Si-Graphite Anode Layer Structure for Stable Nonaqueous Battery Modules
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Solution Overview
Problem
Nonaqueous-electrolyte secondary batteries containing Si materials as negative-electrode active materials experience a decrease in capacity recovery rate after high-temperature storage and an increase in resistance during high-rate charge and discharge.
Innovation Solution
A secondary battery module design with a negative electrode having a two-layered active material structure, where the first layer contains graphite particles and Si particles, and the second layer has a higher compression modulus than the first layer, along with a separator and elastic body with specific compression moduli, to absorb expansion and contraction, thereby maintaining electrolyte retention and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si materials are used as negative-electrode active material to increase capacity, then the battery capacity increases, but the capacity recovery rate decreases after high-temperature storage
Solution Approach 1:
The negative electrode is designed with a two-layer structure where the first layer (near current collector) contains graphite particles with specific BET surface area (1-2.5 m²/g) and the second layer (outer layer) contains Si particles with controlled content (6-13 mass%). This spatial differentiation of material composition and properties optimizes both capacity and stability, with the graphite layer providing structural stability during high-temperature storage and the Si layer contributing high capacity.
Solution Approach 2:
The invention uses a composite negative electrode structure combining graphite particles and Si particles in specific proportions. The graphite component provides dimensional stability and prevents excessive expansion, while the Si component contributes high lithium-ion capacity. This composite approach resolves the contradiction between achieving high capacity and maintaining capacity recovery after high-temperature storage.
2Reliability
If the negative electrode has high compression modulus to retain electrolytic solution, then electrolyte retention improves and resistance increases are suppressed, but the electrode body expansion and contraction are restricted
Solution Approach 1:
The separator is designed with a specific compression modulus range (0.1-0.5 MPa) that is lower than both the first and second layers of the negative electrode. This creates a gradient of compression moduli from the current collector outward, allowing the separator to provide necessary electrolyte retention while the negative electrode layers progressively resist expansion. The elastic body with compression modulus of 0.05-0.2 MPa provides external support without over-constraining the electrode body.
Solution Approach 2:
The invention optimizes the compression modulus parameters of different components: the first layer has compression modulus of 0.5-2.0 MPa, the second layer has 0.3-1.5 MPa, the separator has 0.1-0.5 MPa, and the elastic body has 0.05-0.2 MPa. This parameter gradient allows each component to perform its specific function while working together to maintain overall electrode body stability.
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 design effectively suppresses the increase in resistance during high-rate charge and discharge and maintains capacity recovery rate after high-temperature storage by optimizing the compression moduli of the electrode components.
Implementation Method 1
an elastic body configured to receive a load from the electrode body in the stacking direction of the electrode body
Implementation Method 2
charge carriers are released from the positive-electrode active material constituting the positive-electrode active material layer and are occluded into the negative-electrode active material constituting the negative-material active material layer
Data Source
AI summary
A secondary battery module includes a nonaqueous-electrolyte secondary battery and an elastic body, wherein a negative electrode constituting the nonaqueous-electrolyte secondary battery includes a negative-electrode active material layer, the negative-electrode active material layer includes a first layer, and a second layer that is formed on the first layer and has a higher compression modulus than the first layer, a separator constituting the nonaqueous-electrolyte secondary battery has a lower compression modulus than the first layer, the elastic body has a lower compression modulus than the separator, the graphite particles contained in the first layer have a BET specific surface area of 1 to 2.5 m2/g, and the content of Si particles in the first layer is 6 mass % to 13 mass % relative to the total amount of the negative-electrode active material layer.