Titirici Hard Carbon Microtubes Made from Renewable 2016 Accepted

Hard carbon microtubes derived from renewable cotton as high performance anode material for sodium-ion batteries By Yunming Li, Yong-Sheng Hu*, Maria-Magdalena Titirici*, Liquan Chen, Xuejie Huang Prof Y.-S Hu, Y M Li, Prof L Q Chen, Prof X J Huang Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing100190, China E-mail: yshu@aphy.iphy.ac.cn Prof M.-M Titirici School of Engineering and Materials Science &Materials Research Institute, Queen Mary University of London, London, UK E-mail: m.m.titirici@qmul.ac.uk Keywords: Energy storage; Sodium-ion batteries; Anode; Hard carbon microtubes Abstract Sodium-ion batteries (SIBs) have attracted increasingly more and more attention for scalable electrical energy storage due to the abundance and wide distribution of Na resources However, the anode side still faces several challenges, which hinders poses induces poses grand still remains great challenge for the commercialization application of SIBs Here we report the production of uniform hard carbon microtubes (HCTs) from natural cotton through one simple carbonization process and their application as an anode in SIBs The study shows that the electrochemical performance of our HCTs is seriously affected by the carbonization temperature due to the differences within their microstructure and chemical composition heteroatomic content The HCTs carbonized at 1300oC deliver the highest reversible capacity of 315 mAh g-1 and good rate capability due to their unique tubular structure This contribution is not only providesing a new approach for preparing hard carbon materials with unique tubular mincrostructure using natural inspiration, but it also deepens the fundamental understanding of the sodium storage mechanism Introduction In order to increase the utilization of renewable energies such as wind or solar power to help decarbonize the global economy, more efficient and affordable energy storage technologies are required Electrochemical energy storage technologies based on rechargeable batteries show considerable advances due to their high round-trip efficiency, flexible power, long cycle life, and low maintenance [1,2] Lithium-ion batteries (LIBs) with the advantages of high energy density, good rate capability and long cycle life have been widely applied as the power sources for portable electronic devices and electric vehicles [3] The large-scale application of LIBs would certainly lead to a significant increase in their price as supported by the recent rise in the price of lithium carbonate In addition there are concerns related to the uneven geographical distribution of lithium in the earth crust Sodium-ion batteries (SIBs) have recently attracted significant attention as promising candidates for large-scale stationary energy storage at a lower cost due to the high abundance of sodium coupled with the possibility of using aluminum current collectors for the anode.[4-8] The design of low-cost and high-performance electrode materials including both cathodes and anodes is a key to promote their future commercialization Fortunately, several high performance cathode materials with high sodium storage capacity, high average voltage and high rate capability have been recently discovered These materials include oxides[9-13] and polyanionic compounds[14-17] In particular, layered oxides with a high reversible capacity are ideal candidates for commercial applications due to their simple preparation and high energy Recently, Hu and colleagues made significant progress in copper-based layered oxides and proved a highly reversible Cu2+/Cu3+ redox couple in both P2-phase and O3-phase oxides for the first time.[18-21] However, the discovery of suitable anode materials remains a major challenge and is the main limiting step, which hinders the commercialization of SIBs Graphite is the most used negative electrode in LIBs However, it is not a suitable anode for sodium storage in traditional electrolytes due to the thermodynamic and steric reasons.[22,23] Nevertheless, reversible sodium storage in natural graphite was realized using ether-based or diglyme-based electrolytes, and the Na+-solvent co-intercalation combined with partial pseudocapacitive behaviors were demonstrated [24,25] Natural graphite delivers a reversible capacity of 150 mAh g-1 with an excellent cycling stability, but a poor Coulombic efficiency Expanded graphite was also used as an anode in SIBs and exhibited a high reversible capacity of 284 mAh g -1 at a current density of 20 mA g-1 with good cycling performance.[26] Other anode materials for SIBs extensively studied in the literature include amorphous carbon materials,[27-30] alloys,[31-34] oxides[35-39] and organic compounds[40-42] The Sstructural breakdown caused by a significant volume expansion during the the Na insertion process leads to the loss of electrical contact and capacity fading in the case of alloy-based anode materials The low sodium storage capacity of oxides and the low initial Coulombic efficiency of organic compounds may limit their industrialization application in comercialpractical SIBs Therefore, hard carbons, which are carbons with randomly oriented graphitic layers, are the most promising candidates among all anode materials for SIBs due to their high reversible capacity, low average sodium storage voltage and excellent cycling stability since first reported by Dahn and others [43-52] The fundamentals of sodium storage mechanism in hard carbon materials has also attracteds research attention recently as this is still poorly understood.[53-56] To reduce the cost of hard carbons, we have recently reported the production of low-cost amorphous carbon materials combining hard and soft carbon precursors with a high reversible capacity, good cycling and rate capability [57,58] To control the Mmorphology control in the production of hard carbon materials can be achieved using, processes, such as hydrothermal carbonisationtreatment,[49] templating methods[59] or selfassembly[60] are normally employed, etc These processes have energy and atom economy penalties and thusalso lead to the increase in the cost of carbon materials Here we propose to use a renewable biomass, i.e of natural cotton as a precursor to prepare hard carbon materials with a uniform microtubular shape in a one simple step The electrochemical performance of the resulting hard carbon microtubes (HCTs) as anodes for SIBs was found to be significantly affected by the carbonization temperature The HCTs carbonized at 1300oC exhibit the best sodium storage performance with a high reversible capacity of 315 mAh g -1, a high initial Coulombic efficiency of 83% and excellent cycling stability This work provides a new concept for achieving carbon materials with controlled morphology using bioinspiration Results and discussion Figure 1a and b show a photograph and SEM images of the initial cotton precursor The SEM picture shows a linear fiber shape with diameters around 10-20 µm and a hollow structure After carbonization atin high temperature under Argon gas, the cotton roll turns black, indicating its successful transformation into carbon The carbonized sample cotton maintains its two kinds of typical linear and braided fibrous morphology along with theand hollow structure A reduction in the diameter of fiber to 5-10 µm is noticed in the carbonized samples The hollow tubular structure of hard carbon material facilitates the transport of the electrolyte and reduces the diffusion distance for Na+ ions, improving the electrochemical performance of hard carbon To further study the microstructure of HCT, X-ray diffraction (XRD) and Raman spectroscopy were conducted and the results are shown in Figure 2a and b All XRD patterns exhibit broad peaks at 24° and 43° attributed to the crystallographic planes of (002) and (100) in the disordered carbon structure There is no significant change in the peak patterns of HCT with improving the carbonization temperature, which demonstrates HCT’s nature of hard carbon The (002) peak position shifts a higher angle with increasing heat treatment temperature, indicating the local structural development to short-range ordering and the decrease of d 002 Raman spectra as shown in Figure 2b shows two separate characteristic bands: the of D-band (the defectinduced band) peak at ~1343 cm -1 and G-band (the crystalline graphite band) peak at ~1589 cm-1, confirming the amorphous structure The half width at half maximum (HWHM) of G and D bands in the Raman spectra decreases with increasing carbonization temperature, which further indicates the development of local shortrange ordering structure The La that is calculated from the intensity ratio of D-band over G-band (ID/IG) abnormally decreases at a higher carbonization temperature suggesting the decrease of (100) direction of graphitic microcrystals, which is consistent with previous reports.[49] The results of the XRD and Raman analyses are shown in Table The N2 adsorption-desorption isotherm in Figure 2c shows the BET surface area and the pore structure of the HCT The specific BET surface area of the HCT is directly related to the carbonization temperature The calculated surface area of the HCT decreases with the increasinge theof carbonizationheat treatment temperature., the HCT1000 shows the largest specific BET surface area of 538 m2 g-1 while the HCT1300 and HCT1600 exhibit a smaller specificBET surface area of 38 m2 g-1 and 14 m2 g-1, respectively Theis low surface area of HCT1300 and HCT1600 could limits the induce limited SEI formation and thus improve the initial Coulombic efficiency, which is good agreement consistent with the electrochemical results (Table 1) In addition, the pore size distribution in Figure 2d also shows different pore sizes depending on the carbonization temperature For Tthe HCT1000 material has , a large amount of micropores and mesopores are present, while these pores decrease sharply reduce with the increasinge the of carbonization temperature The pore size distribution of the HCT1300 and HCT1600 materials is mainly centered around 1-1.5 nm The pore evolution in the of the HCT materials is due to a the decrease inof functional groups, and athe poor stacking of C-C aromatic structures and the increase of rotatory graphene layers High-resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) were used for a more detailed investigation of the carbon microstructure The HRTEM micrographs are shown in Figure 2e-g As expected for hard carbons a disordered carbon structure is observed confirming indeed the hard carbon nature of our HCTs Increasing the carbonization temperature, we can clearly observe the development of a local ordered structure containing nanographitic domains At the same time there is also an increase in the amount of nanovoids surrounded by some parallel carbon hexagonal layers A higher amount of nanovoids with a size of 1-2nm can be observed in the HCT1600 sample whichsample, which iscan be related to shifting some of the carbon layers with respect to each other at higher temperatures All SAED patterns exhibit dispersed diffraction rings as a further demonstration of turbostratic carbon structure The diffraction rings become sharper with increasing the carbonization temperature, indicating the development of a more ordered structure The TEM and SAED results are well supported by XRD, Raman spectroscopy and the pore structure distribution from BET measurement using N adsorption The electrochemical performance of HCTs was first tested in half coin cells Figure 3a-c show the CV curves of HCT1000, HCT1300 and HCT1600 at a scanning rate of 0.1 mV s-1 in the voltage range of 0-2 V The irreversible peaks of HCT1300 at 0.38 V and HCT1600 at 0.35 V in the first cathodic process can be assigned to the formation of solid electrolyte interphase (SEI) layer, while the irreversible sharp peak of HCT1000 around V can be ascribed to the irreversible reaction of electrolyte with surface functional groups and the formation of SEI layer The HCT1000 material contains a higher number of functional groups due to lower carbonization temperature In addition, its larger specific surface area, would facilitate more side reactions which lead to a lower initial Coulombic efficiency All reduction peaks disappear during the subsequent cycles in HCT1000 sample, whose CV curves are similar, with capacitance behavior This behaviour indicates a potential adsorption and desorption mechanism of sodium storage in HCT1000 The irreversible area of HCT1300 and HCT1600 electrodes is much smaller as compared to the HCT1000 electrode This corresponds to a higher initial Coulombic efficiency A pair of sharp redox peaks appears at about 0.1 V in both the HCT1300 and HCT1600 electrodes, which can be attributed to the sodium insertion/extraction into/from the nanovoids of hard carbon The HCT1600 electrode has a lower reduction and oxidation peak at position, indicating a lower sodium storage potential Figure 3d displays the typical initial discharge-charge profiles of the three HCT electrodes at a current density of 0.1C (30 mA g -1 or 0.10 mA cm-2) in the voltage range of 0-2 V The HCT1000 delivers a low reversible capacity of 88 mAh g -1 with only a sloping region in the electrochemical curves and an extremely low initial Coulombic efficiency of 26% This is due to very few Na-ion storage sites in the low temperature carbonized material, which is well supported by all the characterization data in particular HRTEM Interestingly both HCT1300 and HCT1600 show high reversible sodium storage capacity of about 300 mAh g-1 and high initial Coulombic efficiency above 80% In particular, the HCT1300 electrode exhibits the highest reversible capacity of 315 mAh g -1 (1.02 mAh cm-2) with a high initial Coulombic efficiency of 83% The HTC1600 has a higher initial Coulombic efficiency compared with the HCT1300 due to less oxygenated groups and a smaller specific surface area, reducing the irreversible sodium loss Comparing the electrochemical curves of HCT1300 with HCT1600, one can find that the HCT1300 has a higher capacity in the sloping region while the HCT1600 has higher capacity in the plateau region In addition, the HCT1300 exhibits a slightly higher sodium storage voltage than that of HCT1600 according to the CV measurements The difference in sodium storage capacity in the sloping and plateau region is due to the difference in the microstructure between the two materials HTC1600 material has less defected sites, more graphitic nanodomains and more nanovoids, indicating that the sloping region corresponds to the sodium storage in defected sites, edges and the surface while the plateau region corresponds to the sodium storage in nanovoids We have also compared the electrochemical properties of different carbonized fibers from the literature with our HCT materials The conclusion is that indeed, our the result shows that the HCT electrode delivers higher initial Coulombic efficiency and reversible capacity (Table S1) The rate performance was also measured to evaluate the kineticsc property of the HCT electrodes carbonized at different temperatures The results are shown in Figure 3e Overall the HCT electrodes exhibit moderate rate capability in half cells as compared with other the hard carbon materials reported before in the literature [48-50] The rate performance deteriorates with increasing the carbonization temperature of HCT, which is in good agreement with the previous results [49] Interestingly, the HCT1300 shows a better rate performance compared with some the monodispersed hard carbon spherules at with a carbonization temperature of 1300oC previously reported by our group, which indicates that the tubular structure of HCT is more beneficial to reduce of the diffusion distance of Na + ions and improve the rate capability The HCT1300 delivers specific capacities of 275 mAh g -1 and 180 mAh g-1 at current rates of 0.5C and 1C, respectively Figure 3f shows the cycling performance of HCT1000, HCT1300 and HCT1600 electrodes at 0.1C for 100 cycles All the HCT electrodes exhibit good cycling stability., Eespecially the HCT1000 has almost no capacity fade duringin the cycling process, indicating the stability of adsorption-desorption during sodium storage in a way that is similar with the capacitive phenomena The cycling stability of HCT1300 and HCT1600 is affected by temperature due to a change in conductivity and polarization, which results in variation of reversible capacity in the plateau region The HCT1300 retains a capacity of 305 mAh g–1 after 100 cycles, corresponding to a capacity retention of 97% To better understand the difference between the samples carbonized at different temperatures in particular with relation to their different rate capabilities, we have employed galvanostatic intermittent titration technique (GITT) to measure the apparent diffusion coefficient of Na+ ions in HCT electrodes with a pulse current at 0.1C for 0.5 h between rest intervals for h The diffusivity coefficient of Na + ions (DNa+) can be estimated based on Fick’s second law with the following simplified equation: 2  m B VM   ∆ES  D= ÷  ÷ πτ  M B S   ∆Eτ  where τ is the pulse duration, m B and MB are the active mass and molar mass of carbon, VM is the molar volume, and S is the active surface area of the HCT electrodes ΔES and ΔEτ can be obtained from the GITT curves As shown in Figure 4c and d, Na+ ions diffusivity coefficient is around 10-9 cm2 s-1 The diffusivity coefficient variation in HCT1300 and HCT1600 electrodes is similar during sodiation and desodiation processes During the sodiation process, the apparent diffusion coefficient of HCT1300 and HCT1600 firstly decreases slowly followed by a steeper decrease The diffusivity coefficient recovers before the cutoff potential During the desodiation process, the apparent diffusion coefficient first decreases until 0.10 V, then increases and finally it decreases again before reaching the cutoff voltage We can notice that the region with the lowest apparent diffusion coefficient is mainly concentrated at the plateau section of discharge/charge curves It can also be observed that the HCT1600 has a lower Na+ ions apparent diffusion coefficient compared with the HCT1300, which sheds some light on the fast fading of the plateau capacity at large current rates explaining the better rate performance of HCT1300 The variation in the diffusivity coefficient value for HCT1000 is similar with the one of HCT1300 and HCT1600 in the sloping region However, for HCT1000 there is no intensively low diffusivity coefficient region, which explains the reason for the good rate capability of HCT1000 The GITT results indicate that the sodium storage mechanism in HCT1000 is consistent with the sloping region of HCT1300 and HCT1600 while the plateau region in HCT1300 and HCT1600 has a different mechanism The difference in the diffusivity coefficient values in sloping and plateau regions suggests that there are different binding energies for the Na-ion-carbon interactions Ex situ TEM and X-ray photoelectron spectroscopy (XPS) were used to investigate the structural changes and the sodium storage mechanism in the HCT materials The results obtained from the best performing material, HCT1300 are shown in Figure TEM images before and after discharge show a disordered carbon structure with the same d-spacing value of 0.404 nm as the initial XRD result on pristine samples, which indicates that there is no obvious intercalation of sodium into graphitic layers The edge of carbon layers and the nanovoids of HCT1300 become ill defined after sodiation, indicating the formation of sodium storage sites The TEM measurement for the HCT1300 sample shows a smooth homogeneous SEI layer with a thickness of about 30nm after 100 cycles (Figure S1) In the XPS profile for the Na 1s for the HCT1300 sample after etching 60nm, we can see the Na 1s spectra at discharging state demonstrating the sodium storage in the HCT1300 The intensity and the value of the binding energy for the Na 1s spectruma increases and approaches the one of metallic Na upon discharging from 0.12V (the over potential of sloping region) to 0V (the over potential of plateau region) Due to a lower binding energy of surface adsorption, we can summarize the sodium storage mechanism as follow: (І) the Na adsorption on disordered graphene sheets corresponding to the sloping region above 0.12V and (ІІ) the nanovoids filling in accordance with the plateau region close to 0V The mechanism can explain the different electrochemical behaviors of HCTs carbonized at different temperatures as supported by GITT results In order to exemplify the actual performance of HCT, we fabricated coin-type full sodium ion batteries with the air-stable Na0.9[Cu0.22Fe0.30Mn0.48]O2 as positive electrode and the HCT1300 as negative electrode Figure 5a shows the typical charge-discharge profiles of Na0.9[Cu0.22Fe0.30Mn0.48]O2 //HCT1300 full cell at a current rate of 0.2C (60 mA g-1) in the voltage range of 1-4.05 V The full cell delivers a high reversible capacity of 290 mAh g-1 (based on negative electrode) after several activation cycles with an initial Coulombic efficiency of 73% and an average voltage of 3.2V The energy density of this system based on positive and negative active materials is calculated to be 207 Wh kg-1 The full cell also exhibited good rate performance with a high capacity of 220 mAh g-1 even at a high current rate of 1C and good cycling stability with a 92% capacity retention after 100 cycles These outstanding properties of full cells demonstrate that the HCT1300 shows promising sodium storage performance as the anode for SIBs Conclusion We have synthesized hard carbon materials with a uniform microtubular morphology from cotton fibers by a simple one step carbonization method The materials were prepared by carbonization at different temperatures from 1000 to 1600°C and exhibited different electrochemical performances These differences in the electrochemical performance were investigated by microstructure-function correlations The HCT1000 electrode delivers a capacity of only 88 mAh g -1 with only a sloping region while the HCT1300 electrode exhibited the highest reversible capacity of 315 mAh g-1 with typical electrochemical curves for hard carbons in SIBs Besides correlation between the electrochemical performance and structure as determined from XRD, TEM, SEM, Raman and nitrogen adsorption we also used GITT to measure the apparent diffusion coefficient of Na + ions in HCT electrodes This helped us to understand more clearly the reason for moderate rate performance in hard carbon anodes The result shows that the low apparent diffusion coefficient of the plateau region in electrochemical curves is mainly responsible for the poor rate capability We have confirmed that indeed the sloping region corresponds to the adsorption of sodium in defected sites, edges and the surface of nanographitic domains while the plateau region is contributed to the nanovoids filling as initially proposed in the literature.[53] The practical feasibility of HCT in full cell was further demonstrated by fabricating full cells with O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2 as cathode and HCT1300 as anode We have obtained a high energy density of 207 Wh kg -1, excellent rate capability with a capacity of 220 mAh g -1 at 1C and good cycling stability Our work shows a simple preparation method for hard carbon materials with controllable morphology by utilizing natural precursors with tubular structure We have also demonstrated that the structural differences in the resulting materials affect the electrochemical performance and serve as good model systems to understanding the electrochemical sodium storage behaviors in hard carbons Experimental Materials synthesis HCT was prepared by the direct pyrolysis of cotton The cotton roll was carbonized for hours in a tube furnace under Argon flow The carbonization temperatures were 1000oC, 1300oC and 1600oC, respectively The fabricated hard carbon microtubes denoted as HCT1000, HCT1300 and HCT1600 were prepared as summarized in Table Materials characterizations The structure was characterized by an X’Pert Pro MPD X-ray diffractometer (XRD) (Philips, Netherlands) using Cu-Kα radiation (1.5405 Å) and Raman spectra (JY-HR 800) The morphologies of the samples were investigated with scanning electron microscope (SEM) (Hitachi S-4800) High-resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) patterns were recorded on a FEI Tecnai F20 transmission electron microscope Nitrogen adsorption and desorption isotherms were determined by nitrogen physisorption on a Micrometritics ASAP 2020 analyzer The X-ray photoelectron spectroscopy (XPS) spectra were recorded with a spectrometer having Mg/Al Kα radiation (ESCALAB 250 Xi, ThermoFisher) All binding energies reported were corrected using the signal of the carbon at 284.8 eV as an internal standard For the ex situ XPS and TEM measurements, the coin cell was disassembled in an argon-filled glove box after discharging and the electrode was washed in dimethyl carbonate (DMC) for three times to remove the NaPF6, then the drying sample was obtained and moved to the machine with Argon-filled sealing tube as transferred box In this process, all samples were exposed to air within 3–4 seconds Electrochemical measurements All the electrochemical tests were conducted in coin cells (CR2032) The working electrode was prepared by spreading the mixed slurry of active material and sodium alginate binder in water solvent with a weight ratio of 9.5:0.5 onto Cu foil, and then dried at 100oC in vacuum for 10 hours The loading mass of hard carbon electrode was controlled between 2.5 ~ 3.5 mg cm -2 The electrolyte was a solution of 0.6 M NaPF6 in ethylene (EC) and dimethyl carbonate (DMC) (1:1 in volume) A sodium foil was used as the counter electrode and glass fiber was used as the separator All the operations were performed in the Argon-filled glove box The discharge and charge tests were carried out on a Land BT2000 battery test system (Wuhan, China) in a voltage range of 0–2 V at various C-rates under room temperature For the galvanostatic intermittent titration technique (GITT) tests, the cell was discharged/charged at 0.1C with current pulse duration of 0.5 h and interval time of h Cyclic voltammetry (CV) was measured using Autolab PGSTAT302N (Metrohm, Switzerland) A sodium-ion full cell was constructed using HCT1300 as the negative electrode and O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2 as the positive electrode in a CR2032 coin-type cell Synthesis method of the Na0.9[Cu0.22Fe0.30Mn0.48]O2 material was a conventional solid state reaction.[21] The weight ratio of the two electrodes (negative/positive) was 1:3.4 The full cells were charged and discharged in a voltage range of 1–4.06 V at 0.2C current rate Supporting Information Supporting Information is available from the Wiley Online Library or from the author Acknowledgements This work was supported by funding from the NSFC (51222210, 11234013, and 51421002), “973” Projects (2012CB932900), and the One Hundred Talent Project of the Chinese Academy of Sciences Y.-S Hu would like to thank to Royal Society via the Newton Fund for an Advanced Newton Fellowship at Queen Mary University of London which triggered this collaboration Author contributions Y.-S H and M.-M T conceived and designed this work; Y M L performed all the synthesis and electrochemical experiments; Y M L., Y.-S H and M.-M T wrote the paper; all the authors participated in analysis of the experimental data and discussions of the results as well as preparing the paper References [1] B Dunn, H Kamath and J M Tarascon, Science 2011, 334, 928–935 [2] D Larcher and J M Tarascon, Nature Chemistry 2015, 7, 19–29 [3] C.-X Zu and H Li, Energy Environ Sci 2011, 4, 2614–2624 [4] S -W Kim, D -H Seo, X Ma, G Ceder and K Kang, Adv Energy Mater 2012, 2, 710–721 [5] V Palomares, M Casas-Cabanas, E Castillo-Martínez, M.H Han, T Rojo, Energy Environ Sci 2013, 6, 2312–2337 [6] H L Pan, Y -S Hu and L Q Chen, Energy Environ Sci 2013, 6, 2338–2360 [7] N Yabuuchi, K Kubota, M Dahbi, and S Komaba, Chem Rev 2014, 114, 11636–11682 [8] D Kundu, E Talaie, V Duffort, L.F Nazar, Angew Chem Int Ed 2015, 54, 3431–3448 [9] M D Slater, D Kim, E Lee, C S Johnson, Adv Funct Mater 2013, 23, 947– 958 [10] S M Oh, S T Myung, C S Yoon, J Lu, J Hassoun, B Scrosati, K Amine and Y K Sun, Nano Lett 2014, 14, 1620–1626 [11] Y S Wang, R J Xiao, Y S Hu, M Avdeev and L Q Chen, Nat Commun 2015, 6, 6954 [12] S Y Xu, Y S Wang, L B Ben, Y C Lyu, N N Song, Z Z Yang, Y M Li, L Q Mu, H T Yang, L Gu, Y.-S Hu, H Li, Z.-H Cheng, L Q Chen and X J Huang, Adv Energy Mater 2015, 5, 1501156 [13] X G Qi, Y S Wang, L W Jiang, L Q Mu, C L Zhao, L L Liu, Y.-S Hu, L Q Chen and X J Huang, Part Part Syst Charact 2015, DOI: 10.1002/ppsc.201500129 [14] Z L Jian, W Z Han, X Lu, H X Yang, Y.-S Hu, J Zhou,Z B Zhou, J Q Li, W Chen, D F Chen and L Q Chen, Adv Energy Mater 2013, 3, 156–160 [15] P Barpanda, G Oyama, S Nishimura, S C Chung and A Yamada, Nat Commun 2014, 5, 4358 [16] C Li, X Miao, W Chu, P Wua and D G Tong, J Mater Chem A 2015, 3, 8265–8271 [17] Y R Qi, L Q Mu, J M Zhao, Y.-S Hu, H Z Liu and S Dai, Angew Chem Int Ed 2015, 54, 9911–9916 [18] S Y Xu, X Y Wu, Y M Li, Y -S Hu and L Q Chen, Chin Phys B 2014, 23, 118202 [19] Y M Li, Z Z Yang, S Y Xu, L Q Mu, L Gu, Y.-S Hu, H Li and L Q Chen, Adv Sci 2015, 2, 1500031 [20] L.-Q Mu, Y.-S Hu, L.-Q Chen, Chin Phys B 2015, 24, 038202 [21] L Q Mu, S Y Xu, Y M Li, Y.-S Hu, H Li, L Q Chen and X J Huang, Adv Mater 2015, 27, 6928–6933 [22] D A Stevens and J R Dahn, J Electrochem Soc 2001, 148, A803–A811 [23] K Nobuhara , H Nakayama , M Nose , S Nakanishi and H Iba, J Power Sources 2013, 243, 585–587 [24] B Jache and P Adelhelm, Angew Chem Int Ed 2014, 53, 10169–10173 [25] H Kim, J Hong, Y.-U Park, J Kim, I Hwang and K Kang, Adv Funct Mater 2015, 25, 534–541 [26] Y Wen, K He, Y J Zhu, F D Han, Y H Xu, I Matsuda, Y Ishii, J Cumings and C S Wang, Nat Commun 2014, 5, 4033 [27] P Thomas, J Ghanbaja and D Billaud, Electrochim Acta 1999, 45, 423–430 [28] L David and G Singh, J Phys Chem C 2014, 118, 28401–28408 [29] T Y Liu, R Kavian, I Kim and S W Lee, J Phys Chem Lett 2014, 5, 4324– 4330 [30] L David, R Bhandavat and G Singh, ACS Nano 2014, 8, 1759–1770 [31] J F Qian, Y Chen, L Wu, Y L Cao, X P Ai and H X Yang, Chem Commun 2012, 48, 7070–7072 [32] Y H Xu, Y J Zhu, Y H Liu and C S Wang, Adv Energy Mater 2013, 3, 128– 133 [33] L F Xiao, Y L Cao, J Xiao, W Wang, L Kovarik, Z M Nie and J Liu, Chem Commun 2012, 48, 3321–3323 [34] J Sun, H.-W Lee, M Pasta, H Yuan, G Zheng, Y Sun, Y Li and Y Cui, Nat Nanotechnol 2015, 10, 980−985 [35] H L Pan, X Lu, X Q Yu, Y -S Hu, H Li, X Q Yang and L Q Chen, Adv Energy Mater 2013, 3, 1186 [36] Y Sun, L Zhao, H L Pan, X Lu, L Gu, Y -S Hu, H Li, M Armand, Y Ikuhara, L Q Chen and X J Huang, Nat Commun 2013, 4, 1870 [37] X Q Yu, H L Pan, W Wan, C Ma, J M Bai, Q P Meng, S N Ehrlich, Y -S Hu and X -Q Yang, Nano Lett 2013, 13, 4721−4727 [38] Y S Wang, X Q Yu, S Y Xu, J M Bai, R J Xiao, Y -S Hu, H Li, X Q Yang, L Q Chen and X J Huang, Nat Commun 2013, 4, 2365 [39] K Zhu, S H Guo, J Yi, S Y Bai, Y J Wei, G Chen and H S Zhou, J Mater Chem A 2015, 3, 22012-22016 [40] L Zhao, J M Zhao, Y S Hu, H Li, Z B Zhou, M Armand and L Q Chen, Adv Energy Mater 2012, 2, 962–965 [41] X Y Wu, J Ma, Q D Ma, S Y Xu, Y.-S Hu, Y Sun, H Li, L Q Chen and X J Huang, J Mater Chem A 2015, 3, 13193–13197 [42] X Y Wu, S F Jin, Z Z Zhang, L W Jiang, L Q Mu, Y.-S Hu, H Li, X L Chen, M Armand, L Q Chen and X J Huang, Sci Adv 2015, 1, e1500330 [43] D A Stevens and J R Dahn, J Electrochem Soc 2000, 147, 1271–1273 [44] Y Cao, L Xiao, M L Sushko, W Wang, B Schwenzer, J Xiao, Z Nie, L V Saraf, Z Yang and J Liu, Nano Lett 2012, 12, 3783–3787 [45] H G Wang, Z Wu, F I Meng, D l Ma, X l Huang, L M Wang and X B Zhang, ChemSusChem 2013, 6, 56–60 [46] T Chen, Y Liu, L Pan, T Lu, Y Yao, Z Sun, D H C Chua and Q Chen, J Mater Chem A 2014, 2, 4117–4121 [47] W Luo, J Schardt, C Bommier, B Wang, J Razink, J Simonsen and X Ji, J Mater Chem A 2013, 1, 10662–10666 [48] L J Fu, K Tang, K P Song, P A van Aken, Y Yu and J Maier, Nanoscale 2014, 6, 1384-1389 [49] Y M Li, S Y Xu, X Y Wu, J Z Yu, Y S Wang, Y -S Hu, H Li, L Q Chen and X J Huang, J Mater Chem A 2015, 3, 71-77 [50] J Ding, H Wang, Z Li, K Cui, D Karpuzov, X Tan, A Kohandehghanab and D Mitlin, Energy Environ Sci 2015, 8, 941–955 [51] L Qie, W M Chen, X Q Xiong, C C Hu, F Zou, P Hu and Y H Huang, Adv Sci 2015, 1500195 [52] S.-W Zhang, W Lv, C Luo, C.-H You, J Zhang, Z.-Z Pan, F.-Y Kang and Q.H Yang, Energy Storage Mater 2015, DOI: 10.1016/j.ensm.2015.12.004 [53] D A Stevens and J R Dahn, J Electrochem Soc 2000, 147, 4428-4431 [54] Y S Yun, K.-Y Park, B Lee, S Y Cho, Y.-U Park, S J Hong, B H Kim, S Lee, Y W Park, H.-J Jin and K Kang, Adv Mater 2015, 27, 6914–6921 [55] B Zhang , C M Ghimbeu , C Laberty , C Vix-Guterl and J.-M Tarascon, Adv Energy Mater 2015, 1501588 [56] C Bommier, T W Surta, M Dolgos and X L Ji, Nano Lett 2015, 15, 5888– 5892 [57] Y M Li, L Q Mu, Y.-S Hu, H Li, L Q Chen and X J Huang, Energy Storage Mater 2016, 2, 139-145 [58] Y M Li, Y.-S Hu, H Li, L Q Chen and X J Huang, J Mater Chem A 2016, 4, 96-104 [59] P Adelhelm, Y.-S Hu, L Chuenchom, M Antonietti, B M Smarsly and Joachim Maier, Adv Mater 2007, 19, 4012–4017 [60] J Tang, J Liu, C L Li, Y Q Li, M O Tade, S Dai and Y Yamauchi, Angew Chem Int Ed 2015, 54, 588 –593 Table Physical parameters and electrochemical properties for HCT Sample HCT1000 HCT1300 HCT1600 HTTsa (oC) d002 (Å) Lc (nm) La (nm) SBET (m2 g-1) RCb (mAh g-1) ICEc(%) 1000 1300 1600 4.14 4.10 4.02 1.60 4.26 1.62 4.03 1.66 3.44 538 38 14 88 315 294 26 83 85 a The heat treatment temperatures The reversible capacity c The initial Coulombic efficiency b Figure Morphology evolution of cotton before and after carbonization a) The schematic illustration of cotton (Inset: the micrograph of cotton fiber); b) A SEM image of cotton; c) A SEM image of the carbonized cotton; d) The magnified SEM images of the carbonized cotton with the details of structure Figure Structure of HCT carbonized at different temperatures a) XRD patterns and b) Raman spectra of HCT with different conditions; c) N2 adsorption-desorption isothermal curve and d) the corresponding pore size distribution of HCT; TEM and SAED images of e) HCT1000, f) HCT1300 and g) HCT1600 Figure Electrochemical performance of the HCT electrodes Cyclic voltammetry (CV) curves of a) HCT1000, b) HCT1300 and c) HCT1600; d) Galvanostatic 1st discharge/charge profiles of HCT at a current rate of 0.1C; e) Rate capability of HCT from 0.1C to 2C; f) Cyclic performance of HCT at a current rate of 0.1C Figure GITT tests GITT potential profiles of HCT for a) sodiation and b) desodiation during the second cycle; Apparent diffusion coefficients calculated from the GITT potential profiles of HCT for c) sodiation and d) desodiation during the second cycle Figure Ex situ characterization of HCT1300 electrodes a) TEM image of the pristine HCT1300 sample; b) TEM image of the HCT1300 sample after discharging to V; c) Ex situ XPS Na 1s spectrum profiles of HCT1300 and Na metal after etching 60nm; d) Potentiogram and schematic of sodium storage mechanism Figure Electrochemical performance of Na0.9[Cu0.22Fe0.30Mn0.48]O2/ HCT1300 full cell a) Charge and discharge curves for the 1st, 5th and 10th cycles at a current rate of 0.2C; b) Rate capability at different constant charge/discharge rates from 0.1C to 2C; c) Cycling performance at a current rate of 0.2C This study reports a novel hard carbon material with microtubulare structure produced contributed from hollow fiber structure of cotton fibers by a simple one step carbonization method The electrochemical sodium storage in difference of hard carbon microtubes with different microstructures and chemical composition carbonization temperature and the sodium storage mechanism were systematically investigated in this work Hard carbon microtubes derived from renewable cotton as high performance anode material for sodium-ion batteries Yunming Li, Yong-Sheng Hu*, Maria-Magdalena Titirici*, Hong Li, Liquan Chen, Xuejie Huang Keywords: Energy storage; Sodium-ion batteries; Anode; Hard carbon microtubes  ... investigation of the carbon microstructure The HRTEM micrographs are shown in Figure 2e-g As expected for hard carbons a disordered carbon structure is observed confirming indeed the hard carbon nature... investigated in this work Hard carbon microtubes derived from renewable cotton as high performance anode material for sodium-ion batteries Yunming Li, Yong-Sheng Hu*, Maria-Magdalena Titirici* , Hong Li,... We have synthesized hard carbon materials with a uniform microtubular morphology from cotton fibers by a simple one step carbonization method The materials were prepared by carbonization at different