CN113437269B - Carbon-coated lithium titanate electrode material and preparation method thereof - Google Patents
Carbon-coated lithium titanate electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a carbon-coated lithium titanate electrode material and a preparation method thereof, wherein the electrode material comprises a substrate and carbon-coated lithium titanate growing on the surface of the substrate in situ, the substrate is a titanium foil, and the electrode material has excellent rate capability. The preparation method comprises the following steps: placing a titanium foil in a hydrothermal kettle, adding a hydrothermal reagent, and carrying out hydrothermal reaction on the hydrothermal reagent containing lithium ions, an etching agent and an organic alcohol aqueous solution at 160-200 ℃ for 4-8 h to obtain a sheet lithium titanate @ polymer precursor composite material; and (3) placing the prepared sheet lithium titanate @ polymer precursor composite material in a tubular furnace, introducing inert gas, annealing at 600-900 ℃ for 1-3 h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material. The preparation method directly grows on the surface of the titanium foil in situ through hydrothermal reaction to obtain the sheet-shaped carbon-coated lithium titanate, and has the characteristics of simple preparation and good rate capability of the obtained cathode material.
Description
Technical Field
The invention relates to the technical field of lithium ion battery electrode materials, in particular to a carbon-coated lithium titanate electrode material and a preparation method thereof.
Background
Lithium ion batteries, as one of the main storage modes of clean energy, have the advantages of high energy, high power density, environmental protection and the like, and are currently applied to various electronic devices and electric vehicles. Among them, the electrode material is one of the key factors affecting the electrochemical performance of the lithium ion battery. At present, the commercial lithium ion battery negative electrode material is mainly made of graphite, but the lithium intercalation potential of the graphite is low (about 0.1V vs. Li +/Li), an SEI film is easily formed, and the volume change is overlarge in the charging and discharging process, so that the application of the lithium ion battery is influenced.
Lithium titanate materials are of great interest because of their "zero strain" because, when used as negative electrode materials for lithium ion batteries, the volume hardly changes during the "lithium intercalation/deintercalation" process, thus having the advantages of high safety performance, long cycle life, and the like. Meanwhile, the charge and discharge potential of lithium titanate is about 1.5V, and the voltage is higher than the formation potential of an SEI film, so that the SEI film cannot be formed on the lithium titanate in the circulation process, and the lithium titanate cannot be influenced by the SEI during charge and discharge under large current, so that the lithium titanate shows excellent rate performance.
However, the electron conductivity of the conventional lithium titanate material (10)－13～10－8S·cm－1) And lithium ion diffusion coefficient (about 10)－15cm2·s－1) The charge-discharge capacity of the lithium ion battery is greatly limited, namely the rate capability of the battery.
In the prior art, the rate capability of a lithium titanate material is improved by controlling the size and the morphology of lithium titanate and performing surface modification, for example, methods such as preparing a lithium titanate material with a nano structure, preparing a lithium titanate material with a sheet structure, preparing a carbon-doped coated lithium titanate material and the like can shorten the diffusion distance of lithium ions and improve the rate capability of the lithium titanate material. However, none of these methods is in situ synthesized on an electrode, the obtained lithium titanate material is in a powder or sheet shape, and when the electrode is prepared by using the lithium titanate material, the lithium titanate and a current collector can be combined by the processes of slurry mixing, coating, vacuum drying and the like by using a binder. Therefore, the lithium titanate synthesized in-situ can complicate the preparation process of the electrode on one hand, and the addition of the binder can reduce the ratio of the titanic acid on the other hand, thereby affecting the quality and capacity of the electrode.
It is seen that improvements and enhancements to the prior art are needed.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a carbon-coated lithium titanate electrode material and a preparation method thereof, and aims to overcome the defects of poor rate capability and complex preparation method of the lithium ion battery electrode material in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the carbon-coated lithium titanate electrode material comprises a substrate and carbon-coated lithium titanate growing on the surface of the substrate in situ, wherein the substrate is a titanium foil.
In the carbon-coated lithium titanate electrode material, the carbon-coated lithium titanate is in a sheet structure.
A method for preparing a carbon-coated lithium titanate electrode material as described above, wherein the method comprises the steps of:
s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: placing a titanium foil in a hydrothermal kettle, adding a hydrothermal reagent, and carrying out hydrothermal reaction on the hydrothermal reagent containing lithium ions, an etching agent and an organic alcohol aqueous solution at 160-200 ℃ for 4-8 h to obtain a sheet lithium titanate @ polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tubular furnace, introducing inert gas, annealing at the temperature of 600-900 ℃ for 1-3 h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step S1, the hydrothermal reagent includes lithium oxalate.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step S1, the etchant is dodecylamine.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step S1, the organic alcohol is one of polyvinyl alcohol, glucose, and sucrose.
In the preparation method of the carbon-coated lithium titanate electrode material, the molecular weight of the polyvinyl alcohol is 200-1000.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step S1, the hydrothermal reagent contains 4-7 g/L of lithium oxalate, 2.5-3.5 g/L of dodecylamine and 0.5-1 g/L of polyvinyl alcohol.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step 1, the reaction temperature of the hydrothermal reaction is 180 ℃.
In the preparation method of the carbon-coated lithium titanate electrode material, in the step S1, the titanium foil further includes surface treatment before hydrothermal reaction, and the surface treatment is polishing the surface of the titanium foil through a sand cloth.
Has the advantages that:
the invention provides a carbon-coated lithium titanate electrode material and a preparation method thereof, wherein the carbon-coated lithium titanate electrode material is carbon-coated lithium titanate obtained by in-situ growth on the surface of a titanium foil, so that when the carbon-coated lithium titanate electrode material is used as a negative electrode material of a lithium ion battery, the carbon-coated lithium titanate is not required to be attached to the surface of a current collector through a binder, the proportion of an active ingredient lithium titanate is greatly improved compared with the prior art, and the carbon-coated lithium titanate electrode material has better rate performance; meanwhile, the titanium foil is grown on the surface of the titanium foil in situ, so that the preparation steps of the electrode material are simpler; moreover, the surface of the lithium titanate is coated with a carbon layer, and the carbon layer can improve the conductivity and the charge-discharge capacity of the negative electrode material. According to the preparation method of the carbon-coated lithium titanate electrode material, an etching reaction is carried out under a weak alkaline condition to obtain a compound of organic titanium and titanium hydroxide, lithium ions react with the compound to prepare sheet lithium titanate, organic alcohol is subjected to dehydration polymerization under an alkaline hydrothermal condition to form a high molecular compound to be coated on the surface of lithium titanate, and the high molecular compound is carbonized through annealing treatment to form the carbon-coated lithium titanate electrode material. The preparation method can obtain the carbon-coated lithium titanate by in-situ growth on the surface of the titanium foil, on one hand, the rate capability of the electrode material is improved, on the other hand, the preparation process of the electrode is simplified, and the carbon-coated lithium titanate can be widely used for producing and manufacturing the cathode material of the lithium ion battery.
Drawings
Fig. 1 is a scanning electron microscope image of the carbon-coated lithium titanate electrode material provided by the invention.
Fig. 2 is an X-ray diffraction pattern of a carbon-coated lithium titanate electrode material.
Fig. 3 is a transmission electron micrograph of the carbon-coated lithium titanate electrode material.
Fig. 4 is a charge-discharge curve diagram of the carbon-coated lithium titanate electrode material.
Fig. 5 is a graph of the cycling stability of a carbon-coated lithium titanate electrode material.
Detailed Description
The invention provides a carbon-coated lithium titanate electrode material and a preparation method thereof, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail below by referring to the attached drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a carbon-coated lithium titanate electrode material, which is a lithium ion battery cathode material and comprises a substrate and carbon-coated lithium titanate growing on the surface of the substrate in situ, wherein the substrate is a titanium foil. The matrix is equivalent to a current collector of a negative electrode material, the lithium titanate is an active substance of the negative electrode material, and in the application, the active material grows on the surface of the current collector in situ, so that the electrode material can be directly used as the negative electrode material of a lithium ion battery, a binder is not needed to connect the lithium titanate with the current collector, the process steps for manufacturing the electrode can be saved, meanwhile, the binder is not added, the occupation ratio of the active ingredient is maximized, and the quality and the capacity of the electrode are greatly improved compared with the prior art. In addition, the surface of the lithium titanate is further coated with a carbon layer, and the carbon layer can improve the conductivity and the charge-discharge capacity of the negative electrode material.
Preferably, in the carbon-coated lithium titanate electrode material with the above structure, the carbon-coated lithium titanate is in a sheet structure, and the carbon-coated lithium titanate with the sheet structure can shorten the diffusion distance of lithium ions and improve the rate capability of the negative electrode material.
The application also provides a preparation method of the carbon-coated lithium titanate electrode material, which comprises the following steps:
s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, firstly polishing the surface of the titanium foil by using No. 2000 abrasive paper, removing surface oxides to facilitate subsequent etching reaction, then placing the polished titanium foil in a hydrothermal kettle, simultaneously adding a hydrothermal reagent, wherein the hydrothermal reagent is an aqueous solution containing lithium ions, an etching agent and organic alcohol, then carrying out hydrothermal reaction for 4-8 h at 160-200 ℃, and obtaining the sheet lithium titanate @ polymer precursor composite material after the reaction is finished.
In the step S1, the reaction process includes performing an etching reaction on the etchant and the polished titanium foil, obtaining a compound of an organic substance of titanium and titanium hydroxide on the surface of the titanium foil through the etching reaction, performing a hydrothermal reaction on the compound and lithium ions under a heating condition to obtain the sheet-shaped lithium titanate, performing a dehydration polymerization reaction on the organic alcohol under an alkaline condition, forming a polymer precursor through dehydration polymerization, and attaching the polymer precursor to the surface of the sheet-shaped lithium titanate to form the sheet-shaped lithium titanate @ polymer precursor composite material.
Specifically, the etchant is organic base, and the selection of the etchant is very important, so that the etchant not only needs to have an etching reaction with the titanium foil, but also needs to avoid the situation that the alkalinity is too strong and the sheet lithium titanate cannot be formed. Therefore, the organic base is selected as the etching agent, because the organic base is weak in alkalinity and can react with the titanium foil at high temperature to obtain organic titanium and titanium hydroxide, and further the subsequent hydrothermal reaction with a lithium source is facilitated to form the sheet lithium titanate. Preferably, the organic base is dodecylamine which is weak in alkalinity and can react with the titanium foil to form a compound of titanium organic matter and titanium hydroxide on the surface of the titanium foil, and the compound can perform hydrothermal reaction with lithium ions to produce the sheet lithium titanate.
In the above step, the hydrothermal reagent contains lithium ions that provide a lithium source for lithium titanate, and the lithium ions react with an organic titanium compound and titanium hydroxide in the hydrothermal reaction process to form lithium titanate. Specifically, the lithium source is lithium oxalate, and the lithium oxalate can react with organic titanium and titanium hydroxide obtained after etching reaction to generate sheet amorphous lithium titanate. The flaky amorphous lithium titanate is an active substance on the surface of a titanium foil, is an active component of a negative electrode material, and influences the conductivity and rate performance of the negative electrode material.
In the step S1, a sheet-shaped lithium titanate precursor is obtained through a hydrothermal reaction, and in the reaction process, the shape of lithium titanate is affected by a titanium source, the reaction temperature and the pH value. In the application, organic titanium and titanium hydroxide formed after an etchant reacts with a titanium foil are used as a titanium source, and the reaction temperature is controlled to be 160-200 ℃, preferably 180 ℃, and the organic titanium and the titanium hydroxide react under the alkalescent condition to obtain the sheet lithium titanate, wherein the sheet lithium titanate has more excellent rate capability. If titanium dioxide or titanium foil is directly used as a titanium source, even under the same hydrothermal reaction condition, the flaky lithium titanate cannot be obtained, and the flaky lithium titanate does not have good rate performance.
Specifically, the organic alcohol provides a carbon source for the carbon coating layer. And the organic alcohol is subjected to dehydration polymerization under an alkaline condition to form a high molecular compound, and the high molecular compound is coated on the surface of the sheet lithium titanate to form a precursor of the carbon coating layer and provide a carbon source for the carbon coating layer. Specifically, the organic alcohol comprises one of polyvinyl alcohol, glucose and sucrose, and is a polyol, the polyol is easy to undergo a dehydration polymerization reaction under a high-temperature alkaline condition to form a high molecular compound, and the high molecular compound is coated on the surface of lithium titanate to form the sheet lithium titanate @ high molecular precursor composite material.
Preferably, the organic alcohol is polyvinyl alcohol, and more preferably, the molecular weight of the polyvinyl alcohol is 200-1000. However, since the molecular weight of the polyvinyl alcohol affects the water solubility thereof, when the molecular weight exceeds 1000, the water solubility thereof is poor, and the dehydration polymerization becomes poor, and a high molecular weight polymer compound cannot be formed, so that the carbon coating effect is reduced and uneven, and the electronic conductivity and the charge and discharge capacity of the negative electrode material are affected. When the polyvinyl alcohol with the molecular weight of 200-1000 is selected, the polyvinyl alcohol has better water solubility, and after dehydration polymerization, a high molecular compound with higher molecular weight can be formed, so that the polyvinyl alcohol has better coating effect.
More preferably, in step S1, the hydrothermal reagent is an aqueous solution containing 4g/L to 7g/L of lithium oxalate, 2.5g/L to 3.5g/L of dodecylamine, and 0.5g/L to 1g/L of polyvinyl alcohol, the reaction temperature of the hydrothermal reaction is 180 ℃, and the sheet lithium titanate having a uniform size can be obtained by the hydrothermal reaction.
S2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tube furnace, introducing inert gas, wherein the inert gas comprises nitrogen or argon, annealing at the temperature of 600-900 ℃ for 1-3 h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material. In the annealing process, on one hand, the polymer precursor is carbonized at high temperature so as to be coated on the surface of lithium titanate in situ, and on the other hand, the sheet lithium titanate formed in the step S1 is amorphous lithium titanate, and is crystallized at high temperature to obtain the sheet lithium titanate with a crystal structure, so that the sheet lithium titanate has better rate capability.
In the annealing process, the annealing temperature can influence the carbonization of the high-molecular precursor, when the temperature is higher, a carbon coating layer with larger proportion of graphite carbon can be formed, and when the temperature is lower, a carbon coating layer with larger proportion of activated carbon can be formed. The larger the graphite carbon proportion is, the better the electronic conductivity of the material is, but the discharge capacity is affected, and meanwhile, when the annealing temperature is too high, the crystal structure of lithium titanate is damaged, and the rate capability of the material is reduced. When the temperature is 600-900 ℃, the conductive performance and rate capability are better.
To further illustrate the carbon-coated lithium titanate electrode material and the preparation method thereof provided by the present invention, the following examples are provided.
Example 1
A method for preparing a carbon-coated lithium titanate electrode material, the method comprising the steps of: s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, polishing and brightening the titanium foil by using No. 2000 abrasive paper, then placing the titanium foil into a hydrothermal kettle, and simultaneously adding a hydrothermal reagent, wherein the hydrothermal reagent comprises an aqueous solution with 6g/L of lithium oxalate, 3g/L of dodecylamine and 0.8g/L of polyvinyl alcohol, the molecular weight of the polyvinyl alcohol is 800, and the hydrothermal reaction is carried out for 6 hours at 180 ℃ to obtain a sheet lithium titanate @ polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tubular furnace, introducing nitrogen protection gas, annealing at 800 ℃ for 2h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
Example 2
A method for preparing a carbon-coated lithium titanate electrode material, the method comprising the steps of: s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, polishing and brightening the titanium foil by using No. 2000 abrasive paper, then placing the titanium foil into a hydrothermal kettle, and simultaneously adding a hydrothermal reagent, wherein the hydrothermal reagent comprises an aqueous solution of 4g/L lithium oxalate, 2.5g/L dodecylamine and 0.5g/L polyvinyl alcohol, the molecular weight of the polyvinyl alcohol is 200, and carrying out hydrothermal reaction for 8 hours at 160 ℃ to obtain a sheet @ lithium titanate polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tube furnace, introducing argon protective gas, annealing at 900 ℃ for 1h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
Example 3
A method for preparing a carbon-coated lithium titanate electrode material, the method comprising the steps of: s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, polishing and brightening the titanium foil by using No. 2000 abrasive paper, then placing the titanium foil into a hydrothermal kettle, and simultaneously adding a hydrothermal reagent, wherein the hydrothermal reagent comprises an aqueous solution of 7g/L lithium oxalate, 3.5g/L dodecylamine and 1g/L polyvinyl alcohol, the molecular weight of the polyvinyl alcohol is 1000, and the hydrothermal reaction is carried out for 4 hours at 200 ℃ to obtain a sheet lithium titanate @ polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tube furnace, introducing inert gas, annealing at 600 ℃ for 3h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
Example 4
A method for preparing a carbon-coated lithium titanate electrode material, the method comprising the steps of: s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, polishing and brightening the titanium foil by using No. 2000 abrasive paper, then placing the titanium foil into a hydrothermal kettle, adding a hydrothermal reagent simultaneously, and carrying out hydrothermal reaction on the hydrothermal reagent for 7 hours at the temperature of 170 ℃, wherein the hydrothermal reagent comprises an aqueous solution of 5g/L lithium oxalate, 3.2g/L dodecylamine and 0.8g/L glucose to obtain a sheet-shaped @ lithium titanate polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tube furnace, introducing inert gas, annealing at 700 ℃ for 2h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
Example 5
A method for preparing a carbon-coated lithium titanate electrode material, the method comprising the steps of:
s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: taking a titanium foil, polishing and brightening the titanium foil by using No. 2000 abrasive paper, then placing the titanium foil into a hydrothermal kettle, adding a hydrothermal reagent simultaneously, and carrying out hydrothermal reaction on the hydrothermal reagent for 7 hours at 170 ℃ to obtain a sheet lithium titanate @ polymer precursor composite material, wherein the hydrothermal reagent comprises an aqueous solution of 5g/L lithium oxalate, 3.2g/L dodecylamine and 0.8g/L sucrose;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tube furnace, introducing inert gas, annealing at 700 ℃ for 2h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
Comparative example 1
A preparation method of a lithium titanate electrode material, which adopts the same steps as in example 1, except that dodecylamine is replaced by sodium hydroxide to obtain needle-shaped carbon-coated lithium titanate growing in situ on the surface of a titanium foil.
Comparative example 2
The preparation method of the lithium titanate electrode material is the same as that in example 1, except that in step S2, the annealing temperature is 1000 ℃ to obtain the sheet lithium titanate electrode material.
Comparative example 3
The preparation method of the lithium titanate electrode material has the same specific steps as those of example 1, and is different from the preparation method in that the needle-shaped lithium titanate is prepared at the hydrothermal temperature of 220 ℃.
Comparative example 4
The preparation method of the lithium titanate electrode material is the same as that in example 1, except that the concentration of lithium oxalate in the hydrothermal reagent is 10g/L, and needle-shaped lithium titanate is prepared.
Characterization and Performance testing
The carbon-coated lithium titanate electrode material prepared in example 1 was scraped from the surface of a titanium foil, and then characterized by a scanning electron microscope, X-ray diffraction, and transmission electron microscope, with specific results shown in fig. 1-3. Meanwhile, the carbon-coated lithium titanate electrode material prepared in example 1 was used as a negative electrode material of a lithium ion battery to perform charge-discharge performance tests and cycle stability performance tests, and the specific results are shown in fig. 4-5.
Fig. 1 is a scanning electron microscope image of the carbon-coated lithium titanate electrode material of example 1, and it can be seen from the image that the carbon-coated lithium titanate electrode material is a sheet-like structure, so that by a hydrothermal reaction under specific conditions, a sheet-like lithium titanate can be prepared, and the sheet-like structure can shorten a diffusion distance of lithium ions and improve a rate capability of the material.
Fig. 2 is an X-ray diffraction pattern of the carbon-coated lithium titanate electrode material described in example 1, in which diffraction peaks at 110, 311, 400, 331, 333, 440, and 531 are all diffraction peaks of a crystal plane of lithium titanate, thereby showing that the material mainly comprises lithium titanate, and it is proved that lithium titanate can be prepared by the actions of step S1 and step S2.
Fig. 3 is a transmission electron microscope image of the carbon-coated lithium titanate electrode material of example 1, wherein dark black represents a nano carbon layer, so that the surface of the lithium titanate is successfully coated with the carbon layer.
Fig. 4 is a charge-discharge curve of the carbon-coated lithium titanate electrode material of example 1 at a magnification of 20C at circle 2, and it can be seen from the graph that the discharge capacity of the carbon-coated lithium titanate electrode material is 172mAh/g, which indicates that the composite material has a higher capacity.
Fig. 5 is a stability test of the carbon-coated lithium titanate electrode material of example 1 at a 20C rate for 1000 cycles, and it can be seen from the figure that the capacity of the negative electrode material is still maintained at 115mAh/g or more after 1000 cycles, which indicates that the material has good cycle stability under large-current charge and discharge.
Meanwhile, examples 1 to 5 and comparative examples 1 to 4 were subjected to a charge and discharge performance test and a cycle stability test at a rate of 20C, and the test results are shown in table 1.
TABLE 1 test results of charge and discharge properties and cycle stability of the negative electrode materials
As can be seen from table 1, in examples 1 to 5, the discharge capacity is greater than 150mAh/g at a high rate of 20C, and the discharge capacity after 1000 cycles at 20C is also better, especially in example 1, because the proportion of lithium oxalate, dodecylamine and polyallylamine in the hydrothermal reagent in example 1 is moderate, and the reaction temperature is moderate, a nano-level sheet carbon-coated lithium titanate can be obtained, and thus the rate performance and the cycle stability are excellent. The reason why the examples 4 and 5 are inferior to the examples 1 to 3 is mainly that the organic alcohol is selected, the dehydration polymerization reaction of short-chain glucose and sucrose is inferior to that of polypropylene alcohol under the conditions of high temperature and high pressure, so that the carbon coating layer on the surface of lithium titanate is inferior to that of the examples 1 to 3, the electronic conductivity is affected, and the rate capability is affected finally.
Comparing the comparative examples 1, 3 and 4 with examples 1-3, the multiplying power performance of the comparative examples 1, 3 and 4 is obviously much lower than that of examples 1-3, and the cycle stability is very poor, which is mainly because the comparative examples 1, 3 and 4 generate needle-shaped lithium titanate. The comparative example 2 is the flaky lithium titanate, which has better discharge capacity at 20C rate, but has poor cycle stability, probably because high-temperature annealing can destroy the crystal structure and affect the rate performance, and in addition, high annealing temperature can increase the ratio of the formed graphite carbon due to carbonization, and the graphite carbon can affect the rate performance of the lithium titanate.
In summary, the sheet-shaped carbon-coated lithium titanate electrode material is generated in situ on the surface of a titanium foil through a hydrothermal reaction, has excellent rate performance and cycle stability, can be widely applied to lithium ion batteries, and has a good market prospect.
It should be understood that equivalents and modifications of the technical solution and inventive concept thereof may occur to those skilled in the art, and all such modifications and alterations should fall within the scope of the appended claims.
Claims (9)
1. A preparation method of a carbon-coated lithium titanate electrode material is characterized by comprising the following steps:
s1, synthesizing a sheet lithium titanate @ polymer precursor composite material: placing a titanium foil in a hydrothermal kettle, adding a hydrothermal reagent containing lithium ions, an etching agent and an organic alcohol aqueous solution, wherein the etching agent is dodecylamine, and performing hydrothermal reaction at 160-200 ℃ for 4-8 h to obtain a sheet lithium titanate @ polymer precursor composite material;
s2, annealing treatment: and (4) placing the sheet lithium titanate @ polymer precursor composite material prepared in the step (S1) in a tubular furnace, introducing inert gas, annealing at the temperature of 600-900 ℃ for 1-3 h, and cooling to obtain the sheet carbon-coated lithium titanate electrode material.
2. The method for preparing a carbon-coated lithium titanate electrode material according to claim 1, wherein in the step S1, the hydrothermal reagent comprises lithium oxalate.
3. The method of claim 1, wherein in step S1, the organic alcohol is one of polyvinyl alcohol, glucose, and sucrose.
4. The method for preparing a carbon-coated lithium titanate electrode material according to claim 3, wherein the polyvinyl alcohol has a molecular weight of 200 to 1000.
5. The method for preparing a carbon-coated lithium titanate electrode material according to claim 1, wherein in step S1, the hydrothermal reagent contains 4 to 7g/L of lithium oxalate, 2.5 to 3.5g/L of dodecylamine, and 0.5 to 1g/L of polyvinyl alcohol.
6. The method for preparing a carbon-coated lithium titanate electrode material according to claim 1, wherein the hydrothermal reaction is performed at a reaction temperature of 180 ℃ in step S1.
7. The method for preparing a carbon-coated lithium titanate electrode material according to claim 1, wherein in the step S1, the titanium foil further comprises a surface treatment before the hydrothermal reaction, wherein the surface treatment is polishing the surface of the titanium foil by using a sand cloth.
8. A carbon-coated lithium titanate electrode material prepared by the method for preparing the carbon-coated lithium titanate electrode material as claimed in any one of claims 1 to 7, wherein the electrode material comprises a substrate and carbon-coated lithium titanate growing on the surface of the substrate in situ, and the substrate is a titanium foil.
9. The carbon-coated lithium titanate electrode material according to claim 8, wherein the carbon-coated lithium titanate has a sheet structure.
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| CN105206814A (en) * | 2015-09-25 | 2015-12-30 | 北京理工大学 | Method for preparing high performance lithium ion battery negative electrode material porous carbon covering exposed (001) active crystal titanium dioxide nanocubes |
| CN109817891A (en) * | 2019-03-06 | 2019-05-28 | 浙江工业大学 | A kind of method of titanium material surface in situ preparation nanostructure |
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| CN105206814A (en) * | 2015-09-25 | 2015-12-30 | 北京理工大学 | Method for preparing high performance lithium ion battery negative electrode material porous carbon covering exposed (001) active crystal titanium dioxide nanocubes |
| CN109817891A (en) * | 2019-03-06 | 2019-05-28 | 浙江工业大学 | A kind of method of titanium material surface in situ preparation nanostructure |
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| "Hydrogenated Li 4 Ti 5 O 12 Nanowire Arrays for High Rate Lithium Ion Batteries ";Laifa Shen等;《Adv. Mater.》;20121005;第24卷;全文 * |
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