Ni-Mn Cathode Material Oxidation Control for High-Rate Lithium Batteries
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Solution Overview
Problem
Lithium secondary batteries face challenges with cathode active materials that have limited structural stability, high cost, and poor electrochemical properties due to the use of cobalt and manganese oxides, which affect their performance and price competitiveness.
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 specific molar ratio of Ni to Mn and Ni2+ to Mn4+, ensuring a stable layered structure and improved electrochemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium cobalt composite oxide (LiCoO2) is used as cathode active material, then long lifespan and good charge/discharge characteristics are achieved, but structural stability is low and cost is high
Solution Approach 1:
The patent uses a composite material system consisting of LiCoO2 coated with LiMn1-xNixO2. This composite approach combines the advantages of both materials: LiCoO2 provides good charge/discharge characteristics while the LiMn1-xNixO2 coating layer enhances structural stability and reduces cost by replacing some cobalt with manganese and nickel.
Solution Approach 2:
The patent replaces expensive cobalt with cheaper manganese and nickel in the coating layer. By using LiMn1-xNixO2 with x=0.01-0.06, the formulation reduces cobalt content while maintaining performance, making the cathode material more cost-effective.
2Stability of the object's composition
If lithium manganese oxides (LiMnO2, LiMn2O4) are used as cathode active material, then thermal stability and low cost are achieved, but capacity and low-temperature characteristics are poor
Solution Approach 1:
The patent creates a composite structure where LiMn1-xNixO2 coating is applied on LiCoO2 core. The nickel addition (x=0.01-0.06) to the manganese-based coating material improves electronic conductivity and lithium ion mobility, thereby enhancing capacity and low-temperature performance while retaining the thermal stability of manganese oxides.
Solution Approach 2:
The patent optimizes the nickel content parameter (x=0.01-0.06) in the LiMn1-xNixO2 coating to achieve the best balance between capacity and thermal stability. This parameter optimization allows sufficient nickel to improve conductivity without excessive replacement of manganese that would compromise thermal stability.
3Quantity of substance
If LiMnO2-based cathode active material is used, then low cost and superior discharge capacity are achieved, but synthesis difficulty and instability increase
Solution Approach 1:
The patent uses LiCoO2 as an intermediary core material that facilitates the synthesis process. The LiMn1-xNixO2 is applied as a coating layer on the LiCoO2 core, which simplifies synthesis compared to trying to directly synthesize stable LiMnO2 with equivalent performance. The core-shell structure acts as an intermediary approach that resolves the synthesis difficulty.
4Reliability
If cobalt content is increased to improve charge/discharge characteristics, then performance is enhanced, but cost increases due to natural resource limitations
Solution Approach 1:
The patent employs a composite structure with LiCoO2 core and LiMn1-xNixO2 coating where only a thin layer (0.5-5 μm) contains cobalt. This composite approach concentrates cobalt where it's most needed for charge/discharge characteristics while using cheaper manganese and nickel in the coating, significantly reducing overall cobalt content and cost.
Solution Approach 2:
The patent applies local quality by concentrating cobalt in the core region where it provides maximum benefit for charge/discharge characteristics, while the outer coating layer uses manganese and nickel. This localized distribution optimizes performance per unit cost of cobalt.
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 +3 or higher, and the lithium transition metal oxide satisfies Equations 1 and 2 below: 1.0<mNi/mMn mNi2+/Mn4+<1 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.