Lithium Metal Composite Oxide with NiO Layer for Thermal Stability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in increasing energy density due to instability in positive electrode active materials, leading to oxygen release during charging, which affects thermal stability and battery performance.
Innovation Solution
A positive electrode active material composed of lithium metal composite oxide with specific ratios of nickel, cobalt, and additional elements, such as Mg or Al, is developed, with a controlled NiO layer thickness and specific surface area to suppress oxygen release and enhance thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel ratio in the positive electrode active material is increased to increase battery capacity, then the charge and discharge capacity is improved, but the thermal stability deteriorates
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the interior contains high-nickel content (0.6≤x≤0.8) for high capacity, while the surface layer contains lower nickel content (0.2≤y≤0.4) for thermal stability. This spatial differentiation of composition allows each region to perform its optimal function without compromising the other.
Solution Approach 2:
The patent uses composite materials by combining lithium-nickel composite oxide particles with a lithium-manganese composite oxide layer. The core material (Li1-aNixCoyMzO2) provides high capacity through nickel's electrochemical activity, while the manganese oxide shell (Li2-yMn2-yO4) provides thermal stability through manganese's structural stability at elevated temperatures.
2Reliability
If two-composition particles are mixed to ensure thermal stability, then thermal stability is improved, but energy density cannot be increased
Solution Approach 1:
The patent merges the high-capacity lithium-nickel composite oxide and the thermally stable lithium-manganese composite oxide into a single integrated particle structure. Rather than mixing separate particles, the manganese oxide is grown as a conformal coating on the nickel oxide particles, creating a unified composite particle that achieves both high energy density (85% theoretical capacity utilization) and thermal stability.
Solution Approach 2:
The patent employs a thin film approach where a relatively thin layer of lithium-manganese composite oxide (containing 5-30 mass% manganese oxide) is deposited on the surface of the lithium-nickel composite oxide particles. This thin protective shell provides sufficient thermal stability while minimizing the amount of lower-capacity material, thereby maintaining high overall energy density.
3Duration of action of moving object
If the positive electrode active material structure becomes unstable due to lithium de-intercalation during charging, then oxygen release occurs, but thermal stability is reduced
Solution Approach 1:
The patent applies preliminary anti-action by pre-coating the high-nickel lithium-nickel composite oxide particles with a lithium-manganese composite oxide layer before charging. This protective shell is in place beforehand to prevent the harmful effect of oxygen release that would otherwise occur during charging when the high-nickel material undergoes lithium de-intercalation and structural instability.
Solution Approach 2:
The lithium-manganese composite oxide layer acts as an intermediary between the high-nickel core material and the electrolyte environment. During charging, this intermediate layer buffers the structural changes in the core material, preventing direct contact between the unstable high-nickel oxide and the electrolyte, thereby suppressing oxygen release and exothermic reactions.
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 effectively suppresses oxygen release during charging, improving thermal stability and battery performance by controlling the NiO layer thickness and specific surface area, thereby enhancing the energy density and cycle characteristics of lithium ion secondary batteries.
Implementation Method 1
Active materials of the negative electrode and the positive electrode are materials that can intercalate and de-intercalate lithium ions
Implementation Method 2
a thickness of a NiO layer is 200 nm or less when particles of the lithium metal composite oxide during charging at 4.3 V (vs. Li+/Li) are observed by STEM-EDS
Implementation Method 3
a specific surface area is 0.7 m2/g or more and 2.0 m2/g or less
Data Source
AI summary
A positive electrode active material for a lithium ion secondary battery contains a lithium metal composite oxide. The lithium metal composite oxide includes lithium (Li), nickel (Ni), cobalt (Co), and an element M (M) in a mass ratio of Li:Ni:Co:M=1+a:1−x−y:x:y (wherein −0.05≤a≤0.50, 0≤x≤0.35, 0≤y≤0.35, and the element M is at least one element selected from Mg, Ca, Al, Si, Fe, Cr, Mn, V, Mo, W, Nb, Ti, Zr, and Ta), wherein a thickness of a NiO layer is 200 nm or less when a particle of the lithium metal composite oxide during charging at 4.3 V (vs. Li+/Li) is observed by STEM-EDS, and wherein a specific surface area is 0.7 m2/g or more and 2.0 m2/g or less.