Solid-state electrolyte diaphragm with conductive gluing layer and preparation method and application of solid-state electrolyte diaphragm

Abstract

The invention discloses a solid electrolyte diaphragm with a conductive gluing layer and a preparation method and application of the solid electrolyte diaphragm. The solid electrolyte membrane comprises a base membrane; one side or two sides of the base membrane is / are coated with a solid electrolyte coating, and the base membrane or the solid electrolyte coating is / are coated with a conductive gluing layer. According to the solid-state electrolyte membrane with the conductive gluing layer, the base membrane is coated with the solid-state electrolyte layer, and compared with traditional materials such as aluminum oxide, the solid-state electrolyte material has an ion conduction effect, so that the conductivity of the membrane is improved. According to the invention, the conductive polymer microspheres are used as a gluing main material, so that the obstruction of LATP in-situ curing of the coating can be effectively avoided. By adopting the composite solid electrolyte diaphragm, the electrical performance of the battery can be effectively improved, and meanwhile, the safety performance of the battery is effectively improved.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte separator with a conductive coating layer, a preparation method and an application thereof, belonging to the field of lithium ion batteries. Background Art

[0002] At present, the lithium ion battery separators widely used are coating separators with a polyolefin porous membrane as the base membrane and an inactive ceramic particle (aluminum oxide, boehmite, etc.) coating on the surface. However, as an inactive substance, the conventional ceramic material reduces the energy density of the battery. At the same time, alumina does not have the ability to conduct lithium. Coated on the membrane surface, it increases the transmission distance of lithium ions and improves the internal resistance of the battery.

[0003] Using a solid electrolyte ceramic material to replace traditional materials such as alumina and coating it on the surface of the base membrane can improve the heat resistance, safety, thermal stability and mechanical strength of the membrane. At the same time, the solid electrolyte material can also play a role in transmitting lithium ions and reduce the internal resistance of the battery. Meanwhile, NASICON-type solid electrolyte material lithium titanium aluminum phosphate (LATP) can form a film in-situ at the low potential of the negative electrode, reduce the content of liquid electrolyte in the battery, protect the negative electrode SEI film, and improve the safety performance of the battery. However, the current common coating methods (oil-based, water-based, PVDF, PMMA, etc.) all have a great hindrance to the in-situ curing of LATP. Therefore, it is necessary to provide a coating solid electrolyte separator that does not hinder the in-situ curing effect of LATP. Summary of the Invention

[0004] The purpose of the present invention is to provide a solid electrolyte separator with a conductive coating layer, which not only has the characteristics of a conventional solid electrolyte separator, but also has a coating layer, and can provide an adhesion effect with the electrode sheet through hot pressing during the battery assembly process.

[0005] The coating layer in the solid electrolyte separator of the present invention has conductivity and does not affect the in-situ curing reaction of the solid electrolyte. It can be used in liquid, semi-solid, quasi-solid and metal lithium batteries, etc. Its preparation method is simple and environmentally friendly, and is suitable for large-scale production.

[0006] The present invention first provides a conductive coating layer, which is made of conductive polymer microspheres; The conductive polymer microspheres are polymer-metal composite conductive microspheres or modified intrinsic conductive polymer microspheres.

[0007] The polymer-metal composite conductive microspheres are polystyrene / copper composite microspheres, and the particle size is 0.1~5um; The modified intrinsic conductive polymer microspheres are modified polyaniline microspheres, such as sulfonated polyaniline microspheres, and the particle size is 0.1~5um.

[0008] The preparation method of the polystyrene / copper composite microspheres is as follows: monodisperse polystyrene (PS) microsphere templates are prepared by microemulsion polymerization, and a metal copper layer is coated on the surface of the PS by electroless copper plating to form core-shell structured composite conductive microspheres.

[0009] The modified polyaniline microspheres are synthesized by interfacial polymerization, and -SO3H groups are introduced through sulfonation reaction for chemical modification to improve conductivity and dispersion stability.

[0010] Based on the conductive coating layer, the present invention also provides a solid electrolyte separator with a conductive coating layer, including a base film; wherein, one side or both sides of the base film are coated with a solid electrolyte coating layer, and the conductive coating layer is coated on the base film or the solid electrolyte coating layer.

[0011] The solid electrolyte coating layer can be coated on one side or both sides according to the design requirements of lithium-ion batteries.

[0012] The separator of the present invention not only has the characteristics of a conventional solid electrolyte separator, but also solves the problem of the hindrance of traditional coatings to the in-situ curing of LATP, improving the electrical performance and safety performance of the battery.

[0013] In particular, since the in-situ curing reaction of the solid electrolyte only occurs at a low potential on the negative electrode side, to reduce costs, the conductive coating layer can be only coated on the surface of the solid electrolyte coating layer on the negative electrode side, and a conventional coating layer can be used on the positive electrode side.

[0014] In particular, if the solid electrolyte coating layer is coated on one side, when the lithium-ion battery is wound or laminated, the solid electrolyte layer needs to face the negative electrode side of the lithium-ion battery to better exert the effect of the solid electrolyte coating layer.

[0015] In the solid electrolyte separator of the present invention, the solid electrolyte used in the solid electrolyte coating layer is a NASCION-type solid electrolyte material, preferably a lithium aluminum titanium phosphate particle coating, where the chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 2x (PO4)3, where x is a number between 0.01 and 0.5, the particle size is 200 nm to 5 μm, and the shape is an irregular polygon; The thickness of the solid electrolyte coating layer is 1 to 5 μm.

[0016] In the solid electrolyte separator of the present invention, the thickness of the conductive coating layer is 1 to 10 μm, and the surface density is 0.1 to 3 g / m 2 。

[0017] In the solid electrolyte separator of the present invention, the base film is a PP film, a PE film, a PET film, a PI film or an aramid film, and the thickness is 5 to 30 μm.

[0018] The present invention also provides a method for preparing the solid electrolyte diaphragm, which comprises the following steps: S1. Coating a solid electrolyte coating slurry containing a solid electrolyte on the surface of the base film and drying to obtain the solid electrolyte coating; S2. Coating a conductive adhesive layer slurry containing conductive polymer microspheres on the surface of the solid electrolyte coating or the base film and drying to obtain the conductive adhesive layer; The mass composition of the solid electrolyte coating slurry is: solid electrolyte: binder: dispersant: wetting agent = 92-99.97%: 0.01-3%: 0.01-3%: 0.01-2%, and the solid content of the slurry is 20-40%; The mass composition of the conductive adhesive coating slurry is: conductive polymer microspheres: binder: dispersant = 94-99.98%: 0.01-3%: 0.01-3%, and the solid content of the slurry is 3-20%; Wherein, the binder can be one or a combination of styrene-butadiene rubber, polyvinylpyrrolidone, acrylate or polyvinyl alcohol; The dispersant can be one or a combination of sodium dodecylbenzenesulfonate, polyacrylate or a copolymer containing a pigment affinity group structure.

[0019] The wetting agent can be a polyether silicone copolymer.

[0020] The method for preparing the solid electrolyte coating slurry comprises the following steps: Stirring and dispersing the solid electrolyte, the dispersant and water for 1-3 h to obtain a dispersion; then adding the binder and the wetting agent to the dispersion and stirring and dispersing for 0.5-2 h, and filtering to obtain; The dispersion treatment can be carried out by a high-speed disperser, such as a double planetary high-speed disperser; Preferably, stirring and dispersing at an autogenous speed of 1000-2000 rpm and a revolution speed of 10-50 rpm for 1-3 h.

[0021] Preferably, stirring and dispersing at an autogenous speed of 100-500 rpm and a revolution speed of 10-50 rpm for 0.5-2 h.

[0022] Preferably, the temperature during dispersion is 20-40 °C.

[0023] Preferably, the mesh number of the filter screen is 100-200 meshes.

[0024] The method for preparing the conductive adhesive coating slurry comprises the following steps: Stir and disperse the conductive polymer microspheres, the dispersant and water for 1 to 3 hours to obtain a dispersion; then add the binder to the dispersion and stir and disperse for 0.5 to 2 hours, and then filter to obtain it; Dispersion treatment can be carried out with a high-speed disperser, such as a double planetary high-speed disperser; Preferably, stir and disperse for 1 to 3 hours at an autogenous speed of 200 to 600 rpm and a revolution speed of 10 to 50 rpm.

[0025] Preferably, stir and disperse for 0.5 to 2 hours at an autogenous speed of 100 to 300 rpm and a revolution speed of 10 to 50 rpm.

[0026] Preferably, the temperature during dispersion is 20 to 40 °C.

[0027] Preferably, the mesh number of the filter screen is 100 to 200 meshes.

[0028] In steps S1 and S2, the coating method used is microgravure roll coating, and the coating speed is 25 to 100 m / min; The drying temperature is 40 to 70 °C.

[0029] Based on the solid electrolyte separator, the present invention further provides a lithium-ion battery, including a positive electrode, a negative electrode and a separator, wherein the separator disposed between the positive electrode and the negative electrode is the solid electrolyte separator of the present invention.

[0030] The solid electrolyte membrane with a conductive coating layer provided by the present invention coats a solid electrolyte layer on a base film. Compared with traditional materials such as alumina, the solid electrolyte material has the function of conducting ions and improves the conductivity of the membrane. At the same time, the used NASCION-type solid electrolyte material lithium aluminum titanium phosphate (LATP) can be in-situ cured into a film at a low negative electrode potential, reducing the content of liquid electrolyte in the battery, protecting the negative electrode SEI film, and improving the battery safety performance. At the same time, in order to improve the interface state of the battery electrode sheet and the hardness of the soft-pack battery, a polymer coating layer is coated on the surface of the solid electrolyte to provide adhesion between the separator and the electrode sheet after the battery core is hot-pressed. The conductive polymer microspheres used as the main coating material can effectively avoid the hindrance of the in-situ curing of LATP in the coating. The composite solid electrolyte separator of the present invention can effectively improve the electrical performance of the battery and effectively enhance the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of the separator prepared in Example 1 of the present invention.

[0032] Figure 2 It is a schematic structural diagram of the separator prepared in Example 2 of the present invention.

[0033] In the figure, 1 represents the lithium-ion battery base film, 2 represents the solid electrolyte coating, and 3 represents the conductive adhesive layer. Detailed implementation mode

[0034] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0035] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained through commercial channels.

[0036] In the following examples, the polystyrene / copper composite microspheres are prepared according to the following method: 1) Wash the styrene monomer 3 times with 5% NaOH solution to remove the inhibitor, and purify it by vacuum distillation; 2) Under nitrogen protection, dissolve the emulsifier in deionized water at 60°C, add the styrene monomer, and stir for pre-emulsification at 500 rpm for 30 min; 3) Raise the temperature to 75°C, add the initiator solution (potassium persulfate dissolved in 20 mL of water), and react for 6 h; 4) After cooling, centrifuge (8000 rpm, 10 min), wash 3 times with ethanol to obtain PS microspheres with a particle size of 0.5 - 3 μm; 5) Ultrasonically disperse the PS microspheres in the plating solution (solid content 5%), and perform activation treatment at 50°C for 30 min; 6) Slowly dropwise add the formaldehyde solution, control the reaction temperature at 50 ± 2°C, and the stirring speed at 200 rpm, and react for 2 h; 7) Centrifuge and separate, wash successively with dilute hydrochloric acid (0.1 M), ethanol, and deionized water, and dry in vacuum at 60°C; 8) Obtain PS / Cu composite microspheres with a copper layer thickness of 50 - 200 nm and an overall particle size of 0.8 - 5 μm.

[0037] In the following examples, the modified polyaniline microspheres are prepared according to the following method: 1) Dissolve SDBS in the HCl solution, add the aniline monomer, and stir in an ice bath for 30 min to form a homogeneous emulsion; 2) Gradually dropwise add the ammonium persulfate solution (dissolved in 50 mL of water), and control the reaction temperature at 0 - 5°C; 3) After continuous reaction for 12 h, perform suction filtration, and wash successively with ethanol and acetone until the filtrate is colorless; 4) Dry in vacuum at 60°C for 24 h to obtain dark green PANI microspheres (original particle size 0.2 - 2 μm).

[0038] 5) Disperse the PANI microspheres in concentrated sulfuric acid, and cool to 0°C in an ice bath; 6) Slowly dropwise add fuming sulfuric acid, control the temperature < 10°C, and raise the temperature to 25°C after dropping and react for 4 h; 7) Pour the mixed solution into ice water to quench the reaction, and centrifuge to collect the precipitate. 8) Wash with deionized water until neutral, and dry at 60 °C to obtain sulfonated polyaniline microspheres.

[0039] Example 1: Preparation of a solid electrolyte membrane with a conductive coating layer The structure of the solid electrolyte diaphragm prepared in this example is as follows: it includes a base film and a solid electrolyte layer coated on one side of the base film, and a conductive coating layer coated on the surface of the solid electrolyte coating and the other side of the base film. Among them, the base film is a polyethylene porous film with a thickness of 12 μm, the thickness of the solid electrolyte layer is 3 μm, and the single-sided surface density of the conductive coating layer is 0.8 g / m 2 .

[0040] The formulation ratio of the solid electrolyte coating slurry is: solid electrolyte powder: binder: dispersant: wetting agent = 95.4 wt%: 2.5 wt%: 2 wt%: 0.1 wt%, and the solid content of the slurry is 30%.

[0041] The formulation ratio of the conductive coating slurry is: conductive polymer microsphere powder: binder: dispersant = 95 wt%: 2.5 wt%: 2.5 wt%, and the solid content of the slurry is 8%.

[0042] The solid electrolyte used in this example is Li 1.3 Al 0.3 Ti 0.6 (PO4)3, the binder is an acrylate binder, the dispersant is sodium dodecylbenzene sulfonate, and the wetting agent is a polyether silicone copolymer.

[0043] The main material of the conductive coating layer used in this example is a conductive polymer microsphere, and the type is a polymer-metal composite conductive microsphere polystyrene / copper composite microsphere.

[0044] Prepare the composite solid electrolyte membrane according to the following steps: 1) Preparation of the solid electrolyte coating slurry: Stir and disperse the main material powder, dispersant and water for 2.5 h to obtain a dispersion; then add the binder and wetting agent to the dispersion and stir and disperse for 2 h, and the temperature during dispersion is 25 °C. Filter through a 200-mesh sieve to obtain the coating slurry; Use a double planetary high-speed disperser for stirring and dispersion, and the conditions are: stir and disperse for 2.5 h at a self-rotation speed of 1500 rpm and a revolution speed of 30 rpm; stir and disperse for 2 h at a self-rotation speed of 2000 rpm and a revolution speed of 35 rpm.

[0045] Preparation of the conductive coating slurry: Stir and disperse the main material powder, dispersant and water for 2.5 h to obtain a dispersion; then add the binder and wetting agent to the dispersion and stir and disperse for 2 h, and the temperature during dispersion is 25 °C. Filter through a 150-mesh sieve to obtain the coating slurry; Stirring and dispersing were carried out using a double planetary high-speed disperser under the following conditions: Stirring and dispersing were carried out at an autogenous rotation speed of 800 rpm and a revolution speed of 15 rpm for 2.5 h; Stirring and dispersing were carried out at an autogenous rotation speed of 1000 rpm and a revolution speed of 20 rpm for 2 h.

[0046] 2) Preparation of the composite solid electrolyte separator: Preparation of the solid electrolyte coating: The solid electrolyte slurry was evenly coated on one side of the base film using a high-precision coater. The coating method was microgravure roll coating, the coating speed was 50 m / min, and the drying temperature was 60 °C.

[0047] Preparation of the conductive adhesive coating: The conductive adhesive coating slurry was evenly coated on the surface of the solid electrolyte coating and the other side of the base film using a high-precision coater. The coating method was microgravure roll coating, the coating speed was 60 m / min, and the drying temperature was 60 °C.

[0048] The structural schematic diagram of the composite solid electrolyte separator prepared in this example is as Figure 1 shown.

[0049] Example 2: Preparation of a solid electrolyte membrane with a conductive adhesive layer The solid electrolyte membrane with a conductive adhesive layer prepared in this example includes a base film, solid electrolyte layers coated on both sides of the base film, and a conductive adhesive layer coated on the surface of the solid electrolyte coating. Among them, the base film is a polyethylene porous membrane with a thickness of 9 μm, the thickness of the single-sided solid electrolyte layer is 1 μm, and the single-sided areal density of the conductive adhesive layer is 0.4 g / m 2 .

[0050] The formulation of the solid electrolyte coating slurry and the formulation of the conductive adhesive coating slurry used in this example are the same as those in Example 1.

[0051] The solid electrolyte and other additives used in this example are the same as those in Example 1.

[0052] The main material of the conductive adhesive layer used in this example is conductive polymer microspheres, and the type is intrinsic conductive polymer microspheres, specifically modified polyaniline microspheres, with a particle size of 0.1 μm to 5 μm.

[0053] The composite solid electrolyte membrane was prepared according to the same method and conditions as in Example 1.

[0054] The structural schematic diagram of the composite solid electrolyte separator prepared in this example is as Figure 2 shown.

[0055] Comparative Example 1 The separator prepared in this comparative example includes a base film, an alumina coating applied to one side of the base film, and a PVDF adhesive layer applied to the surface of the alumina coating and the other side of the base film.

[0056] Among them, the base film is a polyethylene porous film with a thickness of 9 μm, the thickness of the alumina coating is 3 μm, and the areal density of the PVDF adhesive layer is 0.8 g / m 2 .

[0057] The separator is prepared according to the following steps: The formulation of the alumina coating slurry is: alumina powder: binder: dispersant: wetting agent = 95.4 wt%: 2.5 wt%: 2 wt%: 0.1 wt%, and the solid content of the slurry is 30%.

[0058] The formulation of the PVDF coating slurry is: PVDF powder: binder: dispersant = 95 wt%: 2.5 wt%: 2.5 wt%, and the solid content of the slurry is 8%.

[0059] In this comparative example, the binder is an acrylate binder, the dispersant is sodium dodecylbenzenesulfonate, and the wetting agent is a polyether silicone copolymer.

[0060] The comparative example separator is prepared according to the following steps: S1. Preparation of the alumina coating slurry: Stir and disperse the main material powder, dispersant and water for 2.5 h to obtain a dispersion; then add the binder and wetting agent to the dispersion and stir and disperse for 2 h, and the temperature during dispersion is 25 °C. Filter through a 200-mesh sieve to obtain the coating slurry; Use a double planetary high-speed disperser for stirring and dispersion, and the conditions are: stir and disperse at a self-rotation speed of 1500 rpm and a revolution speed of 30 rpm for 2.5 h; stir and disperse at a self-rotation speed of 2000 rpm and a revolution speed of 35 rpm for 2 h.

[0061] Preparation of the PVDF coating slurry: Stir and disperse the main material powder, dispersant and water for 2.5 h to obtain a dispersion; then add the binder and wetting agent to the dispersion and stir and disperse for 2 h, and the temperature during dispersion is 25 °C. Filter through a 150-mesh sieve to obtain the coating slurry; Use a double planetary high-speed disperser for stirring and dispersion, and the conditions are: stir and disperse at a self-rotation speed of 800 rpm and a revolution speed of 15 rpm for 2.5 h; stir and disperse at a self-rotation speed of 1000 rpm and a revolution speed of 20 rpm for 2 h.

[0062] S2. Preparation of the coated separator: Preparation of the alumina coating: Use a high-precision coater to uniformly coat the aqueous alumina slurry on one side of the base film. The coating method is microgravure roll coating, the coating speed is 50 m / min, and the drying temperature is 60 °C.

[0063] Preparation of PVDF coating: A high-precision coating machine was used to uniformly coat the conductive coating paste on the surface of the solid electrolyte coating and the other side of the base film. The coating method was microgravure roll coating, the coating speed was 60 m / min, and the drying temperature was 60 °C.

[0064] The basic physical properties of the separators prepared in Examples 1-2 and Comparative Example 1 are shown in Table 1 (the test method refers to GBT36363-2018).

[0065] Table 1 Test performance of the separators in Examples 1-2 and Comparative Example 1

[0066] It can be seen from the test results in Table 1 that there is no obvious difference in the basic performance of the separators prepared in Examples 1 and 2 compared with Comparative Example 1. They have a certain separator-pole piece adhesion strength, and the ionic conductivity of the separators is significantly better than that of the comparative sample separator.

[0067] The separators prepared in Example 2 and Comparative Example 1, the graphite negative electrode pole piece, the electrolyte, and the NCM712 positive electrode pole piece were assembled into a lithium-ion battery. The battery structure was a square soft package with a nominal capacity of 70 Ah, and the battery performance was tested. The results are shown in Table 2 (the test method refers to GBT 31485).

[0068] It can be seen from the test results in Table 2 that the safety performance of the soft package battery with the conductive coating solid electrolyte separator prepared in Example 2 is significantly better than that of the ordinary separator in the puncture and overcharge tests.

[0069] Table 2 Battery performance test using the separators in Example 2 and Comparative Example 1

[0070] In summary, the present invention provides a solid electrolyte separator with a conductive coating layer, which enables the conventional solid electrolyte separator to have a separator-pole piece adhesion strength without affecting the in-situ curing of the solid electrolyte, and improves the safety performance of the battery.

Claims

1. A conductive paste, which is made of conductive polymer microspheres; The conductive polymer microspheres are polymer-metal composite conductive microspheres or modified intrinsic conductive polymer microspheres; The polymer-metal composite conductive microspheres are polystyrene / copper composite microspheres, and the particle size is 0.1~5um; The modified intrinsic conductive polymer microspheres are sulfonated polyaniline microspheres, and the particle size is 0.1~5um.

2. A solid electrolyte separator with a conductive coating layer, comprising a base film; characterized in that: One side or both sides of the base film are coated with a solid electrolyte coating, and a conductive adhesive layer is coated on the base film or the solid electrolyte coating; The conductive adhesive layer is made of the conductive paste described in claim 1.

3. The solid electrolyte separator according to claim 2, wherein: The solid electrolyte coating is a lithium aluminum titanium phosphate particle coating, where the chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 2x (PO4)3, where x is a number between 0.01 and 0.5, the particle size is 200 nm - 5 μm, and the shape is an irregular polygon; The thickness of the solid electrolyte coating is 1~5um.

4. The solid electrolyte separator according to claim 2 or 3, characterized in that: The thickness of the conductive adhesive layer is 1 to 10 μm, and the areal density is 0.1 to 3 g / m 2 ; The base film is a PP film, a PE film, a PET film, a PI film or an aramid film, and the thickness is 5~30um.

5. The preparation method of the solid electrolyte separator according to any one of claims 2-4, comprising the following steps: S1. Coating a solid electrolyte coating slurry containing a solid electrolyte on the surface of the base film, and drying to obtain the solid electrolyte coating; S2. Coating a conductive adhesive layer slurry containing conductive polymer microspheres on the surface of the solid electrolyte coating or the base film, and drying to obtain the conductive adhesive layer; The mass composition of the solid electrolyte coating slurry is: solid electrolyte: binder: dispersant: wetting agent = 92~99.97%: 0.01~3%: 0.01~3%: 0.01~2%, and the solid content of the slurry is 20~40%; The mass composition of the conductive adhesive coating slurry is: conductive polymer microspheres: binder: dispersant = 94~99.98%: 0.01~3%: 0.01~3%, and the solid content of the slurry is 3~20%.

6. The preparation method according to claim 5, characterized in that: The preparation method of the solid electrolyte coating slurry comprises the following steps: Stirring and dispersing the solid electrolyte, the dispersant and water for 1~3h to obtain a dispersion; then adding the binder and the wetting agent to the dispersion and stirring and dispersing for 0.5~2h, and filtering to obtain; The preparation method of the conductive adhesive coating slurry comprises the following steps: Stirring and dispersing the conductive polymer microspheres, the dispersant and water for 1~3h to obtain a dispersion; then adding the binder to the dispersion and stirring and dispersing for 0.5~2h, and filtering to obtain.

7. The preparation method according to claim 5 or 6, characterized in that: In steps S1 and S2, the coating method used is microgravure roll coating, and the coating speed is 25~100m / min; The drying temperature is 40~70°C.

8. The application of the solid electrolyte separator according to any one of claims 2-4 as a separator for a lithium-ion battery.

9. A lithium-ion battery, comprising a positive electrode, a negative electrode and a separator, characterized in that: A solid electrolyte separator according to any one of claims 2-4 is provided between the positive electrode and the negative electrode.

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