A high-performance flexible nickel-iron battery and a preparation method thereof

Abstract

The application is suitable for the technical field of electrochemical energy storage devices, and provides a high-performance flexible nickel-iron battery and a preparation method thereof, which comprises a fluorine-doped nickel hydroxide positive electrode based on a flexible conductive substrate, an iron-based material negative electrode based on a flexible conductive substrate, and a gel electrolyte; fluorine-doped nickel hydroxide is used as the positive electrode active material, and through controllable fluorine ion doping, the electronic conductivity and structural stability of the nickel hydroxide are significantly improved while the structure of the nickel hydroxide is maintained; the positive electrode and the negative electrode are both loaded on a flexible conductive substrate; and the PVA-KOH gel electrolyte is combined, and through a freeze-thaw solidification process, the electrode and the electrolyte are integrated in a flexible manner. The battery prepared by the application has high energy density, excellent rate performance and cycle stability, and has good electrochemical performance retention under bending, folding and other deformations, and can be applied to the fields of wearable electronic devices and the like.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage device technology, and particularly relates to a high-performance flexible nickel-iron battery and its preparation method. Background Technology

[0002] With the rapid development of wearable devices, flexible display technology, electronic skin, and implantable medical devices, revolutionary requirements have been placed on the matching energy storage systems: not only are high energy density and power density required, but also good mechanical flexibility, safety, and cycle stability.

[0003] Among many energy storage systems, nickel-iron batteries have attracted much attention due to their unique advantages: they use water-based electrolytes, which fundamentally eliminates the risk of combustion and explosion of traditional lithium-ion batteries; raw materials are abundant and inexpensive; they are environmentally friendly and free from heavy metal pollution. However, the industrial application of traditional nickel-iron batteries still faces three major technical bottlenecks: (1) inherent defects of cathode materials: nickel hydroxide, as the active material of the cathode, has poor intrinsic electronic conductivity and unstable structure, which leads to severe polarization of the battery during high-rate charging and discharging and severe capacity decay during long-cycle operation; (2) insufficient mechanical flexibility: traditional nickel-iron batteries use metal current collectors (such as foamed nickel) and liquid electrolytes, and the electrode structure is rigid and cannot withstand bending deformation; liquid electrolytes have leakage risks and are incompatible with flexible application scenarios; (3) poor interface stability: side reactions at the solid-liquid interface can lead to dissolution of active materials and passivation of electrodes, especially under high current density and deep charge and discharge conditions, the battery life is significantly shortened.

[0004] Existing modification strategies mainly focus on carbon material composites and cation doping, but these have significant limitations: carbon materials reduce volumetric energy density; cation doping easily causes lattice distortion, which weakens structural stability. Fluoride ion doping, as an emerging modification strategy, shows great potential due to its unique physicochemical properties: fluoride ions have a similar radius to hydroxide ions, enabling in-situ substitution within the lattice; its high electronegativity effectively modulates the electronic structure and improves conductivity. However, research on the application of fluoride-doped nickel hydroxide in high-performance flexible batteries is relatively limited, and its synergistic integration effect with flexible electrode structures and gel electrolytes warrants further development.

[0005] Therefore, developing a flexible nickel-iron battery based on a high-performance fluorine-doped nickel hydroxide cathode and an iron-based anode is of great significance for promoting the development of flexible energy storage technology. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance flexible nickel-iron battery, which aims to solve the problems mentioned in the background art.

[0007] The present invention is implemented as follows: a high-performance flexible nickel-iron battery includes a fluorine-doped nickel hydroxide positive electrode based on a flexible conductive substrate, an iron-based material negative electrode based on a flexible conductive substrate, and a gel electrolyte.

[0008] The method for preparing the fluorine-doped nickel hydroxide cathode based on a flexible conductive substrate includes the following steps:

[0009] (1) Preparation of fluorine-doped nickel hydroxide material: nickel salt, ammonium fluoride and urea are dissolved in water, and after one-step hydrothermal reaction, washing and drying, fluorine-doped nickel hydroxide material is obtained. The morphology of the fluorine-doped nickel hydroxide material is nanosheet or nanoflower.

[0010] (2) Preparation of fluorine-doped nickel hydroxide cathode: Fluorine-doped nickel hydroxide material, conductive agent and binder are mixed to form a slurry, which is coated on a flexible conductive substrate. After drying and electrochemical treatment, a fluorine-doped nickel hydroxide cathode based on a flexible conductive substrate is obtained.

[0011] The method for preparing the iron-based negative electrode based on a flexible conductive substrate includes the following steps:

[0012] (1) Preparation of iron-based negative electrode: Iron-based active material, conductive agent and binder are mixed to form a slurry, which is coated on a flexible conductive substrate. After drying and electrochemical treatment, an iron-based negative electrode based on a flexible conductive substrate is obtained.

[0013] Another objective of this invention is to provide a method for preparing a high-performance flexible nickel-iron battery, comprising the following steps:

[0014] (1) Preparation of fluorine-doped nickel hydroxide cathode based on flexible conductive substrate;

[0015] (2) Fabrication of iron-based negative electrodes based on flexible conductive substrates;

[0016] (3) Preparation of gel electrolyte;

[0017] (4) Battery assembly: The positive electrode of fluorine-doped nickel hydroxide based on a flexible conductive substrate and the negative electrode of iron-based material based on a flexible conductive substrate are respectively immersed in gel electrolyte to ensure that the positive electrode sheet, the negative electrode sheet and the gel electrolyte are in full contact. One end of the electrode sheet is left uncontacted with the gel electrolyte. The positive electrode sheet and the negative electrode sheet immersed in gel electrolyte are attached together and frozen at -20℃ for 12~20 hours. They are then thawed at room temperature for 3~8 hours to solidify the gel electrolyte and obtain a high-performance flexible nickel-iron battery.

[0018] The high-performance flexible nickel-iron battery provided in this embodiment of the invention has the following advantages:

[0019] 1. Excellent cathode material performance: Fluorine-doped nickel hydroxide prepared by adjusting the ratio of fluorine ions to nickel ions effectively improves the intrinsic conductivity and crystal structure stability of the material. When used as a cathode, it enables the battery to exhibit high specific capacity and excellent rate performance.

[0020] 2. High battery flexibility and integration: The battery adopts a flexible substrate and PVA-KOH gel electrolyte, and achieves tight integration of electrodes and electrolyte through freeze-thaw process. The entire battery structure is flexible and the components have good contact when bent or folded, resulting in stable electrochemical performance.

[0021] 3. Good safety and long cycle life: Fluorine doping enhances the structural stability of the electrode, and the gel electrolyte eliminates the risk of leakage and combustion, giving the battery excellent long cycle performance.

[0022] 4. Simple and environmentally friendly preparation process: The entire preparation process does not require complex equipment or harsh conditions, is simple to operate, has good repeatability, and is suitable for large-scale preparation. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope image of the fluorine-doped nickel hydroxide material prepared in Example 1 of the present invention;

[0024] Figure 2 The elemental distribution diagram of the fluorine-doped nickel hydroxide material prepared in Example 1 of this invention is shown below.

[0025] Figure 3 The X-ray diffraction patterns of the samples prepared in Example 1 and Comparative Example 1 of this invention are compared.

[0026] Figure 4 The graphs show the rate performance of the flexible nickel-iron batteries assembled in Example 1 and Comparative Example 1 of this invention at different current densities.

[0027] Figure 5 The flexible nickel-iron battery assembled for Example 1 and Comparative Example 1 of this invention operates at 6 mA / cm². 2 Long-cycle performance at current density;

[0028] Figure 6 Cyclic volt-ampere curves of the flexible nickel-iron battery assembled in Embodiment 1 of the present invention under flat, bent and twisted states. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0031] Example 1: A high-performance flexible nickel-iron battery, the preparation method of which includes the following steps:

[0032] (1) Preparation of fluorine-doped nickel hydroxide materials:

[0033] Dissolve 2.91g of nickel nitrate hexahydrate, 0.37g of ammonium fluoride and 3.60g of urea in 40mL of deionized water. At this time, the ratio of fluoride ions to nickel ions is 0.5:1.

[0034] The above solution was stirred at 90°C for 12 hours. After the reaction was completed, it was naturally cooled, filtered, and washed three times each with deionized water and ethanol.

[0035] The obtained product was dried in a vacuum oven at 70°C for 10 hours and then ground to obtain the final product.

[0036] The prepared material was analyzed, and its morphology was obtained as follows: Figure 1 As shown, it can be seen that it is a uniform nanosheet; the elemental distribution results are as follows. Figure 2 As shown, the F element is uniformly distributed.

[0037] (2) Preparation of the positive electrode:

[0038] The fluorine-doped nickel hydroxide material, super P and PVDF binder prepared above were mixed at a mass ratio of 8:1:1, an appropriate amount of NMP solvent was added, and the mixture was magnetically stirred for 6 hours to obtain a uniform slurry.

[0039] The above uniform slurry was coated onto a 2 cm × 3 cm carbon cloth and dried at 80°C for 12 hours to obtain a positive electrode sheet with an active material loading of 1 mg / cm³. 2 ;

[0040] Using the dried positive electrode as the working electrode, the positive electrode was electrochemically activated in a 1 mol / L potassium hydroxide solution with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode by cyclic voltammetry scanning 10 times within a voltage range of 0 to 0.6 V.

[0041] (3) Preparation of negative electrode:

[0042] Commercial FeOOH powder, super P and PTFE binder were mixed in a mass ratio of 7:2:1, and a small amount of ethanol was added and stirred into a slurry.

[0043] The above slurry was coated onto another piece of carbon cloth and dried at 60°C to obtain a negative electrode sheet, wherein the active material loading was 2 mg / cm³. 2 ;

[0044] Referring to step (2), the obtained negative electrode sheet was electrochemically activated in a 2 mol / L potassium hydroxide solution using cyclic voltammetry.

[0045] (4) Battery assembly and gel curing:

[0046] Preparation of PVA-KOH gel: Weigh 1 g PVA and 2.8 g KOH and add them to 9 g deionized water. Stir at 90°C for 3 hours until completely dissolved to obtain a gel solution with a PVA mass fraction of 10% and a KOH concentration of about 5 mol / L.

[0047] Immerse the positive electrode prepared in step (2) and the negative electrode prepared in step (3) in the gel solution for ten minutes to allow them to be fully wetted;

[0048] Remove the electrodes, place the positive and negative active surfaces together, and freeze them in a -20°C freezer for 16 hours.

[0049] After removal, thaw at room temperature for 5 hours until the gel is completely solidified to obtain a flexible nickel-iron battery.

[0050] Example 2: Compared with Example 1, the only difference is that the amount of ammonium fluoride in step (1) is adjusted to 0.148g, while other conditions remain unchanged. At this time, the ratio of fluoride ions to nickel ions is 0.4:1. The cathode material is prepared and the battery is assembled under these conditions.

[0051] Example 3: Compared with Example 1, the only difference is that the amount of ammonium fluoride in step (1) is adjusted to 0.74 g, while other conditions remain unchanged. At this time, the ratio of fluoride ions to nickel ions is 2:1. The cathode material is prepared and the battery is assembled under these conditions.

[0052] Comparative Example 1: Compared with Example 1, except that ammonium fluoride was not added in step (1), all other steps were the same as in Example 1, and a fluorine-free nickel hydroxide cathode and the corresponding full cell were prepared.

[0053] Materials characterization and electrochemical performance testing:

[0054] 1. Structural Characterization: The fluorine-doped nickel hydroxide material prepared in Example 1 and the undoped nickel hydroxide material prepared in Comparative Example 1 were analyzed, and the X-ray diffraction patterns were obtained as follows: Figure 3 As shown, the XRD pattern of the sample in Example 1 is consistent with that of the sample in Comparative Example 1.

[0055] 2. Full battery performance test:

[0056] The rate performance of the batteries prepared in Example 1 and Comparative Example 1 was compared, and the results are as follows: Figure 4As shown, it can be seen that the battery of Example 1 performs well at 3, 6, 9, and 12 mA / cm². 2 The discharge specific capacities at the current densities were 0.221, 0.158, 0.124, and 0.112 mA / cm², respectively. 2 When the current density recovers to 3 mA / cm 2 At that time, the capacity recovered to 0.212 mA / cm². 2 The battery in Comparative Example 1 exhibits good rate performance; however, the capacity of the battery in Comparative Example 1 is lower than that in Example 1 at all current densities.

[0057] The batteries prepared in Example 1 and Comparative Example 1 were tested at 6 mA / cm². 2 Charge-discharge cycle tests were conducted at current density, and cycle performance was compared. The results are as follows: Figure 5 As shown, the battery of Example 1 retained 87.6% of its capacity after 200 cycles, demonstrating excellent long-cycle stability; the battery of Comparative Example 1, under the same conditions, retained only 75.4% of its capacity.

[0058] The batteries prepared in Examples 2 and 3 were subjected to rate performance and cycle performance tests, respectively. The battery in Example 2 achieved a rate performance of 3 mA / cm². 2 The discharge specific capacity at the given current density is 0.184 mAh / cm³. 2 After 200 cycles, the capacity retention rate was 81.3%, slightly inferior to Example 1; the battery in Example 3 maintained a capacity retention rate of 3 mA / cm². 2 The discharge specific capacity at the given current density is 0.161 mAh / cm³. 2 (Excessive fluoride content leads to capacity reduction), and the capacity retention rate was 70.8% after 200 cycles;

[0059] Cyclic voltammetry tests were conducted on the battery prepared in Example 1 under flat, bent, and torsional conditions, and the results are as follows. Figure 6 As shown, the curves in the three states almost overlap, demonstrating its excellent mechanical flexibility and interface stability.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance flexible nickel-iron battery, characterized in that, include: Fluorine-doped nickel hydroxide cathode based on flexible conductive substrate, iron-based material anode based on flexible conductive substrate, and gel electrolyte; The method for preparing the fluorine-doped nickel hydroxide cathode based on a flexible conductive substrate includes the following steps: (1) Preparation of fluorine-doped nickel hydroxide material: nickel salt, ammonium fluoride and urea are dissolved in water, and after one-step hydrothermal reaction, washing and drying, fluorine-doped nickel hydroxide material is obtained. The morphology of the fluorine-doped nickel hydroxide material is nanosheet or nanoflower. (2) Preparation of fluorine-doped nickel hydroxide cathode: Fluorine-doped nickel hydroxide material, conductive agent and binder are mixed to form a slurry, which is coated on a flexible conductive substrate. After drying and electrochemical treatment, a fluorine-doped nickel hydroxide cathode based on a flexible conductive substrate is obtained. The method for preparing the iron-based negative electrode based on a flexible conductive substrate includes the following steps: (1) Preparation of iron-based negative electrode: Iron-based active material, conductive agent and binder are mixed to form a slurry, which is coated on a flexible conductive substrate. After drying and electrochemical treatment, an iron-based negative electrode based on a flexible conductive substrate is obtained.

2. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, In the step of preparing fluorine-doped nickel hydroxide material, the nickel salt is at least one selected from nickel nitrate, nickel chloride, and nickel sulfate; The molar ratio of fluoride ions to nickel ions in the nickel salt and ammonium fluoride is (0.2~0.8):1; The hydrothermal reaction is carried out at a temperature of 80~150℃ for 8~24 hours.

3. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, In the step of preparing fluorine-doped nickel hydroxide cathode, the mass ratio of the fluorine-doped nickel hydroxide material, the conductive agent and the binder is (70~85):(10~20):(5~10).

4. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, In the step of preparing the iron-based negative electrode, the iron-based active material is at least one of iron powder, ferrous oxide, iron(II,III) oxide, and iron(III) hydroxyl oxide.

5. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, In the step of preparing the iron-based negative electrode, the mass ratio of the iron-based active material, conductive agent and binder is (70~85):(10~20):(5~10).

6. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, In the steps of preparing the iron-based negative electrode, the electrochemical treatment in the steps of preparing the fluorine-doped nickel hydroxide positive electrode and the steps of preparing the iron-based negative electrode is to carry out electrochemical activation in a potassium hydroxide solution with a concentration of 1~6 mol / L, and the electrochemical activation adopts cyclic voltammetry.

7. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, The flexible conductive substrate is one of carbon cloth, graphene film, nickel mesh, copper mesh, or conductive polymer film.

8. The high-performance flexible nickel-iron battery according to claim 1, characterized in that, The gel electrolyte is a PVA-KOH gel, and its preparation method includes the following steps: Polyvinyl alcohol and potassium hydroxide were added to deionized water and stirred at 80-95℃ to dissolve them, resulting in a homogeneous PVA-KOH gel solution, wherein the mass fraction of PVA was 5-15% and the concentration of KOH was 1-8 mol / L.

9. A method for preparing a high-performance flexible nickel-iron battery as described in any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Preparation of fluorine-doped nickel hydroxide cathode based on flexible conductive substrate; (2) Preparation of iron-based negative electrode material based on flexible conductive substrate; (3) Preparation of gel electrolyte; (4) Battery assembly: The positive electrode of fluorine-doped nickel hydroxide based on a flexible conductive substrate and the negative electrode of iron-based material based on a flexible conductive substrate are respectively immersed in gel electrolyte to ensure that the positive electrode sheet, the negative electrode sheet and the gel electrolyte are in full contact. One end of the electrode sheet is left uncontacted with the gel electrolyte. The positive electrode sheet and the negative electrode sheet immersed in gel electrolyte are attached together and frozen at -20℃ for 12~20 hours. They are then thawed at room temperature for 3~8 hours to solidify the gel electrolyte and obtain a high-performance flexible nickel-iron battery.

Images