Lithium Cobalt Oxide Electrolyte Cycle Stability
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Solution Overview
Problem
Lithium cobalt oxide-based non-aqueous electrolyte secondary cells face challenges with thermal stability and cycle characteristics, particularly when the electrolyte decomposes during charge and discharge cycles, leading to increased internal resistance and reduced cell capacity.
Innovation Solution
Incorporating diethyl carbonate (DEC) at 10 to 30 volume percent in the non-aqueous electrolyte and adding elements like zirconium or magnesium to the lithium cobalt oxide improves the structural stability of the crystal and inhibits electrolyte decomposition, enhancing cycle and low-temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lithium cobalt oxide is used as the positive electrode active material, then high cell capacity and excellent charge and discharge characteristics are achieved, but thermal stability and cycle characteristics are insufficient
Solution Approach 1:
The patent applies composite materials by combining lithium cobalt oxide with metal element compounds (such as titanium oxide, zirconium oxide, magnesium oxide, or aluminum oxide) to form a composite positive electrode active material. This composite structure maintains the high capacity of lithium cobalt oxide while the added metal element compound improves thermal stability and cycle characteristics by forming a protective interface layer that prevents electrolyte decomposition and maintains structural integrity during cycling.
2Stability of the object's composition
If different metal elements are added to lithium cobalt oxide, then thermal stability is improved, but electrolyte decomposition still occurs during charge and discharge cycles
Solution Approach 1:
The patent uses the metal element compound as an intermediary substance between the lithium cobalt oxide and the electrolyte. This intermediary layer (formed by compounds like titanium oxide, zirconium oxide, magnesium oxide, or aluminum oxide) mediates the interaction by providing a stable interface that prevents direct contact between the electrolyte and the lithium cobalt oxide surface, thereby inhibiting electrolyte decomposition while maintaining thermal stability.
3Reliability
If electrolyte decomposition occurs during charge and discharge cycles, then internal resistance increases and cell capacity is reduced
Solution Approach 1:
The patent applies preliminary anti-action by pre-forming a stable interface layer on the lithium cobalt oxide surface through the addition of metal element compounds before the cell begins cycling. This pre-formed protective layer (composed of metal oxides such as titanium oxide, zirconium oxide, magnesium oxide, or aluminum oxide) prevents the harmful decomposition reactions from occurring in the first place, thereby preventing the generation of decomposition products that would increase internal resistance and maintain low internal resistance throughout cycling.
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 significantly improves cycle and low-temperature discharge characteristics, maintaining high cell capacity while reducing internal resistance and electrolyte decomposition, with optimal results achieved when DEC is between 10 to 30 volume percent and the element content is within specified ranges.
Implementation Method 1
open-chain carbonates containing a methyl group (e.g., dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC)) are easily decomposed, and this decomposition is inhibited by adding a certain amount of an open-chain carbonate (diethyl carbonate (DEC)) with no methyl group contained
Implementation Method 2
adding elements like zirconium or magnesium to the lithium cobalt oxide improves the structural stability of the crystal
Data Source
AI summary
The present invention improves the cycle characteristics of a non-aqueous electrolyte secondary cell that uses lithium cobalt oxide as a positive electrode active material. To this end, an element different from cobalt such as zirconium and titanium is added to the lithium cobalt oxide, acting as the positive electrode active material. The non-aqueous electrolyte contains a non-aqueous solvent containing diethyl carbonate at 10 to 30 volume percent on a base of 25 degree Celsius and contains an electrolyte salt.