Layered Positive Electrode Plate for Slurry-Stable Peel Strength
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Solution Overview
Problem
The peel strength of positive electrode plates in lithium-ion batteries, particularly those containing layered oxide materials, is insufficient due to gelation issues in the positive electrode slurry, which affects coating performance and cycling performance.
Innovation Solution
The use of fluorinated monomer-based copolymers as binders in alternately stacked active layers, with controlled pH values and C—F to C—H bond ratios, suppresses slurry gelation and enhances adhesion, resulting in improved peel strength and cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fluorinated monomer homopolymer is used as binder, then adhesion is improved, but slurry gelation occurs due to C—F bond breaking in alkaline environment
Solution Approach 1:
The patent uses copolymer binders containing both fluorinated monomers (for adhesion) and non-fluorinated monomers (for stability). This composite polymer structure combines the advantages of both monomer types: the fluorinated units provide strong adhesion to the active material particles, while the non-fluorinated units reduce the overall C—F bond content, preventing slurry gelation in alkaline environments. The copolymer thus achieves a balance between adhesion and slurry stability.
Solution Approach 2:
The patent controls the ratio of C—F bonds to C—H bonds in the binder polymer by adjusting the composition of fluorinated and non-fluorinated monomers in the copolymer. By optimizing this bond ratio parameter, the patent suppresses the formation of HF and carbon-carbon double bonds that cause gelation, while maintaining sufficient adhesion performance. This parameter optimization resolves the contradiction between adhesion and slurry stability.
2Quantity of substance
If layered oxide active material is used, then energy density is improved, but peel strength is insufficient due to gelation issues
Solution Approach 1:
The patent employs copolymer binders as composite materials that combine fluorinated and non-fluorinated monomer units. The fluorinated units provide strong adhesion to the layered oxide particles, while the non-fluorinated units prevent slurry gelation. This composite binder structure enables the use of high-energy-density layered oxide materials while maintaining sufficient peel strength by preventing gelation-related coating defects.
Solution Approach 2:
The patent applies different functional units within the same binder polymer: fluorinated monomer units localized for adhesion functions and non-fluorinated monomer units localized for stability functions. This local differentiation of polymer chain segments allows simultaneous achievement of strong adhesion (for peel strength) and gelation suppression (for coatability), enabling the use of layered oxide materials with high energy density.
3Strength
If C—F bonds are increased for better adhesion, then adhesive performance is improved, but slurry gelation increases due to HF formation
Solution Approach 1:
The copolymer binder combines fluorinated and non-fluorinated monomer units in controlled ratios. The fluorinated units contribute to adhesive performance through strong C—F bonds, while the non-fluorinated units dilute the overall C—F bond concentration, preventing the formation of HF and carbon-carbon double bonds that cause gelation. This composite structure resolves the contradiction between adhesion and gelation suppression.
Solution Approach 2:
The patent optimizes the C—F to C—H bond ratio in the binder polymer by adjusting copolymer composition. By controlling this parameter, the patent achieves sufficient adhesive performance (requiring some C—F bonds) while suppressing gelation (requiring limited C—F bonds). The optimal ratio balances these competing requirements, resolving the contradiction between adhesive performance and gelation prevention.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents slurry gelation, ensuring coatability and adhesive performance, thereby enhancing the peel strength and cycling performance of the positive electrode film layer.
Implementation Method 1
when a homopolymer contains both a large number of C—F and C—H bonds, the breaking of C—F bonds generates free F ions that combine with free hydrogen from broken C—H bonds to form HF and carbon-carbon double bonds. This leads to crosslinking within or between molecular chains of the homopolymer, resulting in slurry gelation.
Data Source
AI summary
A positive electrode plate for a secondary battery includes a positive electrode current collector and a positive electrode film layer on at least one side of the current collector. The film layer has alternately stacked first and second active layers along the thickness direction. The first active layer contains a layered oxide active material and a first binder including a first copolymer. The second active layer contains a phosphate-based positive electrode active material and a second binder including a fluorinated monomer homopolymer and/or a second copolymer. Monomers forming the first and second copolymers each independently include a fluorinated monomer. The layered configuration and binder compositions improve the peel strength of the positive electrode plate. A secondary battery and an electric apparatus including the positive electrode plate are also provided.