KR100599794B1 - Rechargeable lithium battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery, comprising: a positive electrode having a positive electrode non-coating portion formed on at least one end of a current collector coated with a positive electrode active material; A negative electrode having a negative electrode non-coating portion formed on at least one end of the current collector coated with the negative electrode active material; And an electrolyte solution, wherein an alkali metal layer is formed on at least one of the positive electrode non-coating portion and the negative electrode non-coating portion.

In the lithium secondary battery of the present invention, an alkali metal layer is formed on the non-coated portion of the electrode, thereby efficiently providing a lithium source to compensate for the loss of lithium due to irreversibility.

Alkali metal, lithium secondary battery, anode, irreversible

Description

Lithium Secondary Battery {RECHARGEABLE LITHIUM BATTERY}

1 is a schematic representation of one embodiment of an electrode structure of the present invention;

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

[Industrial use]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery excellent in charge and discharge capacity retention rate due to reduced irreversible capacity.

[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. However, in this case, the density difference between lithium metal and active material is so large that it is difficult to maintain a uniform form during slurry production, coating, and drying process, and the lithium metal powder is dissolved during the initial charging and discharging process, and the remaining pores do not deform the plate in the long term. There is a problem that can lower the life and battery reliability.

An object of the present invention is to efficiently remove the irreversible capacity to provide a charge and discharge capacity retention rate, that is, a lithium secondary battery excellent in life.

In order to achieve the above object, the present invention is a positive electrode having a positive electrode non-coating portion formed on at least one end in the current collector coated with a positive electrode active material; A negative electrode having a negative electrode non-coating portion formed on at least one end of the current collector coated with the negative electrode active material; And an electrolyte solution, and at least one of the positive electrode non-coating portion and the negative electrode non-coating portion provides an lithium secondary battery in which an alkali metal layer is formed.

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 a cathode active material that does not contain lithium such as V ₂ O _5. An alkali metal coating layer, which can be utilized as a source of ions, is formed on an unsupported portion of an electrode to provide a lithium secondary battery exhibiting excellent energy density.

The lithium secondary battery of the present invention includes a positive electrode having a positive electrode non-coating portion formed at least at one end in the current collector coated with a positive electrode active material; A negative electrode having a negative electrode non-coating portion formed on at least one end of the current collector coated with the negative electrode active material; And an electrolyte, wherein at least one of the positive electrode non-coating portion and the negative electrode non-coating portion has an alkali metal layer formed thereon.

As the alkali metal in the alkali metal layer formed on the uncoated portion of the electrode of the present invention, Li, Na or K is preferred, and Li is most preferred.

The alkali metal layer preferably has a thickness of 20 µm or less, preferably 20 µm or less, preferably 20 µm to 0.5 µm, more preferably 10 µm to 0.5 µm, and most preferably 5 µm to 0.5 µm. . When the thickness of the alkali metal coating layer is greater than 20 μm, thermal deformation occurs in the current collector during deposition, which makes it difficult to produce a uniform film, which is not preferable. In addition, when the thickness is thinner than 0.5 mu m, the effect of the alkali metal coating layer, that is, the effect of dose reversal corresponding to irreversible cannot be obtained, which is not preferable.

In the battery of the present invention, the alkali metal layer is formed on the uncoated portion of the electrode, that is, the portion where the negative electrode active material layer is not formed on the current collector. That is, in general, in order to manufacture the electrode of the positive electrode or the negative electrode, except for at least one end of both ends of the current collector to apply the active material composition to form an active material layer, wherein the portion where the active material composition is not applied . Except for both ends of the current collector, the active material layer 20 is formed, and the electrode 100 having the alkali metal layer 30 formed on the uncoated portion 10 positioned at both ends is shown in FIG. 1. .

The alkali metal layer forming step may be any one of a general liquid coating step or a vapor deposition step as long as the alkali metal layer can be formed on the current collector. However, since the alkali metal layer is formed after the active material layer is formed on the current collector, it is not necessary to change the whole process during electrode production, and the process is simple.

When performing the said liquid coating process, the alkali metal powder is added to a solvent, an alkali metal composition is manufactured, and the process of coating this composition on the uncoated part of a current collector is included. The coating process may be any general liquid coating process, for example, knife coating, direct roll coating, reverse roll coating, gravure roll coating, gap coating (gap) coating, spray coating, slot die coating, or tape casting.

Preferable concentration of the alkali metal is 1 to 30 parts by weight, more preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent.

The solvent may be used without particular limitation as long as it has a low boiling point, is easily removed, has low reactivity with alkali metals, and leaves no residue after drying. As a representative example, acetonitrile, acetone, acetone, tetrahydrofurane, dimethyl formamide, N-methyl pyrrolidinone, and the like can be used.

The deposition process may be thermal evaporation, sputtering, ion-beam-assisted deposition or chemical vapor deposition.

The alkali metal layer preferably has a thickness of 20 µm or less, preferably 20 µm to 0.5 µm, more preferably 10 µm to 0.5 µm, and most preferably 5 µm to 0.5 µm in any step.

As the negative electrode active material constituting the negative electrode active material layer in the negative electrode of the present invention, carbon-based materials, Si, Sn, tin oxide, composite tin alloys, transition metal oxides, lithium metal nitrides, or lithium metal oxides may be used. Among them, it is preferable to use a carbon-based material. In particular, it is more preferable to use graphite or carbon black.

In the positive electrode of the present invention, as the positive electrode active material, an electrochemically reversible oxidation / reduction reaction may be possible, and a rithiated intercalation compound generally used in a lithium ion battery may be used, and is generally used in a lithium sulfur battery. Inorganic sulfur (S8) or a sulfur-based compound can also be used.

Examples of the thiolated intercalation compound may be selected from the group consisting of the following Chemical Formulas 1 to 14.

[Formula 1]

LiAO ₂

[Formula 2]

LiMn ₂ O ₄

[Formula 3]

Li _a Ni _b B _c M _d O ₂ (0.95 ≤ a ≤ 1.1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1)

[Formula 4]

Li _a Ni _b Co _c Mn _d M _e O ₂ (0.95 ≤ a ≤ 1.1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1)

[Formula 5]

Li _a AM _b O ₂ (0.95 ≤ a ≤ 1.1, 0.001 ≤ b ≤ 0.1)

[Formula 6]

Li _a Mn ₂ M _b O ₄ (0.95 ≤ a ≤ 1.1, 0.001 ≤ b ≤ 0.1)

[Formula 7]

DX ₂

[Formula 8]

LiDS ₂

[Formula 9]

V ₂ O ₅

[Formula 10]

LiV ₂ O ₅

[Formula 11]

LiEO ₂

[Formula 12]

LiNiVO ₄

[Formula 13]

Li _(3-x) F ₂ (PO ₄ ) ₃ (0 ≤ x ≤ 3)

[Formula 14]

Li (3-x) Fe 2 (PO 4) 3 (0 ≤ x ≤ 2)

(In Chemical Formulas 1 to 14,

A is selected from the group consisting of Co, Ni and Mn,

B is Co or Mn,

D is Ti, Mo or Mn,

E is selected from the group consisting of Cr, V, Fe, Sc and Y,

F is selected from the group consisting of V, Cr, M, Co, Ni and Cu,

M is at least one metal of transition metal or lanthanide metal selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr and V,

X is O or S)

In addition, the sulfur-based compound is selected from the group consisting of Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≥ 2) Can be used.

In the lithium secondary battery 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 _x 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 to 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 By mixing one or more of carbonate, γ-butyrolactone, sulfolane, valerolactone, decanolide, mevalolactone It can be used. 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. 2. 2 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 preferred embodiments of the present invention, and the present invention is not limited to the following examples.

(Comparative Example 1)

A positive electrode active material slurry was prepared by mixing 94 wt% of LiCoO ₂ positive electrode active material, 3 wt% of super P conductive material, and 3 wt% of polyvinylidene fluoride binder in an N-methyl pyrrolidone solvent. 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 except both ends 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 and dried except for both ends of the Cu foil current collector (both ends uncoated), as shown in FIG. 1, 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)

A lithium metal was deposited on a non-coated portion of the negative electrode of Comparative Example 1 by thermal evaporation deposition, except that a negative electrode having a lithium metal layer was formed. The lithium metal coating process was performed after the masking operation to cover the coating site of the negative electrode active material layer using a stainless steel (sus) partition that does not react with lithium so that the lithium metal is not coated on the active material layer. The coating process was performed such that the thickness of the lithium metal layer was 10 μm, and the deposition width was about 5 cm in the length of the plate.

(Example 2)

A lithium metal was deposited on a non-coated portion of the positive electrode of Comparative Example 1 by thermal evaporation deposition, except that a positive electrode having a lithium metal layer was formed. The lithium metal coating process was performed after a masking operation covering the coating site of the positive electrode active material layer using a metal partition so that lithium metal is not coated on the active material layer. The coating process was performed such that the lithium metal layer had a thickness of 10 μm, and the deposition width was about 5 cm in the length of the plate.

According to the method of Examples 1 to 2 and Comparative Example 1, each of five lithium secondary batteries were prepared, and the batteries were charged and discharged, and the results are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Positive electrode active material amount (g) 4.457 4.458 4.827 Anode Active Material Amount (g) 2.200 2.200 2.200 First charge (mAh / g) 713 750 815 First discharge (mAh / g) 620 702 702 Second charge (mAh / g) 620 745 700 Second discharge (mAh / g) 660 700 700 3rd charge (mAh / g) 660 712 700 Third discharge (mAh / g) 690 699 699 4th charge (mAh / g) 699 700 700 Fourth discharge (mAh / g) 699 699 700 5th charge (mAh / g) 699 700 699 5th discharge (mAh / g) 700 700 700

As shown in Table 1, it can be seen that the battery of Examples 1 to 2 exhibits almost the same level of charge and discharge capacity as Comparative Example 1 even when a small amount of the positive electrode active material is used. This is thought to be due to reducing the irreversible capacity of the negative electrode by coating a lithium metal layer on the non-coated portion, and it can be predicted that if the amount of the positive electrode active material can be reduced in this way, the safety can be improved accordingly.

As described above, in the lithium secondary battery of the present invention, an alkali metal layer is formed on the non-coated portion of the electrode, thereby efficiently providing a lithium source to compensate for the loss of lithium due to irreversibility.

Claims (8)

A positive electrode having a positive electrode non-coating portion formed on at least one end of a current collector coated with a positive electrode active material; A negative electrode having a negative electrode non-coating portion formed on at least one end of the current collector coated with the negative electrode active material; And Electrolyte Including; At least one of the positive electrode non-coating portion and the negative electrode non-coating portion is an alkali metal layer formed by a coating process or a deposition process is formed. The lithium secondary battery of claim 1, wherein the alkali metal is selected from the group consisting of Li, Na, and K. 3. The lithium secondary battery of claim 2, wherein the alkali metal is Li. The lithium secondary battery of claim 1, wherein the alkali metal layer has a thickness of 0.5 to 20 μm. The lithium secondary battery of claim 4, wherein the alkali metal layer has a thickness of 0.5 to 10 μm. The lithium secondary battery of claim 5, wherein the alkali metal layer has a thickness of 0.5 to 5 μm. delete The lithium secondary battery of claim 1, wherein the deposition process is selected from the group consisting of thermal evaporation, sputtering, ion-beam-assist-deposition, and chemical vapor deposition.

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