Patent Application
20160133921
The present invention relates to a composite comprising metal fluoride and porous carbon, a method of preparing the same, and a lithium ion battery including the same. More particularly, the present invention relates to a composite, which may be used to realize large capacity, depending on the discharge rate, and high operating voltage, and is thus useful as a cathode material having high energy density in a lithium ion battery, a method of preparing the same, and a lithium ion battery including the same as a cathode material.
Conventional non-rechargeable batteries are referred to as primary batteries, and rechargeable batteries are called secondary batteries. Lithium ion batteries are constructed in a manner in which an organic electrolyte is interposed between a cathode and an anode so that charging and discharging are repeated. As the lithium ions of the anode are moved toward the cathode via the intermediate electrolyte, electricity may be generated. Since lithium ion batteries are lightweight and have high energy density, they may possess high capacity and may thus be utilized in a variety of electronic devices, such as mobile phones, notebook computers, digital cameras, etc.
With the drastic increase in the need for the development of high-capacity electrode materials for lithium ion batteries, thorough research is ongoing into novel electrode materials that are able to replace currently available lithium intercalation/deintercalation-based electrode materials. Materials that may be subjected to conversion or alloying with lithium may exchange several lithium atoms per unit molecule and are receiving attention as next-generation high-capacity electrode materials. However, most of the materials that are able to undergo the above reactions have low operating voltage for lithium exchange, and may be limitedly applied only to the anode.
Useful as an example of metal fluoride, copper fluoride (CuF2) is easily hydrated in air and may easily undergo defluorination in the course of heat treatment, making it difficult to synthesize a nano structure. Furthermore, as copper ions are dissolved in the electrolyte in the electrochemical reaction, reversible charging and discharging cannot be carried out, and thus it is difficult to apply such a fluoride to the cathode for a rechargeable secondary battery.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention is intended to provide a composite, which enables reversible charging and discharging in the electrochemical reaction and may be used as a high-capacity electrode material, and also to provide a superior energy storage device using the composite as a cathode material for a lithium ion battery, thus exhibiting improved energy density and cycling characteristics.
In addition, the present invention is intended to provide a method of preparing a composite, which may be carried out through a solventless reaction, thus minimizing the loss of product attributable to the partial dissolution of a fluoride compound, realizing a very simple synthesis procedure, and obviating the use of a hazardous hydrofluoric acid aqueous solution or toxic gases, which require specific handling equipment, thereby achieving very safe and efficient preparation of the composite.
An aspect of the present invention provides a composite, comprising: a carrier including porous carbon with a plurality of pores; and metal fluoride loaded on the porous carbon.
The metal fluoride may be loaded on the inner wall of the carbon in the pores.
The metal fluoride may comprise at least one selected from among copper fluoride (CuF2), cobalt fluoride (CoF2), iron fluoride (FeF2, FeF3), and nickel fluoride (NiF2).
The pores may have a diameter of 1 to 100 nm.
The metal fluoride may be used in an amount of 30 to 90 wt % based on the total weight of the composite.
Another aspect of the present invention provides a method of preparing a composite, comprising: (a) providing a carrier including porous carbon with a plurality of pores; (b) loading a metal precursor on the porous carbon, thus forming a metal precursor-loaded carrier; (c) mixing the metal precursor-loaded carrier with ammonium fluoride (NH4F), thus obtaining a mixture; and (d) heat-treating the mixture in any one atmosphere selected from among an inert gas, nitrogen gas, and a vacuum, yielding a composite comprising a carrier including porous carbon with a plurality of pores and metal fluoride loaded on the porous carbon.
The metal fluoride may be loaded on the inner wall of the carbon in the pores.
The carrier may be prepared using a hard template process.
The metal precursor may comprise at least one selected from among copper, cobalt, iron, and nickel.
The metal precursor may comprise at least one selected from among Cu(NO3)2.xH2O, CuCl2.xH2O, Cu(OH)2.xH2O, Cu(CH3COO)2.xH2O, CU2(OH)3NO3, (NH4)2CuF4, NH4CuF3, Cu(OH) F, CuO, and Cu2O, where x is 0 to 6.
In the method, (b) may be performed using a wet impregnation process, comprising dissolving the metal precursor in a solvent to obtain a metal precursor solution and impregnating the carrier with the metal precursor solution.
The solvent may comprise at least one selected from among ethanol, methanol, acetone, water, tetrahydrofuran, and chloroform.
After the wet impregnation process, stirring and drying may be performed.
The method may further comprise performing drying at 50 to 100° C., after (b).
The ammonium fluoride in the mixture in (c) may be contained in an amount of two to ten times a molar number of a metal contained in the metal precursor.
The method may further comprise grinding the mixture, after (c).
The inert gas may be argon.
The heat-treating in (d) may be performed at 150 to 300° C.
A further aspect of the present invention provides a lithium ion battery, comprising the above composite as a cathode active material.
The lithium ion battery may comprise a solid electrolyte.
According to the present invention, a composite comprising metal fluoride and porous carbon enables reversible charging and discharging in the electrochemical reaction, and can be used as a high-capacity electrode material. As the composite of the invention can be utilized as a cathode material for a lithium ion battery, energy density and cycling characteristics can be improved.
Also, the preparation of the composite can be carried out through a solventless reaction, thus minimizing the loss of product due to the partial dissolution of a fluoride compound and realizing a very simple synthesis procedure. Furthermore, there is no need for a hazardous hydrofluoric acid aqueous solution or toxic gases, which require specific handling equipment, thereby achieving a safe preparation process.
The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, a detailed description will be given of embodiments of the present invention with reference to the appended drawings so that the present invention may be easily carried out by those skilled in the art to which the present invention belongs.
However, the following description is not intended to limit the present invention to specific embodiments, and a detailed description of the related known technology that may unnecessarily obscure the gist of the present invention will be omitted.
The terms used herein are merely employed to explain specific embodiments, and the present invention is not limited thereby. Unless otherwise stated, the singular expression includes a plural expression. In this application, the terms “include”, “have”, etc. are used to designate the presence of features, numbers, steps, operations, components, or combinations thereof described in the specification, and should be understood as not excluding the presence or additional probability of one or more different features, numbers, steps, operations, components, or combinations thereof.
Below is a description of the composite according to the present invention.
The composite according to the present invention comprises a carrier including porous carbon with a plurality of pores, and metal fluoride loaded on the porous carbon.
Preferably, metal fluoride may be loaded on the inner wall of the carbon in the pores.
Examples of the metal fluoride may include copper fluoride (CuF2), cobalt fluoride (CoF2), iron fluoride (FeF2, FeF3), and nickel fluoride (NiF2), but the present invention is not limited thereto.
Metal fluoride shows a high theoretical operating voltage of 2.5 V or more and has a theoretical capacity of 500 mAh/g or more through a conversion reaction, and is thus expected to be a next-generation high-energy-density cathode material. In particular, copper fluoride (CuF2) has a theoretical operating voltage of 3.55 V, which is regarded as the highest among examples of metal fluoride, and also has a high theoretical capacity exceeding 500 mAh/g, and thus the use thereof as a high-energy-density cathode material is expected.
The pores of the carrier have a diameter of 1 to 100 nm, preferably 3 to 70 nm, and more preferably 10 to 50 nm. Nanoparticles having a size of 10 nm or more may be effectively loaded within the pores.
The amount of metal fluoride is 30 to 90 wt %, and preferably 50 to 70 wt %, based on the total weight of the composite.
Below is a description of the method of preparing the composite according to the present invention with reference to
Specifically, a carrier including porous carbon with a plurality of pores is provided (Step a).
The carrier may be formed using a hard template process, but the present invention is not limited thereto.
The hard template process refers to the synthesis of a mesoporous material using a previously made organic or inorganic template.
Thereafter, a metal precursor is provided, and is then loaded on the porous carbon, thus forming a metal precursor-loaded carrier (Step b).
Specifically, a wet impregnation process, including dissolving the metal precursor in a solvent to obtain a metal precursor solution and impregnating the carrier with the metal precursor solution, may be implemented, but the present invention is not limited thereto.
The solvent, which is contained in the metal precursor solution, may include, but is not limited to, ethanol, methanol, acetone, water, tetrahydrofuran, and chloroform, and any solvent may be used so long as it dissolves the metal precursor.
After the wet impregnation process, stirring and drying are performed, thereby evaporating the solvent.
The metal precursor may include at least one of copper, cobalt, iron, and nickel.
Preferably useful is a copper precursor containing copper, and the copper precursor may include, but is not limited to, Cu(NO3)2.xH2O, CuCl2.xH2O, Cu(OH)2.xH2O, Cu(CH3COO)2.xH2O (where x is 0 to 6), Cu2(OH)3NO3, (NH4)2CuF4, NH4CuF3, Cu(OH) F, CuO, and Cu2O, and any material may be used so long as it reacts with ammonium fluoride to form copper ammonium fluoride.
After Step b, drying may be further performed at 50° C. or more, and preferably 50 to 100° C.
Subsequently, ammonium fluoride (NH4F) is provided, and is then mixed with the metal precursor-loaded carrier, thus obtaining a mixture (Step c).
In the mixture, ammonium fluoride is preferably contained in an amount of at least two times, and more preferably two to ten times, the molar number of the metal contained in the metal precursor.
After Step c, grinding the mixture may be further performed.
The mixture is heat-treated in any one atmosphere selected from among an inert gas, nitrogen gas, and a vacuum, thereby forming a composite comprising a carrier including porous carbon with a plurality of pores and metal fluoride loaded on the porous carbon (Step d).
The inert gas may include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Argon is preferably used.
Here, the heat treatment may be performed at 150 to 300° C.
In addition, the present invention addresses a lithium ion battery comprising the composite as a cathode active material.
The lithium ion battery preferably includes a solid electrolyte.
The solid electrolyte may be exemplified by Li-ion-conducting glass ceramic, but the present invention is not limited thereto, and any solid electrolyte may be used, as long as only lithium ions can selectively pass therethrough.
A better understanding of the present invention may be obtained through the following examples, which are set forth to illustrate, but are not to be construed to limit the present invention.
Mesoporous carbon (mesocellular carbon foam, MSU-F-C) was synthesized by a hard template process using mesocelluar aluminosilicate foam and furfuryl alcohol as a silica template and a carbon precursor, respectively.
A copper precursor was loaded on MSU-F-C through a wet impregnation process. Specifically, a Cu(NO3)2.2.5H2O ethanol solution was incorporated at room temperature, and to impregnate MSU-F-C with 55 wt % CuF2 (e.g. 0.12 g of CuF2+0.1 g of MSU-F-C), 0.1 g of MSU-F-C was impregnated with 0.28 g of a Cu(NO3)2.2.5H2O ethanol solution.
Next, the ethanol solvent was evaporated with stirring, and was then further dried in a vacuum oven at 85° C., thus obtaining a copper precursor/MSU-F-C, which was then mechanically ground using a mortar and pestle together with NH4F in an amount of 0.22 g, which corresponds to five times the molar number of copper contained in the copper precursor. The mixture thus obtained was heat-treated at 210° C. for 1 hr in an argon gas atmosphere, yielding a CuF2/MSU-F-C composite. The composite thus prepared was placed in a glove box filled with argon.
The preparation of the CuF2/MSU-F-C composite in Example 1 is schematically illustrated in
Bulky CuF2 was prepared in the same manner as in Example 1, with the exception that MSU-F-C was not used.
A bulky CuF2/MSU-F-C mixture was prepared by physically mixing the bulky CuF2 of Comparative Example 1 with MSU-F-C.
MSU-F-C was prepared in the same manner as in Preparation Example 1.
A copper precursor/MSU-F-C composite was prepared in the same manner as in Example 1, with the exception that grinding with NH4F and heat treatment were not performed.
0.07 g of the CuF2/MSU-F-C composite of Example 1, 0.02 g of PVDF (polyvinylidene fluoride), 0.01 g of Super P, and 0.9 mL of NMP (N-methyl-2-pyrrolidone) were mixed together and ground to make a paste, which was then applied on an aluminum foil and dried at room temperature for 48 hr in a vacuum, thus forming an electrode.
Subsequently, a portion of the electrode was removed in the form of a circular shape having a diameter of 14 mm, and was thus used as a cathode, and a circular lithium metal foil having a diameter of 8 mm was used as an anode, after which each electrode was fixed to a stainless steel current collector. Also, 1.5 mL of a solution (1M LiPF6 in EC/DMC) of 1 mol LiPF6 in a solvent mixture of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1 was used as a liquid electrolyte, and a solid electrolyte (LTAP) was additionally used, thereby manufacturing a lithium ion battery configured such that the cathode and the anode were physically blocked from each other. The fabrication of the electrode and the lithium ion battery was performed in a glove box filled with argon gas.
A lithium ion battery was manufactured in the same manner as in Device Example 1, with the exception that the bulky CuF2/MSU-F-C mixture of Comparative Example 2, rather than that of Example 1, was used as the cathode material.
A lithium ion battery was manufactured in the same manner as in Device Example 1, with the exception that the MSU-F-C of Comparative Example 3, rather than that of Example 1, was used as the cathode material.
As is apparent from the results of analysis of XRD of
Based on the results of analysis of XRD of
As illustrated in
The conversion of various copper precursors into CuF2 through heat treatment was measured through XRD. The results are illustrated in
As illustrated in
The SEM and TEM images of the CuF2/MSU-F-C composite of Example 1, bulky CuF2 of Comparative Example 1 and MSU-F-C of Comparative Example 3 are illustrated in
The nano-sized active material is loaded on porous carbon to thus realize high dispersibility, and can provide the electron conduction path. Thus, mesoporous carbon, namely MSU-F-C, may be used as the carrier of CuF2.
As illustrated in
As seen in the SEM images of the CuF2/MSU-F-C composite (Example 1), the image of the bulky CuF2 (Comparative Example 1) was not observed, and the overall shape of MSU-F-C was not significantly changed when compared with the image of Comparative Example 3. These results showed that the CuF2 nanoparticles were mostly loaded within the pores of MSU-F-C, and only some of the particles were significantly grown and protruded from the pores.
As seen in the TEM images, the particles were positioned near or on the pores of MSU-F-C, and the size of the particles was similar to the size of the pores.
Based on the results of nitrogen physisorption, loading of CuF2 on MSU-F-C was additionally proven. Specifically, the surface area of CuF2/MSU-F-C and the pore volume thereof were decreased by 25% compared to MSU-F-C, from which it was inferred that the CuF2 particles were distributed within the pores and had an influence on the surface properties of MSU-F-C, taking into consideration the loading of 55% CuF2. Furthermore, the CuF2 particles were neither isolated from the pores nor externally grown.
The pore size distribution indicates easy penetration of the copper precursor and the growth of CuF2 in the pores of MSU-F-C. Since small pores are preferentially filled with the precursor solution due to strong capillary action, the volume of small pores may be significantly decreased compared to that of large pores. This expectation is consistent with the results based on the curved line of the copper precursor/MSU-F-C, which has a single peak of 30 nm or less. After heat treatment with NH4F, the decomposition of the precursor and the growth of the particles occurred together, whereby the small pores were exposed again. Also, the curved line having two peaks, the intensities of which were decreased, was observed in CuF2/MSU-F-C.
As illustrated in
As illustrated in
In the final charging (Curve 7), peaks matching CuF2 were not observed again. This is deemed to be because CuF2, converted again from the discharge material, has smaller crystals or is in an amorphous phase.
As seen in
As shown in
As shown in
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0154463 | Nov 2014 | KR | national |
