Modified lithium titanium aluminum phosphate material, preparation method, cathode material and lithium-ion solid-state battery

Abstract

The present invention provides a modified lithium titanium aluminum phosphate material, a preparation method thereof, a cathode material and a lithium ion solid state battery. The structural formula of the modified lithium titanium aluminum phosphate material is Li x Al y Ti z B a N b (PO4)3, wherein 1.3 ≤ x ≤ 1.5, 0.3 ≤ y ≤ 0.5, 1.5 ≤ z ≤ 1.7, 0.02 ≤ a ≤ 0.05, 0.01 ≤ b ≤ 0.03. The modified lithium titanium aluminum phosphate material prepared by the present invention exhibits excellent electrochemical performance. When it is used as a coating material, the cathode material has a high tap density and excellent thermal stability.

Description

Technical Field

[0001] The present invention relates to the field of solid electrolytes, and more particularly to a modified lithium aluminum titanium phosphate material and a preparation method thereof, a cathode material, and a lithium ion solid state battery. Background Art

[0002] NASICON-type phosphate compounds have good structural stability and high ionic conductivity, enabling lithium ions or sodium ions to be quickly inserted and extracted in the crystal. These excellent physical and electrochemical properties have led to extensive research in the fields of lithium ion and sodium ion energy storage. Among them, lithium aluminum titanium phosphate (LATP) materials have been widely used in the field of lithium ion batteries due to their high ionic conductivity.

[0003] Nowadays, ternary layered materials have gradually become a popular research object for high-capacity cathode materials in lithium batteries. With the change of the component content of ternary materials, their physical and electrochemical properties are different. For example, as the Ni content in the active material system increases, the specific capacity also increases, but the thermal stability and cycle stability decrease. In order to improve the various properties of ternary layered materials as cathode materials for lithium ion batteries, selecting different ratios of ternary cathode materials and optimizing their properties are the main research directions of current scientific researchers. In the prior art, element doping or substitution is usually carried out in ternary cathode materials to effectively improve the electrochemical performance and stability of lithium ion batteries, but this will also lead to a decrease in the capacity and power of the battery.

[0004] It can be seen that the cathode materials in the prior art cannot enable the battery to simultaneously have excellent electrochemical performance and thermal stability. Based on this, there is an urgent need to provide a new cathode material to solve the above problems. Summary of the Invention

[0005] The main object of the present invention is to provide a modified lithium aluminum titanium phosphate material and a preparation method thereof, a cathode material, and a lithium ion solid state battery to solve the problem that the cathode materials in the prior art cannot enable the battery to simultaneously have excellent electrochemical performance and thermal stability.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a modified lithium aluminum titanium phosphate material, and the structural formula of the modified lithium aluminum titanium phosphate material is Li x Al y Ti z B a N b (PO4)3, wherein 1.3 ≤ x ≤ 1.5, 0.3 ≤ y ≤ 0.5, 1.5 ≤ z ≤ 1.7, 0.02 ≤ a ≤ 0.05, 0.01 ≤ b ≤ 0.03.

[0007] Furthermore, the modified lithium titanium aluminum phosphate material is granular, and preferably the average particle size of the modified lithium titanium aluminum phosphate material is 50 to 100 nm.

[0008] According to another aspect of the present invention, there is provided a method for preparing a modified lithium titanium aluminum phosphate material, the preparation method comprising: sintering a lithium source, an aluminum source, a titanium source, a phosphorus source, boric acid and graphitic carbon nitride to obtain the modified lithium titanium aluminum phosphate material.

[0009] Furthermore, the method for preparing the modified lithium titanium aluminum phosphate material comprises the following steps: Step S1, mixing the lithium source, the aluminum source, the titanium source, the phosphorus source and boric acid to obtain a mixture A; Step S2, mixing the mixture A with graphitic carbon nitride and then sintering to obtain the modified lithium titanium aluminum phosphate material.

[0010] Furthermore, in Step S2, take a crucible, and set a nano-grating at the bottom of the crucible, and then add graphitic carbon nitride and the mixture A into the nano-grating for sintering; preferably in Step S2, first lay a layer of graphitic carbon nitride in the nano-grating, and then add the mixture A into the nano-grating for sintering; further preferably, the size of the nano-grating is (50-100) nm × (50-100) nm × (500-1000) nm; further preferably, the laying thickness of the graphitic carbon nitride layer is 100-300 nm; more preferably, the graphitic carbon nitride is layered graphitic carbon nitride.

[0011] Furthermore, the dosage of boric acid accounts for 0.5-1.8 wt% of the total weight of the lithium source, the aluminum source, the titanium source and the phosphorus source; preferably, the contents of the lithium source, the aluminum source, the titanium source and the phosphorus source are mixed according to the chemical stoichiometric ratio of Li:Al:Ti:P of (1.3-1.5):(0.3-0.5):(1.5-1.7):3; preferably, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide or lithium dihydrogen phosphate; preferably, the aluminum source is aluminum trioxide or aluminum hydroxide; preferably, the titanium source is titanium dioxide; preferably, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or lithium dihydrogen phosphate.

[0012] Further, in step S1, the mixing includes: first, mixing a lithium source, an aluminum source, a titanium source, and a phosphorus source at 50-100°C for 1-2 h to obtain a first mixture; then adding boric acid to the first mixture and performing a second mixing at 50-100°C for 1.5-3.0 h to obtain a mixed material A; preferably, the sintering is carried out in an air atmosphere, and the sintering treatment includes a first sintering and a second sintering carried out in sequence; preferably, the treatment temperature of the first sintering is 300-500°C, and the treatment time of the first sintering is 2-4 h; preferably, the treatment temperature of the second sintering is 750-950°C, and the treatment time of the second sintering is 3-8 h; preferably, the air flow rate is 30-70 L / min; preferably, during the process of heating from the treatment temperature of the first sintering to the treatment temperature of the second sintering, the heating rate is 3-10°C / min.

[0013] According to another aspect of the present invention, a positive electrode material is provided. The positive electrode material includes a matrix material and a coating layer coated on its outer surface. The material of the coating layer is the above-mentioned modified lithium aluminum titanium phosphate material, or a modified lithium aluminum titanium phosphate material prepared by the preparation method of the above-mentioned modified lithium aluminum titanium phosphate material.

[0014] According to another aspect of the present invention, a lithium-ion solid-state battery is provided. The lithium-ion solid-state battery includes the above-mentioned positive electrode material.

[0015] The modified lithium aluminum titanium phosphate material prepared by the present invention exhibits excellent electrochemical performance, and when it is used as a coating material, the positive electrode material has a high tap density and excellent thermal stability. Detailed Embodiments

[0016] It should be noted that, without conflict, the embodiments in this 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.

[0017] As described in the background art part of the present invention, the positive electrode materials in the prior art cannot enable the battery to simultaneously have excellent electrochemical performance and thermal stability. To solve this problem, the present invention provides a modified lithium aluminum titanium phosphate material. The structural formula of the modified lithium aluminum titanium phosphate material is Li x Al y Ti z B a N b (PO4)3, where 1.3 ≤ x ≤ 1.5, 0.3 ≤ y ≤ 0.5, 1.5 ≤ z ≤ 1.7, 0.02 ≤ a ≤ 0.05, and 0.01 ≤ b ≤ 0.03.

[0018] In the present invention, B element and N element are doped into the lithium aluminum titanium phosphate material. On the one hand, the introduction of B element can improve the reaction activity of the material, so that when the modified lithium aluminum titanium phosphate material is used as a coating material to coat the outer surface of the conventional ternary cathode material subsequently, the ionic conductivity of the cathode material can be improved. On the other hand, the introduction of N element can play a role in regulating the microstructure of the material. It can block particles and inhibit particle growth, so that the material can be nano-sized. Therefore, when the modified lithium aluminum titanium phosphate material is used as a coating material to coat the outer surface of the conventional ternary cathode material subsequently, the coating uniformity is better, and thus the capacity and thermal stability of the battery can be greatly improved.

[0019] In summary, when the above-mentioned specific modified lithium aluminum titanium phosphate material of the present application is used as a coating material to coat the outer surface of the conventional ternary cathode material subsequently, the battery can simultaneously achieve excellent electrochemical performance and thermal stability.

[0020] In order to further balance the electrochemical performance, thermal stability, capacity and power of the battery, in a preferred embodiment, the modified lithium aluminum titanium phosphate material is in particulate form, and preferably the average particle size of the modified lithium aluminum titanium phosphate material is 50-100 nm.

[0021] Another aspect of the present invention also provides a preparation method of a modified lithium aluminum titanium phosphate material, which includes: sintering a lithium source, an aluminum source, a titanium source, a phosphorus source, boric acid and graphitic carbon nitride to obtain the modified lithium aluminum titanium phosphate material.

[0022] First of all, the addition of boric acid can, on the one hand, improve the liquid-phase mass transfer during the reaction process, thereby reducing the microcracks of the modified lithium aluminum titanium phosphate material. On the other hand, after sintering, the B element in boric acid is doped into the modified lithium aluminum titanium phosphate material, which can further improve the reaction activity of the material, thereby improving the ionic conductivity of the material. Secondly, graphitic carbon nitride will gradually decompose during the sintering process and finally be incorporated into the modified lithium aluminum titanium phosphate material in the form of N element, thereby playing a role in regulating the microstructure of the material. It can block particles and inhibit particle growth, so that the material can be nano-sized. Therefore, when the modified lithium aluminum titanium phosphate material is used as a coating material to coat the outer surface of the conventional ternary cathode material subsequently, the coating uniformity is better, and thus the capacity and thermal stability of the battery can be greatly improved. By incorporating boric acid and graphitic carbon nitride into the lithium aluminum titanium phosphate material together, while they play a synergistic and efficient role, the N in graphitic carbon nitride can also form active species with the B in boric acid, thereby further improving the ionic conductivity of the material and its capacity and thermal stability as a coating material. In summary, when the modified lithium aluminum titanium phosphate material prepared by the above method is used as a coating material to coat the outer surface of the conventional ternary cathode material subsequently, the battery can simultaneously achieve excellent electrochemical performance and thermal stability.

[0023] In order to further balance the electrochemical performance, thermal stability, capacity and power of the battery, in a preferred implementation method, the preparation method of the above-mentioned modified lithium titanium aluminum phosphate material includes the following steps: Step S1, mixing a lithium source, an aluminum source, a titanium source, a phosphorus source and boric acid to obtain a mixture A; Step S2, mixing the mixture A with graphitic carbon nitride and then sintering to obtain the modified lithium titanium aluminum phosphate material. Those skilled in the art can first mix the lithium source, aluminum source, titanium source, phosphorus source and boric acid to obtain a mixture A; then take the above mixture A and mix it with graphitic carbon nitride and then sinter it to obtain the modified lithium titanium aluminum phosphate material.

[0024] Further preferably, in Step S2, first take a crucible and set a nano-grating on the inner bottom wall of the crucible, and then add graphitic carbon nitride and the mixture A into the nano-grating for sintering to obtain the modified lithium titanium aluminum phosphate material. Those skilled in the art can first take a crucible and set a nano-grating at the bottom of the crucible, and then add graphitic carbon nitride and the mixture A into the nano-grating for sintering treatment to obtain the modified lithium titanium aluminum phosphate material. By sintering graphitic carbon nitride and the mixture A in a crucible with a nano-grating set on its inner bottom wall, it can better improve the role of graphitic carbon nitride in further regulating the microstructure of the material during sintering, blocking particles and inhibiting particle growth, further promoting the nanocrystallization of the modified lithium titanium aluminum phosphate material during sintering, thereby further improving the coating uniformity of the modified lithium titanium aluminum phosphate material, and further improving the capacity and thermal stability of the battery. In order to further enable the mixture A and the graphitic carbon nitride layer to be better mixed and contacted, it is further preferably to first lay a graphitic carbon nitride layer inside the nano-grating, and then add the mixture A into the nano-grating for sintering; more preferably, the graphitic carbon nitride is layered graphitic carbon nitride, so as to further promote the nanocrystallization of the modified lithium titanium aluminum phosphate material during sintering, and then make it coat more uniformly as a coating material, improve the coating capacity, and further improve its thermal stability.

[0025] In order to better promote the regulation of the microstructure of materials by graphitic carbon nitride during sintering, the function of blocking particles and inhibiting particle growth, and further promote the nanocrystallization of the modified lithium titanium aluminum phosphate material during sintering, it is preferred that the size parameters of each grid in the nano-grating are (50-100) nm × (50-100) nm × (500-1000) nm, and it is further preferred that the laying thickness of the graphitic carbon nitride layer is 100-300 nm. In order to further improve the liquid-phase mass transfer during the reaction, so that the liquid-phase mass transfer is more uniform, and further reduce the microcracks of the modified lithium titanium aluminum phosphate material and improve its ionic conductivity, it is preferred that the dosage of boric acid accounts for 0.5-1.8 wt% of the total weight of the lithium source, aluminum source, titanium source and phosphorus source. In order to further improve the electrochemical performance of the modified lithium titanium aluminum phosphate material, it is preferred that the lithium source is selected from one or more of lithium carbonate, lithium hydroxide or lithium dihydrogen phosphate, more preferably the aluminum source is selected from aluminum oxide or aluminum hydroxide, more preferably the titanium source is titanium dioxide, and more preferably the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or lithium dihydrogen phosphate.

[0026] In a preferred embodiment, in order to make the mixing of the lithium source, aluminum source, titanium source, phosphorus source and boric acid more uniform, it is preferred that in the preparation method of the modified lithium titanium aluminum phosphate material, in step S1, the mixing includes first mixing the lithium source, aluminum source, titanium source and phosphorus source at 50-100 °C for 1-2 h to obtain a first mixture; then adding boric acid to the first mixture and mixing at 50-100 °C for 1.5-3.0 h to obtain a mixed material A. In order to make the sintering of the lithium source, aluminum source, titanium source, phosphorus source, boric acid and graphitic carbon nitride more sufficient, thereby improving the ionic conductivity of the modified lithium titanium aluminum phosphate material and increasing its coating capacity and thermal stability when used as a coating material subsequently, it is preferred that the sintering is carried out in an air atmosphere, and the sintering treatment includes a first sintering and a second sintering carried out in sequence. Further preferably, the treatment temperature of the first sintering is 300-500 °C, the treatment time of the first sintering is 2-4 h, the treatment temperature of the second sintering is 750-950 °C, and the treatment time of the second sintering is 3-8 h; further preferably, the air flow rate is 30-70 L / min; more preferably, the heating rate from the first sintering to the second sintering is 3-10 °C / min.

[0027] Another aspect of the present invention provides a positive electrode material, which includes a matrix material and a coating layer coated on its outer surface, and the material of the coating layer is the above-mentioned modified lithium titanium aluminum phosphate material, or the modified lithium titanium aluminum phosphate material prepared by the above-mentioned preparation method of the modified lithium titanium aluminum phosphate material. The modified lithium titanium aluminum phosphate material is used as a coating material to coat the positive electrode plate of the ternary positive electrode of the Ni88 system, so that the positive electrode plate coated with the modified lithium titanium aluminum phosphate material exhibits excellent ionic conductivity, and has a high coating capacity and excellent thermal stability.

[0028] On the other hand, the present invention provides a method for preparing a cathode material, which includes ball-milling the above-mentioned modified lithium aluminum titanium phosphate material with a ball mill at a ball-milling speed of 300-400 rpm and a ball-milling time of 4-6 h, so that the average particle size of the obtained modified lithium aluminum titanium phosphate material is 50-100 nm. The cathode material prepared by the above method has excellent ionic conductivity, high coating capacity and excellent thermal stability. Further preferably, the above-mentioned cathode material includes a matrix material and a coating layer coated on its outer surface, and the thickness of the coating layer is 10-20 nm.

[0029] On the other hand, the present invention provides a lithium-ion solid-state battery, which includes the above-mentioned modified lithium aluminum titanium phosphate material, or is obtained by the preparation method of the above-mentioned modified lithium aluminum titanium phosphate material, or is obtained by the above-mentioned cathode material, or is obtained by the preparation method of the above-mentioned cathode material. The lithium-ion battery has good electrochemical performance and cycling performance.

[0030] 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.

[0031] Example 1

[0032] Prepare the modified lithium aluminum titanium phosphate material:

[0033] Step S1, weigh lithium carbonate, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate according to the stoichiometric ratio of Li:Al:Ti:P = 1.4:0.4:1.6:3, add them to a 3D mixer for the first mixing, mix at a temperature of 70 °C for 1.5 h, then add 1 wt% of boric acid, and continue to mix in the 3D mixer for the second mixing, mix at a temperature of 80 °C for 2 h to obtain a mixed material A.

[0034] Step S2, take a sintering crucible, place a nano-grating at its bottom (size: 80 nm × 80 nm × 800 nm), lay a 200-nm-thick layer of graphitic carbon nitride inside the nano-grating, add the above-mentioned mixed material A into it and cut it with a cutting die, and adjust the air intake to reach 50 L / min, and sinter it in a muffle furnace. First, perform the first sintering at 400 °C for 3 h, and then perform the second sintering at 850 °C for 5 h. The heating rate from the first sintering to the second sintering is 5 °C / min. Wait for the sintered material to cool naturally to obtain the modified lithium aluminum titanium phosphate material Li 1.4 Al 0.4 Ti 1.6 B 0.03 N 0.02 (PO4)3.

[0035] Prepare the cathode material:

[0036] The above modified lithium titanium aluminum phosphate material was ball-milled in a ball mill at a rotational speed of 350 rpm for 5 h to obtain a coating material with the modified lithium titanium aluminum phosphate material as the coating layer. The average particle size of the ball-milled modified lithium titanium aluminum phosphate material was 75 nm, and it was used for coating on the ternary NCM811 cathode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), thereby obtaining the coated ternary cathode material.

[0037] Example 2

[0038] Preparation of modified lithium titanium aluminum phosphate material:

[0039] Step S1, Lithium carbonate, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate were weighed according to the stoichiometric ratio of Li:Al:Ti:P of 1.5:0.5:1.5:3, added to a 3D mixer for the first mixing, mixed at a temperature of 50 °C for 1 h, then 0.5 wt% boric acid was added, and the second mixing was continued in the 3D mixer at a temperature of 50 °C for 1.5 h to obtain a mixed material A.

[0040] Step S2, Take a sintering crucible, place a nano-grating at the bottom thereof (with a size of 50 nm × 50 nm × 500 nm, and a 100-nm-thick layer of graphitic carbon nitride was laid inside the nano-grating), add the above mixed material A into it and cut it with a cutting die, and adjust the air intake volume to reach 30 L / min, and sinter it in a muffle furnace. First, perform the first sintering at 300 °C for 2 h, and then perform the second sintering at 750 °C for 3 h. The heating rate from the first sintering to the second sintering was 3 °C / min. After the sintered material was naturally cooled, the modified lithium titanium aluminum phosphate material Li 1.5 Al 0.5 Ti 1.5 B 0.02 N 0.01 (PO4)3 was obtained.

[0041] Preparation of cathode material:

[0042] The above modified lithium titanium aluminum phosphate material was ball-milled in a ball mill at a rotational speed of 300 rpm for 4 h to obtain a coating material with the modified lithium titanium aluminum phosphate material as the coating layer. The average particle size of the ball-milled modified lithium titanium aluminum phosphate material was 50 nm, and it was used for coating on the ternary NCM811 cathode material (LiNi 0.8 Co 0.1 Mn 0.1 O2), thereby obtaining the coated ternary cathode material.

[0043] Example 3

[0044] Preparation of modified lithium titanium aluminum phosphate material:

[0045] Step S1, Weigh lithium carbonate, aluminum oxide, titanium dioxide and ammonium dihydrogen phosphate according to the stoichiometric ratio of Li:Al:Ti:P = 1.3:0.3:1.7:3, add them into a 3D mixer for the first mixing, mix at a temperature of 100 °C for 2 h, then add 1.8 wt% boric acid, and continue the second mixing in the 3D mixer, mix at a temperature of 100 °C for 3 h to obtain the mixed material A.

[0046] Step S2, Take a sintering crucible, place a nano-grating at the bottom thereof (with a size of 100 nm × 100 nm × 1000 nm, and lay a 300-nm-thick layer of graphitic carbon nitride inside the nano-grating), add the above-mentioned mixed material A into it and cut it with a cutting die, and adjust the air intake volume to reach 70 L / min, and sinter it in a muffle furnace. First, conduct the first sintering at 500 °C for 4 h, and then conduct the second sintering at 950 °C for 8 h. The heating rate from the first sintering to the second sintering is 10 °C / min. Wait for the sintered material to cool naturally to obtain the modified lithium titanium aluminum phosphate material Li 1.3 Al 0.3 Ti 1.7 B 0.05 N 0.03 (PO4)3.

[0047] Preparation of the positive electrode material:

[0048] Take the above-mentioned modified lithium titanium aluminum phosphate material and ball-mill it in a ball mill at a rotation speed of 400 rpm for 6 h to obtain a coating material with the modified lithium titanium aluminum phosphate material as the coating layer. The average particle size of the ball-milled modified lithium titanium aluminum phosphate material is 100 nm, and it is used for coating on the ternary Ni88 positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O2) to obtain the coated ternary positive electrode material.

[0049] Comparative Example 1

[0050] The difference from Example 1 is only that boric acid and layered graphitic carbon nitride are not added.

[0051] Comparative Example 2

[0052] The difference from Example 1 is only that the dosage of boric acid is 0.2 wt%.

[0053] Comparative Example 3

[0054] The difference from Example 1 is only that the dosage of boric acid is 2.0 wt%.

[0055] Comparative Example 4

[0056] It is only different from Example 1 in that the laying thickness of the graphitic carbon nitride layer is 50 nm.

[0057] Comparative Example 5

[0058] It is only different from Example 1 in that the laying thickness of the graphitic carbon nitride layer is 400 nm.

[0059] Performance Test

[0060] Ionic conductivity: After pressing the materials milled in the examples and comparative examples into tablets under a pressure of 10 MPa for 30 seconds and sintering at 900 °C for 12 h, the ionic conductivity of the modified lithium titanium aluminum phosphate material was tested.

[0061] Button cell test: The samples in the examples and comparative examples were used as the positive electrode material, a battery-grade lithium sheet was used as the negative electrode material, and a simulated battery assembled with an electrolyte mainly composed of lithium hexafluorophosphate was used. The charge-discharge electrochemical window was 3.0 - 4.3 V.

[0062] Apparent density: The materials prepared in the examples and comparative examples were tested for powder compaction under a pressure of 5 MPa for 30 seconds.

[0063] Thermal stability test: The peak temperature of differential scanning calorimetry was measured for the delithiated positive electrode from room temperature to 400 °C at a heating rate of 10 °C / min; the atmosphere was compressed air.

[0064] The products of the examples and comparative examples were subjected to performance tests, and the specific test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] From the above description, it can be seen that the above examples of the present invention achieve the following technical effects:

[0068] It can be found from the test data of Examples 1, 2, 3 and Comparative Examples 2, 3 that when the preparation method of the modified lithium titanium aluminum phosphate material of the present invention is adopted, and the dosage of boric acid is within the range of 0.5-1.8 wt% of the total weight of the lithium source, aluminum source, titanium source and phosphorus source (for example, 1.0 wt% in Example 1, 0.5 wt% in Example 2, and 1.8 wt% in Example 3), the prepared modified lithium titanium aluminum phosphate material has a high ionic conductivity, and the positive electrode material has a high tap density and excellent thermal stability. When the dosage of boric acid is outside the range of 0.5-1.8 wt% (for example, 0.2 wt% in Comparative Example 2 and 2.0 wt% in Comparative Example 3), since the dosage of boric acid is too small to play an effective liquid mass transfer role, or the dosage of boric acid is excessive, resulting in too much residual B element, the effective active sites of the material are reduced, resulting in a lower ionic conductivity of the prepared modified lithium titanium aluminum phosphate material and a lower tap density of the positive electrode material, and a poor thermal stability.

[0069] It can be found from the test data of Examples 1, 2, 3 and Comparative Examples 4, 5 that when the preparation method of the modified lithium titanium aluminum phosphate material of the present invention is adopted, and the laying thickness of the graphite phase carbon nitride layer is within the range of 100-300 nm (for example, 200 nm in Example 1, 100 nm in Example 2, and 300 nm in Example 3), the prepared modified lithium titanium aluminum phosphate material has a high ionic conductivity, and the positive electrode material has a high tap density and excellent thermal stability. When the laying thickness of the graphite phase carbon nitride layer is outside the range of 100-300 nm (for example, 50 nm in Comparative Example 4 and 400 nm in Comparative Example 5), since too little graphite phase carbon nitride is not easy to form a carbon-nitrogen coating layer or too much graphite phase carbon nitride results in too thick a coating layer, it is difficult for the material properties to play an effective role, resulting in a lower ionic conductivity of the prepared modified lithium titanium aluminum phosphate material and a lower tap density of the positive electrode material, and a poor thermal stability.

[0070] It can be found from the test data of Examples 1, 2, 3 and Comparative Example 1 that when the preparation method of the modified lithium titanium aluminum phosphate material of the present invention is adopted, the prepared modified lithium titanium aluminum phosphate material has a high ionic conductivity, and the positive electrode material has a high tap density and excellent thermal stability. When boric acid and layered graphite phase carbon nitride are not added, since lithium titanium aluminum phosphate is prone to form microcracks and the density is reduced, the ionic conductivity of the prepared modified lithium titanium aluminum phosphate material and the tap density of the positive electrode material are lower, and the thermal stability is poor.

[0071] In summary, compared with the LATP material prepared by the conventional method, the modified lithium titanium aluminum phosphate material obtained by the preparation method of the present invention has significantly improved ionic conductivity, and the capacity and tap density obtained when used as the ternary cathode material are significantly better than those of the conventional LATP. Therefore, the modified lithium titanium aluminum phosphate material prepared by the present invention has excellent ionic conductivity, and has a high coating capacity and exhibits excellent thermal stability when used as a coating material subsequently.

[0072] 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 within the protection scope of the present invention.

Claims

1. A modified lithium titanium aluminum phosphate material, characterized in that, The structural formula of the modified lithium titanium aluminum phosphate material is Li x Al y Ti z B a N b (PO4)3, where 1.3 ≤ x ≤ 1.5, 0.3 ≤ y ≤ 0.5, 1.5 ≤ z ≤ 1.7, 0.02 ≤ a ≤ 0.05, 0.01 ≤ b ≤ 0.03; The preparation method of the modified lithium titanium aluminum phosphate material comprises the following steps: Step S1, mixing a lithium source, an aluminum source, a titanium source, a phosphorus source and boric acid to obtain a mixture A; Step S2, mixing the mixture A with graphitic carbon nitride and then sintering to obtain the modified lithium titanium aluminum phosphate material.

2. The modified lithium titanium aluminum phosphate material according to claim 1, wherein, The modified lithium titanium aluminum phosphate material is granular.

3. The modified lithium titanium aluminum phosphate material according to claim 2, characterized in that The average particle size of the modified lithium titanium aluminum phosphate material is 50 - 100 nm.

4. A method for preparing the modified lithium titanium aluminum phosphate material according to any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: Step S1, mixing a lithium source, an aluminum source, a titanium source, a phosphorus source and boric acid to obtain a mixture A; Step S2, mixing the mixture A with graphitic carbon nitride and then sintering to obtain the modified lithium titanium aluminum phosphate material.

5. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 4, characterized in that, In step S2, take a crucible, set a nano-grating at the bottom of the crucible, and then add the graphitic carbon nitride and the mixture A into the nano-grating for the sintering.

6. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 5, characterized in that, In step S2, first lay a graphitic carbon nitride layer inside the nano-grating, and then add the mixture A into the nano-grating for the sintering.

7. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 6, characterized in that, The size of the nano-grating is (50 - 100) nm × (50 - 100) nm × (500 - 1000) nm.

8. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 6, characterized in that, The laying thickness of the graphitic carbon nitride layer is 100 - 300 nm.

9. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 8, characterized in that, The graphitic carbon nitride is layered graphitic carbon nitride.

10. The preparation method of the modified lithium titanium aluminum phosphate material according to any one of claims 4 to 9, characterized in that, The dosage of the boric acid accounts for 0.5 - 1.8 wt% of the total weight of the lithium source, the aluminum source, the titanium source and the phosphorus source.

11. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 10, wherein, The contents of the lithium source, the aluminum source, the titanium source and the phosphorus source are mixed according to the chemical stoichiometric ratio of Li:Al:Ti:P being (1.3 - 1.5):(0.3 - 0.5):(1.5 - 1.7):

3.

12. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 10, wherein, The lithium source is selected from one or more of lithium carbonate, lithium hydroxide or lithium dihydrogen phosphate.

13. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 10, wherein, The aluminum source is aluminum oxide and / or aluminum hydroxide.

14. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 10, characterized in that, The titanium source is titanium dioxide.

15. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 10, wherein The phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or lithium dihydrogen phosphate.

16. The preparation method of the modified lithium titanium aluminum phosphate material according to any one of claims 4 to 9, characterized in that, In step S1, the mixing includes: first mixing the lithium source, the aluminum source, the titanium source and the phosphorus source at 50 - 100 °C for 1 - 2 h to obtain a first mixture; then adding boric acid to the first mixture and mixing at 50 - 100 °C for 1.5 - 3.0 h to obtain the mixture A.

17. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 16, wherein, The sintering is carried out in an air atmosphere, and the sintering treatment includes a first sintering and a second sintering carried out in sequence.

18. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 17, characterized in that, The treatment temperature of the first sintering is 300 - 500 °C, and the treatment time is 2 - 4 h.

19. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 17, characterized in that, The treatment temperature of the second sintering is 750 - 950 °C, and the treatment time is 3 - 8 h.

20. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 17, characterized in that, The air flow rate of the air in the air atmosphere is 30 - 70 L / min.

21. The preparation method of the modified lithium titanium aluminum phosphate material according to claim 17, characterized in that, When heating from the treatment temperature of the first sintering to the treatment temperature of the second sintering, the heating rate is 3 - 10 °C / min.

22. A cathode material, characterized in that, The positive electrode material includes a matrix material and a coating layer coated on its outer surface, and the material of the coating layer is the modified lithium titanium aluminum phosphate material described in any one of claims 1 to 3, or the modified lithium titanium aluminum phosphate material prepared by the preparation method of the modified lithium titanium aluminum phosphate material described in any one of claims 4 to 21.

23. The cathode material according to claim 22, characterized in that, The thickness of the coating layer is 10 to 20 nm.

24. A lithium-ion solid-state battery, characterized in that, The lithium ion solid state battery includes the positive electrode material described in claim 22 or 23.

Images