Composite Binder for Silicon Negative Electrodes
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Solution Overview
Problem
Existing non-aqueous electrolyte rechargeable batteries, particularly those with silicon-containing negative electrodes, face challenges in maintaining cycle characteristics due to volume changes during charging and discharging, leading to reduced electron conductivity and potential blockage of conductive paths, which existing binders fail to adequately address.
Innovation Solution
A binder system comprising a copolymer (A) derived from (meth)acrylic acid-based and (meth)acrylonitrile monomers, and a copolymer (B) derived from aromatic vinyl and ethylenic unsaturated monomers, which suppresses electrode expansion and improves cycle characteristics even with a small binder content, by forming a core-shell structure that enhances adhesion and dispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aqueous solution of crosslinked sodium polyacrylate copolymer is used as binder, then capacity retention rate is improved, but cracks are generated in the electrode during coating and drying processes
Solution Approach 1:
The patent uses a composite binder system comprising carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a specific weight ratio range (CMC:SBR = 1:4 to 4:1). This composite approach combines the advantages of both materials: CMC provides water solubility and adhesion, while SBR provides elasticity and crack resistance. The synergistic effect of this composite binder system improves capacity retention rate while preventing crack formation during electrode manufacturing processes.
Solution Approach 2:
The patent optimizes the weight ratio parameters of CMC and SBR in the binder system, specifying a range of 1:4 to 4:1. By adjusting these compositional parameters, the binder system achieves optimal balance between adhesion (from CMC) and flexibility/crack resistance (from SBR), thereby improving capacity retention without causing electrode cracking during coating and drying.
2Quantity of substance
If silicon-containing active material is used to increase capacity, then battery capacity is improved, but volume change causes electrode expansion and contract ion leading to reduced electron conductivity and blocked conductive paths
Solution Approach 1:
The patent utilizes styrene butadiene rubber (SBR) as a key component of the binder system. SBR provides flexible, elastic properties that can accommodate the volume changes of silicon-containing active material during lithium intercalation and deintercalation. This flexible binder film maintains continuous contact with the active material particles throughout charging and discharging cycles, preventing conductive path blockage and maintaining electron conductivity despite electrode expansion and contraction.
Solution Approach 2:
The binder system, particularly the SBR component, acts as a cushioning matrix that anticipates and absorbs the mechanical stress from silicon's volume expansion during lithiation. The elastic nature of SBR allows it to deform with the active material particles, maintaining structural integrity and conductive networks before damage can occur, thereby preserving cycle characteristics.
3Reliability
If binder content is increased to suppress electrode expansion, then cycle characteristics are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent employs a composite binder system combining CMC and SBR that achieves effective electrode expansion suppression and improved cycle characteristics through synergistic interaction rather than relying on high binder content. The specific weight ratio range (1:4 to 4:1) optimizes the balance between adhesion and flexibility, allowing the system to function effectively at moderate binder concentrations while maintaining manufacturing simplicity.
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 system effectively reduces negative electrode expansion and enhances cycle performance by maintaining close contacting properties and preventing cracks during the coating and drying processes, thereby improving the overall capacity retention and durability of the rechargeable battery.
Implementation Method 1
the binder system effectively reduces negative electrode expansion and enhances cycle performance by maintaining close contacting properties
Data Source
AI summary
An embodiment provides a binder for a non-aqueous electrolyte rechargeable battery including a copolymer (A) and a copolymer (B), wherein the copolymer (A) includes a unit (a-1) derived from a (meth)acrylic acid-based monomer, and a unit (a-2) derived from a (meth)acrylonitrile monomer, and the copolymer (B) includes a unit (b-1) derived from an aromatic vinyl-based monomer; and a unit (b-2) derived from an ethylenic unsaturated monomer which is at least one of an unsaturated carboxylic acid alkylester monomer, a (meth)acrylic acid-based monomer, a unsaturated carboxylic acid amide monomer, or combinations thereof.