JP6070823B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.

  Currently, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries that are used for mobile devices such as mobile phones have been commercialized. A nonaqueous electrolyte secondary battery generally includes a positive electrode obtained by applying a positive electrode active material or the like to a current collector, and a negative electrode obtained by applying a negative electrode active material or the like to a current collector. It has the structure connected through the electrolyte layer holding electrolyte gel. Then, when ions such as lithium ions are occluded / released in the electrode active material, a charge / discharge reaction of the battery occurs.

  Incidentally, in recent years, it has been required to reduce the amount of carbon dioxide in order to cope with global warming. Thus, non-aqueous electrolyte secondary batteries with a low environmental load are being used not only for portable devices, but also for power supply devices for electric vehicles such as hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. .

  Non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have high output and high capacity. As a positive electrode active material used for a positive electrode of a non-aqueous electrolyte secondary battery for an electric vehicle, a lithium-cobalt composite oxide, which is a layered composite oxide, can obtain a high voltage of 4V and has a high energy density. Has already been put to practical use. However, since cobalt, which is a raw material, is scarce in terms of resources and is expensive, there is anxiety in terms of supply of raw materials, considering the possibility that demand will increase significantly in the future. In addition, the price of cobalt raw materials may rise. Therefore, a composite oxide having a low cobalt content is desired.

A spinel-based lithium manganese composite oxide (LiMn ₂ O ₄ ; also referred to as “LMO” in the present specification) has a spinel structure and functions as a 4V-class positive electrode material between compositions with λ-MnO ₂ . Since the spinel-type lithium manganese composite oxide has a three-dimensional host structure different from the layered structure such as that of LiCoO ₂ or the like, most of the theoretical capacity can be used and is expected to have excellent cycle characteristics. .

  However, in reality, lithium ion secondary batteries using spinel-based lithium manganese composite oxide as the positive electrode material cannot avoid the capacity degradation that gradually decreases in capacity due to repeated charge and discharge. There was a big problem left.

As a technique for solving the problem of capacity deterioration of such spinel-based lithium manganese composite oxide, for example, in Japanese Patent Application Laid-Open No. 2000-77071, a positive electrode material has a predetermined ratio in addition to spinel-based lithium manganese composite oxide. A technique that further uses a lithium nickel composite oxide having a surface area (LiNiO ₂ , Li ₂ NiO ₂ , LiNi ₂ O ₄ , Li ₂ Ni ₂ O ₄ , LiNi _1-x M _x O _2, etc.) is disclosed. According to JP 2000-77071 A, such a configuration suppresses Mn elution from the spinel-based lithium manganese composite oxide and changes in Li concentration in the electrolytic solution. In particular, it is said that a non-aqueous electrolyte secondary battery with greatly improved charge / discharge life at high temperatures can be provided.

  According to the studies by the present inventors, it has been found that sufficient charge / discharge cycle characteristics cannot be achieved even when a battery having a large capacity and a large area is obtained by the technique described in Japanese Patent Application Laid-Open No. 2000-77071. It was issued. Such a decrease in charge / discharge cycle characteristics results from the inclusion of spinel-based lithium manganese composite oxide as the positive electrode active material, and the Joule heat during charge / discharge accompanying the increase in capacity and area of the battery. It was found that the increase was due to the elution of Mn from the composite oxide.

  Therefore, the present invention provides a large-capacity, large-area non-aqueous electrolyte secondary battery containing a spinel-based lithium manganese composite oxide as a positive electrode active material, from the composite oxide resulting from an increase in Joule heat during charge / discharge. An object of the present invention is to provide means capable of suppressing elution of Mn and improving cycle characteristics.

  The inventors of the present invention have accumulated extensive research. As a result, the lithium nickel composite oxide is used in combination with the spinel lithium manganese composite oxide as the positive electrode active material, and the ratio of the discharge depth (DOD) corresponding to the positive electrode potential in a specific range is set to the total discharge depth (total It has been found that the above-mentioned problems can be solved by controlling the DOD) within a predetermined value or less, and the present invention has been completed.

That is, according to one aspect of the present invention, the ratio of the battery area (projected area of the battery including the battery outer package) to the rated capacity is 5 cm ² / Ah or more, and the non-aqueous water has a rated capacity of 3 Ah or more. A positive electrode for a non-aqueous electrolyte secondary battery used for an electrolyte secondary battery is provided. This positive electrode has a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector and containing a spinel-based lithium manganese composite oxide and a lithium-nickel-based composite oxide. The depth of discharge (DOD) corresponding to the positive electrode potential (versus lithium oxidation-reduction potential) in the range of 3.93 to 4.03 V is the total depth of discharge (total DOD) of 100 corresponding to the cell voltage in the range of 3 to 4.25 V. It is characterized in that it is 25% or less with respect to%.

1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat (stacked) bipolar type, which is an embodiment of a nonaqueous electrolyte lithium ion secondary battery. When only the spinel lithium manganese composite oxide is used as the positive electrode active material (curve a shown in FIG. 2), and the mixture of the spinel lithium manganese composite oxide and the lithium nickel composite oxide (mixing ratio) as the positive electrode active material 70:30 (% by weight)) (curve b shown in FIG. 2) and a graph showing a discharge curve for each (graphite is used as the negative electrode active material). It is a graph which expands and shows the area | region (area | region X shown in FIG. 2) whose discharge depth (DOD) in the discharge curve shown in FIG. 2 is 40 to 90%. It is the graph and table | surface which show the relationship between Mn elution and a positive electrode potential quoted from Journal of Power Sources, 136 (2004), p.115-121. In the table shown in FIG. 4, “SOC” represents the depth of discharge (%), and “V / Li ⁺ ” represents the positive electrode potential (vs. lithium oxidation-reduction potential) (V). Are summarized in a table. “V / cell” represents the cell voltage (V), and is a value converted from the values of “SOC” and “V / Li ⁺ ” when graphite (graphite) is used as the negative electrode active material. It is the graph which compared the reduction effect of the Mn elution area | region at the time of using together 2 types of different lithium nickel type complex oxide with spinel type lithium manganese complex oxide, respectively. It is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of a secondary battery.

According to one aspect of the present invention, the ratio of the battery area (projected area of the battery including the battery outer package) to the rated capacity is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. A positive electrode for a nonaqueous electrolyte secondary battery used for a secondary battery, comprising a positive electrode current collector and a surface of the positive electrode current collector, comprising a spinel-based lithium manganese composite oxide and a lithium-nickel-based composite oxide A positive electrode active material layer including a positive electrode active material, and a discharge depth (DOD) corresponding to a positive electrode potential (versus lithium oxidation-reduction potential) in the range of 3.93 to 4.03 V is a cell voltage of 3 to 4.25 V. Provided is a positive electrode for a nonaqueous electrolyte secondary battery that is 25% or less with respect to 100% of the total depth of discharge (total DOD) corresponding to the range. According to the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the discharge profile is changed by using a lithium nickel composite oxide together. In particular, the discharge profile in the region corresponding to the positive electrode potential range (Mn elution region) where Mn elution from the spinel-type lithium manganese composite oxide is likely to occur changes, and the accumulated time that passes through this Mn elution region during charging and discharging is reduced. can do. As a result, elution of Mn from the spinel-based lithium manganese composite oxide due to an increase in Joule heat during charging / discharging is suppressed, and the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.

  Hereinafter, as a preferred embodiment of the nonaqueous electrolyte secondary battery to which the positive electrode according to the present embodiment is applied, a nonaqueous electrolyte lithium ion secondary battery will be described, but the present invention is not limited only to the following embodiment. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 that is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer positive electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost positive electrode current collector is disposed on one or both surfaces of the outermost layer positive electrode current collector. A positive electrode active material layer may be disposed.

  The positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out of the battery exterior material 29 so that it may be pinched | interposed into the edge part. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode via a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  Note that FIG. 1 shows a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Hereinafter, each member will be described in more detail.

[Positive electrode]
The positive electrode has a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector.

(Positive electrode current collector)
There is no particular limitation on the material constituting the positive electrode current collector, but a metal is preferably used. Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

(Positive electrode active material layer)
The positive electrode active material layer includes a positive electrode active material. In this embodiment, the positive electrode active material essentially includes a spinel-based lithium manganese composite oxide and a lithium-nickel-based composite oxide. The ratio of the total amount of spinel-based lithium manganese composite oxide and lithium-nickel-based composite oxide in the total amount of 100% by weight of the positive electrode active material contained in the positive electrode active material layer is preferably 50% by weight or more, and more It is preferably 70% by weight or more, more preferably 85% by weight or more, still more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 100% by weight.

Spinel-based lithium manganese composite oxide Spinel-based lithium manganese composite oxide is a composite oxide that typically has a composition of LiMn ₂ O ₄ and has a spinel structure and essentially contains lithium and manganese. Conventionally known knowledge such as Japanese Patent Application Laid-Open No. 2000-77071 can be appropriately referred to for its specific configuration and manufacturing method.

  The spinel-type lithium manganese composite oxide has a secondary particle configuration in which primary particles are aggregated. And the average particle diameter (average secondary particle diameter) of this secondary particle becomes like this. Preferably it is 5-50 micrometers, More preferably, it is 7-20 micrometers. The average secondary particle diameter is measured by a laser diffraction method.

-Lithium nickel complex oxide The composition of lithium nickel complex oxide is not specifically limited as long as it is a complex oxide containing lithium and nickel. A typical example of a composite oxide containing lithium and nickel is lithium nickel composite oxide (LiNiO ₂ ). However, a composite oxide in which some of the nickel atoms of the lithium nickel composite oxide are substituted with other metal atoms is more preferable. As a preferable example, a lithium-nickel-manganese-cobalt composite oxide (hereinafter simply referred to as “NMC composite”) is preferable. (Also referred to as “oxide”) has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are alternately stacked via an oxygen atomic layer. One Li atom is contained per atom, and the amount of Li that can be taken out is twice that of the spinel-type lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained. In addition, since it has higher thermal stability than LiNiO ₂ , it is particularly advantageous among the nickel-based composite oxides used as the positive electrode active material.

  In the present specification, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Co, d represents the atomic ratio of Mn, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

In the NMC composite oxide, the present inventors charge and discharge the above-mentioned charge and discharge when the metal composition of nickel, manganese and cobalt is not uniform, for example, LiNi _0.5 Mn _0.3 Co _0.2 O _2. It has been found that the influence of strain / cracking of the complex oxide at the time increases. This is presumably because the stress applied to the inside of the particles during expansion and contraction is distorted and cracks are more likely to occur in the composite oxide due to the non-uniform metal composition. Therefore, for example, a complex oxide having a rich Ni abundance ratio (for example, LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ) or a complex oxide having a uniform ratio of Ni, Mn, and Co. Compared with (for example, LiNi _0.3 Mn _0.3 Co _0.3 O ₂ ), the long-term cycle characteristics are significantly reduced. On the other hand, with the configuration according to the present embodiment, surprisingly, even in a complex oxide having a non-uniform metal composition such as LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , the cycle characteristics are surprisingly high. I found it to be improved.

  Therefore, in the general formula (1), composite oxides in which b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26 The positive electrode active material is preferable because the effects of the present invention are remarkably obtained.

  The lithium nickel composite oxide also has a secondary particle configuration in which primary particles are aggregated. And the average particle diameter (average primary particle diameter) of the said primary particle becomes like this. Preferably it is 0.9 micrometer or less, More preferably, it is 0.20-0.6 micrometer, More preferably, it is 0.25-0.5 micrometer. . Moreover, the average particle diameter (average secondary particle diameter) of the secondary particles is preferably 5 to 20 μm, more preferably 5 to 15 μm. Furthermore, the value of these ratios (average secondary particle size / average primary particle size) is preferably greater than 11, more preferably 15 to 50, and even more preferably 25 to 40. The primary particles constituting the lithium nickel composite oxide usually have a hexagonal crystal structure having a layered structure, but the size of the crystallite is correlated with the size of the average primary particle size. Have. Here, “crystallite” means the largest group that can be regarded as a single crystal, and can be measured by a method of refining the crystal structure parameters from the diffraction intensity obtained by powder X-ray diffraction measurement or the like. Although there is no restriction | limiting in particular about the specific value of a crystallite diameter, Preferably it is 1 micrometer or less, More preferably, it is 0.55 micrometer or less, More preferably, it is 0.4 micrometer or less. By adopting such a configuration, it becomes possible to further reduce the amount of displacement during expansion and contraction of the active material, suppressing the occurrence of secondary particle refinement (cracking) due to repeated charge and discharge, and the cycle This can contribute to further improvement of characteristics. In addition, there is no restriction | limiting in particular about the lower limit of the value of a crystallite diameter, Usually, it is 0.02 micrometer or more. Here, in this specification, the value of the crystallite diameter in the positive electrode active material particles is measured by the Rietveld method in which the crystallite diameter is calculated from the diffraction peak intensity obtained by powder X-ray diffraction measurement.

The tap density of the lithium-nickel-based composite oxide is preferably 2.3 g / cm ^3, more preferably 2.4~2.9g / cm ^3. By setting it as such a structure, the high density of the primary particle which comprises the secondary particle of a positive electrode active material is fully ensured, and the improvement effect of cycling characteristics can also be maintained.

Further, BET specific surface area of the lithium nickel composite oxide is preferably 0.1~1.0m ² / g, more preferably 0.3~1.0m ² / g, particularly preferably 0. 3 to 0.7 m ² / g. When the specific surface area of the active material is in such a range, the reaction area of the active material is ensured and the internal resistance of the battery is reduced, so that the occurrence of polarization during the electrode reaction can be minimized.

Further, for the lithium nickel composite oxide, the diffraction peak intensity ratio ((003) / (104)) is the diffraction peak on the (104) plane and the diffraction peak on the (003) plane obtained by powder X-ray diffraction measurement. It is preferably 1.28 or more, more preferably 1.35 to 2.1. The diffraction peak integrated intensity ratio ((003) / (104)) is preferably 1.08 or more, more preferably 1.10 to 1.45. These rules are preferable for the following reasons. That is, the lithium nickel composite oxide has a layered rock salt structure in which a Li ⁺ layer and a Ni ³⁺ layer exist between oxygen layers. However, ^{Ni 3+} is easily reduced to ^{Ni 2+,} and because substantially equal to the ^{Ni 2+} ion radius (0.83Å) is Li ⁺ ion radius (0.90 Å), Ni to Li ⁺ defect occurring during active material synthesized ²⁺ tends to be mixed. When Ni ²⁺ is mixed into the Li ⁺ site, a locally electrochemically inactive structure is formed and Li ⁺ diffusion is prevented. For this reason, when an active material with low crystallinity is used. Battery charge / discharge capacity may decrease and durability may decrease. The above definition is used as an index of the crystallinity. Here, as a method for quantifying crystallinity, as described above, the ratio of the intensity of diffraction peaks of the (003) plane and the (104) plane and the ratio of the integrated intensity of the diffraction peaks by crystal structure analysis using X-ray diffraction. Was used. When these parameters satisfy the above-mentioned rules, defects in the crystal are reduced, and a decrease in battery charge / discharge capacity and a decrease in durability can be suppressed. Such crystallinity parameters can be controlled by the raw material, composition, firing conditions, and the like.

  Lithium nickel composite oxides such as NMC composite oxides can be prepared by selecting various known methods such as coprecipitation method and spray drying method. The coprecipitation method is preferably used because the complex oxide according to this embodiment is easy to prepare. Specifically, as a method for synthesizing the NMC composite oxide, for example, a nickel-cobalt-manganese composite oxide is produced by a coprecipitation method as in the method described in JP2011-105588A, and then nickel-cobalt. -It can be obtained by mixing and firing a manganese composite oxide and a lithium compound. This will be specifically described below.

  A raw material compound of the composite oxide, for example, a Ni compound, a Mn compound, and a Co compound is dissolved in an appropriate solvent such as water so as to have a desired composition of the active material. Examples of the Ni compound, Mn compound, and Co compound include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and halides of the metal elements. Specific examples of the Ni compound, Mn compound, and Co compound include, but are not limited to, nickel sulfate, cobalt sulfate, manganese sulfate, nickel acetate, cobalt acetate, and manganese acetate. In this process, as necessary, for example, Ti, Zr, Nb as a metal element that substitutes a part of the layered lithium metal composite oxide constituting the active material so as to have a desired active material composition. , W, P, Al, Mg, V, Ca, Sr, and a compound containing at least one metal element such as Cr may be further mixed.

  A coprecipitation reaction can be performed by a neutralization and precipitation reaction using the raw material compound and an alkaline solution. Thereby, the metal composite hydroxide and metal composite carbonate containing the metal contained in the said raw material compound are obtained. As the alkaline solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like can be used, but sodium hydroxide, sodium carbonate or a mixed solution thereof is preferably used for the neutralization reaction. . In addition, an aqueous ammonia solution or an ammonium salt is preferably used for the complex reaction.

  The addition amount of the alkaline solution used for the neutralization reaction may be an equivalent ratio of 1.0 with respect to the neutralized amount of all the metal salts contained, but it is preferable to add the alkali excess together for pH adjustment.

  As for the addition amount of the aqueous ammonia solution or ammonium salt used for the complex reaction, the ammonia concentration in the reaction solution is preferably added in the range of 0.01 to 2.00 mol / l. The pH of the reaction solution is preferably controlled in the range of 10.0 to 13.0. The reaction temperature is preferably 30 ° C. or higher, more preferably 30 to 60 ° C.

  The composite hydroxide obtained by the coprecipitation reaction is then preferably suction filtered, washed with water and dried. The particle size of the composite hydroxide can be controlled by adjusting the conditions (stirring time, alkali concentration, etc.) for carrying out the coprecipitation reaction, which is the secondary electrode of the positive electrode active material finally obtained. It affects the average particle size (D50 (A)) of the particles.

  Next, the nickel-cobalt-manganese composite hydroxide is mixed with a lithium compound and fired to obtain a lithium-nickel-manganese-cobalt composite oxide. Examples of the Li compound include lithium hydroxide or a hydrate thereof, lithium peroxide, lithium nitrate, and lithium carbonate.

  The firing process may be performed in one stage, but is preferably performed in two stages (temporary firing and main firing). A composite oxide can be obtained efficiently by two-stage firing. The pre-baking conditions are not particularly limited, and differ depending on the lithium raw material, so that it is difficult to uniquely define them. Here, the factors for controlling the average primary particle size and crystallite size are particularly important as the firing temperature and firing time during firing (temporary firing and main firing in the case of two stages). By adjusting based on the following tendency, the average primary particle diameter and crystallite diameter can be controlled. That is, when the firing time is lengthened, the average primary particle diameter and crystallite diameter increase. Further, when the firing temperature is increased, the average primary particle size and crystallite size are increased. In addition, it is preferable that a temperature increase rate is 1-20 degrees C / min from room temperature. The atmosphere is preferably in air or in an oxygen atmosphere. Here, in the case of synthesizing the NMC composite oxide using lithium carbonate as the Li raw material, the pre-baking temperature is preferably 500 to 900 ° C, more preferably 600 to 800 ° C, and further preferably 650. ~ 750 ° C. Furthermore, the pre-baking time is preferably 0.5 to 10 hours, and more preferably 4 to 6 hours. On the other hand, the conditions for the main firing are not particularly limited, but the rate of temperature rise is preferably from room temperature to 1 to 20 ° C./min. The atmosphere is preferably in air or in an oxygen atmosphere. In the case of synthesizing an NMC composite oxide using lithium carbonate as a Li raw material, the firing temperature is preferably 800 to 1200 ° C, more preferably 850 to 1100 ° C, and still more preferably 900 to 1050. ° C. Furthermore, pre-baking time becomes like this. Preferably it is 1 to 20 hours, More preferably, it is 8 to 12 hours.

  If necessary, when adding a trace amount of a metal element that replaces a part of the layered lithium metal composite oxide constituting the active material, as the method, a method of previously mixing with nickel, cobalt, manganate, Any means such as a method of adding nickel, cobalt and manganate simultaneously, a method of adding to the reaction solution during the reaction, a method of adding to the nickel-cobalt-manganese composite oxide together with the Li compound may be used.

  The lithium nickel composite oxide can be produced by appropriately adjusting reaction conditions such as pH of the reaction solution, reaction temperature, reaction concentration, addition rate, and stirring time.

  One of the features of the positive electrode for a non-aqueous electrolyte secondary battery according to this embodiment is that the discharge depth (DOD) corresponding to the positive electrode potential (versus lithium redox potential) in the range of 3.93 to 4.03 V has a cell voltage of 3 It exists in the point comprised so that it may become 25% or less with respect to 100% of the total depth of discharge (total DOD) corresponding to the range of -4.25V.

  With the configuration as described above, according to the positive electrode for a non-aqueous electrolyte secondary battery according to the present embodiment, when applied to a non-aqueous electrolyte secondary battery having a large capacity and a large area, the Joule at the time of charge and discharge is reduced. The elution of Mn from the spinel-based lithium manganese composite oxide due to the increase in heat is suppressed, and the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved. The mechanism presumed regarding the manifestation of such an excellent effect will be described below with reference to the drawings. FIG. 2 shows a case where only a spinel lithium manganese composite oxide is used as the positive electrode active material (curve a shown in FIG. 2), and a spinel lithium manganese composite oxide and a lithium nickel composite oxide as the positive electrode active material. It is a graph which shows the discharge curve about each when the mixture (mixing ratio 70:30 (weight%)) is used (curve b shown in FIG. 2) (all use graphite as a negative electrode active material). . Here, the discharge curve shown in FIG. 2 is shown as a graph when the horizontal axis represents the active material capacity (DOD (Depth of Discharge); discharge depth [%]) and the vertical axis represents the cell voltage [V]. Has been. Note that the discharge curve as shown in FIG. 2 is usually obtained by charging the battery in a constant current mode to a predetermined cut-off voltage (eg, cell voltage of 4.25 V in FIG. 2), and then further increasing the constant current. It is plotted by discharging to a predetermined cut-off voltage (for example, the cell voltage is 3.0 V in FIG. 2) in the mode. FIG. 3 is an enlarged graph showing a region (region X shown in FIG. 2) where the depth of discharge (DOD) in the discharge curve shown in FIG. 2 is 40 to 90%.

  As shown in FIGS. 2 and 3, the curve b has a steeper slope when passing through the region corresponding to the cell voltage of 3.85 to 3.95 V in the curve b than in the curve a. Here, the cell voltage of 3.85 to 3.95 V corresponds to a positive electrode potential (vs. lithium oxidation-reduction potential) of 3.93 to 4.03 V, and in this positive electrode potential range, from the spinel-based lithium manganese composite oxide. (See the graph and table shown in FIG. 4; quoted from Journal of Power Sources, 136 (2004), p. 115-121). As described above, the curve a and the curve b are different in slope of the discharge curve, so that the cell voltage corresponding to the positive electrode potential (versus lithium oxidation-reduction potential) in the range of 3.93 to 4.03 V is 3.85 to 3. The DOD corresponding to the range of 95V is reduced to 25% in the curve b compared with 33% in the curve a based on the total DOD of 100% (corresponding to the cell voltage of 3.0 to 4.25V). ing.

  According to the studies by the present inventors, it has been found that sufficient charge / discharge cycle characteristics cannot be achieved even when a battery having a large capacity and a large area is obtained by the technique described in Japanese Patent Application Laid-Open No. 2000-77071. It was issued. And, the present inventors searched for the cause, and with the increase in capacity and area of the battery, at the time of charging and discharging that did not manifest in a small capacity and small battery such as a consumer battery. An increase in Joule heat was observed, which was found to promote Mn elution. More specifically, according to the study by the present inventors, in the case of a battery having a large capacity and a large area, a voltage corresponding to a predetermined positive electrode potential at which Mn elution is likely to occur due to an increase in Joule heat. Even with cell voltages other than the above, it has been found that the cell temperature rises during normal use (discharge) and falls into a pseudo high temperature storage mode. Further, the present inventors, due to the occurrence of this pseudo high temperature storage mode, tends to cause Mn elution even if charging and discharging are repeated in the normal mode (that is, deterioration is accelerated). It was found out. In addition, in large-capacity, large-area batteries, the Joule heat generated during charging is difficult to dissipate to the outside, so heat accumulates inside the electrode, which can spur the occurrence of the high-temperature storage mode described above. it was thought.

  In addition, the present inventors have surprisingly found that when a lithium nickel composite oxide is used in combination with a spinel lithium manganese composite oxide, a decrease in charge / discharge cycle characteristics is remarkably suppressed. . And in the battery which concerns on such this form, it confirmed that the integration time which passes Mn elution area at the time of charging / discharging was reduced, and came to complete this invention.

  Therefore, in the positive electrode for a nonaqueous electrolyte secondary battery according to this embodiment, as described above, the discharge depth (DOD) corresponding to the positive electrode potential (with respect to lithium redox potential) of 3.93 to 4.03 V is Two kinds of positive electrodes essential to the positive electrode active material layer may be used as long as they are configured to be 25% or less with respect to 100% of the total depth of discharge (total DOD) corresponding to the voltage range of 3 to 4.25V. There is no restriction | limiting in particular about the mixing ratio of an active material, etc., It is possible to set suitably in the range which satisfy | fills said requirements.

However, as a result of further investigation by the present inventors, the effect of the discharge curve on the reduction of the accumulated time when passing through the Mn elution region depending on the type of the lithium nickel-based composite oxide (as described above, the “predetermined It was found that there was a difference in “DOD / total DOD ratio”). It has also been found that the effect of reducing the integration time varies depending on the amount of nickel atoms contained in the lithium nickel composite oxide added to the spinel lithium manganese composite oxide. For example, FIG. 5 is a graph comparing the reduction effect of the Mn elution region when two different types of lithium nickel composite oxides are used in combination with the spinel lithium manganese composite oxide. As shown in FIG. 5, when LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811) is used as the lithium nickel-based composite oxide, LiNi _0.5 Mn _0.3 Co _0. Compared with the case where ₂ O ₂ (NMC532) is used, a larger effect of reducing the above-mentioned accumulated time was observed with a smaller addition amount. For example, in FIG. 5, the addition amount of the lithium nickel composite oxide required to reduce the Mn elution region by 30% is 38% by weight with respect to the total amount of 100% by weight of the spinel lithium manganese composite oxide in NMC811. In contrast, NMC532 has 43% by weight.

  From the above, in the positive electrode according to the present embodiment, as a preferred embodiment of the mixing ratio of the two types of positive electrode active materials included in the positive electrode active material layer, inclusion in the positive electrode active material layer of spinel-based lithium manganese composite oxide Nickel when the ratio is A [wt%], the content ratio of the lithium nickel composite oxide in the positive electrode active material layer is B [wt%], and the valence of lithium atoms in the lithium nickel composite oxide is 1. When the valence of an atom is x, the following formula 1:

Is preferably satisfied. By adopting such a configuration, it is possible to more reliably reduce the integration time when the discharge curve passes through the Mn elution region, and to contribute effectively to the manifestation of the effect according to the present embodiment. The value of B × x / (A + B) is more preferably 0.24 or more, and further preferably 0.35 or more.

-Other components In addition to the positive electrode active material described above, the positive electrode active material layer is used to increase the conductivity, as necessary, a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and ion conductivity. It further includes other additives such as lithium salts. However, the content of a material that can function as an active material in the positive electrode active material layer and the negative electrode active material layer described later is preferably 85 to 99.5% by weight.

(binder)
Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride fluorine rubber such as rubber (VDF-CTFE fluorine rubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but preferably 0.5 to 15% by weight with respect to the active material layer. More preferably, it is 1 to 10% by weight.

  The positive electrode active material layer further includes other additives such as a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and a lithium salt for enhancing ion conductivity, as necessary.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive auxiliary agent include carbon materials such as carbon black such as ketjen black and acetylene black, graphite, and carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer and the later-described negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. The thickness of each active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. For example, the thickness of each active material layer is about 2 to 100 μm.

[Negative electrode active material layer]
The negative electrode active material layer contains an active material, and other additives such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and a lithium salt to enhance ionic conductivity as necessary. An agent is further included. Other additives such as conductive assistants, binders, electrolytes (polymer matrix, ion conductive polymers, electrolytes, etc.) and lithium salts for improving ion conductivity are those described in the above positive electrode active material layer column. It is the same.

Examples of the negative electrode active material include carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. Is mentioned. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. For the same reason, in the non-aqueous electrolyte secondary battery according to this embodiment, the negative electrode active material preferably includes graphite (graphite), and the negative electrode active material preferably includes graphite as a main component. “The negative electrode active material is mainly composed of graphite” means that the proportion of graphite in the negative electrode active material is 50% by weight or more. In this case, the proportion of graphite in the negative electrode active material is more preferably 70% by weight or more, still more preferably 85% by weight or more, still more preferably 90% by weight or more, and particularly preferably 95% by weight or more. And most preferably 100% by weight.

  Here, in the examples described later, examples using a negative electrode active material mainly composed of graphite (graphite) are disclosed, but even when a negative electrode active material not containing graphite is used, Those skilled in the art can fully understand that the invention can be implemented and the effect of improving the cycle characteristics can be obtained. Hereinafter, this point will be described. The cell voltage is determined as the difference between the potential difference of the positive electrode active material and the potential difference of the positive electrode active material. When a negative electrode active material other than graphite is used, the cell voltage may be in a range different from the examples described later. Nevertheless, as described above, a predetermined positive electrode potential of 3.93 to 4.03 V is used. Since the range of (redox potential against lithium) is a range in which Mn elution is particularly noticeable, the ratio of the DOD corresponding to this range to the total DOD is set to a value equal to or less than the predetermined upper limit value. Similarly, it is obvious that elution of Mn can be suppressed and cycle characteristics can be improved.

  Of course, negative electrode active materials other than those described above may be used.

  The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

  The negative electrode active material layer preferably contains at least an aqueous binder. A water-based binder has a high binding power. In addition, it is easy to procure water as a raw material, and since steam is generated at the time of drying, the capital investment in the production line can be greatly suppressed, and the environmental load can be reduced. There is.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meta ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl methacrylate Relate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer , Polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80. Mol% or more, more preferably 90 mol% or more) and a modified product thereof (saponified product of 1 to 80 mol% of vinyl acetate units of a copolymer of ethylene / vinyl acetate = 2/98 to 30/70 mol ratio) , Poly Nyl alcohol 1-50 mol% partially acetalized product), starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, And their salts), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, alkyl (meth) acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich Denatured body Formalin condensation type resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, and water-soluble polymers such as mannangalactan derivatives Is mentioned. These aqueous binders may be used alone or in combination of two or more.

  The aqueous binder may contain at least one rubber binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose (salt) as a binder. The content weight ratio between the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.1-10, 0 More preferably, it is 5-2.

  Of the binder used in the negative electrode active material layer, the content of the aqueous binder is preferably 80 to 100% by weight, more preferably 90 to 100% by weight, and preferably 100% by weight.

[Separator (electrolyte layer)]
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  In addition, as described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte constituting the electrolytic solution layer has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and the ion conductivity between the layers is easily cut off. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA), and copolymers thereof.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

  The separator is preferably a separator (heat-resistant insulating layer-attached separator) in which a heat-resistant insulating layer is laminated on a porous substrate. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a highly heat-resistant separator having a melting point or a heat softening point of 150 ° C. or higher, preferably 200 ° C. or higher is used. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the battery manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

The inorganic particles in the heat resistant insulating layer contribute to the mechanical strength and heat shrinkage suppressing effect of the heat resistant insulating layer. The material used as the inorganic particles is not particularly limited. Examples thereof include silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. Moreover, only 1 type may be used individually for these inorganic particles, and 2 or more types may be used together. Of these, silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) is preferably used, and alumina (Al ₂ O ₃ ) is more preferably used from the viewpoint of cost.

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . If it is this range, sufficient ion conductivity will be acquired and it is preferable at the point which maintains heat resistant strength.

  The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles or the inorganic particles and the resin porous substrate layer. With the binder, the heat-resistant insulating layer is stably formed, and peeling between the porous substrate layer and the heat-resistant insulating layer is prevented.

  The binder used for the heat-resistant insulating layer is not particularly limited. For example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber A compound such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or methyl acrylate can be used as a binder. Of these, carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. As for these compounds, only 1 type may be used independently and 2 or more types may be used together.

  The binder content in the heat resistant insulating layer is preferably 2 to 20% by weight with respect to 100% by weight of the heat resistant insulating layer. When the binder content is 2% by weight or more, the peel strength between the heat-resistant insulating layer and the porous substrate layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by weight or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The thermal contraction rate of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour at 150 ° C. and ² gf / cm ² . By using such a material having high heat resistance, it is possible to effectively prevent the separator from contracting even if the positive electrode heat generation amount increases and the battery internal temperature reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the positive electrode current collecting plate 27 and the negative electrode current collecting plate 25, and different materials may be used.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Battery exterior]
As the battery outer case 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily and it is easy to adjust to the desired electrolyte layer thickness, the exterior body is more preferably an aluminate laminate.

[Cell size]
FIG. 6 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery. Like this lithium ion secondary battery, according to a preferred embodiment of the present invention, there is provided a flat laminated battery having a structure in which the power generation element is enclosed in a battery outer package made of a laminate film containing aluminum. The

  As shown in FIG. 6, the flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 57 is encased by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Has been. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 1 described above. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

  The lithium ion secondary battery is not limited to a stacked flat shape. The wound lithium ion secondary battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. There is no particular limitation. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit. Preferably, the power generation element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Also, the removal of the tabs 58 and 59 shown in FIG. 6 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  In a general electric vehicle, the battery storage space is about 170L. Since auxiliary devices such as cells and charge / discharge control devices are stored in this space, the storage efficiency of a normal cell is about 50%. The efficiency of loading cells into this space is a factor that governs the cruising range of electric vehicles. If the size of the single cell is reduced, the loading efficiency is impaired, so that the cruising distance cannot be secured.

  Therefore, in the present invention, the battery structure in which the power generation element is covered with the exterior body is preferably large. Specifically, the length of the short side of the laminated cell battery is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the laminated cell battery refers to the side having the shortest length. The upper limit of the short side length is not particularly limited, but is usually 400 mm or less.

[Volume energy density and rated discharge capacity]
In a general electric vehicle, a travel distance (cruising range) by a single charge is 100 km. Considering such a cruising distance, the volume energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Wh or more.

Here, the non-aqueous electrolyte secondary battery in which the positive electrode according to this embodiment is used as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, is large in size due to the battery area and battery capacity. Is defined. Specifically, the nonaqueous electrolyte secondary battery according to this embodiment is a flat laminated battery, and the ratio of the battery area to the rated capacity (projected area of the battery including the battery outer package) is 5 cm ² / It is Ah or more and the rated capacity is 3 Ah or more. Only when the battery has a large area and a large capacity as described above, the cycle characteristics are degraded due to the elution of Mn from the spinel-type lithium manganese composite oxide due to the increase of the Joule heat during charging and discharging as described above. It comes to be. On the other hand, in a battery having a large area and not a large capacity as described above, such as a conventional consumer battery, an increase in Joule heat during charging / discharging does not become obvious, and therefore, from spinel-based lithium manganese composite oxide There is no decrease in cycle characteristics due to elution of Mn (see Comparative Examples 11 to 12 described later).

  Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both required vehicle performance and mounting space can be achieved.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

  A plurality of batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The nonaqueous electrolyte secondary battery of the present invention maintains a discharge capacity even when used for a long period of time, and has good cycle characteristics. Furthermore, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the nonaqueous electrolyte secondary battery can be suitably used as a vehicle power source, for example, a vehicle driving power source or an auxiliary power source.

  Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  Hereinafter, although it demonstrates still in detail using an Example and a comparative example, this invention is not necessarily limited to the following Examples at all.

(1) Preparation of spinel-based lithium manganese composite oxide A spinel-based lithium manganese composite oxide (LiMn ₂ O ₄ ) having an average secondary particle diameter of 15 μm was prepared as a positive electrode active material.

(2) Preparation of lithium nickel composite oxide Sodium hydroxide and ammonia were continuously supplied to an aqueous solution (1 mol / L) in which nickel sulfate, cobalt sulfate and manganese sulfate were dissolved at 60 ° C. to adjust the pH to 11 And a metal composite hydroxide in which nickel, manganese, and cobalt were dissolved at a molar ratio of 80:10:10 by a coprecipitation method.

The metal composite hydroxide and lithium carbonate were weighed so that the ratio of the total number of moles of metals other than Li (Ni, Co, Mn) and the number of moles of Li was 1: 1, and then mixed well. The temperature was raised at a rate of temperature increase of 5 ° C / min, calcined at 900 ° C for 2 hours in an oxygen atmosphere, then heated at a rate of temperature increase of 3 ° C / min, finally baked at 920 ° C for 10 hours, and cooled to room temperature. Thus, an NMC composite oxide (LiNi _0.80 Mn _0.10 Co _0.10 O ₂ ; hereinafter also referred to as “NMC composite oxide (1)”) as a positive electrode active material was obtained. In addition, the average secondary particle diameter of the obtained NMC composite oxide (1) was 10 μm.

Subsequently, similarly to the above, as another positive electrode active material, an NMC composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O having a molar ratio of nickel, manganese, and cobalt of 50:30:20 is used. ₂ ; hereinafter, also referred to as “NMC composite oxide (2)”). In addition, the average secondary particle diameter of the obtained NMC composite oxide (2) was 10 μm.

(3) Production of positive electrode 90% by weight in total of any of the spinel-based lithium manganese composite oxide prepared in (2) and the NMC composite oxide prepared in (2) above, and as a conductive assistant 5% by weight of carbon black (Super-P, 3M), 5% by weight of polyvinylidene fluoride (PVDF) (Kureha, # 7200) as a binder, and N-methyl-2-pyrrolidone (Slurry viscosity adjusting solvent) NMP) is mixed in an appropriate amount to prepare a positive electrode active material slurry, and the obtained positive electrode active material slurry is applied to the surface of an aluminum foil (thickness: 20 μm) as a current collector, dried at 120 ° C. for 3 minutes, A positive electrode active material layer having a rectangular planar shape was produced by compression molding with a roll press. Similarly, a positive electrode active material layer was formed on the back surface to produce a positive electrode in which a positive electrode active material layer was formed on both surfaces of a positive electrode current collector (aluminum foil). In addition, the single-sided coating amount of the positive electrode active material layer was 17 mg / cm ² (excluding the foil). In this way, 11 types of positive electrodes having different compositions of the positive electrode active material were produced as shown in Table 1 below (numbers are% by weight).

  In addition, about the size of each positive electrode, it was set to either □ 1- □ 3 described in Table 2 below. Here, L1 and L2 shown in Table 2 are the vertical and horizontal lengths of the planar rectangular shape of the positive electrode active material layer (L1 ≦ L2), and D is the area per electrode.

(4) Production of negative electrode Artificial graphite (Gr) as a negative electrode active material and silicon powder (Si) as necessary, carbon black (Super-P, manufactured by 3M) as a conductive auxiliary agent, ammonium salt of carboxymethyl cellulose as a binder ( CMC) and styrene-butadiene copolymer latex (SBR) were dispersed in purified water to prepare a negative electrode active material slurry. This negative electrode active material slurry was applied to a copper foil (thickness 10 μm) serving as a negative electrode current collector, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press to produce a negative electrode. In the same manner, a negative electrode active material layer was formed on the back surface to prepare a negative electrode in which a negative electrode active material layer was formed on both sides of a negative electrode current collector (copper foil). The coating amount of the negative electrode active material layer was adjusted so that the A / C ratio was 1.20 with the positive electrode facing when the test cell described later was prepared (the negative electrode active material The single-side coating amount of the material layer was 5.2 to 8.6 mg / cm ² (not including the foil)). In this way, three types of negative electrodes having different compositions of the negative electrode active material layer were produced as shown in Table 3 below (numbers are% by weight).

(5) Production of test cell (I)
The positive electrode produced in the above (3) and the negative electrode produced in the above (4) are selected as shown in Table 4 below, the electrode area is selected from □ 1 or □ 2, and the separator (thickness 25 μm) , Celgard # 2500 (manufactured by Polypore Co., Ltd.) were alternately stacked (positive electrode 3 layers, negative electrode 4 layers) to produce a power generation element. The obtained power generation element was placed in a bag made of an aluminum laminate sheet as an exterior, and an electrolytic solution was injected. As an electrolytic solution, an additive was added to 100% by weight of a solution obtained by dissolving 1.0M LiPF ₆ in a 3: 7 (EC: DEC volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC). What added 1 mass% of vinylene carbonate which was was used. Here, the injection amount of the electrolytic solution was an amount that is 1.40 times the total pore volume (calculated by calculation) of the positive electrode active material layer, the negative electrode active material layer, and the separator. Next, under vacuum conditions, the opening of the aluminum laminate sheet bag was sealed so that the current extraction tabs connected to both electrodes were led out, and a test cell that was a laminated lithium ion secondary battery was completed. . In this way, as shown in Table 4 below, 17 types of test cells (flat plate-type laminate batteries) having different types and sizes of positive electrodes and types of negative electrodes were produced (Examples 1 to 7 and Comparative Examples 1-9 and 11). Table 4 below shows the rated capacity (cell capacity) (Ah) and the ratio of the battery area to the rated capacity (capacity area ratio) (cm ² / Ah) of each test cell obtained.

Further, the positive electrode prepared in the above (3) and the negative electrode prepared in the above (4) are selected as shown in Table 4 below, and the electrode area is set as □ 3, and the layers are laminated through the separator in the same manner as described above. Then, after attaching the current take-out tab, it was wound up and sealed in an outer can, and the electrolyte was injected and sealed. Thus, as shown in Table 4 below, two types of test cells (winding type batteries) with different types of positive electrodes were produced (Comparative Examples 10 and 12). Table 4 below shows the rated capacity (cell capacity) (Ah) and the ratio of the battery area to the rated capacity (capacity area ratio) (cm ² / Ah) of each test cell obtained. Here, the rated capacity of the battery was determined as follows.

≪Measurement of rated capacity≫
The rated capacity of the test battery is left to stand for about 10 hours after injecting the electrolytic solution, and the initial charge is performed. Then, it measures by the following procedures 1-5 in the temperature range of 25 degreeC and the voltage range of 3.0V to 4.15V.

  Procedure 1: After reaching 4.15 V by constant current charging at 0.2 C, pause for 5 minutes.

  Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

  Procedure 3: After reaching 3.0 V by constant current discharge of 0.2 C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.

  Procedure 4: After reaching 4.1 V by constant current charging at 0.2 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.

  Procedure 5: After reaching 3.0 V by constant current discharge of 0.2 C, discharge by constant voltage discharge for 2 hours, and then stop for 10 seconds.

  Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 5 is defined as the rated capacity.

(6) Characteristic evaluation of test cell The battery prepared in (5) above is allowed to stand for 24 hours, and after the open circuit voltage (OCV) is stabilized, the cutoff voltage reaches 4.25 V at a 0.2 C rate. The battery was charged and discharged to a cut-off voltage of 3.0 V after a pause of 1 hour. The discharge depth width (cell voltage 3) corresponding to the cell voltage 3.85 to 3.95 V in the discharge curve (horizontal axis: DOD (discharge depth [%]), vertical axis: cell voltage [V]) obtained at this time. The depth of discharge [%] at .95 V—the depth of discharge [%] at a cell voltage of 3.85 V) was determined, and the ratio of the obtained depth of discharge depth to 100% of the total discharge depth (total DOD) was calculated. The results are shown in Table 4 below.

  In addition, as a durability test simulating an in-vehicle application, a charge / discharge cycle test at a 0.2 C rate was performed in a thermostat at 50 ° C., and a capacity retention rate after 300 cycles was calculated. The results are shown in Table 4 below.

From the results shown in Table 4, in the test cell having a large capacity and a large area (□ 1 and □ 2), a high capacity retention ratio is achieved (the cycle durability is improved) by adopting the configuration of the present invention. I understand that. It can also be seen that when the aspect ratio defined as the aspect ratio of the positive electrode active material layer is in the range of 1 to 3, the effect of improving the cycle durability due to the configuration of the present invention is more remarkably expressed ( Comparative Example 1 using □ 2 (aspect ratio 1.67) compared to the effect of Comparative Example 12 (capacity maintenance ratio 74% → 78%) on Comparative Example 10 using □ 3 (aspect ratio 80.00) (Effect of Example 5 on capacity (capacity maintenance ratio 70% → 79%) is more remarkable). When □ 1 (battery area 100 cm ² ) is used, the rated capacity (cell capacity) is small in the first place (not a test cell having a large capacity and a large area). There is no improvement in cycle durability.

(7) Preparation of test cell (II)
The separator (thickness 25 μm, Celgard # 2500, manufactured by Polypore) with the positive electrode (C11) in which the excellent effect was confirmed in the above (6) and the negative electrode produced in the above (4), with an electrode area of □ 2. A power generation element having a large number of layers was produced by alternately laminating through the layers. Here, the positive electrode 20 layer + the negative electrode 21 layer was used in Example 8, the positive electrode 30 layer + the negative electrode 31 layer was used in Example 9, and the positive electrode 40 layer + the negative electrode 41 layer was used in Example 10. Using the power generation element thus obtained, three types of test cells (flat plate (flat) laminate battery) were produced in the same manner as in (5) above. Table 4 below shows the rated capacity (cell capacity) (Ah) and the ratio of the battery area to the rated capacity (capacity area ratio) (cm ² / Ah) of each test cell obtained. Further, in the same manner as in (6) above, the ratio of the discharge depth width corresponding to the cell voltage of 3.85 to 3.95 V in the discharge curve to the total discharge depth (total DOD) of 100% is calculated. A cycle test was performed, and the capacity retention rate after 300 cycles was calculated. The results are shown in Table 5 below.

  From the results shown in Table 5, according to the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, even in a case where the number of stacks is increased and the cell capacity is increased in the flat laminate type (flat) laminate battery, It can be seen that excellent cycle durability can be exhibited.

  This application is based on Japanese Patent Application No. 2013-054105 filed on Mar. 15, 2013, the disclosure of which is incorporated by reference in its entirety.

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21, 57 power generation element,
25 negative current collector,
27 positive current collector,
29, 52 Battery exterior material,
58 positive electrode tab,
59 Negative electrode tab.

Claims (7)

The value of the ratio of the cell area to rated capacity (projected area of the cell including up battery case body) is not less 5 cm 2 / ^Ah or more, rated capacity Ri der least 3Ah, the power generating element in a battery outer package made of laminated film a non-aqueous electrolyte secondary batteries of flat laminated type having encapsulated becomes a configuration,
A positive electrode having a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector and including a positive electrode active material including a spinel-based lithium manganese composite oxide and a lithium-nickel-based composite oxide;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the negative electrode current collector;
A separator;
A power generation element including
The depth of discharge (DOD) corresponding to the positive electrode potential (versus lithium redox potential) in the range of 3.93 to 4.03 V is 100% of the total depth of discharge (total DOD) corresponding to the range of the cell voltage of 3 to 4.25 V. For 25% or less,
The lithium nickel composite oxide is
General formula: Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x are 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 < c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, b + c + d = 1, M is Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and having a composition represented by at least one a is) selected from the group consisting of cr, a non-aqueous electrolyte secondary batteries. The content ratio of the spinel-based lithium manganese composite oxide in the positive electrode active material layer is A [mass%], the content ratio of the lithium nickel-based composite oxide in the positive electrode active material layer is B [mass%], and the lithium nickel When the molar fraction of nickel atoms is 1 when the molar fraction of lithium atoms in the system composite oxide is 1, the following formula 1:
To satisfy the non-aqueous electrolyte secondary batteries according to claim 1. The non-aqueous solution according to claim 1, wherein b, c, and d satisfy 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, and 0.19 ≦ d ≦ 0.26. electrolyte secondary batteries. 4. The electrode according to claim 1, wherein the positive electrode active material layer has a rectangular shape, and an aspect ratio of the electrode defined as an aspect ratio of the rectangular positive electrode active material layer is 1 to 3. non-aqueous electrolyte secondary batteries. The negative active material comprises as a main component of graphite, a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 , wherein the separator is a separator with a heat-resistant insulating layer. Laminate film is one that includes aluminum, non-aqueous electrolyte secondary battery according to any one of claims 1-6.