KR20050104628A - Electrode for rechargeable lithium battery and rechargeable lithium battery comprising same - Google Patents

Abstract

The present invention relates to a lithium secondary battery electrode and a lithium secondary battery comprising the same, wherein the electrode comprises a core comprising an inert material; And a compound for an electrode including a coating layer including an alkali metal coated on the core.

Since the electrode for a lithium secondary battery of the present invention is coated with an alkali metal on the active material itself or includes a conductive material coated with an alkali metal, the lithium secondary battery electrode has excellent safety and excellent capacity and lifespan.

Description

ELECTRODE FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY COMPRISING SAME

[Industrial use]

The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery comprising the same, and more particularly, an electrode for a lithium secondary battery capable of providing a battery having an initial irreversible capacity and excellent energy density, and a lithium secondary battery comprising the same. It is about.

[Prior art]

Lithium secondary batteries are prepared by reversibly inserting and detaching lithium ions as a positive electrode and a negative electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions are inserted / desorbed at the positive electrode and the negative electrode. When produced, electrical energy is generated by oxidation and reduction reactions.

As a cathode active material, a chalcogenide compound is used. Examples thereof include a composite metal such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), and LiMnO ₂ . Oxides are being studied.

Lithium metal is used as a negative electrode active material of a lithium secondary battery. However, when lithium metal is used, there is a risk of explosion due to a short circuit of the battery due to the formation of dendrite. It is going to be replaced. However, these carbonaceous materials exhibit an irreversible characteristic of 5 to 30% during the initial several cycles, and these irreversible capacities consume lithium ions, preventing them from fully charging or discharging at least one active material, which is disadvantageous in terms of energy density of the battery. It works.

In addition, metal negative electrode active materials such as Si and Sn, which have recently been studied as high-capacity negative electrode active materials, have a larger problem of irreversible characteristics.

In order to solve this problem, U.S. Patent No. 5,948,569 discloses that a Group 1 element is attached to a separator or an electrode using a vacuum deposit method such as evaporation, sputtering, or the like. One method is described for positioning between the positive and negative electrodes. However, because this method uses a deposition process, the initial investment is high, the equipment is difficult to maintain, and the process speed is slow because it takes a lot of time to put the separator or electrode into the vacuum chamber and to make or exhaust the vacuum. have. In addition, Group 1 elements, in particular lithium metal adsorbed in the vacuum chamber during the deposition of lithium metal should be removed regularly, the reactivity is very high, there is a safety problem.

US Patent Publication No. 20020119373 describes a method for producing a negative electrode by uniformly mixing lithium metal powder with an active material. In this case, however, the density difference between the lithium metal and the active material is large, making it difficult to maintain a uniform form in the slurry manufacturing, coating, and drying process. Also, the lithium metal powder is dissolved during the initial charging and discharging process, and the remaining pores cause deformation of the electrode plate in the long term. There is a problem that may lower the life and battery reliability.

An object of the present invention is to provide an electrode for a lithium secondary battery that can reduce the initial irreversible capacity during battery charging and discharging.

Another object of the present invention is to provide a lithium secondary battery including the electrode.

In order to achieve the above object, the present invention comprises a core comprising an inert material; And it provides a lithium secondary battery electrode comprising a compound for electrodes comprising a coating layer comprising an alkali metal coated on the core.

Another object of the present invention is an anode; cathode; And an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises a core including an inert material; And it provides a lithium secondary battery comprising a compound for an electrode comprising a coating layer comprising an alkali metal coated on the core.

Hereinafter, the present invention will be described in more detail.

The present invention prevents a decrease in efficiency of the battery caused by the initial irreversible capacity of the active material when charging and discharging the battery, or when using an active material that does not contain lithium such as V ₂ O _5. By adding an alkali metal which can be utilized as a source of the electrode to remove the irreversible portion, the amount of the positive electrode active material used more than necessary is reduced, thereby increasing the battery capacity and improving safety.

An electrode for a lithium secondary battery of the present invention includes a core containing an inert material; And a compound for an electrode including a coating layer including an alkali metal coated on the core. That is, as shown in FIG. 1, the compound 10 for electrodes of this invention consists of the core 12 and the coating layer 14 formed in this core.

As said alkali metal, Li, Na or K is preferable and Li is the most preferable.

The electrode compound preferably has an average particle size of 70 μm or less, more preferably an average particle size of 50 μm or less, and most preferably an average particle size of 20 μm or less. Since the average particle size of the compound for electrodes does not have to exceed 70 μm and the lower limit cannot be less than 0 μm, it can be seen that the average particle size is larger than 0 μm without limiting the lower limit. If the average particle size of the electrode compound is larger than 70 µm, the high rate characteristic of the battery is lowered, which is not preferable.

The thickness of the coating layer is preferably 50 µm or less, preferably 30 µm or less, more preferably 10 µm or less, and most preferably 5 µm or less. The thickness of the coating layer does not have to exceed only 50 µm, and the lower limit cannot be less than 0 µm.

Ni, Cu, Ti, Au, Pt, Fe, Co, Cr or W may be used as the inert material.

In the electrode compound of the present invention, the amount of the alkali metal is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight based on 100 parts by weight of the total electrode compound. When the amount of the alkali metal is less than 1 part by weight, the effect of adding the alkali metal is hardly obtained, and a capacity improvement and safety improvement effect cannot be obtained. In addition, when the amount of the alkali metal exceeds 30 parts by weight, an excess amount of alkali metal fills the irreversible capacity and a surplus is generated, so that the remaining alkali metal occupies unnecessary space in the battery and may cause problems such as dendrites. Not desirable

The compound for an electrode of the present invention may be used as an active material causing a battery reaction in a lithium secondary battery electrode, or may be used as a material to supplement an irreversible capacity by using an additive together with a general active material. When the electrode compound of the present invention is used as an active material, as shown in FIG. 2, the electrode compound 10 of the present invention is applied to the current collector 20 as a whole to form an active material layer, thereby forming the electrode of the present invention ( 100a). When the electrode compound of the present invention is used as an additive, as shown in FIG. 3, the electrode compound 10 of the present invention is mixed with the active material 30 and coated on the current collector 20 to apply the active material layer. It forms and comprises the electrode 100b of this invention.

In the case of using the electrode compound of the present invention as an additive, as the active material, all of the active materials usable in the lithium secondary battery are generally usable, and thus the active material compounds described above may be used. At this time, the compound for electrodes of the present invention is preferably used in an amount sufficient to calculate the irreversible capacity of the active material and replenish its amount. That is, it is preferable to use the amount calculated by dividing the irreversible capacity by the theoretical capacity of the alkali metal. When the alkali metal is used in excess of an amount sufficient to supplement the irreversible capacity, it is not preferable because the alkali metal remains in the electrode plate, and the remaining alkali metal may cause dendrites and cause short problems.

Hereinafter, a method for preparing an electrode compound of the present invention will be described.

An alkali metal is deposited on the core material including the inert material. Since the materials used as the core material are materials that do not react with the alkali metal, when the alkali metal is deposited on the core material, the alkali metal is coated to form a coating layer on the surface of the core material. In other words, the resultant product is formed on the core material and the surface of the core material, and is composed of a coating layer containing an alkali metal. In FIG. 4, when the central material is Ni and the alkali metal is lithium, a process of performing a thermal evaporation deposition process is schematically illustrated. The lithium melt 406 is placed in the crucible 402, and Ni 404 is placed thereon, and the lithium is evaporated while dispersing using the dispersing propeller 408, whereby a coating layer is formed Ni. 400 is formed.

The deposition process may include sputtering, ion-beam-assist-deposit, or chemical vapor deposition (CVD) in addition to the thermal evaporation described above. It is preferable to implement, and thermal evaporation method is the most preferable among these.

Compared to the conventional process of depositing lithium metal on the electrode plate, the present invention provides alkali metal vapor such as lithium to an inert material and coats the inert material with an alkali metal, thereby producing an alkali metal generated in the method of depositing lithium on the electrode plate. Many shortcomings such as additional process costs such as maintenance due to pollution of the facility due to the facility can be solved. In addition, when the lithium powder is mixed with the active material and used, the disadvantages of structural instability due to pore formation can be solved by continuously supporting the structure as lithium is charged inside the active material through charging and discharging. have. In addition, since the lithium powder itself is not added to the active material composition in the present invention, when the lithium powder is mixed with the active material in the related art, the lithium powder is so light that there is no problem such as layer separation.

The lithium secondary battery of the present invention comprising the electrode compound of the present invention in an electrode includes a positive electrode, a negative electrode and an electrolyte, and at least one of the positive electrode and the negative electrode includes the compound for electrodes of the present invention.

The electrolyte solution contains a non-aqueous organic solvent and a lithium salt.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, one selected from the group consisting of LiCl and LiI Or two or more as supporting electrolytic salts. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. If the concentration of the lithium salt is less than 0.1M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, if it exceeds 2.0M there is a problem that the mobility of the lithium ion is reduced by increasing the viscosity of the electrolyte.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the cell can move. As the non-aqueous organic solvent, benzene, toluene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluoro Robenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1, 2,4-trichlorobenzene, iodobenzene, 1,2-diiobenzene, 1,3-diiobenzene, 1,4-diiobenzene, 1,2,3-triio Dobenzene, 1,2,4-triiodobenzene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3 -Trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene , 1,2,4-trichlorotoluene, iodotoluene, 1,2-dioodotoluene, 1,3-dioodotoluene, 1,4-diodotoluene, 1,2,3-triio Dotoluene, 1,2,4-triiodotoluene, R-CN (wherein R is a straight-chain, branched, or cyclic hydrocarbon group of 2-50 carbon atoms, double bond, aromatic ring, or ether Bonds), dimethylformamide, dimethylacetate, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, dimethyl carbonate, ethylmethyl carbonate, diethyl Carbonate, methylpropyl carbonate, propylene carbonate, methyl propionate, ethyl propionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbonate, propylene One or more of carbonate, γ-butyrolactone, sulfolane, valerolactone, decanolide, mevalolactone Available. The mixing ratio in the case of mixing one or more of the organic solvents can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art.

An example of the lithium secondary battery of the present invention having the above-described configuration is shown in FIG. 5. 5 shows a cathode 2, an anode 3, a separator 4 disposed between the cathode 2 and the anode 3, the cathode 2, the anode 3, and the separator 4. The cylindrical lithium ion battery 1 which consists of an impregnated electrolyte solution, the battery container 5, and the sealing member 6 which encloses the electric container 5 as a main part is shown. Of course, the lithium secondary battery of the present invention is not limited to this shape, and it is natural that any type of square, pouch, etc., including the positive electrode active material of the present invention and capable of operating as a battery, can be formed.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Comparative Example 1)

The LiCoO ₂ positive electrode active material, the super P conductive material, and the polyvinylidene fluoride binder were mixed in an N-methyl pyrrolidone solvent in a 94: 3: 3 weight ratio to prepare a positive electrode active material slurry. In this case, the LiCoO ₂ positive electrode active material is an active material exhibiting a charge capacity of 160mAh / g when the charge up to 0.1V, 4.3V at the initial charge and 157mAg / g when discharged up to 3.0V.

The positive electrode active material slurry was coated on an Al-foil current collector and dried to prepare a positive electrode.

A negative electrode active material slurry was prepared by mixing 90 wt% of the graphite negative active material and 10 wt% of the polyvinylidene fluoride binder having an initial capacity of 370 mAh / g and a reversible capacity of 350 mAh / g in N-methylpyrrolidone. This negative electrode active material slurry was coated on a Cu foil current collector and dried to prepare a negative electrode.

By using the positive electrode and the negative electrode, a polyethylene polymer separator is sandwiched between the positive electrode and the negative electrode so that the N / P ratio representing the amount of the negative electrode active material to the positive electrode capacity is 1: 1.2 based on the reversible capacity. A lithium secondary battery was produced. At this time, a mixed solvent (3: 5: 1: 1 volume ratio) of ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and fluorobenzene in which 1M LiPF ₆ was dissolved was used.

(Example 1)

Fe and lithium are deposited on the Fe, and a conductive additive having an average particle size of 5 to 6 µm is added to the negative electrode active material composition, wherein the mixing ratio of the active material: conductive material: binder: conductive additive is 94: 3: 3: A lithium secondary battery was manufactured in the same manner as in Comparative Example 1 except that the weight ratio was 1.5.

(Example 2)

A lithium secondary battery was manufactured in the same manner as in Example 1 except that lithium and Fe were deposited on the Fe and a conductive additive having an average particle size of 5 to 6 μm was added to the cathode active material composition.

Five lithium secondary batteries were prepared in accordance with the methods of Examples 1 to 2 and Comparative Example 1, respectively, and the batteries were subjected to an overcharge penetration experiment. The results are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Positive electrode active material amount (g) 4.458 4.459 4.827 Anode Active Material Amount (g) 2.200 2.200 2.200 First charge (mAh / g) 711 812 815 First discharge (mAh / g) 704 699 702 Second charge (mAh / g) 702 701 700 Second discharge (mAh / g) 700 698 700 Overcharge Penetration Experiment 5L0 5L0 5L3

* L0: no change, L1: leakage, L2: smoke, L3: exothermic 200 ℃ or less, L4: exothermic 200 ℃ or more, L5: explosion

From the results shown in Table 1, it can be seen that the electricity of Examples 1 to 2 shows almost the same level of battery charge and discharge capacity even when using a smaller amount of the positive electrode active material than Comparative Example 1. These results indicate that the batteries of Examples 1 to 2 are coated with lithium metal, so that the irreversible capacity of the negative electrode can be reduced, and a capacity improving effect can be obtained.

In addition, in Table 1, since 5LO means that all five batteries do not change in the overcharge penetration experiment, it can be seen that the batteries of Examples 1 to 2 are all safe cells that have passed the overcharge penetration experiment. On the contrary, in the battery of Comparative Example 1, all five batteries exhibit heat generation of 200 ° C. or lower, and thus, the battery of Comparative Example 1 is inferior in safety. Therefore, it can be seen that the batteries of Examples 1 to 2 exhibit very high battery charge / discharge capacities with existing batteries, and have excellent safety.

As described above, the electrode for a lithium secondary battery of the present invention has an alkali metal coated on the active material itself or includes a conductive material coated with an alkali metal, and thus has excellent safety and excellent capacity and lifespan.

1 is a cross-sectional view schematically showing the structure of a compound for a lithium secondary battery electrode of the present invention.

Figure 2 is a cross-sectional view schematically showing a cross-sectional view of the electrode for a lithium secondary battery according to an embodiment of the present invention.

3 is a schematic cross-sectional view of an electrode for a rechargeable lithium battery according to another embodiment of the present invention.

4 is a view illustrating a process of partially lithiating a negative electrode active material.

5 is a view showing a schematic structure of a lithium secondary battery of the present invention.

Claims (23)

A core comprising an inert material; And a coating layer comprising an alkali metal coated on the core. Lithium secondary battery electrode comprising a. The lithium secondary battery electrode of claim 1, wherein the alkali metal is selected from the group consisting of Li, Na, and K. 3. The lithium secondary battery electrode of claim 2, wherein the alkali metal is Li. The electrode for a lithium secondary battery of claim 1, wherein the electrode compound has an average particle size of 70 μm or less. The electrode for a lithium secondary battery of claim 4, wherein the electrode compound has an average particle size of 50 μm or less. The electrode for a lithium secondary battery of claim 5, wherein the compound for an electrode has an average particle size of 20 μm or less. The electrode of claim 1, wherein the coating layer has a thickness of 50 μm or less. The electrode of claim 7, wherein the coating layer has a thickness of 30 μm or less. The electrode of claim 8, wherein the coating layer has a thickness of 10 μm or less. The electrode of claim 9, wherein the coating layer has a thickness of 5 μm or less. The electrode of claim 1, wherein the coating layer is formed by a vacuum deposition process. 12. The electrode of claim 11, wherein the vacuum deposition process is selected from the group consisting of thermal evaporation, sputtering, ion-beam-assist-deposition, and chemical vapor deposition. The electrode for a lithium secondary battery of claim 12, wherein the vacuum deposition process is a thermal evaporation method. The electrode of claim 1, wherein the inert material is selected from the group consisting of Ni, Cu, Ti, Au, Pt, Fe, Co, Cr, and W. The electrode for a lithium secondary battery of claim 1, wherein the electrode compound is an active material. The electrode for a lithium secondary battery of claim 1, wherein the electrode compound is a conductive additive. anode; cathode; And Electrolyte solution; Including; At least one of the positive electrode and the negative electrode comprises a core comprising an inert material; And a compound for an electrode including a coating layer including an alkali metal coated on the core. The rechargeable lithium battery of claim 17, wherein the alkali metal is selected from the group consisting of Li, Na, and K. 18. The lithium secondary battery of claim 18, wherein the alkali metal is Li. The lithium secondary battery of claim 17, wherein the electrode compound is an active material. The lithium secondary battery of claim 17, wherein the electrode compound is a conductive additive. 18. The lithium secondary battery according to claim 17, wherein the electrode is a conductive additive which is a compound for the electrode, and the positive electrode or the negative electrode further comprises an active material. 18. The rechargeable lithium battery of claim 17, wherein the inert material is selected from the group consisting of Ni, Cu, Ti, Au, Pt, Fe, Co, Cr, and W.