Is doping NMC with Al through solid-state methods more effective than co-precipitation, as a coating layer generates on the particles? Is it necessary to have a spherical morphology with small primary particles?
I have recently synthesized NMC811, although I have encountered some problems. I would appreciate it if you could guide me. Specifically, I want to know if the synthesis conditions are appropriate. I have attached the SEM results for your reference.
My synthesis conditions are as follows:
- Reactor volume: 500 cc
- Base concentration: 2.75 M
- Feeding ammonia concentration: 1.4 M
- TM concentration: 1.8 M
- pH: 11
- Temperature: 55°C
- Stirring speed: 850 rpm
To optimize the co-precipitation method for synthesizing NMC811 with the proper morphology for Li-ion battery applications, several synthesis parameters need careful consideration. Maintaining a stable pH, such as the 11 you’re using, is crucial, but even small fluctuations can affect particle growth and uniformity. Your stirring speed of 850 rpm seems appropriate, as it generally promotes homogeneity, but adjusting it slightly could help refine the morphology if agglomeration is an issue. The temperature of 55°C is within a reasonable range, though increasing it slightly to around 60–70°C might enhance crystallinity and better control primary particle size. Additionally, the concentration of transition metals and the ammonia feeding rate are important—your TM concentration of 1.8 M looks fine, but balancing these parameters could help minimize size inconsistencies.
Regarding Al doping, using solid-state methods to form a coating layer can be very effective for improving surface stability and reducing degradation during cycling. However, co-precipitation generally provides better control over the distribution of elements within the bulk structure, which can be more beneficial for uniform electrochemical performance. The choice largely depends on whether your priority is enhancing surface stability or optimizing bulk properties.
As for morphology, while spherical shapes with small primary particles are not absolutely necessary, they are typically preferred for better packing density and Li-ion diffusion pathways, which improve overall battery performance. Based on your SEM images, the morphology looks promising, but there’s room to refine the particle size distribution or reduce agglomeration further.
All the best!
Thank you for your time.
the purpose of Al doping is modifying electrochemical function of NMC at high rate for fast charging. So, based on my idea, solid state method could increase surface stability and electrochemical function during high rate current, if it is correct. I am not sure.
moreover, I reduced the stirring speed to 500rpm after feeding (I forgot to tell)
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