Solid electrolyte, preparation method thereof, and solid-state lithium-ion battery

Abstract

The present invention provides a solid electrolyte, a preparation method thereof, and a solid-state lithium-ion battery, belonging to the field of battery technology. The solid electrolyte comprises lithium borate and lithium boron phosphate, wherein the lithium borate and lithium boron phosphate form a solid material, wherein lithium borate is distributed between adjacent particles of the lithium boron phosphate or on the surface of the particles. The electrolyte of the present invention improves the density of the material particles and reduces the grain boundary impedance, so that the inorganic oxide solid electrolyte has high stability while reducing the cost, and solves the problems of poor interface contact tightness and high grain boundary impedance of existing inorganic oxide solid electrolytes. The use of this solid electrolyte is conducive to improving the cycle life and rate performance of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a solid electrolyte and a preparation method thereof and a solid-state lithium-ion battery. Background Art

[0002] Energy storage technology has developed rapidly in recent years, among which lithium-ion batteries are the most representative. They have been widely used in consumer electronics, new energy vehicles, aerospace and other fields.

[0003] When liquid lithium-ion batteries are charging, Li + From the positive electrode into the electrolyte, while the Li + embedded into the negative electrode; on the contrary, during discharge, Li + From the negative electrode into the electrolyte, while the Li + Embedded in the positive electrode. Liquid lithium-ion batteries offer advantages such as high rate performance and long cycle life. However, due to the flammability and volatility of the electrolyte, safety needs to be improved. This has led to the development of all-solid-state batteries, which use solid electrolytes in place of liquid electrolytes. All-solid-state batteries are not only highly safe but also compatible with high-energy-density cathode and anode materials that cannot be used in liquid batteries. Theoretically, solid-state batteries can achieve a specific energy of 2-3 times that of existing lithium-ion batteries.

[0004] Solid-state electrolytes are a diverse range of material systems with varying performance properties. Currently, the solid-state electrolyte materials with the greatest market potential or commercial prospects fall into three main categories: polymers, inorganic oxides, and sulfides. Polymer solid electrolytes include PEO solid polymer systems, polycarbonate systems, polyalkoxy systems, and polymer single-ion conductor-based systems. These electrolytes offer advantages such as flexibility, ease of large-scale preparation, low shear modulus, and resistance to lithium metal reaction. However, they suffer from low ionic conductivity and low oxidation voltage (<4V). Inorganic oxide solid electrolytes include perovskite, garnet, NASICON, and LISICON types. These electrolytes offer advantages such as good mechanical properties and high electrochemical stability, but suffer from poor interfacial contact and high grain boundary resistance. Sulfide solid electrolytes include Thio-LISICON, LGPS, and Li-aegyrodite types. They offer advantages such as high conductivity, excellent mechanical properties, and low grain boundary resistance, but are susceptible to oxidation and are sensitive to water vapor. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a solid electrolyte, a preparation method thereof, and a solid-state lithium-ion battery to solve the problems of poor interface contact tightness and high grain boundary impedance existing in existing inorganic oxide solid electrolytes, improve the density of material particles, and reduce grain boundary impedance, so that the inorganic oxide solid electrolyte has high stability while reducing costs. The use of this solid electrolyte is beneficial to improving the cycle life and rate performance of lithium-ion batteries.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, a solid electrolyte is provided, comprising lithium borate and lithium borophosphate, wherein the lithium borate and lithium borophosphate form a solid material, wherein lithium borate is distributed between adjacent particles of the lithium borophosphate or on the surface of the particles.

[0008] Furthermore, in the solid electrolyte, the mass percentages of lithium borate and lithium borophosphate are 0.5% to 30% and 70% to 99.5% respectively.

[0009] Furthermore, the chemical formula of the lithium borophosphate is Li 0.1 B 0.967 PO4.

[0010] Furthermore, the density of the solid electrolyte is not less than 96%, and the ionic conductivity is not less than 0.45 mS / cm.

[0011] In a second aspect, a method for preparing the above-mentioned solid electrolyte comprises the following steps:

[0012] (3) Preparation of lithium borophosphate: a phosphorus source, a boron source, a lithium source and a solvent are uniformly mixed according to the stoichiometric ratio of lithium borophosphate to form a slurry, the slurry is dried and then calcined to obtain a lithium borophosphate material;

[0013] (4) Preparation of lithium borate: a boron source, a lithium source and a solvent are uniformly mixed in a slurry according to the stoichiometric ratio of lithium borate, the slurry is dried and then calcined to obtain a lithium borate material;

[0014] (3) Preparation of solid electrolyte: The lithium borophosphate material obtained in step (1) and the lithium borate material obtained in step (2) are mixed evenly, and the mixture is calcined after tableting to obtain a solid electrolyte.

[0015] Furthermore, the boron source, lithium source and solvent in step (1) and step (2) are the same or different;

[0016] And / or, the boron source includes at least one of boric acid, metaboric acid and boron oxide;

[0017] And / or, the lithium source includes at least one of lithium hydroxide, lithium nitrate, lithium acetate, lithium carbonate and lithium oxalate;

[0018] and / or, the solvent comprises at least one of deionized water, N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, anhydrous ethanol, glycerol and industrial alcohol;

[0019] And / or, the phosphorus source includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide.

[0020] Furthermore, in step (1) and / or step (2), the mass percentage of the solvent in the slurry is 10% to 60%.

[0021] Furthermore, in step (1) and / or step (2), the drying temperature is 60° C. to 120° C., and the drying time is 0.5 h to 24 h.

[0022] Furthermore, in step (1) and / or step (2) and / or step (3), the calcination temperature is 700°C to 1000°C, the heating rate to the calcination temperature is 0.5 to 10°C / min, and the calcination holding time is 1h to 48h.

[0023] In a third aspect, a solid-state lithium-ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte; the solid electrolyte is the solid electrolyte described above or a solid electrolyte prepared by the above preparation method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The solid electrolyte of the present invention is a composite material composed of a mixture of lithium borate and lithium borophosphate. The lithium borophosphate plays the role of transmitting lithium ions, and the lithium borate mainly plays a wetting and bonding role. In the composite material, due to the close bonding between the particles, the grain boundary impedance can be reduced, the cycle life and rate performance of the all-solid-state lithium-ion battery can be improved, and it has low cost and high stability. The density of the solid electrolyte is not less than 96%, and the ionic conductivity is not less than 0.45mS / cm. It solves the problems of poor interfacial contact tightness and high grain boundary impedance existing in existing inorganic oxide solid electrolytes. When applied to lithium-ion batteries, it is beneficial to improve the cycle life and rate performance of lithium-ion batteries.

[0026] 2. The solid electrolyte preparation method of the present invention is simple and easy. First, lithium borate and lithium borophosphate are prepared by a solid-phase method. The solid-phase raw materials are further dissolved in a solvent to form a slurry to increase the uniformity of the solid-phase raw material mixing and promote the uniform distribution of elements during sintering. Then, a solid-phase method is used to prepare a solid electrolyte. The low-melting-point lithium borate material is first melted between the lithium borophosphate material at a high temperature. With the help of capillary action, it flows and spreads along the gaps between the lithium borophosphate material particles, and dissolves and penetrates the lithium borophosphate material. After solidification, a composite material (solid-state electrolyte) is formed, which enhances the density of the interface, facilitates the diffusion and migration of lithium ions between the material particles, reduces grain boundary impedance, and improves dynamic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram and SEM image of the preparation of the solid electrolyte of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The embodiments of the present invention are implemented on the premise of the technical solutions of the present invention, and detailed implementation methods and processes are given, but the protection scope of the present invention is not limited to the following embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0029] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0030] Throughout this disclosure, unless otherwise specified and / or explained, all values referring to component amounts are expressed as "mass percentages." Process parameters in the following examples, where specific conditions are not specified, generally follow conventional conditions. Reagents and materials used in the following examples, unless otherwise noted, were commercially available.

[0031] According to a first aspect of the present invention, a solid electrolyte is provided, comprising lithium borate and lithium borophosphate, wherein the lithium borate and lithium borophosphate form a solid material, wherein lithium borate is distributed between adjacent particles of the lithium borophosphate or on the surface of the particles.

[0032] In the solid electrolyte of the present invention, lithium borophosphate (Li 0.1 B 0.967 PO4) is an ionic conductor with an ionic conductivity of up to 10 -4 S / cm, which plays a role in transporting lithium ions; lithium borate (Li3BO3) has a slightly lower ionic conductivity and mainly plays a wetting and bonding role. This material has a low melting point (~700°C). After being heated and melted together with other material particles, it can flow and spread along the gaps between other material particles with the help of capillary action, and dissolve and penetrate with other particles, forming a composite material (solid electrolyte) after solidification. In solid electrolytes, the density of the interface between particles is enhanced, which improves the diffusion and migration of lithium ions, reduces the grain boundary impedance, and improves the kinetic performance. This solid electrolyte solves the problems of poor interface contact tightness and high grain boundary impedance in existing inorganic oxide solid electrolytes. Its application in lithium-ion batteries is beneficial to improving the cycle life and rate performance of lithium-ion batteries.

[0033] The solid electrolyte of the present invention has a density of more than 96% (for example, 96%, 97%, 98%, 99%, 100%, etc.), and an ionic conductivity of not less than 0.45 mS / cm (for example, 0.45 mS / cm, 0.55 mS / cm, 0.65 mS / cm, 0.75 mS / cm, 0.85 mS / cm, etc.).

[0034] As an optional embodiment, the solid electrolyte mentioned above has the mass percentages of lithium borate and lithium borophosphate of 0.5% to 30% and 70% to 99.5% respectively.

[0035] In the above technical solution, the mass percentage of lithium borate can be 0.5%, 1%, 3%, 5%, 7%, 9%, 15%, 20%, 25%, 28%, 30%, and the mass percentage of lithium borophosphate can be 70%, 71%, 73%, 75%, 77%, 79%, 85%, 90%, 95%, 98%, 99.5%, and the total of the two is 100%. 0.1 B 0.967 The mass percentage of PO4 is controlled within the above range, so that the solid electrolyte can have a high density without increasing the impedance too much and reducing the battery rate.

[0036] According to a second aspect of the present invention, a method for preparing the aforementioned solid electrolyte is provided, the method comprising the following steps: (1) preparing lithium borophosphate: uniformly mixing a phosphorus source, a boron source, a lithium source and a solvent according to the stoichiometric ratio of lithium borophosphate to form a slurry, drying the slurry and calcining to obtain a lithium borophosphate material; (2) preparing lithium borate: uniformly mixing a boron source, a lithium source and a solvent according to the stoichiometric ratio of lithium borate to form a slurry, drying the slurry and calcining to obtain a lithium borate material; (3) preparing a solid electrolyte: uniformly mixing the lithium borophosphate material obtained in step (1) and the lithium borate material obtained in step (2), preparing the slurry and calcining to obtain a solid electrolyte.

[0037] The preparation method of the present invention is simple and easy to implement. It adopts the solid phase method to synthesize by directly calcining various raw materials. During calcination, the high temperature causes diffusion and migration between atoms, chemical reactions occur, and new substances are formed. Due to the high temperature, other substances are not present, and the new substances are of high purity. During preparation, lithium borate and lithium borophosphate are first prepared by the solid phase method. The solid phase raw materials are further dissolved in a solvent to form a slurry to increase the uniformity of the solid phase raw material mixing and promote the uniform distribution of elements during sintering. Then, the solid electrolyte is prepared by the solid phase method. The low melting point Li3BO3 material is first melted in Li at high temperature. 0.1 B 0.967 Between PO4 materials, by means of capillary action, along the Li 0.1 B 0.967 PO4 material flows and spreads between particles and Li 0.1 B 0.967 PO4 materials dissolve and penetrate each other and solidify to form a composite material (solid electrolyte) (such as Figure 1 Li3BO3 can enhance the density of the interface between composite particles at high temperature, facilitate the diffusion and migration of lithium ions between composite particles, reduce grain boundary resistance, and improve dynamic performance.

[0038] In the preparation method of the present invention, the mixing method of the solid phase and the solvent is not particularly limited, as long as the solid phase and the solvent are mixed before calcination. All solid phases may be mixed to form a mixed solid phase, and then the mixed solid phase is mixed with the solvent. Alternatively, each solid phase may be mixed with the solvent separately to form a different solution, and then all the solutions may be mixed.

[0039] In the preparation method of the present invention, the boron source, lithium source, and solvent in step (1) and step (2) may be the same or different. The boron source is typically, but not limited to, selected from at least one of boric acid, metaboric acid, and boron oxide; the lithium source is typically, but not limited to, selected from at least one of lithium hydroxide, lithium nitrate, lithium acetate, lithium carbonate, and lithium oxalate; the solvent is typically, but not limited to, selected from at least one of deionized water, N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, anhydrous ethanol, glycerol, and industrial alcohol; and the phosphorus source is typically, but not limited to, selected from at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphorus pentoxide.

[0040] In the preparation method of the present invention, the sintering atmosphere during sintering is not particularly limited and can be sintered directly in air or in oxygen. After sintering, the cooling method is not particularly limited and can be sampled after natural cooling to room temperature or after cooling using non-natural cooling methods (such as air cooling, water cooling, etc.).

[0041] In the preparation method of the present invention, the tableting form is not limited and can be tableting by compression or other tableting methods.

[0042] In the preparation method of the present invention, the shape of the tablet is not limited, and is based on the shape suitable for battery use, and can be round, square or other shapes.

[0043] In the above preparation method, as an optional embodiment, in step (1) and / or step (2), the mass percentage of the solvent in the slurry is 10% to 60% (for example, 15%, 20%, 30%, 40%, 50% or 55%).

[0044] In the above preparation method, as an optional embodiment, in step (1) and / or step (2), the drying temperature of the drying is 60°C to 120°C (for example, 70°C, 80°C, 90°C, 100°C, 110°C or 115°C), and the drying time is 0.5h to 24h (for example, 1h, 5h, 10h, 15h, 18h, 20h or 22h).

[0045] In the above preparation method, as an optional embodiment, in step (1) and / or step (2) and / or step (3), the calcination temperature is 700°C to 1000°C (for example, 720°C, 750°C, 800°C, 850°C, 900°C or 950°C), the heating rate to the calcination temperature is 0.5 to 10°C / min (for example, 1°C / min, 2°C / min, 5°C / min, 7°C / min or 9°C / min), and the calcination holding time is 1h to 48h (for example, 1h, 5h, 10h, 15h, 20h, 30h, 40h or 45h).

[0046] According to a third aspect of the present invention, a solid-state lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet and a solid electrolyte; the solid electrolyte is the above-mentioned solid electrolyte or the solid electrolyte prepared by the above-mentioned preparation method.

[0047] The positive electrode sheet and the negative electrode sheet used in the solid-state lithium-ion battery of the present invention are not particularly limited and can be any type of material known in existing lithium battery technology, as long as they can be used to manufacture lithium-ion batteries with energy storage functions.

[0048] In the present invention, the above technical features can be freely combined to form a new technical solution without conflict.

[0049] The following is further described in detail through specific implementation methods:

[0050] Example 1

[0051] A solid electrolyte comprising Li3BO3 (LBO) and Li 0.1 B 0.967 PO4(LBPO), the mass percentages of the two are 10% and 90% respectively. The preparation method comprises the following steps:

[0052] (1) Preparation of Li 0.1 B 0.967 PO4:

[0053] H3BO3, LiOH, and NH4H2PO4 were mixed in a molar ratio of 0.967:0.1:1, and ethanol was added as a solvent to form a slurry, with ethanol accounting for 35% by mass of the slurry. After mixing evenly, the mixture was dried at 90°C for 2 hours; then the temperature was raised to 800°C at a rate of 3°C / min for calcination, the temperature was kept at this temperature for 12 hours, and finally naturally cooled to room temperature to obtain Li 0.1 B 0.967 PO4 powder. The reaction equation is as follows:

[0054] 0.967H3BO3+0.1LiOH+NH4H2PO4+0.74975O2=Li 0.1 B 0.967 PO4+4.5005H2O+0.5N2

[0055] (2) Preparation of Li3BO3:

[0056] H3BO3 and LiOH were mixed in a molar ratio of 1:3, and ethanol was added as a solvent to form a slurry, with ethanol accounting for 35% by mass of the slurry. After mixing evenly, the mixture was dried at 90°C for 2 hours. The mixture was then heated to 700°C at a rate of 3°C / min and calcined for 12 hours. The mixture was then cooled naturally to room temperature to obtain Li3BO3 powder. The reaction equation is as follows:

[0057] H3BO3+3LiOH=Li3BO3+3H2O

[0058] (3) Preparation of solid electrolyte:

[0059] Li3BO3 powder and Li 0.1 B 0.967 PO4 powders were mixed at a mass ratio of 10:90, mixed evenly, and pressed into discs; then the temperature was raised to 800°C at a rate of 3°C / min for calcination, kept at this temperature for 10 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0060] Example 2

[0061] A solid electrolyte comprising Li3BO3 and Li 0.1 B 0.967 PO4, the mass percentages of the two are 15% and 85% respectively. The preparation method comprises the following steps:

[0062] The Li3BO3 powder synthesized in Example 1 and Li 0.1 B 0.967 PO4 powders were mixed at a mass ratio of 15:85, mixed evenly, and pressed into discs; then the mixture was heated to 700°C at a rate of 0.5°C / min for calcination, kept at this temperature for 48 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0063] Example 3

[0064] A solid electrolyte comprising Li3BO3 and Li 0.1 B 0.967 PO4, the mass percentages of the two are 20% and 80% respectively. The preparation method comprises the following steps:

[0065] The Li3BO3 powder synthesized in Example 1 and Li 0.1 B 0.967 PO4 powders were mixed at a mass ratio of 20:80, mixed evenly, and pressed into discs; then the temperature was raised to 850°C at a rate of 5°C / min for calcination, kept at this temperature for 30 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0066] Example 4

[0067] A solid electrolyte comprising Li3BO3 and Li 0.1 B 0.967 PO4, the mass percentages of the two are 25% and 75% respectively. The preparation method comprises the following steps:

[0068] The Li3BO3 powder synthesized in Example 1 and Li 0.1 B0.967 PO4 powders were mixed at a mass ratio of 25:75, and after mixing evenly, pressed into discs; then the temperature was raised to 900°C at a rate of 7°C / min for calcination, kept at this temperature for 15 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0069] Example 5

[0070] A solid electrolyte comprising Li3BO3 and Li 0.1 B 0.967 PO4, the mass percentages of the two are 30% and 70% respectively. The preparation method comprises the following steps:

[0071] The Li3BO3 powder synthesized in Example 1 and Li 0.1 B 0.967 PO4 powders were mixed at a mass ratio of 30:70, and after being mixed evenly, pressed into discs; then the temperature was raised to 1000°C at a rate of 10°C / min for calcination, kept at this temperature for 1 hour, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0072] Comparative Example 1

[0073] The solid electrolyte in this example contains only Li 0.1 B 0.967 PO4.

[0074] The Li synthesized in Example 1 0.1 B 0.967 PO4 powder was pressed into discs; then the temperature was raised to 800°C at a rate of 3°C / min for calcination, kept at this temperature for 10 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0075] Comparative Example 2

[0076] The solid electrolyte in this example contains only Li3BO3.

[0077] Preparation of solid electrolyte:

[0078] The Li3BO3 powder synthesized in Example 1 was pressed into a round pellet; the pellet was then heated to 800°C at a rate of 3°C / min and calcined, kept at this temperature for 10 hours, and finally naturally cooled to room temperature to obtain a solid electrolyte.

[0079] Assembling the battery

[0080] (1) Preparation of positive electrode sheet:

[0081] The positive electrode material NCM622, the binder polyvinylidene fluoride PVDF, the conductive agent superP, and the carbon nanotubes are set to have a mass percentage of 97.1 wt%, 1.5 wt%, 0.7 wt%, and 0.7 wt%, respectively.

[0082] The binder is added to the organic solvent nitrogen methyl pyrrolidone (NMP) and stirred to dissolve. The positive electrode active material and conductive agent are then added according to the set percentages and stirred to disperse evenly to prepare a positive electrode slurry. The mass percentage of NMP in the positive electrode slurry is 35%. The positive electrode slurry is then coated on the surface of the current collector aluminum foil and dried at 90°C. Finally, it is rolled, trimmed, and cut into pieces to form positive electrode discs.

[0083] (2) Preparation of negative electrode:

[0084] Commercial lithium metal sheet is used as the negative electrode.

[0085] (3) Preparation of batteries:

[0086] In an argon atmosphere, the positive electrode sheet is placed on one surface of the solid electrolyte disc, and the metal lithium sheet is placed on the other surface of the solid electrolyte disc. They are pressurized into a stack and placed in a stainless steel casing to make the all-solid-state battery to be tested.

[0087] The solid electrolyte discs are the solid electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 2. When the solid electrolyte disc is the solid electrolyte obtained in Example 1, the all-solid-state battery to be tested is the solid-state lithium-ion battery (solid-state battery) of Example 1, and so on.

[0088] Performance Testing

[0089] (1) Measuring the density of the solid electrolyte using the Archimedes drainage method: The density of the solid electrolytes (solid electrolyte discs) prepared in the above embodiments and comparative examples was tested.

[0090] First, the mass W1 of the solid electrolyte disc was weighed on a balance. Then, the disc was suspended on a balance with a thin wire, placed in a beaker, and placed in a vacuum desiccator equipped with an air extraction port and a water injection port. The vacuum degree was less than 2.66 kPa, and the pressure was maintained for 5 minutes to remove the air. Then, distilled water was slowly injected over 5 minutes to completely immerse the disc. The pressure was maintained for another 5 minutes, and the mass W2 was weighed. Finally, the beaker was removed from the beaker and allowed to stand in air for 30 minutes. The excess water on the surface of the disc was carefully wiped with a towel saturated with distilled water to avoid absorbing water in the disc holes. The mass W3 of the disc in air was immediately weighed. The density was calculated according to ρ = (W1-W2) / (W3-W2). The results are recorded in Table 1.

[0091] (2) Ionic conductivity test of solid electrolyte: The solid electrolytes (solid electrolyte discs) prepared in the above embodiments and comparative examples were subjected to ionic conductivity tests.

[0092] The solid electrolyte disc was sprayed with gold on both sides, and a button battery was made using a CR2330 battery shell. The button battery was clamped in a test clamp and tested using a CHI600E series electrochemical workstation. The frequency range was 0.01 to 10 6 Hz, amplitude 10mV. Ionic conductivity calculation formula: λ=L / (R*S), L is the electrolyte thickness 80μm, S is the electrolyte cross-sectional area 3.46cm 2 , R is the electrolyte impedance. The impedance is measured by the electrochemical workstation and then plugged into the formula to obtain the ionic conductivity. The test data are recorded in Table 1.

[0093] (3) Solid-state battery gram capacity test: The solid-state batteries prepared in the above embodiments and comparative examples were subjected to gram capacity tests.

[0094] Maintaining the ambient temperature at 25±3°C, the battery was charged at 0.33C to a fully charged state of 4.3V, and then discharged at 1C with a discharge cut-off voltage of 2.5V. The average discharge capacity in grams of the positive electrode material for the first five times was calculated and recorded in Table 1.

[0095] (4) Cycling performance and rate performance test of solid-state batteries: Cycling performance and rate performance test were performed on the solid-state batteries prepared in the above embodiments and comparative examples.

[0096] The battery was charged at 0.5C to a cut-off voltage of 4.3V, and then discharged at 1C or 2C with a discharge cut-off voltage of 2.5V for 500 charge and discharge cycles. The capacity retention rate of 1C / 0.5C cycle for 500 cycles and the capacity retention rate of 2C / 0.5C cycle for 500 cycles at 25°C were calculated and recorded in Table 1.

[0097] Table 1 Performance test results

[0098]

[0099] Comparing Example 1 with Comparative Example 1, it can be seen that: 0.1 B 0.967 Solid electrolyte composed of PO4, relative to Li 0.1 B 0.967 PO4 has a higher density, which is beneficial to improving the kinetic properties of lithium ions and can increase the cycle life and rate performance of the battery.

[0100] By comparing and analyzing the examples and comparative examples, it can be seen that adding Li3BO3 helps to improve the density of the solid electrolyte, but the ionic conductivity of Li3BO3 is lower than that of Li 0.1 B 0.967 PO4 is low, and excessive content of the former will cause the ionic conductivity of the solid electrolyte to decrease.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A solid electrolyte, characterized in that The solid electrolyte comprises lithium borate and lithium borophosphate, wherein the lithium borate and lithium borophosphate form a solid material, wherein lithium borate is distributed between adjacent particles of the lithium borophosphate or on the surface of the particles; The chemical formula of the lithium borophosphate is Li 0.1 B 0.967 PO4; Preparation of lithium borophosphate: According to the stoichiometric ratio of lithium borophosphate, a phosphorus source, a boron source, a lithium source and a solvent are uniformly mixed to form a slurry, the slurry is dried and calcined to obtain a lithium borophosphate material, the calcination temperature is 700 ℃ ~ 1000 ℃; In the solid electrolyte, the mass percentages of lithium borate and lithium borophosphate are 15% to 30% and 70% to 85% respectively.

2. The solid electrolyte according to claim 1, wherein The solid electrolyte has a density of not less than 96% and an ion conductivity of not less than 0.45 mS / cm.

3. A method for preparing a solid electrolyte according to any one of claims 1-2, characterized in that: The preparation method comprises the following steps: (1) Preparation of lithium borophosphate: a phosphorus source, a boron source, a lithium source and a solvent are uniformly mixed according to the stoichiometric ratio of lithium borophosphate to form a slurry, the slurry is dried and then calcined to obtain a lithium borophosphate material; (2) Preparation of lithium borate: a boron source, a lithium source and a solvent are uniformly mixed according to the stoichiometric ratio of lithium borate to form a slurry, the slurry is dried and then calcined to obtain a lithium borate material; (3) Preparation of solid electrolyte: The lithium borophosphate material obtained in step (1) and the lithium borate material obtained in step (2) are mixed evenly, and the mixture is calcined after tableting to obtain a solid electrolyte.

4. The preparation method according to claim 3, wherein The boron source, lithium source and solvent in step (1) and step (2) are the same or different; And / or, the boron source includes at least one of boric acid, metaboric acid and boron oxide; And / or, the lithium source includes at least one of lithium hydroxide, lithium nitrate, lithium acetate, lithium carbonate and lithium oxalate; and / or, the solvent comprises at least one of deionized water, N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, acetone, anhydrous ethanol, glycerol and industrial alcohol; And / or, the phosphorus source includes at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide.

5. The preparation method according to claim 3, wherein: In step (1) and / or step (2), the mass percentage of the solvent in the slurry is 10% to 60%.

6. The preparation method according to claim 3, characterized in that: In step (1) and / or step (2), the drying temperature is 60° C. to 120° C., and the drying time is 0.5 h to 24 h.

7. The preparation method according to claim 3, wherein: In step (1) and / or step (2) and / or step (3), the calcination temperature is 700°C to 1000°C, the heating rate to the calcination temperature is 0.5 to 10°C / min, and the calcination holding time is 1h to 48h.

8. A solid-state lithium-ion battery, characterized in that: The solid-state lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet and a solid electrolyte; the solid electrolyte is the solid electrolyte described in any one of claims 1-2 or the solid electrolyte prepared by the preparation method described in any one of claims 3-7.

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