Ni-Rich Cathode Structural Stability via FWHM Control
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Solution Overview
Problem
Lithium nickel composite oxide positive active materials with high Ni ratios in rechargeable lithium ion batteries suffer from structural instability, leading to deteriorated cycle characteristics and initial charge and discharge efficiency due to cation mixing, which compromises discharge capacity and overall battery performance.
Innovation Solution
A lithium nickel composite oxide with a high Ni ratio, characterized by specific X-ray diffraction peak intensity ratios, full width at half maximum, average secondary particle diameter, and specific surface area ranges, is used as a positive active material, prepared through a method involving the addition of a saturated NaOH solution to a mixed aqueous solution of hydrates and subsequent firing under an oxygen atmosphere, to enhance structural stability and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium nickel composite oxide with high Ni ratio is used as positive active material, then discharge capacity and potential are improved, but structural stability deteriorates due to cation mixing
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface region has different composition and properties from the core. The surface is modified with aluminum phosphate coating and controlled cation distribution to suppress cation mixing locally, while the core maintains high Ni ratio (x≥0.80) for high capacity. This local differentiation allows the surface to protect against structural degradation while the bulk provides high discharge capacity.
Solution Approach 2:
The patent uses composite materials by combining lithium nickel composite oxide with aluminum phosphate coating. The composite structure integrates the high-capacity Ni-rich core with the protective Al-rich shell, creating a material that exhibits both high discharge capacity and improved structural stability. The composite nature allows synergistic effects where the coating layer prevents cation mixing while the core provides lithium insertion/extraction sites.
2Productivity
If high Ni ratio is used in lithium nickel composite oxide, then initial charge and discharge efficiency is improved, but cycle characteristics deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-modifying the surface of the lithium nickel composite oxide particles with aluminum phosphate coating before battery assembly. This preliminary surface treatment prevents cation mixing during initial charging cycles, establishing a stable surface structure that maintains both high initial charge-discharge efficiency and good cycle characteristics. The coating is applied in advance to protect against degradation that would otherwise occur during first few cycles.
Solution Approach 2:
The patent changes physical and chemical parameters of the surface region, specifically controlling the full width at half maximum (FWHM) of the (003) diffraction peak to be 0.10-0.165° and the (104)/(003) intensity ratio to be 0.70-1.30. These parameter changes indicate controlled crystallite size and surface structure that suppress cation mixing while maintaining high Ni ratio, thereby achieving both high initial efficiency and good cycle stability.
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 optimized lithium nickel composite oxide improves discharge capacity, initial charge and discharge efficiency, and cycle characteristics by maintaining structural stability and reducing cation mixing, as evidenced by improved diffraction peak intensity ratios and particle properties.
Implementation Method 1
a full width at half maximum (FWHM003) at a (003) plane in X-ray diffraction ranges from about 0.12 to about 0.155
Implementation Method 2
a (I003)/(I104) ratio of a diffraction peak intensity (I003) at a (003) plane and a diffraction peak intensity (I104) at a (104) plane in the X-ray diffraction
Implementation Method 3
adding a saturated NaOH aqueous solution to a mixed aqueous solution including a hydrate of Co and Ni and a M-containing compound in a dropwise fashion so as to maintaining pH to be 8 to 12, and agitating the resulting mixture to prepare a hydroxide salt precursor of a transition metal
Implementation Method 4
mixing the hydroxide salt precursor of the transition metal with a Li compound, and firing the resultant mixture under an oxygen atmosphere at about 700° C. to about 800° C. for about 1 hour to about 10 hours to prepare a lithium nickel composite oxide
Implementation Method 5
firing the resultant mixture under an oxygen atmosphere at about 700° C. to about 800° C.
Data Source
AI summary
A positive active material is disclosed that includes a lithium nickel composite oxide represented by the following Chemical Formula 1, wherein a full width at half maximum (FWHM003) at a (003) plane in X-ray diffraction ranges from about 0.12 to about 0.155, and a rechargeable lithium ion battery including the same.LiaNixCoyMzO2 [Chemical Formula 1]