Ni-Rich NCM Cathode Blend for Thermal Stability and Li-Ion Output
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Solution Overview
Problem
Ni-rich NCM-based lithium composite transition metal oxides face issues with thermal stability, increased resistance, and long Li ion diffusion paths due to over-calcination, leading to deteriorated output performance and surface rock-salt crystal structures.
Innovation Solution
A positive electrode material comprising a mixture of first and second single-particle-type lithium composite transition metal oxides with specific particle diameters and lithium-to-metal molar ratios, optimized through over-calcination, to enhance thermal stability and suppress side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If over-calcination is performed to minimize secondary particle interface and improve thermal stability, then thermal stability is enhanced, but Li ion diffusion path becomes longer and output performance deteriorates
Solution Approach 1:
The positive electrode active material is divided into multiple particles with different mean particle diameters (first particles: 3.5-6.0 μm, second particles: 6.5-9.0 μm). This segmentation allows smaller particles to provide short Li ion diffusion paths for high output performance, while larger particles contribute to thermal stability, resolving the contradiction between thermal stability and output performance caused by over-calcination.
2Quantity of substance
If nickel content is increased to enhance capacity, then capacity increases, but thermal stability deteriorates and side reactions increase
Solution Approach 1:
The invention uses particles with different mean particle diameters (local variation in size) to achieve different functional qualities: smaller particles (3.5-6.0 μm) optimize for capacity and Li ion diffusion, while larger particles (6.5-9.0 μm) enhance thermal stability. This local quality differentiation allows high nickel content for capacity while maintaining thermal stability through appropriate particle size distribution.
3Reliability
If over-calcination is performed to suppress side reactions, then resistance from side reactions decreases, but surface rock-salt crystal structure forms and output performance deteriorates
Solution Approach 1:
The positive electrode active material consists of multiple particles with different mean particle diameters. Smaller particles (3.5-6.0 μm) maintain better crystal structures and shorter Li ion diffusion paths for high output performance, while the overall distribution suppresses side reactions. This segmentation prevents the formation of extensive surface rock-salt structures that occur in uniformly over-calcined materials.
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 improves thermal stability, reduces resistance, and enhances output performance by optimizing particle size and lithium content, addressing the issues of long Li ion diffusion paths and rock-salt crystal structures.
Implementation Method 1
electric energy is produced by a redox reaction when the lithium ions are intercalated/deintercalated into/from the positive electrode and the negative electrode
Implementation Method 2
attempts have been made to improve the deterioration in thermal stability and the increase in side reactions and resistance by minimizing the interface of secondary particles through over-calcination by increasing the calcining temperature when a positive electrode active material is prepared
Data Source
AI summary
The present invention relates to a positive electrode material for a secondary battery, the positive electrode material including a first positive electrode active material and a second positive electrode active material, the first positive electrode active material and the second positive electrode active material being single particle types and lithium composite transition metal oxides including nickel, cobalt, and manganese and having a nickel content accounting for 60 mol% or more of total metals except for lithium, wherein the first positive electrode active material has a mean particle diameter (D50) of 3 µm or less and a molar ratio (Li/M) of lithium to the metals (M) except for lithium of 1.10 to 1.20, and the second positive electrode active material has a mean particle diameter (D50) of greater than 3 µm and a molar ratio (Li/M) of lithium to the metals (M) except for lithium of 1.00 to 1.13.