Li-Rich Cathode Oxide Surface Co Enrichment for Cycle Stability
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Solution Overview
Problem
Existing Li-rich lithium transition metal composite oxides for secondary batteries face challenges in achieving high capacity due to transition metal migration during charging and discharging, and oxygen desorption, which affects cycle characteristics.
Innovation Solution
A positive electrode active material with a lithium transition metal composite oxide represented by the formula Liα[LixMnyCozMe(1-x-y-z)]O2, where Me includes Ni, Fe, Ti, Bi, and Nb, and the Co molar ratio at the surface (Co2) to the Co molar ratio in the entire oxide (Co1) satisfies 1.2 < (Co2/Co1) < 6.0, is used. This material has at least one crystal structure selected from O2, T2, and O6 structures, allowing for Co to be unevenly densely distributed at the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Li-rich lithium transition metal composite oxide having an O3 structure is used, then lithium content in the transition metal layer can be increased, but transition metal migration occurs during charging and discharging which hinders lithium movement and reduces capacity
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of cobalt atoms within the crystal structure. The general formula Liα[LixMnymCozMe(1-x-y-z)]O2 with the constraint 0.05 < z/(x+y+z) < 0.25 indicates that cobalt is preferentially distributed in specific regions (transition metal layers) rather than uniformly throughout the material. This localized enrichment of cobalt in the transition metal layer suppresses transition metal migration during charging/discharging while maintaining high lithium content, thus resolving the contradiction between increasing lithium quantity and maintaining capacity retention reliability
2Reliability
If a conventional Li-rich lithium transition metal composite oxide having an O2 structure is used, then transition metal migration can be suppressed, but oxygen desorption occurs during charging which limits capacity improvement
Solution Approach 1:
The patent employs parameter changes by precisely controlling the compositional parameters in the general formula Liα[LixMnymCozMe(1-x-y-z)]O2. Specifically, the constraints 0.05 < z/(x+y+z) < 0.25 for cobalt concentration and 0.95 < α < 1.05 for lithium excess ratio define an optimized parameter range. These parameter adjustments enable the material to achieve both suppressed transition metal migration (good cycle characteristics) and enhanced battery capacity by preventing oxygen desorption, thus resolving the contradiction between reliability and quantity of substance
3Quantity of substance
If lithium content in the transition metal layer is increased to achieve high capacity, then more lithium can be stored, but transition metal migration increases which hinders lithium movement
Solution Approach 1:
The patent introduces cobalt atoms as an intermediary element in the transition metal layer. The specific concentration range 0.05 < z/(x+y+z) < 0.25 indicates cobalt acts as a mediating species that stabilizes the crystal structure during lithium insertion/extraction. This intermediary cobalt prevents transition metal migration that would otherwise block lithium pathways, thereby maintaining lithium mobility even at high lithium content, resolving the contradiction between lithium storage capacity and lithium mobility
Data Source
AI summary
This lithium transition metal composite oxide, which configures a secondary battery positive electrode active material, is a composite oxide represented by general formula Liα[LixMnyCozMe(1-x-y-z)]O2 (in the formula, Me is at least one species selected from Ni, Fe, Ti, Bi and Nb, and 0.5<α<1, 0.05<x<0.25, 0.4<y<0.7, and 0<z<0.25), and has at least one crystal structure selected from the O2 structure, the T2 structure and the O6 structure. The ratio (Co2/Co1) of the Co molar fraction (Co2) in the surface of the oxide to the Co molar fraction (Co1) in the entire lithium transition metal composite oxide is 1.2<(Co2/Co1)<6.0.