F-doped Carbon Coated Nano-Si Anode

F-doped Carbon Coated Nano-Si Anode nrog lub peev xwm siab: Kev npaj los ntawm Gaseous Fluorination thiab Kev Ua Haujlwm rau Lithium Cia

Tus sau:SU Nan, QIU Jieshan, WANG Zhiyu. F-doped Carbon Coated Nano-Si Anode nrog lub peev xwm siab: Kev npaj los ntawm Gaseous Fluorination thiab Kev Ua Haujlwm rau Lithium Cia. Phau ntawv Journal of Inorganic Materials, 2023, 38(8): 947-953 DOI:10.15541/jim20230009

Abstract

Si anodes hold immense potential in developing high-energy Li-ion batteries. But fast failure due to huge volume change upon Li uptake impedes their application. This work reports a facile yet low-toxic gas fluorination way for yielding F-doped carbon-coated nano-Si anode materials. Coating of nano-Si with F-doped carbon containing high defects can effectively protect Si from huge volume change upon Li storage while facilitating Li+ transport and formation of stable LiF-rich solid electrolyte interphase (SEI). This anode exhibits high capacities of 1540-580 mAh·g-1 at various current rates of 0.2-5.0 A·g-1, while retaining >75% muaj peev xwm tom qab 200 cycles. Txoj kev no tseem hais txog cov teeb meem ntawm tus nqi siab thiab toxicity ntawm cov txheej txheem fluorination ib txwm siv cov khoom siv fluorine xws li XeF2 thiab F2.

Ntsiab lus:Li-ion roj teeb; Yog anode; F-doped carbon; gaseous fluorination txoj kev

Tsim kom muaj zog cia thiab hloov dua siab tshiab thev naus laus zis yuav pab ua kom tiav lub hom phiaj ntawm "carbon peaking thiab carbon neutrality". Cov roj teeb lithium-ion tam sim no yog ib qho ntawm cov khoom siv hluav taws xob siv hluav taws xob ntau tshaj plaws [1]. Txawm li cas los xij, kev lag luam graphite anodes muaj peev xwm cia lithium tsawg, uas txwv tsis pub lub zog ceev ntawm lithium-ion roj teeb [2]. Silicon muaj qhov zoo ntawm qhov tsis tshua muaj peev xwm thiab muaj peev txheej ntau, thiab nws qhov kev xav tau tshwj xeeb muaj peev xwm (4200 mAh·g-1) yog siab dua li ntawm graphite anode, yog li nws tau suav tias yog cov khoom siv anode los hloov graphite [3 ]. Silicon cov ntaub ntawv ua tiav lithium cia raws li qhov thim rov qab alloying cov tshuaj tiv thaiv nrog lithium ions, tab sis cov txheej txheem no yog nrog los ntawm kev hloov pauv loj loj (~ 400%), uas ua rau cov hmoov nplej sai thiab tsis ua haujlwm ntawm cov electrode, dhau los ua qhov tseem ceeb hauv lub raj mis txwv tsis pub siv cov tswv yim siv. silicon anodes [3- 4].

Nyob rau hauv xyoo tas los no, cov kws tshawb fawb tau tsim ntau yam tswv yim los txhim kho kev ruaj ntseg thiab electrochemical kev ua tau zoo ntawm silicon anodes. Xws li: nanometerization [5], structural composite nrog conductive carbon thiab lwm yam ntaub ntawv [6-7], thiab lwm yam. Txhim kho cov qauv stability ntawm silicon anode los ntawm alleviating cov neeg kho tshuab kev nyuaj siab txuam nrog lub ntim expansion ntawm lithium cia ntawm lub microscopic. nplai. Tsim tshiab electrolytes los yog electrolyte additives los txhim kho kev ruaj ntseg thiab Coulombic efficiency ntawm cov khoom electrolyte interface theem (SEI) nyob rau saum npoo ntawm silicon anode [8]. Tsim kom muaj cov ntaub ntawv zoo polymer (xws li sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid-based polyrotaxane [9], thiab lwm yam). Txhim kho lub zog sib txuas ntawm cov khoom siv hluav taws xob, nruab nrab ntawm cov khoom siv hluav taws xob thiab cov khoom siv hluav taws xob, thiab nruab nrab ntawm electrode zaj duab xis thiab cov khoom siv tam sim no [9-10]. Ntawm lawv, carbon txheej yog ib qho zoo tshaj plaws txhais tau tias los txhim kho cov qauv kev ruaj ntseg ntawm silicon anodes thiab modulate nto thiab interface zog [3-4,11]. Txawm li cas los xij, cov txheej txheem nruj heev coated cov pa roj carbon monoxide tseem cuam tshuam kev thauj mus los ntawm lithium ion thiab txwv kev ua haujlwm tag nrho ntawm silicon anode.

Tsis tas li ntawd, qhov rov ua dua ntim ntawm silicon anode thaum lub sij hawm tas mus li thiab cov txheej txheem tawm kuj ua rau SEI zaj duab xis tsis tu ncua tawg thiab loj hlob zuj zus, ua rau tsis tu ncua ntawm cov lithium thiab electrolyte ntawm electrode nto [12]. Hauv kev teb rau cov teeb meem saum toj no, txoj kev tshawb fawb no tau nthuav tawm cov txheej txheem roj-theem fluorination kom zoo rau cov txheej txheem ntawm cov khoom siv silicon anode nrog cov txheej txheem amorphous carbon nplua nuj nyob rau hauv cov ntsiab lus fluorine txhawm rau txhim kho nws cov qauv thiab kev ruaj ntseg. Piv nrog rau cov cuab yeej fluorination ib txwm siv uas siv cov nqi siab thiab cov tshuaj fluorine muaj kuab heev xws li XeF2 lossis F2 [13], lub tswv yim no yooj yim dua thiab tsis muaj tshuaj lom. Cov fluorine-doped carbon txheej txheej txheej saum npoo ntawm cov ntaub ntawv nano-silicon tuaj yeem cuam tshuam qhov ntim ntawm lithium-embedded silicon anodes thaum txhim kho lithium ion thauj peev xwm. Thiab ib qho ruaj khov SEI zaj duab xis nplua nuj nyob rau hauv inorganic fluoride yog tsim nyob rau hauv situ kom ua tiav lub hom phiaj ntawm kev txhim kho lub voj voog stability ntawm silicon anode.

1 Kev sim txoj kev

1.1 Kev npaj khoom siv

Kev npaj ntawm carbon-coated nano-silicon (Si@C): 0.3 g ntawm coj mus muag nanosilica hmoov (particle loj 20~100 nm, Aladdin's reagent) tau ultrasonically dispersed nyob rau hauv 28 mL ntawm ib tug tov hnyav ntawm deionized dej thiab ethanol (ntim piv 5: 2). Tom qab ntxiv 0.4 mL ntawm 3-aminopropyltriethoxysilane, do rau 2 h los ua ib qho kev sib cais A. Dissolve 0.115 g ntawm 4,4-dihydroxydiphenyl sulfide thiab 0.1 g ntawm 3-aminophenol nyob rau hauv 28 mL ntawm ib tug sib tov hnyav ntawm deionized dej thiab ethanol (ntim piv 5:2) los ua ib homogeneous tov B. Sib tov dispersion A thiab tov B sib npaug, ntxiv 0.1 mL ammonia dej, do rau 30 min, tom qab ntawd ntxiv 0.14 mL formaldehyde tov (37% ~ 40%), thiab hnov ​​​​mob tas li stirring ntawm 30 degree rau 12 teev. Tom qab cov tshuaj tiv thaiv, phenolic resin-coated nanosilica (Si@AF) tau txais los ntawm centrifuging thiab ntxuav nrog ethanol thiab deionized dej hloov peb zaug. Nws tau calcined hauv argon roj ntawm 800 degree rau 3 h kom tau carbon-coated nano-silicon (Si@C).

Kev npaj ntawm fluorine-doped carbon-coated nano-silicon (Si@CF): 100 mg Si@C thiab 200 mg polyvinylidene fluoride (PVDF) tau muab tso rau hauv lub qhov cub tiv thaiv argon. Lub nkoj quartz uas muaj PVDF yog nyob rau sab saud ntawm cov huab cua ntws, thiab lub nkoj quartz uas muaj Si@C yog nyob hauv qab ntawm cov huab cua ntws. Nws yog roasted ntawm 600 degree rau 3 h kom tau fluorine-doped carbon-coated nano-silicon (Si@CF).

1.2 Kev sib dhos roj teeb thiab kev kuaj xyuas electrochemical

1.2.1 Roj teeb sib dhos

Sib sau CR2016 khawm roj teeb rau kev sim. Sib tov cov khoom nquag, cov pa roj carbon dub thiab carboxymethylcellulose sodium binder sib npaug hauv qhov sib piv ntawm 7: 2: 1. Deionized dej tau ntxiv raws li cov kuab tshuaj thiab dispersant, thiab cov slurry tau muab sib npaug ntawm cov ntawv ci tooj liab raws li cov electrode ua haujlwm. Cov khoom siv thauj khoom nquag yog 0.8 ~ 1.{{10}}mg·cm-2. Cov ntawv hlau lithium tau siv los ua cov txee electrodes thiab siv electrodes. Cov electrolyte yog DOL/DME cov tshuaj yaj hauv 1. ethylene glycol dimethyl ether, ntim piv 1: 1). Sib sau cov cell hauv lub hnab looj tes uas muaj argon (dej cov ntsiab lus <0.1 μL / L, cov ntsiab lus oxygen < 0.1 μL / L).

1.2.2 Kev ntsuas roj teeb

Siv lub IVIUM Vertex.C.EIS electrochemical workstation los soj ntsuam cov tshuaj tiv thaiv mechanism thiab cov tshuaj tiv thaiv kinetics ntawm lub roj teeb siv Cyclic Voltammetry (CV) txoj kev. Qhov ntsuas hluav taws xob yog {{0}}.01 ~ 1.5 V, thiab tus nqi cheb yog 0.05 ~ 0.5 mV ·s- 1. Electrochemical Impedance Spectroscopy (EIS) tau siv los txheeb xyuas cov electrode dynamics. Qhov ntsuas zaus ntau yog 100 kHz ~ 10 mHz, thiab qhov cuam tshuam qhov voltage amplitude yog 5.0 mV. Av CT2001A roj teeb tester tau siv los kawm txog lithium cia kev ua tau zoo siv cov nqi them tam sim no thiab kev tso tawm. Lub qhov rais voltage yog 0.01 ~ 1.5 V (vs. Li/Li+), thiab qhov ceev tam sim no yog 0.2 ~ 5.0 A·g-1.

2 Cov txiaj ntsig thiab kev sib tham

2.1 Kev soj ntsuam ntawm cov tsos, qauv thiab muaj pes tsawg leeg ntawm cov khoom

Cov txheej txheem kev npaj ntawm fluorine-doped carbon-coated nano-silicon cov ntaub ntawv yog qhia nyob rau hauv daim duab 1. Ua ntej, polymer-coated silicon nanoparticles (Si@AF) yog npaj raws li phenol-aldehyde condensation polymerization cov tshuaj tiv thaiv thiab hloov mus rau hauv amorphous carbon-coated nano. -silicon nanoparticles (Si@C) ntawm qhov kub thiab txias. Tom qab ntawd polyvinylidene fluoride yog siv los ua fluorine qhov chaw, thiab fluorine yog doped rau hauv cov pa roj carbon txheej sab nraum silicon nanoparticles los ntawm cov roj theem fluorination txoj kev ntawm kub. Daim duab 2(a) qhia XRD qauv ntawm Si@C thiab Si@CF cov ntaub ntawv. Diffraction peaks nyob ntawm 2θ=28 degree, 47 degree, 56 degree, 69 degree thiab 76 degree. Lawv sib haum rau (111), (220), (311), (400) thiab (331) siv lead ua dav hlau ntawm ib leeg siv lead ua silicon (JCPDS 77-2108) feem. Lub ncov dav nyob ntawm 2θ=25 degree ~ 26 degree yog ntaus nqi rau cov qauv luv luv uas tau tsim los ntawm carbonization ntawm phenolic condensation polymerization khoom. Cov pa roj carbon txheej txheej nrog cov khoom siv hluav taws xob siab thiab cov txheej txheem zoo heev tuaj yeem txo qis pulverization tsis ua hauj lwm ntawm cov ntaub ntawv silicon thaum lub sij hawm them nqi thiab tawm cov txheej txheem thiab txhim kho cov conductivity ntawm electrode. Daim duab 2(b) yog Raman spectrum ntawm Si@C thiab Si@CF cov ntaub ntawv, nrog pom tseeb nqus peaks tshwm sim ntawm 515, 947, 1350 thiab 1594 cm-1. Ntawm lawv, qhov nqus tau siab tshaj ntawm 515 thiab 947 cm -1 yog cov yam ntxwv peaks ntawm crystalline silicon, uas yog muab los ntawm thawj qhov kev txiav txim photophonon tawg thiab qhov thib ob-order transverse photophonon tawg ntawm silicon feem [14]. Qhov nqus tau siab tshaj plaws ntawm 1350 thiab 1594 cm -1 sib haum rau cov pa roj carbon monoxide configuration stretching vibration (G hom) thiab cov pa roj carbon tsis zoo (D hom), feem. Feem ntau hais lus, qhov sib piv ntawm D hom thiab G hom (ID / IG) tuaj yeem siv los ntsuas qhov ntsuas ntawm qhov tsis xws luag thiab tsis zoo ntawm cov khoom siv carbon [15]. Piv nrog Si@C cov khoom (ID / IG=0.99), ID / IG ntawm Si@CF cov khoom nce mus rau 1.08. Nws qhia tau hais tias cov txheej txheem fluorination tuaj yeem ua rau muaj qhov tsis xws luag ntawm cov pa roj carbon txheej txheej, uas yog qhov zoo rau nruj txheej nano-silicon thaum txhim kho lithium ion thauj peev xwm.

Fig. 1 Schematic illustration of the production of Si@CF

Daim duab 2 (a) XRD qauv, (b) Raman spectra, (c) XPS daim ntawv ntsuam xyuas, (d) high-resolution F1s thiab (e) Si2p XPS spectra ntawm Si@C thiab Si@CF, (f) TGA nkhaus of Si@CF

XPS tag nrho spectrum qhia tau hais tias Si@C cov khoom muaj O, N, C, thiab Si ntsiab (Daim duab 2(c)). Cov atomic feem ntawm F lub hauv paus ntawm Si@CF cov khoom tau txais tom qab kev kho fluorination yog kwv yees li 1.8%. Nyob rau hauv qhov kev daws teeb meem siab F1s XPS spectrum (Daim duab 2(d)), ob lub cim ncov ntawm lub zog khi ntawm 686.3 thiab 687.8 eV sib haum rau CF thiab Si-OF raws, thiab CF yog qhov tseem ceeb. Nws qhia tau hais tias txoj kev kho fluorination tau ua tiav cov txheej txheem fluorine rau hauv amorphous carbon txheej coated rau ntawm nano-silicon. Qhov kev daws teeb meem siab Si2p (Daim duab 2(e)) thiab F1s XPS spectra ua pov thawj tias Si atoms cuam tshuam cov tshuaj nrog F hauv cov txheej txheem carbon los ntawm kev tsim Si-OF bonds, uas muaj txiaj ntsig zoo rau cov txheej txheem nruj ntawm cov pa roj carbon monoxide. silicon nto. Thermogravimetric tsom xam (TGA) qhia tau hais tias qhov loj feem ntawm Si hauv cov khoom Si@CF yog kwv yees li 85.17% (Daim duab 2(f)).

SEM tsom xam qhia tias Si@CF cov khoom yog tsim los ntawm nanoparticles nrog ib tug loj ntawm<100 nm (Figure 3(a~c)). After high-temperature carbonization and gas-phase fluorination treatment, the carbon material is still uniformly coated on the surface of the silicon nanoparticles.

Fig. 3 (ac) SEM images, (df) TEM images and (gi) elemental map of Si@CF

TEM tsom xam qhia tau hais tias cov silicon nanoparticles yog tag nrho thiab tusyees coated nyob rau hauv ib tug carbon txheej nrog ib tug tuab ntawm txog kaum nanometers, tsim ib tug core-plhaub qauv (Daim duab 3(d ~ e)). Silicon nanoparticles muaj ib qho qauv siv lead ua, uas lub lattice spacing ntawm 0.328 nm sib raug rau (111) siv lead ua dav hlau ntawm Si, thiab cov fluorine-doped carbon txheej npog nws muaj cov qauv amorphous (Daim duab 3( f)). Cov khoom faib spectrum ua pov thawj tias C thiab Si cov ntsiab lus sib npaug hauv Si@CF (Daim duab 3 (g ~ i)).

2.2 Electrochemical khoom ntawm cov khoom

Daim duab 4(a, b) yog CV nkhaus ntawm Si@C thiab Si@CF anode cov ntaub ntawv. Lub cheb ceev yog 0.1 mV·s-1 thiab qhov hluav taws xob ntau yog 0.01 ~ 1.5 V. Hauv thawj lub voj voog, qhov tsis muaj zog broad ncov hauv qhov ntau ntawm 0.1~0.4 V sib raug rau cov txheej txheem irreversible electrolyte decomposition los ua ib zaj duab xis SEI; qhov txo qis ntawm 0.01 V sib raug rau cov txheej txheem ntawm crystalline silicon ua silicon-lithium alloy (LixSi) los ntawm cov tshuaj tiv thaiv alloying. Thaum lub sijhawm them nyiaj tom ntej, ob lub oxidation peaks ntawm 0.32 thiab 0.49 V sib haum rau cov txheej txheem ntawm kev xa tawm ntawm LixSi los ua amorphous silicon [16]. Kev kho fluorination tuaj yeem ua tiav cov txheej txheem doping thiab etching teebmeem. Ib tug loj tus naj npawb ntawm cov yam ntxwv tsis xws luag yog nkag mus rau hauv lub amorphous carbon txheej coated nyob rau saum npoo ntawm cov khoom Si los tsim ib tug peb-dimensional lithium ion thauj channel, ceev lithium ion thauj thiab txhim khu cov electrochemical reactivity ntawm cov khoom Si. Yog li ntawd, Si @ CF nthuav tawm lub siab tshaj plaws delithiation oxidation ncov ntawm 0.49 V tshaj Si@C anode yam tsis muaj fluorine doping. Thaum cov txheej txheem tso tawm tom ntej, qhov txo qis tshiab ntawm 0.19 V sib raug rau cov txheej txheem lithium ntxig ntawm amorphous silicon tsim thaum thawj txheej txheem them nyiaj [16-17]. Raws li tus naj npawb ntawm cov voj voog nce, cov haujlwm ntawm oxidation ncov thiab qhov txo qis hauv CV nkhaus tsis hloov lawm, qhia tias Si@C thiab Si@CF anode cov ntaub ntawv ua raws li cov khoom siv lithium zoo sib xws tom qab thawj zaug thiab tawm. Thaum lub sijhawm txheej txheem no, lub ncov oxidation thiab txo qhov ncov maj mam nce, uas qhia txog cov txheej txheem ua kom cov electrode raug.

Fig. 4 (a, b) CV curves ntawm tus nqi scan ntawm 0.1 mV·s-1 thiab charge-discharge voltage curves ntawm (c, d) 0.2 thiab (e, f) 0.4 A·g-1 for (a, c, e) Si@C and (b, d, f) Si@CF anodes

Nyob rau hauv qhov kev ntsuas tam sim no thiab tso tawm, cov khoom siv Si anode tau cycled thiab qhib 4 zaug ntawm qhov qis tam sim no (0.2 A·g-1), thiab tom qab ntawd nws lub voj voog ruaj khov tau sim ntawm ib qhov ceev tam sim no ntawm 0.4 A·g-1. Daim duab 4 (c, d) qhia cov galvanostatic nqi thiab tawm nkhaus ntawm Si@C thiab Si@CF anodes ntawm 0.2 A·g-1, thiab lub qhov rais voltage yog 0 . alloying. Cov txheej txheem no feem ntau nrog rau qhov qis thawj Coulombic efficiency. Thaum lub sij hawm thawj cov txheej txheem them, cov silicon-lithium alloy yog delithiated thiab hloov mus rau hauv amorphous silicon nrog lub zog ua kom qis rau lithium insertion [18], ua rau lithium insertion peev xwm nce mus rau 0.1 ~ 0.3 V tom qab thawj zaug thiab tawm. Piv nrog Si@C, thawj qhov tso tawm tshwj xeeb muaj peev xwm (2640 mAh·g-1) ntawm Si@CF anode qis dua me ntsis. Txawm li cas los xij, thawj tus nqi tshwj xeeb (1739.6 mAh·g{29}}) yog siab dua, thiab thawj Coulombic efficiency (65.9%) yog li 45.8% siab dua li ntawm Si@C anode. Tus nqi-tso tawm nkhaus ntawm SEI cheeb tsam ntawm Si @ CF tsis zoo electrode yog luv dua li ntawm Si@C, qhia tias SEI zaj duab xis ruaj khov yog tsim nyob rau saum npoo. Qhov no yog vim hais tias cov fluorine-doped carbon txheej yog tsim rau inducing tsim ntawm ib tug SEI zaj duab xis uas muaj inorganic Cheebtsam (xws li LiF) thiab siab stability nyob rau saum npoo ntawm silicon anode, li no txo ​​irreversible lithium poob thiab electrolyte noj [19].

Figure 4(e~f) shows the charge and discharge curves of Si@C and Si@C-F negative electrodes at a current density of 0.4 A·g-1 after activation. After 100 cycles, the Si@C-F anode can still maintain a high specific capacity of 1223 mAh·g-1, with a capacity retention rate of >85% (Figure 5(a)). Under the same conditions, the capacity of the Si@C negative electrode without fluorination treatment rapidly decayed during the charge and discharge process, and the capacity retention rate after 100 cycles was only 62%. It shows that the fluorine-doped carbon coating layer has a significant effect on improving the cycle stability of the silicon anode. Commercial nano-silicon anodes without carbon coating will fail after more than 10 cycles due to huge volume expansion and structural powdering during the deintercalation of lithium. During this process, the specific capacity of Si@C-F and Si@C negative electrodes gradually increases in the first 10 to 20 cycles due to the activation effect. At a large current density of 0.2~5.0 A·g-1, the Si@C-F anode can maintain a high specific capacity of 1540~580 mAh·g-1, showing excellent capacity retention (Figure 5(b)). At a high current density of 5.0 A·g-1, its capacity retention rate is approximately 78% higher than that of Si@C. When the current density is further reduced to 0.2 A·g-1, the specific capacity can be restored to 1450 mAh·g-1, indicating that its structure is highly stable during high-rate lithium storage. After 200 charge-discharge cycles at a current density of 0.2 A·g-1, the Si@C-F anode can maintain a specific capacity of >75%. Lub peev xwm tuav tau ntawm Si@C anode yam tsis muaj kev kho fluorination tsuas yog 40% (Daim duab 5(c)). Qhov no anode kuj qhia tau hais tias lithium cia kev ua tau zoo dua li cov khoom siv silicon anode qhia hauv cov ntaub ntawv (Table 1).

Fig. 5 (a) Cycling stability ntawm qhov ceev tam sim no ntawm 0.4 A·g-1 nrog anodes qhib los ntawm 4 lub voj voog ntawm 0.2 A·g-1 ua ntej kev caij tsheb kauj vab, thiab (b) muaj peev xwm muaj peev xwm ntawm ntau qhov ceev tam sim no xws li 0.2 txog 5.0 A·g−1 thiab (c) muaj peev xwm tuav tau ntawm qhov ceev tam sim no ntawm {{13} }.2 A·g-1 rau lithium cia hauv Si@C thiab Si@CF anode

Table 1 Sib piv ntawm Si@CF anode nrog qhia Si-raws li anode hauv electrochemical kev ua tau zoo

At a high current density of 5.0 A·g-1, its capacity retention rate is approximately 78% higher than that of Si@C. When the current density is further reduced to 0.2 A·g-1, the specific capacity can be restored to 1450 mAh·g-1, indicating that its structure is highly stable during high-rate lithium storage. After 200 charge-discharge cycles at a current density of 0.2 A·g-1, the Si@C-F anode can maintain a specific capacity of >75%. The capacity retention rate of the Si@C anode without fluorination treatment is only 40% (Figure 5(c)). This anode also shows better lithium storage performance than the silicon anode material reported in the literature (Table 1). The fluorine doping amount in the coating carbon layer has a significant impact on the lithium storage performance of the Si@C-F anode. When the fluorine doping amount is below 1.8% atomic fraction, the cycling stability of the Si@C-F anode significantly improves as the fluorine doping amount increases (Figure 6). This is due to the enhanced effect of fluorine doping on the lithium ion transport properties of the carbon coating layer and the stability of the SEI film on the surface of the silicon material. When the fluorine doping ratio is too high (>2.7%), cov khoom siv roj carbon-coated Si anode tseem tuav lub voj voog zoo, tab sis lub peev xwm tshwj xeeb poob qis. Qhov no yog vim qhov poob ntawm Si active tshwm sim los ntawm cov roj-theem fluorine hom etching thaum kub-kub fluorination. Thaum cov fluorine doping tus nqi yog 1.8 atomic feem pua, Si@CF anode nthuav tawm lub voj voog zoo thiab muaj peev xwm tshwj xeeb.

Fig. 6 Cycling stability ntawm Si@CF anodes nrog qhov sib txawv F piv ntawm qhov ceev tam sim no ntawm 0.4 A·g-1 nrog anodes qhib los ntawm 4-10 cycles ntawm 0 .2 A·g-1 ua ntej caij tsheb kauj vab

Lub EIS spectra ntawm Si @ C thiab Si @ CF anodes muaj ib nrab arc nkhaus nyob rau hauv nruab nrab- mus rau high-frequency cheeb tsam thiab inclined ncaj kab nyob rau hauv lub low-frequency cheeb tsam (Daim duab 7(a)). Lub semi-arc nkhaus nyob rau hauv nruab nrab-mus rau high-frequency range yog hais txog tus nqi hloov pauv tsis kam (Rct), thiab txoj kab ncaj nraim hauv qhov tsawg zaus feem ntau qhia txog Warburg impedance (ZW) ntawm lithium ion diffusion [26 ]. Ua ntej them thiab tso tawm, Rct ntawm Si @ CF thiab Si @ C tsis zoo electrodes yog qhov zoo sib xws, tab sis cov qub muaj ZW qis dua vim muaj cov fluorine-doped carbon txheej uas tsis zoo heev. Tom qab them nyiaj thiab tso tawm mus, Rct (5.51 Ω) ntawm Si@CF anode yog qhov qis dua li ntawm Si@C anode (21.97 Ω) (Daim duab 7(b)), thiab ZW qis dua li yav tas los. . Qhov no qhia tau hais tias cov fluorine-nplua nuj SEI interface zaj duab xis induced los ntawm fluorine-doped carbon txheej tuaj yeem txhim kho tus nqi cuam tshuam thiab kev thauj mus los lithium ion.

Daim duab 7 Nyquist plots ntawm Si@C thiab Si@CF anodes (a) ua ntej thiab (b) tom qab caij tsheb kauj vab ntawm qhov ceev tam sim no ntawm 0.4 A·g-1

2.3 Cov yam ntxwv ntawm cov qauv electrode tom qab them thiab tawm

SEM tus cwj pwm tom qab them nqi thiab tawm mus (Daim duab 8 (a ~ c)) qhia tau hais tias vim qhov loj ntim nthuav dav ntawm silicon thaum lub sij hawm lithium insertion txheej txheem, lub thickness ntawm Si@C electrode nce 132.3%. Qhov no tsis tsuas yog cuam tshuam kev sib kis ntawm ions thiab electrons, ua rau muaj kev tiv thaiv sab hauv thiab polarization ntawm cov electrode, tab sis kuj ua rau muaj kev ntxhov siab loj heev, ua rau cov electrode tawg thiab sib cais los ntawm cov khoom siv tam sim no, ua rau kev ua haujlwm ntawm Si@C anode. tawg sai sai (Daim duab 5(c)). Nyob rau hauv kev sib piv, lub electrode thickness ntawm Si@CF anode nce los ntawm tsuas yog 26.6% tom qab them thiab tawm mus, thiab tuav zoo electrode qauv stability (Daim duab 8(d ~ f)). Qhov no qhia tau hais tias cov txheej txheem fluorine-doped carbon tau zoo tuaj yeem cuam tshuam qhov ntim nthuav dav ntawm lithium ntxig rau hauv cov ntaub ntawv silicon ntawm micro scale, yog li txhim kho cov qauv kev ruaj ntseg ntawm cov electrode ntawm macro scale los ntawm hauv qab.

Fig. 8 Sab saum toj SEM cov duab ntawm (a) Si@C thiab (d) Si@CF anodes tom qab caij tsheb kauj vab; Hla ntu SEM cov duab ntawm (b, c) Si@C thiab (e, f) Si@CF anodes (b, e) ua ntej thiab (c, f) tom qab caij tsheb kauj vab; High-resolution (g) F1s thiab (h) Li1s XPS spectra ntawm SEI ntawm Si@C thiab Si@CF anodes tom qab caij tsheb kauj vab

Cov muaj pes tsawg leeg ntawm SEI zaj duab xis nyob rau saum npoo ntawm Si@C thiab Si@CF tsis zoo electrodes tom qab them nyiaj thiab tawm mus tau raug tshuaj xyuas los ntawm XPS (Daim duab 8 (g ~ h)). Nyob rau hauv lub high-resolution F1s XPS spectrum, lub binding zog peaks ntawm lub binding zog ntawm 684.8, 688.3, ​​thiab 689.1 eV sib raug rau LiF, CF daim ntawv cog lus, thiab CF2, feem. Ua ke, tseem muaj cov yam ntxwv ncov sib xws rau LiF hom nyob rau hauv high-resolution Li1s XPS spectrum, qhia tias ib tug SEI zaj duab xis uas muaj LiF hom yog tsim nyob rau saum npoo ntawm silicon anode. Piv nrog rau Si@C anode, LiF cov ntsiab lus nyob rau saum npoo ntawm Si @ CF anode yog siab dua, qhia tias LiF hauv SEI zaj duab xis los tsis yog los ntawm decomposition ntawm lithium ntsev hauv cov electrolyte, tab sis kuj los ntawm F hauv fluorine-doped carbon txheej. Qhov tsim ntawm high-modulus LiF tuaj yeem ua kom muaj zog ntawm SEI zaj duab xis thiab inhibit qhov ntim hloov ntawm lithium tso rau hauv cov ntaub ntawv silicon. Nyob rau tib lub sijhawm, qhov dav bandgap thiab insulating zog ntawm LiF tuaj yeem txo qhov SEI thickness thiab txo qhov pib tsis tuaj yeem rov qab lithium poob. LixSi alloy, cov khoom lithiation ntawm LiF thiab Si, muaj lub zog sib cuam tshuam thiab tuaj yeem hloov kho kom zoo dua rau cov yas deformation ntawm lithiated silicon anode thaum caij tsheb kauj vab, yog li ntxiv kev txhim kho cycling stability ntawm electrode [19].

3 Kev xaus

In this study, fluorine-doped carbon-coated nano-silicon materials were prepared through a simple and low-toxic gas-phase fluorination method. Research shows that fluorine doping (1.8% F), on the one hand, increases the defects of the carbon coating layer on the silicon surface, and provides abundant lithium ion transport channels while tightly coating nano-silicon to suppress its volume expansion. On the other hand, a highly stable SEI film rich in LiF is induced on the surface of the nano-silicon material, further improving the stability and Coulombic efficiency of the silicon anode. Thanks to this, the first Coulombic efficiency of the fluorine-doped carbon-coated nano-silicon anode improved to 65.9%. At a current density of 0.2~5.0 A·g-1, it exhibits a high specific capacity of 1540~580 mAh·g-1, and can maintain >75% ntawm qhov pib muaj peev xwm tom qab 200 cycles. Qhov kev ua haujlwm no muab cov tswv yim tshiab rau kev tsim thiab tsim cov khoom siv silicon anode nrog lub peev xwm siab thiab ruaj khov.

Kev siv

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