JP2016119459A - Composite of metal oxide nanoparticle and carbon, method for producing the same, electrode using composite, and electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode having improved output characteristics and electric conductivity, and to provide an electrochemical element using the electrode.SOLUTION: Composite powder in which a precursor of metal oxide nanoparticles is supported on carbon in a highly dispersed manner is subjected to rapid heating treatment in a nitrogen atmosphere, thereby advancing crystallization of metal oxide and allowing the metal oxide nanoparticles to be supported on the carbon in a highly dispersed manner. The precursor of the metal oxide nanoparticles and the carbon nanoparticles, which support the precursor, are prepared by mechanochemical reaction for applying shear stress and centrifugal force to a reactant in a whirling reactor. Preferably, the rapid heating treatment in the nitrogen atmosphere is performed at 400 to 1,000°C. The heated composite is then crushed to eliminate aggregation of the heated composite, thereby homogenizing dispersion degree of the metal oxide nanoparticles. Manganese oxide, lithium iron phosphate, lithium titanate or the like may be used as the metal oxide. A carbon nanofiber or Ketjen black may be used as the carbon.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a composite of metal oxide nanoparticles and carbon, a production method thereof, an electrode using the composite, and an electrochemical device.

  At present, carbon materials that store and release lithium are used as electrodes of lithium batteries, but there is a risk of decomposition of the electrolyte because the negative potential is smaller than the reductive decomposition potential of hydrogen. Thus, as described in Patent Document 1 and Patent Document 2, the use of lithium titanate having a negative potential larger than the reductive decomposition potential of hydrogen has been studied. However, lithium titanate has a problem that output characteristics are low. . Therefore, there is an attempt to improve output characteristics with an electrode in which lithium titanate is made into nanoparticles and supported on carbon.

JP 2007-160151 A JP 2008-270795 A

  The inventions described in these patent documents are dispersed and supported on carbon by a method (generally called mechanochemical reaction) that promotes a chemical reaction by applying shear stress and centrifugal force to a reactant in a rotating reactor. Lithium titanate is obtained. In this case, for example, titanium alkoxide and lithium acetate which are starting materials of lithium titanate, carbon such as carbon nanotube and ketjen black, acetic acid, and the like are used as the reactant.

  Electrodes using carbon carrying lithium titanate nanoparticles described in these patent documents exhibit excellent output characteristics, but recently, in this type of electrode, the output characteristics have been further improved and the electric conductivity has been improved. There is a demand to improve.

  Moreover, not only lithium titanate nanoparticles but also other metal oxide nanoparticles are produced by producing composites in which these are supported on carbon, thereby obtaining electrodes and electrochemical elements having better output characteristics. There are also requests to do so. In particular, it is desired to use a metal oxide that is cheaper than lithium such as manganese oxide.

  The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and the object thereof is to obtain an electrode or an electrochemical element capable of improving output characteristics and electrical conductivity. An object of the present invention is to provide a composite of metal oxide nanoparticles and carbon that can be produced, and a method for producing the same. Another object of the present invention is to provide an electrode and an electrochemical device using the composite.

  In order to achieve the above-mentioned object, the method for producing a composite of metal oxide nanoparticles and carbon according to the present invention comprises a composite powder in which a precursor of metal oxide nanoparticles is supported in a highly dispersed state in a nitrogen atmosphere. In this case, the metal oxide nanoparticles are crystallized and rapidly dispersed on the carbon by rapid heat treatment in the process. In this case, the rapid heating treatment is to heat the composite to 400 to 1000 ° C. in a nitrogen atmosphere, and the metal oxide nanoparticles have a thickness of 1 nm or less at a 2 to 5 atomic layer level. And it is also one aspect | mode of this invention that it is a crystal structure (ultra thin film structure) on a flat plate with a diameter of 5-100 nm. Furthermore, the composite manufactured by the method as described above, and an electrode and an electrochemical device using the composite are also included in the present invention.

  According to the present invention, in the baking process of carbon carrying a precursor of metal oxide nanoparticles, good crystallization of the metal oxide nanoparticles can be progressed by rapid heating treatment. A crystal structure on a flat plate having a thickness of 1 nm or less at the atomic layer level and a diameter of 5 to 100 nm is formed.

FIG. 3 is a drawing-substituting photograph showing an XRD analysis result and a TEM image of the composite of Example 1. FIG. 3 is a drawing-substituting photograph showing an enlarged TEM image of another part of the composite of Example 1. FIG. 3 is a drawing-substituting photograph showing an enlarged TEM image of another part of the composite of Example 1. FIG. The drawing substitute photograph which shows the XRD analysis result and TEM image of the composite_body | complex of Example 2-1. The drawing substitute photograph which shows the TEM image of the other part of the composite_body | complex of Example 2-1. The drawing substitute photograph which shows the expansion TEM image of the other part of the composite_body | complex of Example 2-1. The drawing substitute photograph which shows the high-resolution TEM image of Example 2-1. The graph which shows the charging / discharging characteristic of the electrochemical element which uses the composite_body | complex of Example 2-1. The graph which compared the charging / discharging characteristic of the electrochemical element which uses the composite_body | complex of Example 2-1, and the conventional electrochemical element. The graph which shows the output characteristic of the electrochemical element using the composite_body | complex of Example 2-1. The graph which shows the cycling characteristics of the electrochemical element using the composite_body | complex of Example 2-1. The drawing substitute photograph which shows the high-resolution TEM image of the composite_body | complex of Example 2-2. The drawing substitute photograph which shows the high-resolution TEM image of the composite_body | complex of Example 2-3. The drawing substitute photograph which shows the high-resolution TEM image of the composite_body | complex of Example 2-5. The drawing substitute photograph which shows the TEM image of the composite of the lithium titanate nanoparticle and carbon of Example 3. The drawing substitute photograph which shows the expanded TEM image of the composite of the lithium titanate nanoparticle and carbon of Example 3. The graph which shows the discharge behavior characteristic of the composite_body | complex of lithium titanate nanoparticle of Example 3, and carbon. The graph which shows the output characteristic of the composite_body | complex of lithium titanate nanoparticle of Example 3 and carbon. The graph which shows the characteristic of the high output energy storage device of Example 4. The perspective view which shows an example of the reactor used for the manufacturing method of this invention. The drawing substitute photograph and graph which show the pore distribution of the composite of the lithium iron phosphate nanoparticle and carbon of Example 2-1. 6 is a graph showing charge / discharge characteristics of Example 5. The graph which shows the result of having performed the XRD analysis of Example 5. FIG. The enlarged photograph of Example 2-1, and its schematic diagram. The high resolution TEM image of the composite powder of Example 2-3, and its schematic diagram.

  Hereinafter, modes for carrying out the present invention will be described.

(Mechanochemical reaction)
The reaction method used in the present invention is a mechanochemical reaction similar to the method shown in Patent Document 1 and Patent Document 2 previously filed by the present applicant and the like, and in a reactor that rotates in the course of the chemical reaction. In this method, shear reaction and centrifugal force are applied to the reactant to promote chemical reaction.

  This reaction method can be performed using, for example, a reactor as shown in FIG. As shown in FIG. 20, the reactor includes an outer cylinder 1 having a cough plate 1-2 at an opening, and an inner cylinder 2 having a through hole 2-1 and swirling. By putting the reactant into the inner cylinder of the reactor and turning the inner cylinder, the reactant inside the inner cylinder moves to the inner wall 1-3 of the outer cylinder through the through hole of the inner cylinder by the centrifugal force. . At this time, the reaction product collides with the inner wall of the outer cylinder by the centrifugal force of the inner cylinder, and forms a thin film and slides up to the upper part of the inner wall. In this state, both the shear stress between the inner wall and the centrifugal force from the inner cylinder are simultaneously applied to the reactant, and a large mechanical energy is applied to the thin-film reactant. This mechanical energy seems to be converted into chemical energy required for the reaction, so-called activation energy, but the reaction proceeds in a short time.

  In this reaction, since the mechanical energy applied to the reaction product is large when it is in the form of a thin film, the thickness of the thin film is 5 mm or less, preferably 2.5 mm or less, more preferably 1.0 mm or less. The thickness of the thin film can be set according to the width of the dam plate and the amount of the reaction solution.

This reaction method is considered to be realized by the mechanical energy of the shear stress and the centrifugal force applied to the reactant, and the shear stress and the centrifugal force are generated by the centrifugal force applied to the reactant in the inner cylinder. Thus, the centrifugal force applied to the reactants in the inner cylinder necessary for the present invention is 1500 N (kgms ^-2) or more, preferably 60000N (kgms ^-2) or more, more preferably 270000N (kgms ^-2) or more.

  In this reaction method, mechanical energy of both shear stress and centrifugal force is applied to the reactant at the same time, which seems to be due to the conversion of this energy into chemical energy. Can be promoted.

(Metal oxide)
The metal oxides to produce metal oxide nanoparticles according to the present invention, for example, manganese oxide MnO, lithium iron phosphate LiFePO _4, lithium Li ₄ Ti ₅ O ₁₂ is titanate can be used. As other oxides, metal oxides represented by MxOz, AxMyOz, Mx (DO4) y, AxMy (DO4) z (M: metal element A: alkali metal or lanthanoid element) can also be used. is there.

  In the case of manganese oxide MnO, for example, a manganese source such as sodium permanganate, manganese acetate, manganese nitrate, manganese sulfate and the like as a starting material, and a precursor of manganese oxide nanoparticles are dispersed by the mechanochemical reaction. A supported carbon composite is formed. By rapidly heating this composite in a nitrogen atmosphere, a composite of manganese oxide and carbon, which is the metal oxide of the present invention, is generated.

In the case of lithium iron phosphate LiFePO ₄ , for example, a manganese source such as sodium permanganate, manganese acetate, manganese nitrate, manganese sulfate and the like as a starting material and a precursor of lithium iron phosphate nanoparticles by the mechanochemical reaction. And a carbon composite in which this is dispersed and supported. By rapidly heating the composite in a nitrogen atmosphere, a composite of lithium iron phosphate, which is the metal oxide of the present invention, and carbon is produced.

In the case of lithium titanate Li ₄ Ti ₅ O ₁₂ , for example, a titanium source such as titanium alkoxide, a lithium source such as lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide is used as a starting material, and the mechanochemical reaction is performed. To produce a precursor of lithium titanate nanoparticles. By heating the precursor of the lithium titanate nanoparticles in a nitrogen atmosphere, the lithium titanate nanoparticles of the present invention in which nitrogen is doped at sites of oxygen defects are generated.

(carbon)
By adding a predetermined carbon during the reaction process, carbon in which 5 to 100 nm of lithium titanate is highly dispersed and supported can be obtained. That is, a metal salt, a predetermined reaction inhibitor, and carbon are put into the inner cylinder of the reactor, and the inner cylinder is rotated to mix and disperse the metal salt, reaction inhibitor, and carbon. Further, while turning the inner cylinder, a catalyst such as sodium hydroxide is added to cause hydrolysis and condensation reaction to proceed to produce a metal oxide, and the metal oxide and carbon are mixed in a dispersed state. By rapidly heating this after completion of the reaction, it is possible to form carbon on which metal oxide nanoparticles are supported in a highly dispersed manner.

  Examples of carbon used here include carbon black such as ketjen black and acetylene black, carbon nanotube, carbon nanohorn, amorphous carbon, carbon fiber, natural graphite, artificial graphite, activated carbon, mesoporous carbon, vapor phase carbon fiber, etc. These composite materials can also be used.

(solvent)
As the solvent, alcohols, water, or a mixed solvent thereof can be used. For example, a mixed solvent in which acetic acid and lithium acetate are dissolved in a mixture of isopropanol and water can be used.

(Reaction inhibitor)
When a metal alkoxide is used as a starting material, as described in Patent Document 2, a predetermined compound that forms a complex with the metal alkoxide as a reaction inhibitor is added to the predetermined metal alkoxide to which the mechanochemical reaction is applied. Can be added. Thereby, it can suppress that a chemical reaction accelerates | stimulates too much.

  That is, the reaction can be suppressed and controlled by adding 1 to 3 mol of a predetermined compound such as acetic acid that forms a complex with metal alkoxide to 1 mol of the metal alkoxide to form a complex. I understood that I could do it. It is to be noted that a metal-oxide composite nanoparticle, for example, a lithium-titanium oxide composite nanoparticle, which is a precursor of lithium titanate, is produced by this reaction, and is fired. Thus, a crystal of lithium titanate is obtained.

  Thus, by adding a predetermined compound such as acetic acid as a reaction inhibitor, it is possible to suppress the chemical reaction from being promoted too much because the predetermined compound such as acetic acid can form a stable complex with the metal alkoxide. It is thought that it is for forming.

  Substances capable of forming a complex with a metal alkoxide include acetic acid, carboxylic acids such as citric acid, succinic acid, formic acid, lactic acid, tartaric acid, fumaric acid, succinic acid, propionic acid, and repuric acid, and aminopolyesters such as EDTA. Examples include complexing agents represented by amino alcohols such as carboxylic acid and triethanolamine.

(heating)
The present invention obtains a composite in which a precursor of metal oxide nanoparticles is supported inside a structure of carbon nanoparticles by a mechanochemical reaction, and heats the composite of metal oxide and carbon in a nitrogen atmosphere. By doing so, the crystallization of the metal oxide is promoted, and the capacity and output characteristics of the electrode or electrochemical device using this composite are improved.

  That is, in the firing step of the composite of the obtained metal oxide nanoparticle precursor and the carbon nanoparticle, it is possible to prevent aggregation of the metal oxide nanoparticles by rapid heating from room temperature to 400 to 1000 ° C. It was found that nanoparticles having a small particle size were formed. The rapid heating means rapid heating to such an extent that carbon is not oxidized in an atmosphere having a low oxygen concentration of about 1000 ppm. For example, rapid heating can be performed by a method such as putting a small amount of a metal oxide nanoparticle precursor and carbon nanoparticle composite in a firing furnace set to a firing temperature. The heating temperature has a suitable temperature range depending on the type of metal oxide. That is, the crystallization of the metal oxide proceeds favorably in the above temperature range, and if the temperature is lower than this temperature, the progress of the favorable crystallization cannot be obtained. No good metal oxide can be obtained.

(electrode)
The composite of metal oxide nanoparticles and carbon obtained by the present invention can be kneaded and molded with a binder to be an electrode of an electrochemical element, that is, an electrode for storing electrical energy, and the electrode has high output characteristics. Show high capacity characteristics.

(Electrochemical element)
Electrochemical elements that can use this electrode are electrochemical capacitors and batteries that use an electrolytic solution containing metal ions such as lithium and magnesium. That is, the electrode of the present invention can occlude and desorb metal ions, and operates as a negative electrode and a positive electrode. Therefore, an electrochemical capacitor and a battery can be constituted by using an electrolytic solution containing metal ions and using activated carbon, carbon or metal oxides that occlude and desorb metal ions as a counter electrode.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
A mixed solution of 1 mol of manganese acetate, ethanol and water was prepared. This mixed solution and ketjen black (KB) are put into a swirl reactor, and the inner cylinder is swirled for 5 minutes with a centrifugal force of 66,000 N (kgms ^-2 ) to deposit a thin film of reactants on the inner wall of the outer cylinder. At the same time, shear stress and centrifugal force were applied to the reaction product to promote chemical reaction, and a KB carrying a highly dispersed manganese oxide precursor was obtained.

  The obtained KBN on which the manganese oxide precursor was highly dispersed and supported was dried in vacuum at 80 ° C. for 17 hours to obtain a composite powder in which the manganese oxide precursor was highly dispersed and supported on KB.

  The obtained composite powder in which the precursor of manganese oxide is highly dispersed and supported on KB is rapidly heated to 700 ° C. in a nitrogen atmosphere to promote crystallization of manganese oxide, and manganese oxide nanoparticles are converted to KB. A highly dispersed and supported composite powder was obtained.

  The XRD analysis result and TEM image of the composite powder of Example 1 are shown in FIGS. From the XRD analysis shown in FIG. 1, it can be seen that KB carrying manganese oxide is obtained.

  As can be seen from the TEM images of FIGS. 1 to 3, the carbon nanoparticles (Ketjen black nanoparticles) show the building structure of graphite fragments. In particular, from FIG. 2, the carbon nanoparticles are oxidized with a small diameter (several nm). It can be seen that manganese nanoparticles are encapsulated. Further, according to FIG. 3, Ketjen black graphite is peeled off to form a thin film-like graphene (KB-Graphene), and manganese oxide nanoparticles enter between the graphenes to form a sandwich. Can be observed.

Next, the composite powder of Example 1 configured as described above was put together with polyvinylidene fluoride PVDF as a binder (MnO / KB / PVDF 40:40:20) into a SUS mesh welded on a SUS plate. , Working electrode W.M. E. It was. A separator and a counter electrode on the electrode C.I. E. Then, a Li foil was placed as a reference electrode, and 1.0 M lithium hexafluorophosphate (LiPF 6) / ethylene carbonate EC: dimethyl carbonate DEC (1: 1 w / w) was infiltrated as an electrolyte to obtain a cell. In this state, the energy density was calculated from the charge / discharge characteristics as working voltage 0-2V. The results showed a high energy density of 691 mAh / g (1C) and 418 mAh / g (3C) per manganese oxide.

(Example 2-1)
An aqueous solution of 1.0 mol of phosphoric acid and 1 mol of lithium acetate was prepared with respect to 1 mol of iron acetate. Here, citric acid was used as a reaction inhibitor. This solution and carbon nanofiber (CNF) are put into a swirl reactor, and the inner cylinder is swirled with a centrifugal force of 66,000 N (kgms ^-2 ) for 5 minutes to form a thin film of reactant on the inner wall of the outer cylinder. At the same time, shear reaction and centrifugal force were applied to the reaction product to promote the chemical reaction, and CNF carrying a highly dispersed olivine type lithium iron phosphate precursor was obtained. In this case, the amount of iron acetate, phosphoric acid, lithium acetate and CNF dissolved in the mixed solvent is such that the composition of the resulting composite has a mass ratio (w / w) of 50/50 lithium iron phosphate / CNF. Was set to be.

  The obtained CNF in which the precursor of lithium iron phosphate is highly dispersed and supported is dried at 80 ° C. in a vacuum for 17 hours, whereby a composite powder in which the precursor of lithium iron phosphate is highly dispersed and supported in CNF Got.

  The obtained composite powder in which the precursor of lithium iron phosphate is highly dispersed and supported on CNF is rapidly heated to 700 ° C. in a nitrogen atmosphere to promote the crystallization of lithium iron phosphate, thereby lithium iron phosphate. A composite powder in which the nanoparticles were highly dispersed and supported on CNF was obtained.

  The XRD analysis results and TEM images of the composite powder of Example 2-1 are shown in FIGS. 4 to 6, and the charge / discharge behavior and the capacity calculated from the results are shown in FIGS. From the XRD analysis shown in FIG. 4, it can be seen that CNF supported by lithium iron phosphate is obtained.

  As can be seen from the TEM images of FIGS. 4 to 6, it can be observed that the CNF nanoparticles have a net-entangled structure. A high-resolution TEM image is shown in FIG. FIG. 24 is a further enlarged photograph of FIG. 7 and a schematic view thereof. As can be seen from FIG. 24, lithium iron phosphate nanoparticles are contained in CNF such as green pea. As can be seen from the figure, the crystal structure is seen through, has a thickness of 1 nm or less at the level of 2 to 5 atomic layers, and a lithium iron phosphate crystal structure (ultra-thin film structure) on a flat plate having a diameter of 5 to 100 nm. ).

FIG. 8 is a graph showing the charge / discharge characteristics of an electrochemical device using the composite of Example 2-1. That is, the composite powder of Example 1 configured as described above was put into a SUS mesh welded on a SUS plate together with polyvinylidene fluoride PVDF as a binder (LiFePO ₄ / CNF / PVDF 40:40:20). Working electrode W. E. It was. A separator and a counter electrode on the electrode C.I. E. Lithium foil is placed as a reference electrode, and 1.0M lithium hexafluorophosphate (LiPF ₆ ) / ethylene carbonate (EC): dimethyl carbonate (DEC) (1: 1 w / w) is infiltrated as an electrolyte. And cell. In this state, the charge / discharge characteristics were examined at an operating voltage of 2.0-4.2V.

  As can be seen from FIG. 8, the capacity per composite powder was as excellent as 81 mAh / g. Further, as shown in FIG. 9, the output characteristics were more excellent as compared with the conventional products. That is, FIG. 9 is a graph comparing the capacity per lithium iron phosphate at 60 C of the electrochemical element using this lithium iron phosphate with the approximate capacity of each technology that has been conventionally disclosed. S. BLee (2008), D.C. Kim (2006), Y.M. Wang (2008), B.W. Compared with Kang (2009), the discharge capacity of the device using the composite of this example is increased. Further, FIG. 10 shows the output characteristics and FIG. 11 shows the cycle characteristics. Both the output characteristics and the cycle characteristics are good. The discharge output characteristics of FIG. 10 were measured under the same conditions as in FIG. 8 except that the discharge rate was changed to 1/120/180/240/300 / 360C with respect to the charge rate of 1C and the discharge capacity was measured. Is. As can be seen from FIG. 10, the discharge capacity at 360 C is as high as 70 mAh / g per lithium iron phosphate active material and 35 mAh / g per composite. The cycle characteristics in FIG. 11 were able to maintain a discharge capacity of 89% even at 3000 cycles (10C).

  The composite powder of this example was measured for its pore distribution by the BJH method (Barrett-Joyner-Halenda method). As shown in FIG. 21, the CNF pore distribution was 10 to 50 nm. The pore distribution of this composite was 20 nm, and it was found that lithium iron phosphate nanoparticles were supported in the 50 nm CNF voids, and a composite having a pore distribution of 20 nm was formed. That is, the pore distribution of the composite of this example and CNF was calculated, and these mesopores were observed. In the graph of FIG. 21, the square is a composite and the circle is a CNF plot. First, it can be seen that CNF has more mesopores of 10 to 50 nm than the value of dV / d (logr). Further, when iron phosphate is combined with this CNF, a large change is observed in the pore distribution. The pore diameter of 10 to 50 nm is greatly reduced, and the pore distribution around 20 nm is maintained. In addition, this tendency is remarkably observed in dV / dr. From this result, it can be seen that when iron phosphate is carried by CNF, it occurs in the pores having a pore diameter of 10 to 50 nm of CNF, and further, a network of mesopores having a pore diameter of about 20 nm is constructed. Therefore, it is presumed that this composite electrode can construct a good ion path.

(Example 2-2)
A cell was fabricated in the same manner as in Example 2-1, except that the lithium iron phosphate / CNF was set to a mass ratio (w / w) of 60/40. The capacity of this cell was 71 mAh / g. FIG. 12 shows a high-resolution TEM image of this composite powder. As can be seen from this figure, it can be seen that a lithium iron phosphate crystal structure on a flat plate having a thickness of 1 nm or less at a 2-5 atomic layer level and a diameter of 5-100 nm is supported on CNF.

(Example 2-3)
A cell was produced in the same manner as in Example 2-1, except that ketjen black was used as carbon. The capacity of this cell was 108 mAh / g. FIG. 13 shows a high-resolution TEM image of this composite powder. As can be seen from this figure, the lithium iron phosphate crystal structure on a flat plate having a thickness of 1 nm or less at a 2-5 atomic layer level and a diameter of 5-20 nm is included in Ketjen Black. . FIG. 25 shows a high-resolution TEM image of the composite powder of Example 2-3 and a schematic diagram thereof. In Example 2-3, the structure is such that lithium iron phosphate nanoparticles are contained one by one in hollow, spherical carbon as in the case of a fountain.

(Example 2-4)
A cell was fabricated in the same manner as in Example 2-3 except that the lithium iron phosphate / Ketjen black was set to a mass ratio (w / w) of 60/40. The capacity of this cell was 102 mAh / g.

(Example 2-5)
A cell was produced in the same manner as in Example 2-1, except that BP2000 manufactured by Cabot Corporation was used as carbon. The capacity of this cell was 88 mAh / g. FIG. 14 shows a high-resolution TEM image of this composite powder. As can be seen from this figure, it can be seen that a lithium iron phosphate crystal structure on a flat plate having a thickness of 1 nm or less at a 2-5 atomic layer level and a diameter of 5-100 nm is supported on BP2000.

(Example 2-6)
A cell was fabricated in the same manner as in Example 2-3, except that lithium iron phosphate / BP2000 was set to a mass ratio (w / w) of 60/40. The capacity of this cell was 96 mAh / g.

(Example 3)
A mixed solvent was prepared by dissolving acetic acid and lithium acetate in an amount of 1.8 mol of acetic acid and 1 mol of lithium acetate in a mixture of isopropanol and water with respect to 1 mol of titanium alkoxide. This mixed solvent, titanium alkoxide, and carbon nanofiber (CNF) are put into a swirl reactor, and the inner cylinder is swirled for 5 minutes with a centrifugal force of 66,000 N (kgms ^-2 ), and the reactant is put on the inner wall of the outer cylinder And a chemical reaction was promoted by applying shear stress and centrifugal force to the reaction product to obtain CNF carrying a highly dispersed lithium titanate precursor. In this case, the amount of titanium alkoxide and CNF dissolved in the mixed solvent was set such that the composition of the obtained composite had a mass ratio (w / w) of lithium titanate / CNF of 70/30.

  The obtained CNF in which the lithium titanate precursor is highly dispersed and supported is dried in vacuum at 80 ° C. for 17 hours to obtain a composite powder in which the lithium titanate precursor is highly dispersed and supported in CNF. It was.

  The resulting composite powder in which the precursor of lithium titanate is highly dispersed and supported on CNF is rapidly heated to 800 ° C. in a nitrogen atmosphere to advance crystallization of titanium oxide containing lithium, and titanate A composite powder in which lithium nanoparticles were highly dispersed and supported on CNF was obtained.

  A TEM image of the carbon carrying the lithium titanate nanoparticles of Example 3 thus obtained is shown in FIG. In FIG. 15, it can be seen that 5 to 20 nm lithium titanate nanoparticles are highly dispersed and supported on CNF.

  In particular, as seen in the TEM image of FIG. 15, the “composite of lithium titanate nanoparticles and carbon” of the present invention has a “building structure of graphite fragments” in which CNFs are connected. Lithium titanate nanoparticles are supported in a highly dispersed manner.

  FIG. 16 shows a view of CNF carrying the highly dispersed lithium titanate precursor of Example 3 observed with a high resolution TEM. As can be seen from FIG. 16, the lithium titanate nanoparticles can be seen through the crystal structure, have a thickness of 1 nm or less at the level of 2 to 5 atomic layers, and a lithium titanate crystal on a flat plate with a side of 5 to 10 nm. It is a structure. Such an ultra-thin structure is extremely thin and has a very large surface area per volume. Therefore, high output characteristics can be shown.

  That is, regarding the surface area per volume, the surface area of the sheet whose thickness is infinitely close to zero is the largest, but the sheet of Example 3 has a structure with a thickness of several atomic layers close to zero. The above ultra-thin film structure is formed by a rapid heating treatment after reaction by applying shear stress and centrifugal force to a solution containing a metal oxide starting material and carbon powder in a swirling reactor. It seems that metal oxide nanoparticles other than lithium titanate also have an ultrathin film structure as observed with lithium iron phosphate.

The composite powder obtained in Example 3 configured as described above was welded onto a SUS plate together with polyvinylidene fluoride PVDF as a binder (Li ₄ Ti ₅ O ₁₂ / CNF / PVDF 56:24:20). The working electrode W. E. It was. A separator and a counter electrode on the electrode C.I. E. And a Li foil as a reference electrode, and 1.0 M lithium tetrafluoroborate (LiBF ₄ ) / ethylene carbonate (EC): dimethyl carbonate (DEC) (1: 1 w / w) as an electrolyte. And cell.

  The charge / discharge behavior and the capacity calculated based on the charge / discharge behavior of the cell using the composite powder of Comparative Example 1 heated in vacuum under the same conditions as in Example 3 obtained as described above are shown in FIG. 17 shows the output characteristics. In FIGS. 17 and 18, the graph on the left shows Example 3, and the graph on the right shows Comparative Example 1. In this case, the working voltage is 1.0-3.0V, and the scan rate is 10C.

  As can be seen from FIG. 17, the cell using the composite powder of Example 3 heated in a nitrogen atmosphere has an increased capacity compared to the cell using the composite powder of Comparative Example 1 heated in vacuum. You can see that In particular, the cell using the composite powder heated to 800 ° C. in the vacuum of Comparative Example 1 had the largest capacity in the prior art, but all of the cells of Example 3 greatly exceeded the capacity of Comparative Example 1. ing.

  FIG. 18 is a graph showing the output characteristics of each cell with the C-rate on the horizontal axis and the discharge capacity retention rate (%) on the vertical axis. As can be seen from FIG. 18, the discharge capacity retention rate when the C-rate is 200 C is significantly higher in the cell of Example 3 than in the cell of Comparative Example 1.

Example 4
The working electrode prepared in Example 2-1 was used as the positive electrode, the working electrode prepared in Example 3 was used as the negative electrode, and the electrolyte was 1.0 M lithium hexafluorophosphate (LiPF ₆ ) / ethylene carbonate (EC): An electrochemical device was fabricated using dimethyl carbonate (DMC) (1: 1 w / w). FIG. 19 shows the results of measuring the energy density and power density of this electrochemical element.

  FIG. 19 shows an electrochemical element of Example 4, an electrochemical element using an activated carbon electrode as a positive electrode and a working electrode prepared in Example 3 as a negative electrode, and an electric double layer using activated carbon as a positive electrode and a negative electrode. It is a Ragon plot which measured energy density and output characteristics about each of a capacitor (EDLC). As can be seen from FIG. 19, the electrochemical element of Example 4 realizes a high-output energy storage device having a high energy density and a high output characteristic.

(Example 5)
In the synthesis of the Li ₄ Ti ₅ O ₁₂ / CNF composite, Ti (OC ₄ H ₉ ) ₄ was used as the titanium source and CH ₃ COOLi was used as the lithium source. These precursors were subjected to ultracentrifugation treatment (UC treatment) together with 10 to 40 wt% of CNF or organic solvent with respect to the entire Li ₄ Ti ₅ O ₁₂ / CNF to obtain a precursor. Then, to obtain a highly crystalline nanoparticles _Li 4 _Ti 5 _O 12 / CNF composite by performing a high-temperature short-time firing. This composite was converted into an electrode using PVDF, and electrochemical characteristics were evaluated by a half cell using Li metal as a counter electrode and 1M LiBF ₄ / EC + DMC 1: 1 (in volume) as an electrolyte. As a result of the charge / discharge test, it was found that the output characteristics depend on the weight ratio of Li ₄ Ti ₅ O ₁₂ . As can be seen from FIG. 22, the capacity of 81% (87 mAh / g) of the 10C capacity was maintained even at 600 C where high output characteristics are required, and the capacity of 68% (72 mAh / g) was maintained even at 1200 C.

As a result of XRD analysis of the composite of Example 5, as shown in FIG. 23, the crystal size of the (111) plane with a CNF content ratio of 20% is larger than 30-50%, and lithium titanate The nanoparticle crystals were confirmed to have an ultrathin film structure with a large (111) plane.

Claims (9)

  In a swirling reactor, a composite powder in which the precursor containing metal oxide nanoparticles is supported in a highly dispersed manner by applying shear stress and centrifugal force to the solution containing the metal oxide starting material and carbon powder. The metal oxide is characterized in that the crystallization of the metal oxide is advanced by rapid heating in a nitrogen atmosphere, and the metal oxide nanoparticles having an ultrathin film structure are supported in a highly dispersed state on carbon. A method for producing a composite of nanoparticles and carbon.   The method for producing a composite of metal oxide nanoparticles and carbon according to claim 1, wherein the rapid heating treatment is to heat the composite to 400 to 1000 ° C in a nitrogen atmosphere.   3. The method for producing a composite of metal oxide nanoparticles and carbon according to claim 2, wherein shearing stress and centrifugal force are applied to a solution containing a reaction inhibitor together with a reactant in the reactor. .   The metal oxide is represented by MxOz, AxMyOz, Mx (DO4) y, AxMy (DO4) z (where M: metal element A: alkali metal or lanthanoid element). The manufacturing method of the composite_body | complex of the metal oxide nanoparticle of any one of these, and carbon. The method for producing a composite of metal oxide nanoparticles and carbon according to claim 4, wherein the metal oxide is any one of manganese oxide MnO, lithium iron phosphate LiFePO ₄ , and lithium titanate Li ₄ Ti ₅ O _12. .   A composite of metal oxide nanoparticles and carbon produced by the method according to any one of claims 1 to 5.   An electrode obtained by molding the composite according to claim 6 after mixing with a binder.   An electrochemical device using the electrode according to claim 7. The electrochemical element according to claim 8, wherein lithium iron phosphate LiFePO _{4 is used for} the positive electrode and lithium titanate Li ₄ Ti ₅ O ₁₂ is used for the negative electrode.