Lithium Sulfur Cell

Abstract

The present invention relates to a lithium-sulfur cell, a method for making the lithium-sulfur cell, and a battery comprising the lithium-sulfur cell. a The lithium-sulfur cell includes a working electrode comprising a membrane including a laminated layer of a metal-phase transition metal dichalcogenide of formula (MX2), where a is 0.0-2.0, X is selected from S, Se and Te, and M is a transition metal such as Ti, Hf, V, Nb, Ta, Mo, W, Tc, Re, Pd or Pt. A method for making the lithium-sulfur cell includes the steps of exfoliating the transition metal dichalcogenide to provide a metal-phase transition metal dichalcogenide of formula (I), assembling a working electrode including a membrane including a laminated layer of the metal-phase transition metal dichalcogenide and sulfur or lithium (poly)sulfide, and assembling a lithium-sulfur cell including the working electrode, a counter electrode and an electrolyte.

Description

[Technical field]

[0001] Related Applications This application claims priority to and the benefit of GB2113364.0, filed on September 20, 2021 (20.09.2021), the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to lithium-sulfur cells, methods of making lithium-sulfur cells, and batteries including lithium-sulfur cells. [Background technology]

[0003] The transition to net-zero carbon emissions requires major changes in the performance of electronic devices. Batteries based on new chemistries that overcome the fundamental limitations of lithium-ion batteries will play a key role in enabling the transition to higher performance electronic devices.

[0004] Lithium-sulfur (Li-S) batteries have the potential to offer high energy density, low material cost, and excellent safety. Li-S batteries are based on the conversion reaction between S8 and Li2S and can overcome the limitations of the intercalation oxide cathode and graphite anode used in conventional lithium-ion batteries. However, fundamental challenges such as low sulfur utilization in the cathode, slow reaction rate, self-discharge, poor capacity retention, and short lifespan have hindered the development of Li-S batteries.

[0005] Known Li-S batteries use a sulfur cathode and a lithium metal anode. Sulfur is electrically insulating, meaning that it must be supported on a more conductive host (typically carbon, modified carbonaceous materials, or functional polymeric materials). A binder is often required to hold the sulfur-carbon cathode together. However, a high ratio of carbon and binder "scaffold" to sulfur reduces the overall energy density. This is due to the presence of additional inactive components in the cathode and a high ratio of electrolyte to sulfur.

[0006] Carbon is often hydrophobic and poorly wetted by the electrolyte, which impedes ion diffusion between the electrolyte and the cathode, reducing both capacity and rate capability.

[0007] Furthermore, the weak interaction of sulfur with carbon can lead to the loss of sulfur through dissolution in the electrolyte. x Lithium polysulfides (LiPS) with (2≦x≦8) readily dissolve in the electrolyte and diffuse toward the anode. This effect is particularly pronounced for Li2S6 and Li2S8. This "polysulfide shuttle" effect leads to self-discharge, poor capacity retention, and shortened battery life.

[0008] Typically, Li-S cathodes may also contain a non-conductive electrocatalyst dispersed on a conductive framework, which creates an internal charge transfer resistance at the solid-solid interface, reducing the number of electrons reaching the active side.

[0009] Another problem with conventional sulfur cathodes is their volume expansion during discharge. The conversion between S8 and Li2S can result in a volume expansion of nearly 80%. The mechanical stress caused by this expansion can cause the electrode to fracture, damaging parts of the electrode and reducing the conductivity of the cathode and the battery capacity. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] CN108232164 [Patent Document 2] CN108649194 [Patent Document 3] CN111293293 [Patent Document 4] KR1020200025409 [Patent Document 5] US2019 / 0165365 [Patent Document 6] WO2018 / 226158

Non-licensed literature

[0011] [Non-licensed document 1] Bediako et al. Nature, 2018, Vol.558, pp.425-429.

Non-licensed Document 2

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

Non-licensed Document 7

Non-licensed literature 9

Non-licensed literature 10

[0012] Therefore, there is a need for Li-S batteries with improved energy density, reaction rate, resistance to self-discharge, capacity retention, and life span. [Means for solving the problem]

[0013] The present invention generally relates to a compound of formula (I): Li a MX2(I) (In the formula, a is 0.0 to 2.0, X is selected from S, Se, and Te, and M is a transition metal.) A lithium-sulfur cell (Li-S) is provided having a working electrode comprising a metallic phase transition metal dichalcogenide of

[0014] Accordingly, in a first aspect of the present invention there is provided a lithium-sulfur cell comprising a working electrode, a counter electrode and an electrolyte, the working electrode comprising: Formula (I): Li a MX2(I) (In the formula, a is 0 to 2.0; X is selected from S, Se and Te; M is a transition metal. A laminated layer of a metallic phase transition metal dichalcogenide of Sulfur or lithium (poly)sulfide A lithium-sulfur cell is provided comprising a membrane comprising:

[0015] The inventors have found that the Li-S battery of the first embodiment has excellent electrochemical properties. The metal-phase transition metal dichalcogenide electrode material functions simultaneously as a conductive substrate and an electrocatalyst. Thus, in contrast to typical Li-S electrodes that contain a non-conductive electrocatalyst dispersed on a conductive framework, the electrode material used in the battery of the first embodiment is a single material with no solid-solid interface. This facilitates electron transport to the electrocatalytic active sites, allowing the sulfur reduction reaction (SRR) to proceed efficiently.

[0016] Moreover, the Li-S battery of the first embodiment also has advantageously high gravimetric and volumetric energy densities. The metallic phase transition metal dichalcogenide electrode does not require a binder to fix the sulfur in the electrode. Without wishing to be bound by theory, it is believed that sulfur is securely attached between the nanosheets of the layered transition metal dichalcogenide, and its high affinity to this site eliminates the need for a binder. Also, the self-supporting nature and good electrical conductivity of the metallic phase transition metal dichalcogenide electrode of the present invention means that the cathode can be used without a current collector. This also improves the energy density of the battery.

[0017] Furthermore, the Li-S battery of the first embodiment is less susceptible to electrode material fracture compared to known sulfur cathodes. The volume expansion between S8 and Li2S is absorbed by the layered material. Therefore, the electrode is less susceptible to cracking and damage of the electrode material. This means that the battery is more stable, has improved capacity retention, and has a longer cycle life.

[0018] Preferably, a lithiated metal phase transition metal dichalcogenide is used. Thus, in a second aspect of the present invention, there is provided a lithium-sulfur cell comprising a working electrode, a counter electrode and an electrolyte, wherein the working electrode is Formula (I): Li a MX2(I) (In the formula, a is 0.1 to 2.0; X is selected from S, Se and Te; M is a transition metal. a stacked layer of a lithiated metal phase transition metal dichalcogenide of Sulfur or lithium (poly)sulfide A lithium-sulfur cell is provided comprising a membrane comprising:

[0019] Preferably, metallic phase niobium or molybdenum disulfide is used. Thus, in another aspect of the invention, there is provided a lithium-sulfur cell comprising a working electrode, a counter electrode and an electrolyte, wherein the working electrode is Formula (I): Li a MX2(I) (In the formula, a is 0 to 2.0; X is S, M is Nb or Mo. A laminated layer of a metallic phase transition metal dichalcogenide of Sulfur or lithium (poly)sulfide A lithium-sulfur cell is provided comprising a membrane comprising:

[0020] In some embodiments, a is 0.1 to 2.0. Preferably, the laminated layer of metal-phase transition metal dichalcogenide is pre-lithiated. Preferably, the working electrode includes conductive carbon in an amount of 5% by weight or less, such as 1% by weight or less.

[0021] The inventors have surprisingly found that the Li-S battery of the second aspect has further improved electrochemical properties and improved sulfur utilization. The Li-S battery shown in the examples has a sulfur utilization of more than 85%. As a result, the Li-S battery of the present invention has an advantageously high areal capacity and excellent capacity retention after repeated cycling.

[0022] Without wishing to be bound by theory, this may be due to the improved adsorption of lithium polysulfide provided by the working electrode material, Li + This is believed to be due to the improved ion diffusivity, accelerated electrochemical reaction rate, and excellent electrocatalytic activity for polysulfide conversion.

[0023] Lithiated metal-phase transition metal dichalcogenide electrode materials exhibit improved electrocatalytic activity. Without wishing to be bound by theory, it is believed that lithium intercalated between the layers of the metal-phase transition metal dichalcogenide facilitates the diffusion of Li ions through the material, resulting in enhanced Li ion diffusivity.

[0024] Lithiated metal-phase transition metal dichalcogenide electrode materials retain the excellent conductive properties of non-lithiated materials, eliminating the need for additional conductive components or binders in the electrode. Being free-standing means that the electrode can be used without a current collector. In addition, high concentrations of sulfur can be deposited on the electrode material, further reducing the "scaffold" to sulfur ratio. Thus, excellent gravimetric and volumetric energy densities are obtained.

[0025] Furthermore, the working electrode used in the Li-S battery of the second embodiment has improved electrolyte wettability of the electrode surface. Without wishing to be bound by theory, it is believed that the more lyophilic nature of the electrode material can be attributed to its polarity (e.g., compared to relatively non-polar carbon, which is hydrophobic). It is believed that the lyophilic nature has the advantage of improving ion diffusion between the electrode and the electrolyte, thereby lowering the electrode-electrolyte interfacial resistance. This advantageously results in high rate capability and high reaction rates for the Li-S battery.

[0026] An additional benefit of improved electrolyte wettability is that a smaller volume of electrolyte can be used in the battery, which reduces the mass of the battery and improves its energy density. Furthermore, the smaller electrolyte volume allows for a more efficient use of Li2S x The tendency of components to dissolve in the electrolyte is reduced, reducing the "polysulfide shuttle."

[0027] In this respect, the working electrode used in the Li-S battery of the second embodiment is composed of sulfur and Li2S x Excellent in retaining components. In particular, Li2S, which has high electrolyte solubility x The components (2≦x≦8, especially Li2S6 and Li2S8) have a high affinity for metallic phase transition metal dichalcogenides. Without wishing to be bound by theory, it is believed that the layered transition metal dichalcogenides contain sulfur vacancies that can serve as binding sites for sulfur immobilization. This leads to the Li2S x The tendency of the components to dissolve in the electrolyte is reduced, and Li2S x It is believed that the "polysulfide shuttle," in which components are transported through the electrolyte and irreversibly deposited on the anode, is reduced, which means that the undesirable self-discharge and poor capacity retention characteristics of known Li-S batteries are mitigated, and the battery life is improved compared to known LiS batteries.

[0028] Furthermore, Li + The ions have strong binding affinity with the transition metal dichalcogenides, which is advantageous in minimizing the dissolution of LiPS in the electrolyte.

[0029] The lithiated metal phase transition metal dichalcogenide retains the layered structure of the non-lithiated material. Therefore, the volume expansion between S8 and Li2S is absorbed by the layered material, so the Li-S battery of the second embodiment is less susceptible to electrode material fracture compared to known sulfur cathodes. This means that the battery is more stable, has improved capacity retention, and has a longer cycle life.

[0030] Due to these advantages, the present invention is uniquely suitable for improving the performance of Li-S batteries and can provide a real-world viable Li-S battery.

[0031] In a third aspect of the invention, there is provided a method of making a lithium-sulfur cell comprising the steps of: (a) exfoliating a transition metal dichalcogenide to form a compound of formula (I): Li a MX2(I) (In the formula, a is 0 to 2.0; X is selected from S, Se and Te; M is a transition metal. providing a metal-phase transition metal dichalcogenide of (b) assembling a working electrode comprising a membrane comprising a stacked layer of a metal-phase transition metal dichalcogenide and sulfur or lithium (poly)sulfide; (c) assembling a lithium-sulfur cell comprising a working electrode, a counter electrode, and an electrolyte; A method is provided, comprising:

[0032] In a fourth aspect of the present invention there is provided a lithium-sulphur cell obtained or obtainable by the method of the third aspect.

[0033] The use of lithiated layered transition metal dichalcogenides in the working electrode results in lithium-sulfur cells with improved sulfur utilization. The working electrode exhibits improved electrolyte wettability, improved adsorption of lithium polysulfides, excellent retention of sulfur, and Li +They exhibit improved ion diffusivity, accelerated electrochemical reaction rates, and excellent electrocatalytic activity for polysulfide conversion. The layered electrode materials are resistant to volume expansion and therefore less susceptible to fracture. As a result, Li-S batteries have advantageously high areal capacity and excellent capacity retention after repeated cycling.

[0034] In a fifth aspect of the present invention, there is provided a lithium-sulfur battery comprising a lithium-sulfur cell according to one or more of the first, second or fourth aspects.

[0035] In a sixth aspect of the present invention there is provided a method of charging and / or discharging a lithium-sulphur cell of the first, second or fourth aspects.

[0036] In a seventh embodiment of the present invention, a compound of formula (I): Li a MX2(I) (In the formula, a is 0 to 2.0; X is S, Se or Te; M is a transition metal. The use of the metallic phase transition metal dichalcogenides of the formula (I) is provided.

[0037] The use of the lithiated metal-phase transition metal dichalcogenide of formula (I) as a conductive substrate in the working electrode of a lithium-sulfur cell eliminates the need for conductive carbon, improving the gravimetric and volumetric energy densities of the Li-S of the present invention. Furthermore, the use of a single material means that there are fewer solid-solid interfaces in the electrode, facilitating electron transport to the electrocatalytic active sites and allowing the SRR to proceed efficiently.

[0038] These and other aspects and embodiments of the invention are described in further detail below.

[0039] The invention will now be described with reference to the figures shown below. [Brief description of the drawings]

[0040] [Figure 1] Figure 1a shows a photograph of a free-standing LixMoS2 film. Figure 1b shows a cross-sectional scanning electron microscope image of a LixMoS2 film showing the layered structure of stacked nanosheets (scale bar 1 μm). Figures 1c and 1d show comparative X-ray diffraction patterns (c) and Raman spectra (d) of LixMoS2 (top) and pristine 2H MoS2 powder (bottom). Figure 1e shows a high-resolution XPS spectrum of Mo 3d, showing a concentration of about 85% of the metallic 1T phase (peaks at about 232 eV and 228 eV) compared to the 2H phase (peaks at about 233 eV and 229 eV) of LixMoS2. [Diagram 2] Figure 2a shows galvanostatic charge-discharge curves at a current density of 0.1C. Typical discharge plateaus are seen at 2.4V (Li2S6 to Li2S4) and 2.1V (Li2S4 to Li2S2 / Li2S). 2H MoS2 (left), 2H MoS2 / C (center left), 1T MoS2 (center right), and LixMoS2 (right). Figure 2b shows the specific capacity at different current densities. The rate characteristics of different cathodes 2H MoS2 (bottom), 2H MoS2 / C (second from bottom), 1T MoS2 (second from top), and LixMoS2 (top) when cycled at 0.1C, 0.2C, 0.5C, 1C, and 2C are shown. Figure 2c shows a comparison of the volumetric specific capacity and sulfur loading of the LixMoS2 cathode and the reference cathode. The dashed lines represent the three different gravimetric capacities as indicated. Figure 2d is a graph showing the cycling stability of different cathodes at a current density of 1 C. It shows that the capacity retention of the LixMoS2 cathode at 500 cycles is about 91%, compared to 2H MoS2 (bottom), 2H MoS2 / C (second from the bottom), and 1T MoS2 (second from the top). [Diagram 3]Figure 3a shows the photographs and UV-vis spectra of Li2S4 solutions after exposure to different MoS2 hosts for LiPS adsorption test: Li2S4 (top line; left photo), 2H MoS2 (middle top line; middle left photo), 2H MoS2 / C (middle line; middle photo), 1T MoS2 (middle bottom line; middle right photo) and LixMoS2 (bottom line; right photo). From the photographs, the supernatant liquid in LixMoS2 is transparent, suggesting excellent adsorption of LiPS. From the UV-vis spectra, the absorbance of Li2S4 solution exposed to LixMoS2 host is the lowest, suggesting excellent adsorption of LiPS. Figures 3b and 3c show the cyclic voltammetry curves at various sweep rates for LixMoS2 cathode. Two cathodic and one anodic peaks (b) are shown, along with the corresponding Randles-Sevcik plot of peak current versus square root of sweep rate (c) used to derive DLi values. Figure 3d shows the Nyquist plot at room temperature, 2.1 V, and the equivalent circuit (inset) used to fit the electrochemical impedance spectroscopy profile. Figure 3e shows the Arrhenius plot of LixMoS2 cathode at various voltages. The inverse of the charge transfer resistance is used to describe the polysulfide conversion reaction rate. Figure 3f shows the activation energy of various MoS2 cathodes (2H MoS2 (top), 2H MoS2 / C (second from the top), 1T MoS2 (second from the bottom), and LixMoS2 (bottom)) at various voltages. The reaction rate is revealed by the energy required for each polysulfide conversion step. Peaks are present at 2.4 V and 2.1 V. [Figure 4]Figures 4a and 4b are graphs showing the linear sweep voltammetry (LSV) curves (a) at a sweep rate of 20 mV s-1 and the corresponding Tafel plots (b) for Li2S4 conversion. The order of lines in Figure 4a on the left is: 2H MoS2 (top), 2H MoS2 / C (top center), 1T MoS2 (bottom center), and LixMoS2 (bottom). Figure 4c is a graph showing the LSV curves of LixMoS2 host at a sweep rate of 20 mV s-1 and rotation speeds of 400 rpm (top left), 625 rpm (top center left), 900 rpm (bottom center left), and 1600 rpm (bottom left). Figure 4d is a graph showing the electron transfer numbers of different MoS2 hosts during the Li2S4 conversion process, derived from the LSV curves at different rotation rates according to the Koutecky-Levich equation. [Diagram 5]Figure 5a shows the specific capacity retention versus areal capacity with increasing areal sulfur loading of LixMoS2 cathode. The optimal loading was found to be 7.5 mg cm-2. Figure 5b shows a comparison of areal capacity at different current densities with reported Li-S batteries (triangle symbols) and LIBs (square symbols) fabricated using different types of materials. Figure 5c shows a comparison of gravimetric and volumetric energy densities of LixMoS2-based Ah-level pouch cells with reference Li-S batteries (triangle symbols) with Mo6S8 / C, metal-organic framework / carbon nanotube (MOF / CNT), multi-walled carbon nanotube (MWCNT), and graphitic carbon nitride / graphene (g-C3N4 / G) cathodes; reference Li-S batteries from Oxis Energy and Sion Power (triangle symbols); reference LIBs (square symbols) with LiFePO4 (LFP), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.6Co0.2Mn0.2O2 (NCM622), and LiNi0.8Co0.15Al0.05O2 (NCA) cathodes (BYD, CATL, LG, and Panasonic, respectively); and other reference energy storage technologies (shaded ovals). All presented energy density values ​​are calculated based on the entire device configuration, not just the electrode materials. Figure 5d shows a photograph (inset) of the fabricated LixMoS2-based Li-S pouch cell and a graph showing its cycling stability at a current density of 2 mA cm2. [Figure 6] Figure 6a shows the high-resolution XPS spectrum of Li 1s for LixMoS2. Figure 6b shows the electrochemical lithium extraction measurements in a bare LixMoS2 film cell versus lithium foil. The lithium content in the LixMoS2 sample is about 0.7 (per transition metal). [Figure 7] 1 is a graph showing the thermogravimetric analysis of the LixMoS2 cathode, the sulfur content of the sample is 71.6 wt%. [Figure 8] Figure 1 shows a cross-sectional SEM image of a LixMoS2 cathode (scale bar: 5 μm). [Figure 9] Figure 1 shows the electrolyte wettability of (a) LixMoS2 and (b) 2HMoS2. LixMoS2 is more lyophilic than 2HMoS2. [Figure 10] FIG. 10a is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10b is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10a is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10b is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10b is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10d is a schematic diagram of LixMoS2-based pouch cell construction. FIG. 10c ... [Figure 11] FIG. 1 shows the X-ray diffraction pattern of metallic phase 3R-NbS2 produced by chemical vapor transport method. [Figure 12] 1 is a graph showing galvanostatic charge and discharge curves at a current density of 0.1 C. Typical discharge plateaus are seen at 2.4 V (Li2S6 to Li2S4) and 2.1 V (Li2S4 to Li2S2 / Li2S). The curves shown represent 1T MoS2 (dotted line, top right left line), 3R NbS2 (dashed line, top right center line), and LixMoS2 (solid line, top right right line). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The present invention generally comprises: Li a MX2(I) (In the formula, a is 0 to 2.0, X is selected from S, Se and Te, and M is a transition metal.) A lithium-sulfur (Li-S) cell is provided having a working electrode comprising a metallic phase transition metal dichalcogenide of

[0042] Transition metal dichalcogenides (TMDs) are compounds of transition metals (e.g., Ti, Hf, V, Nb, Ta, Mo, W, Tc, Re, Pd, or Pt) and chalcogens (sulfur, selenium, or tellurium). TMDs typically have the formula MX2, where M is the transition metal and X is the chalcogen. In these materials, the transition metal is sandwiched between layers of chalcogen to form XMX stacks or sheets. TMDs are therefore an example of a "layered material." Layered materials are highly anisotropic and exist in bulk as stacks of two-dimensional (2D) sheets that may join together to form three-dimensional (3D) crystals. The in-plane (i.e., within a layer or sheet) bonds typically involve strong chemical bonds, but the layers themselves are held together by weak forces such as van der Waals forces, allowing them to be exfoliated to form individual nanosheets or monolayers.

[0043] CN111293293 describes a molybdenum disulfide, carbon nanotube-sulfur composite cathode for Li-S cells. The MoS2 is not a metallic phase, but a semiconducting 2H phase, and carbon nanotubes are included to aid in conductivity. CN111293293 does not describe lithiated or exfoliated TMDs.

[0044] KR1020200025409 describes a carbon nanostructure-MoS2 composite as a cathode for LiS cells. The carbon nanostructures are coated with MoS2. The MosS2 is not in the metallic phase but in the semiconducting 2H phase. The electrode contains the carbon nanostructures to provide electrical conductivity to the semiconducting MoS2. The cathode is made by annealing MoS2 at 600°C. At this temperature, all of the metallic phase MoS2 changes to the semiconducting 2H phase MoS2. KR1020200025409 does not describe stacked layers of MoS2, nor does it mention lithiated or exfoliated TMDs.

[0045] CN108232164 describes lithium polysulfide hosts such as Mo, W, Cr, Fe, Co, Ni sulfides supported on carbon nanotubes. The transition metal sulfides are semiconducting phases, not metallic phases. The transition metal sulfides are provided on the carbon nanotube support to aid in electrical conductivity. CN108232164 does not describe stacked layers of TMDs or lithiated TMDs.

[0046] CN108649194 is directed to a reduced graphene oxide supported MoS2 cathode for Li-S batteries. The material is described as a "nanosheet aerogel". MoS2 is reported to be dispersed in the center of graphene oxide lamellae. The MoS2 material is in the semiconducting phase, and the graphene oxide aids in the electrical conductivity of MoS2. CN108649194 does not describe metallic phase TMDs, nor does it mention lithiated or exfoliated TMDs.

[0047] WO2018 / 226158 describes MoS2 coated sulfur particles for LiS cathodes. MoS2 is treated with an organolithium and laminated to the sulfur particles. The MoS2 is in the semiconducting 2H phase when formed into an electrode for a Li-S cell. Metallic MoS2 is not formed during the exfoliation described in WO2018 / 226158. The organolithium is in too low a molar ratio compared to MoS2 and the treatment is too short to form metallic phase MoS2. The electrodes described in WO2018 / 226158 have a MoS2 coated sulfur particle size of 1.5 mg / cm2. 2 The carbon fibers are necessary to provide electrical conductivity to the semiconducting MoS2 phase, as evidenced by the relatively low active material loading of 0.25 μm.

[0048] US2019 / 0165365 relates to anode materials for lithium or sodium ion batteries, including intercalation compounds for lithium ions. Li-S cells are not described. Intercalation compounds for suflur or lithium polysulfides are not described.

[0049] working electrode The Li-S cell of the present invention comprises a working electrode. The working electrode can be a positive electrode (cathode) or a negative electrode (anode), for example during the discharging process. Typically, the working electrode is a positive electrode (cathode).

[0050] The working electrode has the formula (I): Li a Includes (lithiated) transition metal dichalcogenides of MX2(I).

[0051] The group M in formula (I) is a transition metal. The transition metal M can be selected from Ti, Hf, Zr, V, Nb, Ta, Mo, W, Tc, Re, Pd and Pt.

[0052] Preferably, the transition metal M is selected from V, Nb, Ta, Mo and W. More preferably, the transition metal M is selected from V, Nb, Mo and W. Even more preferably, the transition metal is selected from Nb or Mo. Most preferably, the transition metal M is Mo.

[0053] In the example, the working electrode is lithiated molybdenum disulfide (Li x have shown that Li-S cells containing MoS2 have excellent sulfur utilization, excellent capacity retention, and long cycle life. We expect that additional lithiated transition metal dichalcogenides will perform well in Li-S cells based on similar electrochemical properties demonstrated in related systems such as electrocatalytic hydrogen evolution, lithium ion batteries, and supercapacitors (Chhowalla et al., 2013).

[0054] The transition metal dichalcogenides are metallic phases.

[0055] The metallic phase has a Fermi level (E f ) which can occur when the highest occupied electron orbital is partially filled. This is called E fThis contrasts with the semiconductor phase, where the orbital bands lie within the energy gap between the two orbital bands. This can occur when the highest occupied electron orbital is completely filled and there is an energy gap between the highest occupied and lowest unoccupied orbitals. Metallic phase materials are conductors at absolute zero (0 K), while semiconductors are insulators at absolute zero.

[0056] In the metallic phase, Li + The ions have a strong bond with the metallic phase of transition metal dichalcogenides such as MoS2, which is advantageous in minimizing the dissolution of LiPS in the electrolyte.

[0057] The metallic phase is also highly conductive, mitigating the need for additional conductive additives, such as conductive carbon, in the working electrode.

[0058] Transition metal dichalcogenides may have any structure (polymorph) with a metallic phase. Transition metal dichalcogenides may be in the metallic phase of the 1T, 2H, or 3R polymorph, where the letters represent trigonal, hexagonal, and rhombohedral, respectively, and the numbers represent the number of XMX units in the unit cell. For example, the 1T polymorphs of MoS2 and WS2 are metallic, and both the 2H and 3R polymorphs of NbS2 are metallic.

[0059] In a particularly preferred embodiment, the transition metal dichalcogenide is a metallic 1T phase. + The ions have strong binding strength with the 1T phase of MoS2, which is favorable for minimizing the dissolution of LiPS in the electrolyte (Bediako et al., 2018).

[0060] In a further preferred embodiment, the transition metal dichalcogenide is a metal 3R phase. For example, the transition metal dichalcogenide may be NbS2 in the metal 3R phase.

[0061] The working electrode may contain other phases of lithiated transition metal dichalcogenides. Preferably, the proportion of metal phase lithiated transition metal dichalcogenides is 60% to 100%. More preferably, the proportion of metal phase lithiated transition metal dichalcogenides is 70% to 95%, and even more preferably, 80% to 90%.

[0062] The working electrode may contain other phases of lithiated transition metal dichalcogenides. Preferably, the proportion of 1T phase lithiated transition metal dichalcogenides is 60% to 100%. More preferably, the proportion of 1T phase lithiated transition metal dichalcogenides is 70% to 95%, and even more preferably, 80% to 90%.

[0063] The phase of the transition metal dichalcogenides may be known and may be determined using standard techniques such as X-ray photoelectron spectroscopy (XPS).

[0064] The working electrode of the present invention comprises a stacked layer of a transition metal dichalcogenide.

[0065] Thus, the transition metal dichalcogenides are preferably layered materials, in which the transition metal is sandwiched between layers of chalcogen to form XMX stacks or sheets, in which the in-plane (i.e., within the layers or sheets) bonds typically involve strong chemical bonds, but the layers themselves are held together by weaker forces such as van der Waals forces.

[0066] Preferably, the transition metal dichalcogenide is a two-dimensional (2D) material, and thus the working electrode comprises a nanosheet or monolayer of the transition metal dichalcogenide.

[0067] Individual nanosheets can have (geometric) surface areas on the order of μm2, but typically have a thickness of about 1 nanometer. In some embodiments, the nanosheets are about 0.7 nm thick.

[0068] Individual nanosheets or flakes of transition metal dichalcogenides can be restacked to form a film. Thus, the transition metal dichalcogenide preferably comprises a restacked transition metal dichalcogenide, such as restacked flakes of exfoliated transition metal dichalcogenides.

[0069] The restacked film of nanosheets may have a surface area on the order of mm2 and typically has a thickness of 1 to 100 μm. Typically, the restacked film contains 10 or more layers, preferably 20 or more layers, more preferably 50 or more layers, and even more preferably 100 or more layers.

[0070] The 2D transition metal disulfides can be made by exfoliation. Thus, the transition metal dichalcogenide is preferably an exfoliated transition metal dichalcogenide, such as an exfoliated flake, nanosheet, or monolayer of a transition metal dichalcogenide.

[0071] The working electrode comprises a film including stacked layers of transition metal dichalcogenides. Thus, the film has a layered (or laminated) structure. Compared to bulk metal TMD crystals, the layered working electrode can withstand volume expansion, such as that caused by conversion between S8 and Li2S, and therefore has improved cycling stability and is less susceptible to fracture.

[0072] The orientation of each layer (e.g., each nanosheet, monolayer, or flake) is typically parallel to the orientation of the film (i.e., the normal vector of each layer is aligned to within a few degrees, e.g., within 10° or within 5°, of the normal vector of the film).

[0073] As described in more detail below, films can be fabricated by restacking exfoliated metal phase transition metal dichalcogenides, such as individual transition metal disulfide nanosheets, monolayers, or flakes.

[0074] The membrane thickness may depend on the amount of sulfur supported (see below). Typically, the membrane thickness is 1 to 100 μm. Preferably, the membrane thickness is 2 to 10 μm, more preferably 2 to 5 μm, and even more preferably 2 to 3 μm.

[0075] The value a in formula (I) may be referred to as the lithiation ratio. The lithiation ratio a is 0 or more. The upper limit of the lithiation ratio is not particularly limited. Typically, the upper limit of the lithiation ratio is about 2.0.

[0076] In some embodiments, the lithiation ratio is 0.05 or less, such as 0. In such cases, the metal-phase transition metal dichalcogenide is not lithiated, for example, when the cell is constructed.

[0077] Preferably, the transition metal dichalcogenide is lithiated (contains lithium). Lithiation of the transition metal dichalcogenide reduces the amount of Li in the electrode material. + The diffusion rate of ions is increased.

[0078] As described in more detail below, lithiated transition metal dichalcogenides can retain the layered structure of the material. Thus, lithiated transition metal dichalcogenides are two-dimensional (2D) materials, and the working electrode comprises nanosheets or monolayers of lithiated transition metal dichalcogenides. Typically, the lithiated materials have lithium ions (Li) between the sheets. + The metals exist as individual stacks or sheets of transition metal disulfides (X,M,X,X) containing

[0079] Lithiated transition metal dichalcogenides typically contain lithium ions that are not derived from lithium (poly)sulfides. In such cases, the lithiation is distinct from the inclusion of lithium polysulfides in the working electrode. In other words, the lithium ions are not derived from lithium polysulfides.

[0080] Therefore, the lithiation rate a is typically 0.1 to 2.0. The lithiation rate is preferably 0.1 to 1.5, more preferably 0.3 to 1.2, even more preferably 0.5 to 0.9, and most preferably 0.6 to 0.8. In an embodiment, the lithiation rate is about 0.7.

[0081] Preferably, the lithiation occurs before the Li-S cell is formed. Thus, the working electrode may be described as a "prelithiated" electrode. In such a case, the working electrode comprises a laminated layer of a prelithiated metal-phase transition metal dichalcogenide of formula (I). In such a case, the lithiation occurs before sulfur or lithium (poly)sulfide is added to the working electrode (e.g., before operation of the Li-S cell). In other words, the lithium ions do not originate from the lithium polysulfide. The lithium polysulfide can only be introduced during the first cycle of the Li-S cell.

[0082] The lithiated transition metal dichalcogenides can be made by chemical or electrochemical lithiation. Preferably, the lithiated transition metal disulfides are made by chemical lithiation. Thus, the transition metal disulfides are preferably "chemically lithiated" transition metal dichalcogenides.

[0083] The lithiated transition metal dichalcogenide is preferably a layered material as described above. The lithium ions are inserted (intercalated) between the layers of the transition metal dichalcogenide. Thus, the material is a lithium-intercalated transition metal dichalcogenide.

[0084] The working electrode of the present invention comprises sulfur (S8) or lithium (poly)sulfides. Examples of lithium (poly)sulfides include Li2S, Li2S2, Li2S4, Li2S6, and Li2S8.

[0085] The amount of sulfur in the working electrode can be defined using the mass ratio of the (lithiated) transition metal dichalcogenide to sulfur. Typically, the total mass of sulfur, including the sulfur component of the lithium polysulfide, is used to calculate the mass ratio of sulfur.

[0086] Preferably, Li a The mass ratio of MX2 to sulfur is 1:2 to 1:3. More preferably, Li a The mass ratio of MX2 to sulfur is about 1:2.5.

[0087] Alternatively, the amount of sulfur in the working electrode can be defined using the weight percent of sulfur relative to the total weight of sulfur and active material (lithiated transition metal dichalcogenide) in the working electrode. This is sometimes known as the sulfur fraction. Typically, the sulfur fraction is 20% to 90% by weight. Preferably, the sulfur fraction is 40% to 85% by weight, more preferably 50% to 80% by weight, even more preferably 60% to 75% by weight, and most preferably 70% to 75% by weight.

[0088] The amount of sulfur in the working electrode can also be defined using areal sulfur loading, i.e., the mass of sulfur per unit area of ​​the working electrode. Typically, areal sulfur loading is 1 mg cm -2 ~10mgcm -2 Preferably, the areal sulfur loading is 2 mg cm -2 ~9mgcm -2 , more preferably 3 mg / cm -2 ~8mgcm -2 , more preferably 6 mg cm -2 ~8mgcm -2 , most preferably 7 mg / cm -2 ~8mgcm -2 It is.

[0089] The form of the sulfur component, whether it is elemental sulfur or lithium (poly)sulfide, changes during charging and discharging of the electrochemical cell. In the charged state (before discharging), the sulfur component is in the form of elemental sulfur (S8). During discharging, the sulfur component changes to lithium (poly)sulfide.

[0090] The sulfur component, whether elemental sulfur or lithium (poly)sulfide, is typically located between restacked nanosheets of transition metal dichalcogenides.

[0091] Typically, Li-S cells are fabricated in a charged state. Thus, the working electrode contains elemental sulfur (S8). Typically, the working electrode contains a composite of a metallic phase transition metal dichalcogenide and elemental sulfur.

[0092] Metal-phase transition metal dichalcogenides are typically electrical conductors. Therefore, the working electrode does not need to contain additional conductive components such as conductive carbon components. Typical conductive carbon components include carbon black, graphite, nanoparticle carbon powder, carbon fibers, and carbon nanotubes. Specific examples include Ketjen Black and Super P Carbon. A further example is reduced graphene oxide.

[0093] Known working electrodes for Li-S cells (e.g., those using semiconducting phase transition metal dichalcogenides) contain significant amounts of conductive additives (e.g., conductive carbon). These known electrodes may contain conductive carbon in amounts of 10% or more, 20% or more, 30% or more, e.g., 30-40%. When the amount of conductive additive is less than 10%, less than 5%, or less than 1%, the electrodes using semiconducting phase TMDs do not have sufficient conductivity.

[0094] The working electrode may include conductive carbon in an amount of 10% by weight or less, such as 5% by weight or less.

[0095] Typically, the working electrode comprises conductive carbon in an amount of 3% by weight or less. Preferably, the working electrode comprises conductive carbon in an amount of 2% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less. Most preferably, the working electrode is substantially free of conductive carbon.

[0096] The lithiated transition metal dichalcogenides are typically free-standing materials, such as free-standing films. That is, the lithiated transition metal dichalcogenides do not need to depend on or be bonded to a support material. Thus, the working electrode does not need to contain an additional binder component. Typical binder components include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof.

[0097] Typically, the working electrode comprises no more than 3% by weight of binder. Preferably, the working electrode comprises no more than 2% by weight of binder, more preferably no more than 1% by weight, and even more preferably no more than 0.5% by weight. Most preferably, the working electrode is substantially free of binder.

[0098] The working electrode in the Li-S cell of the invention comprises a metal-phase transition metal dichalcogenide of formula (I). The working electrode may consist essentially of a metal-phase transition metal dichalcogenide of formula (I).

[0099] The working electrode may include a current collecting substrate. Any suitable current collecting substrate may be used. Examples of suitable current collecting substrates include aluminum plates or foils. The lithiated transition metal dichalcogenide of formula (I) may be disposed on the surface of the current collecting substrate.

[0100] In a particularly preferred embodiment, there is provided a lithium-sulfur cell comprising a working electrode, a counter electrode and an electrolyte, wherein the working electrode comprises: Formula (IA): NbS2(IA) The metallic phase of niobium disulfide is laminated and Sulfur or lithium (poly)sulfide A lithium-sulfur cell is provided comprising a membrane comprising:

[0101] In some embodiments, NbS2 is a metallic 3R phase.

[0102] In another particularly preferred embodiment, there is provided a lithium-sulfur cell comprising a working electrode, a counter electrode, and an electrolyte, wherein the working electrode comprises: Formula (IB): Li a MoS2(IB) (In the formula, a is 0.5 to 0.9, for example, 0.6 to 0.8.) a laminated layer of lithiated metal phase molybdenum disulfide; Sulfur or lithium (poly)sulfide A lithium-sulfur cell is provided comprising a membrane comprising:

[0103] The metal-phase transition metal dichalcogenides can be prepared by any suitable method. In some embodiments, the metal-phase transition metal dichalcogenides are prepared by the methods described herein. In some embodiments, the metal-phase transition metal dichalcogenides are prepared by known methods such as chemical vapor transport, electrochemical processing, electron beam irradiation, or pressure application (Chhowalla et al., 2015).

[0104] Lithium Sulfur Cell The Li-S cell of the present invention comprises a counter electrode and an electrolyte. The Li-S cell may also comprise a separator. The Li-S cell typically comprises terminals for connection to an external device or power source.

[0105] Typically, the counter electrode is the negative electrode. Any suitable anode active material can be used as the negative electrode. Examples of suitable anode active materials include lithium metal or lithium alloys. Lithium alloys can include alloys of lithium with Mg, Zn, Sn, Sb, Si or Al, such as Li-Sn2O3 and Li-SnO2. Preferably, the counter electrode includes lithium metal.

[0106] The counter electrode may include a current collecting substrate. Any suitable current collecting substrate may be used. Examples of suitable current collecting substrates include copper plates or foils. The anode active material may be disposed on the surface of the current collecting substrate.

[0107] The counter electrode may include a binder to improve adhesion of the active material to the current collecting surface. Typical examples of binders are PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof.

[0108] Typically, the electrolyte of the electrochemical cell is suitable for solubilizing lithium ions. Typically, the electrolyte of a charged and discharged cell contains lithium ions.

[0109] Typically, the electrolyte comprises a lithium salt, such as LiTFSI, (lithium bis(trifluoromethane)sulfonimide, LiPF, LiBF, LiClO, LiNO, LiTF (lithium triflate), and lithium bis(oxalato)borate (LiBOB). Preferably, the electrolyte comprises a lithium salt that has good solubility in an ether solvent, such as LiTFSI, LiClO, LiTF, or LiBOB.

[0110] The electrolyte may be a liquid electrolyte, such as one that is liquid at ambient temperature, for example 25°C.

[0111] Preferably, the electrolyte is a non-aqueous electrolyte. The electrolyte may comprise a polar aprotic solvent. The electrolyte may comprise an organic solvent. Solvents that dissolve lithium ions are well known in the art.

[0112] Preferably, the solvent is one in which sulfur and lithium polysulfide have low solubility.

[0113] Preferably, the solvent is an ether solvent. Lithium polysulfide is poorly soluble in ether solvents. Suitable ether solvents include acyclic ethers, cyclic ethers, and polyethers.

[0114] Examples of suitable acyclic ethers include diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, 1,2-dimethoxypropane, 1,3-dimethoxypropane.

[0115] Examples of suitable cyclic ethers include tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, and trioxane.

[0116] Examples of suitable polyethers include diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), the higher glymes, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethyl ether, butylene glycol ether.

[0117] The electrochemical cell may also include a solid porous membrane disposed between the negative and positive electrodes. The solid porous membrane may be known as a separator. The solid porous membrane may partially or completely replace the liquid electrolyte. The solid porous membrane may include a polymer (e.g., polyethylene, polypropylene, or copolymers thereof), or an inorganic material, such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobium), or a main group metal oxide, such as silicon oxide, which may be in the form of glass fiber.

[0118] Preferably, the solid porous membrane comprises polypropylene.

[0119] The solid non-porous membrane may include lithium ion conductors, such as LLZO (garnet type), LSPO (LISICON type), LGPS (thio-LISICON type), LATP / LAGP (NASICON type), LLTO (perovskite type), and phosphide / sulfide glass-ceramics.

[0120] Manufacturing method The present invention also provides a method of making a lithium-sulfur cell, comprising the steps of: Li a MX2(I) where a, X and M are as defined above and the same precedence applies. The method may include providing a metallic phase transition metal dichalcogenide of

[0121] Metal-phase transition metal dichalcogenides from any source can be used. Metal-phase transition metal dichalcogenides can be made by lithiating non-metallic transition metal dichalcogenides. The phase transition to metal typically accompanies lithiation. The lithium ions may then be removed (see below) and the material will maintain the metallic phase. Chemical or electrochemical lithiation methods can be used.

[0122] The transition metal dichalcogenides may be two-dimensional transition metal dichalcogenides such as nanosheets, monolayers, or flakes of transition metal dichalcogenides. 2D transition metal disulfides can be made by exfoliation.

[0123] Typically, the method includes a step of exfoliating the transition metal dichalcogenide to provide a metallic phase transition metal dichalcogenide, which may be referred to as the exfoliation step, step (a).

[0124] Transition metal dichalcogenides typically have the formula (II): M 2 X 2 2(II) (In the formula, X 2 is selected from S, Se and Te; M 2 is a transition metal) has.

[0125] Transition metal M 2 can be selected from Ti, Zr, Hf, V, Nb, Ta, Mo, W, Tc, Re, Pd and Pt. Preferably, the transition metal M 2 is selected from V, Nb, Ta, Mo and W. More preferably, the transition metal M 2 is Mo.

[0126] Chalcogen X 2 is selected from S, Se and Te. Preferably, chalcogen X 2 is S.

[0127] As mentioned above, transition metal dichalcogenides are layered materials. In layered materials, the bonds within the plane (i.e., within the layers or sheets) typically involve strong chemical bonds, but the layers themselves are held together by weaker forces such as van der Waals forces. Thus, exfoliation is a rapid and efficient means of creating individual nanosheets or monolayers of the material.

[0128] The exfoliation process thus results in flakes, nanosheets, or monolayers of the transition metal dichalcogenide. The flakes, nanosheets, or monolayers are two-dimensional materials. The flakes, nanosheets, or monolayers are sometimes also referred to as "exfoliated" materials (i.e., exfoliated transition metal dichalcogenides).

[0129] Preferably, the exfoliation step comprises chemically exfoliating the transition metal dichalcogenide, for example exfoliating the transition metal dichalcogenide with lithium ions.

[0130] Additionally, the exfoliation step may include chemical exfoliation using any suitable metal ion, including Group 1 metal ions such as lithium ions, sodium ions, potassium ions, etc. Preferably, the metal ion is a lithium ion.

[0131] The chemical exfoliation step results in a metallic phase lithiated transition metal dichalcogenide, which eliminates the need for a subsequent phase transformation step. The exfoliation step can result in a transition metal dichalcogenide of the 1T, 2H or 3R polymorph. In a preferred embodiment, the exfoliation step results in a metallic 1T phase transition metal dichalcogenide.

[0132] Preferably, the stripping step comprises treating the transition metal dichalcogenide with an organolithium compound. Suitable organolithium compounds include alkyllithium compounds and aryllithium compounds. Specific examples of suitable organolithium compounds include butyllithium (e.g., n-butyllithium, sec-butyllithium, iso-butyllithium, tert-butyllithium) and phenyllithium. Preferably, n-butyllithium is used.

[0133] Further, the exfoliation step may include treating the transition metal dichalcogenide with any suitable metal ion source, such as a group 1 metal ion source. Suitable metal ion sources include organometallic compounds, metal borane compounds, Grignard reagents, or metal-metal alloys. Suitable organometallic compounds include alkyl metal compounds and aryl metal compounds. Specific examples of suitable organometallic compounds include butyl lithium (e.g., n-butyl lithium, sec-butyl lithium, iso-butyl lithium, tert-butyl lithium) and phenyl lithium. Preferably, n-butyl lithium is used. Suitable metal borane compounds include NaBH4 and LiBH4, preferably LiBH4. Suitable Grignard reagents include alkyl magnesium chloride or aryl magnesium chloride compounds and alkyl magnesium bromide or aryl magnesium bromide compounds. Suitable metal-metal alloys include sodium-potassium alloys.

[0134] Typically, the molar ratio of the metal ion source to the transition metal dichalcogenide in the peeling step is 1:1 to 5:1. Preferably, the molar ratio of the metal ion source to the transition metal dichalcogenide in the peeling step is 1:1 to 4:1, more preferably 1:2 to 1:3. Typically, the molar ratio of the metal ion source to the transition metal dichalcogenide in the peeling step is 1:1 or more. Preferably, the molar ratio of the metal ion source to the transition metal dichalcogenide in the peeling step is 1:2 or more, more preferably 1:3 or more.

[0135] Typically, the molar ratio of the organolithium reagent to the transition metal dichalcogenide in the stripping step is 1:1 to 5:1. Preferably, the molar ratio of the organolithium reagent to the transition metal dichalcogenide in the stripping step is 1:1 to 4:1, more preferably 1:2 to 1:3. Typically, the molar ratio of the organolithium reagent to the transition metal dichalcogenide in the stripping step is 1:1 or more. Preferably, the molar ratio of the organolithium reagent to the transition metal dichalcogenide in the stripping step is 1:2 or more, more preferably 1:3 or more.

[0136] Typically, the concentration of the metal ion source (e.g., organolithium reagent) is such that it is in excess relative to the transition metal dichalcogenide. In other words, the transition metal dichalcogenide is saturated with respect to the metal ion source (e.g., organolithium reagent). Preferably, the concentration of the metal ion source (e.g., organolithium reagent) is 1M or more, more preferably 1.5M or more, and even more preferably 2M or more. In some embodiments, the concentration can be 1M to 3M, preferably 1.5M to 2.5M.

[0137] Typically, the stripping step is carried out in a solvent. Typically, an organic solvent is used. Most commonly, a non-polar organic solvent is used. Preferably, a hydrocarbon solvent is used.

[0138] The hydrocarbon solvent may be an aliphatic hydrocarbon solvent or an aromatic hydrocarbon solvent.

[0139] Examples of suitable aliphatic hydrocarbon solvents include linear alkanes such as pentane, hexane, heptane and octane; cycloalkanes such as cyclopentane, cyclohexane, cycloheptane and cyclooctane; and petroleum fractions such as kerosene and petroleum ether. Mixtures of these solvents may also be used.

[0140] Examples of suitable aromatic hydrocarbon solvents include benzene, toluene, and xylene.

[0141] Preferably, the organic solvent is an aliphatic hydrocarbon solvent, more preferably, the organic solvent is hexane.

[0142] The stripping step may be carried out at ambient temperature (about 20° C.). Alternatively, the stripping step may be carried out at elevated temperatures (above ambient temperature, about 20° C.). Methods of providing heat during the stripping step are known and include, for example, using a reaction vessel with an external heating jacket.

[0143] Typically, the exfoliation step involves heating the transition metal dichalcogenide at reflux, i.e., at the boiling point of the solvent.

[0144] The stripping step can be carried out for a time sufficient to form a desired amount of lithiated transition metal dichalcogenide, typically until substantially all of the transition metal dichalcogenide is consumed.

[0145] Typically, the exfoliation step involves treating the transition metal dichalcogenide with the organolithium compound for 12 to 72 hours. Preferably, the exfoliation step involves exfoliating the transition metal dichalcogenide for 24 to 72 hours, more preferably for 48 to 72 hours.

[0146] Typically, the exfoliation step involves treating the transition metal dichalcogenide with the organolithium compound for 6 hours or more, 8 hours or more, 10 hours or more, 12 hours or more, and preferably, the exfoliation step involves exfoliating the transition metal dichalcogenide for 24 hours or more, more preferably, 36 hours or more, and even more preferably, 48 hours or more.

[0147] Preferably, the exfoliation is carried out under conditions that result in metallic phase TMDs. For example, the exfoliation is carried out by treating the TMDs with an organolithium compound for a sufficient time and / or in a sufficient molar ratio to result in metallic phase TMDs. The presence of metallic phase TMDs can be confirmed by any suitable analytical method, such as X-ray diffraction, Raman spectroscopy, or XPS. For example, metallic 1T phase Li xThe XPS of MoS2 has peaks at approximately 232 eV and 228 eV, whereas the semiconducting 2H phase has peaks at approximately 233 eV and 229 eV.

[0148] The lithiated transition metal dichalcogenide can be recovered, for example, by filtration, which methods are known in the art.

[0149] The lithiated transition metal disulfide may be washed to ensure removal of any remaining organolithium reagent or organic residues. For example, the lithiated transition metal dichalcogenide may be washed with an organic solvent, typically a non-polar solvent. Preferably, the lithiated transition metal dichalcogenide is washed with a hydrocarbon solvent, such as hexane.

[0150] As discussed above, lithium ions can be removed from the lithiated metal phase transition metal dichalcogenide while maintaining the material in the metal phase. Removal of lithium ions can be accomplished by washing the lithiated transition metal dichalcogenide with an aqueous solvent. Thus, the stripping step can optionally include washing the lithiated transition metal dichalcogenide with water or an aqueous solvent. Washing the lithiated transition metal dichalcogenide with water can reduce the lithiation ratio of the material to 0.05 or less, such as 0.

[0151] Sonication improves the removal of lithium ions. Thus, the aqueous washing step may include sonicating the lithiated transition metal dichalcogenide in water or an aqueous solvent. The sonication step is carried out until substantially all of the lithium ions are removed from the transition metal dichalcogenide. Typically, the sonication step is carried out for 15 minutes to 4 hours, such as 30 minutes to 2 hours, for example about 1 hour.

[0152] The (non-lithiated) metallic-phase transition metal dichalcogenide can be recovered, for example, by filtration or centrifugation.

[0153] The method includes a step of assembling a working electrode comprising a membrane comprising stacked layers of a metal-phase transition metal dichalcogenide and sulfur or lithium (poly)sulfide, which may be referred to as the restacking step, step (b).

[0154] The restacking step may include filtering the suspension containing the metallic phase transition metal dichalcogenide flakes, monolayers, or nanosheets.

[0155] The restacking step also involves loading the working electrode with a lithium sulfide or polysulfide salt.

[0156] Any suitable method can be used to load the sulfur component onto the metallic phase transition metal dichalcogenides, but preferably avoid high temperature annealing or melt diffusion processes, which may induce partial phase transformation from the 1T phase to the less desirable 2H phase.

[0157] The loading is carried out by co-precipitation or solvent-based loading.

[0158] In the co-precipitation method, a suspension of transition metal dichalcogenide and elemental sulfur (S8), such as powdered sulfur, is prepared and mixed. This suspension can be prepared by suspending the material obtained from the exfoliation step in a suitable solvent.

[0159] Preferably, the Li in suspension a The mass ratio of MX2 to sulfur is 1:2 to 1:3. More preferably, Li a The mass ratio of MX2 to sulfur is about 1:2.5.

[0160] Typically, the suspension is prepared in an organic solvent. Suitable solvents include carbon disulfide.

[0161] Typically, the suspension is mixed to ensure that the sulfur and metallic phase transition metal dichalcogenide are uniformly distributed throughout the suspension. Suitable dispersion methods include sonication.

[0162] The suspension is filtered to produce a composite of the metal-phase transition metal dichalcogenide and elemental sulfur. This composite can be removed from the filter and used in the working electrode. Alternatively, the suspension can be filtered through a porous conductive material. The porous conductive material can then be used as a current collector for the working electrode.

[0163] Alternatively, solvent-based loading techniques can be used, in which case a lithium (poly)sulfide solution can be applied to the deposited layered metallic phase transition metal dichalcogenide, e.g., a film of metallic phase transition metal dichalcogenide.

[0164] Suitable lithium (poly)sulfides include Li2S4, Li2S6 and Li2S8. Lithium (poly)sulfides may be purchased commercially. Alternatively, lithium (poly)sulfides may be prepared by reacting lithium sulfide (Li2S) with sulfur in appropriate molar amounts.

[0165] Suitable solvents include the electrolyte solvents described above.

[0166] Preferably, the supporting comprises co-precipitating a metallic phase transition metal dichalcogenide with sulfur.

[0167] The method includes assembling a lithium-sulfur cell that includes a working electrode, a counter electrode, and an electrolyte.

[0168] The assembly process is typically carried out in the absence of oxygen (e.g., an atmosphere containing less than 10 ppm oxygen). The assembly process is typically carried out in the absence of water (e.g., an atmosphere containing less than 10 ppm water vapor).

[0169] Preferably, the assembly process is typically carried out in an inert atmosphere, such as a nitrogen or argon atmosphere.

[0170] Any suitable lithium-sulfur cell configuration may be used. Suitable configurations include coin cells and pouch cells.

[0171] The present invention also provides a lithium-sulfur cell obtained or obtainable by the above-described manufacturing method.

[0172] The lithium-sulfur cells described above and obtained or obtainable by the manufacturing methods described above have excellent electrochemical properties.

[0173] The lithium-sulfur cell of the present invention has excellent sulfur utilization. Sulfur utilization is calculated relative to full utilization of sulfur in the working electrode. Such an electrode produces 1675 mAh of charge per gram of sulfur. That is, 100% utilization corresponds to a gravimetric capacity of 1675 mAhg of sulfur in the cell. -1 is equivalent to.

[0174] Typically, the sulfur utilization of the lithium-sulfur cells of the present invention is 80% or more. Preferably, the sulfur utilization of the lithium-sulfur cells of the present invention is 82% or more, more preferably 83% or more.

[0175] The lithium-sulfur cell of the present invention has excellent capacity retention. Typically, the lithium-sulfur cell of the present invention has a capacity retention of 80% or more at 200 cycles. Preferably, the lithium-sulfur cell of the present invention has a capacity retention of 82% or more at 200 cycles, more preferably 83% or more.

[0176] The lithium-sulfur cells of the present invention have excellent gravimetric energy density. Typically, the lithium-sulfur cells of the present invention have a gravimetric energy density of 350 Whkg. -1 Preferably, the lithium-sulfur cell of the present invention has a gravimetric energy density of 380 Whkg or more. -1 More than 400Whkg, preferably 400Whkg -1 It has a weight energy density of more than 1000g / kg.

[0177] The lithium-sulfur cells of the present invention have excellent volumetric energy density. Typically, the lithium-sulfur cells of the present invention have a volumetric energy density of 600 WhL. -1 Preferably, the lithium-sulfur cell of the present invention has a volumetric energy density of 650 WhL or more. -1 More than 700WhL, preferably 700WhL -1 It has a volumetric energy density of more than or equal to 1000 nm.

[0178] Charging and discharging method The present invention also provides methods of charging and / or discharging the lithium-sulfur cells of the present invention.

[0179] The method includes charging and / or discharging a lithium-sulfur cell in the voltage range of 2.8V to 1.7V.

[0180] The method may include cycling the electrochemical cell through charging and discharging, or discharging and charging. The cycle may be repeated multiple times. Thus, the method of charging and / or discharging may include 2 or more cycles, 5 or more cycles, 10 or more cycles, 20 or more cycles, or 50 or more cycles.

[0181] The electrochemical cells of the present invention exhibit improved capacity retention over extended cycling. In the examples, the pouch cells exhibited a capacity retention of 85.2% after 200 cycles, which corresponds to a capacity loss of 0.074% per cycle. Thus, the charging and / or discharging method preferably includes 100 or more cycles, more preferably 150 or more cycles, even more preferably 200 or more cycles, and most preferably 250 or more cycles.

[0182] battery The present invention also provides a battery comprising one or more lithium-sulfur cells of the present invention.

[0183] When there are multiple cells, the cells can be arranged in series or in parallel.

[0184] The battery of the present invention can be mounted on road vehicles such as automobiles, mopeds, and trucks. Alternatively, the battery of the present invention can be mounted on rail vehicles such as trains and trams. The battery of the present invention can also be mounted on electric bicycles (e-bikes), drones, electric airplanes, electric boats, or hybrid boats. Similarly, the battery of the present invention can be mounted on electric tools such as electric drills and electric saws, gardening tools such as lawnmowers and grass cutters, and home appliances such as toothbrushes and hair dryers.

[0185] The battery of the present invention may also be incorporated into a regenerative braking system.

[0186] The battery of the present invention can be installed in portable electronic devices such as mobile phones, laptops, tablets, etc.

[0187] The battery of the present invention can be installed in a power grid management system.

[0188] use The present invention also relates to a method for producing a lithium-sulfur cell comprising the steps of: Li a MX2(I) (In the formula, a is 0.1 to 1.0, X is selected from S, Se and Te; M is a transition metal. The present invention provides a use of the metallic phase transition metal dichalcogenide of the present invention.

[0189] In particular, the present invention provides the use of a metallic phase transition metal dichalcogenide of formula (I) as a conductive substrate in the working electrode of a lithium-sulfur cell.

[0190] The use of the metal-phase transition metal dichalcogenide of formula (I) as the conductive substrate of the working electrode of the lithium-sulfur cell eliminates the need for additional conductive components such as conductive carbon, thereby improving the gravimetric and volumetric energy densities of the Li-S cells of the present invention. Furthermore, the use of a single material means that there are fewer solid-solid interfaces in the electrode, facilitating electron transport to the electrocatalytic active sites and allowing the SRR to proceed efficiently.

[0191] The priorities regarding a, X, M, and the form and structure of the lithiated transition metal dichalcogenide are as described above.

[0192] definition The voltage values ​​given herein are, as is common in the art, Li + Compliant with / Li.

[0193] The gravimetric capacity is estimated based on the mass of active sulfur in the electrode.

[0194] Sulfur utilization is estimated based on the ratio of actual gravimetric capacity to the theoretical gravimetric capacity of sulfur. For this purpose, the theoretical gravimetric capacity of sulfur is 1675 mAhg -1 It is.

[0195] The volumetric capacitance is calculated based on the gravimetric capacitance multiplied by the sulfur packing density in the working electrode.

[0196] Gravimetric energy density is estimated based on the energy per unit mass of a lithium-sulfur cell.

[0197] Volumetric energy density is estimated based on the energy per unit volume of a lithium-sulfur cell.

[0198] Capacity retention is estimated as the ratio of the original cell capacity to the cell capacity after a specified number of charge-discharge cycles.

[0199] Other priorities Herein, each compatible combination of the above-described embodiments is expressly disclosed as if each combination was individually and explicitly described.

[0200] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in light of the present disclosure.

[0201] As used herein, "and / or" is to be construed as specifically disclosing each of the two specified features or components in the presence / absence of the other. For example, "A and / or B" is to be construed as specifically disclosing each of (i) A, (ii) B, (iii) A and B, as if each were individually set forth herein.

[0202] Unless otherwise dictated by context, the feature descriptions and definitions set forth above are not intended to be limited to any particular aspect or embodiment of the present invention, but apply equally to all aspects and embodiments described. EXAMPLES

[0203] Certain aspects and embodiments of the present invention will now be described, by way of example, with reference to the figures mentioned above.

[0204] Preparation of transition metal compounds 1.1-Li x Preparation of MoS2 Li was obtained by intercalating organolithium reagents into bulk MoS2 powder (2HMoS2). x MoS2 was prepared by immersing bulk MoS2 powder (0.3 g; Alfa Aesar) in hexane (15 ml; Sigma-Aldrich) under argon, then adding n-butyllithium solution (2.5 M in hexane, 2 mL; Sigma-Aldrich) to the mixture and refluxing for 2 days. After cooling, the product was washed with hexane (3 × 50 mL) to remove residual organolithium reagent and organic residues. The resulting Li xThe MoS2 powder was dried and stored in an inert atmosphere to avoid oxidation.

[0205] 1.2-Preparation of 1T MoS2 Li x Dissolve MoS powder (preparation example 1.1) in deionized water (1 mg mL -1 ) for 30 min followed by centrifugation at 10,000 rpm to remove the lithium cations.

[0206] 1.3-Preparation of 2H MoS2 / C 2H MoS2 / C was prepared by ball milling 2H MoS2 (Alfa Aesar) with Super P Carbon (MTI) in a mass ratio of 9:1.

[0207] Further preparation of transition metal compounds 1. Preparation of 4-3R NbS2 3R NbS2 was prepared by chemical vapor transport. A quartz tube containing high-purity Nb (purity 99.99%) and S (purity 99.99%) in a molar ratio of Nb:S of 1:2 was placed in a 10 -6 The tube was evacuated to Torr and sealed. The sealed quartz tube was then inserted into a tubular furnace. The tubular furnace was heated to 900 °C at a heating rate of 3 °C min-1. The reaction time at 900 °C was 18 h, and the furnace was then allowed to cool naturally. Metallic 3R NbS2 crystals were collected from the quartz tube.

[0208] Preparation of sulfur composite materials 2.1-Li x Preparation of MoS2 / S Li x MoS2 sulfur composite (Li x MoS2 / S) was prepared by coprecipitation method. x MoS2 powder (20 mg) and sulfur flower powder (50 mg; Alfa Aesar) were dispersed in carbon disulfide solution (5.0 M hexane solution, 20 ml; Sigma-Aldrich) by ultrasonic treatment. The dispersion was filtered through an anodic aluminum oxide membrane (pore size 0.02 μm; Whatman), dried at room temperature under vacuum, and Li xMoS2 / S was co-precipitated.

[0209] The areal sulfur loading, which is proportional to the film thickness, was adjusted by changing the amount of dispersion liquid of the same concentration.

[0210] The volumetric sulfur loading was calculated based on the areal sulfur loading and the corresponding film thickness.

[0211] Li in the final preparation x The mass ratio of MoS2 to sulfur flowers was 1:2.5 (sulfur fraction = 71.4 mass%).

[0212] 2.2-1T Preparation of MoS2 / S The sulfur composite of 1T MoS2 (1T MoS2 / S) was prepared by coprecipitation method. 1T MoS2 / S was prepared by the same procedure as described in Preparation Example 2.1, except that ethanol solvent was used for dispersion.

[0213] 2.3-Preparation of 2H MoS2 / S The sulfur composite of 2H MoS2 (2H MoS2 / S) was prepared by melt diffusion method. 2H MoS2 (100 mg) was ball-milled with sulfur flowers (250 mg) to obtain fine powder, and 2H MoS2 / S was prepared. The mixture was then sealed in a Teflon-lined autoclave under argon and kept at 155 °C for 12 h. After natural cooling process to room temperature, 2H MoS2 / S was collected.

[0214] 2.4-Preparation of 2H MoS2 / C / S The sulfur composite of 2H MoS2 / C (2H MoS2 / C / S) was prepared by melt diffusion method. 2H MoS2 / C / S was prepared by ball milling 2H MoS2 / C (100 mg) with sulfur flowers (250 mg) to obtain fine powder. The mixture was then sealed in a Teflon-lined autoclave under argon and kept at 155 °C for 12 h. After natural cooling process to room temperature, 2H MoS2 / C / S was collected.

[0215] Further preparation of sulfur composites 2.5-3R Preparation of NbS2 / S The sulfur composite of 3R NbS2 (3R NbS2 / S) was prepared by melt diffusion method. 3R NbS2 / S was prepared by ball milling 3R NbS2 (100 mg) with sulfur flowers (250 mg) to obtain fine powder. The mixture was then sealed in a Teflon-lined autoclave under argon and kept at 155 °C for 12 h. After natural cooling process to room temperature, 3R NbS2 / S was recovered.

[0216] Preparation of electrolyte, LiPS solution, and Li2S4 solution The electrolyte was prepared by dissolving lithium bis(trifluoromethanesulfonyl)imide (1.0 M; Sigma-Aldrich) and lithium nitrate (0.2 M; Sigma-Aldrich) in a solvent of 1,3-dioxolane and 1,2-dimethoxyethane (1:1 by volume; Sigma-Aldrich).

[0217] LiPS solution was prepared by reacting lithium sulfide (Li2S) and sulfur in a stoichiometric ratio in the electrolyte.

[0218] A Li2S4 solution (1.0 M) was prepared by adding Li2S powder (1 mmol; Sigma-Aldrich) and sulfur flowers (3 mmol) to the electrolyte (1 mL) and vigorously stirring overnight at 50 °C in an argon-filled glove box.

[0219] Fabrication of coin cells and pouch cells The electrochemical performance of the MoS2-based cathode was evaluated using a coin cell (CR2032). In an argon-filled glove box, the sulfur composites (Li x A cathode made of MoS2 / S, 1T MoS2 / S, 2H MoS2 / S, 2H MoS2 / C / S, or 3R NbS2 / S), a lithium foil anode, a Celgard separator, and an electrolyte (E / S ratio = 12 μl mg -1) were used to assemble coin cells, which are shown in Table 1 (Coin Cells).

[0220] (Li x The cathodes (MoS2 / S, 1T MoS2 / S, and 3R NbS2 / S) were directly used as cathodes, whereas the 2H MoS2 / S and 2H MoS2 / C / S cathodes were prepared by forming a slurry (90 wt% 2H MoS2 / S or 2H MoS2 / C / S and 10 wt% polyvinylidene fluoride binder; MTI Co., Ltd.) and then a coating process was carried out to fabricate the corresponding cathodes.

[0221] Unless otherwise noted, all cathodes used in coin cells had a sulfur loading of 5 mg.

[0222] [Table 1]

[0223] A pouch cell (dimensions 6 cm x 4.5 cm) was used to measure the Li x The device performance of MoS2-based Li-S batteries was evaluated. The sulfur composite material (Li x A pouch cell was assembled by assembling a cathode made of MoS2 / S) onto an Al current collector (MTI Inc.), a lithium foil anode onto a Cu current collector (MTI Inc.), a Celgard separator onto an Al laminate film (MTI Inc.), and then the electrolyte (E / S ratio = 2.4 μL mg -1 ) and finally sealed in an argon-filled glove box. Al and Ni tabs (MTI) were welded to the cathode and anode, respectively, and introduced for external connection.

[0224] The Ah level pouch cell was assembled by stacking the cathode and anode alternately in layers on the cell core, similar to the pouch cell. xThe stacked configuration of alternating layers of MoS2 cathodes and lithium foil anodes (6 layers of each electrode) is shown in Figure 10b. A pouch cell core providing a total capacity of over 2 Ah (containing 10 layers of each electrode) is shown in Figure 10c.

[0225] Comparative pouch cells are made according to the methods described in the following references, as set forth in Table 2-Comparative pouch cells.

[0226] [Table 2]

[0227] Materials characterization The morphological and structural information of the materials was characterized by SEM (FEI, Magellan 400), XRD (Bruker, D8 Advance powder X-ray diffractometer, CuKα radiation), Raman spectroscopy (Renishaw, InVia, 514 nm laser beam), and X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific, AlKα radiation source).

[0228] The sulfur content was determined by thermogravimetric analysis (Setaram Setsys Evolution 18) in an argon atmosphere.

[0229] LiPS adsorption was performed by immersing the different materials (10 mg) in Li2S4 solution (10 mM, 5 mL) overnight at room temperature. As a control, the same Li2S4 solution was also filled into a blank glass vial. The solutions after LiPS adsorption test were examined by UVvis spectroscopy (Agilent, Cary 7000 Universal measurement spectrophotometer). The contact angle of LiPS was measured by the drop method (droplet: 5 μL of Li2S4 solution) using an optical contact angle meter (FTA1000) in an argon-filled glove box.

[0230] Electrochemical characterization An electrochemical workstation (ModuLab XMECS) was coupled to a rotating disk electrode (RDE) system (AMETEK Scientific Instruments, 636A Rotating Ring-Disk Electrode) and electrocatalysis tests were carried out in an argon-filled glove box.

[0231] To prepare the working electrode, a MoS2 sample (1 mg) was sonicated for 30 min in ethanol (480 μL) and 5 wt% Nafion solution (20 μL; Sigma-Aldrich) and then the catalyst ink (2 mg mL -1 The ink (10 μL) was then applied to a glassy carbon tip (0.2 cm) of an RDE. 2 ) and dried at 60°C, then moved to a glove box.

[0232] Electrochemical measurements were performed using a two-electrode configuration. -2 A MoS2 sample mounted on a sintered body was used as the working electrode, and lithium foil (MTI) was used as both the counter and reference electrodes in a Li2S4 solution (8 mM).

[0233] Cyclic voltammetry (CV) was performed in the non-faradaic range of 3.2 V to 3.0 V with a 10 mVs -1 The sulfur reduction reaction (SRR) activity was then measured at a rate of 20 mVs in the voltage range of 2.3 V to 1.5 V. -1 The electron transfer rate in the SRR process was measured by sweeping linear sweep voltammetry (LSV) at various rotation speeds from 0 to 1600 rpm. Based on the LSV curves, the electron transfer rate in the SRR process was calculated according to the Koutecky-Levich equation: 1 / J = 1 / J D +1 / J K =1 / Bω 1 / 2 +1 / J K (In the formula, J, J D , J Kare the measured current density, the diffusion-limited current density, and the kinetic-limited current density, respectively; ω is the angular velocity of the RDE; and B is the Levich coefficient, which can be defined as: B=0.62nFCD 2 / 3 v -1 / 6 (where n is the electron transfer number, F is the Faraday constant, C is the reactant concentration in the electrolyte, D is the diffusion coefficient of the reactants, and v is the kinetic viscosity of the electrolyte). This method is also described in Bard, AJ & Faulkner, LR Electrochemical Methods: Fundamentals and Applications (Wiley, 2001).

[0234] LSV was also performed on a blank electrolyte containing no LiPS and used as a background curve to separate the contribution of the SRR process.

[0235] Electrochemical measurements of the coin cells were performed in a battery cycler (Biologic MPG-2).

[0236] Galvanostatic charge-discharge (GCD) tests were performed at various C rates (1C=1672mAhg) in the voltage range of 2.8V to 1.7V. -1 The cycling stability was recorded during successive GCD cycles at 1C rate.

[0237] Cyclic voltammetry (CV) curves were collected at various sweep rates and the peak current was calculated according to the Randles-Sevcik equation: P =(2.69×10 5 )n 3 / 2 AD Li 1 / 2 C Li v 1 / 2 where iP is the peak current, n is the number of charge transfers, A is the geometric area of ​​the active electrode, and D Li is the Li ion diffusion coefficient, C Li is the lithium ion concentration in the electrode, and v is the sweep rate) according to the lithium diffusion coefficient (D Li) was used to calculate the charge transport coefficient. This method is also described in Bard, AJ & Faulkner, LR Electrochemical Methods: Fundamentals and Applications (Wiley, 2001).

[0238] Electrochemical impedance spectroscopy (EIS) was performed at open circuit and specific voltage by applying a sinusoidal signal with an amplitude of 10 mV in the frequency range of 100 kHz to 10 mHz. For temperature control during EIS measurements, an oven and a refrigerator were connected to the battery cycler. The activation energies of the various LiPS conversion processes were calculated using the charge transfer resistance (R ct ) was used to calculate the reciprocal of the charge transfer resistance (1 / R ct ) is the Arrhenius equation: k = Ae - E a / RT (where k is the rate constant, T is the absolute temperature, A is the frequency factor, E a was used to express the rate constants for calculating the activation energy of each SRR step according to (where is the activation energy of the reaction, and R is the universal gas constant). This method is also described in Ogihara et al., 2012.

[0239] Electrochemical measurements of the pouch cells were performed at 100% depth of discharge, similar to the coin cells. The energy density of the pouch cells at Ah level is given by the following formula: E 体積 =(C 面積 ×V) / ΣTi,E g =(C 面積 ×V) / Σ(m 面積 )i (where E 体積 and E g are the volumetric energy density and gravimetric energy density, respectively, and C 面積 is the areal capacitance, V is the nominal cell voltage (2.1 V), and T and m 面積 is the cathode, anode, and current collector (ρAl = 2.7 gcm -3 , ρCu=8.96gcm -3 ), separator (ρ=0.95gcm -3), electrolyte (ρ=1.0gcm -3 The thickness of the electrolyte was calculated using E 体積 5b and 5c, Table 7 - Pouch Cell C 面積 and C of Comparative Examples 1 to 10 shown in Table 8 - Pouch Cell Cycle Life 面積 , E 体積 and E g The values ​​of were collected from the literature or calculated in the same way based on reported values.

[0240] Results and Discussion Li as described in the Methods section above. x MoS2 films were prepared.

[0241] Example 1A Li x Morphology and properties of MoS2 Li x The mechanical properties of the MoS2 films were investigated.

[0242] Li x The MoS2 films exhibited considerable mechanical flexibility and strength, as shown in FIG. 1a.

[0243] A typical film (1 mg cm ) is shown in Fig. 1b. -2 Cross-sectional scanning electron microscope (SEM) images of the nanosheets (approximately 2.4 μm) show a compact layered structure in which the nanosheets are closely stacked.

[0244] In the X-ray diffraction (XRD) pattern shown in Figure 1c, a new peak was observed at about 7.8°, which corresponds to the (001) plane due to lithiation. In addition, compared to 2H MoS2, xThe (002) peak shifts to higher angles in MoS2, suggesting a smaller interlayer distance between the nanosheets. Without wishing to be bound by theory, this is believed to be due to the fact that the negatively charged 1T phase MoS2 nanosheets are attracted to the intercalated Li cations.

[0245] Li shown in Fig. 1d x The Raman spectrum of MoS2 shows the usual A 1g and E 1 2g In addition to the peaks in Fig. 1, the J1, J2, and J3 peaks characteristic of the metallic 1T phase are also shown.

[0246] As shown in Fig. 1e, using XXPS, the 1T phase concentration in the lithiated sample was found to be about 85%, which is higher than that of the non-lithiated 1T MoS2, which contains about 70% of the 1T phase.

[0247] Naked Li x Electrochemical lithium extraction measurements in lithium foil versus MoS2 film cells showed that Li x The lithium content in MoS2 was found to be about 0.7 (see Figure 6b). This content was first determined by adding a known excess of dilute HCl to the x This was further confirmed by back titration method where MoS2 was added and then the supernatant was titrated with standard NaOH to determine the exact excess.

[0248] Li x Thermogravimetric analysis of the MoS2 / S composite shows a sulfur content of 71.6 wt.%. x This coincides with the mass ratio of MoS2 to sulfur flowers added being 1:2.5 (see Figure 7).

[0249] Regarding the electrolyte wettability of the cathode surface, Li x MoS2 / S is shown in Figure 9a, and 2HMoS2 / S is shown in Figure 9b. x The contact angle of the electrolyte on MoS2 / S is 14°, whereas on 2HMoS2 / S it is 65°. xMoS2 / S improves the electrolyte wettability of the cathode surface. x MoS2 is more lyophilic than 2HMoS2, which may be due to its polarity, which is advantageous for reducing the electrode-electrolyte interfacial resistance of Li-S battery cathodes.

[0250] Additional Example 1B Characterization of 3R-NbS2 The 3R-NbS2 prepared in preparation 1.4 was characterized by X-ray diffraction (XRD). The XRD pattern shown in Figure 11 confirms that the NbS2 material is a metallic 3R phase. In particular, the peaks at approximately 14.8, 30.1, 45.7, 62.5, and 80.6 correspond to literature values ​​for single crystal XRD diffraction of 3R-NbS2 (see, for example, www.hqgraphene.com / 3R-NbS2.php).

[0251] Metallic NbS2 comprises stacked layers of metallic phase NbS2. The layers or sheets are stacked together with van der Waals forces acting between the sheets. Without wishing to be bound by theory, it is believed that the relatively weak interlayer forces facilitate intercalation between the metallic phase NbS2 layers.

[0252] Example 2 Li in Li-S coin cells x Electrochemical characterization of MoS2 cathode MoS2-based and NbS2-based cathodes were used as sulfur composites (Li x The lithium-ion batteries were fabricated (>70 wt.% sulfur) as Li-S coin cells with lithium metal anodes as described in the Methods section. The coin cells contained 12 μL mg -1 The high E / S ratio, excess lithium, and relatively low amount of active material (area sulfur loading 2.5 mg cm -2 , a total of 5 mg) was used.

[0253] Li xThe galvanostatic charge-discharge (GCD) curves of MoS2 / S, 1T MoS2 / S, 3R-NbS2 / S, and other reference 2H-MoS2 / S and 2H MoS2 / C / S cathodes show typical Li-S battery behavior with two characteristic discharge plateaus at 2.4 V (Li2S6 to Li2S4) and 2.1 V (Li2S4 to Li2S2 / Li2S), respectively, as shown in Figures 2a and 12.

[0254] The specific capacity of the coin cells was measured at 0.1C (see Table 3 - Specific Capacity of Coin Cells).

[0255] [Table 3]

[0256] Li x MoS2 / S cathode is 1425mAhg at 0.1C -1 The specific capacity was 364 mAhg for 2H MoS2. -1 ) and 2H MoS2 / C(728mAhg -1 ) at 0.1C. The 1T MoS2 cathode has a capacity of 1179mAhg -1 The 3R-NbS2 / S cathode showed a specific capacity of 1390 mAhg, which is also significantly higher than the cathodes made from 2H MoS2 and 2H MoS2 / C. -1 , which is higher than the reference 2H MoS2 cathode and slightly higher than the 1T MoS2 cathode (see Figure 12). x The MoS2 / S cathode exhibited a higher specific capacity than the NbS2 cathode at 0.1C.

[0257] In particular, this capacity is x This shows that the sulfur utilization rate of the MoS2 / S cathode is 85.2% (theoretical capacity with 100% sulfur utilization rate is 1672 mAhg -1 ). Furthermore, in these cathodes, Li xMoS2 showed the smallest polarization voltage gap under the same conditions, suggesting faster anode / cathode reactions during the charge / discharge process, which may be due to the improved electrocatalytic activity.

[0258] Furthermore, the specific capacity of the 3R-NbS2 / S electrode indicates a sulfur utilization rate of about 83%. The NbS2 cathode also exhibited a good polarization voltage gap.

[0259] Li x The MoS2 cathode exhibits improved rate capability with 67% capacity retention at 1C (shown in Fig. 2b), which also suggests improved Li-ion diffusivity and kinetics.

[0260] Li x The volumetric capacity and sulfur loading of the MoS2 cathode were compared with different reference cathodes (described in the electrochemical characterization section) as shown in Figure 2c. The values ​​of volumetric sulfur loading with the reference cathodes shown in Figure 2c were either collected from such references or calculated using the same method as described in the Examples section. The Li x MoS2 cathode: 667gL -1 This cathode has a volumetric sulfur loading of 950 AhL -1 It is possible to provide a volumetric capacity of

[0261] By reducing the amount of electrolyte added and confining the sulfur compactly, it is thought that the dissolution of lithium polysulfide (LiPS), which can cause capacity loss due to the shuttle effect, can be minimized. x The capacity retention at 1C, 500 cycles was measured for the MoS2 / S cathode, 1T MoS2, and the comparative cathode (see Figure 2d). x The capacity retention of the MoS2 cathode was 91%, which is higher than the 70% of the 1T MoS2, 47% of the 2H MoS2 / C, and 22% of the 2H MoS2 cathode.

[0262] Without wishing to be bound by theory, Lix The improved performance of MoS2 is attributed to the improved adsorption of LiPS, improved Li-ion diffusivity, and accelerated electrochemical reaction rate. These results lead to high electrocatalytic activity and Li x This results in high capacity and cycling stability for Li-S batteries with MoS2 cathodes, and is believed to minimize the dissolution of lithium polysulfide (LiPS), which can cause capacity loss due to the shuttle effect, by reducing the amount of electrolyte added and confining sulfur compactly.

[0263] Example 3 Li x Lithium polysulfide (LiPS) adsorption, Li-ion diffusivity and electrochemical reaction kinetics of MoS2 cathode Polysulfide adsorption measurements were carried out on different MoS2 hosts using Li2S4 solutions. As can be seen in the photograph in Figure 3a, Li x Most of the Li2S4 was adsorbed on the MoS2 host, and a clear solution was obtained compared to the other hosts. x The high affinity of the MoS2 host for LiPS was quantitatively confirmed by ultraviolet-visible (UVvis) spectroscopy (Fig. 3a).

[0264] Efficient adsorption of the Li2S4 product is important not only to facilitate the conversion process (increasing capacity) but also to minimize the shuttle effect (improving cycling stability). This is because the overall reaction of the Li-S battery (S8 + 16e - +16Li + ⇔8Li2S), of the 16 electrons that move, 12 electrons convert Li2S4 to Li2S (2Li2S4+12e - +12Li + ⇔8Li2S; balanced by an equal amount of sulfur). That is, 75% of the capacity comes from the conversion of Li2S4 to the final Li2S. This also corresponds to the largest discharge plateau at about 2.1 V (see Figure 2a), which usually takes the longest to proceed. The longer exposure of Li2S4 to the electrolyte than the other Li-S species means that there is a higher probability of Li2S4 dissolving and shuttle.

[0265] Li-ion diffusion coefficient (D Li ) was calculated from the cyclic voltammetry (CV) results using the Randles-Sevcik equation (as described in the Methods section). The CV curves show two cathodic and one anodic peaks (Fig. 3b), which correspond to the two discharge and one charge plateaus observed in the GCD curves in Fig. 2a.

[0266] The peak current at various sweep rates was used to measure the D of different cathodes. Li was extracted (Fig. 3c). x D of MoS2 cathode Li is 5.1×10-8cm 2 s -1 and 1T MoS2 cathode (3.0×10-8cm 2 s -1 ) was found to be 71% higher.

[0267] Without wishing to be bound by theory, this is believed to be because the Li intercalated between the metallic MoS2 nanosheets facilitates the diffusion of Li ions through the material. x D of MoS2 cathode Li As a result of the metallic 1T phase, 2H MoS2 / C (4.9×10-9 cm 2 ·s -1 ) is more than an order of magnitude higher than D Li This difference explains the difference in rate performance observed for the MoS2-based cathode (shown in Fig. 2b).

[0268] Li x The Li-ion diffusivity of the MoS2 cathode was also measured by electrochemical impedance spectroscopy (EIS) profiles, as shown in the Nyquist plot in Figure 3d. The large slope in the low frequency region suggests an enhanced ion diffusion behavior. Figure 3d shows the equivalent circuit used to fit the EIS profile. The resistive elements in the circuit are: R sis the combined internal resistance including the interfacial contact resistance between the material and the current collector, the ohmic resistance of the electrolyte, and the intrinsic resistance of the current collector; R 硫黄 is the sulfur deposition resistance caused by the deposition of insoluble LiPS on the electrode surface; R ct is the charge transfer resistance, which represents the resistance to the electrochemical reaction.

[0269] To clarify the electrochemical reaction kinetics, EIS was used to determine the activation energy (E a ) was investigated. The measurements were carried out at different temperatures and at the voltage where the important reaction occurs. The Nyquist plot at 2.1 V (where the important step of Li2S4 conversion occurs) is shown in Figure 3d. Fitting this curve to the equivalent circuit gives the Li x MoS2 cathode has the lowest internal resistance (R s ) and charge transfer resistance (R ct ) Then, using the Arrhenius equation, E a was calculated (Figure 3e). In the Arrhenius equation, the reciprocal of the charge transfer resistance (1 / R ct ) is used to represent the sulfur reduction reaction (SRR) rate because the reaction proceeds with charge transfer. E at different voltages a The values ​​are summarized in Figure 3f.

[0270] For each cathode, E at 2.4 V and 2.1 V a The reaction at 2.1 V, which corresponds to the Li2S4 to Li2S2 / Li2S conversion process, has the highest E value among all voltages. a This indicates that this is the rate-limiting step of the overall Li-S battery reaction. x MoS2 clearly has the lowest E among all polysulfide conversion processes. a For example, at 2.1 V, Li x E of MoS2 cathode a are about 34% and about 70% lower than those of 1T MoS2 and 2H MoS2, respectively.

[0271] This is Li xIt indicates that the LiPS adsorption is improved along with the enhanced Li-ion diffusivity and reaction rate of the MoS2 cathode.

[0272] Example 4 Li using a rotating disk electrode (RDE) system x Electrocatalytic sulfur reduction reaction (SRR) test of MoS2 cathode in Li2S4 solution The SRR characteristics of Li2S4 conversion were investigated by linear sweep voltammetry (LSV). The onset potentials are shown in Table 4 - Onset potentials of cathode materials measured by LSV and in Figure 4a.

[0273] [Table 4]

[0274] From the LSV curves in Fig. 4a, Li x The onset potential of MoS2 is 2.12 V, which is significantly higher than the onset potentials of 1T MoS2 (2.03 V), 2H MoS2 / C (1.95 V), and 2H MoS2 (1.91 V). x The overpotential of MoS2 is the lowest, indicating that the SRR has the highest electrocatalytic activity, which is also indicated by the higher half-wave potential and larger diffusion-limited current density (JD).

[0275] The Tafel slopes obtained from the LSV profiles were recorded and shown in Figure 4b. The slopes of the Tafel slopes are shown in Table 5 - Slopes of Tafel slopes measured by LSV.

[0276] [Table 5]

[0277] The slope of the Tafel slope indicates the kinetics and activity of the electrocatalyst, in the form of the potential required to increase the current density by an order of magnitude. x MoS2 is 1T MoS2 (168mVdec -1), 2H MoS2 / C(195mVdec -1 ), 2H MoS2 (227mVdec -1 ) is significantly smaller than the Tafel slope (66 mVdec -1 ), indicating higher electrocatalytic activity and reaction rate. This is due to the low E a Matches.

[0278] From the LSV curves in Fig. 4a, Li x It can be seen that the JD value of MoS2 is higher than that of other reference MoS2 hosts. Considering that equal loading masses of different materials were used in the measurements, Li x The larger current of MoS2 indicates that more electrons were transferred in the SRR process.

[0279] LSV measurements were performed at different rotation speeds (shown in Figure 4c), which show that the diffusion-limited current density increases with the angular velocity of the RDE.

[0280] The obtained JD is used to calculate the electron transfer number according to the Koutecky-Levich equation (as explained in the Methods section above). The electron transfer numbers of different MoS2 hosts are shown in Figure 4d and Table 6 - Electron transfer numbers of different cathodes.

[0281] [Table 6]

[0282] Li x The electron transfer number of MoS2 is about 10.6, which is larger than those of 1T MoS2 (8.7), 2H MoS2 / C (5.5), and 2H MoS2 (2.8). x This suggests that MoS2 has high electrocatalytic activity. Since a total of 12 electrons are transferred for the complete conversion of Li2S4 to Li2S, this electron transfer number of 10.6 corresponds to a conversion efficiency of 88.3%, which is in good agreement with the sulfur utilization of 85.1% obtained from the coin cell (mentioned above).

[0283] This is because Li x We show that MoS2 exhibits excellent electrocatalytic activity for SRR, enhanced Li-ion diffusivity, accelerated reaction rate, and improved LiPS adsorption that alleviates the shuttle effect. All these attributes are related to the Li x Improve the capacity, rate capability, and cycle stability of MoS2 cathode.

[0284] Example 5 Li x Performance of MoS2-based Li-S pouch cells A pre-optimized E / S ratio of 2.4 μL mg (as described in the Methods section) -1 Use Li x Pouch cells were fabricated using MoS cathodes and lithium metal anodes. Comparative pouch cells PC1-PC10 were fabricated according to the references listed in the Methods section.

[0285] In energy storage devices (e.g., pouch cell-level Li-S batteries and LIBs), the areal capacity (C 面積 ) is an important indicator of performance. 面積 The simplest way to increase the specific capacitance is to increase the areal sulfur loading. However, increasing the loading is usually accompanied by a slowing of ion diffusion across thick electrodes, resulting in a decrease in the specific capacitance and a consequent decrease in C. 面積 also decreases.

[0286] In the pouch cell of the embodiment, as shown in FIG. 5a, the sulfur loading was 7.5 mg cm -2 (The sulfur content in the cathode is constant at 71.4 mass%). 面積 is optimized to 8.21mAhcm -2 C 面積 It can be seen that the above results were obtained. Figure 5b and Table 7 - Pouch Cell C 面積 As shown in Figure 1, 8mAhcm -2 Exceeds C 面積 is superior to known Li-S pouch cells and exceeds the benchmark value of 3 mAhcm for commercial LIBs. -2As shown in Fig. 5b, the Li x MoS2-based pouch cells can provide up to 5mAcm -2 Even at a high current density of 4mAhcm -2 The battery maintains ultra-low charge and exhibits excellent rate capability, which corresponds to a fast charging process that is completed within an hour.

[0287] [Table 7]

[0288] Known Li-S batteries often have low capacities, less than 1 Ah total capacity, which is lower than is needed for practical power sources. For example, most commercially available batteries operate at capacity levels of 1-2 Ah or higher. It is therefore more meaningful to compare the energy densities of batteries operating at levels above 1 Ah.

[0289] The total capacity of the example Ah-level Li-S pouch cell (described in the Methods section above) is 1.33 Ah. This capacity is planned to be increased to over 2 Ah by using industrial manufacturing techniques and optimized configuration. For example, by stacking 10 layers of cathodes, a total capacity of 2.2 Ah can be achieved (as shown in FIG. 10c).

[0290] The energy density of the Ah-level pouch cell was measured and compared with that of a known LIB, Li-S battery, and lead-acid battery. The results are shown in Figure 5c. x MoS2-based pouch cell is 402Whkg -1 High gravimetric energy density of 721WhL -1 These energy densities are excellent for Li-S pouch cells, and are comparable to Li-S batteries from Oxis Energy and Sion Power, LiFePO4 (LFP, manufactured by BYD), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811, CATL), LiNi 0.6 Co 0.2 Mn 0.2O2 (NCM622, manufactured by LG), LiNi 0.8 Co 0.15 Al 0.05 This is superior to commercially available Li-S and LIB systems, including the O2 (NCA, Panasonic) LIB.

[0291] The gravimetric and volumetric energy densities were calculated for the pouch cells at the planned levels above 2 Ah achievable by industrial manufacturing techniques and optimized configuration (see FIG. 10d). This shows that after optimization, the gravimetric and volumetric energy densities are expected to increase by about 30% (E g =520Whkg -1 , E 体積 =940WhL -1 ).

[0292] The cycle life of the pouch cell was measured. The pouch cell showed a capacity retention of 85.2% after 200 cycles, which corresponds to a capacity loss of 0.074% per cycle. As shown in Table 8 - Cycle Life of Pouch Cell, this cycle stability is superior to that of known Li-S batteries. This cycle stability is also superior to that of commercial LIBs, which are designed to retain about 80% of their original capacity for 200 full charge cycles. Li x These results in MoS2-based Li-S pouch cells demonstrate many advantages as energy storage devices.

[0293] [Table 8]

[0294] References A number of publications have been cited above in order to more fully describe and disclose the present invention and the state of the art to which it pertains. Full citations for these references are set forth above. Each of these references is incorporated herein in its entirety.

Claims

1. A lithium-sulfur cell comprising a working electrode, a counter electrode, and an electrolyte, wherein the working electrode comprises: Formula (I): Li ａ MX ２ (I) (In the formula, a is 0 to 2.0; X is selected from S, Se and Te; M is a transition metal. a laminated layer of a metallic phase transition metal dichalcogenide (TMD); Sulfur or lithium (poly)sulfide 1. A lithium-sulfur cell comprising a membrane comprising:

2. A lithium-sulfur cell as described in claim 1, wherein the proportion of lithiated transition metal dichalcogenide in the metal phase is 60% to 100%, or 70% to 95%, or 80% to 90%.

3. 3. The lithium-sulfur cell of claim 1 or 2, wherein the TMDs are two-dimensional TMDs and the working electrode comprises stacked nanolayers or monolayers of the TMDs.

4. 10. The lithium-sulfur cell of claim 1, wherein the TMD is an exfoliated TMD.

5. 2. The lithium-sulfur cell of claim 1, wherein the TMD is prelithiated TMD, for example, a is 0.1 to 2.0, preferably 0.5 to 1.0, more preferably 0.6 to 0.

8.

6. 2. The lithium-sulfur cell of claim 1, wherein a is 0.

7. 2. The lithium-sulfur cell of claim 1, wherein X is S.

8. 2. The lithium-sulfur cell of claim 1, wherein M is selected from V, Nb, Mo, and W, or M is Mo or Nb.

9. Li ａ MX ２ 2. The lithium-sulfur cell of claim 1, wherein the mass ratio of Zn to sulfur is 1:2 to 1:

3.

10. The working electrode is (a) conductive carbon in an amount of 1% by weight or less, and / or (b) a binder in an amount of 1% by weight or less 10. The lithium-sulfur cell of claim 1, comprising:

11. 1. A method of making a lithium-sulfur cell, comprising: (a) exfoliating a transition metal dichalcogenide (TMD) to form a compound of formula (I): Li ａ MX ２ (I) (In the formula, a is 0 to 2.0; X is selected from S, Se and Te; M is a transition metal. providing a metallic phase TMD of (b) assembling a working electrode comprising a laminated layer of metallic phase TMD and a membrane comprising sulfur or lithium (poly)sulfide; (c) assembling a lithium-sulfur cell comprising a working electrode, a counter electrode, and an electrolyte; A method comprising:

12. 12. The method of claim 11, wherein step (a) comprises chemically stripping the TMD, for example by treating the TMD with an organolithium compound, preferably a butyllithium compound.

13. 12. The method of claim 11, wherein step (b) comprises forming a composite material of a transition metal dichalcogenide and sulfur.

14. 12. The method of claim 11, wherein step (b) comprises co-precipitating the transition metal dichalcogenide with sulfur, such as powdered sulfur.

15. In step (b), Li ａ MX ２ The method of claim 11, wherein the mass ratio of sulphur to sulphur is from 1:2 to 1:

3.

16. 12. The method according to claim 11, wherein a is between 0.5 and 1.0, preferably between 0.6 and 0.

8.

17. i) X is S; and / or ii) M is selected from V, Nb, Mo and W, preferably M is Mo; The method of claim 11.

18. 18. A lithium-sulfur cell obtained or obtainable by the method of any one of claims 11 to 17.

19. 10. The lithium-sulfur cell of claim 1 having a sulfur utilization of 80% or greater.

20. 10. The lithium-sulfur cell of claim 1, having a capacity retention rate of 80% or more at 200 cycles.

21. The area of ​​the working electrode with sulfur loading of 6 to 10 mg cm －２ 2. The lithium-sulfur cell of claim 1 , wherein

22. Cell weight energy density is 350Whkg －１ The lithium-sulfur cell of claim 1 .

23. The cell volume energy density is 650WhL －１ The lithium-sulfur cell of claim 1 .

24. A lithium-sulfur battery comprising one or more lithium-sulfur cells according to claim 1.

25. 25. A method of charging and / or discharging the lithium-sulfur cell of claim 1 or the lithium-sulfur battery of claim 24.

26. As a conductive substrate in the working electrode of a lithium-sulfur cell, Li ａ MX ２ (I) (In the formula, a is 0 to 2.0; X is selected from S, Se and Te; M is a transition metal. The use of metallic phase transition metal dichalcogenides.

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