What are the applications of electrospinning technology in the field of lithium-ion batteries?

What are the applications of electrospinning technology in the field of lithium-ion batteries?

Due to the relatively large pore volume and specific surface area of ​​nanomaterials, they have many advantages such as small lithium ion deintercalation depth, small polarization degree, good cycle stability, and high reversibility under high current charge and discharge. Electrode research is more active. In order to obtain electrode materials with the above structures, it is particularly important to select a suitable preparation method. At present, the common methods for preparing lithium-ion battery electrode materials mainly include sol-gel method and hydrothermal synthesis method, as well as thermal evaporation, chemical vapor deposition, pyrolysis and other methods. Among many methods, electrospinning technology is an important method for preparing one-dimensional micro-nano materials developed in recent years.

In recent years, electrospinning technology has also been widely used in the preparation of lithium-ion battery electrode materials. The application of one-dimensional inorganic materials prepared by electrospinning technology in the field of lithium-ion batteries also has many unique advantages. First, due to the small diameter of the nanofibers prepared by electrospinning, the intercalation depth of lithium ions in the nanofibers is shallow and the diffusion path is short, which is conducive to the rapid de-intercalation of lithium ions in the material. Secondly, the nanofibers have a large specific surface area, which helps to reduce the polarization of the electrode during the electrochemical reaction and increase the contact between the electrode and the electrolyte, which is beneficial to the transport of lithium ions. Finally, the nanofibers prepared by electrospinning have many surface defects or lattice defects in the fiber axial direction, which can provide more reaction sites for lithium ions and improve the lithium storage performance of the material. Therefore, in recent years, more and more researchers have paid attention to the application of nanofibers prepared by electrospinning in lithium-ion batteries.

It should be noted that the preparation of inorganic nanofibers by electrospinning technology mainly uses a spinning precursor solution containing polymers (such as polyvinylpyrrolidone, polyacrylonitrile, etc.), which requires further high temperature treatment of the obtained non-woven film. , in order to obtain inorganic nanofibers. If high temperature calcination in air is chosen, the gases formed by the decomposition of the polymer will diffuse, leading to the formation of porous or hollow nanotubes. If high-temperature calcination in an inert gas is chosen, the polymer decomposes and carbonizes to form a composite material containing inorganic compounds dispersed in a conductive matrix. Although further high temperature treatment increases the complexity of the overall process, high temperature calcination also promotes the flexibility, controllability, and most importantly, multifunctionality of inorganic materials prepared by electrospinning technology. It is more beneficial to apply the prepared one-dimensional inorganic materials to lithium-ion batteries.

Since the electrospinning technology was applied to the preparation of lithium-ion battery electrode materials, its development can be roughly divided into three aspects.

① Preparation of one-dimensional inorganic compound electrode materials by electrospinning technology
This kind of material is mainly obtained by directly calcining the obtained non-woven fiber film containing metal salt and polymer at high temperature in air to remove the polymer and promote the formation of inorganic substances. At the same time, by controlling the composition, content and calcination temperature of the precursor liquid, one-dimensional inorganic compound electrode materials with special morphologies, such as nanotubes and nanobelts, can also be obtained. Such electrode materials can greatly improve the cycling stability of electrode materials due to their porous or hollow one-dimensional nanostructures. For example, Mai et al. fabricated ultra-long secondary V2O5 nanowires for lithium-ion battery cathode materials using electrospinning technology and subsequent heat treatment process. Such ultralong nanowires exhibit higher capacity compared to shorter nanorods prepared by hydrothermal method. In fact, the ultra-long secondary nanowires are composed of short nanorods, which greatly reduces the self-aggregation phenomenon of the electrode material and is more conducive to maintaining the effective contact area of ​​the active material, the conductive agent and the electrolyte, so Its electrochemical performance is even better (Figure 1).

What are the applications of electrospinning technology in the field of lithium-ion batteries?
Figure 1 Preparation and battery performance of secondary V2O5 nanowires

② Preparation of one-dimensional inorganic compound/carbon composite electrode materials by electrospinning technology
This kind of material is mainly obtained by calcining the obtained non-woven fiber film containing metal salt and polymer at high temperature in an inert gas to promote the decomposition and carbonization of the polymer to form carbon fiber. By controlling the type, composition and content of the precursor liquid, the core-shell structure of the carbon-coated inorganic compound can be obtained. Due to the conductive carbon fiber coating, this type of electrode material not only improves the conductivity of the material, but also acts as a buffer and protection for inorganic compounds, thereby improving the cycle life and rate performance of the electrode material. For example, Yu et al. successively used uniaxial and coaxial electrospinning techniques to prepare porous, multi-channel carbon nanotubes coated with tin nanoparticles [Figure 2(e)~(g)]. This porous, hollow carbon layer can not only provide enough space to accommodate the volume change of tin nanoparticles during charging and discharging, but also maintain the stability of the tin nanoparticles structure and avoid being oxidized. Therefore, it exhibits excellent performance as a negative electrode material for lithium-ion batteries [Figure 2(d), (h)].

What are the applications of electrospinning technology in the field of lithium-ion batteries?
Figure 2. Preparation and battery performance of inorganic compound/carbon composites

③ Preparation of inorganic compound/carbon flexible composite electrode materials by electrospinning technology
The researchers used the properties of a flexible film that can be obtained by pyrolysis and carbonization of a specific polymer to prepare a self-supporting electrode material that does not require current collectors and binders. This kind of electrode material not only reduces the cumbersome process in the electrode preparation process, but also does not require the use of current collectors and binders, which greatly reduces the cost of lithium-ion battery preparation. For example, Li et al. encapsulated germanium nanoparticles into flexible carbon fibers and used them as self-supporting integrated electrodes. When tested as an anode material for lithium-ion batteries, the electrode exhibited excellent electrochemical performance. In addition, the self-supporting integrated electrode can greatly save the cost of fabrication and will surely become a hot spot of future research.

What are the applications of electrospinning technology in the field of lithium-ion batteries?
Figure 3 Inorganic compound/carbon flexible composite electrode material and battery performance

Of course, these three aspects of research are interwoven with each other, and there is no obvious time limit. Regardless of the structure, the construction of one-dimensional nanomaterials with the above characteristics is of great practical significance for improving the performance of lithium-ion batteries. The application of one-dimensional nanomaterials in lithium-ion battery electrode materials is increasingly valued by researchers, and will become one of the most promising research directions in the field of lithium-ion anode materials in the future.

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