Sodiation Capacity Research Articles

A Venture Synthesis and Fabrication of BiVO4 as a Highly Stable Anode Material for Na‐Ion Batteries

AbstractNeedle‐like BiVO4 anode material for Na‐ion batteries was prepared by a simple solvothermal technique at 100 °C without further calcination. The BiVO4 electrode exhibited initial discharge (sodiation) capacity of 897 mAh /g with coulombic efficiency of 70.68% at 100 mA /g. The average coulombic efficiency was estimated at 93.07% and sodiation capacity predicted at 432 mAh/g upto 200 cycles. The average sodiation/desodiation capacity retention were found to be 52.07 and 68.10%, respectively for more than 100 cycles. The results demonstrate that needle‐like BiVO4 anode material offers an excellent electrochemical performance for large‐scale energy storage applications.

A Red‐Phosphorous‐Assisted Ball‐Milling Synthesis of Few‐Layered Ti3C2Tx (MXene) Nanodot Composite

AbstractLayered two‐dimensional (2D) early transition metal carbides (MXenes) are a new class of 2D materials with established activity for electrochemical energy conversion and storage. The use of MXenes is expected to increase by reducing their lateral size to the nanoscale. Herein, using Ti3C2Tx (T=O, OH, F) MXenes as an example, we show that μm‐sized MXenes can be reduced in size to ≈6 nm nanodots by ball‐milling with red phosphorous (P). It is remarkable almost all starting MXenes were converted to nanodots with this method. The Ti3C2Tx surface O groups interacted with P strongly and chemically to drive the nanodots formation. Ti3C2Tx nanodots (TNDs) with different sizes could also be obtained by ball‐milling Ti3C2Tx with other solid‐state elements such as carbon, sulfur and silicon. The as‐prepared TNDs and P composite was evaluated as a sodium‐ion battery anode material. A good sodiation capacity (≈600 mA h g−1) at 260 mA g−1 and good cycle stability for 150 cycles were shown.

Mechanism of Na‐Ion Storage in Hard Carbon Anodes Revealed by Heteroatom Doping

Hard carbon is the leading candidate anode for commercialization of Na‐ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short‐range local order resembling graphene within each layer, but complete disorder along the c‐axis between layers. A primary challenge holding back the development of Na‐ion batteries is that a complete understanding of the structure–capacity correlations of Na‐ion storage in hard carbon has remained elusive. This article presents two key discoveries: first, the characteristics of hard carbons structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na‐ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low‐voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. The combined experimental studies and first principles calculations reveal that it is the Na‐ion‐defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low‐potential plateau capacity. The understanding suggests a new design principle of hard carbon anode: more reversibly binding defects and dilated turbostratic domains, given that the specific surface area is maintained low.

Highly Stable Intermetallic FeSn2‐Graphite Composite Anode for Sodium‐Ion Batteries

AbstractThe development of anodes with high capacity, long cycle life and good rate capability is essential to expedite the commercialization of sodium‐ion batteries for practical applications, including grid storage and electric vehicles (EV). Herein, we report the facile solvothermal synthesis of nanostructured iron distannide (FeSn2) intermetallic particles as an alloy‐type anode and the improvement of its cycle life by fabricating FeSn2‐graphite composites by a ball‐milling process. The influence of graphite concentration on the sodium storage properties is studied. The composite anode delivered over 400 mAh g−1 sodiation capacity over 200 cycles at a specific current of 100 mA g−1. In addition, the composite anode exhibited excellent rate performance at higher current rates. This result would certainly pave the way for the development of high‐performance anodes that would realize low‐cost sodium‐ion batteries with a longer calendar life.

(Invited) Hard Carbons Made from Cellulose for Na- and K-Ion Batteries

Na-ion batteries are of great interest to realize high energy batteries consisting of abundant elements in the Earth crust. As a negative electrode material for the Na-ion batteries, non-graphitizable carbon, so-called hard carbon, is a promising candidate because of the low operating potential and good cycle stability. Conventional hard carbon prepared at carbonization temperature of 1000 – 1500 ºC delivers ca. 300 mAh g-1 and our group actually reported that hard carbon prepared from sucrose at 1300 ºC delivers 290 mAh g-1with good cycle stability [1]. However, higher capacity is still required to realize comparable energy performance to Li-ion batteries. In this study, we have investigated influence of synthesis condition of hard carbons, such as carbon source and heating temperature, on electrochemical performance as negative electrode of Na-ion battery on the basis of our previous research [1]. Hard carbons were prepared by carbonization of several saccharides which have different molecular structure at 1300 ºC. Figure 1 shows charge/discharge (sodiation/desodiation) curves of hard carbons in Na cells, which are prepared from glucose, amylopectin, glycogen, maltose, and cellulose. Cellulose-derived hard carbon shows the higher sodiation capacity among them which should be due to different nanostructure of hard carbon depending on the starting materials. According to a previous report on carbonization process of cellulose [2], dewatering and following cross-linkage of cellulose occur during pre-heating at around 300 ºC in air followed by carbonization. As the cross-linkage is thought to affect nanostructure and electrochemical properties of hard carbon, we prepared hard carbon with different pre-heating temperatures of cellulose, and the electrochemical properties were examined in Na cells. Figure 2 compares charge/discharge curves of hard carbon prepared by carbonization of cellulose at 1300 ºC with different preheating at 275 – 350 ºC. Although the hard carbons shows quite similar potential variation, hard carbon prepared via pre-heating at 275 ºC delivers higher reversible capacity of 351 mAh g-1, in details, capacity increase depended on a voltage plateau approaching 0 V vs. Na. Small-angle X-ray scattering data reveals that the larger nano-sized pore is formed in the hard carbon synthesized through pre-heating at 275 ºC. Therefore, sodium insertion into the nano-sized pore is believed to be key to increase capacity in the voltage plateau region at close to 0 V. Importantly, the formation of nano-sized pores is influenced by cross-linkage during pre-heating. We additionally examine hard carbons in non-aqueous K cell, as hard carbon is also known to be electrochemically active for potassium insertion [3]. Relation between electrochemical properties and structure of hard carbons is further studied with X-ray diffraction and nitrogen adsorption measurements and will be discussed in the presentation.

The electrochemical performance of super P carbon black in reversible Li/Na ion uptake

Super P carbon black (SPCB) has been widely used as a conducting additive in Li/Na ion batteries to improve the electronic conductivity. However, there has not yet been a comprehensive study on its structure and electrochemical properties for Li/Na ion uptake, though it is important to characterize its contribution in any study of active materials that uses this additive in non-negligible amounts. In this article the structure of SPCB has been characterized and a comprehensive study on the electrochemical Li/Na ion uptake capability and reaction mechanisms are reported. SPCB exhibits a considerable lithiation capacity (up to 310 mAh g–1) from the Li ion intercalation in the graphite structure. Sodiation in SPCB undergoes two stages: Na ion intercalation into the layers between the graphene sheets and the Na plating in the pores between the nano-graphitic domains, and a sodiation capacity up to 145 mAh g–1 has been achieved. Moreover, the influence of the type and content of binders on the lithiation and sodiation properties has been investigated. The cycling stability is much enhanced with sodium carboxymethyl cellulose (NaCMC) binder in the electrode and fluoroethylene carbonate (FEC) in the electrolyte; and a higher content of binder improves the Coulombic efficiency during dis-/charge.

Synthesis of Cu2SnS3 nanosheets as an anode material for sodium ion batteries

Single crystalline Cu2SnS3 nanosheets with exposed (220) planes have been synthesized via a facial solvothermal solution chemical route. The solvent of ethylenediamine hindered the growth along the [110] direction and facilitated the formation of two dimensional nanostructures. Electrochemical performance of Cu2SnS3 electrodes in sodium ion batteries was investigated. Cu2SnS3 electrodes exhibit an initial sodiation capacity of 586 mAh/g and 178 mAh/g after 50 cycles. The electrochemical properties of Cu2SnS3 nanosheets suggest it is a potential anode material for sodium ion batteries.

Experimental Study on Sodiation of Amorphous Silicon for Use as Sodium-Ion Battery Anode

Amorphous Si (a-Si) powders have been synthesized using various synthetic methods, and their electrochemical sodiation behaviours have been studied in detail. These methods include (1) a chemical delithiation method where Si is first lithiated and then delithiated either in an aqueous or organic solution, (2) a mechanical method where crystalline Si is subjected to high-energy ball milling, and (3) a mechanical fusion method where a Si-Sn composite with a Si-Sn atomic ratio of 0.94:0.06 is synthesized through high-energy ball milling. Commercial silicon monoxide (SiO) has also been examined for comparison. It is shown that facile oxidation of a-Si encountered in the methods (1) and (2) has led to low sodiation capacity and huge first-cycle irreversible capacity, similar to those of SiO. By contrast, the mechanically fused Si-Sn composite, which contains a Sn shell that prevents the oxidation of the partially amorphized Si core, exhibits a maximum sodiation capacity of 161mAhg−1 based on active material. This is translated to an estimated sodiation capacity of no more than 230mAhg−1 for the a-Si component in the composite. The presence of the Sn shell considerably reduces the first-cycle irreversible capacity and charge-transfer resistance, resulting in improved rate and cycle performance. This suggests a new material design strategy that may enable the use of the a-Si for Na-ion battery anode applications.

Peanut Shell Hybrid Sodium Ion Capacitor with Extreme Energy - Power Rivals Lithium Ion Capacitors

ABSTRACT: This is the first report of a hybrid sodium ion capacitor (NIC) with the active materials in both the anode and the cathode being derived entirely from a single precursor: peanut shells, which are a green and highly economical waste globally generated at over 6 million tons per year. The electrodes push the envelope of performance, delivering among the most promising sodiation capacity - rate capability - cycling retention combinations reported in literature for each materials class. Hence the resultant NIC also offers a state-of-the-art cyclically stable combination of energy and power, not only in respect to previously published NICs but also as compared to Li ion capacitors (LICs). The ion adsorption cathode based on Peanut Shell Nanosheet Carbon (PSNC) displays a hierarchically porous architecture, a sheet-like morphology down to 15 nm in thickness, a surface area on par with graphene materials (up to 2396 m2g-1) and high levels of oxygen doping (up to 13.51 wt%). Scanned from 1.5 - 4.2 V vs. Na/Na+ PSNC delivers a specific capacity of 161 mAhg-1 at 0.1A g-1 and 73 mAhg-1 at 25.6 Ag-1. A low surface area Peanut Shell Ordered Carbon (PSOC) is employed as an ion intercalation anode. PSOC delivers a total capacity of 315 mAhg-1 with a flat plateau of 181 mAhg-1 occurring below 0.1 V (tested at 0.1 Ag-1), and is stable at 10,000 cycles (tested at 3.2 Ag-1). The assembled NIC operates within a wide temperature range (0 - 65°C), yielding at room temperature (by active mass) 201, 76 and 50 Wh kg-1 at 285, 8500 and 16500 W kg-1, respectively. At 1.5 - 3.5 V, the hybrid device achieved 72% capacity retention after 10,000 cycles tested at 6.4 Ag-1, and 88% after 100,000 cycles at 51.2 Ag-1.

Na-Ion Battery Anodes: Materials and Electrochemistry.

The intermittent nature of renewable energy sources, such as solar and wind, calls for sustainable electrical energy storage (EES) technologies for stationary applications. Li will be simply too rare for Li-ion batteries (LIBs) to be used for large-scale storage purposes. In contrast, Na-ion batteries (NIBs) are highly promising to meet the demand of grid-level storage because Na is truly earth abundant and ubiquitous around the globe. Furthermore, NIBs share a similar rocking-chair operation mechanism with LIBs, which potentially provides high reversibility and long cycling life. It would be most efficient to transfer knowledge learned on LIBs during the last three decades to the development of NIBs. Following this logic, rapid progress has been made in NIB cathode materials, where layered metal oxides and polyanionic compounds exhibit encouraging results. On the anode side, pure graphite as the standard anode for LIBs can only form NaC64 in NIBs if solvent co-intercalation does not occur due to the unfavorable thermodynamics. In fact, it was the utilization of a carbon anode in LIBs that enabled the commercial successes. Anodes of metal-ion batteries determine key characteristics, such as safety and cycling life; thus, it is indispensable to identify suitable anode materials for NIBs. In this Account, we review recent development on anode materials for NIBs. Due to the limited space, we will mainly discuss carbon-based and alloy-based anodes and highlight progress made in our groups in this field. We first present what is known about the failure mechanism of graphite anode in NIBs. We then go on to discuss studies on hard carbon anodes, alloy-type anodes, and organic anodes. Especially, the multiple functions of natural cellulose that is used as a low-cost carbon precursor for mass production and as a soft substrate for tin anodes are highlighted. The strategies of minimizing the surface area of carbon anodes for improving the first-cycle Coulombic efficiency are also outlined, where graphene oxide was employed as dehydration agent and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was used to unzip wood fiber. Furthermore, surface modification by atomic layer deposition technology is introduced, where we discover that a thin layer of Al2O3 can function to encapsulate Sn nanoparticles, leading to a much enhanced cycling performance. We also highlight recent work about the phosphorene/graphene anode, which outperformed other anodes in terms of capacity. The aromatic organic anode is also studied as anode with very high initial sodiation capacity. Furthermore, electrochemical intercalation of Na ions into reduced graphene oxide is applied for fabricating transparent conductors, demonstrating the great feasibility of Na ion intercalation for optical applications.

Ultrafine Manganese Oxide As Sodium-Ion Battery Anode Involving Charge-Transfer Between Mn(III) and Mn(II) Oxides

Our investigation on manganese dioxide (MnO2) as an anode material for sodium (Na)-ion batteries (NIBs) reveals a remarkable size effect within the nanometer range on the electrochemical sodiation activity of the oxide. Space-confined ultrafine (UF)-MnO2, with an average crystal size of 4 nm, synthesized using a porous silicon dioxide templated hydrothermal process exhibits a high reversible sodiation capacity of 392 mAh g−1 compared with the negligible activity shown by the aggregates of larger (14 nm) MnO2 nanocrystallites. To our knowledge, the present study is the first to show that MnO2 is electrochemically active as an NIB anode. The UF-MnO2 anode exhibits exceptional rate and cycle performance, including a reversible sodiation capacity of >100 mAh g−1 at a current density of 7500 mA g−1 and >70% capacity retention after 500 cycles at 150 mA g−1. The enhanced cycle stability may be attributable to the solid-embedding architecture that enables the reduction of the dimensional variations in the active material. In operando synchrotron X-ray absorption near-edge structure analysis reveals combined charge–storage mechanisms involving a unique two-oxide conversion reaction between Mn(III) and Mn(II) oxides, Mn(III)–O1.5 + Na+ + e - « 1/2 Na2O + Mn(II)–O, and non-Mn-centered redox reactions. Figure 1

Peanut Shell Hybrid Sodium Ion Capacitor with Extreme Energy - Power Rivals Lithium Ion Capacitors

This is the first report of a hybrid sodium ion capacitor (NIC) with the active materials in both the anode and the cathode being derived entirely from a single precursor: peanut shells, which are a green and highly economical waste globally generated at over 6 million tons per year. The electrodes push the envelope of performance, delivering among the most promising sodiation capacity - rate capability - cycling retention combinations reported in literature for each materials class. Hence the resultant NIC also offers a state-of-the-art cyclically stable combination of energy and power, not only in respect to previously published NICs but also as compared to Li ion capacitors (LICs). The ion adsorption cathode based on Peanut Shell Nanosheet Carbon (PSNC) displays a hierarchically porous architecture, a sheet-like morphology down to 15 nm in thickness, a surface area on par with graphene materials (up to 2396 m2g-1) and high levels of oxygen doping (up to 13.51 wt%). Scanned from 1.5 - 4.2 V vs. Na/Na+ PSNC delivers a specific capacity of 161 mAhg-1 at 0.1A g-1 and 73 mAhg-1 at 25.6 Ag-1. A low surface area Peanut Shell Ordered Carbon (PSOC) is employed as an ion intercalation anode. PSOC delivers a total capacity of 315 mAhg-1 with a flat plateau of 181 mAhg-1 occurring below 0.1 V (tested at 0.1 Ag-1), and is stable at 10,000 cycles (tested at 3.2 Ag-1). The assembled NIC operates within a wide temperature range (0 - 65°C), yielding at room temperature (by active mass) 201, 76 and 50 Wh kg-1 at 285, 8500 and 16500 W kg-1, respectively. At 1.5 - 3.5 V, the hybrid device achieved 72% capacity retention after 10,000 cycles tested at 6.4 Ag-1, and 88% after 100,000 cycles at 51.2 Ag-1.

Ether-based electrolyte enabled Na/FeS2 rechargeable batteries

Abstract We demonstrate for the first time that by simply substituting ether-based electrolyte (1.0 M NaCF 3 SO 3 in diglyme) for the commonly used carbonate-based electrolyte, the cyclability of FeS 2 towards sodium storage can be significantly improved. A sodiation capacity over 600 mAh/g and a discharge energy density higher than 750 Wh/kg are obtained for FeS 2 at 20 mA/g. When tested at 60 mA/g, FeS 2 presents a sodiation capacity of 530 mAh/g and retains 450 mAh/g after 100 cycles, much better than the cycling performance of Na/FeS 2 tested in carbonate-based electrolyte.