Si-Carbon Negative Electrode Composition for Low-Swelling Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries using high-capacity negative electrode materials face issues with swelling and decreased battery properties due to large volume changes during charge and discharge.
Innovation Solution
A lithium ion secondary battery design that incorporates a negative electrode composition layer on a metal foil current collector, using a mixture of Si and hardly-graphitizable carbon as active materials, with a ratio of 50 to 90 mass % for Si and 10 to 50 mass % for the carbon material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-capacity negative electrode materials (Si, Sn, low crystalline carbon) are used to replace graphite, then battery capacity is improved, but volume change during charge and discharge increases causing swelling and decreased battery properties
Solution Approach 1:
The patent uses a composite negative electrode structure combining high-capacity materials (Si or Sn) with graphite. The high-capacity material provides enhanced lithium storage capacity while graphite provides structural stability. This composite approach allows the battery to achieve higher capacity without suffering from the severe volume expansion problems of pure Si or Sn electrodes.
Solution Approach 2:
The patent distributes high-capacity materials (Si or Sn) as particles within a graphite matrix rather than using them as a continuous phase. This local distribution allows the high-capacity material to contribute to capacity while the surrounding graphite provides a stable structural framework that accommodates local volume changes without causing overall electrode swelling.
2Quantity of substance
If high-capacity negative electrode materials are used, then battery capacity is improved, but the negative electrode transforms largely during repeating charge and discharge
Solution Approach 1:
By creating a composite of high-capacity material particles embedded in a graphite matrix, the patent achieves both high capacity and cycle stability. The graphite component acts as a stable framework that maintains electrode integrity over repeated charge-discharge cycles, preventing the transformation and degradation that would occur with pure high-capacity materials.
Solution Approach 2:
The graphite matrix serves as a pre-established cushioning framework that accommodates the volume expansion of high-capacity materials during lithiation. This pre-configured stable structure prevents catastrophic transformation during cycling by providing a compliant yet stable environment for the high-capacity material particles.
3Quantity of substance
If the ratio of high-capacity negative electrode material is increased to improve battery capacity, then capacity is improved, but swelling and capacity drop increase
Solution Approach 1:
The patent optimizes the ratio of high-capacity material to graphite in the negative electrode. By carefully controlling this compositional parameter, the patent achieves sufficient capacity enhancement from the high-capacity material while the graphite component continues to provide structural stability and minimize swelling and capacity drop during cycling.
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 battery effectively restricts swelling and maintains excellent charge discharge cycle characteristics by controlling the volume change of the negative electrode during charging and discharging.
Implementation Method 1
such a high-capacity negative electrode material shows a very large amount of volume change due to charge and discharge
Data Source
AI summary
The inventive negative electrode for the electrochemical element includes a negative electrode composition layer provided on at least one surface of a current collector made of a metal foil; in which the negative electrode composition layer includes material S comprising Si and a hardly-graphitizable carbon material as a negative electrode active material; in which assuming that the whole amount of the negative electrode active material contained in the negative electrode composition layer is 100 mass %, a ratio of the material S is 50 to 90 mass % and a ratio of the hardly-graphitizable carbon materials is 10 to 50 mass %. The inventive lithium ion secondary battery includes a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte liquid, and the negative electrode is constituted by the negative electrode for the electrochemical element of the present invention.