Zhengdao Auto exhibited the H600 model at this year's Shanghai Auto Show. The biggest highlight of the car is the power combination of “micro-turbine generator range extender + super batteryâ€. It can be said that it is the most eye-catching technology, and its “micro-turbine generator†The power combination of the range extender + super battery is in the category of extended-range electric vehicles. The graphene super battery has a storage density of up to 300 watt-hours per kilogram, and the graphene battery can be continuously charged and discharged more than 40,000 times. The combined fuel-electricity and driving range is over 1000 km, and the acceleration time from 0 to 100 km/h is only 2.9 seconds.
It is reported that the graphene lithium titanate battery is developed by Zhengdao Automobile, which can achieve fast charging in 10~15 minutes. Compared with traditional new energy vehicles, it can improve performance by 30%, and the battery life is up to 10 years. In the case that the driving range becomes the current “chicken rib†of the new energy vehicle, the Zhengdao Automobile can be said to be a problem of charging and driving mileage for the new energy vehicles, bringing a “drugâ€. However, these values ​​are limited to the concept car section. There is still a long period of time from the mass production stage. Whether the super battery can really reach the driving range of more than 1000 kilometers, you need to speak through the actual experience. The Zhengdao H600 has been unveiled at the previous Geneva Motor Show. During the Shanghai Auto Show, the Zhengdao Auto also brought two other concept models, the Zhengdao K550 and the Zhengdao K750.
From the current point of view, graphene is indeed much more advanced than the current technology, but subject to cost and its own characteristics, it is now difficult to replace traditional lithium batteries in various fields. In general, graphene lithium batteries are still a laboratory product, and in the laboratory there have been a series of cool methods such as nanotechnology to improve thermal stability and longevity. Graphene is just one of them. . How the future of graphene batteries will develop will also need to be tested by the market and users.
Study on Phase Transformation Mechanism of Graphite Anode during Charge and Discharge
Modern lithium-ion batteries are developed on the basis of graphite anodes. During the charging process, Li+ is extracted from the cathode lattice structure, diffused to the surface of the graphite anode through the electrolyte, and then embedded in the graphite structure, X-ray diffraction. Both neutron diffraction and other means show that as the amount of Li+ embedded in the graphite structure increases, LiC12 compounds are formed, Li concentration continues to increase, and finally LiC6 compounds are formed. The whole process is divided into many steps. The current research shows that LiC6 is completed. The embedded process can be divided into 4 stages or 8 stages.
Recently, MarTIn Dru?e from Otto Schott Institute of Materials Research, Germany, used XRD technology and metallographic microscope technology to study the phase change of graphite anode in the process of lithium intercalation and deintercalation. The research shows that the graphite anode is embedded in lithium and There are different reaction mechanisms during the deintercalation process, and LiC12 is a non-stoichiometric solid solution compound.
In the experiment, MarTIn Dru?e graphite sheet (SGL Carbon Sigrafine 7500) and metallic lithium powder were synthesized at 330 ° C to synthesize gold LiC6. Other graphite samples in different lithium intercalation state were obtained by calcining LiC6 in a vacuum to volatilize Li. MarTIn Dru?e also prepared graphite sheets with a gradient Li concentration profile, as shown in Figure b below.
The XRD diffraction curve of the sample is shown in the figure below, where Figure a is the XRD pattern of the graphite sheet. It can be seen from the figure that the (002) diffraction peak has a small movement to the low angle, indicating that the C-axis crystal packet parameter has increased. Large, (100) and (101) diffraction peaks widen, and (102) diffraction peaks disappear completely, indicating that the graphite sheet is a disorderly disordered arrangement, which may be the production process of graphite powder compacted into graphite sheets. As a result, the XRD pattern of the LiC6 material shows that the disorderly disordered arrangement of the graphite sheets is retained after lithium insertion.
The following figure shows the original, polished and heat-treated LiC6 material, and the XRD pattern of the graphite material. From the figure, we can see that the original LiC6 material has a (001) diffraction peak at 24.5° and a wide diffraction peak. This may be due to poor crystallinity of the LiC6 material or due to the considerable amount of LiC12.
After polishing, a (002) diffraction peak of LiC12 appeared in the (001) diffraction peak, which may be due to a slight change in structure due to loss of Li during polishing. Graphite materials with different lithium intercalation capacities can be obtained at different treatment times at 330 °C. After 72 h treatment, the (002) diffraction peak of LiC12 is more obvious, and the (001) diffraction peak of LiC6 begins to decrease, indicating that the amount of Li is decreased. The proportion of LiC12 began to increase, and the proportion of LiC6 began to decrease. After 96h treatment, the (001) diffraction peak was no longer contained in the XRD pattern, and the position of the (002) diffraction peak also moved to a larger angle, indicating that LiC6 was not contained in the sample at this time. After 146 h of treatment, the XRD pattern of the sample showed little change compared to the sample heat treated for 96 h. After 240h heat treatment, the (002) diffraction peak shifts significantly to a larger angle (29°), indicating a significant decrease in the c-axis lattice parameter of LiC12, (101) diffraction peak and (004) diffraction of graphite. The peak shows that the Li in the sample is unevenly distributed in the graphite lattice.
The figure below shows the c-axis lattice parameter variation data of different lithium-implanted graphite samples. It can be seen from the figure that the LiC6 component is very stable until the decomposition disappears, and the c-axis lattice parameter of the LiC12 component is very stable. As the Li content decreases, it is likely that a solid solution structure is formed in the graphite structure.
The following figure is a metallographic microscope picture of different lithium-incorporated sample graphite. Figure a is a polished LiC6 sample. It can be seen that the sample contains 10-20um diameter golden yellow particles (LiC6) with a dark red phase around. (LiC12). Figure b is a sample heat treated at 330 ° C for 72 h, which is darker in color and more red in the sample than in the case of no heat treated sample. Figure c is a sample heat treated at 330 ° C for 96 h. It can be seen that there is only a small amount of red area on the image, and the main area has been transformed into blue-violet. Figure d is the original phase structure of graphite. The entire picture area has only one phase and some micropores.
MarTIn Dru?e performed metallographic analysis on samples with gradient Li concentration. The sample was divided into 7 regions as shown in the figure below. The metallographic diagram in region 1 is graph a, which shows a bright yellow color. In the area and the surrounding red area, as the Li concentration decreases (Fig. b, c, d), the yellow area gradually disappears, and the surrounding red area also changes to blue-violet, eventually turning into dark blue and gray (Fig. e, f).
The directly obtained graphite samples of different Li concentrations have very significant differences from the XRD diffraction data of the Li samples obtained after calcination. For example, in the samples obtained by calcination, the c-axis crystal parameters of the LiC6 component do not follow the Li content. The change in the change, and in the directly synthesized Li gradient concentration sample, as the Li concentration decreases, the c-axis crystal packet parameter of LiC6 increases. In addition, the region 3 (Fig. c) in the Li gradient concentration sample has the same composition as the sample obtained after calcination for 72 hours, but the phase composition is significantly different, and the main phases of both are blue-violet, but the sample is obtained by calcination. It still contains a considerable amount of LiC6. This indicates that Li has different reaction mechanisms during the process of inserting and extracting the graphite structure.
Based on the experimental results and other research results, Martin Dru?e believes that the phase change of graphite in the process of lithium intercalation and delithiation is shown in the figure below. The lithium intercalation process (Fig. a) is first formed at a lower Li concentration. The low-concentration phase 2 phase begins to transform into ordered LiC12 as the amount of Li increases, and then transforms into a mixed structure of high-density LiC12 and pseudo-phase 1 phase with the increase of Li, and finally transforms into ultra-density. The LiC12 structure is mixed with LiC6.
In the process of Li taking out the graphite structure (Fig. b), the LiC6 phase and the ultradensity phase 2 phase are first transformed into a low Li concentration layered phase 1 phase and ordered LiC12 mixed structure, and then further with Li De-extraction, conversion to ordered LiC12, and finally to a lower concentration phase 1 phase as the Li concentration is further reduced.
Martin Dru?e's study observed two phases in a sample of LiC6 with high Li concentration, one showing bright yellow LiC6. One that presents a dark red LiC12 is quite different from our general perception. Martin Dru?e believes that LiC12 is a different Li content, and its lattice structure can also have a continuous crystal structure transition in a wide range of Li, indicating that it is more like a solid solution structure. At the same time, the study also shows that Li has different reaction mechanisms when intercalating and extracting graphite. In the process of embedding, a pseudo-phase 1 phase is formed, and at a lower Li concentration, there is a larger lattice parameter. The lattice parameters of LiC6 during the deintercalation process hardly change with the change of Li concentration, indicating that the stack structure of Li and graphite has not changed, but a phase 1 phase with a low Li concentration is formed.
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