In situ analysis of dynamic evolution of the additive-regulated cathode processes in quasi-solid-state lithium-metal batteries

The implementation of high-energy-density storage devices can be facilitated by the built- in situ cathode electrolyte interphase (CEI) between Ni-rich cathodes and gel polymer electrolytes, as it improves interfacial compatibility and enhances security. Understanding the interphase processes of cathode materials, including the structural evolution and the formation of cathode electrolyte interphase upon charging/discharging, is crucial for the design of solid-state lithium batteries. Here, we employed in situ atomic force microscopy (AFM) to investigate the effects of lithium difluoro(oxalato)borate (LiDFOB) on the dynamic evolution of the cathode interphase. In the presence of LiDFOB, the adhesion of nanoparticles and a thin amorphous film on the cathode surface resulted in the formation of a homogeneous CEI, inducing the production of Li x PF y as byproducts. Furthermore, the stable CEI formed between the cathode and electrolyte helps maintain the integrity of the composition and structure, reduces interfacial resistance, and improves the cycle stability of the batteries. The visualization of in situ AFM in quasi-solid-state lithium-metal batteries provides valuable insights into the distinct nanostructures and growth dynamics of LiDFOB-mediated CEI on the LiNi 6 Co 2 Mn 2 O 2 cathode, thus offering a universal and convenient technique for interfacial analysis and a mechanistic understanding of solid-state batteries.