JP2003115325A - Nonaqueous electrolytic solution and nonaqueous electrolytic solution secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution for a secondary battery wherein safety of the battery in overcharge condition can be secured without giving bad influences on battery characteristics such as low-temperature characteristics and storage characteristics. SOLUTION: This is the nonaqueous electrolytic solution used in the secondary battery provided with the negative electrode and the positive electrode, which is possible to occlude/discharge lithium, and this is containing organic solvent(s), lithium salt(s) as the electrolyte and partly hydrogenated substance(s) of terphenyl, and this is the nonaqueous electrolytic solution characterized that the solubility of the partly hydrogenated substance to this electrolytic solution in the room temperature is 0.5 wt.% or more.

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 solution and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution, and more particularly to a secondary battery which can ensure safety even when overcharged. The present invention relates to a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art With the recent lightening and miniaturization of electric products, the demand for lithium secondary batteries having high energy density is increasing. Furthermore, with the expansion of the application fields of lithium secondary batteries, further improvement in battery characteristics is also demanded. Generally, in a lithium secondary battery, a carbon material capable of inserting and extracting lithium ions is used as a negative electrode active material, and LiCoO ₂ , LiMn is used as a positive electrode active material.
A lithium-containing metal oxide such as ₂ O ₄ or LiNiO ₂ is used, and as the non-aqueous electrolyte, a solvent in which a high dielectric constant solvent and a low viscosity solvent are appropriately mixed and a lithium salt is dissolved is used. In such a lithium secondary battery, lithium released from the positive electrode active material by charging is stored in the negative electrode active material, and lithium released from the negative electrode active material by discharging is stored in the positive electrode active material.

The high-dielectric constant solvent is, for example, a cyclic carbonic acid ester such as ethylene carbonate or propylene carbonate or a cyclic carboxylic acid ester such as γ-butyrolactone, and the low-viscosity solvent is Examples thereof include chain carbonates such as diethyl carbonate and dimethyl carbonate, ethers such as dimethoxyethane and the like. In addition, LiClO ₄ , LiP is used as the lithium salt.
F ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF _{3
SO 3) 2, LiN (CF} 3 CF 2 SO 3) is _2, and the like.

When these lithium secondary batteries are overcharged, as the overcharged state progresses, the positive electrode causes excessive release of lithium, while the negative electrode causes excessive storage of lithium. , Metallic lithium is deposited. Both the positive electrode and the negative electrode in such a state are placed in a thermally unstable state, causing decomposition of the electrolytic solution and rapid heat generation, which causes abnormal battery heat generation and impairs battery safety. The problem arises that Such a problem becomes more remarkable as the energy density of the non-aqueous electrolyte battery increases.

In order to solve the above problems, a technique for ensuring the safety of a battery in an overcharged state by adding a small amount of an aromatic compound to the electrolyte of a non-aqueous electrolyte battery has hitherto been available. Has been proposed to. JP-A-9-106
No. 835, biphenyl and 3-R are used as additives.
-Using a small amount of thiophene (R is bromine atom, chlorine atom, fluorine atom), furan, 3-chlorothiophene,
A method of protecting a battery in an overcharged state and a battery containing these additives have been proposed. This method ensures the safety of the battery at the time of overcharging by increasing the internal resistance of the battery by polymerizing the additive at a voltage higher than the maximum operating voltage of the battery. However, when biphenyl is used as the additive, the solubility of the biphenyl in the electrolytic solution is low because it is a solid, and there is a problem that the additive partially deposits at low temperature and the battery characteristics deteriorate. Furan and 3-chlorothiophene are easily oxidized and have a problem that they adversely affect the battery characteristics.

Further, in JP-A-2000-58116, terphenyl and alkyl group-substituted terphenyl are used as additives, and in JP-A-2001-15158,
P-terphenyl is mentioned as an additive, and the use of a small amount of each of them ensures the safety of the battery at the time of overcharge by the same action. Since these additives are also solids, their solubility is low and battery characteristics such as low temperature characteristics are deteriorated. In particular, m-terphenyl,
Since p-terphenyl has a higher melting point, it does not dissolve in a solvent depending on the type of organic solvent, and there is a problem that it is difficult to put it into practical use as a battery.

[0007]

In view of the problems of the above lithium secondary battery, the present invention effectively acts on overcharging without adversely affecting battery characteristics such as low temperature characteristics and storage characteristics. It is an object of the present invention to provide a non-aqueous electrolyte solution containing the additive and a non-aqueous electrolyte secondary battery using the same.

[0008]

The present invention is a non-aqueous electrolyte containing an organic solvent and a lithium salt as an electrolyte, which is used in a secondary battery having a negative electrode and a positive electrode capable of inserting and extracting lithium. The non-aqueous electrolytic solution contains a partial hydride of terphenyl and the solubility of the partial hydride in the electrolytic solution at room temperature is 0.5% by weight or more. Is.

Further, the present invention is used in a secondary battery provided with a negative electrode and a positive electrode capable of inserting and extracting lithium,
A non-aqueous electrolyte solution containing an organic solvent and a lithium salt as an electrolyte, wherein the non-aqueous electrolyte solution contains a partial hydride of m-terphenyl. Furthermore, the present invention is a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte solution containing a lithium salt as an organic solvent and an electrolyte, the non-aqueous electrolyte secondary battery comprising: The electrolytic solution is one described above, which is a non-aqueous electrolytic solution secondary battery.

Since the non-aqueous electrolyte solution according to the present invention contains a partial hydride of terphenyl such as diphenylcyclohexane and cyclohexylbiphenyl, the secondary battery using the same has a positive electrode on the positive electrode when it reaches an overcharged state. An oxidation reaction occurs, and a polymerization reaction occurs with the generation of hydrogen gas. Since this polymer is a compound that is difficult to dissolve in the non-aqueous electrolyte, it acts as a resistor, increases the internal resistance of the battery, and effectively acts to prevent overcharge.

The partial hydride of terphenyl contained in the electrolytic solution in the present invention has a solubility in the electrolytic solution of 0.5% by weight or more at room temperature. In the electrolytic solution containing such a partial hydride, solids are unlikely to be deposited even at low temperatures, so that the problem of deterioration of battery characteristics does not occur. Among the partial hydrides of terphenyl, the partial hydride of m-terphenyl is preferable. Since this is a liquid at normal temperature, there is almost no risk of solids being deposited in the electrolytic solution containing this even at low temperatures.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. (Non-Aqueous Electrolyte) As the solvent of the non-aqueous electrolyte according to the present invention, an aprotic organic solvent that is commonly used for such an electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, etc., having 3 to 10 carbon atoms.
Cyclic carbonates of dimethyl carbonate, diethyl carbonate,
Chain carbonic acid esters having 3 to 10 carbon atoms such as ethylmethyl carbonate; Cyclic carboxylic acid esters having 4 to 10 carbon atoms such as γ-butyrolactone and γ-valerolactone; 3 carbon atoms such as methyl acetate and methyl propionate 10 chain carboxylic acid esters of 10 to 4 carbon atoms such as tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran
And cyclic ethers having 10 to 10 carbon atoms; chain ethers having 3 to 10 carbon atoms such as dimethoxyethane and dimethoxymethane; and sulfur-containing organic solvents having 4 to 10 carbon atoms such as sulfolane and diethyl sulfone. These can be alone or
You may use it in mixture of 2 or more types.

As the lithium salt, for example, LiCl
Inorganic lithium salts such as O ₄ , LiPF ₆ , and LiBF ₄ , L
iCF ₃ SO ₃ , LiN (CF ₃ SO ₃ ) ₂ , LiN
_{(CF 3 CF 2 SO 3)} 2, LiN (CF 3 SO 3)
Fluorine-containing organic lithium salts such as (C ₄ F ₉ SO ₂ ) and LiC (CF ₃ SO ₃ ) ₃ that are known to be usable as the electrolyte of such an electrolytic solution may be used. Particularly, it is preferable to use LiPF ₆ or LiBF ₄ . These lithium salts may be used alone or in combination with
You may use it in mixture of 2 or more types.

The molar concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 2.0 mol / liter. Generally, when the molar concentration is out of this range, problems such as a decrease in electric conductivity of the electrolytic solution and precipitation of a lithium salt at low temperature occur. The terphenyl partial hydride is a compound in which hydrogen has been added to some of the double bonds of the benzene ring of terphenyl, but the double bonds still remain. Terphenyl may be o-, m- or p-, but is preferably m-terphenyl.

The partial hydride of terphenyl may be a single compound or a mixture of a plurality of compounds. For example, a mixture of two or more terphenyl partial hydrides having different hydrogenation rates can be used. It is also possible to use a mixture of partially hydrogenated terphenyls having the same hydrogenation rate but different positions of hydrogenated double bonds.

The terphenyl partially hydrogenated product used in the present invention is required to have a solubility in an electrolytic solution at room temperature of 0.5% by weight or more. An electrolytic solution containing a partial hydride of terphenyl having a solubility in the electrolytic solution of less than 0.5% by weight is unsuitable because of a large risk of solid precipitation at low temperatures. The solubility at room temperature in the electrolytic solution is preferably 1.0% by weight or more, and more preferably 1.5% by weight or more.

The term "room temperature" used to measure the solubility means
Means 25 ° C. The partial hydrogenation rate of terphenyl is 0% when the hydrogen atom is not added to the double bond of the benzene ring of terphenyl, and the complete hydride of terphenyl, that is, all the double bonds. It is a value calculated assuming that the hydrogenation rate of hydrogen atoms added to is 100%, and in the case of a mixture, it is an average value. Since 9 mol of hydrogen molecules can be added to 1 mol of terphenyl, the hydrogenation rate of 1 mol of hydrogen molecules is 11.1 (= 1 /
9 × 100)%.

The partial hydride of terphenyl can be synthesized, for example, by reacting terphenyl with hydrogen in the presence of a hydrogenation catalyst such as platinum, palladium or nickel. The reaction product is usually a mixture of several partial hydrides, but this can be used as it is, or the partial hydride can be obtained as a single compound by separating and purifying by a conventional method. In addition, a partial hydride of terphenyl is obtained by an organic synthetic reaction using cyclohexane, cyclohexylmagnesium halide, cyclohexyllithium, cyclohexene, cyclohexadiene, benzene, cyclohexylbenzene, halogenated benzene, etc. as a raw material, not by hydrogenation reaction of terphenyl. It can also be synthesized.

The lower limit of the hydrogenation rate of the partially hydrogenated terphenyl used in the present invention is preferably 30% or more, particularly 35% or more, from the viewpoint of the storage characteristics of the battery and the solubility in the electrolytic solution. Also, the upper limit is preferably 70% or less, particularly preferably 60% or less. The content of the partial hydride of terphenyl is preferably 0.01% by weight or more, more preferably 0.1% by weight based on the total amount of the non-aqueous electrolyte solution from the viewpoints of the overcharge suppressing effect and the electric conductivity. It is preferably at least 0.5% by weight, particularly preferably at least 0.5% by weight. The upper limit is preferably 10% by weight or less, more preferably 5% by weight.
It is particularly preferably 3% by weight or less.

Further, the non-aqueous electrolyte of the present invention contains a vinylene carbonate compound, vinyl ethylene carbonate, phenyl ethylene carbonate, for the purpose of improving cycle characteristics and charge / discharge efficiency.
Additives such as succinic anhydride can be included.
In particular, the general formula (I):

[0021]

[Chemical 2]

A vinylene carbonate compound represented by the formula (wherein R ₁ and R ₂ are each independently a hydrogen atom or a methyl group) is added in an amount of 0.1 to 1 with respect to the total weight of the non-aqueous electrolyte.
It is preferable to contain 0% by weight. Further, the non-aqueous electrolyte solution of the present invention contains sulfites such as ethylene sulfite, propylene sulfite and dimethyl sulfite; sulfones such as propane sultone, butane sultone, methyl methane sulfonate and methyl toluene sulfonate for the purpose of improving storage characteristics. Acid ester; Sulfate such as dimethyl sulfate and ethylene sulfate; Sulfone such as sulfolane, dimethyl sulfone and diethyl sulfone; Sulfoxide such as dimethyl sulfoxide, diethyl sulfoxide and tetramethylene sulfoxide; Sulfide such as diphenyl sulfide and thioanisole; Diphenyl disulfide, di Additives such as disulfides such as pyridinium disulfide can be included. Further, for the purpose of improving low temperature characteristics, an additive such as fluoro-substituted benzene such as fluorobenzene can be contained. (Negative Electrode) The negative electrode is not particularly limited as long as it can absorb and release lithium, but it is preferable to contain a carbonaceous material capable of absorbing and releasing lithium as a negative electrode active material. Specific examples of the carbonaceous material include thermal decomposition products of organic substances under various thermal decomposition conditions, artificial graphite, natural graphite and the like.

These carbonaceous materials preferably have a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.340 nm as determined by X-ray diffraction by Gakushin method.
It is more preferably 0.335 to 0.337 nm. The ash content in the carbonaceous material is preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less, based on the total weight of the carbonaceous material. preferable. The crystallite size (Lc) determined by X-ray diffraction by Gakshin method is preferably 30 nm or more, more preferably 50 nm or more, and 100 nm.
The above is particularly preferable.

The above charcoal produced by the laser diffraction / scattering method
The median diameter of the substance is preferably 1 to 100 μm.
More preferably, it is 3 to 50 μm or less,
More preferably, it is 40 μm, and it is 7 to 30 μm.
Is particularly preferable. The BET specific surface area is 0.3 to 25.
0m^Two/ G is preferred, 0.5-20.0 m ^Two
/ G is more preferable, 0.7-15.0 m^Two/
More preferably g, 0.8-10.0 m^Two/ G
Is particularly preferable. Also, argon ion laser
-In Raman spectrum analysis using light, 1580
~ 1620 cm ^-1Range peak P_A(Peak intensity I
_A) And 1350-1370 cm^-1Range peak P
_B(Peak intensity I_B) Intensity ratio R = I_B/ I_AIs 0
1.2 is preferable, 1580 to 1620 cm^-1Range of
The half-width of the peak of is 26 cm^{− 1}Below, especially 25 cm
^-1The following is preferable.

Further, amorphous carbon is formed on at least a part of the surface of the carbonaceous material by mixing and firing the carbonaceous material with an organic material or the like, or by using a CVD method or the like. The material can also be suitably used as the carbonaceous material. Examples of such organic matter include coal tar pitch from soft pitch to hard pitch; heavy coal oil such as dry distillation liquefied oil; direct current heavy oil such as atmospheric residual oil and vacuum residual oil; crude oil, naphtha, etc. Examples include petroleum heavy oils such as cracked heavy oils (for example, ethylene heavy ends) that are by-produced during thermal decomposition. Moreover, these heavy oils are heated to 200 to 400 ° C.
It is also possible to use a solid residue obtained by distilling in 1., which is pulverized to 1 to 100 μm. Further, a precursor such as a vinyl chloride resin or a phenol resin or an imide resin can be used.

Examples of the negative electrode active material capable of inserting and extracting lithium other than carbonaceous materials include metal oxide materials such as tin oxide and silicon oxide, lithium metal, and various lithium alloys. These negative electrode active materials containing the carbonaceous material may be used alone or in combination of two or more.
The method for producing a negative electrode using these negative electrode active materials is not particularly limited. For example, a negative electrode can be produced by adding a binder, a thickener, a conductive material, a solvent and the like to the negative electrode active material to form a slurry, applying the slurry to the substrate of the current collector, and drying. it can. Alternatively, the negative electrode active material may be directly roll-formed into a sheet electrode, or may be compression-formed into a pellet electrode.

The binder that can be used in the production of the negative electrode is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolytic solution used in the production of the electrode. For example, polyvinylidene fluoride, polytetrafluoroethylene, styrene
Examples thereof include butadiene rubber, isoprene rubber, butadiene rubber and the like. Examples of the thickener that can be used for producing the negative electrode include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

As the conductive material that can be used for manufacturing the negative electrode, a metal material such as copper or nickel, graphite,
Examples include carbonaceous materials such as carbon black.
As the material of the negative electrode current collector, a metal such as copper, nickel or stainless steel is used, and among these, a copper foil is preferable from the viewpoints of being easily processed into a thin film and cost. (Positive Electrode) The positive electrode constituting the battery of the present invention is not particularly limited as long as it can store and release lithium, but it is preferable to use a lithium transition metal composite oxide as a positive electrode active material. Examples of the lithium transition metal composite oxide include lithium cobalt composite oxide such as LiCoO ₂ , lithium nickel composite oxide such as LiNiO ₂ , and L
Examples thereof include lithium manganese composite oxides such as iMn ₂ O ₄ . In particular, a lithium transition metal composite oxide containing cobalt and / or nickel is preferable. In these lithium-transition metal composite oxides, some of the main transition metal elements are Al, Ti, V, Cr, Mn, Fe, Co,
It can be stabilized by substituting with other metal species such as Li, Ni, Cu, Zn, Mg, Ga, and Zr.
Further, the lithium-transition metal composite oxide thus stabilized is more preferable. These positive electrode active materials alone,
You may use it in mixture of 2 or more types.

The method for producing the positive electrode is not particularly limited, and it can be produced according to the above-mentioned method for producing the negative electrode. Regarding its shape, a binder, a conductive material, a solvent, etc. are added to the positive electrode active material as needed, and mixed, and then coated on a substrate of a current collector to form a sheet electrode, or subjected to press molding. It can be a pellet electrode. Examples of the binder, the conductive agent, the solvent and the like are similar to those mentioned in the above method for producing the negative electrode.

As the material of the positive electrode current collector, a metal such as aluminum, titanium, tantalum, or an alloy thereof can be used. Among these, aluminum or its alloy is particularly lightweight, and thus is desirable in terms of energy density. The material and shape of the separator used in the battery of the present invention are not particularly limited. It is preferable to select from materials that are stable to non-aqueous electrolytes and have excellent liquid retention,
It is preferable to use a porous sheet or non-woven fabric made of polyolefin such as polyethylene or polypropylene as a raw material.

The method for producing the battery of the present invention having at least the negative electrode, the positive electrode and the non-aqueous electrolyte solution is not particularly limited, and can be appropriately selected from the commonly used methods. Further, the shape of the battery is not particularly limited, and for example, a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, and the like. Can be mentioned.

[0032]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples unless it exceeds the gist. Example 1 [Preparation of Non-Aqueous Electrolyte Solution] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3: 7 under a dry argon atmosphere. After sufficiently dried lithium hexafluorophosphate (LiPF ₆ ) was dissolved in this mixed solvent at a rate of 1 mol / liter, a partial hydride of m-terphenyl having a hydrogenation rate of 40% was added to the total weight of the electrolytic solution. To 2% by weight to prepare an electrolytic solution. This electrolytic solution is referred to as electrolytic solution 1. The solubility of this m-terphenyl partial hydride in the electrolytic solution at room temperature was 3% by weight or more.

The partial hydrides of terphenyl used in Examples and Comparative Examples are produced by reacting terphenyl with hydrogen gas under high temperature and pressure conditions in the presence of platinum, palladium, or nickel catalyst. What was done was used. Further, the partial hydrogenation rate was determined as an average value from the composition ratio of the partial hydride of terphenyl obtained by gas chromatography analysis (hereinafter, the same applies to all). [Fabrication of Negative Electrode] As the negative electrode active material, the d value of the lattice plane (002 plane) in X-ray diffraction was 0.336 nm, the crystallite size (Lc) was 100 nm or more (652 nm), the ash content was 0.07% by weight, and the laser was used. The median diameter by the diffraction / scattering method is 12 μm, the BET method specific surface area is 7.5 m ² / g, and the peak P in the range of 1580 to 1620 cm ⁻¹ in the Raman spectrum analysis using an argon ion laser beam.
_A (peak intensity I _A ) and 1350 to 1370 cm ⁻¹
Intensity ratio R = I of peak P _B (peak intensity I _B ) in the range
_B / _{I A} natural graphite powder half width of a peak in the range of 0.12,1580～1620Cm ^-1 is 19.9cm ^-1 (Kansai Thermochemical Co., NG-7) polyvinylidene fluoride 94 parts by weight (PVDF) (KF-1 manufactured by Kureha Chemical Co., Ltd.
000) 6 parts by weight and mixed with N-methyl-2-pyrrolidone (NMP) to form a slurry. This slurry-like mixture was evenly applied to both sides of a copper foil having a thickness of 18 μm, which is a negative electrode current collector, and then passed through a drier to remove NMP used at the time of making the slurry and dried, and then, It was rolled by a roll press machine to obtain a negative electrode plate. [Preparation of Positive Electrode] As a positive electrode active material, 6 parts by weight of carbon black and 9 parts by weight of PVDF (KF-1000, manufactured by Kureha Chemical Co., Ltd.) were added to 85 parts by weight of LiCoO ₂ and mixed to obtain NMP.
To form a slurry. This slurry-like mixture was evenly applied on both sides of a positive electrode current collector, 20 μm thick aluminum foil, and then passed through a drier to remove NMP used during slurry preparation and dried, and then, A positive electrode plate was obtained by rolling with a roll press. [Production of Battery] The negative electrode plate and the positive electrode plate produced as described above are stacked and wound together with a separator made of a microporous film of polyethylene so as not to come into direct contact, and the outermost periphery is fixed with a tape to form a spiral electrode body. did. Then, FIG.
As shown in FIG.
After installing, the electrode body was inserted into the stainless battery case that also functions as the negative electrode terminal formed into a cylindrical shape through the opening. Then, the negative electrode lead 6 connected to the negative electrode of the electrode body is welded to the inner bottom portion of the battery case 1, and the positive electrode lead 5 connected to the positive electrode of the electrode body is increased to a predetermined gas pressure inside the battery. It welded with the bottom part of the current interruption device 8 which operates when it becomes above. Moreover, an explosion-proof valve and a current interrupt device were attached to the bottom of the sealing plate 2. Then, after injecting the electrolytic solution 1, the battery case 1 is sealed at the opening with a sealing plate and an insulating gasket 3 made of polypropylene (PP),
Battery 1 was used. Examples 2 to 6 and Comparative Examples 1 to 3 In Example 1, EC and EMC were mixed at a volume ratio of 3: 7, and LiPF ₆ was dissolved in this mixed solvent at a ratio of 1 mol / liter, and then an additive was added. In addition, batteries 1 to 6 and comparative batteries 1 and 2 were produced in the same manner except that various electrolytic solutions having the compositions shown in Table 1 (electrolytic solutions 1 to 6 and comparative electrolytic solutions 1 and 2) were prepared. The solubility of the terphenyl partial hydride in each of the electrolytic solutions 2 to 6 at room temperature is
All were 3% by weight or more.

As Comparative Example 3, unhydrogenated m-terphenyl was added in an amount of 2% by weight based on the total weight of the electrolytic solution.
However, m-terphenyl was not dissolved and a battery could not be prepared. The batteries 1 to 6 and the comparative batteries 1 and 2 obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were tested for battery safety, low temperature characteristics and storage recovery rate in an overcharged state. [Overcharge test] The above batteries 1 to 6 and comparative batteries 1 to 2
Is charged at room temperature (25 ° C.) with a charging current of 1 C until the battery voltage reaches 4.2 V, and then charged at a constant voltage of 4.2 V for 2.5 hours to be in a fully charged state. Further, as an overcharge test, a charging current of 1 C was applied to each battery for overcharging, and the time from when the current started to flow until the current interrupt device was activated and the maximum temperature of each battery at that time were measured.
The results are shown in Table 1. If the time until the current interruption device operates is short and the maximum temperature of the battery is low, the safety of the battery in overcharging is excellent. [Low temperature characteristics] The above batteries 1 to 6 and comparative batteries 1 and 2 are
1. Charge the battery at room temperature (25 ° C.) until the battery voltage reaches 4.2V with a charging current of 1C, and then 2. at a constant voltage of 4.2V.
It was charged for 5 hours to be in a fully charged state. Furthermore, after resting for 3 hours at room temperature, the battery voltage is 3V with a discharge current of 1C at room temperature.
Discharge from the discharge time to the discharge capacity (m
Ah) was determined.

Next, the above batteries 1 to 6 and the comparative batteries 1 to
2 was charged at a room temperature (25 ° C.) with a charging current of 1 C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V for 2.5 hours to be a fully charged state. Furthermore, 0 ℃
After resting for 3 hours at 0 ° C., the battery was discharged at a discharge current of 1 C until the battery voltage became 3 V, and the discharge capacity (mAh) at room temperature was obtained from the discharge time.

Based on the discharge capacity values at room temperature and 0 ° C. obtained above, the ratio of the discharge capacity at 0 ° C. to the discharge capacity at room temperature was calculated as the low temperature characteristic by the following formula. The results are shown in Table 1. The one having a high low temperature characteristic (%) is excellent in the low temperature characteristic. Low temperature characteristics (%) = (0 ° C. discharge capacity (mAh)) ÷ (room temperature discharge capacity (mAh)) × 100 (%) [Recovery rate after storage] Batteries 1 to 6 and comparative batteries 1 and 2
Was charged at room temperature (25 ° C.) with a charging current of 1 C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V for 2.5 hours to reach a fully charged state. Further, after resting for 3 hours at room temperature, the battery was discharged at room temperature with a discharge current of 1 C until the battery voltage became 3 V, and the discharge capacity (mAh) at room temperature was determined from the discharging time.

Further, with a charging current of 1 C, the battery is charged again at room temperature (25 ° C.) until the battery voltage reaches 4.2 V, and then the battery is charged at a constant voltage of 4.2 V for 2.5 hours to reach a fully charged state. After that, it was stored in an atmosphere of 60 ° C. for 20 days. Next, the above batteries 1 to 6 and comparative batteries 1 and 2 were
The battery is discharged at a discharge current of C until the battery voltage becomes 3V, and then at room temperature (25 ° C) until the battery voltage becomes 4.2V at a charge current of 1C, and then at a constant voltage of 4.2V for 2 Charge the battery for 5 hours to fully charge it. Further, after resting for 3 hours at room temperature, the battery was discharged at room temperature with a discharge current of 1 C until the battery voltage became 3 V, and the discharge capacity (mAh) at room temperature was determined from the discharging time.

Based on the discharge capacity values before storage at 60 ° C. and after storage at 60 ° C., the ratio of the discharge capacity after storage to the discharge capacity before storage was defined as the recovery rate after storage as shown below. Calculated by formula. The results are shown in Table 1. A material having a high recovery rate (%) after storage has excellent storage characteristics. Recovery rate after storage (%) = (discharge capacity after storage (mAh)) /
(Discharge capacity before storage (mAh)) x 100 (%)

[0039]

[Table 1]

From Table 1 above, Comparative Battery 1 containing no additive that suppresses overcharge has excellent low-temperature characteristics and storage characteristics, but bursts after 51 minutes in the overcharge test. Further, the comparative battery 2 using o-terphenyl that is not partially hydrogenated as an additive has a high maximum temperature in the overcharge test, and the low temperature characteristics and the storage characteristics are not preferable. further,
In Comparative Example 3, m-terphenyl that was not partially hydrogenated was used as an additive. However, since m-terphenyl was not dissolved in the electrolytic solution and could not be used as a battery, it was not possible to compare the respective characteristics. It was

On the other hand, in the batteries 1 to 6 of the present invention containing the partial hydride of terphenyl, the current cutoff time was shortened in the overcharge test, and the maximum temperature was suppressed to 80 to 83 ° C.
Excellent low temperature characteristics and storage characteristics.

[0042]

EFFECTS OF THE INVENTION By selecting a partial hydride of terphenyl having a solubility in the electrolyte of a specific value or more as an additive of the electrolyte of the non-aqueous electrolyte secondary battery, low temperature characteristics and storage characteristics can be obtained. It is possible to secure the safety of the battery in the overcharged state without adversely affecting the battery characteristics such as, and to contribute to the miniaturization, high performance and safety of the non-aqueous electrolyte secondary battery. it can.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a cylindrical battery in an example of the present invention and a comparative example.

[Explanation of symbols]

1 battery case 2 Seal plate 3 Insulation gasket 4 spiral electrode body 5 Positive lead 6 Negative electrode lead 7 Insulation ring 8 Current breaker

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Shizuka             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation F term (reference) 5H029 AJ12 AK03 AK18 AL06 AL07                       AL18 AM03 AM04 AM05 AM07                       BJ02 CJ08 HJ00 HJ01 HJ02                       HJ13                 5H050 AA15 BA17 CA08 CA09 CA29                       CB07 CB08 CB29 FA19 GA10                       HA01 HA02 HA13

Claims (9)

[Claims] 1. A non-aqueous electrolyte used in a secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, which is an organic solvent, a lithium salt as an electrolyte, and a partial hydride of terphenyl. And a solubility of the partial hydride in the electrolytic solution at room temperature of 0.5% by weight or more. 2. The non-aqueous electrolyte solution according to claim 1, wherein the terphenyl is m-terphenyl. 3. A non-aqueous electrolytic solution used in a secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, which comprises an organic solvent, a lithium salt as an electrolyte, and m.
A non-aqueous electrolyte solution containing a partial hydride of terphenyl. 4. The hydrogenation rate of a partial hydride of terphenyl is 30 to 70%, wherein
The non-aqueous electrolyte solution according to any one of 3 above. 5. The content of the partial hydride of terphenyl is 0.01 to 10% by weight, based on the total weight of the non-aqueous electrolyte solution, according to any one of claims 1 to 4. The non-aqueous electrolyte solution according to item 1. 6. The non-aqueous electrolyte solution has the general formula (I): (Wherein R ₁ and R ₂ are each independently a hydrogen atom or a methyl group) is contained in an amount of 0.1 to 10% by weight based on the total weight of the non-aqueous electrolyte solution. The non-aqueous electrolyte solution according to any one of claims 1 to 5, wherein 7. A non-aqueous electrolytic solution comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and the non-aqueous electrolytic solution according to any one of claims 1 to 6. Secondary battery. 8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the positive electrode contains a lithium cobalt composite oxide or a lithium nickel composite oxide. 9. The negative electrode has a lattice plane (00
The non-aqueous electrolyte secondary battery according to claim 7 or 8, comprising a carbonaceous material having a d value on the second surface of 0.335 to 0.340 nm.