JP2005327592A - Manufacturing method of nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain increase of manufacturing cost of a battery due to the cost caused by longer hours of a drying process and cost on drying equipment, and even to the cost on manufacturing environment management, to simplify process equipment, and to shorten time taken for battery manufacture. <P>SOLUTION: The manufacturing method of the nonaqueous electrolyte secondary battery made by housing an electrode plate group made by winding around a cathode, an anode, and a separator, and a electrolyte solution comprises: a process of setting a water content of the cathode at 1,000 to 5, 000 ppm; a process of housing the electrode plate group and the electrolyte solution in the battery case; a first aging process; and a second aging process. The first aging process is carried out under conditions of SOC at 40 to 100%, a temperature at 40 to 80°C, and a time of 12 to 72 hours with the battery at a released state, and the second aging is carried out at a temperature lower than in the first aging process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aging treatment method for providing an inexpensive lithium secondary battery in which gas generation during use is suppressed.

  Lithium secondary batteries are widely used in the fields of communication and information devices such as mobile phones and personal computers because of their high energy density. In addition, it is also attracting attention today for electric vehicles, and is expected to be put to practical use at an early stage due to increased awareness of environmental and energy issues.

  In addition, lithium secondary batteries are required to have long-term reliability that can withstand use for over 10 years in a wide temperature range in which electric vehicles are used. In order to promote the popularization of electric vehicles, it is important to keep the cost of batteries low.

  Lithium cobalt composite oxide is the mainstream of the positive electrode active material used in current lithium secondary batteries, but cobalt has a small amount of resources, and because of its supply capacity and material cost, lithium is the main constituent element. Nickel composite oxide is expected as a positive electrode active material.

  Further, since lithium secondary batteries cause capacity deterioration and gas generation when moisture is mixed in the batteries, they are usually completely cut off from the outside by a sealed structure. Therefore, if gas is generated by some reaction inside the battery during use, the gas stays inside, leading to an increase in the internal pressure of the battery, and in some cases discharged to the outside of the battery. However, as described above, since the battery for electric vehicles is expected to be used for more than 10 years, it is necessary to minimize such gas generation.

  Until now, one of the major causes of gas generation has been water content in battery materials, and its gas generation mechanism is that water dissolves in the electrolyte and reacts with lithium on the negative electrode to generate hydrogen gas. It is known to occur. In particular, since acetylene black (AB) having a large specific surface area is used as a conductive additive in the positive electrode mixture, it is more likely to contain a lot of moisture than a negative electrode mixture or a separator. As another cause of gas generation, it is known that gas generation occurs in a process in which a compound containing lithium forms a film on the carbon surface of the negative electrode.

In order to suppress such gas generation, Patent Document 1 discloses an aging method for a lithium secondary battery, in which the assembled battery is stored in a certain temperature range, and thereby the initial charge / discharge characteristics and charge / discharge are determined. It is described to improve cycle characteristics.
JP 2000-340262 A

  However, in the matter described in the cited document 1, if the positive electrode plate is not dried and its water content is not limited to the weight of the positive electrode mixture, there is a sufficient effect for suppressing gas generation during high temperature storage in a charged state. It became clear from our examination that it was not possible to obtain.

In order to limit the moisture content of the electrode plate as described above, it is necessary to dry the electrode plate at a high temperature or high vacuum for a long time. It is also necessary to be performed in a controlled environment. Therefore, there is a problem that the manufacturing cost of the battery increases due to the long time of the drying process, the cost of the drying equipment, the cost of managing the manufacturing environment, and the like.

  The present invention solves the above problems, and is a method for producing a non-aqueous electrolyte secondary battery in which a positive electrode, a negative electrode, a separator and a plate group formed by winding a separator and an electrolytic solution are contained in a battery case. And a step of setting the moisture content of the positive electrode to 1000 to 5000 ppm, a step of accommodating the electrode plate group and the electrolyte in the battery case, a first aging step, and a second aging step, The second aging step is performed under the conditions of SOC (state of charge) of 40 to 100%, temperature of 40 to 80 ° C., time of 12 to 72 hours, and the battery in an open state. The present invention is characterized in that it is performed at a temperature lower than that of the first aging step, and it is possible to suppress the generation of gas even when exposed to a high temperature environment in a charged state, and to provide a good and inexpensive lithium secondary battery. Is possible.

  In the present invention, the positive electrode-containing water content is set to 1000 ppm or more and 5000 ppm or less with respect to the weight of the positive electrode mixture. In order to dry to such a water content, the wound electrode plate group is accommodated in the battery container. It can be carried out by simply vacuum drying at 80 ° C. for 10 to 24 hours. Generally, the electrode plate drying process at 100 ° C. to 250 ° C. performed after coating of the positive electrode plate, In order not to absorb, it is not necessary to store in an environment in which the dew point is limited to a certain temperature or lower, so that not only the process equipment can be simplified, but also the time required for battery production can be greatly shortened.

  It has become clear that the present invention can suppress the generation of gas when stored at a high temperature to a small amount, and is effective in reducing the cost of battery manufacturing equipment and the time required for battery manufacturing.

  A relatively large amount of gas is generated during the initial charge / discharge of the battery using the positive electrode plate having a water content of 1000 to 5000 ppm. This is a hydrogen gas caused by water dissolved in an electrolyte solution, in addition to a gas accompanying the generation of a negative electrode surface film (SEI) such as ethylene gas, which generally occurs in a lithium secondary battery. In particular, when a positive electrode containing a large amount of moisture is used, hydrogen gas is the main component. The mechanism of hydrogen generation occurs when water contained in the electrode dissolves in the electrolyte and reacts with lithium intercalated with the negative electrode carbon. Since time is required for the water in the positive electrode to dissolve in the electrolytic solution, the water still remains on the electrode plate after the initial charge / discharge. Therefore, the battery is first aged at a predetermined SOC and a predetermined temperature, and water contained in the positive electrode is dissolved in the electrolytic solution and reacted with lithium to be removed as hydrogen gas. The reason why the temperature is kept at 40 ° C. to 80 ° C. is to make the dissolution of water and the reaction between lithium and water fast, and the reason why the SOC is made 40% to 100% is because lithium needs to exist in the negative electrode. It is. The reason why the battery is opened after the first aging is to discharge the gas thus generated out of the battery.

  Furthermore, in the second aging, the battery is set to a predetermined SOC, the change of the open circuit voltage (OCV) during the aging period is measured, and the purpose is to select defective products due to an internal short circuit. To do. The sealing of the battery is preferably performed after the first aging is completed and the gas in the battery is discharged, but may be after the second aging is completed.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an example showing an embodiment of the present invention. FIG. 1 is an external view of a lithium secondary battery using an aluminum battery case 1. In this case, an electrode plate group formed by winding a positive electrode plate in which a positive electrode active material is applied to an aluminum foil and a negative electrode plate in which a negative electrode active material is applied to a copper foil via a separator is inserted into the battery case 1. An aluminum lid plate 5 is welded to the battery case 1, and the positive electrode terminal 2 and the negative electrode terminal 3 connected to the positive electrode plate and the negative electrode plate of the electrode plate group are led to the outside through the cover plate 5. These electrode terminals have a structure insulated from the cover plate 5 by a resin made of polyethylene.

  The positive electrode active material used for the lithium secondary battery is mixed with acetylene black (AB) or the like for imparting conductivity, and further combined with a 1% aqueous solution of carboxymethyl cellulose (CMC) to form a paste. It is kneaded with a dispersion (dispersion) of polyethylene terephthalate (PTFE) for imparting adhesion. The solid content rate of this positive electrode active material mixture paste is adjusted to be 45% to 65%. The positive electrode plate is obtained by coating the paste thus prepared on both sides of the aluminum foil using a die coater, a comma coater, or the like, and drying it through a drying furnace adjacent to the coating machine. The moisture content of the positive electrode mixture at this time is about 1% to 5%. The positive electrode plate after coating is wound up in a roll shape, and is dried in vacuum in the range of 80 ° C. to 120 ° C. for 8 hours to 16 hours in this form. The degree of vacuum at this time is preferably controlled to 5.0 torr or less, and the water content of the positive electrode plate obtained through this drying step is in the range of 1000 ppm to 5000 ppm with respect to the weight of the positive electrode mixture. ing.

  A predetermined amount of electrolytic solution is injected into the battery thus manufactured, and initial charge / discharge is performed at room temperature. Initial charging / discharging is performed for the purpose of activating the battery. At this time, a film is formed on the negative electrode and ethylene gas is generated due to the reaction between the lithium that has moved to the negative electrode and the electrolytic solution. Also, water contained in the electrode plate dissolves in the electrolyte and reacts with lithium on the negative electrode to generate hydrogen gas. The gas thus generated is discharged out of the battery through the injection port.

  Next, a first aging process is performed on the lithium secondary battery activated by performing the initial charge / discharge in an environment where the SOC is 60% and the temperature is 60 ° C. At this time, the liquid injection port is sealed with a return type pressure valve, and when the internal pressure of the battery becomes a predetermined atmospheric pressure or higher, the valve opens to allow the gas inside the battery to escape. After the first aging was completed, the battery SOC was adjusted again to a predetermined state of 0% to 100%, and the second aging was performed at 25 ° C. for 72 hours. The battery OCV at the beginning and end of the second aging is measured to confirm that there is no internal short circuit.

Lithium nickel composite oxide represented by the composition formula LiNi _0.8 Co _0.17 Al _0.03 O ₂ is used as the positive electrode active material, AB is added as a conductive agent, PTFE as a binder, and CMC as a solvent. A paste-like mixture was obtained by kneading. This was applied to both sides of a 20 μm thick aluminum foil positive electrode current collector and dried, and then rolled by a roll press so that the density of the mixture layer was 2.1 g / cc to obtain a positive electrode plate. Here, the size of the positive electrode plate was such that the thickness of the mixture on one side was 30 μm, the width was 80 mm, and the length was 2500 mm.

  On the other hand, by adding artificial graphite (MCMB, manufactured by Osaka Gas Co., Ltd.) as a negative electrode active material and adding polyvinylidene fluoride (PVDF) as a binder and N-methyl-2-pyrrolidone (NMP) as a solvent, and kneading. A pasty mixture was obtained. This was applied to both sides of a copper foil negative electrode current collector having a thickness of 10 μm and dried, and then rolled by a roll press so that the density of the mixture layer was 1.3 g / cc to obtain a positive electrode plate. Here, the size of the negative electrode plate was such that the thickness of the mixture on one side was 35 μm, the width was 85 mm, and the length was 2650 mm.

  As the separator, a two-layer porous film made of polypropylene (PP) and polyethylene (PE) having a thickness of 25 μm was used.

  Next, the positive electrode plate and the negative electrode plate are wound through a separator to form a power generation unit, and this power generation unit is inserted into an aluminum rectangular battery case (92 mm × 95 mm × 15 mm), and a battery lid having a liquid inlet is provided. Welded.

As the electrolytic solution, 1M LiPF ₆ dissolved in an organic solvent obtained by mixing ethylene carbonate (EC): dimethyl carbonate (DMC) at a volume ratio of 4: 6 was used. The battery capacity at this time is 5 Ah. And as initial charge-and-discharge conditions, it charged to the upper limit voltage 4.1V with the 0.2C constant current, discharged to the lower limit voltage 3.0V with the 0.2C constant current, and was then constant-current charged to the upper limit voltage 4.1V.

  And in order to confirm the effect of this invention, the battery was created according to said method using two positive electrode plates whose positive electrode containing water content is 500 ppm and 3000 ppm with respect to mixture weight, and initial charge / discharge was performed. Here, a battery having a positive electrode moisture content of 3000 ppm and a first aging temperature of 60 ° C. is compared with the battery of Example 1, a positive electrode moisture content of 3000 ppm, and a first aging temperature of 25 ° C. is compared. The battery of Example 1, the battery with a positive moisture content of 500 ppm and the first aging temperature of 60 ° C., the battery of Reference Example 1, the positive electrode with a moisture content of 500 ppm, and the first aging temperature of 25 ° C. As the battery of Reference Example 2, the first aging was performed. In all the batteries, the second aging was performed under the conditions of 25 ° C./SOC 100% / 7 days. These batteries were sealed, adjusted to SOC 100% again, and left in a 65 ° C. environment for 2 weeks, and the amount of gas generated inside the batteries was measured. The results are shown in Table 1.

実施例１の電池と比較例１の電池から明らかなように、正極に多くの水分が含まれていても、第一のエージングを高温で実施することによって、エージング後の保存によるガス発生量は減少させることができ、実施例１の電池と参考例１、２の電池の結果からその発生量はもともと正極含有水分が少ない電池と同等であることが明らかとなった。

As is clear from the battery of Example 1 and the battery of Comparative Example 1, even if the positive electrode contains a large amount of moisture, by performing the first aging at a high temperature, the amount of gas generated by storage after aging is From the results of the battery of Example 1 and the batteries of Reference Examples 1 and 2, it was clarified that the amount of generation was the same as that of the battery with a low positive electrode-containing water content.

  Next, the temperature is fixed at 60 ° C., the time is fixed at 48 hours, the first aging is performed with the SOC of the battery being 0% to 100%, and then the second aging is performed at 25 ° C./7 days / SOC 100%. went. Thereafter, the battery was sealed, and the battery was adjusted again to SOC 100% and stored at 65 ° C. for 2 weeks. The amount of gas generated by this storage was measured for each battery. The results are shown in Table 2.

この結果から、第一のエージングのＳＯＣが４０％以上で保存によるガス発生量が少なくなることから、第一のエージングの条件としてはＳＯＣが４０％以上であることが好ましい。これは、ＳＯＣが低いと負極のカーボンに充電されたリチウム量が少なくなり、電解液に溶けた水とリチウムの反応が起こりにくいためと考えられる。

From this result, since the amount of gas generated by storage decreases when the SOC of the first aging is 40% or more, the SOC is preferably 40% or more as the condition for the first aging. This is presumably because when the SOC is low, the amount of lithium charged in the carbon of the negative electrode decreases, and the reaction between water and lithium dissolved in the electrolytic solution hardly occurs.

  Next, as the first aging conditions, the SOC is fixed at 60%, the time is fixed at 48 hours, the temperature is set at 20 ° C. to 100 ° C., and then the second aging is performed at 25 ° C./7 days / SOC 100%. I went there. Thereafter, the battery was sealed, and the battery was adjusted again to SOC 100% and stored at 65 ° C. for 2 weeks. The amount of gas generated by this storage was measured for each battery. The results are shown in Table 3.

この結果から、第一のエージング温度は保存によるガス発生量が少なくなる４０℃以上で行うことが好ましいことがわかる。この理由としてはエージング中に起こる水素発生反応が低温ではその進行速度が遅いためと考えられる。

From this result, it can be seen that the first aging temperature is preferably 40 ° C. or higher where the amount of gas generated by storage is reduced. This is probably because the hydrogen generation reaction that occurs during aging is slow at low temperatures.

  On the other hand, when the resistance (DC-IR) after the second aging of the battery prepared under the above conditions is measured, the value of the battery obtained by performing the first aging at 100 ° C. is large as shown in FIG. It became clear.

  This is because the first aging was performed at 100 ° C., so that the separator, which is a porous film, contracted and DC-IR increased, or the electrolytic solution caused a decomposition reaction on the positive electrode and the negative electrode, and the product was extremely A possible reason is that the DC-IR is increased by covering the plate surface.

  In any case, from these results, the temperature condition of the first aging is preferably performed in the range of 40 ° C to 80 ° C. It has been clarified that the same effect can be obtained even if the SOC during aging is changed within the scope of the present invention.

  Furthermore, as the first aging conditions, the SOC is fixed at 60%, the temperature is fixed at 60 ° C., the time is set in the range of 6 hours to 96 hours, and the second aging is performed at 100% SOC / temperature 25 ° C./7. It was carried out under the conditions of the day. These batteries were sealed, adjusted to SOC 100% again, and left in a 65 ° C. environment for 2 weeks, and the amount of gas generated inside the batteries was measured. Further, the DC-IR of the battery was measured after the second aging. The result is shown in FIG.

  From this result, it has been clarified that the effect of suppressing gas generation during storage can be obtained by performing the first aging for 12 hours or more. On the other hand, when aging was performed for 72 hours or more, the problem that the DC-IR of the battery increased was revealed.

  Therefore, it is preferable to perform the first aging time in the range of 12 hours to 72 hours. In addition, it is thought that DC-IR rises by long-term aging because the film | membrane production | generation reaction on the surface of a positive / negative electrode plate advances.

  The amount of positive electrode-containing water allowed in the present invention was examined. After coating the positive electrode, vacuum drying was performed at 120 ° C. The degree of vacuum at this time is 5.0 torr. By adjusting the vacuum drying time, the water content of the positive electrode was adjusted from 1000 ppm to 6000 ppm with respect to the weight of the positive electrode mixture. In order to obtain a positive electrode plate having a water content of less than 1000 ppm, the positive electrode must be dried with hot air at 250 ° C. for 12 hours, and positive electrode plates having a water content of 200 ppm and 500 ppm were obtained by this method. Using these positive electrode plates, a battery manufactured according to the above method was subjected to a first aging condition at a temperature of 60 ° C./SOC 80% / 48 hours, and a second aging condition at a temperature of 25 ° C./SOC 100% / 7 days. This was adjusted again to 100% SOC and allowed to stand in an environment of 65 ° C. for 2 weeks to measure the amount of gas generated inside the battery. The battery sealing is performed when the second aging is completed. The result is shown in FIG.

  From this result, it was found that if it exceeds 5000 ppm, the effect of reducing the amount of gas during storage is small even if high temperature aging is performed. It is considered that this is because when the positive electrode-containing water content is large, it takes a long time to dissolve the water from the electrode plate into the electrolyte, and the water is not consumed during aging and remains in the battery. Moisture can be removed by performing aging at a higher temperature or for a long period of time, and gas generation during high-temperature storage can be suppressed with a small amount. In this case, however, the internal resistance of the battery increases after aging of the battery. It became clear that this occurred. Furthermore, the aging tank which can be controlled at high temperature is required, and the equipment cost is increased, and there is a disadvantage that it is necessary for battery production for a long time.

  As a result of the above studies, the moisture content of the positive electrode is controlled to 5000 ppm or less, the aging conditions that do not adversely affect the battery performance and can suppress gas generation during high temperature storage are 40 ° C. to 80 ° C., SOC 40% to 100%. In range, the period was found to be 12 to 72 hours.

  On the other hand, in order to control the positive electrode-containing water content to less than 1000 ppm, vacuum drying is insufficient, and a hot air drying furnace at about 250 ° C. is required. In order to maintain this level of moisture content, an environment with a dew point of at least −30 ° C. or less is required for storage of the electrode plate after drying. When stored at a dew point higher than this, the electrode plate absorbs moisture in the environment, and the moisture content exceeds 1000 ppm within 48 hours, and the meaning of drying is lost.

  Therefore, it is possible to control the moisture content of the positive electrode to 1000 ppm to 5000 ppm with relatively simple equipment, and it is possible to supply an inexpensive battery.

  Next, as the second aging condition, the purpose of the second aging is to discharge the battery in which the internal short circuit failure has occurred. In order to confirm the effect, in the battery of Example 6, the first aging condition was SOC 60% / 60 ° C./48 hours, and the second aging condition was SOC 100% / 25 ° C./7 days. As the batteries, 200 batteries were produced in which only the first aging condition was performed under the condition of SOC 60% / 60 ° C./48 hours.

  The OCV before and after the second aging was measured for the battery of Example 6, and the OCV before and after the first aging was measured for the battery of Comparative Example 2, and the OCV defective battery was discharged. The determination of the OCV failure was made by measuring the voltage drop amount of all the batteries to obtain the standard deviation (σ), and determining that the battery in which the voltage drop amount was more than three times as bad. Table 4 shows the number of batteries generated in each aging process and the generation rate.

この結果から、第一のエージングだけではＯＣＶ不良を確実に取り除くことはできず、第二のエージングの必要性が確かめられた。ここで第二のエージングを第一のエージングと同じように高温で行うと、図２に示されるようにＤＣ−ＩＲの上昇が起こり得るため、２０℃〜３５℃の室温で行うことが好ましい。このときの電池ＳＯＣは容量変動によるＯＣＶ変化が大きいＳＯＣに設定することが好ましいと考えられるが、ＳＯＣ０％からＳＯＣ１００％までで大きな違いはなく、本実施例では第二のエージング条件をＳＯＣ１００％、２５℃、７日間の条件で行った。また、本実施例では第二のエージングを７日間行っているが、これについても適宜設定されるものである。

From this result, the OCV defect could not be surely removed by the first aging alone, and the necessity of the second aging was confirmed. Here, if the second aging is performed at a high temperature as in the first aging, the DC-IR may increase as shown in FIG. 2, and therefore, it is preferable to perform at a room temperature of 20 ° C. to 35 ° C. It is considered that the battery SOC at this time is preferably set to an SOC in which the OCV change due to capacity fluctuation is large, but there is no significant difference from SOC 0% to SOC 100%. The test was performed at 25 ° C. for 7 days. Further, in this embodiment, the second aging is performed for 7 days, but this is also set as appropriate.

  In the examples of the present invention, lithium secondary batteries using aluminum metal cans have been described. However, other forms, for example, batteries using aluminum laminate sheets as containers, and stainless steel cans as containers. The battery can be implemented, and deformation and rupture of the container due to an increase in battery internal pressure accompanying gas generation when these batteries are stored at high temperatures can be prevented.

  The present invention is useful as a method for producing a non-aqueous electrolyte secondary battery for an electric vehicle.

External view of lithium secondary battery of this example The figure which shows the relationship between the temperature and DC-IR in a present Example. The figure which shows the relationship between the time and storage gas amount in a present Example The figure which shows the relationship between the moisture content and the amount of generated gas in a present Example

Explanation of symbols

1 Battery Case 2 Positive Terminal 3 Negative Terminal 4 Injection Port 5 Lid

Claims (3)

A method for producing a non-aqueous electrolyte secondary battery in which a positive electrode, a negative electrode, an electrode plate group formed by winding a separator, and an electrolyte solution are housed in a battery case,
A step of setting the moisture content of the positive electrode to 1000 to 5000 ppm,
Accommodating the electrode plate group and the electrolyte in the battery case;
A first aging step;
A second aging step,
The first aging step is performed under the conditions of SOC of 40 to 100%, temperature of 40 to 80 ° C., time of 12 to 72 hours, and the battery in an open state,
A method for producing a nonaqueous electrolyte secondary battery, wherein the second aging step is performed at a temperature lower than that of the first aging step.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the second aging step is performed at room temperature. The method for producing a nonaqueous electrolyte secondary battery according to claim 1, further comprising a step of sealing the battery either after the first aging step or after the second aging step.

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