Multilayer Battery Electrode Binder Structure for Low Resistance
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Solution Overview
Problem
Current secondary battery electrodes face issues with adhesion between the current collector and active material, leading to increased electrical resistance and reduced capacity and lifespan due to the use of polyvinylidene fluoride (PVdF) as a binder, which lacks flexibility and causes bonding breakdown with materials like natural graphite or metal-based active materials.
Innovation Solution
A multilayer electrode structure is developed using carboxymethyl cellulose and styrene butadiene rubber as binders, with varying weight average molecular weights and monomer content in each layer to enhance adhesion and cohesion between the current collector and active material, while reducing electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVdF is used as a binder to manufacture an electrode plate, then adhesive strength between current collector and active material is improved, but electrical resistance increases and battery performance deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the binder from PVdF to a copolymer containing carboxylic acid groups (such as polyacrylic acid or polyacrylamide). This parameter change transforms the binder's chemical properties to enable coordination bonding with metal oxides, thereby reducing electrical resistance while maintaining adhesion through a different chemical mechanism.
Solution Approach 2:
The patent employs a composite binder system combining organic polymer matrices with inorganic components or functional groups that can coordinate with metal ions. This composite approach creates a dual-function binder that provides both mechanical adhesion and electrical conductivity pathways, resolving the contradiction between strength and reliability.
2Strength
If PVdF is used as a binder, then adhesive strength is improved, but bonding breaks during charging and discharging due to lack of flexibility, deteriorating cycle characteristics
Solution Approach 1:
The patent modifies the binder's chemical structure by selecting polymers with flexible backbones and incorporating functional groups that can dynamically interact with active material surfaces. This parameter change enables the binder to accommodate volume changes during cycling while maintaining bonding integrity.
Solution Approach 2:
The carboxylic acid-containing polymer acts as an intermediary that mediates between the rigid current collector and the expanding/contracting active material. The coordination bonds formed between the binder's carboxylic acid groups and metal ions create a flexible interface that absorbs mechanical stress during cycling.
3Quantity of substance
If active material loading per unit area is increased, then capacity is improved, but the active material layer is pushed during rolling and loading amount per unit area decreases
Solution Approach 1:
The patent changes the binder's adhesive parameters to achieve stronger bonding between the active material layer and current collector. This enhanced adhesion prevents layer delamination and pushing during the rolling process, allowing higher active material loading densities to be maintained through manufacturing.
Solution Approach 2:
The patent applies preliminary bonding action through the enhanced adhesive properties of the carboxylic acid-containing polymer before the rolling process occurs. This preliminary strong adhesion prevents the active material layer from being pushed or delaminated during subsequent rolling operations, preserving the intended loading density.
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 solution improves adhesion and cohesion, resulting in reduced electrical resistance, increased capacity, and enhanced lifespan characteristics of the secondary battery.
Implementation Method 1
improve the performance of a secondary battery and decrease the resistance within the electrode due to an increase in adhesion between the negative electrode current collector and the active material and the cohesion between the active material and the active material
Implementation Method 2
cohesion between the active material and the active material
Data Source
AI summary
An electrode for a secondary battery includes a current collector, a first electrode mixture layer disposed on at least one surface of the current collector and including styrene butadiene rubber, and a second electrode mixture layer disposed on the first electrode mixture layer and including a second styrene butadiene rubber. The first styrene butadiene rubber and the second styrene butadiene rubber have a repeating unit of styrene derived structure and a repeating unit of a butadiene derived structure, the first styrene butadiene rubber containing 40 to 90 mol % of a butadiene monomer based on total content of a monomer, and the second styrene butadiene rubber having a lower content of a butadiene monomer than the content of the first styrene butadiene rubber.