In modern society, more and more electric devices are coming to our daily lives. The phones, MP3 player, portable power supply and toys are all need batteries to as the energy supply. As a result, the demand for the better-quality and lower-cost batteries of portable devices increases a lot. As of today, the best choice for the anode of the batteries are lithium, which relative technique is enough mature in the industry. However, the anode of the batteries still has development space.
So I try to make a project, Trash to Treasure-preparation of Graphene Battery from Bio-residues, which is using nanotechnology to invest how to use the rice husk (RH) to form the high cost- performance anode of lithium-based batteries with the lowest cost.
In general, there are three main materials to be the anodes of the lithium-based batteries, such as graphite, transition metals oxides and silicon. These materials have their advantages and disadvantages. The first one, graphite is the most common material to as the anodes of the batteries since its good conductivity of the electrons, easiness to accessible and chemical stability.
The electronic capacity of transition metals oxides is around 1000mAh/g. And silicon which is the same group of carbon has similar chemical properties to the graphite and can be extracted from sand conveniently. For silicon, it has a rapid expansion of volume, with 300-400%, causing a reduction in the capacity of the battery when charging or discharging electricity.
Then I choose the graphite carbon which is defined to similar graphene.
Main methods in the industry to get graphene are all not balanced. One method is Chemical Vapor Deposition (CVD). This method needs high purity hydrocarbons to as raw materials and high purity vacuum. The Molecular Turbo Pump creating vacuum are very expensive and easy to break down. The Mechanical stripping is like to use tap to stick one layer of graphite. This method is low efficiency. Another method is Hummers which required concentrated acid and base and hard conditions with low purity.
According to the front information, I come up other method to make the graphene. Compare to the front advantages and disadvantages, rise husks have some special advantages, such as rice husks are rich in fiber, semi-fiber and lignin. It is a good choice as the carbon source and itself have a nanoporous structure which can also increase the electrons and ions transportation. When rice husk was used as carbon source, ZnCl2 was used as an active agent and was activated to prepare carbon materials with porous graphene-like structure. And the utility of ZnCl2 can directly decrease the temperature, apparently 850?, of the carbonation of the rice rush. This temperature is much lower 2000? in CVD. Focusing on this experiment, my aim is to find the ratio of the ZnCl2 to the mass of rice husk weather can influence the properties of batteries.
The specific preparation process is as follows:
The rice husks were washed with deionized water, and then placed in an oven at 80° for drying.
10 g, 20 g, 30 g, and 40 g of ZnCl2 were respectively weighed and dissolved in 200 mL of pure water to prepare a ZnCl2 solution.
Weigh 10 g of dried rice husk and add the ZnCl2 solution prepared in step (2) (the mass ratio of dry rice hull to ZnCl2 is 1:1/1:2/1:3/1:4, respectively), magnetic force. After stirring for 24 hours, it was dried in a 110? blast oven to remove excess water.
The dried mixture was placed in a tube furnace, and the temperature was raised to 850? at a heating rate of 5?/min under a nitrogen atmosphere, and after being kept for 1 h, the furnace was cooled to obtain a sample RH-ZnCl2-850-X (X = 1, 2, 3, 4, the same value of X).
The obtained sample was added to 1M HCl solution and magnetically stirred for 24 h to remove metal salt impurities in the sample. The sample was washed with pure water to pH = 7, and then dried in a forced air oven at 80 ? for 24 hours to obtain a sample RH-SX-850-X (X = 1, 2, 3, 4, the same value of X).
The sample of step (5) was added to a 2M NaOH solution, heated at 60? and mixed by magnetically stirred for 48 h to remove the SiO2 in the sample. The sample was washed with pure water to pH = 7, and then dried in a forced air oven at 80? for 24 hours to obtain a sample RH-C-850-X (X = 1, 2, 3, 4, the same value of X).
Then I took some samples to do the material characterization.
The electrode preparation process is as follows:
After finishing combing each piece of copper to form the galvanic button cell (CR322), then I can take them electrochemical analysis.
After analyzing, I get five graphs: XRD pattern, Raman Shift, BET, SEM&TEM. XRD:
Fig 1.1 shows that the sample RH-C-850-1 the peaks corresponding to SiO2 disappeared after the acid treatment. It indicated that the sharp two peaks (in 20 degrees and27 degree) can be easily leached away by alkali washing. So the RH-C-850-2 can get better conduction.
Figure 2.1 shows a Raman digital plot of a 2D PGC nanosheet structure. The spectral range is between 1200cm and 1700 cm with two distinct peaks. The higher the ratio, the more graphitization and the better the material. Therefore, RH-C-850-2 is better with more ZnCl2.
X-ray diffraction (XRD) of the sample was performed by a diffractometer (D/Max-2400, Rigaku) and Raman spectra were recorded with an in Via Raman spectrometer (Renishaw).
Fig 3.1 shows the TEM diagram, the walls of the porous systems had been quite thin, the thickness starting from several nanometers to 10nm. Having a near study the nanostructures, it is clean that the walls of the pores had been definitely curved graphitic layers with a layer spacing of approximately 0.38 nm, which is greater than the standard price of graphite (0.335 nm). So it proves that the graphite layers have been totally detached and the conclusion from Fig 2.1 is correct.
The morphology of the 2D PGC nanosheets emerges as analyzed via SEM. The graph indicates the SEM pix of the nanosheets. the pattern includes a mass of monodispersed and overlapped nanosheets with a thickness of concerning 10?and a lateral length of about 2?m. achieved on the nanosheets (figure 4.1), electricity dispersive X-ray spectrum analysis organized with SEM become finished on the nanosheets, that additional proof that SiO2 were effectively far away from the reasons sample.
The program proposes a N2 adsorption-desorption isotherm and pore measurement distribution for 2D PGC nanosheets. The RH-C-850-2 model exhibits a raised regression loop with a relative strain range of 0.45-0.96, indicating that the mesoporous structure is as good as the elongated mesoporous size distribution of the PGC nanosheet. In addition, it was observed that the N2 absorption increased sharply above 0.97 and the N2 absorption below 0.45 was slow, indicating that the nanosheets must also have macropores and micropores in their pore structure. The pattern RH-C-850-1 has only micropores.
To analysis this material, we utilize the EIS; CV; Charge and discharge diagram to illustrate those properties
A. Fig 5.1 is the EIS for two diverse proportion of ZnCl2 based on rice-husk anode of cells. The RH-C-850-1 and RH-C-850-2 are in the same diagram. This graph can be divided into two parts, one is the “half cycle”, another one is the straight line. The larger diameter of the cycle, the better electric conductivity. And this part can be equal to a parallel current of resistance and capacitor. Another standard of cells property is the slope of the straight line. The bigger of the slope, the better conductivity of ions transportation. So connecting these theorys to the graph, RH-C-850-2 has better ability to transfer the electrons and ions.
The batteries undergo the 0-3V current to discharging and charging several times. From these two figures, the black curve shows the first round of the charging and discharging is much more different from others, because cells will form SEI film on the internal materials and effect the conductivity of the electrons without rules. In the second and further round, the SEI is more stable and have no change in the electrochemical properties. The left figure has more overlap with second and more curves. That means the RH-C-850-2 has a more stable current and properties.
The RH-C-850-1 and RH-C-850-2 were measured to explore the relationship between the particular capacity and particular voltage. From the left figure, the RH-C-850-2 had the higher particular capacity than the right graph, RH-C-850-2. In this figure, the particular capacity declined as the current influx. Well, in these charts, the RH-C-850-2 will have the better reversibility than RH-C-850-1 when it is under large current charging and discharging. And large particular capacity will be bigger than RH-C-850-1. As a result, the RH-C-850-2 will have higher capacity than RH-C-850-1.
The utility of the rice husk to manufacture graphite carbon with a safer and cheaper method is mainly a success. The total time making a battery needs about 10 days from raw rice husk. But this method still needs improvements. The EIS graph has a different conclusion with other conclusions. I haven’t got the reasonable excuses, but the real properties of batteries depend on many types of materials. But in general, this method will increase the capability of the battery with the lowest risk of manufacturing accidents. Meanwhile, it facilitates the energy pressure of the planet and recycles the useless materials.
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