Calcium-Coated Silicon-Silicate Anodes for Cycle Stability
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Solution Overview
Problem
Lithium silicate-based negative electrodes in non-aqueous electrolyte secondary batteries are prone to dissolution in electrolyte decomposition products, leading to increased surface area and accelerated side reactions, which deteriorate battery capacity over charge-discharge cycles.
Innovation Solution
Incorporating a calcium-containing conductive layer on composite particles with a silicate phase and dispersed silicon phases, where the calcium component reacts with electrolyte decomposition products to stabilize them, reducing contact with the silicate phase and suppressing capacity deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium silicate is used as negative electrode active material, then high theoretical capacity density is achieved, but dissolution in electrolyte decomposition products increases surface area and accelerates side reactions
Solution Approach 1:
A calcium-containing conductive layer is introduced as an intermediary between the lithium silicate particles and the electrolyte decomposition products. The calcium component selectively reacts with HF to form CaF2, preventing HF from attacking the lithium silicate surface. This mediator approach protects the lithium silicate while maintaining electrical conductivity through the conductive layer.
Solution Approach 2:
The negative electrode material is designed as a composite system consisting of lithium silicate particles dispersed in a conductive matrix containing calcium component. This composite structure combines the high capacity of lithium silicate with the protective and conductive properties of the calcium-containing matrix, achieving both high capacity and improved cycle stability.
2Reliability
If calcium component is added to react with electrolyte decomposition products, then side reactions are suppressed, but electrical conductivity may be reduced
Solution Approach 1:
The conductive layer is designed as a composite material combining calcium-containing compounds (such as calcium carbonate or calcium oxide) with conductive materials (such as carbon black or graphite). This composite structure provides both the chemical protection from HF and the necessary electrical conductivity for electrode function.
Solution Approach 2:
The calcium component is controlled within specific quantity ranges (0.1-5.0 mass% relative to lithium silicate) to optimize the balance between protective function and conductivity. The particle size of calcium component is also controlled (1-10 μm) to ensure adequate surface area for HF reaction while maintaining good contact with conductive network.
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 calcium-containing conductive layer stabilizes electrolyte decomposition products, minimizing the increase in lithium silicate surface area and inhibiting side reactions, thereby enhancing the battery's charge-discharge cycle characteristics.
Implementation Method 1
the calcium component reacts with electrolyte decomposition products to stabilize them
Data Source
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AI summary
A negative electrode material for a non-aqueous electrolyte secondary battery includes composite particles, and a conductive layer disposed on a surface of each of the composite particles. The composite particles each have a silicate phase, and silicon phases dispersed in the silicate phase. The conductive layer contains a calcium component.