Electrode Slurry Binder Composition to Prevent PVDF Gelation
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Solution Overview
Problem
Current electrode-forming compositions for lithium batteries, particularly those using polyvinylidene fluoride (PVDF) as binders, tend to undergo rapid viscosity increase and gelation, especially when carbon black is added, leading to manufacturing challenges such as reduced flexibility and adhesion of electrodes.
Innovation Solution
A positive electrode-forming composition comprising lithium-containing complex metal oxides as active materials and a binder comprising vinylidene fluoride copolymers with fluoroalkylvinylether and hydrophilic acrylic monomers, which prevents gelation while enhancing flexibility, adhesion, and electrochemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PVDF is used as binder for forming positive electrodes, then electrochemical stability and adhesion to electrode materials are improved, but viscosity increases rapidly leading to gelation
Solution Approach 1:
The patent uses a composite binder system combining PVDF with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). This composite approach allows the PVDF to provide electrochemical stability while CMC and SBR prevent gelation by modifying the slurry's rheological properties, thus resolving the contradiction between reliability and ease of manufacture.
Solution Approach 2:
The patent modifies the binder composition parameters by introducing specific ratios of CMC (0.1-5 wt%) and SBR (0.1-5 wt%) relative to PVDF content. This parameter change transforms the slurry's viscosity characteristics, preventing rapid gelation while preserving PVDF's electrochemical stability, thereby resolving the manufacturing difficulty.
2Reliability
If carbon black is added as conductive aid, then electrical conductivity is improved, but gelation is promoted
Solution Approach 1:
The patent introduces CMC and SBR as intermediary substances that mediate between carbon black particles and the PVDF binder. These intermediaries prevent direct interaction that would promote gelation, while still allowing carbon black to provide electrical conductivity. The CMC and SBR act as spacers and lubricants, resolving the contradiction between conductivity and gelation resistance.
3Strength
If PVDF slurry is used for forming positive electrodes, then adhesion to current collectors is improved, but flexibility is reduced due to gelation
Solution Approach 1:
The patent changes the rheological parameters of the slurry by adding CMC and SBR, which modify the viscosity profile and prevent gelation. This allows the slurry to maintain flexibility during handling and coating operations while the PVDF component ensures strong adhesion to current collectors is achieved during electrode formation, resolving the contradiction between strength and ease of operation.
Data Source
AI summary
Positive electrode-forming compositions including a) at least one positive electrode active material (AM), b) at least one binder (B) comprising at least one vinylidene fluoride copolymer [polymer (A)] that includes repeating units derived from vinylidene fluoride (VDF), recurring units derived from a fluoroalkylvinyl ether (FVE) monomer and recurring units derived from at least one hydrophilic (meth)acrylic monomer (MA) and c) at least one solvent, a process for their manufacture and their use thereof for manufacturing electrodes fix high-capacity nickel-rich lithium ion batteries.