CN111200119B - SiO (silicon dioxide)2/CoO/graphene composite negative electrode material and preparation method thereof - Google Patents
SiO (silicon dioxide)2/CoO/graphene composite negative electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a SiO2A cobalt-based material and graphene are sequentially modified on the surface of silicon dioxide particles in a layer-by-layer assembly mode, and the excellent characteristics of the cobalt-based material and the graphene material are utilized to modify SiO2Modifying the particles; in the precursor material obtained by adopting the two-step solvothermal method, the cobalt-based material with the sheet structure is more uniformly distributed and is in contact with SiO2Is more tightly bonded and SiO2In the/CoO-2/GS composite material, graphene forms a three-dimensional porous network structure, SiO2the/CoO-2 particles are uniformly dispersed and mostly coated in the conductive network of the graphene, and the impedance test result shows that SiO is2the/CoO-2/GS composite material has smaller capacitive impedance and ohmic impedance. The material has excellent electrochemical performance due to excellent structural characteristics, when the current density is 200mA/g, the first discharge specific capacity is 1568.5mAh/g, no capacity attenuation is caused after the second circulation, and after 10 times of circulation, the specific capacity is still 801 mAh/g.
Description
Technical Field
The invention relates to the technical field of electrochemical energy materials, in particular to SiO2A/CoO/graphene composite negative electrode material and a preparation method thereof.
Background
The increasing scarcity of fossil energy has caused widespread attention to renewable energy and energy storage technologies. Lithium ion batteries are considered to be one of the most distinctive electrochemical energy storage systems based on their excellent performance in energy storage. Electrode materials are the most critical materials in determining the electrochemical performance of lithium ion batteries. The negative electrode material is one of the determining factors affecting the performance of the lithium ion battery, and currently, the most widely studied and applied negative electrode materials of the lithium ion battery mainly include carbon materials, alloy materials, transition metal oxide materials and the like. The three materials can not meet the requirements of large-scale electronic equipment in the modern society due to the problems of low specific capacity, poor cyclicity, low safety and the like. Therefore, the development of more demanding lithium ion battery negative electrode materials is required.
Compared with other materials, the silicon and the silicon-based material have the advantages of rich raw materials, high theoretical specific capacity and the likeAdvantageously, it is considered to be the most desirable anode material. The theoretical specific capacity of silicon is 4200 mAh/g, which is the highest of all known negative electrode materials, and is more than 10 times of the specific capacity of graphite, and the silicon is defined by the U.S. department of energy as a second generation lithium ion battery negative electrode material capable of replacing graphite. The voltage platform of the silicon-based material is about 0.8V, which is higher than that of graphite, lithium dendrite is not easy to form, and the safety is good. Silicon is rich in content on earth, non-toxic and environment-friendly, so that silicon-based materials arouse extensive research interest of scientific researchers. However, silicon materials also have disadvantages in that silicon deintercalates Li+The process of (2) can generate a volume expansion effect of more than 300%, generate great stress, lead the silicon-based material to be easy to pulverize, and fall off from a current collector to lose electric contact, and lead the electrochemical performance to decline. And with the continuous pulverization of the material, more new silicon surfaces are exposed in the electrolyte to form new SEI films and continuously consume Li+Affecting the cycle performance. In addition, the preparation conditions of the nano-silicon with excellent performance are harsh, so that the cost is high.
Silicon dioxide (SiO)2) The material is a silicon-based material with the most abundant content on the earth, the theoretical specific capacity of the material is 1965 mAh/g, and although the material is not as good as silicon, the material is far higher than other types of negative electrode materials. In addition, SiO2The preparation method is simple, the raw materials are low in cost, and therefore, the lithium-ion battery is considered to be an excellent substitute of Si after being reported to have the electrochemical lithium storage characteristic. Reports show that SiO2Has better cycle performance than the Si negative electrode. However, SiO2Similar to nano silicon, the problems of large volume change, low inherent electronic conductivity and the like exist during electrochemical lithium storage, so that the electrochemical performance is not ideal.
For SiO2The negative electrode has problems of poor volume expansion and conductivity, and the like, and is modified by means of particle nanocrystallization, regulation and control to prepare a porous or hollow structure, compounding with a metal base material, compounding with a carbon material, and the like. Wherein, the nanocrystallization can reduce the volume change to a certain extent and reduce the internal stress of the electrode, but the problem of poor conductivity cannot be solved, and the larger surface of the nano-particles can ensure that the nano-particles can be used in the charging and discharging processAgglomeration occurs, resulting in capacity fade. Although the lithium storage capacity of the material can be obviously improved by regulating and controlling the preparation of the porous or hollow structure, the problems of complicated preparation process, low yield and the like exist.
The carbon negative electrode material sold in the market at present has low theoretical specific capacity (372 mAh/g), low power density and low irreversible capacity for the first time, and the electrochemical performance of the lithium ion battery is severely restricted. Therefore, the development of new lithium ion battery anode materials with higher specific capacity, higher rate capability and higher cycle performance is urgent.
Disclosure of Invention
The invention aims to provide SiO with good electrochemical performance2A/CoO/graphene composite negative electrode material and a preparation method thereof.
In order to achieve the purpose, the invention adopts the technical scheme that2The preparation method of the/CoO/graphene composite negative electrode material comprises the following steps:
(1) under magnetic stirring, 0.5-1.5 g of Co (NO) is added in sequence3)2·6H2O, 2-15 mL of oleic acid and 0.5-1.5 g of SiO2Adding the powder into 10-100 ml of absolute ethyl alcohol, fully dispersing, transferring the mixture into a high-pressure reaction kettle, reacting for 2-14 hours at 100-150 ℃, then reacting for 2-14 hours at 160-180 ℃, washing and drying by the absolute ethyl alcohol after the reaction is finished, and thus obtaining the cobalt-based modified SiO2Is named as SiO2/CoO-2；
(2) Dispersing 15-30 mg of graphene oxide in 10-100 ml of absolute ethyl alcohol, and then adding SiO2/CoO-2，SiO2The mass ratio of the/CoO-2 to the graphene oxide is 1: 2-5: 1, the mixture is transferred into a high-pressure reaction kettle, the reaction is carried out for 2-24 hours at the temperature of 140-180 ℃, and the SiO is obtained after freeze drying treatment2/CoO/graphene composite negative electrode material (marked as SiO)2/CoO-2/GS）。
SiO for use in the present invention2The powder can be prepared by common commercial products or by the existing method in the field; preferably, the nano SiO used2The preparation method of the powder comprises the following steps: measuring 23.5 mlSequentially adding ultrapure water, 63.3 ml of isopropanol and 13 ml of ammonia water (25-28 wt%) into a 250 ml three-neck flask, slowly dripping 0.6 ml of tetraethyl orthosilicate into the three-neck flask at the constant temperature of 35 ℃, reacting for 30 minutes under the condition of vigorous stirring to obtain a silicon ball seed solution, dripping 5ml of tetraethyl orthosilicate, continuously reacting for 2 hours at the temperature of 35 ℃, washing and drying to obtain SiO2And (3) powder.
The graphene oxide used in the invention can be prepared by adopting common commercial products or existing methods in the field; preferably, the preparation method of the graphene oxide used in the step (2) is as follows: 2.5g K2S2O8And 2.5g P2O5Sequentially adding the graphite powder into 50 ml of concentrated sulfuric acid, fully dissolving the graphite powder at the temperature of 80 ℃, adding 5g of graphite, stirring the mixture at constant temperature for 6 hours, and then washing and drying the mixture. Adding the above dried product into 115 ml concentrated sulfuric acid, and adding 15 g KMnO under stirring4After being mixed uniformly, the mixture is heated to 35 ℃, stirred for 3.5 hours at constant temperature, added with 400ml of ultrapure water and then added with 30ml of H2O2And uniformly stirring, centrifugally washing for several times (namely washing by adopting a repeated centrifugal mode), and then dialyzing to obtain the graphene oxide.
SiO prepared by the invention2the/CoO/graphene composite material can be used as a lithium ion battery cathode and pure SiO2Compared with the prior art, the performance is obviously improved.
The invention has the following beneficial effects: according to the invention, the cobalt-based material and the graphene are sequentially modified on the surface of the silicon dioxide particles in a layer-by-layer assembly mode, and the excellent characteristics of the cobalt-based material and the graphene material are utilized to modify SiO2Modifying the particles; in the precursor material obtained by adopting the two-step solvothermal method, the cobalt-based material with the sheet structure is more uniformly distributed and is in contact with SiO2Is more tightly bonded and SiO2In the/CoO-2/GS composite material, graphene forms a three-dimensional porous network structure, SiO2the/CoO-2 particles are uniformly dispersed and mostly coated in the conductive network of the graphene, and the impedance test result shows that SiO is2the/CoO-2/GS composite material has smaller capacitive reactance and ohmImpedance. Meanwhile, the material shows excellent electrochemical performance due to excellent structural characteristics, and when the current density is 200mA/g, the first discharge specific capacity is 1568.5mAh/g, which is much higher than that of SiO2CoO-1/GS and pure SiO2The first discharge capacity (967.8 mAh/g and 735.8 mAh/g) and the first coulombic efficiency are 51 percent and are also higher than SiO2CoO-1/GS and pure SiO2A material. The composite material has no capacity attenuation at the beginning of the second cycle, and the specific capacity is still 801mAh/g after 10 cycles.
Drawings
FIG. 1 is SiO2TEM image of/CoO precursor: (a) one-step solvothermal method precursor SiO2TEM image of/CoO-1, (b) two-step solvothermal precursor SiO2TEM image of/CoO-2;
FIG. 2 is SiO2[ solution ]/CoO-1/GS and SiO2CoO-2/GS composite material and pure SiO2XRD profile of (1);
FIG. 3 is SiO2SEM images of two/CoO/GS composites;
FIG. 4 is pure SiO2The charge-discharge curve charts of 1 st, 2 th and 10 th times when the lithium ion battery negative electrode is used for charge-discharge circulation;
FIG. 5 shows a composite SiO2The 1 st, 2 nd and 10 th charging and discharging graphs of/CoO-1/GS when the current density is cycled at 200 mA/g;
FIG. 6 is SiO2The 1 st, 2 th and 10 th charge-discharge curves of the/CoO-2/GS composite material when the current density is 200mA/g cycle;
FIG. 7 is SiO2/CoO-1/GS，SiO2/CoO-2/GS composite material and pure SiO2Comparing the 10 th cycle charging and discharging curve;
FIG. 8 is SiO2/CoO-1/GS，SiO2/CoO-2/GS composite material and pure SiO2The ac impedance diagram of (1).
Detailed Description
The invention will be further illustrated with reference to specific examples, without however restricting the scope of the invention thereto.
SiO used in the following examples2Preparation of powderThe preparation method comprises the following steps: measuring 23.5 ml of ultrapure water, 63.3 ml of isopropanol and 13 ml of ammonia water (25-28 wt%) and sequentially adding the ultrapure water, the isopropanol and the ammonia water into a 250 ml three-neck flask, slowly dripping 0.6 ml of tetraethyl orthosilicate into a constant-temperature water bath kettle at 35 ℃, reacting for 30 minutes under the condition of violent stirring to obtain a silicon ball seed solution, dripping 5ml of tetraethyl orthosilicate, continuously reacting for 2 hours at 35 ℃, washing and drying to obtain SiO2And (3) powder.
The preparation method of graphene oxide used in the following examples is as follows: 2.5g K2S2O8And 2.5g P2O5Sequentially adding the graphite powder into 50 ml of concentrated sulfuric acid, fully dissolving the graphite powder at the temperature of 80 ℃, adding 5g of graphite, stirring the mixture at constant temperature for 6 hours, and then washing and drying the mixture. Adding the above dried product into 115 ml concentrated sulfuric acid, and adding 15 g KMnO under stirring4After being mixed uniformly, the mixture is heated to 35 ℃, stirred for 3.5 hours at constant temperature, added with 400ml of ultrapure water and then added with 30ml of H2O2And uniformly stirring, centrifugally washing for 5 times, and then performing dialysis treatment to obtain the graphene oxide.
Example 1
SiO (silicon dioxide)2The preparation method of the/CoO/graphene composite negative electrode material comprises the following steps:
(1) under magnetic stirring, 0.8g of Co (NO) was added3)2·6H2O, 8mL oleic acid and 0.8g SiO2Adding the powder into 30ml of absolute ethyl alcohol, fully dispersing, transferring the mixture into a 50 ml high-pressure reaction kettle, reacting for 10 hours at 140 ℃, then reacting for 10 hours at 180 ℃, washing and drying by absolute ethyl alcohol after the reaction is finished, and obtaining the cobalt-based modified SiO2Nanospheres, named SiO2/CoO-2；
(2) Dispersing 18 mg of graphene oxide in 30ml of absolute ethyl alcohol, and then adding SiO2/CoO-2，SiO2The mass ratio of/CoO-2 to graphene oxide is 2: 1, transferring the mixture into a high-pressure reaction kettle, reacting at 180 ℃ for 12 hours, and freeze-drying to obtain SiO2/CoO/graphene composite negative electrode material (marked as SiO)2/CoO-2/GS）。
Comparative example 1
SiO (silicon dioxide)2The preparation method of the/CoO/graphene composite negative electrode material comprises the following steps:
(1) under magnetic stirring, 0.8g of Co (NO) was added3)2·6H2O, 8mL oleic acid and 0.8g SiO2Adding the powder into 30ml of absolute ethyl alcohol, fully dispersing, transferring the mixture into a 50 ml high-pressure reaction kettle, reacting for 20 hours at 180 ℃, washing by absolute ethyl alcohol after the reaction is finished, and drying to obtain the cobalt-based modified SiO2Is named as SiO2/CoO-1；
(2) Dispersing 18 mg of graphene oxide in 30ml of absolute ethyl alcohol, and then adding SiO2/CoO-1，SiO2The mass ratio of/CoO-1 to graphene oxide is 2: 1, transferring the mixture into a high-pressure reaction kettle, reacting at 180 ℃ for 12 hours, and freeze-drying to obtain SiO2/CoO/graphene composite negative electrode material (marked as SiO)2/CoO-1/GS）。
Results and analysis
FIG. 1 is SiO2TEM image of/CoO precursor: (a) one-step solvothermal method precursor SiO2TEM image of/CoO-1; (b) two-step solvothermal precursor SiO2TEM image of/CoO-2. As can be seen from FIGS. 1(a) and (b), SiO2For spherical particles, both methods were successful on SiO2The surface is modified with a cobalt-based material having a lamellar stacking structure. Compared with the one-step solvothermal method, the precursor material obtained by the two-step solvothermal method has the advantage that the cobalt-based material is more uniformly distributed and is more uniform than SiO2The bond is tighter. Since CoO particles generally exhibit electropositivity, SiO, which is originally electronegative, can be modified uniformly by CoO particles2The surface modification is electropositive, which is more beneficial to the reaction of the surface modification and the graphene oxide showing electronegativity, and further establishes closer relation with the graphene.
In addition, it is noted that SiO2The particle size of/CoO-2 is smaller than SiO2[ CoO-1 ], which describes SiO in a two-stage solvothermal process2Possibly reacting with oleic acid at a lower temperature to dissolve itThen the solid particles are formed again at higher temperature, and the process is more favorable for SiO2And the equilibrium reaction between the metal raw material occurs, so the product is more uniform.
FIG. 2 is SiO2[ solution ]/CoO-1/GS and SiO2CoO-2/GS composite material and pure SiO2XRD profile of (a). As can be seen from FIG. 2, the two composites exhibited a main peak at 21.6 ° 2 θ with standard SiO2The characteristic peaks are quite consistent, so that amorphous SiO exists in the composite material2. The characteristic peak of about 34.0 degrees 2 theta is well matched with the standard characteristic peak of CoO, which indicates that the main component of the cobalt-based material in the composite is CoO. XRD results show that the invention successfully obtains SiO2And CoO. In addition, no characteristic peak formed by graphene stacking was found in the range of about 25 °, which is due to SiO2the/CoO particles are uniformly dispersed in the graphene, and the stacking phenomenon of the/CoO particles is greatly inhibited.
SiO by using field emission scanning electron microscope2The microstructure of the/CoO/GS composite material is characterized, an SEM image is shown in figure 3, and in the two materials, graphene forms a three-dimensional porous network structure. FIGS. a and b are SiO2SEM image of/CoO-1/GS composite material, it can be seen that SiO2the/CoO-1 particles are dispersed on the surface of the graphene, and a more serious agglomeration phenomenon exists. SiO 22In SEM images (FIGS. c and d) of the/CoO-2/GS composite, SiO having a smaller average particle size2the/CoO-2 particles are uniformly dispersed in the graphene and are mostly coated with the graphene. This fully illustrates the two-step solvothermal preparation of the precursor SiO2The surface of the/CoO-2 is more uniformly positively-charged modified, so that the agglomeration phenomenon can be effectively inhibited, and the particles can be uniformly dispersed and coated in a conductive network of graphene through electrostatic action.
FIG. 4 is pure SiO2The charge-discharge curves of the 1 st, 2 nd and 10 th times when the lithium ion battery negative electrode is subjected to charge-discharge cycles. As shown in FIG. 4, in the first discharge curve, there is a smooth discharge plateau at 0.8V due to SiO2A reaction of being reduced to Si during lithium intercalation. Pure SiO2The first discharge specific capacity of the material is 735.8 mAh/g, the first coulombic efficiency is 33.74%, and after 10 cycles, the reversible capacity is attenuated to 169.2 mAh/g, which shows that pure SiO2Has certain lithium storage activity, but the capacity of the material is greatly attenuated due to poor conductivity and serious volume effect.
FIG. 5 shows a composite SiO2In the first discharge curve, the voltage plateau appearing around 1.4V is attributed to the reduction of CoO in the cobalt-based material to Co, and the voltage plateau appearing at 0.8V is SiO when the/CoO-1/GS is cycled at the current density of 200mA/g according to the 1 st, 2 nd and 10 th charge-discharge graphs2The conversion process is reduced to Si, and the smooth voltage platform at 0.4V is the graphene lithium intercalation process. SiO 22The first discharge specific capacity of the/CoO-1/GS composite material is up to 967.8 mAh/g, which is higher than that of pure SiO2The first discharge capacity is 735.8 mAh/g, the first coulombic efficiency is 48%, after 2 times of circulation, the coulombic efficiency is increased to about 97%, the capacity is attenuated to 465.6 mAh/g, and in the next 10 times of circulation, the specific capacity can be stabilized at 465.6 mAh/g, which shows that the material has better circulation performance.
FIG. 6 is SiO2The graphs of the charge and discharge times 1, 2 and 10 of the/CoO-2/GS composite material at the current density of 200mA/g cycle. In the first discharge curve, a voltage plateau appearing at about 1.4V is a process of reducing CoO in the cobalt-based material into Co, and a voltage plateau appearing at about 0.8V is SiO2The process of being reduced to Si, while the smooth voltage plateau around 0.4V is due to the graphene lithium intercalation process, consistent with fig. 1-5. SiO 22The first discharge specific capacity of the/CoO-2/GS composite material is up to 1568.5mAh/g, which is much higher than that of SiO2967.8 mAh/g of/CoO-1/GS and pure SiO2The first discharge capacity of 735.8 mAh/g is 51 percent of the first coulombic efficiency, and is also higher than SiO2CoO-1/GS and pure SiO2. The composite material has no capacity attenuation at the beginning of the second cycle, and after 10 cycles, the specific capacity is still 801mAh/g, and the excellent cycle performance is shown.
In order to compare the reversible lithium storage performance of several materials more intuitively, the three materials are cycled for the 10 th timeThe charge and discharge curves of (a) were compared. FIG. 7 is SiO2/CoO-1/GS，SiO2/CoO-2/GS composite material and pure SiO2Comparing the 10 th cycle charging and discharging curve, it can be seen from FIG. 7 that the reversible capacity of both composites is higher than that of pure SiO2The double modification of the metal-based material and the graphene can effectively improve SiO2Poor conductivity, serious volume effect and the like, so that the electrochemical performance of the material is greatly improved. In two composite materials, with SiO2SiO in comparison with CoO-1/GS2the/CoO-2/GS has higher first coulombic efficiency and higher specific capacity, because the precursor SiO prepared by the two-step solvothermal method2the/CoO-2 is dispersed in the graphene more uniformly, and forms a better graphene coating structure, so that more excellent electrochemical performance can be obtained.
To further illustrate the difference in electrochemical performance between the two composites and pure silica. The ac impedance of several materials before cycling at 25 c was tested and compared. FIG. 8 is SiO2/CoO-1/GS，SiO2/CoO-2/GS composite material and pure SiO2As can be seen from fig. 8, the ac impedance profile of the sample is composed of two parts: the semi-circular arcs of the high and medium frequency regions are associated with the electrode interface, and the slashes of the low frequency regions represent the Warburg impedance. The semicircle of the high-frequency region is the electrochemical reaction process of the battery, namely the reaction of the cathode material and the electrolyte, the semicircle diameter of the high-frequency region represents the resistance of the sample, mainly consists of the contact resistance between particles and the migration resistance of the particle surface, and reflects the impedance caused by the diffusion of ions in the electrode body phase. The semi-circle of the two composite materials is smaller than that of a pure silicon dioxide battery, which shows that the electronic conductivity of the materials is effectively improved by introducing effective high-conductivity and flexible graphene. And SiO2The semi-circle part in the impedance curve of the/CoO-2/GS composite material is smaller than SiO2[ solution of/[ CoO-1/GS ] for SiO2the/CoO-2/GS composite material has smaller capacitive impedance and ohmic impedance, which are attributed to SiO2The uniform dispersion of particles in/CoO-2/GS and the coating structure of graphene.
Claims (4)
1. SiO (silicon dioxide)2The preparation method of the/CoO/graphene composite negative electrode material is characterized by comprising the following steps of:
(1) under the stirring condition, 0.5-1.5 g of Co (NO) is added in sequence3)2·6H2O, 2-15 mL of oleic acid and 0.5-1.5 g of SiO2Adding the powder into 10-100 ml of absolute ethyl alcohol, fully dispersing, transferring the mixture into a high-pressure reaction kettle, reacting for 2-14 hours at 100-150 ℃, then reacting for 2-14 hours at 160-180 ℃, washing and drying by the absolute ethyl alcohol after the reaction is finished, and thus obtaining the cobalt-based modified SiO2Is named as SiO2/CoO-2；
(2) Dispersing 15-30 mg of graphene oxide in 10-100 ml of absolute ethyl alcohol, and then adding SiO2/CoO-2，SiO2The mass ratio of the/CoO-2 to the graphene oxide is 1: 2-5: 1, the mixture is transferred into a high-pressure reaction kettle, the reaction is carried out for 2-24 hours at the temperature of 140-180 ℃, and the SiO is obtained after freeze drying treatment2the/CoO/graphene composite negative electrode material.
2. SiO as claimed in claim 12The preparation method of the/CoO/graphene composite negative electrode material is characterized in that the SiO is2The preparation method of the powder comprises the following steps: measuring 23.5 ml of ultrapure water, 63.3 ml of isopropanol and 13 ml of ammonia water with the mass fraction of 25-28%, sequentially adding the ultrapure water, the isopropanol and the ammonia water into a 250 ml three-neck flask, slowly dripping 0.6 ml of tetraethyl orthosilicate into the three-neck flask at the constant temperature of 35 ℃, reacting for 30 minutes under the condition of vigorous stirring to obtain a silicon sphere seed solution, dripping 5ml of tetraethyl orthosilicate, continuously reacting for 2 hours at the temperature of 35 ℃, washing and drying to obtain SiO2And (3) powder.
3. SiO as claimed in claim 12The preparation method of the/CoO/graphene composite negative electrode material is characterized in that the preparation method of the graphene oxide in the step (2) is as follows: 2.5g K2S2O8And 2.5g P2O5Sequentially adding into 50 ml of concentrated sulfuric acid, fully dissolving at 80 ℃, adding 5g of graphite, stirring at constant temperature for 6 h,then washing and drying, adding the dried product into 115 ml of concentrated sulfuric acid, and adding 15 g of KMnO under stirring4After being mixed uniformly, the mixture is heated to 35 ℃, stirred for 3.5 hours at constant temperature, added with 400ml of ultrapure water and then added with 30ml of H2O2And uniformly stirring, centrifugally washing, and performing dialysis treatment to obtain the graphene oxide.
4. SiO obtainable by a process according to any one of claims 1 to 32the/CoO/graphene negative electrode material.
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