Application of Asphalt in Anode Materials

Graphite, which is used as a commercial anode material, is increasingly unable to meet the growing demand for high-capacity anode materials due to its limited theoretical capacity. If pitch is used as a carbon precursor for lithium-ion battery anode, it can not only realize the high value-added utilization of pitch, but also provide some new methods and explorations for improving the electrochemical performance of anode materials.

Li P et al. used nano-magnesium oxide particles as template and petroleum pitch as carbon source. After ultrasonic dispersion in liquid phase, they were treated at a high temperature of 800 C for 1 h under nitrogen protection, and the template was removed by pickling to prepare ultra-thin ultra-thin hollow structures with unique hollow structure. Porous Carbon Shell (PACS). Due to the ultrathin lamellae and hierarchically porous structure, PACS provides more active sites for ion transport, with 334 mAh g-1 after 1 000 cycles at a current density of 1 A g-1. reversible capacity and 90% capacity retention.

During the preparation, the cross-linking is promoted by the introduction of oxygen in the air, which avoids the coalescence of the low-softening point asphalt in the emulsion and does not require post-treatment to stabilize its spherical morphology. When used as a negative electrode material for lithium-ion batteries, the gram capacities of PCB are 373.6 mAhg-1 and 125.8 mAhg-1 at current densities of 0.05 Ag-1 and 5 Ag-1, respectively. The capacities are 316.1 mAhcm-3 and 106.4 mAhcm-3, respectively.

The carbon material based on asphalt can be used as the negative electrode to improve the value of asphalt, but because of the complex composition of asphalt, the capacity of asphalt material itself is not high, if it is directly used as the negative material, it needs to carry out the microstructure design, and it is difficult to mass production, and the cost is too high.Therefore, asphalt is usually used as a modified material in the production process to achieve high value-added utilization of asphalt.

Surface coating is one of the most commonly used methods to modify anode materials in industry at present. This method forms a layer of amorphous carbon on the surface of materials by solid phase, liquid phase or gas phase carbonization to build a "core-shell structure".The "shell structure" of the surface can effectively restrain and buffer the volume expansion or structural damage of the active center of the negative electrode material, while increasing the compatibility with the electrolyte and maintaining the stability of the electrode material

Graphite as anode material of lithium ion battery still has many problems, such as in the process of charging and discharging, lithium ion embedment and stripping lead to the lamellar peeling and structure destruction of graphite, graphite and electrolyte compatibility is poor, lithium ion in graphite chemical diffusion coefficient is small.In order to solve these problems, graphite needs to be modified. As a common carbon source of modified graphite, asphalt has been widely concerned by researchers.

The pitch-based anode material has some innovations in its material structure and preparation method, and the capacity and rate performance have made great breakthroughs compared with graphite-based anode materials, but the charge-discharge voltage hysteresis phenomenon is serious, the energy density is reduced, and it is difficult to mass-produce; However, the modification mechanism of asphalt coating is still unclear, and further improving the material properties and maintaining the consistency of the properties of the modified materials is still unclear. Larger room for technical improvement.

Although asphalt is widely used in industry, the composition and structure of asphalt are complex due to the complex sources of asphalt raw materials and the differences in processing technology. During the production process, due to the long screening time of raw asphalt, the instability of the screening process leads to increased costs and low consistency of finished products. Therefore, the development of special asphalt for lithium-ion battery anode materials and the rapid detection of asphalt are also the focus of subsequent asphalt modified anode materials.

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