Cathode Active Material Coating for High-Temperature Battery Life
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Solution Overview
Problem
Lithium nickel cobalt metal oxides used in lithium secondary batteries face issues with low capacity, poor thermal stability, and deteriorated lifespan characteristics due to surface defects from washing processes, necessitating improved high-temperature lifespan and resistance characteristics.
Innovation Solution
A method of forming a first coating layer on the surface of lithium transition metal oxides using a basic aqueous solution containing sodium (Na) and aluminum (Al), followed by a second coating layer using boron (B), through dry-mixing and heat treatment, to create a uniform coating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a washing process is used to remove unreacted residual lithium from the surface of lithium nickel cobalt metal oxide, then the purity of the positive electrode active material is improved, but defects are generated on the surface and lifespan characteristics of the battery are deteriorated
Solution Approach 1:
A coating layer is formed on the surface of the lithium nickel cobalt metal oxide before the washing process. This preliminary coating action protects the surface from damage during subsequent washing, allowing thorough removal of residual lithium without generating surface defects that would harm battery lifespan.
Solution Approach 2:
A coating layer composed of specific metal oxides (such as Al2O3, SiO2, TiO2) serves as an intermediary between the positive electrode active material and the washing solution. This intermediary layer allows the washing process to proceed effectively while preventing direct contact between the washing solution and the active material surface, thus avoiding surface defect formation.
2Quantity of substance
If the content of nickel is increased to increase the capacity of lithium nickel cobalt metal oxide, then the reversible capacity is improved, but thermal stability deteriorates and the battery becomes prone to rupture and ignition
Solution Approach 1:
The coating layer is applied specifically on the surface of the lithium nickel cobalt metal oxide particles, creating a localized region with different properties from the bulk material. This surface coating provides thermal stability and protection against decomposition at high temperatures, while the high-nickel bulk material maintains its high reversible capacity.
Solution Approach 2:
The positive electrode active material is constructed as a composite structure with a core of lithium nickel cobalt metal oxide (providing high capacity) and an outer coating layer of thermally stable metal oxides (providing thermal stability). This composite structure combines the advantages of both materials while mitigating their individual disadvantages.
3Reliability
If a coating layer is formed on the surface of positive electrode active material at low temperature after washing, then the lifespan characteristics are improved, but high-temperature resistance characteristics remain limited
Solution Approach 1:
The coating process is performed at low temperatures (below 900°C, preferably below 700°C) using specific coating materials that form stable compounds at these temperatures. This parameter change allows coating formation without the high temperatures that would cause thermal decomposition, thereby improving lifespan characteristics while maintaining adequate high-temperature resistance.
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 method enhances high-temperature lifespan and resistance characteristics of lithium secondary batteries by uniformly forming a coating layer, improving capacity and resistance characteristics.
Implementation Method 1
forming a first coating layer on a surface of a lithium transition metal oxide using a basic aqueous solution which includes a coating element M1
Implementation Method 2
forming a first coating layer on a surface of a lithium transition metal oxide using a basic aqueous solution
Implementation Method 3
followed by a second coating layer using boron (B), through dry-mixing and heat treatment
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(c)
Figure 3~4
AI summary
The present invention relates to: a method of preparing a positive electrode active material including forming a first coating layer on a surface of a lithium transition metal oxide represented by Formula 1 by using a basic aqueous solution containing a coating element M1 (where M1 includes at least one selected from sodium (Na) and aluminum (Al)), and forming a second coating layer by dry-mixing the lithium transition metal oxide, on which the first coating layer formed, and a raw material containing a coating element M2 (where M2 includes boron (B)) and performing heat treatment on the mixture; a positive electrode active material prepared by the preparation method; a positive electrode for a lithium secondary battery including the positive electrode active material; and a lithium secondary battery.