Wound Electrode Assembly With Radial Capacity Balancing
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Solution Overview
Problem
The existing cylindrical electrode assemblies in lithium secondary batteries experience an imbalance in the N/P ratio (capacity ratio of positive and negative electrodes per unit area) due to varying contact areas between the electrodes, leading to accelerated deterioration and reduced battery lifespan.
Innovation Solution
The electrode assembly is designed with first and second positive/negative electrodes having different capacities per unit area, connected through non-coating portions and tabs, allowing for adjustable capacity distribution to minimize N/P ratio deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform positive electrode is used throughout the electrode assembly, then the manufacturing process is simple, but the N/P ratio deviates between the central hole vicinity and outer edge, causing accelerated deterioration
Solution Approach 1:
The positive electrode is designed with different capacities per unit area at different radial positions. Specifically, the positive electrode has a first capacity in the central hole vicinity and a second capacity in the outer edge vicinity, where the second capacity is greater than the first capacity. This local variation in electrode capacity compensates for the varying contact areas, maintaining uniform N/P ratio throughout the assembly.
Solution Approach 2:
The positive electrode is divided into multiple regions with different capacity characteristics. The electrode can be segmented into a central region and an outer region, each with optimized capacity density. This segmentation allows independent optimization of each region's capacity to match the local contact area requirements.
2Quantity of substance
If the contact area between positive and negative electrodes is increased, then the capacity is improved, but the N/P ratio imbalance is exacerbated due to varying contact areas from central hole to outer edge
Solution Approach 1:
The positive electrode capacity density is locally optimized: higher capacity per unit area at the outer edge where contact area is larger, and lower capacity per unit area at the central hole vicinity where contact area is smaller. This ensures that the total capacity contribution from each region is proportional to its contact area, maintaining overall N/P ratio balance.
3Volume of moving object
If the electrode assembly uses a winding structure with central hole, then the space utilization is improved, but the varying contact area from central hole to outer edge causes N/P ratio deviation
Solution Approach 1:
The winding structure is retained for space efficiency, but the positive electrode is designed with radially varying capacity density. The capacity per unit area is adjusted as a function of radial position, creating a gradient that compensates for the geometric effects of the winding structure and central hole.
Solution Approach 2:
The capacity parameter of the positive electrode is changed as a function of position. By varying the capacity per unit area radially across the electrode assembly, the design compensates for the geometric non-uniformity introduced by the winding structure and central hole.
Data Source
AI summary
An electrode assembly, in which a positive electrode, a separator, a negative electrode are wound in a state of being provided. The positive electrode includes a first positive electrode and a second positive electrode, each of which is manufactured by applying a positive electrode active material on a surface of a positive electrode collector, and the positive electrode active material is not applied on one end of the current collector to form a positive electrode non-coating portion on which the positive electrode collector is exposed, and the positive electrode non-coating portions of the first positive electrode and the second positive electrode are bonded to be connected to each other. An electrode assembly is provided where the negative electrode includes a first negative electrode and a second negative electrode.