Reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators

Abstract

The present application provides a reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators. The polymer-based all-solid-state battery electrode includes at least an electrode active material, a conductive additive, a stationary phase polymer, a mobile phase polymer, and an electrolyte salt. The present application can reduce the diffusion distance of the polymer electrolyte phase in the polymer solid-state battery and eliminate the diffusion dead zone caused by the non-through-hole structure through the activated mode of reverse diffusion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and relates to a reverse diffusion polymer-based all-solid-state battery electrode compatible with a lithium ion battery separator and application of the reverse diffusion polymer-based all-solid-state battery electrode in an all-solid-state battery. BACKGROUND

[0002] With the rapid development of portable electronic devices and electric vehicles in recent years, the performance and safety of power supplies are increasingly required. Today's commercial lithium ion batteries are widely used as power supplies for small electronic devices such as notebook computers and mobile phones, and large devices such as hybrid electric vehicles and pure electric vehicles. Since the commercialization of lithium ion batteries, they have developed rapidly. Due to their high energy density, long cycle life, no memory effect and other characteristics, they have rapidly occupied the markets of portable electronic devices, electric vehicles and the like. Traditional commercial lithium ion batteries use organic liquid electrolytes, which pose a potential safety hazard to the batteries. Compared with traditional lithium ion batteries, solid-state batteries have higher theoretical energy density, longer cycle life and higher safety, which has attracted great attention to solid-state batteries.

[0003] Although solid-state batteries have many advantages, there are still many problems to be solved, such as poor solid-solid interface contact. This leads to an increase in the interface resistance between the battery and the electrode. The performance of the solid-state battery cannot be optimized. However, current commercial lithium ion batteries mainly use liquid electrolytes. These liquid electrolytes based on flammable organic solvents still pose a certain safety risk. Therefore, reducing the content of organic liquid electrolytes in the battery and improving the safety performance, and developing solid-state batteries based on solid-state electrolytes, have become the focus of current lithium secondary battery research and development.

[0004] Solid-state batteries can be mainly classified into oxide electrolytes, sulfide electrolytes, polymer electrolytes, composite electrolytes and other solid-state electrolytes according to the type of solid-state electrolyte. Among them, polymer-based solid-state batteries have been successfully commercialized by some companies due to the similarity of the properties of the polymer electrolyte used to the liquid electrolyte. SUMMARY

[0005] The application proposes a new technical route, which realizes the compatibility of the polymer-based all-solid-state battery assembly process with the current commercial lithium ion battery production process by developing a reverse diffusion polymer-based all-solid-state battery electrode compatible with a lithium ion battery separator.

[0006] A reverse diffusion polymer-based all-solid-state battery electrode includes an electrode active material, a conductive additive, a stationary phase polymer, a mobile phase polymer and an electrolyte salt.

[0007] Compared with the prior art, the application has at least the following beneficial effects:

[0008] The present application provides a reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators. Its technical advantages are: (1) compatible with current lithium-ion battery assembly process; (2) through the reverse diffusion activation mode, it can shorten the diffusion distance of the polymer electrolyte phase in the polymer-based solid-state battery and eliminate the diffusion dead zone caused by the non-through hole structure. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 Schematic diagram of the assembly method of a conventional polymer-based all-solid-state battery.

[0010] Figure 2 Schematic diagram of the assembly process of the reverse diffusion polymer-based all-solid-state battery electrode of the present application.

[0011] Figure 3 Advantage comparison of the reverse diffusion method of the present application and the conventional method.

[0012] Figure 4 Impedance change of the reverse diffusion polymer-based all-solid-state battery activation process in Example 1 of the present application. DETAILED DESCRIPTION

[0013] As Figure 1 shown, the conventional means of the preparation process of the current polymer-based all-solid-state battery can generally be summarized into two ways: (1) prepare an independent self-supporting polymer-based all-solid-state electrolyte film, then assemble it with a porous coated electrode stack to form a battery, and then diffuse the polymer electrolyte into the porous structure of the coated electrode at high temperature; (2) coat the electrode material on the surface of the current collector, then cover the polymer-based electrolyte film on the electrode surface by means of immersion or coating of solution and colloid, in-situ polymerization of monomer precursor, etc., stack the electrode sheet with the polymerized solid-state electrolyte layer on the surface with the electrode sheet or metal negative electrode on the other side to form a battery.

[0014] However, both of these two ways still have their shortcomings to be solved: (1) In order to improve the weight energy density and volume energy density of the battery, it is necessary to limit the thickness of the polymer-based all-solid-state electrolyte film layer to be within 20 microns or even 10 microns, but the polymer-based all-solid-state electrolyte film is generally limited by mechanical strength, so it is difficult to guarantee the independent self-supporting structure under the thinned thickness; (2) The way of introducing the polymer-based all-solid-state electrolyte film layer by immersing or coating the solution and colloid directly on the surface of the coated porous electrode, in-situ polymerization of monomer precursor, etc. generally involves more complex operation steps and / or introduces more complex chemical systems compared with the current commercial lithium ion battery process, which requires corresponding modification of the current commercial lithium ion battery production process. At the same time, both of these two modes involve the post-diffusion of the polymer electrolyte in the coated porous electrode, and this diffusion has poor diffusion ability effect on the coated electrode with thick thickness, and cannot enter the non-through-hole gap structure in the porous electrode. Therefore, it is of great significance to develop a polymer-based all-solid-state battery electrode compatible with the current commercial lithium ion battery separator to simplify the assembly process of the polymer-based all-solid-state battery.

[0015] To at least solve one of the problems in the prior art, embodiments of the present application provide a reverse diffusion polymer-based all-solid-state battery electrode, which at least includes an electrode active material, a conductive additive, a stationary phase polymer, a mobile phase polymer with a melting point above 35 degrees Celsius and below 100 degrees Celsius, and an electrolyte salt.

[0016] In some embodiments, the electrode active material includes commonly used lithium ion positive electrode materials and lithium ion negative electrode materials in the art.

[0017] In some embodiments, the lithium ion positive electrode material is selected from at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium manganate, and lithium nickel manganate; and the lithium ion negative electrode material is selected from at least one of graphite, silicon-carbon composite material, pure silicon negative electrode, and lithium titanate.

[0018] In some embodiments, the conductive additive includes commonly used conductive additives for lithium ion batteries and polymer-based solid-state batteries. The conductive additive includes but is not limited to carbon-based additives, conductive polymers, and metal powder or metal fiber conductors.

[0019] In some embodiments, the carbon-based additive is selected from carbon black, carbon nanotubes, or graphene.

[0020] In some embodiments, the conductive additive is acetylene black.

[0021] In some embodiments, the stationary phase polymer has a melting point greater than 150 degrees Celsius and not higher than 200 degrees Celsius, preferably at least one of modified vinyl chloride, grafted or modified polypropylene, block copolymer polyvinylidene fluoride (Kynar®), oligomeric nylon, polyoxymethylene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate.

[0022] In some embodiments, the modified polypropylene is made by grafting maleic anhydride onto polypropylene (powder) surface, which can be done by conventional methods in the art. In some embodiments, the mobile phase polymer has a melting point above 35 degrees Celsius and below 100 degrees Celsius and is capable of dissolving electrolyte lithium salt; the mobile phase polymer is preferably at least one of polyethylene oxide, polypropylene oxide and block, grafted, modified polymers thereof.

[0023] In some embodiments, the electrolyte salt is a commonly used lithium salt for lithium ion battery polymer electrolytes, preferably at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis-trifluoromethylsulfonylimide.

[0024] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode can further comprise any one or more electrode additives or electrolyte additives known and commonly used in the field of lithium ion battery research for polymer-based solid-state batteries, such as structural reinforcement additives, flame retardant additives, gas generation prevention additives, lithium supplement additives, interface protection film-forming additives, etc.

[0025] In some embodiments, the electrode additives or electrolyte additives include, but are not limited to, structural reinforcement additives such as glass fiber, flame retardant additives, gas generation prevention additives, lithium supplement additives, interface protection film-forming additives, etc., which are known or commonly used in the art.

[0026] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode is a self-supporting independent thin film or sheet structure.

[0027] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode is a structure that is entirely coated on a metal foil current collector.

[0028] The metal foil current collector is commonly used in the field of lithium ion batteries, including copper foil, aluminum foil, and polymer film plated with metal on the surface.

[0029] In some embodiments, the mass ratio of electrode active material, conductive additive, stationary phase polymer, mobile phase polymer, electrolyte salt is (85-92):(2-8):(4-8):(25-65):(1-5), which can be optionally (86-90):(3-7):(5-7):(30-60):(2-4).

[0030] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode comprises lithium iron phosphate, acetylene black, polymethyl methacrylate, polyethylene oxide, and lithium bis-trifluoromethanesulfonimide in a mass ratio of 90:5:5:30:2. The electrode can be coated on a battery-grade aluminum foil.

[0031] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode comprises lithium titanate, acetylene black, polyvinylidene fluoride, polyethylene oxide, and lithium bis-trifluoromethanesulfonimide in a mass ratio of 86:7:7:30:2. The electrode can be coated on a battery-grade aluminum foil.

[0032] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode comprises lithium titanate, acetylene black, modified polypropylene, polyethylene oxide, and lithium bis-trifluoromethanesulfonimide in a mass ratio of 90:3:7:60:4; wherein the modified polypropylene can be prepared by surface grafting maleic anhydride on polypropylene (powder). The reverse diffusion polymer-based all-solid-state battery electrode can be a self-supporting independent thin film or sheet structure.

[0033] In some embodiments, the reverse diffusion polymer-based all-solid-state battery electrode is compatible with lithium ion battery separators.

[0034] The present disclosure also provides a method for preparing the reverse diffusion polymer-based all-solid-state battery electrode described above, which can be prepared by a coating method or a hot extrusion method.

[0035] In some embodiments, the coating method is a high-temperature casting film formation.

[0036] In some embodiments, the coating method comprises:

[0037] The raw materials of the reverse diffusion polymer-based all-solid-state battery electrode are prepared into a solid-phase mixture.

[0038] The solid-phase mixture is coated to form a self-supporting independent thin film or sheet structure; or the solid-phase mixture is coated on a metal foil current collector.

[0039] In some embodiments, the solid-phase mixture is added to a high-temperature casting die, and coating is performed on a conventional current collector of a lithium ion battery.

[0040] In some embodiments, the temperature of the high-temperature casting die needs to be warmed to above the melting point of the fixed-phase polymer and within 200 degrees Celsius.

[0041] In some embodiments, the hot extrusion method comprises: preparing the raw materials of the reverse diffusion polymer-based all-solid-state battery electrode into a solid-phase mixture; and adding the solid-phase mixture to a single-screw extruder or a twin-screw extruder for extrusion; wherein the single-zone extruder extrusion temperature is higher than the melting point of the fixed-phase polymer and lower than 200 degrees Celsius.

[0042] In some embodiments, the hot extrusion method comprises: directly adding raw materials (electrode active material, conductive additive, stationary phase polymer, mobile phase polymer, and electrolyte salt, etc.) of the reverse diffusion polymer-based all-solid-state battery electrode into a twin-screw extruder for mixing extrusion; wherein the twin-screw extrusion is heated at least in three temperature zones, the temperature of the first temperature zone is higher than the melting point of the mobile phase polymer and lower than the melting point of the stationary phase polymer, the temperature of the middle temperature zone is higher than the melting point of the stationary phase polymer and lower than 200 degrees Celsius, and the temperature of the final temperature zone is higher than the melting point of the mobile phase polymer and lower than the melting point of the stationary phase polymer.

[0043] In some embodiments, the method for preparing the solid phase mixture comprises: dissolving the raw materials (electrode active material, conductive additive, stationary phase polymer, mobile phase polymer, and electrolyte salt, etc.) of the reverse diffusion polymer-based all-solid-state battery electrode with a solvent, mixing uniformly, and drying. The solvent can be selected from acetonitrile, acetone, or a mixture of the two. For example, a mixed solvent of acetonitrile and acetone with a volume ratio of 50%:50% is selected.

[0044] In some embodiments, the method for preparing the solid phase mixture comprises: solvent-free mixing of the raw materials (electrode active material, conductive additive, stationary phase polymer, mobile phase polymer, and electrolyte salt, etc.) of the reverse diffusion polymer-based all-solid-state battery electrode under melting, which can be specifically carried out by using a shearing force device (such as an internal mixer and a mixing mill, etc.).

[0045] The embodiments of the present application also provide the use of the above-mentioned reverse diffusion polymer-based all-solid-state battery electrode in the preparation of an all-solid-state battery.

[0046] The embodiments of the present application also provide an all-solid-state battery, which uses the above-mentioned reverse diffusion polymer-based all-solid-state battery electrode at least in one of the positive electrode or the negative electrode, and is assembled using a (conventional commercial) lithium ion battery separator material.

[0047] The above-mentioned all-solid-state battery is activated under heating and optional hot pressing conditions before use.

[0048] The assembly process diagram of the reverse diffusion polymer-based all-solid-state battery electrode of the embodiments of the present application is shown in Figure 2 When stacked or wound with a commonly used separator of a lithium ion battery to assemble a battery, the polymer electrolyte can be activated by hot melting diffusion under a temperature condition of not higher than 100 degrees Celsius and optionally with an increased axial pressure mode. The activation time is not more than 24 hours, and is preferably not more than 12 hours.

[0049] The advantages of the reverse diffusion method of the present application compared with the traditional method can be seen from Figure 3Compared with the prior art, the reverse diffusion polymer-based all-solid-state battery electrode has the following advantages: (1) compatible with current lithium-ion battery assembly process; and (2) through the activation mode of reverse diffusion, the diffusion distance of the polymer electrolyte phase in the polymer-based solid-state battery can be shortened and the diffusion dead zone caused by the non-through-hole structure can be eliminated.

[0050] The following examples are used to illustrate the present application, but not to limit the scope of the present application. If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased through a regular channel.

[0051] Example 1

[0052] This example uses a coating method to prepare a reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators. The preparation steps are as follows: first, take electrode active material lithium iron phosphate, conductive additive acetylene black, polymethyl methacrylate, polyethylene oxide and electrolyte salt lithium bis-trifluoromethylsulfonylimide in a mass ratio of 90:5:5:30:2. Dissolve polymethyl methacrylate, polyethylene oxide and electrolyte salt lithium bis-trifluoromethylsulfonylimide in a mixed solvent of acetonitrile and acetone in a volume ratio of 50:50, then add lithium iron phosphate and conductive additive acetylene black, heat and stir, then evaporate and recover the mixed solvent of acetonitrile and acetone using a three-necked flask and a water cooling device to obtain a solid mixture. Then continue to dry the solid mixture in a vacuum oven at 80 degrees Celsius. Then add the dried solid mixture to a casting hot coating device to coat the electrode on a battery-grade aluminum foil at 160 degrees Celsius.

[0053] After the obtained electrode slice is flattened using a flat plate hot press, it is stacked with commercial lithium-ion battery separators and metal lithium in sequence and packaged using a button cell, and a polymer-based all-solid-state battery is obtained. Then, the packaged button polymer-based all-solid-state battery is placed in a general oven and heated to 110 degrees Celsius, so that the liquefied and flowing polyethylene oxide and lithium bis-trifluoromethylsulfonylimide in the polymer-based all-solid-state battery electrode are filled into the commercial lithium-ion battery separator and contacted with the negative electrode due to capillary action. This process can be monitored by in-situ electrochemical impedance spectroscopy. As shown in Figure 4 As the reverse diffusion of polyethylene oxide and lithium bis-trifluoromethylsulfonylimide electrolyte, the battery impedance gradually decreases during the activation process, and finally reaches a stable state after 20 hours, which proves that the all-solid-state battery has been activated.

[0054] Example 2

[0055] This example uses a coating method to prepare a reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators. The preparation steps are as follows: First, the electrode active material lithium titanate, conductive additive acetylene black, polyvinylidene fluoride, polyethylene oxide, and electrolyte salt lithium bis-trifluoromethanesulfonimide are weighed in a mass ratio of 86:7:7:30:2, respectively. Then, polymethyl methacrylate, polyethylene oxide, and electrolyte salt lithium bis-trifluoromethanesulfonimide are dissolved in acetonitrile solvent, and then lithium titanate and conductive additive acetylene black are added. After heating and stirring, the acetonitrile solvent is recovered by evaporation using a three-necked flask and a water cooling device to obtain a solid mixture. Then, the solid mixture is dried in a vacuum oven at 80 degrees Celsius. Then, the dried solid mixture is added to a casting hot coating device to coat the electrode on a battery-grade aluminum foil at 180 degrees Celsius.

[0056] Example 3

[0057] This example uses a hot extrusion method to prepare a reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators. First, a modified polypropylene is obtained by grafting maleic anhydride onto the surface of polypropylene powder using a method commonly used in the field. Then, the electrode active material lithium titanate, conductive additive acetylene black, modified polypropylene, polyethylene oxide, and electrolyte salt lithium bis-trifluoromethanesulfonimide are weighed in a mass ratio of 90:3:7:60:4, respectively. Then, polyethylene oxide is placed in a beaker and heated to 120 degrees Celsius, then lithium bis-trifluoromethanesulfonimide is added, stirred and dissolved, then lithium titanate and acetylene black are added and stirred uniformly using a shearing device, then the modified polypropylene is added and heated to 180 degrees Celsius for mixing, and finally the obtained mixture is cooled to room temperature. Then, the mixture is cut and added to a single screw extruder, with the extrusion temperature set to 200 degrees Celsius and the extrusion shape set to a rectangle with a thickness of 200 microns. After extrusion, a self-supporting polymer-based all-solid-state battery electrode thick film is obtained. Then, a hot calender is used to calender the electrode thick film to about 150 microns.

[0058] Example 4

[0059] A reverse diffusion polymer-based all-solid-state battery electrode compatible with lithium-ion battery separators is prepared using a hot extrusion method similar to Example 3. The difference is that after obtaining the mixture of electrode active material lithium titanate, conductive additive acetylene black, modified polypropylene, polyethylene oxide, and electrolyte salt lithium bis-trifluoromethanesulfonimide cooled to room temperature, a three-zone twin-screw extruder is used for extrusion. The mixture is cut and added to the barrel of the twin-screw extruder, with the extrusion temperature set to 150, 200, and 180 degrees Celsius in three zones, and the extrusion shape set to a rectangle with a thickness of 200 microns. After extrusion, a self-supporting polymer-based all-solid-state battery electrode thick film is obtained. Then, a hot calender is used to calender the electrode thick film to about 150 microns.

[0060] While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various modifications or changes can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that all such modifications and changes be included within the scope of the application as claimed.

Claims

1. A reverse diffusion polymer-based all-solid-state battery electrode, characterized by, The electrode active material, the conductive additive, the stationary phase polymer, the mobile phase polymer, and the electrolyte salt; The stationary phase polymer has a melting point greater than 150 degrees Celsius and not higher than 200 degrees Celsius; The mobile phase polymer has a melting point greater than 35 degrees Celsius and not higher than 100 degrees Celsius, and is capable of dissolving the electrolyte lithium salt; The mass ratio of the electrode active material, the conductive additive, the stationary phase polymer, the mobile phase polymer, and the electrolyte salt is (85-92):(2-8):(4-8):(25-65):(1-5); The electrode is used to assemble a battery with a porous lithium ion battery separator. Under heating conditions, the mobile phase polymer and the electrolyte salt are back-diffused from the electrode and filled into the pores of the lithium ion battery separator, thereby forming ion transmission channels to complete the activation of the battery. The electrode active material includes lithium ion positive electrode material and lithium ion negative electrode material. The conductive additive includes carbon-based additive, conductive polymer, and metal powder or metal fiber conductor. The stationary phase polymer is at least one of oligomeric nylon, polyformaldehyde, acrylonitrile-butadiene-styrene copolymer, and polymethyl methacrylate. The mobile phase polymer is at least one of polyethylene oxide and polypropylene oxide. The electrolyte salt is at least one of lithium hexafluorophosphate, lithium perchlorate, and lithium bis-trifluoromethylsulfonylimide.

2. The reverse diffusion polymer-based all-solid-state battery electrode of claim 1, wherein, The back-diffusion polymer-based all-solid-state battery electrode further comprises one or more electrode additives or electrolyte additives.

3. The reverse diffusion polymer-based all-solid-state battery electrode of claim 1, wherein, The back-diffusion polymer-based all-solid-state battery electrode is a self-supporting independent thin film or sheet structure; or the back-diffusion polymer-based all-solid-state battery electrode is a structure of being integrally coated on a metal foil current collector.

4. The reverse diffusion polymer-based all-solid-state battery electrode of claim 3, wherein, The metal foil current collector is selected from copper foil, aluminum foil, and polymer film plated with metal on the surface.

5. The reverse diffusion polymer-based all-solid-state battery electrode according to any one of claims 1 to 4, characterized in that, The mass ratio of the electrode active material, the conductive additive, the stationary phase polymer, the mobile phase polymer, and the electrolyte salt is (86-90):(3-7):(5-7):(30-60):(2-4).

6. The method of producing a reverse diffusion polymer-based all-solid-state battery electrode according to any one of claims 1 to 5, characterized by, The back-diffusion polymer-based all-solid-state battery electrode is prepared by a coating method, and the coating method comprises: The raw materials of the back-diffusion polymer-based all-solid-state battery electrode are made into a solid-phase mixture; The solid-phase mixture is coated to form a self-supporting independent thin film or sheet structure; or the solid-phase mixture is coated on a metal foil current collector.

7. The method of producing a reverse diffusion polymer-based all-solid-state battery electrode according to any one of claims 1 to 5, characterized by, The back-diffusion polymer-based all-solid-state battery electrode is prepared by a hot extrusion method, and the hot extrusion method comprises: the raw materials of the back-diffusion polymer-based all-solid-state battery electrode are made into a solid-phase mixture; the solid-phase mixture is added to a single-screw extruder or a twin-screw extruder for extrusion; wherein the single-temperature-zone extruder has an extrusion temperature higher than the melting point of the stationary phase polymer and lower than 200 degrees Celsius; Or the hot extrusion method comprises: the raw materials of the back-diffusion polymer-based all-solid-state battery electrode are directly added to a twin-screw extruder for mixing extrusion; wherein the twin-screw extrusion is heated in at least three temperature zones, the first temperature zone has a temperature higher than the melting point of the mobile phase polymer and lower than the melting point of the stationary phase polymer, the middle temperature zone has a temperature higher than the melting point of the stationary phase polymer and lower than 200 degrees Celsius, and the final temperature zone has a temperature higher than the melting point of the mobile phase polymer and lower than the melting point of the stationary phase polymer.

8. Use of the reverse diffusion polymer-based all-solid-state battery electrode according to any one of claims 1 to 5 for the production of an all-solid-state battery.

9. An all-solid battery, characterized by, The all-solid-state battery uses the reverse diffusion polymer-based all-solid-state battery electrode according to any one of claims 1 to 5 at least in one of the positive electrode or the negative electrode.

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