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In-Situ Synthesis of MnS Hollow Microspheres on Reduced Graphene Oxide Sheets as High-Capacity and LongLife Anodes for Lithium-Ion and Sodium-Ion Batteries Xijun Xu, Shaomin Ji, Mingzhe Gu, and Jun Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b06590 • Publication Date (Web): 03 Sep 2015 Downloaded from http://pubs.acs.org on September 5, 2015

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ACS Applied Materials & Interfaces

In-Situ Synthesis of MnS Hollow Microspheres on Reduced Graphene Oxide Sheets as High-Capacity and Long-Life Anodes for Lithium-Ion and Sodium-Ion Batteries Xijun Xu,a Shaomin Ji,*a Mingzhe Gu,a Jun Liu*a,b

a

Key Laboratory of Low Dimensional Materials & Application Technology, Ministry

of Education, School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China b

School of Materials Science and Engineering, South China University of Technology,

Key Laboratory of Advanced Energy Storage Materials of Guangdong Province Guangzhou 510641, China

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ACS Paragon Plus Environment


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ABSTRACT: Uniform MnS hollow microspheres in-situ crystallized on reduced graphene oxide (RGO) nanosheets via a facile hydrothermal method. The MnS/RGO composite material was the first time used as anode materials for Na-ion batteries and exhibited excellent cycle performance, superior specific capacity, great cycle stability and rate capability for both Li-ion batteries and Na-ion batteries. Compared with non-encapsulated pure MnS hollow microspheres, these MnS/RGO nanocomposites demonstrated excellent charge-discharge stability and long-life cycling life. Li-ion storage testing revealed that these MnS/RGO nanocomposite deliver a high discharge-charge capacities of 640 mAh g–1at 1.0 A g–1 after 400 cycles and 830 mAh g–1 at 0.5 A g–1 after 100 cycles. The MnS/RGO nanocomposite even retained a specific capacity of 308 mAh g–1 at a current density of 0.1A g–1 after 125 cycles as the anode for Na-ion batteries. The outstanding electrochemical of MnS/RGO composite would attribute to the reduced graphene oxide nanosheets greatly improved the electronic conductivity and efficiently mitigated the stupendous volume expansion during the charge and discharge progress.

KEYWORDS: MnS/graphene composites, hollow structures, Na-ion batteries, Li-ion batteries, excellent electrochemical performance, anode

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1. INTRODUCTION Nowadays, rechargeable Na-ion batteries and Li-ion batteries are urgently needed for the next generation of energy storage devices due to the exhaustion of global fossil-fuel resources and ever-growing environmental problems.1,2 So, it is imminent to develop electrode materials with low-cost, green, environment friendly, long stable cycling performance, high specific capacity and high-rate capability. The problem that we are faced with right now is developing high energy density anode material of great urgency because anode materials play a significant role in rechargeable Li-ion batteries and Na-ion batteries.3 It is well known that the traditional graphite material is limited by its theory capacity (372 mAh g–1 for Li-ion batteries).2 Transition metal sulfides with a reversible capacity between 500–1200 mAh g–1 have emerged as alternatives to replace traditional graphite-based anode materials.4–7 Recently, sulfides have attracted intensive attention in the field of energy storage including supercapacitors, solar cells and Li-ion batteries.3,8–14 However, due to the large volume dilation involved in the Li+/Na+ uptake and release, the transition metal sulfide anodes disintegrate resulting in rapid capacity fade and poor cycling performance. As is known to all that constructing hollow/porous structures can enhance the cycling performance.4,15–17 Because hollow/porous structures with large amounts of cavities provide extra active sites for the Li+/Na+ storage, which is benefit for enhancing capacity of the electrode materials.4,9 In addition, this unique hollow structures effectively reduce the diffusion distance of Li+/Na+.1–2,17 Furthermore, the hollow/porous structures with larger surface areas would improve the contacting

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between electrolyte and the electrode materials, hence improving the rate capability.10,16 For example, uniform hollow spheres of CoS2 have been successfully synthesized via a facile solvothermal method and investigated as anode materials for Li-ion batteries, which exhibited good cycling performance.18,19 Our research group also successfully synthesized hollow structured [email protected] and FeF3·0.33H2O cathode materials, with greatly enhanced cycling performance and rate performance.20,21 Reduced graphene oxide (RGO) as a new two-dimensional (2D) carbon material, is an ideal substrate for in-situ growing, anchoring semiconducting and insulating materials for energy storage applications owe to its high mechanical strength, light weight, high structural flexibility, high chemical stability, high conductivity and high surface-to-volume ratio.22–27 The electrochemical performance of various anode materials (e.g. sulfides, oxides and alloys) can be greatly improved by combining them with RGO.28–30 Recently, researchers have showed that growing sulfide particles on RGO effectively prevented the volume expansion, improved the conductivity and active carves of sulfide/RGO composite, to some extent, increased the lithium storage capacity and cycle performance of sulfide/RGO composites.5,31 For example, Xia et al. in-situ synthesized CoS2/RGO nanocomposites with an enhanced electrode performance than pure CoS2 .32 Since the discovery of sulfide materials and have been successfully used in Li-ion batteries, a number of researchers also paid their attention to MnS based materials.4,33–35 Huang`s group synthesized coral-like α-MnS which was embedded in carbon exhibits a high reversible capacity and good cycle stability for

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Li-ion batteries.33 Hollow-structured MnS-carbon nanocomposite powders were synthesized by Kang et al. via a one-pot spray pyrolysis process, which also exhibited a good specific capacity and rate capability.34,35 Tough great progresses have been achieved on the MnS-based anodes for Li-ion batteries, the diversities of micro/nano architecture for long-life and high capacity anode materials based on MnS still need to be greatly expanded for meeting the ever-developing technology and energy demand. As rational designing a hollow structure and combining with reduced graphene oxides can improve their electrochemical performance, herein we successfully in-situ synthesized MnS hollow microspheres on 2D RGO nanosheets as superior anode materials for both Li-ion and Na-ion batteries. The delicate MnS hollow microspheres/RGO composites were successfully prepared through a simple hydrothermal reaction without any template. Most importantly, the MnS hollow microspheres/RGO composites achieved high specific capacity, excellent rate capability and stable cycling ability, make it a promising anode material for rechargeable Li-ion and Na-ion batteries.

2. EXPERIMENT SECTION 2.1 Materials synthesis 2.1.1 Preparation of graphite oxide. In a typical method synthesis, 5 g graphite was added into 230 mL concentrated sulfuric acid at an ice bath and magnetic stirring for 1.5 h, and then 18 g KMnO4 was added under continue magnetic stirring at 35 °C for 1 h, until the solution became viscous. The mixture was stirred at 85 °C for

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another 1 h and diluted with distilled water. 150 ml of 30% H2O2 was finally added to the solution until the color changed to bright yellow. The finally graphite oxide was filtered and washed with 5% hydrochloric acid. 2.1.2 Preparation of pure MnS hollow microspheres. 3.58 g Mn(NO3)2 solvent with 50 wt% concentration, 2.42 g L-cysteine and 0.60 g urea were added into beaker and under magnetic stirring for 0.5 h to form 200 mL mix solution. Then the solution transferred into Teflon-lined stainless steel autoclave and maintained at 160 °C for 24 h. After cooling down to room temperature, the precipitate was filtered, washed with distilled water and anhydrous ethanol three times. Then the precursor was dried at 80 °C for overnight in a vacuum oven. Finally, the products were annealed at 500 °C for 4 h in nitrogen with a rate of 3 °C·min–1. 2.1.3 Preparation of MnS hollow microspheres/RGO. 0.20 g graphite oxide was added into 200 mL distilled water and ultrasonicated at 45 KHz for 1 h. Then 3.58 g Mn(NO3)2 solution with 50% concentration, 2.42 g L-cysteine and 0.60 g urea were added into this graphite oxide solution under magnetic stirring for 0.5 h. Then the solution was transferred into Teflon-lined stainless steel autoclave and maintained at 160 °C for 24 h. After cooling down to room temperature, the precipitate was filtered, washed with distilled water and anhydrous ethanol three times, then the sample was dried at 80 °C for overnight in a vacuum oven. Finally, the products were annealed at 500 °C for 4 h in nitrogen with a rate of 3 °C·min–1. 2.2 Materials characterization. Scanning electron microscopy (SEM) analysis was performed with a JSM-6610LV scanning electron microscope. High-resolution

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transmission electron microscope (HRTEM) analysis was performed with a JEM-2100. The collected products were characterized by X–ray diffractometry (XRD) with a Rigaku-DMax 2400 diffractometer equipped with a graphite-monochromated Cu-Kα 426 radiation source at a scanning rate of 0.02 °·s–1. The thermogravimetric analysis (TGA) was performed from room temperature to 900 °C at a ramp rate of 10 °C·min–1 with an air flow rate of 20 mL·min–1 by using a Q50 thermogravimetric analyzer. The Raman spectra were obtained with a Renishaw Invia Raman microscope. The surface areas of the nanocomposites were measured by the Brunauer Emmett Teller (BET) method, using N2 as the adsorbate gas. 2.3 Electrochemical testing. The electrochemical performances of the as prepared products were measured by charge-discharge test. For the preparation of the working electrode, a mixture of MnS/RGO (or pure MnS), acetylene black, and polyvinylidene fluoride

(PVDF)

in

a

weight

ratio

of

70:20:10

was

ground

with

N-methy1-2-pyrrolidone (NMP) as solvent to make slurry. The slurry was then applied to a Cu foil and dried in vacuum oven at 80 °C for 12 h to from the working electrode. Then the copper foil was punched into circular disks with a diameter 15.8 mm, the active material loading was 1.0 –1.5 mg. The test cells (CR2016) which were assembled in an Ar-filled glove box (H2O and O2

In Situ Synthesis of MnS Hollow Microspheres on ... - ACS Publications

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