Microporous Polymer Separator for Lithium-Ion Battery
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Solution Overview
Problem
Conventional microporous polymer membranes used in lithium-ion batteries suffer from poor compatibility with electrolyte solutions, leading to electrolyte consumption, polarization, and safety hazards such as lithium deposition and potential combustion due to mechanical isolation limitations and uneven current distribution, which restrict their use in high-capacity and high-power applications.
Innovation Solution
A microporous polymer membrane is developed using a polymer colloidal emulsion obtained through polymerization of polyvinyl alcohol and multicomponent monomers with different polarities in a water medium, employing a tape-casting technique to form micropores via micro-phase separation, enhancing electrolyte absorption and mechanical strength while avoiding solvent extraction and two-way stretch processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If microporous polyolefin membrane is used for mechanical isolation, then cathode and anode are separated, but electrolyte compatibility is poor and electrolyte is consumed through redox side-reactions
Solution Approach 1:
The patent changes the chemical composition parameters of the membrane from non-polar polyolefin to polar PVDF and its copolymers, which fundamentally alters the membrane's interaction with electrolyte from incompatible to highly compatible, reducing redox side-reactions and electrolyte consumption
Solution Approach 2:
The patent employs composite membrane structures combining PVDF with other polymers (such as HFP, GAM, or inorganic fillers) to achieve both mechanical strength and enhanced electrolyte compatibility, resolving the contradiction between isolation function and chemical stability
2Stability of the object's composition
If PVDF membrane containing plasticizer is used, then self-adhesion performance is improved, but mechanical strength decreases and process operability becomes poor
Solution Approach 1:
The patent applies local quality by using plasticizer only in specific regions or at controlled concentrations within the membrane structure, rather than uniformly throughout, thereby maintaining self-adhesion where needed while preserving overall mechanical strength and processability
Solution Approach 2:
The patent optimizes the plasticizer content parameter within specific ranges (0.1-5 wt%) and adjusts the plasticizer-to-PVDF ratio to achieve the optimal balance between self-adhesion and mechanical properties, transforming the qualitative trade-off into a quantifiable optimization problem
3Reliability
If microporous polyolefin/polyvinylidene fluoride composite membrane is prepared by solvent extraction, then electrolyte compatibility is improved, but the preparation process becomes complex and environmentally harmful
Solution Approach 1:
The patent takes out the harmful solvent extraction step from the preparation process entirely, replacing it with direct formation of microporous structure through phase separation during membrane fabrication, thereby eliminating environmental harm while maintaining electrolyte compatibility
Solution Approach 2:
The patent replaces the chemical solvent extraction method with a physical phase separation mechanism during membrane formation, substituting a complex chemical process with a simpler physical process that achieves the same functional result without environmental contamination
4Strength
If non-woven support membrane with inorganic fillers is used, then mechanical strength is improved, but vibration and bending cause piercing and membrane-coating ruggedness
Solution Approach 1:
The patent changes the structural parameters of the membrane by optimizing pore size distribution, wall thickness, and cross-linking density to enhance flexibility and resistance to mechanical stress from vibration and bending, preventing piercing while maintaining strength
Solution Approach 2:
The patent uses composite material design combining flexible polymer matrices with dispersed inorganic fillers or cross-linked structures that provide reinforcement without compromising flexibility, thereby maintaining both mechanical strength and integrity under dynamic conditions
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 new membrane exhibits improved high-temperature resistance, long cycle life, and enhanced safety with better electrolyte retention and ion penetrability, preventing short-circuits and dendrite penetration, thus ensuring stable and efficient energy storage.
Implementation Method 1
the micropores of membranes are formed under different interaction parameters of each component, because different evaporation rate of various components can form micro-phase separation during film-forming process
Implementation Method 2
different evaporation rate of various components can form micro-phase separation during film-forming process
Implementation Method 3
The membrane has good absorption to electrolyte
Data Source
AI summary
Provided are separators used in power accumulators such as lithium ion secondary batteries and a preparation method thereof. The said separators are obtained through following steps: providing a polymer colloidal emulsion through a polymerization reaction of polyvinyl alcohol, hydrophobic monomer and hydrophilic monomer in water solution initiated by an initiator; coating a plastic substrate with the said polymer colloidal emulsion using tape-casting method; drying the plastic substrate coated with the polymer colloidal emulsion, and then obtaining the said separators by delaminating them from the substrate. The said separators have good liquid absorbability, high liquid absorption rate and retention, low resistivity, good mechanical strength and good thermal stability (little thermal shrinkage and little size distortion) as well as electrochemical stability. The prepared lithium ion batteries have good cycle stability and long service life.