JP3402233B2 - 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. .

[0005] In such a non-aqueous electrolyte battery, a major problem is to prevent overcharging and overdischarging and to prevent internal short-circuiting due to the miniaturization and high capacity, that is, the dramatic increase in volumetric energy density.

As a measure for preventing overcharge, a method of controlling a charging voltage by a charger, and as a measure for preventing overdischarge, controlling an end-to-end voltage at the time of discharging has become the mainstream. Further, in case of control failure of the charger or the like, or in preparation for the generation of a large current due to an internal short circuit, the battery side is provided with a safety valve and a current cutoff means that are opened when a predetermined battery internal pressure is reached.

In order to solve this problem, some means for preventing overcharge have been proposed. At present, examples include a method of mounting a protection circuit / protection element and a method of utilizing heat blocking of a separator.

However, the use of the protection circuit / protection element imposes great restrictions on the downsizing and cost reduction of the battery pack, and the thermal 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 has been proposed in which the heat generation rate of the positive electrode active material is relaxed and the heat blocking mechanism of the separator is made to work reliably.

[0009]

Generally, as a measure against overcharge, a method of controlling the charging voltage by a charger is adopted. However, when the charger fails, the non-aqueous electrolyte secondary battery is used. When a certain amount of electricity or more is charged, the battery may generate heat and, in the worst case, may ignite.

The main cause of unsafety of the non-aqueous electrolyte secondary battery at the time of 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. It is released, and the oxygen and the electrolytic solution solvent cause a very large exothermic decomposition reaction to cause thermal runaway.

Therefore, according to the present invention, even if the charger fails and becomes overcharged, it is rapidly oxidized and 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.

[0012]

The present invention is directed to a positive electrode having a positive electrode mixture layer containing a positive electrode active host material and a negative electrode compound containing a negative electrode host material capable of inserting and extracting lithium ions as a negative electrode active material. In a non-aqueous electrolyte secondary battery including a negative electrode on which a material layer is formed, 2-methylnaphthalene or
Naphthalene having tertiary hydrogen at α-position of side chain alkyl group
It is characterized by using a non-aqueous electrolyte containing 0.1 to 10 wt% of the electrolyte, and is positive below the potential at which the positive electrode active material transforms into a thermally unstable substance during charging and above the potential range under actual use conditions. It is oxidatively decomposed into, and the separator is shut down by the decomposition heat or Joule heat due to an increase in internal resistance, so that heat generation is effectively prevented so that the battery does not cause thermal runaway.

In the present invention, it is preferable that the naphthalene 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, cadarine and guaiazulene.

Here, "shutdown (heat blocking)" means that in a non-aqueous electrolyte secondary battery, when the battery is short-circuited, a large current flows in a part of the inside of the battery and the temperature becomes locally high. The separator melts due to heat, the pores of the separator are closed, an insulating film is formed, and as a result, the internal resistance of the battery becomes high, and no more current flows,
A mechanism that stops the heat generation and prevents the battery from exploding.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is 2-methylnaphthalene, which is rapidly oxidatively decomposed below a potential at which a positive electrode active material is converted into a thermally unstable substance or below a potential range under actual use conditions. Alternatively, naphthalene having a tertiary hydrogen at the α-position of the side chain alkyl group is added to the electrolytic solution, and examples of the naphthalene having a tertiary hydrogen at the α-position of the side chain alkyl group include isopropylnaphthalene and cadaline. , At least one selected from the group consisting of Guya Azulene,
At least one kind of these compounds may be added to the electrolytic solution.

2-Methylnaphthalene and naphthalene having a tertiary hydrogen at the α-position of the side chain alkyl group are preferred.
This is because the side chain alkyl group is conjugated with the benzene ring to increase reactivity, and is more easily oxidized than a polycyclic aromatic compound whose side chain is not an alkyl group. Further, naphthalene is preferable, in the case of naphthalene having an alkyl group in the side chain,
This is because the reactivity of the ring itself increases and the ring is oxidized before the side chain alkyl group. Furthermore, the reactivity of the side chain alkyl group of the polycyclic aromatic compound is such that the hydrogen at the α-position is
This is because the numbers increase in the order of 2nd class <3rd class.

It is presumed that the oxidative decomposition of these additives prevents the accumulation of thermally unstable substances inside the battery and prevents thermal runaway up to the shutdown temperature of the separator.

As a result, it is possible to effectively suppress the explosive exothermic decomposition reaction at the time of overcharging, which is seen in the conventional non-aqueous electrolyte battery.

[0019]

The addition amount of 2-methylnaphthalene or naphthalene having tertiary hydrogen at the α-position of the side chain alkyl group needs to be in the range of 0.1 to 10 wt% with respect to the electrolytic solution. The reason is that if the added amount is too large, the conductivity of the electrolytic solution is lowered, which adversely affects the charge / discharge characteristics of the battery.On the other hand, if the added amount is too small, heat generated during overcharge or high temperature It is insufficient to reduce a chemically unstable substance to a stable substance.

Positive electrode active material for non-aqueous electrolyte battery according to the present invention
Occlusion and release of lithium and / or lithium ions
Possible compounds include the above-mentioned lithium-containing metal oxides.
It is not limited to. In addition to this, inorganic compounds
As the composition formula LixMO ₂Or LiyM₂O_Four(Ta
However, M is represented by a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2)
Complex oxides, oxides with tunnel-like vacancies, layers
A metal chalcogenide having a structure can be used. So
As a concrete example of₂, LiNiO₂, LiM
n₂O_Four, Li₂Mn₂O_Four, MnO₂, FeO₂, V₂O_Five,
V₆O₁₃, TiO ₂, TiS₂And so on. further
You may mix and use these active materials. Also, the present invention
The negative electrode host material used for the storage of lithium ions
Any substance that can be released may be used. example
For example, graphite, coke, carbon, amorphous
Carbon, SnO, SnO₂, Sn_1-xO (where 0 ≦ x
<1), Si_1-xO (however 0 ≦ x <1)
It can be illustrated. High capacity battery using oxide
Even so, applying the present invention can improve safety.
It is possible.

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.

[0026]

EXAMPLES The present invention will be described below with reference to preferred examples, but it goes without saying that the present invention is not limited to the following unless it exceeds the gist of the present invention.

[Example 1] First, a method for manufacturing a positive electrode plate will be described. A lithium cobalt composite oxide was used as the positive electrode host material as the positive electrode active material, acetylene black was used as the conductive agent, and polyvinylidene fluoride was used as the binder. Lithium cobalt composite oxide, acetylene black and polyvinylidene fluoride in a weight ratio of 91:
The mixture was mixed at a ratio of 3: 6, and NMP (N-methylpyrrolidone) as a solvent was appropriately added to prepare a paste. This paste was applied on both sides of an aluminum foil having a thickness of 20 μm as a current collector material and dried. Then, the positive electrode plate was manufactured by pressing so that the thickness of the positive electrode material mixture layer on each surface was 180 μm, and cutting into a width of 24 mm, leaving a rectangular lead portion.

Next, for the negative electrode plate, graphite as a negative electrode host material and polyvinylidene fluoride as a binder were mixed in a weight ratio of 92: 8, and NMP as a solvent was appropriately added to prepare a paste form. . This paste was applied to both surfaces of a copper foil having a thickness of 10 μm as a current collector material and dried. Then, the negative electrode material mixture layer on each surface was pressed to a thickness of 220 μm, leaving a rectangular lead portion and a width of 26 m.
It was made by cutting into m.

The separator has a thickness of 25 μm and a width of 2
An 8 μm polyethylene microporous membrane was used.

The electrolytic solution contains ethylene carbonate: diethyl carbonate = 1: 1 containing 1 mol / l of LiPF _6.
A mixture was prepared by adding 3 parts by weight of 2-methylnaphthalene to 97 parts by weight of the mixed solvent (volume ratio). The battery in which this electrolytic solution was injected was designated as non-aqueous electrolyte secondary battery A.

FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery A 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, 4 is a positive electrode 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.

The battery case 6 has a thickness of 0.3 mm and inner dimensions of 3
The surface of an iron body of 0.0 × 40.0 × 8.0 mm is plated with nickel having a thickness of 5 μm, and a hole (not shown) for injecting an electrolytic solution is provided on the upper side portion. There is.
7 is a case lid, 8 is a safety valve, 10 is a negative electrode terminal, and 11 is a negative electrode lead.

[Comparative Example 1] As a comparative example, Li was added to the electrolytic solution.
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a mixed solution of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) containing 1 mol / l of PF ₆ was used. This was designated as non-aqueous electrolyte battery B.

After the electrode and the separator are sufficiently wet and a quantity (4 ml) of the electrolyte solution which does not exist in the outside of the electrode group free of pressure is injected under reduced pressure, the injection hole is sealed and the designed capacity is 90%.
Five batteries A and B each with 0 mAh, total 1
0 pieces were produced. These batteries A and B have a power supply voltage of 1
An overcharge test was performed by setting the voltage to 0 V and continuously charging at a current of 2C. As a result, after 2 hours from the start of charging, no abnormality such as smoking or ignition was observed in all the batteries of the battery A according to the present invention, whereas the surface of all the batteries of the battery B of the comparative example was observed. The temperature rises above 200 ° C,
Smoke was seen. [Example 2] Five non-aqueous electrolyte secondary batteries C were produced in the same manner as in Example 1 except that 5 parts by weight of cadarine was added to the electrolytic solution instead of 2-methylnaphthalene. In Battery C, when the power supply voltage was set to 10 V and the battery was continuously charged with a current of 2 C, no abnormalities such as smoking and ignition were observed in Battery C according to the present invention.

[Example 3] Seven kinds of non-aqueous electrolyte secondary batteries similar to Example 1 except that the content of 2-methylnaphthalene in the electrolytic solution was changed between 0.01 and 20.0 wt%. Ten batteries D1 to D7 were produced. For comparison, 10 batteries A produced in Example 1 were also produced. Then, an overcharge test and a charge / discharge test were performed on each of these five batteries.

The overcharge test was performed under the same conditions as described in Example 1, and the state of the battery was observed 2 hours after the start of charging. The charge and discharge cycle test was conducted at room temperature with a current of 1
C constant current charging up to 4.1V, constant voltage charging at 4.1V, total charging time 3 hours, then current 1C
Then, constant current discharge was performed up to 2.7V. The average discharge capacity of the 10th cycle of each battery is summarized in Table 1.

[0037]

[Table 1]

As a result, in the overcharge test, 2
-When the content of methylnaphthalene was less than 0.1 wt%, smoke was generated from the battery. In the charge / discharge test, the content of 2-methylnaphthalene in the electrolytic solution was 15w.
When it was t% or more, the discharge capacity was greatly reduced.

As described above, the content of 2-methylnaphthalene in the electrolytic solution in the non-aqueous electrolyte secondary battery according to the present invention is suitably in the range of 0.1 to 10 wt%.

[0040]

INDUSTRIAL APPLICABILITY The non-aqueous electrolyte secondary battery according to the present invention has an electrolytic solution containing 2-methylnaphthalene or α of side chain alkyl group
0.1-10 wt% of naphthalene having tertiary hydrogen in the -position
I am adding. As a result, at the time of overcharge, the positive electrode active material is rapidly oxidized at a potential equal to or lower than the potential at which it is converted into a thermally unstable material, so that there is an effect of preventing thermal runaway of the battery until the shutdown of the separator is completed.

Therefore, as seen in conventional batteries,
It is possible to effectively prevent the risk of battery smoke, ignition, etc. due to the explosive exothermic decomposition reaction during overcharge. As a result, it is possible to provide a non-aqueous electrolyte secondary battery that not only has a high capacity but also further improved safety. Therefore, the industrial value of the present invention is extremely high.

[0042]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery of an example according to the present invention.

[Explanation of symbols]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 2000-156243 (JP, A) JP 2000-58116 (JP, A) JP 7-302614 (JP, A) JP 10-55822 ( JP, A) JP 5-234618 (JP, A) JP 9-45369 (JP, A) JP 2000-58112 (JP, A) JP 2000-58114 (JP, A) JP 2000- 58115 (JP, A) JP 2000-58117 (JP, A) JP 2000-164251 (JP, A) Special Table 2001-525597 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H01M 10/40

Claims (2)

(57) [Claims] 1. 2-Methylnaphthalene or side chain alkyl
0.1-naphthalene having a tertiary hydrogen at the α-position
A non-aqueous electrolyte solution containing 10 wt% is provided,
Non-aqueous electrolyte secondary battery. 2. A tertiary hydrogen is added to the α-position of a side chain alkyl group.
Naphthalene with isopropyl naphthalene, cabbage
At least one selected from the group consisting of
The non-aqueous electrolyte secondary battery according to claim 1, which is a seed .