Preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte

Abstract

The invention relates to a preparation method of a lanthanum-doped lithium borate coated LATP solid electrolyte, which comprises the following steps: S1, mixing a lithium source, an aluminum source, a lanthanum source, a titanium source and a phosphorus source, putting the mixed material into a dispersing agent, putting into a constant-temperature water bath stirrer, and heating and stirring until the mixture is completely dried to obtain a mixed raw material; s2, performing high-temperature primary sintering on the mixed raw material in an air atmosphere to obtain a composite oxide; s3, performing crushing treatment on a composite oxide, adding lithium borate, and performing uniform mixing to obtain a mixture; the mass ratio of the lithium-containing compound to the composite oxide is (0.01-0.05): 1; and S4, tabletting the mixture, and carrying out high-temperature secondary sintering in an air atmosphere to obtain the finished product lithium titanium aluminum phosphate material. The problems that in an existing scheme, the final calcination temperature of a solid electrolyte is generally up to 1100 DEG C or above, high energy consumption is likely to be caused, meanwhile, Li loss is caused, non-conductive AlPO4 is introduced, the crystal structure is unstable, the powder sintering performance is poor, and the ionic conductivity is reduced are solved.

Description

Technical Field

[0001] The present invention relates to the field of solid-state batteries, and in particular to a method for preparing a lanthanum-doped lithium borate-coated LATP solid-state electrolyte. Background Art

[0002] Lithium-ion batteries generally use liquid electrolytes, which can easily cause thermal runaway of lithium-ion batteries, leading to battery combustion or even explosion. The development of all-solid-state lithium-ion batteries based on solid electrolytes can solve the safety hazards brought by liquid electrolytes. Inorganic solid electrolytes have high room temperature grain conductivity (~10 -3 S / cm), high lithium ion transference number (t≈1.0) and excellent electrochemical stability have attracted much attention.

[0003] At present, the basic skeleton structure of NASICON structure is expressed as M2P3O 12 , that is, two MO6 octahedra and three PO4 tetrahedra are connected at the same corner to form a structural unit. In the framework structure, alkali metals occupy the corner sites of the octahedron and tetrahedron structures, and lithium ions are transported through the structural network formed by the MO6 and PO4 frameworks. Among the many derivative structures, the NASICON-type structural electrolyte Li1+ prepared by Al element doping is x Al x Ti 2-x (PO4)3 (LATP, x = 0.3 ~ 0.5) has attracted widespread attention due to its high ionic conductivity, good electrochemical and chemical stability, and low raw material cost. This structure is also considered to be the most likely material to be used in all-solid-state batteries among many electrolyte structures.

[0004] There are many methods for preparing LATP, such as solid-phase sintering, coprecipitation, sol-gel, etc. In these preparation methods, no matter how the precursors are mixed and dried, the final calcination temperature is usually as high as 1100°C or above, which easily leads to high energy consumption. At the same time, the traditional high-temperature solid-phase method is also prone to Li loss, forming non-conductive AlPO4, resulting in unstable crystal structure, poor powder sintering performance, and reduced electrolyte ion conductivity.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a lanthanum-doped lithium borate coated LATP solid electrolyte, so as to solve the problem that the final calcination temperature of the solid electrolyte in the prior art is usually as high as 1100°C or above, which easily causes high energy consumption, and at the same time causes Li loss and introduces non-conductive AlPO4, resulting in unstable crystal structure, poor powder sintering performance, and decreased ionic conductivity.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for preparing a lanthanum-doped lithium borate-coated LATP solid electrolyte;

[0009] The steps include:

[0010] Step S1, mixing a lithium source, an aluminum source, a lanthanum source, a titanium source, and a phosphorus source, putting the mixed ingredients into a dispersant, placing the mixture in a constant temperature water bath stirrer, heating and stirring until completely dry, to obtain a mixed raw material;

[0011] Step S2, sintering the mixed raw materials once at a high temperature in an air atmosphere to obtain a composite oxide;

[0012] Step S3, crushing the composite oxide, then adding lithium borate, and mixing evenly to obtain a mixture; wherein the mass ratio of the lithium-containing compound to the composite oxide is 0.01-0.05:1;

[0013] Step S4, pressing the mixed material into tablets, and then secondary sintering at high temperature in an air atmosphere to obtain a finished lithium aluminum titanium phosphate material.

[0014] A further technical solution is that in step S1: the lithium source, aluminum source, lanthanum source, titanium source, and phosphorus source are in a molar ratio of Li:Al:La:Ti:P=(1+x+y):x:y:(2-xy):3; wherein x+y=0.3-0.5; the molar ratio of the lanthanum source to the aluminum source is x:y=0.03-0.3:1; and the total metal cation concentration is 1-3 mol / L.

[0015] A further technical solution is that in step S1: the lithium source is one or more of lithium-containing carbonates, hydroxides, and oxides; the aluminum source includes one or more of α-alumina, γ-alumina, and hydrated alumina; the phosphorus source includes one or more of diammonium phosphate, phosphoric acid, and lithium phosphate; the titanium source includes one or a mixture of titanium oxide and titanium chloride; the lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, or lanthanum nitrate; the dispersant includes one or a mixture of anhydrous ethanol or propanol; the stirring speed is 200-400 r / min, the water bath temperature is 50-85°C, and the stirring time is 2-6h.

[0016] A further technical solution is that in step S2: the primary sintering temperature is 600-900°C, the constant temperature time is 4-20h, and the heating rate is 2-5°C / min.

[0017] A further technical solution is that in step S3: the crushing treatment includes: primary crushing by a roller jaw crusher, followed by crushing by a jet mill to obtain a crushed composite oxide with a particle size of 1 to 5 μm;

[0018] The lithium borate includes LiBO2 or Li2B4O7; the mixing method is a combination of one or more of ball milling, mechanical stirring, magnetic stirring or mortar grinding.

[0019] A further technical solution is that in step S4: the tablet pressing pressure is 5-20 MPa, the tablet pressing holding time is 5-30 min, the secondary sintering temperature is 800-1000° C., the heating rate is 3-8° C. / min, and the calcination time is 3-10 h.

[0020] Compared with the prior art, this patent relates to a method for preparing a lanthanum-doped lithium borate coated LATP solid electrolyte, firstly, a soluble salt and a doping element are subjected to a coprecipitation reaction, then the mixture is sintered at a high temperature once, crushed, and then the obtained material is tableted, and lithium supplement / flux is added for secondary sintering, and finally a finished lithium aluminum titanium phosphate material is obtained. The beneficial technical effects of the present invention are as follows: (1) The present invention adopts a two-time sintering process, firstly a sintering process is carried out, and then the product is crushed to reduce the particle size of the material and improve the reaction activity, and then the gas in and between the particles is exhausted again during the tableting process, so that the prepared lithium aluminum titanium phosphate has lower interface resistance, higher density and thermal stability. During the high-temperature secondary sintering, the addition of lithium borate as a coating agent can melt into a glassy state at a lower temperature, coat the surface of the LATP electrolyte and enter the gap between the particles, which can effectively isolate the contact between the metal lithium and the solid electrolyte and improve the overall density. In addition, adding lithium borate can lower the synthesis temperature of the solid electrolyte and reduce energy consumption. At the same time, the lithium element in lithium borate can partially make up for the lithium loss in the sintering process, and it also acts as a flux and lithium supplement.

[0021] (2) The present invention replaces part of the tetravalent Ti by doping trivalent La elements, and achieves the effect of improving ionic conductivity by co-doping Al / La at multiple points, thereby increasing the interstitial Li+ content and thus increasing the conductivity.

[0022] (3) The present invention adopts wet mixing during the precursor mixing process, adding each ingredient into the dispersant and stirring at a constant temperature until the solvent evaporates to make the ingredients more evenly mixed, which is beneficial to the uniformity of the subsequent sintering product.

[0023] (4) Due to the poor interface contact between the solid electrolyte and lithium metal, lithium dendrites are easily generated in places with high current density, penetrating the electrolyte and causing battery short circuit. During the high-temperature secondary sintering of the present invention, adding lithium borate as a coating agent can effectively isolate the contact between metal lithium and the solid electrolyte, thereby avoiding the reaction between the two. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The SEM image of Example Sample 1 in Example 1 of the present invention is shown.

[0025] Figure 2 The XRD test data diagram of example sample 1 in example 1 of the present invention and comparative example sample 3 in comparative example 3 are shown. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the device proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings adopt a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structure, proportion, size, etc. illustrated by the accompanying drawings of this specification are only used to match the content disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effect that the present invention can produce and the purpose that can be achieved, should still fall within the scope of the technical content disclosed by the present invention.

[0027] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0028] Step S1, mixing a lithium source, an aluminum source, a lanthanum source, a titanium source, and a phosphorus source, putting the mixed ingredients into a dispersant, placing the mixture in a constant temperature water bath agitator, heating and stirring until completely dry, to obtain a mixed raw material.

[0029] In step S1: the lithium source, aluminum source, lanthanum source, titanium source and phosphorus source are in a molar ratio of Li:Al:La:Ti:P=(1+x+y):x:y:(2-xy):3. Among them, x+y=0.3-0.5. The molar ratio of lanthanum source to aluminum source is x:y=0.03-0.3:1. The total metal cation concentration is 1-3 mol / L.

[0030] In step S1: the lithium source is one or more of lithium-containing carbonates, hydroxides, and oxides. The aluminum source includes one or more of α-alumina, γ-alumina, and hydrated alumina. The phosphorus source includes one or more of diammonium phosphate, phosphoric acid, and lithium phosphate. The titanium source includes one or a mixture of titanium oxide and titanium chloride. The lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, or lanthanum nitrate. The dispersant includes one or a mixture of anhydrous ethanol or propanol. The stirring speed is 200-400 r / min, the water bath temperature is 50-85°C, and the stirring time is 2-6h.

[0031] Step S2: sintering the mixed raw materials at high temperature once in an air atmosphere to obtain a composite oxide.

[0032] In step S2, the primary sintering temperature is 600-900°C, the constant temperature time is 4-20 hours, and the heating rate is 2-5°C / min.

[0033] Step S3, crushing the composite oxide, then adding lithium borate, and mixing evenly to obtain a mixture, wherein the mass ratio of the lithium-containing compound to the composite oxide is 0.01-0.05:1.

[0034] In step S3: the crushing process includes: primary crushing by roller jaw crusher, and then crushing by air jet mill to obtain crushed composite oxide with a particle size of 1 to 5 um.

[0035] The lithium borate includes LiBO2 or Li2B4O7. The mixing method is a combination of one or more of ball milling, mechanical stirring, magnetic stirring or mortar grinding.

[0036] Step S4, pressing the mixed material into tablets, and then secondary sintering at high temperature in an air atmosphere to obtain a finished lithium aluminum titanium phosphate material.

[0037] In step S4, the tablet pressing pressure is 5-20 MPa, the tablet pressing holding time is 5-30 min, the secondary sintering temperature is 800-1000° C., the heating rate is 3-8° C. / min, and the calcination time is 3-10 h.

[0038] Embodiment 1:

[0039] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0040] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator with a stirring speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0041] Step S2, heating the mixed raw materials to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0042] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0043] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 1: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0044] Embodiment 2:

[0045] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0046] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.29:0.01:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a constant temperature water bath stirrer at 70°C, the stirring speed is 350 r / min, and the mixture is heated and stirred for 4 hours until it is completely dry to obtain a mixed raw material.

[0047] Step S2, heating the mixed raw materials to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0048] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0049] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 2: LiBO2@Li 1.3 Al 0.29 La 0.01 Ti 1.7 (PO4)3.

[0050] Embodiment 3:

[0051] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0052] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.25:0.05:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator, the stirring speed is 350 r / min, and the mixture is heated and stirred for 4 hours until it is completely dry to obtain a mixed raw material.

[0053] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0054] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0055] Step S4: The ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 3: LiBO2@Li 1.3 Al 0.25 La 0.05 Ti 1.7 (PO4)3.

[0056] Embodiment 4:

[0057] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0058] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator with a stirring speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0059] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0060] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is added with 1.2 g of LiBO2 and ball milled evenly.

[0061] Step S4: The ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950°C at a heating rate of 5°C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, i.e., Example Sample 4: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0062] Embodiment 5:

[0063] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0064] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator with a stirring speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0065] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0066] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is added with 4 g of LiBO2 and ball milled to make it uniform.

[0067] Step S4: The ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 5: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0068] Embodiment 6:

[0069] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0070] Step S1, lithium carbonate, γ-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator, the stirring speed is 350 r / min, and the mixture is heated and stirred for 4 hours until it is completely dry to obtain a mixed raw material.

[0071] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0072] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0073] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 6: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0074] Embodiment 7:

[0075] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0076] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and phosphoric acid are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a constant temperature water bath agitator at 70°C, the stirring speed is 350 r / min, and the mixture is heated and stirred for 4 hours until it is completely dry to obtain a mixed raw material.

[0077] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0078] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0079] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 7: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0080] Embodiment 8:

[0081] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0082] Step S1, lithium carbonate, α-alumina, lanthanum hydroxide, titanium oxide, and phosphoric acid are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator with a stirring speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0083] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0084] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0085] Step S4: The ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 8: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0086] Embodiment 9:

[0087] The preparation method of lanthanum-doped lithium borate coated LATP solid electrolyte comprises the following steps:

[0088] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the above mixed ingredients are put into anhydrous ethanol to prepare a mixed solution with a total metal cation concentration of 2 mol / L, and the mixed solution is placed in a 70°C constant temperature water bath agitator with a stirring speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0089] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0090] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide and 2.5 g of LiB4O7 are ball-milled to make them uniform.

[0091] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the insulation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 9: LiB4O7@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0092] Comparative Example 1:

[0093] The steps include:

[0094] Step S1, lithium carbonate, α-alumina, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:Ti:P=1.3:0.3:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a 70°C constant temperature water bath stirrer, the stirring speed is 350r / min, and heated and stirred for 4h until completely dry to obtain a mixed raw material.

[0095] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0096] Step S3, the composite oxide is primarily crushed by a double-roll jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm.

[0097] Step S4: The crushed composite oxide was pressed into tablets at 15 MPa for 15 min, and then the tablets were heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, the tablets were cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material, that is, comparative example sample 1: Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0098] Comparative Example 2:

[0099] Step S1, lithium carbonate, α-alumina, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:Ti:P=1.3:0.3:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a 70°C constant temperature water bath stirrer, the stirring speed is 350r / min, and heated and stirred for 4h until completely dry to obtain a mixed raw material.

[0100] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0101] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0102] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer, that is, comparative example sample 2: LiBO2@Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0103] Comparative Example 3:

[0104] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a 70°C constant temperature water bath stirrer, stirring at a speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0105] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0106] Step S3, the composite oxide is primarily crushed by a double-roll jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm.

[0107] Step S4: the crushed composite oxide was pressed into tablets at 15 MPa for 15 min, and then the tablets were heated to 950°C at a heating rate of 5°C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, the tablets were cooled to room temperature to obtain comparative example sample 3: Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0108] Comparative Example 4:

[0109] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a 70°C constant temperature water bath stirrer, stirring at a speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0110] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0111] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0112] Step S4: The ball-milled mixture was heated to 950°C at a heating rate of 5°C / min in an air atmosphere, and kept warm for 5 hours. After the end of the heat preservation, the mixture was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material having a lithium borate coating layer and doped with La, i.e., Comparative Example 4: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0113] Comparative Example 5:

[0114] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.2:0.1:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a constant temperature water bath stirrer at 70°C, stirring at a speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0115] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0116] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0117] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, comparative example sample 5:: LiBO2@Li 1.3 Al 0.2 La 0.1 Ti 1.7 (PO4)3.

[0118] Comparative Example 6:

[0119] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to the molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, the mixed ingredients are put into anhydrous ethanol, placed in a 70°C constant temperature water bath stirrer, stirring at a speed of 350 r / min, heated and stirred for 4 hours until completely dry, to obtain a mixed raw material.

[0120] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0121] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 8 g of LiBO2 is added and ball-milled to make it uniform.

[0122] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 6: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0123] Comparative Example 7:

[0124] Step S1, lithium carbonate, α-alumina, lanthanum oxide, titanium oxide, and ammonium dihydrogen phosphate are mixed according to a molar ratio of Li:Al:La:Ti:P=1.3:0.275:0.025:1.7:3, and the mixed ingredients are ball-milled to mix evenly to obtain a mixed raw material.

[0125] Step S2, heating the mixture to 850°C at a heating rate of 3°C / min in an air atmosphere, keeping the temperature for 10 hours, and cooling the temperature to room temperature after the end of the heating to obtain a composite oxide.

[0126] Step S3: The composite oxide is crushed by a roller jaw crusher, and then pulverized by a jet mill to obtain a pulverized composite oxide with a particle size of 2 μm. 100 g of the pulverized composite oxide is taken, and 2.5 g of LiBO2 is added and ball-milled evenly.

[0127] Step S4, the ball-milled mixture was pressed into a tablet at 15 MPa for 15 min, and then the tablet was heated to 950 ° C at a heating rate of 5 ° C / min in an air atmosphere, and kept warm for 5 h. After the end of the heat preservation, it was cooled to room temperature to obtain a lithium aluminum titanium phosphate solid electrolyte material with a lithium borate coating layer and La doped, that is, Example Sample 7: LiBO2@Li 1.3 Al 0.275 La 0.025 Ti 1.7 (PO4)3.

[0128] In this application, the density test and ion conductivity test are used for the examples and comparative examples, and the method is as follows:

[0129] 1. Density test: The samples obtained in the above embodiments and comparative examples were measured by the Archimedean drainage method using an electronic balance before and after drainage to determine the actual density of the samples, and then further calculated their relative density to indicate the degree of sintering densification of the samples.

[0130] 2. Ionic conductivity: The samples obtained in the above embodiments and comparative examples were placed in a tablet pressing mold and pressed into a disc with a diameter of 10 mm and a thickness of 1.0 mm by a tablet press at a pressure of 12 tons. Then, the discs were sprayed with gold on both sides, placed in a cylindrical mold, and connected to the electrodes of an electrochemical workstation for AC impedance testing. The working parameters of the electrochemical workstation are: the frequency range is 0.01 Hz to 100 KHz, and other appropriate parameters are selected to measure the AC impedance of the material. Based on the semicircle diameter of the commonly used impedance diagram, the room temperature lithium ion conductivity is obtained by calculation.

[0131] Result analysis:

[0132] Figure 1 The SEM image of Example Sample 1 in Example 1 of the present invention is shown. Figure 2 The XRD test data diagram of example sample 1 in example 1 of the present invention and comparative example sample 3 in comparative example 3 are shown.

[0133] according to Figure 1 Example sample 1: LiBO2@Li1.3Al0.275La0.025Ti1.7(PO4)3 has uniform particle size and small particles, which is convenient for use. Figure 2 When LiBO2 is not used, the sample of Comparative Example 3 generated contains the characteristic peak of TiO2, and the sintering temperature is low, which does not reach the temperature for generating pure phase LATP. Under the same temperature conditions, when LiBO2 is added to Example 1, the product obtained does not contain the characteristic peak of TiO2, and pure phase LATP appears. It is confirmed that the addition of LiBO2 has a fluxing effect, which can reduce the temperature for synthesizing pure phase LATP and reduce energy consumption.

[0134] Table 1 shows the specific implementation steps of various embodiments and comparative examples.

[0135] Table 2 shows the density and conductivity test data of the samples of Examples 1-9 and Comparative Examples 1-7. From Table 2, the relative density of 97.2% and the ionic conductivity of 8.7×10-4 of Example 1 are much higher than the relative density of 80.5% and the ionic conductivity of 0.56×10-4 of Comparative Example 1 without doping, coating, or tableting.

[0136] Example 1 is compared with Comparative Example 2. Comparative Example 2 is not La-doped. The ionic conductivity of Example 1 is higher than that of Comparative Example 2, which proves that doping is beneficial to improving the ionic conductivity of the LATP material.

[0137] Example 1 is compared with Comparative Example 3 and Comparative Example 4. The relative density of Example 1 is higher than the relative density of Comparative Example 3 and the relative density of Comparative Example 4. The addition of lithium borate in Example 1 can melt into a glassy state at a lower temperature, thereby entering the gaps between particles on the surface of the LATP electrolyte, improving the overall density, and then the tableting again exhausts the gas inside and between the particles, so that the prepared lithium aluminum titanium phosphate has a higher density, which proves that coating lithium borate and tableting help to improve the relative density of the LATP material.

[0138] Comparative Example 5 has less La doping, resulting in the ionic conductivity of Comparative Example 5 being lower than that of Example 1, Example 2 and Example 3. Comparative Example 6 adds too much lithium borate, so that the surface of LATP is completely covered with a layer of lithium borate, which is not conducive to the internal Li+ transfer of LATP, resulting in its compaction density and ionic conductivity being lower than those of Example 1. Comparative Example 7 uses solid-phase ball milling when mixing the precursor auxiliary materials in the first step. Compared with the solvent-assisted mixing of Example 1, solid-phase ball milling is difficult to mix evenly, so the final material ionic conductivity of Comparative Example 7 is lower than that of Example 1. In addition, Examples 6-9 confirm that the invention scheme has a certain universality and can be applied to a variety of materials to increase the scope of use.

[0139]

[0140]

[0141] Table 1

[0142]

[0143]

[0144] Table 2

[0145] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0146] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a lanthanum-doped lithium borate-coated LATP solid electrolyte, characterized in that: The steps include: Step S1, mixing a lithium source, an aluminum source, a lanthanum source, a titanium source, and a phosphorus source, putting the mixed ingredients into a dispersant, placing the mixture in a constant temperature water bath stirrer, heating and stirring until completely dry, to obtain a mixed raw material; Step S2, sintering the mixed raw materials once at a high temperature in an air atmosphere to obtain a composite oxide; Step S3, crushing the composite oxide, then adding lithium borate, and mixing evenly to obtain a mixture; wherein the mass ratio of the lithium-containing compound to the composite oxide is 0.01-0.05:1; Step S4, pressing the mixed material into tablets, and then secondary sintering at high temperature in an air atmosphere to obtain a finished lithium aluminum titanium phosphate material.

2. The method for preparing the lanthanum-doped lithium borate coated LATP solid electrolyte according to claim 1, characterized in that: In step S1: the lithium source, aluminum source, lanthanum source, titanium source and phosphorus source are in a molar ratio of Li:Al:La:Ti:P=(1+x+y):x:y:(2-xy):3; wherein x+y=0.3-0.5; the molar ratio of the lanthanum source to the aluminum source is x:y=0.03-0.3:1; and the total metal cation concentration is 1-3 mol / L.

3. The method for preparing the lanthanum-doped lithium borate coated LATP solid electrolyte according to claim 1, characterized in that: In step S1, the lithium source is one or more of lithium-containing carbonates, hydroxides, and oxides; the aluminum source includes one or more of α-alumina, γ-alumina, and hydrated alumina; the phosphorus source includes one or more of diammonium phosphate, phosphoric acid, and lithium phosphate; the titanium source includes one or a mixture of titanium oxide and titanium chloride; the lanthanum source includes one or more of lanthanum oxide, lanthanum hydroxide, or lanthanum nitrate; the dispersant includes one or a mixture of anhydrous ethanol or propanol; the stirring speed is 200-400 r / min, the water bath temperature is 50-85° C., and the stirring time is 2-6 h.

4. The method for preparing the lanthanum-doped lithium borate coated LATP solid electrolyte according to claim 1, characterized in that: In step S2, the primary sintering temperature is 600-900°C, the constant temperature time is 4-20 hours, and the heating rate is 2-5°C / min.

5. The method for preparing the lanthanum-doped lithium borate coated LATP solid electrolyte according to claim 1, characterized in that: In step S3: the crushing process includes: primary crushing by roller jaw crusher, and then crushing by jet mill to obtain crushed composite oxide with a particle size of 1 to 5 μm; The lithium borate includes LiBO2 or Li2B4O7; the mixing method is a combination of one or more of ball milling, mechanical stirring, magnetic stirring or mortar grinding.

6. The method for preparing the lanthanum-doped lithium borate coated LATP solid electrolyte according to claim 1, characterized in that: In step S4, the tablet pressing pressure is 5-20 MPa, the tablet pressing holding time is 5-30 min, the secondary sintering temperature is 800-1000° C., the heating rate is 3-8° C. / min, and the calcination time is 3-10 h.

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