Graphite anode material is currently the most commonly used lithium ion battery anode material, lithium-ion battery charging process, with Li + LiC6 reaction of compounds, the theoretical specific capacity of 372mAh / g, the highest capacity of the current graphite anode material than the actual ratio The capacity of 360mAh / g, has been close to the theoretical capacity, and most of the graphite anode material capacity of 300mAh / g.
With the gradual increase of the specific energy of lithium-ion batteries, the traditional graphite anode materials, such as natural graphite and artificial graphite, can no longer meet the needs of high specific energy lithium-ion batteries. Therefore, many high-capacity anode materials have been developed, of course, graphite materials Did not sit still, a variety of modified technology has been developed, one of the most effective and most attractive is undoubtedly belong to the "nitrogen-doped graphite technology" and "mesoporous carbon technology", these two modification methods significantly improve the graphite material Based on the specific capacity, the material does not reduce the cycle performance, so it has a good prospect.
Recently, Xinyang Yue et al. From Beijing Institute of Technology developed a microporous-mesoporous hollow carbon microspheres lithium ion battery cathode material based on mesoporous carbon technology. The material has a specific surface area of ​​396 m 2 / g. This material not only has high capacity characteristics , And has a good cycle performance, at a current density of 2.5A / g, 1000 times to maintain a specific capacity of 530mAh / g. The material's magnification performance is also very shocking, at a current density of 60A / g (about 100C), the specific capacity of the material is still up to 180mAh / g.
In the study, Xinyang Yue used 370nm silica microspheres as the template, dopamine as the carbon source, PEO-PPO-PEO (P123) as the pore forming medium, Ar protective calcination at 400 ℃ for 3h, then calcined at 800 ℃ for 3h, HF corroded micropores on the surface of the hollow carbon microspheres and removed the silicon template in the material. Finally, after cleaning and vacuum drying, the microporous mesoporous hollow carbon microspheres material was obtained.
In SEM photographs, the material was uniformly dispersed microspheres with a diameter of about 400 nm. The surface of the microspheres formed by HF etching showed a hollow structure with a TEM microscope. Electrochemical tests showed that the current density of 624mAh / g can be obtained at a current density of 0.5A / g, which is much higher than the theoretical specific capacity of 372mAh / g graphite material. The additional capacity mainly consists of material defects produced. However, the material has a high irreversible capacity of 1081 mAh / g, which is mainly due to the large specific surface area of ​​the material resulting in more electrolyte decomposition and more Li consumption during SEI film formation.
Although this material has a high initial irreversible capacity, the material has good cycling properties. The material has a first discharge capacity of 646 mAh / g and a capacity of 50 cycles decreased to 502 mAh / g, but then the specific capacity starts to rise, with a cycle capacity of 563 mAh / g for 400 cycles and a current capacity of 500 mAh / g for 1000 cycles.
The brightest performance of this material is the rate capability at current densities of 1 A / g, 2.5 A / g, 5 A / g, 10 A / g, 20 A / g, 40 A / g and 60 A / g With specific magnifications of 495 mAh / g, 382 mAh / g, 301.3 mAh / g, 254.4 mAh / g, 206.5 mAh / g, 190.7 mAh / g and 189.3 mAh / g, respectively, Performance, ideal for high-power lithium-ion battery.
At present, the biggest problem of the material is the preparation cost is too high, the tap density is low, difficult to commercial applications, and the material for the first time the problem of irreversible capacity can be solved through the anode fill lithium technology. At present, the method still only stays at the laboratory level, and further research is needed to reduce the cost and improve the material performance.
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