Composite positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of battery electrode materials, and discloses a composite positive electrode material and a preparation method and application thereof.The composite positive electrode material comprises a metal aluminum foil current collector, conductive paste is loaded on the surface of the metal aluminum foil current collector, and the conductive paste comprises a copper powder / commercial sulfur-carbon mixture, a conductive agent and a binder according to the mass ratio of 8: (0.1-1.0): (0.2-1.0). The copper powder is added into the positive electrode material, so that the prepared composite positive electrode material has higher initial specific discharge capacity (1347 mAh / g) and better cycle stability; the problems of insufficient electrochemical performance and poor cycle performance of the magnesium-sulfur battery are solved, and the method is suitable for popularization and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery electrode materials, and particularly relates to a composite positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application disclosure and can not constitute the prior art.

[0003] The escalating energy demand and growing environmental concerns have accelerated the pace of developing and deploying clean energy. Lithium-ion batteries (LIBs) have played a key role in powering mobile electronic devices and electric vehicles (EVs) and facilitating the storage of renewable energy. However, the energy density of lithium batteries has reached its theoretical limit, with battery-level energy densities of ≈240 Wh kg −1 and 670 Wh L −1 , which cannot meet the growing energy demand and urgently need to develop new alternative energy storage systems.

[0004] Compared with lithium batteries, rechargeable magnesium batteries have unique advantages: first, the reserves of magnesium in the earth's crust are much higher than those of lithium, which makes the price of metal magnesium much lower than that of lithium; second, magnesium has less chemical activity than lithium, is safer to process and operate, and is less likely to produce dendrites, with high safety; third, magnesium has a higher theoretical volumetric specific capacity than lithium (3832 and 2062 mAh∙cm -3 , respectively). For the above reasons, rechargeable magnesium batteries have the potential to become high-capacity and high-output power batteries, so rechargeable magnesium batteries with magnesium as the negative electrode have become a research hotspot for a new type of battery system.

[0005] The positive electrode materials of rechargeable magnesium batteries include transition metal oxides (such as V2O5, MoO3, MnO2, etc.), transition metal sulfides (such as TiS2, MoS, etc.), polyanion phosphate materials and silicate materials (such as MgMnSiO4, MgFeSiO4), etc. However, there are problems such as very slow kinetic insertion of magnesium, low insertion capacity, high overpotential, and serious decay under multiple cycles, which make the research of magnesium positive electrode materials enter a bottleneck. Therefore, developing positive electrode materials with good reversibility, good safety performance, high capacity, high voltage, and long cycle life is one of the main development directions of rechargeable magnesium batteries. The theoretical specific capacity of sulfur is as high as 1675 mAh / g, which is much higher than that of traditional lithium-ion battery positive electrode materials (such as LiCoO2 of about 140 mAh / g), and adding magnesium to the battery makes the magnesium-sulfur battery have high energy density. And sulfur is an element with abundant reserves on earth, low price and environmental friendliness, which is suitable for large-scale energy storage applications. However, the conductivity of sulfur is poor, the interface of the sulfur positive electrode is unstable when the sulfur loading is high, and the long-term cycle performance is poor, which limits the market application of magnesium-sulfur batteries. SUMMARY

[0006] The present application aims at solving the problem that the current magnesium-sulfur battery cannot balance high energy density and long-term cycle performance, and provides a composite positive electrode material, a preparation method and application thereof, solves the problem of poor conductivity of Al current collector in magnesium-sulfur battery, and improves the performance and cycle life of the battery.

[0007] The technical scheme of the present application is as follows: In one aspect, the present application provides a composite positive electrode material, which comprises a metal aluminum foil current collector, and the surface of the metal aluminum foil current collector is loaded with conductive paste, and the particle size of the paste is 10-30 um. The conductive paste comprises copper powder / commercial sulfur-carbon mixture, conductive agent and binder in a mass ratio of 8:0.1-1.0:0.2-1.0.

[0008] Preferably, the ratio of the copper powder / commercial sulfur-carbon mixture is 1-8:8.

[0009] According to a preferred embodiment, the conductive agent is one or more of Ketjen black, acetylene black, graphene, Super-P carbon black, carbon nanotube, and graphene mixed; According to a preferred embodiment, the binder is one or more of hydroxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA) mixed.

[0010] In another aspect, the present application provides the use of the composite positive electrode material as described above as a positive electrode material of a magnesium-sulfur battery.

[0011] In another aspect, the present application provides the use of the composite positive electrode material as described above as a positive electrode material of a magnesium-sulfur battery in the preparation of a magnesium-sulfur battery.

[0012] A positive electrode of a magnesium-sulfur battery is prepared by using the composite positive electrode material as described above.

[0013] A magnesium-sulfur battery comprises a battery positive electrode, a battery negative electrode and an electrolyte, the battery positive electrode is prepared by using the composite positive electrode material as described above, and the battery negative electrode is prepared by using metal magnesium, preferably metal magnesium foil.

[0014] The addition of Cu powder in the sulfur positive electrode material can well improve the electronic conductivity of the Al current collector, promote the conversion of magnesium sulfide, and thus make the battery exhibit excellent cycle performance. The electrochemical mechanism of the copper powder in the composite material of the present application for improving the performance of the battery is as follows: (1) Strengthening the electronic conduction network High conductivity of copper powder: the volume resistivity of copper is 1.68*10 -8Ω·m) is much lower than carbon (graphite is about ~10 -6 Ω·m), copper powder forms a three-dimensional conductive skeleton in the positive electrode, significantly reducing the electrode sheet resistance and improving the electron transmission efficiency.

[0015] Redundancy of conductive paths: Even if some sulfur active substances are separated from the carbon coating due to volume expansion, copper powder can still provide additional electron paths and reduce the "dead sulfur" area.

[0016] (2) Catalytic conversion of polysulfides Copper adsorption and catalysis of polysulfides: The copper surface can chemically adsorb polysulfides (Cu-S bond formation), inhibiting their dissolution and diffusion, while catalyzing the redox reaction of polysulfides (accelerating the conversion kinetics of MgS and S) and reducing the shuttle effect.

[0017] Reduce polarization: The catalytic effect of copper can reduce the overpotential during charging and discharging, thereby improving voltage efficiency and specific capacity.

[0018] (3) Improve interface stability Mechanical support: The rigid particles of copper powder can buffer the volume change of the sulfur positive electrode, maintain the integrity of the electrode structure, and reduce the shedding of active materials during the cycle.

[0019] Another aspect of the present invention provides a method for preparing a composite positive electrode material, comprising the following steps: Step 1: Weigh a certain amount of copper powder, commercial sulfur carbon, conductive agent and binder according to the mass ratio as mentioned above and grind them in solvent N-methyl-2-pyrrolidone to obtain a slurry; the conductive agent is a mixture of one or more of Ketjen black, acetylene black, graphene, Super-P carbon black, carbon nanotubes, and graphene; the binder is a mixture of one or more of hydroxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA); the mass ratio of powder: solvent N-methyl-2-pyrrolidone is 1:5-10.

[0020] Step 2: The slurry is coated on a metal aluminum foil current collector and dried to obtain a copper powder / sulfur carbon / aluminum ternary composite positive electrode.

[0021] Compared with the existing technology, the beneficial effects of the present invention are: 1. A composite cathode material with a higher initial discharge capacity (1347 mAh / g) than commercial sulfur-carbon / Al foil magnesium-sulfur battery electrode materials without Cu powder addition, and better cycling stability. After 68 cycles at 0.1C, the discharge capacity reached 710 mAh / g, significantly improving battery performance. 2. A composite positive electrode material, wherein a carbon material selected from sulfur-carbon materials is used as a sulfur carrier, provides a conductive network, and simultaneously serves as an adsorbent for polysulfides; and sublimed sulfur is used as an active material. The addition of a conductive agent can improve the conductivity of the electrode material. The addition of copper powder in the present application significantly improves the electrochemical performance of the prepared composite electrode material, and the preparation is simple and easy to obtain. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Cycle performance chart of button cell for Example 1 with Cu powder added and Example 2 without Cu powder added; Figure 2 First cycle charge-discharge curve for Example 1 with Cu powder added; Figure 3 First cycle charge-discharge curve for Example 2 with Cu powder added; Figure 4 First cycle charge-discharge curve for Example 3 with Cu powder added. DETAILED DESCRIPTION

[0023] The specific examples listed in the present application are only used as examples of the present application, and the present application is not limited to the specific examples described below. Any equivalent modifications and alternatives to the examples described below are also within the scope of the present application for those skilled in the art. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present application should be included in the scope of the present application. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer is specified for all reagents or instruments, they are all conventional products that can be purchased on the market. In order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art will understand that the present application can also be implemented without certain specific details. In some embodiments, methods, means, apparatus and steps that are well known to those skilled in the art are not described in detail in order to highlight the main idea of the present application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Unless otherwise specified, the units used in the specification are international standard units, and the numerical values and numerical ranges appearing in the present application should be understood to include the systematic errors that are inevitable in industrial production.

[0025] The selected materials are all commercial products, which have the advantage of being simple to prepare.

[0026] The features and properties of the present application are further described in detail below in conjunction with the examples.

[0027] Example 1 Step one: Cu powder (5-10um), commercial sulfur carbon (particle size: 5-30um), Super-P (1-10um), and polyvinylidene fluoride (PVDF) (particle size: 30-50um) were weighed according to the mass ratio of 3:8:1:1; Step two: the above weighed materials were added to a stirring and grinding device and stirred for 30 min, and mixed uniformly at a stirring speed of 800-1500 r / s; Step three: the powder (0.6g) (particle size: 10-30um) after sufficient grinding was added to 3-5ml N-methyl-2-pyrrolidone to form a uniform slurry, the slurry was placed on a carbon-coated aluminum foil, the coating thickness was 200um, then vacuum dried and cut into positive electrode sheets (sulfur average loading was 1.5mg cm -2 ) with a diameter of 12mm.

[0028] Example 2 Step one: Cu powder, commercial sulfur carbon, Super-P, and polyvinylidene fluoride (PVDF) were weighed according to the mass ratio of 5:8:1:1; Step two: the above weighed materials were added to a stirring and grinding device and stirred for 30 min, and mixed uniformly at a stirring speed of 800-1500 r / s; Step three: the powder (0.6g) (particle size: 10-30um) after 30 min of sufficient grinding was added to 3-5ml N-methyl-2-pyrrolidone to form a uniform slurry, the slurry was placed on a carbon-coated aluminum foil, the coating thickness was 200um, then vacuum dried and cut into positive electrode sheets (sulfur average loading was 1.5mg cm -2 ) with a diameter of 12mm.

[0029] Example 3 Step one: Cu powder, commercial sulfur carbon, Super-P, and polyvinylidene fluoride (PVDF) were weighed according to the mass ratio of 8:8:1:1; Step two: the above weighed materials were added to a stirring and grinding device and stirred for 30 min, and mixed uniformly at a stirring speed of 800-1500 r / s; Step three: the powder (0.6g) (particle size: 10-30um) after sufficient grinding was added to 3-5ml N-methyl-2-pyrrolidone to form a uniform slurry, the slurry was placed on a carbon-coated aluminum foil, the coating thickness was 200um, then vacuum dried and cut into positive electrode sheets (sulfur average loading was 1.5mg cm -2 ) with a diameter of 12mm.

[0030] Comparative Example 1 The preparation method of Comparative Example 1 is the same as that of Example 1, except that in step one, no copper powder is weighed, and commercial sulfur carbon, Super-P, and polyvinylidene fluoride (PVDF) are weighed according to a mass ratio of 8:1:1.

[0031] The above positive electrode sheet is used to prepare a magnesium-sulfur battery, including the following steps: Step one: assemble a coin battery in an Ar atmosphere (water and oxygen content is less than 0.01 ppm) in a glove box.

[0032] Step two: the negative electrode sheet is a magnesium sheet (the surface oxide layer of the magnesium sheet has been removed), the separator is a PP separator with a modified coating, and a boron-based system electrolyte is used.

[0033] Step three: assemble in the order of positive electrode sheet, electrolyte, separator, electrolyte, and magnesium sheet, and then seal with a hydraulic sealer to obtain a magnesium-sulfur battery.

[0034] The first cycle charge-discharge curve of the magnesium-sulfur battery prepared from the positive electrode material of Example 1-3 is shown in Figures 2-4 As can be seen from the figure, the higher the proportion of copper powder, the higher the first cycle discharge capacity of the magnesium battery. The specific discharge capacity of the first cycle of Examples 1-3 is 812 mAh / g, 940 mAh / g, and 1347 mAh / g, respectively. The cycle performance graph of the battery of Example 1 and Comparative Example 1 is shown in Figure 1 As can be seen from the figure, the battery prepared from the positive electrode material of Example 1 with added Cu powder has significantly stronger discharge performance, and the performance does not decrease significantly after cycling for several times, and the cycle performance is excellent.

[0035] The above examples only express the specific embodiments of the present application, which are described in detail and in detail, but should not be construed as limiting the scope of protection of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A composite positive electrode material, characterized in that It includes a metal aluminum foil current collector, the surface of which is loaded with a conductive slurry. The conductive paste comprises a copper powder / commercial sulfur-carbon mixture, a conductive agent and a binder in a mass ratio of 8:0.1-1.0:0.2-1.

0.

2. A composite cathode material according to claim 1, characterized in that: The mass ratio of the copper powder to the commercial sulfur-carbon mixture is 1-8:

8.

3. A composite cathode material according to claim 1, characterized in that: The conductive agent is a mixture of one or more of Ketjen black, acetylene black, graphene, Super-P carbon black, carbon nanotubes, and graphene.

4. A composite cathode material according to claim 1, characterized in that: The binder is one or a mixture of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

5. The method for preparing a composite positive electrode material according to any one of claims 1 to 4, characterized in that: The steps include: Step 1: Weigh a certain amount of copper powder, commercial sulfur carbon, conductive agent and binder according to the mass ratio as mentioned above, mix and grind in N-methyl-2-pyrrolidone to obtain a slurry with a particle size of 10μm-30μm; Step 2: The slurry is coated on a metal aluminum foil current collector and dried to obtain a copper powder / sulfur carbon / aluminum ternary composite positive electrode.

6. Use of the composite positive electrode material according to any one of claims 1 to 4 as a positive electrode material for a magnesium-sulfur battery.

7. Use of the composite positive electrode material according to any one of claims 1 to 4 as a positive electrode material for a magnesium-sulfur battery in the preparation of a magnesium-sulfur battery.

8. A magnesium-sulfur battery positive electrode, characterized in that: The composite positive electrode material is prepared according to any one of claims 1 to 4.

9. A magnesium-sulfur battery, characterized in that: The invention comprises a battery positive electrode, a battery negative electrode and an electrolyte, wherein the battery positive electrode adopts a composite positive electrode material as claimed in any one of claims 1 to 4, and the battery negative electrode adopts metal magnesium.

10. A magnesium-sulfur battery according to claim 9, characterized in that: The negative electrode of the battery is a metal magnesium foil.

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