Core-Shell Positive Active Material for Lithium Battery
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Solution Overview
Problem
Current positive active materials for lithium batteries, such as transition metal oxides, have limited lifespan and electrical capacity due to structural changes during charging and discharging, leading to decreased capacity and voltage.
Innovation Solution
A core-shell structured over-lithiated lithium transition metal oxide is developed, where the shell layer is doped with a metal cation from Period 2 to Period 7 of the Periodic Table, enhancing the material's capacity and lifespan characteristics by suppressing capacity and voltage degradation during high voltage operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If transition metal oxides are used as positive active material, then high capacity can be achieved, but lifespan and voltage characteristics deteriorate due to structural changes during charging and discharging
Solution Approach 1:
The patent employs a core-shell composite structure where the positive active material consists of a Li2MO3-LiM'O2 composite oxide core surrounded by a protective shell layer. This composite structure combines the high capacity characteristics of the over-lithiated core with the structural stability and protection provided by the shell, resolving the contradiction between achieving high capacity and maintaining reliability during cycling.
Solution Approach 2:
The shell layer is selectively applied only to the surface region of the positive active material particles, creating a local quality difference between the core and shell. The shell provides protective functions (structural stability, preventing degradation) at the surface while the core maintains its high capacity characteristics, thus improving lifespan without sacrificing capacity.
2Reliability
If shell layer is added to form core-shell structure, then lifespan and voltage stability improve, but device complexity increases
Solution Approach 1:
The shell layer is designed as a thin film structure that can be applied conformally to the particle surface. This thin film approach provides the necessary protective functions (improving lifespan and voltage stability) while minimizing the additional material volume and structural complexity compared to bulk modifications.
Data Source
AI summary
A positive active material includes an over-lithiated lithium transition metal oxide having a core-shell structure, wherein a shell layer of the core-shell structure includes a metal cation.