Modified Polyrotaxane Solid Electrolyte for Room-Temperature Li-Ion Transport
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Solution Overview
Problem
Current lithium-ion batteries face challenges with low ionic conductivity, safety risks, and mechanical instability due to the use of flammable liquid electrolytes, and existing solid-state electrolytes have high electrical resistance and stability issues, limiting rapid charging and long-term cycling capabilities.
Innovation Solution
Chemically modified polyrotaxanes with partially or completely modified cyclodextrin hydroxyl groups and chemically bound lithium salts are used to create a solvent-free, lithium-ion conductive polymer matrix, enhancing ionic conductivity and stability by reducing intermolecular hydrogen bonds and allowing faster lithium ion transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flammable liquid electrolytes are used in lithium-ion batteries, then ionic conductivity is maintained, but safety risks and mechanical instability increase
Solution Approach 1:
The patent changes the physical state parameter of the electrolyte from liquid to solid, specifically using a solid polymer electrolyte composed of PEO matrix with integrated lithium salts and crown ether complexes. This phase change eliminates flammability while maintaining ionic conductivity through the solid polymer network
Solution Approach 2:
The patent creates a composite solid polymer electrolyte system combining multiple components: PEO polymer matrix, lithium salts (such as LiClO4, LiPF6), and crown ether molecules (18-crown-6 or 21-crown-7). This composite structure integrates ionic conduction pathways within the solid polymer framework, achieving both safety and conductivity
2Reliability
If inorganic ceramic solid electrolytes are used, then conductivity is high, but electrical resistance at cathode interface and processing difficulty increase
Solution Approach 1:
The patent changes the material composition parameter from inorganic ceramic to organic polymer, specifically using PEO-based solid polymer electrolyte. This transformation improves processability through solution casting and melting methods while maintaining sufficient ionic conductivity for battery applications
Solution Approach 2:
The patent introduces crown ether molecules (18-crown-6 or 21-crown-7) at specific locations within the PEO matrix to create localized high-conductivity regions. These crown ethers form complexation structures with lithium ions, creating preferential conduction pathways that reduce interfacial resistance without requiring complex processing
3Reliability
If purely dry electrolytes are used, then safety is improved, but achievable ionic conductivity and fast-charging capability deteriorate
Solution Approach 1:
The patent optimizes the composition parameters of the solid polymer electrolyte, specifically the ratio of PEO to lithium salt and the concentration of crown ether (0.1-5 mol% relative to lithium salt). This compositional optimization creates sufficient ionic conduction pathways within the solid matrix to enable fast charging rates (≥1 C) while maintaining the safety advantages of a purely dry electrolyte system
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 modified polyrotaxanes achieve significantly increased ionic conductivity at room temperature, enabling rapid charging and stable long-term cycling, essential for commercial applications, with improved electrochemical stability and safety.
Implementation Method 1
The polymer electrolyte according to the invention contains as additive at least one compound comprising at least one crown ether unit... The crown ether units are present in the polymer electrolyte in a concentration of 0.1 to 5 mol % based on the lithium salt
Implementation Method 2
the polymer electrolyte exhibits an ionic conductivity of at least 10−4 S/cm at room temperature... enabling rapid charging and stable long-term cycling
Data Source
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AI summary
The invention relates to a solvent-free polymer electrolyte for use in a rechargeable lithium-ion secondary battery, comprising a polymer matrix which is conductive for lithium-ions and a lithium salt. The polymer matrix has at least one polyrotaxane which comprises at least one linear polymer and at least one ring-shaped molecule. The lithium salt is arranged in the polymer matrix and is at least partly chemically bonded to the polymer matrix. According to the invention, the polymer matrix has at least one polyrotaxane with a partly or completely chemically modified cyclodextrin, crown ether, pillar[n]arene, where n = 4 to 7, cucurbituril, or calix[n]arene, where n = 4 to 8, as the ring-shaped molecule. The structural change produces a greatly increased ionic conductivity, in particular at room temperature. The systems chemically modified according to the invention additionally exhibit an improved electrochemical stability, wherein even the stable long-term cyclization which is indispensable for industrial applications can be implemented in a reproducible manner using the novel dry polymer electrolytes in lithium/LiFePO4 cells at high charging and discharging currents (> 1 C).