Core-Shell Positive Electrode Material for Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in maintaining high charge and discharge capacity, cycle performance, reliability, safety, and cost due to issues with the crystal structure of positive electrode active materials, which degrade with repeated charging and discharging.
Innovation Solution
A positive electrode active material composed of lithium, cobalt, nickel, magnesium, and oxygen, with a layered rock-salt crystal structure, where the outermost surface layer has a transition metal site layer and a lithium site layer alternately arranged, and includes a metal element with a larger atomic number than lithium, such as magnesium or cobalt, to enhance stability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional positive electrode active materials are used to achieve high charge and discharge capacity, then the charge and discharge capacity increases, but the cycle performance deteriorates due to crystal structure degradation
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core region contains a different crystal structure (monoclinic or triclinic) compared to the outer shell region (layered rock-salt). This local structural differentiation allows the core to provide stable lithium storage while the shell maintains high capacity, resolving the contradiction between capacity and cycle performance
Solution Approach 2:
The patent uses composite materials by combining two different crystal structures within a single positive electrode active material particle. The composite consists of an inner core with monoclinic or triclinic structure and an outer shell with layered rock-salt structure, leveraging the advantages of both structures to achieve high capacity and excellent cycle performance simultaneously
2Productivity
If the crystal structure is optimized for high capacity, then the charge and discharge capacity increases, but the structural stability deteriorates leading to capacity fade
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core region contains a different crystal structure (monoclinic or triclinic) compared to the outer shell region (layered rock-salt). This local structural differentiation allows the core to provide stable lithium storage while the shell maintains high capacity, resolving the contradiction between capacity and cycle performance
Solution Approach 2:
The patent applies beforehand cushioning by pre-forming a protective outer shell of layered rock-salt structure that stabilizes the crystal structure before cycling begins. This shell prevents structural degradation during charging and discharging, cushioning against capacity fade while maintaining high capacity
Data Source
AI summary
A positive electrode active material having a crystal structure that is unlikely to be broken by repeated charging and discharging is provided. A positive electrode active material with high charge and discharge capacity is provided. A positive electrode active material including lithium, cobalt, nickel, magnesium, and oxygen, in which the a-axis lattice constant of an outermost surface layer of the positive electrode active material is larger than the a-axis lattice constant of an inner portion and in which the c-axis lattice constant of the outermost surface layer is larger than the c-axis lattice constant of the inner portion. A rate of change between the a-axis lattice constant of the outermost surface layer and the a-axis lattice constant of the inner portion is preferably larger than 0 and less than or equal to 0.12, and a rate of change between the c-axis lattice constant of the outermost surface layer and the c-axis lattice constant of the inner portion is preferably larger than 0 and less than or equal to 0.18.