Lithium Positive Electrode Active Material Composition
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Solution Overview
Problem
Current lithium positive electrode active materials for high voltage lithium secondary batteries face challenges in achieving high phase purity, stability, and energy density, with capacity degradation issues and impurities affecting performance.
Innovation Solution
A lithium positive electrode active material with a specific chemical composition of LixNiyMn2-yO4, where 0.95≤x≤1.05 and 0.43≤y≤0.47, is synthesized using precursors with a Li:Ni:Mn ratio of 0.95≤X≤1.05 and 0.42≤Y<0.5, optimizing the Ni content to balance energy density and degradation, and employing methods like SEM, X-ray diffraction, and STEM-EDS for precise composition determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the Ni content is increased to improve energy density, then the capacity and energy density increase, but the material degradation accelerates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Ni content within a narrow range (0.42≤Y<0.5) and adjusting the Li content (0.95≤x≤1.05) to optimize the balance between energy density and material stability. This quantitative parameter optimization resolves the contradiction by finding the optimal composition window where high Ni content provides sufficient energy density while preventing excessive degradation.
2Quantity of substance
If the Li content is increased to improve capacity, then the capacity increases, but the phase purity decreases
Solution Approach 1:
The patent uses parameter changes by defining a specific range for Li content (0.95≤x≤1.05) that balances capacity and phase purity. This controlled parameter adjustment ensures sufficient Li content for high capacity while preventing excessive Li that would lead to impurity phase formation, thus resolving the contradiction between quantity and purity.
3Shape
If the material is heated at high temperature to create spinel morphology, then the desired spinel structure is formed, but oxygen is lost and requires subsequent cooling in oxygen containing medium
Solution Approach 1:
The patent applies preliminary action by performing the high-temperature heat treatment (600-900°C) in a controlled atmosphere to pre-form the spinel morphology, followed by a controlled cooling step in oxygen-containing medium to restore oxygen content. This sequential approach anticipates and compensates for oxygen loss, resolving the contradiction between achieving desired morphology and preventing substance loss.
4Ease of manufacture
If the precursor is prepared by mechanical mixing to obtain homogeneous mixture, then the mixing is simpler, but the preparation difficulty increases and phase purity decreases
Solution Approach 1:
The patent resolves this contradiction by optimizing the precursor composition parameters (Li:Ni:Mn ratios within specific ranges) and controlling the sintering temperature and atmosphere parameters. These parameter optimizations ensure that even with simple mechanical mixing, the final product achieves high phase purity by compensating for potential inhomogeneities through controlled thermal processing.
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 provides a lithium positive electrode active material with high phase purity, low degradation, and balanced energy density, maintaining capacity with minimal fade over cycles, and ensuring stability by controlling the Ni content within a narrow range.
Implementation Method 1
The precursor(s) and product are spherical due to the co-precipitation process. Electrochimica Acta (2014), pp 290-296 discloses a material prepared from precursors obtained by a co-precipitation process followed by sequential sintering (heat treatment) at 500° C., followed by 800° C.
Implementation Method 2
The product obtained is highly crystalline and has a spinel structure after the first heat treatment step (500° C.).
Implementation Method 3
The precursor is heated at 600° C., annealed between 700 and 950° C., and cooled in a medium containing oxygen. It is disclosed that the 600° C. heat treatment step is required in order to ensure that the lithium is well incorporated into the mixed nickel and manganese oxide precursor.
Implementation Method 4
It is also disclosed that the annealing step is generally at a temperature greater than 800° C. in order to cause a loss of oxygen while creating the desired spinel morphology.
Implementation Method 5
It is further disclosed that subsequent cooling in an oxygen containing medium enables a partial return of oxygen.
Data Source
AI summary
The present invention relates to a lithium positive electrode active material for a high voltage secondary battery, where the lithium positive electrode active material comprising a spinel, and the spinel has a chemical composition of LixNiyMn2-yO4, wherein: 0.95≤x≤1.05; and 0.43≤y≤0.47. The lithium positive electrode active material is synthesized from precursors containing Li, Ni, and Mn in a ratio Li:Ni:Mn:X:Y:2−Y, wherein: 0.95≤X≤1.05; and 0.42≤Y<0.5. The present invention also relates to a process of preparing the lithium positive electrode active material as well as a secondary battery comprising the lithium positive electrode active material.