Heterostructure composite material of electronegative carbon nanotube modified manganese oxide, preparation method of heterostructure composite material, positive plate and zinc ion battery

Abstract

The invention relates to the technical field of electrochemical energy storage, in particular to an electronegative carbon nanotube modified manganese oxide (CMO) heterostructure composite material, a preparation method and application thereof, a preparation method of a positive electrode material, a positive plate and a zinc ion battery. The novel positive electrode active material comprises an electronegative carbon nanotube and manganese oxide, manganese dioxide is modified through electronegative carbon nanotubes, and a conductive skeleton network of the electronegative carbon nanotubes (CNTs) enables manganese oxygen materialization to have a shorter ion diffusion path and more proton adsorption active sites, so that rapid electron transmission and reversible structure evolution of manganese oxide are facilitated, more attachment positions are provided for hydrogen ion deintercalation, and the hydrogen ion deintercalation efficiency is improved. Meanwhile, the CNTs network containing the electronegative groups can construct a regional proton enrichment environment on the positive electrode side, and the reaction is promoted. More importantly, carboxyl or hydroxyl groups with electric loads in the carbon nanotubes can promote formation of Mn-O-C interface bonds, dissolution and shuttle side reaction of Mn < 2 + > in the CMO positive electrode are effectively inhibited, and the structural integrity and reaction kinetics of the CMO positive electrode are improved. Therefore, the electronegative group in the functionalized carbon nanotube can effectively limit the dissolution of Mn < 2 + > and inhibit the irreversible deintercalation reaction of Zn < 2 + >, reduce the irreversible Mn < 3 + > disproportionation reaction and the formation of ZnMn2O4, and construct a low-cost and high-stability aqueous zinc-manganese battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage technology, and in particular to a heterostructure composite material of electronegative carbon nanotubes modified with manganese oxide and a preparation method thereof, a positive electrode sheet and a zinc ion battery. Background Art

[0002] In the current field of energy storage technology, aqueous zinc batteries (AZBs) have emerged and attracted much attention. Its zinc negative electrode has the significant advantages of low cost, inherent safety and reliability, coupled with a redox potential as low as -0.76V compared to the standard hydrogen electrode, and a theoretical capacity of up to 820mAh / g, making aqueous zinc batteries expected to be among the most promising energy storage devices. At this stage, researchers have conducted extensive and in-depth explorations on positive electrode materials, and many types of positive electrode materials have come out one after another. However, the road to designing and developing high-energy positive electrode materials is still full of thorns, especially in terms of how to achieve rapid kinetic processes and ensure that the material structure has a high degree of stability. These two key nodes still face severe challenges and need to be overcome. Manganese oxides have attracted much attention due to their diverse crystal structures and high theoretical energy density. However, they have the Jahn-Teller effect and Mn 3+ Disproportionation problem, resulting in irreversible structural changes, Mn 2+ Poor dissolution, cycling stability, and reaction kinetics as well as unclear energy storage mechanisms limit their practical applications.

[0003] To solve these problems, strategies such as transition metal doping, defect engineering, and optimization of electrolyte additives have been adopted. Although some results have been achieved, there are still many problems. For example, doped ions or pre-intercalation may react with Zn 2+ The strong interaction leads to precipitation during the cycle, resulting in structural collapse and capacity decay; the concentration of electrolyte additives is limited, and battery performance can only be improved within a certain range; the commonly used electrodeposition and hydrothermal methods for preparing MnO2 positive electrodes are not conducive to the rapid preparation of modified materials. Therefore, it is necessary to find more effective strategies to achieve MnO2 / Mn 3+ Chemical reversibility and rapid reaction are the key to large-scale application of MnO2 positive electrode materials.

[0004] In order to solve the above problems, this application is proposed. Summary of the invention

[0005] The present application provides a heterostructure composite material of electronegative carbon nanotubes modified manganese oxide and a preparation method thereof, a positive electrode sheet and a zinc ion battery, so as to improve the specific capacity and cycle stability of the manganese dioxide positive electrode of an aqueous zinc ion battery.

[0006] Manganese dioxide is modified by electronegative carbon nanotubes. The conductive skeleton network of electronegative carbon nanotubes (CNTs) makes manganese oxide have a shorter ion diffusion path and more proton adsorption active sites, which is conducive to rapid electron transport and reversible structural evolution of manganese oxide, providing more attachment sites for hydrogen ion deintercalation. At the same time, the CNTs network containing electronegative groups can build a regional proton-enriched environment on the positive electrode side to promote the reaction. More importantly, the charged carboxyl or hydroxyl groups in carbon nanotubes can promote the formation of Mn-OC interface bonds, effectively inhibiting the Mn in the CMO positive electrode. 2+ Therefore, the electronegative groups in functionalized carbon nanotubes can effectively limit the dissolution and shuttling side reactions of Mn 2+ Dissolution and inhibition of Zn 2+ The irreversible deintercalation reaction reduces the irreversible Mn 3+ The disproportionation reaction and the formation of ZnMn2O4 are used to build a low-cost and highly stable aqueous zinc-manganese battery.

[0007] In a first aspect, the present application provides a heterostructure composite material of electronegative carbon nanotubes modified with manganese oxide, the heterostructure composite material comprising: electronegative carbon nanotubes and manganese oxide;

[0008] At least a portion of the electronegative groups of the electronegative carbon nanotubes are not bonded to the manganese oxide.

[0009] The electronegative groups contained in the electronegative carbon nanotubes are selected from: one or more of carboxyl, hydroxyl, and amino groups;

[0010] A portion of the electronegative groups of the electronegative carbon nanotubes are bonded to the manganese oxide.

[0011] For example, when the electronegative group is selected from carboxyl and hydroxyl, a Mn—OC bond is formed between the electronegative carbon nanotube and the manganese oxide.

[0012] When the electronegative group is selected from: amino group, a Mn-NC bond is formed between the electronegative carbon nanotube and the manganese oxide. At least part of the electronegative groups of the electronegative carbon nanotube are not bonded to the manganese oxide, and this part of the electronegative groups can provide more active sites for proton adsorption, and provide more attachment positions for the deintercalation of hydrogen ions. At the same time, the carbon nanotube containing electronegative groups can construct a regional proton-enriched environment on the positive electrode side, promote the reaction, and play a role in improving the specific capacity of the manganese dioxide positive electrode in the zinc ion battery and enhancing the reversibility.

[0013] The electronegative groups of the electronegative carbon nanotubes form bonds with the manganese oxide, which can inhibit the formation of Mn in the C-MnO2 positive electrode. 2+Shuttle, improving the positive electrode structure stability and reaction kinetics.

[0014] The manganese oxide is one or more of manganese dioxide, dimanganese trioxide or trimanganese tetraoxide.

[0015] Preferably, the mass ratio of the electronegative carbon nanotubes to the manganese oxide is (0.1-0.50):1.

[0016] A second aspect of the present application provides a method for preparing a heterogeneous structure composite material, the method comprising the following steps:

[0017] mixing electronegative carbon nanotubes and manganese oxide to obtain a mixture;

[0018] Add the solvent to the mixture, and transfer to stirring after sonication;

[0019] After the stirring is completed, the solid and liquid are separated, and the solid is dried to obtain a heterogeneous structure composite material.

[0020] The mixing method can be hand grinding or mechanical stirring, but ball milling is more uniform.

[0021] The solvent is water or an alcohol solution.

[0022] The stirring can be carried out at room temperature, for example, 15-25° C., or under heating conditions, such as 60-90° C. Heating is beneficial to the reaction.

[0023] Since the present application adopts the method of mixing, ultrasonication and stirring to make the electronegative carbon nanotubes and manganese oxide contact, it is inevitable that a part of the electronegative groups of the electronegative carbon nanotubes will not form a bonding reaction with the manganese oxide during this process. Therefore, a part of the electronegative groups of the electronegative carbon nanotubes will form a chemical bond with the manganese oxide, while another part of the electronegative groups of the electronegative carbon nanotubes will not form a chemical bond with the manganese oxide.

[0024] In addition, since there are many electronegative groups on a carbon tube, some of the electronegative groups of the electronegative carbon nanotube are bonded to the manganese oxide, while the other electronegative groups are not bonded to the manganese oxide.

[0025] The third aspect of the present application provides the use of the heterostructure composite material described in the first aspect as a positive electrode material for a zinc ion battery. Preferably, the heterostructure composite material is used to improve the specific capacity and cycle stability of the manganese dioxide positive electrode of a zinc ion battery.

[0026] More preferably, the heterostructure composite material improves the specific capacity of the manganese dioxide positive electrode of the zinc ion battery by promoting hydrogen ion deintercalation.

[0027] The fourth aspect of the present application provides a method for preparing a positive electrode material, which comprises the following steps: adding a solvent to the heterogeneous structure composite material of the first aspect at a mass ratio of (7 to 9):1 to grind and mix, coating or rolling it onto a current collector, and drying it to obtain a positive electrode material.

[0028] Preferably, the loading amount of the heterogeneous structure composite material on the current collector is 1.0 to 20.0 mg cm -2 .

[0029] Preferably, the current collector is selected from one or more of carbon cloth, titanium foil, carbon felt or stainless steel mesh.

[0030] The drying condition is 60-90°C for 12-24 hours.

[0031] Preferably, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0032] A fifth aspect of the present application provides a positive electrode sheet, the positive electrode sheet comprising: a positive electrode material layer; the positive electrode material layer comprises the heterostructure composite material described in any one of the first aspects.

[0033] A sixth aspect of the present application provides a zinc ion battery, the battery comprising the positive electrode sheet described in the fifth aspect.

[0034] The seventh aspect of the present application provides a method for improving the reversibility of a zinc ion battery, wherein the positive electrode material of the zinc ion battery contains a heterostructure composite material of electronegative carbon nanotubes modified with manganese oxide. In the present application, the reversibility of the zinc ion battery is reflected in the cycle stability.

[0035] Preferably, the zinc ion battery is an electrolyte containing manganese ions. For example, it contains zinc sulfate and a manganese-containing additive. The manganese-containing additive can be one or more of manganese sulfate, manganese acetate, and manganese chloride. The concentration of the manganese-containing additive is 0.1 to 0.4 M to promote the electronegative carbon tubes to absorb Mn in the electrolyte. 2+ adsorption to construct a manganese-rich region at the cathode / electrolyte interface.

[0036] Compared with the prior art, the technical solution of this application has the following advantages:

[0037] 1. The present application modifies manganese oxide (hereinafter taking manganese dioxide as an example) by electronegative carbon nanotubes. The conductive skeleton network of electronegative nanotubes (CNTs) makes α-MnO2 have a shorter ion diffusion path and more proton adsorption active sites, which is conducive to rapid electron transfer and reversible structural evolution of manganese oxide, provides more attachment sites for hydrogen ion deintercalation, and promotes the reaction. Specifically, it is as follows: 1. There are mainly two energy storage mechanisms in zinc ion batteries: zinc ion deintercalation and hydrogen ion deintercalation. Since some electronegative groups of the electronegative carbon nanotubes are not bonded to manganese oxide, these unbonded electronegative groups will construct a regional proton-enriched environment on the surface of the electrode material, promote the adsorption and transmission of ions, and make the deintercalation of hydrogen ions the main conduction reaction, rather than the deintercalation of zinc ions. In this way, the shortcomings such as the Jahn-Teller effect and disproportionation reaction caused by the deintercalation of zinc ions can be avoided. The Jahn-Teller effect will cause the crystal structure to be distorted, destroying the structural stability of the electrode material; the disproportionation reaction will lead to irreversible structural transformation, generating "dead MnO2" and causing serious Mn 2+ dissolution, thereby deteriorating the cycle stability and reaction kinetics of the battery.

[0038] 2. A portion of the electronegative groups of the electronegative carbon nanotubes form bonds with the manganese oxide, and the detached hydroxyl groups will adhere to the material. During the discharge process, they can provide hydrogen ions as a supplementary source of hydrogen ions and thus promote the participation of hydrogen ions in the battery reaction.

[0039] 2. In addition, the charged carboxyl or hydroxyl groups in carbon nanotubes can promote the formation of Mn-OC interface bonds, effectively inhibiting the Mn 2+ The dissolution and shuttling of Mn can improve the structural integrity and reaction kinetics of the CMO cathode. 2+ dissolution and shuttling, reducing irreversible Mn 3+ The disproportionation reaction and the formation of ZnMn2O4 are used to build a low-cost and highly stable aqueous zinc-manganese battery.

[0040] 3. In the preparation method of the present application: after adding deionized water, the powder is dispersed by ultrasound, and then transferred to mechanical stirring to make the electronegative carbon nanotubes and manganese oxide fully contact, so that the electronegative carbon nanotubes and manganese oxide can fully react. Both ultrasound and stirring are to evenly disperse the two materials in the solvent, avoid the formation of agglomerates, and achieve the composite of the two materials, but the two have different effects. Ultrasound acts on the microscopic level and can evenly disperse the materials in the solution to prevent agglomeration. Stirring acts on the macroscopic level and can quickly achieve a uniform mixing state. The combination of ultrasound and stirring is more effective.

[0041] 4. Preferably, in the preparation method of the present application, the mixing is carried out by grinding, and the grinding is carried out in a planetary ball mill. The grinding balls continuously stir and turn the two powders during high-speed motion, so that they are fully mixed in the grinding jar, thereby ensuring the uniformity of the mixing.

[0042] 5. The material of the present application can improve the specific capacity and cycle stability of the manganese oxide positive electrode of aqueous zinc ion batteries. Specifically, it is manifested as follows: Figure 6 It can be seen that at a current density of 0.2A g -1 Under the conditions of , after 120 charge-discharge cycles, the capacity retention rate of the positive electrode material of Example 1 (C-MnO2 in the figure) is 100%; its specific capacity is still maintained at 309 mAh g -1 . Figure 7 , 8 It can be seen that the positive electrode material of Example 1 has a high conductivity at 0.2, 0.5, 1.0, 1.5, 2.0, 3.0 and 5.0A g -1 The average discharge capacities at 1000 mAh g were 302.2, 260.1, 225.5, 195.3, 160.6, 150.7 and 140.2 mAh g -1 At different current densities, the material not only exhibits high capacity output, but also extremely stable performance. Compared with the positive electrode of the unmodified similar material in Example 1 (MnO2 in the figure), its rate performance advantage is significant. Fig. 9 It can be seen that at 1000mA g -1 Under the high current density, the positive electrode material of Example 1 still has a capacity retention rate of 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0045] Figure 1 This is a scanning electron microscope image of the positive electrode material provided in Example 1 of the present application;

[0046] Figure 2 The scanning electron microscope image and EDS of the positive electrode material provided in Example 1 of the present application;

[0047] Figure 3 A high-resolution transmission electron microscopy image of the manganese dioxide material provided in Comparative Example 1 of the present application;

[0048] Figure 4 XRD images of the positive electrode materials provided in Example 1 and Comparative Example 1 of the present application;

[0049] Figure 5 The XPS spectra of C1s and O1s in different states of Example 1 of the present application;

[0050] Figure 6 The positive electrode material provided in Examples 1, 3 and Comparative Examples 1, 2 of the present application is used as a positive electrode of a zinc ion battery at a current density of 200 milliamperes per gram (abbreviated as @0.2A g -1 ) under long charge and discharge cycle diagram (the arrow on the left corresponds to the specific capacity under different number of cycles, and the arrow on the right corresponds to the coulomb efficiency under different number of cycles);

[0051] Figure 7 The rate performance diagram of the positive electrode material provided in Example 1 and Comparative Example 1 of the present application as the positive electrode of a zinc ion battery, the current densities used for constant current charge and discharge are 0.2, 0.5, 1, 1.5, 2, 3, and 5 A g respectively -1 ;

[0052] Figure 8 The positive electrode material provided in Example 1 of the present application is used as the charge and discharge curves of the positive electrode of the zinc ion battery at different current densities; the current densities used for constant current charge and discharge are 0.2, 0.5, 1, 1.5, 2, 3, and 5A g -1 ;

[0053] Fig. 9 The positive electrode materials provided in Example 1 and Comparative Example 1 of the present application are respectively used as positive electrodes of zinc ion batteries at a current density of 1000 milliamperes per gram (abbreviated as @1.0A g -1 ) is a charge-discharge long cycle comparison diagram (the two curves near the left arrow are the specific capacity of C-MnO2 and MnO2 positive electrodes at different numbers of cycles, and the arrow on the right is the Coulomb efficiency of C-MnO2 and MnO2 positive electrodes at different numbers of cycles).

[0054] Fig.10 The positive electrode material provided in Example 1 of the present application is used as a zinc ion battery positive electrode and has a soft-pack battery performance at a current density of 50 mA.

[0055] Fig.11 The positive electrode material provided in Examples 4, 5 and Comparative Example 1 of the present application is used as a positive electrode of a zinc ion battery at a current density of 200 milliamperes per gram (abbreviated as @0.2A g -1 ) under long cycle diagram (the arrow on the left corresponds to the specific capacity under different number of cycles, and the arrow on the right corresponds to the coulomb efficiency under different number of cycles).

[0056] Fig.12The positive electrode material provided in Examples 6, 7 and Comparative Example 1 of the present application is used as a positive electrode material for a zinc ion battery at a current density of 200 milliamperes per gram (abbreviated as @0.2Ag -1 ) under different charge and discharge cycle conditions (the arrow on the left corresponds to the specific capacity under different number of cycles, and the arrow on the right corresponds to the coulombic efficiency under different number of cycles). DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0058] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0059] Hereinafter, manganese dioxide, trimanganese tetraoxide and dimanganese trioxide are all commercially available. Manganese dioxide is α-manganese dioxide.

[0060] Carboxylation carbon nanotubes, hydroxylation carbon nanotubes, and amination carbon nanotubes were all purchased from Xianfeng Nano.

[0061] Example 1

[0062] A method for preparing a positive electrode material, the method comprising:

[0063] S1. adding carboxylated carbon nanotubes and manganese dioxide in a mass ratio of 3:6 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0064] S2. Deionized water was added to the mixed powder for dispersion, and after ultrasonication for 2 h, mechanical stirring was performed and the heating temperature was 60 ° C;

[0065] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carboxylated carbon nanotube@manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-MnO2).

[0066] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and N-methylpyrrolidone (NMP) was added to grind and mix, and then coated on the carbon cloth current collector with a loading of 1.5 mg cm -2 , and dried at 60°C for 24 hours to obtain the carboxylated carbon nanotube@manganese dioxide positive electrode material.

[0067] Example 2

[0068] A method for preparing a positive electrode material, the method comprising:

[0069] S1. adding carboxylated carbon nanotubes and manganese dioxide in a mass ratio of 2:7 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0070] S2. Add ethanol to the mixed powder for dispersion, transfer to mechanical stirring after ultrasonication for 2 h, and heat to 90 ° C;

[0071] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carboxylated carbon nanotube@manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-MnO2).

[0072] S4. The active material and binder (carboxymethyl cellulose, CMC) were mixed in a mass ratio of 9:1 and added with deionized water. After grinding and mixing, the mixture was coated on the stainless steel current collector with a loading of 1 mg cm -2 , and dried at 70°C for 24 hours to obtain the carboxylated carbon nanotube@manganese dioxide positive electrode material.

[0073] Example 3

[0074] A method for preparing a positive electrode material, the method comprising:

[0075] S1. adding carboxylated carbon nanotubes and manganese dioxide in a mass ratio of 1:10 to a ball mill, and grinding to obtain a mixed dispersed powder;

[0076] S2. Add ethanol to the mixed powder for dispersion, transfer to 20 degrees Celsius (room temperature) for mechanical stirring after ultrasonic treatment for 2 hours;

[0077] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carboxylated carbon nanotube@manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-MnO2).

[0078] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 7:1 and N-methylpyrrolidone (NMP) was added to grind and mix, and then coated on the titanium foil current collector with a loading of 20 mg cm -2 , and dried at 80°C for 24 hours to obtain the carboxylated carbon nanotube@manganese dioxide positive electrode material.

[0079] Example 4

[0080] A method for preparing a positive electrode material, the method comprising:

[0081] S1. adding carboxylated carbon nanotubes and manganese tetraoxide into a ball mill in a mass ratio of 1:8, and grinding to obtain a mixed dispersed powder;

[0082] S2. Add ethanol to the mixed powder for dispersion, transfer to mechanical stirring after ultrasonication for 2 h, and heat to 80 °C;

[0083] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carboxylated carbon nanotube@manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-Mn3O4).

[0084] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and N-methylpyrrolidone (NMP) was added to grind and mix, and then coated on the titanium foil current collector with a loading of 2 mg cm -2 , and dried at 80°C for 24 hours to obtain the carboxylated carbon nanotube@manganese tetraoxide positive electrode material.

[0085] Example 5

[0086] A method for preparing a positive electrode material, the method comprising:

[0087] S1. adding carboxylated carbon nanotubes and manganese trioxide in a mass ratio of 1:8 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0088] S2. Add ethanol to the mixed powder for dispersion, transfer to mechanical stirring after ultrasonication for 2 h, and heat to 70 °C;

[0089] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carboxylated carbon nanotube@manganese trioxide active material, which is the heterostructure composite material of the present application (denoted as C-Mn2O3).

[0090] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and N-methylpyrrolidone (NMP) was added to grind and mix, and then coated on the titanium foil current collector with a loading of 2 mg cm -2 , and dried at 80°C for 24 hours to obtain the carboxylated carbon nanotube@manganese trioxide positive electrode material.

[0091] Example 6

[0092] A method for preparing a positive electrode material, the method comprising:

[0093] S1. adding hydroxylated carbon nanotubes and manganese dioxide in a mass ratio of 2:7 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0094] S2. Add ethanol to the mixed powder for dispersion, transfer to mechanical stirring after ultrasonication for 2 h, and heat to 80 °C;

[0095] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the hydroxylated carbon nanotube@manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-MnO2).

[0096] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and added with deionized water. After grinding and mixing, they were coated on the stainless steel current collector with a loading of 1.5 mg cm -2 , and dried at 70°C for 24 hours to obtain hydroxylated carbon nanotube@manganese dioxide positive electrode material.

[0097] Example 7

[0098] A method for preparing a positive electrode material, the method comprising:

[0099] S1. adding the amino carbon nanotubes and manganese dioxide in a mass ratio of 2:7 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0100] S2. Add ethanol to the mixed powder for dispersion, transfer to mechanical stirring after ultrasonication for 2 h, and heat to 80 °C;

[0101] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the amino carbon nanotube @ manganese dioxide active material, which is the heterostructure composite material of the present application (denoted as C-MnO2).

[0102] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and added with deionized water. After grinding and mixing, they were coated on the stainless steel current collector with a loading of 1.5 mg cm -2 , and dried at 70°C for 24 hours to obtain the amino carbon nanotube@manganese dioxide positive electrode material.

[0103] Comparative Example 1

[0104] A method for preparing a positive electrode material, the method comprising:

[0105] S1. Add acetylene black and manganese dioxide in a mass ratio of 3:6 into a ball mill, and grind to obtain a mixed and dispersed powder;

[0106] S2. Deionized water was added to the mixed powder for dispersion, and after ultrasonication for 2 h, mechanical stirring was performed and the heating temperature was 60 ° C;

[0107] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain acetylene black @ manganese dioxide active material, which is the comparative material of this application (denoted as MnO2).

[0108] S4. The active material and binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 9:1 and N-methylpyrrolidone (NMP) was added to grind and mix well, and then coated on the carbon cloth current collector with a loading of 1.5 mg cm -2 , and dried at 60°C for 24 hours to obtain acetylene black@manganese dioxide positive electrode material.

[0109] Comparative Example 2

[0110] A method for preparing a positive electrode material, the method comprising:

[0111] S1. adding carbon nanotubes and manganese dioxide in a mass ratio of 3:6 into a ball mill, and grinding to obtain a mixed dispersed powder;

[0112] S2. Deionized water was added to the mixed powder for dispersion, and after ultrasonication for 2 h, mechanical stirring was performed and the heating temperature was 60 ° C;

[0113] S3. After the stirring is completed, the mixed powder is centrifuged and dried to obtain the carbon nanotube @ manganese dioxide active material, which is the comparative material of the present application (denoted as MnO2).

[0114] S4. The active material (polyvinylidene fluoride, PVDF) was mixed at a mass ratio of 9:1 and N-methylpyrrolidone (NMP) was added to grind and mix, and then coated on the carbon cloth current collector with a loading of 1.5 mg cm -2 , and dried at 60°C for 24 hours to obtain the carbon nanotube@manganese dioxide positive electrode material.

[0115] Material characterization and performance testing:

[0116] The positive electrode materials provided in Examples 1 to 3 and Comparative Example 1 were tested by scanning electron microscopy. Since the results are similar, only the test results of Example 1 are used as an example for illustration below.

[0117] Figure 1 This is a scanning electron microscope image of the positive electrode material provided in Example 1. The structure constructed by the interconnection of manganese dioxide and electronegative carbon nanotubes presents a highly complex and irregular morphology. In the meantime, a large number of nano manganese dioxide are evenly distributed, while the carbon nanotubes are like filamentary structures. The two are intertwined and entangled to build a dense three-dimensional network system with rich pore structure.

[0118] Figure 2 Scanning electron microscope image and EDS of the positive electrode material provided in Example 1. Figure 2The microscopic image of manganese dioxide and electronegative carbon nanotubes tightly combined is clearly presented in the figure. Further elemental analysis can determine the characteristic element of electronegative carbon nanotubes - carbon (C), and the key elements of manganese dioxide - oxygen (O) and manganese (Mn).

[0119] Figure 3 This is a high-resolution transmission electron microscopy image of the manganese dioxide material provided for Comparative Example 1. Figure 3 The microstructure information of manganese dioxide at the nanoscale is shown. Figures a and b show the morphological characteristics of manganese dioxide at the 5nm scale. Through careful analysis, it is found that its lattice size is 0.494nm, which corresponds to the (200) crystal plane of α-manganese dioxide.

[0120] Figure 4 XRD images of the positive electrode materials provided in Example 1 and Comparative Example 1 of the present application. Through XRD (X-ray diffraction) comparative analysis, it can be clearly observed that when the electronegative carbon nanotubes and manganese dioxide are mixed with each other, an obvious diffraction peak of the carbon nanotubes is presented at the 002 crystal plane. This phenomenon strongly indicates that the two materials have been successfully composited.

[0121] Figure 5 The XPS spectra of C1s and O1s in different states of Example 1 of the present application show that Mn-OC is formed. According to the XPS spectra of C1s and O1s, the charged carboxyl groups in the electronegative carbon nanotubes can promote the formation of Mn-OC bonds. Initially, the bond is formed by the interface between manganese dioxide and electronegative carbon nanotubes, and it still exists during charge and discharge. This group can inhibit the formation of Mn in the C-MnO2 positive electrode. 2+ Dissolution shuttling improves the structural integrity and reaction kinetics of the positive electrode.

[0122] The positive electrode materials provided in Examples 1 to 7 and Comparative Example 1 were used with the same concentration of manganese sulfate and 2M zinc salt electrolyte to construct aqueous zinc-manganese batteries. Specifically, the positive electrode materials provided in Examples 1 to 5 and Comparative Example 1 were used as positive electrodes, zinc foil was used as negative electrodes, and the electrolytes were 2M ZnSO4 and 0.2M MnSO4, and the batteries were subjected to charge and discharge tests and charge and discharge long cycle tests.

[0123] The positive electrode materials provided in Examples 1 to 3 were subjected to a long charge and discharge cycle test. Since the results are similar, only the test result of Example 3 is used as an example for illustration below. Figure 6 The positive electrode materials provided in Examples 1, 3 and Comparative Examples 1, 2 are used as positive electrodes for zinc ion batteries at 200 mAg -1 The cycling performance at the current density is given by Figure 6 It can be seen that at a current density of 0.2A g -1Under the conditions of , after 120 charge-discharge cycles, the capacity retention rate of the positive electrode material of Example 1 (C-MnO2 in the figure) remains 100%, and the capacity and stability of Example 3 are slightly lower than those of Example 1, but are significantly better than those of the positive electrode materials of Comparative Examples 1 and 2 (MnO2 in the figure). This shows that the electronegativity modification of the conductive material plays an important role.

[0124] The positive electrode materials provided in Examples 1 to 3 were subjected to charge and discharge tests. Since the results are similar, only the test results of Example 1 are used as an example for illustration below. Figure 7 The rate performance of the positive electrode materials of Example 1 and Comparative Example 1 at different current densities is shown. Figure 8 The charge and discharge curves of the positive electrode material of Example 1 are shown in Figure 1, which are the charge and discharge curves of the positive electrode material of Example 1 (C-MnO2 in the figure) at 0.2, 0.5, 1.0, 1.5, 2.0, 3.0 and 5.0A g -1 The average discharge capacities at 1000 mAh g were 302.2, 260.1, 225.5, 195.3, 160.6, 150.7 and 140.2 mAh g -1 At different current densities, the material not only exhibits high capacity output, but also extremely stable performance. Compared with the positive electrode of the unmodified similar material comparative example 1 (MnO2 in the figure), its rate performance advantage is significant.

[0125] Fig. 9 The charge and discharge long cycle diagram of the positive electrode material provided in Example 1 and Comparative Example 1 as a zinc ion positive electrode at a current density of 1000 mA g-1. Fig. 9 It can be seen that at 1000mA g -1 Under the high current density, the positive electrode material of Example 1 still has a capacity retention rate of 80% after 1200 cycles, while the material of Comparative Example 1 has only a capacity retention rate of 46.3% after about 300 cycles.

[0126] Fig.10 The performance diagram of the positive electrode material provided in Example 1 as a zinc ion positive electrode at a current density of 50 mA. Fig.10 It can be seen that even if the positive electrode material is applied to the soft-pack battery system, its battery performance is still excellent and has significant advantages, specifically, there is still a capacity retention rate of 94.5% after 110 cycles.

[0127] Fig.11 The positive electrode materials provided in Examples 4, 5 and Comparative Example 1 are used as positive electrodes for zinc ion batteries at 200 mA g -1 Cycling performance at current density, from Fig.11It can be seen intuitively that when the manganese dioxide in the positive electrode material is replaced by manganese trioxide or manganese tetraoxide, the battery has achieved significant improvements in capacity and stability. Specifically, after 120 charge and discharge cycles, the capacity of the positive electrode materials of Examples 4 and 5 (Mn3O4 and Mn2O3 in the figure) has no tendency to decay, and the capacity retention rate is 100%, which is significantly better than the positive electrode material of Comparative Example 1 (MnO2 in the figure). This experimental result proves that electronegative carbon nanotubes can play a very significant promoting role in various manganese oxides, helping to improve battery performance.

[0128] Fig.12 The positive electrode materials provided in Examples 6, 7 and Comparative Example 1 are used as positive electrodes for zinc ion batteries at 200 mA g -1 Cycling performance at current density, from Fig.12 We can intuitively observe that the introduction of different electronegative groups has a positive effect on the improvement of battery performance and the enhancement of stability. Among them, the capacity of the positive electrode material of Example 6 shows an upward trend, while the capacity of the positive electrode material of Example 7 remains unchanged, and the capacity retention rate reaches 100%, which is significantly better than the performance of MnO2 as the positive electrode material in Comparative Example 1. This experimental result fully proves that for manganese oxide, carbon nanotubes containing different proton electronegative groups can play a very significant promoting role and effectively improve battery performance.

[0129] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0130] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0131] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A heterostructure composite material of electronegative carbon nanotubes modified with manganese oxide, characterized in that: The heterogeneous structure composite material comprises: electronegative carbon nanotubes and manganese oxide; At least a portion of the electronegative groups of the electronegative carbon nanotubes are not bonded to the manganese oxide.

2. The heterogeneous structure composite material according to claim 1, characterized in that: The electronegative groups contained in the electronegative carbon nanotubes are selected from: one or more of carboxyl, hydroxyl, and amino groups; A portion of the electronegative groups of the electronegative carbon nanotubes are bonded to the manganese oxide.

3. The heterogeneous structure composite material according to claim 1, characterized in that: The mass ratio of the electronegative carbon nanotubes to the manganese oxide is (0.1-0.50):

1.

4. The heterogeneous structure composite material according to claim 1, characterized in that: The manganese oxide is selected from one or more of manganese dioxide, dimanganese trioxide and trimanganese tetraoxide.

5. A method for preparing a heterogeneous structure composite material, characterized in that: The preparation method comprises the following steps: mixing electronegative carbon nanotubes and manganese oxide to obtain a mixture; Add the solvent to the mixture, and transfer to stirring after sonication; After the stirring is completed, the solid and liquid are separated, and the solid is dried to obtain a heterogeneous structure composite material.

6. The method for preparing the heterogeneous structure composite material according to claim 5, characterized in that: The mass ratio of the electronegative carbon nanotubes to the manganese oxide is (0.1-0.50):1; The solvent is water or an alcohol solution.

7. Use of the heterostructure composite material according to claims 1 to 4 as a positive electrode material for zinc ion batteries.

8. A method for preparing a positive electrode material, characterized in that: The preparation method comprises the following steps: adding the heterostructure composite material according to any one of claims 1 to 4 to a binder in a mass ratio of (7 to 9): 1 to a solvent, grinding and mixing, coating or rolling the mixture onto a current collector, and drying the mixture to obtain a positive electrode material.

9. A zinc ion battery, characterized in that: The battery comprises the positive electrode material according to claim 8.

10. A method for improving the reversibility of a zinc ion battery, characterized in that: The positive electrode material of the zinc ion battery contains a heterogeneous structure composite material of electronegative carbon nanotubes modified with manganese oxide.

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