Inorganic composite solid electrolyte and method for preparing the same

Abstract

The application discloses an inorganic composite solid electrolyte and a preparation method thereof, and relates to the technical field of lithium batteries, and specifically discloses an inorganic composite solid electrolyte and a preparation method thereof. The preparation method of the inorganic composite solid electrolyte comprises the following steps: S1, mixing lithium salt, metal oxide A, metal oxide B and ammonium dihydrogen phosphate, wherein the metal oxide B is titanium oxide, and intermittent vibration ball milling is performed to obtain mixed powder; S2, adding lanthanum oxide and germanium oxide into the mixed powder obtained in the step S1, and continuing to perform intermittent vibration ball milling to obtain composite powder; and S3, performing low-temperature sintering on the composite powder obtained in the step S2, and pressing to obtain an inorganic composite solid electrolyte film layer. The preparation method can significantly improve the reaction activity and synergistic effect among raw materials by adopting two-step intermittent vibration ball milling and one-step low-temperature sintering, and the conductivity of the inorganic composite solid electrolyte and the lithium ion transmission performance and cycle life of the solid battery are improved, and meanwhile, no solvent is used in the preparation process, and the sintering cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to an inorganic composite solid electrolyte and its preparation method. Background Technology

[0002] In lithium-ion battery applications, solid electrolytes significantly improve the energy density and safety of lithium-ion batteries compared to traditional liquid electrolytes, thus gaining widespread use. Currently, the synthesis methods for solid electrolytes are mainly divided into traditional solid-state synthesis, solvent synthesis, and mechanical grinding. Among them, traditional solid-state synthesis suffers from low yield and requires high-temperature environments, resulting in high manufacturing costs. While solvent synthesis can scale up production, residual solvents can contaminate the electrolyte. Mechanical ball milling, on the other hand, uses hard balls to intensely impact, grind, and stir the raw materials, creating new reaction surfaces and new particle arrangements. It is an important alternative to traditional solid-state synthesis and solvent synthesis methods for preparing novel battery materials.

[0003] In recent years, mechanical ball milling has become a commonly used method in the synthesis of solid electrolytes. For example, Chinese patent documents, including application number CN202010639364.X, disclose a solid electrolyte and its preparation method, and a lithium secondary solid battery, which discloses the use of ball milling to first crush pre-sintered solid electrolytes, followed by high-temperature sintering, ultimately obtaining a polymer-inorganic composite solid electrolyte membrane; application number CN201910641764.1 discloses a sulfide solid electrolyte and its preparation method and uses, which discloses the use of high-energy mechanical ball milling to mix and ball mill sulfide raw materials, followed by one-step heat treatment to obtain a sulfide solid electrolyte; and application number CN202110548876.X discloses a method for preparing a low-resistivity garnet-type modified LLZO solid electrolyte, which discloses the use of three-dimensional high-energy vibration ball milling to improve the mixing efficiency of raw materials, followed by high-temperature sintering to obtain an Al / Ga-doped modified LLZO solid electrolyte.

[0004] However, the aforementioned patent documents only use mechanical ball milling as a pretreatment or auxiliary step in the electrolyte preparation process. This cannot significantly improve the reactivity of the raw materials in the ball mill, nor can it obtain a high-performance composite oxide inorganic solid electrolyte through one-step low-temperature sintering. As a result, it is difficult to improve the conductivity of the inorganic composite solid electrolyte, and thus difficult to reduce the internal resistance of the solid battery and extend its cycle life. At the same time, the manufacturing cost is also very high, and there are certain technical limitations. Summary of the Invention

[0005] To address the technical problem that in the preparation of solid electrolytes using mechanical ball milling, the low reactivity of the raw materials within the ball mill makes it difficult to improve the conductivity of the solid electrolyte, thereby hindering the reduction of internal resistance and the extension of cycle life in solid batteries, this invention provides an inorganic composite solid electrolyte and its preparation method. This method can significantly improve the reactivity and synergistic effect between the raw materials, thereby enhancing the conductivity of the inorganic composite solid electrolyte, the lithium-ion transport performance of the solid battery, and its cycle life. Furthermore, the preparation process is solvent-free, reducing sintering costs.

[0006] Technical solution

[0007] To solve the above problems, the technical solution provided by the present invention is as follows:

[0008] A method for preparing an inorganic composite solid electrolyte includes the following steps:

[0009] S1. Mix lithium salt, metal oxide A, metal oxide B and ammonium dihydrogen phosphate, wherein metal oxide B is titanium oxide, and intermittently vibratory ball mill to obtain mixed powder;

[0010] S2. Add lanthanum oxide and germanium oxide to the mixed powder obtained in step S1, and continue intermittent vibratory ball milling to obtain composite powder;

[0011] S3. The composite powder obtained in step S2 is sintered at low temperature and pressed to obtain an inorganic composite solid electrolyte membrane layer.

[0012] This application employs a two-step intermittent vibratory ball milling process. In the first step, the intermittent vibration ball milling, with periods of milling followed by periods of cessation, achieves a cooling effect, preventing the raw material from experiencing excessively high local temperatures that could lead to the volatilization of lithium and phosphorus, thus reducing the conductivity of the electrolyte material. Simultaneously, it allows control of the specific surface area of ​​the milled powder, forming a highly surface-active mixed powder (i.e., a NASICON-type lithium-ion electrolyte, such as LATP). Then, lanthanum oxide and germanium oxide are added to the mixed powder, and intermittent vibration ball milling continues—the second step. During this process, lanthanum oxide rapidly reacts with the previously excess titanium oxide to generate LLTO. The generated LLTO then reacts with the mixed powder formed in the first step (i.e., NASICON-type lithium-ion electrolyte, such as LATP). A composite powder (i.e., an inorganic composite solid electrolyte, such as Ge-LLTO-LATP inorganic composite solid electrolyte) is formed by combining NASICON-type lithium-ion electrolytes (such as NASICON-type lithium-ion electrolytes, such as LATP) with added germanium, which permeates into the composite particles. This composite powder exhibits high bulk lithium-ion conductivity but low grain boundary lithium-ion conductivity with LLTO. When LLTO is combined with NASICON-type lithium-ion electrolytes (such as LATP), the LLTO insulator can form a space charge region around the particles, effectively adding space defects to the NASICON-type lithium-ion electrolyte (such as LATP), providing a fast channel for lithium-ion transport and increasing the migration speed of lithium ions. Simultaneously, the amorphous product generated by vibratory ball milling provides even more lithium-ion transport channels. Furthermore, the ionic radii of metal elements (such as germanium) are close to those of aluminum, and doping with them can form rapid three-dimensional lithium-ion transport channels, further improving the conductivity of the composite solid electrolyte. Then, the composite powder is sintered at low temperature and pressed to obtain an inorganic composite solid electrolyte membrane. Compared with the high temperature sintering (above 900°C) in conventional solid-phase reactions, the low temperature sintering used in this application has larger particle lattice parameters, lower elastic modulus and hardness, and the particles are more closely connected after being pressed into a membrane. Furthermore, the particles are not easily broken during charging and discharging.

[0013] Therefore, it can be seen that the preparation method of this application, by adopting a two-step intermittent vibration ball milling and a one-step low-temperature sintering method, can significantly improve the reactivity and synergistic effect between the raw materials. While improving the conductivity of the inorganic composite solid electrolyte and the lithium-ion transport performance and cycle life of the solid battery, the preparation process is solvent-free and reduces the sintering cost.

[0014] Optionally, in step S1, the molar ratio of the lithium salt, metal oxide A, titanium oxide and ammonium dihydrogen phosphate is 1.5-1.9:0.5-0.9:1.0-2.4:2.5-4.0; in step S2, the mass ratio of lanthanum oxide, germanium oxide and mixed powder is 1.5-2.0:1.0-1.5:7.0-9.5.

[0015] Optionally, in step S3, lithium silicate is added during the low-temperature sintering process, with a sintering temperature of 300-500℃ and a sintering time of 4-8h.

[0016] Optionally, the lithium salt is lithium carbonate or lithium hydroxide, and the metal oxide A is one of aluminum oxide, iron oxide, indium oxide, gallium oxide, strontium oxide, calcium oxide, and magnesium oxide.

[0017] Optionally, in step S1, the specific surface area of ​​the powder during the ball milling process is tested. If the specific surface area of ​​the powder during the ball milling process begins to change from large to small, then the intermittent vibratory ball milling is stopped.

[0018] Optionally, in step S1, the intermittent vibratory ball milling time at room temperature is 30-60 min; in step S2, the intermittent vibratory ball milling time at room temperature is 60-120 min, with each ball milling session lasting 30-60 min and the interval between each ball milling session lasting 10-20 min.

[0019] Optionally, in step S2, during the intermittent vibratory ball milling process, a ball milling additive is added. The mass ratio of the ball milling additive to the lanthanum-germanium mixed powder is 5-10:70-90. The lanthanum-germanium mixed powder is the powder obtained in step S1 after mixing with lanthanum oxide and germanium oxide. The ball milling additive is one of polyacrylic acid, polyurethane, ethanol, ethylene glycol, and polyethylene glycol.

[0020] Optionally, in steps S1 and S2, during ball milling, the grinding balls are any one of zirconia balls, alumina balls, stainless steel balls, zirconium silicate balls, and nylon balls, with a ball-to-material ratio of 10-15:10-20, a powder filling ratio of 40-60%, and a vibration frequency of 50-200 Hz.

[0021] Optionally, the average particle size of the lithium salt, metal oxide A, titanium oxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide is 0.3-3 μm; the thickness of the inorganic composite solid electrolyte membrane is 50-150 μm.

[0022] In addition, this application also provides an inorganic composite solid electrolyte, which is prepared by the above-described method for preparing inorganic composite solid electrolyte. Beneficial effects

[0023] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0024] (1) The method for preparing an inorganic composite solid electrolyte proposed in this application involves a two-step intermittent vibratory ball milling process. In the first step, the intermittent vibratory ball milling process, i.e., after each milling period, a period of cessation is performed to achieve a cooling effect, preventing the raw materials from volatilizing lithium and phosphorus due to excessively high local temperatures during the milling process, thereby reducing the conductivity of the electrolyte material. At the same time, the specific surface area of ​​the milled powder can be controlled during the milling process, thereby forming a mixed powder with high surface activity (i.e., NASICON-type lithium-ion electrolyte, such as LATP). Then, lanthanum oxide and germanium oxide are added to the mixed powder, and the intermittent vibratory ball milling continues, i.e., the second step of intermittent vibratory ball milling. During the milling process, lanthanum oxide reacts rapidly with the previously excess titanium oxide to generate LLTO. The generated LLTO reacts with the first step of the process. A composite powder (i.e., a NASICON-type lithium-ion electrolyte, such as LATP) is formed by incorporating germanium into the composite particles, resulting in an amorphous composite powder (i.e., an inorganic composite solid electrolyte, such as a Ge-LLTO-LATP inorganic composite solid electrolyte). In this composite powder structure, LLTO exhibits very high bulk lithium-ion conductivity but very low grain boundary lithium-ion conductivity. When LLTO is combined with (NASICON-type lithium-ion electrolytes, such as LATP), the LLTO insulator can form a space charge region around the particles, effectively adding space defects to the (NASICON-type lithium-ion electrolyte, such as LATP), providing a fast channel for lithium-ion transport and increasing the migration speed of lithium ions. Simultaneously, the amorphous product generated by vibratory ball milling provides even more lithium-ion transport channels. Furthermore, the ionic radii of metal elements (such as germanium) are close to those of aluminum, and doping with them can form rapid three-dimensional lithium-ion transport channels, further improving the conductivity of the composite solid electrolyte. Then, the composite powder is sintered at low temperature and pressed to obtain an inorganic composite solid electrolyte membrane. Compared with the high temperature sintering (above 900°C) in conventional solid-phase reactions, the low temperature sintering used in this application has larger particle lattice parameters, lower elastic modulus and hardness, and the particles are more closely connected after being pressed into a membrane. Furthermore, the particles are not easily broken during charging and discharging.

[0025] Therefore, it can be seen that the preparation method of this application, by adopting a two-step intermittent vibration ball milling and a one-step low-temperature sintering method, can significantly improve the reactivity and synergistic effect between the raw materials. While improving the conductivity of the inorganic composite solid electrolyte and the lithium-ion transport performance and cycle life of the solid battery, the preparation process is solvent-free and reduces the sintering cost.

[0026] (2) The method for preparing an inorganic composite solid electrolyte proposed in this application involves adding lithium silicate during a low-temperature sintering process. The sintering temperature is 300-500℃, and the sintering time is 4-8h. By adding lithium silicate, the density and lithium-ion point conductivity during the sintering process can be improved. At the same time, compared with the high-temperature sintering (above 900℃) in conventional solid-phase reactions, the low-temperature sintering at 300-500℃ results in larger particle lattice parameters, lower elastic modulus and hardness, and tighter contact between particles after pressing into a film. Furthermore, the particles are less prone to breakage during charging and discharging, which helps to improve the conductivity of the electrolyte and the lithium-ion transport performance and cycle life of the solid battery.

[0027] (3) The method for preparing an inorganic composite solid electrolyte proposed in this application involves testing the specific surface area of ​​the powder during the ball milling process. If the specific surface area of ​​the powder during the ball milling process begins to change from large to small, the intermittent vibration ball milling is stopped. This setting can ensure that the mixed powder has the largest specific surface area, the largest specific surface energy, and the highest reactivity, thereby forming a high surface activity NASICON-type lithium-ion electrolyte product, such as LATP.

[0028] (4) The method for preparing an inorganic composite solid electrolyte proposed in the embodiments of this application, the addition of ball milling additives and the limitation of their dosage, can reduce the surface energy of individual particles and change the flowability of particle discharge and suspension, thereby effectively improving the fineness of particles and the flowability of powder, accelerating the reaction rate between solid materials, and improving the electrochemical performance of materials.

[0029] (5) An inorganic composite solid electrolyte proposed in the embodiments of this application is prepared by the preparation method of this application. It has a high conductivity, reduces the impedance of the battery, and improves the lithium-ion transport performance and cycle life of the solid battery. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that all reagents and raw materials involved in this application can be purchased from the market.

[0032] This application provides a method for preparing an inorganic composite solid electrolyte, comprising the following steps:

[0033] S1. Lithium salt, metal oxide A, metal oxide B, and ammonium dihydrogen phosphate are mixed in a high-energy vibratory ball mill, wherein metal oxide B is titanium oxide. Intermittent vibratory ball milling is performed at room temperature to obtain a mixed powder. The molar ratio of lithium salt, metal oxide A, titanium oxide, and ammonium dihydrogen phosphate is 1.5-1.9:0.5-0.9:1.0-2.4:2.5-4.0. The specified amounts of each raw material allow for sufficient reaction between them to generate the corresponding products. The lithium salt is lithium carbonate or lithium hydroxide, and metal oxide A is one of aluminum oxide, iron oxide, indium oxide, gallium oxide, strontium oxide, calcium oxide, and magnesium oxide. The average particle size of the lithium salt, metal oxide A, titanium oxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide is 0.3-3 μm. Generally, during solid particle crushing, the energy loss due to mechanical energy conversion, crushing method, and elastic and permanent deformation is a significant factor. When the particle size of each raw material is controlled within the aforementioned range, the increased power consumed during grinding greatly accelerates the size reduction, while the process energy efficiency does not decrease significantly. The intermittent vibratory ball milling time is 30-60 minutes, and the grinding balls are any one of zirconia balls, alumina balls, stainless steel balls, zirconium silicate balls, and nylon balls. The ball-to-material ratio is 10-15:10-20, the powder filling ratio is 40-60%, and the vibration frequency is 50-200 Hz. These ball milling parameters can improve the reactivity between the raw materials.

[0034] Simultaneously, during the intermittent vibratory ball milling process, the specific surface area of ​​the powder is tested using the BET method. Intermittent vibratory ball milling is stopped when the specific surface area of ​​the powder begins to decrease. Typically, as the milling time progresses, the specific surface area of ​​the powder gradually increases initially, and is immediately stopped when it reaches its maximum value and begins to decrease. This setting ensures that the mixed powder achieves the maximum specific surface area, maximum specific surface energy, and highest reactivity, thereby forming a highly surface-active NASICON-type lithium-ion electrolyte product.

[0035] S2. Add lanthanum oxide and germanium oxide to the mixed powder obtained in step S1, and continue intermittent vibratory ball milling to obtain a composite powder. The mass ratio of lanthanum oxide, germanium oxide, and the mixed powder is 1.5-2.0:1.0-1.5:7.0-9.5. The intermittent vibratory ball milling time is 60-120 min, with each milling session lasting 30-60 min and an interval of 10-20 min between milling sessions. This setting ensures sufficient cooling while maintaining the reactivity between the raw materials, effectively preventing the volatilization of lithium and phosphorus due to localized overheating during ball milling, thus reducing the conductivity of the electrolyte material. The grinding balls are any one of zirconium oxide balls, alumina balls, stainless steel balls, zirconium silicate balls, and nylon balls, with a ball-to-material ratio of 10-15:10-20, a powder filling ratio of 40-60%, and a vibration frequency of 50-200 Hz. These ball milling parameters enhance the reactivity between the raw materials. During intermittent vibratory ball milling, a ball milling additive is added. The mass ratio of the ball milling additive to the lanthanum-germanium mixed powder is 5-10:70-90. The lanthanum-germanium mixed powder is the powder obtained in step S1, which is then mixed with lanthanum oxide and germanium oxide. The ball milling additive is one of polyacrylic acid, polyurethane, ethanol, ethylene glycol, and polyethylene glycol. The addition of the ball milling additive can reduce the surface energy of individual particles and change the particle size distribution and the fluidity of the suspension, thereby effectively improving the fineness of the particles and the fluidity of the powder, accelerating the reaction rate between solid materials, and improving the electrochemical performance of the material.

[0036] In practical applications, the ball milling additive is added in batches. This setting can increase the mixing effect of the ball milling additive with each raw material.

[0037] S3. The composite powder obtained in step S2 is sintered at low temperature in air and pressed under 50-200 standard atmospheres to obtain an inorganic composite solid electrolyte membrane layer with a thickness of 50-150 μm. Lithium silicate is added during the low-temperature sintering process, with a sintering temperature of 300-500℃ and a sintering time of 4-8 hours. The addition of lithium silicate improves the density and lithium-ion point conductivity during sintering. Furthermore, compared to high-temperature sintering (above 900℃) in conventional solid-state reactions, low-temperature sintering at 300-500℃ results in larger particle lattice parameters, lower elastic modulus and hardness, resulting in tighter contact between particles after pressing into a membrane. The particles are also less prone to breakage during charge and discharge, contributing to improved electrolyte conductivity and the lithium-ion transport performance and cycle life of the solid-state battery.

[0038] In summary, this application employs a two-step intermittent vibratory ball milling process. In the first step, the intermittent vibration ball milling, with periods of milling followed by periods of cessation, achieves a cooling effect, preventing the raw material from experiencing excessively high local temperatures that could lead to the volatilization of lithium and phosphorus, thus reducing the conductivity of the electrolyte material. Simultaneously, it allows control of the specific surface area of ​​the milled powder, forming a highly surface-active mixed powder (i.e., a NASICON-type lithium-ion electrolyte, such as LATP). Then, lanthanum oxide and germanium oxide are added to the mixed powder, and intermittent vibration ball milling continues—the second step. During this process, lanthanum oxide rapidly reacts with the previously excess titanium oxide to generate LLTO. The generated LLTO then reacts with the mixed powder formed in the first step (i.e., NASICON-type lithium-ion electrolyte, such as LATP). A composite of CON-type lithium-ion electrolytes, such as LATP, and the addition of germanium, which permeates into the composite particles, forms an amorphous composite powder (i.e., an inorganic composite solid electrolyte, such as a Ge-LLTO-LATP inorganic composite solid electrolyte). In this composite powder structure, LLTO exhibits very high bulk lithium-ion conductivity but very low grain boundary lithium-ion conductivity. When LLTO is combined with (NASICON-type lithium-ion electrolytes, such as LATP), the LLTO insulator can form a space charge region around the particles, effectively adding space defects to the (NASICON-type lithium-ion electrolyte, such as LATP), providing a fast channel for lithium-ion transport and increasing the migration speed of lithium ions. Simultaneously, the amorphous product generated by vibratory ball milling provides even more lithium-ion transport channels. Furthermore, the ionic radii of metal elements (such as germanium) are close to those of aluminum; after doping, they can form a rapid three-dimensional lithium-ion transport channel, further improving the conductivity of the composite solid electrolyte. Then, the composite powder is sintered at low temperature and pressed to obtain an inorganic composite solid electrolyte membrane. Compared with the high temperature sintering (above 900°C) in conventional solid-phase reactions, the low temperature sintering used in this application has larger particle lattice parameters, lower elastic modulus and hardness, and the particles are more closely connected after being pressed into a membrane. Furthermore, the particles are not easily broken during charging and discharging.

[0039] Therefore, it can be seen that the preparation method of this application, by adopting a two-step intermittent vibration ball milling and a one-step low-temperature sintering method, can significantly improve the reactivity and synergistic effect between the raw materials. While improving the conductivity of the inorganic composite solid electrolyte and the lithium-ion transport performance and cycle life of the solid battery, the preparation process is solvent-free and reduces the sintering cost.

[0040] In addition, this application also provides an inorganic composite solid electrolyte, which is prepared by the above-described method for preparing inorganic composite solid electrolyte.

[0041] In addition, this application also provides a solid battery, including the inorganic composite solid electrolyte described above. Example 1

[0042] Lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate were mixed in a high-energy vibratory ball mill and subjected to intermittent vibratory ball milling at room temperature. The molar ratio of lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate was 1.7:0.7:1.8:3.0. Zirconia beads were used as grinding balls, with a ball-to-material ratio of 11:15 and a powder filling ratio of 50%. The vibration frequency was 100 Hz. During the intermittent vibratory ball milling process, the specific surface area of ​​the powder was tested using the BET method. The intermittent vibratory ball milling was stopped when the specific surface area of ​​the powder began to decrease. The milling time was 45 minutes, yielding a mixed powder (LATP). Lanthanum oxide and germanium oxide were then added to the mixed powder, and the intermittent vibratory ball milling continued. The mass ratio of lanthanum oxide, germanium oxide, and the mixed powder was 1.7:1.2:8.0. The average particle size of titanium dioxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide was 1.5 μm. The grinding balls were zirconium beads with a ball-to-powder ratio of 11:15 and a powder filling ratio of 50%. The vibration frequency was 100 Hz. Grinding was carried out at room temperature for 100 min. After each 40 min of ball grinding, a 15 min pause was taken for sufficient cooling. During the pause, polyacrylic acid emulsion was added in batches. The mass ratio of the total mass of the added polyacrylic acid emulsion to the total mass of lanthanum oxide, germanium oxide, and mixed powder was 7:78, resulting in composite powder (i.e., amorphous Ge-LLTO-LATP particles). Then, the composite powder and lithium silicate were sintered in air at 450 °C for 6 h to obtain dense amorphous Ge-LLTO-LATP particles. These particles were then pressed into an inorganic composite solid electrolyte membrane with a thickness of 70 μm under 100 standard atmospheres. Example 2

[0043] Lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate were mixed in a high-energy vibratory ball mill and subjected to intermittent vibratory ball milling at room temperature. The molar ratio of lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate was 1.5:0.5:1.0:2.5. Zirconia beads were used as grinding balls, with a ball-to-material ratio of 10:10 and a powder filling ratio of 40%. The vibration frequency was 80 Hz. During the intermittent vibratory ball milling process, the specific surface area of ​​the powder was tested using the BET method. The intermittent vibratory ball milling was stopped when the specific surface area of ​​the powder began to decrease. The milling time was 30 minutes, yielding a mixed powder (LATP). Lanthanum oxide and germanium oxide were then added to the mixed powder, and the intermittent vibratory ball milling continued. The mass ratio of lanthanum oxide, germanium oxide, and the mixed powder was 1.5:1.0:7.0. The average particle size of titanium dioxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide was 0.5 μm. The grinding balls were zirconium beads with a ball-to-powder ratio of 10:10 and a powder filling ratio of 40%. The vibration frequency was 80 Hz. Grinding was carried out at room temperature for 120 min. After each 60 min of ball grinding, a 10 min pause was taken for sufficient cooling. During the pause, polyacrylic acid emulsion was added in batches. The mass ratio of the total mass of the added polyacrylic acid emulsion to the total mass of lanthanum oxide, germanium oxide, and mixed powder was 7:78, resulting in composite powder (i.e., amorphous Ge-LLTO-LATP particles). Then, the composite powder and lithium silicate were sintered in air at 300 °C for 8 h to obtain dense amorphous Ge-LLTO-LATP particles. These particles were then pressed into an inorganic composite solid electrolyte membrane with a thickness of 150 μm under 100 standard atmospheres. Example 3

[0044] Lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate were mixed in a high-energy vibratory ball mill and subjected to intermittent vibratory ball milling at room temperature. The molar ratio of lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate was 1.8:0.8:2.1:3.5. The grinding balls were made of stainless steel, the ball-to-material ratio was 15:20, the powder filling ratio was 60%, and the vibration frequency was 200 Hz. During the intermittent vibratory ball milling process, the specific surface area of ​​the powder was tested using the BET method. When the specific surface area of ​​the powder began to decrease, the intermittent vibratory ball milling was stopped. The milling time was 60 minutes, yielding a mixed powder (LATP). Lanthanum oxide and germanium oxide were then added to the mixed powder, and the intermittent vibratory ball milling continued. The mass ratio of lanthanum oxide, germanium oxide, and the mixed powder was 2.0:1.5:9.0. The average particle size of titanium dioxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide was 2.5 μm. The grinding balls were made of stainless steel, the ball-to-powder ratio was 15:20, the powder filling ratio was 60%, the vibration frequency was 200 Hz, and grinding was carried out at room temperature for 100 min. After each 30 min of ball grinding, a 15 min pause was taken for sufficient cooling. During the pause, polyacrylic acid emulsion was added in batches. The mass ratio of the total mass of the added polyacrylic acid emulsion to the total mass of lanthanum oxide, germanium oxide, and mixed powder was 10:88, resulting in composite powder (i.e., amorphous Ge-LLTO-LATP particles). Then, the composite powder and lithium silicate were sintered in air at 500 °C for 4 h to obtain densified amorphous Ge-LLTO-LATP particles. These particles were then pressed into an inorganic composite solid electrolyte membrane with a thickness of 50 μm under 200 standard atmospheres. Example 4

[0045] Lithium carbonate, indium oxide, titanium oxide, and ammonium dihydrogen phosphate were mixed in a high-energy vibratory ball mill and subjected to intermittent vibratory ball milling at room temperature. The molar ratio of lithium carbonate, indium oxide, titanium oxide, and ammonium dihydrogen phosphate was 1.7:0.7:1.8:3.0. Zirconia beads were used as grinding balls, with a ball-to-material ratio of 11:15 and a powder filling ratio of 50%. The vibration frequency was 100 Hz. During the intermittent vibratory ball milling process, the specific surface area of ​​the powder was tested using the BET method. The intermittent vibratory ball milling was stopped when the specific surface area of ​​the powder began to decrease. The milling time was 45 minutes, yielding a mixed powder. Lanthanum oxide and germanium oxide were then added to the mixed powder, and the intermittent vibratory ball milling continued. The mass ratio of lanthanum oxide, germanium oxide, and the mixed powder was 1.7:1.2:8.0. The lithium carbonate, indium oxide, titanium oxide, ammonium dihydrogen phosphate, lanthanum oxide, and germanium oxide have an average particle size of 1.5 μm. The grinding balls are zirconium beads with a ball-to-material ratio of 11:15 and a powder filling ratio of 50%. The vibration frequency is 100 Hz. Grinding is carried out at room temperature for 100 min. After each 40 min of ball grinding, a 15 min pause is taken for sufficient cooling. During the pause, polyacrylic acid emulsion is added in batches. The total mass of the added polyacrylic acid emulsion is in a mass ratio of 7:78 to the total mass of lanthanum oxide, germanium oxide, and the mixed powder to obtain a composite powder. Then, the composite powder and lithium silicate are sintered in air at 450°C for 6 h to obtain dense amorphous composite solid electrolyte particles. These particles are then pressed into an inorganic composite solid electrolyte film with a thickness of 70 μm under 100 standard atmospheres.

[0046] Comparative Example 1

[0047] Compared with Example 1, the difference is that Comparative Example 1 uses a one-step ball milling method, in which lithium carbonate, alumina, titanium oxide, ammonium dihydrogen phosphate, lanthanum oxide and germanium oxide are put into a high-energy vibrating ball mill for ball milling, and the other experimental conditions are the same as those in Example 1.

[0048] Comparative Example 2

[0049] Compared with Example 1, the difference is that no ball milling additive polyacrylic acid emulsion was added during the intermittent vibratory ball milling process, while the other experimental conditions were the same as in Example 1.

[0050] Comparative Example 3

[0051] Compared with Example 1, in Comparative Example 3, no lithium silicate was added during the low-temperature sintering process, and the other experimental conditions were the same as in Example 1.

[0052] Comparative Example 4

[0053] Compared with Example 1, lanthanum oxide was not added in Comparative Example 4, and the other experimental conditions were the same as in Example 1.

[0054] Comparative Example 5

[0055] Compared with Example 1, Germanium oxide was not added in Comparative Example 5, and the other experimental conditions were the same as in Example 1.

[0056] Comparative Example 6

[0057] Similar to Example 1, Comparative Example 6 uses a two-step continuous ball milling method, and the remaining experimental conditions are the same as in Example 1.

[0058] Performance testing and evaluation

[0059] The inorganic composite solid electrolyte membranes prepared in Examples 1-4 and the solid electrolyte membranes prepared in Comparative Examples 1-4 were used to prepare corresponding symmetrical coin-type all-solid-state batteries, with 50 μm thick lithium-indium alloy sheets (lithium atom ratio of 60%) as the working electrode and counter electrode, respectively. The performance of the batteries prepared above was then tested and evaluated at room temperature: charge-discharge cycles were performed at a rate of 0.2C within a voltage range of 2.8-3.8V. When a significant short circuit occurred (voltage drop rate ≥ 5mV / min), the battery was considered to have reached the end of its lifespan, and the test was immediately stopped. Simultaneously, the internal resistance of the battery was measured using electrochemical impedance spectroscopy (EIS) with an applied voltage amplitude of 5mV and a frequency range of 1-10. 6 Hz. As shown in Table 1, the performance test results of the inorganic composite solid electrolyte membranes prepared in Examples 1-3 and the solid electrolytes prepared in Comparative Examples 1-4 are presented.

[0060] Table 1

[0061] As shown in Table 1, the inorganic composite solid electrolytes prepared in Examples 1-4 exhibit significantly lower AC impedance and increased cycle life at room temperature compared to Comparative Examples 1-6. Therefore, the inorganic composite solid electrolytes prepared in this application can effectively improve the internal resistance and cycle life of all-solid-state batteries.

[0062] Specifically, based on the data from Example 1 and Comparative Examples 1-3, the two-step intermittent vibratory ball milling method used in this application is more conducive to improving material performance. The first step forms highly surface-active LATP, and the second step involves LLTO composite and Ge doping. The resulting material has an ordered composition distribution and structure. Furthermore, the addition of acrylic emulsion during ball milling can reduce the surface energy of the particles, accelerate the reaction rate and element mobility, and improve the electrochemical performance of the material. Simultaneously, the addition of an appropriate amount of lithium silicate during low-temperature sintering allows lithium elements to distribute and flow along the grain boundaries, which helps improve the conductivity of the final solid electrolyte material.

[0063] Based on the data from Example 1 and Comparative Examples 4-5, it can be seen that the performance of LATP inorganic solid electrolyte is significantly improved after LLTO and Ge composite. LLTO can improve the migration speed of lithium ions, Ge doping can improve the three-dimensional lithium ion transport channels, and the material prepared by ball milling is amorphous, which increases the number of lithium ion transport channels, significantly improves the conductivity of the electrolyte, reduces polarization and prolongs the cycle life of the battery.

[0064] Based on the data from Example 1 and Comparative Example 6, it can be seen that by using intermittent vibratory ball milling, the reactivity between the raw materials can be effectively improved, a dense amorphous inorganic composite solid electrolyte can be obtained, providing more lithium-ion transport channels, thereby improving the conductivity of the electrolyte and extending the cycle life of the battery.

[0065] In summary, the method for preparing the inorganic composite solid electrolyte of this application, by employing a two-step intermittent vibratory ball milling and a one-step low-temperature sintering method, can not only significantly improve the reactivity and synergistic effect between the raw materials, but also improve the conductivity of the inorganic composite solid electrolyte and the lithium-ion transport performance and cycle life of the solid battery. At the same time, the preparation process is solvent-free, reducing sintering costs, and providing a technical reference for the research and development of high-performance all-solid-state batteries.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an inorganic composite solid electrolyte, characterized in that, Includes the following steps: S1. Mix lithium salt, metal oxide A, metal oxide B, and ammonium dihydrogen phosphate, wherein metal oxide B is... Titanium oxide is intermittently vibratory ball-milled to obtain a mixed powder; the lithium salt is lithium carbonate or lithium hydroxide, and the metal oxide A is one of aluminum oxide, iron oxide, indium oxide, gallium oxide, strontium oxide, calcium oxide, and magnesium oxide; S2. Add lanthanum oxide and germanium oxide to the mixed powder obtained in step S1, and continue intermittent vibratory ball milling to obtain composite powder; S3. The composite powder obtained in step S2 is sintered at low temperature and pressed to obtain an inorganic composite solid electrolyte membrane layer. Lithium silicate is added during the low-temperature sintering process, with a sintering temperature of 300-500℃ and a sintering time of 4-8 hours; The molar ratio of the lithium salt, metal oxide A, titanium oxide, and ammonium dihydrogen phosphate is 1.5-1.9:0.5-0.9:1.0-2.4:2.5-4.0; In step S2, the mass ratio of lanthanum oxide, germanium oxide, and the mixed powder is 1.5-2.0:1.0-1.5:7.0-9.5; In step S1, The specific surface area of ​​the powder during the ball milling process is tested. If the specific surface area of ​​the powder during the ball milling process begins to change from large to small, the intermittent vibratory ball milling is stopped. In step S1, the intermittent vibratory ball milling time at room temperature is 30-60 min; in step S2, the intermittent vibratory ball milling time at room temperature is 60-120 min, with each milling session lasting 30-60 min and the interval between milling sessions lasting 10-20 min.

2. The method for preparing the inorganic composite solid electrolyte according to claim 1, characterized in that, In step S2, During the intermittent vibratory ball milling process, a ball milling additive is added. The mass ratio of the ball milling additive to the lanthanum-germanium mixed powder is 5-10:70-90. The lanthanum-germanium mixed powder is the powder obtained in step S1, mixed with lanthanum oxide and germanium oxide. The ball milling additive is one of polyacrylic acid, polyurethane, ethanol, ethylene glycol, and polyethylene glycol.

3. The method for preparing the inorganic composite solid electrolyte according to claim 1, characterized in that, In steps S1 and S2, during ball milling, the grinding balls are any one of zirconia balls, alumina balls, stainless steel balls, zirconium silicate balls, and nylon balls, with a ball-to-material ratio of 10-15:10-20, a powder filling ratio of 40-60%, and a vibration frequency of 50-200Hz.

4. The method for preparing the inorganic composite solid electrolyte according to claim 1, characterized in that, The average particle size of the lithium salt, metal oxide A, titanium oxide, ammonium dihydrogen phosphate, lanthanum oxide and germanium oxide is 0.3-3 μm; the thickness of the inorganic composite solid electrolyte membrane is 50-150 μm.

5. An inorganic composite solid electrolyte, characterized in that, It is prepared by the method of preparing inorganic composite solid electrolyte according to any one of claims 1-4.