Composite Binder Composition for Lithium Ion Battery Electrodes
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Solution Overview
Problem
The existing binder compositions for lithium ion secondary batteries face issues with binding force, electrolyte resistance, and high temperature cycle characteristics, particularly when using small particle diameter active materials, leading to increased resistance and deteriorated cycle characteristics.
Innovation Solution
A binder composition comprising a polymer unit with a nitrile group, (meth)acrylate polymer unit, a polymer unit with hydrophilic groups, and a linear alkylene polymer unit, optimized for swelling degree, solubility, and solubility parameter to enhance binding properties and stability in electrolytic solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fluorine based polymer such as polyvinylidene fluoride is used as binder, then adhesive force against current collector is improved, but internal resistance increases and capacity declines
Solution Approach 1:
The invention uses a composite binder system comprising polyvinylidene fluoride (PVDF) and hydrogenated acrylonitrile-butadiene rubber (H-NBR) in a specific weight ratio (PVDF: 30-70 wt%, H-NBR: 70-30 wt%). This composite approach combines the strong adhesive properties of PVDF with the flexibility and conductivity benefits of H-NBR, achieving both good adhesion and reduced internal resistance
Solution Approach 2:
The invention optimizes the weight ratio parameters of the binder components and controls the total binder content (1-5 wt% of active material weight) to achieve the optimal balance between adhesive force and internal resistance. By precisely controlling these parameters, the patent resolves the contradiction between strong adhesion and low resistance
2Strength
If amount of fluorine based polymer is increased to enhance adhesive force, then binding strength is improved, but internal resistance increases and capacity declines
Solution Approach 1:
The invention controls the total binder content within 1-5 wt% of the active material weight and optimizes the weight ratio between PVDF and H-NBR (30-70/70-30). This parameter optimization ensures sufficient binding strength while preventing excessive binder from increasing internal resistance and reducing battery capacity
Solution Approach 2:
By using a composite binder system instead of pure PVDF, the invention achieves adequate binding strength with lower total binder content. The H-NBR component provides binding capability while contributing less to internal resistance, allowing the system to maintain binding strength without sacrificing battery capacity
3Strength
If binder content is increased to improve adhesion, then adhesive force is improved, but electrode resistance increases and output characteristic deteriorates
Solution Approach 1:
The invention optimizes the binder content parameter to 1-5 wt% of active material weight and controls the PVDF:H-NBR weight ratio (30-70/70-30). This optimization ensures adequate adhesion while minimizing the resistance increase that would deteriorate output characteristics
Solution Approach 2:
The composite binder system provides sufficient adhesion with lower total binder content compared to pure PVDF systems. The H-NBR component contributes to binding strength while having lower resistance impact, thereby maintaining better output 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 binder composition achieves excellent binding properties, stability, and high temperature cycle characteristics by ensuring uniform dispersion and reduced internal resistance, improving the overall performance of lithium ion secondary batteries.
Implementation Method 1
a swelling degree of the binder in an electrolytic solution dissolved with LiPF6 of a concentration of 1.0 mol/L in a mixture solution formed by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) having the volume ratio at 20° C. of EC:DEC=1:2 is 100 to 500%
Implementation Method 2
the polymer which becomes the binder to the liquid solvent such as the water or the organic liquid or so is dispersed or dissolved
Implementation Method 3
the polymer which becomes the binder to the liquid solvent such as the water or the organic liquid or so is dispersed or dissolved
Data Source
AI summary
Provided are a binder composition which has high electrolyte resistance characteristics, and a secondary battery which uses a positive electrode using the binder composition for high-temperature cycle characteristics. [Solution] The binder composition for the secondary battery positive electrode according to the present invention contains a polymerized unit which contains a nitrile group; a polymerized unit of (meth) acrylic acid ester; a polymerized unit which contains a hydrophilic group; and a polymerized unit of linear alkylene having a carbon number of at least four. In a mixed solvent in which a volume ratio EC:DEC between ethylene carbonate (EC) and diethyl carbonate (DEC) at 20° C. is 1:2, a degree of swelling with respect to an electrolyte in which LiPF6 is dissolved to have a concentration of 1.0 mol/L is between 100% and 500%.