CN110998933A

CN110998933A - Core-shell complexes

Info

Publication number: CN110998933A
Application number: CN201880050730.9A
Authority: CN
Inventors: 郑光远; 唐伟; 罗健平
Original assignee: Agency for Science Technology and Research Singapore; National University of Singapore
Current assignee: Agency for Science Technology and Research Singapore; National University of Singapore
Priority date: 2017-06-05
Filing date: 2018-06-05
Publication date: 2020-04-10
Also published as: SG11201911571PA; WO2018226158A1

Abstract

The present invention relates to a core-shell composite and a method for preparing the same, wherein the core-shell composite comprises a core of non-metallic particles having a hollow internal structure, the core being encapsulated in a shell of a transition metal chalcogenide. In a preferred embodiment, the core-shell composite is molybdenum disulfide (MoS)₂) Layer encapsulated hollow sulfur particles. In another embodiment, the core-shell composite may be used as a cathode material.

Description

Core-shell complexes

Cross Reference to Related Applications

The present application claims the benefit of singapore application No. 10201704587U filed on 5.6.2017, which is incorporated herein by reference.

Technical Field

The present invention generally relates to core-shell composites useful as cathode materials. The invention also relates to a method for preparing the core-shell composite and an electrode comprising the core-shell composite.

Background

With the electrification of transportation systems, the use of intermittent renewable energy sources such as solar and wind energy, there is a need to develop rechargeable batteries with higher energy density and lower cost. Lithium-sulfur (Li-S) batteries are considered to be one of the most promising approaches to overcome the above challenges, as

(1) The theoretical capacity of the sulfur cathode is high (1675 mAhg)^-1Based on the original sulfur); and is

(2) The natural abundance of sulfur is high.

However, practical application of Li-S batteries faces several obstacles, such as limited cycle life. This problem is mainly attributed to the intermediate product lithium polysulfide (Li)₂S_x，x>3) Dissolution into the electrolyte, large volume changes (-80%) of sulfur particles, destroying electrode structural integrity and sulfur and Li₂The insulating property of S. Efforts have been made to date to address these problems by trapping soluble lithium polysulphides.

To overcome the above problems, recent studies have involved the encapsulation of sulfur in ordered porous CMK-3 carbon, and the most common strategies have been implemented to encapsulate active sulfur within conductive matrices, such as meso/microporous/hollow carbon, carbon nanotubes/fibers, and conductive polymers, among others. Although improving performance, this physical structure can only partially mitigate polysulfide leakage due to incomplete encapsulation of sulfur. Functional groups have also been introduced as encapsulation building blocks to adsorb lithium polysulphides. In particular, well-designed polymers, functionalized graphene, and nitrogen-doped carbon matrices, among others, are used to achieve strong interactions between lithium polysulfides and polar surfaces. Similar strategies can be achieved by using hydrophilic metal oxides, sulfides, metal organic frameworks, and their derivatives as lithium polysulfide sorbents. However, to date, the above attempts do not appear to solve the above problems, such as complete encapsulation of sulfur in the cathode.

Accordingly, there is a need to provide suitable cathode materials that overcome or at least ameliorate one or more of the disadvantages described above.

Disclosure of Invention

In one aspect, a core-shell composite is provided, the core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide.

The transition metal chalcogenide may have a layered conformal cage structure. Advantageously, each layer of the conformal cage structure may be tightly bonded together by van der Waal's interaction, making the shell mechanically strong and stable while maintaining the morphology of the composite under extreme conditions, such as when subjected to vacuum. More advantageously, the strong van der waals interactions between transition metal chalcogenide layers enable the formation of sealed nanocages for trapping non-metallic particles.

More advantageously, the hollow structure of the core, together with the layered shell (with the aforementioned van der waals interactions), can be balanced against each other to accommodate any inward volume change when the core-shell composite is stressed. When the core-shell composite is used as an electrode material, the core-shell composite undergoes lithiation, which may cause the above-described stress. Thus, the hollow structure of the core can advantageously accommodate inward volume changes during lithiation.

In another aspect, a method is provided for preparing a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide, the method comprising the steps of:

a) mixing a suspension of surfactant-encapsulated non-metallic particles with a transition metal chalcogenide to combine the transition metal chalcogenide with the surfactant; and

b) removing the surfactant to obtain the core-shell complex.

In another aspect, an electrode is provided comprising a plurality of core-shell composites, wherein each composite comprises a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide.

Advantageously, the transition metal chalcogenide of the shell may be multilayered and capable of conforming to the shape of the core, and thus, the transition metal chalcogenide may be considered to have a "layered conformal cage". The transition metal chalcogenide may exhibit good bonding with lithium polysulfide in the core, thereby preventing the intermediate product lithium polysulfide (Li)₂S_x，x>3) Dissolving into the electrolyte. Further advantageously, the core particle may not have any significant volume expansion upon lithiation. As noted above, the transition metal chalcogenide or transition metal dichalcogenide may comprise a multilayered sheet, wherein the sheet may be nano-sized (hence referred to as a nanosheet). The sheet (or nanoplatelets) may have atomic defects. Advantageously, the presence of the above-mentioned atomic defects may promote the interaction between the lithium polysulphides and the core of the complex, when the lithium-sulphide battery undergoes charge-discharge cycles, thus reducing the degradation of the non-metal constituting the core.

Definition of

The following words and terms used herein shall have the indicated meanings:

as used herein, the term "composite" or "composite material" refers to a material system consisting of a mixture or combination of two or more micro-or macro-components that differ in form and chemical composition and are substantially insoluble in each other.

As used herein, the term "encapsulate" refers to the formation of one or more layers of shell material on the surface of a core particle. The encapsulation method is used to avoid dissolution of the core particles in a solvent such as an electrolyte. In addition, such encapsulation also serves to protect the core particle from degradation, for example, when the core particle is exposed to extreme conditions such as high vacuum.

As used herein, the term "exfoliation" refers to the detachment and exfoliation of one or more layers of the transition metal chalcogenide from the bulk of the transition metal chalcogenide.

The word "substantially" does not exclude "completely", e.g., a composition that is "substantially free" of Y may be completely free of Y. The word "substantially" may be omitted from the definition of the invention, if necessary.

Unless otherwise specified, the term "comprising" and grammatical variations thereof is intended to mean "open" or "inclusive" language such that they include the recited elements but also allow for inclusion of additional, unrecited elements.

As used herein, the term "about" in the context of concentrations of ingredients of a formulation generally refers to +/-5% of the stated value, more generally +/-4% of the stated value, more generally +/-3% of the stated value, more generally +/-2% of the stated value, and even more generally +/-1% of the stated value. Even more typically +/-0.5% of the value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It is to be understood that the description of the range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Thus, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as 1 to 6 should be considered to specifically disclose sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as individual numbers within that range such as 1, 2, 3, 4, 5, 6. The interpretation applies regardless of the breadth of the range.

Certain embodiments may also be broadly and generically described herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Detailed Description

Exemplary, non-limiting embodiments of core-shell composites comprising a core of non-metallic particles having a hollow interior structure encapsulated in a shell of a transition metal chalcogenide will now be disclosed.

A transition metal chalcogenide as defined herein may have a layered conformal cage structure. Each layer of the conformal cage structure may be bonded together by van der waals interactions. The layers are advantageously tightly bonded to each other due to van der waals interactions between the layers, such that the shell is mechanically strong and stable while maintaining the morphology of the composite under extreme conditions (e.g., when subjected to vacuum). Strong van der waals interactions between transition metal chalcogenide layers may allow formation of a sealed nanocage for trapping non-metallic particles.

As noted above, the hollow structure of the core, together with the layered shell (with the aforementioned van der waals interactions), can balance each other to accommodate any inward volume change when the core-shell composite is stressed. When the core-shell composite is used as an electrode material, the core-shell composite undergoes lithiation, which may cause the above-described stress. Thus, the hollow structure of the core can advantageously accommodate inward volume changes during lithiation.

The non-metallic particles of the core-shell composite as described above may be sulfur particles, silicon particles, phosphorus particles, or oxides thereof.

The transition metal in the transition metal chalcogenide as defined herein may be selected from the elements of groups 3 to 11 of the periodic table of elements. Non-limiting examples of such transition metals include zinc (Zn), titanium (Ti), vanadium (V), zirconium (Zr), chromium (Cr), molybdenum (Mo), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and tungsten (W). Other suitable transition metal elements not shown here may also be used.

The transition metal chalcogenide may be a transition metal monothio compound, a transition metal dichalcogenide, or a transition metal trichalcogenide. Non-limiting examples of transition metal monothio compounds include ZnX and CdX, where X is sulfur (S), selenium (Se), or tellurium (Te). Thus, such transition metal monochalcogenides may be referred to as zinc sulfide, zinc selenide, zinc telluride, cadmium sulfide, cadmium selenide, and cadmium telluride, respectively.

The transition metal dichalcogenide may be of the formula MX₂Wherein X is similar to the above definition. Non-limiting examples of transition metal dichalcogenides include MoSe₂、WSe₂、NiSe₂、CoSe₂、TiSe₂、MoS₂、WS₂、NiS₂、CoS₂、TiS₂、MoTe₂、WTe₂、NiTe₂、CoTe₂And TiTe₂. It should be understood that other suitable transition metal dichalcogenides may also be used as the shell material.

As mentioned above, transition metal trithionic compounds may also be used as shell materials.

It should be understood that each transition metal chalcogenide may have a particular stoichiometry due to the electronic structure in the transition metal chalcogenide. Thus, for a given transition metal chalcogenide, it may not exist in all of the forms described above, i.e., in the form of transition metal monothiogens, transition metal dichalcogenides, and transition metal trithiogens. For the sake of clarity, for example zinc sulphide, only as ZnS, not as ZnS₂Or ZnS₃Are present. Furthermore, only MoS can be present₂And MoS₃In form, but not as MoS.

The transition metal chalcogenide, which may be a transition metal monothio compound, a transition metal dichalcogenide compound, or a transition metal trichalcogenide compound, may be present in its crystalline form, amorphous form, or mixtures thereof. In preferred embodiments, the transition metal dichalcogenide may be in its crystalline form, amorphous form, or mixtures thereof.

The transition metal chalcogenide may have at least one layer of sheet. When the transition metal chalcogenide has at least two layers of sheets, such transition metal chalcogenide may take a layered structure and thus may be referred to as a layered transition metal chalcogenide. Thus, the transition metal monothio compounds, transition metal dichalcogenides, and transition metal trichalcogenides may be in the form of layered transition metal monothio compounds, layered transition metal dichalcogenides, and layered transition metal trichalcogenides, respectively.

In one embodiment, transition metal chalcogenides such as transition metal dichalcogenides may comprise multilayered sheets, wherein the sheets may be nano-sized (hence referred to as nanosheets). The sheet (or nanoplatelets) may have atomic defects. Defects may be generated during the exfoliation of the sheet or nanoplatelets. The presence of atomic defects in the sheet (or nanoplatelets) can make the core-shell composite, as defined herein, strong and stable. Delamination of the bulk transition metal dichalcogenide may occur due to increased spacing between the multilayered sheets. As will be further noted below, the increased spacing may be caused by the method used to form the core-shell composite.

As noted above, the layered transition metal chalcogenide, such as a layered transition metal dichalcogenide, may be a single layer, a bilayer, or a multilayer transition metal dichalcogenide. For the avoidance of doubt, the layered transition metal dichalcogenide may have 2, 3, 4, 5, 6, 7, 8, 9 or 10 layers. Preferably, the layered transition metal dichalcogenide has 4 to 10 layers, more preferably 5 to 7 layers.

The interlayer spacing of the layered transition metal chalcogenide, such as layered transition metal dichalcogenide, may be in the range of about 0.3nm to about 2nm, such as about 0.3nm to about 0.5nm, about 0.3nm to about 0.8nm, about 0.3nm to about 1nm, about 0.3nm to about 1.5nm, about 0.5nm to about 0.8nm, about 0.5nm to about 1nm, about 0.5nm to about 1.5nm, about 0.5nm to about 2nm, about 0.8nm to about 1nm, about 0.8nm to about 1.5nm, about 0.8nm to about 2nm, about 1nm to about 1.5nm, about 1nm to about 2nm, or about 1.5nm to about 2 nm. The interlayer spacing between the layers of the layered transition metal chalcogenide is preferably from about 0.5nm to about 0.8nm, more preferably from about 0.6nm to about 0.7 nm.

The core-shell composite as defined above may be structurally stable when placed under high vacuum for extended periods of time. As used herein, the term "high vacuum" refers to a pressure of about 10^-4Pascal (Pa) to about 10^-9A range between Pa, e.g. about 10^-4Pa, about 10^-5Pa, about 10^-6Pa, about 10^-7Pa, about 10^-8Pa, about 5X 10^-9Pa, about 2X 10^-9Pa or about 10^-9Vacuum condition of Pa. As used above, "longer period of time" refers to a period of time from about 1 minute to about 5 hours, such as about 1 minute, about 5 minutes, about 10 minutes, about 30 minutes, about 1 hour, about 2 hours, about 3 hours, about 4 hours, or about 5 hours.

The sealing structure of the shell may be capable of protecting the inner core from degradation or phase change, such as sublimation. Thus, advantageously, the core-shell composite can increase the sublimation temperature of the core particle.

The mass loading of the non-metallic particles in the core-shell composite can range from about 40 wt% to about 90 wt%, such as about 40 wt%, about 45 wt%, about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt%, about 70 wt%, about 75 wt%, about 80 wt%, about 85 wt%, or about 90 wt%. The mass loading of the non-metallic particles in the core-shell composite is preferably in the range of about 60 wt% to about 90 wt%.

Furthermore, the core-shell composite as defined above may be a regularly shaped particle, such as a spherical particle, or an irregularly shaped particle.

The particle size of the core-shell composites as defined herein may be in the range of about 50nm to about 5000nm (or about 5 μm), such as about 50nm to about 100nm, about 50nm to about 200nm, about 50nm to about 500nm, about 50nm to about 800nm, about 50nm to about 1000nm, about 50nm to about 2000nm, about 50nm to about 3000nm, about 50nm to about 4000nm, about 100nm to about 200nm, about 100nm to about 500nm, about 100nm to about 800nm, about 100nm to about 1000nm, about 100nm to about 2000nm, about 100nm to about 3000nm, about 100nm to about 4000nm, about 100nm to about 5000nm, about 500nm to about 800nm, about 500nm to about 1000nm, about 500nm to about 2000nm, about 500nm to about 3000nm, about 500nm to about 4000nm, about 500nm to about 5000nm, about 1000nm to about 2000nm, about 3000nm to about 3000nm, about 2000nm, about 3000nm, about 1000 to about 2000nm, about 3000nm, From about 2000nm to about 5000nm, from about 3000nm to about 4000nm, from about 3000nm to about 5000nm, or from about 4000nm to about 5000 nm. Particle size may refer to the diameter or equivalent diameter of an irregularly shaped composite.

The particle size of the core-shell composites as defined herein is preferably in the range of about 100nm to about 1000nm (or about 1 μm), more preferably in the range of about 300nm to about 800 nm.

Thus, with respect to the above aspects, there is also provided a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide, wherein the core is partially or fully (or completely) encapsulated by the shell.

Exemplary, non-limiting embodiments of methods for making a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide will now be disclosed.

There is provided a process for preparing a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide, the process comprising the steps of:

b) the surfactant is removed to obtain the core-shell complex.

The above method can be considered as a self-assembly process in which spontaneous recombination occurs without an external stimulus or initiator due to the binding between the surfactant and the transition metal chalcogenide. When the surfactant is removed, such as in step (b), the transition metal chalcogenide may be considered as a shell that at least partially encapsulates the core of the non-metallic particle having a hollow interior structure. Thus, the shell of the transition metal chalcogenide may substantially entirely or completely encapsulate the core of the non-metallic particle having a hollow interior structure.

The transition metal chalcogenide used in the above method may be a exfoliated transition metal chalcogenide. Accordingly, there is also provided a process for preparing a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, the core of the non-metallic particles being encapsulated in a shell of a transition metal chalcogenide, the process comprising the steps of:

a) mixing a suspension of surfactant-encapsulated non-metallic particles with a exfoliated transition metal chalcogenide to combine the exfoliated transition metal chalcogenide with the surfactant; and

b) the surfactant is removed to obtain the core-shell complex.

Similar to the above, this method can be considered as a self-assembly process in which spontaneous recombination occurs without an external stimulus or initiator due to the bonding between the surfactant and the exfoliated transition metal chalcogenide. When the surfactant is removed, such as in step (b), the exfoliated transition metal chalcogenide may be considered as a shell that at least partially encapsulates the core of the non-metallic particle having a hollow interior structure. Thus, the shell of the exfoliated transition metal chalcogenide may substantially entirely or completely encapsulate the core of the non-metallic particle having a hollow interior structure.

The non-metallic suspension may be highly dispersed, such as monodisperse. As mentioned above, the non-metallic particles may be sulphur particles, silicon particles, phosphorus particles or oxides thereof.

The methods described herein may further comprise: before the mixing step (a), steps a-i) mix the nonmetallic precursor with a surfactant under conditions of a suitable temperature and a suitable medium.

Specifically, the surfactant-encapsulated non-metallic suspension may be prepared by mixing the non-metallic precursor with the surfactant in a suitable medium at room temperature, such as about 20 ℃ to about 30 ℃, and then adding the acid to form a mixture. The room temperature can be about 20 ℃, about 21 ℃, about 22 ℃, about 23 ℃, about 24 ℃, about 25 ℃, about 26 ℃, about 27 ℃, about 28 ℃, about 29 ℃ or about 30 ℃. The mixture is then stirred at room temperature for about 1 to 3 hours (e.g., about 1 hour, about 2 hours, or about 3 hours) to provide a solid product.

Thus, steps a-i) of the methods described herein may further comprise: step a-ii) adding an acid to the mixture obtained from step a-i).

The step of preparing the surfactant encapsulated non-metallic suspension may be performed in a single step at room temperature. Thus, it will be appreciated that this step can be scaled up industrially. The solid product containing the surfactant-encapsulated non-metallic particles can be separated from the reaction medium using suitable separation techniques known in the art. Non-limiting examples of separation techniques used herein are filtration and centrifugation.

The surfactant-encapsulated non-metallic particles obtained from this step may be redispersed in a suitable medium and collected again by a suitable separation technique. Finally, the surfactant encapsulated non-metallic particles obtained from this step may be re-dispersed in distilled water to provide a surfactant encapsulated non-metallic suspension for further use. The concentration of the surfactant encapsulated non-metallic suspension may be about 1mg mL^-1To about 6mg mL^-1E.g. about 1mg mL^-1About 2mg mL^-1About 3mg mL^-1About 4mg mL^-1About 5mg mL^-1Or about 6mg mL^-1Preferably about 4mg mL^-1。

The nonmetallic precursor used to prepare the above-described surfactant-encapsulated nonmetallic suspension may be selected from salts, solvates, or hydrates of the nonmetallic precursor. If surfactant encapsulated sulfur particles are desired, a sulfur-containing salt, such as sodium thiosulfate, can be used. It is to be understood that the sulfur-containing salts provided herein are not limiting and thus can be extended to other suitable sulfur-containing salts.

In the above method, the acid may be selected from weak acids, strong acids, organic acids or inorganic acids. Preferred acids are strong acids, more preferred acids are strong mineral acids such as hydrochloric acid.

Suitable media may be selected from organic solventsAn agent, an aqueous solution or a mixture of an organic medium and an aqueous medium forming a single phase, preferably an aqueous medium of polyvinylpyrrolidone (PVP) solution. When PVP is used, its concentration in solution may be about 0.1M (1M ═ 1mol L)^-1) To about 1M, such as about 0.1M, about 0.2M, about 0.3M, about 0.4M, about 0.5M, about 0.6M, about 0.7M, about 0.8M, about 0.9M, about 1M, preferably about 0.4M.

Furthermore, when a PVP solution is used, the molecular weight of the PVP may be in the range of about 30000Da to about 100000Da, such as about 30000Da, about 40000Da, about 50000Da, about 60000Da, about 70000Da, about 80000Da, about 90000Da or about 100000 Da.

The transition metal chalcogenide or exfoliated transition metal chalcogenide may be prepared by contacting a transition metal chalcogenide with a lithium precursor to form a transition metal chalcogenide or exfoliated transition metal chalcogenide. For the avoidance of doubt, steps a-iii) may be carried out to contact the transition metal chalcogenide with a lithium precursor to form a exfoliated transition metal chalcogenide prior to step (a) of the process described herein. The lithium precursor used may be an organolithium solution as defined below.

The transition metal chalcogenide or exfoliated transition metal chalcogenide may be prepared by lithium intercalation or other suitable methods. When lithium intercalation is used, the transition metal chalcogenide crystals may be dissolved in an organolithium solution in an anhydrous organic solvent under an inert atmosphere to produce Li_x-a transition metal chalcogenide. This product can be recovered with an anhydrous organic solvent through a separation-washing cycle to remove excess lithium and organic residues. The product may then be dried, redissolved in an aqueous medium, and sonicated for about 30 minutes to about 2 hours, such as about 30 minutes, about 60 minutes, about 90 minutes, or about 2 hours, to allow the exfoliation process to occur. The peeling may occur partially or completely. However, it should be understood that complete stripping is desirable.

Li can be achieved by inserting solvent molecules such as water molecules into van der Waal's layers_x-exfoliation of transition metal chalcogenides. Insert water moleculeTo mean forced hydration of lithium intercalation into the transition metal chalcogenide. The exfoliated transition metal chalcogenide suspension may be collected for further use at a concentration of about 0.5mg mL^-1To about 4mg mL^-1In a range of (1), such as about 0.5mg mL^-1About 1mg mL^-1. About 1.5mg mL^-1About 2mg mL^-1About 2.5mgmL^-1About 3mg mL^-1About 3.5mg mL^-1Or about 4mg mL^-1。

The core-shell composite as defined herein may be prepared by mixing the surfactant-encapsulated non-metallic suspension and the exfoliated transition metal chalcogenide suspension with agitation for about 30 minutes to about 2 hours, such as about 30 minutes, about 60 minutes, about 90 minutes, or about 2 hours. The core-shell complex may be collected by at least 3 separation-washing cycles. Thus, the separation-washing cycle may suitably be repeated at least 3, 4, 5, 6, 7, 8, 9, 10 or more times. The separation-washing step can remove surfactants and impurities. The exfoliated transition metal chalcogenide (which may be in the form of a flake) may compact and encapsulate the core after removal of surfactants and impurities. Thus, when the core-shell complex is formed, the complex may be free of solvents or impurities, such as water molecules.

Non-limiting examples of the organolithium solution include a butyllithium solution, a pentyllithium solution, or a hexyllithium solution, and preferably a butyllithium solution. In one embodiment, the organic solvent used may be selected from N-methyl-2-pyrrolidone, pentane, hexane, heptane or octane. In another embodiment, inert atmosphere may refer to an atmosphere substantially free of oxygen or oxidizing agents, and thus may refer to an atmosphere under nitrogen or argon. In one embodiment, the drying process may be performed using a suitable drying technique. Non-limiting examples of drying techniques include vacuum and heat.

The exfoliated transition metal chalcogenide may be as described above. The exfoliated transition metal chalcogenide may be in the form of a sheet or sheet. The lateral dimension of the lamellae as described above may be in the range of about 200nm to about 2 μm (or 2000nm), such as about 200nm to about 400nm, about 200nm to about 600nm, about 200nm to about 800nm, about 200nm to about 1000nm, about 200nm to about 1500nm, about 400nm to about 600nm, about 400nm to about 800nm, about 400nm to about 1000nm, about 400nm to about 1500nm, about 400nm to about 2000nm, about 600nm to about 800nm, about 600nm to about 1000nm, about 600nm to about 1500nm, about 600nm to about 2000nm, about 800nm to about 1000nm, about 800nm to about 1500nm, about 800nm to about 2000nm, about 1000nm to about 1500nm, about 1000nm to about 2000nm, or about 1500nm to about 2000 nm. Such transverse dimension refers to the dimension of one or more faces of the sheet.

When the nonmetal suspension is mixed with the exfoliated transition metal chalcogenide compound and then subjected to a separation-washing cycle as described above, flakes of the exfoliated transition metal chalcogenide compound may adhere or bond to the surfactant on the surface of the hollow structure of the nonmetal particles and may be stacked together due to van der Waal's attraction. The exfoliated transition metal chalcogenide flakes may encapsulate (or at least partially encapsulate) the hollow structure of the non-metallic particles after removal of the surfactant. Due to electrostatic interaction, the flakes can encapsulate the hollow structure of the non-metallic particles. The surfactant is then removed during the separation-wash cycle, as the surfactant is soluble in the solution.

Suitable surfactants used may be polymers containing hydrophilic groups selected from polyvinylpyrrolidone, polyvinylpyridine, polyvinylimidazole, preferably polyvinylpyrrolidone, or non-polymeric surfactants such as sodium stearate or dodecylbenzene sulfonate.

Exemplary, non-limiting embodiments of electrodes comprising a plurality of core-shell composites will now be disclosed, wherein each composite comprises a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide.

The transition metal chalcogenide may have a layered conformal cage structure. As described above, each layer of the conformal cage structure may be bonded together by van der Waals interactions.

Electrodes comprising various core-shell composites as defined above may be used for lithium-sulfide electricityAnd (4) a pool. Advantageously, the layered conformal cage of transition metal chalcogenides exhibits good bonding with lithium polysulfide, thereby preventing intermediate lithium polysulfide (Li)₂S_x，x>3, such as 4, 5, 6, 7, 8, 9 or 10) is dissolved into the electrolyte. Further advantageously, upon lithiation, the core particle does not have any significant volume expansion.

As noted above, the transition metal chalcogenide or transition metal dichalcogenide may comprise a multilayered sheet, wherein the sheet may be nano-sized (hence referred to as a nanosheet). The sheet (or nanoplatelets) may have atomic defects. Advantageously, the presence of the above-mentioned atomic defects promotes the interaction between the lithium polysulphides and the core of the complex when the lithium-sulphide battery undergoes charge-discharge cycles, thereby reducing the degradation of the non-metal constituting the core.

In one embodiment, the loading mass of the core-shell composite loaded into the electrode may be about 0.5mg cm^-2To about 10mg cm^-2E.g. about 0.5mg cm^-2To about 1mg cm^-2About 0.5mg cm^-2To about 2mg cm^-2About 0.5mg cm^-2To about 5mg cm^-2About 1mg cm^-2To about 2mg cm^-2About 1mg cm^-2To about 5mg cm^-2About 1mg cm^-2To about 10mg cm^-2About 2mg cm^-2To about 5mg cm^-2About 2mg cm^-2To about 10mg cm^-2Or about 5mg cm^-2To about 10mg cm^-2。

The electrodes may be prepared according to methods known in the art, except that the material of the electrode is replaced with the core-shell composite disclosed herein. For example, the electrode may be prepared by mixing Vapor Grown Carbon Fiber (VGCF) and polyvinylidene fluoride (PVDF) binder with a core-shell composite in N-methyl-2-pyrrolidone (NMP) to form a slurry. The slurry can be coated onto a copper foil and dried under vacuum overnight.

In one embodiment, the electrode may be used in a battery. The battery may be used in electric vehicles and stationary storage systems. In one embodiment, the electrode can achieve up to about 1660mAhg^-1High specific capacity of (2).The specific capacity may be a discharge capacity. Advantageously, the electrodes can achieve about 500mAhg when charged/discharged at higher rates such as 3C and 5C, respectively^-1To 600mAhg^-1And about 300mAhg^-1To 450mAhg^-1The discharge capacity of (2).

An electrode as defined herein may have long term stability, 1000 cycles at 1C, with a decay of about 0.049% per cycle. Improved electrochemical performance can be observed by discharging the capacity with a current in the range of about 0.1C to about 5C.

As will be appreciated by those skilled in the art, significant problems associated with the practical application of Li-S batteries include the intermediate product lithium polysulfide (Li)₂S_x，x>3) Dissolution into the electrolyte, large volume change of sulfur particles and destruction of electrode structural integrity and sulfur and Li₂The insulating properties of S can be addressed by the disclosure including the invention shown in the examples provided.

Drawings

The drawings illustrate the disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

FIG. 1 shows a schematic view of a

[ FIG. 1 ] A]Is a MoS as described in example 1₂A plurality of images and graphs obtained from characterization of the sheeting. FIG. 1A: MoS₂Scanning Transmission Electron Microscope (STEM) images of the flakes, field of view (FOV)2048 nm; FIG. 1B: MoS₂High resolution STEM images of the lamella, FOV 16 nm; FIG. 1C: MoS₂Atomic STEM image of the flake, FOV 2.5 nm; FIGS. 1D-1F: images from simulation, indicating MoS₂Sulfur vacancy based defects on the flakes. The FOV of FIG. 1D is 1.5 nm; FIG. 1G: vapor Grown Carbon Fiber (VGCF), reduced graphene oxide (rGO), and MoS₂Flakes with 0.005mol L^-1Li of (2)₂S₉A digital image of the solution mixture; FIG. 1H: with Li₂S₉Solution treated MoS₂Raman spectra of the flakes (labeled regions are magnified in fig. 1I).

FIG. 2

[ FIG. 2 ]]Is MoS before and after treatment with 1-undecanethiol as described in example 1₂Fourier transform infrared spectroscopy (FTIR) spectroscopy. The figure also depicts CH₂Asymmetric telescopic, CH₂Symmetrically telescopic, CH₂Characteristic bands of shear and C-S stretch.

FIG. 3

[ FIG. 3 ]]Is a MoS as described in example 1₂And MoS treated with 1-undecanethiol₂(blocked MoS)₂) With 0.005M Li₂S₉A mixed digital image.

FIG. 4

[ FIG. 4 ]]Is a description of the step (a) synthesis procedure and step (b) MoS set forth in example 2₂Schematic representation of lithiation/delithiation process of cage-encapsulated hollow sulfur spheres. FIG. 4A depicts a MoS₂The whole process of the cage-encapsulated hollow sulfur spheres (synthesis process and lithiation/delithiation process). The arrows depict the MoS substantially encapsulating hollow sulfur spheres (or cores)₂A cage; FIG. 4B shows that soluble lithium polysulfides can be effectively trapped in MoS₂Inside the cage. The figure shows the MoS as shown in FIG. 4A₂An enlarged version of the cage-encapsulated hollow sulfur spheres (arrows depict MoS's that substantially encapsulate the hollow sulfur spheres (or sulfur cores)₂A cage).

FIG. 5

[ FIG. 5 ]]Is a MoS as described in example 2₂Characterization of cage-encapsulated hollow sulfur spheres a plurality of Scanning Electron Microscope (SEM) images were obtained. FIGS. 5A-5D: MoS with magnification of 100x, 10000x, 75000x and 65000x respectively₂SEM image of @ S complex; FIG. 5E: SEM image of sulfur ball, magnification is 20000 x; and FIG. 5F: mixing MoS₂Hollow MoS after sulfur removal in cage-encapsulated hollow sulfur spheres₂SEM image of the skeleton at magnification 20000 x.

FIG. 6

[ FIG. 6 ]]Is a MoS as described in example 2₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex) of the sample. FIG. 6A: MoS₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S Complex) Transmission Electron microscope (STEM)) Image, magnification 87000 ×; FIG. 6B: MoS₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex) at a magnification of 87000 x; FIG. 6C: MoS₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S composite) energy dispersive X-ray (EDX) line scans; FIGS. 6D-6F: MoS at magnifications of 435000x (D), 435000x (E) and 620000x (F), respectively₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex); FIGS. 6G-6I: MoS with magnification of 87000x (G), 40000x (H) and 435000x (F), respectively₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex) showing MoS₂The layered stack of cages remains continuous throughout the bending zone.

FIG. 7

[ FIG. 7 ]]Is the MoS described in example 2₂@ S Complex and MoS₂A plurality of charts and tables of EDX analysis of empty cages.

FIG. 8

[ FIG. 8 ]]Is MoS₂Multiple X-ray powder diffraction (XRD) patterns of the @ S complex. Fig. 8B is an enlarged XRD pattern of the marked area of fig. 8A.

FIG. 9

[ FIG. 9 ]]Is a MoS as described in example 2₂@ S composite, pristine sulfur spheres and pristine MoS₂A thermogravimetric analysis (TGA) of (a).

FIG. 10 shows a schematic view of a

[ FIG. 10 ]]Is a MoS as described in example 3₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex) are obtained. FIG. 10A: MoS₂The charge/discharge curves of the @ S complex at different rates; FIG. 10B: MoS₂The circulating capacity of the @ S compound under different multiplying powers; FIG. 10C: MoS₂The long-term cycling ability at 0.5C of @ S composite, rGO (rGO @ S) mixed with sulfur spheres, and original sulfur spheres; FIG. 10D: MoS₂Long-term cycling ability of the @ S complex at 1C; FIG. 10E: based on MoS₂The @ S digital image demonstrating the soft-package battery; FIG. 10F: using MoS-based₂The @ S digital image demonstrating that the soft package battery supplies power to the LED lamp; FIG. 10G: using MoS-based₂Demonstration of @ SAnd the digital image shows that the soft package battery supplies power for the small electric fan.

FIG. 11

[ FIG. 11 ]]Is prepared from MoS before and after lithiation as described in example 4₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S complex) of the sample. FIG. 11A: with loading of MoS₂A digital image of a pouch cell of a glassy carbon substrate of @ S; fig. 11B and 11C: MoS before lithiation₂SEM images of @ S complex at 50000x and 10000x magnification, respectively; fig. 11D and 11E: MoS after lithiation₂SEM images of @ S complex at 50000x and 10000x magnification, respectively; FIG. 11F: MoS before and after lithiation₂@ S particle size statistics.

Examples

Non-limiting examples of the present invention and comparative examples will be further described in more detail by referring to specific examples, which should not be construed as limiting the scope of the present invention in any way.

Example 1: defect modified MoS₂Solution stripping and characterization of flakes

In order to obtain highly dispersed single/multilayer MoS₂Aqueous suspension of flakes, first of all, commercially available MoS₂The powder is intercalated with lithium to form Li_xMoS₂Which is then easily exfoliated by forced hydration with the aid of sonication. As can be seen in the Scanning Transmission Electron Microscope (STEM) image shown in FIG. 1A, a typical MoS₂The thickness of the sheet ranges from a single layer to multiple layers, with transverse dimensions of up to several microns. Typical void defects generated during the lift-off process may be in the MoS₂Clearly observed on the sheets (see fig. 1B). Based on the expanded and simulated STEM images, these defects were shown to have a high concentration of sulfur vacancies (see fig. 1C and 1D).

To detect Li₂S_xTo MoS₂Chemisorption of the flakes to produce 0.005mol L^-1Li₂S₉DOL/DME (1:1v/v) solution and with MoS₂The powders were mixed in an argon-filled glove box (DOL: 1, 3-dioxolane, available from St.Louis, Mo., USAgamma-Aldrich (Sigma-Aldrich); DME: dimethyl ether, available from Sigma-Aldrich of st louis, missouri, usa. As shown in FIG. 1G, yellow Li₂S₉The solution is mixed with a small amount of MoS₂Complete decolorization upon flake powder mixing, indicating MoS₂Flake pair Li₂S_xThe chemical adsorption of (A) is strong. With Li₂S₉After solution treatment, MoS₂Raman spectrum of the flake powder showed 198cm^-1、225cm^-1And 490cm^-1Centered on a new broad peak, they are very close to the characteristic absorbance of the S — S bond in lithium polysulfides (see fig. 1H).

Typical MoS₂Red shift in absorbance to Li₂S_x-MoS₂Evidence is provided for complex formation (see figure 1I). In contrast, no Li was observed after mixing with Vapor Grown Carbon Fiber (VGCF) called conductive additive₂S₉A distinct color change of the solution. When mixed with similar amounts of rGO powder (which has been used as a lithium polysulfide blocker), only slight color decay was observed, indicating that lithium polysulfide vs MoS compared to reduced graphene oxide (rGO) powder₂The capturing of flake powder is more efficient. Lithium polysulfide to MoS₂The strong chemisorption of the flakes was attributed to MoS₂The sulfur vacancy concentration on the flakes is high. To further demonstrate this, 1-undecanethiol (which has been shown to compensate for sulfur vacancies via sulfhydryl groups) was used to block MoS₂Sulfur vacancies in the flakes (see fig. 2). Furthermore, blocking sulfur vacancies significantly reduces lithium polysulfide to MoS as shown in fig. 3₂Binding on the flakes, indicating lithium polysulfide to MoS₂The chemisorption of sulfur vacancies on the flakes was strong.

Example 2: MoS₂Synthesis and characterization of cage-encapsulated hollow sulfur spheres

In addition to the strong chemisorption of lithium polysulfides to sulfur vacancies, the effective physical confinement of sulfur can also enable strong trapping of lithium polysulfides and effective accommodation of outward volume expansion during lithiation. MoS₂The cage encapsulation must be highly conformal to provide consistent protection for each sulfur sphere. Thus, the present embodiment illustratesA unique and easily implemented synthesis method using MoS₂A highly dispersed suspension of flakes and polyvinylpyrrolidone (PVP) encapsulated hollow sulfur spheres was developed as shown in fig. 4A.

a) Preparation of a monodisperse solution of PVP-sulphur particles

A monodisperse solution of PVP-sulfur particles (hereinafter abbreviated to PVP-S) was prepared by a solution synthesis method. In a typical synthesis, 50mL of 80mM aqueous sodium thiosulfate (Sigma-Aldrich, St. Louis, Mo.) is mixed with 50mL of 0.4M PVP (molecular weight-55000, Sigma-Aldrich, St. Louis, Mo.) at room temperature. Then, 0.4mL of concentrated HCl was added to Na with magnetic stirring₂S₂O₃In PVP solution. After stirring at room temperature for 2 hours, the product was collected by centrifugation at 7000rpm for 10 minutes. The product was then redispersed in a 0.4M PVP solution and collected again by centrifugation at 6000rpm for 10 minutes. The product was redispersed in distilled water for use. The resulting solution was designated solution A and had a concentration of about 4mg mL^-1。

b) Peel-off MoS₂Preparation of the suspension of

By intercalating lithium into MoS under sonication₂Forced hydration to prepare MoS₂A dispersion. By mixing 2g of natural MoS in a glove box filled with argon₂Crystals (Sigma-Aldrich from st louis, missouri) were stirred in 20mL of a solution of 1.6M butyllithium (Sigma-Aldrich from st louis, missouri) in anhydrous hexane to effect lithium intercalation. Then, Li was recovered by filtration_xMoS₂And washed with anhydrous hexane to remove excess lithium and organic residues. After vacuum drying, Li is added_xMoS₂Mixed with water and placed in an ultrasonic bath for 1 hour. By insertion of water molecules into the van der Waals layer, Li is achieved_xMoS₂Peeling off. Then, MoS is collected₂A suspension of flakes was kept in reserve at a concentration of about 1mg mL^-1(referred to as solution B).

c)MoS₂@ S compositePreparation of the substance

In a typical synthesis, 20mL of solution a is added to 40mL of solution B with stirring. After stirring for 1 hour, the MoS was collected by filtration₂Encapsulated sulfur particle product (MoS)₂@ S complex) washed with water/methanol (3 times) to remove polymer and impurities.

MoS when mixed with PVP-S suspension₂The flakes adhered to the PVP on the surface of the hollow sulfur spheres, stacked together due to van der waals attraction, and wrapped around the sulfur spheres after the polymer was removed (see fig. 4A and 4B). FIGS. 5A-5D illustrate MoS₂Typical Scanning Electron Microscope (SEM) images of the @ S composite, which exhibited a morphology and spherical diameter similar to its sulfur sphere precursor shown in figure 5E, but with a rough surface with typical wrinkles. These wrinkles result from the 2D flakes being re-stacked on the surface of the sulfur spheres. During SEM characterization, sublimation of sulfur in a high vacuum system can produce significant pores and cracks on the bare sulfur spheres, as shown in fig. 5E. In contrast, conformal MoS₂The cladding may prevent sublimation of the internal sulfur in a high vacuum, indicating effective physical encapsulation of the sulfur. The MoS is depicted in FIG. 5F₂Hollow MoS after sulfur removal in cage-encapsulated hollow sulfur spheres₂SEM image of the skeleton.

The Transmission Electron Microscope (TEM) image shown in FIG. 6A and the STEM image of FIG. 6B clearly show MoS₂The spherical form of the @ S complex. The energy dispersive X-ray (EDX) line scan clearly indicates the distribution of sulfur signal and High Angle Annular Dark Field (HAADF) intensity as shown in fig. 6C. It should be noted that since the Mo La peak and the S Ka peak substantially overlap, the MoS may be adjusted based on additional considerations of the contribution of the Mo Ka line in the EDX pattern shown in FIG. 7₂Composition of sulfur in the @ S complex.

High resolution TEM images show MoS with crystalline sulfur spheres stacked in multiple layers (5-7 layers)₂The sheet is conformally wrapped, as shown in FIGS. 6D and 6E, to form MoS₂A nanocage. FIG. 6F shows a typical MoS₂The nano-cage has a van der Waals gap of about 0.61 nm; the presence of (026) facets in high resolution TEM (HR-TEM) demonstrates the crystalline nature of the sulfur globules. Up to now, the steam pressure of sulfur has been highTherefore, elemental sulfur was not characterized for lattice resolution using high vacuum TEM.

By MoS₂The sulfur spheres can survive for long periods of time in high vacuum TEM under 200KV electron irradiation and can be characterized multiple times without structural degradation. In MoS₂Defects and/or distortions can be observed in HR-TEM images of nanocages (see fig. 6D and 6F, highlighted with blue circles). Multi-layer stack structure allowing MoS₂Defects exist on the nanocages while preventing sublimation of sulfur. In addition to acting as an effective chemisorbent for soluble lithium polysulfides, these defects provide unique channels for transporting lithium ions during lithiation/delithiation.

The X-ray powder diffraction (XRD) pattern as shown in FIG. 8 further confirmed the crystallinity of the hollow sulfur spheres and MoS outside the sulfur particles₂And (4) uniformly wrapping. MoS based on thermogravimetric analysis (TGA) shown in FIG. 9₂The sulfur mass loading in the @ S composite is about 65%, which is a relatively high mass loading. After removal of sulfur spheres by vacuum heating (as evidenced by EDX analysis shown in fig. 7), the free standing MoS₂The structure of the cage remains intact as shown in fig. 6G and 6H. The HR-TEM image in FIG. 6I clearly shows MoS₂The layered stack structure of the cage remains continuous throughout the bending region, which may partially accommodate the outward volume expansion of the sulfur spheres during lithiation.

Example 3: MoS₂Cage-encapsulated hollow sulfur spheres (MoS)₂@ S composite) electrochemical performance

Evaluation of MoS Using Li half-cell (2032 type)₂Electrochemical performance of @ S composite. Vapor Grown Carbon Fiber (VGCF) and polyvinylidene fluoride (PVDF) binder with MoS₂The @ S complex was mixed in N-methyl-2-pyrrolidone (NMP) to form a slurry, thereby preparing a load mass of-1.5 mg cm^-2The working electrode of (1). The slurry was then coated onto copper foil and dried under vacuum overnight. Testing the cell at room temperature at a potential range of 1.6V or 1.8V to 2.6V; and the specific capacity was calculated based on the mass of sulfur only.

When the compound is mixed at different magnifications (0.1C, 0.2C, 0.5C, 1C and 2C, wherein,1C＝1672mAhg^-1) At the time of evaluation, MoS₂@ S exhibits a characteristic Li-S voltage curve, as shown in FIG. 10A. At 0.1C, MoS₂@ S shows 1660mAhg^-1Based on the mass of sulfur, whereas at higher rates of 0.2C, 0.5C, 1C and 2C, 1430mAhg can be obtained, respectively^-1、1137mAhg^-1、930mAhg^-1And 720mAhg^-1The discharge capacity of (2).

Two plateau discharge curves for a typical sulfur cathode can be obtained at various feature rates (fig. 10B). MoS when charged/discharged at higher rates of 3C and 5C₂@ S may be implemented as 508mAhg, respectively^-1And 305mAhg^-1The discharge capacity of (2) is as shown in fig. 10B. MoS considering the insulating properties of sulfur and its lithiated products₂This rate capability of @ S is considered significant.

It is important to note that 2H-MoS₂(semiconductor) will partially convert to a metallic 1-T phase upon lithiation, having 10-100S cm^-1High electrical conductivity. This high conductivity can improve the utilization of insulating sulfur and its lithiated intermediates.

FIG. 10C illustrates MoS₂The cyclability of the @ S complex and control samples (sulfur spheres, sulfur spheres mixed with rGO, abbreviated rGO/S) at 300 cycles at 0.5C. MoS₂The discharge capacity of @ S shows a gradual increase in the initial cycle, which can be explained as sulfur goes through MoS₂Increased accessibility of defect/distortion diffused lithium ions on the sheet, and 2-H MoS₂Gradual conversion to 1-T metal MoS₂The effectiveness of the sulfur is increased. After the initial activation process, by MoS₂@ S the battery exhibited 956mAhg of capacity even after 300 cycles^-1Shows a higher capacity retention of 83.2% (of the initial discharge capacity) with a capacity fade of 0.056% per cycle. In the absence of MoS₂In the case of the cage, the battery made of sulfur spheres showed rapid capacity fade at the initial cycle, and after 300 cycles, the capacity retention rate was only 49.1%, demonstrating MoS₂The cage plays an important role in preventing leakage of the active material during long-term cycling.

As shown in fig. 10C, the mixture of rGO was able to partially mitigate the severe initial capacity fade of the sulfur spheres. However, the capacity retention of the battery made from rGO/S after 300 cycles was about 50.2%, with a capacity fade of 0.166% per cycle (vs MoS)₂Much higher compared to @ S), which is similar to sulfur sphere electrodes, suggesting that rGO with functional groups on the surface can only partially retain polysulfides for a limited number of cycles. When cycling at 1C, by MoS₂The battery made of @ S also exhibited good cycling ability. At 1C, the cell exhibited up to 585mAhg^-1A slight capacity fade of 0.0449% per cycle was achieved (see fig. 10D).

Finally, the mass ratio of the product can be easily increased, since the synthesis step is easy to implement. At load masses up to 30-40mg (based on sulfur mass), pouch cells can be assembled as shown in fig. 10E, which can power LED lamps and can even power small fans, as shown in fig. 10F and 10G.

Example 4: MoS after lithiation₂Characterization of the @ S Complex

To evaluate MoS after lithiation₂Volume expansion of the @ S Complex₂The @ S composite was dispersed and drop cast on a 20 x 1mm glass carbon plate without the addition of carbon conductive and polymeric binders. Using a carrier loaded with MoS₂The pouch cell was assembled in a glove box filled with argon gas using a glassy carbon plate of @ S composite as a working electrode and Li foil as a counter electrode (fig. 11A).

After lithiation to 1.5V at 0.5C, the glassy carbon plates were recovered from the pouch cells and rinsed with a mixed solution of 1,3-DOL and DME (1: 1V/V). MoS on a glassy carbon substrate before and after the first lithiation is depicted in FIGS. 11B-11E₂Typical SEM images of the @ S complex. MoS₂The size distribution of @ S is shown in FIG. 11F. Based on the above results, MoS can be inferred₂The spherical morphology of @ S remains intact after lithiation. In addition, MoS before and after lithiation₂No significant size differences were observed in @ S. The results show that MoS₂The cage can effectively avoid the volume expansion of the sulfur ball, and the hollow space in the sulfur ball can be suitableInward volume expansion upon lithiation. A well-preserved morphology may help maintain a stable electrode-electrolyte interface, limiting leakage of lithium polysulfide into the electrolyte.

Industrial applicability

As described above, since the theoretical capacity of the sulfur cathode is high and the natural abundance of sulfur is high, the Li-S battery is considered to be good. Thus, such rechargeable Li-S batteries with high specific energy may find wide application, such as in electric vehicles (including high altitude long endurance drones or HALE UAVs) as well as in fixed storage systems.

Obviously, various other modifications and adaptations of the present invention will be apparent to those skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention, and all such modifications and adaptations are intended to fall within the scope of the appended claims.

Claims

1. A core-shell complex comprising: a core of a non-metallic particle having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide.

2. The core-shell composite of claim 1 wherein the non-metallic particles are sulfur, silicon, phosphorus particles, or oxides thereof.

3. The core-shell complex of claim 1 or claim 2 wherein the transition metal in the transition metal chalcogenide is selected from the group consisting of group 3 to group 11 elements of the periodic table.

4. The core-shell complex of any one of the preceding claims wherein the transition metal chalcogenide is a transition metal dichalcogenide.

5. The core-shell complex of claim 4 wherein the transition metal dichalcogenide is selected from the group consisting of: MoSe₂、WSe₂、NiSe₂、CoSe₂、TiSe₂、MoS₂、WS₂、NiS₂、CoS₂、TiS₂、MoTe₂、WTe₂、NiTe₂、CoTe₂And TiTe₂。

6. The core-shell complex of claim 4 or claim 5 wherein the transition metal dichalcogenide is in a crystalline form, an amorphous form, or a mixture thereof.

7. The core-shell composite of any of claims 4 to 6 wherein the transition metal dichalcogenide comprises at least one layer of sheet.

8. The core-shell composite of any of claims 4 to 6 wherein the transition metal dichalcogenide comprises at least two layers of sheet material.

9. The core-shell composite of claim 7 or claim 8 wherein the at least one sheet or the at least two sheets of the transition metal dichalcogenide have atomic defects.

10. The core-shell composite of claim 8 wherein the transition metal dichalcogenide comprising at least two layers of sheet material has an interlayer spacing in the range of 0.3nm to 2 nm.

11. The core-shell composite of any of claims 1 to 10 wherein the non-metallic particles are present in a range of 40 wt% to 90 wt% based on the total weight of the core-shell composite.

12. The core-shell complex of any one of claims 1 to 11 wherein the particle size is in the range of 50nm to 5 mm.

13. A process for preparing a core-shell composite comprising a core of non-metallic particles having a hollow interior structure, said core being encapsulated in a shell of a transition metal chalcogenide, said process comprising the steps of:

b) removing the surfactant to obtain the core-shell complex.

14. The method of claim 13, further comprising: before the mixing step (a), steps a-i) mix the nonmetallic precursor with a surfactant under conditions of a suitable temperature and a suitable medium.

15. The method of claim 14, further comprising: step a-ii) adding an acid to the mixture obtained from step a-i).

16. A method according to claim 14 or claim 15, wherein the nonmetallic precursor is in the form of a salt, a solvate, or a hydrate.

17. The method of claim 15, wherein the acid is a weak acid, a strong acid, an organic acid, or an inorganic acid.

18. The method of any of claims 13-17, wherein the transition metal chalcogenide is a exfoliated transition metal chalcogenide.

19. The method as recited in claim 18, further comprising: prior to step (a), steps a-iii) contacting the transition metal chalcogenide with a lithium precursor to form the exfoliated transition metal chalcogenide.

20. The method of claim 18 or claim 19, wherein the exfoliated transition metal chalcogenide is in the form of a flake or sheet.

21. The method of claim 20, wherein the exfoliated transition metal chalcogenide in platelet form has a lateral dimension in the range of 200nm to 2 μ ι η.

22. An electrode comprising a plurality of core-shell composites, wherein each composite comprises a core of non-metallic particles having a hollow interior structure, the core being encapsulated in a shell of a transition metal chalcogenide.