All‐Solid‐State Battery Fabricated by 3D Aerosol Jet Printing

All‐solid‐state battery (ASSB) technology has emerged as a promising solution for developing safe and high‐energy‐density power sources. However, the pronounced interfacial charge transfer resistance between the electrode and the solid electrolyte continues to be a central obstacle in contemporary ASSBs. This work demonstrates the first approach to printing ASSBs using aerosol jet printing technology. A composite cathode, composed of active materials, binder polymer, and conductive filler, is printed onto the current collector. Subsequently, a solventless superionic conducting solid polymer electrolyte is printed on the cathode to form a seamless interface between the electrode and the electrolyte, resulting in a 3D‐printed all‐solid‐state lithium‐ion battery. The active material in the cathode (lithium iron phosphate, LFP) achieves a loading of ≈10 mg cm−2, while the solid polymer electrolyte layer maintains a thickness of a mere 24 μm. Under ambient conditions (30 °C), the half‐cell ASSB exhibits a specific capacity of over 130 mAh g−1 at 0.05 C. Advanced aerosol printed cells with a porous membrane, which allows the batteries to be safely cycled at higher temperature (60 °C), exhibit fast charging/discharging rates. These batteries are capable of cycling at a 0.3 C rate, delivering a specific capacity surpassing 160 mAh g−1.


Introduction
[3][4] Nevertheless, the ever-increasing demand for power, energy density, and safety continues to drive the advancement of LIB technology.A prime safety issue related to the LIBs is the employment of flammable organic solvent-based electrolytes, which pose risks due to thermal runaways that can result in fires and explosions.Recently, all-solid-state batteries (ASSB) have shown great promise by incorporating highly conductive solid-state electrolytes that are notably safer than liquid electrolytes. [5]Furthermore, substituting the liquid electrolyte may decrease the packaging complexity of conventional LIB, reducing their manufacturing cost. [6]espite significant progress, the inferior cycle performance of ASSB is frequently observed, stemming from the high interfacial resistance between electrode and electrolyte materials.Due to the substantial differences between liquid and solid electrolytes, manufacturing techniques for producing ASSBs with low interfacial resistance remain underdeveloped.The production process for fabricating large-format ASSBs is still an open question, and various techniques have been reported over the past decade depending on the solid-state electrolyte materials utilized.Processes involving different wet coating methods, such as doctor blade coating (tape casting), [7][8][9][10][11][12][13] tape casting combined with sintering/pressing, [14][15][16] and electrospinning, [17][18][19] have been used in both polymer solid-state electrolyte and ceramic solid-state electrolyte.Solvent-free techniques, including extrusion, [20][21][22][23] cold pressing, [24,25] high-temperature sintering, [26,27] and diverse film deposition methods, [28][29][30][31][32] have been used for solid-state electrolyte and composite electrode fabrication.The central issue for fabricating ASSB is minimizing the high interfacial charge transfer resistance between the porous cathode and the solid electrolyte due to poor contact.In addition, current methods are not ideal for producing films with a thickness below 25 μm.Therefore, there is an urgent need to develop novel scalable manufacturing techniques to produce high-performance ASSBs.
Additive manufacturing or 3D printing is a technique to fabricate complex 3D objects layer by layer.3D printing technologies have been widely applied in diverse areas such as biomedicine, [33] food, [34] engineering, [35] electronics, [36] and electrochemical energy storage [37] because of their ability to build complex shapes with greater flexibility and precision.Printing-based technologies such as screen printing [38][39][40] have been investigated in battery fabrication.In recent years, 3D printing has also been utilized to manufacture energy devices such as batteries and DOI: 10.1002/adem.202300953All-solid-state battery (ASSB) technology has emerged as a promising solution for developing safe and high-energy-density power sources.However, the pronounced interfacial charge transfer resistance between the electrode and the solid electrolyte continues to be a central obstacle in contemporary ASSBs.This work demonstrates the first approach to printing ASSBs using aerosol jet printing technology.A composite cathode, composed of active materials, binder polymer, and conductive filler, is printed onto the current collector.Subsequently, a solventless superionic conducting solid polymer electrolyte is printed on the cathode to form a seamless interface between the electrode and the electrolyte, resulting in a 3D-printed all-solid-state lithium-ion battery.The active material in the cathode (lithium iron phosphate, LFP) achieves a loading of %10 mg cm À2 , while the solid polymer electrolyte layer maintains a thickness of a mere 24 μm.Under ambient conditions (30 °C), the half-cell ASSB exhibits a specific capacity of over 130 mAh g À1 at 0.05 C. Advanced aerosol printed cells with a porous membrane, which allows the batteries to be safely cycled at higher temperature (60 °C), exhibit fast charging/discharging rates.These batteries are capable of cycling at a 0.3 C rate, delivering a specific capacity surpassing 160 mAh g À1 .
[43][44][45][46][47][48] Compared with the traditional lithium battery manufacturing techniques, 3D printing technologies have shown some advantages [43,49,50] : 1) controlling the structure and thickness of the electrodes; 2) manufacturing solid electrolytes and electrodes with structural stability and safer operation; 3) low cost and ease of technology; and 4) capacity of printing assembled devices with direct integration of packaging.The 3D-printed electrode can be fabricated with a larger surface area and high areal loading density, providing a shorter ion transport distance and improving the battery's energy density and power density.At the same time, 3D printing technologies can be automated processes entirely, potentially reducing battery manufacturing costs.
Due to the versatile methods of 3D printing, the reported 3Dprinted batteries were fabricated by different approaches.Direct ink writing (DIW) is the most popular method used in the 3D printed battery.It has been extensively used for fabricating electrode materials with high areal capacities.In 2013, a 3D-printed Li-ion microbattery composed of anode and cathode microarrays in a submillimeter scale was demonstrated, [51] showing an areal capacity for LiFePO 4 (LFP) half cell of 2.0 mAh cm À2 and LFP/ LTO full cell of 1.5 mAh cm À2 at 1 C.The fabrication method was improved to print LFP/LTO microbattery fully, including the packing frame and separators with an areal capacity of up to 4.45 mAh cm À2 at a current density of 0.14 mA cm À2 . [52]In 2016, a similar work reported a printed full cell LFP/LTO ASSB using graphene oxide-based conducting fillers and a solid-state electrolyte consisting of PVDF-co-HFP and Al 2 O 3 nanoparticles. [53]The device exhibited an average specific capacity of 100 mAh g À at a current density of 50 mA g À1 .This method was further developed to create flexible all-fiber LIBs. [54]More recently, a similar method was used to create high-performance microbatteries with improved cyclability and is suitable for rollto-roll manufacturing. [55,56]59] Stereolithography method was used to fabricate the bicontinuous ceramic electrolyte network to improve the ion transport in the solid-state batteries. [44]Photocrosslinkable polymer electrolyte was printed with the same method to prepare all-solid-state LIBs. [45]Polymer electrolytes and composite electrolytes were also recently printed by the fused deposition modeling (FDM) method. [46,47]ost reported 3D-printed batteries are microbatteries, where the structure of the battery is created with precise control of the printing process.However, those delicate processes are difficult to apply beyond the miniature batteries.Among all 3D printing techniques, material jetting technology makes it suitable to address the fabrication issues for the bulk configuration of printed solid-state batteries.First, material jetting is less restricted by the viscosity limitation as compared to the ink writing method.At the same time, it is possible to provide intimate contact between the electrode and its layers, presenting an advantage over dry processes like FDM.Such a unique property makes the materials jetting technology suitable for all types of solid electrolytes, including ceramics, polymers, or hybrids.Second, material jetting technology can easily accommodate multimaterial deposition, enabling printing electrode and electrolyte materials in different ratios with spatial accuracy in a single print.Third, this process can control micro-to macroscale deposition and tune the thickness between the submicrometer and macroscales without using a mask, rendering it suitable for large-scale fabrication.These factors give material jetting superior to other 3D printing methods for making large batteries, such as DIW and FDM.Material jetting can be divided into inkjet printing (IJP) and aerosol jet printing (AJP).IJP has been shown to produce thin cathodes with high specific capacity.In an early investigation, a 1.2 μm-thick inkjet-printed LiCoO 2 cathode was prepared and exhibited a specific capacity of 120 mAh g À1 at 180 μA cm À2 . [60]In 2015, a study of thin (4 μm) inkjet-printed LFP for microbattery showed a specific capacity of 80 mAh g À1 at 9 C. [61] In another work, a thin (%5 μm) inkjet-printed LFP showed a specific capacity of 160 mAh g À1 at 0.1 C. [62] More recently, a 9 μm-thick LiMn 0.21 Fe 0.79 PO 4 cathode was prepared to obtain a specific capacity of 150 mAh g À1 at a rate of 10 C. [63] AJP has been proved to be more suitable for thick electrolyte and electrode preparation.The first demonstration of the AJP method in battery electrodes was in 2018. [64]In this study, microlattice electrodes with porous solid truss members were prepared by AJP.Previous work has focused on the AJP printed thick electrodes with practical mass loading and demonstrated that AJP could print a thick (170 μm) LFP cathode with micronmeter-scale channels.The half-cell with AJP printed electrode and liquid electrolyte showed a specific capacity of 151 mAh g À1 at a C/15 rate and an areal capacity of 2.5 mAh cm À2 . [65,66]In another study; the AJP technique was demonstrated for fabricating composite electrodes via printing Li-ion conducting solid polymer composite electrolyte on top tape cast cathode.The printed electrolyte, PEO/LiDFOB/alumina (EO:Li = 10:1), showed ionic conductivity >10 À5 S cm À1 at 45 °C.For the half-cell batteries, the printed electrolyte can be cycled at C/15 with a specific capacity >85 mAh g À at 45 °C. [67]his work presents the first aerosol jet-printed composite cathode for a lithium metal battery.The cathode materials were first printed on the current collector by AJP.Then, solvent-free, crosslinkable solid polymer electrolyte (SPE) was printed on top of an aerosol jet printed cathode to form a composite cathode with defined thin electrolyte film.The SPE materials are based on our previous report of a poly(ethylene glycol) diacrylate (PEGDA)based, superionic conductive polymer electrolyte, which exhibits excellent conductivity (>10 À3 S cm À1 at 30 °C) and good electrochemical stability. [68,69]At the relatively high mass loading (%10 mg cm À2 LFP), the composite electrode achieved a specific capacity of >160 mAh g À1 (areal capacity >1.6 mAh cm À2 ) at 60 °C at a 0.3 C rate.Even at room temperature (30 °C), the battery can deliver a specific capacity of 135 mAh g À1 at 0.05 C.This result demonstrated a viable way to prepare ASSBs using AJP techniques.

Electrode and Electrolyte Preparation
The schematic diagram of the aerosol jet printer is shown in Figure 1a.The aerosol jet process uses aerodynamics to deposit inks precisely onto the substrates.The ink is placed into an atomizer, creating a dense mist of loaded droplets between 2 and 5 μm in diameter. [70,71]The aerosol mist moves to the printer head, where a sheath gas focuses it.As the sheath gas and aerosol pass through the nozzle, they accelerate and gather into a tight stream of droplets that flows inside the sheath gas.The resulting highvelocity particle stream remains focused as it travels from the nozzle to the substrate over a distance of 2-10 mm.A sheath gas collimates it for improved print resolution. [72,73]The aerosol jet printer can make patterns without masks or stencils.[76] Figure 1b shows the aerosolprinting procedures investigated in this study.First, LiFePO 4 cathode materials with high mass loading (%10 mg cm À2 ) were aerosol jet printed.Then the cathode material was calendared to a porosity of 60% before SPE was printed on top.Second, the SPE precursor was deposited for 20-30 passes on top of the cathode layer and then UV crosslinked to form a solid composite electrode.The composite electrode can be laminated with lithium metal anode to form half cells.In some half cells, an additional SPE precursor-soaked Solupor solid membrane was used and solidified before lithium metal lamination.Detailed procedures are described in the Experimental Section.
Figure 2 shows the top surface images of the electrodes after different printing steps.As shown in Figure 2a, the printed LFP cathode has high porosity and a rough surface.The sheath gas pressure can control the morphology of the printed cathode.During each printing pass, printed aerosol droplets can undergo partial-to-near-complete drying before the printer head returns for the sequential pass, as the solvent evaporates during the process.When printing these partially dried aerosol droplets, they tend to cling to each other and dry completely, rather than clumping together and forming a wet ink film. [77]After calendaring (Figure 2b), the surface of LFP was flat, but the porous structure remained.The porosity of the electrode film can be controlled by calendaring parameters, and the film shown in Figure 2b has a porosity of %60%. Figure 2c shows the scanning electron microscope (SEM) image of the electrode after SPE printing and crosslinking (10 passes).Most of the pores are filled with SPE material.Unlike the cathode ink, the SPE precursor has no evaporable solvent.The prepolymer PEGDA is liquid at room temperature but will crosslink rather than evaporate when the temperature increases.Therefore, aerosol printing of SPE precursor will form a uniform wet film, and the liquid SPE precursor can infiltrate into the porous cathode until it is crosslinked.
Figure 2d shows the SPE printing/crosslinking after 20 passes, the surface of the composite electrode is smooth due to the formation of a smooth SPE top layer.Additional passes can be applied depending on the desired thickness of SPE formed on top of the cathode.Figure S5, Supporting Information, depicts an optical image showing a printed electrode/electrolyte assembly.The solid electrode and electrolyte assembly disk can be punched out for cell fabrication.
The crosslinked composite cathode was further evaluated by cross-section SEM to elucidate the structure formed after printing and crosslinking.The preparation of the cross-section sample was described in the Experimental Section. Figure 3a shows the SEM image of the cross section of the composite electrode.The current collector, LFP layer, and SPE are indicated in Figure 3a.EDX scans were carried out in strips of about 20 μm thick, as shown in Figure 3a.In Figure 3b, the phosphorus and carbon weight ratios are selected to present the cathode and SPE ratios, respectively.At the bottom part of the electrode (0-20 μm), the carbon wt% is significantly higher than that of the phosphorus.This could be ascribed as the contribution of the carbon-coated aluminum current collector, where a significant amount of carbon existed.Starting from the second strip (20-40 μm), the weight ratio of phosphorus became dominant.There is no noticeable change in the phosphorus-carbon ratio between 20 and 80 μm, indicating a homogeneous distribution of SPE  in the porous LFP cathode film.From %80 μm, the carbon weight ratio increases due to approaching the electrolyte film's top surface.The last strip (100-120 μm) exhibited a much higher weight ratio of carbon over phosphorus, suggesting that the top surface of the composite electrode was covered by polymer electrolyte.Figure 3c,d shows the elemental mapping of carbon and phosphorus, respectfully.The gradient of carbon ad phosphorus is consistent with the observation in Figure 3b.Based on the EDX results, the thickness of the pure SPE top layer is about 25 μm in this sample.

Cell Testing at Room Temperature
The composites electrode was laminated with lithium metal to form half-cell ASSB (details of cell fabrication are described in Experimental Section).The EIS of the composite electrode half cell was conducted under 30 °C and the results are shown in Figure S1, Supporting Information.The EIS revealed a contact resistance of 34 Ω and a charge transfer resistance of around 1.2 kΩ in the coin cell.The results are similar to previous work where the electrolyte was infiltrated into the cathode, [69] suggesting a good interface between the cathode and the electrolyte.To start the long cycling test, the cells were charged and discharged at an electrochemical window of 2.5-3.6 V (vs Li þ /Li) at 0.05 C for the first five cycles to achieve a stable interface layer.To achieve full capacity, the cells were cycled between 2.5 and 3.65 V (vs Li þ /Li) for the subsequent cycles at 0.05 C to 30 °C.A gradual decrease in specific capacity is observed from 113 to 85 mAh g À1 with a capacity retention of 75%.The average Coulombic efficiency is 99.5%.The charge/discharge profiles are plotted in Figure 4b.Considering the mass loading of 9.6 mg cm À2 , the first discharge reached an areal capacity of 1.08 mAh cm À2 .The charge/discharge profiles exhibited a small overpotential around 121.5 mV, gradually increasing to 149.4 mV after 30 cycles.The increase of the overpotential may be caused by the increase in resistance due to possible side reactions on the lithium metal anode.The ratability test of the cell under 30 °C was carried out.As shown in Figure S2, Supporting Information, even though the discharge specific capacity of a cell can reach 131.4 mAh g À1 (areal capacity of 1.37 mAh cm À2 ) at 0.05 C, the specific capacity dropped significantly at a higher rate, exhibiting %80 mAh g À1 at 0.1 C. The decrease of the specific capacity at a high rate can be attributed to the thick electrode (%10 mg cm À2 ) explored in this work, in which case polarization effect limited the discharge capacity at high rates.Therefore, the cells were further tested under a higher temperature (60 °C) to evaluate the high rate capability of the ASSB.

Cell Testing at Elevated Temperature
In order to achieve the practical rate of ASSB (>0.3 C), the high-mass-loading cathode-based ASSB cells were tested under elevated temperature of 60 °C.However, the initial investigation of coin cells with thin solid electrolytes (<30 μm) was not successful due to the short circuit of cells after several cycles.Possible reasons could be the dimensional stability of the SPE at high temperatures and the hazardous lithium dendrite formation.Indeed, the soft short-circuit phenomenon becomes apparent even at lower temperatures when the cycling period is extended.As illustrated in Figure S6, Supporting Information, a typical charging/discharging profile of a degraded cell after prolonged cycling is depicted.As in the charge curve, there are oscillations beyond %60 mAh g À1 .This phenomenon arises from the reduced distance between the cathode and anode due to the protrusion of dendrites, which in turn reduces the overpotential and leads to a descent in the charging plateau.Due to this decreased overpotential, the cell can become overcharged, surpassing its theoretical specific capacity and thus hastening the battery's deterioration.To secure the cell structure for cycling, a porous membrane was integrated with the SPE, as shown in Figure 1b.A porous membrane (Solupor, thickness of 20 μm, porosity of 83%) was first soaked in the SPE precursor and subsequently crosslinked onto the printed SPE/cathode.The total thickness of electrolyte layer is around 70 μm (the soaked membrane and the SPE printed on the composite electrode).This reinforced composite electrolyte and cathode were used for cell fabrication.Figure S3, Supporting Information, shows the EIS result of the reinforced composite electrode half-cell obtained under 30 °C.The EIS revealed a contact resistance of 74 Ω and a charge transfer resistance of around 1.4 kΩ.The contact resistance increased compared to that of membrane-free cells (Figure S1, Supporting Information, 34 Ω), while there is no significant increase in the charge transfer resistance.The testing results of the membrane-reinforced ASSB are summarized in Figure 5. Figure 5a shows ratability tests of cells with the reinforced composite electrode under 60 °C while Figure 5b shows the charge/ discharge profiles of corresponding cycles.The cells were charged and discharged at an electrochemical window of 2.5-3.6 V (vs Li þ /Li) at 0.1 C, 2.5-3.65 V (vs Liþ/Li) at 0.3 C, 2.5-3.7 V (vs Liþ/Li) at 0.5 C, and 2.5-3.8V (vs Liþ/Li) at 1 C, respectively.It is worth noting that the overpotential of the cells changed significantly under different current densities.Therefore, the cut-off voltage of the cells was controlled to achieve the same state of charge without unfavorable overcharging.The battery exhibited reversible specific capacities of 163, 138, 126, 121, and 154 mAh g À1 at corresponding current densities of 0.1, 0.3, 0.5, 1, and 0.1 C (based on 1 C = 170 mAh g À1 ).Considering the mass loading of 9.8 mg cm À2 , it reached the areal capacity of 1.6 mAh cm À2 .The rate and specific capacity of the ASSB are compared with the state-of-the-art printed electrode.(Table S1, Supporting Information) As shown in Table S1, Supporting Information, most reports of printed LIBs utilized printed electrodes with infiltrated liquid electrolytes.The report of fully printed electrode and electrolyte assembly is very rare.In addition, the ASSB cell fabricated in this work exhibited competing performance with those liquid electrolyte-based cells.It is worth to note that the loading of active materials in a 3D-printed electrode is defined in two different ways in the literature, as shown in Figure S4, Supporting Information.In many references, the electrodes are printed as parallel vertical walls (Figure S4a, Supporting Information).In these instances, the loading of active materials is usually calculated by multiple printed electrodes per unit area.Therefore, it is different from the definition of active materials loading in conventional cast electrodes, where the thickness of a single layer of the electrode is taken into account.When the electrode is printed in a horizontal direction (Figure S4b, Supporting Information), the loading of active materials in one layer of the electrode is comparable to that of a conventional cast electrode.Table S1, Supporting Information, clearly shows that all the ultrahighactive-materials loading electrodes are based on such a vertical direction printing procedure, due to varying definitions of "active materials loading".Reports of 3D-printed electrodes with active materials loading approaching 10 mg cm À2 on single electrode (horizontal printing direction) are rare, especially in the context of dense and all-solid-state electrodes.Taking both active materials loading and specific capacity into account, the AJP-printed ASSB presented in this study represents one of the best performances.
The cells underwent further testing for long-term cycling at 0.3 C under 60 °C.As shown in Figure 5c,d, the cells' specific capacity in the initial five cycles is between 160 and 170 mAh g À1 .The specific capacity then gradually decreases over the subsequent 40 cycles (Figure 5c) to 137 mAh g À1 .The overpotential of the cells increased in the initial few cycles and then stabilized (Figure 5d).The phenomenon may be attributed to the interface layer formed between the electrode and electrolyte.Given this observation, we fabricated the cell and maintained it in an uncharged state for approximately four weeks.These "aged" cells were then used in long-term cycling.As shown in Figure 5e, the aged cell exhibited excellent stability.The batteries were tested at 0.3 C for 150 cycles.The average Coulombic efficiency was 99.98%, and the capacity retention reached 97.4% after 150 cycles.The results suggest that an appropriate initiation process could significantly improve the cycling performance of printed ASSB.

Conclusion
In conclusion, a solid-state electrolyte/electrode composite was successfully fabricated using an aerosol jet printer.We developed the procedures to print LiFePO 4 cathode material with controlled porosity.Building upon our previous work of cross-linkable solid-state polymer electrolyte materials, we developed a process to print solvent-free polymer electrolytes onto the printed cathode, forming solid-state composite electrolyte/cathodes through UV light-initiated crosslinking.The aerosol jet printer methodology has enabled the achievement of a high mass-loading composite cathode with a uniform top layer SPE as thin as %20 μm.
The aerosol jet-printed SPE can also penetrate through the printed porous cathode, resulting in smooth interfaces between cathode and electrolyte.Under relatively high mass loading (9.8 mg cm À2 ), the aerosol jet-printed composite electrode exhibited a high specific capacity >130 mAh g À1 at 30 °C (0.05 C) and >160 mAh g À1 at 60 °C (0.3 C).The cell performance at 60 °C is close to the theoretical capacity of 170 mAh g À1 , which indicates that the polymer electrolyte ideally penetrated the cathode body to form a low-resistance electrode/electrolyte interface.In addition, the long-cycling test yielded a Coulombic efficiency of 99.98% and capacity retention of 97.4% after 150 cycles at 0.3 C. Further, the AJP method offers a broader viscosity tolerance range and is capable of printing various types of solid-state electrolytes, including those containing insoluble inorganic particles.This result provides a promising direction for using AJP techniques in the preparation of high-performance, ASSBs for future applications.

Experimental Section
Cathode Ink Formulation and Printing: The LiFePO 4 inks were formulated using LiFePO 4 powder (MTI, Inc.) as the active material, Carbon Super P (MTI, Inc.), and Kynar 1800 (Arkema) with a weight ratio of LFP:CB:PVDF (96:2:2).The solid materials were dispersed in n-methyl-2-pyrrolidone to form the printing solution with a solid to liquid mass ratio of about 1:3.All printing was performed in a dry room using an Optomec Aerosol Jet 200 printer with the procedure developed elsewhere. [65]he distance from the jet and printing plate on a carbon-coated aluminum substrate (MTI, Inc.) was set to 10 mm.The temperature of the substrate was held constant at 50 °C.The temperature of the ink was 21 °C during printing with constant stirring.The flow rate of the slurry ink was set to %9 mg min À1 .The cathode materials with mass loading of %10 mg cm À2 were achieved by 80 passes of cathode ink to a 35 Â 170 mm 2 area.After printing, the sample was placed in a vacuum oven and dried overnight at 90 °C.Later the cathode material was calendared to a porosity of 60% before SPE printing.
SPE Ink Formulation and Printing: The SPE precursor was prepared by mixing succinonitrile (C 4 H 4 N 2 , TCI, 99%), poly(ethylene glycol) diacrylate (PEGDA, Sigma Aldrich, 99%) with a molecular weight of 700 g mol À1 , lithium bis(oxalate)borate (LiBOB, SigmaAldrich), lithium bis(trifluoromethanesulphonyl)imide (LiTFSI, Matrix Scientific), photoinitiator bis(2,4,6trimethyl benzoyl)-phenyl phosphine oxide (Irgacure 819, Sigma Aldrich, 97%), and fluoroethylene carbonate (FEC, Sigma Aldrich 99%). [69]he mass ratio of components in the SPE was Succinonitrile:PEGDA: LITFSI (40:25:35).LiBOB was added to the SPE (with the LiTFSI:LiBOB molar ratio 1:0.085) to improve the electrochemical stability. [78]FEC (5 wt%) was added to improve the stability of the lithium metal anode.The photoinitiator was added to the SPE (with 1 wt%) before printing.After the SPE precursor was prepared, it was used within 36 h in the aerosol jet printer inside the dry room.The precursor SPE was printed on the printed cathode, whose temperature was held constant at 50 °C during the printing.The temperature of the ink was held at 40 °C during printing under constant stirring.The deposition rate was %5 mg min À1 .The SPE precursor was printed at %25 passes on top of the cathode layer and then UV (320 nm) crosslinked.For the UV crosslinking process, the SPE precursor-coated LFP was removed from the printer and sandwiched between 2 glass slides; then, UV light was applied for 2 min to solidify the electrolyte.This procedure yielded %30 μm-thick pure SPE film on top of the filled cathode.
Battery Fabrication and Characterization: The printed SPE and cathode were laid in a coin cell case for membrane-free half cells.A lithium foil (250 μm) was laminated on top of the composite cathode.Spacer and spring were then added, and the cell was crimped.All cells were initialized at 45 °C overnight before testing.For membrane-supported half cells, a treated Solupor membrane was inserted between the composite cathode and lithium metal anode to improve the dimensional stability of the laminated layers.To fabricate the treated Solupor membrane, a Solupor (Lydall, polyethylene membrane with a thickness of 20 μm, porosity of 83%, and Gurley number 1.4 s (50 mL)) membrane was soaked in initiator-free SPE precursor overnight.The membrane then was soaked in SPE precursor with a photoinitiator for 5 min.The soaked membrane was crosslinked to form a solid film with a thickness of around 25 μm.The electrochemical impedance spectroscopy (EIS) (Gamry Instrument 3000) test was conducted within a frequency range of 100 kHz-0.1 Hz with a perturbation potential of 10 mV.The lithium metal batteries were tested by galvanostatic charge/discharge method using the 8 Channel Battery Analyzer (Landt Instruments CT2001A) in isothermal chambers (30 and 60 °C).The first five cycles were performed under a potential window between 2.5 and 3.6 V (vs Li þ /Li) at 0.05 C (1 C = 180 mAh g À1 ), and the following cycles were conducted with a larger potential window of 2.5-3.8V (vs Li þ /Li) at the designed C-rate.
To investigate the cross section of the printed cathode by using energydispersive X-ray spectroscopy (EDX)/SEM (Jeol, JSM-6060), the composite electrode sample was cooled to À60 °C overnight (Tenny Environment Chamber).Then it was cut with scissors to achieve a clear cross-sectional surface.The sample was then mounted on the SEM holder vertically and characterized under 10 kV with a spot size of 25.

Figure 2 .
Figure 2. Schematic diagram of the printing process and corresponding top-view SEM images of a) as-printed LFP, b) printed LFP calendared to %60% porosity, c) electrode after ten SPE printing steps, after UV crosslinking, and d) electrode after 20 SPE printing steps.

Figure 1 .
Figure 1.a) Scheme of the AJP process and b) laminated cathode/electrolyte formation process .

Figure 3 .
Figure 3. a) Cross-section SEM image of the printed electrode material and EDX scan strips.b) Relative weight ratios of phosphorous and carbon elements were measured at different sections of the electrode material.EDX elemental mapping of the c) carbon and d) phosphorous elements.

Figure 4 .
Figure 4. Cell testing of printed ASSB at 30 °C.a) Cycling test of the ASSB at 0.05 C under 30 °C.b) Representative charge/discharge curves of the composite electrode.Cell structure is Li||printed SPE||printed LFP; pure SPE layer is %23 μm thick; cathode mass loading is 9.6 mg cm À2 .

Figure 5 .
Figure 5. a) Rate performance of coin cells with the reinforced composite electrode at 60 °C from 0.1 to 1 C. b) Corresponding charge/discharge profiles of the cells with the reinforced composite electrode at different rates.c) Long cycling test of cells with new reinforced composite electrodes at 0.3 C. d) Representative charge/discharge curves in the first 40 cycles.e) Long cycling performance of "aged" cell with the reinforced composite electrode at 0.3 C under 60 °C.Cathode mass loading is 9.8 mg cm À2 .