Si Alloy Graphite Negative Electrode for Li-Ion Battery Capacity
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in increasing capacity and cycle life due to the high powder resistance of silicon (Si) and limitations in coating amounts of Si-containing negative electrode materials.
Innovation Solution
A lithium ion secondary battery design incorporating a negative electrode with a specific mass ratio of graphite to Si alloy and controlled coating amounts, within the ranges of 0.43 to 9.0 for the mass ratio and 8 to 18 mg/cm² for the coating, to enhance initial capacity and capacity retention rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the mixing ratio of Si is increased to increase capacity, then the initial capacity can be increased, but the capacity retention rate may lower
Solution Approach 1:
The invention changes the physical and chemical parameters of the negative electrode by using Si alloy particles with specific Si content (60-95 mass%) and controlling the mass ratio of graphite to Si alloy (0.43≦x≦9.0). It also optimizes the coating amount (8≦y≦18 mg/cm²) to achieve both high initial capacity and good capacity retention rate
Solution Approach 2:
The invention uses composite materials by combining graphite particles with Si alloy particles to form a negative electrode active material mixture. This composite structure allows the graphite to provide structural stability while the Si alloy provides high capacity, resolving the contradiction between initial capacity and capacity retention rate
2Quantity of substance
If the coating amount of Si is increased to increase capacity, then the initial capacity can be increased, but the cycle life may worsen
Solution Approach 1:
The invention optimizes the coating amount parameter to a specific range (8≦y≦18 mg/cm²) and controls the mass ratio parameter (0.43≦x≦9.0) to achieve both high initial capacity and long cycle life, avoiding the harmful effect of excessive Si coating
Solution Approach 2:
The invention applies different materials in different proportions within the negative electrode - using graphite as the base material and Si alloy as the high-capacity additive in controlled amounts, creating local optimization where each material contributes its strengths without overwhelming the system
Data Source
AI summary
A lithium ion secondary battery includes: a positive electrode including a positive electrode active material; a negative electrode formed by coating a negative electrode active material mixture onto a surface of a negative electrode collector, the negative electrode active material mixture including a negative electrode active material, a conductive additive, and a binder; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, in which the negative electrode active material includes graphite and an Si alloy, inequities of 0.43≦x≦9.0 and 8≦y<18 are satisfied when a mass ratio of the graphite and the Si alloy is defined as x and a coating amount of the negative electrode active material mixture is defined as y (mg/cm2). Thus, an initial capacity thereof can be increased and a capacity retention rate thereof can be improved in the lithium ion secondary battery which includes the Si alloy in the negative electrode.