Cathode Active Material Heat Profile for Low-Cobalt Li-Ion Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The demand for large-sized, high-capacity, high-energy-density rechargeable lithium batteries has increased, but the supply of cobalt, a key component in existing positive electrode active materials, is limited and costly, and replacing cobalt with manganese and nickel leads to structural instability and reduced lithium ion diffusion.
Innovation Solution
A two-step heat treatment process is applied to a nickel-manganese-based composite oxide, involving a primary heat treatment at 200-350°C to reduce cation mixing and a secondary heat treatment at 800-1000°C to promote lithium ion diffusion and enhance structural stability, using a composition represented by Li a1 Ni x1 Mn y1 M 1< z1 M 2< O 2-b1 X b1 , where M 1< and M 2< are selected elements and X is F or S.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cobalt is replaced with nickel and manganese to reduce cost and increase supply availability, then manufacturing cost and material availability improve, but structural stability and lithium ion diffusion deteriorate
Solution Approach 1:
The patent applies parameter changes by implementing a two-step heat treatment process with specific temperature ranges (first step: 200-350°C, second step: 800-1000°C) to optimize the crystal structure of cobalt-free lithium nickel-manganese oxide. This thermal parameter control reduces cation mixing and enhances structural stability, resolving the deterioration caused by cobalt replacement while maintaining the cost and availability benefits.
Solution Approach 2:
The patent uses composite materials by creating a layered structure of lithium nickel-manganese oxide with controlled stoichiometry (Li a1 Ni x1 Mn y1 M 1< z1 M 2< O 2-b1 X b1 where M 1< and M 2< are selected elements). This composite approach combines nickel and manganese in specific ratios with additional elements to achieve both cost reduction and structural stability, overcoming the limitations of simple substitution.
2Quantity of substance
If cobalt content is reduced or eliminated to address supply constraints, then material cost and supply security improve, but capacity and charging-discharging efficiency worsen
Solution Approach 1:
The patent employs parameter changes through precise control of heat treatment temperatures (200-350°C followed by 800-1000°C) and atmospheric conditions to optimize the crystal structure of cobalt-free materials. This enhances lithium ion diffusion pathways and reduces cation mixing, thereby improving capacity and charging-discharging efficiency without cobalt.
Solution Approach 2:
The patent applies local quality by introducing specific elements (M 1< and M 2< from selected groups) at controlled concentrations (0≤z1≤0.05, 0≤w1≤0.05) into specific positions within the crystal structure. This localized compositional optimization enhances lithium ion diffusion and electrochemical performance in the cobalt-free system.
3Speed
If heat treatment temperature is increased to promote lithium ion diffusion, then lithium ion diffusion and capacity improve, but cation mixing and structural instability worsen
Solution Approach 1:
The patent applies segmentation by dividing the heat treatment process into two distinct steps with different temperature ranges and objectives. The first step (200-350°C) addresses lower-temperature transformations, while the second step (800-1000°C) promotes lithium ion diffusion. This segmented approach prevents excessive cation mixing that would occur in a single high-temperature step while still achieving enhanced lithium ion diffusion.
Solution Approach 2:
The patent uses preliminary action by performing the first heat treatment step (200-350°C) before the second step (800-1000°C). This preliminary treatment prepares the crystal structure for the subsequent high-temperature treatment, reducing cation mixing early in the process and creating a more stable framework that can withstand the higher temperatures needed for enhanced lithium ion diffusion.
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 process increases capacity, improves charging and discharging efficiency, and enhances high-temperature cycle-life characteristics by reducing cation mixing and voids, resulting in improved structural stability and lithium ion diffusion.
Implementation Method 1
applying a primary heat treatment at about 200 °C to about 350 °C
Implementation Method 2
applying a secondary heat treatment at about 800 °C to about 1000 °C
Implementation Method 3
promotes diffusion of lithium ions
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method of preparing a positive electrode active material, a positive electrode and a rechargeable lithium battery are provided. The method of preparing the positive electrode active material includes mixing nickel-manganese-based composite hydroxide and a lithium raw material and subjecting them to primary heat treatment at about 200 °C to about 350 °C and secondary heat treatment at about 800 °C to about 1000 °C.