Gradient-porous-structured Ni-rich layered oxide cathodes with high specific energy and cycle stability for lithium-ion batteries

Ni-rich layered oxides (LiNi_xCo_yMn_1-x-yO₂, x > 0.8, NCM) are technologically important cathode (i.e., positive electrode) materials for next-generation high-energy batteries. However, they face challenges in cycle stability and durability due to internal strain accumulation and particle fracture as the batteries cycle. Here we report a simple molten-salt-assisted synthesis route to introduce gradiently distributed pores into the polycrystalline NCM secondary particles. The gradient porous strategy creates void spaces to buffer the anisotropic volume change of the primary particles, effectively mitigating the intergranular fracture and limiting the impedance growth. It not only increases the maximum accessible capacity of the NCM cathodes but also greatly enhances their cycle stability in practical pouch-type batteries and all-solid-state-batteries. It further enables a high nickel, low cobalt cathode (LiNi_0.96Co_0.02Mn_0.02O₂) with a combination of high specific energy (941.2 Wh kg^-1 based on cathode weight at 0.1 C and 25 °C, 1 C = 245 mA g^-1) and high stability during cycling (80.5% capacity retention after 800 cycles at 1 C relative to that of the first cycle) and high-temperature storage (reversible capacity retention >95.5% after 42-day storage at 60 °C at the fully charged state) in pouch cells.