Li-Ion Battery Separator Adhesion for Low-Expansion Cycle Life
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Solution Overview
Problem
Lithium-ion batteries face safety hazards due to increased thickness and potential for fire or explosion as cycle time increases, primarily caused by the deterioration of the interface between the separator and electrode plates, which is attributed to a decrease in adhesive strength over time.
Innovation Solution
A lithium-ion battery design incorporating a non-aqueous electrolyte solution with ethyl propionate and a copolymer of hexafluoropropylene-vinylidene fluoride, where the adhesive layer on the separator maintains a stable adhesive strength between the electrodes, reducing expansion and improving cycle life through a controlled ratio of ethyl propionate to hexafluoropropylene in the copolymer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the battery is used for a long time, then the cycle life increases, but the adhesive strength of the separator decreases causing interface deterioration
Solution Approach 1:
The patent modifies the chemical composition parameters of the adhesive layer by incorporating copolymer of vinylidene fluoride-hexafluoropropylene with specific hexafluoropropylene content (5-30 mass%), and adjusts electrolyte composition with ethyl propionate (5-60 mass%). These parameter changes enable the adhesive layer to maintain stable bonding strength throughout extended cycling, resolving the contradiction between extended cycle life and maintained adhesive strength.
Solution Approach 2:
The patent employs composite material strategies by creating an adhesive layer that combines copolymer of vinylidene fluoride-hexafluoropropylene with ceramic particles (alumina, boehmite, or magnesium oxide). This composite structure provides both adhesive functionality and structural stability, preventing interface deterioration even after prolonged battery operation.
2Duration of action of stationary object
If the battery operates for extended periods, then the cycle life increases, but the battery thickness increases due to expansion leading to safety hazards
Solution Approach 1:
The patent changes the chemical composition parameters of the separator by incorporating heat-resistant layers containing ceramic particles (alumina, boehmite, or magnesium oxide) with specific size ranges (0.1-10 μm). These compositional changes reduce thermal expansion and maintain dimensional stability, preventing battery thickness increase during extended cycling while extending cycle life.
Solution Approach 2:
The patent uses composite materials by integrating ceramic particles into the heat-resistant layer of the separator. This composite structure provides thermal stability and mechanical strength, preventing expansion-induced safety hazards while enabling long cycle life operation.
3Duration of action of stationary object
If the adhesive strength of the separator is increased to prevent interface deterioration, then the cycle life improves, but the device complexity increases
Solution Approach 1:
The patent applies local quality by enhancing only the adhesive layer and heat-resistant layer of the separator with specific functional materials (copolymer with ceramic particles), while keeping the base substrate structure simple. This localized enhancement improves cycle life without requiring complex changes to the entire separator structure.
Solution Approach 2:
The patent uses composite materials in the adhesive and heat-resistant layers, combining copolymer of vinylidene fluoride-hexafluoropropylene with ceramic particles. This composite approach achieves improved adhesion and thermal stability through material composition rather than structural complexity.
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 battery achieves a long cycle life with reduced expansion, enhanced adhesive strength, and improved low-temperature performance by maintaining the adhesive strength within 10% change over 100 cycles, thereby preventing safety hazards and improving stability at high temperatures and voltages.
Implementation Method 1
The adhesive layer includes an adhesive including a copolymer of hexafluoropropylene-vinylidene fluoride
Implementation Method 2
the copolymer of hexafluoropropylene-vinylidene fluoride has a number average molecular weight of 200,000 Da to 2,500,000 Da
Implementation Method 3
a non-aqueous organic solvent including ethyl propionate has a strong swelling effect on PVDF in the separator
Implementation Method 4
ethyl propionate may also reduce a viscosity of the solvent to improve the electrolyte solution wettability
Implementation Method 5
The heat-resistant layer includes ceramic and a binder. A mass percentage of the ceramic in the heat-resistant layer ranges from 20 wt. % to 99 wt. %
Implementation Method 6
The battery achieves a long cycle life with reduced expansion, enhanced adhesive strength, and improved low-temperature performance by maintaining the adhesive strength within 10% change over 100 cycles, thereby preventing safety hazards
Data Source
AI summary
A battery includes a positive electrode plate, a negative electrode plate, a separator, and a non-aqueous electrolyte solution. The non-aqueous electrolyte solution includes a non-aqueous organic solvent including at least ethyl propionate. The separator includes a substrate, a heat-resistant layer, and an adhesive layer, where the heat-resistant layer is disposed on at least one side of the substrate, and the adhesive layer is disposed on the heat-resistant layer. The adhesive layer includes an adhesive including a copolymer of hexafluoropropylene-vinylidene fluoride. A ratio of a mass percentage of ethyl propionate in the non-aqueous electrolyte solution to a mass percentage of hexafluoropropylene in the copolymer of hexafluoropropylene-vinylidene fluoride ranges from 0.2 to 60. The battery in the present disclosure has both a long cycle life and low expansion.