Cation-doped carbon-coated titanium magnesium phosphate composite material as well as preparation method and application thereof

Abstract

The invention provides a cation-doped carbon-coated titanium magnesium phosphate composite material as well as a preparation method and application thereof, the chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg < 0.5 + x > Ti < 2-x > M < x > (PO4) 3 / C, M is selected from at least one of Al and Cr, and x < lt > is more than or equal to 0.01 and less than or equal to 0.01; 0.5, and C is a carbon coating layer. The preparation method comprises the following steps: S1, adding a magnesium source, a titanium source, an M source, a phosphorus source and a carbon source into a solvent, and fully mixing to obtain precursor slurry; s2, transferring the precursor slurry into drying equipment, and fully drying to obtain precursor powder; and S3, heating and calcining the precursor powder in a protective atmosphere, and cooling to obtain the cation-doped carbon-coated titanium magnesium phosphate composite material. The NASICON type cation-doped carbon-coated titanium magnesium phosphate composite material is obtained by introducing a doped metal source and a carbon source material into the mixed slurry, so that the material has relatively high conductivity and capacity retention ratio, and meanwhile, the material can be used as a protective layer of the titanium magnesium phosphate material to prolong the cycle life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a cation-doped carbon-coated titanium magnesium phosphate composite material, a preparation method and application thereof. BACKGROUND

[0002] Sodium superionic conductor (NASICON) structure materials, especially phosphates, have a three-dimensional open framework and flexible structure, and are the most widely researched ion conductive medium. Among them, titanium magnesium phosphate as a NASICON type titanium-based phosphate can stably store alkali metal and alkaline earth metal ions such as Li ions, Na ions, Mg ions, etc., and has excellent properties of all NASICON structure materials.

[0003] However, due to the inherent properties of titanium magnesium phosphate, it inevitably performs poorly in terms of conductivity, limiting its wide application. Moreover, the titanium magnesium phosphate powder prepared by sintering in the prior art has a titanium pyrophosphate impurity phase diffraction peak. The existence of the impurity phase reduces the ionic conductivity of the titanium magnesium phosphate and affects its electrochemical performance.

[0004] Therefore, it is necessary to study how to improve the performance of titanium magnesium phosphate material and improve the electrochemical performance of the battery when it is applied to the battery. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a cation-doped carbon-coated titanium magnesium phosphate composite material, a preparation method and application thereof, which are used to solve the problems of poor conductivity of titanium magnesium phosphate in the prior art, and the existence of a titanium pyrophosphate impurity phase diffraction peak in the titanium magnesium phosphate powder, which reduces the ionic conductivity of the titanium magnesium phosphate and affects its electrochemical performance.

[0006] To achieve the above-mentioned purposes and other related purposes, the present application provides a cation-doped carbon-coated titanium magnesium phosphate composite material, the chemical general formula of which is Mg 0.5+x Ti 2-x M x (PO4)3 / C, wherein M is selected from at least one of Al and Cr, 0.01≤x<0.5, and C is a carbon coating layer.

[0007] Preferably, the material of the carbon coating layer is one of amorphous carbon and crystalline carbon.

[0008] Preferably, the carbon coating layer is at least one of a continuous film, a discontinuous film and closely arranged carbon particles.

[0009] Preferably, the mass percentage is 2.5wt% to 15wt% based on the total mass of the titanium magnesium phosphate.

[0010] The application also provides a preparation method of the cation-doped carbon-coated titanium magnesium phosphate composite material, which comprises the following steps:

[0011] S1, adding a magnesium source, a titanium source, an M source, a phosphorus source and a carbon source into a solvent and mixing them thoroughly to obtain a precursor slurry;

[0012] S2, transferring the precursor slurry to a drying device and drying it thoroughly to obtain a precursor powder;

[0013] S3, heating and calcining the precursor powder in a protective atmosphere, and obtaining the cation-doped carbon-coated titanium magnesium phosphate composite material after cooling.

[0014] Preferably, the magnesium source in step S1 comprises one or a combination of magnesium carbonate, magnesium oxide, magnesium hydroxide and magnesium phosphate.

[0015] Preferably, the titanium source in step S1 comprises one or a combination of titanium dioxide and titanium phosphate.

[0016] Preferably, the M source in step S1 is a doping element source, the doping element is at least one of Al and Cr, and the doping element source is one or a combination of oxides, carbonates, phosphates and oxalates of the doping element.

[0017] Preferably, the phosphorus source in step S1 comprises one or a combination of diammonium hydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate and diphosphorus pentoxide.

[0018] Preferably, the molar ratio of the magnesium source, the titanium source, the M source and the phosphorus source in step S1 is (0.5+x):(2-x):x:3, wherein 0.01≤x<0.5, the magnesium source is calculated based on Mg element, the titanium source is calculated based on Ti element, the M source is calculated based on M doping element, and the phosphorus source is calculated based on P element.

[0019] Preferably, the carbon source in step S1 comprises one or a combination of corn starch, glucose, sucrose, oxalic acid, citric acid, ascorbic acid, polyvinylpyrrolidone and polyethylene glycol.

[0020] Preferably, the solvent in step S1 comprises one or a combination of deionized water, ethanol, propylene glycol and polyvinyl alcohol.

[0021] Preferably, the total mass of the magnesium source, the titanium source, the M source, the phosphorus source and the carbon source in step S1 accounts for 10wt%-30wt% of the mass percentage of the precursor slurry.

[0022] Preferably, the drying method in the drying device in step S2 comprises one of air oven drying, vacuum rake drying and spray dryer drying.

[0023] When air blast oven drying or vacuum rake drying is adopted, the temperature of the air blast oven drying and the temperature of the vacuum rake drying are both 140-210℃, and the drying time is both 6-12h; when the spray dryer is adopted, the outlet temperature of the spray dryer is 280-300℃, the inlet temperature is 110-130℃, and the pressure is 0.4-0.5Mpa.

[0024] Preferably, the step of heating and calcining the precursor powder in a protective atmosphere in step S3 specifically comprises:

[0025] The precursor powder is first calcined in a protective atmosphere, the first calcination temperature is maintained at 350-600℃, the first calcination is maintained for 5-10h, and the first temperature rising rate is 1-3℃ / min;

[0026] Then, the second calcination is carried out in a protective atmosphere, the second calcination temperature is maintained at 1000-1200℃, the second calcination is maintained for 4-12h, and the second temperature rising rate is 2-5℃ / min.

[0027] Preferably, the protective atmosphere is one of nitrogen, helium and argon.

[0028] Preferably, the cation-doped carbon-coated titanium magnesium phosphate composite material obtained in step S3 comprises a carbon coating layer and a titanium magnesium phosphate material, the carbon coating layer is calculated in terms of C element, and the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%-15wt%.

[0029] The application further provides an application of the cation-doped carbon-coated titanium magnesium phosphate composite material in lithium batteries, wherein the cation-doped carbon-coated titanium magnesium phosphate composite material is the above-mentioned cation-doped carbon-coated titanium magnesium phosphate composite material or the cation-doped carbon-coated titanium magnesium phosphate composite material prepared by the above-mentioned preparation method.

[0030] As described above, the cation-doped carbon-coated titanium magnesium phosphate composite material, the preparation method and the application thereof have the following beneficial effects:

[0031] The preparation method provided by the application is simple, easy to operate and low in cost, the doped metal source and the carbon source material are introduced into the mixed slurry, and the NASICON-type cation-doped carbon-coated titanium magnesium phosphate composite material is obtained by one-step sintering or sectional sintering, the doping of the trivalent M cation can maintain the NASICON-type structure of the material and effectively inhibit the formation of the impurity phase titanium pyrophosphate; in addition, the M 3+ Cation substitution Ti 4+The migration channel of lithium ions can be widened, more conductive lithium ions are introduced to maintain electrical neutrality, the number of charge carriers is increased, and the electrical conductivity of the material can also be improved; on this basis, the organic carbon source is mixed with other raw materials to form a mixed slurry, and the organic carbon source is uniformly coated on the surface of the spherical precursor powder in the spray drying process, and the high-temperature sintering uniformly coats the surface of the cation-doped titanium magnesium phosphate with carbon, which is beneficial to further improve the electrical conductivity of the titanium magnesium phosphate, and the coated layer has the characteristics of fast lithium ion conductor, which promotes the migration of Li + inside the material, so that the material has high electrical conductivity and capacity retention rate, and can also serve as a protective layer for the titanium magnesium phosphate material to prolong the cycle life.

[0032] The cation-doped carbon-coated titanium magnesium phosphate composite material provided by the application is applied to lithium batteries, effectively improves the kinetic performance of the batteries, greatly improves the cycle life of the lithium batteries, and has important significance for the sustainable development of future energy. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The XRD patterns of the cation-doped carbon-coated titanium magnesium phosphate composite material in specific embodiments 1-11 of the application and the titanium magnesium phosphate material in comparative example 1 are shown. DETAILED DESCRIPTION

[0034] The embodiments of the application are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the application from the disclosure in the specification. The application can also be implemented or applied in different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the application.

[0035] The application provides a cation-doped carbon-coated titanium magnesium phosphate composite material, the chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.5+x Ti 2-x M x (PO4)3 / C, wherein M is selected from at least one of Al and Cr, 0.01<=x<0.5, and C is a carbon coating layer.

[0036] Specifically, x can include any value within the range of 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, etc., and can be adjusted according to actual conditions.

[0037] As an example, the material of the carbon coating layer is one of amorphous carbon and crystalline carbon.

[0038] As an example, the carbon coating layer is selected from at least one of continuous film, discontinuous film and closely arranged carbon particles.

[0039] As an example, the mass percentage of the carbon coating layer is 2.5wt%-15wt% based on the total mass of the titanium magnesium phosphate.

[0040] Specifically, the cation-doped carbon-coated titanium magnesium phosphate composite material is formed by forming a carbon coating layer on the surface of the cation-doped titanium magnesium phosphate, the material of the carbon coating layer is one of amorphous carbon and crystalline carbon, and the carbon coating layer is selected from at least one of continuous film, discontinuous film and closely arranged carbon particles; the mass percentage of the carbon coating layer can include any value within the range of 2.5wt%, 5wt%, 7wt%, 9wt%, 10wt%, 11wt%, 13wt%, 15wt% and the like based on the total mass of the titanium magnesium phosphate, wherein the carbon coating layer is calculated based on C element.

[0041] The application also provides a preparation method of the cation-doped carbon-coated titanium magnesium phosphate composite material, which comprises the following steps:

[0042] S1, adding a magnesium source, a titanium source, an M source, a phosphorus source and a carbon source into a solvent to mix thoroughly to obtain a precursor slurry;

[0043] S2, transferring the precursor slurry to a drying device to dry thoroughly to obtain a precursor powder;

[0044] S3, heating and calcining the precursor powder under a protective atmosphere, and after cooling, obtaining the cation-doped carbon-coated titanium magnesium phosphate composite material.

[0045] Specifically, in step S1, the magnesium source, the titanium source, the M source, the phosphorus source and the carbon source are added into the solvent to mix thoroughly, and the specific operation is to add the magnesium source, the titanium source, the M source, the phosphorus source and the carbon source into any one of a stirring dispersant, a ball mill and a sand mill, and then add the solvent to disperse thoroughly; when the stirring dispersant is used, the stirring speed of the stirring disperser is 1000rpm-2000rpm, and the stirring time is 1-5h; when the ball mill is used, the rotating speed of the ball mill is 450rpm-650rpm, and the ball milling time is 2h-8h; when the sand mill is used, the average discharge particle size of the sand mill is less than 0.5μm, and the rotating speed is 1500rmp-2000rmp.

[0046] In the specific embodiments of the application, the carbon source is mixed with other raw materials to form a mixed slurry, and in the drying process, the carbon source is uniformly coated on the surface of the spherical precursor powder, and high-temperature sintering uniformly coats the surface of the cation-doped titanium magnesium phosphate with carbon to form a carbon coating layer, the material of the carbon coating layer is one of amorphous carbon and crystalline carbon, and the carbon coating layer is selected from at least one of continuous film, discontinuous film and closely arranged carbon particles.

[0047] As an example, the magnesium source in step S1 includes one or a combination of magnesium carbonate, magnesium oxide, magnesium hydroxide and magnesium phosphate.

[0048] As an example, the titanium source in step S1 includes one or a combination of titanium dioxide, titanium phosphate.

[0049] As an example, the M source in step S1 is a doping element source, the doping element is at least one of Al, Cr, and the doping element source is one or a combination of oxides, carbonates, phosphates, oxalates of the doping element.

[0050] As an example, the phosphorus source in step S1 includes one or a combination of diammonium hydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, and diphosphorus pentoxide.

[0051] As an example, the molar ratio between the magnesium source (calculated as Mg element), the titanium source (calculated as Ti element), the M source (calculated as M doping element), and the phosphorus source (calculated as P element) in step S1 is (0.5+x):(2-x):x:3, wherein 0.01≤x<0.5.

[0052] Specifically, x can include any value within the range of 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, etc., and can be adjusted according to actual conditions; finally, the chemical formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.5+ x Ti 2-x M x (PO4)3 / C, C is a carbon coating layer; M 3+ element substitutes Ti 4+ ion in the structure, and excess Mg 2+ balances the charge, and the additional Mg element can further convert the titanium pyrophosphate impurity phase into a titanium magnesium phosphate conductive crystal phase.

[0053] As an example, the carbon source in step S1 includes one or a combination of corn starch, glucose, sucrose, oxalic acid, citric acid, ascorbic acid, polyvinylpyrrolidone, and polyethylene glycol.

[0054] As an example, the solvent in step S1 includes one or a combination of deionized water, ethanol, propylene glycol, and polyvinyl alcohol.

[0055] As an example, the total mass of the magnesium source, the titanium source, the M source, the phosphorus source, and the carbon source in step S1 accounts for 10wt%-30wt% of the mass percentage of the precursor slurry.

[0056] Specifically, the precursor slurry includes a magnesium source, a titanium source, an M source, a phosphorus source, a carbon source, and a solvent added thereto, and the total mass of the magnesium source, the titanium source, the M source, the phosphorus source, and the carbon source in the precursor slurry (i.e., the solid content of the precursor slurry) can include a value in any range of 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc., and can be specifically adjusted according to actual conditions.

[0057] As an example, the manner of performing sufficient drying in the drying device in step S2 includes one of drum oven drying, vacuum rake dryer drying, and spray dryer drying; when the drum oven drying or the vacuum rake dryer drying is used, the temperature of the drum oven drying and the temperature of the vacuum rake dryer drying are both 80-200°C, and the drying time is both 6-12h; when the spray dryer drying is used, the outlet temperature of the spray dryer is 280-300°C, the inlet temperature is 110-130°C, and the pressure is 0.4-0.5 MPa.

[0058] As an example, the manner of performing sufficient drying in the drying device in step S2 includes one of drum oven drying, vacuum rake dryer drying, and spray dryer drying; when the drum oven drying or the vacuum rake dryer drying is used, the temperature of the drum oven drying and the temperature of the vacuum rake dryer drying are both 80-200°C, and the drying time is both 6-12h; when the spray dryer drying is used, the outlet temperature of the spray dryer is 280-300°C, the inlet temperature is 110-130°C, and the pressure is 0.4-0.5 MPa.

[0059] As an example, the step of heating and calcining the precursor powder in a protective atmosphere in step S3 specifically includes: performing first calcination on the precursor powder in a protective atmosphere, maintaining the first calcination temperature at 350-600°C (such as 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any value in any range thereof), and maintaining the first calcination for 5-10h (such as 5h, 6h, 7h, 8h, 9h, 10h, or any value in any range thereof), and the first temperature rising rate is 1-3°C / min (such as 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, or any value in any range thereof);

[0060] Then, the second calcination is performed under a protective atmosphere, the second calcination temperature is maintained at 1000-1200℃ (such as 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, or any value within any range thereof), and the second calcination is maintained for 4-12h (such as 4h, 6h, 8h, 10h, 12h, or any value within any range thereof), and the second temperature rising rate is 2-5℃ / min (such as 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or any value within any range thereof).

[0061] As an example, the protective atmosphere is one of nitrogen, helium, and argon.

[0062] As an example, the cation-doped carbon-coated titanium magnesium phosphate composite material obtained in step S3 includes a carbon coating layer and a titanium magnesium phosphate material, and the carbon coating layer accounts for 2.5wt%-15wt% of the titanium magnesium phosphate material in terms of C element.

[0063] Specifically, the carbon coating layer accounts for 2.5wt%, 5wt%, 7wt%, 9wt%, 10wt%, 11wt%, 13wt%, 15wt%, or any value within any range thereof of the titanium magnesium phosphate material in terms of C element.

[0064] In addition, the application also provides an application of the above cation-doped carbon-coated titanium magnesium phosphate composite material or the cation-doped carbon-coated titanium magnesium phosphate composite material prepared by the preparation method of the above cation-doped carbon-coated titanium magnesium phosphate composite material in a lithium battery.

[0065] Specifically, the cation-doped carbon-coated titanium magnesium phosphate composite material is used as an additive of a positive electrode active material to prepare a positive electrode sheet, and a button lithium battery is assembled.

[0066] In order to better understand the cation-doped carbon-coated titanium magnesium phosphate composite material, the preparation method, and the application thereof, the cation-doped carbon-coated titanium magnesium phosphate composite material, the preparation method, and the application thereof are described below with reference to specific embodiments, and it should be noted that these embodiments are merely descriptive and do not limit the application in any way.

[0067] Example 1

[0068] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which includes the following steps:

[0069] S1, 15.2 g of magnesium source (magnesium carbonate), 57.6 g of titanium source (titanium dioxide), 0.18 g of M source (aluminum oxide), 40.7 g of phosphorus source (diammonium hydrogen phosphate), and 4.2 g of carbon source (sucrose) were added into 500 g of ethanol, and then transferred into a high-energy ball mill, and mixed at a speed of 500 rpm for 4 h to obtain a precursor slurry;

[0070] S2, the precursor slurry was transferred to a forced air drying oven and dried at 80°C to obtain a precursor powder;

[0071] S3, the precursor powder was transferred to an atmosphere furnace, and heated to 500°C at a heating rate of 2°C / min under a nitrogen atmosphere, and maintained for calcination for 5 h, and then heated to 1000°C at a heating rate of 2°C / min, and maintained for calcination for 6 h, and then naturally cooled to room temperature, and then ground to obtain a cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Al 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0072] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, the chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.51 Ti 1.99 Al 0.01 (PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%, and the mass of the carbon coating layer is in terms of the mass of C element.

[0073] Example 2

[0074] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 1 in that in step S1, 15.2 g of magnesium source (magnesium carbonate), 57.6 g of titanium source (titanium dioxide), 0.18 g of M source (chromium oxide), 40.7 g of phosphorus source (ammonium dihydrogen phosphate), and 4.2 g of carbon source (sucrose) are added into 500 g of ethanol, and then transferred into a high-energy ball mill, and mixed at a speed of 500 rpm for 4 h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 1, and will not be described here again, and finally a cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0075] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, the chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.51 Ti 1.99 Cr 0.01MgTi(PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and titanium magnesium phosphate, and the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5 wt%, and the mass of the carbon coating layer is calculated based on the mass of C element.

[0076] Example 3

[0077] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 1 in that in the step S1, 15.2 g of a magnesium source (magnesium carbonate), 57.6 g of a titanium source (titanium dioxide), 1.25 g of an M source (chromium oxide), 40.7 g of a phosphorus source (ammonium dihydrogen phosphate) and 4.2 g of a carbon source (sucrose) are added into 510 g of ethanol, and then the mixture is fully mixed in a high-energy ball mill at a rotating speed of 500 rpm for 4 h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 1, and details are not described herein again, and finally the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0078] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a general chemical formula of Mg 0.55 Ti 1.95 Cr 0.05 (PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and titanium magnesium phosphate, and the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5 wt%, and the mass of the carbon coating layer is calculated based on the mass of C element.

[0079] Example 4

[0080] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 1 in that in the step S1, 15.2 g of a magnesium source (magnesium carbonate), 57.6 g of a titanium source (titanium dioxide), 1.25 g of an M source (chromium oxide), 40.7 g of a phosphorus source (ammonium dihydrogen phosphate) and 4.2 g of a carbon source (sucrose) are added into 510 g of ethanol, and then the mixture is fully mixed in a high-energy ball mill at a rotating speed of 500 rpm for 4 h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 1, and details are not described herein again, and finally the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0081] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a general chemical formula of Mg 0.6 Ti 1.9 Cr0.1 (PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%, and the mass of the carbon coating layer is calculated according to the mass of C elements.

[0082] Example 5

[0083] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 1 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 1.96g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 4.2g of a carbon source (sucrose) are added into 510g of ethanol, and then the mixture is fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 1, and details are not described herein again. Finally, the cation-doped carbon-coated titanium magnesium phosphate composite material, namely Cr 3+ doped carbon-coated titanium magnesium phosphate composite material is obtained.

[0084] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.7 Ti 1.8 Cr 0.2 (PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%, and the mass of the carbon coating layer is calculated according to the mass of C elements.

[0085] Example 6

[0086] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 1 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 1.96g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 4.2g of a carbon source (sucrose) are added into 510g of ethanol, and then the mixture is fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 1, and details are not described herein again. Finally, the cation-doped carbon-coated titanium magnesium phosphate composite material, namely Cr 3+ doped carbon-coated titanium magnesium phosphate composite material is obtained.

[0087] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.9 Ti1.6 Cr 0.4 (PO4)3 / 2.5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%, and the mass of the carbon coating layer is calculated based on the mass of C element.

[0088] Example 7

[0089] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, comprising the following steps:

[0090] S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 2.28g of a M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 8.41g of a carbon source (citric acid) are added into 500g of ethanol, and then transferred into a high-energy ball mill, and mixed at a rotating speed of 500rpm for 4h to obtain a precursor slurry;

[0091] S2, the precursor slurry is transferred to a gas pressure type spray dryer, the outlet temperature of the spray dryer is 290℃, the inlet temperature is 120℃, and the pressure is 0.4Mpa, and after sufficient drying, loose precursor powder is obtained;

[0092] S3, the precursor powder is transferred to an atmosphere furnace, and heated to 500℃ at a heating rate of 2℃ / min under a nitrogen atmosphere and maintained for calcination for 5h, and then heated to 1000℃ at a heating rate of 2℃ / min, and maintained for calcination for 6h, and then naturally cooled to room temperature, and then ground to obtain a cation-doped carbon-coated titanium magnesium phosphate composite material, i.e. Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0093] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, and the chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.6 Ti 1.9 Cr 0.1 (PO4)3 / 5C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%, and the mass of the carbon coating layer is calculated based on the mass of C element.

[0094] Example 8

[0095] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 7 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 2.28g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 8.41g of a carbon source (sucrose) are added into 600g of ethanol, and then are fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 7, and details are not described herein again, and finally the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0096] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.6 Ti 1.9 Cr 0.1 (PO4)3 / 5C, and includes a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 5wt%, and the mass of the carbon coating layer is calculated according to the mass of C element.

[0097] Embodiment 9

[0098] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 7 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 2.28g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 12.63g of a carbon source (sucrose) are added into 550g of ethanol, and then are fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 7, and details are not described herein again, and finally the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ doped carbon-coated titanium magnesium phosphate composite material.

[0099] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.6 Ti 1.9 Cr 0.1 (PO4)3 / 7.5C, and includes a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 7.5wt%, and the mass of the carbon coating layer is calculated according to the mass of C element.

[0100] Embodiment 10

[0101] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 7 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 2.28g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 16.83g of a carbon source (sucrose) are added into 600g of ethanol, and then are fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 7, and details are not described herein again, and finally, the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ The cation-doped carbon-coated titanium magnesium phosphate composite material.

[0102] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.6 Ti 1.9 Cr 0.1 (PO4)3 / 10C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 10wt%, and the mass of the carbon coating layer is calculated according to the mass of C element.

[0103] Example 11

[0104] The embodiment provides a preparation method of a cation-doped carbon-coated titanium magnesium phosphate composite material, which is different from that in the embodiment 7 in that in the step S1, 15.2g of a magnesium source (magnesium carbonate), 57.6g of a titanium source (titanium dioxide), 2.28g of an M source (chromium oxide), 40.7g of a phosphorus source (ammonium dihydrogen phosphate) and 25.24g of a carbon source (sucrose) are added into 650g of ethanol, and then are fully mixed in a high-energy ball mill at a rotating speed of 500rpm for 4h to obtain a precursor slurry; other steps and methods are the same as those in the embodiment 7, and details are not described herein again, and finally, the cation-doped carbon-coated titanium magnesium phosphate composite material, i.e., Cr 3+ The cation-doped carbon-coated titanium magnesium phosphate composite material.

[0105] The embodiment also provides a cation-doped carbon-coated titanium magnesium phosphate composite material, which has a chemical general formula of Mg 0.6 Ti 1.9 Cr 0.1 (PO4)3 / 15C, the cation-doped carbon-coated titanium magnesium phosphate composite material comprises a carbon coating layer and a titanium magnesium phosphate, the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 15wt%, and the mass of the carbon coating layer is calculated according to the mass of C element.

[0106] Comparative example 1

[0107] The comparative example provides a titanium magnesium phosphate material and a preparation method thereof, the chemical formula of the titanium magnesium phosphate material is Mg 0.5 Ti2(PO4)3.

[0108] The preparation method of the titanium magnesium phosphate material is different from the preparation method in the example 1 in that: no M source and carbon source are added in the step S1, and other steps and methods are the same as those in the example 1, and details are not repeated here.

[0109] Referring to Figure 1 From the XRD patterns of the cation-doped carbon-coated titanium magnesium phosphate composite materials in the examples 1-11 and the titanium magnesium phosphate material in the comparative example 1, it can be seen from the figure that the diffraction peaks of the cation-doped carbon-coated titanium magnesium phosphate composite materials coincide with the diffraction peaks of the titanium magnesium phosphate standard card, which indicates that the cation-doped carbon-coated titanium magnesium phosphate composite materials do not change the lattice structure of the NASICON-type titanium magnesium phosphate main crystal phase; in addition, the doping of appropriate M elements can effectively inhibit the formation of the titanium pyrophosphate impurity phase, since the substitution of the tetravalent Ti ion by the trivalent M ion introduces more Mg elements to maintain electrical neutrality, and the supplemented Mg elements can further convert the titanium pyrophosphate impurity phase into the titanium magnesium phosphate conductive crystal, thereby reducing the adverse effects of these impurities on ion conduction to a certain extent.

[0110] Performance test:

[0111] The cation-doped carbon-coated titanium magnesium phosphate composite materials provided in the examples 1-11 and the titanium magnesium phosphate material in the comparative example 1 are subjected to conductivity test, and the specific test method is as follows: a powder tablet machine is used to press the cation-doped carbon-coated titanium magnesium phosphate composite material or the titanium magnesium phosphate material into a tablet under a pressure of 200 Mpa, then the two surfaces of the tablet are polished by sandpaper and coated with conductive silver paste respectively, and after drying, an electrochemical tester is used to test the electrochemical impedance spectrum (EIS) thereof, and the measured ion conductivity results are shown in Table 1.

[0112] Table 1, ion conductivity of the cation-doped carbon-coated titanium magnesium phosphate composite materials in the examples 1-11 and ion conductivity of the titanium magnesium phosphate material in the comparative example 1

[0113]

[0114]

[0115] From the test data in Table 1, it can be seen that compared with the titanium magnesium phosphate material in the comparative example 1, the ion conductivity of the cation-doped carbon-coated titanium magnesium phosphate composite material obtained in the examples 1-11 is obviously improved, which indicates that the conductivity of the NASICON-type titanium magnesium phosphate is successfully improved by doping M elements; this is mainly because the doping of M elements can effectively inhibit the formation of the titanium pyrophosphate impurity phase, and the substitution of the tetravalent Ti ion by the trivalent M ion introduces more Mg elements to maintain electrical neutrality, and the supplemented Mg elements can further convert the titanium pyrophosphate impurity phase into the titanium magnesium phosphate conductive crystal, thereby reducing the adverse effects of these impurities on ion conduction to a certain extent. 3+Cation-substituted Ti 4+ It can broaden the migration channel of lithium ions, introduce more conductive lithium ions to maintain electrical neutrality, increase the number of carriers, and improve ionic conductivity; According to the results in Table 1, it can be found that with the increase of M 3+ With the increase of the concentration, the corresponding ionic conductivity first increases and then decreases. When the cation doping amount is 0.1, the room temperature ionic conductivity is the highest, which is 7.96×10 -4 S cm -1 This indicates that the content of doping elements should be controlled within a certain range, and it is not advisable to dope too much or too little. Excessive doping of exogenous ions may cause lattice distortion, thereby interfering with the NASICON structure suitable for carrier migration, causing capacity attenuation. Too little substitution will not achieve the required electrochemical performance. In addition, titanium pyrophosphate impurity phase may be produced. Therefore, the content of doping elements should be controlled within a certain range. On this basis, carbon coating the surface of cation-doped magnesium titanium phosphate is beneficial to further improve the ionic conductivity of magnesium titanium phosphate. With the help of the fast lithium ion conductor characteristics of the coating layer, the Li inside the material is + It promotes the migration of magnesium titanium phosphate, making the material have higher electrical conductivity, and can also serve as a protective layer for magnesium titanium phosphate material to extend the cycle life.

[0116] Application Examples

[0117] This application example provides an application of a cation-doped carbon-coated magnesium titanium phosphate composite material in a lithium-ion battery. The cation-doped carbon-coated magnesium titanium phosphate composite materials provided in the above-mentioned Examples 1 to 11 or the magnesium titanium phosphate material in Comparative Example 1 are respectively used as additives to the positive electrode active material to prepare positive electrode sheets, and the positive electrode sheets are assembled into button-type lithium batteries for testing.

[0118] The specific process of assembling button-type lithium batteries is as follows: the positive electrode active material is lithium nickel cobalt manganese oxide, and 2.5% cation-doped carbon-coated titanium magnesium phosphate composite material is added in the process of preparing the positive electrode slurry. The prepared positive electrode slurry is evenly coated on copper foil, vacuum dried at 120°C for 10 hours, and cut to obtain the positive electrode sheet. Then, a metal lithium sheet is used as the negative electrode, a single-layer polyethylene film is used as the separator, and a 1M LiClO4 ethyl acetate solution is used as the electrolyte. The button-type lithium battery is assembled in a closed glove box filled with argon.

[0119] The assembled button-type lithium battery was subjected to a cycle performance test: between 2.5V and 4.3V, the battery was charged and discharged at 0.1C for the first week, and then cycled at a rate of 0.5C. The cycle capacity retention rate after 100 and 300 cycles was tested. The test results are shown in Table 2.

[0120]

[0121]

[0122] From the test results in Table 2, compared with the titanium magnesium phosphate material in Comparative Example 1, the capacity retention rate of the coin lithium battery assembled by the cation-doped carbon-coated titanium magnesium phosphate composite material obtained by Examples 1-11 is obviously improved after 100 weeks and 300 weeks of long cycle, which shows that the cation-doped carbon-coated titanium magnesium phosphate composite material provided in the application can improve the kinetic performance of the lithium battery when used as an additive for preparing the positive electrode sheet, thereby improving the cycle life of the lithium battery.

[0123] In summary, the preparation method provided by the application is simple, easy to operate and low in cost, the doped metal source and the carbon source material are introduced into the mixed slurry, and the NASICON type cation-doped carbon-coated titanium magnesium phosphate composite material is obtained by one-step sintering or sectional sintering, the doping of the trivalent M cation can maintain the NASICON type structure of the material and effectively inhibit the formation of the impurity phase titanium pyrophosphate; in addition, the M 3+ Cation substitution Ti 4+ The migration channel of lithium ions can be widened, more conductive lithium ions can be introduced to maintain electrical neutrality, the number of charge carriers can be increased, and the electrical conductivity of the material can also be improved; on this basis, the organic carbon source is uniformly coated on the surface of the spherical precursor powder in the mixed slurry together with other raw materials in the spray drying process, the surface of the cation-doped titanium magnesium phosphate is uniformly coated with carbon by high-temperature sintering, which is conducive to further improving the electrical conductivity of the titanium magnesium phosphate, and the Li + migration in the material is promoted by the fast lithium ion conductor characteristics of the coating layer, so that the material has high electrical conductivity and capacity retention rate, and can also serve as a protective layer for the titanium magnesium phosphate material to prolong the cycle life; and the cation-doped carbon-coated titanium magnesium phosphate composite material provided by the application is applied to lithium batteries, effectively improves the kinetic performance of the battery, greatly improves the cycle life of the lithium battery, and has important significance for the sustainable development of future energy; therefore, the application effectively overcomes the shortcomings in the prior art and has high industrial utilization value.

[0124] The above examples only exemplarily illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the application should be covered by the claims of the application.

Claims

1. A cation-doped carbon-coated titanium magnesium phosphate composite material, characterized in that: The chemical general formula of the cation-doped carbon-coated titanium magnesium phosphate composite material is Mg 0.5+x Ti 2-x M x (PO4)3 / C, wherein M is selected from at least one of Al, Cr, 0.01≤x<0.5, and C is a carbon coating layer.

2. The cation-doped carbon-coated titamgu phosphate composite material according to claim 1, characterized in that: comprise one or a combination of the following conditions: a material of the carbon-coated layer is one of amorphous carbon and crystalline carbon; the carbon-coated layer is selected from at least one of a continuous film, a discontinuous film, and closely arranged carbon particles; a mass percentage of the carbon-coated layer in a total mass of the titanium magnesium phosphate is 2.5wt%-15wt%.

3. A method for preparing a cation-doped carbon-coated titanium magnesium phosphate composite material, characterized in that: the preparation method comprises the following steps: S1, adding a magnesium source, a titanium source, an M source, a phosphorus source, and a carbon source into a solvent and mixing them thoroughly to obtain a precursor slurry; S2, transferring the precursor slurry to a drying device to dry thoroughly to obtain a precursor powder; S3, heating and calcining the precursor powder under a protective atmosphere, and after cooling, obtaining a cation-doped carbon-coated titanium magnesium phosphate composite material.

4. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 3, characterized in that: In step S1, one or a combination of the following conditions is included: the magnesium source comprises one or a combination of magnesium carbonate, magnesium oxide, magnesium hydroxide, and magnesium phosphate; the titanium source comprises one or a combination of titanium dioxide and titanium phosphate; the M source is a doping element source, the doping element is at least one of Al and Cr, and the doping element source is one or a combination of oxides, carbonates, phosphates, and oxalates of the doping element; the phosphorus source comprises one or a combination of diammonium hydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, and diphosphorus pentoxide; a molar ratio between the magnesium source (calculated based on Mg element), the titanium source (calculated based on Ti element), the M source (calculated based on M doping element), and the phosphorus source (calculated based on P element) is (0.5+x):(2-x):x:3, wherein 0.01≤x<0.5; the carbon source comprises one or a combination of corn starch, glucose, sucrose, oxalic acid, citric acid, ascorbic acid, polyvinylpyrrolidone, and polyethylene glycol.

5. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 3, characterized in that: In step S1, one or a combination of the following conditions is included: the solvent comprises one or a combination of deionized water, ethanol, propylene glycol, and polyvinyl alcohol; a total mass of the magnesium source, the titanium source, the M source, the phosphorus source, and the carbon source accounts for 10wt%-30wt% of the precursor slurry.

6. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 3, characterized in that: In step S2, the drying device is used to dry thoroughly in one of the following ways: air oven drying, vacuum rake drying, and spray dryer drying; when the air oven drying or the vacuum rake drying is used, the temperature of the air oven drying and the temperature of the vacuum rake drying are both 140°C-210°C, and the drying time is both 6-12h; when the spray dryer drying is used, the outlet temperature of the spray dryer is 280-300°C, the inlet temperature is 110-130°C, and the pressure is 0.4Mpa-0.5Mpa.

7. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 3, characterized in that: In step S3, the heating and calcining of the precursor powder under a protective atmosphere comprises the following steps: firstly calcining the precursor powder under a protective atmosphere, maintaining the first calcining temperature at 350-600°C, maintaining the first calcining for 5-10h, and maintaining the first temperature rising rate at 1-3°C / min; Then, the second calcination is carried out under a protective atmosphere, the second calcination temperature is maintained at 1000-1200 DEG C, the second calcination is maintained for 4-12 hours, and the second temperature increasing rate is 2-5 DEG C / min.

8. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 8, characterized in that: The protective atmosphere is one of nitrogen, helium and argon.

9. The method for preparing the cation-doped carbon-coated magnesium titanium phosphate composite material according to claim 3, characterized in that: The cation-doped carbon-coated titanium magnesium phosphate composite material obtained in step S3 comprises a carbon coating layer and a titanium magnesium phosphate material, the carbon coating layer is calculated by C element, and the mass percentage of the carbon coating layer in the titanium magnesium phosphate material is 2.5wt%-15wt%.

10. Use of a cation-doped carbon-coated titanium magnesium phosphate composite material in a lithium battery, characterized in that: The cation-doped carbon-coated titanium magnesium phosphate composite material is the cation-doped carbon-coated titanium magnesium phosphate composite material in claim 1 or 2, or the cation-doped carbon-coated titanium magnesium phosphate composite material prepared by the preparation method in any one of claims 3-9.

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