Author ：Iflowpower – Portable Power Station Supplier
Compared to the battery life mileage, people are more worried about the charging time of electric vehicles, although most electric vehicles launched in recent years have supported 30-40 min fast charge (80% capacity), but still unable to meet people's expectations. At present, the power lithium ion battery used in electric vehicles is substantially a lithium ion battery, and the charging speed limit of lithium ion battery is in a negative gathering in the negative electrode. During the charging process, Li + is taken out from the positive electrode, solvent is solvated in the electrolyte, then diffused to the surface of the negative electrode, and the crystal structure of the graphite negative electrode embedded after solvate.
During the entire reaction, the diffusion of solventification and Li + in the graphite particles is the restriction link of the reaction speed. When the charging speed is too fast, the polarization is added, and the metal Li is precipitated on the surface of the graphite negative electrode. The conventional method of enhancing the negative electrode material is nanofed, improves the contact area of the active material and the electrolyte, reducing the diffusion distance between Li + in the active substance, but this also also brings a series of problems, such as nanoforming The compact density is reduced, and the side effects caused by excessive specific surface area.
Kentj.griffith (first author) and Clarep.grey of the University of Cambridge, British Cambridge, break through the limitations of traditional thinking, starting from the crystal structure, found that if the Ni and W metal oxides are used to build a suitable three-dimensional crystal structure, it can be in microns High-magnification characteristics are realized at level size, and high-pressure solid density and high-magnification characteristics simultaneously.
In the test, Kentj.griffith utilizes NB and W's oxide to synthesize NB16W555 (as shown in Fig. AC) and Nb18W16O93 (as shown in Figure DF shown in Figure DF), wherein Nb16W5O55 is a single-linked crystalline system, and the crystal is composed of a common angle.
, Form a structural unit for every 4x5 octahedral, as shown in Fig. A. The NB18W16O93 material is a orthogonal alkline, and the structure is shown in Figure D.
The two materials are shown in the figure below, and there are three reaction processes between 2.5-1.0V, and the voltage platform is about 1.
55V, and the voltage platform is about 1.55V, and the Li4TI5O12 material (1.55 V) relatively close, but the reversible capacity of the NB16W5O55 material is much higher than the LTO material, reaching 225 mAh / g at the C / 5 ratio, and the NB16W5O55 material also exhibits excellent magnification performance, increase the charging magnification to 5C.
(12min lying) can still reach 171 mAh / g, even at a high magnification of 20c (3min) is still up to 148mAh / g. The NB16W5O55 material is not only in the magnification performance, and there is a strong strength in cycle performance. After 250 cycles of 10C rate, the reversible capacity still reaches 95%, and then the 20C magnification is 750 times cycle, the battery is reversible The capacity retention rate is still as high as 95%.
However, Xiaobian is here to say that the author is here, which is a little tip, which is in the detection of the magnification performance, and the constant voltage charging process is added during the charging process, and the authors in the cycle detection will drop the constant voltage charging process. We all understand that constant pressure charging relates to the charging capacity of new batteries, especially at high charge rates, is very important, so the authors can be so excellent, and the cycle is removed in the cycle is equivalent to decrease The SOC status of the battery is helpful to improve cycle performance. It seems that foreigners will be careful! The electrochemical probe of NB18W16O93 material is also very good, and its voltage platform is 1.
67V, at C / 5 and 1C times, since Nb18W16O93 mole weight is relatively large, the gram is to be 20 mAh / g lower than the NB16W5O55 material, but is more At a high magnification, the NB18W16O93 material is excellent in performance, and the reversible capacity reaches 150 mAh / g under 20C, which can reach 105 and 70 mAh / g at 60C and 100C magnification, preferably from NB16W5O55 material. Excellent magnification performance is forbidden from the high Li + diffusion coefficient of the two materials. From the table below, it is possible to see that the diffusion coefficient of the two materials is about 10-12-10-13m2 / s, which is even higher than Fast charging staminated titanate (10-16-10-15) It is completely sufficient time to complete the diffusion within the particles of 10um diameter, this statement, even if the two materials in the micrometer size can still achieve ultra-high charging speed.
While compared to the traditional graphite materials, the NB16W55 and NB18W16O93 two materials have no advantages on the gram volume and the voltage platform, if we consider the compaction density, we will find that two materials are more High compact density therefore has a very large advantage (as shown in the figure below) in the unit volume (shown below), at 1C magnification, the NB16W5O55 material unit volume capacity can reach 550ah / L, even at 20C magnification It can reach 350AH / L, and the NB18W16O93 material can reach 500ah / L at 1C magnification, still up to 400ah / L at 20C magnification, and the unit volume capacity of the graphite material is only 100ah / L only 100AH / L Left and right, there is almost no capacity at 20C magnification. This statement of the NB16W5O55 and NB18W16O93 two materials cannot match the traditional graphite material on weight energy density, but in volume energy density, it has great advantages, especially at high magnification, and the advantage is almost overpower. Kentj.
Griffith developed NB16W5O55 and NB18W16O93 two materials have very high Li + diffusion coefficients, so that excellent magnification performance can be achieved on the micrometer size, although these two materials are not as good as traditional on weight compared to voltage platforms. The graphite material, but the characteristics of high-pressure real density make the two materials exhibited an overwhelming advantage of the graphite material on the volume energy density, and the material has broad prospects in the future. Prerequisite is to drop in cost).
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