JP2001202965A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery of satisfactory safety in which a heat escaping reaction during an overcharge is restrained effectively. SOLUTION: In a nonaqueous electrolyte secondary battery comprised of a cathode, which includes a material that occludes and emits lithium ions, an anode which includes a material that occludes and emits lithium ions, and a nonaqueous electrolyte, a metal in which an oxidation starts at the voltage between 4.3 V and 5.0 V (vs. Li/Li+) in the organic electrolytic solution of carbonic esters in the mixture of the cathode, is included.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable electronic devices, portable information terminals, and the like, small, lightweight, and high-energy densities are required for batteries as power sources. There is a strong demand for the development of a secondary battery that can repeatedly charge and discharge for a longer period. Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are the most promising secondary batteries that satisfy these requirements, and active research is being conducted.

As a positive electrode active material of a nonaqueous electrolyte secondary battery, titanium disulfide, vanadium pentoxide, molybdenum trioxide and the like have been studied. Recently, as a positive electrode material that occludes and releases lithium ions, a general formula Li _X MO such as lithium cobalt composite oxide, lithium nickel composite oxide, and spinel type lithium manganese oxide has been used.
Various compounds represented by ₂ (where M is one or more transition metals) are being studied.

[0004] Among them, lithium cobalt composite oxide,
Lithium nickel composite oxide, spinel type lithium manganese oxide, and the like charge and discharge at an extremely noble potential of 4 V (vs. Li ^/ Li ⁺ ) or more. Energy density batteries can be realized.

As the negative electrode active material of the non-aqueous electrolyte secondary battery, various materials such as metallic lithium and alloys containing lithium and carbon materials capable of inserting and extracting lithium have been studied. The use of a carbon material has the advantages of obtaining a battery with a long cycle life and high safety.

[0006] The electrolyte of the non-aqueous electrolyte secondary battery, in general a mixed solvent of low viscosity solvent, such as high dielectric constant solvent and dimethyl carbonate and diethyl carbonate such as ethylene carbonate and propylene carbonate, LiPF ₆
And an electrolyte solution in which a supporting salt such as LiBF ₄ is dissolved.

[0007]

However, in such a non-aqueous electrolyte secondary battery, when a power supply circuit or a charging device of an electronic device fails and becomes overcharged, the positive electrode active material and the electrolyte are decomposed. However, abnormal heat generation occurs in the battery, and in extreme cases it is feared that the battery may be damaged or fired.Therefore, the heat generation is effectively suppressed so that the battery does not run away from heat,
Ensuring the safety of batteries has become an important issue.

As a measure for preventing overcharging, a method of controlling a charging voltage by a charger is mainly used. However, at present, the use of protection circuits and protection elements greatly imposes restrictions on miniaturization and cost reduction of battery packs. Therefore, it is desired to ensure safety without protection circuits and protection elements.

[0009]

In order to solve the above-mentioned problems, a battery according to the present invention has the following configuration.

That is, a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a substance that occludes and releases lithium ions, a negative electrode that contains a substance that occludes and releases lithium ions, and a non-aqueous electrolyte. In the positive electrode mixture, 4.3 to 5.0 V (vs. Li / Li) in a carbonate organic electrolyte.
⁺ ) Characterized in that it contains a metal that starts to oxidize.

Further, the present invention is characterized in that the metal contained in the positive electrode mixture is at least one selected from the group consisting of nickel, stainless steel and titanium.

Further, the present invention is characterized in that the content of the metal contained in the positive electrode mixture is 0.1 to 20% by weight or less with respect to the total weight of the positive electrode mixture. It is characterized in that the metal contained has an average particle size of 0.1 μm to 20 μm.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a positive electrode mixture containing 4.3 to 5.0 V (vs. Li) in a carbonate-based organic electrolyte.
/ Li ⁺ ) contains a metal whose oxidation starts. Examples of such a metal include nickel, stainless steel, and titanium, and these can be used alone or as a mixture.

In general, the oxidation potential of a metal in an organic electrolytic solution varies depending on the type of the organic electrolytic solution, that is, the organic solvent and the electrolyte salt constituting the organic electrolytic solution. for that reason,
In the present invention, the oxidation potential of the metal was measured in a carbonate-based organic electrolyte. Here, the carbonate-based organic electrolyte refers to an organic electrolyte in which a solvent constituting the electrolyte contains 50% or more by volume of a carbonate-based organic solvent and a lithium salt as an electrolyte salt.

As the carbonate, a cyclic carbonate such as ethylene carbonate, propylene carbonate, butylene carbonate or vinylene carbonate, or a chain carbonate such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate or methyl propyl carbonate is used. .

In the carbonate-based organic electrolyte,
The potential at which oxidation starts (vs. Li ^/ Li ⁺ ) is about 4.4 V for nickel, about 4.7 V for stainless steel, and about 4.9 V for titanium.

In a non-aqueous electrolyte battery, in a positive electrode mixture,
4.3 to 5.0 V (vs. Li / Li ⁺) With oxidation
If metal is included, this metal substance will be
The overcharge current is consumed by oxidative decomposition, and the positive electrode
Ensures safety during overcharge without decomposing substances and electrolytes
You can do it.

In the positive electrode mixture, 4.3 V (vs. Li) was used.
/ Li ⁺ ) when mixed with a metal that starts to oxidize at a lower potential, decomposes during high-temperature storage or during normal charging, deteriorating battery characteristics. In addition, 5.0 V (vs. Li / L
If a metal that starts to oxidize at a potential higher than i ⁺ ) is mixed, the oxidation does not occur until thermal escape of the positive electrode occurs, and the overcharge current cannot be consumed. 3 to 5.0 V (vs. Li / Li ⁺ )
Oxidation needs to start.

The content of the metal powder with respect to the total weight of the positive electrode mixture is preferably 0.1 to 20% by weight. However, if the content of the metal powder is less than 0.1% by weight, there is no safety effect. If the content of the metal powder exceeds 20% by weight, the weight ratio of the metal powder in the positive electrode mixture is too large, and the capacity of the battery decreases.

Further, the average particle size of the metal contained in the positive electrode mixture is preferably 0.1 to 20 μm. If the average particle size of the metal powder is larger than 20 μm, the effect on safety will be reduced, and If the average particle size of the metal powder is too small, there is a problem in workability in manufacturing an electrode plate.

As the positive electrode active material of the non-aqueous electrolyte secondary battery in the present invention, any substance can be used as long as it can absorb and release lithium ions. Among them,
General formula Li _X MO ₂ (where M is one or more transition metals)
It is preferable to use a compound mainly composed of a single compound or a mixture of two or more compounds. In particular, it is desirable to use a transition metal composed of Co, Ni, and Mn as the transition metal M in view of a high discharge voltage.

As the negative electrode active material, any substance can be used as long as it can absorb and release lithium ions. Among them, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, or metallic lithium, lithium alloys, polyacenes, etc. are used alone or in combination of two or more. In particular, it is desirable to use a carbonaceous material because of its high safety.

Examples of the solvent for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyl lactone, acetyl-γ-butyrolactone, and γ-valero. Lactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolan, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, Dimethyl carbonate, diethyl carbonate,
Methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate and the like can be used alone or in combination of two or more.

The electrolyte salt as a solute of the non-aqueous electrolyte is L
iCLO_Four, LiAsF₆, LiPF ₆, LiBF_Four, Li
CF_ThreeSO_Three, LiCF_ThreeCF_TwoSO_Three, LiCF_ThreeCF_TwoC
F_TwoSO_Three, LiN (CF_ThreeSO_Two)_Two, LiN (C_TwoF_FiveS
O_Two)_TwoEtc. may be used alone or as a mixture of two or more.
Can be. Among them, LiPF₆It is preferable to use
Good.

Further, a solid ion-conductive polymer electrolyte can be used instead of or in addition to the above-mentioned electrolyte salt. In this case, as a configuration of the nonaqueous electrolyte secondary battery,
A combination of a positive electrode, a negative electrode and a separator with an organic or inorganic solid electrolyte and a non-aqueous electrolyte (solvent or a solvent and an electrolyte salt), or an organic or inorganic solid electrolyte membrane and a non-aqueous electrolyte as a positive electrode, a negative electrode and a separator ( Solvent or a combination of a solvent and an electrolyte salt). When the polymer electrolyte membrane is made of polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, the polymer electrolyte membrane is lightweight and flexible, which is advantageous when used for a wound electrode plate. Further, as the electrolyte, other than the polymer electrolyte, an inorganic solid electrolyte or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte can be used.

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, and a combination of a separator and a non-aqueous electrolyte.
A porous polymer membrane such as a porous polyvinyl chloride membrane or an ion-conducting polymer electrolyte membrane can be used alone or in combination.

Further, the shape of the battery is cylindrical, square,
Various shapes such as a coin type, a button type, and a laminate type can be used.

[0028]

Next, preferred embodiments of the present invention will be described in detail.

Example 1 FIG. 1 is a schematic sectional view of a prismatic nonaqueous electrolyte secondary battery used in the present invention. In FIG. 1, 1 is a non-aqueous electrolyte secondary battery, 2 is an electrode group, 3 is a negative electrode,
4 is a positive electrode, 5 is a separator, 6 is a battery case, 7 is a lid,
8 is a safety valve, 9 is a negative electrode terminal, and 10 is a negative electrode lead.

The prismatic non-aqueous electrolyte secondary battery 1 has a positive electrode 4 formed by coating a positive electrode mixture containing a substance capable of occluding and releasing lithium ions on an aluminum current collector, and a lithium current collector on a copper current collector. A flat electrode group 2 in which a negative electrode 3 coated with a negative electrode mixture containing a substance that absorbs and releases ions is wound through a separator 5, and a nonaqueous electrolyte containing an electrolyte salt. Are stored in the battery case 6.

A battery lid provided with a safety valve 8 is attached to the battery case 6 by laser welding, a negative electrode terminal 9 is connected to the negative electrode 3 via a negative electrode lead 10, and the positive electrode 4 contacts the inner wall of the battery case 6. It is electrically connected.

The positive electrode mixture was composed of 87 parts by weight of LiCoO _{2 as} an active material, 5 parts by weight of acetylene black as a conductive material, 3 parts by weight of stainless steel powder having an average particle size of 5 μm as a metal powder, and polyvinylidene fluoride as a binder. And 5 parts by weight,
N-Methyl-2-pyrrolidone was appropriately added and dispersed to prepare a slurry. This slurry was uniformly applied to an aluminum current collector having a thickness of 20 μm, dried, and then compression-molded by a roll press to a thickness of 180 μm.

The negative electrode mixture was prepared by mixing 90 parts by weight of a carbon material capable of inserting and extracting lithium ions and 10 parts by weight of polyvinylidene fluoride, and appropriately adding N-methyl-2-pyrrolidone to prepare a slurry. . This slurry was uniformly applied to a 10 μm-thick copper current collector, dried, and then compression-molded to a thickness of 180 μm by a roll press to produce a negative electrode 3.

As the separator 5, a 25 μm-thick microporous polyethylene film was used. As the non-aqueous electrolyte, an electrolytic solution obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1 and dissolving 1.0 mol / l of LiPF ₆ as an electrolyte salt was used.

The battery of Example 1 having a designed capacity of 600 mAh was manufactured by the above-described components and procedures. This was designated as battery A.

Comparative Example 1 As Comparative Example 1, the positive electrode mixture was composed of 90 parts by weight of LiCoO _{2 as} an active material, 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder. The mixture was mixed, and N-methyl-2-pyrrolidone was appropriately added and dispersed to prepare a slurry. This slurry was uniformly applied to an aluminum current collector having a thickness of 20 μm, dried, and then compression-molded by a roll press to a thickness of 180 μm. A battery was produced as Comparative Example 1 in the above-described components and procedure except for the positive electrode. Battery B
And

Example 2 A battery was manufactured in the same manner as in Example 1 except that nickel powder was used instead of stainless steel powder as the metal powder contained in the positive electrode mixture. This was designated as Battery C.

Example 3 A battery was manufactured in the same manner as in Example 1 except that titanium powder was used instead of stainless steel powder as the metal powder contained in the positive electrode mixture. Battery D
And

[Battery test] The above batteries (Examples 1 to 3,
Using Comparative Example 1), a safety test was performed by overcharging at 25 ° C. and a current of 2 C up to a charge termination voltage of 10.0 V, and the state of the battery at that time was observed.

The above battery was charged and discharged at a current of 25 ° C. and a current of 1 C under the conditions of a final charge voltage of 4.1 V and a final discharge voltage of 2.5 V, and the discharge capacity was determined. The results are shown in Table 1.

[0041]

[Table 1]

From Table 1, it can be seen that the battery A of Example 1 containing stainless powder in the positive electrode mixture showed higher safety at the time of overcharging than the battery B of Comparative Example 1 containing no stainless powder. I understood that. For this reason,
The overcharge current was consumed by the stainless steel causing oxidation near 4.7 V (vs. Li ^/ Li ⁺ ) during overcharge, and the thermal runaway of the battery was suppressed without decomposing the electrolyte or the positive electrode active material. It is supposed to be. Example 2
It is also presumed that thermal escape of the battery was suppressed in the cases of and 3 for the same reason.

[Examples 4 to 10] Next, the batteries of Examples 4 to 8 were prepared by changing the content (wt%) of the nickel powder with respect to the total weight of the positive electrode mixture in the battery of Example 2. And these were designated as batteries EK. A safety test was conducted using 10 of these batteries. Table 2 shows the number of bursts in the safety test.

[0044]

[Table 2]

As can be seen from Table 2, in the battery E of Example 4 in which the content of the nickel powder relative to the total weight of the positive electrode mixture was 0.05 wt%, six batteries burst, whereas
Batteries of Examples 5 to 10 (Battery F
-K), there were no ruptured batteries. However, although the battery K of Example 10 did not burst, the weight ratio of the nickel powder in the positive electrode mixture was too large and the capacity of the battery was reduced. Is preferably 20 wt% or less.

[Examples 11 to 16] Further, in the battery of Example 2, the content of the nickel powder with respect to the total weight of the positive electrode mixture was set to 3 wt%, and the particle diameter of the nickel powder was changed. And these were designated as batteries L to Q. A safety test was conducted using 10 of these batteries. The number of bursts in the safety test was 3.

[0047]

[Table 3]

As can be seen from Table 3, none of the batteries of Examples 11 to 15 (Batteries LP) in which the average particle size of the nickel powder was 20 μm or less was ruptured. However, in Example 16 in which the average particle size of the nickel powder was 25 μm,
In Battery Q, three batteries exploded. That is, when the average particle size of the nickel powder is larger than 20 μm, it is estimated that the effect on safety is reduced. However, in the battery L of Example 11, although the rupture did not occur, the average particle diameter of the nickel powder in the positive electrode mixture was too small, which caused a problem in workability in manufacturing an electrode plate. The average particle size of the nickel powder is preferably 0.1 to 20 μm.

[0049]

In the non-aqueous electrolyte secondary battery according to the present invention, oxidation is carried out at 4.3 to 5.0 V (vs. Li / Li ⁺ ) in the carbonate-based organic electrolyte in the positive electrode mixture. Since the starting metal is contained, this metal is decomposed at the time of overcharging and the overcharge current is consumed.This does not lead to decomposition of the electrolytic solution or decomposition of the positive electrode active material. Safety can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a prismatic battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Negative electrode 4 Positive electrode 5 Separator 6 Battery case 7 Lid 8 Safety valve 9 Negative terminal 10 Negative lead

Claims (4)

[Claims] 1. A positive electrode mixture comprising a positive electrode containing a substance that occludes and releases lithium ions, a negative electrode containing a substance that occludes and releases lithium ions, and a non-aqueous electrolyte, wherein a carbonate-based organic electrolyte is contained in the positive electrode mixture. 4.3-5.0 V (vs. Li
/ Li ⁺ ), wherein the nonaqueous electrolyte secondary battery contains a metal whose oxidation starts. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal contained in the positive electrode mixture is at least one selected from the group consisting of nickel, stainless steel, and titanium. 3. The content of a metal contained in the positive electrode mixture is as follows:
3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount is 0.1 to 20% by weight based on the total weight of the positive electrode mixture. 4. An average particle size of a metal contained in the positive electrode mixture is 0.1 to 20 μm.
Or the non-aqueous electrolyte secondary battery according to 3.