Scientists from Shihezi University in China have reported the use of raw cotton stalk materials to construct novel lithium-ion anode materials for use in energy storage applications. Their research has appeared in the journal Materials Letters.
Study: Nitrogen-doped Cotton Stalk Porous Carbon Composite as Anode Material for Lithium-ion battery. Image Credit: alinabuphoto/Shutterstock.com
Background to the Research
Lithium-ion batteries have found widespread application in electronic devices such as smartphones and computers in recent years. These devices offer the benefits of high energy density, versatility, minimal maintenance, enhanced performance, and longevity.
Conventional lithium-ion batteries typically employ carbon-based materials in the construction of anodes, with metal oxides commonly used for positive electrodes. Lithium salts in organic solvents are used as electrolytes in these devices.
Graphite suffers from low specific capacity and poor rate performance, and these critical limitations have promoted the development of new generations of carbon-based materials for use as anodes in lithium-ion batteries. Anodes can be constructed from several carbon-based materials, including graphene, carbon fiber, carbon nanotubes, and porous carbon.
Amongst these materials, porous carbon produced from biomass has been shown to have particular promise in the field of lithium-ion battery energy storage. This is due to the wide availability and sustainability of biomass materials from agricultural and food industry sources. Another advantage of biomass-derived porous carbon is its favorable transportation and charge transport capabilities.
Heteroatom doping and activators are commonly used to modify biochar to obtain high-performance anode materials. Surface wettability and lithium-ion storage sites are promoted by the use of heteroatom doping, whereas activators promote the development of porous networks which enhance multidimensional electron transport and minimize transport distances between electrode and electrolytes.
Studies have indicated that surface wettability and ion storage have a positive effect on the electrochemical performance of lithium-ion devices, but the synergistic mechanisms are not fully understood at the moment. Understanding the effect of properties such as these will improve the design of high-performance and safe lithium-ion batteries.
The authors have proposed a one-step carbonization process for the preparation of porous carbon materials from cotton stalks for use as anode materials in lithium-ion batteries. The process incorporates the synergistic mechanism of ZnCl2 activation and N-doping. ZnCl2 activators were used in the method, along with urea as a nitrogen source.
The structural characteristics of porous carbon were analyzed to understand this synergistic N-doping/ZnCl2 activation mechanism’s effects on electrochemical performance.
Cotton stalks were prepared by crushing them into powders. Then, the powder was sieved. Stalks were then immersed for 24 h in a urea solution. The resultant slurry was placed in an oven and dried to completely remove any moisture. The dried slurry was mixed with ZnCl2 and pyrolyzed to produce the samples for analysis.
The resulting material was washed with deionized water and hydrochloric acid. The product was denoted N-AC. Another material, N-CSC, was prepared via the same process, but without the addition of ZnCl2, with another material, denoted AC by the authors, prepared without urea and therefore no N-doping. Materials and battery cell construction techniques were thoroughly categorized in the study.
Structural analysis of the biomass-derived activated carbons revealed the influence of ZnCl2 on porosity. N-CSC samples displayed no fragmentation phenomena which leads to mesopore and macropore formation, which is important for rapid ion diffusion. N-AC was revealed to be an amorphous carbon with obvious pore structures. Extra pores were formed on the product’s tube walls.
N-AC samples displayed the highest initial coulombic efficiency, which is crucial for the practical application of anode materials. N-AC also possessed the highest discharge capacities after one hundred cycles.
Although N-AC has a lower pore volume than AC, its better cycle performance indicates that pore structure has a limited effect on electrochemical performance, though the enhanced pore structure of AC provided better cycle performance. N-AC samples also displayed the best rate of performance and specific capacities.
Results indicated that the synergistic effect of N-doping and ZnCl2 activation enhances electrochemical performance by increasing interlayer spacing and relative heteroatom content in the material.
The authors have presented a simple carbonization method that takes advantage of the synergistic effect of ZnCl2 activation and N-doping to manufacture high-performance lithium-ion anodes from raw cotton stalk biomass.
In the study, it was demonstrated that pore development is the basis for improved electrochemical performance in activated carbon, with interlayer spacing and heteroatom content playing a key role. The paper has made an important contribution to the development of new carbon-based anode materials for use in advanced lithium-ion batteries.
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Wang, Y et al. (2022) Nitrogen-doped Cotton Stalk Porous Carbon Composite as Anode Material for Lithium-ion battery Materials Letters 132526 [online, pre-proof] sciencedirect.com. Available at: https://doi.org/10.1016/j.matlet.2022.132526