Negative Electrode Taper Density Layout to Prevent Lithium Deposition
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high energy density while maintaining safety, particularly due to the inefficiencies in the design of the negative electrode, which leads to reduced capacity and potential lithium deposition during charging and discharging.
Innovation Solution
The design includes a lithium ion secondary battery element with a positive electrode and a negative electrode, where both electrodes have active material layers with specific thickness and density gradients, allowing for optimized overlap and reduced lithium deposition, along with an insulating member to prevent short-circuiting, enhancing energy density and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative electrode active material layer is made uniformly thick to increase capacity, then the energy density improves, but lithium deposition occurs during charging and discharging
Solution Approach 1:
The negative electrode active material layer is designed with non-uniform thickness, featuring a thinner portion at the peripheral part and a thicker portion at the central part. This local variation in thickness allows the electrode to accommodate lithium ion insertion and extraction more uniformly, preventing lithium deposition while maintaining high capacity.
2Quantity of substance
If the battery size is reduced to increase volume energy density, then the energy density improves, but the electrode structure becomes more constrained
Solution Approach 1:
By creating local thickness variations in the electrode active material layers, the design optimizes space utilization within the battery structure. The thinner peripheral portions and thicker central portions allow for efficient packing while maintaining electrochemical performance, thereby increasing volume energy density without excessive structural complexity.
3Ease of manufacture
If the positive and negative electrodes are made with identical active material layer shapes for simplicity, then the manufacturing ease improves, but the charging capacity ratio cannot be optimized
Solution Approach 1:
The positive and negative electrodes are designed with different active material layer thickness distributions - the negative electrode has a thinner peripheral part and thicker central part, while the positive electrode has a relatively uniform or different thickness profile. This allows optimization of the charging capacity ratio while maintaining manufacturing feasibility through standard coating processes that can produce controlled thickness variations.
Data Source
AI summary
In a lithium ion secondary battery element, a positive electrode and a negative electrode are overlapped on each other so that a positive electrode active material layer with a generally rectangular shape in the positive electrode and a negative electrode active material layer with a generally rectangular shape in the negative electrode are overlapped on each other substantially perfectly and a positive electrode active material non-applied part of the positive electrode and a negative electrode active material non-applied part of the negative electrode are positioned on opposing sides of the rectangle. A border part between the negative electrode active material applied part and the negative electrode active material non-applied part is positioned closer to a peripheral side of a negative electrode current collector than a peripheral part of a positive electrode current collector. A border part between a negative electrode active material layer flat part and a negative electrode active material layer thin part is positioned closer to a central side of the negative electrode current collector than the peripheral part of the positive electrode current collector. The negative electrode active material layer thin part has a density that is equal to or smaller than that of the negative electrode active material layer flat part.