Group IV-VI compound graphene anode with catalyst

Abstract

An electrode for use in a lithium-ion battery. The electrode comprises a group IV-VI compound and a transition metal group VI compound on a three-dimensional graphene network. A major portion of the transition metal group VI compound is provided on top of the group IV-VI compound or in close proximity to it, whereby the molybdenum group VI compound contributes to the decomposition of a lithium group VI compound at the surface of the group IV-VI compound.

Claims

1. An electrode for use in a lithium-ion battery, the electrode comprising a group IV-VI compound and a transition metal group VI compound on a three-dimensional graphene network, wherein a major portion of the transition metal group VI compound is provided on top of the group IV-VI compound or in close proximity to it, whereby the transition metal group VI compound contributes to the decomposition of a lithium group VI compound at the surface of the group IV-VI compound, the group IV-VI compound being represented by a chemical formula MX2, wherein M is selected from tin, germanium and silicon and X is selected from sulphur, oxygen and selenium, the transition metal group VI compound comprising a transition metal and a group VI element, the group VI element being selected from sulphur, oxygen and selenium.

2. The electrode according to claim 1, wherein a content of the transition metal group VI compound is between 2 and 8 weight percent.

3. The electrode according to claim 1, wherein a molybdenum group VI compound is provided on a material which comprises the group IV-VI compound on a three-dimensional graphene network.

4. The electrode according to claim 1, wherein the transition metal group VI compound is provided in a form of nanosheets.

5. The electrode according to claim 4, wherein the nanosheets of the transition metal group VI compound are provided on larger nanosheets of the group IV-VI compound.

6. The electrode according to claim 1, wherein a loading of the group IV-VI compound is 0.7-1 mg per cubic centimeter of the three-dimensional graphene network.

7. The electrode according to claim 1, wherein the three-dimensional graphene forms a binder-free interconnected porous network.

8. The electrode according to claim 1, wherein the group IV-VI compound is tin disulfide and the transition metal group VI compound is molybdenum disulfide or tungsten disulfide.

9. A lithium-ion battery comprising an electrode according to claim 1, the lithium-ion battery further comprising a casing with a first terminal and a second terminal, a counter electrode and an electrolyte, the electrolyte containing lithium ions, wherein the electrode, the counter electrode and the electrolyte are provided in the casing, the electrode is connected to a first terminal, the counter electrode is connected to the second terminal, and the electrolyte is in contact with the electrode and with the counter electrode.

10. A method of producing an electrode for a lithium-ion battery, the method comprising: depositing a carbon compound on a porous metal scaffold by chemical vapor deposition to obtain a three-dimensional graphene; bringing a group IV compound into contact with the three-dimensional graphene, the group IV compound comprising tin, germanium or silicon; subjecting the group IV compound and the three-dimensional graphene to a hydrothermal treatment to obtain a group IV-VI compound surface structure on the three-dimensional graphene; bringing a transition metal group VI compound into contact with the three-dimensional graphene; and subjecting the transition metal group VI compound and the three-dimensional graphene with the group IV-VI compound surface structure to a hydrothermal treatment to obtain a transition metal group VI compound surface structure on the group IV-VI compound surface structure.

11. The method according to claim 10, wherein preparation of the three-dimensional graphene comprises: flowing a mixture of argon and ethanol over a nickel foam; cooling the reaction product; and etching away the nickel foam.

12. The method according to item 10, wherein preparation of the group IV-VI compound on the three-dimensional graphene comprises: providing a mixture of a group IV tetrachloride, water, thioacetamide and sodium dodecyl sulfate in ethanol, the group IV tetrachloride being selected from tin tetrachloride, germanium tetrachloride and silicon tetrachloride; bringing the mixture and the three-dimensional graphene together; and letting the mixture and the three-dimensional graphene react.

13. The method according to claim 10, wherein preparation of the transition metal group VI compound on the three-dimensional graphene comprises; providing a mixture of a group VI amino acid and sodium transition metal compound in water and ethanol, the group VI amino acid being selected from L-cysteine, selenocysteine and serine; bringing pieces of the three-dimensional graphene with the group IV-VI surface structure and the mixture together; and letting the three-dimensional graphene with the group IV VI compound surface structure and the mixture react.

14. The method according to claim 10 comprising drying the electrode material at a temperature above 100 C.

15. A method for producing a lithium-ion battery comprising: producing an electrode according to claim 10, the method further comprising: providing a counter electrode and a membrane; inserting the electrode, the membrane and the counter electrode into a casing of the coin cell; filling an electrolyte into the casing of the lithium-ion battery; and closing the casing of the lithium-ion battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the present specification is now explained in further detail with respect to the following Figures in which

(2) FIG. 1 shows a SEM image of 3-dimensional interconnected porous network of a three dimensional graphene (3DG) and a high magnification inset,

(3) FIG. 2 shows a SEM image of vertical nanosheets of SnS.sub.2 grown on surfaces of SnS.sub.2 covering the surfaces of the 3DG of FIG. 1 and a high magnification inset,

(4) FIG. 3 shows a SEM image of fine nanosheets of MoS.sub.2 grown on the surfaces of SnS.sub.2 with small clusters of MoS.sub.2 on the edges of SnS.sub.2,

(5) FIG. 4 shows a further view of the nanosheets of FIG. 3 in a higher resolution,

(6) FIG. 5 shows a transmission electron microscope image of a synthesized SnS.sub.2/MoS.sub.2/3DG electrode,

(7) FIG. 6 shows a further transmission electron microscope image of the synthesized SnS.sub.2/MoS.sub.2/3DG electrode,

(8) FIG. 7 shows X-ray diffraction (XRD) patterns of the SnS.sub.2/MoS.sub.2/3DG electrode and the intermediate SnS.sub.2/3DG material,

(9) FIG. 8 shows a Raman spectrum of the synthesized SnS.sub.2/MoS.sub.2/3DG electrode, and for pure SnS.sub.2 and 3DG as references,

(10) FIG. 9 shows thermogravimetric analysis (TGA) curves for the SnS.sub.2/MoS.sub.2/3DG, SnS.sub.2/3DG and 3DG materials,

(11) FIG. 10 shows a cyclic voltammetry (CV) curve of the SnS.sub.2/MoS.sub.2/3DG electrode,

(12) FIG. 11 shows a CV curve of a SnS.sub.2/3DG control electrode,

(13) FIG. 12 shows a CV curve of a Sns.sub.2/MoS.sub.2 control electrode,

(14) FIG. 13 shows a CV curve of a SnS.sub.2 control electrode,

(15) FIG. 14 shows charge-discharge profiles of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG materials,

(16) FIG. 15 shows the rate capability of the SnS.sub.2/MoS.sub.2/3DG electrode and the SnS.sub.2/3DG control electrode,

(17) FIG. 16 shows the coulombic efficiency and the cycling performance of the SnS.sub.2/MoS.sub.2/3DG electrode and the cycling performance of the SnS.sub.2/3DG control electrode at a current density of 200 mA/g,

(18) FIG. 17 shows the cycling performance of the SnS.sub.2/MoS.sub.2/3DG electrode and of the SnS.sub.2/3DG control electrode at a current density of 1000 mA/g,

(19) FIG. 18 shows a high resolution transmission electron microscopy of a SnS.sub.2/MoS.sub.2/3DG electrode after 20 cycles in a fully discharged state,

(20) FIG. 19 shows a high resolution transmission electron microscopy of a SnS.sub.2/MoS.sub.2/3DG electrode after 20 cycles in a fully charged state,

(21) FIG. 20 shows further X-ray diffraction (XRD) patterns of the SnS.sub.2/MoS.sub.2/3DG electrode and the intermediate SnS.sub.2/3DG material,

(22) FIG. 21 shows a further Raman spectrum of the synthesized SnS.sub.2/MoS.sub.2/3DG electrode, and for pure SnS.sub.2 and 3DG as references,

(23) FIG. 22 shows further thermogravimetric analysis (TGA) curves for the SnS.sub.2/MoS.sub.2/3DG, SnS.sub.2/3DG and 3DG materials,

(24) FIG. 23 shows further charge-discharge profiles of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG materials,

(25) FIG. 24 shows a further diagram of the rate capability of the SnS.sub.2/MoS.sub.2/3DG electrode and the SnS.sub.2/3DG control electrode,

(26) FIG. 25 shows a further diagram of the coulombic efficiency and the cycling performance of the SnS.sub.2/MoS.sub.2/3DG electrode and the cycling performance of the SnS2/3DG control electrode at a current density of 200 mA/g,

(27) FIG. 26 shows a further diagram of the cycling performance of the SnS.sub.2/MoS.sub.2/3DG electrode and of the SnS2/3DG control electrode at a current density of 1000 mA/g,

(28) FIG. 27 shows Sn 3d spectra of the electrode in pristine, discharge, and charge state,

(29) FIG. 28 shows an ex-situ HRTEM image of SnS.sub.2/MoS.sub.2/3DG after 30 cycles and being discharged to 0.01 V, and

(30) FIG. 29 shows an ex-situ HRTEM image of SnS.sub.2/MoS.sub.2/3DG after 30 cycles and being charged to 3.0 V.

DETAILED DESCRIPTION

(31) A SnS.sub.2/MoS.sub.2/3DG anode material was prepared in three steps. Molybdenum disulfide (MoS.sub.2) doped on tin disulfide (SnS.sub.2) with a 3-dimensional graphene foam (3DG) base (SnS.sub.2/MoS.sub.2/3DG) was prepared by 3 general steps: (1) chemical vapor deposition (CVD) to obtain 3DG, (2) hydrothermal treatment to obtain SnS.sub.2 on 3DG (SnS.sub.2/3DG), and (3) hydrothermal treatment to obtain MoS.sub.2 on SnS.sub.2/3DG (SnS.sub.2/MoS.sub.2/3DG). The 3 steps are explained in further detail below.

(32) Step 1, Preparation of 3DG foam by CVD and removal of Ni foam: Ni foam (1.6 mm thick, purchased from Alantum Advanced Technology Materials (Shenyang)), was cut into 150 mm45 mm pieces. The rectangular Ni foam pieces were then rolled and placed into a 1 inch quartz tube. Before heat was applied, Argon (Ar) gas was allowed to flow for 10 mins to remove residual air in the tube. Thereafter, a heat rate of 50 C./min was applied to heat the quartz tube to 1000 C. At this temperature, ethanol vapor is mixed with the flowing argon gas through the bubbling of anhydrous ethanol. The mixture Ar/ethanol vapor was allowed to flow for 5 mins. Lastly, the quartz tube was allowed to cool to room temperature rapidly (100 C./min). The Ni foam on 3DG-Ni was removed in an etchant solution of 3M HCl at 80 C. Pure 3DG was washed using deionized (DI) water and ethanol several times before drying at 60 C. The typical loading of this process yields 0.25-0.3 mg/cm.sup.2 of 3DG on Ni foam (3DG-Ni).

(33) Step 2, Synthesis of SnS.sub.2/3DG: SnS.sub.2 grown on 3DG (SnS.sub.2/3DG) was prepared via a simple solvothermal reaction. SnCl.sub.4, 5H.sub.2O (32 mM), thioacetamide (TAA) (80 mM), and sodium dodecyl sulfate (SDS) (0.07 mM) were weighed and dissolved into 35 mL ethanol. Magnetic stirring and mild heat (50 C.) was applied to ensure homogeneity of the precursors. 6 pieces of 3DG (12 mm diameter) were cut and transferred, together with the mixture, into a 50 mL Teflon-line stainless steel autoclave. The reaction proceeded by heating the autoclave at 180 C. for 12 hours. After the reaction, as-synthesized SnS.sub.2/3DG was collected by rinsing with deionized H.sub.2O and ethanol, and drying at 60 C. The loading of SnS.sub.2 on 3DG was between 0.7-1 mg.

(34) Step 3, Synthesis of SnS.sub.2/MoS.sub.2/3DG: MoS.sub.2 grown on SnS.sub.2/3DG (SnS.sub.2/MoS.sub.2/3DG) was prepared by an L-cysteine assisted solvothermal reaction, L-cysteine (0.25 mM) and Na.sub.2MoO.sub.4.H.sub.2O (0.03 mM) was weighed and dissolved in 15 mL deionized H.sub.2O. 15 mL of ethanol was added to the continuously stirred mixture. Six pieces of SnS.sub.2/3DG were added to the mixture and the mixture was transferred to a 50 mL Teflon-lined stainless steel autoclave.

(35) The stainless steel autoclave was heated at 180 C. for 12 h. The as-synthesized SnS.sub.2/MoS.sub.2/3DG was collected by rinsing with deionized H.sub.2O and ethanol, and drying at 60 C. A resulting loading of MoS.sub.2 on SnS.sub.2/3DG is between 0.05-0.1 mg. Lastly, the SnS.sub.2/MoS.sub.2/3DG was annealed in a nitrogen (N.sub.2) at 400 C. for 2 hours at a slow heating rate of 3 C./min.

(36) A SnS.sub.2/MoS.sub.2/3DG anode, comparison anodes and a cathode were prepared as follows. The as-synthesized SnS.sub.2/MoS.sub.2/3DG was used directly as an anode in a two electrode half-cell configuration in which lithium metal acts as the counter electrode or cathode. Control samples of SnS.sub.2/3DG, pure SnS.sub.2 and SnS.sub.2/MoS.sub.2 were also assembled. Pure SnS.sub.2 was synthesized using the procedure described in step 3 by using pure SnS.sub.2 instead of SnS.sub.2/3DG.

(37) Electrodes for the powdered control samples, SnS.sub.2 and SnS.sub.2/MoS.sub.2 were made into a slurry and subsequently coated on Ni foam current collectors (12 mm diameter each). The slurry was prepared by mixing 8 parts of active materials to 1 part of polyvinylidene fluoride (PVDF) binder and 1 part of carbon black in the presence of N-methylpyrrolidone (NMP) solvent.

(38) The SnS.sub.2/3DG was used directly as an electrode. All working electrodes were dried at 120 C. for 12 hours before assembly. A coin cell was assembled in an Ar-filled glove box using standard CR 2032 as casing. Each cell consisted of a Celgard 2400 membrane sandwiched between a working electrode, which contained the active material, and counter electrode, which contained lithium material. The electrolyte used was a mixture of 1M LiPF.sub.6 solution in ethylene carbonate (EC)/Di-methyl carbonate (DMC), with a volume ratio v/v of 1:1.

(39) FIGS. 1 to 6 show the morphology of the products i.e. of 3DG, Sn.sub.2/3DG, and of SnS.sub.2/MoS.sub.2/3DG in scanning electron microscope (SEM) images at different magnifications. FIG. 1 shows the 3-dimensional interconnected porous network of the Ni foam derived 3DG. The inset image shows the smooth nature of the surface of 3DG with crease and folds which are characteristic of the layered graphene/graphite. FIG. 2 shows vertical nanosheets of SnS.sub.2 grown on the surfaces of SnS.sub.2 covering the surfaces of 3DG. The SnS.sub.2 nanosheets are highly dense but also possess gaps to expose its surface to react with lithium during charge-discharge cycles. FIGS. 3 and 4 show fine nanosheets of MoS.sub.2 grown on the surfaces of SnS.sub.2 with small clusters of MoS.sub.2 on the edges of SnS.sub.2.

(40) FIGS. 5 and 6 are high resolution transmission electron microscope (HRTEM) images of the SnS.sub.2/MoS.sub.2/3DG. The low magnification HRETEM of FIG. 5 shows dispersed vertical sheets of SnS.sub.2 of 30 nm thick and 300 nm wide. The inset in FIG. 5 shows that the MoS.sub.2 are grown on both sides of the SnS.sub.2 sheets. High magnification HRTEM in FIG. 6 shows the crystal lattices, which confirms the thick sheet and the thin sheet to be SnS.sub.2, which has a lattice constant of 5.9 and MoS.sub.2, which has a lattice constant of 6.1 , respectively.

(41) FIGS. 7 to 9 show further evidences that the as-synthesized final and intermediate products are indeed composed of SnS.sub.2, MoS.sub.2 and 3DG. FIG. 7 shows X-ray diffraction (XRD) patterns of SnS.sub.2/MoS.sub.2/3DG and intermediate SnS.sub.2/3DG with peaks corresponding well with reference peaks of Joint Committee on powder Diffraction Standards (JCPDS) card no. 65-3656 for MoS2, JCPDS card no. 23-0677 for SnS.sub.2, and JCPDS card no. 75-1621 for graphite.

(42) FIG. 8 shows the Raman spectrum for the synthesized SnS.sub.2/MoS.sub.2/3DG material, and for pure SnS.sub.2 and 3DG as references. The peak at 315/cm corresponds to the Raman mode A.sub.1g of SnS.sub.2, while the peaks at 380/cm and 405/cm correspond to the Raman mode E.sup.1.sub.2g and to the Raman mode A.sub.1g of MoS.sub.2, wherein the Raman modes are denoted by the Mulliken symbols E.sup.1.sub.2g and A.sub.1g. The peaks at 1575/cm and 2715/cm correspond to G and 2D bands of the graphitic layers in 3DG.

(43) FIG. 9 shows the thermogravimetric analysis (TGA) curves for the SnS.sub.2/MoS.sub.2/3DG, SnS.sub.2/3DG and 3DG materials. The initial weight loss of 29.5% for both SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG between 550 C. to 850 C. arises from the combustion of 3DG. Therefore, the final weight composition of the products can be calculated to be about 69% SnS.sub.2 and 31% 3DG in SnS.sub.2/3DG and 66% SnS.sub.2, 5% MoS.sub.2, and 28% 3DG.

(44) FIGS. 10 to 13 show the cyclic voltammetry (CV) curves of all prepared electrodes in the abovementioned experimental setup. Namely, FIG. 10 shows a CV curve of a SnS.sub.2/MoS.sub.2/3DG electrode, FIG. 11 shows a CV curve of a SnS.sub.2/3DG electrode, FIG. 12 shows a CV curve of a Sns.sub.2/MoS.sub.2 electrode and FIG. 13 shows a CV curve of a SnS.sub.2 electrode.

(45) In the first charge-discharge cycles, SnS.sub.2 undergoes an intercalation of lithium ions as described in equation (1) and (2), which leads to the cathodic peaks at 1.75 V for SnS.sub.2/3DG, at 1.76 V for SnS.sub.2/MoS.sub.2, and at 1.03 V for SnS.sub.2. For the 3DG containing samples, the redox pairs at 8.1 V and 0.25 V for SnS.sub.2/MoS.sub.2/3DG and at 0.1V and 0.23V for SnS.sub.2/3DG arise from the intercalation of Li into the graphitic layers.

(46) In subsequent cycles, the redox peaks around 0.2 V and 0.5 V correspond to the reversible alloying/de-alloying reaction as described in equation (4). Furthermore, the redox pairs at 1.15V and 1.85V for SnS.sub.2/MoS.sub.2/3DG, at 1.32 V and 1.88 V for SnS.sub.2/3DG, at 1.28 V and 1.9V for SnS.sub.2/MoS.sub.2, and at 1.35 V and 1.75 V for SnS.sub.2 correspond to the reversible decomposition of Li.sub.2S, which is described by the reverse direction of equation (3)). These peaks correspond well with published results in reference (1) and reference (2).

(47) It can also be observed that except for SnS.sub.2/MoS.sub.2/3DG, the intensity of these peaks reduces significantly from cycles 2 to 3. This implies that the decomposition of Li.sub.2S in these materials is only partially reversible. By contrast, the overlapping peaks for SnS.sub.2/MoS.sub.2/3DG suggest a highly reversible decomposition of Li.sub.2S, which demonstrates the catalytic effect of MoS.sub.2 in the composite. However, the control sample of SnS.sub.2/MoS.sub.2 showed only partial reversibility despite the MoS.sub.2 doping. This could be due to the poor morphology of SnS.sub.2/MoS.sub.2, where the bulk SnS.sub.2 and MoS.sub.2 nanosheets lack a volume change buffer function, which resulted in rapid capacity decay over cycling.

(48) Additional anodic peaks at 1.28 V for SnS.sub.2/MoS.sub.2/3DG and at 1.65 V for SnS.sub.2/3DG, which correspond to the intercalation reaction, and at 2.3 V for SnS.sub.2/MoS.sub.2/3DG and at 2.11 V for SnS.sub.2/3DG, which correspond to the conversion reaction of MoS.sub.2 with lithium, are also present in MoS.sub.2 containing samples and are described by equations (5) and (6) respectively.

(49) During the first charging an insertion reaction takes place at the anode, which is described by the reaction equation
SnS.sub.2+xLi.sup.++xe.sup..fwdarw.Li.sub.xSnS.sub.2(1)

(50) Furthermore, a conversion reaction takes place which is described by the reaction equation
Li.sub.xSnS.sub.2+(4x)Li.sup.++(4x)e.sup..fwdarw.Sn+2Li.sub.2S(2)

(51) Inserting the left hand side of equation (1) into equation (2) yields the simplified conversion reaction equation
SnS.sub.2+4Li.sup.++4e.sup..fwdarw.Sn+2Li.sub.2S(3)

(52) In subsequent charge-discharge cycles an alloying/de-alloying process takes place, which is described by the following equation
Sn+4.4Li.sup.++4.4e.sup..Math.Li.sub.4.4Sn(4)
wherein the left-to-right arrow relates to charging and the right-to-left arrow to discharging.

(53) Moreover, the following reactions involving the catalyzer or catalyst MoS.sub.2 take place at the anode. An insertion reaction is described by
MoS.sub.2+yLi.sup.++ye.sup..fwdarw.Li.sub.yMoS.sub.2(5)
and a conversion reaction is described by
MoS.sub.2+4Li.sup.++4e.sup..Math.Mo+2Li.sub.2S(6),

(54) where x and y are the number of moles of Li.sup.+/e.sup. reacting with SnS.sub.2 and MoS.sub.2, respectively.

(55) The experiments of the present specification were carried out on an experimental lithium-ion battery. A lithium-ion battery according to the present specification may in general comprises various modifications and differences from this experimental setup. For example, the cathode can be provided by a transition metal oxide such as LiMO.sub.2, wherein M is a transition metal such as cobalt or nickel.

(56) Moreover, a production method of the battery may be modified as required to meet requirements such as cost efficiency, mass production, security standards and environmental standards.

(57) FIGS. 14 to 17 illustrate lithium storage improvements brought about by the addition of MoS.sub.2 in SnS.sub.2/3DG.

(58) FIG. 14 shows first galvanostatic discharge and charge curves for SnS2/MoS2/3DG and SnS2/3DG at a current density of 50 mA/g in the potential range of 0.01 V to 3.0 V. In FIG. 14, the charge-discharge profiles of both SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG are fairly similar with the exception of a sharp incline in the charging curve of SnS.sub.2/3DG between 2.0 to 3.0 V, which corresponds well with the CV curves in FIG. 11. On the other hand, SnS.sub.2/MoS.sub.2/3DG displayed a gradual ascending slope between 2.0 to 3.0 V, which is attributed to the decomposition of Li.sub.2S and reactions of MoS.sub.2 with lithium.

(59) In terms of first cycle coulombic efficiency, SnS.sub.2/3DG displayed a large capacity loss (39.6%) due to the formation of a surface electrolyte interface (SEI) layer as well as trapped lithium as a result of a partially reversible formation of Li.sub.2S. By contrast, the decomposition of Li.sub.2S, which is mediated by the catalytic reaction of MoS.sub.2, greatly improved the first cycle coulombic efficiency of SnS.sub.2/MoS.sub.2/3DG from 60.4% to 72.3%.

(60) FIG. 15 illustrates the performance of the SnS.sub.2/MoS.sub.2/3DG anode in the experimental setup. Specifically, FIG. 15 shows the rate capability of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG.

(61) FIGS. 16 and 17 demonstrate the cycling stability of the materials over 50 cycles at 200 mA/g and 1000 mA/g, respectively. Specifically, FIG. 16 shows the cycling performance of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG at a current density of 200 mA/g and the corresponding coulombic efficiency of SnS.sub.2/MoS.sub.2/3DG. The arrows in FIG. 16 indicate the vertical scale that corresponds to the experimental values. FIG. 17 shows the cycling performance of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG at a current density of 1000 mA/g. The cycling stability shows the effectiveness of the 3D hierarchical nanostructures of the SnS.sub.2/MoS.sub.2/3DG composites to mitigate volume changes occurring during alloying/de-alloying and conversion reactions.

(62) The FIGS. 18 and 19 show ex-situ high resolution transmission electron microscopy (HRTEM), which was carried out on SnS.sub.2/MoS.sub.2/3DG to provide additional supporting evidence to show the catalytic effect of MoS.sub.2 to fully reduce Li.sub.2S and release the trapped lithium as described by the typical irreversible/partially reversible reaction of equation (3).

(63) This was carried out by disassembling coin cells that were in either fully charged state at 3.0 V, as shown in FIG. 19, or fully discharged state at 0.01V, as shown in FIG. 18, after 20 charge-discharge cycles and washing the electrodes in N-Methyl-2-pyrrolidone (NMP).

(64) As shown in FIG. 18, at the fully discharged state the presence of Mo suggests the reversible conversion of MoS.sub.2, whereas the absence of SnS.sub.2 implies the complete alloying of Sn with Li, which is described in equations (4) and (5). However, Li.sub.2Sn could not be identified in the HRTEM images, which was possibly due to the non-crystalline phase of Li.sub.2Sn, see reference (4).

(65) In the fully charged state of FIG. 19, lattices of MoS.sub.2 and SnS.sub.2 could be clearly identified. This shows that even after 20 cycles, Li.sub.2S could be decomposed resulting in the formation of SnS.sub.2. Therefore, the reversibility of the reaction in equation (3) is clearly evident.

(66) The FIGS. 20, 21 and 22 provide further evidence of the as-synthesized final and intermediate products to be composed of SnS.sub.2, MoS.sub.2, and 3DG.

(67) FIG. 20 shows X-ray diffraction (XRD) patterns of SnS.sub.2/MoS.sub.2/3DG and intermediate SnS.sub.2/3DG with peaks corresponding well with reference peaks of Joint Committee on Powder Diffraction Standards (JCPDS) card no. 65-3656 for MoS.sub.2, JCPDS card no. 23-0677 for SnS.sub.2, and JCPDS card no. 75-1621 for graphite.

(68) FIG. 21 shows the Raman spectrum for the SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG and 3DG as references. The peak at 315/cm corresponds to A1g mode of SnS.sub.2 while the peaks at 380/cm and 405/cm corresponds to E12g and A1g mode of MoS.sub.2. The peaks at 1575/cm and 2715/cm corresponds to G and 2D bands of the graphitic layers in 3DG.

(69) FIG. 22 shows thermogravimetric analysis (TGA) curves for the SnS.sub.2/MoS.sub.2/3DG, SnS.sub.2/3DG, and 3DG. The initial weight loss of 5% for SnS.sub.2/MoS.sub.2/3DG, SnS.sub.2/3DG between 25 to 150 C. is attributed to the moisture content on the samples. The weight loss of 15% (SnS.sub.2/MoS.sub.2/3DG) and 12% (SnS.sub.2/3DG) between 200 to 550 C. corresponds to the oxidation of SnS.sub.2 and MoS.sub.2. Lastly, the weight loss of 29.5% for both SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG between 550 C. to 850 C. arises from the combustion of 3DG. Therefore, the final weight composition of the products can be calculated to be about 67% SnS.sub.2 and 33% 3DG in SnS.sub.2/3DG and 65% SnS.sub.2, 3% MoS.sub.2, and 32% 3DG.

(70) FIGS. 23 to 26 illustrates properties related to charge and discharge cycles.

(71) FIG. 23 shows first galvanostatic discharge and charge curves for SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG at a current density of 50 mA/g in the potential range of 0.01 to 3.0 V.

(72) FIG. 24 shows a rate capability of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG.

(73) FIG. 25 shows a cycling performance of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG at current density of 200 mA/g and the corresponding coulombic efficiency of SnS.sub.2/MoS.sub.2/3DG.

(74) FIG. 26 shows a cycling performance of SnS.sub.2/MoS.sub.2/3DG and SnS.sub.2/3DG at current density of 1000 mA/g.

(75) As shown in FIGS. 28 and 29, an ex-situ High Resolution Transmission Electron Microscopy (HRTEM) was carried out on SnS.sub.2/MoS.sub.2/3DG to provide additional supporting evidence to show the catalytic effect of MoS.sub.2 to fully reduce Li.sub.2S and release the trapped lithium as described by the typical irreversible/partially reversible reaction in equation (3).

(76) This was carried out by disassembling coin cells that were either in a fully charged state (3.0 V) or in a fully discharged state (0.01V) after 20 charge-discharge cycles and washing the electrodes in NMP. As shown in FIG. 28, at fully discharged state the presence of Mo suggests the reversible conversion of MoS.sub.2 whereas the absence of Sn implies an incomplete alloying of Sn with Li (equations 4 and 6). However, LixSn could not be identified in the HRTEM images possibly due to the non-crystalline phase of LixSn. In the fully charged state, lattices of MoS.sub.2 and SnS.sub.2 could be clearly identified.

(77) Additionally, ex-situ X-ray Photonspectroscopy (XPS) was carried out on the post cycled electrodes as shown in FIG. 27. FIG. 27 shows the high resolution XPS spectra of SnS.sub.2/MoS.sub.2/3DG at different states: initial, discharged, and charged. The peaks at the initial state corresponds to the Sn 3d5/2 and Sn 3d3/2 of Sn4+ in SnS.sub.2. On discharge, these peaks shift towards 493.1 eV and 484.7 eV which corresponds to metallic tin (SnO) implying a reduction of Sn4+. On charge, these peaks return to the initial positions, which indicates that SnO oxidizes to Sn4+ (reformation of SnS.sub.2). Hence, these post-cycled analyses of HRTEM and XPS provide substantial evidence of the reversible decomposition of Li.sub.2S and conversion of Sn to SnS.sub.2.

(78) While at least one exemplary embodiment of the invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a, an or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

LIST OF REFERENCES

(79) US Patent Documents:

(80) (1) U.S. Pat. No. 7,060,390 B2 June 2006 Chen et al., Lithium-Ion battery containing nano-materials, USPC 429/231.8. (2) U.S. Pat. No. 9,120,677 A1 September 2015 Watson et al., Bulk preparation of holey graphene via controlled catalytic oxidation, USPC 423/448. (3) U.S. Pat. No. 8,920,970 B2 December 2014 Sunkara et al., Anode materials for lithium-ion batteries, USPC 409/209. (4) US 20130089796 Sun et al., Lithium-air battery, USPC 429/406.
Research Literature: (5) Seng, K. H., park, M. H., Guo, Z. P., Liu, H. K. and Cho, J. (2013) Catalytic role of Ge in highly reversible GeO.sub.2/Ge/C nanocomposite anode material for lithium batteries, Nano letters, 13(3), 1230-1236. (6) Hwang, J., Jo, C., Kim, M. G., Chun, J., Lim, E., Kim, S., Jeong, Y., Kim and Lee, J. (2015). Mesoporous Ge/GeO.sub.2/Carbon lithium-ion battery anodes with high capacity and high reversibility, ACS nano, 9(5), 5299-5309, s. (7) Zhu, Y. G., Wang, Y., Han, Z. J., Hsi, Y., Wong, J. I., Huang, Z. X., K. K., Ostrikov and Yang, H. Y. (2014), Catalyst engineering for lithium ion batteries: the catalytic role of Ge in enhancing the electrochemic performance of SnO.sub.2 (GeO.sub.2) 0.13/G anodes, Nanoscale, 6(24), 15020-15028. (8) Wang, Y., Huang, Z. X., Shi, Y., Wong, J. I., Ding, M., & Yang H. Y. (2015), Designed hybrid nanostructure with catalytic effect: beyond the theoretical capacity of SnO.sub.2 anode material for lithium-ion batteries, Scientific reports, 5. (9) Zhang, M., et al., Graphene oxide oxidizes stannous ions to synthesize tin sulfide-graphene nanocomposites with small crystal size for high performance lithium-ion batteries, Journal of Materials Chemistry, 2012, 22(43), p. 23091 (10) Qu, B., et al., Origin of the Increased Li+-Storage Capacity of Stacked SnS.sub.2/Graphene Nanocomposite, ChemElectroChem, 2015, 2(8), p. 1138-1143. (11) Wang, Y., et al., Pre-lithiation of onion-like carbon/MoS.sub.2 nano-urchin anodes for high-performance rechargeable lithium-ion batteries, Nanoscale, 2014, 6(15), p. 8884-8890. (12) Wang, Y., et al., Designed hybrid nanostructure with catalytic effect: beyond the theoretical capacity of SnO.sub.2 anode material for lithium-ion batteries, Sci. Rep., 2015, 5, p. 9164. (13) Seng, K. H., Park, M. H., Guo, Z. P., Liu, H. K., & Cho, J. (2013). Catalytic role of Ge in highly reversible GeO.sub.2/Ge/C nanocomposite anode material for lithium batteries, Nano letters, 13(3), 1230-1236. (14) Hwang, J., Jo, C., Kim, M. G., Chun, J., Lim, E., Kim, S., Jeong, Y., Kim & Lee, J. (2015), Mesoporous Ge/GeO.sub.2/Carbon Lithium-ion Battery Anodes with High Capacity and High Reversibility. ACS nano, 9(5), 5299-5309. (15) Huang Z X, Wang Y, Zhu Y G, Shi Y, Wong J I, Yang H Y, 3D graphene supported MoO2 for high performance binder-free lithium ion battery, Nanoscale, 2014, 6(16), 9839-45.