Gradient-Morph LiCoO2 Core-Shell Cathode for High-Voltage Stability
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Solution Overview
Problem
Lithium cobalt oxide (LCO) cathodes in lithium-ion batteries suffer from cycling stability issues at high charging voltages due to oxygen anion and cation-redox reactions, leading to oxygen loss and irreversible phase transformations, which limit their energy density and capacity.
Innovation Solution
A cathode particle design featuring a core-shell structure where the core is a single-crystalline LiCoO2 and the outer layer is a lattice-coherent LiMn1.5Ni0.5O4 shell, preventing oxygen anion redox and loss, and facilitating high-voltage cycling stability by maintaining oxygen in a solid phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LCO cathodes are operated at high charging voltages (>4.5 V) to increase energy density, then volumetric energy density is improved, but cycling stability deteriorates due to oxygen loss and irreversible phase transformations
Solution Approach 1:
The LCO cathode is segmented into a core-shell structure where the core contains the high-energy LCO material and the shell contains a stable spinel coating material (LiMn1.5Ni0.5O4 or similar). This segmentation allows the core to operate at high voltage for high energy density while the shell provides structural stability and prevents oxygen loss during cycling.
Solution Approach 2:
The invention uses composite materials by combining LCO (for high energy density) with spinel-structured LiMn1.5Ni0.5O4 or LiMnAlO4 (for structural stability). The composite core-shell structure enables the cathode to simultaneously achieve high volumetric energy density (>3400 Wh/L) and excellent cycling stability by leveraging the complementary properties of the two materials.
2Reliability
If the outer layer completely prevents oxygen anion redox to stabilize the structure, then cycling stability is improved, but energy density is reduced due to suppressed redox activity
Solution Approach 1:
The invention applies local quality by creating a gradient morphology where the outer layer composition varies with radial distance from the core. The spinel content increases toward the surface while the core retains pure LCO with full oxygen redox activity. This gradient structure allows the core to maximize energy density through oxygen anion redox while the outer shell progressively prevents oxygen loss at the surface, achieving both high energy density and cycling stability.
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 core-shell structure achieves a stable cyclic volumetric energy density exceeding 3400 Wh/L and retains capacity up to 2906 Wh/L after 300 cycles, significantly improving cycling stability and energy density compared to uncoated LCO.
Implementation Method 1
The core facilitates oxygen anion redox activity and M cation redox activity. The outer layer substantially prevents oxygen anion redox and oxygen loss in the outer layer.
Implementation Method 2
The core facilitates oxygen anion redox activity and M cation redox activity.
Implementation Method 3
The outer layer's first crystal structure may be at least one of a layered crystal structure or a spinel crystal structure. The core of the cathode particle may have a second crystal structure that is a layered crystal structure. The two sublattices having a mismatch of about 5% to about 5%.
Implementation Method 4
During step (A), oxygen in the core of the particle is oxidized, and oxygen proximate to and at the surface of the particle is substantially prevented from being oxidized.
Implementation Method 5
During step (B), oxygen in the core of the particle is reduced, and oxygen proximate to and at the surface of the particle is substantially prevented from being reduced.
Data Source
AI summary
A cathode particle has a core and an outer layer. The core includes a lithium (Li) transition metal (M) oxide. The outer layer is disposed conformally around and substantially encloses the core. The core facilitates oxygen anion redox activity and M cation redox activity. The outer layer substantially prevents oxygen anion redox and oxygen loss in the outer layer. The outer layer of the cathode particle may have a first crystal structure. The outer layer's first crystal structure may be at least one of a layered crystal structure or a spinel crystal structure. The core of the cathode particle may have a second crystal structure that is a layered crystal structure. The core may have a single-crystalline structure. The outer layer may be LiMn0.75Ni0.25O2 or LiMn0.5Ni0.5O4.