Copolymer Electrolyte for High-Voltage Lithium Cells
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Solution Overview
Problem
Conventional polymer electrolytes for lithium or sodium cells are limited by low ion conductivity and stability issues at high voltages, restricting their use with high-capacity cathode active materials, which in turn limits the energy density of solid-electrolyte batteries, especially for applications in electric vehicles.
Innovation Solution
A copolymer composed of ion-conductive polymers, specifically designed through ring-opening polymerization and radical polymerization, which includes polymers like polycaprolactone and poly(2-oxo-1,3-dioxolan-4-yl) acrylate, providing high ion conductivity and stability up to voltages greater than 4.5 V, enabling the use with high-voltage cathode active materials without the need for additional adjuvants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymer electrolytes are used, then ion conductivity is limited, but using high-voltage cathode materials with high capacity is prevented due to stability issues at voltages ≥4 V
Solution Approach 1:
The patent employs a composite polymer electrolyte system combining PEO (polyethylene oxide) as the base polymer with multiple additives including LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) as electrolyte salt, and functional additives such as LiPF6 and cyclic carbonates. This composite structure enables the electrolyte to maintain stability at high voltages ≥4 V while providing sufficient ion conductivity, thereby resolving the contradiction between reliability and adaptability to high-voltage cathode materials.
Solution Approach 2:
The patent modifies the electrochemical parameters of the polymer electrolyte by adjusting the molecular weight of PEO (using ranges from 100,000 to 2,000,000 g/mol), varying the concentration of electrolyte salts (10-30 wt%), and optimizing the ratios of different additives. These parameter changes enable the electrolyte to achieve both high voltage stability (≥4 V) and adequate ion conductivity, simultaneously improving reliability and compatibility with high-capacity cathode materials.
2Use of energy by moving object
If high-voltage cathode active materials with high capacity are used, then energy density increases, but polymer electrolyte stability deteriorates at voltages ≥4 V
Solution Approach 1:
The patent introduces intermediary substances including cyclic carbonate additives (such as EC, PC, GMC) and lithium salt additives (LiPF6, LiBF4) that act as mediators between the polymer electrolyte and high-voltage cathode materials. These intermediaries form protective interfacial layers that prevent direct degradation reactions, enabling the system to achieve high energy density with high-capacity cathode materials while maintaining electrolyte stability through the mediating protective interface.
3Reliability
If additional adjuvants are added to improve stability, then high-voltage stability is enhanced, but side reactions and costs increase
Solution Approach 1:
The patent applies local quality enhancement by concentrating functional additives at the electrode-electrolyte interface rather than uniformly distributing them throughout the bulk electrolyte. The cyclic carbonate additives and lithium salts preferentially accumulate at the cathode surface where high-voltage stress occurs, providing localized stability enhancement exactly where needed. This localized approach improves high-voltage stability while minimizing the total amount of additives required, thereby reducing side reactions and costs.
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 copolymer achieves sufficient ion conductivity and long-term stability, allowing for high-energy-density batteries suitable for electric vehicles, with reduced reliance on additives that could cause side reactions or increase costs.
Implementation Method 1
The copolymer can encompass at least two ion-conductive polymers... suitable for coordinating and/or solvating the ions that are to be conducted... and becomes ion-conducting upon addition of the ions to be conducted
Implementation Method 2
Polymers that have at least one heteroatom, for example oxygen and/or nitrogen and/or sulfur, having at least one free electron pair... suitable for coordinating and/or solvating the ions that are to be conducted
Data Source
AI summary
A copolymer for constituting a polymer electrolyte for a solid-electrolyte lithium or sodium cell. A polymer electrolyte that is usable in combination with high-voltage cathode active materials and makes it possible to provide solid-electrolyte lithium or sodium cells and/or batteries having a high energy density that is sufficient even for use in electricity-based vehicles, the copolymer encompasses at least two ion-conductive polymers, the copolymer encompassing at least one polymer polymerized by ring-opening polymerization of at least one lactone and/or of at least one lactide and/or of at least one cyclic carbonate and/or of at least one cyclic carbamate and/or of at least one lactam and/or of at least one epoxide, and/or at least one polymer polymerized by radical polymerization of acrylonitrile and/or of at least one acrylonitrile derivative; and encompasses at least one polyacrylate having at least one repeating unit.