Integrative Interfacial Stabilization of Ni-Rich Cathodes Using Dual Li₃PO₄-Li₂WO₄ Coatings for Improved Cycling Stability

Ni-rich layered oxide materials are gaining significant attention as promising candidates for high-energy, low-cost cathodes for lithium-ion batteries (LIBs) in long-range electric vehicles. However, the phase transition from the layered to rock-salt-like structure severely impedes lithium-ion transport within the cathode, primarily due to the similar ionic radii of lithium ions and divalent nickel ions. In addition to the micro-structural instability, the conventional Ni-rich cathode materials inevitably suffer intergranular cracking after prolonged cycling due to their aggregated particle morphology, thus compromising cathode particle integrity and leading to severe capacity fading.
To address these issues, a wide range of strategies have been explored to enhance the structural and chemical stability of Ni-rich cathodes via surface engineering and morphological modifications. Considering that the parasitic redox reaction occurs at the cathode/electrolyte interface, surface engineering is an ideal strategy to improve the interfacial stability without significantly compromising energy density. For high-performance and long-cycle life LIBs, the surface coating material must function effectively by protecting the cathode surface from electrolyte decomposition, stabilizing the cathode-electrolyte interface to minimize side reactions, and enhancing fast Li⁺ transport across the interface.
In this work, we developed a dual-function in-situ-formed Li-reactive Li₃PO₄-Li₂WO₄ coating on the surface of Ni-rich cathode with secondary particle morphology. The coating is synthesized via reaction between H₃PO₄ and (NH₄)₆H₂W₁₂O₄₀ reacts with the residual lithium compounds, which transformed into Li₃PO₄-Li₂WO₄ coating layer during high-temperature calcination. Conformal dual Li₃PO₄-Li₂WO₄ coating layer not only protects Ni-rich cathode surface from electrolyte decomposition, but also provide facile Li⁺ transport at the cathode-electrolyte interface, achieving improved rate property compared to pristine particles. W and P ions successfully diffuse into the sub-surface of Ni-rich cathodes, resulting in near-surface enrichment of W-O and P-O compounds, which significantly stabilize surface lattice oxygen at deeply de-lithiated states. Atomistic simulations identified the critical combinatorial role of W and P to lower the surface-interface oxygen activity towards electrolyte. Our approach can provide inhibition of the phase transformation, reduction of residual lithium compounds, improved morphological integrity, thus consequently delivering superior cycling performance.