JP2005116321A - Lithium secondary battery and its low-temperature characteristic evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery superior in charge and discharge cycle characteristics (low temperature characteristics ) at the time of low temperature operation. <P>SOLUTION: This the lithium secondary battery comprises as a constituent a positive electrode material containing a lithium transition metal compound oxide as a positive electrode active material, a negative electrode material containing a carbonaceous material as a negative electrode active material, and a non-aqueous electrolytic solution in which a lithium ion electrolyte is dissolved in an organic solvent. Ohmic resistance (Ro (Ω)) at -25°C, charge transfer resistivity (Ra<SB>1</SB>(Ω)) at -25°C, and charge transfer resistivity (Ra<SB>2</SB>(Ω)) at 25°C satisfy at least either of following relationship; Ra<SB>1</SB>/Ro ≤ 40, Ra<SB>1</SB>/Ra<SB>2</SB>≤ 250. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a lithium secondary battery and a method for evaluating low temperature characteristics thereof, and more specifically, a lithium secondary battery having excellent charge / discharge cycle characteristics (hereinafter referred to as “low temperature characteristics” or “low temperature pulse cycle characteristics”) during low temperature operation. The present invention relates to a battery and a method for evaluating low temperature characteristics thereof.

In recent years, portable electronic devices such as mobile phones, VTRs, and notebook personal computers have been increasingly reduced in size and weight. As power batteries, lithium composite oxide is used for the positive electrode active material and carbon is used for the negative electrode active material. Secondary batteries using an organic electrolyte obtained by dissolving a lithium ion electrolyte in an organic solvent as an electrolyte material have been used.

Such a battery is generally referred to as a lithium secondary battery or a lithium ion battery, and has a high energy density and a high single battery voltage of about 4V. In addition to the recent environmental problems, electric vehicles (hereinafter referred to as “EV”) or hybrid electric vehicles (hereinafter referred to as “HEV”) that are actively spreading to the general public as low-pollution vehicles. It is also attracting attention as a motor drive power source.

A lithium secondary battery having a relatively large capacity that is suitably used for EVs, HEVs, etc., has a current collecting tab (positive current collecting tab 5, negative current collecting) as shown in FIG. A wound internal electrode body in which the electrode plates (the positive electrode plate 2 and the negative electrode plate 3) on which the tabs 6) are disposed are wound around the outer periphery of the winding core 13 with the separator 4 interposed therebetween so as not to contact each other. 1 is preferably employed. The positive electrode plate 2 and the negative electrode plate 3 are obtained by forming an electrode active material (positive electrode active material, negative electrode active material) layer on both surfaces of each of a positive electrode metal foil body and a negative electrode metal foil body which are current collecting substrates. The current collecting tab 5 and the negative electrode current collecting tab 6 are formed by using means such as ultrasonic welding during the operation of winding the positive electrode plate 2, the negative electrode plate 3, and the separator 4 around the outer periphery of the winding core 13. The positive electrode metal foil body and the negative electrode metal foil body at the end portion of the plate 3 can be bonded to each other at a predetermined interval.

Moreover, as another form of the internal electrode body, a laminated internal electrode body 7 as shown in FIG. 2 can be exemplified. The laminated internal electrode body 7 has a structure in which positive electrode plates 8 and negative electrode plates 9 having a predetermined area are alternately laminated with a separator 10 interposed therebetween, and at least one electrode plate is provided for each electrode plate. Current collecting tabs (positive electrode collecting tab 11 and negative electrode collecting tab 12) are attached. In addition, the material which comprises the positive electrode plate 8, the negative electrode plate 9, and the separator 10, and these preparation methods are the same as that of the wound type internal electrode body 1 shown in FIG.

Batteries for EVs and HEVs have excellent safety, high energy density, large capacity, and other characteristics, as well as, for example, when mounted on a cold region vehicle. Is required to exhibit sufficient performance even under low-temperature conditions and have excellent low-temperature pulse cycle characteristics, and as a related prior art, the crystal orientation is random and Disclosed are a non-aqueous electrolyte secondary battery having a negative electrode made of graphite powder having a predetermined specific surface area, a negative electrode for a non-aqueous secondary battery having a specific void structure, and a non-aqueous secondary battery using the same. (For example, see Patent Documents 1 to 3).

However, the lithium secondary battery disclosed in Patent Document 1 cannot be said to have sufficient low-temperature pulse cycle characteristics. For this reason, it is necessary to further improve the battery that is planned to be mounted on a vehicle particularly for a cold region, and development of a lithium secondary battery having excellent low-temperature characteristics is expected.

In addition, the low temperature characteristics of the lithium secondary battery could not be judged unless the test (low temperature pulse cycle test) in which charging / discharging was repeated many times under low temperature conditions was performed. Therefore, it is difficult to judge whether the low temperature characteristics of the lithium secondary battery immediately after fabrication are good or not, and the low temperature characteristics of the battery are good without actually repeating charging and discharging many times under low temperature conditions. There was a problem of not being able to know whether or not.
JP 7-226204 A JP-A-6-231766 JP-A-6-295744

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a lithium secondary battery excellent in charge / discharge cycle characteristics (low temperature characteristics) during low temperature operation, and actually Another object of the present invention is to provide a method for evaluating the low temperature characteristics of a lithium secondary battery, which can determine and evaluate the quality of the low temperature characteristics in advance with high accuracy without repeating charging and discharging many times under low temperature conditions.

That is, according to the present invention, a positive electrode material containing a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material containing a carbonaceous material as a negative electrode active material, and a non-aqueous solution obtained by dissolving a lithium ion electrolyte in an organic solvent. A lithium secondary battery comprising an electrolytic solution as a constituent element, an ohmic resistance (Ro (Ω)) at −25 ° C., a charge transfer resistance (Ra ₁ (Ω)) at −25 ° C., and 25 ° C. The lithium secondary battery in which the charge transfer resistance (Ra ₂ (Ω)) in at least one of the following formulas (1) and (2) is satisfied.
Ra ₁ / Ro ≦ 40 (1)
Ra ₁ / Ra ₂ ≦ 250 (2)

In the present invention, the crystal structure of the lithium transition metal composite oxide is preferably a spinel structure.

In the present invention, the lithium transition metal oxide has the general formula _{Li X M a Mn Ya O Z} ( provided that in the general formula, M is a substituted element Mn, a represents the substitution amount, 0 <X, 0 <Y , 0 <Z, 0 ≦ a <Y), and the substitution element M is Li, Fe, Ni, Mg, Zn, Co, Cr, Al, B, Si, Sn, One or more elements selected from the group consisting of P, V, Sb, Nb, Ta, Mo, and W, and Ti are preferable.

In the present invention, the carbonaceous material is preferably an amorphous carbonaceous material or a highly graphitized carbonaceous material.

The lithium secondary battery of the present invention is suitably used for a large battery having a battery capacity of 2 Ah or more, and is suitably used as a power source for starting an engine of an electric vehicle or a hybrid electric vehicle in which a large current is frequently discharged. Used.

Further, according to the present invention, a non-aqueous solution obtained by dissolving a positive electrode material containing a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material containing a carbonaceous material as a negative electrode active material, and a lithium ion electrolyte in an organic solvent. A method for evaluating the quality of a low-temperature characteristic of a lithium secondary battery comprising an electrolytic solution as a constituent element, which is an ohmic resistance (Ro (Ω)) at −25 ° C. and a charge transfer resistance (Ra) at −25 ° C. ₁ (Ω)) and a charge transfer resistance (Ra ₂ (Ω)) at 25 ° C. satisfy at least one of the following formulas (1) and (2): Is provided with a method for evaluating low temperature characteristics of a lithium secondary battery that is judged to have good low temperature characteristics.
Ra ₁ / Ro ≦ 40 (1)
Ra ₁ / Ra ₂ ≦ 250 (2)

The lithium secondary battery of the present invention, the ohmic resistance at -25 ° C. and (Ro (Ω)), charge transfer resistance at _{-25 ℃ (Ra 1 (Ω)} ) and the charge transfer resistance at 25 ℃ (Ra ₂ (Ω )) Satisfies the predetermined relationship, it is excellent in low-temperature pulse cycle characteristics, and is suitable as an in-vehicle battery for cold regions, for example.

Moreover, according to the low temperature characteristic evaluation method of the lithium secondary battery of the present invention, the ohmic resistance (Ro (Ω)) at −25 ° C., the charge transfer resistance (Ra ₁ (Ω)) at −25 ° C., and 25 ° C. When the charge transfer resistance (Ra ₂ (Ω)) in the battery satisfies a predetermined relationship, it is determined that the lithium secondary battery has good low-temperature characteristics. However, the quality of the low temperature characteristics can be determined and evaluated in advance with high accuracy.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and may be appropriately selected based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that design changes, improvements, etc. may be made.

The present invention (first invention) comprises a positive electrode material containing a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material containing a carbonaceous material as a negative electrode active material, and a lithium ion electrolyte dissolved in an organic solvent. A lithium secondary battery comprising a non-aqueous electrolyte as a constituent element, an ohmic resistance (Ro (Ω)) at −25 ° C., a charge transfer resistance (Ra ₁ (Ω)) at −25 ° C., and 25 The charge transfer resistance (Ra ₂ (Ω)) at 0 ° C. satisfies at least one of the relationships of the following formulas (1) and (2). In addition, the present invention (second invention) includes a positive electrode material including a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material including a carbonaceous material as a negative electrode active material, and a lithium ion electrolyte dissolved in an organic solvent. Is a method for evaluating the low-temperature characteristics of a lithium secondary battery comprising a non-aqueous electrolyte as a constituent element, and has an ohmic resistance (Ro (Ω)) at −25 ° C. and charge transfer at −25 ° C. When the resistance (Ra ₁ (Ω)) and the charge transfer resistance (Ra ₂ (Ω)) at 20 to 25 ° C. satisfy at least one of the following formulas (1) and (2): This is a method for evaluating the low temperature characteristics of a lithium secondary battery that is judged to have good low temperature characteristics. The details will be described below.
Ra ₁ / Ro ≦ 40 (1)
Ra ₁ / Ra ₂ ≦ 250 (2)

The lithium secondary battery of the first invention has three kinds of parameters unique to the lithium secondary battery, that is, ohmic resistance (Ro (Ω)) under a predetermined low temperature condition, and charge transfer resistance (Ra ₁ (Ω)). ), And so-called room temperature conditions, the charge transfer resistance (Ra ₂ (Ω)) satisfies a predetermined relationship. The lithium secondary battery of the first invention satisfying such a relationship is excellent in charge / discharge cycle characteristics (low temperature characteristics) during low temperature operation, and specifically, by repeated charge / discharge under low temperature conditions. However, the capacity of the battery is difficult to decrease (capacity maintenance rate is high). Therefore, the lithium secondary battery of the first invention has characteristics suitable as a vehicle-mounted battery for cold regions, for example.

In the low temperature characteristic evaluation method of the second invention, a lithium secondary battery satisfying a predetermined relationship among three kinds of parameters (Ro (Ω), Ra ₁ (Ω), and Ra ₂ (Ω)) has a good low temperature. It is determined that it has characteristics. That is, there is a correlation between the predetermined relationship that these three parameters satisfy and the quality of the low-temperature characteristics of the lithium secondary battery, so that charging and discharging are not actually repeated many times under low-temperature conditions. However, it is possible to determine and evaluate in advance with high accuracy whether or not the battery has a high capacity retention rate because the capacity is not easily reduced by repeated charging and discharging under low temperature conditions.

Here, the ohmic resistance and the charge transfer resistance referred to in the present invention refer to resistances that can be derived by the following procedures (1) to (4).

(1) Charge to 80 to 100% of the maximum charge of the battery to be measured. (2) The AC impedance is measured by changing the frequency from 1 mHz to 10 kHz in an environment of room temperature (25 ° C.) and −25 ° C. The alternating current at this time is fixed to 1/4 to 1/5 of the maximum capacity. (3) Display the measured AC impedance data on the complex plane. Specifically, a complex plane display diagram (call-call plot) as shown in FIG. 4 is created. (4) Let Ro shown in FIG. 4 be ohmic resistance (Ω) at −25 ° C., and Ra ₁ and Ra _{2 be} charge transfer resistance (Ω) at −25 ° C. and 25 ° C., respectively. In FIG. 4, ω is an angular frequency, ω _max is an angular frequency at the apex of the semicircle, and Zw is a diffusion resistance.

Here, in the present invention (first invention), when the value of “Ra ₁ / Ro” in the formula (1) exceeds 40 and / or the value of “Ra ₁ / Ra ₂ ” exceeds 250, the battery This is not preferable because the low temperature characteristics of the resin deteriorate. In the present invention (first invention), Ro, Ra ₁ , and Ra ₂ are all in the relations of the above formulas (1) and (2) from the viewpoint of exhibiting more excellent low temperature characteristics. It is preferable to satisfy. Similarly, in the present invention (first invention), the value of “Ra ₁ / Ro” is 35 or less and “Ra ₁ / Ra ₂ ” is 200 from the viewpoint of exhibiting more excellent low temperature characteristics. The following is preferable.

In the present invention (first invention), the lower limit values of “Ra ₁ / Ro” and “Ra ₁ / Ra ₂ ” are not particularly limited, but the value of “Ra ₁ / Ro” is not limited. The value of “Ra ₁ / Ra ₂ ” is preferably 20 or more and 100 or more.

In the present invention (second invention), if the value of “Ra ₁ / Ro” in the formula (1) exceeds 40 and / or the value of “Ra ₁ / Ra ₂ ” exceeds 250, This is not preferable because the low temperature characteristics are deteriorated. In the present invention (second invention), Ro, Ra ₁ , and Ra ₂ are represented by the formula (1), from the viewpoint of determining and evaluating a lithium secondary battery that exhibits superior low-temperature characteristics. When satisfying both of the relationships of (2), it is preferable to determine that they have good low-temperature characteristics. Similarly, in the present invention (second invention), from the viewpoint of judging and evaluating a lithium secondary battery that exhibits more excellent low temperature characteristics, the value of “Ra ₁ / Ro” is 35 or less, When “Ra ₁ / Ra ₂ ” is 200 or less, it is preferable to determine that it has good low-temperature characteristics.

In the present invention (second invention), the lower limit values of “Ra ₁ / Ro” and “Ra ₁ / Ra ₂ ” are not particularly limited, but the value of “Ra ₁ / Ro” is not limited. The value of “Ra ₁ / Ra ₂ ” may be 20 or more and 100 or more.

Next, the structure of the lithium secondary battery of the present invention, the main members constituting the lithium secondary battery, and the method for manufacturing the lithium secondary battery will be described. FIG. 1 is a perspective view showing an example of a wound electrode body. The positive electrode plate 2 that is a positive electrode material is manufactured by applying and arranging a positive electrode active material on both surfaces of a positive electrode metal foil that is a current collecting substrate. As the positive electrode metal foil body, a metal foil having good corrosion resistance against the positive electrode electrochemical reaction such as an aluminum foil or a titanium foil is used, but punching metal or mesh (net) can be used in addition to the foil. In addition, a lithium transition metal composite oxide is used as the positive electrode active material. Specifically, lithium manganate (LiMn ₂ O ₄ ), lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and the like are preferably used. Can be used. In addition, it is preferable to add carbon fine powders, such as acetylene black, to these positive electrode active materials as a conductive support agent. In the present invention, when a lithium manganate having a cubic spinel structure mainly composed of lithium (Li) and manganese (Mn) (hereinafter simply referred to as “lithium manganate”) is used, This is preferable because the resistance of the internal electrode body can be reduced as compared with the case where a substance is used.

Lithium manganate is not limited to a stoichiometric composition (stoichiometric composition), and a general formula Li _X Ma Mn _Ya O _{Z in which a} part of manganese (Mn) is substituted with one or more other elements. (However, in the general formula, M is a substitution element of Mn, a represents a substitution amount, and 0 <X, 0 <Y, 0 <Z, and 0 ≦ a <Y) Used for. Thus, when a part of manganese (Mn) is substituted with another element, the Li / Mn ratio exceeds 0.5.

The substitution element M is listed below with element symbols, but Li, Fe, Ni, Mg, Zn, Co, Cr, Al, B, Si, Sn, P, V, Sb, Nb, Ta, Mo, and One or more elements selected from the group consisting of W and Ti are preferable from the viewpoint of providing a lithium secondary battery having more excellent low-temperature characteristics, and the substitution element M is more preferably Ni and Ti. . Theoretically, Li is +1 valent, Fe, Mn, Ni, Mg, Zn is +2 valent, B, Al, Co, Cr are +3 valent, Si, Ti, Sn are +4 valent, P, V, Sb, Nb, Ta Is an element which is +5 valent, Mo and W are +6 valent ions and are dissolved in LiMn ₂ O ₄ . However, Co and Sn may be +2 valence, Fe, Sb and Ti may be +3 valence, Mn may be +3 valence and +4 valence, Cr may be +4 and +6 valence.

Therefore, various substitution elements M may exist in a state having a mixed valence, and the amount of oxygen does not necessarily need to be 4 as represented by the stoichiometric composition. It may be missing or excessive in the range for maintaining the structure.

An appropriate amount of the positive electrode active material with respect to a mixture of oxides and / or salts of each element (Li, Mn, and, if necessary, the substitution element M) whose mass ratio is adjusted to a predetermined element ratio Water, and a raw material slurry obtained by dispersing, mixing, and pulverizing the whole while adding water and, if necessary, a binder, and after drying the raw material slurry, an oxidizing atmosphere, 600 to 1000 ° C. It can obtain as a single phase product by baking for 5 to 50 hours in the range. A drying method for drying the raw material slurry is not particularly limited, and a general drying method may be adopted. However, drying the raw material slurry by a spray drying method using a spray dryer instantaneously powders the raw material slurry. The size of the secondary particles (the positive electrode active material is usually composed of secondary particles in which a number of primary submicron particles are bonded) can be adjusted. It is preferable because granulation can be facilitated, raw material mixing can be made uniform, and the particle size of the resulting positive electrode active material can be controlled to some extent.

The oxidizing atmosphere at the time of firing mentioned above refers to an atmosphere having an oxygen partial pressure at which the sample in the furnace causes an oxidation reaction. When the firing temperature is less than 600 ° C., a peak indicating residual material is observed on the XRD chart of the fired product, for example, when lithium carbonate is used as the Li source, a peak indicating lithium carbonate is observed, and a single-phase product is obtained. It may not be possible. On the other hand, if the firing temperature is higher than 1000 ° C., a high-temperature phase product may be produced in addition to the target crystalline compound, and a single-phase product may not be obtained. Therefore, in order to avoid such a case, the firing temperature is preferably 650 to 900 ° C.

Moreover, you may add a vanadium (V) compound and / or a boron (B) compound as an additive to the oxide and / or salt mixture of each element which comprises a positive electrode active material. When these additives are added, the crystallite size of the obtained positive electrode active material (lithium transition metal composite oxide) becomes large, and a transition metal element (for example, Mn) is difficult to elute in the non-aqueous electrolyte. As a result, the capacity reduction of the positive electrode active material itself can be suppressed, and the low-temperature pulse cycle characteristics of the battery can be improved. The additive is preferably added so that vanadium (V) and / or boron (B) is 1 mol% or less with respect to the transition metal element (for example, Mn) constituting the lithium transition metal composite oxide, It is more preferable to add so that it may become 0.5 mol% or less. Examples of the vanadium (V) compound include vanadium pentoxide (V ₂ O ₅ ), and examples of the boron (B) compound include diboron trioxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), and the like. Can be mentioned respectively.

The positive electrode active material is applied by applying a slurry or paste prepared by adding a solvent or a binder to the positive electrode active material powder to the positive electrode metal foil body by a roll coater method or the like and drying it. Do. Then, you may give a press process etc. as needed.

Moreover, the negative electrode plate 3 which is a negative electrode material which comprises the winding type internal electrode body 1 shown in FIG. 1 can be produced similarly to the positive electrode plate 2. As a negative electrode metal foil body which is a current collecting substrate of the negative electrode plate 3, a metal foil having good corrosion resistance against negative electrode electrochemical reaction such as copper foil or nickel foil is preferably used. As the negative electrode active material, amorphous carbonaceous materials such as soft carbon and hard carbon, highly graphitized carbonaceous materials such as artificial graphite and natural graphite, and powders of other carbonaceous materials are used. At this time, it is more preferable that these carbonaceous materials have a specific surface area of 5 m ² / g or more because the current area easily increases.

The separator 4 is preferably a three-layer structure in which a lithium ion permeable polyethylene film (PE film) having micropores is sandwiched between porous lithium ion permeable polypropylene films (PP film). . This also serves as a safety mechanism that suppresses the migration of lithium ions, that is, the battery reaction, when the temperature of the internal electrode body rises, the PE film softens at about 130 ° C. and the micropores collapse. And by sandwiching the PE film with a PP film having a higher softening temperature, even when the PE film is softened, the PP film retains its shape and prevents contact between the positive electrode plate 2 and the negative electrode plate 3 and a short circuit. Thus, it is possible to reliably suppress the battery reaction and ensure safety.

During the winding operation of the positive electrode plate 2, the negative electrode plate 3, and the separator 4, a current collecting tab (positive electrode current collector) is exposed at a portion of the positive electrode plate 2 and the negative electrode plate 3 where the metal foil body not coated with the electrode active material is exposed. The electric tab 5 and the negative electrode current collecting tab 6) are respectively attached. As the positive electrode current collecting tab 5 and the negative electrode current collecting tab 6, foil-like ones made of the same material as the metal foil body constituting each electrode plate are preferably used. The current collector tab can be attached (joined) to each electrode plate by ultrasonic welding, spot welding, or the like.

Next, the non-aqueous electrolyte used for the lithium secondary battery of the present invention will be described. Examples of the solvent include carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and propylene carbonate (PC), and single solvents or mixed solvents such as γ-butyrolactone, tetrahydrofuran, and acetonitrile. Preferably used. In the present invention, a mixed solvent of a cyclic carbonate and a chain carbonate can be suitably used, particularly from the viewpoint of the electric conductivity of the electrolytic solution and the high temperature stability.

Examples of lithium ion electrolytes include lithium complex fluorine compounds such as lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiBF ₄ ), and lithium halides such as lithium perchlorate (LiClO ₄ ). One or more of these are used by dissolving in the organic solvent (mixed solvent) described above. In particular, in the present invention, it is preferable to use LiPF _6, which does not easily undergo oxidative decomposition and has high conductivity of a non-aqueous electrolyte.

Next, a method for assembling the lithium secondary battery will be described based on a cross-sectional view showing an embodiment of the lithium secondary battery of the present invention shown in FIG. In assembling the lithium secondary battery 30 shown in FIG. 3, first, electrical connection between the positive external terminal 15A and the positive current collecting tab 5 and the negative external terminal 15B and the negative current collecting tab 6 for taking out current to the outside is ensured. Meanwhile, the produced wound internal electrode body 1 is inserted into the battery case 20, and one side of the battery case 20 is interposed between the battery lid (the positive battery lid 16 </ b> A and the negative battery lid 16 </ b> B) and the battery case 20 via the packing 18. Seal the end of the. Next, after being held in a stable position, the lithium secondary battery 30 can be assembled by impregnating the non-aqueous electrolyte and sealing the other end of the battery case 20. In FIG. 3, reference numeral 19 denotes a constricted portion.

As described above, the lithium secondary battery according to the present invention has been described with reference to the embodiment mainly using the wound electrode body as an example, but the present invention is limited to the above embodiment. Needless to say, the laminated internal electrode body 7 shown in FIG. 2 may be used. In addition, the lithium secondary battery according to the present invention is preferably used particularly for a large battery having a battery capacity of 2 Ah or more, but does not prevent application to a battery having such a capacity or less. In addition, the lithium secondary battery of the present invention takes advantage of the features of high capacity, low cost, high reliability, and long-term storage, and is used as a battery for vehicles such as EV and HEV, and further, such as EV / HEV. It is preferable as a power source for driving a motor, and can also be particularly suitably used for starting an engine that requires a high output.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Examples 1-3, 6, 7, Comparative Example 1)
A raw material slurry was prepared by mixing oxides or salts of each element so as to have the composition shown in Table 1, and this raw material slurry was spray dried for Example 3 and hot air except for Example 3. Each was dried to obtain a dry powder. The obtained dry powder was fired at the firing temperature shown in Table 1 to obtain a positive electrode active material (lithium transition metal composite oxide). A positive electrode slurry prepared by adding 4% by mass of acetylene black as an external additive to the obtained positive electrode active material and further adding a solvent and a binder was added to both sides of an aluminum foil having a thickness of about 100 μm. A positive electrode plate was prepared by coating to a thickness.

On the other hand, a negative electrode slurry prepared using graphite as a negative electrode active material was applied to both sides of a copper foil having a thickness of 10 μm so as to have a thickness of about 80 μm, thereby preparing a negative electrode plate. The produced positive electrode plate and negative electrode plate were wound through a separator (PP / PE / PP (three layers)) to produce a wound internal electrode body 1 having a configuration as shown in FIG. On the other hand, various organic solvents such as EC, DMC, and DEC are mixed at a volume ratio of 1: 1: 1 to prepare a mixed solvent, which is a lithium ion electrolyte so as to have a concentration of 1 mol / l. LiPF ₆ was dissolved to prepare a non-aqueous electrolyte.

A battery case containing the wound internal electrode body was filled with a non-aqueous electrolyte, and the battery case was sealed to produce lithium secondary batteries (Examples 1 to 3, 6, 7 and Comparative Example 1). All the production was performed by a dry process, and the influence of moisture intrusion from the outside of the battery due to the sealing failure of the battery case was eliminated. Moreover, the battery capacity after the first charge of each battery was about 8 Ah.

(Examples 4, 5, 8, 9)
When the positive electrode active material (lithium transition metal composite oxide) is obtained by firing, the above-described examples are obtained except that the additives shown in Table 1 are added in predetermined addition amounts to the oxides or salts of the respective elements. 1 to 3, 6, 7, and lithium secondary batteries were produced in the same manner as in Comparative Example 1 (Examples 4, 5, 8, and 9). All the raw slurry was dried with hot air. In Table 1, “type” and “B” of “additive” mean boron trioxide (B ₂ O ₃ ), and “V” means vanadium pentoxide (V ₂ O ₅ ). means.

(Measurement of AC impedance)
1. Charge transfer resistance: After charging up to 80 to 100% of the maximum charge of the battery to be measured, change the frequency from 1 mHz to 10 kHz in an environment of room temperature (25 ° C.) and −25 ° C., and measure the AC impedance. The alternating current value at this time is fixed to 1/4 to 1/5 C (discharge rate) of the maximum capacity. Next, based on the measured AC impedance data, a complex plane display diagram (Cole-Cole plot) shown in FIG. 4 is created, and Ra ₁ and Ra ₂ in the figure are charges at −25 ° C. and 25 ° C., respectively. It was measured and calculated as moving resistance (Ω). The results are shown in Table 2. Table 2 shows the value of Ra ₁ / Ra ₂ .

2. Ohmic resistance: A complex plane display diagram (Cole-Cole plot) shown in FIG. 4 is created based on AC impedance data measured by a method similar to that described in “1. Charge transfer resistance” described above. The inside Ro was measured and calculated as ohmic resistance (Ω) at −25 ° C. The results are shown in Table 2. In addition, Table 2 shows the value of Ra ₁ / Ro.

(Low-temperature pulse cycle test)
A low temperature pulse cycle test was performed on the above-prepared battery. For one cycle, a battery in a charged state at a discharge depth of 50% under a temperature condition of −25 ° C. was discharged for 3 seconds at a current equivalent to 20 C (discharge rate) for 3 seconds, then rested for 3 seconds, and then charged at 200 A for 3 seconds. The pattern was again set to 50% charge. In addition, in order to investigate the change in the battery capacity, the capacity measurement was performed with a current stop strength of 1 C and a charge stop voltage of 4.1 V and a discharge stop voltage of 2.5 V. The capacity retention rate (%) was calculated by dividing by the capacity value. The results are shown in Table 2.

As shown in Table 2, the lithium secondary batteries of Examples 1 to 9 satisfying the relationship that the value of “Ra ₁ / Ro” is 40 or less and / or the value of “Ra ₁ / Ra ₂ ” is 250 or less, As compared with the lithium secondary battery of Comparative Example 1 that does not satisfy this relationship, it is apparent that the capacity retention rate (%) after the low-temperature pulse cycle test of 20000 cycles under low temperature conditions is high. Therefore, the superiority of the lithium secondary battery of the present invention could be confirmed.

In addition, the lithium secondary battery (Example 3) using the positive electrode active material prepared by firing the dry powder obtained by drying the raw material slurry by the spray drying method is simply dried with hot air. It is apparent that the capacity retention rate is higher than that of the lithium secondary battery (Example 1) using the positive electrode active material prepared by firing the dry powder obtained.

The lithium secondary battery of the present invention has excellent low-temperature pulse cycle characteristics. Therefore, for example, it has characteristics suitable as a vehicle-mounted battery for cold regions. In addition, the method for evaluating the low temperature characteristics of the lithium secondary battery of the present invention can determine and evaluate the quality of the low temperature characteristics in advance with high accuracy without actually repeating charging and discharging many times under low temperature conditions. A suitable vehicle battery or the like can be selected immediately after fabrication.

It is a perspective view which shows an example of a wound type internal electrode body. It is a perspective view which shows an example of a laminated type internal electrode body. It is sectional drawing which shows one Embodiment of the lithium secondary battery of this invention. It is a complex plane display figure (Cole-Cole plot).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Winding type internal electrode body, 2, 8 ... Positive electrode plate, 3, 9 ... Negative electrode plate, 4, 10 ... Separator, 5, 11 ... Positive electrode current collection tab, 6, 12 ... Negative electrode current collection tab, 7 ... Lamination | stacking Type internal electrode body, 13 ... winding core, 15A ... positive electrode external terminal, 15B ... negative electrode external terminal, 16A ... positive electrode battery cover, 16B ... negative electrode battery cover, 18 ... packing, 19 ... constricted part, 20 ... battery case, 30 ... Lithium secondary battery, Ra ₁ , Ra ₂ ... charge transfer resistance, Rs ... solution resistance, Zw ... diffusion resistance, ω ... angular frequency, ω _max ... angular frequency at the apex of the semicircle.

Claims (9)

A positive electrode material including a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material including a carbonaceous material as a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving a lithium ion electrolyte in an organic solvent are included as constituent elements. A lithium secondary battery
The ohmic resistance at -25 ℃ (Ro (Ω)) , charge transfer resistance at -25 ° C. and (Ra ₁ (Omega)), although the charge transfer resistance at _{25 ℃ (Ra 2 (Ω)} ), the following equation (1 ), A lithium secondary battery that satisfies at least one of the relationships (2).
Ra ₁ / Ro ≦ 40 (1)
Ra ₁ / Ra ₂ ≦ 250 (2) The lithium secondary battery according to claim 1, wherein a crystal structure of the lithium transition metal composite oxide is a spinel structure. The lithium transition metal oxide has the general formula _{Li X M a Mn Ya O Z} ( In the general formula, M is a substituted element Mn, a represents the substitution amount, 0 <X, 0 <Y , 0 < Z, 0 ≦ a <Y), and
The substitution element M is selected from the group consisting of Li, Fe, Ni, Mg, Zn, Co, Cr, Al, B, Si, Sn, P, V, Sb, Nb, Ta, Mo, and W The lithium secondary battery according to claim 1, wherein the lithium element is Ti or the above element. The lithium secondary battery according to claim 1, wherein the carbonaceous material is an amorphous carbonaceous material or a highly graphitized carbonaceous material. The lithium secondary battery according to claim 1, wherein the battery capacity is 2 Ah or more. It is a vehicle-mounted battery, The lithium secondary battery as described in any one of Claims 1-5. The lithium secondary battery according to claim 6, which is used for an electric vehicle or a hybrid electric vehicle. The lithium secondary battery according to claim 6 or 7, which is used for starting an engine. A positive electrode material including a lithium transition metal composite oxide as a positive electrode active material, a negative electrode material including a carbonaceous material as a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving a lithium ion electrolyte in an organic solvent are included as constituent elements. A method for evaluating the quality of the low temperature characteristics of a lithium secondary battery comprising:
The ohmic resistance at -25 ℃ (Ro (Ω)) , charge transfer resistance at -25 ° C. and (Ra ₁ (Omega)), although the charge transfer resistance at _{25 ℃ (Ra 2 (Ω)} ), the following equation (1 ), A method for evaluating low-temperature characteristics of a lithium secondary battery that determines that the lithium secondary battery has good low-temperature characteristics when at least one of the relationships of (2) is satisfied.
Ra ₁ / Ro ≦ 40 (1)
Ra ₁ / Ra ₂ ≦ 250 (2)

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