JP2015095329A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is a lamination type battery arranged by using an NMC complex oxide as a positive electrode active material, and which enables the achievement of less variation in internal resistance regardless of a position in a direction of lamination.SOLUTION: A lithium ion secondary battery 10 is arranged by laminating at least three unit cell layers each having a positive electrode, an electrolytic layer and a negative electrode; the positive electrode includes an NMC complex oxide as a positive electrode active material. In the lithium ion secondary battery, the unit cell layers 3 and 4 located in a center portion in a direction of lamination are higher in positive electrode internal resistance than the unit cell layers 1 and 6 located in an outer portion in the direction of lamination.

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery containing a lithium transition metal composite oxide as a positive electrode active material.

  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 such a battery, there is a technique using a lithium transition metal composite oxide as a positive electrode material.

For example, in the secondary battery of Patent Document 1, as a cathode _{material, Li a Co b Mn c M} d Ni 1- (b + c + d) O 2 (M is B, Al, Si, Ti, Fe, V, Cr, Cu, Zn , Ga, and W, 0 <a <1.2, 0.1 ≦ b <1, 0.05 ≦ c <1, 0 ≦ d <1, 0.15 ≦ b + c + d <The condition of 1 is satisfied). Such a positive electrode material is referred to as a lithium-nickel-manganese-cobalt composite oxide (hereinafter also simply referred to as “NMC composite oxide” or “NMC”).

JP-A-10-289731

  As a battery structure, when multiple batteries are stacked, the battery located at the center in the stacking direction is difficult to dissipate heat, so the battery temperature tends to rise, and the battery located outside the stacking direction tends to dissipate heat, so the center in the stacking direction The temperature is not higher than that of some batteries. On the other hand, NMC composite oxide has a high temperature dependency of resistance. For this reason, when it is set as the structure which laminated | stacked the some battery, the temperature distribution in a lamination direction tends to become large. That is, the battery located at the center in the stacking direction has a low battery temperature because the battery temperature is high. On the other hand, the battery close to the outside in the stacking direction does not increase in temperature as much as the center portion, so the resistance does not decrease so much.

  When such a phenomenon occurs, there is a problem in that the battery in the central portion in the stacking direction in which the resistance is lowered accelerates the battery reaction more quickly than the outer battery, and the deterioration is accelerated.

  Therefore, an object of the present invention is to provide a lithium ion secondary battery in which fluctuation of internal resistance is reduced regardless of the position in the stacking direction in a stacked battery using an NMC composite oxide as a positive electrode active material.

The lithium ion secondary battery of the present invention that achieves the above object has a general formula: Li _a Ni _{b Mc} Co _d O ₂ (where a, b, c, and d are 0.9 ≦ a ≦ 1. .2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, and b + c + d = 1 M is Mn, Ti, Zr, Nb, W, P, Al, Mg, A positive electrode is formed using a positive electrode active material including a lithium nickel-based composite oxide having a composition represented by V, Ca, Sr, and Cr, which is at least one selected from the group consisting of V, Ca, Sr, and Cr. A single battery layer is constituted by the layer and the negative electrode, and three or more single battery layers are laminated. In this lithium ion secondary battery, the internal resistance of the positive electrode of the single battery layer located at the center in the stacking direction is set higher than the internal resistance of the positive electrode of the single battery layer positioned outside in the stacking direction.

  According to the present invention, the internal resistance of the positive electrode of the single cell layer positioned at the center in the stacking direction is set higher than the internal resistance of the positive electrode of the single cell layer positioned at the outer side of the stacking direction. Even if the internal resistance decreases due to heat, the resistance value of the positive electrode of the unit cell located outside can be made comparable. For this reason, the variation in internal resistance of each unit cell during use is reduced, and deterioration of the entire battery can be suppressed.

It is a schematic perspective view which shows the external appearance of a lithium ion secondary battery. It is a schematic sectional drawing which shows the structure of a lithium ion secondary battery. It is explanatory drawing for demonstrating the area | region where resistance value differs in the surface of a positive electrode active material. It is explanatory drawing of the positive electrode for demonstrating the example which changed the resistance value by changing the number of holes for every area | region, Fig.4 (a) is a schematic plan view, FIG.4 (b) is a schematic sectional drawing. It is a schematic sectional drawing for demonstrating the example which adjusts the adjustment of resistance value in a lamination direction by changing the number of holes.

  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 are different from the actual ratios.

[Battery overall structure]
FIG. 1 is a perspective view showing the appearance of a flat lithium ion secondary battery, which is one of the types of stacked batteries applied to this embodiment.

  As shown in FIG. 1, the flat lithium ion secondary battery 10 has a rectangular flat shape, and a positive electrode tab 27 and a negative electrode tab 25 for extracting electric power are drawn out from both sides thereof. Yes. The power generation element 21 is encased in a battery exterior material 29 of the lithium ion secondary battery 10 and its periphery is heat-sealed. The power generation element 21 is sealed with the positive electrode tab 27 and the negative electrode tab 25 pulled out to the outside. Has been. Here, the power generation element 21 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 1 described above. The power generation element 21 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. For this reason, the battery of such a form is also referred to as a stacked battery.

  The tab removal shown in FIG. 1 is not particularly limited. The positive electrode tab 27 and the negative electrode tab 25 may be drawn out from the same side, or the positive electrode tab 27 and the negative electrode tab 25 may be divided into a plurality of parts and taken out from each side. It is not limited to.

  FIG. 2 is a schematic cross-sectional view of the stacked battery according to the present embodiment.

  As shown in FIG. 2, in the laminated lithium ion secondary battery 10 of the present embodiment, 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. It has a stopped structure. 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 negative electrode current collector 11 and the negative electrode active material layer 13) is formed such 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. The electrolyte layer (nonaqueous electrolyte-containing separator 17) and the positive electrode (the positive electrode current collector 12 and the positive electrode active material layer 15) are laminated in this order. Thereby, the adjacent negative electrode, electrolyte layer, and positive electrode constitute one unit cell layer 19. The lithium ion secondary battery 10 shown in FIG. 1 indicates that six single battery layers 19 are stacked (reference numerals 1 to 6 are used for explaining each single battery layer separately for convenience of explanation). Is a sign to do). Of course, an actual battery is not limited to such a number of layers. As a result, each unit cell is configured to be electrically connected in parallel.

  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.

  Since the lithium ion secondary battery 10 has a structure in which the single battery layers 19 are stacked, it is difficult to dissipate heat toward the inner side in the stacking direction. For this reason, the cell layers 3 and 4 located in the central portion in the stacking direction have a higher temperature than the outer cell layers 1 and 6. On the other hand, when NMC is used as the positive electrode active material, there is a characteristic that the internal resistance easily changes due to a temperature change. For this reason, the resistance of the single cell layers 3 and 4 at the center in the stacking direction of the lithium ion secondary battery 10 is more likely to be lower than that of the outer single cell layers 1 and 6. When such a phenomenon occurs, the internal resistance differs between the single cell layers in the stacking direction. If it does so, the cell unit 3 and 4 of the center part with low internal resistance will become easy to flow electricity rather than the outer cell unit 1 and 6, and it will become easy to progress deterioration as a cell unit layer.

  Therefore, in the present embodiment, in order to suppress the difference in internal resistance between the unit cell layers, the electrical resistance of the positive electrode in the unit cell layer at the center in the stacking direction is set higher than the outside. . In addition, as shown in FIG. 2, the central portion in the stacking direction here refers to the two single battery layers 3 and 4 located in the central portion when an even number of single battery layers are stacked in the stacking direction. Become. On the other hand, although not shown, when an odd number of cell layers are stacked in the stacking direction, this is one cell layer located at the center.

  The specific resistance value is preferably about 1.05 to 1.15 times the resistance value of the central portion in the stacking direction with respect to the resistance values of the outermost unit cell layers 1 and 6. In this range, each cell layer in the stacking direction can be used even when the temperature inside the battery is not so high, such as immediately after starting the battery (during discharging or charging) or when the ambient temperature is low. This is to ensure that the internal resistance of the world is not different. Of course, the value is not limited to this value, and may be changed depending on the use environment of the battery, the number of stacked layers, and the like. For example, as the number of layers increases and the amount of heat dissipated in the central portion in the stacking direction decreases, the resistance decreases with respect to the outer side.

  The method of changing the resistance value includes, for example, changing the thickness of the positive electrode active material layer 15 formed on the positive electrode current collector 12 as a positive electrode, forming a plurality of holes or grooves in the positive electrode active material layer 15, etc. The resistance value of the positive electrode as a whole can be made different between the central portion and the outside. In the case where the resistance is adjusted by opening a plurality of holes, the holes themselves do not penetrate the active material and have a so-called concave structure in which the thickness of the active material is partially reduced. Therefore, since the hole of such a concave structure has a thin positive electrode active material layer, the internal resistance in the stacking direction is low. Therefore, as the number of holes per unit area increases, the number of thinned portions increases. If it does so, the resistance of the whole positive electrode will become low. In order to increase the number of holes, if the diameter and depth of the holes are the same, the pitch of the holes (the distance between the centers of the holes) is reduced.

  Therefore, when adjusting the resistance value of the positive electrode active material by making a hole, the positive electrode active material of the single cell layer located in the center in the stacking direction is drilled at a wider pitch than the positive electrode active material of the single cell layer located outside. Do. As a result, the central portion in the stacking direction is high, and the outside has a low resistance value.

  Note that the hole pitch W (W is all of Wa, Wb, W1, and W2) is W / d <2.5 with respect to the film thickness d of the positive electrode active material (see FIG. 4B). It is preferable. This is because if the hole pitch W is far away from the film thickness d of the positive electrode active material, the effect of lowering the resistance value cannot be expected.

  Further, the part having a different resistance value may be the entire surface of the positive electrode, but it is preferable to increase the internal resistance of the inner region by dividing into a region on the outer frame and an inner region surrounded by the region within one positive electrode. . This is because heat is less likely to escape from the center in the stacking direction, but the heat escape at the end is not so bad when viewed in the plane direction. Therefore, the region in the center of the surface direction in which the heat escape is likely to deteriorate even in the surface direction is set to a higher resistance, and the resistance close to the end of the surface is kept low. The positive electrode having a high resistance in the central region in the plane direction is positioned in the central portion in the stacking direction.

  FIG. 3 is an explanatory diagram for explaining in-plane region division in the unit cell layer. The positive electrode shown in the figure is a rectangular (including square) electrode, and the region is divided into a region A and an inner region B (inner region) surrounded by the region A. The area of the region A is Sa, the area of the region B is SB, the resistance value of the positive electrode active material in the region A is Ra, and the resistance value of the positive electrode active material in the region B is Rb.

  Then, the resistance value Rb of the region B is set higher than the resistance value Ra of the region A (that is, Rb> Ra). As a result, in one positive electrode, the resistance value increases toward the inner side in the plane.

  FIG. 4 is an explanatory view of a positive electrode for explaining an example in which the number of holes is changed for each region and the resistance value is changed, FIG. 4 (a) is a schematic plan view, and FIG. 4 (b) is a schematic cross-sectional view. FIG.

  As shown in the figure, the hole 30 has a concave structure as described above. The hole pitch Wa in the region A is narrower than the hole pitch Wb in the region B. The holes 30 have the same diameter and depth regardless of the area. By forming the hole 30 in this way, the resistance value of the inner region B becomes higher than the resistance value of the outer frame region A in the plane.

  By using such a positive electrode as a positive electrode active material located in the center portion in the stacking direction, the single cell layer in the center portion in the stacking direction has a higher resistance value as a whole of each single cell layer than the outer single cell layer. . In addition, in consideration of the difference in in-plane temperature change (heat escape), as a secondary battery having a structure in which a plurality of single battery layers are stacked, variation in internal resistance can be further reduced.

  In addition, in the positive electrode of one single cell layer, the extent of the area ratio between the region A and the region B depends on the area of the positive electrode of one single cell layer and the number of stacked layers. Adjustment may be made so that the resistance fluctuation is reduced between the outside and the outside.

  A case where the resistance value in the stacking direction is adjusted by forming a plurality of holes will be described. FIG. 5 is a schematic cross-sectional view for explaining an example of adjusting the resistance value in the stacking direction by changing the number of holes. In addition, in the figure, the positive electrode 301 of the single battery layer 3 located in the central part in the stacking direction and the positive electrode 101 of the single battery layer 1 positioned in the outermost layer in the stacking direction are shown.

  Here, an example in which the internal resistance of the positive electrode in the stacking direction is changed by changing the hole pitch in the region B will be described.

  As shown in the figure, the positive electrode active material layer of the single cell layer positioned at the center in the stacking direction was formed with respect to the pitch W1 of the holes 30 formed in the positive electrode active material layer of the single cell layer positioned at the outermost layer in the stacking direction. The pitch W2 of the holes 30 is assumed. When the hole pitch is narrower, the number of holes increases, and the portion where the positive electrode active material layer becomes thinner increases accordingly, so the internal resistance decreases. In this case, the hole pitch W1 / W2 is preferably set to 0.75 to 0.95. This is not preferable because the internal resistance will be too different if the hole pitch is significantly different between the outer cell layer and the central cell layer (the hole pitch ratio is large). Conversely, if the hole pitch ratio is too small, the resistance value, which is the original purpose, cannot be adjusted. Of course, it may be appropriately adjusted depending on the number of stacked layers and the area of the positive electrode.

  Here, the single cell layers 3 and 4 positioned in the central portion in the stacking direction and the single cell layers 1 and 7 positioned in the outermost layer in the stacking direction have been described in comparison, but the single cell layers 2 and 5 between them are A resistance value between these is preferable. That is, when the resistance values are arranged from higher to lower, the cell layers 3 and 4> 2 and 5> 1 and 7 are obtained.

  In addition, the structure of the secondary battery demonstrated above is one Embodiment to the last. Therefore, for example, the number of stacked unit cell layers 19 is not limited to six, but may be three or hundreds. However, when the number of layers is large, the resistance value is not different for each layer. For example, when several hundred layers are stacked, every ten layers, every 20 layers, every 50 layers, etc. The resistance value may be different.

  Moreover, although the anode active material layer 13 is disposed on only one side of the outermost layer positive electrode current collector located on both outermost layers of the power generation element 21, active material layers may be provided on both sides. 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.

  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 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 embodiment 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.

  Although the thickness of a positive electrode electrical power collector is not specifically limited, Usually, 1-100 micrometers, Preferably it is about 1-50 micrometers.

(Positive electrode active material)
In the present embodiment, the positive electrode active material includes a lithium nickel composite oxide. Further, it may further contain a spinel manganese positive electrode active material. In this case, the spinel manganese positive electrode active material is not particularly limited, and a lithium manganese composite oxide having a conventional spinel structure is used.

  Next, the lithium nickel composite oxide will be described.

The lithium nickel composite oxide according to the present embodiment is a composite oxide in which a part of nickel atoms of the lithium nickel composite oxide is substituted with another metal atom, and the lithium-nickel-manganese-cobalt composite oxide. (Also referred to as “NMC composite oxide” or “NMC”). 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 order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel 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 embodiment, 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.

Lithium nickel-based composite oxides preferably have a high theoretical discharge capacity, and therefore, general formula (1): LiaNibMcCodO ₂ (where a, b, c, and d are 0.9 ≦ a ≦ 1. 2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, b + c + d = 1, M is Mn, Al, Ti, Zr, Nb, W, P, Mg, V , Ca, Sr, and 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.

  In general, nickel (Ni), manganese (Mn), and cobalt (Co) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving 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.

In addition, in the lithium nickel-based composite oxide, the inventors of the present invention have a non-uniform metal composition of nickel, manganese, and cobalt, such as LiNi _0.5 Mn _0.3 Co _0.2 O _2. The present inventors have found that the influence of strain / cracking of the complex oxide during the 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 composite oxide having a rich abundance ratio of Ni (for example, LiNi _0.8 Mn _0.1 Co _0.1 O ₂ ) or a composite 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 lowered. Therefore, in 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 , a complex having a specific true density is surprisingly obtained. It has been found that the use of an oxide suppresses the deterioration of cycle characteristics. Therefore, in the general formula (1), b, c, and d are 0.49 ≦ b ≦ 0.51, 0.29 ≦ c ≦ 0.31, and 0.19 ≦ d ≦ 0.21. A positive electrode active material of a composite oxide is more preferable.

  The lithium nickel composite oxide 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 this embodiment 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 JP 2011-105588 A, a nickel-manganese-cobalt composite hydroxide, It can be obtained by mixing and baking with a lithium compound.

  This will be specifically described below.

  A raw material compound of a lithium nickel-based composite oxide, for example, a Ni compound, a Co compound, and a Mn 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, Co compound, and Mn compound include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and halides of the metal elements. Specifically, 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 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 composition of the active material. , Nb, 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.

  Next, the nickel-manganese-cobalt composite hydroxide is mixed with a lithium compound and fired to obtain a lithium-nickel-manganese-cobalt composite hydroxide. 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. Although it does not specifically limit as temporary baking conditions, 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. Moreover, it is preferable that it is 700-1000 degreeC, and, as for baking temperature, it is more preferable that it is 650-750 degreeC. Furthermore, the firing time is preferably 3 to 20 hours, 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. Moreover, it is preferable that a calcination temperature is 700-1000 degreeC, and it is more preferable that it is 850-1100 degreeC. 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, as the method, a method of previously mixing with nickel, cobalt, manganate, Any means such as a method of adding nickel, cobalt and manganate at the same time, a method of adding to the reaction solution during the reaction, a method of adding to the nickel-cobalt-manganese composite hydroxide together with the Li compound may be used. .

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

  In addition to the active material described above, the positive electrode active material layer according to the present embodiment enhances the conductivity of the conductive auxiliary, binder, electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and ion conductivity as necessary. In addition, other additives such as lithium salts of

(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 Examples thereof include vinylidene fluoride-based fluororubber such as fluororubber (VDF-CTFE-based fluororubber), 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 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 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) -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]
The negative electrode according to the present embodiment 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 containing water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion, and emulsifies or suspends in water, for example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of the water-based binder 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 Acrylate, 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) 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, (meth) alkyl acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide manni 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 water-based binder may contain at least one rubber-based 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 (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 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.

  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, Li4Ti5O12), metal materials, lithium alloy negative electrode materials, and the like. 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 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 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, 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, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, meta Lil oxymethyl ethylene 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 by 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 the 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. Covering with a tube or the like is preferable.

[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. 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]
As for the cell area in the present embodiment, the effect can be expected for a larger battery. This is because the larger the battery, the less the heat dissipated in the stacking direction, and the more heat is trapped. For example, it is suitable for a battery having a positive electrode area of 160000 mm ² or more. Moreover, it is preferable that the aspect ratio (area / stacking height) of the stacked power generation elements is 1.3 or less.

  In particular, in automobile applications and the like, recently, a large-sized battery has been demanded, so that the effect is more effectively exhibited in the case of a large area battery. Specifically, it is preferable that the positive electrode active material layer has a rectangular shape, and the length of the short side of the rectangle is 100 mm or more. Such a large battery can be used for vehicle applications. Although the upper limit of the length of the short side as a battery structure is not specifically limited, Usually, it is 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 is an enlarged battery 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 enlargement of the battery can be defined by the volume energy density, the single cell rated capacity, or the like. For example, in a general electric vehicle, a travel distance (cruising range) by one charge is 100 km. 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. 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. It is preferable to set the aspect ratio in such a range 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 flat lithium ion secondary batteries 10 shown in FIG. 1 are connected in series or in parallel or connected to both. Capacitance and voltage can be freely adjusted by serialization and / or parallelization.

  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 secondary battery of this embodiment maintains a discharge capacity even when used for a long 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 non-aqueous 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 this embodiment, 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 charging mileage can be formed by installing such a battery. it can. For example, if it is an automobile, it is a hybrid car, a fuel cell car, an electric car (all of which are automobiles (commercial vehicles such as passenger cars, trucks, buses, 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 use 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 positive electrode slurry Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ (average particle diameter 10 μm) as a positive electrode active material, acetylene black as a conductive additive and polyvinylidene fluoride (binder) as a binder (binder) PVDF) was mixed at a weight ratio of 95: 2: 3 to obtain a positive electrode slurry.

2. Production of Positive Electrode (1) While adjusting the viscosity of the positive electrode slurry produced above using NMP (N-methyl-2-pyrrolidone), the amount of active material per unit area on the Al foil was 27.0 mg / cm ^{2 on} one side. Both sides were coated on an Al foil having a thickness of 20 μm. After sufficiently drying, the thickness of the positive electrode (1) is adjusted to 100 μm by using a roll press so that the total thickness of the positive electrode (1) (the total thickness of the Al foil of the positive electrode current collector + the positive electrode active material layer (both sides)) is 100 μm. Adjusted. Three types of coating areas of 100 × 200 mm (area 20000 mm ² ), 400 × 400 mm (area 160000 mm ² ), and 600 × 800 mm (area 480000 mm ² ) were produced.

3. Production of Positive Electrode (2) The positive electrode active material layer (both sides) of the positive electrode (1) was processed with a drill having a diameter of 60 μm at a pitch of 200 μm and a depth of 20 μm to form a plurality of holes on the entire surface of the positive electrode active material layer.

4). Fabrication of positive electrode (3) The positive electrode active material layer (both sides) of the positive electrode (1) was drilled with a diameter of 60 μm in a region A (see FIG. 3, the same applies hereinafter) with a pitch of 100 μm and region B with a pitch of 150 μm. A plurality of holes having a depth of 20 μm were formed. Region B represents the region inside the line connecting the midpoints from the intersection of the diagonal lines of the electrodes to the corners of the electrodes. Region B represents an electrode portion other than region A.

5). Production of Positive Electrode (4) A plurality of holes with a depth of 20 μm were formed in the positive electrode active material layer (both sides) of the positive electrode (1) with a drill having a diameter of 60 μm, with a region A having a pitch of 150 μm, a region B having a pitch of 200 μm.

6). Production of Negative Electrode Natural graphite (average particle size 20 μm) as a negative electrode active material and polyvinylidene fluoride (PVDF) as a binder (binder) were mixed at a weight ratio of 94: 6 to obtain a negative electrode slurry.

While the viscosity of the negative electrode slurry was adjusted using NMP, double-sided coating was applied to a Cu foil having a thickness of 10 μm so that the active material amount per unit area was 9 mg / cm ^{2 on} one side. After sufficiently drying, the thickness of the negative electrode was adjusted using a roll press so that the total thickness of the negative electrode (Cu foil of the negative electrode current collector + negative electrode active material layer (both sides)) was 120 μm.

7). Experiment Using the positive electrodes (1) to (4), the stacked structure batteries of Examples 1 to 3 and Comparative Examples 1 to 6 were produced as shown in Table 1 described later. The negative electrodes were all unified with those prepared in 6 above. That is, when combining the above positive electrode, the above negative electrode 6 and the separator as the constituent parts (members) of the single cell layer, the positive cell (1) to (4) are arranged as shown in Table 1 and the single cell layer is 3 The laminated structure batteries of Examples 1 and 2 and Comparative Examples 1 to 6 in which layers were laminated were produced, and the laminated structure battery of Example 3 in which five single battery layers were laminated was produced.

8). Production of laminated structure battery The positive electrode and the negative electrode obtained by the above procedure and the following separator were further cut (the tab was left without being cut), and 3 to 5 single battery layers (single cells) were laminated. . At that time, a separator (thickness 25 μm), which is a laminated microporous film of polyethylene and polypropylene, is interposed between the positive electrode and the negative electrode. Further, for each of the examples and comparative examples, three layers were laminated so that the positive electrode in each single battery layer (single cell) became the positive electrode ((1) to) shown in the lamination number in Table 1 above. Then, connect the tabs of each stacked single battery layer (single cell) (current collector tab provided by extending a part of the current collector; the thickness of the current collector tab is the same as the current collector) The power generation elements (laminates) (see FIG. 2) of the parallel-type laminated battery were stacked (assembled). Each power generation element (laminate) was put in an aluminum laminate outer package, and after injecting an electrolyte solution (a mixed solution of EC and DEC containing 1 M LiPF ₆ (EC: DEC = 1: 1 molar ratio)), Vacuum-sealing was performed to produce a laminated structure battery for each example and comparative example.

9. Evaluation Method A cycle test (endurance test) was performed under the storage at 25 ° C. using the laminated battery for each example and comparative example prepared in the above procedure. In addition, the produced battery was disassembled, the positive electrodes of the electrode regions A and B were punched out with φ15, a coin cell (half cell) was produced with Li as the counter electrode, and discharged for 10 seconds to measure the direct current resistance (mΩ).

  Cycle conditions were 500 cycles between 4.15V-3.0V at 1C rate.

10. Results Table 2 shows the results of direct current resistance for each layer and each region after disassembling the battery having the laminated structure shown in Table 1 as described in 9 above to create a half cell. In Table 2, 1-A is an electrode taken from region A of the first positive electrode, 1-B is an electrode taken from region B of the first positive electrode, and 2-A is taken from region A of the second positive electrode. The electrode, 2-B, is an electrode taken from the region B of the second-layer positive electrode.

Table 3 shows the capacity retention ratio and the unit area integrated capacity (Ah / cm ² ) before and after the durability test. Here, capacity retention rate (%) = discharge capacity at 500th cycle / discharge capacity at the first cycle × 100. The unit area integrated capacity is a value obtained by dividing the integrated value (total discharge capacity) of the discharge capacity during the durability test by the total positive electrode area.

  In addition, the stacking number in Table 1 (the stacking number of each single cell of the laminated battery in which five single battery layers (single cells) are stacked) is 1 to 5 in order from the bottom.

  The following can be seen from Tables 1-3.

  In the case where the entire positive electrode has the same resistance value, from the results of Comparative Example 1 and Example 1, Comparative Example in which Example 1 in which the resistance in the central portion in the stacking direction is higher does not differ in the resistance value in the stacking direction Compared to 1, the capacity retention rate is improved. In Example 2 having the same structure and an area smaller than that of Example 1, the capacity retention rate is improved as compared with Comparative Example 1.

  When the positive electrode surface was divided into regions, from the results of Comparative Examples 2 and 3 and Examples 3 and 4, the resistance of the central portion was increased in the plane, and the resistance of the central portion in the stacking direction was further increased. However, the capacity retention rate is improved as compared with Comparative Examples 2 and 3 in which the resistance value in the stacking direction is not different. Further, even when the number of stacked layers is increased, the capacity retention rate is improved as compared with other comparative examples as in Example 5.

  Further, when Examples 2 and 5 are compared, the capacity retention rate hardly decreases even when the positive electrode area increases. Therefore, it can be seen that by increasing the resistance of the positive electrode of the unit cell located in the center in the stacking direction, the capacity retention rate can be improved even if the area is increased.

  In Comparative Example 4, the number of stacked layers is two for reference. In this case, since there is almost no temperature difference in the stacking direction, there is no factor that deteriorates the capacity retention rate. And when this comparative example 4 and Examples 1-5 are contrasted, also in the laminated battery which laminated | stacked three or more layers, the capacity | capacitance maintenance factor equivalent to the case of two layers where the temperature distribution of a lamination direction does not appear can be obtained. You can see that

  According to the embodiments and examples described above, the following effects are obtained.

  (1) In a stacked lithium ion secondary battery that uses an NMC composite oxide as a positive electrode active material, the internal resistance of the positive electrode of the single battery layer located at the center in the stacking direction is the single battery positioned outside in the stacking direction. It was higher than the internal resistance of the positive electrode of the layer. As a result, even if the resistance value of the positive electrode of the single cell layer located in the center in the stacking direction in the stacked battery is lowered by heat, it becomes approximately the same as the resistance value of the positive electrode of the single cell located outside. For this reason, the variation in internal resistance for each cell during actual use is reduced, and deterioration of the entire battery can be suppressed.

(2) Particularly effective when the positive electrode area is as large as 160000 mm ² or more. If the area of the positive electrode is originally small, heat escapes from the side surface in the stacking direction even if the single cell layers are stacked, so that the heat rises only to the same extent as the outside even in the central portion in the stacking direction. Therefore, it functions effectively when the positive electrode area is as large as 160000 mm ² or more. Note that the upper limit of the area is not particularly limited as long as it is physically acceptable in manufacturing the battery.

  (3) Moreover, in this embodiment, the resistance value of the positive electrode of the single cell located in the center portion in the stacking direction is 1.05 to 1.15 with respect to the internal resistance of the positive electrode of the single cell positioned in the outermost layer in the stacking direction. It was preferable to double. By adopting such a range, each cell in the stacking direction even when the temperature inside the battery is not so high, such as immediately after the start of the battery (immediately after starting discharge or immediately after charging), or when the environmental temperature is low. The internal resistance of the layers can be kept the same.

  (4) In this embodiment, the resistance value is adjusted by forming a hole having a concave structure in which the thickness of the positive electrode active material is partially reduced. The resistance value can be easily adjusted by reducing the number of such holes at the center in the stacking direction from the outside in the stacking direction, that is, by adjusting the number of holes.

  (5) In particular, in order to adjust the number of holes, the pitch of the holes (the distance between the centers of the holes) is changed. For this reason, it is possible to easily adjust the resistance value only by forming holes having the same diameter and depth by setting the pitches of the holes in advance differently in the central portion and the outer side in the stacking direction.

  (6) Further, the ratio between the pitch W1 of the holes formed in the positive electrode active material of the single cell layer located on the outer side in the stacking direction and the pitch W2 of the holes formed in the positive electrode active material of the single cell layer positioned in the center in the stacking direction. (W1 / W2) was set to 0.75 to 0.95. As a result, it is possible to prevent the internal resistance from being too different between the outer cell layer and the central cell layer.

  (7) When the hole pitch is W and the film thickness of the positive electrode active material is d, the holes satisfy W / d <2. Thereby, the resistance value can be lowered by thinning by forming the hole.

  (8) In one positive electrode, the positive electrode active material was divided into an outer frame-shaped region and an inner region surrounded by the outer frame-shaped region, and the inner region had higher internal resistance than the outer frame-shaped region. Thereby, the variation in internal resistance in the secondary battery having a structure in which a plurality of single battery layers are stacked can be reduced in consideration of the difference in temperature change (heat escape) in the plane of each positive electrode.

  The embodiments and examples to which the present invention is applied have been described above, but the present invention is not limited to the embodiments and examples, and various modifications are possible. The present invention is defined by the claims. It is determined by the stipulated matters.

10 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 power generation elements,
25 Negative electrode current collector (tab),
27 Positive current collector (tab),
29 Battery exterior materials,
30 holes.

Claims (9)

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 Lithium in which a single battery layer is composed of a positive electrode including a positive electrode active material including a lithium nickel-based composite oxide having a composition represented by the following formula: an electrolyte layer and a negative electrode, and three or more single battery layers are laminated In ion secondary batteries,
A lithium ion secondary battery characterized in that the internal resistance of the positive electrode of the single battery layer located in the center in the stacking direction is higher than the internal resistance of the positive electrode of the single battery layer positioned outside in the stacking direction. The lithium ion secondary battery according to claim 1, wherein an area of the positive electrode is 160000 mm ² or more.   The resistance value of the positive electrode of the unit cell located in the central portion in the stacking direction is 1.05 to 1.15 times the internal resistance of the positive electrode of the unit cell positioned in the outermost layer in the stacking direction. The lithium ion secondary battery according to claim 1 or 2.   The internal resistance of the positive electrode is adjusted by forming a hole having a concave structure in which the thickness of the positive electrode active material is partially reduced, and the number of the holes is a single cell layer located at the center in the stacking direction 4. The lithium ion secondary material according to claim 1, wherein the positive electrode active material of the single cell layer positioned on the outer side in the stacking direction is larger than the positive electrode active material of the lithium ion secondary battery. Next battery.   The pitch of the holes formed in the positive electrode active material of the single cell layer positioned on the outer side in the stacking direction is narrower than the pitch of the holes formed in the positive electrode active material of the single cell layer positioned in the center in the stacking direction. The lithium ion secondary battery according to claim 4.   The ratio of the pitch of the holes formed in the positive electrode active material of the single cell layer positioned outside the stacking direction to the pitch of the holes formed in the positive electrode active material of the single cell layer positioned in the center in the stacking direction is 0. The lithium ion secondary battery according to claim 4 or 5, wherein the lithium ion secondary battery is .75 to 0.95.   6. The hole according to claim 4, wherein when the pitch of the holes is W and the film thickness of the positive electrode active material is d, the holes satisfy W / d <2.5. Lithium ion secondary battery.   The positive electrode of the single cell layer located at the central portion in the stacking direction is divided into an outer frame-shaped region and an inner region surrounded by the outer frame-shaped region, and the inner region is more internal than the outer frame-shaped region. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the resistance is high. The b, c and d are 0.49 ≦ b ≦ 0.51, 0.29 ≦ c ≦ 0.31, 0.19.
<= D <= 0.21, The lithium ion secondary battery as described in any one of Claims 1-8 characterized by the above-mentioned.