Bitumen-based Hard Carbon Anode Material Preparation Method
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Update time : 2023-04-14 09:23:05
The development and research of lithium-ion secondary batteries began in the 1970s and it is a new generation of energy storage batteries after NiCd and NiMH batteries. The use of embedded lithium compounds instead of lithium metal as the negative electrode of the battery is a leap forward in the history of secondary batteries. As a new type of high-energy secondary power supply, lithium-ion batteries have the advantages of high specific energy, smooth discharge voltage, high voltage, good low temperature performance, friendly to the environment, superior safety performance, no memory effect and long cycle life, etc. The development of cathode materials plays a decisive role in the development of lithium-ion batteries. At present, the research on carbon anode materials is one of the most active areas in lithium-ion battery research, in which the special structure of hard carbon makes it have the advantages of high capacity and long cycle life, and is one of the most promising alternative materials to graphite in the future.
Lithium battery anode material classification
Li-ion battery anode materials are mainly divided into two categories: carbon and non-carbon materials. Carbon materials are available from a wide range of material sources and in many different structures. Compared to other anode materials, carbon has the advantages of high specific capacity, low electrochemical potential, good cycling performance, low cost, non-toxicity and stability in air, making it the most mature anode material for lithium-ion batteries on the market today. Large-scale commercial lithium-ion battery anodes are now dominated by graphite-based materials, including natural and artificial graphite. However, due to its low energy density (theoretical capacity of 372 mAh-g-1), graphite has been unable to meet the high performance requirements of lithium-ion batteries, which has become the biggest bottleneck shackling the continued development of graphite-based carbon cathodes. Compared to graphite, hard carbon has more lithium ion storage sites, such as the sides of graphite layers, edges, holes around the layer structure and a large number of defects, etc. A variety of lithium embedding methods enable hard carbon to reach a specific capacity of 400 to 700 mAh-g-1, which better meets the requirements of people with high energy storage. In addition, hard carbon has isotropic structural characteristics, and its layer spacing is larger than that of graphite, which facilitates the transport and diffusion of lithium ions; at the same time, it has better cycling and multiplier performance and lower cost.
Hard carbon preparation method
There are many precursors for the preparation of hard carbon, such as sugars, phenolic resins, polymers, biomass, bitumen etc. The different substances used to prepare hard carbon materials show similar charge/discharge curves. Bitumen has advantages as a hard carbon precursor due to its high coking value, easy availability from a wide range of sources and low price. However, untreated bitumen tends to form graphite-like structures during the carbonisation process. Therefore, to use it for the preparation of hard carbon, the bitumen needs to be pre-treated, such as using cross-linking agents to cross-link the bitumen to change its microstructure and hinder the growth of graphite microcrystals during pyrolytic carbonisation, and then solid-phase carbonisation to obtain hard carbon materials; another method is pre-oxidation, i.e. using oxidising agents to pre-oxidise the bitumen to obtain pre-oxidised bitumen with a certain oxygen content. Due to the presence of oxygen heteroatoms, the bitumen does not easily form an ordered structure during the pyrolytic carbonisation process, resulting in a hard carbon material with a three-dimensional cross-linked structure.
Factors affecting the capacity of lithium-ion battery cathode materials
Hard carbon has high capacity, good multiplier performance and low production cost when used as anode in Li-ion batteries, but it has the disadvantage of high irreversible capacity and low first coulomb efficiency, which can lead to the need for excess cathode material to supplement it when assembling the battery, thus reducing the energy density of the battery. Therefore, analysing the reasons for the existence of irreversible capacity and modifying the material can help to improve its first coulomb efficiency and expand its application prospects.
Methods to improve the capacity of lithium battery anode materials
The surface functional groups of hard carbon materials and the heteroatoms in their structure lead to a large irreversible capacity in the charging and discharging process. The purpose of improving the electrochemical properties of hard carbon materials can be achieved by controlling the pretreatment conditions to improve the layer spacing and specific surface area of the materials and controlling the morphology of the materials. For example, in the asphalt modulation process to choose a suitable oxidant to get oxidized asphalt, so that its layer spacing becomes larger, or add polyvinyl alcohol aqueous solution, etc. to get a better sphericity of the precursor, reduce its specific surface area, and further reduce the first effect of the consumption site.
Market prospects for anode materials for lithium batteries
The increasing depletion of non-renewable resources such as petroleum, the greenhouse effect and other environmental protection requirements have led to the importance of new energy vehicles, and the research on power batteries has become particularly important, while there is still relatively little research on hard carbon as an anode material, especially in the study of material structure and lithium inlay mechanism, the optimisation of raw materials and preparation methods, and the modification of materials, which needs to be further strengthened and deepened. It is believed that with the continuous development of research and production, the application of hard carbon in the new energy vehicle industry will increase rapidly. Bitumen is a complex mixture of materials, which can lead to deviations between batches and uneven product quality in the preparation process. Therefore, to bring it to scale, further research is needed to investigate the relationship between raw material bitumen preparation and performance, and to precisely modulate and precisely control the bitumen. In addition, asphalt is prone to environmental impacts such as fumes during processing, and there is also a need to strengthen green production. It is believed that with the continuous development of technology, technical bottlenecks will also be gradually broken through, the conversion of inexpensive asphalt into high value-added carbon electrode materials will have great market potential.
Lithium Battery Anode Material Supplier
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