A preparation method of zinc-air battery composite positive electrode based on 3D printing

Abstract

The present invention discloses a preparation method of a zinc-air battery composite cathode based on 3D printing. Using a mixture of cellulose nanofibers, bacterial cellulose dispersion, and dicyandiamide as a hydrogel ink, it is stacked according to a set model by a 3D printer. The formed three-dimensional hydrogel is freeze-dried and carbonized to obtain a 3D hollow carbon-based three-dimensional framework with ion and electron transport channels. The obtained carbon-based three-dimensional framework is immersed in a Ni(NO3)2 solution to adsorb Ni 2+ , and after freeze-drying, it is placed in a tube furnace together with melamine for heat treatment to grow carbon nanotubes, obtaining a carbon-based three-dimensional framework modified with nickel-based carbon nanotubes. An electroplating solution for depositing Ni is prepared. The obtained carbon-based three-dimensional framework modified with nickel-based carbon nanotubes is fixed with a titanium mesh and forms a three-electrode system with a saturated Hg / HgO electrode and a platinum sheet electrode for electroplating Ni. An electroplating solution for depositing NiCoLDH is prepared. The obtained electrode electroplated with Ni is fixed with a titanium mesh and forms a three-electrode system with a Hg / HgO electrode and a graphite electrode for electroplating NiCoLDH.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and in particular relates to a method for preparing a composite positive electrode of a zinc-air battery. Background Art

[0002] With the rapid development of economy and technology, the shortage of traditional energy such as oil and natural gas has become increasingly prominent, and environmental pollution has become more and more serious. Therefore, the development of clean energy represented by energy storage batteries has become an important goal at present. Although lithium-ion batteries have excellent energy storage performance and are one of the effective ways to solve energy crises and environmental problems, the development of lithium-ion batteries is limited by safety issues such as flammability and poor thermal stability of organic electrolytes. In comparison, zinc-air batteries have a high theoretical energy density (1086Wh kg -1 ), low cost, good safety, environmental friendliness and high stability, and is considered to be an electrochemical energy storage technology with great potential.

[0003] At present, the limiting factors hindering the development of rechargeable zinc-air batteries are mainly the high cost of precious metal catalysts and poor cycle stability in alkaline electrolytes. Therefore, researchers have extensively explored many materials with high electrocatalytic performance, such as non-metallic heteroatom-doped carbon materials, transition metal-based composites, transition metal compounds, and metal-organic frameworks and their derivatives. However, there are few studies on how to concentrate multiple cell reactions on a single electrode, and there are still many challenges. Since the multi-cell reaction in a single electrode places higher requirements on the distribution of active sites, in order to make full use of various active sites and obtain optimization, the constructed electrode needs to have an appropriate spatial structure to improve the electrochemical performance of the electrode. Summary of the invention

[0004] The purpose of the present invention is to propose a method for preparing a composite positive electrode of a zinc-air battery, using 3D printing technology to accurately and controllably construct a suitable 3D structure, reasonably distribute active substances, and obtain a layered composite electrode, which provides a transmission channel for O2 and electrolyte and increases the catalyst loading sites; at the same time, it can well reduce the charging voltage platform, increase the discharge voltage platform, control the reaction ratio of alkaline batteries and zinc-air batteries, and thus optimize the electrochemical performance of the hybrid zinc-air battery.

[0005] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0006] A method for preparing a zinc-air battery composite positive electrode based on 3D printing, comprising the following steps:

[0007] (1) A mixture of cellulose nanofibers, bacterial cellulose dispersion and dicyandiamide is used as hydrogel ink, and stacked according to a set model through a 3D printer. After printing, the formed three-dimensional hydrogel is freeze-dried and carbonized to obtain a 3D hollow carbon-based three-dimensional skeleton with ion and electron transmission channels;

[0008] (2) The obtained carbon-based three-dimensional skeleton was immersed in a Ni(NO3)2 solution to adsorb Ni 2+ , after freeze drying, placed together with melamine in a tube furnace for heat treatment to grow carbon nanotubes, to obtain a carbon-based three-dimensional skeleton modified with nickel-based carbon nanotubes;

[0009] (3) preparing an electroplating solution for depositing Ni, fixing the obtained carbon-based three-dimensional framework modified by nickel-based carbon nanotubes with a titanium mesh, forming a three-electrode system with a saturated Hg / HgO electrode and a platinum sheet electrode, and electro-depositing Ni;

[0010] (4) preparing an electroplating solution for depositing NiCoLDH, fixing the obtained electrode for electrodepositing Ni with a titanium mesh to form a three-electrode system with a Hg / HgO electrode and a graphite electrode, and electrodepositing NiCoLDH.

[0011] According to the above scheme, the composition of the hydrogel ink in step 1 is as follows in parts by weight:

[0012] 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion, and 2 parts of dicyandiamide; the concentration of the bacterial cellulose dispersion is 0.6wt%.

[0013] According to the above scheme, in step 1, the carbonization temperature during the carbonization treatment is 750-850°C, and the heating rate is 4-6°C·min -1 , insulation time 1.5-2.5h, protective gas is N2.

[0014] According to the above scheme, the concentration of the Ni(NO3)2 solution in step 2 is 0.05-0.15M, and the immersion time is 10-20min.

[0015] According to the above scheme, the mass of melamine in step 2 is 2-3g, placed upstream of the air flow, the heat treatment temperature is 850-950℃, and the heating rate is 4-6℃·min -1 , insulation time 2.5-3.5h, protective gas is N2.

[0016] According to the above scheme, the electroplating solution for depositing Ni in step 3 is 0.1M NiSO4, 2M NH4Cl, 2M NaCl solution; the working electrode bias is -6V (relative to the Hg / HgO electrode), and the electroplating time is 100-300s.

[0017] According to the above scheme, the electroplating solution for depositing NiCoLDH in step 4 is 0.05M Ni(NO3)2, 0.05M Co(NO3)2 solution; the current density is 50-100mA cm -2 , the electrodeposition time is 150-600s.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention proposes a method for preparing a micro zinc-air battery composite positive electrode with a three-dimensional structure based on 3D printing technology. Through a set 3D structural model, a hydrogel ink obtained by stirring cellulose nanofibers, bacterial cellulose and dicyandiamide is stacked, freeze-dried and carbonized to obtain a 3D conductive hollow carbon-based skeleton, which provides a transmission channel for O2, ions and electrons and reduces kinetic resistance.

[0020] Ni-carbon nanotubes (Ni-CNTs) were modified on the carbon-based skeleton to increase the specific surface area of ​​the electrode, providing a basis for loading more active materials. Finally, Ni and NiCoLDH were electrodeposited to obtain a multifunctional composite electrode.

[0021] The catalyst loading of the contact part between the zinc-air battery assembled with the composite electrode and the Zn sheet and the electrolyte is adjustable. By adjusting the contact between the electrode and the electrolyte and the air, the reaction ratio of the alkaline battery and the zinc-air battery is controlled, thereby optimizing the electrochemical performance of the zinc-air battery. -2 Under the conditions of current density and charge and discharge time of 5 minutes respectively, it has nearly 2000 stable cycles, with good cycle stability, energy storage performance and energy output efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 : The manufacturing process diagram of the composite electrode of the present invention.

[0023] Figure 2 : SEM image of the electrode obtained when the NiCoLDH deposition time is 150s in Example 1.

[0024] Figure 3 : TEM image of the electrode obtained when the NiCoLDH deposition time is 600s in Example 1 and the corresponding EDS energy spectrum of C, N, O, Ni and Co.

[0025] Figure 4 : XRD diffraction pattern of the electrode obtained when the NiCoLDH deposition time is 450s in Example 1.

[0026] Figure 5: The relationship between voltage and time of a single cycle of the zinc-air battery composed of the electrode and Zn sheet obtained when the NiCoLDH deposition time is 600s in Example 1.

[0027] Figure 6 : Results of a series of stability tests on zinc-air batteries composed of electrodes and Zn sheets obtained when the NiCoLDH deposition time is 300s in Example 1. DETAILED DESCRIPTION

[0028] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0029] The specific implementation method provides a method for preparing a micro three-dimensional zinc-air battery composite positive electrode based on 3D printing:

[0030] (1) A mixture of cellulose nanofibers, bacterial cellulose dispersion and dicyandiamide is used as hydrogel ink, and stacked according to a set model through a 3D printer. After printing, the formed three-dimensional hydrogel is freeze-dried and carbonized to obtain a 3D hollow carbon-based three-dimensional skeleton with ion and electron transmission channels;

[0031] (2) The obtained carbon-based three-dimensional skeleton was immersed in a Ni(NO3)2 solution to adsorb Ni 2+ , after freeze drying, placed together with melamine in a tube furnace for heat treatment to grow carbon nanotubes, to obtain a carbon-based three-dimensional skeleton modified with nickel-based carbon nanotubes;

[0032] (3) preparing a plating solution for depositing Ni, fixing the obtained nickel-based nanotube-modified electrode with a titanium mesh, forming a three-electrode system with a saturated Hg / HgO electrode and a platinum sheet electrode, and electrodepositing Ni;

[0033] (4) preparing an electroplating solution for depositing NiCoLDH, fixing the obtained electrode for electrodepositing Ni with a titanium mesh to form a three-electrode system with a Hg / HgO electrode and a graphite electrode, and electrodepositing NiCoLDH.

[0034] Specifically, the composition of the hydrogel ink in step 1 is as follows by weight: 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion (0.6 wt%), and 2 parts of dicyandiamide. The carbonization temperature during the carbonization treatment is 750-850°C, and the heating rate is 4-6°C min -1 , the holding time is 1.5-2.5h, and the protective gas is N2. Through the set 3D structural model, the hydrogel ink obtained by stirring CNF, BC and dicyandiamide is stacked, freeze-dried and carbonized to obtain a 3D conductive hollow carbon-based skeleton, which provides a transmission channel for O2, ions and electrons and reduces kinetic resistance.

[0035] Specifically, the concentration of the Ni(NO3)2 solution in step 2 is 0.05-0.15M, and the soaking time is 10-20min. The mass of the melamine is 2-3g, and it is placed upstream of the air flow, and the heat treatment temperature is 850-950℃, and the heating rate is 4-6℃min -1 , the holding time is 2.5-3.5h, and the protective gas is N2. The Ni carbon nanotubes (Ni-CNTs) are modified on the carbon-based skeleton to increase the specific surface area of ​​the electrode, providing a basis for loading more active materials.

[0036] Specifically, the electroplating solution for depositing Ni in step 3 is a solution of 0.1M NiSO4, 2M NH4Cl, and 2M NaCl; the working electrode bias voltage is -6V (relative to the Hg / HgO electrode), and the electroplating time is 100-300s.

[0037] Specifically, the electroplating solution for depositing NiCoLDH in step 4 is 0.05M Ni(NO3)2, 0.05M Co(NO3)2 solution; the current density is 50-100mAcm -2 , the electrodeposition time is 150-600s.

[0038] In the specific implementation, the 3D multi-scale hierarchical structure electrode obtained by 3D printing technology has two main characteristics. First, the 3D hollow structure formed by the 3D carbon-based skeleton can provide a transmission channel for ions and oxygen. At the same time, the 3D porous structure increases the specific surface area of ​​the electrode, providing a good foundation for the subsequent loading of active materials. Second, the selected deposited active material itself can not only act as a catalyst to control the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), but also has certain energy storage characteristics. When the electrode and Zn sheet are assembled into a zinc-air battery test, it can be clearly seen that there is a lower charging voltage during charging, a higher alkaline battery voltage platform during discharge, and a lower voltage zinc-air battery voltage platform. By regulating the reaction ratio of alkaline batteries and zinc-air batteries, the electrochemical performance of the hybrid zinc-air battery can be optimized, and the cycle stability and energy output efficiency of the hybrid zinc-air battery can be significantly improved.

[0039] Example 1

[0040] The cellulose nanofiber, bacterial cellulose dispersion and dicyandiamide mixed hydrogel ink were prepared as follows: First, dicyandiamide was added to the BC dispersion and stirred for 30 minutes until it was completely dissolved. Then, CNF was added to the BC / dicyandiamide suspension and stirred several times (Speed ​​Mixer). TMDAC 150.1FVZ) until a highly uniform and translucent hydrogel ink is obtained. The hydrogel ink composition is as follows by weight: 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion (0.6wt%), and 2 parts of dicyandiamide.

[0041] The prepared hydrogel ink was printed by a 3D printer (Cellink TM , BIO-X) according to the set three-dimensional model. After freeze drying, it was heated in a tube furnace with N2 as the protective gas at 5℃min -1 The heating rate was raised to 800°C and kept warm for 2 hours with N2 as the protective gas to obtain a three-dimensional carbon-based skeleton.

[0042] The three-dimensional carbon-based skeleton was immersed in a 0.1M Ni(NO3)2 solution for 15 min, and after freeze-drying, it was heat-treated with melamine in a tubular furnace with N2 as the protective gas. The mass of melamine was 2 g and placed upstream of the tubular furnace. Ni 2+ The three-dimensional carbon-based skeleton is placed downstream. The heat treatment conditions are: heat treatment temperature 900℃, heating rate 5℃min -1 , keeping temperature for 3h, to obtain a carbon-based three-dimensional framework modified with nickel-based carbon nanotubes (C-Ni-CNTs).

[0043] The obtained C-Ni-CNTs were fixed by a titanium mesh and then formed into a three-electrode system with a saturated Hg / HgO electrode and a platinum electrode. By the bubble template method, a -6V bias voltage was applied to the working electrode (relative to the saturated Hg / HgO electrode, using a three-electrode system) in a 0.1M NiSO4, 2M NH4Cl, and 2M NaCl electroplating solution, and electrodeposition was performed for 150s to obtain a C-Ni-CNTs@Ni electrode.

[0044] Loading of NiCoLDH active material: Prepare an aqueous solution of 0.05M Ni(NO3)2 and 0.05M Co(NO3)2, fix the C-Ni-CNTs@Ni electrode through a new titanium mesh, and then form a three-electrode system with a saturated Hg / HgO electrode and a graphite electrode. Constant current electrodeposition of NiCoLDH is carried out in the prepared electroplating solution with an electrodeposition current density of 50-100mA cm -2 The deposition time was controlled to 150, 300, 450 and 600 s to obtain the composite electrode of C-Ni-CNTs@Ni@NiCoLDH.

[0045] Example 2

[0046] The cellulose nanofiber, bacterial cellulose dispersion and dicyandiamide mixed hydrogel ink were prepared as follows: First, dicyandiamide was added to the BC dispersion and stirred for 30 minutes until it was completely dissolved. Then, CNF was added to the BC / dicyandiamide suspension and stirred several times (Speed ​​Mixer). TM DAC 150.1FVZ) until a highly uniform and translucent hydrogel ink is obtained. The hydrogel ink composition is as follows by weight: 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion (0.6wt%), and 2 parts of dicyandiamide.

[0047] The prepared hydrogel ink was printed by a 3D printer (Cellink TM , BIO-X) according to the set three-dimensional model. After freeze drying, it was heated in a tube furnace with N2 as the protective gas at 4℃min -1 The heating rate was raised to 750°C and kept warm for 2 hours with N2 as the protective gas to obtain a three-dimensional carbon-based skeleton.

[0048] The three-dimensional carbon-based skeleton was immersed in a 0.05M Ni(NO3)2 solution for 20 min, and after freeze-drying, it was heat-treated with melamine in a tubular furnace with N2 as the protective gas. The mass of melamine was 3 g and placed upstream of the tubular furnace. Ni 2+ The three-dimensional carbon-based skeleton is placed downstream. The heat treatment conditions are: heat treatment temperature 950℃, heating rate 6℃min -1 , holding time 2.5h, to obtain a carbon-based three-dimensional framework modified with nickel-based carbon nanotubes (C-Ni-CNTs).

[0049] The obtained C-Ni-CNTs were fixed by a titanium mesh and then formed into a three-electrode system with a saturated Hg / HgO electrode and a platinum electrode. By the bubble template method, a -6V bias voltage was applied to the working electrode (relative to the saturated Hg / HgO electrode, using a three-electrode system) in a 0.1M NiSO4, 2M NH4Cl, and 2M NaCl electroplating solution, and electrodeposition was performed for 100s to obtain a C-Ni-CNTs@Ni electrode.

[0050] Loading of NiCoLDH active material: Prepare an aqueous solution of 0.05M Ni(NO3)2 and 0.05M Co(NO3)2, fix the C-Ni-CNTs@Ni electrode through a new titanium mesh, and then form a three-electrode system with a saturated Hg / HgO electrode and a graphite electrode. Constant current electrodeposition of NiCoLDH is carried out in the prepared electroplating solution with an electrodeposition current density of 75mA cm -2, the deposition time is 150s, and the composite electrode of C-Ni-CNTs@Ni@NiCoLDH is obtained. In the test results of the prepared composite electrode in the three-electrode system (the composite electrode is the working electrode, the Pt sheet is the counter electrode, and the Hg / HgO electrode is the reference electrode), the GCD curve shows that the electrode shows almost the same charge / discharge platform at different current densities, where the charging platform is approximately at 0.35-0.45V (vs.Hg / HgO) and the discharge platform is approximately at 0.35-0.25V (vs.Hg / HgO), which corresponds to the oxidation peak of Ni / Co in the CV curve at 0.45-0.5V (vs.Hg / HgO) and the reduction peak at 0.25-0.3V (vs.Hg / HgO). This shows that the operation state of the electrode is stable under different test conditions and has little resistance to the migration of electrons and ions.

[0051] Example 3

[0052] The cellulose nanofiber, bacterial cellulose dispersion and dicyandiamide mixed hydrogel ink were prepared as follows: First, dicyandiamide was added to the BC dispersion and stirred for 30 minutes until it was completely dissolved. Then, CNF was added to the BC / dicyandiamide suspension and stirred several times (Speed ​​Mixer). TM DAC 150.1FVZ) until a highly uniform and translucent hydrogel ink is obtained. The hydrogel ink composition is as follows by weight: 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion (0.6wt%), and 2 parts of dicyandiamide.

[0053] The prepared hydrogel ink was printed by a 3D printer (Cellink TM , BIO-X) according to the set three-dimensional model. After freeze drying, it was heated in a tube furnace with N2 as the protective gas at 6℃min -1 The heating rate was raised to 850°C and kept warm for 2 hours with N2 as the protective gas to obtain a three-dimensional carbon-based skeleton.

[0054] The three-dimensional carbon-based skeleton was immersed in a 0.1M Ni(NO3)2 solution for 10 min, and after freeze-drying, it was heat-treated with melamine in a tubular furnace with N2 as the protective gas. The mass of melamine was 2.5 g and placed upstream of the tubular furnace. Ni 2+ The three-dimensional carbon-based skeleton is placed downstream. The heat treatment conditions are: heat treatment temperature 850℃, heating rate 4℃min -1 , holding time 3.5h, to obtain a carbon-based three-dimensional framework modified with nickel-based carbon nanotubes (C-Ni-CNTs).

[0055] The obtained C-Ni-CNTs were fixed by a titanium mesh and then formed into a three-electrode system with a saturated Hg / HgO electrode and a platinum electrode. By the bubble template method, a -6V bias voltage was applied to the working electrode (relative to the saturated Hg / HgO electrode, using a three-electrode system) in a 0.1M NiSO4, 2M NH4Cl, and 2M NaCl electroplating solution, and electrodeposition was performed for 300s to obtain a C-Ni-CNTs@Ni electrode.

[0056] Loading of NiCoLDH active material: Prepare an aqueous solution of 0.05M Ni(NO3)2 and 0.05M Co(NO3)2, fix the C-Ni-CNTs@Ni electrode through a new titanium mesh, and then form a three-electrode system with a saturated Hg / HgO electrode and a graphite electrode. Constant current electrodeposition of NiCoLDH is carried out in the prepared electroplating solution with an electrodeposition current density of 100mA cm -2 , the deposition time was 300s, and the composite electrode of C-Ni-CNTs@Ni@NiCoLDH was obtained. The prepared composite electrode has a current of 10mA cm -2 The current density was 2.83 mAh cm -2 When the test current density rises to 100 mA cm -2 The capacity retention rate of the electrode is 82.7%, which has good rate performance.

[0057] Figure 1 Figure 2 is a process diagram of the C-Ni-CNTs@Ni@NiCoLDH composite electrode, in which (a) a Ni coating layer is first electrodeposited on the three-dimensional carbon skeleton modified by carbon nanotubes, and then NiCoLDH is electrodeposited; (b) the structural changes of the local deposition of Ni and NiCoLDH on the three-dimensional carbon skeleton modified by carbon nanotubes correspond to each step in (a).

[0058] Figure 2 This is the SEM image of C-Ni-CNTs@Ni@NiCoLDH in Example 1 with a NiCoLDH deposition time of 150 s. From Figure a, it can be seen that the vertical pore width of the electrode is about 400 μm, providing a transmission channel for O2 and the electrolyte. At the same time, it can be observed that the electrode surface presents an uneven morphology; from the local enlarged view of Figure a, Figures bd, it can be speculated that the unevenness is caused by the deposition of Ni and NiCoLDH on Ni-CNTs. From Figure b, it can be seen that Ni-CNTs are grown on the entire electrode, which provides abundant specific surface area for the subsequent loading of NiCoLDH. From Figures c and d, it can be seen that the uniform small particles on the Ni-CNTs are deposited NiCoLDH.

[0059] Figure 3It is a TEM image of C-Ni-CNTs@Ni@NiCoLDH with a NiCoLDH deposition time of 600s in Example 1 and the corresponding EDS energy spectrum of C, N, O, Ni, and Co. The structure of CNTs can be clearly seen in the figure, and multiple CNTs with different lengths and diameters can be seen. This is determined by the size of the Ni salt particles adsorbed on the 3D carbon-based skeleton. The attachment of Ni salt particles of different sizes has given rise to CNTs of different lengths and diameters. The EDS energy spectrum of the C-Ni-CNTs@Ni@NiCoLDH sample was tested. It can be seen from the figure that the distribution of O, N, and C elements shows good consistency, indicating that CNTs have a rich introduction of N elements during growth, which is due to the presence of N in the precursor dicyandiamide vapor. The distribution of Ni and Co elements also shows good consistency, indicating that NiCoLDH is also uniformly deposited on CNTs. CNTs provide a large number of loading sites for NiCoLDH, increasing the specific surface area of ​​the electrode, thereby increasing the loading amount of active materials and making a significant contribution to the ORR and OER of the electrode.

[0060] Figure 4 This is the XRD diffraction pattern of C-Ni-CNTs@Ni@NiCoLDH with a NiCoLDH deposition time of 450s in Example 1. It can be clearly seen from the figure that the peaks related to Ni (located at 44.3°, 51.7° and 76.1°) and the peak related to graphitized carbon (located at 26.6°). In addition to the peaks mentioned above, peaks at 10.2°, 21.4°, 34.4° and 39.4° can also be seen, corresponding to the (0 0 3), (0 0 6), (0 0 9) and (0 1 5) crystal planes of NiCoLDH, respectively, indicating the coexistence of Ni, NiCoLDH and graphite carbon in the composite electrode finally prepared, further confirming that NiCoLDH was successfully deposited on the surface of carbon nanotubes.

[0061] We assembled the composite electrode and Zn sheet into a zinc-air battery in a customized zinc-air battery mold and characterized the full cell performance of the composite electrode. The electrolyte used was 0.2 M zinc acetate and 6 M KOH.

[0062] Figure 5 This is the voltage and time relationship of a single cycle of a zinc-air battery composed of an electrode and a Zn sheet with a NiCoLDH deposition time of 300s in Example 1. It can be seen from the figure that when charging, when the charging voltage platform is around 1.8V, the positive electrode mainly undergoes an alkaline battery reaction: NiCo(OH)4+2OH - →NiCoO2(OH)2+2e - +2H2O, and part of the zinc-air battery reaction: 4OH - →O2+4e -+2H2O, the reaction at the negative electrode is: Zn 2+ +2e - →Zn; During discharge, when the voltage is around 1.5V, the positive electrode first undergoes an alkaline battery reaction: NiCoO2(OH)2+2e-+2H2O→NiCo(OH)4+2OH-, then the voltage begins to drop, and the ORR reaction, i.e., the positive electrode reaction of the air battery, begins: O2+4e-+2H2O→4OH-, and the negative electrode reacts as: Zn→Zn 2+ +2e-, stable when the voltage reaches about 1.1 V. The present invention can optimize the performance of the air battery by regulating the proportion of the two discharge reactions, thereby improving the capacity and energy output efficiency of the battery.

[0063] Figure 6 These are the results of a series of stability tests on the zinc-air battery composed of the electrode with a NiCoLDH deposition time of 300 s and a Zn sheet in Example 1. Figure 6 (a) is 20 mA cm -2 Current density long cycle stability test results, Figure 6 (b) is the comparison of the charge and discharge curves of the system at the 1st, 200th, 400th, 600th, 800th, 1000th, 1200th, 1600th, 1800th, and 2000th cycles. Figure 6(c) is a graph showing the energy efficiency of the system as a function of the number of cycles. For the charging process, the charging voltage shows a slight decrease from the 1st cycle to the 200th cycle. This is because the electrode active material is activated during the cycle, which slightly increases the activity of OER and leads to a decrease in the charging voltage. After the 200th cycle, the charging voltage begins to increase gradually. This is because the active material is partially pulverized or even falls off, and the activity of OER decreases, leading to an increase in the charging voltage. For the discharge process, from the 1st to the 200th cycle, the alkaline battery gradually decays and the capacity contribution ratio gradually decreases. This may be due to the local consumption of electrolyte in the OER process, which makes the electrode material unable to fully contact with the electrolyte; from the 200th to the 600th cycle, the capacity corresponding to the alkaline battery reaction gradually increases, and its reaction ratio also gradually increases, which is mainly due to the gradual penetration of the electrolyte and the activation of the material; by the 600th cycle, the alkaline battery reaction ratio is close to the upper limit, and by the 800-1800th cycle, the platform of the alkaline battery reaction gradually decreases until it disappears, which marks the complete degradation and shedding of the NiCoLDH material. After 1800 to 2000 cycles, the charge / discharge voltage begins to change greatly, indicating that the structure of the electrode has begun to be gradually destroyed at this time, and the activity of the catalyst has gradually lost, making the reaction of the zinc-air battery gradually ineffective. The zinc-air battery composed of the composite electrode and the Zn sheet has a stable cycle of nearly 2000 cycles, indicating that the micro three-dimensional zinc-air battery composite positive electrode prepared by the present invention has good cycle stability and energy output efficiency.

Claims

1. A method for preparing a zinc-air battery composite positive electrode based on 3D printing, characterized in that The following steps are involved: (1) A mixture of cellulose nanofibers, bacterial cellulose dispersion and dicyandiamide is used as hydrogel ink, and stacked according to a set model through a 3D printer. After printing, the formed three-dimensional hydrogel is freeze-dried and carbonized to obtain a 3D hollow carbon-based three-dimensional skeleton with ion and electron transmission channels; (2) The obtained carbon-based three-dimensional framework was immersed in a Ni(NO3)2 solution to adsorb Ni 2+ , after freeze drying, placed together with melamine in a tube furnace for heat treatment to grow carbon nanotubes, to obtain a carbon-based three-dimensional skeleton modified with nickel-based carbon nanotubes; (3) preparing an electroplating solution for depositing Ni, fixing the obtained carbon-based three-dimensional framework modified by nickel-based carbon nanotubes with a titanium mesh, forming a three-electrode system with a saturated Hg / HgO electrode and a platinum sheet electrode, and electro-depositing Ni; (4) preparing an electroplating solution for depositing NiCoLDH, fixing the obtained electrode for electrodepositing Ni with a titanium mesh to form a three-electrode system with a Hg / HgO electrode and a graphite electrode, and electrodepositing NiCoLDH.

2. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that The composition of the hydrogel ink described in step 1 is as follows in parts by weight: 5 parts of cellulose nanofibers, 93 parts of bacterial cellulose dispersion, and 2 parts of dicyandiamide; the concentration of the bacterial cellulose dispersion is 0.6wt%.

3. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that Step 1: During the carbonization process, the carbonization temperature is 750-850°C and the heating rate is 4-6°C·min -1 , insulation time 1.5-2.5h, protective gas is N2.

4. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that The concentration of the Ni(NO3)2 solution in step 2 is 0.05-0.15M, and the immersion time is 10-20min.

5. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that The mass of the melamine in step 2 is 2-3g, which is placed upstream of the air flow, and the heat treatment temperature is 850-950℃, and the heating rate is 4-6℃·min -1 , insulation time 2.5-3.5h, protective gas is N2.

6. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that The electroplating solution for depositing Ni in step 3 is a solution of 0.1M NiSO4, 2M NH4Cl, and 2M NaCl; the working electrode bias voltage is -6V (relative to the Hg / HgO electrode), and the electroplating time is 100-300s.

7. The method for preparing a zinc-air battery composite positive electrode based on 3D printing as claimed in claim 1, characterized in that The electroplating solution for depositing NiCoLDH in step 4 is 0.05M Ni(NO3)2, 0.05M Co(NO3)2 solution; the current density is 50-100mA cm -2 , the electrodeposition time is 150-600s.

Images