Si-Anode Battery Electrolyte Composition for High-Temperature Stability
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Solution Overview
Problem
Lithium-ion secondary batteries using silicon as a negative electrode material face issues with exothermic reactions at elevated temperatures, leading to battery deterioration, especially when using electrolyte solutions with lithium bis(fluorosulfonyl)imide (LiFSI).
Innovation Solution
Incorporating an inorganic lithium salt with a molar concentration greater than or equal to LiFSI into the electrolyte solution, maintaining a concentration ratio of LiFSI to inorganic lithium salt at 1 or less, to suppress exothermic reactions and enhance battery stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrolyte solution containing LiFSI is used to form a firm SEI film at the negative electrode, then low-temperature power output characteristics and high-temperature cycle characteristics are enhanced, but additional exothermic reactions occur at elevated temperatures causing battery deterioration
Solution Approach 1:
The patent introduces a specific additive (cyclic carbonate ester with vinylene carbonate or fluoroethylene carbonate) as an intermediary substance in the electrolyte solution. This additive mediates between the LiFSI and the negative electrode, forming a modified SEI film that prevents harmful exothermic reactions while maintaining the beneficial low-temperature power output characteristics. The additive acts as a buffer that controls the interaction between LiFSI and the electrode at elevated temperatures.
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte solution by specifying precise concentration ranges: LiFSI at 0.1-1.0 mol/L, vinylene carbonate at 0.01-0.5 wt%, and fluoroethylene carbonate at 0.01-0.5 wt%. By changing these compositional parameters within optimized ranges, the SEI film properties are tuned to resist exothermic reactions at high temperatures while preserving low-temperature performance.
2Quantity of substance
If Si material is used as negative electrode active material to increase energy density, then capacity and energy density are improved, but exothermic reactions occur at elevated temperatures leading to battery deterioration
Solution Approach 1:
The patent creates a composite electrolyte system combining LiFSI (inorganic lithium salt) with cyclic carbonate esters containing specific functional groups (vinylene carbonate and/or fluoroethylene carbonate). This composite electrolyte formulation works synergistically with Si-based negative electrode materials to form a stable protective interface, enabling the high energy density of Si materials without suffering from exothermic reaction issues at elevated temperatures.
3Power
If LiFSI concentration is increased to enhance SEI film formation, then low-temperature power output characteristics are improved, but exothermic reactions are more likely to occur at high temperatures
Solution Approach 1:
The patent optimizes the LiFSI concentration parameter within a specific range (0.1-1.0 mol/L) and combines it with controlled amounts of vinylene carbonate (0.01-0.5 wt%) and fluoroethylene carbonate (0.01-0.5 wt%). This parameter optimization ensures sufficient SEI film formation for low-temperature power output while the accompanying cyclic carbonate esters suppress exothermic reactions at high temperatures, achieving a balance between contradictory requirements.
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 an inorganic lithium salt effectively reduces the occurrence of exothermic reactions at elevated temperatures, thereby preventing battery deterioration and improving the safety and performance of silicon-based lithium-ion secondary batteries.
Implementation Method 1
an additional exothermic reaction occurs, and deterioration of the battery proceeds
Implementation Method 2
charging and discharging is achieved by intercalation and deintercalation of lithium ions into graphite crystals
Implementation Method 3
a firm SEI film can be formed at the negative electrode at the time of initial charging
Data Source
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AI summary
Provided is a means that can suppress, in a non-aqueous electrolyte secondary battery that uses a negative electrode active material including a Si material and uses an electrolyte solution including LiFSI, the occurrence of an exothermic reaction that can cause deterioration of the battery even in a case when the battery temperature has risen. A non-aqueous electrolyte secondary battery according to the present invention has a power generating element that includes a positive electrode in which a positive electrode active material layer including a positive electrode active material is formed on a surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer including a negative electrode active material is formed on a surface of a negative electrode current collector, and a separator impregnated with an electrolyte solution. Here, the negative electrode active material includes a Si material that contains silicon and is capable of insertion and removal of lithium ions. The electrolyte solution contains lithium bis (fluorosulfonyl) imide (LiFSI) and an inorganic lithium salt other than the LiFSI, and has a feature that a ratio of a concentration (mol/L) of the LiFSI with respect to a concentration (mol/L) of the inorganic lithium salt (LiFSI/inorganic lithium salt) in the electrolyte solution is 1 or less.