An ultra-long cycle composite supercapacitor positive electrode material N / P-GNTs@NiCoP and its preparation

Abstract

The present invention discloses a positive electrode material for an ultra-long cycle N / P-GNTs@NiCoP composite supercapacitor, belonging to the field of new energy storage. In the present invention, NiCoP nanoparticles are deposited on the surface of N / P-GNTs by a one-step phosphating method, and the NiCoP nanoparticles are firmly anchored on the surface of N / P-GNTs through N-Ni / Co and P-Ni / Co bonds, obtaining an N / P-GNTs@NiCoP composite supercapacitor positive electrode material with an interfacial bonding effect; the N / P-GNTs@NiCoP composite material prepared in the present invention exhibits ultra-long cycle stability, and can still maintain 90% of the original specific capacitance after cycling 75,000 times at 50 Ag-1, which provides a high-quality candidate positive electrode material for constructing a new generation of high-performance supercapacitors.

Description

Technical Field

[0001] The present invention relates to the field of new energy storage, and in particular to an ultra-long cycle N / P-GNTs@NiCoP composite supercapacitor positive electrode material. Technical Background

[0002] Supercapacitors are a new type of energy storage device developed in recent years. They have the advantages of high power density, fast charging speed, long cycle life, wide operating temperature range, good safety performance and environmental protection. They have broad application prospects in new energy vehicles, micro-communication equipment, heavy machinery, aerospace and other fields (Chinese invention patent, application number 201810202685.6). However, compared with rechargeable batteries, supercapacitors have a lower energy density, which seriously restricts their industrial production process (Energy & Environmental Science, 2016, 9, 102-106. Advanced Energy Materials, 2019, 9, 1802928). As we all know, the performance of supercapacitors depends entirely on their electrode materials. Therefore, designing and constructing a new type of electrode material with excellent electrochemical properties is of great significance to improving the energy density of supercapacitors.

[0003] In recent years, traditional carbon materials (such as activated carbon) are often used as supercapacitor electrode materials. Due to their low theoretical specific capacitance, the commercialization process of supercapacitors is seriously restricted. Therefore, researchers often improve the energy density and power density of supercapacitors by designing new positive electrode materials. In recent years, researchers have tried to use transition metal compounds such as NiMoO4, CoNi-MOF, NiCoP / NiCo-OH, MoS2, Fe2O3, NiCoSe2 as positive electrode materials, mainly because they have high theoretical specific capacitance, excellent redox characteristics and electrochemical activity, and advantages such as abundant raw materials, environmental friendliness and low price (Nature Communications, 2017, 8, 14264. Advanced Energy Materials, 2017, 7, 1700294. Advanced Functional Materials, 2018, 28, 1800036. Nature Nanotechnology, 2015, 10, 313-318. Chinese invention patent, application number 201310058911.5; Chinese invention patent, application number 201611200095.7). However, these compounds have the disadvantages of poor cycle stability and rate performance. In order to overcome the above problems, researchers often use carbon materials with good conductivity and large specific surface area as a skeleton to compound with it, effectively improving its low specific capacitance defect (Advanced Energy Materials, 2018, 8, 1702247. Nano Energy, 2017, 35, 331-340. Energy & Environmental Science, 2016, 9, 1299-1307). Although the above-prepared composite electrode material has a higher specific capacitance than a single active material, its cycle stability and rate performance still cannot meet the needs of new high-performance supercapacitors, greatly hindering its practical application in supercapacitors. The reason may be that the composite of the above-mentioned skeleton and the active material is a simple physical adsorption effect. When the composite electrode material is in the process of high current charge and discharge, the rapid insertion / extraction of ions in the electrolyte causes its volume to expand / contract significantly. At the same time, the large alternating stress cycle can cause it to produce stress concentration phenomenon, which leads to the pulverization of the active material and even falls off from the skeleton surface, causing serious collapse of the entire electrode structure. Therefore, how to construct a solid-solid interface between skeleton materials and active materials that has a strong bonding force and is conducive to rapid electron conduction, and systematically explore the influence of the introduction of the above-mentioned solid-solid interface on the high-rate performance and long cycle life of composite electrode materials, is a huge challenge facing this field and a bottleneck problem that must be overcome for the future large-scale application of supercapacitors.

[0004] As we all know, graphene tubes not only have good mechanical properties and physical and chemical stability, large aspect ratio and specific surface area, excellent electrical conductivity and anti-corrosion and anti-oxidation properties, but also they are entangled with each other to form a special network structure. Therefore, the network structure formed by graphene tubes not only makes the active materials evenly dispersed, but also provides a variety of transmission channels for electron conduction during the charging and discharging process; in addition, the graphene tubes have a large diameter (150-200nm), which can be used as a special ion "storage", ensuring a stable supply of electrolyte ions and accelerating the diffusion of ions into the electrode active layer, which makes them a very competitive skeleton material for supercapacitor composite electrodes (Advanced Materials, 2014, 26, 1378-1386. Nano Lett., 2010, 10, 4844. Advanced Materials, 2015, 27, 5943-5949. Advanced Functional Materials, 2018, 28, 1705714). More importantly, N / P co-doping of the graphene tube skeleton can effectively adjust its surface electronic structure, inevitably produce more lone pairs of electrons, and thus induce the formation of strong chemical bonds between the transition metal compound active material and the skeleton. This special chemical bonding can generate a typical internal electric field at their interface, which helps to improve the electron transfer rate and rate characteristics of the interface; at the same time, this strong electrode structure can greatly relieve structural strain, eliminate volume expansion or contraction during the cycle, and ensure the long-term cycle life of the electrode material. In addition, NiCoP, as an important class of transition metal compound electrode materials, is conducive to the storage of charges by Faraday redox reactions because the elements Ni / Co and P are both multivalent. At the same time, compared with similar oxides, they can present metal-like conductivity and have a higher charge transfer rate. Therefore, when nano-NiCoP is bonded to N / P co-doped graphene tubes (N / P-GNTs), it is expected to greatly improve the long-term cycle stability of this composite positive electrode material. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of poor cycle stability of doped graphene@transition metal phosphide composite electrode materials.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] (1) Preparation of N / P-GNTs@NiCoP composites:

[0008] 0.1445 g Ni(NO3)2·6H2O and 0.2990 g Co(NO3)2·6H2O were dissolved in a mixed solution of 15 ml deionized water and 15 ml ethanol and stirred for 30 min to obtain a uniform suspension. Then, N-GNT (1 cm 2 ) graphite substrate; secondly, 1.5 mL of phytic acid (PA) was added dropwise to the mixed solution, followed by vacuum drying at 75 °C for 3 h, and finally calcined at 800-1000 °C in Ar atmosphere for 1 h to obtain N / P-GNTs@NiCoP.

[0009] (2) Electrochemical performance test of N / P-GNTs@NiCoP composites:

[0010] Firstly, a 2M KOH solution was prepared as the electrolyte solution. Then, the N / P-GNTs@NiCoP nanocomposite electrode material, Pt electrode and calomel electrode were used as the working electrode, counter electrode and reference electrode, respectively. The constant current charge and discharge (GCD) of the obtained composite electrode material was tested by an electrochemical workstation to obtain its cycle stability.

[0011] Compared with existing electrode materials, the N / P-GNTs@NiCoP composite electrode material disclosed in the present invention has the following advantages:

[0012] (1) In the present invention, a novel composite electrode material is prepared by bonding NiCoP nanoparticles to N and P co-doped GNTs, and the electrode material exhibits ultra-long cycle stability.

[0013] (2) In the present invention, NiCoP nanoparticles and P-doped N-GNTs are realized in a one-step phosphating process, and the NiCoP nanoparticles are combined with N / P-GNTs through N-Ni / Co and P-Ni / Co chemical bonds. This special interface chemical bond can not only conduct electrons in a timely manner under high current, but also ensure the structural stability of the composite electrode, thereby improving its ultra-long cyclability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0015] Figure 1 SEM and TEM images of N / P-GNTs@NiCoP composites.

[0016] Figure 2 This is the XRD pattern of N / P-GNTs@NiCoP composite material.

[0017] Figure 3N1sXPS spectrum of N / P-GNTs@NiCoP composite material.

[0018] Figure 4 P2pXPS spectrum of N / P-GNTs@NiCoP composite material.

[0019] Figure 5 The cycling stability of N / P-GNTs@NiCoP composite material. DETAILED DESCRIPTION

[0020] Example 1

[0021] Preparation of N-GNTs

[0022] 12.6 g of melamine and 1.4 g of silicon powder mixture were weighed as raw materials, graphite sheets and nickel nitrate were used as substrates and catalysts, and N-doped graphene tubes were prepared on graphite substrates by chemical vapor deposition. The specific steps are as follows: first, nickel nitrate is dripped onto a graphite substrate, soaked in air and dried naturally, and repeated three times; then, a mixture of melamine and silicon powder and a graphite substrate with a catalyst are placed in a graphite reaction chamber, which is then placed in a vacuum furnace, the vacuum furnace cover is sealed, the power supply and the circulating water system are turned on, and then the vacuum system is started, the vacuum is evacuated to 50-80Pa, high-purity argon is introduced into the vacuum furnace to normal pressure and then the vacuum is evacuated again, and the operation is repeated three times; then, the vacuum furnace is heated to 200°C at a heating rate of 10°C / min and kept warm for 10 minutes under the vacuum state; then, high-purity argon is introduced to normal pressure, the vacuum furnace is heated to 1200°C at a heating rate of 10°C / min and kept warm for 30 minutes; finally, the voltage regulator is closed and the vacuum furnace is water-cooled to room temperature.

[0023] Preparation of N / P-GNTs@NiCoP composites

[0024] First, 0.1445 g Ni(NO3)2·6H2O and 0.2990 g Co(NO3)2·6H2O were weighed and dissolved in a mixed solution of 15 ml deionized water and 15 ml ethanol and stirred for 30 min to obtain a uniform suspension. Then, a piece of N-GNT (1 cm 2) on a graphite substrate, and 1.5 mL of phytic acid (PA) was added dropwise, and the mixed solution was then vacuum dried at 75 °C for 3 h; finally, the dried solid mixture was calcined at 800-1000 °C in an Ar atmosphere for 1 h, not only granular NiCoP was obtained, but also P-doped N-GNTs were obtained, and the obtained NiCoP was firmly bonded to the surface of N / P-GNTs through N-Ni / Co bonds and P-Ni / Co bonds (N / P-GNTs@b-NiCoP). At the same time, pure NiCoP was obtained by the same process, and NiCoP was coated on the surface of N / P-GNTs to obtain N / P-GNTs@c-NiCoP. The SEM and TEM images of the N / P-GNTs@NiCoP composite material are shown in Figure 2, respectively. Figure 1 ; The XRD, N1sXPS and P2pXPS characterization results of N / P-GNTs@NiCoP composites are shown in Figure 2 , Figure 3 and Figure 4 .

[0025] Electrochemical performance test of N / P-GNTs@NiCoP composites

[0026] The N / P-GNTs@NiCoP composite electrode material was used as the working electrode, the saturated calomel electrode was used as the reference electrode, and the platinum wire electrode was used as the counter electrode to form a three-electrode system. -1 The cyclic stability was determined in KOH solution. Figure 5 ,from Figure 5 It can be seen that after 75,000 cycles, 90% of the original specific capacitance can still be maintained, which shows that this electrode material has excellent ultra-long cycle stability.

Claims

1. A method for preparing an ultra-long cycle composite supercapacitor positive electrode material N / P-GNTs@NiCoP, characterized in that: Taking N / P-GNTs as the skeleton material, NiCoP nanoparticles were deposited on its surface by a one-step phosphating method to obtain N / P-GNTs@NiCoP composite supercapacitor positive electrode material with interfacial bonding effect, and their interfaces were bonded by N-Ni / Co and P-Ni / Co bonds. Preparation of the N / P-GNTs@NiCoP composite supercapacitor positive electrode material: 0.1445 g Ni(NO3)2·6H2O and 0.2990 g Co(NO3)2·6H2O were dissolved in a mixed solution of 15 ml deionized water and 15 ml ethanol and stirred for 30 min to obtain a uniform suspension. Then, N-GNT (1 cm 2 ) of a graphite substrate; Secondly, 1.5 mL of phytic acid (PA) was added dropwise to the above mixed solution, followed by vacuum drying at 75 °C for 3 h, and finally calcined at 800-1000 °C in Ar atmosphere for 1 h to obtain the N / P-GNTs@NiCoP composite supercapacitor positive electrode material.

2. The preparation method according to claim 1, characterized in that: The N / P-GNTs@NiCoP composite supercapacitor cathode material exhibits ultra-long cycle stability at 50Ag -1 After 75,000 cycles, it can still maintain 90% of the original specific capacitance.

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