Typical cathode materials, such as NCA and NMC, are produced through co-precipitation of transition-metal hydroxide precursor materials, followed by calcination (lithiation and oxidation) with a lithium compound. Co-precipitation is a slow process--starting with nucleation, followed by the growth of primary particles, and finally agglomeration to larger secondary particles. The whole process can take anywhere between 20 to 40 hours, depending on the process and equipments.
Many parameters--including the concentration of ammonia water, slurry composition, pH, temperature, and stirring speed--affect co-precipitation efficiency. Optimizing these parameters plays a key role in the quality and throughput of battery cathode precursor materials. Optimize cathode precursor synthesis process comes from below,
1. The concentration of ammonia water
When the concentration of free ammonia in our precursor reactor is controlled at 9.5-11.5g/l, the surface of spherical particles is smooth, the degree of sphericity and compactness gradually increases, and the dispersion between particles is good.
2. Slurry composition
The slurry composition of the nickel, cobalt, manganese ions and hydroxide ions plays a key role in the particles and shape of the cathode precursors. Precursor particles nucleate, grow and then agglomerate to form larger secondary particles.
3. The influence of pH value
This is the most important factor in all hydroxide synthesis, and it is also the reason why everyone gradually replaces manual control with transmitter PH automatic control.
3. The influence of stirring rate (related to the equipment precursor reactor)
Appropriately increasing the stirring rate can increase the tap density of the precipitated product. Strong stirring can quickly disperse the nickel, cobalt, manganese ions, and hydroxide ions added to the reactor, avoiding a large amount of nucleation caused by excessive local supersaturation of the system during the feeding process, increasing the stirring rate can also accelerate the reaction of ionization. In the mass transfer in the system, more reactants reach the surface crystallization of the crystal per unit of time, which is conducive to crystal growth;
In addition, it can also accelerate the dissolution of small particles and then recrystallize and precipitate on the surface of large particles, so that the particle size distribution of the precipitated product is narrow, the shape is single, and the tap density increases accordingly.
However, when the stirring intensity reaches a certain extreme value, the crystal growth is changed from diffusion control to surface control. At this time, the stirring rate continues to increase, and the crystal growth rate remains basically unchanged.
4. Influence of reaction time
(reaction time affects the particle size and shape of co-precipitation, and directly affects the bulk density of the product) To ensure the highest production efficiency, these particles should grow above their target size in the minimum possible time.
5. The influence of the temperature of the reactor
(the most suitable synthesis temperature is unified at 60°C)
6. The effect of aging
It's to let the grown crystals be ground off by the NH3H2O still present in the cathode precursor solution so that the crystals become round and smooth. Let the lattice structure rules carry out directional rearrangement, showing better crystalline properties.