Positive Electrode Binder for High-Density Lithium-Ion Batteries
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Solution Overview
Problem
Existing positive electrodes for lithium-ion secondary batteries face challenges in maintaining flexibility and binding properties when designed for high density and thickness, leading to issues like electrode active material layer cracking and increased internal resistance, which affects cycle and output characteristics.
Innovation Solution
A positive electrode composition featuring a binder with a fluorine-containing polymer and a second polymer unit having nitrile, hydrophilic, and (meth)acrylate groups, optimized in weight ratio and molecular structure to enhance flexibility, binding, and stability, reducing the risk of cracking and improving high-temperature cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the amount of fluorine based polymer is increased to enhance adhesive force with the current collector, then the adhesive force is improved, but the internal resistance of the battery increases which causes capacity to decline
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by introducing a copolymer with specific functional groups (carboxyl, hydroxyl, or amine groups) in controlled amounts (0.1-10 mmol/g). This parameter change allows optimization of both adhesive force and electrical conductivity, resolving the contradiction between strength and reliability
Solution Approach 2:
The invention creates a composite binder system combining fluorine-based polymer with copolymer containing functional groups. This composite material approach allows the fluorine-based polymer to provide adhesive force while the functional-group-containing copolymer provides sites for conductive agent interaction, thereby maintaining low internal resistance while achieving strong adhesion
2Quantity of substance
If the electrode is designed for high density and thickness to improve energy capacity, then the energy capacity is improved, but the flexibility and binding properties deteriorate leading to cracking
Solution Approach 1:
The invention modifies the binder's molecular structure parameters by incorporating copolymer chains with specific functional group densities. This allows the binder to maintain flexibility and binding properties even in high-density, thick electrode designs, preventing cracking while preserving energy capacity
3Stability of the object's composition
If fluorine based polymer is used as binder for positive electrode, then the polymer resistance against organic electrolytic solution is improved, but the adhesive force against current collector becomes weak
Solution Approach 1:
The invention applies local quality modification by introducing specific functional groups (carboxyl, hydroxyl, or amine) at specific locations within the binder molecular structure. The fluorine-based polymer backbone provides electrolytic solution resistance while the localized functional groups provide enhanced adhesion to the current collector, resolving the contradiction between stability and strength
Data Source
AI summary
[Problem] To provide a positive electrode which exhibits excellent flexibility and binding properties even when designed having a high density and/or a high thickness, and which exhibits a high density even before pressing, and a secondary battery exhibiting excellent cycle characteristics (particularly high-temperature cycle characteristics). [Solution] A positive electrode for a secondary battery according to the present invention is characterized in that: said electrode comprises a collector and a positive electrode active material layer which is stacked upon the collector, and which includes a positive electrode active material, a conductive agent, and a binder; the binder includes a first polymer and a second polymer; the first polymer is a fluorine-containing polymer; the second polymer includes a polymerized moiety having a nitrile group, a polymerized moiety having a hydrophilic group, a polymerized (meth) acrylic acid ester moiety, and a straight-chain polymerized alkylene moiety having a carbon number of at least 4; the proportion of the first polymer and the second polymer in the binder, expressed as a mass ratio, is in the range of 95:5 to 5:95.