JP2012028177A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery simultaneously achieving excellent output characteristics (in particular, low temperature output characteristics) and excellent durability even without an external unit.SOLUTION: The lithium ion secondary battery provided by the present invention includes a positive electrode, a negative electrode and a nonaqueous electrolyte. The positive electrode contains a lithium-containing olivine type compound as a main constituent of a positive electrode active material. The positive electrode further contains 2-20 parts by mass of active carbon relative to 100 parts by mass of the positive electrode active material. The active carbon has an average grain size in a range of from 0.1 to 1 μm and a specific surface measured by a nitrogen absorption method in a range of from 0.1 to 1,000 m/g.

Description

  The present invention relates to a lithium ion secondary battery excellent in output characteristics and durability.

  A lithium ion secondary battery includes positive and negative electrodes capable of reversibly occluding and releasing lithium ions, and an electrolyte interposed between the two electrodes, and the lithium ions in the electrolyte travel between the electrodes. To charge and discharge. Because it is lightweight and has high energy density, it is widely used as a power source for various portable devices. In addition, it is expected to be used in fields that require a large-capacity power source such as a hybrid vehicle and an electric vehicle, and further performance improvement is required. Patent documents 1-4 are mentioned as technical literature about a lithium ion secondary battery.

JP 2003-323984 A JP 2001-110418 A JP 2008-112595 A JP 2002-260634 A International Publication No. 2010/44447

In general lithium ion secondary batteries, the output density tends to decrease in a low SOC (State of Charge) region (low charge state), and the decrease in the output density in the low SOC region can be more remarkable particularly at low temperatures. . A low power density in the low SOC region means that the battery capacity (effective SOC region) that can be used at a power density equal to or higher than a predetermined value is much smaller than the theoretical capacity. Therefore, it is useful to have a lithium ion secondary battery having good output characteristics even at a low temperature (for example, about −10 ° C.).
As means for improving output characteristics, it is common to connect a battery in parallel with a capacitor device. However, such means tends to complicate the battery configuration and system. Further, when the output characteristics are improved without using such an external device, another problem of lowering durability may newly occur. Patent Document 5 is cited as a technical document related to capacitors and the like.

  An object of the present invention is to provide a lithium ion secondary battery that can realize excellent output characteristics (particularly, low temperature output characteristics) and good durability at the same time without being connected to an external device.

  The present inventor has paid attention to the fact that the battery output can be improved by including a predetermined material in the positive electrode active material layer, and has studied a means for avoiding durability deterioration that may occur due to the use of such a material. And it discovered that the improvement of output characteristics and the improvement of durability could be realized simultaneously by using the material which has a predetermined shape, and completed the present invention.

According to the present invention, a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The positive electrode contains a lithium-containing olivine type compound as a main component of the positive electrode active material. The positive electrode further includes 2 to 20 parts by mass of activated carbon with respect to 100 parts by mass of the positive electrode active material. The activated carbon has an average particle size in the range of 0.1 μm to 1 μm. The activated carbon further has a specific surface area measured by a nitrogen adsorption method in the range of 0.1 to 1000 m ² / g. In addition, in this specification, an average particle diameter refers to the volume average diameter calculated | required by the particle size distribution measurement according to the laser diffraction and scattering method. The nitrogen adsorption method refers to a specific surface area measurement method generally referred to as a BET method.

  Since such a battery contains an olivine type compound as a positive electrode active material, a stable voltage can be realized in a wider SOC range. Moreover, since the predetermined amount of activated carbon is included, the temperature dependency of input / output can be reduced, and the output characteristics at least at low temperatures can be improved. Furthermore, since the average particle diameter and specific surface area of the activated carbon are within the predetermined ranges, the battery is excellent in durability against charge / discharge cycles at a relatively high rate (for example, about 2C) in a low temperature environment. Can be. In addition, 1C points out the electric current amount which can charge the battery capacity (Ah) estimated from the theoretical capacity | capacitance of the positive electrode in 1 hour.

In one aspect, the activated carbon preferably has the following property (A).
(A) The pore diameter of the activated carbon is X (nm), the pore volume as a function of X is Y (cm ³ ), and the differential value of Y with respect to X per unit mass is ΔY / ΔX (cm ³ / g · In the pore distribution in which ΔY / ΔX is plotted against X, the maximum value M1 of ΔY / ΔX in the range of 10 nm to 100 nm and the maximum value of ΔY / ΔX in the range of X from 2 nm to 10 nm The ratio value (M1 / M2) to M2 is 1.5 or more and 10 or less. In a lithium ion secondary battery using activated carbon having a value of M1 / M2 in such a range, excellent output characteristics and good durability can be realized at the same time even at low temperatures. In addition, the said pore means here the pore which exists in the activated carbon particle surface.

  As described above, the lithium ion secondary battery disclosed herein is excellent as an output characteristic even in a low temperature environment, and more excellent in durability against charge / discharge at a high rate. Therefore, according to the present invention, as yet another aspect, a vehicle 1 (FIG. 3) provided with the lithium ion secondary battery disclosed herein is provided. In particular, a mode in which such a lithium ion secondary battery is used as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) in the vehicle is preferable.

1 is a perspective view schematically showing one embodiment of a lithium ion secondary battery according to the present invention. It is the II-II sectional view taken on the line in FIG. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery of this invention. It is the figure which plotted SOC50% output ratio and the capacity maintenance rate after a cycle test with respect to the specific surface area about the battery of Examples 1-5. It is the figure which plotted SOC50% output ratio and the capacity maintenance rate after a cycle test with respect to the specific surface area about the batteries of Examples 6-10. It is the figure which plotted SOC50% output ratio and the capacity maintenance rate after a cycle test with respect to M1 / M2 about the batteries of Examples 1-10.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The positive electrode disclosed here contains, as a main positive electrode active material, a lithium-containing compound that can reversibly store and release lithium and has an olivine crystal structure as a main component. For example, use of an olivine type compound represented by the general formula: LiM ¹ PO ₄ ; is preferable. Here, M ¹ is at least one selected from the group consisting of Fe, Co, Mn, and Ni. Examples of the olivine type compound include LiFePO ₄ , LiFe _x Mn _1-x PO ₄ , LiMnPO ₄ , LiFe _x Co _1-x PO _{4, and the} like. A particularly preferred example is LiFePO ₄ . These olivine type compounds can be used singly or in combination of two or more. Here, the main component of the positive electrode active material refers to the positive electrode active material having the largest ratio in the total positive electrode active material. In one aspect, the amount of the olivine-type compound is preferably 50% by mass or more, and more preferably 80% by mass or more of the total positive electrode active material.

In addition to the olivine type compound, the positive electrode active material may further include a lithium-containing compound (also referred to as a non-olivine type compound) having another crystal structure such as a layered rock salt type or a spinel type as an optional component. Examples of the layered rock salt type lithium-containing compound include compounds represented by the general formula: LiM ² O ₂ ; Here, ^{M 2} is at least one selected from the group consisting Co, Ni, from Mn. Specific examples of such layered rock salt type compounds include LiNi _x Mn _1-x O ₂ and LiNi _1-xy Mn _x Co _y O ₂ . Examples of the spinel-type lithium-containing compound include compounds represented by the general formula: LiM ³ ₂ O ₄ ; Here, M ³ is at least one selected from the group consisting of Mn, Co, Ni, Cr, and Fe. Specific examples of such spinel type compounds include LiM ³ _x Mn _2-x O ₂ . Particularly preferable non-olivine type compounds include LiNiO ₂ , LiCoO ₂ , LiMnO ₂ , LiCoNiMnO ₂ , LiNi _0.5 Mn _1.5 O _{4 and the} like. These non-olivine type compounds can be used singly or in combination of two or more. When such a non-olivine type compound is used, the amount used may be appropriately selected within a range where the above-mentioned ΔV _SOC15-95 is 0.5 V or less. For example, the total amount of non-olivine type compounds contained in the positive electrode active material is preferably 50% by mass or less, and more preferably 20% by mass or less. If the amount of the optional component is too large, the effect of improving the low-temperature output characteristics by adding activated carbon may not be sufficiently realized. The positive electrode active material may have a configuration that does not substantially contain these non-olivine type compounds.

The positive electrode further includes activated carbon in addition to the positive electrode active material. The activated carbon has an average particle diameter in the range of 0.1 μm to 1 μm (preferably 0.4 μm to 0.9 μm; for example, 0.4 μm to 0.8 μm), and has a specific surface area measured by a nitrogen adsorption method. In the range of 0.1 to 1000 m ² / g (preferably 100 to 1000 m ² / g). Even activated carbon having such a specific surface area can be obtained with an average particle size of micron level (over 1 μm) and an average particle size of submicron level (about 0.1 μm to 1 μm). In some cases, an excellent output characteristic improvement effect may not be realized. In addition, even if the average particle size is at the micron level or the submicron level, the activated carbon having a specific surface area that is larger than the above range may deteriorate the durability. In other words, activated carbon with an average particle size of micron level tends to decrease durability (for example, capacity retention rate after charge / discharge cycle), although the output characteristics at low temperature improve as the specific surface area increases. is there. On the other hand, in the case of activated carbon having an average particle size of submicron, those having a smaller specific surface area tend to have higher output characteristics improvement effect and better durability. In other words, the reason is not clear, but activated carbon with an average particle diameter of micron level and activated carbon with a submicron level do not change the tendency of the durability to decrease as the specific surface area increases, while the size of the specific surface area is output. The effect on properties tends to reverse.

  In a preferred embodiment, the activated carbon has a characteristic that M1 / M2 obtained from the pore distribution obtained by the following method is 1.5 or more and 10 or less (more preferably, 1.5 or more and 6 or less). . According to the activated carbon in which M1 / M2 falls within such a range, a phenomenon in which durability is lowered at the low temperature against the improvement of output characteristics is suppressed, and these two characteristics can be preferably improved at the same time. If M1 / M2 is too small, the internal resistance increases, and the low-temperature output characteristics may not be sufficiently improved or may deteriorate. If M1 / M2 is too large, a sufficient energy density may not be obtained.

[Pore distribution measurement method]
For each activated carbon sample, the nitrogen gas was adsorbed on the activated carbon at each pressure P while gradually increasing the pressure P (mmHg) of the nitrogen gas in a nitrogen gas atmosphere at a temperature of 77.4K (the boiling point of nitrogen). The nitrogen gas adsorption amount (cm ³ / g) when the equilibrium state is reached is measured. The nitrogen gas adsorption amount measured at each pressure P is plotted as an adsorption isotherm with respect to the relative pressure P / P ₀ (P ₀ is the saturated vapor pressure (mmHg) of nitrogen gas at a temperature of 77.4K). From this adsorption isotherm, the pore distribution (plot of ΔY / ΔX (cm ³ / g · nm) against pore diameter X (nm)) is determined according to the BJH (Barrett-Joyner-Halenda) method. The BJH method is described in, for example, “J. Am. Chem. Soc. (1951), 73, 373-380”.

The activated carbon may have a crystal lattice spacing d ₀₀₂ measured by an X-ray diffraction method of about 0.365 nm to 0.380 nm.

  The activated carbon is prepared by, for example, carbonizing and activating raw materials such as resin, coconut shell, coal, coke, and pitch, and performing treatment such as pulverization (for example, wet centrifugal pulverization) and sieving as necessary. Can do. Carbonization and activation of the raw material can be performed by a conventionally known method. Carbonization and activation may be performed simultaneously or stepwise. The amount of activated carbon contained in the positive electrode is 2 to 20 parts by mass (preferably 5 to 15 parts by mass) with respect to 100 parts by mass of the positive electrode active material. If the amount of activated carbon added is too small, a sufficient output improvement effect may not be realized. If the amount of activated carbon is too large, the durability may decrease or the energy density may decrease.

In a preferred embodiment, the lithium ion secondary battery disclosed herein is a battery for evaluation of correspondence having a configuration in which the activated carbon is removed from the positive electrode (that is, the lithium ion secondary battery according to the present invention except that the activated carbon is not included). The lithium ion secondary battery having the same configuration is charged with a constant current at a temperature of 25 ° C. at a rate of 0.5 C until the voltage between both terminals becomes 4.1 V (SOC at this time). Next, with the same voltage (4.1V), the current value is 0.02C or less as an end condition (typically, until the charging current gradually decreases to reach 0.02C). After charging at a constant voltage, a constant current is discharged at a rate of 0.5 C until the voltage between both terminals reaches 2.5 V, and then the current value of 0.02 C or less is set as an end condition at the same voltage (2.5 V) ( Typically, the discharge current In the case of progressively until it reaches the 0.02C smaller) to a constant voltage discharge, it is below the voltage fluctuation width ΔV _SOC15-95 0.5V in the range SOC15~95%; preferably satisfies the property that. That is, the lithium ion secondary battery disclosed herein preferably has a configuration in which activated carbon is added to the positive electrode of the evaluation battery having such characteristics. In the lithium ion secondary battery having such a configuration, the effect of improving the low-temperature output characteristics by adding an appropriate amount of activated carbon can be suitably realized. The voltage fluctuation range ΔV _SOC15-95 is obtained as the difference between the upper limit value and the lower limit value of the battery voltage in the SOC range of 15 to 95%.

  When the lithium ion secondary battery disclosed herein is configured to include 10 parts by mass of the activated carbon with respect to 100 parts by mass of the positive electrode active material, the SOC 50% output ratio obtained by the following method is 1.15 or more. (For example, 1.20 or more).

[SOC 50% output ratio measurement method]
Each power value (for example, 0.1 W, 0,...) Obtained by varying the evaluation battery adjusted so that the initial SOC is 50% within a predetermined range (for example, 0.1 W to 190 W) at a temperature of −10 ° C. 3W, 1W, 5W, ..., 190W, etc.). At this time, at each power value, the discharge time (seconds) until the voltage between both terminals reaches 2.5 V is measured. The power value (Y axis) is plotted against the charging time (X axis), and the power value when the discharging time is 5 seconds is read. This is converted into an output density D _{out [0]} (input amount per unit mass) (W / kg) at 50% SOC, and this converted value is used as an output reference value.
For the measurement target battery (corresponding lithium ion secondary battery containing 10 parts by mass of activated carbon per 100 parts by mass of the positive electrode active material), the output density D _{out [10]} at 50% SOC is measured in the same procedure, and the above output is referred. The ratio (Dout _[10] / Dout _[0] ) to the value is obtained as the SOC 50% output ratio. For example, if the SOC 50% output ratio of the measurement target battery is 1.15 or more, the SOC 50% output of the measurement target battery is 15% or more higher than the SOC 50% output of the corresponding evaluation battery (that is, by adding activated carbon). This means that the output is improved by 15% or more).

  Hereinafter, with reference to the drawings, for a lithium ion secondary battery to which the technology disclosed herein is applied, a lithium ion secondary battery in which an electrode body and a non-aqueous electrolyte are housed in a rectangular battery case The battery 100 (FIG. 1) will be described in more detail as an example, but the application target of the present invention is not intended to be limited to such an embodiment. That is, the shape of the lithium ion secondary battery according to the present invention is not particularly limited, and the battery case, electrode body, and the like can be appropriately selected in terms of material, shape, size, and the like according to the application and capacity. For example, the battery case may have a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  As shown in FIGS. 1 and 2, the battery 100 according to this embodiment includes a wound electrode body 20 and a flat box-shaped battery case 10 corresponding to the shape of the electrode body 20 together with an electrolyte (not shown). It can be constructed by being housed inside the opening 12 and closing the opening 12 of the case 10 with a lid 14. The lid body 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection so that a part of the terminals protrudes to the surface side of the lid body 14.

  The electrode body 20 includes a positive electrode sheet 30 in which a positive electrode active material layer 34 is formed on the surface of a long sheet-like positive electrode current collector 32, and a negative electrode active material layer on the surface of a long sheet-like negative electrode current collector 42. The negative electrode sheet 40 on which the electrode 44 is formed is rolled up with two long sheet-like separators 50, and the obtained wound body is crushed from the side surface and ablated to form a flat shape. ing. The separator 50 is impregnated with a nonaqueous electrolytic solution in advance. Thereby, an ion conduction path (conduction path) between the electrodes is formed.

  The positive electrode current collector 32 is exposed at one end portion along the longitudinal direction of the positive electrode sheet 30. That is, the positive electrode active material layer 34 is not formed at the end, or is removed after the formation. Similarly, the negative electrode current collector 42 is exposed at one end portion along the longitudinal direction of the wound negative electrode sheet 40. Then, the positive electrode terminal 38 is joined to the exposed end portion of the positive electrode current collector 32, and the negative electrode terminal 48 is joined to the exposed end portion of the negative electrode current collector 42, respectively. The positive electrode sheet 30 or the negative electrode sheet 40 is electrically connected. The positive and negative terminals 38 and 48 and the positive and negative current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The positive electrode active material layer 34 is, for example, a paste or slurry composition (positive electrode mixture) in which the positive electrode active material is dispersed in a suitable solvent together with a conductive material, a binder (binder) or the like as necessary. Is preferably applied to the positive electrode current collector 32 and the composition is dried.

  As the conductive material, a conductive material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. A conductive material can be used alone or in combination of two or more. What is necessary is just to select the quantity of the electrically conductive material contained in the said positive electrode active material layer suitably according to the kind and quantity of a positive electrode active material.

As the binder, for example, a water-soluble polymer that dissolves in water, a polymer that disperses in water, a polymer that dissolves in a non-aqueous solvent (organic solvent), and the like can be appropriately selected and used. Moreover, only 1 type may be used independently and 2 or more types may be used in combination.
Examples of the water-soluble polymer include carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), and polyvinyl alcohol (PVA). It is done.
Examples of the water-dispersible polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetra. Fluorine resin such as fluoroethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), rubbers such as gum arabic, etc. It is done.
Examples of the polymer dissolved in the non-aqueous solvent (organic solvent) include, for example, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer. (PEO-PPO) and the like.
What is necessary is just to select the addition amount of a binder suitably according to the kind and quantity of a positive electrode active material.

  For the positive electrode current collector 32, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. . In the present embodiment, a sheet-like aluminum positive electrode current collector 32 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In such an embodiment, for example, an aluminum sheet having a thickness of about 10 μm to 30 μm can be preferably used.

  The negative electrode active material layer 44 includes, for example, a negative electrode current collector 42 made of a paste or slurry composition (negative electrode mixture) in which a negative electrode active material is dispersed in an appropriate solvent together with a binder (binder) and the like. And the composition can be preferably prepared by drying.

As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. For example, a carbon particle is mentioned as a suitable negative electrode active material. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles such as natural graphite can be preferably used. Since the graphite particles can suitably occlude lithium ions as charge carriers, they are excellent in conductivity. Moreover, since the particle size is small and the surface area per unit volume is large, it can be a negative electrode active material more suitable for rapid charge / discharge (for example, high output discharge).
The amount of the negative electrode active material contained in the negative electrode active material layer is not particularly limited, and is preferably about 90 to 99% by mass, more preferably about 95 to 99% by mass.

  As the binder, the same positive electrode as that described above can be used alone or in combination of two or more. What is necessary is just to select the addition amount of a binder suitably according to the kind and quantity of a negative electrode active material.

  As the negative electrode current collector 42, a conductive member made of a metal having good conductivity is preferably used. For example, copper or an alloy containing copper as a main component can be used. In addition, the shape of the negative electrode current collector 42 may vary depending on the shape of the lithium ion secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. possible. In the present embodiment, a sheet-like copper negative electrode current collector 42 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In this embodiment, for example, a copper sheet having a thickness of about 5 μm to 30 μm can be preferably used.

Moreover, as the separator 50 used by overlapping with the positive electrode sheet 30 and the negative electrode sheet 40, various separators used for a general lithium ion secondary battery can be used without any particular limitation. For example, a porous film made of a polyolefin resin such as polyethylene and polypropylene can be suitably used. The film may be a single layer or a multilayer. A resin film provided with an inorganic filler layer containing one or more ceramic particles such as titania (titanium oxide; TiO ₂ ), alumina, silica, magnesia, zirconia, zinc oxide, iron oxide, ceria, and yttria. May be used. The thickness of the separator may be selected as appropriate.

The nonaqueous electrolytic solution impregnated in the separator 50 can be prepared by dissolving an appropriate electrolyte in a nonaqueous solvent. As the electrolyte, an electrolyte used for a general lithium ion secondary battery can be used without particular limitation. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI, etc. are selected. One or more lithium salts can be used. The concentration of the electrolyte in the electrolytic solution is not particularly limited, and can be, for example, equivalent to the concentration of the electrolytic solution used in a conventional lithium ion secondary battery. Moreover, you may add various additives etc. to the said electrolyte solution in addition to the said electrolyte.

  In addition, as the organic solvent (nonaqueous solvent) used in the nonaqueous electrolytic solution, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane , Tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone (BL), etc. The organic solvents generally used for lithium ion secondary batteries can be used alone or in combination of two or more.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

  The following measurements were performed for activated carbon AJ used in Examples 1-10. The results are shown in Table 1.

[Average particle size measurement]
The average particle diameter (volume average diameter) of the activated carbons A to J uses pure water as a dispersion medium, and has a refractive index of 2.00-0.20i, using a laser diffraction particle size distribution device “SALD-3000”. It was measured.

[Specific surface area measurement]
The specific surface areas of the activated carbons A to J were measured using NOVA-3000 manufactured by Quantachrome in accordance with the nitrogen adsorption method.

[M1 / M2 measurement]
About activated carbon AJ, according to the pore distribution measuring method mentioned above, with the apparatus used for the said specific surface area measurement, pore distribution was obtained and M1 / M2 was calculated | required.

[Measurement of _d002 ]
For the activated carbons A to J, the crystal lattice spacing of the 002 plane was determined using an X-ray diffractometer (manufactured by Rigaku Corporation, model “RINT-2000”).

<Example 1>
Kneaded 35.0 g of carbon black, 35.0 g of PVDF (700 g of 5% NMP solution) and 70 g of activated carbon A, added 700 g of LiFePO ₄ and kneaded, added 400 g of NMP, kneaded overnight, and pasted positive electrode mixture Was prepared. This positive electrode mixture was applied to one surface of an aluminum foil having a thickness of 15 μm so that the amount applied was 12.5 g / cm ² , dried, and then pressed with a 3 t roll press to obtain a positive electrode sheet. Obtained. Incidentally, LiFePO _4, the carbon black, was used by 10 hours by vacuum drying at 120 ° C..
600 g of artificial graphite and 30.0 g of PVDF (600 g of 5% NMP solution) were kneaded, and further kneaded while adding NMP little by little. This was degassed under vacuum to prepare a paste-like negative electrode mixture. This negative electrode mixture was applied to each surface of a copper foil having a thickness of 10 μm so that the amount applied was 5.0 g / cm ² , dried and then pressed with a 3t roll press to obtain a negative electrode sheet. It was.
One negative electrode sheet (7 cm × 5 cm) is sandwiched between two separators (polypropylene porous membrane) impregnated with 1.0 M LiPF ₆ solution (EC: EMC = 3: 7 (volume ratio)), and The positive electrode sheet (6 cm × 4 cm) was sandwiched between two sheets. A laminate type battery was produced using this.

<Example 2>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon B was used instead of activated carbon A.

<Example 3>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon C was used instead of activated carbon A.
<Example 4>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon D was used instead of activated carbon A.
<Example 5>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon E was used instead of activated carbon A.
<Example 6>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon F was used instead of activated carbon A.

<Example 7>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon G was used instead of activated carbon A.
<Example 8>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon H was used instead of activated carbon A.
<Example 9>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon I was used instead of activated carbon A.
<Example 10>
A laminated battery of this example was produced in the same manner as in Example 1 except that activated carbon J was used instead of activated carbon A.
<Example 11>
A laminated battery of this example (a battery for evaluation of the battery of Examples 1 to 10) was prepared in the same manner as in Example 1 except that the activated carbon A was not used.

[Aging process]
Each battery is charged at a constant current (CC) up to 4.1 V at a rate of 0.33 C at a temperature of 25 ° C. (required time is about 3 hours), and then charged at the same voltage (4.1 V). Went. At that time, a current value of 0.02 C or less was set as a constant voltage charging termination condition. Subsequently, constant current discharge was performed at a rate of 0.33 C until the voltage became 2.5 V (required time: about 3 hours), and then constant voltage discharge was performed at the same voltage (2.5 V). At that time, a current value of 0.02 C or less was set as a constant voltage discharge termination condition. Charging and discharging under the above conditions were performed for 3 cycles.

[Measurement of voltage fluctuation range ΔV _SOC15-95 ]
The battery of Example 11 (the battery for evaluation of the battery of Examples 1 to 10) was charged at a temperature of 25 ° C. at a rate of 0.5 C until the voltage between both terminals reached 4.1 V, and then at the same voltage. After charging with a current value of 0.02 C or less as an end condition, the battery is discharged at a rate of 0.5 C until the voltage becomes 2.5 V, and subsequently discharged at the same voltage with a current value of 0.02 C or less as an end condition. The voltage change with respect to the SOC level at this time was monitored. From the difference between the maximum voltage and the minimum voltage in the SOC range of 15 to 95%, the ΔV _SOC15-95 of the battery of Example 11 was 0.15V.

[Measurement of SOC 50% output ratio]
For the evaluation battery (the battery of Example 11), the output reference value P _{out [0]} (W / kg) was determined from the power density at 5 ° C. for 5 seconds according to the SOC 50% output ratio measurement method described above.
Using each battery of Examples 1 to 10 as a measurement target, the output density P _{out [10]} (W / kg) at 50% SOC is measured in the same procedure, and the ratio (P _{out [10]} / Pout _[0] ) was determined as the SOC 50% output ratio.

[Charge / discharge cycle test]
After the aging treatment, each battery of Examples 1 to 10 in which the voltage between both terminals was adjusted to 4.1 V was held at −10 ° C. for 1 hour, and then the upper limit voltage was 4.1 V and the lower limit voltage was 2.5 V. The operation of discharging at a rate of 2C for 0.5 hour and the operation of charging at the same rate for 0.5 hour were taken as one cycle, and this was repeated 500 cycles. As the capacity retention rate, the ratio of the discharge capacity after 500 cycles to the initial discharge capacity was determined.

  For the batteries of Examples 1 to 10, the results of the evaluation tests are shown in Table 1 together with the properties of the activated carbon. Also, with respect to the SOC 50% output ratio and the capacity retention rate after the cycle test, plots with respect to the specific surface area are shown in FIGS. 4 (Examples 1 to 5) and FIG. 5 (Examples 6 to 10), and plots with respect to M1 / M2 are shown. It is shown in FIG.

As is clear from Table 1 and FIG. 5, the batteries of Examples 6 to 10 using activated carbon F to J having an average particle diameter of micron level are compared with the evaluation battery of Example 11 as the specific surface area increases. It was recognized that even when the SOC 50% output was improved, the capacity retention rate (durability) generally tended to decrease.
On the other hand, as shown in Table 1 and FIG. 4, in the batteries of Examples 1 to 5 using the activated carbons A to E having an average particle size of submicron level, the output characteristics observed in the batteries of Examples 6 to 10 In the batteries of Examples 1 to 3 having a specific surface area of 1000 m ² / g or less, the SOC 50% output is remarkably improved as compared with the evaluation battery of Example 11, and the capacity is maintained. The rate was also found to be high. As shown in FIG. 6, when the SOC 50% output ratio and the capacity retention ratio were plotted against M1 / M2, the same difference was observed for these two groups.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Vehicle (Automobile)
20 wound electrode body 30 positive electrode sheet (positive electrode)
32 Positive electrode current collector 35 Positive electrode mixture layer 40 Negative electrode sheet (negative electrode)
42 Anode current collector 45 Anode mixture layer 50 Separator 100 Lithium ion secondary battery

Claims (3)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode includes a lithium-containing olivine type compound as a main component of the positive electrode active material,
The positive electrode further includes 2 to 20 parts by mass of activated carbon with respect to 100 parts by mass of the positive electrode active material,
The activated carbon is a lithium ion secondary battery having an average particle size in a range of 0.1 μm to 1 μm and a specific surface area measured by a nitrogen adsorption method in a range of 0.1 to 1000 m ² / g. The activated carbon has the following characteristics:
The pore diameter is X (nm), the pore volume as a function of X is Y (cm ³ ), the differential value of Y with respect to X per unit mass is ΔY / ΔX (cm ³ / g · nm), and ΔY / ΔX is plotted against X, the ratio value (M1) of the maximum value M1 of ΔY / ΔX in the range of X from 10 nm to 100 nm to the maximum value M2 of ΔY / ΔX in the range of X from 2 nm to 10 nm / M2) is 1.5 or more and 10 or less;
The lithium ion secondary battery according to claim 1, comprising:   A vehicle comprising the lithium ion secondary battery according to claim 1.

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