JP2012216500A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve output characteristics and cycle durability.SOLUTION: A lithium secondary battery 10 comprises a positive electrode sheet 13 in which a positive electrode mixture layer 12 containing a positive electrode active material is formed on a collector 11. The positive electrode mixture layer 12 contains the positive electrode active material containing a lithium-containing oxide, and a carbon material, has a density of 2.0 g/cmor higher, and satisfies that the pore size at which the cumulative volume accounts for 20% of the total pore volume is 0.3 μm or larger in the pore size distribution measured by mercury porosimetry. In addition, the positive electrode mixture layer 12 preferably satisfies that the volume of pores having a size of 0.5 to 10 μm accounts for 40% or more of the total pore volume and the mode pore size is in the range of 0.5 to 10 μm in the pore size distribution measured by mercury porosimetry.

Description

  The present invention relates to a lithium secondary battery.

Conventionally, as a lithium secondary battery, a positive electrode has a structure in which a positive electrode layer containing a lithium composite metal oxide containing nickel and a vinylidene fluoride-based fluororubber is supported on a current collector, and the positive electrode layer is intruded with mercury. in porosity of law 20% to 50%, and those pores of diameter 0.1μm~3μm by mercury porosimetry is 10mm ³ / g~150mm ³ / g has been proposed (e.g., Patent Document 1 reference). This lithium secondary battery is said to improve the energy density and improve the charge / discharge cycle characteristics by improving the positive electrode.

Japanese Patent Laid-Open No. 10-255563

However, in the above-described lithium secondary battery of Patent Document 1, when the pore volume is 150 mm ³ / g or more, the cycle characteristics may be significantly deteriorated. For this reason, the further improvement which raises an output characteristic and cycling durability was calculated | required.

  This invention is made | formed in view of such a subject, and it aims at providing the lithium secondary battery which can improve an output characteristic and cycling durability more.

As a result of diligent research to achieve the above-mentioned object, the present inventors have found that the positive electrode mixture layer having a density of 2.0 g / cm ³ or more has a total pore volume in the pore distribution measured by the mercury intrusion method. Assuming that the pore diameter with an integrated volume of 20% is 0.3 μm or more, it was found that the output characteristics and cycle durability at high temperatures can be improved, and the present invention has been completed.

That is, the lithium secondary battery of the present invention is
A positive electrode mixture layer containing a positive electrode active material containing a lithium-containing oxide and a carbon material is formed on the positive electrode current collector, and has a density of 2.0 g / cm ³ or more and is measured by a mercury intrusion method. A positive electrode having the positive electrode mixture layer having a pore diameter of 0.3 μm or more and an integrated volume with respect to the total pore volume of 20% in the pore distribution;
A negative electrode having a negative electrode active material;
An ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions;
It is equipped with.

The lithium secondary battery of the present invention can further improve output characteristics and cycle durability. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, in the positive electrode, the carbon structure used as the conductive material is important, and the pores resulting from this carbon structure are considered to be 0.3 μm or more. In an electrode having a relatively large pore volume of 20% or more over this pore diameter, that is, an electrode in which this carbon structure has been developed, the density of the positive electrode mixture layer is relatively high at 2.0 mg / cm ³ or more. Assuming that the output performance is particularly effective, the output performance is particularly effective at low temperatures such as -30 ° C, and the endurance performance, especially the cycle durability at high temperatures such as 60 ° C where differences are likely to occur. The

The schematic diagram which shows an example of the lithium secondary battery 10 of this invention. The measurement result of the pore distribution by the mercury intrusion method of Experimental Example 1. The measurement result of the pore distribution by the mercury intrusion method of Experimental Example 2. The measurement result of the pore distribution by the mercury intrusion method of Experimental Example 11. The measurement result of the pore distribution by the mercury intrusion method of Experimental Example 12. The measurement result of the pore distribution by the mercury intrusion method of Experimental Example 13.

  The lithium secondary battery of the present invention includes a positive electrode in which a positive electrode mixture layer containing a positive electrode active material containing a lithium-containing oxide and a carbon material is formed on a positive electrode current collector, a negative electrode having a negative electrode active material, And an ion conducting medium that conducts lithium ions and is interposed between the positive electrode and the negative electrode.

In the positive electrode of the lithium secondary battery of the present invention, a positive electrode mixture layer having a density of 2.0 g / cm ³ or more is formed. When the density of the positive electrode mixture layer is 2.0 g / cm ³ or more, more preferably, the density is 2.1 g / cm ³ or more, the density is relatively high and the battery capacity can be increased. The density of the positive electrode mixture layer is preferably 2.4 g / cm ³ or less in consideration of the contact property with the ion conductive medium.

  The positive electrode of the lithium secondary battery of the present invention has a positive electrode mixture layer having a pore diameter of 0.3 μm or more with an integrated volume with respect to the total pore volume of 20% in a pore distribution measured by a mercury intrusion method. When the pore diameter at which the integrated volume with respect to the total pore volume is 20% is 0.3 μm or more, the output characteristics at a low temperature such as 0 ° C. or lower, particularly at a low temperature of −30 ° C. or lower can be further enhanced. The positive electrode mixture layer preferably has a pore diameter of 0.50 μm or more, more preferably 0.60 μm or more, with an integrated volume of 20% with respect to the total pore volume. That is, it is preferable to have a relatively large pore diameter because lithium ions easily move at a low temperature. The mercury intrusion method is a measurement method that utilizes the large contact angle of mercury, and is a measurement principle that determines the pore diameter by balancing the force that pushes mercury into the pores and the surface tension of mercury that works within the pore diameter. is there. For this reason, in the mercury intrusion method, the size of the entrance of the pore is measured and can be used as an index of the ease of movement of the electrolyte and lithium ions. It can be said that this is a more preferable evaluation method of pores compared to the pore distribution measurement result.

  The positive electrode of the lithium secondary battery of the present invention preferably has a volume of pore diameters of 0.5 μm or more and 10 μm or less in the pore distribution measured by the mercury intrusion method, of 10% or more with respect to the total pore volume, 30% The above is more preferable and 40% or more is still more preferable. When the volume of the pore diameter of 0.5 μm or more and 10 μm or less is 10% or more with respect to the total pore volume, for example, the cycle durability can be further improved at a high temperature of 40 ° C. or higher, particularly at a high temperature of 60 ° C. or higher. . Moreover, it is preferable to have a positive electrode mixture layer having a maximum frequency pore diameter in the range of 0.25 μm to 10 μm. The maximum frequency pore diameter is more preferably from 0.50 μm to 10 μm, and even more preferably from 0.55 μm to 0.65 μm. Particularly, in the pore distribution measured by mercury porosimetry, the volume of the pore diameter of 0.5 μm or more and 10 μm or less is 40% or more with respect to the total pore volume, and the maximum frequency in the range of 0.5 μm or more and 10 μm or less. If there is a hole diameter, the low temperature characteristics can be further improved and the high temperature durability can be further improved.

The positive electrode of the lithium secondary battery of the present invention may have a pore volume measured by a mercury intrusion method of the positive electrode mixture layer of 150 mm ³ / g or less, or may be 150 mm ³ / g or more. Good. Even if the pore volume is 150 mm ³ / g or more, the above-mentioned pore diameter distribution characteristics can further improve the cycle durability at a high temperature as well as the output performance at a low temperature.

The positive electrode of the lithium secondary battery of the present invention is obtained by mixing a positive electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like positive electrode mixture layer. And may be formed by compression to increase the electrode density as necessary. Examples of the positive electrode active material include lithium-containing oxides. For example, an oxide containing lithium and a transition metal element can be used. Specifically, Li _(1-x) MnO ₂ (0 <x <1, etc., the same shall apply hereinafter), lithium manganese composite oxides such as Li _(1-x) Mn ₂ O ₄ , Li _(1-x) CoO lithium cobalt composite oxides such as _2, Li _(1-x) lithium nickel composite oxide such as NiO _2, a lithium vanadium composite oxide such as LiV ₂ O _3, and transition metal oxides such as V ₂ O ₅ is preferably . The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, Carbon materials such as ketjen black, carbon whisker, needle coke, and carbon fiber are preferred. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. The drying temperature can be appropriately set according to the type of the solvent. For example, the drying temperature can be set at 50 ° C. or higher, preferably 100 ° C. or higher and 200 ° C. or lower, more preferably 150 ° C. or higher and 180 ° C. or lower. preferable. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and formed fiber group. The thickness of the current collector is, for example, 1 to 500 μm.

  The positive electrode of the lithium secondary battery of the present invention is prepared by preparing a carbon material-containing paste in which a conductive material and a binder are kneaded, and then kneading the carbon material-containing paste and the positive electrode active material to obtain a positive electrode mixture paste. It is preferable to prepare and apply this positive electrode mixture paste to a positive electrode current collector. The kneading time of the carbon material-containing paste is preferably 0 minutes or more and 200 minutes or less, and more preferably 100 minutes or more and 180 minutes or less. At this time, the kneading time of the positive electrode mixture paste is preferably 100 minutes or more and 300 minutes or less, and more preferably 120 minutes or more and 240 minutes or less. If produced in this way, the pore range of the positive electrode mixture layer can be made more suitable.

  The negative electrode of the lithium secondary battery of the present invention may use an inorganic compound such as lithium, a lithium alloy, or a tin compound as the negative electrode active material. Further, the negative electrode of the lithium secondary battery of the present invention is obtained by mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode mixture layer. It may be applied to the surface of the substrate and dried, and may be compressed to increase the electrode density as necessary. Examples of the negative electrode active material include carbonaceous materials capable of inserting and extracting lithium ions, conductive polymers, and composite oxides containing Ti. Of these, carbonaceous materials are preferable from the viewpoint of safety. The carbonaceous material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as an electrolyte salt. In addition, it is preferable because the irreversible capacity during charging can be reduced. In addition, as the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.

  As the ion conduction medium of the lithium secondary battery of the present invention, a non-aqueous electrolyte solution containing a supporting salt, an ionic liquid, a non-aqueous gel electrolyte solution, or the like can be used. Examples of the solvent for the nonaqueous electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t -Chain carbonates such as butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; Examples include furans such as lan, methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. Further, the ionic liquid is not particularly limited, but 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide, 1-ethyl-3-butylimidazolium tetrafluoroborate, or the like is used. Can do.

The supporting salt contained in the lithium secondary battery of the present invention is, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Examples include LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. This electrolyte salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the electrolyte salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

  The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin fine olefin resin such as polyethylene or polypropylene is used. A porous membrane is mentioned. These may be used alone or in combination.

The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 1 is a schematic diagram showing an example of a lithium secondary battery 10 of the present invention. In the lithium secondary battery 10, a positive electrode sheet 13 in which a positive electrode mixture layer 12 including a positive electrode active material is formed on a current collector 11 and a negative electrode mixture layer 17 including a negative electrode active material are formed on the surface of the current collector 14. The negative electrode sheet 18, the separator 19 provided between the positive electrode sheet 13 and the negative electrode sheet 18, and the nonaqueous electrolyte solution 20 that fills between the positive electrode sheet 13 and the negative electrode sheet 18 are provided. In this lithium secondary battery 10, the separator 19 is sandwiched between the positive electrode sheet 13 and the negative electrode sheet 18, and these are wound and inserted into the cylindrical case 22, and the positive electrode terminal 24 connected to the positive electrode sheet 13 and the negative electrode sheet are connected. A connected negative electrode terminal 26 is provided. This positive electrode mixture layer 12 contains a positive electrode active material containing a lithium-containing oxide and a carbon material, has a density of 2.0 g / cm ³ or more, and has a fine pore distribution measured by a mercury intrusion method. The pore diameter at which the integrated volume with respect to the pore volume is 20% is 0.3 μm or more. Further, the positive electrode mixture layer 12 has a pore size measured by mercury porosimetry of which pore volume of 0.5 μm or more and 10 μm or less is 40% or more of the total pore volume, and 0.5 μm or more and 10 μm. There is a maximum frequency pore size in the following range.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Below, the example which produced the lithium secondary battery of this invention concretely is demonstrated as an experiment example.

[Experimental Example 1]
4 parts by mass of carbon black (TB5500 manufactured by Tokai Carbon Co., Ltd.) as a conductive material, 4 parts by mass of polyvinylidene fluoride (KF polymer manufactured by Kureha Chemical Industry Co., Ltd.) as a binder, and as a dispersant An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and kneaded for 180 minutes to prepare a carbon black-containing paste. Next, 90 parts by mass of lithium nickelate (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) as a positive electrode active material was added and kneaded for 60 minutes to prepare a positive electrode mixture paste. This positive electrode mixture was uniformly applied on both surfaces of an aluminum foil current collector having a thickness of 20 μm and dried at 180 ° C. Thereafter, the density was increased by a roll press to produce a sheet-like positive electrode. This positive electrode is composed of a positive electrode current collector and a positive electrode mixture layer formed on the surface thereof. The sheet-like positive electrode thus produced was cut into a size of width 54 mm × length 450 mm, and used as a positive electrode for the nonaqueous electrolyte lithium secondary battery of Experimental Example 1. Next, artificial graphite is used as the negative electrode active material, 95 parts by mass of the negative electrode active material and 5 parts by mass of polyvinylidene fluoride as the binder are mixed, and an appropriate amount of NMP as a dispersant is added and dispersed. A slurry-like negative electrode mixture was prepared. Next, this negative electrode mixture was uniformly applied to both sides of a 10 μm thick copper foil current collector and dried. Then, it densified with the roll press and produced the sheet-like negative electrode. This negative electrode consists of a negative electrode current collector and a negative electrode mixture layer formed on the surface thereof. The sheet-like negative electrode thus produced was cut into a size of width 56 mm × length 500 mm, and used as the negative electrode for the nonaqueous electrolyte lithium secondary battery of Experimental Example 1. As the electrolytic solution, a solution (manufactured by Kishida Pharmaceutical Co., Ltd.) in which 1M LiPF ₆ was dissolved in a non-aqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 was used. The produced positive electrode sheet and negative electrode sheet were wound in a roll shape through a polyethylene separator having a thickness of 25 μm and a width of 58 mm, and inserted into a 18650 type cylindrical case. At this time, the positive electrode current collecting lead was connected by welding to the positive electrode current collecting tab arranged on the cap side of the battery case, and the negative electrode current collecting lead was connected by welding to the negative electrode current collecting tab arranged at the bottom of the battery case. After injecting the electrolyte into the battery case, the top cap was caulked and sealed to produce a cylindrical lithium secondary battery. In this way, the battery of Experimental Example 1 was obtained. The density of the positive electrode mixture of Experimental Example 1 was 2.1 mg / cm ³ . Table 1 summarizes the mixture ratio, the kneading time of the carbon black-containing paste, the positive electrode mixture kneading time, and the density of the positive electrode mixture layer in Experimental Example 1. In Table 1, the contents of Experimental Examples 2 to 13 are also described.

[Experimental Examples 2 and 3]
A battery obtained through the same steps as in Experimental Example 1 except that the mixing ratio of the positive electrode active material, the conductive material, and the binder was 90: 6: 4 by mass ratio in the production of the positive electrode was designated as Experimental Example 2. did. Moreover, it obtained through the process similar to Experimental example 1 except the compounding ratio of a positive electrode active material, a electrically conductive material, and a binder being 90: 8: 4 by mass ratio, and setting the density to 2.0 mg / cm < ³ >. This battery was designated as Experimental Example 3.

[Experimental Examples 4 to 6]
A battery obtained through the same steps as in Experimental Example 1 except that the kneading time of the carbon black-containing paste was set to 0 minutes when producing the positive electrode was determined as Experimental Example 4. Moreover, it obtained through the process similar to Experimental example 4 except the compounding ratio of a positive electrode active material, a electrically conductive material, and a binder being 90: 6: 4 by mass ratio, and setting the density to 2.0 mg / cm < ³ >. This battery was designated as experimental example 5. In addition, a battery obtained through the same process as Experimental Example 4 was used as Experimental Example 6 except that the mixing ratio of the positive electrode active material, the conductive material, and the binder was 90: 8: 4 by mass ratio.

[Experimental Examples 7 to 10]
In producing the positive electrode, the mixing ratio of the positive electrode active material, the conductive material and the binder was 90: 5: 5 by mass ratio, the kneading time of the carbon black-containing paste was 240 minutes, and the kneading time of the positive electrode mixture was 300. A battery obtained through the same steps as in Experimental Example 1 except for minutes was used as Experimental Example 7. In addition, a battery obtained through the same process as Experimental Example 7 except that the carbon black-containing paste kneading time was 300 minutes and the positive electrode composite kneading time was 360 minutes was designated as Experimental Example 8. Further, a battery obtained through the same process as Experimental Example 7 except that the roll press pressure was changed and the density was 1.9 mg / cm ³ was determined as Experimental Example 9. Further, a battery obtained through the same process as Experimental Example 8 except that the roll press pressure was changed and the density was 1.8 mg / cm ³ was determined as Experimental Example 10.

[Experimental Examples 11 to 13]
Batteries obtained through the same steps as in Experimental Example 1 except that the drying temperature of the positive electrode was set to 50 ° C., 100 ° C., and 150 ° C. were used as Experimental Examples 11 to 13, respectively.

(Measurement of pore size distribution and pore volume of positive electrode mixture)
The pore size distribution and pore volume of the positive electrode mixture were measured using a mercury intruder (Poremaster manufactured by Sysmex Corporation). As the sample, a roll-pressed electrode divided into strips was used. FIG. 2 is a measurement result of pore distribution by the mercury intrusion method of Experimental Example 1, and FIG. 3 is a measurement result of pore distribution by the mercury intrusion method of Experimental Example 2. 4 is a measurement result of pore distribution by the mercury intrusion method of Experimental Example 11, FIG. 5 is a measurement result of pore distribution by the mercury intrusion method of Experimental Example 12, and FIG. 6 is an experimental example. 13 is a measurement result of pore distribution by a mercury intrusion method.

(Low temperature power test)
Using the obtained batteries of Experimental Examples 1 to 13, a low temperature power test was performed. First, the battery was discharged, set to a state of SOC (State Of Charge) 50%, and kept in an environment of −30 ° C. Subsequently, the current of 0.5A, 1A, 2A, 3A, and 5A was passed, the battery voltage after 10 seconds was measured, and the power was determined.

(Charge / discharge test)
Using the obtained batteries of Experimental Examples 1 to 13, the battery capacity at 20 ° C. was measured. Each battery is set to 20 ° C., and is charged to a charging upper limit voltage of 4.1 V at a constant current of a current density of 0.5 mA / cm ² , and then a discharge lower limit voltage of 3 at a constant current of a current density of 0.2 mA / cm ² . One cycle of charging / discharging to discharge to 0 V was performed to determine the discharge capacity.

(Charge / discharge cycle test at high temperature (full charge / discharge))
Using the obtained batteries of Experimental Examples 1 to 13, a charge / discharge cycle test was performed under a temperature condition of 60 ° C. In the charge / discharge cycle test, charging is performed up to a charge upper limit voltage of 4.1 V at a current value of 2 hours rate of battery capacity, and then discharged to a discharge lower limit voltage of 3.0 V at a current value of battery capacity of 2 hours. 1 cycle, and a total of 500 cycles were performed. Then, the discharge capacity is measured for each cycle, and the capacity retention rate at high temperature (high temperature characteristics) Q _H500 (%) is calculated using the formula (discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100. Calculated.

(Experimental result)
Table 2 shows the composition of positive electrode sheets, density (mg / cm ³ ), pore diameter (μm) at an integrated volume of 20% with respect to the total pore volume, and pore diameters of 0.5 μm to 10 μm in Experimental Examples 1 to 13. The volume ratio (%) occupied by the pore volume, pore volume (cm ³ / g), maximum frequency pore diameter (μm), −30 ° C. output characteristics, and high temperature characteristics were exhibited. As shown in Table 2, in Experimental Examples 1 to 6, compared to the batteries of Experimental Examples 7 to 10, the output characteristics and the high temperature characteristics are excellent, and in a wide temperature range from a low temperature to a high temperature, It turns out that the balance is excellent. Further, in Experimental Examples 1 and 2, in which the volume ratio of the pore volume of the pore diameter of 0.5 μm to 10 μm is 40% or more and the maximum frequency pore diameter is in the range of 0.5 μm to 10 μm, It was revealed that the output characteristics and the high temperature characteristics were excellent at −30 ° C. Thus, the density of the positive electrode material layer is relatively dense and 2.0 mg / cm ³ or more, a pore volume in the range of the following pore size 3μm or 0.1μm is 90mm ³ / g~200mm ³ / g Thus, it has been clarified that when the pore diameter at an integrated volume of 20% with respect to the total pore volume is 0.3 μm or more, the output characteristics at -30 ° C. and the high temperature characteristics can be further improved. Moreover, it turned out that the drying temperature has the preferable range of 150 to 180 degreeC.

  DESCRIPTION OF SYMBOLS 10 Lithium secondary battery, 11 Current collector, 12 Positive electrode mixture layer, 13 Positive electrode sheet, 14 Current collector, 17 Negative electrode mixture layer, 18 Negative electrode sheet, 19 Separator, 20 Nonaqueous electrolyte, 22 Cylindrical case, 24 Positive terminal, 26 Negative terminal.

Claims (3)

A positive electrode mixture layer containing a positive electrode active material containing a lithium-containing oxide and a carbon material is formed on the positive electrode current collector, and has a density of 2.0 g / cm ³ or more and is measured by a mercury intrusion method. A positive electrode having the positive electrode mixture layer having a pore diameter of 0.3 μm or more and an integrated volume with respect to the total pore volume of 20% in the pore distribution;
A negative electrode having a negative electrode active material;
An ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions;
Rechargeable lithium battery.   The positive electrode has a pore diameter measured by a mercury intrusion method and a volume of a pore diameter of 0.5 μm or more and 10 μm or less is 40% or more with respect to the total pore volume, and is maximum in a range of 0.5 μm or more and 10 μm or less. The lithium secondary battery according to claim 1, comprising the positive electrode mixture layer having a frequency pore diameter.   The lithium secondary battery according to claim 1, wherein the positive electrode contains carbon black as the carbon material.

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