JP7040290B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

In recent years, various electric vehicles are expected to become widespread in order to solve environmental and energy problems. Secondary batteries are being enthusiastically developed as in-vehicle power sources such as motor drive power sources that hold the key to the spread of these electric vehicles. Non-aqueous electrolyte secondary batteries intended for application to in-vehicle power supplies are required to have high capacity.

Non-aqueous electrolyte secondary batteries often use graphite as a negative electrode active material from the viewpoint of charge / discharge cycle and cost. Further, in the electrolytic solution used for the non-aqueous electrolyte secondary battery, a cyclic carbonate such as propylene carbonate (PC) is used as a solvent because of its high dielectric constant. When graphite is used as the negative electrode active material and propylene carbonate is used as the solvent of the electrolytic solution, propylene carbonate is decomposed by the reaction between graphite and propylene carbonate. A film is formed on the graphite surface by the decomposition product of propylene carbonate. Further, since the entire surface of the graphite is covered with this film, there is a problem that the electrical contact with the conductive auxiliary agent and the current collector is cut off and the capacity cannot be developed. In order to solve such problems, for example, Patent Document 1 describes 0.7 to 4 mol / L lithium bis (fluorosulfonyl) imide, more than 0 to 15% by volume of cyclic carbonate, and 85 to 99% by volume of chain carbonate. A technique for using an electrolytic solution containing and is disclosed.

Japanese Unexamined Patent Publication No. 2015-79636

By the way, in an electric vehicle, a secondary battery having a higher energy density is desired in order to extend the cruising range in one charge. As a means for increasing the energy density of the battery, a method of thickening (thickening) the electrode active material layer per electrode can be mentioned. With such a configuration, the ratio of the volume of the electrode active material layer that contributes to the battery reaction per unit volume of the battery becomes large. As a result, the volumetric energy density is improved.

In particular, as the proportion of the binder contained in the electrode active material layer decreases, the battery capacity per unit volume increases and a battery with a high capacity density can be obtained. Therefore, a method of manufacturing an electrode without using a binder is used. ing.

However, according to the study by the present inventors, in the technique described in Patent Document 1, a negative electrode active material layer composed of a non-binder (without using a binder) containing graphite as a negative electrode active material, a lithium salt, and a propylene carbonate are used. It was found that a high capacity could not be obtained when an electrode was prepared using an electrolytic solution containing.

Therefore, the present invention can develop a high capacity in a non-aqueous electrolyte secondary battery using a negative electrode active material layer made of a non-binder containing graphite as a negative electrode active material and an electrolytic solution containing a lithium salt and propylene carbonate. The purpose is to provide means.

The present inventors have made diligent studies to solve the above problems. As a result, in a non-aqueous electrolyte secondary battery using a negative electrode active material layer made of a non-binder containing graphite as the negative electrode active material and an electrolytic solution containing a lithium salt and propylene carbonate, the molar concentration of propylene carbonate in the electrolytic solution. We have found that it is effective to control the ratio of the molar concentration of the lithium salt to a predetermined range within a predetermined range, and have completed the present invention.

That is, the non-aqueous electrolyte secondary battery according to the present invention has a positive electrode having a positive electrode active material layer containing a positive electrode active material on the surface of a positive electrode current collector and a non-bonding material containing a negative electrode active material on the surface of a negative electrode current collector. It has a power generation element including a negative electrode having a negative electrode active material layer made of a body and an electrolyte layer obtained by impregnating a separator with an electrolytic solution. Here, the negative electrode active material contains graphite, the electrolytic solution contains a lithium salt and a non-aqueous solvent containing propylene carbonate, and the lithium with respect to the concentration (mol / L) of the propylene carbonate in the electrolytic solution. The salt concentration (mol / L) ratio (lithium salt / propylene carbonate) is more than 0.25.

According to the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the non-aqueous electrolyte secondary battery using a negative electrode active material layer made of a non-binder containing graphite as a negative electrode active material and an electrolytic solution containing propylene carbonate. A high capacity can be developed in a battery.

It is sectional drawing which represented typically the bipolar type secondary battery which is one Embodiment of this invention. It is a perspective view which showed the appearance of the flat lithium ion secondary battery which is a typical embodiment of a secondary battery.

One embodiment of the present invention comprises a negative electrode active material layer composed of a positive electrode having a positive electrode active material layer containing a positive electrode active material on the surface of a positive electrode current collector and a non-bonded body containing a negative electrode active material on the surface of the negative electrode current collector. It is a non-aqueous electrolyte secondary battery having a power generation element including a negative electrode having a negative electrode and an electrolyte layer in which a separator is impregnated with an electrolytic solution. Here, the negative electrode active material contains graphite, the electrolytic solution contains a lithium salt and a non-aqueous solvent containing propylene carbonate, and the lithium with respect to the concentration (mol / L) of the propylene carbonate in the electrolytic solution. The salt concentration (mol / L) ratio (lithium salt / propylene carbonate) is more than 0.25. According to the non-aqueous electrolyte secondary battery of this embodiment, the decomposition of propylene carbonate on the graphite surface is suppressed, and the formation of a high resistance film on the graphite surface is suppressed, so that a high capacity can be developed.

The detailed mechanism that exerts the above effect is unknown, but it is presumed as follows. The technical scope of the present invention is not limited to the following mechanism.

The present inventors have attempted to apply the technique described in Patent Document 1 described above to a negative electrode active material made of a non-binding body containing graphite as a negative electrode active material. However, it was found that a high capacity could not be obtained when the electrode was manufactured without using a binder. Therefore, it was considered that the formation of a high resistance film on the graphite surface could be suppressed by reducing the probability of contact between graphite and propylene carbonate. As a result of verification based on this idea, we focused on the molar concentration ratio of lithium salt and propylene carbonate in the electrolytic solution, and set the ratio to more than 0.25 to obtain a high capacity. I found it.

That is, in the non-aqueous electrolyte secondary battery of the present embodiment, the ratio of the lithium salt concentration (mol / L) to the propylene carbonate concentration (mol / L) in the electrolytic solution (lithium salt / propylene carbonate) exceeds 0.25. By doing so, the probability that propylene carbonate will attack graphite is lower than that of lithium salt. Therefore, the decomposition of propylene carbonate on the graphite surface layer can be suppressed, and the formation of a high resistance film on the graphite surface due to the decomposition product of propylene carbonate can be suppressed. Therefore, it is considered that the charge / discharge reaction is facilitated and a high-capacity battery can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. .. Hereinafter, the present invention will be described by taking as an example a bipolar lithium ion secondary battery, which is a form of a non-aqueous electrolyte secondary battery. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. In the present specification, "XY" indicating a range means "X or more and Y or less". Unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) and relative humidity of 40 to 50% RH.

In the present specification, the bipolar lithium ion secondary battery may be simply referred to as a “bipolar secondary battery”, and the electrode for a bipolar lithium ion secondary battery may be simply referred to as a “bipolar electrode”.

<Bipolar secondary battery>
FIG. 1 is a cross-sectional view schematically showing a bipolar secondary battery according to an embodiment of the present invention. The bipolar secondary battery 10 shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated film 29 which is a battery exterior body.

As shown in FIG. 1, in the power generation element 21 of the bipolar secondary battery 10 of the present embodiment, a positive electrode active material layer 13 electrically coupled to one surface of the current collector 11 is formed, and the current collector 11 has a positive electrode active material layer 13. It has a plurality of bipolar electrodes 23 having an electrically coupled negative electrode active material layer 15 formed on the opposite surface. Each bipolar electrode 23 is laminated via an electrolyte layer 17 to form a power generation element 21. The electrolyte layer 17 has a structure in which a separator as a base material is impregnated with an electrolytic solution. At this time, the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other via the electrolyte layer 17. The bipolar electrodes 23 and the electrolyte layers 17 are alternately laminated. That is, the electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23. ing. However, the technical scope of the present invention is not limited to the bipolar secondary battery as shown in FIG. 1, and a plurality of single battery layers as disclosed in, for example, International Publication No. 2016/031688 are electrically formed. Batteries having a similar series connection structure as a result of being stacked in series may be used.

Although not shown, in the bipolar secondary battery 10 of FIG. 1, the negative electrode active material layer 15 contains graphite as the negative electrode active material. Further, the negative electrode active material layer 15 may contain carbon fibers, which are conductive fibers, as a conductive auxiliary agent. Since the negative electrode active material layer 15 contains carbon fibers, the first main surface of the negative electrode active material layer 15 in contact with the electrolyte layer 17 side and the second main surface in contact with the current collector 11 side are electrically connected. A conductive passage can be formed, and the conductive passage and the negative electrode active material can be electrically connected to each other. The negative electrode active material layer 15 does not contain the binder contained in the active material layer of a general non-aqueous electrolyte secondary battery (that is, it is a “non-binding body”). The positive electrode active material layer 13 may contain a binder contained in the active material layer of a general non-aqueous electrolyte secondary battery, but is preferably a non-bundling body.

The adjacent positive electrode active material layer 13, the electrolyte layer 17, and the negative electrode active material layer 15 constitute one cell cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 19 are laminated. Further, a seal portion (insulation layer) 31 is arranged on the outer peripheral portion of the cell cell layer 19. As a result, liquid leakage due to leakage of the electrolytic solution from the electrolyte layer 17 is prevented, adjacent current collectors 11 in the battery come into contact with each other, and the ends of the cell cell layer 19 in the power generation element 21 are slightly uneven. It prevents short circuits caused by the above. The positive electrode active material layer 13 is formed on only one side of the outermost layer current collector 11a on the positive electrode side located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed on only one side of the outermost layer current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21.

Further, in the bipolar secondary battery 10 shown in FIG. 1, a positive electrode current collector plate (positive electrode tab) 25 is arranged so as to be adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior. It is derived from the laminated film 29. On the other hand, the negative electrode current collector plate (negative electrode tab) 27 is arranged so as to be adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminated film 29.

The number of times the cell cell layer 19 is laminated is adjusted according to a desired voltage. Further, in the bipolar type secondary battery 10, the number of times the single battery layer 19 is laminated may be reduced as long as a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar type secondary battery 10, in order to prevent external impact and environmental deterioration during use, the power generation element 21 is vacuum-enclosed in the laminated film 29 which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode collector are collected. It is preferable to have a structure in which the electric plate 27 is taken out from the laminated film 29. Although the embodiment of the present invention has been described here by taking a bipolar secondary battery as an example, the type of non-aqueous electrolyte battery to which the present invention can be applied is not particularly limited, and the single battery layer is used as a power generation element. It can be applied to any conventionally known non-aqueous electrolyte secondary battery such as a so-called parallel laminated battery in the form of being connected in parallel.

Hereinafter, the main components of the above-mentioned bipolar secondary battery will be described.

[Current collector]
The current collector has a function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. The material constituting the current collector is not particularly limited, but for example, a metal or a resin having conductivity may be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, 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. Further, it may be a foil obtained by coating a metal surface with aluminum, or a carbon-coated aluminum foil. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, and the like.

In addition, examples of the latter resin having conductivity include a conductive polymer material or a resin in which a conductive filler is added to a non-conductive polymer material as needed. Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole and the like. 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 the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials may have excellent potential or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. 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 a metal thereof. It is preferable to contain an alloy containing or a metal oxide. Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one species.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally about 5 to 80% by mass.

The current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include a conductive resin layer made of at least a conductive resin. Further, from the viewpoint of blocking the movement of lithium ions between the cells of the cell, a metal layer may be provided on a part of the current collector.

[Negative electrode active material layer]
The negative electrode active material layer is composed of a non-bonded body containing the negative electrode active material. The phrase "consisting of a non-binding body containing a negative electrode active material" means that the electrode active materials are not fixed to each other by a binder (also referred to as a binder). The binder content in the negative electrode active material layer is preferably 1% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.5% by mass or less, based on 100% by mass of the total solid content contained in the negative electrode active material layer. It is preferably 0.2% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass.

Further, in the present specification, whether or not the active material layer is composed of a non-bonded body of the electrode active material is whether or not the active material layer collapses when the active material layer is completely impregnated in the electrolytic solution. It can be confirmed by observing. When the active material layer is made of a binder containing the electrode active material, the shape can be maintained for one minute or more, but when the active material layer is made of a non-bonded body containing the electrode active material, the shape can be maintained. Shape collapse occurs in less than a minute.

(Negative electrode active material)
The negative electrode active material indispensably contains graphite as a main component. Examples of graphite include natural graphite, artificial graphite, expanded graphite and the like. As the natural graphite, for example, scaly graphite, lump graphite and the like can be used. As the artificial graphite, bulk graphite, vapor phase growth graphite, scaly graphite, and fibrous graphite can be used. "The main component is graphite" means that the ratio of graphite to the negative electrode active material is 50% by mass or more. In this case, the proportion of graphite in the negative electrode active material is more preferably 70% by mass or more, further preferably 85% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. It is most preferably 100% by mass.

In addition to graphite, the negative electrode active material includes carbon materials such as soft carbon and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials (tin, silicon), and lithium alloys. Negative electrode materials (for example, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.) can be used in combination.

The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

(Conductive aid)
The negative electrode active material layer preferably further contains a conductive auxiliary agent.

The conductive auxiliary agent has a function of forming an electron conduction path (conductive path) in the negative electrode active material layer. When such an electron conduction path is formed in the negative electrode active material layer, the internal resistance of the battery is reduced, which can contribute to the improvement of output characteristics at a high rate. In particular, at least a part of the conductive auxiliary agent forms a conductive passage that electrically connects the two main surfaces of the negative electrode active material layer (in the present embodiment, it contacts the electrolyte layer side of the negative electrode active material layer). It is preferable to form a conductive passage that electrically connects from the first main surface to the second main surface in contact with the current collector side). By having such a form, the electron transfer resistance in the thickness direction in the negative electrode active material layer is further reduced, so that the output characteristics at a high rate of the battery can be further improved. At least a part of the conductive auxiliary agent forms a conductive passage that electrically connects the two main surfaces of the negative electrode active material layer (in the present embodiment, it contacts the electrolyte layer side of the negative electrode active material layer). Whether or not a conductive passage is formed that electrically connects from the first main surface to the second main surface in contact with the current collector side) is determined by using an SEM or an optical microscope to determine the cross section of the negative electrode active material layer. It can be confirmed by observing.

From the viewpoint of reliably forming such a conductive passage, the conductive auxiliary agent is preferably a conductive fiber having a fibrous form. Specifically, carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers in which a metal having good conductivity or graphite is uniformly dispersed in synthetic fibers, and a metal such as stainless steel are used as fibers. Examples thereof include carbonized metal fibers, conductive fibers in which the surface of organic fibers is coated with metal, and conductive fibers in which the surface of organic fibers is coated with a resin containing a conductive substance. Of these, carbon fiber is preferable because it has excellent conductivity and is lightweight.

However, of course, a conductive auxiliary agent that does not have a fibrous form may be used. For example, a conductive auxiliary agent having a particulate (for example, spherical) morphology can be used. When the conductive auxiliary agent is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, plate, columnar, amorphous, fluffy, and spindle-shaped. The average particle size (primary particle size) when the conductive auxiliary agent is in the form of particles is not particularly limited, but is preferably about 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery. In the present specification, the “particle diameter” means the maximum distance L among the distances between arbitrary two points on the contour line of the conductive auxiliary agent. As the value of the "average particle size", an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used, and the average value of the particle size of the particles observed in several to several tens of fields is used. The calculated value shall be adopted.

Conductive aids having a particulate (eg, spherical) morphology include, for example, metals such as aluminum, stainless steel (SUS), silver, gold, copper, titanium, alloys or metal oxides containing these metals; carbon nanotubes. (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.) and the like, but are not limited thereto. Further, a particulate ceramic material or a resin material coated with the above metal material by plating or the like can also be used as a conductive auxiliary agent. Among these conductive auxiliaries, from the viewpoint of electrical stability, it is preferable to contain at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, and aluminum, stainless steel. It is more preferable to contain at least one selected from the group consisting of silver, gold, and carbon, and even more preferably to contain at least one carbon. Only one kind of these conductive auxiliary agents may be used alone, or two or more kinds thereof may be used in combination.

The content of the conductive auxiliary agent in the negative electrode active material layer is preferably 2 to 20% by mass with respect to 100% by mass of the total solid content of the negative electrode active material layer (total of the solid content of all the members). When the content of the conductive auxiliary agent is in the above range, there is an advantage that the electron conduction path can be satisfactorily formed in the negative electrode active material layer and the decrease in the energy density of the battery can be suppressed.

The thickness of the negative electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 1200 μm, and further preferably 200 to 650 μm. When the thickness of the negative electrode active material layer is 150 μm or more, the energy density of the battery can be sufficiently increased. On the other hand, when the thickness of the negative electrode active material layer is 1500 μm or less, the structure of the negative electrode active material layer can be sufficiently maintained.

The porosity of the negative electrode active material layer is preferably 30 to 60%. When the porosity of the negative electrode active material layer is 30% or more, it is not necessary to increase the pressing pressure when pressing the coating film after applying the negative electrode active material slurry at the time of forming the negative electrode active material layer. As a result, the negative electrode active material layer having a desired thickness and area can be suitably formed. On the other hand, when the void ratio of the negative electrode active material layer is 60% or less, the contact between the electron conductive materials (conductive auxiliary agent, negative electrode active material, etc.) in the negative electrode active material layer can be sufficiently maintained, and the electrons can be sufficiently maintained. It is possible to prevent an increase in movement resistance. In the present specification, the porosity of the negative electrode active material layer shall be measured by the following method. Further, the porosity of the positive electrode active material layer described later can also be measured by the same method.

The porosity of the negative electrode active material layer is calculated according to the following formula (1). The electrolytic solution may be present in a part of the void.
Formula (1): Porosity (%) = 100-Solid content occupied volume fraction (%) of the negative electrode active material layer
Here, the "solid content occupied volume fraction (%)" of the negative electrode active material layer is calculated by the following formula (2).
Equation (2): Solid content occupied volume ratio (%) = (solid material volume (cm ³ ) / negative electrode active material layer volume (cm ³ )) × 100
The volume of the negative electrode active material layer is calculated from the thickness of the negative electrode and the coating area. The volume of solid material is determined by the following procedure.
(A) Weigh the amount of each material added to the negative electrode active material slurry.
(B) After applying the negative electrode active material slurry to the surface of the current collector, the weights of the current collector and the coating film are weighed.
(C) The slurry after coating is pressed, and the weights of the current collector and the coating film after pressing are weighed.
(D) The amount of the electrolytic solution sucked out at the time of pressing is calculated from "the value obtained in (c)-the value obtained in (b)".
(E) From the values of (a), (c) and (d), the mass of each material in the negative electrode active material layer after pressing is calculated. (F) The volume of each material in the negative electrode active material layer is calculated from the mass of each material and the density of each material calculated in (e).
(G) Of the volumes of each material calculated in (f), only the volume of the solid material is added to calculate the volume of the solid material.

The density of the negative electrode active material layer is preferably 0.60 to 1.30 g / cm ³ , more preferably 0.70 to 1.20 g / cm ³ , and further preferably 0.80 to 1.10 g / cm 3. It is cm ³ . When the density of the negative electrode active material layer is 0.60 g / cm ³ or more, a battery having a sufficient energy density can be obtained. On the other hand, when the density of the negative electrode active material layer is 1.30 g / cm ³ or less, it is possible to prevent the above-mentioned decrease in the porosity of the negative electrode active material layer. If the decrease in porosity is suppressed, an electrolytic solution that fills the voids is sufficiently secured, and an increase in ion transfer resistance in the negative electrode active material layer can be prevented. In the present specification, the density of the negative electrode active material layer shall be measured by the following method. Further, the density of the positive electrode active material layer described later can also be measured by the same method.

The density of the negative electrode active material layer is calculated according to the following formula (3).
Equation (3): Electrode density (g / cm ³ ) = solid material mass (g) ÷ electrode volume (cm ³ ).

The mass of the solid material is calculated by adding only the mass of the solid material to the mass of each material in the electrode after pressing obtained in (e) above. The electrode volume is calculated from the thickness of the electrode and the coating area.

(Manufacturing method of negative electrode)
The method for manufacturing the negative electrode is not particularly limited, and the negative electrode can be manufactured by appropriately referring to a conventionally known method. Hereinafter, a method for manufacturing a negative electrode according to an embodiment will be described.

First, the above-mentioned negative electrode active material and the conductive auxiliary agent are mixed with a solvent to prepare a slurry for the negative electrode active material layer.

Here, the method for preparing the slurry for the negative electrode active material layer by mixing the negative electrode active material, the conductive auxiliary agent and the solvent is not particularly limited, and conventionally known knowledge such as the order of addition of members and the mixing method is appropriately referred to. .. At this time, as the solvent, a non-aqueous solvent of a liquid electrolyte described later can be appropriately used. Further, an electrolytic solution further containing a lithium salt, an additive to the electrolytic solution, or the like may be used as it is in place of the solvent in this step.

The concentration of the slurry for the negative electrode active material layer is not particularly limited. However, from the viewpoint of facilitating the application of the slurry in the step described later and the pressing in the subsequent steps, the concentration of the total solid content with respect to 100% by mass of the slurry for the negative electrode active material layer is preferably 35 to 75% by mass. , More preferably 40 to 70% by mass, still more preferably 45 to 60% by mass. When the concentration is within the above range, a negative electrode active material layer having a sufficient thickness can be easily formed by coating.

Next, a coating film of the slurry for the negative electrode active material layer prepared above is formed on the porous sheet, the solvent is removed from the slurry if necessary, and then the current collector is placed on the surface of the coating film. The method for applying the coating film of the slurry is not particularly limited, and conventionally known knowledge such as an applicator is appropriately referred to. Further, there is no limitation on the method for removing the solvent from the slurry, and the solvent can be removed, for example, by performing suction filtration from the surface opposite to the coating film forming surface of the porous sheet.

Here, as the porous sheet, the same one as the microporous membrane, the non-woven fabric, etc. used as the separator in the present technical field can be used. Specifically, examples of the microporous membrane include a microporous membrane made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and glass fiber. Examples of the non-woven fabric include non-woven fabrics in which cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; polyimide, aramid and the like are used alone or in combination. A metal mesh such as a nickel mesh or a stainless mesh may be used as the porous sheet on the premise that the slurry is removed after the application of the slurry (formation of the negative electrode active material layer).

The porous sheet may be removed after the negative electrode active material layer is formed, or the insulating porous sheet may be used as it is as a battery separator. When the porous sheet is used as it is as a separator, the electrolyte layer may be formed by using only the porous sheet as a separator, or a combination of the porous sheet and another separator (that is, two or more separators). ) An electrolyte layer may be formed.

Further, if necessary, a laminate of the coating film of the slurry for the negative electrode active material layer and the porous sheet may be pressed. The press device used at this time is preferably a device that can uniformly apply pressure to the entire surface of the applied slurry for the negative electrode active material layer, specifically, High Pressure Jack J-1 (manufactured by AS ONE Corporation). Can be used. The pressure at the time of pressing is not particularly limited, but is preferably 0.4 to 40 MPa.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material.

(Positive electrode active material)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O ₂ , and lithium such as those in which some of these transition metals are replaced by other elements. Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more kinds of positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used. More preferably, Li (Ni-Mn-Co) O ₂ and a part of these transition metals are substituted with other elements (hereinafter, also simply referred to as "NMC composite oxide"), or lithium-nickel-cobalt. -Aluminum composite oxide (hereinafter, also simply referred to as "NCA composite oxide") or the like is used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni and Co are arranged in an orderly manner) atomic layer are alternately stacked via an oxygen atomic layer. Then, one Li atom is contained in each atom of the transition metal M, and the amount of Li that can be taken out is twice that of the spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

As described above, the NMC composite oxide also includes a composite oxide in which a part of the transition metal element is replaced with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu. , Ag, Zn and the like, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, and more preferably Ti, Zr, P, Al, Mg, It is Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable to use the general formula (1): Li _a Ni _b Mn _{c Code} M _x O ₂ (however, in the formula, a, b, c, d, x). Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 ≦ c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, b + c + d = 1. It has a composition represented by (at least one kind of element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr). Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

Generally, nickel (Ni), cobalt (Co) and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electron conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). The crystal structure is stabilized by solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. As a result, it is considered that the capacity of the battery can be prevented from decreasing even if charging and discharging are repeated, and excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31 and 0.19 ≦ d ≦ 0.26. Is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ includes LiCo O ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , etc., which have been proven in general consumer batteries. Compared with, the capacity per unit mass is large. This has the advantage that the energy density can be improved and a compact and high-capacity battery can be manufactured, which is preferable from the viewpoint of cruising range. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in that it has a larger capacity, but it has a difficulty in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has excellent life characteristics comparable to LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

Of course, a positive electrode active material other than the above may be used. The average particle size of the positive electrode active material is not particularly limited, but the average particle size of the second positive electrode active material contained in the second positive electrode active material layer is preferably 1 to 100 μm from the viewpoint of increasing the output. It is preferably 1 to 20 μm.

The positive electrode active material layer preferably further contains a conductive auxiliary agent, if necessary, in the same manner as described above for the negative electrode active material layer. Further, the positive electrode active material layer may contain a binder.

The binder of the optional component used for the positive electrode active material layer is not particularly limited, and examples thereof include the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, Polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene rubber (SBR), ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and its hydrogen additive , Thermoplastic polymers such as styrene / isoprene / styrene block copolymers and their hydrogenated additives, tetrafluoroethylene / hexafluoropropylene copolymers (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers (PFA). , Fluororesin such as ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylfluorovinyl (PVF), vinylidene fluoride- Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber) Examples thereof include vinylidene fluoride-based fluororubbers such as VDF-PFMVE-TFE-based fluororubber) and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), and epoxy resins. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The compounding ratio of other additives such as the conductive auxiliary agent and the binder that can be contained in the positive electrode active material layer is not particularly limited. Their compounding ratio can be adjusted by appropriately referring to known knowledge about non-aqueous electrolyte secondary batteries. As with the negative electrode active material layer, the positive electrode active material layer preferably does not contain a binder. That is, in a preferred embodiment of the non-aqueous electrolyte secondary battery according to the present embodiment, the positive electrode active material layer is composed of a non-bound body containing a so-called positive electrode active material in which the positive electrode active material is not bound by a binder. The phrase "consisting of a non-bonded body containing a positive electrode active material" means that the electrode active materials are not fixed to each other by a binder, as in the case of the negative electrode active material layer. At this time, the content of the binder in the positive electrode active material layer is preferably 1% by mass or less, more preferably 0.5% by mass or less, based on 100% by mass of the total solid content contained in the positive electrode active material layer. It is more preferably 0.2% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass.

In the non-aqueous electrolyte secondary battery of this embodiment, the thickness of the positive electrode active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of the positive electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 950 μm, and further preferably 200 to 800 μm. When the thickness of the positive electrode active material layer is 150 μm or more, the energy density of the battery can be sufficiently increased. On the other hand, when the thickness of the positive electrode active material layer is 1500 μm or less, the structure of the positive electrode active material layer can be sufficiently maintained.

The porosity of the positive electrode active material layer is preferably 35 to 50%. When the porosity of the positive electrode active material layer is 35% or more, it is not necessary to increase the pressing pressure when pressing the coating film after applying the positive electrode active material slurry at the time of forming the positive electrode active material layer. As a result, the positive electrode active material layer having a desired thickness and area can be suitably formed. On the other hand, when the void ratio of the positive electrode active material layer is 50% or less, the contact between the electron conductive materials (conductive auxiliary agent, positive electrode active material, etc.) in the positive electrode active material layer can be sufficiently maintained, and the electrons can be sufficiently maintained. It is possible to prevent an increase in movement resistance.

The density of the positive electrode active material layer is preferably 2.10 to 3.00 g / cm ³ , more preferably 2.15 to 2.85 g / cm ³ , and further preferably 2.20 to 2.80 g / cm 3. It is cm ³ . When the density of the positive electrode active material layer is 2.10 g / cm ³ or more, a battery having a sufficient energy density can be obtained. On the other hand, when the density of the positive electrode active material layer is 3.00 g / cm ³ or less, it is possible to prevent the above-mentioned decrease in the porosity of the positive electrode active material layer. If the decrease in porosity is suppressed, an electrolytic solution that fills the voids is sufficiently secured, and an increase in ion transfer resistance in the positive electrode active material layer can be prevented.

The positive electrode (positive electrode active material layer) shall be formed by any of a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method and a thermal spraying method, in addition to a method of applying (coating) a normal slurry. Can be done.

[Electrolyte layer]
The electrolyte layer of the non-aqueous electrolyte secondary battery according to this embodiment has a structure in which a separator is impregnated with an electrolytic solution.

The electrolytic solution (liquid electrolyte) has a function as a carrier of lithium ions. The electrolytic solution (liquid electrolyte) constituting the electrolytic solution layer has a form in which a lithium salt is dissolved in a non-aqueous solvent.

In the non-aqueous electrolyte secondary battery according to the present embodiment, the electrolytic solution contains a lithium salt and a non-aqueous solvent containing propylene carbonate, and the concentration of the lithium salt with respect to the concentration (mol / L) of the propylene carbonate in the electrolytic solution. The concentration (mol / L) ratio (lithium salt / propylene carbonate) is more than 0.250. With this configuration, even if graphite is used as the negative electrode active material, the decomposition of propylene carbonate can be suppressed by suppressing the reaction between graphite and propylene carbonate. Therefore, the formation of a high resistance film due to the decomposition product of propylene carbonate on the graphite surface is suppressed, and the charge / discharge reaction easily proceeds. The upper limit of the ratio is not particularly limited, but is preferably 1.43 or less, more preferably 1.15 or less, still more preferably 1.00 or less, and particularly preferably 0.70 or less. When the ratio is 1.43 or less, sufficient battery performance can be ensured.

The non-aqueous solvent contains propylene carbonate (PC). The non-aqueous solvent can contain a non-aqueous solvent other than propylene carbonate as long as the above ratio (lithium salt / propylene carbonate) is satisfied. Examples of non-aqueous solvents other than propylene carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), and methyl acetate (MA). , Methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), ethylene carbonate (EC), butylene carbonate (BC). , And γ-butyrolactone (GBL) and the like. Among them, as the non-aqueous solvent other than PC, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and butylene carbonate (BC) are preferable. , It is preferable to contain ethylene carbonate.

The content of the propylene carbonate in the non-aqueous solvent is preferably 30 to 100 vol% with respect to the total volume of the non-aqueous solvent. The concentration of the propylene carbonate in the non-aqueous solvent is preferably 3.5 to 11.8 mol / L. Within such a range, a higher discharge capacity can be obtained.

Examples of the lithium salt include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ and the like. Among them, LiPF ₆ and Li [(FSO ₂ ) 2N] ₍ LiFSI) are more preferable, and LiPF ₆ is particularly preferable, from the viewpoint of battery output and charge / discharge cycle characteristics.

The concentration of the lithium salt in the electrolytic solution is preferably 0.88 to 5.00 mol / L, more preferably 1.0 to 4.0 mol / L, and more preferably 1.5 to 3.0 mol / L. Is more preferable. Within such a range, a higher discharge capacity can be obtained.

The electrolytic solution may be further mixed with additives other than the above-mentioned components. Further, the additive may be contained in the electrolytic solution. Specific examples of such compounds include, for example, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-divinylethylene carbonate. , 1-Methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylenecarbonate, 1-ethyl-1-vinylethylenecarbonate, 1-ethyl-2-vinylethylenecarbonate, vinylvinylene carbonate, allylethylenecarbonate, vinyl Oxymethylethylene carbonate, allyloxymethylethylene carbonate, acrylicoxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1,1- Examples thereof include dimethyl-2-methyleneethylene carbonate. Only one of these additives may be used alone, or two or more of these additives may be used in combination. When the additive is used in the electrolytic solution, the amount used is preferably 0.5 to 10% by mass, more preferably 0.5 to 5 with respect to 100% by mass of the electrolytic solution before the additive is added. It is mass%.

In the non-aqueous electrolyte secondary battery according to this embodiment, a separator is used for the electrolyte layer. The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

Examples of the form of the separator include a separator of a porous sheet made of a polymer or fiber that absorbs and retains the electrolytic solution, a non-woven fabric separator, and the like.

As the separator of the porous sheet made of a polymer or a fiber, for example, a microporous (microporous membrane) can be used. Specific forms of the porous sheet made of the polymer or fiber include, for example, a polyolefin such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP). Examples thereof include a microporous (microporous film) separator made of a (structured laminate, etc.), a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and glass fiber.

The thickness of the microporous (microporous membrane) separator cannot be uniquely specified because it varies depending on the intended use. To give an example, in applications such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the length is 4 to 60 μm in a single layer or a multilayer. Is desirable. It is desirable that the fine pore size of the microporous (microporous membrane) separator is 1 μm or less at the maximum (usually, the pore size is about several tens of nm).

As the non-woven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. Further, the bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. Further, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

Further, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (separator with a heat-resistant insulating layer). The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a separator having a melting point or a thermal softening point of 150 ° C. or higher, preferably 200 ° C. or higher, having high heat resistance is used. By having the heat-resistant insulating layer, the internal stress of the separator, which increases when the temperature rises, is relaxed, so that the effect of suppressing heat shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is less likely to cause performance deterioration due to a temperature rise. Further, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the film breakage of the separator is less likely to occur. Further, due to the effect of suppressing heat shrinkage and high mechanical strength, the separator is less likely to curl in the battery manufacturing process.

Inorganic particles in the heat-resistant insulating layer contribute to the mechanical strength of the heat-resistant insulating layer and the effect of suppressing heat shrinkage. The material used as the inorganic particles is not particularly limited. For example, silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al _{2O 3} , ZrO ₂ , TIO ₂ ), hydroxides, and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, and mica, or may be artificially produced. Further, only one kind of these inorganic particles may be used alone, or two or more kinds thereof may be used in combination. Of these, from the viewpoint of cost, it is preferable to use silica (SiO ₂ ) or alumina (Al ₂ O ₃ ), and it is more preferable to use alumina (Al ₂ O ₃ ).

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . Within this range, sufficient ionic conductivity can be obtained and heat resistance is preferably maintained.

The binder in the heat-resistant insulating layer has a role of adhering the inorganic particles to each other and the inorganic particles and the resin porous substrate layer. The binder stably forms the heat-resistant insulating layer and prevents peeling between the porous substrate layer and the heat-resistant insulating layer.

The binder used for the heat-resistant insulating layer is not particularly limited, and is, for example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber. , Butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), methyl acrylate and the like can be used as the binder. Of these, carboxymethyl cellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. Only one of these compounds may be used alone, or two or more of these compounds may be used in combination.

The content of the binder in the heat-resistant insulating layer is preferably 2 to 20% by mass with respect to 100% by mass of the heat-resistant insulating layer. When the binder content is 2% by mass or more, the peel strength between the heat-resistant insulating layer and the porous substrate layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by mass or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The heat shrinkage of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour under the conditions of 150 ° C. and 2 gf / cm ² . By using such a material having high heat resistance, it is possible to effectively prevent the separator from shrinking even when the heat generation amount becomes high and the battery internal temperature reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is less likely to cause performance deterioration due to a temperature rise.

[Manufacturing method of non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of this embodiment can be produced by a conventional method. Specifically, a cell may be manufactured by laminating the positive electrode and the negative electrode so as to face each other via the electrolyte layer. Then, the stacking of the electrolyte layer and the electrodes is repeated until the number of cells becomes a desired number, and a laminated body is obtained. Next, the positive electrode tab and the 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 (heating) at the time of joining and can be joined in an extremely short time. Therefore, the electrode active material layer (negative electrode active material) by heat is used. It is excellent in that it can prevent deterioration of the layer and the positive electrode active material layer). At this time, the positive electrode tab and the negative electrode tab can be arranged so as to face each other on the same side (same extraction side). As a result, the positive electrode tabs of each positive electrode can be bundled into one 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 into one and taken out from the exterior body as one negative electrode current collector plate. Further, the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) may be arranged so as to be opposite sides (different extraction sides).

Next, the laminated body is stored in the exterior body. The laminate is a laminate film used for the battery exterior, and 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 from above and below to the outside of the battery exterior body. Insert it.

Next, three sides of the outer peripheral portions (sealing portions) of the upper and lower laminated films are thermocompression bonded to be sealed. A three-sided sealed body is obtained by thermocompression-bonding three sides of the outer peripheral portion to seal the outer peripheral portion. At this time, it is preferable to seal the heat-sealed portion on the side where the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) are taken out. This is because if these positive electrode current collector plates and negative electrode current collector plates are located at the openings during subsequent liquid injection, the electrolytic solution may scatter during liquid injection.

Although the battery having a laminated structure has been described above, the battery is not limited to the laminated type, and various shapes such as a square type, a paper type, a cylindrical type, and a coin type can be adopted as the battery configuration. can.

Next, the electrolytic solution is injected into the inside of the three-sided encapsulant from the opening on the remaining one side of the three-sided encapsulant with the liquid injection device. As a result, an electrolyte layer in which the separator is impregnated with an electrolyte is formed. At this time, the three-sided sealant may be housed in a vacuum box connected to a vacuum pump so that the electrolyte can be impregnated into the laminate inside the three-sided sealant, particularly the separator and the electrode active material layer as soon as possible. preferable. Further, it is desirable to inject the liquid in a state where the pressure is reduced and the inside is in a high vacuum state. After pouring the liquid, the three-sided encapsulant is taken out from the vacuum box, and the remaining one side of the three-sided encapsulant is temporarily sealed to obtain a laminated type (laminated structure) non-aqueous electrolyte secondary battery. The electrolytic solution injected here uses the above-mentioned electrolytic solution, and may have the same composition or a different composition as the electrolytic solution used when forming the electrode active material slurry. It is preferably the same composition.

[Positive current collector plate and negative electrode current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used. As the 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. The same material may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25, or different materials may be used.

[Positive lead and negative electrode lead]
Although not shown, the current collector 11 and the current collector plates (25, 27) may be electrically connected to each other via a positive electrode lead or a negative electrode lead. As the constituent material of the positive electrode and the negative electrode lead, a material used in a known lithium ion secondary battery can be similarly adopted. The part taken out from the exterior is heat-shrinkable with heat-resistant insulation so that it does not affect the product (for example, automobile parts, especially electronic devices) by contacting peripheral devices and wiring and causing electric leakage. It is preferable to cover with a tube or the like.

[Seal part]
The sealing portion (insulating layer) has a function of preventing contact between current collectors and a short circuit at the end of the cell cell layer. As the material constituting the sealing portion, if it has insulating property, sealing property against falling off of solid electrolyte, sealing property against moisture permeation from the outside (sealing property), heat resistance under battery operating temperature, etc. good. For example, acrylic resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber (ethylene-propylene-diene rubber: EPDM), and the like can be used. Further, an isocyanate-based adhesive, an acrylic resin-based adhesive, a cyanoacrylate-based adhesive, or the like may be used, or a hot-melt adhesive (urethane resin, polyamide resin, polyolefin resin) or the like may be used. Among them, polyethylene resin and polypropylene resin are preferably used as constituent materials of the insulating layer from the viewpoints of corrosion resistance, chemical resistance, ease of production (film formation), economy, etc., and mainly non-crystalline polypropylene resin. It is preferable to use a resin obtained by copolymerizing ethylene, propylene, and butene as components.

[Battery exterior]
As the battery exterior, a known metal can case can be used, or a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generation element as shown in FIG. 1, can be used. As the laminated film, for example, a laminated film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminated film is not limited thereto. A laminated film is desirable from the viewpoint of high output, excellent cooling performance, and suitable use for batteries for large equipment for EVs and HEVs. Further, since the group pressure applied to the power generation element from the outside can be easily adjusted and the thickness of the electrolytic solution layer can be easily adjusted, an aluminumate laminate is more preferable for the exterior body.

[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 bipolar secondary battery 50 has a rectangular flat shape, and positive electrode tabs 58 and negative electrode tabs 59 for extracting electric power are pulled out from both sides thereof. There is. The power generation element 57 is wrapped by a battery exterior (laminated film 52) of the bipolar secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. It is sealed in a closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the bipolar secondary battery 10 shown in FIG. 1 described above. The power generation element 57 is formed by stacking a plurality of bipolar electrodes 23 via the electrolyte layer 17.

The lithium ion secondary battery is not limited to a laminated flat battery. The wound lithium-ion secondary battery may have a cylindrical shape, or may be formed by deforming such a cylindrical shape into a rectangular flat shape. There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminated film. By this form, weight reduction can be achieved.

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

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

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

[Volume energy density and rated discharge capacity]
In a general electric vehicle, how to lengthen the mileage (cruising range) by one charge is an important development goal. Considering these points, 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, from the viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to specify the size of the battery from the viewpoint of the battery area and the battery capacity. For example, in the case of a flat laminated laminated battery, the value of the ratio of the battery area (projected area of the battery including the battery exterior) to the rated capacity is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. It is preferable that the present invention is applied to a certain battery. Further, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The aspect ratio of the electrodes is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio within such a range, there is an advantage that both vehicle required performance and mounting space can be achieved.

Further, in the non-aqueous electrolyte secondary battery of the present embodiment, the battery capacity per unit area (cm ² ) is preferably 6 mAh / cm ² or more, more preferably 6.5 mAh / cm, from the viewpoint of a large-sized battery. ² or more.

The battery capacity per unit area is calculated according to the following formula.
Formula: Battery capacity per unit area (mAh / cm ² ) = Discharge capacity per positive electrode active material (mAh / g) x Amount of positive electrode active material (mg / cm ² ) / 10 ³ .

[Battery set]
An assembled battery is configured by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By serializing and parallelizing, it becomes possible to freely adjust the capacity and voltage.

It is also possible to connect a plurality of batteries in series or in parallel to form a small assembled battery that can be attached / detached. Then, by connecting a plurality of small detachable batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle drive power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery with an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be mounted. It may be decided according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery of this embodiment maintains the discharge capacity even after long-term use and has good cycle characteristics. In addition, the volumetric energy density is high. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required and longer life is required compared to electric and portable electronic device applications. .. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

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

Hereinafter, the present invention will be described in more detail by way of examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, "part" means "part by mass". The steps from the preparation of the positive electrode active material slurry and the negative electrode active material slurry to the production of the battery were performed in the glove box. In addition, unless otherwise specified, it was carried out under atmospheric pressure.

[Example 1]
<Preparation of electrolyte>
A lithium salt (LiPF ₆ ) was dissolved in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC) at a ratio of 1.5 mol / L to obtain an electrolytic solution. The concentration ratio of the lithium salt to the propylene carbonate was 0.254.

<Preparation of positive electrode active material slurry>
LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder as positive electrode active material, acetylene black as conductive aid [Denka Black (registered trademark) manufactured by Denka Co., Ltd.] (average particle size (primary particle size): 0 .036 μm), and carbon nanofiber [Showa Denko Co., Ltd., VGCF (registered trademark), aspect ratio 60 (average fiber diameter: about 150 nm, average fiber length: about 9 μm), electrical resistance 40 μΩm, bulk density 0.04 g / Cm ³ ] was used.

As a member, LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, acetylene black and carbon nanofibers were weighed so as to have a mass ratio of 92: 6: 2. An electrolytic solution was added to the above member so that the solid content ratio was 70% by mass. The obtained mixture was mixed at 2000 rpm for 4 minutes using a mixing defoamer (ARE-250, manufactured by Shinky Co., Ltd.). After confirming the slurry properties, the mixture was further mixed at 2000 rpm for 4 minutes to obtain a positive electrode active material slurry.

<Preparation of negative electrode active material slurry>
Graphite as the negative electrode active material, acetylene black as a conductive auxiliary agent [Denka Black (registered trademark) manufactured by Denka Co., Ltd.] (average particle size (primary particle size): 0.036 μm), and carbon nanofiber [manufactured by Showa Denko KK] , VGCF®, aspect ratio 60 (average fiber diameter: about 150 nm, average fiber length: about 9 μm), electrical resistance 40 μΩm, bulk density 0.04 g / cm ³ ] was used.

As a member, graphite, acetylene black, and carbon nanofibers were weighed so as to have a mass ratio of 92: 6: 2. An electrolytic solution was added to the above member so that the solid content ratio was 70% by mass. The obtained mixture was mixed at 2000 rpm for 4 minutes using a mixing defoamer (ARE-250, manufactured by Shinky Co., Ltd.). After confirming the slurry properties, the mixture was further mixed at 2000 rpm for 4 minutes to obtain a negative electrode material slurry.

<Current collector and separator>
Carbon-coated aluminum foil as a positive electrode current collector (manufactured by Showa Denko KK, carbon layer thickness 1 μm, aluminum layer thickness 20 μm, size 61 × 72 mm), copper foil as a negative electrode current collector (Thunk Metal Co., Ltd.) , Thickness 10 μm, size 61 × 72 mm), and separator (5 cm × 5 cm, thickness 23 μm, made of Cellguard 2500 polypropylene) were prepared.

<Manufacturing of positive electrode>
The positive electrode current collector was masked with a PET sheet so that the size of the slurry coated portion was 29 × 40 mm. With the positive electrode current collector fixed on the surface plate under reduced pressure using an adsorption surface plate, the positive electrode active material slurry 1 prepared above is placed on the positive electrode current collector using an applicator to create a gap in the applicator. Was set to be 650 μm and applied. The coating speed was set to 30 mm / s. By applying in this way, an electrode having a positive electrode active material mass (a basis weight of the positive electrode active material) of 40 mg / cm ² was produced.

Six aramid sheets (manufactured by Japan Vilene Co., Ltd., thickness 45 μm) were placed on the surface of the slurry after coating, and pressed using a high pressure jack J-1 (manufactured by AS ONE Corporation). At this time, the press pressure was 0.4 MPa, and the process was repeated until the desired electrode density (electrode porosity) was reached to obtain a positive electrode active material layer. The positive electrode active material layer had a thickness of 250 μm, a porosity of 40%, and a density of 2.55 g / cm ³ . Further, when the cross section of the obtained positive electrode active material layer was confirmed by a scanning electron microscope (SEM), at least a part of the conductive member collected electricity from the first main surface in contact with the electrolyte layer side of the positive electrode active material layer. A conductive passage was formed to electrically connect to the second main surface in contact with the body side.

<Manufacturing of negative electrode>
The dried negative electrode current collector was masked with a PET sheet so that the size of the slurry-coated portion was 33 × 44 mm. With this negative electrode current collector fixed on the surface plate under reduced pressure using an adsorption surface plate, the negative electrode active material slurry 1 prepared above is placed on the negative electrode current collector using an applicator to create a gap in the applicator. Was set to 600 μm and applied. The coating speed was set to 30 mm / s. By applying in this way, an electrode having a total mass of the negative electrode active material and the conductive auxiliary agent of 21 mg / cm ² was produced.

Six aramid sheets (manufactured by Japan Vilene Co., Ltd., thickness 45 μm) were placed on the surface of the slurry after coating, and pressed using a high pressure jack J-1 (manufactured by AS ONE Corporation). At this time, the press pressure was 0.4 MPa, and the process was repeated until the desired electrode density (electrode porosity) was reached to obtain a negative electrode active material layer. The negative electrode active material layer had a thickness of 280 μm, a porosity of 34%, and a density of 1.00 g / cm ³ . Further, when the cross section of the obtained negative electrode active material layer was confirmed by a scanning electron microscope (SEM), at least a part of the conductive member collected electricity from the first main surface in contact with the electrolyte layer side of the negative electrode active material layer. A conductive passage was formed to electrically connect to the second main surface in contact with the body side.

<Manufacturing of lithium-ion batteries>
A separator (5 cm x 5 cm, thickness 23 μm, made of Cellguard 2500 polypropylene) is sandwiched between the positive and negative electrodes to form a battery, and a copper foil (3 cm x 3 cm, thickness 17 μm) with terminals (Ni, 5 mm x 3 cm) and terminals. This battery is sandwiched between carbon-coated aluminum foil (3 cm x 3 cm, thickness 21 μm) with (Al, 5 mm x 3 cm), and it is held by using two commercially available heat-sealed aluminum laminate films (10 cm x 8 cm). Enclosed. Then, after injecting 60 μL of the same electrolytic solution as above, the exterior body was vacuum-sealed to prepare a lithium ion battery.

[Example 2]
A lithium ion battery was produced in the same manner as in Example 1 except that the concentration of the lithium salt in the electrolytic solution was changed from 1.5 mol / L to 2 mol / L. The concentration ratio of the lithium salt to the propylene carbonate was 0.339.

[Example 3]
A lithium ion battery was produced in the same manner as in Example 1 except that the concentration of the lithium salt in the electrolytic solution was changed from 1.5 mol / L to 3 mol / L. The concentration ratio of the lithium salt to the propylene carbonate was 0.508.

[Example 4]
A lithium ion battery was produced in the same manner as in Example 1 except that the concentration of the lithium salt in the electrolytic solution was changed from 1.5 mol / L to 4 mol / L. The concentration ratio of the lithium salt to the propylene carbonate was 0.678.

[Example 5]
A lithium ion battery was produced in the same manner as in Example 2 except that the volume ratio of the mixed solvent of EC and PC in the electrolytic solution was changed from 1: 1 to 2: 1. The concentration ratio of the lithium salt to the propylene carbonate was 0.508.

[Example 6]
A lithium ion battery was produced in the same manner as in Example 3 except that the mixed solvent of EC and PC in the electrolytic solution was changed to a single solvent of PC. The concentration ratio of the lithium salt to the propylene carbonate was 0.254.

[Comparative Example 1]
A lithium ion battery was produced in the same manner as in Example 1 except that the concentration of the lithium salt in the electrolytic solution was changed from 1.5 mol / L to 1 mol / L. The concentration ratio of the lithium salt to the propylene carbonate was 0.169.

[Comparative Example 2]
A lithium ion battery was produced in the same manner as in Comparative Example 1 except that the mixed solvent of EC and PC in the electrolytic solution was changed to a single solvent of PC. The concentration ratio of the lithium salt to the propylene carbonate was 0.085.

[Comparative Example 3]
A lithium ion battery was produced in the same manner as in Comparative Example 2 except that the concentration of the lithium salt in the electrolytic solution was changed from 1 mol / L to 2 mol / L. The concentration ratio of the lithium salt to the propylene carbonate was 0.169.

<Measurement of charge / discharge capacity>
The charge / discharge capacity was measured at 25 ° C. and under the following conditions.
1. 1. Pre-charging conditions The lithium-ion batteries prepared in Examples and Comparative Examples were charged with a constant current (CC) for 10 hours at a current of 0.01 C.
2. 2. Initial charging conditions For the initial charging, CC charging was performed up to 4.2V with a current of 0.05C, and then constant voltage (CV) charging was performed until the current value reached 0.01C.
3. 3. Initial discharge conditions For the initial discharge, CC discharge was performed until 2.5 V was reached with a current of 0.05 C.
4. Charging / discharging conditions Charging conditions: CC charging was performed up to 4.2 V with a current of 0.05 C, and then CV charging was performed until the current value reached 0.01 C;
Discharge conditions: CC discharge is performed until 2.5 V is reached with a current of 0.05 C, and the discharge capacity per unit mass of the positive electrode active material (mAh / g) and the battery capacity per unit area (cm ² ) (mAh / cm ² ). ) Was asked.

The battery capacity per unit area was calculated according to the following formula.
Formula: Battery capacity per unit area (mAh / cm ² ) = Discharge capacity per positive electrode active material (mAh / g) x Amount of positive electrode active material (mg / cm ² ) / 10 ³ .

The results are shown in Table 1.

From the results shown in Table 1, in a non-aqueous electrolyte secondary battery using a negative electrode active material layer made of a non-binder containing graphite as a negative electrode active material and an electrolytic solution containing a lithium salt and propylene carbonate, the electrolytic solution is used. In Examples 1 to 6, in which the ratio (lithium salt / propylene carbonate) of the lithium salt concentration (mol / L) to the propylene carbonate concentration (mol / L) is more than 0.25, the ratio is 0.25. It can be seen that a higher discharge capacity can be obtained as compared with Comparative Examples 1 to 3 below.

Claims (6)

A positive electrode having a positive electrode active material layer containing a positive electrode active material on the surface of a positive electrode current collector,
A negative electrode having a negative electrode active material layer made of a non-binding body containing a negative electrode active material on the surface of the negative electrode current collector, and a negative electrode.
An electrolyte layer in which the separator is impregnated with an electrolytic solution,
Has power generation elements, including
The negative electrode active material contains graphite and contains
The electrolytic solution contains a lithium salt and a non-aqueous solvent containing propylene carbonate, and the ratio of the concentration (mol / L) of the lithium salt to the concentration (mol / L) of the propylene carbonate in the electrolytic solution (lithium salt). / Propylene carbonate) is more than 0.25, a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the propylene carbonate in the non-aqueous solvent is 30 to 100 vol% with respect to the total volume of the non-aqueous solvent. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the ratio is 1.43 or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the concentration of the lithium salt in the electrolytic solution is 1.5 to 3.0 mol / L. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the battery capacity per unit area (cm ² ) is 6 mAh / cm ² or more. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the negative electrode active material layer has a thickness of 200 to 650 μm.

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