In-situ synthesis method of transition metal oxide/graphene composite material
Technical Field
The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to an in-situ synthesis method of a transition metal oxide/graphene composite material.
Background
Compared with the traditional secondary battery, the lithium ion battery has the advantages of high energy density, safety, no pollution, small self-discharge, wide working temperature, long cycle life, no memory effect and the like, and therefore has attracted extensive attention. Lithium ion batteries are widely used in the fields of portable electronic devices (such as mobile phones, digital cameras, video cameras, notebook computers, and the like) and electric tools, and are gradually expanding to the fields of electric bicycles, electric vehicles, new energy storage, and the like.
At present, graphite is the most commonly used material for the negative electrode of the lithium ion battery, and although the graphite has the advantages of high electronic conductivity, long cycle life, low cost, good safety performance and the like, the theoretical specific capacity of the graphite is only 372mAh/g, and the requirements of the lithium ion battery with high performance and high capacity are difficult to meet. The energy density and specific capacity of the transition metal oxide negative electrode material are higher than those of graphite, the transition metal oxide negative electrode material is wide in source, low in price and simple to prepare, and has excellent electrochemical performance, however, the transition metal oxide negative electrode material has a serious volume expansion effect in the charging and discharging processes, the electrode material is pulverized, active species fall off, the capacity of an electrode is greatly attenuated, and the stability performance is difficult to guarantee. A large number of researches show that if a proper conductive carbon material can be selected to modify the metal oxide, the structure and the morphology are reasonably designed, the conductivity of the electrode material can be effectively enhanced, and the volume expansion effect of the electrode material is relieved. Graphene is a two-dimensional lattice structure consisting of a single layer of carbon atoms, and is sp2The honeycomb network structure formed by arranging high-density atomic layers formed by hybridized carbon atoms has excellent electric conductivity and higher specific surface area (2600 m)2/g), excellent thermal and mechanical properties, and is widely used in the fields of nano-electronics, hydrogen storage, supercapacitors and sensors.
The existing preparation method of the graphene composite material comprises the steps of placing a metal simple substance in a graphene oxide aqueous solution, and freeze-drying a black solid product generated after placing to obtain a metal oxide/graphene composite, but the method generally has the problem of volume expansion when being used for a lithium ion battery cathode.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide an in-situ synthesis method of a transition metal oxide/graphene composite material, and the transition metal oxide/graphene composite material with high capacity and high performance is prepared by the in-situ synthesis method and utilizing the excellent conductivity of graphene to further relieve the volume expansion effect of the metal oxide when the metal oxide is used for a lithium ion battery cathode.
In order to achieve the purpose, the invention adopts the following technical scheme:
an in-situ synthesis method of a transition metal oxide/graphene composite material comprises the following steps:
(1) dissolving soluble ferric salt, soluble transition metal salt and soluble cerium salt according to a molar ratio of 1: (0.01-0.5): (0.01-0.1), respectively dissolving in deionized water, and uniformly mixing to form a uniform solution;
(2) dropwise adding a precipitator into the uniform solution, continuously stirring in the dropwise adding process until the pH value of the solution reaches more than 10, stopping dropwise adding, continuously stirring for 1-3h, standing at room temperature, aging for 4h, carrying out hydrothermal reaction, filtering and washing to neutrality, and drying to obtain a transition metal hydroxide compound precipitate, wherein: the hydrothermal reaction temperature is 120-180 ℃, and the time is 3-10 h;
(3) weighing graphite and potassium permanganate according to the mass ratio of 1 (3-4), uniformly mixing, adding the mixture into a three-neck flask filled with mixed acid liquid of concentrated sulfuric acid and phosphoric acid, continuously stirring and reacting for 12 hours to obtain a gray green solution, adding hydroxide for precipitation after an ice water bath is carried out for 1-5 hours, and then slowly adding H with the volume of 1/20-1/5 in the gray green solution2O2And continuously stirring for 30-40min, and then performing ultrasonic dispersion for 1-2h to obtain a suspension of the transition metal hydroxide/graphene oxide which is coated and grown mutually.
(4) Washing and centrifuging the suspension of the transition metal hydroxide/graphene oxide, and drying and roasting to obtain the transition metal composite oxide/graphene, wherein the roasting atmosphere is an oxygen-free atmosphere, the roasting temperature is 500 ℃ below zero, and the roasting time is 3-6 h.
In the step (1), the soluble ferric salt is one of ferric nitrate, ferric sulfate or ferric chloride, and the soluble ferric salt is used as a matrix.
In the step (1), the soluble transition metal salt is one of soluble nitrate, sulfate or chloride of metal cobalt, metal zinc, metal manganese or metal titanium, and one or more of the soluble transition metal salt is added.
In the step (1), the soluble cerium salt is one of cerium nitrate or cerium chloride.
In the step (1), the mass ratio of the deionized water to the soluble ferric salt is (10-25): 1.
in the step (2), the precipitator is one of sodium hydroxide, ammonia water or urea, and the dropping rate is 1-500 drops/min.
In the step (2), the hydrothermal reaction is carried out in a hydrothermal reaction kettle.
In the step (3), the concentration of the concentrated sulfuric acid is 98%, and the ratio of the concentrated sulfuric acid to the phosphoric acid is 1: 1.
In the step (3), the mass percentage of the graphite and the hydroxide precipitate is (0.01-20): 100.
in the step (3), H is added2O2After that, the solution quickly changed from grayish green to bright yellow.
In the step (3), hydroxide precipitation is added in the process of preparing the graphene oxide by adopting an improved Hummers method, so as to obtain a suspension of the transition metal hydroxide/graphene oxide.
In the step (4), the roasting atmosphere is a nitrogen atmosphere or an inert gas atmosphere.
In the step (4), the drying operation is carried out in a vacuum drying oven, and the drying temperature is 60 ℃.
In the step (4), the prepared transition metal composite oxide/graphene composite material is used as a lithium ion battery cathode, the current density is 100mA/g through detection, the specific capacity reaches 1210-1260mAh/g after 100 cycles, and the coulombic efficiency reaches more than 99.5%.
The invention has the beneficial effects that:
(1) in the method, the compound of the transition metal hydroxide is directly added in the process of synthesizing the graphene oxide by adopting an in-situ synthesis method, so that the process is simple and easy to operate, and the production cost is low;
(2) the transition metal oxide/graphene composite material prepared by the method has a porous structure, and the specific surface area reaches 100-200m2/g,CeO2Beneficial to nano-rodAnd the generated graphene is uniformly dispersed among gaps of product particles, and the structure can buffer the volume expansion effect of the metal oxide in the charge-discharge cycle process and improve the electrode reaction dynamic performance.
Description of the figures
Fig. 1 is an XRD pattern of the transition metal oxide/graphene composite material prepared in example 1 of the present invention;
fig. 2 is an SEM image of the transition metal oxide/graphene composite material prepared in example 1 of the present invention;
fig. 3 is a cycle curve diagram of the transition metal oxide/graphene composite material prepared in example 1 of the present invention used as a negative electrode of a lithium ion battery;
fig. 4 is an SEM image of the transition metal oxide/graphene composite material prepared in example 4 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples.
Example 1
(1) Respectively mixing iron nitrate, cobalt nitrate and cerium nitrate in a molar ratio of 1: 0.1: 0.02 is dissolved in deionized water, and a uniform solution is obtained after uniform mixing and stirring; (2) adding ammonia water into the solution at a rate of 100 drops/min until the pH value reaches 10, continuously stirring for 2 hours to completely precipitate, standing and aging at room temperature for 4 hours, placing the solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction at 160 ℃ for 6 hours, filtering and washing the solution to be neutral, and drying the solution to obtain Fe2O3-Co2O3-CeO2Precipitating the composite hydroxide; (3) graphene oxide was prepared using a modified Hummers method: weighing a certain amount of graphite and potassium permanganate, uniformly mixing, adding the graphite and potassium permanganate into a three-neck flask filled with 98% mixed acid solution of concentrated sulfuric acid and phosphoric acid, continuously stirring for reaction for 12 hours to obtain a gray green solution, carrying out ice-water bath for 2 hours, adding hydroxide precipitate (the mass percent of the graphite is 10%), and slowly adding 10mL of H2O2At the moment, the solution is rapidly changed from grey green to bright yellow, and ultrasonic dispersion is carried out for 1h after the solution is continuously stirred for 30min, so that a suspension of transition metal hydroxide/graphene oxide which is mutually coated and grows is obtained; (4) transition metal hydrogenWashing and centrifuging the oxide/graphene oxide suspension, putting the filter cake into a vacuum drying oven at 60 ℃ for fully drying, and roasting at 400 ℃ for 4 hours under the atmosphere of nitrogen to obtain Fe2O3-Co2O3-CeO2Graphene negative electrode material with specific surface area up to 200m2The XRD pattern is shown in figure 1, and the phase is mainly Fe2O3And as shown in an SEM picture of fig. 2, a cycle curve chart of the negative electrode material used as a negative electrode of the lithium ion battery is shown in fig. 3, and after 100 cycles at a current density of 100mA/g, the specific capacity is stabilized at 1254mAh/g, and the coulombic efficiency is 99.57%.
Example 2
(1) Mixing ferric chloride, manganese sulfate and cerium chloride in a molar ratio of 1: 0.5: 0.06 is dissolved in deionized water, and a uniform solution is obtained after uniform mixing and stirring; (2) adding ammonia water into the solution at 300 drops/min until the pH value reaches 10, continuously stirring for 2 hours to completely precipitate, standing and aging at room temperature for 4 hours, placing the solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction at 180 ℃ for 4 hours, filtering, washing with water to be neutral, and drying to obtain Fe2O3-MnO2-CeO2Precipitating the composite hydroxide; (3) graphite oxide was prepared using a modified Hummers method: weighing a certain amount of graphite and potassium permanganate, uniformly mixing, adding the graphite and potassium permanganate into a three-neck flask filled with 98% mixed acid solution of concentrated sulfuric acid and phosphoric acid, continuously stirring for reaction for 12 hours to obtain a gray green solution, carrying out ice-water bath for 2 hours, adding hydroxide precipitate (the mass percent of the graphite is 5%), and slowly adding 10mL of H2O2At the moment, the solution is rapidly changed from grey green to bright yellow, and ultrasonic dispersion is carried out for 1h after the solution is continuously stirred for 30min, so that a suspension of transition metal hydroxide/graphene oxide which is mutually coated and grows is obtained; (4) washing and centrifuging the suspension of the transition metal hydroxide/graphene oxide, putting the filter cake into a vacuum drying oven at 60 ℃ for fully drying, and roasting at 400 ℃ for 5 hours in a nitrogen atmosphere to obtain Fe2O3-MnO2-CeO2Graphene negative electrode material with specific surface area up to 150m2The specific capacity is stabilized at 1219mAh/g after 100 cycles under the current density of 100mA/g, and the coulombic efficiency is 99.53 percent.
Example 3
(1) Respectively mixing ferric sulfate, titanium sulfate and cerium chloride in a molar ratio of 1: 0.3: 0.03 is dissolved in deionized water, and a uniform solution is obtained after uniform mixing and stirring; (2) adding ammonia water into the solution at a rate of 400 drops/min until the pH value reaches 10, continuously stirring for 2 hours to completely precipitate, standing and aging at room temperature for 4 hours, placing the solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction at 140 ℃ for 5 hours, filtering, washing with water to neutrality, and drying to obtain Fe2O3-TiO2-CeO2Precipitating the composite hydroxide; (3) graphite oxide was prepared using a modified Hummers method: weighing a certain amount of graphite and potassium permanganate, uniformly mixing, adding the graphite and potassium permanganate into a three-neck flask filled with 98% mixed acid solution of concentrated sulfuric acid and phosphoric acid, continuously stirring for reaction for 12 hours to obtain a gray green solution, carrying out ice-water bath for 2 hours, adding hydroxide precipitate (the mass percent of the graphite is 20%), and slowly adding 10mL of H2O2At the moment, the solution is rapidly changed from grey green to bright yellow, and ultrasonic dispersion is carried out for 1h after the solution is continuously stirred for 30min, so that a suspension of transition metal hydroxide/graphene oxide which is mutually coated and grows is obtained; (4) washing and centrifuging a suspension product of the transition metal hydroxide/graphene oxide, putting a filter cake into a vacuum drying oven at 60 ℃ for fully drying, and roasting at 500 ℃ for 6 hours in a nitrogen atmosphere to obtain Fe2O3-TiO2-CeO2Graphene negative electrode material with specific surface area of 160m2The specific capacity is stabilized at 1232mAh/g after 100 cycles under the current density of 100mA/g, and the coulombic efficiency is 99.55%.
Example 4
(1) Respectively mixing ferric sulfate, zinc chloride and cerium nitrate in a molar ratio of 1: 0.5: 0.1 is dissolved in deionized water, and a uniform solution is obtained after uniform mixing and stirring; (2) adding ammonia water into the solution at a rate of 500 drops/min until the pH value reaches 10, continuously stirring for 2 hours to completely precipitate, standing and aging at room temperature for 4 hours, placing the solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction at 120 ℃ for 6 hours, filtering, washing with water to neutrality, and drying to obtain Fe2O3-ZnO2-CeO2Precipitating the composite hydroxide; (3) preparation of oxygenates using a modified Hummers processGraphite: weighing a certain amount of graphite and potassium permanganate, uniformly mixing, adding the graphite and potassium permanganate into a three-neck flask filled with 98% mixed acid solution of concentrated sulfuric acid and phosphoric acid, continuously stirring for reaction for 12 hours to obtain a gray green solution, carrying out ice-water bath for 2 hours, adding hydroxide precipitate (the mass percent of the graphite is 15%), and slowly adding 10mL of H2O2At the moment, the solution is rapidly changed from grey green to bright yellow, and ultrasonic dispersion is carried out for 1h after the solution is continuously stirred for 30min, so that a suspension of transition metal hydroxide/graphene oxide which is mutually coated and grows is obtained; (4) washing and centrifuging a suspension product of the transition metal hydroxide/graphene oxide, putting a filter cake into a vacuum drying oven at 60 ℃ for fully drying, and roasting at 400 ℃ for 3 hours in a nitrogen atmosphere to obtain Fe2O3-ZnO2-CeO2The SEM image of the graphene negative electrode material is shown in figure 4, and the specific surface area reaches 180m2The specific capacity is stabilized at 1247mAh/g after 100 cycles under the current density of 100mA/g, and the coulombic efficiency is 99.54 percent.