Spinel Cathode Coating for High-Temperature Cycle Stability
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Solution Overview
Problem
Lithium transition metal oxides used in secondary batteries suffer from energy density degradation during high-temperature charge/discharge due to reactions with electrolyte solutions, leading to transition metal elution and performance degradation.
Innovation Solution
A positive electrode active material is developed with a lithium transition metal oxide having a spinel crystal structure and a coating layer with an orthorhombic structure, composed of specific oxides, which suppresses reactions with electrolyte solutions and enhances lithium ion mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium transition metal oxide is used as positive electrode active material, then high energy density and voltage are achieved, but thermal properties deteriorate due to crystal structure destabilization during de-lithium
Solution Approach 1:
A coating layer comprising lithium nickel oxide or lithium copper oxide is applied on the surface of the lithium transition metal oxide particles. This coating layer acts as an intermediary barrier that prevents direct contact between the electrolyte and the lithium transition metal oxide surface, thereby suppressing transition metal elution and maintaining thermal stability during high-temperature charge/discharge cycles while preserving the high energy density properties of the core material
2Ease of manufacture
If lithium transition metal oxide is used to replace LiCoO2, then cost is reduced, but transition metal elution occurs due to HF formation during high-temperature charge/discharge
Solution Approach 1:
The coating layer of lithium nickel oxide or lithium copper oxide serves as a protective intermediary that prevents HF from reaching the lithium transition metal oxide surface. This eliminates the HF-induced transition metal elution problem that plagues conventional lithium transition metal oxides, thereby maintaining reliability and performance during high-temperature operation while keeping costs lower than LiCoO2
Solution Approach 2:
The coating layer changes the surface chemical environment by providing a stable oxide surface that is resistant to HF attack. This parameter change at the surface level prevents the harmful chemical reactions that would otherwise occur between HF and the lithium transition metal oxide, suppressing transition metal dissolution without affecting the bulk material properties
3Reliability
If lithium transition metal oxide reacts with electrolyte solution during high-temperature charge/discharge, then transition metal elution occurs, but energy density degrades
Solution Approach 1:
The coating layer acts as a thermal-stable intermediary barrier that prevents direct reactions between the electrolyte and lithium transition metal oxide during high-temperature charge/discharge. This suppression of parasitic reactions prevents transition metal elution and maintains the structural integrity of the active material, thereby preserving energy density while improving high-temperature reliability
Solution Approach 2:
A thin film coating layer is formed on the surface of the lithium transition metal oxide particles. This thin film provides sufficient protection against electrolyte penetration and transition metal elution during high-temperature operation, while being thin enough to allow efficient lithium ion transport, thus maintaining high energy density and rate capability
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 coating layer stabilizes the lithium transition metal oxide surface, preventing transition metal elution and improving battery efficiency and capacity during high-temperature cycles.
Implementation Method 1
the coating layer is strongly adsorbed onto the surface of the lithium transition metal oxide, thereby stabilizing the surface structure
Implementation Method 2
stabilizing the surface structure of the lithium transition metal oxide, suppressing a side reaction between the lithium transition metal oxide and an electrolyte solution
Implementation Method 3
improving the diffusivity of lithium ions as well
Data Source
Figure 1~2
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AI summary
The present invention relates to a positive electrode active material, a method for producing the positive electrode active material, a positive electrode including the positive electrode active material, and a lithium secondary battery, the positive electrode active material including a lithium transition metal oxide having a spinel crystal structure, and a coating layer positioned on the surface of the lithium transition metal oxide, wherein the coating layer has an orthorhombic structure, and includes an oxide represented by Formula 1.