A molybdenum dioxide-nano carbon fiber composite and a preparation method and application thereof
By preparing a molybdenum dioxide-carbon nanofiber composite, the volume expansion problem of molybdenum dioxide during charge and discharge was solved, achieving high specific capacity, excellent rate performance, and good cycle performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LUOYANG E-ENERGY STORAGE & TRANSFORMATION SYST CO LTD
- Filing Date
- 2026-05-27
- Publication Date
- 2026-06-23
Smart Images
Figure CN122257154A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a molybdenum dioxide-nanocarbon fiber composite, its preparation method, and its application. Background Technology
[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and low self-discharge, have been widely used in portable electronic devices, electric vehicles, and energy storage systems. The anode material is one of the key factors determining the electrochemical performance of lithium-ion batteries. Currently, graphite is the primary anode material for lithium-ion batteries. While it exhibits good cycle stability and conductivity, its theoretical specific capacity is only 372 mAh·g. -1 The relatively low theoretical specific capacity has limited the development of lithium-ion batteries.
[0003] Currently, molybdenum-based nanomaterials have attracted widespread attention due to their abundant resources, low cost, and high theoretical lithium intercalation capacity. Among them, molybdenum dioxide (MoO2), as a typical transition metal oxide, possesses high electronic conductivity and good electrochemical activity, and is considered a highly promising high-performance anode material. However, molybdenum dioxide exhibits a severe volume expansion effect during charge and discharge, which easily leads to pulverization and cracking of the electrode structure, thereby accelerating capacity decay. Summary of the Invention
[0004] To address the issue of volume expansion of molybdenum dioxide during charging and discharging in existing technologies, this invention provides a molybdenum dioxide-nanocarbon fiber composite, its preparation method, and its application. This composite mitigates the volume expansion of molybdenum dioxide during charging and discharging, exhibiting good cycle performance, high specific capacity, and excellent rate performance.
[0005] To achieve the above objectives, the specific solution adopted by the present invention is as follows: a molybdenum dioxide-nanocarbon fiber composite, which is prepared by using molybdenum disulfide nanosheets and polyacrylonitrile as raw materials, and the molybdenum dioxide in the composite has a monoclinic crystal structure.
[0006] A method for preparing a molybdenum dioxide-carbon nanofiber composite involves dispersing molybdenum disulfide nanosheets and polyacrylonitrile in an organic solvent at a mass ratio of 0.1 to 2:1 to obtain a mixture; electrospinning the mixture to obtain molybdenum disulfide-polyacrylonitrile nanofibers; oxidizing the molybdenum disulfide-polyacrylonitrile nanofibers at 400 to 600 °C to obtain a molybdenum dioxide-polyacrylonitrile composite material; and carbonizing the molybdenum dioxide-polyacrylonitrile composite material under a protective atmosphere and at 700 to 900 °C to obtain the molybdenum dioxide-carbon nanofiber composite.
[0007] As an optimized method for preparing the above-mentioned molybdenum dioxide-nanocarbon fiber composite, the organic solvent is one or more of ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.
[0008] As another optimized method for preparing the above-mentioned molybdenum dioxide-nanocarbon fiber composite, the voltage of the electrospinning is 8~15kV.
[0009] As another optimized method for preparing the above-mentioned molybdenum dioxide-carbon nanofiber composite, the ratio of molybdenum disulfide nanosheets to organic solvent is 0.1~1g:10mL.
[0010] As another optimized method for preparing the above-mentioned molybdenum dioxide-carbon nanofiber composite, the width of the molybdenum dioxide-carbon nanofiber in the molybdenum dioxide-carbon nanofiber composite is 20~200nm.
[0011] As another optimized method for preparing the above-mentioned molybdenum dioxide-carbon nanofiber composite, molybdenum disulfide-polyacrylonitrile nanofibers are oxidized at 450~500℃ for 5~20 min.
[0012] As another optimized method for preparing the above-mentioned molybdenum dioxide-carbon nanofiber composite, the protective atmosphere is one or more of nitrogen, argon, and helium.
[0013] Application of the above-mentioned molybdenum dioxide-carbon nanofiber composite in the negative electrode of lithium-ion battery.
[0014] As an optimized solution for the application of the above-mentioned molybdenum dioxide-nano carbon fiber composite in the negative electrode of lithium-ion battery: the negative electrode is prepared by using molybdenum dioxide-nano carbon fiber composite. The method is as follows: polyvinylidene fluoride, acetylene black and molybdenum dioxide-nano carbon fiber composite are mixed evenly in a mass ratio of 1:1:7~9 to obtain a mixture; N-methylpyrrolidone is added to the mixture and ground to form a slurry, which is then coated on copper foil to form a slurry layer and dried at 120°C; the dried copper foil is then cut to form the negative electrode.
[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a molybdenum dioxide-nanocarbon fiber composite and its preparation method. This material has a low dimensionality (one-dimensional), which is beneficial for the rapid insertion and extraction of lithium ions. In the molybdenum dioxide-nanocarbon fiber composite, the nanocarbon fibers encapsulate molybdenum dioxide, which slows down the volume expansion of molybdenum dioxide during charge and discharge, ensuring the stability of molybdenum dioxide. The battery anode prepared using this material has a large specific capacity, specifically, a specific capacity greater than 950 mAh / g when charged and discharged at a current of 50 mA / g; it has excellent rate performance, that is, a specific capacity greater than 400 mAh / g when charged and discharged at a current of 1000 mA / g; and it also has good cycle performance, specifically, a specific capacity greater than 900 mAh / g after 400 cycles at a current of 50 mA / g.
[0016] 2. In this invention, molybdenum disulfide nanosheets and polyacrylonitrile are used as raw materials, and electrospinning, oxidation and carbonization processes are combined to release sulfur-containing gas during the conversion of MoS2, thereby creating a large number of nanopores in the molybdenum dioxide-carbon nanofiber composite. These pores not only increase the electrolyte wetting area, but also provide a buffer space for volume expansion. The sulfur-containing gas generated during its escape destroys the original crystal lattice and reduces the grain size of molybdenum dioxide, thereby giving the molybdenum dioxide-carbon nanofibers excellent rate performance. Attached Figure Description
[0017] Figure 1 The characterization results of the molybdenum dioxide-carbon nanofiber composite prepared in Example 1 are as follows: Figure 1 In the middle (a) and (b), the images are scanning electron microscope (SEM) images at different magnifications; Figure 1 Image (c) is a transmission electron microscope (TEM) image; Figure 1 Medium (d) High-resolution transmission electron microscopy (HRTEM) image.
[0018] Figure 2 The characterization results of the molybdenum dioxide-carbon nanofiber composite prepared in Example 5 are as follows: Figure 2 In the middle (a) and (b), the images are scanning electron microscope (SEM) images at different magnifications; Figure 2 Image (c) is a transmission electron microscope (TEM) image; Figure 2 Medium (d) High-resolution transmission electron microscopy (HRTEM) image.
[0019] Figure 3 The X-ray photoelectron spectroscopy of the molybdenum dioxide-carbon nanofiber composite prepared in Example 1 is shown. Detailed Implementation
[0020] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments of the present invention should be understood as prior art known or should be known by those skilled in the art.
[0021] A method for preparing a molybdenum dioxide-carbon nanofiber composite includes the following steps: Molybdenum disulfide nanosheets and polyacrylonitrile are dispersed in an organic solvent at a mass ratio of 0.1 to 2:1, with the ratio of molybdenum disulfide nanosheets to organic solvent being 0.1 to 1 g: 10 mL, to obtain a mixed solution. The organic solvent is one or more of ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.
[0022] The mixture is placed in an electrospinning device and electrospinned to obtain molybdenum disulfide-polyacrylonitrile nanofibers; the voltage for electrospinning is 8~15kV.
[0023] Molybdenum disulfide-polyacrylonitrile nanofibers were placed in a muffle furnace and oxidized at 400-600℃ for 5-20 min to obtain a molybdenum dioxide-polyacrylonitrile composite material. During the oxidation process, the temperature was increased to 400-600℃ at a rate of 40℃ / min. Molybdenum disulfide was oxidized in situ to molybdenum dioxide, while polyacrylonitrile underwent pre-oxidation and cyclization reactions to form a stable structure.
[0024] The molybdenum dioxide-polyacrylonitrile composite material was carbonized under a protective atmosphere and at 700~900℃ to obtain a molybdenum dioxide-nano carbon fiber composite material. The protective atmosphere was one or more of nitrogen, argon, and helium, and the carbonization time was 1~3h, so that the polyacrylonitrile was completely converted into the nano carbon fiber matrix.
[0025] One-dimensional molybdenum dioxide-carbon nanofiber composites were prepared by electrospinning. The one-dimensional nanostructure of the material facilitates rapid radial insertion and extraction of lithium ions. The conductive carbon nanofiber matrix not only provides an efficient electron transport network, improving the material's conductivity, but also effectively coats and protects the molybdenum dioxide nanoparticles, significantly mitigating their volume expansion during charge and discharge. Therefore, when used as an anode material for lithium-ion batteries, this composite exhibits high specific capacity, excellent rate performance, and good cycle stability.
[0026] This invention also provides a molybdenum dioxide-carbon nanofiber composite, which is made from molybdenum disulfide nanosheets and polyacrylonitrile, and is composed of molybdenum dioxide-carbon nanofibers with a width of 20-200 nm and a specific surface area of 10-20 m². 2 / g, the molybdenum dioxide in the complex has a monoclinic crystal structure.
[0027] This invention also provides an application of molybdenum dioxide-nanocarbon fiber composite in the negative electrode of a lithium-ion battery, which has a specific capacity greater than 950 mAh / g when charged and discharged at a current of 50 mA / g; a specific capacity greater than 400 mAh / g when charged and discharged at a current of 1000 mA / g; and a specific capacity greater than 900 mAh / g after 400 cycles at a current of 50 mA / g.
[0028] Example 1
[0029] A method for preparing a molybdenum dioxide-carbon nanofiber composite includes the following steps: S1. Add 6g of molybdenum disulfide nanosheets and 12g of polyacrylonitrile to 100mL of N,N-dimethylformamide and disperse evenly by ultrasonication to obtain a mixture.
[0030] S2, the mixture is placed in an electrospinning device and electrospinned at a voltage of 10kV to obtain molybdenum disulfide-polyacrylonitrile nanofibers.
[0031] S3, molybdenum disulfide-polyacrylonitrile nanofibers were placed in a muffle furnace and heated to 450°C at a heating rate of 40°C / min, and then oxidized for 20 min to obtain molybdenum dioxide-polyacrylonitrile composite material.
[0032] S4, molybdenum dioxide-polyacrylonitrile composite material was carbonized at 750℃ for 3 hours under a protective atmosphere to obtain molybdenum dioxide-nanocarbon fiber composite.
[0033] The morphology and structure characterization of the molybdenum dioxide-carbon nanofibers prepared in this embodiment are as follows: Figure 1 As shown, Figure 1 Scanning electron microscope (SEM) images (a) and (b) show that the prepared molybdenum dioxide-carbon nanofibers have an average diameter between 20 and 200 nm and exhibit a uniform one-dimensional fiber morphology. Figure 1 The transmission electron microscopy (TEM) image in (c) further confirms its one-dimensional nanofiber characteristics. Figure 1 The high-resolution transmission electron microscopy (HRTEM) image in (d) shows clear lattice fringes, and its interplanar spacing is measured to be 0.244 nm, consistent with the interplanar spacing of monoclinic molybdenum dioxide (011), confirming that molybdenum dioxide exists in the monoclinic form in the composite. Meanwhile, from Figure 1 It can be seen that the overall structure of the molybdenum dioxide-carbon nanofibers is composed of interwoven fibrous materials, forming a structure in which molybdenum dioxide is encapsulated by carbon nanofibers. Specifically, Figure 1 The microstructure of materials (a) and (b) is that molybdenum dioxide is dispersed in the form of particles in the carbon nanofibers. The morphology of the molybdenum dioxide particles is different depending on the oxidation temperature. Figure 1In (c), the structure of molybdenum dioxide encapsulated in carbon nanofibers can be seen. The molybdenum dioxide is dispersed within the carbon nanofibers, and the crystal lattice of the molybdenum dioxide particles can be observed using a transmission electron microscope. Figure 1 As shown in (d), the particles are proven to be molybdenum dioxide.
[0034] Figure 3 The X-ray photoelectron spectroscopy of the molybdenum dioxide-carbon nanofibers prepared in this embodiment was obtained by... Figure 3 It can be seen that the material contains 6.26% Mo, 69.5% C, and 23.24% oxygen, and also contains Mo-O bonds and exhibits Mo... 4+ .
[0035] The above molybdenum dioxide-nano carbon fiber composite was made into a negative electrode by the following method: polyvinylidene fluoride, acetylene black and the above molybdenum dioxide-nano carbon fiber composite were mixed evenly in a mass ratio of 1:1:8 to obtain a mixture; N-methylpyrrolidone was added to the mixture and ground to form a slurry, which was then coated on a copper foil to form a slurry layer and dried at 120°C; subsequently, it was cut into a disc to make a negative electrode.
[0036] Using the aforementioned negative electrode as the negative electrode and a lithium metal sheet as the positive electrode, a 2025-type coin cell simulated battery was assembled and subjected to constant current charge-discharge testing. The test results were as follows: at a current density of 100 mA / g, the stable specific capacity of this electrode reached 966 mAh / g (higher than 950 mAh / g); at a high current density of 1000 mA / g, the stable specific capacity remained as high as 423 mAh / g (higher than 400 mAh / g); after 400 charge-discharge cycles at 100 mA / g, the specific capacity remained at 923 mAh / g (higher than 900 mAh / g), with a capacity retention rate exceeding 95%. This indicates that the composite material possesses extremely high specific capacity, excellent rate performance, and good cycle stability.
[0037] Example 2
[0038] The preparation method of the molybdenum dioxide-nanocarbon fiber composite in this embodiment is the same as that in Example 1, except that the mass ratio of molybdenum disulfide nanosheets to polyacrylonitrile is 0.2:1.
[0039] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used to fabricate a negative electrode according to the method in Example 1, and corresponding electrochemical performance tests were performed. When preparing the negative electrode, the mass ratio of polyvinylidene fluoride, acetylene black, and the aforementioned molybdenum dioxide-carbon nanofiber composite was 1:1:7. The test results are as follows: at a charge-discharge current of 100 mA / g, the stable specific capacity was 954 mAh / g; at a charge-discharge current of 1000 mA / g, the stable specific capacity was 412 mAh / g; after 400 charge-discharge cycles at a current of 100 mA / g, the specific capacity was 909 mAh / g, with a capacity retention rate of over 95%.
[0040] Example 3
[0041] The preparation method of the molybdenum dioxide-nanocarbon fiber composite in this embodiment is the same as that in Example 1, except that the mass ratio of molybdenum disulfide nanosheets to polyacrylonitrile is 1:1.
[0042] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used to fabricate a negative electrode according to the method in Example 1, and corresponding electrochemical performance tests were performed. When preparing the negative electrode, the mass ratio of polyvinylidene fluoride, acetylene black, and the aforementioned molybdenum dioxide-carbon nanofiber composite was 1:1:9. The test results are as follows: at a charge-discharge current of 100 mA / g, the stable specific capacity was 972 mAh / g; at a charge-discharge current of 1000 mA / g, the stable specific capacity was 441 mAh / g; after 400 charge-discharge cycles at a current of 100 mA / g, the specific capacity was 931 mAh / g, with a capacity retention rate of over 95%.
[0043] Example 4
[0044] The preparation method of the molybdenum dioxide-carbon nanofiber composite in this embodiment is the same as that in Example 1, except that the mass ratio of molybdenum disulfide nanosheets to polyacrylonitrile is 2:1.
[0045] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used as negative electrodes according to the method in Example 1, and their electrochemical performance was tested accordingly. The test results are as follows: the stable specific capacity is 983 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 452 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 939 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of over 95%.
[0046] Example 5
[0047] The preparation method of the molybdenum dioxide-nano carbon fiber composite in this embodiment is the same as that in Example 1, except that the oxidation temperature in step S3 is 400℃.
[0048] The morphology and structure characterization of the molybdenum dioxide-carbon nanofibers prepared in this embodiment are as follows: Figure 2 As shown, SEM images confirm that the fiber width remains within the range of 20–200 nm. HRTEM images show a crystal interplanar spacing of 0.244 nm, confirming that the molybdenum dioxide in the product has a monoclinic crystal structure. Meanwhile, from… Figure 2 It can be seen that the overall structure of the molybdenum dioxide-carbon nanofibers is composed of interwoven fibrous materials, forming a structure in which molybdenum dioxide is encapsulated by carbon nanofibers. Specifically, Figure 2 The microstructure of materials (a) and (b) is that molybdenum dioxide is dispersed in the form of particles in the carbon nanofibers. The morphology of the molybdenum dioxide particles is different depending on the oxidation temperature. Figure 2 In (c), the structure of molybdenum dioxide encapsulated in carbon nanofibers can be seen. The molybdenum dioxide is dispersed within the carbon nanofibers, and the crystal lattice of the molybdenum dioxide particles can be observed using a transmission electron microscope. Figure 2 As shown in (d), the particles are proven to be molybdenum dioxide.
[0049] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used as negative electrodes according to the method in Example 1, and their electrochemical performance was tested accordingly. The test results are as follows: the stable specific capacity is 968 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 427 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 922 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of over 95%.
[0050] Example 6
[0051] The preparation method of the molybdenum dioxide-nano carbon fiber composite in this embodiment is the same as that in Example 1, except that the oxidation temperature in step S3 is 500℃.
[0052] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used as negative electrodes according to the method in Example 1, and their electrochemical performance was tested accordingly. The test results are as follows: the stable specific capacity is 971 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 418 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 928 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of over 95%.
[0053] Example 7
[0054] The preparation method of the molybdenum dioxide-nano carbon fiber composite in this embodiment is the same as that in Example 1, except that the oxidation temperature in step S3 is 600℃ and the carbonization temperature in step S4 is 700℃.
[0055] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used as negative electrodes according to the method in Example 1, and their electrochemical performance was tested accordingly. The test results are as follows: the stable specific capacity is 975 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 427 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 931 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of over 95%.
[0056] Example 8
[0057] The preparation method of the molybdenum dioxide-nano carbon fiber composite in this embodiment is the same as that in Example 1, except that the oxidation temperature in step S3 is 600℃ and the carbonization temperature in step S4 is 900℃.
[0058] The molybdenum dioxide-carbon nanofibers prepared in this embodiment were used as negative electrodes according to the method in Example 1, and their electrochemical performance was tested accordingly. The test results are as follows: the stable specific capacity is 982 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 411 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 935 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of over 95%.
[0059] Comparative Example The preparation method of this comparative molybdenum dioxide-nanocarbon fiber composite is the same as that of Example 1, except that the mass ratio of molybdenum disulfide nanosheets to polyacrylonitrile is 3:1.
[0060] The molybdenum dioxide-carbon nanofibers prepared in this comparative example were used to make a negative electrode according to the method in Example 1, and the corresponding electrochemical performance was tested. The test results are as follows: the stable specific capacity is 862 mAh / g when charged and discharged at a current of 100 mA / g; the stable specific capacity is 398 mAh / g when charged and discharged at a current of 1000 mA / g; and the specific capacity is 801 mAh / g after 400 cycles of charge and discharge at a current of 100 mA / g, with a capacity retention rate of less than 93%.
[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A molybdenum dioxide-nanocarbon fiber composite, characterized by: The composite was prepared using molybdenum disulfide nanosheets and polyacrylonitrile as raw materials, and the molybdenum dioxide in the composite had a monoclinic crystal structure.
2. A method for preparing a molybdenum dioxide-nanocarbon fiber composite, characterized by: Molybdenum disulfide nanosheets and polyacrylonitrile are dispersed in an organic solvent at a mass ratio of 0.1 to 2:1 to obtain a mixture. The mixture is electrospun to obtain molybdenum disulfide-polyacrylonitrile nanofibers. The molybdenum disulfide-polyacrylonitrile nanofibers are oxidized at 400 to 600 °C to obtain a molybdenum dioxide-polyacrylonitrile composite material. The molybdenum dioxide-polyacrylonitrile composite material is carbonized under a protective atmosphere at 700 to 900 °C to obtain a molybdenum dioxide-nanocarbon fiber composite.
3. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: The organic solvent is one or more of ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.
4. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: The voltage for electrospinning is 8~15kV.
5. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: The ratio of molybdenum disulfide nanosheets to organic solvent is 0.1~1g:10mL.
6. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: The width of the molybdenum dioxide-nanocarbon fiber in the molybdenum dioxide-nanocarbon fiber composite is 20~200nm.
7. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: Molybdenum disulfide-polyacrylonitrile nanofibers were oxidized at 450~500℃ for 5~20 min.
8. The method for preparing a molybdenum dioxide-nanocarbon fiber composite as described in claim 2, characterized in that: The protective atmosphere is one or more of nitrogen, argon, and helium.
9. The application of the molybdenum dioxide-nanocarbon fiber composite of claim 1 in the negative electrode of a lithium-ion battery.
10. The application of the molybdenum dioxide-nanocarbon fiber composite as described in claim 9 in the negative electrode of a lithium-ion battery, characterized in that: The negative electrode was prepared using a molybdenum dioxide-nano carbon fiber composite. The method was as follows: polyvinylidene fluoride, acetylene black and molybdenum dioxide-nano carbon fiber composite were mixed evenly in a mass ratio of 1:1:7~9 to obtain a mixture; N-methylpyrrolidone was added to the mixture and ground to form a slurry, which was then coated on a copper foil to form a slurry layer and dried at 120°C; the dried copper foil was then cut to form the negative electrode.