Highly stable Ni-rich layered oxide cathode enabled by a thick protective layer with bio-tissue structure

Abstract Ni-rich layered oxide (LiNixMnyCozO2 (NMC), x > 60%), one of the most promising cathode materials for high-energy lithium ion batteries (LIBs), still suffers from surface instability even with the state-of-art protective coatings, which normally are limited to ≤10 nm to maintain the required kinetics. Here we demonstrate a highly conductive protective layer with bio-tissue structure that can enable high-rate operation of NMC cathodes even with a thickness exceeding 40 nm. With this thick protection layer, the modified LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode retains 90.1% and 88.3% of its initial capacity after 1000 cycles in coin cells and pouch cells, respectively. This novel membrane is composed of crystalline nano-domains surrounded by ~1 nm amorphous phase, which is an effective distance to enable tunneling of electrons and Li+ ions between these domains. The coated NMC811 cathode releases ~55.3% less heat under thermal abuse and largely enhances his safety feature during puncture test. The coating also enables excellent electrochemical stability of NMC811 even after it was exposed to a moist environment for four weeks at 55 °C, which is critical for large-scale production of high-energy-density LIBs.