Voltage-Induced Bromide Redox Enables Capacity Restoration of Fast-Charging Batteries

Abstract

Fast-charging lithium-ion batteries (LIBs) are essential for electric vehicles (EVs) to compete with conventional gasoline ones in terms of charging viability, yet the aggressive capacity drop in fast-charging scenarios gives rise to concerns regarding durability and sustainability. Herein, it is clarified that for fast-charging batteries, the excessive lithium (Li) plating on graphite anode inevitably brings capacity fading, and the concurrent accumulation of Li₂O-dominant passivation species that form dead Li is the main reason for their poor rechargeability. To refresh the passivated graphite, a voltage-induced activation mechanism is developed to leverage bromide (Br⁻/Br₃⁻) redox couple for Li₂O and isolated Li⁰ activation in situ. Along with a tiny amount of lithium bromide (LiBr) added into the electrolyte, the cut-off voltage of activation processes is controlled to initiate and maximize the effectiveness of Br⁻/Br₃⁻ redox couple. The capacity of degraded fast-charging cells can increase from lower than 30 to ≈118 mAh g⁻¹ before and after the activation, respectively. Notably, the process is not one-off; a subsequent activation is feasible. For the same battery that suffered from another round of fast charging, this design still restores the reversible capacity to ≈100 mAh g⁻¹. Such a voltage-mediated mechanism can effectively prolong the service life of practical fast-charging batteries.