Lithium lanthanum zirconium oxide-based solid electrolyte, and preparation method and application thereof

Abstract

The application discloses a lithium lanthanum zirconium oxide-based solid electrolyte and a preparation method and application thereof. The preparation method comprises the following steps: adding a lithium source, a lanthanum source and a zirconium source into water, and obtaining a first mixed solution after mixing; or, adding the lithium source, the lanthanum source, the zirconium source and a doping metal source into water, and obtaining the first mixed solution after mixing; adding a dispersing agent and carbon quantum dots into the first mixed solution, and obtaining a second mixed solution after stirring; mixing the second mixed solution with a precipitant, co-precipitating, drying, and obtaining a co-precipitated precursor; and sintering the co-precipitated precursor, and obtaining the lithium lanthanum zirconium oxide-based solid electrolyte. In the application, the carbon quantum dots are used as nucleation sites and a one-step lithium mixing method is used as a morphology regulator, so that the porous sheet-shaped two-dimensional lithium lanthanum zirconium oxide-based solid electrolyte is prepared. The preparation method provided by the application can maintain the sheet-shaped morphology advantage of the lithium lanthanum zirconium oxide-based solid electrolyte, obtain a larger specific surface area, and effectively improve the conductivity of the composite solid electrolyte.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium batteries, and in particular to a lithium lanthanum zirconium oxy-based solid electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium lanthanum zirconium oxide (LLZO) solid electrolyte powder is often used as a filler in composites with polymer electrolytes to prepare composite solid electrolytes (CSEs) with good electrochemical and mechanical properties. Common powder preparation methods include solid-phase ball milling, liquid-phase sol-gel method, and co-precipitation method. Among these, the liquid-phase method often yields precursors with higher activity, requires lower sintering temperatures, and produces smaller particle sizes because it allows for elemental blending at the ionic level. However, the LLZO particles prepared by these methods often exhibit a spherical morphology (zero-dimensional). In recent years, numerous studies have confirmed that the ionic conductivity of composite solid electrolytes is directly proportional to the effective specific surface area provided by the active filler. Due to the ion exchange behavior and the presence of numerous defects at the two-phase interface, the interface has a higher concentration of conductive lithium ions and lower ion migration energy. Therefore, lithium ions inside the electrolyte tend to be conducted through this interface. Zero-dimensional spherical fillers often struggle to provide continuous ion transport channels, and the reduction in the size of spherical fillers has contradictory effects on improving ionic conductivity and enhancing lithium dendrite suppression. Under the same filler composite ratio, smaller filler particle size results in a larger effective specific surface area, leading to higher ionic conductivity. However, lithium dendrites are also more likely to grow along interconnected interfaces and penetrate the electrolyte membrane, causing short circuits. Therefore, composite solid electrolytes prepared using zero-dimensional fillers often struggle to achieve a simultaneous improvement in ionic conductivity and mechanical properties. To address this issue, researchers have worked on controlling the morphology of fillers, including preparing nanowire (one-dimensional), nanosheet (two-dimensional), and porous framework (three-dimensional) fillers. Compared to zero-dimensional fillers, one-dimensional, two-dimensional, and three-dimensional fillers, due to their larger contact area and interwoven structure, facilitate the construction of effective conduction pathways and improve mechanical properties in composite solid electrolytes. Among these, nanowire fillers have been the most extensively studied. However, the synthesis methods and research on two-dimensional sheet-like fillers for composite solid electrolytes are relatively scarce, and existing methods mostly produce dense, smooth surfaces with relatively small specific surface areas, resulting in limited improvement in ionic conductivity.

[0003] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a lithium lanthanum zirconium oxy-based solid electrolyte and its preparation method and application. It aims to solve the problems that the existing methods for synthesizing two-dimensional fillers with sheet-like morphology for composite solid electrolytes are relatively scarce, and the sheet-like morphology synthesized by the existing methods mostly has a dense and smooth surface, relatively small specific surface area, and the improvement effect on ionic conductivity is not very obvious.

[0005] The technical solution of the present invention is as follows:

[0006] A first aspect of the present invention provides a method for preparing a lithium lanthanum zirconium oxy-based solid electrolyte, comprising the steps of:

[0007] A first mixed solution is obtained by adding a lithium source, a lanthanum source, and a zirconium source to water and mixing them; or, a first mixed solution is obtained by adding a lithium source, a lanthanum source, a zirconium source, and a doped metal source to water and mixing them.

[0008] A dispersant and carbon quantum dots were added to the first mixed solution, and after stirring, a second mixed solution was obtained.

[0009] The second mixed solution was mixed with a precipitant, co-precipitated, and then dried to obtain the co-precipitated precursor.

[0010] The coprecipitated precursor was sintered to obtain the lithium lanthanum zirconium oxy-oxide solid electrolyte.

[0011] Optionally, the lithium source is selected from at least one of lithium nitrate and lithium hydroxide;

[0012] And / or, the lanthanum source is selected from at least one of lanthanum nitrate and lanthanum chloride;

[0013] And / or, the zirconium source is selected from at least one of zirconium oxynitrate and zirconium oxychloride;

[0014] And / or, the metal in the doped metal source is selected from at least one of aluminum, calcium, iron, niobium, titanium, antimony, magnesium, zinc, gallium, and tantalum.

[0015] Optionally, the dispersant is selected from at least one of ethylene glycol and polyethylene glycol;

[0016] And / or, the precipitant is selected from ammonia or lithium hydroxide.

[0017] Optionally, the molar ratio of the dispersant to the metal cation in the first mixed solution is (1-2):1.

[0018] Optionally, the mass ratio of the carbon quantum dots to the lithium lanthanum zirconium oxy-oxide solid electrolyte is (0.01–0.04):1.

[0019] Optionally, after adding a dispersant and carbon quantum dots to the first mixed solution and stirring at a temperature of 40-50°C for 1.5-2 hours, a second mixed solution is obtained.

[0020] Optionally, the step of mixing the second mixed solution with a precipitant, co-precipitating, and then drying to obtain the co-precipitated precursor specifically includes:

[0021] The second mixed solution was added dropwise to the precipitant for mixing and co-precipitation to obtain the co-precipitate precursor solution.

[0022] The coprecipitate precursor solution was stirred in a water bath at 40–50°C for 1–5 hours, then evaporated and concentrated before freeze-drying to obtain the coprecipitate precursor.

[0023] Optionally, the sintering includes a first stage of sintering and a second stage of sintering, wherein the temperature of the first stage of sintering is 400-450℃ and the time is 30-90 min, and the temperature of the second stage of sintering is 750-850℃ and the time is 0.5-2 h.

[0024] In a second aspect, the present invention provides a lithium lanthanum zirconium oxy-based solid electrolyte, wherein the lithium lanthanum zirconium oxy-based solid electrolyte is prepared by the preparation method of the present invention as described above.

[0025] A third aspect of the present invention provides the application of the lithium lanthanum zirconium oxy-based solid electrolyte of the present invention as described above in the preparation of a composite solid electrolyte for solid-state batteries.

[0026] Beneficial Effects: This invention utilizes carbon quantum dots as nucleation sites and morphology modifiers in a one-step lithium mixing method to prepare a porous, sheet-like two-dimensional lithium lanthanum zirconium oxy-based solid electrolyte. The carbon quantum dot surface is rich in hydroxyl and carboxyl functional groups, which can adsorb a large number of metal cations in aqueous solution. During the stirring process before co-precipitation, the metal cations are adsorbed and dissociated on the carbon quantum dot surface, while the carbon quantum dots complex with each other to form a two-dimensional structure. In the subsequent co-precipitation process, the adsorbed metal cations are coated on the carbon quantum dot surface and precipitate, forming a two-dimensional sheet-like co-precipitation precursor. After sintering, the dispersant and carbon quantum dots decompose, releasing gas and yielding a porous, sheet-like pure-phase lithium lanthanum zirconium oxy-based solid electrolyte. Compared to electrolyte fillers synthesized by traditional co-precipitation methods, the preparation method provided by this invention maintains the sheet-like morphology advantage of the lithium lanthanum zirconium oxy-based solid electrolyte while achieving a larger specific surface area, significantly improving the conductivity of the composite solid electrolyte, and significantly enhancing its electrochemical performance and lithium dendrite suppression ability. Attached Figure Description

[0027] Figure 1 Li in Embodiment 1 of the present invention 6.4 Al0.2 La3Zr2O 12 A schematic diagram of the solid electrolyte preparation process.

[0028] Figure 2 In the diagram, (a), (b), and (c) are SEM images of LALZO in Comparative Example 1 of the present invention; (d), (e), and (f) are SEM images of LALZO in Example 1 of the present invention; (g), (h), and (i) are SEM images of LALZO in Example 2 of the present invention; and (j), (k), and (l) are SEM images of LALZO in Example 4 of the present invention.

[0029] Figure 3a Figure 3a shows the XRD patterns of LALZO prepared in Examples 1, 5, 6, and 7 of this invention. Figure 3b shows the XRD patterns of LALZO obtained in Example 1 and Comparative Example 2 of this invention.

[0030] Figure 4a The graph shows the ionic conductivity test results of the composite electro-solid electrolyte in Example 8 and Comparative Example 3 of this invention. Figure 4b The graph shows the cycle life test results of lithium symmetric batteries containing the composite electro-solid electrolytes of Example 8 and Comparative Example 3 of the present invention, respectively. Detailed Implementation

[0031] This invention provides a lithium lanthanum zirconium oxy-based solid electrolyte, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] This invention provides a method for preparing a lithium lanthanum zirconium oxy-based solid electrolyte, comprising the following steps:

[0034] S1. Add lithium source, lanthanum source, and zirconium source to water, mix, and obtain a first mixed solution; or, add lithium source, lanthanum source, zirconium source, and doped metal source to water, mix, and obtain a first mixed solution.

[0035] S2. Add dispersant and carbon quantum dots to the first mixed solution, stir, and obtain a second mixed solution;

[0036] S3. The second mixed solution is mixed with the precipitant, co-precipitated, and then dried to obtain the co-precipitated precursor;

[0037] S4. The co-precipitated precursor is sintered to obtain the lithium lanthanum zirconium oxy-based solid electrolyte.

[0038] This invention employs a one-step lithium mixing method using carbon quantum dots as nucleation sites and morphology modifiers to prepare a porous, sheet-like, two-dimensional pure-phase lithium lanthanum zirconium oxy-based solid electrolyte. The carbon quantum dot surface is rich in hydroxyl and carboxyl functional groups, which can adsorb a large number of metal cations in aqueous solution. During the stirring process before co-precipitation, the metal cations adsorb and dissociate on the carbon quantum dot surface. Simultaneously, due to the adsorption of metal cations, the repulsive effect between carbon quantum dots weakens. To reduce surface tension, the functional groups between carbon quantum dots further complex, forming a two-dimensional structure (i.e., reduction of carbon quantum dots). In the subsequent co-precipitation process, the adsorbed metal cations are coated on the carbon quantum dot surface and precipitate, forming a two-dimensional sheet-like coprecipitation precursor. The dispersant prevents the sheet-like structures from stacking during precipitation. After sintering the obtained two-dimensional sheet-like coprecipitation precursor, the dispersant and carbon quantum dots decompose, and the released gas helps to obtain a loose, dispersed, and porous sheet-like pure-phase lithium lanthanum zirconium oxy-based solid electrolyte powder, ensuring the independence of the sheets and preventing powder accumulation. Compared with electrolyte fillers synthesized by traditional coprecipitation methods, the preparation method provided by this invention achieves a larger specific surface area while maintaining the sheet-like morphology advantage of lithium lanthanum zirconium oxide solid electrolytes. This significantly improves the conductivity of the composite solid electrolyte, as well as the electrochemical performance and lithium dendrite suppression ability of the composite solid electrolyte.

[0039] In step S1, lithium source, lanthanum source, and zirconium source are added to water according to the required stoichiometric ratio of each element in the lithium lanthanum zirconium oxide solid electrolyte. After mixing, a first mixed solution is obtained, and the final product is a porous, sheet-like pure-phase lithium lanthanum zirconium oxide solid electrolyte (LLZO). However, to compensate for lithium loss during the sintering process, the amount of lithium source added must be 10 wt% excess.

[0040] Lithium source, lanthanum source, zirconium source, and doped metal source are added to water according to the desired stoichiometric ratio of elements in the lithium lanthanum zirconium oxy-based solid electrolyte. After mixing, a first mixed solution is obtained, ultimately yielding a porous, plate-like, pure-phase metal-doped lithium lanthanum zirconium oxy-based solid electrolyte. The metal can be at least one of aluminum, calcium, iron, niobium, titanium, antimony, magnesium, zinc, gallium, and tantalum. Metal doping can improve the stability of the highly conductive cubic phase of the lithium lanthanum zirconium oxy-based solid electrolyte at room temperature, and simultaneously increase the lithium vacancy concentration, thereby improving its ionic conductivity. Similarly, to compensate for lithium loss during sintering, the amount of lithium source added should be 10 wt% excess.

[0041] Traditional co-precipitation methods for synthesizing LLZO solid electrolytes typically employ a two-stage lithium mixing process, where metal precipitates such as La, Zr, and Al are dried and then mixed with the lithium source via a solid-state method. This step utilizes a one-stage lithium mixing method, where lithium is mixed with the metal cation solution and participates in the subsequent co-precipitation process. This ensures uniform mixing of lithium ions with each metal cation in the solution, making it easier to achieve molecular-level mixing compared to traditional co-precipitation methods. This improves the sintering activity of the powder, reduces the sintering temperature, and shortens the sintering time.

[0042] In one embodiment, the lithium source is selected from at least one of lithium nitrate (LiNO3) and lithium hydroxide (LiOH·H2O), but is not limited thereto.

[0043] In one embodiment, the lanthanum source is selected from at least one of lanthanum nitrate (La(NO3)3·6H2O) and lanthanum chloride (LaCl3·7H2O), but is not limited thereto.

[0044] In one embodiment, the zirconium source is selected from at least one of zirconium oxynitrate (ZrO(NO3)2·xH2O, where x is 6 to 8) and zirconium oxychloride (ZrOCl2·8H2O), but is not limited thereto.

[0045] In one embodiment, the metal in the doping metal source is selected from at least one of aluminum, calcium, iron, niobium, titanium, antimony, magnesium, zinc, gallium, and tantalum, but not limited thereto. For example, when the metal in the doping metal source is selected from aluminum, the doping metal source may be selected from at least one of aluminum nitrate (Al(NO3)3·9H2O) and aluminum chloride (AlCl3).

[0046] In step S2, in one embodiment, the dispersant is selected from at least one of ethylene glycol and polyethylene glycol. The addition of the dispersant prevents the flake structures from stacking together during precipitation, helping to maintain the independence between the flakes and prevent powder accumulation.

[0047] In a further embodiment, the polyethylene glycol has a molecular weight of 4000.

[0048] In one embodiment, the molar ratio of the dispersant to the metal cations in the first mixed solution is (1-2):1. It is understood that the metal cations in the first mixed solution refer to all metal cations. That is, the ratio of the molar number of the dispersant to the sum of the molar numbers of all metal cations in the first mixed solution is (1-2):1.

[0049] In one embodiment, the mass ratio of the carbon quantum dots to the lithium lanthanum zirconium oxy-coated solid electrolyte is (0.01–0.04):1. That is, the addition of carbon quantum dots needs to be determined based on the mass of the product (lithium lanthanum zirconium oxy-coated solid electrolyte).

[0050] In one embodiment, a dispersant and carbon quantum dots are added to the first mixed solution, and the mixture is stirred at a temperature of 40-50°C for 1.5-2 hours to obtain a second mixed solution.

[0051] In this embodiment, stirring at a temperature of 40–50°C for 1.5–2 hours can promote the adsorption and binding between carbon quantum dots and metal cations, further reduce the repulsion between carbon quantum dots, and allow the functional groups between carbon quantum dots to further complex, forming a two-dimensional sheet-like structure.

[0052] In addition, graphene oxide can also be used as a morphology modifier to replace the carbon quantum dots in step S2. Its surface is also rich in functional groups such as hydroxyl and carboxyl groups, which can be used to prepare porous sheet-like two-dimensional lithium lanthanum zirconium oxy-based solid electrolytes.

[0053] In step S3, in one embodiment, the precipitant is selected from ammonia and lithium hydroxide.

[0054] When the precipitant is ammonia, the amount of ammonia added should ensure that the pH of the solution is between 9.5 and 10 after co-precipitation. During co-precipitation, metal cations precipitate in an alkaline environment (ammonia) to form hydroxides, which are then coated onto the two-dimensional structure surface formed by carbon quantum dot complexes.

[0055] When the precipitant is selected from LiOH·H2O, it also serves as a lithium source, and the number of moles added is 1.1 to 1.2 times that of lithium in the lithium lanthanum zirconium oxy-coated solid electrolyte. That is to say, when the lithium source is selected from LiOH·H2O, it can be directly used as a precipitant, and the number of moles added is 1.1 to 1.2 times that of lithium in the lithium lanthanum zirconium oxy-coated solid electrolyte.

[0056] In one embodiment, the step of mixing the second mixed solution with a precipitant, co-precipitating, and then drying to obtain the co-precipitated precursor specifically includes:

[0057] S31. The second mixed solution is added dropwise to the precipitant for mixing. After co-precipitation, a co-precipitation precursor solution is obtained.

[0058] S32. Stir the coprecipitate precursor solution in a water bath at 40-50°C for 1-5 hours, evaporate and concentrate, and then freeze dry to obtain the coprecipitate precursor.

[0059] In step S31, to ensure that all metal cations precipitate uniformly and simultaneously, when ammonia is used as the precipitant, the second mixture containing metal cations is added dropwise to the ammonia for co-precipitation.

[0060] In step S32, to further improve the phase purity of the lithium lanthanum zirconium oxy-based solid electrolyte synthesized by the co-precipitation method, a constant-temperature water bath stirring and evaporation concentration process were added. This effectively improves the mixing uniformity of the precursor precipitate. Simultaneously, the evaporation concentration process volatilizes excess aqueous solvent and ammonia precipitant, ensuring the lithium salt and precipitate in the aqueous solution are in a relatively saturated state. This prevents stratification of the precipitate and lithium salt solution and the presence of large amounts of ammonium ions during freeze-drying, thus avoiding a decrease in phase purity. Furthermore, to ensure the lamellar morphology of the co-precipitate precursor remains unaffected, freeze-drying is used to remove moisture, maximizing the preservation of the precursor's morphology. Meanwhile, during the freeze-drying process, the water in the gaps between the precipitates can sublimate simultaneously, causing the lithium salt and ethylene glycol in the solution to precipitate uniformly and coat the surface of each precursor particle. This reduces the diffusion distance of elements during subsequent sintering and lowers sintering energy consumption. At the same time, the ethylene glycol dispersant coated on the precursor surface can also generate gas during sintering, preventing the agglomeration between the sheet-like morphologies. Ultimately, a fluffy, porous, and independently dispersed two-dimensional lithium lanthanum zirconium oxide solid electrolyte powder is obtained.

[0061] Furthermore, the evaporation and concentration can be carried out at a temperature of 80–95°C for 1–5 hours. The specific temperature and time can be adjusted according to the actual situation to form a homogeneous co-precipitation precursor mixture with suitable viscosity, ensuring uniform mixing of each precipitate phase. This evaporation and concentration process evaporates excess aqueous solvent and ammonia precipitant, keeping the lithium salt and precipitate in the aqueous solution in a relatively saturated state. This prevents the precipitate from separating from the lithium salt solution and the presence of a large amount of ammonium ions due to settling during freeze-drying, thereby obtaining a high-purity lithium lanthanum zirconium oxy-based solid electrolyte.

[0062] In step S4, in one embodiment, the sintering includes a first stage sintering and a second stage sintering. The temperature of the first stage sintering is 400-450°C and the time is 30-90 min. The temperature of the second stage sintering is 750-850°C and the time is 0.5-2 h.

[0063] In this embodiment, the obtained co-precipitated precursor is subjected to a first-stage sintering and a second-stage sintering at 400–450°C for 30–90 min to remove most of the anions (e.g., nitrate ions) and precipitants (e.g., ammonium ions) from the ethylene glycol, lithium source, lanthanum source, and zirconium source. Then, it is sintered at 750–850°C for 0.5–2 h to decompose the carbon quantum dots, releasing gas and yielding a porous, sheet-like two-dimensional lithium lanthanum zirconium oxy-based solid electrolyte. Furthermore, the gas release helps to obtain a loose, dispersed, and porous lithium lanthanum zirconium oxy-based solid electrolyte powder structure, maintaining the independence between the sheets and preventing the accumulation of lithium lanthanum zirconium oxy-based solid electrolyte powder.

[0064] This invention also provides a lithium lanthanum zirconium oxy-based solid electrolyte, wherein the lithium lanthanum zirconium oxy-based solid electrolyte is prepared using the preparation method described above in this invention. The lithium lanthanum zirconium oxy-based solid electrolyte has a porous, sheet-like microstructure and belongs to the cubic phase.

[0065] This invention also provides an application of the lithium lanthanum zirconium oxy-based solid electrolyte as described in the above embodiments in the preparation of composite solid electrolytes for solid-state batteries.

[0066] Furthermore, a high-performance composite solid electrolyte can be prepared by combining a lithium lanthanum zirconium oxy-based solid electrolyte with an appropriate amount of polymer electrolyte (PEO, PVDF, PAN, PPC, etc.), lithium salt (LiClO4, LiTFSI, LiFSI, etc.) and various ionic liquids (IL) to obtain a uniform slurry, and then using a casting method.

[0067] Taking the preparation of PEO-based composite solid electrolytes as an example:

[0068] ① Take 0.1g of lithium lanthanum zirconium oxy-based solid electrolyte, 0.24g of LiTFSI, and 440μL of ionic liquid (BMIMTFSI) and add them to 25g of anhydrous acetonitrile (CAN) for ultrasonic dispersion;

[0069] ② After ultrasonic dispersion, add 1g PEO (Mw=600000) and magnetically stir for 6-8h to obtain a uniform slurry;

[0070] ③ Pour the above slurry into a circular polytetrafluoroethylene mold, let it dry, and then dry it in a vacuum oven at 40-60°C to remove residual solvent, thus obtaining a uniform composite solid electrolyte film.

[0071] The two-dimensional sheet-like morphology of the lithium lanthanum zirconium oxy-based solid electrolyte has a high aspect ratio, which provides a good physical barrier for the growth of lithium dendrites. At the same time, the two-dimensional plane makes it easier for particles to achieve effective contact, thus providing a more continuous lithium-ion transport path. Compared with the lithium lanthanum zirconium oxy-based solid electrolyte filler synthesized by the traditional co-precipitation method, the lithium lanthanum zirconium oxy-based solid electrolyte provided in this embodiment has a significant effect on improving the electrochemical performance of the composite solid electrolyte and the ability to suppress lithium dendrites.

[0072] The following detailed description uses specific examples.

[0073] Example 1

[0074] Li 6.4 Al 0.2 La3Zr2O 12 Preparation of solid electrolytes, such as Figure 1 As shown:

[0075] According to Li 6.4 Al 0.2 La3Zr2O 12 The stoichiometric ratios of each element were determined by dissolving LiNO3, La(NO3)3·6H2O, ZrO(NO3)2·2H2O, and Al(NO3)3·9H2O in an appropriate amount of deionized water (with LiNO3 added in excess by 10wt% to compensate for lithium loss during sintering). After stirring and dissolving, ethylene glycol (molar ratio of ethylene glycol to metal cations of 2:1) and carbon quantum dots (the amount of carbon quantum dots added accounts for a certain percentage of the product Li) were added. 6.4 Al 0.2 La3Zr2O 12 (1% by mass) to obtain a mixed solution;

[0076] The mixture was ultrasonically dispersed in an ultrasonic machine for 20 minutes to ensure uniform mixing of all components, and then placed in a water bath at 45°C and stirred for 2 hours.

[0077] Coprecipitation was carried out using ammonia as a precipitant. The solution after stirring in a water bath was added dropwise to an excess of ammonia to obtain a coprecipitation precursor solution (pH 9.5).

[0078] The coprecipitation precursor solution was stirred in a constant temperature water bath at 45°C for 2 hours to further improve the uniform mixing of the precipitate. Then, the temperature was increased to 80°C and evaporated and concentrated for 2 hours to form a homogeneous coprecipitation precursor solution with appropriate viscosity, ensuring the uniformity of each precipitate phase.

[0079] Then freeze-drying is performed to remove moisture while maintaining the original two-dimensional morphology, thereby obtaining a dry and dispersed precursor powder.

[0080] The precursor powder was sintered in a muffle furnace in stages. First, the temperature was raised to 450℃ and held for 40 min, then raised to 850℃ and sintered for 0.5 h to obtain porous lamellar two-dimensional cubic phase Li. 6.4 Al 0.2 La3Zr2O 12 Solid electrolyte (LALZO).

[0081] Example 2

[0082] The only difference from Example 1 is that the amount of carbon quantum dots added accounts for a larger proportion of the product Li. 6.4 Al 0.2 La3Zr2O 12 2% of the quality.

[0083] Example 3

[0084] The only difference from Example 1 is that the amount of carbon quantum dots added accounts for a larger proportion of the product Li. 6.4 Al 0.2 La3Zr2O 12 3% of the quality.

[0085] Implementation 4

[0086] The only difference from Example 1 is that the amount of carbon quantum dots added accounts for a larger proportion of the product Li. 6.4 Al 0.2 La3Zr2O 12 4% of the quality.

[0087] Example 5

[0088] The only difference from Example 1 is that the coprecipitated precursor solution was stirred in a constant temperature water bath at 45°C for 0 hours.

[0089] Example 6

[0090] The only difference from Example 1 is that the coprecipitated precursor solution was stirred in a constant temperature water bath at 45°C for 1 hour.

[0091] Example 7

[0092] The only difference from Example 1 is that the coprecipitated precursor solution was stirred in a constant temperature water bath at 45°C for 5 hours.

[0093] Example 8

[0094] Preparation of composite solid electrolytes:

[0095] 0.1g of LLZAO powder from Example 1, 0.24g of LiTFSI, and 440μL of ionic liquid (BMIMTFSI) were added to 25g of anhydrous acetonitrile (CAN) and ultrasonically dispersed until uniform; then 1g of PEO (Mw=600000) was added, and the mixture was magnetically stirred for 8h to obtain a uniform slurry;

[0096] ③ After pouring the above slurry into a circular polytetrafluoroethylene mold and drying it, further dry it in a vacuum oven at 60°C to remove residual solvent and obtain a uniform composite solid electrolyte film.

[0097] Comparative Example 1

[0098] The only difference from Example 1 is that no carbon quantum dots are added, resulting in particulate LLZAO.

[0099] Comparative Example 2

[0100] The only difference from Example 1 is that the step of raising the temperature to 80°C for evaporation and concentration for 2 hours is not performed.

[0101] Comparative Example 3

[0102] The only difference from Example 8 is that granular LLZAO from Comparative Example 1 is used.

[0103] test:

[0104] (1) The LALZO prepared in Examples 1, 2, 4 and Comparative Example 1 were subjected to SEM testing, and the results are as follows: Figure 2 As shown, when carbon quantum dots are not added during the preparation process, the resulting LALZO is granular and randomly aggregated (e.g., Figure 2 As shown in (a), (b), and (c), the addition of a small amount of carbon quantum dots (1 wt%) during the preparation process caused a significant transformation of the LALZO morphology towards a two-dimensional form, resulting in a porous, layered structure (as shown in Figures 1-3). Figure 2 As shown in (d), (e), and (f), when the amount of carbon quantum dots added increases to 4%, a single-layer independent porous sheet-like LLZAO can be prepared (e.g., Figure 2 As shown in (j), (k), and (l).

[0105] (2) XRD tests were performed on the LALZO prepared in Examples 1, 5, 6, and 7. The results are as follows: Figure 3a As shown, it can be seen that when the water bath lasts for 0 hours, La2Li 0.5 Al 0.5 The O5 heterophase peak has a high intensity, La2Li 0.5 Al 0.5 The O5 impurity phase content is high, while La2Li has a high content of impurities when bathed in water for 2-5 hours. 0.5 Al 0.5 The intensity of the O5 impurity peak decreases, La2Li 0.5 Al 0.5 The content of the O5 impurity phase decreased, and the phase purity did not change significantly after stirring in a water bath for more than 2 hours. XRD tests were performed on the LALZO obtained in Example 1 and Comparative Example 2, and the results are as follows: Figure 3bAs shown, it can be seen that the La2Li in the sample obtained by evaporation at 80℃ for 2 hours is higher than that in the sample without this step. 0.5 Al 0.5 The O5 impurity peak has a low intensity, while the La2Li peak has a low intensity. 0.5 Al 0.5 The O5 impurity phase content is low. These results indicate that during the preparation process, the isothermal water bath stirring and evaporation concentration steps after co-precipitation can remove excess solvent water. The isothermal water bath stirring ensures thorough and uniform mixing of the precursors in each precipitate, and the evaporation concentration step effectively prevents the lithium salt dissolved in the aqueous solution from separating from the metal precipitate during cooling, thereby reducing the La2Li content. 0.5 Al 0.5 The intensity of the O5 impurity phase is reduced, effectively improving the purity of the LALZO phase.

[0106] (3) The composite electro-solid electrolytes in Example 8 and Comparative Example 3 were subjected to ionic conductivity tests and lithium symmetric battery cycle life tests at 60°C. The results are as follows: Figure 4a and 4b As shown, the ionic conductivity of the sheet-like LLZAO composite solid electrolyte is 1.7 times that of the particulate LLZAO composite solid electrolyte. The cycle life of the lithium-ion battery prepared using the sheet-like LLZAO composite solid electrolyte is significantly higher than that prepared using the particulate LLZAO composite solid electrolyte. The sheet-like morphology better resists the growth of lithium dendrites, greatly increasing the cycle life of the lithium-ion battery. The results indicate that the porous sheet-like LALZO solid electrolyte prepared in Example 1 can effectively improve the ionic conductivity of the composite solid electrolyte due to its larger specific surface area and the construction of effective conduction pathways.

[0107] In summary, this invention provides a lithium lanthanum zirconium oxy-based solid electrolyte, its preparation method, and its applications. This invention utilizes carbon quantum dots as nucleation sites and morphology modifiers, employing a one-step lithium mixing method to prepare a porous, sheet-like two-dimensional lithium lanthanum zirconium oxy-based solid electrolyte. The surface of carbon quantum dots is rich in hydroxyl and carboxyl functional groups, which can adsorb a large number of metal cations in aqueous solution. During the stirring process before co-precipitation, the metal cations are adsorbed and dissociated on the carbon quantum dot surface, while the carbon quantum dots complex with each other to form a two-dimensional structure. In the subsequent co-precipitation process, the adsorbed metal cations are encapsulated on the carbon quantum dot surface and precipitate, forming a two-dimensional sheet-like co-precipitation precursor. After sintering, the dispersant and carbon quantum dots decompose, releasing gas to obtain a porous, sheet-like pure-phase lithium lanthanum zirconium oxy-based solid electrolyte. Compared to electrolyte fillers synthesized by traditional co-precipitation methods, the preparation method provided by this invention maintains the sheet-like morphology advantage of the lithium lanthanum zirconium oxy-based solid electrolyte while achieving a larger specific surface area, significantly improving the conductivity of the composite solid electrolyte, and significantly enhancing its electrochemical performance and lithium dendrite suppression ability.

[0108] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a lithium lanthanum zirconium oxide-based solid-state electrolyte, characterized by, The method comprises the steps of: adding a lithium source, a lanthanum source and a zirconium source into water, mixing to obtain a first mixed solution; or adding a lithium source, a lanthanum source, a zirconium source and a doping metal source into water, mixing to obtain a first mixed solution; adding a dispersing agent and carbon quantum dots to the first mixed solution, and stirring to obtain a second mixed solution; mixing the second mixed solution with a precipitant, co-precipitating, drying to obtain a co-precipitated precursor; sintering the co-precipitated precursor to obtain a porous sheet-shaped lithium lanthanum zirconium oxide-based solid electrolyte; the step of adding a dispersing agent and carbon quantum dots to the first mixed solution, stirring at a temperature of 40-50 DEG C for 1.5-2 h to obtain a second mixed solution; the step of mixing the second mixed solution with a precipitant, co-precipitating, drying to obtain a co-precipitated precursor specifically comprises: adding the second mixed solution dropwise into a precipitant, mixing, co-precipitating to obtain a co-precipitated precursor solution; stirring the co-precipitated precursor solution in a water bath at 40-50 DEG C for 1-5 h, evaporating and concentrating, and then freeze-drying to obtain a co-precipitated precursor; the evaporation and concentration are carried out at a temperature of 80-95 DEG C for 1-5 h; the sintering comprises first-stage sintering and second-stage sintering; the first-stage sintering is carried out at a temperature of 400-450 DEG C for 30-90 min, and the second-stage sintering is carried out at a temperature of 750-850 DEG C for 0.5-2 h.

2. The method of claim 1, wherein the lithium lanthanum zirconium oxide solid state electrolyte is prepared by the steps of: the lithium source is at least one selected from lithium nitrate and lithium hydroxide; ​ and / or, the lanthanum source is at least one selected from lanthanum nitrate and lanthanum chloride; and / or, the zirconium source is at least one selected from zirconyl nitrate and zirconyl chloride; and / or, the metal in the doping metal source is at least one selected from aluminum, calcium, iron, niobium, titanium, antimony, magnesium, zinc, gallium and tantalum.

3. The method for preparing the lithium lanthanum zirconium oxy-based solid electrolyte according to claim 1, characterized in that, the dispersing agent is at least one selected from ethylene glycol and polyethylene glycol; and / or, the precipitant is one selected from ammonia water and lithium hydroxide.

4. The method for preparing the lithium lanthanum zirconium oxy-based solid electrolyte according to claim 1, characterized in that, the molar ratio of the dispersing agent to the metal cations in the first mixed solution is (1-2):

1.

5. The method for preparing the lithium lanthanum zirconium oxy-based solid electrolyte according to claim 1, characterized in that, the mass ratio of the carbon quantum dots to the lithium lanthanum zirconium oxide-based solid electrolyte is (0.01-0.04):

1.

6. A lithium lanthanum zirconium oxide-based solid state electrolyte, characterized in that, the lithium lanthanum zirconium oxide-based solid electrolyte is prepared by the method according to any one of claims 1-5.

7. Use of the lithium lanthanum zirconium oxide-based solid electrolyte according to claim 6 in the preparation of a composite solid electrolyte for a solid-state battery.

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