JP2016072031A - Positive electrode for power storage element, power storage element using the same, and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage element which has excellent energy density by improving electrode workability of a positive electrode mixture layer containing a positive electrode active material containing lithium vanadium phosphate and using a positive electrode thereof.SOLUTION: A positive electrode for a power storage element includes: a positive electrode current collector; a positive electrode mixture layer containing a positive electrode active material containing lithium vanadium phosphate; and a conductive layer which is located between the positive electrode current collector and the positive electrode mixture layer and contains a carbonaceous material and a binding agent. In the positive electrode 2 for the power storage element, the thickness of the conductive layer is 0.2 to 5 μm, and the power storage element 1 is constituted using the same.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode for a power storage element, a power storage element using the same, and a power storage device.

  In recent years, power storage devices such as lithium secondary batteries having high energy density and low self-discharge and good cycle performance have attracted attention as power sources for portable devices such as mobile phones and notebook computers, and electric vehicles.

  Recently, polyanionic positive electrode active materials having excellent thermal stability have attracted attention. Since this polyanionic positive electrode active material is immobilized by covalently bonding oxygen to an element other than a transition metal, it does not release oxygen even at a high temperature. It is thought that the safety of the secondary battery can be dramatically improved.

As such a polyanionic positive electrode active material, lithium iron phosphate (LiFePO ₄ ) having an olivine structure has been actively studied. However, in addition to lithium insertion and desorption at a low potential of 3.4 V (vs. Li / Li ⁺ ), lithium iron phosphate has electrical conductivity unique to its crystal structure and lithium ion conductivity. Due to the low utilization factor of the active material derived from lowness and low high rate charge / discharge performance, the input / output performance is degraded as compared with conventional lithium-containing transition metal compounds. Then, examination of lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) having a reversible potential in the vicinity of about 4 V (vs. Li / Li ⁺ ) has been conducted.

  On the other hand, regarding the aluminum base material, a technique for coating the surface of the base material with a conductive material has been disclosed for the purpose of improving the decrease in conductivity on the surface of the base material and the elution of aluminum.

  Patent Document 1 states that “a current collector formed of a conductive material is provided with a carbon intermediate film or an intermediate film of a metal nobler than the conductive material, and an active material layer is coated thereon. A method of manufacturing an electrode used for a capacitor or battery to be used. "(Claim 1) is disclosed. According to Patent Document 1, “the thickness of the intermediate film can be appropriately selected in consideration of the type of the electrolyte, the material of the intermediate layer, etc., and the upper limit value can be 1000 nm or 500 nm, for example, and the lower limit value is 10 nm, for example. Alternatively, 30 nm can be adopted ”(paragraph 0009). Moreover, the Example shows the Example of an electric double layer capacitor.

Patent Document 2 states that “the lower layer includes a film containing a compound that does not swell with respect to an organic solvent and carbon fine particles, and the upper layer includes an aluminum foil that includes a film containing a binder, carbon fine particles, and a positive electrode active material. A positive electrode for a secondary battery characterized by the above. "(Claim 6) is disclosed. According to Patent Document 2, “The positive electrode active material used in the present invention is not particularly limited, and any material that can occlude / desorb lithium (ion) may be used. lithium cobaltate which has been used conventionally (LiCoO _2), lithium manganate (LiMn ₂ O _4), lithium nickelate (LiNiO _2), furthermore, Co, Mn, 3 ternary lithium compounds Ni (Li (Co _{x Mn y Ni z) O 2)} , sulfur-based (TiS _2), olivine (LiFePO ₄₎ is preferable, and the like. "(paragraph 0014), the creation of a film and a" film-forming compound and carbon fine particles There is no particular limitation, and a known method can be used, specifically, casting method, bar coater method, dipping method, printing method, etc. Among these methods, the thickness of the film is controlled. The bar coater method, the cast method, etc. are preferred from the viewpoint of easy operation, and a current collector (for positive electrode or negative electrode) can be formed by forming a carbon fine particle-containing film on an aluminum foil or copper foil by the above method. Further, the thickness is preferably 0.1 μm or more and 10 μm or less, and the thickness of 0.1 μm or less is not preferable because a desired effect cannot be obtained, while the thickness of 10 μm or more is not preferable. “The ratio of the active material in a given volume is relatively low, which is not preferable.” (Paragraph 0026). In the examples, the thickness of a film containing an ion-permeable compound and carbon fine particles is 5 μm, and an example (Example 1) in which lithium cobaltate is used as a positive electrode active material is illustrated.

JP 2000-164466 A JP 2007-226969 A

  In Patent Document 1, there is no specific description about providing a carbon intermediate film on a current collector (base material) formed of a conductive material when lithium vanadium phosphate is used as an active material. is there. Patent Document 2 describes many suitable positive electrode active materials. When the positive electrode active material contains lithium vanadium phosphate, a specific example of providing a film containing carbon fine particles as a lower layer is described. There is no description.

  The reversible potential of lithium vanadium phosphate is higher than that of lithium iron phosphate, and it has better electronic and ionic conductivity than lithium iron phosphate. As expected.

  However, in comparison with the case where an active material such as lithium iron phosphate is used, the positive electrode using the active material containing lithium vanadium phosphate is easily peeled off from the aluminum base material in the electrode manufacturing process. For this reason, the present inventors have found that the electrode processability is poor, and in the conventional positive electrode, the density of the active material in the mixture layer containing the active material is low, so that the energy density of the power storage element is low.

  This invention is made | formed in view of the said subject, and it aims at providing the positive electrode for electrical storage elements excellent in electrode workability, and the electrical storage element excellent in the energy density using the same.

  A first aspect of the present invention is located between a positive electrode current collector, a positive electrode mixture layer containing an active material containing lithium vanadium phosphate, and the positive electrode current collector and the positive electrode mixture layer. And a conductive layer containing a carbonaceous material and a binder.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode for electrical storage elements excellent in electrode workability, and the electrical storage element excellent in the energy density using the same can be provided.

1 is an external perspective view showing an embodiment of a power storage device according to the present invention. Schematic showing a power storage device configured by assembling a plurality of power storage elements according to the present invention

  Embodiments and operational effects are as follows. However, the action mechanism described in this specification includes estimation, and its correctness does not limit the present invention.

The present invention is located between a positive electrode current collector, a positive electrode mixture layer containing an active material containing lithium vanadium phosphate, and between the positive electrode current collector and the positive electrode mixture layer, and a carbonaceous material and It is a positive electrode for electrical storage elements provided with the conductive layer containing a binder.
Thus, by providing a conductive layer between the positive electrode current collector and the positive electrode mixture layer, the adhesion of the mixture layer is improved compared to forming the positive electrode mixture layer directly on the positive electrode current collector. Further, peeling of the composite material layer from the positive electrode hardly occurs, and electrode processability such as positive electrode pressing is improved.

  In addition, since the effect of this invention becomes so remarkable that there is much content of lithium vanadium phosphate in a positive electrode active material, the one where the ratio of lithium vanadium phosphate in a positive electrode active material is large is preferable. It is more preferable to use a positive electrode active material containing lithium vanadium phosphate most in the positive electrode active material, that is, lithium vanadium phosphate as a main component.

In addition, an active material containing lithium vanadium phosphate is preferable because the energy density of the power storage element can be increased by controlling the thickness of the conductive layer, as described in Examples below.
From the viewpoint of adhesion between the positive electrode mixture layer and the conductive layer, the thickness of the conductive layer is preferably 0.2 μm or more. On the other hand, from the viewpoint of the energy density of the power storage element, the thickness of the conductive layer is preferably 5 μm or less. In this way, by setting the thickness of the conductive layer to a specific range of 0.2 μm or more and 5 μm or less, the electrode processability due to the improved adhesion between the conductive layer and the mixture layer, and the energy density of the storage element can be further increased. It is preferable because it can be improved.
Furthermore, the thickness of the conductive layer is more preferably 0.2 μm or more and 2.5 μm or less from the viewpoint of high rate charge / discharge performance and energy density of the energy storage device.

  The thickness of the conductive layer in the positive electrode for a storage element is measured with a micrometer or the like at the portion where the positive electrode mixture layer is not present on the surface of the conductive layer, that is, the portion where only the conductive layer is formed on the substrate. Can be confirmed. In addition, it is possible to confirm by measuring the cross section of the electrode for the electricity storage element with a scanning electron microscope (SEM), observation with a transmission electron microscope (TEM), or the like.

The surface resistance of the conductive layer is preferably 10 Ω / cm ² or less. Thereby, since the high rate charge / discharge performance and energy density of an electrical storage element improve, it is preferable.
The surface resistance of the conductive layer can be measured by a four-terminal method using a low resistivity meter (Loresta AX MCP-T370 manufactured by Mitsubishi Chemical Corporation).

Examples of the positive electrode current collector used for the positive electrode for the storage element include metal materials such as aluminum and alloys containing the metal; carbonaceous materials such as carbon cloth and carbon paper. Among these, aluminum is preferable.
As aluminum, a well-known aluminum foil used for lithium batteries can be used. The thickness of the aluminum foil is preferably 10 μm or more from the viewpoint of the strength of the substrate, and is preferably 50 μm or less from the viewpoint of energy density. More preferably, it is 15 micrometers-30 micrometers. Moreover, what etched the surface of aluminum foil is used for a capacitor, a lithium ion capacitor, etc. Such an etched aluminum foil is preferable because it contributes not only to adhesion between the conductive layer and the foil but also to improvement in adhesion between the positive electrode mixture layer and the conductive layer due to surface irregularities.

The carbonaceous material contained in the conductive layer may be any material that has better electronic conductivity than the positive electrode active material, and well-known conductive materials and active materials used for the positive electrode of lithium batteries are used. Examples of such a carbonaceous material include acetylene black, ketjen black, carbon nanofiber, and graphite. Moreover, the carbon containing material obtained by thermally decomposing an organic compound in non-oxygen atmosphere can also be used. Examples of the organic compound as a raw material include polymers such as polyvinyl alcohol and polyethylene glycol, organic acids such as ascorbic acid and citric acid, alcohols such as methanol and ethanol, and organic gases such as acetylene and carbon monoxide.
Moreover, it is preferable that the particle diameter of the carbonaceous material contained in the conductive layer is small. In order to make the conductive layer thin, the average particle size is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less.

  Examples of the binder contained in the conductive layer include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and chitin chitosan. , Pyromellitic acid or the like can be used as one kind or a mixture of two or more kinds. Among these, it is preferable to use a binder containing, as a main component, a material that does not swell in an organic solvent, because the adhesion between the conductive layer and the positive electrode mixture layer can be improved. Among these, a binder mainly composed of chitin chitosan or pyromellitic acid is particularly preferable.

The method for forming the conductive layer is not particularly limited. Specifically, the carbonaceous material, the binder, and other materials are mixed in an organic solvent such as N-methylpyrrolidone and toluene or water and then kneaded to prepare a paste. After coating on the material, it is suitably produced by heat treatment at a temperature of about 50 ° C. to 250 ° C. for about 10 minutes to 120 minutes. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited to.
The content of the carbonaceous material in the paste is preferably 10 to 98% by mass, more preferably 50 to 95% by mass, and 70 to 95% by mass with respect to the mass sum of the carbonaceous material and the binder. Particularly preferred.

  In preparing a positive electrode mixture layer containing lithium vanadium phosphate as a positive electrode active material, in addition to the active material, well-known conductive agents such as acetylene black, ketjen black, carbon nanofiber, polyvinylidene fluoride, silicon butadiene Known binders such as rubber, polytetrafluoroethylene, carboxymethylcellulose and the like can be used in known formulations. Specifically, an active material, a conductive material, a binder, and other materials are mixed in an organic solvent such as N-methylpyrrolidone and toluene or water and then kneaded to prepare a paste for a positive electrode mixture layer. Then, after the obtained paste is applied on the conductive layer, it is preferably produced by heat treatment at a temperature of about 50 ° C. to 250 ° C. for about 10 minutes to 120 minutes.

  The positive electrode for a storage element preferably has a small amount of water contained in the electrode, and specifically, it is preferably less than 1000 ppm. As a means for reducing the amount of moisture, a method of drying the electrode in a high temperature and reduced pressure environment or a method of electrochemically decomposing moisture contained in the positive electrode is suitable.

  The combined thickness of the conductive layer and the positive electrode mixture layer is preferably 10 to 500 μm from the viewpoint of the energy density of the power storage element.

Lithium vanadium phosphate used for the positive electrode active material is represented by the general formula Li ₃ V ₂ (PO ₄ ) ₃ . There are several types of lithium vanadium phosphate corresponding to the crystal structure. Among them, those having a monoclinic crystal (space group P2 ₁ / n) crystal structure have a high reversible potential and are theoretically satisfactory. Since the discharge capacity is as large as 197 mAh / g, it is preferable that the energy density of the power storage element can be increased.
In addition, it does not prevent lithium, vanadium, manganese, phosphorus, and oxygen from being partially substituted with other elements as long as the crystal structure of lithium vanadium phosphate can be maintained. As other elements to be substituted, for example, in the case of lithium, alkali metal or alkaline earth metal such as sodium, potassium and magnesium, and in the case of vanadium or / and manganese, scandium, titanium, chromium, iron, cobalt, nickel In the case where the metal such as zirconium, indium and aluminum is phosphorus, silicon, boron, sulfur and the like are used, and in the case where oxygen is used, fluorine, chlorine and the like are mentioned. Furthermore, for the purpose of improving the performance of an active material for a secondary battery containing lithium vanadium phosphate, impurities may be intentionally coexisted within a range not impairing the effects of the present invention, and further, a synthesis step, etc. In this case, unintended impurities may be mixed.

  The lithium vanadium phosphate containing lithium atoms, vanadium atoms, manganese atoms, phosphorus atoms, and the like can be confirmed by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis. Further, the fact that metal atoms are in solid solution and the crystal structure thereof can be confirmed by powder X-ray diffraction analysis (XRD). In addition, transmission electron microscope observation (TEM), energy dispersive X-ray spectroscopy (EDX), scanning electron microscope X-ray analysis (EPMA), high resolution electron microscope analysis (HRAEM), electron energy loss spectroscopy (EELS), etc. Detailed analysis can be performed by using an analytical instrument in combination.

  Lithium vanadium phosphate may have a carbon compound on the surface or inside of the particles. Thus, it is preferable to provide a carbon compound because it contributes to the improvement of the charge / discharge performance of lithium vanadium phosphate. Here, the particle refers to a primary particle, a secondary particle, or a higher order particle, and a carbon compound such as carbon adheres to the surface or inside of the particle, and is provided in a form such as a coating. It has been.

In addition, lithium vanadium phosphate is preferably used as a powder having an average particle size of secondary particles of 100 μm or less. In particular, the average particle size of the secondary particles is more preferably 0.1 to 50 μm, and the particle size of the primary particles constituting the secondary particles is preferably 1 to 500 nm. Further, the BET specific surface area of the powder particles by the flow method nitrogen gas adsorption method is preferably large to some extent in order to improve the high rate charge / discharge performance of the positive electrode for a storage element, and is preferably 1 to 100 m ² / g. More preferably, it is 5-50 m < ² > / g.

  From the viewpoint of easy handling of the positive electrode mixture layer paste, it is preferable that the amount of water contained in the lithium vanadium phosphate is smaller, specifically, less than 1000 ppm. As a means for reducing the amount of moisture, a method of drying the positive electrode in a high temperature and reduced pressure environment is suitable.

  The counter electrode of the positive electrode for the energy storage device is not limited as long as it can occlude and release lithium. Lithium metal, lithium alloy (lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum- Alloys, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), metal oxides, lithium transition metal composite oxides, polyphosphorus Examples include acid compounds and polyanion compounds. Moreover, you may use lithium vanadium phosphate as an active material of a counter electrode. These can be used according to the kind of electrolyte solution used for an electrical storage element.

  Examples of the solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; formic acid Chain esters such as methyl, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme, etc. Ethers such as acetonitrile, nitriles such as benzonitrile, dioxolane or derivatives thereof, and non-aqueous solvents and water consisting of ethylene sulfide, sulfolane, sultone or derivatives thereof alone or a mixture of two or more thereof You can It is not limited.

Examples of the electrolyte salt include ionic compounds such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiN (CF ₃ SO ₂ ) _2. It can be used alone or in combination of two or more. It is also possible to include an electrolyte salt other than lithium, for example, NaClO _4, and the like. The concentration of the electrolyte salt in the electrolytic solution is preferably 0.5 mol / l or more and 5 mol / l or less, more preferably 1 mol / l or more and 2.5 mol / l, in order to reliably obtain a secondary battery having high battery performance. l or less.

  FIG. 1 is a schematic view of a rectangular nonaqueous electrolyte storage element 1 which is an embodiment of a nonaqueous electrolyte storage element according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, an electrode group 2 is housed in an exterior body 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′. And the nonaqueous electrolyte is hold | maintained in the exterior body and the separator.

  The configuration of the nonaqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include cylindrical, square (rectangular), flat, and other nonaqueous electrolyte storage elements.

  The present invention can also be realized as a power storage device including a plurality of the above nonaqueous electrolyte power storage elements. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

  In the examples described below, a lithium ion secondary battery is exemplified as the nonaqueous electrolyte storage element, but the present invention is not limited to the lithium ion secondary battery, and can be applied to other nonaqueous electrolyte storage elements. .

  First, the manufacturing method of the electrical storage element 10 is demonstrated. In addition, all of the examples described below relate to a lithium ion secondary battery which is a kind of the power storage element 10 according to the above-described embodiment.

Example 1
(Conductive layer)
A conductive layer paste was prepared using a conductive material (acetylene black) and chitin chitosan as binders (Daiichi Seika Kogyo Co., Ltd .: DCN) and NMP as a non-aqueous solvent. Here, the mass ratio of the conductive agent, the binder and the NMP was 20: 1: 19. The conductive layer paste was prepared through a mixing and kneading process using a planetary mixer. After apply | coating this paste for conductive layers on both surfaces of the 15-micrometer-thick aluminum foil base material, the conductive layer was produced by drying at 150 degreeC. In addition, the thickness of the single side | surface of a conductive layer was 2.5 micrometers, and the coating mass of the single side | surface was 0.14 mg / cm < ² >.

(Positive electrode)
Positive electrode active material (lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ), particle size: 20 μm, BET specific surface area: 11.6 m ² / g), conductive agent (acetylene black), polyfluoride as binder A paste for a positive electrode mixture layer was prepared using vinylidene (PVDF) and NMP as a non-aqueous solvent. Here, an 8% NMP solution (# 7208 manufactured by Kureha) was used as the PVDF. The mass ratio of the positive electrode active material, the conductive agent and the binder was 90: 5: 5 (in terms of solid content). The positive electrode mixture layer paste was prepared through a mixing / kneading step using a planetary mixer by adjusting the solid content (mass%) by adjusting the amount of the non-aqueous solvent. In this example, the solid content concentration of the positive electrode paste was adjusted to 30% by mass. This positive electrode paste was applied onto the conductive coating layer and dried at 120 ° C. Next, the positive electrode was produced by pressing with the roll press machine which adjusted the temperature of the roll to 100 degreeC. The active material layer of the produced positive electrode had a single-side coating mass of 13.4 mg / cm ² and a porosity of 40%. The positive electrode was sufficiently vacuum dried and then used for battery production.

(Negative electrode)
A negative electrode mixture layer paste was prepared using a negative electrode active material (graphite), polyvinylidene fluoride (PVDF) as a binder, and NMP as a non-aqueous solvent. Here, the PVDF was used. The mass ratio of the negative electrode active material and the binder was 94: 6. The negative electrode paste was prepared through a kneading step using a planetary mixer after adjusting the solid content (% by mass) by adjusting the amount of the non-aqueous solvent. This negative electrode paste was applied and dried on both sides of a copper foil having a thickness of 10 μm, and then pressed by a roll press to produce a negative electrode. The prepared negative electrode had a mixture layer coating mass of 5.39 mg / cm ² and a porosity of 35%. The negative electrode was sufficiently vacuum dried and then used for battery production.

(Non-aqueous electrolyte)
The nonaqueous electrolyte is prepared by dissolving LiPF ₆ in a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a volume ratio of 1: 1: 1 so that the salt concentration becomes 1 mol / L. It was prepared by adding vinylene carbonate so as to be 1% by mass. The amount of water in the nonaqueous electrolyte was less than 50 ppm.

(Production of battery)
A positive electrode, a negative electrode, and a separator (Asahi Kasei Co., Ltd. product: S6722) are laminated and wound to form an electrode body, and then the positive electrode lead and the negative electrode lead are welded to the positive electrode plate and the negative electrode plate, respectively, and sealed in the container. And the above non-aqueous electrolyte was injected and sealed to prepare a battery. The dimensions of the battery were 112 mm wide, 21 mm thick, and 81 mm high.

(Example 2)
In the production of the positive electrode conductive layer, the thickness of one side of the conductive layer was 0.2 μm, the coating mass on one side was 0.01 mg / cm ² , and the ratio of the positive electrode capacity / negative electrode capacity in the battery of Example 1 A battery of Example 2 was fabricated in the same manner as Example 1 except that the coating mass of the positive electrode mixture layer was adjusted so as to be the same ratio.

(Example 3)
In the production of the positive electrode conductive layer, the thickness of one side of the conductive layer was 1.0 μm, the coating mass on one side was 0.06 mg / cm ² , and the ratio of the positive electrode capacity / negative electrode capacity in the battery of Example 1 A battery of Example 3 was fabricated in the same manner as Example 1 except that the coating mass of the positive electrode mixture layer was adjusted so as to be the same ratio.

Example 4
In the production of the positive electrode conductive layer, the thickness of one side of the conductive layer was 5.0 μm, the coating mass on one side was 0.28 mg / cm ² , and the ratio of the positive electrode capacity / negative electrode capacity in the battery of Example 1 A battery of Example 4 was produced in the same manner as in Example 1 except that the coating mass of the positive electrode mixture layer was adjusted so as to be the same ratio.

(Comparative Example 1)
Comparative Example 1 was carried out in the same manner as in Example 1 except that the same positive electrode paste as in Example 1 was applied to both surfaces of the aluminum foil on which no conductive layer was formed so as to have the same coating mass as in Example 1. An attempt was made to produce a positive electrode. However, the positive electrode mixture layer and the aluminum foil peeled off, and the battery could not be produced.

(Comparative Example 2)
In the production of the positive electrode, the positive electrode active material layer, the conductive agent and the binder were prepared at a mass ratio of 80: 8: 12 (in terms of solid content) to produce a positive electrode mixture layer paste, Similar to Example 1, except that the coating mass of the positive electrode mixture layer was adjusted so that the ratio was the same as the ratio of the positive electrode capacity / negative electrode capacity in the battery of Example 1 and that it was applied to both surfaces. Thus, a battery of Comparative Example 2 was produced.

(Comparative Example 3)
The positive electrode mixture layer paste using lithium iron phosphate (LiFePO ₄ ) as the positive electrode active material was applied to both surfaces of the aluminum foil on which the conductive layer was not formed, and the positive electrode capacity / negative electrode in the battery of Example 1 A battery of Comparative Example 3 was fabricated in the same manner as in Example 1 except that the coating mass of the positive electrode mixture layer was adjusted so as to be the same as the capacity ratio.

(Comparative Example 4)
The coating mass of the positive electrode mixture layer was adjusted so that lithium iron phosphate (LiFePO ₄ ) was used as the positive electrode active material and the same ratio as the positive electrode capacity / negative electrode capacity ratio in the battery of Example 1. Except for this, a battery of Comparative Example 4 was produced in the same manner as in Example 1.

(Comparative Example 5)
Lithium iron phosphate (LiFePO ₄ ) was used as the positive electrode active material, the thickness of one side of the conductive layer was 0.2 μm, the coating mass on one side was 0.01 mg / cm ² , and the battery of Example 1 A battery of Comparative Example 5 was produced in the same manner as in Example 1 except that the coating mass of the positive electrode mixture layer was adjusted so as to have the same ratio as the positive electrode capacity / negative electrode capacity ratio.

Here, the positive electrode capacity is a capacity calculated by the product of the mass of the positive electrode active material in a portion where the positive electrode mixture layer faces the negative electrode mixture layer and a preset capacity of the positive electrode active material in the electrode body. is there. The negative electrode capacity is a capacity calculated by the product of the mass of the negative electrode active material in the portion of the electrode body where the negative electrode mixture layer faces the positive electrode mixture layer and the preset capacity of the negative electrode active material. .
In the examples and comparative examples, the following values were used as the preset capacity of each active material.
Lithium vanadium phosphate: 128 mAh / g
Lithium iron phosphate: 156 mAh / g
Graphite: 340 mAh / g

(Initial activation process)
The battery produced as described above was transferred to a thermostat set at 25 ° C., and an initial activation step was performed. The initial activation process is composed of four charge / discharge cycles.
In the batteries of Example 1, Comparative Example 1 and Comparative Example 2, the initial charging conditions were constant current and constant voltage charging with a current value of 0.1 CmA and a potential of 4.2 V. The charging time was 16 hours from the start of energization. The initial discharge conditions were constant current discharge with a current of 0.1 CmA and a final voltage of 2.0V. Subsequently, the charging conditions for the second to fourth cycles were constant current and constant voltage charging with a current value of 0.2 CmA and a potential of 4.2 V. The charging time was 8 hours from the start of energization. The discharge conditions for the second to fourth cycles were constant current discharge with a current of 0.2 CmA and a final voltage of 2.0 V. In all cycles, a 30 minute rest period was set after charging and discharging.
The batteries of Comparative Example 3 and Comparative Example 4 were set to the same charge / discharge conditions except that the set voltage was 3.6 V in the above charging conditions.
Here, Table 1 shows a current value of 1 CmA applied to each battery.
Further, from the discharge data of the fourth cycle of the initial activation process, the discharge energy of each battery is calculated, and the value obtained by dividing the value by the mass of each battery is referred to as “battery energy density (Wh / g)”. Table 1 shows.

When Example 1 and Comparative Example 1 are compared, when the positive electrode active material contains lithium vanadium phosphate, the positive electrode mixture layer does not peel off in the positive electrode of Example 1 provided with a conductive layer, and the electrode processability is excellent. I know that.
On the other hand, from the result of Comparative Example 3, when lithium iron phosphate is used as the positive electrode active material, the active material is superior in electrode processability to lithium vanadium phosphate, and thus there is no need to provide a conductive layer. I understand that.

  Moreover, when Examples 1-4 and Comparative Example 2 are compared, it turns out that the energy density of a battery is excellent by providing a conductive layer in a positive electrode.

Furthermore, although the energy density of any of the batteries of Examples 1 to 4 is higher than that of the battery of Comparative Example 2, the energy density of the batteries of Comparative Examples 4 and 5 is the battery of Comparative Example 3. Smaller than. In other words, when the positive electrode active material contains lithium vanadium phosphate, the positive electrode provided with the conductive layer improves the energy density of the battery. However, when lithium iron phosphate is used as the positive electrode active material, the positive electrode Even if the conductive layer is disposed, the energy density of the battery is not improved.
From this, it is considered that the battery using lithium vanadium phosphate as the positive electrode active material contributes more to the battery energy density due to the thickness of the conductive layer than the battery using lithium iron phosphate as the positive electrode active material. .

The positive electrode for a power storage device of the present invention is excellent in electrode processability, and the power storage device using this positive electrode for a power storage device has improved energy density, so that the power source for electric vehicles, the power source for electronic devices, the power source for power storage, etc. It can be effectively used for a non-aqueous electrolyte storage element.

Claims (4)

A positive electrode current collector, a positive electrode mixture layer containing an active material containing lithium vanadium phosphate, and positioned between the positive electrode current collector and the positive electrode mixture layer, and includes a carbonaceous material and a binder. A positive electrode for a power storage element comprising a conductive layer. The positive electrode for an electrical storage element according to claim 1, wherein the conductive layer has a thickness of 0.2 μm or more and 5 μm or less. The electrical storage element provided with the positive electrode for electrical storage elements of Claim 1 or 2. A power storage device comprising the power storage element according to claim 3.