Journal of The Electrochemical Society, 163 (8) A1619-A1626 (2016) A1619 0013-4651/2016/163(8)/A1619/8/$33.00 © The Electrochemical Society D-Glucose Derived Nanospheric Hard Carbon Electrodes for Room-Temperature Sodium-Ion Batteries R. V¨ ali, * A. J¨ anes, **, z T. Thomberg, ** and E. Lust ** Institute of Chemistry, University of Tartu, 50411 Tartu, Estonia Electrochemical performance of nanospheric glucose derived hard carbon based electrodes, specially derived from D-glucose via hydrothermal carbonization and subsequent pyrolysis at 1100 ◦ C, has been studied in 1 M NaClO 4 propylene carbonate electrolyte. High Na + electroreduction and Na oxidation peaks were observed in cyclic voltammograms. Galvanostatic charge/discharge mea- surements demonstrated high specific capacity, over 300 mAh g −1 for the first cycle. After 200 th cycle, a specific capacity of 160 mAh g −1 (at 50 mA g −1 cycling rate) has been calculated for the nanospheric hard carbon based half-cells. Raman spec- troscopy, inductively coupled plasma mass spectrometry and energy-dispersive X-ray spectroscopy data indicated accumulation (adsorption/absorption) of Na onto/into the electrochemically polarized porous nanospheric hard carbon material. Impedance data demonstrated that electrode potential has a noticeable influence on the total polarization, and charge transfer resistance as well as on the mass transfer characteristics at the carbon|(1 M NaClO 4 + propylene carbonate) electrolyte interface. © 2016 The Electrochemical Society. [DOI: 10.1149/2.0771608jes] All rights reserved. Manuscript submitted March 16, 2016; revised manuscript received May 20, 2016. Published June 1, 2016. This was Paper 512 from the San Diego, California, Meeting of the Society, May 29-June 2, 2016. Lithium-ion batteries (LIBs) have been studied and used exten- sively for electric vehicle and smart grid applications. 1 Lithium (Li) is the lightest metallic element and lithium electrochemistry has many advantages such as wide voltage region (up to 4 V), high energy density (250–730 Wh L −1 ), high specific power (approximately 250– 340 W kg −1 ) and superior shelf life over a wide temperature range (−20 to 70 ◦ C). 1–7 Li-ion small ionic radius is highly beneficial for mass-transfer step kinetic characteristics, especially in layered solids. However, limited availability and high cost of Li is an increasing con- straint when these batteries are deployed and applied on a large scale. Sodium-ion batteries are considered as promising alternative devices to lithium-ion energy storage systems, since sodium (Na) is an abun- dant and inexpensive element. 1 With growing global energy issues in the 21 st century, sodium-ion electrochemistry has emerged as an attractive alternative energy storage technology to replace LIBs be- cause of sodium abundance and inexpensive raw materials that lower the production cost of sodium-based electrode materials and devices. Sodium-ion batteries (NIBs) utilize similar electrode materials to the ones employed in LIBs; however, the intercalation/accumulation of Na-ion chemistry is slightly different because the Na + ion occupies 1.02 Å in an octahedral coordination site, which is larger than that of Li + (0.76 Å in an octahedral coordination site). 2,3 The choice of sodium is also favored from an electrochemical standpoint as it is char- acterized by a highly negative redox potential and low electrochemical equivalent (0.86 g (A h) −1 ). 1 While Na intercalation cathode materials are gaining attention, 4–9 recent studies have focused on the system- atic development of negative electrode materials. 10–13 Unlike lithium- ion batteries, sodium-ion batteries cannot use graphite materials as negative electrodes, 14 since the formation of binary graphite interca- lation compounds is energetically unfavorable. 15,16 Metallic sodium would be the best negative electrode in terms of theoretical capacity (1166 mAh g −1 ), 17 but extensive dendrite formation during repeated sodium deposition/dissolution steps is a major downside to its ap- plication. However, recent studies of the SEI layer formation on Na metal promise breakthroughs in the near future. 18,19 Among various anode (negative electrode) candidates, hard car- bons have attracted the most attention for NIBs due to their high capacity and relatively high (first) cycle coulombic efficiency. 20,21 However, it should be noted that about 60% of the capacity is con- tributed by sodiation below 0.2 V vs Na + /Na. 22 Recent progress has been made in terms of capacity and reversibility using commercial hard carbons 23,24 such as hard carbons prepared from sugar 25 and pyrolyzed biomass which have not been specifically developed for ∗ Electrochemical Society Student Member. ∗∗ Electrochemical Society Member. z E-mail: alar.janes@ut.ee Na-ion batteries. 26 Specific surface area and optimal graphitization degree are critical parameters that determine high reversible capacity (more than 300 mAh g −1 at C/10 after 120 cycles) and rate capability. 25 A porous hard carbon was used as the anode in sodium ion batteries and exhibited good cycling and rate capability, delivering a moderate capacity of 181 mAh g −1 at 200 mA g −1 after 220 cycles. 26 However, some non-carbonaceous materials such as metals and metal alloys are highly promising electrode materials for NIBs due to their high theoretical gravimetric capacity. 27 Unfortunately, they undergo extensive volumetric changes during charging/discharging, which limits their practical use in large-scale devices. Huang et al. 28 synthesized monodispersed hard carbon spherules (HCS) from an abundant sucrose biomass, and investigated the influence of the car- bonization temperature on the microstructure and electrochemical per- formance of HCS. The initial coulombic efficiency of HCS was in- creased up to 83% by coating its surface with soft carbon by pyrolysis of toluene. The HCS carbonized at 1600 ◦ C showed the highest capac- ity (220 mAh g −1 ) with excellent short-term cycling performance and capacity retention of 93% after 100 cycles. Ji et al. 29,30 developed a graphene oxide-doping strategy for the synthesis of hard carbon with a very low specific surface area. When evaluated as an anode for NIBs, with a high active mass loading of 2.5 mg cm −2 , they reported moder- ate capacity, but one of the highest first-cycle coulombic efficiencies of 83% for NIB carbon anodes (negative electrodes), compared to the 74% demonstrated by hard carbons (HC). Almost no capacity fad- ing was observed (for 300 cycles) for sucrose/graphene oxide derived hard carbon (G-HC), whereas with the conventional HC only 30% of its initial capacity was reversible. When 10 wt% of carbon black was added into the G-HC electrode, the desodiation capacity was increased up to 280 mAh g −1 , while maintaining high cycle life. According to Pyo et al., 31 the porosity and morphology of the sucrose-based hard carbon (SHC) was regulated by varying the amount of bicarbonate salts added during a two-stage sintering process. Reversible capaci- ties of 324 and 289 mAh g −1 were obtained for the first and 100 th cycles at 20 mA g −1 , respectively, in contrast to 251 and 213 mAh g −1 , calculated for SHC. This paper proceeds to demonstrate that the specially designed D-glucose derived hard carbon powder (GDHC), prepared via hy- drothermal carbonization of 2 M D-(+)-glucose solution and sub- sequent controlled pyrolysis, exhibits promising characteristics as a negative electrode material for sodium ion batteries. Experimental Chemicals, reagents and experimental.—D-(+)-glucose (≥99.5% purity, Sigma) was used without further purification for the preparation of the 2 M D-glucose solution in ultrapure water ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 193.40.12.10 Downloaded on 2016-06-05 to IP