Multilayer Secondary Battery Electrode for Adhesion and Cycle Life
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Solution Overview
Problem
Current secondary battery electrodes face issues with adhesion between the current collector and active material, leading to increased electrical resistance and reduced capacity and lifespan due to the use of polyvinylidene fluoride (PVdF) as a binder, which also limits flexibility and active material cohesion.
Innovation Solution
A multilayer electrode structure is developed using carboxymethyl cellulose and styrene butadiene rubber with varying weight average molecular weights in each layer to enhance adhesion and cohesion between the current collector and active material, while reducing electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVdF is used as a binder to manufacture an electrode plate with high adhesive strength, then adhesion between the current collector and active material is improved, but the active material is covered in the same state as the polymer fibers are full, deteriorating the battery performance inherent in the electrode active material in terms of capacity and efficiency
Solution Approach 1:
The patent uses carboxymethyl cellulose (CMC) with different weight average molecular weights (different parameter values) to change the binding characteristics. By selecting specific molecular weight ranges, the patent achieves adequate adhesion while improving electrolyte wettability and active material exposure, thereby resolving the contradiction between adhesive strength and battery performance
Solution Approach 2:
The patent employs a composite binder system combining carboxnymethyl cellulose with styrene butadiene rubber (SBR) in specific weight ratios. This composite material approach allows the electrode to achieve both sufficient adhesion and improved electrolyte interaction, balancing the conflicting requirements of strong bonding and high battery performance
2Strength
If PVdF is used as a binder, then adhesive strength is improved, but the binder lacks flexibility, causing bonding to break when materials with large specific surface area and high expansion and contraction rate like natural graphite are used, deteriorating cycle characteristics
Solution Approach 1:
The patent introduces flexibility by selecting CMC with specific molecular weight parameters and combining it with SBR, which has inherent elastic properties. This parameter optimization allows the binder to maintain adhesion strength while accommodating the expansion and contraction of active materials during cycling, preventing bond breakage and improving cycle characteristics
Solution Approach 2:
By creating a composite binder system of CMC and SBR, the patent combines the adhesive properties of CMC with the flexibility and elasticity of SBR. This composite material provides both strong bonding and the necessary flexibility to withstand volume changes during charging and discharging, resolving the contradiction between adhesion strength and cycle stability
3Quantity of substance
If the amount of active material loading per unit area of the electrode is increased, then capacity is improved, but the active material layer is pushed during rolling and the loading amount per unit area is lower than the originally intended value, increasing manufacturing costs as overall thickness must be increased
Solution Approach 1:
The patent optimizes the molecular weight parameter of CMC to control slurry viscosity and flow characteristics. By adjusting this parameter, the patent achieves better slurry distribution during the coating process, reducing active material loss during rolling and ensuring the intended loading amount per unit area is achieved, thereby improving both capacity and manufacturing precision
Data Source
AI summary
An electrode for a secondary battery includes a current collector, a first electrode mixture layer disposed on at least one surface of the current collector and including carboxymethyl cellulose and styrene butadiene rubber, and a second electrode mixture layer disposed on the first electrode mixture layer and including carboxymethyl cellulose. A weight average molecular weight of the carboxymethyl cellulose included in the first electrode mixture layer is less than a weight average molecular weight of the carboxymethyl cellulose included in the second electrode mixture layer. Adhesion between the electrode current collector and the active material and cohesion between the active materials may be improved, and the resistance within the electrode may be reduced, thereby significantly increasing the capacity and lifespan characteristics of a battery.