JP2009176597A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the safety of a nonaqueous electrolyte secondary battery since heat generation accompanied by an excessive charge in the nonaqueous electrolyte secondary battery is efficiently restrained at favorable responsiveness to heat generation and the thermal runaway of the battery, and to surely prevent the breakage and explosion of the battery. <P>SOLUTION: In the nonaqueous electrolyte secondary battery 10 including a positive electrode 11 having a positive electrode active material layer and a positive electrode collector, a negative electrode 12 having a negative electrode active material layer and a negative electrode collector, a separator 13, and an electrolyte, a conductive material having a positive resistance temperature characteristic at a contact surface between both active materials or the active material and the conductive material is made to exist in the active material layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention mainly relates to an improvement of an electrode plate in a nonaqueous electrolyte secondary battery.

  Lithium ion secondary batteries have high capacity and high energy density, and can be easily reduced in size and weight. For example, mobile phones, personal digital assistants (PDAs), notebook personal computers, electronic dictionaries, video cameras It is widely used as a power source for portable small electronic devices such as headphone stereos and portable game machines. In a typical lithium ion secondary battery, a positive electrode, a separator, a negative electrode, and a separator are stacked in this order and wound, or a wound electrode group, or a stacked electrode group in which a positive electrode, a separator, and a negative electrode are stacked. Is used. In general, a positive electrode containing a lithium cobalt compound as a positive electrode active material is used as a positive electrode, a negative electrode containing a carbon material as a negative electrode active material as a negative electrode, and a polyolefin porous film as a separator. Such a lithium ion secondary battery has high battery capacity and output, good charge / discharge cycle characteristics, and relatively long service life.

  Lithium ion secondary batteries are also at a high level in terms of safety, but due to their high capacity and high output, there is still room for further improvement in terms of safety. For example, when a lithium ion secondary battery is overcharged, there is a risk that problems such as heat generation may occur. In addition, the occurrence of an internal short circuit may cause problems such as heat generation. If the heat is left unattended, the temperature of the battery gradually increases, and there is a risk that the user may be injured such as a burn. In addition, since it contains an electrolyte containing an organic solvent, the organic solvent is electrolyzed to generate gas, the internal pressure of the battery increases, and eventually the battery partially breaks or the battery bursts. It is hard to say that there is no possibility of doing it.

  Currently, when a lithium ion secondary battery is overcharged, the safety of the lithium ion secondary battery is further improved by cutting off the current in the battery and suppressing heat generation. As means for interrupting the current, for example, (a) a method of using a mechanism for detecting the internal pressure of the battery and interrupting the current, such as a safety valve provided in the sealing plate, (b) A method of providing a member made of a PTC (Positive temperature coefficient) element whose electrical resistance increases in response to heat generation, and cutting off current when the PTC element becomes a non-conductor, (c) a separator that melts in response to heat generation of the battery A method of blocking the current by inhibiting the movement of lithium ions between the positive and negative electrodes when the separator is melted is used.

  However, in the method (a), the progress of the decomposition reaction of the electrolytic solution, which is a factor that changes the internal pressure of the battery, is greatly influenced not only by the battery temperature but also by the battery voltage, the environmental temperature, etc. Becomes inaccurate, and the effect of suppressing heat generation becomes insufficient. In the method (b), since the electrode group as the main heating element and the PTC element in the sealing plate are in a positional relationship, the responsiveness to the heat generation of the PTC element is lowered, and the effect of suppressing the heat generation is ineffective. It will be enough. In the method (c), it is necessary to use a separator that melts with high responsiveness to the heat generation of the battery. However, when such a separator is used, an internal short circuit occurs due to a decrease in film strength, or the output of the battery increases. Improvement of charge / discharge cycle characteristics becomes insufficient.

  In addition, an electrode having a positive resistance temperature characteristic has been proposed (see, for example, Patent Document 1). This electrode is a laminated body in which an active material layer, a conductive layer containing a conductive material, and a current collector are stacked in this order, and the active material layer contains the active material, the conductive material, and the binder. In this electrode, positive resistance temperature characteristics are imparted to the active material layer or the conductive layer. As a method for imparting a positive resistance temperature characteristic to the active material layer, (d) a method in which the active material is composed of a part having electrode activity and a part having no electrode activity and having PTC characteristics, (e ) A method of mixing a PTC element into the active material layer, (f) a method of forming secondary particles of the active material obtained by the method (d), and the like.

However, in the method (d), since the portion having electrode activity is exposed, even if the portion having no electrode activity becomes a non-conductor due to the positive resistance temperature characteristic, the current can be weakened. , Can not cut off enough. Therefore, heat generation cannot be sufficiently suppressed. In the method (e), since the PTC element is simply mixed, the active material is exposed in the active material layer, and heat generation cannot be sufficiently suppressed as in the method (d). Further, when secondary particles are formed by the method (f), the thickness of the positive electrode active material layer is limited, and therefore the particle size of the active material itself needs to be very small. Actually, the average particle diameter of the active material used in Example 2 of Patent Document 1 is only 1 μm. When such a small active material is used, there is a problem that the battery capacity and thus the battery performance inevitably deteriorates.
JP-A-10-241665

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which heat generation due to overcharging or the like can be suppressed with good responsiveness to heat generation and safety is further improved.

In the course of research for solving the above problems, the present inventors have repeatedly studied the reason why the technique of Patent Document 1 cannot sufficiently suppress heat generation.
During charging, a desorption reaction of lithium ions from the positive electrode active material proceeds. When the end of the elimination reaction is reached, the ionic conductivity of the positive electrode active material decreases, and the reaction resistance of the positive electrode active material increases. When the charging further proceeds and the battery is overcharged, the reaction resistance of the positive electrode active material is significantly increased. On the other hand, in the positive electrode active material layer, a conductive network is formed by contact between the positive electrode active materials or between the positive electrode active material and the conductive material, and energization is possible. Therefore, the positive electrode active material having increased reaction resistance is energized, Joule heat generation occurs, the temperature of the positive electrode active material rapidly increases, and finally a thermal runaway state in which the heat generation cannot be controlled is reached.

On the other hand, in the technique of Patent Document 1, the dispersion state in the positive electrode active material is as shown in FIG. FIG. 3 is a longitudinal sectional view schematically showing the configuration of the positive electrode 100 in the battery of Patent Document 1. As shown in FIG. The positive electrode 100 includes a current collector 101 and a positive electrode active material layer 102. By dispersing the PTC element 104 in the positive electrode active material layer 102, the conductive network can be partially cut off, so that the amount of current flowing in the positive electrode active material layer is certainly reduced. However, in a portion where the PTC element 104 does not exist, the conductive network connected to the positive electrode active material 103 remains without being interrupted through a conductive material (not shown). Since energization to the positive electrode active material 103 is performed through the conductive network of the unblocked portion, heat generation of the positive electrode active material 103 cannot be sufficiently suppressed. Therefore, the technique of Patent Document 1 cannot sufficiently suppress heat generation during overcharge. Furthermore, the response to heat generation is also poor.
As a result of further studies based on such knowledge, the present inventors have succeeded in obtaining a desired nonaqueous electrolyte secondary battery and completed the present invention.

That is, the present invention is a nonaqueous electrolyte secondary battery including a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator, and a nonaqueous electrolyte,
At least one of the positive electrode active material layer and the negative electrode active material layer is present together with the active material or the active material and the conductive material so as to be in contact with each other between the active materials or between the active material and the conductive material. The present invention relates to a non-aqueous electrolyte secondary battery containing a conductive material having

The content of the conductive material having a positive resistance temperature characteristic is preferably 1 to 15 parts by weight with respect to 100 parts by weight of the active material.
At least one of the positive electrode active material layer and the negative electrode active material layer contains an active material, a conductive material, and a conductive material having a positive resistance temperature characteristic. It is preferable that it is 100-500 weight part with respect to 100 weight part of materials.

It is preferable that a layer containing a conductive material having a positive resistance temperature characteristic is provided on the particle surface of the active material.
The thickness of the layer containing a conductive substance having positive resistance temperature characteristics is more preferably 0.1 to 10 μm.
It is preferable that a plurality of particles containing a conductive material having a positive resistance temperature characteristic adhere to the particle surface of the active material.
Further preferred.
It is preferable that at least a part of the particle surface of the active material is provided with a protrusion that contains a conductive material having a positive resistance temperature characteristic and protrudes outward from the particle surface of the active material.
More preferably, the conductive material having a positive resistance temperature characteristic changes from a conductor to a nonconductor in a temperature range of 130 ° C. or lower.

  According to the present invention, even in an overcharged state, heat generation is suppressed, and an oxidation reaction of an electrolyte solution containing an organic solvent (non-aqueous solvent) hardly occurs, and occurrence of problems such as expansion and rupture is almost certainly prevented. A highly safe non-aqueous electrolyte secondary battery is provided. Furthermore, in the nonaqueous electrolyte secondary battery of the present invention, the mechanism for suppressing heat generation functions with good responsiveness to the heat generation, so the effect of suppressing heat generation is very large.

  The non-aqueous electrolyte secondary battery of the present invention is a conductive material having a positive resistance temperature characteristic on the contact surface between the active materials or between the active material and the conductive material in at least one of the positive electrode active material layer and the negative electrode active material layer. It is characterized by existing. For example, the active material particle surface is coated with a conductive material having a positive resistance temperature characteristic, or the active material particle surface is provided with a protrusion containing a conductive material having a positive resistance temperature characteristic. Break direct contact between each other or the active material and the conductive material.

  FIG. 2 is a cross-sectional view schematically showing the configuration of the electrode 1 in the nonaqueous electrolyte secondary battery of the present invention. The electrode 1 includes a current collector 2 and an active material layer 3. The active material layer 3 contains an active material 4, a conductive material 5 having positive resistance temperature characteristics, a conductive material (not shown), and a binder 6. The conductive material 5 having a positive resistance temperature characteristic exists so as to cover the surface of the active material 4 and functions as a conductor during normal charging / discharging, together with the active material 4 or the active material 4 and the conductive material. A conductive network is formed in the material layer 3. When the battery generates heat due to overcharging or the like, it functions as a nonconductor, and isolates the active material 4 from the conductive network in the active material layer 3. That is, when heat is generated due to overcharge or the like, the conductive material having a positive resistance temperature characteristic is increased in resistance and becomes a nonconductor, and the active material 4 is almost completely cut off from the conductive network in the active material layer 3. As a result, the energization of the active material 4 is almost completely eliminated, the Joule heat generation of the active material 4 is prevented, and the heat generation of the entire battery can be reliably suppressed with good responsiveness.

  On the other hand, in the technique of Patent Document 1, a conductive material having a positive resistance temperature characteristic is not present so that the entire particle surface of the active material does not come into contact with another active material or a conductive material. For this reason, at least a part of the particle surface of the active material is exposed, and it is inevitable to form a conductive network even if partially with other active material or conductive material. As a result, when the battery generates heat, the conductive network is cut off in the portion where the conductive material having the positive resistance temperature characteristic is present, but the conductive network is blocked in the portion where the conductive material having the positive resistance temperature characteristic is not present. Without being interrupted, energization of the active material is performed, and the active material continues to generate heat, resulting in an overheated state.

In this specification, the conductor means various materials having a specific resistance of less than 3 × 10 ³ Ω · cm at a temperature of 25 ° C. The non-conductor or non-conductor means various materials having a specific resistance exceeding 1 × 10 ⁶ Ω · cm at a temperature of 25 ° C.

The nonaqueous electrolyte secondary battery of the present invention is a conventional nonaqueous electrolyte secondary battery except that a conductive material having a positive resistance temperature characteristic is present on the contact surfaces between the active materials or between the active material and the conductive material. The same configuration can be adopted.
The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. In either one or both of the positive electrode and the negative electrode, a conductive material having a positive resistance temperature characteristic is present on the contact surface between the active materials or between the active material and the conductive material.

The positive electrode is provided to face the negative electrode with a separator interposed therebetween, and includes a positive electrode current collector and a positive electrode active material layer.
As the positive electrode current collector, those commonly used in the field of non-aqueous electrolyte secondary batteries can be used, and examples thereof include sheets and foils containing stainless steel, aluminum, titanium and the like. Although the thickness of a sheet | seat and foil is not specifically limited, For example, it is 1-500 micrometers.
The positive electrode active material layer is formed on one or both surfaces in the thickness direction of the positive electrode current collector, contains the positive electrode active material, and may further contain a conductive material, a binder, and the like as necessary.

As the positive electrode active material, those commonly used in this field can be used, and examples thereof include lithium-containing composite metal oxides, olivine-type lithium salts, chalcogen compounds, and manganese dioxide. The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Mn, Al, Co, Ni, Mg and the like are preferable. One kind or two or more kinds of different elements may be used. Among these, lithium-containing composite metal oxides can be preferably used. Specific examples of the lithium-containing composite metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _{z. , Li x Ni 1-y M} y O z, Li x Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F ( in the respective formulas, M is Na, Mg, It represents at least one element selected from the group consisting of Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V and B. x = 0 to 1.2, y = 0-0.9, z = 2.0-2.3). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging. Examples of the olivine type lithium salt include LiFePO ₄ . Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

The particle surface of the positive electrode active material is coated with a conductive material having positive resistance temperature characteristics. That is, the positive electrode active material layer has a coating layer containing a conductive material having positive resistance temperature characteristics on the surface thereof.
As the conductive material having a positive resistance temperature characteristic, various conductive materials conventionally known as PTC elements can be used without any particular limitation. Among them, a PTC element that is a mixture of a conductive material and an organic material is preferable, and a PTC element that is a mixture of a conductive material and an organic material having a softening point at 130 ° C. or lower (preferably 70 to 130 ° C.) is more preferable. . Such a PTC element functions as a conductor in a temperature range below the softening point of the organic material, and functions as a nonconductor in a temperature range above the softening point.

Although it does not restrict | limit especially as an electrically conductive material contained in a PTC element, Preferably, the solid solution in which alkaline earth metal titanates, such as barium titanate, barium strontium titanate, and barium lead titanate, and a dissimilar metal were solid-solubilized, graphite Carbon materials such as acetylene black and carbon black, metal particles such as nickel particles, metal carbides such as WC, B ₄ C, ZrC, NbC, MoC, TiC and TaC, metal nitrides such as TiN, ZrN and TaN, and WSi ₂ and metal silicides such as MoSi ₂ . Although it does not restrict | limit especially as an organic material, For example, polyethylene, a polypropylene, ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polyamide, polystyrene, polyacrylonitrile, heat Examples thereof include a plastic elastomer, polyethylene oxide, polyacetal, thermoplastic modified cellulose, polysulfones, and polymethyl (meth) acrylate. Among these, polyethylene, polypropylene, ethylene-vinyl acetate copolymer (EVA) and the like are preferable. Each of the conductive material and the organic material can be used alone or in combination of two or more. The usage ratio of the conductive material and the organic material is not particularly limited and can be appropriately selected according to various conditions such as the type of the conductive material and the type of the organic material, but is preferably 95: 5 to 50:50 by weight ratio. .

  The coating layer containing the PTC element is, for example, a method of imparting mechanical frictional force to a mixture of an active material and a PTC element, a mechano-fusion method, a theta composer method, an agromaster method, a melt kneader method, a vapor deposition method, a sputtering method, etc. It can be formed according to the coating method. Moreover, it can coat | cover by performing granulation operation with heating with respect to the mixture of an active material and a PTC element.

At this time, the usage ratio of the active material and the PTC element is preferably 1 to 15 parts by weight of the PTC element with respect to 100 parts by weight of the active material. If the amount of the PTC element used is less than 1 part by weight, the active material surface may not be sufficiently covered with the PTC element. Moreover, when the usage-amount of a PTC element exceeds 15 weight part, there exists a possibility of causing the capacity | capacitance fall of a battery.
In the present invention, a coating layer containing a PTC element can be formed on almost the entire surface of the active material particles by employing the above-described coating method and usage ratio.

  In the present invention, a protrusion protruding outward from the surface may be formed on the surface of the active material, and the protrusion may be formed of a PTC element. Thereby, the protrusion part containing a PTC element interposes between active materials or between an active material and a electrically conductive material. That is, the active materials or the active material and the conductive material come into contact with each other through the protrusion. For this reason, at the time of normal charging / discharging, since a projection part is a conductor, a conductive network is formed. On the other hand, when the heat is generated due to overcharge or the like, the protrusion becomes a non-conductor, so that the active material is almost certainly cut off from the conductive network, and the heat generation of the active material is suppressed.

In order to attach a plurality of particles containing the PTC element to the surface of the active material, for example, mechanical friction and impact are applied to the mixture of the active material and the PTC element, and the adhesion force of the PTC element to the active material A method for increasing the cohesive force is also preferred. Examples of methods for imparting mechanical friction and impact include a method using a stirring granulator, a twin-screw kneader, a vibration granulator, a mechanofusion method, and the like.
In this way, an active material in which a plurality of particles containing a PTC element are attached to the surface is obtained. These particles prevent the active materials or the active material and the conductive material from coming into direct contact.

  In order to form the protrusion containing the PTC element on the surface of the active material, for example, a mechanical impact is applied to the mixture of the active material and the PTC element, and the adhesion force and cohesive force of the PTC element to the active material are increased. A method of increasing is preferred. Examples of the method for imparting mechanical impact include a method using a rolling type, fluid type fine particle coating / granulating machine or the like. In this way, an active material surface-treated with the PTC element is obtained.

  As the conductive material contained in the positive electrode active material layer together with the active material surface-treated with the PTC element, for example, carbon black, graphite, carbon fiber, metal fiber, or the like can be used. Examples of carbon black include acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. A conductive material can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  As the binder, for example, polyethylene, polypropylene, fluororesin, rubber particles and the like can be used. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, in consideration of improving the oxidation resistance of the positive electrode active material layer, a binder containing fluorine is preferable. A binder can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture paste to the surface of the positive electrode current collector and drying it. The positive electrode mixture paste is prepared by, for example, adding a positive electrode active material or a positive electrode active material surface-treated with a PTC element to a dispersion medium and mixing with a binder, a conductive material, and the like as necessary. it can. For example, dehydrated N-methyl-2-pyrrolidone (NMP) can be used as the dispersion medium.

The negative electrode is provided so as to face the positive electrode through the separator, and includes a negative electrode current collector and a negative electrode active material layer.
Examples of the negative electrode current collector include sheets and foils containing stainless steel, nickel, copper, and the like. Although the thickness of a sheet | seat and foil is not specifically limited, For example, it is 1-500 micrometers.
The negative electrode active material layer is formed on one or both surfaces in the thickness direction of the negative electrode current collector, contains the negative electrode active material, and further contains a binder, a conductive material, a thickener and the like as necessary. .

The negative electrode active material can form a coating layer containing a PTC element on the surface in the same manner as the positive electrode active material. Moreover, the projection part containing a PTC element can be provided in the surface. Various conditions such as the method for forming the coating layer and the protrusion, the type and amount of use of the PTC element are the same as those for the positive electrode active material.
As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. For example, metallic lithium, carbon material, metal fiber, alloy, tin compound, silicon compound, nitride, and the like can be used. Examples of the carbon material include natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon fiber. A negative electrode active material can be used individually by 1 type, or can be used in combination of 2 or more type.

As the binder and the conductive material, the same binder and conductive material contained in the positive electrode active material layer can be used. However, in consideration of improving the reduction resistance of the negative electrode active material layer, it is preferable to use a binder containing no fluorine. Examples of the thickener include carboxymethyl cellulose.
The negative electrode active material layer can be formed, for example, by applying a negative electrode mixture paste to the surface of the negative electrode current collector and drying. The negative electrode mixture paste is, for example, a negative electrode active material or a negative electrode active material surface-treated with a PTC element, if necessary, added to a dispersion medium together with a binder, a conductive material, a thickener, etc. Can be prepared. For example, water can be used as the dispersion medium.

  A separator is a resin-made porous sheet provided so that it may interpose between a positive electrode and a negative electrode. As the resin constituting the separator, those commonly used in the field of non-aqueous electrolyte secondary batteries can be used, and examples thereof include polyolefins such as polyethylene and polypropylene, polyamides, and polyamideimides. Examples of the form of the porous sheet include a porous sheet-like material, a nonwoven fabric, and a woven fabric. Among these, a microporous sheet having a very small diameter of pores formed therein and usually about 0.05 to 0.15 μm has a high level of ion permeability, mechanical strength, and insulation. It is preferable because it has both. Moreover, although the thickness of a separator is not specifically limited, From a viewpoint of suppressing the excessive increase in impedance, what is necessary is just 10-300 micrometers, for example.

Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, a solid electrolyte (for example, a polymer solid electrolyte), and the like.
The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary. Solutes usually dissolve in non-aqueous solvents. For example, the separator is impregnated with the liquid non-aqueous electrolyte.

As the solute, those commonly used in this field can be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, chloroborane lithium, borates, imide salts and the like. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') and bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate Etc. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate ((CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) NLi) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. A solute may be used individually by 1 type, or may be used in combination of 2 or more type as needed. The amount of the solute dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2 mol / L.

  As the non-aqueous solvent, those commonly used in this field can be used, and examples thereof include cyclic carbonate esters, chain carbonate esters, and cyclic carboxylic acid esters. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, or may be used in combination of 2 or more type as needed.

  Examples of the additive include a material that improves charge / discharge efficiency and a material that inactivates the battery. A material that improves charge / discharge efficiency, for example, decomposes on the negative electrode to form a film having high lithium ion conductivity, and improves charge / discharge efficiency. Specific examples of such materials include, for example, vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4-propyl vinylene. Examples include carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), divinyl ethylene carbonate, and the like. These may be used alone or in combination of two or more. Among these, at least one selected from vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate is preferable. In the above compound, part of the hydrogen atoms may be substituted with fluorine atoms.

The material that inactivates the battery inactivates the battery by, for example, decomposing when the battery is overcharged to form a film on the electrode surface. Examples of such a material include benzene derivatives. Examples of the benzene derivative include a benzene compound containing a phenyl group and a cyclic compound group adjacent to the phenyl group. As the cyclic compound group, for example, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, a phenoxy group and the like are preferable. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether, and the like. A benzene derivative can be used individually by 1 type, or can be used in combination of 2 or more type. However, the content of the benzene derivative in the liquid nonaqueous electrolyte is preferably 10 parts by volume or less with respect to 100 parts by volume of the nonaqueous solvent.
The gel-like non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a polymer material that holds the liquid non-aqueous electrolyte. The polymer material used here is capable of gelling a liquid material. As the polymer material, those commonly used in this field can be used, and examples thereof include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, and polyvinylidene fluoride.

  The solid electrolyte includes a solute (supporting salt) and a polymer material. Solutes similar to those exemplified above can be used. Examples of the polymer material include polyethylene oxide (PEO), polypropylene oxide (PPO), a copolymer of ethylene oxide and propylene oxide, and the like.

  FIG. 1 is a longitudinal sectional view schematically showing a configuration of a cylindrical nonaqueous electrolyte secondary battery 1 which is one embodiment of the present invention. The cylindrical non-aqueous electrolyte secondary battery 1 includes a positive electrode 11, a negative electrode 12, a separator 13, a positive electrode lead 14, a negative electrode lead 15, an upper insulating plate 16, a lower insulating plate 17, a battery case 18, a sealing plate 19, a positive electrode terminal 20, and This is a wound battery including a non-aqueous electrolyte (not shown).

  The positive electrode 11, the negative electrode 12, and the separator 13 are superposed in the order of the positive electrode 11, the separator 13, and the negative electrode 12, and are wound in a spiral shape. Thereby, a wound electrode group is formed. The positive electrode lead 14 has one end connected to the positive electrode 11 and the other end connected to the sealing plate 19. In the present embodiment, the sealing plate 19 is a current blocking valve that is operated by the internal pressure of the battery, or a sealing plate that is not provided with a PTC element that functions when the battery is abnormally hot and energized with a large current. The material of the positive electrode lead 14 is, for example, aluminum. The negative electrode lead 15 has one end connected to the negative electrode 12 and the other end connected to the bottom of the battery race 20 that serves as a negative electrode terminal. The material of the negative electrode lead 15 is, for example, nickel.

  The battery case 18 is a bottomed cylindrical container member, and one end in the longitudinal direction is an opening and the other end is a bottom, and functions as a negative electrode terminal. The upper insulating plate 16 and the lower insulating plate 17 are resin members, are arranged so as to sandwich the wound electrode group from above and below, and insulate the wound electrode group from other members. The material of the battery case 18 is, for example, iron. For example, nickel plating is applied to the inner surface of the battery case 18. The sealing plate 19 includes a positive electrode terminal 20.

  The cylindrical nonaqueous electrolyte secondary battery 1 can be manufactured, for example, as follows. First, the upper insulating plate 16 and the lower insulating plate 17 are attached to the upper end portion and the lower end portion of the wound electrode group, respectively, and housed in the battery case 18 in that state. The positive lead 14 is used for connection. The negative electrode 12 and the bottom of the battery case 18 that also serves as a negative electrode terminal are connected by a negative electrode lead 15. Next, a nonaqueous electrolyte is injected into the battery case 18, and the opening of the battery case 18 is sealed using the sealing plate 19. Thereby, the nonaqueous electrolyte secondary battery 1 is obtained.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
Example 1
(1) Preparation of non-aqueous electrolyte A mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 10:30 was prepared. To this, 2% by weight of vinylene carbonate was added to obtain a mixed solution. LiPF ₆ was dissolved in this mixed solution at a concentration of 1.5 mol / L to prepare a nonaqueous electrolytic solution.
(2) Separator A polyethylene microporous sheet (manufactured by Asahi Kasei Chemicals Corporation) having a thickness of 20 μm was used as the separator.

(3) Production of Positive Electrode Cobalt sulfate and aluminum sulfate were added to an NiSO ₄ aqueous solution so that Ni: Co: Al = 7: 2: 1 (molar ratio) to prepare an aqueous solution having a metal ion concentration of 2 mol / L. While stirring this aqueous solution, a 2 mol / L sodium hydroxide solution was gradually added and neutralized to neutralize a ternary precipitate having a composition represented by Ni _0.7 Co _0.2 Al _0.1 (OH) _2. It was produced by a sedimentation method. This precipitate was separated by filtration, washed with water, and dried at 80 ° C. to obtain a composite hydroxide. As a result of measuring the average particle diameter of the obtained composite hydroxide with a particle size distribution meter (trade name: MT3000, manufactured by Nikkiso Co., Ltd.), the average particle diameter was 10 μm.

This composite hydroxide was heated in the atmosphere at 900 ° C. for 10 hours for heat treatment to obtain a ternary composite oxide having a composition represented by Ni _0.7 Co _0.2 Al _0.1 O. Here, lithium hydroxide monohydrate is added so that the sum of the number of atoms of Ni, Co and Al and the number of atoms of Li are equal, and heat treatment is performed by heating at 800 ° C. for 10 hours in the air. by performing, to obtain a lithium-nickel-containing composite metal oxide having a composition represented by _{LiNi 0.7 Co 0.2 Al 0.1 O 2} . As a result of analyzing this lithium-containing composite metal oxide by powder X-ray diffraction, it was confirmed that the lithium-containing composite metal oxide had a single-phase hexagonal layered structure, and that Co and Al were in solid solution. Thus, a positive electrode active material having an average secondary particle size of 10 μm and a specific surface area by the BET method of 0.45 m ² / g was obtained.

  95 parts by weight of the positive electrode active material powder obtained above and 5 parts by weight of a mixture of acetylene black and polyethylene (PTC element, 5:95 on a weight basis) were mixed, and the resulting mixture was mechanized in an argon gas atmosphere. A fusion apparatus (trade name: AM-15F, manufactured by Hosokawa Micron Corporation, stirring power: 0.5 kW, casing rotational speed: 1200 rpm) was charged, and the surface of the lithium nickelate powder was covered with a PTC element. When the obtained lithium nickelate powder after the coating treatment was observed with a scanning electron microscope, the entire surface of the lithium nickelate powder was covered with the PTC element.

  Mixing 100 parts by weight of the lithium nickelate powder after coating, 2 parts by weight of polyvinylidene fluoride resin (binder, manufactured by Kureha Co., Ltd.) and 40 parts by weight of dehydrated N-methyl-2-pyrrolidone (NMP, dispersion medium) Then, a positive electrode mixture paste was prepared. The positive electrode mixture paste was applied to a positive electrode current collector (thickness: 15 μm) made of an aluminum foil using a comma coater. Thereafter, the positive electrode mixture was dried (at 60 ° C.) and rolled to form a positive electrode mixture layer having a thickness of 130 μm, thereby producing a positive electrode.

(4) Production of negative electrode Artificial graphite powder (negative electrode active material, volume-based median diameter 20 μm, manufactured by Hitachi Chemical Co., Ltd.) 100 parts by weight, polyethylene resin (binder, manufactured by Mitsui Chemicals, Inc.) 1 part by weight And 1 part by weight of carboxymethyl cellulose (thickener, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was mixed. An appropriate amount of water was added to the obtained mixture and kneaded to prepare a negative electrode mixture paste. The negative electrode mixture paste was applied to a negative electrode current collector (thickness 10 μm) made of copper foil. Thereafter, the negative electrode mixture was dried at 100 ° C. for 5 minutes and rolled to form a negative electrode mixture layer having a thickness of 160 μm, thereby preparing a negative electrode.

(5) Production of Cylindrical Battery Using the positive electrode, negative electrode, separator, and nonaqueous electrolyte obtained above, the cylindrical nonaqueous electrolyte secondary battery 1 shown in FIG. 1 was produced.
The positive electrode 11, the separator 13, and the negative electrode plate 12 were superposed in this order and wound in a spiral shape to produce a wound electrode group. An upper insulating plate 16 was attached to the upper part of the wound electrode group, and a lower insulating plate 17 was attached to the lower part. This was housed in an iron battery case 18 having an inner surface plated with nickel. One end of the positive electrode lead 14 made of aluminum was connected to the positive electrode 11, and the other end was connected to the back surface of the sealing plate 19 conducted to the positive electrode terminal 20. One end of the nickel negative electrode lead 15 was connected to the negative electrode 12, and the other end was connected to the bottom of the battery case 18. Next, a predetermined amount of nonaqueous electrolyte was injected into the battery case 18. The opening end of the battery case 18 was caulked to the sealing plate 19 and the opening of the battery case 18 was sealed to produce the cylindrical nonaqueous electrolyte secondary battery of the present invention.

(Example 2)
A nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 1 except that the surface of the lithium nickelate powder was coated with a PTC element using a kneader. The melt kneader method was carried out under the conditions of an inlet temperature of 250 ° C. and an outlet temperature of 210 ° C. using a continuous twin-screw kneader (trade name: KRC Kneader, manufactured by Kurimoto Steel Works). .

(Examples 3 to 6)
Except for changing the usage amount of the active material, the usage amount of the conductive material, the type and usage amount of the PTC element, and the mixing method of the active material and the PTC element, as shown in Table 1, Non-aqueous electrolyte secondary batteries for invention and comparison were prepared. The PTC element of Example 6 was produced in the same manner as Example 1 except that BaTiO ₃ was used instead of acetylene black. In Table 1, AB: acetylene black, KS: graphite, PE: polyethylene.

(Example 7)
95 parts by weight of lithium nickelate powder (positive electrode active material) and 5 parts by weight of a mixture of acetylene black and polyethylene (PTC element, 5:95 by weight) were mixed, and the resulting mixture was stirred in an argon gas atmosphere. A granulator (trade name: SPG-25 type, manufactured by Fuji Powder Co., Ltd., stirring blade 250 rpm, high speed chopper 3000 rpm) was put in, and a plurality of PTC elements were adhered to the surface of the lithium nickelate powder. When the obtained lithium nickelate powder after treatment was observed with a scanning electron microscope, a plurality of PTC elements adhered to the entire surface of the lithium nickelate powder.
A nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 1 except that this lithium nickelate powder with the PTC element attached was used as the positive electrode active material.

(Example 8)
95 parts by weight of lithium nickelate powder (positive electrode active material) and 5 parts by weight of a mixture of acetylene black and polyethylene (PTC element, 5:95 on a weight basis) are mixed, and the resulting mixture is fluidly coated in an argon gas atmosphere. As a method, it was introduced into a multiplex (trade name: MP-01, supply air temperature 80 ° C., rotor rotation speed 300 rpm, supply air flow 40 m ³ / hr, manufactured by POWREC Co., Ltd.), and PTC element on the surface of the lithium nickelate powder The protrusion part which protruded was provided. When the obtained lithium nickelate powder after treatment was observed with a scanning electron microscope, protrusions from which the PTC element protruded were provided on the entire surface of the lithium nickelate powder.
A nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 1 except that this lithium nickelate powder with the PTC element attached was used as the positive electrode active material.

(Comparative Examples 1-3)
Except for changing the usage amount of the active material, the usage amount of the conductive material, the type and usage amount of the PTC element, and the mixing method of the active material and the PTC element, as shown in Table 1, Non-aqueous electrolyte secondary batteries for invention and comparison were prepared. In Table 1, AB: acetylene black, KS: graphite, PE: polyethylene.

About the nonaqueous electrolyte secondary battery obtained in Examples 1-8 and Comparative Examples 1-3, the overcharge test was implemented and the highest ultimate temperature (degreeC) of the battery was calculated | required. The overcharge test was performed as follows.
The nonaqueous electrolyte secondary batteries obtained in Examples 1 to 8 and Comparative Examples 1 to 3 are discharged to a battery voltage of 3.0V. Thereafter, an electric wire was welded to the sealing plate and the bottom of the case, and the suspension plate was suspended in a 25 ° C. constant temperature bath. An overcharge test was performed under the conditions of a current value of 5 A and a maximum voltage of 12 V using a charging power source. A thermocouple was installed at the center of the battery, and the battery temperature was measured.

  From Table 1, the highest attained temperature in the batteries of Examples 1 to 8 is 15 ° C. or more lower than the highest attained temperature in the batteries of Comparative Examples 1 to 3, and the batteries of Examples 1 to 8 have high safety. It is clear that This is because, in the batteries of Examples 1 to 8, a PTC element is interposed between active materials or between an active material and a conductive material, and the PTC element functions as a good conductor in a non-heat generation state, but is not a conductor in a heat generation state. It is presumed that this is caused by blocking the conductive network between the active materials or between the active material and the conductive material. That is, in the present invention, since the PTC element exists as a part of the conductive network in the active material layer, the conductive network is cut off during heat generation, the energization to the active material is stopped, and the heat generation due to the energization to the active material. Can be suppressed.

  On the other hand, in Comparative Examples 2 and 3, since the PTC element does not necessarily exist as a part of the conductive network in the active material layer, even if the PTC element becomes non-conductive due to heat generation of the battery, the conductive network is almost complete. It is not cut off and energization of the active material cannot be avoided. As a result, despite the presence of the PTC element, heat generation of the battery proceeds and the battery tends to be overheated.

  The nonaqueous electrolyte secondary battery of the present invention can be used for the same applications as conventional nonaqueous electrolyte secondary batteries. In particular, it can be suitably used as a power source for various portable electronic devices such as a mobile phone, a notebook personal computer, a portable information terminal, an electronic dictionary, and a game device. When used for such applications, even if the battery is overcharged during charging, heat generation is suppressed, so that thermal runaway, battery rupture, and the like are reliably prevented. The nonaqueous electrolyte secondary battery of the present invention can also be applied to uses such as for power storage, transportation equipment such as electric vehicles and hybrid vehicles.

It is a longitudinal section showing typically the composition of the nonaqueous electrolyte secondary battery which is one of the embodiments of the present invention. It is a longitudinal cross-sectional view which shows typically the structure of the electrode in the nonaqueous electrolyte secondary battery of this invention. 2 is a longitudinal sectional view schematically showing a configuration of a positive electrode in a battery of Patent Document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode 2 Electrode core material 3 Active material layer 4 Active material 5 Conductive material which has positive resistance temperature characteristic 6 Binder 10 Nonaqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead 15 Negative electrode lead 16 Upper insulation Plate 17 Lower insulating plate 18 Battery case 19 Sealing plate 20 Positive terminal

Claims (8)

A non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator and a non-aqueous electrolyte,
At least one of the positive electrode active material layer and the negative electrode active material layer is present together with the active material or the active material and the conductive material so as to be in contact with each other between the active materials or between the active material and the conductive material, and has a positive resistance temperature. A non-aqueous electrolyte secondary battery containing a conductive material having characteristics.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the conductive material having a positive resistance temperature characteristic is 1 to 15 parts by weight with respect to 100 parts by weight of the active material.   At least one of the positive electrode active material layer and the negative electrode active material layer contains an active material, a conductive material, and a conductive material having a positive resistance temperature characteristic, and the content of the conductive material having a positive resistance temperature characteristic is The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the amount is 100 to 500 parts by weight with respect to 100 parts by weight of the material.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a coating layer containing a conductive material having a positive resistance temperature characteristic is provided on the particle surface of the active material.   The nonaqueous electrolyte secondary battery according to claim 4, wherein the thickness of the layer containing a conductive substance having positive resistance temperature characteristics is 0.1 to 10 μm.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a plurality of particles containing a conductive material having a positive resistance temperature characteristic are attached to the particle surface of the active material.   The active material particle surface includes at least part of a conductive material having a positive resistance temperature characteristic, and is provided with a protrusion protruding outward from the active material particle surface. The nonaqueous electrolyte secondary battery as described in any one of these.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the conductive material having a positive resistance temperature characteristic changes from a conductor to a nonconductor in a temperature range of 130 ° C. or less.

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