JP5962961B2 - Positive electrode, manufacturing method thereof, and nonaqueous electrolyte secondary battery using the positive electrode - Google Patents

Description

  The present invention relates to a positive electrode, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery using the positive electrode. More specifically, the present invention relates to a positive electrode used for a non-aqueous electrolyte secondary battery containing a gas generating additive in an electrolyte and a method for producing the same.

In recent years, lithium-ion secondary batteries, nickel-metal hydride batteries, and other secondary batteries have become increasingly important as power sources mounted on vehicles that use electricity as power sources, or power supplies mounted on personal computers, mobile terminals, and other electrical products. ing. In one typical configuration of this type of secondary battery, positive and negative electrodes including an electrode active material layer including an electrode active material capable of reversibly occluding and releasing charge carriers are housed in a battery case together with an electrolyte. ing.
Such a secondary battery is normally used in a state where it is controlled so as to be within a predetermined voltage range of, for example, about 3.0V to 4.2V, but when it is out of the normal state due to various factors. There is a possibility of deviating from a predetermined voltage range and falling into an overcharge state. In this overcharged state, problems such as decomposition of the electrolyte solution and generation of gas in the battery case, or heat generation of the active material and increase of the temperature inside the battery may occur. Therefore, for the purpose of preventing such a problem in advance, it has been proposed to include a mechanism (current interruption mechanism: CID) that detects an overcharge state based on battery temperature, battery internal pressure, etc., and interrupts the current (for example, Patent Document 1).

  In a secondary battery provided with a CID of a type that operates by increasing the internal pressure of the battery, a gas generating additive such as cyclohexylbenzene (CHB) or biphenyl (BP) is included in the electrolyte in order to cause the CID to operate more quickly when overcharged. Is previously added. This gas generating additive has an oxidation potential (that is, a voltage at which the oxidative decomposition reaction starts) lower than that of the electrolyte solvent, and can be rapidly oxidatively decomposed before the electrolyte on the positive electrode surface during overcharge. Due to this oxidative decomposition reaction at the positive electrode, a large amount of gas is generated at the negative electrode, so that the pressure in the battery can be quickly increased and the CID can be operated at an earlier stage. That is, according to such a configuration, it is possible to stop the electrode reaction in the battery in a safer state.

JP 2006-324235 A

  By the way, the oxidative decomposition reactivity of the gas generating additive can be influenced by the kind of the positive electrode active material. Therefore, for example, when a positive electrode active material having a low surface electron conductivity is used, the oxidative decomposition reaction of the gas generating additive at the positive electrode does not proceed rapidly even in an overcharged state, and the amount of gas generated is reduced. It was. Therefore, it takes time until the CID operates, and there is a possibility that it is difficult to cut off the current in the battery in a safe state.

  The present invention has been created in view of such a conventional situation, and an object of the present invention is to provide a positive electrode in which the electron conductivity of the positive electrode active material (active material layer) is improved, and a method for producing the positive electrode, It is a battery comprising a CID and a gas generating additive, and a non-aqueous electrolyte secondary battery in which the oxidative decomposition reactivity of the additive is increased and the amount of gas generated is increased.

That is, as a result of intensive studies by the present inventors, it was considered that the oxidative decomposition reactivity of the gas generating additive in the positive electrode is greatly influenced by the electron conductivity on the surface of the positive electrode active material. In order to increase the reactivity between the positive electrode active material and the gas generating additive, in the overcharged state, the material that increases the reactivity at the interface, that is, the extraction of electrons from the positive electrode active material is promoted, and the electrolyte and the gas generating additive are added. It has been found that arranging a material capable of supplying electrons to the agent is effective in increasing electron conductivity, and the present invention has been conceived.
The positive electrode provided by the present invention is a positive electrode including a positive electrode active material layer including a positive electrode active material, a conductive material, and a binder, and a hole transport material is disposed on at least a part of the surface of the positive electrode active material. It is characterized by being.

For example, in a lithium secondary battery, during discharge, lithium ions as charge carriers are extracted from the graphite as the negative electrode active material into the electrolyte, and the lithium ions are released from the lithium through the electrolyte. (For example, cobalt oxide: CoO ₂ ). Then, on the surface of the positive electrode active material, electrons transported through the external circuit are obtained, and a positive electrode active material (lithium cobalt composite oxide: LiCoO ₂ ) is formed.
Here, the positive electrode active material is inferior in electrical conductivity as compared with graphite or the like that is generally used as a negative electrode active material. Therefore, the presence of a conductive material is indispensable in the positive electrode active material layer. In the positive electrode disclosed herein, a positive electrode active material when a predetermined voltage is generated by disposing a hole transport material on at least a part of the surface of the positive electrode active material separately from the conductive material. The conductivity of the surface of the substance is increased, and the reactivity on the surface of the positive electrode active material when this positive electrode is used in a battery can be increased.

Note that the hole transport material is a material having a high affinity for holes and having a hole transport property for receiving and moving holes under a predetermined electric field. Here, the hole transportability is, for example, that the hole mobility is 50 times greater than the electron mobility, or Time
Only the hole mobility is measured by the OF Flight method (TOF method), and it can be considered as a characteristic that the electron mobility is not measured. Note that the TOF method is a method for measuring electron mobility or hole mobility by measuring a current generated when a carrier generated when a sample surface is irradiated with pulsed light moves within the sample. is there.

  In a preferred embodiment of the positive electrode disclosed herein, at least a part of the surface of the positive electrode active material is covered with the hole transport material. As the arrangement mode of the hole transport agent on the surface of the positive electrode active material, it is preferable that the contact area between the positive electrode active material and the hole transport material is large in order to improve the hole receiving property (electron donating property). Therefore, it is preferable that the positive electrode active material is covered with the hole transport material rather than simply having the hole transport material disposed adjacently. Thereby, the electrical conductivity on the surface of the positive electrode active material is further improved, and a positive electrode having high reactivity is realized.

  In a preferred embodiment of the positive electrode disclosed herein, the positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt, and manganese. A lithium transition metal composite oxide containing nickel, cobalt, and manganese is a so-called ternary positive electrode active material. For example, a positive electrode active material of a lithium secondary battery has a large discharge capacity, but is relatively conductive (electronic conduction). Material). Thus, by imparting electrical conductivity to the surface of the ternary positive electrode active material, a positive electrode having a high capacity and high electrical conductivity can be realized.

  In a preferred embodiment of the positive electrode disclosed herein, the ratio of the hole transport material to the positive electrode active material layer is 0.01% by mass to 1.0% by mass in terms of solid content. It is said. As described above, the hole transport material in the positive electrode enhances the conductivity of the surface of the positive electrode active material when a predetermined voltage is generated. However, during normal use of a battery including this positive electrode, the internal resistance of the battery is reduced. It can be a boost. Therefore, it is not preferable to contain too many hole transport materials. Such a positive electrode can be provided with a good balance between the conductivity of the surface of the positive electrode active material and the internal resistance of the battery by setting the ratio of the hole transport material in the above range.

  In a preferred embodiment of the positive electrode disclosed herein, the hole transport material is N, N′-bis (3-methylphenyl) -N, N′-diphenyl-1,1′-biphenyl-4,4 ′. -It is characterized by being one or more selected from the group consisting of diamine (TPD), polyvinyl carbazole (PVCz), polyaniline and polypyrrole. These are materials that are widely used as hole transport materials, and are preferable because the conductivity of the surface of the positive electrode active material can be suitably increased. In particular, TPD and polyvinylcarbazole (PVCz) can be preferable as a hole transport material from the viewpoint of ionization energy and electron affinity. Therefore, for example, at the time of overcharge, it is preferable because hole injection into the positive electrode active material is promoted more smoothly and the gas generating additive can be efficiently oxidized and decomposed.

  The nonaqueous electrolyte secondary battery provided by the present invention in another aspect is a secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, and includes the positive electrode described in any of the above as the positive electrode. Features. According to this configuration, the positive electrode has the hole transport material disposed on at least a part of the surface of the positive electrode active material. Therefore, when a predetermined voltage at which the hole transport material can exhibit hole transportability is generated in the non-aqueous electrolyte secondary battery, the conductivity of the surface of the positive electrode active material is increased, and the positive electrode is added to the battery. When used, the reactivity between the positive electrode active material and the electrolyte ions can be increased.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte secondary battery further includes a current interrupt mechanism (CID) capable of interrupting a conductive path between the positive electrode and the negative electrode according to an internal pressure in the battery, The water electrolyte includes a gas generating additive having a function of generating gas by being oxidatively decomposed at the positive electrode, and the internal pressure in the battery is increased by the gas generated by the gas generating additive, so that the current interruption mechanism Can cut off the conductive path. According to such a configuration, for example, when the nonaqueous electrolyte secondary battery is overcharged, the electron donating property to the gas generating additive is enhanced at the interface between the positive electrode active material and the gas generating additive. It is possible to oxidatively decompose the gas generating additive more rapidly. This makes it possible to generate a sufficient amount of gas to increase the internal pressure of the battery. As a result, the pressure in the battery can be quickly increased at the time of overcharge, the CID can be operated at an earlier stage, and a safer and more reliable nonaqueous electrolyte secondary battery can be realized. It is possible.

The positive electrode manufacturing method provided by the invention disclosed herein is a positive electrode manufacturing method including a positive electrode current collector including a positive electrode active material layer containing a positive electrode active material. Such a manufacturing method includes the step of disposing a hole transport material on at least a part of the surface of the positive electrode active material, mixing the positive electrode active material layer on which the hole transport material is disposed, a conductive material, and a binder together with a solvent. A step of preparing a composition for forming a positive electrode active material layer (hereinafter sometimes simply referred to as a positive electrode paste), and supplying the composition for forming a positive electrode active material layer onto the positive electrode current collector. Forming an active material layer.
According to this manufacturing method, the hole transport material is first disposed on at least a part of the surface of the positive electrode active material and then blended in the positive electrode paste. Therefore, it is possible to provide a positive electrode in which the hole transport material is disposed on at least a part of the surface of the positive electrode active material layer. That is, it is possible to provide a positive electrode in which the conductivity of the surface of the positive electrode active material is enhanced by the hole transport property of the hole transport material.

  In a preferred embodiment of the production method disclosed herein, the hole transport material is disposed by spraying a solution containing the hole transport material in a state where the positive electrode active material is fluidized, and The method is characterized in that drying is performed in a state where microdroplets of the solution are attached to at least a part of the surface of the substance, and at least a part of the surface of the positive electrode active material is covered with the hole transport material. By disposing the hole transport material with respect to the positive electrode active material, the hole transport characteristics of the hole transport material can be effectively expressed by enhancing the adhesion between the two. Therefore, for example, it is preferable that the hole transport material is made into a solution and adhered to the surface of the positive electrode active material layer because the hole transport material can be disposed on the surface of the positive electrode active material with better adhesion. Thereby, it becomes possible to increase the electroconductivity of a positive electrode active material more effectively with a small amount of hole transport material.

  In a preferred aspect of the production method disclosed herein, the hole transport material is mixed with the positive electrode active material and disposed on at least a part of the surface of the positive electrode active material. Also by this method, the hole transport material can be disposed on at least a part of the surface of the positive electrode active material. As a result, a positive electrode with improved conductivity and reactivity when a predetermined voltage is applied can be suitably produced.

  In a preferred embodiment of the production method disclosed herein, a lithium transition metal composite oxide containing nickel, cobalt, and manganese is used as the positive electrode active material. Such a lithium transition metal composite oxide is a so-called ternary positive electrode active material. For example, a positive electrode active material of a lithium secondary battery is a material having a relatively low electrical conductivity (electron conductivity) although the discharge capacity is large. is there. Thus, by using such a ternary lithium transition metal composite oxide as the positive electrode active material and imparting conductivity to this surface, a high capacity and high conductivity positive electrode can be manufactured.

  In a preferred embodiment of the production method disclosed herein, a positive electrode active material layer forming composition is prepared by using an aqueous solvent as the solvent and using a water-soluble or water-dispersible binder as the binder. It is characterized by. Many of the above hole transport materials are soluble in organic solvents that are typical non-aqueous solvents. Therefore, when an organic solvent is used in the preparation of the positive electrode paste, the hole transport material disposed on the surface of the positive electrode active material is dissolved in the solvent and dispersed in the paste. Therefore, although it is not impossible to use an organic solvent, it is desirable to use an aqueous solvent that does not dissolve the hole transport material as the solvent. Thereby, the positive electrode disclosed here can be manufactured more suitably.

  In a preferred embodiment of the production method disclosed herein, the ratio of the hole transport material in the positive electrode active material layer is 0.01% by mass to 1.0% by mass in terms of solid content. It is characterized by blending. As described above, the hole transport material in the positive electrode disclosed herein can enhance the conductivity of the surface of the positive electrode active material when a predetermined voltage is generated, but in normal use of a battery including the positive electrode, etc. It can also increase the internal resistance of the battery. Therefore, it is not preferable to contain too many hole transport materials. According to this manufacturing method, by setting the ratio of the hole transport material in the above range, it is possible to provide the conductivity of the surface of the positive electrode active material while keeping the internal resistance of the battery low.

It is a perspective view which shows the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the II-II line | wire in FIG. It is a flowchart of the manufacturing method of the positive electrode which concerns on one Embodiment. It is the side view which illustrated the vehicle provided with the nonaqueous electrolyte secondary battery concerning one embodiment. It is a figure which shows an example of the relationship between the addition amount of a positive hole transport material, and battery resistance. It is a figure which shows an example of the relationship between the addition amount of a positive hole transport material, and the gas generation amount at the time of overcharge.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

In the present specification, the “secondary battery” refers to general power storage devices that can be repeatedly charged, such as a lithium secondary battery and a nickel-metal hydride battery. In the present specification, the “lithium secondary battery” refers to a battery that can be repeatedly charged using lithium ions as a charge carrier, and typically includes lithium ion batteries, lithium polymer batteries, and the like.
In addition, the “average particle diameter” in this specification means, unless otherwise specified, a particle diameter (50% integrated value of particle diameter in a particle size distribution measured by a particle size distribution measuring apparatus based on a laser scattering / diffraction method (50 % Volume average particle diameter).

  The positive electrode provided by the present invention includes a positive electrode active material layer including a positive electrode active material, a conductive material, and a binder. The positive electrode active material is capable of reversibly occluding and releasing (typically intercalating and decalating) chemical species that serve as charge carriers in a secondary battery (for example, lithium ions in a lithium ion battery). The conductive material ensures electrical conductivity between the positive electrode active materials and forms a conductive path in the positive electrode active material layer. Further, typically, conductivity between the positive electrode active material layer and the positive electrode current collector holding the positive electrode active material layer is also ensured. The binder plays a role of binding the positive electrode active material and the conductive material, and also has a role of binding the positive electrode active material layer and the positive electrode current collector.

  Therefore, the positive electrode disclosed herein is characterized in that a hole transport material is disposed adjacent to at least a part of the surface of the positive electrode active material. As described above, the hole transport material has a function of transporting and injecting holes into the positive electrode active material under a predetermined voltage. In other words, electrons are extracted from the positive electrode active material to improve electron mobility. That is, since the number of carriers on the surface of the positive electrode increases, electrical characteristics such as conductivity can be improved. Therefore, electron donating property is increased in various reactions using the surface of the positive electrode active material as a reaction field, and the reaction can be smoothly promoted.

  For example, during overcharge when the hole transporting ability of the hole transporting material is expressed and the voltage at which the oxidative decomposition reaction of the gas generating additive added to the electrolyte starts occurs, the reactivity is as follows: Is increased. That is, for example, specifically, (1) at the interface between the positive electrode active material and the hole transport material, the electron transportability from the positive electrode active material is enhanced by the hole transport material, and (2) the hole transport material and the gas At the interface with the generation additive, the electron donating property from the hole transport material to the gas generation additive is enhanced, and as a whole, the gas generation additive can be oxidized and decomposed more rapidly. Thereby, for example, a large amount of gas can be generated in the negative electrode paired with the positive electrode.

  According to such a configuration, for example, even when a positive electrode is produced using a positive electrode active material with low electron conductivity and used for a secondary battery including a CID, a predetermined amount necessary for operating the CID during overcharge Gas can be generated. Therefore, it is not necessary to change various designs such as increasing the amount of the gas generating additive in the electrolyte or resetting the internal pressure for operating the CID to be lower than a predetermined pressure.

  The hole transport material is a material that can be used for an organic electroluminescence (EL) element or the like, and various kinds of materials have been further researched and developed in recent years, and is necessary for developing such hole transport ability. The voltage can be as low as several volts. Therefore, the positive electrode disclosed herein can appropriately select and use a hole transport material so that hole transport characteristics can be obtained in a desired voltage range, thereby promoting an electrode reaction that proceeds in a desired battery. Could be possible.

  Hereinafter, the configuration and manufacturing method of such a positive electrode will be described in more detail by taking the case of a positive electrode for a lithium secondary battery as one embodiment. Needless to say, the technique disclosed herein is not limited to this embodiment. That is, the constituent material, application, shape, manufacturing method, manufacturing apparatus, and the like of the positive electrode disclosed herein are not particularly limited.

As illustrated in the flowchart of FIG. 3, the method for manufacturing a positive electrode disclosed herein essentially includes the following steps.
(S10) Step of disposing a hole transport material on at least a part of the surface of the positive electrode active material (S20) Mixing the positive electrode active material layer in which the hole transport material is disposed, a conductive material and a binder together with a solvent, Typically, a step of preparing a composition for forming a positive electrode active material layer (hereinafter sometimes simply referred to as a positive electrode paste) prepared in a paste (slurry) (S30) A composition for forming a positive electrode active material layer Supplying the positive electrode current collector to form a positive electrode active material layer

[Hole Transport Material Arrangement Step: S10]
In step S10, a hole transport material is disposed on at least part of the surface of the positive electrode active material.
The positive electrode active material may be any positive electrode active material that can be used for a desired battery (the same applies hereinafter). In the present embodiment, one type or two or more types of positive electrode active materials used in conventional lithium secondary batteries can be used without particular limitation. As such a positive electrode active material, a particulate lithium transition metal oxide is typically preferably used, and an oxide having a layered structure or an oxide having a spinel structure can be appropriately selected and used. For example, selected from a lithium nickel oxide (typically LiNiO ₂ ), a lithium cobalt oxide (typically LiCoO ₂ ), and a lithium manganese oxide (typically LiMn ₂ O ₄ ). One or more lithium transition metal oxides can be used.

  Here, for example, “lithium nickel-based oxide” means an oxide having Li and Ni as constituent metal elements, as well as one or more metal elements other than Li and Ni (that is, Li and Ni). It is also meant to include composite oxides containing a transition metal element and / or a typical metal element other than the above in a proportion equal to or less than that of Ni. In addition, when 2 or more types of metal elements other than Li and Ni are included, it is made for all of them to become a ratio smaller than Ni. The metal element is selected from the group consisting of, for example, Co, Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. Or one or more elements.

In addition, for example, the general formula:
_{Li (Li a Mn x Co y} Ni z) O 2
(A, x, y, and z in the formula satisfy a + x + y + z≈1 and xyz ≠ 0.)
So-called ternary lithium transition metal oxides containing three kinds of transition metal elements represented by the general formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
(In the formula, Me is one or more transition metals, and x satisfies 0 <x <1.)
It may be a so-called solid solution type lithium-excess transition metal oxide or the like. These ternary positive electrode active materials and lithium-rich positive electrode active materials have a large discharge capacity as a positive electrode active material for lithium secondary batteries, and are relatively poor in conductivity on the particle surface. Is preferable in that it can be effectively applied.

Further, the positive electrode active material has a general formula of LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and And an anion selected from the group consisting of V.).

  The compound which comprises such a positive electrode active material can be prepared and prepared by a well-known method, for example. For example, some raw material compounds appropriately selected according to the composition of the target positive electrode active material are mixed at a predetermined ratio, and the mixture is fired by an appropriate means. Thereby, the oxide as a compound which comprises a positive electrode active material can be prepared. In addition, the preparation method of a positive electrode active material (typically lithium transition metal oxide) itself does not characterize this invention at all.

  Moreover, although there is no strict restriction | limiting about the shape of a positive electrode active material, the positive electrode active material prepared as mentioned above can be grind | pulverized, granulated, and classified by an appropriate means. For example, a lithium transition metal oxide powder substantially composed of secondary particles having an average particle size in the range of about 1 μm to 25 μm (typically about 2 μm to 15 μm) is used as the positive electrode in the technology disclosed herein. It can preferably be employed as an active material.

  As the hole transport material, one kind or two or more kinds of various materials that exhibit hole transport ability when a predetermined electric field is applied, that is, at a predetermined voltage, can be used without any particular limitation. For example, various hole transport materials used in organic EL elements and the like can be used. As such a hole transport material, for example, from the viewpoint of driving voltage, the ionization energy is about 6.5 eV or less, preferably about 5 eV or more, more preferably 6.2 eV or less, and further It is preferably 6.0 eV or less. Further, the electron affinity is preferably 1.2 eV or more and 3.0 eV or less, more preferably 1.4 eV or more, for example, 1.5 eV or more. Further, for example, a material that exhibits p-type semiconductor characteristics under a predetermined voltage may be used.

Specific examples of such a hole transport material include pyrrole, indole, carbazole, azaindole, azacarbazole, pyrazole, imidazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone. , Styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary amine compound, styrylamine compound, aromatic dimethylidin compound, porphyrin compound, polysilane compound, poly (N-vinylcarbazole), aniline copolymer Examples thereof include conductive polymer oligomers such as coalescence, thiophene oligomer thiophene oligomer, polythiophene, organic silane, carbon film, and derivatives thereof. Among these, the following materials can be mentioned. Among them, N, N′-bis (3-methylphenyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD), polyvinylcarbazole (PVCz), polyaniline, polypyrrole, and the like are included. preferable. It may be a hole transport material made of a polymer compound in which TPD is incorporated in the main chain or side chain.

  The method of disposing the hole transport material on the surface of the positive electrode active material is not particularly limited, but in order to more effectively obtain the hole transport capability of the hole transport material, the hole transport material, the positive electrode active material, It is preferable to form a good contact interface. It is desirable that the interface is in direct contact with each other without using, for example, a binder. Therefore, for example, specifically, by preparing a particulate hole transport material and mixing (powdering) it with the positive electrode active material, the hole transport material is applied to at least a part of the surface of the positive electrode active material. It is preferable to arrange. The average particle diameter of the hole transport material is preferably prepared, for example, with a size of about 1/20 to 1/10 of the average particle diameter of the positive electrode active material as a guide. For example, a preferable example is to use a hole transport material having an average particle diameter of about 0.1 μm to 1 μm.

  In addition to the above method, for example, a method of attaching the hole transport material to the surface of the positive electrode active material by spraying is also suitable. Specifically, for example, a solution containing the hole transport material is prepared by dissolving or dispersing the hole transport material in an organic solvent or the like in advance. Then, by spraying this solution, the hole transport material is made into microdroplets of a predetermined size. At this time, at least a part of the surface of the positive electrode active material can be covered with the hole transport material by allowing the positive electrode active material to flow and attaching a fine droplet-shaped hole transport material and drying. . By disposing the hole transport material in a liquid state, the positive electrode active material and the hole transport material can be attached with good adhesion. Thereby, the hole transport characteristic of a hole transport material can be expressed more effectively.

  In addition, arrangement | positioning of the positive hole transport material by this spraying can be easily implemented, for example using the granulation apparatus etc. which integrated the spray-drying method and the fluidized bed system. The spray drying method is a method of manufacturing a powder by spraying a liquid or a mixture of a liquid and a solid (which may be in a slurry state) into a gas and drying it rapidly. By using an atomizer or a spray nozzle when spraying the liquid or slurry, droplets and powders with controlled average particle diameter can be obtained. The droplets can be dried by typically blowing air or nitrogen gas as a hot air stream. The positive electrode active material can be flowed, for example, by stirring, rolling, or forming a fluidized bed in the vertical direction.

[Step of preparing positive electrode paste: S20]
In step S20, the positive electrode active material layer provided with the hole transport material prepared in step S10, a conductive material, and a binder are mixed together with a solvent to form a paste-like positive electrode active material layer forming composition (positive electrode paste). Prepare. In the present invention, the paste form may include forms such as a slurry form and an ink form.

  The conductive material is not limited to a specific one. For example, various conductive materials conventionally used in this type of lithium secondary battery can be used. Specifically, for example, a carbon material such as carbon powder or carbon fiber can be used as the conductive material. As the carbon powder, carbon black such as acetylene black, furnace black and ketjen black, carbon powder such as graphite powder, and the like can be used. These may be used singly or in combination of two or more. As the conductive material, for example, it is preferable to use a granular conductive material in which the average particle diameter of the constituent particles (typically secondary particles) is in the range of about 100 nm to 2000 nm, for example, about 200 nm to 1000 nm.

As the binder, a polymer that can be dissolved or dispersed in a solvent used for preparing the positive electrode paste can be used. As such a solvent, it is possible to use a solvent-based solvent such as an organic solvent, but it is not preferable to use a solvent that dissolves the hole transport material disposed in the positive electrode active material. For this reason, it is preferable to use an aqueous solvent as the solvent. Accordingly, suitable binders include, for example, carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), and the like as water-soluble (water-soluble) polymer materials. Examples thereof include cellulosic polymers; polyvinyl alcohol (PVA); Further, as polymer materials that are dispersed in water (water dispersible), vinyl polymers such as polyethylene (PE) and polypropylene (PP); polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene- Fluororesin such as hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; styrene butadiene rubber (SBR), acrylic acid modified SBR resin ( Examples thereof include rubbers such as SBR latex).
When a nonaqueous solvent is used as the solvent, a polymer such as polyvinylidene fluoride (PVDF) or polyacrylonitrile (PAN) can be used.

The material constituting the positive electrode active material layer is mixed with a solvent to prepare a positive electrode paste.
As the solvent, an aqueous solvent is preferably used as described above. As an aqueous solvent, it can be set as the composition which consists of water or the mixed solvent which has water as a main component. As the solvent other than water constituting the mixed solvent, one or two or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. In addition, when using a non-aqueous solvent, N-methyl-2-pyrrolidone (NMP) etc. can be used in the range which does not melt | dissolve, peel, etc. of a hole transport material, for example.

In addition, the polymer material illustrated as said binder may be used in order to exhibit the function as additives, such as a thickener of a positive electrode paste other than the function as a binder. Furthermore, in addition to the material constituting the positive electrode active material layer, various additives such as a dispersant and a thickener may be added as necessary.
The mixing means is not particularly limited, and a general kneader conventionally used for preparing the positive electrode paste can be used. For example, an apparatus capable of preparing a paste called a kneader, a stirrer, a disperser, a mixer or the like can be used. However, also in these apparatuses, mixing under a condition in which a strong shearing force acts on the material constituting the positive electrode active material layer is not preferable because it leads to peeling of the hole transport material.

In the preparation of the positive electrode paste, the proportion of the positive electrode active material in the total amount of the positive electrode active material layer is preferably about 50% by mass or more, typically about 50 to 98% by mass, preferably about 60 to 98% by mass. More preferably, it is about 90% by mass.
The hole transport material is preferably blended so that the proportion of the positive electrode active material layer in the solid content is 0.01% by mass to 1.0% by mass. The hole transport material improves the electrical characteristics of the surface of the positive electrode active material even when added in a very small amount, and can sufficiently increase the amount of gas generated during overcharge, for example, but the proportion is 0.01% by mass. If it is less than the range, a sufficient effect may not be obtained, which is not preferable. Further, if the proportion of the hole transport material in the positive electrode active material layer is more than 1.0% by mass, it is not preferable because the internal resistance of the battery is increased. The ratio of the hole transport material is preferably 0.01% by mass to 0.9% by mass, and more preferably 0.01% by mass to 0.8% by mass. This makes it possible to improve the conductivity of the surface of the positive electrode active material and increase the amount of gas generated while keeping the internal resistance of the battery low. In addition, this ratio can be grasped as a ratio of about 0.01% by mass to 1.2% by mass when the positive electrode active material is 100% by mass.
The proportion of the conductive material in the positive electrode active material layer can be about 3 to 25% by mass, preferably about 3 to 15% by mass in terms of solid content.

[Positive electrode active material layer forming step: S30]
In step S30, the positive electrode paste prepared above is supplied onto the positive electrode current collector to form a positive electrode active material layer.
As the positive electrode current collector, a metal having good conductivity, an alloy thereof, and the like similar to the current collector used for the positive electrode of the conventional lithium secondary battery can be used. For example, a metal mainly composed of copper, aluminum, nickel, titanium, iron or the like or an alloy thereof, and more preferably aluminum or an aluminum alloy. Various shapes can be considered for the shape of the positive electrode current collector in accordance with a desired purpose. For example, it may be a rod shape, a plate shape, a sheet shape, a foil shape, a mesh shape, or the like. For example, an aluminum sheet having a thickness of about 10 μm to 30 μm can be suitably used.

About application | coating of the positive electrode paste to the surface of a positive electrode electrical power collector, it can carry out using well-known various coating devices. For example, the paste can be applied to one side or both sides of the current collector using a coater. The coater only needs to be able to apply the paste to the current collector. For example, a slit coater, die coater, gravure coater, roll coater, doctor blade coater, comma coater, etc. Can do. The application of the positive electrode paste may be performed on both surfaces of the positive electrode current collector, or may be performed on either one surface. The coating amount of the positive electrode paste is not particularly limited, and can be arbitrarily set according to target electrode characteristics and the like. In general, if the coating amount is too small, it is difficult to obtain the effect of reducing or interrupting current during overcharge, and if the coating amount is too large, the sheet resistance of the positive electrode tends to increase. Therefore, for example, it can be set appropriately within a range of about 3 to 50 mg / cm ² .

  Next, the positive electrode paste applied to the positive electrode current collector is dried to form a positive electrode active material layer on the positive electrode current collector. The drying is not particularly limited as long as it can remove excess components such as a solvent, and an appropriate means can be adopted as necessary. Typically, for example, an appropriate drying device such as a hot air device, various infrared devices, an electromagnetic induction device, or a microwave device, or drying promoting means such as a blower can be used. After drying, the whole can be pressed as necessary or cut into a desired size to obtain a positive electrode having a desired thickness, porosity, and dimensions. As a pressing (compression) method, for example, a conventionally known compression method such as a roll pressing method or a flat plate pressing method can be employed. In adjusting the thickness of the positive electrode active material layer, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted and compressed several times until the desired thickness is obtained. Thereby, the positive electrode disclosed here can be manufactured.

  Hereinafter, a lithium secondary battery as a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein will be described with reference to the drawings as appropriate. In this embodiment, a square-shaped lithium secondary battery is described, but the present invention is not intended to be limited to this embodiment. Such a lithium secondary battery is not particularly limited except that the characteristic positive electrode as described above is used. In addition, matters other than the particular mention of the configuration of the lithium secondary battery can be grasped as design matters of those skilled in the art based on the prior art in this field. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

FIG. 1 shows an external appearance of the lithium secondary battery 10, and FIG. 2 is a cross-sectional view taken along the line II-II of FIG. The lithium secondary battery 10 includes a wound electrode body 20 including a positive electrode 30, a negative electrode 50, and a separator 70, and a nonaqueous electrolyte containing a gas generation additive (not shown) accommodated in a battery case 80. . At least a part of the nonaqueous electrolyte is impregnated in the electrode body 20.
The positive electrode 30 is configured by the positive electrode disclosed herein. The positive electrode 30 is provided with a positive electrode active material layer 34 containing a positive electrode active material. This positive electrode active material is characterized by having a hole transport material on at least a part of its surface.

  The negative electrode 50 may be the same negative electrode as that used in a conventionally known lithium secondary battery or the like. Specifically, the negative electrode 50 includes a negative electrode active material layer 54 including a negative electrode active material, a conductive material as necessary, and a binder. The negative electrode active material is capable of reversibly occluding and releasing (typically intercalating and decalating) chemical species that serve as charge carriers (for example, lithium ions in a lithium secondary battery). The conductive material is added as necessary for the purpose of ensuring conductivity between the negative electrode active materials and between the negative electrode active material layer 54 and the negative electrode current collector. The binder plays a role of binding the negative electrode active material and the conductive material, and also has a role of binding the negative electrode active material layer 54 and the negative electrode current collector 52.

  As the negative electrode current collector 52, a conductive member made of a highly conductive metal is preferably used. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector 52 may vary depending on the shape of the lithium secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. In the present embodiment, a sheet-like copper negative electrode current collector 52 is used. For example, a copper sheet having a thickness of about 5 μm to 30 μm can be suitably used.

  As the negative electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. For example, a carbon particle is mentioned as a suitable negative electrode active material. Carbon particles are particulate carbon materials that at least partially contain a graphite structure (layered structure), which are so-called graphitic (graphite), non-graphitizable carbonaceous (hard carbon), graphitizable Any carbon material such as a carbonaceous material (soft carbon) and a carbon material having a structure in which these are coated with amorphous carbon or the like may be suitably used. In addition to the carbon material, for example, a metal compound containing Si, Ge, Sn, Pb, Al, Ga, In, As, Sb, Bi, or the like as a constituent metal element, preferably a metal oxide can be used. . For example, specifically, LTO (lithium titanate) or the like. For the negative electrode active material having poor electron conductivity, for example, a carbon coating is provided to cover at least a part of the surface of the metal compound, or the negative electrode active material layer 54 is made to contain a conductive material. You may make it comprise. When the carbon coating is provided, the negative electrode active material layer 54 may not contain a conductive material, or the content of the conductive material may be reduced as compared with the conventional case. The additional aspect of such a negative electrode active material and forms, such as a particle size, can be suitably selected according to a desired characteristic.

  The conductive material, binder, and solvent used for forming the negative electrode active material layer 54 can be appropriately selected from the same materials used for forming the positive electrode active material layer 34. In forming the negative electrode active material layer 54, the binder and the solvent can be either water-based or solvent-based. In consideration of environmental load, it is preferable to use an aqueous (water-soluble or water-dispersible) binder and an aqueous solvent. Although it does not specifically limit, It is preferable that the ratio of the negative electrode active material to the negative electrode active material layer 54 is about 50 mass% or more, for example, about 85-99 mass%, Furthermore, it is 90-97 mass%. It is more preferable. Moreover, the ratio of the binder which occupies for a negative electrode active material layer can be 1-15 mass%, for example, Usually, it is preferable to set it as about 3-10 mass%.

  The above materials are mixed, a paste-like composition for forming a negative electrode active material layer (hereinafter simply referred to as a negative electrode paste) is applied to the negative electrode current collector 52, the solvent is evaporated and dried, and then compressed ( The negative electrode 50 can be obtained by performing pressing and cutting. In addition, methods, such as application | coating, drying, and compression, can be implemented using a conventionally well-known method similarly to the manufacturing method of the above-mentioned positive electrode 30.

  As the separator 70, a conventional separator can be used. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. As a constituent material of such a porous sheet, polyolefin resins such as polyethylene (PE), polypropylene (PP), and polystyrene are preferable. In particular, porous polyolefin such as PE sheet, PP sheet, two-layer structure sheet in which PE layer and PP layer are laminated, and three-layer structure sheet in which one PE layer is sandwiched between two PP layers A sheet can be suitably used. Note that when a solid electrolyte or a gel electrolyte is used as the electrolyte, the separator 70 may be unnecessary because the electrolyte itself can function as a separator.

  The positive electrode 30, the negative electrode 50 and the separator 70 are all formed in a long sheet shape, and are laminated and wound so that two separators 70 are interposed between the positive electrode 30 and the negative electrode 50. A body 20 is formed. In the positive electrode 30, an uncoated portion 33 where the current collector 32 is exposed is provided on one edge along the longitudinal direction of the positive electrode current collector 32 without providing the positive electrode active material layer 34. The uncoated portion 33 is electrically connected to the positive terminal 39 of the lid 82 via the positive lead terminal 36. Similarly, in the negative electrode 50, an uncoated portion 53 where the current collector 52 is exposed is provided on one edge along the longitudinal direction of the negative electrode current collector 52 without providing the negative electrode active material layer 54. . The uncoated portion 53 is electrically connected to the negative electrode terminal 59 of the lid 82 via the negative electrode lead terminal 56.

The non-aqueous electrolyte includes a lithium salt as a supporting salt in an organic solvent (non-aqueous solvent). A nonaqueous electrolyte that is liquid at room temperature (that is, an electrolytic solution) can be preferably used. As the lithium salt, for example, a known lithium salt conventionally used as a supporting salt for a non-aqueous electrolyte of a lithium secondary battery can be appropriately selected and used. Examples of such lithium salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like. These supporting salts can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . The non-aqueous electrolyte is preferably prepared, for example, so that the concentration of the supporting salt is within a range of 0.7 to 1.6 mol / L. As the non-aqueous solvent, an organic solvent used for a general lithium secondary battery can be appropriately selected and used. Particularly preferred non-aqueous solvents include carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC). These organic solvents can be used alone or in combination of two or more.

  Such a non-aqueous electrolyte contains a gas generating additive. As a gas generating additive, the oxidation potential is equal to or higher than the operating voltage of the lithium secondary battery (for example, 4.2 V or higher in the case of a lithium secondary battery that is fully charged at 4.2 V) and is oxidized. Any compound that generates a large amount of gas can be used without particular limitation. If the oxidation potential is close to the operating voltage of the battery, there is a risk of gradually decomposing due to a local voltage increase or the like even at the normal operating voltage. On the other hand, when the decomposition voltage exceeds 4.9 V, the oxidative decomposition of the additive There is a risk that thermal runaway may occur due to the reaction of the main component of the non-aqueous electrolyte and the electrode material before the gas generation due to. Accordingly, a lithium secondary battery that is fully charged at 4.2 V preferably has an oxidation reaction potential in the range of 4.4 V or more and 4.9 V or less. More preferably, the gas generating additive is an aromatic hydrocarbon compound. Examples of such compounds include biphenyl compounds, cycloalkylbenzene compounds, alkylbenzene compounds, organic phosphorus compounds, fluorine atom-substituted aromatic compounds, carbonate compounds, cyclic carbamate compounds, and alicyclic hydrocarbons. More specifically, biphenyl (BP), alkylbiphenyl, terphenyl, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, cyclohexylbenzene (CHB), trans-butylcyclohexyl Benzene, cyclopentylbenzene, t-butylbenzene, t-aminobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, tris- (t-butylphenyl) phosphate, phenyl fluoride, 4-fluorophenyl acetate, diphenyl carbonate, Examples thereof include methyl phenyl carbonate, bicterary butyl phenyl carbonate, diphenyl ether, dibenzofuran and the like. In particular, cyclohexylbenzene (CHB), cyclohexylbenzene derivatives and biphenyl (BP) are exemplified. The usage-amount of the gas generation additive with respect to 100 mass% of nonaqueous electrolytes to be used can be about 0.01-10 mass%, for example, Preferably it is about 0.1-5 mass%.

  The battery case 80 includes a flat cuboid case body 84 having an open upper end, and a lid body 82 that closes the opening. As a material constituting the battery case 80, a metal material such as aluminum or steel is preferably used. Although aluminum is used in the present embodiment, a battery case 80 formed by molding a resin material such as polyphenylene sulfide (PPS) or polyimide resin may be used. On the upper surface of the battery case 80, that is, the lid 82, a positive terminal 39 that is electrically connected to the positive electrode 30 of the wound electrode body 20 and a negative terminal 59 that is electrically connected to the negative electrode 50 of the electrode body 20 are provided. Is provided. Between these electrode terminals 39 and 59, a liquid injection port 86 for injecting an electrolyte and a safety valve 88 for releasing the internal pressure of the battery case are typically provided.

  In addition, a current interruption mechanism 60 that operates when the internal pressure of the battery case 80 increases is provided inside the battery case 80. When the internal pressure of the battery case 80 rises due to gas generation due to the gas generating additive, the current interruption mechanism 60 is charged by cutting a conductive path from at least one of the electrode terminals 39 and 59 to the electrode body 20. It is comprised so that an electric current can be interrupted | blocked. In this embodiment, the current interruption mechanism 60 is provided between the positive electrode terminal 39 fixed to the lid body 82 and the electrode body 20, and reaches the electrode body 20 from the positive electrode terminal 39 when the internal pressure of the battery case 80 rises. The conductive path is configured to be cut.

  The current interrupt mechanism 60 includes a conducting member composed of a first member 62 and a second member 64. When the internal pressure of the battery case 80 increases, at least one of the first member 62 and the second member 64 (here, the first member 62) is deformed and separated from the other, so that the conductive path is cut off. It is configured. In this embodiment, the first member 62 is a deformed metal plate 62, and the second member 64 is a connection metal plate 64 joined to the deformed metal plate 62 at a joint point 66. The deformed metal plate (first member) 62 has an arch shape with a central portion curved downward, and a peripheral portion thereof is connected to the lower surface of the positive electrode terminal 60 via a current collecting lead terminal 65. Further, the tip of the curved portion 63 of the deformed metal plate 62 is joined to the upper surface of the connection metal plate 64. A positive electrode lead terminal 36 is joined to the lower surface (back surface) of the connection metal plate 64, and the positive electrode lead terminal 36 is connected to the positive electrode 30 (positive electrode current collector 32) of the electrode body 20. In this way, a conductive path from the positive terminal 39 to the electrode body 20 is formed.

  The current interrupt mechanism 60 includes an insulating case 61 formed of plastic or the like. The insulating case 61 is provided so as to surround the deformed metal plate 62 and hermetically seals the upper surface of the deformed metal plate 62. The internal pressure of the battery case 80 does not act on the upper surface of the hermetically sealed curved portion 63. The insulating case 61 has an opening into which the curved portion 63 of the deformed metal plate 62 is fitted, and the lower surface of the curved portion 63 is exposed from the opening to the inside of the battery case 80. The internal pressure of the battery case 80 acts on the lower surface of the curved portion 63 exposed inside the battery case 80.

  In the current interrupt mechanism 60 having such a configuration, when the internal pressure of the battery case 80 increases, the internal pressure acts on the lower surface of the curved portion 63 of the deformed metal plate 62, and the curved portion 63 curved downward is pushed upward. The upward pushing force of the curved portion 63 increases as the internal pressure of the battery case 80 increases. When the internal pressure of the battery case 80 exceeds the set pressure, the curved portion 63 is turned upside down and deformed so as to curve upward. Due to the deformation of the curved portion 63, the joint point 66 between the deformed metal plate 62 and the connection metal plate 64 is cut. As a result, the conductive path from the positive terminal 39 to the electrode body 20 is cut, and the charging current is cut off. In this embodiment, the conductive members 62 and 64 that are deformed when the internal pressure is increased are illustrated as being divided into the first member 62 and the second member 64, but the present invention is not limited to this. For example, the conducting member may be a single member. Further, the current interrupt mechanism 60 is not limited to the positive terminal 39 side, and may be provided on the negative terminal 59 side. Moreover, the electric current interruption mechanism 60 is not limited to the mechanical cutting | disconnection accompanied with a deformation | transformation of the deformation | transformation metal plate 62 mentioned above. For example, an external circuit that detects the internal pressure of the battery case 80 with a sensor and interrupts the charging current when the internal pressure detected by the sensor exceeds a set pressure may be provided as the current interrupt mechanism.

  In the positive electrode 30 according to this embodiment, the hole transport material is disposed on at least a part of the surface of the positive electrode active material as described above. For example, when the battery 10 is overcharged, The reactivity is enhanced, and the oxidative decomposition of the gas generating additive can proceed rapidly. Along with this, a large amount of gas is rapidly generated in the negative electrode 50, and the internal pressure of the battery case 80 can rapidly rise to a pressure exceeding the set pressure. Therefore, in the lithium secondary battery 10, when the battery is overcharged, the current interruption mechanism 60 operates early to interrupt the charging current, and the electrode reaction can be stopped in a safer state.

Such a lithium secondary battery 10 can be used as a secondary battery for various applications. For example, as shown in FIG. 4, the lithium secondary battery 10 is used for driving a vehicle 1 such as an automobile that requires particularly high safety and reliability. It can be suitably used as a power source (a power source for a vehicle driving motor). The type of the vehicle 1 on which the lithium secondary battery 10 is mounted is not particularly limited, but typically may be a hybrid vehicle, an electric vehicle, a fuel cell vehicle, or the like. The lithium secondary battery 10 may be used alone or in the form of a battery pack 100 that is connected in series and / or in parallel.
In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte secondary battery further includes a current interrupt mechanism (CID) capable of interrupting a conductive path between the positive electrode and the negative electrode according to an internal pressure in the battery, The water electrolyte includes a gas generating additive having a function of generating gas by being oxidatively decomposed at the positive electrode, and the internal pressure in the battery is increased by the gas generated by the gas generating additive, so that the current interruption mechanism Can cut off the conductive path. According to such a configuration, for example, when the nonaqueous electrolyte secondary battery is overcharged, the electron donating property to the gas generating additive is enhanced at the interface between the positive electrode active material and the gas generating additive. It is possible to oxidatively decompose the gas generating additive more rapidly. This makes it possible to generate a sufficient amount of gas to increase the internal pressure of the battery. As a result, the pressure in the battery can be quickly increased at the time of overcharge, the CID can be operated at an earlier stage, and a safer and more reliable nonaqueous electrolyte secondary battery can be realized. It is possible.

  Therefore, for example, by applying such a configuration to a lithium secondary battery or the like having characteristics such as high energy density, the secondary battery can further have safety and reliability in addition to the inherent characteristics. Such a nonaqueous electrolyte secondary battery having safety can be suitably used as a power source for a vehicle driving motor (electric motor) mounted on a vehicle such as an automobile. Therefore, the present invention can also provide a vehicle provided with the nonaqueous electrolyte secondary battery as a driving power source. The type of such a vehicle is not particularly limited, but may typically be a hybrid vehicle, an electric vehicle, a fuel cell vehicle, or the like. Here, the non-aqueous electrolyte secondary battery may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel.

The following examples further illustrate the present invention. However, it goes without saying that the present invention is not limited to these examples.
[Preparation of positive electrode active material 1]
(A) TPD and (b) PCVz were used as the hole transport material, and this was mixed and dissolved at a ratio of 5 g of the hole transport material to 100 g of toluene as a solvent to obtain a hole transport material solution. The positive electrode active material comprising a lithium transition metal composite oxide having a composition represented by the general formula LiNi _1/3 Co _1/3 Mn _1/3 O ₂ in the form of fine droplets by spray drying method. After spraying on the surface of the film, it was dried by a N ₂ gas stream at 150 ° C. to obtain a particulate positive electrode active material provided with a hole transport material. In this positive electrode active material particle, the ratio of the lithium transition metal composite oxide and the hole transport material was a mass ratio, and the ratio shown in Table 1 shown below.

[Preparation of positive electrode active material 2]
As the hole transport material, (a) TPD having an average particle diameter of 0.2 μm and (b) PCVz having an average particle diameter of 0.5 μm are used, which are expressed by the general formula LiNi _1/3 Co _1/3 Mn _1/3 O. _By mixing with a positive electrode active material comprising a lithium transition metal composite oxide having a composition represented by ₂ , a particulate positive electrode active material provided with a hole transport material on the surface of the lithium transition metal composite oxide was prepared. In this positive electrode active material particle, the ratio of the lithium transition metal composite oxide and the hole transport material was a mass ratio, and the ratio shown in Table 1 shown below.

<Sample 1>
That is, the positive electrode active material of Sample 1 does not include a hole transport material, and is composed only of a normal lithium transition metal composite oxide.
<Sample 2>
The positive electrode active material of Sample 2 includes (a) TPD at a ratio of 0.1% by mass as a hole transport material, and is disposed on the surface of the lithium transition metal composite oxide by spray drying.
<Sample 3>
The positive electrode active material of Sample 3 includes (a) TPD as a hole transport material, and is formed on the surface of the lithium transition metal composite oxide so that the proportion of the total amount of the positive electrode active material layer is 0.5 mass% by spray drying. It is arranged.
<Sample 4>
The positive electrode active material of Sample 4 includes (a) TPD as a hole transport material, and the ratio of the positive electrode active material layer to the whole positive electrode active material layer is obtained by mixing (powder mixing) a granular positive electrode active material and a powdery hole transport material. It is arranged on the surface of the lithium transition metal composite oxide so as to be 0.5% by mass.

<Sample 5>
The positive electrode active material of Sample 5 includes (b) PCVz as a hole transport material, and is formed on the surface of the lithium transition metal composite oxide so that the ratio to the whole positive electrode active material layer is 0.5% by mass by a spray drying method. It is arranged.
<Sample 6>
The positive electrode active material of Sample 6 includes (a) TPD as a hole transport material, and is disposed on the surface of the lithium transition metal composite oxide so that the ratio to the whole positive electrode active material layer is 1% by mass by spray drying. It is what.
<Sample 7>
The positive electrode active material of Sample 7 includes (a) TPD as a hole transport material, and is disposed on the surface of the lithium transition metal composite oxide so that the proportion of the total amount of the positive electrode active material layer is 2% by mass by spray drying. <Sample 8>
The positive electrode active material of Sample 8 is provided with (b) PCVz as a hole transport material, and the ratio of the positive electrode active material layer and the powdery hole transport material is mixed (powder mixed), so that the ratio to the whole positive electrode active material layer is increased. It is arranged on the surface of the lithium transition metal composite oxide so as to be 2% by mass.

[Positive electrode]
The positive electrode active materials of Samples 1 to 8 prepared as described above, acetylene black as a conductive material, CMC as a thickener, and PTFE as a binder were blended in the proportions shown in Table 1, and ion exchange as a solvent. By adding water and mixing, a paste-like composition for forming a positive electrode active material layer (hereinafter also simply referred to as a positive electrode paste) was obtained. In addition, all the positive electrode pastes are blended so that the total amount of the hole transport material and the conductive material is 6% by mass in terms of solid content. This positive electrode paste was applied to both sides of a long aluminum foil having a thickness of 15 μm so that the total weight per unit area was 30 mg / cm ² and dried at a temperature of 120 ° C. The positive electrode sheet was produced by pressing so that the porosity of the layer (ratio of the pore volume in the positive electrode active material layer) was 30%.

[Negative electrode]
Graphite as a negative electrode active material layer, SBR as a binder, and CMC as a thickener are blended at a ratio of 98: 1: 1 when the negative electrode active material: binder: thickener is used. Then, ion-exchanged water was added and mixed to obtain a paste-like composition for forming a negative electrode active material layer (hereinafter also simply referred to as negative electrode paste). This negative electrode paste is applied to both sides of a long copper foil having a thickness of 10 μm so that the opposing capacity ratio to the positive electrode is 1.4, dried at a temperature of 120 ° C., and then pressed. A positive electrode sheet was prepared.

[Construction of evaluation cell]
The positive electrode and the negative electrode were laminated together with two long separators, and the laminated sheet was wound in the longitudinal direction to produce a wound electrode body. As the separator, a microporous sheet having a three-layer structure made of PP / PE / PP was used. After this electrode body was accommodated in the exterior case, a nonaqueous electrolyte was injected to construct a 18650 type (18 mm diameter, 65 mm height) lithium secondary battery. As a non-aqueous electrolyte, 1.0M LiPF ₆ as a lithium source, 1% by mass of CHB as a gas generating additive, and 1% by mass in a solvent in which EC and DEC were mixed at a volume ratio of 3: 7. Of BP was used.

[conditioning]
The evaluation cell constructed as described above was conditioned according to the following procedures 1 and 2.
Procedure 1: After charging at a constant current of up to 4.1V at a charge rate of 1C, pause for 5 minutes.
Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

[SOC adjustment]
The SOC (state of charge) adjustment was performed according to the following procedure. In addition, in order to make the influence by temperature constant, SOC adjustment was performed in a temperature environment of 25 degreeC.
First, a constant current discharge is performed at 1 C until the evaluation cell reaches 3.0 V, and then a constant current charge is performed at a charge rate of 3 V to 1 C to obtain a desired charging state (for example, a charging state (SOC20 %)) To adjust the voltage. Thereafter, constant voltage charging is performed at the voltage for 2.5 hours. Thereby, the evaluation cell is adjusted to a predetermined state of charge. Although the above describes the case where the SOC is adjusted to 20%, the state of charge can be adjusted to an arbitrary state of charge by changing the state of charge to a desired SOC value. For example, when adjusting to SOC 100%, in the procedure 1, the evaluation cell may be set to a charged state (SOC 100%) of 100% of the rated capacity.

[Measurement of internal resistance]
According to the above procedure, each evaluation cell was adjusted to 20% SOC. Next, discharging was performed at 25 ° C. and 10 C for 10 seconds, and a value obtained by dividing the voltage drop ΔV after 10 seconds by the current value was calculated as battery resistance. The measurement results of the battery resistance (mΩ) are shown in Table 1 and FIG.

[Measurement of gas generation amount]
Moreover, according to said procedure, each cell for evaluation was adjusted to SOC100%. Next, overcharge was performed at 25 ° C. until the SOC reached 145%, and the amount of gas generated during this period was measured, and the value divided by the 1C capacity was calculated as the amount of gas generated during overcharge. . The amount of overcharge gas generation (ml / Ah) is shown in Table 1 and FIG. The amount of gas generated was determined by measuring by a liquid replacement method. The liquid replacement method is a method for determining the volume of a measurement object by submerging an evaluation cell as a measurement object in a liquid such as a fluorine-based inert liquid and evaluating the volume change before and after gas generation. It is.

[Evaluation]
As is apparent from Table 1 and FIG. 5, the amount of gas generated during overcharge can be significantly increased by disposing a hole transport material on the surface of a lithium transition metal oxide, which is a conventional positive electrode active material. confirmed. From Table 1 and FIG. 6, it was found that the hole transport material can achieve a sufficient effect by using a very small amount, but if it is too much, the battery resistance is increased. From FIG. 6, it can be seen that it is preferable to dispose a hole transporting material in a proportion of about 0.1 to 1.0% by mass with respect to the lithium transition metal oxide.

  Further, in the hole transport material, there is no significant difference in gas generation amount between (a) TPD and (b) PCVz. On the other hand, as for the arrangement method, it was found that a method that can take a wider adhesion area with the surface of the positive electrode active material, such as a spray dry method, is more effective, although an effect can be obtained even by dry mixing. .

  Moreover, the same effect can be obtained even when an organic p-type semiconductor material such as polypyrrole or polyaniline or a hole transport material is used instead of the above (a) TPD and (b) PCVz as the hole transport material. Was confirmed.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  According to the technology disclosed herein, the electron conductivity of the positive electrode active material layer in an overcharged state is improved, and the oxidative decomposition reactivity between the positive electrode active material and the gas generating additive contained in the electrolyte is efficiently increased. The positive electrode obtained in this way and a manufacturing method thereof can be provided. Moreover, a nonaqueous electrolyte secondary battery provided with this positive electrode is also provided. According to the non-aqueous electrolyte secondary battery including the CID and the gas generating additive, the oxidative decomposition reactivity of the gas generating additive is increased even when the positive electrode active material having low conductivity is used. The amount of gas that can be operated quickly can be generated. Further, it is not necessary to change the design of the battery, and it can be carried out without impairing characteristics such as battery resistance.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Lithium secondary battery 20 Winding electrode body 30 Positive electrode 32 Positive electrode current collector 33 Uncoated part 34 Positive electrode active material layer 36 Positive electrode lead terminal 39 Positive electrode terminal 50 Negative electrode sheet (negative electrode)
52 Negative electrode current collector 53 Uncoated portion 54 Negative electrode active material layer 56 Negative electrode lead terminal 59 Negative electrode terminal 60 Current interruption mechanism 61 Insulating case 62 Deformed metal plate (first member)
63 Curved portion 64 Connection metal plate (second member)
65 Current collecting lead terminal 66 Junction point 70 Separator 80 Battery case 82 Lid body 84 Case body 86 Injection port 88 Safety valve 100 Battery assembly

Claims (10)

A positive electrode for a non-aqueous electrolyte secondary battery comprising a current interrupting mechanism capable of interrupting a conductive path according to an internal pressure in the battery and a gas generating additive having a function of generating gas by being oxidatively decomposed,
E Bei active material layer containing a cathode active material and the electrically conductive material and a binder,
The positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt and manganese,
A positive electrode in which a hole transport material is disposed on at least a part of the surface of the positive electrode active material.   The positive electrode according to claim 1, wherein at least a part of the surface of the positive electrode active material is coated with the hole transport material.   The positive electrode according to claim 1 or 2, wherein a ratio of the hole transport material to the positive electrode active material layer is 0.01% by mass to 1.0% by mass in terms of a solid mass ratio.   The hole transport material is N, N′-bis (3-methylphenyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD), polyvinylcarbazole (PVCz), The positive electrode according to any one of claims 1 to 3, wherein the positive electrode is one or more selected from the group consisting of polyaniline and polypyrrole. A secondary battery comprising a positive electrode, a negative electrode, a current interruption mechanism capable of interrupting a conductive path between the positive electrode and the negative electrode in accordance with an internal pressure in the battery, and a non-aqueous electrolyte,
The non-aqueous electrolyte includes a gas generating additive having a function of generating gas by being oxidatively decomposed in the positive electrode,
The internal pressure in the battery is increased by the gas generated by the gas generating additive, and the current interrupt mechanism can interrupt the conductive path,
A nonaqueous electrolyte secondary battery comprising the positive electrode according to any one of claims 1 to 4 as the positive electrode. Used in a non-aqueous electrolyte secondary battery comprising a current interrupting mechanism capable of interrupting a conductive path according to the internal pressure in the battery and a gas generating additive having a function of generating a gas by oxidative decomposition. body a the nonaqueous positive electrode manufacturing method for the electrolyte secondary battery including a positive electrode active material layer containing a positive electrode active material,
Using a lithium transition metal composite oxide containing nickel, cobalt and manganese as the positive electrode active material, and disposing a hole transport material on at least a part of the surface of the positive electrode active material;
A step of preparing a composition for forming a positive electrode active material layer by mixing a positive electrode active material layer provided with the hole transport material, a conductive material, and a binder together with a solvent; and
Supplying the positive electrode active material layer forming composition onto the positive electrode current collector to form the positive electrode active material layer;
The manufacturing method of the positive electrode including this. Arrangement of the hole transport material,
In a state where the positive electrode active material is flowed, a solution containing the hole transport material is sprayed.
Drying in a state where microdroplets of the solution are attached to at least a part of the surface of the positive electrode active material;
By covering at least part of the surface of the positive electrode active material with the hole transport material,
The manufacturing method according to claim 6 . The manufacturing method according to claim 6 , wherein the hole transport material is mixed with the positive electrode active material and disposed on at least a part of the surface of the positive electrode active material. The production according to any one of claims 6 to 8 , wherein a composition for forming a positive electrode active material layer is prepared by using an aqueous solvent as the solvent and using a water-soluble or water-dispersible binder as the binder. Method. The ratio of the said positive hole transport material to the said positive electrode active material layer is mix | blended so that it may become 0.01 mass%-1.0 mass% by solid content mass, Any one of Claims 6-9. The manufacturing method as described.

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