Gradient Silicon Negative Electrode for Rapid Charging
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Solution Overview
Problem
Lithium-ion secondary batteries with silicon as a negative electrode active material experience capacity degradation during rapid charging due to thick solid electrolyte interphase (SEI) formation, leading to increased irreversible capacity and reduced charge acceptance.
Innovation Solution
A secondary battery design with a negative electrode active material layer containing carbon and silicon compounds, where the silicon content is higher near the current collector and lower on the surface, combined with fluoroethylene carbonate in the nonaqueous electrolyte solution, to control SEI formation and enhance charge acceptance during rapid charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is incorporated into the negative electrode active material layer to increase energy density, then the battery can supply more power, but the battery experiences capacity degradation during rapid charging due to thick SEI formation
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of silicon compounds within the negative electrode active material layer. The silicon content is higher in the lower layer portion (near the current collector) and lower in the upper layer portion (near the electrolyte interface). This non-uniform distribution optimizes both energy density and rapid charging performance by controlling where silicon is present to maximize capacity while minimizing harmful SEI formation.
Solution Approach 2:
The patent changes the concentration parameter of silicon compounds spatially within the electrode layer. By adjusting the silicon content gradient and controlling the thickness ratio between upper and lower layer portions, the patent optimizes the balance between energy density (requiring high silicon content) and rapid charging acceptance (requiring limited silicon exposure to electrolyte).
2Speed
If rapid charging is performed to supply power more quickly, then the charging speed increases, but the battery capacity decreases due to thick SEI formation and increased irreversible capacity
Solution Approach 1:
The patent uses local quality to create a controlled gradient of silicon compounds that allows rapid charging in specific regions while preserving overall capacity. The lower silicon content in the upper layer portion reduces SEI formation at the electrolyte interface during rapid charging, maintaining charge acceptance and preventing excessive capacity loss.
3Quantity of substance
If the silicon content is increased throughout the negative electrode active material layer to maximize energy density, then the theoretical capacity increases, but the charge acceptance during rapid charging deteriorates
Solution Approach 1:
The patent implements local quality by distributing silicon compounds non-uniformly throughout the negative electrode active material layer. High silicon content in the lower layer portion maximizes theoretical capacity, while reduced silicon content in the upper layer portion maintains good charge acceptance during rapid charging by minimizing SEI formation at the electrolyte interface.
Solution Approach 2:
The patent transitions from a uniform two-dimensional distribution of silicon to a three-dimensional gradient distribution. By considering the thickness direction as an additional dimension for compositional variation, the patent achieves both high capacity and good rapid charging performance simultaneously.
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 design suppresses capacity decrease and irreversible capacity increase during rapid charging, maintaining high charge acceptance and extending battery durability.
Implementation Method 1
negative electrodes containing silicon have low charge acceptance in rapid charging and tend to decrease the capacity by rapid charging... thick solid electrolyte interphase (SEI) formation
Implementation Method 2
a material containing silicon that is to be alloyed with lithium is anticipated to be employed as a negative electrode active material having a high theoretical capacity density
Data Source
AI summary
A secondary battery having a suppressed decrease in capacity, even through rapid charging, includes: a positive electrode; a negative electrode including a negative electrode current collector and a negative electrode active material layer formed thereon containing a carbon material and silicon compounds; and an electrolyte solution containing nonaqueous solvents including 10 volume % or more of fluoroethylene carbonate. When: a surface of the negative electrode active material layer that faces the negative electrode current collector and the back side thereof are set as first and second surfaces, respectively; a thickness of the negative electrode active material layer is set as T; and regions from the first and the second surfaces to a depth of 0.5T are set as lower and upper layer portions, respectively, mass M1 of the silicon compounds in the lower layer portion is larger than mass M2 of the silicon compounds in the upper layer portion.