Core-Shell Lithium-Rich Cathode Material for Voltage Decay Control
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Solution Overview
Problem
Existing lithium-nickel-manganese-cobalt oxide cathode active materials suffer from unsatisfactory rate capability, poor cycle life characteristics, and voltage decay due to phase transition during life cycling, which hinder their practical application in lithium secondary batteries.
Innovation Solution
A cathode active material with a lithium composite oxide having a layered structure of overlithiated oxide, featuring a core-shell structure with varying [C2/m]/[R-3m] ratios and phase gradients, which suppresses phase transition and enhances 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 causing voltage decay and reduced cycle life
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface region has different compositional characteristics than the core. The surface is enriched with elements that have higher oxygen affinity (such as Al, Ti, B, or P) to specifically stabilize the surface structure and prevent phase transition, while the core maintains the overlithiated composition for high capacity. This local differentiation allows the material to simultaneously achieve high reversible capacity and stable cycle life.
Solution Approach 2:
The patent employs composite materials by combining the overlithiated layered oxide core with a surface layer containing elements having high oxygen affinity. This composite structure integrates the high capacity advantage of overlithiated materials with the structural stability provided by the surface layer, creating a material that exhibits both high reversible capacity and resistance to phase transition during cycling.
2Ease of manufacture
If conventional Li(NixCoyMnz)O2 is used, then cost is reduced due to small Co content, but rate capability and cycle life at high temperatures are poor
Solution Approach 1:
The patent applies local quality by concentrating the stabilizing elements specifically at the surface region rather than uniformly distributing them throughout the bulk material. This allows the core to maintain the cost-effective Li(NixCoyMnz)O2 composition while the surface layer provides the enhanced rate capability and high-temperature stability through localized structural reinforcement.
Solution Approach 2:
The patent employs parameter changes by modifying the surface composition parameters (elemental ratios, oxidation states) to create a surface layer with optimized properties for high-temperature stability and fast ion transport, while maintaining the bulk composition parameters that provide cost effectiveness. The surface layer parameters are specifically tuned to enhance electrical conductivity and structural stability without compromising the overall material composition.
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 below 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 any 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 crystal structure belonging to space group C2/m is designated as [C2/m], the crystal structure belonging to space group R-3m is designated as [R-3m], and the ratio of the crystal structure belonging to space group C2/m versus the crystal structure belonging to space group R-3m is designated as [C2/m]/[R-3m], the [C2/m]/[R-3m] of the core differs from that of the shell in the secondary particle: [chemical formula 1] rLi2M1O3·(1−r)LiaM2O2.