Negative Electrode Binder Molecular Weight Optimization
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Solution Overview
Problem
Lithium rechargeable batteries face issues with the adherence and impregnation of thick film electrodes, leading to reduced cycle life and performance due to weak adherence to the current collector and potential cracking.
Innovation Solution
A negative electrode composition including carboxylmethyl cellulose with a specific weight average molecular weight range, styrene-butadiene rubber, and polyvinyl alcohol is used, improving flexibility and adherence, and preventing cracking, with a weight ratio of negative active material to binder optimized for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the coating layer is made thicker to increase capacity, then the energy density is improved, but the adherence to current collector deteriorates causing cracks
Solution Approach 1:
The patent changes the molecular weight parameter of carboxylmethyl cellulose binder to a specific range (300,000-500,000 g/mol) to optimize the balance between coating thickness and adherence. This parameter change allows the binder to provide sufficient flexibility and bonding strength even at higher coating thicknesses, preventing crack formation while maintaining good adherence to the current collector.
Solution Approach 2:
The patent uses a composite binder system combining carboxylmethyl cellulose with styrene-butadiene rubber. This composite material approach leverages the complementary properties of both components: CMC provides thickening and suspension capabilities while SBR contributes elasticity and adhesion, together enabling thick coatings to maintain both adherence and flexibility without cracking.
2Strength
If more binder is included to improve adherence, then the adherence is improved, but the impregnation deteriorates
Solution Approach 1:
The patent optimizes the binder content to a specific range (1-3 wt%) and adjusts the molecular weight of carboxylmethyl cellulose to achieve the desired balance. By controlling these parameters, the binder provides sufficient adherence without excessive viscosity that would prevent proper impregnation of the electrode structure, ensuring both good bonding and reliable electrolyte penetration.
Data Source
AI summary
Disclosed herein is a negative electrode for a rechargeable lithium battery including a negative active material and a binder, wherein the binder includes carboxylmethyl cellulose and a styrene-butadiene rubber, and the carboxylmethyl cellulose has a weight average molecular weight of about 300,000 g/mol to about 500,000 g/mol, and a rechargeable lithium battery including the same.