Enabling fast charging of high energy density Li-ion cells with high lithium ion transport electrolytes

Enabling fast charging capability of high energy density Li-ion cells could dramatically increase the widespread adoption of battery electric vehicles. However, fast charging is limited by Li ion depletion in the electrolyte and increasing Li ion transport from cathode to anode is essential. By evaluating different Li salts in the electrolyte, we find lithium bis(fluorosulfonyl)imide (LFSI) has both higher conductivity and higher Li ion transference number compared to the traditional LiPF6 salt. In a 12-minute charge, the electrolyte with LiPF6 salt reaches the cut-off voltage rapidly while the one with LiFSI exhibits a longer constant current charge with more capacity achieved. The LiFSI electrolyte also reflects better cycling performance and less Li plating after repeated fast charging cycles.