A preparation method and application of MnO2NTs / CNFs

Abstract

A preparation method and application of MnO2NTs / CNFs, which relates to a preparation method and application of a MnO2 composite material. The purpose of the present invention is to solve the problem that the existing technology uses material nano-sizing, porous structure and conductive polymer / metal material coating to improve the electrochemical properties of manganese oxide, but there are problems such as complex preparation method, high cost and manganese oxide electrode material directly in contact with electrolyte easily undergoes various side reactions with active electrolyte, affecting the electrochemical reaction rate. Method: 1. Prepare MnO2; 2. Prepare MnO2 nanotubes; 3. Prepare MnO2-PAN polymer; 4. Prepare MnO2 nanotubes / carbon nanofibers. The MnO2NTs / CNFs prepared by the present invention, as a binder-free self-supporting electrode material, have good mechanical properties, higher specific capacity and energy density, greater electrochemical performance and long-term stability.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a MnO2 composite material. Background Art

[0002] In the past few decades, rechargeable lithium-ion batteries have been important energy storage devices. They have become the first choice for electric vehicles and portable electronic products due to their high energy density, long cycle life and environmental friendliness. The negative electrode material in the electrode material is an important component of lithium-ion batteries and plays a decisive role in the overall performance of lithium-ion batteries. So far, graphite is still considered to be the most commonly used negative electrode material for lithium-ion batteries, but its specific capacity is relatively low (372mAhg -1 ), which seriously limits the application of lithium-ion batteries. Therefore, researchers are exploring advanced negative electrode materials to replace graphite.

[0003] Various transition metal oxides (TMOs) have attracted considerable attention due to their excellent electrochemical properties. Among them, manganese oxides (e.g., MnO2, MnO, Mn2O3, and Mn3O4) are considered among the most promising high-theoretical-energy anode materials due to their low cost, high theoretical capacity, diverse crystal structures, and environmental friendliness. However, they suffer from low conductivity and volume expansion during repeated charge and discharge in lithium-ion batteries, resulting in poor electrochemical performance. To address these issues and improve the electrochemical performance of manganese oxides and mitigate their degradation during cycling, numerous effective approaches have been explored, such as material nanostructuring, porous structures, and conductive polymer / metal coatings.

[0004] Sui et al. demonstrated the coating of δ-MnO2 semiconductor polypyridine nanosheet arrays on nickel foam (denoted as MnO2@PPy / NF) by hydrothermal growth of MnO2 followed by electrodeposition of PPy on the anode of the lithium ion battery. The electrode with a PPy coating of ~50 nm thickness exhibited excellent overall electrochemical performance. Lin et al. synthesized a carbonized α-MnO2@ZIF-8 precursor using sea urchin-shaped α-MnO2 microspheres as a template, successfully constructing MnO / C cubic polyhedra. The prepared sample had an irregular polyhedral cubic structure with a thin carbon layer on the surface and exhibited excellent long-term cycling performance and reversible capacity. Cao et al. demonstrated the use of MnO2-loaded hollow carbon nanospheres (denoted as MnO2@HCN) as a negative electrode material for lithium-ion batteries. HCN was prepared by treating 3-aminophenol with formaldehyde resin. MnO2 was loaded onto the outer surface of HCN through reduction with KMnO4, forming a porous core-shell structure. SEM, TEM, and XRD characterizations show that MnO2@HCN has a spherical structure, with a core composed of porous carbon nanoparticles and a shell composed of MnO2 nanoparticles. However, due to the complex methods or high preparation conditions and costs, the manganese oxide electrode material is in direct contact with the electrolyte and is prone to various side reactions with the active electrolyte, affecting the electrochemical reaction rate. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of the existing technology that use material nano-materials, porous structures and conductive polymer / metal material coatings to improve the electrochemical properties of manganese oxides, but there are complex preparation methods, high costs and the manganese oxide electrode materials are directly in contact with the electrolyte and easily undergo various side reactions with the active electrolyte, affecting the electrochemical reaction rate. The present invention provides a preparation method and application of MnO2NTs / CNFs.

[0006] A method for preparing MnO2NTs / CNFs is completed by the following steps:

[0007] 1. Preparation of MnO2:

[0008] Add KMnO4 to water and stir, then add concentrated HNO3, stir evenly and transfer to a Teflon-lined stainless steel reactor, perform hydrothermal reaction at 120°C, cool naturally to room temperature, centrifuge, wash, and dry to obtain MnO2 powder;

[0009] 2. Preparation of MnO2 nanotubes:

[0010] The MnO2 powder was placed in a tube furnace and then heat-treated at 380℃~420℃ in an air atmosphere to obtain MnO2NTs.

[0011] 3. Preparation of MnO2-PAN polymer:

[0012] ① Add MnO2NTs to N,N-dimethylformamide and dissolve them by ultrasonication, then add polyacrylonitrile and dissolve them by ultrasonication to obtain electrospinning solution;

[0013] ②, placing the electrospinning solution into an electrospinning machine for spinning to obtain MnO2-PAN polymer;

[0014] 4. Preparation of MnO2 nanotubes / carbon nanofibers:

[0015] The MnO2-PAN polymer was placed in a tube furnace and then carbonized under an argon atmosphere at a temperature of 600℃~650℃ to obtain MnO2NTs / CNFs.

[0016] Principle of the present invention:

[0017] The present invention uses a hydrothermal method and electrospinning technology to prepare MnO2NTs / CNFs. Electrospinning technology is a low-cost and easy-to-operate processing technology. Manganese oxide composite carbon nanofibers prepared by electrospinning technology retain a large lithium storage capacity while having the good conductivity and stability of carbon fiber, showing better electrochemical properties than pure manganese oxide or graphite.

[0018] Advantages of the present invention:

[0019] 1. Electrospinning technology is a low-cost, easy-to-operate, one-step process that can directly and continuously prepare nanofibers with large specific surface area, good uniformity, and adjustable thickness;

[0020] Second, MnO2NTs are uniformly embedded in carbon nanofibers, effectively alleviating volume expansion during lithium extraction and insertion, thus compensating for the defects caused by a single material.

[0021] 3. The MnO2NTs / CNFs prepared by the present invention have a porous carbon nanofiber structure, which promotes the penetration of electrolyte into the electrode material, increases the reactive sites, and greatly improves the reaction rate;

[0022] Fourth, the electrospun nanofibers have good flexibility and can be used as flexible electrode materials;

[0023] 5. As a binder-free self-supporting electrode material, MnO2NTs / CNFs have good mechanical properties, higher specific capacity and energy density, and have great electrochemical performance and long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a high-magnification SEM image of MnO2NTs prepared in step 2 of Example 1;

[0025] Figure 2This is a low-magnification SEM image of MnO2NTs prepared in step 2 of Example 1;

[0026] Figure 3 This is the SEM image of 5% MnO2NTs / CNFs prepared in Example 1;

[0027] Figure 4 This is the SEM image of 20% MnO2NTs / CNFs prepared in Example 2;

[0028] Figure 5 is the XRD pattern, in which 1 is 5% MnO2NTs / CNFs prepared in Example 1, 2 is 20% MnO2NTs / CNFs prepared in Example 2, 3 is MnO2NTs prepared in step 2 of Example 1, and 4 is JCPDS No.44-0141;

[0029] Figure 6 TEM images and HRTEM images of 20% MnO2NTs / CNFs prepared in Example 2;

[0030] Figure 7 The MnO2NTs prepared in step 2 of Example 1 were scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, 3 is the third time, 4 is the fourth time, and 5 is the fifth time;

[0031] Figure 8 The 5% MnO2NTs / CNFs prepared in Example 1 was scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, and 3 is the third time;

[0032] Figure 9 The 20% MnO2NTs / CNFs prepared in Example 2 were scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, and 3 is the third time;

[0033] Figure 10 5% MnO2NTs / CNFs prepared in Example 1 at 0.1Ag -1 Discharge / charge diagram under current density, in the figure 1 is the 1st time, 2 is the 20th time, and 3 is the 50th time;

[0034] Figure 11 20% MnO2NTs / CNFs prepared in Example 2 at 0.1Ag -1Discharge / charge diagram under current density, in the figure 1 is the 1st time, 2 is the 20th time, and 3 is the 50th time;

[0035] Figure 12 The 5% MnO2NTs / CNFs prepared in Example 1 was heated to a current density of 0.1 A g -1 Cycle curve diagram of 160 cycles;

[0036] Figure 13 The 20% MnO2NTs / CNFs prepared in Example 2 were heated to a current density of 0.1 A g -1 Cycle curve diagram of 200 cycles;

[0037] Figure 14 The rate performance of MnO2NTs prepared in step 2 of Example 1 at different current rates;

[0038] Figure 15 The rate performance of 5% MnO2NTs / CNFs prepared in Example 1 at different current rates;

[0039] Figure 16 The rate performance of 20% MnO2NTs / CNFs prepared in Example 2 at different current rates;

[0040] Figure 17 The microstructure of 20% MnO2NTs / CNFs prepared in Example 2 after 200 cycles. DETAILED DESCRIPTION

[0041] Specific embodiment 1: This embodiment is a method for preparing MnO2NTs / CNFs, which is completed by the following steps:

[0042] 1. Preparation of MnO2:

[0043] Add KMnO4 to water and stir, then add concentrated HNO3, stir evenly and transfer to a Teflon-lined stainless steel reactor, perform hydrothermal reaction at 120°C, cool naturally to room temperature, centrifuge, wash, and dry to obtain MnO2 powder;

[0044] 2. Preparation of MnO2 nanotubes:

[0045] The MnO2 powder was placed in a tube furnace and then heat-treated at 380℃~420℃ in an air atmosphere to obtain MnO2NTs.

[0046] 3. Preparation of MnO2-PAN polymer:

[0047] ① Add MnO2NTs to N,N-dimethylformamide and dissolve them by ultrasonication, then add polyacrylonitrile and dissolve them by ultrasonication to obtain electrospinning solution;

[0048] ②, placing the electrospinning solution into an electrospinning machine for spinning to obtain MnO2-PAN polymer;

[0049] 4. Preparation of MnO2 nanotubes / carbon nanofibers:

[0050] The MnO2-PAN polymer was placed in a tube furnace and then carbonized under an argon atmosphere at a temperature of 600℃~650℃ to obtain MnO2NTs / CNFs.

[0051] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass ratio of KMnO4 to water in step 1 is (0.1g-0.3g):(20mL-30mL); the volume ratio of KMnO4 to concentrated HNO3 in step 1 is (0.1g-0.3g):(1mL-1.5mL). Other steps are the same as specific embodiment 1.

[0052] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the mass fraction of concentrated HNO3 in step 1 is 68%. The other steps are the same as those in specific embodiment 1 or 2.

[0053] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the hydrothermal reaction time in step 1 is 10 to 12 hours. The other steps are the same as those in specific embodiments 1 to 3.

[0054] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the centrifugal speed in step 1 is 10,000 rpm and the stirring time in step 1 is 5 to 10 minutes. The other steps are the same as those in specific embodiments 1 to 4.

[0055] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the heat treatment time in step 2 is 3 hours to 5 hours. The other steps are the same as those in specific embodiments 1 to 5.

[0056] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the mass fraction of MnO2NTs in the electrospinning solution in step 3① is 5% to 20%. The other steps are the same as specific embodiments 1 to 6.

[0057] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the mass fraction of polyacrylonitrile in the electrospinning solution in step 3① is 10% to 14%. The other steps are the same as specific embodiments 1 to 7.

[0058] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the carbonization time in step 4 is 2 to 3 hours. The other steps are the same as those in specific embodiments 1 to 8.

[0059] Specific embodiment 10: This embodiment is a method of using MnO2NTs / CNFs as a negative electrode material for lithium-ion batteries.

[0060] The following examples are used to verify the beneficial effects of the present invention:

[0061] Example 1: A method for preparing MnO2NTs / CNFs is completed by the following steps:

[0062] 1. Preparation of MnO2:

[0063] 0.2 g of KMnO4 was added to 25 mL of water and stirred for 5 minutes. 1.25 mL of 68% HNO3 was added and stirred evenly. The mixture was transferred to a Teflon-lined stainless steel reactor and subjected to a hydrothermal reaction at 120°C for 12 hours. The mixture was naturally cooled to room temperature and centrifuged at 10,000 rpm. The mixture was washed three times with distilled water and dried to obtain MnO2 powder.

[0064] 2. Preparation of MnO2 nanotubes:

[0065] The MnO2 powder was placed in a tube furnace and then heat-treated at 400°C in an air atmosphere for 4 h to obtain MnO2NTs.

[0066] 3. Preparation of MnO2-PAN polymer:

[0067] ① Add MnO2NTs to N,N-dimethylformamide and dissolve them by ultrasonication, then add polyacrylonitrile and dissolve them by ultrasonication to obtain electrospinning solution;

[0068] The mass fraction of MnO2NTs in the electrospinning solution described in step 3① is 5%;

[0069] The mass fraction of polyacrylonitrile in the electrospinning solution described in step 3① is 12%;

[0070] ②Put the electrospinning solution into an electrospinning machine for spinning to obtain a MnO2-PAN polymer with a MnO2NTs mass fraction of 5%;

[0071] 4. Preparation of MnO2 nanotubes / carbon nanofibers:

[0072] The MnO2-PAN polymer with a MnO2NTs mass fraction of 5% was placed in a tube furnace and then carbonized at 600℃ in an argon atmosphere for 2h to obtain MnO2NTs / CNFs (5% MnO2NTs / CNFs).

[0073] Example 2: A method for preparing MnO2NTs / CNFs is completed by the following steps:

[0074] 1. Preparation of MnO2:

[0075] 0.2 g of KMnO4 was added to 25 mL of water and stirred for 5 minutes. 1.25 mL of 68% HNO3 was added and stirred evenly. The mixture was transferred to a Teflon-lined stainless steel reactor and subjected to a hydrothermal reaction at 120°C for 12 hours. The mixture was naturally cooled to room temperature and centrifuged at 10,000 rpm. The mixture was washed three times with distilled water and dried to obtain MnO2 powder.

[0076] 2. Preparation of MnO2 nanotubes:

[0077] The MnO2 powder was placed in a tube furnace and then heat-treated at 400°C in an air atmosphere for 4 h to obtain MnO2NTs.

[0078] 3. Preparation of MnO2-PAN polymer:

[0079] ① Add MnO2NTs to N,N-dimethylformamide and dissolve them by ultrasonication, then add polyacrylonitrile and dissolve them by ultrasonication to obtain electrospinning solution;

[0080] The mass fraction of MnO2NTs in the electrospinning solution described in step 3① is 20%;

[0081] The mass fraction of polyacrylonitrile in the electrospinning solution described in step 3① is 12%;

[0082] ②Put the electrospinning solution into an electrospinning machine for spinning to obtain a MnO2-PAN polymer with a MnO2NTs mass fraction of 20%;

[0083] 4. Preparation of MnO2 nanotubes / carbon nanofibers:

[0084] The MnO2-PAN polymer with a MnO2NTs mass fraction of 20% was placed in a tube furnace and carbonized at 600℃ in an argon atmosphere for 2h to obtain MnO2NTs / CNFs (20% MnO2NTs / CNFs).

[0085] Figure 1 This is a high-magnification SEM image of MnO2NTs prepared in step 2 of Example 1;

[0086] from Figure 1 It can be seen that the MnO2NTs prepared in step 2 of Example 1 are tubular structures with a length of about 3.3 μm. The morphology of the MnO2NTs has good uniformity and almost no impurity particles.

[0087] Figure 2 This is a low-magnification SEM image of MnO2NTs prepared in step 2 of Example 1;

[0088] from Figure 2 It can be seen that the average diameter of the hollow tubes of MnO2NTs prepared in step 2 of Example 1 is 100 nm (±100).

[0089] Figure 3 This is the SEM image of 5% MnO2NTs / CNFs prepared in Example 1;

[0090] Figure 4 This is the SEM image of 20% MnO2NTs / CNFs prepared in Example 2;

[0091] from Figure 3~Figure 4 It can be seen that the diameter of MnO2NTs / CNFs is uniform nanofibers with a diameter of about 300-500 nm, and the nanoparticles are evenly distributed in the high component, indicating that the present invention can prepare uniform MnO2NTs / CNFs.

[0092] Figure 5 is the XRD pattern, in which 1 is 5% MnO2NTs / CNFs prepared in Example 1, 2 is 20% MnO2NTs / CNFs prepared in Example 2, 3 is MnO2NTs prepared in step 2 of Example 1, and 4 is JCPDS No.44-0141;

[0093] from Figure 5 It can be seen that the diffraction peaks of MnO2NTs, 5%MnO2NTs / CNFs prepared in Example 1, and 20%MnO2NTs / CNFs prepared in Example 2 are consistent with the MnO2 standard crystal card (JCPDS NO. 44-0141), and the XRD patterns do not change significantly. The typical diffraction peaks correspond to the (110), (200), (220), (310), (211), (301), (411), (431), (521), (002), (541), (312), and (332) crystal planes of manganese dioxide, respectively, indicating that manganese dioxide has been incorporated into the composite material and the preparation is successful. The 20%MnO2NTs / CNFs prepared in Example 2 have strong and narrow peaks, confirming their good crystallinity and high purity.

[0094] Figure 6TEM images and HRTEM images of 20% MnO2NTs / CNFs prepared in Example 2;

[0095] from Figure 6 It can be seen that the 20% MnO2NTs / CNFs prepared in Example 2 have a nanotube structure with a diameter of 250 nm and are filled with MnO2 particles ( Figure 6 b); Figure 6 In c, the lattice spacing between the nanofibers is 0.182 nm and 0.161 nm, respectively, which is consistent with the (411) plane and (431) plane spacing of MnO2, proving again that the composition of the nanotubes is MnO2.

[0096] The lithium electrochemical performance of the MnO2NTs prepared in step 2 of Example 1, the 5%MnO2NTs / CNFs prepared in Example 1, and the 20%MnO2NTs / CNFs prepared in Example 2 were evaluated using button cells.

[0097] The MnO2NTs prepared in step 2 of Example 1, the 5%MnO2NTs / CNFs prepared in Example 1, and the 20%MnO2NTs / CNFs prepared in Example 2 were tested in the potential range of 0.01-3.0 V at a scan rate of 0.1 mV s -1 When , the CV curves of the first few cycles are as follows Figures 7-9 shown.

[0098] Figure 7 The MnO2NTs prepared in step 2 of Example 1 were scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, 3 is the third time, 4 is the fourth time, and 5 is the fifth time;

[0099] Figure 8 The 5% MnO2NTs / CNFs prepared in Example 1 was scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, and 3 is the third time;

[0100] Figure 9 The 20% MnO2NTs / CNFs prepared in Example 2 were scanned at a rate of 0.1 mVs -1 , Cyclic voltammetry curves with a potential range of 0.01-3.0 V, where 1 is the first time, 2 is the second time, and 3 is the third time;

[0101] and Figure 7 MnO2NTs and Figure 8 Compared with the 5% MnO2NTs / CNFs prepared in Example 1, the first cathode cycle Figure 9 A broad peak of 0.45 V was generated in the cathode cycle, which disappeared in the following cathode cycle, indicating that the reaction was irreversible and the energy difference caused the formation of a solid electrolyte interface (SEI) on the electrode surface. In addition, below 0.35 V, the peak dropped sharply due to the Mn 4+ Reduced to Mn 0 (MnO2+ 4Li + 4e - →Mn + 2Li2O). In the first anodic cycle, the strong peak at 1.32 V corresponds to Li + Dissolved from Li2O, Mn 0 Oxidized to Mn 2+ (Mn + 2Li2O→MnO2+ 4Li + 4e - In other anodic cycles, since the reaction peaks did not change significantly and remained at almost the same positions, the reaction was reversible, showing good electrochemical stability.

[0102] Figure 10 5% MnO2NTs / CNFs prepared in Example 1 at 0.1Ag -1 Discharge / charge diagram under current density, in the figure 1 is the 1st time, 2 is the 20th time, and 3 is the 50th time;

[0103] Figure 11 20% MnO2NTs / CNFs prepared in Example 2 at 0.1Ag -1 Discharge / charge diagram under current density, in the figure 1 is the 1st time, 2 is the 20th time, and 3 is the 50th time;

[0104] Figure 12 The 5% MnO2NTs / CNFs prepared in Example 1 was heated to a current density of 0.1 A g -1 Cycle curve diagram of 160 cycles;

[0105] Figure 13 The 20% MnO2NTs / CNFs prepared in Example 2 were heated to a current density of 0.1 A g -1 Cycle curve diagram of 200 cycles;

[0106] The 5% MnO2NTs / CNFs prepared in Example 1 and the 20% MnO2NTs / CNFs prepared in Example 2 were heated to 0.1Ag. -1 The discharge / charge diagram under current density is as follows Figure 10-11 As shown. Taking the charge and discharge curves of the 1st, 20th and 50th cycles as samples, at about 0.76V ( Figure 10 ) and 0.57V( Figure 11) has an obvious discharge voltage platform, and the first discharge specific capacity is 1023 mA h g -1 and 1094 mA hg -1 In the following cycles, the specific capacity was between 531-558 mA h g -1 and 658-704mA hg -1 Between, a layer of SEI film is formed due to the loss of capacity, which is irreversible and is consistent with the cycle curve ( Figure 12-13 ), demonstrating the alloy's lithiation mechanism. Furthermore, the charge-discharge capacity of the 20% MnO2NTs / CNFs prepared in Example 2 was consistently higher than that of the 5% MnO2NTs / CNFs prepared in Example 1, demonstrating that the battery not only exhibits excellent performance but also good reversibility.

[0107] At a current density of 0.1Ag -1 When the 5% MnO2NTs / CNFs prepared in Example 1 were cycled 160 times, and the 20% MnO2NTs / CNFs prepared in Example 2 were cycled 200 times, the cycle performance was as follows: Figure 12-13 The initial discharge / charge specific capacities of 20% MnO2NTs / CNFs prepared in Example 2 were 1094 mA h g -1 and 687mA hg -1 , which is higher than that of 5% MnO2NTs / CNFs prepared in Example 1. As the number of cycles increases, the specific capacity of 5% MnO2NTs / CNFs prepared in Example 1 remains at 610 mAh g during the 117th to 160th cycles. -1 The specific capacity of 20% MnO2NTs / CNFs prepared in Example 2 remained at 835 mAh g during the 133rd to 200th cycles. -1 Throughout the entire process, the Coulombic efficiencies of the 5% MnO2NTs / CNFs prepared in Example 1 and the 20% MnO2NTs / CNFs prepared in Example 2 remained at approximately 98.9% and 99.5%, respectively. The Coulombic efficiency of the 20% MnO2NTs / CNFs prepared in Example 2 was significantly higher, indicating that a greater proportion of MnO2 nanotubes in the 20% MnO2NTs / CNFs prepared in Example 2 resulted in better reversibility and structural stability.

[0108] Figure 14 The rate performance of MnO2NTs prepared in step 2 of Example 1 at different current rates;

[0109] Figure 15 The rate performance of 5% MnO2NTs / CNFs prepared in Example 1 at different current rates;

[0110] Figure 16 The rate performance of 20% MnO2NTs / CNFs prepared in Example 2 at different current rates;

[0111] In order to compare the discharge / charge capabilities, the -1 The rate performance of MnO2NTs, 5%MnO2NTs / CNFs prepared in Example 1 and 20%MnO2NTs / CNFs prepared in Example 2 were tested at different current rates ( Figures 14 to 16 MnO2NTs do not contain MnO2NTs / CNFs, so the structure is easily damaged and the cycle is unstable ( Figure 14 Due to the presence of carbon nanofibers, the 5% MnO2NTs / CNFs prepared in Example 1 and the 20% MnO2NTs / CNFs prepared in Example 2 have good structural stability, but the capacity of the 20% MnO2NTs / CNFs prepared in Example 2 is higher, and the corresponding reversible capacities are 0.1, 0.2, 0.3, and 0.5 Ag -1 796, 611, 552, 486 mAhg -1 When 0.1, 0.2, 0.3 Ag -1 When tested again under the same conditions, it can reach 835, 620, 565mAhg -1 The reversible capacity of the samples was not significantly different from that of the samples before, but the value was higher than that before, which may be due to the fact that the residual MnO2NTs / CNFs also participated in the reaction.

[0112] In order to further prove the relationship between fiber structure and cycle stability, the electrode was disassembled after the cycle was completed. The microstructure observed by scanning electron microscopy is as follows Figure 17 As shown;

[0113] Figure 17 The microstructure of 20% MnO2NTs / CNFs prepared in Example 2 after 200 cycles;

[0114] from Figure 17 It can be seen that it still maintains the fiber structure, and the pores in the fiber can effectively release the expansion volume of the alloy during the lithiation process, thereby maintaining the stability of the structure and improving the battery cycle stability.

[0115] This paper studies the method of using MnO2NTs / CNFs as a high-performance anode. MnO2NTs / CNFs are prepared by electrospinning technology, and the electrochemical performance of MnO2NTs, 5% MnO2NTs / CNFs and 20% MnO2NTs / CNFs are analyzed. In comparison, the 20% MnO2NTs / CNFs anode has a low electrochemical performance at 0.1 mA g -1 The initial reversible capacity is 1094 mA h g-1 , and still maintained 835mA hg after 133 cycles -1 The results show that 20% MnO2NTs / CNFs have the advantages of good structural stability, high specific capacity, good reversibility, long cycle period, and good ionic conductivity, which provides ideas and prospects for the preparation of high-performance negative electrode materials for lithium-ion batteries.

Claims

1. A method for preparing MnO2 NTs / CNFs, characterized in that The preparation method is completed according to the following steps:

1. Preparation of MnO2: Add KMnO4 to water and stir, then add concentrated HNO3, stir evenly and transfer to a Teflon-lined stainless steel reactor, perform hydrothermal reaction at 120°C, cool naturally to room temperature, centrifuge, wash, and dry to obtain MnO2 powder; The mass ratio of KMnO4 to water described in step 1 is (0.1g~0.3g):(20mL~30mL); The mass ratio of KMnO4 to concentrated HNO3 described in step 1 is (0.1g~0.3g):(1mL~1.5mL); 2. Preparation of MnO2 nanotubes: The MnO2 powder was placed in a tube furnace and then heat-treated at 380℃~420℃ in an air atmosphere to obtain MnO2NTs. The heat treatment time in step 2 is 3h~5h; 3. Preparation of MnO2-PAN polymer: ① Add MnO2NTs to N,N-dimethylformamide and dissolve them by ultrasonication, then add polyacrylonitrile and dissolve them by ultrasonication to obtain electrospinning solution; The mass fraction of MnO2NTs in the electrospinning solution described in step 3① is 20%; The mass fraction of polyacrylonitrile in the electrospinning solution in step 3① is 10% to 14%; ②, placing the electrospinning solution into an electrospinning machine for spinning to obtain MnO2-PAN polymer; 4. Preparation of MnO2 nanotubes / carbon nanofibers: The MnO2-PAN polymer was placed in a tube furnace and carbonized at 600℃~650℃ under argon atmosphere to obtain MnO2 NTs / CNFs; The carbonization time in step 4 is 2h~3h.

2. The method for preparing MnO2 NTs / CNFs according to claim 1, characterized in that The mass fraction of concentrated HNO3 described in step 1 is 68%.

3. The method for preparing MnO2 NTs / CNFs according to claim 1, characterized in that The hydrothermal reaction time in step 1 is 10 h to 12 h.

4. The method for preparing MnO2 NTs / CNFs according to claim 1, characterized in that The centrifugal speed in step 1 is 10000 r / min; the stirring time in step 1 is 5 min to 10 min.

5. Application of MnO2 NTs / CNFs prepared by the preparation method according to claim 1, characterized in that MnO2 NTs / CNFs are used as negative electrode materials for lithium-ion batteries.

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