Single-Crystal Cathode Material With Low Lattice Strain
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Solution Overview
Problem
Current single-crystal cathode materials for lithium ion batteries face challenges such as high lattice strain, slow lithium ion diffusion, and poor rate performance due to internal lattice microstress and uneven element distribution.
Innovation Solution
A single-crystal cathode material with a chemical formula of LixNiaCobMncNdO2 is developed, where the lattice strain is reduced to less than 0.2%, and the distribution uniformity of Ni, Co, and Mn elements is improved, leading to enhanced lithium ion diffusion coefficients and reduced Direct Current Resistance (DCR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monocrystalline ternary material is used to eliminate grain boundaries and inhibit cracking, then cycling performance is improved, but diffusion path of Li becomes long causing slow transmission power and poor rate performance
Solution Approach 1:
The cathode material is designed as a composite structure with primary single crystal particles (1-5 μm) agglomerated to form secondary particles (10-20 μm). This segmentation allows the material to combine the advantages of single crystals (no grain boundaries, high cycling stability) with shorter diffusion paths at the primary particle level, resolving the contradiction between cycling performance and rate performance.
Solution Approach 2:
The patent employs a nested structure where primary single crystal particles are embedded within secondary particle aggregates. The primary particles maintain their single crystal integrity for excellent cycling performance, while the secondary particle formation creates a hierarchical structure that facilitates Li ion transport. This nested architecture effectively addresses both the cycling stability and rate performance requirements.
2Stability of the object's composition
If sintering is performed at high temperature to form single-crystal cathode material, then crystallinity is improved, but uneven growth rate causes concentrated stress and internal lattice microstress cracks
Solution Approach 1:
The patent uses a co-precipitated hydroxide precursor with uniformly distributed Ni, Co, and Mn elements before sintering. This preliminary uniform distribution of elements ensures that during high-temperature sintering, the single crystals grow evenly without concentrated stress or internal lattice microstress cracks, while still achieving high crystallinity and reduced lattice strain (<0.2%).
Solution Approach 2:
The patent optimizes sintering parameters including temperature (900-950°C), time (12-24 hours), and atmosphere control to achieve uniform crystal growth. By carefully controlling these parameters, the material achieves high crystallinity with minimal internal stress and lattice strain, resolving the contradiction between crystallinity and internal stress.
3Speed
If element distribution in ternary material is improved to reduce lattice strain, then lithium ion diffusion coefficients are increased, but manufacturing precision requirements are increased
Solution Approach 1:
The patent employs a co-precipitation method to create a hydroxide precursor where Ni, Co, and Mn elements are uniformly distributed at the molecular level before sintering. This preliminary uniform distribution is maintained through controlled sintering, achieving standard deviation of element content ≤0.03. This approach enables high lithium ion diffusion coefficients while managing manufacturing precision through a controlled chemical process.
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 resulting single-crystal cathode material exhibits improved rate performance, reduced impedance, and enhanced cycling stability due to the reduced lattice strain and improved element distribution, leading to better structural stability and electrochemical performance.
Implementation Method 1
the lattice strain is reduced to less than 0.2%
Implementation Method 2
diffusion energy barriers of lithium ions among crystallite can be reduced, and Li ion diffusion coefficients are increased
Data Source
AI summary
A cathode material precursor, a single-crystal cathode material and a preparation method thereof, and a lithium ion battery are provided. A general chemical formula of the single-crystal cathode material is LixNiaCobMncNdO2, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, or Y; a standard deviation of a mass content of each element of Ni, Co, and Mn in the single-crystal cathode material is ≤0.03; and lattice strain is ε<0.2%.