Electrolyte diluent with large electrostatic potential difference for fast charging and slow discharging lithium metal batteries

Progress in extending the cycle life of lithium metal batteries has primarily been achieved through strategies focused on slow charging and fast discharging conditions, with limited practical impact. However, accelerated performance degradation under the opposite operation protocols—fast charging and slow discharging—remains a challenge. Here, we introduce (difluoromethyl)trimethylsilane with a large electrostatic potential difference as a diluent for localized high-concentration electrolytes. The presence of this diluent limits the size of ion clusters and promotes the transfer of Li ions through the swollen solid-electrolyte-interphase layer for robust fast charging. The diluent also increases electrode polarization, which leads to spatially uniform Li stripping sites and allows reliable discharging even at low current densities. As a result, the electrolyte achieves an average Coulombic efficiency of 98.12% even at 12 mA cm−2 in Li | |Cu asymmetric cells. In full cells, a state-of-charge of 77.3% is achieved within 6 minutes while retaining 81.3% capacity after 200 cycles at a 10 C charging rate, demonstrating their stability under fast-charging and slow-discharging protocols. Fast-charging and slow-discharging operation of lithium metal batteries is limited by ion depletion and uneven charge transfer. Here, authors present a (difluoromethyl)trimethylsilane diluent with a large electrostatic potential difference to stabilize long cycling under 6 min fast charging.