WO2008136561A1

WO2008136561A1 - Anode material of secondary battery and secondary battery using the same

Info

Publication number: WO2008136561A1
Application number: PCT/KR2007/005433
Authority: WO
Inventors: Kyung-Hee Han; Jeong-Hun Oh; Jong-Sung Kim; Chul Youm; Jeong-Min Han
Original assignee: Ls Mtron, Ltd.
Priority date: 2007-05-03
Filing date: 2007-10-31
Publication date: 2008-11-13
Also published as: JP2010526409A; KR100817977B1

Abstract

The present invention relates to an anode material of a secondary battery and a secondary battery using the same. The anode material of a secondary battery according to the present invention is made of a mixture of a first core carbon material having sphericity greater than 10 but not greater than 100; and a second core carbon material having sphericity greater than 0 but not greater than 10, wherein a mixing weight ratio of the first core carbon material to the second core carbon material is 1:1 to 9: 1. The present invention reduces a phenomenon that the anode material is broken by a compression process in the manufacture of an electrode, thereby maintaining a high initial capacity and improving efficiency and cycleability of the battery.

Description

ANODE MATERIAL OF SECONDARY BATTERY AND SECONDARY BATTERY USING THE SAME

Technical Field

[1] The present invention relates to an anode material of a secondary battery and a secondary battery using the same, and in particular, to an anode material of a secondary battery, which is made of a mixture of a first core carbon material having sphericity greater than 10 but not greater than 100 and a second core carbon material having sphericity greater than 0 but not greater than 10, and thus can reduce a breakage phenomenon by a compression process in the manufacture of an electrode, thereby maintaining a high initial capacity and improving efficiency and cycleability of the battery, and a secondary battery using the same. Background Art

[2] As various portable electronic equipments such as video cameras, wireless phones, mobile phones or notebook computers spread into daily life rapidly, the demand for a secondary battery as a power source increased considerably. Among the secondary battery, a lithium secondary battery has excellent battery characteristics such as large capacity and high energy density, and thus is used more widely than other secondary batteries.

[3] The lithium secondary battery comprises basically a cathode, an anode and an electrolyte, and accordingly research and development of the lithium secondary battery includes largely studies about a cathode material, an anode material and an electrolyte.

[4] A natural graphite used as an anode material of the lithium secondary battery has an excellent initial capacity, but low efficiency and cycleability. It is known that this drawback results from a decomposition reaction of an electrolyte liquid occurring at an edge portion of the natural graphite of high crystallinity.

[5] To solve the problem, Japanese Patent Application No. 2002-084836 discloses characteristics of graphite, in which an edge portion of a crystal of a core carbon material is partially or wholly coated with a carbon material for coating. The above-mentioned patent application teaches a coating technique for improving characteristics when preparing an anode material. However, the above-mentioned patent application does not mention a technique for mixing carbon materials having different sphericities to improve characteristics.

[6] And, in the case that a natural graphite is used as an anode material, the anode material itself has an edge portion, and furthermore during a compression process in the manufacture of an anode, the anode material does not maintain its shape and is broken, and thus the edge portion of the anode material is increased. Accordingly, a battery using the natural graphite as the anode material experiences severer reduction of efficiency and cycleability.

[7] Therefore, attempts have been made in the related industry to solve the above- mentioned conventional problems, and the present invention was devised under this technical background. Disclosure of Invention Technical Problem

[8] An object of the present invention is to provide an anode material of a secondary battery, which can solve a phenomenon that efficiency and cycleability of a battery are reduced when a natural graphite is used as an anode material of a battery, and a secondary battery using the same. Technical Solution

[9] In order to achieve the above-mentioned object, an anode material of a secondary battery is made of a mixture of a first core carbon material having sphericity greater than 10 but not greater than 100; and a second core carbon material having sphericity greater than 0 but not greater than 10, wherein a mixing weight ratio of the first core carbon material to the second core carbon material is 1:1 to 9: 1.

[10] Preferably, the first core carbon material is a spherical natural graphite.

[11] Preferably, the second core carbon material is a plate-shaped natural graphite.

[12] And, the first core carbon material or the second core carbon material may be surface-coated with a low crystallinity carbon.

[13] In order to achieve the above-mentioned object, a secondary battery comprises an anode made of the above-mentioned anode material. Best Mode for Carrying Out the Invention

[14] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[15] The present invention coats a natural graphite with a low crystallinity carbon and mixes core carbon materials having different sphericities with each other to reduce a phenomenon that an anode material is broken during a compression process and to improve efficiency and cycleability of a battery as proved through a charge/discharge test of the battery.

[16] Hereinafter, the sphericity used in the present invention may be deducted from the following Math Rgure 1 by measuring 110 surface intensity and 004 surface intensity of a graphite material using an X-ray diffractometer.

[17] MathHgure 1

[Math.l]

SPHERICITY - INTENSITY OF 110 SURFACE

INTENSITY OF 004 SURFACE

[18] The anode material of a secondary battery according to the present invention is a mixture of a first core carbon material having sphericity greater than 10 but not greater than 100, and a second core carbon material having sphericity greater than 0 but not greater than 10, wherein a mixing weight ratio of the first core carbon material to the second core carbon material is 1: 1 to 9:1.

[19] Preferably, the first core carbon material is a spherical natural graphite. In the case that the sphericity of the first core carbon material meets the above-mentioned numerical range, it is preferable because a sub-reaction between an anode active material and an electrolyte liquid is maintained at a proper level. And, in the case that the first core carbon material is a spherical natural graphite, it is preferable because a sub-reaction between an anode active material and an electrolyte liquid occurs to a proper level and a filling density of the anode active material is proper.

[20] Preferably, the second core carbon material is a plate-shaped natural graphite. In the case that the sphericity of the second core carbon material meets the above-mentioned numerical range, it is preferable because a characteristics improving effect obtained by mixing the core carbon materials is sufficient. And, in the case that the second core carbon material is a plate-shaped natural graphite, it is preferable because a characteristics improving effect, especially a compression characteristics effect obtained by mixing the core carbon materials is proper. [21] It is preferable to mix the first core carbon material with the second core carbon material with a mixing weight ratio of 1 : 1 to 9: 1. In the case that the mixing weight ratio of the core carbon materials having different sphericities meets the above- mentioned range, it is preferable because a mixing effect of the core carbon materials is sufficiently and an unnecessary sub-reaction with an electrolyte liquid does not occur.

[22] And, the first core carbon material and second core carbon material may be coated with a low crystallinity carbon, each or both, if necessary.

[23] The low crystallinity carbon may be pitch, tar, a phenol resin, a furan resin or a furfurly alcohol. At this time, efficiency and cycleability of a battery may vary depending on a surface energy ratio of the low crystallinity carbon to the core carbon material. Therefore, it is preferable to select the kind of the low crystallinity carbon properly.

[24] The core carbon material may be coated by the following method.

[25] Hrst, a low crystallinity carbon and a core carbon material are dry-mixed. Next, the mixture is sintered at temperature of 800 to 3,000 ⁰C for 1 to 5 hours, and classified to remove fine powder. The core carbon material is surface-coated such that an edge portion of the core carbon material is partially or wholly coated with the low crystallinity carbon.

[26] A conductive agent or binder may be selectively added with a small amount to a slurry for manufacturing an electrode plate including the above-mentioned anode material according to necessity.

[27] The content of the conductive agent or binder may be adjusted properly to a typical level used in the prior art, and the content range does not influence the present invention.

[28] The conductive agent is not limited to a specific material if it is an electronically conductive material that does not bring about a chemical change in the battery. For example, the conductive agent may be carbon black such as acetylene black, Ketjen black, furnace black or thermal black; a natural graphite; an artificial graphite; or a conductive carbon fiber, and in particular, it is preferable to use carbon black, graphite powder or carbon fiber.

[29] The binder may be a thermoplastic resin, a thermosetting resin or a mixture thereof.

In particular, preferably the binder may be polyvinylidene fluoride (PVDF) or polyte- trafluoroethylene (PTFE), more preferably polyvinylidene fluoride.

[30] The slurry for manufacturing an electrode plate including the anode material and se- lectively at least one of the conductive agent and the binder is coated on an electrode collector, and dried to remove a solvent or dispersion medium, so that anαie materials are stuck to the electrode collector and the anode materials are stuck together.

[31] The electrode collector is not limited to a specific material if it is made of a conductive material, however in particular, it is preferable to use a foil made of copper, gold, nickel, a copper alloy or combination thereof.

[32] And, in a secondary battery of the present invention comprising a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte, the anode is made of the anode material prepared by the above-mentioned preparing me thod.

[33] The secondary battery of the present invention may be manufactured by a typical method used in the prior art, i.e. interposing a porous separator between a cathode and an anode and adding an electrolyte.

[34] The electrolyte is a non-aqueous electrolyte liquid including a lithium salt and an electrolyte liquid compound, and the lithium salt may be at least one compound selected from the group consisting of LiClO , LiCF SO , LiPF , LiBF , LiAsF and

4 3 3 6 4 6

LiN(CF SO ) . And, the electrolyte liquid compound may be at least one compound selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and methyl propyl carbonate (MPC).

[35] Preferably, the separator of the present invention is a porous separator, for example polypropylene-based, polyethylene-based or poly-olefin-based porous separator.

[36] The secondary battery of the present invention is not limited to a specific shape, however may be manufactured in various shapes without limitation, for example cylindrical, angular, pouch-shaped or coin-shaped using a can. Mode for the Invention

[37] Hereinafter, the present invention will be described in detail through examples and comparative examples for better understanding.

[38] The sphericity of the following examples and comparative examples was measured using an X-ray dffractometer. At this time, a scan range was 20 to 80°, a step size was 0.02°, and a scanning speed was 0.4 s/step. And, a standard material was Si powder (-325 mesh, 99%). The Si powder was mixed with a content of about 15 to 20 weight% in each sample, and a peak location of the measured data was compensated using data measured from Si powder only. The sphericity was measured from an intensity value of a peak (77.6°) representing 110 surface and an intensity value of a peak (53.2 to 54.7°) representing 004 surface using XRD data measured by the above-mentioned method.

[39] Example 1

[40] 20 weight% of pitch was dry-mixed with a spherical natural graphite at a high speed for about 10 minutes to produce a mixture. The mixture was sintered at 1,100⁰C and 2,200⁰C for 1 hour, respectively, and classified to remove fine powder, thereby preparing an anode material having sphericity of 37.1. At this, time, sphericity was measured through XRD analysis. 90 weight% of the natural graphite having sphericity of 37.1 was mixed with 10 weight% of a natural graphite having sphericity of 5.3 at a low speed.

[41] 100 g of the anode material prepared by mixing the carbon materials having different sphericities were put into a reactor of 500 m-d, and N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added with a small amount. And, the mixture was mixed using a mixer to prepare a slurry for manufacturing an electrode plate. Next, the prepared slurry for manufacturing an electrode plate was compression- dried on a copper foil and used as an electrode.

[42] Example 2

[43] This example 2 was carried out by the same method as the example 1 , except that a natural graphite having sphericity of 37.1 was used with a content of 80 weight%, and a natural graphite having sphericity of 5.3 was used with a content of 20 weight%.

[44] Example 3

[45] This example 3 was carried out by the same method as the example 1, except that a natural graphite having sphericity of 37.1 was used with a content of 70 weight%, and a natural graphite having sphericity of 5.3 was used with a content of 30 weight%.

[46] Example 4

[47] This example 4 was carried out by the same method as the example 1 , except that a natural graphite having sphericity of 37.1 was used with a content of 60 weight%, and a natural graphite having sphericity of 5.3 was used with a content of 40 weight%.

[48] Example 5

[49] This example 5 was carried out by the same method as the example 1, except that a natural graphite having sphericity of 37.1 was used with a content of 50 weight%, and a natural graphite having sphericity of 5.3 was used with a content of 50 weight%.

[50] Example 6

[51] 10 weight% of pitch was dry-mixed with a spherical natural graphite at a high speed for about 10 minutes to produce a mixture. The mixture was sintered at 1,100⁰C and 2,200⁰C for 1 hour, respectively, and classified to remove fine powder, thereby preparing a carbon material having sphericity of 37.1. At this time, sphericity was measured through XRD analysis.

[52] Next, 5 weight% of pitch was dry-mixed with a plate-shaped natural graphite at a high speed for about 10 minutes to produce a mixture. The mixture was sintered at 1,100⁰C for 1 hour and classified to remove fine powder, thereby preparing a carbon material having sphericity of 8.9.

[53] 90 weight% of the natural graphite having sphericity of 37.1 was dry-mixed with 10 weight% of the natural graphite having sphericity of 8.9 at a low speed.

[54] 100 g of an anode material prepared by mixing the carbon materials having different sphericities was put into a reactor of 500 rn-C, and N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added with a small amount. Next, the mixture was mixed using a mixer to prepare a slurry for manufacturing an electrode plate. And, the prepared slurry for manufacturing an electrode plate was compression- dried on a copper foil and used as an electrode.

[55] Comparative example 1

[56] 20 weight% of pitch was dry-mixed with a spherical natural graphite at a high speed for about 10 minutes to produce a mixture. The mixture was sintered at 1,100⁰C and 2,200⁰C for 1 hour, respectively, and classified to remove fine powder, thereby preparing an anode material having sphericity of 37.1. At this time, sphericity was measured through XRD analysis.

[57] 100 g of the anode material was put into a reactor of 500 m-6, and N- methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added with a small amount. Next, the mixture was mixed using a mixer to prepare a slurry for manufacturing an electrode plate. Subsequently, the prepared slurry for manufacturing an electrode plate was compression-dried on a copper foil and used as an electrode.

[58] Comparative example 2

[59] This comparative example 2 was carried out by the same method as the example 1, except that 15 weight% of pitch was dry-mixed with a spherical natural graphite at a high speed for about 10 minutes to produce a mixture.

[60] Coin cells were manufactured using the electrodes of the above examples 1 to 6 and the comparative examples 1 and 2. Next, charge and discharge characteristics of the coin cells were tested by the following method, and results of the test are shown in the following Table 1.

[61] First, the charge/discharge test was performed such that the coin cell was charged with a charge current of 0.5 mA/crf until a voltage is 0.01 V while an electrical potential was limited to the range of 0 to 1.5 Y and was continuously charged until the charge current is 0.02 mA/cπf while maintaining the voltage at 0.01 V. And, discharge was performed with a discharge current of 0.5 mA/cnf until the voltage is 1.5 V. In the following Table 1, the charge/discharge efficiency is a ratio of a discharged electrical capacity to a charged electrical capacity.

[62] Table 1 [Table 1] [Table ]

[63] As shown in the above Table 1, it is found that, when compared with the comparative examples 1 and 2, the examples 1 to 6 each maintains an advantage of a natural graphite, i.e. a high initial capacity and improves efficiency and cycleability of a battery.

[64] As such, the preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability

[65] The present invention reduces a phenomenon that an anode material is broken by a compression process in the manufacture of an electrode, thereby maintaining a high initial capacity and improving efficiency and cycleability of a battery.

Claims

[1] An anode material of a secondary battery, made of a mixture comprising: a first core carbon material having sphericity greater than 10 but not greater than

100; and a second core carbon material having sphericity greater than 0 but not greater than 10, wherein a mixing weight ratio of the first core carbon material to the second core carbon material is 1:1 to 9: 1. [2] The anode material of a secondary battery according to claim 1, wherein the first core carbon material is a spherical natural graphite. [3] The anode material of a secondary battery according to claim 1, wherein the second core carbon material is a plate-shaped natural graphite. [4] The anode material of a secondary battery according to claim 1, wherein the first core carbon material is coated with a low crystallinity carbon. [5] The anode material for a secondary battery according to claim 1, wherein the second core carbon material is coated with a low crystallinity carbon. [6] The anode material of a secondary battery according to claim 4 or 5, wherein the low crystallinity carbon is any one selected from the group consisting of pitch, tar, a phenol resin, a furan resin and a furfurly alcohol, or mixtures thereof. [7] A secondary battery, comprising an anode made of the anode material defined in any one of claims 1 to 6.