Negative Electrode with Gradient Binding Agents for Silicon Anodes
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries using silicon-containing materials as negative electrodes face issues with reduced electronic conductivity and ionic diffusivity due to expansion and contraction during charge and discharge cycles, leading to poor cycle characteristics.
Innovation Solution
A negative electrode configuration with a higher amount of binding agent A and conductive agent on the current collector-side region and a lower amount on the surface-side region, utilizing a rubber polymeric binding agent A and a water-soluble binding agent B, enhances electronic conductivity and ionic diffusivity by preventing agglomeration and ensuring even charge/discharge reactions across the electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing material is used as negative electrode active material, then high capacity is expected, but cycle characteristics are poor due to expansion and contraction causing pulverization and isolation
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of binding agents within the electrode structure. Specifically, the first binding agent is concentrated in the deep portion near the current collector, while the second binding agent is distributed in the entire mixture layer including the surface portion. This localized differentiation ensures that each region receives the appropriate binding characteristics needed to handle the expansion and contraction of silicon-containing materials, thereby improving cycle characteristics while maintaining high capacity.
2Duration of action of moving object
If charge and discharge are repeated, then electronic conductivity and ionic diffusivity are reduced by expansion and contraction, but cycle characteristics are reduced
Solution Approach 1:
The patent applies parameter changes by utilizing the distinct properties of two different binding agents with varying characteristics. The first binding agent (polymerizable compound) provides structural stability and adhesion to the current collector, while the second binding agent (water-soluble polymer) maintains flexibility and ionic conductivity. By adjusting the types and amounts of these binding agents, the electrode can maintain both electronic conductivity and ionic diffusivity even after repeated charge and discharge cycles, thereby improving cycle characteristics.
3Reliability
If binding agent is added to prevent pulverization, then cycle characteristics improve, but electronic conductivity may be reduced
Solution Approach 1:
The patent applies composite materials by combining two different types of binding agents with complementary properties. The first binding agent (polymerizable compound) provides strong adhesion and structural support to prevent pulverization, while the second binding agent (water-soluble polymer) maintains electrical conductivity and ionic transport. This composite approach allows the electrode to achieve both improved cycle characteristics and maintained electronic conductivity, as each binding agent compensates for the limitations of the other.
Data Source
AI summary
A negative electrode for nonaqueous electrolyte secondary batteries including a negative electrode current collector and a negative electrode mixture layer placed on the negative electrode current collector. The negative electrode mixture layer is a layer of a mixture of a negative electrode active material, a binding agent, and a conductive agent. The binding agent includes a binding agent A made of a rubber polymeric compound and a binding agent B made of a water-soluble polymeric compound. In the case where a through-thickness cross section of the negative electrode mixture layer is halved into a current collector-side region and a surface-side region, the amount of the binding agent A in the current collector-side region is larger than the amount of the binding agent A in the surface-side region and the amount of the conductive agent in the current collector-side region is larger than the amount of the conductive agent in the surface-side region.