Non-aqueous Electrolyte for Lithium Battery SEI Stability
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Solution Overview
Problem
Rechargeable lithium batteries face capacity and cycle-life deterioration due to the instability of the Solid Electrolyte Interface (SEI) layer, especially at high temperatures, which affects their performance and longevity.
Innovation Solution
A non-aqueous electrolyte composition comprising a lithium salt, an ester-based solvent (such as methyl propionate) with lithium difluoro(oxalate) borate and tris(trialkylsilyl)phosphate or related additives, which forms a stable SEI layer and enhances ion conductivity, preventing capacity and output degradation at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If propionate-based solvent is used to improve low temperature characteristic and prevent gas generation at high temperature, then low temperature performance is improved, but capacity and power output deteriorate at negative electrode
Solution Approach 1:
The patent combines multiple additives (lithium difluoro(oxalate) borate and tris(trialkylsilyl)phosphate or tris(trialkylsilyl)borate) with the propionate-based solvent to create a synergistic effect that maintains the low temperature performance benefits while preventing the capacity and power output deterioration caused by the solvent alone
Solution Approach 2:
The electrolyte uses a composite approach by combining the propionate-based solvent with specific additive compounds that form a stable SEI layer, creating a multi-component system that achieves both low temperature performance and maintains capacity/power output
2Reliability
If SEI layer is formed to protect negative electrode, then ion tunnel effect is achieved, but SEI layer deteriorates during repetitive charge and discharge
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing specific additives (lithium difluoro(oxalate) borate and tris(trialkylsilyl)phosphate/borate) that modify the SEI layer formation process, creating a more stable and durable SEI layer that maintains ion tunneling capability throughout the battery's cycle life
Solution Approach 2:
The additives act as intermediaries that facilitate the formation of a stable SEI layer, mediating between the electrolyte and the negative electrode to create a protective interface that resists deterioration during repetitive charge and discharge cycles
3Reliability
If SEI layer is used to prevent electrolyte decomposition, then stable charge and discharge is maintained, but SEI layer is easily destroyed at high temperature
Solution Approach 1:
The patent modifies the thermal stability parameters of the SEI layer by incorporating specific additives that raise the decomposition temperature and improve the thermal resistance of the SEI layer, allowing it to maintain stability at high operating temperatures while continuing to provide stable charge and discharge
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 proposed electrolyte composition improves battery capacity, cycle-life, and performance at low temperatures while maintaining stability and output at high temperatures, thereby extending the battery's lifespan and efficiency.
Implementation Method 1
lithium ions come out from a positive active material such as a lithium metal oxide and the like, move toward a negative active material such as graphite and the like, and then, are inserted between negative active material layers
Implementation Method 2
an electrolyte solution reacts with a lithium salt on the surface of a negative active material such as graphite and the like, producing a compound such as Li 2 CO 3, Li 2 O, LiOH, and the like. These compounds form a so-called SEI (Solid Electrolyte Interface) layer
Implementation Method 3
The SEI layer plays a role of an ion tunnel and thus, passes only lithium ions. Thus, the SEI layer brings about an ion tunnel effect that organic solvent molecules with a big molecular weight are prevented from being inserted between negative active material layers
Implementation Method 4
a non-aqueous electrolyte prepared by appropriately dissolving a lithium salt in a mixed organic solvent
Data Source
Figure 1
AI summary
According to one aspect of the present invention there is provided a non-aqueous electrolyte for a rechargeable lithium battery comprising: - a lithium salt; - a non-aqueous organic solvent including more than 50 wt% of an ester-based solvent based on the total weight of the non-aqueous organic solvent; - a first additive of lithium difluoro(oxalate) borate (LiF2OB); and - a second additive selected from the group consisting of tris(trialkylsilyl)phosphate, tris(trialkylsilyl)phosphite, tris(trialkylsilyl)borate, and mixtures thereof.