Design Strategies of Safe Electrolytes for Preventing Thermal Runaway in Lithium Ion Batteries

Abstract

The safety problems of lithium ion batteries (LIBs) have been the main obstacles that hinder their broad applications in portable electronic devices, electric vehicles, and energy storage. Such problems originate from flammable solvent-containing liquid electrolytes that could be easily oxidized upon excessive heat, leading to further heat accumulation and, subsequently, thermal runaway. The design strategies of a safe electrolyte could control the flammability and volatility of the liquid electrolyte, might prevent the thermal runaway, and ultimately ensure the risk-free and fire-free operation of LIBs. This work is to explore the mechanism of thermal runaway and review the state-of-the-art of the designs of a safe electrolyte for LIBs, including the additions of flame retardant additives, overcharge additives, and stable lithium salts and the adoption of solid-state electrolytes, ionic liquid electrolytes, and thermosensitive electrolytes. The features, advantages, and drawbacks of these strategies are systematically summarized, compared, and discussed, while the development direction of a safer electrolyte for future LIBs is proposed in the end.

A Review of Degradation Mechanisms and Recent Achievements for Ni‐Rich Cathode‐Based Li‐Ion Batteries

“…The reactions involved in the gas release are typically exothermic, triggering a series of chain reactions and eventually leading to a severe risk of catastrophic self‐combustion of the battery. [ 45 ] The gaseous decomposition products are generally CO 2 and O 2 . In Ni‐rich cathodes, the origins of gas generation arise from three aspects, as schematically shown in Figure 10 a: 1) Electrolyte/surface mixed reactivity, including lattice oxygen loss induced by the structural defects (cation disorder and surface reconstruction as discussed above), lithium hydroxides, and unreacted precursors at the surface; 2) decomposition of Li 2 CO 3 and reaction with the electrolyte; 3) direct electrolyte oxidation.…”

“…To optimize the electrolytes, many additives with various functional groups have been studied to restrain the decompositions of lithium salts and organic solvents in the electrolyte. [ 45,110,111 ] Some up‐to‐date and representative approaches for improving cathode, anode, and electrolyte in Ni‐rich cathode‐based LIBs will be discussed below.…”

Bioinspired Thermal Runaway Retardant Capsules for Improved Safety and Electrochemical Performance in Lithium‐Ion Batteries

“…[17][18][19][20] The commonly used flame-retardant additives include phosphorus, triazine, ionic liquids, fluorine-containing additives, bisphenol, etc. [17][18][19][20] Similar to flame-retardant additives, another effective method for controlling TR in the first and second stages is to use electrolyte poisons, including benzylamine (BA), dibenzylamine (DBA), and trihexylamine (THA), diols, diamines, 1,1′-(methylenedi-4,1-phenylene) bismaleimide (BMI), etc. [21][22][23][24] These flame retardants and poisoning agents prevent the occurrence or delay the development of TR.…”

“…However, in most cases, huge amounts of TRRs are required to ensure a high level of cell safety, which consequently degrades the overall ionic conductivity of the electrolyte, resulting in poor electrochemical performance. [11,[17][18][19][20][21][22][23][24] Encapsulation can solve the problems faced by the above two methods by avoiding direct contact between the TRR and electrolyte, which is inspired by the functions of core-shell structures such as seeds, eggs, and fruits in nature. [25] In these capsule structures, the shell isolates the core from the outside, so that the core and the outside do not affect each other.…”

Bidentate Phosphonate‐Functionalized Ionic Liquid Exhibiting Better Ability in Improving the Performance of Lithium‐Ion Battery

“…However, the applications of such organic carbonate‐based electrolytes have been limited by their intrinsic features such as flammability, [8] volatility, moisture sensitivity and redox instability [9] . Harsh working conditions, especially in cases of abuse or short circuit, [10] can cause a fire [11] or even an explosion [12] . Therefore, the search for electrolyte with good safety [13] while maintaining high electrochemical performance still remains challenging [14] .…”