Crosslinked Polymer Binder for Secondary Battery Electrodes
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Solution Overview
Problem
Existing binders for secondary battery electrodes, while improving binding ability, face challenges such as increased viscosity in electrode mixture layer slurries with higher molecular weight polymers, leading to poor coating performance, and limited improvement in binding ability with crosslinked polymers, which affects the durability and energy density of lithium-ion batteries due to volume changes in active materials during charging and discharging.
Innovation Solution
A binder containing a crosslinked polymer or salt with a water swelling degree of 5.0 to 10.0 at pH 8 and 2.0 to 10.0 at pH 4, incorporating structural units derived from ethylenically unsaturated carboxylic acid monomers, crosslinked with a crosslinkable monomer, and neutralized to a degree of 80% to 100%, providing excellent adhesiveness and dispersion stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the molecular weight of the polymer in the binder is increased to improve binding ability, then the binding ability is improved, but the viscosity of the electrode mixture layer slurry increases, leading to poor coating performance
Solution Approach 1:
The patent changes the molecular weight parameter of the polymer binder to optimize the balance between binding ability and slurry viscosity. By selecting polymers with specific molecular weights within defined ranges, the invention achieves sufficient binding strength while maintaining acceptable coating performance
Solution Approach 2:
The patent uses composite binder systems combining multiple polymer components with different molecular weights and functionalities. This composite approach allows the system to achieve high binding ability through synergistic effects while the lower molecular weight components help maintain manageable slurry viscosity
2Ease of manufacture
If the concentration of active material, binder and the like in the slurry is decreased to reduce viscosity, then the viscosity is decreased, but productivity is reduced
Solution Approach 1:
The patent optimizes the concentration parameters of all slurry components to achieve the right balance. By carefully controlling the amounts of active material, binder, and additives within specific ranges, the invention maintains low enough viscosity for good processability while keeping productivity high through efficient slurry formulation
3Strength
If the primary chain length of the crosslinked polymer is increased to improve binding ability, then the binding ability is improved, but the improvement effect is limited
Solution Approach 1:
The patent optimizes the primary chain length parameter of crosslinked polymers within specific molecular weight ranges. By controlling this parameter along with crosslinking density, the invention achieves improved binding ability while ensuring sufficient durability, avoiding the diminishing returns of excessive chain length
Solution Approach 2:
The patent employs composite crosslinked polymer systems where polymers with different primary chain lengths are combined. This allows the system to achieve optimal binding ability through the longer chains while shorter chains contribute to maintaining durability and preventing over-softening of the electrode structure
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 binder achieves enhanced binding ability and adhesiveness to the collector, maintaining electrode integrity and improving durability by suppressing deterioration from volume changes in active materials, while maintaining good coating properties and energy density.
Implementation Method 1
the viscosity is not greatly affected even if the molecular weight (primary chain length) is increased. However, the inventors' researches have shown that simply increasing the primary chain length of the crosslinked polymer has only a limited improvement effect of binding ability.
Implementation Method 2
neutralized to a degree of 80% to 100%, providing excellent adhesiveness and dispersion stability
Data Source
AI summary
An aqueous binder for secondary batteries, which has a binding capacity superior than conventional binders while having fine coating property; a secondary battery electrode mixture layer composition and a secondary battery electrode which are acquired by using the binder. This binder for secondary battery electrodes contains: a crosslinked polymer or a salt thereof having a water-swelling degree of 5.0-100 at pH8.