CN111430788A - Composite solid electrolyte membrane, preparation method and solid lithium battery - Google Patents

Abstract

The invention discloses a composite solid-state electrolyte membrane, a preparation method and a solid-state lithium battery. The composite solid-state electrolyte membrane comprises: a supporting membrane, an organic-inorganic composite coating A coated on the positive side surface of the supporting membrane, and a coating on the supporting membrane The organic-inorganic composite coating B on the negative side surface of , one or more of polyvinyl chloride; coating B contains organic polymer B, lithium salt, nano-inorganic solid electrolyte; organic polymer B is polyethylene oxide, polypropylene carbonate, polycarbonate, polysanya One or more of methyl carbonates. Aiming at the different requirements of the positive and negative electrode layers for the electrolyte membrane in the solid-state lithium battery, the present invention uses the graphene oxide membrane as a support, and designs electrolyte membranes containing different polymer groups on both sides of the graphene oxide membrane, thereby further improving the comprehensive performance of the battery.

Description

A composite solid-state electrolyte membrane, preparation method and solid-state lithium battery

technical field

The invention relates to the technical field of solid-state lithium batteries, in particular to a composite solid-state electrolyte membrane, a preparation method and a solid-state lithium battery.

Background technique

Lithium-ion batteries have been widely used in many aspects of the national economy. However, with the continuous improvement of the energy density and safety performance requirements of lithium-ion batteries in consumer electronics and electric vehicles, it is urgent to develop high-performance lithium-ion batteries that take into account both performances. However, traditional liquid lithium-ion batteries have potential safety hazards such as easy leakage, volatility, and combustion due to the use of liquid electrolytes, and the safety needs to be further improved. Meanwhile, the energy density of liquid lithium batteries is approaching its upper limit. Therefore, realizing the transition from liquid lithium-ion batteries to all-solid-state lithium batteries as soon as possible is an important way to solve battery safety performance and energy density. The development of high-performance all-solid-state electrolytes has become the focus of both scientific research and industry. All-solid-state electrolytes are divided into two categories: inorganic all-solid-state electrolytes and all-solid-state polymer electrolytes. Inorganic all-solid-state electrolytes can maintain chemical stability in a wide temperature range, and have better mechanical strength and higher ionic conductivity at room temperature, but they are more brittle and have poor processability. In comparison, solid polymer electrolytes have low ionic conductivity, but they are easy to form and more suitable for mass production, so they have better development prospects.

According to the groups of the polymer matrix, polymer electrolytes can be divided into polyethylene oxide, polyester-based, polyvinylidene fluoride, polyacrylonitrile and other polymers. The structure of polyethylene oxide polymer electrolyte is conducive to the rapid migration of ions, high electrochemical stability, and excellent solvation ability for many lithium salts, but its room temperature ionic conductivity is low. Polycarbonate polymers have good room temperature ionic conductivity, interfacial compatibility and chemical stability, but poor mechanical properties. Polyvinylidene fluoride and polyacrylonitrile polymers have wide electrochemical windows and high room temperature ionic conductivity, but have poor interfacial compatibility with lithium. It can be seen from this that the main problems facing solid polymer electrolytes are low ionic conductivity at room temperature (generally lower than 10 ^-4 S/cm), high interface impedance and low mechanical strength.

Therefore, it is necessary to modify and compound the polymer solid electrolyte, design and optimize its structure, so that the solid electrolyte membrane has good ionic conductivity, interface compatibility, chemical stability and mechanical properties at the same time to meet the development needs of solid-state batteries. , and further developed a solid-state lithium battery with excellent comprehensive performance.

SUMMARY OF THE INVENTION

In view of this, the first object of the present invention is to provide a composite solid electrolyte membrane and a preparation method thereof with good ionic conductivity, interface compatibility, thermal stability and mechanical properties at the same time, so as to solve the problem of existing solid polymer electrolytes. The defects of the membrane; the second purpose of the present invention is to provide a solid-state lithium battery comprising the above-mentioned composite solid-state electrolyte membrane, which can effectively improve the cycle stability, rate performance and thermal stability performance of the solid-state lithium battery.

In order to achieve the above object, the present invention provides a composite solid electrolyte membrane, which comprises: a support membrane, an organic-inorganic composite coating A coated on the positive electrode side surface of the support membrane, and a coating on the support membrane The organic-inorganic composite coating B on the negative side surface of the membrane; wherein, the organic-inorganic composite coating A comprises: an organic polymer A, a lithium salt, and a nano-inorganic solid electrolyte, and the organic polymer A is polyvinylidene fluoride One or more of ethylene, polyvinylidene fluoride copolymer, polyacrylonitrile, and polyvinyl chloride; the organic-inorganic composite coating B includes: organic polymer B, lithium salt, and nano-inorganic solid electrolyte; The organic polymer B is one or more of polyethylene oxide, polypropylene carbonate, polycarbonate and polytrimethylene carbonate.

Preferably, the support film is a graphene oxide film.

Preferably, the thickness of the support film is 10-50 μm.

Preferably, the thickness of the organic-inorganic composite coating A is 30-100 μm, and the thickness of the organic-inorganic composite coating B is 30-100 μm.

Preferably, the lithium salt comprises: lithium bistrifluoromethylimide, lithium bisfluorosulfonimide, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium oxalatedifluoroborate, One or more of lithium difluorophosphates.

Preferably, the nano inorganic solid electrolyte is one of NASICON type inorganic solid electrolyte, garnet type solid electrolyte and LISICON type inorganic solid electrolyte.

The present invention also provides the above-mentioned preparation method of the composite solid electrolyte membrane, which comprises the following steps:

Step 1: mixing organic polymer A, lithium salt, nano-inorganic solid electrolyte and solvent to obtain organic-inorganic composite slurry A, the solid content of the slurry is 2-8%;

Step 2: mixing organic polymer B, lithium salt, nano-inorganic solid electrolyte and solvent to obtain organic-inorganic composite slurry B, the solid content of the slurry is 2-8%;

Step 3: The organic-inorganic composite slurry A and the organic-inorganic composite slurry B are respectively coated on both sides of the support membrane, and a composite solid-state electrolyte membrane is obtained after drying.

Preferably, the solvent is one or a mixture of two or more selected from acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone and acetone.

The present invention also provides a solid-state lithium battery, comprising: the above-mentioned composite solid-state electrolyte membrane.

Preferably, the positive electrode active material in the positive electrode layer of the battery is one of lithium cobalt oxide, lithium manganate, lithium iron phosphate, nickel-cobalt-manganese ternary material and nickel-cobalt-aluminum ternary material.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The composite solid-state electrolyte membrane provided by the present invention has a structure similar to a sandwich, and adopts a graphene oxide film as a supporting film, which has the following three advantages:

①Increase the mechanical properties of the solid electrolyte membrane;

② Coating the composite coating on the surface of the graphene oxide film, the enriched functional groups on graphene oxide can interfere with the reorganization of the polymer chain and interact with the polar groups of the polymer through Lewis acid-base reaction, bringing about more high ionic conductivity;

③ The covalent oxygen functional groups on graphene oxide have excellent compatibility with polar solvents. On the one hand, the existence of graphene oxide can improve the compatibility of organic polymers, lithium salts, nano-inorganic solid electrolytes and solvents, which is more conducive to Film formation, on the other hand, is beneficial to stabilize the skeleton formed by the organic-inorganic composite polymer film, maintain its original pore structure, and improve the electrochemical stability and thermal stability of the solid electrolyte membrane.

(2) In the solid-state lithium battery provided by the present invention, the coating on the side of the composite solid-state electrolyte membrane near the positive electrode layer mainly contains polyvinylidene fluoride and polyacrylonitrile polymers, which can bring higher ionic conductivity and a wide electrochemical window, suitable for all kinds of even high-voltage cathode materials, thereby improving the capacity and rate performance of solid-state battery active materials; the coating near the lithium anode layer mainly contains polyvinylidene fluoride, polypropylene Nitrile polymers have good interfacial compatibility and are stable to lithium, thereby improving the cycle stability of solid-state batteries.

Description of drawings

FIG. 1 is a schematic structural diagram of a solid-state lithium battery of the present invention.

FIG. 2 is a SEM image of the composite solid electrolyte membrane prepared in Example 1 of the present invention.

FIG. 3 is a comparison diagram of the ionic conductivity test impedance of the composite solid electrolyte membrane and the single-layer electrolyte membrane prepared in Example 1 of the present invention at room temperature.

4 is a cycle performance curve of the lithium solid-state battery prepared in Example 3 of the present invention.

FIG. 5 is a rate performance curve of the lithium solid-state battery prepared in Example 3 of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

As shown in FIG. 1 , which is a schematic cross-sectional view of a solid-state lithium battery provided by the present invention, the battery body is formed by stacking a positive electrode layer 1 , a composite solid-state electrolyte membrane 2 and metal lithium 3 in sequence. The composite solid electrolyte membrane 2 includes: a supporting membrane 22, an organic-inorganic composite coating A21 coated on the side of the supporting membrane 22 close to the positive electrode layer 1, and an organic-inorganic composite coating A21 coated on the side close to the negative electrode (closer to the metal lithium 3). Coating B23. The organic-inorganic composite coating A21 includes an organic polymer A, a lithium salt, and a nano-inorganic solid electrolyte, and the organic-inorganic composite coating B23 includes an organic polymer B, a lithium salt, and a nano-inorganic solid electrolyte.

The organic polymer A is one or more of polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyacrylonitrile, and polyvinyl chloride.

The organic polymer B is one or more of polyethylene oxide, polypropylene carbonate, polycarbonate and polytrimethylene carbonate.

The support film is a graphene oxide film.

The thickness of the support film is 10-50 μm, the thickness of the coating layer A is 30-100 μm, and the thickness of the coating layer B is 30-100 μm.

The lithium salt is lithium bistrifluoromethylimide (LiTFSI), lithium bisfluorosulfonimide (LiFSI), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ) ₄ ), one or more of lithium dioxalate borate (LiBOB), lithium difluoroborate oxalate (LiDFOB), and lithium difluorophosphate (LiPF ₂ O ₂ ).

The nano inorganic solid electrolyte is one of NASICON type inorganic solid electrolyte, garnet type solid electrolyte and LISICON type inorganic solid electrolyte.

The positive electrode layer is made of the positive electrode active material, the conductive agent, and the binder mixed evenly and then pressed into a tablet. The positive electrode layer active material is one of lithium cobalt oxide, lithium manganate, lithium iron phosphate, nickel-cobalt-manganese ternary material and nickel-cobalt-aluminum ternary material.

The composite solid electrolyte membrane in the present invention adopts a graphene oxide membrane as a support layer, which can effectively improve the ionic conductivity, thermal stability and mechanical properties of the composite electrolyte membrane. The positive and negative electrode layers are respectively in contact with the composite coating electrolyte with different characteristics, which can effectively improve the utilization rate of the positive electrode active material while improving the interface compatibility and suppress the side reaction of metallic lithium. The application of the composite solid electrolyte membrane to solid lithium batteries can bring about comprehensive improvements in capacity development, cycle stability, rate performance and thermal stability.

The specific preparation method of the present invention is as follows:

(1) Preparation of positive electrode sheet

Step 1: Add the binder, the conductive agent, and the positive electrode active material to the NMP solvent in sequence to disperse and stir to obtain a positive electrode slurry; Step 2: Use a coating machine to coat the positive electrode slurry on the aluminum foil, and the coating machine The drying temperature is 120 °C, the coiled pole pieces are dried in a vacuum oven at 100 °C for 24 hours, the dried electrode pieces are rolled, and the positive pole pieces are obtained by punching;

(2) Preparation of composite solid electrolyte membrane

Step 1: Mix organic polymer A, lithium salt, nano-inorganic solid electrolyte and solvent to obtain organic-inorganic composite slurry A, and the solid content of the slurry is 2-8%; Step 2: Combine organic polymer B, lithium salt, nanometer The inorganic solid electrolyte and the solvent are mixed to obtain an organic-inorganic composite slurry B, and the solid content of the slurry is 2-8%; Step 3: The organic-inorganic composite slurry A and the organic-inorganic composite slurry B are respectively coated on both sides of the supporting membrane , and the composite solid electrolyte membrane was obtained after drying.

(3) Preparation of solid-state batteries

The positive electrode layer, the composite solid electrolyte membrane and the metal lithium were sequentially filled into the stainless steel shell of the button battery in a stacked manner, and the button battery was assembled and tested in the glove box.

The specific embodiments of the present invention will be further described below with reference to the embodiments and the accompanying drawings.

Example 1:

(1) Preparation of positive electrode plate

Step 1: The binder PVDF, the conductive agent SuperP, and the positive electrode active material LiFePO ₄ are sequentially added to the NMP solvent in a mass ratio of 10:10:80 for dispersion and stirring to obtain a positive electrode slurry; Step 2: Use a coating machine to coat the positive electrode slurry The material is coated on the aluminum foil, the drying temperature of the coating machine is 120 °C, the coiled pole piece is dried in a vacuum oven at 100 °C for 24 hours, the dried electrode piece is rolled and punched to obtain the positive pole piece ;

(2) Preparation of composite solid electrolyte membrane

Step 1: Mix 0.3g polyvinylidene fluoride PVDF, 0.1g LiTFSI, 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g DMF to obtain organic-inorganic composite slurry A; Step 2: Mix 0.3g polyethylene oxide PEO, 0.1g LiTFSI, 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g acetonitrile were mixed to obtain organic-inorganic composite slurry B; Step 3: Apply organic-inorganic composite slurry A and organic-inorganic composite slurry B on both sides of the supporting membrane respectively , put it in a vacuum drying box to dry for 12h, and then dry to obtain a composite solid electrolyte membrane.

(3) Preparation of solid-state batteries

The positive electrode layer, the composite solid electrolyte membrane and the metal lithium were sequentially filled into the stainless steel shell of the button battery in a stacked manner, and the button battery was assembled and tested in the glove box.

The SEM image of the composite solid-state electrolyte membrane prepared in Example 1 is shown in Figure 2, and the upper side is the coating layer A. It can be seen that the presence of graphene oxide makes the organic-inorganic electrolyte membrane of the coating layer A in the formation of In the process, the intact pore structure is retained, which has good stability and facilitates the transport of lithium ions.

FIG. 3 is a comparison diagram of the ionic conductivity test impedance of the single-layer electrolyte membrane and the composite solid-state electrolyte membrane prepared in Example 1 of the present invention at room temperature. After calculation, it can be concluded that the room temperature ionic conductivity of the composite solid electrolyte membrane prepared in Example 1 of the present invention can reach 8.1×10 ^-4 S/cm, while the ionic conductivity of the single-layer electrolyte membrane at room temperature is only 3.9× 10 ^-4 S/cm, the room temperature ionic conductivity was improved.

Example 2:

(1) Preparation of positive electrode plate

Step 1: The binder PVDF, the conductive agent SuperP, and the positive electrode active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are sequentially added to the NMP solvent in a mass ratio of 10:10:80 for dispersion and stirring to obtain a positive electrode slurry; step 2: using The coating machine coats the positive electrode slurry on the aluminum foil. The drying temperature of the coating machine is 120 ° C. The coiled pole piece is dried in a vacuum oven at 100 ° C for 24 hours. Die cutting to get the positive pole piece;

(2) Preparation of composite solid electrolyte membrane

Step 1: Mix 0.3g polyvinylidene fluoride PVDF, 0.1g LiTFSI, 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g DMF to obtain organic-inorganic composite slurry A; Step 2: Mix 0.3g polyethylene oxide PEO, 0.1g LiTFSI, 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g acetonitrile were mixed to obtain organic-inorganic composite slurry B; Step 3: Apply organic-inorganic composite slurry A and organic-inorganic composite slurry B on both sides of the supporting membrane respectively , put it in a vacuum drying box to dry for 12h, and then dry to obtain a composite solid electrolyte membrane.

(3) Preparation of solid-state batteries

The positive electrode layer, the composite solid electrolyte membrane and the metal lithium were sequentially filled into the stainless steel shell of the button battery in a stacked manner, and the button battery was assembled and tested in the glove box.

Example 3:

(1) Preparation of positive electrode plate

Step 1: The binder PVDF, the conductive agent SuperP, and the positive electrode active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are sequentially added to the NMP solvent in a mass ratio of 10:10:80 for dispersion and stirring to obtain a positive electrode slurry; step 2: using The coating machine coats the positive electrode slurry on the aluminum foil. The drying temperature of the coating machine is 120 ° C. The coiled pole piece is dried in a vacuum oven at 100 ° C for 24 hours. Die cutting to get the positive pole piece;

(2) Preparation of composite solid electrolyte membrane

Step 1: Mix 0.3g polyacrylonitrile PAN, 0.1g LiClO ₄ , 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g acetonitrile to obtain organic-inorganic composite slurry A; Step 2: Mix 0.3g polypropylene carbonate PPC, 0.1g Mix gLiTFSI, 0.05g Li ₇ La ₃ Zr ₂ O ₁₂ and 10g acetonitrile to obtain organic-inorganic composite slurry B; Step 3: apply organic-inorganic composite slurry A and organic-inorganic composite slurry B on both sides of the supporting membrane respectively , put it in a vacuum drying box to dry for 12h, and then dry to obtain a composite solid electrolyte membrane.

(3) Preparation of solid-state batteries

The positive electrode layer, the composite solid electrolyte membrane and the metal lithium were sequentially filled into the stainless steel shell of the button battery in a stacked manner, and the button battery was assembled and tested in the glove box.

The cycle performance curve of the solid-state lithium battery prepared in Example 3 is shown in Figure 4. The battery was charged and discharged at a current density of 15 mA/g and at room temperature in a voltage range of 2.8 to 4.3 V. The specific capacity of the first discharge was 164.0 mAh/g, which is higher than that of the solid-state battery with conventional single-layer solid-state electrolyte membrane (124.9mAh/g), the utilization rate of active materials is significantly improved, and the capacity can still be maintained at 162.8.0mAh/g after 20 cycles, while the single-layer solid-state electrolyte The capacity of the membrane solid-state battery rapidly decays to 80.1 mAh/g, and the use of the composite membrane significantly improves the cycle stability of the solid-state battery.

Figure 5 is the rate performance curve of the solid-state lithium battery prepared by Example 3 of the present invention. Even at a relatively high rate of 1C, the solid-state battery containing the composite solid-state electrolyte membrane can obtain a stable capacity of 111.4mAh g ^-1 , This is much higher than the capacity of a solid-state battery (48.7 mAhg ^-1 ) using a single-layer solid-state electrolyte membrane. This benefits from the high ionic conductivity of the composite membrane, which not only enables fast ion transport between the cathode and the solid electrolyte membrane in the battery, but also ensures stable interfacial contact.

In summary, when polymer electrolyte membranes or single-layer organic-inorganic composite electrolyte membranes are used as electrolyte membranes for solid-state lithium batteries, there are often problems of poor mechanical properties, low ionic conductivity or poor interfacial compatibility, and cannot take into account the performance of various properties. . In view of this, the present invention aims at the different requirements for the electrolyte membrane of the positive and negative electrode layers in the solid-state lithium battery, and uses the graphene oxide film as a support to design organic-inorganic composite electrolyte membranes containing different polymer groups on both sides of the positive and negative electrodes. , to obtain a composite solid electrolyte membrane with high room temperature ionic conductivity, strong interface compatibility, good thermal stability and mechanical properties, thereby further improving the overall performance of the battery.

While the content of the present invention has been described in detail by way of the above preferred embodiments, it should be appreciated that the above description should not be construed as limiting the present invention. Various modifications and alternatives to the present invention will be apparent to those skilled in the art upon reading the foregoing. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims (10)

1. A composite solid-state electrolyte membrane, characterized in that, comprising: a support film, an organic-inorganic composite coating A coated on the positive side surface of the support film, and a negative electrode side coated on the support film Surface organic-inorganic composite coating B; wherein, The organic-inorganic composite coating A includes: an organic polymer A, a lithium salt, and a nano-inorganic solid electrolyte, and the organic polymer A is polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyacrylonitrile, polyacrylonitrile, and polyvinylidene fluoride. One or more of vinyl chloride; The organic-inorganic composite coating B comprises: organic polymer B, lithium salt, nano-inorganic solid electrolyte; the organic polymer B is polyethylene oxide, polypropylene carbonate, polycarbonate, polytrimethylene carbonate One or more of esters. 2 . The composite solid-state electrolyte membrane according to claim 1 , wherein the supporting membrane is a graphene oxide membrane. 3 . 3 . The composite solid-state electrolyte membrane according to claim 1 , wherein the thickness of the support membrane is 10-50 μm. 4 . 4 . The composite solid electrolyte membrane according to claim 1 , wherein the organic-inorganic composite coating A has a thickness of 30-100 μm, and the organic-inorganic composite coating B has a thickness of 30-100 μm. 5 . 5 . The composite solid-state electrolyte membrane according to claim 1 , wherein the lithium salt comprises: lithium bistrifluoromethylimide, lithium bisfluorosulfonimide, lithium perchlorate, lithium hexafluorophosphate, One or more of lithium fluoroborate, lithium dioxalatoborate, lithium difluoroborate oxalate, and lithium difluorophosphate. 6 . The composite solid electrolyte membrane according to claim 1 , wherein the nano inorganic solid electrolyte is one of NASICON type inorganic solid electrolyte, garnet type solid electrolyte and LISICON type inorganic solid electrolyte. 7 . 7. The preparation method of the composite solid-state electrolyte membrane according to any one of claims 1 to 6, characterized in that, comprising the following steps: Step 1: mixing organic polymer A, lithium salt, nano-inorganic solid electrolyte and solvent to obtain organic-inorganic composite slurry A, the solid content of the slurry is 2-8%; Step 2: mixing organic polymer B, lithium salt, nano-inorganic solid electrolyte and solvent to obtain organic-inorganic composite slurry B, the solid content of the slurry is 2-8%; Step 3: The organic-inorganic composite slurry A and the organic-inorganic composite slurry B are respectively coated on both sides of the support membrane, and a composite solid-state electrolyte membrane is obtained after drying. 8. The method for preparing a composite solid electrolyte membrane according to claim 7, wherein the solvent is one of acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, and acetone or A mixture of two or more. 9 . A solid-state lithium battery, comprising: the composite solid-state electrolyte membrane according to any one of claims 1 to 6 . 10 . 10. The solid-state lithium battery according to claim 9, wherein the positive electrode active material in the positive electrode layer of the battery is lithium cobalt oxide, lithium manganate, lithium iron phosphate, nickel cobalt manganese ternary material and nickel cobalt aluminum One of the ternary materials.

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