JP5290819B2 - Non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery having a high capacity and excellent charge and discharge cycle characteristics and also having a high reliability such as safety. <P>SOLUTION: The non-aqueous secondary battery is provided with a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte. As the positive electrode active material, a lithium-containing transition metal oxide which has as a body at least one of transition metal element selected from a group of Co and Ni and contains at least one of metal element selected from a group of Mn, Mg, Ti, Zr, Ge, Nb, Al and Sn is used, and the non-aqueous electrolyte contains at least one of compound selected from sulfonic acid anhydride and sulfonate derivative, and a dinitrile compound. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a non-aqueous secondary battery having high capacity, excellent charge / discharge cycle characteristics, and high reliability such as safety.

  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. . In particular, 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 as a positive electrode active material and metal lithium as a negative electrode active material has an electromotive force of 4 V or more, so that high energy density can be achieved. I can expect.

However, the current LiCoO ₂ as the positive electrode active material, a LiCoO ₂ based secondary battery using a carbon material such as graphite as the negative electrode active material, the charge voltage is usually 4.2V or less, in the charging condition LiCoO The charge amount is about 60% of the theoretical capacity of ₂ . Although it is possible to increase the power capacity by making the end-of-charge voltage higher than 4.2 V, as the amount of charge increases, the LiCoO ₂ crystal structure collapses and the charge / discharge cycle life is shortened. Since the crystal structure of LiCoO ₂ becomes less stable, there arises a problem that the thermal stability is lowered.

In order to solve this problem, many attempts have been made to add a different metal element to LiCoO ₂ , and attempts have been made to use the battery in a high voltage region of 4.2 V or higher (Patent Documents 1 to 5).

  In addition to increasing the capacity, secondary batteries are required to have high reliability including charge / discharge cycle characteristics and safety.

  Conventionally, various techniques for solving problems such as battery safety, a decrease in charge / discharge cycle, and battery swelling have been proposed. For example, a lithium ion secondary battery that has already been put into practical use mainly includes a non-aqueous electrolyte having a mixed solvent of a cyclic ester such as ethylene carbonate and a chain ester such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. However, there is a technique for solving the above-mentioned problems that occur in lithium ion secondary batteries by adding an additive such as a specific cyclic sulfate to the non-aqueous electrolyte (for example, Patent Documents). 6-9). When a lithium ion secondary battery having a non-aqueous electrolyte containing the above additive is charged, a dense film derived from the above additive is formed on the negative electrode surface, and the organic solvent and the negative electrode in the non-aqueous electrolyte are formed by this film. It is considered that the charge / discharge cycle characteristics and the like of the battery can be improved.

  Further, when a lithium-containing composite oxide having a layered structure containing manganese as a constituent element or a lithium-containing composite oxide having a spinel structure containing manganese as a constituent element is used as a positive electrode active material, vinylene carbonate, It has been proposed to improve the charge / discharge cycle characteristics and high-temperature storage characteristics of a battery by adding a sulfonic acid anhydride or a sulfonic acid ester derivative (see Patent Document 10).

JP 07-176202 A Japanese Patent Laid-Open No. 2001-167663 JP 2004-296098 A JP 2001-176511 A JP 2002-270238 A JP-A-10-189041 JP-A-11-162511 Japanese Patent No. 3213459 Japanese Patent No. 3438636 JP 2006-344391 A

  However, there is still room for study in terms of increasing the battery capacity, further safety, and improving high-temperature storage characteristics. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous secondary battery having high capacity, excellent charge / discharge cycle characteristics, and high reliability such as safety.

The present invention is a non-aqueous secondary battery including a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte, and the general formula Li _x M ¹ _y M ² _{z is} used as the positive electrode active material. O ₂ (wherein M ¹ is one or more elements including at least one transition metal element selected from the group consisting of Co and Ni, and M ² is Mn, Mg, Ti, Zr, It is at least one metal element selected from the group consisting of Ge, Nb, Al and Sn, and M ¹ is an element other than Li, Co, Ni and M ² within a range of 5 mol% or less in the total amount. A lithium-containing transition metal oxide represented by the following formula: 0.97 ≦ x <1.02, 0.55 ≦ y <1.02, 0.002 ≦ z ≦ 0.4. contained, and the density of the positive electrode mixture layer is 3.5 g / cm ³ or more, the A non-electrolyte containing at least one compound selected from a sulfonic acid anhydride represented by the following general formula (1) and a sulfonic acid ester derivative represented by the following general formula (2) as a water electrolyte and a dinitrile compound: It is characterized by using a water electrolyte.

[In the general formula (1), R ₁ and R ₂ each independently represents an organic residue having 1 to 10 carbon atoms. Further, in the above general formula (2), _{R 3} and _{R 4} each independently represents an organic residue having 1 to 10 carbon atoms. ]

In the non-aqueous secondary battery of the present invention, the density of the positive electrode mixture layer is set to 3.5 g / cm ³ or more, and the filling amount of the positive electrode active material in the positive electrode mixture layer is increased to achieve high capacity, By using a lithium-containing transition metal oxide that contains a metal element and has high stability even in a charged state as a positive electrode active material, the collapse of the positive electrode active material is suppressed even when the battery is repeatedly charged and discharged. Charge / discharge cycle characteristics can be ensured.

In the nonaqueous secondary battery of the present invention, as the nonaqueous electrolyte,
By using a non-aqueous electrolyte containing at least one compound selected from sulfonic acid anhydrides and sulfonic acid ester derivatives and a dinitrile compound, the additive acts on the surface of the positive electrode or the negative electrode, It seems that the reaction of can be suppressed.

  Therefore, according to the present invention, it is possible to provide a non-aqueous secondary battery having high capacity, excellent charge / discharge cycle characteristics, and high reliability such as safety.

  As the positive electrode according to the present invention, a positive electrode mixture layer containing a positive electrode active material or the like can be used, for example, having a structure formed on one side or both sides of a current collector.

Positive electrode mixture layer in the present invention has a density, 3.5 g / cm ³ or higher, preferably 3.6 g / cm ³ or more, more preferably 3.8 g / cm ³ or more, the battery of the present invention, By increasing the density of the positive electrode mixture layer related to the positive electrode as described above, the filling amount of the positive electrode active material is increased to achieve high capacity. However, if the density of the positive electrode mixture layer is too high, the wettability of the non-aqueous electrolyte is lowered. Therefore, the density is preferably 4.6 g / cm ³ or less, for example, 4.4 g / cm ³ or less. It is more preferable that it is 4.2 g / cm ³ or less.

  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.

  A lithium-containing transition metal oxide represented by the following general formula (3) is used for the positive electrode active material of the positive electrode mixture layer.

Li _x M ¹ _y M ² _z O ₂ (3)
[In the general formula (3), M ¹ is one or more elements including at least one transition metal element selected from the group consisting of Co and Ni, and M ² is Mn, Mg, It is at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn, and M ¹ is in a range of 5 mol% or less in the total amount, and Li, Co, Ni and M ² Other elements may be included, and 0.97 ≦ x <1.02, 0.55 ≦ y <1.02, and 0.002 ≦ z ≦ 0.4. ]

  The lithium-containing transition metal oxide having a metal element as described above has good stability (particularly stability in a charged state), and thus can improve reliability such as battery safety. Further, in the lithium-containing transition metal oxide having the above metal element, since the stability thereof is improved, the collapse when the charge / discharge cycle of the battery is repeated is suppressed. The charge / discharge cycle characteristics of the battery can also be improved by using.

In the lithium-containing transition metal oxide, in order to improve the stability in a charged state, M ² is at least one metal selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al, and Sn. It is desirable to include an element, and it is more desirable that the lithium-containing transition metal oxide represented by the general formula (3) further satisfies the composition represented by the following general formula (4).

Li _x M ¹ _y Mn _u M ³ _v O ₂ (4)
[In the general formula (2), M ¹ is one or more elements including at least one transition metal element selected from the group consisting of Co and Ni, and M ³ is Mg, Ti, At least one metal element selected from the group consisting of Zr, Ge, Nb, Al and Sn, and M ¹ is in a range of 5 mol% or less in the total amount, and Li, Co, Ni, Mn and M ³ May contain other elements than 0.97 ≦ x <1.02, 0.55 ≦ y <1.02, 0.002 ≦ v ≦ 0.05 and 0.002 ≦ u + v ≦ 0.4. is there. ]

Note that v 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, as the content of M ³ increases, the effect of improving the charge / discharge cycle characteristics and safety of the battery becomes larger. On the other hand, from the viewpoint of the electrical characteristics of the battery, the content of M ³ should be as low as possible. This is desirable.

Further, the positive electrode active material is a mixture of two or more lithium-containing transition metal oxides having different average particle diameters, or in a particle size distribution curve obtained by the following average particle diameter measurement method, d ₁₀ and d ₉₀ it is preferred to have a particle size frequency peak to a larger diameter than the arithmetic mean d _M. or having a particle size frequency peak to a larger diameter than the arithmetic mean d _M of the d ₁₀ and d _90, or a large lithium-containing transition metal oxide having an average particle diameter and a small lithium-containing transition metal oxide having an average particle diameter In the positive electrode mixture layer, the gap between the lithium-containing transition metal oxides having a large particle diameter can be filled with the lithium-containing transition metal oxide having a small particle diameter. Thus, a high-density positive electrode mixture layer can be easily formed. More desirably, two or more lithium-containing transition metal oxides having different average particle diameters are used. The most desirable is a mixture of two or more types of lithium-containing transition metal oxides having different average particle sizes, and in the particle size distribution curve obtained by the following average particle size measurement method, the arithmetic average d of d ₁₀ and d _{90 It} has a particle size frequency peak in a particle size larger than _M. By using two or more types of lithium-containing transition metal oxides having different average particle sizes, it is possible to increase the density of the electrodes by allowing small particles to enter the gaps between the large particles. Further, when having a particle size frequency peak to a larger diameter than the arithmetic mean d _M of the d ₁₀ and d _90, since the attained small particles is reduced density desired. When the average using two or more different lithium-containing transition metal oxide particle size, having a particle size frequency peak to a larger diameter than the arithmetic mean d _M of the d ₁₀ and d ₉₀ is smaller in a gap large particles This is desirable because particles can enter and excessively small particles can be reduced to achieve higher density.

The “average particle diameter” of the lithium-containing transition metal oxide used in the present specification is a value measured using a microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd. The 50% diameter value (d ₅₀ ) median diameter in the volume-based integrated fraction in the case of obtaining the integral volume. _{Similarly, d 10} 10% _{diameter, d 90} is the 90% size. Here, the particle size distribution curve is created by connecting the frequency at each particle size with a curve.

As described above, the “two or more lithium-containing transition metal oxides having different average particle sizes” have a particle size larger than the arithmetic average d _M of d ₁₀ and d ₉₀ in the particle size distribution curve of these mixtures. preferably has a frequency peak (hereinafter, the grain size in the presence of the particle size frequency peak and d _p). More preferably, d _p / d _M is 1.05 or more, further preferably d _p / d _M is 1.2 or more, and particularly preferably d _p / d _M is 1.3 or more. Further, d _p / d _M is more preferably 1.6 or less, further preferably 1.5 or less, and particularly preferably 1.45 or less. More preferably, there are two or more peaks in the particle size distribution curve. For example, even when the same d _p / d _M = 1.3, two or more peaks are present in the particle size distribution curve. The density of the positive electrode mixture layer is improved by 0.1 g / cm ³ or more. 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. From the above, the average particle diameter (d ₅₀ ) of the lithium-containing transition metal oxide and the mixing ratio thereof can be determined.

  When the above-mentioned “two or more types of lithium-containing transition metal oxides having different average particle sizes” are used in combination, the average particle size of the one having the maximum average particle size [hereinafter referred to as “positive electrode active material (A)”] , Where A is the average particle diameter of B having the smallest average particle diameter [hereinafter referred to as “positive electrode active material (B)”], the ratio B / A of B to A is 0.15 or more and 0.00. It is preferable that it is 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 make the positive electrode mixture layer have a high density. 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 is difficult to fill the gap between the lithium-containing transition metal oxide particles having a large particle diameter in the positive electrode mixture layer. It may be difficult to increase the density of the mixture layer. On the other hand, if the average particle diameter of the positive electrode active material (B) is too small, the void volume between the small particles increases, and therefore the density tends to be difficult to increase. For example, the average particle diameter is 2 μm or more. Preferably, it is 3 μm or more, more preferably 4 μm or more.

  As the positive electrode active material, only two kinds of lithium-containing transition metal oxides having different average particle diameters are used, 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-containing transition metal oxides having different diameters can also be used. When three or more lithium-containing transition metal 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). The lithium-containing transition metal oxide may be used together with the positive electrode active materials (A) and (B).

  Of the lithium-containing transition metal oxide of the positive electrode, the content of the positive electrode active material (B) having the smallest average particle size is, for example, preferably 5% by mass or more, and more preferably 10% by mass or more. Preferably, it is 20 mass% or more. When the positive electrode active material (B) is contained in the above amount, the gaps between the lithium-containing transition metal 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-containing transition metal oxide of the positive electrode is too large, it becomes difficult to make the positive electrode mixture layer high in density. 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less.

  Therefore, for example, when the lithium-containing transition metal oxide possessed by the positive electrode is two types of the positive electrode active material (A) and the positive electrode active material (B), the average particle size of the two active materials is The content of the larger positive electrode active material (A) 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, it is desirably 80% by mass or less.

  As described above, when two types of lithium-containing transition metal oxides having different average particle sizes are used, the positive electrode active material (A) whose content ratio can be made higher than that of the positive electrode active material (B) The lithium-containing transition metal oxide represented by the formula (3) or (4) is desirable from the viewpoint of increasing the capacity.

In addition, since the positive electrode active material (B) has a smaller average particle diameter than the positive electrode active material (A), there is a possibility that the positive electrode active material (B) may easily react with the electrolytic solution as compared with the positive electrode active material (A). In order to improve the reliability and ensure the reliability such as the safety of the battery, the positive electrode active material (B) is at least one selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al and Sn containing metal elements M ^5, for example, it is preferable to use a lithium-containing transition metal oxide represented by the following general formula (5).

^{_{Li s M 4 t M 5 w}} O 2 (5)

Here, in the general formula (5), M ⁴ is at least one transition metal element of Co, Ni, or Mn, and M ⁵ is made of Mg, Ti, Zr, Ge, Nb, Al, and Sn. It is at least one metal element selected from the group, and M ³ may contain elements other than Li, Co, Ni, Mn, and M ⁴ in the total amount of 5 mol% or less 0.97 ≦ s <1.02, 0.8 ≦ t <1.02 and 0.002 ≦ w ≦ 0.05. Note that w 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, as the content of M ⁵ increases, the effect of improving the charge / discharge cycle characteristics and safety of the battery becomes larger. On the other hand, from the viewpoint of the electrical characteristics of the battery, the content of M ⁵ should be as low as possible. This is desirable.

The element selected in M ³ of the general formula (4) and the element selected in M ⁵ of the general formula (5) may be different, but the improvement in battery safety is more effective. For this reason, it is preferable to contain at least Mg, and it is preferable that M ³ and M ⁵ are contained in common.

Further, since the density of the positive electrode mixture layer can be increased as the Co ratio in the lithium-containing transition metal oxide is higher, for example, the Co ratio in M ¹ in the general formulas (3) and (4), The Co ratio in M ⁴ in the formula (5) is preferably 10 mol% or more, more preferably 30 mol% or more, and still more preferably 65 mol% or more.

  X in the general formulas (3) and (4) and s in the general formula (5) are values that change depending on the charge / discharge of the battery, but are 0.97 or more and less than 1.02 when the battery is manufactured. It is preferable. x and s 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.

In the positive electrode active material (B), from the viewpoint of more effectively exerting the effect of containing Mg, the content thereof is, for example, 0.1 mol with respect to M ⁴ in the general formula (5). % Or more, 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 is based on M ⁴ from the viewpoint of more effectively exerting the above-described effect by containing these. It is preferably 0.05 mol% or more, more preferably 0.08 mol% or more, and further preferably 0.1 mol% or more. Furthermore, in the case where the positive electrode active material (B) contains Al or Sn, the total amount thereof is less than 0. ^{4 with} respect to M ⁴ from the viewpoint of more effectively exerting the above-described effects by containing these. It is preferably 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), the content of Mg is too large, since the load characteristics of the battery tends to decrease, and the content thereof, for example, with respect to M ^4, at less than 2 mol% Preferably, it is less than 1 mol%, more preferably less than 0.5 mol%, 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 M ⁴ , and 0.25 More preferably, it is less than mol%, and still more preferably less than 0.15 mol%. It positive electrode active material (B) is, when containing Al or Sn is the total amount thereof, with respect to ^{M 4,} it is preferably less than 1 mol%, less than 0.5 mol% Is more preferable, and it is still more preferable that it is less than 0.3 mol%.

On the other hand, in the positive electrode active material (A), from the viewpoint of more effectively exerting the effect of containing Mg, the content thereof is, for example, relative to M ¹ in the general formulas (3) and (4), The amount is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and further preferably 0.07 mol% or more.

Further, when the positive electrode active material (A) contains Ti, Zr, Ge, or Nb, the total amount is based on M ¹ from the viewpoint of more effectively exerting the above-described effect by containing these. Thus, it is preferably 0.005 mol% or more, more preferably 0.008 mol% or more, and still more preferably 0.01 mol% or more. Furthermore, when the positive electrode active material (A) contains Al or Sn, the total amount thereof is set to 0. ^{1 with} respect to M ¹ from the viewpoint of more effectively exerting the above-described effects by containing them. It is preferably at least 01 mol%, more preferably at least 0.05 mol%, and even more preferably at least 0.07 mol%.

However, even in the positive electrode active material (A), if the content of Mg is too large, the load characteristics of the battery tend to be reduced. Therefore, the content is, for example, 0.5 mol% with respect to M ¹ . It is preferably less than 0.2 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, the positive electrode active material (A) is, in the case of containing Ti, Zr, Ge or Nb, the total amount of preferably against ^{M 1,} it is less than 0.3 mol%, 0.1 It is more preferably less than mol%, and still more preferably less than 0.05 mol%. Also, the positive electrode active material (A) is, when containing Al or Sn is the total amount thereof, with respect to ^{M 1,} preferably less than 0.5 mol%, less than 0.2 mol% More preferably, it is less than 0.1 mol%.

In the positive electrode active material (A), the positive electrode active material (B), and other lithium-containing transition metal oxides, there are no particular restrictions on the way in which the metal elements M ³ and M ⁵ are contained, for example, they exist on the particles. Even if it is present as a solid solution in the active material, it may be unevenly distributed with a concentration distribution inside the active material, or a layer may be formed as a compound on the surface. It is preferable that they are uniformly dissolved.

Although the stabilizing elements M ³ and M ⁵ contribute to improving the stability of the lithium-containing transition metal oxide, if the content is too large, the effect of occluding and releasing Li ions is impaired. The characteristics may be deteriorated.

Since the positive electrode active material (B) has a small particle size and tends to be low in stability, it is preferable that the content of the stabilizing element M ⁵ is high to some extent, while the particle size is small and the surface area is large. The activity is high, and the influence on the occlusion and release action of Li ions is small even when M ⁵ is contained.

On the other hand, since the positive electrode active material (A) having a larger particle size than the positive electrode active material (B) is more stable than the positive electrode active material (B), the positive electrode active material (B) has a greater M ^3. On the other hand, since the surface area is smaller and the activity is lower than that of the positive electrode active material (B), the action of occluding and releasing Li ions is easily impaired by the inclusion of M ³ .

Therefore, the content of the metal element M ³ in the positive electrode active material (A) is preferably smaller than the content of the metal element M ⁵ in the positive electrode active material (B).

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

In addition, when two or more types of lithium-containing transition metal oxides having different average particle sizes are used, those having different average particle sizes may have the same composition, and compositions having different average particle sizes have different compositions. It may have. For example, when the lithium-containing transition metal oxide is a positive electrode active material (B) having a minimum average particle size and a positive electrode active material (A) having a maximum average particle size, the positive electrode active material (A) is LiCo _{0. .998} Mg _0.0008 Ti _0.0004 Al _0.0008 O ₂ and the positive electrode active material (B) is LiCo _0.334 Ni _0.33 Mn _0.33 Mg _0.0024 Ti _0.0012 Al _0.0024 O ₂ may be combined.

The positive electrode active material (lithium-containing transition metal oxide) is formed through a specific synthesis process and a specific battery manufacturing process. For example, in order to obtain a lithium-containing transition metal oxide containing Co as the transition metal element M ^{1 and} having different particle diameters, an alkali such as NaOH is generally added dropwise to an acidic aqueous solution of Co. Precipitate as (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 and the planetary ball mill is mixed. 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 inductively coupled plasma (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.

  The positive electrode is produced, for example, by the following method. First, if necessary, a conductive additive (eg, graphite, carbon black, acetylene black, etc.) is added to the lithium-containing transition metal oxide that is the positive electrode active material, and further a binder (eg, polyvinylidene fluoride, polytetrafluoroethylene, etc.). A positive electrode mixture is prepared by adding fluoroethylene or the like). 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. When two or more kinds of lithium-containing transition metal oxides having different average particle diameters [for example, positive electrode active material (A) and positive electrode active material (B)] are used as the positive electrode active material, these lithium-containing transitions are used. What is necessary is just to use for the subsequent process the positive electrode mixture prepared by mixing a metal oxide at a predetermined mass ratio and adding the conductive assistant and binder to the mixture. 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, it is difficult to achieve high capacity, and the density of the positive electrode mixture layer is also difficult to increase. This is because the formability of the positive electrode 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 includes, for example, an electrode body having a laminated structure in which a positive electrode and a negative electrode having a positive electrode mixture layer are stacked with a separator interposed therebetween, and a winding structure in which this is further wound in a spiral shape The electrode body and the like are sealed together with the non-aqueous electrolyte in the exterior body.

  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.

  In the nonaqueous secondary battery of the present invention, at least one compound selected from a sulfonic acid anhydride represented by the following general formula (1) and a sulfonic acid ester derivative represented by the following general formula (2), and a dinitrile A nonaqueous electrolytic solution (nonaqueous electrolyte) containing the compound is used.

[In the general formula (1), R ₁ and R ₂ each independently represents an organic residue having 1 to 10 carbon atoms. Further, in the above general formula (2), _{R 3} and _{R 4} each independently represents an organic residue having 1 to 10 carbon atoms. ]

  The above additive has a function of forming a surface protective film on the surface of the positive electrode active material during charging of the battery (particularly during initial charging), and the reaction between the positive electrode and the nonaqueous electrolyte is caused by the surface protective film. Therefore, the temperature rise of the battery due to such a reaction can be suppressed, and the safety is excellent.

R ₁ and R ₂ in the above general formula (1) representing the sulfonic acid anhydride, and R ₃ and R ₄ in the general formula (2) representing the sulfonic acid ester derivative each independently have 1 carbon atom. More than 10 organic residues. R ₁ , R ₂ , R ₃ and R ₄ are preferably alkyl groups having 1 to 10 carbon atoms in which some or all of the hydrogen atoms may be substituted with fluorine atoms, specifically, , Methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group and the like. R ₁ , R ₂ , R ₃ and R ₄ may be an aromatic group having 1 to 10 carbon atoms. R ₁ , R ₂ , R ₃ and R ₄ preferably have 2 or more carbon atoms, and preferably 6 or less carbon atoms. R ₄ is more preferably an alkyl group having 1 to 6 carbon atoms or a benzyl group. In sulfonic acid anhydrides and sulfonic acid ester derivatives in which R ₁ , R ₂ , R _3, and R ₄ have more than 10 carbon atoms, the solubility in a non-aqueous electrolyte solvent is reduced, so that the effect is hardly exhibited.

  The sulfonic acid anhydride may be a symmetric anhydride, an asymmetric anhydride derived from two different acids (also referred to as a mixed anhydride), or an acid anhydride ester-anhydride containing a partial ester as an acid residue. It is. Specific examples thereof include ethanemethanesulfonic anhydride, propanesulfonic anhydride, butanesulfonic anhydride, pentanesulfonic anhydride, hexanesulfonic anhydride, heptanesulfonic anhydride, butaneethanesulfonic anhydride, Examples include butanehexanesulfonic acid anhydride and benzenesulfonic acid anhydride. These sulfonic acid anhydrides may be used alone or in combination of two or more. Of these, propanesulfonic anhydride, butanesulfonic anhydride, butanepentanesulfonic anhydride, pentanesulfonic anhydride, and hexanesulfonic anhydride are particularly preferable.

  Specific examples of the sulfonate derivative include methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, isobutyl methanesulfonate, methyl ethanesulfonate, pentanyl methanesulfonate, hexyl methanesulfonate, and ethanesulfone. Ethyl acetate, propyl ethanesulfonate, isobutyl ethanesulfonate, ethyl propanesulfonate, propyl propanesulfonate, butyl propanesulfonate, methyl butanesulfonate, ethyl butanesulfonate, propyl butanesulfonate, methyl pentanesulfonate, pentanesulfone Ethyl acetate, ethyl hexanesulfonate, methyl hexanesulfonate, propyl hexanesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, benzenesulfonic acid (Chain) alkyl sulfonates such as propyl, phenyl methanesulfonate, phenyl ethanesulfonate, phenyl propanesulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, benzyl propanesulfonate; methyl benzylsulfonate, benzylsulfone Examples thereof include chain aromatic sulfonates such as ethyl acrylate and propyl benzyl sulfonate; fluorinated products of the respective sulfonates described above. These sulfonic acid ester derivatives may be used alone or in combination of two or more. Of these, ethyl propanesulfonate, methyl butanesulfonate, ethyl butanesulfonate, methyl pentanesulfonate, and ethyl pentanesulfonate are particularly preferable. One or more of the sulfonic acid anhydrides and one or more of the sulfonic acid ester derivatives can be used in combination.

  The content of the sulfonic acid anhydride in the total amount of the non-aqueous electrolyte used for producing the battery of the present invention is, for example, 0.2% by mass or more, more preferably 0.3% by mass or more, and 2% by mass. Hereinafter, it is desirable that the content is 1% by mass or less. In addition, the content of the sulfonic acid ester derivative in the total amount of the non-aqueous electrolyte used for manufacturing the battery of the present invention is, for example, 0.2% by mass or more, more preferably 0.3% by mass or more, It is desirable that the content is not more than mass%, more preferably not more than 3 mass%. If the content of the sulfonic acid anhydride or the sulfonic acid ester derivative in the non-aqueous electrolyte is too small, the effects of using these (the safety improvement effect, the charge / discharge cycle characteristics and the high temperature storage characteristics If the amount is too large, the film formed by the reaction with the positive and negative electrodes becomes thick and the resistance is increased, making it difficult to construct a high-performance battery.

  Moreover, as said dinitrile compound, the compound represented by general formula NC-R-CN (however, R is a C1-C10 linear or branched hydrocarbon chain) is preferable, for example. R in the above general formula is more preferably a linear alkylene chain having 1 to 10 carbon atoms or a branched alkylene chain.

  Specific examples of the dinitrile compound represented by the above general formula include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6 -Dicyanodecane, 2,4-dimethylglutaronitrile, etc. are mentioned.

  The content of the above compound in the non-aqueous electrolyte is preferably 0.01% by mass or more and more preferably 0.05% by mass or more from the viewpoint of more effectively ensuring the effect of the use of the compound. More preferred. However, if the amount of the compound is too large, the charge / discharge cycle characteristics tend to deteriorate. Therefore, the content of the compound in the nonaqueous electrolytic solution is more preferably 1% by mass or less, and 0.5% by mass. % Or less is particularly preferable.

  By adding the sulfonic acid anhydride or sulfonic acid ester derivative and the dinitrile compound in an appropriate content, the effect can be enhanced by the synergistic action.

  Although it does not specifically limit as a solvent of a nonaqueous electrolyte, For example, chain esters, such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propion carbonate; High dielectric constants, such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate Cyclic ester; mixed solvent of chain ester and cyclic ester; and the like, and a mixed solvent with a cyclic ester having a chain ester as a main solvent is particularly suitable. In order to further enhance the effect of the additive, it is preferable to contain vinylene carbonate or a derivative thereof, and the addition amount is preferably 0.3% by mass or more and 5% by mass or less. Is preferred.

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

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.

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 the load characteristics may be deteriorated in a high-density negative electrode. 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. This is because if the specific surface area of graphite is not large to some extent, the characteristics tend to deteriorate, while if it 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.

  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.

  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. In addition, the amount of the NMP solution of polyvinylidene fluoride (PVDF) having a concentration of 10% by mass was adjusted so that the solid content concentration during kneading was always 94% by mass. Was fed into a twin-screw kneader-extruder while being controlled so as to be a predetermined amount per unit time, and kneaded to prepare a positive electrode mixture-containing paste.

  In addition, the composition of the positive electrode active material (A) and the positive electrode active material (B) is a value obtained by dissolving each in aqua regia and confirming the ratio of contained elements by ICP analysis and atomic absorption analysis. .

Next, 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 auxiliary agent: 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 (positive electrode density) is 3.86 g / cm ³ , and the thickness of the positive electrode mixture layer (the thickness of both surfaces, that is, the total thickness of the positive electrode, the aluminum of the positive electrode current collector). The thickness obtained by subtracting the thickness of the foil (hereinafter the same) was 135 μm.

The particle size distribution of the mixture of the positive electrode active materials (A) and (B) was measured using a Microtrac particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd. The particle size frequency peak d _p was present at 12 μm and 5 μm, while d ₁₀ was 4.3 μm, d ₉₀ was 13.8 μm, and the d _M value was 9 μm. D _p / d _M was 1.3.

  Here, the positive electrode active material (A) has 0.08 mol% Mg, 0.04 mol% Ti, and 0.08 mol% Al with respect to Co. Moreover, when the concentration of Mg, Ti, and Al in the particle cross section was measured using an electron beam microanalyzer “EPMA1600” manufactured by Shimadzu Corporation, all the elements were uniformly distributed.

  Further, the positive electrode active material (B) is 0.24 mol% Mg, 0.12 mol% Ti, 0.24 mol% Al, and positive electrode active material with respect to Co. With respect to (A), on a molar basis, Mg was 3 times, Ti was 3 times, and Al was 3 times.

  Regarding the positive electrode active material (B), the cross section of the particles was observed in the same manner as the positive electrode active material (A), but Mg, Ti and Al were uniformly distributed.

<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 carboxymethylcellulose, and 1 part by mass of styrene butadiene rubber are mixed in the presence of water to form a slurry. A negative electrode mixture containing paste was prepared in the. 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 was dissolved in a mixed solvent in which methyl ethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed at a volume ratio of 3: 1: 2 so as to have a concentration of 1.2 mol / l. A nonaqueous electrolytic solution was prepared by adding 0.2% by mass of succinonitrile by mass%.

<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 and sufficiently infiltrating the non-aqueous electrolyte into the separator, etc., partial charge to 25% charge state, after discharging the gas generated by the partial charge, The inlet was sealed and sealed. Thereafter, charging and aging were performed to obtain a rectangular non-aqueous secondary battery having a width of 34.0 mm, a thickness of 4.0 mm, and a height of 50.0 mm.

(Examples 2 to 8)
Instead of ethyl propanesulfonate, butanesulfonic anhydride (Example 2), butanepentanesulfonic anhydride (Example 3), methyl propanebutanesulfonate (Example 4), methyl butanesulfonate (Example 5) ), Ethyl butanesulfonate (Example 6), methyl pentanesulfonate (Example 7) or ethyl hexanesulfonate (Example 8), respectively, and 0.5% by mass relative to the total mass of the non-aqueous electrolyte. A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the non-aqueous electrolyte was used, and a non-aqueous secondary battery was fabricated in the same manner as in Example 1 except that this non-aqueous electrolyte was used.

Example 9
LiPF ₆ was dissolved in a mixed solvent in which methyl ethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed at a volume ratio of 3: 1: 2 so as to have a concentration of 1.2 mol / l. A non-aqueous electrolyte solution was prepared by adding 0.2% by mass of succinonitrile and 1.0% by mass of vinylene carbonate. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the nonaqueous electrolyte was used.

(Example 10)
A non-aqueous secondary battery was fabricated in the same manner as in Example 1 except that LiCo _0.9965 Mg _0.0014 Ti _0.0007 Al _0.0014 O ₂ (average particle size 8 μm) was used alone as the positive electrode active material. did. The density of the positive electrode mixture layer after the pressure treatment (the density of the positive electrode) was 3.76 g / cm ³ . This positive electrode active material has a particle size frequency peak d _p at a particle size of 9.6 μm, d ₁₀ is 4 μm, d ₉₀ is 12.4 μm, d _M is 8.2 μm, and d _p / d _M is 1.2.

(Example 11)
Example 1 except that the positive electrode active material (B) was changed to LiCo _0.334 Ni _0.33 Mn _0.33 Mg _0.0024 Ti _0.0012 Al _0.0024 O ₂ (average particle size 5 μm) A non-aqueous secondary battery was produced in the same manner. The density of the positive electrode mixture layer after the pressure treatment (the density of the positive electrode) was 3.72 g / cm ³ . The positive electrode active material (B) has 0.24 mol% Mg, 0.12 mol% Ti, and 0.24 mol% Al with respect to the total amount of Co, Ni, and Mn. And on the molar basis with respect to the positive electrode active material (A), Mg was 3 times, Ti was 3 times, and Al was 3 times. The particle size frequency peak d _p of the whole positive electrode active material was present at 12 μm and 5 μm, while d ₁₀ was 4.1 μm, d ₉₀ was 14.1 μm, and d _M value was 9.1 μm. D _p / d _M was 1.3.

(Comparative Example 1)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that ethyl propanesulfonate and succinonitrile were not added to the electrolytic solution.

(Comparative Example 2)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that succinonitrile was not added to the electrolytic solution.

(Comparative Example 3)
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that ethyl propanesulfonate was not added to the electrolytic solution.

(Comparative Example 4)
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that LiCoO ₂ (average particle size 8 μm) was used alone as the positive electrode active material.

  The following characteristic evaluation was performed about the non-aqueous secondary battery of Examples 1-6 and Comparative Examples 1-4.

<Discharge capacity after charge / discharge cycle>
About each battery of Examples 1-11 and Comparative Examples 1-4, after charging with a constant current of 0.2 C to 4.2 V, constant voltage charging was performed until the total charging time was 8 hours, followed by 0.2 C A constant current discharge was performed until the battery voltage was 3.3 V, and the discharge capacity at that time was determined as the initial capacity. In addition, the voltage of the lithium standard positive electrode at the time of the said constant current charge means 4.3V). Furthermore, charge / discharge under the same conditions was repeated 400 times, and the discharge capacity at the 400th cycle was evaluated as the discharge capacity after the cycle. The results are shown in Table 1. In these tables, the discharge capacity after the charge / discharge cycle obtained for each battery is a relative value when the discharge capacity at the charge / discharge cycle of the battery of Comparative Example 1 is 100. Show.

<Overcharge test>
For each of the batteries of Examples 1 to 11 and Comparative Examples 1 to 4, the following tests were performed three by three. After charging at a constant current of 0.2 C to 4.2 V, charge at a constant voltage until the total charging time is 8 hours, and then perform a 5 V overcharge test at 1 A to determine the number of explosion-proof mechanisms (vents) activated. Examined. The results are shown in Table 1.

<Battery swelling>
About each battery of Examples 1-11 and Comparative Examples 1-4, after charging with a constant current of 0.2 C up to 4.2 V, constant voltage charging was performed until the total charging time was 8 hours, and then the temperature was set to 85 ° C. The battery was stored for 4 hours in a thermostatic bath, and the battery thickness before and after storage was measured. Changes in battery thickness before and after storage are shown in Table 1 as battery swelling.

  As is apparent from the results shown in Table 1, the nonaqueous secondary batteries of Examples 1 to 11 are superior in discharge capacity and charge / discharge cycle characteristics as compared to the nonaqueous secondary batteries of Comparative Examples 1 to 4. High safety during overcharge and excellent durability at high temperatures.

Claims (8)

A non-aqueous secondary battery comprising a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode and a non-aqueous electrolyte,
As the positive electrode active material, the general formula _{^{Li x Co y Mg z1 M 6}} z2 M 7 (z-z1-z2) O 2 or _{Li x Co y1 Ni (y-} y1) Mn z1 Mg z2 M 6 z3 M 7 (z _{-z1-z2-z3) O 2} ( provided that at least M ⁶ is at least one metal element selected Ti, Zr, Ge or from the group consisting of Nb,, M ⁷ is selected from Al or Sn One metal element, 0.97 ≦ x <1.02, 0.55 ≦ y <1.02, 0 <y1 <y, 0.002 ≦ z ≦ 0.4, 0 <z1, z2, z3 <z.) containing a lithium-containing transition metal oxide represented by:
The density of the positive electrode mixture layer is 3.5 g / cm ³ or more,
As the non-aqueous electrolyte, at least one compound selected from a sulfonic acid anhydride represented by the following general formula (1) and a sulfonic acid ester derivative represented by the following general formula (2), and succinonitrile: A non-aqueous secondary battery using a non-aqueous electrolyte contained therein.

[In the general formula (1), R ¹ and R ² each independently represents an alkyl group having 1 to 6 carbon atoms. Similarly, the general formula (2), ^{R 3} and ^{R 4} are each independently, carbon atoms an alkyl group having 1 to 6. ]   M in the general formula of the lithium-containing transition metal oxide ⁶ Is Ti and M ⁷ The nonaqueous secondary battery according to claim 1, wherein is Al. The nonaqueous secondary battery according to claim 1, wherein in the particle size distribution curve of the positive electrode active material, the d ₅₀ value is larger than the arithmetic average value of the d ₁₀ value and the d ₉₀ value.   The nonaqueous secondary battery according to claim 1 or 2, wherein a nonaqueous electrolyte containing 0.2 to 5% by mass of the sulfonic acid anhydride represented by the general formula (1) is used.   The nonaqueous secondary battery according to claim 1 or 2, wherein a nonaqueous electrolyte containing 0.2 to 5% by mass of the sulfonic acid ester derivative represented by the general formula (2) is used.   The sulfonic acid anhydride represented by the general formula (1) is butanesulfonic acid anhydride or butanepentanesulfonic acid anhydride,
  The sulfonic acid ester derivative represented by the general formula (2) is any one of ethyl propanesulfonate, methyl butanebutanesulfonate, methyl butanesulfonate, ethyl butanesulfonate, methyl pentanesulfonate, and ethyl hexanesulfonate. The nonaqueous secondary battery according to any one of claims 1, 2, 4, and 5. The nonaqueous secondary battery according to any one of claims 1 to 6 , wherein a nonaqueous electrolyte containing 0.05 to 0.5 mass% of succinonitrile is used. The nonaqueous secondary battery according to any one of claims 1 to 7 , wherein a nonaqueous electrolyte containing 0.3 to 5% by mass of vinylene carbonate is used.