JP2009245922A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of exhibiting excellent charge discharge cycle characteristics and high temperature storage characteristics even if high voltage charge discharge is performed. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a positive electrode containing a lithium-containing composite oxide represented by general formula: Li<SB>1+x+α</SB>M<SB>1-x</SB>O<SB>2</SB>(wherein M represents at least two element containing at least one element selected from Co and Ni and at least one element selected from Al and Mg, a ratio of Co to Ni of the element M is 50-99.8 atom% in total; -0.05≤x≤0.1; -0.05≤α≤0.1) and a nonaqueous electrolyte to which a silane compound represented by general formula (1) is added. In general formula (1), R<SP>1</SP>to R<SP>4</SP>are 1-6C organic substituent or halogen element; and either one of R<SP>1</SP>to R<SP>4</SP>is 3-6C alkenyl group or 2-6C alkynyl group, and hydrogen in the organic substituent may be substituted with a halogen element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery having a non-aqueous electrolyte that has a high voltage and a high capacity and is excellent in charge / discharge cycle performance and high-temperature storage characteristics.

  Non-aqueous electrolyte secondary batteries are characterized by high voltage (operating voltage 4.2V) and high energy density, so they are widely used in the field of portable information devices, and their demand is rapidly expanding. Position as a standard battery for mobile information devices such as mobile phones and notebook computers has been established. Of course, along with higher performance and multi-functionality of portable devices, etc., even higher performance (for example, higher capacity and higher energy density) will be provided for non-aqueous electrolyte secondary batteries as power sources. It has been demanded. In order to meet this demand, various methods such as higher density by improving the filling rate of electrodes, improvement of the depth of use of current active materials (especially negative electrodes), development of new high-capacity active materials, etc. have been carried out. Yes. In reality, the capacity of the non-aqueous electrolyte secondary battery is reliably increased by these methods.

Further, in order to further increase the capacity of the non-aqueous electrolyte secondary battery, improvement in the utilization rate of the positive electrode active material and development of a high voltage material are required. Among these, the improvement of the utilization depth of the positive electrode active material due to the increase in the charging voltage has attracted attention. For example, a cobalt composite oxide (LiCoO ₂ ), which is an active material of a non-aqueous electrolyte secondary battery with an operating voltage of 4.2 V class, has a charge capacity of about 155 mAh / g when charged to 4.3 V based on the current Li standard. On the other hand, when charged to 4.50 V, it is about 190 mAh / g or more. Thus, the utilization rate of a positive electrode active material becomes large by the improvement of a charging voltage.

  However, as the voltage of the battery increases, the capacity and energy density of the battery improve, while problems such as deterioration of charge / discharge cycle characteristics and swelling during high-temperature storage occur.

  Conventionally, various techniques for solving problems such as a decrease in charge / discharge cycle of a battery and swelling of the battery have been proposed. For example, non-aqueous electrolyte secondary batteries that have already been put into practical use mainly include non-aqueous electrolytes having a mixed solvent of cyclic esters such as ethylene carbonate and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Although an electrolytic solution is used, a technique for solving the above-mentioned problems occurring in a non-aqueous electrolyte secondary battery by adding an additive such as vinylene carbonate and a specific cyclic sulfate to the non-aqueous electrolyte. (For example, see Patent Documents 1 to 4). When a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing the additive is charged, a dense film derived from the additive is formed on the negative electrode surface, and this film forms an organic solvent in the non-aqueous electrolyte. And the negative electrode are continuously suppressed. Therefore, it is considered that the battery capacity can be prevented from decreasing and the battery is swollen due to gas generation as the subsequent charge / discharge cycle progresses, and the charge / discharge cycle characteristics of the battery can be improved.

Also suitable for use in high-temperature atmospheres by using non-aqueous electrolytes of secondary batteries and primary batteries to which cyclic sultone derivatives and acid anhydrides are added to suppress swelling due to gas generation in the batteries. There has also been proposed a technique for providing a battery (Patent Document 5).
JP-A-10-189042 JP 2003-151623 A JP 2003-308875 A JP 2004-22523 A JP 2004-47413 A

  However, the techniques of Patent Documents 1 to 5 do not assume a case where the potential of the positive electrode in a charged state of the battery becomes a high voltage such as 4.35 V or more on the basis of Li. However, it is not possible to sufficiently achieve reduction in charge / discharge cycle characteristics in secondary batteries charged at such a high voltage and suppression of swelling during high-temperature storage.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery that can exhibit excellent charge / discharge cycle characteristics and high-temperature storage characteristics even when high-voltage charging is performed. There is to do.

The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein the positive electrode has a general composition formula Li _{1 + x + α} M _1-x O ₂ (where M represents two or more elements including at least one element selected from Co and Ni and at least one element selected from Al and Mg; The ratio of Co and Ni in the element M is 50 to 99.8 atomic% in total, and is represented by −0.05 ≦ x ≦ 0.1 and −0.05 ≦ α ≦ 0.1. The lithium-containing composite oxide is contained, and the nonaqueous electrolytic solution is characterized in that a silane compound represented by the following general formula (1) is added.

［前記一般式（１）中、Ｒ^１〜Ｒ^４は、炭素数が１〜６の有機置換基またはハロゲン元素であり、Ｒ^１〜Ｒ^４のいずれか１つは、炭素数が３〜６のアルケニル基または炭素数が２〜６のアルキニル基であり、前記有機置換基の水素は、少なくとも一部がハロゲン元素で置換されていてもよい。］

[In General Formula (1), R ^{1 to} R ⁴ are an organic substituent having 1 to 6 carbon atoms or a halogen element, and any one of R ^{1 to} R ⁴ has 3 to 6 carbon atoms. Or an alkynyl group having 2 to 6 carbon atoms, and at least a part of hydrogen of the organic substituent may be substituted with a halogen element. ]

  In a non-aqueous electrolyte secondary battery charged at a high voltage, the metal oxide, which is the positive electrode active material, exhibits a very strong oxidizing property in a high potential state. Reacts with solvent and decomposes. As a result of intensive studies, the present inventors have determined that such a decomposition reaction of the non-aqueous electrolyte solvent causes deterioration of charge / discharge cycle characteristics in a non-aqueous electrolyte secondary battery charged at a high voltage and swelling during high-temperature storage. I found out that it was the cause of the outbreak. Then, by combining a positive electrode containing a specific lithium-containing composite oxide as an active material and a non-aqueous electrolyte containing a silane compound having a specific functional group, the above-described decomposition reaction of the non-aqueous electrolyte solvent is suppressed. Thus, the present inventors have found that charge / discharge cycle characteristics and high-temperature storage characteristics can be improved in a non-aqueous electrolyte secondary battery charged at a high voltage, and the present invention has been completed.

  ADVANTAGE OF THE INVENTION According to this invention, even if it performs high voltage charge, the nonaqueous electrolyte secondary battery which can exhibit the outstanding charging / discharging cycling characteristics and high temperature storage characteristic can be provided.

  In the positive electrode according to the battery of the present invention, for example, a conductive additive or a binder such as polyvinylidene fluoride is appropriately added to the positive electrode active material, and these are dissolved in a solvent such as N-methyl-2-pyrrolidone (NMP).・ Dispersed positive electrode mixture-containing composition (paste, slurry, etc.) is applied to one or both sides of a current collector such as an aluminum foil, and the solvent is removed to form a strip-shaped molded body (positive electrode mixture layer). Used. However, the manufacturing method of the positive electrode is not limited to the above-described examples.

The positive electrode active material includes a general composition formula Li _{1 + x + α} M _1-x O ₂ (where M is at least one element selected from Co and Ni and at least one element selected from Al and Mg). 2 or more elements are included, and the ratio of Co and Ni in the element M is 50 atomic% or more and 99.5 atomic% or less in total, −0.05 ≦ x ≦ 0.1, −0.05 ≦ a lithium-containing composite oxide represented by α ≦ 0.1 is used. Since the lithium-containing composite oxide has good stability in a high-voltage charge state, by using this as a positive electrode active material, a non-aqueous electrolyte secondary battery can be used, for example, the potential of the positive electrode after charging. Can be used under the condition that the utilization rate of the positive electrode active material is increased by charging under the condition that is 4.35 V or more on the basis of Li, so that the capacity of the battery can be easily increased. Moreover, the safety of the battery at the time of overcharge can also be improved.

  The lithium-containing composite oxide may contain only one of Co and Ni as the element M, or may contain both, but the capacity and the thermal stability are further improved. In order to make it favorable, it is preferable to contain both. Moreover, the said lithium containing complex oxide may contain any one among Al and Mg as the element M, and may contain both. In the lithium-containing composite oxide, if the ratio of Co and Ni in the element M is too small, the capacity of the battery is reduced. Therefore, the ratio of Co and Ni in the element M is a total (however, Co Or, when only one of Ni is contained, the ratio of one of them is the same hereinafter.), 50 atomic% or more, and preferably 60 atomic% or more. On the other hand, in the lithium-containing composite oxide, if the proportion of Co and Ni in the element M is too large, the proportion of Al and Mg becomes small, and the stability of the lithium-containing composite oxide in a high-voltage charge state decreases. Therefore, the ratio of Co and Ni in the element M is 99.8 atomic% or less in total, and preferably 99.5 atomic% or less.

  In the general composition formula relating to the lithium-containing composite oxide, in order to increase the uniformity of the composite oxide and increase the capacity, −0.05 ≦ x ≦ 0.1 and −0.05 ≦ α. ≦ 0.1.

  In the lithium-containing composite oxide, the ratio of Al and Mg in the element M is a total (however, in the case where only one of Al and Mg is contained, in order to improve charging stability at high voltage, One proportion (the same applies hereinafter)) is preferably 0.5 atomic percent or more, and in order to maintain high capacity, the total content is preferably 5 atomic percent or less.

  Further, as element M, in addition to Co, Ni, Al, and Mg, Mn, Zr, Fe, Ti, Ca, Nb, V, Cr, Mo, W, Cu, Zn, Ge, Si, Sn, and the like are included. Can do.

In the battery of the present invention, a positive electrode active material other than the lithium-containing composite oxide can be used in combination. As such a positive electrode active material, for example, Li _a CoO ₂ and a lithium-cobalt composite oxide having a layered structure including at least one additional element such as Al, Ge, Ti, Zr; Li _a NiO ₂ and further Ge Lithium / nickel composite oxide or lithium / titanium composite oxide having a layered structure containing at least one additive element such as Ti, Zr, and Al; metal oxides such as manganese dioxide, vanadium pentoxide, and chromium oxide; disulfide Examples thereof include metal sulfides such as titanium and molybdenum disulfide. Two or more of these may be used in combination and in combination.

  In the positive electrode of the present invention, the total content of the lithium-containing composite oxide in the total amount of the positive electrode active material to be used is, for example, preferably 80% by mass or more, and more preferably 90% by mass or more. In addition, all (namely, 100 mass%) of the positive electrode active material may be the lithium-containing composite oxide. By setting the amount of the lithium-containing composite oxide in the total amount of the positive electrode active material to be equal to or higher than the lower limit value, the effect of using this can be better ensured.

  As a composition in the positive mix layer in a positive electrode, content of a positive electrode active material is 90-98 mass%, content of a conductive support agent is 1-5 mass%, and content of a binder is 1-5, for example. It is preferable that it is mass%.

  The thickness of the positive electrode mixture layer is preferably 30 to 80 μm per one side of the current collector. Moreover, it is preferable that the thickness of a positive electrode electrical power collector is 5-25 micrometers.

  In the non-aqueous electrolyte secondary battery of the present invention, as described above, since the lithium-containing composite oxide is used as the positive electrode active material, the potential of the positive electrode after charging is 4.35 V or more on the basis of Li. High voltage charging is possible, thereby increasing the utilization rate of the positive electrode active material and improving the battery capacity. Note that the upper limit of the positive electrode potential in the charged state is not particularly limited, and may be set as appropriate depending on, for example, the stability of the active material and the voltage resistance of the current collector and the nonaqueous electrolyte solvent. In general, it is preferably 4.6 V or less, and more preferably 4.5 V or less, based on Li. Incidentally, the open circuit voltage of the non-aqueous electrolyte secondary battery is determined by the combination of the positive electrode potential and the negative electrode potential. For example, when a negative electrode using a high-crystal carbon material is used, the positive electrode potential is 4. When it is 35 V, the open circuit voltage of the battery is about 4.25 V (that is, there is a difference of about 0.1 V between the positive electrode potential and the open circuit voltage of the battery).

  In the positive electrode using the lithium-containing composite oxide, as described above, even when charged so that the potential is 4.35 V or more, these active materials are structurally and thermally stable at room temperature, for example. . However, when the positive electrode is charged at such a high potential and stored at a high temperature of, for example, 60 ° C. or higher, a reaction between the positive electrode active material and the non-aqueous electrolyte solvent occurs, and the battery swells and is charged / discharged. Since deterioration of characteristics and the like is likely to occur, the high-temperature storage characteristics of the battery are not necessarily sufficient.

  However, in the present invention, since the silane compound represented by the general formula (1) is contained in the non-aqueous electrolyte, the reaction with the non-aqueous electrolyte solvent on the positive electrode surface can be suppressed thereby. In addition to improving the charge / discharge cycle characteristics of the battery, the high-temperature storage characteristics can be enhanced such that swelling of the battery during high-temperature storage can be suppressed and good battery characteristics can be maintained. Moreover, the safety of the battery at the time of overcharge can also be improved.

As the nonaqueous electrolytic solution according to the battery of the present invention, a solution prepared by dissolving an electrolyte salt in an organic solvent which is an electrolytic solution solvent is used. The non-aqueous electrolyte contains a silane compound represented by the general formula (1). The non-aqueous electrolyte containing the silane compound may be prepared by adding and dissolving the silane compound in a solution obtained by dissolving the electrolyte salt in an organic solvent in advance. It may be added together and dissolved.

In the general formula (1) representing the silane compound, any one of R ^{1 to} R ⁴ is an alkenyl group having 1 to 6 carbon atoms (1-propenyl group, 2-propenyl group, 1 -Butenyl group, 2-butenyl group, 3-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, etc.) or an alkynyl group having 2 to 6 carbon atoms (ethynyl group, 1 -Propynyl group, 2-propynyl group, 1-butynyl group, 2-butynyl group, 1-pentynyl group, 2-pentynyl group, 1-hexynyl group, 2-hexynyl group and the like, and alkenyl having 3 to 4 carbon atoms It is preferably a group. In the alkenyl group or alkynyl group, at least a part of hydrogen may be substituted with a halogen element (F, Cl, Br, etc.).

In the general formula (1) representing the silane compound, among R ^{1 to} R ⁴ , those other than the alkenyl group having 3 to 6 carbon atoms and the alkynyl group having 2 to 3 carbon atoms have carbon numbers. 1 to 6 organic substituents or halogen elements (F, Cl, Br, etc.), which may be the same or different. Examples of the organic substituent having 1 to 6 carbon atoms include alkyl groups (methyl group, ethyl group, propyl group, butyl group, etc.), alkoxy groups, aryl groups, and the like. May be substituted with a halogen element (F, Cl, Br, etc.).

  The silane compound is also considered to have a function of forming a SEI (Solid Electrolyte Interface) film on the surface of the negative electrode. By forming the SEI film derived from the silane compound on the negative electrode surface, for example, even if elution of Co or Ni occurs from the positive electrode active material, precipitation on the negative electrode surface is suppressed.

  In addition, the silane compound has a feature that gas is hardly generated on the surface of the positive electrode. In conventional non-aqueous electrolyte secondary batteries, vinylene carbonate has often been used as an additive for forming an SEI film on the negative electrode. There was a risk of generating gas and causing battery swelling during high-temperature storage. However, since the silane compound is hardly oxidatively decomposed on the surface of the positive electrode, in the non-aqueous electrolyte secondary battery of the present invention, there is a possibility that the silane compound may be caused by gas generated due to oxidative decomposition of the additive for forming the SEI film. The deterioration of the discharge cycle characteristics and the high temperature storage characteristics can be suppressed.

  The content of the silane compound in the total amount of the non-aqueous electrolyte used in the battery of the present invention is 0.2% by mass or more from the viewpoint of ensuring the above-described effect better by using this. Preferably, it is 0.3 mass% or more. However, if the amount of the silane compound in the non-aqueous electrolyte is too large, the formed film becomes thick and the resistance may be increased. Therefore, the silane in the total amount of the non-aqueous electrolyte used in the battery The content of the compound is preferably 5% by mass or less, and more preferably 3% by mass or less.

  The organic solvent in the non-aqueous electrolyte preferably has a high dielectric constant, for example, ethers and esters are preferable. For example, the organic solvent preferably contains esters having a dielectric constant of 30 or more. Examples of esters having such a high dielectric constant include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfur-based esters (ethylene glycol sulfite, etc.), and the like. Among these, cyclic esters are preferable, and cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate are particularly recommended.

In addition to the above solvents, polar chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate (low viscosity polar chain carbonates); chain alkyl esters such as methyl propionate; trimethyl phosphate, etc. An organic solvent such as a chain phosphate triester; a nitrile solvent such as 3-methoxypropionitrile; and the like can be used.

Furthermore, a fluorine-based solvent can also be used. Examples of the fluorine-based solvent include H (CF ₂ ) ₂ OCH ₃ , C ₄ F ₉ OCH ₃ , H (CF ₂ ) ₂ OCH ₂ CH ₃ , H (CF ₂ ) ₂ OCH ₂ CF ₃ , H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H or the like, or (perfluoroalkyl) alkyl ether having a linear structure such as CF ₃ CHFCF ₂ OCH ₃ , CF ₃ CHFCF ₂ OCH ₂ CH ₃ , or iso (par Fluoroalkyl) alkyl ethers, that is, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ethyl ether, 2-trifluoromethyl hexafluoropropylpropyl ether, 3-trifluorooctafluorobutyl methyl ether 3-trifluorooctafluorobutyl ethyl ether, 3- Rifluorooctafluorobutylpropyl ether, 4-trifluorodecafluoropentyl methyl ether, 4-trifluorodecafluoropentyl ethyl ether, 4-trifluorodecafluoropentylpropyl ether, 5-trifluorododecafluorohexyl methyl ether, 5- Trifluorododecafluorohexyl ethyl ether, 5-trifluorododecafluorohexyl propyl ether, 6-trifluorotetradecafluoroheptyl methyl ether, 6-trifluorotetradecafluoroheptyl ethyl ether, 6-trifluorotetradecafluoroheptylpropyl ether 7-trifluorohexadecafluorooctyl methyl ether, 7-trifluorohexadecafluorooctyl ethyl ether, 7-trifluorohexadecafluorohexyl octyl ether Le and the like. Further, the iso (perfluoroalkyl) alkyl ether can be used in combination with the linear structure (perfluoroalkyl) alkyl ether.

Moreover, you may add the various additive which can improve the performance of a battery to the said non-aqueous electrolyte. For example, when a compound having a C═C unsaturated bond other than the silane compound is added to the electrolytic solution, the deterioration of the charge / discharge cycle characteristics of the battery may be further suppressed. Examples of the compound having such an unsaturated bond include fluorinated aliphatic compounds such as H (CF ₂ ) ₄ CH ₂ OOCCH═CH ₂ and F (CF ₂ ) ₈ CH ₂ CH ₂ OOCCH═CH ₂ . , Fluorine-containing aromatic compounds, vinylene carbonate, and the like.

  However, since the compound having a C═C unsaturated bond other than the silane compound may cause the battery to swell if the amount used is too large, the total amount of the non-aqueous electrolyte is used when using them. The amount in it is preferably 10% by mass or less.

As the electrolyte salt used in the non-aqueous electrolyte, lithium perchlorate, organoboron lithium salt, fluorine-containing compound salt represented by trifluoromethanesulfonate, imide salt, and the like are preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCnF _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ (Rf is a fluoroalkyl group) These may be used alone, or these may be used alone or in combination of two or more. Among these, LiPF ₆ and LiBF ₄ are preferable in that the charge / discharge characteristics of the battery are good. This is because such a fluorine-containing organic lithium salt is highly anionic and easily dissociates ions, so that it is easily dissolved in the solvent.

  The concentration of the electrolyte salt in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.5 mol / l or more, more preferably 0.8 mol / l or more, and preferably 1.7 mol. / L or less, more preferably 1.2 mol / l or less.

  The non-aqueous electrolyte secondary battery of the present invention is not limited as long as it has the positive electrode and the non-aqueous electrolyte, and there are no particular restrictions on other configurations and structures. Various configurations and structures used in secondary batteries can be employed.

  That is, the negative electrode according to the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and a negative electrode employed in a conventionally known nonaqueous electrolyte secondary battery can be used. For example, a negative electrode mixture containing a conductive additive, a binder such as polyvinylidene fluoride, styrene butadiene rubber, etc., as appropriate, added to the negative electrode active material, and dissolved and dispersed in a solvent such as water. A composition (paste, slurry, etc.) is applied to one or both sides of a current collector such as a copper foil, and the solvent is removed to form a strip-shaped molded body (negative electrode mixture layer). However, the manufacturing method of the negative electrode is not limited to the above-described examples.

  As the negative electrode active material, materials capable of inserting and extracting lithium can be used. For example, graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon micro beads, carbon fibers , Carbon materials such as activated carbon, metals composed of elements that can be alloyed with lithium, such as Si and Sn, or alloys containing the elements.

Among the negative electrode active material, an alloy containing the (002) plane of graphite plane spacing _{d 002} is less 0.340nm or metal consists of lithium can be alloyed elements, or said element _{preferably, d 002} Is particularly preferable. This is because the use of such an active material can realize further increase in capacity of the battery. The lower limit value of d ₀₀₂ is not particularly limited, but is theoretically about 0.335 nm.

In graphite with d ₀₀₂ of 0.340 nm or less, the crystallite size Lc in the c-axis direction in the crystal structure is preferably 3 nm or more, more preferably 8 nm or more, and 25 nm or more. Is more preferable. This is because, when such Lc is contained, insertion and extraction of lithium becomes easier. The upper limit of Lc is not particularly limited, but is usually about 200 nm. The average particle size of the graphite is preferably 3 μm or more, more preferably 5 μm or more, preferably 15 μm or less, more preferably 13 μm or less, and its purity is 99.9% or more. Is preferred. This is because the graphite having such a particle size and purity is easy to obtain, with no trouble in properties and low cost. In the present specification, d ₀₀₂ and Lc in the graphite are values measured by an X-ray diffraction method.

In particular, when highly crystalline graphite such as graphite having a d ₀₀₂ of 0.340 nm or less is used as the negative electrode active material, the nonaqueous electrolyte solvent tends to be reductively decomposed on the negative electrode surface. By containing the silane compound represented by the above general formula in the electrolytic solution, for example, in the above-described content, the secondary decomposition of the nonaqueous electrolytic solution with excellent battery characteristics is suppressed by suppressing the reductive decomposition of the organic solvent. It can be a battery.

  As the composition in the negative electrode mixture layer in the negative electrode, for example, when a negative electrode active material that requires the use of a binder is used, the content of the negative electrode active material is 90 to 98% by mass, and the binder is contained. The amount is preferably 1 to 5% by mass. Moreover, when using a conductive support agent, it is preferable that content of the conductive support agent in a negative mix layer is 1-5 mass%, for example.

  The thickness of the negative electrode mixture layer is preferably 50 to 100 μm per side of the current collector, and the thickness of the negative electrode current collector is preferably 5 to 15 μm.

  In the non-aqueous electrolyte secondary battery of the present invention, as the separator, it is preferable that the separator has sufficient strength and can hold a large amount of the electrolyte. From such a viewpoint, the thickness is 10 to 50 μm and the aperture ratio is 30 to 70. %, A microporous film or a nonwoven fabric containing polyethylene, polypropylene, or ethylene-propylene copolymer is preferable.

  In addition to the separator, a separator layer (I) composed of a microporous film mainly composed of a thermoplastic resin having a melting point of 80 to 140 ° C. and a porous layer mainly comprising inorganic particles having a heat resistant temperature of 150 ° C. or more. A laminated separator having a separator layer (II) can be used.

  The laminated separator preferably contains plate-like particles in at least one of the separator layer (I) and the separator layer (II).

  The separator layer (I) in the laminated separator is mainly for ensuring a shutdown function. When the temperature of the electrochemical element incorporating the separator reaches or exceeds the melting point of the thermoplastic resin of the separator layer (I), the thermoplastic resin melts to block the pores of the separator, and the electrochemical reaction proceeds. Causes a shutdown to be suppressed.

  In addition, the separator layer (II) in the laminated separator has an original function of the separator, mainly a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode, and an inorganic particle having a heat resistant temperature of 150 ° C. or higher. The function is secured by. That is, in the temperature range where an electrochemical element is normally used by the separator layer (II), when the positive electrode and the negative electrode are pressed through the separator to form an electrode body, the positive electrode active material penetrates the separator and the negative electrode The occurrence of a short circuit due to contact with can be prevented. In addition, when the electrochemical device is at a high temperature, even if the separator layer (I) shrinks, the separator layer (II) which does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally contracted. It is also possible to prevent short circuit due to contact. Except for the porous substrate described later, “heat-resistant temperature is 150 ° C. or higher” in this specification means that deformation such as softening is not observed at least at 150 ° C.

  Furthermore, in the laminated separator, it is preferable that at least one of the separator layer (I) and the separator layer (II) contains plate-like particles. When at least one of the separator layer (I) and the separator layer (II) contains plate-like particles, a path between the positive electrode and the negative electrode in the separator, that is, a so-called curvature is increased. Therefore, in the non-aqueous electrolyte secondary battery using the laminated separator, even when dendrite is generated, the dendrite is difficult to reach from the negative electrode to the positive electrode, and the reliability against a dendrite short can be improved. When the separator layer (II) contains plate-like particles, the plate-like particles can also serve as “inorganic particles having a heat-resistant temperature of 150 ° C. or higher”, and the inorganic particles contained in the separator layer (II) At least a part can be composed of plate-like particles.

  In the separator layer (I) in the present specification, “having a thermoplastic resin as a main component” means a solid content ratio in the microporous film constituting the separator layer (I), and the thermoplastic resin is 50% by volume or more. It means that. Further, in the separator layer (II) in this specification, “mainly containing inorganic particles having a heat-resistant temperature of 150 ° C. or higher” means a solid content ratio in the layer (however, in the case of having a porous substrate described later) The solid content ratio excluding the porous substrate) means that the inorganic particles having a heat-resistant temperature of 150 ° C. or more are 50% by volume or more.

  The thermoplastic resin in the separator layer (I) has a melting point of 80 to 140 ° C. The melting point of the thermoplastic resin can be determined by, for example, the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

  As the thermoplastic resin, there is an electrochemically stable material that has electrical insulation, is stable with respect to the electrolyte solution of the electrochemical element, and is not easily oxidized and reduced in the operating voltage range of the battery. preferable. Specific examples include polyethylene (PE), copolymerized polyolefin, or polyolefin derivative (such as chlorinated polyethylene), polyolefin wax, petroleum wax, carnauba wax, and the like. Examples of the copolymer polyolefin include an ethylene-vinyl monomer copolymer, more specifically, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer (EVA), an ethylene-methyl acrylate copolymer, and ethylene. Examples thereof include ethylene-acrylic acid copolymers such as ethyl acrylate copolymer. The ethylene-derived structural unit in the copolymerized polyolefin is desirably 85 mol% or more. Moreover, polycycloolefin etc. can also be used. As the thermoplastic resin, one of the above exemplified resins may be used alone, or two or more of them may be used.

  Among the materials exemplified above, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is preferably used as the thermoplastic resin. Further, the thermoplastic resin may contain various known additives (for example, antioxidants) added to the resin as necessary.

  The separator layer (I) is composed of a microporous film containing the above resin as a main component. As such a microporous film, for example, a microporous film made of a polyolefin (such as a copolymer polyolefin such as PE or ethylene-propylene copolymer) used in an electrochemical element such as a conventionally known lithium secondary battery That is, it is possible to use a film or sheet formed using a polyolefin mixed with inorganic particles or the like and formed with fine pores by uniaxial or biaxial stretching. In addition, the above thermoplastic resin and other resin are mixed to form a film or sheet, and then the film or sheet is immersed in a solvent that dissolves only the other resin, so that only the other resin is mixed. What melt | dissolved and formed the void | hole can also be used as a separator layer (I).

  In order to make it easier to obtain the shutdown effect, the content of the thermoplastic resin in the laminated separator is preferably as follows, for example. The volume of the thermoplastic resin in all the constituent components of the separator is preferably 10% by volume or more, and more preferably 20% by volume or more. Further, the volume of the thermoplastic resin is preferably 50% by volume or more, more preferably 70% by volume or more, and more preferably 80% by volume or more in all the constituent components of the separator layer (I). preferable. Furthermore, the porosity of the separator layer (II) obtained by the method described later is 10 to 50%, and the volume of the thermoplastic resin is 50% or more of the pore volume of the separator layer (II). preferable.

  The inorganic particles in the separator layer (II) have heat resistance and electrical insulation, are stable to the electrolyte and the solvent used in the production of the separator, and are oxidized and reduced within the operating voltage range of the battery. Any material that is difficult and electrochemically stable may be used.

Specific examples of the constituent material of the inorganic particles include inorganic oxides such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , and ZrO ₂ ; inorganic nitrides such as aluminum nitride and silicon nitride; Insoluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate; Covalent crystals such as silicon and diamond; clays such as montmorillonite; Here, the inorganic oxide may be a mineral resource-derived substance such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or an artificial product thereof. In addition, the surface of a conductive material exemplified by metal, SnO ₂ , conductive oxide such as tin-indium oxide (ITO), carbonaceous material such as carbon black, graphite, etc., is a material having electrical insulation ( For example, the particle | grains which gave electrical insulation property by coat | covering with said inorganic oxide etc. may be sufficient. Among the above inorganic oxides, Al ₂ O ₃ , SiO ₂ and boehmite are particularly preferably used.

The shape of the inorganic particles may be, for example, a shape close to a sphere or a plate shape, but is preferably a plate-like particle from the viewpoint of preventing a short circuit. Typical examples of the plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite.

  The inorganic particles are preferably fine particles from the viewpoint of dispersion and the like, and the average particle size is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 15 μm or less. Preferably it is 5 micrometers or less. The average particle size of the fine particles [inorganic particles, plate-like particles described later, thermoplastic resin described later] used in the present specification is, for example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). In the case of inorganic particles, the number average particle diameter measured by dispersing these fine particles in a medium that does not dissolve them in the case of thermoplastic resins, and in the case of thermoplastic resins in a medium that does not swell these resins (for example, water) Can be prescribed.

  In order to improve the effect of preventing internal short circuit, the content of the inorganic particles is preferably 20% by volume or more and more preferably 50% by volume or more in all the constituent components of the separator. Moreover, in order to ensure the content of the resin in the separator and maintain the shutdown characteristics, the content of the inorganic particles in all the constituent components of the separator is preferably suppressed to 80% by volume or less.

  The separator layer (II) mainly containing inorganic particles can contain the following fibrous material, the above resin, and other additive particles. As described above, the separator layer (II) is mainly used. In addition, it is intended to ensure the original function as a separator for preventing a short circuit between the positive and negative electrodes. If the content of inorganic particles in the separator layer (II) is small, it is difficult to ensure this function. Therefore, the content of inorganic particles in the separator layer (II) is 50% by volume or more in the total solid content (when using the porous substrate described later, the total solid content excluding the porous substrate). Is more preferable, 70% by volume or more is more preferable, and 80% by volume or more is further preferable.

  In the separator, it is preferable that at least one of the separator layer (I) and the separator layer (II) contains plate-like particles. When the separator layer (II) contains plate-like particles, the plate-like particles can also serve as the inorganic particles as described above.

  Examples of the method for incorporating the plate-like particles into the separator layer (I) include the following methods. For example, as a separator layer (I), a microporous film produced through a process of forming fine pores by uniaxially or biaxially stretching a film or sheet formed using polyolefin mixed with inorganic particles or the like In the case of using, a method of using plate-like particles is mentioned as the inorganic particles for pore formation. In addition, the above thermoplastic resin and other resin are mixed to form a film or sheet, and then the film or sheet is immersed in a solvent that dissolves only the other resin, so that only the other resin is mixed. In the case of using a microporous membrane prepared through a step of dissolving and forming pores, a plate-like particle is further mixed with a mixture of a thermoplastic resin and another resin to produce a microporous membrane. The method to use is mentioned.

  As the form of the plate-like particles, it is desirable that the aspect ratio is 5 or more, more preferably 10 or more, and 100 or less, more preferably 50 or less. Further, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction (length in the major axis direction / length in the minor axis direction) of the flat plate surface of the grain is 3 or less, more preferably 2 or less and close to 1. It is desirable to be a value.

  In addition, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface in the plate-like particles can be obtained, for example, by image analysis of an image taken with a scanning electron microscope (SEM). it can. Further, the above aspect ratio of the plate-like particles can also be obtained by image analysis of an image taken by SEM.

  Further, the average particle size of the plate-like particles may be smaller than the thickness of the separator, and is preferably 1/100 or more of the thickness of the separator. More specifically, the number average particle diameter measured by the above-described measurement method is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 5 μm or less. It is.

  The presence form of the plate-like particles in the separator is preferably such that the flat plate surface is substantially parallel to the surface of the separator. More specifically, for the plate-like particles near the surface of the separator, the flat plate surface and the separator The average angle with the surface is preferably 30 ° or less [most preferably, the average angle is 0 °, that is, the plate-like flat plate surface near the surface of the separator is parallel to the surface of the separator] . Here, “near the surface” refers to a range of about 10% from the surface of the separator to the entire thickness. When the presence state of the plate-like particles is as described above, it is possible to more effectively prevent an internal short circuit from occurring due to the lithium dendrite deposited on the electrode surface or the projection of the active material on the electrode surface.

As the plate-like particles, in addition to the inorganic fine particles (typically plate-like Al ₂ O ₃ and plate-like boehmite) exemplified above as specific examples of the plate-like inorganic particles, the heat resistant temperature is 150 ° C. The above resin materials can also be used. Two or more kinds of the constituent materials of the plate-like particles can be used in combination.

  In addition, in order to exhibit the effect by including a plate-like particle in at least one of the separator layer (I) and the separator layer (II) more effectively, the content of the plate-like particle is the total component of the separator. It is preferably 25% or more, more preferably 40% or more, in the total volume (however, when a porous substrate described later is used, in the total volume of all components excluding the porous substrate). 70% or more is more preferable.

  The plate-like particles are more preferably contained in the separator layer (II), and in the separator layer (II), the inorganic particles are more preferably plate-like particles.

  The separator layer (II) preferably contains an organic binder for ensuring the shape stability of the separator. As the organic binder, EVA (with a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, fluorine-based rubber, styrene-butadiene rubber (SBR), Examples include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. A heat-resistant binder having a heat-resistant temperature is preferably used. As the organic binder, those exemplified above may be used alone or in combination of two or more. The content of the organic binder in the separator layer (II) is preferably 1 or more with respect to the inorganic particles 100 in terms of weight ratio in order to improve the shape stability of the separator.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar's EEA, Daikin Industries'" Daiel Latex Series (Fluororubber) ", JSR's" TRD-2001 (SBR) ", Nippon Zeon's" EM-400B " (SBR) ".

  In addition, when using said organic binder, what is necessary is just to use it with the form of the emulsion dissolved or disperse | distributed to the solvent of the composition for separator layer (II) formation mentioned later.

  Further, in order to ensure the shape stability and flexibility of the separator, a fibrous material or the like may be mixed with inorganic particles in the separator layer (II). The fibrous material has a heat-resistant temperature of 150 ° C. or higher, has an electrical insulation property, is electrochemically stable, and further uses an electrolyte solution described in detail below and a solvent used in manufacturing a separator. If it is stable, the material is not particularly limited. The “fibrous material” in the present specification means an aspect ratio [length in the longitudinal direction / width in the direction perpendicular to the longitudinal direction (diameter)] of 4 or more. The ratio is preferably 10 or more.

  Specific examples of the constituent material of the fibrous material include, for example, cellulose and modified products thereof [carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), etc.], polyolefin [polypropylene (PP), propylene copolymer, etc.], Polyesters [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.], polyacrylonitrile (PAN), polyaramid, polyamideimide, polyimide and other resins; glass, alumina, zirconia, silica and other inorganic materials An oxide; etc. can be mentioned, and two or more of these constituent materials may be used in combination to form a fibrous material. The fibrous material may contain various known additives (for example, an antioxidant in the case of a resin) as necessary.

  Moreover, in order to improve the handleability when the laminated separator is used as an independent film, a porous substrate can be used in the separator layer (II). The porous substrate has a heat resistant temperature of 150 ° C. or more formed by forming a sheet-like material such as a woven fabric or a nonwoven fabric (including paper), and a commercially available nonwoven fabric or the like is used as the substrate. Can do. In the separator of this aspect, it is preferable to contain inorganic particles in the voids of the porous substrate, but the above organic binder can also be used to bind the porous substrate and the inorganic particles.

  The “heat resistance” of the porous substrate means that a substantial dimensional change due to softening or the like does not occur, and the change in the length of the object, that is, the porous substrate with respect to the length at room temperature. The heat resistance is evaluated based on whether or not the upper limit temperature (heat resistance temperature) at which the shrinkage ratio (shrinkage ratio) can be maintained at 5% or less is sufficiently higher than the shutdown temperature. In order to increase the safety of the electrochemical device after shutdown, the porous substrate preferably has a heat resistant temperature that is 20 ° C. or more higher than the shutdown temperature. More specifically, the heat resistant temperature of the porous substrate is 150 ° C. It is preferable that the temperature is higher than or equal to ° C, and more preferably higher than or equal to 180 ° C.

  When the separator layer (II) is formed using a porous substrate, inorganic particles (including plate-like particles) or when using fine particles of thermoplastic resin fine particles in the separator layer (II) In addition, it is preferable that all or part of the inorganic particles and these fine particles exist in the voids of the porous substrate. By setting it as such a form, the effect | action of an inorganic particle etc. can be exhibited more effectively.

  The diameter of the fibrous material (including the fibrous material constituting the porous substrate and other fibrous materials) may be equal to or less than the thickness of the separator layer (II), and is, for example, 0.01 to 5 μm. Is preferred. If the diameter is too large, the entanglement between the fibrous materials is insufficient. For example, when a porous substrate is formed by forming a sheet-like material, the strength may be reduced and handling may be difficult. On the other hand, if the diameter is too small, the gap of the separator becomes too small, and the ion permeability tends to be lowered, and the load characteristics of the electrochemical device may be lowered.

  The content of the fibrous material in the separator is, for example, 10% by volume or more, more preferably 20% by volume or more, and 90% by volume or less, more preferably 80% by volume or less, in all the constituent components. desirable. The state of the presence of the fibrous material in the separator is, for example, that the angle of the long axis (long axis) with respect to the separator surface is preferably 30 ° or less on average, and more preferably 20 ° or less. .

  When the fibrous material is used as the porous substrate, the content of other components is adjusted so that the proportion of the porous substrate is 10% by volume or more and 90% by volume or less in all the constituent components of the separator. It is desirable to adjust.

  The separator layer (II) may contain the above thermoplastic resin. The form of the resin to be contained in the separator layer (II) is not particularly limited. In addition to fine particles, for example, in the separator layer (II), the fibrous material constituting the porous substrate is used as a core material on the surface. A separator may be contained in the separator layer (II) by attaching a thermoplastic resin or coating the surface thereof with a thermoplastic resin. Further, the separator layer (II) may be contained in the separator layer (II) in the form of a core-shell structure in which the above-mentioned “inorganic particles having a heat-resistant temperature of 150 ° C. or higher” in the separator layer (II) or the like is used as the core. . As the thermoplastic resin, it is preferable to use fine particles.

  In the case of a particulate thermoplastic resin, it is sufficient that these particle sizes at the time of drying are smaller than the thickness of the separator, but preferably have an average particle size of 1/100 to 1/3 of the thickness of the separator. Specifically, the average particle size of the thermoplastic resin is preferably 0.1 to 20 μm. When the particle size of the thermoplastic resin is too small, the gap between the particles becomes small, the ion conduction path becomes long, and the battery characteristics may deteriorate. On the other hand, if the particle size is too large, the thickness of the separator layer (I) or the separator layer (II) is increased, which is not preferable because the energy density of the battery is reduced.

  From the viewpoint of further improving the short-circuit preventing effect in the electrochemical device, ensuring the strength of the separator and improving the handleability, the thickness of the separator is preferably 3 μm or more, and more preferably 5 μm or more. On the other hand, from the viewpoint of further increasing the energy density of the electrochemical element, the thickness of the separator is preferably 30 μm or less, and more preferably 20 μm or less.

  The thickness of the separator layer (I) is preferably 1 μm or more, more preferably 3 μm or more, preferably 15 μm or less, more preferably 10 μm or less. And the thickness of separator layer (II) becomes like this. Preferably it is 1 micrometer or more, More preferably, it is 2 micrometers or more, Preferably it is 20 micrometers or less, More preferably, it is 10 micrometers or less.

Further, the porosity of the laminated separator is preferably 15% or more, and preferably 20% or more in a dried state in order to ensure the amount of electrolyte retained and to improve ion permeability. It is more preferable. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing internal short circuit, the porosity of the separator is preferably 70% or less, more preferably 60% or less, in a dry state. The porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula.
P = 100− (Σa _i / ρ _i ) × (m / t)
[Wherein, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of separator (g / cm ² ) , T is the thickness (cm) of the separator. ]

In the above formula, m is the mass per unit area (g / cm ² ) of the separator layer (II), and t is the thickness (cm) of the separator layer (II). The porosity of the separator layer (II): P (%) can also be determined. As described above, the porosity of the separator layer (II) obtained by this method is preferably 10 to 50%.

The laminated separator is formed by a method in accordance with JIS P 8117, and the Gurley value indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ² is 10 to 300 sec. It is desirable. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  The shutdown characteristic of the separator can be determined, for example, by the temperature change of the internal resistance of the electrochemical element. Specifically, it can be measured by placing the electrochemical element in a thermostat, increasing the temperature from room temperature at a rate of 1 ° C. per minute, and determining the temperature at which the internal resistance of the electrochemical element increases. is there. In this case, the internal resistance of the electrochemical element at 150 ° C. is preferably 5 times or more of room temperature, and more preferably 10 times or more.

  In the laminated separator, at least the separator layer (II) can have a heat shrinkage rate at 150 ° C. of 1% or less by adopting the above-described configurations. That is, even when the inside of the electrochemical element reaches about 150 ° C., the separator layer (II) hardly contracts, so that a short circuit due to contact between the positive and negative electrodes can be prevented, and the safety of the electrochemical element at high temperature Can be increased. Further, for example, in the case of a separator in which the separator layer (I) and the separator layer (II) are integrated, the presence of the separator layer (II) reduces the thermal contraction rate at 150 ° C. of the entire separator to 1%. It can also be as follows. The “150 ° C. heat shrinkage” in the separator or separator layer (II) means that the separator or separator layer (II) is placed in a thermostatic bath, the temperature is raised to 150 ° C. and left for 30 minutes, and then taken out. The percentage of reduction in size obtained by comparing with the size of the separator or separator layer (II) before entering the thermostatic bath is expressed as a percentage.

  As a method for producing the laminated separator, for example, the following method (a) or (b) can be adopted. In the production method (a), a separator layer (II) forming composition containing inorganic particles (such as a liquid composition such as a slurry) is applied to a porous substrate, and then dried at a predetermined temperature. The composition is applied and then dried at a predetermined temperature to form a separator layer (II), which is superposed on a microporous film mainly composed of a thermoplastic resin for forming the separator layer (I). In this method, one separator is used. In this case, the separator layer (I) and the separator layer (II) may be integrated with each other, and each of the separator layers (I) and the separator layer (II) may be integrated into the nonaqueous electrolyte secondary battery by assembling the nonaqueous electrolyte secondary battery. It may function as an integrated separator in a state of being overlapped with each other.

  In order to integrate the separator layer (I) and the separator layer (II), for example, a method in which the separator layer (I) and the separator layer (II) are superposed and bonded together by a roll press or the like can be mentioned.

  As the porous substrate in the above case, specifically, a woven fabric composed of at least one kind of fibrous material containing each of the above exemplified materials as a constituent component, or a structure in which these fibrous materials are entangled with each other. Examples thereof include porous sheets such as non-woven fabrics. More specifically, non-woven fabrics such as paper, PP non-woven fabric, polyester non-woven fabric (PET non-woven fabric, PEN non-woven fabric, PBT non-woven fabric, etc.) and PAN non-woven fabric can be exemplified.

  Separator layer (II) formation composition contains a thermoplastic resin, an organic binder, etc. as needed other than inorganic particles (it can also be considered as plate-like particles), and these contain a solvent (dispersion medium). The same shall apply hereinafter). The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the separator layer (II) may be any one that can uniformly disperse the thermoplastic resin, inorganic particles, and the like, and can uniformly dissolve or disperse the organic binder. In general, organic solvents such as aromatic hydrocarbons such as tetrahydrofuran, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The composition for forming the separator layer (II) preferably has a solid content including inorganic particles, a thermoplastic resin, and an organic binder of, for example, 10 to 80% by mass.

  When the pore diameter of the porous substrate is relatively large, for example, when it is 5 μm or more, this tends to cause a short circuit of the electrochemical element. Therefore, in this case, it is preferable to have a structure in which all or part of inorganic particles, plate-like particles, thermoplastic resin, and the like are present in the voids of the porous substrate. In order to allow inorganic particles, plate-like particles, thermoplastic resin, etc. to exist in the voids of the porous substrate, for example, after applying the separator layer (II) forming composition containing them to the porous substrate, a certain gap A process such as drying after removing excess composition may be used.

  In order to increase the orientation of the plate-like particles contained in the separator and to make its function work more effectively, the separator layer (II) forming composition containing the plate-like particles is applied to the porous substrate and impregnated. Then, a method of applying a shear or a magnetic field to the composition may be used. For example, as described above, the composition for forming the separator layer (II) containing plate-like particles is applied to the porous substrate and then passed through a certain gap, whereby the composition can be shared.

  Further, in order to more effectively exert the action of each constituent such as inorganic particles, plate-like particles, thermoplastic resin, etc., the constituents are unevenly distributed and parallel or substantially parallel to the separator film surface. It is good also as a form which the structure gathered in layers.

  In the separator production method (b), the separator layer (II) -forming composition further contains a fibrous material as necessary, and this is applied onto a substrate such as a film or a metal foil, and is subjected to a predetermined temperature. And then drying from the substrate. In the method (b), as in the method (a), the separator layer (I) composed of a microporous film mainly composed of a thermoplastic resin and the separator layer (II) mainly composed of inorganic particles are respectively It is good also as an independent structure and it is good also as an integrated structure. In order to integrate the separator layer (I) and the separator layer (II), the separator layer (II) and the separator layer (I) that are separately formed are bonded together by a roll press or the like. A method of forming the separator layer (II) directly on the surface of the separator layer (I) by applying the composition for forming the separator layer (II) on the surface of (I) and drying it may be employed.

  Further, the separator (II) may be formed on the surface of at least one of the positive electrode and the negative electrode constituting the electrochemical element by the method (b), and the separator and the electrode may be integrated.

  Further, in the case of employing any of the manufacturing methods (a) and (b), the separator layer (I) may be integrated with at least one of the positive electrode and the negative electrode. In order to integrate the separator layer (I) with the electrode, for example, a method of roll pressing the microporous film serving as the separator layer (I) and the electrode can be employed. Further, by the production method (b), the separator layer (II) is formed on one surface of the positive electrode or the negative electrode, and the microporous film that becomes the separator layer (I) is attached to the surface of the other electrode and integrated. It is good to integrate the separator layer (I) and separator layer (II) produced by the production method (a) or (b) by attaching them to the surface of either the positive electrode or the negative electrode. May be. In order to attach and integrate the separator in which the separator layer (I) and the separator layer (II) are integrated on the surface of the electrode, for example, a method of roll pressing the separator and the electrode can be employed.

  The separator layer (I) composed of a microporous film mainly composed of a thermoplastic resin and the separator layer (II) mainly composed of inorganic particles do not have to be one each, and a plurality of layers are not required. It may be in the separator. For example, the separator layer (I) may be arranged on both sides of the separator layer (II), or the separator layer (II) may be formed on both sides of the separator layer (I). However, increasing the number of layers may increase the thickness of the separator, leading to an increase in internal resistance and a decrease in energy density. Therefore, it is not preferable to increase the number of layers, and the number of separator layers is five. The following is preferable. Further, the thermoplastic resin may be present in the form of particles and may be partly fused to a fibrous material or the like. In addition, as described above, the separator layer (I) and the separator layer (II) are each an independent component other than constituting the separator as an independent film, and at the stage where the electrochemical element is assembled, It can also be made to function as a separator interposed between the positive electrode and the negative electrode by being superposed in the electrochemical element. Furthermore, the separator layer (I) and the separator layer (II) do not need to be in contact with each other, and another layer, for example, a fibrous layer constituting a porous substrate may be interposed between them. Good.

  By using the laminated separator described above, it is possible to configure a non-aqueous secondary battery that is excellent in safety when the non-aqueous electrolyte secondary battery is abnormally heated and in reliability with respect to an internal short circuit and a short circuit due to dendrite.

  In the nonaqueous electrolyte secondary battery of the present invention, the shape thereof is not particularly limited. For example, any of a coin shape, a button shape, a sheet shape, a laminated shape, a cylindrical shape, a flat shape, a square shape, a large size used for an electric vehicle, etc. may be used.

  Next, the nonaqueous electrolyte secondary battery of the present invention will be described with reference to the drawings. The non-aqueous electrolyte secondary battery shown in the drawings is merely an example of the present invention, and the non-aqueous electrolyte secondary battery of the present invention is not limited to those illustrated in these drawings. 1 is an external perspective view showing an example of the non-aqueous electrolyte secondary battery of the present invention, and FIG. 2 is a cross-sectional view taken along the line II of FIG. In the following description, the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte are the same as those described above, and thus detailed description thereof is omitted.

  In FIG. 1, a non-aqueous electrolyte secondary battery 1 includes a rectangular battery case 2 and a cover plate 3. The battery case 2 is formed of a metal such as an aluminum alloy and serves as a battery exterior material. The battery case 2 also serves as a positive electrode terminal. The cover plate 3 is also formed of a metal such as an aluminum alloy and seals the opening of the battery case 2. Further, the lid plate 3 is provided with terminals 5 made of metal such as stainless steel through an insulating packing 4 made of synthetic resin such as polypropylene.

  In FIG. 2, the nonaqueous electrolyte secondary battery 1 includes a positive electrode 6, a negative electrode 7, and a separator 8. The positive electrode 6 and the negative electrode 7 are wound in a spiral shape via a separator 8 and then pressed so as to be flattened to form an electrode winding body 9 having a flat winding structure in a non-aqueous electrolyte solution in the battery case 2. It is stored with. However, in FIG. 2, in order to avoid complication, the metal foil, the non-aqueous electrolyte, and the like used as the current collector used in the production of the positive electrode 6 and the negative electrode 7 are not illustrated. Further, the inner peripheral side portion of the electrode winding body 9 is not cross-sectional.

  In addition, an insulator 10 formed of a synthetic resin sheet such as a polytetrafluoroethylene sheet is disposed at the bottom of the battery case 2, and the electrode winding body 9 is connected to one end of each of the positive electrode 6 and the negative electrode 7. The positive electrode lead body 11 and the negative electrode lead body 12 are drawn out. The positive electrode lead body 11 and the negative electrode lead body 12 are made of a metal such as nickel. A lead plate 14 made of a metal such as stainless steel is attached to the terminal 5 via an insulator 13 made of a synthetic resin such as polypropylene.

  The cover plate 3 is inserted into the opening of the battery case 2, and the opening of the battery case 2 is sealed and the inside of the battery is sealed by welding the joint of both.

  In FIG. 2, by directly welding the positive electrode lead body 11 to the lid plate 3, the battery case 2 and the lid plate 3 function as positive electrode terminals, and the negative electrode lead body 12 is welded to the lead plate 14. The terminal 5 functions as a negative electrode terminal by connecting the negative electrode lead body 12 and the terminal 5 via 14. However, depending on the material of the battery case 2, the sign may be reversed. is there.

  As the battery case 2, a metal square case is used, but a metal cylindrical case or a laminate case made of a metal (aluminum, etc.) laminate film can also be used.

  The manufacturing method of the non-aqueous electrolyte secondary battery 1 is not particularly limited, but after the positive electrode 6, the negative electrode 7, the separator 8 and the non-aqueous electrolyte are stored in the battery case 2 and before the battery is completely sealed. It is preferable to perform charging. Thereby, the gas generated at the initial stage of charging and the residual moisture in the battery can be removed outside the battery.

  The non-aqueous electrolyte secondary battery of the present invention can be charged at a high voltage, has a high capacity, is excellent in charge / discharge cycle characteristics and high-temperature storage characteristics, and has good safety during overcharge. Therefore, the non-aqueous electrolyte secondary battery of the present invention is widely used as a power source for various devices such as secondary batteries for driving power sources of mobile information devices such as mobile phones and notebook personal computers, taking advantage of these characteristics. Can be used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
An electrode was prepared and a non-aqueous electrolyte was prepared as described below, and a non-aqueous electrolyte secondary battery having the same structure as that shown in FIGS. 1 and 2 was prepared.

<Production of electrode>
The positive electrode was produced as follows. First, 94 parts by mass of LiCo _0.995 Mg _0.005 O ₂ (positive electrode active material), which is a lithium-containing composite oxide, was added with 3 parts by mass of carbon black as a conductive additive and mixed, and this mixture was combined with polyvinylidene fluoride. A solution in which 3 parts by mass was dissolved in NMP was added and mixed to form a positive electrode mixture-containing slurry, which was passed through a 70-mesh net to remove large particles. After this positive electrode mixture-containing slurry is uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm and dried, and then compression-molded by a roll press machine to a total thickness of 136 μm This was cut and welded with an aluminum lead body to produce a strip-like positive electrode.

The negative electrode was produced as follows. As the negative electrode active material, high crystal artificial graphite synthesized by the following method was used. That is, 100 parts by mass of coke powder, 40 parts by mass of tar pitch, 14 parts by mass of silicon carbide, and 20 parts by mass of coal tar were mixed in air at 200 ° C. and then pulverized, and heat-treated at 1000 ° C. in a nitrogen atmosphere. Furthermore, it was heat-treated at 3000 ° C. in a nitrogen atmosphere and graphitized to obtain artificial graphite. The obtained artificial graphite had a BET specific surface area of 4.0 m ² / g, d ⁰⁰² measured by X-ray diffraction of 0.336 nm, c-axis direction crystallite size Lc of 48 nm, total pores The volume was 1 × 10 ⁻³ m ³ / kg.

  Using this artificial graphite, styrene butadiene rubber as a binder, carboxymethyl cellulose as a thickener, these are mixed at a mass ratio of 98: 1: 1, and further mixed with water to mix the negative electrode. An agent-containing paste was obtained. This negative electrode mixture-containing paste was uniformly applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm and dried, and then compression-molded by a roll press machine to a total thickness of 138 μm. It cut | disconnected and the lead body made from nickel was welded, and the strip | belt-shaped negative electrode was produced.

<Preparation of non-aqueous electrolyte>
To a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / l in a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate at a volume ratio of 10:10:30, 2-propenyltrimethylsilane manufactured by Shin-Etsu Chemical Co., Ltd. The nonaqueous electrolyte solution was prepared by adding 3.0% by mass with respect to the total mass of the nonaqueous electrolyte solution.

<Production of battery>
After the strip-like positive electrode is wound on the strip-like negative electrode through a microporous membrane separator made of PE (thickness 22 μm, porosity 49%, average pore diameter 0.09 μm, melting point 135 ° C.) and wound in a spiral shape Then, an electrode wound body having a flat wound structure was formed by applying pressure so as to be flat, and this electrode wound body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a prismatic battery case made of aluminum alloy having outer dimensions of 4.0 mm (thickness), 34 mm in width, and 50 mm in height, and the lead body is welded, and the aluminum alloy The made lid plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte solution was injected from the electrolyte solution injection port provided on the cover plate, and was allowed to stand for 1 hour. In the nonaqueous electrolyte secondary battery of this example, the design electric capacity when charged to 4.4 V (the positive electrode potential is 4.5 V on the basis of Li) was 820 mAh. Incidentally, when the non-aqueous electrolyte secondary battery is charged to 4.2 V (the positive electrode potential is 4.3 V with respect to Li), the design electric capacity is 720 mAh.

  Next, the battery was charged in a dry room having a dew point of −30 ° C. under the following conditions. That is, charging was performed for 1 hour at a constant current of 0.25 CmA (205 mA) so that the amount of charge was 25% (205 mAh) of the design electric capacity (820 mAh) of the battery. During this time, the gas generated from the inside of the battery was spontaneously released out of the battery case from the electrolyte solution inlet. After charging, the electrolyte injection port was sealed to seal the inside of the battery. The produced battery was charged at 0.3 CmA (246 mA) to 4.1 V and then stored at 60 ° C. for 12 hours. Thereafter, the battery is charged at 0.3 CmA (246 mA) to 4.4 V, then charged at a constant voltage of 4.4 V for 3 hours, discharged at 1 CmA (820 mA) to 3 V, and an evaluation battery (non-aqueous electrolysis). Liquid secondary battery).

Example 2
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the silane compound added to the nonaqueous electrolytic solution was changed from 2-propenyltrimethylsilane to ethynyltrimethylsilane (manufactured by Shin-Etsu Chemical Co., Ltd.). A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the electrolyte was used.

Example 3
The separator is an organic binder SBR emulsion (solid content ratio 40 mass%): 100 g and water: 4000 g are put in a container and stirred at room temperature until uniformly dispersed, and the dispersion is heat-resistant fine particles. Boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10): 4000 g was added in 4 portions, and stirred with a disper at 2800 rpm for 5 hours to prepare a uniform slurry, and a polyethylene porous membrane (porous layer) (I): The slurry was applied on a microgravure coater on a thickness of 16 μm, a porosity of 40%, an average pore diameter of 0.02 μm, and a melting point of 135 ° C., and dried to form a heat resistant porous layer (porous layer (II )) To obtain a separator having a thickness of 22 μm (a volume ratio of 91% by volume of heat-resistant fine particles in the heat-resistant porous layer, a heat-resistant porous layer) 48% porosity), the positive electrode, the negative electrode, and the separator are stacked with the resin porous membrane (porous layer (I)) facing toward the negative electrode, and wound in a spiral shape to form a wound electrode A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the group was produced.

Comparative Example 1
A nonaqueous electrolyte solution was prepared in the same manner as in Example 1 except that 2-propenyltrimethylsilane was not added, and a nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this nonaqueous electrolyte solution was used. Produced.

Comparative Example 2
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that vinylene carbonate was added instead of adding 2-propenyltrimethylsilane, and the same procedure as in Example 1 was conducted except that this nonaqueous electrolytic solution was used. A water electrolyte secondary battery was produced.

Comparative Example 3
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that trimethylvinylsilane was added instead of adding 2-propenyltrimethylsilane, and the same procedure was performed as in Example 1 except that this nonaqueous electrolytic solution was used. A water electrolyte secondary battery was produced.

Comparative Example 4
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that diallyldimethylsilane was added instead of adding 2-propenyltrimethylsilane, and in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used. A non-aqueous electrolyte secondary battery was produced.

  The following evaluation was performed about the nonaqueous electrolyte secondary battery of Examples 1-3 and Comparative Examples 1-4. The results are shown in Table 1.

<High temperature storage characteristics>
The batteries of Examples 1 to 3 and Comparative Examples 1 to 4 were charged at 4.4 ° C. at 410 mA (0.5 C) at 20 ° C. until further charged to 4.4 V, and further charged for 3 hours at a constant voltage of 4.4 V. The thickness of the battery at this time was measured. Then, it discharged to 3V at 1C at 20 degreeC, and measured the discharge capacity before storage. In addition, about the battery of Example 1 (battery different from what was used for the said measurement), it charges on the same conditions as the above except having changed only the charging voltage into 4.2V among the said charging conditions. The battery thickness and storage capacity before storage were measured.

  Next, each battery was charged in the same manner as described above, and then stored in a thermostatic bath at 80 ° C. for 5 days. The battery after storage was naturally cooled to 20 ° C., the thickness of the battery was measured, and the swelling of the battery after storage was determined from comparison with the thickness of the battery case before storage.

<Charge / discharge cycle characteristics>
For each of the batteries of Examples 1 to 3 and Comparative Examples 1 to 4, another battery that was not subjected to the high temperature storage characteristic test was charged to 4.4 V at 0.5 C at 20 ° C. A charge / discharge cycle in which the battery was fully charged by charging at a constant voltage of 4V for 3 hours and then discharged to 3V at 1C was repeated 200 times, and the discharge capacity at the first cycle and the discharge capacity at the 200th cycle were measured. Subsequently, using the discharge capacity at the first cycle and the discharge capacity at the 200th cycle, the capacity retention rate was calculated by the following formula, and the charge / discharge cycle characteristics were evaluated.
Capacity retention rate (%) = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100

  Moreover, about the battery of Example 1 (battery different from what was used for the said charging / discharging cycle characteristic evaluation), it charged / discharged on the same conditions except having changed only the charging voltage into 4.2V among the said charging conditions. Cycle characteristics were evaluated. In addition, the description of the voltage of Example 1 in Table 1 means a charging voltage.

  As can be seen from Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 to 3 have a high capacity, and have a high capacity retention rate after the charge / discharge cycle and excellent charge / discharge cycle characteristics, Furthermore, battery swelling after high-temperature storage is small, and high-temperature storage characteristics are also good. In contrast, the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 4 configured using the non-aqueous electrolyte not containing the silane compound represented by the general formula (1) maintain the capacity after the charge / discharge cycle. The rate is low and the charge / discharge cycle characteristics are inferior, or the battery swells after high-temperature storage is large, and the high-temperature storage characteristics are inferior.

  Further, in the battery of Example 1, when the charge voltage is 4.4 V, the discharge capacity is larger than when the charge voltage is 4.2 V, and the utilization rate of the positive electrode active material is increased to increase the capacity. Has been achieved. In the battery of Example 1, excellent charge / discharge cycle characteristics and high-temperature storage characteristics can be secured as described above even when high voltage charging is performed at 4.4 V.

  About the separator of the lithium secondary battery of Examples 1-3, it was left to stand in a 150 degreeC thermostat for 3 hours, and the shrinkage rate was measured. The shrinkage rate was measured as follows.

  A separator test piece cut into 4 cm × 4 cm was sandwiched between two glass plates with a thickness of 5 mm fixed with clips, left in a thermostatic bath at 150 ° C. for 3 hours, taken out, and the length of each test piece was measured. Measured, and the rate of decrease in length compared to the length before the test was taken as the shrinkage rate. Table 2 shows the measurement results.

  As shown in Table 2, the heat shrinkage rate at 150 ° C. of the laminated separator used in the nonaqueous electrolyte secondary battery of Example 3 was 0%, and the heat shrinkage at a high temperature was suppressed. .

  Moreover, the following evaluation was performed about each lithium secondary battery of Examples 1-3. First, the shutdown temperature of the separator used for each battery was determined by the following method. The discharged battery was placed in a thermostatic bath, heated from 30 ° C. to 150 ° C. at a rate of 1 ° C. per minute, and heated, and the temperature change of the internal resistance of the battery was determined. The temperature at which the resistance value increased to 5 times or more the value at 30 ° C. was taken as the shutdown temperature.

  In addition, constant current charging was performed until the battery voltage reached 4.25 V at a current value of 0.2 C, and then constant current-constant voltage charging in which constant voltage charging at 4.25 V was performed. The total charging time until the end of charging was 15 hours. The battery charged under the above conditions was heated from 30 ° C. to 150 ° C. at a rate of 5 ° C. per minute and then allowed to stand at 150 ° C. for 3 hours to measure the surface temperature of the battery and the battery voltage. Further, an external short circuit test was conducted in which the positive and negative electrodes were short-circuited through a 100 mΩ resistor of the battery, and the maximum temperature on the battery surface was measured. The evaluation results are shown in Table 3.

  As shown in Table 3, in Example 3, a shutdown occurs in an appropriate temperature range to ensure the safety of the battery at a high temperature, and the surface temperature of the battery significantly increases even in the external short-circuit test. No abnormality was found, and a battery with higher safety than before could be constructed. Moreover, the effect of the silane compound used in the present invention was not inhibited.

It is an external appearance perspective view which shows an example of the nonaqueous electrolyte secondary battery of this invention. It is the II sectional view taken on the line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Battery case 3 Cover plate 4 Insulation packing 5 Terminal 6 Positive electrode 7 Negative electrode 8 Separator 9 Electrode winding body 10 Insulator 11 Positive electrode lead body 12 Negative electrode lead body 13 Insulator 14 Lead plate

Claims (4)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The positive electrode has a general composition formula Li _{1 + x + α} M _1-x O ₂ (wherein M includes at least one element selected from Co and Ni and at least one element selected from Al and Mg) It represents an element of seeds or more, and the ratio of Co and Ni in the element M is 50 to 99.8 atomic% in total, -0.05 ≦ x ≦ 0.1, −0.05 ≦ α ≦ 0.1 A lithium-containing composite oxide represented by
The non-aqueous electrolyte secondary battery is characterized in that a silane compound represented by the following general formula (1) is added.

[In General Formula (1), R ^{1 to} R ⁴ are an organic substituent having 1 to 6 carbon atoms or a halogen element, and any one of R ^{1 to} R ⁴ has 3 to 6 carbon atoms. Or an alkynyl group having 2 to 6 carbon atoms, and at least a part of hydrogen of the organic substituent may be substituted with a halogen element. ]   The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of Al and Mg in the element M is 0.5 to 5 atomic% in total.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the silane compound has an alkenyl group having 3 or 4 carbon atoms.   A separator is provided between the positive electrode and the negative electrode, and the separator has a separator layer (I) composed of a microporous film mainly composed of a thermoplastic resin having a melting point of 80 to 140 ° C. and a heat resistant temperature of 150 ° C. or higher. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte secondary battery is a laminated separator having a porous separator layer (II) containing mainly inorganic particles.

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