Unraveling Asymmetric Electrochemical Kinetics in Low-Mass-Loading LiNi1/3Mn1/3Co1/3O2 (NMC111) Li-Metal All-Solid-State Batteries

In this study, we fabricated a Li-metal all-solid-state battery (ASSB) with a low mass loading of NMC111 cathode electrode, enabling a sensitive evaluation of interfacial electrochemical reactions and their impact on battery performance, using Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) as the solid electrolyte. The electrochemical behavior of the battery was analyzed to understand how the solid electrolyte influences charge storage mechanisms and Li-ion transport at the electrolyte/electrode interface. Cyclic voltammetry (CV) measurements revealed the <i>b</i>-values of 0.76 and 0.58, indicating asymmetry in the charge storage process. A diffusion coefficient of 1.5 × 10^-9 cm²⋅s^-1 (oxidation) was significantly lower compared to Li-NMC111 batteries with liquid electrolytes, 1.6 × 10^-8cm²⋅s^-1 (oxidation), suggesting that the asymmetric charge storage mechanisms are closely linked to reduced ionic transport and increased interfacial resistance in the solid electrolyte. This reduced Li-ion diffusivity, along with the formation of space charge layers at the electrode/electrolyte interface, contributes to the observed asymmetry in charge and discharge processes and limits the rate capability of the solid-state battery, particularly at high charging rates, compared to its liquid electrolyte counterpart.