Flame-Retardant Electrolyte Composition for High-Ni/High-Si Li-Ion Batteries
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Solution Overview
Problem
High-ni/high-Si lithium-ion batteries face challenges in achieving both high energy density and safety performance due to thermal runaway causing gas generation and flammability, primarily from electrolyte decomposition.
Innovation Solution
An electrolyte containing additives like trimethyl phosphate (TMP) and ethoxy(pentafluoro)cyclotriphosphazene (PFPN) with specific mass ratios, optionally combined with lithium difluorophosphate (LiPO2F2) and tripropargyl phosphate (TPP), to inhibit gas generation and enhance safety through radical capture and film formation, reducing impedance and improving electrochemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-nickel ternary materials and silicon-based materials are applied to achieve high energy density, then the energy density is improved, but the safety performance deteriorates due to thermal runaway and gas generation
Solution Approach 1:
The patent introduces a fluorinated cyclic phosphazene compound as an intermediary substance in the electrolyte that mediates between the high-energy-density electrodes (high-nickel ternary and silicon-based materials) and the thermal runaway process. This compound acts as a flame retardant and gas generation inhibitor, capturing free radicals and forming protective films that prevent thermal propagation while allowing the high-capacity electrodes to function.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by incorporating fluorinated cyclic phosphazene compounds with specific molecular structures and ratios. This parameter change transforms the electrolyte's thermal and electrochemical properties, enabling it to resist thermal runaway and suppress gas generation while maintaining compatibility with high-nickel and silicon-based electrodes.
2Productivity
If conventional electrolytes are used in high-Ni/high-Si batteries, then the electrochemical performance is maintained, but gas generation and flammability increase during thermal runaway
Solution Approach 1:
The patent converts the harmful thermal runaway process into a beneficial controlled reaction by using fluorinated cyclic phosphazene compounds that decompose endothermically to absorb heat and release flame-retardant gases. The compound transforms the uncontrolled exothermic decomposition of conventional electrolytes into a controlled endothermic process that suppresses fire and reduces gas generation.
Solution Approach 2:
The patent creates a composite electrolyte system combining fluorinated cyclic phosphazene compounds with conventional electrolyte components. This composite material integrates the high ionic conductivity of conventional electrolytes with the flame-retardant and gas-suppression properties of the phosphazene compound, achieving both electrochemical performance and safety.
3Use of energy by moving object
If electrolyte decomposition occurs during thermal runaway, then energy release is achieved, but combustible gases are generated causing flammability and explosiveness
Solution Approach 1:
The fluorinated cyclic phosphazene compound serves as an intermediary that intercepts the decomposition pathway of the electrolyte. Instead of direct decomposition into combustible gases, the phosphazene compound decomposes first to form protective char layers and release non-flammable gases, mediating the energy release process to prevent explosive gas generation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The electrolyte significantly reduces gas generation and flammability, enhances safety performance, and improves electrochemical and cycling performance, extending the cycling service life of lithium-ion batteries.
Implementation Method 1
the first additive releases a large number of free radicals capable of capturing combustion radicals (H−, O2*, HO−) in the gas phase during the heating process
Implementation Method 2
N2 and ammonia produced by the combustion process of nitrogen in PFPN form a protective layer, which inhibits the supply of oxygen
Implementation Method 3
both the TMP and PFPN have properties of low combustion heat, so that the electrolyte shows excellent flame retardant effect under the synergistic effect of phosphorus in TMP and fluorine in PFPN
Data Source
AI summary
The electrolyte includes a first additive, in which a mass fraction of the first additive in the electrolyte is 2.5-5.5%, the first additive contains trimethyl phosphate (TMP) and ethoxy (pentafluoro) cyclotriphosphazene (PFPN), and a mass ratio of the TMP to the PFPN is (0.5-2):(2-3.5). The electrolyte is added with the first additive containing TMP and PFPN, and both the TMP and PFPN have properties of low combustion heat, which enhances the flame retardant effect of the electrolyte. By applying the electrolyte in a lithium-ion battery, it not only reduces the risk of the lithium-ion battery becoming flammable and explosive, when suffering thermal runaway, caused by the generation of flammable gases due to the reduction and decomposition of the electrolyte, improving the safety performance of the batteries, but also reduces the gas generation of the battery stored at high temperatures, and improves the battery storage performance at high temperatures.