Preparation method of low-cost LAGP nanofiber solid electrolyte

Abstract

The present invention discloses a low-cost method for preparing LAGP nanofiber solid electrolytes, comprising: 1. preparing an LAGP precursor solution comprising a lithium source, an aluminum source, a germanium source, a phosphorus source, a polymer, a solvent, and an organic acid; 2. preparing LAGP precursor fibers by electrospinning; and 3. crystallizing the LAGP precursor fibers. This method uses GeO2, the lowest-cost germanium source, and the entire precursor solution preparation process is performed in an air environment, significantly reducing costs and equipment requirements. The resulting LAGP precursor fibers, upon crystallization at a relatively low temperature, yield well-crystallized, complete fiber morphology, a high aspect ratio, and no beading. This method facilitates the preparation of high-performance composite solid electrolytes.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of energy materials, and particularly relates to a preparation method of a low-cost LAGP nanofiber solid electrolyte. BACKGROUND

[0002] Since the advent of lithium-ion batteries (LIBs), high energy density, low self-discharge, long life, environmental protection and other advantages have enabled them to be widely used in portable electronic devices, electric vehicles, aerospace and national defense and military fields. With the rapid development of electric vehicles in recent years and the construction of large-scale energy storage devices, people's requirements for the energy density, charging speed and service life of LIBs are becoming higher and higher. In addition, the flammable carbonate-based solvent liquid electrolyte is prone to fire and explosion when exposed to high temperature, overcharge and accidental short circuit, so safety is another big problem faced by the development of LIBs.

[0003] All-solid-state lithium-ion batteries are an ideal way to solve the above problems, in which the solid electrolyte can essentially overcome the potential safety problems of organic electrolyte and can hinder the surface dendrite growth of lithium metal, which is considered to be an ideal anode. An ideal solid electrolyte not only needs high room temperature ionic conductivity, wide electrochemical window and good electrode compatibility, but also has good stability to O2 / H2O. Solid polymer electrolytes have low room temperature ionic conductivity, narrow electrochemical window and poor electrode material compatibility; sulfides in inorganic solid electrolytes have high room temperature ionic conductivity, but are not stable to O2 and H2O; oxides and phosphates have high air stability and good ionic conductivity, but thin film, brittleness and interface problems with electrodes are difficult to solve; polymer composite solid electrolytes have the advantages of polymer / ceramic solid electrolytes and become the most ideal solid electrolyte material for solid-state lithium-ion batteries. Studies have shown that composite solid electrolytes with continuous polymer / active ceramic interfaces have higher ionic conductivity (Zhang Z Y, Chen H, Liu Z L, et al. Front. Energy 2022, 16(5): 706-733, Ding Y, He B, Wang D, et al. Energy Mater. Adv. 2023; 4: Article 0041), and fiberization of ceramic solid electrolytes is the most effective way to improve their film-forming performance, interface / ceramic phase ionic conduction ability.

[0004] There are articles and patents on oxide ceramic nanofibers, such as patent CN201810119950.4 discloses a solid-state lithium lanthanum zirconium oxide ceramic nanofiber electrolyte film and its preparation, and patent CN202210246386.9 discloses a acrylic-based ceramic composite nanofiber solid electrolyte and its preparation method. In contrast, the electrospinning precursor solution used for phosphate (such as LATP and LAGP) ceramic nanofibers has not been disclosed in patents due to stability problems, and only a few articles have been reported (Lancel G, Stevens P, Toussaint G, et al. Langmuir 2017, 33, 9288-9297; Monaca A L, Girard G, Savoie S, et al. J. Mater. Chem. A, 2021, 9, 13688; Monaca A L, Girard G, Savoie S, et al. Nanoscale, 2022, 14, 5094), but all use expensive GeCl4 as raw material. In addition, LAGP nanofibers use soluble germanium salt (GeCl4) and in large quantities, and the precursor solution needs to be prepared in an inert atmosphere glove box, which is extremely costly and has a small aspect ratio, seriously hindering the development and application of LAGP nanofiber-based composite solid electrolytes. SUMMARY

[0005] The purpose of the present application is to provide a low-cost LAGP nanofiber solid electrolyte preparation method, which has the characteristics of low raw material cost, can be carried out in an atmospheric environment, and the aspect ratio of the LAGP nanofiber can be adjusted.

[0006] Technical scheme: The low-cost LAGP nanofiber solid electrolyte preparation method of the present application comprises the following steps:

[0007] Step 1, preparation of LAGP precursor solution: the precursor solution comprises a lithium source, an aluminum source, a germanium source, a phosphorus source, a polymer, a solvent and an organic acid, and the germanium source is GeO2;

[0008] Step 2, electrospinning preparation of LAGP precursor fiber: set the electrospinning parameters for the LAGP precursor fiber preparation of the LAGP precursor solution of step 1, and the electrospinning parameters include voltage, relative humidity, flow rate and spinning distance;

[0009] Step 3, LAGP precursor fiber crystallization treatment: dry the LAGP precursor fiber of step 2 and perform high-temperature crystallization treatment to obtain a LAGP nanofiber solid electrolyte.

[0010] Further, in step 1, the molar ratio of the lithium source, the aluminum source, the germanium source, and the phosphorus source is 1.5-1.65:0.5:1.5:3-3.3.

[0011] Preferably, in step 1, the molar ratio of the lithium source, the aluminum source, the germanium source, and the phosphorus source is 1.6:0.5:1.5:3.2.

[0012] Further, in step 1, the lithium source is LiOH; the aluminum source is at least one of aluminum chloride and aluminum nitrate; the phosphorus source is phenyl phosphoric acid C6H7O3P; and the polymer is at least one of polyvinyl alcohol PVA, polyvinylidene fluoride PVDF, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, polyvinylpyrrolidone PVP, polyacrylonitrile PAN, and polyethylene oxide PEO.

[0013] Further, in step 1, the solvent is a mixed solvent, wherein the solvent for dissolving the lithium source, the aluminum source, the germanium source, and the phosphorus source is water, the organic solvent for dissolving the polymer is at least one of DMF and DMA, and the volume ratio of water to the organic solvent is 3:7 to 7:3.

[0014] Further, in step 1, the organic acid is at least one of tartaric acid, acetic acid, oxalic acid, citric acid, malic acid, maleic acid, salicylic acid, and succinic acid.

[0015] Preferably, the organic acid is tartaric acid, the pH value is 3-4, and the molar ratio of the complexing agent to the metal ion is 1:1.5.

[0016] Further, in step 2, the LAGP precursor fiber is prepared by setting the electrospinning parameters for the LAGP precursor solution of step 1, specifically: the germanium source is added to the alkaline lithium source solution and stirred to dissolve, then the pH value is adjusted to be acidic (2

[0017] Further, in step 3, the LAGP precursor fiber of step 2 is dried and subjected to high-temperature crystallization treatment, specifically: the LAGP precursor fiber is first dried by blowing air at 50-100 DEG C to remove the solvent, and then subjected to crystallization treatment at a temperature of 700-850 DEG C at a rate of 1-10 DEG C / min for 0-8 h to obtain the LAGP nanofiber solid electrolyte.

[0018] Preferably, the crystallization treatment is performed at a rate of 2-5 DEG C / min to a temperature of 750 DEG C for 2 h.

[0019] Further, the LAGP nanofiber solid electrolyte has an average diameter of 100-1000 nm, an internal grain size of 50-250 nm, and a room-temperature ionic conductivity of >10 -4 S cm -1 .

[0020] Advantages: Compared with the prior art, the present application has the following remarkable advantages:

[0021] (1) The present application uses the cheapest germanium source GeO2 (unit price less than 20 yuan / g), compared with the expensive soluble germanium source (GeCl4 unit price higher than 110 yuan / g, tetraethyl germanium, tetramethyl germanium and tetrabutyl germanium unit price higher than 210 yuan / g), thereby greatly reducing the cost.

[0022] (2) The toxic gases released in the subsequent heat treatment crystallization process of the raw materials such as LiOH and aluminum nitrate used to dissolve GeO2 in the present application are less and less toxic than the toxic gases produced by using chlorides as raw materials.

[0023] (3) The preparation of the electrospun precursor solution in the present application can be carried out in the atmospheric environment, without the need for inert atmosphere environment and glove box using GeCl4 as raw material, which is convenient to operate and can greatly reduce the cost and equipment demand.

[0024] (4) The present application can prepare LAGP nanofiber solid electrolyte with good crystallinity, complete fiber morphology, large aspect ratio and no beads at a lower crystallization temperature, which is beneficial to the preparation of high-performance composite solid electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM image of the LAGP precursor fiber prepared according to Example 1 of the present application;

[0026] Figure 2 XRD pattern of the LAGP nanofiber solid electrolyte prepared according to Example 1 of the present application;

[0027] Figure 3 SEM image of the LAGP nanofiber solid electrolyte prepared according to Example 1 of the present application;

[0028] Figure 4 SEM image of the LAGP nanofiber solid electrolyte prepared according to the present application in Example 2;

[0029] Figure 5 EIS image of the LAGP nanofiber solid electrolyte prepared according to the present application in Example 2;

[0030] Figure 6 SEM image of the LAGP nanofiber solid electrolyte prepared according to the present application in Example 3;

[0031] Figure 7 SEM image of the LAGP nanofiber solid electrolyte prepared according to the present application in Example 4. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further described below in combination with the drawings.

[0033] Example 1

[0034] A preparation method of a low-cost LAGP nanofiber solid electrolyte, the specific steps are as follows:

[0035] (1) 1.5 mmol of GeO2 (156.96 mg) was weighed and added to a 10 mL aqueous solution containing 1.65 mmol of LiOH·H2O (69.3 mg), and stirred at 60°C for 15 min to dissolve. 1.5 g of citric acid was added, and the solution was stirred thoroughly until it was uniform and clear for 1 h, and then concentrated to 2 mL at 90°C. Then 3 mmol of C6H7O3P (474.3 mg) was weighed and added to a 1 mL aqueous solution containing 0.5 mmol of Al(NO3)3·9H2O (187.6 mg), and stirred thoroughly. The concentrated solution containing germanium was added dropwise to the aqueous solution containing the phosphorus source, and stirred for 30 min until the solution was uniform. Finally, 0.6 g of PVP was dissolved in 3.65 g of DMF, and then mixed with the above solution, stirred uniformly and left to stand for 2 h to obtain a transparent electrospinning precursor solution.

[0036] (2) The above precursor solution was sucked into a syringe, and electrospinning was performed using a 19G needle, adjusting the humidity to 20, the voltage to 12 kV, the flow rate to 0.6 mL / h, and the receiving plate to be 15 cm away from the needle, to obtain a LAGP precursor fiber membrane (such as Figure 1 ).

[0037] (3) The LAGP precursor fiber membrane was placed in an oven at 100°C for 2 h to remove the solvent that was not completely volatilized, and then placed in a muffle furnace, set the heating rate to 5°C / min, and raised from room temperature to 750°C and kept for 2 h, and then naturally cooled to obtain a LAGP ceramic nanofiber (such as Figure 2 andFigure 3 )。

[0038] Example 2

[0039] A preparation method of a low-cost LAGP nanofiber solid electrolyte, the specific steps are:

[0040] (1) 1.5 mmol of GeO2 (156.96 mg) was weighed and added to a 10 mL aqueous solution containing 1.65 mmol of LiOH·H2O (69.3 mg), and stirred at 60°C for 15 minutes to dissolve. 1.5 g of tartaric acid was added, and the solution was stirred until it was uniform and clear for 1 h, and then concentrated to 2 mL at 90°C. Then 3 mmol of C6H7O3P (474.3 mg) was weighed and added to a 1 mL aqueous solution containing 0.5 mmol of Al(NO3)3·9H2O (187.6 mg), and stirred well. The concentrated germanium-containing solution was added dropwise to the phosphorus-containing aqueous solution, and stirred for 30 min until the solution was uniform. Finally, 0.4 g of PVP was dissolved in 3 g of DMF, and then mixed with the above solution, stirred uniformly and left to stand for 2 h to obtain a transparent electrospinning precursor solution.

[0041] (2) The above precursor solution was sucked into a syringe, a 19G needle was used, the humidity was adjusted to 20, the voltage was 8 kV, the flow rate was 0.6 mL / h, the receiving plate was 15 cm away from the needle, and electrospinning was carried out to obtain a LAGP precursor fiber membrane.

[0042] (3) The LAGP precursor fiber membrane was placed in a 90°C oven for 4 h to remove the solvent that was not completely volatilized, and then it was placed in a muffle furnace, the heating rate was set to 5°C / min, and the temperature was raised from room temperature to 750°C and kept for 2 h, and then naturally cooled to obtain LAGP ceramic nanofiber (as shown in Figure 4 ). The average diameter of the LAGP nanofiber solid electrolyte was about 500 nm, the average size of the internal grains was 150 nm, and the room temperature ionic conductivity of the ceramic fiber powder and the composite solid electrolyte prepared with PEO and LiTFSI was 1.64×10 -4 S cm -1 ( Figure 5 )。

[0043] Example 3

[0044] A preparation method of a low-cost LAGP nanofiber solid electrolyte, the specific steps are:

[0045] (1) 1.5 mmol of GeO2 (156.96 mg) was weighed and added to a 10 mL aqueous solution containing 1.65 mmol of LiOH H2O (69.3 mg), and dissolved by stirring at 60°C for 15 minutes. 1.5 g of tartaric acid was added, and the solution was stirred thoroughly until it was uniform and clear for 1 h, and then concentrated to 2 mL by evaporation at 90°C. Then 3 mmol of C6H7O3P (474.3 mg) was weighed and added to a 1 mL aqueous solution containing 0.5 mmol of Al(NO3)3 9H2O (187.6 mg), and stirred thoroughly. The concentrated solution containing germanium was added dropwise to the aqueous solution containing the phosphorus source, and the solution was stirred for 30 min until it was uniform. Finally, 0.4 g of PVP was dissolved in 3 g of DMF, and then mixed with the above solution, stirred uniformly, and left to stand for 2 h to obtain a transparent electrospinning precursor solution.

[0046] (2) The above precursor solution was sucked into a syringe, and electrospinning was performed using a 19G needle, with a humidity of 20, a voltage of 15 kV, a flow rate of 0.6 mL / h, and a receiving plate 15 cm from the needle, to obtain a LAGP precursor fiber membrane.

[0047] (3) The LAGP precursor fiber membrane was placed in an oven at 100°C for 2 h to remove the solvent that was not completely volatilized, and then placed in a muffle furnace, with a temperature increase rate of 5°C / min, and heated from room temperature to 750°C and held for 2 h, and then naturally cooled to obtain a LAGP ceramic nanofiber (as shown in Figure 6 ).

[0048] Example 4

[0049] A method for preparing a low-cost LAGP nanofiber solid electrolyte, the specific steps being:

[0050] (1) 1.5 mmol of GeO2 (156.96 mg) was weighed and added to a 10 mL aqueous solution containing 1.65 mmol of LiOH H2O (69.3 mg), and dissolved by stirring at 60°C for 15 minutes. 1.5 g of tartaric acid was added, and the solution was stirred thoroughly until it was uniform and clear for 1 h, and then concentrated to 2 mL by evaporation at 90°C. Then 3 mmol of C6H7O3P (474.3 mg) was weighed and added to a 1 mL aqueous solution containing 0.5 mmol of Al(NO3)3 9H2O (187.6 mg), and stirred thoroughly. The concentrated solution containing germanium was added dropwise to the aqueous solution containing the phosphorus source, and the solution was stirred for 30 min until it was uniform. Finally, 0.4 g of PVP was dissolved in 3 g of DMF, and then mixed with the above solution, stirred uniformly, and left to stand for 2 h to obtain a transparent electrospinning precursor solution.

[0051] (2) The precursor solution is sucked into a syringe, electrospinning is performed with a 19G needle, humidity is adjusted to 20, voltage is 10 kV, flow rate is 0.8 mL / h, the receiving plate is 15 cm away from the needle, and a LAGP precursor fiber membrane is obtained.

[0052] (3) The LAGP precursor fiber membrane is directly placed into a muffle furnace, the temperature rising rate is set to 5 ℃ / min, the temperature is raised from room temperature to 850 ℃ and kept for 2 h, and a LAGP ceramic nanofiber is obtained after natural cooling (as shown in FIG. 4). Figure 7 )。

[0053] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For those skilled in the art in the technical field of the present application, a number of simple deductions or replacements can be made without departing from the concept of the present application, and all of them shall be regarded as falling within the protection scope of the present application.

Claims

1. A method for preparing a low-cost LAGP nanofiber solid electrolyte, characterized in that: The following steps are involved: Step 1, preparing a LAGP precursor solution: the precursor solution includes a lithium source, an aluminum source, a germanium source, a phosphorus source, a polymer, a solvent and an organic acid, wherein the germanium source is GeO2; The molar ratio of the lithium source, aluminum source, germanium source and phosphorus source is 1.5-1.65:0.5:1.5:3-3.3; The lithium source is LiOH; the aluminum source is at least one of aluminum chloride and aluminum nitrate; the phosphorus source is phenyl phosphate C6H7O3P; the polymer is at least one of polyvinyl alcohol PVA, polyvinylidene fluoride PVDF, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, polyvinyl pyrrolidone PVP, polyacrylonitrile PAN, and polyethylene oxide PEO; The solvent is a mixed solvent, wherein the solvent for dissolving the lithium source, aluminum source, germanium source, and phosphorus source is water, and the organic solvent for dissolving the polymer is at least one of DMF and DMA, and the volume ratio of water to the organic solvent is 3:7 to 7:3; Step 2, electrospinning to prepare LAGP precursor fibers: setting electrospinning parameters to prepare LAGP precursor fibers from the LAGP precursor solution in step 1, wherein the electrospinning parameters include voltage, relative humidity, flow rate, and spinning distance; Step 3, LAGP precursor fiber crystallization treatment: drying the LAGP precursor fiber of step 2 and performing high-temperature crystallization treatment on it to obtain LAGP nanofiber solid electrolyte.

2. The method for preparing a low-cost LAGP nanofiber solid electrolyte according to claim 1, characterized in that: In step 1, the organic acid is at least one of tartaric acid, acetic acid, oxalic acid, citric acid, malic acid, maleic acid, salicylic acid, and succinic acid.

3. The method for preparing a low-cost LAGP nanofiber solid electrolyte according to claim 1, characterized in that: In step 2, the electrospinning parameters are set to prepare LAGP precursor fibers from the LAGP precursor solution of step 1, specifically: a germanium source is added to an alkaline lithium source solution and stirred to dissolve, and then an organic acid is added to adjust the pH value to acidic, and complexed with metal ions to prevent precipitation, and fully stirred and concentrated to obtain a germanium source solution; a phosphorus source is added to an aqueous solution containing an aluminum source, and stirred evenly to obtain a phosphorus source solution; the germanium source solution is added to the phosphorus source solution, and mixed evenly to obtain a clarified LAGP raw material solution; the polymer is dissolved in an organic solvent to prepare a solution with a concentration of 0.1~0.2 g / mL, and then mixed evenly with the LAGP raw material solution to obtain a LAGP electrospinning precursor solution having a raw material content of 5~15 wt% and a polymer content of 5~15 wt%; the electrospinning parameters are specifically: relative humidity of 20~50%, spinning voltage of 8~20 kV, spinning flow rate of 0.3~1.5 mL / h, and spinning distance of 10~25 cm.

4. The method for preparing a low-cost LAGP nanofiber solid electrolyte according to claim 1, characterized in that: In step 3, the LAGP precursor fiber of step 2 is dried and subjected to high-temperature crystallization treatment. Specifically, the LAGP precursor fiber is first dried at 50-100 °C by air blast to remove the solvent, and then the temperature is raised to 700-850 °C at a rate of 1-10 °C / min for crystallization treatment for 2-8 h to obtain a LAGP nanofiber solid electrolyte.

5. The method for preparing a low-cost LAGP nanofiber solid electrolyte according to claim 4, characterized in that: The LAGP nanofiber solid electrolyte has an average diameter of 100-1000 nm, an internal grain size of 50-250 nm, and a room temperature ionic conductivity of >10 -4 S cm -1 .

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