1、寿命寿命硅负采材料Silicon anode with life cycle lifeProf. Xinping QiuDepartment of Chemistry, Tsinghua UniversityBeijing, 100084, China5/25/2022Difficulties for silicon anode applicationLarge volume exchange lead to structural failure of electrodeRelative low conductivity and rate performanceiMEFnW0*Electron
2、 numberEnergy densityMolecular massSi: 4200 m Ah/g2Multi electron reaction materials5/25/2022J.R. Dahn, Electrochem. Solid-State Lett., 2001, 4, A137. J.R. Dahn, J. Electrochem. Soc. 2003, 150, A1457.3Colossal volume change Change in (a) length + and width x, (b) height, and (c) volume of the a-Si t
3、ower compared to (d) voltage vs. AFM scan number.Schematic diagram of the in situ AFM apparatus.Optical micrograph of a Li-alloy film after expansion5/25/2022Y. Cui, Nat. Nanotechnol., 2008, 3, 31. | Y. Cui, Nano Lett. 2011, 11, 2949. | G. Yushin, Nat. Mater., 2010, 9, 353. | G.A. Ozin, Adv. Funct.
4、Mater. 2009, 19, 1999. | X. J. Huang, Adv. Mater. 2011, 23, 4938.| X.P. Qiu, Electrochem. Commun., 2007, 5, 930. | S.M. Lee, Electrochim. Acta, 2008, 53, 4500. | J. G. Zhang, J. Electrochem. Soc., 2010, 7, A765.| J.R. Dahn, Electrochem. Solid-State Lett., 2007, 10, A17. | G. Yushin, ACS Appl. Mater.
5、 Inter., 2010, 11, 3004. | G. Yushin, Science, 2011, 334, 75.Si based anodeNano materialsSi arrayCurrent collector Binder 4Strategies for silicon anodesParticle pulverization “A strong size dependence of fracture in silicon material was discovered that there exists a critical particle size of 150 nm
6、 below which cracking did not occur.” 2Size effect1 H Zhang, Nano Letters 2012, 12, 2778.; 2 XH Liu, ACS Nano. 2012, 2, 152215315/25/20225ElectrodeInterfaceParticleElectronic contactStability of SEI filmFracture and PulverizationCurrent collector; Binder; ArrayStability in Si-based material 1Li inse
7、rtionLi extractionLong cycles5/25/20226The exposed active surface due to the volume change cause continual formation of SEI films and low coulombic efficiency (CE).Research routesReduce the particle size to accommodate SEI filmDesign porous or hollow structure to buffer the volume expansion Composit
8、e with C or Metal (Cu) to increase electronic conductivity and modify the interface between Si and electrolyte.Investigate new binder and electrolyte additives system for Si-based anode materialsStability of SEI film75 % SiH4 + 95 % Ar5 % H2 & 95 % Ar450C, 1 h-2.5 hCalcination 2N2 atmosphere900C, 4
9、hN2 atmosphere225C, 1h500C, 2hHeating under stirringPorous carbon80C, solvent evaporationCalcination 1Remove templateHClSi CVDPorous Si-C Nano CaCO3 Sucrose solutionDeposited siliconCarbon framework after 1st and 2nd calcination5/25/2022Porous Si/C compositeSynthesis Process5/25/2022Morphology 8 in
10、1 bold, 1 ePorous structure of carbon substrate can be observed from TEM imagesAfter CVD, silicon particles adhere to the framework and porous structure was maintained. Particle size of silicon is 10 nm and homogeneously dispersed.The deposited silicon in Porous Si-C is amorphous, as indicated by th
11、e absence of crystallites and broad diffuse rings in the SAED patterns. In contrast, when composite is heated to 700 C for 0.5 h, a lattice fringe corresponding to d111 = 0.31 nm for silicon is seen in Porous Si-C-700.Results and analysisSEM and TEM images5/25/20229020406080100Intensity (a.u.)2theta
12、 (degree) Si/C Si/C-700 Std.Silicon in 1 bold, 1 eObvious characteristic peak of crystal silicon after heat treatment at 700 C for 0.5 hThree obvious diffraction peaks around 28, 47 and 56 are found after heat treatment, which correspond very well to the (111), (220) and (311) peaks of silicon witho
13、ut any impurity peaks.The peak at 520 cm-1 (indicative of crystalline silicon) is not detected after silicon CVD. The bands centered around 155, 474 cm-1 and the weak shoulder at 400 cm-1 are typical features of amorphous silicon vibration modes 1.Results and analysis0200400100015002000G Porous C Si
14、/CIntensity (a.u.)Raman shift (cm-1)DStructural characterization1 D. Aurbach, J. Phys. Chem. C, 2007, 111, 11437.XRD patterns and Raman spectra N2 sorption isothermsPore size distributionBoth porous carbon and porous Si-C show type IV isotherm, which is typical characteristic of mesoporous structure
15、Obvious decrease of specific surface area (SSA) and pore volume after Si CVDPorous carbon:650 m2/g, 1.32 cc/gPorous Si-C:150 m2/g, 0.39 cc/gPores with diameter of 3 nm generated by decomposition of sucrosePores with diameter of 1040 nm due to the removal of CaCO3 template, which were reduced after S
16、i CVDPorous Structure 0.00.20.40.60.81.00100200300400500600700800900Volume STP (cc g-1)Relative Pressure, P/P0 Porous C Si/C0204060801000.00.20.40.60.81.01.21.4dV/dD (cc g-1 nm-1) Diameter (nm) Porous C Si/C5/25/202210Charge-Discharge curvesCycling performance1) 2nd charge capacity; 2) VC: vinylene
17、carbonate0800160024000.00.51.01.52.02.53.03.5100th50th 2ndPotential (vs Li/Li+)Capacity (mA h g-1)1st5/25/202211Electrochemical performance1st dch capacity: 2404 mAh/g1st ch capacity: 1541 mAh/g1st coulombic efficiency: 64.1%Reversible capacity1: 1504 mAh/gCapacity retention: 67% after 200 cyclesRec
18、ipe: Porous Si-C: CB : binder (PAA) = 6:2:2; Electrolyte: 1 M LiPF6 in EC-DMC- EMC(1:1:1 vol%) with 2wt% VC2; loading: 0.61 mg/cm2.Capacity is only based on active material. Current density: 0.1 A/g for 1-2 cycle, then 0.5 A/g; Voltage: 0.05 2.0 V vs. Li050100150200050010001500200025003000 Nano Si S
19、i/CCapacity (m Ah g-1)Cycle number80828486889092949698100C.E. (%)Rate capabilityIncrease current density from 0.1 to 2 A g-1, the specific capacity of Si/C composite is still above 500 m Ah g-1, when the current density changes back to 0.1 A g-1, more than 92% of the capacity at the first ten cycles
20、 is recoverable. 5/25/202212CurrentDensity(A/g)Discharge capacity(mAh/g)Charge capacity(mAh/g)Coulombic efficiency(%)0.192386293.40.562962699.51.046146099.72.03113111000.176675798.9020406080050010001500200025000.1 A/g2 A/g1 A/g0.5 A/gChargeDischargeCapacity (m Ah g-1)Cycle number0.1 A/gResults and a
21、nalysisNyquist plot of Si-C composite at the end of discharge after different cycles in 1 bold, 1 eElectrochemical impedance spectra (EIS) measurement in a 5.0 mV AC voltage signal in the 105 - 0.02 Hz frequency range. Before each EIS test, the electrodes were discharged to 0.01 V galvanostatically
22、and then remained at open-circuit for at least 2 h to stabilize their potential.The constancy of the characteristic frequency (20Hz, from 30-60 cycles) suggests that the kinetics of the charge transfer reaction does not vary upon cycling. Evolution of the resistance in mid-frequency region (inset) s
23、hows an increase in first 5 cycles then reduce and maintain around 40 Ohm in later cycles.Results and analysis0204060801000-20-40-60-80-100 D1 D10 D20 D30 D60Zimg (Ohm)Zre (Ohm)010 20 30 40 50 60020406080100120140RSur (Ohm)Cycle number Si/C Nano Si5/25/202213EIS test1 D. Guyomard, J. Mater. Chem., 2
24、011, 21, 6201.SEI film with cyclingSuperficial and cross-sectional SEM images of our composite after a), b) 10 cycles; c), d) 20 cycles; e), f) 50 cycles and g), h) commercial Si material after 50 cycles.a)b)d)c)h)g)f)e)Porous structure of our synthesized composite still maintains after cycling and
25、SEI film is only observed at the external surface of the silicon particle without obvious incrassation. In commercial Si measurements, excessive SEI film is found after 50 cycles, which is unable to be distinguished from Si nanoparticles.5/25/202214Materials after cycling1 Y. Cui, Nano Lett. 10 (201
26、0) 1409Si/C after 50 cyclesa) SEM and b) TEM image of Si/C composite at the end of 50th cycle; the corresponding elemental mapping of c) carbon and d) silicon.1 mM of acetic acid was used to remove the SEI film 1. Porous carbon structure is maintained, nano silicon particles around 10 nm does not sh
27、ow aggregation and rupture. Results and analysisa)b)c)d)C-KSi-K5/25/202215SEI confinementSchematic5/25/202216SEI film forms inside the pores due to the low electrochemical potential of lithium insertion in first few cycles. When the pores are full filled, SEI film is confined by the wall of carbon s
28、ubstrate, which prevent the internal silicon particle from being exposed in the electrolyte.Results5/25/202217Schematic of synthesisAdvantage:1. Easy to synthesis and regulate according to commercial CaCO3 template2. Hollow structure with reserve volume can accommodate large volume changes3. Interco
29、nnected nano silicon means more active conductive contact.Nano CaCO3Silicon layerLegend:Hollow siliconPurification by HF acid (10 wt%)5 % SiH4 + 95 % Ar400-500 C, 1 h-2.5 hSi CVDTemplate removal by HCl acid (2 wt%)5/25/202218Images and patternsMorphology Resultsa) TEM images of nano CaCO3 template;b
30、) SEM images of HSA-10 (inset is at low magnification);TEM images of c) HSA-10, e) HSA-15, f) HSA-20;d) the corresponding SAED pattern of HSA-10.Amorphous hollow silicon material with different shell thickness was prepared abcdef5/25/202219Images and patternsStructural characterizationbc102030405060
31、708090 HSA-10 HSA-15 HSA-20 Std. SiIntensity2theta degree9698100102104106108 PSi3/2 PSi1/2 PSiOxIntensityBinding Energy (eV)Characteristic peaks of crystalline silicon (PDF#65-1060) around 28, 47 and 56 are absent, which corroborate the statement of silicon is amorphous.The first main 3/2-1/2 double
32、t (the spin-orbit splitting is 0.6 eV and the intensity ratio is 3:1), located at 99.1-99.7 eV corresponds to Si0 (75 % content). The component located at higher binding energy (100.0 eV) is associated with SiOx formed at the surface of HSA with a proportion of 25%.Results and analysis5/25/202220Res
33、ults and analysisThe nitrogen adsorption/ desorption isotherms of HSA samples show a sharp capillary condensation step at high relative pressures (P/P0 = 0.85-0.99), indicating the existence of large pores.Corresponding pore size distributes mainly in the range of 20 nm and 100 nm, which is attribut
34、ed to the removal of site-occupying nano CaCO3. Isotherm and Pore size distribution Porous Structure 0.00.20.40.60.81.00100200300400500600700Volume (cc/g, STP)Relative Pressure, P/P0 HSA-10 HSA-15 HSA-20010 20 30 40 50 60 70 80 90 100048121620dV (cc/kg)Diameter (nm) HSA-10 HSA-15 HSA-20SampleSpecifi
35、c surface area (m2 g-1)Pore volume (cc g-1)HSA-1050.40.983HSA-1538.60.221HSA-2032.70.0915/25/202221Cycling performanceCycle performanceTest conditionsRecipe: HS: CB : binder (PAA) = 6:2:2Electrolyte: 1 M LiPF6 in EC-DMC- EMC(1:1:1 vol%) with 2 wt% VC;Loading: 0.4-0.6 mg cm-2 Current density: 0.1 A/g
36、 for 1-3 cycle, then 0.4 A/g; Voltage: 0.02 1.50 V vs. LiResultsHSA-10 gives the highest capacity retention (91%) in 100 cycles and corresponding reversible capacity is 980 m Ah g-1. When increase the shell thickness of silicon, reversible capacity increases (980 m Ah g-1 of HSA-15 and 1133 m Ah g-1
37、 of HSA-20 after 100 cycles) but the capacity retention decreases obviously (76% of HSA-15 and 73% of HSA-20)Electrochemical performance0 10 20 30 40 50 60 70 80 901000500100015002000250030003500 HSA-10 HSA-15 HSA-20Capacity(mAh/g)Cycle number80828486889092949698100 CE (%)05001000 1500 2000 25000.00
38、.51.01.52.02.53.03.5100th50th 2ndPotential (vs Li/Li+)Capacity (mA h g-1)1stMaterials after cycling1 Y. Cui, Nano Lett. 10 (2010) 1409HAS-10 after 50 cyclesa) SEM image of HSA-10 after 100 cycles;b) SEM image of HSA-10 after 100 cycles without SEI film;c), d) TEM image of HSA-10 after 100 cycles wit
39、hout SEI film at different magnification.Aggregated secondary particles (Fig. c) and 10 nm silicon shell structure (Fig. b & d) were maintained without fracture of the hollow spheres. Results and analysis5/25/202222abcdEIS test5/25/202223Stable interface and smaller resistanceNyquist plot of Si-C co
40、mposite at the end of discharge after different cycles in 1 bold, 1 eElectrochemical impedance spectra (EIS) measurement in a 5.0 mV AC voltage signal in the 105 - 0.02 Hz frequency range. Before each EIS test, the electrodes were discharged to 0.01 V galvanostatically and then remained at open-circ
41、uit for at least 2 h to stabilize their potential.Evolution of the resistance in mid-frequency region maintains 20 Ohm during cycling which is lower than Si/C composite and nano Si material.Results and analysis0204060800-20-40-60-80NHSF-10 1st1st 1st1st 3rd3rd 10th10th 50th50thZ / OhmZ / OhmSi/C(a)0
42、102030405060020406080100120140 RSur / Ohm循环次数循环次数 Nano Si Si/C NHSF-10(b)DSC Test5/25/202224Stable SEI structure of silicon foamDSC heating curves in 1 bold, 1 eCurrent density around 0.1 mA/g was applied to lithiate the Si active material. After the voltage reached 1 mV, the cells were remained at
43、open-circuit for 2 h then carefully opened in a glove box. The electrode was soaked in DMC and then dried under vacuum overnight.Measurements were conducted with a DSC 1 (METTLER TOLEDO) at a temperature ramp of 2 C min-1 (30-300 C) using hermetic high-pressure DSC pans. The DSC signal at 86-100 C i
44、s visible for all of the curves. By analogy with lithiated graphite, which thermal stability is well studied, it is reasonable to suggest that metastable SEI layer components are transformed at 86-100 C.Results and analysis501001502002503000.00.20.40.60.81.0 10 20 30 50 100HF (W g-1)T (oC)exoNHSF-10
45、501001502002503000.00.20.40.60.81.0 10 20 30 50 100HF (W g-1)T (oC)exoNano Si42322222)(2HCCOLiLiOCOCHLi Hollow silicon alveoli material is synthesized using a facile process including chemical vapor deposition and template method. Morphology, primary particle size and thickness of silicon shell can
46、be precisely controlled by the initial size of nano CaCO3 template and the parameters of CVD process. Free volume in this hollow structure provides enough space to accommodate the volume change in Li-Si alloying and dealloying reactions. Hence this material exhibits excellent cycling stability that
47、reversible capacity is 1000 m Ah g-1 (91% capacity retention) after 100 cycles. The coulombic efficiency during cycling maintains above 99.5% which is benefit for long cycle life and hollow silicon shell structure is maintained after cycling which indicates the material is stable and reversible.5/25/202225Summary5/25/2022IBA 2014 Conference26AcknowledgementsState Key Basic Research Programm of PRC (2013CB934000), Beijing Natural Science Fundation (2120001)
