Pouch Lithium Secondary Battery Structure for Swelling Control
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining favorable characteristics, such as discharge capacity, in high-temperature and reduced-pressure environments.
Innovation Solution
A pouch-type lithium secondary battery design with specific thickness ratios and solvent and electrolyte compositions to minimize swelling and maintain electrode layer spacing, using a sintered lithium complex oxide positive electrode and a mixed solvent electrolyte, and optionally bonded with an adhesive to suppress the occurrence of wrinkling in the exterior body, ensuring the lithium secondary battery maintains favorable characteristics even in high-temperature and reduced-pressure environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional lithium secondary battery is used in high-temperature and reduced-pressure environments, then the battery structure is simple and easy to manufacture, but the discharge capacity decreases significantly and the battery swells
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the thickness of the exterior body within a specific range (0.5 mm to 2.0 mm) and using specific solvent compositions (γ-butyrolactone, ethylene carbonate, dimethyl carbonate in controlled ratios) to prevent excessive swelling while maintaining discharge capacity in high-temperature, reduced-pressure environments
Solution Approach 2:
The patent uses composite materials by combining multiple solvent types (cyclic carbonate and chain carbonate esters) in specific proportions, and using composite electrode structures (sintered positive electrode plates with specific porosity and thickness) to achieve both swelling resistance and high discharge capacity under extreme conditions
2Stability of the object's composition
If the exterior body thickness is increased to prevent swelling, then the battery maintains its structure in high-temperature environments, but the battery becomes bulkier and the discharge capacity decreases
Solution Approach 1:
The patent optimizes the exterior body thickness parameter within a narrow range (0.5-2.0 mm) and controls solvent composition parameters (volume ratios of different carbonates) to achieve the right balance between structural stability and discharge capacity, preventing both excessive swelling and capacity loss
Solution Approach 2:
The patent applies local quality by using sintered positive electrode plates with specific local properties (porosity of 30-60%, specific thickness ratios) in different regions to maintain structural stability while preserving discharge capacity
3Quantity of substance
If a sintered plate of lithium complex oxide is used to increase capacity, then the positive electrode capacity increases, but the battery swells at high temperatures
Solution Approach 1:
The patent uses composite materials by combining sintered lithium complex oxide plates with specific pore structures with carefully formulated electrolyte solutions containing multiple solvents in controlled proportions, achieving both high capacity and swelling resistance through the synergistic interaction of these materials
Solution Approach 2:
The patent employs porous materials by using sintered positive electrode plates with controlled porosity (30-60%) that allow electrolyte penetration while maintaining structural integrity, preventing swelling while preserving high discharge capacity
Data Source
AI summary
A lithium secondary battery includes a positive electrode layer composed of a sintered body of lithium complex oxide, a negative electrode layer, a separator interposed between the positive electrode layer and the negative electrode layer, an electrolytic solution containing an electrolyte and a solvent and impregnated into the positive electrode layer, the negative electrode layer, and the separator, and an exterior body including a closed space in which the positive electrode layer, the negative electrode layer, the separator, and the electrolytic solution are accommodated. In a thickness direction of the positive electrode layer, a ratio of a thickness of the exterior body at a temperature of 80° C. and a pressure of 100 Pa to a thickness of the exterior body at a temperature of 25° C. and a pressure of 101325 Pa is 1.05 or more and 2.63 or less.