This is the submitted version of the journal article: Li, Junshan; Xu, Xijun; Yu, Xiaoting; [et al.]. «Monodisperse CoSn and NiSn nanoparticles supported on commercial carbon as anode for lithium- and potassium-ion batteries». ACS applied materials & interfaces, Vol. 12 issue 4 (Jan 2020), p. 4414-4422. DOI 10.1021/acsami.9b16418 This version is available at https://ddd.uab.cat/record/235999 under the terms of the license Page 1 of 11 ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 Monodisperse CoSn and NiSn Nanoparticles Supported on 8 9 Commercial Carbon as Anode for Lithium- and Potassium-ion 10 Batteries 11 12 Junshan Li,∑,¤, Xijun Xu,§,ŋ, Xiaoting Yu,∑,¤ Xu Han,Ś Ting Zhang,e Yong Zuo,∑ Chaoqi Zhang,∑ 13 Dawei Yang,∑ Wang Xiang,∑ Zhishan Luo,Ǽ Jordi Arbiol,Ś,∆ Jordi Llorca,φ Jun Liu,§,ŋ* Andreu 14 15 Cabot∑,∆* 16 ∑ Catalonia Institute for Energy Research - IREC, Sant Adrià de Besòs, Barcelona, 08930, Spain 17 18 ¤ Departament d’Electrònica, Universitat de Barcelona, 08028 Barcelona, Spain 19 § Guangdong Provincial Key Laboratory of Advanced Energy Storage Materials, School of Materials Science and 20 Engineering, South China University of Technology, Guangzhou 510641, P. R. China 21 ŋ SUNWODA-SCUT Joint Laboratory for Advanced Energy Storage Technology, South China University of 22 Technology, Guangzhou 510641, P. R. China 23 Ś Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 24 Barcelona, Spain 25 26 Ǽ Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong 27 518055, P. R. China 28 ∆ ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain 29 φ Institute of Energy Technologies, Department of Chemical Engineering and Barcelona Research Center in Multiscale 30 Science and Engineering. Universitat Politècnica de Catalunya, EEBE, 08019 Barcelona, Spain 31 32 KEYWORDS: Colloidal nanoparticles; bimetallic alloys; anode; lithium-ion batteries; potassium-ion batteries. 33 34 35 36 ABSTRACT: Monodisperse CoSn and NiSn nanoparticles were prepared in solution and supported on commercial carbon 37 black. The obtained nanocomposites were applied as anodes for Li- and K-ion batteries. CoSn@C delivered stable average 38 capacities of 850, 650 and 500 mAh g-1 at 0.2, 1.0 and 2.0 A g-1, respectively, well above those of commercial graphite 39 anodes. The capacity of NiSn@C retained up to 575 mAh g-1 at a current of 1.0 A g-1 over 200 continuous cycles. Up to 40 74.5% and 69.7% pseudocapacitance contribution for Li-ion batteries were measured for CoSn@C and NiSn@C, 41 respectively, at 1.0 mV s-1. CoSn@C was further tested in full-cell lithium ion batteries with a LiFePO4 cathode to yield a stable capacity of 350 mAh g-1 at a rate of 0.2 A g-1. As electrode in K-ion batteries, CoSn@C composites presented a stable 42 capacity of around 200 mAh g-1 at 0.2 A g-1 over 400 continuous cycles, and NiSn@C delivered a lower capacity of around 43 100 mAh g-1 over 300 cycles. 44 45 46 47 INTRODUCTION interesting due to their abundance, low cost and large 48 With an ever increasing demand for portable electrical conductivity. 49 electronics, the market for rechargeable lithium-ion A critical challenge for these anode materials and 50 batteries (LIBs) have exponentially grown since their first particularly Sn is a poor cycling performance associated 51 commercialization in 1991.1,2 However, current LIBs still with a large volume variation upon lithium ion 52 do not meet the desired targets on safety, durability and insertion/extraction.11–14 To buffer these volume changes, 53 energy density.3 Centering on the anode, commercial LIBs several stratagems have been developed, including the 54 currently use graphite, which presents moderate nanostructuring of the electroactive elements, its alloying 55 theoretical capacities , 372 mAh g-1,4 leaving plenty of with additional metals, its encapsulation within a shell, 56 room for improvement. Beyond graphite, Sn, Sb, Si and and its combination with carbon-based materials.15-26 57 Ge can alloy with Li to provide much higher energy On the other hand, the limited availability of lithium 58 densities.5–10 Among them, Sn and its alloys are especially and the related high price of this element may soon 59 constrain the LIBs market growth, especially in 60 ACS Paragon Plus Environment ACS Applied Materials & Interfaces Page 2 of 11 applications requiring large-scale storage. Thus, the heating mantle and the flask was shortly cooled to 1 rechargeable batteries based on more abundant and low- ambient temperature in a water bath. NiSn NPs were 2 cost raw materials are highly desirable. In this direction, synthesized using the same procedure, but replacing 3 sodium-ion batteries (SIBs) and potassium-ion batteries Co(acac)2 by Ni(acac)2. NPs were centrifuged at a high 4 (KIBs) are gathering increasing interest owing to the high speed after adding a proper amount of acetone. Then, 5 abundance of Na and K.26–31 chloroform was used to disperse the precipitate. A small 6 Recently we reported a series of monodisperse NixSn portion of solution was dropt on a Cu mesh for electron 7 and CoxSn nanoparticles (NPs) as anodes for LIBs and microscopy analyses. Then the NPs were collected again 8 SIBs.29,30 We found the best stoichiometry to be close to with the help of acetone and they were repeatedly washed 9 x=1. In this work, we report a significant increase of with acetone and chloroform. 10 stability of these anodes by proper ligand removal and by CoSn and NiSn NP-carbon nanocomposites: Before 11 supporting the NPs on carbon black. The material supporting the NPs on carbon black, surface ligands were 12 performance is analyzed not only in half-cell removed using a mixture of diluted hydrazine hydrate in 13 electrochemical experiments, but also in full-cell LIBs acetonitrile, following a previously reported protocol (see 14 with LiFePO4 as cathode. Additionally, we study here the details in the SI).32 Ligand-free NPs were subsequently 15 electrochemical performance of CoSn and NiSn as anode supported on commercial CB as follows: First, 100 mg 16 material in KIBs. dried NPs and 30 mg CB together with 25 ml ethanol were 17 mixed into a 50 ml vial. Afterward the mixture was 18 vigorously sonicated for 1 hour at ambient temperature. EXPERIMENTAL 19 Then, the material was centrifuged and dried in vacuum Chemicals: Cobalt(II) acetylacetonate (Co(acac)2, 99%, for over 2 nights. The product was kept in the glove box 20 Sigma-Aldrich), nickel(II) acetylacetonate until further use. The terminology CoSn@C and NiSn@C 21 (Ni(acac)2·xH2O (x2), 95%, Sigma-Aldrich), tin(II) was used to label these two nanocomposites. 22 acetate (Sn(oac)2, 95%, Fluka), oleic acid (OAc, Sigma- 23 Sn@C nanocomposites: SnO2 hollow nanospheres Aldrich), oleylamine (OAm, 80-90%, TCI), borane tert- 24 were fabricated by a one-pot hydrothermal treatment, butylamine complex (TBAB, 97%, Sigma-Aldrich), tri-n- 25 according to our previous work.33 Simply, 0.48 g urea and octylphosphine (TOP, 97%, Strem), urea 26 0.384 g K2SnO3·3H2O were dissolved in a mixture of ( C7H7BrN2O, >98.0%, Aladdin), potassium stannate 27 ethanol and distilled water. Then this mixture was located trihydrate (K2SnO33H2O, 95%, Aladdin), glucose 28 into an autoclave containing a Teflon liner that was (C6H12O6, 99.5%, Aladdin), acetonitrile (CH3CN, extra dry, 29 heated at 190 °C for 15 h. The product of the hydrothermal Fisher), carbon black (CB, Vulcan XC72), hydrazine 30 reaction was collected, washed with ethanol and distilled monohydrate (N2H4, 64-65%, reagent grade, 98%, Sigma- 31 water, and then dried under vacuum. To obtain Sn@C, Aldrich), Carbon Super P (Super P, KJ group), N-methy1- 32 0.17 g of as-prepared SnO2 hollow nanospheres and 0.68 g 2-pyrrolidone (NMP, 99%, Aladdin), polyvinylidene glucose were treated in a sealed autoclave at 190 °C for a 33 fluoride (PVDF, KJ group), ethylene carbonate (EC), period of 10 h and subsequently annealed at 650 °C in an 34 fluoroethylene carbonate (FEC), diethyl carbonate (DEC), H2/Ar flow for 6 h to reduce the SnO2 to Sn. 35 potassium bis-trifluoromethanesulfonylimide (KTFSI), 36 and diglyme (DME) were used without further Characterization: The structure of the NPs and 37 purification. Analytical-grade acetone, chloroform and nanocomposites was analyzed by means of X-ray 38 ethanol were purchased from different supplier. A small diffraction (XRD) on a Bruker AXS D8 Advance X-ray 39 glove-box filled with Ar was used for the manipulation diffractometer with Cu K radiation. NPs size and and storage of sensitive chemicals. morphology were observed by transmission electron 40 microscopy (TEM) on a Zeiss Libra 120. Scanning TEM 41 Synthesis of CoSn and NiSn NPs: Syntheses of (STEM) and high-resolution TEM (HRTEM) were 42 monodisperse NPs were conducted in a three-necked performed on a FEI Tecnai F20 microscope. Electron 43 flask with a thermocouple, condenser, and septum. In a energy loss spectroscopy (EELS) and high angle annular 44 typical synthesis of CoSn NPs, 0.6 mmol Sn(oac)2, 0.9 dark-field (HAADF) STEM were carried out using a Gatan 45 mmol Co(acac)2 20 mL of OAm and 1.0 mL of OAc were Quantum filter. Energy dispersive X-ray spectroscopy 46 loaded into a 50 mL flask with a magnetic bar. (EDS) analysis was carried out at 20 kV within a ZEISS 47 Subsequently, the flask was kept at 80 °C under vacuum Auriga scanning electron microscope (SEM). 48 for 2 hours to remove water and other organics. Then, the Compositions were obtained by averaging results from at 49 flask was protected with a gentle flow of Ar, 5 mL TOP least 3 points. X-ray photoelectron spectroscopy (XPS) 50 were injected, and subsequently the temperature was spectra were obtained with a SPECS system in normal 51 ramped at 5 °C min-1 to 180 °C. In the meantime, 5 mmol emission. The presence of surface ligands was determined 52 of TBAB was sonicated in 5 mL OAm for 0.5 hours and using a Alpha Bruker Fourier transform infrared 53 then degassed with Ar for 1 hour. Upon injection of this spectrometer (FTIR). The materials’ pore size distribution 54 reductant to the flask containing the Co and Sn and specific surface area were analyzed by means of N2 55 precursors at 180 °C, the solution immediately turned adsorption using a Tristar II 3020 Micromeritics system. black. The flask was maintained for 1 hour at this 56 Specific surface areas were determined by means of the temperature to enable the NPs to grow. Then we removed 57 Brunauer−Emmet−Teller (BET) approach, considering 58 59 60 ACS Paragon Plus Environment Page 3 of 11 ACS Applied Materials & Interfaces equally spaced points in the P/Po range. The pore size a b 1 distribution was calculated from the isotherms desorption 6.0  0.8 nm Intensity (a.u.) 2 Carbon black Counts (a. u.) branches using the Barrett-Joyner-Halenda (BJH) 3 approach. CoSn@C 4 Electrochemical measurements: The performance of JCPDS 03-065-8982 5 NP-based electrodes was analyzed using a battery test 10 20 30 40 50 60 6 system (CT2001A, LAND). Half cells were fabricated in an 2 4 6 8 10 Size (nm) 2 (degrees) 7 argon-filled glove box with H2O and O2 level lower than c d ADF C 8 0.1 ppm using Celgard2400 as separator. The ink was 9 obtained by mixing NPs, PVDF and Super P (80:10:10 in Co Co-Sn 10 weight ratio) with NMP. Then, to prepare the working 11 electrode, the mixture was coated on Cu and it was (20-1) 12 subsequently dried in vacuum at 80 °C during 24 h. Then, (201)b Sn Co-Sn-C 13 disks with a diameter of 12 mm were cut from the foil. The (002) [010] Co3Sn2 PNMA 20 nm 14 electrolyte for LIBs was composed of a 1 M LiPF6 solution e C 1s Sn 3d5/2 Co 2p3/2 15 in EC/DEC (1:1 in volume) with 5 wt% FEC as additive. For Intensities (a. u.) Intensities (a. u.) Intensity (a. u.) Co2+ electrochemical measurements, cyclic voltammetry (CV) 2 2+/4+ 16 C sp Sn Satellite 17 was conducted on an electrochemical workstation (Gamry C sp3 0 Sn Co0 18 Interface 1000) in the potential window 0.01–3.0 V using COO- 19 scan rates in the range 0.1-1 mV s-1. Electrochemical 20 impedance spectroscopy (EIS) measurements were 294 291 288 285 282 490 488 486 484 482 Binding Energy (eV) 790 785 780 775 Binding Energy (eV) Binding Energy (eV) 21 performed using a 5 mV modulation amplitude in a 22 frequency range 0.1-106 Hz. For the lithium-ion full-cell, Figure 1. a) Representative TEM micrograph of CoSn 23 LiFePO4 on Al foil (MTI Corporation, 10.95 mg cm-2) was NPs and their size distribution histogram. b) XRD used as cathode materials. The anodic capacities were patterns of CoSn NPs and a CoSn@C composite. c) 24 normalized to the mass of the whole materials in both HRTEM micrograph of a CoSn@C composite and detail of 25 half- and full-cell experiments. For potassium ion half- the yellow square with its corresponding power spectrum. 26 cell, 3 M KTFSI in DME was used as electrolyte, Whatman d) STEM-HAADF micrograph and EELS elemental maps 27 GF/D as the separator and K flakes as counter electrodes. of a CoSn@C composite showing individual Co L2,3-edges 28 at 779 eV (red), Sn M-edge at 485 eV (green) and C K- 29 edge at 284 eV (blue) as well as their composites: Co-Sn 30 RESULTS AND DISCUSSION and Co-Sn-C. e) XPS spectra of the C 1s, Sn 3d5/2 and Co 31 Colloidal CoSn (6 ± 0.8 nm) and NiSn NPs (4.2 ± 0.7 2p3/2 regions of the CoSn@C composite. 32 nm) were produced in solution from the reduction of XRD patterns of the carbon black and a CoSn@C 33 proper precursors in a solution containing OAm, OAc and composite are displayed in Figure 1b. The broad peak at 34 TOP (see the experimental details, Figures 1a and S1).29,30 25o was ascribed to the (002) crystallographic plane of 35 After purifying the NPs by multiple precipitation and re- carbon. The two peaks at around 31o and 44o observed in 36 dispersion steps, surface organic ligands were removed, as the nanocomposite XRD pattern matched with the Co3Sn2 37 confirmed by FTIR spectroscopy (Figure S2). phase.34 HRTEM micrographs and power spectra analyses 38 Subsequently, Sn-based NPs and carbon black were confirmed the crystallographic phase of CoSn alloy NPs to 39 physically mixed in solution by sonication for 1 hour. A match with the Co3Sn2 orthorhombic phase in PNMA 40 uniform distribution of the two phases within the space group. From the crystalline domain in Figure 1c, the 41 CoSn@C and NiSn@C nanocomposites was evidenced by Co3Sn2 lattice fringe distances were 0.328 nm, 0.403 nm, 42 SEM-EDS elemental maps (Figures S3 and S4). According and 0.330 nm, at 63.46º and 47.61º which were assigned to 43 to EDS analysis, atomic ratios for CoSn and NiSn NPs the Co3Sn2 orthorhombic phase, visualized along the [010] 44 were Co/Sn1 and Ni/Sn1, respectively (Figure S5). zone axis. The unit cell parameters were a = 7.1450, b = 45 Figure S6a shows the type IV adsorption−desorption 5.2500 Å and c = 8.1730 Å (Figure 1d). EELS elemental 46 isotherms obtained from the as-prepared nanocomposites composition maps revealed a uniform distribution of Co 47 and carbon black. High BET specific surface areas of 51.5 and Sn (Figure 1d). Besides, XRD and HRTEM analyses 48 m2 g-1 and 56.2 m2 g-1, were calculated for NiSn@C and evidenced the structure of NiSn NPs to match the Ni3Sn2 CoSn@C. As displayed in Figure S6b, BJH plots revealed 49 orthorhombic phase, consistently with our previous the composites to be characterized by broad pore size report (Figure S7).29 50 distribution in the mesoporous and microporous range, 51 similar to carbon black. 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment ACS Applied Materials & Interfaces Page 4 of 11 0.2 0.2 CoSn@C NiSn@C 1 a b a 3.0 b 3.0 Current (mA) Current (mA) 2 0.0 0.0 2.5 4 th 1 st 2.5 th 1 st Voltage (V) 4 Voltage (V) 2.0 2.0 3 -0.2 1st cycle -0.2 1st cycle 1.5 1.5 4 2nd cycle 2nd cycle 1.0 1.0 3rd cycle 3rd cycle 5 -0.4 CoSn@C -0.4 NiSn@C 4th cycle 4th cycle 0.5 0.5 6 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0 300 600 900 1200 1500 0.0 0 300 600 900 1200 1500 Voltage (V) Voltage (V) 7 1800 Capacity (mAh g ) -1 Capacity (mAh g ) -1 8 c c 2000 d 2000 Capacity (mAh g ) Charge -1 1500 100 100 9 Discharge Capacity (mAh g ) Capacity (mAh g ) -1 1600 1600 0.1 A g -1 -1 Efficiency (%) Efficiency(%) 80 80 1200 CoSn@C 10 0.2 A g -1 1200 0.1 1.0 60 1200 0.1 60 900 0.2 1.0 11 800 40 800 40 600 CoSn 12 Sn@C 400 Unit: A g -1 20 400 Unit: A g -1 20 300 13 0 0 40 80 0 120 160 200 0 0 40 80 0 120 160 200 14 0 10 20 30 40 50 60 70 80 90 100 Cycle number Cycle number Cycle number 15 Figure 3. a-b) Initial 4 CV curves at 0.1 A g-1 for 16 Figure 2. Initial cyclic voltammograms obtained in the CoSn@C and NiSn@C electrodes. c-d) Charge-discharge 17 voltage window 0-3.0 V vs. Li+/Li at 0.1 mV s-1 from capacity and its coulombic efficiency over 200 cycles at 1.0 18 nanocomposite electrode: a) CoSn@C, b) NiSn@C. c) A g-1: activated at 0.1 A g-1 for 10 cycles each. For the 19 Charge-discharge capacity and the related coulombic CoSn@C electrode, additional 10 activation cycles were 20 efficiency over 100 cycles at a current density of 0.2 A g-1 conducted at 0.2 A g-1. 21 for CoSn@C, bare CoSn and Sn@C electrodes: activated at Figure 2c compares the cycling performance of 22 0.1 A g-1 for 10 cycles each. CoSn@C, unsupported CoSn and Sn@C electrodes at 0.2 23 The XPS spectra of CoSn@C are shown in Figures 1e A g-1. For the CoSn-based electrode, the stability and 24 and S8. The C 1s region was fitted with three peaks at capacity were significantly enhanced with the presence of 25 284.3 eV, 285.3 eV and 288.1 eV, matching C sp3, sp2 and carbon. Note that the capacity values plotted in this figure 26 COO- respectively. Two tin chemical states were are referred to the whole mass of material coated on the 27 identified, at 484.7 eV (Sn 3d5/2) and 486.7 eV (Sn 3d5/2), Cu support, i.e. it takes into account both the mass of NPs 28 assigned to a metallic Sn0 environment and a Sn2+ or Sn4+ and carbon in the case of CoSn@C composites. If 29 oxidized state, respectively. Co was present in two capacities were referred to the amount of NPs, differences 30 different chemical states, metallic Co0 at 777.8 eV (Co between CoSn@C and unsupported CoSn would be much 31 2p3/2) and Co2+ at 781.5 eV (Co 2p3/2). The surface more evident. In other words, properly supporting the 32 oxidation was consistent with the exposure of the NPs to NPs on carbon black allowed replacing part of the active ambient atmosphere during purification, ligand removal material with carbon while maintaining similar overall 33 and handing.35–38 The surface atomic ratio of CoSn NPs capacities. The enhanced cycling performance of CoSn@C 34 measured by XPS was Sn/Co=2.6. This result indicated compared with bare CoSn was ascribed to the 35 that the NPs surface was Sn rich, which could be accommodation of structural strain of CoSn within the 36 associated with a preferential diffusion of Sn toward the carbon matrix, the improved electrical conductivity of the 37 surface during oxidation. 30,39 composite, the high NP dispersion and the shorter charge 38 Initial electrochemical tests were performed in Li-ion transportation lengths for Li ions due to the higher 39 half-cells with elemental lithium as counter and reference electrode porosity.42 40 electrode. Electrodes were printed from slurries Besides, when compared with Sn@C, CoSn@C delivered 41 containing 80 wt% of nanocomposites as active material, a twofold increase of the average capacity, up to 800 42 10 wt% PVDF as binder and 10 wt% Super P as conductive mAh g-1 over 100 continuous cycles. The higher capacities 43 additive. Figure 2ab display CV curves for CoSn@C and experimentally obtained in the present work for alloy NPs 44 NiSn@C obtained at 0.1 mV s-1 in the applied potential compared when with bare Sn may be partially related to 45 range 0-3.0 V vs. Li/Li+. Both electrodes displayed similar the smaller size of the alloy NPs and the different 46 CV curves. During the first charging process, a broad peak synthesis protocols used (Figure S9). However, taking 47 at 1.2-2.0 V was clearly displayed, but disappear in the into account previous literature on Sn-based LIBs, we 48 following few circles. This peak was attributed to the associated the improved capacity of our alloys with 49 growth of the solid-electrolyte interface (SEI) layer and respect to Sn@C to a size change buffering effect 50 the irreversible lithiation of the surface oxidized layer associated to the presence of Co,43 and a very large 51 formed during NP washing, handing and ligand-removing pseudocapacitive contribution in the alloy electrodes, as 52 processes.40,41 The well-overlapped 2nd-4th CV curves discussed below. 53 indicated a good cycling performance of CoSn@C and As shown in Figures 3a and 3c, at a higher charge- 54 NiSn@C anode. discharge rate, 1.0 A g-1, the initial coulombic efficiency for 55 CoSn@C electrodes was 59.5% with high reversible 56 capacities (848.4 mA g-1) and discharge capacities (1426 57 58 59 60 ACS Paragon Plus Environment Page 5 of 11 ACS Applied Materials & Interfaces mA g-1). For the following 10 cycles at 0.1 A g-1, the capacity NiSn@C, but with a smaller charge-transfer resistance. 1 decreased, which was associated with the SEI formation The inclined line in the low frequency part of the Nyquist 2 and an irreversible Li+ insertion in the surface oxide layer. plots, reflecting the kinetics of the Li+ uptake/release, 46 3 After additional 10 cycles at 0.2 A g-1, the capacity was was linearly fitted with the square root of angular 4 relatively stable at around 700 mAh g-1 for over 180 cycles frequency (ω), see Figure S11c.47 From this fitting, the 5 at 1.0 A g-1 with a coulombic efficiency up to 100%. lithium ion diffusion coefficient for LIBs was calculated to 6 Actually, a slight increase of capacity was obtained with be 9.25 × 10-15 cm2 s-1 for CoSn@C and 2.34×10-15 cm2 s-1 for 7 the cycle number above 40 cycles. This increase of NiSn@C (see details in the SI). Surprisingly, the ohmic 8 capacity is a common observation in Sn-based transition resistance and charge-transfer resistance between the 9 metal alloys and is assigned to several factors, including anode and the electrolyte obtained from the semicircle in 10 restructuration of the material, creation of additional the medium-frequency range was significantly larger for 11 paths for electrolyte diffusion, increase of CoSn@C than for NiSn@C (Table S2). 12 pseudocapacitive contribution, and increased rate of a 2.5 b 1500 3.0 13 lithiation/delithiation of the material.43–45 1200 100 Efficiency (%) 80 Voltage (V) Capacity (mAh g ) 5.0 0.1 0.1 0.2 -1 14 When comparing the electrochemical performance of 2.0 900 0.10.2 0.5 0.5 60 1.5 15 LIBs at the same charging-discharging rate, the capacity 600 1.0 2.0 40 1.0 1.0 16 for NiSn@C was lower than that of CoSn@C electrode, -1 Unit: A g 0.5 300 20 -1 5.0 17 which is in good agreement with our earlier report.29,30 0.0 0 Unit: A g 0 0 150 300 450 600 750 900 0 20 40 60 80 100 18 NiSn@C electrodes provided an average capacity of 500 -1 Capacity (mAh g ) Cycle number 19 mAh g-1 (Figures 3b and 3d) at 1.0 A g-1 and 400 mAh g-1 20 over 200 cycles at 2.0 A g-1 (Figure S10). The origin of the c d 2000 100 21 higher performance of CoSn- with respect to NiSn-based 1600 Efficiency (%) Capacity (mAh g ) -1 80 22 electrodes is not clear at this point, but it may be related 1200 60 23 to the higher pseudocapacitance provided by the former 800 0.1 A g -1 40 24 or to a higher rate of oxidation of the smaller NiSn NPs Seperator 400 20 compared with CoSn. CoSn@C 25 Stainless shell LiFePO4 0 0 10 20 30 40 0 50 26 Overall, Sn-based NPs@C nanocomposites provided Cycle number 27 enhanced performance when compared with graphite and Figure 4. Li-ion storage performance of the CoSn@C 28 most previous Sn-based alloys (Table S1). We associated composite electrode: a) Charge-discharge CV curves at 29 the superior electrochemical performance of our anodes rates: 0.1, 0.2, 0.5, 1.0, 2.0, 5.0A g-1. b) The corresponding 30 to the very small size of the alloy domains, their excellent rate performance. c) Schematic drawing of the full-cell set 31 dispersion over the carbon support and the large surface up. d) Galvanostatic charge-discharge curves of a lithium- 32 area and porous character of the overall composite, which ion full-cell battery with CoSn@C as anode and LiFePO4 provided a high electrode-electrolyte interface and a large 33 as cathode materials. density of Li-ion diffusion avenues through an electrically 34 To further investigate the applicability of CoSn@C highly conductive and mechanically stable support. 35 composites as anode in LIBs, full cells were assembled 36 To evaluate the rate capability, galvanostatic cycling and tested using LiFePO4 as cathode material (Figure 4c). 37 was conducted at various current rates ranging from 0.1 to CoSn@C//LiFePO4 cells were cycled galvanostatically at a 38 5 A g-1. As displayed in Figures 4a and 4b, CoSn@C current density of 0.1 A g-1 in the potential window 0.5-3.2 39 electrodes delivered a discharge capacity of 882.3, 846.2, V. As shown in Figure 4d, a fast loss in the capacity was 735.1, 640.8, 526.8, 298.2 mA g-1 at 0.1, 0.2, 0.5, 1.0, 2.0 and 40 obtained with the formation of the SEI layer within the 5.0 A g-1, respectively. NiSn@C delivered lower rate 41 initial 10 cycles at 0.1 A g-1. Afterward, the capacity was capability, with 798.6, 668, 497.9, 376.3, 279.3, 162.6 mA g- 42 1 at the same testing rates (Figure S11). Additionally, the stabilized at 350 mAh g-1 with around 95% coulombic 43 efficiency over the following 40 cycles. CoSn@C anode delivered a stable capacity at 0.1, 0.2, 0.5 44 The capacitive contribution of CoSn@C anodes was and 1.0 A g-1 after 60 cycles at variable charging rates. We 45 associated the excellent cycling performance and rate further studied using CV measurements. Figure 5a 46 capability of CoSn@C to the nanometric size of the presents the CV curves at various scan rates 0.1-1.0 mV s-1 47 electroactive material, its proper composition and its in the potential range 0-3.0 V vs. Li+/Li. Two obvious 48 combination with a high surface area and porous carbon anodic peaks were identified at around 0.57 and 1.49 V, 49 matrix that prevented NP aggregation and disconnection, with a peak current that increased with the scan rate. 50 and facilitated Li+ diffusion and charge transport. Generally, the measured current (i) is considered as a 51 function of scan rate (ν) as follows: We further investigated the electrode kinetics using 52 EIS. The Nyquist plots measured from CoSn@C and 𝑖 = 𝑎𝑣𝑏 53 NiSn@C and the equivalent circuits are displayed in where a and b are empirical values.48–51 In previous 54 Figure S12 and the fitted values are summarized in Table reports, a diffusion-controlled process was characterized 55 S2. At high frequencies, the diffusion resistance of by b = 0.5, whereas b = 1 was associated with an ideal 56 CoSn@C was observed to be slightly larger than that of capacitive behavior. From our measurements, the b value 57 58 59 60 ACS Paragon Plus Environment ACS Applied Materials & Interfaces Page 6 of 11 at the two peaks was calculated to be 0.68 and 0.85 Beyond Li+, K+ can be also reversibly stored and 1 respectively (Figure 5b), which was consistent with a fast released from Sn-based anode materials, although with a 2 kinetics arising from an important pseudocapacitive relatively lower theoretical capacity of 226 mAh g-1.56 3 effect. Despite its lower maximum capacity, the use of K finds 4 We further divided the capacity contribution at each advantages in terms of resource availability and cost, 5 scan rage and potential into the diffusion-controlled which are two main drawbacks of LIBs in a large scale 6 (k1ν1/2) and the capacitance contribution (k2ν) using the energy storage scenario. 7 following equation:52–55 a 0.1 b 800 8 100 𝑖(𝑉) = 𝑘1𝑣1/2 + 𝑘2𝑣 Capacity (mAh g ) Current (mA) 0.0 600 9 Efficiency (%) -1 Unit: A g -1 80 10 which can be rewritten as: -0.1 rd 3 cycle 400 0.1 60 nd 0.2 0.1 𝑖 (𝑉 ) 𝑣1/2 = 𝑘1 + 𝑘2𝑣1/2 2 cycle 0.5 40 11 -0.2 st 200 1.0 2.0 5.0 1 cycle 20 12 k1 and k2 were determined from the dependence of -0.3 0 0 13 i(V)/ν1/2 vs. ν1/2. Figure 5c shows the CV profiles at 1.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Voltage (V) 0 20 40 60 Cycle number 14 mV s-1 where the capacitive current (in red filling) is c d 3.0 800 15 differentiated from the total current (blue line). Similarly, 100 2.5 st st 16 4 1 Efficiency (%) Capacity (mAh g ) contributions of the capacitive part at 0.1, 0.2, 0.4, 0.6 and 600 -1 80 Voltage (V) 2.0 17 0.8 mV s-1 are presented in Figure S13, and summarized in 1.5 400 -1 60 0.1 A g 18 Figure 5d for comparison. When increasing sweep rates 1.0 200 0.2 A g -1 40 19 from 0.1 to 1.0 mV s-1, the capacitive contribution 0.5 20 0.0 0 0 20 increased from 45.8% to 74.5%. These capacitive values 0 150 300 450 600 750 0 100 200 300 400 -1 Capacity (mAh g ) Cycle number 21 are lower than those measured for bare CoSn NPs under 22 the same scanning rates.30 A similar trend was observed Figure 6. Potassium-ion storage performance of the 23 for NiSn@C composites, with a capacity contribution CoSn@C electrode: a) Initial CV curves obtained in the 24 increase from 39.0% to 69.7%, slightly lower than those of voltage window 0-3.0 V vs. K+/K at 0.1 mV s-1. b) Rate 25 CoSn@C (Figure S14). These results are in good performance at 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 A and 0.1 A g-1. c) 26 agreement with the superior rate performance of CoSn@C Initial charge-discharge curves at 0.1 A g-1. d) Charge- 27 when compared with NiSn@C electrodes. Besides, the discharge capacity and its coulombic efficiency over 400 28 above analysis evidenced that pseudocapacitance had a cycles at 0.2 A g-1: activated at 0.1 A g-1 for 10 cycles. 29 dominant role in the measured electrode capacity. KIB half cells were assembled in the same way as LIBs, 30 a 1.0 Peak 1 Peak 2 b -0.2 except for the use of 3 M KTFSI in DME as K+ electrolyte. Peak 2 31 0.5 -0.4 b = 0.85 Figure 6a shows CV profiles of a CoSn@C composite Current (mA) 32 measured at 0.1 mV s-1 in the applied potential range of 0- Log i (A g ) 0.0 -1 -0.6 33 -0.5 0.1 mV s -1 -0.8 3.0 V vs. K+/K. The significant differences obtained 34 -1.0 -1.0 Peak 1 between the initial and the following cycles were b = 0.68 associated to the formation of SEI and the irreversible K -1 35 -1.5 1.0 mV s -1.2 36 0.0 0.5 1.0 1.5 2.0 2.5 3.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1 insertion in the oxide layer. The rate capability of the Voltage (V) Log  (mV s ) 37 CoSn@C composite was analyzed in the range between 0.1 38 c 0.8 d 1.2 Diffusion controlled to 5 A g-1. As can be seen in Figure 6b, the CoSn@C 39 0.4 1.0 Capacitive electrode delivered a discharge capacity of 351, 286.9, ) -1 Contribution ratio 0.0 221.5, 161.8, 115.2 and 76.7 mA g-1 at 0.1, 0.2, 0.5, 1.0, 2.0 and Current (A g 0.8 40 -0.4 41 0.6 5.0 A g-1, respectively. As shown in Figure S15ab, NiSn@C -0.8 0.4 delivered lower capacities, with 322.4, 259.8, 184.3, 125.6, 70.2% 74.5% -1 65.2% 60.0% 1.0 mV s 52.9% 45.8% 42 -1.2 0.2 73.8 and 44.8 mAh g-1 at the same testing rate. The 43 -1.6 0.0 0.1 0.2 0.4 0.6 0.8 1.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 slightly higher capacitances obtained for CoSn are 44 Voltage (V) -1 Scan rate (mV s ) consistence with results obtained for LIBs and may also 45 Figure 5. Kinetic analysis of CoSn@C as Li-ion anode: find its origin on a higher relative oxidation of NiSn and a 46 a) CV curves with scan rates from 0.1 to 1.0 mV s-1. b) CV larger pseudocapacitance associated to Co. 47 peak current as a function of the sweep rate. c) Capacitive 48 The cycling performance of these two composites was (shaded region) and diffusion current contributions at 1.0 obtained by galvanostatic charging-discharging at a high 49 mV s-1. d) Normalized capacitive- and diffusion-controlled 50 current density of 0.2 A g-1 (Figure 6cd). CoSn@C contribution at different scan rate. electrodes delivered very large initial capacities, but 51 Based on the detailed electrochemistry and structural displayed an obvious capacity loss during the first few 52 analysis, the superior performance of CoSn@C electrodes cycles associated with the formation of the SEI layer. After 53 in LIBs could be associated with its hierarchical structure. additional 390 cycles, the capacities were stabilized at 54 The well-defined CoSn NPs with carbon supports could around 200 mAh g-1 with high coulombic efficiency. As in 55 buffer the volume expansion to maintain the structural LIBs, the NiSn@C composite presented lower 56 integrity of CoSn@C anode upon cycling. electrochemical performance towards KIBs as displayed in 57 58 59 60 ACS Paragon Plus Environment Page 7 of 11 ACS Applied Materials & Interfaces Figure S15cd. A comparison of our results with those (ENE2016-77798-C4-3-R). J. Li is grateful for the China 1 obtained for other Sn-related materials as KIB anode Scholarship Council (CSC) support. This project was also 2 materials is provided in Table S3. supported by the National Natural Science Foundation of 3 China (no. 51771076), the “1000 plan”, and the Project of EIS spectra obtained in KIBs was similar to that 4 Public Interest Research and Capacity Building of obtained in LIBs (Figure S16a). However, larger resistance 5 Guangdong Province (no. 2017A010104004). H. Xu, T. Zhang values were obtained in KIBs than in LIBs when using the and J. Arboil thank the funding from Generalitat de 6 same fitting circuit (Table S4, Figure S16b). Besides, the K+ Catalunya 2017 SGR 327 and the Spanish MINECO ENE2017- 7 diffusion coefficient for CoSn@C and NiSn@C was 85087-C3. ICN2 acknowledges support from the Severo 8 1.38×10-14 cm2 s-1 and 1.08×10-14 cm2 s-1, higher than those Ochoa Programme (MINECO, Grant no. SEV-2013-0295) and 9 obtained for Li+ diffusion. Overall, EIS result were is funded by the CERCA Programme / Generalitat de 10 consistent with the larger radius of K+ than Li+ and the Catalunya. J. Llorca is a Serra Húnter Fellow and is grateful to 11 fact that each Sn is able to accommodate 1 K+ and 4.4 Li+. ICREA Academia program and to MINECO/FEDER grant 12 ENE2015-63969-R and funding from Generalitat de Catalunya 13 Conclusions 2017 SGR 128. H. Xu and T. Zhang thank the CSC-UAB PhD 14 scholarship program. Part of the present work has been In conclusion, monodisperse CoSn and NiSn NPs were performed in the framework of Universitat Autònoma de 15 synthesized via a facile solution-based approach. After Barcelona Materials Science PhD program. 16 removing the surface ligands, NPs were supported on 17 commercial carbon materials. The obtained nanocomposites ABBREVIATIONS 18 were tested as anode materials in half-cell LIBs and KIBs and 19 NPs nanoparticles full-cell LIBs. CoSn@C electrodes displayed an excellent LIBs lithium-ion batteries 20 performance, with LIB half-cell charge-discharge capacities SIBs sodium-ion batteries 21 over more than one hundred cycles above 850, 650 and 500 KIBs potassium-ion bat-teries 22 mAh g-1 at current densities of 0.2, 1.0 and 2.0 A g-1, CB carbon black 23 respectively. These values were significantly larger than the OAm, oleylamine 24 theoretical maximum of graphite. As for LIB full-cells, OAc oleic acid 25 CoSn@C electrodes delivered average capacities of 400 mAh TOP tri-n-octylphosphine g-1 at a rate of 0.1 A g-1. Through the kinetic analysis of 26 PVDF polyvinylidene fluoride CoSn@C and NiSn@C nanocomposite by CV, it was found 27 that charge-discharge capacities included very large NMP N-methy1-2-pyrrolidone 28 EC ethylene carbonate pseudocapacitive contributions up to 74.5% at 1 mV s-1 for 29 DEC diethyl car-bonate CoSn@C and 69.7% for NiSn@C. These materials were also 30 FEC fluoroethylene carbonate tested as anodes in KIBs. KIB capacities were stabilized at KTFSI potassium bis-trifluoromethanesulfonylimide 31 around 200 mAh g-1 with high coulombic efficiency over 400 DME diglyme 32 cycles for CoSn@C and 100 mAh g-1 for NiSn@C over 300 XRD X-ray power diffraction 33 cycles. SEM scanning electron microscopy 34 TEM transmission electron microscopy 35 Conflicts of interest STEM scanning TEM 36 There are no conflicts to declare. HRTEM high-resolution TEM 37 HAADF High angle annular dark-field 38 ASSOCIATED CONTENT EELS electron energy loss spectroscopy 39 EDS energy dispersive X-ray spectroscopy Supporting Information. This material is available free of 40 XPS X-ray photoelectron spectroscopy charge via the Internet at http://pubs.acs.org.” For instance, 41 FTIR Fourier transform infrared spectrometer additional TEM, XRD, ligand removal, FT-IR, SEM-EDS, XPS BET Brunauer−Emmet−Teller 42 and additional electrochemical performance in LIBs and KIBs BJH Barrett-Joyner-Halenda 43 are presented. CV cyclic voltammetry 44 EIS Electrochemical impedance spectroscopy 45 AUTHOR INFORMATION SEI solid-electrolyte interface 46 Corresponding Author 47 * Andreu Cabot: acabot@irec.cat REFERENCES 48 * Jun Liu: msjliu@scut.edu.cn (1) Palacín, M. R. Recent Advances in Rechargeable 49 Battery Materials: A Chemist’s Perspective. 50 Author Contributions Chem. Soc. Rev. 2009, 38 (9), 2565–2575. 51  J. Li and X. Xu equally contributed to this work. 52 (2) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-Ion 53 ACKNOWLEDGMENT Battery Materials: Present and Future. 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