Composite ceramic solid electrolyte diaphragm material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a composite ceramic solid electrolyte diaphragm material and a preparation method and application thereof. Wherein the lithium ion conductor filler is LLZTO (lithium zinc oxide) nano particles coated with polydopamine; the mass dosage of the polydopamine is not more than 2 times that of the LLZTO nanoparticles, and the thickness of a coating layer formed by the polydopamine is less than 10nm. Compared with the prior art, the problems of dispersity and contact of nano solid electrolyte particles in a polymer substrate in the prior art are solved. According to the scheme, the contact interface of LLZTO nanoparticles and PVDF-HFP is optimized by introducing the interface layer and particularly utilizing the bidirectional cohesiveness of polydopamine, and the distribution of the nanofiller in a polymer is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a composite ceramic solid electrolyte diaphragm material and a preparation method and application thereof. Background Art

[0002] With the advancement of science and technology, modern society's demand for energy is increasing. Faced with environmental pollution and global resource constraints caused by fossil fuels, electrochemical energy sources, represented by lithium-ion batteries, are attracting increasing attention. Traditional organic solvent electrolytes offer strong lithium-ion conductivity and excellent wettability at the interfaces between the positive and negative electrodes. However, they are volatile, leaky, toxic, dendrite-resistant, and flammable, raising safety concerns.

[0003] Solid-state electrolytes have higher thermal stability and the ability to block dendrites, and can be roughly divided into two categories: inorganic solid electrolytes and polymer solid electrolytes. Inorganic solid electrolytes are stronger, sufficient to resist the damage caused by dendrite penetration, and are non-flammable. However, the brittleness of inorganic solid electrolytes and various interface issues have hindered their development. The soft surface of polymers alleviates the problem of interface contact, and their plasticity also opens up more application possibilities. However, their inherent ionic conductivity is low, and their excessive softness makes them unable to resist dendrite penetration during long-term lithium ion cycling. Therefore, the composite gel polymer electrolyte obtained by compounding polymers with lithium ion conductor fillers and activating them with plasticizers has become popular. This composite polymer electrolyte combines the strength of solid electrolytes with the ionic conductivity of organic electrolytes.

[0004] An excellent composite polymer electrolyte should meet the following characteristics: (1) It has sufficient ionic conductivity to ensure that lithium ions can pass through the electrolyte smoothly; (2) It has sufficient strength to withstand the puncture threat brought by lithium dendrites; (3) When used in lithium-oxygen batteries, it should be stable to oxygen, air and water. Therefore, when designing a solid electrolyte that can be used in lithium-oxygen batteries, the above conditions should be taken into consideration. Common polymer substrates include PEO, PAN, PMMA, PVDF, PVDF-HFP, etc. They each have their own advantages and disadvantages. For example, PEO has low ionic conductivity at room temperature and needs to be used at higher temperatures. PAN and PMMA are hard and brittle. In this regard, people have modified PVDF by using PVDF and other polymer monomers to form a co-block polymer, thereby improving its ionic conductivity. Therefore, PVDF-HFP has become one of the more commonly used polymer substrates. Solid electrolytes, such as LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ), which has the characteristics of high ionic conductivity, high strength and easy preparation.

[0005] For example, the prior art CN120015917A discloses a composite gel polymer electrolyte, a preparation method, and a battery containing the same, and CN118213612A discloses a co-doped asymmetric composite solid electrolyte, a battery, and a preparation method thereof, both of which construct a PVDF-HFP / LLZTO mixed electrolyte composite material; however, there are dispersion and contact problems with the nano-solid electrolyte particles in the polymer matrix, resulting in the following risks when the material is used as an electrolyte separator: uneven ion channel distribution, reduced lithium ion transmission efficiency, and the risk of inducing dendrite growth. Summary of the Invention

[0006] The present invention aims to address at least one of the aforementioned issues by providing a composite ceramic solid electrolyte membrane material, its preparation method, and its application, addressing the existing dispersion and contact issues of nano-solid electrolyte particles in polymer substrates. This solution optimizes the contact interface between LLZTO nanoparticles and PVDF-HFP by introducing an interface layer, specifically by leveraging the bidirectional bonding properties of polydopamine, thereby improving the distribution of the nanofiller in the polymer.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a composite ceramic solid electrolyte diaphragm material, which is composed of a polymer substrate and a lithium ion conductor filler;

[0009] in,

[0010] The lithium ion conductor filler is polydopamine-coated LLZTO nanoparticles;

[0011] The mass dosage of the polydopamine is no more than 2 times that of the LLZTO nanoparticles, and the thickness of the coating layer formed by the polydopamine is less than 10 nm.

[0012] Preferably, the polymer substrate includes PEO, PAN, PMMA, PVDF and PVDF-HFP.

[0013] Preferably, the polymer substrate is PVDF-HFP.

[0014] The solid electrolyte membrane of this scheme is prepared using a polymer substrate. Compared with conventional membranes, if a conventional membrane is used as a substrate, the ionic conductivity of the entire solid electrolyte membrane prepared will be reduced. This is because the membrane is a non-ionic conductor. If the electrolyte solidifies on the surface and in / on the pores of the membrane during the preparation process, the ion path will be blocked, affecting the ionic conductivity.

[0015] The second aspect of the present invention discloses a method for preparing a composite ceramic solid electrolyte membrane material as described above, comprising the following steps:

[0016] S1: adding dopamine hydrochloride to the buffer solution to adjust the pH, then adding LLZTO nanoparticles, and reflux reaction. The reaction product is filtered, washed and dried to obtain polydopamine-coated LLZTO nanoparticles;

[0017] S2: Adding a polymer substrate and polydopamine-coated LLZTO nanoparticles to an NMP solution, mixing them evenly, and then coating them on a substrate, and drying them to obtain the composite ceramic solid electrolyte membrane material.

[0018] Preferably, in step S1,

[0019] The buffer solution is an ethanol solution of tris(hydroxymethylaminomethane); and / or,

[0020] The pH adjustment is to adjust the pH of the mixed solution to a weak alkaline state using dilute hydrochloric acid; and / or,

[0021] The reflux reaction is carried out by condensing and refluxing at 50-80° C. and stirring for 20-36 hours.

[0022] More preferably, the weak alkalinity is pH=7.5-9; further preferably 8.5.

[0023] More preferably, the reflux reaction is carried out at 60° C. with condensation reflux and stirring for 24 hours.

[0024] Preferably, in step S1,

[0025] The LLZTO nanoparticles are prepared by the following steps:

[0026] LiOH, La2O3, ZrO2 and Ta2O5 were weighed and mixed according to the element ratio of LLZTO, and then ball-milled again after pre-calcination and tableting, and then sintered, crushed and ball-milled to obtain LLZTO nanoparticles;

[0027] The mass ratio of dopamine hydrochloride to LLZTO nanoparticles is 1.1-2:1.

[0028] More preferably, the mass ratio of dopamine hydrochloride to LLZTO nanoparticles is 1.2:1, that is, 120 mg of dopamine hydrochloride and 100 mg of LLZTO nanoparticles.

[0029] Preferably, the LLZTO nanoparticles are prepared by the following steps:

[0030] LiOH, La2O3, ZrO2 and Ta2O5 are weighed and mixed by ball milling according to the element ratio of LLZTO, wherein the amount of LiOH is 1.05-1.2 times the theoretical calculated amount; the mixed raw materials are ball milled for 1-2 hours, and then pre-calcined at 600-900°C for 2-5 hours to obtain a pre-calcined powder; the pre-calcined powder is ball milled again and pressed into tablets, and then sintered at 800-1200°C for 5-10 hours to obtain an LLZTO ceramic electrolyte; the LLZTO is crushed and ball milled for 8-20 hours to obtain LLZTO nanoparticles.

[0031] More preferably, the LLZTO nanoparticles are prepared by the following steps:

[0032] LiOH, La2O3, ZrO2 and Ta2O5 were weighed and mixed by ball milling according to the element ratio of LLZTO, wherein the amount of LiOH was 1.1 times the theoretical calculated amount; the mixed raw materials were ball milled for 1.5 hours and then pre-calcined at 700°C for 2 hours to obtain a pre-calcined powder; the pre-calcined powder was ball milled again and pressed into tablets, and then sintered at 900°C for 6 hours to obtain an LLZTO ceramic electrolyte; the LLZTO was crushed and ball milled for 10 hours to obtain LLZTO nanoparticles.

[0033] Preferably, in step S2, the polymer substrate is PVDF-HFP;

[0034] The mass ratio of the polymer substrate to the polydopamine-coated LLZTO nanoparticles is 200:35-60.

[0035] More preferably, the mass ratio of the polymer substrate to the polydopamine-coated LLZTO nanoparticles is 200:50.

[0036] The third aspect of the present invention discloses an application of any of the composite ceramic solid electrolyte membrane materials described above in lithium-ion batteries, such as lithium-lithium symmetrical batteries and lithium-oxygen batteries.

[0037] Preferably, the lithium-ion battery is prepared by the following steps:

[0038] T1: punching the composite ceramic solid electrolyte diaphragm material into sheets, and plasticizing it with LITFSI / TEGDME to obtain a diaphragm;

[0039] T2: Take metal pole pieces as the positive electrode and the negative electrode respectively, and then assemble the positive electrode, the negative electrode and the separator under a protective atmosphere to obtain the lithium-ion battery.

[0040] The working principle of the present invention is:

[0041] Dopamine is a biomaterial rich in hydroxyl and amino groups and has adhesive properties. It can generate polydopamine through oxidation, recombination, self-polymerization and other reactions in an alkaline solution environment. Polydopamine has adhesive properties and can adhere to the surfaces of most substances in nature, making it widely used in surface modification materials. This scheme uses the bidirectional adhesion of polydopamine to optimize the contact interface between LLZTO nanoparticles and PVDF-HFP, improve the distribution of nanofillers in the polymer, and prepare a composite ceramic solid electrolyte membrane. By adding polydopamine-coated LLZTO particles, the crystallinity of the polymer is improved, and more ion transmission channels are provided for the electrolyte. Polydopamine optimizes the binding interface between the nanofiller and the polymer, making the ion channel distribution more uniform, and improving the physical and electrochemical properties of the electrolyte membrane.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This scheme uses the bidirectional adhesion of polydopamine to optimize the contact interface between LLZTO nanoparticles and PVDF-HFP, improves the distribution of nanofillers in the polymer, and prepares a composite ceramic solid electrolyte membrane. By adding polydopamine-coated LLZTO particles, the crystallinity of the polymer is improved, and more ion transmission channels are provided for the electrolyte. Polydopamine optimizes the bonding interface between the nanofiller and the polymer, making the ion channel distribution more uniform, and improving the physical and electrochemical properties of the electrolyte membrane. The prepared PH-PDA@LLZTO composite ceramic solid electrolyte membrane can withstand a stress of 13MPa and can withstand a heating test at 150°C. The overall uniformity of the electrolyte is enhanced, the contact with the electrode is good, and the battery cycle is smoother. The PH-PDA@LLZTO composite ceramic solid electrolyte membrane is used to assemble a lithium-lithium symmetrical battery. At 0.1mA·cm -2 It can stably cycle for more than 1000 hours at the current density, which gives it certain application prospects in the future.

[0044] Compared to existing technologies, this proposal combines polydopamine, a solid electrolyte, and a polymer matrix into an electrolyte membrane, leveraging the synergistic effects of these three materials to develop a polymer electrolyte membrane with superior performance. The electrolyte membrane consists of two main components: a polymer matrix and an active filler. Polymer matrixes typically include PEO, PAN, PMMA, and PVDF, each with its own advantages and disadvantages. PEO has low ionic conductivity at room temperature and requires higher temperatures, while PAN and PMMA are hard and brittle. PVDF is often used in co-block copolymers with other monomers. Modification of PVDF improves its ionic conductivity, making PVDF-HFP a commonly used polymer matrix. The solid electrolyte LLZTO offers high ionic conductivity, strength, stability to water and oxygen, and ease of preparation, making it ideal as an active filler. Dispersion and contact issues with solid electrolyte nanoparticles in polymers can be addressed by introducing an interfacial layer. Dopamine is a biomaterial rich in hydroxyl and amino groups and exhibits adhesive properties. It can be converted into polydopamine through oxidation, recombination, and self-polymerization in an alkaline solution. Polydopamine has good adhesion and can adhere to the surfaces of most substances in nature. It is widely used in surface modification materials.

[0045] This patented method utilizes an excellent coating process to uniformly coat LLZTO nanoparticles with a small amount of polydopamine on a solid electrolyte membrane with a large surface area. The amount of polydopamine is up to twice that of the active filler, and the coating thickness is less than 10 nm. This achieves excellent electrical performance, far less than that achieved with conventional solid electrolyte coating technologies. The coated solid electrolyte is then composited with PVDF-HFP and activated with LITFSI / TEGDME to produce a composite gel polymer electrolyte. The electrolyte membrane has an ionic conductivity of up to 9.4×10 -4 S cm -1 , exceeding the existing related technology by more than 10%. At the same time, the electrolyte membrane has high mechanical strength and can effectively suppress lithium dendrites. The solid-state battery cycle can reach more than 1000 cycles, exceeding the level achieved by existing technologies. The electrolyte membrane has good adhesion to the positive and negative electrode interfaces, which can further reduce the interfacial impedance. This is also the key reason for its stable cycle of more than 1000 cycles.

[0046] This patent enables the direct preparation of solid electrolyte membranes, with a simple process suitable for mass production and large-scale production. Compared to existing technologies, such as the solution disclosed in CN115621535B, which requires separate film formation on the surfaces of the positive and negative electrodes and then lamination, it also overcomes the problems of cumbersome assembly processes and the battery's tendency to short-circuit, which makes it unsuitable for mass production. This is mainly due to the multi-directional bonding effect of the polydopamine coating, which improves the dispersion and binding of the nanoparticles in the polymer, allowing the LLZTO nanoparticles to better combine with PVDF-HFP. At the same time, in the interface layer, the multi-directional bonding effect of the polydopamine coating also allows for closer contact between the positive and negative electrodes and the solid electrolyte membrane, achieving better ion conductivity.

[0047] In addition, the technical solution in CN115621535B requires the positive and negative electrodes to be bonded together before the gel electrolyte precursor solidifies. This process is prone to uneven thickness of the intermediate electrolyte membrane, which can easily lead to the problem of lithium dendrites and even safety issues such as direct contact between the positive and negative electrodes. Compared with this existing technology, the solution of this patent directly prepares a solid electrolyte membrane. The membrane has high ionic conductivity, uniform thickness, high mechanical strength and toughness, can be well bonded to the positive and negative electrodes, and inhibit the growth of lithium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 (a) SEM image and (b) particle size distribution of LLZTO particles.

[0049] Figure 2 (a) is the infrared absorption spectra of LLZTO, PDA@LLZTO and pure PDA, and (b) is the TEM image of PDA@LLZTO.

[0050] Figure 3 (a) is the optical image of PH-LLZTO and PH-PDA@LLZTO, and (b) is the optical image of PH-PDA@LLZTO after bending.

[0051] Figure 4 (a) is the SEM image of PH-LLZTO and the corresponding optical image, (b) is the SEM image of PH-PDA@LLZTO and the corresponding optical image.

[0052] Figure 5 Stress-strain curves of PH-PDA@LLZTO, PH-LLZTO and PH film.

[0053] Figure 6 Thermal stability tests of (a) PH-PDA@LLZTO and (b) PH-LLZTO.

[0054] Figure 7 (a) EIS spectra and (b) ionic conductivity of PH-PDA@LLZTO, PH-LLZTO, and PH.

[0055] Figure 8 (a) is 0.1 mA cm -2 Time-voltage curves of (a) Li / PH / Li symmetric cells and (b) Li / PH / Li.

[0056] Figure 9 (a) is the time-voltage curve of the lithium symmetric battery formed by PH-PDA@LLZTO assembly at different rates, and (bc) are the local enlarged views of (a).

[0057] Figure 10 SEM images of the lithium anode of a symmetrical battery assembled with (a) PH-PDA@LLZTO and (b) PH-LLZTO after 50 cycles. DETAILED DESCRIPTION

[0058] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] In the following description, unless otherwise specified, the reagents used are conventional commercial products, the methods used are well known in the art, and other matters not covered may adopt existing technologies.

[0060] A composite ceramic solid electrolyte diaphragm material, composed of a polymer substrate and a lithium ion conductor filler;

[0061] in,

[0062] The lithium ion conductor filler is polydopamine-coated LLZTO nanoparticles;

[0063] The mass dosage of the polydopamine is no more than 2 times that of the LLZTO nanoparticles, and the thickness of the coating layer formed by the polydopamine is less than 10 nm.

[0064] Specifically, the polymer substrate includes PEO, PAN, PMMA, PVDF and PVDF-HFP; in particular, the polymer substrate is preferably PVDF-HFP.

[0065] A method for preparing a composite ceramic solid electrolyte diaphragm material comprises the following steps:

[0066] S1: adding dopamine hydrochloride to the buffer solution to adjust the pH, then adding LLZTO nanoparticles, and reflux reaction. The reaction product is filtered, washed and dried to obtain polydopamine-coated LLZTO nanoparticles;

[0067] S2: Adding a polymer substrate and polydopamine-coated LLZTO nanoparticles to an NMP solution, mixing them evenly, and then coating them on a substrate, and drying them to obtain the composite ceramic solid electrolyte membrane material.

[0068] Among them, in step S1,

[0069] The buffer solution is an ethanol solution of tris(hydroxymethylaminomethane); and / or,

[0070] The pH adjustment is to adjust the pH of the mixed solution to a weak alkaline state using dilute hydrochloric acid; and / or,

[0071] The reflux reaction is carried out at 50-80° C. with condensation and reflux and stirring for 20-36 hours; more preferably, the reflux reaction is carried out at 60° C. with condensation and reflux and stirring for 24 hours.

[0072] The LLZTO nanoparticles are prepared by the following steps:

[0073] LiOH, La2O3, ZrO2 and Ta2O5 were weighed and mixed according to the element ratio of LLZTO, and then ball-milled again after pre-calcination and tableting, and then sintered, crushed and ball-milled to obtain LLZTO nanoparticles;

[0074] Specifically:

[0075] LiOH, La2O3, ZrO2 and Ta2O5 are weighed and mixed by ball milling according to the element ratio of LLZTO, wherein the amount of LiOH is 1.05-1.2 times (preferably 1.1 times) the theoretical calculated amount; the mixed raw materials are ball milled for 1-2 hours (preferably 1.5 hours), and then pre-calcined at 600-900°C for 2-5 hours (preferably 700°C for 2 hours) to obtain a pre-calcined powder; the pre-calcined powder is ball milled again and tableted, and then sintered at 800-1200°C for 5-10 hours (preferably 900°C for 6 hours) to obtain an LLZTO ceramic electrolyte; the LLZTO is crushed and ball milled for 8-20 hours (preferably 10 hours) to obtain LLZTO nanoparticles;

[0076] The dosage ratio of dopamine hydrochloride to LLZTO nanoparticles is 1.1 to 2:1, preferably 1.2:1, i.e., 120 mg of dopamine hydrochloride and 100 mg of LLZTO nanoparticles.

[0077] In step S2, the polymer substrate is PVDF-HFP;

[0078] The mass ratio of the polymer substrate to the polydopamine-coated LLZTO nanoparticles is 200:35-60, and more preferably 200:50.

[0079] The composite ceramic solid electrolyte membrane material is prepared to form an electrolyte membrane to be assembled into a lithium-ion battery, such as a lithium-lithium symmetrical battery and a lithium-oxygen battery. Specifically, the composite ceramic solid electrolyte membrane material is prepared to form an electrolyte membrane by the following steps:

[0080] T1: punching the composite ceramic solid electrolyte diaphragm material into sheets, and plasticizing it with LITFSI / TEGDME to obtain a diaphragm;

[0081] T2: Take metal pole pieces (such as lithium pole pieces) as the positive electrode and the negative electrode respectively, and then assemble the positive electrode, the negative electrode and the separator under a protective atmosphere to obtain the lithium-ion battery.

[0082] Example 1

[0083] (1) Preparation of nano-LLZTO particles: According to the element ratio of LLZTO, LiOH, La2O3, ZrO2, and Ta2O5 were weighed as raw materials to prepare LLZTO. Among them, an additional 10% of the original amount of LiOH was added to the total amount of LiOH to supplement the volatilization of the lithium source during the preparation process. The mixed raw materials were ball milled for 1.5 hours, mixed evenly, and pre-calcined at 700°C for 2 hours. The obtained pre-calcined powder was ball milled, pressed into tablets, and finally sintered at 900°C for 6 hours to obtain LLZTO ceramic electrolyte. After manually crushing LLZTO, it was ball milled for 10 hours using a ball mill to obtain nano-LLZTO particles.

[0084] (2) Preparation of polydopamine (PDA)-coated LLZTO nanoparticles: Prepare a buffer solution using 60 ml of anhydrous ethanol and 72.6 mg of tris(hydroxymethyl)aminomethane. Add 120 mg of dopamine hydrochloride, dissolve thoroughly, and titrate to pH 8.5 with dilute hydrochloric acid. Add LLZTO nanoparticles to the solution, reflux under condensation at 60°C, and stir for 24 hours. After filtration, washing, and drying, polydopamine-coated LLZTO nanoparticles are obtained.

[0085] (3) Preparation of a composite ceramic solid electrolyte membrane: 200 mg of PVDF-HFP was dissolved in NMP, and 50 mg of polydopamine-coated LLZTO particles were added. After the solution was mixed thoroughly, it was coated on a glass plate using a 250 μm-thick doctor blade. The resulting membrane was then transferred to a vacuum oven and dried at 80°C for 24 h to obtain a PH-PDA@LLZTO composite ceramic solid electrolyte membrane.

[0086] (4) Assembly of lithium-lithium symmetric cells: The prepared PH-PDA@LLZTO composite ceramic solid electrolyte membrane was punched into 16 mm discs using a punching machine and plasticized with 1M LITFSI / TEGDME. The lithium-lithium battery consists of a negative electrode, an electrolyte, and a positive electrode. Both the positive and negative electrodes are directly 12 mm lithium metal discs. The entire assembly process is completed in an argon glove box. After the battery is allowed to rest, it is tested at 25°C.

[0087] Comparative Example 1

[0088] (1) Preparation of nano-LLZTO particles: According to the element ratio of LLZTO, LiOH, La2O3, ZrO2, and Ta2O5 were weighed as raw materials to prepare LLZTO. Among them, an additional 10% of the original amount of LiOH was added to the total amount of LiOH to supplement the volatilization of the lithium source during the preparation process. The mixed raw materials were ball milled for 1.5 hours, mixed evenly, and pre-calcined at 700°C for 2 hours. The obtained pre-calcined powder was ball milled, pressed into tablets, and finally sintered at 900°C for 6 hours to obtain LLZTO ceramic electrolyte. After manually crushing LLZTO, it was ball milled for 10 hours using a ball mill to obtain nano-LLZTO particles.

[0089] (2) Preparation of a composite ceramic solid electrolyte membrane: 200 mg of PVDF-HFP was dissolved in NMP, and 50 mg of LLZTO particles were added. After the solution was mixed thoroughly, it was coated on a glass plate using a scraper of the same thickness as in Example 1. The resulting solution was then transferred to a vacuum oven and dried at 80°C for 24 h to obtain a PH-LLZTO composite ceramic solid electrolyte membrane.

[0090] (3) Assembly of lithium-lithium symmetric battery: The prepared PH-LLZTO composite ceramic solid electrolyte membrane was punched into 16 mm discs using a punching machine and plasticized with 1M LITFSI / TEGDME. The lithium-lithium battery consists of a negative electrode, electrolyte, and positive electrode. Both the positive and negative electrodes are directly 12 mm lithium metal discs. The entire assembly process is completed in an argon glove box. After the battery is allowed to stand, it is tested at 25°C.

[0091] Comparative Example 2

[0092] (1) Preparation of PVDF-HFP membrane: 200 mg of PVDF-HFP was dissolved in NMP. After the solution was mixed evenly, it was coated on a glass plate using a scraper of the same thickness as in Example 1. The resulting solution was then transferred to a vacuum oven and dried at 80°C for 24 h to obtain a pH membrane.

[0093] (2) Assembly of lithium-lithium symmetric cells: The prepared pH diaphragm was punched into 16 mm discs using a punching machine and plasticized with 1 MLITFSI / TEGDME. The lithium-lithium battery consists of a negative electrode, an electrolyte, and a positive electrode. Both the positive and negative electrodes are directly 12 mm lithium metal discs. The entire assembly process is completed in an argon glove box. After the battery is allowed to rest, it is tested at 25°C.

[0094] like Figure 1 As shown in (a), it can be observed that most particles are small in size. At the same time, the particle size distribution of LLZTO particles was statistically analyzed. Statistical results Figure 1 (b) shows that most of the particle sizes are distributed between 200nm and 400nm, with an average particle size of 288.3nm. Compared with the SEM images of the particles, it can be concluded that after the ball milling process, the LLZTO particles are broken into small-sized nanoparticles.

[0095] like Figure 2 As shown, it can be observed that PDA@LLZTO and pure PDA have the same peak at 2975 cm -1 There is a peak representing CH stretching vibration at 3403cm on the PDA@LLZTO spectrum, but there is no such peak on pure LLZTO, which indicates that organic matter exists on the surface of LLZTO after the coating process. -1 The peak at 1623 cm represents the stretching vibration peak of NH or OH. -1 , 1500cm -1 、1455cm -1 The peak at 1281 cm represents the C=C skeleton vibration peak of the benzene ring, and the peak at 1281 cm -1 CO and 1044cm -1 CN stretching vibration peak. These groups are consistent with the structural composition of polydopamine. This shows that PDA exists on the surface of LLZTO after the coating experiment. In order to determine the form of polydopamine on the surface of LLZTO, TEM ( Figure 2 (b) Observation of the structural composition of PDA@LLZTO. The image clearly shows the LLZTO lattice stripes and the polymer layer attached to the LLZTO surface. There are no obvious gaps or faults between the two. The coating is evenly distributed, with an overall thickness of approximately 7.2 nm. This indicates that a very thin layer of polydopamine is uniformly coated on the surface of the LLZTO particles.

[0096] The use of polydopamine-coated LLZTO particles and PVDF-HFP composites first brings about a change in appearance. Optical pictures such as Figure 3As shown, the color of PH-PDA@LLZTO changes to brownish-yellow. This is because the powder changes from white to brownish-yellow after the coating experiment, while the coating layer itself is brownish-yellow. Furthermore, distinct particles can be observed in the appearance of PH-LLZTO, while PH-PDA@LLZTO has a uniform texture. Furthermore, the introduction of the coating layer does not affect the flexible nature of the polymer electrolyte, allowing it to withstand changes such as bending and reduction.

[0097] At the same time, SEM images of the surfaces of PH-PDA@LLZTO and PH-LLZTO were taken ( Figure 4 Due to their small size and high surface energy, LLZTO nanoparticles agglomerate during polymer compounding, resulting in uneven distribution of the filler within the polymer matrix. The introduction of a polydopamine coating effectively improves this phenomenon. The bidirectional bonding effect of polydopamine improves the dispersion and binding of the nanoparticles within the polymer, enabling better integration of the LLZTO nanoparticles with PVDF-HFP.

[0098] The improvement of the polydopamine coating on the composite polymer electrolyte is first reflected in the physical properties, and the overall strength of the membrane has been improved. Tensile tests were conducted on PH-PDA@LLZTO, PH-LLZTO and PVDF-HFP. Figure 5 PVDF-HFP itself has excellent flexibility and can be stretched to 1.33 times its original length, but its strength is insufficient, and it can only withstand a tensile force of 3MPa. After the introduction of fillers, although some stretchability is sacrificed, the overall stress tolerance is improved. With the addition of polydopamine, the stress and strain tolerance are further improved, more than doubling.

[0099] Thermal safety is also important for batteries. Once dendrites penetrate, the battery will release a large amount of heat due to short circuit, which will further affect the diaphragm. Therefore, a heating test is used to test the heat resistance of the electrolyte. Figure 6 As shown in Figure 2, after heating at 150°C for 10 min, PVDF-HFP quickly experienced thermal shrinkage and deformation ( Figure 6 (b)), indicating that it has poor thermal stability and cannot maintain its shape at higher temperatures. In contrast, PH-PDA@LLZTO can still maintain its shape after heating without obvious deformation ( Figure 6 (a)), indicating that PH-PDA@LLZTO has good thermal stability.

[0100] The improvement of PVDF-HFP crystallinity improves the ionic conductivity of solid electrolyte. Figure 7As shown in the figure, due to the poor crystallinity of polymers, the ionic conductivity of PVDF-HFP, also a polymer, is relatively low, only 1.2×10 -5 S cm -1 After adding lithium ion conductor fillers, the ionic conductivity of PH-LLZTO is 3.08×10 -4 S cm -1 The ionic conductivity of PH-PDA@LLZTO is 9.4×10 -4 S cm -1 The ionic conductivity of both materials has been significantly improved compared to pure polymers. The ionic conductivity of PH-PDA@LLZTO is slightly lower than that of PH-LLZTO. This is because the polydopamine layer itself cannot conduct lithium ions, which slightly affects the overall ionic conductivity, but does not have a significant impact, and is at a comparable level to PH-LLZTO.

[0101] In order to explore the lithium deposition / stripping behavior and characteristics of the composite polymer electrolyte in the battery, a lithium-lithium symmetric battery was first assembled to perform constant current charge and discharge tests. Figure 8 As shown. At 0.1 mA·cm -2Under the test conditions, the charge and discharge overpotential of PH-PDA@LLZTO is 0.05V. The overpotential of PH-LLZTO is close to that of the former, but it can be observed from the image that its overpotential is slightly lower than that of the former. Although the overpotentials of the two are very close, PH-PDA@LLZTO far exceeds PH-LLZTO in terms of cycle time. The former can be stably cycled for more than 1000h, while the latter has a short circuit inside the battery when it cycles to about 160h, resulting in a sudden voltage drop. This is because lithium dendrites grow on the negative electrode side. PH-LLZTO cannot withstand the dendrites due to its own strength problems. Eventually, the dendrites pierce the diaphragm, causing the battery to fail. The growth of lithium dendrites conforms to the "tip discharge" effect. Due to the uneven dispersion of LLZTO in the polymer and the unevenness of PH-LLZTO itself, lithium dendrites are more inclined to break through the weak points of the diaphragm, thereby accelerating the death of the battery. In PH-PDA@LLZTO, thanks to the bidirectional adhesion of the polydopamine layer, the bonding interface between LLZTO and PVDF-HFP is optimized, thereby improving the overall strength of the electrolyte and significantly improving the cycle life of the battery. In contrast, pure PVDF-HFP has a lower intrinsic ionic conductivity and a polarization potential much higher than the previous two, with an overpotential of around 0.1V and poor self-strength. The battery short-circuited after about 60 hours of cycling. At the same time, it can be seen that the charge and discharge potential of PH-PDA@LLZTO remains very stable, with no obvious voltage changes. Comparing the charge and discharge platforms of PH-LLZTO and PH-PDA@LLZTO, it can be clearly seen that the charge and discharge platform of PH-PDA@LLZTO is more stable. Through these phenomena, it can be concluded that by introducing the polydopamine coating layer, the ion transport process of the composite polymer electrolyte is more stable, the overall strength is enhanced, and the battery cycle life is improved.

[0102] Then, the lithium-lithium symmetric battery using PH-PDA@LLZTO as the electrolyte was tested at different current densities. Figure 9 As shown, PH-PDA@LLZTO at 0.1 mA·cm -2 , 0.2mA·cm -2 , 0.5mA·cm -2 The battery can be cycled stably at all three rates, with polarization potentials of approximately 45mV, 75mV, and 180mV at the three rates, and the polarization potential of the battery can remain stable at each rate. Figure 9 As shown in (a), after continuous cycling at three current densities, the battery returns to 0.1 mA cm -2When the battery is fully charged, the battery can still cycle stably, and the potential before and after does not change significantly. The cycle time exceeds 200h, indicating that PH-PDA@LLZTO can withstand the influence of changes in current at different rates, showing the good rate performance of PH-PDA@LLZTO. Figure 9 (b) Figure 9 (c) As can be seen, the curves remain consistent when the charge and discharge currents vary, showing no signs of short-circuiting. Therefore, the rate test demonstrates that the symmetrical PH-PDA@LLZTO battery has excellent rate performance. PH-PDA@LLZTO can withstand a wide range of current variations, demonstrating its excellent ion transport, physical strength, and electrochemical stability.

[0103] In order to explore the reason why PH-PDA@LLZTO resists dendrites, the deposition and growth of dendrites were observed in the work. -2 After 50 cycles, the lithium sheet on one side of the battery was removed and the surface morphology was observed using a scanning electron microscope. Figure 10 As shown in the figure, the lithium metal surface corresponding to PH-PDA@LLZTO is relatively smooth, while the lithium metal surface corresponding to PH-LLZTO has a large number of cracks. This shows that under the action of polydopamine, the interface between PVDF-HFP and LLZTO is improved, the distribution of ion transport channels in the polymer matrix is ​​optimized, and the ion distribution becomes more uniform. Therefore, the negative electrode forms a more uniform deposition during the cycle, thus showing that PH-PDA@LLZTO has a strong ability to inhibit dendrites.

[0104] Example 2

[0105] The preparation method of this embodiment is basically the same as that of Example 1, with the main differences being that in step (2), the pH is adjusted to 7.5; and the reflux reaction is carried out by condensing and refluxing at 50° C. and stirring for 36 h.

[0106] Example 3

[0107] The preparation method of this embodiment is basically the same as that of Example 1, with the main differences being that in step (2), the pH is adjusted to 9; and the reflux reaction is carried out by condensing and refluxing at 80° C. and stirring for 20 h.

[0108] Example 4

[0109] The preparation method of this embodiment is basically the same as that of Example 1, with the main difference being that in step (3), the amount of polydopamine-coated LLZTO particles used is 35 mg.

[0110] Example 5

[0111] The preparation method of this embodiment is basically the same as that of Example 1, with the main difference being that in step (3), the amount of polydopamine-coated LLZTO particles used is 60 mg.

[0112] Example 6

[0113] The preparation method of this embodiment is basically the same as that of Example 1, with the main difference being that in step (1), pre-calcination is performed at 600° C. for 5 h; and sintering is performed at 1200° C. for 8 h.

[0114] Example 7

[0115] The preparation method of this embodiment is basically the same as that of Example 1, with the main difference being that in step (1), pre-calcination is performed at 900° C. for 2 h; and sintering is performed at 800° C. for 20 h.

[0116] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A composite ceramic solid electrolyte membrane material, characterized in that: It is composed of a polymer substrate and a lithium ion conductor filler; in, The lithium ion conductor filler is polydopamine-coated LLZTO nanoparticles; The mass dosage of the polydopamine is no more than 2 times that of the LLZTO nanoparticles, and the thickness of the coating layer formed by the polydopamine is less than 10 nm.

2. A composite ceramic solid electrolyte membrane material according to claim 1, characterized in that: The polymer substrate includes PEO, PAN, PMMA, PVDF and PVDF-HFP.

3. The composite ceramic solid electrolyte membrane material according to claim 1, characterized in that: The polymer substrate is PVDF-HFP.

4. A method for preparing a composite ceramic solid electrolyte membrane material according to any one of claims 1 to 3, characterized in that: The steps include: S1: adding dopamine hydrochloride to the buffer solution to adjust the pH, then adding LLZTO nanoparticles, and reflux reaction. The reaction product is filtered, washed and dried to obtain polydopamine-coated LLZTO nanoparticles; S2: Adding a polymer substrate and polydopamine-coated LLZTO nanoparticles to an NMP solution, mixing them evenly, and then coating them on a substrate, and drying them to obtain the composite ceramic solid electrolyte membrane material.

5. The method for preparing a composite ceramic solid electrolyte diaphragm material according to claim 4, characterized in that: In step S1, The buffer solution is an ethanol solution of tris(hydroxymethylaminomethane); and / or, The pH adjustment is to adjust the pH of the mixed solution to a weak alkaline state using dilute hydrochloric acid; and / or, The reflux reaction is carried out by condensing and refluxing at 50-80° C. and stirring for 20-36 hours.

6. The method for preparing a composite ceramic solid electrolyte diaphragm material according to claim 4, characterized in that: In step S1, The LLZTO nanoparticles are prepared by the following steps: LiOH, La2O3, ZrO2 and Ta2O5 were weighed and mixed according to the element ratio of LLZTO, and then ball-milled again after pre-calcination and tableting, and then sintered, crushed and ball-milled to obtain LLZTO nanoparticles; The mass ratio of dopamine hydrochloride to LLZTO nanoparticles is 1.1-2:

1.

7. The method for preparing a composite ceramic solid electrolyte diaphragm material according to claim 6, characterized in that: The LLZTO nanoparticles are prepared by the following steps: LiOH, La2O3, ZrO2 and Ta2O5 are weighed and mixed by ball milling according to the element ratio of LLZTO, wherein the amount of LiOH is 1.05-1.2 times the theoretical calculated amount; the mixed raw materials are ball milled for 1-2 hours, and then pre-calcined at 600-900°C for 2-5 hours to obtain a pre-calcined powder; the pre-calcined powder is ball milled again and pressed into tablets, and then sintered at 800-1200°C for 5-10 hours to obtain an LLZTO ceramic electrolyte; the LLZTO is crushed and ball milled for 8-20 hours to obtain LLZTO nanoparticles.

8. The method for preparing a composite ceramic solid electrolyte diaphragm material according to claim 4, characterized in that: In step S2, the polymer substrate is PVDF-HFP; The mass ratio of the polymer substrate to the polydopamine-coated LLZTO nanoparticles is 200:35-60.

9. Use of the composite ceramic solid electrolyte membrane material according to any one of claims 1 to 3 in a lithium-ion battery.

10. The use according to claim 9, characterized in that The lithium-ion battery is prepared by the following steps: T1: punching the composite ceramic solid electrolyte diaphragm material into sheets, and plasticizing it with LITFSI / TEGDME to obtain a diaphragm; T2: Take metal pole pieces as the positive electrode and the negative electrode respectively, and then assemble the positive electrode, the negative electrode and the separator under a protective atmosphere to obtain the lithium-ion battery.

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