JP2010015852A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery for realizing each intrinsic performance a plurality of active substances it uses. <P>SOLUTION: The cylindrical lithium-ion secondary battery 10 includes a battery can 6 of a bottomed cylindrical shape. The battery can 6 houses an electrode group 11 with a cathode plate and an anode plate with a strip shape wound around via a separator 5. The cathode plate includes a cathode active material layer 2 containing a cathode active material coated on either side of a cathode collector 1. The anode plate includes an anode active material layer 4a containing graphite system carbon powder coated on one face of an anode collector 3, as well as an anode active material layer 4b containing amorphous system carbon powder coated on the other. Both anode active material layers 4a, 4b are exposed to a surface of the anode plate. Each active material exerts its intrinsic performance on the surface of the anode plate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery, and in particular, an electrode group in which an active material layer containing an active material is applied to a current collector and an electrode group in which a negative electrode plate is disposed via a separator, and electrolysis that infiltrates the electrode group The present invention relates to a secondary battery including a liquid and a battery container that houses an electrode group and an electrolytic solution.

Among secondary batteries, a lithium secondary battery using a non-aqueous electrolyte has a high energy density, and is therefore widely used as a power source for portable devices such as VTR cameras, notebook computers, and mobile phones. On the other hand, hybrid electric vehicles (HEV) are beginning to spread due to recent global warming and oil depletion problems. In addition, development of plug-in hybrids (PHEV) and electric vehicles (EV) is urgently required for further improvement in fuel consumption, and they are also used as power sources for these. In HEV, a motor is used for power assist when starting or accelerating, and the secondary battery used as a power source at this time has a high output type, that is, a high discharge rate characteristic capable of discharging a large current in a short time. It is required to be. On the other hand, in PHEV and EV, since a motor is used even during steady running, a secondary battery having a high capacity and a high discharge rate characteristic is required. Furthermore, it is required to extend the battery life in order to cope with a long use period.

  Conventionally, in a lithium secondary battery, an active material layer containing an active material capable of occluding and releasing lithium ions is applied to the positive and negative electrode current collectors. In general, a lithium-containing composite oxide is used for the positive electrode active material, and a carbon material such as a graphite-based carbon material such as natural graphite or artificial graphite or an amorphous carbon material obtained by firing a furan resin or the like as the negative electrode active material. Is used. When a graphite-based carbon material is used for the negative electrode active material, the irreversible capacity is smaller than that of the amorphous carbon material and the voltage characteristics are flat, so that a high-capacity lithium secondary battery can be obtained. However, since the volume change of the crystal accompanying charging / discharging is larger than that of the amorphous carbon material, the lifetime is reached early. In contrast, when an amorphous carbon material is used, the charge / discharge characteristics at a large current density are superior to those of a graphite-based carbon material, and the volume change of crystals accompanying charge / discharge is smaller than that of a graphite-based carbon material. Since it is small, a lithium secondary battery having high cycle characteristics and high discharge rate characteristics can be obtained. However, since the irreversible capacity is larger than that of the graphite-based carbon material, it is difficult to increase the capacity of the lithium secondary battery.

  As described above, it is difficult to satisfy all requirements such as high capacity, long life and high discharge rate with a single active material used for lithium secondary batteries, so there is a method of using a plurality of active materials in combination. Conceivable. As a method of using a plurality of active materials, a technique of laminating and coating two active material layers containing different active materials on a negative electrode current collector is disclosed (for example, see Patent Document 1).

JP-A-8-138671

  However, in the technique of Patent Document 1, the active material contained in the active material layer applied to the lower layer of the negative electrode current collector has a reaction rate higher than that of the active material contained in the active material layer applied to the upper layer. It will be slow and not fully perform. On the other hand, when an active material layer containing a mixed active material in which a plurality of active materials are mixed is applied to the positive and negative electrode current collectors, active materials having different properties are present randomly in the active material layer. The performance of each active material is difficult to demonstrate.

  In view of the above circumstances, the present invention provides a secondary battery that can exhibit the original performance of each active material using a plurality of active materials and can improve both high output and high capacity characteristics. Let it be an issue.

  In order to solve the above problems, the present invention provides an electrode group in which an active material layer containing an active material is applied to a current collector and an electrode group in which a negative electrode plate is disposed via a separator, and infiltrates the electrode group A plurality of active material layers each including a different active material is applied to at least one current collector of the positive and negative electrode plates. The plurality of active material layers are all exposed on the surface of the positive electrode plate or the negative electrode plate.

  In the present invention, at least one current collector of the positive and negative electrode plates is coated with a plurality of active material layers each containing a different active material, and any active material layer is exposed on the surface of the positive electrode plate or the negative electrode plate. Therefore, the original performance of each active material can be exhibited, and high output and high capacity characteristics can be improved.

  In this case, the plurality of active material layers may be coated with active material layers containing different active materials on both surfaces of at least one current collector of the positive and negative electrode plates, and at least one current collector of the positive and negative electrode plates. It may be applied in stripes on at least one surface of the electric body. Moreover, it is desirable that at least one of the positive and negative electrode plates is a positive electrode plate, and different active materials are in the same operating potential range.

  According to the present invention, at least one of the current collectors of the positive and negative electrode plates is coated with a plurality of active material layers each containing different active materials, and any active material layer is applied to the surface of the positive electrode plate or the negative electrode plate. Since it is exposed, the original performance of each active material can be exhibited, and the effect that high output and a high capacity | capacitance characteristic can be improved can be acquired.

(First embodiment)
Hereinafter, a first embodiment of a cylindrical lithium ion secondary battery to which the present invention is applied will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1, the columnar lithium ion secondary battery 10 according to the present embodiment includes a nickel-plated iron-made bottomed cylindrical battery can 6 serving as a battery container. The battery can 6 accommodates an electrode group 11 in which a belt-like positive electrode plate and a negative electrode plate are wound in a spiral shape through a separator 5. An insulation coating (not shown) is applied to the entire outer peripheral surface of the electrode group 11. In this example, the separator 5 is a polyethylene porous film having a thickness of 25 μm and a width that intersects the longitudinal direction (hereinafter simply referred to as a width) of 58 mm. The rated voltage of the lithium ion secondary battery 10 is set to 4V.

  On the upper side of the electrode group 11, a ribbon-like positive electrode tab terminal 8 made of aluminum and having one end joined to the positive electrode current collector 1 is led out. The other end of the positive electrode tab terminal 8 is joined to the lower surface of the disc-shaped upper lid 7 which is disposed on the upper side of the electrode group 11 and serves as a positive electrode external terminal. The upper lid 7 incorporates a current cutoff switch (not shown) that operates in response to an increase in battery internal pressure and a safety valve mechanism (not shown) that operates at a pressure higher than the pressure at which the current cutoff switch operates. On the other hand, a ribbon-like negative electrode tab terminal made of copper having one end bonded to the negative electrode current collector 3 is led out below the electrode group 11. The other end of the negative electrode tab terminal is joined to the inner bottom surface of the battery can 6. Therefore, the negative electrode plate and the battery can 6 are electrically connected, and the battery can 6 also serves as a negative electrode external terminal.

The upper lid 7 is caulked and fixed to the upper part of the battery can 6 via an insulating gasket 9. For this reason, the inside of the lithium ion secondary battery 10 is sealed. In addition, a non-aqueous electrolyte (not shown) is injected into the battery can 6. In the non-aqueous electrolyte, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent in which ethylene carbonate, dimethyl carbonate and diethyl carbonate are mixed at a volume ratio of 30:50:20. Is used. In this example, 5 ml of the non-aqueous electrolyte is injected into the battery can 6.

(Positive electrode plate)
The positive electrode plate is produced using a single active material. Lithium-manganese-cobalt-nickel composite oxide (LiMn _0.33 Co _0.33 Ni _0.33 O ₂ ) as a positive electrode active material, graphite powder having an average particle diameter of 0.5 μm as a conductive material, and a binder Polyvinylidene fluoride (KF # 1120 manufactured by Kureha Chemical Co., Ltd.) is mixed at a weight ratio of 80:10:10, and the solvent is N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP). A mixture slurry is produced by dispersing the mixture almost uniformly. In this example, an aluminum foil having a thickness of 20 μm is used as the positive electrode current collector 1, and the mixture slurry is applied on both surfaces of the positive electrode current collector 1 approximately uniformly by a roll-to-roll method transfer. At this time, uncoated portions of the mixture slurry for joining the positive electrode tab terminals 8 are formed at both longitudinal ends of the positive electrode current collector 1. After drying, it is press-integrated and the positive electrode active material layers 2 are applied to both surfaces of the positive electrode current collector 1. Increasing the press pressure increases the density of the positive electrode active material layer 2, that is, the density of the positive electrode active material, and improves battery performance. However, if the press pressure is too high, the positive electrode current collector 1 is stretched and changes in dimensions. , Pressed in a pressure range that does not change dimensions. In this example, the thickness of the positive electrode plate is set to 160 to 165 μm, and the density of the positive electrode active material layer 2 is set to 3.5 g / cm ³ . Thereafter, by cutting, a belt-like positive electrode plate having a width of 54 mm and a length of 450 mm is produced.

(Negative electrode plate)
The negative electrode plate is produced using two types of active materials, graphite-based carbon powder having high capacity characteristics and amorphous-based carbon powder having high discharge rate characteristics. Graphite-based carbon powder and amorphous carbon powder are mixed with a binder of polyvinylidene fluoride (KF # 9130, manufactured by Kureha Chemical Industry Co., Ltd.) at a weight ratio of 90:10, respectively, and each of them is mixed with NMP as a solvent. Two kinds of mixture slurry are produced by dispersing the mixture almost uniformly. A copper foil having a thickness of 10 μm is used as the negative electrode current collector 3. Each is uniformly applied by roll-to-roll transfer. Similarly to the positive electrode plate, uncoated portions of the mixture slurry for joining the negative electrode tab terminals are formed at both ends in the longitudinal direction of the negative electrode current collector 3. After drying, two negative electrode active material layers 4 that are press-integrated and that contain different active materials on both sides of the negative electrode current collector 3 are applied. That is, a negative electrode active material layer 4a containing graphite-based carbon powder is coated on one surface of the negative electrode current collector 3, and a negative electrode active material layer 4b containing amorphous carbon powder is coated on the other surface. Similar to the positive electrode plate, the negative electrode current collector 3 is pressed in a pressure range in which the dimension does not change due to elongation. In this example, the thickness of the negative electrode plate is set to 160 to 165 μm, and the density of the negative electrode active material layer 4 is set to 1.1 to 1.7 g / cm ³ . Thereafter, by cutting, a strip-shaped negative electrode plate having a width of 56 mm and a length of 500 mm is produced.

(Second Embodiment)
Next, a second embodiment of the cylindrical lithium ion secondary battery 10 to which the present invention is applied will be described. In this embodiment, instead of the negative electrode plate shown in the first embodiment, a negative electrode plate in which negative electrode active material layers 4 containing different active materials are applied in a stripe shape is used. In addition, in this embodiment, the same code | symbol is attached | subjected to the component same as 1st Embodiment, the description is abbreviate | omitted, and only a different location is demonstrated.

(Negative electrode plate)
The negative electrode plate of this embodiment is produced using a mixture slurry containing graphite-based carbon powder and amorphous carbon powder, respectively, as in the first embodiment. As shown in FIG. 2, amorphous carbon powder, graphite carbon powder, and amorphous carbon powder are respectively formed on both sides of the negative electrode current collector 3 in a stripe shape along the longitudinal direction of the negative electrode current collector 3. The mixed slurry containing is applied substantially uniformly and with a substantially uniform width. Uncoated portions of the mixture slurry are formed on the side edges on both sides in the longitudinal direction of the negative electrode current collector 3. After drying, it is press-integrated and three negative electrode active material layers 4 are applied to both surfaces of the negative electrode current collector 3. That is, the negative electrode active material layer 4a containing graphite-based carbon powder at the center in the width direction of the negative electrode current collector 3 and the negative electrode active material layer 4b containing amorphous carbon powder at both ends in the width direction are approximately equal in width. It is painted with.

  Next, examples of the lithium ion secondary battery 10 manufactured according to the above embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
In Example 1, according to the first embodiment, the negative electrode active material layer 4a containing graphite-based carbon powder on one surface of the negative electrode current collector 3 and the negative electrode active material layer 4b containing amorphous carbon powder on the other surface are respectively provided. The lithium ion secondary battery 10 was produced using the coated negative electrode plate.

(Example 2)
In Example 2, in accordance with the second embodiment, the negative electrode active material layer 4a including the graphite-based carbon powder in the central portion in the width direction of the negative electrode current collector 3 includes two pieces including the amorphous carbon powder in the both ends in the width direction. The lithium ion secondary battery 10 was produced using the negative electrode plate by which the negative electrode active material layer 4b was apply | coated with the substantially equal width | variety, respectively (refer FIG. 2).

(Comparative Example 1 and Comparative Example 2)
In Comparative Example 1 and Comparative Example 2, lithium ion secondary batteries were produced in the same manner as in the above embodiment except that a negative electrode plate different from the negative electrode plate used in Example 1 and Example 2 was used. In Comparative Example 1, a negative electrode plate in which a negative electrode active material layer containing a mixed active material in which an amorphous carbon powder and a graphite carbon powder were mixed at a weight ratio of 50:50 was coated on both surfaces of a negative electrode current collector A lithium ion secondary battery was fabricated using In Comparative Example 2, a negative electrode plate in which a negative electrode active material layer containing an amorphous carbon powder is laminated and coated on both sides of a negative electrode current collector on a negative electrode active material layer containing a graphite carbon powder is used. Thus, a lithium ion secondary battery was produced. That is, in the lithium ion secondary battery of Comparative Example 2, only the negative electrode active material layer containing amorphous carbon powder is exposed on the surface of the negative electrode plate.

(Battery evaluation test)
About the produced lithium ion secondary battery of each Example and a comparative example, discharge capacity and a load factor characteristic were evaluated. In the evaluation of the discharge capacity, the discharge capacity of each lithium ion secondary battery in the fifth cycle in which charge and discharge were repeated in consideration of the irreversible capacity was measured. The ratio of the discharge capacity of each example and the lithium ion secondary battery of the comparative example when the discharge capacity of the lithium ion secondary battery of the comparative example 1 is 100% is shown in Table 1 below. Further, in the evaluation of the load factor characteristics, each lithium ion secondary battery charged at a 5-hour rate (discharge rate 0.2C) is 1 hour rate (1C), 0.5 hour rate (2C), 0.3 hour. The discharge capacity of each lithium ion secondary battery was measured when discharged to the final voltage at a rate (3C), a 0.2 hour rate (5C), and a 0.1 hour rate (10C). All the evaluation tests were performed at room temperature (25 ° C.) with a charge end voltage of 4.1 V and a discharge end voltage of 3.0 V. When the discharge capacity at 1C of the lithium ion secondary battery of Comparative Example 1 is 100%, the ratio of the discharge capacity of each Example and Comparative Example lithium ion secondary battery is defined as the discharge capacity maintenance rate, and the discharge capacity maintenance rate FIG. 3 is a graph showing the load factor characteristics plotted with respect to the discharge rate.

  As shown in Table 1, it is clear that the lithium ion secondary batteries 10 of Example 1 and Example 2 have higher discharge capacities than the lithium ion secondary batteries of Comparative Example 1 and Comparative Example 2. Became. Further, as shown in FIG. 3, in the lithium ion secondary batteries of Comparative Examples 1 and 2, the discharge capacity greatly decreased as the discharge rate increased and the discharge current increased. On the other hand, in the lithium ion secondary battery 10 of Example 1 and Example 2, it became clear that even if the discharge rate was increased, the decrease in the discharge capacity was suppressed. Therefore, the lithium ion secondary battery 10 of Example 1 and Example 2 has both a high capacity characteristic and a high discharge rate characteristic (load factor characteristic) as compared with the lithium ion secondary battery of each comparative example. Was confirmed.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 10 of the above embodiment will be described.

  In the first embodiment, the negative electrode active material layer 4a containing graphite-based carbon powder is coated on one surface of the negative electrode current collector 3, and the negative electrode active material layer 4b containing amorphous carbon powder is coated on the other surface. In other words, the negative electrode current collector is coated with a plurality of active material layers each containing a different active material, and all of the active material layers are exposed on the surface of the negative electrode plate. For this reason, the active material contained in the active material layer can quickly exchange lithium ions and the like on the surface of each active material layer, that is, on the surface of the negative electrode plate. In addition, since each active material layer contains one type of active material substantially uniformly, interference between active materials such as when different active materials randomly exist in one active material layer. Performance degradation can be prevented. Therefore, the original performance of each active material can be exhibited using a plurality of active materials.

  In the second embodiment, the negative electrode active material layer 4a containing graphite-based carbon powder at the center in the width direction of the negative electrode current collector 3 and the negative electrode active material layer 4b containing amorphous carbon powder at both ends in the width direction. Are each applied with a substantially uniform width. That is, two or more active material layers are respectively applied in stripes on both sides of the negative electrode current collector. For this reason, the ratio of the active material layer in which active materials having different characteristics are included can be arbitrarily adjusted. Therefore, as described above, the original performance of each active material can be exhibited, and by adjusting the ratio of the active material layer that exhibits the characteristics of the active material, the characteristics of each active material can be balanced as desired. It can be demonstrated with.

  Furthermore, in the above embodiment, the negative electrode active material layer 4a including the graphite-based carbon powder having high capacity characteristics in the negative electrode current collector 3 and the negative-electrode active material layer including the amorphous carbon powder having high discharge rate characteristics. 4b is applied. For this reason, it is possible to improve both high output (high discharge rate) and high capacity characteristics that are difficult to achieve with a single type of active material.

  In the above embodiment, two types of negative electrode active materials, ie, graphite-based carbon powder and amorphous carbon powder, are exemplified as different active materials, but the present invention is not limited to this. For example, a carbon material such as graphitizable carbon can be used, and usually, a plurality of negative electrode active materials used for the secondary battery can be used without being limited to two types. For example, by using three kinds of active materials, it is possible to provide high capacity, high output, and long life.

  In the second embodiment, an example in which three negative electrode active material layers 4 are applied to both surfaces of the negative electrode current collector 3 in a stripe shape along the longitudinal direction of the negative electrode current collector 3 has been described. The invention is not limited to this. For example, the negative electrode active material layer 4 may be applied so as to be striped in a direction crossing the longitudinal direction of the negative electrode current collector 3 or in an oblique direction. Furthermore, it goes without saying that the type of active material contained in the negative electrode active material layer 4 and the width and number of the negative electrode active material layers 4 may be arbitrarily set. Further, different striped negative electrode active material layers 4 may be applied to both surfaces of the negative electrode current collector 3, or the striped negative electrode active material layers 4 may be applied to only one surface.

  Further, in the above-described embodiment, an example in which a plurality of active material layers each including different active materials is applied to the negative electrode current collector is shown, but the present invention is not limited to this, and the positive electrode plate is used as the negative electrode. You may produce similarly to a board. That is, a positive electrode plate in which a plurality of active material layers each containing a different active material is applied to the positive electrode current collector and all of the active material layers are exposed on the surface may be used. In the above embodiment, the operating potential (range), that is, the rated voltage is 4 V is exemplified, but the operating potential (range) is 3 V, for example, is also applicable. However, if the operating potential range differs greatly between different active materials, the operating potential range of the battery is limited to the common potential range for the active material used, so the original performance of each active material may not be fully demonstrated. There is sex. Therefore, in the case of the positive electrode plate, it is preferable to use an active material within the same operating potential range. Further, a plurality of active material layers may be applied to both the positive electrode plate and the negative electrode plate.

Furthermore, in the above embodiment, lithium-manganese-cobalt-nickel composite oxide (LiMn _0.33 Co _0.33 Ni _0.33 O ₂ ) is exemplified as the positive electrode active material, but the present invention is not limited to this. For example, a composite of lithium and a transition metal such as lithium-manganese-nickel composite oxide (LiMn _0.5 Ni _0.5 O ₂ ), lithium manganate (LiMn ₂ O ₄ ), or lithium cobaltate (LiCoO ₂ ) Oxides can be used.

  Furthermore, in the above-described embodiment, the non-aqueous electrolyte was prepared by dissolving 1 mol / liter of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate. It is not limited, and any of those normally used for secondary batteries can be used. As an electrolytic solution other than the above-described embodiment, a non-aqueous electrolytic solution in which a general lithium salt is used as an electrolyte and dissolved in an organic solvent can be used, and the lithium salt and the organic solvent are not particularly limited. Further, the mixing ratio of the organic solvent and the content of the lithium salt are not particularly limited.

  Moreover, in the said embodiment, although the winding type cylindrical lithium ion secondary battery 10 was illustrated as a secondary battery, this invention is not limited to this, Any secondary battery using electrolyte solution It is also applicable to. In other words, the battery type, battery capacity, size, shape and the like are not limited. Examples of batteries other than the winding type to which the present invention can be applied include batteries having a structure in which a positive and negative electrode plate in which an active material layer is coated on a current collector is laminated via a separator. Further, the battery structure to which the present invention can be applied may be other than a battery having a structure in which the upper lid is caulked and sealed to the battery can described above. As an example of such a structure, a battery in a state where positive and negative external terminals penetrate through the battery lid and are pressed through the shaft core in the battery container can be mentioned.

  The present invention provides a secondary battery that can exhibit the inherent performance of each active material using a plurality of active materials and can improve both high output and high capacity characteristics. Since it contributes to manufacturing and sales, it has industrial applicability.

It is sectional drawing which shows the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is a top view which shows typically the negative electrode plate which comprises the cylindrical lithium ion secondary battery of 2nd Embodiment, and was coated with the different active material layer in stripe form. It is a graph of the load factor characteristic (high discharge rate characteristic) which shows the change of the discharge capacity maintenance factor with respect to the discharge rate in the lithium ion secondary battery of an Example and a comparative example. The

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode active material layer 3 Negative electrode collector 4 Negative electrode active material layer 4a Negative electrode active material layer containing graphite type carbon powder 4b Negative electrode active material layer containing amorphous type carbon powder 5 Separator 6 Battery can ( Battery container)
10 Cylindrical lithium ion secondary battery (secondary battery)
11 Electrode group

Claims (4)

An electrode group in which a positive electrode plate and a negative electrode plate on which an active material layer containing an active material is applied to a current collector are disposed via a separator;
An electrolyte solution infiltrating the electrode group;
A battery container containing the electrode group and the electrolyte;
With
At least one current collector of the positive and negative electrode plates is coated with a plurality of active material layers each containing a different active material, and each of the plurality of active material layers is exposed on the surface of the positive electrode plate or the negative electrode plate. A secondary battery characterized by that.   The secondary material according to claim 1, wherein the plurality of active material layers are coated with active material layers containing different active materials on both surfaces of at least one current collector of the positive and negative electrode plates. battery.   The secondary battery according to claim 1, wherein the plurality of active material layers are applied in a stripe pattern on at least one surface of one of the current collectors of the positive and negative electrode plates.   The secondary battery according to claim 1, wherein at least one of the positive and negative plates is a positive plate, and the different active materials are in the same operating potential range.

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