Electrochemically Derived Interfacial Li-Ion Conductor Enables High-Rate and Long-Cycling in Ni-Rich Layered Cathodes

The fast-charging capability has become a critical performance requirement for next-generation lithium-ion batteries (LIBs). Layered high-nickel transition metal oxides (LiNi_xCo_yMn_(1-x-y)O₂, x ≥ 0.8) have emerged as the most promising candidates due to their high specific capacity and energy density toward fast-charging LIBs. However, their practical implementation under fast-charging conditions is severely hindered by sluggish Li⁺ diffusion kinetics and interfacial instability. While a high Ni content effectively boosts capacity, it inevitably compromises structural robustness and accelerates surface degradation. Conventional surface coating methods, which typically target secondary particles, often suffer from nonuniform coverage and incomplete interfacial protection. To overcome these bottlenecks, we propose a novel surface engineering strategy that electrochemically constructs a conformal fast-ion-conducting layer directly on the primary particles of Ni-rich cathodes. High-resolution transmission electron microscopy equiped with energy-dispersive X-ray spectroscopy combined with time-of-flight secondary ion mass spectrometry (ToF-SIMS) verify the conformal and homogeneous nanoscale Li₂SeO₄ coating on primary particles, while Galvanostatic Intermittent Titration technique and Density Functional Theory calculations collectively demonstrate its fast Li⁺-ion transport characteristics, featuring a migration barrier as low as 260 meV. This strategy significantly improves high-rate performance (180.6 mAh·g^-1 at 10C) and cycling durability (94.2% capacity retention after 100 cycles). This work presents a versatile and scalable interfacial engineering approach for advancing fast-charging layered cathode materials.