Non-Aqueous Electrolyte With Isopropyl Acetate for LFSI Film Stability
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Solution Overview
Problem
Long-term cycling of non-aqueous electrolyte secondary batteries, particularly lithium ion batteries, results in significant capacity reduction due to excessive reactions at the positive electrode surface, leading to inactivation of the lithium bis(fluorosulfonyl)imide (LFSI) film and increased resistance.
Innovation Solution
Incorporating isopropyl acetate into the liquid electrolyte at specific concentrations (50 ppm to 1000 ppm) to suppress excessive reactions of LFSI on the positive electrode surface, forming a protective layer that maintains capacity and prevents film inactivation, while ensuring isopropyl acetate is gradually consumed to sustain its effect over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium bis(fluorosulfonyl)imide (LFSI) is added to the liquid electrolyte to improve long life, then reliability is improved, but excessive reactions occur at the positive electrode surface during long-term cycling, leading to capacity reduction
Solution Approach 1:
Isopropyl acetate serves as an intermediary substance that mediates between LFSI and the positive electrode surface. It preferentially reacts with alkaline components on the positive electrode to form a protective layer, preventing excessive reactions of LFSI with the electrode surface while maintaining the electrolyte's long-life benefits
Solution Approach 2:
The invention changes the chemical composition parameters of the electrolyte by introducing isopropyl acetate at specific concentrations (50-1000 ppm). This parameter change modifies the reaction dynamics at the electrode surface, suppressing excessive LFSI reactions while preserving capacity and extending battery life
2Productivity
If isopropyl acetate is added to suppress excessive LFSI reactions, then capacity maintenance is improved, but the content of isopropyl acetate must be precisely controlled to avoid harmful effects
Solution Approach 1:
The invention establishes specific parameter ranges for isopropyl acetate content (50-1000 ppm) to optimize its beneficial effects while avoiding harmful consequences. This parameter control transforms the complex composition issue into a manageable specification
Solution Approach 2:
The protective layer formed by isopropyl acetate acts as a model or template for ideal electrode surface protection. This self-assembled layer copies the desired protective function without requiring complex external control mechanisms
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 use of isopropyl acetate in the electrolyte enhances long-term cycle characteristics by maintaining capacity ratios during repeated charge and discharge cycles, preventing excessive LFSI film inactivation and reducing resistance, thereby improving battery performance.
Implementation Method 1
Isopropyl acetate produces alkoxy radicals in a battery, e.g., by a reaction such as the following Reaction Scheme (1). It is believed that the alkoxy radicals adsorb on the surface of the positive electrode material to form a protective layer which inhibits the reaction of LFSI on the surface of the positive electrode
Implementation Method 2
Lithium bis(fluorosulfonyl)imide (also referred to as LFSI) forms a film (hereafter referred to as LFSI film) on the positive and negative electrode surfaces which is excellent in lithium-ion conductivity and inhibits oxidative degradation of the liquid electrolyte
Implementation Method 3
Isopropyl acetate produces alkoxy radicals in a battery, e.g., by a reaction such as the following Reaction Scheme (1). It is believed that the alkoxy radicals adsorb on the surface of the positive electrode material to form a protective layer which inhibits the reaction of LFSI on the surface of the positive electrode
Data Source
AI summary
A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode and a liquid electrolyte, wherein the liquid electrolyte contains a lithium salt and isopropyl acetate, and the lithium salt includes lithium bis(fluorosulfonyl)imide, and a content of isopropyl acetate in the liquid electrolyte is 1000 ppm or less with respect to a mass of the liquid electrolyte.