JP5312751B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve adhesiveness of an electrode and a separator of a nonaqueous electrolyte secondary battery with the electrode and separator adhered by using the separator carrying a reactive polymer. <P>SOLUTION: The method of manufacturing the nonaqueous electrolyte secondary battery includes a process A for housing an electrode group, which includes a positive electrode and negative electrode capable of reversibly storing and emitting lithium, and a separator sandwiched by the positive electrode and negative electrode and carrying the reactive polymer on both surfaces, in a battery case together with nonaqueous electrolyte, a process B for charging the electrode group filled with the nonaqueous electrolyte after the process A, a process C for adhering the positive electrode and the separator, and the negative electrode and the separator respectively by polymerizing at least a part of the reactive polymer after the process B. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery, and more particularly to a method for producing a non-aqueous electrolyte secondary battery in which a separator carrying a reactive polymer is used to adhere an electrode and a separator. .

  In recent years, consumer electronic devices such as cellular phones, portable personal computers, and portable video cameras are rapidly becoming portable and cordless. For this reason, as a drive power source for these electronic devices, there is an increasing demand for a secondary battery that is small and light and has a high energy density.

  Lithium ion secondary batteries are widely used as secondary batteries having such characteristics. Lithium ion secondary batteries generally consist of a sheet-like positive electrode and negative electrode wound or laminated via a microporous membrane separator made of polyolefin to form an electrode group. It is manufactured by injecting and sealing an electrolytic solution after being housed in a metal case.

  However, in recent years, portable devices have been made lighter and thinner, and lithium ion secondary batteries are also required to be lighter and thinner as a power source. For this reason, lithium ion secondary batteries using a lightweight laminate film as an outer case instead of a heavy metal case are becoming widespread.

  When such a laminate film is used as an exterior case, it is difficult to apply a sufficient surface pressure to the electrode group as compared with a case where a metal case is used. For this reason, due to the expansion and contraction of the electrodes during charging / discharging, the distance between the electrodes varies within the electrode surface, the uniformity of the charging / discharging reaction is lost, and the cycle characteristics deteriorate.

  As one means for solving such a problem, it has been proposed to provide an adhesive layer between the separator and the electrode, and to bond and integrate the separator and the electrode. For example, it has been proposed to provide an adhesive layer mainly composed of polyvinylidene fluoride resin between the separator and the electrode (Patent Documents 1 to 5). However, in such a method, in order to obtain a sufficient adhesive force between the separator and the electrode, it is necessary not only to increase the thickness of the adhesive layer, but also to limit the amount of electrolyte that can be contained in the adhesive layer. Therefore, the internal resistance of the battery is increased, resulting in a problem that the high-load discharge characteristics are deteriorated.

  On the other hand, a precursor capable of generating a polymer gel is blended in advance in the electrolytic solution, and after injecting the electrolytic solution into the case, a polymer gel containing the electrolytic solution is generated by a technique such as thermal polymerization, thereby separating the separator and the electrode. Adhesion has been proposed (Patent Document 6). However, in such a method, since all of the injected electrolyte solution is gelled, the ionic conductivity of the electrolyte solution is lowered, the internal resistance of the battery is increased, and as a result, the high load discharge characteristics are lowered. Arise.

As a method of suppressing an increase in the internal resistance of the battery caused by bonding the separator and the electrode, a reactive polymer is supported on the separator, an electrode group is formed with the positive electrode and the negative electrode, and after impregnating the electrolytic solution, the reactive polymer is added. It has been proposed that a part of the electrolytic solution is gelled by crosslinking and curing, and the separator and the electrode are bonded (Patent Documents 7 to 9).
Japanese Patent Laid-Open No. 10-255849 Japanese Patent Laid-Open No. 2003-77545 JP-A-10-177865 Japanese Patent Laid-Open No. 10-189054 JP-A-10-172606 JP 2006-32237 A JP 2004-241172 A JP 2004-335210 A JP 2006-131808 A

  The amount of current consumed by a portable device tends to increase as the functionality of the device increases. For this reason, in designing a lithium secondary battery, it is not preferable to sacrifice the high-load discharge characteristics of the battery. A conventionally proposed method of bonding between a separator and an electrode using a polyvinylidene fluoride resin, or a method of gelling an electrolyte solution using a precursor capable of generating a polymer gel and bonding between the separator and the electrode Then, although it is possible to adhere | attach firmly between a separator and an electrode, the subject that a high load discharge characteristic falls will generate | occur | produce. Therefore, these methods are not suitable as a method for integrating the separator and the electrode.

  On the other hand, according to the manufacturing method in which the separator and the electrode are bonded using the conventionally proposed reactive polymer, only the electrolyte solution in the vicinity of the interface between the separator and the electrode is gelled. When the ionic conductivity is considered as a whole, a decrease in the ionic conductivity can be minimized. As a result, it is possible to suppress an increase in the internal resistance component caused by bonding the separator and the electrode, and to exhibit excellent high load discharge characteristics. However, since the separator and the electrode are bonded by gelation of a very small amount of the electrolyte, the separator and the electrode may not be bonded with sufficient strength.

  In particular, as a result of examination by the inventors of the present application, it has been found that although the positive electrode and the separator exhibit a sufficient adhesive strength, the adhesive strength between the negative electrode and the separator is extremely low, which is insufficient. In the case of a battery using an electrode group in which a separator and an electrode are integrated, the reaction uniformity during charging and discharging can be obtained only when both the positive electrode and the separator and the negative electrode and the separator are sufficiently bonded. If the adhesion state is insufficient in any one of them, it is difficult to obtain excellent cycle characteristics because the uniformity of the reaction during charge / discharge cannot be obtained. So far, there is no public information referring to this cause, and no improvement proposal has been made.

  In view of the above problems, an object of the present invention is to provide a manufacturing method for manufacturing a non-aqueous electrolyte secondary battery having sufficient adhesion between a separator and positive and negative electrodes and excellent in high-load discharge characteristics. And

The method for producing a non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode and a negative electrode capable of reversibly occluding and releasing lithium, and sandwiched between the positive electrode and the negative electrode, and carrying a cationically polymerizable reactive polymer on both sides A step (A) of storing the electrode group including the separator in a battery case together with a non-aqueous electrolyte containing at least one selected from the group consisting of lithium hexafluorophosphate and lithium tetrafluoroborate; After (A), charging the electrode group filled with the non-aqueous electrolyte (B), and after the step (B), polymerizing at least a part of the reactive polymer, A step (C) of bonding the separator and the negative electrode and the separator, respectively.

  In a preferred embodiment, in the step (B), the battery voltage is maintained at 3.5 V or higher for a predetermined time.

  In a preferred embodiment, in the step (B), the battery voltage is maintained at 3.5 V or more for a time of 51 minutes or more and 336 minutes or less, and the open circuit voltage at the end of charging is 4.3 V or less. Thus, the charging voltage, the charging current and the sustain time are determined.

  In a preferred embodiment, the nonaqueous electrolytic solution contains at least one solvent selected from the group consisting of ethylene carbonate and propylene carbonate.

  In a preferred embodiment, the electrode group includes a plurality of at least one of the positive electrode and the negative electrode and the separator, and at least one of the positive electrode and the negative electrode is laminated via the separator.

  In a preferred embodiment, in the step (C), at least a part of the reactive polymer and the non-aqueous electrolyte are polymerized to gel the non-aqueous electrolyte, and the positive electrode and the separator, and The negative electrode and the separator are bonded together by the gel.

  In a preferred embodiment, the method for producing a non-aqueous electrolyte secondary battery further includes a step of performing a pressure press treatment on the electrode group between the step (B) and the step (C). .

  In a preferred embodiment, the method for producing a non-aqueous electrolyte secondary battery further includes a step of reducing the pressure inside the battery case between the step (B) and the step (C).

  According to the method for producing a non-aqueous electrolyte secondary battery of the present invention, by performing charging before bonding the electrode and the separator, the gas accompanying the solid-electrolyte interface reaction or impurities in the non-aqueous electrolyte can be obtained. Generates gas from decomposition of water contained. Since these gases are mainly generated only at the time of the first charge, the reactive polymer is then reacted to join the positive electrode and the separator, and the negative electrode and the separator, respectively. It is possible to maintain strong adhesion without being affected by gas generation.

  Therefore, the adhesive strength between the negative electrode and the separator is improved, and even when charging and discharging are repeated, high reaction uniformity can be maintained, and displacement of the electrode within the electrode group can be suppressed against dropping and impact. And a non-aqueous electrolyte secondary battery having excellent cycle characteristics and reliability can be provided.

  The inventor of the present application has earnestly studied the cause of the decrease in the adhesive strength between the negative electrode and the separator when using the production method in which the separator and the electrode are bonded using a reactive polymer, and the following knowledge. .

  Specifically, according to the conventional manufacturing method, when the reactive polymer is polymerized and a part of the electrolytic solution is gelled, the separator and the negative electrode are bonded to each other with sufficient strength. It was found that peeling occurs at the interface between the separator and the negative electrode when charging the electrode group integrated with the separator. In addition, this peeling is caused by gas generated by SEI (Solid-Electrolyte-Interface) formation reaction that occurs on the surface of the electrolytic solution and the negative electrode active material at the time of initial charge, and moisture mixed as impurities in the battery system. It was found that the internal pressure in the negative electrode mixture layer was increased by the gas generated by the electrolysis of the electrode and the adhesive interface between the separator and the negative electrode was destroyed.

  Based on these findings, the method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention performs initial charging before the step of bonding the electrode and the separator. The initial charge causes SEI formation reaction and water electrolysis, and the gas generated on the surface of the negative electrode active material does not increase the internal pressure in the negative electrode mixture layer, and promptly increases the amount of the separator carrying the negative electrode and the reactive polymer. It is guided out of the electrode group through a gap. Then, the negative electrode and the separator are bonded with sufficient strength by bonding the negative electrode and the separator. Since the SEI formation reaction and water electrolysis are unique phenomena at the time of initial charge, there is almost no gas generation even after repeated charge and discharge, so that deterioration of the adhesive strength between the negative electrode and the separator is suppressed. The

  Hereinafter, embodiments of a method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings.

  FIG. 1 is a flowchart showing a procedure of a method for manufacturing a nonaqueous electrolyte secondary battery according to the present embodiment. As shown in FIG. 1, first, an electrode group is produced (step 101). Next, the produced electrode group is accommodated in a battery case (step 102), a nonaqueous electrolyte is injected (step 103), and then the battery case is sealed (step 104). Thereafter, initial charging is performed (step 105), and the electrode and the separator are bonded (step 105) to complete the nonaqueous electrolyte secondary battery. Hereinafter, each process will be described in detail.

(Production of electrode group)
First, an electrode group including a positive electrode, a negative electrode, and a separator is prepared. FIG. 2 schematically shows an enlarged cross section of the electrode group 13. The electrode group 13 includes a positive electrode 1, a negative electrode 2, and a separator 3. The positive electrode 1 and the negative electrode 2 can occlude and release lithium reversibly, respectively.

  The positive electrode 1 includes a positive electrode current collector 1a and a positive electrode mixture 1b supported on one surface of the positive electrode current collector 1a. As the positive electrode current collector 1a, a material known as a positive electrode current collector for a lithium secondary battery, such as aluminum, nickel, and a nickel-based alloy (main additive elements such as aluminum, silicon, and carbon) can be used. The positive electrode mixture 1b contains a positive electrode active material, and is formed into a paste together with a conductive material such as acetylene black and a binder such as polyvinylidene fluoride, if necessary, and is applied to the positive electrode current collector 1a and dried. It is carried on one side of the current collector 1a.

As the positive electrode active material, a known positive electrode active material that occludes and releases lithium is used. For example, Li _x CoO ₂ (0.95 ≦ x ≦ 1.05), Li _x NiO ₂ (0.95 ≦ x ≦ 1.05), Li _x MnO ₂ (0) conventionally used for positive electrode active materials. .9 ≦ x ≦ 1.05), Li _x Co _y Ni _(1-y) O ₂ (0.95 ≦ x ≦ 1.05, 0 <y ≦ 0.80), Li _x Ni _y Mn _z Co _{( 1-yz)} Layered lithium-containing composite oxides such as O ₂ (0.95 ≦ x ≦ 1.05, 0 <y ≦ 0.80, 0 <z ≦ 0.50) and some of these metal elements Examples include those substituted with other elements, spinel-type lithium-containing composite oxides such as Li _x Mn ₂ O ₄ (0.90 ≦ x ≦ 1.20), and those obtained by substituting part of Mn with other elements. It is done.

  The negative electrode 2 includes a negative electrode current collector 2a and a negative electrode mixture 2b supported on one surface of the negative electrode current collector 2a. As the negative electrode current collector 2a, a material known as a current collector of a negative electrode for a lithium secondary battery, such as copper, nickel, and stainless steel, can be used. The negative electrode mixture 2b contains a negative electrode active material, and if necessary, conductive materials such as acetylene black, graphite powder and fibrous carbon material, binders such as styrene butadiene rubber and polyvinylidene fluoride, and carboxymethyl cellulose and the like. It is pasted together with the adhesive, applied to the negative electrode current collector 2a, and dried to be carried on one side of the negative electrode current collector 2a. The negative electrode mixture 2b containing the negative electrode active material may be formed on the foil-like negative electrode current collector 2a by vapor deposition or sputtering.

  A known negative electrode active material that absorbs and releases lithium is used as the negative electrode active material. In particular, the effect of the present invention is great when the negative electrode active material reacts with the electrolytic solution during initial charging to form SEI and the decomposition product of the electrolytic solution is gasified. As such a negative electrode active material, for example, graphite materials such as natural graphite and artificial graphite conventionally used for non-aqueous electrolytes, amorphous carbon materials, and alloying with Li are known. Examples include compounds such as Al, Sn, and Si, and oxides.

  The separator 3 includes a microporous membrane 3a and a reactive polymer 3b supported on both sides of the microporous membrane 3a. As the microporous membrane 3a, a membrane having a large ion permeability and having a predetermined mechanical strength and insulating property is used. Preferably, the pores are closed at a temperature of 100 ° C. or higher and 200 ° C. or lower, and a function of increasing the resistance of ion permeability is provided. From the viewpoint of excellent organic solvent resistance and hydrophobicity, a polyolefin resin in which polypropylene, polyethylene or the like is used alone or in combination is preferable. The pore diameter of the microporous membrane 3a is preferably in a range in which the active material, binder, and conductive agent detached from the positive electrode mixture 1b and the negative electrode mixture 2b do not permeate, for example, 0.01 to 1 μm. Is preferred. The thickness of the microporous membrane 3a is generally selected in the range of 5 to 100 μm. The porosity is determined according to the permeability of the electrons and ions, the material, and the film pressure, but is generally preferably 30 to 80%. As the microporous membrane 3a, a laminate of microporous membranes having different compositions may be used. For example, a multilayer film of polypropylene and polyethylene may be used from the viewpoints of heat resistance and pore blocking properties.

  The reactive polymer 3b to be carried on the separator 3 can be any polymer that functions to gel at least the electrolyte near the interface between the separator 3 and the electrode by the polymerization reaction of the reactive group and to adhere the separator and the electrode. Good. The polymerization reaction may be a radical polymerization reaction or a cationic polymerization reaction. However, in the case of radical polymerization reaction, it is necessary to add a highly reactive radical polymerization initiator and a side reaction with the electrolytic solution may occur. Therefore, the reactive polymer 3b that is polymerized by cationic polymerization may be used. preferable.

  As such a reactive polymer, a polyfunctional crosslinking polymer having a plurality of reactive groups capable of reacting with an isocyanate group and a cationic polymerizable functional group in the molecule as disclosed in Patent Document 8 is used. At least one kind of reactivity selected from a 3-oxetanyl group and an epoxy group in the molecule as disclosed in Patent Document 9 or a reactive polymer partially having a crosslinked structure by reacting with isocyanate. By reacting a crosslinkable polymer having a group with an acid anhydride, a reactive polymer having a partially cross-linked structure may be mentioned.

  In the positive electrode 1 and the negative electrode 2, the electrode group 13 is configured by sandwiching the separator 3 so that the positive electrode mixture 1b and the negative electrode mixture 2b are in contact with the reactive polymer 3b.

(Storage in battery case)
Next, the electrode group 13 is housed in a battery case. FIGS. 3A and 3B are a perspective view and a sectional view showing the electrode group 13 housed in the battery case 14. As the battery case 14, a metallic battery can such as Al or Fe or a laminate film obtained by laminating a resin film on both surfaces of a metal foil can be used. In order to realize a lightweight and thin secondary battery, it is preferable to use a battery case made of a laminate film. An aluminum lead 11 and a nickel lead 12 for external connection are attached to the positive electrode current collector 1a of the positive electrode 1 and the negative electrode current collector 2a of the negative electrode 2, respectively.

(Non-aqueous electrolyte injection)
Subsequently, a nonaqueous electrolytic solution is injected into the battery case 14. The nonaqueous electrolyte is usually injected at room temperature and normal pressure. However, when the viscosity of the non-aqueous electrolyte is high, it may be injected in a heated or pressurized state. Further, after injecting the non-aqueous electrolyte, it is preferable to deaerate the inside of the battery case by reducing the pressure, and then to promote the impregnation of the non-aqueous electrolyte into the electrode group by returning to normal pressure. . The injected nonaqueous electrolytic solution is filled in the gaps of the positive electrode mixture 1b, the negative electrode mixture 2b, and the microporous membrane 3a, and the electrode group 13 is filled with the nonaqueous electrolytic solution.

  The non-aqueous electrolyte is composed of a non-aqueous solvent and a lithium salt that dissolves in the non-aqueous solvent. As the non-aqueous solvent, known ones can be used without particular limitation. For example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Acyclic ethers such as dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane , Formamide, Acetamide, dimethylformamide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl Examples include aprotic organic solvents such as 2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, and N-methylpyrrolidone. Use a mixture of seeds or more.

  In particular, when the non-aqueous solvent reacts with the negative electrode active material during the initial charge to form a reduced coating called SEI and the decomposition product is gasified, the production method according to the present invention is suitably used. For this reason, the effect of the present invention remarkably appears when a non-aqueous solvent containing EC, PC, DMC, DEC, and EMC, which is known to cause SEI formation reaction with the negative electrode active material, is used. In order to obtain excellent high-load discharge characteristics, it is preferable that at least one of EC and PC having a large relative dielectric constant is contained in the non-aqueous solvent.

Any known lithium salt that can be dissolved in the non-aqueous solvent can be used without particular limitation. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate and the like, and a nonaqueous solvent using these may be used alone or in combination of two or more It can be dissolved and used.

Among the lithium salts mentioned above, in particular, LiBF ₄ (lithium hexafluoroborate) and LiPF ₆ (lithium hexafluorophosphate) themselves effectively function as a cationic polymerization catalyst, so that LiBF ₄ and LiPF ₆ It is preferable to include at least one in the electrolytic solution. When LiBF ₄ or LiPF ₆ is not used as the lithium salt contained in the electrolytic solution, it is preferable to separately add a catalyst for promoting the cationic polymerization reaction of the reactive polymer supported on the separator to the electrolytic solution. As such a cationic polymerization catalyst, an onium salt is preferable.

(Battery case sealing)
After injecting the non-aqueous electrolyte, the inside of the battery is sealed by sealing the opening of the battery case. At this time, when the battery case 14 made of a laminate film is used, it is preferable to seal the opening by heat welding. Moreover, when sealing the opening part of a battery case, the inside of a battery case can also be made into a pressure reduction state.

For the purpose of simplifying the handling of the electrode group 13 in the assembly process and improving productivity, the separator 3 carrying the electrode and the reactive polymer is pressed by pressing the stacked electrode group 13. Temporary pressure bonding can also be performed. At this time, the applied pressure needs to be within a range that does not crush the fine holes of the separator 3, and the applied pressure is preferably 5 N / cm ₂ or less.

(First charge)
The non-aqueous electrolyte secondary battery thus manufactured is first charged before the step of bonding the separator 3 supporting the reactive polymer to the positive electrode 1 and the negative electrode 2. In the initial charge, the negative electrode active material and the electrolytic solution react to form SEI, and it is preferable to hold the battery above the voltage at which gas generation occurs due to decomposition of the electrolytic solution. For this reason, it is preferable to apply a voltage of 3.5 V or more between the positive electrode 1 and the negative electrode 2 as the battery voltage. On the other hand, when the voltage between the positive electrode 1 and the negative electrode 2 is higher than 4.3 V, the battery characteristics of the nonaqueous electrolyte secondary battery are deteriorated, which is not preferable. More preferably, the battery voltage is set to 3.5 V or higher and held for a certain period of time so that the generation of gas due to the SEI reaction and the decomposition of the electrolyte solution described above is almost completely completed.

When the negative electrode potential becomes lower than a predetermined value due to charging, as shown in FIG. 4, the solvent such as EC or PC in the non-aqueous electrolyte 15 held in the gap of the negative electrode mixture 2b is decomposed, and the negative electrode mixture SEI is formed on the surface of the negative electrode active material in 2b. At this time, one part of the solvent molecule is cut, and gas 16 is generated as a side reaction. For example, it is known that CH ₄ , CO, CO _{2 and the} like are generated in a solvent containing EC. SEI gradually grows and stabilizes as the reductive decomposition of the solvent proceeds. For this reason, gas generation continues until the SEI formation reaction is completed, and a certain time is required until gas generation converges. As a result of detailed experiments, it was found that the time for maintaining the battery voltage at 3.5 V or higher is preferably 51 minutes or longer.

  There is no particular limitation on the upper limit of the time for holding the battery voltage at 3.5 V or higher. However, since the productivity decreases as the charging time becomes longer, it is preferable that the time for holding the battery voltage at 3.5 V or higher is not so long. Specifically, shorter than about 336 minutes is preferable. If the time for maintaining the battery voltage at 3.5 V or higher is 51 minutes or longer, the gas generation reaction is considered to have ended. Therefore, considering productivity, the time is more preferably closer to 51 minutes.

  In the initial charge, it is preferable to hold the secondary battery at a temperature of 30 ° C. or lower in order to suppress the progress of the polymerization reaction of the reactive polymer 3b. When charging with a large current, the charging current value at the time of initial charging is such that metal lithium is electrodeposited on the negative electrode and the battery capacity may decrease, so that the charge / discharge rate current value (1C) or less is 1 hour or less. It is preferable to do.

As shown by the arrows in FIG. 4, the gas generated by the initial charge is a slight gap between the separator 3 carrying the negative electrode mixture 2b and the reactive polymer 3b immediately without increasing the internal pressure in the negative electrode mixture layer. Through the electrode group 13 is guided. In order to introduce the gas existing between the separator 3 and the negative electrode 2 carrying the reactive polymer completely and more quickly, the secondary battery is preferably pressure-pressed after the initial charge. The pressing pressure is preferably 0.5 N / cm ² or more and 5 N / cm ² or less. When the pressure is less than 0.5 N / cm ² , the effect of pushing out the gas from the electrode group is small. Further, if it is 5 N / cm ² or more, there is a possibility of crushing the fine pores of the separator. Moreover, in order to obtain the same effect, initial charging may be performed in a state where the secondary battery is pressurized or restrained.

  It is also preferable to discharge the gas generated by the initial charge to the outside of the battery case 14. In this case, after the initial charging step, one end of the battery case 14 is opened and deaerated under a reduced pressure environment. When the battery case 14 made of a laminate film is used, the battery case 14 can be sealed again by thermally welding the opening portion.

(Adhesion between electrode and separator)
After the initial charge, at least a part of the reactive polymer 3b is polymerized to bond the positive electrode 1 and the separator 3, and the negative electrode 2 and the separator 3, respectively. When a cationic polymerizable polymer is used as the reactive polymer 3b, the secondary battery is held in a heated environment. Thereby, the cationic polymerization reaction of the reactive polymers 3b starts, and a crosslinking reaction occurs between the reactive polymers 3b or in the reactive polymer molecules. At this time, the solvent is embraced by the polymerized reactive polymer 3b and gels. As shown in FIG. 5, the electrolyte solution in the vicinity of the interface between the positive electrode mixture 1b and the microporous film 3a and in the vicinity of the interface between the negative electrode mixture 2b and the microporous film 3a gels to generate a gel 15 '. As a result, it is possible to obtain a non-aqueous electrolyte secondary battery in which the positive electrode 1 and the separator 3 and the negative electrode 2 and the separator 3 are firmly bonded by the gel 15 ′. In order to improve the uniformity of the adhesion between the electrode and the separator, it is preferable to bond the secondary battery in a pressurized or constrained state, that is, to polymerize the reactive polymer 3b.

  The temperature at which the secondary battery for carrying out the polymerization reaction of the reactive polymer 3b is preferably 40 ° C. or higher and 80 ° C. or lower. When the temperature is lower than 40 ° C., polymerization does not occur at a practical reaction rate, resulting in low productivity. On the other hand, the higher the temperature, the more the reaction is promoted. However, when the temperature is higher than 80 ° C., problems such as deterioration of battery characteristics and separator shrinkage occur.

  On the other hand, if the heating time for the reaction is too short, gelation of the reactive polymer and the non-aqueous electrolyte does not proceed sufficiently, and the adhesive strength between the electrode and the separator is not sufficient. On the other hand, if the length is too long, battery characteristics may deteriorate. For this reason, it is preferable that heating time shall be 12 hours or more and 48 hours or less.

  If the battery voltage when stored in a warm environment is too low, the battery characteristics are deteriorated due to overdischarge due to self-discharge during warm storage. On the other hand, when the battery voltage is too high, warming storage deterioration occurs and battery characteristics deteriorate. Therefore, it is preferable to keep the battery voltage at 3.7V or higher and 4.0V or lower while being stored in a warm environment.

(Completion of non-aqueous electrolyte secondary battery)
A nonaqueous electrolyte secondary battery is completed through the above steps. According to the method for producing a non-aqueous electrolyte secondary battery of the present invention, charging is performed to form SEI on the surface of the negative electrode active material before bonding the electrode and the separator. As a result, the gas accompanying the SEI reaction and the gas accompanying the decomposition of the water contained as impurities in the non-aqueous electrolyte can be generated, and such a gas generated only at the first charge can be excluded from the negative electrode mixture. it can. Since then, such gas is hardly generated even after repeated charging. For this reason, after the initial charge, the reactive polymer is reacted, and the positive electrode and the separator and the negative electrode and the separator are bonded to each other, so that the non-water that can maintain the strong adhesion between the electrode and the separator even when charging and discharging are repeated. An electrolyte secondary battery can be obtained.

  As a result, even if charging / discharging is repeated, the bonding state between the electrode and the separator is prevented from changing or a gap is prevented between the electrode and the separator. The change in battery characteristics is suppressed. In addition, since the electrode and separator are bonded with high strength and the bonding strength is maintained, the positive electrode and the negative electrode do not shift within the electrode group even when subjected to dropping or impact, and excellent cycle characteristics and reliability are achieved. Can be obtained.

  In the above-described embodiment, a non-aqueous electrolyte secondary battery manufacturing method is exemplified by using a non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode in which a mixture containing an active material is formed on one side of each current collector. However, the present invention is not limited to the structure of the nonaqueous electrolyte secondary battery described in the above embodiment. For example, a non-aqueous electrolyte secondary battery using an electrode group in which a positive electrode and a negative electrode in which a mixture containing an active material is formed on both sides of a current collector and a separator supporting a reactive polymer are alternately stacked to increase the number of layers The present invention can also be applied to the manufacture of Further, the present invention can be similarly applied to a non-aqueous electrolyte secondary battery using a wound electrode group in which a positive electrode and a negative electrode are wound through a separator carrying a reactive polymer. Furthermore, the shape of the battery is not particularly limited, and may be any of a cylindrical shape, a flat shape, and a square shape.

  Examples of the present invention will be specifically described below.

<Example 1>
(Preparation of a separator carrying a reactive polymer)
As shown in FIG. 2, a microporous membrane 3a made of polyethylene and having a thickness of 20 μm was prepared as the microporous membrane 3a. The average pore diameter of the microporous membrane 3a is 0.1 μm, and the porosity is 41%.

  As the reactive polymer, a substance prepared by the method disclosed in the example of Patent Document 9 was used. Specifically, first, 60.0 g of methyl methacrylate, 16.0 g of 3-ethyl-3-oxetanylmethyl methacrylate, and 3,4-epoxycyclohexylmethyl acrylate were added to a 500 ml three-necked flask equipped with a reflux condenser. 0 g, 226.6 g of ethylene carbonate and 0.15 g of N, N′-azobisisobutyronitrile were added, mixed with stirring for 30 minutes while introducing nitrogen gas, and then heated to 70 ° C. to perform radical polymerization. I went for 8 hours. After this, the resulting reaction mixture was cooled to 40 ° C. To this reaction mixture, 226.6 g of diethyl carbonate and 0.15 g of N, N′-azobisisobutyronitrile were added, and the mixture was heated again to 70 ° C., and radical polymerization was further performed for 8 hours. Thereafter, the resulting reaction mixture was cooled to 40 ° C. to obtain an ethylene carbonate / diethyl carbonate mixed solvent solution (concentration: 15% by weight) of the crosslinkable polymer.

  Next, 100 g of this polymer solution was added to 600 ml of methanol while stirring with a high-speed mixer to precipitate the polymer. The polymer was filtered off, washed several times with methanol, placed in a drying tube, dried by circulating dry nitrogen gas (dew point temperature −70 ° C. or lower) in which liquid nitrogen was vaporized, A crosslinkable polymer was obtained by vacuum drying in a desiccator for 6 hours.

  The crosslinkable polymer was dissolved in ethyl acetate at room temperature to obtain a 10 wt% crosslinkable polymer solution. Separately, an ethyl acetate solution of phthalic anhydride having a concentration of 5% by weight was prepared. While stirring the crosslinkable polymer solution, the phthalic anhydride solution was slowly added dropwise thereto to prepare a mixed solution of the crosslinkable polymer and phthalic anhydride. The ratio of the number of moles of acid anhydride of phthalic anhydride to the number of moles of reactive groups possessed by the crosslinkable polymer was 0.025.

After this mixed solution of the crosslinkable polymer 3b and phthalic anhydride is applied to one side of the microporous membrane 3a, it is heated to 50 ° C. to volatilize ethyl acetate, and then applied to the other side in the same manner. The ethyl acetate was stripped. As a result, a separator 3 having a crosslinkable polymer supported on both sides at a coating density of 2.5 g / m ² per side was obtained. Next, the separator carrying the crosslinkable polymer is put in a thermostat at 50 ° C. for 60 hours, and the crosslinkable polymer carried on the separator is reacted with phthalic anhydride to partially crosslink the crosslinkable polymer. Thus, the separator 3 carrying the reactive polymer 3b on both sides was obtained.

(Preparation of positive electrode)
LiCoO ₂ (average particle size: 8 μm, specific surface area by BET method: 4.2 m ² / g) is used as the positive electrode active material, 3 parts by weight of acetylene black as a conductive agent is added to 100 parts by weight of this active material as a binder. 4 parts by weight of a certain polyvinylidene fluoride and an appropriate amount of N-methyl-2-pyrrolidone were added and stirred and mixed to obtain a slurry-like positive electrode mixture 1b. Polyvinylidene fluoride was used in a state of being previously dissolved in N-methyl-2-pyrrolidone.

  Next, the slurry-like positive electrode mixture 1b was applied to one side of a current collector 1a made of an aluminum foil having a thickness of 20 μm, the coating film was dried, and rolled with a roller. The obtained electrode plate was punched out to the dimensions shown in FIG. 6, and the positive electrode mixture 1 b at the tab portion as the lead attachment portion was peeled off to obtain the positive electrode 1. The positive electrode current collector 1a to which the positive electrode mixture 1b is applied has a square shape with one side having a length of 20 mm.

The method for preparing LiCoO ₂ used as the positive electrode active material is as follows.

  First, an aqueous metal salt solution in which cobalt sulfate was dissolved was prepared. The aqueous metal salt solution was maintained at 50 ° C. with stirring, and an aqueous solution containing 30% by weight of sodium hydroxide was dropped into the aqueous solution and neutralized to generate a cobalt hydroxide precipitate. The cobalt hydroxide precipitate was filtered, washed with water, dried in air, and then calcined at 400 ° C. for 5 hours to obtain cobalt oxide. The obtained cobalt oxide was confirmed to be a single phase by powder X-ray diffraction.

Next, the obtained cobalt oxide and lithium carbonate were mixed so that the ratio of the number of Co atoms to the number of Li atoms was 1: 1. This mixture was calcined at 950 ° C. for 10 hours. Thereafter, the fired product was pulverized to obtain a powder having a cumulative 50% particle size of 8 μm obtained by a laser diffraction method, thereby obtaining the target LiCoO ₂ . The obtained LiCoO ₂ was confirmed to have a single-phase hexagonal crystal structure by powder X-ray diffraction.

(Preparation of negative electrode)
100 parts by weight of natural graphite (average particle size: 18 μm, specific surface area by BET method: 3.2 m ² / g), 6 parts by weight of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone In addition, stirring and mixing were performed to obtain a slurry-like negative electrode mixture. Polyvinylidene fluoride was used in a state of being previously dissolved in N-methyl-2-pyrrolidone.

Next, the slurry-like negative electrode mixture was applied to one side of a current collector 2a made of a copper foil having a thickness of 15 μm, and the coating film was dried and rolled with a roller. The packing density of the active material in the negative electrode mixture layer was 1.4 g / cm ³ . The obtained electrode plate was punched into the dimensions shown in FIG. 6 to obtain a negative electrode.

(assembly)
Using the obtained positive electrode 1 and negative electrode 3 and separator 3, a thin nonaqueous electrolyte secondary battery (thickness 0.5 mm, width 40 mm, height 50 mm, design capacity 14 mAh) as shown in FIG. 3 is assembled. It was. First, the positive electrode 1 and the negative electrode 2 were laminated | stacked through the separator 3 which carry | supported the reactive polymer, and the electrode group 13 was produced. An aluminum positive electrode lead 11 and a nickel negative electrode lead 12 were welded to the positive electrode 1 and the negative electrode 2, respectively. The electrode group was accommodated in a battery case 14 made of aluminum laminate film having a wall thickness of 0.12 mm and opened in three directions, and fixed to the inner surface of the aluminum laminate film with PP tape. The two openings including the opening from which the positive electrode lead 11 and the negative electrode lead 12 protrude are thermally welded to form a battery case 14 made of an aluminum laminate film into a bag shape. Then, a predetermined amount of non-aqueous electrolyte was injected from the opening, and after decompression and deaeration, the opening was thermally welded under reduced pressure to seal the inside of the battery. As the non-aqueous electrolyte, a solution of LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 30:70 so as to have a concentration of 1.0 mol / L was used.

(First charge)
The sealed secondary battery is sandwiched between two glass plates with a thickness of 3 mm and fixed with clips, so that the electrode group in the battery is uniformly pressurized, and then the current value is 1. Constant current charging was performed at 4 mA for 120 minutes. The open circuit voltage (OCV) after completion of charging was 3.75 V, and the time during which the battery voltage was maintained at 3.5 V or higher was 101 minutes.

(Adhesion of positive electrode and negative electrode to separator)
The battery pressed with the clip was subjected to constant current discharge to 3.7 V at a current value of 1.4 mA in an environment of 20 ° C., and then stored in an environment of 60 ° C. for 24 hours.

<Example 2>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 30 minutes at a current value of 2.8 mA in the initial charging step, and discharging was not performed in the bonding step of the positive electrode, the negative electrode, and the separator. . The OCV after the completion of charging in the initial charge gas generation step was 3.66 V, and the battery voltage was maintained at 3.5 V or higher for 21 minutes.

<Example 3>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 60 minutes at a current value of 2.8 mA in the initial charging step. The OCV after the completion of charging was 3.75V, and the time during which the battery voltage was maintained at 3.5V or higher was 51 minutes.

<Example 4>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 300 minutes at a current value of 2.8 mA in the initial charging step. The OCV after the end of charging was 4.14V, and the time during which the battery voltage was maintained at 3.5V or higher was 291 minutes.

<Example 5>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 345 minutes at a current value of 2.8 mA in the initial charging step. The OCV after the completion of charging was 4.30 V, and the time during which the battery voltage was maintained at 3.5 V or higher was 336 minutes.

<Example 6>
A battery was fabricated in the same manner as in Example 1 except that in the initial charging gas generation step, the charging condition was a constant current value of 380 minutes at a current value of 2.8 mA. The OCV after the completion of charging was 4.42 V, and the time during which the battery voltage was maintained at 3.5 V or higher was 371 minutes.

<Example 7>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 24 minutes at a current value of 7.0 mA in the initial charging step. The OCV after the completion of charging was 3.75V, and the battery voltage was maintained at 3.5V or higher for 20 minutes.

<Example 8>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 12 minutes at a current value of 14.0 mA in the initial charging step. The OCV after the completion of charging was 3.75 V, and the time during which the battery voltage was maintained at 3.5 V or higher was 10 minutes.

<Example 9>
In the initial charging process, constant current charging was performed for 60 minutes at a current value of 2.8 mA, the glass plate and the clip were removed after the charging was completed, and 6N for 1 minute was performed in a 25 ° C environment. A battery was produced in the same manner as in Example 1. The OCV after the completion of charging was 3.75V, and the time during which the battery voltage was maintained at 3.5V or higher was 51 minutes.

<Example 10>
A battery was fabricated in the same manner as in Example 1 except that constant current charging was performed for 60 minutes at a current value of 2.8 mA in the initial charging step, and decompression and deaeration were performed after the completion of charging. The OCV after the completion of charging was 3.75V, and the time during which the battery voltage was maintained at 3.5V or higher was 51 minutes.

  After charging, remove the glass plate and clip, cut one end of the sealing part of the aluminum laminate case and leave it open, leave the entire battery in a reduced pressure environment, degas the gas present in the battery, While the pressure was reduced, the open part was heat welded again to seal the inside of the battery.

<Comparative Example 1>
A battery was fabricated in the same manner as in Example 1 except that the discharge was not performed in the step of bonding the positive electrode and the separator and the negative electrode and the separator without performing the initial charging step. The OCV after sealing the battery was 0.21V.

<Battery evaluation>
(Evaluation of adhesive strength between separator and electrode)
The prepared batteries of Examples 1 to 10 and Comparative Example 1 were prepared one by one, discharged at a constant current of 1.4 mA at a current value of 1.4 mA in a 25 ° C. environment, and then in a 25 ° C. environment. The battery was charged with a constant current up to 4.2 V at a current value of 2.8 mA. Thereafter, the battery was disassembled, the electrode group housed in the battery was taken out, and the adhesion between the positive electrode and the separator and the negative electrode and the separator was evaluated. At this time, in any of the batteries of Examples and Comparative Examples, it was visually confirmed that the electrolyte solution at the interface between the positive electrode and the separator and the negative electrode and the separator was gelled.

  The case where the electrode and the separator were not adhered at all was judged as x, the case where less than 60% of the electrode plate area was adhered was judged as Δ, and the case where 60% or more was adhered was judged as ○.

(Evaluation of battery capacity)
Prepare the batteries of Examples 1 to 10 and Comparative Example 1 one by one, discharge at a constant current of 3.0 mA at a current value of 1.4 mA in an environment of 25 ° C., and then in an environment of 25 ° C. The battery was charged at a constant current of 4.2 V at a current value of 2.8 mA, and further charged at a constant voltage of 4.2 V until the current value was attenuated to 0.7 mA. Thereafter, each battery was subjected to constant current discharge to 3.0 V at a current value of 1.4 mA in an environment of 25 ° C., and the discharge capacity obtained at this time was measured as the initial discharge capacity.

  In Table 1, the evaluation results of Examples 1 to 10 and Comparative Example 1 are displayed together with the production conditions.

  From (Table 1), the negative electrode and the separator were adhered in the batteries of any of the examples in which the initial charging step was performed. On the other hand, in the battery of Comparative Example 1 in which the initial charging process was not performed, the negative electrode and the separator were not adhered. From these results, by using the production method of the present invention, it is possible to bond the negative electrode to the separator, which was difficult with a non-aqueous electrolyte secondary battery produced using a separator carrying a conventional reactive polymer. It turns out that it became.

  Further, as can be seen from Examples 3 to 6, when the current value of the initial charging process is constant and the charging time is changed, the charging time is maintained for 60 minutes or more, that is, the battery voltage is maintained at 3.5 V or more. If the elapsed time is 51 minutes or more, the negative electrode and the separator are more reliably bonded. As can be seen from Example 2, if the time kept at 3.5 V or more is only 21 minutes, the adhesion between the negative electrode and the separator is slightly worse than in Examples 3-6.

  In each of Examples 1, 3, 7, and 8, the charging current value and the charging time are changed so that the OCV at the end of charging is 3.75V. The battery of Example 1 and Example 3 in which the battery voltage was maintained at 3.5 V or higher was 51 minutes or longer, and the battery voltage was held in the battery voltage of 3.5 V or higher was less than 51 minutes. Compared with the batteries of Example 7 and Example 8, the area where the negative electrode and the separator are bonded is larger. On the other hand, the battery of Example 6 in which the battery voltage was maintained at 3.5 V or higher was 371 minutes, while the adhesion between the separator and the negative electrode was ensured, but the initial discharge capacity was different from that of the other examples. Somewhat smaller. This is probably because the charging time is increased because the charging time is increased, the positive electrode active material charged at a high potential is deteriorated, and as a result, the initial charging capacity is decreased. This can be seen from the fact that the OCV at the end of the initial charging of the battery of Example 6 is 4.42 V, which is significantly higher than the charging voltage of 4.2 V for a general lithium ion secondary battery.

  From the above results, the charging condition in the initial charging step is that the battery voltage is maintained at 3.5 V or higher for 51 minutes or more and 336 minutes or less, and the OCV at the end of charging is 4.3 V or less. Is preferred.

  Furthermore, the battery of Example 9 is subjected to a pressure press process at the end of the initial charge, and the battery of Example 10 is subjected to a vacuum degassing process after the end of the initial charge. These batteries have a larger adhesion area between the separator and the negative electrode than those of Example 3 manufactured under the same conditions except that these treatments are not performed at the end of the initial charge, and are almost 100% adhered. I was able to confirm.

  From these results, it can be seen that after the initial charging step, the pressure press treatment or the vacuum degassing treatment is effective as a means for increasing the adhesive strength between the separator and the negative electrode.

  According to the method for producing a non-aqueous electrolyte secondary battery of the present invention, since the separator and the positive electrode and the separator and the negative electrode can be firmly bonded, the non-water having excellent cycle characteristics and drop resistance / impact reliability. An electrolyte secondary battery can be obtained. Therefore, the present invention provides, for example, a non-aqueous electrolyte secondary battery that can be used as a power source for portable electronic devices that require high reliability, a large battery used for electric vehicles and power storage, etc. It is suitably used for production.

It is a flowchart which shows the procedure of one Embodiment of the manufacturing method of the nonaqueous electrolyte secondary battery by this invention. It is sectional drawing which shows typically the structure of the electrode group of the nonaqueous electrolyte secondary battery manufactured by this embodiment. (A) And (b) is the perspective view and sectional drawing which show the form after inserting the electrode group shown in FIG. 2 in a battery case. It is typical sectional drawing explaining the gas which generate | occur | produces at an initial charging process. It is sectional drawing which shows typically the structure of the electrode group after an adhesion process. It is a figure explaining the magnitude | size of an electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 1b Positive electrode mixture 2 Negative electrode 2a Negative electrode collector 2b Negative electrode mixture 3 Separator 3a Microporous film 3b Reactive polymer 11 Positive electrode lead 12 Negative electrode lead 13 Battery case

Claims (6)

An electrode group including a positive electrode and a negative electrode capable of reversibly occluding and releasing lithium, and a separator sandwiched between the positive electrode and the negative electrode and carrying a cationic polymerizable reactive polymer on both sides, is formed of lithium hexafluorophosphate and Storing in a battery case with a non-aqueous electrolyte containing at least one selected from the group consisting of lithium tetrafluoroborate;
After the step (A), the step of charging the electrode group filled with the non-aqueous electrolyte while maintaining the electrode group at 30 ° C. or lower (B),
After the step (B), the positive electrode and the separator, and the negative electrode and the separator are bonded to each other by polymerizing at least a part of the reactive polymer at 40 ° C. or higher and 80 ° C. or lower. Step (C),
It encompasses,
In the step (B), the battery voltage is maintained at 3.5 V or more for a time of 51 minutes or more and 336 minutes or less, and the open circuit voltage at the end of charging is 4.3 V or less. A method for producing a non-aqueous electrolyte secondary battery that determines a charging current and a maintenance time .   The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains at least one solvent selected from the group consisting of ethylene carbonate and propylene carbonate.   2. The nonaqueous electrolytic solution according to claim 1, wherein the electrode group includes a plurality of at least one of the positive electrode and the negative electrode and the separator, and at least one of the positive electrode and the negative electrode is laminated via the separator. A method for manufacturing a secondary battery.   In the step (C), the positive electrode and the separator, and the negative electrode and the separator are obtained by polymerizing at least a part of the reactive polymer and the nonaqueous electrolytic solution to gel the nonaqueous electrolytic solution. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the gel is adhered by the gel.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1, further comprising a step of performing a pressure press treatment on the electrode group between the step (B) and the step (C).   The method for producing a non-aqueous electrolyte secondary battery according to claim 1, further comprising a step of reducing the pressure in the battery case between the step (B) and the step (C).

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