A 4.8 V Reversible Li2CoPO4F/Graphite Battery Enabled by Concentrated Electrolytes and Optimized Cell Design

Abstract

AbstractElevating the voltage of lithium‐ion batteries (currently 3.8 V) is a simple and pragmatic way to achieve high‐density energy storage. Many so‐called “5 V‐class” cathodes have been discovered over the past decade; however, they have been studied below 5 V (vs. Li/Li+) because of the severe oxidation of electrolytes and other cell components. Here, highly reversible charge‐discharge cycling of Li2CoPO4F/graphite full‐cells up to a cut‐off voltage of 5.2 V is demonstrated for the first time. This result is achieved with synergetic effects of an optimized cell design and a newly designed concentrated electrolyte based on LiBF4, propylene carbonate (PC), and fluoroethylene carbonate (FEC). As an electrolyte design rationale, two important properties of high oxidation stability and anode‐passivation ability are clearly allocated for LiBF4 and FEC, respectively. Besides, all other cell components (e. g., conductive carbon, separator, and binder) are reconsidered and customized for use at >5 V. The new concentrated electrolyte and optimized cell design presented here will pave the way for developing over‐5 V rechargeable batteries.