Overlithiated Cathode Material Structure for Capacity-Stability Balance
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Solution Overview
Problem
Conventional overlithiated lithium manganese-based oxides suffer from stability degradation and low discharge capacity and rate capability due to excessive lithium and manganese, which limits their commercial viability as positive electrode active materials in lithium secondary batteries.
Innovation Solution
A positive electrode active material is developed, comprising an overlithiated lithium manganese-based oxide with a solid solution structure containing phases of C2/m and R3-m space groups, where the proportions of these phases vary across different regions, optimizing nickel content to mitigate instability and enhance discharge capacity and rate capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If an overlithiated lithium manganese-based oxide with excessive lithium and manganese is used to increase discharge capacity, then the theoretical capacity is improved, but stability degradation occurs due to cation mixing and crystal structure instability
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region has a different phase composition (C2/m and R3-m phases) compared to the shell region. The shell has a higher proportion of R3-m phase which provides structural stability, while the core contains the overlithiated composition for high capacity. This spatial differentiation allows the material to simultaneously achieve high discharge capacity and stability by assigning different functional characteristics to different regions of the particle.
Solution Approach 2:
The patent creates a composite material system by forming a solid solution of C2/m and R3-m phases within the lithium manganese-based oxide. This composite phase structure combines the high capacity characteristics of the C2/m phase with the structural stability of the R3-m phase, resolving the contradiction between capacity and stability through phase composition rather than pure phase formation.
2Productivity
If nickel content is increased to improve rate capability, then the electrical conductivity is improved, but cation mixing between lithium and nickel increases causing instability
Solution Approach 1:
The patent applies local quality by concentrating nickel in the core region where it can enhance electrical conductivity and rate capability without excessive cation mixing. The shell region has reduced nickel content and higher proportion of R3-m phase, which minimizes cation mixing and maintains structural stability. This spatial distribution of nickel allows the material to achieve both high rate capability and stability.
Solution Approach 2:
The patent changes the phase composition parameter by forming a solid solution of C2/m and R3-m phases. The R3-m phase has a lower tendency for cation mixing compared to the C2/m phase. By adjusting the proportion of R3-m phase in the shell region, the patent reduces cation mixing while maintaining acceptable rate capability, thus resolving the contradiction between rate capability and stability.
3Quantity of substance
If lithium content is increased beyond the stoichiometric ratio to achieve high capacity, then the discharge capacity is improved, but the crystal structure becomes unstable due to excessive lithium
Solution Approach 1:
The patent applies local quality by concentrating the excessive lithium content in the core region where it contributes to high discharge capacity. The shell region has a more stoichiometric composition with higher proportion of R3-m phase, which maintains crystal structure stability. This spatial separation allows the material to tolerate excessive lithium without compromising overall structural stability.
Solution Approach 2:
The patent creates a composite phase structure where C2/m and R3-m phases coexist in a solid solution. The R3-m phase acts as a stabilizing component that compensates for the structural instability introduced by excessive lithium in the C2/m phase. This phase composite allows the material to maintain crystal structure stability while achieving high capacity through overlithiation.
Data Source
AI summary
The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, to a positive electrode active material, which includes an overlithiated lithium manganese-based oxide, which is a solid solution with a phase belonging to a C2/m space group and a phase belonging to an R3-m space group and in which stability degradation caused by excessive amounts of lithium and manganese in the lithium manganese-based oxide is mitigated and/or prevented because there are regions with different proportions of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group in the lithium manganese-based oxide, and a lithium secondary battery including the same.