JP2008123705A - Positive electrode plate for lithium-ion secondary battery and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode plate for obtaining a lithium-ion secondary battery having stable characteristics. <P>SOLUTION: The positive electrode plate for the lithium-ion secondary battery is formed by applying paste-like positive electrode mixture 12 in which a positive-electrode active material is dispersed in the solvent of an alkaline aqueous solution to the surface of a collector 11 comprising aluminum and drying it. The alkaline aqueous solution contains the aluminum ions of the same element as the aluminum constituting the collector 11. Also, the positive-electrode active material comprises a lithium compound oxide, and the alkaline aqueous solution contains lithium ions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode plate for a lithium ion secondary battery and a method for producing the same.

  Lithium ion secondary batteries are small and have a high capacity, and thus are attracting attention as power sources for driving electric vehicles in addition to electronic devices such as notebook computers and mobile phones.

  A positive electrode plate of a lithium ion secondary battery has a positive electrode active material (for example, a lithium-containing composite oxide) on a surface of a current collector (for example, aluminum) and a conductive material, a binder, and the like in a solvent. It is formed by applying a dispersed positive electrode mixture. In order to apply this positive electrode mixture in paste form to the current collector, an organic solvent (for example, N-methylpyrrolidone) is usually used as a solvent for dispersing the positive electrode active material.

  By the way, in order to increase the capacity of the lithium ion secondary battery, it is effective to increase the electrode area. However, the amount of the mixture to be applied to the current collector also increases. As a result, a reduction in the production cost of the positive electrode mixture is required, and in order to cope with this, a method of using an aqueous solution instead of an organic solvent as a solvent for dispersing an active material has been studied.

  However, when a lithium-containing composite oxide is used as the positive electrode active material, the lithium-containing composite oxide reacts with water and the contained lithium dissolves in the aqueous solution, resulting in a decrease in the capacity of the lithium-containing composite oxide. The problem of end up occurs.

In order to solve this problem, Patent Document 1 discloses a method in which lithium ions (Li ions) are dissolved in advance in an aqueous solution by using an alkaline aqueous solution (for example, a lithium hydroxide aqueous solution) as a solvent. Are listed. Thereby, it can suppress that lithium melt | dissolves in aqueous solution from lithium containing complex oxide.
JP 2005-228679 A JP 2001-143703 A

  The inventors of the present application use a current collector made of aluminum foil and a positive electrode active material made of a lithium-containing composite oxide, and the method described in Patent Document 1, that is, a lithium hydroxide aqueous solution (alkaline aqueous solution) as a solvent. As a result, the characteristics of the positive electrode plate formed by applying the positive electrode mixture to the surface of the current collector were examined, and the battery capacity was compared with that obtained by adjusting the positive electrode mixture using an organic solvent. I noticed that there was a big variation.

  When examining the positive electrode plate of the battery with large variations, as shown in the micrograph of FIG. 3, there are many bubbles B on the surface A of the positive electrode plate coated with the positive electrode mixture. Observed. When the positive electrode mixture was wiped off and the surface of the aluminum foil (current collector) was observed, it was found that the surface of the aluminum foil corresponding to the position where the bubbles B were generated was corroded.

  The cause of the corrosion of the surface of the aluminum foil is considered as follows. That is, when a positive electrode mixture containing an alkaline aqueous solution as a solvent is applied to the surface of the aluminum foil, it is considered that aluminum is dissolved in the alkaline aqueous solution, and as a result, hydrogen gas is generated as bubbles.

  If the cause of corrosion of the aluminum foil is dissolution of the above-mentioned aluminum in an alkaline aqueous solution, it is predicted that the same phenomenon will occur even when an aqueous solution in which Li ions are not dissolved in advance is used as a solvent. That is, as described above, when a lithium-containing composite oxide is used as the positive electrode active material, the lithium-containing composite oxide reacts with water and the contained lithium dissolves in the aqueous solution. Show. Therefore, since aluminum has a property of dissolving in an alkaline aqueous solution, bubbles B can be generated even when an aqueous solution in which Li ions are not previously dissolved in the aqueous solution is used as a solvent. However, even when the positive electrode mixture was prepared using ion-exchanged water as a solvent, it was observed that bubbles were generated on the surface of the positive electrode plate coated with this positive electrode mixture.

  From the above considerations, the variation in battery capacity in the lithium ion secondary battery described above is a problem inherent to a positive electrode plate in which a positive electrode mixture prepared using an alkaline aqueous solution as a solvent is applied to the surface of a current collector made of aluminum. It can be said that there is. If the cause of bubbles is due to dissolution of aluminum, it is expected that the bubbles are present not only on the surface of the positive electrode plate but also inside.

  When a positive electrode plate in which such bubbles are present is rolled with a press, density unevenness or thickness unevenness of the positive electrode mixture occurs in the plane of the positive electrode plate. In addition, when applying the positive electrode mixture to both surfaces of the current collector, the thickness unevenness at the time of applying the front surface is superimposed on the thickness unevenness at the time of applying the back surface, so when the positive electrode plate is pressed in this state, Density unevenness or thickness unevenness becomes more prominent.

  Such a positive electrode mixture, that is, uneven density or uneven thickness of the positive electrode active material causes variations in battery capacity. In addition, even in an electrode group formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, reaction unevenness due to density unevenness of the positive electrode active material occurs, resulting in a problem that the cycle life of the battery is reduced. Also occurs. In addition, the pressure applied during pressing changes due to uneven thickness, which may cause problems such as electrode plate breakage during processing of the positive electrode plate or formation of the electrode group.

  The present invention has been made on the basis of such knowledge, and its main object is to provide a positive electrode plate for obtaining a lithium ion secondary battery having stable characteristics.

  The inventors of the present application are that the variation in battery capacity in the lithium ion secondary battery described above is due to the fact that the aluminum constituting the positive electrode current collector is dissolved in the alkaline aqueous solution that is the solvent for the positive electrode mixture. Attention has been paid to the fact that the aluminum aqueous solution can contain aluminum ions (Al ions), which are the same elements as the material constituting the current collector, so that the dissolution of the aluminum can be effectively suppressed.

  That is, the method for manufacturing a positive electrode plate for a lithium ion secondary battery according to the present invention is a method for manufacturing a positive electrode plate for a lithium ion secondary battery in which a positive electrode active material is formed on the surface of a current collector, and is made of aluminum. A step of preparing the current collector, and a step of applying a positive electrode mixture in which a positive electrode active material is dispersed in a solvent comprising an alkaline aqueous solution to the surface of the current collector and then drying the positive electrode mixture; The alkaline aqueous solution contains Al ions.

  According to such a method, due to the presence of Al ions, dissolution of aluminum constituting the current collector into the alkaline aqueous solution is suppressed, and as a result, generation of bubbles in the positive electrode mixture can be prevented. Thereby, density unevenness or thickness unevenness of the positive electrode mixture can be reduced, and a lithium ion secondary battery having stable characteristics can be obtained.

  Here, the alkaline aqueous solution preferably further contains Li ions. Thereby, it can suppress that lithium elutes from aqueous solution in a positive electrode active material, and can prevent the capacity | capacitance fall of a positive electrode active material by this. Although the alkalinity of the alkaline aqueous solution is further increased by further containing Li ions, the effect of suppressing dissolution of aluminum is not lost because the alkaline aqueous solution already contains Al ions.

  The alkaline aqueous solution is preferably a lithium hydroxide aqueous solution. By using Li ions, other alkali metal ions can be prevented from being replaced with Li of the active material, and the physical properties of the active material can be kept unchanged.

  The positive electrode active material is made of a composite lithium oxide, and the composite lithium oxide is preferably a lithium nickel composite oxide. Lithium-nickel composite oxide is liable to dissolve in an alkaline aqueous solution, so the alkalinity of the alkaline aqueous solution increases and the dissolution of aluminum may be accelerated, but by including Al ions in the alkaline aqueous solution, The drowning can be resolved.

  According to the present invention, by containing Al ions, which are the same elements as aluminum constituting the current collector, in an alkaline aqueous solution that is a solvent for the positive electrode mixture, dissolution of aluminum is suppressed, and as a result, the positive electrode mixture The generation of bubbles in can be prevented. Thereby, the density nonuniformity or thickness nonuniformity of a positive mix (positive electrode active material) can be reduced, and the lithium ion secondary battery which has the stable characteristic is realizable.

  Further, when Al ions are present in the solvent of the positive electrode mixture, when the positive electrode mixture applied to the surface of the current collector is dried, the surface of the positive electrode active material or / and the positive electrode active material and the current collector An aluminum hydroxide or oxide can be formed on the surface of the current collector or / and on the surface of the current collector. This prevents direct contact with the electrolyte solution at each interface, thereby suppressing undesirable reactions with the electrolyte solution due to the positive electrode potential, and as a result, realizing a lithium ion secondary battery with excellent cycle characteristics. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of simplicity. In addition, this invention is not limited to the following embodiment.

  1A and 1B are process cross-sectional views schematically showing a method for manufacturing a positive electrode plate for a lithium ion secondary battery in the present embodiment.

  First, as shown in FIG. 1A, a current collector 11 made of aluminum is prepared. Here, the current collector 11 is preferably an aluminum foil having a thickness of about 15 μm in order to obtain a large capacity lithium ion secondary battery.

  Next, a positive electrode mixture to be applied to the surface of the current collector 11 is prepared. Here, as the positive electrode mixture, a paste in which a positive electrode active material is dispersed in a solvent of an alkaline aqueous solution is used. Further, the alkaline aqueous solution contains Al ions of the same element as the aluminum constituting the current collector 11.

  As the positive electrode active material, for example, a composite lithium oxide such as a lithium nickel composite oxide can be used. Moreover, lithium hydroxide aqueous solution can be used for alkaline aqueous solution, for example. Furthermore, Al ions (referred to as “aluminate ions” in the alkaline aqueous solution) can be contained in the alkaline aqueous solution by charging and dissolving the aluminum powder in the alkaline aqueous solution. In addition to the conductive agent (for example, acetylene black) and the binder (for example, tetrafluoroethylene resin), it is preferable to mix a thickener (for example, carboxymethyl cellulose) with the positive electrode mixture.

  Next, as shown in FIG.1 (b), after apply | coating the positive mix 12 adjusted to the paste form on both surfaces of the electrical power collector 11, the positive mix 12 is dried and a positive electrode plate is obtained.

  FIG. 2 is a photomicrograph of the surface of the positive electrode plate obtained by the above method when the Al ion concentration in the alkaline aqueous solution is 0.01 mol / l (in terms of Al metal). It can be seen that the generation of bubbles C is reduced compared to the surface of the positive electrode plate formed by the conventional method shown in FIG. That is, by containing Al ions that are the same element as the aluminum constituting the current collector 11 in the alkaline aqueous solution that is the solvent of the positive electrode mixture 12, dissolution of aluminum is suppressed, and as a result, bubbles in the positive electrode mixture Can be suppressed. Thereby, the density nonuniformity or thickness nonuniformity of a positive mix (positive electrode active material) can be reduced, and the lithium ion secondary battery which has the stable characteristic is realizable.

  In order to effectively suppress dissolution of aluminum, the concentration of Al ions contained in the alkaline aqueous solution is preferably 0.01 mol / liter or more.

  In the present embodiment, when a lithium hydroxide aqueous solution containing Li ions is used as the alkaline aqueous solution, it is possible to suppress dissolution of Li ions from the composite lithium oxide that is the positive electrode active material in the alkaline aqueous solution. Thereby, the fall of the capacity | capacitance of lithium containing complex oxide can be prevented.

  Further, when Al ions are present in the solvent of the positive electrode mixture, when the positive electrode mixture applied to the surface of the current collector is dried, the surface of the positive electrode active material or / and the positive electrode active material and the current collector It is possible to achieve an effect of covering the interface or the surface of the current collector with an aluminum hydroxide or oxide. As a means for improving the cycle characteristics of the battery, a method of covering the surface of the positive electrode active material with an aluminum hydroxide or oxide is known (see, for example, Patent Document 2), but the positive electrode mixture is adjusted. Prior to this, a special coating process is required, which raises an increase in manufacturing cost. In the present invention, in the step of applying the positive electrode mixture to the surface of the current collector, in addition to the effect of suppressing the dissolution of aluminum, the effect of covering the surface of the positive electrode active material with an aluminum hydroxide or oxide, etc. You can play at the same time. Thereby, it is possible to realize a lithium ion secondary battery having stable characteristics and excellent cycle characteristics.

  Furthermore, in the present invention, not only the surface of the positive electrode active material but also the interface between the positive electrode active material and the current collector or / and the surface of the current collector are covered with an aluminum hydroxide or oxide. As a result, since it does not come into direct contact with the electrolyte at each interface, it is possible to suppress undesirable reactions with the electrolyte due to the positive electrode potential, and as a result, a lithium ion secondary battery with excellent cycle characteristics is realized. It becomes possible to do.

  Furthermore, among the lithium composite oxides that are positive electrode active materials, when a lithium nickel composite oxide with a large amount of nickel added is used, the alkalinity of the aqueous alkali solution increases because the contained lithium is easily dissolved in the alkaline aqueous solution. Thus, the dissolution of aluminum may be accelerated, but the inclusion of Al ions in the alkaline aqueous solution can also be solved.

  Next, in order to evaluate the positive electrode plate in the present invention, a positive electrode plate was produced according to the following examples, a battery was produced using the obtained positive electrode plate, and the battery capacity characteristics were evaluated.

(Example 1)
Lithium hydroxide was dissolved in ion-exchanged water to prepare a 1 mol / l lithium hydroxide aqueous solution. To this, Al powder was added, stirred and dissolved to obtain an aqueous lithium hydroxide solution having an Al ion concentration of 0.05 mol / l in terms of Al metal.

  100 parts by weight of a positive electrode active material powder (LiNi0.81Co0.14Al0.05O2) made of Ni, Co, and Al, 2.5 parts by weight of acetylene black as a conductive agent, and a fluorine-based binder (ethylene tetrafluoride as a binder) 4 parts by weight of resin) and carboxymethyl cellulose as a thickener were mixed in an aqueous lithium hydroxide solution containing Al ions to prepare a positive electrode mixture paste. Note that the lithium hydroxide aqueous solution containing Al ions was 50 mL with respect to 100 parts by weight of the positive electrode active material powder.

  This paste was applied to both sides of a 15 μm thick aluminum foil as a current collector and dried. After application, the time until the start of drying was 2 minutes. This was rolled to a uniform thickness with a flat roll press, cut into a size of 100 μm in thickness, 37 mm in width, and 300 mm in length to obtain a positive electrode plate a.

(Example 2)
Positive electrode plates b to e were produced in the same manner as in Example 1 except that the amount of Al powder to be added was changed. In addition, when Al powder was charged and stirred in the lithium hydroxide aqueous solution, a part of Al might not be completely dissolved as an oxide and a hydroxide, but the paste as it was was applied to the current collector.

(Comparative Example 1)
A positive electrode plate f was produced in the same manner as in Example 1 except that a lithium hydroxide aqueous solution without using Al powder was used.

(Comparative Example 2)
A positive electrode plate g was produced in the same manner as in Example 1 except that ion-exchanged water was used instead of the lithium hydroxide aqueous solution containing Al ions.

  Next, using the positive electrode plates a to g obtained by the above method, a laminate battery was produced by the following method.

First, 10 locations of the positive electrode plates a to g are punched out to a size of 10 mm square (there is a tab portion for lead attachment in addition to the 10 mm square), and the mixture on the surface of the tab portion for lead attachment is peeled off. A lead was attached. The punched positive electrode plate was sandwiched with 12 mm square Li metal attached with Ni leads via a separator, and inserted into an Al laminate. Furthermore, an electrolytic solution in which 1 mol / l LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 3 was injected into an Al laminator. Thereafter, the Al laminator was heat sealed in a vacuum to produce 10 laminated batteries for each of the positive plates a to g.

  The laminate battery was charged at a constant current until reaching 4.2 V at 1 mA in a 25 ° C. atmosphere, then left for 10 minutes and discharged to 2.5 V at 1 mA. The variation in discharge capacity at this time was measured. The variation (dispersion) Y was determined by the following equation (1).

  Here, An is the discharge capacity of the nth laminate battery, and B is the average value of the discharge capacity of the 10 laminate batteries.

  Table 1 shows the results obtained for the positive plates a to g. In addition, the Al ion concentration in a table | surface shows the value in conversion of Al metal of the Al ion concentration in lithium hydroxide aqueous solution.

  Table 1 shows that the positive electrode plates a to e in Examples 1 and 2 have smaller capacity variations than the positive electrode plates f and g in Comparative Examples 1 and 2. This is because, in the positive electrode plates in Examples 1 and 2, since the Al ions are dissolved in the positive electrode mixture paste applied to the current collector, the dissolution of aluminum constituting the current collector is suppressed. As a result, it is considered that the generation of hydrogen gas accompanying the dissolution of aluminum was suppressed. That is, as shown in FIG. 2, the generation of hydrogen gas is suppressed, and as a result, the bubbles C in the positive electrode plate are reduced. As a result, density unevenness or thickness unevenness of the positive electrode mixture can be reduced. It seems that the variation was reduced.

  In addition, the positive electrode plate b in the present embodiment has a larger variation than the other positive electrode plates in the present embodiment. This is presumably because the effect of suppressing dissolution of aluminum was small because the Al ion concentration in the aqueous alkali solution was small compared to other samples. From this, the concentration of Al ions in the alkaline aqueous solution is preferably 0.01 mol / l or more. Moreover, the capacity | capacitance of the positive electrode plate g in the comparative example 2 is small compared with the other sample. This is presumably because the Li ion in the active material was dissolved in the ion exchange water used as the solvent for the positive electrode mixture, and the capacity of the active material was reduced.

  Next, a wound type lithium ion secondary battery was produced using the positive electrode plate of the present invention, and the cycle characteristics were evaluated.

(Example 3)
Using the positive electrode plate a of Example 1, a lithium ion battery A was produced by the following method.

  100 parts by weight of graphite as a negative electrode active material and 6 parts by weight of PVDF as a binder were respectively charged and mixed in an N-methylpyrrolidone (NMP) solution, which is an organic solvent, to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a 10 μm thick copper foil as a current collector, dried and rolled, and cut into a size of 39 mm width and 340 mm length to obtain a negative electrode plate.

A current collecting lead is welded to the exposed portion of each of the current collector of the positive electrode plate a produced in Example 1 and the negative electrode plate produced by the above method, and the positive electrode plate is passed through a polyethylene separator having a thickness of 20 μm. The electrode group was produced by winding a and the negative electrode in a spiral shape. The electrode group was housed in a stainless steel bottomed cylindrical container having an outer diameter of 17.5 mm and a height of 50 mm together with the electrolytic solution, and then the container was sealed to prepare a cylindrical lithium ion secondary battery A. Note that the electrolytic solution, EC and EMC and 1: was prepared by dissolving of LiPF ₆ 1 mol / l in a solvent mixture in the third volume.

(Comparative Example 3)
Lithium hydroxide was dissolved in ion exchange water to prepare 1 L of 1 mol / l lithium hydroxide aqueous solution. To this aqueous solution, 1 kg of positive electrode active material powder (LiNi0.81Co0.14Al0.05O2) and 6.75 g of Al powder were added and stirred. The positive electrode mixture slurry thus obtained was dried at 80 ° C., so that the surface of the positive electrode active material was covered with Al hydroxide or oxide. At this time, the Al amount of the Al compound relative to 100 parts by weight of the positive electrode active material was 0.675 parts by weight in terms of Al metal.

  100 parts by weight of this positive electrode active material, 2.5 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of polyvinylidene fluoride (PDVF) as a binder, each of which is an organic solvent, N-methylpyrrolidone (NMP) The solution was charged and mixed to prepare a positive electrode mixture paste. After applying this paste on both sides of a 15 μm thick aluminum foil as a current collector, it was dried and further rolled to a uniform thickness with a flat roll press to cut out a positive electrode plate h to a size of 37 mm width and 300 mm length. Produced. And using this positive electrode plate h, the lithium ion secondary battery H was produced by the method similar to Example 3. FIG.

(Comparative Example 4)
100 parts by weight of the positive electrode active material powder (LiNi0.81Co0.14Al0.05O2), 2.5 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of PDVF as a binder, are each put into an NMP solution that is an organic solvent. And mixing to prepare a positive electrode mixture paste. This paste was applied to both sides of an aluminum foil having a thickness of 15 μm as a current collector, then dried, and further rolled to a uniform thickness with a flat plate roll press, cut into a size of 37 mm in width and 300 mm in length, and positive electrode plate i was cut. Produced. And using this positive electrode plate i, the lithium ion secondary battery I was produced by the method similar to Example 3. FIG.

  Next, the lithium ion secondary batteries A, H, and I obtained by the above method were aged in a 45 ° C. atmosphere for 3 days while being charged to 4.1 V at 50 mA. Then, it discharged to 2.5V at 50 mA in 25 degreeC atmosphere. After charging to 4.2 V at 50 mA again, impedance (hereinafter referred to as “impedance before cycle”) was measured at a frequency of 0.1 Hz by the AC impedance method.

  Furthermore, after carrying out constant current charge until it reached 4.2V at 50mA in 45 degreeC atmosphere, the cycle discharged to 2.5V at 50mA was repeated 300 cycles. Then, after charging to 4.2 V at 50 mA, impedance after cycling (hereinafter referred to as “impedance after cycling”) was measured again at a frequency of 0.1 Hz by the AC impedance method.

  The impedance measured in this evaluation is particularly important for an electric vehicle or the like that performs pulse-like discharge, and an increase in internal impedance due to the cycle leads to a decrease in output characteristics accompanying the cycle.

Table 2 shows the increase rate of the internal impedance obtained for the lithium ion secondary batteries A, H, and I. The increase rate ΔS of the internal impedance was obtained by the following formula (2).
ΔS = (S2−S1) / S1 × 100 [%] (2)
Here, S1 is the impedance before the cycle, and S2 is the impedance after the cycle.

  From Table 2, it can be seen that lithium ion batteries A and H have a smaller impedance increase rate than battery I and have excellent cycle characteristics. In the batteries A and H, the positive electrode active material is coated with Al hydroxide or oxide, whereas in the battery I, the positive electrode active material is coated with Al hydroxide or oxide. It is thought that it is caused by not being done.

  Moreover, in the lithium ion batteries A and H, although the Al amount in terms of metal with respect to the active material in the positive electrode is the same, the battery A has a smaller impedance increase rate than the battery H. The reason is considered as follows. That is, the positive electrode active material of the battery H is coated with Al hydroxide or oxide, whereas the positive electrode active material of the battery A is coated with Al hydroxide or the like. This is presumably because Al hydroxides and oxides are also present at the interface between the substance and the current collector and the surface of the current collector.

  Next, in order to further investigate the effect of the coating of the positive electrode active material with such an Al hydroxide, a positive electrode plate was produced by changing the Al ion concentration in the alkaline aqueous solution as the solvent of the positive electrode mixture.

Example 4
Lithium hydroxide was dissolved in ion-exchanged water to prepare a 1 mol / l lithium hydroxide aqueous solution. In this aqueous solution, Al powder was added, stirred and dissolved, and the concentration of Al ions was 0.05 mol / l in terms of Al metal.

  100 parts by weight of a positive electrode active material powder (LiNi1 / 3Co1 / 3Mn1 / 3O2) composed of Ni, Co, and Mn, 2.5 parts by weight of acetylene black as a conductive agent, and a fluorine-based binder (ethylene tetrafluoride as a binder) Resin) and 4 parts by weight of carboxymethyl cellulose as a thickener were added to and mixed with the lithium hydroxide aqueous solution to prepare a positive electrode mixture paste. Note that the lithium hydroxide aqueous solution was 50 mL with respect to 100 parts by weight of the positive electrode active material powder. In this case, the Al amount of the Al compound formed on the surface of the positive electrode active material or the interface between the positive electrode active material and the current collector by Al ions contained in the lithium hydroxide aqueous solution is 0.675 parts by weight in terms of Al metal. is there.

  This paste was applied to both sides of an aluminum foil having a thickness of 15 μm as a current collector, dried, further rolled to a uniform thickness with a flat plate roll press, cut into a size of 37 mm in width and 300 mm in length. It was.

(Example 5)
Except changing the quantity of Al powder thrown in, it carried out similarly to Example 4, and produced the positive electrode plates kn. In addition, when Al powder was added and stirred in the lithium hydroxide aqueous solution, a part of Al might not be completely dissolved as an oxide or a hydroxide, but it was used as a paste as it was.

(Comparative Example 5)
A positive electrode plate o was produced in the same manner as in Example 4 except that ion-exchanged water was used instead of the lithium hydroxide aqueous solution containing Al ions.

(Comparative Example 6)
Lithium hydroxide was dissolved in ion exchange water to prepare 1 L of 1 mol / l lithium hydroxide aqueous solution. To this aqueous solution, 1 kg of positive electrode active material powder (LiNi1 / 3Co1 / 3Mn1 / 3O2) and 6.75 g of Al powder were added and stirred. The slurry thus obtained was dried at 80 ° C. to obtain a positive electrode active material whose surface was coated with Al hydroxide or oxide. In this case, the Al amount of the Al compound with respect to 100 parts by weight of the positive electrode active material is 0.675 parts by weight in terms of Al metal.

  100 parts by weight of this positive electrode active material, 2.5 parts by weight of acetylene black as a conductive agent, 4 parts by weight of a fluorine-based binder as a binder, and carboxymethyl cellulose as a thickener are charged and mixed with ion-exchanged water, respectively. Then, a positive electrode mixture paste was produced. This paste was applied to both sides of a 15 μm thick aluminum foil as a current collector, dried, and then rolled to a uniform thickness with a flat roll press, cut into a size of 37 mm in width and 300 mm in length, and the positive electrode plate p was cut. Produced.

  Next, 100 parts by weight of graphite as a negative electrode active material and 6 parts by weight of PVDF as a binder were respectively charged and mixed in an NMP solution as an organic solvent to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a 10 μm thick copper foil as a current collector, dried and rolled, and cut into a size of 39 mm width and 340 mm length to obtain a negative electrode plate p.

  Using the positive electrode plates j to p thus obtained, lithium ion secondary batteries J to P were produced in the same manner as in Example 3 (in the comparative example 6, the negative electrode plate p was used).

  Table 3 shows the increase rate of the internal impedance obtained by using the same measurement method as that shown in Table 2 for the lithium ion secondary batteries J to P. In the table, Al parts by weight indicate the amount of Al in terms of metal of the Al compound formed on the surface of the positive electrode active material or the interface between the positive electrode active material and the current collector by Al ions contained in the lithium hydroxide aqueous solution (positive electrode active material). (Parts by weight in terms of Al metal relative to 100 parts by weight).

  From Table 3, it can be seen that the rate of increase in impedance in the lithium ion secondary batteries J to N of this example is smaller than that of the lithium ion secondary battery O of the comparative example, and the cycle characteristics are excellent. Further, the reason why the impedance increase rates of the batteries K and N are larger than those of the batteries J, L, and M in the other examples is considered to be as follows. That is, if the amount of Al is less than 0.1 parts by weight, the amount of coating on the surface of the positive electrode active material, the positive electrode active material and the current collector, or the surface of the current collector by an Al hydroxide or the like is not sufficient. In addition, if the amount of Al exceeds 2 parts by weight, the amount of Al hydroxide, oxide, etc. is too large, thereby reducing the electronic conductivity between the active materials or between the active material and the current collector. As a result, it is considered that the rate of increase in impedance is increased. Therefore, in order to improve the cycle characteristics more effectively, it can be said that the amount of Al in terms of metal of the Al compound is preferably in the range of 0.1 to 2 parts by weight.

  On the other hand, when comparing the lithium ion secondary battery J of this example and the lithium ion secondary battery P of the comparative example, the amount of Al in terms of metal is the same, but the rate of increase in impedance is smaller in the battery J. Yes. This is because, in the positive electrode produced in this example, as described above, the active material surface coating form is different from that of the comparative example, the current collector surface, the current collector / active material interface, This is probably because Al hydroxide or oxide is also present on the surface of the current collector.

As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, in the above embodiment, the material constituting the current collector of the positive electrode plate is aluminum. However, the present invention is not limited to this, and for example, similar effects can be obtained even in an alloy containing aluminum. Moreover, although the composite lithium oxide was used as the material of the positive electrode active material, there is no particular limitation as long as it absorbs and releases lithium ions. Further, the aqueous alkaline solution is preferably a lithium hydroxide aqueous solution (LiOH), but is not limited thereto, and for example, NaOH, KOH, Ca (OH) ₂ , Ba (OH) _2, or the like can be used.

  The present invention provides a positive electrode plate for obtaining a lithium ion secondary battery having stable characteristics, and is useful as a power source for driving an electric vehicle or the like in addition to the use of an electronic device such as a notebook computer or a mobile phone. It is.

It is process sectional drawing which showed the manufacturing method of the positive electrode plate in embodiment of this invention. It is the surface photograph of the positive electrode plate produced by the method in the Example of this invention. It is the surface photograph of the positive electrode plate produced by the conventional method.

Explanation of symbols

11 Current collector
12 Positive electrode mixture

Claims (7)

A method for producing a positive electrode plate for a lithium ion secondary battery in which a positive electrode active material is formed on a current collector surface,
Preparing the current collector made of aluminum;
A step of applying a positive electrode mixture in which the positive electrode active material is dispersed in a solvent comprising an alkaline aqueous solution to the surface of the current collector, and then drying the positive electrode mixture;
The method for producing a positive electrode plate for a lithium ion secondary battery, wherein the alkaline aqueous solution contains aluminum ions.   The method for producing a positive electrode plate for a lithium ion secondary battery according to claim 1, wherein the alkaline aqueous solution further contains lithium ions.   The method for producing a positive electrode plate for a lithium ion secondary battery according to claim 2, wherein the aqueous alkaline solution is an aqueous lithium hydroxide solution.   2. The method for producing a positive electrode plate for a lithium ion secondary battery according to claim 1, wherein the concentration of aluminum ions contained in the alkaline aqueous solution is 0.01 mol / liter or more.   The method for manufacturing a positive electrode plate for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material is composed of composite lithium oxide.   The method of manufacturing a positive electrode plate for a lithium ion secondary battery according to claim 5, wherein the composite lithium oxide is a lithium nickel composite oxide. A positive electrode plate for a lithium ion secondary battery in which a positive electrode active material is formed on a current collector surface,
The current collector is made of aluminum;
The positive electrode active material is formed by applying a positive electrode mixture in which the positive electrode active material is dispersed in a solvent composed of an alkaline aqueous solution containing aluminum ions to the surface of the current collector. Secondary battery positive electrode plate.