Structural and interfacial stability of a coated Ni-rich layered oxide cathode at high-voltage operation

Abstract

By increasing the cutoff potential of Ni-rich layered oxide cathodes, specifically LiNi0.8Co0.1Mn0.1O2 (NMC811), Li-ion batteries (LIBs) can deliver higher energy densities; a desirable performance trait in electric vehicle battery systems. However, this strategy compromises the structural and interfacial stability of NMC811, leading to a shorter operational lifetime. In this work, LixWyOz (LWO) coating is formed on the surface of a NMC811 active material to address the instability issues. LWO-NMC811 reports an improved cycling stability compared with an uncoated NMC811 at a high-voltage operation of 3.0–4.6 V. Operando X-ray diffraction and operando dilatometry are combined with ex-situ characterization techniques to elucidate the degradation mechanisms that occur in the cathode material from initial cycling to after 100 charge-discharge cycles. The multiscale analyses show that LWO-NMC811 experiences a suppressed H2→H3 contraction at the high state-of-charge, which results in lesser particle cracking and electrode thickness change. The LWO coating also diminishes the parasitic side reactions and supports the agile movement of Li+ at the electrode-electrolyte interface. Overall, this work demonstrates an inter-mapping of the complex deterioration processes that occur during high-voltage cycling of Ni-rich NMC, which is useful in optimizing electrode design to achieve high performance LIBs.