JP6075633B2 - Electroconductive material encapsulating material and method for producing the same - Google Patents

Description

  The present invention relates to an electronically conductive material encapsulating material and a method for producing the same.

  The number of products using secondary batteries continues to increase, and in general, secondary batteries are recognized as essential for portable devices such as mobile phones and laptop computers. Among secondary batteries, lithium ion secondary batteries are widely used because of their small size and large capacity, and are also used in aircraft and automobiles. In recent years, research on lithium ion secondary batteries has been actively conducted for the purpose of providing better lithium ion secondary batteries. Research from the viewpoint of safety has also been conducted, and Patent Literatures 1-3 disclose a technique for improving safety when a lithium ion secondary battery becomes high temperature.

  Patent Document 1 discloses a technique for forming a shell using a PTC (positive temperature coefficient) material whose resistance increases with an increase in temperature on the outer surface of an active material, and the safety of a battery using the technique is disclosed. It is described that the property is high.

  Patent Documents 2 and 3 disclose a technique of adding an electron conductive material or a PTC material to an active material layer, and describe that the safety of a battery employing the technique is high.

  Patent Documents 4 to 8 disclose Curie temperatures of various materials.

Special table 2011-51012 gazette JP-A-10-241665 JP-A-2005-123185 JP 2013-14508 A JP 2008-63188 A JP 2013-35704 A JP 2010-232666 A JP 2001-332125 A

  Since lithium ion secondary batteries are used in aircraft and automobiles, the level of safety required for lithium ion secondary batteries is higher. Therefore, there is a need for a new technology that can be an option for ensuring the safety of lithium ion secondary batteries.

  This invention is made | formed in view of such a situation, and it aims at providing the technique which can improve the safety | security of a lithium ion secondary battery by methods other than the above.

  This inventor earnestly examined about the technique which can ensure the safety | security of a lithium ion secondary battery. Then, the present inventor recalls an electron conductive material-containing active material in which an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. is introduced into the active material. I recalled introducing an electron-conducting material at the same time. Furthermore, it has been found that the actually produced electron conductive material encapsulating material has a high resistance at high temperatures, and the present invention has been completed.

  The electron conductive material encapsulating material of the present invention is characterized in that it contains an electron conductive material having a Curie temperature in the range of 30 to 400 ° C.

  The method for producing an active material in an electron conductive material of the present invention comprises a mixing step of mixing an active material and an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. to obtain a mixture, and the mixture and the carrier gas. Mixing into a fluid, introducing the fluid into plasma, melting step to melt the mixture to form a melt, cooling the melt, the active material and the electron conductive material, And a solid solution forming step of forming the solid solution.

  Since the resistance of the electron conductive material encapsulating material of the present invention increases at a temperature equal to or higher than the Curie temperature, the safety of the lithium ion secondary battery can be improved.

2 is a scanning electron micrograph of a cut surface of an electron conductive material-containing active material of Example 1. FIG. 2 is a scanning electron micrograph of a cut surface of an electron conductive material-containing active material of Example 1. FIG. 6 is a graph showing the resistance (electrical resistivity) in the range of 0 ° C. to 140 ° C. of the electronically conductive material-containing active material-containing film of Application Example 1. FIG. 6 is a graph showing a relative dielectric constant in a range of 0 ° C. to 140 ° C. of the electron conductive material-containing active material-containing film of Application Example 1. FIG. 6 is a graph showing the magnetic flux density in the range of 0 ° C. to 140 ° C. of the electron conductive material-containing active material-containing film of Application Example 1. FIG.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

  The electron conductive material encapsulating material of the present invention is characterized in that it contains an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. That is, the electron-conductive material-containing active material of the present invention includes an electron-conductive material having a Curie temperature in the range of 30 to 400 ° C. inside a conventional active material used for a secondary battery. .

  The active material may be a positive electrode active material or a negative electrode active material.

A well-known thing may be sufficient as a positive electrode active material. For example, in the case of a positive electrode active material for a lithium secondary battery, any material capable of occluding and releasing lithium ions may be used, such as a cobalt composite oxide such as LiCoO ₂ , manganese such as LiMn ₂ O ₄ and Li ₂ MnO _3. composite oxide, nickel composite oxide such as _{LiNiO 2, LiFePO 4, Li 2} FeSO 4, LiFeVO iron composite oxides such as _{4, Li a Ni b Co c} Mn d D e O f (0.2 ≦ a ≦ 1 , B + c + d + e = 1, 0 ≦ e <1, D is at least one element selected from Li, Fe, Cr, Cu, Zn, Zr, Ca, Mg, S, Si, Na, K, Al, 1.7 ≦ f ≦ 2.1), Li ₂ MnO ₂ , Li ₂ MnO ₃ , LiFePO ₄ , Li ₂ FeSO ₄ , LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (formula M in the middle is selected from at least one of Co, Ni, Mn, and Fe).

The positive electrode active material for lithium secondary batteries, from the viewpoint of high _{capacity, Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1, b + c + d + e = 1,0 of the layered rock-salt structure < b <1, 0 <c <1, 0 <d <1, 0 ≦ e <1, D is from Li, Fe, Cr, Cu, Zn, Zr, Ca, Mg, S, Si, Na, K, Al Preferably at least one element selected, 1.7 ≦ f ≦ 2.1), of which 0 <b <70/100, 0 <c <50/100, 10/100 <d <1 And preferably within the range of 1/3 ≦ b ≦ 50/100, 20/100 ≦ c ≦ 1/3, 1/3 ≦ d <1, b = 1/3, c = 1 / 3, d = 1/3, or b = 50/100, c = 20/100, d = 30/100 are particularly preferred. About a, e, and f, if it is a numerical value within the above-mentioned range, there will be no restriction | limiting in particular. For example, a = 1, e = 0, and f = 2 can be exemplified.

  A known negative electrode active material may be used. For example, in the case of a negative electrode active material for a lithium secondary battery, a carbon material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that has an element that can be alloyed with lithium, and the like can be given.

  Examples of the carbon material include non-graphitizable carbon, artificial graphite, natural graphite, cokes, graphites, glassy carbons, carbon fibers, activated carbon, and carbon blacks.

  Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn capable of inserting and extracting lithium with a high capacity is particularly preferable.

Specific examples of compounds having elements that can be alloyed with lithium include CuSn, CoSn, ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , and CoSi _{2. , NiSi 2, CaSi 2, CrSi} 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, Si 3 N 4, Si 2 N 2 O, SiO v (0 <V ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 or LiSnO can be exemplified, and particularly SiO _x (0.5 ≦ x ≦ 1.7) capable of inserting and extracting lithium with a high capacity. Is preferred.

The electron conductive material will be described. The electron conductive material as used in the present invention is a ferroelectric material having a Curie temperature in the range of 30 to 400 ° C. The Curie temperature is a transition temperature at which a ferroelectric changes to a paraelectric, and is a temperature at which a ferroelectric loses spontaneous polarization. For example, PbZr _x Ti _1-x O ₃ (0 ≦ x ≦ 1) known as lead zirconate titanate is a ferroelectric tetragonal crystal whose crystal structure is spontaneously polarized at room temperature, but exceeds the Curie temperature. And transition to a paraelectric cubic crystal that has lost its spontaneous polarization. The electron conductive material of the present invention loses spontaneous polarization at 30 to 400 ° C., and becomes an insulator that does not participate in the movement of electrons in the active material. Therefore, the electronically conductive material encapsulating material exhibits high resistance at a temperature equal to or higher than the Curie temperature. The electron conductive material of the present invention can also be grasped as a PTC material whose resistance increases at 30 to 400 ° C.

  A material having a Curie temperature of less than 30 ° C. is not preferable as an electron conductive material included in the active material because it has a high resistance at a normal temperature at which a secondary battery is normally used. When the Curie temperature exceeds 400 ° C, the resistance becomes high near the decomposition temperature or combustion temperature of the organic matter that constitutes the secondary battery. Even if high resistance is exhibited at such temperature, it contributes to the safety of the secondary battery. Since it cannot be said, it is not preferable. From this point of view, the electron conductive material of the present invention has a Curie temperature in the range of 30 to 400 ° C, but preferably has a Curie temperature in the range of 50 to 300 ° C. Those within the range of ° C are more preferred, and those within the range of 90 to 150 ° C are particularly preferred.

Examples of the electron conductive material of the present invention include BaTiO ₃ , PbZr _x Ti _1-x O ₃ (0 <x <1), Pb _1-x La _x Ti _1-y Zr _y O ₃ (0 <x <1, A ferroelectric composite metal oxide can be given at room temperature (25 ° C.) such as 0 <y <1). A sintered body obtained by sintering a material obtained by adding a compound containing a metal element such as an alkali metal, an alkaline earth metal, or a rare earth element to these materials may be used as the electron conductive material of the present invention. Such a material is, for example, a general formula Ba _1-x Ti _1-y M ¹ _x M ² _y O ₃ (M ¹ and M ² are each one or more kinds of metal elements. 0 ≦ x <1, 0 ≦ y <1). M ¹ and M ² include Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, lanthanoid, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, Fr, Ra, and actinoid are mentioned.

KNbO _{3, which} is known as a ferroelectric substance, is not an electron conductive material of the present invention because its Curie temperature is 435 ° C., but a material obtained by adding a metal compound to KNbO ₃ is sintered and the Curie temperature is increased. The reduced sintered body may be used as the electron conductive material of the present invention. This material has the general formula ^{_{K 1-x Nb 1-y}} M 1 x M 2 y O 3 (M 1, M 2 is one or more kinds of metal elements each .0 ≦ x <1,0 ≦ y < 1, 0 <x + y <2). M ¹ and M ² include Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, lanthanoid, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, Fr, Ra, and actinoid are mentioned.

Furthermore, as the electron conductive material of the present invention, a ferroelectric general formula Ti _v M ¹ _W M ² _x M ³ _y O _z (M ¹ , M, which is known to have a lower relative dielectric constant than BaTiO ₃ is used. ² and M ³ are each a metal element, such as 0 ≦ v ≦ 1, 0 ≦ w ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 <z ≦ 3). it can. M ¹ , M ² , M ³ include Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge , As, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, lanthanoid, Hf, Ta, W, Re, Os, Ir , Pt, Au, Hg, Tl, Pb, Bi, Po, Fr, Ra, and actinoids. Specific examples represented by the material by the general formula ^{_{Ti v M 1 W M 2 x}} M 3 y O z, cited _{Ti v Sr W Ca x Zr y} O 2, Sr w Ca x O, the _Ti v Zr _y O be able to.

These materials may be used singly or in combination as the electron conductive material of the present invention. The Curie temperature of the above material is clarified in many documents such as Patent Documents 4 to 8. For example, the Curie temperature of BaTiO ₃ is around 120 ° C., and the Curie temperature of Ba _0.94 Sn _0.06 TiO ₃ is around 80 ° C. Curie temperature of PbZr _x Ti _1-x O 3, known as lead zirconate titanate (0 <x <1) is approximately from 200 to 330 ° C. is dependent on the value of x. Curie temperature of _{Pb 1-x La x Ti 1} -y Zr y O 3 , known as lead lanthanum zirconate titanate (0 <x <1,0 <y <1) is depends on the values of x and y It is about 70-350 degreeC.

  The active material included in the electron conductive material of the present invention includes an active material containing an electron conductive material having a Curie temperature in the range of 30 to 400 ° C., and the active material and the electron conductive material are integrated. It is. Here, the state of the electron conductive material and the active material in the electron conductive material encapsulating material is preferably a solid solution in which both are mixed to form a solid phase, and particularly the crystal structure of the electron conductive material is electron conductive. What is maintained in the active material inclusion material is good.

  The mass ratio of the active material to the electron conductive material in the electron conductive material encapsulating material of the present invention is preferably in the range of active material: electron conductive material = 100: 1 to 1: 1, 19: 1 to 3: 1. : 2 is more preferable, and the range of 9: 1 to 13: 7 is particularly preferable. If the mass of the electron conductive material is too large, the performance of the electron conductive material-encapsulating material as an active material may be extremely inferior.

  The method for producing an active material in an electron conductive material according to the present invention includes an introducing step of introducing an active material and an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. into the plasma, and the active material and the active material in the plasma A melting step of melting the electron conductive material to form a melt, and a solid solution forming step of cooling the melt to form a solid solution of the active material and the electron conductive material. To do.

  The introducing step is a step of introducing an active material and an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. into the plasma. In the introduction step, the mass ratio of the active material introduced into the plasma and the electron conductive material is preferably in the range of active material: electron conductive material = 100: 1 to 1: 1, and 19: 1 to 3: 2 Is more preferable, and the range of 9: 1 to 13: 7 is particularly preferable.

  As a specific introduction step, an active material and an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. are mixed to form a mixture, and the mixture and carrier gas are mixed to form a first fluid. A first introduction step of introducing a fluid into plasma, or an active material and a carrier gas are mixed to form a second fluid, and an electron conductive material and a carrier gas having a Curie temperature in the range of 30 to 400 ° C. are mixed. The third fluid can be used, and one of the second introduction steps of introducing the second fluid and the third fluid into the plasma can be exemplified.

  In the first introduction step, an active material and an electron conductive material having a Curie temperature in the range of 30 to 400 ° C. are mixed to form a mixture, and the mixture and carrier gas are mixed to form a first fluid. Is introduced into the plasma.

  First, an active material and an electron conductive material are added and mixed in a suitable container to obtain a mixture. The container preferably has a stirring device. The amount of the electron conductive material in 100 parts by mass of the mixture is preferably in the range of more than 0 parts by mass and not more than 50 parts by mass, more preferably in the range of 5 to 40 parts by mass, and in the range of 10 to 35 parts by mass. Particularly preferred. If the amount of the electron conductive material is too large, the performance of the electron conductive material-containing active material as the active material may be remarkably deteriorated.

  The carrier gas is a gas for transporting the mixture to a high temperature region where plasma is generated through an introduction tube communicating with a plasma generation site. Argon can be mentioned as a kind of carrier gas.

  A negative pressure pipe (which is negative pressure due to a vacuum pump or a carrier gas flow of the introduction pipe) that is joined to the introduction pipe is brought close to the mixture in the container to bring the mixture into the negative pressure pipe. Suction. In addition, it is preferable that the said mixture continues stirring in a container. The sucked mixture is mixed with the carrier gas at the junction of the negative pressure tube and the introduction tube to become the first fluid. The first fluid moves in the introduction tube and is introduced into a high temperature region where plasma is generated. The flow rate of the carrier gas may be set appropriately as appropriate.

  The plasma is generated in a chamber of a plasma generator such as a high frequency induction thermal plasma generator. The gas to be plasmified may be any of argon, argon and oxygen, argon and hydrogen. The temperature of the plasma may be higher than the melting temperature of the active material and the electron conductive material, but the temperature is sufficiently high to melt the active material and the electron conductive material, and the plasma is generated stably. The temperature is preferably around 10000 ° C.

  In the second introduction step, the active material and the carrier gas are mixed to form a second fluid, the electron conductive material having a Curie temperature in the range of 30 to 400 ° C. and the carrier gas are mixed to form a third fluid, This is a step of introducing the second fluid and the third fluid into the plasma.

  First, an active material or an electron conductive material is placed in a suitable container. The container preferably has a stirring device.

  Next, the active material or the electron conductive material in the container is brought close to the negative pressure tube that joins the introduction tube, and the active material or the electron conductive material is sucked into a separate negative pressure tube. The active material or the electron conductive material is preferably kept stirred in the container. The sucked active material or electron conductive material is mixed with the carrier gas at the junction of each negative pressure tube and the introduction tube to become the second fluid or the third fluid, respectively.

  The second fluid or the third fluid moves in the introduction pipe and is introduced into the high temperature region where plasma is generated at a predetermined ratio. The second fluid and the third fluid may be mixed at a predetermined ratio before being introduced into the plasma, moved in the same introduction tube, and introduced into the plasma, or in separate introduction tubes. May be introduced into the plasma at a predetermined ratio. The predetermined ratio is preferably such that the mass of the electron conductive material is more than 0 parts by mass and not more than 50 parts by mass with respect to 100 parts by mass of the total amount of the active material and the electron conductive material introduced into the plasma. The range of 5 to 40 parts by mass is more preferable, and the range of 10 to 35 parts by mass is particularly preferable. When the ratio of the electron conductive material is too high, the performance of the electron conductive material-containing active material as the active material may be remarkably deteriorated.

  The carrier gas, the introduction tube, the negative pressure tube, the plasma, and the like are the same as those described in the first introduction step except for those specially explained in the second introduction step. The flow rate of the carrier gas may be set appropriately as appropriate.

  The active material and the electron conductive material used in the introduction step are preferably in powder form. The average particle diameter of the powder is preferably within the range of 10 nm to 100 μm, preferably within the range of 100 nm to 50 μm, and particularly preferably within the range of 200 nm to 10 μm. If the average particle size of the powder is too large, it may be difficult to introduce it into the plasma in the introduction step.

  The melting step is a step of melting the active material and the electron conductive material into a melt in plasma. The active material and the electron conductive material introduced into the high temperature region where plasma is generated in the introduction step are immediately melted into a melt. Depending on the material contained in the active material and the electron conductive material, vaporization may occur in the melting step. In the present invention, the term melt is used in the sense of including the material vaporized in the melting step. The melt is gradually transported away from the plasma generation site by the carrier gas flow and the plasma flow.

The solid solution forming step is a step of cooling the melt to form a solid solution of the active material and the electron conductive material. The melt transported far from the plasma generation site is gradually cooled. And the melted material cooled below the melting point of each material becomes solid for each material. At this time, since there is a difference in the melting point of each material, the material having the higher melting point becomes solid particles first, and the material having the next melting point adheres around the particles of the previous material and becomes solid. Here, a solid solution forming step of a melt using SiO _x (0.5 ≦ x ≦ 1.7) as an active material and BaTiO ₃ as an electron conductive material will be considered. In SiO _x (0.5 ≦ x ≦ 1.7), the melting point of Si, which is the main component, is 1414 ° C., and the melting point of BaTiO ₃ is 1625 ° C. Then, when the melt is cooled, solid particles of BaTiO ₃ are first formed, and then solid with Ba adhering to the BaTiO ₃ particles (or aggregates thereof), resulting in the BaTiO ₃ particles being Encapsulated Si is formed. Depending on the material used, the solidification order of the active material and the electron conductive material may be reversed, but even in such a case, the mass ratio of the active material to the electron conductive material is the active material: electron If it is in the range of conductive material = 100: 1 to 1: 1, it can be said that the active material contains the electron conductive material because the matrix in the active material included in the electron conductive material becomes the active material. In view of this manufacturing method, the melting point of the active material (or the melting point of the main component of the active material) is preferably lower than the melting point of the electron conductive material.

  In this way, the electron conductive material encapsulating material of the present invention is produced. The shape of the electronically conductive material encapsulating material of the present invention is generally spherical because it is produced by cooling the melt in the space in the chamber. In addition, the particle size of the electron conductive material encapsulating material can be controlled by controlling the temperature distribution in the chamber.

  The electron conductive material encapsulating material of the present invention includes an electron conductive material having a Curie temperature in the range of 30 to 400 ° C., that is, a PTC material whose resistance increases at 30 to 400 ° C. Therefore, when the lithium ion secondary battery using the electronically conductive material encapsulating material of the present invention becomes the Curie temperature or higher, the resistance of the electroconductive material encapsulating material increases, and excess current flows. Suppress. Therefore, it can be said that the active material for inclusion of an electron conductive material of the present invention is an active material for a lithium ion secondary battery suitable for ensuring safety. When using the electron conductive material inclusion active material of the present invention as the active material of the lithium ion secondary battery, it is preferable to use the electron conductive material inclusion active material of the present invention alone as the active material. It may be used in combination with a substance.

  A lithium ion secondary battery usually has a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode and the negative electrode each have a current collector and an active material layer bound to the surface of the current collector.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given. The current collector may be covered with a known protective layer. The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 10 μm to 100 μm.

  The active material layer includes an active material and, if necessary, a binder and / or a conductive aid.

  As the active material, the electron-conductive material-containing active material of the present invention may be used as at least one of the positive electrode active material and the negative electrode active material, but a known active material may be used in combination. The known active material is as described above.

  The binder plays a role of binding the active material to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to. The blending ratio of the binder in the active material layer is preferably a mass ratio of active material: binder = 1: 0.05 to 1: 0.5. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Examples of the conductive assistant include carbon black, natural graphite, artificial graphite, acetylene black, ketjen black (registered trademark), and vapor grown carbon fiber (VGCF) which are carbonaceous fine particles. These conductive assistants can be added to the active material layer alone or in combination of two or more. Although there is no restriction | limiting in particular about the usage-amount of a conductive support agent, For example, it can be 0.5-30 mass parts with respect to 100 mass parts of active materials.

  In order to form an active material layer on the surface of the current collector, the surface of the current collector can be formed using a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method. What is necessary is just to apply | coat an active material to. Specifically, a mixture containing an active material and, if necessary, a binder and a conductive additive is prepared, and an appropriate solvent is added to the mixture to form a paste-like active material layer forming composition. The active material layer forming composition is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. Examples of the separator include a porous film using one or more synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene, or a ceramic porous film.

  The electrolytic solution is a medium for ions to move between the positive electrode and the negative electrode, and includes a solvent and an electrolyte dissolved in the solvent.

  Examples of the solvent used for the electrolyte solution of the lithium ion secondary battery include non-aqueous solvents such as cyclic esters, chain esters, and ethers. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. A plurality of the above-described solvents may be used in combination as the solvent for the electrolytic solution. In particular, it is preferable to use three types of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in combination.

Examples of the electrolyte of the lithium ion secondary battery include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ . The concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 1.7 mol / L.

  An example of a method for manufacturing a lithium ion secondary battery will be described. A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal connected to the outside with a current collecting lead or the like, an electrolyte is added to the electrode body to obtain a lithium ion secondary battery. . The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, a coin shape, and a laminated shape can be employed.

  The lithium ion secondary battery may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. In addition to vehicles, lithium ion secondary batteries can be used in personal computers, portable communication devices, various home appliances driven by batteries, home-use distributed storage systems, office equipment, industrial equipment, and the like.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
The electron conductive material encapsulating material of the present invention was produced as follows.

7 g of commercially available SiO _x (0.5 ≦ x ≦ 1.7) as an active material and ₃ g of commercially available BaTiO ₃ as an electron conductive material were mixed in a container equipped with a stirring portion to obtain a mixture. Note that the Curie temperature of BaTiO ₃ is around 120 ° C.

The high-frequency induction thermal plasma generator was activated, and plasma was generated in the device under the following conditions.
High frequency output: 6 kW, gas: argon, gas flow rate: 30 L / min. , Pressure in the chamber: 7 to 100 kPa
The negative pressure tube joined to the argon introduction tube of the high frequency induction thermal plasma generator was brought close to the mixture stirred at a speed of 4000 rpm in the container, and the mixture was sucked into the negative pressure tube. The sucked mixture was mixed with argon gas at the junction of the negative pressure tube and the argon inlet tube to form a fluid. The fluid moved in the argon introduction tube and was introduced into the high temperature region where the plasma was generated in the high frequency induction thermal plasma generator.

  The mixture introduced into the high temperature region where the plasma was generated melted immediately and became a melt. Then, the melt was gradually transported away from the plasma generation site by an argon gas flow and cooled to powder. This powder is the electron conductive material inclusion material of Example 1.

When the obtained electron-conductive material-encapsulating material was measured with a powder X-ray diffractometer, a peak derived from the raw material BaTiO ₃ crystal and a peak derived from the Si crystal contained in the raw material SiO _x were observed.

Furthermore, when the particles of the obtained electron-conducting material-encapsulating material were divided with a laser and the cut surface of the obtained fragment was observed with a scanning electron microscope, the particles contained SiO _x as a matrix, and BaTiO was incorporated in the inside. ₃ was found to be a solid solution. 1 and 2 show scanning electron micrographs of the electron conductive material encapsulating material of Example 1. FIG.

(Application 1)
A slurry was prepared by mixing 45 parts by mass of the electron-conductive material encapsulating material of Example 1, 40 parts by mass of natural graphite powder, 5 parts by mass of acetylene black, and 33 parts by mass of the binder solution. As the binder solution, a solution in which polyamideimide resin was dissolved in N-methyl-2-pyrrolidone at a concentration of 30% by mass was used. This slurry was applied to the surface of a glass plate, and N-methyl-2-pyrrolidone was volatilized to form a rectangular electron-conductive material-containing active substance-containing film. The electron conductive material-containing active material-containing film corresponds to the negative electrode active material layer in the lithium ion secondary battery. Another glass plate was placed on the electron conductive material-containing material. An electron conductive material-containing active substance-containing film sandwiched between glass plates is placed on a hot plate, and the resistance (electric resistivity) and ratio of the electron-conductive material-containing active substance-containing film in the range of 0 to 140 ° C. The dielectric constant and magnetic flux density were measured.

  Resistance (electrical resistivity) was measured using a four-probe method, relative dielectric constant was measured using an impedance measurement method using a network analyzer, and magnetic flux density was measured using a gauss meter. The measurement results are graphed and shown in FIGS.

  As is apparent from the graphs shown in FIGS. 3 to 5, the resistance (electrical resistivity) and relative dielectric constant of the film containing the electron-conductive material-containing active material increase with increasing temperature from around 100 ° C., and the magnetic flux density is Diminished. In particular, the fluctuations in resistance (electrical resistivity), relative dielectric constant and magnetic flux density around 120 ° C. are remarkable.

This result can be explained by the characteristic change of BaTiO ₃ having a Curie temperature of around 120 ° C. included in the electron conductive material-containing active material-containing film. That is, the resistance (electric resistivity) of the BaTiO ₃ encapsulating material-containing film was changed as BaTiO ₃ which was a tetragonal structure and ferroelectric at room temperature changed to a cubic structure paraelectric through a Curie temperature. It can be said that the relative permittivity and the magnetic flux density have changed. The above results mean that the electronically conductive material-encapsulating material of the present invention functions as a PTC material. Therefore, even if the lithium ion secondary battery using the electron conductive material encapsulating material of the present invention generates heat due to an internal short circuit or the like, the electron conductive material will be used when the battery temperature exceeds the Curie temperature of the electron conductive material. Since the encapsulated active material has high resistance, generation of excess current between the electrodes can be suppressed. It was confirmed that the electron-conductive material-encapsulating material of the present invention improves the safety of the lithium ion secondary battery.

Claims (3)

An introducing step of introducing an active material and BaTiO ₃ into the plasma;
A melting step of melting the active material and the BaTiO ₃ in the plasma to form a melt;
A solid solution forming step of cooling the melt and forming a solid solution of the active material and the BaTiO ₃ ;
A method for producing a BaTiO ₃ encapsulating material, comprising: 2. The inclusion of BaTiO _{3 according} to claim 1, wherein in the introduction step, a mass ratio between the active material introduced into the plasma and the BaTiO ₃ is in a range of active material: BaTiO ₃ = 100: 1 to 1: 1. A method for producing an active material. BaTiO ₃ inclusion active material which is a solid solution of BaTiO _{3 and an} active material.