Can starch be used as an electrode material for rechargeable batteries? This creative and novel idea is being proposed and verified by Chinese scientists.
Recently, the team of Chen Chengmeng, a researcher at the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, used oxygen-rich esterified starch to prepare anode materials for sodium-ion batteries-hard carbon through chemical reactions and studied the precursors of reaction intermediates. Effect of Bulk Oxygen Content on Electrochemical Performance of Hard Carbon Anode Materials
On July 4, related papers were published in the journal "of for Hard: the of by Low-" (of hard: the in by low-). Song Mingxin, a doctoral student at the Institute of Coal Chemistry, is the first author of the paper, and researcher Chen Chengmeng and associate researcher Xie Lijing are the co-corresponding authors of the paper.
(Source: )
The reviewers of the paper spoke highly of the research work. One of the reviewers commented: "This work is an important study of biomass-based hard carbon materials that expands our understanding of changes in oxygen content in biomass precursors and the corresponding microstructure of derived hard carbons. The development of hard carbon materials with high capacity and high first-time Coulombic efficiency provides a new reference."
At present, the mainstream of the rechargeable battery market is lithium-ion batteries. A technology that emerged half a century ago, lithium-ion batteries still account for 80% of the market today. Since most of my country's lithium resources currently rely on imports, it is not conducive to the overall transformation of the traditional energy structure. In recent years, the rapid development of my country's new energy and battery-related industries shows that lithium-ion battery replacement technology has become a strategic direction that needs to be developed in this field.
The emerging sodium-ion battery technology is expected to replace lithium-ion batteries in many fields such as new energy vehicles and energy storage grids due to lower cost and higher safety. This is a promising battery technology.
However, Na-ion batteries also have some technical bottlenecks. Due to the large atomic radius and relative atomic mass, the diffusion of sodium ions is slow during the charging and discharging process of the battery, the volume of the existing electrode materials changes drastically, and the sodium storage performance is not good (it is generally believed that the capacity of the battery is the same as the capacity of the battery (and the capacity of the negative electrode to store cations) It is difficult to obtain good electrochemical performance. Therefore, the development of anode materials with higher sodium storage efficiency, low cost, and good stability is a key step toward the large-scale application of sodium-ion batteries.
▲Picture | Researcher Chen Chengmeng (Source: Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences)
Chen Chengmeng's team used a low-temperature hydrogen reduction strategy to chemically treat esterified starch raw materials adjusted the oxygen content in the reaction product precursor by changing the reaction temperature in the tube furnace, and then prepared hard carbon materials at high temperatures with different precursor samples. The microstructure of the final product hard carbon is tuned by varying the oxygen content.
The process from raw starch to final hard carbon product in this experiment is roughly divided into three steps: first, corn starch and maleic anhydride are used to prepare esterified starch; 1:5), carry out hydrogen reduction reaction with esterified starch, and the reaction product starch is used as the precursor of the final product; finally, with argon as the protective gas, the starch precursor is subjected to high-temperature carbonization reaction at 1100 ° C to complete the hard carbon material. preparation.
▲Figure | Schematic diagram of the preparation route from esterified starch to hard carbon materials (source: marked by the author of this article)
To study the effect of different hydrogen reduction reaction temperatures on the oxygen content of the precursor and the final structure of the hard carbon material, the team selected multiple reduction temperatures (200°C, 300°C, 400°C), and to eliminate the effect of the temperature on the hydrogen reduction reaction Given the direct impact on the product, a hydrogen-free precursor was prepared at 300 °C as a control sample.
The morphological characteristics of the prepared samples are shown in the figure below. It can be seen that almost all product samples are around 10 microns in size. The highly disordered amorphous carbon structure is circled in the TEM image.
▲Figure | Scanning electron microscope images (ad) and high-resolution transmission electron microscope images (eh) of different hard carbon samples (source: )
The team performed structural characterization of hard carbon samples under different conditions, and the results are shown in the figure below. Curves of different colors represent different hard carbon samples, and 200, 300, and 400 respectively correspond to the above reaction temperatures. Figure A is the adsorption-desorption curve of various hard carbon samples, which can be used to calculate the specific surface area of the material; Figure B represents the size distribution of micropores in different samples; Figure C is the X-ray diffraction curve of the sample, with a slight deviation in peak position The shift is due to the difference in oxygen content in the precursors. It can be roughly seen from the characterization diagram that the adsorption capacity and pore size of different samples vary greatly.
▲Figure | Structural representation of different hard carbon samples (source: cropped by the author of this article)
By testing the electrochemical performance of hard carbon materials, the research team found that when it is used as the anode material for sodium-ion batteries, the first Coulombic efficiency of the sample numbered H300-1100 is as high as 82.5% (that is, half of the first charge-discharge cycle battery, the ratio of its charge-discharge capacity) and the specific capacity of 369.8 mAh/g (i.e., the ratio of the electrode material capacity to its mass), strongly confirm the effect of oxygen content on the properties of hard carbon materials.
The team also used the time-resolved Raman spectroscopy system of the H300-1100 sample to study the sodium storage behavior of hard carbon materials and verified the "adsorption-intercalation-filling" sodium storage mechanism of sodium ions in hard carbon materials.
▲Figure | Mechanism of sodium ion intercalation (source: cropped by the author of this article)
At the end of the paper, a full battery experiment was carried out on the hard carbon anode material, which further verified the high specific capacity and stable high Coulombic efficiency of the H300-1100 sample in actual use.
When Chen Chengmeng recalled the whole research work, he mentioned that the exploration spirit of tracing back to the source played a great role in this project. The hard carbon material obtained in the early stage of the experiment has a large specific surface area, resulting in a low first Coulomb effect. Through continuous tracking and a large number of exploratory experiments, the team found that the oxygen content in the precursor is the key factor to balance the structural stability and specific surface area of hard carbon materials.
After identifying this core issue, the research team adopted a simple low-temperature hydrogen reduction method to adjust the oxygen content of the reaction product to prepare high-performance hard carbon materials. Through comparative experiments, structural analysis, and other means, the influence of the oxygen content in the precursor on the microstructure of the final product was finally revealed.
Chen Chengmeng said: "Scientific research may not necessarily produce the results we expected, but as long as we are good at summarizing, summarizing, and reviewing our experimental phenomena, data, and conclusions in the process, we will eventually open a new window and discover hidden truths. Truth. Answers after confusion.
For the next step of this work, Chen Chengmeng said that although the team's research has laid a good foundation for the subsequent development of high-performance hard carbon materials, the microstructure and electrochemical properties of the materials still need to be explored in depth.
To this end, the team will start with raw materials, build a structural model of the material, establish a corresponding database; and in-depth study of the sodium storage mechanism of hard carbon materials, to further clarify the storage and transport mechanism of sodium ions in the material, as well as the structure of the material. The dependence between sodium storage performance and physical structure, and the development of hard carbon materials for specific application scenarios, such as high power, ultra-low temperature, and high temperature, etc. In addition to the electrode material itself, the team will continue to focus on the compatibility of sodium-ion battery electrolytes, separators, etc. with hard carbon materials.
When introducing the application prospects of this research, Chen Chengmeng said: In recent years, sodium-ion batteries have attracted extensive attention and strategic layout from academia and industry due to their advantages of low production cost and high safety performance.
As the electrode material of this type of battery, hard carbon has inherent advantages and prospects in practical sodium ions due to its structural characteristics and advantages that are more suitable for storing sodium ions with a larger radius, low cost, and green and sustainable. Ion batteries are wide.
"We believe that sodium-ion batteries with hard carbon as the negative electrode will go out of the laboratory and enter people's lives. Combined with the cost and energy density of sodium-ion batteries, it has a wide range of applications in low-speed vehicles, large vehicles, and other fields." Scale Energy storage, smart grid, and other application prospects. Chen Chengmeng said.