Boosting stability in Ni-rich cathodes: a synergistic approach to surface and bulk modifications for advanced lithium-ion batteries

Abstract

Nickel-rich layered oxides, with the general formula LiNi_xCo_yMn_zO₂ (0.8 ≤ × < 1), have emerged as highly promising cathode materials owing to their high operating-voltage for high-energy-density applications. However, the major challenge impeding the industrial viability of nickel-rich single-crystal cathodes is the instability of the electrode's surface and cathode–electrolyte interface. The dissolution of transition metal ions, the release of lattice oxygen, and triggered reactions are crucial for maintaining a battery's stable electrochemical performance. Herein, a synergistic approach is proposed to prevent bulk and surface degradation in Ni-rich cathodes. We applied a thin TiNb₂O₇ (TNO) coating on single-crystal LiNi_0.83Mn_0.06Co_0.11O₂ (SCNMC), whereby Ti⁴⁺ ions diffused inward during high-temperature annealing, as confirmed by XPS depth profile analysis. The TNO coating helped suppress side reactions and synergistically reduced lithium/nickel mixing, thereby enhancing lithium diffusion in the bulk electrode. The prepared TiNb₂O₇-coated LiNi_0.83Mn_0.06Co_0.11O₂ (SCNMC/TNO) exhibited a higher capacity retention of 81.92% compared with that (58.55%) exhibited by pristine SCNMC for cells cycled at 1C. Postmortem analysis revealed that the SCNMC/TNO cathode retained its stable crystalline structure, unlike pristine SCNMC. The surface engineering strategy presented in this study is broadly effective for enhancing electrochemical performance and ensuring a stable interface after long cycling of nickel-rich single-crystal cathode materials.