KR100786942B1 - Lithium secondarty battery additives - Google Patents

Abstract

In the lithium secondary battery having improved high temperature storage characteristics, the cathode and the electrolyte of the battery are characterized in that they include metal hydroxide and cyclohexylbenzene (CHB), respectively.

The present invention minimizes the capacity reduction problem during high temperature storage in a lithium secondary battery using CHB, an overcharge preventing agent, by using a metal hydroxide, thereby improving the high capacity storage lithium as well as the safety during overcharging by the existing CHB. A secondary battery can be provided.

Cyclohexylbenzene, Metal Hydroxide, Overcharge, High Temperature Storage, Lithium Secondary Battery

Description

Lithium Secondary Battery Additives {LITHIUM SECONDARTY BATTERY ADDITIVES}

1 is a schematic diagram showing an insertion electrode roll and a square battery can.

The present invention relates to a lithium secondary battery having improved high temperature storage characteristics by preventing a decrease in battery capacity during high temperature storage due to an electrolyte additive used to prevent problems when overcharging such a dangerous situation such as explosion of a battery.

In recent years, with the trend of miniaturization and weight reduction of electronic devices, miniaturization and weight reduction of batteries acting as power sources are also required. BACKGROUND ART Lithium-based secondary batteries have been put to practical use as small, light weight, high capacity rechargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers.

The lithium secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte, and transfers energy while reciprocating both electrodes such that lithium ions from the positive electrode active material are inserted into a negative electrode active material, such as carbon particles, and are detached again when discharged. Since it is possible to charge and discharge.

In the case where the lithium secondary battery is overcharged over a predetermined operating voltage range, the reactivity of the positive electrode and the electrolyte increases, resulting in degradation of the surface of the positive electrode and oxidation of the electrolyte. In addition, there is a problem of lack of battery safety, such as lithium dendrite growth and the resulting membrane destruction, rapid exothermic reaction, explosion.

In order to solve the above problems, an electrolyte additive for forming a non-conductor film on the surface of the anode during overcharging to suppress heat generation was developed, and currently commercially available additives include Japanese Patent Application Publication Nos. 01-015158 and 98-074537. Cyclo Hexyl Benzene (CHB) published in the issue.

When CHB reaches the potential of the battery during overcharging, an electropolymerization reaction is performed to form an insulator film on the surface of the anode, which delays the operation of the battery and prevents the battery from ignition due to overheating. However, even when the battery is exposed to high temperature for a long time within the normal operating voltage range, the electrolytic polymerization reaction of CHB proceeds and thus the capacity of the battery is greatly reduced.

The present inventors have found that the addition of a small amount of metal hydroxide in the preparation of the slurry for the cathode active material can minimize the capacity reduction during high temperature storage generated in a battery using CHB, an overcharge inhibitor.

The present invention is based on the above findings, and an object thereof is to provide a high capacity lithium secondary battery which is safe even when overcharged and whose high temperature storage characteristics are improved.

The present invention is a lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a positive electrode prepared from a positive electrode active material containing a metal hydroxide, the electrolyte is characterized in that it comprises cyclohexylbenzene (CHB) It provides a secondary battery.

Hereinafter, the present invention will be described in detail.

The electrolyte of the present invention comprises a CHB additive in a conventional electrolyte consisting of an electrolyte solution and a lithium salt.

In the above, when CHB is overcharged at about 4.7V or more at room temperature, an electropolymerization reaction proceeds as described below to form a non-conductive film on the surface of the anode, thereby preventing the ignition or explosion of the battery.

The amount of CHB added is preferably 3 to 5% by weight per 100% by weight of electrolyte. If the content is less than 3% by weight, the formation of the film due to electropolymerization may not be sufficient, and thus, the desired safety improvement may not be achieved. If the content is more than 5% by weight, the reaction may not be improved by forming a local reaction rather than forming an effective film over the entire range.

In the above, the lithium salt may be at least one selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ) ₂ .

In the above, the electrolyte solution is ethylene co (carbonate), propylene carbonate, butylene carbonate, vinylene carbonate, sulfolane, γ-butylo lactone, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxy ethane, tetra At least one selected from the group consisting of hydrofuran and mixtures thereof can be used.

The lithium secondary battery containing CHB, an overcharge inhibitor, in the electrolyte has an electrolytic polymerization reaction at a voltage lower than 4.7V when stored at a high temperature for a long time, thereby inhibiting the charge transfer reaction of the positive electrode active material and increasing the positive electrode resistance. Capacity reduction problem will occur.

Accordingly, the present invention can solve the problem of capacity reduction of the battery by adding a metal hydroxide in the production of the slurry of the positive electrode active material.

Hydroxyl groups (-OH) in the metal hydroxide evenly distributed on the surface of the anode can minimize capacity degradation during storage at high temperature by delaying and suppressing the electrolytic polymerization of CHB generated on the surface of the anode during high temperature storage . In addition, when the battery is stored at high temperature, it reacts with HF to elevate the electrode dissolution and the formation of lithium fluoride (LiF) on the surface of the anode, such as a metal fluoride hydroxide or a metal fluoride such as Al (OH) ₂ F, Al (OH) F ₂ or By forming AlF ₃ , it is possible to exhibit a synergistic effect of preventing the capacity reduction problem during high temperature storage of the lithium secondary battery.

As the cathode active material of the present invention, a conventional lithium transition metal composite oxide may be used, and non-limiting examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNi _1-X Co _X M _Y O ₂ (Where M = Al, Ti, Mg, Zr, 0 <X ≤ 1, 0 ≤ Y ≤ 0.2), LiNi _X Co _Y Mn _1-XY O ₂ (where 0 <X ≤ 0.5, 0 <Y ≤ 0.5) or LiM _x M ' _y Mn _(2-xy) O ₄ (M, M' = V, Cr, Fe, Co, Ni, Cu, 0 <X ≤ 1, 0 <Y ≤ 1), and the like. .

The metal hydroxide added to the cathode active material slurry of the present invention may be any metal hydroxide capable of forming a hydroxide, and non-limiting examples thereof include Al (OH) ₃ , Mg (OH) ₂ , and Ca (OH) _2. , LiOH, NaOH or mixtures thereof.

The metal hydroxide may vary in effect of delaying electrolytic polymerization and preventing formation of lithium fluoride depending on the number and degree of ionization of the hydroxyl groups.

While the metal hydroxide may improve the high temperature storage characteristics of the battery, on the other hand, since it cannot absorb and release lithium ions, there is a need to minimize the reduction of battery capacity by minimizing the amount of metal hydroxide added to the positive electrode of the battery. have. Therefore, the amount of the metal hydroxide added is preferably 0.1 to 10% by weight per 100% by weight of the positive electrode active material. If the amount of the metal hydroxide is less than 0.1% by weight, the effect of delaying the electrolytic polymerization reaction and preventing the formation of lithium fluoride by the hydroxyl group may be insufficient.If the amount of the metal hydroxide exceeds 10% by weight, the high temperature storage characteristics are improved due to excessive initial resistance increase. Will not be.

The negative electrode active material of the present invention may use a carbon material, a lithium metal or an alloy thereof that may occlude and release lithium ions, and other TiO ₂ and SnO ₂ that may occlude and release lithium and have a potential for lithium less than 2V. And metal oxides such as Li ₄ Ti ₅ O ₁₂ may also be used.

The slurry of the positive electrode according to the present invention may be obtained by mixing the positive electrode active material and the negative electrode active material, respectively, with a binder, a dispersion medium, and the like, and preferably include a small amount of a conductive agent or a viscosity modifier.

Any conductive material that does not cause chemical change in the battery configured can be used for the conductive agent. For example, carbon black, such as acetylene black, Ketjen black, Farnes black, and thermal black; Natural graphite, artificial graphite, conductive yarn fibers, and the like can be used. Carbon black, graphite powder and carbon fiber are particularly preferable.

As the binder, any one of a thermoplastic resin and a thermosetting resin may be used, or a combination thereof may be used. Among these, polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) is preferable, and PVdF is particularly preferable.

As the dispersion medium, an organic dispersion medium such as an aqueous dispersion medium or N-methyl-2-pyrrolidone can be used.

The lithium secondary battery of the present invention can be produced by conventional methods. In one example, the production of the positive electrode of the battery can be usually obtained by applying, rolling and drying the slurry of the positive electrode prepared above on the current collector, respectively. The porous separator may be placed between the positive electrode and the negative electrode, and then prepared by adding an electrolyte.                     

The separator may be a porous separator, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

The external shape of the lithium secondary battery manufactured by the above method is not limited, but may be cylindrical, square, pouch type, or coin type using a can.

The present invention will be described in more detail based on the following Examples and Experimental Examples. However, the Examples and Experimental Examples are for illustrating the present invention and are not limited thereto.

Example 1. Fabrication of Lithium Secondary Battery

1-1. Manufacture of anode

LiCoO ₂ was used as a positive electrode active material, and NMP (N), which was a solvent, was composed of 94.5 wt% of LiCoO ₂ , 0.5 wt% of Al (OH) ₃ , 2.5 wt% of Super-P (conductive agent), and 2.5 wt% of PVdF (binder). -methyl-2-pyrrolidone) to prepare a positive electrode mixture slurry, and then coated on an aluminum current collector to prepare a positive electrode.

1-2. Preparation of Cathode

Artificial graphite was used as the negative electrode active material, and the negative electrode mixture slurry was prepared by adding 95.3% by weight of artificial graphite, 0.7% by weight of Super-P (conductive agent), and 4% by weight of PVdF (binder) to NMP as a solvent. It was coated on a copper current collector to prepare a negative electrode.

1-3. Preparation of Electrolyte

As an electrolyte, an EC / EMC solution was used in 1M LiPF ₆ , and 3 wt% of CHB was added thereto.

1-4. Manufacture of batteries

The positive electrode, the porous separator and the negative electrode manufactured by the above method were wound as shown in FIG. 1 to form a roll, and a rectangular battery was prepared (see FIG. 1).

1 shows a roll and a can inserted into a rectangular battery, in which (a) is a cathode active material coated on an Al foil, (b) is a porous separator, and (c) is on a Cu foil The negative electrode active material is coated, rolled up the details, and inserted into a can to prepare a rectangular battery.

[Comparative Example 1-3]. Fabrication of Lithium Secondary Battery

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that CHB was not used in the electrolyte (see Table 1).

Comparative Example 2

Lithium secondary battery was prepared in the same manner as in Example 1 except that 95 wt% of LiCoO ₂ was used instead of Al (OH) ₃ and CHB was not used in the electrolyte. See Table 1).

Comparative Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 95 wt% of LiCoO ₂ was used instead of Al (OH) ₃ when preparing the cathode (see Table 1).

Experimental Example 1. High Temperature Storage Experiment of Lithium Secondary Battery

The high temperature preservation experiment was performed on the battery of Example 1 prepared according to the present invention and the batteries of Comparative Examples 1 to 3 as follows.

Each battery was charged to 4.2V with a charging current of 1C and 1C discharged to 3V to confirm the initial discharge capacity (A) .Then, the battery was stored at 80 ° C for 5 days and then discharged at 1C. (B) was measured. After measuring the remaining capacity, charging and discharging was carried out three times to confirm the recovery capacity (C). The remaining capacity ratio (B / A) and recovery capacity ratio (C / A) obtained by converting the remaining capacity (B) or recovery capacity (C) to the initial capacity (A) of the battery as a percentage are described in Table 1, respectively. .

battery Al (OH) ₃ (anode) CHB (electrolyte) Remaining capacity rate (%) Recovery capacity rate (%) Example 1 O O 64.6 77.9 Comparative Example 1 O X 65.5 73.8 Comparative Example 2 X X 61.1 74.9 Comparative Example 3 X O 45.2 57.0

As shown in Table 1, the battery of Comparative Example 3 using CHB in the electrolyte solution was shown to significantly reduce the remaining capacity rate and recovery capacity rate compared to the battery of Comparative Example 2 is not added any conventional additives. This means that an electrolytic polymerization reaction occurs even at a low voltage state in which CHB is maintained at high temperature and not at the time of overcharging, thereby forming an insulator film on the positive electrode, thereby causing a significant decrease in capacity of the battery. In contrast, the batteries of Example 1 and Comparative Example 1 including the positive electrode to which Al (OH) ₃ was added showed that the residual capacity rate and recovery capacity rate were significantly increased after high temperature storage at 80 ° C.

As a result, it was confirmed that the present invention minimizes the decrease in battery capacity during high temperature storage caused by CHB, an overcharge preventing agent, using metal hydroxides.

Experimental Example 2. Overcharge Experiment of Lithium Secondary Battery

The overcharge experiment was performed on the battery of Example 1 prepared in accordance with the present invention, and the batteries of Comparative Examples 1 and 3 as follows.

The charge and discharge voltage range of the battery was 0 to 10V ( vs. Li / Li ⁺ ), and the current was 3C (1950 mA), and the battery was operated at room temperature (25 ° C.).

As a result of the experiment, the battery of Comparative Example 1, in which CHB was not added to the electrolyte, had a temperature of the battery increased to 357 ° C due to overcharging, and ignition and explosion of the battery occurred. In contrast, the cells of Example 1 and Comparative Example 3 to which the CHB was added, the temperature was increased up to about 110 ℃ due to overvoltage charging, but there was no problem of overcharge such as further smoke, fire and explosion of the battery ( Table 2), and showed stability over time.

As a result, it was confirmed that the lithium secondary battery of the present invention can solve the problem of capacity reduction at the time of high temperature storage by CHB due to the metal hydroxide added to the positive electrode active material, while achieving the existing purpose of CHB, an overcharge preventing agent.                     

battery Fire explosion Acting Temperature (℃) result Example 1 X X X 109.95 Pass Comparative Example 1 O O O 357.13 failure Comparative Example 3 X X X 110.01 Pass

The present invention can minimize the reduction in battery capacity during the high temperature storage caused by the CHB added to the electrolyte in order to improve the safety of the lithium secondary battery during overcharging by adding a metal hydroxide.

Claims (4)

A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is a positive electrode prepared from a positive electrode active material including a metal hydroxide, and the electrolyte includes cyclohexylbenzene (CHB). The lithium secondary battery of claim 1, wherein the amount of cyclohexylbenzene is 3 to 5 wt% per 100 wt% of the electrolyte. The lithium secondary battery of claim 1, wherein the metal hydroxide is at least one selected from the group consisting of Al (OH) ₃ , Mg (OH) ₂ , Ca (OH) ₂ , LiOH, and NaOH. The lithium secondary battery of claim 1, wherein the amount of the metal hydroxide is about 0.1 wt% to about 10 wt% per 100 wt% of the positive electrode active material.

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