Improving Intrinsic Safety of Ni-Rich Layered Oxide Cathode by Modulating Its Electronic Surface State

Abstract

Safety risks and severe capacity degradation at elevated temperature of Ni-rich layered oxides hamper their application in power batteries for electric vehicles. In this work, the polymethacrylate-N-dibenzenesulfonimide ester (PM-NDIE) is proposed to penetrate into the interstices of primary particles of LiNi_0.85Co_0.1Mn_0.05O₂. During in-situ polymerization, nucleophilic oxygen and electrophilic sulfur atoms chemically bond with undercoordinated Ni and oxygen on the surface, respectively, modulating the electronic surface state. The in-situ XRD/XAFS/TEM analyses and DFT calculations corroborate that PM-NDIE contributes to slowing down the covalency increase of TM-O bond and preserving atomic coordination integrity even under highly delithiated state, thereby maintaining the integral layered structure during cycling. NCM with the PM-NDIE-engineered surface (P-NCM) demonstrates a distinct thinner inorganics-dominant cathode/electrolyte interphase and enables exceptional interfacial stability. P-NCM delivers a 47% reduction in voltage decay in self-discharge test at 55°C, a 27.4% improvement in capacity retention over 100 cycles at 1C/55°C, and maintains 93.66% capacity after 400 cycles under 1C in Ah-level pouch-cell. Moreover, a significantly inhibited thermal-induced phase transition and a delayed thermal runaway critical temperature of pouch-cells provide further evidence that a major driving force for heat-/oxygen- release spontaneous reaction of NCM has been cut off by stabilizing its electronic surface state.