JP2005327489A - Positive electrode for power storage element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for power storage element used in a hybrid automobile for example capable of making compatible high capacity and high output performance. <P>SOLUTION: The positive electrode for the power storage element has a battery mix layer and a capacitor layer on a current collector, the battery mix layer contains a positive active material mainly comprising a lithium-containing composite oxide, the capacitor layer contains activated carbon, the battery mix layer is placed on the current collector, and the capacitor layer is placed on the battery mix layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a positive electrode for a power storage element.

  In recent years, electronic devices are rapidly becoming smaller and lighter, and there is an increasing demand for smaller, lighter, and higher capacity batteries as power sources, and high energy density energy storage devices have been put to practical use. ing. Also in the automobile field, development of an electric vehicle or a hybrid vehicle using an engine and a power storage element in combination is active, and some of them have been put into practical use.

  A power storage element used in a hybrid vehicle or the like is required to have a large output, that is, a large current discharge characteristic, for a certain period of time in order to perform power assist during starting, starting and acceleration. In addition, there is a demand for input characteristics that enable efficient recovery even for large regenerative energy during deceleration. Such high load pulse characteristics are required at a high level.

  Furthermore, since it is assumed that it will be used in various parts of the world, the usage environment temperature is wide from high to low, and stable and good battery characteristics are required in these wide temperature ranges. A high level input / output characteristic is required in a severe environment at an extremely low temperature such as ° C.

  In addition, secondary batteries and capacitors are often compared as power storage elements, but when considering from the viewpoint of a power assist source for automobiles, batteries generally provide a high amount of energy, but are accompanied by a battery reaction, resulting in high output. The capacitor can store only a small amount of energy, but it has the advantages and disadvantages of being able to obtain high output.So far, secondary batteries and electric double layer capacitors have been shared. Composite elements have been proposed.

In Patent Document 1, a composite element of an electric double layer capacitor and a lithium secondary battery is used, a battery mixture layer is provided on one side of the shared current collector foil, and a capacitor layer is provided on the other side. A composite element in which they are connected in parallel, or an element in which a layer in which a battery mixture and a capacitor material are mixed is arranged on both sides of the current collector foil is shown.
JP 2001-351688 A

  However, in the matter described in Patent Document 1, in order to form the battery mixture layer only on one side of the current collector foil, in order to obtain the same battery capacity as that obtained by forming the battery mixture layer on both sides of the current collector foil Therefore, it is necessary to double the thickness of the battery mixture layer on one surface of the current collector foil. As a result, the mixture thickness is increased and the electron conductivity is deteriorated, so that the battery resistance is increased, the output performance is not sufficiently improved, and the life characteristics are deteriorated due to the increase in the thickness of the battery mixture layer.

In addition, activated carbon is shown as the capacitor material. However, when a mixed layer of battery material and capacitor material is formed, the press filling property of the activated carbon is poor, so that it is difficult to achieve high filling of the battery material, which increases the energy density. It becomes difficult to achieve.
An object of the present invention is to solve these problems and to provide a positive electrode for a storage element that has a high capacity and is compatible with a high output performance.

  In order to achieve the above object, the present invention provides a positive electrode for a storage element comprising a battery mixture layer and a capacitor layer on a current collector, wherein the battery mixture layer mainly comprises a lithium-containing composite oxide. The capacitor layer includes activated carbon, has the battery mixture layer on the current collector, and further has the capacitor layer on the battery mixture layer. It is what.

  Since the positive electrode for a storage element of the present invention has the above-described configuration, a battery mixture layer and a capacitor layer are formed on both sides of the current collector foil, so that high output performance can be obtained by applying a capacitor component without increasing battery resistance. In addition, since the battery layer and the capacitor layer are laminated, the battery layer can be highly filled by pressing, and an energy storage device capable of achieving high capacity and high energy density can be obtained.

  The present invention is a positive electrode for a storage element having a battery mixture layer and a capacitor layer on a current collector, the battery mixture layer comprising a positive electrode active material mainly composed of a lithium-containing composite oxide, The capacitor layer includes activated carbon, has the battery mixture layer on the current collector, and further has the capacitor layer on the battery mixture layer, and has a high capacity. And the positive electrode for electrical storage elements which has high output performance can be obtained.

  Further, the same effect can be obtained even in a configuration having the capacitor layer on the current collector and further having the battery mixture layer on the capacitor layer.

  Furthermore, a uniform positive electrode can be obtained by applying the battery mixture layer and the capacitor layer. To do.

  Note that reduction in resistance and increase in electric double layer capacity are important for improving the input / output characteristics of the power storage element, and these improvements enable large input / output.

Here, the battery and the capacitor will be described in detail. FIG. 1 is a basic equivalent circuit of a battery reaction. As shown in FIG. 1, a battery is an electromotive force E of a battery that changes due to charging / discharging of the battery, and a component resistance R _bp such as a collector foil or a collector component. The electrode resistance layer is divided into six components: the electronic resistance R _{be of} the electrode mixture layer, the electrolyte resistance R _bs , the electric double layer capacity C _b generated at the electrode plate / electrolyte interface, and the battery reaction resistance R _bct . With this basic equivalent circuit, the battery is charged and discharged using a storage phenomenon caused by an electrochemical reaction in the positive and negative electrode active materials.

Next, FIG. 2 shows a basic equivalent circuit of the capacitor. The capacitor is shown in FIG.
It is divided into four components: component resistance R _cp of current collector foil and current collector component, electronic resistance R _ce of the mixture layer, electrolyte resistance R _cs , and capacitor capacitance C _c . Capacitors generally have a shape in which a dielectric is sandwiched between two opposing electrodes, but an electric double layer capacitor is not a dielectric, but uses an interface electric double layer as a dielectric function. This capacitor is a device that utilizes an electricity storage phenomenon caused by an adsorption / desorption reaction of an ion adsorption layer formed on the surface of an activated carbon electrode used for both positive and negative electrodes, that is, an electric double layer.

  Here, FIG. 3A shows a cross-sectional view of the positive electrode plate when the battery mixture layer is formed on one surface of the current collector foil and the capacitor layer is formed on the other surface. A negative electrode is formed so as to face these layers, and a battery mixture layer is provided on one side of the current collector foil, and a capacitor layer on the opposite side is connected in parallel.

On the other hand, FIG. 4A shows a cross-sectional view of a positive electrode plate in which a battery mixture layer and a capacitor layer are laminated on both surfaces of the current collector foil of the present invention. A negative electrode is configured to face these stacked layers, and is configured to be connected in parallel by stacked battery layers and capacitor layers on both sides of the current collector foil. Here, in order to make the battery capacity of FIG. 3 and FIG. 4 the same, when the electrode plate length is the same, the positive electrode plate of FIG. 3 (a) is the battery mixture layer on one side of the positive electrode plate of FIG. 4 (a). It is necessary to form a battery mixture layer having a thickness twice as large as the above. Similarly, in order to obtain the same capacitor capacity, the capacitor layer also needs to be formed twice as thick. FIG. 4B shows a positive electrode mixture portion equivalent circuit in that case.

Here, in order to make the battery capacities of FIG. 3 and FIG. 4 the same, even if the electrode plate length is the same, even if the amount of the battery mixture layer in the entire power storage element is the same, FIG. 4), it is necessary to form a battery mixture layer having a thickness twice that of the battery mixture layer on one side of the positive electrode plate in FIG. Similarly, in order to obtain the same capacitor capacity, the capacitor layer also needs to be formed twice as thick. Therefore, when the thickness of the layer shown in FIG. 4A is used as a basis, the positive electrode mixture portion equivalent circuit of FIG. 3A has a battery mixture layer and capacitor layer thickness of 2 as shown in FIG. 3B. Thus, an equivalent circuit is formed in which the electronic resistance components R _be and R _{ce of the} battery layer and the capacitor layer are configured in series, and the positive electrode mixture circuit impedance increases as compared with the configuration of FIG. As a result, in the element as shown in FIG. 3, sufficient output performance cannot be obtained, and further, the influence of the increase in the electronic resistance component of the battery mixture layer and the capacitor layer due to the cycle on the increase in the battery impedance is increased, resulting in a lifetime. Problems such as deterioration of characteristics, that is, deterioration of output performance due to cycles occur.

On the other hand, in the case of the configuration of the present invention as shown in FIG. 4A, each resistance component is based on parallel connection, so that the impedance of the element is lower than that in the configuration shown in FIG. And output performance is improved. Here capacitance C _c component capacitor function is given by the lamination structure because it is the current collector allows the electronic resistance R _BE of the battery mixture layer as a conductive path. In addition, the increase in each resistance component due to the cycle is based on a parallel circuit, so that the increase in resistance of the entire circuit can be suppressed. Therefore, the lifetime characteristic is better than that in the configuration of FIG.

  FIG. 5 is a cross-sectional view of a power storage device manufactured using the positive electrode of the present invention, and is composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like. Hereinafter, each element will be described in detail.

  The positive electrode manufacturing method starts with a positive electrode active material, a conductive agent, a binder, a solvent, and further a battery mixture paste having a battery function kneaded with a thickener as necessary, and activated carbon, a conductive agent, a binder. A capacitor mixture paste having a capacitor function in which an agent and a solvent are kneaded is prepared. For example, first, a battery mixture paste is applied to both sides of an aluminum foil current collector foil, dried, and rolled to a predetermined thickness by pressing as necessary. Thereafter, the capacitor mixture paste is applied onto the battery mixture layer, dried, pressed as necessary, and rolled to a predetermined thickness, and the battery mixture layer and the capacitor layer are laminated on both sides of the current collector foil. To do. Thereafter, the sheet is processed into a predetermined size by slitting as necessary to produce a sheet-like positive electrode plate.

As the positive electrode active material, a material capable of inserting and extracting lithium is used. For example, a lithium metal composite oxide represented by LiCoO ₂ , LiNiO ₂ or LiMn ₂ O ₄ is used. It is also possible to use other element substitution types such as those in which a part of the above Co, Ni or Mn is further substituted with Co, Mn, Al, etc., or those substituted with Li. It is not limited to the above as long as it is an active material capable of inserting and extracting lithium and capable of charge / discharge reaction.

  The conductive agent is for increasing electrical conductivity in order to efficiently perform the charge / discharge reaction of the positive electrode mixture. For example, carbon materials such as acetylene black (AB), ketjen black (KB), or graphite Can be used alone or in combination.

The binder has a bonding function between the mixture and an adhesion function between the mixture and the core material. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or the like is used. When water is used as a solvent, a water-soluble dispersion of PTFE is particularly used.

  As the thickener, a water-soluble polymer such as carboxymethyl cellulose (CMC) is used when water is used as a solvent.

On the other hand, for the activated carbon used for the positive electrode capacitor layer, the raw material is an organic raw material such as coconut shell, coal, phenol, etc., and carbonized and activated (alkali, steam activated, etc.) materials are used according to the suitability of the battery, Its specific surface area is 1000 to 3000 m ² / g.

  A mixture paste is prepared by kneading these materials, but the mixture mixture ratio can be arbitrarily adjusted according to the suitability of the battery.

  On the other hand, the negative electrode is composed of a negative electrode mixture layer composed of a negative electrode active material, a binder and the like on a copper foil as a current collector, and a mixture paste is prepared in the same manner as the positive electrode. It is applied to a foil, dried, and then processed into a predetermined size by pressing and slitting as necessary to obtain a sheet-like negative electrode.

  As the negative electrode active material, a material capable of inserting and extracting lithium ions is used. For example, a carbon material such as natural graphite, artificial graphite, or coke can be used. As the binder, PVdF, styrene butadiene rubber (SBR) or the like is used, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) or water is used as a solvent for dispersing these active materials and the binder. Can do.

  The separator has a function of insulating between the positive electrode and the negative electrode and further holding an electrolyte solution. The separator is made of a thin microporous film such as polyethylene (PE), polypropylene (PP), or a laminate thereof. However, the present invention is not limited to these as long as the necessary functions can be obtained.

The electrolytic solution is obtained by dissolving a lithium salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), A chain carbonate such as ethyl methyl carbonate (EMC) or the like alone or in a mixed system is used. As the lithium salt, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like is used.

  In addition, the shape of the power storage element configured may be any of a cylindrical shape, a square shape, or a stacked shape, and a positive electrode and a negative electrode are stacked via a separator to produce an electrode group, and a positive current collector A current collecting terminal is connected to the body and the negative electrode current collector, inserted into the battery outer case, injected with an electrolyte, and sealed to produce a battery.

  Examples of the present invention will be described with respect to a 17500 type cylindrical battery in which various electrode plates are actually produced and configured using the electrode plates.

(Example 1)
As the positive electrode active material, a lithium nickel composite oxide represented by a composition formula LiNi _0.7 Co _0.2 Al _0.1 O ₂ was used. A predetermined ratio of Co and Al sulfate was added to the NiSO ₄ aqueous solution to prepare a saturated aqueous solution. While stirring this saturated aqueous solution, an alkaline solution in which sodium hydroxide is dissolved is slowly added dropwise and neutralized to neutralize a ternary nickel hydroxide Ni _0.7 Co _0.2 Al _0.1 (OH) ₂ precipitate by a coprecipitation method. Generated. The precipitate was filtered, washed with water, and dried at 80 ° C. The obtained nickel hydroxide had an average particle size of 10 μm.

Thereafter, the obtained Ni _0.7 Co _0.2 Al _0.1 (OH) ₂ was heat-treated in the atmosphere at 900 ° C. for 10 hours to obtain nickel oxide Ni _0.7 Co _0.2 Al _0.1 O. The obtained oxide was confirmed to be single phase nickel oxide by powder X-ray diffraction. Then, lithium hydroxide monohydrate was added so that the sum of the number of atoms of Ni, Co, and Al and the number of atoms of Li were equal, and heat treatment was performed at 800 ° C. in dry air for 10 hours. LiNi _0.7 Co _0.2 Al _0.1 O ₂ was obtained. The obtained lithium nickel composite oxide was confirmed by powder X-ray diffraction to have a single-phase hexagonal layered structure and that Co and Al were dissolved. Then, a positive electrode active material powder was obtained through pulverization and classification. The average particle size was 9.5 μm, and the specific surface area by the BET method was 0.4 m ² / g.

AB having a specific surface area of 68 m ² / g was used as the conductive agent. PTFE water-soluble dispersion liquid was used as the binder, and CMC was used as the thickener. These active materials, AB, PTFE, and CMC were adjusted at a solid content ratio of 100: 5: 2: 1 weight ratio, and kneaded with water as a solvent to prepare a positive electrode mixture paste.

  Next, a capacitor mixture was prepared. The activated carbon used was manufactured by Kansai Thermal Chemical Co., Ltd. AB was used as the conductive agent, PTFE water-soluble dispersion liquid was used as the binder, and CMC was used as the thickener. These activated carbon, AB, PTFE, and CMC were adjusted at a solid content ratio of 100: 10: 2: 2 weight ratio, and kneaded with water as a solvent to prepare a capacitor mixture paste.

  The positive electrode current collector foil was alloy 1N30, tempered H18, and 20 μm thick aluminum foil. The positive electrode mixture paste was applied to both sides and dried, and then the battery mixture layer was pressed to a thickness of 60 μm. A capacitor mixture paste was applied on both sides of the mixture layer in a laminated manner and dried to form a capacitor layer having a thickness of 20 μm, and then slit processing was performed to produce a positive electrode plate having a thickness of 100 μm, a width of 37 mm, and a length of 440 mm. .

  For the negative electrode, artificial graphite was used as the active material, and SBR water-soluble dispersion was used as the binder. CMC is used as the thickener, and the active material, the binder, and the thickener are each adjusted to a solid content ratio of 96: 3: 1% by weight, and kneaded using water as a solvent to mix the negative electrode A paste was prepared. This was applied to both sides of a 10 μm thick copper foil, dried, and then rolled and slitted to produce a negative electrode plate having a thickness of 77 μm, a mixture width of 39 mm, and a length of 460 mm.

After the aluminum and nickel current collector leads were joined to the positive electrode and the negative electrode described above, they were dried in a drying furnace at 100 ° C. for 10 hours and 80 ° C. for 10 hours, respectively, for the purpose of removing residual moisture. Thereafter, a group in which the positive electrode and the negative electrode were wound through a 25 μm thick polyethylene separator was produced. The group was inserted into the battery case, the negative electrode lead was resistance welded to the bottom of the case, and the positive electrode lead was laser welded to the sealing plate. And after inject | pouring electrolyte solution in a case, the case was sealed with the sealing board and the battery A was produced. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a solute at a concentration of 1 mol / dm ³ in a mixed solvent in which EC and EMC were mixed at a mixing ratio of 1: 3 by volume was used.

(Example 2)
A battery B was fabricated in the same configuration as the battery A except that the capacitor layer was formed to a thickness of 40 μm.

(Example 3)
A battery C was fabricated in the same configuration as the battery A except that the capacitor layer was formed to a thickness of 60 μm.

Example 4
A battery D was fabricated in the same configuration as the battery A except that the capacitor layer was formed with a thickness of 80 μm.

(Example 5)
A battery E was produced in the same configuration as the battery A except that a capacitor layer was formed on both surfaces of the aluminum current collector foil with a thickness of 40 μm, a mixture layer was formed on the capacitor layer in a laminated shape, and then pressed.

(Comparative Example 1)
A battery F was fabricated in the same configuration as the battery A except that no capacitor layer was formed.

(Comparative Example 2)
In order to make the negative electrode receiving load for the positive electrode mixture layer the same as that of the battery A with respect to the positive electrode in which the mixture layer is formed on one side of the aluminum current collector foil and 60 μm is formed on the opposite surface of the current collector foil, the negative electrode A battery G was manufactured in the same configuration as the battery A except that the thickness was 144 μm.

  The batteries A to G were charged and discharged under a condition of a charge upper limit voltage of 4.2 V and a discharge lower limit voltage of 3.0 V at a constant current of 50 mA in an environment of 25 ° C., and a capacity test was performed. As a result, the capacity was about 250 mAh.

  Thereafter, the output at 25 ° C. was measured by the following procedure. Each battery is charged at a constant current up to 50% charge in an environment of 25 ° C., left for 1 hour in an environment of 25 ° C., and then at a constant current while increasing the current value in the range of 250 to 2500 mA. Charge and discharge pulses were applied to the battery for 10 seconds, the voltage at 10 seconds after each pulse application was measured, and plotted against the current value. An output test was performed in which the current at 3.0 V was calculated from the data of two sections across the battery voltage 3.0 V on the discharge side, and the output value was calculated by the product of 3.0 V and the current value.

  In addition, a charge / discharge cycle test is performed in a voltage range of 4.2 to 3.0 V at a constant current of 500 mA under an environment of 25 ° C., and the capacity test and output test described above are performed every 100 cycles. A life test was conducted to confirm the change in capacity and output accompanying the test.

  Table 1 shows a list of output values of various batteries obtained from the above tests. In addition, the output value of the battery F is shown as a ratio with 100.

表１に示すように電池Ａ〜Ｄはキャパシタ層を形成していない電池Ｆと比較して、キャパシタ層形成厚みを厚くすることにより、電気二重層容量が増加し、出力値が増加していることがわかる。また電池Ｂと電池Ｅのように積層する電池合剤層とキャパシタ層の順番が逆であっても同様な効果が得られていることがわかる。それに対し電池Ｇは図２に示されるような構成であり、電池容量を確保するために合剤層の厚みを他の電池の集電箔片側形成厚みの２倍の厚みで形成している。そのため直列接続による抵抗増加のため、同じ層厚みを集電箔両面に分配している電池Ｂと比較し、出力値が低下していることがわかる。

As shown in Table 1, the batteries A to D increase the electric double layer capacity and increase the output value by increasing the capacitor layer formation thickness compared to the battery F in which the capacitor layer is not formed. I understand that. Moreover, it turns out that the same effect is acquired even if the order of the battery mixture layer and capacitor layer which are laminated | stacked like the battery B and the battery E is reverse. On the other hand, the battery G has a configuration as shown in FIG. 2, and the thickness of the mixture layer is formed to be twice the thickness of the current collector foil formed on the other battery in order to ensure the battery capacity. Therefore, it can be seen that the output value is lower than that of the battery B in which the same layer thickness is distributed on both sides of the current collector foil because of the increase in resistance due to series connection.

  6 to 12 show the life test results of the respective batteries plotted with the capacity maintenance ratio with respect to the initial capacity and the output decrease ratio with respect to the initial output every 100 cycles. Here, as shown in FIG. 12, the battery G has a tendency to decrease in capacity and output as compared with other batteries, and this is remarkably battery because the increase in the mixture resistance accompanying the charge / discharge cycle is serialized. It appears that resistance increases and as a result, capacity and output decrease.

  From the above results, the present invention is for a storage element in which a mixture layer containing a positive electrode active material mainly composed of a lithium-containing composite oxide and a capacitor layer containing activated carbon are laminated on both sides of a current collector foil. With the positive electrode, it is possible to obtain a power storage element that has high output while maintaining battery capacity, and further exhibits good life characteristics.

  The present invention is useful as a positive electrode for a storage element having high output characteristics.

Basic equivalent circuit diagram of the battery Basic equivalent circuit diagram of capacitor (A) Conventional positive electrode cross-sectional view (b) Conventional positive electrode mixture portion equivalent circuit diagram (A) Positive electrode cross-sectional view of the present invention (b) Positive electrode mixture portion equivalent circuit diagram of the present invention Cross-sectional view of cylindrical power storage device of this example Life characteristics of battery A Life characteristics of battery B Life characteristics of battery C Life characteristics diagram of battery D Life characteristics of battery E Life characteristics of battery F Life characteristics of battery G

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery mixture layer 2 Capacitor layer 3 Positive electrode 4 Negative electrode 5 Separator 6 Case 7 Sealing plate

Claims (3)

A positive electrode for a storage element having a battery mixture layer and a capacitor layer on a current collector,
The battery mixture layer includes a positive electrode active material mainly composed of a lithium-containing composite oxide,
The capacitor layer includes activated carbon;
A positive electrode for a storage element, comprising: the battery mixture layer on the current collector; and the capacitor layer on the battery mixture layer. A positive electrode for a storage element having a battery mixture layer and a capacitor layer on a current collector,
The battery mixture layer includes a positive electrode active material mainly composed of a lithium-containing composite oxide,
The capacitor layer includes activated carbon;
The positive electrode for electrical storage elements which has the said capacitor layer on the said electrical power collector, and also has the said battery mixture layer on the said capacitor layer. The positive electrode for a storage element according to claim 1, wherein the battery mixture layer and the capacitor layer are applied.

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