High-Concentration Electrolytes for Enhanced Stability

High-concentration electrolytes (HCEs) with salt-to-solvent ratios >1:3 have emerged as a promising strategy for improving battery stability and performance. HCEs based on lithium bis(fluorosulfonyl)imide (LiFSI) in dimethyl carbonate (DMC) solvents have achieved ionic conductivities of ~10 mS/cm while forming robust SEIs on both anodes and cathodes. These electrolytes exhibit exceptional oxidative stability (>5 V vs Li/Li+), enabling compatibility with high-voltage cathodes like LiCoO2 (LCO). Recent studies have shown that HCEs can increase cycle life by >50% compared to conventional electrolytes.

Localized high-concentration electrolytes (LHCEs), which dilute HCEs with inert solvents like hydrofluoroethers (HFEs), offer improved viscosity (~5 cP) and wettability while retaining the benefits of HCEs. LHCEs using LiFSI:DMC:HFE mixtures have demonstrated Coulombic efficiencies >99% in lithium-metal batteries while suppressing dendrite growth even at current densities of up to 5 mA/cm². These systems also reduce electrolyte decomposition rates by ~70%, extending cycle life beyond 1,000 cycles in NMC811||Li cells.

HCEs have been particularly effective in addressing challenges associated with silicon anodes (>4x higher capacity than graphite). For instance, HCEs based on LiFSI:ethylene carbonate (EC):ethyl methyl carbonate (EMC) mixtures have enabled stable cycling of silicon anodes for over 500 cycles with capacity retention >80%. The formation of fluorine-rich SEIs reduces volume expansion-induced cracking by ~50%, significantly improving electrode integrity.

Despite their advantages,HCEs face challenges related to cost (~30% higher than conventional electrolytes)and low-temperature performance(conductivity drops below -20°C).Recent advancements in solvent design(e.g.,using fluorinated carbonates)and salt optimization(e.g.,lithium difluoro(oxalato)borate(LiDFOB))have mitigated these issues,making HCEs more viable for commercial applications.

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