JP3105204B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary battery,
In particular, the present invention relates to a nonaqueous electrolyte secondary battery provided with a positive electrode containing a lithium-containing compound as an active material.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries have attracted attention. This is considered to be largely due to the successful development of a relatively safe anode material and the realization of a high voltage battery by increasing the decomposition voltage of the non-aqueous electrolyte. Among such non-aqueous electrolyte secondary batteries, a secondary battery using lithium ions has a particularly high discharge potential, and thus is expected to realize a battery having a high energy density. The positive electrode of the nonaqueous electrolyte secondary battery using lithium ions is composed of an oxide of a transition metal called an active material, a binder, and a conductive agent for imparting necessary conductivity to the active material in general. I have.

[0003] In this case, the conductive agent is required to have, in addition to high electrical conductivity, oxidation resistance which is not easily oxidized by contact with the active material, and furthermore, the active material is effectively electrically connected to each other. A structure for contacting, for example, a fibrous structure is required. In addition to the above conditions, in consideration of lighter weight and cost, conventionally, carbon-based acetylene black or the like has been used as a conductive agent. In fact, in a secondary battery using LiCoO ₂ as a positive electrode active material, relatively satisfactory characteristics are obtained by using the above-described conductive agent.

[0004]

By the way, recently, Co
In view of the increase in material costs and the pursuit of batteries with higher energy density, search for active materials using substances other than Co-based materials and research and development have been promoted. Some of these new active materials have high energy densities, but may not have sufficient thermal stability after charging compared to Co-based active materials, and may have problems such as relatively high oxidizing power. It is becoming clear. For this reason, various attempts have been made to improve the active material itself, as well as to improve the material around the active material such as an electrolytic solution.

As for the conductive agent, it has been pointed out that carbon-based conductive agents which have been used conventionally do not always have sufficient oxidation resistance and may burn or ignite. A decrease in safety is expected.

Therefore, there is a demand for a conductive agent having higher oxidation resistance and higher safety than conventional carbon-based conductive agents.

Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery which realizes high energy density and is excellent in safety.

[0008]

In order to achieve the above object, a nonaqueous electrolyte secondary battery according to the present invention comprises a nonaqueous electrolyte comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a nonaqueous electrolyte. In the liquid secondary battery, the conductive agent contained in the positive electrode may be: (a) ABO ₃ (where A is at least one selected from the group consisting of a divalent typical element, a lanthanoid element, and a combination thereof)
B is a species, wherein B is a group IVa, Va, VIa, VIIa
An oxide having a perovskite structure represented by at least one selected from the group consisting of transition elements of Group III, Group VIII and Group Ib), (b) the following formula: A ₂ BO ₄ (where A is a divalent typical element) , At least one selected from the group consisting of lanthanoid elements or a combination thereof
B is a species, wherein B is a group IVa, Va, VIa, VIIa
An oxide having a K ₂ NiF ₄ type structure represented by at least one selected from transition elements of Group III, Group VIII and Group Ib); and (c) a mixture of the above (a) and (b); A non-aqueous electrolyte secondary battery comprising an oxide selected from the group consisting of: a conductive oxide having free electrons.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to the present invention will be described below based on one embodiment (cylindrical non-aqueous electrolyte secondary battery) shown in FIG.

In the cylindrical nonaqueous electrolyte secondary battery shown in FIG. 1, an insulator 2 is arranged at the bottom of a cylindrical container 1 having a bottom made of, for example, stainless steel. The electrode group 3 is housed in the container 1.

The electrode group 3 has a structure in which a strip formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5 is formed of, for example, a synthetic resin nonwoven fabric, a porous polyethylene film, or a porous porobylene film. The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is disposed at the upper opening of the container 1 and the vicinity of the upper opening is caulked inward to fix the sealing plate 8 to the container 1 in a liquid-tight manner. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6
Is connected to the container 1 serving as a negative electrode terminal via a negative electrode lead (not shown). Next, the configurations of the positive electrode 4, the negative electrode 6, and the non-aqueous electrolyte will be described more specifically. (1) Configuration of Positive Electrode 4 The positive electrode 4 is made of, for example, a lithium-containing cobalt oxide (LiCoO ₂ ), a lithium-containing nickel oxide (LiNiO ₂ ), or a lithium-containing manganese oxide (Li
Mn ₂ O ₄ ) or those obtained by adding or partially substituting another element in the crystal of the active material can be used.

In the present invention, as the conductive agent contained in the positive electrode, a conductive oxide containing a transition metal element and a conductive composite oxide containing both a typical element and a transition metal element can be used.

That is, in the present invention, a preferred conductive agent is (A) the following formula ABO ₃ (where A is at least one selected from the group consisting of a divalent typical element, a lanthanoid element, and a combination thereof)
B is a species, wherein B is a group IVa, Va, VIa, VIIa
An oxide having a perovskite structure represented by at least one selected from the group consisting of transition elements of Group III, Group VIII and Group Ib), (b) the following formula: A ₂ BO ₄ (where A is a divalent typical element) , At least one selected from the group consisting of lanthanoid elements or a combination thereof
B is a species, wherein B is a group IVa, Va, VIa, VIIa
An oxide having a K ₂ NiF ₄ type structure represented by at least one selected from transition elements of Group III, Group VIII and Group Ib); and (c) a mixture of the above (a) and (b); And an oxide selected from the group consisting of conductive oxides having free electrons.

Preferred examples of the conductive oxide include lanthanum nickel composite oxide (LaNiO ₃ ), strontium vanadate (SrVO ₃ ), calcium vanadate (CaVO ₃ ), and strontium ferrate (SrF ₃ ).
eO ₃ ), lanthanum titanate (LaTiO ₃ ), lanthanum strontium nickel composite oxide (LaSrNiO)
₄₎ strontium chromate (SrCrO), calcium chromate (CaCrO _3), calcium ruthenate (CaRuO _3), strontium ruthenate (Sr
RuO ₃ ), strontium iridate (SrIrO)
Conductive composite oxides such as ₃ ) can be preferably used.

Of the above, SrVO ₃ , SrFeO
₃ , SrCrO ₃ , La _1-x Sr _x MnO ₃ (0.15 ≦
x ≦ 0.6), and those selected from the group consisting of LaNiO ₃ , LaSrNiO ₄ and LaCuO ₃ are particularly preferable.

In the present invention, a carbon black conductive agent such as carbon black, acetylene black or Ketjen black may be used in combination with the conductive oxide as the conductive agent.

The positive electrode can be prepared by suspending the active material, the conductive agent and the binder in a suitable solvent, applying the suspension to a current collector, and drying to form a thin plate.

In the present invention, the specific resistance of the conductive agent is not particularly limited to a specific value, but in general, when the specific resistance of the conductive agent is 1 × 10 ⁻³ (Ωm) or more, the positive electrode The insufficient electron conductivity tends to cause an increase in overvoltage and internal stress during charge and discharge, which results in a decrease in discharge voltage and capacity and a decrease in cycle life, which is not desirable. Further, the lower limit of the specific resistance value of the conductive agent is not particularly limited,
In the present invention, a superconducting material (for example, La _1.85 S
r _0.15 CuO ₄ ) also includes a specific resistance value of zero realized at a low temperature.

On the other hand, the reason why the conductive oxide is limited to the compound containing the specific transition metal element as described above is as follows. In other words, oxides of typical elements are essentially semiconductors, and the electrical conductivity is caused by a slight deviation of the ratio of elements from the stoichiometric ratio. In addition to this, when it comes into contact with a strong oxidizing agent such as a positive electrode active material, oxidation proceeds from the surface, and due to this, the conductivity tends to be further reduced.

The binder is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) Etc. can be used.

As the current collector, for example, aluminum foil, stainless steel foil, titanium foil and the like are preferably used. 2) Configuration of Negative Electrode 6 As the negative electrode 6, for example, a substance capable of inserting and extracting lithium ions (for example, a carbonaceous substance or a chalcogen compound)
, And those made of light metal can be used. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that stores and desorbs lithium ions is preferable in terms of improving battery characteristics such as the cycle life of the secondary battery.

Examples of the carbonaceous material for absorbing and desorbing lithium ions include coke, carbon fiber, pyrolytic vapor growth carbon material, graphite, resin fired body, mesoface pitch-based carbon fiber, and mesophase spherical carbon. And the like. Of these, mesoface pitch-based carbon fibers or mesophase spherical carbons graphitized at 2500 ° C. or higher are particularly preferable because of their high electrode capacity.

The above-mentioned carbonaceous material is particularly 70% by differential thermal analysis.
Exothermic peak at a temperature of 0 ° C or higher, more preferably 800 ° C
As described above, the exothermic peak is present, and the intensity ratio P101 / P100 of the (101) diffraction peak (P101) and the (100) diffraction peak (P100) of the graphite structure by X-ray diffraction is in the range of 0.7 to 2.2. Is preferred. Since the negative electrode containing such a carbonaceous substance can rapidly insert and extract lithium ions, the rapid charge and discharge performance of the secondary battery can be significantly improved. Further, the negative electrode containing such a carbonaceous substance is excellent in that the possibility of ignition of the negative electrode during overheating can be significantly reduced.

The chalcogen compounds that occlude and desorb lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbS).
e ₂ ). When such a chalcogen compound is used for the negative electrode, although the voltage of the secondary battery may decrease, the capacity of the negative electrode significantly increases, so that the capacity characteristics of the secondary battery can be improved. Further, since such a negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Preferred examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like. A negative electrode containing a substance that occludes and desorbs lithium ions is produced, for example, by suspending the above-described substance and a binder in a suitable solvent, applying the suspension to a current collector, drying, and then pressing. Can be done.

As the binder in this case, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SB
R), carboxymethyl cellulose (CMC) and the like can be used.

As the current collector of the negative electrode, it is preferable to use, for example, a copper foil, a stainless steel foil, a nickel foil or the like. 3) Configuration of Nonaqueous Electrolyte Solution As the nonaqueous electrolyte solution, a solution in which an electrolyte (lithium salt) is dissolved in a nonaqueous solvent is preferably used.

Specific examples of preferable non-aqueous solvents in this case include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Carbonate (DE
Chain carbonates such as C), dimethoxyethane (DM
E), chain ethers such as diethoxyethane (DEE) and ethoxymethoxyethane, and tetrahydrofuran (TH
F) and 2-methyltetrahydrofuran (2-MeTH
Cyclic ethers such as F), crown ethers, fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), sulfolane (S
L) and sulfur compounds such as dimethylsulfoxide (DMSO). The non-aqueous solvents may be used alone or in combination of two or more. Among them, one composed of at least one selected from EC, PC and γ-BL, and at least one selected from EC, PC and γ-BL and DMC, EMC, DEC, DM
It is particularly desirable to use a mixed solvent comprising at least one selected from E, DEE, THF, 2-MeTHF and AN. Further, when using a negative electrode containing a carbonaceous material that occludes and desorbs lithium ions, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC, γ-BL, EC and PC and EMC, EC and PC and DEC, EC and PC and DEE, E
C and AN, EC and EMC, PC and DMC, PC and DE
It is desirable to use a mixed solvent composed of C, EC and DEC.

Preferred examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium borofluoride (L
iBF4), lithium hexafluoroarsenate (LiAsF _6),
Lithium triple olometasulfonate (LiCF ₃ S
O ₃ ) and lithium salts such as pistrifluoromethylsulfonylimitolithium (LiN (CF ₃ SO ₂ ) ₂ ). Among these, LiPF ₆ , Li
It is preferable to use BF ₄ or LiN (CF ₃ SO ₂ ) ₂ because conductivity and safety are improved. The amount of the electrolyte dissolved in the non-aqueous solvent is 0.1 mol / 1 to 3. It is preferred to be in the range of O mol / 1.

By incorporating a positive electrode containing the above-described conductive oxide as a positive electrode conductive agent into a secondary battery, high safety can be realized even in a secondary battery having a high capacity. Actually, as shown in the results of Examples and Comparative Examples described later, the secondary battery according to the present invention using a conductive oxide as a positive electrode conductive agent has a heat generation property of an electrode in an electrode heating test after charging. Is suppressed,
It has been recognized that a conventional secondary battery electrode using a carbon-based conductive agent generates heat or a combustion reaction at a certain temperature.

[0031]

Embodiments of the present invention will be described below with reference to the results shown in the accompanying drawings and the like. It should be noted that the present invention is not limited to the following embodiments at all, and can be implemented with appropriate changes within a scope that does not change the gist of the present invention.

Example 1 <Preparation of positive electrode> Li _1.075 Ni _0.755 Co as active material
_0.17 O _1.9 F _0.1 powder and conductive agent LaN as conductive agent
iO ₃ powder and Teflon powder as a binder were mixed at a weight ratio of 80: 17: 3 to prepare a positive electrode mixture.

The positive electrode mixture thus obtained was attached to a stainless steel net as a current collector, 10 mm square × 0.1 mm.
A 25 mm positive electrode was produced. <Production of Negative Electrode> A 20 mm square negative electrode was produced by attaching a lithium metal foil to a stainless steel net as a current collector.

<Preparation of Reference Electrode> A 10 mm square negative electrode was prepared by attaching a lithium metal foil to a stainless steel net as a current collector.

<Preparation of Nonaqueous Electrolyte> A nonaqueous electrolyte was prepared by dissolving LiClO ₄ as an electrolyte at a concentration of 1 mol / l in a mixed solvent composed of propylene carbonate and dimethoxyethane.

<Preparation of Electrode for Evaluation of Positive Electrode>
After the negative electrode, the reference electrode, and the nonaqueous electrolyte were sufficiently dried, a beaker-type glass cell-type evaluation battery shown in FIG. 3 was assembled using these members in an argon atmosphere. That is, the non-aqueous electrolyte 22 is provided in the glass cell 21.
Is housed. The positive electrode 23 and the negative electrode 24 housed in the bag-shaped separator are stacked with a separator 25 interposed therebetween, and are immersed in the electrolytic solution 22 in the glass cell 21. The two holding plates 26 sandwich the laminate between them. The reference electrode 27 housed in the bag-shaped separator is connected to the electrolyte solution 22 in the glass cell 21.
Is immersed in. One end of each of the three glass filters 28 projects through the upper surface of the glass cell 21 and the other end is connected to the positive electrode 23, the negative electrode 24, and the reference electrode 27, respectively. Such a glass cell 21 is sealed to prevent air from entering during the charge / discharge test.

Example 2 (Reference Example) The positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode conductive agent was used. Chromium oxide (CrO ₂ ) powder was used as the conductive agent.

Example 3 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the positive electrode conductive agent shown below was used. Strontium vanadate (SrV
O ₃ ) powder was used.

Example 4 A positive electrode evaluation battery as shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode conductive agents were used. The conductive agent was used La _0.5 Sr _0.5 MnO ₃ powder.

Example 5 A positive electrode evaluation battery as shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode conductive agents were used. As a conductive agent, strontium chromate (SrCr)
O ₃ ) powder was used.

Example 6 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode active materials were used. Li _1.075 Ni _0.755 A as positive electrode active material
l _0.17 O _1.9 F _0.1 powder was used.

Example 7 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode active materials were used. Li _1.075 Ni _0.705 Al _0.22 O as positive electrode active material
_1.9 F _0.1 powder was used.

Example 8 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode active materials were used. LaSrNiO ₄ powder was used as a positive electrode active material.

COMPARATIVE EXAMPLE 1 A battery for evaluating a positive electrode as shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode conductive agents were used. Iron oxide (Fe ₃ O ₄ ) powder was used as the conductive agent.

Comparative Example 2 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the positive electrode conductive agent shown below was used. Acetylene black powder was used as the conductive agent.

COMPARATIVE EXAMPLE 3 A positive electrode evaluation battery as shown in FIG. 3 was assembled in the same manner as in Example 1 except that the following positive electrode conductive agents were used. Carbon black powder was used as the conductive agent.

COMPARATIVE EXAMPLE 4 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the positive electrode conductive agent shown below was used. Vapor-grown carbon fiber (VGCF) powder was used as the conductive agent.

COMPARATIVE EXAMPLE 5 The above-described positive electrode evaluation battery shown in FIG. 3 was assembled in the same manner as in Example 1 except that the positive electrode conductive agent shown below was used. Tin oxide (SnO ₂ ) powder was used as the conductive agent.

The obtained Examples 1 to 8 and Comparative Examples 1 to 5
After the battery reached 4.4 V at a current value of 1 mA, the battery was continuously charged with a current value of 0.05 m.
When the voltage drops below A, the current stops. Thereafter, the glass cell is disassembled in an argon atmosphere, the positive electrode is taken out and sufficiently dried, and the thermal stability of the positive electrode is measured as follows. The positive electrode taken out was peeled off from the current collector, and the temperature was increased at a rate of 2 ° C./min (DSC), and the exothermic temperature and calorific value estimated from the exothermic peak were measured. Also,
The charge / discharge cycle characteristics of the cell using the conductive agent were also measured. The results are shown in Table 1 below and FIG.

As is clear from Table 1, the electrodes of Examples 1 to 8 have a high exothermic peak temperature or no exotherm is observed. On the other hand, it is understood that the electrodes of Comparative Examples 1 to 5 have low peak heat generation and large heat generation. Also,
It can be seen that the cycle characteristics of the electrode of Comparative Example 5 were significantly reduced due to insufficient conductivity of the conductive agent. As a result of the comprehensive judgment, all of the examples were judged to be superior to the comparative examples. (In the table, ◎: extremely good, ：: good, Δ: almost good, ×: bad)

[0051]

[Table 1]

[0052]

As described in detail above, according to the nonaqueous electrolyte secondary battery of the present invention, by using a specific conductive oxide as a conductive agent for the positive electrode, the thermal stability of the charged battery can be improved. A more reliable secondary battery having high energy density and excellent safety can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 2 is a graph showing cycle characteristics of non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples of the present invention.

FIG. 3 is a schematic view showing a positive electrode evaluation battery used in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 3 Electrode group 4 Positive electrode 5 Negative electrode 6 Separator 8 Sealing plate

Continuation of front page (72) Inventor Motoki Kanda 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. Toshiba Corporation Kawasaki Office (56) References JP, A) JP-A-53-46636 (JP, A) JP-A-8-213022 (JP, A) JP-A-11-67212 (JP, A) JP-A-5-135759 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/38-4/62 H01M 10/40

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a non-aqueous electrolyte,
The conductive agent contained in the positive electrode may be represented by the following formula: A ₂ BO ₄ (where A is at least one selected from the group consisting of a divalent typical element, a lanthanoid element, and a combination thereof)
B is a species, wherein B is a group IVa, Va, VIa, VIIa
Group, characterized by comprising a conductive oxide having free electrons an oxide having a K ₂ NiF ₄ -type structure represented by at least one selected from the transition elements of group VIII and Group Ib) Non-aqueous electrolyte secondary battery. 2. The substance constituting the negative electrode has a heat generation peak at a temperature of 700 ° C. or more in differential thermal analysis, and a (101) diffraction peak (P101) and a (100) diffraction peak of a graphite structure by X-ray diffraction. (P100) intensity ratio P101 / P10
0 is in the range of 0.7 to 2.2, or titanium disulfide (TiS ₂ ), molybdenum disulfide (Mo).
S ₂₎ and containing the selected chalcogen compound from the group consisting of niobium selenide (NbSe _2), the non-aqueous electrolyte secondary battery according to claim 1.