Li-Rich Cathode Oxide Surface Chemistry for Capacity Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional lithium transition metal composite oxides face challenges in achieving high capacity and maintaining capacity retention due to transition metal migration during charging and discharging, as well as oxygen desorption issues, particularly in Li-rich composite oxides with O3 and O2 structures.
Innovation Solution
A lithium transition metal composite oxide with a main O2 structure, represented by Li α [Li x Mn y Co z Me (1-x-y-z]O 2, where Co and Mn molar ratios at the surface are unevenly distributed to suppress oxygen desorption and enhance capacity, with Co2/Co1 ranging from 1.2 to 6.0 and Mn2/Mn1 from 0.5 to 1.0, achieved through controlled synthesis methods like ion exchange and surface coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Li-rich lithium transition metal composite oxide with O3 structure is used, then high capacity can be achieved, but transition metal migration occurs during charging and discharging which hinders Li movement
Solution Approach 1:
The patent applies local quality by creating an asymmetric concentration distribution of Co and Mn elements between the surface and interior of the composite oxide particles. The surface region has a different compositional ratio compared to the interior, with specific Co concentration at the surface (Co1) and different Co concentration in the interior (Co2), where Co1/Co2 falls within 0.1 to 10. This localized compositional variation suppresses transition metal migration at the surface while maintaining high capacity in the interior, thereby resolving the contradiction between capacity and cycle characteristics.
2Reliability
If a conventional Li-rich lithium transition metal composite oxide with 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 applies parameter changes by precisely controlling the Co concentration ratio between surface and interior (Co1/Co2 within 0.1 to 10) and the overall Li excess parameter (δ). By adjusting these compositional parameters, the material achieves suppression of transition metal migration (improving cycle characteristics) while preventing oxygen desorption (maintaining high capacity). The specific parameter ranges optimize both stability and capacity simultaneously.
3Quantity of substance
If lithium content is increased to achieve high capacity, then capacity retention rate deteriorates due to structural instability during charge/discharge cycles
Solution Approach 1:
The patent applies local quality by creating compositional gradients where the surface and interior have different Li and transition metal ratios. The surface region with controlled Co concentration (Co1) provides structural stability during cycling, while the interior region with different composition (Co2) maintains high Li content for capacity. This localized differentiation allows the material to achieve both high capacity and good capacity retention by distributing functional roles across different regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a secondary battery with improved capacity and cycle characteristics, demonstrating higher discharge capacity and better retention rates compared to conventional materials.
Implementation Method 1
achieved through controlled synthesis methods like ion exchange and surface coating
Data Source
Figure 1
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.