Hard carbon negative electrode materials make energy storage a "rookie"?

Tech 2023-06-05 09:04:16 Source: Network

Reporter Li He from our newspaperHard carbon is a type of carbon that does not undergo graphitization after high-temperature treatment. Its internal crystal arrangement is disordered and the interlayer spacing is large, which allows the hard carbon negative electrode to store more charges at the same volume, improving the energy density and endurance of sodium ion batteries

Reporter Li He from our newspaper

Hard carbon is a type of carbon that does not undergo graphitization after high-temperature treatment. Its internal crystal arrangement is disordered and the interlayer spacing is large, which allows the hard carbon negative electrode to store more charges at the same volume, improving the energy density and endurance of sodium ion batteries. During the discharge process, the expansion and contraction of the hard carbon negative electrode are more uniform, which increases its cycling stability, charging and discharging performance, and extends the cycling service life of the sodium ion battery.

With the rapid expansion of renewable energy generation such as solar and wind energy, research on new materials for energy storage batteries is also constantly deepening. At the 15th Shenzhen China International Battery Technology Exhibition, a company released a new generation of hard carbon negative electrode materials for sodium ion batteries, which can achieve a charging and discharging efficiency of 90% for the first time.

China is rich in sodium resources, and sodium ion batteries are considered the most suitable new type of battery for large-scale energy storage, which is expected to alleviate the problems of limited energy storage development caused by the shortage and uneven distribution of lithium resources. What are the advantages of hard carbon materials compared to other negative electrode materials for sodium ion batteries? What is the current development status of China's hard carbon material industry? How far is there to go from large-scale application? With these questions in mind, a reporter from Science and Technology Daily interviewed relevant experts.

Hard carbon is the preferred negative electrode material for sodium ion batteries

Sodium ion batteries are mainly composed of positive electrode, negative electrode, electrolyte, separator, etc., and their working principle is similar to that of lithium-ion batteries. The negative electrode material of sodium ion batteries, as the main body of sodium storage in batteries, achieves the insertion or detachment of sodium ions during the charging and discharging process. Therefore, the capacity of the battery is positively correlated with the ability of the negative electrode to store sodium ions. The selection of negative electrode materials plays a decisive role in the development of sodium ion batteries.

Professor Zhou Xiangyang from Central South University said that from the classification of negative electrode materials for sodium ion batteries, they can be roughly divided into five categories. First, carbon based anode materials, mainly including graphite, amorphous carbon, nano carbon, etc., of which amorphous carbon is most likely to take the lead in achieving industrialization; The second is alloy type negative electrode materials, which have high theoretical capacity, but have severe volume expansion and poor cycling performance after electronic sodium insertion; The third is metal oxide and sulfide based negative electrode materials, which have high theoretical capacity but poor conductivity; The fourth is an embedded titanium based negative electrode material with small volume change but low capacity; The fifth is organic negative electrode materials, which have low cost but poor conductivity and are easily soluble in the electrolyte.

Carbon based negative electrode materials have excellent conductivity, flexible preparation methods, low cost, and environmentally friendly, making them the primary choice for negative electrode materials in sodium ion batteries. Among them, hard carbon and soft carbon materials in amorphous carbon are considered as potential negative materials for sodium ion batteries. Soft carbon refers to the carbon that can be graphitized after high temperature treatment. It is usually processed and manufactured with low-cost anthracite as the precursor, but its sodium storage capacity is low, charging speed is slow, and low-temperature performance is poor.

Hard carbon is a type of carbon that does not undergo graphitization after high-temperature treatment. Its internal crystal arrangement is disordered and the interlayer spacing is large, which allows the hard carbon negative electrode to store more charges at the same volume, improving the energy density and endurance of the battery. Due to the larger pore structure of hard carbon, which can accommodate more sodium ions, the expansion and contraction of the electrode during discharge are more uniform, which increases the cycling stability and charge discharge performance of the hard carbon negative electrode, and prolongs the cycling service life of sodium ion batteries.

Zhou Xiangyang said that by comparing the performance of different types of carbon negative electrode materials, it can be found that hard carbon is currently the preferred solution for the commercialization of sodium ion batteries, and is expected to be the first to achieve industrialization.

Biomass becomes the mainstream in the preparation of hard carbon materials

The source of raw materials for hard carbon precursors is abundant, and the selection of precursors and the accumulation of process technology are key factors in the development of hard carbon negative electrode materials, "Zhou Xiangyang said.

The common precursors for preparing hard carbon materials include biomass, synthetic polymers, and fossil fuels. Hard carbon materials prepared with different precursor systems have significant performance differences. Due to the different sources of precursor raw materials, the cost composition of hard carbon materials also varies significantly. Among them, biomass has a wide range of raw materials, such as coconut shells, fruit shells, pomelo peels, and animal and plant tissues, with relatively low costs, making it the preferred choice for preparing hard carbon materials. Synthetic polymers mainly include chemical synthetic materials such as phenolic resin and polyacrylonitrile, which have good electrochemical performance, controllable raw materials, and good product consistency, but have high costs. Fossil fuels mainly include asphalt, coal tar and related mixtures. The source of raw materials is wide and the cost is low, but the product capacity is low. Because asphalt and other volatile substances contain more, additional waste gas and wastewater treatment is required in the production process, which increases the production cost.

At present, the preparation process of hard carbon is multiple and parallel, and hard carbon negative electrode materials are constantly being developed. For example, the team led by Chen Chengmeng, a researcher from Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, prepared starch into hard carbon anode material through chemical reaction, and its achievements were published in the academic journal Energy Storage Materials.

Chen Chengmeng's team also achieved the regulation of the microstructure of hard carbon by changing the reaction temperature in the tubular furnace and adjusting the oxygen element content in the precursor of the reaction product, confirming the influence of oxygen element content on the electrochemical performance of hard carbon negative electrode materials.

Chen Chengmeng emphasized that although the team's research has laid the foundation for the subsequent development of high-performance hard carbon materials, it is still necessary to deeply explore the microstructure and electrochemical properties of the material.

In addition, Professor Xia Yongyao and others from Fudan University immersed the fruit shell biomass materials in hydrochloric acid alcohol solution and sulfuric acid solution in sequence and stirred them to obtain a suspension; Then disperse the suspension in water, filter and dry to obtain the precursor. They heated the precursor under inert gas protection for pre carbonization treatment, cooled it, and then ball milled it to obtain pre carbon powder; The pre carbon powder is then heated under inert gas protection for high-temperature carbonization treatment and cooling to obtain efficient biomass hard carbon negative electrode materials for sodium ion batteries.

The market size of hard carbon negative electrode materials industry will continue to grow

Sodium ion batteries have become a hot research and industrialization topic both domestically and internationally. The Fourteenth Five Year Plan for Renewable Energy Development issued by nine departments, including the National Development and Reform Commission and the National Energy Administration, proposes to research and develop high energy density energy storage, such as sodium ion batteries, liquid metal batteries, solid lithium ion batteries, metal air batteries, lithium sulfur batteries, etc.

Zhou Xiangyang said that currently, researchers have proposed multiple models for the sodium storage mechanism of hard carbon, but there is no unified understanding of its sodium storage mechanism. Therefore, further research is needed to reveal the structure-activity relationship between hard carbon materials and electrochemical reaction mechanisms, providing theoretical guidance and scientific basis for improving the performance of hard carbon. In addition, the impact of physical parameters such as particle size, compacted density, and mass load on the electrochemical performance of hard carbon materials also needs to be further explored to synergistically improve the performance of the materials when applied to sodium ion battery systems.

The "2023-2029 China Hard Carbon Negative Electrode Industry Market Special Survey and Investment Prospect Analysis Report" released by Beijing Zhiyan Kexin Consulting Co., Ltd. points out that with the support of the country for the development of new energy vehicles and energy storage equipment, the market size of China's hard carbon negative electrode material industry will further increase. According to market forecasts, the market size of China's hard carbon negative electrode material industry will reach 8.65 billion yuan in 2025, and the average annual growth rate of the hard carbon negative electrode material industry will reach 15.3% in the next five years.

At present, due to the relatively short development time of the domestic hard carbon negative electrode material industry, most enterprises and research institutions are still in the stage of technological research and optimization. However, major domestic manufacturers are actively laying out the production of hard carbon negative electrode materials. In April of this year, Guangdong Rongna New Energy Technology Co., Ltd. announced that the annual production of 10000 tons of hard carbon negative electrode material precursors project was officially put into operation in the Graphene and Graphene Industrial Park in Yong'an City, Fujian Province, mainly using plant-based biomass as raw materials. Ningbo Shanshan Co., Ltd. stated that the hard carbon negative electrode materials used in sodium ion batteries have achieved tons of sales in China, and it is expected that the mass production scale will reach thousands of tons this year.

Ye Yindan, a researcher at the Bank of China Research Institute, believes that sodium ion batteries perform better than lithium-ion batteries in terms of performance indicators such as low temperature, safety, and fast charging. Although there is still room for improvement in energy density, cycle life, and other aspects, considering the abundant sources of materials, they still have great development potential. With the breakthrough of key technologies such as hard carbon negative electrode materials for sodium ion batteries and the rapid growth of energy storage demand, the application scenarios and scale of sodium ion batteries will also be rapidly developed.

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