JP2012028225A - Nonaqueous electrolyte secondary battery and method for manufacturing positive electrode mixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has high thermal stability and electrodes having high energy density, and a method for manufacturing a positive electrode mixture.SOLUTION: The positive electrode is composed by forming a positive electrode mixture layer consisting of a positive electrode active material 10a, conductive agents 10b, 20, 30 and binder on a surface of a positive electrode current collector 5. The nonaqueous electrolyte secondary battery 100 has a positive electrode in which the amount of the positive electrode mixture layer is equal to or more than 125 g/mper on side of the positive electrode current collector 5. The positive electrode mixture layer 5 contains olivine type lithium-containing phosphate represented by a specific formula (1) as the positive electrode active material 10a, amorphous carbon 10b, lump graphite 20 and carbon black 30 as conductive agents, polyacrylonitrile and polyvinylidene fluoride as the binder. And the positive electrode active material 10a is coated with amorphous carbon 10b, in an amount of 2 wt.% to 5 wt.% based on the whole positive electrode mixture layer, and contained amounts of conductive agents 10b, 20, 30 are equal to or more than 6 wt.% based on the whole positive electrode mixture layer.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for producing a positive electrode mixture.

  For example, nonaqueous electrolyte secondary batteries (lithium ion secondary batteries) are attracting attention for use in power systems such as smart grids, use in vehicles such as railways and automobiles, and use in information equipment. As the positive electrode active material contained in the positive electrode of the nonaqueous electrolyte secondary battery, lithium cobaltate has been the mainstream. However, since the raw material cobalt is small in output and expensive, a non-aqueous electrolyte secondary battery using lithium cobaltate as a positive electrode active material has been expensive. Further, such a non-aqueous electrolyte secondary battery using lithium cobaltate has a problem in safety when the battery temperature rises at the end of charging.

  For the above reasons, the use of, for example, lithium manganate, lithium nickelate, and the like as a positive electrode active material that replaces lithium cobaltate is currently being studied. However, non-aqueous electrolyte secondary batteries using lithium manganate as a positive electrode active material have problems such as insufficient discharge capacity and elution of manganese when the battery temperature rises. In addition, a nonaqueous electrolyte secondary battery using lithium nickelate as a positive electrode active material has problems such as a decrease in discharge voltage and a decrease in battery thermal stability at the end of charging.

In view of such a problem, recently, olivine type lithium iron phosphate such as LiFePO ₄ is used as a positive electrode active material. Has attracted attention. The olivine-type lithium-containing phosphate is represented by the chemical formula LiMPO ₄ (where M represents one or more elements selected from the group consisting of Co, Ni, Mn, and Fe). The battery voltage can be arbitrarily selected according to the type of M. A battery using such an olivine-type lithium-containing phosphate as a positive electrode active material has a relatively high battery capacity of about 140 mAh / g or more and about 170 mAh / g or less, so the battery capacity per unit weight is increased. There is an advantage that you can. In particular, for example, lithium iron phosphate (LiFePO ₄ ) in which M is Fe is advantageous in that it can greatly reduce the production cost of a non-aqueous electrolyte secondary battery using lithium iron phosphate from the viewpoint of high yield and low cost. have.

  Among olivine-type lithium-containing phosphates, for example, lithium iron phosphate is known to be iron phosphate having high thermal stability when a battery using the lithium phosphate is in a charged state. Further, the charging end potential is 3.6 V based on lithium metal, and the battery is charged 100% at 4.2 V or less, which is the decomposition potential of cyclic carbonates and chain carbonates usually used as the main component of the non-aqueous electrolyte. Is possible. Therefore, non-aqueous electrolyte secondary batteries using lithium iron phosphate are highly durable because iron does not deposit during charging and cause a short circuit inside the battery. It is expected as a positive electrode active material that can suppress the above.

  However, lithium iron phosphate has a NASICON structure, which is an ionic conductor, and therefore has poor electron conductivity, and has a strong crystal structure, so that lithium ion diffusion is limited. Accordingly, it is known that only one-dimensional diffusion path exists, so that lithium ion diffusibility is poor. Therefore, despite the above advantages, lithium iron phosphate has a problem that it is difficult to use as a positive electrode active material because of its low electronic conductivity.

  In order to solve such problems, the surface of the lithium iron phosphate particles is coated with a highly conductive carbon material to improve the electron conductivity, and the particle diameter of the particles is set to 1 μm or less to provide a reactive path. Patent Document 1 describes use as a positive electrode active material by short-circuiting and increasing the reaction rate.

  Patent Document 2 describes that a conductive agent is used to improve the electron conductivity in the electrode, and in addition, in order to form the electrode on the aluminum foil, the contact between the positive electrode active material particles is ensured. . Patent Document 3 describes the use of polyacrylonitrile for the purpose of improving interparticle contact.

JP 2002-110162 A JP 2008-181850 A JP 2005-251554 A

Table 1 shows the capacity density (mAh) obtained by the product of the discharge capacity (mAh / g) and the true density (g / cm ³ ) for lithium iron phosphate and lithium cobaltate obtained by the study of the present inventors. / Cm ³ ).

※ リン酸鉄リチウムの放電容量は、Ｌｉ金属を対極として３．８Ｖまで充電した場合の放電容量を表し、コバルト酸リチウムの放電容量は、Ｌｉ金属を対極として４．３Ｖまで充電した場合の放電容量を表す。
また、理論エネルギー密度は、平均電位と放電容量と真密度との積を表す。

* The discharge capacity of lithium iron phosphate represents the discharge capacity when Li metal is charged to 3.8V, and the discharge capacity of lithium cobaltate is the discharge capacity when charged to 4.3V using Li metal as the counter electrode. Represents capacity.
The theoretical energy density represents the product of average potential, discharge capacity, and true density.

Although both lithium iron phosphate and lithium cobaltate show similar discharge capacities, the true density of lithium iron phosphate is lower than that of lithium cobaltate (specifically, about 3/4). ), And the theoretical capacity density is about 25% lower. In addition, in order to increase the reaction activity of lithium iron phosphate, the particle size of lithium iron phosphate is reduced, and in order to further increase the conductivity, a low-density carbon material and lithium iron phosphate are combined. Therefore, since the content of lithium iron phosphate in the positive electrode becomes lower, the electrode density of the positive electrode is usually adjusted in the range of 1.7 g / cm ³ or more and 2 g / cm ³ or less.

  The potential of the positive electrode containing lithium iron phosphate as a positive electrode active material is usually about 3.4V. Therefore, the energy density when lithium iron phosphate is used is lower than the energy density of a positive electrode (usually about 4.2 V) containing lithium cobalt oxide as a positive electrode active material. That is, when it is intended to achieve the same energy density as a battery having a positive electrode containing lithium cobaltate as a positive electrode active material using a positive electrode containing lithium iron phosphate as a positive electrode active material, the positive electrode active material in the positive electrode Although it is important to increase the content of, it is necessary to increase the amount of the mixture layer by about 25% as compared with the conventional positive electrode because the filling property to the positive electrode is low. Therefore, the positive electrode becomes thicker than the conventional one.

  When the thickness of the positive electrode is increased, the distance from the positive electrode current collector to the electrode surface is increased, so that the electron conduction path and the lithium ion diffusion path in the electrode are also increased. That is, as the thickness of the positive electrode increases, the internal resistance of the battery increases. In addition, a larger amount of binder may be required due to an increase in inter-particle contact between the positive electrode active material particles, but the binder usually has almost no electron conductivity, and the electron conduction path and lithium ion in the electrode. The diffusion path may be hindered by the binder. Therefore, the internal resistance may also increase with an increase in the binder amount. As described above, there is a problem that the resistance inside the battery increases as the thickness of the positive electrode increases.

  The present invention has been made to solve the above-described problems, and has as its object to provide a nonaqueous electrolyte secondary battery having a high thermal stability and a high energy density, and a method for producing a positive electrode mixture. Is to provide.

  As a result of intensive studies to solve the above problems, the present inventor has added a plurality of other conductive agents and a binder in addition to the positive electrode active material coated with a specific amount of a conductive agent in the positive electrode, thereby increasing the heat. The present invention was completed by finding that a nonaqueous electrolyte secondary battery having high mechanical stability and a high energy density electrode and a method for producing a positive electrode mixture can be provided.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having a high thermal stability and a high energy density electrode, and a method for producing a positive electrode mixture.

It is sectional drawing which showed typically the structure of the positive electrode active material coat | covered with the amorphous carbon as a electrically conductive agent based on the form for implementing this invention. In the positive electrode of the nonaqueous electrolyte secondary battery according to the embodiment for carrying out the present invention, a positive electrode active material coated with amorphous carbon as a conductive agent and two other conductive agents are bonded together It is sectional drawing which shows this typically. It is a perspective view which shows typically the internal structure of the nonaqueous electrolyte secondary battery based on one form for implementing this invention. In the positive electrode produced in Examples 1-3 and Comparative Examples 1-3, it is the graph which made the amount of mixture layers of the positive mix in the horizontal axis | shaft, and normalized DC resistance value in the vertical axis | shaft. In the positive electrodes produced in Examples 1 to 3 and Comparative Examples 1 and 2, the horizontal axis represents the ratio of graphite to graphite and carbon black, and the vertical axis represents resistance change.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment” as appropriate) will be described in detail, but the present embodiment is not limited to the following contents and does not depart from the gist thereof. Any change can be made within the range.

（上記式（１）中、ｘは０＜ｘ≦１を満たす数を表し、Ｍ^１は、Ｔｉ，Ｚｒ，Ｍｏからなる群より選ばれる１種以上の元素で一部が置換されていてもよい、Ｆｅ及び／又はＭｎを表す。） [1. Nonaqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery according to this embodiment is a positive electrode in which a positive electrode mixture layer including a positive electrode active material, a conductive agent, and a binder is formed on the surface of a positive electrode current collector, and the amount of the positive electrode mixture layer is In the non-aqueous electrolyte secondary battery having a positive electrode of 125 g / m ² or more per side of the positive electrode current collector, the positive electrode mixture layer is an olivine type represented by the following formula (1) as the positive electrode active material: Lithium-containing phosphate (hereinafter referred to as “lithium-containing phosphate (1)” as appropriate), amorphous carbon, massive graphite and carbon black as the conductive agent, and polyacrylonitrile and polyfluoride as the binder. And the positive electrode active material is coated with the amorphous carbon in an amount of 2 wt% or more and 5 wt% or less with respect to the whole positive electrode mixture layer, and the content of the conductive agent Is the positive electrode It is 6% by weight or more based on the whole agent layer.

(In the above formula (1), x represents a number satisfying 0 <x ≦ 1, and M ¹ may be partially substituted with one or more elements selected from the group consisting of Ti, Zr, and Mo. Represents Fe and / or Mn.)

[1-1. Positive electrode mixture layer]
The positive electrode included in the nonaqueous electrolyte secondary battery according to this embodiment (hereinafter referred to as “the positive electrode according to this embodiment” as appropriate) has a positive electrode mixture layer formed on the surface of the positive electrode current collector. . Hereinafter, in the nonaqueous electrolyte secondary battery according to the present embodiment, the positive electrode mixture layer formed on the surface of the positive electrode current collector is appropriately referred to as a “positive electrode mixture layer according to the present embodiment”.

  The positive electrode mixture layer according to the present embodiment includes a positive electrode active material, a conductive agent, and a binder.

[Positive electrode active material]
Lithium-containing phosphate (1) is used as the positive electrode active material contained in the positive electrode mixture layer according to the present embodiment. Here, the “olivine-type lithium-containing phosphate” represents a lithium-containing phosphate having an olivine-type crystal structure. Since the olivine-type lithium-containing phosphate is excellent in thermal stability, a battery having a positive electrode using the olivine-type lithium-containing phosphate as a positive electrode active material can be expected to have good thermal stability.

In the above formula (1), x represents a number greater than 0 and 1 or less. M ¹ represents Fe and / or Mn, and a part thereof may be substituted with one or more elements selected from the group consisting of Ti, Zr, and Mo. When a part of Fe and / or Mn is substituted with one or more elements selected from the group consisting of Ti, Zr, and Mo, the substitution ratio is arbitrary as long as the effects of the present invention are not significantly impaired.

Specific examples of such olivine-type lithium-containing phosphate include LiFePO ₄ , LiMnPO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiFe _1/3 Mn _1/3 Ti _1/3 PO ₄ , LiFe _{1 / 3} Mn _1/3 Zr _1/3 PO ₄ , LiFe _1/3 Mn _1/3 Mo _1/3 PO _{4 and the} like. Especially, as a positive electrode active material contained in the positive electrode mixture layer according to the present embodiment, LiFePO ₄ (lithium iron phosphate) is preferable from the viewpoint of easy availability. In addition, a positive electrode active material may be contained individually by 1 type, and 2 or more types may be contained by arbitrary ratios and combinations. In addition to the lithium-containing phosphate (1), any known positive electrode active material may be included as the positive electrode active material.

  The shape of the positive electrode active material contained in the positive electrode mixture layer according to this embodiment is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually in the form of particles. When the shape of the positive electrode active material contained is particulate, its particle size is arbitrary as long as the effects of the present invention are not significantly impaired, but the average particle size is preferably 0.5 μm or less. Since the ion conductivity is very low compared with, for example, lithium cobaltate and lithium manganate generally used as the positive electrode active material, the reactivity of the positive electrode active material is increased by setting the average particle size within this range. be able to. In addition, the average particle diameter of a positive electrode active material can be measured using a particle size distribution measuring apparatus.

  The amount of the positive electrode active material contained in the positive electrode mixture layer according to the present embodiment is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 85% by weight or more based on the total amount of the positive electrode mixture layer. The amount is usually 87% by weight or less.

[Conductive agent]
As the conductive agent contained in the positive electrode mixture layer according to the present embodiment, amorphous carbon, massive graphite, and carbon black are used. However, in the positive electrode mixture layer according to the present embodiment, as shown in FIG. 1, the positive electrode active material is formed by coating the positive electrode active material 10 a with amorphous carbon 10 b as a conductive agent. It exists as the positive electrode active material 10.

  As described above, the positive electrode active material included in the positive electrode mixture layer according to this embodiment is coated with amorphous carbon. The coating amount of the amorphous carbon is usually 2% by weight or more, preferably 3% by weight or more, and the upper limit is usually 5% by weight or less with respect to the whole positive electrode mixture layer. If the coating amount of amorphous carbon is too small, the surface of the positive electrode active material cannot be uniformly coated, so that sufficient conductivity may not be imparted to the positive electrode active material, and the coating amount is too large Since the specific surface area of the amorphous carbon-coated positive electrode active material is increased, a larger amount of binder may be required to bond the positive electrode active materials to each other. Accordingly, the contents of graphite and carbon black (both described later) are relatively reduced, and the electron conductivity in the positive electrode mixture layer may be lowered.

Moreover, the specific surface area of the positive electrode active material after coating with amorphous carbon is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 10 m ² / g or more and usually 20 m ² / g or less. The specific surface area can be measured, for example, according to the BET method.

  One kind of amorphous carbon may be included alone, or two or more kinds of amorphous carbon may be included in any ratio and combination.

(Lumped graphite)
As the block graphite contained in the positive electrode mixture layer according to the present embodiment, any known one can be used as long as the effects of the present invention are not significantly impaired. Therefore, the physical properties of the massive graphite are arbitrary as long as the effects of the present invention are not significantly impaired. For example, the bulk graphite has a mean particle size of usually 5 μm or more, preferably 10 μm or more, and its upper limit is usually 20 μm or less. In addition, the average particle diameter of massive graphite can be measured using a particle size distribution measuring apparatus.

The tap density of the massive graphite is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.6 g / cm ³ or more, preferably 0.8 g / cm ³ or more, and the upper limit is usually 1 .2g / cm ³ or less, preferably 1.0 g / cm ³ or less. If the tap density is too small, the particles are small and tend to agglomerate, and the conductivity may be lowered, and if it is too large, the particles may be large and the number of particles may be reduced to reduce the conductivity. . The tap density can be measured according to the method of JIS Z2512.

  In addition, 1 type of lump graphite may be contained independently, and 2 or more types may be contained by arbitrary ratios and combinations.

(Carbon black)
The carbon black contained in the positive electrode mixture layer according to the present embodiment is uniformly dispersed in the portion where the particles are in contact with each other, and imparts electron conductivity to the positive electrode mixture layer. In addition, by including carbon black in the positive electrode mixture layer, the positive electrode mixture layer also has a function of holding the nonaqueous electrolytic solution impregnated in the voids that are normally included. Therefore, bulky carbon black is used in the positive electrode mixture layer according to this embodiment.

Any known carbon black may be used as the carbon black contained in the positive electrode mixture layer according to the present embodiment as long as the effects of the present invention are not significantly impaired. Therefore, the physical properties of the carbon black are arbitrary as long as the effects of the present invention are not significantly impaired. For example, the BET specific surface area of carbon black is usually 40 m ² / g or more, preferably 80 m ² / g or more, and the upper limit is usually 1000 m ² / g or less, preferably 800 m ² / g or less. If the BET specific surface area is too small, the particles may be large and the conductivity may decrease. If it is too large, the particles may be small and aggregate to reduce the conductivity. The BET specific surface area can be measured using a specific surface area measuring device.

  In addition, carbon black may be contained individually by 1 type and 2 or more types may be contained by arbitrary ratios and combinations.

(Content of conductive agent in positive electrode mixture layer according to this embodiment)
In the positive electrode mixture layer according to this embodiment, the content of the conductive agent is usually 6% by weight or more and usually 8% by weight or less with respect to the whole positive electrode mixture layer.

In the conductive agent contained in the positive electrode mixture layer, it is preferable that the ratio of massive graphite is 0.3 or more and 0.7 or less with respect to the total quantity of massive graphite and carbon black contained.
That is, in the battery according to the present embodiment, the positive electrode mixture layer has a positive electrode active material content of 85 wt% or more and 87 wt% or less, a conductive agent content of 8 wt% or less, It is preferable that the ratio of the block graphite contained in the agent is 0.3 or more and 0.7 or less with respect to the total amount of the block graphite and carbon black.

  The positive electrode mixture layer according to the present embodiment may contain any known conductive agent in addition to the above conductive agent as long as the effects of the present invention are not significantly impaired.

[Binder]
As the binder contained in the positive electrode mixture layer according to the present embodiment, polyacrylonitrile (hereinafter referred to as “PAN” as appropriate) and polyvinylidene fluoride (hereinafter referred to as “PVDF” as appropriate) are used. The physical properties of PAN are arbitrary as long as the effects of the present invention are not significantly impaired. However, the weight average molecular weight of PAN is usually 10,000 or more, preferably 15,000 or more, and the upper limit is usually 25,000 or less, preferably 20,000 or less. When the molecular weight is too small, there is a possibility that sufficient interparticle binding properties may not be obtained. When the molecular weight is too large, the positive electrode mixture layer becomes hard and easily cracked, and the interparticle binding may be reduced.

  Further, the physical properties of PVDF are arbitrary as long as the effects of the present invention are not significantly impaired. However, the weight average molecular weight of PVDF is usually 280,000 or more, preferably 500,000 or more, and the upper limit is usually 1,000,000 or less, preferably 80 or less. When the molecular weight is too small, there is a possibility that sufficient interparticle binding properties may not be obtained. When the molecular weight is too large, the positive electrode mixture layer becomes hard and easily cracked, and the interparticle binding may be reduced.

  The amount of the binder in the positive electrode mixture layer according to the present embodiment is arbitrary as long as the effect of the present invention is not significantly impaired, and is appropriately determined according to the amount of the positive electrode active material and the conductive agent in the positive electrode mixture layer. That's fine. However, the ratio of PAN in the positive electrode mixture layer is preferably 0.3 or more and 0.7 or less with respect to the total amount of PAN and PVDF contained in the positive electrode mixture layer. Moreover, when a positive electrode mixture layer does not contain PAN but contains only PVDF, the positive electrode mixture layer surface may become excessively hard. That is, when the amount of PVDF is too large, this phenomenon may cause the positive electrode mixture layer to become brittle.

  In addition to the above binder, the positive electrode mixture layer according to the present embodiment may include any known binder as long as the effects of the present invention are not significantly impaired.

[Amount of cathode mix]
The positive electrode mixture layer according to this embodiment can be formed, for example, by applying a positive electrode mixture (described later) to a positive electrode current collector and drying it. The positive electrode mixture layer in the present embodiment is formed on one surface of the positive electrode current collector with a thickness such that the amount of the positive electrode mixture layer is 125 g / m ² . In the formed positive electrode mixture layer, as shown in FIG. 2, the amorphous carbon-coated positive electrode active material 10, the massive graphite 20, and the carbon black 30 are bonded to each other by a binder (not shown). It has become a thing. In FIG. 2, a space is provided between the particles of the amorphous carbon-coated positive electrode active material 10 for the sake of clarity. In practice, however, the amorphous carbon-coated positive electrode active material 10 has a large size. The portion is in contact with the adjacent amorphous carbon-coated positive electrode active material 10.

  In general, in the case of a non-aqueous electrolyte secondary battery mounted on a vehicle such as a railroad or an automobile, it is required to improve the fuel consumption by increasing the distance traveled by the motor. In addition, in the case of a nonaqueous electrolyte secondary battery mounted on a small precision device such as a notebook personal computer, it is required to increase the driving time. That is, non-aqueous electrolyte secondary batteries are strongly required to improve energy density. In response to such demands, lithium iron phosphate has attracted attention as a positive electrode active material that uses iron that is excellent in thermal stability, abundant in resources, and inexpensive. However, as described above, in order to obtain an electrode having the same energy density as that of a conventional non-aqueous electrolyte secondary battery, the electrode mixture layer such as the positive electrode mixture layer is usually thickened to form a positive electrode in the electrode. It is extremely important to reduce the occupied volume of the electrode current collector such as the current collector and the separator and increase the content of the active material such as the positive electrode active material in the electrode.

For example, a conventional non-aqueous electrolyte secondary battery mounted on an electric tool and using lithium cobalt oxide as a positive electrode active material is usually an 18650 type battery and has a battery capacity of about 1.5 to 2 Ah. Such a nonaqueous electrolyte secondary battery is known to contain about 9.6 to 12.7 g of lithium cobaltate in one side of the positive electrode mixture layer. Assuming that the total electrode area of the positive electrode is about 0.1 m ² and the positive electrode active material content is about 87%, the amount of the positive electrode mixture layer containing lithium cobaltate present on one side of the positive electrode is It is calculated to be about 100 to 150 g / m ² .

As shown in Table 1 above, the content of the positive electrode active material in the positive electrode mixture layer is obtained when lithium iron phosphate is used as the positive electrode active material and the battery capacity is about the same as that of the battery using lithium cobalt oxide. And increasing the amount of lithium iron phosphate used by about 25% is extremely important. That is, it is important to form a positive electrode mixture layer containing lithium iron phosphate on one side of the positive electrode so as to be about 125 to 190 g / m ² . Accordingly, in order to provide a non-aqueous electrolyte secondary battery having high thermal stability while maintaining a battery capacity comparable to that of a conventional non-aqueous electrolyte secondary battery (that is, maintaining an energy density). In this embodiment, the amount of the positive electrode mixture layer is set to 125 g / m ² or more on one side of the positive electrode current collector.

The upper limit of the abundance of the positive electrode mixture layer containing lithium iron phosphate is not particularly limited.For example, when the shape of the nonaqueous electrolyte secondary battery according to the present embodiment is a cylindrical one, the abundance The upper limit is usually 200 g / m ² or less on one side, preferably 150 g / m ² or less. When this upper limit is exceeded, the thickness of the positive electrode becomes excessively thick and it may be difficult to wind the positive electrode. In addition, when the shape of the nonaqueous electrolyte secondary battery according to the present embodiment is, for example, a coin-like shape, the upper limit value of the abundance is not particularly limited, but when it is excessively thick, drying after applying the positive electrode mixture May take too long.
In addition, although lithium iron phosphate was mentioned as a suitable example of a lithium containing phosphate (1), and said description was carried out, lithium containing phosphate (1) is not restrict | limited to lithium iron phosphate. The above description applies to other cases as well.

[1-2. Positive electrode current collector]
In the positive electrode according to the present embodiment, the positive electrode mixture layer is formed on the surface of the positive electrode current collector. As such a positive electrode current collector, any known material can be used. Usually, a metal having conductivity is used, but aluminum is particularly preferable.

  Further, the shape of the positive electrode current collector can be any shape as long as the effects of the present invention are not significantly impaired. For example, the shape of the positive electrode current collector can be a foil shape. By making the shape of the positive electrode current collector into a foil shape, the positive electrode can be easily wound, so that the nonaqueous electrolyte secondary battery according to this embodiment can be a cylindrical nonaqueous electrolyte secondary battery.

  In addition, when the shape of the positive electrode current collector is a foil shape, the thickness is not particularly limited. However, in order to minimize the occupied volume of the positive electrode current collector in the battery, the thickness is as thin as possible. Is preferred.

  In the present embodiment, a positive electrode mixture layer is provided on the surface of the positive electrode current collector. When the positive electrode current collector has a foil shape, the positive electrode mixture layer may be provided on both surfaces of the positive electrode current collector or only on one surface. However, from the viewpoint of achieving higher battery capacity, it is preferable that a positive electrode mixture layer is provided on both surfaces of the positive electrode current collector. When the positive electrode mixture layer is provided on both surfaces of the positive electrode current collector, the positive electrode mixture layer provided on each surface is the above [1-1. The physical properties described in [Positive electrode mixture layer] may be satisfied.

Moreover, the electrode density of the positive electrode is arbitrary as long as the effects of the present invention are not significantly impaired. However, from the viewpoint of ensuring interparticle contact between the positive electrode active material particles, it is usually 1.6 g / cm ³ or more, preferably 1. 7 g / cm ³ or more, and the upper limit is usually 2.2 g / cm ³ or less, preferably 2 g / cm ³ or less.

[1-3. Other configurations]
As long as the nonaqueous electrolyte secondary battery according to the present embodiment has a positive electrode made of a positive electrode current collector on which the positive electrode mixture layer is formed, the other configurations are arbitrary and can have a known configuration. . Therefore, the nonaqueous electrolyte secondary battery according to the present embodiment usually includes a negative electrode, a separator, and a nonaqueous electrolytic solution containing a nonaqueous electrolyte and a nonaqueous solvent in addition to the positive electrode. Hereinafter, the nonaqueous electrolyte secondary battery according to this embodiment will be described on the assumption that the nonaqueous electrolyte secondary battery according to this embodiment includes a negative electrode, a separator, and a nonaqueous electrolyte in addition to the above positive electrode.

[Negative electrode]
The negative electrode (hereinafter referred to as “the negative electrode according to this embodiment”) of the nonaqueous electrolyte secondary battery according to the present embodiment has the same configuration as that of any negative electrode used in a known nonaqueous electrolyte secondary battery. It can be. For example, a negative electrode mixture containing a negative electrode active material and a binder can be applied to a negative electrode current collector such as copper to produce a negative electrode.

  As the negative electrode active material, for example, silicon or a tin alloy can be used. However, the initial charge efficiency of a battery having a negative electrode using such a negative electrode active material tends to be low. Therefore, in consideration of reversibility of charge / discharge and the possibility of voltage drop in a battery using lithium-containing phosphate (1) as the positive electrode active material, graphite or a mixture containing graphite is used as the negative electrode active material. Is preferred. Specifically, the negative electrode active material is preferably graphite or a mixture of graphite and amorphous carbon. By using graphite or a mixture containing graphite as the negative electrode active material, the initial charge / discharge efficiency can be improved. When graphite or a mixture of graphite and amorphous carbon is used as the negative electrode active material, it is preferable that the graphite has a value of L002 of 0.3335 nm to 0.3375 nm in any case.

  Further, when a mixture of graphite and amorphous carbon is used as the negative electrode active material, the mixture may be simply a mixture of graphite and amorphous carbon. Those coated with crystalline carbon, and composite particles obtained by combining graphite particles and amorphous carbon particles are preferable.

  The amount of the negative electrode active material contained in the negative electrode is not particularly limited, but is usually 94% by weight or more and 98% by weight or less with respect to the total amount of the negative electrode mixture. However, the weight ratio of the positive electrode active material to the negative electrode active material is preferably a value obtained by dividing the weight of the positive electrode active material by the weight of the negative electrode active material, and is usually 1.5 or more and 3.5 or less. When the weight ratio is within this range, the characteristics of the lithium-containing phosphate (1) used as the positive electrode active material can be maximized.

  However, when an alloy containing an element capable of being alloyed with lithium, a lithium-containing composite nitride, and a mixture containing these materials are used as the negative electrode active material, the negative electrode capacity increases when the weight ratio is as described above. In some cases, the weight ratio is preferably 4 or more and 7 or less.

  As described above, the negative electrode usually contains a binder. Examples of the binder contained in the negative electrode include PVDF, styrene butadiene rubber (SBR), and the like. When PVDF is used as the binder, the form of PVDF used is not particularly limited, but a PVDF binder solution is preferably used. Depending on the type of the negative electrode active material contained in the negative electrode, it is preferable to use PVDF having a higher molecular weight from the viewpoint of adhesion between the negative electrode active material and the binder.

  The negative electrode current collector to which the negative electrode mixture is applied is not particularly limited, but for example, copper foil is suitable.

  Furthermore, the negative electrode mixture may contain a thickener such as carboxymethylcellulose (CMC). By including a thickener in the negative electrode mixture, the viscosity of the negative electrode mixture can be increased. In particular, when an aqueous binder such as a rubber binder is used in combination with PAN and PVDF as a binder, it is preferable to use a thickener together. The content of the thickener is not particularly limited, but may be included so that the negative electrode mixture has a desired viscosity.

[Separator]
Any known separator can be used as the separator of the nonaqueous electrolyte secondary battery according to the present embodiment (hereinafter referred to as “the separator according to the present embodiment” as appropriate). For example, the separator according to the present embodiment is preferably a separator having sufficient strength and capable of holding a large amount of non-aqueous electrolyte (that is, excellent in wettability). Specifically, the separator according to the present embodiment has a thickness of 5 μm or more and 50 μm or less, and the material is polypropylene, polyethylene, a microporous film made of polyolefin such as a copolymer of propylene and ethylene, and Nonwoven fabrics are preferred. In particular, when a separator having a thickness of 5 μm or more and 20 μm or less is used, there is usually a possibility that the charge / discharge cycle characteristics may be deteriorated and the battery characteristics may be deteriorated during high-temperature storage. However, since the lithium-containing phosphate (1) having high thermal stability is used as the positive electrode active material in the battery according to the present embodiment, the battery functions stably even when such a thin separator is used. be able to. Therefore, since the occupied volume of the separator in the battery can be reduced by using a thin separator, the occupied volume of the electrode can be increased to increase the energy density.

  Moreover, when using polyolefin as a separator, the layer which consists of oxides, such as aluminum oxide, magnesium oxide, and silicon dioxide, can be provided in the said separator surface. By providing such a layer, the thermal shrinkage of the separator at 150 ° C. or higher can be suppressed, so that the thermal stability of the battery according to this embodiment can be further improved. The thickness of such a layer is not particularly limited, but is usually 3 μm or more and 5 μm or less.

[Non-aqueous electrolyte]
In addition to the positive electrode, the battery according to this embodiment usually has a non-aqueous electrolyte containing a non-aqueous electrolyte and a non-aqueous solvent. As such a non-aqueous electrolyte and a non-aqueous solvent, any non-aqueous electrolyte and non-aqueous solvent that are used in known lithium ion secondary batteries can be used.

The non-aqueous electrolyte contained in the nonaqueous electrolytic solution in the battery according to the present embodiment, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCnF _{2n + 1} SO ₃ (n ≧ 2) and the like. Among these, LiPF ₆ and LiC ₄ F ₉ SO ₃ are preferable from the viewpoint of obtaining good charge / discharge characteristics. In addition, a nonaqueous electrolyte may be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations.

  The concentration of the nonaqueous electrolyte in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.3 mol / L or more, preferably 0.4 mol / L or more, and the upper limit is usually 1.7 mol / L or less, preferably Is 1.5 mol / L or less.

  As the nonaqueous solvent contained in the nonaqueous electrolytic solution in the battery according to the present embodiment, for example, an organic solvent, a polymer containing the organic solvent, or the like can be used. The type of the non-aqueous solvent is not particularly limited, but it is preferable to include a chain ester from the viewpoint of battery load characteristics. Examples of the chain ester include chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, ethyl acetate, methyl propionate, and the like. When the non-aqueous solvent contains a chain ester, the content of the chain ester in the non-aqueous solvent is preferably 50% by volume or more and more preferably 65% by volume or more from the viewpoint of improving the low-temperature characteristics of the battery.

The nonaqueous solvent preferably contains an ester having a high dielectric constant (specifically, a dielectric constant of 30 or more) in addition to the chain ester from the viewpoint of improving the discharge capacity of the battery. Examples of such esters include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, γ-butyrolactone, and ethylene glycol sulfite. Among these, cyclic carbonate is preferable, and ethylene carbonate and propylene carbonate are particularly preferable among the cyclic carbonates. These non-aqueous solvents may contain 1 type independently, and may contain 2 or more types by arbitrary ratios and combinations.
When the non-aqueous solvent contains an ester having a high dielectric constant, the content of the ester in the non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more from the viewpoint of the discharge capacity of the battery, and the upper limit thereof. Is usually 40% by volume or less, preferably 30% by volume or less, from the viewpoint of the load characteristics of the battery.

  Examples of the solvent that can be contained in the nonaqueous solvent other than the above solvents include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, and the like. In addition, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used. In addition, these solvents may contain 1 type independently, and may contain 2 or more types by arbitrary ratios and combinations.

  In addition to the nonaqueous electrolyte and the nonaqueous solvent, the nonaqueous electrolytic solution included in the battery according to this embodiment may include an aromatic compound from the viewpoint of improving the safety and storage characteristics of the battery. Such an aromatic compound is not particularly limited, and for example, benzenes having an alkyl group such as cyclohexylbenzene and t-butylbenzene, biphenyl, or fluorobenzenes are suitable. One of these aromatic compounds may be used alone, or two or more thereof may be used in any ratio and combination.

[2. Manufacturing method of non-aqueous electrolyte secondary battery]
The battery according to the present embodiment can be manufactured by any method. Hereinafter, although the manufacturing method of the battery which concerns on this embodiment is given as an example, the manufacturing method of the battery which concerns on this embodiment is not limited to the method described below. However, it is preferable to manufacture the said positive electrode mixture with the manufacturing method of the positive electrode mixture described below.

The battery according to this embodiment is mainly manufactured through the following steps.
(1) Preparation of positive electrode mixture and production of positive electrode by application of positive electrode mixture to positive electrode current collector (2) Negative electrode by preparation of negative electrode mixture and application of negative electrode mixture to negative electrode current collector (3) Preparation of Nonaqueous Electrolyte (4) Assembly of Battery Using Positive Electrode, Negative Electrode and Nonaqueous Electrolyte Hereinafter, the method for producing a battery according to this embodiment will be described separately for each process.

(1) Preparation of positive electrode mixture and preparation of positive electrode by application of the positive electrode mixture to a positive electrode current collector What is necessary is just to mix and prepare each component so that it may become a density | concentration as described in a positive mix layer. However, in the battery according to this embodiment, it is particularly preferable to prepare the positive electrode mixture by the following procedure.

  The lithium-containing phosphate (1), massive graphite, carbon black, PAN and PVDF contained in the positive electrode mixture layer can be prepared by any known method so as to have desired physical properties, and are commercially available. Goods can also be used. For example, flake graphite powder (flaky graphite) can be used as the bulk graphite, and acetylene black can be used as the carbon black.

  The lithium-containing phosphate (1) can be produced, for example, by a solid phase firing method or a hydrothermal synthesis method, and a positive electrode mixture can be produced using these materials. In addition, this invention can be applied irrespective of the manufacturing method of lithium containing phosphate (1), and is not limited to the method as described in this embodiment.

  As described above, the positive electrode mixture layer in the positive electrode according to the present embodiment includes amorphous carbon, massive graphite, and carbon black as a conductive agent, and PAN and PVDF as binders. Among these, it is particularly preferable that the amorphous carbon is pre-coated with the positive electrode active material. Therefore, as a process for preparing the positive electrode mixture layer, massive graphite and carbon black are respectively made of PAN and It is particularly preferable to mix an amorphous carbon-coated positive electrode active material with the N-methylpyrrolidone solution of PVDF.

  However, according to the study of the present inventors, even when trying to disperse lump graphite and carbon black in an N-methylpyrrolidone solution of PAN and PVDF simply as a whole, they are not uniformly dispersed, and a uniform positive electrode mixture It turned out to be difficult to produce. The reason for this is considered to be that PAN becomes a high-viscosity solvent and the dispersibility of carbon black is lowered according to the study of the present inventors. Therefore, in this embodiment, a dispersion in which massive graphite is dispersed in an N-methylpyrrolidone (NMP) solution of PAN is prepared, and further, a dispersion in which carbon black is dispersed in an NMP solution of PVDF is separately prepared. Then, by mixing the prepared dispersions, a dispersion in which massive graphite and carbon black are uniformly dispersed can be prepared. A uniform cathode mixture can be prepared by dispersing the amorphous carbon-coated cathode active material in such a uniformly dispersed dispersion.

  As described above, the reason why the components can be uniformly dispersed by preparing the dispersion liquid in two stages is as follows. This is considered to be due to dispersion with the NMP solution.

  There is no particular limitation on the solvent of the dispersion liquid dispersed in the massive graphite and PAN solution, and the solvent of the dispersion liquid dispersed in the carbon black and PVDF solution, but as described above, N-methylpyrrolidone is preferable in any case. . Moreover, there is no restriction | limiting in particular in the quantity of the dispersion medium to be used, What is necessary is just to use the quantity of the grade which can disperse | distribute each component uniformly. However, if the amount of the dispersion medium is too large, an excessive time may be required for drying after application of the positive electrode mixture. Therefore, the amount of the dispersion medium used is preferably as small as possible.

The method for dispersing each component in the dispersion medium is not particularly limited, and for example, a planetary mixer or the like can be used. Further, the mixing method of the two types of dispersions after dispersing the respective components is not particularly limited, and the two types of dispersions can be put in one container and mixed using a known stirring device.
Further, a dispersion of massive graphite and PAN (hereinafter referred to as “dispersion A” as appropriate), a dispersion of carbon black and PVDF (hereinafter referred to as “dispersion B” as appropriate), and amorphous carbon. There is no restriction | limiting in particular in the order which mixes a covering positive electrode active material. For example, after mixing dispersion A and dispersion B, an amorphous carbon-coated positive electrode active material may be further mixed. Further, for example, after the dispersion A and the amorphous carbon-coated positive electrode active material are mixed, the dispersion B may be further mixed. Further, for example, the dispersion liquid A, the dispersion liquid B, and the amorphous carbon-coated positive electrode active material may be mixed together. Therefore, if the positive electrode mixture finally prepared is a mixture of the dispersion liquid A and the dispersion liquid B, it falls within the category of the present invention.

  The positive electrode mixture prepared as described above is applied onto a positive electrode current collector such as an aluminum foil, dried at an arbitrary temperature and time, and then pressed and cut to a desired electrode density. Thus, a positive electrode can be produced. Although it does not restrict | limit especially as temperature at the time of drying, Usually, it can be 100 degreeC or more and 120 degrees C or less. Also, since the drying time varies depending on the drying temperature, it cannot be generally stated. For example, when the drying temperature is 120 ° C., the drying time is usually about 15 minutes.

Further, the pressure during the pressing is not particularly limited, but the electrode density of the positive electrode is usually 1.6 g / cm ³ or more, preferably 1.7 g / cm ³ or more, and the upper limit is usually 2.2 g / cm ³ or less. The pressing is preferably performed at a pressure of 2 g / cm ³ or less.

(2) Preparation of Negative Electrode Mixture and Production of Negative Electrode by Applying Negative Electrode Mixture to Negative Electrode Current Collector Also in the negative electrode in the battery according to the present embodiment, first, the negative electrode mixture The negative electrode can be prepared by preparing and applying the negative electrode mixture to the negative electrode current collector. Specifically, the above [1-3. For example, a negative electrode active material, a binder, a thickener and the like are mixed to prepare a negative electrode mixture so that the concentration described in [Negative Electrode] of [Other Configurations] is obtained, and the negative electrode mixture is applied to the negative electrode current collector. That's fine.

  Although there is no restriction | limiting in particular in the dispersion medium which disperse | distributes each component, For example, N-methylpyrrolidone or water is suitable. Moreover, there is no restriction | limiting in particular in the quantity of the dispersion medium to be used, What is necessary is just to use the quantity which can disperse | distribute each component uniformly. However, if the amount of the dispersion medium is too large, an excessive time may be required for drying after application of the negative electrode mixture. Therefore, the amount of the dispersion medium used is preferably as small as possible.

  Also, the method for dispersing each component in the dispersion medium is not particularly limited, and after adding a negative electrode active material, a binder, a thickener, etc., the components may be dispersed using, for example, a planetary mixer. .

  The negative electrode mixture prepared as described above is applied onto a negative electrode current collector such as a copper foil, dried at an arbitrary temperature and time, and then pressed and cut to a desired electrode density. Thus, a negative electrode can be produced. Although it does not restrict | limit especially as temperature at the time of drying, Usually, it can be 100 degreeC or more and 120 degrees C or less. In addition, although the drying time varies depending on the drying temperature, it cannot be generally stated. For example, when the drying temperature is 100 ° C., the drying time is usually about 15 minutes.

Further, the pressure during pressing is not particularly limited, but the electrode density of the negative electrode is usually 1.3 g / cm ³ or more, and the upper limit is usually 1.7 g / cm ³ or less, and nonaqueous electrolysis to the negative electrode mixture layer From the viewpoint of ensuring the impregnation of the liquid, it is preferable to press at a pressure of 1.5 g / cm ³ or less.

(3) Preparation of non-aqueous electrolyte The non-aqueous electrolyte is the above-mentioned [1-3. The non-aqueous electrolyte can be mixed with a non-aqueous solvent so as to have the content of each component described in [Non-aqueous electrolyte solution] in [Other configuration]. There is no particular limitation on the mixing method, and for example, the non-aqueous electrolyte can be prepared by putting each component in one container and mixing them using a known stirring device.

(4) Assembly of battery using positive electrode, negative electrode and non-aqueous electrolyte Using positive electrode, negative electrode and non-aqueous electrolyte obtained in the above (1) to (3), and a known separator as necessary. The battery according to the present embodiment can be manufactured by assembling into an arbitrary shape. Examples of the shape of the battery include a cylindrical shape and a coin shape. Among the cylindrical shapes, examples of the shape include a cylindrical shape and a prismatic shape. In the next item, the structure of the battery according to one embodiment of the present invention will be specifically described.

[3. Non-aqueous electrolyte secondary battery structure]
The specific structure of the battery according to this embodiment is arbitrary as described above. Hereinafter, the structure of the battery according to one embodiment of the present invention will be described with reference to FIG. 3, but the structure of the battery according to the present embodiment is not limited to the contents described in FIG. 3 and the following.

  FIG. 3 is a schematic perspective view of the internal structure of the battery according to one embodiment (first embodiment) of the present invention. The battery 100 according to the first embodiment shown in FIG. 3 includes a battery container 1, a gasket 2, an upper lid 3, an upper lid case 4, a positive current collector plate 5, a negative current collector plate 6, and an electrode group 8. And the positive electrode lead 9.

  The battery container 1 houses a positive electrode current collector plate 5, a negative electrode current collector plate 6, an electrode group 8, a positive electrode lead 9, and a non-aqueous electrolyte (not shown). In the battery 100 according to the present embodiment, the battery container 1 has a cylindrical shape, but may have a rectangular shape. Moreover, it is preferable to use the metal which is not corroded by the nonaqueous electrolyte solution accommodated as a material of the battery container 1.

  The gasket 2 is provided between the battery container 1 and the upper lid case 4. The battery container 1 is sealed by the gasket 2 and the battery container 1 is electrically insulated from the upper lid 3 and the upper lid case 4. As the material of the gasket 2, a known sealing member such as an elastic resin can be used.

The upper lid 3 is an external terminal for taking out the electric power obtained by the battery 100 to the outside, specifically, a positive external terminal.
The upper lid case 4 is integrally formed of the same material as the upper lid 3, and the upper lid 3 and the upper lid case 4 are electrically connected. As the material of the upper lid 3 and the upper lid case 4, a conductive metal can be used. The upper lid case 4 and the positive electrode current collector plate 5 are electrically connected via a positive electrode lead 9 made of metal.

  The positive electrode current collector plate 5 and the negative electrode current collector plate 6 are electrically connected to a positive electrode tab 12 and a negative electrode tab 13 described later, respectively. This electrical connection can be performed by, for example, ultrasonic welding. In addition, a hole is provided in the central portion of the positive electrode current collector plate 5 and the negative electrode current collector plate 6, and an axial center 7 (described later) is fitted into the hole, whereby the positive electrode current collector plate 5 and the negative electrode current collector plate. The electric plate 6 is fixed to the shaft center 7. As a material for the positive electrode current collector plate 5 and the negative electrode current collector plate 6, a conductive metal is used.

  The negative electrode current collector plate 6 is electrically connected to the bottom of the battery case 1, and the bottom of the battery case 1 functions as a terminal for taking out the electric power obtained by the battery 100, specifically, as a negative electrode external terminal. is doing. Therefore, the bottom part and the side part of the battery container 1 are insulated from each other by an insulator (not shown).

  The shaft center 7 is located at the center of the electrode group 8 and winds the positive electrode 14, the negative electrode 15, and the separator 18. Further, the upper and lower ends of the shaft center 7 penetrate through the positive electrode current collector plate 5 and the negative electrode current collector plate 6. The shape of the shaft center is arbitrary, but a hollow cylinder is used in the first embodiment. As the material, for example, a resin or the like that does not have conductivity or has extremely low conductivity can be used.

  The electrode group 8 includes a separator 18, a positive electrode 14 provided with a positive electrode mixture (positive electrode mixture layer) 16 after drying, and a negative electrode mixture (negative electrode mixture layer) 17 after drying on both surfaces thereof. Are alternately laminated with separators 18 interposed therebetween. And the separator 18 is provided in the outermost periphery. The electrode group 8 is fixed to the separator 18 provided on the outermost periphery by a winding member 19 so that the winding of the electrode group 8 cannot be unwound. Further, a positive electrode tab 12 is provided above the positive electrode 14, and a negative electrode tab 13 is provided below the negative electrode 15.

  The positive electrode tab 12 and the positive electrode 14 are made of a metal such as aluminum, and [1-2. This corresponds to the positive electrode current collector described in “Positive electrode current collector]. A positive electrode mixture layer 16 is provided on both surfaces of the positive electrode 14. The positive electrode mixture layer 16 is obtained by applying the positive electrode mixture to the positive electrode 14 and then drying it, and the above [1-1. This corresponds to the positive electrode mixture layer described in [Positive electrode mixture layer].

  The negative electrode tab 13 and the negative electrode 15 are made of a metal such as copper, and the above [1-3. This corresponds to the negative electrode current collector described in “Other configuration”. A negative electrode mixture layer 17 is provided on both surfaces of the negative electrode 15. The negative electrode mixture layer 17 is a layer obtained by applying the negative electrode mixture to the negative electrode 15 and then drying it. This corresponds to the negative electrode mixture described in “Other configuration”.

  Further, the positive electrode 14 and the negative electrode 15 are provided via a separator 18. The separator 18 is porous and has an insulating property, and any known separator that can be used for a lithium ion secondary battery can be used.

  The battery 100 according to this embodiment can be charged from the outside of the battery container 1 or discharged to the outside of the battery container 1 by having the configuration described above and shown in FIG. 3. That is, for example, when the battery 100 is discharged, electrons generated at the negative electrode 15 of the electrode group 8 are taken out through the negative electrode tab 13, the negative electrode current collector plate 6, and the bottom of the battery container 1 in this order. On the other hand, electrons reach the positive electrode 14 of the electrode group 8 from the outside via the upper lid 3, the upper lid case 4, the positive electrode lead wire 9 and the positive electrode tab 12.

[4. Application of battery according to this embodiment]
The battery according to this embodiment can be used for any known application. Among them, the battery according to the present embodiment is excellent in thermal stability in addition to high energy density, and can suppress metal deposition at high temperatures, so that it may be exposed to high temperatures, for example, railways, It can be particularly suitably used as a battery for automobiles.

  Hereinafter, the present embodiment will be described in more detail with reference to examples. However, the present embodiment is not limited to the following examples, and may be arbitrarily modified without departing from the scope of the present invention. Can do.

Example 1
-Production of non-aqueous electrolyte secondary battery First, a positive electrode was produced.
5.35 g of LiH ₂ PO ₄ (manufactured by Aldrich), 8.75 g of FeC ₂ O ₄ .2H ₂ O (manufactured by Koyo Chemical Co., Ltd.) and 0.82 g of dextrin (manufactured by Wako Pure Chemical Industries, Ltd.) A zirconia grinding ball was put into the pot and mixed with a planetary ball mill (manufactured by Frichche) at a rotation speed of 3 levels for 30 minutes. The mixed powder was put into an alumina crucible and calcined at 400 ° C. for 10 hours under an argon flow of 0.3 L / min. Once pulverized in an agate mortar, again put into an alumina crucible and subjected to main baking at 700 ° C. for 10 hours under an argon flow of 0.3 L / min, the powder obtained was pulverized in an agate mortar. After crushing, the particle size was adjusted with a 45 μm mesh sieve to obtain the desired material. As a result of carrying out composition analysis by ICP measurement (manufactured by Shimadzu Corporation), the content of Li _1.0 Fe _0.98 P _1.02 O ₄ carbon was 3.0% by weight. The coating with amorphous carbon was confirmed using a scanning electron microscope (manufactured by Hitachi, Ltd.) and a powder X-ray diffractometer (manufactured by Rigaku Corporation).

  Next, the weight ratio of the lithium iron phosphate, the conductive agent, and the binder in the dried positive electrode mixture (that is, the positive electrode mixture layer) is 85: 8: 7 (among others, amorphous carbon, graphite, and carbon black). 0.88 g of lithium iron phosphate coated with the above amorphous carbon so that the weight ratio is 3: 3.5: 1.5, and the weight ratio of PAN and PVDF is 7: 3). 0.35 g of N-methylpyrrolidone (NMP) dispersion containing 10% by weight of graphite and 10% by weight of acrylonitrile was thoroughly mixed using a small kneader.

Then, 0.15 g of an NMP dispersion containing 10% by weight of carbon black and 10% by weight of PVDF was added to the mixture and further mixed to prepare a positive electrode mixture. The excess and deficiency of the binder was added in an amount of 0.1 g each to prepare a predetermined blend composition using a separately prepared PAN and PVDF 10 wt% solution. The prepared positive electrode mixture was applied onto an aluminum foil such that the positive electrode mixture layer amounts were 100 g / m ² , 125 g / m ² and 150 g / m ^2, and dried at 120 ° C.

The aluminum foil provided with the positive electrode mixture layer (hereinafter simply referred to as “mixture layer”) was pressed into a circular shape having a diameter of 10 mm after being pressed so that the electrode density was 1.7 g / cm ^3. It cut | disconnected and created 3 types of positive electrodes.

Next, a lithium metal is used as the negative electrode, a polyolefin porous film is used as the separator, and a mixed solution (volume ratio 1: 3) of ethylene carbonate and ethyl methyl carbonate containing 1 M LiPF ₆ is used as the non-aqueous electrolyte. A secondary battery was manufactured.

-Characteristic evaluation of non-aqueous electrolyte secondary battery With respect to the manufactured non-aqueous electrolyte secondary battery, the current value is 0.1 mA / cm ² with a current value of 1.0 mA / cm ² and an upper limit voltage value of 3.6 V. The battery was charged until Next, the battery was discharged at a current value of 1.0 mA / cm ² to a voltage value of 2.0V. The capacity of the battery after discharge is defined as a discharge depth of 0%. And the capacity | capacitance of the battery after charging on the same conditions again is defined as the charge depth of 100%.

The battery was discharged from a state of charge depth of 100% to a discharge depth of 50% and left for 1 hour to make the battery voltage an open circuit voltage. Thereafter, 0.5 mA ^/ cm 2 at room temperature (25 ° C.), and pulse discharge at a constant current of 1.0 mA / cm ² and 2.0 mA / cm ^2, DC resistance by linear approximation with 5 th second closed circuit voltage Was calculated.

When the direct current resistance in a battery having a mixture layer amount of 100 g / m ² is defined as 100 (ie, when normalized), the direct current resistance values in batteries having a mixture layer amount of 125 g / m ² and 150 g / m ² are Calculated. Table 2 shows the calculated results. Table 2 also shows the results of calculating the amount of change in DC resistance with respect to the mixture layer amount.

(Example 2)
Example 1 except that the weight ratio of amorphous carbon, graphite and carbon black was 3: 2.5: 2.5 in the conductive agent, and the weight ratio of PAN and PVDF was 5: 5 in the binder. Similarly, a non-aqueous electrolyte secondary battery was manufactured, and the characteristics of the manufactured battery were evaluated. The results are shown in Table 2. Table 2 also shows the results of calculating the amount of change in direct current resistance with respect to the mixture layer amount according to the same method as in Example 1.

(Example 3)
Example 1 except that the weight ratio of amorphous carbon, graphite and carbon black was 3: 2.5: 2.5 in the conductive agent, and the weight ratio of PAN and PVDF was 3: 7 in the binder. A non-aqueous electrolyte secondary battery was manufactured, and the characteristics of the manufactured battery were evaluated. The results are shown in Table 2. Table 2 also shows the results of calculating the amount of change in direct current resistance with respect to the mixture layer amount according to the same method as in Example 1.

(Comparative Example 1)
In the conductive agent, the weight ratio of amorphous carbon, graphite, and carbon black was set to 3: 2.5: 2.5, and the binder was not mixed with PVDF, and the whole amount was PAN. A non-aqueous electrolyte secondary battery was manufactured, and the characteristics of the manufactured battery were evaluated. The results are shown in Table 2. Table 2 also shows the results of calculating the amount of change in direct current resistance with respect to the mixture layer amount according to the same method as in Example 1.

(Comparative Example 2)
In the conductive agent, the same as in Example 1 except that the weight ratio of amorphous carbon, graphite and carbon black was 3: 2.5: 2.5, and the binder was not mixed with PAN and the whole amount was PVDF. A non-aqueous electrolyte secondary battery was manufactured, and the characteristics of the manufactured battery were evaluated. The results are shown in Table 2. Table 2 also shows the results of calculating the amount of change in direct current resistance with respect to the mixture layer amount according to the same method as in Example 1.

  In the positive electrode mixture after drying, the weight ratio of lithium iron phosphate, the conductive agent, and the binder is 90: 5: 5 (in the conductive agent, the weight ratio of amorphous carbon, graphite, and carbon black is 3 1: 1, and in the binder, a nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the weight ratio of PAN and PVDF was 2.5: 2.5) The characteristics of the manufactured battery were evaluated. The results are shown in Table 2. Table 2 also shows the results of calculating the amount of change in direct current resistance with respect to the mixture layer amount according to the same method as in Example 1.

※ ＣＢはカーボンブラックを表す。

* CB represents carbon black.

  Further, FIG. 4 is a graph in which the horizontal axis represents the mixture layer amount and the vertical axis represents the normalized DC resistance value. Further, a graph with the horizontal axis representing the ratio of graphite to carbon black and the vertical axis representing the resistance change is shown in FIG.

As shown in FIG. 4, in any of Examples 1 to 3, the increase in DC resistance accompanying the increase in the amount of the mixture layer could be suppressed as compared with Comparative Examples 1 to 3. Specifically, in Examples 1 to 3, the value of the DC resistance is 20 to 30% by increasing the amount of the mixture layer from 100 g / m ² to 150 g / m ² (that is, the film thickness is increased). Although the increase remained, in Comparative Examples 1 to 3, the increase rate was 40 to 60%, which was a maximum of 3 times as compared with the case of Example (relationship between Example 1 and Comparative Example 3). increased.

  Moreover, as shown in FIG. 5, when graphite and carbon black were used as the conductive agent (Examples 1 to 3), the resistance change (that is, the rate of increase in resistance) was small. On the other hand, when only one of graphite and carbon black was used (Comparative Examples 1 and 2), the resistance change was large. In Comparative Example 3, graphite and carbon black are used as the conductive agent. However, the content of the conductive agent is not included in the range defined in the present invention, and the resistance change is particularly large, so the description is omitted in FIG. is doing.

  In particular, as shown in FIG. 5, the resistance change was smaller when the ratio was 0.3 or more and 0.8 or less. In particular, in the range where the ratio is 0.3 or more and 0.7 or less, since the slope of the straight line is small, for example, there is a stable battery in which the resistance change is small even with respect to the variation in film thickness that normally occurs at the time of manufacturing the electrode. I found that it can be manufactured.

  According to the inventor's study, such a phenomenon is confirmed by the graphite particles having a high electron conductivity and a large particle diameter to ensure the electron conductivity in the thickness direction, while the bulky carbon black improves the adhesion of the graphite particles. It is considered that the increase in resistance due to the electrode thickness can be suppressed by providing the electrode with the retention of the non-aqueous electrolyte. Accordingly, when an olivine type lithium-containing phosphate is used as the positive electrode active material, a large current can be taken out by increasing the film thickness, and further, an increase in generated resistance can be suppressed. That is, the electrode included in the battery according to the present embodiment has a high energy density.

  On the other hand, in Comparative Example 1 in which carbon black is not used as the conductive agent, the retention of the non-aqueous electrolyte in the electrode is lower than in Examples 1 to 3, so that the lithium ions in the non-aqueous electrolyte are reduced. It is thought that the reactivity decreased and the resistance change became large.

  In Comparative Example 2 in which graphite was not used as the conductive agent, it was considered that the resistance change became large because the electron conductivity in the thickness direction was lowered.

  Furthermore, even if amorphous carbon, graphite, and carbon black are used as the conductive agent, as shown in Comparative Example 3, if the content of the conductive agent is not equal to or greater than a specific amount, sufficient conductivity is provided inside the positive electrode mixture layer. It is thought that the resistance change due to the thick film became large because the net was not constructed.

DESCRIPTION OF SYMBOLS 10 Amorphous carbon covering positive electrode active material 10a Positive electrode active material 10b Amorphous carbon 20 Lump graphite 30 Carbon black 1 Battery container 100 Battery (nonaqueous electrolyte secondary battery)
12 Positive electrode tab 13 Negative electrode tab 14 Positive electrode 15 Negative electrode 16 Positive electrode mixture layer 17 Negative electrode mixture layer 18 Separator 19 Winding member 2 Gasket 3 Upper lid 4 Upper lid case 5 Positive electrode current collector plate 6 Negative electrode current collector plate 7 Axis 8 Group 9 Positive lead

Claims (5)

A positive electrode mixture layer including a positive electrode active material, a conductive agent, and a binder is formed on the surface of the positive electrode current collector, and the amount of the positive electrode mixture layer is 125 g / m ² per side of the positive electrode current collector. In the non-aqueous electrolyte secondary battery having the positive electrode as described above,
The positive electrode mixture layer is
As the positive electrode active material, an olivine-type lithium-containing phosphate represented by the following formula (1):
As the conductive agent, amorphous carbon, massive graphite and carbon black,
As the binder, polyacrylonitrile and polyvinylidene fluoride;
Including
The positive electrode active material is coated with the amorphous carbon in an amount of 2 wt% or more and 5 wt% or less with respect to the entire positive electrode mixture layer;
The non-aqueous electrolyte secondary battery, wherein the content of the conductive agent is 6% by weight or more based on the whole positive electrode mixture layer.

(In the above formula (1), x represents a number satisfying 0 <x ≦ 1, and M ¹ may be partially substituted with one or more elements selected from the group consisting of Ti, Zr, and Mo. Represents Fe and / or Mn.) 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein an electrode density of the positive electrode is 1.6 g / cm ³ or more and 2.2 g / cm ³ or less. In the positive electrode mixture layer,
The content of the positive electrode active material is 85 wt% or more and 87 wt% or less,
The content of the conductive agent is 8% by weight or less,
The proportion of the massive graphite contained in the conductive agent is 0.3 or more and 0.7 or less with respect to the total amount of the massive graphite and the carbon black. Non-aqueous electrolyte secondary battery. The ratio of the polyacrylonitrile contained in the binder is 0.3 or more and 0.7 or less with respect to the total amount of the polyacrylonitrile and the polyvinylidene fluoride. 2. The nonaqueous electrolyte secondary battery according to item 1. A method for producing a positive electrode mixture comprising bulk graphite, carbon black, polyacrylonitrile and polyvinylidene fluoride,
A dispersion in which massive graphite and polyacrylonitrile are dispersed in a dispersion medium;
A method for producing a positive electrode mixture, comprising a step of mixing a dispersion in which carbon black and polyvinylidene fluoride are dispersed in a dispersion medium.

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