Using Artificial Solid-Electrolyte Interphase Coatings for Enhancing Safety of High-Energy Li-Ion Batteries from Material Level

Abstract

The development of high-energy-density Li-ion batteries (LIBs) to meet the demand for electric vehicles and sustainable energy storage applications simultaneously brings about more safety issues. On the anode side, graphite has been a major anode material for high-energy LIBs and is anticipated to continuously play an important role even for the high-capacity Si-graphite (Si-Gr) composite anodes in the near future. The low lithiation electrochemical potential of graphite enables a lower anode potential allowing higher energy for a full cell but is vulnerable to the plating of metallic Li dendrite, which could easily arise from either over-lithiation, due to heterogeneity in the negative electrode, or fast charging. Li dendritic deposits could penetrate through the separator to trigger cell short-circuit and eventually thermal runaway. On the cathode side, the high surface reactivity and low oxygen lattice stability of the Ni-rich layered oxide cathodes lower the thermal stability. This study focuses on enhancing the safety of LIB full-cells by modifying the properties and stability of the solid-electrolyte interphases (SEIs) respectively on the anode and cathode electrodes. A polymeric artificial SEI for the anode is developed not only to improve the electrode performance but also effectively suppress SEI and Li dendrite formation. Meanwhile, a composite coating for the cathode is derived to simultaneously enhance the cycle stability and thermal stability, due to the altered thermal decomposition pathway, of an NCM811 cathode. The overall enhanced safety of the full cells is illustrated with the nail penetration test, and the safety-enhancing mechanisms are revealed by conducting post-mortem and synchrotron-based operando studies.