Operando X-Ray Diffraction and Dilatometry Analysis of Coated Ni-Rich Layered Oxide Material at High-Voltage Operation

By extending the cutoff potential of a Ni-rich layered metal oxide cathode material, specifically LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811), lithium-ion batteries (LIB) can effectively deliver higher energy density output. However, this approach negatively impacts the structural and interfacial stability of NMC811 during cycling, which leads to poor electrochemical performance and shorter cycling duration. The application of a protective coating on the surface of Ni-rich NMC has been recognized as an effective procedure in improving the cycling stability of NMC-based LIBs. However, there is limited analysis available on the structural and interfacial evolution experienced by a coated Ni-rich NMC cathode during cycling at a high voltage operation.<br/><br/>In this work, a Li_xW_yO_z (LWO) coating is developed on the NMC811 active material to address the instability issues. The coated NMC811 sample reports a higher capacity retention at 85% compared with an uncoated NMC811 at 80% after 100 charge-discharge cycles at 1C with a high cutoff potential of 4.6 V vs Li/Li⁺. Operando X-ray diffraction (XRD) and operando electrochemical dilatometry are combined with ex-situ characterization techniques to provide an inter-mapping and compare the degradation mechanisms that occur in the uncoated and coated Ni-rich NMC. The multiscale analysis show that the coated Ni-rich NMC experiences a suppressed lattice contraction along the c-axis at high state-of-charge (SOC), consequently producing lesser particle cracking and electrode thickness change compared with the uncoated sample. Moreover, the coating shields the bulk material from the electrolyte which mitigates the parasitic side reactions and facilitates the ease of Li⁺ movement across the electrode-electrolyte interface. The results can help elucidate the role of surface coatings in enhancing the cycling stability of Ni-rich NMC at an extended voltage operation and assist in developing more advanced coating strategies to optimize electrode design for high energy density LIBs.