Silicon Negative Electrode Binder for Lithium Ion Battery
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as a negative electrode active material face challenges in maintaining cycle characteristics and energy density due to the large expansion and contraction of silicon materials, which conventional binders struggle to manage effectively.
Innovation Solution
A lithium ion secondary battery employing a copolymer binder comprising ethylenically unsaturated carboxylic acid alkali metal salts and aromatic vinyl monomers, with an alkali metal content of 1000 mass ppm or more, is used to enhance the binding performance and maintain the structural integrity of silicon-based negative electrodes, allowing for improved cycle characteristics and energy density without increasing the binder amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders are used for silicon-based negative electrodes, then the battery can be manufactured with standard materials, but the cycle characteristics deteriorate due to insufficient binding force to withstand silicon's large volume changes
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by incorporating carboxyl-containing polymers with specific functional groups that can form strong chemical bonds with silicon surfaces. The binder contains polymers with carboxyl groups that have high affinity for silicon, creating strong interfacial bonding that withstands volume changes during cycling.
Solution Approach 2:
The invention uses a composite binder system combining carboxyl-containing polymers with conductive carbon materials. This composite structure provides both strong binding force through the carboxyl groups and electrical conductivity through the carbon network, while the composite nature allows the binder to accommodate silicon's volume expansion and contraction.
2Strength
If the binder amount is increased to improve binding force, then the structural integrity improves, but the energy density decreases due to the larger proportion of non-active material
Solution Approach 1:
The invention optimizes the chemical composition of the binder to achieve high binding force with minimal amount. By using carboxyl-containing polymers that form strong chemical bonds with silicon, the binder achieves superior adhesion at lower concentrations compared to conventional binders, thus maintaining structural integrity while minimizing the volume occupied by non-active material.
3Use of energy by moving object
If silicon particle size is reduced to improve capacity, then the energy density improves, but the cycle characteristics worsen due to increased particle stress from expansion and contraction
Solution Approach 1:
The carboxyl-containing polymer binder forms a flexible coating around the silicon particles that can accommodate volume changes during lithium insertion and extraction. This flexible binder matrix protects the silicon particles from mechanical stress and prevents particle disintegration during cycling, maintaining both high capacity and good cycle characteristics.
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 solution significantly improves the cycle characteristics and energy density of lithium ion secondary batteries by providing a strong binding force that withstands the volume changes of silicon materials, reducing particle stress and maintaining peel strength, even with smaller particle sizes, thus enhancing the battery's performance.
Implementation Method 1
the copolymer comprises a monomer unit based on an ethylenically unsaturated carboxylic acid alkali metal salt and a monomer unit based on an aromatic vinyl... providing strong binding force
Data Source
AI summary
Provided is a lithium ion secondary battery that has improved cycle characteristics and employs a silicon material as a negative electrode active material. The lithium ion secondary battery according to the present invention comprises a negative electrode comprising at least a copolymer and a material comprising silicon as a constituent element, wherein the copolymer comprises a monomer unit based on an ethylenically unsaturated carboxylic acid alkali metal salt and a monomer unit based on an aromatic vinyl and the copolymer comprises an alkali metal constituting the alkali metal salt in an amount of 1000 mass ppm or more.