JP5670671B2 - Method for producing positive electrode for battery and method for producing lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode for a battery, and a lithium ion secondary battery having a positive electrode produced by the production method.

  In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small and light weight and high capacity have been required.

  In order to increase the capacity of the secondary battery, for example, it is known that a technique of increasing the density of the positive electrode mixture layer in the positive electrode and thereby increasing the filling amount of the positive electrode active material is effective. And in order to raise the density of a positive mix layer, various techniques are proposed (patent documents 1-5 etc.).

JP 2006-86116 A JP 2006-339026 A JP 2007-200681 A JP 2009-301727 A JP 2010-92835 A

  In addition to the techniques described in Patent Documents 1 to 5, a plurality of positive electrode active materials having different particle sizes are used, and positive electrode active material particles having a small particle size are arranged between positive electrode active material particles having a large particle size. Thus, it is conceivable to increase the density of the positive electrode mixture layer and increase the filling amount thereof.

  However, since it is not always easy to ideally arrange positive electrode active material particles having different particle diameters in the positive electrode mixture layer, development of a technique that can achieve this by a simple method is required.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a positive electrode for a battery having a high density mixture layer, and a lithium ion secondary battery having a positive electrode produced by the method. It is to provide.

The method for producing a positive electrode for a battery according to the present invention that has achieved the above object comprises a step of preparing a positive electrode mixture-containing composition containing at least a positive electrode active material A, a positive electrode active material B, a conductive additive, a binder, and a medium. A step of applying the positive electrode mixture-containing composition on one or both sides of the current collector and drying to form a positive electrode mixture layer on the current collector; and a positive electrode mixture layer formed on the current collector The cathode active material A includes an average particle diameter d _A1 at the stage used for preparing the positive electrode mixture-containing composition, and an average particle diameter d _A2 after the calendar treatment. The ratio (d _A1 / d _A2 ) is 0.8 to 1.2, and the positive electrode active material B has an average particle diameter d _B1 at the stage used for the preparation of the positive electrode mixture-containing composition, and a calendar treatment. the ratio of the average particle diameter _{d B2} after _(d B1 _/ d _B2) is 2.0 to 5.0 There, the ratio of the _{d A2} and the _{d B2 (d B2 / d A2} ) is characterized in that it is a 0.10 to 0.5.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the positive electrode is manufactured by the method for manufacturing a positive electrode for a battery of the present invention. It is a feature.

  ADVANTAGE OF THE INVENTION According to this invention, the method of manufacturing the positive electrode for batteries which has a mixture layer with a high density, and the lithium ion secondary battery which has a positive electrode manufactured by this method can be provided. That is, according to the lithium ion secondary battery of the present invention, a high capacity can be achieved satisfactorily.

It is a schematic diagram which shows an example of the lithium ion secondary battery of this invention, (a) Top view, (b) Cross-sectional view. FIG. 2 is a perspective view of FIG. 1.

  A positive electrode used in a battery such as a lithium ion secondary battery is, for example, a composition containing a positive electrode mixture by dispersing a positive electrode active material, a conductive additive and a binder in a medium such as N-methyl-2-pyrrolidone (NMP). (However, the binder may be dissolved in the medium) is applied to one or both sides of the current collector and dried to form the positive electrode mixture layer, and then the positive electrode mixture layer. Manufactured through a calendaring process.

  In this case, in order to increase the density of the positive electrode mixture layer, when a positive electrode active material particle having a large particle size and a positive electrode active material particle having a small particle size are used in combination, a positive electrode having a close particle size is prepared during the preparation of the positive electrode mixture-containing composition. Active material particles tend to gather together, and it is not easy to uniformly disperse them in a medium. Therefore, it is not always easy to increase the density of the positive electrode mixture layer by arranging the positive electrode active material particles having a large particle diameter and the positive electrode active material particles having a small particle diameter in an ideal state in the positive electrode mixture layer. There wasn't.

  Therefore, in the method for producing a positive electrode for a battery according to the present invention (hereinafter simply referred to as “positive electrode”), the particle size of the positive electrode mixture-containing composition is adjusted and after the calender treatment is performed on the positive electrode mixture layer. The positive electrode active material A, which hardly changes, and the positive electrode active material B, which has a smaller particle size than the preparation stage of the positive electrode mixture-containing composition after the calendar treatment of the positive electrode mixture layer, were used. Thus, in the method of the present invention, after the positive electrode is manufactured (after the calendering of the positive electrode mixture layer), the relationship between the particle diameter of the positive electrode active material A and the particle diameter of the positive electrode active material B is determined as follows. While making it possible to adjust so that the density can be increased satisfactorily, at the time of preparing the positive electrode mixture-containing composition, the relationship between the particle diameter of the positive electrode active material A and the particle diameter of the positive electrode active material B The positive electrode active material can be adjusted so that it can be uniformly dispersed in the medium, and a positive electrode capable of constituting a high-capacity battery can be easily produced.

  The method for producing a positive electrode of the present invention includes a step of preparing a positive electrode mixture-containing composition containing at least a positive electrode active material, a conductive additive, a binder and a medium (positive electrode mixture-containing composition preparation step), and one side of a current collector Alternatively, the positive electrode mixture-containing composition is applied to both sides and dried to form a positive electrode mixture layer on the current collector (positive electrode mixture layer forming step), and the positive electrode mixture formed on the current collector And a step of performing a calendar process on the agent layer (calendar process step).

  In the positive electrode mixture-containing composition preparation step, the following positive electrode active material A and positive electrode active material B are used as the positive electrode active material.

  The positive electrode active material A has a relatively small change between the particle size at the stage of use for preparing the positive electrode mixture-containing composition and the particle size after the calendar treatment.

Specifically, when the average particle diameter of the positive electrode active material A used for the preparation of the positive electrode mixture-containing composition is d _A1 and the average particle diameter of the positive electrode active material A after the calendar treatment is d _A2 , these ratios “D _A1 / d _A2 ” is 0.8 or more, preferably 0.9 or more, and 1.2 or less, preferably 1.1 or less from the viewpoint of favorably increasing the density of the positive electrode mixture layer. .

  Further, the positive electrode active material B has a particle size smaller than that used in the preparation of the positive electrode mixture-containing composition after the calendar treatment. That is, the positive electrode active material B is located between the particles of the positive electrode active material A having a large particle diameter in the positive electrode mixture layer, filling the voids, and contributing to the improvement of the density of the positive electrode mixture layer.

Specifically, when the average particle diameter of the positive electrode active material B used for the preparation of the positive electrode mixture-containing composition is d _B1 and the average particle diameter of the positive electrode active material B after the calendar treatment is d _B2 , these ratios “D _B1 / d _B2 ” is 2.0 or more, preferably 2.5 or more, and 5.0 or less, preferably 4.0 or less. If the value of d _B1 / d _B2 is too small, the positive electrode active material B particles cannot enter between the positive electrode active material A particles in the positive electrode mixture layer, and the density of the positive electrode mixture layer is increased. There is a risk of not getting. Further, if the value of d _B1 / d _B2 is too large, the difference between the particle size of the positive electrode active material A and the particle size of the positive electrode active material B may become large during the preparation of the positive electrode mixture-containing composition. There is a possibility that the dispersion of the positive electrode active material A and the positive electrode active material B in the medium is not uniform, and the density of the positive electrode mixture layer cannot be increased satisfactorily.

In preparing the positive electrode mixture-containing composition, for the positive electrode active material A, for example, primary particles having the average particle diameter d _A1 may be used. In the case of primary particles, since the particle size be subjected to calendering to the positive electrode mixture layer is hardly changed, the choice of d _A1, can be adjusted d _{A1 /} d _A2 to the value of the. On the other hand, the positive electrode active material B used for the preparation of the positive electrode mixture-containing composition is, for example, secondary particles (aggregates of primary particles), and constitutes the average particle diameter of the secondary particles and the secondary particles. It is preferable that the ratio of the average particle diameter of the primary particles to be satisfied satisfies the above d _B1 / d _B2 . In the case of the positive electrode active material B of the secondary particles, the secondary particles collapse into the primary particles by the calendering treatment in the positive electrode mixture layer, so that the particle size after the calendering treatment is changed to the positive electrode mixture containing composition. It can be easily made smaller than the preparation step.

Further, the ratio “d _B2 / d _A2 ” between the average particle diameter d _B2 of the positive electrode active material B after the calendar process and the average particle diameter d _A2 of the positive electrode active material A after the calendar process is the density of the positive electrode mixture layer From the viewpoint of improving the thickness, it is 0.10 or more, preferably 0.2 or more, and 0.5 or less, preferably 0.4 or less.

Furthermore, the average particle diameter d _B1 of the positive electrode active material B in the stage used for preparing the positive electrode mixture-containing composition, and the average particle diameter of the positive electrode active material A in the stage used for preparing the positive electrode mixture-containing composition the ratio of d _{A1 "d} B1 _{/ d A1",} from the viewpoint of enhancing the positive electrode active dispersion of the uniformity of the material a and positive electrode active material B in the medium, preferably at least 0.7, 0.9 More preferably, it is preferably 1.3 or less, and more preferably 1.1 or less.

The average particle diameter d _A1 of the positive electrode active material A at the stage of use for preparing the positive electrode mixture-containing composition is preferably 10 to 20 μm. The average particle diameter d _B1 of the positive electrode active material B at the stage used to prepare the positive electrode mixture-containing composition is preferably 10 to 20 [mu] m.

The average particle diameter d _A1 of the positive electrode active material A and the average particle diameter d _B1 of the positive electrode active material B at the stage used for the preparation of the positive electrode mixture-containing composition referred to in this specification are a laser diffraction scattering type particle size distribution measuring device. The particle diameter (d _50% ) is _{50% as} a cumulative volume frequency measured by dispersing them in a medium in which the positive electrode active material A and the positive electrode active material B are not dissolved. Moreover, the average particle diameter d _A2 of the positive electrode active material A and the average particle diameter d _B2 of the positive electrode active material B after the calendering treatment referred to in this specification are values measured by the methods used in the examples described later.

  The ratio of the positive electrode active material A and the positive electrode active material B used for the preparation of the positive electrode mixture-containing composition is the sum of the positive electrode active material A and the positive electrode active material B from the viewpoint of favorably increasing the density of the positive electrode mixture layer. Is 100 mass%, the positive electrode active material A is preferably 50 mass% or more, more preferably 60 mass% or more, and preferably 90 mass% or less, and 80 mass%. % Or less is more preferable. In other words, when the total of the positive electrode active material A and the positive electrode active material B is 100% by mass, the positive electrode active material B is preferably 10% by mass or more, and more preferably 20% by mass or more. Moreover, it is preferable to set it as 50 mass% or less, and it is more preferable to set it as 40 mass% or less.

As the positive electrode active material A, for example, primary particles having a relatively large capacity and a large particle size can be easily obtained, and therefore, a lithium-containing composite oxide represented by the following general composition formula (1) is used. preferable.
Li _{1 + x} M ¹ O ₂ (1)
[In the general composition formula (1), −0.15 ≦ x ≦ 0.15, and M ¹ represents an element group containing Co, Mg, and Ti, and in each element constituting M ¹ When the ratios (mol%) of Co, Mg and Ti are a, b and c, respectively, b ≦ 3, c ≦ 3 and a + b + c = 100. ]

In the general composition formula (1), M ¹ is an element group including Co, Mg and Ti, and the total number of elements of the element group M ¹ , that is, the Co ratio a, the Mg ratio b, and the Ti ratio c. The total a + b + c is 100 mol%.

  In the lithium-containing composite oxide represented by the general composition formula (1), Co is a component that contributes to an increase in capacity.

  In addition, by including Mg in the lithium-containing composite oxide represented by the general composition formula (1), the structure of the lithium-containing composite oxide particles grown by promoting the growth of primary particles can be stabilized. Since the thermal stability can be improved, it is possible to obtain a positive electrode capable of constituting a lithium ion secondary battery with higher safety. In addition, when the phase transition of the lithium-containing composite oxide occurs due to the detachment and insertion of Li during battery charging / discharging, the irreversible reaction is mitigated by the rearrangement of Mg to the Li site, and the crystal structure of the lithium-containing composite oxide Therefore, a positive electrode capable of constituting a lithium ion secondary battery having a long charge / discharge cycle life can be obtained.

However, since Mg has little involvement in the charge / discharge reaction, increasing the content of the lithium-containing composite oxide may cause a decrease in capacity. Therefore, in the general formula (1) representing the lithium-containing composite oxide, the total number of elements in the element group ^{M 1} is taken as 100 mol%, it is preferable that the ratio b of Mg less 3 mol%. On the other hand, in order to better secure the above-mentioned effect by containing Mg, in the general composition formula (1) representing the lithium-containing composite oxide, the total number of elements in the element group M ¹ is set to 100 mol%. In some cases, the Mg ratio b is preferably 0.02 mol% or more.

  Further, the lithium-containing composite oxide represented by the general composition formula (1) also contains Ti. However, in the lithium-containing composite oxide, a synergistic effect is exhibited by containing Ti together with Mg. The charge / discharge cycle characteristics and stability of a battery using a positive electrode containing a lithium-containing composite oxide can be further improved, and the density of the positive electrode mixture layer in the positive electrode can be further increased. Can also be achieved.

In the general formula (1) representing the lithium-containing composite oxide, the total number of elements in the element group M ¹ is taken as 100 mol%, the ratio c of Ti, from the viewpoint of satisfactorily ensuring the effect of the, It is preferable to set it as 0.01 mol% or more, and it is more preferable to set it as 0.1 mol% or more. However, when the content of Ti increases, Ti does not participate in charging / discharging, so that the capacity may be reduced, or a heterogeneous phase such as Li ₂ TiO ₃ may be easily formed, leading to deterioration in characteristics. Therefore, in the general formula (1) representing the lithium-containing composite oxide, the total number of elements in the element group ^{M 1} is taken as 100 mol%, the ratio c of Ti is preferably set to less 3 mol%.

  The lithium-containing composite oxide represented by the general composition formula (1) has a large true density, particularly when the composition is close to the stoichiometric ratio. In this case, −0.15 ≦ x ≦ 0.15 is preferable, and the true density and reversibility can be improved by adjusting the value of x in this way.

As the positive electrode active material B, for example, primary particles having a capacity larger than that of the lithium-containing composite oxide represented by the general composition formula (1) and having a small particle size can be easily obtained. It is preferable to use the lithium-containing composite oxide represented by (2).
Li _{1 + y} M ² O ₂ (2)
[In the general composition formula (2), −0.15 ≦ y ≦ 0.15, and M ² represents a group of four or more elements including at least Ni, Co, Mn, and Mg, and M ² When the ratio (mol%) of Ni, Co, Mn, and Mg is d, e, f, and g, respectively, 50 ≦ d ≦ 97, e ≦ 49, f ≦ 49, g ≦ 3 and 3 ≦ e + f + g ≦ 50. ]

The lithium-containing composite oxide represented by the general formula (2) contains at least Ni, Co, four or more elements group M ² including Mn and Mg. Ni is a component that contributes to an increase in capacity of the thium-containing composite oxide represented by the general composition formula (2).

  In the general composition formula (2) representing the lithium-containing composite oxide, it is preferable to increase the Ni ratio in order to achieve high capacity. However, if the Ni ratio is too large, Ni becomes a Li site. When introduced, it tends to have a non-stoichiometric composition. In the lithium-containing composite oxide, the average valence of Ni varies depending on the composition. In the range represented by the general composition formula (2), for example, Ni has an average valence of 2.2 to 2.9, and divalent and trivalent coexist, but trivalent Ni is unstable. Therefore, the average valence of Ni is likely to be lowered from the original average valence of the composition, and it becomes difficult to control the oxidation number of Ni by, for example, firing in the atmosphere (for the synthesis method of the lithium-containing composite oxide) (It will be described later.) In addition, when the valence of Ni is lowered, the capacity is usually lowered or the reversibility is lost.

Standpoint Therefore, in the general formula representing the lithium-containing composite oxide (2), when the total number of elements in the element group M ² was 100 mol%, the ratio d of Ni is to improve the capacity increase of the lithium-containing composite oxide Therefore, it is preferably 50 mol% or more, and from the viewpoint of avoiding the above-mentioned problem due to the excessive Ni ratio, it is preferably 97 mol% or less.

Further, in the general formula (2) representing the lithium-containing composite oxide, the total number of elements in the element group ^{M 2} is taken as 100 mol%, the ratio e of Co as below 49 mol%, in the crystal lattice Co If present, the irreversible reaction resulting from the phase transition of the lithium-containing composite oxide due to the detachment and insertion of Li during charge / discharge of the battery can be mitigated, and the reversibility of the crystal structure of the lithium-containing composite oxide can be improved. Therefore, a battery having a long charge / discharge cycle life can be formed. In addition, in order to ensure the above-mentioned effect by containing Co more satisfactorily, when the total number of elements in the element group M is 100 mol% in the general composition formula (2) representing the lithium-containing composite oxide. In addition, the Co ratio e is preferably 1 mol% or more.

Further, in the general formula (2) representing the lithium-containing composite oxide, the total number of elements in the element group ^{M 2} is taken as 100 mol%, the fraction f of Mn as less 49 mol%, in the crystal lattice Mn Can stabilize the layered structure together with divalent Ni and improve the thermal stability of the lithium-containing composite oxide, so that a positive electrode capable of constituting a safer battery can be obtained. it can. Incidentally, the better secure the effect of the by the inclusion of Mn is in the general formula (2) representing the lithium-containing composite oxide, the total number of elements in the element group M ² was 100 mol% Sometimes, it is preferable to set the ratio f of Mn to 1 mol% or more.

  In addition, by adding Mg to the lithium-containing composite oxide represented by the general composition formula (2), the structure of the lithium-containing composite oxide particles grown by promoting the growth of primary particles can be stabilized. Since the thermal stability can be improved, a positive electrode capable of constructing a battery with higher safety can be obtained. In addition, when the phase transition of the lithium-containing composite oxide occurs due to the detachment and insertion of Li during battery charging / discharging, the irreversible reaction is mitigated by the rearrangement of Mg to the Li site and the crystal structure of the lithium-containing composite oxide Therefore, a positive electrode capable of constituting a battery having a long charge / discharge cycle life can be obtained.

However, since Mg has little involvement in the charge / discharge reaction, increasing the content of the lithium-containing composite oxide may cause a decrease in capacity. Therefore, in the general formula (2) representing the lithium-containing composite oxide, the total number of elements in the element group ^{M 2} is taken as 100 mol%, it is preferable that the ratio g of Mg less 3 mol%. On the other hand, in order to better secure the effect of the by the inclusion of Mg is, in the general formula (2) representing the lithium-containing composite oxide, the total number of elements in the element group M ² was 100 mol% Sometimes, it is preferable that the Mg ratio g is 0.02 mol% or more.

In the general composition formula (2) representing the lithium-containing composite oxide, when the total number of elements in the element group M ² is 100 mol%, the Co ratio e, the Mn ratio f, and the Mg ratio g And the total may be 3 mol% or more and 50 mol% or less.

Element group ^{M 2} in the general formula (2) representing the lithium-containing composite oxide, Ni, Co, may contain elements other than Mn and Mg, for example, Ti, Al, Cr, Fe , Cu Zn, Ge, Sn, Ca, Sr, Ba, Ag, Ta, Nb, Mo, B, P, Zr, W, and Ga may be included. However, the represented to better secure the effect of the use of lithium-containing composite oxide is in the general formula (2), when the total number of elements in the element group M ² was 100 mol%, Ni, The ratio of elements other than Co, Mn and Mg is preferably 10 mol% or less, and more preferably 3 mol% or less. Elements other than Ni, Co, Mn and Mg in the element group M ^2, which may be uniformly distributed in the lithium-containing composite oxide, also may be segregated like particles surfaces.

The lithium-containing composite oxide represented by the general composition formula (2) has a large true density of 4.55 to 4.95 g / cm ³ and is a material having a high volume energy density. Note that the true density of the lithium-containing composite oxide containing Mn in a certain range varies greatly depending on the composition, but the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. It is considered to be a large value close to the true density of LiCoO ₂ . Moreover, the capacity | capacitance per mass of lithium containing complex oxide can be enlarged, and it can be set as the material excellent in reversibility.

The lithium-containing composite oxide represented by the general composition formula (2) has a higher true density especially when the composition is close to the stoichiometric ratio. Specifically, the lithium-containing composite oxide has the general composition formula (2). In this case, −0.15 ≦ y ≦ 0.15 is preferable, and the true density and reversibility can be improved by adjusting the value of y in this way. y is more preferably −0.05 or more and 0.05 or less. In this case, the true density of the lithium-containing composite oxide can be set to a higher value of 4.6 g / cm ³ or more. .

The lithium-containing composite oxide represented by the general composition formula (1) includes a Li-containing compound (such as lithium hydroxide), a Co-containing compound (such as cobalt sulfate), a Mg-containing compound (such as magnesium sulfate), and a Ti-containing compound ( Ti oxide such as TiO ₂ ) is mixed, and this raw material mixture can be fired. In order to synthesize the lithium-containing composite oxide with higher purity, a composite compound (hydroxide, oxide, etc.) containing Co and Mg, a Li-containing compound and a Ti-containing compound are mixed, and this raw material mixture Is preferably calcined.

The lithium-containing composite oxide represented by the general composition formula (2) includes a Li-containing compound (such as lithium hydroxide), a Ni-containing compound (such as nickel sulfate), a Co-containing compound (such as cobalt sulfate), and a Mn-containing compound. A compound (manganese sulfate, etc.), a Mg-containing compound (magnesium sulfate, etc.) and a compound containing other elements contained in the element group M ² (Ti oxide such as TiO ₂ , aluminum sulfate, etc.) are mixed, and this raw material mixture Can be produced by baking. Incidentally, in synthesizing the lithium-containing composite oxide with higher purity, composite compound containing a plurality of elements included in the element group M ² (hydroxides, oxides, etc.) and a Li-containing compound is mixed, It is preferable to fire this raw material mixture.

  The firing conditions of the raw material mixture for synthesizing the lithium-containing composite oxide represented by the general composition formula (1) and the lithium-containing composite oxide represented by the general composition formula (2) are, for example, 800 to Although it can be made into 1 to 24 hours at 1050 degreeC, it preheats by once heating to the temperature (for example, 250-850 degreeC) lower than a calcination temperature, and after that, to calcination temperature It is preferable to increase the temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

In addition, in the lithium-containing composite oxide containing a large amount of Ni like the lithium-containing composite oxide represented by the general composition formula (2), an alkali component (LiOH or Li ₂ CO ₃ ) derived from the Li raw material is an impurity It tends to remain in large quantities. Since these alkali components contained in the lithium-containing composite oxide cause gas generation during high-temperature storage of the battery, a battery using a lithium-containing composite oxide containing a large amount of alkaline components as the positive electrode active material swells during high-temperature storage. Will occur.

  Therefore, the lithium-containing composite oxide represented by the general composition formula (2) is preferably used after being washed with water and dried after the firing. Thereby, the amount of alkali components in the lithium-containing composite oxide can be reduced, thereby avoiding the above-described problems. Moreover, the secondary particle | grains of lithium containing complex oxide represented by the said general composition formula (2) can be obtained by performing the said water washing.

  The conductive auxiliary agent used for the preparation of the positive electrode mixture-containing composition only needs to be chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metallic powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle, and positive electrode productivity is improved.

  As the binder used for the preparation of the positive electrode mixture-containing composition, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoro Propylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoro Ethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoro Ethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, or , Ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, and Na ion cross-linked products of these copolymers. May be used alone or in combination of two or more. Among these, PVDF, PTFE, and PHFP are preferable in consideration of the stability in the battery and the characteristics of the battery. In addition, these are used together, or a copolymer formed of these monomers is used. Also good.

  The medium used for the preparation of the positive electrode mixture-containing composition is not particularly limited, and a medium (an organic material such as NMP) used at the time of forming the positive electrode mixture layer in the positive electrode of a conventionally known lithium ion secondary battery. Solvent etc.) can be used.

  As the composition of the positive electrode mixture (all components other than the medium) used in the positive electrode mixture-containing composition, the amount of the positive electrode active material (total amount of the positive electrode active material A and the positive electrode active material B) is 80 to 99% by mass. It is preferable that the conductive auxiliary is 0.5 to 10% by mass and the binder is 0.5 to 10% by mass.

  In the positive electrode mixture-containing composition preparation step, for example, a positive electrode active material A, a positive electrode active material B, a binder, a conductive auxiliary agent, and the like are mixed to prepare a positive electrode mixture, and a medium is added to the positive electrode mixture. The mixture may be dispersed to prepare a paste-like or slurry-like positive electrode mixture-containing composition. Note that the binder may be dissolved in the medium. Alternatively, the binder may be dissolved or dispersed in the medium, and this may be added to a mixture of the positive electrode active material A, the positive electrode active material B, and the conductive additive, and further mixed to prepare a positive electrode mixture-containing composition. Good.

  In the positive electrode mixture layer forming step according to the method of the present invention, first, the positive electrode mixture-containing composition is applied to one side or both sides of a current collector. The material of the current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the battery. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. For the positive electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above-described material is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  Examples of the coating method for applying the positive electrode mixture-containing composition to the surface of the current collector include: a substrate lifting method using a doctor blade; a coater method using a die coater, comma coater, knife coater, etc .; screen printing, letterpress Printing methods such as printing can be adopted.

  After coating the positive electrode mixture-containing composition on the surface of the current collector, drying is performed according to a conventional method, and the medium is removed to form a positive electrode mixture layer.

  The current collector is preferably provided with an exposed portion that does not form the positive electrode mixture layer in order to connect to a terminal in the battery.

  In the calendering process according to the present invention method, the positive electrode material mixture layer formed on the current collector is calendered, and the pressure (linear pressure) at that time is preferably 100 kN / cm or less, It is preferably 1 kN / cm or more. By performing the calendering treatment under such conditions, the density of the positive electrode mixture layer can be increased satisfactorily by causing the secondary particles of the positive electrode active material B to collapse well and reducing the particle size.

The thickness of the positive electrode mixture layer after the calendar treatment is preferably 15 to 200 μm per one side of the current collector. Further, after the calendar treatment, the density of the electrode mixture layer is preferably 3.5 g / cm ³ or more. By using a positive electrode having such a high-density positive electrode mixture layer, the capacity of a battery using this can be increased. However, if the density of the positive electrode mixture layer is too large, the porosity is decreased, and the permeability of the non-aqueous electrolyte of the battery may be reduced. Is preferably 4.0 g / cm ³ or less.

  The density of the positive electrode mixture layer referred to in the present specification is a value measured by the method used in Examples described later.

  In addition, before or after the calendar processing step, if necessary, a lead body for connection with a terminal in the battery or the like may be attached to the exposed portion of the current collector (portion where the positive electrode mixture layer is not formed). You may attach according to.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the positive electrode may be any of the positive electrodes manufactured by the method of the present invention. There is no restriction | limiting in particular about the structure and structure employ | adopted with the lithium ion secondary battery known conventionally.

  For the negative electrode, for example, a negative electrode active material, a binder, and, if necessary, a negative electrode mixture layer comprising a negative electrode mixture containing a conductive additive can be used on one or both sides of the current collector. .

Examples of the negative electrode active material include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and metals that can be alloyed with lithium (Si , Sn, etc.) or alloys thereof, silicon oxides such as Li _3/4 Ti _5/3 O ₄ , SiO, SiO ₂ and the like. Moreover, the same thing as what was illustrated previously as what can be used in the positive electrode manufactured by this invention method can be used for a binder and a conductive support agent.

  The material of the current collector of the negative electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. For the current collector of the negative electrode, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials can be used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  The negative electrode is, for example, a negative electrode mixture-containing composition in which a negative electrode active material and a binder, and further, if necessary, a negative electrode mixture containing a conductive additive are dispersed in a medium (a binder is dissolved in the medium) May be applied to one or both sides of the current collector and dried to form a negative electrode mixture layer. The negative electrode is not limited to the one obtained by the above production method, and may be one produced by another method. The thickness of the negative electrode mixture layer is preferably 10 to 300 μm per one side of the current collector.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator is made of a thermoplastic resin having a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  As the non-aqueous electrolyte, a solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone, etc. Aprotic organic solvents, and the like, may be used these alone, or in combination of two or more of these. Also, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can be used. Among these, a mixed solvent of EC, MEC, and DEC is preferable. In this case, it is more preferable to include DEC in an amount of 15% by volume to 80% by volume with respect to the total volume of the mixed solvent. This is because such a mixed solvent can enhance the stability of the solvent during high-voltage charging while maintaining the low temperature characteristics and charge / discharge cycle characteristics of the battery high.

As the electrolyte salt related to the non-aqueous electrolyte, a salt of a fluorine-containing compound such as lithium perchlorate, lithium organic boron, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) 3, LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ [where Rf Represents a fluoroalkyl group. These may be used alone or in combination of two or more thereof. Among these, LiPF ₆ and LiBF ₄ are more preferable because of good charge / discharge characteristics. This is because these fluorine-containing organic lithium salts have a large anionic property and are easily ion-separated, so that they are easily dissolved in the solvent. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 to 1.7 mol / L.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, and fluorobenzene are used for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of the non-aqueous electrolyte. An additive such as t-butylbenzene may be added as appropriate. When the positive electrode active material (lithium-containing composite oxide) relating to the positive electrode constituting the battery contains Mn, it is particularly preferable to add an additive containing sulfur element to the non-aqueous electrolyte. Thus, the surface activity of the positive electrode active material can be stabilized.

  The lithium ion secondary battery of the present invention includes, for example, an electrode laminate obtained by laminating a positive electrode manufactured by the method of the present invention and the negative electrode with the separator interposed therebetween, and an electrode obtained by winding this in a spiral shape. A wound body is prepared, and such an electrode body and the non-aqueous electrolyte are enclosed in an exterior body according to a conventional method. As the form of the battery, similarly to the conventionally known lithium ion secondary battery, a cylindrical battery using a cylindrical (cylindrical or rectangular) outer can, or a flat shape (circular in plan view) A flat battery using a rectangular flat-shaped outer can, a soft package battery using a metal-deposited laminated film as an outer package, and the like. The outer can can be made of steel or aluminum.

  The lithium ion secondary battery of the present invention is used for power sources of various electronic devices such as portable electronic devices such as mobile phones and laptop computers, for example, power tools, automobiles, bicycles, and power storages where safety is important. It can also be applied to other uses.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

  In this example, the following measuring method was adopted.

<Average particle diameter d _A1 of positive electrode active material A and average particle diameter d _B1 of positive electrode active material B used for preparing the positive electrode mixture-containing composition>
According to the method described above, measurement was performed using “Microtrac HRA” manufactured by Nikkiso Co., Ltd.

<Average Particle Diameter d _A2 of Positive Electrode Active Material A and Average Particle Diameter d _B2 of Positive Electrode Active Material B after Calendar Treatment>
First, the positive electrode active material A and the positive electrode active material B before the preparation of the positive electrode mixture-containing composition were observed with a scanning electron microscope (SEM, “JSM-6380” manufactured by JEOL Ltd.) at a magnification of 2000 times. Next, the cross section of the positive electrode mixture layer was observed using the SEM at a magnification of 2000 times, and compared with the previously observed SEM image of the positive electrode active material A, particles having the same shape and size were observed. The positive electrode active material A was identified, a SEM image was taken of a sample of 100 particles, the diameter was measured for each particle with a JIS grade 1 metal ruler, averaged, and the positive electrode active material after calendering The average particle diameter d _A2 of the substance A was determined.

Further, the cross section of the positive electrode mixture layer was observed at a magnification of 2000 times using the above SEM, and the presence of particles having a small size compared to the SEM images of the positive electrode active material A and the positive electrode active material B observed previously. Qualitative analysis is performed by elemental mapping using an energy dispersive X-ray analyzer attached to the SEM, and the particles present at the site where C (carbon) appears are identified as the conductive assistant, and the site where Ni appears The existing particles were identified as positive electrode active material B. And the SEM image was image | photographed about the sample of 100 particle | grains of the positive electrode active material B, and it carried out similarly to the case of the positive electrode active material A, and calculated _| required the average particle diameter dB2 of the positive electrode active material B after a calendar process.

<Density of positive electrode mixture layer after calendar treatment>
The positive electrode was cut into a predetermined area, the mass was measured using an electronic balance with a minimum scale of 0.1 mg, and the mass of the electrode mixture layer was calculated by subtracting the mass of the current collector. On the other hand, the total thickness of the positive electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the positive electrode mixture layer was calculated from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. did. Then, the density of the positive electrode mixture layer was calculated by dividing the mass of the positive electrode mixture layer by the volume.

Example 1
<Positive electrode active material A>
A lithium-containing composite oxide (positive electrode active material Aa) represented by LiCo _0.94 Mg _0.03 Ti _0.03 O ₂ was used.

<Synthesis of positive electrode active material B>
Aqueous ammonia whose pH was adjusted to about 11 by addition of sodium hydroxide was placed in a reaction vessel, and while stirring vigorously, nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate were each added to 2.69 mol. / Dm ³ , 0.84 mol / dm ³ , 0.63 mol / dm ³ , 0.04 mol / dm ³ of a mixed aqueous solution and 25% by mass of ammonia water, respectively, at 23 cm ³ / min, A coprecipitation compound (spherical coprecipitation compound) of Ni, Co, Mn, and Mg was synthesized by dropping using a metering pump at a rate of 5.2 cm ³ / min. At this time, the temperature of the reaction solution is maintained at 50 ° C., and an aqueous sodium hydroxide solution having a concentration of 3.0 mol / dm ³ is dropped so that the pH of the reaction solution is maintained at around 11. Further, nitrogen gas was bubbled at a flow rate of 0.3 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co, Mn and Mg in a molar ratio of 64: 20: 15: 1. 2 mol of this hydroxide and 2 mol of LiOH.H ₂ O were uniformly mixed for 40 minutes with a high-speed stirring mixer to obtain a mixture. Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The lithium-containing composite oxide as the positive electrode active material B was synthesized by firing for a period of time. The obtained lithium-containing composite oxide was sieved with 200 mesh and stored in a desiccator.

When the composition of the lithium-containing composite oxide powder was measured with an ICP emission analyzer, a composition represented by LiNi _0.64 Co _0.2 Mn _0.15 Mg _0.01 O ₂ [the general composition formula In (2), it was found that y = 0, d = 64 mol%, e = 20 mol%, f = 15 mol%, g = 1 mol%, and e + f + g = 36 mol%]. This was designated as a positive electrode active material Ba.

<Preparation of positive electrode>
Positive electrode active material Aa: 70 parts by mass, positive electrode active material Ba: 30 parts by mass, 100 parts by mass of a mixture, 20 parts by mass of an NMP solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite and 1 part by mass of ketjen black, which are agents, were kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  The positive electrode mixture-containing paste is applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode mixture layer on both sides of the aluminum foil. Formed. Thereafter, calendering is performed at a linear pressure of 70 kN / cm, the thickness and density of the positive electrode mixture layer are adjusted, a nickel lead body is welded to the exposed portion of the aluminum foil, and a strip shape having a length of 375 mm and a width of 43 mm is obtained. A positive electrode was prepared.

<Production of negative electrode>
To 97.5 parts by mass of natural graphite having a number average particle size of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener, Were added and mixed to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was applied to both sides of a copper foil having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form negative electrode mixture layers on both sides of the copper foil. Thereafter, calendering was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead was welded to the exposed portion of the copper foil to produce a strip-shaped negative electrode having a length of 380 mm and a width of 44 mm. The negative electrode mixture layer in the obtained negative electrode had a thickness of 65 μm on one side.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent having a volume ratio of EC: MEC: DEC of 2: 3: 1 to prepare a non-aqueous electrolyte.

<Battery assembly>
The belt-like positive electrode is stacked on the belt-like negative electrode through a microporous polyethylene separator (porosity: 41%) having a thickness of 16 μm, wound in a spiral shape, and then pressed so as to be flat. An electrode winding body having a flat winding structure was formed, and the electrode winding body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having an outer dimension of 4.0 mm in thickness, 34 mm in width, and 50 mm in height to weld the lead body, and a lid made of aluminum alloy The plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte is injected from the inlet provided on the cover plate, and left for 1 hour, and then the inlet is sealed, and the lithium ion secondary having the structure shown in FIG. 1 and the appearance shown in FIG. A battery was obtained. In addition, the design electric capacity of the said lithium ion secondary battery was 1000 mAh.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 and then pressed into a flat shape to form a flat electrode winding body 6 in a rectangular (square tube) battery case 4 together with a non-aqueous electrolyte. Contained. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. An insulator 5 made of a polyethylene sheet is arranged at the bottom of the battery case 4, and is connected to one end of each of the positive electrode 1 and the negative electrode 2 from the flat electrode winding body 6 made of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the battery case 4 and the cover plate 9 function as positive terminals by directly welding the positive electrode lead body 7 to the cover plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
All except that Ab shown in Table 1 was used as the positive electrode active material A and Bb shown in Table 2 was synthesized as the positive electrode active material B by adjusting the molar concentration of nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate. A positive electrode was produced in the same manner as in Example 1. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Example 3
All except for using Ac shown in Table 1 as the positive electrode active material A and Bc shown in Table 2 synthesized as the positive electrode active material B by adjusting the molar concentration of nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate. A positive electrode was produced in the same manner as in Example 1. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Example 4
All except that Ad shown in Table 1 was used as the positive electrode active material A and Bd shown in Table 2 was synthesized as the positive electrode active material B by adjusting the molar concentrations of nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate. A positive electrode was produced in the same manner as in Example 1. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Example 5
All except that Ae shown in Table 1 was used as the positive electrode active material A and Be shown in Table 2 was synthesized as the positive electrode active material B by adjusting the molar concentration of nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate. A positive electrode was produced in the same manner as in Example 1. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Example 6
A positive electrode was produced in the same manner as in Example 1 except that Af shown in Table 1 was used as the positive electrode active material A and Be shown in Table 2 was used as the positive electrode active material B. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Example 7
Ad shown in Table 1 as the positive electrode active material A and Bf shown in Table 2 were synthesized as the positive electrode active material B by adjusting the molar concentrations of nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate, and LiOH.H ₂ O. A positive electrode was produced in the same manner as in Example 1 except that was used. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that Ag shown in Table 1 was used as the positive electrode active material A and Ba shown in Table 2 was used as the positive electrode active material B. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 2
A positive electrode was produced in the same manner as in Example 1 except that Ah shown in Table 1 was used as the positive electrode active material A and Ba shown in Table 2 was used as the positive electrode active material B. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 3
Aa shown in Table 1 as the positive electrode active material A and Bg shown in Table 2 synthesized as the positive electrode active material B by adjusting the molar concentrations of nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate and LiOH.H ₂ O. A positive electrode was produced in the same manner as in Example 1 except that was used. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 4
Ah shown in Table 1 as the positive electrode active material A and Bh shown in Table 2 were synthesized as the positive electrode active material B by adjusting the molar concentrations of nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate and LiOH.H ₂ O. A positive electrode was produced in the same manner as in Example 1 except that was used. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 5
Bi shown in Table 2 was synthesized by adjusting Ab as shown in Table 1 as the positive electrode active material A and adjusting the molar concentration of nickel sulfate, cobalt sulfate, manganese sulfate, magnesium sulfate and LiOH.H ₂ O as the positive electrode active material B. A positive electrode was produced in the same manner as in Example 1 except that was used. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 6
A positive electrode was produced in the same manner as in Example 1 except that Ab shown in Table 1 was used as the positive electrode active material A and Bg shown in Table 2 was used as the positive electrode active material B. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 7
A positive electrode was produced in the same manner as in Example 1 except that Ah shown in Table 1 was used as the positive electrode active material A and Bg shown in Table 2 was used as the positive electrode active material B. And the lithium ion secondary battery was produced like Example 1 except having used the said positive electrode.

Table 1 shows the composition of the positive electrode active material A (positive electrode active materials Aa to Ah) used in the batteries of Examples and Comparative Examples, and Table 2 shows the composition of the positive electrode active material B (positive electrode active materials Ba to Bi). Further, Table 3 shows positive electrode active material A and positive electrode active material B, d _A1 , d _A2 , d _B1 , d _B2 , d _A1 / d _A2 , d _B1 / d used in the batteries of the examples and comparative examples. _B2 , _dB2 / _dA2 , and _dB1 / _dA1 are shown.

  Moreover, each evaluation below was performed about the lithium ion secondary battery of each Example and the comparative example. Table 4 shows the results and the density of the positive electrode mixture layer relating to the positive electrode used in each battery.

<Discharge capacity measurement>
Each battery of the example and the comparative example was stored at 60 ° C. for 7 hours, and then the discharge capacity was measured at 20 ° C. Charging was performed at a constant current of 200 mA. After the charging voltage reached 4.2 V, the charging was performed at a constant voltage until the current became 1/10. Next, discharging was performed at a constant current of 200 mA until the battery voltage reached 2.5 V, and the capacity at this time was defined as the discharge capacity of the battery. In addition, discharge capacity measured about 100 batteries with each battery, and the average value was made into the discharge capacity of each Example and a comparative example.

<Charge / discharge cycle test>
The charge / discharge cycle test was performed as follows for each of the batteries of the examples and comparative examples (after the discharge capacity measurement). Charging was performed at a constant current of 1000 mA, and after the battery voltage reached 4.2 V, the battery was charged for a total of 3 hours by a method of maintaining the constant voltage. Next, the battery was discharged at a constant current of 1000 mA until the battery voltage dropped to 3V. The charge / discharge cycle was repeated 500 cycles. The capacity retention rate at the 500th cycle was calculated by the following formula.
Capacity maintenance rate (%)
= 100 × (500th cycle discharge capacity / 1st cycle discharge capacity)

  It can be said that the larger the capacity retention rate, the better the charge / discharge cycle characteristics of the battery. In addition, the charge / discharge cycle test was performed on 10 batteries for each battery, and the average value of the capacity maintenance rates was defined as the capacity maintenance rates of the examples and comparative examples.

As is clear from Table 4, the positive electrode according to the battery of the example using the positive electrode active material in which d _A1 / d _A2 , d _B1 / d _B2 and d _B2 / d _A2 are suitable is calendered at the same linear pressure. However, the density of the positive electrode mixture layer is increased, the capacity of the lithium ion secondary battery is large, and the charge / discharge cycle characteristics are also good.

In contrast, the positive electrode according to the comparative battery using the positive electrode active material in which one or more values of d _A1 / d _A2 , d _B1 / d _B2, and d _B2 / d _A2 deviate from the preferred values The density of the agent layer is lower than that of the positive electrode according to the battery of the example, and the capacity of the lithium ion secondary battery is also low. Furthermore, the lithium ion secondary battery of the comparative example is inferior to the battery of an Example also in charging / discharging cycling characteristics.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (5)

A step of preparing a positive electrode mixture-containing composition comprising at least a positive electrode active material A, a positive electrode active material B, a conductive additive, a binder, and a medium;
Applying the positive electrode mixture-containing composition to one or both sides of the current collector and drying to form a positive electrode mixture layer on the current collector;
And a step of calendering the positive electrode mixture layer formed on the current collector,
The positive electrode active material A is a general composition formula Li _{1 + x} M ¹ O ₂ [wherein −0.15 ≦ x ≦ 0.15, and M ¹ represents an element group containing only Co, Mg, and Ti, In each element constituting M ¹ , when the ratios (mol%) of Co, Mg and Ti are a, b and c, respectively, 0.02 ≦ b ≦ 3, 0.01 ≦ c ≦ 3 and a + b + c = 100], the average particle size d _A1 at the stage of use in the preparation of the positive electrode mixture-containing composition, and the average particle size d _A2 after the calendar treatment, The ratio (d _A1 / d _A2 ) is 0.8 to 1.2,
The positive electrode active material B is a general composition formula Li _{1 + y} M ² O ₂ [wherein −0.15 ≦ y ≦ 0.15, and M ² is at least four kinds including at least Ni, Co, Mn, and Mg. 50 ≦ d ≦ 97, where the ratio (mol%) of Ni, Co, Mn and Mg in each element constituting M ² is d, e, f and g, respectively. 1 ≦ e ≦ 49, 1 ≦ f ≦ 49, 0.02 ≦ g ≦ 3, and 3 ≦ e + f + g ≦ 50], for preparing a positive electrode mixture-containing composition The ratio (d _B1 / d _B2 ) between the average particle diameter d _B1 at the stage of use and the average particle diameter d _B2 after the calendar treatment is 2.0 to 5.0,
A positive electrode manufacturing method for a battery, wherein the ratio of the _{d A2} and the _{d B2 (d B2 / d A2} ) is from 0.10 to 0.5. 2. The method for producing a battery positive electrode according to claim 1, wherein a ratio of d _B1 to d _A1 (d _B1 / d _A1 ) is 0.7 to 1.3. The method for producing a positive electrode for a battery according to claim 1 or 2 , wherein the pressure of the calendar treatment is 100 kN / cm or less. A method for producing a lithium ion secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator,
The positive electrode manufacturing process comprises:
A step of preparing a positive electrode mixture-containing composition comprising at least a positive electrode active material A, a positive electrode active material B, a conductive additive, a binder, and a medium;
Applying the positive electrode mixture-containing composition to one or both sides of the current collector and drying to form a positive electrode mixture layer on the current collector;
And a step of calendering the positive electrode mixture layer formed on the current collector,
The positive electrode active material A has a general composition formula Li _{1 + x} M ¹ O ₂ [wherein −0.15 ≦ x ≦ 0.15, and M ¹ represents an element group containing only Co, Mg, and Ti. , M ¹ , where the ratio (mol%) of Co, Mg, and Ti is a, b, and c, respectively, 0.02 ≦ b ≦ 3, 0.01 ≦ c ≦ 3 And a + b + c = 100], and an average particle size d _A1 at the stage of use in the preparation of the positive electrode mixture-containing composition and an average particle size d _A2 after the calendar treatment. The ratio (d _A1 / d _A2 ) to 0.8 to 1.2,
The positive electrode active material B is a general composition formula Li _{1 + y} M ² O ₂ [wherein −0.15 ≦ y ≦ 0.15, and M ² includes at least four types including Ni, Co, Mn, and Mg. When the ratio (mol%) of Ni, Co, Mn, and Mg is d, e, f, and g in each element that represents the above element group and constitutes M ² , 50 ≦ d ≦ 97 1 ≦ e ≦ 49, 1 ≦ f ≦ 49, 0.02 ≦ g ≦ 3, and 3 ≦ e + f + g ≦ 50], and a preparation of a positive electrode mixture-containing composition The ratio (d _B1 / d _B2 ) between the average particle size d _B1 at the stage of use to the average particle size d _B2 after the calendar treatment is 2.0 to 5.0,
Method for manufacturing a lithium ion secondary battery, wherein the ratio of the _{d A2} and the _{d B2 (d B2 / d A2} ) is from 0.10 to 0.5. d _B1 And d _A1 Ratio (d _B1 / D _A1 ) Is 0.7 to 1.3. The method for producing a lithium ion secondary battery according to claim 4.