JP2006294597A - Non-aqueous electrolytic liquid secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic liquid secondary battery superior in safety and capable of suppressing reduction in capacity at the time of high-temperature storage. <P>SOLUTION: The non-aqueous secondary battery is equipped with a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a non-aqueous electrolytic liquid, and a separator. The separator includes a heat resistant resin having chlorine atom as an end group, and the positive electrode active material contains a lithium-contained compound oxide having aluminum atom in the composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to a highly safe non-aqueous electrolyte secondary battery.

  In recent years, consumer electronic devices have become increasingly portable and cordless. As a power source for driving such an electronic device, there is an increasing demand for a battery that is small, lightweight, and has a high energy density. In particular, since lithium ion secondary batteries have high voltage and high energy density, they are expected to grow greatly as power sources for portable electronic devices such as notebook computers, mobile phones, and AV devices.

Lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ are used as positive electrode active materials for lithium ion secondary batteries. In such a positive electrode active material, crystal structure destruction, particle cracking, and the like occur with expansion and contraction due to charge and discharge. For this reason, when the charge / discharge cycle is repeated, the capacity decreases and the internal resistance increases.

  For example, in order to improve the cycle characteristics and safety of the battery, a part of Co and Ni contained in the lithium-containing composite oxide is replaced with an element such as Mg to stabilize the crystal structure of the lithium-containing composite oxide. Has been proposed (see Patent Document 1).

Among the positive electrode active materials as described above, LiNiO ₂ has a large theoretical capacity, but on the other hand, the reversibility of the crystal structure change accompanying charge / discharge is significantly reduced. In order to solve such a problem, a proposal has been made to relax a change in crystal structure by replacing a part of Ni with an element such as Co (for example, see Patent Document 2).
Furthermore, it has been proposed that nickel and / or cobalt in lithium-containing nickel cobalt oxide is replaced with inexpensive Mn to obtain Li (NiMnCo) O ₂ and this oxide is used as a positive electrode active material ( For example, see Patent Document 3). Thereby, a low-cost and high-performance battery can be obtained.

  A separator used for a lithium ion secondary battery often uses a porous film made of a thermoplastic resin, for example, polyolefin, from the viewpoint of safety. This is because such a separator has a so-called shutdown function. Here, the shutdown function means that, for example, when an external short circuit occurs and the battery temperature suddenly increases, the separator softens, the pores are blocked, and the ionic conductivity decreases. This is a function that prevents current from flowing.

  However, even if the shutdown function is activated, when the temperature of the battery further rises, the separator is melted and thermally contracted, so that there is a problem of so-called meltdown in which the positive electrode and the negative electrode are short-circuited on a large scale. On the other hand, when the thermal meltability of the separator is increased in order to improve the shutdown function, there is a problem that the meltdown temperature of the separator is lowered.

Therefore, in order to improve both shutdown property and meltdown resistance, many composite separators including a porous layer made of polyolefin as described above and a layer made of a heat resistant resin have been proposed. For example, a separator in which a layer made of a heat-resistant nitrogen-containing aromatic polymer such as aramid or polyamideimide and ceramic powder and a porous film layer are laminated has been proposed (for example, see Patent Document 4).
JP 2002-198051 A Japanese Patent No. 3232943 JP 2004-31091 A Japanese Patent No. 3175730

  When the heat resistant resin as described above is used, the safety of the battery can be improved. However, there is a problem that the capacity drop during high temperature storage becomes large. Specifically, aramid is obtained by polymerizing an organic substance having an amine group typified by paraphenylenediamine and an organic substance having a chlorine group typified by terephthalic acid chloride. As a group, a chlorine group remains. Similarly, since polyamideimide is obtained by reacting trimellitic anhydride monochloride with diamine, a chlorine group remains as a terminal group in the produced polyamideimide. Such chlorine groups are liberated in the electrolytic solution under a high temperature environment. On the other hand, the positive electrode active material is likely to elute main constituent elements (transition metals such as Co) of the positive electrode active material in a high temperature and high potential environment. If the liberated chlorine is present in the vicinity of the positive electrode active material, a complexing reaction between the transition metal eluted from the positive electrode active material and chlorine continues to occur. For this reason, a large amount of constituent elements are eluted from the positive electrode active material into the electrolytic solution, and the number of sites that function as the positive electrode active material is reduced.

  The present invention has been made in view of the above problems, and an object thereof is to provide a non-aqueous electrolyte secondary battery that is excellent in safety and can suppress a decrease in capacity during high-temperature storage. And

The present invention comprises a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a non-aqueous electrolyte, and a separator, the separator including a heat resistant resin having a chlorine atom as a terminal group, The present invention relates to a non-aqueous electrolyte secondary battery in which the substance includes a lithium-containing composite oxide having an aluminum atom in the composition.
The heat resistant resin preferably contains at least one selected from the group consisting of aramid and polyamideimide.

  The separator may have a film containing a heat resistant resin and a film containing a polyolefin laminated thereon. The separator may have a film containing polyolefin and a layer containing a heat resistant resin and a filler formed on the film.

The lithium-containing composite oxide has the following formula:
_{Li x M 1-y Al y} O 2 (1)
(1 ≦ x ≦ 1.05, 0.001 ≦ y ≦ 0.2, M is at least one selected from the group consisting of Co, Ni, Mn, and Mg).

The lithium-containing composite oxide includes the following formula among the composite oxides of the formula (1):
Li _a Co _1-bc Mg _b Al _c O ₂ (2)
(1 ≦ a ≦ 1.05, 0.005 ≦ b ≦ 0.1, 0.001 ≦ c ≦ 0.2)
The following formula:
Li _a Ni _1-bc Co _b Al _c O ₂ (3)
(1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, 0.001 ≦ c ≦ 0.2)
The following formula:
Li _a Ni _{1- (b + c + d)} Mn _b Co _c Al _d O ₂ (4)
(1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.5, 0.1 ≦ c ≦ 0.5, 0.001 ≦ d ≦ 0.2, 0.2 ≦ b + c + d ≦ 0.75) The composite oxide represented may be sufficient.

  According to the present invention, even when chlorine atoms are released from the heat-resistant resin contained in the separator into the non-aqueous electrolyte during high temperature storage, the positive electrode active material reacts preferentially with the aluminum contained in the positive electrode active material. Other components of the material do not elute from the positive electrode active material. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that has high safety and excellent high-temperature storage characteristics.

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a non-aqueous electrolyte, and a separator. A positive electrode active material contains the lithium containing complex oxide which has an aluminum atom in a composition. The separator includes a heat resistant resin having a chlorine atom as a terminal group.

  In the present invention, the lithium-containing composite oxide that is the positive electrode active material contains a predetermined amount of aluminum atoms. A complex composed of an aluminum atom and a chlorine atom has a higher stability constant than a complex composed of a main constituent element of a lithium-containing composite oxide (for example, a transition metal such as C, Ni, or Mn) and a chlorine atom. . For this reason, an aluminum atom tends to form a complex with a chlorine atom preferentially. Therefore, even when chlorine atoms, which are terminal groups, are released from the heat-resistant resin contained in the separator into the non-aqueous electrolyte during high-temperature storage, the chlorine atoms are preferentially combined with aluminum atoms contained in the positive electrode active material. To form a complex. Therefore, it is possible to suppress the constituent elements contained in the positive electrode active material other than aluminum from being eluted into the non-aqueous electrolyte solution, and avoid a decrease in battery capacity during high-temperature storage.

  The heat resistant resin having a chlorine atom as a terminal group preferably contains at least one selected from the group consisting of aramid and polyamideimide. This is because aramid and polyamideimide are soluble in polar organic solvents, so that they are easy to form, and the porous film made of these has extremely high holding power and heat resistance for the non-aqueous electrolyte.

The heat-resistant resin preferably has a glass transition point, a melting point, and a thermal decomposition starting temperature accompanied by a chemical change, and more specifically, a high mechanical strength under high heat.
For example, it is desirable that the heat-resistant resin has a heat distortion temperature of 260 ° C. or higher which is obtained by a test method ASTM-D648 of the American Society for Testing Materials, that is, a load deflection temperature measurement at 1.82 MPa. This is because the higher the heat distortion temperature, the more the shape of the separator can be maintained even when heat shrinkage occurs. When the heat distortion temperature is 260 ° C. or higher, sufficiently high thermal stability can be exhibited even when the battery temperature further rises due to heat storage during battery overheating (usually about 180 ° C.).

  The amount of chlorine contained in the separator is preferably 300 to 3000 μg per 1 g of the separator. The amount of chlorine contained in a predetermined weight of the heat resistant resin is affected by the degree of polymerization of the heat resistant resin. If the amount of chlorine is too small, the degree of polymerization of the heat-resistant resin becomes too high, and the flexibility is lowered. For this reason, the workability of heat resistant resin falls. When the amount of chlorine is large, the degree of polymerization of the heat resistant resin is small, and the heat distortion temperature of the heat resistant resin is lowered. Therefore, it is considered that the function of the heat resistant resin is sufficiently performed when the amount of chlorine is in the above range.

  In the present invention, a porous film containing the above heat-resistant resin may be used as a separator. The separator may be a laminated film in which, for example, a porous film containing a polyolefin such as polyethylene or polypropylene and a porous film containing the heat resistant resin are laminated. Furthermore, the separator may be a laminate having a porous film containing polyolefin and a porous layer formed on the porous film containing the heat-resistant resin and filler.

For example, the porous film containing the heat resistant resin can be produced as follows.
First, the heat resistant resin is dissolved in a polar solvent such as N-methylpyrrolidone. The obtained solution is applied on a substrate such as a glass plate or a stainless plate and dried. The obtained porous membrane is peeled from the substrate. In this way, a porous film containing the heat resistant resin can be obtained.

  A laminated film obtained by laminating a porous film containing polyolefin and a porous film containing the heat resistant resin is obtained by dissolving the heat resistant resin in a polar solvent, and applying the solution onto the porous film containing polyolefin. It can be produced by drying.

A laminate having a porous film containing polyolefin and a porous layer containing the heat resistant resin and filler formed thereon can be produced as follows.
The heat resistant resin is dissolved in a polar solvent, and a filler is added to the solution. The obtained mixture is applied onto a porous membrane containing polyolefin and dried. Thus, it is possible to obtain a laminate having a porous film containing polyolefin and a porous layer formed on the porous film containing the heat-resistant resin and filler.

  The filler used is preferably chemically stable and highly pure so as not to adversely affect the battery characteristics even when immersed in a non-aqueous electrolyte or under the oxidation-reduction potential of the active material. Examples of such a filler include inorganic oxide fillers. Examples of the inorganic oxide filler include inorganic porous materials such as alumina, zeolite, silicon nitride, silicon carbide, titanium oxide, zirconium oxide, magnesium oxide, zinc oxide, and silicon dioxide.

  Among these, since the heat resistance is higher, it is preferable to use a laminate having a porous film containing polyolefin and a porous layer containing the porous film containing the heat-resistant resin and filler formed thereon as a separator. .

  When the separator is a laminate having a porous film containing polyolefin and a porous layer containing a heat resistant resin and a filler, the thickness of the porous layer containing the heat resistant resin layer and the filler is not particularly limited, 1-20 micrometers is preferable from the ensuring of safety | security by prevention of an internal short circuit, and the balance of battery capacity, and it is more preferable that it is 2-10 micrometers. When the thickness is less than 1 μm, the porous layer containing the heat-resistant resin and the filler becomes less effective in suppressing heat shrinkage of the porous layer containing polyolefin in a high temperature environment. When the thickness exceeds 20 μm, the porosity of the porous layer containing the heat resistant resin and the filler is relatively low, and the ionic conductivity is lowered. For this reason, an impedance rises and the charging / discharging characteristic of a battery may fall a little.

  From the viewpoint of ensuring ion conductivity, the porosity of the porous layer containing the heat resistant resin and the filler is preferably 20 to 70%. This porosity can be controlled by adjusting the coating speed and drying conditions (temperature and air volume) of the mixture containing the heat-resistant resin and the filler, the particle size and shape of the filler, and the like.

  When the separator has a porous film containing polyolefin and a porous layer containing heat-resistant resin and filler formed thereon, the total thickness of the separator is not particularly limited, but safety, various battery characteristics When considering the battery design capacity comprehensively, it is preferably 5 to 35 μm.

  The pore diameter of the porous membrane containing polyolefin is preferably 0.01 to 10 μm from the viewpoint of achieving both ion conductivity and mechanical strength.

  In the case of the separator containing the heat resistant resin, the thickness of the separator is preferably 5 to 20 μm, and more preferably 10 to 20 μm, from the viewpoint of ensuring safety by preventing internal short circuit and the battery capacity. The porosity of the separator containing the heat resistant resin is preferably 20 to 70%. The porosity of the separator can be controlled by adjusting the application rate of the heat resistant resin solution and the drying conditions.

Next, a lithium-containing composite oxide having an aluminum atom in the composition, which is a positive electrode active material, will be described.
As described above, in a high temperature and high potential environment, even if a chlorine atom remaining as a terminal group is liberated in a heat resistant resin, the chlorine atom preferentially forms a complex with an aluminum atom. In the present invention, a lithium-containing composite oxide containing a predetermined amount of aluminum is used.

Among such lithium-containing composite oxides, the following formula:
_{Li x M 1-y Al y} O 2 (1)
(1 ≦ x ≦ 1.05, 0.001 ≦ y ≦ 0.2, M is at least one selected from the group consisting of Co, Ni, Mn, and Mg.) Can be used. This is because the lithium-containing composite oxide represented by the formula (1) has a large capacity and can occlude and release lithium ions even under a high voltage.

The molar ratio x of lithium is preferably 1 ≦ x ≦ 1.05. When the molar ratio x of lithium is less than 1, the lithium salt is reduced in the raw material mixture for producing the lithium-containing composite oxide. For this reason, electrochemically inactive impurities such as cobalt oxide are present in the obtained product, and the battery capacity may be reduced. When the molar ratio x of lithium exceeds 1.05, an excess of lithium salt is present in the raw material mixture. For this reason, lithium salts may remain as impurities in the product, and the battery capacity may be reduced.
Note that the molar ratio x of lithium is a value immediately after the production of the lithium-containing composite oxide represented by the formula (1). However, the x value changes beyond the range of the x value due to charging / discharging of the battery.

  The molar ratio y of aluminum is preferably 0.001 ≦ y ≦ 0.2, and more preferably 0.005 ≦ y ≦ 0.2. When the molar ratio y of aluminum is less than 0.001, the above-described action is not sufficient, and a sufficient improvement effect may not be expected. When the molar ratio y exceeds 0.2, the amount of the metal atom M contributing to the charge / discharge reaction decreases, and the battery capacity may be reduced.

Although the manufacturing method of the lithium containing complex oxide represented by Formula (1) is not specifically limited, For example, it can produce as follows.
At least one salt selected from the group consisting of a cobalt salt, a nickel salt, a manganese salt, and a magnesium salt, a lithium salt, and a magnesium salt are mixed at a predetermined ratio. The lithium-containing composite oxide of formula (1) can be obtained by firing the obtained raw material mixture at high temperature in an oxidizing atmosphere.

Among the lithium-containing composite oxides represented by the above formula (1), the following formula:
Li _a Co _1-bc Mg _b Al _c O ₂ (2)
(1 ≦ a ≦ 1.05, 0.005 ≦ b ≦ 0.1, 0.001 ≦ c ≦ 0.2)
A lithium-containing composite oxide represented by the formula can be used. The lithium-containing composite oxide represented by the formula (2) contains magnesium. By including magnesium, even if the positive electrode active material repeatedly expands and contracts due to charge and discharge, distortion of the crystal lattice, structural breakdown thereof, or cracking of the active material particles can be suppressed. As a result, the reduction in discharge capacity is alleviated and the cycle characteristics are improved.

  The molar ratio b of magnesium is preferably 0.005 ≦ b ≦ 0.1. If the molar ratio b is less than 0.005, the above effect may not be obtained. When the molar ratio b exceeds 0.1, the battery capacity may be slightly reduced.

  The molar ratio c of aluminum is preferably 0.001 ≦ c ≦ 0.2. When the molar ratio c is less than 0.001, the effect of Al is not sufficiently exhibited. When the molar ratio c exceeds 0.2, the amount of metal atoms contributing to the charge / discharge reaction is slightly insufficient.

  The preferable range of the molar ratio a of lithium and the reason why the range is preferable are the same as in the case of the lithium-containing composite oxide of the formula (1).

Although the manufacturing method of the lithium containing complex oxide represented by Formula (2) is not specifically limited, For example, it can produce as follows.
A lithium salt, a magnesium salt, a cobalt salt, and an aluminum salt are mixed in a predetermined ratio. The lithium-containing composite oxide of formula (2) can be obtained by firing the obtained raw material mixture at high temperature in an oxidizing atmosphere.

  In addition, you may use the composite salt containing 2 or more types of elements chosen from the group which consists of cobalt, magnesium, and aluminum instead of each salt of the element contained in composite salt. For example, a eutectic hydroxide containing cobalt, magnesium and aluminum or an eutectic oxide thereof can be used instead of the cobalt salt, the magnesium salt and the aluminum salt.

Similarly, the following formula:
Li _a Ni _1-bc Co _b Al _c O ₂ (3)
(1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, 0.001 ≦ c ≦ 0.2)
It is also possible to use a lithium-containing composite oxide represented by It is known that a LiNiO ₂ based material has a large crystal structure change due to charge / discharge in spite of a high capacity density, and the reversibility of the structure change is poor. On the other hand, the lithium-containing composite oxide of formula (3) further contains cobalt and aluminum in its composition. The presence of cobalt atoms or aluminum atoms in the crystal structure, particularly in the lithium diffusion layer, suppresses the shrinkage of the crystal lattice when lithium is desorbed from the composite oxide. For this reason, the structural change amount at the time of charging / discharging can be made small.
Further, the lithium-containing composite oxide of the formula (3) is less expensive than a LiCoO ₂ based material, and is particularly useful as a positive electrode material for large battery applications.

  The molar ratio b of cobalt is preferably 0.1 ≦ b ≦ 0.35. When the molar ratio b is less than 0.1, it is difficult to obtain the effects described above. When the molar ratio b exceeds 0.35, the battery capacity slightly decreases.

  The preferable range of the molar ratio a of lithium and the molar ratio c of aluminum and the reason why the range is preferable are the same as in the case of the lithium-containing composite oxide of the formula (1).

The lithium-containing composite oxide represented by the formula (3) can be produced, for example, as follows.
Nickel salt, cobalt salt and aluminum salt are dissolved in water at a predetermined mixing ratio. The obtained aqueous solution is neutralized and precipitated as a nickel-cobalt-aluminum ternary composite hydroxide by coprecipitation. The obtained composite hydroxide and lithium salt are mixed at a predetermined mixing ratio, and the mixture is fired to obtain a lithium-containing composite oxide of the formula (3).
In addition, you may use the composite salt containing 2 or more types of elements chosen from the group which consists of nickel, cobalt, and aluminum instead of each salt of the element contained in composite salt.

Furthermore, the following formula:
Li _a Ni _{1- (b + c + d)} Mn _b Co _c Al _d O ₂ (4)
(1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.5, 0.1 ≦ c ≦ 0.5, 0.001 ≦ d ≦ 0.2, 0.2 ≦ b + c + d ≦ 0.75)
It is also possible to use a lithium-containing composite oxide represented by The lithium-containing composite oxide represented by the formula (4) can maintain stable battery characteristics while being inexpensive.

  The molar ratio b of manganese is preferably 0.1 ≦ b ≦ 0.5. When the molar ratio b is less than 0.1, the amount of manganese contained in the composite oxide is small, so that it is difficult to reduce the cost. When the molar ratio b exceeds 0.5, the battery capacity slightly decreases.

  The molar ratio c of cobalt is preferably 0.1 ≦ c ≦ 0.5. If the molar ratio c is less than 0.1, the complex oxide crystals may be slightly unstable, and the cycle characteristics may be deteriorated or the safety of the battery may be somewhat deteriorated. When the molar ratio c exceeds 0.5, the battery capacity slightly decreases.

  In order to exhibit various battery characteristics in a balanced manner, it is preferable that 0.2 ≦ b + c + d ≦ 0.75.

  The preferable ranges of the molar ratio a of lithium and the molar ratio d of aluminum are the same as those of the lithium-containing composite oxide of the formula (1).

  The lithium-containing composite oxide of the formula (4) is prepared by mixing, for example, a lithium salt, a nickel salt, a cobalt salt, a manganese salt, an aluminum salt, and the like at a predetermined mixing ratio. It can obtain by baking with.

  Similarly to the above, a composite salt containing two or more elements selected from the group consisting of nickel, cobalt, manganese, and aluminum may be used in place of each salt of the elements contained in the composite salt. For example, a eutectic hydroxide containing cobalt, magnesium, manganese, and aluminum or an eutectic oxide thereof can be used instead of the nickel salt, cobalt salt, manganese salt, and aluminum salt.

As the lithium salt used for the synthesis of the lithium-containing composite oxide, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, and lithium oxide can be used.
Examples of magnesium salts that can be used include magnesium oxide, basic magnesium carbonate, magnesium chloride, magnesium fluoride, magnesium nitrate, magnesium sulfate, magnesium acetate, magnesium oxalate, magnesium sulfide, and magnesium hydroxide.
As the cobalt salt, for example, cobalt oxide and cobalt hydroxide can be used.
As the aluminum salt, for example, aluminum hydroxide, aluminum nitrate, aluminum oxide, aluminum fluoride, and aluminum sulfate can be used.
As the nickel salt, for example, nickel oxide and nickel hydroxide can be used.
As the manganese salt, for example, manganese oxide, manganese hydroxide, manganese carbonate, manganese nitrate, manganese sulfate, manganese fluoride, manganese chloride, and manganese oxyhydroxide can be used.

  In the lithium-containing composite oxide represented by the above formula (1), the effect of the present invention can be obtained even if the composite oxide contained therein is used alone or in combination of two or more. . For example, a mixture containing two or more lithium-containing composite oxides represented by formulas (1) to (4) can be used as the positive electrode active material.

A mixture of a lithium-containing composite oxide that does not contain an aluminum atom in the composition, for example, a mixture of Li _a Co _1-b O ₂ and Li _a Ni _{1- (b + c)} Mn _b Co _c O ₂ is used. When used as a substance, the potential of each composite oxide in the charged state is derived from the valence of the transition metal contained. In these two types of composite oxides, since the types of transition metals contained are different, the potentials of the respective composite oxides have different values. For this reason, variations in the potential distribution are likely to occur in the mixture. Therefore, when a chlorine atom contained as a terminal group in the heat-resistant resin is liberated, the main constituent element (transition metal such as Co) of the positive electrode active material may be easily eluted into the non-aqueous electrolyte. Furthermore, when the charging voltage is high, the transition metal contained in the positive electrode active material is likely to be oxidized in a high voltage environment, and the main constituent elements (transition metals such as Co) are likely to elute.
However, since the lithium-containing composite oxide used in the present invention contains Al, even when chlorine atoms contained in the heat-resistant resin are liberated in the nonaqueous electrolyte, Al is selectively selected from the composite oxide of the positive electrode. Elution, and the elution of other main components is suppressed. For this reason, the battery which is excellent in safety | security and the capacity | capacitance fall at the time of high temperature storage is suppressed can be obtained.

  Next, the positive electrode, the negative electrode, and the nonaqueous electrolytic solution will be described.

The positive electrode may include, for example, a positive electrode current collector and a positive electrode mixture layer supported thereon.
The positive electrode mixture layer includes a positive electrode active material, a conductive agent, a binder, and the like. As described above, the positive electrode active material includes a lithium-containing composite oxide having an aluminum atom in the composition.

Examples of the binder used for the positive electrode include polytetrafluoroethylene, modified acrylonitrile rubber particles (for example, BM-500B manufactured by Nippon Zeon Co., Ltd.), and poly having both binding properties and thickening properties. Examples thereof include vinylidene fluoride and modified products thereof. These may be used alone or in combination of two or more.
The polytetrafluoroethylene and the modified acrylonitrile rubber particles may be used in combination with carboxymethylcellulose, polyethylene oxide, or soluble modified acrylonitrile rubber (for example, BM-720H manufactured by Nippon Zeon Co., Ltd.) having a thickening effect. .

  As the conductive agent, acetylene black, ketjen black, and various graphites can be used. These may be used alone or in combination of two or more.

  Similar to the positive electrode, the negative electrode may also include a negative electrode current collector and a negative electrode mixture layer carried thereon. The negative electrode mixture layer includes a negative electrode active material. The negative electrode mixture layer may contain a binder, a conductive agent, and the like as necessary.

  The negative electrode active material includes at least one element selected from the group consisting of lithium metal, materials that can be alloyed with lithium, various types of natural graphite, artificial graphite, silicon-based composite materials such as silicide, tin, aluminum, zinc, and magnesium. And various alloy materials can be used. These may be used alone or in combination of two or more.

Among these, from the viewpoint of increasing the capacity, for example, at least one selected from the group consisting of a material that can be alloyed with lithium, lithium metal, and the above lithium alloy is preferably used as the negative electrode active material.
Examples of materials that can be alloyed with lithium include silicon simple substance, silicon oxide (eg, SiO _x (0 <x <2)), tin simple substance, tin oxide (eg, SnO), and Ti. It is done.

  The negative electrode mixture layer may be formed by directly depositing a negative electrode active material on a current collector. Moreover, you may form a negative mix layer by apply | coating the mixture containing a negative electrode active material and a small amount of arbitrary components to a collector, and drying.

As the binder used in the negative electrode, various resin materials such as polyvinylidene fluoride and modified products thereof can be used as in the positive electrode.
Among these, from the viewpoint of improving overcharge safety, it is more preferable to use a mixture of a water-soluble binder containing, for example, a styrene-butadiene copolymer or a modified product thereof and a cellulose resin such as carboxymethylcellulose.

  The nonaqueous electrolytic solution includes a nonaqueous solvent and a solute dissolved in the nonaqueous solvent. As the non-aqueous solvent, a solvent generally used in this field can be used. Examples of such a solvent include ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These may be used alone or in combination of two or more.

As the solute, a lithium salt generally used in this field can be used. Examples of such lithium salts include LiPF ₆ and LiBF ₄ . Such lithium salt may be used independently and may be used in combination of 2 or more type.

  In addition, the nonaqueous electrolytic solution may contain, for example, vinylene carbonate, cyclohexylbenzene, and / or a modified product thereof in order to form a good film on the positive and negative electrodes.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

(Example 1-1)
(A) Production of positive electrode An aqueous solution containing cobalt sulfate at a concentration of 0.999 mol / L and aluminum sulfate at a concentration of 0.001 mol / L was continuously supplied to the reaction vessel. Co _0.999 Al _0.001 (OH) ₂ was synthesized by dropping sodium hydroxide into the reaction vessel so that the pH of the aqueous solution was 10 to 13. Thereafter, the hydroxide was sufficiently washed with water and dried to obtain a positive electrode active material precursor.

The obtained precursor and lithium carbonate were mixed so that the molar ratio of lithium, cobalt, and aluminum was 1.02: 0.999: 0.001. The mixture was calcined at 600 ° C. for 10 hours and pulverized. Next, the pulverized fired product was fired again at 900 ° C. for 10 hours, pulverized, and classified to obtain a lithium-containing composite oxide represented by the formula Li _1.02 Co _0.999 Al _0.001 O ₂ . This lithium-containing composite oxide was designated as a positive electrode active material 1-1.

  N-methylpyrrolidone (hereinafter referred to as NMP) solution containing 3 kg of the obtained positive electrode active material and 12% by weight of polyvinylidene fluoride as a positive electrode binder (# 1320 (trade name) manufactured by Kureha Chemical Industry Co., Ltd.) 1 kg, 90 g of acetylene black as a conductive agent, and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a positive electrode mixture paint.

This paint was applied to both surfaces of a 15 μm thick aluminum foil as a positive electrode current collector. At this time, the paint was not applied to the connection portion of the positive electrode lead.
Next, the applied paint was dried and rolled with a roller to form a positive electrode mixture layer having an active material density (active material weight / mixture layer volume) of 3.3 g / cm ³ . The total thickness of the positive electrode current collector and the positive electrode mixture layer was 160 μm.

  Thereafter, the obtained electrode plate precursor was slit into a width that could be inserted into a battery case of a cylindrical battery (diameter 18 mm, length 65 mm) to obtain a positive electrode plate.

(B) Production of Negative Electrode An aqueous dispersion containing 3 kg of artificial graphite as a negative electrode active material and 40% by weight of a modified styrene-butadiene copolymer as a negative electrode binder (“BM-” manufactured by Nippon Zeon Co., Ltd.) 400B (trade name) ") 75 g, 30 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water were stirred with a double-arm kneader to prepare a negative electrode mixture paint. The obtained coating material was apply | coated on both surfaces of the 10-micrometer-thick copper foil which is a negative electrode collector. At this time, this paint was not applied to the connecting portion of the negative electrode lead.

The applied paint was dried and rolled with a roller to form a negative electrode mixture layer having an active material density of 1.4 g / cm ³ . The total thickness of the copper foil and the negative electrode mixture layer was controlled to 180 μm.
After that, the obtained electrode plate precursor was slit to a width that can be inserted into the battery can of the cylindrical battery described above to obtain a negative electrode plate.

(C) Production of Separator A laminated film including a porous film made of polyethylene (PE) having a thickness of 16 μm and a film made of an aramid resin, which is a heat-resistant resin, is formed thereon, and this laminated film is used as a separator. Using.
A method for manufacturing the laminated film will be described below.
6.5 parts by weight of dry anhydrous calcium chloride was added to 100 parts by weight of NMP. This mixture was heated to 80 ° C. in a reaction vessel to completely dissolve anhydrous calcium chloride in NMP.
After the obtained solution was returned to room temperature, 3.2 parts by weight of paraphenylenediamine was added to this solution and completely dissolved. Thereafter, the reaction vessel containing the solution containing paraphenylenediamine was placed in a constant temperature bath at 20 ° C. While maintaining at 20 ° C., 5.8 parts by weight of terephthalic acid dichloride was dropped into this solution over 1 hour and reacted to obtain polyparaphenylene terephthalamide (hereinafter referred to as PPTA).
Thereafter, the solution containing PPTA was allowed to stand in a constant temperature bath at 20 ° C. for 1 hour. After completion of the reaction, the solution containing PTAA was placed in a vacuum bath and deaerated for 30 minutes while stirring under reduced pressure.
The obtained polymerization solution was further diluted with an NMP solution to which calcium chloride was added to prepare an NMP solution of PTAA having a PPTA concentration of 1.4% by weight.

The NMP solution of PTAA thus obtained was thinly coated on a polyethylene porous thin film with a doctor blade and dried with hot air at 80 ° C. (wind speed 0.5 m / sec). Thereafter, the obtained PTAA membrane was sufficiently washed with pure water to remove calcium chloride, thereby making the membrane porous, and then drying again. Thus, a laminated film including a polyethylene porous thin film and a PTAA porous film formed thereon was produced.
When the amount of residual chlorine in this laminated film was measured by chemical analysis, the amount of residual chlorine was 650 μg per 1 g of laminated film.

(D) Preparation of Nonaqueous Electrolytic Solution LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 2: 3: 3. Vinylene carbonate was added to this solution to prepare a non-aqueous electrolyte. The amount of vinylene carbonate was 3 parts by weight per 100 parts by weight of the non-aqueous electrolyte.

(E) Battery assembly A cylindrical battery as shown in FIG. 1 was produced.
The positive electrode plate and the negative electrode plate obtained as described above were cut into predetermined lengths to obtain the positive electrode 11 and the negative electrode 12. One end of the positive electrode lead 14 was connected to the positive electrode lead connection portion of the positive electrode 11. One end of the negative electrode lead 15 was connected to the negative electrode lead connection portion of the negative electrode 12.
A separator 13 was disposed between the positive electrode 11 and the negative electrode 12, and these were wound to produce a cylindrical electrode group. At this time, the separator 13 was disposed between the positive electrode 11 and the negative electrode 12 so that the PTAA layer was disposed on the positive electrode side. The outermost periphery of the electrode group was covered with the separator 13.

  The obtained electrode group was sandwiched between an upper insulating ring 16 and a lower insulating ring 17 and accommodated in a battery can 18. Next, 5 g of the non-aqueous electrolyte (not shown) was injected into the battery can 18. Thereafter, the inside of the battery can 18 was depressurized to 133 Pa and left until no nonaqueous electrolyte residue was found on the surface of the electrode group, thereby impregnating the electrode group with the nonaqueous electrolyte solution.

  Next, the other end of the positive electrode lead 14 was welded to the back surface of the battery lid 19 with the insulating packing 20 disposed on the periphery, and the other end of the negative electrode lead 15 was welded to the inner bottom surface of the battery can 18. Finally, the opening end of the battery can 18 was caulked to the insulating packing 20 of the battery lid 19 to close the opening of the battery can 18 to complete a cylindrical lithium ion secondary battery. The obtained battery was designated as the battery of Example 1-1.

(Examples 1-2 to 1-4)
When synthesizing the precursor of the positive electrode active material, except that the concentration ratio of cobalt sulfate and aluminum sulfate is 0.95: 0.05, 0.80: 0.20, or 0.75: 0.25. A battery was produced in the same manner as in Example 1-1. The obtained batteries were referred to as Examples 1-2 to 1-4, respectively.

(Example 1-5)
When synthesizing the precursor of the positive electrode active material, iron sulfate was further added, and the concentration ratio of cobalt sulfate, iron sulfate and aluminum sulfate was set to 0.9: 0.05: 0.05. A battery was produced in the same manner as in 1-1. The obtained battery was designated as the battery of Example 1-5.

(Examples 1-6 to 1-9)
When synthesizing the positive electrode active material, the precursor of the positive electrode active material and lithium carbonate have a molar ratio of lithium, cobalt, and aluminum of 0.98: 0.95: 0.05, 1: 0.95: 0. 0.05, 1.05: 0.95: 0.05, or 1.08: 0.95: 0.05 did. The obtained batteries were referred to as batteries of Examples 1-6 to 1-9.

(Example 1-10)
A battery was fabricated in the same manner as in Example 1-2, except that a laminated film in which a film made of polyamideimide resin was formed on the polyethylene porous thin film instead of the PTAA film was used as a separator. The obtained battery was referred to as battery of Example 1-10.

A method for producing a laminated film including a polyethylene porous thin film and a film made of polyamideimide resin formed thereon will be described below.
Trimellitic anhydride monochloride and diamine were added to NMP at room temperature and mixed to obtain an NMP solution of polyamic acid. The NMP solution was thinly applied onto a polyethylene porous thin film with a doctor blade. The coating film was dried with hot air at 80 ° C. (wind speed 0.5 m / sec) to dehydrate the polyamic acid, cyclize it, and convert it to polyamideimide. Thus, a laminated film including the polyethylene porous thin film and the polyamideimide film formed thereon was produced. The total thickness of this laminated film was 20 μm.
When the amount of residual chlorine in this laminated film was measured by chemical analysis, the amount of residual chlorine was 830 μg per 1 g of laminated film.

(Example 1-11)
A battery was fabricated in the same manner as in Example 1-2, except that a porous film made only of aramid was used as the separator. The obtained battery was referred to as battery of Example 1-11.

Below, the preparation method of the porous film which consists only of aramids is shown.
A predetermined amount of aramid resin was dissolved in NMP as described above. Next, the NMP solution was applied onto a smooth stainless steel plate using a doctor blade. The obtained coating film was dried with hot air at 80 ° C. (wind speed 0.5 m / sec) to obtain a porous film made only of aramid. The thickness of this porous film was 20 μm.
When the amount of residual chlorine in the porous membrane was measured by chemical analysis, the amount of residual chlorine was 1800 μg per 1 g of porous membrane.

(Example 1-12)
A battery was fabricated in the same manner as in Example 1-2, except that a laminate having a polyethylene thin film and a layer containing a filler and an aramid resin formed thereon was used as a separator. The obtained battery was referred to as battery of Example 1-12.

Below, the preparation methods of the said laminated body are shown.
Alumina fine particles were added to the NMP solution of aramid resin prepared in Example 1-1 and stirred. The amount of alumina fine particles added was 200 parts by weight per 100 parts by weight of the aramid resin contained in the NMP solution.
The obtained dispersion was thinly applied onto a polyethylene porous thin film with a doctor blade, and the coating film was dried with hot air at 80 ° C. (wind speed 0.5 m / sec). In this way, a laminate having a polyethylene porous film and a layer containing filler and aramid formed thereon was obtained.
When the residual chlorine content of this laminate was measured by chemical analysis, the residual chlorine content was 600 μg per 1 g of separator.

(Comparative Example 1)
In the same manner as in Example 1-1, cobalt hydroxide was synthesized from only cobalt sulfate, and lithium carbonate and cobalt hydroxide were mixed so that the molar ratio of lithium to cobalt was 1.02: 1. A lithium-containing composite oxide was synthesized. A battery was fabricated in the same manner as in Example 1-1 except that this lithium-containing composite oxide was used as the positive electrode active material. The obtained battery was used as the battery of Comparative Example 1.

(Comparative Example 2)
A battery was fabricated in the same manner as in Example 1-2, except that a polyethylene porous film having a thickness of 20 μm was used as the separator. The obtained battery was used as the battery of Comparative Example 2.

  Each of the obtained batteries was discharged at a constant current of 400 mA until the battery battery dropped to 3 V, and then subjected to preliminary charging and discharging twice at a constant current of 1400 mA until the battery voltage reached 4.2 V. . Next, the battery after charging was stored at 45 ° C. for 7 days. The battery after storage was evaluated as follows.

[Evaluation]
(I) Measurement of discharge capacity The battery after storage was charged at 20 ° C. at a constant voltage of 4.2 V until the current value decreased to 100 mA, and then the battery after charging was charged at a constant current of 2000 mA. The first charge / discharge cycle was discharged once until the battery voltage dropped to 3V. The discharge capacity at this time was defined as the initial discharge capacity. The results are shown in Table 1.

(Ii) Safety test The battery after storage was charged at 20 ° C. with a constant voltage of 4.2 V until the current value decreased to 100 mA. Thereafter, the charged battery was placed in a thermostatic bath at 130 ° C., and the maximum temperature on the battery surface was measured. The results are shown in Table 1.

(Iii) High-temperature storage characteristics First, the initial discharge capacity was measured as described above. Thereafter, the battery was charged at 20 ° C. with a constant voltage of 4.2 V until the current value decreased to 100 mA. Next, the battery after charging was placed in a constant temperature bath at 90 ° C. and stored for 24 hours. The battery after storage was discharged at a constant current of 2000 mA, and the discharge capacity after storage was determined. The value representing the ratio of the discharge capacity after storage to the initial discharge capacity as a percentage was taken as the capacity recovery rate. The results are shown in Table 1.
Table 1 also shows the composition of the positive electrode active material and the type of separator used in the examples and comparative examples.

From Table 2, in the battery of Comparative Example 2 in which the separator did not contain a heat resistant resin, the maximum temperature on the battery surface increased to 156 ° C. Therefore, it can be seen that when the separator does not contain a heat resistant resin, the safety of the battery is lowered.
Even if the separator includes a heat resistant resin, it can be seen that the capacity recovery rate is significantly reduced according to the result of Comparative Example 1 when the positive electrode active material does not include an aluminum atom. This is because the chlorine group contained as a terminal group in the heat-resistant resin is liberated in the non-aqueous electrolyte under a high-temperature environment and promotes the elution of the main constituent element of the positive electrode active material (cobalt in the case of Comparative Example 1). It is thought that it was because.

  On the other hand, as in the batteries of Examples 1-1 to 1-12, when a positive electrode active material containing a heat-resistant resin and containing aluminum atoms in the composition is used, safety and storage in a high-temperature environment It can be seen that both characteristics can be achieved. Aluminum atoms in the positive electrode active material form stable complex ions with chlorine liberated from aramid (or polyamideimide), so that the aluminum atoms are selectively eluted from the positive electrode active material and other components of the positive electrode active material. This is thought to be due to the suppression of elution. In addition, such an effect is the same also when the positive electrode active material which contains metals, such as iron other than cobalt, in the composition like the battery of Example 1-5.

  As shown in the results of Examples 1-1 to 1-4, as the amount of aluminum contained in the positive electrode active material increases, the maximum temperature of the battery decreases and the capacity recovery rate improves. However, as shown in Example 1-4, when the amount of aluminum is too large, the ratio of the main constituent element in the positive electrode active material is decreased, and the initial discharge capacity is decreased.

  In addition, from the results of Examples 1-2 and 1-6 to 1-8, it can be seen that the initial discharge capacity decreases even if the amount of lithium contained in the positive electrode active material is small or large. If the amount of lithium in the positive electrode active material is small, it is considered that impurities such as cobalt oxide that do not contribute to the battery capacity increase and the battery capacity decreases. If the amount of lithium is too large, it is considered that excess lithium remains as impurities in the positive electrode active material, and the initial discharge capacity decreases.

Therefore, in the lithium-containing composite oxide represented by Li _x Co _1-y Al _y O ₂ , 1 ≦ x ≦ 1.05 and preferably 0.001 ≦ y ≦ 0.2.

  Furthermore, from the results of Examples 1-10 to 1-12, the effect described above is that, even when a laminated film including a film made of a porous thin film and a heat resistant resin is used as the separator, the porous film made of the heat resistant resin is used. It can be seen that even when a membrane is used, a porous thin film and a laminate having a layer containing a filler and an aramid resin are used.

(Examples 2-1 to 2-12)
When synthesizing the precursor of the positive electrode active material, magnesium sulfate was further added, and the concentration ratio of cobalt sulfate, magnesium sulfate and aluminum sulfate was changed as shown in Table 2, and the same as in Example 1-1. Thus, precursors 2-1 to 2-12 were synthesized. Further, the mixture ratio of the obtained precursors 2-1 to 2-12 and lithium carbonate was changed as shown in Table 2, and in the same manner as in Example 1-1, the positive electrode active material 2- 1-2-12 were synthesized. Using these positive electrode active materials, a battery was fabricated in the same manner as in Example 1-1. The obtained batteries were referred to as Examples 2-1 to 2-12, respectively.

  Each of the obtained batteries was subjected to preliminary charge / discharge similar to that in Example 1 twice. The battery after charging was stored at 45 ° C. for 7 days. About the battery after a preservation | save, it carried out similarly to Example 1, and measured the initial stage discharge capacity, the maximum temperature of a battery surface, and a capacity | capacitance recovery rate. The results are shown in Table 2.

(Iv) Capacity Maintenance Rate In this example, the capacity maintenance rate was further measured for the battery after being stored at 45 ° C. for 7 days. The capacity retention rate was measured as follows. The said 1st charging / discharging cycle was repeated 200 times at 45 degreeC with respect to the battery after a preservation | save. A value representing the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle as a percentage value was defined as a capacity maintenance rate. The results are shown in Table 2.

  In Table 2, the capacity maintenance rate of each battery is 80% or more. Therefore, it can be seen that when the positive electrode active material contains magnesium, expansion and contraction of the positive electrode active material accompanying charge / discharge are alleviated, and a decrease in discharge capacity is suppressed.

From the results of Examples 2-2 and 2-5 to 2-8, the capacity retention ratio is improved as the molar ratio b of magnesium in the positive electrode active material is increased. However, in Example 2-5 in which the molar ratio b is 0.001, the capacity retention rate is 80%, and sufficient cycle characteristics cannot be obtained.
Moreover, when the molar ratio b of magnesium increases, the ratio of the main constituent element in the positive electrode active material tends to decrease, and the initial discharge capacity tends to decrease. That is, in Example 2-8 in which the molar ratio b is 0.15, a sufficient initial discharge capacity cannot be obtained.

  Further, as shown in Examples 2-1 to 2-4 and Examples 2-9 to 2-12, the amounts of aluminum and lithium have the same tendency as in Example 1.

Therefore, in the lithium-containing composite oxide represented by Li _a Co _1-bc Mg _b Al _c O ₂ , 1 ≦ a ≦ 1.05, 0.005 ≦ b ≦ 0.1, 0.001 ≦ c ≦ It is preferable that it is 0.2.

(Examples 3-1 to 12)
When synthesizing the precursor of the positive electrode active material, nickel sulfate, cobalt sulfate, and aluminum sulfate were used, and the concentration ratio thereof was changed as shown in Table 3, and the same as in Example 1-1. Precursors 3-1 to 3-12 were synthesized. Further, the mixture ratio of the obtained precursors 3-1 to 3-12 and lithium carbonate was changed as shown in Table 3, and in the same manner as in Example 1-1, the positive electrode active material 3- 1-3-12 were synthesized. Using these positive electrode active materials, a battery was fabricated in the same manner as in Example 1-1. The obtained batteries were designated as batteries of Examples 3-1 to 3-12, respectively.

  Each of the obtained batteries was subjected to preliminary charge / discharge similar to that in Example 1 twice. The battery after charging was stored at 45 ° C. for 7 days. For the battery after storage, the initial discharge capacity, the maximum temperature of the battery surface, the capacity recovery rate, and the capacity retention rate were measured in the same manner as in Example 2. The results are shown in Table 3.

From the results of Table 3, it can be seen that when the positive electrode active material contains nickel and cobalt and the amount of nickel is large, the initial discharge capacity and the capacity retention rate are improved.
Moreover, as can be seen from the results of Examples 3-5 to 3-8, the initial discharge capacity increases as the amount of nickel contained in the positive electrode active material increases, that is, as the amount of cobalt decreases. However, in Example 3-8 in which the molar ratio b of cobalt is 0.45, a sufficient initial discharge capacity may not be obtained.
Moreover, in Example 3-5 in which the molar ratio b of cobalt is 0.005, the capacity retention rate was somewhat lowered. This is considered to be because the expansion and contraction of the positive electrode active material accompanying charge / discharge are not sufficiently relaxed.

  Furthermore, as shown in Examples 3-1 to 3-4 and Examples 3-9 to 3-12, the amount of aluminum and the amount of lithium have the same tendency as in Example 1.

Therefore, in the lithium-containing composite oxide represented by Li _a Ni _1-bc Co _b Al _c O ₂ , 1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, and It is preferable that 001 ≦ c ≦ 0.2.

(Examples 4-1 to 19)
When synthesizing the precursor of the positive electrode active material, nickel sulfate, manganese sulfate, cobalt sulfate, and aluminum sulfate were used, and the concentration ratio thereof was changed as shown in Table 4 to obtain Example 1-1. Similarly, precursors 4-1 to 4-19 were synthesized. Further, the mixture ratio of the obtained precursors 4-1 to 4-19 and lithium carbonate was changed as shown in Table 4, and in the same manner as in Example 1-1, the positive electrode active material 4- 1-4-19 were synthesized. Using these positive electrode active materials, a battery was fabricated in the same manner as in Example 1-1. The obtained batteries were referred to as batteries of Examples 4-1 to 4-19, respectively.

The obtained battery was subjected to the same preliminary charging / discharging as in Example 1 twice. The battery after charging was stored at 45 ° C. for 7 days. About the battery after a preservation | save, it carried out similarly to Example 1, and measured the initial stage discharge capacity, the maximum temperature of a battery surface, and a capacity | capacitance recovery rate. The results are shown in Table 4.
Table 4 also shows the value of b + c + d.

  When the positive electrode active material contains manganese in addition to nickel and cobalt, an inexpensive positive electrode active material can be obtained while maintaining stable battery characteristics. In order to reduce costs, a certain amount or more of manganese is required. In the case of Example 4-11 in which the molar ratio b of manganese is 0.05, the maximum temperature on the battery surface becomes high, and the safety of the battery is somewhat lowered. In Examples 4-16 and 4-18 in which the molar ratio b of manganese is 0.6, the initial discharge capacity is reduced.

  Further, as can be seen from Example 4-11, when the molar ratio c of cobalt is 0.05, the maximum temperature of the battery surface becomes high. In Examples 4-17 and 4-19 in which the molar ratio c of cobalt is 0.6, the initial discharge capacity is reduced.

  Furthermore, as shown in Examples 4-1 to 4-4 and Examples 4-7 to 4-10, the amounts of aluminum and lithium have the same tendency as in Example 1.

Therefore, in the lithium-containing composite oxide represented by Li _a Ni _{1- (b + c + d)} Mn _b Co _c Al _d O ₂ , 1 ≦ a ≦ 1.05, and 0.1 ≦ b ≦ 0.5, and preferably 0.1 ≦ c ≦ 0.5 and 0.001 ≦ d ≦ 0.2.

  In Examples 4-18 and 4-19 where b + c + d was 0.85, the initial discharge capacity tended to decrease. In Example 4-11 in which b + c + d was 0.15, the maximum temperature on the battery surface increased, and the safety of the battery tended to decrease somewhat. Therefore, it can be seen that when 0.2 ≦ b + c + d ≦ 0.75, a battery having an excellent balance of the three characteristics can be obtained.

  In the following examples, when a mixture of a plurality of types of lithium-containing composite oxides is used as the positive electrode active material, the positive electrode active material is exposed to a high voltage environment, and the type of the negative electrode active material is changed. The battery characteristics were evaluated.

(Example 5-1)
50 parts by weight of the positive electrode active material (Li _1.02 Co _0.95 Al _0.05 O ₂ ) used in Example 1-2 and the positive electrode active material (Li _1.01 Ni _0.32 Mn _0.32 Co _0.32 Al _0.05 O ₂ ) used in Example 4-2 ) Was mixed with 50 parts by weight to obtain a positive electrode active material 5-1. A battery was fabricated in the same manner as in Example 1-1 except that this positive electrode active material was used. The obtained battery was designated as the battery of Example 5-1.

(Example 5-2)
A battery was fabricated in the same manner as in Example 1-2 except that the active material density of the positive electrode mixture layer was 3.3 g / cm ³ and the thickness of the positive electrode plate was 144 μm. The obtained battery was referred to as battery of Example 5-2.

(Example 5-3)
A battery was fabricated in the same manner as in Example 4-2, except that the active material density of the positive electrode mixture layer was 3.3 g / cm ³ and the thickness of the positive electrode plate was 144 μm. The obtained battery was referred to as battery of Example 5-3.

(Example 5-4)
An aqueous dispersion (BM-400B manufactured by Nippon Zeon Co., Ltd.) )) 750 g, 600 g of acetylene black as a conductive agent, 300 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water as a dispersion medium are stirred with a double-arm kneader to prepare a negative electrode mixture paste. did. The negative electrode mixture paste was applied to both surfaces of a strip-shaped negative electrode current collector made of a copper foil having a thickness of 10 μm. The applied negative electrode mixture paste was dried and rolled with a rolling roll to produce a negative electrode plate. A battery was fabricated in the same manner as in Example 3-2 except that this negative electrode plate was used. The obtained battery was referred to as battery of Example 5-4.

(Example 5-5)
A battery was fabricated in the same manner as in Example 5-4, except that SiO powder (median diameter 8 μm) was used instead of silicon powder, and the dimensions of the positive electrode and the negative electrode were changed as appropriate. The obtained battery was referred to as battery of Example 5-5.

(Example 5-6)
The following negative electrode was produced using the vacuum evaporation apparatus provided with the water cooling roller in the vacuum chamber.
Electrolytic Cu foil (made by Furukawa Circuit Foil Co., Ltd., thickness 20 μm) serving as a current collector was attached to a water-cooled roller in a vacuum vapor deposition apparatus and fixed. A graphite crucible containing silicon (manufactured by Furuuchi Chemical Co., Ltd., ingot with a purity of 99.999%) was placed immediately below. A nozzle was installed in the vacuum chamber so that oxygen gas was introduced between the crucible and the Cu foil. The flow rate of oxygen gas (manufactured by Nippon Oxygen Co., Ltd., purity 99.7%) from the nozzle was set to 20 sccm (flow rate of 20 cm ³ per minute). In order to prevent excessive silicon from adhering, a stainless steel shielding plate having an opening was disposed between the crucible and the water cooling roller. The width of the opening was 10 mm in the rotation direction of the roller. In order to prevent evaporation and adhesion until the evaporation temperature is reached, a shutter is disposed at the opening of the shielding plate.

Silicon was deposited on the current collector using an electron gun. The acceleration voltage of the electron beam was -8 kV, and the emission of the electron beam was 150 mA.
At this time, the degree of vacuum in the vacuum chamber was 1.5 × 10 ⁻¹ Pa, and the water-cooled roller was rotated at a speed of 10 cm / min. The surface temperature of the water cooling roller was 20 ° C.

After vapor-depositing an active material containing silicon and oxygen on one side of the current collector, the active material was vapor-deposited in the same manner on the other side. Thus, a negative electrode carrying a thin film made of an active material on both sides of the current collector was produced.
The composition of the negative electrode active material was quantified by elemental analysis. As a result, the composition of the negative electrode active material was SiO _0.6 .

  A battery was fabricated in the same manner as in Example 5-4, except that such a negative electrode was used and the dimensions of the positive electrode and the negative electrode were appropriately changed. The obtained battery was referred to as battery of Example 5-6.

  The batteries of Examples 5-1 and 5-4 to 5-6 were subjected to the same preliminary charging / discharging as in Example 1 twice. The battery after charging was stored at 45 ° C. for 7 days. About the battery after a preservation | save, it carried out similarly to Example 1, and measured the initial stage discharge capacity, the maximum temperature of a battery surface, and a capacity | capacitance recovery rate. The results are shown in Table 5.

  About the battery of Example 5-2 and 5-3, it used for the preliminary | backup charge / discharge similar to Example 1 twice except having changed the charge end voltage to 4.4V. The battery after charging was stored at 45 ° C. for 7 days. Next, the battery after storage was evaluated as follows.

(V) Measurement of discharge capacity The battery after storage was charged at 20 ° C. with a constant voltage of 4.4 V until the current value decreased to 100 mA. Thereafter, the charged battery was discharged at a constant current of 2000 mA until the battery voltage dropped to 3 V, and the initial discharge capacity was determined. The results are shown in Table 5.

(Vi) Safety test The battery after storage was charged at 20 ° C. with a constant voltage of 4.4 V until the current value decreased to 100 mA. Thereafter, the charged battery was placed in a thermostatic bath at 130 ° C., and the maximum temperature on the battery surface was measured. The results are shown in Table 5.

(Vii) High-temperature storage characteristics First, the initial discharge capacity was measured as described above. Thereafter, the battery was charged at 20 ° C. with a constant voltage of 4.4 V until the current value decreased to 100 mA. Next, the battery after charging was placed in a constant temperature bath at 90 ° C. and stored for 24 hours. The battery after storage was discharged at a constant current of 2000 mA, and the discharge capacity after storage was determined. The value representing the ratio of the discharge capacity after storage to the initial discharge capacity as a percentage was taken as the capacity recovery rate. The results are shown in Table 5.

  As shown in Table 5, in any of the batteries of Examples, the initial discharge capacity and the capacity recovery rate were excellent, and the maximum temperature on the battery surface was not so high. Therefore, when a mixture containing two types of lithium-containing composite oxide is used as the positive electrode active material (Example 5-1), when the positive electrode active material is exposed to a high voltage environment (Examples 5-2 to 5- 3) and when a high capacity negative electrode active material is used (Examples 5-4 to 5-6), it can be seen that a battery excellent in safety and high-temperature storage characteristics can be obtained.

  According to the present invention, since the positive electrode active material contains an appropriate amount of aluminum, even if chlorine atoms contained as end groups in the heat-resistant resin contained in the separator are liberated in the non-aqueous electrolyte, the main component of the positive electrode active material Elution of components into the non-aqueous electrolyte can be suppressed. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that has excellent safety and improved high-temperature storage characteristics. Such a battery can be used, for example, as a power source for equipment that requires excellent battery characteristics even in a high temperature environment.

It is a longitudinal cross-sectional view which shows schematically the cylindrical lithium secondary battery produced in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead 15 Negative electrode lead 16 Upper insulating ring 17 Lower insulating ring 18 Battery can 19 Battery cover 20 Insulating packing

Claims (8)

A positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a non-aqueous electrolyte, and a separator,
The separator includes a heat resistant resin having a chlorine atom as a terminal group,
The positive electrode active material is a non-aqueous electrolyte secondary battery including a lithium-containing composite oxide having an aluminum atom in the composition.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the heat resistant resin includes at least one selected from the group consisting of aramid and polyamideimide.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator includes a film containing the heat resistant resin and a film containing polyolefin laminated on the film containing the heat resistant resin.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator includes a film containing polyolefin and a layer containing the heat-resistant resin and filler formed on the film containing polyolefin. The lithium-containing composite oxide has the following formula:
_{Li x M 1-y Al y} O 2 (1)
(1 ≦ x ≦ 1.05, 0.001 ≦ y ≦ 0.2, M is at least one selected from the group consisting of Co, Ni, Mn, and Mg). Non-aqueous electrolyte secondary battery. The lithium-containing composite oxide has the following formula:
Li _a Co _1-bc Mg _b Al _c O ₂ (2)
The nonaqueous electrolyte secondary battery according to claim 5, represented by (1 ≦ a ≦ 1.05, 0.005 ≦ b ≦ 0.1, 0.001 ≦ c ≦ 0.2). The lithium-containing composite oxide has the following formula:
Li _a Ni _1-bc Co _b Al _c O ₂ (3)
The nonaqueous electrolyte secondary battery according to claim 5, represented by (1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.35, 0.001 ≦ c ≦ 0.2). The lithium-containing composite oxide has the following formula:
Li _a Ni _{1- (b + c + d)} Mn _b Co _c Al _d O ₂ (4)
(1 ≦ a ≦ 1.05, 0.1 ≦ b ≦ 0.5, 0.1 ≦ c ≦ 0.5, 0.001 ≦ d ≦ 0.2, 0.2 ≦ b + c + d ≦ 0.75) The nonaqueous electrolyte secondary battery according to claim 5 represented.