Method for preparing aluminum-doped nickel hydroxide through hydrothermal synthesis and application
Aluminum-doped α-phase nickel hydroxide is prepared by hydrothermal synthesis, which solves the problems of doping unevenness and poor stability in the existing technology, and realizes an electrode material with high specific capacity and excellent cycle stability, which is suitable for nickel-iron batteries and nickel hydroxide electrodes.
Patent Information
- Application Number
- CN202511135913.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-14
- Publication Date
- 2025-10-17
AI Technical Summary
The existing preparation methods of aluminum-doped nickel hydroxide have problems such as uneven doping, poor product phase, poor morphology control and poor doping stability, which makes it difficult to meet the needs of high-performance electrode materials.
A hydrothermal synthesis method was adopted, hexamethylenetetramine was used to provide an alkaline environment, and aluminum-doped α-phase nickel hydroxide was prepared using nickel nitrate hexahydrate and aluminum nitrate nonahydrate as raw materials. This solved the problem of uneven local ion distribution caused by the difference in precipitation rates of nickel ions and aluminum ions, and improved the doping uniformity and stability.
The prepared aluminum-doped nickel hydroxide has a nanoflower structure, which has better dispersibility and contact area with the electrolyte, improves the performance of the electrode material, shows high specific capacity and excellent cycle stability, and is suitable for high-capacity, high-performance electrode materials.
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Figure CN120794033A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of battery materials, and relates to a method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis and application thereof. BACKGROUND
[0002] Nickel hydroxide has a wide application prospect in the fields of energy storage and electrode materials such as nickel-hydrogen batteries and nickel-iron batteries. By doping modification, the crystal structure, electrochemical performance and stability of nickel hydroxide can be controlled. Among them, aluminum-doped nickel hydroxide has significant advantages in improving the cycle life and charge-discharge efficiency of electrode materials. However, there are still many problems to be solved in the preparation technology of aluminum-doped nickel hydroxide at present.
[0003] Firstly, in the aspect of doping process, the existing technology generally uses the coprecipitation method to realize the doping of aluminum elements. In actual operation, due to the difference in precipitation rate and reaction activity between nickel ions and aluminum ions, phase separation phenomenon is easily caused. Specifically, in the generated precipitate, part of the area is mainly nickel hydroxide, and the other part is mainly aluminum hydroxide, and the two are difficult to form a uniform mixed system, which not only seriously affects the composition uniformity of the product, but also causes the performance stability of the material to decrease significantly, which cannot meet the application requirements of high-performance scenes.
[0004] Secondly, from the crystal structure of the product, the nickel hydroxide prepared by the coprecipitation method is mostly β phase, and its comprehensive performance in theoretical specific capacity and proton diffusion capacity is not as good as that of α phase nickel hydroxide, which limits the further application of nickel hydroxide in the field of high-capacity and high-performance electrode materials. In the aspect of morphology control of the product, the spherical morphology of the nickel hydroxide produced by coprecipitation as the electrode material of the nickel-iron battery, due to the difficulty in achieving the ideal state of the parameters such as the packing density and porosity of the spherical structure, will cause the insufficient contact area between the electrode material and the electrolyte, the too long ion diffusion path, and then affect the charge-discharge performance and cycle stability of the nickel-iron battery, which cannot meet the use requirements of high-performance nickel-iron batteries.
[0005] In addition, some existing technologies use surface doping to introduce aluminum elements, which can only form an enrichment of aluminum elements on the surface of the nickel hydroxide particles, and cannot realize the uniform distribution of aluminum elements in the whole particle. Surface doping not only causes significant differences in chemical composition and crystal structure between the core region and the surface region of the material, affecting the overall performance consistency of the material, but also in the long-term charge-discharge cycle process, the aluminum elements on the surface are easy to fall off or migrate, causing the performance of the material to decay quickly, which seriously reduces the service life and reliability of the aluminum-doped nickel hydroxide.
[0006] In summary, the existing preparation methods of aluminum-doped nickel hydroxide have obvious defects in doping uniformity, product phase state, morphology control and doping stability, and a new preparation method is needed to overcome the above problems to obtain aluminum-doped nickel hydroxide material with uniform composition, excellent phase state, suitable morphology and stable performance, to meet the urgent needs of high-performance materials in related fields. SUMMARY
[0007] In view of the above deficiencies of the prior art, the purpose of the present application is to provide a method for hydrothermally synthesizing aluminum-doped nickel hydroxide, which provides an alkaline environment by heating hexamethylenetetramine, thereby preparing aluminum-doped alpha-phase nickel hydroxide by hydrothermal synthesis method, solving the problem of local ion distribution imbalance caused by co-precipitation rapid aluminum-doped nickel hydroxide, and improving the doping uniformity of aluminum-doped nickel hydroxide product, improving the product phase state and doping stability.
[0008] Another purpose of the present application is to provide the application of the above preparation method in the preparation of nickel hydroxide electrode and nickel-iron battery.
[0009] In order to achieve the above purpose, the technical solution adopted by the present application is:
[0010] A method for hydrothermally synthesizing aluminum-doped nickel hydroxide, taking hexamethylenetetramine, nickel nitrate, aluminum nitrate and water, and preparing aluminum-doped nickel hydroxide by hydrothermal synthesis method;
[0011] The molar ratio of the hexamethylenetetramine, nickel nitrate and aluminum nitrate is 2:1:0.09-0.13.
[0012] The nickel hydroxide in the aluminum-doped nickel hydroxide is alpha-phase nickel hydroxide.
[0013] The hexamethylenetetramine acts as a catalyst.
[0014] Further, the hexamethylenetetramine can also be replaced by other substances that provide an alkaline environment.
[0015] As a limitation of the present application, the nickel nitrate is hexahydrate nickel nitrate.
[0016] As another limitation of the present application, the aluminum nitrate is nine-hydrate aluminum nitrate.
[0017] As a further limitation of the present application, the following steps are carried out in sequence:
[0018] As a further limitation of the present application, the reactants of the hydrothermal synthesis method are treated by mixing, and the mixing treatment is uniform stirring.
[0019] As a further limitation of the present application, the reaction temperature of the hydrothermal synthesis method is 90-120 DEG C, and the aging time is greater than 10h, wherein the reaction kettle liner with a specification of 50ml-100ml is used to provide the reaction pressure.
[0020] The reaction temperature and the aging time of the hydrothermal synthesis method affect the yield of the reaction product, for example, the yield at 80 DEG C is extremely low, which affects the production preparation efficiency and cost.
[0021] The present application also provides a use of the method for preparing the aluminum-doped nickel hydroxide by the hydrothermal synthesis in preparation of an aluminum-doped nickel hydroxide electrode.
[0022] As a further limitation of the present application, the aluminum-doped nickel hydroxide, acetylene black and polyvinylidene fluoride (PVDF) are taken in a mass ratio of 8:1:1, an organic solvent is added, and then mixed to obtain electrode slurry;
[0023] The electrode slurry is coated on a carbon-based conductive substrate material, dried to obtain an aluminum-doped nickel hydroxide electrode.
[0024] After mixing, the density of the electrode slurry is uniform;
[0025] The acetylene black serves to enhance the conductivity, and the PVDF serves as an adhesive;
[0026] The organic solvent is N-methyl pyrrolidone (NMP).
[0027] Further, the amount ratio of the organic solvent to the polyvinylidene fluoride is 4ml:0.025g.
[0028] As a further limitation of the present application, the carbon-based conductive substrate material is carbon cloth.
[0029] The present application also provides a use of the method for preparing the aluminum-doped nickel hydroxide by the hydrothermal synthesis in preparation of a nickel-iron battery. The aluminum-doped nickel hydroxide electrode is used as an electrode of the nickel-iron battery.
[0030] The main principle of the present application is shown in the following chemical equation:
[0031] (CH2)6N4+6H2O+4H + →6HCHO+4NH4 +
[0032]
[0033] Due to the above technical solutions, the present application has the following technical progress compared with the prior art:
[0034] The preparation method of the aluminum-doped nickel hydroxide of the present application adopts a hydrothermal synthesis method, and solves the problem that, in the preparation process by the coprecipitation method, nickel ions and aluminum ions are difficult to form a uniform mixed system in the generated precipitate due to the difference in precipitation rate and reactivity, thereby affecting the stability of the product performance.
[0035] The preparation method of the aluminum-doped nickel hydroxide of the present application utilizes the thermal decomposition of hexamethylenetetramine to provide an alkaline environment, and uses nickel nitrate hexahydrate and aluminum nitrate nonahydrate as raw materials without introducing other metal ions, thereby improving the purity and yield of the aluminum-doped nickel hydroxide product, and the product stability and purity are both higher compared to improving the specific capacity by doping Co, Fe and other variable valence elements, which is conducive to industrialization.
[0036] The aluminum-doped nickel hydroxide prepared by the present application has a nanoflower size of about 200 nm, and compared to the aluminum-un-doped nickel hydroxide nanoflower with a size of about 6 um, the dispersibility is better, and the contact area with the electrolyte is large, thereby improving the performance as an electrode material. It is detected that the specific capacity of the aluminum-doped nickel hydroxide with 11% doping can reach 184 mAh / g at a current density of 5 A / g, and when the aluminum doping amount is 11%, the electrode material exhibits an excellent specific capacity of 276 mAh / g at a current density of 1 A / g, which is about 100% higher than that of the undoped sample (120 mAh / g), and the capacity remains stable after 100 cycles of charge and discharge at a high current density of 5 A / g.
[0037] The aluminum-doped nickel hydroxide prepared by the present application has an alpha phase structure, has outstanding theoretical specific capacity and proton diffusion capacity, is suitable for the advantages of aluminum-doped nickel hydroxide in the field of high-capacity and high-performance electrode materials, and is proved by XRD test to be lattice doping rather than surface doping, and has a stable structure, which is conducive to maintaining stability and prolonging service life during long-term charge and discharge cycles.
[0038] The present application is suitable for industrial production of nickel hydroxide electrode material and nickel-iron battery. BRIEF DESCRIPTION OF DRAWINGS
[0039] Figure 1 SEM result graph of 0% and 11% aluminum-doped nickel hydroxide in the experimental verification example of the present application;
[0040] Figure 2 TEM detection result graph of aluminum-doped nickel hydroxide in the experimental verification example of the present application;
[0041] Figure 3 EDS test result graph of aluminum-doped nickel hydroxide with different proportions in the experimental verification example of the present application;
[0042] Figure 4 XRD analysis result graph of aluminum-doped nickel hydroxide with different proportions in the experimental verification example of the present application;
[0043] Figure 5 XPS analysis results of different proportions of aluminum-doped nickel hydroxide in the experimental verification example of the present application;
[0044] Figure 6 CV scan results of different proportions of aluminum-doped nickel hydroxide in the experimental verification example of the present application;
[0045] Figure 7 CV scan results of 11% aluminum-doped nickel hydroxide at different scan speeds in the experimental verification example of the present application;
[0046] Figure 8 Discharge curve of different proportions of aluminum-doped nickel hydroxide at a current density of 5 A / g in the experimental verification example of the present application;
[0047] Figure 9 Discharge curve of 11% aluminum-doped nickel hydroxide at different current densities in the experimental verification example of the present application;
[0048] Figure 10 Cycle stability test results of different proportions of aluminum-doped nickel hydroxide at a current density of 5 A / g for 100 cycles in the experimental verification example of the present application;
[0049] Figure 11 Specific capacity value results of different proportions of aluminum-doped nickel hydroxide at a current density of 5 A / g after 100 cycles of charge and discharge in the experimental verification example of the present application;
[0050] Figure 12 Electrochemical impedance spectroscopy test results in the experimental verification example of the present application;
[0051] Figure 13 Magnified image of impedance in the high frequency region in the electrochemical impedance spectroscopy test results in the experimental verification example of the present application. DETAILED DESCRIPTION
[0052] The present application will be further described in detail by specific embodiments and drawings. It should be understood that the described embodiments are only for explaining the present application and do not limit the present application.
[0053] The experimental methods used in the following examples are conventional methods in the art unless otherwise specified.
[0054] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.
[0055] Example 1
[0056] This embodiment is a method for hydrothermally synthesizing aluminum-doped nickel hydroxide, which is specifically as follows:
[0057] According to a molar ratio of 1:2, 1.16 g of nickel nitrate hexahydrate and 1.1215 g of methenamine (urotropine) are weighed, and aluminum nitrate nonahydrate is added so that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 9%, and 40 ml of UP water is additionally taken, the above reaction is added to a polytetrafluoroethylene liner with a specification of 50 mL, a high-pressure reaction kettle is set, the reaction temperature is set to 120°C, and aging is performed for 12 h, the hydrothermal synthesis is ended, the product is washed with distilled water, and drying is performed at 60°C, thereby obtaining 9% aluminum-doped nickel hydroxide.
[0058] Example 2
[0059] The present example is a method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis, and the details are as follows:
[0060] According to a molar ratio of 1:2, 1.16 g of nickel nitrate hexahydrate and 1.1215 g of methenamine (urotropine) are weighed, and aluminum nitrate nonahydrate is added so that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 11%, and 40 ml of UP water is additionally taken, the above reaction is added to a polytetrafluoroethylene liner with a specification of 50 mL, a high-pressure reaction kettle is set, the reaction temperature is set to 120°C, and aging is performed for 12 h, the hydrothermal synthesis is ended, the product is washed with distilled water, and drying is performed at 60°C, thereby obtaining 11% aluminum-doped nickel hydroxide.
[0061] Example 3
[0062] The present example is a method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis, and the details are as follows:
[0063] According to a molar ratio of 1:2, 1.16 g of nickel nitrate hexahydrate and 1.1215 g of methenamine (urotropine) are weighed, and aluminum nitrate nonahydrate is added so that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 13%, and 40 ml of UP water is additionally taken, the above reaction is added to a polytetrafluoroethylene liner with a specification of 50 mL, a high-pressure reaction kettle is set, the reaction temperature is set to 120°C, and aging is performed for 12 h, the hydrothermal synthesis is ended, the product is washed with distilled water, and drying is performed at 60°C, thereby obtaining 13% aluminum-doped nickel hydroxide.
[0064] Comparative Example 1
[0065] The present comparative example is different from Example 1 only in that no nickel nitrate hexahydrate is added, i.e., no aluminum doping is performed, and only nickel hydroxide is prepared, i.e., 0% aluminum-doped nickel hydroxide.
[0066] Comparative Example 2
[0067] The present comparative example is different from Example 1 only in that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 5%, thereby obtaining 5% aluminum-doped nickel hydroxide.
[0068] Comparative Example 3
[0069] The difference between the present comparative example and Example 1 is that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 5%, obtaining 7% aluminum-doped nickel hydroxide.
[0070] Comparative Example 4
[0071] The difference between the present comparative example and Example 1 is that the molar ratio of aluminum nitrate nonahydrate to nickel nitrate hexahydrate is 5%, obtaining 7% aluminum-doped nickel hydroxide.
[0072] Example 4
[0073] The present example is the application of aluminum-doped nickel hydroxide prepared in the above examples or comparative examples in the preparation of nickel hydroxide electrodes, specifically: the prepared aluminum-doped nickel hydroxide is weighed as a precursor together with acetylene black and polyvinylidene fluoride (PVDF) according to a mass ratio of 8:1:1, N-methyl pyrrolidone (NMP) is weighed according to 0.025 g of PVDF per 4 mL of NMP, and the mixture is stirred uniformly to obtain electrode slurry with uniform density.
[0074] 2 mg of the obtained electrode slurry is coated on a 1x1 cm carbon cloth (carbon-based conductive base material), and the coated carbon cloth is dried to obtain aluminum-doped nickel hydroxide electrodes with different proportions.
[0075] The prepared aluminum-doped nickel hydroxide electrodes with different proportions are used to prepare different nickel-iron batteries.
[0076] In some embodiments, carbon paper is used as the carbon-based conductive base material.
[0077] In other embodiments, the reaction temperature of the hydrothermal synthesis method is 90-120°C, the inner liner of the reaction kettle is a polytetrafluoroethylene liner with a specification of 50 mL or 100 mL, and the aging time is greater than a certain value in 10 h, such as 90°C, 110°C or 120°C for the reaction temperature; and 10 h, 13 h or 15 h for the aging time.
[0078] Experimental verification example
[0079] (I) Characterization experiment of aluminum-doped nickel hydroxide with different proportions
[0080] SEM is used to analyze the morphology of 0% and 13% aluminum-doped nickel hydroxide electrode samples, XRD is used for diffraction analysis, TEM detection and EDS testing are performed, and XPS is used to analyze the element content, wherein the SEM results are as follows: Figure 1 , the TEM detection results are as follows: Figure 2 , the EDS test results are as follows: Figure 3 , the XRD analysis results are as follows: Figure 4 , and the XPS analysis results are as follows: Figure 5 .
[0081] (1) SEM results: Figure 1 a Figure 1 c are SEM results of 0% aluminum-doped nickel hydroxide at different magnifications (scale bars are 1 μm, 100 nm, and 50 nm), Figure 1 d Figure 1 f are SEM results of 11% aluminum-doped nickel hydroxide at different magnifications (scale bars are 1 μm, 100 nm, and 50 nm), and it can be seen that the 11% aluminum-doped nickel hydroxide has finer and more rough nanoflower grains, indicating that Al3+ inhibits the growth of grains by replacing Ni2+ and introduces lattice distortion; in Figure 1 d, uniform distribution of grains can be observed without agglomeration; in Figure 1 b of 0% aluminum-doped nickel hydroxide, typical flaky nickel hydroxide nanosheets can be found, Figure 1 a stacking of nanosheets is observed, which will affect the ion transmission efficiency and the contact area with the electrolyte. Therefore, the preparation method of the present application can prepare Al-doped nickel hydroxide with a nanoflower structure, and the aluminum-doped nickel hydroxide prepared has a nanoflower size of about 200 nm, while the nickel hydroxide nanoflower without doping aluminum element has a size of about 6 um.
[0082] (2) TEM detection results: further TEM detection of 11% aluminum-doped nickel hydroxide, results as Figure 2 , Figure 2 a lattice fringes are marked, Figure 2 b is the TEM result corresponding to the diffraction, and the (012) plane diffraction ring is marked.
[0083] (3) EDS test results: to analyze the element composition, 11% aluminum-doped nickel hydroxide was subjected to EDS test, results as Figure 3 , Figure 3 a is the EDS surface total scanning, Figure 3 b corresponds to O element, Figure 3 c corresponds to Ni element, Figure 3 d corresponds to Al element, indicating that aluminum element is successfully doped and there is no other metal element impurity.
[0084] (4) XRD analysis results: Figure 4XRD patterns of Ni(OH)2and Al-Ni(OH)2samples with different Al doping amounts. The XRD patterns of Ni(OH)2and the sample with 7% doping amount are almost the same. The diffraction peaks at 33.5°, 38.7° and 60.0° (JCPDS, No. 38-0715) correspond to the (101), (015) and (110) crystal planes of hexagonal phase α-Ni(OH)2, respectively. For the samples with 11%, 13% and 15% doping amounts, the diffraction peaks at 33.5° and 60.0° shift to higher angles. According to Bragg's law, the lattice of Al-doped Ni(OH)2shrinks. The disappearance of the diffraction peak at 38.7° is due to the disappearance of interlayer water in pure Ni(OH)2. After doping Al, the lattice shrinkage and the elimination of interlayer water occur simultaneously, so the diffraction peak corresponding to the (015) crystal plane also disappears. The XRD results show that Al atoms replace Ni atoms and are successfully doped into the Ni(OH)2lattice.
[0085] (5) XPS analysis results: To further study the chemical valence and element composition of Ni(OH)2and Al-Ni(OH)2, X-ray photoelectron spectroscopy (XPS) analysis was performed. Figure 5 XPS spectra of Ni(OH)2and Al-Ni(OH)2samples. All spectra were charge-corrected with 248.8 eV as the reference. Figure 5 a The results show that no characteristic peak of Al is detected in the spectrum of Ni(OH)2. The peak at 74.5 eV in the Al 2p spectrum is attributed to Al 3+ , and is split into two peaks. Figure 5 b shows that the characteristic peak of O 1s shifts from 531.6 eV to 531.9 eV after Al doping, indicating a decrease in the electron density of O atoms. This shift can be attributed to the substitution of Al 3+ for Ni 2+ : O atoms directly coordinated with Al 3+ experience stronger Coulomb attraction, resulting in a decrease in the electron density of these O atoms and an increase in the O 1s binding energy. Figure 5 c is the Ni 2p fitted spectrum of Ni(OH)2, which contains two spin-orbit doublets (at 856.7 eV and 874.3 eV, with a spin energy separation of 17.6 eV, corresponding to Ni 2p3 / 2 and Ni 2p1 / 2) and two satellite peaks (labeled "sat."). In addition, after the introduction of Al in Ni(OH)2, the peak positions of Ni 2p3 / 2 and Ni 2p1 / 2 shift to 856.5 eV and 874.2 eV, with a spin energy separation of 17.7 eV, indicating that the introduction of Al has a relatively small effect on the electron density around Ni. Therefore, the XPS results show that the introduction of Al changes the electron density around Ni and O, but the bonding environment between nickel and oxygen remains unchanged.
[0086] (ii) Electrode performance test experiment
[0087] The electrode samples of different proportions of aluminum-doped nickel hydroxide prepared in Example 4 were subjected to the following electrode performance tests: electrochemical tests were performed in a three-electrode electrolytic cell at room temperature, a Hg / HgO electrode was selected as the reference electrode, the prepared electrode was used as the working electrode, a platinum sheet electrode was selected as the counter electrode, and the electrode size was 1x1 cm 2 . The electrolyte was a 4 mol / L potassium hydroxide solution. CV tests were performed between 0.0 V and 0.65 V at scan rates of 1 mV / s, 2 mV / s, 5 mV / s, 10 mV / s, and 15 mV / s, respectively. Then, constant current charge and discharge tests were performed, with a constant current charge and discharge starting voltage of 0 V, a terminal voltage of 0.5 V, a static time of 2 s, a current density of 1 A / g, 2 A / g, 4 A / g, 6 A / g, 8 A / g, and 10 A / g. Electrochemical impedance spectroscopy tests were performed at a bias voltage of 0.5 V, a perturbation voltage of 5 mV, and a frequency range of 10 kHz to 0.1 Hz.
[0088] (1) CV test results
[0089] The CV test results of different proportions of aluminum-doped nickel hydroxide electrodes at a scan rate of 10 mV / s are as follows Figure 6 , and the CV test results of 11% aluminum-doped nickel hydroxide electrodes at scan rates of 1, 2, 5, 10, and 15 mV / s are as follows Figure 7 ;
[0090] Figure 6 The CV scan results show that when the doping amount is 0%, the redox peak is between 0.45 V and 0.5 V, the corresponding redox peak current is 0.061 A, and there is only one redox peak, and the corresponding Faraday process is the conversion of nickel hydroxide to hydroxyl nickel oxide. When the doping amount is 5%, the oxidation peak decreases and the high and sharp peak changes to a low and short wide peak. As the doping amount gradually increases, when the doping amount is 7% and 9%, two redox peaks appear, which indicates that the addition of Al element has modified the active material, causing the material to undergo a phase change and affecting the oxidation reaction of the polarization process, causing certain changes in the chemical reaction process. When the doping amount is 11%, the redox peak current is 0.086 A, the corresponding peak voltage is 0.54 V, and the oxidation peak is slightly offset by 0.05 V. As the doping amount continues to increase to 13% and 15%, the oxidation peak slightly decreases and moves backward, and the doping double peak at 15% becomes less obvious than the previous one.
[0091] Figure 7CV images of 11% doping under different scanning speeds are given, and the oxidation peak gradually shifts backward with the increase of scanning speed. It can be observed that when the scanning speed is lower than 10 mV / s, two peaks appear between 0.4 V and 0.5 V in the CV curve, so it can be seen that the introduction of Al element changes the original structure distribution of nickel hydroxide, so that the discharge process begins to be carried out step by step.
[0092] The above results show that, in the process of electrode polarization, OH ions in the electrolyte are adsorbed on the surface of nickel hydroxide, and when the voltage rises to the chemical reaction voltage, the protons on the surface of the material and OH - The Faraday process of the conversion of nickel hydroxide into nickel oxyhydroxide corresponds to the first oxidation peak on the CV curve, and with further polarization of the voltage, the nickel hydroxide inside the active material also joins the reaction, thereby generating a second oxidation peak.
[0093] (2) Constant current charge and discharge test results
[0094] Figure 8 The discharge curve of aluminum-doped nickel hydroxide material with different doping ratios at a current density of 5 A / g is shown in the figure. The results show that the discharge time is 68 s when the doping amount is 0%, and the discharge time decreases when the doping amount is 5% and 7%. The discharge time gradually increases with the increase of the doping amount, and reaches the maximum when the doping amount is 11%, the discharge time is 97 s, which increases the discharge time by 42%. When the doping amount is further increased, the specific capacity begins to decrease.
[0095] Figure 9 The discharge curve of 11% doping under different current densities is shown in the figure. The results show that the maximum discharge time reaches 664 s at a low current density of 1 A / g, and the relative specific capacity is 276 mAh / g.
[0096] Figure 10 The cycle stability test of the material at a current density of 5 A / g for 100 cycles under different doping ratios is shown in the figure. The specific capacity of the 11% sample tends to be constant after the first 10 activation cycles, and the specific capacity does not decrease after 100 cycles. The specific capacity of the 0% doped sample tends to be stable after nearly 30 activation cycles. When the doping amount is 5%, the specific capacity is very low, but it gradually increases with the charging and discharging. When the doping amount is 13% and 15%, the specific capacity of the material reaches a peak after activation, but it gradually decreases with the charging and discharging. It can be seen that when the doping content is high, it has a negative impact on the specific capacity. The 11% doped sample is cycled and discharged for 100 times, and the initial specific capacity is small because the material has not been fully activated. With the increase of discharge times, the specific capacity tends to be stable, and the specific capacity does not change after 100 discharges. The activation to stable times is much lower than 0%, and the specific capacity does not decrease with the charging and discharging, Figure 11The specific capacity value after 100 cycles of charging and discharging, thus it can be seen that the active material with the doping ratio of 11% has higher specific capacity and better cycle stability, and the specific capacity is not reduced after 100 cycles of charging and discharging at a high current density of 5 A / g, and is maintained at 201 mAh / g.
[0097] (3) Test results of electrochemical impedance spectroscopy
[0098] The test results of electrochemical impedance spectroscopy are as follows Figure 12 and Figure 13 wherein, Figure 13 The high-frequency magnified image of impedance. The semicircular response area of all samples in the high-frequency region corresponds to the synergistic effect of charge transfer resistance (Rct) and electric double layer capacitance (Cdl), but no significant difference is shown between the doped samples and the undoped aluminum sample, which indicates that Al 3+ substitutes Ni 2+ The doping behavior of the Al site mainly changes the kinetic path of the electrode reaction, rather than the surface electrochemical process thereof. Among them, the slope of the EIS curve of the 5% Al doped sample is lower than that of the other samples, and the slopes of the EIS curves of the remaining samples gradually increase with the increase of the doping level. When the doping amount is higher than 11%, the EIS curves are almost coincident, indicating that the Al substitution doping of Ni helps to improve the internal diffusion rate of Ni(OH)2, and when the doping concentration is greater than 11%, the improvement of the proton diffusion rate has reached saturation.
[0099] The above results show that the specific capacity of the 11% Al doped nickel hydroxide prepared by the method of the present application can reach 184 mAh / g at a current density of 5 A / g. When the Al doping amount is 11%, the electrode material exhibits excellent specific capacity, which is about 100% higher than that of the undoped sample (120 mAh / g), and the capacity remains stable after 100 cycles of charging and discharging at a high current density of 5 A / g, and the comprehensive performance is outstanding. The alpha phase nickel hydroxide prepared has obvious advantages over the beta phase nickel hydroxide in terms of electrochemical performance and structural stability, and has higher specific capacity and better electrochemical reactivity.
[0100] Therefore, the present application is suitable for preparing Al doped nickel hydroxide, and is suitable for preparing Al doped nickel hydroxide electrode and nickel-iron battery.
[0101] It should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the claims of the present application.
Claims
1. A method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis, characterized in that: Hexamethylenetetramine, nickel nitrate, aluminum nitrate and water are used to prepare aluminum-doped nickel hydroxide through a hydrothermal synthesis method. Wherein, the molar ratio of hexamethylenetetramine, nickel nitrate and aluminum nitrate is 2:1:0.09-0.13; The nickel hydroxide in the aluminum-doped nickel hydroxide is α-phase nickel hydroxide.
2. The method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to claim 1, characterized in that: The nickel nitrate is nickel nitrate hexahydrate.
3. The method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to claim 1, characterized in that: The aluminum nitrate is aluminum nitrate nonahydrate.
4. A method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to any one of claims 1 to 3, characterized in that: The reactants of the hydrothermal synthesis method are mixed uniformly.
5. The method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to claim 4, characterized in that: The reaction temperature of the hydrothermal synthesis method is 90~120℃, and the aging time is greater than 10h.
6. Use of the method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to any one of claims 1 to 5 in preparing aluminum-doped nickel hydroxide electrodes.
7. Application of a method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis in preparing aluminum-doped nickel hydroxide electrodes, characterized in that: The aluminum-doped nickel hydroxide prepared according to any one of claims 1 to 5, acetylene black, and polyvinylidene fluoride are taken in a mass ratio of 8:1:1, an organic solvent is added, and the mixture is mixed to obtain an electrode slurry; The electrode slurry is coated on a carbon-based conductive substrate material and dried to obtain an aluminum-doped nickel hydroxide electrode.
8. The use according to claim 7, characterized in that The organic solvent is N-methylpyrrolidone; and the carbon-based conductive base material is carbon cloth.
9. Use of the method for preparing aluminum-doped nickel hydroxide by hydrothermal synthesis according to any one of claims 1 to 5 in the preparation of nickel-iron batteries.