Lithium-Rich Cathode Material for Stable Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using lithium-rich cathode active materials experience a significant decrease in discharge capacity after 50 charge and discharge cycles, compromising their cycle characteristics.
Innovation Solution
A cathode active material comprising a lithium-containing composite oxide with specific structural and compositional characteristics, represented by the formula aLi(Li1/3Mn2/3)O2.(1−a)LiMO2, where M is a transition metal element, and optimized parameters such as integral breadths, peak ratios, and molar ratios of Ni, Co, and Mn, which enhance the stability and performance of the battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium-rich cathode active material is used to increase discharge capacity, then the discharge capacity per unit mass is improved, but the cycle characteristics deteriorate due to sudden decrease after 50 cycles
Solution Approach 1:
The patent applies parameter changes by precisely controlling the stoichiometric ratios of Li, Mn, Ni, Co, and other elements in the cathode active material formula Li1+aMn2-x-yNixCoyAlzO2. By optimizing parameters such as the Li excess amount (a), Ni content (x), Co content (y), and Al content (z), the patent achieves both high discharge capacity and good cycle characteristics, resolving the contradiction between capacity and reliability.
Solution Approach 2:
The patent uses composite materials by combining multiple transition metal elements (Mn, Ni, Co, Al) in specific proportions within the spinel crystal structure. This composite approach leverages the advantages of each element: Mn provides high capacity, Ni enhances voltage, Co improves stability, and Al strengthens structural integrity, thereby achieving both high discharge capacity and excellent cycle characteristics.
2Duration of action of moving object
If the charge and discharge cycle is conducted more than 50 times, then the battery operates longer, but the discharge capacity suddenly decreases
Solution Approach 1:
The patent applies beforehand cushioning by incorporating Al elements and optimizing the Li excess amount in advance to prevent structural degradation before it occurs. The Al elements strengthen the spinel structure and suppress Jahn-Teller distortion, while the controlled Li excess compensates for capacity fade during cycling, thereby maintaining discharge capacity over extended operational durations beyond 50 cycles.
3Quantity of substance
If high Li and Mn contents are increased to improve discharge capacity, then the discharge capacity is improved, but the cycle characteristics decrease
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of elements within the cathode material structure. Specifically, Al elements are positioned at specific sites in the spinel structure to locally strengthen the framework, while the Li excess is concentrated in specific layers to provide buffer capacity. This localized optimization allows high Li and Mn contents for high capacity while maintaining overall structural stability and cycle characteristics.
Data Source
AI summary
To provide a cathode active material with which it is possible to obtain a lithium ion secondary battery having a high discharge capacity and being excellent in the cycle characteristic even after 50 cycles; a positive electrode using it; and a lithium ion secondary battery. A cathode active material, which comprises a lithium-containing composite oxide represented by the formula: aLi(L1/3Mn2/3)O2.(1−a)LiMO2 wherein M is at least one transition metal element selected from Ni, Co and Mn, and 0<a<1; wherein when the lithium-containing composite oxide is electrochemically oxidized to a potential of 4.5 V vs. Li/Li+, in an X-ray diffraction pattern, the integral breadth of a peak of (003) plane assigned to a crystal structure with space group R-3m is at most 0.38 deg, and the integral breadth of a peak of (104) plane assigned to a crystal structure with space group R-3m is at most 0.54 deg.