Lithium Phosphate Positive Electrode Flexibility Without Cracking
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Solution Overview
Problem
Lithium transition metal phosphate-based positive electrodes in lithium secondary batteries face challenges with poor flexibility and adhesion, leading to increased risk of cracking and reduced energy density, while existing solutions compromise coating and drying productivity.
Innovation Solution
A positive electrode with a lithium transition metal phosphate active material and a fluorine-based binder, featuring a specific porosity ratio and molecular weight range, is developed to enhance flexibility and adhesion, incorporating a carbon nanotube conductive material and hydrogenated nitrile-based butadiene rubber, which improves energy density without reducing productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the size of lithium transition metal phosphate particles is reduced to improve lithium mobility and electrical conductivity, then the specific surface area increases, but particle agglomeration severely occurs, leading to reduced positive electrode adhesion
Solution Approach 1:
The patent changes the particle size parameter of lithium transition metal phosphate to an optimal range (3 μm ≤ D50 < 6 μm) to balance lithium mobility/conductivity with adhesion prevention. It also adjusts binder content (1-3 wt%) and slurry solid content (5-15 wt%) to optimize the balance between particle dispersion and adhesion without causing excessive agglomeration
Solution Approach 2:
The patent uses a composite binder system comprising fluorine-based binder (e.g., PVDF) and carboxymethyl cellulose (CMC) in specific ratios. This composite binder system improves both adhesion and particle dispersion, preventing agglomeration while maintaining strong electrode structure
2Quantity of substance
If the rolling density of the positive electrode is increased to improve energy density, then the flexibility is reduced, making it difficult to manufacture without cracking
Solution Approach 1:
The patent optimizes the porosity parameter of the positive electrode to a specific range (20-40%) to balance flexibility and rolling density. It also controls the thickness of the active material layer and the properties of the binder to maintain flexibility while achieving high rolling density for improved energy density
3Ease of operation
If a polymer binder with high molecular weight is selected to improve the flexibility of the lithium transition metal phosphate-based positive electrode, then the viscosity of the positive electrode slurry rapidly increases, causing a decrease in coating productivity
Solution Approach 1:
The patent uses a composite binder system combining fluorine-based binder (e.g., PVDF with molecular weight 300,000-750,000) and carboxymethyl cellulose (CMC). This composite system provides the necessary flexibility while maintaining lower slurry viscosity compared to using only high molecular weight polymer binders, thus preserving coating productivity
4Productivity
If the solid content in the slurry is lowered to reduce the viscosity of the positive electrode slurry, then the drying time increases due to increased solvent content
Solution Approach 1:
The patent optimizes the solid content parameter of the slurry to a specific range (5-15 wt%) that balances viscosity and drying time. It also adjusts the molecular weight and type of binder to control slurry rheology, achieving low enough viscosity for good coating productivity while maintaining reasonable drying times
Data Source
AI summary
A positive electrode according to one embodiment of the present technology is a positive electrode including a positive electrode active material layer disposed on at least one surface of a positive electrode current collector, the positive electrode active material layer includes a lithium transition metal phosphate and a fluorine-based binder, and, in a flexibility evaluation, in which the positive electrode is lifted after bringing measuring rods for each phi (Φ) into contact with the positive electrode active material layer, a ratio value (=P/D) of a porosity (P) of the positive electrode active material layer calculated by the disclosed Equation 1 to a maximum phi value (D) of the measuring rod at which a crack occurs is greater than or equal to 10.