Binder Composition Suppressing Positive Electrode Expansion
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Solution Overview
Problem
Lithium ion secondary batteries face performance degradation due to excessive expansion of the positive electrode during lithium ion insertion and desorption, which has not been adequately addressed by conventional binder compositions.
Innovation Solution
A binder composition for lithium ion secondary battery positive electrodes is developed, incorporating a copolymer with a nitrile group-containing monomer unit, a conjugated diene monomer unit, and an alkylthio group, with specific properties such as a degree of swelling in electrolysis solution and storage elastic modulus, to suppress the expansion of the positive electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binder compositions (fluorine-based polymer and hydrogenated nitrile rubber) are used for positive electrodes, then the battery can be manufactured with standard materials, but the positive electrode expands excessively during lithium ion insertion and desorption cycles
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by introducing a copolymer with specific functional groups (carboxyl, hydroxyl, or amine groups) and controlling the ratio of nitrile groups to other groups. This compositional parameter change enables the binder to effectively suppress positive electrode expansion during lithium ion cycles, resolving the dimensional stability issue while maintaining battery performance reliability
Solution Approach 2:
The patent uses a composite binder system comprising a copolymer with specific functional groups in combination with conventional binder materials. This composite approach leverages the advantageous properties of both the functional copolymer (expansion suppression) and conventional binders (adhesion and flexibility), achieving both dimensional stability and manufacturing compatibility
2Productivity
If the positive electrode density is increased to improve battery performance, then higher energy density is achieved, but the positive electrode becomes more susceptible to expansion during cycling
Solution Approach 1:
The patent modifies the binder composition parameters to include a copolymer with specific functional groups and controlled nitrile group ratios, which provides enhanced binding strength and expansion resistance. This enables the use of higher density positive electrode materials without suffering from excessive expansion, thus achieving both high energy density and structural stability
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 proposed binder composition effectively reduces the expansion of the positive electrode, thereby enhancing the performance and longevity of lithium ion secondary batteries by minimizing performance degradation caused by thermal stress and cycling.
Implementation Method 1
a degree of swelling in electrolysis solution of at least 200 mass% and no greater than 700 mass%
Implementation Method 2
a storage elastic modulus of a binder coating resulting from film formation of the binder composition under specific conditions is at least 1 × 10^4
Data Source
AI summary
Provided is a binder composition for a lithium-ion secondary cell positive electrode with which swelling of the positive electrode can be minimized. This binder composition for a lithium-ion secondary cell positive electrode contains a solvent and a copolymer including a nitrile group-containing monomer unit and a conjugated diene monomer unit. The electrolyte swelling degree of the copolymer is 200-700% by mass, and the storage elasticity of a binder film obtained by forming the binder composition into a film is 1×104Pa to 1×109Pa.