Positive Electrode Sheet Additives for Gelation and DCR Control
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Solution Overview
Problem
Secondary batteries with strong alkaline positive electrodes face issues of gelation phenomena, brittleness, poor direct current resistance (DCR), and degraded cycle performance, which affect their energy density and safety.
Innovation Solution
A positive electrode sheet is developed with specific additives, including a first additive made from acrylonitrile and a monomer represented by formula I, and a second additive that is a vinylidene fluoride modified polymer, along with a lithium-rich additive, to improve processability, reduce DCR, and enhance cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a strong alkaline substance is used in a positive electrode sheet, then the energy density is improved, but gelation phenomena occur and the cycle performance degrades
Solution Approach 1:
A water-soluble polymer additive is introduced as an intermediary substance in the positive electrode slurry. This additive mediates between the strong alkaline substance and the slurry components, preventing harmful gelation while allowing the strong alkaline substance to maintain high energy density. The polymer acts as a buffer and stabilizer, enabling the coexistence of high energy density materials with slurry stability.
Solution Approach 2:
The chemical parameters of the slurry system are modified by adding the water-soluble polymer additive. This changes the rheological and chemical properties of the slurry, preventing gelation phenomena that would otherwise occur with strong alkaline substances. The parameter change enables the system to maintain both high energy density and good cycle performance.
2Use of energy by moving object
If a strong alkaline substance is used in a positive electrode sheet, then the energy density is improved, but the positive electrode sheet becomes brittle
Solution Approach 1:
The water-soluble polymer additive serves as a protective intermediary that prevents direct harmful interactions between the strong alkaline substance and the electrode sheet matrix. This intermediary layer maintains the structural integrity and flexibility of the electrode sheet while allowing the strong alkaline substance to provide high energy density.
3Use of energy by moving object
If a strong alkaline substance is used in a positive electrode sheet, then the energy density is improved, but the direct current resistance increases
Solution Approach 1:
The addition of water-soluble polymer additive modifies the electrical and chemical parameters of the positive electrode slurry. This parameter modification prevents the formation of high-resistance phases that would otherwise form with strong alkaline substances, thereby maintaining low direct current resistance while achieving high energy density.
Data Source
AI summary
A positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on at least one surface of the positive electrode current collector and including an additive. The additive includes a structural unit made from acrylonitrile and a structural unit made from a monomer represented by following formula:where R1, R2, R3, and R4 are each independently selected from hydrogen, an alkyl group with 1-8 carbon atoms, or a saturated carboxylic acid group with 1-8 carbon atoms, and at least one of R1, R2, R3, or R4 is selected from the saturated carboxylic acid group with 1-8 carbon atoms.