Preparation method of nickel-iron-based alloy and application of nickel-iron-based alloy in positive electrode of lithium-sulfur battery

Abstract

The invention relates to a preparation method of a nickel-iron-based alloy and application of the nickel-iron-based alloy in a positive electrode of a lithium-sulfur battery. The method comprises the following steps: firstly, dissolving polyvinylpyrrolidone and potassium ferrocyanide in deionized water; and aging the obtained mixture for 24 hours, and centrifugally collecting the obtained blue powder (Fe-MOF). Then, Fe-MOF powder prepared in advance, nickel chloride hexahydrate, polyacrylonitrile and N, N-dimethylformamide are mixed to be prepared into an electrostatic spinning solution; and then preparing FeNi3 / NC by combining an electrostatic spinning method with a heat treatment method. And finally, assembling the FeNi3 / NC serving as a positive electrode material and a lithium sheet serving as a negative electrode material into a button cell for electrochemical testing. Benefited from the efficient adsorption performance of FeNi3 / NC on polysulfide and the capability of accelerating catalytic conversion of the FeNi3 / NC, the product obtained by the invention has high specific capacity, excellent rate capability and stable cycle performance.

Description

Technical Field

[0001] The invention belongs to the field of lithium-sulfur battery preparation, and specifically relates to a method for preparing a nickel-iron based alloy and application of the alloy in a positive electrode of a lithium-sulfur battery. Background Art

[0002] With the increasing demand for efficient mobile power in electric vehicles and portable electronic devices, research on energy storage technology has received extensive attention. Compared with lithium-ion batteries (LIBs), lithium-sulfur batteries have a higher energy density (2600W h kg -1 ), and sulfur reserves are abundant and environmentally friendly. Therefore, lithium-sulfur batteries are considered to be a potential alternative system that can overcome the energy density limitations of current lithium batteries. However, the commercialization of lithium-sulfur batteries is limited by several technical barriers. First, the poor conductivity of sulfur and its discharge products (Li2S2 / Li2S) may reduce the utilization of sulfur. Second, the soluble polysulfide intermediates (Li2S n , 4≤n≤8) may lead to poor cycle stability and low Coulombic efficiency. The "shuttle effect" mainly comes from the following two reasons. One is the dissolution of LiPS in the electrolyte, and the other is the slow transformation of these LiPS and insufficient reaction kinetics. In order to achieve a high-activity reaction of sulfur, an ideal contact between sulfur and the electrolyte is required, which makes it difficult to avoid LiPS dissolution.

[0003] Based on the above discussion, there are two effective ways to mitigate the "shuttle effect". One is to effectively confine LiPS in the cathode body, and the other is to accelerate the redox kinetics of LiPS. In response to these two points, great efforts have been made to introduce functional catalysts into the cathode to anchor LiPS and improve the performance of lithium-sulfur batteries; and to use porous carbon to encapsulate sulfur in its porous network. However, due to the physical interaction with LiPS and volume expansion during discharge, they can only partially confine polysulfides. On this basis, the introduction of electrocatalytically active substances into the sulfur cathode is considered to be an effective method to accelerate the surface reaction kinetics. The rapid surface reaction helps to improve the utilization of active materials, while mitigating the "shuttle effect" of soluble intermediates, effectively solving the capacity decay. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of existing template technology, provide a new method for preparing nickel-iron-based alloy and apply it to the positive electrode material of lithium-sulfur batteries. The method prepares Fe-MOF cubic block powder as a precursor by a hydrothermal method, and constructs FeNi3 / NC material by combining electrospinning and heat treatment. Finally, FeNi3 / NC is used as the positive electrode material and lithium sheets are used as the negative electrode material to assemble button batteries for electrochemical testing. Thanks to the efficient adsorption performance of FeNi3 / NC for polysulfides and its ability to accelerate their catalytic conversion, the product obtained by the present invention has high specific capacity, excellent rate performance and stable cycle performance.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a nickel-iron-based alloy and application thereof in a positive electrode of a lithium-sulfur battery, the method comprising the following steps:

[0007] (1) Preparation of Fe-MOF powder precursor: First, polyvinyl pyrrolidone and potassium ferrocyanide were dissolved in deionized water. The resulting mixture was heated and aged at 80°C for 24 h, and the resulting blue powder (Fe-MOF) was collected by centrifugation;

[0008] (2) Preparation of FeNi3 / NC nanofiber membrane: The Fe-MOF powder precursor obtained in the previous step was mixed with nickel chloride hexahydrate, polyacrylonitrile and N,N-dimethylformamide to prepare an electrospinning solution. FeNi-MOF@PAN fiber membrane was prepared by electrospinning. Then, the FeNi-MOF@PAN fiber membrane was prepared under argon atmosphere at 5℃min -1 The temperature was raised to 700℃ at a speed of 100℃ and then kept at this temperature for 2h to obtain FeNi3 / NC fiber membrane;

[0009] (3) Assembly of button cells: All the required tools and materials are placed in the glove box, including: the electrode (FeNi3 / NC) after weighing and recording, lithium sheet (high purity), diaphragm (diameter 16mm), gasket, shrapnel, positive and negative battery shell (2032 type), electrolyte (2.0% LiNO3), tablet pressing mold, pipette gun (100uL), and insulated tweezers. The assembly process is described as follows: First, place the metal lithium sheet in the negative electrode shell, and pay attention to keep it in the middle of the battery shell. Second, place the diaphragm on the lithium sheet, and then use the pipette gun to add electrolyte. Third, use insulated tweezers to place the electrode (diameter 14mm), gasket, and shrapnel on the top of the diaphragm in turn, and finally buckle the positive electrode shell. The preliminarily assembled battery positive electrode shell is placed downward on the hydraulic packaging machine for sealing. It is worth noting that during the assembly process, pay attention to using insulated tweezers to adjust the position so that the material is located in the center of the battery shell. The electrolyte used in this experiment is: 1.0M LiTFSI+2.0% LiNO3+DME+DOL+S+Li2S (wherein V DME:V DOL=1:1; MS:M Li2S=5:1). The sealed battery was placed in a glove box overnight and tested the next day.

[0010] The essential features of the present invention are:

[0011] The present invention first uses a hydrothermal method to prepare a Fe-MOF precursor material with a cubic structure and regular size. Then, Fe-MOF is used as a precursor to prepare a FeNi-MOF@PAN fiber membrane by an electrostatic spinning method. Then, a heat treatment method is used to carbonize the FeNi3 / NC fiber membrane under an argon atmosphere. Using the fiber membrane as the positive electrode material of a lithium-sulfur battery can achieve efficient adsorption of polysulfides and accelerate its reaction kinetics, thereby inhibiting the "shuttle effect" and ultimately achieving a lithium-sulfur battery with high specific capacity, excellent rate performance and stable cycle performance.

[0012] The beneficial effects of the present invention are:

[0013] 1. The present invention uses Fe-MOF cubes as reaction precursors and prepares FeNi3 / NC fiber membranes by combining simple electrospinning and heat treatment methods. The operation is simple, the yield is high, the preparation is controllable, and the repeatability is strong;

[0014] 2. The FeNi3 / NC fiber membrane material prepared by the present invention has abundant chemically active sites on its surface, which can effectively adsorb and transform polysulfides, thereby inhibiting the "shuttle effect";

[0015] 3. The Li-S button battery assembled with FeNi3 / NC prepared in the present invention as the positive electrode material has high specific capacity, excellent rate performance and stable cycle performance. Description of the drawings:

[0016] Figure 1 This is the XRD pattern of the FeNi3 / NC fiber membrane prepared in the present invention.

[0017] Figure 2 This is the SEM image of the FeNi3 / NC fiber membrane prepared in the present invention.

[0018] Figure 3 The FeNi3 / NC fiber membrane prepared in the present invention is used as the positive electrode material to assemble into a Li-S button battery and the cycle performance curve is tested.

[0019] Figure 4 The rate performance curve of the FeNi3 / NC fiber membrane prepared in the present invention was tested after being assembled into a Li-S button battery as the positive electrode material. DETAILED DESCRIPTION

[0020] Example 1

[0021] Step 1: Dissolve 0.7 g PVP in 50 ml 0.1 M HCl solution, and then add 2.6 g K4Fe(CN)6·3H2O. After stirring for 30 minutes, transfer the solution to a glass bottle and then age it in an oven at 120 °C for 10 hours. Collect the resulting Prussian blue crystals, wash them with a centrifuge, and vacuum dry them at 60 °C to obtain Fe-MOF powder.

[0022] Step 2: First, 1.2 g of polyacrylonitrile (PAN, Mw = 150000) was dissolved in 10 ml of N, N-dimethylformamide (DMF) and stirred at 60 ° C overnight. Then, 0.2 g of Fe-MOF powder and 0.4 g of nickel chloride hexahydrate were added to the obtained solution and stirred vigorously at room temperature for 8 h to prepare a uniform electrospinning precursor. The electrospinning machine was set with a high voltage power supply of 24 kV and a 0.12 mL h -1 The feed rate was 100 rpm and the collector speed was 100 rpm. The electrospun fabric was collected on an aluminum foil 20 cm away from the stainless steel needle tip. The original fabric was collected and carbonized in an Ar atmosphere tube furnace at 700 °C for 2 h to obtain FeNi3 / NC fabric.

[0023] Step 3: Use the prepared FeNi3 / NC as the positive electrode, lithium foil as the anode, and PP as the separator to assemble a coin cell (CR2032). Drip 30μL of Li2S6 electrolyte (0.50M) on the positive electrode side to assemble a button cell, and perform the next performance test using the Blue Electric electrochemical workstation and Chenhua electrochemical workstation.

[0024] Figure 1 This is the XRD pattern of the FeNi3 / NC fiber membrane prepared in the present invention.

[0025] Figure 2This is the SEM image of the FeNi3 / NC fiber membrane prepared in the present invention.

[0026] Figure 3 The cycle performance curve of the Li-S button battery assembled with the FeNi3 / NC fiber membrane prepared in the present invention as the positive electrode material; it can be seen from the figure that FeNi3 / NC as the positive electrode material makes the battery have an ultra-high initial capacity density (1200mAh g -1 ), and stable cycle performance.

[0027] Figure 4 The rate performance curve of the Li-S button battery after the FeNi3 / NC fiber membrane prepared in the present invention is assembled as the positive electrode material; it can be seen from the figure that FeNi3 / NC as the positive electrode material makes the battery have excellent rate performance.

[0028] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a nickel-iron-based alloy and its application in a positive electrode of a lithium-sulfur battery, characterized in that the method comprises the following steps: (1) First, polyvinyl pyrrolidone and potassium ferrocyanide were dissolved in deionized water. The resulting mixture was aged for 24 hours, and the resulting blue powder (Fe-MOF) was collected by centrifugation. Then, the pre-prepared Fe-MOF powder, nickel chloride hexahydrate, polyacrylonitrile and N,N-dimethylformamide were mixed to prepare an electrospinning solution; (2) FeNi-MOF@PAN fiber membrane was prepared by electrospinning and then heated at 5 °C min-1 in an argon atmosphere. -1 The temperature was raised to 700°C at a rate of 100 °C and then kept constant for 2 h to obtain FeNi3 / NC fiber membrane.

2. The method for preparing a nickel-iron based alloy as claimed in claim 1, wherein the diameter of the nanocube is about 750 nm.

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