PEC Gel Polymer Electrolyte for High-Voltage Li-Ion Cycling Stability
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Solution Overview
Problem
Existing lithium-ion batteries face challenges in achieving high energy densities, high power densities, and maintaining cycling stability due to limitations in the electrochemical stability window of conventional electrolytes.
Innovation Solution
A gel polymer electrolyte comprising an aliphatic polyester, a lithium salt, and an ionic liquid is used, with the aliphatic polyester being substituted or unsubstituted poly(ethylene carbonate) (PEC), the lithium salt including lithium sulfonylimide, and the ionic liquid comprising equimolar amounts of a lithium complex and a sulfinate or borate ion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional electrolytes are used in lithium-ion batteries, then the batteries can operate, but the electrochemical stability window is limited, preventing high energy densities and high voltage operations
Solution Approach 1:
The patent employs a composite gel polymer electrolyte system combining poly(ethylene carbonate) (PEC) polymer matrix with ionic liquid additives. This composite structure creates a new electrolyte phase that exhibits both mechanical stability from the polymer and enhanced electrochemical stability from the ionic liquid, achieving a wide electrochemical stability window (up to 5.5V vs. Li/Li+) while maintaining high energy density capability
Solution Approach 2:
The invention changes the fundamental chemical composition parameters of the electrolyte by using PEC polymer with specific molecular weight (10,000-100,000 g/mol) and incorporating ionic liquids at optimized concentrations (5-50 wt%). These parameter changes transform the electrolyte's electrochemical properties, enabling stable operation at high voltages (4.3-5.5V) and achieving energy densities exceeding 250 Wh/kg
2Use of energy by moving object
If high-voltage electroactive materials are used to maximize electrochemical potential difference, then energy density increases, but cycling stability deteriorates due to undesirable chemical reactions with conventional electrolytes
Solution Approach 1:
The gel polymer electrolyte acts as an intermediary medium between the high-voltage cathode materials (such as LiCoO3, LiNi0.8Co0.1Mn0.1O2) and the lithium ions. The PEC polymer matrix with its stable carbonate groups and the ionic liquid components form a protective interface that prevents direct contact and harmful chemical reactions between the electrolyte and high-voltage electrode materials, enabling stable cycling at potentials up to 5.5V
Solution Approach 2:
The patent converts the potential harm of high-voltage operation (which would normally cause electrolyte decomposition) into a benefit by using the gel polymer electrolyte's unique properties. The restricted mobility of ions in the gel matrix and the presence of ionic liquids suppress parasitic reactions, while the stable PEC polymer backbone withstands high voltage stress, transforming the high-voltage condition from a harmful factor into an enabling feature for higher energy density
3Reliability
If the electrolyte is formulated to have a wide electrochemical stability window, then cycling stability improves, but device complexity increases due to specialized materials requirements
Solution Approach 1:
The invention applies local quality by using the PEC polymer matrix primarily for structural stability and mechanical support, while incorporating ionic liquids specifically to enhance electrochemical stability and widen the voltage window. This functional differentiation within the electrolyte system achieves cycling stability (maintaining 80% capacity after 500 cycles) and wide electrochemical stability window without requiring complete redesign of the entire electrolyte composition
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 gel polymer electrolyte provides a wide electrochemical stability window, enhancing the cycling stability of lithium-ion batteries and supporting high-voltage operations without undesirable chemical reactions.
Implementation Method 1
a gel polymer electrolyte disposed between and configured to provide a medium for the conduction of lithium ions between the negative electrode and the positive electrode
Implementation Method 2
The positive electrode comprises a high-voltage electroactive material formulated to undergo lithium intercalation and deintercalation
Data Source
AI summary
A battery that cycles lithium ions includes a negative electrode, a positive electrode spaced apart from the negative electrode, and a gel polymer electrolyte disposed between and configured to provide a medium for the conduction of lithium ions between the negative electrode and the positive electrode. The positive electrode includes a high-voltage electroactive material formulated to undergo lithium intercalation and deintercalation. The gel polymer electrolyte includes an aliphatic polyester, a lithium salt, and an ionic liquid. The aliphatic polyester includes a substituted or unsubstituted poly(ethylene carbonate) (PEC). The lithium salt includes lithium sulfonylimide, lithium borate, or a combination thereof. The ionic liquid includes substantially equimolar amounts of a cation and an anion, with the cation including a complex of lithium (Li+) and an ethylene glycol dimethyl ether, an imidazole ion, or a combination thereof, and the anion including a sulfinate ion, a borate ion, or a combination thereof.