Non-aqueous Electrolyte for Lithium Battery SEI Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high-temperature and low-temperature cycle characteristics and capacity due to irreversible decomposition reactions and poor SEI formation caused by propylene carbonate and ethylene carbonate, leading to reduced battery performance.
Innovation Solution
A non-aqueous electrolyte solution comprising propylene carbonate, ethylene carbonate, lithium bis(fluorosulfonyl)imide, and a lithium salt with a specific molar ratio, which forms a robust SEI on the anode, improving low-temperature and room temperature output characteristics and capacity retention after high-temperature storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If propylene carbonate is used as a non-aqueous organic solvent, then room temperature output characteristics are improved, but irreversible decomposition reaction occurs with graphite material
Solution Approach 1:
The patent combines propylene carbonate and ethylene carbonate in a specific ratio (5:95 to 45:55 by volume) to create a mixed solvent system. This merging allows the electrolyte to simultaneously achieve the high room temperature output characteristics of propylene carbonate while avoiding its irreversible decomposition reaction with graphite, as ethylene carbonate provides stability.
Solution Approach 2:
The patent changes the concentration parameters of lithium salt and lithium bis(fluorosulfonyl)imide within specific ranges (0.5-2.0 M and 0.05-1.5 M respectively) to optimize SEI formation. This parameter optimization enables robust SEI formation that prevents decomposition while maintaining good output characteristics.
2Reliability
If ethylene carbonate is used as a non-aqueous organic solvent, then high-temperature cycle characteristics are improved, but low-temperature performance is reduced due to high melting point
Solution Approach 1:
The patent merges ethylene carbonate and propylene carbonate in a balanced ratio to create a solvent system that exhibits both high-temperature stability from ethylene carbonate and low-temperature fluidity from propylene carbonate, thereby resolving the temperature performance contradiction.
Solution Approach 2:
The electrolyte uses a composite solvent system combining two different carbonate solvents with complementary properties. This composite approach allows the electrolyte to maintain stable SEI formation at high temperatures while remaining fluid and conductive at low temperatures.
3Reliability
If robust SEI is formed on the anode, then high-temperature cycle characteristics and capacity retention are improved, but manufacturing complexity increases due to specific composition requirements
Solution Approach 1:
The patent defines specific parameter ranges for solvent ratios and lithium salt concentrations that reliably produce robust SEI. By establishing these clear parameter specifications, the manufacturing process becomes more controllable and less complex, as operators can simply maintain concentrations within the specified ranges to achieve consistent SEI formation.
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 high-temperature and room temperature cycle characteristics and capacity retention by forming a stable SEI, preventing decomposition and oxidation reactions, thereby improving the overall performance of lithium secondary batteries.
Implementation Method 1
Charge and discharge of the lithium secondary battery is performed while a process of intercalating and deintercalating lithium ions from a lithium metal oxide cathode into and out of a graphite anode is repeated
Implementation Method 2
The SEI may only pass the lithium ions by acting as an ion tunnel
Implementation Method 3
since lithium is highly reactive, lithium reacts with the carbon electrode to form Li 2 CO 3, LiO, or LiOH
Data Source
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AI summary
Provided are a non-aqueous electrolyte solution, which includes a non-aqueous organic solvent including propylene carbonate (PC) and ethylene carbonate (EC), and lithium bis(fluorosulfonyl)imide (LiFSI), and a lithium secondary battery including the non-aqueous electrolyte solution. The lithium secondary battery of the present invention may improve low-temperature and room temperature output characteristics, high-temperature and room temperature cycle characteristics, and capacity characteristics after high-temperature storage by forming a robust solid electrolyte interface (SEI) on an anode during initial charge of the lithium secondary battery.