Layered Organic Electrode Prevents Overdischarge Degradation
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Solution Overview
Problem
Lithium-ion capacitors with graphite negative electrodes are prone to degradation due to overdischarge, necessitating restrictive discharge cutoff voltages to prevent cell degradation.
Innovation Solution
An electricity storage device featuring a negative electrode with a layered structure composed of an organic backbone layer containing aromatic dicarboxylate anions and an alkali metal element layer, coordinated with oxygen, along with a positive electrode providing electric double-layer capacity and a nonaqueous electrolyte solution containing an alkali metal salt, which inhibits overdischarge by increasing internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If graphite negative electrodes are used in lithium-ion capacitors, then the cell can operate at higher voltages, but the cell becomes prone to degradation due to overdischarge
Solution Approach 1:
The patent applies preliminary action by pre-doping the graphite negative electrode with lithium ions before the capacitor is put into service. This pre-doping creates a buffer that prevents the graphite from undergoing harmful phase transformations during normal operation, thereby preventing cell degradation while maintaining high voltage operation capability
2Reliability
If discharge cutoff voltage is restricted to prevent overdischarge degradation, then cell reliability is improved, but the usable capacity and energy output are reduced
Solution Approach 1:
By pre-doping the graphite negative electrode with lithium ions in advance, the patent creates a protective buffer that allows the cell to discharge to lower voltages without suffering degradation. This enables the cell to maintain both high reliability and high usable capacity, as the pre-doped lithium prevents harmful reactions even at extended discharge depths
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 prevents cell degradation from overdischarge by rapidly increasing internal resistance, thereby shutting down current flow and maintaining the cell's integrity, even when pre-doping with alkali metal ions is used.
Implementation Method 1
when a predetermined amount or more of ions absorbed in the layered structure is released by discharge, the resistance increases rapidly to make it difficult to pass a current
Implementation Method 2
a positive electrode providing electric double-layer capacity
Data Source
AI summary
An electricity storage device includes a negative electrode having a layered structure that includes an organic backbone layer containing an aromatic compound having an aromatic ring structure, the aromatic compound being in the form of dicarboxylate anions, and an alkali metal element layer containing an alkali metal element coordinated with oxygen in the dicarboxylate anions to form a backbone, a positive electrode that provides electric double-layer capacity, and a nonaqueous electrolyte solution provided between the negative electrode and the positive electrode, the nonaqueous electrolyte solution containing an alkali metal salt. The layered structure may be provided in layers by a π-electron interaction of the aromatic compound and may have a monoclinic crystal structure belonging to the space group P21/c. The positive electrode may contain activated carbon having a specific surface area of 1,000 m2/g or more.