Interfacial Li+ Diffusion Booster Accelerated by Enhanced Metal‐Organic Framework Sieving and Wettability for High‐Voltage Solid‐State Lithium Metal Batteries

An ion-selective SSE is proposed with an accelerated Li+ migration feature, where the metal organic framework functions as a molecular sieve to selectively block bulky anions and the ionic liquid acts as Li ion bridge. Consequently, The as-prepared full cell exhibited high capacity and retention under the upper voltage of 4.3 V.

Solid-state lithium metal batteries (SSLMBs) are promising for realizing higher energy density. However, the poor interfacial Li⁺ transport kinetics and Li dendrite growth inhibit SSLMBs, leading to sluggish interfacial ion diffusion and depressive lifespan, which is attributed to high barriers blocked by anions or interface space in solid-state electrolytes. Herein, a flexible solid-state polymer skeleton employed with ionic liquid and metal-organic frameworks (PIM) electrolyte is proposed to strengthen interfacial Li ion exchange by improving the Li⁺ sieving effect and interfacial wettability. Thanks to the immobilization effect of TFSI⁻ anions affected by positive metal atom centers and pore morphology, the PIM electrolyte exhibits exceptional properties, i.e., a high ionic conductivity up to 3.1 mS cm⁻¹ at 60 °C and an improved Li⁺ transference number of 0.65, enabling symmetric cells of Li metal to run steadily for over 1000 h with lower voltage hysteresis (25 mV). Meanwhile, matching with high-voltage electrodes, the solid-state PIM electrolyte exhibits good compatibility and stability toward LiNi_0.6Co_0.2Mn_0.2O₂ and LiFePO₄ electrodes, showing the capacity retentions of 85.5% and 96.5% after 120 and 400 cycles, respectively. This work suggests low interfacial diffusion resistances and high compatibility for make it a promising candidate for future solid-state battery.

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