Scaling‐Up Insights for Zinc–Air Battery Technologies Realizing Reversible Zinc Anodes

Zinc–air battery (ZAB) technology is considered one of the promising candidates to complement the existing lithium‐ion batteries for future large‐scale high‐energy‐storage demands. The scientific literature reveals many efforts for the ZAB chemistries, materials design, and limited accounts for cell design principles with apparently superior performances for liquid and solid‐state electrolytes. However, along with the difficulty of forming robust solid‐electrolyte interphases, the discrepancy in testing methods and assessment metrics severely challenges the realistic evaluation/comparison and commercialization of ZABs. Here, strategies to formulate reversible zinc anodes are proposed and specific cell‐level energy metrics (100−500 Wh kg−1) and realistic long‐cycling operations are realized. Stabilizing anode/electrolyte interfaces results in a cumulative capacity of 25 Ah cm−2 and Coulomb efficiency of >99.9% for 5000 plating/stripping cycles. Using 1–10 Ah scale (≈500 Wh kg−1 at cell level) solid‐state zinc–air pouch cells, scale‐up insights for Ah‐level ZABs that can progress from lab‐scale research to practical production are also offered.


Introduction
Lithium-ion batteries (LIBs) are the worldwide leading scaleup technology, manufacturing hundreds of GWh yr -1 for electrified transportation, electronic markets, and grid-energy storage.However, LIBs intercalation chemistry cannot satisfy the ever-growing electrical transportation market demands of celllevel specific energy ≥500 Wh kg −1 , pack-level cost below Fundamental illustrations for all-solid-state zinc-air pouch cells: Optimizing cell-level energy density with key cell parameters.a) Increase of specific cell energies in stepwise order by optimizing active/inactive cell parameters in pouch configurations.The baseline cells display the specific energy ≤ 50 Wh kg −1 with active and inactive components reported typically in the literature (N/P ratio ≥ 25, E/C ratio ≥ 150 μL mg −1 , cathode mass of 1-2 mg cm −2 ).The reduction of excess electrolytes, inactive materials (packing and current collectors), and N/P, E/C, and E/A ratios are required with advanced Zn intercalation chemistry for the specific cell energy ≥ 500 Wh kg −1 .b) Estimation of cell energy density (gravimetric and volumetric) vs N/P ratio considering cathode and anode mass loading at fixed anode and cathode mass, respectively.c) Estimation of cell energy density vs E/C ratio considering cathode and electrolyte loading amounts at fixed electrolyte and cathode amounts, respectively.d) Estimation of cell energy density vs E/A ratio considering electrolyte and anode amounts at fixed anode and electrolyte amounts, respectively.e) Projection of cell-level energy (gravimetric and volumetric) vs cell capacities (0.1-1.5 Ah) with different voltages (1-1.6 V) for a single cell.f) Ragone plots for the reported energy densities for the representative state-of-the-art Zn-air and Zn-ion batteries including liquid and solid electrolytes.The theoretical limit of cell energy and the year 2030 cell energy target for the United States, Department of Energy (US DOE) are shown.Two black dotted lines display the boundaries of 60% and 5% depth of discharge (DOD).Square and circle symbols correspond to the reported values from zinc-air and zinc-ion batteries, respectively, and the filled color reflects the number of operating cycles.The E g is the reported gravimetric energy density.Please see the Experimental Section and Tables 1 and  S1,Supporting Information for more details about specific energy and cell parameters.The dotted lines in (b), (c), (d), and (e) show the optimal values for ultrahigh energy densities with long cycle life.lithium batteries.[36] Pouch cells can be a superior cell format to enhance specific energy due to the feasibility of multilayered bipolar stacking, flexible cell dimensions, and minimal weight of packing materials compared to those of coin, cylindrical, homemade, and prismatic types.Since there are few reports on pouch cell designs with upgraded performances, [4] no comprehensive analysis has been reported on cell-level energy metrics and cycle life for practically complete Zn cells.The insights of key design battery parameters at the cell level are critically indispensable for high-energy Zn-based batteries.
This Perspective provides the essential conditions for the practical realization of ZABs to achieve cell-level specific energy ≥ 500 Wh kg −1 as a standardized reference for bridging academic and commercial efforts with pouch cell configurations.A con-ceivable gap in the case of ZAB cycling is the utilization of excess electrolyte and Zn -much higher than that required for highenergy cells -that challenges executing the careful experiments desired to guarantee robust and dendrite-free cycling.Precise quantification of electrochemistry and thermodynamics of Zn inspires compatibility with electrolytes to prolong calendar life by regulating interface and charge-transfer kinetics.We present central performances of rechargeable Zn-air cells prepared using 1-10 Ah-scale pouches (≈500 Wh kg −1 at cell level) and cylindrical format, alongside insights into materials selectivity and process design parameters for upscaling ZABs.and packing shields, and encounter various parameters such as high specific energy, operational cycle life for wide temperatures, and chemical/mechanical robustness.First, we evaluate the scenario of cell-level specific and volumetric energies with different fundamental cell parameters considering all the active and inactive components for multilayered pouch cells (see methods for details).[5] A meaningfully high energy density zinc battery will never be achievable under such unrealistic conditions.This is a major source of misleading the research pathways between the lab and practical pouch cells under working conditions.Finding optimal cell parameters to obtain desired specific/volumetric cell energies (E SP /E Vol ) with long-term cycle life in practical Zn-air pouch cells (ZPCs) is highly challenging.[3] The specific cell energy can be enhanced by decreasing electrolyte volume, increasing cathode mass, and controlling the inactive materials (see second-to-fourth bars in Figure 1a).
Typically, the literature reports the electrochemical performances based solely on the reversible capacity of cathodes or anodes, but the cell energy is a crucial metric for practical applications.Thus, reasonable calculations of cell energy in half-cells are critically important.Cell energy can be relative potential vs reference/counter (Zn metal) and reversible capacity with potential vs standard SHE references for cathode and anode, respectively.More precisely, the anode retains the character of higher electrochemical potentials (vs M n+ /M), lowering the energy density.Excessive use of Zn and electrolyte greatly influences both final energy density and the overall performance of the cells, requesting in-depth insight into the capacity coupling in the solid electrolyte interphase (SEI) region.For example, Coulombic efficiency (CE) and N/P ratios are key test parameters for commercial LIBs.In ZPC case, CE cannot be considered similar to LIBs due to irreversible consumption of Zn and small fraction utilization (<1%) per cycle. [37,38]e suggest five testing parameters for effective verification of ZPCs: capacity pairing for anode-to-cathode (or N/P ratio), E/C ratio, electrolyte-to-anode (E/A) ratio, average voltage, and capacity, which are vital indicators predicting the battery cycle life and energy density.First, we examine the relation between specificcell and volumetric energy with the N/P ratio per cathode and anode mass loadings (Equations ( 7)-( 13)).As N/P decreased from 50 to 10, E SP and E Vol increased slowly, but it considerably improved from 177 to 600 Wh kg −1 and 241 to 1346 Wh L −1 by reducing N/P ratio from 10 to 1 (Figure 1b).
Second, the correlation of E/C to the E SP and E Vol at a constant N/P of 1.8 clarifies the significant improvement in both energies from 136 to 765 Wh kg −1 and 240 to 2904 Wh L −1 as the E/C ratio decreases from 50 to 2 μL mg −1 (Figure 1c).However, indefinite reduction in E/C ratio cannot be suitable for specific capacity and cycle life so that optimal range is critical for cell design.Third, the influence of E/A to E SP and E Vol vindicates the comparable E SP of 680 Wh kg −1 above the E/A ratio 10 μL mg −1 and then consid-erable decreases from 680 to 11 Wh kg −1 by lowering E/A from 10 to 1 μL mg −1 for anode mass loadings.While for electrolyte volume, E SP increases from 22 to 700 Wh kg −1 by lowering E/A from 60 to 1 μL mg −1 .In contrast, E Vol increases in both anode and electrolyte mass loadings (Figure 1d).Fourth, both E SP and E Vol energies increase with a discharge voltage of 1 to 1.6 V from 390 to 660 Wh kg −1 and 1183 to 1924 Wh L −1 at fixed N/P and E/C or E/A ratios.
Finally, with the increasing cell capacity from 0.1 to 1.5 Ah, both E SP and E Vol considerably achieve the promising range of 31 to 750 Wh kg −1 and 100 to 2200 Wh L −1 (Figure 1e), which illustrates N/P, E/C or E/A, and cell capacity are the critical parameters for obtaining high energy targets of US DOE in the year of 2030.Notably, the literature reports high gravimetric energy density for liquid/solid-state Zn-ion (200-460 Wh kg −1 ) and Znair (600-1400 Wh kg −1 ) batteries with different Zn-chemistries.Typically, these values are solely normalized to the mass of active cathode (1-5 mg cm −2 ) and consumed Zn (0.02-1 g cm −2 ), the expense of sacrificing other decisive parameters, and limited for operating depth of discharge (DOD) 5-10% (Figure 1f, Table 1, and Table S1, Supporting Information).  Consiing practical full-cells (including the total mass of active/inactive components -electrolyte, anode, separator, currentcollectors, cathode, and packaging), the resultant cell-level energies are recalculated to Zn-ion (10-15 Wh kg −1 ) and Zn-air (1-146 Wh kg −1 ) batteries, which correspond to ≈5% of reported values.It is worth noticing that a significant gap remains between reported and actual commercial battery parameters due to imprecise valuation for ZB-full-cells conditions.Recently, Shinde et al. reported practical cell-level-high-energy (460 Wh kg −1 ) ZPCs considering commercially utilized parameters. [4]Thus, the following key design parameters are recommended for practical ZPCs with desired energy densities: 1.For E SP of 100 Wh kg −1 , the N/P ≤7.5, E/C ≤37, E/A ≥1.2, capacity ≥ 0.5 Ah, and cathode mass ≥ 3 mg cm −2 ; 2. For 300 Wh kg −1 , the N/P ≤2.4,E/C ≤12, E/A ≥1.4,capacity ≥ 0.8 Ah, and cathode mass ≥ 10 mg cm −2 ; and 3.For 500 Wh kg −1 , the N/P ≤1.8, E/C ≤8.0, E/A ≥2.6, capacity ≥1.0 Ah, and cathode mass ≥ 15 mg cm −2 .

Thermodynamics and Kinetics of Zn Reversibility
Figure 2 represents the five crucial parameters for designing practical Zn-metal anodes relevant to high-energy cell cycling in the commercial and academic state-of-the-art; 1) The cumulative capacity of plated Zn (or capacity of Zn metal plated per cycle), 2) Zn-electrolyte-interfacial reactions, 3) Zn utilization (or DOD), 4) Plating/stripping current density, and 5) CEs.Commercial targets of ZBs are 100% CE with 2000 cycles and a cumulative capacity of 10 Ah cm −2 , which competes with the goal of Li-metal cells (5 mAh cm −2 with 80% DOD/cycle, 2C or 10 mA cm −2 ). [3,26,38]or this, at least one-order-of-magnitude performance improvement is required for five key parameters.39] However, the insights over universal Zn-anodes are highly challenging.Design of sustainable in-situ SEI that can play a decisive   The state-of-the-art of liquid (alkaline, neutral, acid, and hybrid electrolytes) and solid-state reversible Zn-air batteries.[26]   a) The stated values as of the published articles. b) Calculated from the electrochemical measurements, if it is not mentioned in the respective articles.). e) Cathode mass was evaluated based on the stated mass loadings for the current collectors such as carbon paper, carbon cloth, and stainless steel mesh. f) Liquid-state cells was constructed with excess electrolytes from 1 to 10 mL with several time electrolyte exchange. g) The cell-level capacity and energy density are calculated by using Equations ( 7)- (13). h) The calculated cell capacity without consideration of packing materials mass.role in the construction of robust Zn-metal anode can prolong the cycle-life of high-energy practical cells while controlling over Zn-affinity to reduce nucleation barrier, inhomogeneous Zn(OH) 2 − and ZnO-based depositions, volumetric expansions of Zn-anode, decomposition/depletion of electrolytes, and local current density in liquid/solid-state electrolytes (Figure 2a).Fundamental understanding between hexagonal close-packed (hcp) Zn-crystal structures and interfacial environments during charge-discharge processes can be the key to new Zn-chemistry with controlling epitaxial growth of preferred crystal orientations and compositions. [39,40]Dense packing and anisotropy of hcp crystal structures have superior atomic coordination, facilitating the lower dissolution affinity than loosely packing crystal planes.
We present the design of surface atomic structures of Zn anodes with F − /S − passivation using Zn(TFSI) 2 , and/or Zn(OTf) 2 , and/or ZnFSI via immersion processes (see the Experimental Section).Electrochemical stability and reversibility of Zn-anodes were investigated by finding relevance between F − /S − mass loadings (5-30 at%) on Zn-surface and their preferred crystal orientations out of ( 101), ( 100), ( 102), (103), and (002).X-ray diffraction results show the well-defined hexagonal crystal structures along these preferential crystal facets for Zn-anodes (JCPDS: 03-065-5973, Figure 2b).Preferentially orientated Zn-anode ensures strong binding affinity of F − /S − atoms and Zn-ions for stimulating homoepitaxial growth of Zn-F/Zn-S with increasing the nucleation overpotentials, thus facilitating reversible dendrite-free Zn anode with persistent cycle lifespan even for high current densities.However, pristine Zn suffers from severe dendritic growth due to the absence of F − /S − -interactions as well as uneven electric field distributions alongside corrosion reactions.
Sand's model [43] highlights that the metal-dendrite formation can be regulated by dynamic parameters such as current density (I), ion-transport (t), conductivity (), shear modulus (G), and surface tension (S).Density functional theory (DFT) calculations [44] elucidate the design of advanced SEI adjusting metal-surface reactivity, surface tension, and transport.Combining DFT calculation and Sand's model can estimate the ideal conditions for completely dendrite-free anodes as "lower the surface diffusion barriers of metal ions for higher the surface energies" and "the shear modulus of separator or electrolyte needs to be greater than that of a metal anode (G separator/electrolyte > G anode )." Considering these parameters, Tikekar et al. extracted the analytical relevance between G, S, I, t, and  (Equation ( 17)) [45] for determining the Zn deposition stability at the anode surface, in which the dendritic growth index (/I) of zinc seeds correlates critically with a current density.Figure 2g reveals that lower current densities are beneficial for more negative values (zincophilic) of /I, allowing larger seed sizes for stable deposition leading to dendrite-free Znanodes.The current density reflects the kinetic equilibrium between alleviating influences of separator mechanics, undermining transports, and alteration with surface tension.Theoretically, /I = 0 is a boundary between stable and unstable (dendritic) growth domains./I remains zero or negative at low current densities (<10 mA cm −2 ), so the dendritic growth can be suppressed despite the crystal growth of zinc seeds ( ≈ 0.1 mm).The trend of dendritic growth likely increases at mid-current densities (10-100 mA cm −2 ), manifesting that the threshold seed size ( th ) for inhibiting dendritic growth decreases accordingly with increasing current densities.Higher current densities (100-1000 mA cm −2 ) cause unstable kinetics with /I beyond the  th .High CEs (>99.6%)obtained by Zn-F/Zn-S chemistry offer the elastic SEI with stable kinetics for crystal-oriented Zn(101) anodes, and their lower permeability diminishes the parasitic corrosion reactions between electrolytes/cathodes/anodes.
DFT calculations were conducted to explore the fundamental mechanism for elastic SEI formation, diffusion kinetics for higher CEs, and desirable Zn dendrite suppression by employing F − /S − -chemistries (Figure 3a,b and Figure S1, Supporting Information).Compared to pristine and other (002), (102), (103) surfaces, DFT reveals the Zn(101) has lowest surface diffusion barriers and high surface energies for S, F, and Zn-sites along with minimal compressive strain, which facilitates the spontaneous reorientation of Zn crystallites epitaxial to the electrode surface favorable for SEI.The Zn(101) exhibits the robust 3D diffusion trend after the initial nucleation stage within 7 s (dotted line, Figure 3c), implying absorption of Zn 2+ ions on the surface with a local reduction to Zn 0 and restricted 2D surface diffusion.The stable, time-independent current behavior is indicative of a 3D diffusion promoting the uniform nucleation sites with directional Zn 2+ flow. [39]The time-dependent change of current density for pristine Zn implies a 2D diffusion behavior that involves the lateral dispersal of adsorbed ions along the surface to determine promising active sites for charge transfer. [28]Low diffusion barriers are preferable because the growth rate relies upon exponential-in-proportion to barrier height with the order of several kT.Further, we could experimentally observe that the areal nucleation density was lowest in case of Zn(101) compared to other crystal orientations (Figure 3d).When the areal density of nucleation increases, nearby dense nuclei compete to secure zinc ions, so lateral 2D diffusion becomes dominant and the growth rate decreases.DFT calculations also vindicate the highest diffusion barriers for pristine and Zn(002) anodes, which initiate specific nucleation locations on the Zn-surface with a 2D diffusion behavior with uneven dendrite growth as "tip effect" due to the accumulation of numerous active sites continue to grow vertically. [39]Conclusively, the preference of Zn-anodes is the order of Zn(101) > Zn(100) > Zn(102) > Zn(103) > Zn(002) > Zn due to steric interactions and strength of ionic bonds in the

F/S-Reinforced Chemistry for Zn Reversibility
Pristine Zn displays polarization values of 126 and 159 mV for solid and aqueous electrolytes, respectively, and fails within 600 cycles with CE from 70.7−95.2%(Figure 4a and Figure S2, Supporting Information).We employed chitosan biocellulosics (CBCs) [4] as the solid electrolyte and aqueous 2 m ZnSO 4 solution as the liquid electrolyte for comparison.In contrast to pristine zinc, Zn(101) reveals small polarizations of 52 mV and 89 mV for CBCs and aqueous electrolytes, respectively, even after 5000 plating/stripping cycles (5 mAh cm −2 per cycle) with average CEs of 99.9 and 99.6% at 10 mA cm −2 for a cumulative capacity of 25 Ah cm −2 , which is 2.5 times higher than the commercial/DOE targets. [3,26,38]Even for commercial-scale arealcapacity of 10 mAh cm −2 per cycle, Zn(101)||Zn(101) cells exhibit >2000 cycles with an overpotential of 56 mV, while pristine Zn lasts only a few cycles (Figure 4b).This elucidates the significance of F − /S − anions interactions (via TFSI/OTF Zn-salts and Me 3 EtNOTF) in forming robust ZnF 2 /ZnS-rich SEI with lowest interphase resistance (Figure 2e).Scanning electron microscopy (SEM; Figure 4c) images exhibit substantial cracks, characteris-tic dendrites, and a mossy morphology for pristine Zn, while the Zn(101)-anode shows compact and smooth morphology after 50 plating/stripping cycles.SEM displays uniform, dense particleslike morphology even after the 5000th plating/stripping cycles (Figure S3, Supporting Information).The mechanical flexibility of CBCs accommodates volume changes without cracks via interfacial stretch during electroplating, enabling uniform Zn plating.Symmetric cells of pristine Zn display apparent inhomogeneous Zn plating with dendritic protrusions after an initial 10 min, whereas Zn(101) remains uniform and smooth morphology even after 60 min (10 mAh cm −2 ; Figure 4d).remaining as Zn 2+ , not Zn 0 states.][48] Depth profiles of ToF-SIMS confirm the 10.2 nm thin ZnF 2 /ZnS-rich interphase for Zn(101) with decreasing concentrations of S − , F − , and O − with etching, as comparable to the SEI of commercial LIBs (graphite and Limetal anodes).This thin, robust SEI layer serves as an electron barrier inhibiting parasitic reactions and reduction of electrolyte during Zn 2+ reaction kinetics (Figure 4h).However, pristine Zn does not show such interphase due to serious decomposition of electrolyte, formation of irreversible ZnO, and secondary CO 3 2− /COOR components (Figure S7a-d, Supporting Information). [3]The SEI formation mechanism can be estimated as follows: TFSI/OTf 2 yields S − /F − anions through nucleophilic reactions with OH − ; then, S − and F − anions can rapidly coordinate with Zn 2+ cations to generate the ZnF 2 −ZnS layers during higher voltages (charging).
The chemical kinetics of cycled Zn(101) and pristine Zn anodes was evaluated using XPS (Figure 4i,j and Figure S8a-f, Supporting Information).Pristine Zn was observed to form irreversible ZnO just after the first cycle with high polarization, featuring the difficulty of zinc nucleation during plating (Figure 4i, and Figure S8a,b, Supporting Information).The growth of dead Zn fibrils at the interface is generally associated with clear squaring along the edges of voltage profiles with internal short circuits due to uncontrolled Zn deposits at the local regions of electrodes (left images in Figure 4c,d).In contrast, XPS spectra of Zn(101) display retention of stable ZnF 2 /ZnS bindings after 5000 plating/stripping cycles (Figure 4j and Figure S8c-f, Supporting Information).F − /S − -treated Zn(101) surface reveals the formation of inorganic Zn-S/Zn-F, Zn(OH) 2 , and sulfurized/fluorinated oxide species during 5000 cycles. [3,26]It can be seen that the presence of Zn-S/Zn-F bonds well inhibits the formation of irreversible ZnO even after the long-term operation of more than 5000 cycles.O 1s, S 2p, and F 1s spectra also demonstrated the absence of loosely bound S-species and organic fluorinated CF 3 after 5000 cycles.Note that the Arrhenius behavior of ZnF 2 /ZnSrich SEI boosts the ion conductivity at lower temperatures, and the higher thermal robustness of the ZnF 2 /ZnS-rich interfaces significantly enhances the high temperature (80-100 °C) electrochemical performances for both cathodes/anodes.
39a-c] Previous studies on zinc crystal planes have overlooked the critical need for a robust SEI that can be induced by surface F/S bindings.The previous research derived the basal (002) plane of the ideal zinc hcp crystal as the optimal crystal plane by considering only uniform plating/stripping by lattice matching.So, a smooth equipotential surface and homogeneous interfacial charge density distribution can be attributed to a more even nucleation site formation along the parallel direction in the initial Zn deposition.3a-d] Further, the water decomposition forms Zn(OH) 4  2− (zincate) for local high pH regions that subsequently convert to insoluble and electrochemically inert ZnO.The inhomogeneous morphology of Zn(OH) 2 − and ZnObased depositions on Zn electrode leads to the dendritic growth degrading the cycle life and safety.
This feature clearly indicates the need for water removal for the formation of robust SEI in between the electrolyte and zinc anode to realize the long life required for commercialization.In this Perspective, the utilization of bis(trifluoromethane)sulfonimide (TFSI − ), trifluoromethanesulfonate (OTF − ), and bis(fluorosulfonyl)imide (FSI − ) anions in the electrolytes and anodes processing improved Zn reversibility and cathode surface by removal of water from the inner Helmholtz layer that can meet the requirement of commercial battery technology standards.This work demonstrates the facile and scalable design strategies for various robust and reversible single preferred crystal oriented (>95-100%) Zn metal anodes [(002), (100), (101), (102), and (103)] using chemical immersion process with sulfonyl imide salts.Engineering preferred Zn(101) with ZnS/ZnF 2 bindings at the interface significantly controls the interfacial charge distributions and facilitates the superior ion kinetics, mainly because of preferred crystal orientations, close-packed layer, and flexible thinnest SEI layer.Notably, ZnS/ZnF 2 phases act as discerning crystal interfaces and superior corrosion-resistant durable coating.SEI layer formed with preferred Zn(101) orientation displays the thinnest SEI layer of ≈10.2 nm (similar to LIBs SEI thickness; Table S2 and Figure S5b, Supporting Information) compared to those of other orientations such as (002), (100), (102), and (103), which is consistent with chemical activity of crystal planes and lowest surface diffusion barriers (Figure S1, Supporting Information).The minimal compressive strains of Zn(101) [i.e., with ZnF 2 (111) and ZnS(111)] manifests the lower lattice-mismatch interphases over the Zn foil, facilitating the direct nucleation and growth via stable electrodeposition.In contrast, (002) crystal surface likely devastates interfacial durability due to the uncontrolled growth of thick SEI and Zn deposit under harsh operating conditions and high capacity scale (i.e., DOD, rate-capacity, areal capacity, and operating temperature).Theoretical and experimental analyses display that the Zn(101) anodes exhibit exceptional overall capacity, operational life, chemical/thermodynamic stability, reversibility, and half-/full-cells energy/power activities satisfying the commercial requirements.
Constructing symmetric-cell-configurations with Zn(101) enables a >10 times increase in capacity/energy at the cell level, which offers pathways to reach 2030 DOE targets.This strategy also decreases 50% Zn consumption while increasing active cell area by two times larger.Stable internal resistance is possible with reduced overpotentials.Symmetric-cell configurations can also measure the chemical and electrochemical stability of both electrode and electrolyte at the charge-balanced state, which evaluates full-cell performance metrics comparable to practical applications.However, conventional asymmetric cells (excess charge state) normally present inhomogeneous surfaces with unavoidable side reactions, irreversible crossover, and decay of intrinsic stability at current collectors (left, Figure 5b), resulting in severe zinc loss during cycling.The excess charge operation minimizes the negative impact on the electrode and electrolyte by sacrificing overall cell energy and stability at the full cell level.Therefore, obtaining high energy with long-term stability is critically challenging.N/P ratio also locally varies depending considerably on the location at first charging, causing a disastrous capacity loss in practical cells (uneven utilization of cathodes/anodes).This approach is recommended only for assessing capacity-limited stability in the early stages of research when the energy density is not considered critical.Since no such critical issues have been observed from the symmetric cell configuration (right, Figure 5b), the charge-balanced full-cell configuration is recommended.
Combining symmetric-cell-configurations with solid-state electrolytes enforces the thermal and safety management for the cell-to-pack-level.F − /S − -adopted Zn(101) anode further optimizes mass and volume by inducing the stable SEI during electrochemical reactions (Figures 2-4, and a third bar in Figure 5a).Employing solid electrolytes enables bipolar cell stackings in a single pack without short-circuit while minimizing dead space for high power applications.Three-to-ten Ah-scale cells can be integrated by combining bipolar cell stacking with a gas diffusion layer (GDL) capable of enhancing air permeability (fourth-to-fifth bars in Figure 5a).Compressive pressure can improve the wettability of electrodes with increasing double-layer capacitance and reducing R ct without change in morphology of electrodes (sixth bar, Figure 5a).The pressure of <100 psi likely concentrates along the cell boundaries.At pressures around 200 psi, the pressure can be evenly distributed over the entire cell area without generating a locally concentrated pressure.Particulate cracking of the cathodes and electrolyte degradation severely occur under high pressures of 300-1000 psi. [50]igure 5c-e displays the electrochemical performances of CPS||CBCs||Zn(101) pouch and cylindrical cells.Discharge capacities of pouch cells correspond to 2.2, 5.1, and 10.6 Ah for different cell areas of 10, 60, and 120 cm 2 , respectively, alongside the cell energy density of 300-500 Wh kg cell −1 .We have also fabricated the cylindrical format of cells, in which discharge capacity was obtained to increase from the types of AAAA (1.1 Ah), AAA (2.6 Ah), AA (5.6 Ah), and A (8.8 Ah), but the energy density decreased from 500 to 100 Wh kg cell −1 at the expense of excess electrolyte.The total area of cylindrical cells increased from AAAA to A with increasing the content of excess electrolyte and inactive cell-packing materials, which elucidates a significant decrease in energy density.We compared the calculated battery pack cost versus the driving range of electric vehicles (EVs) between different batteries of LIB, LiS (Li-sulfur), and ZPC.Cycle/calendar life, self-discharge rate, and efficiency/power are significant parameters for reliable EV operation.Compared to LIB and LiS, a twoto-three times cheaper battery-pack cost is estimated for 1000 km driving (Figure 5f, Equation 18, and Tables S4-S6, Supporting Information).
Combining GDL and external pressure of 200 psi enabled the fabrication of 10-Ah bipolar-stacked ZPCs (10 layers), revealing 89% capacity after 1000 cycles with unprecedented 100% DOD and average 100% CEs.However, applying GDL without pressure gradually decays capacity, i.e., 58% retention over 470 cycles (Figure 5g).ZPCs without GDL provided ≈7 Ah for just 81 cycles with rapid capacity drop associated with enhanced interfacial impedance.Optimized ZPCs display notable reversibility and almost flat discharge plateaus after 230 charge-discharge cycles under practical operating conditions (fast charging and 100% DOD, Figure 5h).Symmetrically designed ZPCs provided specific energy (500 Wh kg −1 cell ) with an estimated production cost of 34 US$ kWh −1 , intrinsically safer, and wide-temperature operations, [4] which are noticeably attractive for emerging EV markets.
We also focus on standard testing protocols essential for electrochemical measurements of high-energy ZPCs in liquid-and solid-based electrolytes under a balanced or excess charge state.Precise assessment of SOC (state of charge at initial-to-final state), temperature, internal resistance, cycle life, and overheating protection must be considered.Figure 6a-c displays testing protocols such as constant current-constant time (CC-CT), constant current-constant voltage (CC-CV), and constant currentconstant capacity (CC-CC) modes.In conventional CC-CT (or CV-CT) protocol, the charging current rate and polarization voltage are the significant factors influencing the battery's performance.The major challenges are finding proper values of charging current/voltage that can justify the capacity utilization, charging time, and electrolyte decomposition.A high current level induces cell failure, generating toxic gases at 10-80% SOC and reducing active materials.The low current yields an inferior charging rate, which is inappropriate for EV applications.At a highenergy scale, fast charging at the initial phase requires a large amount of charging current instantaneously, then gradually decreases with increasing SOC, resulting in severe degradation of cell performances.Therefore, optimal charging protocols considering minimal cell-capacity decay and charge time are desirable.
In the CC-CV protocol, CC and CV steps are responsible for the charging time and capacity utilization, respectively.The CV step after CC measurement compensates reduction in energy density while utilizing all active materials without ohmic losses.Since the mass-transport resistance limits the SOC in the CV step, choosing proper redox-potentials far away from the boundaries of the electrolyte-stability window can mitigate the resistance.The CC-CV protocol is beneficial for forming elastic SEI on the anode, enhanced capacity and SOC retention, lower internal resistance of Zn-anode, and protection of Zn-anode against electrolyte corrosion and volume changes.This protocol also provides a feasible charging state and obtains the practical tradeoff between energy efficiencies and charge rates as per the demanded applications.Like in LIBs, precharging (6-12 h) with a small current (0.1-1.0 mA cm −2 ) is highly recommended at the initial stage of charging ZABs before the formal high-current charging.Direct fast charging causes severe damage to cell electrodes, operational life, and safety hazards due to the high-energy ratio of ZABs.The CC-CV protocol combined with precharging in small currents can improve the overall ZABs performances by 50-80% compared to other testing protocols (CC-CT, CV-CT, CC, or CV; Figure S9, Supporting Information).
Note that capacity/voltage decay rates should be normalized with cycle numbers or time of operations for standardized current rates, the so-called C-rate.Battery operation lifetime can be estimated using Eq.19.The charge-balanced full-cell configurations are recommended to achieve high-energy and long-life cycling simultaneously, which matches realistic operations.Capacity fading should be analyzed at DOD/SOC of 100%.Since the lifespan of battery cells depends mainly on the C-rate and DOD, a moderate rate of 10 mA cm 2 or 1C, and CC-CV protocol are re-quired to compare reasonably with commercial LIBs.Secondary ZBs adopting TFSI/OTF/FSI-based solid-state electrolytes deliver a promising cell energy density (>400 Wh kg cell -1 ) and operation lifetime as competent to incumbent LIBs technology. [4,5,37,48]pscaling from lab-scale in ZBs technology requires the specifications summarized for the key parameters (Table 2).The cost Table 2. Requirements for the principal testing parameters in lab-scale measurements of Zn batteries.

Principal parameters
Specifications required for each parameter

Cell dimension
Active cell dimension, dead cell dimension (area or volume), design structures, the total weight of cells (homemade-, coin-, or prototype-cell), mass or specification for packing and tab materials

Cell operations
Minimum applied current density should be greater than the following conditions; 1) Diffusion current limitations 2) For CC-CC mode operation, preferably ≥1 C to compare with LIBs 3) For, CC/CV, or CC-CT operation, preferably ≥10 mA cm −2 for liquid electrolytes or 20-25 mA cm −2 for solid-state electrolytes with a charge-discharge cycle time of >40-80% depth of discharge/state of charge (DOD/SOC) 4) For CC-CV mode operation, preferably ≥1C to compare with LIBs

Cathodes (C)
The mass loading of all cathode components (binder, active materials, additives/carbon black) needs to be at least ≈10 mg cm −2 , comparable to a commercial level.Stoichiometric characteristics and loaded mass of each component should be given with the mass/thickness of current collectors.The density change of the cathode needs to be compared before and after testing.
Electrolytes (E) Type of electrolytes, electrolyte-to-cathode ratio (E/C to be ≤12 μL mg −1 ), amount of liquid electrolytes, thickness and mass of solid-state electrolytes, removal of excess electrolytes Separators (S) Type of materials (polymer or glassy carbon), thickness and mass, specified dimensions Zinc anodes (A) Thickness, mass of anode, active and inactive dimensions, anode-to-cathode ratio (N/P to be ≤ 2.4), number of replacement for anodes, removal of excess anodes, consumed Zn mass, electrolyte-to-anode ratio (E/A to be ≥ 1. Electrochemical parameters Precharging (6-12 h) with small current of 0.1-0.5 mA cm −2 , Power density, specific or gravimetric capacity and energy density (at 50% and 100% DOD/SOC), cycle life at 40-80% DOD/SOC, capacity retention of >80%, EE of ≥99.5%, Coulombic efficiencies (CE) of ≥99.9% reduction of cell constituents utilizing Zn(TFSI/FSI/OTF) and optimized electrode designs will be a notable inspiration for fueling ZABs research.

Perspective Towards Zinc-Ion Batteries (ZIBs)
57a-c] Typically, lab-scale research did not observe the diffusion limitations and polarization effects due to minimal mass loading (1 mg cm −2 ) that provides artificially improved performance.However, the realistic ZIBs require active mass loadings of 7-10 (aqueous/liquid) and 10-15 mg cm −2 (solid), relatively comparable to the areal capacity of 2-5 mAh cm −2 .Ideally, the Zn-anode utilization should be 100% (DOD), and relative mass loadings should be perfectly balanced regarding the charge.However, practical results show that Zn-anode utilization is limited to 10-50%, implying 2-8 times oversized anode relative to cathode capacities.Such a low active-material-loading of cathodes seriously induces the poor utilization (DOD) of the Zn anode (Equation 20), which illustrates large, unbalanced electrodes with a lower specific energy of ZIBs.In general, all lab-scale reports follow the cathode-mass-loading, which is 100-150 times lower than that of anodes (i.e., cathode: 1-2 mg cm −2 and anode: 150-300 mg cm −2 ).This approach is unrealistic to obtain meaningfully high specific energy and CEs for ZIBs.
In aqueous ZIBs, the major parasitic reactions are based on the H 2 -evolution during Zn plating.57d,e] Whereas excess electrolytes diminish specific energies, electrolyte starving condition amplifies the negative influence of parasitic reactions due to depleted Zn 2+ ions, resulting in lower cycle life.Parasitic electrochemical reactions of Zn with electrolytes and kinetically inactive dead Zn lead to irreversible capacity and reduced CE.We recommend the optimal cathode loadings of 10 mg cm −2 with an E/C ratio of ≈10-12 for ZIBs.58a,b] Maintaining high electronic conductivity and ion-diffusion capability with high-mass loading is challenging.Specific energy degrades by 50-80% with an increase over 20 mg cm −2 in mass loading, implying significant polarization and underutilization of thicker electrodes for higher charging rates.Lower charge transfer resistance and Warburg impedance ascribe the favorable Zn-ion diffusion in the cathodes.
In our work, Zn(101) consists of an inorganic ZnF 2 /ZnSderived SEI layer.This SEI promoted the Zn 2+ diffusion and regulated Zn electrodeposition along (101) orientation without H 2 evolution (Figures 2-4).Typically, the electric double layer (EDL) has a crucial impact on creating a favorable condition for SEI before cycling.The internal structure of EDL at the Zn surface is denoted as the inner Helmholtz plane with a nanoscale thickness.A negatively charged metal surface (S − /F − ) enables the enriched cations in the EDL, inhibiting the side reactions and dendrites by regulating the Zn 2+ diffusion over Zn(101) surface.This distinctive SEI possesses ensuing advantages: 1) Redistribution of Zn 2+ flux with smooth/dense deposit.2) Low energy barriers for desolvation.3) Low corrosion current/potential with suppression of tip effects.4) Low LUMO energy levels lead to the transfer of electrons to favorable solvated structures.58c-e] Equation (21) defines that the ion diffusion is dominant for b = 0.5.In contrast, for b = 1, surface capacitance is dominant through charge and discharge processes that explain the ZIBs kinetics operating for both effects.58h] Figure 3b-d displays the smallest diffusion barriers with minimal compressive strain, 3D diffusion, and lowest nucleation density for Zn(101), illustrating the prospects of Zn(101) as an optimal anode for both ZIBs and ZABs.The suitable pore structures (i.e., shape, diameter, and tortuosity) of separators (liquid-electrolytes) or solid electrolytes and mechanical strengths can regulate the Zn 2+ flux and diffusion kinetics.CBCs solid-electrolyte adopted in this work has exceptional mechanical stress-strain characteristics for favorable electrochemical kinetics. [4]59c,d] However, excess Zn is critically required for rechargeable average cycle life, implying N/P ratio should be >1.A larger N/P ratio severely decreases the practical energy density to 83 and 47 Wh kg −1 for N/P of 5. N/P ratio 2-3 can be considered for better energy density and cycle life practice.In general, aqueous ZIBs can reach 80 Wh kg −1 with a suitable cell design approach; however, 100 Wh kg −1 is practically unreasonable under decent cycle life.

Conclusions
Herein, we have suggested new insights for understanding specific cell-level and volumetric energy densities with standard key parameters as imperious screening tools for evaluating the practical relevance of ZABs.Emerging fluorinated/sulfonated (Zn-TFSI/FSI/OTF) chemistries effectively controlled the electrochemical reactions along Zn/electrolyte interphase while suppressing corrosion and hydrogen evolution reactions.Different crystal orientations of the zinc anode greatly affected the SEI formation, so Zn(101) was the optimal anode structure interfaced with the electrolytes.Conclusively, constructing a symmetric cell configuration with F − /S − -adopted Zn(101) anode enabled robustness for redox potentials, per-cycle utilization, and Zn nucleation inhibiting dendritic growth.Qualitative understanding of the SEI provided the precise kinetics and diffusion, thermodynamics, interface ion-transport, and ideal operating regime (current density, SOC/DOD) for realistic high-energy long-life ZABs.Finally, design guidelines were proposed for production-worthy high-performance Ah-level ZABs with cycling protocols and performance metrics.This approach can make fair evaluations with different laboratories (employing Zn, Al, Mg, Na, Si, K, Fe, Ca) and commercial Li-benchmarks for dynamic and intricate environments.

Experimental Section
Determination of Key Performance Metrics: The cell-level capacity, specific and volumetric energies, operational cycle-life, SOC/DOD, and weight/volume of utilized cell components were evaluated considering all active and inactive materials such as cathode, electrolyte, anode, separator, packing materials (PM), and GDL in comparison with theoretical values (Equations ( 1)-( 16)).Table 1 and Table S1, Supporting Information, summarize the cell-level performance analysis reported in the literature.The average voltage was evaluated using discharge curves provided in reported articles, if not stated.The fraction of consumed Zn was assessed by considering the thickness and areal capacity per cycle compared to the total Zn electrode thickness.Note that the n is the number of electrons per mole, F is the Faraday constant, MW, M Zn , and M Cathode are the molecular weight, c is concentration (mol l −1 ), v is the volume (ml), I is current (mA), A is the active area, Q dis is the discharge capacity, T dis or T ch is the discharge or charge time, V nom is the nominal cell voltage, V cell is the cell volume, A C is the area of cathode, L AC , and L AA are the loading of active cathode and anode, R E/C and R E/A is the ratio of electrolyte to cathode and electrolyte to anode, T fC is the total cathode fraction, f C and f B are the fraction of carbon black and binder, t Zinc is the thickness (μm), and  E is the density of electrolyte.R is the total vehicle range, E T is total energy of pack (kWh), E BP is energy of battery pack (Wh kg −1 ), W BP is weight of battery pack (kg), ECE V is energy consumption efficiency of vehicle (Wh kg −1 km −1 ), W V is vehicle weight excluding battery pack (kg), i dis is current rate, N is number of cycles, CE is Coulombic efficiency (%), n cathode is the number of utilized cathodes,  Sep , t Sep , and A Sep are the porosity, thickness, and area of separator, respectively.

Theoretical cathode capacity,
Theoretical areal anode capacity, The stored discharge or charge capacities compared to those of theoretical capacity Depth of discharge, DOD = The specified power per unit area of cathodes or cells at the definite DOD/SOC values Specific power density, The specific discharge or charge capacities per unit cell or per unit volume of cells Specific capacity, The capacity obtained per unit area of cathodes or total area of cells Areal capacity, The specified energy densities per unit cell weight and for pack-level case including weight of pack as Specific energy density, (10)   Weight of active materials, Specified energy densities per unit cell volume of all cell components and total volume of practical cell including tabs for cell-level consideration as Volumetric energy density, where As known, the ratio of discharge to charge capacities of specific electrodes or ratio of total charge (M + or e − ) flow to/from electrodes defined as the CE: Coulombic efficiency, CE(%) = The Zn dendrite growth index The /I is the dendritic growth index depending on current density, L is the electrolyte separator thickness, G is the shear stress of separator or electrolyte membrane, t Zn is the Zn transfer number, S is the surface tension,  is the ion conductivity,  is seed size,  is the partial molar volume of cation.
Driving range, and vehicle and battery-pack costs for mid-size vehicles with lower and upper boundaries for energy-cost characteristics of LIBs, LiS, and Zn-air cells are evaluated by following equation (see details in Table S4, Supporting Information) Battery operating life = The cost was evaluated with identifying three parameters such as material inputs cost, processing cost (in comparison with LIBs), and integrated metals, separators and other components (see in Tables S5 and S6, Supporting Information).ZIBs gravimetric energy density is calculated using following equations where E is the gravimetric energy density for ZIBs, Q cathode and Q anode are the specific capacities of the cathodes and anodes, ΔV cell or U is the difference in average discharge voltage of cells, k is the mass fraction of cathode/anode or all components, R is cell balance (i.e., N/P ratio) and b is slope.Materials Synthesis: Zinc trifluoromethanesulfonate [Zn(OTf) 2 , 99%], trifluoromethanesulfonic acid (TFSA, 98%), Zinc bis(trifluoromethylsulfonyl)imide (ZnTFSI, 98%), and triethyl(methyl)ammonium iodide were purchased from Tokyo Chemical Industry.Zinc sulfate heptahydrate (ZnSO 4 •7H 2 O), potassium hydroxide (KOH), and acetonitrile were from Daejung chemicals.Zn foil and stainless steel (SUS) mesh were from MTI Corporation.
The preferentially oriented Zn-anodes along the crystal planes of (101), (102), (102), (103), and (002) were fabricated by the ionimmersion reactions method.First, to prepare the trimethylethyl ammonium trifluoromethanesulfonate, the trifluoromethanesulfonic acid and triethyl(methyl)ammonium iodide were dissolved in the acetonitrile in the desired stoichiometric proportions.Then, the reaction mixture was treated for two days at 25 °C under magnetic stirring.After the reaction, the precipitate was washed three times with ethyl ether and ethyl acetate.Finally, the trimethylethyl ammonium trifluoromethanesulfonate was obtained after vacuum drying.Further, Zn foil was treated for the mixture of ethanol, acetone, and deionized water under sonication before utilizing for further reactions.After that, the reaction suspension of trimethylethyl ammonium trifluoromethanesulfonate and zinc bis(trifluoromethylsulfonyl)imide (or zinc trifluoromethanesulfonate or zinc bis(fluorosulfonyl)imide) was prepared in deionized water with appropriate molar concentrations and followed immersion of Zn foil for 5-30% loading of S − and F − bindings.The obtained Zn anodes were washed three times with deionized water and dried overnight under a vacuum.Please note that the detailed S and F compositions along with their preferential crystal orientations are displayed in the Table S2 (Supporting Information).Chitosan biocellulosics (CBCs) electrolyte membrane and copper phosphosulfide (CPS) cathodes were prepared using the synthesis method adopted in our previous report. [4]lectrochemical Measurements: The copper phosphosulfide (CPS) cathodes were fabricated by employing 90% CPS active materials, 5% carbon black, and 5% polytetrafluoroethylene (PTFE) in Nmethylpyrrolidinone (NMP) solvent.After that, the obtained slurries were layered on to the stainless steel mesh, vacuum dried at 80 °C for 20 min for solvent removal prior to pressing, punched in required different dimensions, dried at 80 °C for 12 h, and then weighed before cell-manufacturing.For symmetric cells, the 2032 coin cells were assembled for pristine Zn and preferentially oriented Zn(101) anodes with solid CBCs and aqueous 2 m ZnSO 4 electrolytes.Whatman GF/A glass fiber separator was utilized during aqueous cells.The cylindrical cells were assembled using CPS air-cathodes, CBCs gel electrolytes, the designed helical spring type Zn(101)-anodes, and Celgard 3501 separator.The pouch cells with ≈0.5 to ≈10 Ah capacities were fabricated under asymmetric (cathode//electrolyte//anode) and symmetric (sandwichtype, cathode//electrolyte//anode//electrolyte//cathode) layered configurations with different dimensions.All the electrodes were stacked in the laminating bags, vacuum sealed, and then pressurized.After that, the cells were removed from laminating bags, and then nickel metal tabs were applied to the anode and cathode terminals.Further, the cells were then packed into an aluminum laminating material with vacuum sealing again.The 200 psi external pressure was retained for all electrochemical measurements.The cathode mass loading was 15 mg cm −2 .The thickness of the electrolyte was 50 μm.The in situ Zn plating images were conducted on Dino-Lite digital optical microscope attached with a monochromator and EMCCD.These real-time morphological changes of Zn-based anode surfaces were conducted in homemade cuvette cells with a two-parallel Zn electrode configuration.Galvanostatic chargedischarge experiments were performed using WonATech multichannel battery test systems at room temperature.A CHI 760D electrochemical workstation was utilized for the linear sweep voltammetry experiments.
Materials Characterizations: The morphologies of Zn-based anodes were examined by JEOL JSM-6700F field emission scanning electron microscope.X-ray photoelectron spectroscopy (XPS) results were performed using a Perkin-Elmer PHI-1600 spectrometer (monochromatic Al K radiation).The C 1s peak (284.6 eV) was applied as the reference for binding energies calibration.All electrodes for XPS characterizations were collected from full cells after electrochemical cycling with several-times washing and vacuum drying.Ar + sputtering depth rate was ≈0.5 nm s −1 .The fundamental elements distributions for various depths of cycled Zn-based anodes were conducted by time-offlight secondary-ion mass spectroscopy (ToF-SIMS) for accelerated voltage of 20 kV (current ≈ 1 nA) with TESCAN GAIA3 focused-ion beam-SEM.X-ray diffraction (XRD) results were recorded with Rigaku Smartlab D/max 2500Pc diffractometer (Cu K radiation,  = 1.5406Å and 40 kV).
Computation: The electronic structure calculations were performed using the density functional theory (DFT) codes with the Vienna Ab initio Simulation Package (VASP 5.4.4). [51,52]The projector augmented wave (PAW) method [53,54] was exploited and the exchange-correlation interactions treated by Perdew-Burke-Ernzerhof (PBE) [55] functional under the generalized gradient approximation (GGA).The electron occupations were smeared with a Gaussian distribution function with a smearing width of 2 meV.The plane waves were incorporated till a high energy cut-off of 500 eV.Lattice constants and internal atomic positions were fully optimized until the residual forces were less than 0.04 eV Å −1 .The vacuum slab space of a unit cell in the z-direction was set to 15 Å to avoid interactions between layers.Here, ZnF 2 (111) and ZnS(111) surfaces were specifically used, which can minimize the lattice mismatching and form the chemical bonds of Zn-F and Zn-S with five different Zn surfaces ((100), ( 101), ( 102), ( 103), (002)) based on the experimental XRD re-sult (Figure 2a).The Monkhorst-Pack k-point grid was used, and maximum symmetry was applied to reduce the number of k-points in all calculations. [56]

Figure 1 .
Figure 1.Fundamental illustrations for all-solid-state zinc-air pouch cells: Optimizing cell-level energy density with key cell parameters.a) Increase of specific cell energies in stepwise order by optimizing active/inactive cell parameters in pouch configurations.The baseline cells display the specific energy ≤ 50 Wh kg −1 with active and inactive components reported typically in the literature (N/P ratio ≥ 25, E/C ratio ≥ 150 μL mg −1 , cathode mass of 1-2 mg cm −2 ).The reduction of excess electrolytes, inactive materials (packing and current collectors), and N/P, E/C, and E/A ratios are required with advanced Zn intercalation chemistry for the specific cell energy ≥ 500 Wh kg −1 .b) Estimation of cell energy density (gravimetric and volumetric) vs N/P ratio considering cathode and anode mass loading at fixed anode and cathode mass, respectively.c) Estimation of cell energy density vs E/C ratio considering cathode and electrolyte loading amounts at fixed electrolyte and cathode amounts, respectively.d) Estimation of cell energy density vs E/A ratio considering electrolyte and anode amounts at fixed anode and electrolyte amounts, respectively.e) Projection of cell-level energy (gravimetric and volumetric) vs cell capacities (0.1-1.5 Ah) with different voltages (1-1.6 V) for a single cell.f) Ragone plots for the reported energy densities for the representative state-of-the-art Zn-air and Zn-ion batteries including liquid and solid electrolytes.The theoretical limit of cell energy and the year 2030 cell energy target for the United States, Department of Energy (US DOE) are shown.Two black dotted lines display the boundaries of 60% and 5% depth of discharge (DOD).Square and circle symbols correspond to the reported values from zinc-air and zinc-ion batteries, respectively, and the filled color reflects the number of operating cycles.The E g is the reported gravimetric energy density.Please see the Experimental Section and Tables1 and S1,Supporting Information for more details about specific energy and cell parameters.The dotted lines in (b), (c), (d), and (e) show the optimal values for ultrahigh energy densities with long cycle life.
is determined from the standard thickness of Zn foil (0.3 and 0.5 mm; 0.22 and 0.4 g cm−2

Figure 2 .
Figure 2. Thermodynamics and kinetics for designing high-capacity-dendrite-free reversible Zn-metal anodes.a) Schematics showing failure mechanisms and the comprehensive design considerations for high-performance Zn anodes.b) X-ray diffraction patterns for pristine Zn, Zn(101), Zn(100), Zn(102), and Zn(002) anodes in comparison with theoretical Zn (JCPDS: 03-065-5973, P63/mmc(194), hexagonal structure).The symbols "•" and " * " denote the ZnS(111) and ZnF 2 (111) phases with the reference JCPDS: 05-0566 (F-43m(216), ZnS, cubic structure) and 07-0214 (P42/mnm(136), ZnF 2 , tetragonal structure).c) Evans diagram for electrochemical corrosion of pristine and preferred (101) orientation of Zn.The dotted blue and orange lines denote the Zn dissolution kinetics (including corrosion current) and electrochemical redox potential of pristine and designed Zn(101) anodes, respectively.Cathodic and anodic Tafel slopes are shown by solid orange and blue lines.The blue-shaded area defines the range of electrochemical potentials and current distributions from pristine to Zn(101) or other Zn(100), Zn(102), Zn(103), and Zn(002) anodes.d) Comparison of corrosion inhibition efficiency, equilibrium potential, and HER overpotential for pristine, and preferentially orientated (002), 103), (102), (100), and (101) Zn anodes.e) Normalized charge transfer resistance (R ct ) as a function of depth of discharge for pristine and preferentially oriented Zn anodes at 10 mA cm −2 of current density.The optimal DOD range (gray shaded area) is depicted by a rapid increase in normalized R ct for pristine Zn. f) Comparison of Zn utilization efficiencies vs discharge rate for pristine and preferentially aligned Zn anodes.Pristine Zn reveals a lack of utilization due to severe corrosion reactions even for lower current densities.g) The dendritic growth index vs current density for Zn(101) metal anodes. is the size of zinc seeds, and /I = 0 is a boundary between stable and unstable (dendritic) growth domains./I < 0 denotes the stable deposition during recharging while /I > 0 represents the continued dendritic growth by a highly unstable Zn surface.

Figure 4 .
Figure 4. Quantifying structural and chemical kinetics of Zn-metal anodes in symmetric cells.a) Galvanostatic Zn plating/stripping cycles for pristine and Zn(101) anodes in symmetric cells configuration under aqueous 2 m ZnSO 4 and CBCs electrolytes for capacity of 5 mAh cm −2 at 10 mA cm −2 .b) Zn plating/stripping in symmetric cells for pristine and Zn(101) anodes under CBCs electrolyte at 10 mA cm −2 and capacity of 10 mAh cm −2 .c) SEM images of pristine Zn (left) and Zn(101) (right) anodes after 50 plating/stripping cycles for CBCs electrolyte at 10 mA cm −2 and 5 mAh cm −2 .State: Plating.Scale: 10 μm.d) The real-time optical images of the Zn-deposit over pristine (left) and Zn(101) (right) metal anodes for a test time of 10 and 60 min in aqueous electrolyte (2 m ZnSO 4 ) at a current density of 10 mA cm −2 .Scale 300 μm.The brown layer displays the plated Zn (right, Figure4d).e-g) High-resolution XPS results of F 1s (e), S 2p (f), and Zn 2p (g) for ZnF 2 /ZnS inorganic SEI layer on the Zn(101) metal anode.h) Time-of-flight secondary-ion mass spectrometry depth profiles of F − , S − , O − , and Zn + secondary ions for Zn(101) metal anodes.i,j) XPS results of Zn 2p core-state for pristine Zn cycled to 100th (i), and Zn(101) cycled to 5000th (j) for plating/stripping in CBCs electrolytes, respectively.The pink and black dotted lines correspond to ZnO and metal zinc positions, respectively.

Figure 5 .
Figure 5. Design strategies for >10 Ah-scale pouch cells and their electrochemical performance.a) Scale-up insights of cell capacity depending on major cell parameters.For example, even if cell design and electrode interface/transport are successfully optimized, it means that it is difficult to massproduce and manufacture pouch cells with a maximum capacity of 5 Ah or more with bipolar stacking without GDL.b) Conventional (asymmetric, left) vs symmetric (right) cell design of Zn-batteries.c) Digital photo of 10.6 Ah-scale zinc-air pouch cell.(Symmetric cell design using a pouch dimension: 6.5 × 7.5 cm 2 , cell-level energy: 468 Wh kg −1 ).Scale: 2 cm.d) Discharge capacities at 10 mA cm −2 for asymmetrically designed pouch cells of different cell areas (cell 1: 10 cm 2 cell area, cell 2: 60 cm 2 cell area, and cell 3: 120 cm 2 cell area).e) Discharge capacity of cylindrical cell formats at 10 mA cm −2 [AAAA (D × H = 0.84 cm × 4.25 cm), AAA (D × H = 1.05 cm × 4.45 cm), AA (D × H = 1.45 cm × 5.05 cm), and A (D × H = 1.7 cm × 5.0 cm) types], where D and H are diameter and height of cells.f) Estimated battery pack cost vs EV driving range for LIB, LiS, and ZPC (see Tables S4-S6 in the Supporting Information for details).A possible driving range and cost span are displayed by colored area for each battery type.g) Cycling performance and Coulombic efficiency of Zn-air pouch cells vs critical parameters such as GDL and external pressure.Ten bipolar layers were stacked for applying 10 mA cm −2 .h, Galvanostatic cycling under practical operating conditions of fast charging and 100% DOD.(Conditions: charge current density of 100 mA cm −2 and discharge current density of 10 mA cm −2 , Zn anode thickness of 300 μm and N/P ratio of ≈2.0).

Figure 6 .
Figure 6.Testing protocols and key performance metrics.a,b) Testing protocols schematics for Zn-batteries under constant current-constant capacity (a) and constant current-constant time as well as constant current-constant voltage (b) modes.c) Symmetric/asymmetric cells configuration capacitytime and voltage-time analysis limitations for commercial approaches.CE and EE denote the Coulombic and energy efficiency.The 80% capacity and 90% voltage retention under testing protocols are highly recommended for commercial standards (black dotted lines).

4 μL mg − 1 )
, 10-15 nm thin SEI layer is recommended Cumulative capacity of Zn anode Preferably ≥10 Ah cm −2 Operating temperature (T) Measurement temperatures (−20 to 80 °C) and atmosphere Operating voltage windows Charge-discharge cut-off voltages (at least 0.8-2.5 V), DOD, SOC, energy efficiencies (EE) Oxygen or air flow Flow rate of oxygen or air Rate performances High rate performance is preferable.It depends on the materials and electrode parameters.C rate should be evaluated for areal current density (mA cm −2 ) instead of cathode mass (mA g −1 ) Total number of M + ions back to cathode Total number of M + ions departing from cathodeCE (%) =Total number of e − back to cathode Total number of e − departing from cathode(15)  Capacity or voltage decay rate = Capacity per cycle∕initial capacity or Voltage per cycle∕initial voltage(16)