Single [0001]-oriented zinc metal anode enables sustainable zinc batteries

Zinc metal anodes suffer from dendrite growth that reduces Coulombic efficiency and can short-circuit cells. Exposing the closest-packed Zn(0002) planes is known to enhance corrosion resistance and lower surface energy, promoting planar deposition. Prior approaches using pseudomorphic substrates, electrolyte optimization, or reconstructing the Zn matrix have not yielded single (0002)-textured Zn anodes that can sustain epitaxial growth over extended cycling. Epitaxy quality is controlled by chemical potential and lattice mismatch; homoepitaxy is favored when mismatch is minimized. The authors hypothesize that a Zn substrate with a single [0001] orientation (single Zn(0002) texture) will eliminate lattice mismatch at the epitaxial interface, enabling ultra-sustainable homoepitaxial Zn growth that suppresses dendrites and improves reversibility, even under high depth of discharge and high areal capacity.

Research has pursued dendrite-free Zn deposition by: (i) constructing pseudomorphic substrates with tolerable lattice misfit (<18%) to Zn(0002); (ii) electrolyte engineering to direct dense surface formation; and (iii) reconstructing Zn matrix to regulate crystallographic orientation and expose Zn(0002). While these efforts can favor hexagonal textures, achieving a purely single (0002)-textured Zn anode that maintains continuous epitaxial growth remains challenging. Epitaxy theory indicates lattice mismatch drives misfit dislocations and limits the critical thickness (te) of epitaxial layers. Homoepitaxy, which removes chemical disparity, still requires minimal mismatch, ideally with a single substrate orientation. In battery-relevant kinetic regimes (high current), growth can deviate from thermodynamic predictions, further complicating sustained epitaxy when multiple textures exist in the substrate.

Fabrication of Zn(0002) metal anodes: Direct-current electrodeposition onto pre-cleaned Cu foil (100 µm) was performed in H3BO3/Zn-based electrolytes with vigorous stirring to suppress side reactions. For single-textured Zn(0002), the electrolyte contained 100 g/L ZnSO4·6H2O and 20 g/L H3BO3; deposition used a Cu cathode disk (15 mm) and Zn plate anode with ~5 cm spacing, stirred at 700 rpm, 25 °C, pH 2, 30 mA cm−2 for 1 h, yielding ~127 µm Zn. To create an intermediate-state electrode (IMS-Zn(0002), predominantly (0002) with minor other textures), 5 g/L Zn(CH3COO)2·2H2O was added to the above solution. Comparative electrodes were prepared by replacing ZnSO4 with ZnCl2 or Zn(CH3COO)2·2H2O under identical conditions. Substrate pre-treatment included rinsing Cu foil with 1% H2SO4 to remove oxides. Characterization: XRD (Rigaku MiniFlex 600, Cu-Kα, 40 kV, 100 mA) tracked texture evolution during plating/stripping and quantified relative texture coefficients (RTC). SEM (FEI Nova NanoSEM 430, BSE VCD detector) assessed morphology and grain size; EBSD (NordlysMax2, HKL Channel 5e) mapped textures and pole figures. TEM/HRTEM (Tecnai G2 F20, 200 kV; JEOL 2010) examined lattice orientations; FFT/SAED used for crystallography. Cross-sectional foils across the epitaxial interface were prepared by FIB for HAADF-STEM and nano-beam electron diffraction (NBED) to resolve epitaxial relationships and atomic stacking. Residual stresses were evaluated pre- and post-deposition. Surface roughness during in situ plating was measured by confocal LSM; in situ optical microscopy observed deposition dynamics in transparent Zn||Zn cells. Electrochemistry: CR2025 coin cells used glass fiber separators (Whatman GF/C, 260 µm). Zn||Cu half-cells measured Coulombic efficiency at various current densities/capacities; Zn||Zn symmetric cells assessed cycling stability and polarization, including thin Zn (45 µm, 26.3 mAh cm−2) at DODZn = 75.2% (current density 11.3 mA cm−2, areal capacity 19.8 mAh cm−2). Full cells paired Zn anodes with NH4V4O10 (NVO) cathodes (loading 1.2–1.5 mg cm−2; 7:2:1 NVO:carbon:PVDF) in 3 M ZnSO4 (100 µL), tested between 0.4–1.4 V at currents up to 20 A g−1. EIS determined charge transfer resistance (Rct); Tafel/LSV in a 3-electrode setup (Pt counter, Ag/AgCl reference) evaluated HER behavior; CV probed kinetics. Pouch cells (30×30 mm, ~2 mAh cm−2) were cycled under controlled pressure at 25 °C. Cathode synthesis: NVO prepared hydrothermally by reacting NH4VO3 with oxalic acid at 140 °C, 3 MPa for 48 h, followed by washing and drying. Theory: DFT calculations (VASP, PBE-GGA, PAW, 520 eV cutoff, DFT-D3, Gaussian smearing 0.05 eV; force convergence <0.01 eV Å−1; energy convergence <1e−7 eV) computed surface energies of Zn low-index planes using slab models (>12 Å thickness, 15 Å vacuum). VASPsol accounted for solvation effects. Adsorption of anions (Cl−, SO4^2−, CH3COO−) was modeled to obtain modified surface energies and guide Wulff constructions for predicted equilibrium shapes and surface coverage ratios.

• Single-textured [0001]-uniaxial Zn(0002) anodes were electrodeposited by anion regulation (SO4^2− in ZnSO4/H3BO3), yielding a dominant (002) XRD peak and EBSD-confirmed single <0001> texture; average grain size 1.51 ± 0.60 µm versus 25.58 ± 0.55 µm for commercial Zn (com-Zn) and 8.40 ± 0.30 µm for IMS-Zn(0002).
• DFT shows anion-specific adsorption lowers surface energies; SO4^2− markedly reduces Zn(0002) surface energy, increasing its exposure. Wulff constructions predict preferential (0002) facets in ZnSO4, consistent with experiment.
• Lattice mismatch analysis: Zn(0002) on Zn(0002) has f = 0%; Zn(1010) or Zn(1011) on Zn(0002) exhibit f ≈ 6.67% and 42.29%, respectively. Even minor off-[0001] textures in the substrate induce misfit dislocations; beyond a critical epitaxial thickness, growth becomes disordered and dendritic.
• HAADF-STEM/NBED reveal sharp interfaces and identical lattice orientation between deposited Zn and Zn(0002) substrate. High-resolution imaging confirms ABABAB stacking of (0002) planes during homoepitaxial growth.
• Mechanical state: Residual stress remains nearly unchanged for Zn(0002) upon deposition (14.8 → 15.7 MPa) but increases drastically for IMS-Zn(0002) (16.5 → 60.8 MPa) and com-Zn (22.8 → 110.7 MPa) after 1 h plating at 4 mA cm−2.
• Deposition morphology: Zn(0002) supports planar, hexagonal, dendrite-free growth with lower surface roughness (~0.3 µm) compared to IMS-Zn(0002) (~1.9 µm) and com-Zn (~2.8 µm) after 1 h plating; com-Zn/IMS develop loose, uneven deposits and pores on stripping; Zn(0002) shows orderly stripping and higher corrosion resistance.
• Electrochemistry (half cells): Cu||Zn(0002) achieves average CE 99.6% for 330 cycles at 1 mA cm−2/1 mAh cm−2; at 5 mA cm−2/5 mAh cm−2, cycles stably for 220 cycles with CE 99.5%. Zn(0002) shows more negative HER onset than com-Zn, indicating suppressed HER.
• Symmetric cells under high utilization: With thin Zn (45 µm, 26.3 mAh cm−2) at DODZn = 75.2% and current density 11.3 mA cm−2 (19.8 mAh cm−2 per cycle), Zn(0002)||Zn(0002) cycles >250 h; com-Zn||com-Zn short-circuits at ~51 h.
• Full cells (Zn||NVO): At 0.5 A g−1 and 5 A g−1, Zn(0002) anodes deliver up to 98% capacity retention over 600 and 3500 cycles, respectively, with lower voltage hysteresis than com-Zn. Initial Rct is 31.35 Ω for Zn(0002)||NVO vs 60.37 Ω for com-Zn||NVO; Zn(0002) maintains lower Rct even after 1000 cycles, attributed to higher exchange current density. SEM after 1000 cycles shows intact Zn(0002) grains.
• Pouch cells (~2 mAh cm−2): Zn(0002)||NVO retains 80% capacity after 450 cycles, whereas com-Zn||NVO retains 61% after 100 cycles with unstable CE; Zn(0002) pouch cells power small devices stably.

The findings demonstrate that enforcing a single [0001] orientation in Zn anodes eliminates lattice mismatch at the epitaxial interface, enabling continuous homoepitaxial growth of Zn with ABAB stacking. This crystallographic control stabilizes interfacial mechanics (minimal residual stress increase), maintains planar deposition, and suppresses dendrite formation, thereby improving Coulombic efficiency and cycle life. In contrast, substrates with even small fractions of off-[0001] textures introduce misfit dislocations; beyond the critical epitaxial thickness, growth becomes random, elevating stress and promoting dendrites. The anion-driven reduction of Zn(0002) surface energy in ZnSO4 electrolytes rationalizes the formation of single-textured Zn(0002) during electrodeposition. Electrochemical metrics across half-cells, symmetric cells under high DOD, and full cells (coin and pouch) corroborate that homoepitaxy translates into superior kinetics (lower Rct, higher i0), reduced HER and corrosion, and durable high-rate cycling, highlighting a practical pathway for sustainable Zn-metal batteries.

This work establishes a strategy to fabricate [0001]-uniaxial, single (0002)-textured Zn metal anodes via electrolyte anion regulation, enabling ultra-sustainable homoepitaxial Zn growth. Atomic-scale HAADF-STEM/NBED confirm ABAB stacking continuity from substrate to deposit. The single-texture design suppresses dendrites, minimizes residual stress, inhibits HER and corrosion, and yields high reversibility: near-unity CE over hundreds of cycles in half-cells, robust symmetric-cell operation at 75.2% DODZn, and long-life Zn||NVO coin and pouch cells with low Rct and high capacity retention. These insights into epitaxial control suggest generalizable routes to stabilize other metal anodes through crystallographic orientation engineering. Future research could extend this approach to different metals and electrolytes, integrate with interphase/coating strategies, and optimize scalable deposition protocols for practical large-format cells under diverse operating conditions.

Sustained homoepitaxy requires a strictly single [0001] substrate orientation; even minor fractions of other Zn textures lead to misfit dislocations and failure beyond a critical thickness. The epitaxial theory applied assumes single-orientation substrates and is challenged under kinetic-dominated high-current conditions typical of batteries. Demonstrations used specific electrolytes (3 M ZnSO4) and an NVO cathode; generalization to other chemistries and practical stack designs needs verification. The electrodeposited Zn(0002) requires controlled deposition conditions (acidic pH, boric acid additive, stirring), and scalability and tolerance to manufacturing variances were not assessed. Long-term stability under varying temperatures, pressures, and real-world duty cycles remains to be evaluated.