Silicon Anode Buffer Layer for Battery Volume Expansion
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Solution Overview
Problem
Silicon-based materials as negative electrode active materials in secondary batteries experience significant volume expansion and contraction during charging and discharging, leading to structural damage, reduced cycling performance, and safety hazards such as thermal runaway due to excessive internal resistance and lithium precipitation.
Innovation Solution
The use of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide as positive electrode active materials, combined with silicon-based materials in the negative electrode, where the volume changes of both electrodes are matched to minimize the 'breathing effect', and the inclusion of carbon materials for improved structural stability, along with specific film thickness and compaction densities to maintain electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used as negative electrode active material to increase energy density, then the energy density of secondary batteries is improved, but the volume expansion and contraction during charging and discharging causes structural damage to the electrode plate
Solution Approach 1:
The negative electrode is divided into multiple layers including a buffer layer and a silicon-based material layer. The buffer layer segments the volume expansion stress from the current collector, preventing structural damage while allowing the silicon-based material to expand and contract during charging and discharging cycles.
Solution Approach 2:
The negative electrode uses a composite structure combining a buffer layer (made of carbon material or metal) with silicon-based material layers. This composite design allows the buffer layer to provide structural stability while the silicon-based material provides high capacity, resolving the contradiction between energy density and structural strength.
2Quantity of substance
If silicon-based materials are used as negative electrode active material, then the energy density is improved, but the cycling performance deteriorates due to volume expansion at full charged state
Solution Approach 1:
A buffer layer is placed between the silicon-based material and the current collector to beforehand cushion the volume expansion stress. This buffer layer absorbs the mechanical stress during charging, preventing structural damage that would otherwise occur during subsequent cycling operations.
Solution Approach 2:
The invention changes the structural parameters of the negative electrode by introducing a buffer layer with specific thickness and material properties. This parameter modification allows the electrode to accommodate volume changes during cycling, improving reliability while maintaining high energy density from the silicon-based material.
3Stability of the object's composition
If the negative electrode film layer compaction density is increased to improve structural stability, then the structural stability is improved, but the lithium ion diffusion resistance increases
Solution Approach 1:
The negative electrode is segmented into a buffer layer and a silicon-based material layer with different compaction densities. The buffer layer can be compacted for stability, while the silicon-based material layer maintains lower compaction density to facilitate lithium ion diffusion, thus resolving the contradiction between structural stability and ion diffusion.
Solution Approach 2:
Different regions of the negative electrode have different local qualities: the buffer layer has higher compaction density for structural stability, while the silicon-based material layer has optimized lower density for lithium ion diffusion. This local differentiation allows both requirements to be satisfied simultaneously.
Data Source
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AI summary
The present application relates to a secondary battery and a battery module, a battery pack and an apparatus containing the secondary battery. In particular, the secondary battery includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte, characterized in that: the secondary battery satisfies the following formula I: 2≤|(AF/AE-1)/(CE/CF-1)|≤7 (Formula I) in which CF represents an unit cell volume as measured when the positive electrode active material is prepared into a button battery and the button battery is charged to 100% SOC at a rate of 0.05C; CE represents an unit cell volume as measured when the positive electrode active material is prepared into a button battery and the button battery is discharged to 0% SOC at a rate of 0.05C; AF represents a volume of the negative electrode active material particles as measured when the silicon-based material is prepared into a single-particle battery, and the single-particle battery is charged to 100% SOC at a rate of 0.5C; and AE represents a volume of the negative electrode active material particles as measured when the silicon-based material is prepared into a single-particle battery, and the single-particle battery is discharged to 0% SOC at a rate of 0.5C.