Aqueous VDF Binder for Battery Electrodes
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Solution Overview
Problem
Existing aqueous vinylidene fluoride (VDF) polymer binder compositions for non-aqueous-type electrochemical devices face challenges in achieving good cohesion within powdery electrode material particles and adhesion to metal collectors, leading to high electrical resistance and low capacity, especially during charging and discharging cycles.
Innovation Solution
An aqueous composition comprising an aqueous latex of vinylidene fluoride polymer with recurring units derived from vinylidene fluoride and (meth)acrylic monomers, combined with powdery electrode material, where the polymer is in the form of primary particles less than 1 μm in size, providing enhanced stability and adhesion without the need for isolating and drying the polymer powder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aqueous vinylidene fluoride polymer binder compositions are used, then environmental friendliness is improved by avoiding organic solvents, but adhesion to metal collectors and cohesion within electrode material particles deteriorates
Solution Approach 1:
The patent changes the molecular weight parameters of the VDF polymer binder, specifically using polymers with weight average molecular weights of 100,000-500,000 and number average molecular weights of 50,000-200,000. This parameter optimization enables the polymer to achieve sufficient adhesion and cohesion in aqueous form without requiring organic solvents, thus resolving the contradiction between environmental friendliness and binding strength
Solution Approach 2:
The patent creates a composite binder system by combining vinylidene fluoride polymer with specific additives including carboxymethyl cellulose and starch derivatives. This composite approach enhances the adhesion and cohesion properties of the aqueous binder, allowing it to perform effectively without organic solvents while maintaining environmental friendliness
2Stability of the object's composition
If VDF polymer powder is isolated and dried before redispersion, then processing stability is improved, but manufacturing complexity and time consumption increase
Solution Approach 1:
The patent performs preliminary stabilization by conducting the polymerization reaction directly in aqueous medium with controlled molecular weight parameters, creating a pre-stabilized polymer latex that can be directly used without isolation and redispersion steps. This preliminary action eliminates subsequent processing steps while maintaining composition stability
Solution Approach 2:
The patent extracts the problematic isolation and drying steps from the manufacturing process by developing a polymerization method that produces directly usable aqueous binder. This removes the unnecessary intermediate steps of powder isolation, drying, and redispersion, simplifying the overall manufacturing process while maintaining product stability
3Ease of manufacture
If conventional VDF polymer binders are used, then ease of manufacture is improved, but electrical resistance increases and capacity decreases during charging and discharging cycles
Solution Approach 1:
The patent optimizes molecular weight parameters (weight average MW: 100,000-500,000; number average MW: 50,000-200,000) and compositional parameters (VDF content: 80-95 mol%) to achieve the right balance between ease of manufacture and electrical performance. These parameter changes enable the binder to provide sufficient adhesion while maintaining low electrical resistance and high capacity during battery cycling
Solution Approach 2:
The patent develops a composite binder formulation combining VDF polymer with specific additives (carboxymethyl cellulose at 0.1-5 wt%, starch derivatives at 0.1-5 wt%) that work synergistically to reduce electrical resistance and improve capacity while maintaining ease of manufacture through aqueous processing
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 enables the manufacture of electrodes with improved capacity values during charging and discharging cycles, ensuring better cohesion and adhesion, thus reducing electrical resistance and enhancing overall performance.
Implementation Method 1
The role of the organic solvent is typically to dissolve the VDF polymer in order to bind the powdery electrode material particles to each together and to the metal collector
Implementation Method 2
ensuring good cohesion within the particulate active material and good adhesion between these particles and the metal collector
Implementation Method 3
ensuring good cohesion within the particulate active material and good adhesion between these particles and the metal collector upon evaporation of the organic solvent
Data Source
AI summary
The present invention pertains to an aqueous composition comprising: (A) an aqueous latex comprising at least one vinylidene fluoride (VDF) polymer [polymer (F)] comprising recurring units derived from vinylidene fluoride (VDF) and at least one (meth)acrylic monomer (MA) having formula (I) here below: wherein: —R1, R2 and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and —ROH is a hydrogen atom or a C1-C5 hydrocarbon moiety comprising at least one hydroxyl group, (B) at least one powdery electrode material, and (C) optionally, less than 10% by weight, based on the total weight of the aqueous composition, of at least one organic solvent (S), wherein the polymer (F) in the aqueous latex is under the form of primary particles having an average primary particle size of less than 1 μm, as measured according to ISO 13321. The present invention also pertains to a process for manufacturing an electrode using said aqueous composition, to an electrode comprising a metal substrate coated on at least one surface with said aqueous composition and to use of said electrode for manufacturing a non-aqueous-type electrochemical device.