Electronic Supplementry Informtion Assemling cron-coted hollow α-fe 2 nnohorns on the CNT ckone for superior lithium storge cpility Corresponding uthor: Xiong Wen (Dvid) Lou* School of Chemicl nd Biomedicl Engineering, Nnyng Technologicl University, 70 Nnyng Drive, Singpore, 637457. Emil: xwlou@ntu.edu.sg; Tel: +65 63168879 Experimentl Detils Pre-tretment of cron nnotues Cron nnotues (CNTs) used in this work re provided y X2 Lwres Pte. Ltd., of which the dimeter is in rnge of 20 60 nm nd the length is round severl micrometers. 3 g of the CNTs is refluxed in 90 ml of HN (65 wt.%) t 120 o C for 6 h. After tht, the cid treted CNTs re rinsed with DI wter until neutrl ph vlue is reched. Then they re collected y filtrtion nd dried t 60 o C for further use. Synthesis of the CNT@FeOOH hierrchicl structure For the growth of β-feooh nnospindles on CNT ckones, 5 mg of the CNTs is dispersed in 10 ml of queous solution of FeCl 3 (0.12 M) y ultr-soniction for 30 60 min in cpped ottle. After thorough mixing, the suspension is kept in n oil th under stirring t 75 o C for 5 h. The finl products re collected y severl rinse-centrifugtion (2000 rpm) cycles efore drying t 60 o C. Synthesis of the CNT@Fe 2 hierrchicl structure For the formtion of hollow α-fe 2 nnohorns on CNT ckones, certin mount of CNT@FeOOH hierrchicl structures is nneled in ir t 400 o C for 4 h with slow rmp rte of 0.5 o C min -1. Cron coting of CNT@Fe 2 hierrchicl structures For the cron coting of CNT@Fe 2 hierrchicl structures, 20 mg of the CNT@Fe 2 smples is dispersed in 40 ml of queous solution of glucose (0.06 M). After thorough mixing, the suspension is trnsferred into 50 ml Teflon-lined stinless steel utoclve nd kept in n oven t 180 o C for 6 h. The otined products re collected y severl rinse-centrifugtion (2000 rpm) cycles efore drying t 60 o C. Mterils chrcteriztion All smples were chrcterized y field-emission scnning electron microscope (FESEM, JEOL, JSM-7600F), trnsmission electron microscope (TEM, JEOL, JEM-2010 nd JEM-2100F), powder X-ry diffrction (XRD, Bruker, D8-Advnce X-ry Diffrctometer, Cu Kα, λ = 1.5406 Å), nitrogen dsorption/desorption (Quntchrome Instruments, Autosor AS-6B) nd thermogrvimetric nlysis (TGA, Shimdzu, DRG-60). The electrochemicl mesurements were conducted using two-electrode Swgelok cells with pure lithium foil s the counter nd reference electrode t room temperture. The S1
working electrode consists of test mteril (e.g., CNT@Fe 2 with or without cron coting), cron lck (Super-P-Li) nd polyvinylidene difluoride (PVDF) in weight rtio of 7:2:1. The electrolyte used is 1.0 M LiPF 6 in 50:50 (w/w) mixture of ethylene cronte nd diethyl cronte. Cell ssemly is crried out in n Ar-filled gloveox with concentrtions of moisture nd oxygen elow 1.0 ppm. The glvnosttic chrge/dischrge tests were performed using Newre ttery tester t different current densities with cut-off voltge window of 0.01 3.0 V. The clcultion of the specific cpcity is sed on the overll mss of the composite mteril synthesized, for exmple, cron coted CNT@Fe 2 structures. Electrochemicl impednce spectroscopy (EIS) ws performed using n CHI660C electrochemistry worksttion y pplying n c mplitude of 5 mv over the frequency rnge from 0.1 to 10 5 Hz. CNT@FeOOH nnostructures CNT@Fe 2 nnostructures Intensity (.u.) (002) CNT (130) (012) (002) CNT (400) (211) (301) (104) (110) (113) (202) (411) (024) (600) (251) 20 30 40 50 60 2Thet (degree) Figure S1 XRD profiles of CNT@FeOOH nd CNT@Fe 2 hierrchicl structures. CNT FeOOH CNT Fe 2 Figure S2 HRTEM imges of CNT@FeOOH nd CNT@Fe 2 hierrchicl structures. S2
c d Figure S3 TEM imges of the smples otined y the hydrolysis of FeCl 3 with vrious initil concentrtion: (, ) 0.03 M, (c) 0.06 M, (d) 0.36 M. Figure S4 TEM imges of CNT@Fe 2 structures otined y nneling t different temperture: () 250 o C, () 300 o C. Figure S5 N 2 dsorption/desorption isotherms of () CNT@FeOOH, () CNT@Fe 2 nd (c) cron coted CNT@Fe 2 hierrchicl structures. S3
Weight (wt. %) 100 95 90 85 80 75 70 65 60 55 50 100 200 300 400 500 600 Temperture o C 30 wt. % Figure S6 Thermogrvimetric nlysis of cron coted CNT@Fe 2 structures. The test ws conducted in ir with rmpe rte of 10 o C min -1. Cron Figure S7 TEM imge showing the presence of uniform cron nnocoting round the scffold of CNT@Fe 2 hierrchicl structures. 100 Coulomic Efficiency (%) 90 80 70 60 50 40 30 20 10 0 0 20 40 60 80 100 Cycle Numer Figure S8 Coulomic efficiency of cron coted CNT@Fe 2 structures cycled etween 0.01 3V t current density of 500 ma g -1. S4
1400 Cron coted CNT@Fe 2 -Fe 2 nnoprticles 1200 1000 Z im /ohm 800 600 400 200 0 0 200 400 600 800 1000 1200 Z re /ohm Figure S9 Nyquist plots of the electrodes composed of the hierrchicl structures of cron coted CNT@Fe 2 or α-fe 2 nnoprticles. S5