A solid electrolyte, a preparation method thereof, a separator, a battery, and an electricity-related device

Abstract

The present invention provides a solid electrolyte, a preparation method thereof, a separator, a battery and an electricity-related device, relating to the technical field of lithium batteries. The solid electrolyte is a core-shell composite structure with LATP as the core and a Mg-Sn alloy as the shell coated on the outer surface of the core. The core-shell structured solid electrolyte of the present invention has LATP as the core and a Mg-Sn alloy as the shell, enhancing the air stability, preventing the generation of Li2CO3 impurities, maintaining high ionic conductivity and a wide electrochemical window, and improving the stability and mechanical strength. The corrosion resistance and tear resistance of the alloy enhance the battery safety, while the aluminum element in LATP improves the alloy strength, optimizing the battery performance and charge-discharge efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular, to a solid electrolyte and a preparation method thereof, a separator, a battery, and an electricity-related device. Background Art

[0002] As an efficient energy storage device, lithium-ion batteries play an important role in modern electronic devices, electric vehicles and other fields. With the progress of technology and the growth of energy demand, lithium-ion battery technology has become one of the key technologies in the new energy field. However, with the expansion of the application scope, its safety and performance issues have gradually become the main bottleneck restricting its further development.

[0003] In the prior art, lithium-ion batteries mainly use organic liquid electrolytes. Although such electrolytes have high ionic conductivity, their chemical stability is poor. These safety problems limit the application of lithium-ion batteries in extreme environments such as high temperature and high pressure, and also increase the complexity and cost of the battery management system.

[0004] In the research of solid electrolytes, garnet-type oxide solid electrolytes such as LATP have attracted attention due to their high ionic conductivity and good mechanical properties. However, the stability of LATP solid electrolyte in air is poor, and it is easy to react with water vapor, carbon dioxide, etc. to generate Li2CO3 impurities with low ionic conductivity. This reaction not only reduces the performance of the electrolyte, but may also cause damage to the internal structure of the battery, affecting the long-term stability and reliability of the battery.

[0005] In addition, the existing LATP solid electrolyte still needs to be improved in terms of ionic conductivity and cycle stability. The insufficient ionic conductivity limits the charge and discharge rate and power density of the battery, while the insufficient cycle stability affects the service life and performance retention of the battery. These problems are particularly prominent in high-power applications and long-cycle operations, and have become the main obstacles to the development of solid-state battery technology.

[0006] In summary, the existing lithium-ion battery technology has many defects in terms of safety, stability and performance. The safety hazards of liquid electrolytes, the air instability of solid electrolytes, and the deficiencies in ionic conductivity and cycle stability are all the main challenges faced by current lithium-ion battery technology. These defects limit the application of lithium-ion batteries in a wider range of fields and pose higher requirements for their future technological development.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] The object of the present invention is to provide a solid electrolyte, a preparation method thereof, a separator, a battery and an electricity-related device. The solid electrolyte has good electrical conductivity and thermal conductivity, can improve the electrical conductivity of the battery, reduce the internal resistance of the battery, and thus improve the charge and discharge efficiency of the battery.

[0009] In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0010] In the first aspect, the present invention provides a solid electrolyte, which is a core-shell composite structure with LATP as the core and a Mg-Sn alloy as the shell coated on the outer surface of the core.

[0011] The LATP is Li y Al x Ti 2-x (PO4)3; where y - x = 1, 0 < x < 2, 1 < y < 3;

[0012] The mass fraction of the Mg-Sn alloy in the solid electrolyte is 1% - 10%.

[0013] In an optional embodiment, in the LATP, y - x = 1, 0.5 ≤ x < 2, 1 < y < 3; and / or, the molar ratio of Mg to Sn in the Mg-Sn alloy is 1:4; and / or, the mass fraction of the Mg-Sn alloy in the solid electrolyte is 4% - 10%.

[0014] In the second aspect, the present invention provides a preparation method of the solid electrolyte according to any one of the foregoing embodiments, including:

[0015] Ball-milling LATP and the Mg-Sn alloy together, and then obtaining the solid electrolyte after sintering treatment and cooling treatment.

[0016] In an optional embodiment, the sintering treatment is to sequentially perform the following treatment steps:

[0017] A. Sintering in air at 200°C - 250°C for 1 hour - 2 hours;

[0018] B. Calcining at 650°C - 700°C for 2 hours - 4 hours;

[0019] C. Sintering at 700°C - 750°C for 1 hour - 2 hours.

[0020] In an optional embodiment, the preparation method of the Mg-Sn alloy includes:

[0021] Mixing magnesium powder and tin powder to obtain a mixed powder;

[0022] Perform ball milling, pressing and sintering on the mixed powder to obtain the Mg-Sn alloy.

[0023] In an alternative embodiment, the time for the ball milling is 2 to 8 hours; and / or, the pressure for the pressing is 5 to 10 t; and / or, the sintering temperature for the sintering is 200 to 400 °C; and / or, the sintering time for the sintering is 4 to 12 hours.

[0024] In an alternative embodiment, the method for preparing the LATP includes:

[0025] Mix a lithium source, a phosphorus source, an aluminum source and a titanium source according to a stoichiometric ratio with the lithium source being 5% to 15% in excess, add a sintering aid, and obtain the LATP through calcination.

[0026] In an alternative embodiment, the lithium source includes: Li2CO3; and / or, the phosphorus source includes: (NH4)H2PO4; and / or, the aluminum source includes: Al2O3; and / or, the titanium source includes: TiO2; and / or, the sintering aid includes at least one of aluminum oxide, lithium tetrafluoroborate, tetrabutylammonium tetrafluoroborate and ammonium tetrafluoroborate; and / or, the mass fraction of the sintering aid is 1% to 2%.

[0027] In a third aspect, the present invention provides a separator, including the solid electrolyte as described in any one of the foregoing embodiments; or, the solid electrolyte obtained by the preparation method of the solid electrolyte as described in any one of the foregoing embodiments.

[0028] In a fourth aspect, the present invention provides a battery, including the separator as described in the foregoing embodiments.

[0029] In a fifth aspect, the present invention provides an electricity-related device, including the battery as described in the foregoing embodiments.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The present invention proposes a solid electrolyte with a core-shell composite structure, where LATP is used as the core and is coated with a Mg-Sn alloy shell on the outer layer. This design significantly improves the air stability of the solid electrolyte because the Mg-Sn alloy shell can effectively isolate water vapor and carbon dioxide in the air, preventing the LATP core from reacting with the air, thus avoiding the generation of impurities such as Li2CO3 with low ionic conductivity. The combination of the high ionic conductivity of the Mg-Sn alloy and the LATP inner core further improves the ionic conductivity of the overall electrolyte. At the same time, the shell can also inhibit the ionic migration of the core, enhancing the structural and electrochemical performance stability of the electrolyte during the battery cycle. In addition, the wide electrochemical window of the LATP inner core is maintained, and the addition of the Mg-Sn alloy shell does not reduce its electrochemical window, ensuring that the electrolyte can maintain a wide electrochemical window. The combination of the high mechanical strength of the Mg-Sn alloy shell and the LATP inner core enhances the overall mechanical strength and impact resistance of the electrolyte. The excellent corrosion resistance, tear resistance, and puncture resistance of the Mg-Sn alloy further improve the safety and stability of the battery system. The aluminum element in LATP promotes the formation of the Mg2Sn phase, further enhancing the strength of the Mg-Sn alloy. This core-shell structured solid electrolyte shows significant advantages in improving battery performance and safety. At the same time, its good electrical and thermal conductivity helps to improve the electrical conductivity of the battery, reduce the internal resistance, and enhance the charge and discharge efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic cross-sectional structure diagram of the solid electrolyte particles in the embodiment of the present application;

[0034] Figure 2 It is a schematic diagram of the results of investigating the ionic conductivity and high-temperature shrinkage rate in Test Experiment 1 of the present application;

[0035] Figure 3 It is a schematic diagram of the results of investigating the electrochemical performance in Test Experiment 2 of the present application.

[0036] Reference numerals:

[0037] 100, solid electrolyte; 1, LATP; 2, Mg-Sn alloy. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The embodiments of the present invention will be described in detail below in conjunction with the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0039] Reference Figure 1 , in the embodiments of the present application, a solid electrolyte is provided. The solid electrolyte is a core-shell composite structure with LATP as the core and a Mg-Sn alloy as the shell coated on the outer surface of the core. The LATP is Li y Al x Ti 2-x (PO4)3; where y - x = 1, 0 < x < 2, 1 < y < 3; the mass fraction of the Mg-Sn alloy in the solid electrolyte is 1% - 10%. Among them, the mass fraction can be, for example, 1%, 2%, 4%, 6%, 8%, 10%, etc.

[0040] It should be noted that as a Nasicon-type oxide solid electrolyte, LATP has attracted attention due to its high ionic conductivity (10 -4 S / cm) at room temperature and good chemical stability. LATP shows good stability in humid air or a carbon dioxide environment and has a relatively high oxidation potential, which makes LATP an ideal solid electrolyte material suitable for high-voltage solid-state batteries.

[0041] The Mg-Sn alloy is selected as the shell material because of its good strength and hardness and is coated on the surface of LATP. This alloy not only improves the strength and durability of the separator but also enhances the safety and stability of the entire battery system due to its excellent corrosion resistance, tear resistance, and puncture resistance. In addition, the electrical and thermal conductivity of the Mg-Sn alloy helps to improve the electrical conductivity of the battery, reduce the internal resistance of the battery, and thus improve the charge and discharge efficiency of the battery.

[0042] The adoption of the core-shell structure solves the problem of poor stability of LATP in air. The Mg-Sn alloy shell effectively blocks water vapor and carbon dioxide in the air, preventing LATP from reacting with air to generate Li2CO3 impurities with low ionic conductivity, thereby improving the air stability of the solid electrolyte. At the same time, the high ionic conductivity of the Mg-Sn alloy is combined with the LATP core to enhance the ionic conductivity of the overall solid electrolyte.

[0043] The Mg-Sn alloy shell can also inhibit the ion migration of the LATP core, improving the structural stability and electrochemical performance stability of the solid electrolyte during battery cycling. The LATP core has a wide electrochemical window, and the introduction of the Mg-Sn alloy shell does not reduce this property, enabling the core-shell structured solid electrolyte to maintain a wide electrochemical window.

[0044] In summary, the solid electrolyte technical solution in the embodiments of this application, through the design of the core-shell structure, fully utilizes the core advantages of LATP and, with the help of the characteristics of the Mg-Sn alloy shell, comprehensively improves the air stability, ionic conductivity, cycling stability, and electrochemical window of the solid electrolyte, providing a high-performance solid electrolyte material for the development of all-solid-state batteries.

[0045] In addition, the role of aluminum element in the Mg-Sn alloy is to promote the formation of the Mg2Sn phase. Mg2Sn is a precipitation phase in the Mg-Sn alloy and has excellent precipitation hardening effect. In the alloy, Sn and Mg form the Mg2Sn phase, which forms at the grain boundaries and significantly improves the strength and hardness of the alloy. The addition of aluminum element can improve the precipitation behavior of the Mg2Sn phase in the Mg-Sn alloy, thereby enhancing the precipitation hardening effect of the alloy.

[0046] The addition of aluminum element in LATP can significantly improve the interfacial stability of the Mg-Sn alloy. According to the first-principles calculation, the doping of aluminum element at the Mg(0001) / Mg2Sn(022) interface can reduce the interfacial energy and enhance the adhesion work of the interface. Especially when aluminum atoms occupy specific doping positions, the strength of the Al-Sn bond at the interface dominates, which helps to improve the stability of the interface.

[0047] Aluminum element can also refine the Mg2Sn phase, thereby improving the mechanical properties of the alloy. Experimental studies have shown that the addition of aluminum element can significantly change the distribution and morphology of Mg2Sn, playing a role in refining Mg2Sn and improving the mechanical properties of the Mg-Sn alloy.

[0048] The addition of aluminum element increases the strength of the Mg-Sn alloy. This is because the addition of aluminum element can inhibit the coarsening of the Mg2Sn phase, playing a role in refining Mg2Sn, thereby improving the mechanical properties of the alloy. In addition, the solid solution strengthening effect of aluminum element is also higher than that of other elements such as zinc (Zn), and it can more effectively improve the yield strength and tensile strength of the alloy.

[0049] In summary, the aluminum element in LATP significantly improves the performance of the Mg-Sn alloy through multiple effects such as promoting the formation of the Mg2Sn phase, enhancing interfacial stability, refining the Mg2Sn phase, and increasing the alloy strength. This strengthening effect is of great significance for improving the overall performance and stability of the solid electrolyte.

[0050] In an alternative embodiment, in the LATP chemical formula Li y Al x Ti 2-x (PO4)3, the conditions satisfied by x and y are: y - x = 1, 0.5 ≤ x < 2, 1 < y < 3.

[0051] In an alternative embodiment, the molar ratio of Mg to Sn in the Mg - Sn alloy is 1:4.

[0052] In an alternative embodiment, the mass fraction of the Mg - Sn alloy in the solid electrolyte is 4% - 10%. For example, it can be 4%, 5%, 6%, 8%, 9%, 10%, etc.

[0053] In a second aspect, the present invention provides a method for preparing a solid electrolyte as described in any one of the foregoing embodiments, including:

[0054] Performing ball - milling treatment on LATP and the Mg - Sn alloy together, and then obtaining the solid electrolyte after sintering treatment and cooling treatment.

[0055] The present invention provides a method for preparing a solid electrolyte as described in the foregoing embodiments. The sintering treatment is performed by sequentially performing the following treatment steps:

[0056] A. Sintering in air at 200°C - 250°C for 1 hour - 2 hours; for example, the sintering temperature can be 200°C, 220°C, 240°C, 250°C, etc.; the time can be 1 hour, 1.5 hours, 2 hours, etc.

[0057] B. Calcining at 650°C - 700°C for 2 hours - 4 hours; for example, the calcining temperature can be 650°C, 680°C, 690°C, 700°C, etc. The calcining time can be 2 hours, 3 hours, 4 hours, etc.

[0058] C. Sintering at 700°C - 750°C for 1 hour - 2 hours. For example, the sintering temperature can be 700°C, 720°C, 740°C, 750°C, etc.; the sintering time can be 1 hour, 1.5 hours, 2 hours, etc.

[0059] In an alternative embodiment, the method for preparing the Mg - Sn alloy includes:

[0060] Mixing magnesium powder and tin powder to obtain a mixed powder;

[0061] Performing ball - milling treatment, pressing - forming treatment and sintering treatment on the mixed powder to obtain the Mg - Sn alloy.

[0062] In an alternative embodiment, when preparing the Mg-Sn alloy, the ball milling treatment time is 2 hours to 8 hours; for example, the time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, and so on.

[0063] In an alternative embodiment, when preparing the Mg-Sn alloy, the pressure of the pressing forming treatment is 5t to 10t; for example, the pressure can be 5t, 6t, 7t, 8t, 10t, and so on.

[0064] In an alternative embodiment, when preparing the Mg-Sn alloy, the sintering temperature of the sintering treatment is 200°C to 400°C; for example, the temperature can be 200°C, 300°C, 400°C, and so on.

[0065] In an alternative embodiment, when preparing the Mg-Sn alloy, the sintering time of the sintering treatment is 4 hours to 12 hours. For example, the sintering time can be 4 hours, 5 hours, 6 hours, 7 hours, 9 hours, 10 hours, 12 hours, and so on.

[0066] The mass fraction of the Mg-Sn alloy is 1% to 5%. For example, the mass fraction can be 1%, 3%, 4%, 5%, and so on.

[0067] In an alternative embodiment, the preparation method of the LATP includes:

[0068] Mix the lithium source, phosphorus source, aluminum source, and titanium source according to a stoichiometric ratio with the lithium source being 5% to 15% in excess. After adding a sintering aid, the LATP is obtained through a calcination treatment.

[0069] As described above, during the preparation of the LATP (lithium aluminum titanium phosphate) solid electrolyte, an excessive amount of the lithium source, such as lithium carbonate, is mainly added to compensate for the loss of lithium element during the high-temperature calcination process. Lithium, as an active alkali metal element, is prone to volatilization at high temperatures, resulting in insufficient lithium content in the final product. To ensure the accurate stoichiometric ratio of lithium in the LATP material and thus obtain an ideal chemical composition and crystal structure, it is necessary to add an excessive amount of the lithium source in the starting materials to compensate for this loss. In addition, the excessive lithium source can also improve the accuracy of the stoichiometric ratio, enhance the conductivity and other physical properties of the electrolyte. When preparing LATP by the solid-phase method, if the lithium source is insufficient, it may lead to the formation of impurity phases such as AlPO4 and TiO2, and these impurity phases will reduce the ionic conductivity of the electrolyte. Therefore, adding an excessive amount of the lithium source helps to reduce the formation of these impurity phases and improve the performance of the electrolyte. Generally speaking, adding an excessive amount of the lithium source is to ensure the chemical stability and electrochemical performance of the LATP electrolyte, which is crucial for improving the efficiency, safety, and cycle life of the battery.

[0070] In an alternative embodiment, the lithium source includes: Li2CO3.

[0071] In an alternative embodiment, the aluminum source includes: Al2O3.

[0072] In an alternative embodiment, the titanium source includes: TiO2.

[0073] In an alternative embodiment, the phosphorus source includes: (NH4)H2PO4.

[0074] In an alternative embodiment, the sintering aid includes at least one of aluminum oxide, lithium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, and ammonium tetrafluoroborate.

[0075] In an alternative embodiment, the mass fraction of the sintering aid is 1% to 2%. For example, it can be 1%, 1.5%, 2%, etc.

[0076] An embodiment of the present application provides a separator, including the solid electrolyte as described in any one of the foregoing embodiments; or, the solid electrolyte obtained by the preparation method of the solid electrolyte as described in any one of the foregoing embodiments.

[0077] An embodiment of the present application provides a battery, including the separator as described in the foregoing embodiment.

[0078] Correspondingly, the present application further provides a preparation method of the above-mentioned separator, which may include the following steps: melt-extruding polyolefin and the above-mentioned solid electrolyte to obtain a cast film; performing a stretching treatment on the cast film to obtain a stretched film; winding and slitting the stretched film to obtain the separator.

[0079] During the preparation process of the above-mentioned separator, the weight of the solid electrolyte material is less than the weight of the polyolefin. That is, the weight ratio of the solid electrolyte to the polyolefin is less than 50:50, such as 49:51, 40:60, 30:70, 20:80, 10:90, etc.

[0080] In some embodiments, the average particle size of the above-mentioned solid electrolyte is ≤1 μm, such as 1 μm, 0.8 μm, 0.6 μm, 0.5 μm, or 0.2 μm, etc.

[0081] In some embodiments, the weight-average molecular weight of the polyolefin can be 100,000 to 5,000,000, such as 100,000, 500,000, 1,000,000, 2,000,000, 3,000,000, 4,000,000, or 5,000,000, etc.

[0082] In addition, the equipment used in each step of the above-mentioned separator and other preparation conditions (for example, the preparation raw materials further include a pore former, the selection and dosage of the pore former, stretching parameters, etc.) can all refer to the prior art and will not be elaborated here too much.

[0083] Furthermore, an electric-related device is provided in an embodiment of the present application, including a battery as described in the foregoing embodiment, which contains the above-mentioned separator.

[0084] This battery has the advantages of high safety, excellent low-temperature rate charging and discharging capabilities, no lithium precipitation during low-temperature charging, and a high low-temperature charging constant current ratio.

[0085] Table 1. Main components and parameters of solid electrolytes in examples and comparative examples

[0086]

[0087] In the above table, the Mg-4Sn alloy represents an Mg-Sn alloy with a molar ratio of Mg to Sn of 1:4, and the same applies hereinafter.

[0088] Example 1

[0089] In this example, a solid electrolyte was prepared. Among them, the solid electrolyte is a core-shell composite structure with Li 1.1 Al 0.2 Ti 1.8 (PO4)3 as the core and an Mg-4Sn alloy as the shell coated on the outer surface of the core, namely Li 1.1 Al 0.2 Ti 1.8 (PO4)3@Mg-4Sn, and its preparation method is as follows:

[0090] (1) Prepare the shell material: Ball-mill magnesium powder and tin powder according to a molar ratio of 1:4 for 2 h, press and mold at a pressure of 5 t, and then sinter. The sintering temperature is 200 °C and the time is 4 h to form an Mg-4Sn alloy.

[0091] (2)Prepare LATP: Prepare lithium carbonate, ammonium hydrogen phosphate, titanium dioxide, and aluminum oxide according to the stoichiometric ratio of Li 1.1 Al 0.2 Ti 1.8 (PO4)3. Add lithium carbonate in an amount 5% in excess of the stoichiometric ratio and another 1% by mass of tetrabutylammonium tetrafluoroborate, and then calcine to obtain LATP [Li 1.1 Al 0.2 Ti 1.8 (PO4)3]; The calcination temperature is 600 °C and the time is 1 h.

[0092] (3)Prepare the solid electrolyte: Mix LATP [Li 1.1 Al 0.2 Ti 1.8(PO4)3 was sintered with Mg-4Sn alloy with a mass fraction of 1%, and the sintering was carried out in three stages. The first stage was sintered at 200 °C for 1 h, the second stage was sintered at 650 °C for 2 h, and the third stage was sintered at 700 °C for 1 h, and then cooled to obtain a solid electrolyte.

[0093] (4)Preparation of separator: The solid electrolyte and polyolefin (PP) were melt-extruded to obtain a cast film; the cast film was stretched to obtain a stretched film; the stretched film was wound and slit to obtain a separator.

[0094] Example 2

[0095] In this example, the preparation of the solid electrolyte was carried out. The preparation method used in this example was basically the same as that in Example 1, and the differences (specific components and parameters can be referred to Table 1) were as follows:

[0096] Replace Li 1.1 Al 0.2 Ti 1.8 (PO4)3 with Li 1.1 Al 0.3 Ti 1.7 Replace the mass fraction of Mg-4Sn alloy with 2%

[0097] Example 3

[0098] In this example, the preparation of the solid electrolyte was carried out. The preparation method used in this example was basically the same as that in Example 1, and the differences (specific components and parameters can be referred to Table 1) were as follows:

[0099] Replace Li 1.1 Al 0.2 Ti 1.8 (PO4)3 with Li 1.1 Al 0.4 Ti 1.6 Replace the mass fraction of Mg-4Sn alloy with 3%

[0100] Example 4

[0101] In this example, the preparation of the solid electrolyte was carried out. The preparation method used in this example was basically the same as that in Example 1, and the differences (specific components and parameters can be referred to Table 1) were as follows:

[0102] Replace Li 1.1 Al 0.2 Ti 1.8 (PO4)3 with Li 1.1 Al 0.5 Ti 1.5 Replace the mass fraction of Mg-4Sn alloy with 4%

[0103] Example 5

[0104] In this example, a solid electrolyte was prepared. The preparation method used in this example was basically the same as that in Example 1, with the difference (specific components and parameters can be referred to Table 1) being that:

[0105] Li 1.1 Al 0.2 Ti 1.8 (PO4)3 was replaced with Li 1.1 Al 0.6 Ti 1.4 (PO4)3, and the mass fraction of the Mg-4Sn alloy was replaced with 5%

[0106] Example 6

[0107] In this example, a solid electrolyte was prepared. The preparation method used in this example was basically the same as that in Example 1, with the difference (specific components and parameters can be referred to Table 1) being that:

[0108] Li 1.1 Al 0.2 Ti 1.8 (PO4)3 was replaced with Li 1.3 Al 0.5 Ti 1.4 (PO4)3, and the mass fraction of the Mg-4Sn alloy was replaced with 4%

[0109] Example 7

[0110] In this example, a solid electrolyte was prepared. The preparation method used in this example was basically the same as that in Example 1, with the difference (specific components and parameters can be referred to Table 1) being that:

[0111] Li 1.1 Al 0.2 Ti 1.8 (PO4)3 was replaced with Li 1.3 Al 0.5 Ti 1.5 (PO4)3, and the mass fraction of the Mg-4Sn alloy was replaced with 5%

[0112] Comparative Example 1

[0113] In this comparative example, a solid electrolyte was prepared. The preparation method used in this comparative example was basically the same as that in Example 1, with the difference (specific components and parameters can be referred to Table 1) being that:

[0114] Mg-4Sn alloy coating was not used. That is, step (1) was not carried out, and the solid electrolyte directly used LATP, and then the diaphragm was directly prepared in step (4) to obtain the diaphragm.

[0115] Transverse test experiment:

[0116] 1. Test experiment 1: Investigation of ionic conductivity and high-temperature shrinkage rate.

[0117] A. Test method:

[0118] (1) Ionic conductivity: For the solid electrolytes prepared in Examples 1 - 7 and Comparative Example 1, they were pressed into solid electrolyte membranes (separators), and then the solid electrolyte membranes were cut into circular pieces with a diameter of 19 mm. The circular pieces were sandwiched between two stainless steel gaskets to assemble a symmetrical cell; then an electrochemical workstation was connected, and impedance tests were carried out at room temperature of 25 °C to obtain the bulk impedance values of the samples to be tested. According to the formula σ = L / (A×Rb), the ionic conductivity was calculated, where σ is the ionic conductivity, with the unit of S / cm; L is the thickness of the pressed tablet, with the unit of cm; A is the area of the pressed tablet, with the unit of cm 2 ; Rb is the bulk impedance of the sample to be tested, with the unit of Ω. Among them, L is 0.015 cm, and A is 2.84 cm 2 .

[0119] (2) High-temperature shrinkage rate: The separators prepared in the above examples and the separators listed in the comparative examples were cut into samples with dimensions of 10 cm×10 cm, and the longitudinal length l of each sample was recorded 原始 , placed at 130 °C for 10 h, and the longitudinal length l of each sample was tested 保温 , and the shrinkage rate was calculated. The shrinkage rate = (l 保温 / l 原始 )×100%.

[0120] B. Experimental results and analysis:

[0121] Table 2. Transverse test experimental results of examples and comparative examples

[0122]

[0123] (1) Referring to the experimental results in Table 2 and Figure 2 , the ionic conductivities of Examples 1 - 7 are all in the range of 9.0×10 −4 ~9.6×10 −4 S / cm, showing relatively close ionic conductivity values, indicating that the solid electrolytes obtained by the method in this application and the separators prepared therefrom can all achieve high ionic conductivity, and the influence of different Mg-4Sn alloy mass fractions and LATP composition ratios on ionic conductivity is small.

[0124] (2) The ionic conductivity of Comparative Example 1 (without Mg-4Sn alloy coating) is the lowest, which is 5.5×10 −4S / cm, significantly lower than all the examples, indicating that the addition of Mg-4Sn alloy significantly improves the ionic conductivity of the solid electrolyte.

[0125] (3) The high-temperature shrinkage rates of Examples 1 to 7 are all between 4.2% and 4.5%, showing good thermal stability.

[0126] (4) The high-temperature shrinkage rate of Comparative Example 1 is 7.1%, higher than all the examples, indicating that the addition of Mg-4Sn alloy helps to significantly reduce the shrinkage rate of the solid electrolyte at high temperature, thereby improving its thermal stability.

[0127] 2. Test Experiment 2: Investigation of electrochemical performance.

[0128] A. Preparation and testing methods:

[0129] The diaphragms obtained in Examples 1, 4, 5, 6, and 7 were made into batteries, and then the electrochemical performance was investigated. The specific methods include:

[0130] (1) The binder PVDF was added to NMP according to a mass ratio of 1:8 and stirred to obtain a glue solution. Then, the commercial ternary lithium nickel cobalt manganese oxide TLP813 material, conductive agent acetylene black, and the glue solution were mixed according to a mass ratio of 97:1:2, and stirred in a vacuum mixer until the system became homogeneous to obtain the positive electrode slurry.

[0131] (2) The positive electrode slurry was evenly coated on the positive electrode current collector, air-dried at room temperature, transferred to an oven for further drying, and then cold-pressed and cut into the required specifications to obtain the positive electrode sheet.

[0132] (3) The negative electrode active material graphite, conductive agent acetylene black, thickening agent CMC, and binder SBR were mixed according to a mass ratio of 96.2:0.8:1.2:1.8. Then, deionized water as a solvent was added to the resulting mixture, and stirred in a vacuum mixer until the system became homogeneous to obtain the negative electrode slurry.

[0133] (4) The negative electrode slurry was evenly coated on the negative electrode current collector, air-dried at room temperature, transferred to an oven for further drying, and then cold-pressed and cut into the required specifications to obtain the negative electrode sheet.

[0134] (5) The above positive electrode sheet, diaphragm (diaphragms prepared in Examples 1, 4, 5, 6, and 7), and negative electrode sheet were stacked in sequence to obtain a battery cell after assembly.

[0135] (6) Place the battery cell assembly into the inner cavity of the battery case. After drying, inject electrolyte into the inner cavity of the battery case. The electrolyte solvent is ethylene carbonate, and the solute is lithium hexafluorophosphate (1 mol / L). Through processes such as sealing, standing, formation, and grading, a prismatic lithium-ion battery is obtained. The capacity of the prismatic battery is 20 Ah, the thickness is 15 mm, the width is 119 mm, and the height is 208 mm.

[0136] (7)Test the retention rate [at room temperature (25 ± 5) °C and 1500 cycles] of each prismatic lithium-ion battery.

[0137] B. Experimental results and analysis:

[0138] Table 3. Retention rate of prismatic lithium-ion batteries in the examples

[0139]

[0140] (1)Referring to the experimental results of the retention rate in Table 3 and Figure 3 It can be seen that the cycle retention rate of Example 1 is 88.72%, which is relatively low. The cycle retention rates of Examples 4 to 7 all exceed 90%. Among them, the cycle retention rate of Example 7 is the highest, which is 91.39%.

[0141] (2)Examples 4 to 7 show higher cycle retention rates compared to Example 1, which indicates that when the mass fraction of Mg-4Sn alloy increases to 4% or more (mass fraction ≥ 4%), and the value of x in LATP satisfies 0.5 ≤ x < 2, the cycle performance of the battery is significantly improved, indicating that the addition of Mg-Sn alloy (Mg-4Sn) and the optimization of the specific LATP composition ratio contribute to improving the battery performance.

[0142] (3)The core-shell structured solid electrolyte in the examples exhibits excellent battery cycle performance. The core-shell structure design utilizes the core advantages of LATP and, with the help of the characteristics of the Mg-4Sn alloy shell, comprehensively improves the air stability, ionic conductivity, cycle stability, and electrochemical window of the solid electrolyte.

[0143] (4)The cycle retention rate of Example 7 is higher than that of Example 1. Supported by data, it is attributed to the fact that the aluminum element in the Mg-4Sn alloy promotes the formation of the Mg2Sn phase, further enhancing the strength of the Mg-4Sn alloy, making the core-shell structured solid electrolyte show significant advantages in improving battery performance. At the same time, good electrical and thermal conductivity helps to improve the electrical conductivity of the battery, reduce the internal resistance, and enhance the charge and discharge efficiency of the battery.

[0144] (5)The excellent corrosion resistance, tear resistance, and puncture resistance of the Mg-4Sn alloy further improve the safety and stability of the battery system.

[0145] In summary, based on the test experimental results, through the core-shell structure design and the application of the Mg-Sn alloy, the present application can improve the ionic conductivity, cycle stability, and electrochemical window of the solid electrolyte, thereby enhancing the cycle retention rate and overall performance of the battery. These improvements provide a high-performance solid electrolyte material for the development of all-solid-state batteries and contribute to the progress of lithium battery technology.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte has a core-shell composite structure with LATP as the core and a Mg-Sn alloy as the shell coated on the outer surface of the core; wherein, the molar ratio of Mg to Sn in the Mg-Sn alloy is 1:4; in the Mg-Sn alloy, Mg and Sn form a Mg2Sn phase, and the role of aluminum element in the Mg-Sn alloy is to promote the formation of the Mg2Sn phase; The LATP is Li y Al x Ti 2-x (PO4)3; where y - x = 1, 0 < x < 2, 1 < y < 3; The mass fraction of the Mg-Sn alloy in the solid electrolyte is 1% to 10%.

2. The solid electrolyte according to claim 1, characterized in that, In the LATP, y - x = 1, 0.5 ≤ x < 2, 1 < y < 3.

3. The solid electrolyte according to claim 1, characterized in that, The mass fraction of the Mg-Sn alloy in the solid electrolyte is 4% to 10%.

4. A method for preparing a solid electrolyte according to any one of claims 1-3, characterized in that, Comprising: LATP and the Mg-Sn alloy are subjected to ball milling treatment together, and then the solid electrolyte is obtained after sintering treatment and cooling treatment.

5. The preparation method of the solid electrolyte according to claim 4, characterized in that, The sintering treatment is sequentially carried out as follows: A. Sinter at 200°C to 250°C in air for 1 hour to 2 hours; B. Calcinate at 650°C to 700°C for 2 hours to 4 hours; C. Sinter at 700°C to 750°C for 1 hour to 2 hours.

6. The preparation method of the solid electrolyte according to claim 4, wherein, The preparation method of the Mg-Sn alloy includes: Mix magnesium powder and tin powder to obtain a mixed powder; The mixed powder is subjected to ball milling treatment, pressing molding treatment and sintering treatment to obtain the Mg-Sn alloy.

7. The preparation method of the solid electrolyte according to claim 6, characterized in that, The time of the ball milling treatment is 2 hours to 8 hours.

8. The method for preparing the solid electrolyte according to claim 6, characterized in that, The pressure of the pressing molding treatment is 5t to 10t.

9. The preparation method of the solid electrolyte according to claim 6, characterized in that, The sintering temperature of the sintering treatment is 200°C to 400°C.

10. The method for preparing a solid electrolyte according to claim 6, wherein The sintering time of the sintering treatment is 4 hours to 12 hours.

11. The preparation method of the solid electrolyte according to claim 4, characterized in that, The preparation method of the LATP includes: Mix a lithium source, a phosphorus source, an aluminum source and a titanium source according to a stoichiometric ratio with the lithium source being 5% to 15% in excess, add a sintering aid, and then obtain the LATP after calcination treatment.

12. The preparation method of the solid electrolyte according to claim 11, characterized in that, The lithium source includes: Li2CO3.

13. The preparation method of the solid electrolyte according to claim 11, characterized in that, The aluminum source includes: Al2O3.

14. The preparation method of the solid electrolyte according to claim 11, characterized in that, The titanium source includes: TiO2.

15. The preparation method of the solid electrolyte according to claim 11, wherein The phosphorus source includes: (NH4)H2PO4.

16. The preparation method of the solid electrolyte according to claim 11, characterized in that, The sintering aid includes at least one of aluminum oxide, lithium tetrafluoroborate, tetrabutylammonium tetrafluoroborate and ammonium tetrafluoroborate.

17. The method for preparing the solid electrolyte according to claim 11, wherein The mass fraction of the sintering aid is 1% to 2%.

18. A diaphragm, characterized in that, Comprising the solid electrolyte according to any one of claims 1 - 3; or, comprising the solid electrolyte obtained by the preparation method of the solid electrolyte according to any one of claims 4 - 17.

19. A battery, characterized in that, Comprising the separator according to claim 18.

20. An electric-related device, characterized in that, Comprising the battery according to claim 19.

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