JP2014035859A - Positive electrode active material composite material and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material composite material produced by coating the surface of positive electrode active material particles with a conductive material or other target material, in a state having a sufficient fixing force difficult to peel off the coating material.SOLUTION: A positive electrode active material composite material (1) for use in the positive electrode of a nonaqueous electrolyte secondary battery contains core particles (2) composed of a positive electrode active material, a binding agent (4) imparted to the surface of the core particles, a conductive carbon material (3) composed of an amorphous carbon having a structure capable of holding the nonaqueous electrolyte, and distributed on the surface of the core particles, and a conductive coating material (6) mainly composed of graphite and distributed on the core particles so as to coat the binding agent and the conductive carbon material.

Description

  The present invention relates to a positive electrode material for use in a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a positive electrode material mainly composed of positive electrode active material particles whose surface is coated with a carbon material, and a non-aqueous electrolyte secondary battery using the material.

  A non-aqueous electrolyte secondary battery such as a lithium secondary battery uses a non-aqueous electrolyte (for example, a non-aqueous electrolyte) as an electrolyte and typically has a positive electrode combined with the surface of a positive electrode current collector made of aluminum foil or the like. A negative electrode mixture layer (mainly composed of a negative electrode active material) is formed on the surface of a negative electrode current collector composed of a positive electrode on which a material layer (mainly composed of a positive electrode active material and is mainly composed of a positive electrode active material) and copper foil is formed. Therefore, it is also referred to as a “negative electrode active material layer”). These electrodes are housed in a predetermined battery case together with a non-aqueous electrolyte, and the case is sealed.

By the way, as one form of the positive electrode active material used in this type of lithium secondary battery, the surface of particles (hereinafter referred to as “positive electrode active material core particles”) composed of a compound constituting the positive electrode active material is carbon black or the like. And a composite material coated with a conductive carbon material. By covering the surfaces of the positive electrode active material core particles with the conductive carbon material (conductive material), the conductivity of the positive electrode mixture layer can be improved, and the battery performance can be improved.
As a technique related to coating the surface of such positive electrode active material core particles with other substances, for example, Patent Document 1 discloses a positive electrode active material (powder made of lithium cobaltate, lithium manganate, lithium nickelate, etc.). Body) and a carbon material such as carbon black are mixed in a predetermined powder processing apparatus, and a mechanochemical treatment called a mechanofusion treatment is performed, so that the carbon material adheres to the surface of the positive electrode active material. A method for producing a composite particulate material is described. Patent Document 2 describes composite particles in which other inorganic substances are attached to the surface of the positive electrode active material by performing a so-called mechanochemical treatment, and the inorganic substances are integrated with the active material surface by a mechanochemical reaction. Has been.

JP 2003-086174 A JP 2009-217946 A

Covering the surface of the positive electrode active material core particles with a desired substance (typically a conductive material such as carbon black) by mechanochemical treatment (or mechanofusion treatment) as described in the above-mentioned patent document, to some extent Is possible.
However, the fixing force for maintaining the coating material on the surface of the positive electrode active material core particles (that is, the performance that is difficult to peel off) is not yet sufficient, and a desired amount of the target substance is uniformly dispersed on the surface of the positive electrode active material core particles. It was difficult to maintain the state of being covered (fixed) in the state of being applied. For example, when preparing a slurry for forming a positive electrode mixture layer using positive electrode active material particles whose surfaces are coated with a conductive material as a material, the mixed positive electrode active material particles are mixed (kneaded) with a solvent, a binder, a conductive material, or the like. When a part of the conductive material is peeled off by the received torque (shearing force), it becomes difficult to maintain the uniform dispersed state.

  Therefore, the present invention has been created to solve the above-described problems, and the object of the present invention is to have a sufficient fixing force that makes it difficult to peel off the conductive material and other target substances on the surface of the positive electrode active material core particles. Provided with a technology for coating in the state, and in addition, a positive electrode active material composite material in which a target material such as a conductive material is coated on the surface of the positive electrode active material core particles in a state of being highly dispersed throughout, and using the composite material It is to provide a constructed secondary battery.

In order to achieve the above object, the positive electrode active material composite material used for the positive electrode of the non-aqueous electrolyte secondary battery disclosed herein includes a core particle made of a positive electrode active material and a binding applied to the surface of the core particle. And a conductive carbon material dispersed on the surface of the core particle. Here, the conductive carbon material has an amorphous structure having a structure capable of holding a non-aqueous electrolyte (typically a structure having a dibutyl phthalate (DBP) oil absorption amount of 100 mL / 100 g or more according to JIS K6217-4 (2008)). Made of carbon. The structure refers to the degree of development of an aggregate (typically a state in which particles are connected in a bunch of grapes) composed of particles constituting a conductive carbon material.
The positive electrode active material composite material disclosed herein further includes a conductive coating material mainly composed of graphite dispersedly disposed on the core particles so as to cover the binder and the conductive carbon material.
The present invention also provides a non-aqueous electrolyte secondary battery using any of the positive electrode active material composite materials disclosed herein. Typically, a nonaqueous electrolyte secondary battery including a positive electrode in which a positive electrode mixture layer containing a positive electrode active material is formed on the surface of a positive electrode current collector, the positive electrode mixture layer mainly comprising a positive electrode active material The positive electrode active material composite material includes the positive electrode active material composite material having the above structure.

In the positive electrode active material composite material having the above configuration, the conductive carbon material is dispersedly disposed on the surface of the positive electrode active material core particles with a binder interposed therebetween. Thereby, the usage-amount of a conductive carbon material can be reduced compared with the case where a conductive carbon material is unevenly distributed partially on the core particle surface. The reduction in the amount of the conductive carbon material used is that of the amount of the organic solvent in preparing the slurry for forming the positive electrode mixture layer (including the paste or ink composition for forming the positive electrode mixture layer; the same applies hereinafter). As a result, the battery manufacturing cost can be reduced by reducing the amount of heat required for volatilization (removal) of the solvent when the positive electrode mixture layer is produced using the slurry.
In the positive electrode active material composite material having the above-described configuration, the conductive coating material mainly composed of graphite is dispersedly arranged on the positive electrode active material core particles so as to cover the binder and the conductive carbon material. This coats (protects) the conductive carbon material having the above structure, which is easily peeled off by the torque (shearing force) received when preparing the slurry for forming the positive electrode mixture layer, and the conductive carbon material becomes the positive electrode active material core particles during slurry preparation. Can be prevented from being peeled off, and the dispersed arrangement state can be maintained. Therefore, high electron conductivity can be ensured even with a relatively small amount of conductive carbon material. In addition, the presence of a conductive coating material mainly composed of graphite can also contribute to improvement of electron conductivity.
Furthermore, the battery capacity can be increased by increasing the positive electrode active material content in the positive electrode mixture layer while realizing sufficient electronic conductivity along with the reduction of the usage fee of the conductive carbon material. Accordingly, by using the positive electrode active material composite material disclosed herein, it is possible to provide a non-aqueous electrolyte secondary battery such as a high-performance lithium secondary battery having a high battery capacity and excellent high-speed charge / discharge characteristics. it can.

In a preferred embodiment of the positive electrode active material composite material (and a secondary battery using the composite material) disclosed herein, the binder is decomposed to generate gas when a predetermined battery voltage is exceeded. Organic compounds constituting possible gas generants are used.
When a positive electrode active material composite material using such an organic compound as a binder is used as a positive electrode mixture, a current interrupt device (CID) that cuts off current by increasing the gas pressure in the battery is further provided. It can operate suitably.
That is, such a current interruption mechanism is configured to cut off the charging path of the battery and prevent further overcharge when the pressure in the battery case exceeds a predetermined value. When the battery voltage is exceeded, a positive electrode active material (core particle) is typically obtained by using a compound (gas generating agent) that can be decomposed at a lower potential than a nonaqueous electrolyte (nonaqueous solvent) to generate gas (gas generating agent) as the binder. ) Can be contained in the positive electrode mixture layer in a state of being applied to the surface. Here, the “overcharged” state typically means a state where the depth of charge (SOC) exceeds 100%. In the operating voltage range in which the SOC can be reversibly charged / discharged, the state of charge in which the upper limit voltage is obtained (that is, the fully charged state) is 100%, and the state of charge in which the lower limit voltage is obtained is 0%. It shows the state of charge when
As described above, the gas generating agent is contained in the non-aqueous electrolyte (non-aqueous solvent) by arranging the gas generating agent in advance on the surface of the positive electrode active material which is a reaction site where gas generation occurs during overcharge. Compared to the conventional battery, the gas can be generated more efficiently during overcharging. For this reason, a highly accurate current interruption mechanism is realizable. Moreover, it is not necessary to mix a wasteful amount of a gas generating agent in the nonaqueous electrolyte, which contributes to a reduction in the manufacturing cost of the secondary battery.
Preferably, an organic compound having an oxidation potential of 4.6 V or less based on a lithium metal electrode standard (vs. Li / Li ⁺ ) is used as the organic compound. By generating gas at a relatively low potential, a more accurate current interruption mechanism can be constructed.

In another preferable embodiment of the positive electrode active material composite material (and the secondary battery using the composite material) disclosed herein, the content of the binder is 5 with respect to 100 parts by mass of the positive electrode active material. It is -20 mass parts, It is characterized by the above-mentioned.
By including the binder at such a blending ratio, a sufficient binding force (fixing force) between the conductive carbon material and the core particles can be maintained while suppressing an increase in the internal resistance of the battery.

  In another preferred embodiment of the positive electrode active material composite material disclosed herein, the core particle is composed of at least one lithium transition metal composite oxide, and is used as a positive electrode material for a lithium secondary battery. The positive electrode active material composite material disclosed here can be suitably used for the construction of a lithium secondary battery.

In order to achieve the above object, the present invention provides, as another aspect, a method for producing any one of the positive electrode active material composite materials disclosed herein.
That is, the manufacturing method of the positive electrode active material composite material disclosed here is:
(1) Mixing particles made of a predetermined positive electrode active material prepared as a core particle material, a binder, and a conductive carbon material made of amorphous carbon having a structure capable of holding a nonaqueous electrolyte, and the mixture By stirring the mixture while applying mechanical energy so that the temperature is maintained in a temperature range above and below the melting point of the substance constituting the binder, the binder is applied to the surface of the core particles. And preparing a first composite particle in which a conductive carbon material is dispersed and arranged on the surface of the core particle;
(2) The first composite particles and a conductive coating material mainly composed of graphite are mixed, and the mixture is applied while applying mechanical energy to the mixture of the first composite particles and the conductive coating material. And a step of preparing second composite particles in which the conductive coating material is dispersedly arranged on the first composite particles so as to cover the binder and the conductive carbon material by stirring. To do.
By carrying out the (1) first composite particle preparation step and (2) the second composite particle preparation step, a positive electrode active material composite material used for the positive electrode of the non-aqueous electrolyte secondary battery having the above-described configuration is obtained. It can manufacture suitably.

Preferably, (1) the first composite particle preparation step and (2) the second composite particle preparation step each impart mechanical energy so as to cause a mechanochemical reaction in the mixture in each step. However, it is performed continuously.
By preparing the first composite particles in a state where a mechanochemical reaction can occur, and then preparing the second composite particles, the first composite particles having excellent fixing power of the conductive carbon material, the conductive coating material Second composite particles having excellent fixing force can be prepared.

Preferably, as the binder, an organic compound constituting a gas generating agent capable of decomposing and generating gas when a predetermined battery voltage is exceeded is used. As such an organic compound, it is particularly preferable to use an organic compound having an oxidation potential of 4.6 V or less based on a lithium metal electrode standard (vs. Li / Li ⁺ ).
According to the manufacturing method of this aspect, a positive electrode active material composite material suitable for a secondary battery having a current interruption mechanism can be manufactured.

In another preferred embodiment of the method for producing a positive electrode active material composite material disclosed herein, the additive amount of the binder is 5 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. To do.
By including the binder at such a blending ratio, it is possible to produce a positive electrode active material composite material capable of maintaining a sufficient binding force between the conductive carbon material and the core particles while suppressing an increase in the internal resistance of the battery. it can.

Another preferred embodiment of the method for producing a positive electrode active material composite material disclosed herein is a particle comprising a lithium transition metal composite oxide that can be used as a positive electrode active material for a lithium secondary battery as the core particle material. It is characterized by using.
By this, the positive electrode active material composite material which can be utilized suitably for construction of a lithium secondary battery can be manufactured.

It is a perspective view which shows typically the external shape of the secondary battery (lithium secondary battery) which concerns on one Embodiment. It is a figure which shows typically the cross-sectional structure in the II-II line of the secondary battery of FIG. It is a partially broken perspective view which shows typically the structure of the winding electrode body with which the secondary battery of FIG. 1 is equipped. It is a manufacturing flowchart of the positive electrode active material composite material which concerns on one Embodiment. It is a schematic diagram which shows the structure of the 1st composite particle which concerns on one Embodiment. It is a schematic diagram which shows the structure of the 2nd composite particle (positive electrode active material composite material) which concerns on one Embodiment.

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 this specification, the “secondary battery” generally refers to a rechargeable power storage device in general, a so-called storage battery such as a lithium secondary battery (typically a lithium ion battery), a nickel hydrogen battery, a nickel cadmium battery, and the like. It is a term that encompasses power storage elements (physical batteries) such as electric double layer capacitors. In the present specification, the “electrode active material” refers to a material capable of reversibly occluding and releasing (typically inserting and detaching) chemical species serving as a charge carrier in a secondary battery. The “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes. A secondary battery generally called a lithium ion battery (or a lithium ion secondary battery) is a typical example included in the lithium secondary battery in this specification.

  Hereinafter, a preferred embodiment relating to a lithium secondary battery (lithium ion battery) as an example of the secondary battery disclosed herein will be described with reference to the drawings. Although not intended to be particularly limited, in the following, a sealed lithium secondary in a form in which the wound electrode body and the nonaqueous electrolyte (nonaqueous electrolyte) are accommodated in a rectangular (that is, rectangular box shape) case. A battery will be described as an example. The dimensions (length, width, thickness, etc.) in each figure do not reflect actual dimensional relationships. Further, members / parts having the same action are denoted by the same reference numerals, and redundant description is omitted or simplified.

FIG. 1 is a perspective view schematically showing an outer shape of a sealed nonaqueous electrolyte secondary battery 100 according to the present embodiment. FIG. 2 is a diagram schematically showing a cross-sectional structure taken along line II-II of the sealed secondary battery shown in FIG. FIG. 3 is a partially broken perspective view schematically showing the configuration of the wound electrode body 80.
As shown in FIGS. 1 and 2, the secondary battery 100 according to this embodiment includes a wound electrode body 80 and a battery case (outer container) 50. The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface of the battery case 50 (that is, the lid 54), a positive terminal 70 for external connection that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode of the electrode body 80. Is provided. In addition, the lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case 50 to the outside of the case 50, similarly to the battery case of the conventional nonaqueous electrolyte secondary battery.

Inside the battery case 50, a long sheet-like positive electrode (positive electrode sheet) 10 and a long sheet-like negative electrode (negative electrode sheet) 20 are flattened via two long sheet-like separators 40A and 40B. A wound electrode body (winding electrode body) 80 is accommodated together with a non-aqueous electrolyte (not shown). Specifically, as shown in FIG. 3, as a result of the winding electrode body 80 being wound while being slightly shifted in the lateral direction with respect to the winding direction, a part of the ends of the positive electrode sheet 10 and the negative electrode sheet 20 are respectively It protrudes outward from the wound core portion 82. A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are provided on the positive electrode side protruding portion (that is, a non-formed portion of the positive electrode mixture layer 14 described later) 16 and the negative electrode side protruding portion (that is, a portion where the negative electrode mixture layer 24 is not formed) 26. The lead terminals 74 and 76 are electrically connected to the positive terminal 70 and the negative terminal 72 described above, respectively.
In addition, the material itself of each member constituting the wound electrode body 80 may be the same as the electrode body provided in the conventional lithium secondary battery, and there is no particular limitation. For example, the positive electrode current collector 12 of the positive electrode sheet 10 is made of a metal foil such as an aluminum foil. The negative electrode current collector 22 of the negative electrode sheet 20 is made of a metal such as copper foil. Although the thickness of these foil-shaped current collectors is not particularly limited, those having a thickness of about 5 μm to 50 μm (typically 8 μm to 30 μm) can be used in consideration of the capacity density of the battery and the strength of the current collector. As the separators 40A and 40B, the same separators as in the past can be used. For example, a porous sheet (porous film) made of a polyolefin resin can be used.

The positive electrode mixture layer 14 is formed on both surfaces of the positive electrode sheet 10 constituting the core portion 82. Similarly, the negative electrode mixture layer 24 is formed on both surfaces of the negative electrode sheet 20 constituting the core portion 82. Yes. In the present embodiment, the positive electrode active material composite material disclosed in this specification is used as a positive electrode active material, and the positive electrode mixture layer 14 is formed on the positive electrode current collector 12. The formation method itself of the layer 24 may be the same as that of the prior art, and no special treatment is required for carrying out the present invention. Details of the production of the positive electrode active material composite and the method of forming the positive electrode mixture layer will be described later.
In the present embodiment, the negative electrode mixture layer 24 may be manufactured using the same material and manufacturing method as those of conventional lithium secondary batteries, and is not particularly limited. For example, the negative electrode active material may be any material that can occlude and release lithium ions, such as a carbon material such as graphite, an oxide material such as lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), Examples include alloy materials made of alloys such as tin (Sn), aluminum (Al), zinc (Zn), and silicon (Si). A typical example is a powdery carbon material made of graphite or the like. In particular, the graphite particles can be a negative electrode active material more suitable for rapid charge / discharge (for example, high-power discharge) because the particle size is small and the surface area per unit volume is large.
A slurry-like composition for forming a negative electrode mixture layer can be prepared by dispersing and kneading such a powdery active material material together with an appropriate binder in an appropriate dispersion medium. By applying an appropriate amount of this slurry onto the negative electrode current collector 22 and further drying and pressing, the negative electrode mixture layer 24 can be produced. The density of the negative electrode mixture layer 24 is, for example, 1.0 g / cm ³ or more (typically 1.2 g / cm ³ or more, for example, 1.3 g / cm ³ or more), and 1.5 g / cm ³ or less. It can be.

Moreover, the lithium secondary battery according to the present embodiment includes the current interrupt mechanism 30 as described above. That is, as shown in FIG. 2, the battery case 50 is provided with a current interrupt mechanism 30 that operates when the internal pressure of the battery case increases. The current interruption mechanism 30 only needs to be configured to cut a conductive path (for example, a charging path) from at least one electrode terminal to the electrode body 80 when the internal pressure of the battery case 50 increases, and has a specific shape. It is not limited to. For example, in the form shown in FIG. 2, the current interrupt mechanism 30 is provided between the positive electrode terminal 70 fixed to the lid body 54 and the electrode body 80, and when the internal pressure (gas pressure) of the battery case 50 rises, the positive electrode terminal 70. It is comprised so that the electrically conductive path | route from to the electrode body 80 may be cut | disconnected.
Specifically, the current interrupt mechanism 30 can include, for example, a first member 32 and a second member 34. When the internal pressure of the battery case 50 rises, at least one of the first member 32 and the second member 34 is deformed and separated from the other, thereby cutting the conductive path. In this embodiment, the first member 32 is a deformed metal plate, and the second member 34 is a connection metal plate joined to the deformed metal plate 32. The deformed metal plate (first member) 32 has an arch shape in which a central portion is curved downward, and a peripheral portion thereof is connected to the lower surface of the positive electrode terminal 70 via a current collecting lead terminal 35. Further, the tip of the curved portion 33 of the deformed metal plate 32 is joined to the upper surface of the connection metal plate 34. A positive current collector plate 74 is joined to the lower surface (back surface) of the connection metal plate 34, and the positive current collector plate 74 is connected to the positive electrode 10 of the electrode body 80. In this way, a conductive path from the positive electrode terminal 70 to the electrode body 80 is formed.

The current interrupt mechanism 30 includes an insulating case 38 made of plastic or the like. The insulating case 38 is provided so as to surround the deformed metal plate 32 and hermetically seals the upper surface of the deformed metal plate 32. The internal pressure of the battery case 50 does not act on the upper surface of the hermetically sealed curved portion 33. The insulating case 38 has an opening into which the curved portion 33 of the deformed metal plate 32 is fitted, and the lower surface of the curved portion 33 is exposed from the opening to the inside of the battery case 50. The internal pressure of the battery case 50 acts on the lower surface of the curved portion 33 exposed inside the battery case 50. In the current interrupt mechanism 30 having such a configuration, when the internal pressure of the battery case 50 increases, the internal pressure acts on the lower surface of the curved portion 33 of the deformed metal plate 32, and the curved portion 33 curved downward is pushed upward. The upward push of the curved portion 33 increases as the internal pressure of the battery case 50 increases. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is inverted so as to be bent up and down. Due to the deformation of the curved portion 33, the joint point 36 between the deformed metal plate 32 and the connection metal plate 34 is cut. As a result, the conductive path from the positive electrode terminal 70 to the electrode body 80 is cut, and the overcharge current is cut off.
The current interrupt mechanism 30 is not limited to the positive terminal 70 side, and may be provided on the negative terminal 72 side. Further, the current interrupt mechanism 30 is not limited to the mechanical cutting accompanied by the deformation of the deformed metal plate 32 described above. For example, the internal pressure of the battery case 50 is detected by a sensor, and the internal pressure detected by the sensor sets the set pressure. An external circuit that cuts off the charging current when exceeded can be provided as a current cut-off mechanism.

Hereinafter, the positive electrode active material composite material according to the present embodiment and the production thereof will be described in detail.
The positive electrode active material composite material disclosed here is a material contained as a positive electrode active material in the positive electrode mixture layer, and is a positive electrode material mainly composed of a predetermined positive electrode active material. That is, as shown in FIG. 6, the positive electrode active material composite material 1 according to this embodiment includes a core particle 2 made of a positive electrode active material, a binder 4 applied to the surface of the core particle 2, and a non-aqueous solution. A conductive carbon material 3 made of amorphous carbon having a structure capable of holding an electrolyte, the conductive carbon material 3 dispersed on the surface of the core particle 2, and the binder 4 and the conductive carbon material 3 are covered. In this way, the conductive coating material 6 mainly composed of graphite arranged in a dispersed manner on the core particle 2 is formed.

As the positive electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without particular limitation. As a preferred example, an oxide containing lithium and a transition metal element as constituent metal elements such as lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), and lithium manganese oxide (for example, LiMn ₂ O ₄ ). And a phosphate containing lithium and a transition metal element as constituent metal elements such as lithium oxide (lithium transition metal composite oxide), lithium manganese phosphate (LiMnPO ₄ ), and lithium iron phosphate (LiFePO ₄ ).
For example, a lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having a layered structure including lithium element, nickel element, cobalt element, and manganese element as a constituent element is used as a main component. A positive electrode active material (typically, a positive electrode active material substantially made of a lithium nickel cobalt manganese composite oxide) can be preferably used because it has excellent thermal stability and can realize a high energy density. Here, the lithium-nickel-cobalt-manganese composite oxide is an oxide containing lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn) as a constituent metal element, or Li, Ni, Co, Mn. It is meant to include oxides partially substituted with at least one other metal element (transition metal elements other than Li, Ni, Co, and Mn and / or typical metal elements). Such metal elements include, for example, magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo ), Tungsten (W), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga) ), Indium (In), tin (Sn), lanthanum (La), and cerium (Ce). The same applies to lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. The amount of the substitutional constituent element is not particularly limited. For example, it is 0.05% by mass or more (typically 0.1% by mass with respect to the total of 100% by mass of the substitution element, Ni, Co, and Mn. % Or more, for example, 0.2% by mass or more) and 5% by mass or less (typically 3% by mass or less, for example, 2.5% by mass or less).
A granular positive electrode active material composed of such a compound can be used as the core particle 2.
The composite oxides constituting the various positive electrode active materials as described above include several kinds of supply sources (compounds) appropriately selected according to the constituent elements of the composite oxides and their atomic compositions at a predetermined molar ratio. It can be obtained by mixing and baking the mixture at a predetermined temperature by an appropriate means. For example, a positive active material comprising a lithium transition metal composite oxide having a desired composition by mixing an appropriate lithium source compound and one or more transition metal source compounds, firing, pulverizing and granulating Can be obtained.
After firing, the obtained composite oxide (positive electrode active material) is pulverized by an appropriate means, and if necessary, granulated, to prepare positive active material core particles having a desired average particle size Can do. The properties of the core particles are not particularly limited. For example, the average particle size based on the laser diffraction / light scattering method is preferably about 1 μm to 20 μm (for example, 1 μm to 10 μm). The specific surface area of the core particles is 0.1 m ² / g or more (typically 0.5 m ² / g or more, preferably 1 m ² / g or more), and 30 m ² / g or less (typically 20 m ² / g or less, preferably 10 m ² / g or less). When the properties of the positive electrode active material core particles are within the above range, a dense and highly conductive positive electrode mixture layer can be produced. Moreover, since a moderate space | gap can be hold | maintained in this positive electrode compound material layer, a non-aqueous electrolyte can be easily immersed and battery resistance can be reduced. Further, since a wide reaction field with the gas generating agent can be secured, reliability during overcharge can be secured.

The conductive carbon material 3 for constituting the positive electrode active material composite material 1 disclosed here is not particularly limited as long as it is amorphous carbon having a structure capable of holding a nonaqueous electrolyte. Typically, carbon black such as acetylene black, furnace black, ketjen black, channel black, lamp black, and thermal black can be used. Here, the degree of “structure” can be defined by the DBP oil absorption based on JIS K6217-4 (2008). The DBP oil supply amount is suitably 100 mL / 100 g or more, preferably 200 mL / 100 g or more. For example, carbon black such as acetylene black and ketjen black is an amorphous carbon material having a structure that meets such requirements, and can be suitably used as a conductive carbon material for the positive electrode active material composite material disclosed herein. it can.
The average particle diameter (primary particles) based on observation of the conductive carbon material with an electron microscope is preferably 100 nm or less, and particularly preferably 50 nm or less. The specific surface area may be 50 to 1000 m ² / g, or 1000 m ² / g or more, but those having a relatively small specific surface area are preferred. For example, carbon black (acetylene black or the like) having a specific surface area of about 50 to ²⁰⁰ m ² / g can be suitably used.
Moreover, the addition amount of the conductive carbon material is suitably about 2 to 10 parts by mass, preferably about 3 to 6 parts by mass with respect to 100 parts by mass of the positive electrode active material.

The binder 4 for constituting the positive electrode active material composite material 1 disclosed here is an organic compound conventionally contained as a binder (binder) in the positive electrode mixture layer (for example, vinylidene fluoride such as PVDF). In the case of being used for a secondary battery including the current interruption mechanism 30 such as the lithium secondary battery 100 according to the present embodiment, the organic compound that functions as the gas generating agent is bound. It is preferable to use as the material 4.
As the gas generating agent, a compound capable of decomposing and generating gas when a predetermined battery voltage is exceeded (that is, the oxidation potential is equal to or higher than the operating voltage of the nonaqueous electrolyte secondary battery, and the battery is in an overcharged state) If it becomes a compound that decomposes to generate gas when it becomes, it can be used without any particular limitation.
Specific examples include aromatic compounds such as biphenyl compounds, alkylbiphenyl compounds, cycloalkylbenzene compounds, alkylbenzene compounds, organic phosphorus compounds, fluorine atom-substituted aromatic compounds, carbonate compounds, cyclic carbamate compounds, and alicyclic hydrocarbons. . More specific compounds (and the oxidation potential (vs. Li ^/ Li ⁺ ) of the compound with respect to the lithium metal electrode) include biphenyl (4.5 V), cyclohexylbenzene (4.6 V), 1-fluoro- 2-cyclohexylbenzene (4.8V), 1-fluoro-3-cyclohexylbenzene (4.8V), 1-fluoro-4-cyclohexylbenzene (4.8V), 1-bromo-4-cyclohexylbenzene (4.8V) ), Trans-butylcyclohexylbenzene (4.6V), cyclopentylbenzene, tert-butylbenzene (4.9V), tert-pentylbenzene (4.8V), 1-fluoro-4-tert-butylbenzene (4.9V) ), 1-chloro-4-tert-butylbenzene (4.9V), 1-bromo-4-t rt-butylbenzene (4.9V), tert-pentylbenzene (4.8V), 1-fluoro-4-tert-pentylbenzene (4.8V), 1-chloro-4-tert-pentylbenzene (4.8V) ), 1-bromo-4-tert-pentylbenzene (4.8V), tert-aminobenzene, terphenyl, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o -Cyclohexyl fluorobenzene, p-cyclohexyl fluorobenzene, tris- (t-butylphenyl) phosphate (4.8V), phenyl fluoride (4.9V), 4-fluorophenyl acetate (4.7V), diphenyl carbonate (4 .9V), methyl phenyl carbonate (4.8) ), Bicester tertiary butyl phenyl carbonate (4.7V), diphenyl ether, dibenzofuran, and the like. It is preferable to use an organic compound having a boiling point (for example, a boiling point of 160 ° C. or higher, preferably 200 ° C. or higher) exceeding the temperature at which the positive electrode mixture layer 14 formed on the positive electrode current collector 12 is dried.
The gas generating agent is preferably selected according to the design (operating voltage) of the battery. For example, the gas generating agent has an oxidation potential higher by about 0.1 V (or 0.2 V or 0.3 V) than the operating upper limit voltage of the battery. What it has can be selected preferably. Therefore, there is an oxidation potential at a relatively low potential such as cyclohexylbenzene (4.6 V) and biphenyl (4.5 V), and gas is generated at a lower potential (eg, 4.6 V or less) than the nonaqueous electrolyte component, for example. The resulting organic compound is particularly preferred. The oxidation potential can be measured in the same manner as the charge carrier occlusion start potential by, for example, cyclic voltammetry (CV).

  The content of the binder (for example, the gas generating agent) 4 is not particularly limited. However, when the content is too small, the fixing force for fixing the positive electrode active material core particles 2 and the conductive carbon material 3 is not preferable. On the other hand, if the content is too large, the internal resistance of the battery is increased, which is not preferable. Therefore, about 3-30 mass parts is suitable for this content with respect to 100 mass parts of positive electrode active materials, and about 5-20 mass parts is preferable with respect to 100 mass parts of positive electrode active materials. By setting the content within the above range, an increase in internal resistance (typically, an increase in charge transfer resistance) accompanying the addition of a binder (for example, the gas generating agent) can be suppressed to a low level, and high fixation is achieved. Both strength and excellent battery performance can be achieved.

The conductive coating material 6 for constituting the positive electrode active material composite material 1 disclosed here is a conductive coating material 6 mainly composed of graphite (typically made of graphite). It is a carbon material that is clearly different from the material 3. As long as the conductive coating material 6 can function as a coating material for maintaining the conductive carbon material 3 dispersed and disposed on the surface of the positive electrode active material core particles 2, the type of graphite used is not particularly limited. From the viewpoint of being suitable for the application disclosed herein, highly crystalline spherical or scale (flaky) graphite is preferred. For example, scale-like graphite having an average particle diameter based on a light scattering method or microscopic observation of about 1 to 20 μm is preferable, and an interlayer distance (inter-face distance) between carbon hexagonal network layers in X-ray diffraction (XRD). A highly crystalline graphite having a d ₀₀₂ of 0.337 nm or less (particularly preferably 0.336 nm or less) is particularly suitable.
Moreover, the addition amount of the conductive coating material is suitably about 2 to 10 parts by mass, preferably about 3 to 6 parts by mass with respect to 100 parts by mass of the positive electrode active material.

Thus, the positive electrode active material composite material 1 is manufactured using the materials described above. Specifically, as shown in the manufacturing flow of FIG. 4, first, three materials of the positive electrode active material core particle 2, the conductive carbon material 3, and the binder 4 are mixed at an appropriate blending ratio, and the mixture is mixed. On the other hand, while maintaining the temperature of the mixture in a temperature range higher than the melting point of the substance constituting the binder 4 and lower than the boiling point, moderate mechanical energy such as collision (impact), compression, friction, etc. (if necessary, further (1) A first composite particle 5 (see FIG. 5) preparation step is performed by applying thermal energy) and stirring the mixture.
The degree of mechanical energy such as collision (impact), compression, friction, etc. applied at this time is such that the conductive carbon material 3 is dispersed almost uniformly over the surface of the core particle 2 via the binder 4. What is necessary is just to implement | achieve arrangement | positioning and it does not specifically limit. It is preferable to apply mechanical energy to such a degree that a so-called mechanochemical reaction can occur in the stirring mixture.
Here, the mechanochemical reaction is a reaction that utilizes a phenomenon in which a physicochemical property of a substance is changed and a reaction with a surrounding substance is caused by applying mechanical energy to the target substance. For example, applying a large mechanical energy to a solid that may cause collisions (impacts), compression, friction or grinding, or other shearing or shear stresses will change the crystal structure of the solid surface or activate the solid surface. Can change the physicochemical properties and cause a chemical reaction at the interface with the surroundings.
Therefore, by controlling the level of the mechanical energy to be applied to such an extent that such a mechanochemical reaction can occur, the conductive carbon material can be made uniform on the surface of the positive electrode active material core particle 2 through the binder 4 efficiently. Can be fixed in a dispersed state.

In addition, although there is no restriction | limiting in particular as an apparatus which provides the mechanical energy of the grade which can produce a mechanochemical reaction, What is necessary is just an apparatus which can provide mechanical energy, such as friction, compression, a collision, and it does not specifically limit. For example, various commercially available planetary ball mills, kneading / dispersing devices, powder mixing devices, and hybridization systems using a high-speed in-air impact method can be preferably used. However, these are only examples and do not limit the implementation of the present invention.
The planetary ball mill is a kind of ball mill device in a broad sense, and has a structure in which several pots or cylindrical mills revolve around an axis parallel to the rotation axis while rotating. With the complex movement of the mill, the balls in the mill and the mixture of the three materials also exhibit complex movement and can impart moderate mechanical energy to the mixture.
A kneading and dispersing apparatus, for example, Miracle KCK (manufactured by Asada Tekko Co., Ltd.) is an apparatus for kneading by applying a strong shearing force in a solid state. It is a uniaxial continuous type using slices of a fixed disk cavity and a rotating disk cavity, and can impart appropriate mechanical energy such as compression and shearing to the mixture of the above three materials.
Alternatively, as another preferable apparatus, a powder mixing apparatus such as Nobilta (manufactured by Hosokawa Micron) can be used. Such an apparatus is a high-speed rotating mixing apparatus in which a stirring blade (blade) rotates at a high speed in a horizontal cylindrical mixing container (for example, rotates at a high speed of about 40 to 80 m / s), and impacts each particle constituting the mixture. (Collision), compression and shearing force can be applied uniformly.
As another preferable apparatus, a hybridization system using a high-speed air-flow impact method can be used. Such a device can be stirred in a short time while imparting mechanical energy such as compression, friction, shearing force and the like while being dispersed in the device by the action of a rotor, a stator and a circulation circuit that rotate at high speed.

As shown in FIG. 5, the mechanical energy is applied as described above, and the mixture is typically stirred as the mixture is heated by the application of energy (for example, heated to about 50 to 80 ° C.). 1st composite particle 5 can be prepared.
Next, preferably, continuously, a preparation step of the second composite particles (that is, composite particles constituting the positive electrode active material composite material) 1 is performed. That is, as shown in FIG. 4, the conductive coating material is added to the prepared first composite particles, and the mixture is mixed and the mixture is given a predetermined mechanical energy. Stir. At this time, it is preferable to apply a large mechanical energy that may generate a collision force (impact), compression, friction or grinding, or other shearing force or shear stress, as in the case of the first composite particle preparation step. is there.
The time for these preparation steps is not particularly limited. If the treatment time is too long, the conductive carbon material once immobilized on the surface of the core particle 2 may be peeled off by excessive treatment, which is not preferable. On the other hand, if the treatment time is too short, the fixing force between the core particle 2 and the conductive carbon material 3 is insufficient, or the fixing force between the first composite particle 5 and the conductive coating material 6 is insufficient. For example, the first composite particle preparation step is preferably about 1 to 10 minutes, and the second composite particle preparation step is preferably about 1 to 5 minutes.

The positive electrode active material composite material 1 (FIG. 6) thus obtained is used in the same manner as a conventional positive electrode material (positive electrode active material) to form the positive electrode mixture layer 14.
Specifically, the positive electrode mixture layer 14 is obtained by mixing the powdered positive electrode active material composite material 1 obtained as described above in a suitable solvent together with a suitable binder and, if necessary, a conductive material. It can be formed by preparing a slurry composition, applying the slurry for forming the positive electrode mixture layer on the positive electrode current collector 12 in the longitudinal direction of the sheet, drying, and pressing as necessary.
Although not particularly limited, the proportion of the positive electrode active material in the entire positive electrode mixture layer 14 is 50% by mass or more (typically 70% by mass or more and less than 100% by mass, for example, 80% by mass or more and 99% by mass or less). It is preferable that The density of the positive electrode mixture layer 14 is, for example, 2.0 g / cm ³ or more (typically 2.5 g / cm ³ or more) and 4.5 g / cm ³ or less (typically 4.2 g / cm ³ ). ³ or less).

As the binder to be used, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be used without particular limitation. For example, a polymer material that is dispersed or dissolved in an organic solvent can be preferably used. Examples of the polymer material include polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide, and the like.
In addition, when adding a conductive material, various carbon blacks, coke, graphite (natural graphite and modified products thereof, artificial graphite), carbon fiber (PAN-based carbon fiber, pitch-based carbon fiber), nanocarbon, etc. 1 type or 2 types or more selected from these carbon materials are mentioned. By using the positive electrode active material composite material 1 disclosed here, the amount of the conductive material in the free state can be reduced. Alternatively, the use of a conductive material in a free state can be eliminated. By not using or reducing the amount of the conductive material in the free state, the amount of organic solvent used (content) can be reduced, resulting in the formation of a positive electrode mixture layer having a high solid content concentration. A slurry can be prepared, and it becomes easy to form the high-density, high-capacity positive electrode mixture layer 14. The ratio of the conductive material in the entire positive electrode mixture layer 14 is not particularly limited, but may be, for example, 15% by mass or less. Preferably it can be 10 mass% or less.

Examples of the organic solvent used for preparing the slurry include amide, alcohol, ketone, ester, amine, ether, nitrile, cyclic ether, and aromatic hydrocarbon. More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl ethyl ketone, methyl propenoate, cyclohexanone, acetic acid Methyl, ethyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran, dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide, dichloromethane, trichloromethane, dichloroethane, etc. Typically, NMP can be used.
The solid content concentration (NV) of the positive electrode active material layer forming slurry disclosed herein can be about 60% by mass to 80% by mass (for example, 60% by mass to 75% by mass).

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not intended to be limited to those shown in the specific examples.

  First, a total of seven types of positive electrode active material composite materials used as a positive electrode material of a lithium secondary battery (lithium ion battery) were prepared as follows. Subsequently, using each positive electrode active material composite material, a total of seven types of positive electrode mixture layer forming slurries were prepared as follows.

<Sample 1>
As the positive electrode active material core particles, layered lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) powder having an average particle diameter of about 7.4 μm was prepared.
Solid biphenyl (BP) was prepared as a binder.
Acetylene black having a specific surface area of 78 m ² / g was prepared as a conductive carbon material.
In addition, a scaly graphite powder having an average particle diameter of about 6.4 μm was prepared as a conductive coating material.

Thus, 5 g of binder (BP) and 3 g of conductive carbon material (acetylene black) are added to 100 g of the positive electrode active material core particles, and these mixtures are mixed with a commercially available high-speed powder mixer (manufactured by Hosokawa Micron). It was housed in a horizontal cylindrical container with a high-speed rotating stirring blade (blade). Subsequently, the rotational speed of the stirring blade was set to 60 m / s, and stirring and mixing were performed for 3 minutes. The mixture (powder) in the container is heated by friction and other mechanical energy generated during mixing and stirring. In this example, the amount of water circulating in the water jacket provided on the outer wall of the container and the water temperature are adjusted. Thus, the temperature of the mixture (powder) in the container was maintained at 73 ° C. The temperature of the mixture (powder) was measured by a contact thermocouple provided in the container.
Subsequently, 3 g of a conductive coating material (flaky graphite) was added to 100 g of the positive electrode active material core particles in a container, and stirring and mixing were further performed for 1 minute while maintaining the above stirring and temperature conditions. Thus, a positive electrode active material composite material of Sample 1 was obtained.
Next, the positive electrode active material composite material and polyvinylidene fluoride (PVDF) as a binder are mixed so as to have a mass ratio of 97: 3, and NMP is used as a solvent when the total solid content is 100. A positive electrode active material layer forming slurry of Sample 1 was prepared by adding and mixing in an amount corresponding to 30% by mass.

<Sample 2>
Except for changing the addition amount of the binder (BP) to 100 g of the positive electrode active material core particles to 20 g and changing the temperature condition at the time of stirring and mixing to 78 ° C., the same treatment as in the preparation of Sample 1 was performed, A positive electrode active material composite material of Sample 2 was obtained.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 30% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 2 having substantially the same viscosity as the positive electrode active material layer forming slurry of sample 1 was prepared.

<Sample 3>
A positive electrode active material composite material of Sample 3 was obtained in the same manner as in Preparation of Sample 1, except that the amount of binder (BP) added to 100 g of the positive electrode active material core particles was changed to 2 g.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 40% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 3 having substantially the same viscosity as the positive electrode active material layer forming slurry of samples 1 and 2 was prepared.

<Sample 4>
The positive electrode active material composite material of Sample 2 was obtained in the same manner as in Preparation of Sample 1, except that the temperature condition during stirring and mixing was changed to 30 ° C.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 53% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 4 having substantially the same viscosity as the positive electrode active material layer forming slurries of samples 1 to 3 was prepared.

<Sample 5>
The treatment was performed in the same manner as in the preparation of Sample 1 without adding the binder (BP) to obtain a positive electrode active material composite material of Sample 5 that does not contain the binder.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 54% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 5 having substantially the same viscosity as the positive electrode active material layer forming slurry of samples 1 to 4 was prepared.

<Sample 6>
Although the mixing ratio of each material was the same, a positive electrode active material composite material of Sample 6 was obtained, in which the stirring and mixing process itself by the high-speed powder mixing apparatus was not performed.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 52% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 6 having substantially the same viscosity as the positive electrode active material layer forming slurry of samples 1 to 5 was prepared.

<Sample 7>
The positive electrode active material of Sample 7 was treated in the same manner as Sample 6 (that is, the stirring and mixing treatment itself was not performed) except that the amount of conductive carbon material (acetylene black) added to 100 g of the positive electrode active material core particles was changed to 6 g. A composite material was obtained.
Next, the positive electrode active material composite material and PVDF are mixed so as to have a mass ratio of 97: 3, and NMP is added and mixed in an amount corresponding to 71% by mass when the total solid content is 100. Thus, a positive electrode active material layer forming slurry of sample 7 having substantially the same viscosity as the positive electrode active material layer forming slurry of samples 1 to 6 was prepared.
Table 1 below shows the characteristics of the positive electrode active material composite material and slurry of each sample in terms of the production and manufacturing characteristics.

<Construction of lithium secondary battery>
As a lithium secondary battery for evaluation tests, a sealed lithium secondary battery (lithium ion battery) having a structure in which a wound electrode body was housed in a rectangular battery case as shown in FIGS. In the following description, the batteries of Samples 1 to 7 are referred to as they correspond to the types (Samples 1 to 7) of the positive electrode mixture layer forming slurry (that is, the positive electrode active material composite material) used.

<Positive electrode>
An aluminum foil having a width dimension of 116 mm, a sheet length of 4500 mm, and a thickness of 15 μm was prepared as a positive electrode current collector.
Thus, using the slurry of any of Samples 1 to 7 above, leaving the uncoated portion (that is, the portion where the positive electrode active material layer is not formed) along one end of the aluminum foil, the positive electrode active material per unit area Was coated on both sides and dried so that the coating amount (weight per unit area) was 30 mg / cm ² on both sides. After drying, rolling was performed with a rolling press so that the density of the positive electrode mixture layer was approximately 3.0 g / cm ^3, and positive electrode sheets of Samples 1 to 7 corresponding to any one of the above slurries were produced.

<Negative electrode>
Spherical graphite (negative electrode active material), styrene butadiene block copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of 98: 1: 1. A slurry for forming a negative electrode mixture layer was prepared by mixing with ion-exchanged water so that Further, a copper foil having a width direction dimension of 119 mm, a sheet length of 4700 mm, and a thickness of 10 μm was prepared as a negative electrode current collector.
Thus, the slurry has a negative electrode active material coating amount (weight per unit area) on both sides while leaving an uncoated part (that is, a negative electrode mixture layer non-formed part) along one end of the copper foil. Both sides were applied and dried so as to be 15 mg / cm ² . After drying, rolling was performed with a rolling press so that the density of the negative electrode mixture layer was about 1.4 g / cm ³ , thereby preparing a negative electrode sheet.

<Construction of evaluation test battery>
A lithium secondary battery for evaluation test was constructed using any of the positive electrode sheet and the negative electrode sheet.
That is, as shown in FIG. 3, the positive electrode and the negative electrode are arranged with the separator interposed therebetween, so that the non-mixed material layer non-forming portion is located on the opposite side, and the negative electrode mixed material layer is the positive electrode mixed material layer. Winding electrode by laminating so as to cover in the width direction and winding it into an ellipsoidal shape so that both ends in the width direction of the separator do not cover the negative electrode mixture layer and the positive electrode mixture layer, and then letting it into a flat shape The body was made.
Then, the wound electrode body is housed in a prismatic battery case having a current interruption mechanism made of aluminum as described above together with a non-aqueous electrolyte, and sealed to provide a high energy density type evaluation lithium of about 285 kWh / m ^3. Secondary batteries (Samples 1 to 7) were constructed. The non-aqueous electrolyte was prepared by mixing LiPF ₆ as a lithium salt in a mixed solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at 3: 3: 4 (volume ratio). What was added so that it might become 1.1 mol / L was used.
The battery thus obtained was placed in a constant temperature bath at 25 ° C., and constant current and constant voltage charging (CC charging) was performed at 1 C up to 4.1 V, and a voltage value of 4.1 V was maintained for about 1.5 hours. Subsequently, aging was completed by leaving it to stand in a 60 degreeC thermostat for 24 hours.

<Evaluation test 1: Measurement of battery internal resistance>
The battery resistance (internal resistance: IV resistance value) of each battery was measured. Specifically, the SOC (state of charge) is adjusted to 60%, discharged at a rate of 2C at −30 ° C. for 5 seconds, and the internal resistance (IV resistance value (mΩ)) is calculated from the voltage drop at that time. did. The results are shown in the corresponding column of Table 2.

<Evaluation test 2: Overcharge test>
For each battery, overcharging was started from an SOC of 100% at a current density of 1 C at an environmental temperature of 25 ° C. Then, the presence or absence of the action | operation of a current interruption mechanism (CID) was confirmed. In addition, the presence or absence of the operation | movement of CID recognized that the thing which was cooled to room temperature without the temperature rise resulting from an overcharge having the operation of CID. The results are shown in the corresponding column of Table 2.

As is clear from the above results, the batteries of Sample 1 and Sample 2 showed lower values of battery internal resistance than other batteries. In addition, it was confirmed that a lithium secondary battery having a high capacity and a high energy density can be constructed with a small amount of NMP used.
Also, the CID operates well, and the use of the positive electrode active material composite material of the present invention can realize the operation of the CID more efficiently than a conventional type battery in which a gas generating agent is added to the nonaqueous electrolyte. confirmed.

On the other hand, for the battery of sample 3 in which the battery internal resistance is relatively higher than those of samples 1 and 2, the amount of the binder added is small, and therefore the conductive carbon material fixed on the surface of the positive electrode active material core particles is It is thought that it was relatively less. In addition, since the amount of the binder added was small, it was considered that the gas generation amount was insufficient and the CID operation was not achieved. In such a case, it is preferable to supplement the gas generating agent in the positive electrode mixture layer and / or the electrolyte solution in an auxiliary manner. In addition, since the battery of sample 4 had a low stirring temperature, the function of the binder could not be exhibited well, so that the conductive carbon material fixed on the surface of the positive electrode active material core particles was relatively small, It is thought that resistance became high.
For the batteries of Samples 5 to 7, the positive electrode active material composite material (that is, the second composite particles) disclosed herein is formed due to reasons such as the absence of a binder and the absence of mechanical energy. No increase in battery resistance or non-operation of CID was observed.

As is clear from the above examples, by using the positive electrode active material composite material disclosed here as the positive electrode material, high electron transferability can be realized with a small amount of conductive material. Therefore, the battery capacity per volume can be increased by reducing the amount of the conductive material in the positive electrode mixture layer.
In addition, by using a gas generating agent such as BP as a binder, gas can be efficiently generated during overcharging, and low cost and reliability without excessively adding the gas generating agent to the non-aqueous electrolyte. A high-performance non-aqueous electrolyte secondary battery having a high current interruption mechanism can be provided.
Accordingly, the present invention also provides a set comprising a nonaqueous electrolyte secondary battery such as a lithium secondary battery disclosed herein as a single battery, and a plurality of the single batteries connected to each other. A battery can be provided. In addition, a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV) including the assembled battery as a driving power source can be provided.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Positive electrode active material composite material (second composite particle)
2 Core particle 3 Conductive carbon material 4 Binder 5 First composite particle 6 Conductive coating material 10 Positive electrode sheet 12 Positive electrode current collector 14 Positive electrode composite material layer 20 Negative electrode sheet 22 Negative electrode current collector 24 Negative electrode composite material layer 30 Current interruption Mechanism 40A, 40B Separator 50 Battery case 52 Case body 54 Lid 55 Safety valve 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium secondary battery

Claims (8)

A positive electrode active material composite material used for a positive electrode of a nonaqueous electrolyte secondary battery,
Core particles made of a positive electrode active material;
A binder applied to the surface of the core particles;
A conductive carbon material made of amorphous carbon having a structure capable of holding a non-aqueous electrolyte and dispersed on the surface of the core particles; and
A positive electrode active material composite material, comprising: a conductive coating material mainly composed of graphite dispersedly disposed on the core particles so as to cover the binder and the conductive carbon material.   The positive electrode active material composite material according to claim 1, wherein an organic compound constituting a gas generating agent capable of decomposing and generating gas when a predetermined battery voltage is exceeded is used as the binder. The positive electrode active material composite material according to claim 2, wherein an organic compound having an oxidation potential of 4.6 V or less based on a lithium metal electrode standard (vs. Li / Li ⁺ ) is used as the organic compound.   The positive electrode active material composite material according to any one of claims 1 to 3, wherein a content of the binder is 5 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material.   The said core particle is comprised from the at least 1 sort (s) of lithium transition metal complex oxide, and is used as a positive electrode material of a lithium secondary battery, The positive electrode active material composite material as described in any one of Claims 1-4 .   The nonaqueous electrolyte secondary battery using the positive electrode active material composite material as described in any one of Claims 1-5. A method for producing a positive electrode active material composite material used for the positive electrode of the nonaqueous electrolyte secondary battery according to any one of claims 1 to 5,
(1) Mixing particles made of a predetermined positive electrode active material prepared as a core particle material, a binder, and a conductive carbon material made of amorphous carbon having a structure capable of holding a nonaqueous electrolyte, and the mixture By stirring the mixture while applying mechanical energy so that the temperature of the material is maintained in a temperature range not lower than the melting point and lower than the boiling point of the substance constituting the binding material, the surface of the core particles can be bonded. And preparing a first composite particle in which a conductive carbon material is dispersed and arranged on the surface of the core particle;
(2) The first composite particles and a conductive coating material mainly composed of graphite are mixed, and the mixture is applied while applying mechanical energy to the mixture of the first composite particles and the conductive coating material. A step of preparing second composite particles in which the conductive coating material is dispersedly arranged on the first composite particles so as to cover the binder and the conductive carbon material by stirring;
Manufacturing method. The (1) first composite particle preparation step and the (2) second composite particle preparation step each impart mechanical energy so as to cause a mechanochemical reaction in the mixture in each step. The manufacturing method according to claim 7, which is continuously performed.

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