LFP Cathode Rolling Sequence to Prevent Layer Delamination
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Solution Overview
Problem
The challenge in manufacturing a high-density positive electrode for lithium secondary batteries using lithium iron phosphate as the active material is the deintercalation of the active material layer from the current collector due to mechanical property differences, which is exacerbated by high rolling rates needed for density, and increasing binder content to prevent this increases resistance and reduces capacity.
Innovation Solution
A method involving multiple stages of rolling with controlled thickness changes, specifically limiting the thickness change to 3.5% or less after the first rolling, to prevent deintercalation while maintaining a low binder content, using lithium iron phosphate with a monolith structure and optimized carbon coating, and employing a controlled rolling process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional method (not using a crosslinking catalyst) is used for crosslinking the binder, then the manufacturing process is simple, but the crosslinking reaction is incomplete and battery performance is insufficient
Solution Approach 1:
A crosslinking catalyst (metal complex catalyst) is introduced as an intermediary substance to facilitate the crosslinking reaction between the binder and crosslinking agent. The catalyst mediates the reaction to proceed completely and efficiently, achieving high battery performance without requiring complex manufacturing processes. The catalyst is used in small amounts (0.01-5 parts by weight per 100 parts of binder) and can be easily removed or deactivated after crosslinking.
Solution Approach 2:
The invention changes the chemical reaction parameters by introducing a catalyst that lowers the activation energy and accelerates the crosslinking reaction. This allows the reaction to proceed to completion under milder conditions (lower temperature, shorter time) compared to uncatalyzed reactions, thereby improving battery performance while simplifying the manufacturing process.
2Reliability
If a metal complex catalyst is used for crosslinking, then complete crosslinking and high battery performance are achieved, but residual catalyst may remain in the battery
Solution Approach 1:
The invention uses a crosslinking catalyst that can be easily removed or deactivated after serving its purpose. The catalyst is used in small amounts and can be eliminated through simple washing or thermal treatment, leaving no harmful residues in the battery. This approach allows complete crosslinking during manufacturing while ensuring the final product is free from harmful catalyst residues.
Solution Approach 2:
The invention converts the potential harm of residual catalyst into a benefit by selecting catalysts that can be completely removed or decomposed after crosslinking. The catalyst performs its beneficial function during manufacturing (achieving complete crosslinking) and then is eliminated, leaving no harmful effects in the final battery product.
3Reliability
If crosslinking is performed at high temperature for long time, then crosslinking completeness is improved, but production time increases and productivity decreases
Solution Approach 1:
The invention changes the temperature and time parameters of the crosslinking reaction by introducing a catalyst. The catalyst enables the reaction to proceed to completion at lower temperatures (50-200°C) and shorter times (1-24 hours) compared to uncatalyzed reactions that require high temperatures and long durations. This dramatically increases production speed while maintaining complete crosslinking.
Solution Approach 2:
The catalyst is introduced before the crosslinking reaction to pre-enable the reaction pathway. This preliminary action of adding the catalyst allows the crosslinking to proceed rapidly and completely under mild conditions, avoiding the need for subsequent high-temperature prolonged heating that would reduce productivity.
4Strength
If binder content in the electrode is increased to improve adhesion, then adhesion is improved, but lithium ion mobility decreases and battery performance deteriorates
Solution Approach 1:
The invention applies local quality by creating a binder network with different properties in different regions. The crosslinked binder forms a rigid adhesive network at the electrode substrate interface for strong adhesion, while maintaining a more open, flexible structure in the bulk that allows lithium ion transport. This spatial differentiation of binder properties simultaneously achieves strong adhesion and good ion mobility without increasing overall binder content.
Solution Approach 2:
The invention creates a composite binder system consisting of crosslinked polymer networks with specific chemical structures (e.g., polyacrylic acid crosslinked with polyethylene glycol diacrylate). This composite structure combines the adhesive properties of the polymer matrix with the ion-conducting properties of the crosslinked network, achieving both strong adhesion and good lithium ion mobility without increasing binder content.
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
This approach enables the production of a high-density positive electrode with improved adhesive force and reduced resistance, enhancing battery capacity by maintaining the integrity of the active material layer and minimizing electrode defects.
Implementation Method 1
crosslinking catalyst which catalyzes the crosslinking reaction of the binder
Implementation Method 2
the positive electrode has a porous structure and absorbs a specific amount of electrolyte solution in a specific range
Data Source
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AI summary
Disclosed herein relates to a method for manufacturing a positive electrode for a lithium secondary battery including: (S1) forming a positive electrode active material layer by applying a positive electrode slurry composition comprising lithium iron phosphate and a binder onto a current collector and drying it; (S2) rolling a positive electrode active material layer N times (N is an integer greater than or equal to 2), wherein in the rolling step, during the first rolling, the rate of change in thickness of a positive electrode active material layer according to Equation 1 below is 5% to 15%, and during rolling after the first rolling, the rate of change in thickness of a positive electrode active material layer according to Equation 1 below is 3.5% or less. Rateofchangeinthickness%=thicknessofK−1timesrolledpositiveelectrodeactivemateriallayer−thicknessofKtimesrolledpositiveelectrodeactivemateriallayer×100/thicknessofpositiveelectrodeactivemateriallayerbeforerollingstep In Equation 1, K is an integer greater than or equal to 1 and smaller than or equal to N.