Separator Surface Layer Deformation for Battery Pressure Resistance
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Solution Overview
Problem
Lithium ion secondary batteries using silicon or tin as negative electrode materials face issues with pressure-induced expansion, leading to collapsed separator pores and reduced ion permeability, as well as oxidation of polyolefin separators, which lowers battery characteristics such as cycle performance.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a separator with a substrate layer and a surface layer containing polyvinylidene fluoride and inorganic material particles, where the surface layer has a higher deformation under pressure than the substrate layer, preventing pore collapse and enhancing oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin separator is used, then the separator provides shutdown function and insulation, but the pores collapse under pressure from negative electrode expansion, reducing ion permeability
Solution Approach 1:
The separator is constructed as a composite material combining polyolefin base material with silane-modified polyethylene crosslinked network. This composite structure provides both the shutdown function of polyolefin and the pressure resistance of crosslinked network, preventing pore collapse while maintaining ion permeability.
Solution Approach 2:
The separator undergoes parameter change through crosslinking modification. By introducing crosslinked network structure into the polyolefin matrix, the mechanical strength and pressure resistance are enhanced, allowing the separator to maintain its pore structure under electrode expansion pressure while retaining ion transport capability.
2Reliability
If a polyolefin separator is used, then the separator provides insulation and shutdown function, but the separator strength is lowered upon oxidation
Solution Approach 1:
The crosslinked composite structure creates a more robust separator that resists oxidation. The crosslinked network provides structural integrity that prevents strength degradation from oxidation, while the polyolefin matrix maintains the shutdown function through its melting characteristics.
3Reliability
If a polyolefin separator is used, then the separator provides shutdown function, but pores become clogged by oxide, lowering battery characteristics
Solution Approach 1:
The crosslinked composite structure provides a more stable pore architecture that resists clogging by oxide particles. The enhanced mechanical strength from crosslinking prevents pore deformation and maintains open pathways for ion transport, preventing battery characteristic degradation.
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 design effectively suppresses the lowering of battery characteristics by absorbing pressure from negative electrode expansion and improving separator strength, maintaining ion permeability and cycle performance.
Implementation Method 1
an amount of deformation against pressure of the surface layer is larger than that of the substrate layer
Implementation Method 2
a pressure generated due to expansion of the negative electrode active material
Implementation Method 3
oxidation resistance of the separator can be enhanced
Implementation Method 4
ion permeability of the separator is lowered
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator includes a substrate layer and a surface layer formed on at least one principal plane of the substrate layer, the surface layer contains polyvinylidene fluoride and an inorganic material particle, and an amount of deformation against pressure of the surface layer is larger than that of the substrate layer.