JP5196392B2 - Positive electrode for non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a novel positive electrode for a nonaqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries typified by lithium ion batteries have become widespread for reasons such as high energy density. In such a lithium ion battery, the principle of charging and discharging is performed by moving lithium ions between the positive electrode and the negative electrode. LiCoO ₂ , LiMn ₂ O _{4 and the} like are used as the positive electrode material, and lithium ions are used as the negative electrode material. A carbon material that can be occluded and released uses a microporous thin film as a separator and an organic solvent in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an electrolyte.

In particular, for positive electrode materials, LiCoO ₂ is the mainstream and widely used. LiMn ₂ O ₄ has also been put to practical use because it can greatly solve the resource depletion problem and the price problem.

However, even in these materials, further improvement in discharge capacity is required as a future problem. In addition, LiMn ₂ O ₄ has a problem that Mn dissolves in the electrolyte due to an increase in battery temperature. In addition to these materials, LiNiO _{2 and the} like have also been developed, but both the discharge capacity and voltage are low, and further improvement is necessary.

Incidentally, in a lithium ion battery, a metal foil is generally used as a current collector (support) to which a positive electrode material or a negative electrode material is attached. Such current collectors have many porous bodies such as punching metal, screen, and expanded metal, as well as three-dimensional porous bodies such as foam and nonwoven fabric, for the purpose of high output, high capacity, and long life. It has been proposed (Patent Documents 1 to 4). For example, Patent Document 1 discloses a three-dimensional network porous body whose surface is made of aluminum, an alloy, or stainless steel as a positive electrode current collector. Patent Document 2 discloses a current collector such as a sheet made of a metal such as aluminum, copper, zinc, or iron, or a conductive polymer such as polypyrrole or polyaniline, or a mixture thereof, a sheet having holes, or a three-dimensional porous body. It is disclosed. Patent Document 3 discloses a current collector such as aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony alone or an alloy, and a stainless alloy. Patent Document 4 discloses foamed aluminum, foamed nickel, and the like as the positive electrode current collector.
JP-A-11-233151 JP2000-195522 JP2005-078991 JP2006-032144

  By the way, in order to increase the output and capacity of the secondary battery as a whole, it is desired that the current collector adopts a three-dimensional structure having a higher porosity than the two-dimensional structure. In particular, the positive electrode current collector is easily oxidized by the electrolyte under a high charge / discharge voltage, so that oxidation resistance and electrolyte resistance are also required.

  However, for the following reasons, the lithium-based non-aqueous electrolyte secondary battery has an oxidation resistance and an electrolyte resistance, a large porosity, and a positive electrode current collector suitable for industrial production. Is not provided.

  In order to increase the porosity of the current collector, the surface of the porous organic resin is generally plated, as represented by a nickel porous body, and the organic resin is removed by incineration if necessary. Is called.

  However, the nickel porous body is easily oxidized in the lithium non-aqueous electrolyte secondary battery, and is dissolved in the electrolyte solution, so that sufficient charging cannot be performed by long-term charge / discharge.

  On the other hand, in aluminum, which is the main material of the current positive electrode current collector, it is necessary to process in a very high temperature molten salt state for the plating process, so organic resin cannot be used as the object to be plated. It is difficult to plate the surface of the organic resin. Therefore, a porous current collector made of aluminum is not currently provided.

  Stainless steel is also widely used as a material for the positive electrode current collector, but for the same reason as stainless steel, it is difficult to obtain a highly porous current collector by plating the organic resin surface. It is.

  As for stainless steel, there is provided a method for obtaining a porous body by making it into a powder form, applying it to an organic resin porous body and sintering it.

  However, stainless steel powder is very expensive. Moreover, since the organic resin porous body to which the powder adheres is removed by incineration, there is a problem that the strength is reduced and it cannot be used.

  Therefore, it is desired to provide a current collector that has oxidation resistance and electrolytic solution resistance, has a high porosity, and is suitable for industrial production, and further provides a positive electrode obtained by using this current collector.

  In view of the above problems, the present inventors have intensively researched and, as a result, have adopted the current collector having a specific structure and have solved the above problems. That is, the present invention relates to the following positive electrode for a nonaqueous electrolyte secondary battery.

  Item 1. A positive electrode for a non-aqueous electrolyte secondary battery in which a current collector is filled with a positive electrode active material, and the current collector sequentially performs a conductive treatment, an electrolytic nickel plating treatment, and a chromium plating treatment on a foamed resin, A positive electrode for a nonaqueous electrolyte secondary battery, which is obtained by removing the foamed resin and annealing in a reducing atmosphere.

  Item 2. Item 2. The positive electrode according to Item 1, wherein the positive electrode active material is olivine type lithium phosphate.

  Item 3. Item 3. The positive electrode according to Item 2, wherein the olivine-type lithium phosphate contains lithium iron phosphate.

  Item 4. Item 2. The positive electrode according to Item 1, wherein the positive electrode active material is a lithium metal oxide.

  Item 5. Item 5. The positive electrode according to Item 4, wherein the lithium metal oxide includes an oxide of at least one metal selected from the group consisting of cobalt, manganese, and nickel.

  Item 6. Item 6. The positive electrode according to any one of Items 1 to 5, wherein the foamed resin has an average pore diameter of 30 to 80 µm.

  Item 7. Item 7. The positive electrode according to any one of Items 1 to 6, wherein the porosity of the foamed resin is 85 to 97%.

Item 8. Item 8. The positive electrode according to any one of Items 1 to 7, wherein the basis weight of the nickel plating layer formed by the treatment is 150 to 300 g / m ² .

Item 9. Item 9. The positive electrode according to any one of Items 1 to 8, wherein the basis weight of the chromium plating layer formed by the chromium plating treatment is 50 to 250 g / m ² .

  The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is a positive electrode in which a current collector is filled with a positive electrode active material, and the current collector is a conductive resin, electrolytic nickel plating treatment and chromium in a foamed resin. It is characterized by being obtained by sequentially performing plating treatment, removing the foamed resin, and annealing in a reducing atmosphere. By having this feature, the nonaqueous electrolyte secondary battery of the present invention has good battery performance such as high output, high capacity and long life. The present invention is described in detail below.

Current collector The current collector used in the present invention is obtained by sequentially conducting a conductive treatment, electrolytic nickel plating treatment and chromium plating treatment on a foamed resin, removing the foamed resin, and annealing in a reducing atmosphere. It is done.

  As the foamed resin, any known or commercially available one can be used as long as it is porous, and examples thereof include foamed urethane and foamed styrene. Among these, urethane foam is preferable from the viewpoint of particularly high porosity.

  The porosity of the foamed resin is usually about 85 to 97 vol%, preferably about 90 to 96 vol%.

  The average pore diameter of the foamed resin is usually about 20 μm to 200 μm, preferably about 30 μm to 80 μm. In addition, the average particle diameter of this invention is calculated | required by measuring by the bubble point method.

  The thickness of the porous body before filling with the positive electrode active material is not limited and is appropriately determined according to the use of the non-aqueous electrolyte secondary electrode, etc., but is usually about 200 μm to 900 μm, preferably about 400 μm to 800 μm.

  The foamed resin is sequentially subjected to conductive treatment, electrolytic nickel plating treatment and chromium plating treatment.

  The conductive treatment is not limited as long as a conductive layer can be provided. Examples of a material constituting the conductive layer (conductive plating layer) include graphite, in addition to metals such as nickel, titanium, and stainless steel. Among these, nickel is particularly preferable.

  As specific examples of the conductive treatment, for example, when nickel is used, electroless plating treatment, sputtering treatment, and the like are preferably exemplified. For example, in the case of using a material such as titanium, stainless steel, or a material such as graphite, a treatment obtained by applying a mixture obtained by adding a binder to fine powder of these materials to a foamed resin is preferable. As the binder in this case, the same material as the active material paste described later can be used.

  As an electroless plating treatment using nickel (electroless nickel plating treatment), for example, a foamed resin is immersed in a known electroless nickel plating bath such as a nickel sulfate aqueous solution containing sodium hypophosphite as a reducing agent. That's fine. If necessary, before immersion in the plating bath, the foamed resin may be immersed in an activation solution containing a small amount of palladium ions (manufactured by Kanisen Co., Ltd.) and washed.

  The sputtering process using nickel (nickel sputtering process) is not limited as long as nickel is used as a target, and may be performed according to a conventional method. For example, after attaching a foamed resin to the substrate holder, while introducing an inert gas, a DC voltage is applied between the holder and the target (nickel) to remove the ionized inert gas (such as argon) from nickel. The nickel particles blown off by the collision may be deposited on the foamed resin surface.

  Next, electrolytic nickel plating is applied to the foamed resin for forming a conductive plating layer. What is necessary is just to perform an electrolytic nickel plating process in accordance with a conventional method. As the plating bath used for the electrolytic nickel plating treatment, a known or commercially available bath can be used, and examples thereof include a watt bath, a chloride bath, a sulfamic acid bath, and the like.

  Next, a chromium plating treatment is applied to the conductive plating layer / nickel plating layer forming foamed resin. The chromium plating process may be performed according to a conventional method, and the chromium plating process is not limited, and examples thereof include an electrolytic plating method, an electroless plating method, and a sputtering method. In the present invention, a chromium plating layer formed by an electrolytic plating method is preferable.

As the electroplating bath used in the electroplating method, a known or commercially available bath can be used. For example, a sergeant bath (typical composition is CrO ₃ : 250 g / l and sulfuric acid H ₂ SO ₄ : 2.5 g / l). And a fluorination bath (typical composition is CrO ₃ : 250 g / l and fluorine component F: 0.6 g / l (or SiF ₆ : 2.5 g / l)).

  The basis weight (adhesion amount) of each of these plating layers is not particularly limited. In the present invention, the conductive plating layer only needs to be formed continuously on the foamed resin surface, and the electrolytic nickel plating layer only needs to be formed on the conductive plating layer to the extent that the conductive plating layer is not exposed. The chromium plating layer should just be formed on the said electrolytic nickel plating layer to such an extent that an electrolytic nickel plating layer is not exposed. In addition, when a conductive plating layer is a nickel layer, the chromium plating layer should just be formed so that the said conductive plating layer (nickel layer) and an electrolytic nickel plating layer may not be exposed.

Basis weight of the conductive plating layer is not limited, usually 5g / m ² ~12g / m ^2, preferably about may be set to 6g / m ² ~10g / m ² approximately.

Basis weight of the electrolytic nickel plating layer is not limited, usually 100g / m ² ~300g / m ^2, preferably about may be set to 150g / m ² ~250g / m ² approximately. When nickel is used for the conductive treatment, the total basis weight of the nickel plating layer formed by the conductive treatment and the electrolytic nickel treatment is preferably about 150 to 300 g / m ² .

Basis weight of the chromium plating layer is not limited, usually 50g / m ² ~250g / m ^2, preferably about may be set to 70g / m ² ~200g / m ² approximately.

These conductive plating layer, the total amount of the basis weight of the electroless nickel plating layer and the chromium plating layer is preferably 250g / m ² ~450g / m ^2, more preferably about 300g / m ² ~400g / m ² about . If the total amount is below this range, the strength of the current collector may be reduced. On the other hand, if the total amount exceeds this range, the filling amount of the positive electrode active material is reduced or the cost is disadvantageous.

  Next, the foamed resin component in the conductive plating layer / nickel plating layer / chromium plating layer forming foamed resin obtained as described above is removed. Although the removal method is not limited, it may be removed by incineration. Specifically, the heating may be performed in an oxidizing atmosphere such as air of about 600 ° C. or higher. Moreover, you may heat at about 750 degreeC or more in reducing atmosphere, such as hydrogen. By these, the porous body which consists of a conductive plating layer, a nickel plating layer, and a chromium plating layer is obtained.

  Next, the current collector of the present invention can be produced by annealing the porous body in a reducing atmosphere. This current collector is a three-dimensional structure having a large porosity. By this annealing treatment, the porous body made of the conductive layer, nickel plating and chrome plating can be reduced. By this reduction action, nickel and chromium are alloyed, and the resistance to electrolytic solution and oxidation is further improved. Can be improved.

  Although it does not specifically limit as reducing atmosphere, Preferably the mixed gas of nitrogen and hydrogen, such as decomposition | disassembly ammonia, etc. are mentioned.

  The heating temperature is not limited as long as it is a temperature at which the chromium and nickel are reduced, but is usually about 600 to 1100 ° C, preferably about 700 to 950 ° C. Moreover, you may carry out by a normal pressure and you may carry out under reduced pressure.

Positive electrode The positive electrode of the present invention is formed by filling the current collector with a positive electrode active material. In the positive electrode of the present invention, since the current collector has a large porosity, it becomes possible to fill more positive electrode active material. Further, since the positive electrode active material is enclosed in the voids in the porous body, the content of a binder or the like (insulator) for bonding the positive electrode active material and the current collector can be reduced. Accordingly, it is possible to increase the output and capacity of the battery. In addition, since the current collector has resistance to electrolytic solution and oxidation, the life of the battery can be extended.

The positive electrode active material is not particularly limited as long as it can be used for a non-aqueous electrolyte secondary battery. In the present invention, olivine type lithium phosphate (LiMPO ₄ ) is particularly preferable. Examples of the metal component M constituting the olivine-type lithium phosphate include iron (Fe), manganese (Mn), chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn), and aluminum (Al). And at least one selected from the group consisting of and the like. Among these, iron and the like are particularly preferable, that is, olivine type lithium iron phosphate and the like are preferable. In this olivine type lithium iron phosphate, a part of iron may be substituted with other metals such as Mn, Cr, Cu, Ni, Zn, Al.

  In the present invention, a known or commercially available lithium metal oxide (LiM′Ox) (where 1 ≦ x ≦ 4) can also be used as the positive electrode active material. Examples of such a lithium metal oxide M ′ include at least one metal selected from the group consisting of Co, Mn, Ni, and the like.

The filling amount of the positive electrode active material is not limited, and may be appropriately determined according to the use, purpose, etc. of the non-aqueous electrolyte secondary battery to be manufactured, but is usually about 40 mg to 150 mg per 1 cm ^{2 of} the current collector, preferably What is necessary is just about 50 mg-100 mg.

  In addition to the positive electrode active material, the material to be filled in the current collector may contain, for example, known additives such as a conductive additive and a binder.

  As the conductive assistant, known or commercially available ones can be used. For example, acetylene black, ketjen black, graphite and the like are preferable. The content of the conductive assistant is usually 5 parts by weight or less, preferably about 0.5 to 2 parts by weight with respect to 100 parts by weight of the positive electrode active material. Thereby, the discharge capacity etc. of a battery can be improved.

  A known or commercially available binder can be used. For example, polyvinylidene fluoride (PVdf), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and the like. Among these, PVdf is preferable. Thereby, the binding strength between the positive electrode active material and the current collector can be improved.

  The addition amount of the binder is appropriately determined according to the kind of the binder and the like, but is usually about 0.1 to 5 parts by weight with respect to 100 parts by weight of the positive electrode active material. By setting it as this range, it is possible to improve the binding strength while preventing an increase in electrical resistance and a decrease in discharge capacity.

  The positive electrode of the present invention is obtained by filling the current collector with a positive electrode active material. For example, the current collector may be filled with a paste containing the positive electrode active material by a known method such as a press-fitting method. .

  Examples of the press-fitting method include a method of immersing the current collector in a positive electrode active material paste and reducing the pressure as necessary, a method of filling the positive electrode active material paste while pressing with a pump from one side of the current collector, etc. Is mentioned.

  The positive electrode active material paste only needs to contain a positive electrode active material and a solvent, and the blending ratio thereof is not limited. The solvent is not limited, and examples thereof include N-methyl-2-pyrrolidone and water. In particular, when polyvinylidene fluoride is used as a binder, N-methyl-2-pyrrolidone may be used as a solvent. When polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, or the like is used as a binder, water may be used as a solvent.

  In the positive electrode of the present invention, the solvent in the paste may be removed by performing a drying treatment after filling the positive electrode active material paste, if necessary.

  If necessary, the positive electrode of the present invention may be compression molded by pressurizing the paste with a roller press after filling. The thickness before and after compression is not limited, but the thickness before compression is usually 250 μm to 800 μm, preferably 300 μm to 700 μm, and the thickness after compression molding is usually about 150 μm to 600 μm, more preferably 200 μm to 550 μm. It should be about.

  According to the positive electrode of the present invention, the current collector has oxidation resistance, electrolyte resistance, porosity, and high strength. Therefore, the non-aqueous electrolyte secondary battery such as a lithium ion battery has high output and high power. Capacitance and long life can be achieved. Further, since the material is inexpensive and easy to manufacture, it is suitable for industrial production.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

(Preparation of current collector)
As the foamed resin, a urethane foam resin (commercially available product, average pore diameter 80 μm, thickness 1.2 mm, porosity 95%) was used.

By performing sputtering treatment using nickel as a target for the foamed urethane resin, a conductive plating layer (nickel layer) was formed on the surface of the foamed urethane resin. The basis weight of the conductive plating layer was 8 g / m ² .

Subsequently, the electroplating process was performed to the obtained electroconductive plating layer formation foaming urethane resin. As an electrolytic nickel plating bath, a Watt bath (nickel sulfate 330 g / L, nickel chloride 50 g / L, boric acid 40 g / L) was used. A titanium basket containing nickel pieces was used as the counter electrode. The electrodeposition conditions were a bath temperature of 60 ° C. and a current density of 30 A / dm ² . The basis weight of the electrolytic nickel plating layer was 192 g / m ² . As a result, the total amount of plating layers formed by the conductive plating layer and the electrolytic nickel plating layer was 200 g / m ² .

Next, electrolytic chrome plating was performed. As the plating bath, a Sargent bath (chromic acid 250 g / l and sulfuric acid 2.5 g / l) was used. As the counter electrode, an electrode coated with a lead alloy with copper as a core was used. The electrodeposition conditions were a bath temperature of 50 ° C. and a current density of 40 A / dm ² . The basis weight of the chromium plating layer was 110 g / m ² . At this time, the current collector had an average thickness of 800 μm.

  Next, this conductive plating layer / electrolytic nickel plating layer / chromium plating layer-forming foamed urethane resin was washed with water and dried, and then heated to about 600 ° C. in air to incinerate and remove the urethane resin. Furthermore, a current collector having a three-dimensional structure was prepared by performing reduction and annealing in a decomposed ammonia atmosphere at about 750 ° C. for 20 minutes.

  The porous bodies thus obtained were adjusted to three thicknesses of 350 μm, 430 μm, and 520 μm, respectively, and were designated as current collectors a, b, and c of the present invention.

・ Production of positive electrode 100 parts by weight of LiFePO ₄ powder as a positive electrode active material, 2.5 parts by weight of ketjen black as a conductive additive, and 5 parts by weight of polyvinylidene fluoride as a binder are mixed and mixed as a solvent for the binder A positive electrode active material paste was prepared by adding 25 parts by weight of N-methyl-2-pyrrolidone.

This paste was filled into current collectors a, b, and c using a press-fitting method using a pump. Filling amount of the positive electrode active material, a current collector a At 40 mg / cm ^2, current collectors b At 52 mg / cm ^2, was the current collector c 69mg / cm ^2.

  Next, these three kinds of current collectors were dried at 90 ° C. for 1 hour with a dryer, and then pressed with a roller press machine (slit: 100 μm) having a roller diameter of 500 mm. The thickness after pressing was 170 μm, 260 μm, and 310 μm, respectively. Thereafter, it was further dried at 150 ° C. under reduced pressure for 3 hours to obtain positive electrodes A, B and C of Examples 1 to 3.

Comparative Examples 1-3
As the current collector, an aluminum foil (commercial product, thickness 25 μm) was used. In this case, the positive electrode active material paste prepared in the example was applied by the doctor blade method so that the total on both sides was 30 mg / cm ² , but the positive electrode active material was sufficiently aluminum because the adhesive strength was insufficient. Could not adhere to the foil.

Therefore, a positive electrode active material paste similar to that produced in the example was produced except that the polyvinylidene fluoride was changed to 10 parts by weight. The paste was applied to both surfaces of an aluminum foil by a doctor blade method, dried and pressed to produce positive electrodes d, e, and f of Comparative Examples 1 to 3. The coating amount of the positive electrode active material, 11 mg / cm ² in the positive electrode d, 15mg / cm ² in the positive electrode e, was the positive electrode f 19mg / cm ^2. The thicknesses of these positive electrodes were 70 μm, 125 μm, and 175 μm, respectively.

Comparative Example 4
As the current collector, foamed nickel (commercial product, porosity 96 vol%, average pore diameter 150 μm, thickness 550 μm) was used. The positive electrode active material produced in Example 1 was filled in the same manner as in Example 1 so as to be 70 mg / cm ^2, and then further pressurized and dried to produce the electrode of Comparative Example 4.

Preparation of Battery and Test Examples 1-3 and Comparative Examples 1-3 were cut into 5 cm × 5 cm, and batteries A to C (using current collectors a to c of Examples) and batteries D to F (using the current collectors d to f of the comparative example) was prepared. As the negative electrode, lithium metal having a sufficiently large capacity compared to the positive electrode was used, and as the electrolyte, 1.0 mol / l of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 4: 6). A non-aqueous electrolyte was used, a microporous polyolefin film (thickness 20 μm, porosity 55%) was used as a separator, and a laminate film was used as a battery case.

  These batteries A to F were charged to 4.1 V with a current of 0.1 C, and charged / discharged to discharge to 2 V with a discharge current of 0.2 C was repeated 10 times for chemical conversion. Next, each battery was charged at ambient temperature of 40 ° C. to 4.1 V at 0.2 C, and discharged to 0.5 V, 1 C, and 1.5 C to a final voltage of 2 V. Table 1 shows the capacity per unit weight obtained from the measured values.

  Further, charging up to 4.1 V at 0.2 C and discharging up to 2 V at 0.5 C were performed at an ambient temperature of 25 ° C. Table 1 also shows the capacity retention rate at 200 cycles with respect to the initial capacity at this time.

  The battery produced using the positive electrode of Comparative Example 4 was repeatedly formed and charged / discharged under the same conditions as above, but could not be charged in only 10 cycles (not shown in Table 1).

As is clear from the evaluation table 1, it was found that the batteries A to C of the present invention were superior in capacity density and capacity retention rate than the batteries D to F of the comparative example. Thus, it was found that if the positive electrode of the present invention is used, the non-aqueous electrolyte secondary battery can be increased in output, capacity, and life.

  In addition, in the batteries A to C of the present invention, the reason why the decrease in the capacity density is small even when the charge / discharge cycle is repeated is that the positive electrode active material of the present invention is a current collector having a two-dimensional structure like the batteries D to F of the comparative example. This is because it is not applied to the surface of the body but is encased in a current collector excellent in electrolytic resistance and oxidation resistance, and this causes swelling of the positive electrode material (positive electrode active material, conductive additive and binder). It is thought that the increase in electrical resistance due to the is suppressed.

  From the above, it has been clarified that the effects of the present invention are exhibited with respect to olivine-type lithium phosphate having a slightly lower charge / discharge potential than those of general-purpose lithium metal oxides in Examples 1-3.

  Further, when at least one lithium metal oxide selected from the group consisting of cobalt, manganese, nickel and the like is used as the other positive electrode active material, the effects of the present invention are also exhibited.

Claims (9)

A positive electrode for a non-aqueous electrolyte secondary battery in which a current collector is filled with a positive electrode active material,
The current collector is obtained by sequentially conducting conductive treatment, electrolytic nickel plating treatment and chromium plating treatment on the foamed resin, removing the foamed resin, and annealing in a reducing atmosphere.
A positive electrode for a non-aqueous electrolyte secondary battery.   The positive electrode according to claim 1, wherein the positive electrode active material is olivine type lithium phosphate.   The positive electrode according to claim 2, wherein the olivine-type lithium phosphate includes lithium iron phosphate.   The positive electrode according to claim 1, wherein the positive electrode active material is a lithium metal oxide.   The positive electrode according to claim 4, wherein the lithium metal oxide includes an oxide of at least one metal selected from the group consisting of cobalt, manganese, and nickel.   The positive electrode according to claim 1, wherein the foamed resin has an average pore diameter of 30 to 80 μm.   The positive electrode according to claim 1, wherein the foamed resin has a porosity of 85 to 97%. The positive electrode according to claim 1, wherein the basis weight of the nickel plating layer formed by the treatment is 150 to 300 g / m ² . The basis weight of the chromium plating chrome plating layer formed by it is 50 to 250 g / m ^2, a positive electrode according to claim 1.