Si-Graphite Negative Electrode Composition for Low-Swelling Batteries
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Solution Overview
Problem
Si-containing particles in negative electrodes of nonaqueous electrolyte secondary batteries tend to swell significantly during charge and discharge cycles, leading to potential malfunctions and reduced battery reliability due to increased stress and risk of conductive path breakage.
Innovation Solution
A negative electrode with a low spring constant, achieved by using a combination of graphite and Si-containing particles with specific properties, such as average 10% yield strength ≤12 MPa and BET specific surface area between 0.5-3.5 m2/g, and a binder composition that includes carboxymethyl cellulose, poly acrylic acid, and styrene butadiene rubber, to mitigate stress and prevent swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-containing particles are used as negative electrode active material to increase capacity, then specific capacity is improved, but swelling rate increases during charge and discharge cycles
Solution Approach 1:
The patent uses a composite material system consisting of Si-containing particles (such as silicon oxide) combined with graphite particles and amorphous carbon material. This composite structure allows the high capacity of Si-containing particles to be utilized while the graphite and carbon components provide structural stability to counteract swelling, thus resolving the contradiction between high capacity and low swelling rate
Solution Approach 2:
The patent optimizes specific parameters including the spring constant of the negative electrode (700-3000 kN/mm), the ratio of Si-containing particles to graphite particles, and the properties of amorphous carbon material. By adjusting these parameters, the electrode achieves both high capacity and resistance to swelling during charge-discharge cycles
2Strength
If the negative electrode is made rigid to maintain structural integrity, then strength is improved, but stress concentration increases leading to conductive path breakage
Solution Approach 1:
The patent incorporates amorphous carbon material that forms a flexible coating or matrix around the active material particles. This flexible carbon layer acts as a buffer that absorbs swelling stress while maintaining structural integrity, preventing stress concentration that would lead to conductive path breakage
Solution Approach 2:
The composite structure of rigid Si-containing particles embedded in a more compliant matrix of graphite and amorphous carbon creates a hierarchical material system. The harder particles provide capacity while the softer matrix distributes and absorbs stress, preventing localized stress concentration
Data Source
AI summary
The herein disclosed negative electrode is a negative electrode for a nonaqueous electrolyte secondary battery that includes a current collector, and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer includes a negative electrode active material and a binder, and a graphite particle and a Si-containing particle are included as the negative electrode active material. An average 10% yield strength of the graphite particle is equal to or less than 12 MPa. A BET specific surface area of the graphite particle is equal to or more than 0.5 m2/g and not more than 3.5 m2/g. A spring constant in a thickness direction of the negative electrode is equal to or less than 200 kN/mm. A 90° peel strength between the current collector and the negative electrode active material layer is equal to or more than 1.5 N/m.