CN115832414A

CN115832414A - Composite solid electrolyte membrane, preparation method and application thereof, and lithium ion battery

Info

Publication number: CN115832414A
Application number: CN202211602913.1A
Authority: CN
Inventors: 刘宏超; 葛明政; 何宏刚; 汤育欣
Original assignee: University of Macau
Current assignee: University of Macau
Priority date: 2022-12-13
Filing date: 2022-12-13
Publication date: 2023-03-21

Abstract

The invention discloses a composite solid electrolyte membrane, a preparation method and application thereof, and a lithium ion battery. The preparation method comprises the following steps: and (3) standing, drying and hot-pressing the organic suspension containing the inorganic particles. The invention realizes the gradient distribution of inorganic particles in the vertical direction in the solid electrolyte membrane, so that the concentration of the inorganic particles on the side contacting with the lithium metal cathode is lower, and the interface impedance is reduced; the other side with higher concentration of the inorganic particles is contacted with the anode, so that the rapid transmission of lithium ions is realized, the transmission rate of the lithium ions in the solid electrolyte is improved, the mechanical strength of the composite electrolyte membrane is improved by utilizing the excellent mechanical property of the inorganic particles, and the problems that the polymer solid electrolyte membrane is easy to pierce due to the growth of lithium dendrites and the ionic conductivity is low are solved.

Description

Composite solid electrolyte membrane, preparation method and application thereof, and lithium ion battery

Technical Field

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

Background

With the improvement of quality of life, various electronic devices, such as electronic watches, smart phones, notebook computers, new energy vehicles, etc., are more and more widely used, and the performance requirements of the devices on batteries are higher and higher. The liquid lithium ion battery is mainly used at present, the potential safety hazard of the battery is very large, organic electrolyte is mainly used, if leakage occurs, the lithium battery is easy to combust and explode, the safety is low, and meanwhile, the theoretical capacity density of the liquid lithium ion battery is limited and is not enough to support the increasing energy requirement. The lithium metal is used as the cathode of the all-solid-state lithium battery, so that the theoretical capacity of the battery can be improved, and the solid electrolyte used by the all-solid-state lithium battery has higher mechanical strength and nonflammability compared with a liquid electrolyte, so that the lithium battery has more excellent safety performance while loading an electrode with higher energy density.

Through decades of continuous research on solid electrolytes, the existing solid electrolytes are mainly divided into two categories, one category is polymer solid electrolytes, the interface contact of the electrolyte and a lithium metal negative electrode is good, the interface impedance is low, and the flexibility is good, but the ionic conductivity and the mechanical strength are poor, the growth of lithium dendrites is difficult to inhibit, the lithium dendrites are easy to puncture to cause short circuit of a battery, the electrochemical stability is low, the electrochemical window is narrow, and the redox reaction is easy to occur when the voltage is high to cause the failure of the electrolyte; the other is an inorganic solid electrolyte which is prepared by calcining garnet type powder at high temperature, has the characteristics of high ionic conductivity and large electrochemical window, has high mechanical strength, can effectively prevent the battery short circuit caused by the puncture of lithium dendrite, but has poor flexibility and strong brittleness, is easy to form a plurality of gaps with a lithium cathode, and can cause the generation of space charge effect, so that the lithium ions are unevenly deposited on the lithium metal cathode to cause the growth of the lithium dendrite, the interface impedance is high, and simultaneously, the battery assembly is also difficult.

Therefore, both the existing polymer solid electrolyte and inorganic solid electrolyte have certain performance defects, and a solid electrolyte with better flexibility and mechanical strength, low interface impedance, and higher ionic conductivity and electrochemical stability is needed.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a composite solid electrolyte membrane, a preparation method and application thereof and a lithium ion battery, so as to improve the technical problem.

The invention is realized by the following steps:

in a first aspect, the present invention provides a composite solid electrolyte membrane including an organic phase bulk and inorganic particles, the composite solid electrolyte membrane having a first surface and a second surface opposite to the first surface, the particle content of the inorganic particles gradually increasing in a direction extending from the first surface to the second surface.

In a second aspect, the present invention also provides a method for producing the above composite solid electrolyte membrane, comprising: and (3) standing, drying and hot-pressing the organic suspension containing the inorganic particles.

In a third aspect, the present invention further provides a lithium ion battery, which includes a positive electrode, a lithium metal negative electrode, and the composite solid electrolyte membrane, wherein a first surface of the composite solid electrolyte membrane is connected to the lithium metal negative electrode, and a second surface of the composite solid electrolyte membrane is connected to the positive electrode.

In a fourth aspect, the invention also provides an application of the composite solid electrolyte membrane in preparation of a lithium ion battery or a flexible energy storage device.

The invention has the following beneficial effects: by regulating and controlling the gradient distribution of the inorganic particles from small concentration to large concentration in the solid electrolyte membrane, the side with lower inorganic particle concentration can be used for contacting with a lithium cathode, so that the interface contact is tight, the interface resistance between an organic layer and an inorganic layer does not exist, the interface impedance is greatly reduced, and meanwhile, the side with higher inorganic particle concentration is used for contacting with an anode, the quick transmission of lithium ions is realized, and the transmission rate of the lithium ions in the solid electrolyte is improved. Meanwhile, the inorganic particles can endow the solid electrolyte membrane with better mechanical properties, and the inorganic particles can also keep better flexibility when being distributed in an organic phase, so that the problems that the polymer solid electrolyte membrane is easy to pierce due to the growth of lithium dendrites and the ionic conductivity is low are solved. In addition, the preparation method of the composite solid electrolyte membrane is simple and safe, low-cost and large-scale industrial application can be realized, and the prepared symmetrical battery can be stably circulated for a long time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a schematic flow chart of a method for manufacturing a lithium ion battery according to an embodiment of the present invention;

FIG. 2 is an SEM image of a PEO/LLZTO solid electrolyte membrane prepared in example 1 of the present invention: (a) SEM pictures of the low-concentration side of LLZTO, and (b) SEM pictures of the high-concentration side of LLZTO; (c) is a cross-sectional SEM image of the composite electrolyte membrane; (d) is an element map of Zr element on the section of the composite electrolyte; (e) elemental map of La element of composite electrolyte cross section;

FIG. 3 is an XRD pattern of a PEO/LLZTO solid electrolyte membrane prepared in example 1 of the present invention;

FIG. 4 shows the assembly of the solid electrolyte membrane prepared in example 1 of the present invention into a symmetrical cell at 0.1mAh cm ^-2 Test pattern (Current Density of 0.1mA cm) ^-2 )；

FIG. 5 is a graph showing the rate performance and cycle performance of a full cell assembled from the solid electrolyte membrane prepared in example 1 of the present invention;

FIG. 6 is an SEM photograph of a PAN/LLZO solid electrolyte membrane prepared in example 2 of the present invention: (a) is an SEM image of the low concentration side of LLZO; (b) SEM picture of LLZTO high concentration side;

FIG. 7 is an SEM image of a PVDF/LATP solid electrolyte membrane prepared in example 3 of the present invention: (a) is an SEM image of the low LATP concentration side; (b) is an SEM photograph of the high concentration side of LLZTO.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The composite solid electrolyte membrane, the preparation method and the application thereof, and the lithium ion battery provided by the invention are specifically described below.

The inventors found through studies that the mechanical strength and lithium ion transport ability of the organic electrolyte can be improved by the following methods: (1) The organic-inorganic frameworks are added to enhance the strength of the electrolyte, and meanwhile, the frameworks can form a conductive network to rapidly transmit lithium ions. (2) The organic solution is cast on the inorganic electrolyte to obtain the organic-inorganic composite electrolyte, and the advantages of high lithium ion transmission capacity of the inorganic electrolyte and excellent interface contact performance of the organic electrolyte can be combined by the method, but the electrolyte is complex in preparation process, high-temperature sintering is needed in the preparation process, and the danger is high. (3) The inorganic particles are mixed into the organic electrolyte to improve the performance of the organic electrolyte. Although the method for blending organic and inorganic particles has a certain improvement with a pure organic electrolyte, the improvement on mechanical strength and ionic conductivity is limited, and the uniform distribution of the inorganic particles can cause the surface smoothness of an electrolyte membrane in contact with a lithium metal negative electrode to be low, so that gaps occur, and the gaps can generate a space charge effect, so that lithium ions are unevenly deposited, lithium dendrites rapidly grow, and a battery is short-circuited.

In view of this, the following technical solutions have been proposed through further research and practice.

Some embodiments of the present invention provide a composite solid electrolyte membrane including an organic phase bulk and inorganic particles, the composite solid electrolyte membrane having a first surface and a second surface opposite to the first surface, the particle content of the inorganic particles gradually increasing in a direction extending from the first surface to the second surface.

The performance of the electrolyte can be further improved by regulating and controlling the concentration gradient distribution of the inorganic particles between the first surface and the second surface, so that the concentration of the inorganic particles on the first surface for contacting a lithium cathode is reduced, the interface contact is tight, and the interface impedance is reduced.

The inorganic particles are uniformly distributed in the cross section of the composite solid electrolyte membrane parallel to the first surface or the second surface, and the uniform distribution of the inorganic particles on the parallel cross section (generally a horizontal plane) is beneficial to ensuring that the performance of the composite solid electrolyte is uniform at different parts. It should be noted that the uniform distribution of the inorganic particles herein refers to a relatively uniform dispersion state after being sufficiently mixed, and is not absolutely uniform.

Specifically, in some embodiments, the inorganic particles have a particle size of 200nm to 8 μm, for example, which may be selected as: 200nm to 800nm, 300nm to 1 μm, and the like, and generally, the more uniform the particle diameter of the inorganic particles, the better the performance of the composite solid electrolyte membrane. The inorganic particles in the market particle size range are selected to enable the composite solid electrolyte membrane to have better mechanical properties, and meanwhile, the inorganic particles are beneficial to realizing gradient dispersion of concentration, so that the electrochemical performance of the composite solid electrolyte membrane is improved.

In some embodiments, the inorganic particles are selected from any one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide, and tantalum-doped lithium lanthanum zirconium oxide.

In some embodiments, the total mass content of the inorganic particles in the composite solid electrolyte membrane is controlled to be 0.3g to 1g in order to balance flexibility and mechanical strength, conductivity, and the like;

in some embodiments, the composite solid electrolyte membrane has a thickness of 100 μm to 400 μm;

further, some embodiments of the present invention also provide a method for producing the above composite solid electrolyte membrane, which includes: and (3) standing, drying and hot-pressing the organic suspension containing the inorganic particles.

And (3) naturally settling the inorganic particles in the suspension through a standing and drying process to form a vertical concentration gradient, and solidifying by hot pressing to obtain the composite solid electrolyte membrane.

In order to control the sedimentation rate of the inorganic particles and the concentration of the formed gradient, the concentration of the inorganic particles in the organic suspension needs to be limited, and in some embodiments, the mass ratio of the inorganic particles to the solvent in the organic suspension is (0.5-1.5): (10 to 100). For example, 1.

Some embodiments of the present invention also provide a method for preparing the above composite solid electrolyte membrane, which specifically includes:

s1, preparing a composite electrolyte suspension.

And uniformly mixing the polymer powder, the inorganic particles and the lithium salt in a solvent to prepare a suspension.

Specifically, the mixing operation may be performed in a glove box, the mixing manner may be magnetic stirring, in order to enable uniform dispersion between the components, the stirring speed may be selected from 10rpm to 1500rpm, for example, 10rpm, 20rpm, 30rpm, 40rpm, 50rpm, 60rpm, 70rpm, 80rpm, 90rpm, 100rpm, 110rpm, 120rpm, 130rpm, 140rpm, 150rpm, or the like may be selected, and the stirring time may be selected from 12h to 48h, for example, 12h, 14h, 15h, 18h, 20h, 22h, 24h, 25h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, or 48h may be selected.

In the mixing process, the polymer powder and the lithium salt are completely dissolved in the solvent, and the particle diameter is not required.

In some embodiments, the mass ratio of the polymer powder, the inorganic particles, and the lithium salt is (0.5 to 1): (0.5-1.5): (0.3 to 1), for example, 0.5:1:0.3, 1:1:0.6 or 0.7:1:0.5, etc. In some embodiments, the molecular weight of the polymer powder is 100000 to 800000.

In some embodiments, the lithium salt comprises LiTFSI powder, liPSTFSI powder, or LiClO ₄ At least one of (1).

In some embodiments, the solvent is selected from any one of acetonitrile, N-dimethylformamide, and N-methylpyrrolidone.

S2, standing and drying the suspension solution.

Specifically, the suspension is poured into a mold and placed into a vacuum oven for drying.

In some embodiments, the vacuum oven is pre-dried before drying to complete drying. Illustratively, the pre-drying is performed at 20 to 40 ℃ (e.g., 20 ℃, 25 ℃, 28 ℃,30 ℃, 32 ℃, 35 ℃, or 40 ℃, etc.) for 2 to 6 hours (e.g., 2, 3, 4, 5, 6, 7 hours), and then the drying is performed at 50 to 80 ℃ (e.g., 50, 55, 60, 65, 70, 75 ℃, or 80 ℃, etc.) for 12 to 24 hours (e.g., 12, 13, 14, 15, 16, 17, 18, 19, 20, or 24 hours, etc.).

The method comprises the steps of providing sufficient inorganic particle settling time through low-temperature pre-drying, enabling the inorganic particle settling time to generate the characteristic of concentration gradient distribution in the composite electrolyte, enabling the composite electrolyte membrane to be converted from a liquid state to a solid state, and then completely removing a solvent in the composite electrolyte through high-temperature drying.

And S3, performing film pressing treatment on the composite electrolyte membrane.

Specifically, the composite electrolyte membrane prepared by drying is firstly calendered at high temperature and high pressure through a hot press, and then is cooled through water cooling. The thickness of the composite electrolyte is further reduced through calendering, so that the impedance of lithium ions in the composite electrolyte during transmission is reduced, and the ionic conductivity of the composite electrolyte is improved.

In some embodiments, the hot pressing is performed by first pressing at a temperature of 40 ℃ to 70 ℃ (e.g., 40 ℃, 45 ℃,50 ℃,55 ℃, 60 ℃, 65 ℃, or 70 ℃, etc.) for 0.5h to 2h (e.g., 0.5h, 1h, 1.5h, or 2 h) with a pressure of 5MPa to 20MPa (e.g., 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, 11MPa, 12MPa, 13MPa, 15MPa, 16MPa, 18MPa, 19MPa, or 20MP, etc.), and maintaining the pressure stable during the pressing.

In some embodiments, the preparation method further comprises reducing the temperature to 20-30 ℃ after hot pressing, wherein the temperature reduction process is carried out under the pressure of 5-20 MPa for 0.5-1 h, and the pressure is kept stable during the temperature reduction process. The purpose is to prevent the phenomenon that the thickness of the composite electrolyte rises back and local position is uneven in the cooling process.

It should be noted that the pressure in the cooling process is the same as that in the hot pressing process.

Some embodiments of the present invention also provide a lithium ion battery, which includes a positive electrode, and a lithium metal negative electrode, wherein a first surface of the composite solid electrolyte membrane is connected to the lithium metal negative electrode, and a second surface of the composite solid electrolyte membrane is connected to the positive electrode. Referring to fig. 1, the preparation process of the lithium ion battery may be that a composite solid electrolyte membrane is prepared first by the above embodiment, and then the battery is assembled.

Some embodiments of the invention also provide applications of the composite solid electrolyte membrane of the above embodiments in preparing lithium ion batteries or flexible energy storage devices.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The preparation process of the composite solid electrolyte membrane provided in this embodiment is as follows:

0.5g of polyethylene oxide (PEO), 1g of tantalum-doped lithium lanthanum zirconium oxide (LLZTO Li) _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ ) 0.3g of LiTFSI powder is dispersed in 12g of anhydrous Acetonitrile (ACN), wherein the particle size of LLZTO is 200nm-8 μm, the molecular weight of PEO is 200000, 800rmp is continuously stirred for more than 12h to obtain a uniformly dispersed milky suspension, the milky suspension is poured into a polytetrafluoroethylene evaporation dish, and the milky suspension is dried in a vacuum ovenAnd (3) drying, namely pre-drying for 3h at 30 ℃, then drying for 12h at 60 ℃, putting the obtained film under a hot press for hot pressing, keeping the pressure at 10MPa and the temperature at 60 ℃ for 1h, then cooling to 30 ℃ by water cooling, keeping the pressure at 10MPa and the duration for 0.5h, and obtaining the solid electrolyte film.

The composite solid electrolyte membrane prepared in example 1, i.e., the solid electrolyte membrane of a gradient-distributed polyethylene oxide @ garnet-type oxide lithium metal battery, was analyzed:

wherein FIG. 2 is SEM images of the low concentration side and the high concentration side of LLZTO of the solid electrolyte membrane prepared in example 1 of the present invention. It can be seen from fig. 2a that the particles of LLZTO on the side contacting the lithium negative electrode are few, and the particles of LLZTO on this side are mostly the smaller ones, and the diameter is about 3 μm or so. From FIG. 2b, it can be seen that the LLZTO particles on the other side are much more abundant, and have higher concentration, and are uniformly dispersed in the horizontal direction. From fig. 2c, it can be seen that the bright points of the inorganic particles gradually decrease from top to bottom, and the concentration of the inorganic particles gradually decreases from top to bottom; the elemental maps of Zr and La elements in fig. 2d and 2e further confirm that the concentration gradient distribution of LLZTO in the vertical direction is achieved in the electrolyte membrane, demonstrating that the expected effect is achieved.

Fig. 3 is an XRD pattern of the solid electrolyte membrane prepared in example 1 of the present invention. From the XRD pattern, it can be seen that all diffraction peaks in this material can be well aligned with LLZTO (JCPDSNO.80-0457), and that the peaks detected at 18.4 °,22.5 °,24.9 °,26.8 °,30.1 °,33.2 °,37.3 °,42.3 °,50.2 °,51.2 °,52.3 °,55.2 °,56.3 ° correspond to the (221), (220), (321), (400), (420), (422), (521), (532), (640), (633), (642), (732) and (800) crystal planes of LLZTO. It was demonstrated that LLZTO did not deteriorate or react with other substances throughout the test.

FIG. 4 shows the assembly of the solid electrolyte membrane prepared in inventive example 1 into a symmetrical cell at 0.1mAh cm ^-2 Test pattern (Current Density of 0.1mA cm) ^-2 ). As can be seen from FIG. 5, at 0.1mAh cm ^-2 Bottom assembled symmetrical electricThe cell can stably run for 900 hours without obvious short circuit and polarization phenomena, and the cell is proved to have good cycle performance.

FIG. 5 shows that in example 1 of the present invention, PEO/LLZTO composite solid electrolyte membrane is used as an electrolyte, and LiNi is used _1/ ₃ Co _1/3 Mn _1/3 O ₂ (NCM) is the anode, and the electrochemical performance test chart is obtained after the battery is assembled into the full battery, the test voltage is 2.5-4.3V, the charge-discharge current is 0.1-5C, and the long-cycle charge-discharge current is 1C. As can be seen from the figure, the composite solid electrolyte has the characteristics of good interface contact, high ionic conductivity, high mechanical strength, good flexibility and the like, so that the full battery has better rate performance and cycle performance. The initial specific discharge capacity at 0.1C was 153.4mAh g ^-1 The coulomb efficiency was 96.1%. At higher current densities of 0.2C and 0.5C, the cells maintained 146.5 and 132.7mAh g, respectively ^-1 The specific capacity of (a) was restored to a level similar to that before high rate cycling when it was restored to 0.2C and 0.1C after high rate cycling. The battery can maintain a capacity retention rate of 85.3% after being cycled 200 times at 1C and 60 ℃, and has a high coulombic efficiency of 90.3%.

In conclusion, the test results show that the preparation method provided by the invention successfully prepares the organic/inorganic composite solid electrolyte membrane with the gradient distribution characteristic. The solid electrolyte membrane of the polyethylene oxide @ garnet-type oxide lithium metal battery with the gradient distribution characteristics in example 1 realizes uniform dispersion of the LLZTO nanoparticles in the PEO electrolyte solution by simple solution mixing and stirring, effectively improves the strength and ion conduction capability of the PEO-based electrolyte by using the excellent mechanical properties and lithium ion transmission capability of the LLZTO nanoparticles, and regulates and controls the vertical concentration distribution of the LLZTO nanoparticles in the electrolyte, so that the concentration of the LLZTO nanoparticles on one side contacting the lithium negative electrode is lower, the interface impedance is reduced, and the concentration of the other side is higher, thereby realizing rapid transmission of lithium ions. In addition, the symmetric cell assembled with this electrolyte membrane can be stably cycled for 900 hours. In addition, the solid electrolyte membrane has good flexibility, can be used for preparing a flexible energy storage device besides being applied to the field of lithium ion batteries, continuously supplies power for wearable electronic equipment, and has good application prospect.

Example 2

The preparation process of the composite solid electrolyte membrane provided by the embodiment is as follows:

1g of Polyacrylonitrile (PAN), 1g of Lithium Lanthanum Zirconium Oxide (LLZO) and 0.6g of LiTFSI powder are dispersed in 10ml of N, N-Dimethylformamide (DMF), wherein the particle size of LLZO is 200nm-8 mu m, the mixture is continuously stirred for more than 12 hours at 800rmp to obtain uniformly dispersed yellow suspension, the yellow suspension is poured into a polytetrafluoroethylene evaporation dish and dried in a vacuum oven, the yellow suspension is pre-dried at 30 ℃ for 3 hours, then dried at 60 ℃ for 12 hours, the obtained film is placed under a hot press for hot pressing, the pressure is kept at 10MPa, the temperature is 60 ℃, the duration time is 1 hour, then the temperature is reduced to 30 ℃ by water cooling, the pressure is kept at 10MPa, and the duration time is 0.5 hour, so that the solid electrolyte film is prepared.

By analyzing the composite solid electrolyte membrane provided in this example and produced in this example 2, the results are shown in FIG. 6, and FIG. 6 is an SEM photograph of the LLZO low concentration side and the LLZO high concentration side of the composite solid electrolyte membrane produced in this example 2. It can be seen from fig. 6a that the particles of LLZO at the side contacting the lithium negative electrode are fewer, and that the particles of LLZO at this side are mostly smaller ones, having a diameter of about 3 μm or so. It can be seen from fig. 6b that the LLZO particles on the other side are present in a large amount and have a high concentration, and are uniformly dispersed in the horizontal direction, thus proving that the LLZO in the electrolyte membrane realizes a gradient distribution of concentration in the vertical direction, achieving the desired effect, and further proving that an organic/inorganic composite solid electrolyte membrane having a gradient distribution characteristic can be prepared by a natural sedimentation method.

Example 3

0.7g of polyvinylidene fluoride (PVDF), 1g of Lithium Aluminum Titanium Phosphate (LATP) and 0.5g of LiTFSI powder are dispersed in 10ml of DMF, wherein the particle size of the LATP is 200nm-8 mu m, the LATP is continuously stirred for more than 12h at 800rmp to obtain a uniformly dispersed milky suspension, the milky suspension is poured into a polytetrafluoroethylene evaporation dish and dried in a vacuum oven, the milky suspension is firstly pre-dried for 3h at 30 ℃, then dried for 12h at 60 ℃, the obtained film is put under a hot press for hot pressing, the pressure is kept at 10MPa, the temperature is 60 ℃, the duration time is 1h, then the water cooling is carried out to reduce the temperature to 30 ℃, the pressure is kept at 10MPa, and the duration time is 0.5h, thus obtaining the solid electrolyte film.

By analyzing the organic-inorganic composite solid electrolyte prepared in example 3, the results are shown in fig. 7, and fig. 7 is an SEM image of the low concentration side and the high concentration side of the LATP of the organic-inorganic composite solid electrolyte membrane prepared in example 3. It can be seen from fig. 7a that the LATP on the side contacting the lithium negative electrode has fewer particles, and the LATP on this side has many particles of which are smaller, having a diameter of about 3 μm or so. As can be seen from fig. 7b, the LATP particles on the other side are much in content, high in concentration, and uniformly dispersed in the horizontal direction, which proves that the LATP in the electrolyte membrane realizes the gradient distribution of concentration in the vertical direction, achieving the expected effect, and further proves that an organic/inorganic composite solid electrolyte membrane with the gradient distribution characteristic can be prepared by the natural sedimentation method.

It should be noted that the short names of letters in the present invention are all fixed short names in the field, and some of the short names of letters are explained as follows: SEM image: electronic scanning and image display; XRD pattern: an X-ray diffraction pattern; SEI: a solid electrolyte interface film.

In summary, the composite solid electrolyte membrane of the embodiment of the present invention has the following features compared to the prior art:

(1) The uniform electrolyte membrane prepared by directly mixing the polymer powder and the inorganic particles has poor interface contact, is easy to cause the uneven deposition of lithium ions, leads the rapid growth of lithium dendrites, pierces the diaphragm to cause the short circuit of the battery, and compared with the electrolyte membrane, the electrolyte membrane for regulating and controlling the vertical concentration gradient of the inorganic nanoparticles in the organic electrolyte can reduce the concentration of the inorganic particles on one side contacting with the lithium cathode, has tight interface contact, reduces the interface impedance, realizes the rapid transmission effect of the lithium ions by gradually increasing the concentration of the inorganic particles in the vertical direction, and has better safety performance while loading a higher energy density electrode.

(2) The method adopts a natural sedimentation method for preparation, achieves the effect of the organic-inorganic composite electrolyte membrane, does not have an interface layer of the organic-inorganic composite electrolyte, can realize faster lithium ion transmission, has simple preparation method, and is suitable for large-scale industrial production.

(3) The invention provides a preparation method of an organic/inorganic composite solid electrolyte membrane with gradient distribution characteristics, which comprises the steps of uniformly dispersing inorganic particles in a solution through magnetic stirring, and enabling the inorganic particles to have gradient distribution in the vertical direction through a natural sedimentation mode; the electrolyte separator is subsequently thinned by means of hot and cold pressing, and rapid shuttling of lithium ions therein can be achieved.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite solid electrolyte membrane comprising an organic phase body and inorganic particles, the composite solid electrolyte membrane having a first surface and a second surface opposite to the first surface, the particle content of the inorganic particles gradually increasing in a direction of extension of the first surface to the second surface.

2. The composite solid electrolyte membrane according to claim 1, wherein the inorganic particles are uniformly distributed in a cross section of the composite solid electrolyte membrane parallel to the first surface or the second surface.

3. The composite solid electrolyte membrane according to claim 1, wherein the inorganic particles have a particle diameter of 200nm to 8 μm;

preferably, the total mass content of the inorganic particles in the composite solid electrolyte membrane is 0.3g to 1g;

preferably, the inorganic particles are selected from any one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide and tantalum-doped lithium lanthanum zirconium oxide;

preferably, the thickness of the composite solid electrolyte membrane is 100 μm to 400 μm.

4. The method for producing a composite solid electrolyte membrane according to any one of claims 1 to 3, characterized by comprising: and (3) standing, drying and hot-pressing the organic suspension containing the inorganic particles.

5. The method according to claim 4, wherein the mass ratio of the inorganic particles to the solvent in the organic suspension is (0.5 to 1.5): (10-100);

preferably, the organic suspension further contains a polymer powder and a lithium salt dissolved therein, and more preferably, the mass ratio of the polymer powder, the inorganic particles and the lithium salt is (0.5-1): (0.5-1.5): (0.3 to 1), more preferably, the molecular weight of the polymer powder is 100000 to 800000;

preferably, the lithium salt includes LiTFSI powder, liPSTFSI powder or LiClO ₄ At least one of (1).

6. The method according to claim 5, wherein the step of preparing the organic suspension containing inorganic particles comprises: uniformly mixing polymer powder, inorganic particles and LiTFSI powder in a solvent, preferably stirring, more preferably, the stirring speed is 10-1500 rpm, and the stirring time is 12-48 h;

preferably, the solvent is selected from any one of acetonitrile, N-dimethylformamide and N-methylpyrrolidone.

7. The production method according to any one of claims 4 to 6, wherein the standing drying is performed in a mold;

preferably, drying is carried out in a vacuum oven;

preferably, the pre-drying is carried out at the temperature of 20-40 ℃ for 2-6 h, and then the drying is carried out at the temperature of 50-80 ℃ for 12-24 h.

8. The preparation method according to any one of claims 4 to 6, wherein the hot pressing is performed by continuously pressing at a temperature of 40 ℃ to 70 ℃ for 0.5h to 2h under a pressure of 5MPa to 20MPa, and the pressure is kept stable during the pressing;

preferably, the preparation method further comprises the steps of reducing the temperature to 20-30 ℃ after hot pressing, wherein the temperature reduction process is carried out under the pressure of 5-20 MPa, the duration is 0.5-1 h, and the pressure is kept stable in the temperature reduction process.

9. A lithium ion battery comprising a positive electrode, a lithium metal negative electrode, and the composite solid electrolyte membrane of any one of claims 1 to 3, wherein the first surface of the composite solid electrolyte membrane is connected to the lithium metal negative electrode and the second surface is connected to the positive electrode.

10. Use of a composite solid electrolyte membrane according to any one of claims 1 to 3 for the preparation of a lithium ion battery or a flexible energy storage device.