Electrochemically tuned crystal tectonics in crack-resistant textured oxide cathode films for electrochemical energy storage

Electro-chemo-mechanical degradation pathways which significantly impact performance of ceramic (e.g., LiCoO2) battery electrodes are a strong function of bulk crystallographic texture, crystal size and interfacial misorientation angle. Via electrodeposition, deterministic synthesis of textured thick (>10 µm) films of LiCoO2 with iso-oriented crystalline domains having controlled size dispersity and interfaces enabling study and control of these degradation pathways is demonstrated. The crystal morphogenesis stem from the growth parameters (current density and growth temperature), resulting in a bouquet of textures and microstructures. Columnar grained <110>||ND textured films with a finer crystallite size (f4-8µm=0.617) can be synthesized in kinetic regimes of growth (T=275°C, supersaturation>0.367), whereas <003>||ND films with coarse, polygonal crystals (f8-15µm=0.597) originate in thermodynamic regimes of growth (T=275°C, supersaturation<0.036; T=350°C, supersaturation independent). Interestingly, Σ3 coincident site lattice (CSL) boundaries are controllably incorporated in the <110>||ND films as low energy interfaces (f = 0.337), whereas <003>IIND films only possesses high angle crystal interfaces (HACIs, f = 1.0). The morpho-structural evolution of the crystal assembly under electro-chemo-mechanical stimuli is rooted in the crystal tectonics and co-related anisotropic ionic diffusion differences. Stochastic analysis of microstructures of electrochemically cycled films via electron backscatter diffraction (EBSD) and Raman spectroscopy indicates interface, size and texture-dependent degradation modes. On electrochemical cycling, <003>||ND electrode degrades by both intercrystal and intracrystal cracking (13.3% retention, critical size 1.79 µm), whereas <110>||ND electrode is only susceptible to intercrystal cleavage (89.2% retention, critical size 2.25 µm). The cracks initiate at local lithiation heterogeneities near coarser crystals and always propagate along HACIs; with all the CSL boundaries remaining mechanically robust. Our discoveries highlight how careful orchestration of orientation and interfaces leads to unique chemomechanical stabilization strategies.