Synergistic sulfur-chlorine battery chemistry towards efficient energy storage

Conversion-type batteries with high energy storage efficiencies are crucial to minimize the energy loss during energy storage. However, current conversion-type batteries generally show relatively low energy storage efficiencies of (59-95)% with large charge-discharge overpotentials of 200-1500 mV. Here we report a rechargeable battery with a maximum energy storage efficiency of 99.5% and a small overpotential of 9 mV, based on a S-Cl synergistic chemistry with fast reaction kinetics. We verify that the in situ formed Cl₂ during charging can trigger highly efficient SO₂/SO₂Cl₂ conversion with a maximum current density of 400 mA/cm², which is one to three orders of magnitude higher than those of state-of-the-art conversion-type batteries. In addition, the high energy storage efficiencies of (93 - 97)% have been validated under a variety of harsh yet practical conditions, e.g., at a low temperature of - 20 °C and a high areal capacity of 13.5 mAh/cm². We further demonstrate their potential applications by producing a 250 mAh pouch cell, an on-chip microbattery, and a wearable fiber battery, which exhibit high electrochemical properties and practicability.