At present, the development of the power battery can be mainly divided into two directions: 1) high specific energy direction; 2) fast charging direction, although under the current subsidy policy for new energy vehicles, high specific energy batteries have become the main power battery manufacturers. Research direction. However, in order to increase the specific energy of lithium-ion batteries, we also need to continuously improve the charging characteristics of lithium-ion batteries. The charging capability of lithium-ion batteries is mainly affected by the dynamic characteristics of the negative electrodes. The traditional graphite negative electrodes have poor dynamic characteristics. In the rapid charge, it is easy to cause the precipitation of metal Li on the surface of the negative electrode. At the same time, the theoretical specific energy of the negative electrode of graphite is only 372 mAh/g. Therefore, it is difficult to meet the design requirements for high specific energy and fast-charging batteries. The transition made by using the MOFs method is difficult. The metal oxide negative electrode material, because of its small particle size and a large number of micropores, significantly improves the material's rate performance and is one of the best choices to solve this problem.
Recently, Guangyu Zhao of Harbin Institute of Technology used Co-electrochemically assisted MOFs to synthesize Co3O4 on a Ti nanowire substrate. The electrode exhibited excellent rate performance and cycling performance. At an ultra-high rate of 20 A/g, the electrode still remains. The capacity of 300 mAh/g can be exerted, and there is no significant capacity decline after 2000 cycles. It is of great significance to develop a lithium ion battery with high specific energy and fast charge characteristics at a current density of 1 A/g.
The thin film materials prepared by the MOFs method generally have poor adhesion to the substrate. To solve this problem, Guangyu Zhao uses a Ti foil with a vertical Ti nanowire structure as a substrate, and then the precursor of the MOFs process is electrochemically deposited. In the matrix above, the direction of high specific energy; 2) fast charge direction, although under the current subsidy policy for new energy vehicles, high specific energy batteries have become the main research direction of major power battery manufacturers. However, in the increase of lithium-ion battery ratio At the same time of energy, we also need to continuously improve the charging characteristics of lithium-ion batteries. The charging capability of lithium-ion batteries is mainly affected by the dynamic characteristics of the negative electrodes. The traditional graphite negative electrodes have poor dynamic characteristics and are easily formed on the surface of negative electrodes during rapid charging. The precipitation of metal Li, while the theoretical specific energy of the negative electrode of graphite is only 372 mAh/g, so it is difficult to meet the design requirements for high specific energy and fast charging batteries. The transition metal oxide negative electrode material prepared by MOFs method has a relatively small particle size. Small, and with a large number of micro-holes, which significantly improves the material's rate performance, and is the best choice to solve this problem. Choose one.
Recently, Guangyu Zhao of Harbin Institute of Technology used Co-electrochemically assisted MOFs to synthesize Co3O4 on a Ti nanowire substrate. The electrode exhibited excellent rate performance and cycling performance. At an ultra-high rate of 20 A/g, the electrode still remains. The capacity of 300 mAh/g can be exerted, and there is no significant capacity decline after 2000 cycles. It is of great significance to develop a lithium ion battery with high specific energy and fast charge characteristics at a current density of 1 A/g.
The thin film materials prepared by the MOFs method generally have poor adhesion to the substrate. To solve this problem, Guangyu Zhao uses a Ti foil with a vertical Ti nanowire structure as a substrate, and then the precursor of the MOFs process is electrochemically deposited. On the above substrate (as shown above in the synthesis process), this not only enhances the adhesion between the matrix and the precursor, but also ensures good electronic conductivity, thus greatly improving the rate capability of the material.
The morphology of the Co3O4/Ti electrode prepared by the above process is shown in the following figure. After 600 s deposition at -2.0 V, we can see that the surface of the Ti nanowires is covered with a layer of nanoparticles (as shown in Figure c below), after XRD Crystal structure analysis of these nanoparticles is metal Co, and then through the MOFs process the zeolite imidazole metal organic framework material ZIF67 deposited on the Co/Ti composite structure, at this point we can observe some polyhedral MOFs at the top of Ti nanowires, At the same time, we noticed that the surface of the Ti nanowires became smooth at this time, indicating that Co was already consumed during the deposition of ZIF67 (as shown in Figure d below). The above precursor was then pyrolyzed from In the figure below, g, h, and f, we can see that the pyrolysis-generated Co3O4 still maintains the morphology of the precursor, is uniformly dispersed on the Ti nanowires, and is firmly held by the Ti nanowires. This self-supporting The characteristics of the structure determine that it does not require a binder and a conductive agent, and good dispersion properties significantly improve the material's rate performance.
In the following electrochemical performance tests, the Co3O4/Ti structure electrode exhibited excellent rate performance and cycle stability as expected. From the rate performance test results of the following figure, we can see that Co3O4 prepared by the above process is used. The /Ti electrode (below in figure a) can exert a capacity of 700mAh/g at a current density of 1A/g. Even if the current density is increased to a staggering 50A/g, the material can still exert a specific capacity of 180mAh/g. On the other hand, the Co3O4 material deposited on a smooth thin Ti substrate using the same MOFs process is very poor (Figure b). After the current density reaches 5A/g or more, almost no capacity can be achieved. Guangyu Zhao believes that This may be due to the poor dispersibility and cohesiveness of Co-MOFs prepared by traditional MOFs on Ti foil substrates.
The following figure shows the cycling performance of a Co3O4/Ti electrode prepared using a Ti nanowire matrix. From the figure, we can see that the cycle is 2000 times at a charge-discharge rate of 20 A/g, and there is almost no decrease in the capacity of the Co3O4/Ti electrode. The main benefit is that the Ti nanowire structure not only firmly immobilizes the Co3O4 particles, but also provides good electronic conductivity. In addition, the good dispersion of Co3O4 also greatly reduces the diffusion resistance of Li+ and improves the cycle performance of the electrode. .
The preparation process developed by Guangyu Zhao uses the Ti nanowire matrix to solve the problem of poor adhesion between the film and the substrate prepared by the MOFs process, and the poor cycling performance and rate performance caused by uneven dispersion of the active material of the film. The wire firmly holds Co3O4 on the substrate and also provides highly efficient electron transport channels. In addition, the good dispersion of Co3O4 particles on the substrate reduces the diffusion resistance of Li+, which has helped the Co3O4/Ti material to achieve an amazing magnification. Performance: The capacity can reach 700mAh/g at a current density of 1A/g, and at a current density of 50A/g, it can still exert a capacity of 180mAh/g. More importantly, the material has a current density of 20A/g. The charge-discharge cycle was 2000 times, and there was almost no loss in capacity. This made it possible for lithium-ion batteries with high specific energy and fast charge characteristics.
