Exploring the Mechanisms\nof LiNiO<sub>2</sub> Cathode\nDegradation by the Electrolyte Interfacial Deprotonation Reaction

Nickel-rich layered oxides stand as ideal cathode candidates\nfor\nhigh specific capacity and energy density next-generation lithium-ion\nbatteries. However, increasing the Ni content significantly exacerbates\nstructural degradation under high operating voltage, which greatly\nrestricts large-scale commercialization. While strategies are being\ndeveloped to improve cathode material stability, little is known about\nthe effects of electrolyte–electrode interaction on the structural\nchanges of cathode materials. Here, using LiNiO<sub>2</sub> in contact\nwith electrolytes with different proton-generating levels as model\nsystems, we present a holistic picture of proton-induced structural\ndegradation of LiNiO<sub>2</sub>. Through ab initio molecular dynamics\ncalculations based on density functional theory, we investigated the\nmechanisms of electrolyte deprotonation, protonation-induced Ni dissolution,\nand cathode degradation and the impacts of dissolved Ni on the Li\nmetal anode surfaces. We show that the proton-transfer reaction from\nelectrolytes to cathode surfaces leads to dissolution of Ni cations\nin the form of NiOOH<sub><i>x</i></sub>, which stimulates\ncation mixing and oxygen loss in the lattice accelerating its layered-spinel–rock-salt\nphase transition. Migration of dissolved Ni<sup>2+</sup> ions to the\nanode side causes their reduction into the metallic state and surface\ndeposition. This work reveals that interactions between the electrolyte\nand cathode that result in protonation can be a dominant factor for\nthe structural stability of Ni-rich cathodes. Considering this factor\nin electrolyte design should be of benefit for the development of\nfuture batteries.