硅负极材料的相关应用介绍.ppt

1、寿命寿命硅负采材料Silicon anode with life cycle life,Prof. Xinping Qiu Department of Chemistry, Tsinghua University Beijing, 100084, China,9/2/2020,Si: 4200 m Ah/g,1,Multi electron reaction materials,9/2/2020,J.R. Dahn, Electrochem. Solid-State Lett., 2001, 4, A137. J.R. Dahn, J. Electrochem. Soc. 2003, 150,

2、 A1457.,2,Colossal volume change,Change in (a) length + and width x, (b) height, and (c) volume of the a-Si tower compared to (d) voltage vs. AFM scan number.,Schematic diagram of the in situ AFM apparatus.,Optical micrograph of a Li-alloy film after expansion,9/2/2020,Y. Cui, Nat. Nanotechnol., 200

3、8, 3, 31. | Y. Cui, Nano Lett. 2011, 11, 2949. | G. Yushin, Nat. Mater., 2010, 9, 353. | G.A. Ozin, Adv. Funct. 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. Electroche

4、m. Soc., 2010, 7, A765.| J.R. Dahn, Electrochem. Solid-State Lett., 2007, 10, A17. | G. Yushin, ACS Appl. Mater. Inter., 2010, 11, 3004. | G. Yushin, Science, 2011, 334, 75.,3,Strategies for silicon anodes,Particle pulverization,“A strong size dependence of fracture in silicon material was discovere

5、d that there exists a critical particle size of 150 nm below which cracking did not occur.” 2,Size effect,1 H Zhang, Nano Letters 2012, 12, 2778.; 2 XH Liu, ACS Nano. 2012, 2, 15221531,9/2/2020,4,Current collector; Binder; Array,Stability in Si-based material,?,1,9/2/2020,5,The exposed active surfac

6、e due to the volume change cause continual formation of SEI films and low coulombic efficiency (CE).,Research routes,Reduce the particle size to accommodate SEI film Design porous or hollow structure to buffer the volume expansion Composite with C or Metal (Cu) to increase electronic conductivity an

7、d modify the interface between Si and electrolyte. Investigate new binder and electrolyte additives system for Si-based anode materials,Stability of SEI film,6,9/2/2020,Porous Si/C composite,Synthesis Process,9/2/2020,Morphology,7,in 1 bold, 1 e Porous structure of carbon substrate can be observed f

8、rom TEM images After 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 the absence of crystallites and broad diffuse rings in the SAED p

9、atterns. 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 analysis,SEM and TEM images,9/2/2020,8,in 1 bold, 1 e Obvious characteristic peak of crystal silicon after heat treatment at 700 C f

10、or 0.5 h Three 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 without any impurity peaks. The peak at 520 cm-1 (indicative of crystalline silicon) is not detected after silicon CVD. The bands ce

11、ntered around 155, 474 cm-1 and the weak shoulder at 400 cm-1 are typical features of amorphous silicon vibration modes 1.,Results and analysis,Structural characterization,1 D. Aurbach, J. Phys. Chem. C, 2007, 111, 11437.,XRD patterns and Raman spectra,N2 sorption isotherms,Pore size distribution,Bo

12、th porous carbon and porous Si-C show type IV isotherm, which is typical characteristic of mesoporous structure Obvious decrease of specific surface area (SSA) and pore volume after Si CVD,Porous carbon: 650 m2/g, 1.32 cc/g,Porous Si-C: 150 m2/g, 0.39 cc/g,Pores with diameter of 3 nm generated by de

13、composition of sucrose Pores with diameter of 1040 nm due to the removal of CaCO3 template, which were reduced after Si CVD,Porous Structure,9/2/2020,9,Charge-Discharge curves,Cycling performance,1) 2nd charge capacity; 2) VC: vinylene carbonate,9/2/2020,10,Electrochemical performance,1st dch capaci

14、ty: 2404 mAh/g 1st ch capacity: 1541 mAh/g 1st coulombic efficiency: 64.1% Reversible capacity1: 1504 mAh/g Capacity retention: 67% after 200 cycles,Recipe: 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

15、 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. Li,Rate capability,Increase 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

16、 92% of the capacity at the first ten cycles is recoverable.,9/2/2020,11,Results and analysis,Nyquist plot of Si-C composite at the end of discharge after different cycles,in 1 bold, 1 e Electrochemical impedance spectra (EIS) measurement in a 5.0 mV AC voltage signal in the 105 - 0.02 Hz frequency

17、range. Before each EIS test, the electrodes were discharged to 0.01 V galvanostatically 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

18、does not vary upon cycling. Evolution of the resistance in mid-frequency region (inset) shows an increase in first 5 cycles then reduce and maintain around 40 Ohm in later cycles.,Results and analysis,9/2/2020,12,EIS test,1 D. Guyomard, J. Mater. Chem., 2011, 21, 6201.,SEI film with cycling,Superfic

19、ial 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.,Porous structure of our synthesized composite still maintains after cycling and SEI film is only observed at the external surface of the s

20、ilicon 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.,9/2/2020,13,Materials after cycling,1 Y. Cui, Nano Lett. 10 (2010) 1409,Si/C after 50 cycles,a) SEM and b) TEM image of

21、 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 show aggregation and rupture.,Results and analysis,a),

22、b),c),d),C-K,Si-K,9/2/2020,14,SEI confinement,Schematic,9/2/2020,15,SEI 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 substrate, which prevent the internal sili

23、con particle from being exposed in the electrolyte.,Results,9/2/2020,16,Schematic of synthesis,Advantage: 1. Easy to synthesis and regulate according to commercial CaCO3 template 2. Hollow structure with reserve volume can accommodate large volume changes 3. Interconnected nano silicon means more ac

24、tive conductive contact.,Hollow silicon,9/2/2020,17,Images and patterns,Morphology,Results,a) TEM images of nano CaCO3 template; b) 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 silic

25、on material with different shell thickness was prepared,9/2/2020,18,Images and patterns,Structural characterization,b,c,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 doublet (

26、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 analysis,9/2/2020,19,Res

27、ults and analysis,The 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 attrib

28、uted to the removal of site-occupying nano CaCO3.,Isotherm and Pore size distribution,Porous Structure,9/2/2020,20,Cycling performance,Cycle performance,Test conditions Recipe: HS: CB : binder (PAA) = 6:2:2 Electrolyte: 1 M LiPF6 in EC-DMC- EMC(1:1:1 vol%) with 2 wt% VC; Loading: 0.4-0.6 mg cm-2 Cur

29、rent density: 0.1 A/g for 1-3 cycle, then 0.4 A/g; Voltage: 0.02 1.50 V vs. Li Results HSA-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 H

30、SA-15 and 1133 m Ah g-1 of HSA-20 after 100 cycles) but the capacity retention decreases obviously (76% of HSA-15 and 73% of HSA-20),Electrochemical performance,Materials after cycling,1 Y. Cui, Nano Lett. 10 (2010) 1409,HAS-10 after 50 cycles,a) SEM image of HSA-10 after 100 cycles; b) SEM image of

31、 HSA-10 after 100 cycles without SEI film; c), d) TEM image of HSA-10 after 100 cycles without 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 analysis,9/2/

32、2020,21,a,b,c,d,EIS test,9/2/2020,22,Stable interface and smaller resistance,Nyquist plot of Si-C composite at the end of discharge after different cycles,in 1 bold, 1 e Electrochemical impedance spectra (EIS) measurement in a 5.0 mV AC voltage signal in the 105 - 0.02 Hz frequency range. Before eac

33、h EIS test, the electrodes were discharged to 0.01 V galvanostatically and then remained at open-circuit 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

34、 and analysis,DSC Test,9/2/2020,23,Stable SEI structure of silicon foam,DSC heating curves,in 1 bold, 1 e Current 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 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 is visible for all of the curves. By analogy with