Lithium-Ion Battery Electrolyte Ratios for Graphite SEI Stability
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Solution Overview
Problem
Lithium-ion batteries using natural graphite as negative electrode material face issues with non-uniform particle size, surface defects, and volume expansion, leading to internal stress, reduced service life, and safety concerns, particularly affecting cycle performance and high-temperature storage.
Innovation Solution
A lithium-ion battery design incorporating an electrolytic solution with vinylene carbonate and fluoroethylene carbonate, where the weight percentages of these components and the OI value of the negative active material are optimized to form a tough SEI film, reducing damage from volume expansion and enhancing cycle and high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used as negative electrode material, then capacity and compacted density are improved, but particle uniformity and surface quality deteriorate
Solution Approach 1:
The patent applies local quality by treating the surface of natural graphite particles with a coating layer that has different properties from the bulk material. The coating layer is designed to provide uniform surface characteristics and defect repair locally, while maintaining the high capacity and compacted density of the natural graphite core.
Solution Approach 2:
The patent uses composite materials by combining natural graphite with a coating layer formed from electrolyte components. This composite structure integrates the high capacity of natural graphite with the surface protection and uniformity provided by the coating, resolving the contradiction between capacity and particle uniformity.
2Quantity of substance
If natural graphite is used as negative electrode material, then capacity and compacted density are improved, but service life and safety performance deteriorate
Solution Approach 1:
The patent applies preliminary action by forming a protective coating layer on the natural graphite surface before the battery undergoes cycling. This pre-formed coating layer prevents surface defects from causing damage during subsequent charging and discharging cycles, thereby extending service life while maintaining high capacity.
Solution Approach 2:
The patent uses beforehand cushioning by creating a buffer coating layer that absorbs and mitigates the harmful effects of surface defects and volume expansion during battery cycling. This coating acts as a cushion that protects the underlying natural graphite from damage, improving reliability without sacrificing capacity.
3Strength
If vinylene carbonate and fluoroethylene carbonate are added to electrolytic solution, then SEI film toughness is improved, but internal resistance increases
Solution Approach 1:
The patent applies parameter changes by optimizing the concentrations and ratio of vinylene carbonate and fluoroethylene carbonate in the electrolyte. By carefully adjusting these parameters, the patent achieves sufficient SEI film toughness while minimizing the increase in internal resistance, resolving the contradiction between film strength and electrical resistance.
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 composition significantly reduces internal resistance and improves both cycle and high-temperature storage performance by forming a resilient SEI film on the negative electrode, addressing the issues of volume expansion and side reactions.
Implementation Method 1
The electrolytic solution includes vinylene carbonate and fluoroethylene carbonate... form a tough SEI film, reducing damage from volume expansion
Implementation Method 2
the particles of the natural graphite are not uniform in size, and include relatively many surface defects, and therefore, are scarcely compatible with an electrolytic solution, incur relatively many side reactions, and tend to expand in volume during cycling, thereby increasing the internal stress of the battery
Data Source
AI summary
A lithium-ion battery includes an electrolytic solution and a negative electrode plate. The electrolytic solution includes vinylene carbonate and fluoroethylene carbonate. The negative electrode plate includes a negative active material. An OI value of the negative active material is a. Based on a weight of the electrolytic solution, a weight percent of the vinylene carbonate is b %, and a weight percent of the fluoroethylene carbonate is c %; and a, b, and c satisfy: 0.3≤a/(b+c)≤6; 0.02≤b+c≤10; and 0.1<b/c<3.