Non-Aqueous Battery Electrolyte With Carboxylic Acid for DCIR Stability
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Solution Overview
Problem
In non-aqueous electrolyte secondary batteries, the direct current resistance (DCIR) increases over time during high-temperature storage due to a reaction between the alkaline component in the positive electrode and lithium difluorophosphate, forming an inert surface film on the positive electrode active material.
Innovation Solution
Incorporating a non-aqueous electrolyte with a lithium salt, including lithium difluorophosphate, and a carboxylic acid, where the carboxylic acid content is between 5 ppm and 900 ppm, which helps form a high-quality surface film and inhibits the inactivation of the positive electrode active material, thereby suppressing the increase in DCIR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium difluorophosphate is added to improve battery storage characteristics, then storage characteristics are improved, but DCIR increases due to formation of inert surface film on positive electrode
Solution Approach 1:
A carboxylic acid component is introduced as an intermediary substance that mediates between the alkaline component of the positive electrode and lithium difluorophosphate. The carboxylic acid reacts preferentially with the alkaline component to form a protective film, preventing the harmful reaction between alkaline component and lithium difluorophosphate that would otherwise form an inert surface film increasing DCIR.
Solution Approach 2:
The carboxylic acid component converts the potentially harmful reaction between alkaline component and lithium difluorophosphate into a beneficial process. By controlling the reaction to form a specific surface film composition through the carboxylic acid, the film becomes protective rather than inert, maintaining low DCIR while preserving storage characteristics improvement.
2Object-affected harmful factors
If carboxylic acid content is increased to suppress DCIR increase, then DCIR stability is improved, but excessive carboxylic acid may cause other side reactions
Solution Approach 1:
The carboxylic acid content is precisely controlled within the range of 5 ppm to 900 ppm. This parameter optimization ensures sufficient carboxylic acid to suppress DCIR increase by forming protective films, while preventing excessive carboxylic acid that would cause unwanted side reactions. The specific concentration range balances film formation effectiveness with reaction selectivity.
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 combination of lithium difluorophosphate and carboxylic acid in the non-aqueous electrolyte effectively reduces the growth of an inert surface film on the positive electrode, maintaining battery performance during long-term high-temperature storage by suppressing the increase in DCIR.
Implementation Method 1
the reaction between the alkaline component in the positive electrode and the lithium difluorophosphate proceeds gradually, forming an inert surface film on the outer layer of the positive electrode active material
Implementation Method 2
the carboxylic acid helps form a high-quality surface film and inhibits the inactivation of the positive electrode active material
Data Source
AI summary
A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a lithium salt and a carboxylic acid, and the lithium salt includes lithium difluorophosphate. The content of the carboxylic acid in the non-aqueous electrolyte is 5 ppm or more and 900 ppm or less with respect to the mass of the non-aqueous electrolyte.