Amorphous Lithium Fluoride and Phosphate Coating for Li-Ion Battery
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Solution Overview
Problem
Lithium ion secondary batteries using lithium nickel manganese oxide as a positive electrode active material face challenges in improving cycle characteristics due to insufficient reduction in lithium ion diffusion resistance, despite the addition of insoluble lithium compounds like Li3PO4 or LiF.
Innovation Solution
A method involving the formation of a coating film containing amorphous lithium fluoride and amorphous lithium phosphate on the surface of the positive electrode active material, achieved by exposing lithium nickel manganese oxide to fluorine-based gas and adding a phosphate compound, followed by charging to create an amorphous lithium phosphate coating, which reduces lithium ion diffusion resistance and enhances cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating film is formed on the positive electrode active material surface, then lithium ion diffusion resistance is reduced, but the complexity of the manufacturing process increases
Solution Approach 1:
The coating film is formed on the positive electrode active material surface before battery assembly. This preliminary action ensures that the surface modification is completed in advance, allowing for controlled formation of the amorphous coating structure without adding complex post-assembly processes
Solution Approach 2:
The coating film acts as an intermediary layer between the positive electrode active material and the electrolyte. This intermediate structure facilitates lithium ion transport while protecting the active material, reducing diffusion resistance without requiring direct modification of the bulk material
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 amorphous coating film significantly improves the cycle characteristics of lithium ion secondary batteries by reducing lithium ion diffusion resistance, leading to better capacity retention and inhibiting the adverse effects of hydrogen fluoride in the electrolyte.
Implementation Method 1
exposing lithium nickel manganese oxide, which is a positive electrode active material, to fluorine-based gas to form a coating film containing amorphous lithium fluoride on a surface of the positive electrode active material
Implementation Method 2
charging the formed lithium ion secondary battery to form a coating film containing amorphous lithium phosphate on the surface of the positive electrode active material
Implementation Method 3
the amorphous coating film has lower lithium ion diffusion resistance (in other words, higher lithium ion conductivity) than that of a crystalline coating film. Accordingly, by forming the amorphous coating film on the surface of the positive electrode active material, the lithium ion diffusion resistance of the surface of the positive electrode active material can be reduced
Data Source
AI summary
In a method of manufacturing a lithium ion secondary battery, first, lithium nickel manganese oxide which is a positive electrode active material is exposed to fluorine-based gas to form a coating film containing amorphous lithium fluoride on a surface of the positive electrode active material. Next, a phosphate compound is added to the positive electrode active material on which the coating film containing the lithium fluoride is formed. After a lithium ion secondary battery which includes a positive electrode including the positive electrode active material is formed, the lithium ion secondary battery is charged to form a coating film containing amorphous lithium phosphate on the surface of the positive electrode active material.