WO2014142280A1 - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

[Problem] To provide a means that is capable of suppressing changes in resistance associated with the depth of discharge and improving discharge rate characteristics in a battery that is intended particularly for high output use (with an internal resistance as small as 10 mΩ/Ah (SOC 50%) or less) among large-size non-aqueous electrolyte secondary batteries capable of being used for driving electric vehicles, for example. [Solution] This non-aqueous electrolyte secondary battery comprises a power-generating element including: a positive electrode in which a positive-electrode active material layer including a positive-electrode active material is formed on the surface of a positive-electrode charge collector; a negative electrode in which a negative-electrode active material layer including a negative-electrode active material is formed on the surface of a negative-electrode charge collector; and a separator. In this secondary battery: the positive-electrode active material includes a spinel-type manganese positive-electrode active material and a lithium-nickel complex oxide; the rate of mixture of said lithium-nickel complex oxide to 100 wt% of said positive-electrode active material is 30 wt% or greater; and the internal resistance is 10 mΩ/Ah or less (SOC 50%).

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery.

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 in which a positive electrode active material or the like is applied to a current collector, and a negative electrode in which a negative electrode active material or the like is applied to a current collector. It has the structure connected through the electrolyte layer holding electrolyte gel. Then, ions such as lithium ions are occluded / released in the electrode active material, thereby causing a charge / discharge reaction of the battery.

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.

Lithium manganese composite oxide (LiMn ₂ O ₄ ) has a spinel structure and functions as a 4V-class positive electrode material between the composition and λ-MnO ₂ . Since the spinel structure lithium manganese composite oxide has a three-dimensional host structure different from the layered structure of LiCoO ₂ and the like, most of the theoretical capacity can be used, and excellent cycle characteristics are expected. Yes.

However, in actuality, lithium ion secondary batteries using lithium manganese composite oxide as a positive electrode material cannot avoid capacity deterioration that gradually decreases in capacity due to repeated charge and discharge, which is great for practical use. The problem remained.

As a technique for solving the problem of capacity deterioration of such a lithium manganese composite oxide, for example, Japanese Patent Application Laid-Open No. 2000-77071 discloses a lithium material having a predetermined specific surface area as a positive electrode material in addition to a lithium manganese composite oxide. A technique of further using a nickel-based composite oxide (LiNiO ₂ , Li ₂ NiO ₂ , LiNi ₂ O ₄ , Li ₂ Ni ₂ O ₄ , LiNi _1-x MxO _2, etc.) is disclosed. According to Japanese Patent Application Laid-Open No. 2000-77071, as a result of suppressing the elution of Mn from the lithium manganese composite oxide and the change in the Li concentration in the electrolytic solution, the charge / discharge cycle characteristics (particularly high temperature) It is said that a non-aqueous electrolyte secondary battery having a greatly improved charge / discharge life) can be provided.

However, the technique related to Japanese Patent Laid-Open No. 2000-77071 does not take into account the required performance of a large battery for an electric vehicle. According to the study by the present inventors, it has been found that even if the technique proposed in the conventional consumer use is applied as it is to a large battery for an electric vehicle, sufficient battery performance is not exhibited. More specifically, a large battery for an electric vehicle requires a high output and a large capacity secondary battery. However, the secondary battery disclosed in Japanese Patent Application Laid-Open No. 2000-77071 is under a high output condition. It has been found that the resistance change with the progress of the depth of discharge is large and the amount of electricity that can be taken out decreases at the end of the discharge.

Therefore, the present invention is assumed to be used particularly at a high output among large-sized nonaqueous electrolyte secondary batteries that can be used for driving electric vehicles and the like (internal resistance is 10 mΩ / Ah (SOC 50%) or less). It is an object of the present invention to provide means for suppressing a change in resistance accompanying the depth of discharge and improving discharge rate characteristics in a small battery.

The present inventors have accumulated earnest research. As a result, in the positive electrode active material including the spinel-based manganese positive electrode active material and the lithium nickel-based composite oxide, the above-described problem is solved by setting the mixing ratio of the lithium nickel-based composite oxide within a specific range. I found.

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 non-aqueous electrolyte secondary battery. It is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of a nonaqueous electrolyte secondary battery. Battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at charge depth SOC 50% to SOC 20% and discharge capacity obtained at 0.2 C ampere and 2 C ampere of full cells prepared in Examples 1 to 5 and Comparative Examples 1 and 2 It is a graph which shows the discharge rate characteristic (2C / 0.2C) calculated | required from (2). Obtained from the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at the charging depth SOC 50% to SOC 20% of the full cell prepared in Examples 6 to 7 and Comparative Example 3, and the discharge capacity obtained at 0.2 C ampere and 2 C ampere. 5 is a graph showing the discharge rate characteristics (2C / 0.2C). Obtained from the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at the charge depth SOC 50% to SOC 20% of the full cells prepared in Examples 8 to 9 and Comparative Example 4 and the discharge capacity obtained at 0.2 C ampere and 2 C ampere. 5 is a graph showing the discharge rate characteristics (2C / 0.2C). From the charge depth SOC 50% to SOC 20% of the full cell produced in Examples 10 to 11 and Comparative Example 5, the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) and the discharge capacity obtained at 0.2 C ampere and 2 C ampere were obtained. 5 is a graph showing the discharge rate characteristics (2C / 0.2C). Obtained from the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at the charge depth SOC 50% to SOC 20% of the full cells prepared in Examples 12 to 13 and Comparative Example 6 and the discharge capacity obtained at 0.2 C ampere and 2 C ampere. 5 is a graph showing the discharge rate characteristics (2C / 0.2C). Discharges obtained from the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at the charge depth SOC 50% to SOC 20% of the full cells prepared in Examples 1 and 14 to 17 and the discharge capacity obtained at 0.2 C amperes and 2 C amperes. It is a graph which shows a rate characteristic (2C / 0.2C). Discharges obtained from the battery internal resistance change rate (DCR ₂₀ / DCR ₅₀ ) at charge depth SOC 50% to SOC 20% and discharge capacities obtained at 0.2 C amperes and 2 C amperes of the full cells prepared in Examples 1 and 18 to 21 It is a graph which shows a rate characteristic (2C / 0.2C).

According to one embodiment of the present invention, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of a positive electrode current collector, and a negative electrode active material layer containing a negative electrode active material on the surface of the negative electrode current collector are provided. A power generation element including a formed negative electrode and a separator; wherein the positive electrode active material includes a spinel-based manganese positive electrode active material and a lithium nickel-based composite oxide; and the positive electrode active material is 100% by weight. A non-aqueous electrolyte secondary battery is provided in which the mixing ratio of the lithium nickel-based composite oxide is 30% by weight or more and the internal resistance is 10 mΩ / Ah or less (SOC 50%). According to the configuration of the present invention, since the lithium nickel-based composite oxide sufficiently contributes to the discharge even at the end of discharge, it is possible to suppress a change in resistance associated with the depth of discharge and improve the amount of electricity that can be taken out at the end of discharge. As a result, a non-aqueous electrolyte secondary battery having excellent discharge rate characteristics can be provided, particularly in a large non-aqueous electrolyte secondary battery having a small internal resistance of 10 mΩ / Ah (SOC 50%) or less.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 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.

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing an outline of a stacked battery as an embodiment of the battery of the present invention. In the present specification, the flat type (stacked type) lithium ion secondary battery shown in FIG. 1 will be described in detail as an example, but the technical scope of the present invention is only such a form. Not limited to.

First, the overall structure of the nonaqueous electrolyte secondary battery of the present invention will be described with reference to the drawings.

[Battery overall structure]
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 type (stacked type) 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 so that they are electrically connected in parallel.

In addition, although the negative electrode active material layer 13 is arrange | positioned only at one side in the outermost layer positive electrode collector 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, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 1 so that the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the single-sided positive electrode active material of the outermost layer positive electrode current collector Layers may be arranged.

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 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) 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.

Hereafter, each member which comprises the nonaqueous electrolyte lithium ion secondary battery which is one Embodiment of this invention is demonstrated.

[Positive electrode]
The positive electrode according to the present invention has a configuration in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of a positive electrode current collector.

The positive electrode current collector is made of a conductive material. The conductive material is not particularly limited as long as it has conductivity, and conventionally known materials such as metals and conductive polymers can be appropriately used. Specifically, at least one selected from the group consisting of Fe, Cr, Ni, Mn, Ti, Mo, V, Nb, Al, Cu, Ag, Au, Pt and carbon, for example, two or more The current collector material such as stainless steel made of the above alloy can be preferably used. In the present embodiment, a Ni / Al clad material, a Cu / Al clad material, or a plating material obtained by combining these current collector materials can be preferably used. The current collector may be a current collector in which the surface of a metal (excluding Al) as the current collector material is coated with Al as the other current collector material. Moreover, you may use the electrical power collector which bonded together the metal foil which is two or more said electrical power collector materials depending on the case.

The thickness of the positive electrode current collector is not particularly limited, but is usually 1 to 100 μm, preferably about 1 to 50 μm.

In the present invention, in the case of a large current, the weight per unit area of the positive electrode is preferably 30 mg / cm ² or less, and preferably 25 mg / cm ² or less, from the viewpoint of suppressing a rapid decrease in battery discharge rate characteristics. Is more preferable. Note that the lower limit of the basis weight of the electrode is not particularly defined from the viewpoint of the battery discharge rate characteristics, but is more preferably 10 mg / cm ² or more from the viewpoint of the electrode preparation process or the battery energy density. Further, the basis weight on both surfaces of the electrode may be the same or different, but is more preferably the same.

In the present invention, it is preferable that the packing density of the positive electrode is 2.5 to 3.5 g / cm ³ from the viewpoint of suppressing a rapid decrease in battery discharge rate characteristics in the case of a large current. More preferably, it is set to ˜3.3 g / cm ³ .

Furthermore, in the positive electrode according to the present invention, it is preferable to satisfy at least one of the preferable range of the basis weight and the preferable range of the packing density, and more preferable to satisfy both the preferable range of the basis weight and the preferable range of the packing density. .

(Positive electrode active material)
In the present invention, the positive electrode active material includes a spinel manganese positive electrode active material and a lithium nickel composite oxide.

The spinel manganese positive electrode active material is not particularly limited, and a conventional lithium manganese composite oxide having a spinel structure is used.

Next, the lithium nickel composite oxide will be described.

The composition of the lithium nickel composite oxide according to the present invention is not specifically limited as long as it is composed of a composite oxide containing lithium and nickel. A typical example of a composite oxide containing lithium and nickel is lithium nickel-based composite oxide (LiNiO ₂ ). However, a composite oxide in which a part of nickel atoms of a lithium nickel composite oxide is substituted with another metal atom is more preferable. A preferable example is a lithium-nickel-manganese-cobalt composite oxide (hereinafter simply referred to as “NMC”). Or a lithium-nickel-cobalt-aluminum composite oxide. Here, the NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in an orderly manner) atomic layers 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-based lithium manganese oxide, that is, the supply capacity is doubled, and 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 invention, the NMC composite oxide includes a composite oxide in which a part of the transition 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.

The lithium-nickel-based composite oxide, since the theoretical discharge capacity is high, preferably the general formula _{(1): Li a Ni b} M c Co d O 2 ( In the formula, a, b, c, d is 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, and b + c + d = 1, where M is Mn, Al, Ti, Zr, Nb, W, P, Mg, V, Ca, Sr, Cr, and at least one kind of element. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of M, and d represents the atomic ratio of Co. 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.

Generally, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electronic conductivity. Ti and the like partially replace 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 <c ≦ 0.5 in the general formula (1). Since at least one selected from the group consisting of Mn, Al, Ti, Zr, Nb, W, P, Mg, V, Ca, Sr and Cr is dissolved, the crystal structure is stabilized. It is considered that even when charging and discharging are repeated, a decrease in battery capacity can be prevented and excellent cycle characteristics can be realized.

Moreover, in the lithium nickel-based composite oxide, the inventors of the present application have non-uniform metal compositions of nickel, manganese, and cobalt, such as LiNi _0.5 Mn _0.3 Co _0.2 O _2. It was found that the influence of strain / cracking of the composite oxide at the time of charge / discharge is increased. 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. In the present invention, 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 , a complex oxide having a specific true density is surprisingly obtained. It has been found that, when used, deterioration of cycle characteristics is suppressed.

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 according to the present invention can be prepared by selecting various known methods such as a coprecipitation method and a spray drying method. The coprecipitation method is preferably used because the composite oxide of the present invention is easy to prepare. Specifically, for example, after producing a nickel-manganese-cobalt composite hydroxide by a coprecipitation method as in the method described in JP2011-105588A, nickel-manganese-cobalt composite hydroxide; It can be obtained by mixing and baking with a lithium compound.

The details will be described below.

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

The coprecipitation reaction can be performed by neutralization and precipitation reaction using the above 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 content of all the metal salts contained, but it is preferable to add the alkali excess together for pH adjustment.

The addition amount of the aqueous ammonia solution or ammonium salt used for the complex reaction is preferably such that the ammonia concentration in the reaction solution is 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.

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

The firing treatment 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, 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. The firing temperature is preferably 700 to 1000 ° C., more preferably 650 to 750 ° C. Furthermore, the firing time is preferably 3 to 20 hours, and more preferably 4 to 6 hours. 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. The firing temperature is preferably 700 to 1000 ° C., more preferably 850 to 1100 ° C. Furthermore, the firing time is preferably 3 to 20 hours, and more preferably 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, the method includes, in advance, nickel, cobalt, manganate or aluminum Method of mixing, method of adding simultaneously with nickel, cobalt, manganate or aluminumate, method of adding to reaction solution during reaction, nickel-cobalt-manganese composite hydroxide or nickel-cobalt-aluminum together with Li compound Any means such as a method of adding to the composite hydroxide may be used.

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

As a result of diligent research on the fact that a secondary battery for consumer use as described in JP 2000-77071 A (corresponding to WO0013250A1) described above cannot achieve sufficient discharge rate characteristics, So identified the cause. That is, in a lithium ion secondary battery having a positive electrode including a spinel-based manganese positive electrode active material and a lithium nickel-based composite oxide, reaction potential profiles in which the lithium ion desorption reaction proceeds in the two types of positive electrode active materials are different. Specifically, the reaction ratio of the spinel-based manganese positive electrode active material increases at the initial stage of discharge, but the reaction ratio of the lithium nickel-based composite oxide increases at the end of the reaction. In particular, in the region where the SOC is 20% or less, almost only the lithium nickel composite oxide is in a reaction state. For this reason, in a secondary battery with a small mixing ratio of the lithium nickel composite oxide, the current flowing through the lithium nickel composite oxide becomes very large, the apparent internal resistance increases remarkably, and the discharge operating voltage suddenly increases. It will decline. As a result, it has been found that the amount of electricity that can be taken out decreases and the discharge rate characteristics deteriorate.

In addition, the present inventors are proceeding with studies to solve the above problems in a non-aqueous electrolyte secondary battery having an internal resistance of 10 mΩ / Ah or less (SOC 50%), which is assumed to be used under high output conditions. It was. Here, the internal resistance of the battery is one of indexes indicating its input / output performance. In particular, it is preferable that the internal resistance of a large secondary battery used in an automobile or the like is as small as possible within a designable range. In this respect, the inventors of the present invention have assumed that the non-aqueous electrolyte secondary battery targeted by the present invention is a battery whose internal resistance is 10 mΩ / Ah (SOC 50%) or less as a battery expected to be used under high output conditions. We decided to proceed with the investigation.

As a result, the inventors have found that excellent discharge rate characteristics can be obtained by setting the mixing ratio of the lithium nickel composite oxide to 100% by weight of the positive electrode active material to 30% by weight or more. In addition, the positive electrode active material according to the present invention may be composed of only two types of active materials of a spinel-based manganese positive electrode active material and a lithium nickel-based composite oxide, and other positive electrode active materials as long as the effects of the present invention are not impaired. May be included. In the case of being composed of only two kinds of active materials, spinel manganese positive electrode active material and lithium nickel composite oxide, the mixing ratio of the lithium nickel composite oxide with respect to 100% by weight of the positive electrode active material is 30% by weight. This means that the weight ratio of the lithium nickel composite oxide and the spinel manganese positive electrode active material is 30:70.

The mixing ratio of the lithium nickel composite oxide to 100% by weight of the positive electrode active material is preferably 30 to 90% by weight, more preferably 50 to 80% by weight. As described above, when the mixing ratio of the lithium nickel composite oxide is less than 30% by weight, particularly in a secondary battery having an internal resistance of 10 mΩ / Ah or less (SOC 50%), the lithium nickel composite is at the end of discharge. The reaction ratio of the oxide is increased, and the discharge rate characteristics are deteriorated.

Further, the positive electrode active material layer of the present invention includes a positive electrode material having a core portion containing the lithium nickel composite oxide and a shell portion containing a lithium metal composite oxide different from the lithium nickel composite oxide. But you can. Such a core-shell structure further improves the cycle characteristics of the nonaqueous electrolyte secondary battery. In the study by the present inventors, when the lithium nickel composite oxide particles after the cycle endurance test were analyzed, a decrease in Ni valence was confirmed only in the particle surface layer portion. From this, the present inventors set a hypothesis that Ni may be deactivated in the particle surface layer portion and may not substantially contribute to charge / discharge. In addition, it was considered that the arrangement of an NMC composite oxide having a low Ni concentration or a material other than Ni in the local portion that is likely to deteriorate would lead to further improvement in cycle characteristics. Such a core-shell type positive electrode active material can be produced by the method described in Japanese Patent Application Laid-Open No. 2007-213866.

In the positive electrode active material of the present invention, primary particles are aggregated to form secondary particles. There are voids between the primary particles in the secondary particles. In the present invention, the porosity of the secondary particles is preferably 2 to less than 10% from the viewpoint of cycle characteristics and volume energy density. Here, the porosity refers to the area ratio of the void portion to the sum of the area of the primary particle and the area of the void portion in the cross section of the secondary particle.

The average particle size of the positive electrode active material is not particularly limited, but is preferably 6 to 11 μm, more preferably 7 to 10 μm in terms of secondary particle size from the viewpoint of increasing output. The average particle diameter of the primary particles is 0.4 to 0.65 μm, more preferably 0.45 to 0.55 μm. The “particle diameter” in the present specification means the maximum distance L among the distances between any two points on the particle outline. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A value calculated as a value is adopted.

The positive electrode active material of the present invention preferably has a specific surface area of 0.30 to 1.0 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 electrode reaction can be minimized. The occurrence of polarization causes side reactions such as decomposition of the electrolytic solution and oxidative decomposition of the surface of the electrode material. Therefore, it is preferable to minimize the occurrence of polarization. More preferably, the specific surface area is 0.30 to 0.7 m ² / g.

The lithium nickel composite oxide of the present invention has (1) a true density of 4.40 to 4.80 g / cm ³ , or (2) a specific surface area of 0.30 to 1.0 m ² / g. It is preferable to satisfy at least one of the above, and it is more preferable to satisfy both (1) and (2).

In the present invention, the positive electrode active material content in the positive electrode active material layer is preferably 85 to 99.5% by weight.

In addition to the active material described above, the positive electrode active material layer according to the present invention is provided with a conductive additive, a binder, an electrolyte (such as a polymer matrix, an ion conductive polymer, an electrolytic solution) and an ion conductivity as necessary. It further includes other additives such as lithium salts.

(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 fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene 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 Examples thereof include vinylidene fluoride fluorine rubber such as fluorine 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 conductive assistant means an additive blended to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant 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, Li (CF ₃ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , and LiCF ₃ SO _3. It is done.

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

The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer described later 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. As an example, the thickness of each active material layer is about 2 to 100 μm.

[Negative electrode]
The negative electrode according to the present invention has a configuration in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of a negative electrode current collector. The negative electrode current collector is composed of a conductive material. About the kind and the thickness of the electroconductive material which comprise a negative electrode collector, since the form similar to having mentioned above about the positive electrode collector can be employ | adopted, detailed description is abbreviate | omitted here.

(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.

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, ) 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 Such as tacrylate), 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 (a 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) 1 to 50 mol% partially acetalized polyvinyl alcohol), 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 man Dech, modified formalin resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, mannangalactan derivative, etc. And water-soluble polymers. 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 styrene-butadiene rubber because of good binding properties.

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 (such as 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 of the styrene-butadiene rubber to the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.1 to 10; More preferably, it is 5 to 2.

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

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. 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.

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

As the separator of the porous sheet made of 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, and is preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

Also, 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, Li (CF 3 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6 A compound that can be added to the active material layer of the electrode, such as LiTaF ₆ and LiCF ₃ SO _3, 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, vinyl vinylene carbonate, allyl ethylene 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 above 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.

Further, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (a separator with a heat-resistant insulating layer). 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 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 adhering the inorganic particles and the inorganic particles to 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 the 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 leaking electricity. 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. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used. However, 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. In addition, the exterior body is more preferably an aluminum laminate because the group pressure applied to the power generation element applied from the outside can be easily adjusted and can be easily adjusted to a desired electrolyte layer thickness.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery.

As shown in FIG. 2, 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 tabs 58 and 59 shown in FIG. 2 are 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 automobile applications and the like, recently, larger batteries are required. The effect of the present invention of improving the discharge rate characteristics by suppressing the increase in internal resistance at the end of discharge when discharged under high output conditions is more effectively exhibited in the case of a large area battery. . Therefore, in this invention, it is preferable in the meaning that the effect of this invention is exhibited more that the battery structure which covered the electric power generation element with the exterior body is large sized. Specifically, the negative electrode active material layer is preferably rectangular, and the length of the short side of the rectangle 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 negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the length of the short side of the battery structure is not particularly limited, but is usually 250 mm or less.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, 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. In some batteries, the battery area per unit capacity is large, which is advantageous for discharging under high output conditions. Therefore, it is more preferable that the nonaqueous electrolyte secondary battery according to the present embodiment is a battery that is enlarged as described above, together with the merit due to the manifestation of the effects of the present invention. Further, as the non-aqueous electrolyte secondary battery according to this embodiment, it is more preferable that it is a large-sized lithium ion secondary battery for automobiles, together with the merit due to the manifestation of the effects of the present invention.

Furthermore, the size of the battery can be specified by the volume energy density, the single cell rated capacity, and the like. For example, in a general electric vehicle, a travel distance (cruising range) by one charge is 100 km, which is a market requirement. Considering such cruising distance, the single cell rated capacity is preferably 20 Wh or more, and the volume energy density of the battery is preferably 153 Wh / L or more. The volume energy density and the rated discharge capacity are measured by the methods described in the following examples. Further, 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. Setting the aspect ratio in such a range is preferable because the gas generated during charging can be discharged uniformly in the surface direction.

[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.

It is also possible to form a small assembled battery that can be attached and detached by connecting a plurality of batteries in series or in parallel. 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 the 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 in detail using an Example and a comparative example, this invention is not necessarily limited only to the following Examples.

[Example 1]
(1) Preparation of positive electrode active material Sodium hydroxide and ammonia are continuously supplied to an aqueous solution (1.0 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved so as to have a pH of 11.0. A metal composite hydroxide formed by solid solution with a molar ratio of nickel, cobalt and manganese of 50:20:30 was prepared by the method.

The metal composite oxide and lithium carbonate were weighed so that the ratio of the total number of moles of metals other than Li (Ni, Co, Mn) to the number of moles of Li was 1: 1, and then mixed sufficiently. The temperature was raised at a temperature rate of 5 ° C./min, pre-baked at 900 ° C. for 2 hours in an air 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. A lithium nickel composite oxide having a chemical composition of LiNi _0.50 Mn _0.30 Co _0.20 O ₂ was obtained. The lithium nickel composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) had an average primary particle size of 0.5 μm and an average secondary particle size of 10.0 μm.

Next, electrolytic manganese dioxide and aluminum hydroxide were mixed and heat-treated at 750 ° C. to obtain manganese sesquioxide, and then lithium carbonate was added and mixed so that the Li / (Mn + Al) molar ratio was 0.55. The spinel lithium manganate having the chemical composition LiMn ₂ O ₄ was obtained by baking at 20 ° C. for 20 hours. The average secondary particle diameter of the spinel lithium manganate (LiMn ₂ O ₄ ) was 10.0 μm.

Then, the obtained lithium nickel composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) and lithium spinel manganate (LiMn ₂ O ₄ ) were mixed at 30:70 (weight ratio). A positive electrode active material was prepared.

(2) Production of positive electrode 95% by weight of the positive electrode active material obtained in the above (1), 2% by weight of acetylene black (average particle size: 38 nm) as a conductive additive, 3% by weight of polyvinylidene fluoride (PVDF) as a binder, And an appropriate amount of N-methyl-2-pyrrolidone (NMP) which is a slurry viscosity adjusting solvent was mixed to prepare a positive electrode active material slurry, and the obtained positive electrode active material slurry had a basis weight of 15 mg / cm ² (single side) Then, it was applied to one side of an aluminum foil (thickness: 20 μm) as a current collector and dried. After sufficiently drying, the electrode thickness was adjusted using a roll press so that the packing density of the electrode mixture was 3.0 g / cm ^3, and a positive electrode having positive electrode active material layers on both sides was produced.

(3) Production of negative electrode A carbon negative electrode active material using natural graphite (average particle size 20 μm) coated with amorphous carbon as a negative electrode active material was prepared, 94% by weight of the negative electrode active material, and polyvinylidene fluoride (PVDF) as a binder An appropriate amount of 6% by weight and N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent was mixed to prepare a negative electrode slurry.

This slurry was applied to both surfaces of a copper foil (thickness 10 μm) serving as a negative electrode current collector, and the coating amount per unit area was 1 for each AC ratio (negative electrode charge capacity / positive electrode charge capacity). .2 was set. After sufficiently drying, the electrode thickness was adjusted using a roll press so that the electrode mixture filling density was 1.4 g / cm ^3, and a negative electrode having negative electrode active material layers on both sides was produced.

(4) Preparation of Electrolytic Solution A solution was prepared by dissolving 1.0M LiPF ₆ in a mixed solvent (volume ratio of 1: 1) of ethylene carbonate (EC) and dimethyl carbonate (DMC). Vinylene carbonate was added thereto in an amount corresponding to 2% by weight with respect to the weight of the electrolytic solution to obtain an electrolytic solution. Note that “1.0 M LiPF ₆ ” means that the lithium salt (LiPF ₆ ) concentration in the mixture of the mixed solvent and the lithium salt is 1.0 M.

(5) Production of full cell The positive electrode produced in (1) above is a square with a side of 20 cm, the negative electrode produced in (2) above is a square with a side of 20.5 cm, and a separator (polyethylene / polypropylene microporous film, thickness 25 μm) Are cut into a square with a side of 21 cm and laminated alternately (5 layers of positive electrode, 6 layers of negative electrode, 10 layers of separator). At this time, both ends are negative electrodes, and a separator is interposed between the positive electrode and the negative electrode. It was. Parallel cells were stacked by connecting the tabs of each layer. The obtained power generation element was put in an aluminum laminate outer package, the electrolyte prepared in (1) above was injected, and vacuum sealed to prepare a full cell for evaluation. The projected area of the battery including the full cell aluminum laminate outer package obtained was 484 cm ² .

[Examples 2-5, Comparative Examples 1-2]
In preparation of the positive electrode active material described in Example 1, the mixing ratio of lithium nickel-based composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) and lithium spinel manganate (LiMn ₂ O ₄ ) A full cell for evaluation was produced in the same manner as in Example 1 except that a positive electrode active material produced by changing the composition as described in Table 1 was used.

[Examples 6 to 7, Comparative Example 3]
In the preparation of the lithium nickel-based composite oxide described in Example 1, the preparation conditions were changed by the coprecipitation method so that the molar ratio of nickel, cobalt, and manganese was 1/3: 1/3: 1/3. Further, a positive electrode active material prepared according to a mixing ratio of lithium nickel-based composite oxide (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) and lithium spinel manganate (LiMn ₂ O ₄ ) described in Table 1 Each full cell for evaluation was produced in the same manner as in Example 1 except that was used.

[Examples 8 to 9, Comparative Example 4]
In the preparation of the lithium nickel-based composite oxide described in Example 1, the preparation conditions were changed by a coprecipitation method so that the molar ratio of nickel, cobalt, and manganese was 80:10:10. Except that a positive electrode active material prepared according to a mixing ratio of lithium nickel-based composite oxide (LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ) and spinel lithium manganate (LiMn ₂ O ₄ ) was used. Each evaluation full cell was produced in the same manner as in Example 1.

[Examples 10 to 11, Comparative Example 5]
In the preparation of the lithium nickel-based composite oxide described in Example 1, the preparation conditions were changed by a coprecipitation method so that the molar ratio of nickel, cobalt, and manganese was 60:20:20. Except that a positive electrode active material prepared according to a mixing ratio of lithium nickel-based composite oxide (LiNi _0.6 Mn _0.2 Co _0.2 O ₂ ) and lithium spinel manganate (LiMn ₂ O ₄ ) was used. Each evaluation full cell was produced in the same manner as in Example 1.

[Examples 12 to 13, Comparative Example 6]
In the production of the lithium nickel composite oxide described in Example 1, aluminum sulfate is used instead of manganese sulfate so that the molar ratio of nickel, cobalt, and aluminum is 80:10:10 by coprecipitation. The preparation conditions were changed, and further according to the mixing ratio of lithium nickel-based composite oxide (LiNi _0.8 Co _0.1 Al _0.1 O ₂ ) and spinel lithium manganate (LiMn ₂ O ₄ ) listed in Table 1 Each evaluation full cell was produced like Example 1 except having used the produced positive electrode active material.

[Examples 14 to 17]
In the production of the positive electrode described in Example 1, a full cell for each evaluation was produced in the same manner as in Example 1 except that the basis weight (one side) of the positive electrode was changed according to the description in Table 2.

[Examples 18 to 21]
In the production of the positive electrode described in Example 1, each evaluation full cell was produced in the same manner as in Example 1, except that the packing density of the positive electrode was changed according to the description in Table 3.

[Evaluation methods]
In the present invention, unless otherwise specified, the following various measurements are all performed at 25 ° C.

(1) Rate of change of battery internal resistance (DCR) First, the full cell produced in each example and comparative example was charged to a SOC of 50% SOC (state of charge) SOC, 0.2C ampere, 0.5C ampere, The battery was discharged for 10 seconds at a current value of 1 C ampere and the voltage after each discharge was measured. Then, the internal resistance DCR ₅₀ is obtained from the slope of a straight line graph with these current values on the horizontal axis and the measured voltage on the vertical axis, and the results are shown in Table 1.

Next, the battery was charged to a charge depth SOC of 20%, and the same operation as in the case of the SOC of 50% was performed to obtain DCR ₂₀ , and the results are shown in Table 1.

Thereafter, the battery internal resistance change rate (ΔDCR = DCR ₂₀ / DCR ₅₀ ) in the full cell produced in each example and comparative example was determined, and the results are shown in Tables 1 to 3. For easy comparison, the results of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in FIG. 3-1, and the results of Examples 6 to 7 and Comparative Example 3 are shown in FIG. 3-2. The results of Examples 8 to 9 and Comparative Example 4 are shown in FIG. 3-3, the results of Examples 10 to 11 and Comparative Example 5 are shown in FIG. 3-4, and the results of Examples 12 to 13 and Comparative Example 6 are shown in FIG. The results of Examples 1 and 14 to 17 are shown in FIG. 4, and the results of Examples 1 and 18 to 21 are shown in FIG.

In the present invention, the 4.15V full charge state is SOC 100%, the 3V full discharge state is SOC 0%, the state in which the capacity of 20% from the full discharge state is charged is SOC 20%, and the full discharge state is 50%. The state in which the capacity is charged is defined as SOC 50%.

(2) Discharge rate characteristics First, charging of the full cell produced in each example and comparative example was started at a constant current of 1 C ampere, and continued at a constant voltage of 4.15 V when the voltage reached 4.15 V. Charging was continued, and when the current value reached 0.02 C ampere, charging was completed (cut off), and the charge capacity at 1 C ampere was measured. Next, discharge was started at constant currents of 0.2 C ampere and 2 C ampere, and when the voltage reached 3.0 V, the discharge was completed (cutoff), and each discharge capacity at 0.2 C ampere and 2 C ampere Was measured.

Then, the ratio% (abbreviated as “2C / 0.2C”) of the discharge capacity obtained at each discharge rate was obtained, and the results are shown in Tables 1 to 3. For easy comparison, the results of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in FIG. 3-1, and the results of Examples 6 to 7 and Comparative Example 3 are shown in FIG. 3-2. The results of 8-9 and Comparative Example 4 are shown in FIG. 3-3, the results of Examples 10-11 and Comparative Example 5 are shown in FIG. 3-4, and the results of Examples 12-13 and Comparative Example 6 are shown in FIG. The results of Examples 1 and 14 to 17 are shown in FIG. 4, and the results of Examples 1 and 18 to 21 are shown in FIG.

In addition, the rated capacity of the full cell produced by each Example and the comparative example was calculated | required by the following.

The rated capacity is about 10 hours after injecting the electrolyte for the test battery, and the battery is initially charged after the battery voltage becomes 2.0 V or higher. Thereafter, the measurement is performed by the following procedures 1 to 4 at a temperature of 25 ° C. and a voltage range of 3.0 V to 4.15 V.

Procedure 1: After reaching 4.15 V by constant current charging at 0.2 C amp, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

Procedure 2: After reaching 3.0 V by constant current discharge of 0.2 C amp, pause for 5 minutes.

Procedure 3: After reaching 4.15 V by constant current charging at 1 C amp, charge for 2.5 hours by constant voltage charging, and then rest for 5 minutes.

Procedure 4: Discharge until reaching 3.0V by constant current discharge of 0.2C ampere.

Rated capacity: The discharge capacity obtained from the constant current discharge in step 4 is the rated capacity.

Table 1 shows the rated discharge capacity (Ah) and the ratio of the battery area to the rated capacity (cm ² / Ah) of each full cell measured as described above.

From the above results, in the batteries having an internal resistance of 10 mΩ / Ah or less (SOC 50%), the full cells of Examples 1 to 21 using the positive electrode with a mixing ratio of 30% by weight or more in any lithium nickel composite oxide. , The increase in resistance at the end of discharge was suppressed, and excellent discharge rate characteristics were obtained.

In the full cell, excellent discharge rate characteristics could be obtained by controlling the basis weight of the positive electrode to 30 mg / cm ² or less and the packing density to 2.5 to 3.5 g / cm ³ .

This application is based on Japanese Patent Application No. 2013-054103 filed on March 15, 2013, the disclosure of which is incorporated by reference as a whole.

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 (10)

1. A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of the positive electrode current collector;
   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 positive electrode active material includes a spinel manganese positive electrode active material and a lithium nickel composite oxide, and a mixing ratio of the lithium nickel composite oxide with respect to 100% by weight of the positive electrode active material is 30% by weight or more. ,
   A non-aqueous electrolyte secondary battery having an internal resistance of 10 mΩ / Ah or less (SOC 50%).
2. The lithium nickel composite oxide is
   General _{formula: Li a Ni b M c Co} d O 2 ( In the formula, a, b, c, d is, 0.9 ≦ a ≦ 1.2,0 <b <1,0 <c ≦ 0. 5, 0 <d ≦ 0.5, b + c + d = 1, M is at least 1 selected from the group consisting of Mn, Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr The nonaqueous electrolyte secondary battery according to claim 1, which has a composition represented by:
3. The non-aqueous electrolyte 2 according to claim 2, wherein b, c, and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, and 0.19 ≦ d ≦ 0.26. Next battery.
4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a weight per unit area (one side) of the positive electrode is 30 mg / cm ² or less.
5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a filling density of the positive electrode is 2.5 to 3.5 g / cm ³ .
6. 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.
7. The ratio of the battery area to the rated capacity (projected area of the battery including the battery outer casing) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. The non-aqueous electrolyte secondary battery described in 1.
8. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein an aspect ratio of the electrode defined as an aspect ratio of the rectangular positive electrode active material layer is 1 to 3.
9. A separator that is interposed between the positive electrode, the negative electrode, the positive electrode and the negative electrode, and holds a liquid electrolyte or a gel electrolyte;
   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, wherein a power generation element having the structure is enclosed in an exterior body that is a laminate film containing aluminum.
10. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 9, which is a large-sized lithium ion battery for automobiles.

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