Lithium diffusion detection by Kelvin Probe Force Microscopy

Lithium-ion batteries play an integral role in our daily lives. However, due to the limited energy and power density of lithium-ion batteries, alternatives are being sought after. Solid state batteries (SSBs) based on lithium conducting solid electrolytes are promising candidates for high energy density storage. However, SSBs are prone to lithium dendrite formation resulting in low cycling stability. The cycling stability of SSBs is directly related to the initial nucleation of lithium. Therefore, the detection and analysis of initial nucleation is essential to seek strategies for improvement. Local detection of lithium nucleation in batteries during operation is limited due to the high reactivity of lithium. Conventional techniques, such as methods based on electron microscopy, suffer from beam damage. Beam-induced electron injection can reduce lithium ions to metallic lithium, potentially affecting battery operation. Here we report a new approach to lithium detection based on Kelvin Probe Force Microscopy (KPFM) and Photo induced Force Microscopy. We show that KPFM allows to assess the inhomogeneity of the lithium flux at the interface between the solid electrolyte (SE) and the current collector (CC). We further propose a method to quantitatively measure the local current density at the SE/CC interface.