JP2007165224A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in a nonaqueous electrolyte secondary battery that a large current flows and an open circuit voltage is decreased and a heating may be caused, in case an internal short circuit occurs between an uncoated part of a cathode collector and an anode plate coated by an anode active substance. <P>SOLUTION: The nonaqueous electrolyte secondary battery is composed of a group of electrodes wound with a separating membrane in-between by a cathode plate of which the cathode collector is coated by a cathode active substance and an anode plate of which an anode collector 1 is coated by an anode active substance 2. The cathode plate has an uncoated part other than an end part in a length-wise direction, and a cathode lead 7 is connected with the uncoated part of the cathode plate, and the cathode lead is covered by a tape and furthermore a heat-resisting protective membrane is formed on the anode plate surface facing the uncoated part of the cathode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to the structure of a positive electrode plate and a negative electrode plate.

  In recent years, electronic devices such as AV devices and personal computers have been rapidly becoming portable and cordless, and the demand for non-aqueous electrolyte secondary batteries having a small size, light weight, and high energy density as driving power sources has increased. ing. Lithium ion secondary batteries, which are representative of non-aqueous electrolyte secondary batteries, are particularly expected as batteries with high voltage and high energy density, and competition for development of high capacity, high output, and high reliability has intensified. ing. In a non-aqueous electrolyte secondary battery, a separator is usually used as a separator between a positive electrode plate coated with a positive electrode active material on both sides of the positive electrode current collector and a negative electrode plate coated with a negative electrode active material on both sides of the negative electrode current collector. And an electrode group wound in a spiral shape. There was a possibility that the uncoated portion of the positive electrode current collector and the negative electrode plate face each other with the separator interposed therebetween, and the uncoated portion of the positive electrode current collector and the negative electrode plate were short-circuited to generate heat. .

In order to prevent this heat generation, in the positive electrode plate and the negative electrode plate located at the winding start end and the winding end end of the electrode group, a part of the uncoated part facing the other electrode in at least one current collector or It has been proposed to provide a heat-resistant protective film on all (see, for example, Patent Document 1).
JP 2004-63343 A

  As a test for confirming the safety of the non-aqueous electrolyte secondary battery, an internal short circuit test using a foreign material was adopted. This test is performed by, for example, embedding a metal foreign object such as iron in advance on the negative electrode plate in order to intentionally cause an internal short circuit when the electrode group is manufactured. Then, it is a test of generating an internal short circuit by repeating charging and discharging several times. The test result is a method in which a thermocouple is attached to the battery in advance and it is determined that the battery has generated heat when the battery temperature reaches 100 ° C. or higher. If this internal short circuit occurs between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material, a large current flows, which may cause a significant decrease in open circuit voltage or abnormal heat generation. There was a problem that there was.

  Patent Document 1 has the following problems. When a heat-resistant protective film is provided on a part or all of the uncoated part facing the other electrode of one current collector, it is necessary to form the heat-resistant protective film on the surface of the current collector. There was a problem that the adhesion between the current collector and the current collector was lowered, and the heat-resistant protective film was peeled off during the production of the electrode group. The uncoated part is recessed compared to the electrode part to which the active material is applied, and the heat-resistant protective film is applied only to the uncoated part (so that the heat-resistant protective film is not applied to the coated part of the active material) However, there is a problem that it is difficult in the manufacturing process.

  Further, when a lead is connected to an uncoated portion, it is difficult in the manufacturing process to form a heat-resistant protective film densely for the same reason. In the case of a cylindrical non-aqueous electrolyte secondary battery in which a positive electrode lead is provided on the current collector of the uncoated part at the winding start end of the electrode group, the positive electrode lead is welded to the innermost peripheral side where the radius of curvature is the smallest. Therefore, there is a new problem that the edge portion of the positive electrode lead damages the positive electrode plate on the outer peripheral side and the positive electrode plate is cut.

The present invention solves such a conventional problem, and does not form a heat-resistant protective film on the uncoated portion of the positive electrode current collector, but is provided on the negative electrode mixture portion facing the uncoated portion. Accordingly, it is possible to provide a non-aqueous electrolyte secondary battery that can form a negative electrode mixture layer with very few irregularities and a dense heat-resistant protective film with high adhesion, and can suppress heat generation during an internal short circuit.

In order to solve the above problems, the non-aqueous electrolyte secondary battery of the present invention is
A positive electrode plate in which a positive electrode active material is applied to a positive electrode current collector; and a negative electrode plate in which a negative electrode active material is applied to a negative electrode current collector. An uncoated part is provided in addition to the end in the length direction of the plate, a positive electrode lead is connected to the uncoated part, the positive electrode lead is covered with a tape, and the negative electrode is opposed to the uncoated part A heat-resistant protective film is formed on the plate surface.

  In another non-aqueous electrolyte secondary battery of the present invention, an uncoated part is provided in addition to an end in the length direction of the positive electrode plate, a positive electrode lead is connected to the uncoated part, and A heat resistant protective film is formed on the surface of the negative electrode plate facing the uncoated portion.

  By doing so, it is possible to suppress heat generation at the time of an internal short circuit occurring between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material, which has the highest risk of heat generation.

  According to the present invention, when an internal short circuit occurs between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material, the heat generation does not become high. Compared to the case where the entire negative electrode plate is covered with a heat-resistant protective film by protecting only between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material, a non-aqueous electrolyte solution There is also an advantage that the energy density per volume of the secondary battery can be increased. In addition, by arranging the uncoated portion of the positive electrode current collector in a portion other than the end portion of the positive electrode plate, for example, by setting the welded portion of the positive electrode lead to the central portion of the positive electrode plate, The wound diameter of the portion is not reduced, and the electrode plate damage due to the lead edge portion can be greatly reduced.

  A non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode plate in which a positive electrode active material is applied to a positive electrode current collector, and a negative electrode plate in which a negative electrode current collector is applied with a negative electrode active material, In the non-aqueous electrolyte secondary battery having the electrode group wound through, an uncoated portion is provided in addition to the end portion in the length direction of the positive electrode plate, and a positive electrode lead is provided on the positive electrode plate uncoated portion. , The positive electrode lead is covered with a tape, and a heat-resistant protective film is formed on the surface of the negative electrode plate facing the uncoated positive electrode plate portion.

  By doing so, the heat-resistant protective film can be formed densely with good adhesion, and the highest risk of heat generation between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material Heat generation at the time of internal short circuit that occurred can be suppressed.

  The non-aqueous electrolyte secondary battery according to another embodiment of the present invention has an uncoated portion other than an end portion in the length direction of the positive electrode plate, and a positive electrode lead is provided on the positive electrode plate uncoated portion. A heat-resistant protective film is formed on the surface of the negative electrode plate that is connected and faces the positive electrode uncoated portion.

By doing so, the heat-resistant protective film can be formed densely with good adhesion, and the highest risk of heat generation between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material Heat generation at the time of internal short circuit that occurred can be suppressed. Further, even if there is no tape attached to prevent an internal short circuit due to “flash” generated in the positive electrode lead, there is no danger of heat generation, so that the energy density per volume can be further increased. In the preferred embodiment of the non-aqueous electrolyte secondary battery, the positive electrode active material has the general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (x is a variable that changes with charge and discharge, and 0 <x <1.1, 0 <y ≦ 0.5, 0 ≦ z <0.5, M is Al, Mn, Mg, Ca, Fe, Ti, Zn, S
and at least one element selected from the group consisting of r, Ba, Zr, Y, B, and Ta.

  By doing so, the heat-resistant protective film can be formed densely with good adhesion, and the highest risk of heat generation between the uncoated portion of the positive electrode current collector and the negative electrode plate coated with the negative electrode active material Heat generation at the time of internal short circuit that occurred can be suppressed.

  Hereinafter, the positive electrode will be described in detail.

As the positive electrode active material, a lithium-containing transition metal oxide such as lithium cobaltate (LiCoO ₂ ) or lithium nickelate (hereinafter abbreviated as LiNiO ₂ ) can be used. Further, a spinel-type composite oxide such as lithium manganate (LiMn ₂ O ₄ ) using relatively inexpensive manganese as a raw material can also be used.

  As the thickener for the positive electrode, carboxymethyl cellulose (hereinafter abbreviated as CMC), methyl cellulose (MC), hydroxymethyl cellulose (HMC), ethyl cellulose, polyvinyl alcohol (PVA), oxidized starch, phosphorylated starch, and casein are used. Good.

  The conductive agent may be anything as long as it is an electron conductive material. For example, graphite such as natural graphite (such as flake graphite), artificial graphite, expanded graphite, carbon black such as acetylene black, channel black, furnace black, and thermal black, conductivity such as carbon fiber, metal fiber, etc. Fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and carbon fiber are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1-30 weight% is preferable with respect to a negative electrode active material, Furthermore, 1-10 weight% is preferable.

  As the material of the current collector of the positive electrode, a metal such as aluminum (Al), titanium (Ti), and tantalum (Ta) or an alloy thereof can be used. Al) or its alloys are preferably used.

  Hereinafter, the negative electrode will be described in detail.

  Examples of the negative electrode active material include carbon materials such as graphite and amorphous materials, mixtures thereof, alloys, metal compounds, and the like, and these can be used alone or in admixture of two or more. The alloy preferably comprises at least one element selected from the group consisting of silicon, tin, aluminum, zinc, magnesium, titanium, and nickel. The metal compound is at least one selected from the group consisting of silicon, tin, aluminum, zinc, magnesium, titanium, and nickel oxides and carbides. Although the average particle diameter of a negative electrode active material is not specifically limited, 1-30 micrometers is preferable.

  The current collector of the negative electrode plate can be anything as long as it is an electrochemically stable electron conductor, and metals such as copper, nickel, and stainless steel can be used. Copper foil is preferred. Although thickness is not specifically limited, 5-25 micrometers is preferable.

The binder used in the production of the positive electrode plate and the negative electrode plate is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), isopropylene rubber, butadiene rubber, ethylene propylene diethane polymer (EPDM), or the like may be used.

  Hereinafter, the nonaqueous electrolyte will be described in detail.

  The non-aqueous solvent is preferably a carbonate ester. The carbonate ester can be either cyclic or chain. Suitable cyclic carbonates include propylene carbonate (hereinafter abbreviated as PC), ethylene carbonate (EC), butylene carbonate (BC), and the like. These high dielectric constant solvents may be used alone or in combination of two or more. Examples of the chain carbonate ester include dimethyl carbonate (hereinafter abbreviated as DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), di-n-propyl carbonate, methyl-n-propyl carbonate, and ethyl-i-propyl. And carbonate. These low viscosity solvents may be used alone or in combination of two or more. A cyclic carbonate and a chain carbonate can be arbitrarily selected and used in combination.

As the electrolyte salt, an inorganic lithium salt selected from lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium tetrafluoroborate (LiBF ₄ ), LiCF ₃ SO ₃ , LiN Fluorine-containing organolithium such as (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), and LiC (CF ₃ SO ₂ ) ₃ Examples include salts. Among these electrolyte salts, LiPF ₆ or LiBF ₄ is preferable. These electrolyte salts can be used alone or in combination of two or more. These electrolyte salts are preferably prepared and used in the non-aqueous solvent described above so that the concentration is usually 0.1 to 3.0 mol / L, preferably 0.5 to 2.0 mol / L.

  The non-aqueous electrolyte may contain an additive that increases resistance to overcharge. As the additive, a benzene derivative composed of a phenyl group and a cyclic compound group adjacent thereto is preferably used. Examples of such benzene derivatives include biphenyl, cyclohexylbenzene, diphenyl ether, and phenyllactone.

  The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are stacked Etc. can be used.

    The method for producing the nonaqueous electrolyte secondary battery is not particularly limited, and can be appropriately selected from commonly employed methods.

  Hereinafter, an embodiment of the present invention will be described.

Example 1
First, a method for producing a positive electrode plate will be described. Acetylene black, a positive electrode active material composed of lithium cobaltate (hereinafter abbreviated as LiCoO ₂ ) obtained by mixing lithium carbonate (Li ₂ CO ₃ ) and tricobalt tetroxide (Co ₃ O ₄ ) and firing in air at 900 ° C. (N-methyl-) obtained by mixing a conductive material made of (hereinafter abbreviated as AB) and a binder made of polyvinylidene fluoride (hereinafter abbreviated as PVDF) so as to have a weight ratio of 100: 2: 3. A positive electrode paste was prepared by kneading and dispersing 2-pyrrolidone (hereinafter abbreviated as NMP) as a dispersion medium. The positive electrode paste was applied to an aluminum foil having a thickness of 15 μm as a current collector and dried. Then, it rolled so that the density of the mixture layer containing a positive electrode active material might be set to 3.5-3.6 g / cm < ³ >, and the total thickness of the positive electrode plate was 0.17 mm. The uncoated part was cut so that the total length including 6.5 mm was 612 mm and the width was 57 mm. At this time, the uncoated portion was disposed at a position of 40 to 46.5 mm from the longitudinal end portion of the electrode plate.

  Next, positive electrode plates 1 and 2 described below were produced.

  First, the positive electrode lead 7 was connected to the uncoated portion of the electrode plate composed of the above-mentioned coated portion and uncoated portion by ultrasonic welding to produce a positive electrode plate α.

  Next, in order to protect the lead of the positive electrode plate α, a positive electrode plate β on which a 9 mm wide polypropylene (hereinafter abbreviated as PP) tape was attached was prepared.

  At this time, the positive leads 7 of the positive plates [alpha] and [beta] were set so that "flash" of 50 to 200 [mu] m appeared in the direction opposite to the positive plate.

  1 and 2 are schematic sectional views of the positive plates α and β, respectively.

Next, a method for manufacturing the negative electrode plate will be described. A negative electrode active material made of artificial graphite and a binder made of PVDF mixed at a weight ratio of 100: 6 were kneaded and dispersed using NMP as a dispersion medium to prepare a negative electrode paste. The negative electrode paste was applied to a copper foil having a thickness of 10 μm as a current collector and dried. Then, it rolled so that the density of the mixture layer containing a negative electrode active material might be set to 1.57 g / cm < ³ >.

  The total thickness of the negative electrode plate was 0.17 mm. Thereafter, after cutting to a width of 59 mm and a total length of 645 mm, a negative electrode lead was welded to the outermost peripheral portion, and a negative electrode plate α in which PP tape was attached only to the peripheral portion of the negative electrode lead was produced.

  And the heat-resistant protective film demonstrated below was formed in the "location facing the positive electrode lead 7" at the time of electrode group preparation on the negative electrode plate (alpha).

  As used herein, “location facing the positive electrode lead” refers to a location facing a range of 15 mm in the longitudinal direction including 6.5 mm of the uncoated portion of the positive electrode plate α or β.

  The heat resistant protective film was produced as follows. 960 g of alumina having a median diameter of 0.3 μm as an inorganic oxide filler, 500 g of modified acrylonitrile rubber as a binder, and an appropriate amount of NMP were put into a double-arm kneader and stirred to prepare a heat-resistant protective film precursor paste. . A heat-resistant protective film precursor paste was applied on the negative electrode plate 1 facing the positive electrode lead 7. Then, it dried and formed the 6-micrometer-thick heat-resistant protective film, and produced the negative electrode plate (beta).

  Next, as the inorganic oxide filler, titania was used instead of alumina, and a negative electrode plate γ was produced in the same manner as the negative electrode plate α except for this.

  Non-aqueous electrolyte secondary batteries were prepared by combining the positive plates α, β thus obtained and the negative plates α, β, and γ, and the combinations are shown in Table 1. A microporous polyethylene resin having a thickness of 16 μm was used as a separator, and a positive electrode plate and a negative electrode plate were wound therethrough to produce electrode groups a to f. 3 and 4 are schematic cross-sectional views of the vicinity of the positive electrode lead 7 connected in the electrode groups c and f, respectively.

The electrode groups a to f produced as described above were housed in an iron cylindrical battery case 1 plated with nickel (Ni), and polypropylene (PP) insulating plates were arranged on both upper and lower surfaces of the electrode group. In order to collect current from each of the positive and negative electrode plates, the positive and negative electrode leads were led out from the current collectors of the positive and negative electrode plates, respectively, and the negative electrode lead was connected to the battery case 1 by resistance welding.

Next, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 1 in the battery case 1 in which the electrode group is housed, and 1 mol / L lithium hexafluorophosphate (LiPF) is mixed. ₆ ) A non-aqueous electrolyte dissolved in was injected. Then, the positive electrode lead 7 led out from the electrode group was welded to a sealing plate in which a gasket was previously incorporated. Thereafter, the sealing plate was attached to the battery case 1 and sealed with caulking to prepare nonaqueous electrolyte secondary batteries A to F. Table 1 shows the electrode group used for each battery.

100 cells of each of the batteries A to F were prepared, and charging and discharging were repeated 100 cycles at 25 ° C. The charging conditions were a constant current / constant voltage system with a voltage of 4.2 V, the maximum current was 1500 mA, and the end current was 100 mA. The discharge conditions were a constant current method, the current was 400 mA, and the final voltage was 3.0V. Since the battery produced this time intentionally has a “flash” on the positive electrode lead, there is a possibility of heat generation due to an internal short circuit due to the “flash” of the positive electrode lead during charge / discharge. Table 2 shows the heat generation rate generated during 100 cycles.

From the results in Table 2, the batteries B, C, E, and F had a higher heat generation rate than the batteries A and D, and the difference was clear. For this reason, batteries such as batteries B, C, E, and F, in which a porous insulator is applied to the surface of the negative electrode plate, do not generate heat. When disassembling the batteries A and D where heat generation occurred and confirming the short-circuited part, it was found that the separator at the position facing the positive electrode lead was blackened, and heat was generated due to “flash” of the positive electrode lead.

(Example 2)
Next, a case where a positive electrode active material other than lithium cobaltate is used as the positive electrode active material will be described.

Nickel sulfate and cobalt sulfate were dissolved in water so that the molar ratio of Co to Ni was 20% to prepare a nickel sulfate-cobalt mixed solution. Nickel-cobalt hydroxide was obtained by adding sodium hydroxide to the nickel sulfate-cobalt mixed solution to cause coprecipitation. The obtained nickel-cobalt hydroxide was washed with water and dried at 80 ° C. to form a powder, thereby producing a nickel-cobalt hydroxide (Ni _0.8 Co _0.2 (OH) ₂ ).

The nickel-cobalt hydroxide thus prepared was mixed with lithium hydroxide-hydrate so that the molar ratio of Li / (Ni + Co) was 1/1. It was calcined for 20 hours at a temperature of 700 ° C. in an oxygen atmosphere, and pulverized to obtain LiNi _0.8 Co _0.2 O ₂ .

The positive electrode active material LiNi _0.8 Co _0.2 O ₂ thus produced, AB as the conductive material, and PVDF as the binder were mixed so that the weight ratios thereof were 100: 2: 3. A positive electrode paste prepared by kneading and dispersing using NMP as a dispersion medium was applied, rolled and cut in the same manner as in Example 1. Then, in the same manner as the positive plates α and β described in Example 1, the positive leads 7 were connected by ultrasonic welding to produce positive plates γ and δ.

  Also in this case, the “flash” of 50 to 100 μm is projected in the direction opposite to the positive electrode plate on the positive electrode leads 7 of the positive electrode plates γ and δ.

  Then, the same negative electrode plates α, β, and γ as in Example 1 and positive electrode plates γ, δ were combined to prepare electrode groups g to l by the same manufacturing method as in Example 1. Nonaqueous electrolyte secondary batteries G to L were produced using the electrode groups g to l. Table 3 shows the positive electrode plate, the negative electrode plate, and the electrode group used in the batteries G to L.

100 cells of each of the batteries G to L were prepared, and 100 cycles of charging and discharging were performed at 25 ° C. The charge / discharge conditions are the same as in Example 1. Since the battery produced this time has a “flash” on the positive electrode lead, it may generate heat during charging and discharging. Table 4 shows the heat generation rate that occurred during 100 cycles.

From the results in Table 4, the batteries H, I, K, and L had higher heat generation rates than the batteries G and J, and the difference was clear. For this reason, batteries such as batteries H, I, K, and L in which a porous insulator is applied to the surface of the negative electrode plate do not generate heat. When disassembling the batteries G and J where heat generation occurred and confirming the short-circuited portion, it was found that the separator at the position facing the positive electrode lead was blackened and heat was generated due to “burrs” of the positive electrode lead.

  From the above, even if the “flash” of the positive electrode lead is as large as 100 μm, it is possible to provide a safe non-aqueous electrolyte secondary battery without generating heat due to an internal short circuit due to the “flash” of the positive electrode lead. .

  Moreover, although the lithium secondary battery has been described as the nonaqueous electrolyte secondary battery, the same effect can be obtained in a nonaqueous electrolyte secondary battery such as a magnesium secondary battery other than the lithium secondary battery. is there.

  The nonaqueous electrolyte secondary battery of the present invention is useful as a main power source for electronic devices and the like. For example, it is suitable for use as a main power source for consumer mobile tools such as mobile phones and laptop computers, a main power source for power tools such as an electric screwdriver, and an industrial main power source such as an EV car.

Schematic sectional view of positive electrode plate α used in the examples of the present invention Schematic sectional view of positive electrode plate β used in the examples of the present invention Schematic cross-sectional view near the positive electrode lead position of the electrode group c used in the example of the present invention Schematic cross-sectional view of the vicinity of the positive electrode lead position of the electrode group f used in the example of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode active material 3 Separator 4 Positive electrode collector 5 Positive electrode active material 6 PP tape 7 Positive electrode lead 8 Porous insulating film

Claims (3)

A non-aqueous electrolyte secondary having an electrode group in which a positive electrode plate coated with a positive electrode active material on a positive electrode current collector and a negative electrode plate coated with a negative electrode active material on a negative electrode current collector are wound through a separator In batteries,
An uncoated part is provided in addition to the end in the length direction of the positive electrode plate, a positive electrode lead is connected to the uncoated part, the positive electrode lead is covered with a tape, and is opposed to the uncoated part. A non-aqueous electrolyte secondary battery in which a heat-resistant protective film is formed on the surface of the negative electrode plate. A non-aqueous electrolyte secondary having an electrode group in which a positive electrode plate coated with a positive electrode active material on a positive electrode current collector and a negative electrode plate coated with a negative electrode active material on a negative electrode current collector are wound through a separator In batteries,
A non-coated portion is provided in addition to the lengthwise end of the positive electrode plate, a positive electrode lead is connected to the non-coated portion, and a heat-resistant protective film is formed on the negative electrode plate surface facing the non-coated portion. A non-aqueous electrolyte secondary battery in which is formed. The positive electrode active material has a general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (x is a variable that changes with charge and discharge, and 0 <x <1.1, 0 <y ≦ 0.5, 0 ≦ z <0.5, wherein M is at least one element selected from the group consisting of Al, Mn, Mg, Ca, Fe, Ti, Zn, Sr, Ba, Zr, Y, B, and Ta) Item 3. The nonaqueous electrolyte secondary battery according to Item 1 or 2.