Core-Shell Cathode Material with Differential Porosity for Ni-Rich Stability
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Solution Overview
Problem
Positive electrode materials with high levels of nickel face issues such as fast capacity decay, structural instability, and safety risks due to phase transitions, lithium ion distribution disorders, and electrolyte oxidation, which affect the performance and safety of lithium-ion batteries.
Innovation Solution
A positive electrode material is designed with a core and shell structure where the core has a higher porosity than the shell, facilitating lithium ion transport and enhancing structural stability by allowing for increased pore volumes under pressure, thereby improving cycling performance and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the porosity of the positive electrode material is increased to facilitate lithium ion transport, then the rate performance is improved, but the structural stability deteriorates due to increased voids and potential particle fracture
Solution Approach 1:
The positive electrode material is segmented into a core-shell structure where the core region has high porosity for fast lithium ion transport and the shell region has lower porosity for structural stability. This spatial segmentation allows both high rate performance and structural integrity to coexist.
Solution Approach 2:
Different regions of the particle are assigned different porosity characteristics: the core has high porosity (50-90%) to facilitate rapid lithium ion diffusion, while the shell has lower porosity (10-50%) to maintain structural stability and resist particle fracture during cycling.
2Quantity of substance
If the nickel level in the ternary material is increased to improve energy density, then the capacity is enhanced, but the safety and structural stability deteriorate due to phase transitions and internal stress
Solution Approach 1:
The particle is divided into core and shell regions with different nickel concentrations. The core contains high nickel content (0.90-0.98) for high energy density, while the shell has lower nickel content (0.80-0.95) to reduce internal stress and prevent particle fracture during lithium insertion/extraction cycles.
Solution Approach 2:
The nickel distribution is optimized locally: the core region maintains high nickel content to maximize energy density, while the shell region has reduced nickel content and increased protective doping elements to enhance structural stability and safety during cycling.
3Stability of the object's composition
If a dense shell structure is formed to improve structural stability, then the safety is enhanced, but the lithium ion transport capability deteriorates due to restricted diffusion channels
Solution Approach 1:
The shell is designed with controlled porosity (10-50%) that balances structural stability and lithium ion transport. Unlike a completely dense shell, this partially porous structure maintains mechanical integrity while preserving sufficient diffusion channels for lithium ion transport.
Solution Approach 2:
The shell contains controlled porosity with pore sizes of 0.003-0.03 μm that provide diffusion pathways for lithium ions while maintaining structural stability. The porous shell prevents complete densification, allowing both safety and rate performance to be achieved.
4Duration of action of stationary object
If the porosity is increased to reduce internal stress and prevent particle fracture, then the cycling performance is improved, but the manufacturing precision deteriorates due to difficulty in controlling pore structure
Solution Approach 1:
The porosity control is segmented into two distinct regions with different target porosity ranges. The core is designed with high porosity (50-90%) while the shell has controlled lower porosity (10-50%), making the overall porosity control more manageable than attempting to uniform porosity throughout the entire particle.
Solution Approach 2:
The core-shell structure with differential porosity is formed during the co-precipitation process itself, preliminarily establishing the porous framework before final calcination. This preliminary structuring guides the subsequent heat treatment and ensures consistent pore formation during manufacturing.
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 with differential porosity improves lithium ion transport, reduces stress-induced cracks, and enhances structural stability, leading to improved rate and cycling performance of lithium-ion batteries.
Implementation Method 1
the core has a porosity greater than that of the shell... the voids between the primary particles in the core are greater than those between the primary particles in the shell
Implementation Method 2
subjecting a solution of soluble salts containing Ni, Co and M and a dispersion containing D to the first co-precipitation, to form the core of the secondary particles; subjecting a solution of soluble salts containing Ni, Co and M and a dispersion containing G to a second co-precipitation in the presence of the core in step (1), to form the shell on the core
Implementation Method 3
contacting the secondary particles obtained in step (2) with a lithium source material at 300-900°C to obtain the positive electrode material
Data Source
Figure 1~2
Figure 3~4
AI summary
The present disclosure relates to a positive electrode material and the preparation method therefor. The positive electrode material in accordance with the present disclosure is in a form of secondary particles having a core and a shell, wherein the core has a porosity greater than that of the shell. By forming larger particle voids in the cores of secondary particles, the present invention may reduce the stress concentration due to the volume deformation during the lithium ion intercalation/deintercalation, and improve the stability, rate performance, safety and cycle life of the material, which makes the material particularly suitable for lithium-ion batteries of high energy density.