Battery Electrolyte Composition for High-Temperature Cycling Stability
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Solution Overview
Problem
Existing electrolytes in batteries suffer from poor high-temperature cycling performance due to the instability of ethylene carbonate (EC) at high temperatures and the poor thermal stability of electrolyte salts, leading to increased side reactions and reduced ionic conductivity.
Innovation Solution
A non-aqueous electrolyte composition comprising ethylene carbonate (EC) at 5%-25% weight content, a first electrolyte salt with specific formula (1), and a second electrolyte salt with formula (2), balanced by weight ratios x/y of 0.75≤x/y≤5 and x/z of 120≤x/z≤3000, forms a synergistic effect to enhance thermal stability, reduce hydrolysis, and form a flexible interfacial film, thereby improving high-temperature cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene carbonate (EC) is used as a solvent in the electrolyte, then the ionic conductivity is improved, but the thermal stability deteriorates at high temperatures
Solution Approach 1:
The patent combines EC with chain carbonates (EMC, DEC, DMC) in specific ratios to create a composite electrolyte system. This composite approach allows the electrolyte to benefit from EC's high dielectric constant and ionic conductivity while the chain carbonates provide thermal stability and flexibility, resolving the contradiction between ionic conductivity and thermal stability at high temperatures.
Solution Approach 2:
The patent optimizes the weight percentage of EC within a specific range (5-25%) rather than using it in excess. By controlling the concentration parameter of EC and balancing it with other components, the electrolyte achieves sufficient ionic conductivity while preventing the thermal degradation issues that occur with high EC content at elevated temperatures.
2Reliability
If electrolyte salt content is increased to improve ionic conductivity, then the conductivity is improved, but the thermal stability deteriorates
Solution Approach 1:
The patent employs a composite electrolyte salt system combining lithium hexafluorophosphate (LiPF6) with lithium fluorosulfonate (LiFSO3) or lithium bis(oxalato)borate (LiBOB). This composite salt approach enables the electrolyte to achieve high ionic conductivity through LiPF6 while the alternative salts contribute to thermal stability and reduced hydrolysis, resolving the contradiction between conductivity and thermal stability.
Solution Approach 2:
The patent assigns different functional roles to different electrolyte salt components: LiPF6 primarily provides ionic conductivity, while LiFSO3/LiBOB specifically enhance thermal stability and reduce hydrolysis. This functional differentiation within the electrolyte salt system allows simultaneous optimization of conductivity and thermal stability.
3Reliability
If EC content is increased to improve solvation, then the solvation ability is improved, but side reactions increase at high temperatures
Solution Approach 1:
The patent limits EC content to a specific weight percentage range (5-25%) in the non-aqueous solvent system. By optimizing this concentration parameter, the electrolyte achieves adequate solvation ability for lithium ions while preventing the excessive side reactions and decomposition that occur with high EC content at elevated temperatures.
Solution Approach 2:
The chain carbonates (EMC, DEC, DMC) act as intermediary components that mediate between EC's solvation ability and thermal stability requirements. These intermediaries provide a balanced environment that maintains sufficient solvation while reducing the direct exposure of EC to high-temperature conditions, thereby minimizing side reactions.
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 optimized electrolyte composition enhances the battery's high-temperature cycling performance by reducing side reactions, maintaining ionic conductivity, and forming a durable interfacial film, thus extending the battery's cycle life under high-temperature conditions.
Implementation Method 1
the poor thermal stability of electrolyte salts, leading to increased side reactions
Data Source
AI summary
An electrolyte includes a non-aqueous solvent and an electrolyte salt, where the non-aqueous solvent includes ethylene carbonate (EC), and a weight content of the EC in the non-aqueous solvent is denoted by x, based on a total weight of the non-aqueous solvent; the electrolyte salt includes a first electrolyte salt represented by formula (1) and a second electrolyte salt represented by formula (2), and a weight content of the first electrolyte salt in the electrolyte is denoted by y, and a weight content of the second electrolyte salt is denoted by z, based on a total weight of the electrolyte; R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, R3 includes a fluorine atom or a C1-C6 fluoroalkyl group, and M1 and M2 each independently include one or more of Li, Na, and K; where 5%≤x≤25%, 0.75≤x/y≤5, and 120≤x/z≤3000.