A high specific capacity modified nickel oxide cathode

Abstract

The present invention discloses a high-specific-capacity modified nickel oxide cathode, which uses a modified nickel foil. The modified nickel foil is prepared by depositing a nanometer-scale nickel film on the surface of a nickel foil substrate. Monosilane is then reacted with the nickel film deposited on the surface of the nickel foil to generate nickel silicide nanowires, thereby obtaining a nickel foil modified with nickel silicide nanowires. Highly conductive nickel silicide is deposited on the surface of the nickel foil using hot-wire chemical vapor deposition (HWCVD) technology, effectively resolving the problem of poor conductivity of nickel oxide as a semiconductor material, thereby increasing the specific capacity of the active nickel oxide by more than 80%. As the number of cycles increases, the gap between the electrode material and the nickel foil gradually widens, resulting in poor contact of the active material and causing capacity decay. The introduction of a nickel silicide buffer layer can significantly improve the contact. The introduction of a nickel silicide buffer layer can significantly improve the reversibility of the active material, improving the cycle performance by more than 35%.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a high-specific-capacity modified nickel oxide cathode. Background Art

[0002] Currently, commonly used secondary batteries, such as nickel-cadmium, nickel-metal hydride, and lithium-ion batteries, have high specific energy but low power density, generally not exceeding 500W / kg. Supercapacitors are secondary energy storage devices that can directly store charge. Compared to secondary batteries, they offer higher power density, longer cycle life, faster charging, higher energy efficiency, and a wider operating temperature range.

[0003] Supercapacitors can be divided into electrochemical double-layer capacitors and faradaic pseudocapacitors. Carbon materials have the advantages of high specific surface area, low cost, and long cycle life, but their specific capacitance is less than 300F / g, which limits their commercial application. Transition metal oxides have high specific capacitance and excellent cycle reversibility, but are relatively expensive. Among them, nano-nickel oxide has the characteristics of high specific surface area, wide operating temperature range, and low cost. Nickel oxide (NiO) has a very high theoretical specific capacitance (2584F / g), but the actual specific capacitance is far lower than the theoretical value, mainly due to the poor conductivity of NiO and the low electron transfer rate.

[0004] Chinese invention patent CN105761951A discloses that a three-dimensional nickel oxide / graphene composite material was prepared to improve the specific capacitance and surface area of ​​the material, but the maximum capacitance was only 123 F / g.

[0005] Chinese invention patent CN103560018B discloses the preparation of a carbon nanotube / nickel oxide composite material, which utilizes the good electrical conductivity of carbon nanotubes to achieve a specific capacitance of 120-400 F / g.

[0006] However, the specific capacitance of the materials prepared by the above methods is still far from the theoretical capacity. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention provides a high-specific-capacity modified nickel oxide cathode, which can significantly improve the electrode capacity and reversibility. The electrode material prepared by the present invention has a higher energy density and a short charging time. The technical solution is mature and belongs to the field of materials technology.

[0008] A method for preparing a modified nickel foil comprises the following steps:

[0009] (1) depositing a nano-scale nickel film on the surface of a nickel foil substrate;

[0010] (2) using monosilane to react with the nickel thin film deposited on the surface of the nickel foil obtained in step (1) to generate nickel silicide nanowires, thereby obtaining a nickel foil modified with nickel silicide nanowires.

[0011] Preferably, in step (1), the nickel thin film is deposited using a hot-wire chemical vapor deposition technique, wherein the nickel foil is hung on a coiled tungsten wire and thermally evaporated with a hydrogen flow in a vacuum environment to deposit the nickel thin film onto the substrate nickel foil;

[0012] In step (2), using hot-wire chemical vapor deposition technology, monosilane and hydrogen are introduced separately under a vacuum environment and then dissociated and deposited on the surface of the nickel foil to react and form nickel silicide nanowires. The nickel nanofilm and monosilane react completely to form NiSi nanowires.

[0013] More preferably, in step (1), the substrate temperature is 100-300° C., the thermal evaporation pressure is 0.1-5 mbar, the hydrogen flow rate is 10-500 sccm, and the deposition thickness is 30-50 nm;

[0014] In step (2), a high temperature filament is used for dissociation, the temperature of the high temperature filament is 1200-2200°C, the dissociation time is 5-60 min, the flow rate of monosilane is 0.5-50 sccm, the flow rate of hydrogen is 10-500 sccm, the substrate temperature is 150-800°C, the deposition pressure is 0.1-5 mbar, and the base pressure is 1-20×10 -7 mbar.

[0015] The present invention further provides a modified nickel foil prepared by the preparation method.

[0016] The present invention also provides a high specific capacity modified nickel oxide cathode, which is obtained by mixing the cathode active material nickel oxide with a conductive agent and a binder, and preparing a slurry with a solvent, which is then coated on the modified side surface of the modified nickel foil.

[0017] Preferably, the mass ratio of nickel oxide, conductive agent and binder is 80-90:5-10:5-10.

[0018] Preferably, the cathode active material nickel oxide is graphene oxide-modified nickel oxide, and the graphene oxide-modified nickel oxide is synthesized using a sol-gel method.

[0019] More preferably, the method for preparing graphene oxide-modified nickel oxide comprises the following steps:

[0020] (a) adding a nickel nitrate solution to a graphene oxide solution to obtain a nickel nitrate / graphene oxide solution;

[0021] (b) preparing a gelatin solution, adding the nickel nitrate / graphene oxide solution obtained in step (a) to the gelatin solution, stirring and heating to react to obtain a black gel;

[0022] (c) heating the black gel obtained in step (b) to obtain the graphene oxide-modified nickel oxide.

[0023] Preferably, the conductive agent is at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, graphene, and Ketjen black;

[0024] The binder is at least one of styrene-butadiene rubber, sodium hydroxymethyl cellulose, polyacrylic acid, polyacrylonitrile, sodium alginate, polyvinylidene fluoride and polytetrafluoroethylene.

[0025] Preferably, the cathode coating surface density is 2 to 3 mg / cm 2 .

[0026] The present invention provides a method for preparing a high specific capacity modified nickel oxide cathode, which has the following beneficial effects:

[0027] (1) Highly conductive nickel silicide is deposited on the surface of nickel foil using hot wire chemical vapor deposition (HWCVD) technology, which can effectively solve the problem of poor conductivity of nickel oxide as a semiconductor material, thereby increasing the specific capacity of active nickel oxide by more than 80%;

[0028] (2) As the number of cycles increases, the gap between the electrode material and the nickel foil gradually expands, resulting in poor contact of the active material and causing capacity decay. The introduction of the nickel silicide buffer layer can significantly improve the contact;

[0029] (3) The introduction of the nickel silicide buffer layer can significantly improve the reversibility of the active material and the cycle performance can be improved by more than 35%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The cyclic voltammetry curves of the electrode in Example 1 and the electrode in Comparative Example 1 at a scan rate of 30 mV / S are shown.

[0031] Figure 2 2 are discharge curves obtained for the electrode of Example 1 and the electrode of Comparative Example 1 at a current density of 0.1 A / g.

[0032] Figure 3 1 is a graph showing the relationship between the retained capacitance value and the number of charge / discharge cycles of the electrode of Example 1 and the electrode of Comparative Example 1.

[0033] Figure 4 The cyclic voltammetry curves of the electrode of Example 3 and the electrode of Comparative Example 2 at a scan rate of 30 mV / S are shown.

[0034] Figure 5 2 are discharge curves obtained for the electrode of Example 3 and the electrode of Comparative Example 2 at a current density of 0.1 A / g.

[0035] Figure 6 Graph showing the relationship between the retained capacitance and the number of charge / discharge cycles for the electrode of Example 3 and the electrode of Comparative Example 2. DETAILED DESCRIPTION

[0036] Example 1

[0037] S1: Nickel foil is suspended on a coiled tungsten wire and thermally evaporated in a vacuum environment using a hydrogen flow rate of 150 sccm. The evaporation pressure is controlled at 0.5 mbar. The evaporated gas is then deposited onto the surface of a nickel foil substrate through a cooling device. The nickel foil substrate is heated to 200°C during deposition, and the deposition thickness is controlled to 50 nm. A nickel foil substrate with a nanoscale nickel film deposited on its surface is obtained.

[0038] S2: Monosilane and hydrogen are introduced into the coating chamber through mass flow meters, with flow rates controlled at 5 sccm and 120 sccm, respectively. A Roots pump is used to maintain the system vacuum environment. After being dissociated by a high-temperature filament at 1700°C for 15 minutes, they are deposited onto the surface of the nickel foil obtained in step S1 through a cooling device. The nickel foil is heated to 500°C. The nano-scale nickel film deposited in step S1 reacts with monosilane to form NiSi nanowires, thereby obtaining a nickel foil modified with NiSi nanowires. The deposition pressure is controlled at 0.9 mbar and the substrate pressure is controlled at 3×10 -7 mbar.

[0039] Nickel oxide (NiO): PVDF (polyvinylidene fluoride): SP (conductive carbon black) in a mass ratio of 80:10:10 was prepared into a slurry using NMP solvent and applied to the modified side surface of the NiSi nanowire-modified nickel foil obtained in step S2, with an area density of 3 mg / cm 2 , dried at 120℃ and assembled into batteries for testing.

[0040] Example 2

[0041] S1: Nickel foil is suspended on a coiled tungsten wire and thermally evaporated in a vacuum environment using a hydrogen flow rate of 300 sccm. The evaporation pressure is controlled at 0.4 mbar. The evaporated gas is then deposited onto the surface of a nickel foil substrate through a cooling device. The nickel foil substrate is heated to 150°C during deposition, and the deposition thickness is controlled to 30 nm. A nickel foil substrate with a nanometer-scale nickel film is obtained.

[0042] S2: Monosilane and hydrogen are introduced into the coating chamber through mass flow meters, with flow rates controlled at 5 sccm and 120 sccm, respectively. A Roots pump is used to maintain the system vacuum environment. After being dissociated by a high-temperature filament at 2000°C for 10 minutes, they are deposited onto the surface of the nickel foil obtained in step S1 through a cooling device. The nickel foil is heated to 450°C. The nano-scale nickel film deposited in step S1 reacts with monosilane to form NiSi nanowires, thereby obtaining a nickel foil modified with NiSi nanowires. The deposition pressure is controlled at 0.6 mbar and the substrate pressure is controlled at 1×10 -7 mbar.

[0043] A slurry of nickel oxide: PVDF: SP = 90:5:5 was prepared using NMP solvent and applied to the modified side surface of the NiSi nanowire-modified nickel foil obtained in step S2 at a surface density of 2 mg / cm 2 , dried at 120℃ and assembled into batteries for testing.

[0044] Example 3

[0045] S1: Hang the nickel foil on the coiled tungsten wire and perform thermal evaporation with a hydrogen flow rate of 200 sccm in a vacuum environment. The evaporation pressure is controlled at 0.3 mbar. The evaporated gas flow is then deposited onto the surface of the nickel foil substrate through a cooling device. During deposition, the nickel foil substrate is heated to 300°C and the deposition thickness is controlled at 50 nm.

[0046] S2: Monosilane and hydrogen are introduced into the coating chamber through mass flow meters, with flow rates controlled at 5 sccm and 120 sccm, respectively. A Roots pump is used to maintain the system vacuum environment. After being dissociated by a high-temperature filament at 2000°C for 15 minutes, they are deposited onto the surface of the nickel foil obtained in step S1 through a cooling device. The nickel foil is heated to 550°C. The nano-scale nickel film deposited in step S1 reacts with monosilane to form NiSi nanowires, thereby obtaining a nickel foil modified with NiSi nanowires. The deposition pressure is controlled at 1 mbar and the substrate pressure is controlled at 2×10 -7 mbar.

[0047] S3: 320 ml of H2SO4 (0.1 M), 80 ml of H3PO4 (0.1 M), 3 g of graphite flakes and 18 g of KMnO4 were slowly added to the reactor and mixed using a magnetic stirrer to oxidize the graphite. The color of the mixture changed from dark purple-green to dark brown. Then 30 ml of a 30% volume concentration of H2O2 solution was added to stop the oxidation process, and the color of the mixture changed to bright yellow. The formed graphite oxide was washed three times with a 1 M HCl aqueous solution to a pH of 4-5 and repeatedly washed with deionized water. It was repeatedly washed with deionized water in a centrifuge, leaving only the insoluble matter in the lower layer. During the washing process with deionized water, the graphite oxide underwent exfoliation, causing the graphene solution to thicken and form a GO (graphene oxide) gel.

[0048] S4: Dissolve 4g of Ni(NO₃)₂6H₂O in 20mL of deionized water and stir for 30 minutes to obtain a nickel nitrate solution. Dissolve 0.04g of GO (obtained in step S3) in 20mL of deionized water and stir for 30 minutes to obtain a GO solution. The nickel nitrate solution is then very slowly added to the GO solution to obtain a nickel nitrate / GO solution. Simultaneously, dissolve 2g of gelatin in 40mL of deionized water and stir at 60°C for 45 minutes to obtain a clear gelatin solution. The nickel nitrate / GO solution is then added to the gelatin solution and heated in a 60°C water bath with stirring to dissolve the gelatin and crosslink to form a gel. Stirring is continued for 15 hours to obtain a honey-like black gel. The black gel is placed in a furnace and heated from room temperature to 300°C at a rate of 25°C / min. After maintaining the final temperature for 2 hours, the water is removed to obtain a powdered material. The furnace is then cooled naturally to room temperature to obtain a nano-nickel oxide / graphene (NiO / GO) composite material.

[0049] A slurry with a mass ratio of NiO / GO:PVDF:SP=85:5:10 was prepared using NMP solvent and coated on the modified side surface of the NiSi nanowire-modified nickel foil obtained in step S2 with a surface density of 2 mg / cm 2 , dried at 120℃ and assembled into batteries for testing.

[0050] Comparative Example 1

[0051] Nickel oxide (NiO): PVDF: SP = 80:10:10 mass ratio was prepared into slurry using NMP solvent and coated on the surface of unmodified nickel foil with an area density of 3 mg / cm 2 , dried at 120℃ and assembled into batteries for testing.

[0052] Comparative Example 2

[0053] The composite cathode material NiO / GO synthesized by the sol-gel method in Example 3 was prepared into a slurry with a mass ratio of NiO / GO:PVDF:SP=85:5:10 using NMP solvent and coated on the surface of unmodified nickel foil with an area density of 2 mg / cm 2 , dried at 120℃ and assembled into batteries for testing.

[0054] Test Example 1

[0055] Cyclic voltammetry was performed on Example 1 and Comparative Example 1 at a scan rate of 30 mV / s. The results are shown in FIG. Figure 1 As shown, the area under the CV curve of the electrode of Example 1 is larger, the potential window is wider, and the lower ohmic resistance allows relatively smooth charge transfer between the substrate and the electrode material.

[0056] Table 1: Comparison of the capacities of the electrode of Comparative Example 1 and the electrode of Example 1 at different scan rates by CV

[0057]

[0058] Cyclic voltammetry tests were performed on Example 1 and Comparative Example 1 at scan rates of 1, 5, 15, 20, and 30 mV / s, respectively. The results are shown in Table 1, and the following conclusions can be drawn:

[0059] 1) Compared with the electrode of comparative example 1, the electrode of example 1 shows a higher capacity at 1mV / S -1 and 30mV / S -1 The specific capacity increased by 87% and 46% at the same scan rate, respectively.

[0060] 2) Compared with the electrode of comparative example 1, the potential window between the redox peaks of the electrode of example 1 is 1mV / S -1 and 30mV / S -1 The reversibility decreased by 22% at all scan rates.

[0061] Test Example 2

[0062] The charge and discharge tests were carried out on Example 1 and Comparative Example 1 at a current density of 0.1 A / g to detect the first cycle capacity. The results are as follows: Figure 2 As shown, it can be seen that the capacity of Example 1 is increased by 15% compared with Comparative Example 1.

[0063] Test Example 3

[0064] The charge and discharge tests were performed on Example 1 and Comparative Example 1 at a current density of 0.1 A / g to detect the capacity retention rate.

[0065] Table 2: Comparison of charge and discharge of the electrode of Example 1 and the electrode of Comparative Example 1

[0066]

[0067] The results are as follows Figure 3 As shown in Table 2, it can be seen that the capacitance retention rates of the electrode of Example 1 and the electrode of Comparative Example 1 after 1000 cycles are 82.1% and 60.3%, respectively.

[0068] Test Example 4

[0069] Cyclic voltammetry tests were performed on Example 3 and Comparative Example 2 at scan rates of 1, 5, 15, 20, and 30 mV / S, respectively. The results are shown in Table 3. Figure 4 A comparison of cyclic voltammetry of the electrode of Example 3 and the electrode of Comparative Example 2 at a scan rate of 30 mV / s is shown.

[0070] Table 3: Comparison of the capacities of the electrodes of Example 3 and Comparative Example 2 at different scan rates by CV

[0071]

[0072] Through Table 3 and Figure 4 The following conclusions can be drawn:

[0073] 1) Compared with the electrode of Comparative Example 2, the electrode of Example 3 shows a higher capacity at 1mV / S -1 and 30mV / S -1 The specific capacity increased by 51% and 48% at the same scan rate, respectively.

[0074] 2) Compared with the electrode of Comparative Example 2, the potential window between the redox peaks of the electrode of Example 3 is 1 mV / S -1 The reversibility decreased by 54% at a scan rate of 30 mV / S. -1 Scan rate increased by 46%.

[0075] Test Example 5

[0076] The charge and discharge tests were performed on Example 3 and Comparative Example 2 at a current density of 0.1 A / g to detect the first cycle capacity. Figure 5 As shown, it can be seen that the capacity of Example 3 is increased by 16% compared with Comparative Example 2.

[0077] Test Example 6

[0078] The charge and discharge tests were performed on Example 3 and Comparative Example 2 at a current density of 0.1 A / g to detect the capacity retention rate.

[0079] Table 4: Comparison of charge and discharge of the electrode of Example 3 and the electrode of Comparative Example 2

[0080]

[0081] The results are as follows Figure 6 As shown in Table 4, it can be seen that the capacitance retention rates of the electrode of Example 3 and the electrode of Comparative Example 2 after 1000 cycles are 78.2% and 27.5%, respectively.

Claims

1. A method for preparing a modified nickel foil, characterized in that: The following steps are involved: (1) Depositing a nano-scale nickel film on the surface of a nickel foil substrate; (2) using monosilane to react with the nickel film deposited on the surface of the nickel foil obtained in step (1) to generate nickel silicide nanowires, thereby obtaining nickel foil modified with nickel silicide nanowires; In step (1), the nickel thin film is deposited using hot wire chemical vapor deposition technology, the nickel foil is hung on a coiled tungsten wire, and thermally evaporated with hydrogen flow in a vacuum environment to deposit it on the substrate nickel foil; In step (1), the substrate temperature is 100-300°C, the thermal evaporation pressure is 0.1-5 mbar, the hydrogen flow rate is 10-500 sccm, and the deposition thickness is 30-50 nm; In step (2), using hot-wire chemical vapor deposition technology, monosilane and hydrogen are introduced separately under a vacuum environment and then dissociated and deposited on the surface of the nickel foil to react and generate nickel silicide nanowires; In step (2), a high-temperature filament is used for dissociation, the high-temperature filament temperature is 1200-2200°C, the dissociation time is 5-60 min, the silane flow rate is 0.5-50 sccm, the hydrogen flow rate is 10-500 sccm, the substrate temperature is 150-800°C, the deposition pressure is 0.1-5 mbar, and the base pressure is 1-20×10 -7 mbar.

2. The modified nickel foil prepared by the preparation method according to claim 1.

3. A high specific capacity modified nickel oxide cathode, characterized in that: The nickel oxide cathode is obtained by mixing the cathode active material nickel oxide with a conductive agent and a binder, and adding a solvent to prepare a slurry which is coated on the modified side surface of the modified nickel foil according to claim 2.

4. The high specific capacity modified nickel oxide cathode according to claim 3, characterized in that: The mass ratio of nickel oxide, conductive agent and binder is 80~90:5~10:5~10.

5. The high specific capacity modified nickel oxide cathode according to claim 3, characterized in that: The cathode active material nickel oxide is graphene oxide-modified nickel oxide, and the graphene oxide-modified nickel oxide is synthesized by a sol-gel method.

6. The high specific capacity modified nickel oxide cathode according to claim 5, characterized in that: The preparation method of graphene oxide modified nickel oxide comprises the following steps: (a) adding nickel nitrate solution to graphene oxide solution to obtain nickel nitrate / graphene oxide solution; (b) preparing a gelatin solution, adding the nickel nitrate / graphene oxide solution obtained in step (a) to the gelatin solution, stirring and heating to react to obtain a black gel; (c) heating the black gel obtained in step (b) to obtain the graphene oxide-modified nickel oxide.

7. The high specific capacity modified nickel oxide cathode according to claim 3, characterized in that: The conductive agent is at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene; The binder is at least one of styrene-butadiene rubber, sodium hydroxymethyl cellulose, polyacrylic acid, polyacrylonitrile, sodium alginate, polyvinylidene fluoride and polytetrafluoroethylene.

8. The high specific capacity modified nickel oxide cathode according to claim 3, characterized in that: The cathode coating surface density is 2~3mg / cm 2 .

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