JP3402237B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art With the rapid reduction in size and weight of electronic equipment, there is an increasing demand for developing a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged with respect to a battery as a power source. . In addition, due to environmental problems such as air pollution and increase in carbon dioxide, early commercialization of electric vehicles is desired, and development of excellent secondary batteries having characteristics such as high efficiency, high output, high energy density, and light weight. Is required.

As a secondary battery satisfying these requirements, a secondary battery using a non-aqueous electrolyte has been put into practical use. This battery has an energy density several times that of a battery using a conventional aqueous electrolyte solution. As an example, cobalt composite oxide, nickel composite oxide or spinel type lithium manganese oxide is used for the positive electrode, and lithium is occluded in the negative electrode.
A high-energy and long-life 4V class non-aqueous electrolyte secondary battery using a releasable carbon material and an organic electrolyte as an electrolyte has been put into practical use.

Further, a high-capacity non-aqueous electrolyte secondary battery using a high-capacity amorphous carbon or / and an oxide or the like for a negative electrode has been developed, and technological development for miniaturization and high capacity is rapidly progressing. . In such a non-aqueous electrolyte battery, there is a big problem to prevent overcharging and over-discharging, prevent internal short-circuiting, and the like, which is accompanied by miniaturization and high capacity, that is, a dramatic increase in volume energy density.

As a measure for preventing overcharge, a method of controlling a charge voltage by a charger and a method for controlling an end voltage at the time of discharge as a measure for preventing overdischarge have become mainstream. Further, in case of control failure of a charger or the like or occurrence of large current due to internal short circuit, the battery side is provided with a safety valve and a current cutoff means that are cleaved when a predetermined battery internal pressure is reached. As means for preventing overcharging, at present, several methods such as a method of mounting a protection circuit / protection element and a method of utilizing thermal blocking of a separator have been proposed.

However, the use of the protection circuit / protection element imposes great restrictions on the downsizing and cost reduction of the battery pack, and the heat blocking of the separator utilizes the exothermic reaction at the time of non-safety. Therefore, when heat is generated rapidly, it may not work effectively. Therefore, as one means for achieving safety during overcharge, a method of relaxing the heat generation rate of the positive electrode active material and allowing the heat blocking mechanism of the separator to operate reliably can be considered.

[0007]

Generally, as a measure for preventing overcharge, a method of controlling the charging voltage by a charger is adopted. However, assuming a case where the charger fails, a non-aqueous electrolyte secondary battery is used. If the battery is charged with a predetermined amount of electricity or more, the battery may generate heat and, in the worst case, may ignite. In addition, even if a nail is stuck in the center of the battery, assuming that an internal short circuit occurs for some reason during charging, the battery may be ignited in the worst case.

The main cause of unsafety in a non-aqueous electrolyte secondary battery during overcharge is a positive electrode active material such as a lithium-containing metal oxide that occludes and releases lithium and / or lithium ions (hereinafter referred to as "positive electrode"). Host material)) changes to a thermally unstable substance due to desorption of lithium during overcharge, and when the battery temperature reaches the critical temperature, oxygen becomes unstable from the unstable positive electrode active material. The released oxygen causes a very large exothermic decomposition reaction of the solvent of the electrolytic solution and the like, resulting in heat escape.

Therefore, according to the present invention, even if the charger fails and becomes overcharged, it is rapidly oxidatively decomposed below the potential generated by the thermally unstable substance and above the actual use potential range. An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the separator is shut down (thermally closed) by decomposition heat or Joule heat due to an increase in internal resistance, and heat generation can be effectively suppressed so that the battery does not cause thermal runaway. To do.

Here, "shutdown (heat blocking)" means that in a non-aqueous electrolyte secondary battery, when the battery temperature rises abnormally due to a large current due to an external short circuit or the like, the separator heat-shrinks to cause ionization. The function of blocking heat generation by blocking the hole that is the passage of, and stopping the flow of short-circuit current after that.

[0011]

The present invention is capable of occluding and releasing lithium ions, and a positive electrode having a positive electrode mixture layer containing a lithium-containing metal oxide capable of occluding and releasing lithium ions as a positive electrode active material. In a non-aqueous electrolyte secondary battery comprising a negative electrode on which a negative electrode mixture layer containing a host material as a negative electrode active material is formed, the non-aqueous electrolyte solution is at the α-position of 2-methylnaphthalene and a side chain alkyl group. Simultaneously containing a benzene compound having a tertiary hydrogen, the total amount of the 2-methylnaphthalene and the benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group is the 2-methylnaphthalene and the pendant compound. It is characterized in that it is contained in an amount of 1 to 10% by weight with respect to the non-aqueous electrolyte except the benzene compound having a tertiary hydrogen at the α-position of the chain alkyl group.

A second invention is the invention according to claim 1,
The benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group is at least one selected from the group consisting of isopropylnaphthalene, cumene, cadarine, and guaiazulene.

[0013]

[0014]

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is directed to a positive electrode on which a positive electrode mixture layer having a lithium-containing metal oxide capable of occluding and releasing lithium ions is formed, and a negative electrode mixture having a host material capable of occluding and releasing lithium ions. In a non-aqueous electrolyte secondary battery provided with a layered negative electrode, the positive electrode active material is below a potential at which it is converted into a thermally unstable substance during overcharging, and when fully charged during actual use. 2-methylnaphthalene and a benzene compound having a tertiary hydrogen at the α-position of a side chain alkyl group, which undergoes oxidative decomposition preferentially at a potential nobler than the positive electrode potential, are simultaneously contained. 2-Methylnaphthalene and a benzene compound having a tertiary hydrogen at the α-position of a side chain alkyl group are substances that keep the battery safe until the separator shuts down by preventing the accumulation of unstable substances inside the battery. . A polycyclic aromatic compound having a side chain and a benzene compound are effective in improving safety during overcharge when used alone, but when used together, a further dramatic improvement in safety can be obtained. It was also found that the actual use performance did not deteriorate.

Therefore, since a thermally unstable substance does not accumulate in the battery, it is possible to effectively suppress the explosive exothermic decomposition reaction at the time of overcharging which occurs in a conventional battery. .

Here, the 2-methylnaphthalene and the benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group preferably have an oxidation potential at a potential nobler than the positive electrode potential at the time of full charge. The reason is that 2-methylnaphthalene and the benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group should not be oxidized in the potential range of the actual use conditions of the battery.

Furthermore, the reason why 2-methylnaphthalene is used is that in naphthalene having a methyl group as a substituent, the reactivity of the aromatic ring itself increases and the ring is oxidized before the side chain methyl group.

[0021]

Further, the use of a benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group is because the reactivity of the side chain alkyl group of the benzene compound is such that the hydrogen at the α position is primary < This is because the numbers increase in the order of second grade <third grade.

In the present invention, the total amount of 2-methylnaphthalene and the benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group is such that the amount of 2-methylnaphthalene and the α-position of the side chain alkyl group are equal to each other. 1 to 10% by weight with respect to the non-aqueous electrolyte except the benzene compound having tertiary hydrogen. The reason is that if the addition amount is too large, the conductivity of the electrolytic solution decreases, which adversely affects the charge and discharge characteristics of the battery.
On the other hand, if the amount added is too small, it is insufficient to reduce the thermally unstable substance generated at the time of overcharge or high temperature to a stable substance.

The benzene compound having a tertiary hydrogen at the α-position of the side chain alkyl group is isopropylnaphthalene, cumene,
It is preferably at least one selected from the group consisting of kadarin and guaiazulen. At least one benzene compound having a tertiary hydrogen at the α-position of these side chain alkyl groups may be added to the electrolytic solution. The compound capable of inserting and extracting lithium and / or lithium ions as the positive electrode active material of the non-aqueous electrolyte battery according to the present invention is not limited to the above-mentioned lithium-containing metal oxide. In addition to this, as the inorganic compound, the composition formula L
i _x MO ₂ or Li _y M ₂ O ₄ (where M is a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), a composite oxide, an oxide having tunnel-shaped vacancies, and a layered structure. Metal chalcogenides can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ ,
Li ₂ Mn ₂ O ₂ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V
₆ O ₁₃ , TiO ₂ , TiS _{2 and the} like can be mentioned. Further, these active materials may be mixed and used.

The negative electrode host material used in the present invention may be any material as long as it can store and release lithium ions. For example, graphite, coke, carbon, amorphous carbon, SnO, SnO
₂ , substances such as Sn _1-x O (where 0 ≦ x <1) and Si _1-x O (where 0 ≦ x <1) can be exemplified. Even if a high capacity battery is formed by using an oxide, the safety can be improved by applying the present invention.

The lithium salt which can be dissolved in the electrolytic solution includes LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiCF ₃ C.
O ₂ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN
(SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and L
A salt such as iN (COCF ₂ CF ₃ ) ₂ or a mixture thereof can be used.

As the solvent of the electrolytic solution, cyclic carbonic acid esters such as propylene carbonate and ethylene carbonate, chain carbonic acid esters such as diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate may be used alone or in a mixture thereof. it can.

The non-aqueous electrolyte secondary battery according to the present invention usually comprises a combination of a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution. The separator is a porous polyvinyl chloride film. Porous polymer membranes such as and lithium ion or ion conductive polymer electrolyte membranes can be used alone or in combination.

When the polymer electrolyte membrane is polyethylene oxide, polyacrylonitrile, polyethylene glycol, or modified products thereof, it is lightweight and flexible, which is advantageous when used for a wound electrode plate. Furthermore, the ion conductive polymer electrolyte membrane and the organic electrolyte can be used in combination. As the electrolyte, in addition to the polymer electrolyte, known materials such as an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used.

[0030]

EXAMPLES A non-aqueous electrolyte secondary battery according to the present invention containing a polycyclic aromatic compound having a side chain in an electrolyte and a benzene compound will be described below with reference to examples.

[Example 1] Four types of prismatic non-aqueous electrolyte secondary batteries having spiral electrode groups were prepared. The positive electrode plate is obtained by holding a lithium-cobalt composite oxide as a lithium-containing metal oxide that absorbs and releases lithium ions on an aluminum foil having a thickness of 20 μm as a current collector. The positive electrode plate was prepared by mixing 6 parts by weight of polyvinylidene fluoride as a binder and 3 parts by weight of acetylene black as a conductive agent together with 91 parts by weight of lithium-cobalt composite oxide to prepare NMP (N-methylpyrrolidone) as a solvent. After being appropriately added to form a paste, the current collector material is coated on both sides, dried, and pressed to a thickness of 180 μm, and cut into a width of 24 mm while leaving a rectangular lead portion.

The negative electrode plate is a copper foil having a thickness of 10 μm serving as a current collector and holding graphite serving as a host material. The negative electrode plate was prepared by mixing 92 parts by weight of graphite and 8 parts by weight of polyvinylidene fluoride as a binder, and using NMP as a solvent.
Was added to form a paste, which was applied to both sides and dried. Then, it was rolled to a thickness of 220 μm and cut to a width of 26 mm while leaving a rectangular lead portion. The separator was a polyethylene microporous film having a thickness of 25 μm and a width of 28 μm.

FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery according to the present invention. In the figure, 1 is a non-aqueous electrolyte secondary battery, 2 is an electrode group, 3 is a negative electrode plate, and 4 is a positive electrode. A plate, 5 is a separator, and 6 is a battery case. The configuration of the non-aqueous electrolyte secondary battery 1 is a prismatic battery in which a negative electrode plate 3, a positive electrode plate 4, a spiral electrode group 2 including a separator 5 and an electrolytic solution are housed in a battery case 6, and 7 is a lid, 8 is a safety valve, 10 is a negative electrode terminal, and 11 is a negative electrode lead.

The battery case 6 has a thickness of 0.3 mm and inner dimensions of 3
The surface of a 0 × 40 × 8.0 mm iron main body is plated with nickel having a thickness of 5 μm, and a hole (not shown) for injecting an electrolytic solution is provided in the upper side portion.

The basic electrolyte is LiPF ₆ at 1 mo.
A mixed solution of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) containing 1 / l was prepared. A battery prepared by injecting an electrolyte solution obtained by adding 3 parts by weight of 2-methylnaphthalene and 3 parts by weight of cumene to 100 parts by weight of this basic electrolyte solution is referred to as Battery A, and 100 parts by weight of the basic electrolyte solution contains only 2-methylnaphthalene. Battery B in which 6 parts by weight of the electrolyte solution was injected, Battery B, battery C in which the electrolyte solution of 6 parts by weight of cumene was added was battery C, and battery B in which the basic electrolyte solution was injected
And

The electrolyte and the separator were sufficiently moistened with each electrolyte, and the amount of free electrolyte not present outside the electrode group was reduced by pressure injection (4 ml) to seal the electrolyte injection hole, and the designed capacity 9
Ten 00 Ah batteries A, B, C, and D were manufactured, and a total of 40 batteries were manufactured.

Five of each of these batteries A, B, C and D were used, and 4.1 V at 900 mA in an environment of 45 ° C.
Charge at constant voltage for 2 hours, then at 900mA 2.
The charge / discharge cycle was repeated under the condition of discharging up to 75V.
Table 1 shows the average discharge capacity at the 300th cycle and the average battery thickness after the 300th cycle. In addition, an overcharge test was performed under the condition that each of the five batteries was charged with a power supply voltage of 10 V and a current of 2700 mA for 1 hour. Table 2 shows the changes in the battery status after the overcharge test.

[0038]

[Table 1]

[0039]

[Table 2]

From these test results, the battery A using the electrolytic solution according to the present invention has a discharge capacity of 720 mAh at the 300th cycle, the battery swells small, and the battery state does not change even in the overcharge test. There wasn't.

On the other hand, in the battery B in which only 2-methylnaphthalene was added to the basic electrolytic solution, the battery C in which only cumene was added to the basic electrolytic solution, and the battery D in which only the basic electrolytic solution was used, the discharge capacity at the 300th cycle Significantly decreased, the battery swelled, or the battery leaked, smoked, or exploded in the overcharge test.

[Example 2] Four kinds of batteries exactly the same as in Example 1 except for the electrolytic solution used were prepared.

The basic electrolyte is LiPF ₆ at 1 mo.
A mixed solution of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) containing 1 / l was prepared. A battery in which 100 parts by weight of this basic electrolytic solution was infused with an electrolytic solution prepared by adding 0.1 parts by weight of 2-methylnaphthalene and 0.1 parts by weight of cumene was designated as a battery E. In addition, a battery prepared by injecting an electrolyte solution prepared by adding 0.5 parts by weight of 2-methylnaphthalene and 0.5 parts by weight of cumene to 100 parts by weight of the basic electrolyte solution is referred to as Battery F and 100 parts by weight of the basic electrolyte solution.
A battery in which 5 parts by weight of 2-methylnaphthalene and 5 parts by weight of cumene are added to parts by weight of the battery is battery G, and 10 parts by weight of 2-methylnaphthalene and 10 parts by weight of cumene are added to 100 parts by weight of the basic electrolyte. The battery in which the prepared electrolytic solution was injected was designated as Battery H.

The electrolyte and the separator were sufficiently moistened with each electrolyte, and the amount of free electrolyte not present outside the electrode group was reduced pressure injection (4 ml) to seal the electrolyte injection hole, and the designed capacity 9
For each of the 00 mAh batteries E, F, G, and H, a total of 40 batteries were manufactured.

Five of each of these batteries E, F, G, and H were used and 4.1 V at 900 mA in an environment of 45 ° C.
Charge at constant voltage for 2 hours, then at 900mA 2.
The charge / discharge cycle was repeated under the condition of discharging up to 75V.
Table 3 shows the average discharge capacity at the 300th cycle and the average battery thickness after the 300th cycle. In addition, an overcharge test was performed under the condition that each of the five batteries was charged with a power supply voltage of 10 V and a current of 2700 mA for 1 hour. Table 4 shows changes in the battery state after the overcharge test.

[0046]

[Table 3]

[0047]

[Table 4]

From these test results, in the battery F in which the total amount of 2-methylnaphthalene and cumene added to the basic electrolytic solution was 1 part by weight and the battery G in which the total amount was 10 parts by weight, the discharge capacity at the 300th cycle was found. It was 700 mAh or more, the swelling of the battery was small, and the state of the battery did not change even in the overcharge test.

On the other hand, in the battery E in which the total amount of 2-methylnaphthalene and cumene added to the basic electrolyte was 0.2 parts by weight, the discharge capacity at the 300th cycle was 700 mAh or more, and the battery swelled was small. All batteries burst in the overcharge test. In addition, the total amount of 2-methylnaphthalene and cumene added to the basic electrolyte is 20
In the battery H, which is a part by weight, the state of the battery did not change at all in the overcharge test, but the discharge capacity at the 300th cycle was significantly reduced, or the battery swelled.

[0050]

INDUSTRIAL APPLICABILITY According to the present invention, a benzene compound having a tertiary hydrogen at the α-position of a side-chain alkyl group and 2-methylnaphthalene, which is added to a battery in an amount of 1 to 10% by weight, is used during overcharge. To prevent the accumulation of unstable substances, the positive electrode is preferentially subjected to oxidative decomposition at a potential below the potential at which it becomes a thermally unstable substance, and at a potential nobler than the positive electrode potential at the time of full charge during actual use. You can keep the battery safe until your shut down.

Further, 2-methylnaphthalene and a benzene compound having a tertiary hydrogen at the α-position of a side chain alkyl group are effective in improving safety during overcharge even if they are used alone. When used together, it is possible to dramatically improve safety and maintain actual use performance.

Therefore, the actual use performance remains the same as that of the conventional battery, and the explosive exothermic decomposition reaction at the time of overcharging which occurs in the conventional battery can be effectively suppressed. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that not only has a high capacity but can further improve safety. Therefore, the industrial value of the present invention is extremely high.

[0053]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to a first embodiment.

[Explanation of symbols]

1 Non-aqueous electrolyte secondary battery 2 electrode group 3 Negative electrode plate 4 Positive plate 5 separator 6 battery case 7 lid 8 safety valve 10 Negative electrode terminal 11 Negative electrode lead

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-55822 (JP, A) JP-A-7-302614 (JP, A) JP-A-9-45369 (JP, A) JP-A-5- 36439 (JP, A) JP-A-6-150970 (JP, A) JP-A-2000-58116 (JP, A) JP-A-2000-156243 (JP, A) JP-A-5-234618 (JP, A) Special Table 2001-525597 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte solution is 2-methylnaphthalene and side.
Of Benzene Compounds with Tertiary Hydrogen at α-position of Chain Alkyl Group
And 2-methylnaphthalene and the side
Of Benzene Compounds with Tertiary Hydrogen at α-position of Chain Alkyl Group
The total amount of the 2-methylnaphthalene and the side chain
A benzene compound having a tertiary hydrogen at the α-position of the rukyl group
The non-aqueous electrolyte secondary battery is characterized by containing 1 to 10 wt% with respect to the non-aqueous electrolyte solution excluding . 2. A tertiary hydrogen is added to the α-position of a side chain alkyl group.
Benzene compounds have isopropyl naphthalene,
Selected from the group consisting of
The non-aqueous electrolyte secondary battery according to claim 1, wherein the even without a kind.