Solid Electrolyte Separator Film Balancing Conductivity and Strength
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Solution Overview
Problem
Current solid electrolytes for Li-ion batteries face challenges in achieving a balance between high ion conductivity, electrochemical stability, and temperature stability, while also ensuring mechanical strength and safety, particularly in preventing dendrite growth and flammability.
Innovation Solution
A solid electrolyte composition comprising a copolymer of vinylidene fluoride (VDF) and a compatible comonomer, mixed with an ionic liquid and a plasticizer, and a lithium salt, which forms a non-porous film with high ion conductivity and mechanical strength, suitable for use as a separator in Li-ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid electrolytes are used to improve safety and prevent dendrite growth, then reliability is improved, but ion conductivity deteriorates compared to liquid electrolytes
Solution Approach 1:
The invention uses a composite material system consisting of P(VDF-HFP) copolymer matrix combined with ionic liquid and plasticizer. This composite structure allows the solid electrolyte to achieve ion conductivity comparable to liquid electrolytes while maintaining the safety and dendrite prevention benefits of solid materials. The copolymer provides mechanical strength and stability, while the ionic liquid-plasticizer mixture provides high ion conductivity.
2Quantity of substance
If gelled membranes are used to improve ion conductivity through swelling, then ion conductivity is improved, but mechanical strength deteriorates
Solution Approach 1:
The invention changes the physical and chemical parameters of the electrolyte system by using a copolymer with specific HFP content (5-45% by weight) and combining it with ionic liquid and plasticizer in controlled ratios. This parameter optimization allows the membrane to maintain adequate swelling for ion conductivity while retaining sufficient mechanical strength for handling and battery operation.
3Strength
If polyolefins are used as separators to ensure mechanical strength, then mechanical strength is improved, but affinity with electrolyte deteriorates
Solution Approach 1:
The invention modifies the local chemical properties of the polymer matrix by using P(VDF-HFP) copolymer with controlled HFP content. The HFP units provide localized regions with high electrolyte affinity, while the overall copolymer structure maintains good mechanical properties. This local quality modification resolves the contradiction between mechanical strength and electrolyte affinity.
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 solution provides a safer and more efficient electrolyte with ion conductivity comparable to liquid electrolytes, resistance to dendrite growth, and stability up to 80°C, enhancing energy density and electrochemical performance.
Implementation Method 1
a mixture of at least one ionic liquid and of at least one plasticizer... exhibiting a very good compromise between ion conductivity
Implementation Method 2
a low viscosity promotes the ionic diffusion which plays an essential role, among other parameters, in the rates of charge and discharge of the electrochemical system
Implementation Method 3
at least one copolymer of vinylidene fluoride (VDF) and of at least one comonomer compatible with VDF... exhibiting a very good compromise between ion conductivity, electrochemical stability, high-temperature stability and mechanical strength
Implementation Method 4
c) at least one lithium salt... The electrolyte consists of a lithium salt, generally lithium hexafluorophosphate
Implementation Method 5
The use of solid electrolytes makes it possible to overcome these difficulties, while avoiding the use of flammable liquid components. A further advantage of solid or virtually solid electrolytes is to make possible the use of lithium metal at the negative electrode, preventing the formation of dendrites which can cause short-circuits during the cycling
Implementation Method 6
The electrochemical stability has to make possible the use of the electrolyte with cathode materials which can operate at high voltage (>4.5 V). Likewise, the solid electrolyte has to operate at least up to 80° C. and not catch fire below 130° C.
Implementation Method 7
high-temperature stability... the solid electrolyte has to operate at least up to 80° C. and not catch fire below 130° C
Implementation Method 8
The liquid electrolytes composed of solvent(s), lithium salt(s) and additive(s) have a good ion conductivity but are liable to leak or catch fire if the battery is damaged. The use of solid electrolytes makes it possible to overcome these difficulties, while avoiding the use of flammable liquid components
Data Source
AI summary
The invention relates to a composition of a solid electrolyte which makes possible the manufacture of a film exhibiting a very good compromise between ion conductivity, electrochemical stability, high-temperature stability and mechanical strength. This film is intended for a separator application, in particular for Li-ion batteries. The invention also relates to a Li-ion battery comprising such a separator.