Modified Lithium Titanium Aluminum Phosphate Solid Electrolyte, Its Preparation Method and Application

Abstract

The present invention provides a modified lithium titanium aluminum phosphate solid electrolyte, a preparation method thereof and an application. The solid electrolyte includes an inner layer and a coating layer coated on the surface of the inner layer. The inner layer is Li 1+ x Al x Ti 2‑x (PO4)3, and the coating layer is (In 0.5 Nb 0.5 ) y Ti 1‑y O2, where 0.1 ≤ x ≤ 0.5 and 0.4 ≤ y ≤ 0.8. The present invention uses indium, niobium, titanium composite oxide (In 0.5 Nb 0.5 ) y Ti 1‑y O2 as the coating layer to modify the inner layer of lithium titanium aluminum phosphate Li 1+x Al x Ti 2‑x (PO4)3, so as to reduce the holes and gaps of lithium titanium aluminum phosphate while stabilizing the lithium titanium aluminum phosphate material, improve the density and ionic conductivity of lithium titanium aluminum phosphate, and give full play to the electrochemical activity of lithium titanium aluminum phosphate, and can take into account good ionic conductivity, density and thermal stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular, to a modified lithium aluminum titanium phosphate solid electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] In order to thoroughly solve the problems of poor cycle performance and great safety hazards of traditional lithium-ion batteries, more and more researchers have begun to focus on the development and application of all-solid-state lithium-ion batteries. Traditional lithium-ion batteries use organic electrolytes with low ionic resistance as electrolytes. The flammable and easily leaky characteristics of organic electrolytes easily lead to safety problems. All-solid-state batteries using solid electrolytes with non-flammable characteristics can avoid these problems. Relatively speaking, compared with traditional liquid lithium-ion batteries, all-solid-state batteries are considered to be safer, and have longer cycle life, higher energy density, and fewer packaging requirements. It is expected to be widely used in large-scale power storage systems such as electric vehicles and electronic devices relying on its high energy density and good safety performance.

[0003] NASICON-type materials LM2(PO4)3 (L = Li, Na, K; M = Ge, Ti, Sn, Hf, Zr) have been widely studied because of their high ionic conductivity, and lithium aluminum titanium phosphate (Li 1+x Al x Ti 2-x (PO4)3, LATP) has received more extensive attention. Currently, the most widely used methods for preparing LATP solid electrolytes are sol-gel method, molten salt quenching method, water cooling method, and high-temperature solid-phase method. In the solid-phase method, Al2O3 is used as the aluminum source. In the preparation related to solution such as sol-gel or hydrothermal method, aluminum nitrate and the like are generally used as the aluminum source (S. Duluard et, al. Lithium conducting solid electrolyte Li 1.3 Al 0.3 Ti 1.7 (PO4)3 obtained via solution chemistry, journal of the European Ceramic society 33(6): 1145 - 1153.).

[0004] For a solid electrolyte to achieve conductivity, it depends on the migration of conductive ions. The faster the ion migration rate, the better the conductivity of the electrolyte. The tightness of the crystal arrangement inside the lithium-ion conductor has an important influence on the ion migration rate inside the conductor. Low ionic conductivity and low tightness are the main problems affecting the performance of LATP materials. Summary of the Invention

[0005] The main object of the present invention is to provide a modified lithium aluminum titanium phosphate solid electrolyte, a preparation method thereof, and an application, so as to solve the problems of low ionic conductivity, low density, and poor thermal stability of lithium aluminum titanium phosphate solid electrolytes in the prior art.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a modified lithium aluminum titanium phosphate solid electrolyte, which includes an inner layer and a coating layer coated on the surface of the inner layer. The inner layer is Li 1+x Al x Ti 2-x (PO4)3, and the coating layer is (In 0.5 Nb 0.5 ) y Ti 1-y O2, where 0.1 ≤ x ≤ 0.5 and 0.4 ≤ y ≤ 0.8.

[0007] According to another aspect of the present invention, there is provided a preparation method of the above-mentioned modified lithium aluminum titanium phosphate solid electrolyte, which includes the following steps: Step S1, respectively weighing a lithium source, an aluminum source, a first titanium source, and a phosphorus source, dispersing them in a first solvent to obtain a precursor dispersion liquid, and then sequentially performing first drying and first sintering to obtain a lithium aluminum titanium phosphate precursor; Step S2, respectively weighing an indium source, a niobium source, and a second titanium source, dispersing them in a second solvent to obtain a coating dispersion liquid; Step S3, adding the lithium aluminum titanium phosphate precursor to the coating dispersion liquid to obtain a mixed dispersion liquid, and then sequentially performing second drying and second sintering to obtain a modified lithium aluminum titanium phosphate solid electrolyte; wherein, both the first sintering and the second sintering are carried out in an air atmosphere.

[0008] Further, in Step S1, among the lithium source, the aluminum source, the first titanium source, and the phosphorus source, the molar ratio of the elements Li, Al, Ti, and P is (1 + x): x: (2 - x): 3, where 0.1 ≤ x ≤ 0.5; preferably, in Step S2, among the indium source, the niobium source, and the second titanium source, the molar ratio of the elements In, Nb, and Ti is 0.5y: 0.5y: (1 - y), where 0.4 ≤ y ≤ 0.8.

[0009] Further, in Step S3, the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid is (97 - 100): 1.

[0010] Further, in Step S1, the lithium source includes one or more of lithium oxide, lithium hydroxide, and lithium carbonate; preferably, the aluminum source includes one or more of aluminum oxide, aluminum hydroxide, and aluminum chloride; preferably, the first titanium source includes titanium oxide and / or titanium chloride; preferably, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0011] Further, in Step S2, the indium source includes indium nitrate, the niobium source includes niobium pentachloride, and the second titanium source includes titanium dioxide.

[0012] Furthermore, the first solvent is absolute ethanol, the second solvent is an absolute ethanol solution of citric acid, and the mass fraction of citric acid is 20-40%; preferably, the mass ratio of indium source to citric acid is (4-5):1.

[0013] Furthermore, in step S1, the temperature of the first drying is 60-100°C and the time is 4-8h; preferably, the temperature of the first sintering is 300-500°C and the time is 2-6h; more preferably, before the first drying, a step of ball-milling the precursor dispersion is further included, the rotation speed of the ball-milling is 200-500 rpm, and the time is 2-10h.

[0014] Furthermore, in step S3, the temperature of the second drying is 100-120°C and the time is 2-3h; preferably, the temperature of the second sintering is 850-950°C and the time is 8-12h; more preferably, before the second drying, a step of stirring the mixed dispersion is further included, the temperature of the stirring is 100-160°C, and the time is 4-6h.

[0015] According to another aspect of the present invention, there is provided an application of the modified lithium titanium aluminum phosphate solid electrolyte of the present invention in a lithium ion solid battery.

[0016] Applying the technical solution of the present invention, using lithium titanium aluminum phosphate Li 1+x Al x Ti 2-x (PO4)3 as the inner layer and using indium, niobium, titanium composite oxide (In 0.5 Nb 0.5 ) y Ti 1-y O2 as the coating layer to modify lithium titanium aluminum phosphate, so as to reduce the holes and gaps of lithium titanium aluminum phosphate while stabilizing the lithium titanium aluminum phosphate material, improve the density and ionic conductivity of lithium titanium aluminum phosphate, and give full play to the electrochemical activity of lithium titanium aluminum phosphate. At the same time, it can also reduce the activation energy of the modified lithium titanium aluminum phosphate electrolyte, which is more conducive to the transmission of lithium ions and improve the comprehensive performance of the material. In addition, when the modified lithium titanium aluminum phosphate solid electrolyte of the present invention is applied to a lithium ion battery such as ternary materials, a dense oxide can be generated on the surface of the ternary materials, so that it can effectively coat the surface of the ternary materials, the formed coating layer is not easy to fall off, the differential scanning calorimetry peak temperature is increased, thereby increasing the thermal stability of the ternary materials and improving the safety performance of the ternary materials. Specific Embodiments

[0017] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] It should be noted that in the claims and the specification of the present invention, the terms "first" and "second" are only used to distinguish similar operations in different steps, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0019] It should be noted that unless otherwise specified, the raw materials of the present invention can be conveniently obtained from the market.

[0020] As described in the background art of the present invention, in the prior art, there are problems such as low ionic conductivity, low density, and poor thermal stability of lithium aluminum titanium phosphate solid electrolyte, especially the problem that ionic conductivity, density, and thermal stability cannot be taken into account at the same time. To solve the above problems, in a typical embodiment of the present invention, a modified lithium aluminum titanium phosphate solid electrolyte is provided, which includes an inner layer and a coating layer coated on the surface of the inner layer. The inner layer is Li 1+x Al x Ti 2-x (PO4)3, and the coating layer is (In 0.5 Nb 0.5 ) y Ti 1-y O2, where 0.1 ≤ x ≤ 0.5 and 0.4 ≤ y ≤ 0.8.

[0021] The present invention uses indium, niobium, titanium composite oxide (In 0.5 Nb 0.5 ) y Ti 1-y O2 as the coating layer to modify the inner layer of lithium aluminum titanium phosphate Li 1+x Al x Ti 2-x (PO4)3. While ensuring the stability of lithium aluminum titanium phosphate, it reduces the holes and gaps of lithium aluminum titanium phosphate, improves the density and ionic conductivity of lithium aluminum titanium phosphate, fully exerts the electrochemical activity of lithium aluminum titanium phosphate, and can also effectively increase the differential scanning calorimetry peak temperature and improve the safety performance such as the thermal stability of the material. By optimizing the element ratio of LATP and the coating layer within the above range, the LATP material can be further stabilized, and the hole and gap defects of LATP can be further reduced, thereby further improving the density and ionic conductivity of the material and achieving better thermal stability.

[0022] In another typical embodiment of the present invention, a method for preparing the modified lithium titanium aluminum phosphate solid electrolyte of the present invention is further provided, including the following steps: Step S1, respectively weigh a lithium source, an aluminum source, a first titanium source, and a phosphorus source, disperse them in a first solvent to obtain a precursor dispersion liquid, and then successively perform first drying and first sintering to obtain a lithium titanium aluminum phosphate precursor; Step S2, respectively weigh an indium source, a niobium source, and a second titanium source, disperse them in a second solvent to obtain a coating dispersion liquid; Step S3, add the lithium titanium aluminum phosphate precursor to the coating dispersion liquid to obtain a mixed dispersion liquid, and then successively perform second drying and second sintering to obtain the modified lithium titanium aluminum phosphate solid electrolyte; wherein, both the first sintering and the second sintering are carried out in an air atmosphere.

[0023] In the present invention, first, the lithium source, the aluminum source, the first titanium source, and the phosphorus source are dispersed in the first solvent. After mixing them evenly, first drying and first sintering are successively carried out to volatilize and remove the first solvent to obtain the lithium titanium aluminum phosphate precursor; then, the indium source, the niobium source, and the second titanium source are dispersed in the second solvent. After mixing them evenly, the coating dispersion liquid is obtained for standby; finally, the lithium titanium aluminum phosphate precursor is added to the coating dispersion liquid. After mixing them evenly, second drying and second sintering are successively carried out, so that the lithium titanium aluminum phosphate precursor and the indium source, the niobium source, and the second titanium source form a molecular-level mixture, realizing the introduction of the indium, niobium, and titanium composite oxide coating layer, and obtaining the modified lithium titanium aluminum phosphate solid electrolyte with an indium, niobium, and titanium composite oxide coating layer on the surface. Thus, while stabilizing the lithium titanium aluminum phosphate material, the pores and gaps of the lithium titanium aluminum phosphate are reduced, and the density and ionic conductivity of the lithium titanium aluminum phosphate are improved. At the same time, during the second air sintering, since the material reacts with air when forming the coating layer, the further heat release can also reduce the activation energy of the modified lithium titanium aluminum phosphate electrolyte sheet, which is more conducive to the transport of lithium ions and improves the comprehensive performance of the material. In addition, after applying it to a lithium-ion battery such as a ternary material battery, it can also effectively increase the differential scanning calorimetry peak temperature, thereby increasing the thermal stability of the ternary material and improving the safety performance of the ternary material, and thus simultaneously solving the problems of low ionic conductivity, low density, and poor thermal stability of the lithium titanium aluminum phosphate solid electrolyte in the prior art.

[0024] To further improve the ionic conductivity of the modified LATP material, in a preferred embodiment, in step S1, among the lithium source, aluminum source, first titanium source, and phosphorus source, the elemental molar ratio of Li, Al, Ti, and P is (1 + x):x:(2 - x):3, where 0.1 ≤ x ≤ 0.5; preferably, in step S2, among the indium source, niobium source, and second titanium source, the elemental molar ratio of In, Nb, and Ti is 0.5y:0.5y:(1 - y), where 0.4 ≤ y ≤ 0.8. By optimizing the proportion of metal element raw materials of LATP and the coating layer within the above range, the present invention can further stabilize the lithium aluminum titanium phosphate material, and further reduce the pore and gap defects of the lithium aluminum titanium phosphate during the subsequent coating of the second sintering, thereby further improving the density and ionic conductivity of the material.

[0025] When the coating layer is too thin, it cannot fully play the role of improving the density and ionic conductivity of lithium aluminum titanium phosphate. When it is too thick, it cannot further improve the material performance, but instead causes waste of raw materials. Therefore, to further improve the ionic conductivity of the modified LATP solid electrolyte, in a preferred embodiment, in step S3, the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid is (97 - 100):1. The mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid includes but is not limited to the above range. When within the above range, it can achieve greater improvement in comprehensive properties such as density, ionic conductivity, thermal stability, and activation energy at a lower cost.

[0026] For the raw materials of the lithium aluminum titanium phosphate precursor, conventional materials in the art can be used. For the purpose of further improving the stability of the lithium aluminum titanium phosphate precursor and at the same time giving full play to the electrochemical activity of the lithium aluminum titanium phosphate, in a preferred embodiment, in step S1, the lithium source includes one or more of lithium oxide, lithium hydroxide, and lithium carbonate; preferably, the aluminum source includes one or more of aluminum oxide, aluminum hydroxide, and aluminum chloride; preferably, the first titanium source includes titanium oxide and / or titanium chloride; preferably, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0027] In a preferred embodiment, in step S2, the indium source includes indium nitrate, the niobium source includes niobium pentachloride, and the second titanium source includes titanium dioxide. The above raw materials are more suitable for the coating of the lithium aluminum titanium phosphate precursor of the present invention. They can further stabilize the lithium aluminum titanium phosphate material while further reducing the pores and gaps of the lithium aluminum titanium phosphate, and better improve the density and ionic conductivity of the lithium aluminum titanium phosphate.

[0028] The present invention places no restrictions on the types of solvents used, as long as they can achieve good dissolution of each raw material. In a preferred embodiment, the first solvent is absolute ethanol, which facilitates the smooth removal of the first solvent during the first drying and first sintering processes, reducing the subsequent coating burden. The second solvent is an absolute ethanol solution of citric acid, and the mass fraction of citric acid is 20 - 40%. As an acidic complexing agent, citric acid can be ionized and chelated with indium, niobium, and titanium metal cations during the dispersion process in step S2, making their dispersion more uniform. When the mass ratio of the above metal cations to citric acid is too low, the acidity of the solution will be too strong, resulting in side reactions. When it is too high, step S2 will not be completed fully. Therefore, preferably, the mass ratio of the indium source to citric acid is (4 - 5):1.

[0029] To fully remove the volatile components in the LATP material and facilitate the smooth formation of the LATP structure during the subsequent sintering process, in a preferred embodiment, in step S1, the temperature of the first drying is 60 - 100°C, and the time is 4 - 8 h; preferably, the temperature of the first sintering is 300 - 500°C, and the time is 2 - 6 h. The above process conditions can further improve the stability of lithium titanium aluminum phosphate and facilitate the more fully exertion of the electrochemical activity of lithium titanium aluminum phosphate. For the purpose of further improving the mixing uniformity of the LATP raw materials, more preferably, before the first drying, there is also a step of ball-milling the precursor dispersion liquid. The rotation speed of the ball-milling is 200 - 500 rpm, and the time is 2 - 10 h.

[0030] In a preferred embodiment, in step S3, the temperature of the second drying is 100 - 120°C, and the time is 2 - 3 h; preferably, the temperature of the second sintering is 850 - 950°C, and the time is 8 - 12 h, so as to more quickly and fully achieve the coating of the indium, niobium, and titanium composite oxide on the lithium titanium aluminum phosphate precursor. To make the components of the lithium titanium aluminum phosphate precursor and the coating dispersion liquid more uniformly mixed before the second sintering, more preferably, before the second drying, there is also a step of stirring the mixed dispersion liquid. The temperature of the stirring is 100 - 160°C, and the time is 4 - 6 h.

[0031] In another typical embodiment of the present invention, there is also provided the application of the modified lithium titanium aluminum phosphate solid electrolyte of the present invention in a lithium-ion solid battery, such as its application in a ternary battery. During use, in addition to having good electrochemical performance, it can also effectively increase the differential scanning calorimetry peak temperature, thereby enhancing the safety performance of the ternary battery.

[0032] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0033] Example 1

[0034] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0035] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium carbonate, aluminum oxide, titanium oxide, and ammonium dihydrogen phosphate according to the elemental molar ratio of Li:Al:Ti:P of 1.1:0.1:1.9:3, disperse them in absolute ethanol, ball-mill at 200 rpm for 2 h, dry at 60 °C for 4 h, and pre-calcine in an air atmosphere at 300 °C for 2 h to obtain a lithium aluminum titanium phosphate precursor;

[0036] S2. Weigh indium nitrate, niobium pentachloride, and titanium dioxide according to the elemental molar ratio of In:Nb:Ti of 0.2:0.2:0.6, dissolve and disperse them in an absolute ethanol solution of citric acid with a mass fraction of 20%, to form a coating dispersion liquid, where the mass ratio of indium nitrate to citric acid is 4:1;

[0037] S3. Add the lithium aluminum titanium phosphate precursor in S1 to the coating liquid in S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating liquid is 97:1, stir at 100 °C for 4 h to obtain a gel, dry the gel in an oven at 100 °C for 2 h, grind to obtain a powder, and calcine the powder at 850 °C for 8 h at a constant temperature in an air atmosphere under normal pressure to obtain an (In 0.5 Nb 0.5 ) 0.4 Ti 0.6 O2-coated modified Li 1.1 Al 0.1 Ti 1.9 (PO4)3 solid electrolyte material.

[0038] Example 2

[0039] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0040] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium hydroxide, aluminum chloride, titanium oxide, and ammonium dihydrogen phosphate according to the elemental molar ratio of Li:Al:Ti:P of 1.2:0.2:1.8:3, disperse them in absolute ethanol, ball-mill at 250 rpm for 4 h, dry at 70 °C for 5 h, and pre-calcine in an air atmosphere at 350 °C for 3 h to obtain a lithium aluminum titanium phosphate precursor;

[0041] S2. Weigh indium nitrate, niobium pentachloride, and titanium dioxide according to the elemental molar ratio of In:Nb:Ti of 0.25:0.25:0.5, dissolve and disperse them in an absolute ethanol solution of citric acid with a mass fraction of 25%, to form a coating dispersion liquid, where the mass ratio of indium nitrate to citric acid is 4.2:1;

[0042] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 97.5:1, stir at 110 °C for 4.5 h to obtain a gel, dry the gel in an oven at 110 °C for 2.5 h, grind to obtain a powder, and calcine the powder at 870 °C for 10 h under normal pressure in an air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.5 Ti 0.5 O2-coated and modified Li 1.2 Al 0.2 Ti 1.8 (PO4)3 solid electrolyte material.

[0043] Example 3

[0044] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0045] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid according to the element molar ratio of Li:Al:Ti:P of 1.3:0.3:1.7:3, disperse them in absolute ethanol, ball mill at 350 rpm for 6 h, dry at 80 °C for 6 h, and pre-calcine at 400 °C for 4 h in an air atmosphere to obtain the lithium aluminum titanium phosphate precursor;

[0046] S2. Weigh indium nitrate, niobium pentachloride, and titanium dioxide according to the element molar ratio of In:Nb:Ti of 0.3:0.3:0.4, and dissolve and disperse them in an absolute ethanol solution of citric acid with a mass fraction of 30% to form a coating dispersion, where the mass ratio of indium nitrate to citric acid is 4.5:1;

[0047] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 98.5:1, stir at 130 °C for 5 h to obtain a gel, dry the gel in an oven at 110 °C for 2.5 h, grind to obtain a powder, and calcine the powder at 900 °C for 10 h under normal pressure in an air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated and modified Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte material.

[0048] Example 4

[0049] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0050] S1. Preparation of lithium aluminum titanium phosphate precursor: Lithium carbonate, aluminum chloride, titanium chloride, and diammonium hydrogen phosphate were weighed respectively according to the molar ratio of Li:Al:Ti:P of 1.4:0.4:1.6:3, and dispersed in absolute ethanol. Ball milling was carried out at 400 rpm for 7 h, followed by drying at 80 °C for 4 h and pre-calcination in air atmosphere at 450 °C for 3 h to obtain the lithium aluminum titanium phosphate precursor;

[0051] S2. According to the molar ratio of In:Nb:Ti of 0.35:0.35:0.3, indium nitrate, niobium pentachloride, and titanium dioxide were weighed respectively, and dissolved and dispersed in an absolute ethanol solution of citric acid with a mass fraction of 25% to form a coating dispersion liquid, where the mass ratio of indium nitrate to citric acid is 5:1;

[0052] S3. The lithium aluminum titanium phosphate precursor in S1 was added to the coating dispersion liquid in S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid is 98:1. Stirring was carried out at 150 °C for 5 h to obtain a gel. The gel was dried in an oven at 105 °C for 2 h and ground to obtain a powder. The powder was calcined at 950 °C for 8 h under normal pressure in air atmosphere to obtain the (In 0.5 Nb 0.5 ) 0.7 Ti 0.3 O2-coated and modified Li 1.4 Al 0.4 Ti 1.6 (PO4)3 solid electrolyte material.

[0053] Example 5

[0054] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0055] S1. Preparation of lithium aluminum titanium phosphate precursor: Lithium carbonate, aluminum hydroxide, titanium chloride, and phosphoric acid were weighed respectively according to the molar ratio of Li:Al:Ti:P of 1.2:0.2:1.8:3, and dispersed in absolute ethanol. Ball milling was carried out at 450 rpm for 9 h, followed by drying at 80 °C for 6 h and pre-calcination in air atmosphere at 350 °C for 4 h to obtain the lithium aluminum titanium phosphate precursor;

[0056] S2. According to the molar ratio of In:Nb:Ti of 0.2:0.2:0.6, indium nitrate, niobium pentachloride, and titanium dioxide were weighed respectively, and dissolved and dispersed in an absolute ethanol solution of citric acid with a mass fraction of 40% to form a coating dispersion liquid, where the mass ratio of indium nitrate to citric acid is 4.7:1;

[0057] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2. The mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 97.7:1. Stir at 140 °C for 5 h to obtain a gel. Dry the gel in an oven at 100 °C for 2 h, grind to obtain a powder, and calcine the powder at 850 °C for 8 h under normal pressure in an air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.4 Ti 0.6 O2-coated and modified Li 1.2 Al 0.2 Ti 1.8 (PO4)3 solid electrolyte material.

[0058] Example 6

[0059] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0060] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium oxide, aluminum chloride, titanium chloride, and diammonium hydrogen phosphate according to the elemental molar ratio of Li:Al:Ti:P of 1.5:0.5:1.5:3, and disperse them in anhydrous ethanol. Ball mill at 500 rpm for 10 h, dry at 100 °C for 8 h, and pre-calcine at 500 °C for 6 h in an air atmosphere to obtain the lithium aluminum titanium phosphate precursor;

[0061] S2. Weigh indium nitrate, niobium pentachloride, and titanium dioxide according to the elemental molar ratio of In:Nb:Ti of 0.4:0.4:0.2, and dissolve and disperse them in an anhydrous ethanol solution of citric acid with a mass fraction of 40%. The mass ratio of indium nitrate to citric acid is 5:1 to form a coating dispersion;

[0062] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2. The mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 100:1. Stir at 160 °C for 6 h to obtain a gel. Dry the gel in an oven at 120 °C for 3 h, grind to obtain a powder, and calcine the powder at 950 °C for 12 h under normal pressure in an air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.8 Ti 0.2 O2-coated and modified Li 1.5 Al 0.5 Ti 1.5 (PO4)3 solid electrolyte material.

[0063] Example 7

[0064] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0065] S1. Preparation of lithium aluminum titanium phosphate precursor: Lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid were weighed respectively according to the molar ratio of Li:Al:Ti:P of 1.3:0.3:1.7:3, and dispersed in absolute ethanol. Ball milling was carried out at 350 rpm for 6 h, drying was carried out at 80 °C for 6 h, and pre-calcination was carried out at 400 °C in air atmosphere for 4 h to obtain the lithium aluminum titanium phosphate precursor;

[0066] S2. According to the molar ratio of In:Nb:Ti of 0.3:0.3:0.4, indium nitrate, niobium pentachloride, and titanium dioxide were weighed respectively, and dissolved and dispersed in an absolute ethanol solution of citric acid with a mass fraction of 30% to form a coating dispersion liquid, in which the mass ratio of indium nitrate to citric acid was 4.5:1;

[0067] S3. The lithium aluminum titanium phosphate precursor in S1 was added to the coating dispersion liquid in S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid was 95:1. Stirring was carried out at 130 °C for 5 h to obtain a gel. The gel was dried in an oven at 110 °C for 2.5 h and ground to obtain a powder. The powder was calcined at 900 °C for 10 h under normal pressure in air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated and modified Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte material.

[0068] Example 8

[0069] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0070] S1. Preparation of lithium aluminum titanium phosphate precursor: Lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid were weighed respectively according to the molar ratio of Li:Al:Ti:P of 1.3:0.3:1.7:3, and dispersed in absolute ethanol. Ball milling was carried out at 350 rpm for 6 h, drying was carried out at 80 °C for 6 h, and pre-calcination was carried out at 400 °C in air atmosphere for 4 h to obtain the lithium aluminum titanium phosphate precursor;

[0071] S2. According to the molar ratio of In:Nb:Ti of 0.3:0.3:0.4, indium nitrate, niobium pentachloride, and titanium dioxide were weighed respectively, and dissolved and dispersed in an absolute ethanol solution of citric acid with a mass fraction of 30% to form a coating dispersion liquid, in which the mass ratio of indium nitrate to citric acid was 4.5:1;

[0072] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2. The mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 105:1. Stir at 130 °C for 5 h to obtain a gel. Dry the gel in an oven at 110 °C for 2.5 h, grind to obtain a powder, and calcine the powder at 900 °C for 10 h under atmospheric pressure in an air atmosphere to obtain (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated and modified Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte material.

[0073] Example 9

[0074] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0075] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid according to the molar ratio of elements Li:Al:Ti:P of 1.05:0.05:1.95:3, disperse them in absolute ethanol, ball mill at 150 rpm for 1 h, dry at 50 °C for 3 h, and pre-calcine at 250 °C for 1 h in an air atmosphere to obtain the lithium aluminum titanium phosphate precursor;

[0076] S2. Weigh indium nitrate, niobium pentachloride, and titanium dioxide according to the molar ratio of elements In:Nb:Ti of 0.15:0.15:0.7, dissolve and disperse them in an absolute ethanol solution of citric acid with a mass fraction of 15% to form a coating dispersion, where the mass ratio of indium nitrate to citric acid is 3.5:1;

[0077] S3. Add the lithium aluminum titanium phosphate precursor of S1 to the coating dispersion of S2. The mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion is 95:1. Stir at 90 °C for 3 h to obtain a gel. Dry the gel in an oven at 90 °C for 1.5 h, grind to obtain a powder, and calcine the powder at 800 °C for 7 h under atmospheric pressure in an air atmosphere to obtain less (In 0.5 Nb 0.5 ) 0.3 Ti 0.7 O2-coated and modified Li 1.05 Al 0.05 Ti 1.95 (PO4)3 solid electrolyte material.

[0078] Example 10

[0079] A preparation method of a modified lithium aluminum titanium phosphate solid electrolyte, comprising the following steps:

[0080] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid respectively according to the molar ratio of Li:Al:Ti:P being 1.6:0.6:1.4:3, disperse them in anhydrous ethanol, ball-mill at 600 rpm for 12 h, dry at 120 °C for 10 h, and pre-calcine in an air atmosphere at 600 °C for 7 h to obtain the lithium aluminum titanium phosphate precursor;

[0081] S2. According to the molar ratio of In:Nb:Ti being 0.45:0.45:0.1, weigh indium nitrate, niobium pentachloride, and titanium dioxide respectively, and dissolve and disperse them in an anhydrous ethanol solution of citric acid with a mass fraction of 45% to form a coating dispersion liquid, where the mass ratio of indium nitrate to citric acid is 5.5:1;

[0082] S3. Add the lithium aluminum titanium phosphate precursor in S1 to the coating dispersion liquid in S2, where the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid is 95:1, stir at 170 °C for 7 h to obtain a gel, dry the gel in an oven at 130 °C for 3.5 h, grind to obtain a powder, and calcine the powder at 1000 °C for 13 h at a constant temperature in an air atmosphere under normal pressure to obtain a (In 0.5 Nb 0.5 ) 0.9 Ti 0.1 O2-coated and modified Li 1.6 Al 0.6 Ti 1.4 (PO4)3 solid electrolyte material.

[0083] Comparative Example 1

[0084] A preparation method of a lithium aluminum titanium phosphate solid electrolyte includes the following steps:

[0085] S1. Preparation of lithium aluminum titanium phosphate precursor: Weigh lithium hydroxide, lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid respectively according to the molar ratio of Li:Al:Ti:P being 1.3:0.3:1.7:3, disperse them in anhydrous ethanol, ball-mill at 350 rpm for 6 h, dry at 80 °C for 6 h, and pre-calcine in an air atmosphere at 400 °C for 4 h to obtain the lithium aluminum titanium phosphate precursor;

[0086] S2. Grind the lithium aluminum titanium phosphate precursor in S1 to obtain a powder, and calcine the powder at 900 °C for 10 h at a constant temperature in an air atmosphere under normal pressure to obtain Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte material.

[0087] Comparative Example 2

[0088] A preparation method of a lithium aluminum titanium phosphate solid electrolyte includes the following steps:

[0089] S1. Preparation of lithium aluminum titanium phosphate precursor: Lithium oxide, aluminum chloride, titanium chloride, and phosphoric acid were weighed respectively according to the molar ratio of Li:Al:Ti:P of 1.3:0.3:1.7:3, and dispersed in absolute ethanol. Ball milling was carried out at 350 rpm for 6 h, drying was carried out at 80 °C for 6 h, and pre-calcination was carried out at 400 °C for 4 h in an air atmosphere to obtain the lithium aluminum titanium phosphate precursor;

[0090] S2. The lithium aluminum titanium phosphate precursor obtained in S1 was dissolved and dispersed in an absolute ethanol solution of citric acid with a mass fraction of 30%, and a mixed solution was formed. Stirring was carried out at 130 °C for 5 h to obtain a gel. The gel was dried in an oven at 110 °C for 2.5 h and ground to obtain a powder. The powder was calcined at 900 °C for 10 h at a constant temperature in an air atmosphere under normal pressure to obtain the Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte material.

[0091] The solid electrolytes in Examples 1 to 10 and Comparative Examples 1 to 2 were tested, and the results are shown in Table 1.

[0092] It should be noted that in the examples and comparative examples, the Archimedes drainage method was used, and the mass before and after was measured with an electronic balance to determine the actual density of the sample, so as to calculate the relative density. The solid electrolyte material was made into a sample wafer to be measured. Using an electrochemical workstation, the AC impedance at different response frequencies was recorded, and different electrode processes with different reaction time constants were analyzed. The ionic conductivity of the material was obtained through fitting, analysis, and calculation. The peak temperature of differential scanning calorimetry was tested for the delithiated cathode from room temperature to 400 °C, with a heating rate of 10 °C / min, in a compressed air atmosphere.

[0093] Table 1

[0094]

[0095]

[0096] As can be seen from the above, compared with the comparative examples, each example of the present invention can take into account good ionic conductivity, relative density, and thermal stability. The relative density of the modified LATP material prepared in Example 3 is 96.63%, the ionic conductivity is 3.32×10 -4 S / cm, the peak temperature of differential scanning calorimetry is 222.1 °C, and the activation energy is only 0.28 ev, which is significantly better than the uncoated and modified LATP materials in Comparative Example 1 and Comparative Example 2. It can be seen that the examples of the present invention use indium, niobium, titanium composite oxide (In 0.5 Nb 0.5 ) y Ti 1-y O2 as a coating layer for the inner layer of lithium aluminum titanium phosphate Li 1+x Al xTi 2-x (PO4)3 is modified to reduce the pores and gaps of lithium titanium aluminum phosphate while ensuring its stability, improve the density and ionic conductivity of lithium titanium aluminum phosphate, fully exert its electrochemical activity, and effectively increase the peak temperature of differential scanning calorimetry and improve the safety performance such as the thermal stability of the material.

[0097] In addition, it can be seen that in Example 7, too little (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated modified LATP material is used. In Example 8, too much (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated modified LATP material is used. The element ratios and process parameters of Examples 9 and 10 are outside the preferred scope of the present invention, and the obtained modified LATP has poor performance, indicating that (In 0.5 Nb 0.5 ) 0.6 Ti 0.4 O2-coated LATP can significantly improve the comprehensive properties such as density, ionic conductivity, peak temperature of differential scanning calorimetry (thermal stability), and activation energy only within the ranges of element ratio, coating ratio, and process parameters of this solution.

[0098] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modified lithium titanium aluminum phosphate solid electrolyte, characterized in that, The modified lithium titanium aluminum phosphate solid electrolyte includes an inner layer and a coating layer coated on the surface of the inner layer. The inner layer is Li 1+x Al x Ti 2-x (PO4)3, and the coating layer is (In 0.5 Nb 0.5 ) y Ti 1−y O2, where 0.1 ≤ x ≤ 0.5 and 0.4 ≤ y ≤ 0.

8.

2. The preparation method of the modified lithium titanium aluminum phosphate solid electrolyte according to claim 1, characterized in that, It includes the following steps: Step S1: Weigh a lithium source, an aluminum source, a first titanium source, and a phosphorus source respectively, disperse them in a first solvent to obtain a precursor dispersion liquid, and then perform first drying and first sintering in sequence to obtain a lithium aluminum titanium phosphate precursor; Step S2: Weigh an indium source, a niobium source, and a second titanium source respectively, disperse them in a second solvent to obtain a coating dispersion liquid; Step S3: Add the lithium aluminum titanium phosphate precursor to the coating dispersion liquid to obtain a mixed dispersion liquid, and then perform second drying and second sintering in sequence to obtain the modified lithium aluminum titanium phosphate solid electrolyte; Among them, both the first sintering and the second sintering are carried out in an air atmosphere.

3. The preparation method according to claim 2, characterized in that, In step S1, among the lithium source, the aluminum source, the first titanium source, and the phosphorus source, the elemental molar ratio of Li, Al, Ti, and P is (1 + x): x: (2 - x): 3, where 0.1 ≤ x ≤ 0.

5.

4. The preparation method according to claim 3, characterized in that, In step S2, among the indium source, the niobium source, and the second titanium source, the elemental molar ratio of In, Nb, and Ti is 0.5y: 0.5y: (1 - y), where 0.4 ≤ y ≤ 0.

8.

5. The preparation method according to any one of claims 2 to 4, characterized in that, In step S3, the mass ratio of the lithium aluminum titanium phosphate precursor to the coating dispersion liquid is (97 - 100):

1.

6. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The lithium source includes one or more of lithium oxide, lithium hydroxide, and lithium carbonate.

7. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The aluminum source includes one or more of aluminum oxide, aluminum hydroxide, and aluminum chloride.

8. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The first titanium source includes titanium oxide and / or titanium chloride.

9. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

10. The preparation method according to any one of claims 2 to 4, characterized in that, In step S2, the indium source includes indium nitrate, the niobium source includes niobium pentachloride, and the second titanium source includes titanium dioxide.

11. The preparation method according to any one of claims 2 to 4, characterized in that, The first solvent is anhydrous ethanol, the second solvent is an anhydrous ethanol solution of citric acid, and the mass fraction of citric acid is 20 - 40%.

12. The preparation method according to claim 11, characterized in that, The mass ratio of the indium source to citric acid is (4 - 5):

1.

13. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The temperature of the first drying is 60 - 100 °C, and the time is 4 - 8 h.

14. The preparation method according to any one of claims 2 to 4, characterized in that, In step S1, The temperature of the first sintering is 300 - 500 °C, and the time is 2 - 6 h.

15. The preparation method according to any one of claims 2 to 4, characterized in that In step S1, Before the first drying, it further includes a step of ball-milling the precursor dispersion liquid, the rotation speed of the ball-milling is 200 - 500 rpm, and the time is 2 - 10 h.

16. The preparation method according to any one of claims 2 to 4, characterized in that, In step S3, The temperature of the second drying is 100 - 120 °C, and the time is 2 - 3 h.

17. The preparation method according to any one of claims 2 to 4, characterized in that, In step S3, The temperature of the second sintering is 850 - 950 °C, and the time is 8 - 12 h.

18. The preparation method according to any one of claims 2 to 4, characterized in that, In step S3, Before the second drying, it further includes a step of stirring the mixed dispersion liquid, the temperature of the stirring is 100 - 160 °C, and the time is 4 - 6 h.

19. Application of the modified lithium aluminum titanium phosphate solid electrolyte according to claim 1 in a lithium-ion solid battery.

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