Lithium-Ion Battery Electrolyte for Stable SEI and Low Gas Generation
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Solution Overview
Problem
Lithium-ion batteries with high compaction density and specific surface area negative electrodes experience severe side reactions and high gas production, leading to reduced cycling performance and storage issues due to the lack of a stable solid electrolyte interface (SEI) film and excessive lithium evolution.
Innovation Solution
A lithium-ion battery design incorporating a negative electrode with a compaction density of ≥1.4 g/cm3, using a non-aqueous electrolyte containing vinylene carbonate, fluoro ethylene carbonate, an unsaturated phosphate, and LiFSI, which forms a stable SEI film and improves conductivity, thereby reducing side reactions and gas production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative electrode has high compaction density and high specific surface area, then the energy density is improved, but side reactions with electrolyte increase and gas production increases
Solution Approach 1:
The patent introduces a multi-component electrolyte system comprising vinylene carbonate (VC), fluoro ethylene carbonate (FEC), and unsaturated phosphate esters as intermediary substances. These additives mediate the interaction between the high-surface-area negative electrode and the bulk electrolyte, forming a protective interface layer that suppresses harmful side reactions while allowing beneficial lithium insertion/extraction processes to proceed efficiently.
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte by incorporating specific ratios of VC (0.1-3%), FEC (0.1-30%), and unsaturated phosphate esters (0.1-2%). This parameter change transforms the electrolyte's interfacial properties, enabling it to form a stable SEI film on high-surface-area electrodes that prevents excessive side reactions and gas generation while maintaining high energy density performance.
2Reliability
If high content of FEC is added to form stable SEI film, then side reactions are suppressed, but lithium evolution occurs and oxidation reactions increase at high voltage
Solution Approach 1:
The patent creates a composite electrolyte system combining three different additive types (VC, FEC, and unsaturated phosphate esters) that work synergistically. VC provides initial SEI formation, FEC enhances SEI stability and lithium conductivity, and unsaturated phosphate esters suppress oxidation at high voltage. This composite approach achieves stable SEI film formation without the harmful side effects of high FEC content alone.
Solution Approach 2:
The patent applies different electrolyte additives at different functional locations: VC and FEC primarily act at the negative electrode interface to form stable SEI, while unsaturated phosphate esters primarily protect the high-voltage positive electrode from oxidation. This localized functional distribution optimizes protection where needed while minimizing unwanted side reactions throughout the battery system.
3Quantity of substance
If the negative electrode material layer has high coating weight, then the capacity is improved, but lithium evolution occurs with thick SEI film
Solution Approach 1:
The electrolyte additives act as intermediaries that enable high coating weight electrodes to function without lithium evolution. The unsaturated phosphate esters and FEC form an interface layer that mediates between the high-capacity electrode material and the electrolyte, preventing the thick SEI formation that would otherwise trap lithium ions and cause evolution, while still allowing sufficient lithium transport for high capacity utilization.
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 solution enhances the cycling performance and storage stability of lithium-ion batteries by forming a dense SEI film, reducing battery impedance, and inhibiting gas production, while maintaining optimal viscosity and conductivity for improved charge and discharge rates at various temperatures.
Implementation Method 1
adding an appropriate amount of fluoroethylene carbonate (FEC) to lithium batteries with negative electrodes (or silicon-doped graphite negative electrodes) of higher specific surface area favors forming a stable solid electrolyte interface (SEI) film on surfaces of the negative electrodes to suppress the side reactions
Implementation Method 2
the non-aqueous electrolyte includes solvent, an electrolyte salt, vinylene carbonate, fluoro ethylene carbonate and an unsaturated phosphate shown in formula 1
Implementation Method 3
a high content of FEC easily participates in oxidation reactions in high-voltage positive electrodes, causing the battery to generate a large amount of gas at high temperatures
Data Source
AI summary
In order to overcome the problems in existing lithium ion batteries having high compactness and high-specific-surface-area negative electrodes of serious side reactions of electrolytes and high gas production, the present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode material layer, the compaction density of the negative electrode material layer is greater than or equal to 1.4 g/cm3, and the negative electrode material layer comprises a negative electrode active material, and the non-aqueous electrolyte comprises a solvent, an electrolyte salt, a vinylene carbonate, a fluoroethylene carbonate, and an unsaturated phosphate represented by structural formula 1, and the electrolyte salt comprises LiPF6 and LiFSI. The lithium ion battery provided by the present invention has good cycle performance, high and low temperature storage performance, and lithium precipitation resistance.