Size-Dependent Composition in Li-Ion Cathode Materials
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Solution Overview
Problem
Lithium-ion batteries face challenges with LiCoO2-based cathode materials due to high cost, low capacity, and safety issues related to particle size and composition, particularly with LNMCO materials, which require a compromise between power and safety performance.
Innovation Solution
Development of lithium metal oxide powders with a specific formula LiaNixCoyMnzM′mO2±eAf, where the Ni and Mn content varies with particle size, allowing for a continuous Ni/Mn ratio, and a process involving mixing transition metal precursors with different particle sizes and lithiation firing to achieve superior electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LNMCO cathode materials are used to reduce cost and increase capacity compared to LiCoO2, then raw material cost decreases and discharge capacity increases, but thermal stability decreases and safety deteriorates
Solution Approach 1:
The patent applies local quality by creating size-dependent composition gradients within particles. Small particles have higher Mn content (better safety) while large particles have higher Ni content (better capacity). This is achieved by controlling precipitation conditions during synthesis, where Mn precipitates first in smaller particles and Ni precipitates later in larger particles, allowing each particle size to have optimized local composition for its specific function.
Solution Approach 2:
The patent changes the compositional parameters (Ni and Mn content) as a function of particle size. By varying the Ni/Mn ratio across different particle sizes rather than maintaining a homogeneous composition, the material achieves both high capacity (from Ni-rich large particles) and good safety (from Mn-rich small particles). The precipitation process parameters are controlled to achieve this gradient composition.
2Speed
If particle size is reduced to improve power behavior and rate performance, then rate capability increases, but safety deteriorates due to increased surface area and higher reactivity
Solution Approach 1:
The patent applies local quality by assigning different compositional characteristics to different particle size ranges. Small particles (D10) are enriched with Mn which provides thermal stability and safety, while large particles (D90) contain more Ni for high capacity. This size-dependent composition ensures that even though small particles have high surface area, their Mn-rich composition compensates by providing better thermal stability.
Solution Approach 2:
The patent creates a composite material system where particles of different sizes with different compositions are distributed throughout the cathode material. The overall material behaves as a composite of Mn-rich small particles and Ni-rich large particles, combining the rate performance benefits of small particles with the safety benefits of Mn content, while maintaining high capacity through Ni content in larger particles.
3Ease of manufacture
If homogeneous composition is used for all particles, then manufacturing is simplified, but performance is compromised due to inability to optimize both power and safety simultaneously
Solution Approach 1:
The patent introduces dynamics by making the composition variable rather than static. Instead of a fixed homogeneous composition, the Ni and Mn content dynamically varies with particle size. The precipitation process naturally creates this variation through controlled nucleation and growth, where Mn precipitates first in smaller particles and Ni precipitates later in larger particles, achieving compositional optimization without complex post-processing.
Solution Approach 2:
The patent changes the compositional parameters as a function of particle size. By controlling the precipitation conditions (pH, temperature, addition rate), the material achieves a continuous variation of Ni/Mn ratio across the particle size distribution. This parameter change approach allows optimization of both safety (Mn content) and capacity (Ni content) within a single synthesis 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 solution results in improved reversible capacity, rate performance, and cycling stability, enhancing both power and safety characteristics of lithium-ion batteries while maintaining cost-effectiveness.
Implementation Method 1
lithium metal oxide powder for use as a cathode material in a rechargeable battery
Implementation Method 2
bulk diffusion rate of lithium
Implementation Method 3
heating the mixture at a temperature of at least 800° C.
Data Source
AI summary
The invention relates to cathode materials for Li-ion batteries having a size dependent compositions. The lithium metal oxide powder has a general formula LiaNixCoyMnzM′mO2±eAf, with 0.9<a<1.1, 0.2≦x≦0.9, 0<y≦0.4, 0<z≦0.7, 0≦m≦0.35, e<0.02, 0≦f≦0.05 and 0.9<(x+y+z+m+f)<1.1; M′ consisting of either one or more elements from the group Al, Mg, Ti, Cr, V, Fe and Ga; A consisting of either one or more elements from the group F, C, Cl, S, Zr, Ba, Y, Ca, B, Sn, Sb, Na and Zn. The powder has a particle size distribution defining a D10 and a D90; wherein either x1−x2≧0.005; or z2−z1≧0.005; or both x1−x2≧0.005 and z2−z1≧0.005; x1 and z1 being the values of x and z of particles having a particle size D90; and x2 and z2 being the values of x and z of particles having a particle size D10.