KR20190073758A - Method for purifying graphite materials and graphite materials - Google Patents

Abstract

The present invention relates to a method for purifying a graphite material, which provides a graphite material of high purity by improving a removal rate of metal impurities, and a graphite material thereof. The method for purifying a graphite material of the present invention comprises the steps of: preparing a graphite material; and heat-treating the graphite material in an atmosphere including a reductive reaction gas.

Description

METHOD FOR PURIFYING GRAPHITE MATERIALS AND GRAPHITE MATERIALS FIELD OF THE INVENTION [0001]

The present invention relates to a method for purifying graphite materials and graphite materials.

As the price of energy sources increases due to the depletion of fossil fuels and the interest of environmental pollution is amplified, environmentally friendly alternative energy sources become indispensable factors for future life. In particular, as technology development and demand for mobile devices increase, the demand for rechargeable batteries as an environmentally friendly alternative energy source is rapidly increasing.

Lithium secondary batteries conventionally used lithium metal as a cathode, but the risk of short-circuiting of the battery due to formation of dendrite and explosion thereof is a problem, reversible intercalation and desorption of lithium ions are possible , And the use of carbon-based active materials that maintain their structural and electrical properties.

As carbon-based active materials, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon have been applied and carbon-based compounds capable of intercalating and desorbing reversible lithium ions while maintaining structural and electrical properties, In particular, graphite based materials are mainly used, and graphite based materials are most widely used as graphite based active materials capable of ensuring lifetime characteristics of lithium secondary batteries with excellent reversibility.

Since the discharge voltage of the graphite-based active material is as low as -0.2 V, the battery using the graphite-based active material can exhibit a high discharge voltage of 3.6 V, thereby providing many advantages in terms of energy density of the lithium battery, Side compounds such as the theoretical maximum capacity limit, the deterioration of the battery productivity due to the hydrophobicity of the carbon-based compound, and the alloying of metal impurities except for insertion and desorption of ions generated in the graphite cathode during charging and discharging of the secondary battery, Which negatively affects the performance and safety of the secondary battery.

An object of the present invention is to provide a method for purifying a graphite material, which is capable of effectively removing metal impurities in a graphite material to produce a high-purity graphite material.

The present invention provides a purified graphite material by the method for purifying graphite material according to the present invention.

The present invention provides an electrode material comprising the graphite material of the present invention.

The present invention provides an electrode including the electrode material according to the present invention.

The present invention provides a lithium secondary battery comprising the electrode according to the present invention.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

According to one embodiment of the present invention,

Preparing a graphite material; And heat treating the graphite material in an atmosphere containing a reducing reaction gas; To a process for purifying graphite material.

According to an embodiment of the present invention, the reducing reaction gas may include chlorine gas.

According to one embodiment of the present invention, the chlorine-containing gas may be one containing HCl, Cl _2, or both.

According to an embodiment of the present invention, the chlorine-containing gas may be 0 to 50 vol% or less of the gas forming the atmosphere.

According to one embodiment of the present invention, the step of heat-treating may be performed at a heat treatment temperature of 1500 ° C to 2500 ° C for 1 to 30 days.

According to an embodiment of the present invention, the step of heat-treating may include heating the substrate to a heat treatment temperature in a vacuum or an inert atmosphere, injecting a reducing reaction gas at the reaction temperature, and heat-treating the substrate.

According to one embodiment of the present invention, the graphite material after the heat treatment may contain less than 1 ppm to less than 200 ppm metal impurities.

According to an embodiment of the present invention, among the graphite materials after the heat treatment, Fe may be 0.1 ppt to 100 ppm or less.

The total amount of Cr, Zn, Ni, Cu, Co, Al, Si, K, Mn, Ca and Mg in the graphite material after the heat treatment may be 1 ppm to 200 ppm have.

Another aspect of the present invention relates to a graphite material which is heat-treated by the method of purifying graphite material according to the present invention and contains metallic impurities of 1 ppm to less than 200 ppm.

Another aspect of the present invention relates to an electrode active material comprising a graphite material according to the present invention.

Another aspect of the present invention relates to an electrode comprising an electrode active material according to the present invention.

Another aspect of the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the negative electrode comprises the electrode according to the present invention.

The present invention can improve the removal efficiency of metal impurities in a graphite material to provide a high-purity graphite material, suppress side reactions occurring in the electrodes of the energy storage device, and improve the performance and safety of the energy storage device.

In the following, embodiments will be described in detail with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

Various modifications may be made to the embodiments described below. It is to be understood that the embodiments described below are not intended to limit the embodiments, but include all modifications, equivalents, and alternatives to them. The terms used in the examples are used only to illustrate specific embodiments and are not intended to limit the embodiments. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like refer to the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this embodiment belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

The present invention relates to a method of purifying graphite materials.

According to an embodiment of the present invention, the manufacturing method can effectively remove metal impurities in the graphite material through the heat treatment cleaning using a reducing reaction gas to provide a high purity graphite material.

According to one embodiment of the present invention, the method comprises: preparing a graphite material; And heat treating the graphite material; . ≪ / RTI >

As an example of the present invention, the step of preparing the graphite material may be prepared in the form of a powder or bulk of a graphite material, and the graphite material may be processed for heat treatment cleaning.

For example, the graphite material may include at least one selected from the group consisting of graphite, carbon black, natural graphite, artificial graphite, and expanded graphite.

For example, the graphite material may have a thickness of 1 占 퐉 or more; Average 1 占 퐉 to 50 占 퐉; Or an average particle size of 5 [mu] m to 100 [mu] m, the graphite material being capable of controlling the particle size, if necessary, by a pulverizing process.

For example, the milling process may utilize mechanical milling, and the mechanical milling may be accomplished using a variety of methods, including rotor milling, mortar milling, ball milling, planetary ball milling, jet milling, bead milling, (air classifier mill, ACM), and atraction milling.

For example, the graphite material may use anisotropic graphite and isotropic graphite, respectively, and may include mixed graphite, wherein the mixed graphite has a mixing ratio of anisotropic graphite to isotropic graphite of 1: 0.1 to 0.1: 1 (w / w). When the graphite material is applied to an electrode, a high capacity by anisotropic graphite and a reversible effect by isotropic graphite can be combined to improve electrode performance.

In one embodiment of the present invention, the step of heat-treating the graphite material is a step of introducing the graphite material obtained after the step of preparing the graphite material into a heat treatment equipment and heat-treating the graphite material.

For example, the heat treatment equipment may be an electric furnace, an induction furnace, a microwave sintering furnace, or the like.

For example, in the step of heat-treating the graphite material, the graphite material may be cleaned by heat treatment in an atmosphere containing a reducing reaction gas.

For example, the reducing reaction gas may be a chlorine-containing gas, for example, HCl, Cl _2, or both, and the reducing reaction gas may increase the removal rate of metal impurities in the graphite material at a high temperature .

For example, the removal rate of the specific metal in the graphite material may be increased depending on the kind and / or mixing ratio of the reducing reaction gas, and the mixing ratio of HCl to Cl ₂ is 1: 0.1 to 1 (v / v); 1: 0.2 to 8 (v / v); Or 1: 0.5 to 7 (v / v).

For example, the atmosphere containing the reducing reaction gas may include the reducing reaction gas alone or a mixed gas of the reducing reaction gas and the inert gas.

For example, the reducing reaction gas, for example, the chlorine-containing gas may be used in an amount of more than 0 to 50% by volume of the gas forming the atmosphere; 5 to 50% by volume; 10 to 20% by volume. If it is contained in the above volume percentage, metal impurities can be removed smoothly.

For example, the step of heat treating the graphite material may be performed at a temperature of 1500 to 2500 占 폚; 1700 DEG C to 2500 DEG C; Or at a heat treatment temperature (or reaction temperature) of 1900 ° C to 2500 ° C for 1 day or more; 1 to 10 days; 2 to 20 days; Or for 4 to 30 days. If the temperature is within the time range, the removal rate of metal impurities in the graphite material can be increased.

For example, the step of heat-treating the graphite material may include heating the graphite material to a heat treatment temperature in an atmosphere of vacuum, an inert gas atmosphere or both, A lower temperature of 200 DEG C or lower than the heat treatment temperature; A low temperature of 100 DEG C or lower; A low temperature of 50 캜; A low temperature of 10 DEG C or lower; Or by introducing a reducing reaction gas at the same temperature as the heat treatment temperature. This makes it possible to prevent the coagulation and porosity between the graphite materials due to the heat treatment at a high temperature due to sufficient heat transfer in the graphite material and to improve the removal rate of metal impurities in the graphite material by the introduction of the reducing reaction gas. This is because the reducing reaction gas can form an atmosphere with the composition, the ratio, and the like as mentioned above.

For example, the heating rate may be 5 ° C / min or more; 30 DEG C / min or more; 5 DEG C / min to 500 DEG C / min; Or 100 [deg.] C / min to 300 [deg.] C / min.

The present invention relates to a high purity graphite material obtained by high purification by the method of purifying graphite material according to the present invention.

In one embodiment of the present invention, the high purity graphite material has a purity of less than 1 ppm to less than 200 ppm; 1 ppm to 150 ppm; 1 ppm to 100 ppm of metal impurities. The graphite material of high purity can reduce the content of metal impurities such as Fe and minimize the side reaction when applied to an energy storage device such as an electrode of a lithium secondary battery, thereby preventing deterioration due to electrode expansion and collapse .

For example, Fe in the high purity graphite material may be in the range of 0.1 ppt to 100 ppm or less; 0.1 ppb to 80 ppm; 1 ppt to 50 ppm; Or from 1 ppt to 30 ppm.

For example, the total amount of Cr, Zn, Ni, Cu, Co, Al, Si, K, Mn, Ca and Mg in the high purity graphite material is 1 ppm to 200 ppm; 1 ppb to 300 ppm; Or from 1 ppb to 400 ppm.

For example, the content of the metallic impurities may be measured by GDMS (Glow Discharge Mass Spectrometer) or ICP-MS (inductively coupled plasma mass spectrometer) analysis method.

The present invention relates to an electrode material comprising a high purity graphite material produced by the method for purifying graphite according to the present invention.

According to an embodiment of the present invention, since the electrode material uses a high-purity graphite material, it is possible to provide an electrode and an energy storage device capable of minimizing side reactions due to an alloying reaction due to metal impurities and stable operation.

In one embodiment of the present invention, the electrode material is a negative electrode active material of a lithium secondary battery, for example, a high purity graphite material according to the present invention; Alternatively, the high purity graphite material may be further mixed with a conventional negative electrode active material used in the technical field of the present invention.

For example, the conventional negative electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. More specifically, for example, carbon, a lithium metal, a lithium-based alloy, a silicon- Metal alloys, metal oxides, carbon, etc., and more specifically, lithium titanium oxide (LTO); _{Li x Fe 2 O 3 (0} <x≤1), Li x WO 2 (0 <x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge, Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen, 0 < x < Lithium metal; A lithium alloy (Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd or an alloy of Si and lithium); Silicon alloy; Tin alloy; Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO ₂ , GeO ₂ , Bi ₂ O ₃ , SiO x (0 <x <2), SnO ₂ , SnO ₂ , PbO, PbO ₂ , ₂ O ₃ , Bi ₂ O ₄ , MoO ₂ , MoO ₃ , V ₂ O ₅ , Li _{1 + x} V _{1 - x} O ₂ And Bi ₂ O ₅ ; Tin oxide compounds; Titanium oxide; A conductive polymer such as polyacetylene, a Li-Co-Ni-based material, a soft carbon, a hard carbon, and the like, but is not limited thereto.

The present invention relates to an electrode including an electrode material according to the present invention.

According to an embodiment of the present invention, the electrode may be a cathode of an energy storage device, for example, a lithium secondary battery.

In one example of the present invention, the negative electrode includes a negative electrode collector and an electrode material according to the present invention. For example, a mixture of a negative electrode active material, a conductive material and a binder is coated on the negative electrode collector, followed by drying and rolling . Further, the mixture may further contain a filler.

For example, the negative electrode collector may have a thickness of from 3 탆 to 500 탆, preferably from 8 탆 to 300 탆, and if it does not cause a chemical change in an energy storage device, for example, a lithium secondary battery, For example, copper, aluminum or stainless steel surface-treated with copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or carbon, nickel, titanium, silver or the like; A polymer substrate coated with a conductive metal and the like and may have various shapes such as a foil, a film, a sheet, a net, a porous body, a foam, and a nonwoven fabric, and the adhesive force of an electrode material (for example, an anode active material) Fine irregularities may be formed on the surface of the current collector in order to raise it, but the present invention is not limited thereto.

For example, the conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in an energy storage device, for example, a lithium secondary battery, for example, graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives; Or the like, but is not limited thereto.

For example, the binder is a component that assists in binding of the components in the mixture and bonding of the electrode material to the substrate to be coated, and is used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the electrode material (for example, the negative electrode active material) And may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) But are not limited to, sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber or various copolymers.

For example, the filler is a component that suppresses the expansion of the negative electrode and is not particularly limited as long as it does not cause chemical changes in an energy storage device, for example, a lithium secondary battery, and is a fibrous material. , Olefin polymers such as polypropylene; Fibrous materials such as glass fibers and carbon fibers; Or the like, but is not limited thereto.

For example, the mixture may further comprise an additive applicable to form a negative electrode according to the technical field of the present invention, and this specification is not specifically referred to.

The present invention relates to an energy storage device comprising an electrode according to the present invention.

According to an embodiment of the present invention, the energy storage device may be a lithium secondary battery, and the lithium secondary battery may include a negative electrode; An anode, a separator, and an electrolyte, and the cathode may include an electrode according to the present invention.

In one example of the present invention, the anode includes a cathode current collector and a cathode active material. For example, the anode active material, the solvent, the conductive material, and the electrode material slurry of the binder are coated on the cathode current collector, followed by drying and rolling . Further, the mixture may further contain a filler.

For example, the positive electrode collector may have fine unevenness on the surface like the negative electrode collector to increase the adhesion of the positive electrode active material, and may have various shapes. The cathode can be produced by a conventional method in the art, and the present specification is not specifically referred to.

For example, the cathode active material is a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound), and more specifically, a transition metal such as cobalt, manganese, nickel, or aluminum Or a lithium-transition metal oxide including lithium. Further, the lithium transition metal oxide may be a lithium-nickel-manganese-cobalt oxide, a lithium-nickel-aluminum-cobalt oxide, a lithium-manganese oxide, a lithium- More specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (NiaCobMnc) O ₂ (where 0 <a <1, 0 <b < 1, a + b + c = 1), Li (NiaCobAlc) O ₂ (where 0 <a < _{LiNi 1 - Y Co Y O 2} , LiCo 1 - Y Mn Y O 2, LiNi 1 - Y Mn Y O 2 ( here, 0≤Y <1), Li ( Ni a Co b Mn c) O 4 (0 2, 0 <b <2, a + b + c = 2), LiMn _{2 - z} Ni _z O ₄ , LiMn _{2 - z} Co _z O ₄ where 0 <Z _{<2), LiCr x Mn 2} - x O 4 (0≤x≤0.5), LiCo x Mn 2 - x O 4 (0≤x≤1.0), LiNi x Mn 2-x O 4 (0≤x≤0.5 ), LiCu _x Mn _{2 - x} O ₄ (0? _X ? 0.5), xLi ₂ MnO _{3 - (1-x)} LiNi _a Co _b Mn _c O ₂ (a + b + c = 1) It is not limited.

In one embodiment of the present invention, the electrolytic solution is a nonaqueous electrolytic solution and may be impregnated into the positive electrode, negative electrode and separator. For example, the non-aqueous liquid electrolyte may include a lithium salt; Organic solvent; And conventional additives such as LiBF ₄ , LiClO ₄ , LiPF ₆ , LiSbF ₆ , LiAsF ₆ , Li (C ₂ F ₅ SO ₃ ) ₂ N, LiCF ₃ SO ₃ , Li (CF _{3 SO 2) 2 N, LiC} 4 F 9 SO 3, Li (CF 3 SO 2) 3 C, LiBPh 4, LiAlO 4, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y + ₁ SO ₂ ) ( ₁ ? X? 3 and ₁ ? Y? ₃ ), LiB (C ₂ O ₄ ) ₂ , LiBF ₂ C ₂ O ₄ And LiB ₁₂ H _{12 - x} F _x (0 _{? X? 12} ). The organic solvent may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, At least one cyclic carbonate-based organic solvent selected from the group consisting of 2,3-pentylene carbonate; And dimethyl carbonate, DEC (dimethyl carbonate), EMC (ethylmethyl carbonate), DME (1,2-dimethoxyethane), DPC (dipropyl carbonate), MPC (methyl propyl carbonate) Linear or higher carbonate-based organic solvents; Ester solvents such as methyl acetate, ethyl acetate, -butyrolactone, and epsilon -caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; And ketone-based solvents such as cyclohexanone, and the like, but are not limited thereto.

In one embodiment of the present invention, the separation membrane is provided between the anode and the cathode to block electrical contact between the anode and the cathode, and moves the lithium ion. The separator is disposed between the anode and the cathode, and has insulating properties with high ion permeability and mechanical strength. It may be a thin film having porosity. For example, the separation membrane may have a thickness of 3 to 500 μm, preferably 5 to 300 μm, and may be formed of a sheet, a multilayer, an olefinic polymer such as polyethylene or polypropylene, Film, woven fabric, and nonwoven fabric, and may be an inorganic or organic composite porous separator prepared from a slurry containing inorganic particles, a binder polymer, and a solvent and having a greatly enhanced safety, but the present invention is not limited thereto.

The lithium secondary battery according to the present invention can be further modified and added to the known constitution in the technical field of the present invention and manufactured by a method known in the technical field of the present invention, but the present application is not specifically mentioned.

The present invention is not limited thereto but may be embodied in other specific forms without departing from the spirit or scope of the present invention as set forth in the following claims, The present invention can be variously modified and changed.

Example 1

HCl and Cl ₂ gas (HCl: Cl ₂ = 1: 1) and N ₂ gas were injected into the electric furnace, and the graphite (product name: HCl-20, particle size: 20 μm) To form an atmosphere composed of 20 vol% of HCl gas and heat-treated.

Example 2

Graphite (trade name: HCl-20, particle size: 20 ㎛) were placed in an electric furnace, heated in a vacuum atmosphere, and after the reaction temperature reached by injecting a HCl gas and the N ₂ gas atmosphere consisting of HCl / Cl ₂ gas 20% by volume And heat treated.

Example 3

Graphite (trade name: HCl-20, particle size: 20 ㎛) were placed in an electric furnace, to form an atmosphere consisting of a Cl ₂ gas of 20 volume% by heating in a vacuum atmosphere, and after the reaction temperature reached injecting a Cl ₂ gas and the N ₂ gas And heat treated.

Comparative Example

Graphite was highly purified in the same manner as in Example 1 except that HCl and Cl ₂ gas were not introduced and heat treatment was conducted.

Test Example

The content of metal impurities was measured using ICP-MS of high-purity graphite of Examples 1 to 3 and Comparative Examples, and it is shown in Table 1.

metal
(ppm) Fe Cr Zn Ni Ca Al Cu Si Mg K Co Mn Example 1 58.6 26.9 4.3 8.4 25.4 6.2 0.2 8.5 50.5 2.5 0.3 0.6 Example 2 55.0 13.5 2.4 91.2 40.7 5.7 0.2 7.5 72.3 3.6 0.4 0.6 Example 3 54 18.4 2.2 89.4 41.0 7.0 0.21 6.4 73.5 4.0 0.4 0.61 Comparative Example 1210 26.9 4.3 90.4 123.1 25.3 0.3 366.7 76.5 5.8 0.6 1.5

As shown in Table 1, it can be confirmed that the content of the metal impurities is significantly lowered in the case of the heat treatment purification using the reducing reaction gas according to the present invention, as compared with the comparative example in which the heat treatment is performed using the inert gas. This can effectively remove metal impurities by the reducing reaction gas in a high-temperature heat treatment environment, and can provide a lithium secondary battery which can minimize the side reaction in the lithium secondary battery and can operate stably.

Various modifications and variations may be made by those skilled in the art without departing from the scope of the present invention. For example, if the techniques described are performed in a different order than the described methods, and / or if the described components are combined or combined in other ways than the described methods, or are replaced or substituted by other components or equivalents Appropriate results can be achieved. Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (13)

Preparing a graphite material; And
Heat treating the graphite material in an atmosphere containing a reducing reaction gas;
/ RTI &gt;
Method of purifying graphite material.
3. The method of claim 2,
Wherein the reducing reaction gas comprises a chlorine-containing gas.
Method of purifying graphite material.
3. The method of claim 2,
Wherein the chlorine containing gas comprises HCl, Cl _2, or both.
Method of purifying graphite material.
3. The method of claim 2,
Wherein the chlorine-containing gas is 0.01 to 50 volume% of the gas forming the atmosphere.
Method of purifying graphite material.
The method according to claim 1,
Wherein the heat treatment is performed for 1 to 30 days at a heat treatment temperature of 1500 ° C to 2500 ° C.
Method of purifying graphite material.
The method according to claim 1,
Wherein the heat treatment step is a step of raising the temperature to a heat treatment temperature in a vacuum or an inert atmosphere and injecting a reducing reaction gas at the reaction temperature and performing heat treatment.
Method of purifying graphite material.
The method according to claim 1,
Wherein the graphite material after the heat treatment comprises less than 1 ppm to less than 200 ppm metal impurities.
Method of purifying graphite material.
The method according to claim 1,
Wherein, among the graphite materials after the heat treatment, Fe is 0.1 ppt to 100 ppm or less.
Method of purifying graphite material.
The method according to claim 1,
Wherein the total amount of Cr, Zn, Ni, Cu, Co, Al, Si, K, Mn, Ca and Mg in the graphite material after the heat treatment is 200 ppm or less.
Method of purifying graphite material.
A heat treatment method as claimed in claim 1,
RTI ID = 0.0 &gt; 1 ppm to &lt; / RTI &gt; 200 ppm,
Graphite material.
A graphite material according to claim 10,
Electrode material.
The electrode assembly of claim 11,
electrode.
An anode, a cathode, a separator, and an electrolyte,
Wherein the cathode comprises the electrode of claim 12. &lt; RTI ID = 0.0 &gt;
Lithium secondary battery.