JP2015005350A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nonaqueous electrolyte secondary battery by which the amount of gas generating from a positive electrode active material at the time of charging can be reduced and consequently, battery characteristics can be enhanced in the nonaqueous electrolyte secondary battery.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery comprises: a step of preparing a nonaqueous electrolyte secondary battery including a positive electrode arranged by use of a positive electrode active material expressed by the compositional formula (1), Li[NiCoMnc[Li]]O(1) (where a, b, c and d satisfy 0<a<1.4, 0≤b<1.4, 0<c<1.4, 0<d≤0.5, a+b+c+d=1.5, and 1.0≤a+b+c<1.5); a first charging step of charging the nonaqueous electrolyte secondary battery to a potential lower than a plateau potential; a first degassing step of removing gas from inside the nonaqueous electrolyte secondary battery; and a second charging step of charging the nonaqueous electrolyte secondary battery to a potential equal to or higher than the plateau potential in turn.

Description

  The present invention relates to a method for manufacturing a nonaqueous electrolyte secondary battery.

  In recent years, in order to cope with global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there is an expectation for the reduction of carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electricity such as secondary batteries for motor drive is the key to the practical application of these. Device development is actively underway.

  As secondary batteries for driving motors, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries having high theoretical energy are attracting attention and are being developed rapidly. A non-aqueous electrolyte secondary battery generally has a positive electrode in which a positive electrode active material or the like is applied to a current collector and a negative electrode in which a negative electrode active material or the like is applied to a current collector through an electrolyte positioned between them. Connected to each other. Then, when ions such as lithium ions are occluded / released in the electrode active material, a charge / discharge reaction of the battery occurs.

In such a non-aqueous electrolyte secondary battery for driving a motor, spinel lithium manganate (for example, LiMn ₂ O ₄ ) and layered lithium nickel oxide (for example, LiNi _1-x Co _x O ₂ ) are used as the positive electrode active material. ) Etc. are used. When such a positive electrode active material is used, the solvent in the electrolytic solution is decomposed at the time of initial charge, and a small amount of gas is generated. In particular, solid solution positive electrode active material materials are charged to a plateau potential or higher for activation, and it is known that further gas is generated. Therefore, in the production of the nonaqueous electrolyte secondary battery, it is preferable to carry out a step of degassing. This is because the appearance of the battery not only changes the appearance of the gas but also affects the battery characteristics.

  With respect to gas generation from an electrode active material, a conventional technique for manufacturing an electrochemical device is known which includes a step of charging the electrode active material to a plateau potential or higher and a step of removing gas (Patent Document 1 below). ).

Special table 2009-505367

  However, in the above-described conventional technology, a small amount of gas generated at the time of initial charge less than the plateau potential is retained between the electrodes. Due to the stagnation of gas during the initial charge, the charge above the plateau potential becomes non-uniform. As a result, it was found that an overcharged part was formed, and further gas was generated at this part. As a result, in the secondary battery, cycle durability is deteriorated, the appearance of the battery is changed, and the like.

  Accordingly, an object of the present invention is to provide means for reducing the amount of gas generated from a positive electrode active material during charging in a method for producing a nonaqueous electrolyte secondary battery, and as a result, improving battery characteristics. .

The present inventor has intensively studied to solve the above problems. As a result, when a solid solution positive electrode active material is used, after the step of charging to a potential lower than the plateau potential, the step of removing the gas, and the step of charging to the potential higher than the plateau potential, I found it to be solved. As a solid solution positive electrode active material, the following composition formula (1):
Li _1.5 [Ni _a Co _b Mnc [Li] _d ] O ₃ (1)
Wherein a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0 <d ≦ 0.5, a + b + c + d = 1.5, 1.0 ≦ a + b + c <1.5 is satisfied,
The positive electrode active material represented by these is used.

  The production method of the present invention can prevent the gas generated during the initial charge from staying between the electrodes by removing the gas before the step of charging to a plateau potential or higher. Thereby, the electrode reaction proceeds uniformly during charging at a plateau potential or higher, and gas generation at that time can be suppressed. As a result, the battery characteristics of the nonaqueous electrolyte secondary battery can be improved.

1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat (stacked) bipolar type, which is an embodiment of a non-aqueous electrolyte secondary battery. It is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of a secondary battery. It is a figure for demonstrating a plateau area | region.

  The present embodiment is a method for manufacturing a nonaqueous electrolyte secondary battery. First, a typical example of a non-aqueous electrolyte secondary battery that can be manufactured by the manufacturing method of the present embodiment will be described with reference to the drawings. Below, a nonaqueous electrolyte lithium ion secondary battery is demonstrated as preferable embodiment of a nonaqueous electrolyte secondary battery. However, it is not limited only to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

[Overall configuration of non-aqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 that is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer positive electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 2, the outermost layer positive electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost layer positive electrode current collector is disposed on one or both surfaces. A positive electrode active material layer may be disposed.

  The positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out of the battery exterior material 29 so that it may be pinched | interposed into the edge part. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  Note that FIG. 1 shows a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

[Method for producing non-aqueous electrolyte secondary battery]
The manufacturing method of the nonaqueous electrolyte secondary battery of the present embodiment includes at least a step of preparing an uncharged nonaqueous electrolyte secondary battery using a specific positive electrode active material, a first charging step, a first degassing step, A 2nd charge process is implemented in order. The first charging step charges the battery to a potential below the plateau potential, and the second charging step charges to a potential equal to or higher than the plateau potential. As a preferred embodiment, the second degassing step is performed after the second charging step. In a more preferred embodiment, an aging process and a third gas venting process are performed after the second gas venting process. Moreover, a pre 1st charge process may be implemented before a 1st charge process, and an auxiliary charge process may be performed after a 2nd charge process. Hereinafter, each step will be described.

<Step of preparing an uncharged non-aqueous electrolyte secondary battery>
The step of preparing an uncharged non-aqueous electrolyte secondary battery includes a positive electrode forming step using a positive electrode slurry, a negative electrode forming step using a negative electrode slurry, and a positive electrode, a negative electrode and a separator obtained in the forming step are laminated. Forming a laminate, and injecting an electrolyte into the laminate. An uncharged non-aqueous electrolyte secondary battery means a battery immediately after assembling a non-aqueous electrolyte secondary battery and injecting an electrolytic solution, that is, a non-aqueous electrolyte secondary battery that has never been charged. Hereinafter, each step will be described.

[I] Positive Electrode Formation Step The positive electrode formation step [I] using the positive electrode slurry is not particularly limited except that a specific positive electrode active material is used, and a conventionally known method can be applied. In the positive electrode formation step [I], from the viewpoint of mass production (production efficiency), first, (1) a positive electrode slurry preparation step is performed. Next, (2) the obtained positive electrode slurry is applied to the surface of the current collector, the positive electrode slurry is applied, dried, and roll-pressed to perform a positive electrode raw material preparation step for preparing a positive electrode raw material. Thereafter, (3) the positive electrode raw material is cut into a desired shape and size using a cutting means, and a positive electrode manufacturing step is carried out to obtain a positive electrode through drying.

(1) Positive electrode slurry preparation process (Preparation method of positive electrode slurry)
This process should just be able to prepare a positive electrode slurry. Specifically, the slurry is prepared by adding a slurry viscosity adjusting solvent (NMP or the like) in which a binder is dissolved in a positive electrode active material, a conductive auxiliary agent, and the like, and further adding a solvent and mixing to adjust the viscosity. That is, the positive electrode slurry is slurried (inked) from the slurry viscosity adjusting solvent and the solid content using a homogenizer or a kneader.

(Composition of positive electrode slurry)
In addition to the positive electrode active material, the positive electrode slurry optionally includes a conductive additive, a binder, a slurry viscosity adjusting solvent, and the like.

In the present embodiment, as the positive electrode active material, the following composition formula (1):
_{Li 1.5 [Ni a Co b Mn} c [Li] d] O 3 (1)
Wherein a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0 <d ≦ 0.5, a + b + c + d = 1.5, 1.0 ≦ a + b + c <1.5 is used.

The positive electrode active material represented by the formula (1) includes an electrochemically inactive layered Li ₂ MnO ₃ and an electrochemically active layered LiMO ₂ (where M is Co, Ni, Mn and A layered lithium-containing transition metal oxide comprising a solid solution with a transition metal such as Fe). This layered lithium-containing transition metal oxide has a portion that changes to a spinel structure when subjected to charge or charge / discharge in a predetermined potential range, and partially has a spinel phase after the battery is completed. It is in a state. After a predetermined charge / discharge cycle treatment, the lithium-containing transition metal oxide is useful as a material capable of obtaining a large electric capacity exceeding 200 mAh / g.

  As an average particle diameter of a positive electrode active material, it is preferable that it is 10-20 micrometers, and it is more preferable that it is 12-18 micrometers. It is preferable that the average particle size is 10 μm or more because elution of manganese can be suppressed. On the other hand, when the average particle size is 20 μm or less, it is preferable that foil breakage, clogging, and the like can be suppressed in the application step to the current collector during the production of the positive electrode. The average particle diameter is measured by a laser diffraction / scattering particle size distribution measuring device. The average particle diameter can be measured, for example, using a particle size distribution analyzer (model LA-920) manufactured by Horiba.

  Examples of conductive assistants include carbon powders such as acetylene black, carbon black, channel black, thermal black, ketjen black, graphite, various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark), expanded graphite, etc. Is mentioned. Content of the conductive support agent with respect to the whole quantity of a positive electrode active material layer is 0-30 mass% normally, Preferably it is 1-10 mass%, More preferably, it is 3-7 mass%.

  The binder is added for the purpose of maintaining the electrode structure by binding the constituent members in the active material layer or the active material layer and the current collector. The binder is not particularly limited, but polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinyl acetate, acrylic resin, polyimide, epoxy resin, polyurethane resin, urea resin, styrene- Examples thereof include a synthetic rubber binder such as butadiene rubber (SBR). The content of the binder with respect to the total amount of the positive electrode active material layer is usually 0 to 50% by mass, preferably 5 to 45% by mass, more preferably 10 to 25% by mass, and particularly preferably 15 to 20%. % By mass.

  Examples of the slurry viscosity adjusting solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like.

  The viscosity of the positive electrode slurry can be applied in a wide viscosity range. The viscosity of the positive electrode slurry is preferably 500 to 10000 mPa · s, more preferably 800 to 9000 mPa · s, and still more preferably 1000 to 8000 mPa · s. In the positive electrode slurry, the solid content concentration is 40 to 90% by mass, more preferably 50 to 70% by mass. When the viscosity of the positive electrode slurry is 500 mPa · s or more, the positive electrode slurry can be uniformly applied to a predetermined thickness on the current collector foil to be conveyed using a coating machine (coater or the like). In the positive electrode obtained as a result, a positive electrode active material layer having a uniform and flat surface can be formed. If the viscosity of the positive electrode slurry is 100000 mPa · s or less, the positive electrode slurry can be uniformly applied to a predetermined thickness on the current collector foil conveyed using a coating machine (coater, etc.), and then Can be dried in a short time. In the positive electrode obtained as a result, a positive electrode active material layer having a uniform and flat surface can be formed.

(2) Positive Electrode Fabrication Step In this step, the obtained positive electrode slurry is applied to the surface of the current collector, dried and pressed to produce a positive electrode fabric.

(Slurry application)
The method for applying the positive electrode slurry is not particularly limited, and for example, a coating method using a coater, a patterning coating method such as an ink jet method or a screen printing method can be used. Preferably, application to the surface of the current collector is performed while continuously conveying the current collector from the unwinding roll. A guide roll or the like provided at a predetermined interval can be used so that the current collector traveling between the winding roll and the winding roll can be stably conveyed. In slurry application, it is desirable that the coating is generally performed so that the weight per unit area or the accuracy of the application mass is within a range of about ± 5% by mass (any part).

  The current collector is made of a conductive material, and a positive electrode active material layer is disposed on one side or both sides thereof. There is no particular limitation on the material constituting the current collector, and for example, a conductive resin in which a conductive filler is added to a metal or a conductive polymer material or a non-conductive polymer material may be employed.

  Examples of the metal include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, or copper is preferably used from the viewpoint of conductivity and battery operating potential.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Examples of non-conductive polymer materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide ( PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals. It is preferable to include an alloy or metal oxide. Further, the conductive carbon is not particularly limited, but is at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. Preferably it contains seeds. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. Although there is no restriction | limiting in particular also about the thickness of a collector, Usually, it is about 1-100 micrometers.

(Drying; Removal of slurry viscosity adjusting solvent)
Next, the current collector on which the positive electrode slurry coating film is formed is dried, and the slurry viscosity adjusting solvent contained in the slurry coating film is removed. Although there is no restriction | limiting as drying conditions, Usually, 40-150 degreeC, Preferably it is 80-130 degreeC, and is 5 minutes-20 hours. The drying atmosphere is preferably performed in an air atmosphere from the viewpoint of production cost. As the drying means (apparatus), a drying means using hot air drying and infrared (IR) drying capable of normal continuous drying can be used, and a drying means using vacuum drying can also be used. Moreover, you may use the drying means which used hot air drying and IR drying together.

  The coating and drying are performed on one surface of the current collector, and then the same surface is applied and dried on the other surface of the current collector to form a dry coating film on both surfaces of the current collector. Can do. In addition, you may perform the said application | coating and drying simultaneously on both surfaces. When carrying out the above application and drying simultaneously on both sides, from the viewpoint of preventing the slurry on the lower surface side from dripping, the conveying direction of the current collector is changed from the horizontal direction to the vertical direction (from top to bottom, or from bottom to top). You may go by the method of heading). In this case, a conveying device, a coating (coating) device, a drying device, and the like may be installed from horizontal to vertical (or from vertical to horizontal). In the case of a bipolar electrode, a dry coating film (positive electrode active material layer) is formed on one surface using the positive electrode slurry, and a dry coating film (negative electrode active material layer) is formed on the other surface using a negative electrode slurry. ) May be formed. Also in this case, the application and drying may be performed in order of each surface, or both surfaces may be performed simultaneously.

(Dry coating press)
Next, by pressing the current collector having the dried coating film after drying the slurry coating film and adjusting the slurry dried coating film (positive electrode active material layer) to have a target density, obtain.

As conditions for pressing, for example, a slurry dry coating film (positive electrode active material layer) has a target density of 0.90 to 3.00 g / cm ³ by roll pressing while continuously transporting a current collector having a dry coating film on both sides. Adjust so that it is within the range. However, the target density may be appropriately determined in consideration of the purpose of use of the battery (output importance, energy importance, etc.), ion conductivity, and the like. The press method may be either a cold press or a hot press.

  In addition, the collector which has a dry coating film can be normally obtained as a roll-form positive electrode raw material by roll-rolling, carrying continuously, and winding on a winding roller. Preferably, the positive electrode fabric (current collector having a dried coating film) to be conveyed after the pressing may be cut by the following cutting means without being wound by a winding roller.

(3) Positive electrode production process In this process, the positive electrode raw material obtained above is cut (cut) into a desired shape and size using a cutting means, and a positive electrode is obtained through drying.

(Cut positive electrode fabric (cutting))
As a method of cutting, the positive electrode raw material wound up in a roll shape is again attached to the unwinding roller, and since the positive electrode original material is not unwound, use a cutting means such as a slitter to match the target electrode size. And cut into a rectangular shape. Note that the cutting means is, for example, a rectangular shape or the like according to the target electrode size using a cutting means such as a slitter for the positive electrode material conveyed after the pressing process without being wound by a winding roller. It can also be cut. This method is desirable in that the man-hour can be reduced.

(Drying; removal of adhering water)
Next, the cut positive electrode is dried to remove moisture adhering to the drying in the positive electrode raw material preparation step (2). Drying conditions are determined according to the size of the positive electrode and cannot be uniquely defined, but are usually dried at 70 ° C. or higher for 7 hours or longer using a vacuum dryer. There is no particular limitation on the drying atmosphere, and after substitution with an inert gas (nitrogen gas), vacuum drying can be performed under reduced pressure. Moreover, you may use the drying means which used vacuum drying and IR drying together. Through the drying, a positive electrode having a desired target density, size, and shape can be obtained.

[II] Negative Electrode Formation Step As the negative electrode formation step [II], from the viewpoint of mass production (production efficiency), first, (1) a negative electrode slurry preparation step is performed. (2) Next, the obtained negative electrode slurry is applied to the surface of the current collector, dried and pressed to perform a negative electrode raw material preparation step for preparing a negative electrode raw material. Thereafter, (3) the negative electrode raw material obtained above is cut into a desired shape and size using a cutting means and dried to obtain a negative electrode.

(1) Negative electrode slurry preparation process This process does not have a restriction | limiting in particular, What is necessary is just to be able to prepare a negative electrode slurry. Specifically, the negative electrode active material, conductive additive, binder, slurry viscosity adjusting solvent (NMP, etc.) and the like are added and mixed, and the solvent is further added to adjust the viscosity.

(Composition of negative electrode slurry)
In addition to the negative electrode active material, the negative electrode slurry thus obtained optionally includes a conductive additive, a binder, a slurry viscosity adjusting solvent, and the like.

The negative electrode active material has a composition capable of releasing lithium ions during discharging and occluding lithium ions during charging. The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium. Examples of the negative electrode active material include metals such as Si and Sn, TiO, Ti ₂ O ₃ , TiO ₂ , or Metal oxides such as SiO ₂ , SiO, SnO ₂ , composite oxides of lithium and transition metals such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN, Li—Pb alloys, Li—Al alloys , Li, or carbon powder, natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or carbon material such as hard carbon is preferably exemplified. Among these, by using an element that forms an alloy with lithium, it becomes possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a conventional carbon-based material. The negative electrode active material may be used alone or in the form of a mixture of two or more. The element alloying with lithium is not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like.

  Among the negative electrode active materials, it is preferable to include a carbon material and / or at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. Or Sn is more preferable, and it is particularly preferable to use a carbon material. A carbon material is preferable because a high energy density can be obtained by using it in combination with the above solid solution positive electrode active material and a non-aqueous electrolyte.

  The carbon material is preferably a carbonaceous particle having a low lithium relative discharge potential, such as natural graphite, artificial graphite, a blend of natural graphite and artificial graphite, a material obtained by coating natural graphite with amorphous, soft carbon, hard Carbon or the like can be used. The shape of the carbonaceous particles is not particularly limited and may be any shape such as a lump shape, a sphere shape, and a fiber shape, but is preferably not a scale shape, and preferably a sphere shape and a lump shape. Those that are not scaly are preferred from the viewpoints of performance and durability. The carbonaceous particles may be those whose surfaces are coated with amorphous carbon. By covering the surfaces of the carbonaceous particles with amorphous carbon, it is possible to prevent the graphite and the electrolytic solution from reacting during charging and discharging of the battery.

The BET specific surface area of the negative electrode active material is preferably 0.8 to 1.5 m ² / g. If the specific surface area is in the above range, the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved. Moreover, it is preferable that the tap density of a negative electrode active material is 0.9-1.2 g / cm < ³ >. It is preferable from the viewpoint of energy density that the tap density is in the above range.

  The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm and more preferably 1 to 20 μm from the viewpoint of increasing the capacity, reactivity, and cycle durability of the negative electrode active material. preferable.

  The conductive additive, binder and slurry viscosity adjusting solvent that can be used for the negative electrode are the same as those that can be used for the positive electrode. In the negative electrode slurry, the solid content concentration is preferably 30 to 80% by mass, more preferably 45 to 65% by mass.

  Since the (2) negative electrode raw material preparation step and (3) the negative electrode preparation step are the same steps except that the negative electrode slurry is used instead of the positive electrode slurry, detailed description is omitted here.

[III] Step of Forming Laminate In this step [III], a positive electrode and a negative electrode obtained in the positive electrode formation step [I] and the negative electrode formation step [II] and a separator are laminated to form a laminate. To do.

(Method for forming laminate)
The positive electrode and the negative electrode obtained in the positive electrode forming step [I] and the negative electrode forming step [II], and a separator are alternately stacked in the order of a positive electrode, a separator, a negative electrode, a separator, and a positive electrode. By doing so, it can be set as the laminated body which consists of desired lamination | stacking number (cell number).

  The separator is obtained in the same manner as the positive electrode and the negative electrode, for example, by purchasing a microporous membrane (thickness of about 25 μm) made of polyethylene (PE) with a roll. It is desirable to cut (cut) the raw material of the separator into a desired shape and size using a cutting means, and obtain the separator through drying. The method for cutting the separator raw is not particularly limited. Specifically, the separator web wound in a roll shape is attached to the unwinding roller, and since the separator web is unwound, using a cutting means such as a slitter, the desired shape, size, What is necessary is just to cut into a rectangular shape according to the target separator size.

  Specific examples of the separator include a microporous film made of a polyolefin such as polyethylene or polypropylene, a hydrocarbon such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, or the like.

(Drying; removal of adhering water)
Next, the cut separator is dried to remove the attached moisture. The drying conditions are not particularly limited and are determined according to the separator size and the like. Usually, drying is performed at 70 ° C. or higher for 7 hours or longer using a vacuum dryer. The drying atmosphere is not particularly limited, but it is desirable to perform vacuum drying under reduced pressure after replacement with an inert gas (nitrogen gas). As the drying means (apparatus), a drying means using a vacuum drying apparatus can also be used. Moreover, you may use the drying means which used vacuum drying and IR drying together. Through the above drying, a separator having a desired target density, size, and shape can be obtained.

(Lamination method)
Lamination of the positive electrode, separator, and negative electrode may be performed manually or may be automated (mechanical). For automation (mechanization), a commercially available lamination machine may be used, or an in-house produced lamination machine may be used. A laminated body is obtained by alternately laminating positive electrodes, separators, negative electrodes, separators, positive electrodes,.

(Tab welding)
Next, a positive electrode tab and a negative electrode tab are joined to the obtained laminate by welding. If necessary, it is desirable to remove excess tabs and the like by trimming after welding. The joining method is not particularly limited, but the ultrasonic welding machine does not generate heat (heat) during joining and can be joined in a very short time, preventing deterioration of the electrode active material layer due to heat. It is excellent in that it can be done. At this time, the positive electrode tab and the negative electrode tab can be arranged so as to face (opposite) each other on the same side (the same extraction side). Thereby, the positive electrode tab of each positive electrode can be bundled together and taken out from the exterior body as one positive electrode current collector plate. Similarly, the negative electrode tabs of each negative electrode can be bundled together and taken out from the outer package as one negative electrode current collector. Moreover, you may arrange | position so that a positive electrode current collecting plate (positive electrode current collecting tab) and a negative electrode current collecting plate (negative electrode current collecting tab) may become an opposite side (different extraction side).

  Alternatively, the separator may be laminated by forming an adhesive layer. Thereby, even if an electrode (a positive electrode thru | or negative electrode) and a separator are laminated | stacked, it can laminate | stack stably, without shifting | deviating. Therefore, it is excellent in that it is possible to omit the trouble of providing inspection items and inspecting whether there is a deviation so that the electrode does not protrude from the separator at the end portion to cause a micro short circuit.

  The material constituting the current collector plate (tab) is not particularly limited, and a known highly conductive material can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable.

[IV] Step of Injecting Electrolytic Solution into Laminated Body In this step, an electrolytic solution is injected into the laminated body. The laminated body is sandwiched and stored from above and below with a laminate film used for the battery exterior body. After storage, the three sides of the exterior body are sealed to form a three-side sealed body. Further, an electrolytic solution is injected from the opening on one side where the three-side sealing body remains.

(Storing the laminate in the exterior)
The laminate is a laminate film used for the battery outer package, and from above and below, the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) can be taken out of the battery outer package, Sandwich. In addition, you may provide an insulation reinforcement sheet inside the edge | side which takes out a positive electrode collector plate and a negative electrode collector plate outside among the upper and lower laminate films. As a result, even if an unexpected accident such as unexpected strong vibration or impact, or a user accidentally scratching with a blade during use, some of the upper and lower laminate films are damaged, and the internal Al foil is damaged. It can be prevented from being exposed. As a result, the positive electrode current collector plate and the negative electrode current collector plate are excellent in that the safety of the battery can be significantly improved without contacting the Al foils in the upper and lower laminate films.

  A conventionally known metal can case can be used as the exterior material. In addition, the laminate may be packed using a laminate film as an exterior material. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order. By using such a laminate film, it is possible to easily open the exterior material, add the capacity recovery material, and reseal the exterior material.

  As the configuration of the battery, various shapes such as a square shape, a paper shape, a laminated shape, a cylindrical shape, and a coin shape can be adopted.

(Preparation of three-side sealed body)
Next, three sides of the outer peripheral portions (sealing portions) of the upper and lower laminate films are sealed by thermocompression bonding. A three-side sealed body is obtained by thermocompressing and sealing three sides of the outer peripheral portion. Under the present circumstances, it is preferable to seal the heat sealing part of the edge | side which takes out a positive electrode current collecting plate (positive electrode current collecting tab) and a negative electrode current collecting plate (negative electrode current collecting tab). This is because, if the positive electrode current collector plate and the negative electrode current collector plate are in the opening during the subsequent injection, the electrolyte may be scattered during the injection.

(Liquid injection)
Next, the liquid injection device provided at the tip of the electrolyte solution transport line connected to the electrolyte storage tank inside the three-side sealed body from the opening on one side where the three-side sealed body remains in the liquid injection device The electrolyte is injected from the nozzle. As a result, an electrolyte layer in which the separator is impregnated with the electrolytic solution is formed. At this time, the three-side sealing body is accommodated in a vacuum box connected to a vacuum pump so that the electrolyte solution can be impregnated in the laminate inside the three-side sealing body, particularly the separator and the electrode active material layer as soon as possible. Furthermore, it is desirable to perform liquid injection in a state where the pressure is reduced and the inside is in a high vacuum state. After the injection, the three-side sealed body is taken out from the vacuum box, and the remaining one side of the three-side sealed body is temporarily sealed to obtain a laminate type (laminated structure) nonaqueous electrolyte secondary battery.

  The electrolytic solution has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), fluorine-containing cyclic carbonate (fluoroethylene carbonate (FEC), etc.), fluorine-containing chain carbonate, fluorine-containing chain ether, and fluorine-containing chain ester. Can be mentioned.

Further, it is preferable to use at least LiPF ₆ as the lithium salt. In addition, LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSO ₃ CF _{3 and the} like can be used. The lithium salt concentration is preferably 0.1 to 5 mol / L, more preferably 0.1 to 2 mol / L.

  Furthermore, the additive contains at least one of an organic sulfone compound, an organic disulfone compound, a vinylene carbonate derivative, an ethylene carbonate derivative, an ester derivative, a divalent phenol derivative, a terphenyl derivative, a phosphate derivative, and a lithium fluorophosphate derivative. Is preferred. Of these, lithium fluorophosphate derivatives such as lithium monofluorophosphate and lithium difluorophosphate are more preferable. Use of these additives is preferable from the viewpoints of performance and life characteristics. The additive is preferably contained in the electrolyte at 0.1 to 5% by mass, and more preferably 0.5 to 3.5% by mass.

[V] First impregnation step In the present embodiment, an electrolyte was injected into the laminate and the remaining side was temporarily sealed, and then the three-side sealing body was allowed to stand for a certain period of time as a first impregnation step. It is preferable to impregnate the electrolytic solution. Usually, by leaving it to stand for about 10 to 80 hours, the electrolyte injected from the opening can be impregnated into the separator and the active material layer. Depending on the case, using a vacuum box or a vacuum pump used in the liquid injection step, it may be performed in an environment in which the battery is easily impregnated with the electrolyte solution by repeatedly increasing and decreasing pressure. Also, the atmosphere is preferably performed in a dry environment containing no moisture, for example, in a dry inert gas atmosphere. Moreover, depending on the case, you may make it accelerate | stimulate that an electrolyte solution is impregnated by applying the gentle ultrasonic vibration of the grade which does not destroy an electrode.

[VI] Pre-initial charging step As a preferred embodiment, it is preferable to perform pre-initial charging of the three-side sealed body after the first impregnation step at a predetermined charging rate. Usually, it may be performed within a range of 10 to 30% of SOC (State of Charge) indicating a fully charged state at a charging rate of 0.01 C to 20.0 C for about 0.5 to 5.0 hours. As a result, defective products can be easily found and removed.

[VII] Second impregnation step In this step, after obtaining a non-aqueous electrolyte secondary battery, the three-side sealed body after sealing three sides or after pre-initial charging is left for a certain period of time to impregnate the electrolyte. To promote. Although it is not limited to this, normally, by leaving it to stand for 24 hours or more (up to about several days), it is possible to promote the impregnation of the electrolytic solution particularly into the corners of the separator and the active material layer. Depending on the case, using a vacuum box or a vacuum pump used in the liquid injection step, it may be performed in an environment in which the battery is easily impregnated with the electrolyte solution by repeatedly increasing and decreasing pressure. Also, the atmosphere is preferably performed in a dry environment containing no moisture, for example, in a dry inert gas atmosphere. In some cases, impregnation with the electrolytic solution may be promoted by applying gentle ultrasonic vibration that does not destroy the electrode.

<First charging process>
[VIII] First charging step (step of charging to a potential lower than the plateau potential; initial charging step)
In the first charging step, initial charging is performed at a predetermined charging rate up to a potential lower than the plateau potential. The method of the initial charging is not particularly limited, but specifically, before applying a voltage higher than the potential plateau region of the positive electrode active material, 0.01 to 1.0 C and 40% to 80% of SOC (typical In the range of the applied voltage of about 3.7 V to 4.4 V), one or more charge / discharge treatments are performed at a voltage lower than the potential plateau region. This is because the re-resistance treatment of the negative electrode active material and the activation treatment that changes a part of the crystal structure of the positive electrode active material (changes 20% or less of the final structural variable). The SOC of the battery can be determined by preparing a sample in advance and measuring it.

  By such charging / discharging treatment, a film can be re-formed on the surface of the negative electrode active material expanded by increasing the charge amount. In addition, by passing through a state in which the crystal structure of the positive electrode active material is partially changed, fine deterioration (crystal breakdown) of the crystal structure on the surface of the positive electrode active material particles occurs with a large voltage change. Can be suppressed. Further, when a voltage higher than the potential plateau region described later is applied, the structure change of the positive electrode active material is preferably improved, the charge / discharge capacity is improved, and the change of the crystal structure of the surface of the positive electrode active material is also preferably improved. The durability of can be improved.

[IX] First Aging Step After the first charging step, it is preferable to perform a first aging step. The first aging step is performed by a process of holding the three-side sealed body in a predetermined charged state for a predetermined time. Typically, the “predetermined charging state” is a charging state of 40% to 80% of the SOC, and the “predetermined time” is a time of 1 hour or more and 7 days or less.

By such treatment, water contained in the electrolytic solution can be decomposed and removed. Further, the electrolyte solution is infiltrated into the electrode to secure a path for inserting lithium ions (Li ⁺ ) into the graphite structure (interlayer) of the negative electrode active material.
<First degassing process>
[X] First degassing step In this step, the gas generated up to the previous step is removed. In the first charging step, a film is formed on the surface of the negative electrode active material, and at that time, a solvent such as ethylene carbonate in the electrolytic solution is decomposed to generate a small amount of gas. This embodiment is characterized in that a step of removing this small amount of gas is provided before a second charging step described later, that is, a step of charging to a potential equal to or higher than the plateau potential. Without removing the small amount of gas generated in the initial charging process, and performing a charging process above the plateau potential in order to activate the solid solution positive electrode active material, gas stays between the electrodes, It is not uniformly charged and is exposed to overvoltage conditions. In this overvoltage state, the decomposition of the solvent in the electrolytic solution is promoted, a larger amount of gas is generated, and the amount of the electrolytic solution is reduced. Further, the phase transition of the positive electrode active material is excessively promoted to cause deterioration, and the conductive auxiliary agent in the electrode is also deteriorated. In the present embodiment, the occurrence of the overvoltage state can be prevented by providing the first degassing step. As a result, the non-aqueous electrolyte secondary battery can be reduced in impedance, increased in charge / discharge capacity, and improved in rate characteristics. Furthermore, deterioration of the electrolytic solution, the positive electrode active material, and the conductive additive can be prevented, and cycle durability is improved.

  Although there is no restriction | limiting in particular in removing gas from a 3 side sealing body, The following methods are employable. In this case, the remaining one side of the three-side sealing body is not sealed (thermally sealed), but can be opened and closed by a clip or the like so that the gas generated by precharging or initial charging can be discharged from the exterior body. It is desirable to keep it. After the first charging step, the clip or the like is removed to open one side of the three-side sealed body, and the generated gas is easily discharged from the exterior body by reducing the pressure to 1 to 20 hPa, more preferably 5 to 15 hPa. be able to. In addition, after the first charging step in a closed state with a clip or the like, for example, from the side opposite to the unsealed side of the exterior body, the surface pressure is 0.1 to 1.0 MPa, more preferably 0.3 to The gas generated inside the battery may be pushed to the unsealed side of the outer package (the inner space portion of the gap between the outer package and the laminated body) by rolling at 0.7 MPa. Then, the generated gas can be easily and reliably discharged from the exterior body by removing the clip and opening one side of the three-side sealing body.

<Second charging step>
[XI] Second charging step (step of charging to a plateau potential or higher; activation step)
The positive electrode active material represented by the composition formula (1) is initially composed of an electrochemically inactive layered Li ₂ MnO ₃ and an electrochemically active layered LiMO ₂ (M is Co, Ni , A layered lithium-containing transition metal oxide comprising a solid solution with a transition metal such as Mn. This layered lithium-containing transition metal oxide has a portion that changes to a spinel structure when subjected to charge or charge / discharge in a predetermined potential range, and partially has a spinel phase after the battery is completed. It is in a state.

  A 2nd charge process is performed by applying a predetermined voltage between both poles and performing a charging / discharging process. Typically, it is carried out by applying a voltage of 4.30 to 4.75 V at 0.05 to 0.5 C, and performing charge and discharge once or more until the potential plateau interval of the positive electrode active material to be used. . Such charging and discharging treatment (charging / discharging cycle treatment) may of course be performed twice or more, but the capacity of the positive electrode active material can be increased by such positive electrode activation treatment. Note that the potential plateau region of the positive electrode active material used in this embodiment typically corresponds to an applied voltage of 4.30 to 4.75V.

  In this embodiment, the constant current charging method is used and the electrochemical pretreatment method when the voltage is set as the termination condition is introduced as an example. However, the charging method may be a constant current constant voltage charging method. . Further, as the termination condition, a charge amount or time may be used in addition to the voltage.

  By exposing the positive electrode active material to the potential plateau region or more once or more, the crystal structure of the positive electrode active material can be changed to a suitable state, and the diffusibility of Li ions in the crystal structure (mobility during charge / discharge) And the capacity (mAh / g) is increased. Specifically, it changes into a spinel structure by performing charging or charging / discharging in a predetermined potential range, which is dissolved in the crystal structure of the layered lithium-containing transition metal oxide represented by the above formula (1). The part to form partially forms a spinel phase. Thereby, a large amount of Li ions can be moved while maintaining the crystal structure, and the charge capacity and discharge capacity can be increased.

  The rate at which the layered lithium-containing transition metal oxide changes into a spinel phase can be indicated by a k value. In the present invention, the k value is a theoretical structural change amount of 0.25 to 1. 0.0, that is, 0.25 ≦ k <1.0 is preferably satisfied. If the k value deviates from this range, the capacity of the positive electrode active material may not increase as intended.

The theoretical structural change amount of the positive electrode active material can be determined in advance as follows. “Spinel structure change ratio” means that by performing charge or charge / discharge in a predetermined potential range, the layered structure Li ₂ MnO ₃ in the solid solution lithium-containing transition metal oxide was changed to the spinel structure LiMn ₂ O ₄ The ratio is specified. That is, the spinel structure change ratio when the Li ₂ MnO ₃ having a layered structure in the solid solution lithium-containing transition metal oxide is all changed to LiMn ₂ O ₄ having a spinel structure is set to 1. Specifically, it is defined by the following formula.

  Regarding the definition of “spinel structure change ratio”, for a battery assembled using a positive electrode in which the solid solution lithium-containing transition metal oxide is used as a positive electrode active material, a charge charged from initial state A before charging to 4.5 V A case as shown in FIG. 3 will be described as an example, in which the state is set to state B, further passed through a plateau region, overcharged state C charged to 4.8V, and discharged state D further discharged to 2.0V. To do.

The “actual capacity of the plateau region” in the above formula is the plateau region in FIG. 1 (specifically, the region from 4.5 V to 4.8 V (the actual capacity V _BC of the region BC from the charged state B to the overcharged state C) _. ) And the region resulting from the change in the crystal structure.

Actually, in the solid solution lithium-containing transition metal oxide of the composition formula (1), the actual capacity V _{AB in} the region AB from the initial state A to the charged state B charged to 4.5 V is a layered structure portion. It corresponds to the composition (y) and theoretical capacity (V _L ) of a certain LiMO ₂ , and the actual capacity V _BC of the region BC in the overcharged state C charged from 4.5 V to 4.8 V is Since it corresponds to the composition ratio (x) and the theoretical capacity (V _S ) of Li ₂ MnO ₃ which is a spinel structure site, the actual capacity (V _T ) measured from the initial state A to a predetermined plateau region is expressed as (V _T = V _AB + V _BC ) Since V _AB = y (V _L ) and V _BC = x (V _S ) K, it can also be calculated using the following formula (M is nickel (Ni), Less selected from the group consisting of cobalt (Co) and manganese (Mn) It is also shown one.).

Furthermore, the “composition ratio of Li ₂ MnO _{3 in} the solid solution” can be calculated from the composition formula of the solid solution lithium-containing transition metal oxide. In addition, the presence or absence of the layered structure site and the spinel structure site in the solid solution lithium-containing transition metal oxide can be determined by the presence of a peculiar peak in the layered structure and the spinel structure by X-ray diffraction analysis (XRD), and the ratio is It can be determined from the measurement and calculation of the capacity as described above.

  In addition, the spinel structure change ratio does not become 1.0, and when it is less than 0.25, a discharge capacity and a capacity retention rate similar to those of a conventional solid solution lithium-containing transition metal oxide can be realized even if high. Only a solid solution lithium-containing transition metal oxide is obtained.

  In the present embodiment, in the positive electrode activation process, the charge rate is less than or equal to the discharge rate, that is, charge rate ≦ discharge rate, with respect to the charge / discharge process in which a voltage less than the potential plateau section of the positive electrode active material is applied once or more. It is preferable to carry out with a constant current cycle By changing the charge rate and the discharge rate stepwise and satisfying the charge rate ≦ the discharge rate, a voltage higher than the potential plateau interval is applied while protecting the coating formed on the surface of the negative electrode active material layer.

  In the charge / discharge cycle treatment in which a voltage less than the potential plateau region is applied, the structure change of the positive electrode active material is improved, the charge / discharge capacity is improved, and the formation of the SEI film (protective film) on the surface of the negative electrode active material is also preferable. In particular, the durability of the negative electrode active material can be improved. Therefore, by changing the charging rate and the discharging rate of the applied voltage stepwise and satisfying the charging rate ≦ the discharging rate, the potential plateau section is protected while protecting the film formed on the surface of the negative electrode active material layer. The above voltage can be applied.

<Second degassing process>
[XI] Second Degassing Step In the present embodiment, it is preferable to perform the second degassing step after the second charging step. By the second degassing step, it is possible to remove a large amount of gas generated in the second charging step of charging to a potential equal to or higher than the plateau potential. Thereby, the external appearance change of the battery by gas generation can be prevented, and the adhesiveness of an electrode can be aimed at. In addition, since the uniformity of charge and discharge of the electrode can be maintained and improved, the production of byproducts containing Li can be suppressed, and the life characteristics are improved. Further, since it is possible to suppress the gap between the electrodes, it is possible to further improve the decrease in charge / discharge capacity, the increase in impedance, the decrease in C rate characteristics due to overvoltage, and the like.

  Since the details of the second degassing step are the same as those of the first degassing step, the description thereof is omitted.

[XII] Second Aging Step It is preferable to carry out the second aging step after the second degassing step. The second aging step is a charge / discharge cycle treatment in which the maximum charge state corresponding to 60% or more and less than 100% of the SOC, desirably 80% or more and less than 100%, is typically maintained for 1 hour or more and 30 days or less. It is preferable to carry out.

  More specifically, after performing the above-described negative electrode aging treatment and positive electrode activation treatment, the practical SOC is less than 60 to less than 100% at 0.05 to 0.5 C (for example, the upper limit potential 4.4 to be actually used) 4.5V) for 1 hour to 10 days. In the meantime, you may heat at 30-55 degreeC. Thereby, the structural change of the positive electrode active material can be further promoted, and the performance and durability can be improved.

<Third degassing process>
[XIII] Third Degassing Step In the present embodiment, when the second aging step is performed, it is preferable to perform a third degassing step thereafter. A small amount of gas that can be generated in the second aging step can be removed by the third degassing step. Thereby, the external appearance change of the battery by gas generation can be prevented, and the adhesiveness of an electrode can be aimed at. In addition, since the uniformity of charge and discharge of the electrode can be maintained and improved, the production of byproducts containing Li can be suppressed, and the life characteristics are improved. Further, since it is possible to suppress the gap between the electrodes, it is possible to further improve the decrease in charge / discharge capacity, the increase in impedance, the decrease in C rate characteristics due to overvoltage, and the like.

  The details of the third degassing step are the same as those of the first degassing step, and thus the description thereof is omitted.

  Finally, the three-side sealed body is taken out, and the remaining one side of the three-side sealed body is sealed (heat sealed) to complete a laminate type (laminated structure) nonaqueous electrolyte secondary battery. In the present embodiment, the finished product refers to a non-aqueous electrolytic secondary battery that has been charged by performing the first and second charging steps as described above. In addition, you may implement a sail charge process after heat sealing as needed.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery.

  As shown in FIG. 2, the flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 57 is encased by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Has been. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 illustrated in FIG. 2 described above. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

  The lithium ion secondary battery is not limited to a stacked flat shape. The wound lithium ion secondary battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. There is no particular limitation.

  Further, the removal of the tabs 58 and 59 shown in FIG. 2 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  In a general electric vehicle, the battery storage space is about 170L. Since auxiliary devices such as cells and charge / discharge control devices are stored in this space, the storage efficiency of a normal cell is about 50%. The efficiency of loading cells into this space is a factor that governs the cruising range of electric vehicles. If the size of the single cell is reduced, the loading efficiency is impaired, so that the cruising distance cannot be secured.

  Therefore, in the present invention, the battery structure in which the power generation element is covered with the exterior body is preferably large. Specifically, the length of the short side of the laminated cell battery is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the laminated cell battery refers to the side having the shortest length. The upper limit of the short side length is not particularly limited, but is usually 400 mm or less.

[Volume energy density and rated discharge capacity]
In a general electric vehicle, a travel distance (cruising range) by a single charge is 100 km. Considering such a cruising distance, the volume energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Wh or more.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, the value of the ratio of the battery area to the rated capacity (projected area of the battery including the battery outer casing) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. In a certain battery, since the battery area per unit capacity is large, the problem to be solved by the present embodiment is more likely to become apparent. Therefore, it is preferable that the nonaqueous electrolyte secondary battery according to the present embodiment is a battery that is enlarged as described above, from the viewpoint of greater merit due to the manifestation of the operational effects of the embodiment. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both required vehicle performance and mounting space can be achieved.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

  A plurality of batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery manufactured according to this embodiment maintains a discharge capacity even when used for a long period of time, and has good cycle characteristics. Furthermore, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the nonaqueous electrolyte secondary battery can be suitably used as a vehicle power source, for example, a vehicle driving power source or an auxiliary power source.

  Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  Hereinafter, although this embodiment is concretely demonstrated through an Example, this embodiment is not limited to the following Examples.

[Production Example 1: Production of positive electrode]
(Positive electrode active material)
As the positive electrode active material, the composition formula:
Li _1.5 [Ni _0.25 Co _0.25 Mn _0.75 [Li] _0.25 ] O ₃
a + b + c + d = 1.5, d = 0.25, a + b + c = 1.25
The positive electrode active material was used. The charge capacity of the positive electrode active material was 280 mAh / g.

(Composition of slurry for positive electrode)
Active material: Li _1.5 [Ni _0.25 Co _0.25 Mn _0.75 [Li] _0.25 ] O ₃ 100 parts by mass Conductive aid: flake graphite 1.0 part by mass
3.0 parts by mass of acetylene black Binder: 3.0 parts by mass of polyvinylidene fluoride (PVDF) Solvent: 65 parts by mass of N-methylpyrrolidone (NMP).

(Production of positive electrode slurry)
A positive electrode slurry having the above composition was prepared as follows. First, a binder solution was prepared by dissolving 3.0 parts by mass of a binder in 30 parts by mass of NMP. Next, the mixed powder of 4.0 parts by weight of the conductive agent and 100 parts by weight of the positive electrode active material powder is kneaded with a planetary mixer (PVM100, manufactured by Asada Tekko Co., Ltd.) in addition to 33.0 parts by weight of the binder solution. Then, 35 parts by mass of NMP was added to the kneaded product to obtain a positive electrode slurry (solid content concentration: 62% by mass).

(Application and drying of positive electrode slurry)
While the 20 μm thick aluminum foil current collector foil was run at a running speed of 1 m / min, the positive electrode slurry was applied to one side of the current collector foil by a die coater. Subsequently, the current collector foil coated with the positive electrode slurry is dried in a hot air drying oven (100 ° C. to 110 ° C., drying time 3 minutes), and the amount of NMP remaining in the electrode active material layer is 0.02% by mass. It was as follows.

  Further, coating and drying were performed on the back surface of the aluminum foil in the same manner as above to form a sheet-like electrode having electrode active material layers on both sides.

(Electrode press)
The sheet-like electrode was compression-molded by applying a roller press and cut to prepare a positive electrode C1 having a mass of about 10 mg / cm ² , a thickness of about 50 μm, and a density of 2.70 g / cm ³ of the active material layer on one side.

(Dry electrode)
Next, the positive electrode C1 was subjected to a drying process in a vacuum drying furnace. After the positive electrode C1 was placed inside the drying furnace, the pressure in the drying furnace was reduced at room temperature (25 ° C.) (100 mmHg (1.33 × 10 ⁴ Pa)) to remove the air in the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, the pressure was reduced again at 120 ° C., and the nitrogen in the furnace was kept exhausted for 12 hours, The temperature was lowered. In this way, a positive electrode C11 was obtained.

[Production Example 2: Production of positive electrode]
(Positive electrode active material)
As the positive electrode active material, the composition formula:
Li _1.5 [Ni _0.3 Co _0.3 Mn _0.7 [Li] _0.2 ] O ₃
a + b + c + d = 1.5, d = 0.25, a + b + c = 1.3
The positive electrode active material was used. The charge capacity of the positive electrode active material was 277 mAh / g.

  In this production example, positive electrode C22 was obtained according to Production Example 1.

[Production Example 3; Production of positive electrode]
(Positive electrode active material)
As the positive electrode active material, the composition formula:
Li _1.5 [Ni _0.45 Mn _0.85 [Li] _0.20 ] O ₃
a + b + c + d = 1.5, d = 0.20, a + b + c = 1.3
The positive electrode active material was used. Moreover, the discharge capacity of the positive electrode active material was 288 mAh / g.

  In this production example, positive electrode C33 was obtained according to Production Example 1.

[Production Example 4; Production of positive electrode]
(Positive electrode active material)
As the positive electrode active material, the composition formula:
Li _1.5 [Ni _0.525 Mn _0.825 [Li] _0.15 ] O ₃
a + b + c + d = 1.5, d = 0.15, a + b + c = 1.35
The positive electrode active material was used. The charge capacity of the positive electrode active material was 267 mAh / g.

  In this production example, positive electrode C44 was obtained according to Production Example 1.

[Production Example 5: Production of negative electrode]
(Composition of slurry for negative electrode)
Active material: Natural graphite 100 parts by mass Conductive agent: Acetylene black 1.0 part by mass Binder: Polyvinylidene fluoride (PVDF) 5.0 parts by mass Solvent: N-methylpyrrolidone (NMP) 97 parts by mass.

(Manufacture of negative electrode slurry)
A negative electrode slurry having the above composition was prepared as follows. First, a binder solution was prepared by dissolving 5.0 parts by mass of a binder in 50 parts by mass of NMP. Next, in addition to 55.0 parts by mass of the binder solution, the mixed powder of 1.0 part by mass of the conductive agent and 100 parts by mass of natural graphite powder is kneaded with a planetary mixer (PVM100, manufactured by Asada Tekko). 47 parts by mass of NMP was added to the kneaded material to prepare a negative electrode slurry (solid content concentration 52 mass%).

(Application and drying of slurry for negative electrode)
Negative electrode coating amount (mg / cm ^2), the one surface of the coating amount was about 9.50mg / cm ^2. The negative electrode slurry was applied to one surface of the current collector foil by a die coater while the 10 μm thick electrolytic copper foil current collector foil was run at a running speed of 1.5 m / min. Subsequently, the current collector foil coated with the negative electrode slurry was dried in a hot air drying oven (100 ° C. to 110 ° C., drying time 2 minutes), and the amount of NMP remaining in the electrode active material layer was 0.02% by mass. It was as follows.

  Further, coating and drying were performed on the back surface of the electrolytic copper foil in the same manner as described above to form a sheet-like electrode having electrode active material layers on both sides.

(Electrode press)
The sheet-like electrode was compression-molded using a roller press and cut to prepare a negative electrode A1 having a mass of about 11.5 mg / cm ² and a density of 1.45 g / cm ³ of the active material layer on one side. When the surface of the negative electrode A1 was observed, no cracks were observed.

(Dry electrode)
Next, a drying process was performed in a vacuum drying furnace using the negative electrode A1 produced by the above procedure. After the negative electrode A1 was placed inside the drying furnace, the air in the drying furnace was removed by reducing the pressure (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.). Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 135 ° C. at 10 ° C./min, the pressure was again reduced at 135 ° C., and the nitrogen in the furnace was kept exhausted for 12 hours, The temperature was lowered. In this way, negative electrode A11 was obtained.

[Example 1]
[Production of battery]
A tab was welded to the current collector foil portions of positive electrode C11 (active material layer area length: 3.6 cm × width: 5.3 cm) and negative electrode A11 (active material layer area length: 3.8 cm × width: 5.5 cm). A porous polypropylene separator (S) (4.5 cm long × 6.0 cm wide, 25 μm thick, porosity 55%) is sandwiched between the negative electrode A11 and the positive electrode C11 welded with these tabs. A battery element of stacked type (stacked example, A11- (S) -C11- (S) -A11) was produced. Next, both sides were sandwiched between aluminum laminate films (length 5.0 cm × width 6.5 cm), and the battery element was housed by thermocompression sealing at three sides. In this battery element, ethylene carbonate (EC) 30 vol. % And diethyl carbonate (DEC) 70 vol. After dissolving 1.0 mol / liter of LiPF ₆ in 1% of a mixed solvent, 1.0% by mass of vinylene carbonate (VC), 1.0% by mass of 1,3-propane sultone, lithium difluorophosphate as additives 1.0% by mass was dissolved to obtain an electrolytic solution. After injecting this electrolyte solution 0.6 cm ³ / cell, the remaining one side was temporarily sealed by thermocompression bonding to produce a laminate type cell. In order to sufficiently infiltrate the electrolyte into the electrode pores, the electrolyte was held at 25 ° C. for 24 hours while being pressurized at a surface pressure of 0.5 Mpa.

  Thereafter, the battery element was set on an evaluation cell attachment jig, and a positive electrode lead and a negative electrode lead were attached to each tab end portion of the battery element to perform a test.

  The battery produced as described above was subjected to an initial charging process and an activation process under the following conditions.

[Evaluation of battery characteristics]
[Pre-initial charging step; first charging step; first aging step]
At 25 ° C., 0.05 C, 4 hours of charging (SOC about 20%) was performed by a constant current charging method (pre-initial charging step). Subsequently, it charged to 4.35V at a 0.1C rate at 25 degreeC (1st charge process; initial charge process). Thereafter, the charging was stopped, and the state (SOC about 70%) was maintained for about 2 days (48 hours) (first aging step).

[First degassing step; gas removal treatment (1)]
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding was performed again to perform temporary sealing. Furthermore, pressure was applied with a roller (surface pressure 0.5 ± 0.1 MPa), and the electrode and the separator were sufficiently adhered.

[Second charging step; activation treatment]
After charging at 25 ° C. until the voltage reaches 4.45 V at 0.2 C by the constant current charging method, the cycle of discharging to 0.2 V at 0.2 C to 2.0 V becomes 4.55 V at 0.2 C. Then, the battery was discharged twice at 0.2 C to 2.0 V.

[Second degassing step; gas removal treatment (2)]
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding was performed again to perform main sealing. Furthermore, pressure was applied with a roller (surface pressure 0.5 ± 0.1 MPa), and the electrode and the separator were sufficiently adhered.

[Life Evaluation]
In the battery life test, charging / discharging at a 1.0 C rate was repeated 300 cycles at 45 ° C. The battery is evaluated by a constant current / constant voltage charging method in which the battery is charged at a rate of 0.2 C until the maximum voltage reaches 4.5 V and then held for about 1 hour to 1.5 hours. It was performed by a constant current discharge method in which discharge was performed at a 0.2 C rate until the minimum voltage became 2.0V. All were performed at room temperature.

  The ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle was compared as a capacity retention rate.

[DCR increase rate]
The ratio of the DCR at the 300th cycle to the direct current resistance (DCR) at the first cycle in the life evaluation was compared as the DCR increase rate.

[Thickness change rate]
The thickness change rate was determined by measuring the thickness of the cell before and after the above 300 cycles of charge / discharge using a micrometer.

[Example 2]
A cell was produced using positive electrode C22 and negative electrode A11 according to Example 1. Further, after performing the initial charging process, the gas removal process (1), the activation process and the gas removal process (2) according to Example 1, the life evaluation, the DCR increase rate measurement, and the thickness change rate measurement were performed.

[Example 3]
A cell was fabricated using positive electrode C33 and negative electrode A11 according to Example 1. Further, after performing the initial charging process, the gas removal process (1), the activation process and the gas removal process (2) according to Example 1, the life evaluation, the DCR increase rate measurement, and the thickness change rate measurement were performed.

[Example 4]
A cell was produced using positive electrode C44 and negative electrode A11 according to Example 1. Further, after performing the initial charging process, the gas removal process (1), the activation process and the gas removal process (2) according to Example 1, the life evaluation, the DCR increase rate measurement, and the thickness change rate measurement were performed.

[Example 5]
In accordance with Example 1, after performing [Gas removal treatment (2)], the following treatment was further performed.

[Third charging step; aging treatment]
After charging at 25 ° C. until the voltage reaches 4.45 V at 0.2 C by the constant current charging method, the charging is stopped, and in that state (SOC approximately 90% or more), the temperature of the thermostat is 45 ° C., Hold for about 5 days (120 hours). Thereafter, the temperature of the thermostatic bath was set to 25 ° C., and further maintained for about 2 days (48 hours).

[Third degassing step; gas removal treatment (3)]
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding was performed again for sealing. Furthermore, pressure was applied with a roller (surface pressure 0.5 ± 0.1 MPa), and the electrode and the separator were sufficiently adhered.

  Then, according to Example 1, performance evaluation and lifetime evaluation were performed.

[Example 6]
According to Example 1, the gas removal treatment (2) was not performed, and life evaluation, DCR increase rate measurement, and thickness change rate measurement were performed.

[Comparative Example 1]
According to Example 1, the gas removal treatments (1) and (2) were not performed, and life evaluation, DCR increase rate measurement, and thickness change rate measurement were performed.

[Comparative Example 2]
According to Example 1, the gas removal treatment (1) was not performed, and life evaluation, DCR increase rate measurement, and thickness change rate measurement were performed.

  The results of the performance evaluation and life evaluation are shown in Table 1 below. As shown in Table 1, the example in which the first degassing step was performed showed excellent results in all of the thickness change rate, the capacity retention rate, and the DCR change rate as compared with the comparative example. Examples 1-4 which implemented the 2nd degassing process became a result superior in all the evaluation values compared with Example 6 only of the 1st degassing process. Moreover, Example 5 which implemented the 3rd degassing process was a result in which all the evaluation values were further excellent compared with Examples 1-4 until the 2nd degassing process.

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21, 57 power generation element,
25 negative current collector,
27 positive current collector,
29, 52 Battery exterior material,
58 positive electrode tab,
59 Negative electrode tab.

Claims (5)

The following composition formula (1):
Li _1.5 [Ni _a Co _b Mnc [Li] _d ] O ₃ (1)
Wherein a, b, c and d are 0 <a <1.4, 0 ≦ b <1.4, 0 <c <1.4, 0 <d ≦ 0.5, a + b + c + d = 1.5, 1.0 ≦ a + b + c <1.5 is satisfied,
A step of preparing an uncharged non-aqueous electrolyte secondary battery including a positive electrode using a positive electrode active material represented by:
A first charging step of charging the non-aqueous electrolyte secondary battery to a potential lower than a plateau potential;
A first degassing step of removing gas from the non-aqueous electrolyte secondary battery;
A second charging step of charging the non-aqueous electrolyte secondary battery to a potential equal to or higher than a plateau potential;
The manufacturing method of the nonaqueous electrolyte secondary battery which contains these in order.   The method for producing a nonaqueous electrolytic secondary battery according to claim 1, further comprising a second degassing step of removing gas after the second charging step. After the second degassing step, an aging step for maintaining a state charged to 4.5 V or less,
The method for producing a nonaqueous electrolytic secondary battery according to claim 2, further comprising a third degassing step of removing gas after the aging step.   The method for producing a nonaqueous electrolytic secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material of the nonaqueous electrolyte secondary battery is a carbon material.   The method for producing a nonaqueous electrolytic secondary battery according to any one of claims 1 to 4, wherein the plateau potential is in the range of 4.3 to 4.75V.