Cyclic Carbonate Electrolyte for Sulfide Cathode Cycle Retention
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving high charge/discharge cycle performances and initial coulombic efficiency due to the reaction of lithium-free transition metal sulfides with electrolyte solutions, leading to capacity loss and cycle degradation.
Innovation Solution
A nonaqueous secondary battery electrolyte solution with a cyclic carbonate compound content of 80 to 100 vol % and a chain carbonate compound content of 0 to 20 vol %, along with specific additives such as vinylene carbonate and lithium difluoro(oxalato)borate, is used to improve the charge/discharge cycle performances and initial coulombic efficiency by controlling the depth of discharge within a predetermined range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a less reactive electrolyte solution is used to suppress the reaction between lithium-free transition metal sulfide and electrolyte, then charge/discharge cycle performances improve, but initial coulombic efficiency decreases
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte solution by specifying precise ratios of cyclic carbonate (80-100 vol%) to chain carbonate (0-20 vol%), and adding specific additives at controlled concentrations (0.01-5 wt%). This parameter optimization resolves the contradiction by finding the optimal balance between reactivity suppression and efficiency maintenance.
Solution Approach 2:
The patent creates a composite electrolyte system combining multiple components: cyclic carbonate solvents, chain carbonate solvents, and specific additives (vinylene carbonate, fluoroethylene carbonate, lithium difluoro(oxalato)borate). This composite approach allows the electrolyte to simultaneously provide reaction suppression and maintain high initial coulombic efficiency through synergistic effects of the components.
2Quantity of substance
If the depth of discharge is set to 100%, then battery capacity utilization is maximized, but charge/discharge cycle performances deteriorate due to deposition of byproducts and decrease in electrode active material components
Solution Approach 1:
The patent recommends setting the depth of discharge to 70-90% rather than 100%, applying partial action principle. This prevents excessive stress on the electrode materials and electrolyte, reducing byproduct deposition and material degradation while maintaining acceptable capacity utilization, thus resolving the contradiction between capacity and cycle 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 solution significantly enhances the charge/discharge cycle performances and initial coulombic efficiency of lithium-free transition metal sulfide-based batteries, reducing capacity loss and improving overall battery performance.
Implementation Method 1
the deposition of byproducts due to the reaction of a lithium-free transition metal sulfide with an electrolyte solution
Implementation Method 2
Lithium-ion secondary batteries
Data Source
AI summary
An electrolyte solution that satisfies at least one of the following (A) and (B) can improve the charge/discharge cycle performances of nonaqueous secondary batteries containing a lithium-free transition metal sulfide as a cathode active material and can also improve initial coulombic efficiency when a specific additive is used: (A) the nonaqueous secondary battery electrolyte solution contains an organic solvent containing a cyclic carbonate compound, and the content of the cyclic carbonate compound is 80 to 100 vol %, and the content of a chain carbonate compound is 0 to 20 vol %, based on the total amount of the organic solvent taken as 100 vol %; and (B) the nonaqueous secondary battery electrolyte solution contains an organic solvent containing a cyclic carbonate compound and an additive. A method for discharging a nonaqueous secondary battery containing a lithium-free transition metal sulfide as a cathode active material, including setting the depth of discharge during a charge-and-discharge cycle to 70 to 90%, can improve the charge/discharge cycle performances of nonaqueous secondary batteries containing a lithium-free transition metal sulfide as a cathode active material.