Lithium Battery Electrolyte Additive for Polysulfide-Stable SEI Formation
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Solution Overview
Problem
Lithium-sulfur secondary batteries face challenges with the lifetime characteristics due to the use of ether-based solvents, which lead to polysulfide leaching, dendrite growth, and electrolyte decomposition, especially when the electrolyte content is minimized, affecting the battery's energy density and stability.
Innovation Solution
Incorporating a benzo-dioxole-based or benzo-dioxane-based compound with a hydrogen or electron-donating group at a carbon position between two oxygen atoms into the electrolyte solution to reduce polysulfide reactivity and form a stable film on the negative electrode, preventing decomposition and improving battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ether-based solvent is used to improve sulfur reactivity, then polysulfide solubility and reactivity are improved, but lifetime characteristics deteriorate due to polysulfide leaching and electrolyte decomposition
Solution Approach 1:
The patent introduces a lithium nitrate compound as an intermediary substance in the electrolyte solution. This compound acts as a mediator that suppresses the direct harmful interaction between polysulfide and the ether-based solvent, thereby preventing polysulfide leaching and electrolyte decomposition while maintaining the beneficial reactivity enhancement. The lithium nitrate compound serves as a protective intermediary layer that reconciles the contradiction between reactivity improvement and lifetime deterioration.
Solution Approach 2:
The patent creates a composite electrolyte solution by combining ether-based solvent with lithium nitrate compound. This composite formulation integrates the reactivity-enhancing properties of the ether-based solvent with the stabilizing effects of lithium nitrate, achieving both improved sulfur reactivity and extended battery lifetime. The composite material approach allows the system to simultaneously exhibit properties that individually address both aspects of the contradiction.
2Quantity of substance
If electrolyte solution content is minimized to increase energy density, then energy storage density is improved, but viscosity increases rapidly and overvoltage increases during charging/discharging
Solution Approach 1:
The patent modifies the chemical composition parameters of the electrolyte solution by introducing lithium nitrate compound at specific concentrations (0.1-10 wt%). This parameter change fundamentally alters the solution's physical properties, including viscosity and conductivity characteristics. The optimized composition allows the electrolyte to maintain low viscosity and acceptable overvoltage levels even when the total electrolyte content is minimized, thereby enabling high energy storage density without excessive overvoltage penalties.
3Quantity of substance
If sulfur loading amount is increased to achieve high energy density, then energy storage capacity is improved, but polysulfide loss increases and lifetime characteristics worsen
Solution Approach 1:
The lithium nitrate compound functions as an intermediary protective agent that suppresses polysulfide loss mechanisms. By introducing this compound, the system can accommodate higher sulfur loading amounts without proportionally increasing polysulfide leaching. The lithium nitrate acts as a buffer that mediates between the high sulfur content and the electrolyte, preventing excessive polysulfide dissolution and maintaining substance retention even at elevated energy storage capacities.
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 addition of the benzo-dioxole-based or benzo-dioxane-based compound enhances the battery's lifetime characteristics by suppressing polysulfide loss and forming a stable Solid Electrolyte Interphase (SEI) film, thereby improving the battery's capacity retention and overall performance.
Implementation Method 1
forming a stable film on the negative electrode, preventing decomposition and improving battery performance
Implementation Method 2
the oxidation reaction of lithium is a process by which lithium metal releases electron and is converted to lithium cation form. In addition, the reduction reaction of sulfur is a process by which the S—S bond accepts two electrons and is converted to a sulfur anion form. The lithium cation produced by the oxidation reaction of lithium is transferred to the positive electrode through the electrolyte
Implementation Method 3
the reduction reaction of sulfur is a process by which the S—S bond accepts two electrons and is converted to a sulfur anion form. Specifically, sulfur before discharging has a cyclic S8 structure, which is converted to lithium polysulfide (LiSx) by the reduction reaction
Implementation Method 4
an ether-based solvent such as dioxolane and dimethoxy ethane, which are highly soluble for lithium polysulfide, is used as a solvent for the electrolyte solution
Data Source
AI summary
The present invention relates to an electrolyte solution for a lithium secondary battery comprising lithium salt, non-aqueous solvent, and a benzo-dioxole-based compound or benzo-dioxane-based compound, in which hydrogen or an electron donating group is substituted at the carbon position between two oxygen atoms, and a lithium secondary battery containing the same.