CN114566705A

CN114566705A - Preparation method of polymer solid electrolyte of lithium metal battery

Info

Publication number: CN114566705A
Application number: CN202210213064.4A
Authority: CN
Inventors: 陆文强; 史天泽; 康帅
Original assignee: Chongqing Institute of Green and Intelligent Technology of CAS
Current assignee: Chongqing Institute of Green and Intelligent Technology of CAS
Priority date: 2022-02-28
Filing date: 2022-03-04
Publication date: 2022-05-31

Abstract

The present invention provides a method for preparing a polymer solid electrolyte of a lithium metal battery, which includes a substrate preparation and previous material preparation step S1, which provides a substrate and previous materials for the prepared polymer solid electrolyte of a lithium metal battery; and step S2, preparing the polymer solid electrolyte. The invention can prepare the novel polymer solid electrolyte with a special surface structure and has the advantages of simple process flow, short time consumption, low cost, high quality and the like.

Description

Preparation method of polymer solid electrolyte of lithium metal battery

Technical Field

The invention belongs to the technical field of preparation of solid electrolyte of a chemical power supply, and particularly relates to a preparation method of polymer solid electrolyte of a lithium metal battery.

Background

Lithium ion batteries are widely studied as the main core components of electric vehicles and portable electronic devices due to their advantages of long cycle life, high energy density, no memory effect, and the like. However, the liquid electrolyte used in the current commercial lithium ion battery often contains a highly volatile and flammable organic solvent, and has huge potential safety hazards such as ignition and explosion. These safety concerns limit the safety of the battery over long-term use. Meanwhile, in commercial lithium ion battery systems, energy density and capacity are related to electrolyte content, and too little electrolyte results in loss of capacity and battery life.

In recent years, researchers have studied a very large number of solid electrolytes, attempting to replace lithium ion battery liquid electrolytes with other substances and solving these problems. For example, in order to obtain polymer solid electrolytes with high ionic conductivity, high mechanical strength, and high lithium ion transport number, researchers have adopted various methods including casting, electrospinning, solution casting, phase inversion, etc., wherein solution casting is the most promising and economically efficient controllable synthesis method for large-area, high-quality polymer electrolytes. The existing solution casting method mainly uses a glass substrate or a polytetrafluoroethylene substrate, but focuses on electrolyte material selection, and lacks attention to substrate selection and electrolyte surface appearance. Therefore, attempts to replace the liquid electrolyte of lithium ion batteries with other materials and to solve the problems of the prior art have not been substantially solved.

Disclosure of Invention

In order to solve the above problems, the present inventors have made many studies and designs to provide a method for preparing a polymer solid electrolyte for a lithium metal battery.

According to the technical scheme of the invention, the preparation method of the polymer solid electrolyte of the lithium metal battery comprises the following steps:

step S1, substrate preparation and precursor material preparation, which provides a substrate and precursor materials for the polymer solid electrolyte of the fabricated lithium metal battery;

and step S2, preparing a polymer solid electrolyte.

Wherein the substrate preparation in step S1 includes the steps of: taking a clean glass plate, and sticking the modified polytetrafluoroethylene sticker on the surface of the glass plate; and then sequentially adding acetone, absolute ethyl alcohol and deionized water, placing the mixture in an ultrasonic cleaning instrument for ultrasonic treatment for 3min to 30min to remove impurities on the surface of the substrate, taking out the substrate after all the impurities are removed, and placing the substrate in a nitrogen environment for drying to obtain the modified polytetrafluoroethylene substrate with a clean surface and no impurities.

Preferably, the modified polytetrafluoroethylene sticker is completely adhered to the surface of the glass plate. The ultrasonic treatment time is 8-20 min.

Preferably, a small amount of detergent, acetone, absolute ethyl alcohol and deionized water are adopted to ultrasonically clean the modified polytetrafluoroethylene sticker, and the modified polytetrafluoroethylene sticker has the function of removing oil stains, insoluble substances, impurities soluble in organic solvents and other pollutants or stubborn particles on the surface of the modified polytetrafluoroethylene sticker, so that a clean substrate can be obtained.

And additionally, sequentially adding acetone, absolute ethyl alcohol and deionized water, and completely immersing the surface of the modified polytetrafluoroethylene substrate in an ultrasonic cleaning instrument.

Further, the preparation of the early-stage material comprises the following steps: the mass ratio of polyvinylidene fluoride powder to lithium perchlorate is 3:1 weighing polyvinylidene fluoride powder and lithium perchlorate respectively, placing the polyvinylidene fluoride powder and the lithium perchlorate in different beakers, placing the beakers in a vacuum oven, and drying the beakers in vacuum for 10 to 48 hours (h) at the temperature of between 60 and 90 ℃ to prepare the organic solvent.

Preferably, the preparation of the polymer solid electrolyte of step S2 includes step S21, taking a 100ml clean beaker, adding a magnetic stirrer, adding N, N-dimethylformamide to the beaker, then adding dried polyvinylidene fluoride powder, and sealing the beaker with a flexible thermoplastic sealing film to avoid excessive evaporation of the solvent during dissolution.

Additionally, the preparation of the polymer solid electrolyte of the step S2 includes the step S22 of turning on a magnetic heating stirring table, adding 200ml of water into a 500ml beaker, placing the beaker on the stirring table to heat 200ml of water in the beaker, placing the beaker filled with N, N-dimethylformamide and polyvinylidene fluoride into the 500ml beaker when the temperature of the beaker rises to 50 ℃, starting heating and stirring for 2 hours to 6 hours until polyvinylidene fluoride powder is completely dissolved in the N, N-dimethylformamide solvent.

Further, the preparation of the polymer solid electrolyte of step S2 includes step S25, the solid electrolyte after knife coating is placed in a vacuum oven to be vacuum dried for 24h at 60 ℃, and the polymer electrolyte membrane is obtained.

Compared with the prior art, the preparation method of the polymer solid electrolyte of the lithium metal battery has the following technical advantages:

1. compared with the prior art, the invention can prepare the novel polymer solid electrolyte with a special surface structure and has the advantages of simple process flow, short time consumption, low cost, high quality and the like.

2. Compared with the prior art, the novel polymer solid electrolyte with a special surface structure can be prepared by adopting the method, the surface appearance is compact, the surface almost has no pores, and the electrochemical stability is obviously improved.

3. Compared with the prior art, the polymer solid electrolyte prepared by the method obviously improves the micro short circuit phenomenon of the battery caused by the penetration of local lithium dendrites in the battery charging process in the battery cycle, and improves the battery cycle stability.

Drawings

FIG. 1 is one of the scanning electron micrographs of a modified polytetrafluoroethylene substrate used in the invention;

FIG. 2 is a second scanning electron microscope image of a modified PTFE substrate used in the present invention;

FIG. 3 is a scanning electron microscope image of a polymer electrolyte obtained under a modified polytetrafluoroethylene substrate according to the invention;

FIG. 4 is a second scanning electron microscope image of the polymer electrolyte obtained under the modified PTFE substrate of the present invention;

fig. 5 is a schematic structural view of a lithium metal battery manufactured using the process of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

According to the preparation method of the polymer solid electrolyte of the lithium metal battery, the poly-modified tetrafluoroethylene is selected as the substrate, micron-sized attachment sites are provided for electrolyte forming when a solvent is volatilized, a sample is ensured to have a compact surface appearance, and the contact between the polymer solid electrolyte and an electrode material is facilitated. The preparation method of the polymer solid electrolyte of the lithium metal battery ensures that the solvent is continuously volatilized and separated out in the forming process of the electrolyte membrane, and simultaneously, the residual gas in the mixture is separated out to reduce the porosity of the electrolyte membrane in the final forming process.

According to the preparation method of the polymer solid electrolyte of the lithium metal battery, the lithium ion battery based on the solid electrolyte can reduce the using amount of the liquid electrolyte under the condition of not using a diaphragm, so that higher energy density of the battery is realized, and the safety and the service life of the battery are improved.

As shown in fig. 5, the lithium metal battery manufactured by using the polymer solid electrolyte of the present invention includes a negative electrode case, a lithium sheet, a polymer electrolyte, a positive electrode, and a positive electrode case, the negative electrode case, the lithium sheet, the polymer electrolyte, the positive electrode, and the positive electrode case are sequentially stacked together, the negative electrode case and the positive electrode case are both half-enclosed case-shaped structures, the negative electrode case covers the lithium sheet, the positive electrode case covers the positive electrode, the exposed lithium sheet corresponds to the exposed positive electrode, and the polymer electrolyte is disposed between the lithium sheet and the positive electrode. Further, a gap of 100nm to 500nm is formed between the positive electrode can and the negative electrode can. The lithium metal battery is a lithium ion battery, preferably a button battery or a soft package battery.

The function or use, or manufacturing material of each component in the lithium metal battery of the present invention is as follows:

the cathode shell is made of a CR2025 shell and is made of stainless steel;

the lithium sheet is used as the cathode of the lithium metal battery, and compared with a graphite material, the energy density of the battery is greatly improved;

the polymer electrolyte comprises the main components of polyvinylidene fluoride and lithium perchlorate, and lithium ions are transmitted between the anode material and the cathode material of the battery;

a positive electrode, which can be selected from lithium intercalation compounds and is used as a positive electrode of the lithium metal battery;

the positive electrode shell is made of a CR2025 shell and stainless steel.

The preparation method of the polymer solid electrolyte of the lithium metal battery comprises the following steps:

step S1, substrate preparation and precursor material preparation, which provides a substrate and precursor materials for the polymer solid electrolyte of the fabricated lithium metal battery.

The substrate preparation comprises the steps of: taking a clean glass plate, sticking a modified polytetrafluoroethylene sticker on the surface of the glass plate, preferably completely sticking the modified polytetrafluoroethylene sticker on the surface of the glass plate, sequentially adding acetone, absolute ethyl alcohol and deionized water, placing the glass plate in an ultrasonic cleaning instrument for ultrasonic treatment for 3min to 30min to remove impurities on the surface of the substrate, taking out the substrate after all the materials are finished, and placing the substrate in a nitrogen environment for drying to obtain the modified polytetrafluoroethylene substrate with a clean surface and no impurities. In the preferred embodiment, the ultrasound time is 8min-20 min. In another embodiment, the modified polytetrafluoroethylene sticker is ultrasonically cleaned by a small amount of detergent, acetone, absolute ethyl alcohol and deionized water, and the modified polytetrafluoroethylene sticker has the functions of removing oil stains, insoluble substances, impurities soluble in organic solvents and other pollutants or stubborn particles on the surface of the modified polytetrafluoroethylene sticker respectively, so that a clean substrate can be obtained.

The surface of the polytetrafluoroethylene is modified by a chemical treatment method, when corrosive liquid is contacted with the polytetrafluoroethylene, partial fluorine atoms on the surface of the polytetrafluoroethylene are removed, and polar groups such as a carbonized layer, C-O, COOH and the like are left on the surface, so that the surface energy of the material is increased, the wettability is improved, and the material is changed from difficult adhesion to adhesive adhesion.

And sequentially adding acetone, absolute ethyl alcohol and deionized water, and completely immersing the surface of the modified polytetrafluoroethylene substrate in an ultrasonic cleaning instrument.

Preferably placing the mixture in an ultrasonic cleaning instrument for ultrasonic treatment for 10min, wherein the time is too short, and the surface impurities are not completely removed; the modified polytetrafluoroethylene is easy to separate from the glass plate after the time is too long.

And (3) drying the mixture in a nitrogen environment at the temperature of between 20 and 35 ℃, preferably at 26 ℃.

The preparation of the early-stage material comprises the following steps:

the mass ratio of polyvinylidene fluoride powder to lithium perchlorate is 3:1 weighing polyvinylidene fluoride powder and lithium perchlorate respectively, placing the polyvinylidene fluoride powder and the lithium perchlorate in different beakers, placing the beakers in a vacuum oven, and drying the beakers in vacuum for 10 to 48 hours (h) at the temperature of between 60 and 90 ℃ to prepare the organic solvent. Preferably, the mixture is placed in a vacuum oven to be dried in vacuum for 24 hours at 80 ℃. The moisture impurities in the lithium metal battery can be removed through vacuum drying, so that the material is favorably dissolved in an organic solvent, and side reactions generated when the solid electrolyte is applied to the lithium metal battery are avoided.

Step S2, preparing a polymer solid electrolyte; which comprises the following steps:

and step S21, adding a magnetic stirrer into a 100ml clean beaker, adding N, N-dimethylformamide into the beaker, then adding dried polyvinylidene fluoride powder, and sealing the beaker by using a flexible thermoplastic sealing film so as to avoid excessive volatilization of the solvent in the dissolving process. The high-performance waterproof sealing film is preferred, in another embodiment, a parafilm sealing film is selected, and the parafilm sealing film seals the beaker to prevent the organic solvent from volatilizing in the magnetic heating and stirring process and prevent external moisture and impurities from being mixed into the raw materials.

Step S22, opening a magnetic heating stirring table, adding 200ml of water into a 500ml beaker, placing the beaker on the stirring table to heat 200ml of water in the beaker, placing the beaker filled with N, N-dimethylformamide and polyvinylidene fluoride into the 500ml beaker when the temperature of the beaker is raised to 50 ℃, starting to heat and stir for 2-6 hours, preferably 4 hours until polyvinylidene fluoride powder is completely dissolved in N, N-dimethylformamide solvent; after the polyvinylidene fluoride powder is completely dissolved in the N, N-dimethylformamide solvent, adding lithium perchlorate, keeping the temperature of 50 ℃ for constant heating and continuing stirring for 1 hour until the lithium perchlorate is completely dissolved; the constant temperature heating is preferably a water bath heating mode. The magnetic heating stirring is beneficial to fully dissolving the mixture, and the constant-temperature water bath heating keeps the constant temperature of the stirring process all the time after the preset temperature is reached, so that the solubility of the polyvinylidene fluoride and the lithium perchlorate in the organic solvent is improved.

Step S23, placing the completely dissolved mixture solution in a vacuum oven, standing for 15-50 min, preferably 30min, at 50 ℃ in vacuum, setting a vacuum condition to exhaust gas in the solution, wherein the time is too short, the gas is not sufficiently exhausted, and the time is too long, so that the solvent is easily volatilized too much, and the coating is not facilitated; the mixture solution is placed in a vacuum oven, which is helpful for discharging gas in the solution, and prevents the solid electrolyte membrane from generating bubbles during vacuum drying, so that the solid electrolyte membrane keeps uniform shape.

Step S24, uniformly coating the uniformly stirred mixture on the modified polytetrafluoroethylene substrate prepared in step S1 by using an automatic coating machine; coating at normal temperature (preferably 26 deg.C), and adjusting thickness of scraper to obtain polymer solid electrolyte membranes with thickness of 20-200 μm. Preferably, the height of the scraper is set to be 200 mu m, and the coating speed is 20 cm/min-100 cm/min; more preferably 30 cm/min. The film coating speed is not too fast, and the film coating speed is too fast, so that the solution is not favorably dispersed uniformly.

And step S25, drying the polymer solid electrolyte membrane in a vacuum oven at 60-100 ℃. The drawdown coated solid electrolyte is preferably placed in a vacuum oven to be dried in vacuum for 24h at 60 ℃ to obtain the polymer electrolyte membrane. Too high drying temperature, uneven solvent volatilization, poor electrolyte film forming effect, too short drying time and unfavorable complete solvent volatilization;

furthermore, in step S1 of the present invention, poly-modified tetrafluoroethylene is selected as the substrate, the surface of the modified polytetrafluoroethylene substrate has micron-sized columnar protrusions, which provide micron-sized attachment sites for electrolyte molding when the solvent is volatilized, so as to ensure that the sample has a dense surface morphology, which is beneficial for the contact between the polymer solid electrolyte and the electrode material.

Step S22 adopts a water bath heating mode, constant temperature water bath heating not only improves the solubility of polyvinylidene fluoride and lithium perchlorate in N, N-dimethylformamide solvent, but also avoids the excessive violence and temperature uncontrollable property caused by direct heating, can heat stably and accurately control the heating temperature, controls the mixture to be heated uniformly, and keeps the whole temperature uniform.

And step S23, placing the mixture in a vacuum oven to be kept still at 50 ℃ in vacuum, on one hand, keeping the temperature to ensure that the mixture does not generate phase transition when being kept still, and simultaneously providing a vacuum environment to discharge gas components dissolved in the mixture to avoid gas from being separated out to destroy the appearance of the electrolyte when the film is formed later.

And step S24, adjusting the final polymer electrolyte thickness by adjusting the height of the automatic film coating scraper. In step S25, the solid electrolyte after blade coating is placed in a vacuum oven and dried in vacuum at 60 ℃ for 24h, while a vacuum environment and a constant temperature of 60 ℃ are provided to ensure that the solvent is continuously volatilized and separated out during the formation of the electrolyte membrane, and the residual gas in the mixture is separated out to reduce the porosity of the electrolyte membrane during the final formation. The main factors influencing the film formation of the polymer solid electrolyte in the invention are substrate morphology, vacuum drying time and temperature, selection of solvent, proportion of each component and the like.

The preparation method has the advantages of simple preparation process, lower cost, more compact structure and wider application range after the modified polytetrafluoroethylene substrate is adopted, and has very important practical significance.

The preparation method of the polymer solid electrolyte of the lithium metal battery of the invention is explained below with reference to the accompanying drawings, fig. 1 and fig. 2 are scanning electron microscope images of the modified polytetrafluoroethylene substrate, as can be seen from fig. 1, the surface of the modified polytetrafluoroethylene substrate has micron-sized columnar protrusions with the uniform width of about 1-2 μm, and micron-sized attachment sites are provided for electrolyte molding when a solvent is volatilized; as can be seen from fig. 2, the micro-scale protrusions are uniformly and densely distributed on the surface of the substrate, i.e., the entire surface of the substrate has uniform and dense attachment sites for the electrolyte membrane.

Fig. 3 and 4 are scanning electron microscope images of polymer electrolytes obtained under a modified polytetrafluoroethylene substrate, and as can be seen from fig. 3, the polymer electrolytes are aggregated according to attachment sites to form a compact and compact surface morphology, and no micron-sized pores or granular accumulation exists after the modified polytetrafluoroethylene substrate is used, which is significantly different from the morphology of a conventional polymer electrolyte membrane; as can be seen from FIG. 4, the polymer electrolyte membrane exhibits uniform surface morphology in a large range, is dense on the surface and has few pores, and forms a polymer matrix network around the attachment sites, thereby facilitating polymer segment movement and lithium ion transmission.

The details of the method for preparing the polymer solid electrolyte for a lithium metal battery according to the present invention are given below:

step W1, use of Pre-polyvinylidene fluoride (PVDF) and lithium perchlorate (LiClO)₄) Vacuum drying at 80 deg.C for 24 hr to remove water;

step W2, dissolving polyvinylidene fluoride (PVDF) in N, N-Dimethylformamide (DMF) according to the mass ratio of 3 parts of polyvinylidene fluoride (PVDF) to 26 parts of N, N-Dimethylformamide (DMF), adding DMF into a 100ml clean beaker, adding a magnetic stirrer, then adding dried polyvinylidene fluoride powder, and sealing the beaker by taking a parafilm sealer;

step W3, opening a magnetic heating stirring table, adding 200ml of water into a 500ml beaker, and heating the beaker on the stirring table; when the water temperature rises to 50 ℃, putting the beaker filled with DMF and PVDF into a 500ml beaker, starting heating and stirring, and keeping the heating and stirring conditions at 50 ℃ until the PVDF is completely dissolved in the DMF solvent;

step W4, LiClO is added according to the mass ratio₄With PVDF LiClO₄Add to beaker solution at 3:1 mass ratio and continue stirring for 1 hour until LiClO₄Completely dissolving;

step W5, placing the uniformly dissolved solution in a vacuum oven heated to 50 ℃, standing for 30 minutes in a constant temperature and vacuum manner, and taking out;

step W6, after standing, uniformly coating the uniformly stirred mixture on a modified polytetrafluoroethylene plate by using an automatic film coating machine and a scraper at normal temperature;

step W7, the electrolyte solution was further vacuum-dried in a vacuum oven at 60 ℃ for 24 hours to remove the DMF solvent, yielding a polymer electrolyte membrane.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

1. A method for preparing a polymer solid electrolyte of a lithium metal battery is characterized by comprising the following steps:

and step S2, preparing a polymer solid electrolyte.

2. The method for preparing a polymer solid electrolyte for a lithium metal battery according to claim 1, wherein the substrate preparation in step S1 comprises the steps of: and (3) taking a clean glass plate, and sticking the modified polytetrafluoroethylene sticker on the surface of the glass plate.

3. The method for preparing a polymer solid electrolyte of a lithium metal battery according to claim 2, wherein the modified polytetrafluoroethylene sticker is completely attached to the surface of a glass plate, then acetone, absolute ethyl alcohol and deionized water are sequentially added, the mixture is placed in an ultrasonic cleaning instrument for 3min to 30min by ultrasound to remove impurities on the surface of the substrate, and after all the impurities are removed, the substrate is taken out and placed in a nitrogen environment for drying, so that the modified polytetrafluoroethylene substrate with a clean surface and no impurities is obtained.

4. The method for preparing a polymer solid electrolyte for a lithium metal battery according to claim 2, wherein the ultrasonic time is 8min to 20 min.

5. The method for preparing the polymer solid electrolyte of the lithium metal battery according to claim 2, wherein the modified polytetrafluoroethylene sticker is ultrasonically cleaned by a small amount of detergent, acetone, absolute ethyl alcohol and deionized water, and the method has the function of removing oil stains, insoluble substances, impurities soluble in organic solvents and other pollutants or stubborn particles on the surface of the modified polytetrafluoroethylene sticker, and is beneficial to obtaining a clean substrate.

6. The method of claim 2, wherein acetone, absolute ethyl alcohol and deionized water are sequentially added to completely immerse the surface of the modified polytetrafluoroethylene substrate in an ultrasonic cleaning apparatus.

7. The method for preparing a polymer solid electrolyte for a lithium metal battery according to claim 2, wherein the preliminary material preparation comprises the steps of: the mass ratio of polyvinylidene fluoride powder to lithium perchlorate is 3:1 weighing polyvinylidene fluoride powder and lithium perchlorate respectively, placing the polyvinylidene fluoride powder and the lithium perchlorate in different beakers, placing the beakers in a vacuum oven, and drying the beakers in vacuum for 10 to 48 hours (h) at the temperature of between 60 and 90 ℃ to prepare the organic solvent.

8. The method of claim 2, wherein the step S2 of preparing the polymer solid electrolyte comprises the steps S21 of taking a 100ml clean beaker, adding a magnetic stirrer, adding N, N-dimethylformamide into the beaker, adding dried polyvinylidene fluoride powder, and sealing the beaker with a flexible thermoplastic sealing film to avoid excessive evaporation of the solvent during the dissolution process.

9. The method of claim 2, wherein the step S2 of preparing the polymer solid electrolyte comprises the step S22 of turning on a magnetically heated stirring table, adding 200ml of water into a 500ml beaker, placing the beaker on the stirring table to heat 200ml of water in the beaker, placing the beaker filled with N, N-dimethylformamide and polyvinylidene fluoride into the 500ml beaker after the temperature of the beaker water rises to 50 ℃, and starting heating and stirring for 2-6 hours until polyvinylidene fluoride powder is completely dissolved in the N, N-dimethylformamide solvent.

10. The method of claim 2, wherein the step S2 of preparing the polymer solid electrolyte comprises a step S25 of vacuum drying the solid electrolyte in a vacuum oven at 60 ℃ for 24h to obtain the polymer electrolyte membrane.