KR101468542B1 - Anode material with graphynes, and a lithium ion battery having the same - Google Patents

Abstract

So that the present invention is combined, sp- related to the lithium cell anode material with fine and sp ² - Yes, two-dimensional layer of carbon atoms of the bond pine can be used as an effective energy storage material by having a large surface area, the present invention The Li potential energy can have an appropriate energy range that can be used as a negative electrode material through the first-principle density function calculation, and the structure of the multilayer α-graphene and γ-graphene intercalated Li layer is C ₆ Li ₃ And 1117 mAh / g, which is approximately three times larger than graphite in the specific capacity. In addition, the volume capacities of multilayer-graphene and γ-graphene intercalated Li interlayer are 1364 mAh / ㎤ and 1589 mAh / ㎤ respectively, which is considerably larger than 818 mAh / ㎤, which is the volume capacity of graphite, As shown in FIG.

Description

Anode material with graphynes and a lithium ion battery having the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode material for a lithium battery using graphene and, more particularly, to a negative electrode material for a lithium battery which can improve energy storage capacity as compared with a conventional graphite negative electrode material by using α- or γ- Lt; / RTI >

Lithium-ion batteries are one of the most important technologies in the development of portable electronic devices because they have a higher energy density compared to other rechargeable batteries. Lithium metal cathodes were used because of their high specific capacity of 3860 mAh / g [refs. 1, 2]. However, lithium metal cathodes have some problems in terms of dendrite formation and stability. On the other hand, graphite is widely used as a cathode material of a lithium ion battery because of high lithium diffusion property (high power) of lithium ion and high stability (small volume change) by intercalation of lithium interlayer. The maximum arrangement of Li intercalated graphite is that one Li atom is located on all six carbon atoms, the structure of which is C ₆ Li, where the specific capacity is 372 mAh / g [Ref. 3-5] . On the other hand, researches on new materials that can surpass graphite have been extensively carried out to increase the capacity of lithium ion batteries. As cathode materials, silicon, germanium, and tin have been proposed to have high specific capacities of ~ 4000 mAh / g, 1600 mAh / g, and 1000 mAh / g, respectively [6,7]. However, it is known that these cathode materials have a problem of crystal expansion which causes a large volume change (~ 400%) in the process of inserting and separating lithium ions. This is a serious obstacle to use as a cathode material, as it has low electron conductivity (semiconductor) and lithium diffusion of low lithium ions. On the other hand, it is expected that the materials having the layer structure can effectively solve the volume change problem because the volume change is small due to the interlayer intercalation between the Li layers. In addition, the cathode material must meet various requirements. Since Li has a bulk cohesive energy of ~ 1.6 eV and Li maximum energy for a lithium-ion battery cathode material is ~ 3 eV, the binding energy of Li atoms must have an energy in the range of ~ 1.6-3.0 eV [References 2]. On the other hand, if the binding energy is less than ~ 1.6 eV, separation of lithium occurs, and if the binding energy is more than ~ 3 eV, it will not function as a negative electrode material. Also, the specific capacity and volume capacity should be larger than graphite, and the volume change due to lithium insertion should be as small as that of graphite.

Last sp- and sp ² - a two-dimensional structure consisting of a carbon atom of the coupling α-, β-, and 6,6,12 (hereinafter, "γ") - graphyne (graphyne) is symmetric as considerably interesting electronic properties It has been reported to have red and asymmetric Dirac cones. This shows different properties from graphene such as electron collimation transport [Ref 8-11]. Another interesting feature is that graphene can be seen as a sheet with a very large surface area of the one-dimensional carbon-chain network because the hexagonal region is considerably larger than graphene (about 8 times larger than graphene). From an application point of view, the properties of graphene can be various potential applications as energy storage materials. For example, graphene with calcium or lithium atoms can be used as a high-capacity hydrogen storage material by having a large surface area [Refs. 12-14]. Moreover, graphene can have a high electronic conductivity due to its metallic nature.

[references]

[1] Reddy TB, Hossain S. Rechargeable Lithium Batteries, in Handbook of Batteries, ed. L

[2] Landi BJ, Ganter MJ, Cress CD, DiLeo RA, and Raffaelle RP 2009 Energy Environ Sci 2 638.

[3] Dahn JR 1991 Phys Rev B 44 9170.

[4] Satoh A, Takami N and Ohsaki T 1995 Solid State Ionics 80 291.

[5] Stura E and Nicolini C 2006 Anal Chim Acta 568 57.

[6] Chan CK, Zhang XF and Cui Y 2008 Nano Lett 8 307.

[7] Meduri P, Pendyala C, Kumar V, Sumansekera GU and Sunkara MK 2009 Nano Lett 9 612.

[8] Idota Y, Kubota T, Matsufujia, Maekawa Y and Miyasaka T 1997 Science 276 1395.

[9] Malko D, Neiss C, Vines F and Gorlinge 2012 Phys Rev Lett 108 086804.

[10] Coluci VR, Braga SF, Galvao DS and Baughman RH 2004 Nanotechnology 15 S142.

[11] Kang, J .; Li, J .; Wu, F .; Li, S.-S .; Xia, J.-B. 2011 J. Phys. Chem . C 115 20466.

[12] Hwang, HJ; Kwon, Y .; Lee, H. 2012 J. Phys . Chem . C, DOI: 10.1021 / jp306222v .

[13] Guo, Y .; Jiang, K .; Xu, B .; Xia, Y .; Yin, J .; Liu, Z. 2012 J. Phys. Chem . C 116 13837.

[14] Li, C .; Li, J .; Wu, F .; Li, S.-S .; Xia, J.-B .; Wang, L.-W. 2011 J. Phys. Chem.C 115 23221.

In the present invention, it has been confirmed that the Li potential energy has an energy range suitable for the negative electrode between the respective layers of? - or? -Grapeine in which nanoporous sheets are laminated, and by using graphene, And to provide a negative electrode material for a lithium battery.

In order to accomplish the above object, the present invention provides a negative electrode material for a lithium battery, a lithium ion dispersed between respective layers of? - or? -Grapeine comprising laminated nanoporous sheets, .

Preferably, in the present invention, the unit lattice structure of the α-graphene composite in which Li ions are eccentrically positioned at the center of the hexagonal lattice plane of the α-graphene, and more preferably, the Li ion is inserted is C ₆ Li _x (0 < _x ? 3).

Preferably, in the present invention, Li ions are located on the upper or lower hollow portion of the triangular lattice plane of? -Grape, more preferably, a unit of? -Grapein complex The lattice structure is characterized by being C ₆ Li _x (0 < _x ? 3).

The negative electrode material for a lithium battery according to the present invention is effective as a negative electrode material for a lithium battery because it can be inserted or separated into Li ions between respective layers of? - or? -Grapeane in which nanoporous sheets are laminated, Compared to cathode materials using graphite, it has an excellent effect of having a specific capacity of 2 to 3 times larger.

Particularly, in the negative electrode material for a lithium battery according to the present invention, since alpha-graphene does not cause volume change during insertion / separation of Li ions, it can be used as a stable negative electrode material for lithium batteries.

1 (a) and 1 (b) are diagrams showing the atomic structure of 2x2? -Grapeine and? -Grapeane with Li atoms attached thereto (carbon atoms are gray points and lithium atoms are pink)
2 (a) and 2 (c) show the calculated Li bond energies per Li atom with respect to the concentration x, and (b) and (d) show 2 × 2 α- Drawings showing atomic structure in graphene and gamma-graphene,
Fig. 3 (a) shows the calculated Li bond energies per Li atom of AB-laminated a-graphene intercalated with Li as a function of concentration (x) (C ₆ Li _x ) Are views showing side and cross-sectional views of the atomic structure when x = 3, respectively;
4 (a) shows the calculated Li bond energies per Li atom of AA-laminated y-graphene intercalated into Li as a function of concentration (x) (C ₆ Li _x ) &Lt; / RTI &gt; are side and cross-sectional views of the atomic structure when x = 3, respectively.

In the present invention, it was confirmed that graphene can exert excellent functions as a lithium ion battery cathode material by using a first-principle density-functional theory calculation. Grafine is able to fabricate graphene from a carbon network in dehydrobenzoanulene using a bottom-up approach [Ref. 15]. In the present invention, the bond required for Li bond energies It was confirmed that Li atoms could be intercalated into a multi-layered graphene without Li separation. The Li-intercalated α-graphene and γ-graphene composites have a specific capacity of 1117 mAh / g with C ₆ Li ₃ and are three times larger than the specific capacity of graphite (372 mAh / g). The calculated volume capacities of the α-graphene and γ-graphene composites are 1364 mAh / ㎤ and 1589 mAh / ㎤, respectively, and the graphene (818 mAh / ㎤) is considerably larger. As a result, graphene, which is a multilayer structure according to the present invention, can be used as a lithium ion battery negative electrode material.

Hereinafter, embodiments of the present invention will be described in detail.

Example

In this embodiment, the first principles based on the density function theory (Reference 16) implemented in the VASP (Vienna Ab-initio Simulation Package) provided with the projector-augmented-wave (PAW) Method.

A standard gradient approximation (GGA) is used in the PBE (Perdew-Burke-Ernzerhof) method [Ref. 14] and the kinetic energy cutoff is 400 eV.

In the present embodiment, the α- (γ-) graphene system used in the model is a 2 × 2 hexagonal supercell with 32 (48) C atoms. Optimization of the geometry of Li-dispersed graphene is based on the assumption that the Hellman-Feynman forces acting on each atom in a fixed 2 x 2 number of percels from an isolated graphene equilibrium lattice constant are 0.01 eV / &Lt; / RTI &gt; The first Brillouin zone integral was made by the Monkhorst-Pack scheme [19]. 4 × 4 × 1 k-point sampling was performed on 2 × 2 graphene. A vacuum layer of 10 angstroms was taken in each of the non-periodic directions to eliminate spurious interactions between neighboring structures by periodic calculations. In the present invention, a test calculation was performed on a Li adsorbed graphene model system and the calculated binding energy (0.69 eV / Li) of Li in 4 x 4 graphene was consistent with the 0.67 eV / Li value in Reference 20 The reliability of the approach in the present invention was confirmed.

<Result>

Graphyne is sp- and sp ² - and has a range of phase (phase), such as a hexagon, a triangle and a rectangle having a different local geometric structure consisting of carbon having a coupling. In the present invention, it has been confirmed that Li adsorption depends only on local geometry such as hexagons and triangles. Therefore, in this embodiment, a single layer, which is typically? - and? -Grape, is selected.

Figs. 1 (a) and 1 (b) show the atomic structure of? - and? -Grape, in which Li is dispersed, respectively, and are obtained from calculations for graphene 2 × 2 water cells. In 2 × 2 graphene, the binding energy of Li atoms as a function of Li concentration x was calculated, where x is defined from C ₆ Li _x . The binding energy of Li atoms is defined as follows.

[Equation 1]

는 Li 원자의 농도 x를 갖는 Li 분산된 2×2 그래파인의 전체 에너지이며, E _C 는 2×2 고립된 그래파인의 전체 에너지이며, E _Li 는 진공에서 고립된 Li 원자의 전체 에너지이다. 2×2 γ-그래파인의 경우에, N=8x로써 C₄₈Li_N은 C₆Li_x으로 표현될 수 있다.Where N is the number of Li atoms attached per 2 x 2 cells to the concentration x,

Is the total energy of the Li dispersed 2 x 2 graphene with a concentration x of Li atoms, E _c is the total energy of graphene isolated 2 x 2, and E _Li is the total energy of Li atoms isolated in vacuum. In the case of 2 x 2 gamma-graphene, C ₄₈ Li _N can be expressed as C ₆ Li _x with N = 8x.

(A) C ₆ Li _0.188 and (b) C ₆ Li _{0 .125,} respectively, of the Li- dispersed α- and γ-graphene complexes shown in FIG. Yes Pine and the mounting position of the various Li atom is present, for example, the top of the carbon atom, sp - may be combined inside a triangle - with sp ² - and the hollow portion of the associated hexagonal, sp. As shown in Fig. 1 (a), in the case of the attachment of Li-atoms of alpha -grapein, the most preferred adsorption position is a somewhat eccentric position at the center of the hexagonal plane, and between the C atoms at the closest position to Li atoms Is 2.23 Å, and the binding energy of Li atoms is 2.21 eV / Li.

As shown in Fig. 1 (b), in Li-graphene, one Li atom has a binding energy of 2.69 eV / Li and is bonded to the hollow portion of the triangle. At this time, Li and C atoms have a shortest distance of 2.26 Å, and Li atoms are located at a height of 0.95 Å above the graphene sheet.

)의 응집에너지보다 작은 값의 Li 결합 에너지를 갖는 그래핀, 탄소나노튜브 및 풀러렌은 리튬 이온 배터리 음극물질로써 적합하지 않을 수 있다. 한편, 그래파인의 Li 결합에너지는

보다 상당히 크며, 따라서 Li 분리 없이 그래파인 상에서 Li 원자가 분산될 수가 있음을 알 수 있다.
The calculated binding energy of the Li atom in graphene is calculated from the corresponding GGA values of 1.10 eV / Li [Ref. 20], 1.80 eV / Li of C ₆₀ [Reference 21] 0.34 eV / Li (inner shell) and 0.41 eV / Li (outer shell) [Reference 22]. Thus, the theoretical and experimental values are 1.58 eV and 1.84 eV, respectively, and bulk Li (

), Graphene, carbon nanotubes and fullerenes having Li-bond energies less than the cohesive energy of lithium ion battery anode materials may not be suitable as lithium-ion battery cathode materials. On the other hand, the ligand binding energy of graphene is

And thus it can be seen that Li atoms can be dispersed on graphene without Li separation.

), Li 분산된 그래파인의 x 배열은 벌크 Li과 그래파인으로 분리된 상(phase)보다 에너지적으로 더 안정적이다. 도 2의 (a)(c)에서 굵은 점은 농도 x에 대해 가장 안정된 배열의 Li 결합에너지를 표시하고 있으며, 중공 점은 에너지 최소화 과정에서 확인된 다양한 국소 최소 배열의 Li 결합에너지를 나타내고 있다. 이로부터 알 수 있듯이, 단층(single layer) α- 또는 γ-그래파인에서의 Li 결합에너지는 여기서 고려된 Li 농도(x<3) 모두에 대해 응집에너지 보다 크다(또는 상당히 비슷). 다층(multilayer) 그래파인에서 Li 결합에너지는 레이어-레이어 상호작용에 의해 보다 증가할 수가 있다. α-그래파인의 또 다른 우수한 특징으로써 Li 원자는 면내(in-plane) 위치에서 흡착이 이루어지기 때문에 Li 삽입 또는 탈리 시에 체적 변화가 아주 작다는 것이다. 이러한 결과들에 의해 다층 그래파인은 음극물질로서 매우 효율적일 수 있다.Next, Li dispersion stability was examined in a single layer graphene. In a single layer of graphene, Li dispersion is easily generated and nucleation of Li atoms can occur. Fig. 2 shows the optimized geometry of the graphene in which Li is dispersed together with the binding energy of Li atoms in 2x2 graphene as a function of Li concentration x. FIG. 2 (b) shows an arrangement of x = 3 in alpha-graphene, and exactly four Li atoms are contained in each hexagon of the somewhat modified graphene. In the multi-layer graphene, since Li atoms are dispersed on one side of each graphene sheet, it is understood that only the one side of the sheet is adsorbed on the side in? -Grape. The x = 2 arrangement of γ-grapefine is shown in FIG. 2 (d), and most of the Li atoms are dispersed in the upper part of the triangle. When the Li bonding energy for the arrangement of the concentration x is larger than the cohesive energy (

), The x arrangement of Li dispersed graphene is more energetically stable than the phases separated by bulk Li and graphene. The thick points in FIGS. 2A and 2C indicate the Li binding energies of the most stable arrangement with respect to the concentration x, and the hollow points represent the Li binding energies of various local minimum arrangements confirmed in the energy minimization process. As can be seen from this, the Li bond energy in the single layer? - or? -Grapeane is greater than (or significantly similar to) the cohesive energy for all the Li concentrations here (x <3). Li bond energies in multilayer graphenes can be increased by layer-layer interactions. Another excellent feature of α-graphene is that the volume change is very small at the time of Li insertion or desorption because Li atoms are adsorbed in-plane. These results enable multilayer graphene to be very efficient as a cathode material.

The main advantages of intercalation compounds such as graphite in cathode materials are their high Li diffusion, small volume change due to intercalation of Li, long lifetime due to excellent reversibility of Li insertion / removal and excellent expandability. Similar to graphite, graphene having a multi-layer structure has excellent advantages as a lithium ion battery cathode.

In this embodiment, a multi-layer structure inserted between Li layers based on? - and? -Graffin was calculated. As described above, the stabilized graphene structure of a multi-layer structure inserted between Li layers was predicted by calculation of Li dispersion in a single-layer graphene. FIG. 3 shows an optimized geometry of a multi-layered a-graphene intercalated with Li bonding energy with Li bonding energy for different concentrations. In the α-graphene of the multilayer structure, it was confirmed that the laminate structure of the AB-type is preferable to the interlayer of Li interlayer. Figures 3 (b) and 3 (c) show side and cross-sectional views of a Li-intercalated α-graphene with x = 3 concentration, where the distance between layers is 3.1 Å. As shown in FIG. 3, as in the case of a single layer? -Grapeine, Li atoms are intercalated into an in-plane position of graphene, and up to four Li atoms are accommodated in the hexagons . On the other hand, in the γ-graphene of the multi-layer structure, AA-type lamination is advantageous for Li interlayer intercalation, and Li interlayer intercalation is performed between layers. Figures 4 (b) and 4 (c) show side and cross-sectional views of Li-intercalated γ-graphene, respectively, with x = 3 concentration, where the distance between the layers is 4.1 Å, Lt; RTI ID = 0.0 &gt; Li &lt; / RTI &gt; It was confirmed that the distance between the layers in the Li interlayer-inserted graphene was weakly dependent on the concentration (x). As expected, the binding energy of Li atoms in the graphene of the multi-layer structure increases somewhat compared to the graphene of the single-layer structure.

As shown in FIG. 4 (a), in the γ-graphene of the multi-layer structure, the Li bonding energy is larger than the cohesive energy of the bulk Li at a concentration lower than x = 3, and the Li atoms are intercalated without separation. In addition, Li clustering occurs at a high concentration (x> ~ 3), and the distance between layers can be increased up to ~ 50% from 4.1 Å due to Li clustering. On the other hand, the large nucleation barrier is related between the Li nucleation arrays and the x = 3 arrays, so the structure of the Li intercalated γ-grapple maximal complex can be expected to be C ₆ Li ₃ . On the other hand, due to the large nucleation threshold between the array with the concentration (x) of ~ 2.5 and the Li separation array, the Li bond energy near the ~3 concentration is somewhat smaller than the aggregation energy of the bulk Li, Li atoms can also be intercalated without the separation of Li in? -Graffin. Therefore, the structure of the maximal complex for Li intercalated α-graphene is expected to be C ₆ Li ₃ as well for Li clustering at x> 3. The specific capacity of this complex corresponds to 1116 mAh / g. Furthermore, the calculated volume capacities of α-graphene and γ-graphene intercalated multilayer structures are 1364 mAh / ㎤ and 1589 mAh / ㎤, respectively, which are all 818 mAh / ㎤, the capacity of graphite [ . This shows that the multi-layered graphene can be used as a lithium ion battery cathode material.

As described above, the present invention can be applied to the structure of Li layer intercalated multi-layered graphene as a lithium ion battery negative electrode material by using the principle principle of the first principle density function, The potential energy has an energy range suitable for the cathode material. The Li specific capacity of graphene of the multi-layer structure is considerably larger than the Li specific capacity (372 mAh / g) of graphite at about 1000 mAh / g. The volume capacity is ~ 1500 mAh / cm3, which is considerably larger than the volume capacity of graphite ~ 800 mAh / cm3. From the present invention, it can be seen that the multi-layered graphene is remarkably excellent as a high-capacity lithium ion battery cathode material.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. It will be apparent to those of ordinary skill in the art.

[references]

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[19] Monkhorst, HJ; Pack, JD 1976 Phys Rev B 13 5188.

[20] Chan, KT; Neaton, JB; Cohen, ML 2008 Phys Rev B 77 235430.

[21] Sun, Q .; Wang, Q .; Jena, P .; Kawazoe, Y. 2005 J Am Chem Soc 127 14582.

[22] Zhou, Z .; Gao, X .; Yan, J .; Song, D .; Morinaga, M. 2004 J Phys Chem B 108 9023.

Claims (6)

delete delete 1. A negative electrode material for a lithium battery capable of intercalating or deintercalating Li ions dispersed between respective layers of? -Grapeine in which nanoporous sheets are laminated,
The unit lattice structure of the α-graphene composite in which Li ions are positioned and eccentrically located at the center of the hexagonal lattice plane of the α-graphene and in which Li ions are inserted is C ₆ Li ₃ and the distance between the layers is 3.1 Å As a cathode material for lithium batteries. delete 1. A negative electrode material for a lithium battery capable of intercalating or deintercalating Li ions dispersed between respective layers of? -Grape, wherein nano-porous sheets are laminated,
The Li-ion is located on the upper or lower hollow portion of the triangular lattice plane of y-grape, and the unit lattice structure of the y-graphene complex into which Li ions are inserted is C ₆ Li ₃ , 4.1 &lt; RTI ID = 0.0 &gt; A. &lt; / RTI &gt; A lithium ion battery comprising the cathode material of claim 3 or claim 5.

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