Positive Electrode Layer Stacking to Prevent Slurry Gelation
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Solution Overview
Problem
Lithium-ion batteries face issues with insufficient peel strength and gelation of the positive electrode slurry due to the alkalinity of layered oxide materials, which affects the coating performance and cycling performance of the battery cell.
Innovation Solution
The use of alternately stacked first and second active layers in the positive electrode plate, where the first layer includes a layered oxide active material and a first binder with a fluorinated copolymer, and the second layer includes a phosphate-based active material and a fluorinated monomer homopolymer or copolymer, to suppress gelation and enhance adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a layered oxide active material is used in the positive electrode, then the energy density is improved, but the slurry gelates due to alkalinity causing insufficient peel strength
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by using fluorinated monomers (vinylidene fluoride, vinyl fluoride) instead of conventional polymers. This parameter change suppresses the alkaline-induced gelation while maintaining adhesion, resolving the contradiction between energy density and peel strength
Solution Approach 2:
The patent creates a composite binder system using fluorinated polymers (PVDF, PVAE) combined with specific additives (carboxymethyl cellulose, styrene-butadiene rubber) to achieve both gelation suppression and strong adhesion, thereby maintaining high energy density while improving peel strength
2Strength
If a fluorinated monomer homopolymer is used as binder, then the adhesion is improved, but the slurry gelates due to C-F bond breaking in alkaline environment
Solution Approach 1:
The patent modifies the binder composition by using copolymers containing fluorinated monomers (vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene copolymer) instead of homopolymers. This changes the chemical structure parameters to reduce C-F bond density and suppress gelation while maintaining adhesion performance
Solution Approach 2:
The patent introduces intermediary substances (carboxymethyl cellulose, styrene-butadiene rubber) that mediate between the fluorinated binder and the alkaline active material, preventing direct harmful interactions while maintaining the adhesion benefits of fluorinated polymers
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
This configuration improves the peel strength and cycling performance of the positive electrode film layer by preventing slurry gelation and ensuring effective adhesion, thereby enhancing the overall battery performance.
Implementation Method 1
The first copolymer and the second copolymer for the fluorinated monomers utilize the fluorinated monomers to provide excellent adhesion, and utilize combination of fluorinated monomers and other monomers to adjust the ratio of C-F bonds to C-H bonds. This suppresses the reaction that forms HF and carbon-carbon double bonds, making the positive electrode slurry used for coating to form the first active layer less prone to gelation.
Implementation Method 2
Since C-F bonds are prone to break in an alkaline environment to produce free F ions, 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.
Implementation Method 3
The first copolymer and the second copolymer for the fluorinated monomers utilize the fluorinated monomers to provide excellent adhesion
Data Source
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AI summary
This application provides a positive electrode plate, a secondary battery, and an electric apparatus. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, where the positive electrode film layer includes one or more first active layers and one or more second active layers arranged along a thickness direction of the positive electrode current collector, the first active layers and the second active layers being alternately stacked; the first active layer includes a layered oxide active material and a first binder, the first binder including a first copolymer; and the second active layer includes a phosphate-based positive electrode active material and a second binder, the second binder including a fluorinated monomer homopolymer and/or a second copolymer, where monomers forming the first copolymer and the second copolymer each independently include a fluorinated monomer. This enhances peel strength of the positive electrode plate.