Fast Charging of High Energy Density Li-Ion Batteries with High Li Ion Transport Electrolyte

Abstract

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 the accompanying Li plating over graphite anodes. This phenomenon was pointed out as a major reason for cell performance degradation and failure. One of the solutions for enabling extreme fast charging while retaining most of the battery energy can be achieved through the significant enhancement of the Li-ion mass-transport in electrolytes such that enough Li ions are available for intercalation in graphite.Researchers at ORNL have developed high performance electrolytes with optimized Li salt, solvents, and additives. The electrolytes have both higher Li ion conductivity and Li ion transference number, compared to state-of-the-art electrolyte. The electrolyte development is ideal for higher Li ion transport and has been identified as a significant step towards realizing cells with XFC capabilities.The electrolytes were filled into NMC622||graphite Li-ion cells (1.5 Ah pouch cells) and the cells were tested under 6C (10 minutes) XFC protocol in Figure 1. The cell with ORNL V2 electrolyte has 89% capacity retained after 500 XFC cycles, which is better than the targeted goal (80% after 500 cycles), and much better than the 64% retention for the Gen2 baseline electrolyte (1.2 M LiPF6 in EC:EMC 30:70 wt%). Continued cycling of the cells show 80% capacity retention after 1000 cycles. The cell can have an energy density of ~180 Wh/Kg (when scaled up to 50 Ah), which has met the targeted goal for energy density. After 1000 XFC cycles, the cell still has 141 Wh/kg energy density. When the cell was charged/discharged at C/3 after 1000 XFC cycles, it can still deliver 193 Wh/kg. This demonstrates the excellent performance of Li-ion cell using ORNL V2 electrolyte formulation for XFC capability.