It is energetically favorable to localize this charge and surround it with a local distortion of the crystal lattice. Lithium-ion batteries (LIBs) are considered a good candidate for energy applications due to their response time, high cycle efficiency, and so on. In this paper we studied on 2D Si flake @ PPy synthesized by vapor phase polymerization and 2D Si flake @ SO3 doped PANI to refine the problem of Si anode.
In the case of 2D Si flakes@PPy, the initial coulombic efficiency (ICE) was 85%, as overoxidation occurs during synthesis. 2D Si flakes@PPy and 2D Si flakes@SO3 doped PANI were synthesized to improve the disadvantages of Si anode. 2D Si flake@PPy adopted vapor phase polymerization to simplify the coating method, but it was difficult to obtain a uniformly coated sample and overoxidation reaction occurs due to the reaction.
On the other hand, 2D Si flake@SO3-doped PANI exhibited uniformly coated Si anode and prevented overoxidation by dissolution and reconstruction in NMP solution. Moreover, 2D Si flake@SO3-doped PANI showed high initial coulombic efficiency, good cyclic performance and suppressed expansion.
Introduction
Overview of Global Energy
Review of electrical energy storage technologies and systems and their potential for the United Kingdom.
Lithium-Ion Batteries
- Basic Principles of Lithium-Ion Batteries
- Components of Lithium-Ion Batteries
- Cathode materials
- Anode materials
- Separators
- Electrolytes
Meanwhile, cathode materials release lithium ions from their lattice structure during the lithiation process, anode materials store lithium ions in their lattice, and they deliver large electromotive force through the charge-discharge reaction. When two electrodes of different electrical potential create a potential difference in the electrolyte, the separator acts as a "shield" to prevent physical contact between electrodes in a battery system. The electrolytes consist of lithium salt and non-aqueous organic solvent with electrochemical, thermal and chemical stabilities in the range of working voltage.11.
This is why the rush in industry to develop next-generation LIBs, which have higher power and greater energy density, has normally focused on investigating new, higher-performance cathode materials. Materials in the second group have more open structures, such as many of the vanadium oxides, manganese dioxide tunneling compounds, and more recently transition metal phosphates, such as LiFePO4 olivine. The first group, because of their more compact grids, will have a natural advantage in stored energy per unit volume, but some in the second group, such as LiFePO4, are potentially much lower cost.
One way to compensate for this loss of capacity would be to develop a material containing a polyatomic anion capable of reversibly inserting two lithium ions onto a redox-active metal ion. The potential associated with the electrochemical reactions must be very similar to the electrochemical potential of metallic lithium. Because the anode has a large specific capacitance per unit mass, it is more difficult to intercalate or deintercalate lithium ions compared to the cathode.
As such, the design of the anode must take into account the rapid movement of lithium ions to improve the performance of Li batteries. Moreover, graphite anodes exhibit only a moderate intrinsic specific capacity (372 mA h/g) and serious safety concerns due to lithium plating and further formation of lithium dendrites. To overlap these matters, there are several types of anode materials that can be classified according to their reaction with lithium ions as follows (Table formation of metal alloy (group Ⅳ elements (metalloids); silicon, tin, germanium, aluminum and antimony, etc.),18- 20 and 2) Conversion reaction with lithium (transition metal oxides; Fe2O3, Fe3O4, CuO, Cu2O, NiO, Ni2O, MnO, MnO2, etc.)21.
The separation membrane separates two electrodes and serves as an 'aisle' for lithium ion transport between two electrodes to control the number of lithium ions and their mobility. During this process, electricity is stored in the battery in the form of chemical energy. On the other hand, during a discharge process, lithium ions move back across the electrolyte to the cathode, releasing electrons to the outer circuit to do the electrical work.
Although they easily get wet in the electrolyte, they must not curl and lie flat to separate between two electrodes. Yamada, Y, Sagane, F. et al., Kinetics of lithium ion transfer at the interface between Li0.35La0.55TiO3 and binary electrolytes.
Conducting Polymers
- Introduction of Conducting Polymers
- Basic Principles of Conducting Polymers
- Polymerization mechanisms
- Applications of Conducting Polymers
Silva et al., Battery separators based on vinylidene fluoride (VDF) polymers and copolymers for lithium-ion battery applications. Kang et al., Shell- and diatom-inspired silica coating on separators provides improved power and safety in lithium-ion batteries. Figure 1.3.1.1 shows a comparison of CP conductivity with the conductivity of conventional conductors.
The initial work on CPs was initiated by three Nobel Laureates, Alan Heeger, Alan MacDiarmid and Hideki Shirakawa.2,3 They discovered an increase of nearly 10 orders of magnitude in the electrical conductivity of polyacetylene (PA) when doped with iodine or acceptors others.4 Since Heeger et al. As can be seen in Figure 1.3.3., the conjugated structure with alternating single and double bonds or conjugated segments associated with atoms that provide p-orbitals8 for a continuous orbital overlap (e.g. N, S ) appears to be necessary for the polymers to become intrinsically directional. Since most organic polymers do not have internal charge carriers, the required charge carriers are provided by partial oxidation (p-doping) of the polymer chain with electron acceptors (eg I2, AsF5).
Not only partial oxidation of the polymer remains, there is another example: partial reduction (n-doping) with electron donors (e.g. Na, K). CP can be doped with many molecules, such as small salt ions, peptides, or polymers, including polysaccharides and proteins. Conductive polymers exhibit not only conductive properties but also some extraordinary properties such as electronic, magnetic, wetting, optical, mechanical and microwave absorbing properties.
The properties of hybrid conducting polymers mainly depend on the size, shape, aspect ratio, dispersion and alignment of the filler (organic-inorganic) in the matrix. For polymerization, the first step is the oxidation of the monomer, resulting in the formation of a radical cation, which then reacts with another monomer or radical cation to form a dimer. Monomer/oxidizing agent concentration, temperature, pH parameter and reaction time can be variable for this method.
Among other things, chemical polymerization has several possibilities with regard to covalent modification of the CP backbone.17-22. In addition, this process provides better control over the shape, size, and physical properties of CPs by tuning the source of the initiator, light intensity, and temperature. The increasing number of academic, government and industrial laboratories worldwide involved in basic research and evaluation of possible applications of conducting polymers shows that this field is interdisciplinary in nature.
Deng, J.; Wang, X. et al., Effect of oxidant/monomer ratio and washing post-treatment on the electrochemical properties of conducting polymers. Zhang, X.; Wang, S.; et al., Effect of anion doping on the structure and properties of electropolymerized polypyrrole counter electrodes for use in dye-sensitized solar cells.,.
Study on Si-conducting polymer core-shell anodes for lithium-ion batteries
- Introduction
- Experimental Section
- Synthesis of 2D Silicon flake (Si flake)
- Synthesis of 2D Si flake @ Polypyrrole (PPy)
- Synthesis of 2D Si flake @ SO 3 doped polyaniline (PANI)
- Characterization
- Electrochemical measurements
- Results and Discussion
- Conclusion
Synthesis of 2D Silicon Flake (Si Flake): The 2D Si flake was synthesized by magnesiothermal reduction reaction and subsequent simple acid leaching process. Synthesis of 2D Si flake @ Polypyrrole (PPy): To synthesize PPy, vapor phase polymerization method was used in this process. First mix as synthesized 2D Si flake and Fe(NO3)3. 1:2 wt%) Place this mixture flat in the entrance of the three-neck round flask.
Synthesis of 2D Si flake @ SO3 doped PANI: Uniformly mix polyaniline salt and camphorsulfonic acid (CSA) in a weight ratio of 1:4. Scanning electron microscopy (SEM, S-4800, Hitachi) at an accelerating voltage of 10kV was used to characterize morphologies of 2D Si-flake and 2D Si-flake @-conducting polymer samples. The dimensions and internal structures of 2D Si flake and 2D Si flake @ conducting polymer were determined using TEM (JEOL-2100) at an accelerating voltage of 200 kV.
A scanning electron microscopy (SEM) image of 2D Si flakes shows that Figure 2.3.3. a) shows the X-ray diffraction (XRD) patterns of the as-synthesized 2D Si flake. It adopts 2D Si flakes containing all-silicon structures without by-products through magnesiothermal reduction reaction and HCl leaching process. In the case of 2D Si flakes@PPy, the particle diameters are found to consist of porous flake materials of a few micrometer sizes, covered with some submicron size particles.
On the other hand, in the case of 2D Si flakes @ SO3 doped PANI shows that the particles covered more brittle particles than 2D Si flakes @ PPy. In the case of 2D Si flakes @ PPy, although its content was more than 50 wt. % in the EDS data, was partially coated with Si. The thickness distribution of the sample was too large to show a uniformly coated core-shell structure, while the 2D Si flakes @ SO3 doped PANI was coated with 10-20 nm on the sample.
Based on this data, we can say that 2D Si flakes@SO3-doped PANI were more uniformly coated than 2D Si flakes@PPy, due to the coating method. The electrochemical performance of 2D Si flake@PPy and 2D Si flake@SO3 doped PANI electrodes was tested in the potential range of 0.005-1.5 V (vs. Li/Li+) in a coin-type half-cell (2016R). For both conductive polymer-coated samples, an initial coulombic efficiency drop occurred, causing the percentage of silicon to be lower than that of bare 2D Si flakes.
On the other hand, the initial thickness of the 2D Si flake @ SO3 doped PANI electrode was 20 μm and after 50 cycles it was 37 μm. In summary, 2D Si flake @ PPy and 2D Si flake @ SO3 doped PANI were synthesized to improve the disadvantages of Si anode.
