JP5072248B2 - Non-aqueous secondary battery and method of using the same - Google Patents

Description

  The present invention relates to a non-aqueous secondary battery and a method for using the same.

  2. Description of the Related Art In recent years, secondary batteries have become one of the essential components that are indispensable as power sources for personal computers and mobile phones, and as power sources for electric vehicles and power storage.

  In particular, in mobile communication applications such as portable computers and personal digital assistants, further miniaturization and weight reduction are required. However, it is difficult to make the system compact and lightweight because the power consumed by the backlight and drawing control of the liquid crystal display panel is high and the capacity of the secondary battery is still insufficient. . Particularly in personal computers, power consumption tends to increase due to multi-functionalization due to DVD (digital versatile disk) mounting. Therefore, there is an urgent need to increase the power capacity, particularly the discharge capacity when the voltage of the unit cell is 3.3 V or higher.

  Furthermore, with the growing global environmental problems, electric vehicles that emit no exhaust gas or noise are attracting attention. Recently, parallel hybrid electric vehicles (HEVs) have been gaining popularity because they use a system in which regenerative energy at the time of braking is stored in a battery for effective use, or electric energy stored in the battery is used at the start to increase efficiency. ing. However, because the current battery has a low power capacity, it is necessary to increase the number of batteries to increase the voltage, which causes problems such as a narrow space in the vehicle and poor vehicle stability. ing.

Among secondary batteries, a lithium secondary battery using a non-aqueous electrolyte is attracting attention because of its high voltage, light weight, and high energy density. In particular, a lithium secondary battery using a lithium-containing transition metal oxide typified by LiCoO ₂ disclosed in Patent Document 1 as a positive electrode active material and metal lithium as a negative electrode active material has an electromotive force of 4 V or more. Therefore, high energy density can be expected.

JP-A-55-136131

  By the way, in order to achieve higher capacity of the battery, it is effective to increase the filling amount of the active material in the positive and negative electrodes in addition to the improvement of the active material. For example, in a normal non-aqueous secondary battery, a positive electrode mixture layer containing a positive electrode active material, a conductive auxiliary agent, a binder and the like is formed on the surface of a conductive substrate (metal foil or the like) serving as a current collector. In this positive electrode, it is conceivable to increase the density of the positive electrode mixture layer in order to improve the filling amount of the active material.

However, in the positive electrode using LiCoO ₂ as the positive electrode active material, when the density of the positive electrode mixture layer is increased, the load characteristics of the battery are degraded.

In order to increase the power capacity of the battery, it can be considered that the battery is used in a higher voltage region. For example, in a conventional LiCoO ₂ positive electrode active material battery, if the discharge end voltage is higher than 3.2 V, the discharge end stage is reached. Since the potential drop at is large, complete discharge cannot be performed, and the discharge electricity quantity efficiency with respect to charging is significantly reduced. And since complete discharge cannot be performed, the crystal structure of LiCoO ₂ tends to collapse, and the charge / discharge cycle life is shortened. This phenomenon appears more prominently in the above high voltage region.

  Furthermore, under the charging conditions where the final voltage at full charge is 4.2 V or higher, in addition to the decrease in charge / discharge cycle life and thermal stability due to the collapse of the crystal structure of the positive electrode active material, the active point of the positive electrode active material Due to the increase, the electrolytic solution (solvent) may be oxidatively decomposed to form a passive film on the surface of the positive electrode, resulting in an increase in internal resistance and poor load characteristics.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous secondary battery having high voltage, high capacity, and excellent load characteristics, and a method of using the same.

The nonaqueous secondary battery of the present invention that has achieved the above object is a nonaqueous secondary battery comprising a positive electrode having a positive electrode mixture layer containing lithium cobalt oxide as an active material, a negative electrode, and a nonaqueous electrolyte. The lithium cobalt oxide contains at least a part of Co substituted with another metal element, and when the positive electrode is subjected to XRD (X-ray diffraction spectroscopy) analysis. The ratio I ₀₀₆ / I ₁₀₁ of the peak intensity I ₀₀₆ of the (006) plane to the peak intensity I ₁₀₁ of the (101) plane is 0.6-3.

  Further, in using the non-aqueous secondary battery of the present invention, the non-aqueous secondary battery is charged so that the positive electrode potential at full charge is 4.35 to 4.6 V at the Li reference potential. Are also included in the present invention.

  For example, in the above usage method, when the non-aqueous secondary battery of the present invention has a graphite negative electrode (a negative electrode containing graphite as a negative electrode active material) having a Li reference potential of 0.1 V when fully charged, the battery voltage is Charging at 4.45V or higher is considered to be charging at which the positive electrode potential is substantially 4.35V or higher.

  In the method of using the non-aqueous secondary battery according to the present invention, the “full charge” is a constant current charge at a current value of 0.2 C up to a predetermined voltage, and then at the predetermined voltage. It refers to charging under conditions where constant voltage charging is performed and the total time of the constant current charging and the constant voltage charging is 8 hours.

  According to the present invention, it is possible to provide a non-aqueous secondary battery having high voltage, high capacity, and excellent load characteristics.

  Moreover, according to the usage method of this invention, the non-aqueous secondary battery of this invention is applicable to the use for which a higher output is requested | required.

As described above, in the positive electrode using LiCoO ₂ as the positive electrode active material, when the density of the positive electrode mixture layer is increased to achieve high capacity, the load characteristics of the battery are impaired. Since the present inventors have increased the crystal orientation of LiCoO ₂ so as to cause a decrease in the Li ion diffusion rate as the density of the positive electrode mixture layer is increased, such a decrease in load characteristics is observed. I found

Then, when an XRD (X-ray diffraction) analysis of the positive electrode, is in the (101) ratio _I 006 _{/ I 101} of the peak intensity _{I 006} of (006) plane to the peak intensity _{I 101} of the surface is 0.6 to 3 In some cases, the positive electrode active material crystal is oriented so that the diffusion rate of Li ions decreases, and the load characteristics of the battery are improved, while the density of the positive electrode mixture layer is increased, that is, the capacity of the battery is increased. I found out that I can do it.

Further, by using at least a part of the lithium cobalt oxide as the positive electrode active material in which a part of Co is substituted with another metal element, the above-mentioned I ₀₀₆ can be _achieved even if the density of the positive electrode mixture layer is increased. / I ₁₀₁ can be controlled to 0.6 or more and 3 or less, and furthermore, by using such a positive electrode active material, it has been found that its stability can be improved and it can be used in a higher voltage region. It was.

  Based on the above findings, the present inventors have completed the present invention. Hereinafter, the present invention will be described in detail.

The non-aqueous secondary battery of the present invention contains lithium cobalt oxide as a positive electrode active material. When the XRD analysis is performed on the positive electrode, the (006) plane of the (101) plane with respect to the peak intensity I _{101 is} measured. The ratio I ₀₀₆ / I _{101 of the} peak intensity I ₀₀₆ is 0.6 or more and 3 or less.

The (006) plane corresponds to a portion (crystal layer) where Li ions enter and exit in a lithium cobalt oxide crystal that is a positive electrode active material contained in the positive electrode mixture layer. The ratio I ₀₀₆ / I ₁₀₁ between the peak intensity I ₁₀₁ on the ( ₁₀₁ ) plane and the peak intensity I ₀₀₆ on the (006) plane in the XRD curve obtained by XRD analysis can allow Li ions to enter and exit the lithium cobalt oxide crystal. It becomes an index of the orientation between the layers and the surface of the positive electrode.

That is, a large I ₀₀₆ / I ₁₀₁ value means that the layer in which lithium ions can enter and exit in the lithium cobalt oxide crystal is oriented more parallel to the surface of the positive electrode. Therefore, in this case, Li ions hardly enter and exit the lithium cobalt oxide crystal, so that the diffusion rate of Li ions decreases, and the load characteristics are impaired in a battery using such a positive electrode. For example, when only LiCoO ₂ is used as the positive electrode active material, when the density of the positive electrode mixture layer is increased, the value of I ₀₀₆ / I ₁₀₁ in the positive electrode increases rapidly.

Therefore, in the present invention, the I ₀₀₆ / I ₁₀₁ value is controlled to a low value of 0.6 or more and 3 or less while increasing the density of the positive electrode mixture layer in order to achieve a higher capacity of the battery, and the diffusion rate of Li In order to improve the load characteristics of the battery while maintaining high, use is made of at least a part of the lithium cobalt oxide that is the positive electrode active material in which a part of Co is substituted with another metal element. That is, if lithium cobalt oxide in which a part of Co is substituted with another metal element, the I ₀₀₆ / I ₁₀₁ value can be controlled to a low value even if the density of the positive electrode mixture layer is increased. The load characteristics can be maintained with the increase in capacity.

  In addition, lithium cobalt oxide in which a part of Co is substituted with another metal element is more stable than lithium cobalt oxide that does not have a metal element that substitutes Co (especially stability under high voltage). ) And is unlikely to break down. Therefore, by using this as a positive electrode active material, the battery can be used in a high voltage region.

In addition, in the lithium cobalt oxide crystal, the crystal plane showing the portion where Li ions can enter and exit is, for example, the (003) plane in addition to the (006) plane. In the present invention, the (006) plane is adopted. The reason is as follows. In the XRD curve, the diffraction peak of the (006) plane appears at a position close to the diffraction peak of the (101) plane [the peak position of the (006) plane is 2θ = 3 8 . 4 °, the peak position of the (101) plane is 2θ = 3 7 . This is because the accuracy of the ratio of the peak intensity to the peak intensity of the (101) plane is higher than that of the (003) plane where the peak is at a position farther from the peak position of the (101) plane.

The I ₀₀₆ / I ₁₀₁ value is 3 or less, preferably 2 or less. If the value of I ₀₀₆ / I ₁₀₁ is too large, the lithium cobalt oxide that is the positive electrode active material will be oriented too much so as to reduce the diffusion rate of Li, and the load characteristics (and thermal stability) of the battery will be impaired. It is.

Further, the I ₀₀₆ / I ₁₀₁ value is 0.6 or more, and preferably 0.7 or more. From the standpoint of ensuring the load characteristics and thermal stability of the battery, the I ₀₀₆ / I ₁₀₁ value should be low. However, if it is too low, the density of the positive electrode mixture layer will be reduced, and the capacity of the battery will be increased. Cannot be achieved.

In order to control the I ₀₀₆ / I ₁₀₁ value to the specific value, lithium cobalt oxide in which a part of Co is substituted with another metal element may be used as at least a part of the positive electrode active material. Such a lithium cobalt oxide and lithium cobalt oxide (LiCoO ₂ ) having no substitution metal element may be used in combination, or all of the positive electrode active material may be partially substituted with other metal elements. Lithium cobalt oxide may also be used.

In the case where a lithium cobalt oxide in which a part of Co is substituted with another metal element and a lithium cobalt oxide (LiCoO ₂ ) having no substitution metal element are used in combination, for example, a part of Co is It is desirable that the lithium cobalt oxide substituted with another metal element is 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more in the total positive electrode active material.

The density of the positive electrode mixture layer of the positive electrode according to the present invention, for example, 3.5 g / cm ³ or more, more preferably 3.6 g / cm ³ or more, more preferably it is preferred to 3.8 g / cm ³ or more . As a result, the capacity of the battery can be increased, and even if the positive electrode mixture layer has a high density as described above, a reduction in load characteristics of the battery due to the orientation of the positive electrode active material can be suppressed. However, if the density of the positive electrode mixture layer is too high, the wettability of the non-aqueous electrolyte (described later) is lowered. Therefore, the density is preferably 4.6 g / cm ³ or less, for example, 4.4 g. / Cm ³ or less is more preferable, and 4.2 g / cm ³ or less is still more preferable.

  In addition, the density of the positive mix layer as used in this specification is a value calculated | required with the following measuring methods. The positive electrode is cut out in a predetermined area, the weight thereof is measured using an electronic balance having a minimum scale of 1 mg, and the weight of the positive electrode mixture layer is calculated by subtracting the weight of the current collector from this weight. Further, 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 and the area obtained by subtracting the thickness of the current collector from this thickness. The density of the positive electrode mixture layer is calculated by dividing the weight of the positive electrode mixture layer.

  In order to form a high-density positive electrode mixture layer as described above, it is preferable that the lithium cobalt oxide as the positive electrode active material contains two or more types having different average particle diameters. By using lithium cobalt oxide having a large average particle size and lithium cobalt oxide having a small average particle size in combination, in the positive electrode mixture layer, a small particle size is formed in the gap between the lithium cobalt oxides having a large particle size. Since the lithium cobalt oxide can be filled, it is easier to increase the density of the positive electrode mixture layer and achieve a higher capacity.

The “average particle size” of lithium cobalt oxide as used in the present specification refers to the case where the integral volume is obtained from particles having a small particle size distribution measured using a microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd. The value of 50% diameter (d ₅₀ ) and median diameter in the volume-based integrated fraction.

The “two or more lithium cobalt oxides having different average particle diameters” relating to the positive electrode have three or more inflection points, preferably four or more, in the particle size distribution curve of these mixtures. In this particle size distribution curve, two or more peaks may be present, or a distribution in which a shoulder is seen in one or more peaks may be used. In the case of such a particle size distribution curve, a general peak separation method is used to divide the particle size distribution into a large particle size distribution and a small particle size distribution. each average particle diameter of the lithium cobalt oxide and (d _50), it is possible to obtain the mixing ratio.

  Among lithium cobalt oxides used for the positive electrode, those having the largest average particle diameter [hereinafter referred to as “positive electrode active material (A)”] having an average particle diameter A and those having the smallest average particle diameter [hereinafter “ When the average particle size of the “positive electrode active material (B)” is B, the ratio B / A to B is preferably 0.15 or more and 0.6 or less. When the ratio between the average particle diameter of the positive electrode active material (A) having the maximum average particle diameter and the average particle diameter of the positive electrode active material (B) having the minimum average particle diameter is such a value, The density of the positive electrode mixture layer can be increased more easily.

  In addition, about a positive electrode active material (A), it is preferable that the average particle diameter is 5 micrometers or more, for example, it is more preferable that it is 8 micrometers or more, and it is still more preferable that it is 11 micrometers or more. If the average particle size of the positive electrode active material (A) is too small, it may be difficult to increase the density of the positive electrode mixture layer. On the other hand, if the average particle size of the positive electrode active material (A) is too large, the battery characteristics tend to deteriorate. For example, the average particle size is preferably 25 μm or less, and preferably 20 μm or less. More preferably, it is 18 μm or less.

  Moreover, about the positive electrode active material (B), it is preferable that the average particle diameter is 10 micrometers or less, for example, it is more preferable that it is 7 micrometers or less, and it is still more preferable that it is 5 micrometers or less. If the average particle diameter of the positive electrode active material (B) is too large, it becomes difficult to fill the gap between the lithium cobalt oxide particles having a large particle diameter in the positive electrode mixture layer with the positive electrode active material (B). It may be difficult to increase the density of the layer. On the other hand, if the average particle size of the positive electrode active material (B) is too small, even if it is too small, the void volume between small particles tends to increase, and thus the density tends to be difficult to increase. Therefore, the average particle diameter of the positive electrode active material (B) is, for example, preferably 2 μm or more, more preferably 3 μm or more, and further preferably 4 μm or more.

  The positive electrode active material according to the present invention may be only two types of lithium cobalt oxides having different average particle diameters as in the case of only the positive electrode active material (A) and the positive electrode active material (B). Three or more (for example, three, four, five, etc.) lithium cobalt oxides having different average particle diameters may be used. When three or more types of lithium cobalt oxides having different average particle sizes are used, for example, the average particle size is between the average particle size of the positive electrode active material (A) and the average particle size of the positive electrode active material (B). A certain lithium cobalt oxide may be used together with the positive electrode active materials (A) and (B).

  Of the lithium cobalt oxide of the positive electrode, the content of the positive electrode active material (B) having the smallest average particle diameter is, for example, preferably 5% by mass or more, more preferably 10% by mass or more, More preferably, it is 20 mass% or more. When the positive electrode active material (B) is contained in the above amount, the gap between the lithium cobalt oxide particles having a large particle diameter can be easily filled, and the density of the positive electrode mixture layer can be easily increased. On the other hand, if the content of the positive electrode active material (B) in the lithium cobalt oxide of the positive electrode is too large, it is difficult to increase the density of the positive electrode mixture layer. Therefore, the content is, for example, 60% by mass or less. Preferably, it is 50% by mass or less, and more preferably 40% by mass or less.

  Therefore, for example, when the lithium cobalt oxide of the positive electrode is only the positive electrode active material (A) and the positive electrode active material (B), the inclusion of the positive electrode active material (A) in the total lithium cobalt oxide The amount is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and 95% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less. Is desirable.

  In addition, among the lithium cobalt oxides that the positive electrode has, the positive electrode active material (B) has, for example, the above average particle diameter, but the lithium cobalt oxide with such a small particle diameter has a high voltage, for example. In the charged state, the stability is poor, and the reliability such as the safety and storage characteristics of the battery is impaired.

  Therefore, in the battery of the present invention, when two or more lithium cobalt oxides having different average particle diameters are used as the positive electrode active material, at least a positive electrode active material (lithium cobalt oxide having a minimum average particle diameter) ( B) is preferably a lithium cobalt oxide in which a part of Co is substituted with another metal element. As described above, the lithium cobalt oxide in which a part of Co is substituted with another metal element has improved stability (particularly, stability in a charged state at a high voltage). Therefore, since collapse in the high voltage region is suppressed, battery characteristics (for example, charge / discharge cycle characteristics) can be improved, and reliability such as battery safety and storage characteristics can be improved. .

  In addition, in the positive electrode active material according to the positive electrode, it can be confirmed by the following method that the lithium cobalt oxide having at least the minimum average particle diameter is one in which a part of Co is substituted with another metal element. . The particle size distribution curve of the positive electrode active material related to the positive electrode is obtained, and when the above-described peak separation is performed on the peak and the like existing in the curve, the particles belonging to the peak of the smallest particle size are, for example, electrons It is confirmed that a metal element other than Li and Co is contained by means of a line micro part analyzer (EPMA) or ICP.

  When two or more types of lithium cobalt oxides having different average particle diameters are used as the positive electrode active material, the positive electrode active material (B) having the smallest average particle diameter is replaced with a part of Co by another metal element. The lithium cobalt oxide is preferably a lithium cobalt oxide other than the positive electrode active material (B) [the positive electrode active material (A) having the largest average particle diameter, etc.], but a part of Co is also other More preferably, it is a lithium cobalt oxide substituted with a metal element. When a part of Co in the lithium cobalt oxide other than the positive electrode active material (B) is substituted with another metal element, the stability (particularly the stability in a charged state at a high voltage) is improved. Therefore, for example, reliability such as charge / discharge cycle characteristics, safety, and storage characteristics of the battery can be further improved.

  In the above-described lithium cobalt oxide in which a part of Co is substituted with another metal element, examples of the metal element that substitutes a part of Co include Mg, Ti, Zr, Ge, Nb, and Al. And at least one metal element selected from the group consisting of Sn. This is because these metal elements have an excellent effect of increasing the stability of the lithium cobalt oxide.

Among the positive electrode active materials, the lithium cobalt oxide in which a part of Co is substituted with another metal element is preferably a lithium cobalt oxide represented by the following general formula (1).
Li _x Co _y M ¹ _z M ² _v O ₂ (1)

Here, in the general formula (1), M ¹ is at least one metal element selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al, and Sn, and M ² is Li, Co. and an element other than ^{M 1,} is 0.97 ≦ x <1.02,0.8 ≦ y < 1.02,0.002 ≦ z ≦ 0.05,0 ≦ v ≦ 0.05. Note that z is more preferably 0.004 or more, further preferably 0.006 or more, more preferably less than 0.02, and still more preferably less than 0.01. This is because if z is too small, the effect of improving the charge / discharge cycle characteristics and safety of the battery is not sufficient, and if it is too large, the electrical characteristics of the battery begin to deteriorate.

  When two or more types of lithium cobalt oxides having different average particle sizes are used as the positive electrode active material, the positive electrode active material (B) having the minimum average particle size is represented by the lithium represented by the general formula (1). Cobalt oxide is preferred.

Moreover, when using 2 or more types of lithium cobalt oxides from which an average particle diameter differs as a positive electrode active material, as lithium cobalt oxide [a positive electrode active material (A) is included] other than a positive electrode active material (B), it is as follows. The lithium cobalt oxide represented by the general formula (2) is preferable.
^{_{Li a Co b M 1 c M}} 2 d O 2 (2)

Here, in the general formula (2), M ¹ and M ² are the same as those in the general formula (1), and 0.97 ≦ a <1.02, 0.8 ≦ b <1.02, 0 ≦ c ≦ 0.02 and 0 ≦ d ≦ 0.02. M ¹ and M ² are selected from the same elements as in the general formula (1). However, the element types and the constituent ratios to be selected may be different for each active material having a different average particle diameter. For example, in the positive electrode active material (B), M ¹ may be Mg, Ti, and Al, while in the positive electrode active material (A), M ¹ may be a combination of Mg and Ti. However, as also shown in this example, it is preferable that the common element is at least one among the M ^1, the common elements in the M ¹ is more preferably 2 or more, is 3 or more More preferably.

In the case of the positive electrode active material (A), c is more preferably 0.0002 or more, further preferably 0.001 or more, more preferably less than 0.005, still more preferably less than 0.0025. . In the case of the positive electrode active material (A), d is more preferably 0.0002 or more, further preferably 0.001 or more, more preferably less than 0.005, still more preferably less than 0.0025. . Since the positive electrode active material (A) has a large particle size, an effect can be obtained even if the addition amount of M ¹ or the like is smaller. However, if the amount is too small, the effect on the charge / discharge cycle characteristics and safety of the battery is small. This is because if the amount is too large, the electric characteristics of the battery tend to deteriorate.

  X in the general formula (1) and a in the general formula (2) vary depending on the charge / discharge of the battery, but are preferably 0.97 or more and less than 1.02 when the battery is manufactured. x and a are more preferably 0.98 or more, further preferably 0.99 or more, more preferably 1.01 or less, and further preferably 1.00 or less.

  Y in the general formula (1) and b in the general formula (2) are preferably 0.8 or more, more preferably 0.98 or more, and still more preferably 0.99 or more. It is less than 02, more preferably less than 1.01, and still more preferably less than 1.0.

In the lithium cobalt oxide other than the positive electrode active material (B) represented by the general formula (1) and the positive electrode active material (B) represented by the general formula (2), the safety improvement of the battery is more effective. Therefore, it is preferable that M ¹ contains Mg. In the lithium-containing transition metal oxide other than the positive electrode active material (B) represented by the general formula (1) and the positive electrode active material (B) represented by the general formula (2), as M ¹ , It is preferable to contain at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn together with Mg. In this case, these in a charged state at a high voltage The stability of the lithium-containing transition metal oxide is further improved.

  In the positive electrode active material (B), the content thereof is, for example, 0.1 mol% or more with respect to the Co content from the viewpoint of more effectively exerting the effect of containing Mg. It is preferably 0.15 mol% or more, more preferably 0.2 mol% or more.

  Further, when the positive electrode active material (B) contains Ti, Zr, Ge, or Nb, the total amount thereof is, for example, Co from the viewpoint of more effectively exerting the above-described effect by containing these. The content is preferably 0.05 mol% or more, more preferably 0.08 mol% or more, and further preferably 0.1 mol% or more. Furthermore, when the positive electrode active material (B) contains Al or Sn, the total amount thereof is, for example, relative to the Co content from the viewpoint of more effectively exerting the above-described effects by containing these. Thus, it is preferably 0.1 mol% or more, more preferably 0.15 mol% or more, and further preferably 0.2 mol% or more.

  However, in the positive electrode active material (B), if the content of Mg is too large, the load characteristics of the battery tend to be lowered. Therefore, the content is, for example, 2 mol% with respect to the Co content. Is preferably less than 1 mol%, more preferably less than 0.5 mol%, and particularly preferably less than 0.3 mol%.

  In addition, if the content of at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al, and Sn is too large in the positive electrode active material (B), the battery capacity improvement effect is reduced. Sometimes. Therefore, when the positive electrode active material (B) contains Ti, Zr, Ge, or Nb, the total amount is preferably less than 0.5 mol% with respect to the Co content, for example. More preferably, it is less than 0.25 mol%, and still more preferably less than 0.15 mol%. When the positive electrode active material (B) contains Al or Sn, the total amount is preferably less than 1 mol%, for example, 0.5 mol% with respect to the Co content. Is more preferably less than 0.3 mol%.

  Furthermore, in the positive electrode active material (A), the content thereof is, for example, 0.01 mol% or more with respect to the Co content from the viewpoint of more effectively exerting the effect of containing Mg. It is preferably 0.05 mol% or more, more preferably 0.07 mol% or more.

  Further, when the positive electrode active material (A) contains Ti, Zr, Ge, or Nb, the total amount thereof is, for example, Co from the viewpoint of more effectively exerting the above-described effect by containing these. The content is preferably 0.005 mol% or more, more preferably 0.008 mol% or more, and still more preferably 0.01 mol% or more. Furthermore, in the case where the positive electrode active material (A) contains Al or Sn, the total amount is, for example, relative to the Co content from the viewpoint of more effectively exerting the above-described effects by containing them. It is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and even more preferably 0.07 mol% or more.

  However, even in the positive electrode active material (A), if the Mg content is too large, the load characteristics of the battery tend to be lowered. Therefore, the content is, for example, 0.5% relative to the Co content. It is preferably less than mol%, more preferably less than 0.2 mol%, and even more preferably less than 0.1 mol%.

  Also, in the positive electrode active material (A), if the content of at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn is too large, the battery capacity improvement effect is small. May be. Therefore, when the positive electrode active material (A) contains Ti, Zr, Ge, or Nb, the total amount is preferably less than 0.3 mol% with respect to the Co content, for example. More preferably, it is less than 0.1 mol%, and still more preferably less than 0.05 mol%. When the positive electrode active material (A) contains Al or Sn, the total amount is preferably less than 0.5 mol% with respect to the Co content, for example, 0.2 More preferably, it is less than mol%, and further preferably less than 0.1 mol%.

  In addition, when a lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B) is used, the lithium-containing transition metal oxide is more effective in containing Mg. From the viewpoint of exhibiting effectively, the content thereof is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, for example, relative to the Co content, and 0.07 More preferably, it is at least mol%.

  In addition, when the lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B) contains Ti, Zr, Ge, or Nb, the above-described effects due to the inclusion thereof are more effective. From the viewpoint of exhibiting, the total amount is, for example, preferably 0.005 mol% or more, more preferably 0.008 mol% or more, relative to the Co content, % Or more is more preferable. Further, when the lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B) contains Al or Sn, the viewpoint of more effectively exerting the above-described effect by containing them. Therefore, the total amount is, for example, preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and 0.07 mol% or more with respect to the Co content. More preferably.

  However, even in lithium-containing transition metal oxides other than the positive electrode active material (A) and the positive electrode active material (B), if the content of Mg is too large, the load characteristics of the battery tend to deteriorate. Is, for example, preferably less than 2 mol%, more preferably less than 10.2 mol%, still more preferably less than 0.5 mol%, relative to the Co content. It is particularly preferred that it is less than 3 mol%.

  Also, in the lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B), at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al, and Sn If the content of is too large, the effect of improving the battery capacity may be reduced. Therefore, when the lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B) contains Ti, Zr, Ge, or Nb, the total amount is, for example, the content of Co Is preferably less than 0.5 mol%, more preferably less than 0.25 mol%, and still more preferably less than 0.15 mol%. When the lithium-containing transition metal oxide other than the positive electrode active material (A) and the positive electrode active material (B) contains Al or Sn, the total amount is, for example, the Co content, It is preferably less than 1 mol%, more preferably less than 0.5 mol%, and even more preferably less than 0.3 mol%.

In the positive electrode active material (B) and other lithium cobalt oxide, the way of containing the metallic element M ¹ is not particularly limited, for example, need only be present on the particle, uniformly dissolved in the active material Even if it exists, it may be unevenly distributed in the active material with a concentration distribution, or a layer as a compound may be formed on the surface, but it is preferable that it is uniformly dissolved.

The element M ^{2 according} to the general formula (1) and the general formula (2) representing the positive electrode active material (B) and other lithium cobalt oxides is an element other than Li, Co, and M ¹ . The positive electrode active material (B) and other lithium cobalt oxides may or may not contain M ² within a range that does not impair the effects of the present invention.

Examples of the element M ² include alkali metals other than Li (such as Na, K, and Rb), alkaline earth metals other than Mg (such as Be, Ca, Sr, and Ba), and group IIIa metals (such as Sc, Y, and La). ), Group IVa metals other than Ti and Zr (such as Hf), Group Va metals other than Nb (such as V and Ta), Group VIa metals (such as Cr, Mo and W), and Group VIIb metals other than Mn (Tc, Re) Etc.), Group VIII metals excluding Co and Ni (Fe, Ru, Rh etc.), Group Ib metals (Cu, Ag, Au etc.), Group IIIb metals other than Zn, Al (B, Ca, In etc.), Sn, etc. IVb group metals other than Pb (such as Si), P, Bi and the like.

Although the metal element M ¹ contributes to improving the stability of the lithium cobalt oxide, if the content is too large, the diffusion of Li ions in the solid layer is impaired, and thus the battery characteristics may be deteriorated. Since the positive electrode active material (B) having the smallest average particle size has a small particle size and a large surface area, the activity is high and the stability is low. Therefore, the content of M ¹ that is a stabilizing element is somewhat The positive electrode active material (B) preferably has a high particle size and a large surface area. Therefore, the positive electrode active material (B) has high activity, and the inclusion of M ¹ has little influence on the diffusion of Li ions in the solid layer.

On the other hand, lithium cobalt oxide having a relatively large particle size [lithium cobalt oxide other than the positive electrode active material (B)] has higher stability than the positive electrode active material (B). While it is not necessary to contain M ¹ as in B), since the surface area is small and the activity is low compared to the positive electrode active material (B), the diffusion of Li ions in the solid layer is easily impaired by the inclusion of M ¹ .

Therefore, the content of the metal element M ¹ of the cathode active material (B) having the smallest average particle diameter is preferably larger than the content of M ¹ of the lithium cobalt oxide other than the positive electrode active material (B).

  That is, it is preferable that z in the general formula (1) and c in the general formula (2) satisfy the relationship of z> c. z is more preferably 1.5 times or more of c, further preferably 2 times or more, and particularly preferably 3 times or more. On the other hand, if z is too large with respect to c, the load characteristics of the battery tend to deteriorate. Therefore, z is more preferably less than 5 times c, more preferably less than 4 times. It is particularly preferable that the ratio is less than 5 times.

When using lithium cobalt oxide relating to the positive electrode having three or more average particle diameters, the maximum average particle diameter of the lithium cobalt oxide other than the positive electrode active material (B) having the minimum average particle diameter. There is no particular limitation on the relationship of the content of M ¹ between the positive electrode active material (A) and the other lithium cobalt oxide, and the former may contain more M ¹ , The latter may contain more M ^1, and the content of both M ¹ may be the same. More preferably, the lithium cobalt oxide having a smaller average particle diameter is an embodiment in which the content of M ¹ is increased. That is, for example, in the case of using lithium cobalt oxide having three kinds of average particle diameters, the positive electrode active material (B) having the smallest average particle diameter has the largest M ¹ content, and then the positive electrode active material ( many average M ¹ content of the lithium-containing metal oxide having a particle size of between a) the cathode active material (B), M ¹ content of the positive electrode active material (a) having a maximum average particle size of most Less embodiments are more preferred.

Moreover, as lithium cobalt oxide which is a positive electrode active material which concerns on this invention, when using two or more types from which an average particle diameter differs, those from which an average particle diameter differs may have the same composition, average Each having a different particle size may have a different composition. For example, when the lithium cobalt oxide according to the present invention is the positive electrode active material (B) having the minimum average particle size and the positive electrode active material (A) having the maximum average particle size, the positive electrode active material (A) is A combination in which LiCo _0.9975 Mg _0.001 Ti _0.0005 Al _0.001 O ₂ and the positive electrode active material (B) is LiCo _0.9925 Mg _0.003 Ti _0.0015 Al _0.003 O ₂ It does not matter.

The positive electrode active material (lithium cobalt oxide) according to the present invention is formed through a specific synthesis process and a specific battery manufacturing process. For example, in order to obtain lithium cobalt oxides of different particle sizes, generally an alkali such as NaOH is dropped into an acidic aqueous solution of Co and precipitated as Co (OH) ₂ . In order to obtain a uniform precipitate, a coprecipitated compound with a different element can be used, followed by firing to produce Co ₃ O ₄ . The particle size of the precipitate can be controlled by controlling the time for producing the precipitate, and the particle size of the precipitate at this time is the dominant factor in the particle size of Co ₃ O ₄ after firing.

  In synthesizing the positive electrode active material, it is necessary to select specific mixing conditions, baking temperature, baking atmosphere, baking time, starting material, and specific battery manufacturing conditions. As for the mixing conditions for the synthesis of the positive electrode active material, for example, ethanol or water is preferably added to the raw material powder and mixed for 0.5 hour or more in a planetary ball mill, and ethanol and water are mixed at a volume ratio of 50:50, It is more preferable to mix for at least 20 hours. By this mixing step, the raw material powder can be sufficiently pulverized and mixed to prepare a uniform dispersion. This is dried with a spray dryer or the like while maintaining uniformity. A preferable baking temperature is 750 to 1050 ° C, and a more preferable baking temperature is 950 to 1030 ° C. A preferable firing atmosphere is in the air. A preferable baking time is 10 to 60 hours, and a more preferable baking time is 20 to 40 hours.

Regarding the above positive electrode active material, Li ₂ CO ₃ is preferable as the Li source, and different metal sources such as Mg, Ti, Ge, Zr, Nb, Al, and Sn are nitrates, hydroxides, or 1 μm or less of those metals. An oxide having a particle size is preferable, and using a hydroxide coprecipitate is more preferable because different elements are easily distributed uniformly in the active material.

  The amount of metal element in the positive electrode active material in the positive electrode mixture layer is determined by measuring the amount of each element by ICP analysis. Further, the amount of Li can be separately measured using atomic absorption or the like. Normally, in the state of the electrode (positive electrode), for the positive electrode active materials having different particle diameters, it is possible to separate the large active material particles and the small active material particles from each other and measure the element amount. difficult. Therefore, using an active material mixture with a known mixing amount as a standard, EPMA (electron beam microanalysis device) etc. is used to compare the content and content ratio of elements in small and large particles. You can go. Further, the electrode (positive electrode) is treated with N-methyl-2-pyrrolidone (NMP) or the like, the active material particles are peeled off from the electrode to precipitate the particles, and after washing and drying, the particle size distribution of the obtained particles is determined. When measuring or performing peak separation of particle size distribution and determining that it has two or more particle sizes, the particles are classified into large particles and small particles. The point or element amount may be measured by ICP.

  In the ICP analysis for measuring the amount of metal element in the positive electrode active material in this specification, about 5 g of the active material is precisely weighed and put into a 200 ml beaker, 100 ml of aqua regia is added, and the liquid volume is about 20 to 25 ml. After heating and concentrating until cooled, the solids were separated with a quantitative filter paper “No. 5B” manufactured by Advantech Co., Ltd., and the filtrate and washings were placed in a 100 ml volumetric flask and diluted to a constant volume. A method of measurement using a sequential type ICP analyzer “IPIS1000” manufactured by Ash Corporation is adopted.

  Among the two or more types of lithium-containing transition metal oxides having different average particle diameters of the positive electrode mixture layer, the lithium-containing transition metal oxides having the minimum average particle diameter are analyzed by the above ICP, Mg, Ti Lithium-containing transition metals other than lithium-containing transition metal oxides having a content (I) of at least one metal element selected from the group consisting of Zr, Ge, Nb, Al and Sn and a minimum average particle size About the oxide, the content of at least one metal element selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al and Sn analyzed by the above ICP, The ratio (I) / (II) between the metal element related to the content (I) and the content (II) of the same metal element is the z in the general formula (1) and the general formula ( 2) In The value of (I) / (II) is more preferably 1.5 or more, further preferably 2 or more, and particularly preferably 3 or more. preferable. On the other hand, if z is too large with respect to c, the load characteristics of the battery tend to deteriorate. Therefore, the value of (I) / (II) is more preferably less than 5, and preferably less than 4. More preferably, it is particularly preferably less than 3.5.

In the present invention, the positive electrode is produced, for example, by the following method. First, lithium cobalt oxide as a positive electrode active material (at least in part, in which a part of Co is substituted with other metal elements M ^1), if necessary, a conductive additive (e.g., graphite, Carbon black, acetylene black, etc.) are added, and a binder (for example, polyvinylidene fluoride, polytetrafluoroethylene, etc.) is further added to prepare a positive electrode mixture. This positive electrode mixture is made into a paste using a solvent (the binder may be dissolved in a solvent in advance and then mixed with the positive electrode active material) to prepare a positive electrode mixture-containing paste. The obtained positive electrode mixture-containing paste is applied to a positive electrode current collector made of aluminum foil or the like, dried to form a positive electrode mixture layer, and rolled as necessary to obtain a positive electrode. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

  The thickness of the positive electrode mixture layer is preferably, for example, 30 to 200 μm. Moreover, it is preferable that the thickness of the electrical power collector used for a positive electrode is 8-20 micrometers, for example.

  In the positive electrode mixture layer, the content of the lithium-containing transition metal oxide as the active material is 96% by mass or more, more preferably 97% by mass or more, and further preferably 97.5% by mass or more, It is desirable that it is 99 mass% or less, More preferably, it is 98 mass% or less. Further, the content of the binder in the positive electrode mixture layer is, for example, 1% by mass or more, more preferably 1.3% by mass or more, still more preferably 1.5% by mass or more, and 4% by mass or less. Preferably it is 3 mass% or less, More preferably, it is 2 mass% or less. And content of the conductive support agent in a positive mix layer is 1 mass% or more, for example, More preferably, it is 1.1 mass% or more, More preferably, it is 1.2 mass% or more, Comprising: 3 mass% or less More preferably, it is 2% by mass or less, and further preferably 1.5% by mass or less.

  This is because if the proportion of the active material in the positive electrode mixture layer is small, the capacity cannot be increased, and the density of the positive electrode mixture layer cannot be increased. It is because the formability of may be impaired. Also, if the content of the binder in the positive electrode mixture layer is too large, it will be difficult to increase the capacity, and if it is too small, the adhesiveness with the current collector will be reduced, and the possibility of electrode dusting will occur. It is desirable to have the above preferred composition. Furthermore, if the content of the conductive additive in the positive electrode mixture layer is too large, it is difficult to sufficiently increase the density of the positive electrode mixture layer, and it may be difficult to increase the capacity. This is because it leads to deterioration of charge / discharge cycle characteristics and load characteristics of the battery.

  The non-aqueous secondary battery of the present invention is not limited as long as it has the above-described positive electrode, and there are no particular restrictions on other components and structures, and various constituent elements employed in conventionally known non-aqueous secondary batteries. And structure can be applied.

The negative electrode active material for the negative electrode is not particularly limited as long as it can be doped / undoped with Li ions. For example, graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbons Examples of the carbon material include microbeads, carbon fibers, and activated carbon. Also, alloys such as Si, Sn, In, etc., oxides such as Si, Sn that can be charged and discharged at a low potential close to Li, and compounds such as Li and Co nitrides such as Li _2.6 Co _0.4 N are also available. It can be used as a negative electrode active material. Furthermore, a part of graphite can be replaced with a metal or oxide that can be alloyed with Li. When graphite is used as the negative electrode active material, the voltage at the time of full charge can be regarded as about 0.1 V on the basis of Li. Therefore, the potential of the positive electrode is calculated for convenience by adding 0.1 V to the battery voltage. Therefore, it is preferable that the charge potential of the positive electrode is easy to control.

As a form of graphite, for example, it is preferable that an interplanar spacing (d ₀₀₂ ) of the 002 plane is 0.338 nm or less. This is because the higher the crystallinity, the easier it is to make the negative electrode (negative electrode mixture layer described later) dense. However, if d ₀₀₂ is too large, the discharge characteristics and load characteristics of the high-density negative electrode may be deteriorated. Therefore, d ₀₀₂ is preferably 0.335 nm or more, and more preferably 0.3355 nm or more. preferable.

  Further, the crystallite size (Lc) in the c-axis direction of graphite is preferably 70 nm or more, more preferably 80 nm or more, and still more preferably 90 nm or more. This is because the larger the Lc, the flatter the charging curve, the easier to control the positive electrode potential, and the larger the capacity. On the other hand, if Lc is too large, the battery capacity tends to decrease in a high-density negative electrode, so Lc is preferably less than 200 nm.

Furthermore, the specific surface area of the graphite is preferably at 0.5 m ² / g or more, more preferably ^{1 m} 2 / g or more, further preferably ^2m 2 / g or more,, ^{6 m} 2 / g or less is preferable, and 5 m ² / g or less is more preferable. If the specific surface area of graphite is not large to some extent, the characteristics tend to deteriorate. On the other hand, if the specific surface area is too large, the influence of the reaction with the nonaqueous electrolyte tends to occur.

  The graphite used for the negative electrode is preferably made of natural graphite as a raw material, and a mixture of two or more types of graphite having different surface crystallinity is more preferable from the viewpoint of increasing the capacity. Since natural graphite is inexpensive and has a high capacity, it can be a negative electrode with high cost performance. Normally, natural graphite is likely to have a reduced battery capacity due to densification of the negative electrode. However, a decrease in battery capacity can be reduced by mixing and using graphite whose surface crystallinity has been reduced by surface treatment.

The crystallinity of the surface of graphite can be determined by Raman spectrum analysis. R value of Raman spectrum when excited graphite in argon laser with a wavelength of 514.5nm is _[R = _{I 1350} / _I 1580 (the ratio of the Raman intensity and 1580cm Raman intensity at around ^-1 around 1350 cm ^-1)] If it is 0.01 or more, it can be said that the crystallinity of the surface is slightly lower than that of natural graphite. Therefore, as the graphite whose surface crystallinity is reduced by the surface treatment, for example, the R value is 0.01 or more, more preferably 0.1 or more, and 0.5 or less, more preferably 0.3 or less. More preferably, it is preferably 0.15 or less. The content ratio of the graphite whose surface crystallinity is reduced is preferably 100% by mass in order to increase the density of the negative electrode, but in order to prevent a decrease in battery capacity, 50% by mass in the total graphite. % Or more, more preferably 70% by mass or more, and particularly preferably 85% by mass or more.

  Moreover, since the irreversible capacity | capacitance will become large if the average particle diameter of graphite is too small, it is preferable that it is 5 micrometers or more, it is more preferable that it is 12 micrometers or more, and it is still more preferable that it is 18 micrometers or more. From the viewpoint of increasing the density of the negative electrode, the average particle diameter of graphite is preferably 30 μm or less, more preferably 25 μm or less, and further preferably 20 μm or less.

  The negative electrode can be produced, for example, by the following method. If necessary, a binder or the like is added to the negative electrode active material and mixed to prepare a negative electrode mixture, which is dispersed in a solvent to obtain a paste. The binder is preferably dissolved in a solvent in advance and then mixed with the negative electrode active material or the like. The negative electrode mixture-containing paste is applied to a negative electrode current collector made of a copper foil or the like, dried to form a negative electrode mixture layer, and a negative electrode can be obtained through a pressure treatment step. Note that the method for manufacturing the negative electrode is not limited to the above method, and other methods may be adopted.

The density of the negative electrode mixture layer (the density after the pressure treatment step) is preferably 1.70 g / cm ³ or more, and more preferably 1.75 g / cm ³ or more. From the theoretical density of graphite, the upper limit of the density of the negative electrode mixture layer is 2.1 to 2.2 g / cm ³ , but from the viewpoint of affinity with the nonaqueous electrolyte, the density of the negative electrode mixture layer is 2 more preferably .0g / cm ³ or less, further preferably 1.9 g / cm ³ or less. In the above pressure treatment step, since the negative electrode can be pressed more uniformly, it is preferable to perform a plurality of pressure treatments rather than a single pressure treatment.

  The binder used in the negative electrode is not particularly limited, but from the viewpoint of increasing the active material ratio and increasing the capacity, it is preferable to reduce the amount used as much as possible, and for this reason, an aqueous resin having the property of being dissolved or dispersed in water. A mixture of styrene and a rubber-based resin is preferred. This is because the water-based resin contributes to the dispersion of the graphite even in a small amount, and the rubber-based resin can prevent the negative electrode mixture layer from peeling from the current collector due to the expansion and contraction of the electrode during the charge / discharge cycle of the battery.

  Examples of the water-based resin include cellulose resins such as carboxymethyl cellulose and hydroxypropyl cellulose, and polyether resins such as polyvinyl pyrrolidone, polyepichlorohydrin, polyvinyl pyridine, polyvinyl alcohol, polyethylene oxide, and polyethylene glycol. Examples of the rubber resin include latex, butyl rubber, fluorine rubber, styrene butadiene rubber, nitrile butadiene copolymer rubber, ethylene-propylene-diene copolymer, polybutadiene, and ethylene-propylene-diene copolymer (EPDM). . For example, it is more preferable to use a cellulose ether compound such as carboxymethyl cellulose in combination with a butadiene copolymer rubber such as styrene butadiene rubber from the viewpoint of dispersion of the graphite and prevention of peeling. It is particularly preferred to use carboxymethyl cellulose in combination with a butadiene copolymer rubber such as styrene butadiene rubber or nitrile butadiene copolymer rubber. This is because cellulose ether compounds such as carboxymethyl cellulose mainly exert a thickening effect on the negative electrode mixture-containing paste, and rubber binders such as styrene / butadiene copolymer rubber bind to the negative electrode mixture. This is because it exerts a wearing action. Thus, when using together cellulose ether compounds, such as carboxymethylcellulose, and rubber-type binders, such as a styrene butadiene rubber, as a ratio of both, 1: 1-1: 15 are preferable by mass ratio.

  The thickness of the negative electrode mixture layer is preferably 40 to 200 μm, for example. Moreover, it is preferable that the thickness of the electrical power collector used for a negative electrode is 5-30 micrometers, for example.

  In the negative electrode mixture layer, the content of the binder (the total amount when a plurality of types are used in combination) is 1.5% by mass or more, more preferably 1.8% by mass or more, and further preferably 2%. It is desirable that it is 0.0 mass% or more, less than 5 mass%, more preferably less than 3 mass%, and still more preferably less than 2.5 mass%. This is because if the amount of the binder in the negative electrode mixture layer is too large, the discharge capacity may decrease, and if it is too small, the adhesion between the particles decreases. In addition, it is preferable that content of the negative electrode active material in a negative mix layer exceeds 95 mass%, and is 98.5 mass% or less, for example.

  In the non-aqueous secondary battery of the present invention, as the non-aqueous electrolyte, for example, non-aqueous solvent-based electrolysis in which an electrolyte salt such as a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent from the viewpoint of electrical characteristics and ease of handling. A liquid is preferably used, but even a polymer electrolyte or gel electrolyte can be used without any problem.

  Although it does not specifically limit as a solvent of nonaqueous electrolyte solution, For example, dielectric constants, such as chain esters, such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propion carbonate; ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate High cyclic ester; mixed solvent of chain ester and cyclic ester;

  In addition to the above esters, examples of the solvent include chain phosphate triesters such as trimethyl phosphate, 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, and the like. These ethers, nitriles, dinitriles, isocyanates, halogen-containing solvents, and the like can also be used. Further, amine-based or imide-based organic solvents, sulfur-based organic solvents such as sulfolane, and the like can also be used.

  Furthermore, the non-aqueous electrolyte preferably contains a nonionic aromatic compound. Specifically, compounds in which an alkyl group is bonded to an aromatic ring such as cyclohexylbenzene, isopropylbenzene, t-butylbenzene, t-amylbenzene, octylbenzene, toluene, xylene; fluorobenzene, difluorobenzene, trifluorobenzene, chlorobenzene Compounds in which a halogen group is bonded to an aromatic ring, such as: Compounds having an alkoxy group bonded to an aromatic ring, such as anisole, fluoroanisole, dimethoxybenzene, diethoxybenzene, etc .; phthalic acid esters (dibutyl phthalate, di-2- Ethyl hexyl phthalate), aromatic carboxylic acid ester such as benzoic acid ester; carbonate ester having a phenyl group such as methyl phenyl carbonate, butyl phenyl carbonate, diphenyl carbonate; Examples include phenyl lopionate; biphenyl; and the like. Among them, a compound in which an alkyl group is bonded to an aromatic ring is preferable, and cyclohexylbenzene is particularly preferably used.

  These aromatic compounds are compounds capable of forming a film on the active material surface of the positive electrode or the negative electrode in the battery. These aromatic compounds may be used alone or in combination, but when two or more of these aromatic compounds are used in combination, an excellent effect is exhibited. Particularly, a compound in which an alkyl group is bonded to an aromatic ring, and a lower potential than that. By using in combination with an aromatic compound such as biphenyl that is oxidized at a particularly favorable effect in improving the safety of the battery.

  A method for adding an aromatic compound to the nonaqueous electrolytic solution is not particularly limited, but a method of adding the aromatic compound to the nonaqueous electrolytic solution in advance before assembling the battery is common.

  The preferred content of the aromatic compound in the non-aqueous electrolyte is, for example, 4% by mass or more from the viewpoint of safety and 10% by mass or less from the viewpoint of load characteristics. When two or more aromatic compounds are used in combination, the total amount should be within the above range, particularly when a compound in which an alkyl group is bonded to an aromatic ring and a compound that is oxidized at a lower potential are used in combination. The content of the compound in which an alkyl group is bonded to the aromatic ring in the nonaqueous electrolytic solution is 0.5% by mass or more, more preferably 2% by mass or more, and 8% by mass or less, more preferably 5% by mass. The following is desirable. On the other hand, the content in the non-aqueous electrolyte of the compound that is oxidized at a lower potential than the compound in which an alkyl group is bonded to the aromatic ring is 0.1% by mass or more, more preferably 0.2% by mass or more. It is desirable that the content be 1% by mass or less, more preferably 0.5% by mass or less.

Further, the non-aqueous electrolyte includes at least one of an organic halogen solvent such as a halogen-containing carbonate, an organic sulfur solvent, a fluorine-containing organic lithium salt, a phosphorus-containing organic solvent, a silicon-containing organic solvent, and a nitrogen-containing organic compound. By adding the seed compound, a surface protective film can be formed on the surface of the positive electrode active material during the initial charging of the battery. Organic fluorine-based solvents such as fluorine-containing carbonates, organic sulfur-based solvents, fluorine-containing organic lithium salts and the like are particularly preferable. Specifically, F-DPC [C ₂ F ₅ CH ₂ O (C═O) OCH ₂ C _{2 F 5], F-DEC} [CF 3 CH 2 O (C = O) OCH 2 CF 3], HFE7100 (C 4 F 9 OCH 3), butyl sulfate _{(C 4 H 9 OSO 2 OC} 4 H 9), Methyl ethylene sulfate [(—OCH (CH ₃ ) CH ₂ O—) SO ₂ ], butyl sulfone (C ₄ H ₉ SO ₂ C ₄ H ₉ ), polymer imide salt [[—N (Li) SO ₂ OCH ₂ ( _{CF 2) 4 CH 2 OSO 2} - ] _n (where n in formula 2 to 100), and the like _{(C 2 F 5 SO 2)} 2 NLi, _{[(CF 3) 2} CHOSO 2] ₂ NLi Et That.

  Such additives can be used alone, but it is particularly preferable to use an organic fluorine-based solvent and a fluorine-containing organic lithium salt in combination. The amount of addition is 0.1% by mass or more, more preferably 2% by mass or more, further preferably 5% by mass or more, and 30% by mass or less, more preferably 10% by mass or less, based on the total amount of the non-aqueous electrolyte. It is desirable that This is because if the addition amount is too large, the electrical characteristics may be lowered, and if it is too small, it is difficult to form a good film.

  By charging (particularly, high voltage charging) a battery having a non-aqueous electrolyte containing the above additives, a surface protective film containing F (fluorine) or S (sulfur) is formed on the surface of the positive electrode active material. . The surface protective film may contain F or S alone, but is more preferably a film containing both F and S.

  The atomic ratio of S in the surface protective film formed on the surface of the positive electrode active material is preferably 0.5 atomic% or more, more preferably 1 atomic% or more, and 3 atomic% or more. Is more preferable. However, if the atomic ratio of S on the surface of the positive electrode active material is too large, the discharge characteristics of the battery tend to deteriorate. Therefore, the S atomic ratio is preferably 20 atomic% or less, and preferably 10 atomic% or less. It is preferable that it is 6 atomic% or less. Further, the atomic ratio of F in the surface protective film formed on the surface of the positive electrode active material is preferably 15 atomic% or more, more preferably 20 atomic% or more, and 25 atomic% or more. Is more preferable. However, if the atomic ratio of F on the surface of the positive electrode active material is too large, the discharge characteristics of the battery tend to deteriorate. Therefore, the F atomic ratio is preferably 50 atomic% or less, and 40 atomic% or less. It is preferable that it is 30 atomic% or less. The positive electrode active material (lithium-containing transition metal oxide particles) having such a surface protective film is not formed by charging the battery as described above, but the surface protective film containing F or S in the positive electrode active material. ) May be used to produce a positive electrode (battery).

In order to improve the charge / discharge cycle characteristics of the battery, (—OCH═CHO—) C═O, (—OCH═C (CH ₃ ) O—) C═O, (− Vinylene carbonate or derivatives thereof such as OC (CH ₃ ) ═C (CH ₃ ) O—C = O, or (—OCH ₂ —CHFO—) C═O, (—OCHF—CHFO—) C═O, etc. It is preferable to add at least one fluorine-substituted ethylene carbonate. The amount added is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 2% by mass or more in the total amount of the non-aqueous electrolyte. In addition, since there exists a tendency for the load characteristic of a battery to fall when there is too much content of said additive, content in the nonaqueous electrolyte solution whole quantity is 10 mass% or less, More preferably, it is 5 mass% or less. More preferably, the content is 3% by mass or less.

As the non-aqueous electrolyte electrolyte salt to be dissolved in a solvent In the preparation of, 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 (RfSO ₂ ) (Rf′SO ₂ ), LiC (RfSO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [ Here, Rf and Rf ′ are fluoroalkyl groups, etc., and these may be used alone or in combination of two or more. Among the above electrolyte salts, fluorine-containing organic lithium salts having 2 or more carbon atoms are particularly preferable. This is because the fluorine-containing organolithium salt is highly anionic and easily ion-separated, so that it is easily dissolved in the solvent. The concentration of the electrolyte salt in the nonaqueous electrolytic solution is not particularly limited, but is, for example, 0.3 mol / l or more, more preferably 0.4 mol / l or more, and 1.7 mol / l or less, more preferably 1. 5 mol / l or less is desirable.

  In the present invention, as the non-aqueous electrolyte, a gel polymer electrolyte can be used in addition to the above non-aqueous electrolyte. Such a gel polymer electrolyte corresponds to a gel obtained by gelling the non-aqueous electrolyte with a gelling agent. For gelation of the non-aqueous electrolyte, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or a copolymer thereof; a polyfunctional monomer that is polymerized by irradiation with actinic rays such as ultraviolet rays or electron beams ( For example, tetrafunctional or higher acrylates such as pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, dipentaerythritol hexaacrylate, and tetrafunctional or higher methacrylates similar to the above acrylates. Etc.); etc. are used. However, in the case of a monomer, the monomer itself does not gel the electrolyte solution, but a polymer obtained by polymerizing the monomer acts as a gelling agent.

  When the non-aqueous electrolyte is gelled using a polyfunctional monomer as described above, if necessary, as a polymerization initiator, for example, benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides, Acetophenones, thioxanthones, anthraquinones, and the like can be used, and alkylamines, amino esters, and the like can also be used as sensitizers for the polymerization initiator.

  In the present invention, a solid electrolyte can also be used as the non-aqueous electrolyte in addition to the non-aqueous electrolyte and the gel polymer electrolyte. As the solid electrolyte, either an inorganic solid electrolyte or an organic solid electrolyte can be used.

  The separator according to the present invention has directionality in tensile strength, maintains good insulation, and reduces thermal shrinkage, and the thickness thereof is 5 μm or more, more preferably 10 μm or more, and still more preferably. Is preferably 12 μm or more, less than 25 μm, more preferably less than 20 μm, and still more preferably less than 18 μm. Further, the air permeability of the separator is, for example, preferably 500 seconds / 100 ml or less, more preferably 300 seconds / 100 ml or less, and further preferably 120 seconds / 100 ml or less. The smaller the air permeability of the separator, the better the load characteristics. However, since the internal short circuit easily occurs, the air permeability is preferably 50 seconds / 100 ml or more. As the heat shrinkage rate in the TD direction of the separator is smaller, an internal short circuit is less likely to occur when the temperature rises. Therefore, it is preferable to use a separator having a heat shrinkage rate as low as possible. For example, the heat shrinkage rate is 10% or less. Is more preferable, and 5% or less is still more preferable. In order to suppress thermal shrinkage, it is preferable to use a separator that has been heat-treated at a temperature of about 100 to 125 ° C. in advance. It is recommended that a battery having such a heat shrinkage rate be combined with the positive electrode material according to the present invention to stabilize the behavior at a higher temperature.

  The thermal contraction rate in the TD direction of the separator means the contraction rate of the portion contracted to the maximum in the TD direction when a 30 mm square separator is allowed to stand at 105 ° C. for 8 hours.

Further, the strength of the separator is, for example, preferably 6.8 × 10 ⁷ N / m ² or more, more preferably 9.8 × 10 ⁷ N / m ² or more as the tensile strength in the MD direction. . The tensile strength in the TD direction is preferably smaller than that in the MD direction. For example, the ratio of the tensile strength in the TD direction to the tensile strength in the MD direction (TD tensile strength / MD tensile strength) is 0.95 or less. Is more preferable, 0.9 or less is further preferable, and 0.1 or more is more preferable. In addition, TD direction is a direction orthogonal to the take-up direction (MD direction) of film resin in separator manufacture.

  Furthermore, the piercing strength of the separator is preferably 2.0 N or more, and more preferably 2.5 N or more. The higher this value is, the more difficult the battery is short-circuited. However, the upper limit value is generally almost determined by the constituent material of the separator. For example, in the case of a polyethylene separator, the upper limit value is about 10N.

  In the conventional non-aqueous secondary battery, when the positive electrode potential is charged at a high voltage of 4.35 V or more on the basis of Li and discharged at a voltage termination higher than 3.2 V, the crystal structure of the positive electrode active material collapses. This has been impractical due to problems such as a decrease in capacity and a problem that heat stability is reduced and the battery generates heat. For example, even if a positive electrode active material to which a different element such as Mg or Ti is added can be reduced in safety and capacity reduction due to charge / discharge cycles, it is still insufficient. Moreover, the filling property of the positive electrode is insufficient, and the battery tends to swell.

  On the other hand, the present invention is a non-aqueous secondary battery that has improved high capacity characteristics, charge / discharge cycle characteristics, safety, and suppression of swelling by adopting the above-described configuration. 4.2V) is effective, but the positive electrode is charged to a high voltage of 4.35V (battery voltage 4.25V) on the basis of Li, and the discharge is terminated at a battery voltage higher than 3.2V. However, the crystal structure of the positive electrode active material is more stable, and the decrease in capacity and the decrease in thermal stability are suppressed.

  In addition, since the positive electrode active material related to the conventional non-aqueous secondary battery has a low average voltage, when the charge / discharge cycle test is repeated under the condition that the end-of-charge voltage of the unit cell is 4.35 V or more on the basis of Li, the positive electrode Put in and out a large amount of Li ions. This is the same as a charge / discharge cycle test of the battery under overcharge conditions. Therefore, under such severe conditions, when a conventional positive electrode active material is used, the crystal structure cannot be maintained, resulting in inconveniences such as a decrease in thermal stability and a short charge / discharge cycle life. On the other hand, if the positive electrode active material according to the battery of the present invention is used, such inconvenience can be eliminated, so that the positive electrode potential at the time of full charge is high such that the Li reference potential is 4.35 to 4.6V. A non-aqueous secondary battery that can be reversibly charged and discharged even under voltage can be provided.

  The non-aqueous secondary battery of the present invention takes advantage of the high voltage, high capacity, and high safety as described above, for example, notebook computers, pen input computers, pocket computers, notebook word processors, pocket word processors. , Electronic book player, mobile phone, cordless phone, pager, handy terminal, portable copy, electronic notebook, calculator, LCD TV, electric shaver, electric tool, electronic translator, car phone, transceiver, voice input device, memory card , Backup power supply, tape recorder, radio, headphone stereo, portable printer, handy cleaner, portable CD, video movie, navigation system and other power supplies, refrigerator, air conditioner, TV, stereo, water heater, microwave oven, dishwasher Machine, washing machine, dry Machine, game equipment, lighting equipment, can be used toys, sensor devices, load conditioners, medical equipment, motor vehicles, electric vehicles, golf carts, electric cart, security system, as a power source, such as a power storage system. In addition to consumer use, it can also be used for space use. In particular, a small portable device is highly effective in increasing the capacity, and is desirably used for a portable device having a weight of 3 kg or less, and more desirably for a portable device having a weight of 1 kg or less. Further, the lower limit of the weight of the portable device is not particularly limited, but in order to obtain a certain degree of effect, it is preferably about the same as the battery weight, for example, 10 g or more.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
<Preparation of positive electrode>
LiCo _0.998 Mg _0.0008 Ti _0.0004 Al _0.0008 O ₂ [average particle size 12 μm, positive electrode active material (A)] and LiCo _0.994 Mg _0.0024 Ti _0.0012 Al _0.0024 O ₂ A powder supply apparatus comprising 97.3 parts by mass of [average particle diameter of 5 μm, positive electrode active material (B)] mixed at a mass ratio of 65:35, and 1.5 parts by mass of carbon material as a conductive auxiliary agent. The amount of 10% strength by weight polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) is adjusted so that the solid concentration during kneading is always 94. The material adjusted so as to be in mass% was charged into a biaxial kneader-extruder while being controlled so as to have a predetermined input amount per unit time and kneaded to prepare a positive electrode mixture-containing paste. The obtained positive electrode mixture-containing paste was put into a planetary mixer, diluted with an NMP solution of PVDF having a concentration of 10% by mass and NMP, and adjusted to a coatable viscosity. The diluted positive electrode mixture-containing paste is passed through a 70-mesh net to remove large inclusions, and then uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm and dried to form a film. A positive electrode mixture layer was formed. The solid content ratio of the positive electrode mixture layer after drying is 97.3: 1.5: 1.2 in terms of positive electrode active material: conductive aid: PVDF mass ratio. Then, after pressurizing and cutting to a predetermined size, an aluminum lead body was welded to produce a sheet-like positive electrode. The density of the positive electrode mixture layer after the pressure treatment (the density of the positive electrode) is 3.8 g / cm ³ .

The above positive electrode was measured using a Rigaku X-ray diffractometer “RINT2500VPC” under the conditions of tube Cu, 50 kV, 150 mA, scan 2 ° / min, and the I ₀₀₆ / I ₁₀₁ value was determined. The results are shown in Table 1.

<Production of negative electrode>
Graphite-based carbon material (A) as a negative electrode active material [purity 99.9% or more, average particle diameter 18 μm, inter-surface distance (d ₀₀₂ ) = 0.3356 nm, crystallite size in the c-axis direction (Lc ) = 100 nm, R value (ratio of peak intensity around ₁₃₅₀ cm ⁻¹ and peak intensity around 1580 cm ⁻¹ in the Raman spectrum when excited by an argon laser with a wavelength of 514.5 nm [R = I ₁₃₅₀ / I ₁₅₈₀ ] ) = 0.18]: 70 parts by mass and graphite-based carbon material (B) [purity 99.9% or more, average particle diameter 21 μm, d ₀₀₂ = 0.3363 nm, Lc = 60 nm, R value = 0.11. : 30 parts by mass, and 98 parts by mass of this mixture, 1 part by mass of carboxymethyl cellulose and 1 part by mass of styrene butadiene rubber are mixed in the presence of water to form a slurry. The negative electrode mixture containing paste was prepared. The obtained negative electrode mixture-containing paste was applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried to form a negative electrode mixture layer, and the density of the negative electrode mixture layer was 1 with a roller. A pressure treatment was performed until the pressure became 0.75 g / cm ^3, and after cutting into a predetermined size, a nickel lead was welded to prepare a sheet-like negative electrode.

<Preparation of non-aqueous electrolyte>
LiPF ₆ is dissolved to a concentration of 1.2 mol / l in a mixed solvent in which methyl ethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed at a volume ratio of 1.5: 0.5: 1. (FB) 3% by mass, biphenyl (BP) 0.2% by mass, propane sultone (PS) 0.5% by mass, C ₄ F ₉ OCH ₃ (HFE) 10% by mass, vinylene carbonate (VC) 3% by mass. In addition, a non-aqueous electrolyte was prepared.

<Production of non-aqueous secondary battery>
The positive electrode and the negative electrode are made of a microporous polyethylene film [porosity 53%, MD direction tensile strength: 2.1 × 10 ⁸ N / m ² , TD direction tensile strength: 0.28 × 10 ⁸ N / m ^2. Thickness 16 μm, air permeability 80 seconds / 100 ml, thermal shrinkage 3% in TD direction after 105 ° C. × 8 hours, puncture strength: 3.5 N (360 g)] After forming the electrode structure with a round structure, the electrode body was pressed to be inserted into a rectangular battery case to obtain an electrode body with a flat winding structure. Insert it into a rectangular battery case made of aluminum alloy, weld the positive and negative electrode lead bodies and laser weld the open end of the lid plate to the battery case, and then insert it from the inlet on the lid plate for sealing. After injecting the above non-aqueous electrolyte into the battery case, fully infiltrating the non-aqueous electrolyte into the separator, etc., perform partial charging, discharge the gas generated by partial charging, and seal the injection port And sealed. Thereafter, charging and aging are performed, the structure shown in FIG. 1 has the appearance shown in FIG. 2, the width is 34.0 mm, the thickness is 4.0 mm, and the height is 50.0 mm. A non-aqueous secondary battery was obtained.

  The battery shown in FIGS. 1 and 2 will now be described. The positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3 as described above, and then pressed so as to be flattened, thereby forming a flat winding structure. The electrode laminate 6 is housed in a rectangular battery case 4 together with a non-aqueous electrolyte. However, in order to avoid complication, in FIG. 2, the metal foil, electrolyte solution, etc. as a collector used in producing the positive electrode 1 and the negative electrode 2 are not shown.

  The battery case 4 is made of an aluminum alloy and constitutes the main part of the battery exterior material. The battery case 4 also serves as a positive electrode terminal. An insulator 5 made of a polytetrafluoroethylene sheet is disposed at the bottom of the battery case 4, and the flat electrode structure 6 made of the positive electrode 1, the negative electrode 2, and the separator 3 has the positive electrode 1 and A positive electrode lead body 7 and a negative electrode lead body 8 connected to one end of the negative electrode 2 are drawn out. A stainless steel terminal 11 is attached to the aluminum lid plate 9 that seals the opening of the battery case 4 via an insulating packing 10 made of polypropylene, and the terminal 11 is made of stainless steel via an insulator 12. A steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the said battery case 4, and the opening part of the battery case 4 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 1, an electrolyte solution inlet 14 is provided in the lid plate 9, and the electrolyte solution inlet 14 is welded and sealed by, for example, laser welding or the like with a sealing member inserted. Thus, the sealing property of the battery is ensured (therefore, in the battery of FIGS. 1 and 2, the electrolyte inlet 14 is actually the electrolyte inlet and the sealing member, but the explanation is easy. In order to achieve this, it is shown as an electrolyte inlet 14). Furthermore. The cover plate 9 is provided with an explosion-proof vent 15.

  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, and this FIG. 2 is shown for the purpose of showing that the battery is a square battery. Fig. 1 schematically shows a battery, and shows a specific battery component.

Example 2
Non-aqueous secondary as in Example 1, except that the density of the positive electrode mixture layer after pressure treatment (positive electrode density) was adjusted to 4.0 g / cm ³ by adjusting the pressure of the pressure treatment. A battery was produced. Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Example 3
Non-aqueous secondary as in Example 1 except that the density of the positive electrode mixture layer after pressure treatment (positive electrode density) was 3.6 g / cm ³ by adjusting the pressure of the pressure treatment. A battery was produced. Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Example 4
Non-aqueous secondary as in Example 1 except that the density of the positive electrode mixture layer after pressure treatment (positive electrode density) was set to 3.5 g / cm ³ by adjusting the pressure of the pressure treatment. A battery was produced. Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Example 5
A non-aqueous secondary battery was prepared in the same manner as in Example 1 except that the positive electrode active material was changed to only LiCo _0.9975 Mg _0.001 Ti _0.0005 Al _0.001 O ₂ (average particle diameter 12 μm). Produced. The density of the positive electrode mixture layer after the pressure treatment (the density of the positive electrode) was 3.9 g / cm ³ . Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Example 6
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material was changed to only LiCo _0.9964 Mg _0.0024 Ti _0.0012 O ₂ (average particle diameter 5 μm). The density of the positive electrode mixture layer after pressure treatment (positive electrode density) was 3.5 g / cm ³ . Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Example 7
_Except for using LiCoO ₂ having an average particle diameter of 12 μm as the positive electrode active material (A) and using LiCo _0.9988 Mg _0.0008 Ti _0.0004 O ₂ (average particle diameter of 5 μm) as the positive electrode active material (B). A nonaqueous secondary battery was produced in the same manner as in Example 1. The density of the positive electrode mixture layer after the pressure treatment (positive electrode density) was 3.8 g / cm ³ . Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Comparative Example 1
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material was changed to only LiCoO ₂ (average particle size 12 μm). The density of the positive electrode mixture layer after the pressure treatment (the density of the positive electrode) was 3.7 g / cm ³ . Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Comparative Example 2
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the positive electrode active material was changed to only LiCoO ₂ (average particle diameter 5 μm). The density of the positive electrode mixture layer after the pressure treatment (positive electrode density) was 3.6 g / cm ³ . Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

Comparative Example 3
Non-aqueous secondary as in Example 1 except that the density of the positive electrode mixture layer after pressure treatment (the density of the positive electrode) was set to 3.4 g / cm ³ by adjusting the pressure of the pressure treatment. A battery was produced. Table 1 shows the I ₀₀₆ / I ₁₀₁ values of the positive electrode obtained in the same manner as in Example 1.

  The following characteristic evaluation was performed about the non-aqueous secondary battery of Examples 1-7 and Comparative Examples 1-3. The results are shown in Table 2.

<Discharge capacity>
About each battery of Examples 1-7 and Comparative Examples 1-3, after charging until it becomes 4.4V with a constant current of 0.2C, constant voltage charging is performed at 4.4V until the total charging time is 8 hours, Subsequently, constant current discharge was performed until the battery voltage was 3.3 V at 0.2 C, and the discharge capacity at that time was determined. In Table 2, the discharge capacity obtained for each battery is shown as a relative value when the discharge capacity of the battery of Comparative Example 1 is set to 100.

<Load characteristics>
About each battery of Examples 1-7 and Comparative Examples 1-3, after charging until it becomes 4.4V with a constant current of 0.2C, constant voltage charging is performed at 4.4V until the total charging time is 8 hours, Subsequently, a constant current discharge was performed at 2.0 C until the battery voltage was 3.3 V, and the discharge capacity at that time was determined. The value obtained by dividing the discharge capacity by the discharge capacity when discharged at 0.2 C was expressed as a percentage to obtain the load characteristics of the battery.

<Storage characteristics>
About each battery of Examples 1-7 and Comparative Examples 1-3, it charges on the same conditions as the said discharge capacity measurement, measures the battery thickness before storage, and after storing for 20 days in a 60 degreeC environment after that, a battery is used. It left still until it became normal temperature, the battery thickness after storage was measured, and the increase amount (battery swelling) of battery thickness was measured. This value was expressed as an index, with the amount of increase in thickness of the battery of Comparative Example 1 being 1, and the level of swelling. For example, if this is 0.5, it indicates that the amount of swelling is reduced to half that of Comparative Example 1.

<Safety evaluation>
About each battery of Examples 1-7 and Comparative Examples 1-3, it charges on the same conditions as the charge conditions in the case of the said discharge capacity evaluation, Then, it heats for 10 minutes in a 150 degreeC thermostat, and each at that time The maximum temperature (surface temperature) of the battery was measured. The lower the temperature of the battery after heating, the better the safety at high temperatures.

Table 1 and as can be seen from Table 2, the nonaqueous secondary battery of the _I 006 _{/ I 101} value good Examples 1-7 in the positive electrode, compared _I 006 _{/ I 101} value is unsuitable in the positive electrode Examples 1-3 Compared with the non-aqueous secondary battery, the battery has a high capacity, excellent load characteristics, and excellent battery storage characteristics and stability.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically an example of the non-aqueous secondary battery of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the non-aqueous secondary battery shown in FIG.

Explanation of symbols

1 Positive electrode 2 Negative electrode 3 Separator

Claims (7)

A non-aqueous secondary battery comprising a positive electrode having a positive electrode mixture layer containing lithium cobalt oxide as an active material, a negative electrode, and a non-aqueous electrolyte,
The lithium cobalt oxide includes at least a part of Co substituted with another metal element,
When the XRD analysis is performed on the positive electrode, the ratio I ₀₀₆ / I ₁₀₁ of the peak intensity I ₀₀₆ on the (006) plane to the peak intensity I ₁₀₁ on the ( ₁₀₁ ) plane is 0.6-3. Non-aqueous secondary battery. The nonaqueous secondary battery according to claim 1, wherein the positive electrode mixture layer has a density of 3.5 g / cm ³ or more.   The non-aqueous secondary battery according to claim 1, wherein the positive electrode mixture layer contains two or more types of lithium cobalt oxides having different average particle diameters.   4. The non-aqueous secondary battery according to claim 3, wherein at least one of the two or more lithium cobalt oxides having a minimum average particle diameter is substituted with a part of Co by another metal element. 5.   In the lithium cobalt oxide having the minimum average particle size, at least one selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al, and Sn is used as the metal element replacing a part of Co. The nonaqueous secondary battery according to any one of claims 1 to 4, which is a seed metal element.   The lithium cobalt oxide having the minimum average particle size has an Mg content of less than 2 mol% with respect to Co, and is composed of at least one metal element selected from the group consisting of Ti, Zr, Ge, and Nb. The non-aqueous secondary battery according to claim 5, wherein the total content is less than 0.5 mol% with respect to Co, and the total content of Al and / or Sn is less than 1 mol% with respect to Co. . In using the nonaqueous secondary battery according to any one of claims 1 to 6,
A method of using a non-aqueous secondary battery, wherein charging is performed such that the positive electrode potential at full charge is 4.35 to 4.6 V at a Li reference potential.
Here, the full charge is a constant current charge up to a predetermined voltage at a current value of 0.2 C, and then a constant voltage charge is performed at the predetermined voltage, so that the constant current charge and the constant voltage charge are performed. And charging under the condition that the total time is 8 hours.

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