WO2014048390A1

WO2014048390A1 - Composite electrode material and preparation method therefor, positive electrode, and batteries having the positive electrode

Info

Publication number: WO2014048390A1
Application number: PCT/CN2013/084613
Authority: WO
Inventors: 陈璞; 张永光; 李晶
Original assignee: 苏州宝时得电动工具有限公司
Priority date: 2012-09-29
Filing date: 2013-09-29
Publication date: 2014-04-03
Also published as: CN103715399A

Abstract

Disclosed is a composite electrode material comprising elemental sulphur, a conducting polymer, and graphene or reduced graphene oxide. The composite electrode material has a layered structure, wherein the graphene or reduced graphene oxide, as a substrate, provides the composite electrode material with an effective electron conduction network and a stable structure, enabling the composite electrode material to have a good cycle life, good rate performance, and a high discharge capacity. Also disclosed are a method for preparing the composite electrode material, a positive electrode using the composite electrode material, and a battery having the positive electrode.

Description

Electrode composite material and preparation method thereof, positive electrode, battery having the same

The invention relates to an electrode composite.

The invention also relates to a method of preparing an electrode composite.

The invention further relates to a positive electrode having the electrode composite.

The invention also relates to a battery having the positive electrode.

Background technique

In recent years, with the development of science and technology, the demand for energy, especially renewable green energy, has become more and more prominent. The battery as an energy storage and conversion device is playing an irreplaceable role. Lithium-ion batteries attract a lot of attention because of their high mass-to-weight ratio energy. Low-cost, high-energy density, long cycle life, green secondary batteries are currently the development of lithium-ion batteries. The current commercial cathode materials are mainly layered or spinel-structured lithium transition metal oxides (such as cobalt acid). Lithium phosphate, lithium manganate) and lithium iron phosphate of olivine structure. Lithium cobaltate (LiCo0 ₂ ) has a relatively large theoretical capacity of 275 mAh/g, but its price is high and it is toxic. Moreover, the positive electrode material is prone to exothermic decomposition reaction when overcharged, which not only causes a significant decrease in battery capacity, but also It also poses a threat to battery safety; the theoretical capacity of lithium manganate (LiMn ₂ 0 ₄ ) is 148 mAh/g, and the actual capacity is less than 130 mAh/g. The stability of the positive electrode material is not good, and it is easy to cause lattice during charge and discharge. The deformation causes the cycle efficiency to be low; the theoretical capacity of lithium iron phosphate (LiFeP0 ₄ ) is 172 mAh/g, and the conductivity of the positive electrode material is poor, so that the reversible capacity of the battery is lowered. The capacity of the above-mentioned common lithium ion battery cathode materials is generally not high, and there are also some problems, which cannot meet the battery development needs.

The theoretical specific capacity of elemental sulfur is 1675 mAh/g, and the theoretical specific energy of assembling lithium metal into a battery can reach 2600 mAh/g, which is much higher than the currently commercialized cathode material, and has become the main trend of current battery development. Elemental sulfur and sulfur-containing inorganic sulfides, organic sulfides, polyorganodisulfides, organic polysulfides, polysulfides, and carbon-sulfur polymers have attracted attention as high-capacity cathode materials, but these materials remain There are some problems.

First, the conductivity of elemental sulfur and sulfide itself is very poor, and a large amount of conductive agent needs to be added to increase its conductivity. Secondly, when elemental sulfur is used as the positive electrode active material, although elemental sulfur and complete discharge are present on the positive electrode when fully charged. The existing Li ₂ S is insoluble in the polar organic electrolyte, but the lithium polysulfide present in the partial charge and discharge positive electrode is easily soluble in the polar organic electrolyte. In addition, the small molecular sulfide generated during the discharge of the polyorganosulfide is also easily soluble in organic Electrolytes affect the cycle performance of the battery. So how Improving the conductivity of materials, solving the problem of dissolution of charge and discharge intermediates, and improving the cycle performance of batteries are the focus of research on sulfur-containing cathode materials.

Summary of the invention

The present invention provides an electrode composite having high electrode capacity, good electrochemical reversibility, and cycle stability.

The present invention provides an electrode composite comprising elemental sulfur, a conductive polymer, and graphene or reduced graphene oxide.

Preferably, the conductive polymer is selected from one of polypyrrole and polyacrylonitrile.

Preferably, the electrode composite has a layered structure.

Preferably, the elemental sulfur is attached to the conductive polymer.

Preferably, the graphene or the reduced graphene oxide has a nano-layered structure, and the elemental sulfur and the conductive polymer are attached to the graphene or the reduced graphene oxide.

Preferably, in the electrode composite, the specific gravity of the elemental sulfur ranges from 30 to 90%, and the specific gravity of the conductive polymer ranges from 9 to 50%, and the graphene or the reduced graphene oxide The specific gravity ranges from 1 to 20%.

Preferably, in the electrode composite, the mass ratio of polyacrylonitrile to reduced graphene oxide is 45:1 - 10:1.

The present invention also provides a positive electrode comprising the electrode composite as described above. The present invention also provides a battery comprising a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, the positive electrode including at least the electrode composite material as described above.

The invention also provides a preparation method of an electrode composite material, the preparation method comprising the following steps:

Acrylonitrile, elemental sulfur, graphene and an initiator are dissolved in a solvent, stirred at a preset temperature, stirred, washed and dried, and the dried product is subjected to heat treatment under a protective gas atmosphere.

Preferably, the drying temperature ranges from 60 to 80 °C.

Preferably, the heat treatment temperature ranges from 200 to 400 °C.

Preferably, the initiator is selected from the group consisting of potassium persulfate and sodium lauryl sulfate.

Preferably, the solvent is at least one selected from the group consisting of water, methanol, ethanol, N-methylpyrrolidone, dimethylformamide, and acetonitrile.

Preferably, the washing is a centrifugal washing, and the detergent in the centrifugal washing is water.

The invention also provides a preparation method of an electrode composite material, the preparation method comprising the following steps: The elemental sulfur, polyacrylonitrile and graphene are dispersed in a dispersing agent, mechanically mixed, and dried, and the dried product is subjected to heat treatment under a protective gas atmosphere.

Preferably, the drying temperature ranges from 60 to 80 °C.

Preferably, the heat treatment temperature ranges from 200 to 400 °C.

Preferably, the dispersing agent comprises an organic solvent selected from at least one of methanol, ethanol, N-methylpyrrolidone, dimethylformamide, and acetonitrile.

Preferably, the machine is mixed for ball milling mixing.

Preferably, the rotational speed of the ball milling is 500-1000 rpm, and the milling time is 3-9 h.

The polyacrylonitrile solution and the reduced graphene oxide oxide suspension are mixed under weak alkaline conditions, deposited, and the deposited product is filtered and dispersed, and the dispersion is mechanically mixed with elemental sulfur and dried, and dried. The product is heat treated.

Preferably, the redispersing is to redisperse the polyacrylonitrile and the reduced graphene oxide in methanol, ethanol, N-methylpyrrolidone, dimethylformamide or acetonitrile.

Preferably, the drying temperature ranges from 60 to 80 °C.

Preferably, the heat treatment temperature ranges from 200 to 400 °C.

Preferably, the machine is mixed for ball milling mixing.

Preferably, the ball milling is wet ball milling.

The composite of polypyrrole and graphene is added to a suspension containing elemental sulfur, mixed and dried, and the dried product is subjected to heat treatment under a protective gas atmosphere.

Preferably, the composite of polypyrrole and graphene is prepared by in-situ polymerization, and comprises the following steps:

The graphene is ultrasonically dispersed in a mixed solvent of methanol and acetonitrile, pyrrole is added, and a ferric chloride solution is added while ultrasonic treatment, and a precipitate is obtained by filtration, and the precipitate is washed and dried to obtain a composite of polypyrrole and graphene. Polypyrrole is formed on graphene.

Preferably, the mixing is ultrasonic mixing.

Preferably, the drying temperature ranges from 60 to 80 °C.

Preferably, the heat treatment temperature ranges from 150 to 350 °C.

Preferably, the ferric chloride solution is added dropwise. Preferably, the detergent at the time of washing is deionized water and ethanol.

The invention provides an electrode composite material, wherein the electrode composite material has a layered structure, graphene or reduced graphene oxide as a base, which provides an effective electron conduction path and a stable structure for sulfur, and the stable structure The electrode composite can be subjected to volume change well during charge and discharge, so that the electrode composite has excellent electrical conductivity and cycle stability. The invention also provides a preparation method of the electrode composite material, which is simple and easy to manufacture, and has industrial application prospects.

DRAWINGS

The invention will now be further described with reference to the drawings and embodiments.

Figure 1 is a diagram of RGO in the first embodiment;

Figure 2 is an SEM image of RGO/PAN/S after ball milling in Example 1;

3 is an SEM image of RGO/PAN/S after heat treatment in Example 1, wherein RGO:PAN=l:30; FIG. 4 is an SEM image of RGO/PAN/S after heat treatment in Example 1, wherein RGO:PAN= l: 15; Figure 5 is an infrared spectrum of Ppy, Ppy/GNS and S/Ppy/GNS;

Figure 6 is an XRD pattern of Ppy, S and S/Ppy/GNS;

Figure 7 is an SEM image of Ppy/GNS;

Figure 8 is an SEM image of S/Ppy/GNS;

Figure 9 is an SEM image of PAN/S after heat treatment in Comparative Example 1;

Figure 10 is a graph showing the charge-discharge voltage versus specific capacity of the battery in Example 3 and Comparative Example 2; Figure 11 is a graph showing the charge and discharge cycle performance of the battery in Example 3 and Comparative Example 2; Figure 12 is an example. Fig. 13 is a graph showing the charge and discharge cycle performance of the battery in Example 3 and Comparative Example 2; Fig. 14 is a charge and discharge cycle of the battery in Example 3; Cycle performance chart;

Figure 15 is a graph showing the cycle performance of a battery with a charge and discharge of 0.2 C in Comparative Example 2;

Figure 16 is a CV diagram of the battery in Embodiment 4;

Figure 17 is a graph showing the cycle performance of a battery in Example 4 at a charge and discharge cycle of 0.1C;

Figure 18 is a graph showing the cycle performance of a battery in Example 4 at a charge and discharge cycle of 0.5C;

Figure 19 is a graph showing the relationship between the charge and discharge voltage and the capacity of the battery in Example 5 in Example 5;

Figure 20 is a graph showing the relationship between the charge and discharge voltage and the capacity of the battery in Comparative Example 3 at 0.1 C;

Figure 21 is a graph showing the relationship between the discharge capacity and the number of cycles of the battery in Example 5 and Comparative Example 3; Figure 22 is a graph showing the cycle performance of the battery in Example 5 at different discharge rates;

Figure 23 is a graph showing the cycle performance of a battery in Example 6 at a charge and discharge of 0.1C; Figure 24 is a graph showing the relationship between charge and discharge voltage and capacity of a battery in Example 8 in Example 8; Figure 25 is a CV diagram of the battery in Example 8;

Figure 26 is a graph showing the cycle performance of the batteries of Example 8 and Example 9 at different discharge rates; Figure 27 is a graph showing the charge and discharge cycle performance of the battery of Example 8 in Example 8.

detailed description

An electrode composite with high electrode capacity and good electrochemical reversibility. The electrode composite includes elemental sulfur, a conductive polymer, and graphene or reduced graphene oxide.

Preferably, in the electrode composite, the specific gravity of the elemental sulfur ranges from 30 to 90%, the specific gravity of the conductive polymer ranges from 9 to 50%, and the specific gravity of the graphene or reduced graphene oxide ranges from 1 to 20%.

Preferably, in the electrode composite, the specific gravity of elemental sulfur is 46%.

Preferably, in the electrode composite, graphene or reduced graphene oxide has a specific gravity of 10%.

Preferably, in the electrode composite, the specific gravity of the graphene or the reduced graphene oxide is

19%.

Preferably, in the electrode composite, the conductive polymer has a specific gravity ranging from 51.5 to 55%.

The electrode composite has a layered structure, and the elemental sulfur (S) is a micron or submicron or nanometer-sized particle, and S is attached to the conductive polymer. Graphene (GNS, graphene nano-sheet) or reduced graphene oxide (RGO) is a nano-layered structure, GNS is a single-atom graphite layer, and RGO is generally 2-3 atoms thick graphite. Layer, GNS or RGO has a large specific surface area and strong adsorption capacity. S and conductive polymer are attached to GNS or RGO together. Similar to sandwich structure, conductive polymer with S attached to the layer of GNS or RGO. Between the layers.

Elemental sulfur has a considerable theoretical specific capacity, but elemental sulfur at room temperature is an insulator of electrons and ions, and a lithium-sulfur battery composed of an elemental sulfur positive electrode having a sulfur content of 100% is unlikely to be charged and discharged at room temperature. Therefore, certain electron and ion conductors must be added to the sulfur-based positive electrode. The present invention aims to improve the electrical conductivity of a sulfur-containing electrode composite material, and to improve the stability and cycle performance of the electrode.

The conductive polymer is selected from one of polyacrylonitrile (PAN) and polypyrrole (Ppy). PAN undergoes pyrolysis reaction at a certain temperature, including cyclization, dehydrogenation, conjugate, cross-linking, etc. of cyano group to form a conjugated polypyrrole having conductive properties. The low-temperature pyrolysis property of PAN is a preparation of electrode composite material. A good carrier is provided, which is introduced into elemental sulfur. The elemental sulfur S ₈ has a crown structure. At a certain temperature, the elemental lanthanum is in a molten state, and the molten ruthenium is embedded in the PAN, that is, an S ₈ ring is embedded in In the four dehydrogenated PAN rings, S is attached to the PAN to form a complex of S and PAN, thereby increasing the conductivity of S. ability. Ppy is a kind of polymer with excellent conductivity. It is widely used in electrode surface modification and electrode materials. Ppy has strong adsorption capacity, and S can be adsorbed on Ppy, which also improves the conductivity of elemental sulfur.

Graphene (GNS), also known as single-layer graphite or two-dimensional graphite, is a two-dimensional carbon atom crystal with a single atomic thickness, which has a high specific surface area, outstanding thermal and mechanical properties, and electron transport properties. It is introduced into the electrode composite material, a GNS having a nano-layered structure is used as a substrate, S and a conductive polymer are adsorbed on the surface thereof, and a GNS layer is superposed with the layer to obtain an electrode composite material having a sandwich structure, S and conductive polymerization. The object is sandwiched between the GNS layers. Thus, the GNS provides an effective electron conduction path and a stable structure for the electrode composite. This stable structure allows the electrode composite to withstand volume changes during charge and discharge. The electrical conductivity and cycle stability of the electrode composite can be improved, that is, the cycle performance and rate performance of the electrode composite are improved.

The reduced graphene oxide (RGO) is a nano-layered structure containing a graphite layer of 2-3 atoms thick, and the graphite is oxidized, stripped and then reduced to obtain RGO. In the oxidation process of strong oxidant, an oxygen-containing group such as a carboxyl group, a phenolic hydroxyl group and an epoxy group appears on the graphite layer, and the obtained graphite oxide interlayer distance is increased by using any appropriate known technique such as ultrasonic or mechanical stirring. , the graphite oxide is stripped into graphene oxide (GO, graphene oxide), but GO is thermodynamically unstable, and decomposition at about 200 °C is mainly due to pyrolysis of unstable oxygen-containing functional groups; The numerous oxygen-containing groups on the graphene oxide destroy the sp ² hybrid system of graphene, which makes the conductivity of GO worse. Therefore, the removal of thermodynamically unstable oxygen-containing functional groups by chemical reduction reaction can be passed. Controlling the amount of reducing agent to control the degree of reduction of GO, so that not only the obtained RGO has good thermodynamic stability and electrical conductivity, but also due to the ionization of the remaining oxygen-containing functional groups, RGO is negatively charged, due to electrostatic repulsion, RGO can be well dispersed in water, and because RGO has a large specific surface area and strong adsorption capacity, S and PAN are evenly attached. On RGO, RGO also provides an effective electron conduction path and stable structure for the electrode composite, which makes the electrode composite have excellent electrical conductivity and stable structure, and improve the cycle performance and magnification of the electrode composite. performance.

Preferably, in the electrode composite, the mass ratio of polyacrylonitrile PAN to reduced graphene oxide RGO is 45:1 - 10:1.

At this ratio, sufficient contact between the polyacrylonitrile PAN and the reduced graphene oxide RGO can be ensured, the agglomeration of the RGO can be avoided, and the effective communication between the RGO fingers can be ensured, and the conductivity of the electrode composite material can be enhanced.

In a preferred embodiment, in the electrode composite, polyacrylonitrile PAN and reduced graphite The mass ratio of the olefin oxide RGO is 13:1 -25:1.

In another preferred embodiment, in the electrode composite, the mass ratio of polyacrylonitrile PAN to reduced graphene oxide RGO is 26:1 - 44:1.

The electrode composite material provided by the invention introduces a conductive polymer, GNS or RGO into elemental sulfur, so that the electrode composite material has excellent electrical conductivity, and GNS or RGO as a substrate provides an effective electron conduction path for S and Stable structure, this stable structure can make the electrode composite can withstand the volume change well during the charging and discharging process, so that the conductivity and cycle stability of the electrode composite can be improved. The electrode composite layered structure, the conductive polymer with S attached is sandwiched between the layers of the nano-layered structure of GNS or RGO, inhibits the dissolution of the charge and discharge intermediate lithium polysulfide, and improves the utilization ratio of S. The shuttle effect is reduced, and the cycle performance and rate performance of the electrode composite material are significantly improved.

The present invention also provides a positive electrode, wherein the electrode composite material described above can be used as a positive electrode active material, and the electrode composite material and the positive electrode current collector together constitute a positive electrode.

The present invention also provides a battery comprising a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.

The positive electrode includes at least a positive electrode active material. The positive electrode active material contains the above electrode composite material, and the electrode composite material accounts for 50-90% of the total weight of the positive electrode active material, and the positive electrode active material may further contain a conductive agent and a binder as needed.

The conductive agent is selected from, but not limited to, one or more of a conductive polymer, activated carbon, graphene, carbon black, carbon fiber, metal fiber, metal powder, and metal flake.

The binder is selected from, but not limited to, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyimide, polyester, polyether, fluorinated polymer, polydivinyl polyethylene glycol, polyethylene One of an alcohol diacrylate, polyethylene glycol dimethacrylate, or a mixture and derivative of the above polymers.

In a specific embodiment, the positive electrode further includes a positive electrode current collector, and the positive electrode current collector is selected from the group consisting of, but not limited to, metallic nickel, metallic aluminum or stainless steel, wherein the metallic nickel may be in the form of a foamed nickel or nickel mesh; the metallic aluminum may be in the form of aluminum foil. Or aluminum sheet; the shape of stainless steel can be stainless steel mesh.

The negative electrode includes a negative electrode current collector and a negative electrode active material, and the negative electrode active material is selected from the group consisting of lithium metal, lithium alloy, lithium carbon, carbon-based or silicon-based material. The lithium alloy includes a lithium-aluminum alloy, a lithium-magnesium alloy or a lithium-tin alloy; the carbon material in the lithium carbon is not limited, including crystalline carbon, amorphous carbon, or a mixture thereof; the carbon-based material includes but is not limited to graphite; The base material is selected from at least one of elemental silicon, silicon alloy, metal-coated silicon, and metal-doped silicon. Silicon alloys include silicon-carbon alloys, silicon-lithium alloys, and silicon-manganese alloys. In order to improve the electrical conductivity of the material silicon, it is generally coated on the surface of silicon or doped with metal in silicon. Since but not limited to copper, tin, silver, etc. with good electron conductivity.

The negative electrode current collector is selected from, but not limited to, one of copper foil, copper mesh, aluminum foil, nickel foam or stainless steel mesh. When the negative electrode active material is metallic lithium, metallic lithium itself can also be used as a negative electrode current collector.

In order to ensure that there is a deintercal-embedded ion between the positive and negative electrodes of the battery during charge and discharge, such as lithium ions, the selected sulfur-based material and the silicon-based material do not contain the elution-embedded lithium ions, and the positive electrode and/or Or the negative electrode is pre-intercalated with lithium. The specific pre-embedding method is not limited, including lithium intercalation in chemical reaction or lithium intercalation in electrochemical reaction.

In a specific embodiment, the electrolyte includes at least an electrolyte lithium salt and a mixed organic solvent. In a specific embodiment, the electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC) containing lithium hexafluorophosphate (LiPF ₆ ), and A mixed solution of diethyl carbonate (DEC).

The electrolyte lithium salt may include, but is not limited to, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiC10 ₄ ), lithium trifluoromethyl hydride (LiCF ₃ S0 ₃ ), ditrifluoroa Lithium hexyl imide (LiN(CF ₃ S0 ₂ ) ₂ ). The addition of a lithium salt to the electrolyte can effectively increase the ionic conductivity of the electrolyte.

The solvent of the electrolyte may be a usual organic solvent such as dimethoxyethane (DME), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), 1,3-dioxane. Pentane (DIOX), various ethers, glyme, lactone, sulfone, sulfolane or a mixture of the above. For example, using 1,3 _ dioxolane (DIOX); it can also be a polymer such as PVDF, polyvinylidene fluoride-polymethyl methacrylate copolymer (PVDF-PMMA), polyvinylidene fluoride-six Fluoropropylene copolymer (PVDF-HFP), polyethylene glycol borate esters (PEG-borate esters).

The electrolyte is placed in the battery in the form of a gel, which helps to prevent leakage of the potential battery electrolyte, avoids environmental pollution, and also improves the safety of the battery. In a battery provided by a specific embodiment of the present invention, if a diaphragm is required in the battery structure, the separator is an organic porous material or a glass fiber material, and the separator has a pore diameter of 0.001 to 100 μm and a porosity of 20 to 95%.

In a specific embodiment, the electrode composite material, the conductive agent, and the binder are mixed, and an organic solvent is added as a dispersing agent to prepare a positive electrode slurry. The prepared positive electrode active material slurry is deposited on the surface of the positive electrode collector by any method which can provide a substantially uniform coating layer on the entire surface of the positive electrode current collector. For example, it may be by a doctor blade, a wire draw draw method, screen printing or the like. The solvent can be removed from the positive electrode active material slurry layer by atmospheric or low pressure and evaporation at ambient temperature or high temperature, and the rate of solvent removal is preferably kept substantially constant along the surface of the slurry. The obtained positive electrode was then assembled into a battery together with a negative electrode, an electrolyte, and a separator.

The invention also provides a preparation method of an electrode composite material, the preparation method comprising the following steps: Acrylonitrile, sulfur, graphene and an initiator are dissolved in a solvent, stirred at a preset temperature, stirred, washed, dried after washing, and the dried product is subjected to heat treatment under a protective gas atmosphere.

The solvent is at least one selected from the group consisting of water, methanol, ethanol, N-methylpyrrolidone, dimethylformamide, and acetonitrile. Specifically, the solvent is water.

Stirring at a preset temperature is to achieve better polymerization of acrylonitrile. Specifically, the preset temperature range is 60-80 °C.

^3⁄4 and graphene may be added to the solvent as a solid or a suspension. Specifically, the nanometer-sized sulfur may be dispersed in a solvent to obtain a sulfur-containing suspension, so that the sulfur can be sufficiently and uniformly dispersed, and the solvent includes It is not limited to one of water, methanol, ethanol, N-methylpyrrolidone, dimethylformamide, acetonitrile; graphene can be dispersed in a solvent to obtain a graphene-containing suspension, so that graphene can be sufficiently and uniformly Dispersion, likewise, solvents include, but are not limited to, one of water, methanol, ethanol, N-methylpyrrolidone, dimethylformamide, acetonitrile.

According to the method of chemical oxidation in situ polymerization, the polyacrylonitrile is sufficiently mixed with the elemental sulfur in the presence of the acrylonitrile monomer, and the acrylonitrile monomer is oxidatively polymerized by the initiator to form polyacrylonitrile, in order to complete the reaction. The mixture was vigorously stirred at a preset temperature of 60-8 CTC for 10 hours, and the stirred particles were washed by centrifugation. Specifically, the detergent for washing was water. Initiators include, but are not limited to, potassium persulfate and sodium lauryl sulfate.

After thorough washing, the water is removed by drying. The drying can be carried out under vacuum or a protective gas atmosphere. The drying temperature ranges from 60 to 8 CTC, and the drying time ranges from 1 to 5 hours to completely remove water.

The dried product is subjected to heat treatment. In order to avoid introduction of impurities and unnecessary side reactions, the heat treatment is carried out in a protective gas atmosphere. Specifically, the shielding gas is an inert gas, and the inert gas includes, but is not limited to, argon gas. The temperature range of the heat treatment is 200-400 °C, and the heat treatment time is l -5h. When the temperature rises, the elemental sulfur becomes molten, and the dehydrogenation reaction with polyacrylonitrile occurs, and the elemental sulfur is embedded in the desulfurization reaction. In the polyacrylonitrile ring of hydrogen, that is, elemental sulfur is attached to the polyacrylonitrile. Due to the large specific surface area and strong adsorption capacity of graphene, polyacrylonitrile with elemental sulfur attached to graphene, graphene is a nano-layered structure, and the graphene layer and the layer are sandwiched with elemental substances. The sulfur polyacrylonitrile, that is, the electrode composite obtained has a layered structure.

Specifically, acrylonitrile, potassium peroxylate, sodium lauryl sulfate, a suspension of nanoquinone, and a suspension of nanographene are dissolved in deionized water. In order to polymerize AN, the above mixture was vigorously stirred at 70 ° C for 10 h, and the obtained granules were thoroughly washed with water by centrifugation, washed and dried in a vacuum oven at 60 ° C for 3 h to remove solvent water, and then under an argon atmosphere, Heat treatment at 350 °C in a tube furnace In hours, the sulfur is melted and reacted with polyacrylonitrile, and the sulfur is embedded in the polyacrylonitrile, and then attached to the stone.

The preparation method provided by the invention combines in-situ polymerization and heat treatment, firstly mixing the monomer of polyacrylonitrile and elemental sulfur, and oxidizing and polymerizing the acrylonitrile monomer on the surface of graphene by an initiator in the presence of elemental sulfur. Poly! 3⁄4 olefinonitrile, at which point a part of the sulfur has been bound together with the poly(3⁄4) acrylonitrile, and then the sulfur is melted during the heat treatment, and the unbound and bound elemental sulfur reacts with the polyacrylonitrile and is embedded in In polyacrylonitrile, the degree of mixing of polyacrylonitrile and elemental sulfur is increased by in-situ polymerization, and then sulfur and polyacrylonitrile are reacted by heat treatment, sulfur is embedded in the polyacrylonitrile ring, and conductive property is aggregated. Acrylonitrile not only enhances the conductivity of sulfur, but also ensures sulfur activity during charge and discharge, and improves sulfur utilization. Further, the graphene has a nano-layered structure, and a polyacrylonitrile-embedded polyacrylonitrile is adhered between the layers of the graphene. Graphene has a strong ability to conduct electrons. As a substrate, it provides an effective electron conduction network and a stable structural framework, which not only enables the electrode composite to better withstand the volume effect during charge and discharge, but also improves the electrode. The electrical conductivity and power performance of the composite material; In addition, the polyacrylonitrile embedded with elemental sulfur can effectively inhibit the dissolution of the lithium polysulfide intermediate in the charge and discharge cycle, improve the utilization of elemental sulfur, and make the electrode composite excellent. Cycle performance. The electrode composite material obtained by the preparation method provided by the invention has excellent electrochemical performance, and the process is simple and easy, and has industrial application prospects.

The invention also provides a preparation method of the electrode composite material, the preparation method comprises the following steps: dispersing elemental sulfur, polyacrylonitrile and graphene in a predetermined proportion in a dispersing agent, mechanically mixing, mixing and drying, after drying The product is heat treated in a protective gas atmosphere.

The dispersing agent is selected from, but not limited to, an organic solvent including, but not limited to, one or more of methanol, ethanol, acetonitrile, dimethylformamide (DMF), and N-methylpyrrolidone (NMP). The dispersant mainly serves the purpose of thoroughly mixing elemental sulfur (S), polyacrylonitrile (PAN) and graphene (GNS), and then dispersing it by mechanical mixing. Specifically, mechanical mixing includes but is not limited to ball milling mixing. The speed range of ball milling is 500-1000 rpm, and the time range of ball milling mixing is 3-9h. In the ball milling, the ball mill can be zirconia ball milled, in order to prevent the ball mill from being damaged, and the elemental S, PAN and GNS are sufficiently ground and uniformly dispersed. The preferred ball mill speed is 800 rpm and the ball milling time is 6 h.

The ball milled mixture is dried to remove the dispersant, and the drying may be carried out under vacuum or a protective gas atmosphere, the drying temperature is in the range of 60-80 ° C, and the drying time is in the range of 8-16 h. Remove the dispersant.

The dried product is subjected to heat treatment, and the heat treatment is carried out in a protective gas atmosphere. The shielding gas is an inert gas, and the inert gas includes, but is not limited to, argon. The temperature range of the heat treatment is 200-400 °C, and the heat treatment time range is 3-9h. When the temperature rises, the elemental enthalpy becomes molten, and the dehydrogenation reaction with polyacrylonitrile occurs, and the elemental sulfur is embedded in the desulfurization reaction. In the polyacrylonitrile ring of hydrogen, that is, elemental sulfur is attached to the polyacrylonitrile.

Specifically, the elemental S, PAN and GNS were mixed at a weight ratio of 4:1: 0.25, and NMP was used as a dispersing agent, and ball-milled at 800 rpm for 6 hours. The ball milled product was further dried in a vacuum oven at 60 ° C for 12 h to remove the dispersant NMP, and then heat treated at 350 ° C for 6 h in an argon atmosphere tube furnace to melt and react with PAN, GNS was The nano-layered structure has a large specific surface area and a strong adsorption capacity. The PAN embedded with S is attached to the GNS, and the prepared electrode composite has a layered structure, and the nano-layered structure is interposed between the GNS. The PAN of S.

The preparation method provided by the invention combines ball milling mixing and heat treatment, ball milling mixing to mix the components of the electrode composite material, and then heat treatment to react sulfur and polybutene, and sulfur is embedded in the polyacrylonitrile ring. Among them, the polyacrylonitrile having electrical conductivity not only improves the conductivity of sulfur, but also ensures the activity of sulfur during charging and discharging, improves the utilization of sulfur, and finally produces sulfur/polyacrylonitrile/graphene having a layered structure. Electrode composite. Further, the graphene has a nano-layered structure, and a polyacrylonitrile-embedded polyacrylonitrile is adhered between the layers of the graphene. Graphene has a strong ability to conduct electrons. As a substrate, it provides an effective electron conduction network and a stable structural framework, which makes the electrode composites have a good tolerance to volume changes during charging and discharging, and the electrode is improved. The conductivity and power performance of the composite material; In addition, the polyacrylonitrile embedded with elemental sulfur can effectively inhibit the dissolution of the lithium polysulfide intermediate in the charge and discharge cycle, improve the utilization of elemental sulfur, and make the electrode composite excellent. Cycle performance. The electrode composite material obtained by the preparation method provided by the invention has excellent electrochemical performance, and the process is simple and easy, and has industrial application prospects.

The invention also provides a preparation method of an electrode composite material, the preparation method comprising the steps of: mixing a polyacrylonitrile solution and a reduced graphene oxide suspension under weak alkaline conditions, and dispersing the deposition product after deposition; The dispersion is mechanically mixed with elemental sulfur, mixed and dried, and the dried product is subjected to heat treatment.

In a polyacrylonitrile (PAN) solution, the solvent may be selected from organic solvents including, but not limited to, dimethylformamide (DMF) at a temperature ranging from 50 to 80 ° C to sufficiently dissolve the polyacrylonitrile. Specifically, PAN was dissolved in DMF at 60 °C.

The reduced graphene oxide (RGO) is dispersed in a suitable solvent such as water, methanol, ethanol, acetonitrile, N-methylpyrrolidone or dimethylformamide to obtain an RGO suspension.

RGO is prepared by the modified Hummers method. First, the graphite oxide was synthesized by the Hummers method. The compound is then stripped to obtain graphene oxide (GO). However, GO is thermodynamically unstable and has poor electrical conductivity. The decomposition of GO at about 200 °C is mainly due to the pyrolysis of unstable oxygen-containing functional groups. This produces carbon monoxide, carbon dioxide and water vapor. On the other hand, the thermodynamic stability of RGO is much better than GO. Therefore, the thermodynamically unstable oxygen-containing functional group in GO is further removed by a chemical reduction reaction to convert GO into RGO to increase its thermodynamic stability and electrical conductivity. In addition, the degree of reduction of graphene can be controlled by controlling the amount of reducing agent, which not only makes RGO have good thermodynamic stability and electrical conductivity, but also negatively charges RGO due to ionization of unreduced oxygen-containing functional groups. Due to the electrostatic repulsion, RGO is well dispersed in water.

Specifically, the PAN/DMF solution and the RGO suspension are mixed under weakly alkaline conditions, and the weakly alkaline environment is to make the RGO suspension more stable, preferably weakly alkaline to a pH of less than 9. The weak alkaline reagent selected is ammonia water. Specifically, the ammonia aqueous solution is added under vigorous stirring. The mass concentration of the aqueous ammonia solution is 0.5 wt%, and then the stirring is continued for 12-24 h. The RGO is better dispersed due to the polarity of DMF. PAN tends to deposit on the RGO surface with a layered structure, and the deposition rate is slow, obtaining a uniform PAN/RGO composite.

After mixing evenly, PAN and RGO are deposited. The specific deposition method is by centrifugation. The speed range during centrifugation is 8000-12000 rpm, the time of centrifugation is 10 min-lh, and the dispersion is dispersed after deposition. The specific dispersant includes but is not limited to ethanol. Specifically, the PAN/RGO complex is redispersed in ethanol after centrifugation, and then subjected to wet ball milling with elemental sulfur. The ball milling speed is 400-800 rpm. For sufficient mixing, the ball milling time is 0.5-2 h.

After the ball mill is mixed, it is dried to remove the solvent therein, and the drying may be carried out under vacuum or a protective gas atmosphere at a drying temperature of 60-8 CTC and a drying time of l - 4 h.

The dried product is subjected to heat treatment. In order to avoid introduction of impurities and unnecessary side reactions, the heat treatment is carried out in a protective gas atmosphere. Specifically, the shielding gas is an inert gas, and the inert gas includes, but is not limited to, argon gas. The temperature range of heat treatment is 200-400 °C, and the heat treatment time is l -5h. When heating, the elemental sulfur becomes molten as the temperature increases, dehydrogenation reaction with polyacrylonitrile, and elemental sulfur is embedded into dehydrogenation. In the polyacrylonitrile ring, that is, elemental sulfur is attached to the polyacrylonitrile. Due to the large specific surface area and strong adsorption capacity of RGO, polyacrylonitrile with elemental sulfur attached to RGO, RGO is a nano-layered structure containing 2-3 monoatomic graphite layers, layers and layers of RGO The polyacrylonitrile to which elemental sulfur is attached is interposed, that is, the obtained electrode composite has a layered structure.

Specifically, the PAN powder was dissolved in DMF at 60 °C. The PAN/DMF solution was mixed with the suspension containing RGO, and 0.5 wt% aqueous ammonia solution was added under vigorous stirring, followed by vigorous stirring. 24 hours. The gray material was obtained by centrifugation at a temperature of l OOOO rpm for 10 minutes, and then the gray matter and the elemental sulfur were subjected to wet ball milling, and ethanol was used as a dispersing agent at a rotation speed of 600 rpm and ball milling for 30 minutes. The ball milled mixture was dried in a vacuum oven at 60 ° C for 2 hours. Then, the dried product was heat-treated in a tube furnace at 320 ° C for 3 hours and annealed. Finally, an electrode composite is obtained.

The preparation method provided by the present invention uses centrifugal and ball milling to thoroughly mix the components of the electrode composite. RGO is a nano-layered structure containing 2-3 monoatomic graphite layers. RGO contains oxygen-containing groups such as carboxyl groups, phenolic hydroxyl groups and epoxy groups. Due to the ionization of these groups, RGO is negatively charged due to electrostatic repulsion. , RGO can be well dispersed in water, and because RGO has a large specific surface area and strong adsorption capacity, sulfur and polyacrylonitrile are attached to RGO, and then heat treatment, melting sulfur, reacting with PAN, embedding In the PAN, the finally obtained electrode composite has a layered structure, and a PAN in which sulfur is embedded is adhered between the RGO layer and the layer.

The polyacrylonitrile having electrical conductivity not only improves the conductivity of sulfur, but also ensures the activity of sulfur during charging and discharging, and improves the utilization of sulfur. Furthermore, RGO has strong conductivity and thermal stability, and as a substrate, it provides an effective electronic conduction network and a stable structural frame, which improves the electrical conductivity and power performance of the electrode composite; The single-sulfur polyacrylonitrile can effectively inhibit the dissolution of the lithium polysulfide intermediate in the charge-discharge cycle, improve the utilization of elemental sulfur, and make the electrode composite have excellent cycle performance. The electrode composite obtained by the preparation method provided by the invention has excellent electrochemical performance, and the process is simple and easy, and has industrial application prospects.

The invention also provides a preparation method of an electrode composite material, which comprises the following steps: adding a composite of polypyrrole and graphene to a sulfur-containing suspension, mixing and drying, and drying the product in a protective gas Heat treatment in an atmosphere.

Specifically, the nano-sized sulfur is dispersed in a dispersant to obtain a sulfur-containing suspension, so that the sulfur can be sufficiently and uniformly dispersed, and the dispersing agent includes but is not limited to water.

Specifically, the mixture is ultrasonically mixed, and after ultrasonication, the mixed polypyrrole and graphene composite and the sulfur-containing suspension are dried to remove the solvent therein, and the drying may be in a vacuum condition or a protective gas atmosphere. The drying temperature range is 60-8 CTC and the drying time range is l -5 h. Specifically, the drying temperature was 65 ° C and the drying time was 3 h.

The dried product is subjected to heat treatment. In order to avoid introduction of impurities and unnecessary side reactions, the heat treatment is carried out in a protective gas atmosphere. Specifically, the shielding gas is an inert gas, and the inert gas includes, but is not limited to, argon gas. The temperature range of the heat treatment is 150-350 °C, and the heat treatment time is l -5h. When the temperature rises, the elemental ruthenium becomes molten, and the polypyrrole has a ruthenium. Strong adsorption capacity, elemental sulfur is adsorbed into polypyrrole, that is, elemental sulfur is attached to polypyrrole. Because graphene has a large specific surface area and a strong adsorption capacity, polypyrrole attached to elemental sulfur adheres to graphene, graphene is a nano-layered structure, and elemental sulfur is adhered between the graphene layer and the layer. The polypyrrole, that is, the electrode composite obtained has a layered structure.

Specifically, the composite of polypyrrole and graphene is prepared by in situ polymerization, and includes the following steps:

In order to control the reaction rate, the ferric chloride solution is added dropwise, and the pyrrole is polymerized on the graphene. After the pyrrole is polymerized, the precipitated polypyrrole/multiwalled carbon nanotubes are filtered, and the precipitate is passed through deionized water and ethanol. Washing, drying after washing, drying can be carried out in a vacuum drying oven, drying temperature range of 60-8 CTC, drying time range of 5-12 h. Specifically, it was dried under vacuum at 70 ° C overnight.

Specifically, polypyrrole is synthesized from a pyrrole monomer by a chemical oxidation process using FeCl ₃ as an initiator. Polypyrrole-attached graphene is obtained by in-situ polymerization of pyrrole on graphene. First, the graphene was dispersed in a mixed solvent of methanol and acetonitrile (volume ratio of 1:1) by a sonicator at room temperature, and sonicated for 2 hours. Pyrrole was added to the above solution, stirred for 0.5 h, and then FeCl ₃ solution was added dropwise, and ultrasonication was continued at room temperature. Finally, the final Ppy/GNS was separated by filtration, washed thoroughly with deionized water and ethanol, and dried overnight at 70 ° C under vacuum.

The prepared Ppy/GNS was added to a suspension containing nano-sulfur, sonicated for 0.5 h to uniformly disperse the mixture, and then the mixture was placed in a vacuum drying oven and dried at 65 ° C for 3 hours to remove the solvent. Finally, the mixture was heated to 150 ° C in Ar atmosphere for 3 h to obtain an electrode composite having a layered structure.

The nano-sized S is highly dispersed on the surface of the Ppy/GNS composite. Due to the excellent electron conductivity and good lithium ion migration path of the GNS, the sulfur-based electrode composite has excellent large-rate discharge capacity. In addition, Ppy with a porous structure can not only withstand the large bond during charging and discharging.

The preparation method of the electrode composite material provided by the invention combines ultrasonic treatment, in-situ polymerization and heat treatment, so that the components of the electrode composite material can be more uniformly dispersed, and the electrode composite material obtained by the preparation method has a layer. The polypyrrole to which the elemental sulfur is attached is attached to the graphene of the layered structure, and the polypyrrole to which sulfur is adsorbed is adhered between the layers of the graphene. Graphene has Strong conductivity, as a substrate, provides an effective electronic conduction network and a stable structural framework, improving the conductivity and power performance of the electrode composite; in addition, the adsorption of sulfur-containing polypyrrole can effectively inhibit The dissolution of lithium polysulfide, the intermediate product during the charge and discharge cycle, improves the utilization of elemental sulfur, and the electrode composite has excellent cycle performance. The electrode composite material obtained by the preparation method provided by the invention has excellent electrochemical performance, and the process is simple and easy, and has industrial application prospects.

The invention is further illustrated by the following examples.

Example 1

The ig graphite was ground in an agate mortar for 10 minutes with 50 g of sodium chloride to remove contaminants from the graphite and finely ground. The mixture of graphite and sodium chloride was then washed several times with distilled water and vacuum filtered to remove sodium chloride, and the membrane pore size was 0.2 μm. After filtration, the graphite was placed in a vacuum drying oven and dried at 70 ° C for 20 min to remove residual moisture. After drying, the obtained solid was mixed with 23 ml of concentrated sulfuric acid in a 250 ml round bottom flask, and stirred at 25 ° C for 24 hours without interruption. To the above dispersion, 100 mg of sodium nitrate was added, and the mixture was stirred for 5 minutes to be dissolved. Then, the flask was placed in a water bath, the temperature was kept below 20 ° C, 3 g of potassium permanganate was added to the suspension, and then heated to 40 ° C for 30 min, 3 ml of ultrapure water, 5 min, and then 3ml ultra-pure water from Likou, 5min, and 40ml ultra-pure water. Thereafter, the suspension was heated to 100 ° C and kept for 15 minutes, then 140 ml of ultrapure water and 10 ml of hydrogen peroxide (H ₂ O ₂ , 30 wt ) were added to stop the reaction. The suspension was further stirred for 5 min, then washed twice with 5% hydrochloric acid, and washed several times with ultrapure water. The resulting precipitate was dispersed in 150 ml of ultrapure water and sonicated for 30 min to obtain a brown, homogeneous suspension. Finally, the suspension was dialyzed to completely remove the remaining salts and acid to obtain a graphite oxide.

The obtained graphite oxide was diluted to 0.05 wt% by ultrapure water, and after being sonicated for 30 min, the graphene oxide was peeled off, and then centrifuged at 5000 rpm for 15 min to remove the remaining unpeeled graphite oxide. Subsequently, 100 ml of a homogeneous suspension, 100 ml of ultrapure water, a solution of ΙΟΟμΙ ( (35 wt, Aldrich) and 0.7 ml of an aqueous ammonia solution (28\¥1%) were mixed in a 250 ml round bottom flask. The mass ratio of 肼 to graphene oxide is about 7:10. After vigorous agitation for 5 min, the round bottom flask was immersed in an oil bath for 1 h, and the temperature was maintained at about 95 °C. In order to obtain a stable suspension, the excess hydrazine is further removed by dialysis in a 0.5 wt% aqueous ammonia solution after the reduction reaction, and the resulting pale black fraction suspension, ie, reduced graphene oxide (RGO), is subjected to ultrasonication for 30 minutes. Processing to control the lateral length of the RGO slice.

5 g of polyacrylonitrile powder was dissolved in 850 ml of dimethylformamide solution (DMF) at 60 °C. Mix 64ml of PAN/DMF solution with 33.3ml, 50ml, 100ml RGO solution, respectively. Stir vigorously for 15 minutes. The mass ratio of RGO to PAN is 1:45, 1:30 and 1:15, respectively. A 0.5 wt% aqueous ammonia solution was then added to the beaker until it reached 500 ml, followed by vigorous stirring for 24 h. Next, a gray composite was obtained by centrifugation at 1000 rpm for 10 minutes, and then the gray composite was wet-milled with 1.6 g, the dispersant was ethanol, the ball mill was rotated at 600 rpm, and ball milled for 30 minutes. The resulting mixture was dried in a vacuum oven at 60 ° C for 2 h. Then, 0.7 g of the dried product was heated in a 320 ° C tube oven for 3 h and annealed. Finally, an electrode composite of RGO/PAN/S was obtained. The sulfur content was measured by an elemental analyzer.

Fig. 1 is a transmission electron microscope (TEM) image of RGO prepared in Example 1, from which it can be seen that the peeling of graphite oxide to graphene oxide by ultrasonic treatment is well realized.

2 is a scanning electron microscope (SEM) image of RGO/PAN/S after ball milling in Example 1, from which it can be inferred that after wet ball milling, the surface of the PAN/RGO composite is covered by S, and is subjected to heat treatment, that is, annealing. S reacts with PAN while the surface excess sulfur is evaporated.

Fig. 3 and Fig. 4 are scanning electron microscope (SEM) images of RGO/PAN/S after heat treatment in Example 1, in which RGO: PAN = 1:30, and Fig. 4 RGO: PAN = 1:15. Figure 3 shows that polyacrylonitrile is uniformly deposited on the surface of RGO. When the content of RGO is increased, as shown in Fig. 4, some RGOs are not covered by PAN/S, and the edge cross section of the massive particles can clearly see the electrolytic composite. The layered structure has a thickness of about 10 nm.

Example 2

Polypyrrole was synthesized from a pyrrole monomer (Aldrich, purity 98%) by a chemical oxidation process using FeCl ₃ as an initiator. Polypyrrole-attached graphene (Ppy/GNS) was obtained by in-situ polymerization of pyrrole on graphene. First, O.lg's graphite women (US research nano-materials Inc) were dispersed in 40 mL of methanol and acetonitrile mixed solvent (1:1 by volume) by ultrasonication (Fisher Scientific, FB120), sonicated for 2 h. . 0.2 g of pyrrole was added to the solution, stirred for 0.5 h, then 15 mL, 0.5 mol/L of FeCl _{3 was} added dropwise to the above solution, and ultrasonication was continued at room temperature, and Ppy/GNS was separated by filtration, and then passed. The ionized water and ethanol were thoroughly washed and dried overnight at 70 ° C in a vacuum atmosphere.

The Ppy/GNS Φ1 obtained from Φ1 contained a suspension of 6 g of endogenous stone (US research nano-materials Inc, 10 wt%), which was ultrasonically sonicated for 0.5 h, so that the mixture was uniformly dispersed, and then the mixture was placed in a vacuum. The solvent was removed by drying in a drying oven at 65 ° C for 3 h. Finally, the mixture was heated to 150 ° C in an Ar atmosphere for 3 h to obtain an S/Ppy/GNS electrode composite, and the elemental sulfur in the electrode composite was measured by a chemical analyzer (CHNS, Vario Micro Cube, Elementar). The content is 41%. Ppy, Ppy/GNS and Pitch were studied by Fourier transform infrared spectroscopy (FTIR, 520, Nicolet)

The chemical structure of S/Ppy/GNS. Figure 5 shows the infrared spectra of Ppy, Ppy/GNS and S/Ppy/GNS. In the figure, the characteristic peak indicated by I corresponds to the vibration of the =CH plane, II corresponds to the C-N stretching vibration, and III corresponds to the basic vibration of the pyrrole ring. Fig. 5 shows that Ppy is successfully produced by the in-situ polymerization method of the present invention, and the characteristic peak of Ppy also appears in the infrared spectrum of Ppy/GNS and S/Ppy/GNS, except that the intensity of the peak is lowered.

The crystal structure of the sample was examined by an X-ray diffractometer (XRD, D8 Dis-cover, Bruker). Figure 6 shows the XRD patterns of the prepared Ppy, S and S/Ppy/GNS. As can be seen from the figure, Ppy is amorphous, elemental sulfur is Fddd orthorhombic, and S/Ppy/GNS is located at 2Θ=24.5. And 2Θ=42.8. The broad peak at the point can be attributed to the characteristic peak of graphene, and the characteristic peak of S is not observed in S/Ppy/GNS, indicating that the nano-sized S has been well adsorbed in the composite.

Figure 7 and Figure 8 show SEM images of Ppy/GNS and S/Ppy/GNS, respectively. Figure 7 shows that after polymerization, Ppy is formed and fixed on the surface of GNS, and the pyrrole monomer is adsorbed on GNS having a large specific surface area by a π-mono bond, hydrogen bond and van der Waals force. It is apparent in Figure 8 that the staggered nanosheet-like S/Ppy/GNS are irregularly stacked together and have a rough surface coated with dense sulfur particles. This can be attributed to the strong adsorption capacity of Ppy for S. Figures 7 and 8 demonstrate the layered structure of the electrolytic composite of the present invention.

Comparative example 1

5 g of polyacrylonitrile powder was wet-milled with 1.6 g of sulfur at 60 ° C, the dispersant was ethanol, the ball mill was rotated at 600 rpm, and ball milled for 30 min. The resulting mixture was dried in a vacuum oven at 60 ° C for 2 h. Then, the dried product was heated in a tube furnace at 320 ° C for 3 hours and annealed. Finally, a PAN/S composite is obtained.

Figure 9 is a SEM image of the composite PAN/S after heat treatment provided in Comparative Example 1. Compared with Fig. 2, the composite material in Fig. 9 is mainly elliptical particles, and the agglomeration phenomenon is obvious. In Fig. 9, the particle size and dispersion of the electrode composite material are relatively uniform.

Example 3

The electrochemical performance of the S/PAN/RGO electrode composite was investigated by assembling a button cell CR2032.

The electrode composite S/PAN/RGO, the conductive agent Ketjen black KB600 and the binder PVDF were mixed in NMP according to a weight ratio of 8:1:1, and then the slurry was applied to a foam having a diameter of 12 mm. On the nickel current collector, the working electrode was dried at 80 ° C for 12 hours, and the weight ratio of RGO to PAN in the electrode composite was 1:30. As a counter electrode in the metal, the electrolyte is a solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dinonyl carbonate (DMC) (volume ratio 1:1:1) containing 1 M of LiPF ₆ . The diaphragm is ENTEK ET20-26 and is fitted with a CR2032 button battery in an argon-filled glove box. Then, through the New Ware battery test system, the battery was charged and discharged at a constant current density at room temperature, and the open circuit voltage range was 1-3V.

Comparative example 2

In Comparative Example 2, the composite material was PAN/S, and the remaining battery compositions and assembly methods were the same as in the examples.

3.

10 is a graph showing the relationship between charge and discharge voltage and specific capacity at a rate of 0.5 C in the batteries provided in Example 3 and Comparative Example 2. The average charge and discharge voltages of the batteries provided in Comparative Example 2 were 2.3 V and 1.7 V, respectively, showing Strong electrochemical polarization, and the introduction of graphene greatly reduced this electrochemical polarization. In Example 3, the discharge voltage of the battery increased from 1.7V to 1.8V, and the charging voltage dropped from 2.3V to 2.25V. Figures 11 and 12 are graphs showing the charge-discharge cycle performance of the batteries provided in Example 3 and Comparative Example 2 at 0.2C and 0.5C rates, respectively. It can be seen from the figure that: in the comparative example 2, the battery is rapidly attenuated after the cycle of 40 times, and in the case of the battery in the third embodiment, the specific capacity is stable after the previous cycles, and the capacity is maintained at 60 cycles. The retention rate is close to 95%, indicating that the electrode composite with a layered structure distributes the soluble intermediate polysulfide between the layers, increasing the utilization of sulfur, and the layered structure is enhanced to some extent. Battery cycle life and stability.

Figure 13 is a graph showing the performance test of the batteries provided in Example 3 and Comparative Example 2 at gradually increasing magnification. After the battery was cycled 10 times at a rate of 0.2 C, the current density was gradually increased to 0.5 C, 1 C, and 2 C, and then reduced to 0.2 C. For the battery in Example 3, the stable capacities corresponding to 0.2C, 0.5C, 1 C and 2C are about 1333, 1249, 1166, 800 mAh/g, respectively, and the specific capacity of the battery 2C ratio in Comparative Example 2 under the same conditions. Only 440mAh/g, about half of it. This phenomenon indicates that the presence of graphene does improve the rate performance of the electrode composite.

Figures 14 and 15 are graphs showing the relationship between the charge-discharge specific capacity and the coulombic efficiency and the number of cycles at the 0.1 C and 0.2 C rates for the batteries of Example 3 and Comparative Example 2, respectively. In Fig. 14, the initial specific capacity of the battery is 1827 mAh/g, which is higher than the theoretical specific capacity due to side reactions. After 10 cycles, it gradually decreases to a relatively stable value of 1352 mAh/g, after 90 cycles relative to the tenth time. The discharge specific capacity retention rate is 90%, indicating that the PAN/RGO/S electrode composite has good cycle stability. In Fig. 15, after the battery is cycled 200 times, the specific capacity is still 1050 mAh/g, the capacity retention ratio is 82% with respect to the tenth discharge ratio, and the first reversible discharge specific capacity retention rate is 77%. It is indicated that the layered electrode composite can absorb polysulfide between layers, which helps to improve the cycle life and power performance of the battery.

Example 4 Study on the electrochemical properties of S/Ppy/GNS electrode composites by assembling CR2025 button cells

H.

The battery includes: a lithium metal negative electrode, a S/Ppy/GNS positive electrode, a pore polypropylene membrane, and a tetraethylene glycol II impregnated with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, Aldrich, purity 96%). Methyl ether (Aldrich, purity 99%) electrolyte. The positive electrode preparation process is: 80wt% S/Ppy/GNS, 10wt binder PVDF (Kynar, HSV900) and 10wt3⁄4^々 conductive agent acetylene black (MTI, purity 99.5 %) in NMP (NMP, Sigma-Aldrich, purity) A positive electrode slurry was prepared by mixing in ≥99.5%.

The prepared positive electrode slurry was spread on a circular foamed nickel having a diameter of 1 cm, and dried in a vacuum drying oven at 60 ° C for 12 hours. In order to make the positive electrode material and the foamed nickel contact well after drying, 8 Mpa was passed through a hydraulic press. The pressure is pressed against the positive electrode. In the argon-filled Braun glove box, the button battery is assembled, and the battery is subjected to constant current charging and discharging at different current densities through a multi-channel battery tester (BT-2000). The voltage range is 1-3V, and the potentiostat is passed. VMP3, Bio-logic) for cyclic voltammetry (CV) testing with a voltage range of 1 -3V and a scan rate of 0.5mV/s. All electrochemical tests were performed at room temperature.

Figure 16 is a CV diagram of the battery provided in Example 4. As can be seen from the figure, during the cycle, the voltage and peak current of the cathode and anode peaks are small, indicating a good capacity retention of the electrode composite, CV. The results show that Ppy/GNS plays a very important role in hindering the diffusion of lithium polysulfide from the electrode.

Figure 17 is a graph showing the discharge capacity and coulombic efficiency vs. cycle number of the battery provided in Example 4 at 0.1 C charge and discharge. The battery showed a lower coulombic efficiency of 91.8% on the first cycle, and the further cycle coulombic efficiency was improved, and the reversible performance of the battery was improved due to the good contact of the remaining S with the porous Ppy. The Coulomb efficiency after the cycle of 50 times reached 99.5%, that is, the shuttle effect decreased as the number of cycles increased. On the other hand, the battery showed better cycle performance. The reversible capacity of the battery after 50 cycles was maintained at 715.8 mAh/g. Compared with the S/Ppy composite without GNS, the reversible specific capacity was increased by at least 200 mAh/g. And it is under twice the charge and discharge rate. The increase in reversible performance indicates that GNS provides an efficient electron conduction path and a layered structure of S/Ppy/GNS provides a very stable structure for sulfur.

Figure 18 is a graph showing the charge-discharge cycle performance of the battery in Example 4 at a rate of 0.5 C. The battery capacity is 8751 mAh/g. After 50 cycles, the capacity is still 597 mAh/g, indicating that the battery has good cycle stability performance. The decay rate of the cycle was 0.64%. At 1 C rate, better battery cycle performance was obtained with a decay rate of 0.54% per cycle, which is attributed to a decrease in the shuttle effect at higher current densities.

Example 5 S (Sigma-Aldrich, powder particle size 100 mesh), polyacrylonitrile (PAN, Sigma-Aldrich) and graphene (GNS, US research nano-materials Inc) were mixed at a weight ratio of 4:1:0.25 at 800 rpm. The ball was milled for 6 h, and NMP was used as a dispersing agent. After ball milling, it was dried in a vacuum oven at 60 ° C for 12 h to remove the solvent, and then heat-treated at 350 ° C for 6 h in an argon atmosphere tube furnace to melt and react with PAN.

The electrode composite S/PAN/GNS, the conductive agent acetylene black and the binder PVDF were mixed at a weight ratio of 8:1:1 in NMP to prepare a slurry, and then the slurry was applied to a foamed nickel current collector having a diameter of 1 cm. The working electrode was obtained by vacuum drying at 60 ° C for 12 hours. For the positive electrode material to be in good contact with the foamed nickel current collector, the electrode was rolled by a hydraulic press at a pressure of 8 MPa. The prepared electrodes were made to have the same weight and thickness by precisely weighing, pressing and controlling the geometry. Metal lithium is used as the counter electrode, and the electrolyte is a solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (volume ratio 1:1:1) containing 1 M of LiPF ₆ , and the separator is Polypropylene, equipped with a CR2032 button cell in an argon-filled glove box.

The battery was subjected to constant current charging and discharging at different current densities through a multi-channel battery tester (BT-2000, Arbin Instruments) with a voltage range of 1-3V.

Comparative example 3

In Comparative Example 3, the electrode material was S/PAN, and the preparation process of S/PAN, the composition of the battery, and the test method were the same as those in Example 5.

19 and FIG. 20 are graphs showing the relationship between charge and discharge voltage and capacity of the battery in Example 5 and Comparative Example 3 at a rate of 0.1 C. It can be seen from the figure: Compared with Comparative Example 3, the charge and discharge of the battery in Example 5 Electrodeization is significantly reduced, indicating a decrease in voltage difference during charge and discharge. The kinetics of the electrode composite with the addition of graphene is improved, the polarization is lowered, and the energy and power density of the battery are increased.

Fig. 21 is a graph showing the relationship between the discharge capacity and the number of cycles of the battery in Example 5 and Comparative Example 3 at a rate of 0.1 C. The electrochemical performance of the battery in Example 5 was remarkably improved, indicating that the shuttle effect in the battery was suppressed. In Comparative Example 3, the capacity of the battery was quickly attenuated, and the battery capacity was reduced by 38% from the initial after 50 charge and discharge cycles.

Figure 22 is a graph showing the cycle performance of the battery in Example 5 at different discharge rates. The excellent high-rate capacity of the battery is due to the excellent electrical conductivity of the electrode composite graphene. In particular, after initial charge and discharge cycles of 1C and 2C, the discharge capacity is gradually increased, and the capacity is almost no during the 100 cycles. Attenuation, indicating that the battery has very stable cycle performance.

Example 6

0.62 mL of acrylonitrile (ACROS, purity 99%), 10 mg of potassium persulfate (EMD, purity 99%), O.lg sodium lauryl sulfate (Sigma-Aldrich, purity ≥99%), 19.72g nanosulphur suspension (US research nano-materials Inc, weight percentage 10\¥1%) and 0.616g nanographene suspension (US research nano-materials Inc, 2% by weight by weight) was dissolved in 20 mL of deionized water. In order to polymerize acrylonitrile, the mixture was vigorously stirred at 70 ° C for 10 h, and then thoroughly washed by centrifugation with water. The washed product was dried in a vacuum oven at 60 ° C for 3 h to remove the solvent, and then heat-treated in a tube furnace under an argon atmosphere at 350 ° C for 3 hours to melt the sulfur and react with PAN to obtain a layered structure. Structure of S/PAN/GNS.

Further, the obtained S/PAN/GNS electrode composite was assembled as a positive electrode active material. The remaining composition of the battery and the test method are the same as those in the embodiment 5.

Fig. 23 is a graph showing the charge and discharge cycle performance of the battery of Example 6 at a rate of 0.1 C. When the battery first discharges, the specific capacity reaches 1588.9 mAh/g, the capacity of the battery is almost no attenuation during 100 cycles of charging and discharging, and the Coulomb efficiency is about 100%, indicating that the shuttle effect in the battery is suppressed, further verifying that the present invention provides The electrode composite obtained by the preparation method has excellent cycle performance.

Example 7

The ig graphite and 50 g of sodium chloride were ground in an agate mortar for 10 minutes to remove contaminants from the graphite and finely ground. The mixture of graphite and sodium chloride was then washed several times with distilled water and vacuum filtered to remove sodium chloride, and the membrane pore size was 0.2 μm. After filtration, the graphite was placed in a vacuum oven and dried at 70 ° C for 20 min to remove residual moisture. After drying, the obtained solid was mixed with 23 ml of concentrated sulfuric acid in a 250 ml round bottom flask, and stirred at 25 ° C for 24 hours without interruption. To the above dispersion, 100 mg of sodium nitrate was added, and the mixture was stirred for 5 minutes to be dissolved. Then, the flask was placed in a water bath, the temperature was kept below 20 ° C, 3 g of potassium permanganate was added to the suspension, and then heated to 40 ° C for 30 min, 3 ml of ultrapure water, 5 min, and then 3ml ultra-pure water for people with force, and 5min ultra-pure water for people with 5ml. Thereafter, the suspension was heated to 100 ° C and kept for 15 minutes, then 140 ml of ultrapure water and 10 ml of hydrogen peroxide (H ₂ O ₂ , 30 wt ) were added to stop the reaction. The suspension was further stirred for 5 min, then washed twice with 5% hydrochloric acid, and washed several times with ultrapure water. The resulting precipitate was dispersed in 150 ml of ultrapure water and sonicated for 30 min to obtain a brown, homogeneous suspension. Finally, the suspension was dialyzed to completely remove the remaining salts and acid to obtain a graphite oxide.

The obtained graphite oxide was diluted to 0.05 wt% by ultrapure water, and after being sonicated for 30 min, the graphene oxide was peeled off, and then centrifuged at 5000 rpm for 15 min to remove the remaining unpeeled graphite oxide. Subsequently, 100 ml of a homogeneous suspension, 100 ml of ultrapure water, a solution of ΙΟΟμΙ ( (35 wt, Aldrich) and 0.7 ml of an aqueous ammonia solution (28 \¥1%) were mixed in a 250 ml round bottom flask.肼 The mass ratio to graphene oxide is about 7:10. After vigorous stirring for 5 min, the round bottom flask was immersed in an oil bath for 1 hour, and the temperature was maintained at about 95 °C. In order to obtain a stable suspension, the excess hydrazine is further removed by dialysis in a 0.5 wt% aqueous ammonia solution after the reduction reaction, and the resulting pale black fraction suspension, ie, reduced graphene oxide (RGO), is subjected to ultrasonication for 30 minutes. Processing to control the lateral length of the RGO slice.

64 ml of a PAN/DMF solution with a concentration of 5.88 g/L was mixed with different amounts of RGO solution to make the mass ratio of RGO to PAN 1:16 and 1:32, respectively; vigorous stirring for 15 min. Water was then added to the beaker until it reached 600 ml, followed by vigorous stirring for 24 h. Next, a gray composite was obtained by centrifugation at 100 rpm for 10 minutes, and then the gray composite was wet-milled with 1.6 g of sulfur, the dispersant was ethanol, the ball mill was rotated at 600 rpm, and ball milled for 30 minutes. The resulting mixture was dried in a vacuum oven at 60 ° C for 2 h. Then, 0.7 g of the dried product was heated in a tube furnace at 150 ° C for 1 h and at 320 ° C for 3 h for annealing. Finally, an electrode composite of S/PAN/RGO was obtained, which was designated as S/PAN/RGO-16, S/PAN/RGO-32, respectively. Among them, the sulfur content in both was about 44% by weight as measured by an elemental analyzer.

Example 8

The electrochemical performance of the electrode composite S/PAN/RGO-16 was investigated by assembling a button cell CR2032.

The electrode composite material S/PAN/RGO-16, the conductive agent Ketchen Black KB600 and the binder PVDF were mixed in NMP according to a weight ratio of 8:1:1, and then the slurry was applied to a diameter of 12 mm. The working electrode was prepared by drying at 80 ° C for 12 hours on a foamed nickel current collector. Metal lithium is used as the counter electrode, and the electrolyte is a solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) (volume ratio 1:1:1) containing 1 M of LiPF ₆ , and the separator is ENTEK ET20-26, equipped with a CR2032 button battery in an argon-filled glove box. Then, through the New Ware battery test system, the battery was charged and discharged at a constant current density at room temperature, and the open circuit voltage range was 1-3V.

Example 9

Different from Example 8, the electrochemical properties of the electrode composite S/PAN/RGO-32 were studied by replacing S/PAN/RGO-16 with S/PAN/RGO-32.

Fig. 24 is a graph showing the relationship between the charge and discharge voltage and the specific capacity at a rate of 0.1 C in the battery of Example 8. As can be seen from Figure 24, the initial discharge capacity of the composite S/PAN/RGO-16 is approximately greater than 1800 mAh/g (calculated based on sulfur). This is much larger than the theoretical capacity of sulfur of 1672 mAh/g, because irreversible lithium is inserted into the PAN backbone of the conjugated π system. In the second cycle, the composite exhibited a reversible capacity of 1470 mAh/g, which represents a sulfur utilization of approximately 90%. At the same time, it can be seen from Fig. 24 that in the first cycle, there is a small voltage platform at 2.35 V (the arrow pointing in Fig. 24), and there is a large voltage platform at 1.65V. These two voltage platforms are difficult to distinguish between the second and subsequent cycles. In fact, the only voltage platform is around 1.8V. In addition, from the 1st to the 10th, the charge and discharge platform is converted to a higher value.

Figure 25 is a CV curve of the battery of Example 8, the scan rate is 0. l mV / s. In the first cycle, a small cathode peak appeared at 2.35V (indicated by the arrow in Fig. 25), and a large cathode peak appeared at 1.21 V. This indicates a two-step reaction between lithium and sulfur. There is a large anode peak at 2.4V, which desorbs LiS _n for lithium ions. In the subsequent cycle, the 2.35V cathode peak disappeared, while the 1.21 V cathode peak shifted significantly, and in the 10th cycle it was transferred to 1.69V. In addition, the anode peak has a very small displacement. This is consistent with Figure 24.

Figure 26 is a graph showing the performance test of the batteries of Example 8 and Example 9 at gradually increasing magnification. The battery was cycled 10 times at a rate of 0.2 C, 10 cycles of 0.5 C, 10 cycles of 1 C, and 10 cycles of 2 C, and then recycled to 0.2 C for 10 cycles. As can be seen from Fig. 26, the stable capacities of the batteries of Example 8 at 0.2C, 0.5C, 1C and 2C were approximately 1353 mAh/g, 1292 mAh/g, 1180 mAh/g, and 828 mAh/g, respectively. This indicates that the battery of Example 8 has more excellent rate performance.

In addition, the battery of Example 8 also had good capacity recovery performance, and 0.2C still had an initial capacity retention rate of 96% after high-rate cycling, indicating that the composite S/PAN/RGO-16 has a very stable structure.

Fig. 27 is a graph showing the charge and discharge cycle performance of the battery of Example 8 and Comparative Example 2. As can be seen from Fig. 27, the capacity characteristics of Comparative Example 2 during the first 20 cycles were substantially similar to those of Example 8, and after 40 cycles, the capacity began to rapidly decrease, and after 100 cycles, it almost decreased to 0 mAh/g. This indicates that the active substance has been substantially inactivated. The root cause of the inactivation of the active substance is the dissolution of polysulfide and the shuttle effect. On the other hand, in Example 8, after 10 cycles, a reversible specific capacity of about 1385 mAh/g was obtained. After 200 cycles, it remains at 1100 mAh/g and achieves a capacity retention of 80% of the stable capacity. In addition, after 20 cycles, its Coulomb efficiency is close to 100%. This indicates that the composite material S/PAN/RGO-16 has very excellent cycle performance, which effectively suppresses the dissolution of polysulfide and the shuttle effect.

Although the inventors have made a detailed description and enumeration of the technical solutions of the present invention, it should be understood that modifications and/or variations or equivalents of the above-described embodiments are obvious to those skilled in the art. The present invention is not limited to the spirit and scope of the present invention, and the terminology used in the present invention is not intended to limit the invention.

Claims

Right J book

An electrode composite characterized by: the electrode composite material comprising elemental sulfur, a conductive polymer, and graphene or a reduced graphene oxide.

The electrode composite according to claim 1, wherein the conductive polymer is one selected from the group consisting of polypyrrole and polyacrylonitrile.

The electrode composite according to claim 1, wherein the electrode composite has a layered structure.

The electrode composite according to claim 3, wherein the elemental sulfur is attached to the conductive polymer.

The electrode composite according to claim 3, wherein the graphene or the reduced graphene oxide has a nano-layered structure, and the elemental sulfur and the conductive polymer are attached to the graphene together Or reduced graphene oxide.

The electrode composite according to claim 1, wherein in the electrode composite, the specific gravity of the elemental sulfur ranges from 30 to 90%, and the specific gravity of the conductive polymer ranges from 9 to 50. %, the graphene or reduced graphene oxide has a specific gravity ranging from 1 to 20%.

The electrode composite according to claim 2, wherein in the electrode composite, a mass ratio of polyacrylonitrile to reduced graphene oxide is 45:1 - 10:1.

A positive electrode, characterized in that the positive electrode comprises the electrode composite material according to any one of claims 1 to 7.

A battery comprising a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, the positive electrode comprising at least the electrode composite material according to any one of claims 1 to 7.

10. A method of preparing an electrode composite, characterized in that: the preparation method comprises the following steps:

The preparation method according to claim 10, wherein the predetermined temperature range is 60-80 °C.

12. A method of preparing an electrode composite, characterized in that: the preparation method comprises the following steps:

The elemental sulfur, polyacrylonitrile and graphene are dispersed in a dispersing agent, mechanically mixed, and dried, and the dried product is subjected to heat treatment under a protective gas atmosphere.

13. A method of preparing an electrode composite, characterized in that: the preparation method comprises the following steps Step:

The polyacrylonitrile solution and the reduced graphene oxide suspension are mixed under weak alkaline conditions. After deposition, the deposited product is filtered out and redispersed, and the dispersion is mechanically mixed with elemental sulfur and dried, and dried. The product is heat treated under a protective gas atmosphere.

The preparation method according to claim 12 or 13, wherein the mechanical mixing is ball milling mixing.

The preparation method according to any one of claims 10 to 14, wherein the heat treatment temperature ranges from 200 to 400 °C.

16. A method of preparing an electrode composite, characterized in that: the preparation method comprises the following steps:

The preparation method according to claim 16, wherein the composite of polypyrrole and graphene is prepared by in-situ polymerization, and comprises the following steps:

The graphene is ultrasonically dispersed in a mixed solvent of methanol and acetonitrile, pyrrole is added, and the ferric chloride solution is added while ultrasonic treatment, and the precipitate is obtained by filtration, and the precipitate is washed and dried to obtain polypyrrole/graphene, and polypyrrole is formed. On graphene.

The preparation method according to claim 16, wherein the heat treatment temperature ranges from 150 to 350 °C.

The preparation method according to any one of claims 10 to 16, wherein the drying temperature ranges from 60 to 80 °C.