A monoclinic sulfide electrolyte, its preparation method and application

Abstract

The present invention relates to the technical field of all-solid-state sulfide electrolyte materials. Specifically, the present invention relates to a monoclinic sulfide electrolyte and its preparation method and application. The chemical formula of the novel monoclinic sulfide electrolyte is LiM1M2S 4， where M1 is a rare earth element, including scandium (Sc), yttrium (Y), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu); M2 is a Group IVA element, including silicon (Si), germanium (Ge), tin (Sn); and it is made from Li2S3, M1 elemental substance (powder), M2 elemental substance (powder), and sulfur (S) elemental substance (powder) through mixing, ball milling, and sintering. The monoclinic sulfide electrolyte of the present invention has good compatibility with lithium metal, can effectively inhibit lithium dendrites, and realizes a high-performance all-solid-state lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state battery electrolyte materials. Specifically, the present invention relates to a monoclinic sulfide electrolyte and its preparation method and application, and particularly to a monoclinic sulfide electrolyte for all-solid-state lithium metal batteries and its preparation method. Background Art

[0002] In today's energy field, with the growing demand for high-energy-density energy storage devices, solid-state batteries have become the focus of research. Although traditional liquid electrolyte batteries have certain performance advantages, they have many safety hazards, such as leakage and flammability. Solid electrolytes can effectively solve these safety problems and thus have received extensive attention.

[0003] In recent years, argyrodite-type electrolytes have become a research hotspot in the field of solid-state batteries due to their excellent ionic conductivity. With its unique cubic crystal structure and composition, this material has advantages that cannot be compared with traditional liquid electrolytes, making it play an important role in the next-generation high-energy-density batteries.

[0004] Compared with other solid electrolytes, argyrodite-type electrolytes have a relatively high lithium-ion conductivity at room temperature, comparable to or even exceeding some liquid electrolytes. Argyrodite-type electrolytes have a relatively wide electrochemical window and can be compatible with a variety of cathode materials.

[0005] However, in the process of moving towards commercialization in practical applications, argyrodite-type electrolytes have exposed some problems that need to be solved urgently. In terms of the interaction with the electrode interface, there is a large interfacial contact impedance between it and the electrode material. This impedance will cause an increase in the internal resistance of the battery, an increase in power loss during charge and discharge, and thus affect the overall performance of the battery, such as reducing the charge and discharge efficiency and decreasing the actual available charge of the battery.

[0006] The problem of lithium dendrite growth is also severe. During the battery cycling process, lithium dendrites are prone to grow at the electrolyte / electrode interface. The growth of lithium dendrites not only pierces the electrolyte, causing the positive and negative electrodes to come into direct contact and form a short-circuit path, but also continuously consumes the lithium source, reducing the active lithium available for charge and discharge in the battery, ultimately leading to a significant reduction in the cycle life of the battery and unable to meet the demand for long battery life in practical applications. Therefore, it is urgent to develop a new type of electrolyte that can retain the advantages of argyrodite-type electrolytes and overcome the existing problems. The emergence of the new electrolyte is expected to promote new breakthroughs in the field of solid-state batteries and lay a foundation for the large-scale commercial application of high-energy-density batteries. Summary of the Invention

[0007] In view of this, the present invention provides a monoclinic sulfide electrolyte and a preparation method and application thereof. The material has the following advantages: the monoclinic sulfide electrolyte can have the advantages of high ionic conductivity and wide electrochemical window of argyrodite-type electrolyte, and can also overcome the compatibility problem between electrolyte and electrode interface and the problem of lithium dendrite growth. The electrolyte of the present invention is applied to all-solid-state lithium metal batteries and can still maintain more than 90% of the capacity after 500 cycles, and the cycle life is greatly improved.

[0008] The technical solution provided by the present invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a monoclinic sulfide electrolyte for an all-solid-state lithium metal battery, comprising the following steps:

[0010] S1, mixing Li2S3, M1, M2, and S, and performing a ball milling; wherein M1 is a rare earth element, and the rare earth element is selected from one or more of scandium (Sc), yttrium (Y), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); M2 is a Group IVA element, and the Group IVA element is selected from one or more of silicon (Si), germanium (Ge), and tin (Sn);

[0011] The Li2S3 is prepared by a liquid ammonia method; the method comprises the following steps:

[0012] 1) Weigh lithium and sulfur according to the stoichiometric ratio and place them in a pressure-resistant reaction vessel; cool the pressure-resistant reaction vessel containing the reactants, evacuate the reaction vessel, and introduce liquid ammonia until the reaction vessel is full of liquid ammonia; react at low temperature for a period of time:

[0013] 2) Slowly heat the reaction container to room temperature, release liquid ammonia, and dry the solid product to obtain the Li2S3.

[0014] In step S1, the molar ratio of Li2S3:M1:M2:S is (0.4 - 0.6): (0.9 - 1.1): (0.9 -1.1): (2.4 - 2.6). Preferably, it is 0.5:1:1:2.5.

[0015] In step 1), the metallic lithium is washed with a hydrocarbon solvent;

[0016] and / or, the hydrocarbon solvent comprises n-hexane;

[0017] And / or, the cooling method adopts liquid nitrogen cooling, or adopts dry ice / acetone bath cooling;

[0018] And / or, in the low temperature reaction step, the reaction temperature ranges from -78°C to -33°C, and the reaction time is 5-10 hours.

[0019] In step S1, the primary ball milling conditions are as follows: the ball-to-material ratio (the mass ratio of zirconia balls to reactant raw materials) is (5 - 30):1, the ball milling speed is 100 - 150 r / min, and the ball milling time is 1 - 2 h.

[0020] In step S2, the secondary ball milling conditions are as follows: ball milling at a rotational speed of 500 r / min - 600 r / min for 24 - 48 h, with a stop of 10 - 20 minutes every 1 - 2 h of ball milling.

[0021] Step S3 is specifically as follows: The mixture after ball milling in step S2 is heated to 700 - 900 °C under vacuum conditions and held for 8 - 10 h to obtain the monoclinic sulfide electrolyte. The heating rate is 0.5 - 10 °C / min.

[0022] In a second aspect, the present invention provides a monoclinic sulfide electrolyte prepared by the preparation method as described above.

[0023] The chemical formula of the monoclinic sulfide electrolyte is LiM1M2S4. M1 is a rare earth element, and the rare earth element is selected from one or more of scandium, yttrium, erbium, thulium, ytterbium, and lutetium; M2 is an element of Group IVA, and the Group IVA element is selected from one or more of silicon, germanium, and tin.

[0024] In a third aspect, the present invention provides a all-solid-state lithium metal secondary battery, including a lithium metal negative electrode or a metal lithium composite negative electrode, a positive electrode, and the monoclinic sulfide electrolyte as described above.

[0025] Compared with the all-solid-state lithium metal battery in the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. In the prior art, due to the fact that the ionic conductivity of the argyrodite-type electrolyte cannot be further improved, it affects the overall performance of the battery. Therefore, the present invention uses the liquid ammonia method combined with the ball milling and sintering method to prepare a monoclinic sulfide electrolyte, which has abundant lithium ion vacancies. Coupled with the introduction of rare earth elements, by occupying specific lattice positions, the structure of the electrolyte is adjusted, forming more lithium ion migration channels, thereby greatly improving the diffusion coefficient of lithium ions.

[0027] 2. The interfacial contact impedance between the argyrodite-type electrolyte and the electrode material is relatively large, which affects the overall performance of the battery. Therefore, there is a strong interaction between the rare earth elements of the monoclinic sulfide electrolyte of the present invention and the electrode material, which can effectively reduce the contact impedance at the electrolyte / electrode interface and improve the interfacial compatibility. At the same time, the rare earth elements form a stable passivation film at the interface, inhibiting the side reaction between the electrolyte and the electrode, and improving the cycle stability of the battery.

[0028] 3. In the prior art, due to the uneven deposition of lithium ions, lithium dendrites are prone to grow at the electrolyte / electrode interface during cycling, resulting in battery short - circuit and affecting the cycle life of the battery. In the present invention, the lattice structure of the electrolyte is further stabilized by rare - earth elements, inhibiting the decomposition of the electrolyte during charge and discharge, thereby broadening the electrochemical window of the electrolyte. On the other hand, rare - earth elements make the distribution of lithium ions in the electrolyte more uniform, slowing down the aggregation of lithium ions in local areas, thus inhibiting the growth of lithium dendrites. Therefore, the monoclinic sulfide electrolyte can combine the advantages of high ionic conductivity and wide electrochemical window of the argyrodite - type electrolyte, and can also overcome the problems of the compatibility between the electrolyte and the electrode interface and the growth of lithium dendrites.

[0029] The novel monoclinic electrolyte used in the present invention has high lithium - ion conductivity, which can ensure the uniform distribution of lithium ions at the interface, avoiding the growth of dendrites caused by too high local lithium - ion concentration. Moreover, it has the advantage of lattice structure. There are a large number of lithium - ion vacancies in the lattice structure of the novel electrolyte, providing channels for the rapid migration of lithium ions and contributing to the uniform distribution of lithium ions at the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the following detailed description of non - restrictive embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent:

[0031] Figure 1 XRD diffraction pattern of Li2S3 in Preparation Example 1;

[0032] Figure 2 XPS spectrum of Li2S3 in Preparation Example 1;

[0033] Figure 3 EDS spectrum of Example 1;

[0034] Figure 4 SEM image of Example 1;

[0035] Figure 5 XRD diffraction pattern of Example 1;

[0036] Figure 6 Cycling performance graph of the electrolyte of Example 1 applied to all - solid - state lithium metal;

[0037] Figure 7 Coulombic efficiency graph of the electrolyte of Example 1 applied to all - solid - state lithium - metal battery;

[0038] Figure 8 Structure diagram of LiM1M2S4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several adjustments and improvements can still be made. These all fall within the protection scope of the present invention.

[0040] In the specific implementation mode of the present invention, the manufacturers and specifications of the raw materials are as follows. On the premise of not affecting the effect of the present invention, raw materials from other manufacturers can also be selected.

[0041] Sc: Powder, Adamas, purity > 99.9%

[0042] Y: Powder, Adamas, purity > 99.9%

[0043] Er: Powder, Adamas, purity > 99.9%

[0044] Tm: Powder, Adamas, purity > 99.9%

[0045] Yb: Powder, Adamas, purity > 99.9%

[0046] Lu: Powder, Adamas, purity > 99.9%

[0047] Si: Powder, Adamas, purity > 99.9%

[0048] Ge: Powder, Adamas, purity > 99.9%

[0049] Sn: Powder, Adamas, purity > 99.9%

[0050] S: Powder, Adamas, purity > 99.9%

[0051] Li2S: Powder, Adamas, purity > 99.9%

[0052] P2S5: Powder, Adamas, purity > 99.9%

[0053] LiCl: Powder, Adamas, purity > 99.9%

[0054] GeS2: Powder, Adamas, purity > 99.9%.

[0055] The structural diagram of LiM1M2S4 prepared by the present invention is as Figure 8As shown. First, monoclinic sulfide electrolytes were synthesized in the manner of Examples 1-4, and then high-quality single crystals were screened under an electron microscope. The crystal structure data of this sulfide electrolyte was collected and analyzed using a Bruker single-crystal diffractometer. The X-ray source was Mo Kα radiation monochromatized by a graphite monochromator, with a wavelength λ = 0.71073 Å. It should be noted that the voltage and current of the X-ray tube were set to 50 kV and 30 mA, respectively. Finally, the crystal structure was directly solved using the SHELXTL software package, and the structure of the monoclinic sulfide electrolyte was refined using matrix least squares; finally, this structure was obtained.

[0056] Preparation Example Preparation of Li2S3

[0057] The Li2S3 was synthesized by the liquid ammonia method, and its synthesis steps are as follows:

[0058] (1) Prepare high-purity raw materials: Metallic lithium needs to be cleaned with a hydrocarbon solvent (specifically n-hexane in this preparation example); sulfur powder needs to be of high purity and dried in an oven to ensure dryness; liquid ammonia needs to be dried to ensure anhydrous and oxygen-free.

[0059] (2) Weigh and mix: Weigh metallic lithium and sulfur powder according to the stoichiometric ratio and put them into a stainless-steel pressure-resistant container (Lei Yunsen 500 ml stainless-steel digestion tank).

[0060] (3) Vacuumize and fill with ammonia: Place the pressure-resistant reaction kettle containing the reactants in a liquid nitrogen or dry ice / acetone bath for cooling (liquid nitrogen is used in this preparation example). Connect a vacuum pump to evacuate the reaction kettle to remove the air inside; introduce liquid ammonia until the reaction kettle is filled with liquid ammonia.

[0061] (4) Low-temperature reaction: The reaction temperature range is -78°C to -33°C, and the reaction is carried out at low temperature for 5-10 hours (in this preparation example, the reaction temperature is -50°C, and the reaction is carried out at low temperature for 8 hours).

[0062] (5) Post-treatment: Take the reaction kettle out of the low-temperature bath, slowly warm it up to room temperature, open the valve, and slowly release the liquid ammonia. Take out the solid product in the reaction kettle and place it in a glove box for drying and grinding.

[0063] Figure 1 XRD diffraction pattern of Li2S3 in Preparation Example 1; compared with that in the literature (literature source: Fabrication ofmesoporous Li2S–C nanofibers for high performance Li / Li2S cell cathodes.

[0064] F. Ye, Y. Hou, M. Liu, W. Li, X. Yang, Y. Qiu, et al. Nanoscale 2015 Vol. 7 Issue 21 Pages 9472-9476. DOI: 10.1039 / C5NR00480B) The positions of the main peaks in the XRD diffraction pattern related to Li2S3 are basically the same.

[0065] Figure 2 XPS spectrum of Li2S3 in Preparation Example 1.

[0066] Example 1 LiYGeS4

[0067] This example provides a monoclinic electrolyte and its preparation method. The raw materials used in this example are Y, Ge, elemental S, and Li2S3 synthesized by the liquid ammonia method in Preparation Example 1.

[0068] The preparation method of the monoclinic electrolyte includes the following steps:

[0069] S1. Add each raw material according to the molar ratio: Li2S3:Y:Ge:S = 0.5:1:1:2.5 into a vacuum ball milling jar and mix evenly using a ball mill. Use zirconia balls (diameter 5 mm) as the ball milling medium, and the mass ratio of the ball milling medium to the raw materials is 10:1. Under the condition of a vacuum degree of 100 Pa, use a ball mill for mixing, the rotation speed of the ball mill is 110 r / min, and the ball milling time is 1 hour;

[0070] S2. Intermittent ball milling: Adjust the rotation speed of the ball mill to 500 r / min and ball mill for 24 hours, where for every 1 hour of ball milling, the ball mill stops and cools for 10 minutes;

[0071] S3. Seal the ball milled mixture in a quartz tube under vacuum conditions, adjust the temperature control program to a heating rate of 0.646 °C / min, slowly heat the quartz tube to 800 °C, and keep it in the program furnace for 10 hours. After this program, a LiYGeS4 powder sample is obtained.

[0072] S4. Crystal structure analysis of monoclinic LiYGeS4 electrolyte:

[0073] Through the analysis of the data of the Bruker single crystal diffractometer, the crystal structure parameters and atomic coordinates and other information of the monoclinic LiYGeS4 electrolyte are determined.

[0074] Diffraction data obtained from a Bruker single-crystal diffractometer were used to directly solve the crystal structure using the SHELXTL software package, and the structure of the monoclinic sulfide electrolyte was refined by matrix least squares. Finally, the crystal structure parameters and atomic coordinates of the monoclinic LiYGeS4 electrolyte were determined.

[0075] The unit cell parameters are as follows:

[0076] a = 6.71187800 Å; b = 6.54213100 Å; c = 8.70463875 Å

[0077] α = 72.67936380 Å; β = 90.00000000 Å; γ = 90.00000000 Å

[0078] Unit cell volume: 364.88824410; Number of formula units in the unit cell: Z = 2

[0079] Structural chemical formula: LiYGeS4; Total chemical formula: Li2Y2Ge2S8

[0080] The atomic coordinates and occupancies are shown in Table 1:

[0081] Table 1

[0082]

[0083] Result analysis

[0084] 1). Crystal system determination: Through the crystal parameters, it can be determined that this crystal belongs to the monoclinic crystal system.

[0085] 2). Atomic distribution: Through the atomic coordinates, the specific positions of Li, Y, Ge, and S atoms in the unit cell can be clearly understood.

[0086] Through the detailed analysis of the Bruker single-crystal diffractometer data in this example, the crystal structure of the monoclinic LiYGeS4 electrolyte was successfully determined.

[0087] Figure 3 This is the EDS spectrum of Example 1; the proportions of each element are shown in Table 2:

[0088] Table 2

[0089]

[0090] Figure 4 This is the SEM spectrum of Example 1;

[0091] Figure 5 This is the XRD diffraction pattern of Example 1.

[0092] Example 2: LiScSnS4

[0093] This example provides a novel monoclinic electrolyte and its preparation method. The raw materials used in this example are Sc, Sn, elemental S, and Li2S3 synthesized by the liquid ammonia method in Preparation Example 1.

[0094] The preparation method of the monoclinic electrolyte includes the following steps:

[0095] S1. Add appropriate amounts of each raw material with a molar ratio of Li2S3:Sc:Sn:S = 0.5:1:1:2.5 into a vacuum ball milling tank and uniformly mix them using a ball mill. Use zirconia balls (diameter 5 mm) as the ball milling medium, and the mass ratio of the ball milling medium to the raw materials is 10:1. Under the condition of a vacuum degree of 100 Pa, use the ball mill for mixing. The rotation speed of the ball mill is 110 r / min, and the ball milling time is 1 hour;

[0096] S2. Adjust the rotation speed of the ball mill to 500 r / min and ball mill for 24 hours. Among them, every 1 hour of ball milling, the ball mill stops for cooling for 10 minutes;

[0097] S3. Seal the ball-milled mixture in a quartz tube under vacuum conditions, adjust the temperature control program to a heating rate of 0.646 °C / min, slowly heat the quartz tube to 800 °C, and keep it in the program furnace for 10 hours. After this procedure, a LiScSnS4 powder sample is obtained.

[0098] Example 3

[0099] This example provides a novel monoclinic electrolyte and its preparation method. The raw materials used in this example are Li2S3 synthesized by the liquid ammonia method in Preparation Example 1, as well as Er, Si, and S.

[0100] The preparation method of the novel electrolyte includes the following steps:

[0101] S1. Add appropriate amounts of each raw material with a molar ratio into a vacuum ball milling tank and uniformly mix them using a ball mill. Use zirconia balls (diameter 5 mm) as the ball milling medium, and the mass ratio of the ball milling medium to the raw materials is 10:1. Under the condition of a vacuum degree of 100 Pa, use the ball mill for mixing. The rotation speed of the ball mill is 110 r / min, and the ball milling time is 1 hour;

[0102] S2. Adjust the rotation speed of the ball mill to 500 r / min and ball mill for 24 hours. Among them, every 1 hour of ball milling, the ball mill stops for cooling for 10 minutes;

[0103] S3. Seal the ball-milled mixture in a quartz tube under vacuum conditions. Adjust the temperature control program to a heating rate of 0.646 °C / min, slowly heat the quartz tube to 800 °C, and hold it in the programmed furnace for 10 hours. After this procedure, a LiErSiS4 powder sample is obtained.

[0104] Example 4

[0105] This example provides a novel monoclinic electrolyte and its preparation method. The raw materials used in this example are Li2S3, Yb, Ge, and S synthesized by the liquid ammonia method of Preparation Example 1.

[0106] The preparation method of the novel electrolyte includes the following steps:

[0107] S1. Add appropriate amounts of each raw material in accordance with the molar ratio to a vacuum ball mill tank and mix evenly using a ball mill. Use zirconia balls (diameter 5 mm) as the ball milling medium, and the mass ratio of the ball milling medium to the raw materials is 10:1. Under the condition of a vacuum degree of 100 Pa, use the ball mill for mixing. The rotation speed of the ball mill is 110 r / min, and the ball milling time is 1 hour;

[0108] S2. Adjust the rotation speed of the ball mill to 500 r / min and ball mill for 24 hours. Among them, every 1 hour of ball milling, the ball mill stops to cool for 10 minutes;

[0109] S3. Seal the ball-milled mixture in a quartz tube under vacuum conditions. Adjust the temperature control program to a heating rate of 0.646 °C / min, slowly heat the quartz tube to 800 °C, and hold it in the programmed furnace for 10 hours. After this procedure, a LiYbGeS4 powder sample is obtained.

[0110] Comparative Example 1

[0111] This comparative example provides a Li6PS5Cl electrolyte and its preparation method. The raw materials used in this comparative example are Li2S, P2S5, and LiCl (commercial Li6PS5Cl is from Ganfeng Lithium Industry)

[0112] The preparation method of the electrolyte includes the following steps:

[0113] S1. Raw material preparation and mixing: Weigh Li2S, P2S5, and LiCl according to the stoichiometric ratio and mix them evenly in the ball mill tank;

[0114] S2. Mechanical ball milling: Put the mixture into the ball mill and improve the reaction activity through the grinding action of the ball milling medium;

[0115] S3. High-temperature reaction: React the pre-burned sample at high temperature to generate Li6PS5Cl;

[0116] S4. Cooling and grinding: After natural cooling, the product is ground into fine particles.

[0117] Comparative Example 2

[0118] This comparative example provides a kind of Li 5.5 PS 4.5 Cl 1.5 electrolyte and its preparation method (literature source: Parvin Adeli, J. David Bazak, Kern Ho Park, Ivan Kochetkov, Ashfia Huq, Gillian R. Goward, Linda F. Nazar. Boosting Solid-State Diffusivity and Conductivity in Lithium Superionic Argyrodites by Halide Substitution[J]. Angewandte Chemie International Edition, 2019, 58(18): 6040 - 6044. DOI: 10.1002 / anie.201814222). The raw materials used in this comparative example are Li2S, P2S5, and LiCl.

[0119] The preparation method of the electrolyte includes the following steps:

[0120] S1. Raw material preparation and mixing: Weigh Li2S, P2S5, and LiCl according to the stoichiometric ratio and mix them evenly in a ball milling jar;

[0121] S2. Mechanical ball milling: Put the mixture into a ball mill and improve the reaction activity through the grinding action of the ball milling medium;

[0122] S3. High-temperature reaction: React the pre-burned sample at high temperature to generate Li 5.5 PS 4.5 Cl 1.5 ;

[0123] S4. Cooling and grinding: After natural cooling, the product is ground into fine particles.

[0124] Comparative Example 3

[0125] This comparative example provides a kind of Li 10 GeP2S 12 electrolyte and its preparation method. The raw materials used in this comparative example are Li2S, P2S5, LiCl, and GeS2 (commercial Li 10 GeP2S 12From Tokyo Chemical Industry (Shanghai) Chemical Industry Development Co., Ltd.

[0126] The preparation method of the electrolyte comprises the following steps:

[0127] S1. Raw material preparation and mixing: Weigh Li2S, P2S5 and GeS2 according to the stoichiometric ratio and mix them evenly in a ball milling jar.

[0128] S2. Mechanical ball milling: Put the mixture into a ball mill and improve the reaction activity through the grinding action of the ball milling medium.

[0129] S3. High-temperature reaction: React the pre-burned sample at high temperature to generate Li 10 GeP2S 12 ;

[0130] S4. Cooling and pulverization: After natural cooling, pulverize the product into fine particles.

[0131] Comparative Example 4

[0132] The difference between this comparative example and Example 1 is that the intermittent ball milling in S2 is modified to continuous ball milling, specifically:

[0133] S3. The material after ball milling in step S1 is ball milled at 500 r / min for 24 hours.

[0134] Comparative Example 5

[0135] The difference between this comparative example and Example 1 is that only one ball milling is carried out. The specific steps of this comparative example are as follows:

[0136] S1. Add each raw material according to the molar ratio: Li2S3:Y:Ge:S = 0.5:1:1:2.5 to a vacuum ball milling jar and ball mill at 600 r / min for 24 hours using a ball mill. For every 1 hour of ball milling, the ball mill stops for cooling for 10 minutes.

[0137] S2. Seal the ball milled mixture in a quartz tube under vacuum conditions, adjust the temperature control program to a heating rate of 0.646 °C / min, slowly heat the quartz tube to 800 °C, and hold it in the program furnace for 10 hours. After this program, a LiYGeS4 powder sample is obtained.

[0138] Comparative Example 6

[0139] This comparative example uses Li2S3 synthesized by the ethanol method. The steps for synthesizing Li2S3 by the ethanol method are as follows:

[0140] S1. Weigh lithium sulfide (Li2S) and sulfur (S) according to the stoichiometric ratio in a glove box.

[0141] S2. Put Li2S and S into 20 mL of anhydrous ethanol (C2H5OH);

[0142] S3. Stir for 30 minutes at room temperature to form a brown solution of Li2S3;

[0143] S4. Heat the Li2S3 solution at 60 °C for 5 hours to obtain Li2S3 powder.

[0144] It should be noted that Li2S is sensitive to water. Therefore, the entire experimental process must be carried out in a glove box to avoid contact between Li2S and water.

[0145] The preparation method of LiYGeS4 is the same as that of Example 1.

[0146] Performance test:

[0147] Measure the AC impedance values of the inorganic sulfide electrolytes prepared in Examples 1-4 and Comparative Examples 1-6 using an electrochemical workstation, and calculate the ionic conductivity. The calculation formula is σ = L / RS. Where S is the area of the electrolyte sheet, L is the thickness of the electrolyte sheet, R is the impedance value, and σ is the ionic conductivity. In the examples and comparative examples, 120 mg of the electrolyte was weighed and pressed into a tablet, and all were pressed into a thin sheet with an area of 0.785 cm 2 and a thickness of 1 mm. Then, the bulk impedance (R) of the electrolyte was tested, and the bulk impedance of different electrolyte sheets was measured using electrochemical impedance spectroscopy (EIS) on an Es-Lab. Two stainless steels (SS) were used as blocking electrodes, and the measurement was carried out at room temperature in the frequency range of 7000 kHz – 100 mHz and an AC amplitude of 10 mV.

[0148] Assemble the products prepared in the above examples and comparative examples: In an inert gas glove box with a water and oxygen content ≤ 0.01 ppm, grind the target electrolyte taken out after sintering and use it as the electrolyte layer. The positive electrode is a pole piece with a unit area NCM811 loading of 10 mgcm -2 and the lithium metal is the negative electrode layer to assemble a all-solid-state lithium metal battery. Finally, perform cyclic charge and discharge. First, charge and discharge at 0.1C for two cycles, and then perform a long-term cyclic test at 0.5C. Test its initial efficiency and the capacity retention rate after 500 cycles.

[0149] The results are shown in Table 3 below: It can be seen from Table 1 that the novel monoclinic sulfide electrolyte can exhibit higher initial efficiency and capacity retention as an electrolyte, improving the performance of the all-solid-state lithium metal battery life. Figure 6 It can be seen that it has excellent cycling ability and capacity retention rate.

[0150] Figure 7 It is the Coulomb efficiency diagram of the electrolyte of Example 1 applied to the all-solid-state lithium metal battery.

[0151] Table 3

[0152]

[0153] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a monoclinic sulfide electrolyte, characterized in that: The steps include: S1, mixing Li2S3, M1, M2, and S, and performing a ball milling; wherein M1 is a rare earth element, and the rare earth element is selected from one or more of scandium, yttrium, erbium, thulium, ytterbium, and lutetium; M2 is a Group IVA element, and the Group IVA element is selected from one or more of silicon, germanium, and tin; The Li2S3 is prepared by a liquid ammonia method; the method comprises the following steps: 1) Weigh lithium and sulfur according to the stoichiometric ratio and put them into a pressure-resistant reaction vessel; cool the pressure-resistant reaction vessel containing the reactants, evacuate the reaction vessel, introduce liquid ammonia until the reaction vessel is full of liquid ammonia, and react at low temperature for a period of time; 2) slowly heating the reaction vessel to room temperature, releasing liquid ammonia, and drying the solid product to obtain the Li2S3; S2, performing secondary ball milling on the material after ball milling in step S1; S3, sintering the product after the secondary ball milling to obtain the monoclinic sulfide electrolyte; In step S1, the first ball milling conditions are: ball milling speed 100-150r / min; ball milling time 1-2h; In step S2, the secondary ball milling conditions are: ball milling at a speed of 500 r / min-600 r / min for 24-48 hours, wherein each ball milling is 1-2 hours and stopped for 10-20 minutes; Step S3 specifically comprises: heating the mixture after the secondary ball milling in step S2 to 700-900° C. under vacuum conditions, and keeping the temperature for 8-10 hours to obtain the monoclinic sulfide electrolyte.

2. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of Li2S3:M1:M2:S is 0.4-0.6:0.9-1.1:0.9-1.1:2.4-2.

6.

3. The preparation method according to claim 1, characterized in that: In step 1), the lithium metal is washed with a hydrocarbon solvent; the hydrocarbon solvent used to wash the lithium metal includes n-hexane; And / or, in step 1), the cooling method is liquid nitrogen cooling, or dry ice / acetone bath cooling; And / or, in step 1), in the low-temperature reaction step, the reaction temperature ranges from -78°C to -33°C, and the reaction time is 5-10 hours.

4. The preparation method according to claim 1, characterized in that: In step S3, the heating rate is 0.5-10°C / min.

5. A monoclinic sulfide electrolyte prepared by the preparation method according to any one of claims 1 to 4.

6. The monoclinic sulfide electrolyte according to claim 5, characterized in that: The chemical formula of the monoclinic sulfide electrolyte is LiM1M2S4; M1 is a rare earth element, and the rare earth element is selected from one or more of scandium, yttrium, erbium, thulium, ytterbium, and lutetium; M2 is a Group IVA element, and the Group IVA element is selected from one or more of silicon, germanium, and tin.

7. An all-solid-state lithium metal secondary battery, characterized in that: The invention comprises a lithium metal negative electrode or a metal lithium composite negative electrode, a positive electrode and a monoclinic sulfide electrolyte prepared by the preparation method according to any one of claims 1 to 4.

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