CN108039466B - A kind of preparation method of titanium silicide-coated lithium iron phosphate composite material - Google Patents

Abstract

The invention discloses a preparation method of a titanium silicide-coated lithium iron phosphate composite material, comprising the following steps: weighing a lithium source, an iron source and a Phosphorus source; wet ball milling of lithium source, iron source and phosphorus source, dried and crushed to obtain LiFePO ₄ precursor; put LiFePO ₄ precursor into a tube furnace, under protective atmosphere, at 2-8℃/ The temperature was raised to 680-750℃ for 6-12h at the rate of min, the protective atmosphere was stopped, the silicon source and titanium source were added, and the deposition reaction was carried out for 5-30min, then calcined for 0-6h in the protective atmosphere, and then cooled to room temperature The titanium silicide-coated lithium iron phosphate composite material is obtained. The preparation method of the titanium silicide-coated lithium iron phosphate composite material proposed by the invention has the advantages of simple process, improved electronic conduction performance of the lithium iron phosphate material, and improved rate performance and cycle performance.

Description

A kind of preparation method of titanium silicide-coated lithium iron phosphate composite material

technical field

The invention relates to the technical field of positive electrode materials for lithium ion batteries, in particular to a preparation method of a titanium silicide-coated lithium iron phosphate composite material.

Background technique

With the development of lithium-ion battery technology, secondary lithium batteries have been widely used in electronic products, electric vehicles, hybrid vehicles, large power grids and new energy storage devices. Compared with other lithium battery cathode materials, lithium iron phosphate has the characteristics of high safety, long cycle life, high specific capacity, good stability, abundant resources, low price, non-toxic and environmentally friendly, and is widely regarded as the most promising technology. One of the cathode materials for lithium batteries. In addition, lithium iron phosphate has good high temperature cycling performance without explosion. Lithium iron phosphate is also an excellent cathode material for large-scale lithium-ion battery packs, and has a large application space in large-scale power batteries.

However, the structural characteristics of lithium iron phosphate with an olivine structure determine that lithium ions can only conduct one-dimensional conduction along the (010) direction during charging and discharging, resulting in low electronic conductivity (10 ^-9 -10 ^-10 S·cm ^-1 ). The low electronic conductivity limits the high-rate charge-discharge performance of lithium iron phosphate batteries, thereby limiting the application of lithium iron phosphate in fields requiring high current and rapid charge and discharge. The most common method to solve this problem is the surface carbon coating technology. Although carbon coating can improve the battery performance of lithium iron phosphate to a certain extent, there are many difficulties and challenges in practical production. For example, when the carbon content is low, a complete and uniform coating layer cannot be formed on the surface of lithium iron phosphate, and sufficient electrical conductivity cannot be obtained; as the carbon content increases, the coating layer thickens, which not only reduces the vibration of the active material density and hinder the diffusion channels of lithium ions.

Titanium silicide compound not only has excellent electrical conductivity, but also has extremely high chemical stability and corrosion resistance, and is not easy to decompose. As a modified substance, it will not affect the progress of the main reaction due to the generation of impurities. Due to the above properties, titanium silicide compounds have a very significant effect on the modification of lithium iron phosphate battery materials.

SUMMARY OF THE INVENTION

Based on the technical problems existing in the background technology, the present invention proposes a preparation method of a titanium silicide-coated lithium iron phosphate composite material, which has a simple process, can improve the electronic conductivity of the lithium iron phosphate material, and improve its rate performance and cycle performance. .

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1-1.05:1:1; Obtain LiFePO ₄ precursor;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, and in a protective atmosphere, the temperature is raised to 680-750 ℃ at a rate of 2-8 ℃/min for 6-12 hours, and the protective atmosphere is stopped. After adding a silicon source and a titanium source, a deposition reaction is performed for 5-30 minutes, and then calcined in a protective atmosphere for 0-6 hours and then cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material.

Preferably, in S1, the lithium source is a mixture of one or more of lithium carbonate, lithium acetate, lithium oxalate, lithium dihydrogen phosphate, and lithium hydroxide.

Preferably, in S1, the iron source is a mixture of one or more of ferric oxide, ferric tetroxide, ferrous oxide, ferric hydroxide, ferric phosphate, and ferrous oxalate.

Preferably, in S1, the phosphorus source is a mixture of one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

Preferably, in S2, the protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

Preferably, in S2, the silicon source and the titanium source are gaseous SiH ₄ and liquid TiCl ₄ respectively, and N ₂ is used as a carrier gas.

Preferably, the TiCl ₄ is maintained at 30-40 °C by heating in a water bath, and the temperature of the TiCl ₄ pipeline is maintained at 45-55 °C.

Preferably, by bubbling N ₂ , TiCl ₄ is passed into the gas mixing chamber and mixed with SiH ₄ to obtain a mixed gas and then enter the reaction chamber for deposition reaction, and the total flow of the mixed gas is controlled at 500-1200 sccm.

Preferably, in the mixed gas, the molar percentage of SiH ₄ is 0.33-0.5%, and the molar percentage of TiCl ₄ is 0.33-1.67%.

Preferably, the molar ratio of TiCl ₄ to SiH ₄ is 1-3:1.

Preferably, the titanium silicide is one or a mixture of Ti ₅ Si ₃ and TiSi ₂ .

In the preparation method of the titanium silicide-coated lithium iron phosphate composite material of the present invention, a titanium silicide-coated lithium iron phosphate composite material is synthesized by chemical vapor deposition by introducing a titanium source and a silicon source during the preparation of the lithium iron phosphate calcination process. In the synthesis process, the thickness and morphology of the coating layer can be adjusted by adjusting the molar ratio of silicon to titanium, the deposition time, and the reaction temperature to obtain a titanium silicide-coated lithium iron phosphate composite material; compared with the prior art, the present invention has the beneficial effects It is shown in: 1. The coating of the titanium silicide prepared by the present invention is very uniform on the lithium iron phosphate, and has no hindering effect on the diffusion of lithium ions; 2. The conductivity of the titanium silicide-coated lithium iron phosphate composite material prepared by the present invention is The rate performance and cycle performance of the lithium iron phosphate material are greatly improved; 3. The lithium iron phosphate composite material coated by this method has an increased tap density, which is more conducive to the miniaturization of high-capacity lithium-ion batteries.

Description of drawings

FIG. 1 is the charge-discharge curve of the battery assembled with the titanium silicide-coated lithium iron phosphate composite material prepared in Example 1 of the present invention at different rates.

Detailed ways

Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments.

Example 1

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh lithium carbonate, ferrous oxalate and ammonium dihydrogen phosphate according to the molar ratio of lithium element, iron element and phosphorus element as 1:1:1 respectively for preparation; Ball milling, vacuum drying and then ball milling and crushing to obtain LiFePO ₄ precursor;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, in a protective nitrogen atmosphere, heat up to 680 ℃ for 10h at a rate of 5 ℃/min, turn off the protective nitrogen, and use N ₂ by bubbling The TiCl ₄ was introduced into the gas mixing chamber and mixed with SiH ₄ to obtain a mixture of TiCl ₄ , SiH ₄ and N ₂ , and the uniformly mixed mixture of TiCl ₄ , SiH ₄ and N ₂ was introduced into the reaction chamber to carry out the deposition reaction for 10min, Wherein, the molar ratio of TiCl ₄ to SiH ₄ is 3:1, the total flow of the mixed gas is 1000sccm, the mixed gas is turned off, then calcined under protective nitrogen for 2 h, cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite Material.

The titanium silicide-coated lithium iron phosphate composite material prepared in this example is a titanium silicide-coated lithium iron phosphate composite material according to the weight ratio: SP:PVDF=8:1:1 to assemble a button battery, using Clgard2300 type diaphragm, metal The lithium sheet was used as the counter electrode, and the charge and discharge tests were carried out at different rates. The results are shown in Figure 1. It can be seen from Figure 1 that the specific capacity of 0.2C discharge is 165mAh/g, the specific capacity of 1C discharge is 160mAh/g, and the specific capacity of 2C discharge is 160mAh/g. It is 158mAh/g, and the 3C discharge capacity is 155mAh/g.

Example 2

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh lithium hydroxide, ferrous oxalate and ammonium dihydrogen phosphate respectively according to the molar ratio of lithium element, iron element and phosphorus element as 1.02:1:1 for preparation; Wet ball milling, vacuum drying, ball milling and crushing to obtain LiFePO ₄ precursor;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under the protective argon atmosphere, heat up to 700 ℃ for 8 hours at a rate of 2 ℃/min, and then turn off the protective argon gas. The mixed gas of TiCl ₄ , SiH ₄ and N ₂ was introduced into the reaction chamber for deposition reaction for 15min, wherein the molar ratio of TiCl ₄ to SiH ₄ was 2:1, and the total flow of the mixed gas was 800sccm. calcined under argon for 2 h, and cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material.

Example 3

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh lithium carbonate and iron phosphate respectively according to the molar ratio of lithium element, iron element and phosphorus element as 1.05:1:1 for material preparation; wet ball milling of lithium carbonate and iron phosphate, vacuum drying and then ball milling and crushing to obtain LiFePO ₄ Precursor;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, in a protective nitrogen atmosphere, heat up to 730 ℃ for 10h at a rate of 8 ℃/min, turn off the protective nitrogen, and put the uniformly mixed TiCl ₄ The mixed gas of , SiH ₄ and N ₂ was introduced into the reaction chamber for deposition reaction for 20min, wherein the molar ratio of TiCl ₄ to SiH ₄ was 1:1, the total flow rate of the mixed gas was 1200sccm, the mixed gas was closed, and then under protective nitrogen Cooling to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material.

Example 4

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh lithium carbonate, ferrous oxalate and ammonium dihydrogen phosphate respectively according to the molar ratio of lithium element, iron element and phosphorus element as 1.01:1:1 for preparation; Ball milling, vacuum drying and then ball milling and crushing to obtain LiFePO ₄ precursor;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under the protective nitrogen atmosphere, heat up to 750 ℃ for 6 h at a rate of 4 ℃/min, turn off the protective nitrogen, and put the uniformly mixed TiCl ₄ The mixed gas of , SiH ₄ and N ₂ was introduced into the reaction chamber for deposition reaction for 30min, wherein the molar ratio of TiCl ₄ to SiH ₄ was 3:1, the total flow of the mixed gas was 500sccm, the mixed gas was closed, and then under protective nitrogen After calcining for 4 hours, cooling to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material.

Example 5

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1:1:1; wet ball milling of lithium source, iron source and phosphorus source, dry and crush to obtain LiFePO ₄ precursors;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under a protective atmosphere, heat up to 750 ℃ for 6 hours at a rate of 2 ℃/min, stop the protective atmosphere, add silicon source and titanium source Then, the deposition reaction is carried out for 30 minutes, and then cooled to room temperature in a protective atmosphere to obtain the titanium silicide-coated lithium iron phosphate composite material.

Example 6

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1.05:1:1; wet ball milling of lithium source, iron source and phosphorus source, dry and crush to obtain LiFePO ₄ precursors;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under a protective atmosphere, heat up to 680 ℃ for 12 hours at a rate of 8 ℃/min, stop the protective atmosphere, add silicon source and titanium source After that, the deposition reaction is carried out for 5 minutes, then calcined for 6 hours in a protective atmosphere, and cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material.

Example 7

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1.03:1:1; wet ball milling of lithium source, iron source and phosphorus source, dry and crush to obtain LiFePO ₄ precursors; wherein, the lithium source is lithium carbonate; the iron source is ferric oxide; the phosphorus source is ammonium dihydrogen phosphate;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under a protective atmosphere, heat up to 690 ℃ for 11 hours at a rate of 3 ℃/min, stop the protective atmosphere, add silicon source and titanium source After that, the deposition reaction was carried out for 16 minutes, then calcined in a protective atmosphere for 2 hours, and cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material; wherein, the protective atmosphere was a nitrogen atmosphere; the silicon source and the titanium source were respectively It is gaseous SiH ₄ and liquid TiCl ₄ , and N ₂ is used as the carrier gas; the TiCl ₄ is maintained at 30 ° C by heating in a water bath, and the temperature of the TiCl ₄ pipeline is maintained at 55 ° C _; TiCl ₄ is passed into the mixing chamber and mixed with SiH ₄ to obtain a mixed gas and then enters the reaction chamber for deposition reaction, and the total flow of the mixed gas is controlled at _{600sccm ;} The mole percent is 1.67%.

Example 8

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1.01:1:1; wet ball milling of lithium source, iron source and phosphorus source, dry and crush to obtain LiFePO ₄ precursors; wherein, the lithium source is a mixture of lithium carbonate and lithium acetate, and the weight ratio of lithium carbonate and lithium acetate is 3:2; the iron source is ferric tetroxide; the phosphorus source is diphosphate Ammonium hydrogen;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, under a protective atmosphere, heat up to 720 ℃ for 7 h at a rate of 7 ℃/min, stop the protective atmosphere, add silicon source and titanium source After that, the deposition reaction is carried out for 25 minutes, then calcined for 5 hours in a protective atmosphere, and cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material; wherein, the protective atmosphere is a nitrogen atmosphere; the silicon source and the titanium source are respectively It is gaseous SiH ₄ and liquid TiCl ₄ , and N ₂ is used as a carrier gas; the TiCl ₄ is maintained at 40 ° C by heating in a water bath, and the temperature of the TiCl ₄ pipeline is maintained at 55 ° C _; TiCl ₄ is passed into the gas mixing chamber and mixed with SiH ₄ to obtain a mixed gas and then enters the reaction chamber for deposition reaction, and the total flow of the mixed gas is controlled at _{1100sccm ;} The mole percent is 0.33%.

Example 9

The preparation method of a titanium silicide-coated lithium iron phosphate composite material proposed by the present invention comprises the following steps:

S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1.02:1:1; wet ball milling of lithium source, iron source and phosphorus source, dry and crush to obtain LiFePO ₄ precursors; wherein, the lithium source is a mixture of lithium carbonate, lithium oxalate, and lithium hydroxide, and the weight ratio of lithium carbonate, lithium oxalate, and lithium hydroxide is 3:2:1; the iron source is trioxide A mixture of ferrous iron, ferrous oxide, and ferrous oxalate, and the weight ratio of ferrous trioxide, ferrous oxide, and ferrous oxalate is 4:3:2; the phosphorus source is ammonium dihydrogen phosphate, diammonium hydrogen phosphate mixture, and the weight ratio of ammonium dihydrogen phosphate and diammonium hydrogen phosphate is 4:5;

S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, in a protective atmosphere, heat up to 700 ℃ for 8 hours at a rate of 5 ℃/min, stop the protective atmosphere, add silicon source and titanium source After that, the deposition reaction is carried out for 20 minutes, then calcined in a protective atmosphere for 3 hours, and cooled to room temperature to obtain the titanium silicide-coated lithium iron phosphate composite material; wherein, the protective atmosphere is an argon atmosphere; the silicon source and the titanium source are Gaseous SiH ₄ and liquid TiCl ₄ respectively, and N ₂ is used as the carrier gas; the TiCl ₄ is maintained at 35 °C by heating in a water bath, and the temperature of the TiCl ₄ pipeline is maintained at 50 ° C; N ₂ is used by bubbling The TiCl ₄ is passed into the gas mixing chamber and mixed with SiH ₄ to obtain the mixed gas, and then enters the reaction chamber of the tube furnace to carry out the deposition reaction, and the total flow of the mixed gas is controlled at 800sccm; in the mixed gas, the mole percentage of SiH ₄ is 0.38 %, the mole percentage of _TiCl4 is 1.2%.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (11)

1. a preparation method of titanium silicide-coated lithium iron phosphate composite material, is characterized in that, comprises the following steps: S1. Weigh the lithium source, iron source and phosphorus source according to the molar ratio of lithium element, iron element and phosphorus element as 1-1.05:1:1; Obtain LiFePO ₄ precursor; S2. Add the LiFePO ₄ precursor in S1 into the tube furnace, and in a protective atmosphere, the temperature is raised to 680-750 ℃ at a rate of 2-8 ℃/min for 6-12 hours, and the protective atmosphere is stopped. By bubbling N ₂ , TiCl ₄ was passed into the gas mixing chamber and mixed with SiH ₄ to obtain a mixed gas, and then entered the reaction chamber for deposition reaction for 5-30 min, and then calcined in a protective atmosphere for 0-6 h and cooled to room temperature to obtain the obtained The titanium silicide-coated lithium iron phosphate composite material is described. 2. the preparation method of titanium silicide-coated lithium iron phosphate composite material according to claim 1, is characterized in that, in S1, described lithium source is lithium carbonate, lithium acetate, lithium oxalate, lithium dihydrogen phosphate, hydroxide A mixture of one or more of lithium. 3. according to the preparation method of the described titanium silicide-coated lithium iron phosphate composite material of claim 1 and 2, it is characterized in that, in S1, described iron source is ferric oxide, ferric oxide, ferrous oxide, Ferric hydroxide, ferric phosphate, ferrous oxalate. 4. The preparation method of titanium silicide-coated lithium iron phosphate composite material according to claim 1 or 2, characterized in that, in S1, the phosphorus source is lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate A mixture of one or more of them. 5. The preparation method of titanium silicide-coated lithium iron phosphate composite material according to claim 3, characterized in that, in S1, the phosphorus source is lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. one or more mixtures. 6 . The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to claim 1 or 2 , wherein, in S2 , the protective atmosphere is a nitrogen atmosphere or an argon atmosphere. 7 . 7 . The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to claim 3 , wherein, in S2 , the protective atmosphere is a nitrogen atmosphere or an argon atmosphere. 8 . 8 . The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to claim 4 , wherein, in S2 , the protective atmosphere is a nitrogen atmosphere or an argon atmosphere. 9 . 9 . The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to claim 1 , wherein the TiCl ₄ is maintained at 30-40° C. by heating in a water bath, and the temperature of the TiCl ₄ pipeline is maintained at 45-55 ℃. 10 . °C. 10 . The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to claim 1 , wherein, in the mixed gas, the molar percentage of SiH ₄ is 0.33-0.5%, and the molar percentage of TiCl ₄ is 0.33-1.67 %. 11 . %; the molar ratio of TiCl ₄ to SiH ₄ is 1-3:1. 11. The method for preparing a titanium silicide-coated lithium iron phosphate composite material according to any one of claims 1-2, 5, and 7-10, wherein the titanium silicide is one of Ti ₅ Si ₃ and TiSi ₂ one or a mixture of both.

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