硅负极材料的相关应用介绍ppt课件.pptx

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1、寿命寿命硅负采材料Silicon anode with life cycle life,Prof.Xinping QiuDepartment of Chemistry,Tsinghua UniversityBeijing,100084,China,1/10/2023,Si:4200 m Ah/g,1,Multi electron reaction materials,1/10/2023,J.R.Dahn,Electrochem.Solid-State Lett.,2001,4,A137.J.R.Dahn,J.Electrochem.Soc.2003,150,A1457.,2,Colossal

2、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,1/10/2023,Y.Cui,Nat.Nanotechnol.,2008,3,31.|Y.Cui,Nano Lett.2011,11,29

4、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 discovered that there exists a critical particle size of 150 nm below which cracking did not occur.”2,Size effect,1 H Zhang,Na

5、no Letters 2012,12,2778.;2 XH Liu,ACS Nano.2012,2,15221531,1/10/2023,4,Current collector;Binder;Array,Stability in Si-based material,?,1,1/10/2023,5,The exposed active surface due to the volume change cause continual formation of SEI films and low coulombic efficiency(CE).,Research routes,Reduce the

6、 particle size to accommodate SEI filmDesign porous or hollow structure to buffer the volume expansion Composite 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 mater

7、ials,Stability of SEI film,6,1/10/2023,Porous Si/C composite,Synthesis Process,1/10/2023,Morphology,7,in 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 1

8、0 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 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 Po

9、rous Si-C-700.,Results and analysis,SEM and TEM images,1/10/2023,8,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

10、)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 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 analysis,Structural

11、characterization,1 D.Aurbach,J.Phys.Chem.C,2007,111,11437.,XRD patterns and Raman spectra,N2 sorption isotherms,Pore size distribution,Both porous carbon and porous Si-C show type IV isotherm,which is typical characteristic of mesoporous structureObvious decrease of specific surface area(SSA)and por

12、e 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 decomposition of sucrosePores with diameter of 1040 nm due to the removal of CaCO3 template,which were reduced after Si CVD,Porous Structure,1/10/2023,9,Charge-Discharge cur

13、ves,Cycling performance,1)2nd charge capacity;2)VC:vinylene carbonate,1/10/2023,10,Electrochemical performance,1st dch capacity:2404 mAh/g1st ch capacity:1541 mAh/g1st coulombic efficiency:64.1%Reversible capacity1:1504 mAh/gCapacity retention:67%after 200 cycles,Recipe:Porous Si-C:CB:binder(PAA)=6:

14、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.Li,Rate capability,Increase current density from 0.1 to 2 A g-1,the specific capacity of Si/C composi

15、te 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 is recoverable.,1/10/2023,11,Results and analysis,Nyquist plot of Si-C composite at the end of discharge after different cycles,in 1 bold,1 eElectrochemical impedanc

16、e 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-circuit for at least 2 h to stabilize their potential.The constancy of the characteristic frequency(20H

17、z,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)shows an increase in first 5 cycles then reduce and maintain around 40 Ohm in later cycles.,Results and analysis,1/10/2023,12,EIS test,1

18、 D.Guyomard,J.Mater.Chem.,2011,21,6201.,SEI film with cycling,Superficial 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 an

19、d 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.,1/10/2023,13,Materials after cycling,1 Y.Cui,Nano Lett.10(2010

20、)1409,Si/C after 50 cycles,a)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 show aggr

21、egation and rupture.,Results and analysis,a),b),c),d),C-K,Si-K,1/10/2023,14,SEI confinement,Schematic,1/10/2023,15,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 carb

22、on substrate,which prevent the internal silicon particle from being exposed in the electrolyte.,Results,1/10/2023,16,Schematic of synthesis,Advantage:1.Easy to synthesis and regulate according to commercial CaCO3 template2.Hollow structure with reserve volume can accommodate large volume changes3.In

23、terconnected nano silicon means more active conductive contact.,Hollow silicon,1/10/2023,17,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 HS

24、A-10.Amorphous hollow silicon material with different shell thickness was prepared,1/10/2023,18,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

25、 main 3/2-1/2 doublet(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,

26、1/10/2023,19,Results 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

27、is attributed to the removal of site-occupying nano CaCO3.,Isotherm and Pore size distribution,Porous Structure,1/10/2023,20,Cycling performance,Cycle performance,Test 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

28、density:0.1 A/g 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

29、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 HSA-10 after 100 cycles with

30、out 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,1/10/2023,21,a,b,c,d,EIS test,1/10/2023,22,St

31、able interface and smaller resistance,Nyquist 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

32、.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 and analysis,DSC Test,1/10/2023,23,Stable SEI s

33、tructure of silicon foam,DSC 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 open-circuit for 2 h then carefully opened in a glove box.The electrode was soaked in DMC and then dried u

34、nder 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 lithiated graphite,which thermal stability is well studied,it is

35、 reasonable to suggest that metastable SEI layer components are transformed at 86-100 C.,Results and analysis,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

36、can 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 tha

37、t 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.,1/10/2023,24,Summary,Thanks for your attention!,1/10/2023,IBA2014Conference,25,AcknowledgementsState Key Basic Research Programm of PRC(2013CB934000),Beijing Natural Science Fundation(2120001),

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