Ti-induced surface stabilization for enhanced capacity of aqueous-processed Ni-rich cathodes

Abstract

Aqueous processing offers an environmentally friendly alternative to conventional organic solvent-based methods for producing Ni-rich cathodes for lithium-ion batteries (LIBs). However, interaction with water can drive phase reconstruction at the cathode surface region, increasing activation polarization and charge transfer resistance, which can partially lower specific capacity. This study investigates the beneficial effect of Ti(IV) incorporation on single-crystalline Ni-rich LiNi_0.8Mn_0.1Co_0.1O₂ (SNMC) cathodes and demonstrates that the resulting Ti-rich, Ni-depleted surface layer enhances overall structural stability. Specifically, high-resolution scanning transmission electron microscopy images reveal that titanium suppresses undesirable rock-salt phase formation during aqueous processing, electrochemical impedance spectroscopy shows that Ti-incorporated SNMC cathodes exhibit lower charge transfer resistance compared to the conventional SNMC electrodes, and soft X-ray photoelectron spectroscopy exhibits a thinner cathode electrolyte interphase (CEI) layer with Ti incorporation. Improved cycling capacity was evidenced down to the atomic scale by utilizing operando X-ray absorption spectroscopy measurements, revealing stronger changes in the formal valence of all transition metals (or higher redox activity/charge compensation) during battery cycling for Ti-incorporated SNMC electrodes compared to the conventional SNMC electrodes. These results highlight that controlled surface modification using titanium can effectively stabilize the surface structure and reduce charge transfer resistance, offering a viable strategy to improve the structural and electrochemical performance of aqueous-processed Ni-rich cathode materials.