Ionic Liquid Electrolyte for Lithium-Ion Battery Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with high irreversible capacity, decomposition of electrolytic solutions at high temperatures, and reduced charge/discharge capacity due to the volatility and flammability of organic solvents used in electrolytes, which limits their operating temperature range and reliability.
Innovation Solution
A power storage device design incorporating a positive electrode, negative electrode, and a separator with an electrolytic solution containing an alkali metal salt and an ionic liquid, where the positive electrode overlaps with the negative electrode, and the negative electrode active material layer has a thinner, higher resistance layer to inhibit decomposition reactions and enhance stability, using an ionic liquid with an imidazolium cation to improve conductivity and reduce irreversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If organic solvents (ethylene carbonate) are used in electrolytic solutions to achieve high ionic conductivity, then the power storage device can maintain stable performance, but the device becomes vulnerable to temperature rise, bursting, and fire due to volatility and flammability
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolytic solution by replacing traditional organic solvents with ionic liquids. This parameter change eliminates volatility and flammability while maintaining ionic conductivity, directly resolving the contradiction between reliability and harmful factors.
Solution Approach 2:
The patent uses ionic liquids which, although more expensive than traditional solvents, eliminate the need for safety precautions against fire and explosion, effectively making the system safer and more reliable despite the higher material cost.
2Object-affected harmful factors
If ionic liquid is used as electrolytic solution to eliminate flammability and volatility, then safety is improved, but the device exhibits high irreversible capacity and decomposition at high temperatures
Solution Approach 1:
The patent employs a composite electrolytic solution system combining ionic liquid with specific additives and uses composite electrode structures with coating layers. This composite approach enhances the stability of ionic liquid-based systems, reducing irreversible capacity and high-temperature decomposition while maintaining safety benefits.
Solution Approach 2:
The patent applies different functional layers to electrode surfaces, creating local quality variations. The coating layers on electrodes provide specific local properties that prevent ionic liquid decomposition at high temperatures and reduce irreversible capacity, while the bulk ionic liquid maintains its safety advantages.
3Loss of energy
If the negative electrode active material layer is made thinner to reduce resistance, then conductivity is improved, but the decomposition reaction of electrolytic solution increases at high temperature
Solution Approach 1:
The patent creates local quality differences within the electrode structure by adding protective coating layers on specific regions of the thin active material layer. This allows the electrode to maintain low bulk resistance while the surface coating prevents electrolyte decomposition at high temperatures, resolving the contradiction between conductivity and 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 design achieves a power storage device with high capacity, reduced irreversible capacity, and extended operating temperature range by inhibiting electrolyte decomposition, leading to improved reliability and performance in lithium-ion secondary batteries.
Implementation Method 1
an ionic liquid with low viscosity, a low melting point, and high conductivity
Implementation Method 2
the decomposition reaction of an electrolytic solution is inhibited and a decrease in capacity with the increasing number of charge and discharge cycles is prevented
Data Source
AI summary
A power storage device with high capacity, a power storage device with high energy density, a highly reliable power storage device, and a long-life power storage device are provided. The power storage device includes a positive electrode, a separator, a negative electrode, and an electrolytic solution. The electrolytic solution contains an alkali metal salt and an ionic liquid. The separator is located between the positive electrode and the negative electrode. At least part of the positive electrode overlaps with the negative electrode. At least part of an end portion of the negative electrode is located inside a region between end portions of the positive electrode.