A Scalable Dendritic Si‐Clad NiSn Anode via One‐Step Electrodeposition with Ultrahigh Areal Capacity for Micro Lithium‐Ion Battery

High energy density, long cyclability, and enhanced stability in a small footprint achieved through microfabrication are crucial for micro lithium‐ion batteries. Herein, a 3D Si‐clad NiSn anode characterized by a dendritic NiSn network and silicon nanoparticles is proposed. The dendritic network facilitates fast ion/electron transfer and provides expansion space for the silicon, while the uniformly distributed silicon enhances capacity and stability. The anode, scalable to the hundred‐micron scale, is fabricated via one‐step electrodeposition incorporating the dynamic template technique. This technique generates interconnected pores extending from the inner to the outer surface of the anode, facilitating electrolyte penetration and ion transport. As a result, the anodes in the Swagelok cells exhibit an ultrahigh areal capacity of up to 28.2 mAh cm−2 and an enhanced stability of 91% capacity retention after 300 cycles. The dendritic Si‐clad NiSn anode, based on microfabrication, presents an excellent opportunity to advance micro energy systems.


Introduction
Lithium-ion batteries (LIBs) show potential as an energy supply of microsystems due to their high capacity, long cycle life, and lightweight attributes. [1,2]5] Therefore, developing novel designs for micro lithium-ion batteries (μLIBs) is critical, especially in terms of capacity enhancement and microfabrication compatibility.
Furthermore, advancements in silicon nanoforms and anode configurations are crucial to achieving high capacity and prolonged cyclability in μLIBs.The 3D structure of nano-Si anodes is considered optimal, significantly increasing the specific surface area of the electrode/electrolyte interface. [27,28]For instance, Westover et al. demonstrated graphene-passivated on-chip porous Si arrays with a capacity of 0.1 mAh cm À2 over 10 000 cycles [29] ; Yue et al. proposed Si/Ge 3D micropits with a honeycomb TiN interlayer for μLIB anode, [8] achieving a reversible areal capacity of 0.26 mAh cm À2 at a current density of 0.4 mA cm À2 .However, most 3D designs encounter scalability constraints, as active materials in deeper sites are not fully utilized in thicker anodes, resulting in a capacity that is not proportional to thickness. [30,31]o overcome diffusion limitations and enhance power densities, researchers have concentrated on developing internal pores within thick electrodes to offer additional channels for lithiumion movement.This focus has led to extensive research on 3D electrodes, facilitated by advanced porous engineering.The predominant manufacturing methods are categorized into additive/subtractive manufacturing and templating.However, these methods often involve additional process steps and lack scalability. [32]Recently, electrodeposition using the dynamic hydrogen bubble template (DHBT) method has gained attention for its ability to fabricate scalable interconnected porous structures in situ.The formation of hydrogen bubbles on the substrate surface occurs through the reduction of H þ ions and progresses through three distinct stages: nucleation, growth, and detachment. [33,34]Concurrently, metal cations are deposited using the hydrogen bubbles as a dynamic template, leading to the formation of a porous network.The DHBT method is notable for its rapid and straightforward production of electrodes with high specific surface areas and controlled morphologies, offering significant potential for energy storage devices. [35,36]n this article, we report a scalable dendritic Si-clad NiSn anode for μLIBs.The high capacity and excellent stability of this anode are attributed to the Si-clad NiSn, featuring a dendritic NiSn network that facilitates fast ion/electron transfer and provides expansion space for silicon nanoparticles.The uniformly distributed silicon enhances both capacity and stability.The anode, scalable to a hundred-micron scale, is fabricated through a one-step electrodeposition process that incorporates the dynamic template technique.This method generates interconnected pores extending from the inner to the outer surface of the thick anode, thereby enhancing electrolyte penetration and ion transport.As a result, the anodes in Swagelok cells exhibit ultrahigh areal capacity of up to 28.2 mAh cm À2 and advanced stability, maintaining 91% capacity retention after 300 cycles.

Anode Design and Fabrication
The 3D anode, comprising fractal dendrites of NiSn clad with silicon nanoparticles (SiNPs), is proposed, as shown in Figure 1a.To counter the low conductivity of silicon and its volume effect, the NiSn alloy functions as a metallic framework, enhancing electrical conductivity and leveraging the lithium storage properties of Sn.It also buffers volume expansion stress and particle aggregation during repeated lithiation and delithiation processes.In addition, to scale up the thickness of the anode while avoiding capacity limitations due to liquid phase impedance and polarization, we designed interconnected micropores with the target size of tens of microns (30-50 μm) to serve as channels for electrolyte penetration and ion diffusion, [31] as illustrated in Figure 1b.This architecture results from NiSn and Si composite electroplating.The ion-diffusion-limited state at high currents during NiSn nucleation and growth leads to fractal dendritic deposits, as shown in Figure 1c. [37]Simultaneously, overpotential and hydrodynamic conditions influence the uniform cladding of SiNPs.Moreover, the micropores are created using the DHBT method, as illustrated in Figure 1d.In this process, Ni 2þ , Sn 2þ , and H þ are reduced by gaining electrons at the cathode, allowing NiSn and SiNPs to be deposited concurrently with the nucleation, growth, and detachment of hydrogen bubbles.
The prepared composite nanomaterials feature SiNPs clad on NiSn dendrites, as illustrated in Figure 1e and S1, Supporting Information.The abundant arrangement of nanopores facilitates the expansion of the SiNPs and provides a larger specific surface area (Figure 1f ), thus offering more reaction sites. [38]The continuous evolution of bubbles serves as a dynamic template, [33,34] forming interpenetrating channel configurations, as evidenced by the top view of the electrode morphology in Figure 1g.Compared to alternative deposition techniques, such as physical vapor deposition or chemical vapor deposition, the one-step electrodeposition with DHBT stands out for its remarkable speed, achieving a deposition rate of several microns per second for the 3D dendritic Si-clad NiSn anode.The 5 min electrodeposition process resulted in an anode with a thickness of 308 μm, as confirmed by the cross-sectional scanning electron microscopy (SEM) image depicted in Figure 1h.

Dendritic Si-Clad NiSn Anode Characterization
We characterized the elemental composition and nanoscale distribution of the anode to investigate the characteristics of NiSn dendrites clad with SiNPs.Transmission electron microscopy (TEM) analyses confirmed the angular dendritic and spherical frames for NiSn and SiNPs, respectively.The interstitial spacing within the dendritic network was several nanometers, as shown in  emerged and remained consistent through subsequent discharge processes.Based on relevant literature, [39][40][41][42][43] we deduced the lithium storage mechanism of the NiSn alloy during chargedischarge cycles, involving an initial activation step in the electrochemical process of the Ni-Sn intermetallic compound, represented as: followed by the main reversible electrochemical process: Although the initial activation step was irreversible, the subsequent steps were, in principle, reversible and signify the steady-state electrochemical operation of the electrode.
The mass fractions of Si, Sn, and Ni were determined through inductively coupled plasma optical emission spectrometry (ICP-OES).The analysis revealed that the mass fractions were 27.1 wt% for Si, 42.9 wt% for Sn, and 20.9 wt% for Ni, respectively, as shown in the inset of Figure 2d.Additionally, we evaluated the optimization of structural design using a traditional slurry-coated anode with the exact proportions and loading masses, referred to as the slurry NiSn/Si anode as a control group (Figure S3, Supporting Information).
The X-ray photoelectron spectrometry (XPS) of the anode material was used to determine the elemental species and chemical states of the Si-clad NiSn anode, as demonstrated in Figure 2e-g.Figure 2e illustrates the Ni 2p spectrum, where the peaks at 856.5 and 874.0 eV corresponded to Ni 2þ 2p 3/2 and 2p 1/2 states, respectively.The peaks at 862.0 and 879.7 eV were identified as satellite peaks. [44,45]The peaks at 852.4 and 869.6 eV were indicative of the metallic state of Ni. [46,47] The Sn 3d spectrum, as depicted in Figure 2f, showed peaks at 484.5 eV (Sn 3d 5/2) and 492.9 eV (Sn 3d 3/2 ) related to metallic Sn.The peaks at 486.0, 486.7, 494.4,and 495.1 eV were attributed to Sn 3d 3/2 and Sn 3d 5/2 of Sn 2þ and Sn 4þ , arising from the oxidation of Sn, which indicated that the NiSn surface undergoes inevitable oxidation in air. [41,48]Furthermore, in the highresolution Si 2p XPS spectrum (Figure 2g), peaks at binding energies of 98.8 and 99.5 eV corresponded to Si 2p 1/2 and Si 2p 3/2 .The fitting peaks from 100.3 to 103.2 eV were ascribed to the Si-O bond of SiOx, derived from the inevitable oxidation of monatomic Si. [49,50]

Electrochemical Performance
The electrochemical properties of the Si-clad NiSn anode were evaluated using cyclic voltammetry (CV) and galvanostatic charge/discharge experiments.The CV testing was carried out from 0.01 to 1.5 V at a scan rate of 0.1 mV s À1 .Two irreversible broad reduction peaks at 0.4-0.6 and 0.7-1.2V were observed during the first cathodic scan, primarily attributed to the formation of the solid electrolyte interface (SEI) and the reduction of oxides on the surface of Sn and SiNPs, [51] as demonstrated in Figure 3a.The subsequent cathodic scans displayed a reduction peak at 0.2 V, corresponding to the conversion of Si to Li x Si.In comparison, the oxidation peak at 0.52 V in the anodic scan was related to the delithiation reaction of Li x Si. [52] Meanwhile, the reduction peak at 0.62 V was associated with the lithiation of Sn, and the oxidation peaks between 0.7 and 0.85 V were related to the delithiation of Li x Sn. [53,54] The Si-clad NiSn anode with a mass loading of 35 mg cm À2 was tested in galvanostatic charge/ discharge experiments to determine the areal capacity.At a current density of 0.5 mA cm À2 , an ultrahigh areal capacity of 28.2 mAh cm À2 and an initial Coulombic efficiency (CE) of 79.4% were observed (Figure 3b).At a current density of 2 mA cm À2 , an areal capacity of 17.39 mAh cm À2 and a capacity retention rate of 93.2% were observed after 100 cycles.
The diminishing marginal effect of increasing the anode thickness to improve the mass loading and enhance the areal capacity is a challenge for traditional μLIBs.We investigated the capacity and capacity retention of Si-clad NiSn anodes with varying mass loadings, as depicted in Figure 3c.The anodes were precycled for five cycles at a constant current of 0.8 mA cm À2 and subsequently charged/discharged at a current of 2 mA cm À2 .The initial capacities of the anodes with mass loadings of 15, 25, 35, and 40 mg cm À2 were 6.19, 11.35, 17.39, and 20.06 mAh cm À2 , respectively.After 100 cycles, their capacities only marginally decreased to 5.99, 10.68, 16.21, and 17.16 mAh cm À2 , with capacity retention of 96.8%, 94.1%, 93.2%, and 85.5%, respectively.Furthermore, the areal capacity was proportional to the mass loading of the active material at various current densities, as shown in Figure 3d.The micron-scale pores in the thick anode reduced the Li-ion diffusion distance in the composite framework and decreased the liquid phase resistance.This configuration served to mitigate the increase in series resistance at the electrode-electrolyte interface and averts anode collapse caused by the increased thickness.Therefore, ion transport channels that interpenetrate within the thick anode effectively overcame transport restrictions and enabled higher areal capacities.The absence of mass loading limitations, even at high mass loadings of 40 mg cm À2 and high currents of 4 mA cm À2 , suggests the potential to further increase mass loading to achieve even higher areal capacities (>25 mAh cm À2 ), surpassing those of current anode technologies.These results demonstrate that Si-clad NiSn anodes exhibit exceptional capacity utilization.
The rate performances of the Si-clad NiSn anode and traditional slurry NiSn/Si anode were evaluated to assess the charge/discharge capacities.Anodes with a mass loading of 25 mg cm À2 were analyzed under various charge/discharge rates, as depicted in Figure 3e.As the current densities increased from 1 mA cm À2 to 2, 3, and 5 mA cm À2 , the capacities of the Si-clad NiSn anode gradually decreased from 8.5 mAh cm À2 to 7.3, 6.3, and 4.7 mAh cm À2 , respectively.When the areal current density returned to 1 mA cm À2 , the capacity recovered to 7.9 mAh cm À2 , achieving a capacity recovery of 92.9%.The capacity results demonstrate both stability and high reversibility throughout the cycling process.In contrast, the capacities of the slurry NiSn/Si anode decreased significantly from 9.8 mAh cm À2 to 8.8, 5.5, and 2.8 mAh cm À2 at the same current densities.This decline illustrates that conventional slurry thick anodes, with highly tortuous paths from the top surface to the interior, pose a significant barrier to ion transport at high charge and discharge rates. [55]As a result of the tortuous paths for ion transport, the accessibility of Li-ion decreased and a sharp decline in capacity was observed.Moreover, the capacity of the slurry NiSn/Si anode failed to recover when the areal current density returned to 1 mA cm À2 , indicating that high currents cause irreversible damage to the internal network of the anode.Notably, the slurry NiSn/Si exhibited a higher specific capacity in the initial cycles under low current conditions.This higher capacity in the initial cycles can be attributed to several factors.First, the dense slurry anodes, processed through milling mixing and rolling, exhibited a more uniform distribution of active and conductive materials, contributing to the overall capacity.Second, the larger specific surface area of the porous Si-clad NiSn anodes led to the formation of the SEI layer during the initial cycles, resulting in lower initial capacity.In contrast, the interface between the slurry NiSn/Si anode and the electrolyte was more stable during initial cycles, leading to a higher specific capacity.Additionally, longterm cycling comparisons revealed an initial increase followed by a decrease in the capacity of the porous Si-clad NiSn anode, suggesting a process of enhanced electrolyte penetration and activation during the initial cycles.

Investigation of Cycle Stability
We investigated the long-term cycling stability of the Si-clad NiSn anode.At a current density of 1 mA cm À2 and with a mass loading of 10 mg cm À2 , the anode achieved an areal capacity of 3.6 mAh cm À2 and maintained a capacity retention of up to 91% after 300 cycles, as shown in Figure 4a.In contrast, the slurry NiSn/Si anode exhibited significantly lower capacity retention, maintaining only 22.9% after 300 cycles.These results emphasize the superior long-term cycling stability of the Si-clad NiSn anode, a crucial attribute for practical applications.
During the charge/discharge process, we observed an initial increase in capacity to a maximum, followed by a gradual decline.To understand this change in capacity, we conducted electrochemical impedance and CV analysis, as illustrated in Figure 4b and S5, Supporting Information.The increase in charge transfer resistance after the fifth precycle suggested the formation of the SEI layer and irreversible reactions during initial cycling.Concurrently, the first cathodic scan in the CV test revealed an irreversible broad reduction peak between 0.4 and 1.2 V, principally attributed to the SEI formation and the reduction of surface oxides on Sn or Si nanoparticles. [51]The capacity reaches its maximum after several tens of cycles, accompanied by a decrease in impedance, which indicates maximum activation of active materials and interembedding in Sn and Si, thereby enhancing the transport and storage of Li ions. [38]This trend was paralleled in the CV analyses, where an increase in redox peak intensities was noted as cycling progressed, reaching nearmaximal values after about 50 cycles.Additionally, the initial increase in capacity may also be attributed to the reorganization of crystal structures from the continuous intercalation and deintercalation of lithium ions coupled with the expansion and contraction of Si and Sn.This reorganization could reduce electrochemical impedance and increase overall capacity. [71,72]he modest increase in charge transfer resistance in subsequent cycles signified the stability of the SEI, effective functioning of the charge transfer channels, and resilience of the overall structure.
The Si-clad NiSn anodes were assembled with a lithium iron phosphate (LFP) cathode to demonstrate its practical application in full cells, particularly in scenarios where the total amount of Li ions is limited.Before full-cell testing, the anodes were first cycled with lithium metal in half-cells and LFP cathodes with appropriate loading were prepared.The charge/discharge curves of a typical full cell were cycled at various current densities between 1.9 and 3.4 V, as depicted in Figure 4c.The full cell exhibited an areal capacity of 2.95 mAh cm À2 at a current density of 0.2 mA cm À2 and maintained a capacity retention of 90.7% over 40 cycles, as shown in Figure 4d, demonstrating exceptional capacity and cyclability.
SEM images of the Si-clad NiSn anode materials, both pre-and postcycling, were compared.The precycled anode, incorporating lithium polyacrylic acid (LiPAA) and Super P wrapped around the dendrites to act as binder and conductive additives, is illustrated in Figure 5a,c, and S6, Supporting Information.Postcycling SEM images, as shown in Figure 5b, revealed an increase in anode thickness from 138.6 to 170 μm.The postcycled anode exhibited unchanged morphology of the dendritic structure and intact micron-scale pores even after hundreds of cycles, as seen in Figure 5d-f.Notably, the cut cross-section in Figure 5f revealed SEI growth at the periphery of the dendrites.The internal dendritic NiSn conductive channels remained effective, with most SiNPs retaining structural integrity postcycling.Even the ruptured SiNPs remained encapsulated within the structure, preserving their electrical connectivity and functionality.These observations confirm the anode's high structural stability and integrity during cycling, contributing to its excellent capacity retention.

Discussion
Evaluation of the influence of micro-and nanopores on ion and electron transport is essential to understanding the structural advantages of the thick Si-clad NiSn anode in enhancing charge transport.Utilizing a bottom-up DHBT preparation method, the resulting anode extends in the z-direction by hundreds of microns with increasing electrodeposition time.The bubbles released during the DHBT method undergo deformation and agglomeration during their ascent [73] and serve as dynamic templates to establish different porosity profiles within the bulk structure.The size and distribution of pores in the Si-clad NiSn anode were analyzed using SEM images processed with ImageJ software.The results reveal that the surface pore size enlarges as the thickness increases, a conclusion corroborated by characterizing the change in pores from bottom to top.This characterization utilized X-ray nanocomputed tomography, as detailed in the supplementary material, and is further supported by the pore size distribution histogram presented in Figure S7, Supporting Information.These pores of varying sizes were instrumental in the Si-clad NiSn architecture's efficiency in ion transport. [74]The N 2 adsorption-desorption measurements were conducted to characterize the specific surface area and nanoscale pore size distribution.The resulting isotherm at 77 K exhibited a typical type IV curve with a hysteresis loop, indicating the existence of mesoporous structures, as depicted in Figure 6a.The specific surface area, which provided sites for electrochemical reactions and reduced polarization, was calculated to be 8.98 m 2 g À1 using Brunauer-Emmett-Teller (BET) analysis.The nanopore size distribution, ranging from 5 to 15 nm, facilitated the rapid material transfer and promoted electrochemical reactions, [75,76] as determined by Barrett-Joyner-Halenda analysis and illustrated in the inset of Figure 6a.
Impedance analyses were conducted to investigate performance optimization through structural design.The anodes, assembled with lithium foil, were configured into half-cells for electrochemical impedance spectroscopy (EIS) analysis.Nyquist diagram fitting analysis, based on an equivalent circuit model shown in Figure 6b, revealed lower ohmic resistance in the Si-clad NiSn anode compared to the slurry NiSn/Si anode.This lower resistance indicates that the conductive NiSn dendritic network formed efficient electron transfer channels and reduced internal cell resistance.Furthermore, the Si-clad NiSn anode exhibited a significantly smaller charge transfer resistance (25.6 Ω) compared to the slurry NiSn/Si anode (102.5 Ω).This improvement was primarily due to the optimization of surface morphology and activity by the nanostructure in the Si-clad NiSn anode.Moreover, the lithium-ion diffusion coefficient in the anode, calculated from the Warburg impedance coefficient (slope of Z w vs ω À1/2 curve), highlighted the Si-clad NiSn anode's superior Li-ion diffusion coefficient.This coefficient for the slurry NiSn anode was 5.68 times higher, as illustrated in Figure 6c.
The electrochemical properties of thick, porous electrodes differ significantly from planar electrodes.This is primarily attributed to the increased electrolyte solution resistance in the pores, which intensifies with the distance along the tortuous path to the electrode's depth.Therefore, the transmission line model (TLM) was applied to analyze the ionic resistance in the solution, with additional analyses presented in supplemental material Figure S8, Supporting Information.Nyquist plots of symmetric cells with unlithiated electrodes (0% state of charge (SOC)) depict non-Faraday processes, with both electrodes exhibiting similar 45°slopes in the mid-frequency range (5-100 Hz) and quasivertical lines at low frequencies (<1 Hz).The ionic resistance was determined by fitting the experimental data to the TLM.In this model, the projection length of the 45°slope onto the real axis is equivalent to one-third of the ion resistance in the electrolyte.This relationship is depicted in Figure 6d and reflects the ion resistance of the electrolyte-filled pores within the 3D electrode.The calculated ionic resistance of the Si-clad NiSn anode (108.3Ω) was lower than that of the slurry NiSn/Si anode (234.3Ω).This reduction was attributed to the interconnected channels provided by micron-scale pores in the Si-clad NiSn anode.These channels shorten the Li-ion diffusion distance, enable rapid Li-ion transport along direct paths created by the dynamic template, and prevent severe polarization effects caused by excessive concentration gradients in electrolytes.
The galvanostatic intermittent titration technique (GITT) was employed to evaluate the ion diffusion characteristics during charging and discharging.The Li-ion diffusion coefficient, which significantly influences the rate of Li-ion movement through thick anodes, is illustrated in Figure 6e,f, with the original GITT curves in the insets.For the Si-clad NiSn anode, the calculated transport coefficient was 10 À11 cm 2 s À1 , an order of magnitude higher than that of the slurry NiSn/Si anode.The Li-ion diffusion coefficient versus the SOC curves exhibited the typical "W" shape observed in Si-based anode materials. [77]Notably, the ion transport in the Si-clad NiSn showed improvement when compared to previous studies, where Li-ion diffusion coefficients in modified silicon anodes ranged from 10 À14 to 10 À10 cm 2 s À1 . [78]

Conclusion
We proposed a scalable Si-clad NiSn anode via one-step electrodeposition with ultrahigh areal capacity for μLIBs.The anode features uniformly distributed SiNPs on the dendritic NiSn network, which enhances fast ion/electron channels and provides expansion space.The anodes in the Swagelok cells exhibit an ultrahigh areal capacity of up to 28.2 mAh cm À2 and demonstrate an enhanced stability of 91% capacity retention after 300 cycles.By integrating the dynamic template technique with the one-step electrodeposition process, interconnected pores are generated within the anode.This structural design facilitates electrolyte penetration and ion transport, particularly in thick anodes that extend to hundreds of microns.The scalable dendritic Siclad NiSn anode, applicable to thick electrodes in μLIBs, offers valuable insights for advancing next-generation micro energy systems.

Experimental Section
Fabrication of Si-Clad NiSn Anode: The electrodeposition process utilized DHBTs, with a metallic copper substrate serving as the cathode and inert platinum metal as the anode.The electrodeposition bath (20 mL) consisted of SiNPs (50 mg mL À1 ), NiCl 2 •6H 2 O(0.4 M), SnCl 2 •2H 2 O (0.04 M), and H 2 SO 4 (ranging from 0.1 to 2 M).High electrodeposition current densities, varying between 0.5 and 3 A for different durations, resulted in samples with diverse loading masses.Given the limited mass of the anodes used in our experiments (approximately 50 mg), the concentrations of Ni 2þ , Sn 2þ , H þ , and SiNPs were considered constant throughout the electrodeposition process.The solution composition and electrodeposition parameters critically influence the porosity properties of the electrodes.Therefore, the effects of metal salt concentration, sulfuric acid concentration, electrodeposition current, pulse on-off ratio, additives, and other conditions were extensively explored in prior experiments to determine the optimal preparation conditions.Here, the porous anodes were formed under typical preparation conditions of H 2 SO 4 (0.5 M) and the current density of 1 A cm À2 , denoted as Si-clad NiSn.For comparison, traditionally slurry-coated electrodes with the same proportions and loading masses of Ni, Sn, and Si were referred to as the slurry NiSn/Si group.
Characterization: The morphology and microstructure of the samples were investigated using field-emission SEM (ZEISS Merlin) and TEM (JEM-2100).The cross-sections of electrodes were obtained using focused ion beam SEM (ZEISS Auriga).To characterize the crystal structure and chemical composition of the materials, XRD (D/max-2550), EDS (Zeiss Merlin), and inductively coupled plasma emission spectroscopy (ICP-TEOS, iCAP 6300) were employed.The porous properties of the materials were measured using a specific surface and pore analyzer (BET, Quantachrome NOVA 1000e).
Electrochemical Testing: The fabricated anodes were vacuum-dried in a solution containing 10 wt% LiPAA and carbon black (Super P) for 24 h to achieve conformal encapsulation of the conductive additive and binder within the micron pores.Subsequently, Swagelok cells were encapsulated in a glove box.The electrolyte was 1 M LiPF 6 in ethylene carbonate: diethyl carbonate = 1:1 vol% with 10% fluoroethylene carbonate.Half-cells were assembled using lithium metal foil as the counter electrode, while full cells were prepared employing LFP (LiFePO 4 ) films as the counter electrodes.CV curves were obtained at a scan rate of 0.1 mV s À1 in the potential range of 0.01 to 1.5 V (vs Li/Li þ ).EIS were recorded using a 5 mV AC voltage test over a frequency range from 0.01 Hz to 100 kHz.Galvanostatic chargedischarge tests were conducted using a battery-comprehensive test system (Neware BTS-3000).

Figure 1 .
Figure 1.Design and fabrication of the dendritic Si-clad NiSn anode.a) Dendritic NiSn clad with SiNPs.b) Microinterpenetrating channels for electrolyte penetration and Li-ion transport.c) Dendritic Si-clad NiSn fractals fabricated at high currents.d) One-step electrodeposition based on the DHBT.e) Highresolution SEM of spherical SiNPs clad uniformly in dendritic NiSn.f ) Dendritic NiSn network to increase conductivity and nanopores to provide space for Si expansion.g) Top view of the fabricated anode with interpenetrating channel configurations.h) Cross-section of the anode with a thickness of 308 μm.

Figure 2a .
The lattice distance of 0.324 nm for the spherical SiNPs corresponded to the d-spacing of the (111) plane, as depicted in the high-resolution TEM (HRTEM) image in Figure 2b.The corresponding selected area electron diffraction (SAED) pattern closely matched with the Si (111), (220), and (311) planes.Furthermore, the frame area consisted of Ni 3 Sn 4 and metastable NiSn phases, as the apparent lattice spacing of 0.29 nm validated the (111) plane of Ni 3 Sn 4 , with the SAED pattern indicating the (111) and (À511) planes of Ni 3 Sn 4 .The binding of SiNPs to the dendritic NiSn structure was tight based on TEM observations, resulting in fast electron transport channels and improved electrical conductivity in the Si-based anode.The energy dispersive X-ray spectroscopy (EDS) mappings were utilized to evaluate the elemental distribution of both NiSn and Si components in Figure 2c.It was observed that SiNPs uniformly covered the NiSn structure, enhancing the Si loading and avoiding clustering issues in the nanomaterials.The composition and crystalline structure of the anodes were further analyzed by X-ray diffractometry (XRD), as depicted in Figure 2d.The peaks located at 28.5°, 47.3°, and 56.2°corresponded to the (111), (220), and (311) planes of crystalline Si (JCPDS NO. 27-1402).The (111), (202), and (À511) planes of Ni 3 Sn 4 (JCPDS NO. 04-0845) were discernible at 30.3°, 42.0°, and 44.0°, respectively, with metastable NiSn (JCPDS NO. 26-1289) peaks emerging at 42.6°and 46.7°.These results confirm the stability of the crystalline phase of NiSn produced by electrodeposition and the preservation of SiNPs properties during fabrication.In addition, XRD characterization of the anode at various charge-discharge stages, including before cycling, after initial lithiation, upon reaching the first discharge voltage plateau, and after complete delithiation, were shown in Figure S2, Supporting Information.As the anode progressed through charge-discharge stages, the characteristic peaks of silicon, Ni 3 Sn 4 , and NiSn x diminished, while peaks indicative of Ni

Figure 2 .
Figure 2. Characterization of the dendritic Si-clad NiSn anode.a) TEM image distinguishes the angular dendritic frame as NiSn and the spherical shape as SiNPs.b) HRTEM image with insets of the corresponding SAED of NiSn and Si.c) TEM and EDS elemental mapping images demonstrated that Si is uniformly covered on the NiSn network.d) XRD analysis on composition and crystalline structure, with ICP-OES in the inset confirmed mass fractions of 27.1, 42.9, and 20.9 wt% for Si, Sn, and Ni.e-g) XPS characterization of the Si-clad NiSn anode.

Figure 3 .
Figure 3. Electrochemical performance.a) CV curve of the Si-clad NiSn anodes at 0.1 mV s À1 scan rate.b) Constant current charge/discharge curves with a mass loading of 35 mg cm À2 achieve an ultra-high specific capacity of 28.2 mAh cm À2 at the current density of 0.5 mA cm À2 .c) Cycling performances for different mass loadings between 15 and 40 mg cm À2 .d) Correlation between areal capacity and mass loading for Si-clad NiSn anodes at different current densities: the capacity can be adjusted proportionally to the mass.e) Comparison of the rate performance between Si-clad NiSn anode and slurry NiSn/Si anode.f ) The comparison of areal performance metrics of Si-clad NiSn anode with other reported electrodes.

Figure 4 .
Figure 4. Cycling stability and full-cell performance.a) Long-term cycling stability of the anodes with capacity retention of 91% after 300 cycles.b) EIS at critical nodes for long-term cycling.c) Voltage-capacity curve profiles at different current densities for full cells made by pairing Si-clad NiSn anodes with LFP cathodes.d) Cycling performance of full cells.

Figure 5 .
Figure 5. SEM images of the Si-clad NiSn anodes before and after cycling.a) Cross-sectional SEM image of the anode before cycling.b) Cross-sectional SEM image of the anode after cycling.c) The LiPAA and super P wrap around the periphery of the dendritic anode before cycling.d) Surface morphology and micron pores after cycling, with the dendritic anode remaining unaltered and the micron-scale pores well retained.e) Surface morphology of the dendritic structure after cycling.f ) Cross-section of the dendritic structure after cycling.

Figure 6 .
Figure 6.Structural analysis.a) The specific surface area is 8.98 m 2 g À1 and nanoscale pores are mainly distributed in the range of 5-10 nm.b) Half-cell EIS analysis: Si-clad NiSn anode has a smaller charge transfer resistance of 25.6 Ω than slurry NiSn/Si anode of 102.5 Ω. c) Nyquist diagram analysis: the Warburg coefficient for Si-clad NiSn anode is 174.4Ω S À1 , while the Warburg coefficient for slurry NiSn/Si anode is 999.3Ω S À1 .d) Ion-resistance in non-Faraday processes with TLM: ion resistance in electrolytes (108.3Ω) of Si-clad NiSn anode is smaller than that of slurry NiSn/Si anode (234.3Ω). e,f ) GITT measurement to evaluate the Li-ion diffusion characteristics of Si-clad NiSn anode and slurry NiSn/Si anode: the Li-ions transport coefficient of the Si-clad NiSn anode is 10 À11 cm 2 s À1 , while that of NiSn/Si anode is 10 À12 cm 2 s À1 .