Interfacial reactions take the lead: elucidating the dominant role of cathode–electrolyte interactions in triggering thermal runaway of high-nickel lithium-ion batteries†
Abstract
Ni-rich layered oxide cathodes have garnered considerable attention for their high energy density but suffer from notorious safety concerns in lithium-ion batteries (LIBs). During thermal runaway (TR) of LIBs, the cathode surface induced electrolyte decomposition and oxygen release from bulk crystal structure transitions are both responsible for accelerating the rapid self-heating, yet their specific roles and contributions have never been explicitly elucidated, leaving uncertainty of safety enhancing strategies regarding bulk crystal structure modification versus interphase regulation. Here, we systematically analyzed the thermal runaway characteristics of varied Ni-rich layered cathode LIBs, from cell level to material level. Quantificational comparisons between the TR temperature of LIBs and phase transition point of cathode materials reveal that for ultrahigh Ni (≥80%) cathode LIBs, exothermic interfacial parasitic reactions dominate the TR process, while for those with relatively low Ni content (≤60%), it is the O2 escaping from the phase transition and the following oxidization it involves that govern the TR behavior. Moreover, the underlying reaction pathways of cathode/electrolyte reactions are explored in detail by deconvoluting the electrochemical–thermo–mechanical evolution process during TR. Stress accumulation from phase inhomogeneity aggravates interfacial reaction and gassing, while the gaseous species trapped in turn drives crack propagation upon temperature argument, constituting a self-sustaining loop consequently developing into catastrophic TR. This work bridges a critical knowledge gap in understanding the correlation between TR performance and microstructures, and highlights the necessity of promoting interfacial compatibility for safe Ni-rich cathode LIBs.