High Li + Coordination Entropy Reducing the Interaction between Li + and Polymer Chains to Improve Li + Transport for Solid‐State Lithium Metal Batteries

Abstract High ionic conductivity and Li + transference number are crucial for ensuring the high safety and high energy density of solid‐state batteries, particularly those using lithium metal anodes (LMAs). However, the performance of current polymer electrolytes in these areas remains suboptimal, primarily due to the insufficient Li + transport properties hindered by strong coordination between Li + ions and the polymer chains. In this work, the coordination entropy of Li + is modulated through using four types of anions (TFSI − , DFOB − , BF 4 − , and FSI − ) to reduce the coordination strength between Li + and the polymer chains, thereby lowering the energy barrier for Li + transport. Additionally, these anions promote the formation of a uniform F‐ and B‐rich solid electrolyte interphase on LMA surface. As a result, the fabricated solid‐state polymer electrolyte with high Li + coordination entropy (HESPE) exhibits high ionic conductivity of 0.238 mS cm −1 and high Li + transference number of 0.707 at room temperature. The assembled Li/HESPE/LiFePO 4 batteries demonstrate improved Li plating/stripping behavior and present stable cycling for 1000 cycles without a short circuit at a current density of 1.5 C. The high‐entropy strategy presents a promising approach for the design and industrial application of solid‐state lithium metal batteries with enhanced stability and safety.