Solid electrolyte, preparation method and solid-state battery

Abstract

The invention provides a solid-state electrolyte, a preparation method and a solid-state battery, and belongs to the technical field of solid-state batteries, and the preparation method of the solid-state electrolyte comprises the following steps: disassembling a waste lithium iron phosphate battery to obtain a positive pole piece; carrying out acidolysis on the positive pole piece to obtain mixed slurry; sequentially grinding and drying the mixed slurry to obtain a dried material; calcining the dried material for the first time to obtain a first material; and mixing the first material with an additive, and carrying out secondary calcination to obtain the solid electrolyte. According to the method, the positive pole piece of the waste lithium iron phosphate battery is subjected to acidolysis, grinding, drying and primary calcination in sequence to remove the aluminum foil in the positive pole piece, and the first material without the aluminum foil is mixed with the additive for secondary calcination, so that the solid electrolyte with good dispersity and relatively high ionic conductivity can be prepared at low cost.

Description

Technical Field

[0001] The present application relates to the field of solid-state battery technology, and in particular to a solid-state electrolyte, a preparation method, and a solid-state battery. Background Art

[0002] With the increasing popularity and development of electronic products and new energy vehicles, lithium-ion batteries (Li-ion batteries), known for their high power, high energy content, and long lifespan, have gained widespread use. Conventional Li-ion batteries typically use flammable organic solvents as their electrolyte, posing significant safety risks. Compared to conventional Li-ion batteries, solid-state batteries (SSBs) offer higher energy density, faster charging speeds, and improved safety due to the absence of flammable organic solvents.

[0003] The core of solid-state batteries lies in solid electrolytes. Oxide solid electrolytes have become the focus of attention at this stage due to their wide electrochemical window and high thermal stability. However, the current preparation process of oxide solid electrolytes usually involves directly calcining after mixing metal salts. The resulting product is a ceramic material with high hardness, no obvious interface between primary particles, difficult to control particle size, poor dispersibility, and unfavorable processing. In addition, the high preparation cost and low ionic conductivity limit its widespread application in solid-state batteries. Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a solid electrolyte, a preparation method and a solid-state battery, aiming to solve the technical problems of high preparation cost, poor dispersibility and low ionic conductivity of existing solid electrolytes.

[0005] In a first aspect, an embodiment of the present application provides a method for preparing a solid electrolyte, comprising the following steps: Dismantle the waste lithium iron phosphate battery to obtain the positive electrode sheet; Acid hydrolyzing the positive electrode sheet to obtain a mixed slurry; Grinding and drying the mixed slurry in sequence to obtain a dried material; calcining the dried material once to obtain a first material; The first material is mixed with an additive and subjected to secondary calcination to obtain a solid electrolyte.

[0006] In the technical solution of the embodiment of the present application, waste lithium iron phosphate batteries are used as raw materials, and the aluminum foil is dissolved by acid hydrolysis to obtain an aluminum-containing mixed slurry; the aluminum-containing mixed slurry is then ground and dried to obtain an aluminum-containing dried material, which is then subjected to a primary calcination treatment to volatilize and remove the aluminum salt in the aluminum-containing dried material to obtain a first material with the aluminum element removed; the first material with the aluminum element removed is mixed with additives and subjected to a secondary calcination treatment to obtain a composite solid electrolyte. The preparation method of the present application is simple, using waste lithium iron phosphate batteries as raw materials, not only is the cost low and realizes the resource utilization of waste, but the resulting solid electrolyte is easy to disperse and process and has high ionic conductivity.

[0007] In some embodiments, the step of acid-hydrolyzing the positive electrode sheet to obtain a mixed slurry includes: adding an acidic solution to the positive electrode sheet to obtain an intermediate slurry, and controlling the pH of the intermediate slurry to 1.5-2.5, and then reacting for 2-4 hours to obtain a mixed slurry.

[0008] In this embodiment, an acidic solution is used to acid-hydrolyze the positive electrode sheet at a pH of 1.5-2.5, and the acid-hydrolysis time is controlled to 2-4 hours, which is conducive to fully dissolving the aluminum foil in the positive electrode sheet, thereby ensuring that the aluminum element is fully removed after one calcination, and avoiding incomplete removal of aluminum in the positive electrode sheet, which affects the product quality of the prepared solid electrolyte.

[0009] In some embodiments, the concentration of the acidic solution is 2-4 mol / L; and / or the particle size of the mixed slurry obtained after grinding is 0.3-3 μm; and / or the particle size of the dried material obtained after drying is 3-10 μm.

[0010] In this embodiment, by controlling the concentration of the acidic solution, the aluminum foil can be fully dissolved in a relatively short time. The particle size of the mixed slurry is controlled to be 0.3-3 μm, which facilitates subsequent full drying and improves the drying efficiency. By controlling the particle size of the dried material to be 3-10 μm, the specific surface area of ​​the first material after the first calcination can be increased, and the degree of mixing with the additive can be improved. At the same time, the densification rate during the secondary calcination process can be increased, thereby increasing the sintering rate, and the dispersibility of the solid electrolyte obtained after calcination is also improved, making the prepared solid electrolyte easy to process.

[0011] In some embodiments, the primary calcination comprises: introducing gas into the dried material during the calcination process, wherein the volume ratio of the gas introduced per unit time to the dried material is (50-100):1; the gas is air or an inert gas.

[0012] In this embodiment, by introducing air or inert gas during a single calcination process, the aluminum-containing waste gas generated during the calcination process is conveniently led out of the calcination furnace in a timely manner, thereby removing the aluminum in the positive electrode plate; at the same time, the volume ratio of the gas introduced per unit time to the drying material is controlled within an appropriate range, avoiding the drying material being blown out along with the waste gas due to excessive gas flow, and at the same time, avoiding the aluminum-containing waste gas not being discharged in a timely manner due to excessively small gas flow.

[0013] In some embodiments, the conditions for the primary calcination include: a calcination temperature of 250-400° C., and a calcination time of 3-6 hours.

[0014] In this embodiment, the aluminum salts in the dried material are completely removed by controlling the calcination temperature and calcination time of the primary calcination. If the calcination temperature is less than 250°C, the aluminum salts in the dried material cannot be fully volatilized; if the calcination temperature is greater than 400°C, the energy consumption is excessive, increasing costs. If the calcination time is less than 3 hours, the aluminum salts cannot be completely removed, and if the calcination time is greater than 6 hours, the time cost is increased.

[0015] In some embodiments, the additive is at least one compound formed by a metal element and a non-metal element; wherein the metal element is at least one of aluminum, titanium, manganese, iron, and lithium, and the non-metal element is at least one of boron, phosphorus, sulfur, fluorine, chlorine, and oxygen.

[0016] In this embodiment, the additive is a compound formed by a metal element and a non-metal element. The first material is mixed with the additive containing metal and non-metal and subjected to secondary calcination. During this process, a solid electrolyte composed of multiple metal oxides and multiple non-metal oxides is formed, thereby improving the ionic conductivity of the prepared solid electrolyte.

[0017] In some embodiments, the molar ratio of the additive to the lithium element in the first material is (0.05-0.15):1.

[0018] In this embodiment, the molar ratio of the additive to the lithium element in the first material affects the electrochemical properties of the solid electrolyte. If the molar ratio of the additive to the lithium element in the first material is greater than 0.15:1, the doping amount of the doping element is too high, resulting in excessive defective aggregates, a decrease in the effective oxygen vacancy concentration, and severe lattice distortion, thereby reducing the ionic conductivity of the prepared solid electrolyte. If the molar ratio of the additive to the lithium element in the first material is less than 0.05:1, the doping amount of the doping element is too small and the ionic conductivity of the prepared solid electrolyte cannot be effectively improved.

[0019] In some embodiments, the conditions for the secondary calcination include: an oxygen volume content of ≥15%, a calcination temperature of 700-850° C., and a calcination time of 10-20 h.

[0020] In this embodiment, the secondary calcination conditions were optimized. A high temperature of 700-850°C accelerated ion diffusion, resulting in improved sphericity, good dispersibility, and easier processing of the resulting primary particles. By performing the secondary calcination in an aerobic environment with an oxygen content of 15% or more by volume, the additives and the metallic and non-metallic elements in the first material were completely oxidized, resulting in a composite oxide solid electrolyte with excellent dispersibility and ionic conductivity.

[0021] In a second aspect, an embodiment of the present application provides a solid electrolyte, which is prepared by the preparation method described in the first aspect.

[0022] In the technical solution of the embodiment of the present application, the solid electrolyte is prepared by the preparation method described in the first aspect, so the solid electrolyte has low cost, is easy to process and disperse, and has high ionic conductivity.

[0023] In a third aspect, an embodiment of the present application provides a solid-state battery, which includes the solid-state electrolyte described in the second aspect.

[0024] In the technical solution of the embodiment of the present application, the solid-state battery includes the solid-state electrolyte described in the second aspect, and thus has low cost and good electrochemical performance.

[0025] Compared with the prior art, the advantages of this application include: The present application uses waste lithium iron phosphate batteries as raw materials, and undergoes acid hydrolysis treatment to dissolve the aluminum foil therein to obtain an aluminum-containing mixed slurry; the aluminum-containing mixed slurry is ground and dried, and then subjected to a primary calcination treatment to volatilize and remove the aluminum salt in the dried material, thereby obtaining a first material from which the aluminum element has been removed; the first material is then mixed with additives and subjected to a secondary calcination treatment to obtain a composite solid electrolyte. The preparation method is simple, and using waste lithium iron phosphate batteries as raw materials not only reduces costs and realizes resource utilization of waste, but also the obtained solid electrolyte is easy to disperse and process, and has high ionic conductivity.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0028] Figure 1 This is a SEM image of the solid electrolyte prepared in Example 1 of the present application; Figure 2 This is a particle size distribution diagram of the solid electrolyte prepared in Example 1 of the present application; Figure 3 This is the XRD pattern of the solid electrolyte prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0031] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0032] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0034] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0035] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0037] The preparation process of oxide solid electrolytes in the existing technology usually involves directly calcining the metal salts after mixing. The resulting product is a ceramic material with high hardness, no obvious interface between primary particles, difficult to control particle size, poor dispersibility, and is not conducive to processing. In addition, the preparation cost is high and the ionic conductivity is low, which limits its widespread application in lithium-ion solid-state batteries.

[0038] In order to solve the technical problem that the existing technology cannot prepare solid electrolytes with good dispersibility and high ionic conductivity at low cost, the present application provides a solid electrolyte, a preparation method and a solid-state battery, wherein the positive electrode plates of waste lithium iron phosphate batteries are acid-lyzed, ground, dried and calcined once, and then the aluminum foil is removed, and the first material after removing the aluminum foil is mixed with additives and calcined twice to prepare a solid electrolyte with good dispersibility and high ionic conductivity. The solid-state battery prepared using the above-mentioned solid electrolyte with good dispersibility and high ionic conductivity has low cost, good electrochemical performance, and can be used on a large scale.

[0039] In a first aspect, an embodiment of the present application provides a method for preparing a solid electrolyte, comprising the following steps: Dismantle the waste lithium iron phosphate battery to obtain the positive electrode sheet; Acid hydrolyzing the positive electrode sheet to obtain a mixed slurry; Grinding and drying the mixed slurry in sequence to obtain a dried material; calcining the dried material once to obtain a first material; The first material is mixed with an additive and subjected to secondary calcination to obtain a solid electrolyte.

[0040] In the technical solution of the embodiment of the present application, waste lithium iron phosphate batteries are used as raw materials, and the aluminum foil therein is dissolved by acid hydrolysis treatment to obtain a mixed slurry containing aluminum salts; the mixed slurry containing aluminum salts is ground and dried to obtain a dried material containing aluminum salts, and the aluminum salts in the dried material containing aluminum salts are volatilized and removed after a primary calcination treatment to obtain a first material from which the aluminum salts are removed; then the first material from which the aluminum element is removed is mixed with additives and subjected to a secondary calcination treatment to obtain a composite solid electrolyte. The preparation method is simple, and waste lithium iron phosphate batteries are used as raw materials, which not only has low cost and realizes resource utilization of waste, but also the solid electrolyte obtained after the primary and secondary calcination treatments is easy to disperse and process, and has high ionic conductivity.

[0041] Furthermore, in some embodiments, the step of acid-hydrolyzing the positive electrode sheet to obtain a mixed slurry includes: adding an acidic solution to the positive electrode sheet to obtain an intermediate slurry, and controlling the pH of the intermediate slurry to be 1.5-2.5, and then reacting for 2-4 hours to obtain a mixed slurry.

[0042] In the technical solution of the embodiment of the present application, an acidic solution is used to acid-lyze the positive electrode sheet at a pH of 1.5-2.5, and the acid-lysis time is controlled to 2-4 hours, which is conducive to fully dissolving the aluminum foil in the positive electrode sheet, thereby ensuring that the aluminum element is fully removed after one calcination, and avoiding the influence of incomplete removal of aluminum in the positive electrode sheet on the purity and electrochemical properties of the prepared solid electrolyte. If the pH of the intermediate slurry is less than 1.5, the acidity is too high, which will lead to the dissolution loss of valuable metals in the positive electrode sheet; if the pH of the intermediate slurry is greater than 2.5, the aluminum foil will not be completely dissolved and cannot be fully removed. If the acid-lysis time is too long, it will lead to excessive dissolution of other metals such as iron and lithium; and if the acid-lysis time is too short, the dissolution and removal rate of aluminum will be reduced.

[0043] Furthermore, in some embodiments, the acidic solution is selected from one or more of hydrochloric acid and nitric acid.

[0044] In the technical solution of the embodiment of the present application, hydrochloric acid or nitric acid is used to acidify the positive electrode plate to form a mixed slurry containing aluminum chloride or aluminum nitrate, which is convenient for volatilization and removal at a lower calcination temperature, thereby reducing energy consumption and saving production costs.

[0045] Furthermore, in some embodiments, the concentration of the acidic solution is 2-4 mol / L; and / or the particle size of the mixed slurry obtained after grinding is 0.3-3 μm; and / or the particle size of the dried material obtained after drying is 3-10 μm.

[0046] In the technical solution of the embodiment of the present application, by controlling the concentration of the acidic solution, the aluminum foil can be fully dissolved in a relatively short time. The particle size of the mixed slurry is controlled to be 0.3-3 μm, which facilitates subsequent full drying and improves the drying efficiency. By controlling the particle size of the dried material to be 3-10 μm, the specific surface area of ​​the first material obtained after the first calcination can be increased, and the degree of mixing with the additive can be improved, thereby improving the sintering rate of the secondary calcination, and it is convenient to control the particle size of the solid electrolyte obtained after calcination, and improve the degree of mixing with other materials when preparing solid-state batteries. If the particle size of the obtained solid electrolyte is too large, it will affect its dispersibility and processing performance.

[0047] Furthermore, in some embodiments, the drying is spray drying, the inlet air temperature of the spray drying is 200-250°C, and the outlet temperature of the spray drying is 80-90°C.

[0048] In the technical solution of the embodiment of the present application, a granular material with uniform particle size can be obtained by spray drying, thereby obtaining a solid electrolyte with spherical primary particles, easy to crush, and good processing dispersibility.

[0049] Furthermore, in some embodiments, the primary calcination includes: introducing gas into the dried material during the calcination process, wherein the volume ratio of the gas introduced to the dried material per unit time is (50-100):1; the gas is air or an inert gas.

[0050] In the technical solution of the embodiment of the present application, by introducing gas during a single calcination process, the aluminum-containing waste gas generated during the calcination process is easily led out of the calcination furnace in a timely manner, thereby removing the aluminum in the positive electrode plate; at the same time, the volume ratio of the gas introduced per unit time to the drying material is controlled within an appropriate range, avoiding the problem of excessive gas flow causing the drying material to be blown out along with the waste gas, resulting in raw material loss, and also avoiding the problem of aluminum-containing waste gas not being able to be discharged in time due to too small a gas flow, thereby affecting product quality.

[0051] Furthermore, in some embodiments, the conditions of the primary calcination include: a calcination temperature of 250-400° C., and a calcination time of 3-6 hours.

[0052] In the technical solution of the embodiment of the present application, the aluminum salt in the dried material is completely removed by controlling the calcination temperature and calcination time of the primary calcination. If the calcination temperature is less than 250°C, the aluminum salt in the dried material cannot be fully volatilized; if the calcination temperature is greater than 400°C, the energy consumption is excessive, increasing costs; if the calcination time is less than 3 hours, the aluminum salt cannot be completely removed; if the calcination time is greater than 6 hours, the time cost is increased.

[0053] Furthermore, in some embodiments, the additive is at least one of the compounds formed by metal elements and non-metal elements; wherein the metal element is at least one of aluminum, titanium, manganese, iron, and lithium, and the non-metal element is at least one of boron, phosphorus, sulfur, fluorine, chlorine, and oxygen.

[0054] In the technical solution of the embodiments of the present application, the additive is a compound formed from a metal element and a non-metal element. A first material is mixed with the metal and non-metal additive and subjected to a secondary calcination process. During this process, a solid electrolyte composed of multiple metal oxides and multiple non-metal oxides is formed, thereby improving the ionic conductivity of the prepared solid electrolyte. Specifically, compounds formed from metal elements and non-metal elements include, but are not limited to, lithium borate, lithium fluoride, iron oxide, titanium tetrachloride, aluminum sulfate, and the like.

[0055] Furthermore, in some embodiments, the molar ratio of the additive to the lithium element in the first material is (0.05-0.15):1.

[0056] In the technical solution of the embodiment of the present application, the molar ratio of the additive to the lithium element in the first material will affect the electrochemical properties of the solid electrolyte. If the molar ratio of the additive to the lithium element in the first material is greater than 0.15:1, the doping amount of the doping element will be too high, resulting in excessive defective aggregates, a decrease in the effective oxygen vacancy concentration, and severe lattice distortion, thereby reducing the ionic conductivity of the prepared solid electrolyte; and if the molar ratio of the additive to the lithium element in the first material is less than 0.05:1, the doping amount of the doping element will be too small and the ionic conductivity of the prepared solid electrolyte cannot be effectively improved.

[0057] Specifically, the molar ratio of the additive to the lithium element in the first material is 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.12:1, 0.14:1, 0.15:1, or any ratio within the above range.

[0058] Furthermore, in some embodiments, the conditions for the secondary calcination include: an oxygen volume content ≥ 15%, a calcination temperature of 700-850° C., and a calcination time of 10-20 h.

[0059] In the technical solution of the embodiment of the present application, the conditions for the secondary calcination are optimized, and the high temperature of 700-850°C can accelerate the diffusion of ions, so that the generated primary particles have better sphericity, good dispersibility, and are easy to process. If the calcination time is too long, the time cost is increased, and if the calcination time is too short, the oxidation reaction is insufficient, thereby affecting the purity and electrochemical properties of the prepared solid electrolyte. By performing a secondary calcination in an aerobic environment with an oxygen volume content of ≥15%, the metal elements and non-metallic elements in the additive and the first material can be completely oxidized, thereby obtaining a composite oxide solid electrolyte with good dispersibility and good ionic conductivity.

[0060] In a second aspect, an embodiment of the present application provides a solid electrolyte, which is prepared by the preparation method described in the first aspect.

[0061] In the technical solution of the embodiment of the present application, the solid electrolyte is prepared by the preparation method described in the first aspect, so the solid electrolyte has low cost, is easy to process and disperse, and has high ionic conductivity.

[0062] In a third aspect, an embodiment of the present application provides a solid-state battery, which includes the solid-state electrolyte described in the second aspect.

[0063] In the technical solution of the embodiment of the present application, the solid-state battery includes the solid-state electrolyte described in the second aspect, and thus has low cost and good electrochemical performance.

[0064] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0065] 1. Preparation method Example 1 (1) Dismantle the waste lithium iron phosphate battery to obtain the positive electrode sheet, and add 3 mol / L hydrochloric acid to the positive electrode sheet and stir it to obtain an intermediate slurry with a pH of 2.1. Then, stir and react at this pH for 3 hours to obtain a mixed slurry.

[0066] (2) The mixed slurry is ground until the particle size of the mixed slurry is 1.6 μm, and then the mixed slurry is spray-dried to obtain a dry material with a particle size of 6 μm. Thereafter, the obtained dry material is placed in a calcining furnace for a single calcination. The temperature of the single calcination is 350°C and the time of the single calcination is 5 hours. During the single calcination process, air is introduced into the calcining furnace, and the volume ratio of the air introduced per unit time to the dry material entering the furnace is controlled to be 75:1. At the same time, the hot exhaust gas in the calcining furnace is led out of the furnace body by an induced draft fan, and the drawn hot exhaust gas is cooled to a temperature of 135°C and then dusted, so that aluminum chloride can be recovered, and the remaining exhaust gas is discharged after being sprayed and absorbed.

[0067] (3) The first material obtained after the primary calcination is mixed with the additive lithium borate and placed in a rotary kiln, and air is blown in for secondary calcination, wherein the molar ratio of lithium borate to lithium in the first material is 0.1:1; the volume content of oxygen in the rotary kiln is higher than 15%, the temperature of the secondary calcination is 780°C, and the secondary calcination time is 15 hours. Thereafter, the material obtained from the secondary calcination is subjected to air flow pulverization at a gas source pressure of 0.55 MPa, pulverized three times, and then classified using a classifying wheel. After iron removal and packaging, an iron-lithium-phosphorus composite oxide solid electrolyte is obtained, whose chemical formula is 0.65Li2O·0.5Fe2O3·0.5P2O5·0.05B2O5.

[0068] Example 2 The difference from Example 1 is that in step (1), an intermediate slurry with a pH of 1.5 is obtained.

[0069] Example 3 The difference from Example 1 is that in step (1), an intermediate slurry with a pH of 2.5 is obtained.

[0070] Example 4 The difference from Example 1 is that in step (1), an intermediate slurry with a pH of 3 is obtained.

[0071] Example 5 The difference from Example 1 is that the temperature of the primary calcination in step (2) is 250°C.

[0072] Example 6 The difference from Example 1 is that the temperature of the primary calcination in step (2) is 400°C.

[0073] Example 7 The difference from Example 1 is that the temperature of the primary calcination in step (2) is 500°C.

[0074] Example 8 The difference from Example 1 is that in step (3), the molar ratio of lithium borate to the lithium element in the first material is 0.05:1.

[0075] Example 9 The difference from Example 1 is that in step (3), the molar ratio of lithium borate to the lithium element in the first material is 0.15:1.

[0076] Example 10 The difference from Example 1 is that in step (3), the molar ratio of lithium borate to the lithium element in the first material is 0.2:1.

[0077] Example 11 The difference from Example 1 is that the additive in step (3) is titanium chloride.

[0078] Example 12 The difference from Example 1 is that the additive in step (3) is manganese sulfide.

[0079] Comparative Example 1 Lithium oxide, red iron oxide, phosphorus pentoxide, boron oxide, and aluminum trioxide were added and mixed according to the molar ratio of lithium, iron, phosphorus, boron, and aluminum in the finished product of Example 1. The mixture was then ground to a particle size of 400 nm and calcined in a rotary kiln at a high temperature of 780° C. for 15 h. The mixture was then pulverized and the obtained product was tested. The results are shown in Table 1.

[0080] 2. Test Method 1. The performance of the solid electrolytes prepared in Examples 1 to 12 and Comparative Example 1 was tested. The element content was tested using an inductively coupled plasma emission spectrometer (ICP), the specific surface area was tested using the nitrogen adsorption BET test method, with reference to the standard GB / T 19587-2017; the tap density was tested using a tap density meter, with reference to the standard GB / T 5162-2021; the bulk density was tested using the funnel method, the angle of repose was tested using the injection method, and the particle size was tested using a laser particle size analyzer. The test results are shown in Table 1. The SEM, particle size distribution and XRD of Example 1 are shown in Table 1. Figures 1-3 shown.

[0081] 2. The ionic conductivity of the solid electrolytes prepared in Examples 1 to 12 and Comparative Example 1 was tested by AC impedance method. Specifically, the prepared solid electrolytes were made into a 50 μm thick and 0.785 cm 2 The electrolyte sheet is tested by AC impedance tester to obtain the volume resistance of the sample, and then the ionic conductivity is calculated; The calculation formula for ionic conductivity is:

[0082] Where σ is the ionic conductivity, I is the thickness of the solid electrolyte, S is the area of ​​the solid electrolyte, and R is the volume resistance. The test results are shown in Table 1.

[0083] 3. Analysis of test results of various embodiments and comparative examples Table 1 Test data of solid electrolytes of Examples and Comparative Examples

[0084] From the data of Examples 1 to 4, it can be seen that the pH value of the acid dissolution of waste lithium iron phosphate batteries affects the content of aluminum in the prepared solid electrolyte, and thus affects its specific surface area and ionic conductivity. From the data of Examples 1 and Examples 5-7, it can be seen that with the increase of the primary calcination temperature, the content of aluminum in the prepared solid electrolyte gradually decreases, but its ionic conductivity shows a trend of first increasing and then decreasing. Among them, when the primary calcination temperature is 350°C, the obtained solid electrolyte has better ionic conductivity. From the data of Examples 1 and Examples 8-10, it can be seen that with the increase of the additive content, the ionic conductivity of the prepared solid electrolyte first increases and then decreases. Among them, when the molar ratio of the additive to the lithium element in the first material is 0.1:1, the ionic conductivity of the obtained solid electrolyte is better. From the data of Examples 1 and Examples 11-12, it can be seen that the introduction of titanium or manganese elements into lithium iron phosphate has a lower ionic conductivity than the introduction of boron elements into it.

[0085] Comparison of Example 1 with Comparative Example 1 shows that the present invention removes the aluminum foil from the positive electrode sheet of the waste lithium iron phosphate battery by acid decomposition, grinding, drying and primary calcination in sequence, and mixes the first material after removing the aluminum foil with an additive for secondary calcination. The prepared solid electrolyte has good dispersibility and high ionic conductivity.

[0086] Figure 1 From the SEM image of the solid electrolyte prepared in Example 1, it can be seen that the primary particles of the solid electrolyte prepared in the embodiment of the present application are spherical particles with high sphericity, a primary particle size of about 200 nm, and high dispersibility. Therefore, when it is used to prepare solid-state batteries, it is easy to process and has good compatibility with other solid electrolytes.

[0087] Figure 2 This is a particle size distribution diagram of the solid electrolyte prepared in Example 1. It can be seen that the solid electrolyte prepared in this example of the present application has a small particle size and a narrow particle size distribution.

[0088] Figure 3This is the XRD pattern of the solid electrolyte prepared in Example 1. It can be seen that the solid electrolyte prepared by the method of the present application is a pure phase iron-lithium-phosphorus composite oxide material.

[0089] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a solid electrolyte, characterized in that: The following steps are involved: Dismantle the waste lithium iron phosphate battery to obtain the positive electrode sheet; Acid hydrolyzing the positive electrode sheet to obtain a mixed slurry; Grinding and drying the mixed slurry in sequence to obtain a dried material; calcining the dried material once to obtain a first material; The first material is mixed with an additive and subjected to secondary calcination to obtain a solid electrolyte.

2. The method for preparing a solid electrolyte according to claim 1, wherein: The step of acid-hydrolyzing the positive electrode sheet to obtain a mixed slurry comprises: adding an acidic solution to the positive electrode sheet to obtain an intermediate slurry, controlling the pH of the intermediate slurry to be 1.5-2.5, and then reacting for 2-4 hours to obtain a mixed slurry.

3. The method for preparing a solid electrolyte according to claim 2, wherein: The concentration of the acidic solution is 2-4 mol / L; and / or, The particle size of the mixed slurry obtained after grinding is 0.3-3 μm; and / or, The particle size of the dried material obtained after the drying is 3-10 μm.

4. The method for preparing a solid electrolyte according to claim 1, wherein: The primary calcination includes: introducing gas into the dried material during the calcination process, wherein the volume ratio of the gas introduced per unit time to the dried material is (50-100):1; the gas is air or an inert gas.

5. The method for preparing a solid electrolyte according to claim 1, wherein: The conditions for the primary calcination include: a calcination temperature of 250-400° C. and a calcination time of 3-6 hours.

6. The method for preparing a solid electrolyte according to claim 1, wherein: The additive is at least one of compounds formed by a metal element and a non-metal element; wherein the metal element is at least one of aluminum, titanium, manganese, iron, and lithium, and the non-metal element is at least one of boron, phosphorus, sulfur, fluorine, chlorine, and oxygen.

7. The method for preparing a solid electrolyte according to claim 1, wherein: The molar ratio of the additive to the lithium element in the first material is (0.05-0.15):

1.

8. The method for preparing a solid electrolyte according to claim 1, wherein: The conditions for the secondary calcination include: the volume content of oxygen is ≥15%, the calcination temperature is 700-850° C., and the calcination time is 10-20 hours.

9. A solid electrolyte, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. A solid-state battery, characterized in that: Comprising the solid electrolyte as claimed in claim 9.

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