The increase in the demand for clean and sustainable energy has prompted intense effort towards the realization of high-performance energy storage technologies. Among the many available energy storage technologies, lithium(Li)-ion batteries with Li-intercalation compounds as positive electrodes have achieved great success for use in portable electronic devices [1, 2]. A typical rechargeable Li-ion battery requires heavy host compounds (e.g., CoO₂) to accommodate guest atoms (e.g., Li), which greatly limits its energy density to less than 210 Wh kg^-1. On the other hand, a Li-sulfur (S) battery as a typical integration reaction battery system [4] may open a new horizon for electric vehicles.  As the sulfur cathode has a theoretical specific capacity of 1672 mAh g^-1, a Li-S battery can achieve an energy density of 2654 Wh kg^-1 when combined with a lithium metal anode, which is 3-5-fold higher than those of current Li-ion batteries [5]. In addition, sulfur is a highly abundant element source on earth and is not geographically isolated [6], which may reduce the cost of cathode materials. However, Li-S batteries have serious problems [7-9], including low utilization of the active material and a poor cycle life because of the insulating property of sulfur and the high solubility of lithium polysulfides in organic electrolytes. To overcome the above-mentioned problems, much effort has been devoted to designing S-based cathodes, thus far. Various elegantly designed carbons have been studied for use as sulfur hosts to enhance the electronic conductivity of sulfur and trap polysulfides within a carbon framework simultaneously. However, carbon is an electrochemically inactive material in the integration reaction of Li-S batteries, and therefore its quantity in the electrode should be reduced as much as possible.

Vanadium pentoxide (V₂O₅) is one of the most common cathode materials in the field of Li batteries and has a few advantages when used as an additive in sulfur cathodes. It is an electrochemically active material in the cut-off voltage range from 1.5 to 4 V, which closely matches that for sulfur cathodes (from 1.5 to 3 V), and it also positively contributes to the capacity of sulfur cathodes. In this study, S/Carbon/porousV₂O₅ nanocomposites were prepared by a novel synthesis route and their physical and electrochemical properties were further investigated.

Porous V₂O₅ particles were firstly prepared by spray pyrolysis (SP) with NH₄NO₃ additive. The pore structure of obtained samples were analyzed by N₂ adsorption-desorption isotherm measurements. The V₂O₅ particles with pore size less than 100 nm could be prepared at 500 ºC by SP with a 0.272 mol L-1 NH₄NO₃ additive, and the porous V₂O₅ electrode exhibited a first discharge capacity of 400 mAh g^-1 at 20 mA g^-1.

The as-prepared porous V₂O₅ were packed with acetylene black and S at a targeted ration in a closed reactor. The reactor was heated at different temperatures ranging from 120 to 200 ºC. The effect of S content, heating temperature and heating time were investigated systematically.

Figure 1 shows the cycle performance of the S/C/porous V₂O₅ composite electrode at a charge-discharge rate of 100 mA g^-1. The cycle performance of the S/C composite electrode is also shown in the figure as a comparison. The S/C/porous V₂O₅ composite electrode exhibits a discharge capacity of 666 mAh g^-1 at 50^th cycles, while the S/C composite electrode shows a discharge capacity of 379 mAh g^-1 at 50^th cycles . As seen from this fact, the S/C/porous V₂O₅ composite electrode shows larger discharge capacities and better cycle performance than the S/C composite electrode. This fact indicate that the V₂O₅ additive to the S/C composite electrode leads to enhance its electrochemical performance.

References

[1] Bruce et. al., Nat. Mater. 11 (2012), 19–29.

[2] Armand et. al., Nature, 451 (2008), 652–657.

[3] Manthiram et. al., Chem. Rev. 114 (2014), 11751–11787.