Oswald ripening mechanism (Ostwald ripening) is a classical mechanism in the process of crystal nucleation growth. Ostwald ripening process is different from dissolution recrystallization process. Generally speaking, this process refers to the competitive growth of large particles by ingesting small particles during crystal growth. The driving force for this process is the reduction in the total interfacial free energy resulting from the reduction in the total surface area of the particles. Because in the early stage of nucleation, the energy of small particles is higher and unstable, and after being absorbed by large particles, the energy of the system is lower and tends to be stable. The electrochemical Oswald ripening (Electrochemical Ostwald ripening,EOR) process involves the transfer of electrons and ions from smaller nanocrystals to large grains. EOR leads to non-uniform deposition of metals, which is very important for the study of metal-ion batteries, such as lithium-ion batteries and sodium-ion batteries. The research group of Huang Jianyu of Yanshan University studied the deposition process of sodium and lithium using in situ transmission electron microscope technology, and found that lithium/sodium metal has electrochemical Oswald ripening process (EOR) in the early growth process. Sodium and lithium are randomly nucleated at the initial stage of growth, and then grow. In the process of growth, small particles will be absorbed by large particles to form a larger grain. The research results were published in Nano Research under the title of "In situ observation of electrochemical Ostwald ripening during sodium deposition". teachers Huang Jianyu, Zhang Liqiang and Tang Yongfu of Yanshan university were the co-corresponding authors of the paper, and Geng Lin (1/2) and Liu Qiannan (2/2) were the co-first authors of the paper. In-situ link: https://doi.org/10.1007/s12274-021-3861-6

Figure 1 The PicoFemto of Zeyu Technology (ZepTools) was used in this study.®The series of in-situ TEM-STM sample rods set up an in-situ test environment.

Figure 3 Electrochemical Oswald Ripening Path 1

Figure 4 Deposition EOR process of sodium/lithium metal on MWCNT/Na2CO3 or Li2CO3/CO2

Figure 5 Electrochemical Oswald ripening path 2

In summary, researchers have observed two EOR paths in the study of sodium and lithium deposition processes. The first (EOR1) is as shown in Figure 1(a)& (B) of the experimental process. Large grains and small grains begin to grow in distant square nuclei respectively. Electrons and ions are transported through MWCNT to consume small grains and realize that large grains gradually become larger. The other (EOR2) is the experimental process shown in Figure 2(c), (d), (e), two or three sodium or lithium particles are grown next to each other by direct contact transporting electrons and ions. With further growth of the large crystals, the Na2CO3 or Li2CO3 shell near the contact points of the nanocrystals is broken, and subsequent growth is chemical Ostwald ripening.

Figure In-situ TEM sample rod used during the experiment