NMC Cathode Material Firing with Two-Step Low-Oxygen Sintering
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Solution Overview
Problem
Conventional methods for preparing lithium nickel-manganese-cobalt oxide-based positive electrode active materials face challenges such as reduced productivity, quality variation, and the generation of unnecessary gases like CO2 during the firing process.
Innovation Solution
A two-step heat treatment method is employed, where a reaction mixture is first treated at 500-800°C to form a pre-sintered mixture, which is then pulverized and subjected to a second heat treatment at 700-1000°C under a low oxygen partial pressure to produce a lithium nickel-manganese-cobalt-based positive electrode active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel-manganese-cobalt precursor and lithium-raw material are mixed to increase volume, then the amount of raw material added into the crucible is reduced, but productivity deteriorates
Solution Approach 1:
The invention performs preliminary heat treatment at 500-800°C to form a pre-sintered mixture before the final firing step. This preliminary action removes moisture and volatile components, preventing gas generation during the main firing process and enabling higher raw material loading without quality degradation, thus resolving the contradiction between quantity and productivity
2Productivity
If the amount of raw material added into the crucible is increased to improve productivity, then productivity improves, but quality variation of the positive electrode active materials occurs
Solution Approach 1:
The preliminary heat treatment at 500-800°C performs critical preparatory work by removing moisture and volatile components before the main firing. This ensures that even when large amounts of raw material are loaded, the subsequent firing at 900-1000°C proceeds uniformly without gas generation, maintaining quality consistency while enabling high productivity
Solution Approach 2:
The invention extracts and removes harmful volatile components and moisture during the preliminary heat treatment step at 500-800°C. By taking out these problematic substances before the main firing process, the invention enables loading of large raw material quantities without compromising quality uniformity, thus resolving the contradiction between productivity and manufacturing precision
3Reliability
If firing is performed in an oxygen atmosphere to oxidize Ni+2 to Ni+3, then the positive electrode active material is formed, but temperature variation severely occurs and firing time increases
Solution Approach 1:
The preliminary heat treatment at 500-800°C performs the oxidation of Ni+2 to Ni+3 in advance before the main firing step. By completing the oxidation reaction during the low-temperature preliminary treatment, the subsequent high-temperature firing at 900-1000°C only needs to complete the sintering process without requiring oxygen atmosphere, thus significantly reducing firing time while maintaining reliable oxidation
Solution Approach 2:
The invention segments the firing process into two distinct stages: (1) preliminary heat treatment at 500-800°C in air atmosphere to perform oxidation and remove volatiles, and (2) main firing at 900-1000°C in inert or reducing atmosphere to complete sintering. This segmentation allows the oxidation step to be completed separately at lower temperature, avoiding the need for long high-temperature oxygen atmosphere firing, thus resolving the contradiction between reliable oxidation and firing time
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 method results in a positive electrode active material with excellent physical properties and electrochemical characteristics, improved productivity, and uniform quality, while minimizing the generation of unwanted gases.
Implementation Method 1
performing a first heat treatment at a temperature of 500-800° C. to form a pre-sintered mixture
Implementation Method 2
performing a second heat treatment at a temperature of 700-1000° C. under an atmosphere in which an oxygen partial pressure is 20% or less to form a lithium nickel-manganese-cobalt-based positive electrode active material
Data Source
AI summary
A method for preparing a positive electrode active material includes: a step for adding a reaction mixture containing a lithium-raw material and a nickel-manganese-cobalt precursor into a first crucible and performing a first heat treatment at a temperature of 500-800° C. to form a pre-sintered mixture; a step for extracting the pre-sintered mixture from the first crucible and pulverizing or classifying the same; and a step for adding the pulverized or classified pre-sintered mixture into a second crucible and performing a second heat treatment at a temperature of 700-1000° C. under an atmosphere in which an oxygen partial pressure is 20% or less to form a lithium nickel-manganese-cobalt-based positive electrode active material, wherein a volume of the pre-sintered mixture formed after the first heat treatment is reduced to a volume that is 20-50% of a volume of the reaction mixture added into the first crucible.