JP5654820B2 - Positive electrode material, method for producing the same, and power storage device - Google Patents

Description

  The present invention relates to a positive electrode material for a non-aqueous lithium storage element, a method for producing the positive electrode material, and a storage element.

  In recent years, midnight power storage systems, home-use distributed power storage systems based on solar power generation technology, power storage systems for electric vehicles, etc. have attracted attention from the viewpoint of global environment conservation and effective use of energy for resource saving. Yes.

  In these power storage systems, the first requirement is that the energy density of the power storage element used is high. As a promising candidate for a high energy density storage element capable of meeting such demands, development of lithium ion batteries has been energetically advanced.

  The second requirement is high output characteristics. For example, a combination of a high-efficiency engine and a power storage system (for example, a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (for example, a fuel cell electric vehicle) requires high output discharge characteristics in the power storage system during acceleration. ing.

  Currently, as a high power storage element, an electric double layer capacitor using activated carbon as an electrode (hereinafter also simply referred to as “capacitor”) has been developed, and durability (particularly cycle characteristics and high temperature storage characteristics) is high. It has an output characteristic of about 0.5 to 1 kW / L. These electric double layer capacitors have been considered as the most suitable storage element in the field where the above high output is required, but the energy density is only about 1 to 5 Wh / L, and the output duration time is not practical. It is a footpad.

  On the other hand, nickel-metal hydride batteries currently used in hybrid electric vehicles realize high output equivalent to electric double layer capacitors and have an energy density of about 160 Wh / L. However, research is underway energetically to further increase the energy density and output, further improve the stability at high temperatures, and increase the durability.

  In addition, research for higher output is also being conducted in lithium ion batteries. For example, a lithium-ion battery has been developed that can obtain a high output exceeding 3 kW / L at a discharge depth (that is, a value representing what percentage of the device discharge capacity is discharged) 50%. It is 100 Wh / L or less, and is designed to deliberately suppress the high energy density, which is the greatest feature of lithium ion batteries. Further, its durability (particularly cycle characteristics and high temperature storage characteristics) is inferior to that of an electric double layer capacitor. Therefore, in order to give practical durability, a lithium ion battery can be used only in a range where the depth of discharge is narrower than the range of 0 to 100%. For this reason, the capacity that can be actually used is further reduced, and research for further improving the durability is being actively pursued.

  As described above, there is a strong demand for practical use of a power storage element having high output density, high energy density, and durability. However, the existing power storage element described above has advantages and disadvantages. Therefore, a new power storage element that satisfies these technical requirements has been demanded, and development of a power storage element called a lithium ion capacitor has been actively developed as a promising candidate.

  A lithium ion capacitor is a type of storage element that uses a non-aqueous electrolyte containing an electrolyte containing lithium ions (that is, a non-aqueous lithium storage element), and in the positive electrode, an anion similar to an electric double layer capacitor is used. It is a power storage element that performs charge and discharge by a non-Faraday reaction by adsorption / desorption, and a Faraday reaction by occlusion / release of lithium ions in the negative electrode similar to a lithium ion battery.

  As described above, an electric double layer capacitor that charges and discharges by a non-Faraday reaction in both the positive electrode and the negative electrode has excellent output characteristics but low energy density. On the other hand, a lithium ion battery that is a secondary battery that charges and discharges by a Faraday reaction in both the positive electrode and the negative electrode is excellent in energy density but inferior in output characteristics. A lithium ion capacitor is a new power storage element that aims to achieve both excellent output characteristics and high energy density by performing charge and discharge by a non-Faraday reaction at the positive electrode and a Faraday reaction at the negative electrode.

  As such a lithium ion capacitor, activated carbon is used as a positive electrode active material, natural graphite or artificial graphite, graphitized mesophase carbon microspheres, graphitized mesophase carbon fiber, graphite whisker, graphitized carbon fiber, etc. A power storage element using the above has been proposed (see Patent Document 1). In addition, a power storage element using activated carbon as a positive electrode active material and non-graphitizable carbon or graphite as a negative electrode active material has been proposed (see Patent Document 2).

Moreover, hydrogen / carbon different from normal activated carbon as a positive electrode active material is 0.05 to 0.5, BET specific surface area is 300 to 2000 m ² / g, and mesopore volume by BJH method is 0.02 to 0.3 ml / g. , Using a hydrocarbon material having a pore structure with a total pore volume of 0.3 to 1.0 ml / g by the MP method, and using a material obtained by activating an optically anisotropic carbon substance excluding graphite as a negative electrode An element has been proposed (see Patent Document 3).

  Further, activated carbon or a polyacene organic semiconductor having a polyacene skeleton structure in which the atomic ratio of hydrogen atoms / carbon atoms is 0.05 to 0.50 is used as the positive electrode active material, and hydrogen atoms / carbon atoms are used as the negative electrode material. A power storage element using non-graphitizable carbon having a number ratio of 0 or more and less than 0.05 has been proposed (see Patent Document 4).

  On the other hand, the negative electrode material of the lithium ion capacitor is a carbonaceous material obtained by depositing a carbonaceous material on the surface of activated carbon, and the amount of mesopores derived from pores having a diameter of 20 mm or more and 500 mm or less is Vm1 (cc / g), When the amount of micropores derived from pores having a diameter of less than 20 mm is Vm2 (cc / g), a negative electrode material for an electricity storage element satisfying 0.01 ≦ Vm1 ≦ 0.20 and 0.01 ≦ Vm2 ≦ 0.40 is obtained. It has been proposed (see Patent Document 5).

  In addition, a power storage device has been proposed that uses non-porous charcoal instead of activated carbon as a positive electrode active material and a carbon material capable of reversibly occluding and desorbing lithium ions as a negative electrode active material (see Patent Document 6). .

  Here, considering the upper limit value of the working voltage of the nonaqueous lithium storage element (set to a withstand voltage or lower), most lithium ion batteries have an upper limit value of 4.2 V, while the lithium ion capacitor Then, an upper limit is 3.8-4.0V.

Japanese Patent Laid-Open No. 8-1007048 JP-A-9-283383 JP 2005-93778 A JP 2007-115721 A JP 2003-346801 A JP 2007-294539 A

  As described above, in the conventional lithium ion capacitor, the upper limit value of the working voltage is 3.8 to 4.0 V, and thus there is a problem that the obtained energy is lowered. In addition, when using in parallel to assist the lithium ion battery taking advantage of the excellent output characteristics of the lithium ion capacitor, the upper limit voltage is lower than the lithium ion battery, so the number of cells increases, The big problem was that there was a lot of loss, such as the need for a converter.

  Accordingly, the present invention provides a non-aqueous lithium storage element that can solve the above-described problems and has excellent output characteristics and high withstand voltage, a positive electrode material for a non-aqueous lithium storage element that provides the non-aqueous lithium storage element, and a method for manufacturing the same. With the goal.

  As a result of intensive studies to solve the above problems, the present inventors have paid attention to the difference in the positive electrode active material as a cause of the withstand voltage of the lithium ion capacitor being lower than that of the lithium ion battery. As a result of the investigation, by using a composite material in which a carbonaceous material is used as a core and the core is covered with a shell that is a substance that is difficult to oxidatively decompose the organic solvent that constitutes the electrolyte solution, the output characteristics are improved. It has been found that a non-aqueous lithium storage element having an excellent withstand voltage can be obtained.

That is, the present invention provides the following positive electrode material for a non-aqueous lithium storage element, a method for producing the same, and a non-aqueous lithium storage element.
[1] A composite material having a core and a shell covering the surface of the core,
The core material constituting the core is a carbonaceous material,
The shell material constituting the shell is a requirement of the following (1):
(1) A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 M / L in a solvent obtained by mixing ethylene carbonate and methyl ethyl carbonate at a mass ratio of 4: 1, a working electrode comprising the shell material, And a triode cell having a counter electrode and a reference electrode made of lithium metal, the oxidative decomposition potential of the solvent at the working electrode is 4.2 V (vsLi / Li ⁺ ) or more at 25 ° C.
A positive electrode material for a non-aqueous lithium storage element that satisfies the above requirements.
[2] The positive electrode material for a non-aqueous lithium storage element according to [1], wherein the carbonaceous material is activated carbon.
[3] The positive electrode material for a non-aqueous lithium storage element according to [1] or [2], wherein the shell material is made of a compound containing at least one of aluminum and lithium.
[4] The positive electrode for a non-aqueous lithium storage element according to any one of [1] to [3], wherein the shell material is made of at least one compound selected from the group consisting of oxides, carbonates and carbides. material.
[5] The positive electrode material for a non-aqueous lithium storage element according to any one of [1] to [4], wherein the shell has an average thickness of 0.05 nm to 3 nm.
[6] The carbonaceous material is activated carbon, and the activated carbon is
The amount of mesopores derived from pores with a diameter of 20 to 500 mm calculated by the BJH method is V1 (cc / g), and the amount of micropores derived from pores with a diameter of less than 20 mm calculated by the MP method is V2 (cc / g ) Satisfies 0.3 <V1 ≦ 0.8 and 0.5 ≦ V2 ≦ 1.0,
The positive electrode material for a non-aqueous lithium storage element according to any one of [1] to [5], which has a specific surface area of 1500 m ² / g or more and 3000 m ² / g or less as measured by a BET method.
[7] A method for producing a positive electrode material for a non-aqueous lithium storage element according to any one of [1] to [6],
A step of obtaining a core dispersion by dispersing the core in a medium obtained by dispersing or dissolving the shell material or a precursor thereof in a solvent;
Removing a part or all of the solvent from the core dispersion to obtain a coated core; and firing the coated core in an inert gas atmosphere;
The manufacturing method of the positive electrode material for non-aqueous lithium-type electrical storage elements containing this.
[8] A positive electrode including the positive electrode material for a non-aqueous lithium-type energy storage device according to any one of [1] to [6] as a positive electrode active material, a negative electrode including a negative electrode active material, and a non-electrode composed of an organic solvent and a lithium salt. A non-aqueous lithium storage element having an aqueous electrolyte.
[9] The negative electrode active material is a composite porous material obtained by depositing a carbonaceous material on the surface of activated carbon, and the composite porous material is
The amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method is Vm1 (cc / g), and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method is Vm2 (cc / g ) Satisfying 0.010 ≦ Vm1 ≦ 0.250, 0.001 ≦ Vm2 ≦ 0.200, and 1.5 ≦ Vm1 / Vm2 ≦ 20.0, the nonaqueous lithium type according to [8] Power storage element.
[10] The organic solvent is one or more cyclic carbonates selected from the group consisting of ethylene carbonate and propylene carbonate, and one or more acyclic carbonates selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; The nonaqueous lithium storage element according to [8] or [9], comprising:

  INDUSTRIAL APPLICABILITY According to the present invention, there are provided a non-aqueous lithium storage element having excellent output characteristics and high withstand voltage, a positive electrode material for a non-aqueous lithium storage element that provides the non-aqueous lithium storage element, and a method for producing the same.

  Hereinafter, embodiments of the present invention will be described in detail.

[Positive electrode material]
One embodiment of the present invention is a composite material including a core and a shell that covers the surface of the core, the core material that forms the core is a carbonaceous material, and the shell material that forms the shell is (1 ) Requirements, (1) a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 M / L in a solvent obtained by mixing ethylene carbonate and methyl ethyl carbonate at a mass ratio of 4: 1, from the shell material And a triode cell having a counter electrode and a reference electrode made of lithium metal, and the oxidative decomposition potential of the solvent at the working electrode is 4.2 V (vsLi / Li ⁺ ) or more at 25 ° C. And a positive electrode material for a non-aqueous lithium storage element (hereinafter, also referred to as a positive electrode material of the present invention) is provided.

<Core>
First, the carbonaceous material that is the core material in the present invention will be described. As the carbonaceous material, a carbonaceous material that can be adsorbed / desorbed to form an electric double layer by an anion that forms an electrolyte can be used. Specific examples of the carbonaceous material include, for example, activated carbon, graphite, graphitizable carbon material, non-graphitizable carbon material, amorphous carbonaceous material such as polyacene-based material, carbon black such as ketjen black and acetylene black, Examples thereof include carbon nanotubes, fullerenes, carbon nanophones, and fibrous carbonaceous materials. Among them, a carbonaceous material having a large specific surface area is preferable from the viewpoint that the electric double layer capacity can be increased. Specifically, activated carbon and carbon nanotube are preferable from this viewpoint. Furthermore, activated carbon which is cheap in production cost and can take a larger specific surface area is more preferable.

In the activated carbon, it is preferable to optimally control the pores of the activated carbon in order to achieve both high capacity (that is, high energy density) and high output characteristics (that is, high output density). Specifically, the amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method is V1 (cc / g), and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method is calculated. When V2 (cc / g) is satisfied, 0.3 <V1 ≦ 0.8 and 0.5 ≦ V2 ≦ 1.0 are satisfied, and the specific surface area measured by the BET method is 1500 m ² / g or more and 3000 m ^2. Activated carbon that is less than / g is preferred.

  The mesopore amount V1 is preferably a value larger than 0.3 cc / g from the viewpoint of increasing the output characteristics when the positive electrode material of the present invention is incorporated in a power storage element, and also reduces the capacity of the power storage element. From the viewpoint of suppressing, it is preferably 0.8 cc / g or less. V1 is more preferably 0.35 cc / g or more and 0.7 cc / g or less, and further preferably 0.4 cc / g or more and 0.6 cc / g or less.

  On the other hand, the micropore volume V2 is preferably 0.5 cc / g or more in order to increase the specific surface area of the activated carbon and increase the capacity, and also suppresses the bulk of the activated carbon and increases the density as an electrode. From the viewpoint of increasing the capacity per unit volume, it is preferably 1.0 cc / g or less. The V2 is more preferably 0.6 cc / g or more and 1.0 cc / g or less, and further preferably 0.8 cc / g or more and 1.0 cc / g or less.

  The ratio of the mesopore volume V1 to the micropore volume V2 is preferably in the range of 0.3 ≦ V1 / V2 ≦ 0.9. That is, V1 / V2 is preferably 0.3 or more from the viewpoint of increasing the ratio of the mesopore amount to the micropore amount to such an extent that the decrease in output characteristics can be suppressed while obtaining a high capacity. V1 / V2 is preferably 0.9 or less from the viewpoint of increasing the amount of micropores relative to the amount of mesopores to such an extent that a decrease in capacity can be suppressed while obtaining high output characteristics. A more preferable range is 0.4 ≦ V1 / V2 ≦ 0.7, and a further preferable range is 0.55 ≦ V1 / V2 ≦ 0.7.

  In the present invention, the micropore volume and mesopore volume are values determined by the following method. That is, the sample is vacuum-dried at 500 ° C. all day and night, and the adsorption and desorption isotherm is measured using nitrogen as an adsorbate. Using the isotherm on the desorption side at this time, the micropore volume is calculated by the MP method, and the mesopore volume is calculated by the BJH method.

  The MP method uses a “t-plot method” (BC Lippens, JH de Boer, J. Catalysis, 4319 (1965)), and uses a micropore volume, a micropore area, and a micropore. Is a method for obtaining the distribution of M.M. It is a method devised by Mikhail, Brunauer, Bodor (RS Mikhal, S. Brunauer, EE Bodor, J. Colloid Interface Sci., 26, 45 (1968)). The BJH method is a calculation method generally used for analysis of mesopores and was proposed by Barrett, Joyner, Halenda et al. (EP Barrett, LG Joyner and P. Halenda, J Amer. Chem. Soc., 73, 373 (1951)).

  The average pore diameter of the activated carbon as the core material is preferably 17 mm or more, more preferably 18 mm or more, and most preferably 20 mm or more in order to maximize the output. Further, from the point of maximizing the capacity, it is preferably 25 mm or less. The average pore diameter described in the present specification is obtained by dividing the total pore volume per weight obtained by measuring each equilibrium adsorption amount of nitrogen gas at each relative pressure at the liquid nitrogen temperature by the BET specific surface area. Point to what you asked for.

The BET specific surface area of the activated carbon as the core material is preferably 1500 m ² / g or more and 3000 m ² / g or less, and more preferably 1500 m ² / g or more and 2500 m ² / g or less. When the BET specific surface area is less than 1500 m ² / g, it is difficult to obtain a good energy density. On the other hand, when the BET specific surface area exceeds 3000 m ² / g, a large amount of binder is used to maintain the strength of the electrode. The performance per electrode volume tends to be low.

  The activated carbon having the above-described characteristics can be obtained using, for example, raw materials and processing methods as described below.

  The carbon source used as a raw material for activated carbon in the present invention is not particularly limited. For example, plant raw materials such as wood, wood flour, coconut husk, by-products during pulp production, bagasse, and molasses; peat, lignite , Fossil materials such as lignite, bituminous coal, anthracite, petroleum distillation residue components, petroleum pitch, coke, coal tar, etc .; phenol resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, celluloid, epoxy resin, Examples include various synthetic resins such as polyurethane resin, polyester resin, and polyamide resin; synthetic rubber such as polybutylene, polybutadiene, and polychloroprene; other synthetic wood, synthetic pulp, and their carbides. Among these raw materials, plant-based raw materials such as coconut shells and wood flour, and carbides thereof are preferable, and coconut shell carbides are particularly preferable.

  As a method of carbonization and activation for using these raw materials as the activated carbon, known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method can be employed.

  As a carbonization method of these raw materials, nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, an exhaust gas such as combustion exhaust gas, or other gases mainly composed of these inert gases. The method of baking for about 30 minutes-about 10 hours at about 400-700 degreeC (preferably 450-600 degreeC) using mixed gas is mentioned.

  As a method for activating the carbide obtained by the carbonization method, a gas activation method in which firing is performed using an activation gas such as water vapor, carbon dioxide, or oxygen is preferably used. Among these, a method using water vapor or carbon dioxide as the activation gas is preferable.

  In this activation method, the carbide is supplied for 3 to 12 hours (preferably 5 to 11) while supplying the activation gas at a rate of 0.5 to 3.0 kg / h (preferably 0.7 to 2.0 kg / h). It is preferable to activate by heating to 800 to 1000 ° C. over a period of time, more preferably 6 to 10 hours.

  Furthermore, prior to the activation treatment of the carbide, the carbide may be activated in advance. In this primary activation, the carbonaceous material can usually be fired at a temperature of less than 900 ° C. using an activation gas such as water vapor, carbon dioxide, oxygen, etc. to activate the gas.

  Producing activated carbon having the above-described characteristics, which can be used in the present invention, by appropriately combining the firing temperature and firing time in the carbonization method with the activation gas supply amount, the heating rate and the maximum activation temperature in the activation method. Can do.

  The average particle diameter of the core material is preferably 1 to 20 μm. The average particle size described in the present specification is the particle at which the cumulative curve becomes 50% when the cumulative curve is determined with the total volume being 100% when the particle size distribution is measured using a particle size distribution measuring device. Diameter (ie 50% diameter (Median diameter)).

  If the average particle size is less than 1 μm, the capacity per electrode volume tends to be low because the density of the active material layer is low. Furthermore, a small average particle size may lead to a drawback of low durability. On the other hand, when the average particle size is larger than 20 μm, it tends to be unsuitable for high-speed charge / discharge. The average particle diameter of the core material is preferably 2 to 15 μm, more preferably 3 to 10 μm.

<Shell>
Next, the shell material in the present invention will be described. The shell material is a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 M / L in a solvent obtained by mixing ethylene carbonate and methyl ethyl carbonate at a mass ratio of 4: 1, and a working electrode comprising the shell material. And a triode cell having a counter electrode and a reference electrode made of lithium metal, the oxidative decomposition potential of the solvent at the working electrode is 4.2 V (vsLi / Li ⁺ ) or more at 25 ° C.

  The shell material can be selected from various types such as an inorganic compound containing an alkali metal or an alkaline earth metal, an inorganic compound containing a transition metal, an inorganic compound containing a noble metal, an organic metal compound containing various metals, an organic polymer compound, or the like. Among these, from the viewpoint of cost and the viewpoint of stability in a non-aqueous electrolyte, it is preferable to include at least one compound selected from the group consisting of oxides, carbonates, and carbides. Is more preferable. Specifically, alkali metal oxides such as lithium oxide, sodium oxide, and potassium oxide, alkaline earth metal oxides such as magnesium oxide, calcium oxide, strontium oxide, and barium oxide, alkaline earth metal carbides such as aluminum carbide, Inorganic compounds made of alkali metals or alkaline earth metals such as alkali metal carbonates such as lithium carbonate are preferred.

  The shell material preferably contains a compound containing at least one of aluminum and lithium, and more preferably consists of the compound. This is because the compound containing at least one of aluminum and lithium is a material in which the oxidative decomposition potential of the organic solvent constituting the electrolytic solution becomes extremely high when used on the positive electrode side of the non-aqueous lithium storage element. Specific preferred specific examples of the compound containing at least one of aluminum and lithium include aluminum oxide, aluminum carbide, aluminum fluoride, lithium carbonate, lithium oxide, lithium fluoride, and lithium nitride.

  In addition, the said shell material may be used individually by 1 type, and may mix and use 2 or more types.

  In the case of an inorganic compound, the composition of the shell material in the present invention can be determined by X-ray diffraction analysis. However, when the average thickness of the shell is small, for example, 0.5 nm or less, it may be difficult to analyze the composition of the shell material by X-ray diffraction. In such a case, measurement using X-ray photoelectron spectroscopy (XPS) with a measurement depth of generally 5 nm or less is performed on both the composite material in the present invention and the carbonaceous material that is the core material. And the composition of the shell material can be identified by the difference between these measurements. In addition, approximately, as defined in the present invention, a composite material in which the core is coated with a shell material that is larger than the preferable average thickness defined in the present invention is manufactured, and the composition of the shell material is measured. It may represent the shell composition of a composite material in which the core is coated with a shell material having a preferred average thickness.

  On the other hand, when the shell material is an organic compound such as an organic polymer compound, a method of measuring by an organic chemical analysis method typified by infrared spectroscopy (IR) or a shell material extracted by pretreatment is used. It is also possible to identify by a method of measuring by an organic chemical analysis method such as nuclear magnetic resonance spectroscopy (NMR), IR, mass spectrometry (MS).

  The average thickness of the shell is preferably 0.05 nm or more and 3 nm or less. When the average thickness is less than 0.05 nm, the electrolytic solution and the carbonaceous material that is the core material may directly contact each other in a large area, and the oxidative decomposition reaction with the solvent constituting the non-aqueous electrolytic solution may be promoted. Therefore, the upper limit of the withstand voltage may be lowered. On the other hand, if the average thickness is greater than 3 nm, it is difficult to store electric charges by the electric double layer between the anion in the electrolyte and the core, and the energy density of the electric storage element may be significantly reduced. The average thickness of the shell is more preferably 0.5 nm or more and 2 nm or less.

  In the present invention, the average thickness of the shell is directly observed using a transmission electron microscope (TEM), or the specific element of the carbonaceous material constituting the core (XPS) is used (XPS). Carbon) and the ratio of the number of atoms of the material forming the shell (shell material) with a specific element (for example, lithium in the case of lithium carbonate) and the specific gravity of the shell determined from the shell composition obtained by the above-described method. It can also be calculated. It should be noted that the specific element selected to determine this atomic ratio is easy to analyze (for example, less peak overlap, strong peak intensity, and preferably only one of the core / shell). It is selected as appropriate.

  In addition, for example, using a time-of-flight secondary ion mass spectrometry (TOF-SIMS) apparatus, the composition distribution is obtained while etching, and the shell thickness is obtained using the etching thickness until the change in the composition becomes apparent. it can.

  When the core material is a non-porous material, it can be simply calculated from the specific gravity of the shell and core materials, the amount of the raw material used, and the average particle diameter of the core.

  In the present invention, the composite material shell may cover the core completely or partially. When the shell partially covers the core, the average thickness of the shell means the average thickness of the shell over the entire core surface.

  In addition, in the non-aqueous lithium storage element using the positive electrode material of the present invention, which is the composite material described above, as a positive electrode active material, from the viewpoint of improving the energy density of the storage element as an additional positive electrode active material, A metal oxide that occludes and releases lithium ions, for example, lithium cobaltate, may be further used as a positive electrode active material for a secondary battery. However, in order not to impair the effect of the positive electrode material of the present invention, when a metal oxide that occludes and releases lithium ions is used in combination, the ratio of the positive electrode material of the present invention to the total positive electrode active material is 50% by mass or more. It is preferable.

[Method for producing positive electrode material]
The method for producing the positive electrode material of the present invention is not particularly limited as long as it can form a composite material having the target composition of the present invention. For example, the precursor and the core are mixed using a precursor of a vaporizable shell material. After the coated core is obtained, the shell is formed on the core surface by firing the coated core. The shell material itself is applied to the core surface using a solution medium. And a method of bonding the two by a chemical reaction with the surface functional group of the.

  In particular, the following production method is preferable from the viewpoints of forming a uniform shell on the core surface as much as possible, strong bonding between the core and the shell, and considering a mass production process and cost.

  That is, another aspect of the present invention is a method for producing the above-described positive electrode material for a non-aqueous lithium electricity storage device of the present invention, wherein the shell material or a precursor thereof is dispersed or dissolved in a solvent. A non-aqueous lithium type comprising a step of dispersing a core to obtain a core dispersion, a step of removing a part or all of the solvent from the core dispersion to obtain a coated core, and a step of firing the coated core A method for producing a positive electrode material for a storage element is provided. Below, the typical procedure of the said manufacturing method is demonstrated.

  First, a core dispersion is obtained by dispersing a core in a medium in which a shell material or a precursor thereof is dispersed or dissolved in a solvent. The solvent can be appropriately selected according to the kind of the shell material or its precursor, and for example, a mixed solvent of water and alcohol (methanol / ethanol), dimethylformamide, toluene or the like can be used.

  The precursor of the shell material means a compound that can form the target shell material by the step of firing the above-described coated core (also referred to as “firing step”), and includes an organic metal compound and an inorganic metal compound.

  Specific examples of the organic metal compound include organic acid metal salts such as acetates, oxalates, formates, and benzoates, low molecular organic metal compounds such as metal alkoxides, and polyacrylic acid metal salts. High molecular organometallic compounds can be exemplified. Examples of inorganic metal compounds include nitrates, sulfates, chloride salts, phosphates and silicates. For example, when the shell material is lithium carbonate, precursors thereof include lithium oxalate and lithium acetate. Further, when the shell material is aluminum oxide, the precursor thereof may be aluminum stearate. Moreover, when the shell material is magnesium oxide, magnesium oxalate can be cited as a precursor thereof.

  Next, a part or all of the solvent is removed from the core dispersion to obtain a coated core. The method for removing the solvent is not limited, and for example, vacuum removal with a rotary evaporator or the like can be used.

  Next, the above coated core is fired. There is no restriction | limiting in particular about the atmospheric gas and temperature at the time of baking, According to the objective, it selects suitably. However, in the present invention, since the core material is a carbonaceous material, an inert gas atmosphere is preferable to prevent disappearance of the carbonaceous material due to carbon dioxide during high-temperature firing. Regarding the firing temperature, when a shell material precursor is used at the time of dispersion in the previous step, it is necessary to fire at a temperature at which the precursor can be completely composed of the target shell material. . Exemplary firing conditions include firing at 500 ° C. for 1 hour in a nitrogen gas atmosphere. For example, the positive electrode material of the present invention can be manufactured by the procedure as described above.

[Non-aqueous lithium storage element]
Next, a non-aqueous lithium storage element using the positive electrode material of the present invention will be described.

  Another aspect of the present invention is a non-aqueous electrolyte comprising a positive electrode including the above-described positive electrode material for a non-aqueous lithium storage element of the present invention as a positive electrode active material, a negative electrode including a negative electrode active material, and an organic solvent and a lithium salt. A non-aqueous lithium-type energy storage device (hereinafter also referred to as the energy storage device of the present invention) is provided. Each of the positive electrode and the negative electrode is typically formed as an electrode body in which an active material layer containing an active material (a positive electrode active material or a negative electrode active material) is fixed to a current collector.

<Positive electrode active material>
The positive electrode active material included in the positive electrode in the electricity storage device of the present invention includes at least the positive electrode material of the present invention described above. In addition to the positive electrode material of the present invention, the positive electrode active material can further include an additional positive electrode active material as described above. As described above, the ratio of the positive electrode material of the present invention to the total positive electrode active material is preferably 50% by mass or more.

<Negative electrode active material>
First, the negative electrode active material in the electricity storage device of the present invention will be described.

  The negative electrode active material included in the negative electrode of the electricity storage device of the present invention can be a material that occludes and releases lithium ions, such as a carbonaceous material, a lithium titanium composite oxide, and a conductive polymer. The negative electrode active material is preferably a carbonaceous material that occludes and releases lithium ions. For example, a carbonaceous material such as non-graphitizable carbon, graphitizable carbon, and the composite porous material disclosed in Patent Document 5 above. Can be mentioned. More preferably, the negative electrode active material is a composite porous material obtained by depositing a carbonaceous material on the surface of activated carbon, and pores having a diameter of 20 to 500 mm calculated by the BJH method in the composite porous material. When the amount of mesopores derived is Vm1 (cc / g) and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method is Vm2 (cc / g), 0.010 ≦ Vm1 ≦ 0.250 , 0.001 ≦ Vm2 ≦ 0.200, and 1.5 ≦ Vm1 / Vm2 ≦ 20.0.

  The negative electrode active material may be used alone or in combination of two or more.

  The composite porous material can be obtained, for example, by heat-treating activated carbon and a carbonaceous material precursor in the coexistence state.

  Regarding the activated carbon used as a raw material for the composite porous material, as long as the obtained composite porous material exhibits desired characteristics, there are no particular restrictions on the raw material for obtaining the activated carbon, and petroleum-based, coal-based, plant-based, Commercial products obtained from various raw materials such as molecular systems can be used. In particular, it is preferable to use activated carbon powder having an average particle diameter of 1 μm or more and 15 μm or less. The average particle diameter is more preferably 2 μm or more and 10 μm or less. In addition, the measuring method of the said average particle diameter is the same as the measuring method used for the average particle diameter of the carbonaceous material which is a core of the above-mentioned positive electrode material.

  On the other hand, the carbonaceous material precursor used as a raw material for the composite porous material is an organic material that can be dissolved in a solid, liquid, or solvent, by which the carbonaceous material can be deposited on activated carbon by heat treatment. Examples thereof include synthetic resins such as pitch, mesocarbon microbeads, coke, and phenol resin. Among these carbonaceous material precursors, it is preferable in terms of production cost to use an inexpensive pitch. Pitch is roughly divided into petroleum pitch and coal pitch. Examples of petroleum pitches include crude oil distillation residue, fluid catalytic cracking residue (decant oil, etc.), bottom oil from thermal crackers, ethylene tar obtained during naphtha cracking, and the like.

  When the pitch is used, the composite porous material is obtained by depositing a carbonaceous material on the activated carbon by thermally reacting a volatile component or a pyrolysis component of the pitch on the surface of the activated carbon. In this case, at a temperature of about 200 to 500 ° C., the deposition of pitch volatile components or pyrolysis components into the activated carbon pores proceeds, and at 400 ° C. or higher, the reaction in which the deposited components become carbonaceous materials proceeds. To do. The peak temperature during the heat treatment is appropriately determined according to the characteristics of the composite porous material to be obtained, the thermal reaction pattern, the thermal reaction atmosphere, etc., but is preferably 400 ° C. or higher, more preferably 450 ° C. to 1000 ° C. More preferably, the peak temperature is about 500 to 800 ° C. Moreover, the time which maintains the peak temperature at the time of heat processing should just be 30 minutes-10 hours, Preferably they are 1 hour-7 hours, More preferably, they are 2 hours-5 hours. For example, when heat treatment is performed at a peak temperature of about 500 to 800 ° C. for 2 to 5 hours, the carbonaceous material deposited on the activated carbon surface is considered to be a polycyclic aromatic hydrocarbon.

  Examples of the method for producing the composite porous material include a method in which activated carbon is heat-treated in an inert atmosphere containing hydrocarbon gas volatilized from a carbonaceous material precursor, and the carbonaceous material is deposited in a gas phase. . In addition, a method in which activated carbon and a carbonaceous material precursor are mixed in advance and heat-treated, or a method in which a carbonaceous material precursor dissolved in a solvent is applied to activated carbon and dried is then heat-treated.

  The composite porous material is obtained by depositing a carbonaceous material on the surface of the activated carbon, but the pore distribution after the carbonaceous material is deposited inside the pores of the activated carbon is important. And can be defined by the micropore volume. In the present invention, the ratio of mesopore amount / micropore amount is particularly important as well as the absolute values of mesopore amount and micropore amount. That is, in one embodiment of the present invention, the amount of mesopores derived from pores having a diameter of 20 mm or more and 500 mm or less calculated by the BJH method in the composite porous material is Vm1 (cc / g), and the diameter of 20 mm calculated by the MP method is used. When the amount of micropores derived from pores less than Vm2 (cc / g) is 0.010 ≦ Vm1 ≦ 0.250, 0.001 ≦ Vm2 ≦ 0.200, and 1.5 ≦ Vm1 / Vm2 ≦ 20.0 is preferred.

  The mesopore amount Vm1 is more preferably 0.010 ≦ Vm1 ≦ 0.225, and further preferably 0.010 ≦ Vm1 ≦ 0.200. About micropore amount Vm2, 0.001 <= Vm2 <= 0.150 is more preferable, and 0.001 <= Vm2 <= 0.100 is still more preferable. The ratio of mesopore amount / micropore amount is more preferably 1.5 ≦ Vm1 / Vm2 ≦ 15.0, and further preferably 1.5 ≦ Vm1 / Vm2 ≦ 10.0. If the mesopore volume Vm1 is less than or equal to the upper limit (Vm1 ≦ 0.250), high charge / discharge efficiency with respect to lithium ions can be maintained, and the mesopore volume Vm1 and the micropore volume Vm2 are equal to or greater than the lower limit (0.010 ≦ Vm1, 0. If 001 ≦ Vm2), high output characteristics can be obtained.

  In addition, since mesopores with a large pore diameter have higher ionic conductivity than micropores, a mesopore amount is necessary to obtain high output characteristics. Since impurities such as moisture, which are thought to adversely affect the properties, are difficult to desorb, it is considered necessary to control the amount of micropores in order to obtain high durability. Therefore, it is important to control the ratio between the amount of mesopores and the amount of micropores. When the ratio is equal to or higher than the lower limit (1.5 ≦ Vm1 / Vm2), that is, the carbonaceous material is deposited on the micropores more than the mesopores of the activated carbon. When the composite porous material after deposition has a large amount of mesopores and a small amount of micropores, high energy density, high output characteristics and high durability (cycle characteristics, float characteristics, etc.) can be obtained. When the ratio between the mesopore amount and the micropore amount is not more than the upper limit (Vm1 / Vm2 ≦ 20.0), high output characteristics can be obtained.

  In the present invention, the amount of micropores and the amount of mesopores are the same as those in the measurement method for the positive electrode material described above.

  In one embodiment of the present invention, as described above, the mesopore / micropore ratio after the carbonaceous material is deposited on the surface of the activated carbon is important. In order to obtain a composite porous material having a pore distribution range defined in the present invention, the pore distribution of activated carbon used as a raw material is important.

  In the activated carbon used for forming the composite porous material as the negative electrode active material, the mesopore amount derived from the pores having a diameter of 20 to 500 mm calculated by the BJH method is V1 (cc / g), the diameter calculated by the MP method. When the amount of micropores derived from pores less than 20 mm is V2 (cc / g), 0.050 ≦ V1 ≦ 0.500, 0.005 ≦ V2 ≦ 1.000, and 0.2 ≦ V1 / V2 It is preferable that ≦ 20.0.

  About mesopore amount V1, 0.050 <= V1 <= 0.350 is more preferable, and 0.100 <= V1 <= 0.300 is still more preferable. The micropore amount V2 is more preferably 0.005 ≦ V2 ≦ 0.850, and further preferably 0.100 ≦ V2 ≦ 0.800. The ratio of mesopore amount / micropore amount is more preferably 0.22 ≦ V1 / V2 ≦ 15.0, and further preferably 0.25 ≦ V1 / V2 ≦ 10.0. When the upper limit is exceeded, that is, when the mesopore volume V1 of the activated carbon is greater than 0.500 and when the micropore volume V2 is greater than 1.000, the pore structure of the composite porous material of one embodiment of the present invention is obtained. Needs to deposit many carbonaceous materials and tends to make it difficult to control the pore structure. On the other hand, when below the lower limit, that is, when the mesopore volume V1 of the activated carbon is less than 0.050, when the micropore volume V2 is less than 0.005, when V1 / V2 is less than 0.2, and when V1 / V2 is 20 If it is larger than 0.0, it tends to be difficult to obtain the pore structure of the composite porous material of one embodiment of the present invention from the pore distribution of the activated carbon.

  The average particle size of the composite porous material in the present invention is preferably 1 μm or more and 10 μm or less. About a lower limit, More preferably, it is 2 micrometers or more, More preferably, it is 2.5 micrometers or more. About an upper limit, More preferably, it is 6 micrometers or less, More preferably, it is 4 micrometers or less. If the average particle size is 1 μm or more and 10 μm or less, good durability is maintained. The measurement method of the average particle diameter of the composite porous material is the same as the measurement method used for the average particle diameter of the carbonaceous material that is the core of the positive electrode material.

  In the above composite porous material, the atomic ratio of hydrogen atoms / carbon atoms (hereinafter also referred to as H / C) is preferably 0.05 or more and 0.35 or less, and 0.05 or more and 0.15. The following is more preferable. When H / C exceeds the upper limit, the structure of carbonaceous material (typically polycyclic aromatic conjugated structure) deposited on the activated carbon surface may not be sufficiently developed. (Energy density) and charge / discharge efficiency are lowered. On the other hand, when H / C is lower than the lower limit, carbonization may proceed excessively and a sufficient energy density may not be obtained. H / C is measured by an elemental analyzer.

The composite porous material usually has an amorphous structure derived from the activated carbon as a raw material and a crystal structure derived mainly from the deposited carbonaceous material. According to the X-ray wide angle diffraction method, the composite porous material preferably has a structure with low crystallinity in order to exhibit high output characteristics, and has a structure with high crystallinity in order to maintain reversibility in charge and discharge. From the (002) plane spacing d ₀₀₂ is 3.60 to 4.00 mm, and the crystallite size Lc in the c-axis direction obtained from the half width of this peak is 8.0 to 20.0 mm. Some are preferable, d ₀₀₂ is 3.60 to 3.75 Å, and the crystallite size Lc in the c-axis direction obtained from the half width of this peak is 11.0 to 16.0 よ り. preferable.

<Other components>
In addition to the positive electrode active material and the negative electrode active material described above, the nonaqueous lithium electricity storage device of the present invention includes a current collector, a component other than the active material in the active material layer, a nonaqueous electrolyte solution, a separator, an exterior body, and the like. . Hereinafter, these components will be described.

(Current collector)
The material of the current collector is usually a metal foil that does not deteriorate such as elution and reaction in the power storage element, and is not particularly limited, and examples thereof include copper foil and aluminum foil. In the electricity storage device of the present invention, the positive electrode current collector is preferably an aluminum foil and the negative electrode current collector is preferably a copper foil.

  The current collector may be a normal metal foil having no through hole, or a metal foil having a through hole. The thickness of the current collector is not particularly limited, but when the thickness is smaller than 1 μm, the shape and strength of the electrode body (positive electrode and negative electrode in the present invention) formed by fixing the active material layer to the current collector cannot be sufficiently maintained. If it is larger than 100 μm, the weight and volume of the electricity storage device become too large, and the performance per weight and volume tends to be low, so 1 to 100 μm is preferable.

  As the active material layer, a known component contained in the active material layer of a known lithium ion battery, a capacitor, or the like can be used. In addition to the above-described positive electrode active material or negative electrode active material, the active material layer can contain known components such as a binder, a conductive filler, a thickener, and the like, and the type thereof is not particularly limited. Hereinafter, the details of the components of the active material layer in the non-aqueous lithium storage element will be described.

  The active material layer can contain a conductive filler, such as carbon black, if necessary. 0-30 mass parts is preferable with respect to 100 mass parts of active materials, and, as for the usage-amount of an electroconductive filler, 1-20 mass parts is more preferable. The conductive filler is preferably used from the viewpoint of high output density. However, if the amount used is more than 30 parts by mass, the proportion of the amount of the active material in the active material layer is low and the output density per volume is small. Tend.

  In order to fix the above-mentioned active material and further the conductive filler used as necessary on the current collector as an active material layer, as a binder, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluorine Rubber, styrene butadiene copolymer, cellulose derivative and the like can be used. The amount of the binder used is preferably in the range of 3 to 20 parts by mass and more preferably in the range of 5 to 15 parts by mass with respect to 100 parts by mass of the active material. When the amount of the binder used is more than 20 parts by mass, the binder covers the surface of the active material, and ions tend to enter and exit slowly, making it difficult to obtain a high output density. Further, when the amount of the binder used is less than 3 parts by mass, it tends to be difficult to fix the active material layer on the current collector.

  The electrode body in the present invention may be one in which the active material layer is formed only on the upper surface (one surface) of the current collector, or may be formed on the upper and lower surfaces (both surfaces).

  In the electrode body in which the active material layer is fixed to the current collector, the thickness of the active material layer is usually preferably about 30 to 200 μm. When the thickness of the active material layer is less than 30 μm, the proportion of the active material amount with respect to the entire power storage element decreases, and the energy density tends to decrease. On the other hand, when the thickness of the active material layer is larger than 200 μm, the resistance inside the electrode is increased and the output density tends to be lowered.

  The electrode body can be manufactured by an electrode manufacturing technique such as a known lithium ion battery or an electric double layer capacitor. For example, various materials including an active material are slurried with water or an organic solvent, and the active material layer is formed. It is obtained by coating on a current collector, drying, and pressing as necessary. Further, various materials including an active material can be dry-mixed without using a solvent, the active material can be press-molded, and then attached to the current collector using a conductive adhesive.

  The formed positive electrode body and negative electrode body are laminated or wound around via a separator, and inserted into an outer package formed from a metal can or a laminated film. As the separator, a polyethylene microporous film or a polypropylene microporous film used in a lithium ion secondary battery, a cellulose nonwoven paper used in an electric double layer capacitor, or the like can be used.

  The thickness of the separator is preferably 10 μm or more and 50 μm or less. When the thickness is less than 10 μm, self-discharge due to internal micro-shorts tends to increase. Moreover, when the thickness exceeds 50 μm, not only the energy density of the electricity storage element tends to be low, but also the output characteristics tend to be low.

  As a metal can which can be used for an exterior body, the thing made from aluminum is preferable. Moreover, as a laminate film that can be used for the exterior body, a film in which a metal foil and a resin film are laminated is preferable, and an example of a three-layer structure including an outer layer resin film / metal foil / interior resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used. The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel and the like can be suitably used. The interior resin film protects the metal foil from the electrolyte contained therein and melts and seals it at the time of heat sealing. Polyolefin, acid-modified polyolefin, and the like can be suitably used.

  The non-aqueous electrolyte used for the electricity storage device of the present invention comprises an organic solvent and a lithium salt. Examples of the organic solvent include cyclic carbonates represented by ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates represented by diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (MEC). , Lactones such as γ-butyrolactone (γBL), and mixed solvents thereof can be used. The mixed solvent includes one or more cyclic carbonates selected from the group consisting of ethylene carbonate and propylene carbonate, and one or more acyclic carbonates selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. Is preferable because a non-aqueous electrolyte solution having both a high dielectric constant and a low viscosity can be obtained.

In one embodiment of the present invention, the electrolyte dissolved in these organic solvents is a lithium salt. Examples of preferred lithium salts include LiBF ₄ , LiPF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₄ H) and mixed salts thereof.

  The electrolyte concentration in the non-aqueous electrolyte is preferably in the range of 0.5 to 2.0 mol / L. If it is less than 0.5 mol / L, anions are insufficient and the capacity of the electricity storage element tends to be low. On the other hand, if it exceeds 2.0 mol / L, undissolved lithium salt precipitates in the electrolyte solution, or the viscosity of the electrolyte solution becomes too high. There is a tendency to decrease.

  In the present invention, the negative electrode body can be previously doped with lithium ions. As a method for doping, a known method, for example, a method in which a negative electrode body is assembled in a state where a lithium metal foil is laminated on a negative electrode active material layer, and this is put in a nonaqueous electrolytic solution can be used. By doping with lithium ions, the capacity and operating voltage of the power storage element can be controlled.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

<Example 1>
[Production of cathode material]
The crushed palm shell carbide was carbonized in nitrogen in a small carbonization furnace at 500 ° C. for 3 hours. The treated carbide is placed in an activation furnace, 1 kg / h of steam is heated in a preheating furnace, and the temperature is raised to 900 ° C. over 8 hours. To obtain activated carbon. The obtained activated carbon was washed with water for 10 hours and then drained. Then, after drying for 10 hours in an electric dryer maintained at 115 ° C., pulverization was performed for 1 hour with a ball mill to obtain activated carbon as a core. It was 4.2 micrometers as a result of measuring an average particle diameter using the Shimadzu Corporation laser diffraction type particle size distribution measuring device (SALD-2000J). In addition, the pore distribution was measured with a pore distribution measuring apparatus (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics. As a result, the BET specific surface area was 2360 m ² / g, the mesopore volume (V1) was 0.52 cc / g, and the micropore volume (V2) was 0.88 cc / g.

Next, lithium oxalate as a precursor of the shell material and the activated carbon as the core described above are mixed well in a mixed solvent of water and ethanol (1: 1 by volume), and an ultrasonic homogenizer is used. A core dispersion was obtained by sufficiently dispersing. The solvent was removed from the core dispersion with an evaporator and dried to obtain a coated core. The obtained coated core powder was baked at 500 ° C. for 1 hour in an electric furnace under a nitrogen gas atmosphere to obtain a positive electrode material 1. Using a powder X-ray diffractometer (RINT-2500) manufactured by Rigaku Denki Co., Ltd., measurement with CuKα rays revealed that the composition of the shell material was identified as Li ₂ CO ₃ . As a result of TEM observation, the average thickness of the shell was 0.25 nm.

  Here, the following work was performed in order to measure the oxidative decomposition potential of the shell material.

After commercially available Li ₂ CO ₃ was dispersed with a water-ethanol mixed solution, it was dropped and dried on a glassy carbon electrode (No. 002417 manufactured by BAS Co., Ltd.). Next, a small amount of diluted PVdF solution (solvent is NMP) was dropped, and then dried to completely remove NMP. This electrode is a working electrode, Li metal is used as a counter electrode and a reference electrode, and LiPF ₆ is dissolved at a concentration of 1 M / L in an organic solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a mass ratio of 4: 1. A triode cell as an electrolyte was prepared. Using this triode cell, the oxidative decomposition potential was measured in an environment of 25 ° C. and found to be 5.05 V (vsLi / Li +).

[Preparation of positive electrode body]
80.8 parts by mass of positive electrode material 1, 6.2 parts by mass of ketjen black, 10 parts by mass of PVDF (polyvinylidene fluoride), 3.0 parts by mass of PVP (polyvinylpyrrolidone), and NMP (N-methylpyrrolidone) Were mixed to obtain a slurry. Next, the obtained slurry was applied to one side of an aluminum foil having a thickness of 15 μm, dried, and pressed to obtain a positive electrode body having an active material layer thickness of 55 μm.

[Preparation of negative electrode body]
With respect to commercially available coconut shell activated carbon, the pore distribution was measured using nitrogen as an adsorbate with a pore distribution measuring device (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics. The specific surface area was determined by the BET single point method. Further, as described above, using the isotherm on the desorption side, the mesopore amount was determined by the BJH method, and the micropore amount was determined by the MP method. As a result, the BET specific surface area was 1,780 m ² / g, the mesopore volume was 0.198 cc / g, the micropore volume was 0.695 cc / g, V1 / V2 = 0.29, and the average pore diameter was 21.2 mm. there were.

150 g of this coconut shell activated carbon is placed in a stainless steel mesh basket, placed on a stainless steel bat containing 270 g of a coal-based pitch (softening point: 50 ° C.), and an electric furnace (effective size in the furnace 300 mm × 300 mm × 300 mm) It installed in and performed the heat reaction. Heat treatment is performed in a nitrogen atmosphere by raising the temperature to 600 ° C. in 8 hours and holding at that temperature for 4 hours. Subsequently, after cooling to 60 ° C. by natural cooling, the composite porous material that is taken out from the furnace and becomes a negative electrode material The material 1 was obtained. When the obtained composite porous material 1 was measured in the same manner as the positive electrode core material, the BET specific surface area was 262 m ² / g, the mesopore volume (Vm1) was 0.1798 cc / g, and the micropore volume (Vm2) was 0. 0.0843 cc / g and Vm1 / Vm2 = 2.13.

  83.4 parts by mass of the composite porous material 1, 8.3 parts by mass of acetylene black, 8.3 parts by mass of PVDF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) are mixed to prepare a slurry. Obtained. Next, the obtained slurry was applied to one side of a copper foil having a thickness of 15 μm, dried and pressed to obtain a negative electrode body having an active material layer thickness of 60 μm. The electrode body was electrochemically doped with lithium ions corresponding to 760 mAh / g per unit weight of the composite porous material 1 using a lithium metal foil.

[Assembly and performance of storage element]
A cellulose nonwoven fabric separator (thickness: 30 μm) is laminated between the obtained negative electrode body and the positive electrode body, inserted into an outer package formed from a laminate film, and injected with an electrolyte solution. Sealed and assembled a non-aqueous lithium storage element. A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a mass ratio of 1: 4 was used as an electrolytic solution.

  The produced power storage element was charged to 4.0 V with a current amount of 1.5 C, and then subjected to constant current constant voltage charging for applying a constant voltage of 4.0 V for 2 hours. Subsequently, the battery was discharged to 2.0 V with a current amount of 1.5 C. Next, the same charge as described above was performed, and the battery was discharged to 2.0 V with a current amount of 350C. The ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 69.5%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. The resistance magnification here is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.05. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 1.10. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 1.24.

<Example 2>
[Production of cathode material]
A positive electrode material 2 was obtained in the same manner as in Example 1 except that aluminum oxalate n-hydrate was used as a precursor of the shell material. By analyzing in the same manner as in Example 1, the composition of the shell material was identified as Al ₂ O ₃ . The average thickness of the shell was 0.38 nm.

As a result of evaluation in the same manner as in Example 1 except that Al ₂ O ₃ was used instead of Li ₂ CO ₃ , the oxidative decomposition potential was 4.97 V (vsLi / Li +) in a 25 ° C. environment.

[Preparation of positive electrode body]
In the same manner as in Example 1, a positive electrode body was obtained.
[Preparation of negative electrode body]
The same one as in Example 1 was used.
[Assembly and performance of storage element]
A power storage element was assembled in the same manner as in Example 1.

  As a result of evaluation in the same manner as in Example 1, the ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 70.5%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. The resistance magnification here is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.07. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 1.15. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 1.28.

<Example 3>
[Production of cathode material]
A positive electrode material 3 was obtained in the same manner as in Example 1 except that calcium oxalate monohydrate was used as a precursor of the shell material. By analyzing in the same manner as in Example 1, the composition of the shell material was identified as CaCO ₃ . The average thickness of the shell was 0.41 nm.

As a result of evaluation in the same manner as in Example 1 except that CaCO ₃ was used instead of Li ₂ CO ₃ , the oxidative decomposition potential was 4.92 V (vsLi / Li +) in a 25 ° C. environment.

[Preparation of positive electrode body]
In the same manner as in Example 1, a positive electrode body was obtained.
[Preparation of negative electrode body]
The same one as in Example 1 was used.
[Assembly and performance of storage element]
A power storage element was assembled in the same manner as in Example 1.

  As a result of evaluation in the same manner as in Example 1, the ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 72.1%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. The resistance magnification here is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.10. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 1.21. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 1.31.

<Example 4>
[Production of cathode material]
The cured phenol resin was placed in a stainless steel dish and allowed to react by heat. The thermal reaction was performed in a nitrogen atmosphere, the temperature was raised until the inside of the furnace reached 630 ° C., kept at the same temperature for 4 hours, and then naturally cooled. The obtained material was pulverized using a planetary ball mill to obtain a non-graphitizable carbon material as a core. The physical properties of the non-graphitizable carbon material were evaluated in the same manner as in Example 1. BET specific surface area of 390m ² / g, mesopore Anaryou (V1) is 0.0251cc / g, the micropore volume (V2) is 0.121cc / g, d ₀₀₂ is 0.383, and the average particle size in the 4.2μm there were.

Next, a positive electrode material 4 was obtained in the same manner as in Example 2 except that the non-graphitizable carbon material was used as the core. By analyzing in the same manner as in Example 1, the composition of the shell material was identified as Al ₂ O ₃ . The average thickness of the shell was 0.38 nm.

[Preparation of positive electrode body]
In the same manner as in Example 1, a positive electrode body was obtained.
[Preparation of negative electrode body]
The same one as in Example 1 was used.
[Assembly and performance of storage element]
A power storage element was assembled in the same manner as in Example 1.

  As a result of evaluation in the same manner as in Example 1, the ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 67.8%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. Here, the resistance magnification is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.02. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 1.08. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 1.14.

<Comparative Example 1>
[Production of cathode material]
The activated carbon that is the core of Example 1 was used as the positive electrode material as it was.
[Preparation of positive electrode body]
In the same manner as in Example 1, a positive electrode body was obtained.
[Preparation of negative electrode body]
The same one as in Example 1 was used.
[Assembly and performance of storage element]
A power storage element was assembled in the same manner as in Example 1.

  As a result of evaluation in the same manner as in Example 1, the ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 70.7%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. Here, the resistance magnification is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.50. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 2.50. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 3.50.

<Comparative example 2>
[Production of cathode material]
The non-graphitizable carbon material that is the core of Example 4 was used as the positive electrode material.
[Preparation of positive electrode body]
In the same manner as in Example 1, a positive electrode body was obtained.
[Preparation of negative electrode body]
The same one as in Example 1 was used.
[Assembly and performance of storage element]
A power storage element was assembled in the same manner as in Example 1.

  As a result of evaluation in the same manner as in Example 1, the ratio of the discharge capacity at 350 C to the discharge capacity at 1.5 C was 68.4%.

  The durability test of the assembled electricity storage device was performed at 60 ° C. First, it carried out on condition of 4.2V application. The resistance magnification was measured at the start of the test (0 h) and after 100 h had elapsed. The resistance magnification here is a numerical value represented by (resistance value at 0.1 Hz after 100 hours) / (resistance value at 0.1 Hz at 0 h). The resistance magnification after 100 hours was 1.35. Next, it carried out on the conditions of 4.4V application. When evaluated in the same manner as described above, the resistance magnification was 2.01. Furthermore, it carried out on the conditions of 4.6V application. When evaluated in the same manner as described above, the resistance magnification was 3.05.

  From the above, it can be seen that the power storage device according to the present invention has excellent output characteristics and high withstand voltage.

  The positive electrode material for non-aqueous lithium storage element and the storage element of the present invention are, for example, in the field of a hybrid drive system that combines an internal combustion engine or a fuel cell, a motor, and a storage element in an automobile, and further assists in instantaneous power peak. It can be suitably used for purposes.

Claims (8)

A non-aqueous lithium storage element having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte solution comprising an organic solvent and a lithium salt,
The positive electrode active material is a composite material having a core and a shell covering the surface of the core;
The core material constituting the core is a carbonaceous material,
The shell material constituting the shell is a requirement of the following (1):
(1) A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 M / L in a solvent obtained by mixing ethylene carbonate and methyl ethyl carbonate at a mass ratio of 4: 1, a working electrode comprising the shell material, And a triode cell having a counter electrode and a reference electrode made of lithium metal, the oxidative decomposition potential of the solvent at the working electrode is 4.2 V (vsLi / Li ⁺ ) or more at 25 ° C.
Meet the,
The negative electrode active material is a composite porous material formed by depositing a carbonaceous material on the surface of activated carbon, and the composite porous material comprises:
The amount of mesopores derived from pores having a diameter of 20 to 500 mm calculated by the BJH method is Vm1 (cc / g), and the amount of micropores derived from pores having a diameter of less than 20 mm calculated by the MP method is Vm2 (cc / g ) Satisfying 0.010 ≦ Vm1 ≦ 0.250, 0.001 ≦ Vm2 ≦ 0.200, and 1.5 ≦ Vm1 / Vm2 ≦ 20.0. Wherein the carbonaceous material of the positive electrode active material is activated carbon, non-aqueous lithium electric storage element according to claim 1. The shell material is a compound containing at least one of aluminum and lithium, nonaqueous lithium-type electric storage element according to claim 1 or 2. The shell material is an oxide composed of at least one compound selected from the group consisting of carbonates and carbides, nonaqueous lithium-type electric storage element according to any one of claims 1 to 3. The average thickness of the shell is 3nm or less than 0.05 nm, a non-aqueous lithium electric storage element according to any one of claims 1 to 4. The carbonaceous material of the positive electrode active material is activated carbon, and the activated carbon is
The amount of mesopores derived from pores with a diameter of 20 to 500 mm calculated by the BJH method is V1 (cc / g), and the amount of micropores derived from pores with a diameter of less than 20 mm calculated by the MP method is V2 (cc / g ) Satisfies 0.3 <V1 ≦ 0.8 and 0.5 ≦ V2 ≦ 1.0,
Having the following measured by a specific surface area of 1500 m ² / g or more 3000 m ² / g by BET method, the non-aqueous lithium electric storage element according to any one of claims 1 to 5. The organic solvent includes one or more cyclic carbonates selected from the group consisting of ethylene carbonate and propylene carbonate, and one or more acyclic carbonates selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. The non-aqueous lithium storage element according to any one of claims 1 to 6 . A method of manufacturing a nonaqueous lithium-type electric storage element according to any one of claims 1 to 7
A step of obtaining a core dispersion by dispersing the core in a medium obtained by dispersing or dissolving the shell material or a precursor thereof in a solvent;
Removing part or all of the solvent from the core dispersion to obtain a coated core; and firing the coated core;
The positive active material includes producing, manufacturing method of a non-aqueous lithium electric storage element by a process comprising the.