Preparation method of binder-free electrode suitable for low-temperature battery

Abstract

The invention discloses a preparation method of a binder-free electrode suitable for a low-temperature battery, the electrode is a NiO C / Ni composite film, and the preparation process comprises the following steps: dissolving a nickel salt, an amide compound and villiaumite in deionized water, uniformly mixing, and then placing in a reaction kettle; placing foamed nickel in the mixed solution, performing hydrothermal reaction in a constant-temperature box, then taking out the foamed nickel, and cleaning to obtain a precursor; putting the precursor into a Tris solution containing dopamine, and soaking at a constant temperature to obtain an intermediate product; and placing the intermediate product in an inert atmosphere tube furnace, and calcining to obtain the NiO-coated C / Ni composite film. The composite film can be directly used as a battery electrode, use of a binder is avoided, the problem of electrode failure caused by binder embrittlement at low temperature can be effectively solved, and the composite film has excellent performance in low-temperature nickel-iron battery application; in addition, the preparation process is simple, a complex blade coating film preparation process is avoided, and large-scale application and popularization are easy.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology and relates to a method for preparing a binderless electrode suitable for low-temperature batteries. Background Technology

[0002] To meet the rapid development of aerospace, deep-sea submersible, and polar scientific research, and to ensure the convenient life of military and civilian personnel in plateau areas, it is crucial to develop stable and efficient low-temperature battery systems. In recent years, with the continuous development of battery system design and related theories, the low-temperature performance of batteries has been significantly improved, with both low-temperature specific capacity and cycle life increasing. The freezing of the electrolyte and the decrease in ionic conductivity at low temperatures are the main reasons for the decline in the low-temperature performance of low-temperature batteries. A large number of studies have successfully achieved high-performance low-temperature batteries by regulating the electrolyte. Specific regulation strategies include: (1) introducing suitable salt additives; (2) introducing organic co-solvents; and (3) configuring quasi-solid-state gel electrolytes. The above strategies utilize the interaction between the introduced anions and cations, co-solvents, or polar molecules on the polymer chains and water molecules to disrupt their ordered hydrogen bond structure, lower their freezing point, and improve their conductivity, thereby improving the low-temperature performance of the battery.

[0003] However, the reasons for battery performance degradation at low temperatures are multifaceted. Besides the electrolyte system, the electrochemical performance of the electrodes at low temperatures is also crucial. For electrodes, the slowed ion diffusion rate at low temperatures is a significant cause of battery performance degradation. Conventional battery active materials are powder materials, requiring binders and coating processes to prepare electrodes. Binders are a crucial component of electrodes, mostly polymeric compounds, functioning to adhere the active materials to the conductive current collector. Their performance directly affects the battery's specific capacity, lifespan, and safety. In low-temperature environments, the performance of binders drops sharply or even fails, severely impacting the electrode's ion diffusion rate. For example, polyvinylidene fluoride (PVDF) is a commonly used battery binder. When the temperature drops to 0 °C, its viscosity and mechanical properties weaken. When the temperature drops to its glass transition temperature of -43 °C, PVDF becomes completely embrittled, causing the electrode to collapse and fail completely. Therefore, the low-temperature limit for normal operation of batteries using this type of binder is ~ -20 °C. Styrene-butadiene rubber / carboxymethyl cellulose (SBR / CMC) is also a commonly used binder, but its glass transition temperature is only ~ -5 ℃. In environments of ~ -10 ℃, its electrodes and cells completely fail. Therefore, how to avoid battery failure caused by the low-temperature performance degradation of binders is crucial for the research, development, and application of low-temperature batteries. Summary of the Invention

[0004] Therefore, the purpose of this invention is to develop a method for preparing a binder-free electrode suitable for low-temperature batteries. This electrode is a NiO@C / Ni composite electrode, wherein the active material NiO@C is uniformly grown on a foamed Ni conductive substrate, completely avoiding the use of binders and complex coating processes. This electrode can be directly used as the positive electrode of nickel-iron batteries, exhibiting excellent low-temperature electrochemical performance, achieving high specific capacity and long cycle life in a -45 °C environment. Furthermore, this electrode has low production costs, a simple preparation process, and is suitable for mass production.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing a binder-free electrode suitable for low-temperature batteries, the specific preparation process of which includes the following steps: (1) Dissolve the nickel salt, amide compound, and fluoride salt in deionized water, stir to mix them evenly, and then transfer the mixed solution into the polytetrafluoroethylene liner of the reactor. (2) Place the nickel foam in the mixed solution and carry out the hydrothermal reaction in a constant temperature electric heating oven. After a certain period of time, cool it naturally, take out the nickel foam, wash it, and obtain the precursor. (3) The precursor was placed in a Tris solution containing dopamine, and then placed in an electric heating oven and soaked at a constant temperature for a certain period of time to obtain the intermediate product; (4) The intermediate product is placed in a tube furnace with inert gas and calcined to obtain NiO@C / Ni composite material.

[0006] In some embodiments of the present invention, in step (1), the nickel salt is one of nickel formate dihydrate, nickel acetate tetrahydrate, nickel oxalate tetrahydrate, nickel carbonate, and nickel sulfate; the amide compound is one of urea, formamide, and acetamide; and the fluoride salt is one of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0007] In some embodiments of the present invention, in step (1), the molar ratio of nickel salt, amide compound and fluoride salt in the mixed solution is 1:3:1 to 1:10:3.

[0008] In some embodiments of the present invention, in step (2), the temperature of the hydrothermal reaction is 60~200 ℃ and the reaction time is 1~10 hours.

[0009] In some embodiments of the present invention, in step (2), the cleaning method is rinsing with deionized water or anhydrous ethanol.

[0010] In some embodiments of the present invention, in step (3), the dopamine content in the Tris solution is 0.1 to 10 g / L.

[0011] In some embodiments of the present invention, in step (3), the temperature of constant temperature soaking is 40~100 ℃ and the time is 3~10 hours.

[0012] In some embodiments of the present invention, in step (4), the inert gas is either high-purity argon or nitrogen, the calcination temperature is 300~700 ℃, and the calcination time is 1~5 hours.

[0013] The NiO@C / Ni composite film prepared by the above synthesis method can be directly used as a positive electrode material in nickel-iron batteries. Compared with the prior art, the advantages of this invention are: (1) Compared with NiO@C powder electrodes prepared by traditional blade coating technology, the nickel-iron battery assembled by this NiO@C / Ni composite electrode has excellent low-temperature electrochemical performance, with a specific capacity of 0.1 mAh / cm³ in an environment of -45 ℃. 2 It can be stably charged and discharged for 500 cycles, and its performance parameters such as reaction kinetics, specific capacity and cycle life far exceed those of conventional powder electrodes.

[0014] (2) The active material of the electrode is grown directly on the conductive substrate, avoiding the use of binders and eliminating the complex powder coating process. The electrode has low production cost, simple preparation process, and adopts industrially compatible hydrothermal and calcination technology, making it easy to scale up production and promote application. Attached Figure Description

[0015] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 (ab) Scanning electron microscope (SEM) images of the NiO@C / Ni composite thin film in the example; (c) X-ray diffraction (XRD) pattern and (d) Raman spectrum.

[0016] Figure 2 For the examples of NiO@C / Ni composite films and comparative examples of NiO@C powder electrodes, the temperature was -45°C. Comparison of linear voltammetry (CV) curves in a ℃ environment.

[0017] Figure 3 Comparison of (a) CV and (b) constant current charge-discharge (GCD) curves of nickel-iron batteries assembled with NiO@C / Ni composite thin films in the example and NiO@C powder electrodes in the comparative example at -45°C.

[0018] Figure 4 This is a comparison of the long-term cycling performance of nickel-iron batteries assembled with NiO@C / Ni composite thin films in the example and NiO@C powder electrodes in the comparative example, at -45°C. Detailed Implementation

[0019] The preferred embodiments of the present invention will now be described in detail with reference to the examples. The described embodiments are only a part of the embodiments of the present invention, and not all of them. The scope of the present invention should not be construed as limited to the embodiments described below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Example 1

[0020] 1. Preparation of a binder-free electrode suitable for low-temperature batteries: (1) Dissolve 1 g nickel acetate tetrahydrate (C4H6NiO4·4H2O), 1.5 g urea (CO(NH2)2) and 0.3 g ammonium fluoride (NH4F) in 50 mL of deionized water, stir to dissolve completely and mix evenly, and then transfer it to the polytetrafluoroethylene liner of the autoclave.

[0021] (2) Clean the nickel foam substrate, place it in the above mixed solution, seal the reaction vessel, and place it in a 130 ℃ electric heating oven for hydrothermal reaction for 5 hours. After the reaction vessel cools naturally, remove the nickel foam to obtain nickel foam with a basic nickel carbonate (Ni2(OH)2CO3) precursor.

[0022] (3) Rinse the precursor nickel foam with deionized water, then soak it in 100 mL Tris buffer containing 50 mg dopamine for 6 hours in a constant temperature oven at 60 °C to achieve surface modification and obtain the intermediate nickel foam. Then remove it and dry it in a 60 °C oven for later use.

[0023] (4) The dried intermediate product, nickel foam, was placed in a tube furnace and calcined at 550°C for 1 hour under an argon atmosphere to obtain a NiO@C / Ni composite film.

[0024] (5) The NiO@C / Ni composite film can be directly used as a battery electrode. (1) Dissolve 1 g nickel acetate tetrahydrate (C4H6NiO4·4H2O), 1.5 g urea (CO(NH2)2) and 0.3 g ammonium fluoride (NH4F) in 50 mL of deionized water, stir to dissolve completely and mix evenly, and then transfer it to the polytetrafluoroethylene liner of the autoclave.

[0025] (2) Seal the reaction vessel and place it in a 130°C electric heating oven for hydrothermal reaction for 5 hours. After the reaction vessel cools naturally, remove the powder material from the solution to obtain basic nickel carbonate (Ni2(OH)2CO3) precursor powder.

[0026] (3) The precursor powder was washed in deionized water and then filtered to obtain the powder. The powder was then soaked in 100 mL of Tris buffer containing 50 mg of dopamine and incubated at 60 °C for 6 hours to achieve surface modification. The intermediate product powder was then filtered and dried in an oven at 60 °C for later use.

[0027] (4) The dried intermediate product powder was placed in a tube furnace and calcined at 550 °C for 1 hour under an argon atmosphere to obtain NiO@C powder.

[0028] (5) NiO@C powder, acetylene black conductive agent and PVDF binder are ground and mixed evenly in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone solvent is added, and the mixture is stirred at room temperature for 12 hours to obtain a black viscous slurry. The slurry is evenly coated onto the nickel foam current collector with a scraper, and after drying, the NiO@C electrode is obtained. The active material loading of the electrode is about ~2 mg / cm³. 2 .

[0029] The difference between Example 1 and Comparative Example 1 is that in the hydrothermal reaction process, a nickel foam substrate was added to the reaction solution in Example 1, and the Ni2(OH)2CO3 precursor was directly grown on the nickel foam. The final product was a NiO@C / Ni composite film, which could be directly used as a battery electrode, avoiding the need for binders and complex bulk coating processes to prepare the electrode. In Comparative Example 1, no substrate was added in the hydrothermal reaction, and the final product was NiO@C powder, requiring the use of binders and a powder coating process to prepare the electrode.

[0030] The SEM morphology of the NiO@C / Ni composite film is as follows: Figure 1 As shown in ab, NiO@C grows in the form of nanosheets, uniformly and upright on a nickel foam substrate. The nanosheets are interwoven to form a porous network structure. Its XRD test results ( Figure 1 The diffraction peaks of c) match those of NiO (JCPDS card number: 47-1049). Its Raman spectra ( Figure 1 d) at 1350 cm -1 and 1572 cm -1 A vibration peak appears at this point, corresponding to the D and G peaks of material C.

[0031] 2. Low-temperature electrochemical performance testing of the NiO@C / Ni composite thin film electrode: A three-electrode testing system was assembled using the aforementioned NiO@C / Ni composite thin film as the working electrode, an Ag / AgCl electrode as the reference electrode, a platinum wire as the counter electrode, and a 7.5 M KOH aqueous solution as the electrolyte. The electrode system was subjected to CV testing at a scan rate of 10 mV / s in an environment of -45 °C. For comparison, the NiO@C powder electrode prepared in Comparative Example 1 was used as the working electrode, with all other conditions kept consistent.

[0032] The low-temperature CV curves of NiO@C / Ni composite films and NiO@C powder electrodes are compared as follows: Figure 2 As shown, both electrode systems exhibit a distinct pair of redox peaks located at 0.46V / 0.64V, corresponding to Ni. 2+ / Ni 3+ The redox reaction was observed. Among them, the redox peak signal of the NiO@C / Ni composite thin film electrode was stronger and the area of ​​the CV pattern was larger, proving that the binder-free electrode has better electrochemical reaction kinetics under low temperature conditions.

[0033] 3. Low-temperature electrochemical performance testing of the nickel-iron battery assembled with this NiO@C / Ni composite thin film electrode: A full cell was assembled using the aforementioned NiO@C / Ni composite thin film positive electrode, foamed iron negative electrode, and 7.5 M KOH aqueous solution electrolyte. The electrochemical performance of the full cell was tested at -45 °C: CV testing was performed at a scan rate of 5 mV / s, and the electrochemical performance was measured at 1 mA / cm². 2 GCD tests were performed at a current density of 1 mA / cm² to verify the electrochemical reaction kinetics and specific capacity of the battery; 2 The battery was repeatedly charged and discharged at a certain current density to verify its cycle stability.

[0034] The CV curves of the full cell under low-temperature conditions are shown in the following figure. Figure 3 As shown in Figure a, the CV curve of the nickel-iron battery assembled with the NiO@C / Ni composite thin film cathode exhibits more pronounced redox peaks and a larger CV area, while the CV curve of the battery assembled with the NiO@C powder cathode shows multiple pairs of irregular and weak reaction peak signals. This may be related to the ion transport lag caused by the performance degradation of PVDF in a low-temperature environment, demonstrating that the NiO@C / Ni composite thin film electrode has superior low-temperature electrochemical kinetic characteristics. A comparison of the GCD curves of the full cell is shown below. Figure 3 As shown in b, the GCD curve of the binder-free system exhibits a longer charge-discharge reaction plateau, and its specific capacity can be calculated to reach 0.1 mAh / cm³. 2Furthermore, its charge-discharge plateau overpotential difference is smaller; while the NiO@C powder cathode battery exhibits a larger overpotential and a lower specific capacity, further confirming the superior electrochemical reaction kinetics and larger specific capacity of the binder-free battery system in low-temperature environments.

[0035] The long-cycle comparison chart of all batteries is shown below. Figure 4 As shown, the nickel-iron battery assembled with NiO@C / Ni cathode can stably cycle for 500 cycles with a coulombic efficiency of ~100%; while the battery assembled with NiO@C powder cathode exhibits large fluctuations in specific capacity and coulombic efficiency during cycling, with a coulombic efficiency of only ~60%, and the battery completely fails after 320 cycles. This result confirms that the binder-free battery system has superior cycle stability in low-temperature environments.

[0036] The above embodiments are only used to illustrate preferred embodiments of the present invention, and are not intended to limit the concept and scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a binderless electrode suitable for low-temperature batteries, characterized in that: Its specific preparation process includes the following steps: (1) Dissolve the nickel salt, amide compound, and fluoride salt in deionized water, stir to mix them evenly, and then transfer the mixed solution into the polytetrafluoroethylene liner of the reactor. (2) Place the nickel foam in the mixed solution and carry out the hydrothermal reaction in a constant temperature electric heating oven. After a certain period of time, cool it naturally, take out the nickel foam, wash it, and obtain the precursor. (3) The precursor was placed in a Tris solution containing dopamine, and then placed in an electric heating oven and soaked at a constant temperature for a certain period of time to obtain the intermediate product; (4) The intermediate product is placed in a tube furnace with inert gas and calcined to obtain NiO@C / Ni composite material.

2. The preparation method according to claim 1, characterized in that: In step (1), the nickel salt is one of nickel formate dihydrate, nickel acetate tetrahydrate, nickel oxalate tetrahydrate, nickel carbonate, and nickel sulfate; the amide compound is one of urea, formamide, and acetamide; and the fluoride salt is one of ammonium fluoride, sodium fluoride, and potassium fluoride.

3. The preparation method according to claim 1, characterized in that: The molar ratio of nickel salt, amide compound, and fluoride salt in the mixed solution is 1:3:1 to 1:10:

3.

4. The preparation method according to claim 1, characterized in that: In step (2), the temperature of the hydrothermal reaction is 60~200 ℃ and the reaction time is 1~10 hours.

5. The preparation method according to claim 1, characterized in that: In step (2), the cleaning method is rinsing with deionized water or anhydrous ethanol.

6. The preparation method according to claim 1, characterized in that: In step (3), the dopamine content in the Tris solution is 0.1~10 g / L.

7. The preparation method according to claim 1, characterized in that: In step (3), the constant temperature soaking temperature is 40~100 ℃ and the time is 3~10 hours.

8. The preparation method according to claim 1, characterized in that: In step (4), the inert gas is either high-purity argon or nitrogen, the calcination temperature is 300~700 ℃, and the calcination time is 1~5 hours.

9. A binder-free electrode suitable for low-temperature batteries prepared by any one of claims 1 to 8, characterized in that: The electrode is a NiO@C / Ni composite film, in which NiO@C nanosheets are uniformly grown on foamed Ni to form a three-dimensional hierarchical network structure. This composite material uses foamed Ni as a conductive substrate and NiO@C as an active material, and can be directly used as an electrode for batteries. The electrode does not contain binders, and the preparation process avoids complex powder coating processes.

10. The application of the electrode material according to claim 9 in a low-temperature battery, characterized in that, Using the above-mentioned NiO@C / Ni composite film as the positive electrode, iron foam as the negative electrode, and potassium hydroxide aqueous solution as the electrolyte, a secondary battery can be assembled, and its test temperature can be as low as -45 ℃.

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