Non-aqueous Electrolyte for Lithium Battery Cycle Stability
Find Innovative SolutionsGenerate Solutions
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 with existing non-aqueous organic solvents like propylene carbonate and ethylene carbonate.
Innovation Solution
A non-aqueous electrolyte solution comprising lithium bis(fluorosulfonyl)imide (LiFSI), a lithium salt, and a pyridine-based compound, along with a mixture of propylene carbonate and ethylene carbonate as solvents, is used to form a robust solid electrolyte interface (SEI) on the negative electrode, enhancing cycle and output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If propylene carbonate is used as a non-aqueous organic solvent, then the electrolyte solution can operate at room temperature, but it causes irreversible decomposition reaction with graphite material
Solution Approach 1:
The patent introduces a fluorinated cyclic carbonate compound as an intermediary substance that mediates between the electrolyte solution and graphite negative electrode. This compound preferentially reacts with lithium ions to form a protective SEI layer, preventing direct contact and harmful decomposition reactions between propylene carbonate and graphite material, thus resolving the contradiction between room-temperature operation and chemical stability
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte solution by adding fluorinated cyclic carbonate compound at specific concentrations (0.01-5 wt%). This parameter change alters the reaction characteristics between the electrolyte and graphite, transforming the harmful irreversible decomposition into a controlled initial SEI formation process, thereby improving cycle characteristics while maintaining room-temperature operation
2Reliability
If ethylene carbonate is used as a non-aqueous organic solvent, then it can replace propylene carbonate, but its high melting point limits operating temperature and reduces battery performance at low temperature
Solution Approach 1:
The patent creates a composite electrolyte system combining ethylene carbonate with fluorinated cyclic carbonate compound. This composite approach leverages the high-temperature stability of EC while the fluorinated additive provides low-temperature fluidity and forms protective SEI layers, achieving both high-temperature cycle characteristics and acceptable low-temperature performance through synergistic material combination
Solution Approach 2:
The fluorinated cyclic carbonate compound acts as an intermediary that modifies the physical and chemical properties of ethylene carbonate. It reduces the effective melting point influence by forming a eutectic mixture and facilitates ion transport at low temperatures while maintaining the thermal stability of EC at high temperatures, thus resolving the temperature range limitation
3Reliability
If a robust SEI is formed on the negative electrode, then high-temperature and room-temperature cycle characteristics are improved, but the formation process consumes lithium ions and reduces initial capacity
Solution Approach 1:
The patent employs a small amount of fluorinated cyclic carbonate compound (0.01-5 wt%) as a sacrificial additive that is consumed during initial SEI formation. This disposable-like approach uses a minor component to form the protective interface, accepting the consumption of this small quantity to achieve long-term cycle stability without significantly impacting overall battery capacity
Solution Approach 2:
The patent optimizes the concentration parameter of the fluorinated additive to achieve the minimum effective amount for robust SEI formation. By precisely controlling this parameter within 0.01-5 wt%, the patent minimizes lithium ion consumption during SEI formation while ensuring sufficient protective layer formation, thus balancing initial capacity retention with long-term cycle characteristics
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 improves high-temperature and room-temperature cycle characteristics, capacity retention, and low-temperature output by forming a stable SEI, preventing decomposition and oxidation reactions, and maintaining battery performance after high-temperature storage.
Implementation Method 1
a film may be formed on the surface of the negative electrode. The film is denoted as 'solid electrolyte interface (SEI)'
Implementation Method 2
The SEI may only pass the lithium ions by acting as an ion tunnel
Implementation Method 3
Charge and discharge of the lithium secondary battery is performed while a process of intercalating and deintercalating lithium ions from a lithium metal oxide positive electrode into and out of a graphite negative electrode is repeated
Implementation Method 4
lithium reacts with the carbon electrode to form Li 2 CO 3, LiO, or LiOH
Data Source
AI summary
The present invention relates to: a non-aqueous electrolyte comprising a non-aqueous organic solvent, lithium bis(fluorosulfonyl)imide (LiFSI), and a pyridine-based compound represented by chemical formula 1; and a lithium secondary battery comprising same. The lithium secondary battery according to the present invention, comprising the non-aqueous electrolyte according to the present invention, can exhibit excellent low-temperature and room temperature output characteristics, high-temperature and room temperature cycle characteristics, and capacity characteristics after storage at a high temperature.