CN115241457A - Three-dimensional strip-shaped graphene compound conductive paste for metal ion battery - Google Patents

Abstract

The invention provides a high-performance metal ion battery conductive slurry and a preparation method thereof. The method comprises the steps of obtaining three-dimensional banded graphene through a liquid nitrogen quenching method, mixing the three-dimensional banded graphene and conductive carbon black according to a certain proportion, and performing liquid phase ball milling in a dispersing agent to obtain the high-performance metal ion battery conductive slurry. The conductive paste combines a good space cross-linking network of three-dimensional strip graphene with excellent conductivity of conductive carbon black, and a 'surface-point'/'point-point' contact combination is constructed in an electrode, so that a novel conductive electrode system with a long-range bridging conductive network and a three-dimensional ion migration channel is realized, and a good synergistic effect is realized. The conductive paste has the advantages of simple preparation method, low raw material cost, excellent performance and good application value and prospect.

Description

A three-dimensional ribbon graphene composite conductive paste for metal-ion batteries

technical field

The invention belongs to the technical field of metal ion battery conductive agents, and in particular relates to a high-performance metal ion battery conductive paste and a preparation method thereof.

Background technique

Metal-ion batteries (lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, etc.) are an energy storage device that uses compounds that can intercalate metal ions as positive and negative electrode materials, and metal ions shuttle back and forth through the electrolyte to achieve energy storage and release. . Metal-ion batteries are mainly composed of positive electrodes, negative electrodes, separators, electrolytes, current collectors and shells. The positive and negative electrodes of the battery are mainly composed of active materials, conductive agents, binders and current collectors. The active materials in the electrodes are mainly used to store metal ions, and the conductive agents are used to enhance the charge transport capacity of the electrodes and promote the electron transfer inside the electrodes. Conductive, the binder firmly bonds the active material, conductive agent and current collector together to ensure the integrity of the electrode during charging and discharging.

Although conductive agents account for a small proportion of metal-ion battery components, they are crucial for improving the rate performance of batteries and assisting active materials to fully exert their capacity and cycle stability. The traditional conductive agents are mainly carbon black and acetylene black. Its microscopic morphology is that carbon nanoparticles of ten to several tens of nanometers are cross-linked with each other, forming a coral-like structure in space. The traditional conductive agent and the active material particles mainly improve the conductivity of the electrode through "point-to-point" contact. During the charging and discharging process, it is easy to cause the loss of electrical contact between the active material and the conductive agent, resulting in a sharp decline in the electrochemical performance of the electrode. . In recent years, new multi-dimensional conductive agents such as carbon nanotubes (ACS Nano 2021, 15, 6735-6746) and graphene conductive agents (Nano Energy 2012, 1, 429-439; Journal of Energy Chemistry 2019, 30, 19-26) have increasingly attracted people's attention. Compared with the traditional zero-dimensional conductive agent, the new multi-dimensional conductive agent has significant advantages: 1) The contact mode between the conductive agent and the active material particles has changed from "point-point" contact to "line-point" (carbon nanotubes) and " Surface-to-point" (graphene) contact increases the contact area and improves the efficiency of the use of conductive agents; 2) Line-type and surface-type conductive agents contribute to the construction of conductive networks and improve the transmission efficiency of electrons/ions. However, there are also some key problems when carbon nanotubes and graphene are directly used as conductive agents. The contact between the two is insufficient, resulting in the insignificant improvement of the cycle stability and rate performance of the electrode; the planar structure of graphene will hinder the transport of metal ions to a certain extent (especially under high current), affecting the Rate capability of electrode materials.

The three-dimensional ribbon graphene structure (patent authorization number: CN105947973B) developed by the applicant is formed by spatially cross-linking graphene nanoribbons. In this work, it was found that when three-dimensional ribbon graphene is used as a conductive agent for metal-ion batteries, its unique neural network-like multi-antenna structure can tightly wrap the active materials together, effectively preventing the "electrode" during charging and discharging. Loss of electricity” and structural crushing of the active material. At the same time, the three-dimensional ribbon structure can provide a continuous three-dimensional conductive network and improve the electron/ion transport efficiency in the electrode. And compared with graphene, the graphene nanoribbons forming the three-dimensional ribbon graphene structure have a large aspect ratio, and the steric hindrance to the transport of metal ions is greatly reduced.

The three-dimensional ribbon graphene structure and traditional conductive carbon black are compounded to construct a high-performance metal-ion battery conductive paste (Figure 1). Combined, the disadvantage of simply relying on short-range "point-point" contact and insufficient utilization of conductive agent between traditional conductive agents and active materials is changed, and a "surface-point"/"point-point" contact combination is constructed inside the electrode, with long-range bridges The new conductive electrode system connecting the conductive network and the three-dimensional ion migration channel achieves a good synergistic effect, thereby improving the electron/ion transmission efficiency in the electrode and the stability of the electrode. The performance comparison of several typical conductive agents is shown in Table 1.

Table 1 Performance comparison of different conductive agents

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to construct a high-performance metal ion battery conductive paste. The second purpose of the present invention is to provide a preparation method of a high-performance metal ion battery conductive paste.

The high-performance metal ion battery conductive paste of the present invention is prepared by mixing three-dimensional ribbon graphene, conductive carbon black, a liquid dispersion medium and a dispersion aid. The mass ratio of solid in the conductive paste is 30% to 90%, the mass ratio of three-dimensional ribbon graphene in the solid is a, and the mass ratio of carbon black is b, a+b=100%, 5%≤a≤90% .

Further, the preparation of the three-dimensional ribbon graphene is carried out according to the patent we have authorized (patent authorization number: CN105947973B), and the specific preparation parameters are slightly adjusted: the improved Hummers method is used to prepare the graphene oxide dispersion, and the solvent is to remove Ionized water, the concentration of graphene oxide dispersion is 0.3mg/mL, then the graphene oxide dispersion is sprayed into liquid nitrogen at a rate of 5mL/min, freeze-dried and heat treated under nitrogen protection to obtain three-dimensional ribbon graphene, heat treatment The temperature range is 250-1200℃, and the heat treatment time is 0.2-10h.

Further, the preparation method of the high-performance metal-ion battery conductive paste is to first weigh a specific proportion of three-dimensional ribbon graphene and carbon black, and uniformly disperse the above three-dimensional ribbon graphene and carbon black in a solvent. It can be used in combination of one or more of high-speed stirring, ultrasonic treatment, liquid phase grinding, and high-speed homogenization, wherein the dispersing speed of high-speed stirring is 300-12000 rpm, the ultrasonic processing frequency is 40 kHz, and the ultrasonic output power is 60 ~600W, the mass ratio of liquid phase grinding balls is 5:1, and the dispersion time is 10-2400 minutes. The obtained dispersion liquid is vacuum filtered to obtain a premix, and the premix is added to a suitable liquid dispersion medium and added to a certain amount. Amount of dispersing aid, liquid phase ball milling for 10-2400 minutes to obtain high-performance metal ion battery conductive paste.

The present invention mainly has the following beneficial effects:

The high-performance metal ion battery conductive paste of the present invention changes the short-range "point-point" contact mode of the traditional conductive agent, constructs a "surface-point"/"point-point" contact combination inside the electrode, and has a long-range bridging conductive network and a three-dimensional Novel conductive electrode systems for ion transport channels. At the same time, the three-dimensional ribbon-shaped graphene with certain mechanical strength and toughness can effectively prevent the "power loss" and structure crushing of the active material during the charging and discharging process, and improve the cycle stability of the electrode system. The preparation method of the high-performance metal ion battery conductive paste provided by the invention can realize the high performance and long cycle construction of the metal ion battery, and has good application value and prospect.

Description of drawings

Fig. 1 Scanning electron microscope photo of conductive paste for high performance metal ion battery;

Fig. 2 uses the cycle performance comparison diagram of the lithium ion battery that the experiment of the present invention and comparative example make;

FIG. 3 is a comparison diagram of electrochemical impedance spectra of lithium ion batteries prepared by using the experiment of the present invention and the comparative example after 300 cycles of charging and discharging.

Detailed ways

In order to more clearly demonstrate the objectives, technical solutions and advantages of the present invention, the implementation process of the present invention is described below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

Preparation of Si-based negative electrode using high-performance metal-ion battery conductive paste.

Mix 10mg three-dimensional ribbon graphene and 10mg carbon black in 20mL of ethanol using a high-speed shear homogenizer for 20min, vacuum filter and freeze-dry to obtain a premix, which is dispersed in 5mL of deionized water. And liquid-phase ball milling at 500 r/min for 1 h to make a high-performance metal-ion battery conductive paste (Figure 1). 60mg of nano-Si (particle diameter distribution range is 30-100nm) and 20mg of sodium alginate are added to the conductive paste for high-performance metal ion batteries prepared above, and the electrode paste is prepared through the process of mixing/slurrying/mixing/beating Then, the Si-based negative pole piece is prepared through the processes of coating, baking, rolling and die-cutting. In the glove box, the Si-based negative electrode plate and the positive and negative electrode shell, gaskets, shrapnel, lithium plate, diaphragm, and electrolyte were assembled into a button-type half-cell and left for 12 hours to ensure that the inside of the battery was fully infiltrated.

Comparative Example 1

The Si-based negative pole piece was prepared using carbon black as the conductive agent.

Mix 60mg of nano-Si (with a particle diameter distribution range of 30-100nm), 20mg of carbon black and 20mg of sodium alginate and ball-milled in 5mL of deionized water at a speed of 500 rpm for 1h. The electrode slurry was prepared by the slurry mixing/beating process, and then the Si-based negative pole piece of the comparative example was prepared through the processes of coating, baking, rolling and die-cutting. In a glove box, the comparative Si-based negative electrode piece and the positive and negative electrode shell, gasket, shrapnel, lithium piece, diaphragm, and electrolyte were assembled into a button half-cell and left for 12 hours to ensure that the inside of the battery was fully infiltrated.

Example 2

Lithium iron phosphate-based positive electrode sheets were prepared using high-performance metal-ion battery conductive paste.

5mg three-dimensional ribbon graphene and 5mg carbon black were mixed in 10mL ethanol using a high-speed shear homogenizer for 20min, vacuum filtered and freeze-dried to obtain a premix, and the above premix was dispersed in 5mL N-formaldehyde. pyrrolidone (NMP) and liquid-phase ball milling at 500 r/min for 1 h to make a high-performance metal-ion battery conductive paste. 80mg of lithium iron phosphate and 10mg of polyvinylidene fluoride (PVDF) were added to the above-prepared conductive paste for high-performance metal ion batteries, and the electrode paste was prepared through the process of mixing/slurrying/sizing/beating, and then by coating The process of cloth, baking, rolling and die-cutting obtains the lithium iron phosphate-based positive pole piece. In the glove box, the lithium iron phosphate-based positive electrode piece and the positive and negative electrode shell, gasket, shrapnel, lithium piece, diaphragm, and electrolyte were assembled into a button-type half-cell and left for 12 hours to ensure that the inside of the battery was fully infiltrated.

Comparative Example 2

Lithium iron phosphate-based positive electrode sheets were prepared using carbon black as a conductive agent.

80mg lithium iron phosphate, 10mg carbon black and 10mg polyvinylidene fluoride (PVDF) were mixed uniformly and ball-milled in 5mL N-methylpyrrolidone (NMP) at 500 rpm for 1h in liquid phase, after mixing/slurrying Electrode slurry was prepared in the process of mixing/sizing/beating, and then through the processes of coating, baking, rolling, and die-cutting to prepare a lithium iron phosphate-based positive electrode piece of comparative example. In the glove box, the comparative lithium iron phosphate-based negative pole piece and the positive and negative pole shell, gasket, shrapnel, lithium piece, diaphragm, and electrolyte were assembled into a button half-cell and left for 12 hours to ensure that the inside of the battery was fully infiltrated.

The electrochemical performance tests of the above four button half-cells are carried out, and the specific test steps and results are as follows:

The electrochemical cycle performance test was carried out on the button-type half-cells prepared in the examples and comparative examples. First, they were activated for 5 cycles at a current density of 0.5A/g, and then the cycle performance test was carried out at a current density of 1A/g. The performance comparison results are shown in Figure 2. It was found that after 300 cycles of charge and discharge at 1A/g, the capacity retention rate of Comparative Example 1 was only 24.3%, while that of Example 1 was as high as 69.3%, and the electrode capacity was still as high as 1031.4mAh/g after 300 cycles of charge and discharge. . By studying the electrochemical impedance (EIS) spectrum of the electrode after 300 cycles of charge and discharge, we found that the electrode of Example 1 still maintained a low interfacial resistance and good electron/ion transport performance after 300 cycles of cycling, on the contrary to the electrode of Comparative Example 1. The interfacial resistance becomes larger after cycling, and the electron/ion transport performance deteriorates. We believe that the structure of 3D ribbon-shaped graphene-wrapped active Si particles avoids the direct contact between Si particles and the electrolyte and reduces the generation of interfacial side reactions, and the addition of 3D ribbon-shaped graphene helps to form a layer of quality The thin and stable solid electrolyte (SEI) film avoids the influence of thick SEI film formed in conventional pure carbon black electrodes on electron/ion transport and continuous consumption of electrolyte.

Table 2 Comparison of discharge specific capacity and cycle performance results

project First lap capacity (mAh/g) Capacity retention rate after 300 cycles (%) Example 1 2117 69 Comparative Example 1 1824 twenty four Example 2 173 98% Comparative Example 2 169 94%

In particular, those skilled in the art should realize that the above embodiments are only used to illustrate the present invention, but not to limit the present invention. As long as they are within the scope of the description of the present invention, changes and modifications to the above embodiments will fall within the protection scope of the present invention.

Claims (3)

1. A high-performance metal ion battery conductive paste is characterized in that: the graphene material is prepared by mixing three-dimensional banded graphene, conductive carbon black, a liquid dispersion medium and a dispersion auxiliary agent.

2. The high-performance metal-ion battery conductive paste of claim 1, wherein: the mass ratio of the solid is 30-90%, the mass ratio of the three-dimensional strip graphene in the solid is a, the mass ratio of the conductive carbon black is b, a + b =100%, and a is more than or equal to 5% and less than or equal to 90%; the conductive carbon black is one or more of commercially available conductive acetylene black, super P conductive carbon black and Ketjen black; the liquid dispersion medium consists of a solvent and a dispersion auxiliary agent, wherein the solvent can be one or more of deionized water, N-methyl pyrrolidone, N-dimethyl amide and dimethyl sulfoxide for combined use, the dispersion auxiliary agent is one or more of polyvinylpyrrolidone, polyacrylamide, sodium dodecyl sulfate and ethanol for combined use, and the mass percentage of the dispersion auxiliary agent in the liquid dispersion medium is 0-2.0%.

3. A preparation method of high-performance metal ion battery conductive slurry is characterized by comprising the following steps: 1) Obtaining three-dimensional strip-shaped graphene through a liquid nitrogen quenching method and heat treatment, wherein the three-dimensional strip-shaped graphene is formed by spatially crosslinking graphene strips, the length range of the graphene strips is 0.1-200 mu m, the width range of the graphene strips is 0.01-1 mu m, the heat treatment temperature range is 250-1200 ℃, and the heat treatment time is 0.2-10h; 2) Weighing three-dimensional strip graphene and conductive carbon black in a specific ratio; 3) Uniformly dispersing the three-dimensional banded graphene and the conductive carbon black in a solvent, wherein the dispersion method can be one or more of high-speed stirring, ultrasonic treatment and liquid-phase grinding, the high-speed stirring dispersion speed is 300-12000 r/min, the ultrasonic treatment frequency is 40kHz, the ultrasonic output power is 60-600W, and the liquid-phase grinding ball material mass ratio is 5:1, dispersing for 10-2400 minutes; 4) And carrying out vacuum filtration on the obtained dispersion liquid to obtain a premix, adding the premix into a proper liquid dispersion medium, adding a certain amount of dispersing auxiliary agent, and carrying out liquid phase ball milling for 10-2400 minutes to obtain the high-performance metal ion battery conductive slurry.

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