Nickel-Rich Cathode Core-Shell Coating for Cycling Stability
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Solution Overview
Problem
Current lithium ion secondary battery cathode materials, such as LiNiO2, face challenges with cycling stability and thermal stability due to the generation of Ni4+ ions, which react with the electrolyte, leading to increased inner resistance and reduced battery life, and conventional surface coatings often compromise conductivity and capacity.
Innovation Solution
A nickel-rich cathode material with a bulk portion of lithium-nickel composite oxide and a thin coating portion of lithium transition metal oxide with no electrochemical activity at 4.2V, providing physical isolation and maintaining high capacity and thermal stability, is developed. The coating portion acts as a protective layer, preventing the bulk material from reacting with the electrolyte and ensuring stable lithium ion migration and electron conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiNiO2 is used as cathode material to achieve high capacity, then the specific capacity exceeds 200 mAh/g, but the cycling stability and thermal stability deteriorate due to Ni4+ reaction with electrolyte
Solution Approach 1:
The cathode material is segmented into a core region (Li1+δ[Ni1−x−yCoxAly]O2 providing high capacity) and a shell region (Li2MO3 or Li2MO4 providing stability), where each region performs its specialized function to resolve the contradiction between high capacity and cycling stability
Solution Approach 2:
A composite core-shell structure is constructed combining nickel-rich cathode material with high capacity and lithium transition metal oxide with high stability, creating a material that exhibits both high specific capacity and excellent cycling stability simultaneously
2Reliability
If surface coating is applied to improve cycling stability, then the contact between cathode material and electrolyte is reduced, but the conduction capability for lithium ions and electrons deteriorates
Solution Approach 1:
The shell coating is designed with specific thickness (0.1-5 nm) and composition (lithium transition metal oxide) to provide localized protection at the electrolyte interface while maintaining bulk conduction properties, ensuring cycling stability without compromising electron and lithium ion transport
3Quantity of substance
If the cathode material is charged to high voltage to achieve high capacity, then Ni4+ is generated which reacts with electrolyte, but the thermal stability and safety deteriorate
Solution Approach 1:
The stable lithium transition metal oxide shell is formed preliminarily on the cathode material surface to prevent Ni4+ from reacting with the electrolyte and generating heat, thereby maintaining thermal stability even when charged to high voltage for high capacity
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 solution achieves high charging-discharging rate, excellent cycling stability, and enhanced thermal stability, while maintaining high capacity and energy density, with the coating portion ensuring the cathode material remains inactive at 4.2V, preventing electrolyte reactions and maintaining electrochemical performance.
Implementation Method 1
the coating material works in two aspects. One aspect is the physical isolation, although the coating material cannot cover all the surface of the particle, the coating material can, to a certain extent, reduce the contact between the cathode material and the electrolyte
Implementation Method 2
ensuring stable lithium ion migration and electron conduction
Implementation Method 3
ensuring stable lithium ion migration and electron conduction
Data Source
AI summary
The present invention discloses a cathode material for lithium ion secondary battery. The cathode material is in the form of powder particles. The powder particle includes a bulk portion and a coating portion coated on the outer surface of the bulk portion. The bulk portion is formed of at least one first cathode material which is a lithium-nickel based composite oxide. The first cathode material has electrochemical activity and has high charging-discharging specific capacity at a charged voltage of 4.2V versus Li/Li+. The coating portion is formed of at least one second cathode material. The second cathode material has no electrochemical activity or has low charging-discharging specific capacity at a charged voltage of 4.2V versus Li/Li+. Lithium ion secondary battery using the cathode material has high energy density, cycling stability, security, and output power.