Lithium Transition Metal Oxide Cathode for High-Rate Battery Performance
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Solution Overview
Problem
Lithium secondary batteries face challenges with cathode active materials that have limited structural stability, low capacity, and poor electrochemical properties due to the conventional approach of adjusting the average oxidation number of transition metals to +3, which leads to issues like Ni2+ intercalation into the lithium layer and decreased performance under high-rate charge/discharge conditions.
Innovation Solution
A lithium transition metal oxide with an α-NaFeO2 layered crystal structure, where the transition metal blend of Ni and Mn has an average oxidation number higher than +3, with a molar ratio of Ni to Mn greater than 1 and a lower ratio of Ni2+ to Mn4+, resulting in a stable layered structure and improved electrochemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the average oxidation number of transition metals is adjusted to +3, then the structural stability is improved, but the capacity and electrochemical properties deteriorate
Solution Approach 1:
The patent changes the oxidation number parameter from the conventional +3 to a range of +3.01 to +3.5, which fundamentally alters the electronic structure and ion mobility characteristics of the cathode material, enabling simultaneous achievement of structural stability and high capacity
Solution Approach 2:
The patent uses a composite cathode material containing Li, Ni, and Mn elements with specific compositional ratios (0.97≤x≤1.03 and 0.4≤y≤0.6), creating a composite structure that combines the structural stability benefits of Mn with the high capacity benefits of Ni at optimized ratios
2Reliability
If Ni2+ is present in the structure, then the electrochemical activity is improved, but Ni2+ intercalates into the lithium layer causing structural degradation
Solution Approach 1:
By increasing the average oxidation number to +3.01-+3.5, the patent reduces the concentration of Ni2+ ions and increases Ni3+ content, which decreases the ionic radius and reduces the tendency of Ni ions to migrate into the lithium layer, thereby maintaining layered structure stability while preserving electrochemical activity
3Quantity of substance
If the molar ratio of Ni to Mn is increased, then the battery capacity is improved, but the structural stability deteriorates
Solution Approach 1:
The patent optimizes the Ni/Mn ratio parameter within the range 0.4≤y≤0.6, which balances the high capacity contribution of Ni with the structural stability contribution of Mn, achieving optimal performance when combined with the elevated oxidation number
4Ease of manufacture
If conventional cathode materials are used, then the manufacturing cost is reduced, but the high-rate charge/discharge characteristics are poor
Solution Approach 1:
By changing the oxidation number parameter to +3.01-+3.5, the patent enhances lithium ion mobility and electrode reaction kinetics, enabling superior high-rate charge/discharge characteristics while maintaining compatibility with conventional manufacturing processes and cost-effective Ni-Mn composite materials
Data Source
AI summary
Provided is a lithium transition metal oxide having an α-NaFeO2 layered crystal structure, as a cathode active material for lithium secondary battery, wherein the transition metal includes a blend of Ni and Mn, an average oxidation number of the transition metals except lithium is more than +3, and the lithium transition metal oxide satisfies Equations 1 and 2 below:1.0<m(Ni)/m(Mn) (1)m(Ni2+)/m(Mn4+)<1 (2)wherein m(Ni)/m(Mn) represents a molar ratio of nickel to manganese and m(Ni2+)/m(Mn4+) represents a molar ratio of Ni2+ to Mn4+.The cathode active material of the present invention has a uniform and stable layered structure through control of oxidation number of transition metals to a level higher than +3, in contrast to conventional cathode active materials, thus advantageously exerting improved overall electrochemical properties including electric capacity, in particular, superior high-rate charge/discharge characteristics.