LiNiCoMnO Cathode Core-Shell Structure for Power Safety Trade-off
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Solution Overview
Problem
Lithium-nickel-manganese-cobalt-oxide (LiNixCoyMny′M′zO2) cathode materials face a compromise between safety and electrochemical performance due to their complex synthesis and particle size-dependent properties, where smaller particles require higher inert doping for safety but reduce power performance, and larger particles compromise safety for better performance.
Innovation Solution
A lithium metal oxide powder with a non-homogeneous Ni/M′ ratio in particles of varying sizes, where the Ni content increases and M′ content decreases with particle size, maintaining a constant Co and Mn content to optimize power and safety performance, achieved through a process involving precursor powders with different particle size distributions and mixing with lithium carbonate before high-temperature sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If smaller particle size is used to improve power performance, then power performance is improved, but safety deteriorates
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region has high Ni content for power performance while the shell region has high M′ content for safety. This spatial differentiation of composition allows small particles to simultaneously achieve both high power (through high Ni core) and high safety (through protective M′-rich shell), resolving the contradiction between power performance and safety that plagues conventional homogeneous small particles.
2Reliability
If higher M′ doping is used to improve safety, then safety is improved, but power performance deteriorates
Solution Approach 1:
The patent concentrates M′ doping in the shell region rather than distributing it uniformly throughout the particle. This localized high M′ content in the shell provides the necessary safety stabilization at the particle surface and interface, while the Ni-rich core maintains high electrochemical activity and power performance. Thus, safety is improved without sacrificing power performance.
Solution Approach 2:
The patent segments the particle into functionally distinct core and shell regions. The core segment (Ni-rich) handles electrochemical reactions and power delivery, while the shell segment (M′-rich) handles safety stabilization and structural protection. This segmentation allows each region to be optimized for its specific function, resolving the trade-off between safety and power performance.
3Reliability
If larger particle size is used to improve safety, then safety is improved, but power performance deteriorates
Solution Approach 1:
The patent enables small particles (which inherently provide good power performance) to achieve the safety characteristics of large particles through the M′-rich shell. The shell provides the same protective function that would require large particle size in homogeneous materials, thus decoupling the size-safety relationship and allowing small particles to simultaneously achieve both safety and power performance.
4Ease of manufacture
If homogeneous composition is used to simplify manufacturing, then manufacturing complexity is reduced, but overall performance deteriorates due to compromise
Solution Approach 1:
The patent segments the particle composition into core and shell regions with different compositions. This can be achieved by sequential precipitation or controlled synthesis methods where the core forms first with high Ni content, followed by shell formation with high M′ content. While slightly more complex than homogeneous synthesis, the segmentation enables simultaneous optimization of power and safety, resulting in superior overall performance that compensates for the increased manufacturing complexity.
Solution Approach 2:
The patent employs preliminary action by first forming the Ni-rich core structure, then subsequently adding the M′-rich shell layer. This sequential approach allows precise control over the core-shell composition gradient and ensures that the high-Ni core is established before the protective shell is formed, optimizing both power performance (from core) and safety (from shell).
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
This approach enhances both power and safety performance by optimizing Ni and M′ content in larger particles and smaller particles respectively, maintaining the layered structure and electrochemical stability, resulting in improved capacity and rate performance compared to conventional materials.
Implementation Method 1
heating the mixture at a temperature of at least 800° C.
Data Source
AI summary
The invention relates to a LiaNixCoyMny′M′zO2 composite oxide for use as a cathode material in a rechargeable battery, with a non-homogenous Ni/M′ ratio in the particles, allowing excellent power and safety properties when used as positive electrode material in Li battery. More particularly, in the formula 0.9<a<1.1, 0.3≦̸x≦̸0.9, 0<y≦̸0.4, 0<y′≦̸0.4, 0<z≦̸0.35, e<0.02, 0≦̸f≦̸0.05 and 0.9<(x+y+y′+z+f)<1.1; M′ consists of either one or more elements from the group Al, Mg, Ti, Cr, V, Fe, Mn and Ga; N consists of either one or more elements from the group F, Cl, S, Zr, Ba, Y, Ca, B, Sn, Sb, Na and Zn. The powder has a particle size distribution defining a D10, D50 and D90; and the x and z parameters varying with the particles size of the powder, and is characterized in that either one or both of: x1−x2≧0.005 and z2−z1≧0.005; x1 and z1 being the parameters corresponding to particles having a particle size D90; and x2 and z2 being the parameters corresponding to particles having a particle size D10.