Aqueous Positive Electrode Sheet With Graded Porosity for Lower Resistance
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Solution Overview
Problem
Current aqueous positive electrode sheets for secondary batteries face challenges in reducing membrane resistance and improving dynamic performance, with existing binders and solvents like PVDF and NMP being costly, environmentally harmful, and inefficient in energy storage.
Innovation Solution
An aqueous positive electrode sheet with a non-uniform structure, featuring greater porosity and larger average particle sizes of active materials on the surface compared to the inner area, combined with an aqueous binder and conductive agents, reduces membrane resistance and enhances battery performance through multi-layer die head extrusion coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PVDF and NMP are used as binder and solvent in positive electrode sheet preparation, then the electrode sheet can be formed with good binding performance, but the cost increases and environmental pollution occurs
Solution Approach 1:
The patent replaces expensive and environmentally harmful PVDF/NMP system with a cheaper, biodegradable starch-based aqueous binder system. The starch binder is derived from renewable resources and can be disposed of without environmental contamination, directly addressing both cost reduction and pollution elimination while maintaining electrode integrity through its adhesive properties
Solution Approach 2:
The patent fundamentally changes the binder system from organic-based (PVDF in NMP) to water-based starch binder, altering the chemical composition parameters. This parameter change enables the use of aqueous slurry instead of organic slurry, eliminating NMP volatilization and pollution while reducing costs through the use of abundant, inexpensive starch materials
2Stability of the object's composition
If PVDF and NMP are used as binder and solvent, then the electrode sheet can be prepared with stable structure, but the energy consumption increases due to complex synthesis and post-treatment processes
Solution Approach 1:
The patent eliminates the need for complex energy-intensive processes by using a starch-based aqueous binder that requires no sophisticated synthesis or post-treatment. The simple aqueous system can be processed at lower temperatures and without the need for energy-consuming NMP recovery operations, directly reducing stationary energy consumption while maintaining electrode structural stability
Solution Approach 2:
The patent changes the processing parameters from high-energy organic solvent-based processes to low-energy aqueous processes. The aqueous starch binder system allows for lower drying temperatures and eliminates the need for energy-intensive solvent recovery, fundamentally altering the energy consumption profile of electrode manufacturing while preserving structural integrity
3Ease of manufacture
If uniform structure is used in positive electrode active substance layer, then the manufacturing process is simple, but the membrane resistance and impedance are high
Solution Approach 1:
The patent applies local quality by creating a vertically non-uniform particle size distribution within the electrode layer. Larger particles are positioned in the surface area while smaller particles are positioned in the inner area near the current collector. This local differentiation optimizes ion transport pathways, reducing membrane resistance and impedance while maintaining a relatively simple one-step coating manufacturing process
Solution Approach 2:
The patent transitions from a uniform one-dimensional structure to a vertically stratified structure with different particle sizes at different depths. This dimensional organization within the electrode thickness direction creates optimized ion transport channels that reduce resistance without complicating the horizontal manufacturing process, effectively adding structural complexity only where needed for performance
4Quantity of substance
If larger particle size is used in positive electrode active material, then the capacity is high, but the rate performance deteriorates
Solution Approach 1:
The patent applies local quality by positioning larger particles (0.8-2.5 μm) in the surface area where they provide high capacity, while positioning smaller particles (0.5-1.5 μm) in the inner area where they facilitate faster ion diffusion. This spatial differentiation allows the electrode to simultaneously achieve high overall capacity through large particles and good rate performance through small particles near the current collector, resolving the capacity-rate performance trade-off
Data Source
AI summary
The present application relates to an aqueous positive electrode sheet, which may include a current collector and a positive electrode active substance layer provided on at least one surface of the current collector, the positive electrode active substance layer may include an aqueous binder, where the porosity of a surface area of the positive electrode active substance layer may be greater than the porosity of an inner area of the positive electrode active substance layer, and the average particle size of the positive electrode active material in the surface area may be greater than the average particle size of the positive electrode active material in the inner area. The present application further relates to a secondary battery including the aqueous positive electrode sheet, a battery pack including the secondary battery, and a power consumption apparatus including the battery pack.