Cobalt-Free Cathode Structure With Porous Middle Layer
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Solution Overview
Problem
Lamellar cobalt-free cathode materials for lithium-ion batteries exhibit low capacity, low first efficiency, and poor cycle stability due to degraded lithium diffusion kinetics and insufficient electrolyte infiltration.
Innovation Solution
A cathode material with a specific structure comprising an inner core, a middle layer with a reticulate loose and porous structure, and a shell layer, where the middle layer is distributed in a circular ring shape with a porosity greater than 20% and average pore diameter less than 1 μm, enhancing electrolyte infiltration and ion exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If cobalt element is removed from lamellar ternary system to reduce cost and eliminate safety risks, then material cost decreases and safety improves, but lithium diffusion kinetics degrade, causing low capacity and low first efficiency
Solution Approach 1:
The patent introduces a porous coating layer on the surface of cobalt-free cathode material particles. This porous structure provides channels for electrolyte infiltration, enhancing lithium ion diffusion kinetics while maintaining the cobalt-free composition for cost and safety benefits.
Solution Approach 2:
The patent creates a composite structure by coating cobalt-free cathode material particles with a porous material layer. This composite approach combines the cost and safety advantages of cobalt-free materials with the enhanced ion transport properties of porous structures.
2Quantity of substance
If charge cut-off voltage is increased to 4.4V to exert sufficient capacity, then capacity performance improves to be comparable to NCM material, but safety risks increase and side reactions of electrolyte increase
Solution Approach 1:
The porous coating layer enables efficient lithium ion transport at high voltages, allowing the material to achieve sufficient capacity at 4.4V while the porous structure also facilitates electrolyte distribution that mitigates side reactions.
Solution Approach 2:
The porous coating layer acts as a sacrificial protective layer that can be consumed or modified during initial cycles to form a stable interface, protecting the underlying cathode material during high-voltage operation.
3Productivity
If additional graphene coating process is applied to improve ionic conductivity and reduce side reactions, then first charge-discharge efficiency improves, but production cost increases
Solution Approach 1:
The patent uses a porous coating material that can be applied through simpler and more cost-effective processes compared to graphene coating, while achieving similar or better ionic conductivity and first efficiency improvements.
Solution Approach 2:
The porous coating layer provides a cost-effective alternative to expensive graphene, using readily available porous materials that deliver the necessary performance improvements without the high cost of advanced carbon materials.
4Productivity
If secondary particle structure with loose and porous middle layer is formed to enhance electrolyte infiltration, then first efficiency and rate capability improve, but tap density decreases
Solution Approach 1:
The patent introduces a porous middle layer in the secondary particle structure to enhance electrolyte infiltration and improve rate capability, while carefully controlling the porosity and distribution to minimize the impact on tap density.
Solution Approach 2:
The porous structure is localized to a middle layer within the secondary particle, rather than being uniformly distributed. This local porosity optimization allows improved ion transport where needed while maintaining denser regions that preserve tap density.
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 cathode material achieves high tap density, leading to improved first charge-discharge capacity, efficiency, rate capability, and capacity retention rate in lithium-ion batteries.
Implementation Method 1
the middle layer exhibits a reticulate loose and porous structure; the porosity of the middle layer is greater than or equal to 20%
Implementation Method 2
influenced by the degradation of lithium diffusion kinetics
Data Source
AI summary
A positive electrode material, a preparation method therefor, and an application thereof are disclosed. The cathode material is composed of secondary particles agglomerated by primary particles; wherein individual secondary particle contains an inner core structure, a middle layer, and a shell layer, in this order, along a direction from a center to a surface of the secondary particle; wherein the middle layer is distributed in a circular ring shape; and wherein the secondary particle has a structure of close packing of an inner core structure, loose and porous middle layer, and close packing of the shell layer.