Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a PANI @ CN/SnS lithium ion battery anode material and a preparation method thereof, wherein high-conductivity polyaniline is coated on C3N4SnS electrode material surface, intended to solve the existing C3N4SnS electrode material due to g-C3N4Poor conductivity and poor electrochemical performance of the battery caused by large volume expansion of SnS in the charge and discharge processes.
In order to realize the purpose, the invention provides a PANI @ CN/SnS lithium ion battery cathode material which comprises SnS and g-C3N4The composite nano sheet is constructed, and the carbon layer is coated on the surface of the composite nano sheet, wherein the carbon layer is made of polyaniline; in the negative electrode material, the mass fraction of the carbon element is 30-40%.
According to another aspect of the present invention, there is also provided a method for preparing a PANI @ CN/SnS lithium ion battery anode material, comprising the steps of:
s1, preparation g-C3N4;
S2, g-C prepared by step S13N4Directly mixing and stirring the polyaniline and a tin source and a sulfur source for reaction, and then adding protonic acid, an aniline monomer and an initiator to synthesize polyaniline in situ under an acidic condition to obtain a PANI @ CN/SnS precursor;
s3, heating and preserving the PANI @ CN/SnS precursor prepared in the step S2, then carbonizing at high temperature in a protective atmosphere, and cooling to obtain the PANI @ CN/SnS lithium ion battery negative electrode material.
Preferably, in step S1, g-C is prepared3N4The specific process is as follows: heating the raw materials to 500-600 ℃ at a heating rate of 3-5 ℃/min, and calcining for 2-4 h to obtain the final productTo g-C3N4(ii) a Wherein the raw material is at least one of dicyandiamide, urea, melamine and thiourea.
Preferably, in step S2, the sulfur source is at least one of thioacetamide and thiourea.
Preferably, in step S2, the Sn source and the S source are mixed in a molar ratio of Sn element to S element of 1 (1-2).
Preferably, in step S2, the protonic acid is at least one of hydrochloric acid and sulfuric acid, and the initiator is at least one of persulfate, dichromate, and hydrogen peroxide.
Preferably, the protonic acid is hydrochloric acid, the initiator is ammonium persulfate, and the molar ratio of the hydrochloric acid to the aniline monomer to the ammonium persulfate is (1-1.5):1 (1-3).
Preferably, in step S2, the temperature during the synthesis of polyaniline is controlled below 5 ℃, and the reaction time is 10h-14 h.
Preferably, in step S3, the PANI @ CN/SnS precursor is heated and preserved for 10h to 12h in an oil bath, and the temperature of the oil bath is 60 ℃ to 85 ℃.
Preferably, in step S3, the protective atmosphere is argon-hydrogen mixed gas, and the high-temperature carbonization process is performed at a temperature rise rate of 5 ℃/min to 10 ℃/min, and after the temperature is raised to 700 ℃ to 900 ℃, the temperature is maintained for 2h to 4 h.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
(1) the invention coats C by using polyaniline with high conductivity as a carbon layer3N4The negative electrode material of the lithium ion battery is obtained by the SnS compound, the volume expansion of the material in the SnS charge and discharge process can be effectively relieved by the porous lamellar structure of the material, more active sites are exposed, and the transmission path of ions and electrons is shortened, so that the material has higher specific capacity and excellent cycling stability, the specific capacity can still be maintained at about 760mAh/g after being cycled for 100 circles under the current density of 200mA/g, and the material has important reference value for the practical application of lithium ion energy storage equipment with excellent electrochemical performance.
(2) At present, g-C is generally3N4Preparing C with a tin source and a sulfur source by a hydrothermal method3N4SnS complex, but the hydrothermal method requires high temperature and pressure steps, making it more dependent on production equipment; and the hydrothermal method has poor experimental repeatability and is not convenient to be amplified into batch experiments due to the lack of deep research on the control of influencing factors in the crystal nucleus forming process and the crystal growth process of the hydrothermal method. The method utilizes the one-step method of solution to prepare the high-conductivity PANI-coated C in situ3N4The SnS electrode material has the advantages of simple operation steps, good repeatability, high yield of the obtained product, uniform dispersion of components and excellent electrochemical performance.
(3) The preparation method has the advantages of abundant available synthetic raw materials, no strict limitation, no pollution, simple equipment, low energy consumption and low cost.
(4) The preparation method of the invention strictly controls the concentration of reactants for polymerizing the polyaniline and the reaction temperature to be C3N4And a polyaniline carbon layer with uniform shape and high conductivity is formed on the surface of the SnS composite, so that the performance of the battery cathode material is improved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. 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 PANI @ CN/SnS lithium ion battery cathode material which comprises SnS and g-C3N4The composite nano sheet is constructed, and the carbon layer is coated on the surface of the composite nano sheet, wherein the carbon layer is made of polyaniline; in the negative electrode material, the mass fraction of the carbon element is 30-40%.
Polyaniline (PANI) has the characteristics of high specific capacity, good redox reversibility, high conductivity, simple synthesis method, low cost and the like, and is used as C3N4The coating carbon layer of the SnS precursor can improve the electrode conductivity and well relieve the volume expansion of the SnS in the charge-discharge reaction process. g-C3N4And in combination with the polyaniline carbon layer, nitrogen atoms can be doped in the PANI crystal lattice, and the nitrogen-doped carbon matrix can further reduce the energy barrier of lithium ion penetration and promote the rapid diffusion of lithium ions and electrons. Meanwhile, the polyaniline carbon layer and SnS can form a C-S-C heterocyclic configuration, and the reaction kinetics of the material are improved.
By utilizing thermogravimetric analysis and battery performance tests, a large number of experiments prove that if the content of carbon in the negative electrode material is too high, the specific discharge capacity of the material is low; if the content of the carbon element is too low, the capacity fading is fast. The PANI @ CN/SnS lithium ion battery cathode material provided by the invention has excellent electrochemical performance, and the specific capacity of the PANI @ CN/SnS lithium ion battery cathode material can still maintain about 760mAh/g after being cycled for 100 circles under the current density of 200 mA/g.
As shown in fig. 1, the preparation method of the PANI @ CN/SnS lithium ion battery anode material provided by the present invention comprises the following steps:
s1, preparation g-C3N4;
S2, g-C prepared by step S13N4Directly mixing and stirring the polyaniline and a tin source and a sulfur source for reaction, and then adding protonic acid, an aniline monomer and an initiator to synthesize polyaniline in situ under an acidic condition to obtain a PANI @ CN/SnS precursor;
s3, heating and preserving the PANI @ CN/SnS precursor prepared in the step S2, then carbonizing at high temperature in a protective atmosphere, and cooling to obtain the PANI @ CN/SnS lithium ion battery negative electrode material.
In some embodiments, step S1 uses a calcination process to prepare g-C3N4The preparation raw materials can be selected from various nitrogen-rich precursors, and the preparation method has the characteristics of short process flow, less used equipment, low requirement on equipment, short preparation time and the like. The raw material can be at least one of dicyandiamide, urea, melamine and thiourea. The specific preparation process comprises heating the raw materials to 500-600 deg.C at a heating rate of 3-5 deg.C/min, calcining for 2-4 h, and naturally cooling to room temperature to obtain g-C3N4。
In some embodiments, in step S2, the tin source may be stannous chloride dihydrate, and the sulfur source may be at least one of thioacetamide and thiourea. The tin source and the sulfur source are mixed according to the molar ratio 1 (1-2) of the Sn element to the S element.
The invention adopts a chemical oxidative polymerization method to synthesize polyaniline, and uses an initiator to perform oxidative polymerization on aniline monomers under an acidic condition. Protonic acid is an important factor influencing the oxidative polymerization of aniline, and on the one hand, provides the pH value required by the reaction medium; on the other hand, the polyaniline skeleton is endowed with certain conductivity in the form of a dopant. The polymerization is carried out simultaneously with in-situ doping, and the polymerization and doping are completed simultaneously. The synthesis reaction is influenced by the type and concentration of protonic acid, the type and concentration of initiator, the concentration of aniline monomer, the reaction temperature, the reaction time and other factors. The protonic acid used for synthesizing polyaniline is at least one of hydrochloric acid and sulfuric acid, and the initiator is at least one of persulfate, dichromate and hydrogen peroxide, so that the reaction temperature is controlled to be C3N4The surface of the SnS compound is used for synthesizing polyaniline more uniformly, and a surfactant can be added in the synthesis process, wherein the surfactant can adopt at least one of polyvinylpyrrolidone (PVP), dodecylbenzene sulfonic acid (DBSA) and sodium dodecylbenzene sulfonate (SDBS). Because the polyaniline of the coating layer is synthesized in situ in the cathode material, the reaction environment is complicated, and the method is used for preparing the polyaniline in C3N4The SnS compound has uniform surface formation form, high conductivity and air spaceThe invention discloses a polyaniline carbon skeleton with a stable core structure, which is characterized in that a large number of experiments are carried out to screen out a preferred embodiment, wherein, hydrochloric acid is selected as protonic acid, ammonium persulfate is selected as initiator, and the molar ratio of hydrochloric acid to aniline monomer to ammonium persulfate is (1-1.5) to (1-3); the temperature is controlled below 5 ℃ in the synthesis process, and the reaction time is 10-14 h. If the reaction temperature is too high, side reactions during the production of polyaniline may increase, and more by-products may be produced.
In some embodiments, in step S3, the PANI @ CN/SnS precursor is heated and held in an oil bath at a temperature of 60 ℃ to 85 ℃ for 10h to 12 h. The PANI @ CN/SnS precursor is heated more uniformly by the oil bath, and water vapor is not generated in the heating process, so that better crystallization of SnS is facilitated. The protective atmosphere in the carbonization process is argon-hydrogen mixed gas, the temperature is raised to 700-900 ℃ at the temperature raising rate of 5-10 ℃/min, and then the temperature is kept for 2-4 h. Ar/H2The carbon skeleton with uniform appearance and large specific surface area can be obtained by controlling proper carbonization temperature in the reducing atmosphere of gas, and the electrical property and specific capacity of the battery cathode material can be effectively improved by carbonization treatment.
The above technical solution is described in detail below with reference to specific examples.
Example 1
The embodiment provides a PANI @ CN/SnS lithium ion battery cathode material, and the preparation method comprises the following steps:
(1)g-C3N4the preparation of (1): heating urea to 550 ℃ at the heating rate of 5 ℃/min, carrying out heat preservation and calcination for 2h, and naturally cooling to room temperature to obtain g-C3N4。
(2) Preparation of PANI @ CN/SnS precursor: adding 0.5 mmol-C into 50mL of ethanol3N4Ultrasonic dispersing, then adding 1mmol SnCl2·2H2And performing O ultrasonic treatment for 2h, then adding 1mmol thioacetamide, and stirring for reaction for 2 h. And adding 0.1mmol PVP, 0.5mmol hydrochloric acid and 0.5mmol aniline monomer into the original system, slowly adding 0.5mmol ammonium persulfate, and carrying out polymerization reaction in an ice bath environment for 12 hours to obtain a PANI @ CN/SnS precursor.
(3) Preparing a PANI @ CN/SnS lithium ion battery anode material: polymerizing the polymer prepared in the step (2)The latter system was reacted for 12h with stirring directly in a 65 ℃ oil bath. Then placed in a tube furnace at Ar/H2And (3) heating to 800 ℃ at a heating rate of 5 ℃/min in a gas atmosphere, calcining at a constant temperature for 2h, and cooling to obtain the PANI @ CN/SnS lithium ion battery negative electrode material.
The PANI @ CN/SnS lithium ion battery anode material prepared in this example was observed with a scanning electron microscope, and as can be seen from fig. 2 and 3, the material as a whole showed a lamellar structure with holes visible on the surface. The lamellar structure can provide convenience for lithium ion de-intercalation and can relieve volume expansion in the SnS charge-discharge process; the surface defects expose more active sites, and shorten the transmission path of ions and electrons, so that the material as a lithium ion negative electrode shows excellent electrochemical performance. An X-ray diffraction pattern (XRD) is shown in figure 4, and the lithium ion battery cathode material has obvious characteristic peaks of SnS besides obvious carbon peaks, which indicates that the carbon layer successfully coats SnS.
Electrochemical tests are carried out on the lithium ion battery cathode material of the embodiment, as can be seen from fig. 5, the charge and discharge curves of the cycle 2 nd circle and the cycle 10 th circle almost coincide, which indicates that the electrode has high reversibility; as can be seen from FIG. 6, the specific discharge capacity of the PANI @ CN/SnS electrode is maintained to be stable under the current density of 200mA/g, and 760mAh/g can be maintained after 100 cycles.
Example 2
The embodiment provides a PANI @ CN/SnS lithium ion battery cathode material, and the preparation method comprises the following steps:
(1)g-C3N4the preparation of (1): heating melamine to 500 ℃ at the heating rate of 5 ℃/min, carrying out heat preservation and calcination for 4h, and naturally cooling to room temperature to obtain g-C3N4。
(2) Preparation of PANI @ CN/SnS precursor: adding 0.5 mmol-C into 50mL of ethanol3N4Ultrasonic dispersing, then adding 1mmol SnCl2·2H2And performing O ultrasonic treatment for 2 hours, then adding 1.5mmol thioacetamide, and stirring for reaction for 2 hours. And adding 0.75mmol of hydrochloric acid and 0.5mmol of aniline monomer into the original system, slowly adding 1mmol of ammonium persulfate, and carrying out polymerization reaction in an ice bath environment for 10 hours to obtain a PANI @ CN/SnS precursor.
(3) Step (3) of this example is the same as step (3) of example 1.
Through detection, the PANI @ CN/SnS lithium ion battery cathode material prepared by the embodiment has excellent electrochemical performance, the discharge capacity of the PANI @ CN/SnS lithium ion battery cathode material is maintained at 760mAh/g after 100 cycles of circulation at a current density of 200 mA/g.
Example 3
The embodiment provides a PANI @ CN/SnS lithium ion battery cathode material, and the preparation method comprises the following steps:
(1)g-C3N4the preparation of (1): heating thiourea to 600 ℃ at the heating rate of 3 ℃/min, carrying out heat preservation and calcination for 2h, and naturally cooling to room temperature to obtain g-C3N4。
(2) Step (2) of this example is the same as step (2) of example 1;
(3) preparing a PANI @ CN/SnS lithium ion battery anode material: and (3) directly stirring the polymerized system prepared in the step (2) in an oil bath kettle at the temperature of 75 ℃ for reaction for 10 hours. Then placed in a tube furnace at Ar/H2And (3) heating to 800 ℃ at a heating rate of 10 ℃/min in a gas atmosphere, calcining at a constant temperature for 3h, and cooling to obtain the PANI @ CN/SnS lithium ion battery negative electrode material.
Through detection, the PANI @ CN/SnS lithium ion battery cathode material prepared by the embodiment has excellent electrochemical performance, the discharge capacity of the PANI @ CN/SnS lithium ion battery cathode material is maintained at 758mAh/g after 100 cycles of circulation under the current density of 200 mA/g.
Example 4
The embodiment provides a PANI @ CN/SnS lithium ion battery cathode material, and the preparation method comprises the following steps:
(1)g-C3N4the preparation of (1): step (1) of this example is the same as step (1) of example 1.
(2) Preparation of PANI @ CN/SnS precursor: 50mL of ethanol was added with 0.5mmol of C3N4Ultrasonic dispersing, then adding 1mmol SnCl2·2H2And performing O ultrasonic treatment for 1h, then adding 2mmol thioacetamide, and stirring for reaction for 2 h. Adding into the original strain0.1mmol of PVP, 0.5mmol of hydrochloric acid and 0.5mmol of aniline monomer, then slowly adding 1.5mmol of ammonium persulfate, and carrying out polymerization reaction in an ice bath environment for 14 hours to obtain a PANI @ CN/SnS precursor.
(3) Preparing a PANI @ CN/SnS lithium ion battery anode material: and (3) directly stirring the polymerized system prepared in the step (2) in an oil bath kettle at 65 ℃ for reaction for 12 hours. Then placed in a tube furnace at Ar/H2And (3) heating to 700 ℃ at a heating rate of 8 ℃/min in a gas atmosphere, calcining at a constant temperature for 4h, and cooling to obtain the PANI @ CN/SnS lithium ion battery negative electrode material.
Through detection, the PANI @ CN/SnS lithium ion battery cathode material prepared by the embodiment has excellent electrochemical performance, the discharge capacity of the PANI @ CN/SnS lithium ion battery cathode material is maintained at 778mAh/g after 100 cycles of circulation at a current density of 200 mA/g.
The embodiments show that the PANI @ CN/SnS lithium ion battery cathode material prepared by the invention has excellent electrochemical performance, high specific capacity and good cycling stability.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.