KR20060087333A - Fabrication process for lithium secondary battery and lithium secondary battery applying the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery employing the same, and more specifically, (1) preparing an electrode assembly by interposing a separator on a positive electrode plate and a negative electrode plate; (2) inserting the electrode assembly into a packaging material and injecting electrolyte to seal the electrode assembly; (3) filling the sealed electrode assembly; (4) allowing the charged electrode assembly to stand at high temperature to generate gas which may occur later; And (5) to a lithium secondary battery manufacturing method comprising a degassing step of removing the above-generated gas and a lithium secondary battery employing the same. According to the present invention, there is an advantage in that a lithium secondary battery excellent in high temperature standing performance and high temperature charging / discharging characteristics can be obtained.

Lithium Secondary Battery, High Temperature, Degassing Process, Degassing

Description

Lithium secondary battery manufacturing method and lithium secondary battery using the same {Fabrication Process for Lithium Secondary Battery and Lithium Secondary Battery Applying the Same}             

1 is a graph comparing charge and discharge characteristics at room temperature of a lithium secondary battery according to an embodiment and a comparative example of the present invention; And

2 is a graph comparing charge and discharge characteristics at 60 ° C. of a rechargeable lithium battery according to Examples and Comparative Examples of the present invention.

The present invention relates to a method for manufacturing a lithium secondary battery having improved high temperature leaving performance and high temperature charging and discharging characteristics, and a lithium secondary battery employing the same.

The lithium secondary battery is composed of a cathode / cathode active material, a current collector, and an electrolyte, and the cathode / cathode active material plays a role of generating a potential difference through insertion and detachment of lithium ions, and is a lithium-transition metal oxide. This is used, and a lithium metal, a lithium alloy, carbon or a carbon composite material is used as the negative electrode active material. The current collector serves to transfer electrons generated and consumed in the cathode / cathode active material through low resistance, and aluminum is used as the cathode current collector, and copper or nickel is used as the anode current collector. In addition, the electrolyte is a passage for delivering lithium ions generated and consumed in the cathode / cathode active material, and is composed of a non-aqueous organic solvent, lithium salt, and other additives.

In addition, a lithium secondary battery having such a configuration generates electricity by an electrochemical oxidation / reduction reaction, and is mainly used as a power source of a portable electronic device, and in particular, an electronic device such as a mobile phone, a notebook computer, an MP3 player, a PDA, and the like. Used as a power source.

Lithium secondary batteries generally have a rectangular shape, and a method of manufacturing the same is a method of manufacturing a cathode film and a cathode film by using a cathode / cathode active material, and applying the cathode / cathode film to a current collector together with a separator as an insulator. The electrode assembly is manufactured by winding or laminating, storing the electrode assembly in a packaging material, injecting and sealing an electrolyte solution, charging and discharging, and finally degassing to remove gas generated at the initial stage of charging. Consists of performing. However, according to the above process, since a large amount of gas is additionally generated at high temperature after shipment of the product, it may be a fatal problem in battery deterioration and battery life.

As such, when a pouch-type secondary battery increases its internal voltage in a severe use environment such as overcharging or high temperature, the pressure and temperature of the battery increase, in particular, a gas is generated and the battery pack expands. There is a risk of explosion, which is a big problem for safety.

Attempts have been made to solve the safety problem of such secondary batteries. For example, the Republic of Korea Patent Publication No. 2003-0044258 is charged by the initial charging after the electrode assembly manufacturing step, the electrode assembly is contained in the packaging material and sealed, injecting and sealing the electrolyte solution, and then full charge Disclosed is a method of manufacturing a lithium secondary battery that eliminates the degassing process by dividing the gas in two times to release the gas in advance during initial charging.

Korean Patent Laid-Open Publication No. 2004-0023964 No. 98-44210 and 2004-0037579 are provided with a capillary pressure-resistant release means on the sealing surface of the battery case, so that the internal pressure is rapidly released to the outside at high temperature. A pouch type lithium secondary battery provided with a safety device for improving battery safety is disclosed. However, in order to install the safety device as described above requires a separate additional process there is a problem that the productivity is lowered.

Korean Patent Laid-Open Publication Nos. 2004-0037053 and 2004-0037054 disclose additives to electrolytes, namely 2-SULFOBENZOIC ACID CYCLIC ANHYDRIDE and DIVINYL SULFONE, Is disclosed for a swelling inhibiting lithium secondary battery electrolyte which suppresses the collapse of the SEI film by mixing.

U. S. Patent No. 6,586, 131 discloses an alkali metal secondary battery provided with a gas discharge valve in a casing for discharging gas inside the cell to the outside. In addition, US Patent No. 6,686,087 discloses a nonaqueous electrolyte secondary battery having a safety valve for degassing when the internal pressure of the battery exceeds a predetermined value. However, this also requires a further process, there is a problem that contributes little to the improvement of productivity.

As such, some active materials used in lithium secondary batteries generate very high gas at high temperatures. The use of such active materials causes gas to be generated at high temperatures, thereby degrading the performance of the battery.

The present invention is to solve the above problems, without the need for a safety device or a gas outlet, a simple process, due to the gas generated under overheating conditions deteriorate the performance of the battery or repeated expansion and contraction during charging and discharging of the battery SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a lithium secondary battery having improved high-temperature standing performance and high temperature charge / discharge characteristics, which can prevent the phenomenon of swelling of a battery in advance, and a lithium secondary battery employing the same.

In order to achieve the above object, the present invention provides:

(1) manufacturing an electrode assembly by interposing a separator on the positive electrode plate and the negative electrode plate;

(2) inserting the electrode assembly into a packaging material and injecting electrolyte to seal the electrode assembly;

(3) filling the sealed electrode assembly;

(4) allowing the charged electrode assembly to stand at high temperature to generate gas which may occur later; And

(5) It provides a lithium secondary battery manufacturing method comprising a degassing step of removing the gas generated in advance.

In the method of manufacturing a lithium secondary battery according to the present invention, the high temperature standing in step 4 is characterized in that it is carried out for 0.5 to 24 hours at 70 ~ 100 ℃.

According to the present invention, there is an advantage in that a lithium secondary battery having improved high temperature leaving performance and high temperature charging and discharging characteristics can be obtained.

Hereinafter, the present invention will be described in detail.

According to the present invention, the gas may be generated in advance during the manufacturing process, and may be generated in advance, and the gas generated during the high temperature standing after the product is shipped after degassing is removed. The main feature of the present invention is that it can reduce the occurrence.

The present invention includes a lithium secondary battery having improved high temperature leaving performance and high temperature charging / discharging characteristics.

First, step 1 is to prepare an electrode assembly through a separator on the positive electrode plate and the negative electrode plate.

The electrode assembly may be prepared by including a cathode / cathode active material and a current collector, and the electrode assembly may be manufactured by a conventional method in the art. In one example, a cathode film and a cathode film are manufactured using a cathode / cathode active material, and a separator film which is an insulator is also produced. Thereafter, the cathode / cathode film is pretreated to coat and dry, and the prepared cathode / cathode film is applied to a current collector to be wound or laminated together with a separator as an insulator to manufacture a battery. In this case, the materials used in the production of the cathode / cathode active material, the current collector, and the separator may be used as materials commonly used in the art, but are not limited thereto.

Step 2 may be configured to insert the electrode assembly of the step 1 into the packaging material and then inject the electrolyte solution to seal.

The packaging material of the electrode assembly is to be used as the packaging material for packaging the battery after the injection of the electrolyte, it can be used aluminum laminate pouch. The aluminum laminate pouch is a film approximately 100 μm thick consisting of a layer of nylon-aluminum-polypropylene, wherein the polypropylene inside the battery pack is absorbed by heat ranging from 160 to 210 ° C. and pressure ranging from 1 to 3 kg _f / cm 3. It melts and performs sealing.

Step 3 has a configuration consisting of filling the sealed electrode assembly. The charging and discharging step may be performed by a conventional method, but more preferably, after sealing, the battery may be charged and discharged several times with a voltage of 3.0 to 4.2 V.

Step 4 is a major feature of the invention, characterized in that the charged electrode assembly is left at high temperature to generate gas which may subsequently occur.

Pouch-type batteries are very vulnerable to high temperature, since they directly lead to changes in appearance when gas is generated compared to can-type batteries. In order to compensate for this, when the battery material is replaced for high performance and low price, the high temperature leaving performance is often deteriorated. Although electrolyte additives may be added to improve the high temperature leaving performance, they are expensive, have limited performance, and have limitations that may deteriorate other performances. Alternatively, the electrolyte base composition may be changed. However, in this case, low temperature performance, high rate discharge performance, and cycle performance may deteriorate. However, according to the present invention, since no special material is consumed, it is possible to obtain an advantage of significantly improving the high temperature leaving performance at low cost.

Therefore, a preferred high temperature leaving method according to the present invention is to leave the supercharged battery in the step 3 for 70 to 100 ℃, 0.5 to 24 hours, more preferably at 85 ℃ for 4 hours. At this time, if the leaving temperature is less than 70 ℃ does not reach the desired amount of gas generation on the other hand, if the leaving temperature exceeds 100 ℃ is not preferable because there is a risk of ignition or explosion of the battery. In addition, when the leaving time is less than 0.5 hours or more than 24 hours, since no significant gas is generated, it is not preferable.

In general, an electrode material according to a lithium ion battery has a structure in which lithium (Li ⁺ , Li-ion) in an ionic state is reversibly inserted into the inside and then exits again. In other words, lithium in the LiCoO ₂ or LiMn ₂ O ₄ is discharged to move along the electrolyte and enter the carbon inside the lithium ion battery is a charge, the movement in the opposite direction corresponds to the discharge.

When lithium enters or exits the material, there is a slight difference, but it is accompanied by expansion and contraction of the volume. In addition, while the non-aqueous solvent reacts at the electrode surface to form a solid electrolyte film, gas is generated inside the battery, thereby increasing the internal pressure of the battery.

On the other hand, in the pouch type secondary battery, when the internal voltage increases due to overcharging, gas may be generated to cause the battery pack to expand and explode. In particular, a lithium ion battery releases gases such as carbon dioxide and carbon monoxide as the liquid electrolyte decomposes due to overcharging, thereby increasing the internal pressure of the battery.

In addition, when an overcurrent flows due to overdischarge or short circuit, the temperature inside the battery rises and the liquid electrolyte turns into a gas, thereby increasing the pressure and temperature inside the battery, and in particular, there is a risk of ignition.

As a result, the deterioration of the electrode is one of the main causes affecting the battery life, the presence of gas in the cell leads to a poor appearance of the battery.

Therefore, the lithium ion battery manufactured through the above process is evaluated under such overload conditions, which are several times higher than the actual use conditions, so that the battery can not only show a significantly stable performance under actual use conditions but also improve the battery life. Will be.

The gas inside the battery generated as described above is generated in advance during the battery manufacturing process and discharged in advance through the following step 5.

In step 5, the degassing process is performed by removing the battery from step 4. When the battery is taken out under the stand-by temperature condition according to step 4, gas is generated from the active material inside the battery and the battery is swollen. The degassing process of the present invention returns to the gas free state. Through this, the gas inside the battery is discharged, which may cause an appearance defect, or the battery may be prevented from igniting or exploding.

In general, degassing is a method of removing the internal gas of a pouch-type battery. The cell is opened or a portion of the pouch is removed, a vacuum state of -750 mmHg is applied for 10 seconds, and then the opened pouch part is opened by heat. After bonding, it is made into a normal pressure.

In summary, the present invention is characterized in that the amount of gas generated after shipment of the product can be reduced by making the high-temperature standing condition after shipment of the product before the degassing process.

In conclusion, when the lithium secondary battery manufactured according to an embodiment of the present invention was subjected to the high temperature standing conditions, the battery thickness increase rate was less than 5%, and the high temperature standing performance was very excellent.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are provided to illustrate the present invention, but the scope of the present invention is not limited or limited by the following examples.

Example 1 Fabrication of Lithium Secondary Battery of the Present Invention

(Step 1) Preparation of Electrode Assembly

91% by weight of LiMnO ₄ , 4% by weight of PVDF and 5% by weight of graphite were dispersed using N-methylpyrrolidone (NMP) as a solvent, and the product obtained was coated on both sides of an aluminum foil as a current collector. The applied aluminum foil is dried at 100 ° C. for 24 hours under reduced pressure. The resulting aluminum foil is pressed in a roll press. The compressed product is cut and used as an anode.

91% by weight of artificial graphite and 9% by weight of PVdF were dispersed using N-methylpyrrolidone (NMP) as a solvent, and a mixed product was applied to a copper foil as a current collector, and the product applied to the current collector was 100 ° C. under reduced pressure. Dry for 24 hours. The resulting negative foil is also pressurized in a roll press. The compressed product is cut and used as a negative electrode.

The prepared positive electrode and the negative electrode were laminated with a 20 μm-thick porous PE separator interposed therebetween to fabricate an electrode assembly having a design capacity of 5500 mAh.

(Step 2) Battery Pouring and Sealing

After forming the aluminum laminate packaging material of 100 ㎛ thickness to put the electrode assembly to make a space, and put the electrode assembly prepared in step 1 and sealing the remaining three sides except one side to make an electrode assembly.

The molded electrode assembly was impregnated with 3 g of EC: EMC (4: 6) nonaqueous electrolyte of LiPF ₆ 1M, and then sealed by thermocompression bonding in a vacuum state.

(Step 3) charge and discharge

After sealing, the battery was charged and discharged three times at a voltage of 3.0 to 4.2 V to manufacture a lithium secondary battery.

(Step 4) high temperature left

The prepared lithium secondary battery was left at 85 ° C. for 4 hours to generate gas to be generated after product shipment.

(Step 5) Degassing Process

The high-temperature left battery was taken out and a vacuum of −750 mmHg was added for 10 seconds to remove the internal gas generated in step 4, switch to normal pressure, and heat bond to prepare a lithium secondary battery.

Comparative Example 1 Preparation of General Electrode Assembly

A lithium secondary battery was manufactured in the same manner as in Example 1 except that the high temperature leaving step was performed before the degassing step in Example 1.

Experimental Example 1 High Temperature Anti-Static Performance Test of Lithium Secondary Battery

The high temperature standing performance of the lithium secondary battery prepared in Example 1 and Comparative Example 1 was measured. Specifically, after the constant current at 0.5C, 4.2V, after constant voltage charging, it was left at 85 ℃ for 4 hours to measure the thickness change, the results are shown in Table 1 below.

As can be seen from Table 1, the lithium secondary battery of Example 1 according to the present invention has a small thickness change compared to the lithium secondary battery of Comparative Example 1, it can be seen that the high temperature stability is improved.

Thickness change after leaving 85 ℃ for 4 hours (%) Voltage Internal resistance thickness Example 1 -1.10% 36.1% 18.7% Comparative Example 1 -1.03% 17.6% 4.6%

Experimental Example 2 Room Temperature Charge / Discharge Characteristics

The batteries produced by the methods of Example 1 and Comparative Example 1 were charged to 4.2 V with a charging current of 5,500 mA (1C) in a room temperature atmosphere, and after reaching 4.2 V, until the charging current became 550 mA or less, 4.2 V. After the constant voltage charging, the battery is stopped for 10 minutes, and repeated 300 times of 4.2 V-5,500 ㎃ constant current-constant voltage charging and 5,500 ㎃ constant current discharging to discharge until 5,500 ㎃ (1C) discharge current reaches 3.0 V. It was.

The results are shown in Figure 1;

It was confirmed that the battery produced by the method of Example 1 had better performance at room temperature charge and discharge than the battery produced by the method of Comparative Example 1.

Experimental Example 3 60 ° C Charge-Discharge Characteristics

 Charge and discharge were tested in the same manner as in Experimental Example 2 except that the charge and discharge execution temperature was 60 ° C.

The results are shown in Fig.

It was confirmed that the battery produced by the method of Example 1 had a smaller initial capacity decrease at high temperature charge / discharge than the battery produced by the method of Comparative Example 1, and the late capacity maintenance also had excellent performance. It is thought that the battery produced by the method of Example 1 has an improved 60 ° C charge and discharge performance because the gas generation amount is small during 60 ° C charge and discharge.

According to the present invention having the above structure, even a simple process without the installation of a safety device or a gas discharge port, due to the gas generated under overheating conditions, the performance of the battery is reduced, or the battery is repeatedly expanded and contracted during charging and discharging of the battery. It is possible to provide a lithium secondary battery having excellent high temperature leaving performance and high temperature charging / discharging characteristics that can prevent the phenomenon of gas swelling in advance.

Claims (3)

(1) manufacturing an electrode assembly by interposing a separator on the positive electrode plate and the negative electrode plate; (2) inserting the electrode assembly into a packaging material and injecting electrolyte to seal the electrode assembly; (3) filling the sealed electrode assembly; (4) allowing the charged electrode assembly to stand at high temperature to generate gas which may occur later; And (5) A lithium secondary battery manufacturing method comprising a degassing step of removing the previously generated gas. The method of claim 1, wherein the high temperature in step 4 is carried out at 70 ~ 100 ℃ for 0.5 to 24 hours. A lithium secondary battery prepared according to claim 1.

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