Silicon-Based Anode Gradient Shell Structure for Better Cycle Life
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Solution Overview
Problem
Conventional lithium ion batteries using graphite as anode material face limitations due to low theoretical capacity, and silicon-based anode materials suffer from poor cycle performance and high lithium consumption during the first charge-discharge cycle, making them unsuitable for commercial applications.
Innovation Solution
A silicon-based anode material for secondary batteries is developed, comprising an inner core of Si particles and silicon oxide SiOx1, a first shell layer of MySiOz and C particles with increasing M and C content from the inner core to the outer side, and a second shell layer of a carbon film or composite film layer. This structure improves the first charge-discharge cycle capability and reduces production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based anode material is used to replace graphite, then theoretical capacity is improved (4200 mAh/g vs 372 mAh/g), but cycle performance deteriorates due to serious volume effect
Solution Approach 1:
The silicon-based anode material is divided into small particles with diameter of 0.5-5 μm, and further organized into a composite structure with silicon oxide matrix and carbon coating layers. This segmentation reduces the volume effect impact on overall structure and improves cycle performance while maintaining high capacity.
Solution Approach 2:
The patent creates a composite material structure consisting of silicon particles embedded in silicon oxide matrix (SiOx where 0.5 < x ≤ 1.5), surrounded by a carbon-containing compound coating layer. This composite structure combines the high capacity of silicon with the stability of silicon oxide and carbon, resolving the cycle performance issue.
2Quantity of substance
If lithium supplementation process is applied to improve capacity, then lithium content is increased, but safety performance deteriorates and excessive Si grain growth occurs reducing cycle life
Solution Approach 1:
The patent performs preliminary lithium supplementation during the sintering process at 300-1000°C, where lithium compounds are pre-introduced into the silicon oxide matrix before final electrode assembly. This preliminary action ensures uniform lithium distribution without causing excessive grain growth or safety issues that occur with post-assembly lithium plating.
Solution Approach 2:
The patent changes the parameters of lithium supplementation by using lithium compounds (such as lithium carbonate, lithium hydroxide, or lithium nitrate) and controlling the lithium content parameter to be 1-15 mass% of the total anode material. This parameter control prevents excessive lithium that would cause grain growth while ensuring sufficient lithium for high capacity.
3Quantity of substance
If silicon oxide material is used as anode, then capacity is improved, but first cycle Coulombic efficiency deteriorates due to generation of irreversible substances
Solution Approach 1:
The patent optimizes the silicon oxide composition parameter (SiOx where 0.5 < x ≤ 1.5) to balance capacity and Coulombic efficiency. By controlling the oxygen content parameter, the material achieves sufficient capacity while reducing irreversible lithium consumption during the first cycle, improving overall efficiency.
Solution Approach 2:
The patent creates a composite structure where silicon particles are embedded in silicon oxide matrix and coated with carbon-containing compounds. This composite structure reduces the direct exposure of silicon oxide to electrolyte, minimizing irreversible substance generation while maintaining high capacity through the silicon core.
4Reliability
If conventional lithium ion battery uses graphite anode, then cycle performance is stable, but theoretical capacity is limited to 372 mAh/g
Solution Approach 1:
The patent develops a composite anode material combining silicon (high capacity) with silicon oxide and carbon-containing compounds (providing structural stability). This composite structure achieves both high theoretical capacity (4200 mAh/g) and stable cycle performance, overcoming the limitations of pure graphite anodes.
Solution Approach 2:
The patent applies different materials to different parts of the anode structure: silicon core for high capacity, silicon oxide matrix for structural stability, and carbon coating for surface protection. This local quality assignment allows each component to perform its optimal function, achieving both high capacity and stability.
Data Source
AI summary
A silicon-based anode material for secondary batteries, a preparation method thereof and a secondary battery are provided. The silicon-based anode material includes: an inner core including an Si particle and silicon oxide SiOx1, where 0<x1<2, a first shell layer including a compound of the general formula MySiOz (0<y≤4, 0<z≤5, and z≥x1) and a C particle, wherein the first shell layer covers the inner core, and the contents of M and C in the first shell layer gradually increase from a side thereof close to the inner core to another side thereof far away from the inner core; and a second shell layer including a carbon film layer or a composite film layer formed by a carbon film layer and a conductive additive, the second shell layer covers the first shell layer. The first charge-discharge cycle capability of the silicon-based anode material is improved, and the manufacturing cost is reduced.