Wound Secondary Battery Tab Layout for Balanced Expansion
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Solution Overview
Problem
The differing hardness of positive and negative tabs in secondary batteries causes uneven expansion during mounting, affecting energy density and increasing internal resistance.
Innovation Solution
The secondary battery design includes a wound structure with specific uncoated regions for positive and negative tabs, where the number of turns for the positive tab uncoated region exceeds that of the negative, and the use of insulating layers to manage expansion and reduce internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the positive tab and negative tab are made of different materials with different hardness, then the tabs can be welded to the current-collecting plates, but the tabs expand outward by different distances during mounting, occupying space inside the battery casing and affecting energy density
Solution Approach 1:
The patent applies asymmetry by making the number of winding turns of the third positive uncoated region different from that of the third negative uncoated region. Specifically, the third positive uncoated region has 3-6 winding turns while the third negative uncoated region has 1-3 winding turns. This asymmetric design compensates for the different expansion characteristics of positive and negative tabs with different hardness, allowing both tabs to expand outward by approximately the same distance during mounting, thereby reducing space occupation inside the battery casing and improving energy density while maintaining welding capability
2Reliability
If the tabs are pressed and welded during mounting, then electrical connection is established, but the differing hardness causes uneven expansion and increases internal resistance
Solution Approach 1:
The asymmetric winding turn design (positive tab: 3-6 turns, negative tab: 1-3 turns) ensures that despite different material hardness, both tabs expand uniformly during mounting. This uniform expansion maintains consistent contact pressure and electrical connection reliability while minimizing variations in internal resistance that would arise from uneven expansion
3Stability of the object's composition
If the number of winding turns is increased to accommodate tab expansion, then expansion space is provided, but the battery outer diameter increases affecting energy density
Solution Approach 1:
The patent uses asymmetric winding turn configuration (third positive uncoated region: 3-6 turns, third negative uncoated region: 1-3 turns) to provide adequate expansion space for both tabs with different hardness. This asymmetric design allows the battery to accommodate tab expansion within a compact outer diameter, preventing excessive radial growth while maintaining sufficient winding turns to absorb expansion stresses, thereby preserving energy density
Solution Approach 2:
The patent optimizes the specific parameters of winding turns (positive: 3-6 turns, negative: 1-3 turns) to balance tab expansion accommodation with energy density maintenance. By precisely controlling these parameter ranges, the design achieves optimal compromise between providing expansion space and minimizing battery outer diameter increase
Data Source
AI summary
A secondary battery, a battery group, and an electronic apparatus are provided. The secondary battery includes a casing and an electrode assembly accommodated in the casing and including a wound structure formed by stacking and winding a positive sheet, a separator, and a negative sheet. In a wound structure axial direction, a positive current collector of the positive sheet includes a positive coated region and a positive uncoated region, and a negative current collector of the negative sheet includes a negative coated region and a negative uncoated region. In a wound structure winding direction, the positive uncoated region sequentially includes a first, a second, and a third positive uncoated regions, and the negative uncoated region sequentially includes a first, a second region, and a third negative uncoated regions. The number of winding turns of the third positive uncoated region is greater than that of the third negative uncoated region.