KR20070082379A - Method for peparation of lithium secondary battery through high temperature aging - Google Patents

Abstract

A method for manufacturing a lithium secondary battery through a high temperature pretreatment step is provided to control the storage temperature, storage period and state of charge of the battery adequately, to minimize degradation of the quality of the battery, and to inhibit swelling of the battery. A method for manufacturing a lithium secondary battery comprises the steps of: (a) introducing an electrode assembly, formed by stacking a cathode, an anode and a separator disposed between the cathode and the anode, into a battery casing; (b) injecting an electrolyte into the battery casing; (c) carrying out formation of the battery; and (d) aging the battery, wherein the aging step(d) is carried out at 60-100 deg.C in such a manner that the state of charge of the battery ranges from 0 to 100%.

Description

Manufacturing Method of Lithium Secondary Battery by High Temperature Pretreatment Process {METHOD FOR PEPARATION OF LITHIUM SECONDARY BATTERY THROUGH HIGH TEMPERATURE AGING}

1 is a graph showing the thickness change of the battery according to the aging time of the battery prepared in Examples 1 to 3 and Comparative Example 1.

The present invention relates to a method for manufacturing a lithium secondary battery in which the swelling characteristics of the battery are improved without deteriorating the performance of the 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. The lithium secondary battery may be classified into a liquid electrolyte battery and a polymer electrolyte battery according to the type of electrolyte. Generally, a battery using a liquid electrolyte is called a lithium ion battery, and a battery using a polymer electrolyte is called a lithium polymer battery.

In general, a lithium secondary battery is formed by applying an electrode active material, optionally a binder and a conductive material, to a positive electrode current collector and a negative electrode current collector to produce a positive electrode and a negative electrode, and stacking them on both sides of a separator to form a battery part having a predetermined shape. The battery pack is inserted into the battery case and sealed to complete the battery pack. In order to ensure the performance of the battery, it is almost essential to go through the formation (aging) and aging (aging) process.

The formation process is to activate the battery by repeatedly charging and discharging the battery after assembling the battery. Lithium ions from the lithium metal oxide used as the anode during charging are moved to and inserted into the carbon electrode used as the cathode. Due to its high reactivity, it reacts with the carbon anode to form compounds such as Li ₂ CO ₃ , LiO, LiOH, and these form a solid electrolyte interface (SEI) film on the surface of the cathode. In addition, the aging step is to stabilize the battery which is activated as described above for a certain period of time. A lithium secondary battery completed by such a manufacturing process is generally prohibited from being exposed to high temperatures due to an accelerated electrolyte decomposition reaction or a decrease in charge / discharge capacity of the lithium secondary battery at a high temperature. In the state in which the electrolyte was injected, it was left to stand at room temperature for a period of time to charge and discharge.

On the other hand, lithium secondary batteries, in particular nickel-based and ternary-based polymer battery caused a lot of problems due to the swelling (phenomena) of the battery due to the generation of gas during high temperature storage. In the case of the nickel-based cathode active material, since unreacted lithium salts are present in the synthesis, the swelling phenomenon appears in the battery manufacturing due to their hygroscopicity. Conventionally, an electrode, an electrolyte additive, and the like have been added to the inside of a cell to reduce the above-mentioned cell swelling, but in this case, an increase in cost and a deterioration of the battery are required.

In view of the above-described problems, the present inventors perform the aging process performed in the conventional battery manufacturing process without additional costs due to the use of an electrode and an electrolyte additive, but control the storage remaining capacity (SOC), storage temperature and storage time. It has been found that not only the swelling of the battery is significantly reduced, but the performance degradation due to high temperature exposure is minimized.

Accordingly, an object of the present invention is to provide a method for manufacturing a lithium secondary battery through a high temperature aging process.

The present invention comprises the steps of (a) injecting a battery unit formed by interposing a separator between a positive electrode, a negative electrode, a positive electrode in a battery case; (b) pouring an electrolyte solution into the battery case; (c) forming the battery; And (d) aging the battery, wherein the aging step (d) has a battery state of charge (SOC) in the range of 0 to 100% and a temperature in the range of 60 to 100 ° C. It provides a method of manufacturing a lithium secondary battery, characterized in that to perform aging.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is characterized in that by using the aging step of the conventional battery manufacturing process as it is, by changing the storage remaining capacity (SOC), storage temperature and storage time.

When performing the aging step under the above conditions, it is possible to improve the swelling (swelling) characteristics without deteriorating the performance of the battery.

That is, conventional batteries have generally undergone chemical conversion and aging in order to determine whether they are defective and to ensure battery performance, in particular, stability of life, but increase the internal pressure of the battery by accelerating the decomposition of the electrolyte at a high temperature and thereby the battery. It may cause a deterioration of the lifespan of the battery and a decrease in the charge / discharge capacity of the battery.

On the other hand, in the present invention, by performing the aging step by adjusting the temperature, SOC, time, etc., the electrolyte components or other reactive impurity components that cause the battery swelling phenomenon during the actual battery reaction are thermodynamically reacted at a high temperature in advance. Since the stabilization process, the gas by the reaction product to be produced at a high temperature is removed beforehand. Therefore, it is possible to significantly reduce the swelling phenomenon of the battery due to the components during the charge and discharge of the battery in the future.

In addition, an SEI film is formed on the surface of the cathode through a chemical conversion process, and the SEI film is generally stabilized by standing at room temperature for a certain period of time, that is, at room temperature. On the other hand, the present invention can be confirmed that even when the high temperature aging process does not cause problems such as reduced stability or decomposition of the SEI film due to high temperature, it is possible to extend the temperature constraints of the aging process that was only performed at room temperature. There is an advantage.

In addition, it is possible to remove not only gases such as carbon dioxide and methane generated during SEI film formation, but also electrolyte component gases that may cause the battery to swell later, thereby minimizing overall performance degradation of the battery caused by the gases. can do. In fact, as a result of a comparative experiment with a battery manufactured through a conventional room temperature aging process, it was confirmed that the equivalent or better performance improvement effect.

According to the present invention, one embodiment of a method of manufacturing a lithium secondary battery through a high temperature aging process is as follows.

1) A battery unit is formed by interposing a separator between the positive electrode, the negative electrode, and the positive electrode, and put the battery into the battery case.

The positive electrode may be prepared using a conventional method known in the art, for example, a positive electrode slurry is prepared by mixing a positive electrode active material and a negative electrode active material, respectively, a binder, a dispersion medium, and the like, and the prepared slurry It can obtain by apply | coating, rolling, and drying on the electrical power collector which consists of metal foils, respectively. At this time, the electrode slurry preferably contains a small amount of a conductive agent.

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 , SnO ₂ , which may occlude and release lithium and have a potential for lithium less than 2V. Metal oxides such as Li ₄ Ti ₅ O ₁₂ may also be used.

The positive electrode active material of the present invention is _a lithium transition metal complex oxide such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , LiNiO _2, and the lithium nickel oxide, LiCoO _2, and so was the replaced by the lithium cobalt oxide and manganese oxide of these, nickel and other transition metal for a portion of cobalt and the like (for example, Li (NiMn) _{1-2 x} Co _x O ₂₎ Or lithium-containing vanadium oxide, or the like, or a chalcogen compound (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, or the like).

The current collector is not particularly limited as long as it is made of a conductive material. Examples of the current collector include a mesh made of copper or aluminum, a foil, and the like.

The separator may be a polypropylene-based, polyethylene-based, or polyolefin-based porous separator, but is not limited thereto. In addition, as a process of applying the separator to a battery, a lamination (stacking) and a folding process of the separator and the electrode may be performed in addition to the general winding process.

The battery case is not particularly limited, but cans are cylindrical, coin-shaped, square or pouch types.

2) After the electrolyte is injected into the battery case, charging or charging / discharging is performed to perform a formation process.

The electrolyte according to the present invention comprises a conventional electrolyte solvent and a lithium salt, wherein the lithium salt is 1 from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ) ₂ . More than one species can be selected, and the electrolyte solvent is ethylene co (carbonate), propylene carbonate, butylene carbonate, vinylene carbonate, sulfolane, γ-butylarolactone, dimethyl carbonate, diethyl carbonate, 1,2-dimeth One or more selected from the group consisting of oxyethane, tetrahydrofuran and mixtures thereof can be used.

Formation process is a step of forming a SEI film on the surface of the negative electrode by performing a part of charge and discharge to activate the battery, generally proceeds to repeat the charge and discharge with a constant current or constant voltage of a range.

The condition of the above step is not particularly limited, and may be half charged at 1.0 to 3.8V or full charge at 3.8 to 4.3V. If possible, the C-RATE is preferably charged at a current density of 0.1 C to 2 C for 5 minutes to 1 hour.

3) The lithium secondary battery of the present invention is completed by performing a high temperature aging process following the chemical conversion process.

The aging step is preferably carried out within a temperature range of 60 to 100 ℃. When the temperature is less than 60 ° C., the above-described effect of reducing battery swelling may be insignificant. When the temperature is more than 100 ° C., the exterior material may rupture or the battery may ignite due to evaporation of the electrolyte. In addition, the remaining capacity SOC of the battery may be in any range from 100% when the battery is fully charged to 0% due to discharge. In addition, the storage time is not particularly limited, but is preferably about 1 hour to 1 week.

As described above, the high temperature aging process may evaporate the electrolyte or other components that may cause the battery to swell, thereby minimizing the swelling that occurs during battery reaction and causes deterioration of battery safety and performance.

In addition to the above-described steps, the method of manufacturing a lithium secondary battery according to the present invention may include a degassing step of removing a gas after an aging process, through which gases such as carbon dioxide and methane generated during formation of the SEI film in the formation step may be used. However, the gas and the like of the aforementioned components, which occur in the high temperature aging step and cause the battery bulge later, are removed in advance.

The manufacturing method described above is not limited thereto, and in some cases, the above-described processes may optionally add or exclude pre- and post-steps or merge them into one.

The lithium secondary battery produced by the above method includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery, and the like, and particularly a polymer battery which is nickel-based or ternary.

The invention is explained in more detail based on the following examples and experimental examples. However, Examples and Experimental Examples are for illustrating the present invention and are not limited to these.

[ Example  1 to 3]

Example  1. Lithium Secondary Battery Manufacturing

(Anode manufacturing)

A slurry was prepared by mixing 95 wt% of LiCoO ₂ having a particle size of 10 μm, 2.5 wt% of a conductive agent, and 2.5 wt% of a binder, and then uniformly applying the slurry to both sides of an aluminum thin plate having a thickness of 15 μm and rolling it. To prepare a positive electrode.

(Cathode production)

A negative electrode slurry was prepared by adding and mixing 95.3 wt% graphite material, 4.0 wt% binder, and 0.7 wt% conductive material, and uniformly applying and rolling the negative electrode slurry on both sides of a 10 μm thick copper plate to prepare a negative electrode.

(Electrolyte preparation)

An electrolyte solution was prepared by dissolving 1 mol of LiPF ₆ in a solution having a volume ratio of 1: 2 of ethylene carbonate (EC) and dimethyl carbonate (DMC).

(Battery manufacturing)

After the separator was interposed between the positive electrode, the negative electrode, and the positive electrode manufactured by the above method, the pouch-type battery case was introduced into the pouch-type battery case, and the electrolyte solution prepared above was infused. After injection, the solution was stored in a 30 ° C. chamber for about 3 days, and then charged by 475 mA for 12 minutes to form. Thereafter, an aging process was performed at 65 ° C. for one week with a state of charge (SOC) of 100 without a discharge process, and then the final battery was completed after the degassing process.

Example  2

Except that the aging process was performed for 1 day with the remaining capacity (SOC) of the battery being 0 due to the discharge carried out after the chemical conversion process at 80 ℃, lithium was carried out in the same manner as in Example 1 Secondary batteries were prepared.

Example  3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the aging process was performed for one day while the battery has a residual capacity (SOC) of 100 at 80 ° C.

Comparative example  One

A lithium secondary battery was manufactured by the same method as Example 1, except that the room temperature (25 ° C.) aging process was performed.

Experimental Example 1. Evaluation of swelling characteristics of a lithium secondary battery

The swelling characteristic evaluation experiment was performed on the lithium secondary battery manufactured through the high temperature aging process according to the present invention as follows.

Batteries of Examples 1 to 3 prepared through high-temperature aging processes under different conditions were used, and the batteries of Comparative Example 1, which had undergone the same aging process as the conventional method, were used as a control. Each battery was fully charged at 4.2 V, and then stored at 65 ° C. for one week with a storage SOC of 100. The thickness change of each battery was then described in Table 1 below.

As a result, the lithium secondary batteries of Examples 1 to 3 manufactured according to the high temperature aging process according to the present invention are reduced by at least 60% compared to the bulging phenomenon of the battery of Comparative Example 1 subjected to the room temperature aging process as in the conventional method. It was found (see Table 1 and FIG. 1). This occurs when the actual battery reaction proceeds and removes the electrolyte components or other components to be reacted, which are caused after the battery swells, through the high temperature aging process. The swelling phenomenon seems to decrease.

Therefore, it can be seen that the lithium secondary battery manufactured through the high temperature aging process according to the present invention has an excellent effect of reducing the swelling of the battery, and it can be confirmed that it is appropriate to apply the high temperature aging process to the conventional battery manufacturing process. there was.

battery Aging condition Battery condition after 168 hours SOC Temperature time Increased battery thickness (mm) Thickness increase rate (%) Example 1 100 65 ℃ 7 days 0.949 34% Example 2 0 80 ℃ 1 day 1.178 43% Example 3 100 80 ℃ 1 day 0.992 36% Comparative Example 1 100 25 ℃ 7 days 2.753 100%

Experimental Example 2. Performance Evaluation of Lithium Secondary Battery

According to the present invention, the following experiment was performed on a lithium secondary battery manufactured through a high temperature aging process.

The batteries of Examples 1 to 3, which were prepared through different high temperature aging processes, were used, and the batteries of Comparative Example 1, which had undergone the same aging process as the conventional method, were used as a control.

Each battery was charged to 4.2 V with a charging current of 1 C, and 1 C discharge was performed to 3 V to confirm the initial discharge capacity. Then, after charging to 4.2V under the same conditions as above, the battery was discharged at 1C to measure the remaining capacity (SOC) of the battery, and then charged and discharged three times to measure the recovery capacity of the battery. Since these results are shown in Table 2 below.

As a result, the lithium secondary batteries of Examples 1 to 3 manufactured by the high temperature aging process according to the present invention showed superior capacity retention and recovery capacity ratio compared to the battery of Comparative Example 1 which had undergone the normal temperature aging process ( See Table 2).

For this reason, it could be confirmed that the lithium secondary battery manufactured through the high temperature aging process according to the present invention had a comparable or superior effect in terms of performance as compared with the battery according to the conventional battery manufacturing process.

battery Aging condition Retention rate (%) Recovery (%) SOC Temperature time Example 1 100 65 ℃ 7 days 80.0% 90.89% Example 2 0 80 ℃ 1 day 68.14% 88.5% Example 3 100 80 ℃ 1 day 76.68% 88.75% Comparative Example 1 100 25 ℃ 7 days 72.45% 86.6%

The method for manufacturing a lithium secondary battery according to the present invention significantly affects battery performance by appropriately adjusting storage temperature, storage time, and storage remaining capacity (SOC) during an aging step performed in a conventional lithium secondary battery manufacturing process. The battery swelling at high temperatures can be significantly reduced without any additional cost, and further economics can be achieved since no additional processing is required.

Claims (5)

(a) inserting a battery unit formed by interposing a separator between a positive electrode, a negative electrode, and a positive electrode into a battery case; (b) pouring an electrolyte solution into the battery case; (c) forming the battery; And (d) aging the battery It includes, wherein the aging step (d) is a battery state of charge (SOC) is 0 to 100% range, the temperature is 60 to 100 ℃ manufacturing of a lithium secondary battery characterized in that to perform the aging in the range Way. The method of claim 1, wherein the aging step (d) is performed for 1 minute to 1 week. A lithium secondary battery prepared by the method of claim 1. The battery of claim 3, wherein the lithium secondary battery is a lithium ion battery or a lithium polymer battery. The battery of claim 4, wherein the lithium polymer battery is nickel-based or ternary.

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