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1、 Supporting_Information Nano-scale coating of LiMO2(M=Ni,Co,Mn)nanobelts with Li+-conductive Li2TiO3:Towards better rate capabilities for Li-ion battery Jun Lu,Qing Peng*,Weiyang Wang,Caiyun Nan,Lihong Li and Yadong Li Department of Chemistry,State Key Laboratory of Low-Dimensional Quantum Physics,T
2、singhua University,Beijing 100084 SI-2 Experimental 1.Synthesis.Synthesis of MC2O4xH2O nanobelts.All reagents were purchased from China National Medicines Corp.,L.T.D.,and used without further purification.The preparation of MC2O4xH2O nanobelts was based on our unpublished results,applying a solvoth
3、ermal method with mixed polyethylene glycol 400(PEG 400)and ethylene glycol(EG)as the solvent.Typically,5 mmol transition metal chlorides are added into the solvent with a volume ratio of PEG 400:EG=30:10 under stirring.Afterwards,5 mmol oxalate and 10 mmol urea were added into the solution.After st
4、irring for 15 min,the transparent solution was transferred into a Teflon-lined autoclave,and kept at 200 oC for 12 hours.The product was washed with de-ionized water and ethanol several times,and dried in an oven at 70 oC for more than 12 h.Coating Procedure.Another solvothermal process was carried
5、out to coat TiO2 on the nanobelts.0.2 g MC2O4xH2O was dispersed into 10 mL absolute ethanol,followed by addition of 0.020 g Ti(OC4H9)4 diluted in 0.2 mL absolute ethanol.The mixture was maintained at 150 oC for 5 hours.During the solvothermal process,the phase of MC2O4xH2O remain unchanged.Then,the
6、product was washed with ethanol,and collected by centrifugation.Synthesis of surface-Li2TiO3-rich LiMO2 materials.After coating treatment,the nanobelts were dispersed in ethanol,and mixed with about 0.050 g LiOH?H2O.The amount of LiOH?H2O is calculated by the following equation:)n2n(molg96.41mTi)MnC
7、oNi(1OHLiOH2+=+The mixture was stirred under 80 oC until it was dry.Then,the blend was collected and calcinated at 800 oC for 3 hours,with heat rate of 4 oC?min-1.2.Characterizations The XRD patterns of all samples were collected on a diffractometer(Rikagu D/max 2500 with CuK radiation,=0.15418 nm).
8、The morphologies were characterized by field-emission scanning electron microscopy(FESEM)(LEO-1530),and high resolution transmission electron microscopy(HRTEM)(FEI Tecnai G2 F20 S-Twin working at 200kV).Also,energy dispersive X-ray spectroscopy(EDS)was carried out on OXFORD 7426 as the attachment of
9、 SEM,with the acceleration voltage of 20 kV.Thermo gravimetric analyzer 2050(TGA 2050)was applied on the metal oxalates precursors from room temperature to 800 oC at a heating rate of 15 oC/min under air flow.The specific surface areas of Ti433 and 433 nanobelts were determined by Brunauer-Emmett-Te
10、ller(BET)method using Autosorb-1(Quantachrome).X-ray photoelectron spectroscopy(XPS)characterization was carried out on 250XI,with the detection spot size of 650 m.Carbon monoxide temperature programmed reductions(CO-TPR)of Ti433 and 433 were carried out on ChemBET PULASR TPR/TPD(Quantachrome),with
11、a 50 mLmin-1 in gas flow of CO/N2=1:1 in volume,and a heating rate of 5 oC min-1.3.Electrochemical measurements.CR2016 coin-type cells were applied for electrochemical test.Blends of active material,acetylene black and PVDF in the mass ratio of 8:1:1 were fully mixed,pasted on aluminum foil and cut
12、into wafers.After drying in a 120 oC vacuum oven for 12 h,the wafers were fabricated into CR2016 cells in an Ar-filled glove box,using lithium metal as the counter electrode and 1 M LiPF6 solution in DMC/EC(1:1 in volume)as the electrolyte.The rate tests were carried out on battery testing system(BT
13、S-5 V 5 mA,Neware)at a voltage range of 3.0-4.3 V,from 0.5 to 10 C(1C=140 mA g-1)under 25 oC and 55 oC.For electrochemical impedance spectroscopy(EIS),CHI 660D electrochemical station was applied on the cycled batteries discharged to 3.30 V with the frequency range of 10 kHz to 1.0 Hz and RMS potent
14、ial of 10 mV.SI-3 Figure SI 1.The TGA curves(a)for metal oxalates precursors,and the line scan of the TiO2 coated MC2O4 nanobelts(b,c).The reactions taking place for the samples could be expressed as follows:42ba1baC300242ba1baOC)MnCoNi(OxHOC)MnCoNi(o)b177.0a5.05.1(ba1baC300,O42ba1baO)MnCoNi(OC)MnCo
15、Ni(o2 The molecular weight for 811,622 and 433 oxalates were determined to be 168.2,167.6 and 162.7,respectively.In addition,the variation x for H2O was in the range of 0.8-1.2 for 811,622 and 433 samples.For coating TiO2 with Ti:M=5:100,only 0.1 mol H2O for per mol of MC2O4 nanobelts was required.I
16、n other words,H2O given off by a 0.1%weight loss of the sample below 150 oC was sufficient for the coating process,as the red horizontal line drawn in the inset.a)b)c)SI-4 Figure SI 2.The XRD pattern for the nanobelts with a Ti:M ratio of 15:100 in mole.SI-5 Figure SI 3.The SEM images for pristine 8
17、11(a),622(b)and 433(c)nanobelts.SI-6 Figure SI 4.Energy dispersive X-ray spectrum(EDS)of Ti 433 nanobelts.SI-7 1400 1200 10008006004002000CTiOMnCoIntensity(Counts)Binding energy(eV)Ni Figure SI 5.X-ray photoelectron spectrum of Ti433 nanobelts.The surface content of Ti element in mole was calculated
18、,assuming that:1)the depth of XPS detection is 9 nm,the average of 810 nm for XPS detection depth;1 2)the crystal densities of LiMO2 and Li2TiO3 which are 5.04 and 3.45 g cm-3 respectively,are applied regardless of density variation;3)the XPS quantification result which obtained on 650 m is represen
19、tative for the total materials.The processes for calculations are as follows:1.The total surface volume per gram(Vs)Ti433 sample is determined by the product of specific surface area(ABET)and detection depth(LD):DBETsLAV=2.The surface volume consists of two parts,the volume for LiMO2(V1),and the vol
20、ume for Li2TiO3(V2):21sVVV+=3.The volumes for LiMO2 and Li2TiO3 are relevant with the densities(1,2),molecular weights(M1,M2)as well as the surface mole ratio of LiMO2 and Li2TiO3,and Ti:M ratio in the following expression:23:100:222111=MVMV 4.The mole content of surface Ti of the total mass can be
21、determined by the following equation:222 MVmassTotalnTi=5.Given that the molar masses are 96.6 and 109.7 gmol-1 for for LiMO2 and Li2TiO3 respectively,the mole content of surface Ti is calculated in the below equation:1464s211221gmol109.41091022.645.36.9610004.57.1092304.545.323VM100M2323=+=+Actuall
22、y,the coating layer would be thinner than the estimated value,as part of Ti ions migrate into the host structure.1 Philippe,B.;Dedryvre,R.;Allouche,J.;Lindgren,F.;Gorgoi,M.;Rensmo,H.;Gonbeau,D.;Edstrm,K.Chem.Mater.2012,24,1107-1115.SI-8 Table SI 1 Retrieved crystal lattice parameters for pristine an
23、d coated samples(Range:10-80 o;Step length:0.02 o/step;Scan rate:2 o/min)Sample 811 Ti811 622 Ti622 433 Ti433 a/A 2.8260 2.8304 2.8436 2.8442 2.858 2.8626 c/A 14.0939 14.1198 14.165 14.1745 14.1944 14.2222 Table SI 2.The fitted solution resistances(Rs),charge transfer resistances(Rct)and constant ph
24、ase elements(CPE)for the Nyquist plots of Ti433 and 433 samples.Sample Rs Rct CPE Value Error%Value Error%CPE-T Error%CPE-P Error%Ti433 5.12 1.83 48.2 0.79 1.13E-5 5.67 0.76 0.72 433 4.40 4.86 172 1.29 1.09E-5 5.42 0.70 0.76 Table SI 3 Calculated Li+ion diffusion coefficient(D)in LMO2 from EIS resul
25、t(3.9 Hz0.06 Hz,after cycling for 100 cycles under 2C;data for 622 is missing as the test failed for 611 cells)Sample 811 Ti811 Ti622 433 Ti433 D(cm2/s)4.7E-15 3.6E-15 2.2E-15 5.1E-15 3.9E-15 Table SI 4 Capacity retention of the coated and pristine samples after cycling for 100 cycles at 2 C under 25 oC Sample 811 622 433 Coated Pristine Coated Pristine Coated Pristine Highest capacity(mAh/g)132.0 117.1 128.8 101.3 109.8 107.9 Final capacity(mAh/g)119.7 96.3 112.3 79.0 96.3 70.1 Capacity retention(%)90.7 82.2 87.2 78.0 87.7 65.0