Lithium-Rich Cathode Core-Shell Gradient for Stable Cycling
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Solution Overview
Problem
Lithium-nickel-manganese-cobalt oxide cathode active materials for secondary batteries face issues with rate capability, cycle life, and voltage decay due to phase transitions during life cycling, leading to unsatisfactory discharge capacity and structural instability.
Innovation Solution
A cathode active material with a layered structure of overlithiated oxide, where the core and shell of secondary, primary, and crystallite particles have distinct oxidation states of nickel, cobalt, and manganese, forming a core-shell structure with a concentration gradient, enhancing lithium ion mobility and structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If overlithiated layered oxide is applied to increase reversible capacity, then charge/discharge capacity is improved, but phase transition occurs during life cycling leading to voltage decay and cycle life deterioration
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the shell region has a different oxidation state composition (Mp+/M ratio) than the core. This local differentiation allows the shell to suppress phase transitions and protect the overlithiated core material, thereby maintaining both high capacity and structural stability during cycling. The shell acts as a protective layer with tailored chemical properties that prevent harmful phase changes while preserving the high-capacity characteristics of the overlithiated interior.
2Ease of manufacture
If conventional Li(NixCoyMnz)O2 is used to reduce cost, then manufacturing cost is reduced, but rate capability and cycle life at high temperatures are poor
Solution Approach 1:
The patent applies parameter changes by modifying the oxidation state parameters (Mp+/M ratios) of transition metals in the core-shell structure. By controlling the Ni2+/Ni3+, Mn3+/Mn4+, and Co2+/Co3+ ratios differently in the core and shell regions, the material achieves improved electronic conductivity and structural stability. This parameter optimization enables better rate capability and high-temperature performance while maintaining cost-effectiveness through controlled metal composition.
3Reliability
If phase transition is suppressed to improve cycle life, then structural stability is improved, but lithium ion mobility may be affected
Solution Approach 1:
The patent applies segmentation by dividing the particle into core and shell regions with distinct functional roles. The core region maintains the overlithiated structure for high capacity, while the shell region provides structural stability to suppress phase transitions. This segmented architecture allows lithium ions to move freely through the core while the shell provides protective structural framework, thereby achieving both high ion mobility and improved cycle life without compromising either property.
Data Source
AI summary
A positive electrode active material for a secondary battery according to an embodiment of the present invention comprises a lithium composite oxide represented by chemical formula 1 and containing a layer-structured lithium excess oxide, wherein the lithium composite oxide comprises a secondary particle; the secondary particle comprises at least one primary particle; the primary particle comprises at least one crystallite; at least one selected from the secondary particle, the primary particle, and the crystallite comprises a core and a shell occupying at least a portion of the surface of the core; and when the number of moles of at least one element having an oxidation number, selected from among nickel (Ni), cobalt (Co) and manganese (Mn) relative to the total number of moles of M1 and M2 in chemical formula 1 is Mp+/M, the Mp+/M in the core differs from that in the shell in the secondary particle: [Chemical formula 1] rLi2M1O3(1-r) LiaM2O2.