JP4359678B2 - Secondary battery electrode and secondary battery using the same - Google Patents

Description

  The present invention relates to an electrode for a secondary battery and a secondary battery using the same.

  In recent years, various secondary batteries have been used in many applications such as portable devices and mobile devices. For example, as a secondary battery used for small devices such as portable devices and personal computers, the use of lithium ion batteries in addition to nickel-hydrogen batteries is expanding.

On the other hand, a nickel-hydrogen battery or the like is mainly used as a power source for high output, for example, a power tool, a shaver, a remote toy, a vacuum cleaner, and the like. In addition, as an application that requires higher output, there is a battery for a hybrid vehicle driven by an engine and a battery that has been attracting attention recently. Hybrid vehicles are greatly characterized by energy saving and low pollution. Automakers are aggressive in commercialization, and are expected to spread widely in the future.

  In this way, secondary batteries are widely used as power sources for various applications, and in addition to characteristics such as high capacity and high output, various characteristics such as long life, low pollution, reliability, and low cost are required. In addition, nickel-hydrogen batteries and lithium ion batteries are being developed and put into practical use.

Among these secondary batteries, the nickel-hydrogen battery is a battery that uses a nickel electrode as a positive electrode and a hydrogen electrode filled with an alloy capable of occluding and releasing hydrogen as a negative electrode. An electrode obtained by applying a paste containing hydrogen storage alloy powder to a core material made of punching metal and pressurizing it is used.

  On the other hand, the nickel electrode of the positive electrode has been improved by coating nickel hydroxide, which is an active material, with a cobalt compound to improve conductivity, but it is still more conductive than the metal, which is the active material of the negative electrode. Is insufficient. For this reason, in the nickel electrode, the performance is improved, in particular, the capacity is increased by adopting a three-dimensional structure in which a sintered body or a foamed porous body is filled with an active material.

  With respect to the nickel electrode of such a nickel-hydrogen battery, it is desirable to use a porous body having a two-dimensional structure such as a screen, an expanded metal, or a punching metal in consideration of cost. However, the two-dimensional base material cannot sufficiently meet the demands for improving the utilization rate, increasing the capacity, and increasing the output. For this reason, for example, a conductive layer made of a conductive powder and a thermoplastic polymer is formed on a punching metal, an expanded metal, a foamed metal porous body, or the like (see Patent Document 1 below), and the electrode support is made corrugated. It has been proposed to form a fine concavo-convex layer made of nickel, cobalt or a mixture of both on the surface (see Patent Document 2 below). Further, improved sintered nickel electrodes, foamed nickel electrodes, and the like have been proposed (see Patent Documents 3 to 5 below).

  However, with a conventional nickel electrode, not only when a three-dimensional structure base is used, but also when a two-dimensional structure base such as punching metal is used, there are defects due to protrusions, burrs, and the like present in the processed portion of the hole. There is a possibility of short-circuiting during operation. For this reason, the separator cannot be sufficiently thinned due to the necessity of short circuit prevention. Since a sintered body or a foam is often used as the positive electrode at present, a relatively thick nonwoven fabric of about 0.12 mm or more is used as the separator. For this reason, in the nickel-hydrogen battery, there is a limit to increase the capacity and output by reducing the thickness of the separator.

On the other hand, a general lithium ion battery adopts the same cylindrical or square shape as the nickel-hydrogen battery as the basic structure, but a thin electrode is used because the conductivity of the organic electrolyte used is inferior. Furthermore, since it is necessary to reduce the distance between the electrodes, an extremely thin separator is used.

  In this case, if a two-dimensional structure such as a sintered body or a foamed body or a two-dimensional structure such as a punching metal is used as a base material for an electrode, when a wound structure is used, There is a possibility that a short circuit may occur due to damage to the separator.

  For this reason, in a lithium ion battery, a metal foil that can be thinned and does not generate burrs during winding is used as an electrode base material. For example, as the positive electrode, a base material made of a strip-shaped aluminum foil is used, and a surface containing a positive electrode active material such as lithium cobaltate, lithium manganate, or lithium nickelate is used on the surface. A base material mainly made of a strip-shaped copper foil is used, and a negative electrode material layer made of a carbon material such as graphite is formed on the surface (see Patent Documents 6 and 7 below).

  Then, a thin microporous separator is sandwiched between the positive electrode and the negative electrode and wound much more than a nickel-hydrogen battery to form a spiral electrode body, and the electrode body and the electrolyte are contained in a battery container. A battery is configured.

The lithium ion battery having such a structure can be made thin by using a metal foil as a base material, but further improvement in the utilization rate of the electrode material and extension of the life of the electrode are desired.
Japanese Patent Laid-Open No. 5-236190 Japanese Unexamined Patent Publication No. 7-15912 JP-A-4-33803 Japanese Unexamined Patent Publication No. 9-3341139 JP-A-9-341140 Japanese Patent Laid-Open No. 2002-216761 JP 09-293498 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to cope with higher output and higher capacity of various secondary batteries such as nickel-hydrogen batteries and lithium ion batteries. An electrode for a secondary battery that has a high utilization factor of an active material and has a long life, and a secondary battery using this electrode.

The present inventor has intensively studied to achieve the above-described object. As a result, it has been found that a metal foil obtained by pressing metal powder or metal fiber has extremely fine irregularities and a high porosity, unlike a metal foil obtained by electrolytic method or metal rolling. And when such a metal foil is used as an electrode base material and a paste containing an active material is applied to make an electrode, the adhesion between the electrode base material and the active material paste is improved, It has been found that the electrolytic solution is held in the gap, and the utilization factor and life of the active material are improved. In addition, when such a metal foil is used as an electrode substrate, even if the electrode body has a wound structure, no burrs are generated on the substrate, and a very thin separator can be used. The inventors have found that it is possible to increase the output and capacity of the secondary battery. The present invention has been completed based on these findings.

That is, the present invention provides the following battery electrode and secondary battery.
1. A secondary battery electrode comprising a metal foil having a porosity of 5 to 40% and a thickness of 7 to 50 µm as a base material.
2. An electrode for a secondary battery, wherein a paste containing an active material is applied to an electrode substrate made of a metal foil having a porosity of 5 to 40% and a thickness of 7 to 50 µm.
3. The secondary battery electrode according to claim 1 or 2, wherein the metal foil is obtained by pressurizing at least one raw material selected from metal powder and metal fiber.
4). The secondary battery electrode according to any one of claims 1 to 3, wherein the metal foil is made of at least one metal selected from the group consisting of nickel, copper, aluminum and iron.
5. The electrode for a secondary battery according to any one of claims 1 to 4, which is a nickel electrode of a nickel-hydrogen battery, a hydrogen storage alloy electrode of a nickel-hydrogen battery, a positive electrode of a lithium ion battery, or a negative electrode of a lithium ion battery.
6). 6. The electrode according to claim 5, wherein the electrode is a nickel electrode for a nickel-hydrogen battery having a metal foil mainly composed of nickel as a base material.
7). The electrode according to claim 5, which is a hydrogen storage alloy electrode for a nickel-hydrogen battery based on a metal foil composed mainly of at least one metal selected from nickel, copper and iron.
8). 6. The electrode according to claim 5, wherein the electrode is a positive electrode for a lithium ion battery mainly comprising a metal foil made of aluminum.
9. 6. The electrode according to claim 5, wherein the electrode is a negative electrode for a lithium ion battery mainly comprising a metal foil made of copper.
10. A secondary battery comprising the electrode according to claim 1 as a constituent element.
11. A secondary battery comprising the electrode according to any one of claims 1 to 9 and a separator having a thickness of 0.1 mm or less as constituent elements.

  In the secondary battery electrode of the present invention, it is necessary to use a metal foil having a porosity of 5 to 40% and a thickness of 7 to 50 μm as the electrode substrate.

  Such a metal foil can be produced, for example, by pressing at least one selected from metal powder and metal fiber into a foil shape by pressing.

  The metal powder used as a raw material can be generally produced by mechanical pulverization such as jet mill pulverization. In addition, metal powder produced by reduction of oxide, carbonyl nickel, carbonyl iron, or the like can also be used. The particle size of the metal powder is not particularly limited, but usually the average particle size is preferably about 0.1 to 30 μm, more preferably about 0.5 to 10 μm. In this case, as the particle size decreases, the mechanical strength improves, but the cost tends to increase.

  The metal fibers are not particularly limited, but those having a length of about 10 to 40 μm and a diameter of about 1 to 5 μm are preferable.

  In the present invention, only one or both of metal powder and metal fiber can be used as a raw material. In particular, the metal powder is advantageous in that the cost is lower than that of the metal fiber.

About the kind of metal, what is necessary is just to determine suitably according to the kind of battery to be used, for example, nickel, copper, aluminum, iron, etc. can be used individually by 1 type or in mixture of 2 or more types. Specifically, nickel - as the base material of the nickel electrode for hydrogen batteries, it is preferable to use a metal foil mainly made of nickel, nickel - as the base material of the negative electrode of a hydrogen storage alloy electrode of hydrogen batteries, mainly nickel, It is preferable to use a metal foil made of at least one metal selected from copper and iron. Moreover, it is preferable to use a metal foil mainly made of aluminum as the base material of the positive electrode of the lithium ion battery, and it is preferable to use a metal foil mainly made of copper as the base material of the negative electrode of the lithium ion battery. In each of these metal foils, the main metal component described above is preferably contained in the metal foil in an amount of about 60% by weight or more.

  As a method for producing the metal foil, the above-described metal powder and / or metal fiber may be used as a raw material and pressed to obtain a foil having a predetermined thickness. The pressure at this time is not particularly limited, but is usually about 10 to 1000 MPa.

  As a specific forming method, for example, methods such as pressure forming and roll forming can be applied. In particular, when embossing is performed as a pressurizing method, pressurization is performed while partially pressing the protrusions of the mold, whereby elongation during pressurization can be suppressed and mechanical strength can be increased. Moreover, after pressurization, it is also possible to raise mechanical strength by heat-processing at about 400-800 degreeC, for example.

Since the metal foil obtained by the above-described method is obtained by pressing metal powder and / or metal fiber as a raw material, it has extremely fine irregularities and is used as an electrode base material for a conventional lithium ion battery. Compared to the metal foil used, it has a very high porosity. The metal foil used in the present invention is required to have a porosity of about 5 to 40%, and preferably about 10 to 30%. By the this having such porosity, improved adhesion between the electrode substrate and the active material paste, the gap of the metal foil is held electrolyte, utilization of the active material and the electrode life Will improve. On the other hand, if the porosity is too low, the above-described effects are not sufficiently exhibited. On the other hand, if the porosity is too high, mechanical strength, conductivity, etc. are insufficient, which is not preferable.

  In the present specification, the porosity is the weight (calculated weight) calculated from the product of the apparent volume and the specific gravity of the metal obtained from the thickness of the metal foil measured with a micrometer, as shown in the following formula, The difference from the weight of the metal foil (measured weight) divided by the calculated weight.

Porosity (%) = (calculated weight−measured weight) × 100 / calculated weight The thickness of the metal foil used in the present invention needs to be about 7 to 50 μm, and preferably about 15 to 30 μm. . If the metal foil is too thin, mechanical strength, conductivity, etc. are likely to be insufficient. On the other hand, if the metal foil is too thick, the proportion of the base material in the electrode increases and the capacity density decreases, which is not preferable.
The electrode for a secondary battery of the present invention is obtained by using a metal foil having a porosity of 5 to 40% and a thickness of 7 to 50 μm as a base material and applying a paste containing an active material thereto. .

  The electrode for a secondary battery of the present invention is suitable for applications such as a positive electrode (nickel electrode) and a negative electrode (hydrogen storage alloy electrode) in a nickel-hydrogen battery, and a positive electrode and a negative electrode in a lithium ion battery. In particular, when the nickel electrode of a nickel-hydrogen battery is used, it is very useful in that the output can be increased by thinning the separator, which is difficult with the conventional nickel electrode.

  The composition of the paste containing the active material is not particularly limited, and a paste containing a normally used active material may be used depending on the type of electrode. Such a paste usually contains an active material, a conductive agent, a thickener, a binder, a solvent, etc., although it varies depending on the type of electrode.

For example, in a nickel electrode for a nickel-hydrogen secondary battery, nickel hydroxide is usually used as an active material, but it is particularly preferable to use nickel hydroxide whose surface is coated with a cobalt compound such as cobalt hydroxide. . Nickel hydroxide whose surface is coated with a cobalt compound has good conductivity and excellent utilization rate and discharge rate. It can be a nickel electrode.

  As the binder, a known binder may be used depending on the type of electrode. Specifically, a binder that is excellent in alkali resistance, oxidation resistance, binding property, and the like and that satisfies conditions such as the generation of no harmful compounds may be appropriately selected and used. For example, a known binder can be used as the binder for the nickel electrode, and polyolefin is particularly preferred because it is excellent in both performance and life. Polyolefin may be used alone or in combination with a fluororesin.

  In addition, when using a binder in the form of a solution instead of an emulsion or dispersion binder, for example, an N-methylpyrrolidone solution of polyvinylidene fluoride, a part of the binder solution enters the gap of the electrode substrate. As a result, the binding property between the active material and the base material is improved, and a long-life electrode can be obtained.

  The method for applying the paste containing the active material to the above-described metal foil is not particularly limited, and a known method for producing a paste-type electrode can be appropriately applied. For example, a desired electrode can be obtained by applying a paste to a metal foil, then drying, and if necessary, pressurizing to a predetermined thickness and drying.

  The thickness of the electrode is preferably about 0.35 mm or less. The electrode of the present invention uses the above-described metal foil as an electrode base material, so that the adhesion of the active material paste is good even when the thickness is very thin, and the utilization rate and life of the active material are sufficient. It will have. As a result, a very thin electrode of about 0.35 mm or less can be obtained, which makes it possible to increase the output and capacity of the secondary battery.

  The structure of the secondary battery using the electrode of the present invention may be the same as that of a known secondary battery. The electrode of the present invention uses the above-described specific metal foil as a base material, so that no burrs are generated even in a wound structure. For this reason, even if it is a case where it is a case where it is a case where it is set as the structure which winds and comprises an electrode group using a thin film thickness separator, it does not short-circuit. In this case, in particular, by using a thin separator having a thickness of about 0.1 mm or less, preferably about 0.04 to 0.08 mm, a high capacity and high output secondary battery can be obtained. As the material of the separator, polyethylene, polypropylene, or the like is usually used.

  The electrode for a secondary battery of the present invention uses a metal foil having a fine concavo-convex structure as a substrate for an electrode, has good adhesion of the active material paste, and further has an electrolyte solution in the gap portion of the substrate. Therefore, the active material has a high utilization rate and a long life.

  In addition, since the metal foil used as the base material does not generate burrs even in a wound structure, a short circuit does not occur even when a thin film separator is used. For this reason, it can be set as the secondary battery which has high capacity | capacitance and high output by setting it as the structure which wound the electrode group using the separator with thin film thickness.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
60 parts by weight of carbonyl nickel powder having an average particle diameter of 8 μm and 40 parts by weight of nickel powder having an average particle diameter of 3 μm obtained by pulverization with a jet mill are sufficiently mixed, and a roll having fine irregularities is used to give approximately 200 MPa. The nickel foil was obtained by embossing under pressure. This nickel foil is similar in appearance to a normal nickel foil, and has no irregularities or burrs that penetrate the separator during winding.
As a result of measuring the thickness of the obtained nickel foil with a micrometer, the average was 28 μm.
The calculated value of the nickel weight was obtained from the product of the volume of the nickel foil obtained from this measured value and the specific gravity of nickel of 8.9, and the weight of the nickel foil was measured to obtain the porosity of the nickel foil. As a result, the porosity of the nickel foil described above was 15%, and it was confirmed that the nickel foil had extremely fine irregularities. The weight per unit area of the nickel foil was 202 g / m ² .

  On the other hand, nickel hydroxide powder whose surface was coated with 4% by weight of cobalt oxyhydroxide was used as the positive electrode active material, and 92 parts by weight of nickel hydroxide was mixed with 4 parts by weight of cobalt hydroxide and 1 part by weight of carboxymethylcellulose aqueous solution. Then, 2 parts by weight of a polyethylene emulsion and 1 part by weight of a fluororesin dispersion were added to obtain a paste containing an active material.

  The paste containing the active material thus obtained was applied to the above-described nickel foil one by one by the doctor knife method. After that, it was dried and pressed with a roller press to have an average thickness of 0.22 mm, and dried to obtain a paste-type nickel electrode. The nickel electrode thus obtained is defined as a nickel electrode a.

  On the other hand, for comparison, a punching metal made of nickel-plated iron with a two-dimensional structure and a porosity of 50% was used as a base material, and the same active material paste as described above was applied thereto. The paste was smoothed by passing between slits with a spacing of 0.38 mm formed using a steel member. After drying, pressure was applied with a roller press to obtain a nickel electrode having an average thickness of 0.22 mm. The nickel electrode thus obtained is referred to as a nickel electrode b.

  Furthermore, about the general-purpose foamed nickel electrode, the thickness was adjusted before the active material filling, and the thickness of the finished foamed nickel electrode was 0.22 mm to obtain a nickel electrode. This nickel electrode is referred to as a nickel electrode c.

  Using the nickel electrodes a to c described above as the positive electrode, a nickel-hydrogen battery having the following structure was produced.

First, 99 parts by weight of an MmNiCoAlMn alloy, which is a known ternary hydrogen storage alloy in which Al, Mn and Co are added to an MmNi alloy, is added to 1 part by weight of an aqueous carboxymethylcellulose solution to form a paste, which is usually 30 μm thick. The nickel foil was applied. This was passed between slits made of steel members set at an interval of 0.22 mm, dried, and then pressed with a roller press to produce a negative electrode having a thickness of 0.17 mm. The actual capacity of this negative electrode was set to 17.0% with respect to the positive electrode capacity.

As the separator, a polypropylene non-woven fabric having a thickness of 0.07 mm was used. The electrode group was wound and inserted into a known SubC battery case. As an electrolytic solution, an aqueous solution in which 25 g / liter of lithium hydroxide was dissolved in a 30% aqueous potassium hydroxide solution was added. After sealing, a battery was produced by a known tabless method.

  A battery obtained using the nickel electrode a is referred to as a battery A, a battery obtained using the nickel electrode b is referred to as a battery B, and a battery using the nickel electrode c is referred to as a battery C.

However, as for battery C, when 100 cells were manufactured, a short circuit was observed in about 30% of the cells.

The batteries A, B, and C thus obtained were subjected to chemical conversion treatment by repeating 150 times charging at 0.1 C and discharging to 0.1 V at 0.1 C to a final voltage of 0.9 V three times. Then, as a result of investigating the capacity | capacitance in 0.1C discharge by the full charge of each battery, the battery A was 3.32Ah, the battery B was 3.30Ah, and the battery C was 3.10Ah.

Next, a charge / discharge cycle consisting of charging by 1C ΔV-5 mV system and discharging to 1C at a final voltage of 0.95 V was repeated at an ambient temperature of 30 ° C. Table 1 shows the measurement results of the discharge capacity at each discharge current performed in the vicinity of 40 cycles. The charge before this discharge was 120% of the discharge capacity, and the ambient temperature was 30 ° C. The final voltage was 0.9 V until a discharge current of 5 A, and 0.7 V for a discharge current higher than that.

表1から明らかなように、本発明方法によって得られたニッケル極ａを用いた電池Ａは、
特に大電流放電において優れた利用率を示すことがわかる。なお、電池Ｂについては、放電電流の増加とともに容量が大きく低下した。電池Ｃはセパレータが厚く、正極負極の極間距離が大きいために、同じ終止電圧では、電池Ａと比較して放電電流が大きい場合に容量低下が大きい結果であった。

As is clear from Table 1, the battery A using the nickel electrode a obtained by the method of the present invention is
In particular, it can be seen that an excellent utilization rate is exhibited in large current discharge. In addition, about the battery B, the capacity | capacitance fell large with the increase in the discharge current. Battery C had a thick separator and a large distance between the positive and negative electrodes. Therefore, the same end voltage resulted in a large capacity drop when the discharge current was large compared to battery A.

Next, for batteries A, B, and C, the relationship between discharge current and discharge average voltage (intermediate value) is shown in Table 2 below.
Shown in Also in this case, the charge before the measurement was performed up to 120% of the discharge capacity at an ambient temperature of 30 ° C., and the measurement was performed near 80 cycles.

表２から明らかなように、電池Ａは、各放電電流において、電池Ｂ及び電池Cよりも高い
放電電圧を示し、高出力特性に優れていることがわかる。一方、汎用のパンチングメタルを電極基材とした電池Ｂは活物質の利用率が低いために電圧特性が劣り、電池Ｃは極間距離が大きいために高放電電流における電圧低下が大きい結果であった。

As is clear from Table 2, it can be seen that the battery A exhibits a higher discharge voltage than the batteries B and C at each discharge current, and is excellent in high output characteristics. On the other hand, the battery B using a general-purpose punching metal as an electrode base material has poor voltage characteristics due to the low utilization rate of the active material, and the battery C has a large voltage drop at a high discharge current due to a large distance between the electrodes. It was.

  Next, the life of each battery was examined. As a method, a charging / discharging cycle consisting of a 1C ΔV-5 mV charging and a 1C discharging with a final voltage of 0.95 V was repeated at an ambient temperature of 30 ° C.

The relationship between the number of cycles and the capacity retention rate is shown in Table 3 below. The capacity retention rate is expressed as the capacity at each cycle number when the capacity at 10 cycles is 100.

以上の結果から明らかなように、ニッケル極ａを用いた電池Ａは、電池Bよりもはるかに
長寿命であり、高価な発泡状ニッケル極と同程度の寿命を有するものであった。

As is clear from the above results, the battery A using the nickel electrode a has a much longer life than the battery B, and has a life similar to that of the expensive foamed nickel electrode.

  The cycle characteristics of the battery A are superior to the battery B because the nickel electrode b uses a porous base material, and therefore there is a portion where the distance between the active material layer and the base material is large. The nickel electrode a has no large holes on the surface of the base material at all, the contact degree between the active material and the base material is high, and the electrical conductivity is excellent. This is thought to be due to the fact that the loss of the active material is suppressed.

Example 2
A copper powder having an average particle diameter of 3 μm obtained by jet milling was pressed into a plate shape with a roll having a smooth surface, and then heat-treated at 600 ° C. for 15 minutes in a decomposed ammonia atmosphere to obtain a copper foil. This copper foil is similar in appearance to a normal copper foil, and has no irregularities or burrs that penetrate the separator during winding.

As a result of measuring the obtained copper foil with a micrometer, the thickness was 18 μm on average. The calculated value of the copper foil was obtained from the product of the volume of the copper foil and the specific gravity of the copper obtained from the measured value, and the weight of the copper foil was measured. Based on this, the porosity of the copper foil was obtained. As a result, the porosity of the copper foil described above was 13%, and it was confirmed that the copper foil had extremely fine irregularities. In addition, the weight per unit area of this copper foil was 190 g / m < ² >.

  Using the obtained copper foil as a negative electrode substrate, a lithium ion battery was produced by the following method.

First, a N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride is added to 93 parts by weight of natural graphite so that the amount of polyvinylidene fluoride is 7 parts by weight, and kneaded to obtain a paste containing an active material for a negative electrode. Prepared. This paste was applied to both sides of the above copper foil, dried and compressed to a thickness of 0.21 mm, which was cut into 50 × 300 mm to obtain a negative electrode. This negative electrode is defined as negative electrode d.

  A paste containing an active material for a negative electrode was prepared by adding 8 parts by weight of N, N dimethylformamide and polyvinylidene fluoride as a binder to 92 parts by weight of mesophase bitch graphite powder. This paste was applied to both sides of the above copper foil, dried, compressed to a thickness of 0.2 mm, and cut into 50 × 300 mm to obtain a negative electrode. This negative electrode is defined as negative electrode e.

As a comparison, a negative electrode was obtained in the same manner as negative electrodes d and e, except that a copper foil containing no gaps obtained by a rolling method was used as a base material. These negative electrodes are referred to as negative electrodes d ′ and e ′, respectively. As a positive electrode used as a counter electrode, 5 parts by weight of graphite conductive agent and NMP solution in which polyvinylidene fluoride is dissolved are added to 90 parts by weight of LiCoO ₂ as an active material so that the amount of polyvinylidene fluoride is 5 parts by weight. A paste was prepared, applied to both sides of an aluminum foil having a thickness of 20 μm, dried and pressed, and an electrode having a thickness of 0.18 mm was used.

  In the negative electrode, an aluminum ribbon was caulked and crimped to a copper foil as a lead, and in the positive electrode, an aluminum ribbon was caulked and crimped to a lead.

Next, a bottom insulating plate and an electrode group consisting of a positive electrode, a separator, and a negative electrode were inserted into the metal battery case, and after the negative electrode lead plate was welded to the battery case, the insulating plate was attached and the battery case was grooved. Thereafter, the positive electrode lead plate was welded to the sealing body through the hole of the insulating plate, and the electrolytic solution was injected. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of LiPF ₆ as a supporting electrolyte in a 55:45 mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used. After injecting the electrolytic solution, the opening of the battery case was covered with a sealing body through an insulating packing, and was crimped and sealed to obtain a lithium ion battery. The batteries obtained using the negative electrodes d, e, d ′, and e ′ are referred to as batteries D, E, D ′, and E ′, respectively.

  About each lithium ion battery obtained by the above-mentioned method, the battery life was investigated by the charge / discharge cycle test. As a test method, after charging at a constant current of 1 C (550 mA), charge at a constant voltage of 4.15 V for 3 hours, pause for 15 minutes, and then discharge to 2.75 V at a constant current of 1 C (550 mA). Then, after a pause of 15 minutes, the cycle of entering the next charge was repeated, and the change in the discharge capacity was examined. The results are shown in Table 4.

表４から明らかなように、間隙部を有する銅箔を負極用基材とした電池Ｄ及びＥは、間隙部のない銅箔を負極用基材とした電池Ｄ´及びＥ´と比較して、充放電サイクルを繰り返した際の容量低下が少ないことがわかる。

As is apparent from Table 4, the batteries D and E using the copper foil having gaps as the negative electrode base material are compared with the batteries D 'and E' using the copper foil having no gap parts as the negative electrode base material. It can be seen that there is little decrease in capacity when the charge / discharge cycle is repeated.

  This is considered to be due to the fact that in the batteries D and E, the electrolyte was held up to the inside of the negative electrode by using the negative electrode base material having a gap.

  In addition, when the battery was disassembled after repeating charge and discharge, the negative electrode constituent material was partially peeled off in the negative electrodes of the batteries D ′ and E ′, whereas in the batteries D and E, the negative electrode constituent material was No peeling was observed. This is because the negative electrode base material used in the batteries D and E had fine irregularities on the surface, which suppressed the decrease in the binding property of the negative electrode constituent material, and the use of a solution-like binder, It is considered that a part of the liquid permeates into the gap portion of the negative electrode base material when the paste is applied, thereby improving the binding property between the base material and the active material layer.

Next, in order to investigate the sustainability of the high output characteristics in the charge / discharge cycle, the capacity retention rate at a high discharge current when the charge / discharge cycle was repeated was examined. The results are shown in Table 5. Table 5 shows the 2C discharge capacity (end voltage 2.2V) in each cycle when the 0.1C discharge capacity in 5 cycles is 100.

表５から明らかなように、充放電サイクルの初期では、容量維持率に大きな差は無いが、１００サイクル以降では、間隙部を有する銅箔を用いた電池Ｄ及びＥが高い容量維持率を示すことがわかる。

As is apparent from Table 5, there is no significant difference in capacity retention rate at the beginning of the charge / discharge cycle, but after 100 cycles, the batteries D and E using the copper foil having the gap portion show a high capacity retention rate. I understand that.

Claims (2)

  An electrode for a secondary battery obtained by pressurizing carbonyl nickel powder and using a metal foil having a porosity of 5 to 15% and a thickness of 7 to 50 µm as a base material.   An electrode for a secondary battery obtained by applying a paste containing an active material to an electrode substrate made of a metal foil having a porosity of 5 to 15% and a thickness of 7 to 50 μm obtained by pressurizing carbonyl nickel powder.