Revealing the role of Li content on the structural stability of textured LiCoO 2 battery electrodes along fast diffusing <11x> directions

Facile ion transport in layered battery cathode systems require (11x) terminating facets. However, the facets that provide accelerated transport also amplify deleterious phase transitions and chemical reactions. The coupling between initial intercalant ion content (nominal lithium-ion stoichiometry), ionic mobility and phase transformations along the fastest diffusing facets remain understudied. Here, the coupling is elucidated using electrodeposited highly textured <11x>||(sample normal direction, ND) LiCoO2 (LCO) electrodes with controlled texture, facet presentation, and initial lithium content. Contrary to powdered systems with untextured particles, here we show that minute variations in lithium content drive distinct interphase formation at (110) terminating facets and impact ion diffusivity in cathodes possessing identical <110>IIND texture, indicating the unique importance of control of lithium content in highly oriented systems. While Lithium-poor <110>IIND LCO cathodes provide initial good ion diffusivity, they exhibit accelerated interfacially originated degradation along <110> directions via rapid rocksalt formation. Lithium-rich <110>IIND LCO electrodes exhibit elevated interfacial degradation due to the poorly conducting Li2CO3 on the surface. Lithium-balanced textured LCO electrodes suppress kinetically driven degradation pathways, even at (110) terminating facets, and provide both good ion diffusivity and structural stability. The dual control of lithium content and crystallographic orientation along the fastest diffusing directions provided by the textured electrodeposited cathodes enables deterministic design of energy-dense cathodes with good ion transport kinetics and low surface reactivity, both in thin and thick electrode formats, a combination which is difficult to achieve in untextured slurry systems presenting a range of surface facets.