High Oxidation Potential ≈6.0 V of Concentrated Electrolyte toward High‐Performance Dual‐Ion Battery

Dual‐ion batteries (DIBs) show the advantages of high working voltage, cost‐effectiveness, and environmental friendliness, but conventional electrolytes commonly cannot satisfy simultaneously the requirements of wide voltage range and high‐concentration, leading to poor cycling durability and limited energy density. In this work, an electrolyte system with 4.0 m lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in tetramethylene sulfone, which shows merits of i) high oxidation potential ≈6.0 V to enable the insertion/deinsertion of FSI − reversibly at the graphite cathode, ii) dramatically suppressed gas formation under high working voltage, and iii) significantly elevated full‐cell DIB energy density, is developed. The DIB constructed with such an electrolyte is able to exhibit 113.3 mAh g −1 capacity and ≈4.6 V medium discharge voltage at 200 mA g −1 , along with 94.7% capacity retention after 1000 cycles. Moreover, this DIB delivers an energy density of ≈180 Wh kg −1 (including electrolyte which contributes to the capacity and electrode materials), one of the best performances amongst the related work on DIBs.