Gel Electrolyte Flame Retardancy Capacity Maintenance
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Solution Overview
Problem
Lithium ion secondary batteries face issues with long-term reliability due to reductive decomposition of phosphate esters and halogen-substituted phosphate esters, leading to increased resistance and decreased safety and capacity maintenance, while existing solutions either require high amounts of halogen-substituted carbonate esters, which decrease ionic conductivity, or fail to maintain flame retardancy over time.
Innovation Solution
A gel electrolyte comprising a lithium salt, a copolymer of specific monomers, an oxo-acid ester derivative of phosphorus, and a disulfonate ester, with the oxo-acid ester derivative and disulfonate ester concentrations optimized to suppress reductive decomposition and maintain high flame retardancy and capacity over a long period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If phosphate esters or halogen-substituted phosphate esters are used as electrolyte additives to improve flame retardancy, then safety is improved, but reductive decomposition occurs on the negative electrode leading to increased resistance and decreased capacity maintenance over time
Solution Approach 1:
The patent introduces a specific copolymer as an intermediary substance that mediates between the phosphate ester additive and the negative electrode. This copolymer forms a protective interface layer that prevents direct contact and reductive decomposition between the phosphate ester and the electrode, while still allowing the phosphate ester to perform its flame retardant function in the bulk electrolyte.
Solution Approach 2:
The patent optimizes the concentration parameters of both the phosphate ester (0.1-10 wt%) and the copolymer (1-20 wt%) to achieve a balance between flame retardancy and electrode protection. By carefully controlling these parameters, the system maintains adequate flame suppression while minimizing reductive decomposition through the protective copolymer layer.
2Reliability
If high amounts of halogen-substituted carbonate esters are used to suppress reductive decomposition, then capacity maintenance is improved, but ionic conductivity decreases
Solution Approach 1:
The copolymer acts as an intermediary that protects the negative electrode from reductive decomposition without requiring high concentrations of halogen-substituted carbonate esters. This intermediary mechanism maintains capacity while preserving ionic conductivity.
Solution Approach 2:
The patent creates a composite electrolyte system combining the copolymer, phosphate ester, and halogen-substituted carbonate ester in specific proportions. This composite approach leverages the protective interface formed by the copolymer while using minimal amounts of halogen-substituted carbonate ester, thus maintaining both capacity maintenance and ionic conductivity.
3Object-affected harmful factors
If phosphate esters are used to achieve flame retardancy, then safety is improved, but the flame retardant effect decreases over long-term usage due to decomposition
Solution Approach 1:
The copolymer provides beforehand cushioning by forming a protective layer on the negative electrode before the phosphate ester can decompose. This protective interface prevents the phosphate ester from undergoing reductive decomposition that would otherwise eliminate its flame retardant properties over time.
Solution Approach 2:
The copolymer serves as a stable intermediary that remains intact over long periods, continuously protecting the phosphate ester from decomposition and maintaining its flame retardant function throughout the battery's operational life.
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 electrolyte achieves high flame retardancy and good capacity maintenance over a long period by suppressing reductive decomposition and maintaining ionic conductivity, providing enhanced safety and performance.
Implementation Method 1
phosphate esters and halogen-substituted phosphate esters are reductively decomposed on a negative electrode during long-period usage
Implementation Method 2
these carbonates tend to have a low flash point and be combustible though having a high dielectric constant and a high ionic conductivity of lithium ions
Data Source
AI summary
An object of the present invention is to provide a gel electrolyte for a lithium ion secondary battery having flame retardancy over a long period and a good capacity maintenance rate. The gel electrolyte for a lithium ion secondary battery according to the exemplary embodiment contains a lithium salt, a copolymer of at least one first monomer selected from compounds represented by chemical formulae (1) and (2) and a second monomer represented by chemical formula (4), at least one oxo-acid ester derivative of phosphorus selected from compounds represented by chemical formulae (5) to (7), and at least one disulfonate ester selected from a cyclic-chain type disulfonate ester represented by chemical formula (8) and a linear-chain type disulfonate ester represented by chemical formula (9).