Silicon Negative Electrode Slurry for Crack-Resistant Cycle Stability
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Solution Overview
Problem
The expansion of silicon-containing negative electrodes in rechargeable lithium-ion batteries due to lithium intercalation/deintercalation leads to decreased electronic conductivity and cycle characteristics, and the use of acrylic acid-based polymers as binders can result in cracks during the coating and drying processes.
Innovation Solution
A negative electrode slurry comprising a silicon-containing active material, an acrylic acid-acrylonitrile-based copolymer as a binder, and a particulate dispersed body, with specific weight percentages and viscosity ranges to suppress expansion and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-containing active material is used to increase capacity, then the battery capacity is improved, but the negative electrode mixture layer expands and contracts violently during charge and discharge, decreasing electronic conductivity and isolating the silicon-containing active material
Solution Approach 1:
The invention changes the physical and chemical parameters of the binder by using a copolymer with specific composition ratios (acrylic acid-based monomer 40-70 wt%, acrylonitrile-based monomer 30-60 wt%) and controlled glass transition temperature (-50°C to 0°C). This modifies the binder's mechanical properties to accommodate silicon's volume expansion while maintaining electrical conductivity.
Solution Approach 2:
The invention creates a composite binder system combining organic polymer (acrylic acid-acrylonitrile copolymer) with inorganic particles (at least one type selected from metal oxide, metal nitride, metal carbide, or carbon material). This composite structure provides both flexibility to accommodate expansion and conductive pathways to maintain electrical connectivity.
2Reliability
If an acrylic acid-based polymer with relatively high hardness is used as a binder to suppress expansion, then the negative electrode expansion is reduced, but cracks occur in the negative electrode during coating and drying processes
Solution Approach 1:
The invention precisely controls the glass transition temperature of the binder within -50°C to 0°C by adjusting the monomer composition ratios. This parameter optimization provides the right balance between flexibility (to prevent cracking during manufacturing) and expansion suppression (for battery performance).
Solution Approach 2:
The invention creates different functional zones within the binder: the acrylic acid-based segments provide flexibility and adhesion to prevent cracking during coating, while the acrylonitrile-based segments and inorganic particles provide expansion suppression during battery operation. This local differentiation of properties resolves the contradiction.
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 effectively reduces the expansion of the negative electrode, prevents cracking during coating and drying, and improves the cycle maintenance rate of the batteries.
Implementation Method 1
the binder includes a particulate dispersed body and a water-soluble polymer including a copolymer including an acrylic acid-based monomer and an acrylonitrile-based monomer
Implementation Method 2
a binder for binding the negative active material
Implementation Method 3
a solvent for dispersing the negative active material and the binder in the negative electrode slurry
Implementation Method 4
a water-soluble polymer including a copolymer including an acrylic acid-based monomer and an acrylonitrile-based monomer
Data Source
AI summary
A negative electrode slurry includes a negative active material including a first active material in an amount of greater than or equal to about 5 wt % and less than or equal to about 100 wt %, a binder for binding the negative active material, and a solvent for dispersing the negative active material and the binder in the negative electrode slurry, wherein the first active material contains silicon atoms in an amount of greater than or equal to about 20 wt % and less than or equal to about 100 wt %, the binder includes a particulate dispersed body and a water-soluble polymer containing an acrylic acid-acrylonitrile-based copolymer, and when a sum of an amount of the negative active material and an amount of the binder is 100 wt %, an amount of the water-soluble polymer is greater than or equal to about 0.5 wt % and less than or equal to about 2 wt %.