Enabling Superior Cycling Stability of LiNi_0.9Co_0.05Mn_0.05O₂ with Controllable Internal Strain

Abstract Intergranular cracking of Ni‐rich layered LiNi 1‐x‐y Co x Mn y O 2 (1‐x‐y ≥ 0.8) cathode particles deteriorate the chemo–electro–mechanical stability of high‐energy lithium‐ion batteries (LIBs), thus presenting a challenge to typical modification methods to establish robust structures with highly efficient lithium‐ion storage. Herein, the ZrTiO 4 (ZTO) as an epitaxial layer to enhance mechanical stability of ultrahigh‐Ni LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM90) is reported for the first time. Intensive exploration from structure characterizations (X‐ray absorption spectroscopy and in situ X‐ray diffraction techniques), multi‐physics field analysis, and first‐principles calculations disclose that the conformal ZTO layers and Zr doping effectively suppresses the internal strain and the release of lattice oxygen, which prodigiously restrains the local stress accumulation during whole (de)lithiation processes, thereby maintaining good mechanical stability of the materials. Meanwhile, the protective ZTO layer also prevents electrolyte erosion, thus keeping an intact surface structure of NCM90. Notably, ZTO‐modified NCM90 achieves significantly improved cyclability under high‐voltage (4.5 V) operation, expressing a 17% increase in capacity retention (71% vs 88%) after 100 cycles. Overall, this work reveals the role of internal strain in the original degradation behavior and effectiveness of surface engineering strategy to solve the challenge, emphasizing that the conformal surface protection mitigates the internal stress of Ni‐rich NCM by anchoring the lattice oxygen.