Enhancing Li⁺ Transport in NMC811||Graphite Lithium‐Ion Batteries at Low Temperatures by Using Low‐Polarity‐Solvent Electrolytes

Abstract

LiNi_x Co_y Mn_z O₂ (x+y+z=1)||graphite lithium-ion battery (LIB) chemistry promises practical applications. However, its low-temperature (≤ -20 °C) performance is poor because the increased resistance encountered by Li⁺ transport in and across the bulk electrolytes and the electrolyte/electrode interphases induces capacity loss and battery failures. Though tremendous efforts have been made, there is still no effective way to reduce the charge transfer resistance (R_ct ) which dominates low-temperature LIBs performance. Herein, we propose a strategy of using low-polarity-solvent electrolytes which have weak interactions between the solvents and the Li⁺ to reduce R_ct , achieving facile Li⁺ transport at sub-zero temperatures. The exemplary electrolyte enables LiNi_0.8 Mn_0.1 Co_0.1 O₂ ||graphite cells to deliver a capacity of ≈113 mAh g^-1 (98 % full-cell capacity) at 25 °C and to remain 82 % of their room-temperature capacity at -20 °C without lithium plating at 1/3C. They also retain 84 % of their capacity at -30 °C and 78 % of their capacity at -40 °C and show stable cycling at 50 °C.