CN114335454B - Titanium-based composite material with multi-layer structure and preparation method thereof - Google Patents
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Abstract
The invention relates to a titanium-based composite material with a multi-layer structure and a preparation method thereof, belonging to the technical field of lithium ion batteries. The invention discloses a titanium-based composite material with a multi-layer structure, which has a core-shell structure, wherein the inner core is lithium titanate, the first coating layer is titanium niobate, and the second coating layer is a carbon layer; the mass ratio of each material in the composite material is respectively 60-80% of lithium titanate, 20-40% of titanium niobate and 1-5% of carbon source. The invention also discloses a preparation method of the titanium-based composite material with the multi-layer structure, which comprises the following steps: grinding a titanium source and a lithium source, performing ultrasonic dispersion treatment, and then drying, granulating and calcining to obtain nano lithium titanate microspheres; dispersing nano lithium titanate microspheres in a surfactant mixed solution, then adding a soluble titanium compound and a soluble niobium compound, stirring at constant temperature, aging and drying to obtain a composite material precursor; and mixing the composite material precursor with a carbon source, and calcining and crushing under an inert gas atmosphere to obtain the titanium-based composite material with the multi-layer structure.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a titanium-based composite material with a multi-layer structure and a preparation method thereof.
Background
As one of the most widely used energy storage systems, lithium Ion Batteries (LIBs) have been widely used in consumer electronics in the last twenty years, and the application range of Electric Vehicles (EVs), hybrid Electric Vehicles (HEVs), power grid energy storage and other fields has been greatly expanded in recent 10 years. As one of the key components of the battery. The graphite carbon cathode material is the first choice of the current commercial lithium ion battery, but the lithium ion migration rate in the graphite material is slow, the working voltage is low, the problems of poor charge-discharge rate performance, poor working safety at fast charge and low temperature and the like exist, and the application requirements of high-rate and high-safety working conditions cannot be met. Therefore, a lithium ion battery anode material having both high magnification and high safety is urgently required to be developed.
The properties of the niobium titanium oxide are similar to those of lithium titanate, a relatively safe charge-discharge platform (-1.6V) is provided, and the material structure is more stable in the charge-discharge process of the structure in the Li+ intercalation and deintercalation process, but the theoretical capacity of the titanium niobate anode material is almost 2 times of that of the lithium titanate, and the capacity of the titanium niobate anode material reaches 387mAh/g. Therefore, the titanium niobate negative electrode material becomes a fast-charge type lithium ionResearch hotspots on anode materials. However, since the band gap of titanium niobate is wide (-2.9 eV), and wherein Ti 4+ And Nb (Nb) 5+ All in the highest valence state, no unpaired electrons, resulting in material conductivity and poor, almost insulating. In addition, li of titanium niobate + The diffusion coefficient is also low, resulting in a large interfacial resistance between the titanium niobate anode material and the electrolyte. The defects in the two aspects lead to lower electronic conductivity and ionic conductivity of the titanium niobate anode material, thus severely limiting the coulombic efficiency and the multiplying power performance of the titanium niobate anode material, and the defects limit the commercialization application of the titanium niobate anode material in lithium ion batteries.
CN201910442680.5 provides a titanium niobate/lithium titanate composite material, which is obtained by spraying titanium niobate powder into atomized lithium titanate solution, and fully mixing the powder to obtain a core-shell structure material, but the material is only the mixture among particles and has no other coating layer. The existing composite material cannot simultaneously play the role of solving the high capacity characteristic of titanium niobate and the high rate capability of lithium titanate, and cannot better isolate the gas production reaction of lithium titanate.
Disclosure of Invention
The invention aims at solving the problems existing in the prior art and provides a titanium-based composite material with a multi-layer structure, which has the high capacity characteristic of titanium niobate and the high rate capability of lithium titanate.
The invention adopts the following technical scheme: a titanium-based composite material with a multi-layer structure is provided, wherein the composite material has a core-shell structure, the inner core is lithium titanate, the first coating layer is titanium niobate, and the second coating layer is a carbon layer.
The composite material core 1 is lithium titanate, the first coating layer 2 is titanium niobate, the second coating layer 3 is a carbon layer, and the structural schematic diagram is shown in fig. 1.
Preferably, the mass ratio of each material in the composite material is respectively 60-80% of lithium titanate, 20-40% of titanium niobate and 1-5% of carbon source.
Further preferably, the carbon layer has a thickness of 30-80nm.
Preferably, the specific surface area of the composite material is 1-20m 2 /g, median particleThe diameter is 4-6 μm, and the pH value is 9.0-11.
Further preferably, the specific surface area of the composite material is 3-10m 2 /g。
The invention also provides a preparation method of the titanium-based composite material with the multi-layer structure, which comprises the following steps: grinding a titanium source and a lithium source, performing ultrasonic dispersion treatment, and then drying, granulating and calcining to obtain nano lithium titanate microspheres; dispersing nano lithium titanate microspheres in a surfactant mixed solution, then adding a soluble titanium compound and a soluble niobium compound, stirring at constant temperature, aging and drying to obtain a composite material precursor; and mixing the composite material precursor with a carbon source, and calcining and crushing under an inert gas atmosphere to obtain the titanium-based composite material with the multi-layer structure.
Preferably, the titanium source is titanium dioxide.
Preferably, the lithium source is one or more of lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate and lithium hydroxide monohydrate.
Preferably, the Li/Ti molar ratio is 4 (4.5-5.0).
Further preferably, the Li/Ti molar ratio is 4 (4.7-4.9).
Preferably, the grinding process is wet grinding, the linear velocity is 12-18m/s, and the time is 2-6h.
Further preferably, the milling process slurry has a solids content of 20-40%.
Preferably, the inlet temperature of the drying and granulating process is 220-260 ℃, the outlet temperature is 90-110 ℃, and the particle D50 is 2-5 mu m.
Preferably, the calcination process is carried out in a muffle furnace at 800-1000 ℃ at a heating rate of 3-8 ℃/min for 6-15h.
Preferably, the specific surface area of the nano lithium titanate microsphere is 4-15m 2 And/g, median particle diameter 2-3 μm.
Preferably, the surfactant comprises Dodecyl Trimethyl Ammonium Bromide (DTAB), tetradecyl Trimethyl Ammonium Bromide (TTAB), hexadecyl trimethyl ammonium bromide (CTAB), octadecyl trimethyl ammonium bromideAmmonium (OTAB), 3-alkoxy-2-Hydroxypropyl Trimethyl Ammonium Bromide (HTAB), cetyl trimethyl ammonium salicylate (C) 16 TASal).
Preferably, the solvent of the surfactant is one or more of absolute ethyl alcohol, ethylene glycol, isopropanol and glycerol; the concentration is 0.05-0.5mol/L.
Further preferably, the concentration of the surfactant mixed solution is 0.1 to 0.3mol/L.
Still more preferably, the solid content of the surfactant mixed solution is 20 to 50%.
The lithium titanate belongs to a indissolvable substance, and the surfactant can improve the dispersion effect of the lithium titanate and provide conditions for the subsequent uniform coating of the titanium niobate precursor on the surface of the titanium niobate precursor. In addition, the surfactant can regulate the pH value of the solution, slow down the reaction rate of the hydrolysis reaction of tetrabutyl titanate and ammonium niobium oxalate and control the size of the titanium niobate nano particles.
Preferably, the soluble titanium compound is one or more of titanyl sulfate, titanium tetrafluoride, titanium tetraisopropoxide, titanium sulfate, potassium titanium oxalate, titanium tetrachloride, titanium trichloride and tetrabutyl titanate.
Preferably, the soluble niobium compound is one or more of niobium oxalate, ammonium niobium oxalate, niobium ethoxide and niobium pentachloride.
According to the invention, the coating of the titanium niobate on the surface of the lithium titanate is carried out by a sol-gel method, the soluble niobium salt and the titanium source can provide niobium ions and titanium ions, and the insoluble niobium source and the titanium source can not generate the titanium niobate precursor, so that the coating of the titanium niobate precursor on the surface of the lithium titanate can not be satisfied. The molecular formula of the titanium niobate is TiNb 2 O 7 The theoretical molar ratio of Ti to Nb is 1:2, and increasing the proportion of a niobium source is beneficial to improving the cycle stability and the multiplying power performance of the material; in addition, excessive niobium can reduce the overall pH of the composite material and improve the processing performance of the material, but excessive niobium addition causes the reduction of specific capacity and the increase of cost.
Preferably, the Ti/Nb molar ratio is 1 (2.0-2.3).
Further preferably, the Ti/Nb molar ratio is 1 (2.05-2.1).
Preferably, the constant temperature stirring is carried out in an oil bath, the solution temperature is 80-160 ℃, and the reaction time is 12-48h.
The constant-temperature stirring aims to control the generation rate of the titanium niobate precursor and ensure the uniform coating of the titanium niobate precursor on the surface of lithium titanate.
Preferably, the aging process comprises: the system is kept stand under the condition of unchanged system, after the sediment is generated in the open beaker, the sediment is placed for a period of time together with the mother liquor, and irreversible recrystallization process occurs in the sediment.
By aging, a crystalline form is intact, large and pure precipitate can be obtained. The aging process can be accelerated by properly increasing the temperature; the longer the time, the more complete the aging.
Preferably, the drying is one or more of forced air drying, press filtration drying and spray drying.
Preferably, the mixing process of the composite material precursor and the carbon source is one of a solid-phase coating method or a gas-phase coating method.
Further preferably, the solid phase coated carbon source is selected from one or more of pitch, sucrose, glucose, citric acid; the gas phase coated carbon source is one or more of methane, acetylene, ethylene and the like.
The gas phase cladding method comprises the steps of placing a precursor of the composite material in an atmosphere protection rotary furnace, introducing nitrogen to remove residual air in the furnace, then introducing organic carbon source gas, and cracking the carbon source at 500-1000 ℃, thereby forming a compact and uniform carbon cladding layer on the surface of the composite material, and enabling the carbon content to be 1-5%.
Preferably, the mass ratio of the composite material precursor to the solid phase coated carbon source is (8-14): 1.
Preferably, the calcination process is carried out under nitrogen at a temperature of 800-1000 ℃ for a time of 5-16 hours.
Compared with the prior art, the invention has the following beneficial effects:
1. the prepared titanium-based composite material with the multi-layer structure has a core-shell structure, lithium titanate is taken as an inner core, a first coating layer is titanium niobate, and a second coating layer is a carbon layer.
2. According to the invention, the titanium niobate is introduced to make up for the disadvantage of lower theoretical specific capacity of lithium titanate, and the prepared composite material has both the high capacity characteristic of titanium niobate and the high rate capability of lithium titanate.
3. According to the invention, the pH of the lithium titanate and the surface characteristics of the lithium titanate core can be reduced by coating the titanium niobate, and the carbon second coating layer can increase the conductivity of the composite material and promote the circulation stability.
4. The preparation method can improve the processing stability of the material and inhibit the gas production phenomenon of lithium titanate in the charge and discharge process.
5. The preparation method of the invention has the advantages of simple and controllable operation, simple process flow, lower cost and high degree of automation.
Drawings
FIG. 1 is a schematic structural view of a titanium-based composite material of a multi-layered structure.
FIG. 2 is a scanning electron microscope image of the lithium titanate core produced in example 1.
FIG. 3 is a scanning electron microscope image of the titanium-based composite material of the multi-layered structure prepared in example 1.
Fig. 4 is a transmission electron microscope image of the titanium-based composite material of the multi-layered structure prepared in example 2.
Detailed Description
The following are specific examples of the present invention, and the technical solutions of the present invention are further described, but the present invention is not limited to these examples.
Example 1
1000.0g of titanium dioxide and 385.0g of lithium carbonate powder are added into a sand mill, water is added to adjust the solid content to 30%, grinding is carried out for 6 hours at the linear speed of 14m/s, then the grinding slurry is transferred and spray drying treatment is carried out, the temperature of a spray feeding hole is 230 ℃, the temperature of a discharge hole is 110 ℃, the lithium titanate precursor with the median particle diameter of 3 mu m is obtained, then the lithium titanate precursor is placed into a muffle furnace to react for 10 hours at the temperature of 800 ℃, and finally the nanometer lithium titanate microsphere core with the median particle diameter of 3 mu m is obtained, and a scanning electron microscope image is shown in figure 2.
Then CTAB is dissolved in absolute ethyl alcohol to prepare suspension with the concentration of 0.15mol/L, then 600.0g of nano lithium titanate microspheres are dispersed in the suspension, then the solution is sequentially added into the mixed solution, the solid content is adjusted to 35%, then the solution is subjected to oil bath for 24 hours at the constant temperature of 160 ℃, and finally the precursor of the titanium-based composite material is obtained through ageing, press filtration and drying.
And then mixing the dried titanium-based composite precursor with citric acid according to the weight ratio of 9:1, transferring into a nitrogen atmosphere box-type furnace, and carrying out high-temperature treatment for 6 hours at 900 ℃ to finally obtain the titanium-based composite with the multi-level structure. The scanning electron microscope image is shown in fig. 3, and the thickness of the carbon coating layer is shown in fig. 4.
The composite material is then: PVDF: super P is prepared according to a mass ratio of 82:8:10, mixing, dissolving and dispersing uniformly by using N-methyl pyrrolidone, coating on an aluminum foil, drying and rolling to prepare the pole piece. The composite pole piece is used as a working electrode, the lithium piece is used as a counter electrode and a reference electrode, and 1mol of LiPF is used 6 (EC: DMC: emc=1:1:1 v/v) as electrolyte, polypropylene fiber as separator, and assembled into a battery in a glove box. The assembled battery was activated with a 1C current cycle of 5 cycles, setting a charge-discharge range of 1.0-2.5V, followed by a 1C cycle of 50 cycles. After the composite material is subjected to rate performance test in 1C for 5 circles, the composite material is respectively subjected to 2C, 5C, 10C and 20C for 5 circles, and then the composite material is recovered in 1C for 5 circles. The 20C/1C capacity retention results are shown in Table 1.
Example 2
In comparison with example 1, the difference was that 1000.0g of titanium dioxide and 437.3g of lithium hydroxide monohydrate powder were added to a sand mill, water was further added to adjust the solid content to 30%, grinding was carried out at a linear speed of 15m/s for 6 hours, and then the grinding slurry was transferred and subjected to spray drying treatment. The PH of the composite material obtained thereafter is shown in table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Example 3
Compared with example 1, the method is characterized in that 600.0g of nano lithium titanate microspheres are dispersed in an absolute ethanol suspension containing CTAB, 408.5g of niobium pentachloride and 117.5g of titanyl sulfate are added, then oil bath is carried out for 24 hours at a constant temperature of 150 ℃, and finally, the titanium-based composite precursor is obtained through ageing and air drying. The PH of the composite material obtained thereafter is shown in table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Example 4
Compared with the embodiment 1, the method is characterized in that the dried titanium-based composite precursor and citric acid are mixed according to the weight ratio of 9:1, then the mixture is transferred into a nitrogen atmosphere box-type furnace, and the mixture is treated at the high temperature of 800 ℃ for 6 hours, and finally the titanium-based composite with the multi-level structure is obtained. The pH of the resulting composite is shown in Table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Example 5
Compared with the embodiment 1, the difference is that the precursor of the titanium-based composite material is transferred into a rotary furnace protected by nitrogen, then acetylene gas is introduced, the flow rate is 1.5L/min, the reaction is carried out for 4 hours at 800 ℃, the cooled precursor is continuously subjected to heat treatment for 6 hours at 900 ℃ in an atmosphere protection box-type furnace, and finally the titanium-based composite material with the multi-level structure is obtained. The pH of the resulting composite is shown in Table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Comparative example 1
1000.0g of titanium dioxide and 385.0g of lithium carbonate powder are added into a sand mill, water is added to adjust the solid content to 30%, grinding is carried out for 6 hours at the linear speed of 14m/s, then the grinding slurry is transferred and spray drying treatment is carried out, the temperature of a spray feeding hole is 220 ℃, the temperature of a discharge hole is 110 ℃, a lithium titanate precursor is obtained, then the lithium titanate precursor is placed into a muffle furnace, and the reaction is carried out for 10 hours at the temperature of 800 ℃, thus finally obtaining the nano lithium titanate microsphere. The pH of the lithium titanate obtained is shown in Table 1; the assembled battery was subjected to performance test, and the results of the performance test are shown in table 1.
Comparative example 2
CTAB is dissolved in absolute ethyl alcohol to prepare a suspension with the concentration of 0.15mol/L, 460.0g of ammonium niobium oxalate and 250.0g of tetrabutyl titanate are sequentially added into the suspension, the solid content is adjusted to be 30 percent, then the suspension is subjected to oil bath for 24 hours at the constant temperature of 150 ℃, and finally the suspension is aged, press-filtered and dried and then is subjected to glucose mixing according to the mass ratio of 8:1, transferring the mixture into a tube furnace in a nitrogen atmosphere, and treating the mixture for 6 hours at 900 ℃ to obtain the carbon-coated titanium niobate material. The pH of the product is shown in Table 1; the assembled battery was subjected to performance test, and the results of the performance test are shown in table 1.
Comparative example 3
Compared with example 1, the method is characterized in that 430.0g of ammonium niobium oxalate and 250.0g of tetrabutyl titanate are added, then oil bath is carried out for 24 hours at the constant temperature of 160 ℃, and finally aging and forced air drying are carried out to obtain the titanium-based composite material precursor. The PH of the composite material obtained thereafter is shown in table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Comparative example 4
Compared with example 1, the method is characterized in that 600.0g of the nano lithium titanate microspheres are dispersed in an absolute ethanol suspension containing CTAB, 190.1g of ammonium niobium oxalate and 103.7g of tetrabutyl titanate are added, then oil bath is carried out for 24 hours at a constant temperature of 150 ℃, and finally, the titanium-based composite precursor is obtained through ageing and forced air drying. The PH of the composite material obtained thereafter is shown in table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Comparative example 5
Compared with example 1, the method is characterized in that 600.0g of the nano lithium titanate microspheres are dispersed in an absolute ethanol suspension containing CTAB, 1079.0g of ammonium niobium oxalate and 589.2g of tetrabutyl titanate are added, then oil bath is carried out for 24 hours at a constant temperature of 150 ℃, and finally, the titanium-based composite precursor is obtained through ageing and forced air drying. The PH of the composite material obtained thereafter is shown in table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
Comparative example 6
Compared with example 1, the titanium-based composite precursor and asphalt are different in mass ratio of 11:1, then transferring the mixture into a nitrogen atmosphere box-type furnace, and carrying out high-temperature treatment for 4 hours at 1100 ℃ to finally obtain the titanium-based composite material with the multi-level structure. The pH of the resulting composite is shown in Table 1; performance testing was performed after assembly into a battery, and the performance test results are shown in table 1.
TABLE 1 PH value and Battery Performance Table of titanium-based composite Material of Multi-layer Structure
As can be seen from Table 1, the pH of the composite material of example 1 was 10.6, the prepared CR2430 type battery had a reversible specific capacity of 218.3mAh/g for the first time at a current density of 1C, a capacity retention rate after 100 cycles was 97.1%, the battery capacity remained 184.1mAh/g at a current density of 20C, and a capacity retention rate of 20C/1C was 84.3%, and the composite material of example 1 exhibited good cycle performance and rate performance. Example 2 the lithium source used to prepare lithium titanate was replaced with lithium hydroxide monohydrate, and the subsequent continuous heat treatment resulted in an increase in the initial particle size of lithium titanate, and eventually in a deterioration in the cycle and rate performance of the multi-layered titanium-based composite material, due to the lower melting point and greater basicity of lithium hydroxide. Example 3 the electrochemical properties of the composite material prepared in example 1 were not significantly different from those of the titanium source and niobium source species required for the preparation of titanium niobate. Example 4 to reduce the firing and carbonization temperatures of titanium niobate, the crystallinity of titanium niobate is reduced, the specific capacity of the composite material is increased, the cycle and rate performance are slightly increased, but the initial effect is reduced. In example 5, the solid phase coating was adjusted to the gas phase coating, and the cycle stability and rate performance of the composite material were improved due to the uniformity of the carbon coating. Comparative example 1 is a pure-phase prepared nano lithium titanate, which has high initial efficiency, excellent cycle and rate performance, but lower specific capacity. While comparative example 2 is a carbon-coated titanium niobate material having a higher capacity but a lower initial efficiency and poor cycle and rate performance. Comparative example 3 is to reduce the Ti/Nb molar ratio in titanium niobate, and both the cycle stability and rate performance of the composite material are reduced. In comparative example 4, in order to reduce the coating proportion of titanium niobate, the capacity increase of the composite material is not obvious, the coating effect is not uniform, and the processing stability of the material is not obviously improved. In example 5, the coating ratio of titanium niobate was increased, but the side reaction was increased, the initial effect was significantly reduced, and the cycle stability and rate capability were poor. Comparative example 6 is to improve the crystallinity of titanium niobate, but the particle size is significantly increased, the capacity is reduced, the initial effect is increased, and the cycle stability and the rate performance are significantly deteriorated.
In conclusion, the preparation method is simple and controllable in operation, simple in process flow, low in cost and high in automation degree; the prepared titanium-based composite material with the multi-layer structure has a core-shell structure, lithium titanate is taken as an inner core, a first coating layer is titanium niobate, and a second coating layer is a carbon layer; the coating of the titanium niobate and the carbon layer can reduce the pH of the lithium titanate and the surface characteristics of the lithium titanate inner core, improve the processing stability of the material and inhibit the gas production phenomenon of the lithium titanate in the charge and discharge process, and the titanium niobate is introduced to make up for the disadvantage of lower theoretical specific capacity of the lithium titanate, and the carbon material coating layer can increase the conductivity of the composite material and improve the cycling stability of the battery.
The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.
Claims (9)
1. The titanium-based composite material with the multi-layer structure is characterized by having a core-shell structure, wherein the inner core is lithium titanate, the first coating layer is titanium niobate, and the second coating layer is a carbon layer;
the preparation method of the titanium-based composite material with the multi-layer structure comprises the following steps:
grinding a titanium source and a lithium source, performing ultrasonic dispersion treatment, and then drying, granulating and calcining to obtain nano lithium titanate microspheres; dispersing nano lithium titanate microspheres in a surfactant mixed solution, then adding a soluble titanium compound and a soluble niobium compound, stirring at constant temperature, aging and drying to obtain a composite material precursor; mixing a composite material precursor with a carbon source, and calcining and crushing under an inert gas atmosphere to obtain a titanium-based composite material with a multi-layer structure;
the inlet temperature of the drying and granulating process is 220-260 ℃, the outlet temperature is 90-110 ℃, and the particle D50 is 2-5 mu m.
2. The composite material according to claim 1, wherein the mass ratio of each material in the composite material is respectively 60-80% of lithium titanate, 20-40% of titanium niobate and 1-5% of carbon source.
3. A method of preparing the titanium-based composite material of multi-layered structure according to claim 1, comprising the steps of: grinding a titanium source and a lithium source, performing ultrasonic dispersion treatment, and then drying, granulating and calcining to obtain nano lithium titanate microspheres; dispersing nano lithium titanate microspheres in a surfactant mixed solution, then adding a soluble titanium compound and a soluble niobium compound, stirring at constant temperature, aging and drying to obtain a composite material precursor; and mixing the composite material precursor with a carbon source, and calcining and crushing under an inert gas atmosphere to obtain the titanium-based composite material with the multi-layer structure.
4. The method of claim 3, wherein the titanium source is titanium dioxide; the lithium source is one or more of lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate and lithium hydroxide monohydrate.
5. The method according to claim 3, wherein the molar ratio of Li/Ti in the titanium source and the lithium source is 4 (4.5-5.0).
6. The method according to claim 3, wherein the soluble titanium compound is one or more of titanyl sulfate, titanium tetrafluoride, titanium tetraisopropoxide, titanium sulfate, potassium titanium oxalate, titanium tetrachloride, titanium trichloride, tetrabutyl titanate; the soluble niobium compound is one or more of niobium oxalate, ammonium niobium oxalate, niobium ethoxide and niobium pentachloride.
7. The method according to claim 3 or 5, wherein the Ti/Nb molar ratio in the soluble titanium compound and the soluble niobium compound is 1 (2.0 to 2.3).
8. A method of preparation according to claim 3, wherein the surfactant comprises one or more of dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), hexadecyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium bromide (OTAB), 3-alkoxy-2-hydroxypropyl trimethylammonium bromide (HTAB), hexadecyltrimethylammonium salicylate (C16 TASal).
9. The method according to claim 3, wherein the calcination process is carried out in a muffle furnace at 800-1000 ℃ at a heating rate of 3-8 ℃/min for a reaction time of 6-15h.
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