Secondary Battery Bacterial Cellulose Electrode Deformation
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Solution Overview
Problem
Secondary batteries with wound electrode assemblies face deformation and property deterioration due to expansion and contraction during repetitive charge/discharge cycles, leading to reduced capacity retention and potential precipitation issues during low temperatures and high outputs.
Innovation Solution
Incorporating bacterial cellulose with specific particle diameters and thicknesses in the surface layer and edge regions of the negative electrode active material layer, which inhibits deformation and precipitation, and enhances the durability and performance of the battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a wound electrode assembly is used to increase reaction area and energy density, then the battery can achieve high output and elevated energy density, but the electrode assembly undergoes deformation and buckling during repetitive charge/discharge cycles leading to property deterioration
Solution Approach 1:
The invention introduces an uncoated region (active material layer-free region) at specific locations on the electrode sheets, creating local structural differences. This uncoated region acts as a buffer zone that accommodates expansion and contraction stresses during charge/discharge cycles, preventing deformation and buckling while maintaining high reaction area in the coated regions.
Solution Approach 2:
The uncoated region is pre-designed and positioned on the electrode sheets before winding into the spiral configuration. This preliminary structural arrangement ensures that the buffer zones are already in place to handle anticipated expansion/contraction forces during operation, preventing deformation before it occurs.
2Ease of operation
If the uncoated region is disposed as a strip on both sides at one edge to raise current collection efficiency, then current collection is improved, but the electrode assembly becomes susceptible to deformation and buckling during charge/discharge
Solution Approach 1:
The invention positions the uncoated regions of positive and negative electrode sheets asymmetrically, with each uncoated region located at opposite edges in the width direction. This asymmetric arrangement optimizes current collection pathways while creating a balanced structural configuration that resists deformation during charge/discharge cycles.
Data Source
AI summary
A secondary battery includes a wound electrode assembly in which a positive electrode sheet, a negative electrode sheet and a separator are stacked and wound. The positive electrode sheet is provided with a long positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on the positive electrode current collector. The negative electrode sheet is provided with a long negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the negative electrode current collector. The separator is interposed between the positive electrode sheet and the negative electrode sheet. The negative electrode current collector has a first active material layer-free region at one edge of the negative electrode current collector in a winding direction of an axis of the wound electrode assembly. The first active material layer-free region is a region where the negative electrode active material layer is not formed. The positive electrode current collector has a second active material layer-free region at one edge of the positive electrode current collector in a winding direction of an axis of the wound electrode assembly. The second active material layer-free region is a region where the positive electrode active material layer is not formed. The negative electrode current collector and the positive electrode current collector are disposed, with the first active material layer-free region and the second active material layer-free region being projected toward opposite sides in the winding direction of the axis of the wound electrode assembly. A width of the negative electrode active material layer is wider than a width of the positive electrode active material layer and a bacterial cellulose is disposed in at least a surface layer of the negative electrode active material layer that faces the second active material layer-free region.