JP2004355977A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a nonaqueous electrolyte secondary battery, having a high discharge capacity and suppressing expansion of the battery even when stored at a high temperature. <P>SOLUTION: The method comprises the steps of housing a power generating element having a positive electrode, negative electrode, and a nonaqueous electrolyte into a container, obtaining a provisionally sealed secondary battery by provisionally sealing an opening of the container, applying initial charging to the provisionally sealed secondary battery, storing the provisionally sealed secondary battery in an atmospheric temperature of 40-80 °C, releasing the provisional sealing of the opening of the container in the provisionally sealed secondary battery to leave it, discharging at least a part of the gas existing inside the container to outside, and permanently sealing the opening of the container. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１０７】
表１から明らかなように、本発明の製造方法に従った実施例１〜８の非水電解質二次電池は、初充電後のガス放出を行わなかった比較例４の非水電解質二次電池とほぼ同等の高い放電容量を実現しながら、２４時間貯蔵後の電池膨れを小さくできている。また、実施例１〜８の二次電池は、ＣＨＢ無添加の比較例５の非水電解質二次電池とほぼ同等の高い放電容量を持ちつつ、９６時間貯蔵後の電池膨れを小さくすることができ、本発明の方法がＣＨＢによる膨れ抑制の効果に影響を及ぼさないことを確認できた。
【０１０８】
また、実施例３および実施例６の非水電解質二次電池の試験結果から、貯蔵時間を同じ４８時間とした場合、貯蔵温度を５０〜７０℃の範囲とすることにより、高い放電容量を維持しながら、電池膨れをさらに小さくすることができることを確認できた。
【０１０９】
これに対して、高温貯蔵時の雰囲気温度を４０℃未満にした比較例１及び比較例２の非水電解質二次電池は、貯蔵時間を１時間としても、６０時間としても、実施例１〜８の非水電解質二次電池と比較して、２４時間貯蔵後の電池膨れが大きかった。
【０１１０】
高温貯蔵時の雰囲気温度を８０℃を超える温度にした比較例３の非水電解質二次電池は、高温貯蔵時の電池膨れは小さかったものの、実施例１〜８の非水電解質二次電池と比較して放電容量が低かった。
【０１１１】
なお、前述した実施例では、分解抑制用添加剤としてＣＨＢを用いる例を説明したが、分解抑制用添加剤には充電状態の非水電解質二次電池を高温に貯蔵した際の非水溶媒の分解を抑制する効果を有するものであればいかなるものを用いてもよい。
【０１１２】
また、前述した実施例では、金属製容器を用いた非水電解質二次電池について説明したが、本願発明は、ラミネートフィルム製容器を用いる非水電解質二次電池にも適用することができる。
【０１１３】
また、前述した実施例においては、正極とセパレータと負極とが偏平状に捲回された電極群を用いる例を説明したが、この代わりに、正極とセパレータと負極との積層物からなる電極群、正極とセパレータと負極との積層物が１回以上折り曲げられた構造の電極群を用いても良い。
【０１１４】
【発明の効果】
以上詳述したように本発明によれば、高温貯蔵した際の電池膨れが抑制され、かつ優れた放電容量を有する非水電解質二次電池の製造方法を提供することができる。
【図面の簡単な説明】
【図１】実施例１の方法により製造される角形非水電解質二次電池を示す部分切欠斜視図。
【図２】実施例１の製造方法における初充電工程及び高温貯蔵工程を説明するための模式図。
【符号の説明】
１…外装缶、２…絶縁体、３…電極群、４…負極、５…セパレータ、６…正極、７…スペーサ、８…蓋体、９…取出穴、１０…注液孔、１１…封止蓋、１２…負極端子、１３…絶縁材、１４…負極リード、１５…絶縁封口板、１６…外装チューブ、２１…型枠。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, many electronic devices such as personal computers and telephones have been reduced in size and made portable due to advances in electronic technology and packaging technology. Accordingly, higher performance is required for secondary batteries used as power supplies for these electronic devices.
[0003]
As such a secondary battery, LiMnO 2 is used as a positive electrode active material. ₄ , LiCoO ₂ Using a carbonaceous material or a chalcogen compound that occludes and releases lithium ions in the negative electrode active material; ₄ , LiPF ₆ A non-aqueous electrolyte secondary battery using an electrolytic solution obtained by dissolving a lithium salt such as in a non-aqueous solvent such as ethylene carbonate, propylene carbonate, methyl ethyl carbonate, γ-butyrolactone, and tetrahydrofuran has been developed. Among them, LiCoO is used for the positive electrode. ₂ At present, lithium ion secondary batteries using a carbonaceous material that stores and releases lithium ions in the negative electrode, such as graphite, spherical carbon, and carbon fibers, are widely used.
[0004]
By the way, when such a non-aqueous electrolyte secondary battery is stored at a high temperature in a charged state, the non-aqueous solvent used in the electrolyte is decomposed and gasified, thereby increasing the internal pressure of the battery and expanding the battery. The problem arises.
[0005]
In order to solve this problem, an additive having an effect of suppressing the decomposition of the non-aqueous solvent has been added to the non-aqueous electrolyte. For example, Patent Document 1 discloses an electrolytic solution in which an organic solvent contains an alkylbenzene derivative having a tertiary carbon adjacent to a phenyl group or a cycloalkylbenzene derivative as an additive.
[0006]
However, among the above additives, for example, a non-aqueous electrolyte secondary battery including an electrolytic solution containing an additive such as cyclohexylbenzene, when stored at high temperatures for a long period of several days or more, the battery swells due to the effect of the additive. However, when high-temperature storage is performed for a short period of about 24 hours, battery swelling may be increased rather than a nonaqueous electrolyte secondary battery containing no additive. Various criteria are set by the user for the time until the battery swells in the non-aqueous electrolyte secondary battery, so that these criteria can be satisfied by a single battery specification. In addition, there is a need for a non-aqueous electrolyte secondary battery that suppresses battery swelling not only during long-term high-temperature storage but also during short-term high-temperature storage.
[0007]
[Patent Document 1]
JP 2001-15155 A
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a method of manufacturing a nonaqueous electrolyte secondary battery having a high discharge capacity and suppressing battery swelling when stored at a high temperature.
[0009]
[Means for Solving the Problems]
The method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention includes a step of housing a power generation element including a positive electrode, a negative electrode, and a nonaqueous electrolyte in a container,
A step of temporarily sealing the opening of the container to obtain a temporarily sealed secondary battery,
Performing a first charge on the temporarily sealed secondary battery,
Storing the temporarily sealed secondary battery at an ambient temperature in the range of 40 to 80 ° C;
By releasing the temporary sealing of the container opening in the temporarily sealed secondary battery and leaving it to stand, a step of releasing at least a part of the gas present inside the container to the outside,
A step of permanently sealing the opening of the container;
It is characterized by having.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for manufacturing a nonaqueous electrolyte secondary battery of the present invention will be described.
[0011]
(Battery assembly process)
An electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. Next, the power generation element including the electrode group and the non-aqueous electrolyte is housed in a container.
[0012]
Hereinafter, the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte will be described.
[0013]
1) Positive electrode
The positive electrode includes a current collector and a positive electrode active material-containing layer, and can be manufactured by, for example, a method described below.
[0014]
A positive electrode active material, a binder, and a conductive agent, if necessary, are suspended in an appropriate organic solvent to form a mixture slurry, and the mixture slurry is applied to one or both surfaces of a current collector substrate in a desired size. The positive electrode can be manufactured by applying a large area, drying the sheet, and cutting the sheet into a desired size. Alternatively, the positive electrode can be prepared by kneading the positive electrode active material together with a binder and, if necessary, a conductive agent, and then attaching the kneaded sheet to a current collector.
[0015]
A ball mill, a bead mill, a dissolver, a sand grinder, a roll mill, or the like is used as a dispersing device for producing the mixture slurry.
[0016]
The thickness of the positive electrode active material-containing layer formed on the current collector surface (excluding the thickness of the current collector) is desirably in the range of 50 μm or more and 200 μm or less.
[0017]
Examples of the current collector include an aluminum foil, a stainless steel foil, and a titanium foil. Particularly, it is most preferable to use an aluminum foil because it is excellent in workability and inexpensive. When an aluminum foil is used as the current collector, the thickness is preferably in the range of 10 μm or more and 40 μm or less because sufficient foil strength can be obtained and the capacity of the secondary battery can be increased.
[0018]
As the positive electrode active material, for example, Li _x MO ₂ (Where M is a transition metal such as Co, Ni, Mn, and the value of 0.05 ≦ x ≦ 1.10.) ₂ , LiNiO ₂ , LiNi _y Co _(1-y) O ₂ , LiMnO ₂ And the like.
[0019]
As the binder, vinylidene fluoride-based fluororesin can be used.
[0020]
Examples of the vinylidene fluoride-based fluororesin include polyvinylidene fluoride, terpolymer of vinylidene fluoride-tetrafluoroethylene-6-propylene fluoride, copolymer of vinylidene fluoride-pentafluoropropylene, and vinylidene fluoride-chlorotrifluoride. Examples thereof include a copolymer of fluoroethylene or a copolymer of vinylidene fluoride and another fluorine-based monomer.
[0021]
Examples of the copolymer of such another fluorine-based monomer and vinylidene fluoride include a copolymer of tetrafluoroethylene-vinylidene fluoride and a terpolymer of tetrafluoroethylene-perfluoroalkylvinyl ether (PFA) -vinylidene fluoride. Copolymer, terpolymer of tetrafluoroethylene-hexafluoropropylene (FEP) -vinylidene fluoride, terpolymer of tetrafluoroethylene-ethylene-vinylidene fluoride, copolymer of chlorotrifluoroethylene-vinylidene fluoride And a terpolymer of chlorotrifluoroethylene-ethylene-vinylidene fluoride and a copolymer of vinyl fluoride-vinylidene fluoride. As the binder, these compounds can be used alone or in combination with other compounds. The types of other compounds to be contained in the binder can be one or more.
[0022]
In particular, it is preferable to use polyvinylidene fluoride as the binder because excellent battery characteristics are obtained and electrode production is easy.
[0023]
Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), ethyl acetate, acetone, and toluene.
[0024]
Examples of the conductive agent include acetylene black, Ketjen black, graphite and the like.
[0025]
The amount of the binder is preferably in the range of 2 to 10 parts by weight based on 100 parts by weight of the total of the positive electrode active material and the conductive agent. When the amount of the binder is within the above range, battery production becomes easy, and excellent battery characteristics and excellent electrode strength can be maintained. When the amount is larger than the above range, the large current characteristics and cycle characteristics of the nonaqueous electrolyte secondary battery may be deteriorated. On the other hand, when the amount is smaller than the above range, the binding force between the positive electrode active materials and the adhesion to the current collector Power cannot be maintained, and battery characteristics may be degraded.
[0026]
The amount of the conductive agent is preferably in the range of 1 part by weight to 20 parts by weight based on 100 parts by weight of the positive electrode active material.
[0027]
The compounding amount of the organic solvent is preferably in the range of 50 parts by weight to 150 parts by weight based on 100 parts by weight of the total of the positive electrode active material, the binder, and the conductive agent. When the compounding amount of the organic solvent is larger than the above range, the stability of the mixture slurry may be deteriorated, and it may be difficult to obtain an electrode having a uniform film thickness. May increase, and the coating property may be deteriorated.
[0028]
The positive electrode has a coating amount of the positive electrode active material-containing layer of 100 to 400 g / m ² Is preferable in terms of battery characteristics or ease of battery manufacture.
[0029]
2) Negative electrode
The negative electrode includes a current collector and a negative electrode active material-containing layer, and can be manufactured by, for example, a method described below.
[0030]
A negative electrode active material, a binder, and a conductive agent, if necessary, are suspended in an appropriate organic solvent to form a mixture slurry, and the mixture slurry is formed on one or both surfaces of a current collector substrate in a desired size. The negative electrode can be manufactured by applying a large area, drying the sheet, and cutting the sheet into a desired size. Further, the negative electrode can be prepared by kneading the negative electrode active material together with a binder and, if necessary, a conductive agent, and attaching the kneaded sheet to a current collector.
[0031]
As the dispersing device for producing the mixture slurry, the same device as that described for the positive electrode is employed.
[0032]
The thickness of the negative electrode active material-containing layer formed on the surface of the current collector (excluding the thickness of the current collector) makes it easy to manufacture the electrode, and has good electrolyte impregnation and electrochemical characteristics. From the viewpoint of being obtained, it is desirable to set the range of 50 μm or more and 200 μm or less.
[0033]
As the current collector, for example, a copper foil, a nickel foil, and the like can be given. However, in consideration of electrochemical stability, flexibility at the time of winding, and the like, it is most preferable to use a copper foil. When a copper foil is used as the current collector, the thickness is desirably in the range of 8 μm or more and 20 μm or less, since sufficient strength of the foil can be obtained and the capacity of the secondary battery can be increased.
[0034]
Examples of the negative electrode active material include a material containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions, and a material formed of a light metal. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of a secondary battery can be improved.
[0035]
Examples of the carbonaceous material that occludes / releases lithium ions include coke, carbon fiber, pyrolytic gas-phase carbonaceous material, graphite, fired resin, fired mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. Above all, it is preferable to use mesophase pitch-based carbon fiber or mesophase spherical carbon that has been graphitized at 2500 ° C. or higher because the electrode capacity is increased.
[0036]
Chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiS). ₂ ), Molybdenum disulfide (MoS ₂ ), Niobium selenide (NbSe) and the like. When such a chalcogen compound is used for the negative electrode, the voltage of the secondary battery decreases, but the capacity of the negative electrode increases, so that the capacity of the secondary battery can be improved. , The rapid charge / discharge performance of the secondary battery can be improved.
[0037]
Examples of the light metal include aluminum, an aluminum alloy, a lithium metal, and a lithium alloy.
[0038]
Examples of the binder include polytetrafluoroethylene (PTFE), vinylidene fluoride-based fluororesin, polyvinylidene fluoride (PVdF), ethylene-propylene-diene terpolymer (EPDM), and styrene-butadiene rubber (SBR). And the like.
[0039]
Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), acetone and the like.
[0040]
The amount of the binder is preferably in the range of 2 parts by weight to 15 parts by weight with respect to 100 parts by weight of the negative electrode active material, from the viewpoint of maintaining battery characteristics and electrode strength.
[0041]
In particular, when a carbonaceous material is used as the negative electrode active material, it is desirable to use polyvinylidene fluoride as the binder, and the compounding amount is in the range of 2 parts by weight to 15 parts by weight with respect to 100 parts by weight of the negative electrode active material. Is preferable in terms of maintaining battery characteristics and electrode strength.
[0042]
The compounding amount of the organic solvent is preferably in the range of 50 parts by weight to 150 parts by weight based on 100 parts by weight of the total of the negative electrode active material and the binder. When the compounding amount of the organic solvent is larger than the above range, the stability of the mixture slurry may be deteriorated, and it may be difficult to obtain an electrode having a uniform film thickness. May increase, and the coating property may be deteriorated.
[0043]
The negative electrode has a coating amount of the negative electrode active material-containing layer of 50 to 300 g / m3 per side. ² Is preferable in terms of battery characteristics or ease of battery manufacture. When a carbonaceous material is used as the negative electrode active material, the coating amount of the negative electrode active material-containing layer is adjusted to 50 to 200 g / m 2 per side. ² Is preferable in terms of battery characteristics or ease of battery manufacture.
[0044]
3) Separator
The separator is formed from a porous material such as a synthetic resin nonwoven fabric, a polyethylene porous film, and a polypropylene porous film.
[0045]
4) Non-aqueous electrolyte
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. The non-aqueous electrolyte has a liquid or gel form.
[0046]
Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), and chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). , 2-dimethoxyethane (DME), diethoxyethane (DEE) and other chain ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF) such as cyclic ethers and crown ethers such as γ-butyrolactone (γ -BL), for example, nitrogen compounds such as acetonitrile (AN), for example, sulfur compounds such as sulfolane (SL) and dimethylsulfoxide (DMSO), and aromatic compounds such as cyclohexylbenzene (CHB). Group compounds and the like. The type of the non-aqueous solvent used can be one or more.
[0047]
Above all, a non-aqueous electrolyte containing an aromatic compound such as cyclohexylbenzene (CHB) is added to the non-aqueous electrolyte secondary battery to prevent decomposition of the non-aqueous solvent when the non-aqueous electrolyte secondary battery is stored at a high temperature in a charged state. Since it acts as an agent, oxidative decomposition of the non-aqueous electrolyte can be suppressed.
[0048]
It is desirable that the compounding amount of CHB in the non-aqueous electrolyte is in the range of 0.1 to 5% by weight. This is for the reason described below. If the amount of CHB is less than 0.1% by weight, the swelling during high-temperature charging and long-term storage may increase. On the other hand, when the compounding amount of CHB exceeds 5% by weight, the amount of gas generated by the decomposition reaction of CHB increases, so that the production method of the present invention may not be able to suppress swelling. A more preferable range of the amount of CHB is 0.5 to 2% by weight.
[0049]
Further, for the purpose of improving the characteristics of the non-aqueous electrolyte secondary battery, it is possible to add an additive other than the decomposition suppressing additive.
[0050]
The non-aqueous electrolyte containing CHB contains a solvent other than CHB (hereinafter, referred to as another solvent), and the composition of the other solvent is preferably as follows.
[0051]
That is, at least one selected from the group consisting of EC, PC and γ-BL, and at least one selected from the group consisting of EC, PC and γ-BL, and DMC, MEC, DEC, DME, DEE, THF, 2- A mixed solvent comprising at least one selected from the group consisting of MeTHF and AN is desirable. In particular, when a negative electrode containing a carbonaceous material that occludes and releases lithium ions is used, other solvents include EC, PC, and γ-BL from the viewpoint of improving the cycle life of the nonaqueous electrolyte secondary battery. It is desirable to use a mixed solvent composed of EC, PC and MEC, EC and PC and DEC, EC and PC and DEE, EC and AN, EC and MEC, PC and DMC, PC and DEC, or EC and DEC.
[0052]
As the electrolyte, for example, lithium perchlorate (LiClO ₄ ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium tetrafluoroborate (LiBF ₄ ), Lithium hexafluoroarsenate (LiAsF) ₆ ), Lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), Lithium aluminum tetrachloride (LiAlCl ₄ ), Lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] And the like. Among them, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ The use of is preferred because conductivity and safety are improved.
[0053]
The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2 mol / L.
[0054]
(Temporary sealing step)
The opening of the container is temporarily sealed to obtain a temporarily sealed secondary battery. Here, the term "temporarily sealed secondary battery" means a secondary battery which is assembled on the premise that the battery is temporarily opened after the temporary sealing and is in a state capable of being initially charged and discharged.
[0055]
(First charging process)
The initial charging is performed by, for example, charging of a constant current / constant voltage method.
[0056]
When the form of the non-aqueous electrolyte secondary battery is rectangular or thin, it is desirable to perform the initial charging step while pressing both surfaces orthogonal to the thickness direction of the temporarily sealed secondary battery. This is because the containers used for the prismatic and thin secondary batteries are formed of a thin and easily deformable material (for example, a metal such as aluminum or an aluminum alloy), so that once they swell, they return to their original shape. It is difficult to return. This pressurization can suppress an increase in the thickness of the secondary battery due to expansion of the container due to a gas generated by a decomposition reaction of a cyclic carbonate such as EC or a chain carbonate such as MEC in the initial charging step.
[0057]
(High temperature storage process)
The temporarily sealed secondary battery is stored at a high temperature in an ambient temperature range of 40 to 80C.
[0058]
In the high-temperature storage step, the atmosphere temperature is set in the above range for the reason described below.
[0059]
If the ambient temperature is lower than 40 ° C., decomposition of the decomposition suppressing additive such as CHB does not sufficiently proceed in the high-temperature storage step, and even if the gas in the container is completely released in the subsequent gas release step, Since unreacted components are decomposed during high temperature storage during use, suppression of battery swelling cannot be achieved. On the other hand, when the ambient temperature exceeds 80 ° C., not only the decomposition reaction of the decomposition suppressing additive but also the decomposition reaction of other non-aqueous solvents occur, so that the loss amount of the non-aqueous electrolyte increases, Due to the organic film formed on the surface of the positive electrode by the reaction, the internal resistance increases, and the discharge capacity or charge / discharge cycle characteristics decrease. A more preferable range of the ambient temperature is 50 to 70 ° C.
[0060]
The present inventors have found that a decomposition reaction (gasification reaction) of a decomposition suppressing additive such as cyclohexylbenzene (CHB) tends to occur after about 24 hours has passed during high-temperature storage in a charged state. . As a result of further experiments, it was found that the storage time is preferably in the range of 2 to 48 hours from the viewpoint of suppressing battery swelling without impairing battery characteristics. Hereinafter, the reason for limiting the storage time to the above range will be described in detail.
[0061]
If the storage time is less than 2 hours, the process proceeds to the gas release step before the decomposition reaction of the decomposition suppressing additive is completed, and there is a possibility that the unreacted decomposition reaction may occur during the high-temperature storage during charging during use. On the other hand, if the storage time exceeds 48 hours, a decomposition reaction between the decomposition suppressing additive and the other non-aqueous solvent occurs, which may lower the discharge capacity or charge / discharge cycle characteristics of the secondary battery.
[0062]
When the form of the non-aqueous electrolyte secondary battery is rectangular or thin, the high-temperature storage step is desirably performed while applying pressure to both surfaces orthogonal to the thickness direction of the temporarily sealed secondary battery. To suppress battery swelling, it is desirable to perform this pressurization at least in the high-temperature storage step, and in order to obtain a sufficient effect, continue from the initial charging step to the high-temperature storage step, and place the container as described above. It is desirable to fix.
[0063]
(Gas release process)
By releasing the temporary sealing of the container opening in the temporary sealed secondary battery and leaving it unattended, at least a part of the gas present inside the container is released to the outside.
[0064]
The release of the temporary sealing is preferably performed after the temporary sealing secondary battery is cooled by leaving it in an atmosphere in a temperature range of 15 to 30 ° C. This is for the reason described below.
[0065]
Since the non-aqueous solvent contained in the non-aqueous electrolyte, especially methyl ethyl carbonate (MEC), which is widely used, has a low boiling point, the temperature of the temporarily sealed secondary battery exceeds 30 ° C. When the sealing is released, the non-aqueous solvent volatilizes to cause loss of the non-aqueous electrolyte, and the discharge capacity may be reduced. For this reason, it is preferable that the temporary sealing secondary battery is cooled to a temperature lower than the boiling point of the non-aqueous solvent of 30 ° C. or lower, and then the temporary sealing is released. However, even when cooling to a temperature lower than 15 ° C., energy loss due to supercooling only increases, and there is a possibility that significant improvement in suppression of volatilization of the non-aqueous solvent may not be expected. It is desirable to set it in the range of -30 ° C.
[0066]
The gas releasing step is preferably performed in an inert gas atmosphere having a dew point of −15 ° C. or less.
[0067]
As the inert gas, it is preferable to use an argon gas from the viewpoint of suppressing the characteristic deterioration due to opening the secondary battery and reducing the manufacturing cost.
[0068]
The reason why the dew point of the inert gas atmosphere is set to −15 ° C. or less is that if the dew point of the inert gas atmosphere is higher than −15 ° C., the positive electrode active material may be deteriorated by moisture mixed in the container due to dew condensation. It is. The lower the dew point, the more moisture (condensation) can be prevented from entering the container. However, since excessive cooling causes deterioration of energy efficiency, the dew point is set to −80 ° C. or higher. Is preferred.
[0069]
(Main sealing step)
The opening of the container is completely sealed.
[0070]
This sealing is desirably performed after the internal pressure of the container returns to normal pressure. This means that if the main sealing is performed in a state where the internal pressure of the container is higher than the normal pressure, the main sealing will be performed in a state where the decomposition gas is dissolved in the non-aqueous electrolyte, and during high-temperature storage during use, This is because the decomposition gas may be released from the non-aqueous electrolyte to cause swelling. By performing the main sealing after the internal pressure of the container returns to normal pressure, the solubility of the decomposition gas of the nonaqueous electrolyte can be reduced to the solubility at normal pressure, and the decomposition gas can be sufficiently released to the outside of the container. it can.
[0071]
Note that this sealing step is preferably performed in an inert gas atmosphere under the same conditions as described in the gas releasing step.
[0072]
According to the method of manufacturing a non-aqueous electrolyte secondary battery according to the present invention described above, it is possible to suppress swelling when the charged secondary battery is stored at a high temperature without impairing the discharge capacity.
[0073]
That is, after the initially charged secondary battery is initially charged and stored at an ambient temperature in the range of 40 to 80 ° C., the nonaqueous electrolyte can be forcibly decomposed to generate gas. Next, the temporary sealing of the container opening of the temporarily sealed secondary battery is released and left to allow at least a part of the decomposed gas to be released to the outside of the container. Then, the non-aqueous electrolyte secondary battery obtained by performing the encapsulation can achieve a high discharge capacity, and almost no decomposition reaction of the non-aqueous electrolyte occurs during high temperature storage during charging. Therefore, the amount of gas generated can be reduced, and swelling can be suppressed.
[0074]
In particular, the present invention is highly effective in suppressing swelling within 24 hours during charging high-temperature storage of a secondary battery including a non-aqueous electrolyte containing an additive such as CHB. A non-aqueous electrolyte secondary battery with less swelling in both storage for a longer period can be provided.
[0075]
Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention at the stage of implementation. Various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.
[0076]
【Example】
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
[0077]
(Example 1)
First, a prismatic nonaqueous electrolyte secondary battery obtained by the method of Embodiment 1 will be described with reference to FIG.
[0078]
As shown in FIG. 1, a bottomed rectangular cylindrical outer can 1 made of metal, for example, aluminum, also serves as, for example, a positive electrode terminal, and an insulator 2 is disposed on the inner surface of the bottom. The flat electrode group 3 is housed in the outer can 1. The electrode group 3 is manufactured by spirally winding the negative electrode 4, the separator 5, and the positive electrode 6 so that the positive electrode 6 is located at the outermost periphery, and then press-forming the flat shape.
[0079]
A spacer 7 made of, for example, a synthetic resin and having a lead extraction hole near the center is disposed on the electrode group 3 in the outer can 1. The metal lid 8 is liquid-tightly joined to the upper end opening of the outer can 1 by, for example, laser welding. The lid 8 has an injection hole 10 for injecting a non-aqueous electrolyte. A sealing lid 11 is liquid-tightly joined to the portion of the lid 8 including the liquid injection hole 10 by, for example, laser welding so as to cover the liquid injection hole 10. In the vicinity of the center of the lid 8, an extraction hole 9 for a negative electrode terminal is opened. The negative electrode terminal 12 is hermetically sealed in the extraction hole 9 via an insulating material 13 made of glass or resin. A negative electrode lead 14 is connected to the lower end surface of the negative electrode terminal 12, and the other end of the negative electrode lead 14 is connected to the negative electrode 4 of the electrode group 3. The insulating sealing plate 15 is arranged on the upper surface of the lid 8. The insulating outer tube 16 covers the side and bottom edges of the outer can 1 and the edge of the insulating sealing plate 15.
[0080]
Hereinafter, a method for manufacturing the secondary battery will be described.
[0081]
<Preparation of positive electrode>
First, a lithium cobalt oxide (LiCoO) having an average particle diameter of 3 μm as a positive electrode active material was used. ₂ 100 parts by weight of powder, 3 parts by weight of acetylene black and 3 parts by weight of graphite as conductive agents, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder (based on 100 parts by weight of active material and conductive agent in total) Was dissolved in N-methyl-2-pyrrolidone (NMP) as an organic solvent, and the mixture was dispersed and mixed with a general-purpose disperser for 4 hours to obtain a mixture slurry.
[0082]
Next, the obtained mixture slurry was coated with 200 to 300 g / m ² Was applied to both surfaces of an aluminum foil (thickness: 15 μm) as a current collector substrate, dried, and then pressed to produce a positive electrode 6.
[0083]
<Preparation of negative electrode>
First, after mesophase pitch carbon fiber (MCF) using mesophase pitch as a raw material is carbonized at 1000 ° C. in an argon atmosphere, 90 volume% is present in an average fiber length of 20 μm, an average fiber diameter of 8 μm, and a particle size of 1 to 80 μm. Then, after appropriately pulverizing so that particles having a particle size of 0.5 μm or less become 5% or less, a carbonaceous material was produced by graphitizing at 3000 ° C. in an argon atmosphere.
[0084]
Next, the obtained carbonaceous material was added to a solution obtained by dissolving polyvinylidene fluoride as a binder in N-methyl-2-pyrrolidone as an organic solvent, and dispersed and mixed with a general-purpose disperser for 3 hours. Prepared a mixture slurry composed of 5 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the carbonaceous material.
[0085]
The obtained mixture slurry is coated with a coating amount per side of 100 to 150 g / m. ² Was applied to both surfaces of a copper foil as a current collector substrate, dried, and then pressed to produce a negative electrode 4.
[0086]
<Preparation of non-aqueous electrolyte>
In a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2), lithium hexafluorophosphate (LiPF) was used as an electrolyte. ₆ ) Was dissolved in 1M, and 1% by weight of cyclohexylbenzene (CHB) was dissolved as an additive for suppressing non-aqueous solvent decomposition to prepare a non-aqueous electrolyte.
[0087]
<Assembly of battery>
The positive electrode 6, the separator 5 made of a polyethylene porous film, and the negative electrode 4 are laminated in this order, and then spirally wound so that the positive electrode 6 is located on the outside. ² To form a flat electrode group 3.
[0088]
The electrode group 3 is housed in an outer can 1 formed by molding an aluminum sheet having a thickness of 0.2 mm so as to have a thickness of 4.1 mm, a width of 30 mm, and a height of 50 mm. After sealing the electrode group 3 by laser seam welding of the electrode 8, a non-aqueous electrolyte was injected from the liquid injection hole 10 of the lid 8 under reduced pressure.
[0089]
Next, a fluoro rubber stopper (not shown) is inserted into the liquid injection hole 10 and hermetically sealed. The liquid rubber is sandwiched with a clamp (not shown) so as to press the top of the fluoro rubber stopper and the bottom of the battery container. Temporarily sealed tightly to produce a temporarily sealed secondary battery. The reason why the clamp is used is to prevent the plug from being removed from the liquid injection hole 10 when the internal pressure of the battery container is increased due to generation of gas or the like. Instead of using a rubber stopper as described above, a rubber plate is put on the lid 8 including the liquid injection hole 10 to close the liquid injection hole 10, and the upper surface of the rubber plate and the battery The battery container can also be temporarily sealed in a liquid-tight manner by sandwiching it with a clamp or the like so as to press the bottom surface of the container.
[0090]
Next, as shown in FIG. 2, a rectangular mold 21 made of a heat-resistant resin such as polypropylene or polyphenylene sulfide is fitted to the outer can 1 of the temporarily sealed secondary battery, thereby forming a wide surface of the outer can 1. The battery was initially charged at a constant current and a constant voltage (1 C, 4.2 V) for 6 hours while holding down (a surface orthogonal to the thickness direction of the battery), and then stored at an ambient temperature of 60 ° C. for 24 hours.
[0091]
After cooling the temporarily sealed secondary battery by leaving it in an atmosphere of 25 ° C., remove the fluoro rubber plug for temporary sealing in an argon gas atmosphere having a dew point of −70 ° C., and leave it for 30 minutes to keep the internal pressure constant. After returning to the pressure, the mold 21 was removed, and the sealing lid 11 was laser-seam welded to the lid 8 including the liquid injection hole 10 to completely seal the liquid injection hole 10. Subsequently, the insulating sealing plate 15 is disposed on the lid 8 and is covered with the outer tube 16, thereby having the structure shown in FIG. 1 described above. The non-rated dimensions are 4.4 mm in thickness, 30 mm in width, and 30 mm in height. A square non-aqueous electrolyte secondary battery having a size of 48 mm and a discharge capacity of 0.2 C of 620 mAh was manufactured.
[0092]
(Example 2)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was 40 ° C. and the storage time was 2 hours.
[0093]
(Example 3)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during the high-temperature storage was 40 ° C. and the storage time was 48 hours.
[0094]
(Example 4)
A prismatic non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was 80 ° C. and the storage time was 2 hours.
[0095]
(Example 5)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was set to 80 ° C. and the storage time was set to 36 hours.
[0096]
(Example 6)
A prismatic non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was 60 ° C. and the storage time was 48 hours.
[0097]
(Example 7)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was 40 ° C. and the storage time was 1 hour.
[0098]
(Example 8)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was set to 80 ° C. and the storage time was set to 1 hour.
[0099]
(Comparative Example 1)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the ambient temperature during high-temperature storage was 30 ° C. and the storage time was 1 hour.
[0100]
(Comparative Example 2)
A prismatic nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the ambient temperature during high-temperature storage was 30 ° C. and the storage time was 60 hours.
[0101]
(Comparative Example 3)
A rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the atmosphere temperature during high-temperature storage was set to 100 ° C. and the storage time was set to 2 hours.
[0102]
(Comparative Example 4)
After the injection of the non-aqueous electrolyte, the sealing is performed not by the temporary sealing, but by the final sealing, that is, the sealing lid 11 is laser seam-welded to the lid 8 including the injection hole 10, and then the initial charging is performed in the same manner as in the first embodiment. By performing this, a prismatic nonaqueous electrolyte secondary battery was manufactured.
[0103]
(Comparative Example 5)
As a non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2), and lithium hexafluorophosphate (LiPF) as an electrolyte ₆ ) Was dissolved in 1M, that is, a non-aqueous solvent containing no CHB was prepared. Immediately after the injection of the non-aqueous electrolyte, the sealing lid 11 was attached to the lid 8 including the injection hole 10. The injection hole 10 was completely sealed by laser seam welding, and the battery was initially charged in the same manner as in Example 1 to produce a prismatic nonaqueous electrolyte secondary battery.
[0104]
<Storage test>
Five rectangular non-aqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared and charged at a constant current and a constant voltage (1 C, 4.2 V) for 3 hours. The battery was stored at a temperature of 80 ° C. for 24 hours or 96 hours, and the difference between the thicknesses of the battery container before and after the storage was measured. The average value is shown in Table 1 below as battery swelling (mm).
[0105]
<Discharge test>
Five rectangular non-aqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared, and charged at a constant current and a constant voltage (1 C, 4.2 V) for 3 hours. The discharge capacity (mAh) when the battery was discharged to 3 V at 0.2 C was measured, and the average value is also shown in Table 1 below.
[0106]
[Table 1]

[0107]
As is clear from Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 to 8 according to the production method of the present invention were non-aqueous electrolyte secondary batteries of Comparative Example 4 in which gas was not released after the first charge. The battery swelling after storage for 24 hours can be reduced while realizing a high discharge capacity almost equivalent to that of. Further, the secondary batteries of Examples 1 to 8 have a high discharge capacity almost equivalent to that of the non-aqueous electrolyte secondary battery of Comparative Example 5 without the addition of CHB, and can reduce battery swelling after storage for 96 hours. It was confirmed that the method of the present invention did not affect the effect of suppressing swelling by CHB.
[0108]
Also, from the test results of the non-aqueous electrolyte secondary batteries of Example 3 and Example 6, when the storage time was set to the same 48 hours, a high discharge capacity was maintained by setting the storage temperature to a range of 50 to 70 ° C. However, it was confirmed that battery swelling could be further reduced.
[0109]
On the other hand, the non-aqueous electrolyte secondary batteries of Comparative Examples 1 and 2 in which the ambient temperature during high-temperature storage was set to less than 40 ° C., even when the storage time was 1 hour or 60 hours, In comparison with the nonaqueous electrolyte secondary battery of No. 8, the battery swelled after storage for 24 hours was large.
[0110]
The non-aqueous electrolyte secondary battery of Comparative Example 3 in which the ambient temperature during high-temperature storage was set to a temperature exceeding 80 ° C., although the battery swelling during high-temperature storage was small, the non-aqueous electrolyte secondary batteries of Examples 1 to 8 The discharge capacity was low in comparison.
[0111]
In the above-described embodiment, an example in which CHB is used as the decomposition-suppressing additive has been described. However, the decomposition-suppressing additive uses a nonaqueous solvent when the charged nonaqueous electrolyte secondary battery is stored at a high temperature. Any material may be used as long as it has an effect of suppressing decomposition.
[0112]
Further, in the above-described embodiment, the non-aqueous electrolyte secondary battery using the metal container has been described. However, the present invention can be applied to a non-aqueous electrolyte secondary battery using a laminate film container.
[0113]
Further, in the above-described embodiment, an example was described in which the electrode group in which the positive electrode, the separator, and the negative electrode were wound flat was used, but instead, the electrode group formed of a laminate of the positive electrode, the separator, and the negative electrode was used. Alternatively, an electrode group having a structure in which a laminate of a positive electrode, a separator, and a negative electrode is bent at least once may be used.
[0114]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a method for manufacturing a nonaqueous electrolyte secondary battery in which battery swelling during high-temperature storage is suppressed and which has excellent discharge capacity.
[Brief description of the drawings]
FIG. 1 is a partially cutaway perspective view showing a prismatic nonaqueous electrolyte secondary battery manufactured by the method of Example 1.
FIG. 2 is a schematic diagram for explaining an initial charging step and a high-temperature storage step in the manufacturing method according to the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Outer can, 2 ... Insulator, 3 ... Electrode group, 4 ... Negative electrode, 5 ... Separator, 6 ... Positive electrode, 7 ... Spacer, 8 ... Lid, 9 ... Extraction hole, 10 ... Liquid injection hole, 11 ... Sealing Stop lid, 12: negative electrode terminal, 13: insulating material, 14: negative electrode lead, 15: insulating sealing plate, 16: exterior tube, 21: formwork.

Claims (2)

A step of housing the power generating element including the positive electrode, the negative electrode and the non-aqueous electrolyte in a container,
A step of temporarily sealing the opening of the container to obtain a temporarily sealed secondary battery,
Performing a first charge on the temporarily sealed secondary battery,
Storing the temporarily sealed secondary battery at an ambient temperature in the range of 40 to 80 ° C;
By releasing the temporary sealing of the container opening in the temporarily sealed secondary battery and leaving it to stand, a step of releasing at least a part of the gas present inside the container to the outside,
And a step of permanently sealing the opening of the container. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the gas releasing step is performed in an inert gas atmosphere having a dew point of -15 ° C or less.

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