Gel Electrolyte Flame Retardancy and Capacity Retention
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Solution Overview
Problem
Lithium ion secondary batteries face issues with capacity retention and safety due to the reductive degradation of phosphazene compounds over time, leading to increased resistance and decreased flame retardancy, especially at high temperatures, and are prone to solution leakage.
Innovation Solution
A gel electrolyte composition containing a lithium salt, a copolymer, a phosphazene compound, and specific disulfonate and sultone additives that suppress reductive degradation and provide high flame retardancy, eliminating the need for radical polymerization initiators and reducing solution leakage risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphazene compounds are used as flame retardants in electrolyte solutions, then flame retardancy is improved, but capacity retention deteriorates due to reductive degradation over time
Solution Approach 1:
The patent introduces sultone compounds and cyclic carbonate esters as intermediary substances that form protective films on electrode surfaces. These intermediaries prevent direct contact between phosphazene compounds and electrode surfaces, thereby suppressing reductive degradation while maintaining flame retardancy. The protective film acts as a barrier that mediates the interaction between the flame retardant and the electrode.
Solution Approach 2:
The patent optimizes the concentration ratios of phosphazene compounds, sultone compounds, and cyclic carbonate esters in the electrolyte solution. By adjusting these parameters within specific ranges, the patent achieves a balance between flame retardancy and capacity retention, preventing excessive reductive degradation while maintaining safety properties.
2Reliability
If phosphazene compounds are used as flame retardants, then safety is improved, but resistance increases due to reductive degradation
Solution Approach 1:
Sultone compounds and cyclic carbonate esters serve as intermediary substances that form protective films on electrode surfaces. These films prevent direct reductive degradation of phosphazene compounds, thereby suppressing the increase in resistance while maintaining the flame retardancy and safety properties of the electrolyte solution.
3Reliability
If electrolyte solutions are used, then ionic conductivity is improved, but solution leakage occurs
Solution Approach 1:
The patent utilizes the phase transition properties of gel polymers to transform the electrolyte from a liquid state to a gel state. This phase transition allows the electrolyte to maintain high ionic conductivity similar to liquid electrolytes while gaining the mechanical stability and leakage prevention characteristics of gel structures.
Solution Approach 2:
The patent creates a composite gel electrolyte system by combining gel polymers with phosphazene compounds, sultone compounds, and cyclic carbonate esters. This composite structure integrates the ionic conductivity benefits of liquid electrolytes with the leakage prevention advantages of gel structures, achieving both high performance and safety.
4Reliability
If high concentrations of phosphazene compounds are used for flame retardancy, then safety is improved, but charge/discharge efficiency deteriorates
Solution Approach 1:
Sultone compounds and cyclic carbonate esters act as intermediaries that form protective films on electrode surfaces, enabling the use of higher phosphazene concentrations without excessive reductive degradation. This intermediary protection maintains charge/discharge efficiency while allowing sufficient flame retardancy through optimized phosphazene content.
Solution Approach 2:
The patent optimizes the concentration of phosphazene compounds within specific ranges (0.1-10% by mass) and adjusts the ratios of sultone compounds and cyclic carbonate esters to achieve the best balance between flame retardancy and charge/discharge efficiency, preventing both under-protection and excessive degradation.
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 enhances safety and life characteristics by maintaining capacity retention and flame retardancy over long periods, reducing gas generation during charging, and ensuring good contact between electrodes, thereby improving battery performance and safety.
Implementation Method 1
a gel electrolyte composition containing a lithium salt, a copolymer, a phosphazene compound, and specific disulfonate and sultone additives that suppress reductive degradation
Implementation Method 2
Lithium ion secondary batteries use aprotic solvents such as cyclic carbonates and chain carbonates as electrolyte solvents; and these carbonates are characterized by having a low flash point and being combustible though having a high dielectric constant and a high ionic conductivity of lithium ion
Implementation Method 3
A gel electrolyte composition containing a lithium salt, a copolymer, a phosphazene compound
Implementation Method 4
One means of further enhancing the safety of lithium ion secondary batteries is making electrolyte solutions flame-retardant. As a technique for making electrolyte solutions flame-retardant, methods of adding a phosphazene compound as a flame retardant are disclosed
Data Source
AI summary
There is provided a lithium ion secondary battery which has high safety and good life characteristics. There is also provided a gel electrolyte for a lithium ion secondary battery, which contains a lithium salt, a copolymer of specific monomers, a compound having a specific phosphazene structure, and at least one compound selected from a specific cyclic disulfonate ester, a specific chain disulfonate ester and a specific sultone compound.