Lithium Ion Battery High Potential Electrolyte Separator
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Solution Overview
Problem
Lithium ion secondary batteries using high operating potential materials face issues with decomposition and degradation of electrolytic solutions, leading to decreased charge and discharge cycle characteristics, especially at high temperatures, and oxidative deterioration of separators.
Innovation Solution
A lithium ion secondary battery design incorporating a positive electrode with a 4.5 V or higher operating potential, a cellulose or cellulose derivative separator with a porosity of 50% to 95%, and an electrolytic solution containing fluorinated solvents to enhance high-temperature cycle performance and prevent oxidative decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a positive electrode active material with high operating potential (4.5 V or more) is used to increase energy density, then the battery's energy density and operating potential are improved, but the electrolytic solution decomposes and the separator undergoes oxidative deterioration, leading to decreased cycle characteristics
Solution Approach 1:
A fluorinated solvent is introduced as an intermediary substance in the electrolytic solution to mediate between the high-potential positive electrode and the conventional electrolyte components. The fluorinated solvent suppresses oxidative decomposition and protects the separator from deterioration, enabling the system to maintain both high energy density and reliable cycle characteristics at 4.5 V or higher operating potentials
Solution Approach 2:
The chemical composition parameter of the electrolytic solution is changed by incorporating a fluorinated solvent. This parameter change fundamentally alters the electrochemical stability window and oxidation resistance of the electrolyte system, allowing it to withstand the high operating potential of 4.5 V or more without decomposing the electrolyte or oxidizing the separator
2Object-affected harmful factors
If a polyolefin microporous film separator is used to provide shutdown function, then the safety of the battery is maintained, but the separator undergoes oxidative deterioration at high operating potentials, leading to gas generation and internal short circuits
Solution Approach 1:
The fluorinated solvent acts as a protective intermediary that surrounds and protects the polyolefin microporous film separator from direct contact with oxidative species generated at the high-potential positive electrode. This mediation prevents oxidative deterioration while preserving the separator's shutdown function for safety
Solution Approach 2:
The fluorinated solvent creates an inert electrochemical environment around the separator by suppressing the generation of oxidative species. This inert environment prevents oxidation of the polyolefin material while maintaining the separator's original safety functions
3Volume of moving object
If the operating potential is increased to 4.5 V or more to reduce the number of series batteries, then the size and weight of the battery module are reduced, but decomposition products are deposited on the separator, causing internal short circuits
Solution Approach 1:
The fluorinated solvent converts the potentially harmful high-potential environment into a beneficial protective atmosphere. Instead of allowing decomposition products to form and deposit on the separator, the fluorinated solvent suppresses decomposition at the source, transforming the high-potential condition from a harmful factor into an opportunity to demonstrate the solvent's superior stability
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 effectively improves the high-temperature cycle characteristics and reduces gas generation, maintaining capacity retention and preventing internal short circuits in lithium ion secondary batteries.
Implementation Method 1
the separator comprises cellulose or a cellulose derivative... having excellent heat resistance and high load characteristics
Implementation Method 2
an electrolytic solution containing fluorinated solvents to enhance high-temperature cycle performance and prevent oxidative decomposition
Implementation Method 3
a separator between the positive electrode and the negative electrode... the porosity of the separator is 50% or more and 95% or less
Data Source
Figure 1
AI summary
It is an object of this exemplary embodiment to provide a lithium ion secondary battery using a positive electrode active material having an operating potential of 4.5 V or more, the lithium ion secondary battery having excellent high temperature cycle characteristics. This exemplary embodiment is a lithium ion secondary battery comprising a positive electrode and a negative electrode capable of intercalating and deintercalating lithium, a separator between the positive electrode and the negative electrode, and an electrolytic solution containing a nonaqueous electrolytic solvent, wherein the positive electrode comprises a positive electrode active material operating at a potential of 4.5 V or more versus lithium, the separator comprises cellulose, a cellulose derivative, or a glass fiber, and the nonaqueous electrolytic solvent comprises a fluorinated solvent.