Mg/F-Doped LiCoO2 Cathode Particles for Cycle-Stable Capacity
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving high output performance, discharge capacity, cycle performance, reliability, safety, and cost, with existing positive electrode active materials prone to capacity degradation and structural breakdown during charge and discharge cycles.
Innovation Solution
A positive electrode active material particle composed of magnesium, fluorine, and lithium cobalt oxide, with specific layer substitutions and crystal structures, including a layered rock-salt structure and rock-salt crystal structures in the surface and inner portions, respectively, to enhance stability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional positive electrode active materials are used, then the battery can operate, but discharge capacity decreases and structural breakdown occurs during charge and discharge cycles
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core maintains the original layered rock-salt crystal structure for high capacity, while the outer shell transforms to a stable rock-salt crystal structure for structural protection. This spatial differentiation of material properties resolves the contradiction between capacity and stability.
Solution Approach 2:
The patent creates a composite material system combining two crystal structures (layered rock-salt and rock-salt) within a single particle. The composite structure allows the inner portion to provide high discharge capacity while the outer portion provides structural stability during cycling.
2Quantity of substance
If high capacity positive electrode materials are used, then discharge capacity increases, but structural breakdown occurs during cycling
Solution Approach 1:
The patent segments the positive electrode active material particle into distinct inner and outer portions with different crystal structures. The inner portion is optimized for high discharge capacity while the outer portion is optimized for structural integrity, resolving the contradiction between quantity and strength.
Solution Approach 2:
The patent creates a shell-like outer portion with rock-salt crystal structure that envelops the inner core. This shell structure provides mechanical protection and structural flexibility that prevents breakdown while allowing the inner high-capacity material to function.
3Reliability
If existing positive electrode materials are used, then the battery can function, but safety and reliability are insufficient
Solution Approach 1:
The patent changes the crystal structure parameter of the positive electrode material from a single-phase layered rock-salt structure to a two-phase composite structure with both layered rock-salt and rock-salt phases. This parameter change enhances safety and reliability while the complexity is managed through controlled synthesis.
Data Source
AI summary
A lithium-ion secondary battery with favorable charge and discharge cycle performance is provided. The lithium-ion secondary battery includes a positive electrode and a negative electrode. The positive electrode includes positive electrode active material particles containing magnesium, fluorine, and lithium cobalt oxide. When a surface of the positive electrode active material particle observed in a cross-sectional STEM image of a plane where lithium is inserted and extracted is a first layer, the positive electrode active material particle includes a region where magnesium is substituted for part of cobalt sites in a second layer to a sixth layer. Magnesium has a function of relieving a distortion between the layered rock-salt crystal structure and the rock-salt crystal structure, and fluorine has a function of promoting transfer of the magnesium into an inner portion of the positive electrode active material particle.