CN114613944B - A method of preparing solid-state battery electrodes through microwave technology - Google Patents

Abstract

The invention discloses a method for preparing a solid-state battery electrode by a microwave process, which comprises the following steps: (1) coating the wave-absorbing material outside the active substance; (2) Uniformly mixing the active material with the core-shell structure, the conductive agent and the additive to obtain electrode mixed powder; the electrode mixed powder obtained in the step (3) is pressed into a film; (4) And (5) putting the film into a special microwave die, and then performing microwave processing to generate the battery electrode. The invention obtains the positive electrode precursor through the spraying process, so that the microwave absorbing material used as the binder is uniformly distributed, the particles are well coated, the electrode is compact and the components are more uniform at the same time through the subsequent microwave processing, and the defects and limitations of the traditional dry process can be overcome.

Description

A method of preparing solid-state battery electrodes through microwave technology

Technical field

The invention belongs to the technical field of secondary battery electrode materials, and specifically relates to a method for preparing solid-state battery electrodes through microwave technology.

Background technique

The organic liquid electrolyte in traditional lithium-ion batteries poses a major safety hazard due to its flammability. The risk of thermal runaway of all-solid-state lithium batteries is much lower than that of traditional lithium-ion batteries, and due to the good mechanical properties of the electrolyte, it can effectively block the lithium dendrites generated by the negative electrode during the charge and discharge process, thereby reducing dead lithium and improving battery cycle life and energy. Density, therefore the development of all-solid-state batteries has become an important direction for the development of a new generation of energy storage technology.

Solid electrodes are the core components of all-solid-state batteries. The main problem currently is that there are large gaps between the active materials, conductive agents and solid electrolyte particles inside the electrodes, and there are a large number of point-to-point contacts, resulting in large interfacial resistance between solid particles. , restricting the transmission of lithium ions inside the electrode, thus weakening the rate performance and capacity performance of the battery. Therefore, preparing a dense cathode with high ionic conductivity has become one of the bottlenecks in the development of all-solid-state batteries.

Commercially available solid-state battery cathodes all use a wet coating process. The wet process means that after the binder is fully dissolved or dispersed in the solvent, it is evenly mixed with the active material and conductive agent in the liquid phase, and then the slurry is coated. After application, the volatile solvent is dried to obtain a positive electrode. The wet process is widely used in lithium battery manufacturers, and the binder is evenly dispersed and the bonding effect is good. However, the use of solvents (such as NMP) is not environmentally friendly, has high costs, has poor conductivity, is prone to cracking of thick electrode plates, and generates residual solvents. Disadvantages such as side reactions. Even more fatal is the large porosity electrode piece left after the solvent evaporates, resulting in high interface resistance and poor lithium ion conductivity, which in turn causes battery rate performance and capacity performance problems.

In contrast, the dry process is simple and has the advantage of reducing the need for solvents and thus reducing pores. At present, there are many technical routes for dry electrodes, among which Maxwell's technology is the most mature, which specifically includes the following: Mix the active material, conductive agent and polytetrafluoroethylene (PTFE) in a mixer, and extrude the powder mixture It is extended into a continuous self-supporting electrode film, and finally the thin electrode and the current collector are pressed together to form the battery pole piece. The traditional dry process has the disadvantage that each component is not easily dispersed in the polymer melt, resulting in phase separation within the resulting electrode film and poor mechanical properties. At the same time, dry electrodes require a long period of hot rolling or extrusion processing, which consumes a lot of energy and can easily lead to thermal degradation of polymers and other materials. Therefore, it is very necessary to develop a process to solve the above existing problems.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing solid-state battery electrodes through microwave technology. The positive electrode precursor is obtained through a spraying process, so that the microwave absorbing material used as a binder is evenly distributed and better coats the particles. Subsequent microwave processing makes the electrode dense and the composition more uniform, which can solve the problems of traditional dry processes. Disadvantages and limitations.

In order to achieve the above objectives, one of the technical solutions of the present invention is a method for preparing solid-state battery electrodes through microwave technology, which specifically includes the following steps:

(1) Coat the active material with the absorbing material;

(2) Mix evenly the active material that has formed a core-shell structure in step (1) with the conductive agent and additives to obtain an electrode mixed powder;

(3) Press the electrode mixed powder obtained in step (2) into a film;

(4) Put the film prepared in step (3) into a special microwave mold and perform microwave processing. A microwave-absorbing melting reaction occurs inside the electrode, forming a dense electrode.

In a preferred embodiment of the present invention, the coating process in step (1) is a spraying process or a vapor deposition process.

In a preferred embodiment of the present invention, the absorbing material in step (1) includes one or more of absorbing carbon materials, iron-based absorbing materials, absorbing ceramic materials, and absorbing polymer materials.

Further, the absorbing carbon material is preferably conductive graphite, graphene, carbon nanotubes, and carbon fiber, the iron-based absorbing material is preferably ferrite, the absorbing ceramic material is preferably silicon carbide, silicon nitride, and the absorbing polymer The material is preferably an organic material containing polar functional groups, such as polyaniline, polyethylene glycol, polythiophene, polypyrrole, etc.

Furthermore, the absorbing polymer material needs to be doped with lithium salts before use. The lithium salts include tetrafluoroboric acid (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and lithium hexafluoroarsenate (LiAsF ₆ ), lithium hexafluorophosphate

(LiPF ₆ ), lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium bisdifluorosulfonyl imide (LiFSI), and lithium bistrifluoromethanesulfonyl imide (LiTFSI) species or several species.

Furthermore, the wave-absorbing polymer material is preferably at least one of polyethylene glycol and its derivatives.

Furthermore, the lithium salt is preferably lithium perchlorate (LiClO ₄ ) or lithium bistrifluoromethylsulfonimide (LiTFSI).

Further, the mass ratio of the lithium salt to the wave-absorbing polymer material is 0.01-0.8:1.

In a preferred embodiment of the present invention, the ion conductivity of the absorbing material in step (1) is 10-10-10-1S/cm.

In a preferred embodiment of the present invention, the active materials in step (1) include lithium iron phosphate, lithium cobalt oxide, lithium manganate, ternary cathode materials and their derivatives, elemental sulfur, sulfur-containing compounds and One or more of its derivatives and organic materials with redox activity and their derivatives.

In a preferred embodiment of the present invention, the coating method in step (1) includes mechanical mixing method, solid phase reaction method, physical and chemical vapor deposition method, dip coating method, sol-gel method, hydrothermal method Method, co-precipitation method, electrodeposition method, ball milling method, spray coating method, microwave method, electrostatic spray method.

In a preferred embodiment of the present invention, the thickness of the coating layer in step (1) is 1 nm-1 cm.

In a preferred embodiment of the present invention, the mass fraction of the absorbing material in the electrode mixed powder in step (2) is 0.1%-90%.

In a preferred embodiment of the present invention, the type of conductive agent in step (2) is one or more of carbon black, conductive graphite, Ketjen black, Super P, carbon fiber, carbon nanotube, and graphene. kind.

In a preferred embodiment of the present invention, the additive in step (2) is one or more of polymer binder, solid electrolyte, and electrolyte.

In a preferred embodiment of the present invention, the types of pressing in step (3) include vacuum hot pressing, atmosphere hot pressing, isostatic pressing, hot isostatic pressing, reaction hot pressing, vibration hot pressing, and equilibrium heat pressing. Pressure and ultra-high pressure sintering.

In a preferred embodiment of the present invention, the pressure used for pressing in step (3) is 0.1-3000MPa, and the temperature is 30-1500°C.

In a preferred embodiment of the present invention, the film thickness of the pressed film in step (3) is 5 nm-1 cm.

In a preferred embodiment of the present invention, the microwave in step (4) is an electromagnetic wave with a frequency between 300MHz and 300GHz. The frequency range of microwave heating is 300MHz-300GHz. The form of the wave can be sine wave, cosine wave, Square waves, transverse waves, longitudinal waves, and any combination thereof.

In a preferred embodiment of the present invention, the microwave power in step (4) is 10-9000W, and the microwave time is 0.01-3600S.

In order to achieve the above objects, the second technical solution of the present invention is a solid-state battery electrode obtained by preparing a solid-state battery electrode through a microwave process.

Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

1. The method of the present invention can make the microwave absorbing material used as a binder evenly distributed, thereby better coating the particles; the selected conductive agent not only plays a role in improving the electronic conductivity, but also has good microwave absorption properties. ; The pressure of the completely dried powder enables closer contact between the components, increasing the electrode density, which is beneficial to the preparation of thick electrodes, improves cycle performance, and increases battery life;

2. Compared with the wet process, the method of the present invention performs pressure treatment on the powder, which solves the problem of poor contact between particles inside the electrode;

3. Compared with the traditional dry method, the method of the present invention can achieve better binder distribution, and subsequent microwave processing melts the binder, further filling the internal pores of the electrode, making the electrode more dense and assembled at the same time. The distribution of points becomes more even;

4. The process of the present invention is simple and does not require excessive mechanical stirring links, which greatly reduces material loss; due to the high heating efficiency and short time of the microwave process, it is more energy-saving and efficient than the traditional dry process; and because the microwave process can The controllability is good, so the repeatability of the sample is good.

Description of the drawings

Figure 1 is a basic flow chart for preparing solid-state electrodes by microwave technology according to the present invention;

Figure 2 is a schematic diagram of the active material of the present invention undergoing coating and microwave treatment;

Figure 3 is a TEM image of an active material coated with a microwaveable material in Example 1 of the present invention;

Figure 4 is an SEM image of the cross-section of the electrode treated by microwave processing and without microwave processing in Example 1 and Comparative Example 1 of the present invention;

Figure 5 shows the all-solid-state battery data of the electrodes prepared in Examples 1-2 and Comparative Example 1 of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in more detail below with reference to the drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

A method of preparing solid-state battery electrodes through microwave technology:

(1) Coat the active material with the absorbing material;

(2) Mix evenly the active material that has formed a core-shell structure in step (1) with the conductive agent and additives to obtain an electrode mixed powder;

(3) Press the electrode mixed powder obtained in step (2) into a film;

(4) Put the film prepared in step (3) into a special microwave mold and perform microwave processing. A microwave-absorbing melting reaction occurs inside the electrode, forming a dense electrode.

Example 1

Polyethylene glycol is used as the absorbing material and coated using a spraying process. At room temperature, weigh 200 mg of PEG particles with a molecular weight of 600,000, add 10 ml of deionized water and stir until it is completely dissolved. Weigh 700mg LCO and 100mg acetylene black, mix evenly, grind with a mortar for 15 minutes and then add the PEG aqueous solution. After 30 minutes of even dispersion, add the slurry to the spray gun while stirring. Cut an appropriate size of aluminum foil and place it tightly against the heating platform, place the heating platform upright, and heat to 250°C. Spray the slurry evenly on the aluminum foil. After spraying, remove the aluminum foil and send it to an 80°C oven for 3 hours. After drying, scrape off the powder on the aluminum foil and collect it. The mass was weighed as 850mg. Take 90mg and place it in the press mold. The pressure is 1.2MPa and the pressure is maintained for 10 minutes. After taking it out, cut it into a disc size of 12mm in diameter and 150μm in thickness. Put the cut product into the microwave mold. Adjust the microwave to 700W power. After microwave processing for 30 seconds, take it out to obtain a 120 μm thick positive electrode piece.

The TEM image of the active material coated with the microwaveable material in this embodiment is shown in Figure 3. It can be seen from Figure 3 that the active material exhibits a complete coating layer.

Example 2

Titanium nitride is used as the absorbing material, and the vapor deposition process is used for coating. Place 700 mg of LCO in the reaction chamber. Repeatedly vacuuming and filling with nitrogen, under the protection of nitrogen, using titanium tetrachloride and ammonia as precursors, the two gases enter the reaction chamber through independent gas paths. Among them, nitrogen is used as a carrier gas to load vaporized titanium tetrachloride into the reaction chamber through a series bubbler. The carrier gas flow rates of ammonia and titanium tetrachloride are 80 and 150 ml/min respectively, and the nitrogen flow rate as protective gas is 670 ml/min. The deposition temperature is 580°C, and the deposition time is 360S. After the deposition is completed, take it out and put it into an oven at 80°C for 3 hours. After drying, scrape off the powder on the aluminum foil and collect it. The mass was weighed as 800mg. Take 90 mg and place it in the press mold. The pressure is 5MPa and the pressure is maintained for 50 minutes. After taking it out, cut it into a disc size of 12mm in diameter and 150μm in thickness. Put the cut product into the microwave mold. Adjust the microwave oven to 800W power. After microwave processing for 500 seconds, take it out to obtain a 90 μm thick positive electrode piece.

Comparative example 1

This comparative example provides a traditional lithium-ion battery in which the positive electrode of the battery is prepared according to the traditional liquid coating preparation method and does not include the positive electrode piece of the microwave coating process described in the present invention. Weigh 700mg LCO and 100mg acetylene black, grind and mix them evenly, then add them to the NMP solvent of polyvinylidene fluoride (PVDF). Continue grinding for 15 minutes and then use a coater to pattern on the aluminum foil to obtain a positive electrode with a thickness of 100 μm.

The porosity of the solid-state battery positive electrodes prepared in Examples 1, 2 and Comparative Example 1 is as shown in the table below.

Table 1 Porosity of different samples

sample Porosity Comparative ratio 34% Example 1 3% Example 2 2%

Figure 4 is an SEM image of the electrode cross section of Example 1 and Comparative Example 1 with and without microwave treatment; it can be seen from the figure that the electrode after microwave treatment is denser.

Example 3

The positive electrode sheets prepared in Example 1, Example 2 and Comparative Example 1 were respectively assembled into solid-state batteries, and solid-state battery assembly tests were performed. The test results are shown in Figure 5. It can be seen from the figure that the electrodes that have undergone microwave processing (Examples 1 and 2) exhibit better cycle performance.

The above embodiments are only optimized implementation methods of the present invention and are used to illustrate the principles and effects of the present invention, but are not intended to limit the present invention. It should be noted that any person skilled in the art may make modifications to the above embodiments without departing from the spirit and scope of the invention, and these modifications shall also be considered as the protection scope of the invention.

Claims (8)

1. A method for preparing solid-state battery electrodes through microwave technology, characterized in that it includes the following steps: (1) Cover the active material with an absorbing material; the absorbing material is an absorbing polymer material, and the absorbing polymer material includes polyaniline, polythiophene, polypyrrole, polyethylene glycol, and polyamide. , at least one of polyimide, polyester, polyether, polysulfone and their derivatives; (2) Mix evenly the active material that has formed a core-shell structure in step (1) with the conductive agent and additives to obtain an electrode mixed powder; (3) Press the electrode mixed powder obtained in step (2) into a film; (4) Put the film prepared in step (3) into a mold and perform microwave processing to generate battery electrodes. 2. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the absorbing polymer material needs to be doped with lithium salt before use, and the lithium salt includes lithium perchlorate , one or more of lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bisoxaloborate, lithium difluoroxaloborate, lithium bisdifluorosulfonimide and lithium bistrifluoromethanesulfonimide. 3. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the ion conductivity of the absorbing material in step (1) is 10 ^-10 -10 ^-1 S/ cm. 4. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the coating method in step (1) includes mechanical mixing method, solid phase reaction method, physical and chemical vapor phase Deposition method, dip coating method, sol-gel method, hydrothermal method, coprecipitation method, electrodeposition method, ball milling method, spray coating method, microwave method, electrostatic spray method. 5. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the conductive agent in step (2) is carbon black, conductive graphite, Ketjen black, carbon fiber, carbon nanoparticles One or more of tubes, graphene and their mixed conductive agents, and the additive is one or more of polymer binder, solid electrolyte, and electrolyte. 6. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the types of pressing in step (3) include vacuum hot pressing, atmosphere hot pressing, isostatic pressing, Hot isostatic pressing, reaction hot pressing, vibration hot pressing, balanced hot pressing, ultra-high pressure sintering. 7. A method for preparing solid-state battery electrodes through microwave technology according to claim 1, characterized in that the microwave in step (4) is an electromagnetic wave with a frequency between 300 MHz and 300 GHz, and the wave form is sinusoidal. Wave, cosine wave, square wave, transverse wave and their combination, microwave power is 10-9000W, microwave time is 0.01-3600S. 8. A solid-state battery electrode obtained by the method according to any one of claims 1-7.