Nonaqueous Electrolyte Stabilizing Negative Electrode Film
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges with unstable negative electrode coating films, poor cycle performance, and overcharging issues due to reactivity with solvents and additives, leading to safety concerns and reduced retention characteristics.
Innovation Solution
Incorporating a tertiary carboxylate ester and cyclic acid anhydrides such as succinic anhydride, glutaric anhydride, and glycolic anhydride in the nonaqueous electrolyte to stabilize the negative electrode coating film, improving lithium ion penetrativity and battery properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a nonaqueous solvent mixture (cyclic carbonate ester and chain-shaped carbonate ester) is used to achieve excellent discharging properties, then discharging performance is improved, but oxidation resistance and reactivity with lithium become unstable, causing poor safety
Solution Approach 1:
The patent changes the chemical composition parameters of the nonaqueous electrolyte by introducing a carboxylate ester component and controlling the ratios of cyclic carbonate ester, chain-shaped carbonate ester, and carboxylate ester. This parameter modification stabilizes the SEI film while maintaining discharging properties and improving oxidation resistance.
Solution Approach 2:
The patent creates a composite electrolyte system combining cyclic carbonate ester, chain-shaped carbonate ester, and carboxylate ester. This composite approach leverages the advantages of each component: cyclic carbonate for SEI formation, chain carbonate for conductivity, and carboxylate ester for stability, achieving both excellent discharging properties and reliable oxidation resistance.
2Use of energy by moving object
If diethyl carbonate (DEC) is used as a nonaqueous solvent, then discharging properties are improved, but uncontrollable exothermic reaction with lithium occurs at around 90°C, causing safety issues
Solution Approach 1:
The carboxylate ester acts as an intermediary substance that modifies the interaction between the electrolyte and lithium. It forms a stable SEI film that prevents direct contact and exothermic reaction between DEC and lithium, while still allowing ionic conductivity for normal discharging operations.
Solution Approach 2:
The carboxylate ester performs preliminary protective action by forming a stable SEI film on the electrode surface before any harmful exothermic reaction can occur. This pre-formed protective layer prevents the uncontrollable exothermic reaction with lithium at elevated temperatures.
3Reliability
If dimethyl carbonate (DMC) is used as a nonaqueous solvent, then reactivity with lithium is reduced, but flash point is low and cycle performance is poor
Solution Approach 1:
The patent modifies the electrolyte composition parameters by adding carboxylate ester and optimizing the ratio of DMC to other components. This parameter change increases the flash point of the electrolyte system and stabilizes the SEI film, thereby improving cycle performance while maintaining low reactivity with lithium.
4Reliability
If aromatic hydrocarbon or redox shuttle agent is added to improve overcharging performance, then overcharging protection is enhanced, but high temperature retention characteristics and cycle performance are significantly lowered when added amount is enlarged
Solution Approach 1:
The patent changes the protective mechanism by using carboxylate ester that forms a stable SEI film, replacing or supplementing aromatic hydrocarbons and redox shuttle agents. This parameter change in the protective mechanism allows for better high temperature retention and cycle performance while still providing overcharging protection.
5Object-affected harmful factors
If ethylene carbonate (EC) or propylene carbonate (PC) is used to increase flash point, then safety is improved, but oxidation resistance is poor, causing lowered retention characteristics and cycle performance
Solution Approach 1:
The patent creates a composite electrolyte system combining cyclic carbonate ester (for flash point), chain-shaped carbonate ester, and carboxylate ester (for oxidation resistance). This composite approach allows the system to simultaneously achieve high flash point and good oxidation resistance, resolving the contradiction between safety and reliability.
6Reliability
If carboxylate ester is used as a nonaqueous solvent, then oxidation resistance is strong and reactivity with positive electrode is moderate, but reactivity with negative electrode is high causing unstable coating film and poor cycle performance
Solution Approach 1:
The patent applies local quality by using carboxylate ester specifically at the negative electrode interface where it forms a stable SEI film. The carboxylate ester's unique chemical properties are localized to where they are most needed (at the negative electrode surface), providing stability without compromising overall battery performance.
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 enhances cycle performance, retention characteristics, and overcharging performance by stabilizing the negative electrode coating film, reducing gas generation during high-temperature charging, and improving the overall battery stability and safety.
Implementation Method 1
it has become an important task not only to form a coating film on the surface of the negative electrode, but also to control the formed state and the properties of the coating film
Implementation Method 2
a positive electrode having a positive electrode active material capable of intercalating/deintercalating lithium ions; a negative electrode having a negative electrode active material capable of intercalating/deintercalating lithium ions
Implementation Method 3
a nonaqueous electrolyte in which an electrolyte composed of a lithium salt is dissolved in a nonaqueous solvent
Implementation Method 4
a nonaqueous electrolyte composed of a nonaqueous solvent and an electrolyte is used
Data Source
AI summary
In a nonaqueous electrolyte secondary battery according to an embodiment of the invention, a nonaqueous electrolyte contains: a tertiary carboxylate ester represented by the following general formula (1) in an amount of a range of 3% by mass or more and 80% by mass or less based on the total mass of the nonaqueous solvent:where R1, R2, R3, R4 represent a (C1 to 4) alkyl group, respectively, and one or more acid anhydride selected from succinic anhydride, glutaric anhydride, and glycolic anhydride in an amount of a range of 0.1% by mass or more and 5% by mass or less based on the total mass of the nonaqueous electrolyte. By containing such a constitution, in other words, by containing a nonaqueous solvent capable of stabilizing the coating film of the negative electrode, a nonaqueous electrolyte secondary battery in which not only can satisfactory cycle performance and retention characteristics be obtained, but also the overcharging performance is largely improved, can be provided.