CN115571889A - Lithium iron silicate cathode material, preparation method thereof and lithium ion battery - Google Patents
Lithium iron silicate cathode material, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention discloses a lithium iron silicate positive electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium batteries. The preparation method has the advantages that the silicon dioxide nanotube is used as a silicon source, the precursor mixed liquid containing the iron source, the lithium source and the silicon source is evaporated to dryness to obtain a solid precursor, the solid precursor is sintered, the lithium iron silicate anode material is prepared by combining a hard template method and a solid phase reaction method, the hollow structure is provided, the full contact between an electrochemical active substance and an electrolyte is facilitated, the charge diffusion distance can be shortened, the ion transport capacity and the electronic conductivity of the lithium iron silicate anode material are greatly improved, and the capacity of a product under a low-rate condition can be remarkably improved.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a lithium iron silicate positive electrode material, a preparation method thereof and a lithium ion battery.
Background
In recent years, rapid development of portable electronic products and electric vehicles has promoted a huge economic market for high-performance lithium ion batteries. At present, the performance of lithium ion batteries mainly depends on positive electrode materials, and traditional positive electrode materials represented by spinel type lithium manganate and olivine type lithium iron phosphate are widely applied to a plurality of energy storage fields, however, the performance of the traditional positive electrode materials is pushed to a limit level along with the increase of the market demand for high specific capacity positive electrode materials. Therefore, in the process of searching for the next-generation cathode material, whether the cathode material has the advantages of low cost, high specific capacity and good safety must be considered. Polyanion cathode materials represented by lithium iron silicate are concerned about due to high specific capacity (the theoretical specific capacity is 330 mAh/g) and good safety and stability, and are cathode materials with great development potential.
Although lithium iron silicate has the advantages of low cost, high specific capacity and good safety performance, the characteristics of low electronic conductivity and slow ion transmission capability hinder the high reversible capacity of the lithium iron silicate. To date, various methods such as carbon coating cladding, metal ion doping, composite morphology control, and nanocomposite construction have been developed to solve this problem, and the preparation of lithium iron silicate composites with relatively high relative capacity remains a significant challenge.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a lithium iron silicate positive electrode material, a preparation method thereof and a lithium ion battery, and aims to remarkably improve the specific capacity of a product under a low-rate condition.
The invention is realized by the following steps:
in a first aspect, the present invention provides a method for preparing a lithium iron silicate positive electrode material, using a silicon dioxide nanotube as a silicon source, and using a hard template method to prepare the lithium iron silicate positive electrode material, including:
and evaporating the precursor mixed solution containing the iron source, the lithium source and the silicon source to dryness to obtain a solid precursor, and sintering the solid precursor.
In an alternative embodiment, the preparation process of the precursor mixed solution comprises: mixing a silicon source with a mixed solution containing an iron source, a lithium source and a carbon source;
the dosage of the lithium source, the iron source and the silicon source is controlled to be that the molar ratio of the lithium element to the iron element to the silicon element is 2.5-1.5;
preferably, the lithium source, the iron source and the silicon source are used in such amounts that the molar ratio of the lithium element, the iron element and the silicon element is controlled to be 2.9-1.1.
In an alternative embodiment, the iron source is selected from at least one of ferrous acetate and ferric citrate;
the lithium source is at least one of lithium acetate, lithium formate, lithium citrate and lithium tartrate;
in an alternative embodiment, the solvent used in preparing the mixed solution is selected from at least one of ethanol and deionized water.
In alternative embodiments, the carbon source is selected from at least one of polyvinylpyrrolidone, citric acid, and ammonium citrate.
In an alternative embodiment, the amount of carbon source is controlled to 5% to 10% by mass of the carbon in the product.
In an optional embodiment, the silicon source and the mixed solution are stirred for 100min to 150min, and then dried at 70 ℃ to 90 ℃ to evaporate the solvent.
In an optional embodiment, the solid precursor is sintered for 3 to 6 hours at the temperature of 300 to 500 ℃ and then sintered for 4 to 8 hours at the temperature of 600 to 800 ℃;
the temperature rise rate is controlled to be 4-6 ℃/min in the sintering process.
In a second aspect, the present invention provides a lithium iron silicate positive electrode material prepared by the preparation method according to any one of the foregoing embodiments.
In a third aspect, the present invention provides a lithium ion battery including the lithium iron silicate positive electrode material of the foregoing embodiment.
The invention has the following beneficial effects: the preparation method has the advantages that the silicon dioxide nanotube is used as a silicon source, the precursor mixed solution containing the iron source, the lithium source and the silicon source is evaporated to dryness to obtain a solid precursor, the solid precursor is sintered, the lithium iron silicate anode material is prepared by combining a hard template method and a solid phase reaction method, the hollow structure is favorable for full contact of electrochemical active substances and electrolyte, the charge diffusion distance can be shortened, the ion transmission capacity and the electronic conductivity of the lithium iron silicate anode material are greatly improved, and the capacity of the product under the low-rate condition can be remarkably improved.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a view showing a tubular Li in example 1 2 FeSiO 4 A scanning electron microscope image of the/C nano material;
FIG. 2 is a view showing a tubular Li in example 1 2 FeSiO 4 The first charge-discharge performance curve of the/C nano material;
FIG. 3 is a view showing a tubular Li example 1 2 FeSiO 4 Second charge and discharge performance curve of/C nanometer material.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The inventors found that Li 2 FeSiO 4 The difficulty in breaking through the high reversible capacity is mainly due to the poor ion transmission capability and electron conductivity of the electrode material, the structure and the morphology are two key factors for controlling the electrochemical performance of the electrode material, and the Li is improved by constructing a tubular structure 2 FeSiO 4 The ion transport ability and the electron conductivity of the electrolyte, thereby enhancing the electrochemical performance of the electrolyte.
The embodiment of the invention provides a preparation method of a lithium iron silicate anode material, which is synthesized by taking a silicon dioxide nanotube as a silicon source and combining a hard template method and a solid-phase reaction method and comprises the following steps:
s1, preparation of silicon dioxide nano tube
The preparation method of the silica nanotube is not limited, and the existing preparation process can be adopted, and is not limited herein.
In some embodiments, the silica nanotubes can be prepared by the following method: dissolving DL-tartaric acid, mixing with ammonia water, adding ethyl orthosilicate dropwise into the mixed system, standing for crystallization for 8-12h to obtain white gel, drying the white gel at 70-90 deg.C (such as drying for 1-3 h), and sintering at 500-700 deg.C for 2-5h.
Specifically, the preparation process of the silica nanotube comprises the following steps: weighing 0.104g of DL-tartaric acid, dissolving the DL-tartaric acid in a certain amount of absolute ethyl alcohol, adding 4mL of ammonia water at room temperature, slowly dropwise adding 1.57mL of Tetraethoxysilane (TEOS) under the condition of continuously stirring, standing and crystallizing for 10 hours after 1 hour of dropwise adding. And drying the obtained white gel at 80 ℃ for 2h, then placing the dried sample in a muffle furnace, heating to 600 ℃ at the speed of 5 ℃/min, preserving heat for 3h, and naturally cooling to room temperature to obtain the silicon dioxide nanotube. DL-tartaric acid is used as a template, tetraethoxysilane is hydrolyzed under alkaline conditions to generate silica nanotubes, and specific products and reaction principles can be referred to documents (Zheng bin, li Yuanqing, zhuluping, yangyang, shushao cloud, template method for preparing silica nanotubes and characterization thereof, chemical science and report, 2007, 58 (10): 2641-2646) to obtain silica nanotube products after sintering.
It is necessary to supplement that the silica nanotube is an inorganic functional material with large specific surface area, strong surface adsorption capacity, good dispersibility, good thermal stability and excellent mechanical stability. It is widely used in the storage and transportation of adsorbents, carriers of catalysts, drugs and proteins, and the manufacture of silicon-based materials. The good mechanical and thermal stability of the silica nanotubes helps them to maintain the hollow nanostructure and morphology during high temperature sintering. Thus, silica nanotubes are Li with a unique hollow structure 2 FeSiO 4 An ideal template. In addition, the silicon dioxide nanotube synthesis raw material is cheap and easy to obtain, and the synthesis process is simple and easyCan be commercially produced and can be used for synthesizing tubular Li on a large scale 2 FeSiO 4 And (3) a positive electrode material.
S2, mixing materials
And evaporating the precursor mixed solution containing the iron source, the lithium source and the silicon source to dryness to obtain a solid precursor, and evaporating to dryness to remove the solvent to obtain the solid raw material containing the iron source, the lithium source and the silicon source.
In order to improve the uniformity of raw material mixing, the preparation process of the precursor mixed liquid comprises the following steps: mixing a silicon source with a mixed solution containing an iron source, a lithium source and a carbon source, stirring the silicon source and the mixed solution for 100-150 min, and drying at 70-90 ℃ to evaporate the solvent. The raw materials can be fully contacted and mixed through long-time stirring, and then the mixture is heated and evaporated to dryness to obtain a fluffy precursor; and doping by introducing a carbon source to further improve the electrochemical performance of the material.
Specifically, the mixing and stirring can be performed at normal temperature, the stirring time can be 100min, 110min, 120min, 130min, 140min, 150min and the like, the drying temperature can be 70 ℃, 80 ℃, 90 ℃ and the like, and the drying time can be determined according to the situation, so that the purpose of evaporating the solvent can be achieved.
In order to further ensure the electrochemical properties such as the capacity and the like of the prepared cathode material, the inventor optimizes the dosage of each raw material: the lithium source, the iron source and the silicon source are used in such a manner that the molar ratio of the lithium element to the iron element to the silicon element is controlled to be within a range from 0.5 to 1.5, preferably from 2; the amount of the carbon source is controlled to 5-10% of the mass fraction of carbon in the product.
Specifically, the molar ratio of the lithium element, the iron element, and the silicon element may be 2.5.
Specifically, the carbon content of the final product can be controlled by controlling the amount of the carbon source, generally, the carbon content of the product after sintering 100g of the carbon source (such as polyvinylpyrrolidone PVP) is about 10g, and the amount of the carbon source in the raw material can be controlled according to the carbon content of the product. The carbon content in the product is controlled to be 5%, 7.5%, 10% and the like.
In some embodiments, the iron source is selected from at least one of ferrous acetate and ferric citrate and the lithium source is selected from at least one of lithium acetate, lithium formate, lithium citrate and lithium tartrate. The iron source and the lithium source may be any one or more of the above materials, and are not limited herein.
In some embodiments, the solvent used in preparing the mixed solution is at least one selected from ethanol and deionized water, and any one or more of the above solvents may be used in preparing the mixed solution, so long as the iron source and the lithium source are well dissolved.
In some embodiments, the carbon source is at least one selected from polyvinylpyrrolidone, citric acid and ammonium citrate, and the above carbon sources are all suitable for being doped in the lithium iron silicate, and the carbon source may be any one or more of the above raw materials.
S3, sintering
And sintering the solid precursor, and carrying out solid-phase reaction in the sintering process to obtain a lithium iron silicate product, wherein the product is doped with carbon in some embodiments.
In some embodiments, the solid precursor is sintered for 3-6 hours at 300-500 ℃ and then sintered for 4-8 hours at 600-800 ℃; the temperature rise rate is controlled to be 4-6 ℃/min in the sintering process. By further controlling the sintering temperature and time to promote the reaction, uniform tubular Li is obtained 2 FeSiO 4 a/C nano material product.
The embodiment of the invention provides a lithium iron silicate cathode material which is prepared by the preparation method, has a tubular structure and higher capacity under a low-rate condition, and can be further prepared into a lithium ion battery so as to further improve the electrochemical performance of the battery.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a preparation method of a lithium iron silicate cathode material, which comprises the following steps:
(1) Preparation of silica nanotubes
0.104g of DL-tartaric acid is weighed and dissolved in 5mL of absolute ethyl alcohol, 4mL of ammonia water is added at room temperature, 1.57mL of Tetraethoxysilane (TEOS) is slowly and dropwise added under the condition of continuous stirring, and after 1 hour of dropwise addition, standing and crystallizing are carried out for 10 hours. And drying the obtained white gel at 80 ℃ for 2h, then placing the dried sample in a muffle furnace, heating to 600 ℃ at a speed of 5 ℃/min, preserving heat for 3h, and naturally cooling to room temperature to obtain the silicon dioxide nanotube.
(2) Tubular Li 2 FeSiO 4 Preparation of/C
Firstly weighing 0.6g of the silicon dioxide nano-tube prepared in the step (1), and mixing SiO 2 Nanotube pouring into 20mL LiCH 3 COO.2H 2 O, anhydrous Fe (CH) 3 COO） 2 And PVP in absolute ethanol, with continuous mechanical stirring. Silica nanotube, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled to be 1. Stirring the mixture for 120min to obtain a fluffy precursor. And then putting the precursor into a vacuum drying oven for drying for 6 hours at the temperature of 80 ℃.
Putting the dried precursor into a tubular resistance furnace in an argon atmosphere, heating to 400 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 4h, heating to 700 ℃ and keeping the temperature for 6h, and naturally cooling to room temperature to obtain tubular Li 2 FeSiO 4 C nanometer material (carbon content in product is 4.9%).
And (3) performance testing: according to the mass ratio of 8:1: 1. weighing tubular Li 2 FeSiO 4 Placing the/C nano material, super P (carbon black conductive agent) and LA132 aqueous adhesive in an agate mortar, taking absolute ethyl alcohol as a dispersing agent, mixing and grinding, uniformly coating the slurry on an aluminum foil with the thickness of 20 mu m, and preparing a circular positive plate with the diameter of 12mm by using a puncher after drying. Then, a metal lithium sheet is taken as a negative electrode, a Cellgard-2400 type polypropylene membrane is taken as a diaphragm, and the electrolyte is 1.0 mol/L LiPF 6 [ Ethylene Carbonate (EC) + ethylmethyl carbonate (EMC) + diethyl carbonate (DEC) ] [ m (EC): m (EMC): m (DEC) = 1:1 ] was assembled into a CR2032 type button cell in a glove box filled with high-purity argon gas.
Sample tubular Li prepared in example 1 2 FeSiO 4 The scanning electron microscope image of the/C nano material is shown in figure 1, and the tubular Li 2 FeSiO 4 the/C can be clearly observed in FIG. 1.
FIGS. 2 and 3 are respectively a tubular Li 2 FeSiO 4 The first discharge specific capacity of the charge-discharge curve of the/C nano material at the first time under 0.1C is 189.7mAh/g, and the second discharge specific capacity is 186.2mAh/g.
Measuring tubular Li in the voltage range of 1.5 to 4.8V 2 FeSiO 4 The rate and cycle performance of the positive electrode material. The specific discharge capacities of the materials are 189.7, 148.6, 111.9, 109.3, 73.5, 51.5 and 179.3mAh/g at 0.1C, 0.5C, 1C, 2C, 5C, 10C and counter-test 0.1C. Tubular Li 2 FeSiO 4 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 84.6%.
Example 2
The embodiment provides a preparation method of a lithium iron silicate cathode material, which is different from the embodiment 1 only in the parameter value in the step (2), and specifically includes the following steps:
firstly weighing 0.6g of the silicon dioxide nano tube prepared in the step (1), and pouring the silicon dioxide nano tube into 20mL of LiCH 3 COO.2H 2 O, anhydrous Fe (CH) 3 COO） 2 And PVP in absolute ethanol, with continuous mechanical stirring. Silica nanotube, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled to be 0.5. Stirring the mixture for 100min to obtain a fluffy precursor. Then the precursor is put into a vacuum drying oven to be dried for 9 hours at 70 ℃.
Putting the dried precursor into a tubular resistance furnace in an argon atmosphere, heating to 300 ℃ at a heating rate of 4 ℃/min, preserving heat for 6h, then heating to 600 ℃ and preserving heat for 8h, and then naturally cooling to room temperature to obtain tubular Li 2 FeSiO 4 C nanometer material (the carbon content in the product is 7.6%).
And (3) performance testing: the procedure was the same as in example 1.
Through detection: tubular Li 2 FeSiO 4 The first discharge specific capacity of the/C nano material is 186.5mAh/g, and the second discharge specific capacity is 187.1mAh/g. The specific discharge capacities of the materials are 186.5, 147.9, 112.3, 110.8, 76.4, 52.6 and 180.7mAh/g respectively at 0.1C, 0.5C, 1C, 2C, 5C, 10C and counter-test 0.1C. Tubular Li 2 FeSiO 4 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 87.9%.
Example 3
The embodiment provides a preparation method of a lithium iron silicate cathode material, which is different from the embodiment 1 only in the parameter value in the step (2), and specifically includes the following steps:
firstly weighing 0.6g of the silicon dioxide nano tube prepared in the step (1), and pouring the silicon dioxide nano tube into 20mL of LiCH 3 COO.2H 2 O, anhydrous Fe (CH) 3 COO） 2 And PVP in absolute ethanol, with continuous mechanical stirring. Silica nanotube, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled to be 1.5. Stirring the mixture for 150min to obtain a fluffy precursor. Then the precursor is put into a vacuum drying oven to be dried for 3 hours at the temperature of 90 ℃.
Putting the dried precursor into a tubular resistance furnace in an argon atmosphere, heating to 500 ℃ at a heating rate of 6 ℃/min, keeping the temperature for 3h, heating to 800 ℃ and keeping the temperature for 4h, and naturally cooling to room temperature to obtain tubular Li 2 FeSiO 4 C nanometer material (carbon content in product is 10.1%).
And (4) performance testing: the procedure was the same as in example 1.
Through detection: tubular Li 2 FeSiO 4 The first discharge specific capacity of the/C nano material is 191.4mAh/g, and the second discharge specific capacity is 190.7mAh/g. The specific discharge capacities of the materials are 191.4, 149.4, 113.6, 110.5, 75.1, 53.3 and 183.2mAh/g at 0.1C, 0.5C, 1C, 2C, 5C, 10C and 0.1C in counter test. Tubular Li 2 FeSiO 4 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 90.2%.
Example 4
The only difference from example 1 is: silica nanotube, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled to be 1.5.
And (3) performance testing: the procedure was the same as in example 1.
Through detection: tubular Li 2 Fe 1.5 S i1.5 O 4 The first discharge specific capacity of the/C nano material is 150.2mAh/g, and the second discharge specific capacity is 149.7mAh/g. The specific discharge capacities of the materials are 150.2, 109.3, 83.1, 70.3, 62.7, 33.8 and 150.5mAh/g respectively at 0.1C, 0.5C, 1C, 2C, 5C, 10C and counter-test 0.1C. Tubular Li 2 Fe 1.5 S i1.5 O 4 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 81.9%.
Example 5
The only difference from example 1 is: silica nanotube, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled to be 0.5.
And (3) performance testing: the procedure was the same as in example 1.
Through detection: tubular Li 2 Fe 0.5 S i0.5 O 3.5 The first discharge specific capacity of the/C nano material is 95.5mAh/g, and the second discharge specific capacity is 94.7mAh/g. The specific discharge capacities of the materials are 95.5, 80.4, 63.5, 52.7, 41.6, 28.7 and 95.7mAh/g respectively at 0.1C, 0.5C, 1C, 2C, 5C, 10C and counter-test 0.1C. Tubular Li 2 Fe 0.5 S i0.5 O 3.5 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 81.9%.
Comparative example 1
The comparative example provides a preparation method of a traditional lithium iron silicate positive electrode material, which comprises the following specific steps:
first, 0.6g of nano-silica is weighed, and the nano-silica is poured into 20mL of LiCH 3 COO.2H 2 O, anhydrous Fe (CH) 3 COO） 2 And PVP in absolute ethanol, with continuous mechanical stirring. Nano silicon dioxide, fe (CH) 3 COO） 2 And LiCH 3 COO.2H 2 The molar ratio of O is controlled at 1. Stirring the mixture for 120min to obtain a fluffy precursor. Then the precursor is put into a vacuum drying oven to be dried for 6 hours at the temperature of 80 ℃.
Drying the precursorPutting the mixture into a tubular resistance furnace in an argon atmosphere, heating to 400 ℃ at a heating rate of 5 ℃/min, preserving heat for 4h, then heating to 700 ℃ and preserving heat for 6h, and then naturally cooling to room temperature to obtain the nano Li 2 FeSiO 4 C (carbon content in the product is 5.1%).
And (3) performance testing: the procedure was the same as in example 1.
Through detection: nano Li 2 FeSiO 4 The first discharge specific capacity of the/C is 141.4mAh/g, and the second discharge specific capacity is 139.8mAh/g. The specific discharge capacities of the materials are 141.3, 123.6, 100.9, 79.3, 48.5, 31.5 and 137.6mAh/g respectively at 0.1C, 0.5C, 1C, 2C, 5C, 10C and counter-test 0.1C. Tubular Li 2 FeSiO 4 The capacity retention rate of the/C nano material after 100 times of circulation at 1C is 81.6%.
The present invention has been described in terms of the preferred embodiment, and it is not intended to be limited to the embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of a lithium iron silicate cathode material is characterized in that a silicon dioxide nanotube is used as a silicon source, and the preparation method is carried out by using a hard template method, and comprises the following steps:
and evaporating the precursor mixed solution containing the iron source, the lithium source and the silicon source to dryness to obtain a solid precursor, and sintering the solid precursor.
2. The method according to claim 1, wherein the precursor mixture is prepared by a process comprising: mixing the silicon source with a mixed solution containing an iron source, a lithium source and a carbon source;
the dosage of the lithium source, the iron source and the silicon source is controlled in a manner that the molar ratio of lithium element to iron element to silicon element is 2.5-1.5.
3. The production method according to claim 2, wherein the iron source is selected from at least one of ferrous acetate and ferric citrate;
the lithium source is selected from at least one of lithium acetate, lithium formate, lithium citrate and lithium tartrate.
4. The method according to claim 2, wherein the solvent used in preparing the mixed solution is at least one selected from the group consisting of ethanol and deionized water.
5. The method of claim 2, wherein the carbon source is selected from at least one of polyvinylpyrrolidone, citric acid, and ammonium citrate.
6. The method of claim 5, wherein the carbon source is used in an amount to control the mass fraction of carbon in the product to 5-10%.
7. The preparation method according to claim 2, wherein the silicon source and the mixed solution are stirred for 100min to 150min and then dried at 70 ℃ to 90 ℃ to evaporate the solvent.
8. The preparation method according to claim 1, characterized in that the solid precursor is sintered for 3-6h at 300-500 ℃ and then for 4-8h at 600-800 ℃;
the temperature rise rate is controlled to be 4-6 ℃/min in the sintering process.
9. A lithium iron silicate positive electrode material, characterized by being produced by the production method according to any one of claims 1 to 8.
10. A lithium ion battery comprising the lithium iron silicate positive electrode material according to claim 9.
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