Tin-functionalized silicon oxycarbide as a stable, high-capacity anode material for Na-ion batteries

Currently, MXenes have been identified as promising candidate electrode materials for Na-ion batteries because of their excellent energy storage and electrical conductivity. Among them, dual transition metal MXenes have attracted attention due to their excellent properties as anode materials for Na-ion batteries. In order to explore the reason why dual transition metal MXenes outperform single transition metal MXenes, we systemically investigated and compared the performance of TiNbC-based dual transition metal MXenes (TiNbC, TiNbCF2, and TiNbCO2) with that of Nb2C-based single transition metal MXenes (Nb2C, Nb2CF2, and Nb2CO2) as anode materials for Na-ion batteries based density functional theory calculations. The results showed that TiNbC, TiNbCO2, Nb2C, and Nb2CO2 are promising anode materials for Na-ion batteries due to the low diffusion barrier and high capacity of Na on their surfaces. Compared with the Nb2C-based single transition metal MXenes, the TiNbC-based dual transition metal MXenes have better adsorption performance, diffusion rate, and theoretical storage of Na atoms. The higher adsorption ability of TiNbC and TiNbCO2 to Na atoms was attributed to the synergistic effect of Ti and Nb which increases the interaction between the substrate and Na. This conclusion provides a new insight for the development of other high-performance MXenes-based anode materials for Na-ion batteries.

First-principles study of a substitutionally doped phosphorene as anode material for Na-ion batteries

First-principles study of two-dimensional zirconium nitrogen compounds: Anode materials for Na-ion batteries

Sodium (Na)-ion batteries have received widespread attention due to their low cost and good safety. The possibility of two-dimensional vanadium boride (V2B2, MBene) as the anode material for Na-ion batteries is explored by first principles. It is found that V2B2 has good dynamic stability, thermodynamic stability, and conductivity. V2B2 has a good performance as anode material: it can adsorb nearly 3 layers of Na ions, and the maximum capacity reaches 814 mAhg–1. It is found that V2B2 has a very low Na ion diffusion barrier, about 0.011 eV, which represents the ultrahigh ion diffusion rate of Na ions on the surface of V2B2. The average open circuit voltage of V2B2 is 0.65 V, and good metallicity is maintained during the entire Na ion adsorption process. The results indicate that two-dimensional V2B2 has a low diffusion barrier, low open circuit voltage, and high theoretical capacity and is a potential anode material for Na-ion batteries.

Recently demand for Li-ion batteries is growing as power sources for various applications such as electric vehicles and electric energy storage systems, because their high energy density and light weight properties are suitable for these applications. However, lithium resources may be insufficient to meet the increasing demand for these applications. Na-ion batteries could be a promising alternative to Li-ion batteries thanks to the natural abundance and lower cost of sodium. Non-graphitized carbon materials such as hard carbon are well-studied as high capacity anode materials for Na-ion batteries. The discharge capacity of 200 - 300 mAh/g, which is lower than conventional graphite anode materials for Li-ion batteries, has been reported [1,2]. In addition, the insertion mechanism of Na-ion into non-graphitized carbon materials is proposed that Na-ions are first inserted between stacked graphene layers in the voltage range from 2.0 V to 0.2 V (vs. Na metal), and then inserted into nano-pores in the voltage range from 0.2 V to 0.0 V (vs. Na metal) [2]. In this study, we focused on the pore structure of carbon materials and investigated the relationship between the carbon structures and electrochemical properties to clarify the optimum pore structure and propose a new carbon material as anode for high energy Na-ion batteries. Non-graphitized carbon samples were synthesized by heating various raw materials at between 1000 and 2600 °C under flowing argon. The pore structure of the synthesized carbon samples was characterized by using argon and nitrogen adsorption measurement and helium gas densitometry. Electrochemical properties were evaluated by using laminate-type cell with Na metals as the counter electrode and the reference electrode. Open and closed pore volumes of the synthesized carbons were calculated and the relationship between the reversible capacity and pore volume was investigated. As seen in Figure 1, an almost linear relationship between the reversible capacity in the voltage range from 0.2 to 0.0 V (vs. Na metal) and the closed pore volume was confirmed. Some carbon materials with large closed pore volume on the basis of this relationship were designed and successfully synthesized. Figure 2 shows charge/discharge curves of one of synthesized carbon samples. This carbon sample had the closed pore volume of 0.37 cc/g and its discharge capacity reached 413 mAh/g. This result suggests that Na-ion could be inserted reversibly in the closed pore and non-graphitized carbons with large closed pore volume may be promising for high capacity anode materials for Na-ion batteries. [1] D. A. Stevens et al, J. Electrochem. Soc., 148 (2001) A803 [2] S.Komaba et al, ACS Appl. Mater. Interfaces, 3 (2011) 4165 Figure 1

Anatase TiO2 nanoparticles for high power sodium-ion anodes

First principles calculations based on density functional theory (DFT) were studied to carry out the systematical investigation of electrochemical properties of Mo2N MXene. The Na adsorbed metal atom is strongly bounded to respective monolayer at the top of upper Mo-layer (Mo1 atom). The metallic character of Na-adsorbed Mo2N monolayer indicates the high electronic conduction which suggest its potential application for being used as an electrode material in Na-ion batteries. Moreover, the charge transfers from Na-adsorbed atom to the monolayer indicate the cationic state of adsorbed metal atom. The Sodiation potential of Mo2N for single Na-adsorbed atom lying in the range of 0.1-1.0 eV suggests it to be a promising anode material for Na-ion batteries to be used for low charging battery applications.

Fluorine-doped and carbon-coated porous SnO2-NiO composite as a high performance anode material for lithium ion batteries

Graphene-based phosphorus-doped carbon (GPC) is prepared through a facile and scalable thermal annealing method by triphenylphosphine and graphite oxide as precursor. The P atoms are successfully doped into few layer graphene with two forms of P–O and P–C bands. The GPC used as anode material for Na-ion batteries delivers a high charge capacity 284.8 mAh g−1 at a current density of 50 mA g−1 after 60 cycles. Superior cycling performance is also shown at high charge−discharge rate: a stable charge capacity 145.6 mAh g−1 can be achieved at the current density of 500 mA g−1 after 600 cycles. The result demonstrates that the GPC electrode exhibits good electrochemical performance (higher reversible charge capacity, super rate capability, and long-term cycling stability). The excellent electrochemical performance originated from the large interlayer distance, large amount of defects, vacancies, and active site caused by P atoms doping. The relationship of P atoms doping amount with the Na storage properties is also discussed. This superior sodium storage performance of GPC makes it as a promising alternative anode material for sodium-ion batteries.

Lithium-ion batteries (LIBs) have been recognized as major part in the development of electrical devices such as portable device, energy storage system (ESS) and electric vehicle (EV) due to high energy storage-demand. Graphite material is the most widely used as anode part in commercial LIBs due to its low cost and good cycle life. However, due to limited capacity (~372mAh/g) of graphite, alternative anode materials based on conversion or alloying reaction have been extensively studied, which shows exceptional high capacity. Among these anode materials, SnO2 has been attracted as one of the promising anode materials, which stores high electric energy by conversion and alloying reaction during first discharge process: (1) SnO2 + 4Li++ 4e- → Sn + 2Li2O (Conversion reaction; 711mAh/g), (2) Sn + xLi++ xe- → LixSn (0<<x<<4.4) (Alloying reaction; 993mAh/g of Sn or 783mAh/g of SnO2). In this lithium storage mechanism, only alloying reaction has been contributed to reversible capacity after the first irreversible discharge process.[1] Currently, there are several reports that some nano-structured and composite SnO2 materials deliver exceptional high reversible capacity beyond their theoretical capacity based on alloying reaction without clear explanation of additional capacity.[2,3] In our previous work, for elucidating the additional capacity and the detailed lithium storage mechanism of nano-structured SnO2, we performed systematic analysis about the mesoporous SnO2 anode material using synchrotron radiation based analyses such as XRD and XAS, and reported novel electrochemical reaction mechanism. Ordered mesoporous SnO2 prepared by hard templating showed a reversible capacity of about 1100 mAh/g, which is higher than the predicted value based on the alloying reaction mechanism of Sn, formed from conversion reaction of SnO2 with lithium. Synchrotron XAS analysis combined with XRD revealed that some portion of the Li2O phase decomposes to form the SnOx phase with Sn upon delithiation (additional conversion reaction), parallel with dealloying of LixSn (alloying reaction), which leads to unexpected high capacity of an ordered mesoporous SnO2 material.[4] Namely, high performance of SnO2 anode material is highly related to the additional conversion reaction during electrochemical cycling and stable structure for accommodating volume expansion. In this study, to understand the main reason for the difference in electrochemical performance between bulk and mesoporous SnO2, we performed XAS experiment about bulk SnO2 anode material in same procedure with our previous report, and carried out quantitative analysis using EXAFS spectra of bulk and mesoporous sample as well. Besides, for maximizing the performance of SnO2 anode material for LIBs, we prepared SnO2/rGO composite, synthesized by simple refluxing method using graphene oxide, SnCl4 and ascorbic acid. Composition of metal oxide nanoparticles and rGO systems is the efficient methods to improve electrochemical performance in terms of rate performance and cyclability. In metal oxide/rGO composite anode materials, rGO provide faster lithium ion diffusion pathway through rGO sheets and metal-O-C linkage at the interface, and ensure stable structure during volume expansion aroused from electrochemical cycling by strong interaction between rGO sheets and metal oxide nanoparticles.[5] The discharge/charge capacity of bulk, mesoporous, and SnO2/rGO composite were 1644, 1073mAh/g; 2059, 1148mAh/g; and 1752, 1185mAh/g, respectively. Except the irreversible capacity during the initial discharge, reversible capacity is similar to each other. However, compared to bulk and mesoporous SnO2, SnO2/rGO composite material shows prominent cyclability, and its capacity retention after 100th cycles is over 100%. This phenomenon may be related to the stable rGO source and exfoliation process during electrochemical cycling, respectively.[6] Using synchrotron radiation based techniques, we found that high reversible capacity of SnO2/rGO composite comes from alloying reaction and partial conversion reaction as same as bulk and mesoporous SnO2. Additionally, through further XAS experiment using cycled samples, we confirmed key factors in the high performance of SnO2/rGO composite anode material. More detailed discussion will be presented at the time of meeting. Reference [1] I. A. Courtney et al., Journal of The Electrochemical Society 144 (1997) 2045-2052 [2] Z. Ying et al., Appl. Phys. Lett. 87 (2005) 113108 [3] J. Lin et al., ACS Nano 7, (2013) 6001–6006 [4] H. Kim et al., Chemistry of materials 26 (2014) 6361-6370 [5] X.-Y. Shan et al., J. Mater. Chem. A 2 (2014) 17808–17814 [6] J. Wang et al., J. Am. Chem. Soc. 133 (2011) 8888–8891

Due to inherent theoretical capacity limitations and safety issues associated with commonly used anode materials in lithium-ion batteries, carbon nanotubes (CNTs), with their unique one-dimensional tubular structure and superior mechanical, electrical, and thermal properties, can partially address these deficiencies and enhance lithium storage capacity. Therefore, this paper concentrates on the impacts of carbon nanotubes as electrode materials on energy storage for lithium-ion batteries. It discusses three aspects in detail: the use of CNTs as direct anode materials, as composite anode materials, and as flexible electrode materials. Each application will be examined in terms of its specific advantages, existing challenges, and corresponding solutions to improve battery performance. The paper also evaluates the role of CNTs in enhancing the electrochemical stability, improving cycle life, and achieving higher power densities, which makes them highly promising for next-generation energy storage solutions, particularly for portable and flexible electronic devices. Additionally, the unique ability of CNTs to form a highly conductive network facilitates efficient charge transport and reduces internal resistance, further contributing to the overall performance of the battery. Future research directions may focus on optimizing the synthesis methods and improving the interface interactions between CNTs and other active materials, to fully leverage their properties for enhanced safety, higher efficiency, and lower costs. As such, carbon nanotubes are seen as key materials that could play an important role in meeting the growing demand for advanced energy storage systems.

Silicon (Si) anode materials have received much attention on account of their unparalleled theoretical specific capacity, but they suffer from huge volumetric expansion and particle pulverization, which leads to rapid capacity fading and poor electrical conductivity as well. In this work, a quaternary silicon/carbon (Si/C) composite anode material is proposed which combines the advantages of both graphene and the three-dimensional carbon framework through rational structural design and simple synthesis methods. Nanosilicon/carbon nanofibers/pyrolytic carbon (SCC) composite particles are first synthesized by spray drying and pyrolysis, which are then wrapped by graphene nanosheets through a second spray drying and pyrolysis process to obtain the final product (SGCC). In this composite, a 3D carbon skeleton composed of carbon nanofibers and pyrolytic carbon serves as an electric conductive matrix that supports and stabilizes Si nanoparticles, while graphene nanosheets wrapped on the surface further improve the conductivity and structure stability of the composite particles, and isolate the particles from direct contact with electrolytes. Meanwhile, the rich pores of the composite particles can effectively provide space for the volume expansion of Si during lithiation. As a consequence, the as-prepared SGCC composite shows a high initial Coulomb efficiency of 84.7%, a high reversible capacity of 2150.8 mA h g–1, and a good capacity retention rate of 83.75% after 100 cycles.

In-situ preparation of LixSn-Li2O–LiF/reduced graphene oxide composite anode material with large capacity and high initial Coulombic efficiency

Recent progress in rational design of anode materials for high-performance Na-ion batteries

Because of the low cost and plentiful resources of sodium as compared to lithium, sodium-ion batteries (SIBs) are becoming promising alternatives to lithium-ion batteries for large-scale electrochemical energy storage applications. However, the non-availability of appropriate anode materials restricts the use of SIBs. We have herein made an attempt to investigate the suitability of a triformylphloroglucinol (TP) and triazine triamine (TT)-based bilayer organic framework (TPTT) as an anode material for SIBs using density functional theory-based computations. Our study reveals that the bilayer TPTT is a direct band gap semiconductor with a band gap value of 2.64 eV. The triazine framework undergoes a transition from semiconductor to metal after adsorption of sodium at the most favorable carbonyl oxygen (C═O) site, thus ensuring good electrical conductivity. The good electrical conductivity, moderate diffusion barrier (0.56 eV), high theoretical specific capacity (855 mA h/g), average voltage (0.43 V) in the range required for suitable anode materials (0.1–1.00 V), and structural flexibility compel us to infer that the bilayer TPTT may be a potential candidate as an anode material for SIBs.