Solvent polarizability governs Li⁺ transport kinetics for high energy lithium metal batteries

Fast Li⁺ kinetics are essential for high energy lithium metal batteries, yet the factors governing these kinetics remain unclear. Here, we decipher a quantitative structure-kinetics relationship by demonstrating that polarizability dictates Li⁺ desolvation and transport. Specifically, the inert solvents with low polarizability generate weak induced dipoles under interfacial electric fields, which keeps the structural integrity of anion-rich solvates. These intact solvates improve the Li⁺ kinetics via coupling Li⁺ hopping and electrostatic repulsion to anions, as evidenced by the linear relationship between polarizability and desolvation energy. Meanwhile, the induced more inorganic-rich solid-electrolyte interphase further accelerates the Li⁺ kinetics. Accordingly, the tailored electrolyte enables Li | |LiNi_0.8Co_0.1Mn_0.1O₂ cells to achieve a stable cycling (0.2 C charge/0.5 C discharge, 1 C = 200 mA g^-1 based on the NCM811 positive electrode) with 95% capacity retention after 200 cycles at -35 °C and powers a 7.5-Ah lithium metal pouch cell (0.1 C charge/0.3 C discharge, 1 C = 200 mA g^-1 based on the NCM811 positive electrode) with a specific energy of 541.6 Wh kg^-1 (based on the full cell mass). This work decodes the polarizability-governed Li⁺ kinetics and establishes practical electrolyte guidelines for realizing high energy lithium metal batteries.