Nonflammable Electrolytes for Lithium-Ion Battery Safety

Lithium-ion batteries underpin modern portable electronics and electric vehicles, yet their widespread adoption is constrained by safety risks associated with flammable organic electrolytes. Nonflammable electrolytes offer a route to mitigate thermal runaway, the rapid exothermic cascade that can lead to fire or explosion. Strategies to achieve nonflammability encompass the use of intrinsically flame-retardant solvents (such as phosphates, fluorinated ethers or ionic liquids), high salt concentrations which suppress solvent volatility, and locally highly concentrated electrolytes combining a coordinating solvent with inert diluents to maintain low viscosity. These formulations must preserve a wide electrochemical window, ensure rapid ion transport and foster the formation of a stable solid electrolyte interphase. Advances in understanding the interplay between solvation structure, electrode–electrolyte interfacial chemistry and thermal stability have spurred the design of safer electrolytes with minimal performance penalty. Nonflammable electrolyte research carries global significance, promising higher-energy-density storage systems with enhanced tolerance to abuse, while facilitating regulatory approval and public confidence in large-scale energy applications.

Research from Nature Portfolio

Recent studies have interrogated the limits of concentrated formulations in preventing thermal runaway. Investigations into lithium bis(fluorosulfonyl)imide-based highly concentrated electrolytes revealed that although these systems are non-flammable in isolation, reduction reactions at the graphite anode trigger exothermic processes and cell overheating. This work emphasises that non-flammability under oxidative conditions does not guarantee safety under reductive, cell-level operation. Mechanistic analyses have guided a design philosophy that integrates both thermal stability and reduced electrolyte reactivity, pointing towards tailored salt anions and engineered interfacial layers as keys to truly safer lithium-ion cells.

Nonflammable Electrolytes for Lithium-Ion Battery Safety publication trend

The graph below shows the total number of articles in nonflammable electrolytes for lithium-ion battery safety across all publications each year (not limited to Nature Index journals).

Technical terms

Thermal runaway: A self-accelerating exothermic sequence in a battery that leads to rapid temperature rise and potential fire.

Electrochemical window: The voltage range over which an electrolyte remains electrochemically stable without decomposition.

Highly concentrated electrolyte (HCE): An electrolyte in which the salt-to-solvent ratio is sufficiently high to alter solvation dynamics and reduce flammability.

Locally highly concentrated electrolyte (LHCE): An HCE diluted with inert, non-coordinating solvents to lower viscosity while retaining concentrated solvation structures.

Solid electrolyte interphase (SEI): A passivation layer formed on electrode surfaces that controls ion transport and protects against continuous electrolyte decomposition.

References

1. Thermal runaway of Lithium-ion batteries employing LiN(SO2F)2-based concentrated electrolytes. Nature Communications (2020).
2. Recent Advances in Non-Flammable Electrolytes for Safer Lithium-Ion Batteries. Batteries (2019).
3. Is Nonflammability of Electrolyte Overrated in the Overall Safety Performance of Lithium Ion Batteries? A Sobering Revelation from a Completely Nonflammable Electrolyte. Advanced Energy Materials (2022).
4. A comparative analysis of the influence of hydrofluoroethers as diluents on solvation structure and electrochemical performance in non-flammable electrolytes. Journal of Materials Chemistry A (2023).