CN113745486B - In-situ carbon-doped lithium titanium phosphate for water-based lithium ion battery and preparation method and application thereof - Google Patents
In-situ carbon-doped lithium titanium phosphate for water-based lithium ion battery and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of water-system lithium ion batteries, and discloses in-situ carbon-doped lithium titanium phosphate for a water-system lithium ion battery, and a preparation method and application thereof. The method comprises the following steps: (1) in the presence of a solvent I, carrying out first contact mixing on lithium acetate dihydrate and a titanium source to obtain a first mixed solution; and in the presence of a solvent II, carrying out second contact mixing on a carbon source and phosphoric acid with the concentration of 80-85 wt% to obtain a second mixed solution; (2) under a closed condition, carrying out a first contact reaction on the first mixed solution and the second mixed solution to obtain a gel precursor, and evaporating the gel precursor to obtain a xerogel; (3) the xerogel is calcined. When the in-situ carbon-doped lithium titanium phosphate provided by the invention is used in a water-based lithium ion battery, the cycle performance and the rate capability of the battery can be obviously improved.
Description
Technical Field
The invention relates to the technical field of water-system lithium ion batteries, in particular to in-situ carbon-doped lithium titanium phosphate for a water-system lithium ion battery, and a preparation method and application thereof.
Background
In recent years, safety accidents of lithium ion batteries frequently occur, and in order to solve the safety problem of the lithium ion batteries, water-based lithium ion batteries are gradually paid attention by researchers. Compared with the traditional organic electrolyte lithium ion battery, the aqueous lithium ion battery adopts non-flammable lithium salt aqueous solution as the electrolyte, and has the remarkable advantage of high safety performance.
On the other hand, the aqueous lithium ion battery can be assembled under a non-inert gas condition, and the production cost is lower than that of the organic lithium ion battery. In addition, the ionic conductivity of the aqueous electrolyte is generally two orders of magnitude higher than that of the organic electrolyte, so that the aqueous lithium ion battery has good electrochemical performance and application prospect.
However, the decomposition voltage of water is low, and when the intercalation potential of the electrode material exceeds the decomposition voltage window of water, obvious hydrogen evolution and oxygen evolution phenomena will occur, which affects the normal use of the water-based battery.
The lithium intercalation potential of the anode material of the traditional organic lithium battery, such as lithium cobaltate, lithium manganate, lithium nickelate and the like, is lower than the oxygen evolution potential, and the anode material can be applied to a water system environment, while the commercial anode material graphite can not be applied to the water system environment, because the lithium intercalation potential of the graphite is not in the stable voltage window of the water system electrolyte. Therefore, the development of aqueous lithium ion batteries focuses on the preparation of novel negative electrode materials.
The lithium titanium phosphate belongs to a rhombohedral crystal system, a space group is R-3c, the lithium titanium phosphate has a three-dimensional lithium ion transmission channel, the lithium titanium phosphate has high ionic conductivity and stable structure, the theoretical specific capacity is 138mAh/g, and a voltage platform is positioned in a stable window of a water system electrolyte and is suitable for being used as a negative electrode material of a water system lithium ion battery.
At present, titanium lithium phosphate is mostly synthesized by a high-temperature solid-phase method, the method has simple process flow, but the production energy consumption is higher, the particle size of the product is larger, and the electrochemical performance needs to be improved. In addition, pure-phase lithium titanium phosphate has the problem of low electronic conductivity, the capacity of the pure-phase lithium titanium phosphate is attenuated quickly in an aqueous electrolyte, and the cycle performance and the rate performance are required to be further improved.
Therefore, it is of great significance to develop a lithium titanium phosphate with high electronic conductivity and good electrochemical performance so as to obtain a water-based battery with high cycle performance and rate performance.
Disclosure of Invention
The invention aims to overcome the defects of poor cycle performance and rate capability of a water-based battery caused by low electronic conductivity and poor electrochemical performance of a titanium lithium phosphate battery in the prior art.
In order to achieve the above object, a first aspect of the present invention provides a method for preparing in-situ carbon-doped lithium titanium phosphate for an aqueous lithium ion battery, the method comprising:
(1) in the presence of a solvent I, carrying out first contact mixing on lithium acetate dihydrate and a titanium source to obtain a first mixed solution; the titanium source is tetrabutyl titanate and/or isopropyl titanate; and
in the presence of a solvent II, carrying out second contact mixing on a carbon source and phosphoric acid with the concentration of 80-85 wt% to obtain a second mixed solution; the carbon source comprises the following components in percentage by mass of 1: 0.1-0.9 of citric acid and lactic acid;
(2) under a closed condition, carrying out first contact reaction on the first mixed solution and the second mixed solution to obtain a gel precursor, and carrying out evaporation treatment on the gel precursor to obtain a xerogel;
(3) calcining the xerogel;
wherein the amount of the carbon source accounts for 10-35 wt% of the total amount of the lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid.
In a second aspect, the invention provides in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries, which is prepared by the method of the first aspect.
In a third aspect, the invention provides the use of the in-situ carbon-doped lithium titanium phosphate according to the second aspect in a water-based lithium ion battery.
According to the invention, lithium acetate dihydrate is used as a lithium source, citric acid and lactic acid with a specific mixing ratio are used as carbon sources, phosphoric acid with the concentration of 80-85 wt% is used as a phosphorus source, and the formed in-situ carbon-doped lithium titanium phosphate is used in a water-based lithium ion battery, so that the cycle performance and the rate capability of the battery can be obviously improved.
Drawings
FIG. 1 is an XRD pattern of in-situ carbon-doped lithium titanium phosphate prepared in example 1;
FIG. 2 is a thermogravimetric plot of in situ carbon-doped lithium titanium phosphate prepared in example 2;
FIG. 3 is a graph of the cycling performance at 1C rate for a cell assembled from in situ carbon doped lithium titanium phosphate of example 3;
FIG. 4 is an SEM image of in-situ carbon-doped lithium titanium phosphate prepared in example 3;
FIG. 5 is the EDS surface-swept carbon element profile of in-situ carbon-doped lithium titanium phosphate prepared in example 3.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
As previously mentioned, a first aspect of the present invention provides a method of preparing in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries, the method comprising:
(1) in the presence of a solvent I, carrying out first contact mixing on lithium acetate dihydrate and a titanium source to obtain a first mixed solution; the titanium source is tetrabutyl titanate and/or isopropyl titanate; and
in the presence of a solvent II, carrying out second contact mixing on a carbon source and phosphoric acid with the concentration of 80-85 wt% to obtain a second mixed solution; the carbon source comprises the following components in percentage by mass of 1: 0.1-0.9 of citric acid and lactic acid;
(2) under a closed condition, carrying out a first contact reaction on the first mixed solution and the second mixed solution to obtain a gel precursor, and evaporating the gel precursor to obtain a xerogel;
(3) calcining the xerogel;
wherein the amount of the carbon source accounts for 10-35 wt% of the total amount of the lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid.
The method adopts a one-time calcination process, directly calcines the xerogel to obtain a target product, does not need pre-calcination, and can effectively shorten the process flow and reduce the production energy consumption.
In the present invention, the sealing condition means that a reaction system formed by the first mixed solution and the second mixed solution is isolated from the outside and does not leak gas, and for example, a sealing film may be used to form the sealing condition.
Preferably, the carbon source is used in an amount of 20 to 30 wt% based on the total amount of the lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid. The inventors have found that, according to the preferred embodiment, a titanium lithium phosphate electrode material having a higher carbon content can be obtained, and an aqueous lithium ion battery having more excellent cycle performance can be obtained.
Preferably, lithium acetate dihydrate calculated by the element lithium, the titanium source calculated by the element titanium and the phosphoric acid calculated by the element phosphorus are used in a molar ratio of 1: 1-3: 3-5.
Preferably, in the step (1), the carbon source is a mixture of carbon sources with a content mass ratio of 1: 0.2-0.8 of citric acid and lactic acid. The inventors have found that, according to the preferred embodiment, an aqueous lithium ion battery having a higher specific capacity and more excellent cycle performance and rate performance can be obtained.
Preferably, in step (1), the conditions of the first contact mixing and the second contact mixing each independently comprise: the stirring speed is 300-400rpm, the temperature is 50-60 ℃, and the time is 2-3 h.
Preferably, in step (2), the conditions of the first contact reaction include at least: the stirring speed is 300-400rpm, the temperature is 50-60 ℃, and the time is 2-3 h.
Preferably, in step (2), the conditions of the evaporation treatment include at least: the temperature is 70-90 ℃ and the time is 2-3 h.
Preferably, in step (3), the calcination conditions include at least: the heating rate is 4-10 ℃/min, the calcination temperature is 650-850 ℃, and the time is 4-6 h.
Preferably, the calcined vessel is a graphite boat. The inventor finds that the graphite boat is used as a calcining container, no sticking phenomenon occurs after calcining, and a sample is easy to recover.
Preferably, in step (3), the method further comprises: and crushing the material obtained after the calcination to obtain the in-situ carbon-doped lithium titanium phosphate with the average particle size of 60-100 nm.
Preferably, the pulverization treatment is carried out by using a planetary ball mill. The inventor finds that the agglomeration effect of the product can be effectively reduced by crushing the calcined material, and coarse particles are converted into nano-scale fine particles, so that the interface wettability of the electrolyte to the electrode material is improved, and the circulation stability and the rate capability of the electrolyte are improved.
Preferably, in the step (3), the conditions of the pulverization treatment include at least: the rotating speed is 500-600r/min, and the time is 2-3 h.
The present invention is not particularly limited in the kind and amount of the solvent I and the solvent II, and the solvent I and the solvent II are, for example, absolute ethyl alcohol.
Preferably, the amount of the solvent I is 10 to 100mL relative to the total amount of the lithium acetate dihydrate and the titanium source used of 1 g.
Preferably, the amount of the solvent II is 10 to 100mL relative to the total amount of the phosphoric acid and the carbon source used of 1 g.
As described above, the second aspect of the present invention provides the in-situ carbon-doped lithium titanium phosphate for the aqueous lithium ion battery prepared by the method of the first aspect.
As previously mentioned, a third aspect of the invention provides the use of the in situ carbon doped lithium titanium phosphate according to the second aspect in an aqueous lithium ion battery.
The present invention will be described in detail below by way of examples. In the following examples, various raw materials used are commercially available ones unless otherwise specified.
Lithium acetate dihydrate: from Shandong and Xia chemical industries, Inc.;
tetrabutyl titanate: from Shandong and Xia chemical industries, Inc.;
phosphoric acid: purchased from Tianjin Fuchen chemical reagents, Inc.;
citric acid: purchased from Beijing Yinaoka technologies, Inc.;
lactic acid: purchased from yinaoka technologies ltd, beijing.
Example 1
The embodiment provides a method for preparing in-situ carbon-doped lithium titanium phosphate for an aqueous lithium ion battery, which comprises the following steps:
(1) 0.2555g of lithium acetate dihydrate and 1.7065g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 300rpm for 2 hours to obtain a first mixed solution;
0.8952g of phosphoric acid with a concentration of 82 wt% and 0.7140g of a carbon source (the amount of the carbon source accounts for 20 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid and comprises 0.4762g of citric acid and 0.2378g of lactic acid, namely, the mass ratio of the amount of the citric acid to the amount of the lactic acid is 1:0.5) are dissolved in a beaker containing 80mL of absolute ethanol at 50 ℃, and stirred at 400rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by using tin foil paper, stirring at the constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 80 ℃ for 3 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a 650 ℃ tubular heating furnace under the protection of argon gas, calcining for 6h at the heating rate of 5 ℃/min, and then grinding the calcined material for 2h by adopting a planetary ball mill at the rotating speed of 500r/min to obtain the in-situ carbon-doped lithium titanium phosphate LTP-1.
Example 2
The embodiment provides a method for preparing in-situ carbon-doped lithium titanium phosphate for an aqueous lithium ion battery, which comprises the following steps:
(1) 0.2567g of lithium acetate dihydrate and 1.7128g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 300rpm for 3 hours to obtain a first mixed solution;
0.9247g of phosphoric acid with the concentration of 80 wt% and 0.9651g of carbon source (the amount of the carbon source accounts for 25 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid and comprises 0.6433g of citric acid and 0.3218g of lactic acid, namely, the mass ratio of the amounts of the citric acid and the lactic acid is 1:0.2) are dissolved in a beaker containing 90mL of absolute ethyl alcohol at 60 ℃, and stirred at 300rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 60 ℃, sealing the mouth of the beaker by using tin foil paper, stirring at the constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 80 ℃ for 3 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a tubular heating furnace at 750 ℃ under the protection of argon gas, calcining for 5h at the heating rate of 6 ℃/min, and then grinding the calcined material for 2h by adopting a planetary ball mill at the rotating speed of 550r/min to obtain the in-situ carbon-doped lithium titanium phosphate LTP-2.
Example 3
The embodiment provides a method for preparing in-situ carbon-doped lithium titanium phosphate for an aqueous lithium ion battery, which comprises the following steps:
(1) 0.2522g of lithium acetate dihydrate and 1.6875g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃, and stirred at 400rpm for 3 hours to obtain a first mixed solution;
0.8550g of phosphoric acid with a concentration of 85 wt% and 1.1979g of a carbon source (the amount of the carbon source accounts for 30 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid and comprises 0.6655g of citric acid and 0.5324g of lactic acid, namely, the mass ratio of the amounts of the citric acid and the lactic acid is 1:0.8) are dissolved in a beaker containing 100mL of anhydrous ethanol at 60 ℃, and stirred at 350rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by using tin foil paper, stirring at constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained dry gel in a graphite boat, placing the graphite boat in a 850 ℃ tubular heating furnace under the protection of argon gas, calcining for 4 hours at the heating rate of 7 ℃/min, and then grinding the calcined material for 3 hours by adopting a planetary ball mill at the rotating speed of 600r/min to obtain the in-situ carbon-doped lithium titanium phosphate LTP-3.
Example 4
The embodiment provides a method for preparing in-situ carbon-doped lithium titanium phosphate for an aqueous lithium ion battery, which comprises the following steps:
(1) 0.2537g of lithium acetate dihydrate and 1.6928g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 300rpm for 3 hours to obtain a first mixed solution;
0.8600g of phosphoric acid with the concentration of 85 wt% and 1.5112g of carbon source (the amount of the carbon source accounts for 35 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid and comprises 0.8394g of citric acid and 0.6718g of lactic acid, namely, the mass ratio of the amount of the citric acid to the amount of the lactic acid is 1:0.8) are dissolved in a beaker containing 100mL of absolute ethyl alcohol at 60 ℃, and stirred at 300rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by using tin foil paper, stirring at constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a tubular heating furnace at 850 ℃ under the protection of argon gas, calcining for 4h at the heating rate of 7 ℃/min, and then grinding the calcined material for 3h by adopting a planetary ball mill at the rotating speed of 600rpm to obtain the in-situ carbon-doped lithium titanium phosphate LTP-4.
Example 5
The embodiment provides a method for preparing in-situ carbon-doped lithium titanium phosphate for a water-based lithium ion battery, which comprises the following steps:
(1) 0.2563g of lithium acetate dihydrate and 1.7101g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 300rpm for 3 hours to obtain a first mixed solution;
0.8692g of phosphoric acid with the concentration of 85 wt% and 0.3154g of carbon source (the dosage of the carbon source accounts for 10 wt% of the total dosage of lithium acetate dihydrate, titanium source, carbon source and phosphoric acid, and the dosage mass ratio of citric acid to lactic acid is 1:0.8) are dissolved in a beaker containing 100mL of absolute ethyl alcohol at the temperature of 60 ℃, and stirred for 2 hours at 400rpm to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by adopting tin foil paper, stirring for 3 hours at constant temperature of 400rpm to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained dry gel in a graphite boat, placing the graphite boat in a 850 ℃ tubular heating furnace under the protection of argon gas, calcining for 4 hours at the heating rate of 4 ℃/min, and then grinding the calcined material for 3 hours by adopting a planetary ball mill at the rotating speed of 500rpm to obtain the in-situ carbon-doped lithium titanium phosphate LTP-5.
Comparative example 1 (without addition of carbon Source)
The present comparative example provides a method of preparing pure phase lithium titanium phosphate for aqueous lithium ion batteries, comprising the steps of:
(1) 0.2563g of lithium acetate dihydrate and 1.7101g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 300rpm for 3 hours to obtain a first mixed solution;
0.8692g of phosphoric acid with a concentration of 85 wt% was dissolved in a beaker containing 50mL of absolute ethanol at 60 ℃ and stirred at 300rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by using tin foil paper, stirring at constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a tubular heating furnace at 850 ℃ under the protection of argon gas, calcining for 4h at the heating rate of 4 ℃/min, and then grinding the calcined material for 3h by adopting a planetary ball mill at the rotating speed of 550rpm to obtain pure-phase lithium titanium phosphate DLTP-1.
Comparative example 2
The present comparative example provides a method of preparing in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries, comprising the steps of:
(1) 0.2502g of lithium acetate dihydrate and 1.6691g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 400rpm for 3 hours to obtain a first mixed solution;
0.8480g of phosphoric acid with the concentration of 85 wt% and 0.1458g of carbon source (the amount of the carbon source accounts for 5 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid, and the mass ratio of the amount of citric acid to the amount of lactic acid is 1:0.8) are dissolved in a beaker containing 100mL of anhydrous ethanol at 60 ℃, and stirred at 350rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by adopting tin foil paper, stirring for 3 hours at the constant temperature of 300rpm to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a tubular heating furnace at 850 ℃ under the protection of argon gas, calcining for 4h at the heating rate of 7 ℃/min, and then grinding the calcined material for 3h by adopting a planetary ball mill at the rotating speed of 600rpm to obtain the in-situ carbon-doped lithium titanium phosphate DLTP-2.
Comparative example 3
This comparative example in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries was prepared similarly to example 3, except that in step (2), phosphoric acid was used at a concentration of 50 wt%.
The remaining steps were the same as in example 3.
And obtaining the in-situ carbon-doped lithium titanium phosphate DLTP-3.
Comparative example 4
The present comparative example provides a method of preparing in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries, comprising the steps of:
(1) 0.2561g of lithium acetate dihydrate and 1.7086g of tetrabutyl titanate were dissolved in a beaker containing 100mL of anhydrous ethanol at 50 ℃ and stirred at 400rpm for 3 hours to obtain a first mixed solution;
0.8652g of ammonium dihydrogen phosphate and 1.2132g of a carbon source (the amount of the carbon source accounts for 30 wt% of the total amount of lithium acetate dihydrate, the titanium source, the carbon source and the ammonium dihydrogen phosphate, and the mass ratio of the amounts of citric acid and lactic acid is 1:0.8) are dissolved in a beaker containing 100mL of anhydrous ethanol at 60 ℃, and stirred at 350rpm for 2 hours to obtain a second mixed solution;
(2) adding all the obtained second mixed solution into the first mixed solution at 50 ℃, sealing the beaker mouth by using tin foil paper, stirring at constant temperature of 300rpm for 3 hours to obtain a gel precursor, removing the tin foil paper, and evaporating all the obtained gel precursors at 90 ℃ for 2 hours to obtain dry gel;
(3) and placing the obtained xerogel in a graphite boat, placing the xerogel in a tubular heating furnace at 850 ℃ under the protection of argon gas, calcining for 4h at the heating rate of 7 ℃/min, and then grinding the calcined material for 3h by adopting a planetary ball mill at the rotating speed of 600rpm to obtain the in-situ carbon-doped lithium titanium phosphate DLTP-4.
Test example
The titanium phosphate lithium electrode materials prepared in the examples and the comparative examples are assembled into a CR2016 type button cell, and the assembled cell is subjected to constant-current charge-discharge test and rate test, wherein the specific test results are shown in Table 1.
Wherein, the assembly process of the battery is as follows:
the titanium phosphate lithium electrode materials prepared in the examples and the comparative examples are mixed with acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, uniformly coated on a stainless steel foil with the thickness of 75 mu m, dried for 12 hours at 80 ℃ in vacuum (the vacuum degree is 0.1MPa), and then prepared into a circular electrode slice with the diameter of 12mm,
at 100. mu.L of 2mol/L Li 2 SO 4 As an electrolyte, LiMn is used 2 O 4 The prepared round electrode plate containing the lithium titanium phosphate is used as a negative electrode material, and the round electrode plate is assembled into a CR2016 type button cell.
The specific test conditions were as follows: testing the assembled water-based battery by using a battery testing system (Land-CT2001A, purchased from Wuhan blue electric company) at 25 ℃, respectively testing the first discharge specific capacity and the coulombic efficiency of the battery at 1C multiplying power, and the discharge specific capacity and the coulombic efficiency after 50 cycles, wherein the testing voltage range is 0.7-1.8V, and calculating the capacity retention rate;
wherein, the calculation formula of the capacity retention rate is as follows: (specific discharge capacity after 50 cycles/specific first discharge capacity) x 100%.
TABLE 1
The results in table 1 show that the aqueous lithium ion battery assembled by using the in-situ carbon-doped lithium titanium phosphate provided by the invention as a negative electrode material has excellent cycle performance and rate capability.
The invention exemplarily provides an XRD (X-ray diffraction), a thermogravimetric graph, an SEM (scanning electron microscope) graph and an EDS (electron-dispersive spectroscopy) surface scanning carbon element distribution diagram of the prepared in-situ carbon-doped lithium titanium phosphate, and the cycle performance graphs of the battery assembled by the in-situ carbon-doped lithium titanium phosphate prepared by the invention under the 1C multiplying power are respectively shown in figures 1-5.
Wherein, fig. 1 is an XRD pattern of in-situ carbon-doped lithium titanium phosphate prepared in example 1, fig. 2 is a thermogravimetric plot of in-situ carbon-doped lithium titanium phosphate prepared in example 2, fig. 3 is a cycle performance plot at 1C rate of a battery assembled from in-situ carbon-doped lithium titanium phosphate prepared in example 3, fig. 4 is an SEM image of in-situ carbon-doped lithium titanium phosphate prepared in example 3, and fig. 5 is an EDS surface-scanning carbon element distribution diagram (red element represents carbon element) of in-situ carbon-doped lithium titanium phosphate prepared in example 3.
As can be seen from figure 1, the in-situ carbon-doped lithium titanium phosphate prepared by the method disclosed by the invention has good correspondence with standard card PDF #35-0754, has a sharp XRD peak type, does not have a mixed peak, and shows that the material has good crystallinity and does not have an impurity phase.
As can be seen from FIG. 2, the in-situ carbon-doped lithium titanium phosphate prepared in example 2 of the present invention has a carbon content of 2.28 wt%.
As can be seen from fig. 3, the initial specific discharge capacity of the battery assembled by the in-situ carbon-doped lithium titanium phosphate prepared in embodiment 3 of the present invention is 105.2mAh/g at a rate of 1C, and after 50 cycles, the specific discharge capacity is 82.9mAh/g, and the capacity retention rate is 78.8%.
As can be seen from FIG. 4, the in-situ carbon-doped lithium titanium phosphate prepared in example 3 of the present invention has an average particle size of 60 nm.
As can be seen from FIG. 5, the carbon element in the in-situ carbon-doped lithium titanium phosphate prepared by the method of the present invention has good dispersibility, and the method of the present invention can achieve uniform carbon doping effect.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (9)
1. A method of preparing in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries, the method comprising:
(1) in the presence of a solvent I, carrying out first contact mixing on lithium acetate dihydrate and a titanium source to obtain a first mixed solution; the titanium source is tetrabutyl titanate and/or isopropyl titanate; and
in the presence of a solvent II, carrying out second contact mixing on a carbon source and phosphoric acid with the concentration of 80-85 wt% to obtain a second mixed solution; the carbon source comprises the following components in percentage by mass: 0.1-0.9 of citric acid and lactic acid;
(2) under a closed condition, carrying out first contact reaction on the first mixed solution and the second mixed solution to obtain a gel precursor, and carrying out evaporation treatment on the gel precursor to obtain a xerogel;
(3) calcining the xerogel; the conditions of the calcination include at least: the heating rate is 4-10 ℃/min, the calcination temperature is 650-850 ℃, and the time is 4-6 h;
wherein the amount of the carbon source accounts for 20-30 wt% of the total amount of the lithium acetate dihydrate, the titanium source, the carbon source and the phosphoric acid;
the molar ratio of the lithium acetate dihydrate calculated by lithium element, the titanium source calculated by titanium element and the phosphoric acid calculated by phosphorus element is 1: 1-3: 3-5.
2. The method according to claim 1, wherein in the step (1), the carbon source is a mixture of carbon sources with a content mass ratio of 1: 0.2-0.8 of citric acid and lactic acid.
3. The method of claim 1, wherein in step (1), the conditions of the first contacting and the second contacting and the mixing each independently comprise: the stirring speed is 300-400rpm, the temperature is 50-60 ℃, and the time is 2-3 h.
4. The method according to any one of claims 1 to 3, wherein in step (2), the conditions of the first contact reaction comprise at least: the stirring speed is 300-400rpm, the temperature is 50-60 ℃, and the time is 2-3 h.
5. The method according to any one of claims 1 to 3, wherein in step (2), the conditions of the evaporation treatment comprise at least: the temperature is 70-90 ℃ and the time is 2-3 h.
6. The method according to any one of claims 1-3, wherein in step (3), the method further comprises: and crushing the calcined material to obtain the in-situ carbon-doped lithium titanium phosphate with the average particle size of 60-100 nm.
7. The method according to claim 6, wherein in step (3), the conditions of the pulverization treatment include at least: the rotating speed is 500-600r/min, and the time is 2-3 h.
8. The in-situ carbon-doped lithium titanium phosphate for aqueous lithium ion batteries prepared by the method of any one of claims 1 to 7.
9. Use of the in situ carbon-doped lithium titanium phosphate according to claim 8 in a water-based lithium ion battery.
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