JP5709010B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

  Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are important as, for example, power supplies mounted on vehicles that use electricity as a drive source, or power supplies used in personal computers, portable terminals, and other electrical products. It is growing. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferable as a high-output power source mounted on a vehicle.

  In a typical example of a non-aqueous electrolyte secondary battery, charge and discharge are performed by charge carriers (for example, metal ions such as lithium ions) traveling between the positive electrode and the negative electrode through the non-aqueous electrolyte. Is done. Such a positive electrode includes a positive electrode current collector (conductive member) and a positive electrode mixture layer. Such a positive electrode mixture layer is prepared by, for example, adding a positive electrode active material, a binder, and the like to a suitable amount of a solvent and kneading the paste-like composition (the paste-like composition includes a slurry-like composition and an ink). Is formed, and this is coated on a positive electrode current collector (conductive member) and dried.

  When producing, for example, a lithium ion secondary battery as a non-aqueous electrolyte secondary battery including a wound electrode body formed by winding the positive electrode and the negative electrode as described above, the non-aqueous electrolyte is used as the positive electrode mixture layer. Injection is performed from both ends in the winding axis direction, and the wound electrode body is impregnated with the electrolytic solution. At this time, there is a possibility that the central portion is not sufficiently impregnated with the non-aqueous electrolyte injected from both ends of the positive electrode mixture layer in the winding axis direction. If the non-aqueous electrolyte is not sufficiently impregnated in the central portion, metallic lithium may be deposited in the portion during charging and discharging. When metallic lithium is deposited in this manner, lithium ions used during charging and discharging are reduced, and battery performance (for example, cycle characteristics) is deteriorated. Patent document 1 is mentioned as a prior art regarding the impregnation of electrolyte solution. Patent Document 1 describes a lithium ion battery configured such that the amount of electrolyte solution retained per unit volume at the center in the winding axis direction of the electrode body is greater than at both ends.

JP 2009-211956 A

By the way, in order to satisfactorily impregnate the positive electrode mixture layer with the non-aqueous electrolyte solution, when an active material having a large absorption amount of the non-aqueous electrolyte solution is used as the positive electrode active material included in the positive electrode mixture layer, the positive electrode mixture layer The non-aqueous electrolyte is sufficiently impregnated in the central portion in the winding axis direction. However, due to the expansion and contraction of the positive electrode active material during charge / discharge, the nonaqueous electrolytic solution containing lithium salt or the like in the positive electrode mixture layer flows out from the positive electrode mixture layer (rolled electrode body). There is a fear. As a result, the capacity maintenance rate of the lithium ion secondary battery (nonaqueous electrolyte secondary battery) provided with the positive electrode is reduced due to the decrease in the nonaqueous electrolyte contained in the positive electrode mixture layer (non-uniform concentration of the nonaqueous electrolyte). (In other words, the cycle characteristics may be degraded).
On the other hand, when an active material that absorbs a small amount of non-aqueous electrolyte is used as the positive electrode active material included in the positive electrode mixture layer, it is possible to prevent the non-aqueous electrolyte from flowing out from the positive electrode mixture layer to the outside during charge and discharge. However, when the positive electrode mixture layer (rolled electrode body) is impregnated with the nonaqueous electrolyte solution, the central portion of the positive electrode mixture layer is not sufficiently impregnated with the nonaqueous electrolyte solution. May be insufficient (for example, in a state of no impregnation).
Therefore, the present invention has been created to solve the above-described conventional problems, and its purpose is to improve the impregnation property of the central portion of the positive electrode mixture layer in the winding axis direction and at the time of charging and discharging. An object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in battery performance by preventing the non-aqueous electrolyte from flowing out from a positive electrode mixture layer.

In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery comprising a wound electrode body including a positive electrode sheet and a negative electrode sheet, and a nonaqueous electrolyte solution. That is, in the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode sheet includes a long positive electrode current collector, and a positive electrode compound including at least a positive electrode active material formed on the surface of the positive electrode current collector. And a material layer. Both end portions of the positive electrode mixture layer in the winding axis direction of the wound electrode body are mainly composed of a first positive electrode active material. The central portion including at least the center of the positive electrode mixture layer in the winding axis direction is mainly composed of the second positive electrode active material. The DBP absorption amount [mL / 100 g] based on JIS K6217-4 is different between the first positive electrode active material and the second positive electrode active material. The DBP absorption amount A [mL / 100 g] of the first positive electrode active material is smaller than the DBP absorption amount B [mL / 100 g] of the second positive electrode active material.
In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery including a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt (supporting electrolyte) in a non-aqueous solvent). . The term “secondary battery” refers to a general battery that can be repeatedly charged and discharged, and is a term that includes a so-called chemical battery such as a lithium ion secondary battery and a physical battery such as an electric double layer capacitor.

In the non-aqueous electrolyte secondary battery provided by the present invention, the positive electrode composite in the winding axis direction of the wound electrode body (that is, the width direction of the positive electrode mixture layer formed on the long positive electrode current collector). The DBP absorption amount A of the first positive electrode active material (that is, the main component of both end portions of the positive electrode mixture layer) contained in both end portions of the material layer is the central portion (that is, positive electrode) including the center of the positive electrode mixture layer in the same direction. The DBP absorption amount B of the second positive electrode active material contained in the main component of the central portion of the composite material layer is smaller.
As described above, the DBP absorption amount B of the second positive electrode active material included in the central portion of the positive electrode mixture layer is larger than the DBP absorption amount A of the first positive electrode active material included in both end portions. The impregnation property of the nonaqueous electrolytic solution is improved in the central portion. For this reason, when the non-aqueous electrolyte is injected from both ends of the wound electrode body and the wound electrode body is impregnated with the non-aqueous electrolyte, the non-aqueous electrolyte is entirely covered including the central portion of the positive electrode mixture layer. The electrolyte is well impregnated. Thereby, precipitation of the substance (for example, metals, such as metal lithium) derived from a charge carrier in the said center part at the time of charging / discharging can be prevented.
Furthermore, the DBP absorption amount A of the first positive electrode active material included in both end portions of the positive electrode mixture layer is smaller than the DBP absorption amount B of the second positive electrode active material included in the center portion. For this reason, during the charge / discharge, the second positive electrode active material contained in the central portion of the positive electrode mixture layer expands and contracts, so that the nonaqueous electrolyte present in the positive electrode mixture layer becomes the positive electrode mixture layer. Even if it moves to the outside of the winding axis direction (width direction) (in the direction of both end portions), both end portions of the positive electrode mixture layer have low impregnation properties, so that the nonaqueous electrolyte in the winding axis direction (width direction) The movement will be suppressed. Thereby, it can prevent effectively that a non-aqueous electrolyte flows out of the positive electrode compound-material layer (winding electrode body). As a result, an increase in the internal resistance of the positive electrode (that is, the wound electrode body) due to the nonaqueous electrolyte flowing out of the positive electrode mixture layer can be suppressed.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the DBP absorption amount A is smaller than the DBP absorption amount B as described above, and the DBP absorption amount A [mL / mL of the first positive electrode active material]. 100 g] is 10 mL / 100 g to 30 mL / 100 g, and the DBP absorption amount B [mL / 100 g] of the second positive electrode active material is 30 mL / 100 g to 80 mL / 100 g. Preferably, the DBP absorption amount B of the second positive electrode active material is at least 5 mL / 100 g larger than the DBP absorption amount A of the first positive electrode active material.
According to such a configuration, since a good impregnation property is obtained in the central portion of the positive electrode mixture layer, the nonaqueous electrolyte can be satisfactorily impregnated in the central portion of the wound electrode body. Furthermore, it is possible to effectively prevent the non-aqueous electrolyte from flowing out from the positive electrode mixture layer during charging and discharging.

In another preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the length of the positive electrode mixture layer in the winding axis direction is L, and the length of the central portion in the winding axis direction is L Lp / L is 0.15 to 0.85 (for example, 0.2 to 0.6), where Lp is Lp.
According to this configuration, the non-aqueous electrolyte secondary battery is excellent in the impregnation performance of the non-aqueous electrolyte solution in the central portion of the positive electrode mixture layer and the anti-flow performance of the non-aqueous electrolyte solution from the positive electrode mixture layer during charging and discharging. Can be.
Preferably, both the first positive electrode active material and the second positive electrode active material are active material particles having a hollow structure. From the size of the hollow portion of the active material particles having a hollow structure, it can be said that the movement of the non-aqueous electrolyte during expansion and contraction is relatively large compared to the active material particles having no hollow structure. Therefore, the effect of the present invention becomes more remarkable when such hollow structure active material particles are used.

In another preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the length of the positive electrode mixture layer in the winding axis direction is at least 40 mm.
When the length of the positive electrode mixture layer in the winding axis direction is at least 40 mm, the impregnating property of the non-aqueous electrolyte in the central portion of the positive electrode mixture layer is not sufficient. The effect of adopting the configuration of the present invention that includes a positive electrode active material having a large absorption amount can be particularly exerted.

  Further, according to the present invention, there is provided an assembled battery as a driving power source for a vehicle in which a plurality of unit cells are electrically connected to each other, and any one of the nonaqueous electrolyte solutions disclosed herein as the unit cell. An assembled battery is provided in which a secondary battery is used. As described above, any of the non-aqueous electrolyte secondary batteries disclosed herein is a substance (for example, a metal) derived from a charge carrier particularly at a high rate (for example, 5C to 50C, preferably 10C to 30C) charge and discharge. Non-aqueous electrolysis that maintains excellent battery performance as a result of excellent performance in preventing the precipitation of electrolytes to the outside of the positive electrode mixture layer (winding electrode body). It can be a liquid secondary battery. For this reason, an assembled battery in which a plurality of such secondary batteries (for example, about 10 or more, preferably about 10 to 30) are electrically connected to each other is a vehicle (typically an automobile, particularly a hybrid automobile, an electric automobile). In addition, it can be preferably used as a drive power source of a vehicle equipped with an electric motor such as a fuel cell vehicle.

It is a perspective view which shows typically the external shape of the non-aqueous-electrolyte secondary battery which concerns on one Embodiment of this invention. FIG. 2 is a sectional view taken along line II-II in FIG. It is sectional drawing which shows typically the structure of the winding electrode body of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the structure of the positive electrode of the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention. It is a perspective view which shows typically the external shape of the assembled battery which concerns on one Embodiment of this invention. It is a side view which shows typically the vehicle (automobile) provided with the nonaqueous electrolyte secondary battery which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  As a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, a lithium ion secondary battery will be described in detail as an example, but the application target of the present invention is such a non-aqueous electrolyte solution. It is not intended to be limited to secondary batteries. For example, the present invention can also be applied to a non-aqueous electrolyte secondary battery using other metal ions (for example, magnesium ions) as a charge carrier.

As shown in FIG. 3, the lithium ion secondary battery according to the present embodiment includes a wound electrode body 50 including a positive electrode sheet 64 and a negative electrode sheet 84, and a nonaqueous electrolytic solution. As shown in FIG. 4, the positive electrode sheet (positive electrode) 64 includes a long (sheet shape) positive electrode current collector 62 and at least a positive electrode active material 68 formed on the surface of the positive electrode current collector 62. And a positive electrode mixture layer 66. Such a positive electrode mixture layer is formed in layers from, for example, an electrode material such as a positive electrode active material 68, a conductive material (not shown), and a binder.
As shown in FIG. 4, both end portions 66A and 66A of the positive electrode mixture layer 66 in the winding axis direction (that is, the width direction of the positive electrode mixture layer 66) of the wound electrode body 50 (see FIG. 3) The cathode active material 68A (68) is the main constituent. Both end portions 66A may contain a small amount of positive electrode active material that does not cause a problem in obtaining the effects of the present invention in addition to the first positive electrode active material 68A.
The central portion 66B of the positive electrode mixture layer 66 in the winding axis direction of the wound electrode body 50 (see FIG. 3) is mainly composed of the second positive electrode active material 68B (68). The central portion 66B can contain a small amount of the positive electrode active material that does not cause a problem in obtaining the effects of the present invention in addition to the second positive electrode active material 68B.
Here, the central portion 66B of the positive electrode mixture layer 66 in the winding axis direction (width direction) is a region including the center of the positive electrode mixture layer 66 in the winding axis direction, as shown in FIGS. When the length of the positive electrode mixture layer 66 in the winding axis direction is L and the length of the central portion 66B in the winding axis direction is Lp, the value of Lp / L is about 0.15. It is preferable that the region be ˜0.85 (for example, 0.2 to 0.6, preferably 0.4 to 0.6). Further, both end portions 66A of the positive-electrode mixture layer 66, cause material density between 66A and the central portion 66B may be substantially the same, which may be for example 2.2g ^/ cm ³ ~3.4g ^/ cm 3 .

  As the positive electrode current collector 62, a conductive member made of a metal having good conductivity is preferably used, as in the current collector used in the positive electrode of a conventional lithium ion secondary battery. For example, an aluminum material or an alloy material mainly composed of an aluminum material can be used. The thickness of the long positive electrode current collector is, for example, about 10 μm to 30 μm.

The positive electrode active material 68 (68A, 68B) is a material capable of occluding and releasing lithium ions, and is a lithium-containing compound (for example, a lithium transition metal oxide) containing a lithium element and one or more transition metal elements. ). For example, lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (for example, LiCoO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or lithium nickel cobalt manganese composite oxide (for example, LiNi _{1). / 3} Co _1/3 Mn _1/3 O ₂ ), a ternary lithium-containing composite oxide.
In addition, a polyanionic compound (for example, LiFePO ₄₎ whose general formula is represented by LiMPO _4, LiMVO _4, or Li ₂ MSiO ₄ (wherein M is at least one element of Co, Ni, Mn, and Fe), etc. ₄ , LiMnPO ₄ , LiFeVO ₄ , LiMnVO ₄ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ CoSiO ₄ ) may be used as the positive electrode active material.
The positive electrode active material 68 may be in the form of secondary particles in which primary particles are collected, and the average particle size (median diameter d50) of the secondary particles is, for example, 1 μm to 50 μm. Preferably they are 3 micrometers-10 micrometers. Further, the first positive electrode active material 68A and the second positive electrode active material 68B may have substantially the same average particle diameter. The average particle diameter can be easily measured by a particle size distribution measuring apparatus based on various commercially available laser diffraction / scattering methods.

In the present embodiment, between the first positive electrode active material 68A included in both end portions 66A and 66A of the positive electrode mixture layer 66 and the second positive electrode active material 68B included in the central portion 66B of the positive electrode mixture layer 66. , DBP absorption [mL / 100 g] based on JIS K6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP absorption” is different from each other. Further, the DBP absorption amount A [mL / 100 g] of the first positive electrode active material 68A is smaller than the DBP absorption amount B [mL / 100 g] of the second positive electrode active material 68B.
Here, the DBP absorption amount A [mL / 100 g] of the first positive electrode active material 68A is approximately 10 mL / 100 g to 30 mL / 100 g (for example, approximately 15 mL / 100 g to 25 mL / 100 g). When the DBP absorption amount A is too larger than 30 mL / 100 g, the nonaqueous electrolyte solution is discharged from both end portions 66A, 66A to the outside during charging / discharging of the lithium ion secondary battery (nonaqueous electrolyte secondary battery). There is a risk of leaking. On the other hand, when the DBP absorption amount A is too smaller than 10 mL / 100 g, the impregnation property of the non-aqueous electrolyte in the both end portions 66A and 66A of the positive electrode mixture layer 66 is not sufficient, and the central portion 66B is sufficiently non-aqueous. There is a risk that the electrolyte will not spread.
Further, assuming that the DBP absorption amount B [mL / 100 g] of the second positive electrode active material 68B is larger than the DBP absorption amount A [mL / 100 g] of the first positive electrode active material 68A, for example, about 30 mL. / 100g-80mL / 100g (for example, about 30mL / 100g-60mL / 100g, usually about 40mL / 100g-50mL / 100g). When the DBP absorption amount B is too smaller than 30 mL / 100 g, the impregnating property of the central portion 66B of the positive electrode mixture layer 66 is not sufficient, so There is a possibility that the water electrolyte is not sufficiently impregnated in the central portion 66B (particularly the central portion in the width direction of the positive electrode mixture layer 66).
Preferably, the DBP absorption amount B of the second positive electrode active material 68B is at least 5 mL / 100 g (for example, 20 mL / 100 g) larger than the DBP absorption amount A of the first positive electrode active material 68A.

  In general, the DBP absorption amount of a positive electrode active material (for example, a lithium transition metal oxide powder having a layered structure) composed of dense solid-structure particles is approximately 10 mL / 100 g to 20 mL / 100 g. If other conditions (particle size and the like) are about the same, the DBP absorption amount of the porous or hollow structure particles tends to be larger than the DBP absorption amount of the solid particles. The positive electrode active material 68 (68A, 68B) in the technology disclosed herein may be a particle having such a porous structure or a hollow structure.

  Here, the porous structure refers to a structure (sponge-like structure) in which a substantial part and a void part are mixed over the entire particle. As a typical example of a positive electrode active material having a porous structure, a positive electrode active material obtained by a so-called spray baking method (sometimes referred to as a spray dry method) (typically a secondary in which primary particles are collected). It takes the form of particles.). The hollow structure refers to a structure having a shell portion and a hollow portion (cavity portion) inside thereof. In a preferred embodiment, the shell portion may have a through hole that allows the outside of the particle to communicate with the hollow portion (hereinafter, the hollow structure having the through hole in the shell portion is referred to as a “perforated hollow structure”. The active material particles having such a structure are sometimes referred to as “porous hollow active material particles”. The particles of such a hollow structure (meaning that it includes a perforated hollow structure unless otherwise specified) are such that the substantial part is biased toward the shell part, and a space is secured in the hollow part. In this respect, the particles having a porous structure are clearly distinguished from each other in terms of structure.

As the material of the active material particles having such a hollow structure, lithium transition metal oxide (typically, lithium transition metal oxide having a layered structure) is preferable. Particularly preferred is a lithium transition metal oxide (typically lithium nickel oxide) containing at least Ni (preferably further Mn) as a transition metal.
≪Method for producing perforated hollow active material particles≫
The porous hollow active material particles having the lithium transition metal oxide as a constituent material can be preferably produced, for example, as follows. The production method includes an aqueous solution containing at least one of transition metal elements contained in the lithium transition metal oxide constituting the active material particles (in a preferred embodiment, all of the metal elements other than lithium contained in the oxide). It includes precipitating the transition metal hydroxide from a solution under appropriate conditions (raw material hydroxide generation step). Moreover, the transition metal hydroxide and the lithium compound are mixed (mixing step). Furthermore, it can include firing the mixture (firing step). Hereinafter, a preferred embodiment of such a production method will be described in detail by taking as an example the case of producing a perforated hollow active material particle composed of a LiNiCoMn oxide having a layered structure. It is not intended to be limited to hollow active material particles.

In a preferred embodiment of the method for producing positive electrode active material particles disclosed herein, the raw material hydroxide generation step supplies ammonium ions (NH ₄ ⁺ ) to an aqueous solution of a transition metal compound, and then from the aqueous solution. Depositing particles of transition metal hydroxide. The solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component. As the solvent other than water constituting the mixed solvent, an organic solvent (such as a lower alcohol) that can be uniformly mixed with water is preferable. The aqueous solution of the transition metal compound (hereinafter also referred to as “transition metal solution”) constitutes the lithium transition metal oxide in accordance with the composition of the lithium transition metal oxide constituting the active material particles as the production target. It contains at least one (preferably all) transition metal elements (here, Ni, Co and Mn). For example, a transition metal solution containing one or more compounds that can supply Ni ions, Co ions, and Mn ions in an aqueous solvent is used. As the metal ion source compound, sulfates, nitrates, chlorides, and the like of the metals can be appropriately employed. For example, a transition metal solution having a composition in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in an aqueous solvent (preferably water) can be preferably used.

The NH ₄ ⁺ may be supplied to the transition metal solution in the form of an aqueous solution (typically an aqueous solution) containing NH ₄ ⁺ , for example, and supplied by directly blowing ammonia gas into the transition metal solution. These supply methods may be used in combination. An aqueous solution containing NH ₄ ⁺ can be prepared, for example, by dissolving a compound (ammonium hydroxide, ammonium nitrate, ammonia gas, or the like) that can be an NH ₄ ⁺ source in an aqueous solvent. In a preferred embodiment, NH ₄ ⁺ is supplied in the form of an aqueous ammonium hydroxide solution (ie, aqueous ammonia).

≪Nucleation stage≫
In a preferred embodiment, the raw material hydroxide generation step comprises a step of depositing transition metal hydroxide nuclei from the transition metal solution (nucleation generation step) and a step of growing the nuclei (particle growth step). Including. In a preferred embodiment, both the nucleation step and the particle growth step are performed in the presence of ammonium ions. At least the particle growth step is preferably performed while controlling the ammonium ion concentration (ammonia concentration) in the solution (for example, controlling it to a predetermined value or less). The particle growth stage is preferably carried out under alkaline conditions at a pH lower than that in the nucleation stage.

  From the viewpoint that it is easy to obtain porous hollow active material particles with little variation (for example, a small number ratio of particles whose particle size or particle structure is greatly deviated from the average), in the nucleation stage, from the transition metal solution, It is preferable to deposit a large number of nuclei within a short time (eg, almost simultaneously). For example, the nuclei may be precipitated from a solution in which the transition metal hydroxide is in a supersaturated state (for example, by allowing the solution to reach a critical degree of supersaturation). In order to suitably realize such a precipitation mode, it is advantageous to perform the nucleation step under a condition of pH 12 or more (typically pH 12 or more and 14 or less, for example, pH 12.2 or more and 13 or less).

The NH ₄ ⁺ concentration (ammonium ion concentration) in the nucleation stage is not particularly limited, but usually it is suitably about 25 g / L or less, for example, about 3 to 25 g / L. The pH and NH ₄ ⁺ concentration can be adjusted by appropriately balancing the usage amount of the ammonia water and the usage amount of an alkaline agent (a compound having an action of tilting the liquidity to alkalinity). The amount used can be grasped as a supply rate to the reaction system, for example. As the alkaline agent, for example, sodium hydroxide, potassium hydroxide and the like can be typically used in the form of an aqueous solution. In a preferred embodiment, an aqueous sodium hydroxide solution is used. In addition, in this specification, the value of pH shall mean pH value on the basis of liquid temperature of 25 degreeC.

≪Particle growth stage≫
In the particle growth stage, the transition metal hydroxide nuclei (typically particles) precipitated in the nucleation stage are preferably grown under alkaline conditions at a lower pH than in the nucleation stage. For example, the growth may be performed at a pH of less than 12 (typically a pH of 10 or more and less than 12, preferably a pH of 10 or more and 11.8 or less, such as a pH of 11.0 or more and 11.8 or less). The transition metal hydroxide particles (raw material hydroxide particles) obtained through this particle growth stage preferably have a structure in which the density inside the particles is lower than the density of the outer surface portion of the particles. In order to stably obtain transition metal hydroxide particles having such a structure, it is important not to make the NH ₄ ⁺ concentration too high (suppress it low) in the particle growth stage. This increases the deposition rate of the transition metal hydroxide (here, the composite hydroxide containing Ni, Co, and Mn), and the raw material water suitable for the formation of the apertured hollow active material particles disclosed herein. Oxide particles (in other words, raw material hydroxide particles that easily form a fired product having a perforated hollow structure) can be effectively produced. Usually, it is appropriate that the NH ₄ ⁺ concentration in the particle growth stage is 25 g / L or less, preferably 15 g / L or less, more preferably 10 g / L or less (for example, 8 g / L or less). The lower limit of the NH ₄ ⁺ concentration is not particularly limited. However, from the viewpoints of ease of management of production conditions, quality stability, mechanical strength (for example, hardness) of the obtained active material particles, etc., the NH ₄ ⁺ concentration is usually set. It is appropriate to set it to 1 g / L or more (preferably 3 g / L or more). The pH and NH ₄ ⁺ concentration in the particle growth stage can be adjusted in the same manner as in the nucleation stage.

In a preferred embodiment, the NH ₄ ⁺ concentration in the particle growth stage is 7 g / L or less (typically 1 to 7 g / L, for example, 3 to 7 g / L). NH ₄ ⁺ concentration in the particle growth step, for example, may be a substantially the same level as NH ₄ ⁺ concentration in the nucleation stage may be lower than NH ₄ ⁺ concentration in the nucleation stage. In addition, the precipitation rate of the transition metal hydroxide is, for example, the transition metal ions contained in the liquid phase of the reaction liquid with respect to the total number of moles of transition metal ions contained in the transition metal solution supplied to the reaction liquid. It can be grasped by examining the transition of the total number of moles (total ion concentration).

  In each of the nucleation stage and the particle growth stage, the temperature of the reaction solution is preferably controlled so as to be a substantially constant temperature (for example, a predetermined temperature ± 1 ° C.) in a range of about 30 ° C. to 60 ° C. The temperature of the reaction solution may be approximately the same in the nucleation stage and the particle growth stage. Moreover, it is preferable to maintain the reaction liquid and the atmosphere in the reaction tank in a non-oxidizing atmosphere through the nucleation stage and the particle growth stage. Further, the total number of moles (total ion concentration) of Ni ions, Co ions and Mn ions contained in the reaction solution is set to, for example, about 0.5 to 2.5 mol / L through the nucleation stage and the particle growth stage. It is preferably about 1.0 to 2.2 mol / L. The transition metal solution may be replenished (typically continuously supplied) in accordance with the deposition rate of the transition metal hydroxide so that the total ion concentration is maintained. The amounts of Ni ions, Co ions, and Mn ions contained in the reaction solution correspond to the composition of the active material particles as the target product (that is, the molar ratio of Ni, Co, and Mn in the LiNiCoMn oxide constituting the active material particles). It is preferable to set the quantity ratio.

≪Mixing process≫
In a preferred embodiment, the transition metal hydroxide particles thus produced (here, composite hydroxide particles containing Ni, Co and Mn) are separated from the reaction solution, washed and dried. Then, the transition metal hydroxide particles and the lithium compound are mixed at a desired quantitative ratio to prepare an unfired mixture (mixing step). In this mixing step, typically, the quantitative ratio corresponding to the composition of the active material particles as the target (that is, the molar ratio of Li, Ni, Co, Mn in the LiNiCoMn oxide constituting the active material particles) Li compound and transition metal hydroxide particles are mixed. As the lithium compound, lithium compounds that can be converted into oxides upon heating, such as lithium carbonate and lithium hydroxide, can be preferably used.

≪Baking process≫
And the said mixture is baked and the active material particle of a hole hollow structure is obtained (baking process). This firing step is typically performed in an oxidizing atmosphere (for example, in the air). The firing temperature in this firing step can be set to 700 ° C. to 1100 ° C., for example. It is preferable that the maximum baking temperature be 800 ° C or higher (preferably 800 ° C to 1100 ° C, for example, 800 ° C to 1050 ° C). According to the maximum firing temperature within this range, the sintering reaction of the primary particles of the lithium transition metal oxide (preferably Ni-containing Li oxide, here LiNiCoMn oxide) can proceed appropriately. Preferably, the fired product is crushed and sieved after the firing step to adjust the particle size of the active material particles.

  In a preferred embodiment, the mixture is calcined at a temperature T1 of 700 ° C. to 900 ° C. (that is, 700 ° C. ≦ T1 ≦ 900 ° C., for example, 700 ° C. ≦ T1 ≦ 800 ° C., typically 700 ° C. ≦ T1 <800 ° C.). A second firing step, and a result obtained through the first firing step is fired at a temperature T2 of 800 ° C. to 1100 ° C. (that is, 800 ° C. ≦ T2 ≦ 1100 ° C., for example, 800 ° C. ≦ T2 ≦ 1050 ° C.) And a firing step. By this, the active material particle of a perforated hollow structure can be formed more efficiently. T1 and T2 are preferably set so that T1 <T2.

  The first firing stage and the second firing stage are performed continuously (for example, by holding the mixture at the first firing temperature T1, and subsequently raising the temperature to the second firing temperature T2 and maintaining the temperature at T2. Alternatively, after maintaining at the first firing temperature T1, it is once cooled (for example, cooled to room temperature) and, if necessary, crushed and sieved before being subjected to the second firing stage. Good.

  In the technique disclosed herein, the first firing stage is a temperature T1 in which the sintering reaction of the target lithium transition metal oxide proceeds and is lower than the melting point and lower than the second firing stage. It can be grasped as a stage for firing. Further, the second firing stage should be understood as a stage in which the sintering reaction of the target lithium transition metal oxide proceeds and the firing is performed at a temperature T2 that is lower than the melting point and higher than the first firing stage. Can do. It is preferable to provide a temperature difference of 50 ° C. or higher (typically 100 ° C. or higher, for example, 150 ° C. or higher) between T1 and T2.

  As described above, the DBP absorption amount A [mL / 100 g] is 10 mL / 100 g to 30 mL / 100 g of the first positive electrode active material 68A, and the DBP absorption amount B [mL / 100 g] is 30 mL / 100 g to 80 mL / 100 g. A preferred example of the second positive electrode active material 68B, here, porous hollow active material particles can be produced.

In addition to the positive electrode active material 68 (first positive electrode active material 68A and second positive electrode active material 68B), the positive electrode mixture layer 66 (that is, both end portions 66A and 66A and the central portion 66B) includes a conductive material and a binder. Any component such as (binder) may be contained as necessary.
The conductive material is not limited to a specific conductive material as long as it is conventionally used in the positive electrode of this type of lithium ion secondary battery. For example, carbon materials such as carbon powder and carbon fiber can be used. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black, etc.), carbon powders such as graphite powder can be used. Among these, you may use together 1 type, or 2 or more types. The amount of the conductive material used is not particularly limited. For example, the conductive material is used in an amount of 1% by mass to 20% by mass with respect to 100% by mass of the first positive electrode active material 68A (or the second positive electrode active material 68B). (Preferably 5% by mass to 15% by mass).

  As said binder, the thing similar to the binder used for the positive electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when a solvent-based paste-like composition (a paste-like composition includes a slurry-like composition and an ink-like composition) is used as the composition for forming the positive electrode mixture layer, a polyfluoride is used. Polymer materials that dissolve in an organic solvent (non-aqueous solvent) such as vinylidene chloride (PVDF) and polyvinylidene chloride (PVDC) can be used. Alternatively, when an aqueous paste composition is used, a polymer material that can be dissolved or dispersed in water can be preferably used. For example, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be mentioned. In addition, the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder. Although the usage-amount of a binder is not specifically limited, For example, 0.5 mass%-10 mass% with respect to 100 mass% of said 1st positive electrode active materials 68A (or said 2nd positive electrode active material 68B). It can be.

  Here, the “solvent-based paste-like composition” is a concept indicating a composition in which the dispersion medium of the first positive electrode active material 68A (or the second positive electrode active material 68B) is mainly an organic solvent. As the organic solvent, for example, N-methyl-2-pyrrolidone (NMP) can be used. “Aqueous paste-like composition” refers to a composition using water or a mixed solvent mainly composed of water as a dispersion medium for the first positive electrode active material 68A (or the second positive electrode active material 68B). It is. As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

The positive electrode sheet (positive electrode) 64 of the lithium ion secondary battery disclosed here can be produced as follows, for example. A paste-like composition for forming a positive electrode mixture layer (composition for the central portion) in which the second positive electrode active material 68B and other optional components (the conductive material, binder, etc.) are dispersed in an appropriate solvent is prepared. Then, the prepared composition is applied to a predetermined portion (a portion corresponding to the central portion 66B of the positive electrode mixture layer 66) on the surface of the long positive electrode current collector 62. Next, a paste-like composition for forming a positive electrode mixture layer (composition for an end portion) in which the first positive electrode active material 68A and other optional components (the conductive material, binder, etc.) are dispersed in an appropriate solvent is prepared. prepare. Then, the prepared composition is applied to a predetermined portion on the surface of the positive electrode current collector 62 (portions corresponding to both end portions 66A and 66A of the positive electrode mixture layer 66). Then, after the composition for center part and the composition for edge part are dried and the positive mix layer 66 is formed, it is compressed (pressed) as needed. Thereby, the positive electrode sheet 64 provided with the positive electrode current collector 62 and the positive electrode mixture layer 66 formed on the positive electrode current collector 62 can be produced. At this time, the coating amount of the central portion composition and the coating amount of [mg / cm ^2] and the end portions composition [mg / cm ^2] may be substantially the same.
In addition, as a method of apply | coating each said composition on the positive electrode electrical power collector 62, the technique similar to a conventionally well-known method is employable suitably. For example, the composition can be suitably applied to the positive electrode current collector 62 by using an appropriate application device such as a die coater, a slit coater, or a gravure coater. At this time, the center portion composition and the end portion composition may be applied onto the positive electrode current collector 62 at the same time.
Moreover, as a compression (pressing) method, conventionally known compression methods such as a roll press method and a flat plate press method can be employed.

As shown in FIG. 4, the positive electrode sheet 64 produced as described above includes a positive electrode current collector 62 and a positive electrode mixture layer 66 including at least a positive electrode active material 68 formed on the current collector 62. It has. The central portion 66B of the positive electrode mixture layer 66 includes, as a main component, a second positive electrode active material 68B having a DBP absorption amount larger than that of the first positive electrode active material 68A included in both end portions 66A and 66A. For this reason, the impregnation property of the central portion 66B is higher than both end portions 66A and 66A. Therefore, in the positive electrode mixture layer 66, when the non-aqueous electrolyte is injected from both end portions 66A and 66A of the wound electrode body 50 (see FIG. 3), the wound electrode body 50 is impregnated with the non-aqueous electrolyte. Moreover, the nonaqueous electrolyte is satisfactorily impregnated over the entire portion including the central portion 66B of the positive electrode mixture layer 66. Thereby, precipitation of metallic lithium can be effectively prevented in the central portion 66B during charging and discharging.
Furthermore, both end portions 66A and 66A of the positive electrode mixture layer 66 contain the first positive electrode active material 68A having a DBP absorption amount smaller than that of the second positive electrode active material 68B included in the central portion 66B as a main component. For this reason, at the time of charge / discharge, the second positive electrode active material 68B included in the central portion 66B of the positive electrode mixture layer 66 expands and contracts, so that the nonaqueous electrolytic solution is in the winding axis direction of the positive electrode mixture layer 66. Even when moving toward the outside in the (width direction), the non-aqueous electrolyte is suppressed from moving at both end portions 66 </ b> A and 66 </ b> A of the positive electrode mixture layer 66. As a result, it is possible to suppress an increase in internal resistance of the positive electrode sheet 64 (that is, the wound electrode body 50) due to the non-aqueous electrolyte flowing out of the positive electrode mixture layer 66. In FIG. 4, illustration of a conductive material, a binder, and the like is omitted.

Next, the negative electrode sheet (negative electrode) 84 provided in the lithium ion secondary battery disclosed here will be described. As shown in FIG. 3, the negative electrode sheet 84 includes a negative electrode current collector 82 and a negative electrode mixture layer 88 including at least a negative electrode active material formed on the negative electrode current collector 82.
As the negative electrode active material, one or more materials conventionally used for negative electrodes of lithium ion secondary batteries can be used without particular limitation. For example, carbon materials such as graphite (graphite), oxide materials such as lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), metals such as tin, aluminum (Al), zinc (Zn), silicon (Si), or Examples thereof include metal materials composed of metal alloys mainly composed of these metal elements.

The negative electrode mixture layer 88 can contain any component such as a binder (binder) and a thickener as needed in addition to the negative electrode active material.
As said binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when an aqueous paste composition is used to form the negative electrode mixture layer 88, a polymer material that is dissolved or dispersed in water can be preferably employed. Polymer materials that disperse in water (water dispersible) include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber; fluorine resins such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE); vinyl acetate Examples thereof include copolymers.

  Moreover, as the thickener, a polymer material that is dissolved or dispersed in water or a solvent (organic solvent) can be employed. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol ( PVA); and the like.

  The negative electrode mixture layer 88 is, for example, a paste-like negative electrode mixture layer formed by dispersing the negative electrode active material and other optional components (binder, thickener, etc.) in an appropriate solvent (for example, water). Preparation (preparation, purchase, etc.), applying (applying) the composition to the surface of the negative electrode current collector 82, drying the composition, and then pressing (compressing) as necessary. Thus, the negative electrode mixture layer 88 is formed. As a result, a negative electrode sheet (negative electrode) 84 including the negative electrode current collector 82 and the negative electrode mixture layer 88 can be produced.

Hereinafter, one embodiment of the lithium ion secondary battery 10 including the positive electrode sheet 64 and the negative electrode sheet 84 disclosed herein will be described with reference to the drawings. However, the present invention is not intended to be limited to the embodiment. Absent. That is, as long as the positive electrode sheet 64 is employed, the shape (outer shape and size) of the lithium ion secondary battery to be manufactured is not particularly limited. In the following embodiment, a description will be given by taking as an example the lithium ion secondary battery 10 having a configuration in which the wound electrode body 50 and the nonaqueous electrolytic solution are housed in a rectangular battery case 15.
In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing a lithium ion secondary battery (nonaqueous electrolyte secondary battery) 10 according to the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.
As shown in FIG. 1, the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable). The case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20. The lid body 25 seals the opening 20 of the case main body 30 by welding or the like. The upper surface of the case 15 (that is, the lid body 25) is provided with a positive electrode terminal 60 that is electrically connected to the positive electrode sheet 64 of the wound electrode body 50 and a negative electrode terminal 80 that is electrically connected to the negative electrode sheet 84 of the electrode body. It has been. In addition, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. . In the case 15, the positive electrode sheet 64 and the negative electrode sheet 84 are laminated together with a total of two separator sheets 90, wound in the longitudinal direction, and then the obtained wound body is crushed from the side surface and kidnapped. The flat wound electrode body 50 and the non-aqueous electrolyte to be produced are accommodated.

2 and 3, the positive electrode mixture layer non-formation portion 63 of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66, as shown in FIGS. 2 and 3) ) And the negative electrode mixture layer non-forming portion 83 of the negative electrode sheet 84 (that is, the portion where the negative electrode current collector 82 is exposed without forming the negative electrode mixture layer 88) protrudes from both sides of the separator sheet 90 in the width direction. In addition, the positive electrode sheet 64 and the negative electrode sheet 84 are overlapped with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 50, the electrode mixture layer non-formed portions 63 and 83 of the positive electrode sheet 64 and the negative electrode sheet 84 are respectively wound core portions (that is, the positive electrode mixture of the positive electrode sheet 64). The layer 66, the negative electrode mixture layer 88 of the negative electrode sheet 84, and the two separator sheets 90 are closely wound around).
As shown in FIG. 2, the positive electrode terminal 60 is joined to the positive electrode mixture layer non-forming portion 63 to electrically connect the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape. Connecting. Similarly, the negative electrode terminal 80 is joined to the negative electrode mixture layer non-forming portion 83, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

As said non-aqueous electrolyte, the thing similar to the non-aqueous electrolyte conventionally used for the lithium ion secondary battery can be used without limitation. Such a non-aqueous electrolyte typically has a composition in which a supporting salt is contained in an appropriate organic solvent (non-aqueous solvent). As the organic solvent, for example, one or more selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like are used. be able to. Further, as the supporting salt (supporting electrolyte), for _{example, LiPF 6, LiBF 4, LiAsF} 6, Li (CF 3 SO 2) 2 N, lithium salt containing as a constituent element fluorine (F), such as LiCF ₃ SO ₃ Is preferably used. Further, difluorophosphate (LiPO ₂ F ₂ ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
Moreover, as said separator sheet, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. A porous polyolefin resin sheet such as polyethylene (PE) or polypropylene (PP) is preferred. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which PP layers are laminated on both sides of the PE layer, and the like can be suitably used.

Next, an example of an assembled battery (typically an assembled battery in which a plurality of single cells are connected in series) 200 including the lithium ion secondary battery 10 as a single battery and a plurality of the single batteries will be described. .
As shown in FIG. 5, the assembled battery 200 includes a plurality of (typically 10 or more, preferably about 10 to 30, for example, 20) lithium ion secondary batteries (unit cells) 10 respectively. The wide surfaces of the battery case 15 are arranged in the facing direction (stacking direction) while being inverted one by one so that the positive electrode terminals 60 and the negative electrode terminals 80 are alternately arranged. A cooling plate 110 having a predetermined shape is sandwiched between the arranged cells 10. The cooling plate 110 functions as a heat dissipating member for efficiently dissipating the heat generated in each unit cell 10 during use, and preferably a cooling fluid (typically air) between the unit cells 10. ) (For example, a shape in which a plurality of parallel grooves extending vertically from one side of the rectangular cooling plate to the opposite side are provided on the surface). A cooling plate made of metal having good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.

A pair of end plates (restraint plates) 120 and 120 are disposed at both ends of the unit cell 10 and the cooling plate 110 arranged as described above. One or a plurality of sheet-like spacer members 150 as length adjusting means may be sandwiched between the cooling plate 110 and the end plate 120. The unit cell 10, the cooling plate 110, and the spacer member 150 arranged above have a predetermined restraining pressure in the stacking direction by a tightening restraining band 130 attached so as to bridge between the end plates 120, 120. Restrained to join. More specifically, by tightening and fixing the end portion of the restraining band 130 to the end plate 120 with screws 155, the unit cells and the like are restrained so that a predetermined restraining pressure is applied in the arrangement direction. Thereby, restraint pressure is also applied to the wound electrode body 50 housed in the battery case 15 of each unit cell 10.
In addition, between the adjacent unit cells 10, one positive electrode terminal 60 and the other negative electrode terminal 70 are electrically connected by a connection member (bus bar) 140. Thus, the assembled battery 200 of the desired voltage is constructed | assembled by connecting each cell 10 in series.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Preparation of positive electrode sheet]
<Example 1>
The mass ratio of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (DBP absorption A: 15 mL / 100 g) as the positive electrode active material, acetylene black as the binder, and PVDF as the binder is 87. : Weighed so as to be 10: 3, and dispersed these materials in NMP to prepare paste-form positive electrode mixture layer forming composition A (end portion composition A). Furthermore, the mass ratio of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (DBP absorption B: 42 mL / 100 g), acetylene black, and PVDF as the positive electrode active material is 87: 10: 3. Thus, these materials were dispersed in NMP to prepare a paste-like positive electrode mixture layer-forming composition B (center portion composition B). Each composition was applied onto a positive electrode current collector (aluminum foil) A having a thickness of 20 μm and a length in the width direction of 78 mm. That is, the center of the positive electrode mixture layer is placed on the remaining positive electrode current collector in the width direction of 58 mm excluding the 20 mm region (that is, the portion where the positive electrode mixture layer is not formed) from the edge in the width direction of the positive electrode current collector. The center portion partial composition B is applied at a coating amount of 13.5 mg / cm ² so that the length Lp in the width direction (winding axis direction) of the portion is 11.6 mm, and the end portion of the positive electrode mixture layer The end portion composition A was applied at a coating amount of 13.5 mg / cm ² so that the lengths in the width direction were 23.2 mm. Thereafter, the composition A and the composition B are dried and subjected to a rolling treatment, whereby a composite material density (positive electrode composite material density) of 2.8 g / cm ³ and a width direction length L are formed on the surface of the positive electrode current collector. Produced a positive electrode sheet according to Example 1 in which a positive electrode mixture layer having a thickness of 58 mm was formed. At this time, the value of Lp / L was 0.2.

<Example 2>
Example 2 is the same as Example 1 except that the composition A for end portion and the composition B for center portion are applied onto the positive electrode current collector A so that the value of Lp / L is 0.4. A positive electrode sheet was produced.

<Example 3>
Example 3 is the same as Example 1 except that the composition A for end portion and the composition B for center portion are applied onto the positive electrode current collector A so that the value of Lp / L is 0.6. A positive electrode sheet was produced.

<Example 4>
A positive electrode sheet according to Example 4 was produced in the same manner as in Example 1 except that only the central portion composition B was applied onto the positive electrode current collector A so that the value of Lp / L was 1.

<Example 5>
Example 5 is the same as Example 1 except that the composition A for end portion and the composition B for center portion are applied onto the positive electrode current collector A so that the value of Lp / L is 0.1. A positive electrode sheet was produced.

<Example 6>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (DBP absorption: 40 mL / 100 g), acetylene black, PVDF were weighed so that the mass ratio was 87: 10: 3, and these materials were A paste-like composition for forming a positive electrode mixture layer C was prepared by dispersing in NMP. The composition was applied onto the positive electrode current collector A at a coating amount of 13.5 mg / cm ² . Thereafter, the composition is dried and subjected to a rolling treatment to produce a positive electrode sheet according to Example 6 in which a positive electrode mixture layer having a width direction length L of 58 mm is formed on the surface of the positive electrode current collector. did.

<Example 7>
DBP absorption instead of _LiNi 1/3 _Mn 1/3 _Co 1/3 _{O 2} in 40 mL / 100 g, DBP absorption using _LiNi 1/3 _Mn 1/3 _Co 1/3 _{O 2} in 20 mL / 100 g Otherwise, the positive electrode sheet according to Example 7 was produced in the same manner as in Example 6.

[Bending amount measurement test]
Two positive electrode sheets according to Examples 1 to 7 were prepared, and the amount of bending of the positive electrode sheet according to each example was measured. That is, each positive electrode sheet is cut so that the length in the longitudinal direction is 1 m, the positive electrode sheet according to each cut example is placed on a flat desk, and the desk surface of the most curved part The height from was measured and the average value was obtained. The measurement results are shown in Table 1.

  As shown in Table 1, in the positive electrode sheets according to Examples 4 and 6, there is only one type of positive electrode active material contained in the positive electrode mixture layer, and the DBP absorption amount of the positive electrode active material is as large as 40 mL / 100 g or more. Therefore, it was confirmed that the bending amount was greatly curved as 3 mm or more. On the other hand, a case where the central portion includes the second positive electrode active material having a large DBP absorption amount and the both end portions include the first positive electrode active material having a DBP absorption amount smaller than that of the second positive electrode active material (Example 1 to Example) 3 and Example 5), or when the positive electrode active material contained in the positive electrode mixture layer is only one kind and the DBP absorption amount of the positive electrode active material is as small as 20 mL / 100 g (Example 7), It was confirmed that the amount of bending was 0.6 mm or less and almost no bending.

[Production of wound electrode body]
<Example 1 to Example 7>
Weigh the natural graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener so that the mass ratio is 98: 1: 1, and disperse these materials in ion-exchanged water. A paste-like composition for forming a negative electrode mixture layer was prepared. The composition was applied on a negative electrode current collector (copper foil) having a thickness of 10 μm and a length in the width direction of 80.9 mm, and an application amount of 7.4 mg / cm ² . Then, the negative electrode sheet according to Example 1 in which a negative electrode mixture layer having a length in the width direction of 60.9 mm is formed on the surface of the negative electrode current collector by drying the composition and rolling the composition. Was made.
Then, the prepared positive electrode sheet according to Example 1 and the negative electrode sheet according to Example 1 are wound through two separator sheets (polyethylene porous membrane) having a length of 63 mm in the width direction, and the wound electrode body according to Example 1 is obtained. Produced. A wound electrode body according to Examples 2 to 7 was produced in the same manner as Example 1 except that the positive electrode sheet according to Examples 2 to 7 was used instead of the positive electrode sheet according to Example 1.

[Winding deviation measurement test]
100 wound electrode bodies according to Examples 1 to 7 were prepared, and the presence or absence of winding deviation of the wound electrode bodies according to each example was confirmed. That is, by using an X-ray fluoroscopy method, a winding misalignment is defined as an end portion of the wound electrode body on the outer side of the negative electrode mixture layer facing the positive electrode mixture layer at the end in the winding axis direction. . Here, the following formula: (number of winding misalignment / 100) was taken as the winding misalignment rate [%]. The measurement results are shown in Table 1.

  As shown in Table 1, it was confirmed that winding misalignment occurred in the wound electrode body (Example 4 and Example 6) provided with the positive electrode sheet having a large bending amount. On the other hand, in the wound electrode body (Examples 1 to 3, Example 5 and Example 7) including the positive electrode sheet having a small amount of bending and almost not curved, no winding misalignment occurred.

[Production of lithium ion secondary battery]
<Example 1 to Example 7>
A lithium ion secondary battery according to Example 1 having a rated capacity of 25 Ah was fabricated by housing the wound electrode body according to Example 1 above in a rectangular case together with a non-aqueous electrolyte. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / L LiPF ₆ in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3: 5: 2 is used. used. Lithium ion secondary batteries according to Examples 2 to 7 were produced in the same manner as Example 1 except that the wound electrode bodies according to Examples 2 to 7 were used instead of the wound electrode bodies according to Example 1. .

[Impregnation test]
Five lithium ion secondary batteries according to Examples 1 to 7 were prepared. Then, after injecting each non-aqueous electrolyte solution (after fabrication), each lithium ion secondary battery is allowed to stand for 1 hour, 4 hours, 8 hours, 12 hours, and 24 hours, and then each lithium ion secondary battery is disassembled to form a positive electrode. The sheet was taken out. The degree of impregnation of the non-aqueous electrolyte in the positive electrode sheet (that is, the positive electrode mixture layer) at this time was examined. The measurement results are shown in Table 1.
In addition, those in which the entire positive electrode mixture layer is sufficiently impregnated with the nonaqueous electrolyte solution (that is, those in which the nonaqueous electrolyte solution floats on the surface of the positive electrode mixture layer) are sufficiently impregnated with the nonaqueous electrolyte solution. In Table 1, it is indicated by “◎”. Also, the whole positive electrode mixture layer is impregnated with a non-aqueous electrolyte (that is, the whole positive electrode mixture layer is wet and has no white part (part not impregnated with a non-aqueous electrolyte)) It was judged that the non-aqueous electrolyte was impregnated, and the result is shown in FIG. Further, the positive electrode mixture layer is not impregnated with the nonaqueous electrolyte in the central portion in the winding axis direction (width direction) (that is, the white portion (nonaqueous electrolyte is impregnated in the central portion of the positive electrode mixture layer) The remaining part)) was determined to be insufficiently impregnated with the non-aqueous electrolyte, and indicated by Δ in Table 1. Further, the non-aqueous electrolyte solution is hardly impregnated over the entire positive electrode mixture layer (that is, almost the entire positive electrode mixture layer is made of a white portion (a portion not impregnated with the non-aqueous electrolyte solution). It was determined that the non-aqueous electrolyte was hardly impregnated, and the result was shown as x in Table 1.

  As shown in Table 1, in the lithium ion secondary batteries shown in Examples 1 to 3 and Example 6, after 8 hours have passed since the nonaqueous electrolyte was injected into the wound electrode body, the electrode body was sufficiently It was confirmed that the non-aqueous electrolyte was impregnated. Further, as in Example 7, it was confirmed that the positive electrode mixture layer composed of only the positive electrode active material having a relatively small DBP absorption amount of 20 mL / 100 g was inferior in the impregnation property of the non-aqueous electrolyte. Furthermore, from the results of Examples 1 to 5, Lp / L when the length L of the positive electrode mixture layer in the winding axis direction (width direction) and the length of the central portion in the winding axis direction are Lp. When the value of is 0.1 or less, it was confirmed that the impregnation property of the central portion of the positive electrode mixture layer was not sufficient.

[Capacity maintenance rate measurement test]
About the lithium ion secondary battery which concerns on the produced said Example 1-Example 7, charge / discharge was repeated 1000 cycles and the capacity | capacitance maintenance factor [%] after 1000 cycles was calculated | required. In other words, under a temperature condition of 25 ° C., an operation of charging at a constant current and a constant voltage up to 4.2 V (SOC 100%) at a charging rate of 10 C (240 A) (CC-CV charging) and 2 at a discharging rate of 10 C (240 A) The operation of discharging at a constant current and a constant voltage up to 5 V (CC-CV discharge) was repeated 1000 times. The ratio of the discharge capacity after 1000 cycles ((discharge capacity after 1000 cycles / initial capacity) × 100 (%)) to the discharge capacity (initial capacity) after 1 cycle was calculated as the capacity retention rate (%). Each of the discharge capacities is determined by charging the lithium ion secondary battery after each cycle to 4.2 V at 1 C (24 A) by a constant current constant voltage (CCCV) method, and then 2 at 1 C (24 A) by the CCCV method. This is the capacity obtained when discharging to 5V. The above measurement results are shown in Table 1.

As shown in Table 1, it was confirmed that the lithium ion secondary batteries according to Examples 1 to 3 had a higher capacity retention rate than the lithium ion secondary batteries according to Examples 4 to 7. . In particular, when Lp / L was 0.4 to 0.6 (Example 2 and Example 3), it was confirmed that the capacity retention rate was excellent.
From the above results, the lithium ion secondary batteries according to Examples 1 to 3 were provided with the positive electrode sheet with a small amount of bending, and therefore, the occurrence of winding misalignment when the wound electrode body was produced was prevented. . The positive electrode mixture layer is sufficiently impregnated with the non-aqueous electrolyte, and the central portion of the positive electrode mixture layer in the winding axis direction (width direction) holds a sufficient amount of the non-aqueous electrolyte. Therefore, deposition of metallic lithium in the central portion is prevented, and a decrease in capacity maintenance rate based on this is prevented. Further, in the lithium ion secondary batteries according to Examples 1 to 3, outflow of the non-aqueous electrolyte from the positive electrode mixture layer to the outside during high rate charge / discharge was suppressed, and a high capacity retention rate was provided.

  The non-aqueous electrolyte secondary battery according to the present invention is well impregnated with the non-aqueous electrolyte over the entire positive electrode mixture layer, and has cycle characteristics (for example, capacity during charge / discharge). Because of its excellent maintenance rate, it can be used as a non-aqueous electrolyte secondary battery for various applications. For example, as shown in FIG. 6, it can be suitably used as a power source (drive power source) for a vehicle drive motor mounted on a vehicle 100 such as an automobile. The lithium ion secondary battery 10 used for the vehicle 100 may be used alone, or may be used in the form of an assembled battery 200 that is connected in series and / or in parallel.

10 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
15 Battery Case 20 Opening 25 Cover 30 Case Body 40 Safety Valve 50 Winding Electrode Body 60 Positive Electrode Terminal 62 Positive Electrode Current Collector 63 Positive Electrode Mixing Layer Non-Forming Portion 64 Positive Electrode Sheet (Positive Electrode)
66 Positive electrode mixture layer 66A End portion 66B Central portion 68 Positive electrode active material 68A First positive electrode active material 68B Second positive electrode active material 80 Negative electrode terminal 82 Negative electrode current collector 83 Negative electrode mixture layer non-formed portion 84 Negative electrode sheet (negative electrode) )
88 Negative electrode composite material layer 90 Separator sheet 100 Vehicle (automobile)
110 Cooling plate 120 End plate 130 Restraint band 140 Connection member 150 Spacer member 155 Screw 200 Battery assembly

Claims (6)

A non-aqueous electrolyte secondary battery comprising a wound electrode body including a positive electrode sheet and a negative electrode sheet, and a non-aqueous electrolyte solution,
The positive electrode sheet includes a long positive electrode current collector, and a positive electrode mixture layer including at least a positive electrode active material formed on the surface of the positive electrode current collector,
Both end portions of the positive electrode mixture layer in the winding axis direction of the wound electrode body are mainly composed of the first positive electrode active material, and at least the center of the positive electrode mixture layer in the winding axis direction is formed. The central part including the second positive electrode active material is mainly composed of the DBP absorption amount [mL between the first positive electrode active material and the second positive electrode active material according to JIS K6217-4. / 100g] are different from each other,
The DBP absorption amount A [mL / 100 g] of the first positive electrode active material is smaller than the DBP absorption amount B [mL / 100 g] of the second positive electrode active material. Next battery. The DBP absorption amount A [mL / 100 g] of the first positive electrode active material is 10 mL / 100 g to 30 mL / 100 g,
2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the DBP absorption amount B [mL / 100 g] of the second positive electrode active material is 30 mL / 100 g to 80 mL / 100 g.   The value of Lp / L when the length of the positive electrode mixture layer in the winding axis direction is L and the length of the central portion in the winding axis direction is Lp is 0.15 to 0.85. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein   4. The non-aqueous electrolyte according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are both active material particles having a hollow structure. Secondary battery.   5. The non-aqueous electrolyte secondary battery according to claim 1, wherein a length of the positive electrode mixture layer in a winding axis direction is at least 40 mm. 6.   A non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the unit battery is an assembled battery as a driving power source for a vehicle in which a plurality of unit cells are electrically connected to each other. A battery pack, characterized in that is used.

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