JP2003157892A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery having high safety upon overcharge, and superior in high temperature storage characteristic. SOLUTION: This nonaqueous secondary battery has metallic oxide as a positive electrode active material, a carbon material or an Li insertable material as a negative electrode active material, and a nonaqueous electrolyte, and includes a compound A of bonding an alkyl group to benzene ring and a phosphate B in the nonaqueous electrolyte, and is constituted by setting the content of a triester phosphate B to 0.1 mass % to 10 mass % to the compound A. Cyclohexyl benzene is desirable as the compound A. The triester phosphate such as a trioctyl phosphate, a diester phosphate such as a dioctyl phosphate, and a monoester phosphate such as an octyl phosphate are desirable as the phosphate B. This invention is desirably applied to the nonaqueous secondary battery having a battery form of a square battery and a laminate battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery, and more particularly to a non-aqueous secondary battery having high safety during overcharge and excellent high temperature storage characteristics.

[0002]

2. Description of the Related Art A non-aqueous secondary battery represented by a lithium ion battery using a metal oxide as a positive electrode active material and a carbon material as a negative electrode active material has high voltage and high energy density. The demand is increasing. However, since safety decreases as the energy density increases, improving safety becomes more important in a high energy density battery. Moreover, since the energy density tends to decrease in the usual safety measures, it is desired to improve the safety while maintaining the energy density.

In order to meet the above demands, biphenyl (Japanese Patent Laid-Open No. 9-171840) and cyclohexylbenzene (Japanese Patent Laid-Open No. 2001) have been used as compounds for polymerizing at a high voltage to improve safety during overcharge. -015
No. 155) has been proposed. These additives facilitate the operation of the current cutoff valve due to the generation of gas at the time of overcharge, and the safety is ensured by the combined use with the current cutoff valve.

However, in the prismatic battery, since the current cutoff valve is not normally installed, the safety improving effect of these additives is sufficient compared with the cylindrical battery in which the current cutoff valve is installed. There wasn't. For example, the inventors of the present invention have studied that adding a small amount, that is, about 2% by mass has little effect of improving safety during overcharge,
In addition, the stability of the additive itself is not sufficient in the charged state, so if the battery is left at high temperature for a long time, the positive electrode reacts with the electrolytic solution to cause decomposition of the electrolytic solution and the decomposition of the electrolytic solution. There is a problem that the gas generated by this causes the battery to swell and the internal resistance to increase.

When the electrolytic solution is decomposed and gas is generated inside the battery as described above, the cylindrical battery has a high pressure resistance of the battery case as an outer packaging material, and therefore, the increase in the internal pressure of the battery is sufficient. However, in a prismatic battery or a laminated battery (a battery in which a laminated film having a metal foil such as an aluminum foil as a core material is packaged) is not sufficiently resistant to pressure, the battery swells (swells), and The external dimensions change, so that the battery does not fit in the predetermined space and cannot be completely filled, or the appearance is deteriorated. Therefore, it is desired to establish a means for generating less gas during storage and improving safety during overcharge.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the problems in the non-aqueous secondary battery as described above, has high safety during overcharge, has less gas generation during high temperature storage, and has high temperature storage. An object is to provide a non-aqueous secondary battery having excellent characteristics.

[0007]

According to the present invention, a metal oxide is used as a positive electrode active material, a carbon material or a material into which Li can be inserted is used as a negative electrode active material, and a non-aqueous electrolytic solution (hereinafter simply referred to as "electrolytic solution") is used. In the non-aqueous secondary battery having a), a compound (A) having an alkyl group bonded to a benzene ring and a phosphoric acid ester (B) are contained in an electrolytic solution, and the content of the phosphoric acid ester (B) is The above problem is solved by adjusting the content of the compound (A) to 0.1% by mass or more and 10% by mass or less.

In the present invention, the phosphoric acid ester (B) is represented by the general formula (R ₁ O) ₃ P═O (R _{1 is} an alkyl group having 1 or more carbon atoms), and is generally a phosphoric acid triester. The phosphoric acid diester represented by the formula (R ₂ O) ₂ P (OH) = O (R ₂ : an alkyl group having 1 or more carbon atoms) and the general formula (R ₃ O) P (OH) ₂ = O (R ₃ : Alkyl group having 1 or more carbon atoms), at least one selected from the group consisting of phosphoric acid monoesters represented by formula (3), wherein the compound (A) having an alkyl group bonded to the benzene ring is 3% by mass in the electrolytic solution.
The content of the phosphoric acid ester (B) is 0.1 mass% or more and 5 mass% or less with respect to the compound (A), and the form of the non-aqueous secondary battery is a prismatic battery or A preferred embodiment is a laminated battery.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is necessary that the electrolytic solution contains a compound (A) having an alkyl group bonded to a benzene ring and a phosphoric acid ester (B).
Examples of the compound (A) include cyclohexylbenzene, isopropylbenzene, n-butylbenzene,
Examples thereof include octylbenzene, toluene, xylene, and derivatives thereof. Particularly, cyclohexylbenzene having a carbon bonded to a benzene ring having hydrogen or a derivative thereof is preferable because it improves safety during overcharge.
In addition, the alkyl group is preferably long to some extent (having 4 or more carbon atoms) and has a sterically bulky structure such as a branched structure. Among such compounds (A), cyclohexylbenzene and derivatives thereof are particularly preferable.

The content of the compound (A) having an alkyl group bonded to the benzene ring in the electrolytic solution is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 4% by mass or more, and 10 mass% or less is preferable, 7 mass% or less is more preferable, and 6 mass% or less is further preferable. That is, by setting the content of the compound (A) in the electrolytic solution in the range of 1 to 10 mass% as described above, the swelling of the battery due to high temperature storage is suppressed and the safety during overcharge is improved. be able to.

The phosphoric acid ester (B) is not particularly limited, but for example, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, trihexyl phosphate, trioctyl phosphate and the like are commonly used. Phosphoric acid triester represented by the formula (R ₁ O) ₃ P═O (R ₁ : an alkyl group having 1 or more carbon atoms), dimethyl phosphate, diethyl phosphate, dipropyl phosphate, dibutyl phosphate, phosphoric acid Dihexyl, dioctyl phosphate, and other general formulas (R ₂ O) ₂ P (O) (OH) (R ₂ : alkyl group having 1 or more carbon atoms) and the like, diester phosphate, methyl phosphate, ethyl phosphate , Propyl phosphate, butyl phosphate, hexyl phosphate, octyl phosphate, etc.
A phosphoric acid monoester represented by ( ₃ O) P (O) (OH) ₂ (R ₃ : an alkyl group having 1 or more carbon atoms) or the like is preferable. The carbon numbers of R ₁ , R ₂ and R ₃ may be large even if they are large, but it is practical that all of them are about 10.

Compound (A) of the above phosphoric acid ester (B)
To 10% by mass or less, preferably 5% by mass or less, more preferably 2.5% by mass or less, and 0.1% by mass or more, and 1% by mass. % Or more is preferable, and 2% by mass or more is more preferable. Regarding the action of this phosphoric acid ester (B),
At present, it is not always clear, but it is estimated as follows. That is, by mixing a small amount of the phosphoric acid ester (B) with the compound (A), the phosphoric acid ester (B) reacts with the active site of the positive electrode before charging the active site of the positive electrode during charging. It is considered that since the reaction of the compound (A) on the positive electrode is adjusted by partially discharging the compound and forming a thin film on the surface of the positive electrode, swelling of the battery can be suppressed. However, when the amount of the phosphoric acid ester (B) is larger than that of the compound (A), the phosphoric acid ester (B) also affects the swelling of the battery and increases the impedance. 10 mass% or less. If the amount of the phosphoric acid ester (B) is too small, the discharge at the active site of the positive electrode will be insufficient or a sufficient film cannot be formed. Therefore, it is necessary to mix it in a certain amount. It is necessary that the content is 0.1% by mass or more based on the compound (A).

In the present invention, the electrolytic solution is usually used in a liquid state, but it may be used in the form of gel with a gelling agent.

As the electrolytic solution, a nonaqueous electrolytic solution prepared by dissolving an electrolyte salt such as a lithium salt in a nonaqueous solvent such as an organic solvent is used, and the nonaqueous solvent is, for example, ethylene carbonate. Carbonates such as propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, and esters such as γ-butyrolactone and methyl acetate can be used. In addition to the above, non-aqueous solvents such as ethers such as 1,3-dioxolane and 1,2-dimethoxyethane, sulfur compounds such as sulfolane, nitrogen-containing compounds, silicon-containing compounds, fluorine-containing compounds, phosphorus-containing compounds, etc. They can be used alone or in combination of two or more.

In preparing the electrolytic solution, examples of the electrolyte salt to be dissolved in the non-aqueous solvent include LiPF ₆ and LiC.
_{F 3 SO 3 LiC n F 2n} + 1 SO 3 , such as (n> 1), L
iClO ₄ , LiBF ₄ , LiAsF ₆ , (C _n F _{2n + 1}
SO ₂ ) (C _m F _{2m + 1} SO ₂ ) NLi (m, n ≧ 1),
(RfOSO ₂ ) ₂ NLi [Rf is an alkyl group containing a halogen having 2 or more carbon atoms, Rf may be the same or different, and Rf's are bonded to each other. It may be bonded, for example, in a polymer form. Examples of Rf bound to a polymer include, for example, (CH ₂ (CF ₂ ) ₄ CH ₂ OSO ₂ N
(Li) SO ₂ O) _n (where n is an integer), or the like, and two or more of them may be used in combination. In particular, LiPF ₆ and C 2 or more may be used. Fluoroorganic lithium salts and the like are preferable. The electrolyte salt is usually added to the non-aqueous solvent in an amount of 0.1 to 2 mol.
It is preferable to dissolve about 1 / l.

In order to gelate the above-mentioned electrolytic solution into a gel, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or vinylidene fluoride-hexafluoropropylene copolymer is used. , A method in which the linear polymer is dissolved in an electrolytic solution by heating, and then the electrolytic solution is gelated by cooling, or a monomer or prepolymer that can be polymerized by active rays such as ultraviolet rays is used in the electrolytic solution. A method is employed in which the monomer, prepolymer, etc. are polymerized by irradiating the electrolytic solution in which the monomer, prepolymer, etc. are dissolved, with active light, and the polymer is gelled with the polymer.

Also, the sulfur compound may be contained in the electrolytic solution.
This helps to reduce the swelling of the battery.
It is preferable because As the sulfur compound, especially -O
SO ₂Those having a bond are preferred, such io
Specific examples of the compound include, for example, 1,3-propane
Sultone, methyl ethyl sulfonate, diethyl monkey
And the like, particularly 1,3-propane salt
Is preferred. And in the electrolyte of this sulfur compound
The content is preferably 0.5% by mass or more, and 1% by mass
% Or more is more preferable, and 10% by mass or less is preferable.
5 mass% or less is more preferable.

In the present invention, a metal oxide is used as the positive electrode active material, and as such a metal oxide,
For example, lithium cobalt oxide such as LiCoO ₂ ,
LiMn ₂ O ₄ and other lithium manganese oxides, LiN
LiNiO ₂ and other lithium nickel oxide, LiNiO ₂ LiCo _x Ni _1-x O in which a part of Ni is replaced with Co
₂ (0 <x <1), manganese oxide, vanadium pentoxide,
Examples include chromium oxide, but especially LiNiO ₂ ,
LiCoO ₂ , LiMn ₂ O ₄ , LiCo _x Ni _{1- x} O
Positive open circuit voltage when charged, such as ₂ Li
A lithium composite oxide showing 4.2 V or more as a standard is preferable, and a lithium composite oxide showing 4.3 V or more as a Li standard is particularly preferable.

In preparing the positive electrode, a conductive auxiliary agent and a binder are usually used in addition to the above positive electrode active material.
Various materials can be used as the conductive additive, but especially a carbon material is used, and the amount in the positive electrode mixture (that is, the mixture of the positive electrode active material, the conductive additive and the binder) is 5% by mass or less. Preferably. This is because when the amount of the carbon material as the conductive additive in the positive electrode mixture is more than 5% by mass, gas may be generated due to the reaction with the electrolytic solution solvent in the charged state. The amount of the carbon material is preferably 3% by mass or less in the positive electrode mixture, more preferably 2.5% by mass or less, and if too small, the conductivity of the positive electrode is lowered. Since it tends to deteriorate the battery characteristics, it is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more.

The carbon material of the conductive additive in the positive electrode is not particularly limited, but it is preferable to use carbon black having low crystallinity because the swelling of the battery during high temperature storage can be suppressed. It is preferable to partially use graphite having high crystallinity in combination with this carbon black having low crystallinity because the conductivity is improved and the amount of the conductive additive used can be reduced. As described above, when carbon black having low crystallinity and graphite having high crystallinity are used together as the conductive additive, the amount of carbon black having low crystallinity is preferably 50% by mass or more based on the total conductive additive. More preferably 70% by mass or more, and 95% by mass
It is preferably not more than 80% by mass, more preferably not more than 80% by mass.

In producing the positive electrode, as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, styrene butadiene rubber, fluororubber, etc. can be used.

For the positive electrode, a positive electrode mixture is prepared by adding a conductive additive and a binder to the positive electrode active material and mixing them, and the positive electrode mixture is dispersed in a solvent to prepare a positive electrode mixture-containing paste ( The binder may be dissolved or dispersed in a solvent in advance and then mixed with a positive electrode active material, a conductive auxiliary agent, or the like), and the positive electrode mixture-containing paste is applied to a positive electrode current collector such as an aluminum foil, It is prepared by drying to form a positive electrode material mixture layer and, if necessary, undergoing pressure molding. However, the method for producing the positive electrode is not limited to the above-exemplified method, and another method may be used.

A carbon material or a material into which Li can be inserted is used as the active material of the negative electrode. Examples of the carbon material include graphite, pyrolytic carbons, cokes, glassy carbons, and organic materials. A high-molecular compound fired body, mesocarbon microbeads, carbon fiber, activated carbon, graphite, carbon colloid, and the like are preferably used.
Examples of insertable materials include metal oxides and metal nitrides into which Li can be inserted, and examples of the metal oxide into which Li can be inserted include metal oxides containing tin and silicon (for example, S _n O _x , SiO _x, etc.) are preferably used.

For the negative electrode, a binder similar to that used in the case of the positive electrode and a conductive auxiliary agent, if necessary, are added to the negative electrode active material and mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent. To prepare a negative electrode mixture-containing paste (the binder may be dissolved or dispersed in a solvent in advance and then mixed with a negative electrode active material, etc.), and the negative electrode mixture-containing paste is applied to a negative electrode current collector, It is prepared by drying to form a negative electrode mixture layer and, if necessary, a step of pressure molding. However, the method for producing the negative electrode is not limited to the above-described example, and other methods may be used.

Examples of the current collector used for producing the positive electrode and the negative electrode include foils of aluminum, copper, nickel, stainless steel, punching metal, net, expanded metal, etc., but the positive electrode current collector is aluminum foil. It is particularly preferably used, and a copper foil is particularly preferably used as the negative electrode current collector.

The positive electrode and the negative electrode are usually wound with a separator interposed therebetween to form a wound structure laminate,
Although it is formed into a laminated body by bending or laminating a plurality of layers, the discharge capacity per unit volume of the electrode laminated body is preferably 130 mAh / cm ³ or more in order to increase the capacity. In the present invention, the volume of the electrode laminate means a bulk volume of a positive electrode, a negative electrode and a separator folded or laminated, or a positive electrode, a negative electrode and a separator wound (when they have tabs or the like, In the case of the latter wound, the through hole in the center of the wound body based on the shaft used for winding is not included in the volume. The point is the volume occupied by the positive electrode, negative electrode, separator, etc. These three volumes are important factors that determine the capacity of the battery, and regardless of the size of the battery, the discharge capacity per unit volume of the electrode stack. By calculating (discharge capacity / volume of electrode stack), the capacity densities of the batteries can be compared. In addition, the discharge capacity referred to here is the discharge capacity when the battery is charged and discharged under standard use conditions. The standard operating conditions are 1C at 25 ° C.
3. With constant current of (current that can discharge the battery in 1 hour).
After charging up to 2V and reaching 4.2V, it means charging at a constant voltage of 4.2V for 2.5 hours, and then discharging at 0.2C to 2.75V at that time. The discharge capacity of the electrode laminate is measured to obtain the discharge capacity per unit volume of the electrode laminate. From the viewpoint of achieving higher capacity, the discharge capacity per unit volume of the electrode laminate is 140 mA.
h / cm ³ or more is more preferable, and 150 mAh / cm ³
The above is more preferable.

The form of the non-aqueous secondary battery of the present invention is not limited to a particular one. However, the present invention is not limited to a prismatic battery or a laminated battery which is prone to battery swelling in the prior art, and can be stored at high temperature. Since the swelling can be suppressed, the effect is remarkably exhibited particularly when applied to a prismatic battery or a laminated battery.

[0028]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only those examples.

Example 1 First, after dissolving LiPF ₆ in ethylene carbonate, methyl ethyl carbonate was added and mixed, and 1 volume of LiPF ₆ was added to a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1: 2. .2 mol / l
Correspondingly, 4% by mass of cyclohexylbenzene and 0.1% by mass of trioctyl phosphate were dissolved as additives, and further 2% by mass of 1,3-propane sultone was dissolved to prepare an electrolytic solution.

The positive electrode was composed of LiCoO ₂ 93.5 parts by mass, carbon black 2.0 parts by mass and graphite [Lonza KS-.
6 (trade name)] 0.5 part by mass was added and mixed, and the resulting mixture was mixed with 4 parts by mass of polyvinylidene fluoride in advance.
-A positive electrode mixture-containing paste was prepared by adding and mixing the solution dissolved in methylpyrrolidone. The obtained positive electrode mixture-containing paste was uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm (however, an electrode having a winding structure in which the produced positive electrode was wound with a negative electrode via a separator). In the laminated body, the positive electrode mixture-containing paste was not applied to the inner surface side portion of the innermost peripheral portion that did not face the negative electrode), and the positive electrode mixture layer was dried to form a positive electrode mixture layer. After pressure molding, cut into a predetermined size,
The lead body was welded to produce a strip-shaped positive electrode. The amount of the conductive additive (carbon black and graphite) in the positive electrode mixture was 2.5% by mass.

Separately from this, 95 parts by mass of mesocarbon microbeads were added to and mixed with a solution prepared by dissolving 5 parts by mass of polyvinylidene fluoride in N-methylpyrrolidone in advance to prepare a paste containing a negative electrode mixture. . The obtained negative electrode mixture-containing paste was applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 10 μm (however, the prepared negative electrode was wound with a positive electrode through a separator to form an electrode laminate having a winding structure). In, the outer surface side of the outermost peripheral portion that does not face the positive electrode was not coated with the negative electrode mixture-containing paste), dried to form the negative electrode mixture layer, and then pressure-molded by a roller press machine, After cutting to size, weld the lead body,
A strip-shaped negative electrode was produced.

Next, a current collecting tab is attached to each of the positive electrode and the negative electrode, and the positive electrode and the negative electrode have a thickness of 25 μm.
After being laminated via a separator made of the microporous polyethylene film, wound in a spiral shape, and pressed into a flat shape to form a laminated electrode body having a flat winding structure, an insulating tape is attached, and Square battery case with dimensions of 5 mm x 30 mm x 48 mm [thickness (depth) 5 mm, width 30 m
m, 48 mm high prismatic battery case], the lead body is welded and the lid plate for sealing is laser-welded to the opening end of the battery case, and the electrolyte injection port is provided on the lid plate for sealing. From the above electrolyte solution is injected into the battery case, after the electrolyte solution has sufficiently penetrated into the separator, etc., the electrolyte solution injection port is sealed and sealed, and then precharged and aged.
A prismatic non-aqueous secondary battery having a structure as shown in FIG. 1 and having an appearance as shown in FIG. 2 was produced.

The battery shown in FIGS. 1 and 2 will now be described. The positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3 as described above, and then pressed into a flat shape to be flattened. The electrode laminate 6 having a wound structure is housed in the prismatic battery case 4 together with the electrolytic solution. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolytic solution or the like as a current collector used in the production of the positive electrode 1 and the negative electrode 2 is not shown.

The battery case 4 is made of aluminum alloy and serves as a battery exterior material, and the battery case 4 also serves as a positive electrode terminal. An insulator 5 made of a polytetrafluoroethylene sheet is arranged at the bottom of the battery case 4, and the positive electrode 1 and the negative electrode are formed from the electrode laminate 6 having a flat winding structure composed of the positive electrode 1, the negative electrode 2 and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 connected to one end of each of the two are drawn out. Further, a stainless steel terminal 11 is attached to an aluminum alloy cover plate 9 for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and the terminal 11 is connected via an insulator 12. A lead plate 13 made of stainless steel is attached.

The cover plate 9 is inserted into the opening of the battery case 4 and the joint between the two is welded to seal the opening of the battery case 4 and seal the inside of the battery.

In the battery of Example 1, the positive electrode lead body 7
The battery case 4 and the lid plate 9 function as a positive electrode terminal by directly welding the negative electrode lead body 8 to the lead plate 13, and the negative electrode lead body 8 and the terminal via the lead plate 13. 11 is electrically connected to the terminal 11
Function as a negative electrode terminal, but depending on the material of the battery case 4 and the like, the positive and negative may be reversed.

FIG. 2 is a perspective view schematically showing the appearance of the battery shown in FIG. 1, and this FIG. 2 is shown for the purpose of showing that the battery is a prismatic battery. In FIG. 2, the battery is schematically shown, and only specific components of the battery are shown. Also, in FIG. 1, the inner peripheral portion of the electrode laminate is not shown in cross section.

Example 2 As in Example 1, LiPF ₆ was dissolved in ethylene carbonate, methyl ethyl carbonate was added and mixed, and LiPF ₆ was added to a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1: 2. ₆ to 1.2 m
equivalent to ol / l, 4% by mass of cyclohexylbenzene was dissolved as an additive, and 0.1% by mass of dioctyl phosphate was dissolved in place of the trioctyl phosphate used in Example 1, and further 1,3 A prismatic nonaqueous secondary battery was produced in the same manner as in Example 1 except that 2% by mass of propane sultone was dissolved to prepare an electrolytic solution, and the electrolytic solution was used.

Comparative Example 1 A prismatic nonaqueous secondary battery was prepared in the same manner as in Example 1 except that an electrolytic solution was prepared in the same manner as in Example 1 except that trioctyl phosphate was not contained. Was produced.

Comparative Example 2 A prismatic non-aqueous secondary battery was prepared in the same manner as in Example 1 except that an electrolytic solution was prepared in the same manner as in Example 1 except that cyclohexylbenzene was not contained. Was produced.

The batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were discharged to 3.0 V at 1 CmA at room temperature and charged at a constant current of 1 C until the battery voltage reached 4.2 V. 0.2m after charging at a constant voltage of 2V for 2.5 hours
A was discharged to 3.0 V and the discharge capacity was measured. The discharge capacity was divided by the bulk volume of the electrode laminate (sum of the volumes of the electrode, the separator, and the tab) to obtain the discharge capacitance per unit volume of the electrode laminate (mAh / cm ³ ). The results are shown in Table 1. The positive electrode potential when charged to 4.2 V as described above was 4.3 V based on Li.

Further, in order to investigate the safety of the battery during overcharge, an overcharge safety test was conducted as shown below. That is, the batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were
After charging to 4.2V with CmA and after reaching 4.2V, it is charged to a full charge state by a constant voltage of 4.2V for 2.5 hours, and after charging, 0.5V, 1A with 6V as the upper limit voltage.
The battery was overcharged with current values of A, 2A and 5A. At the time of the overcharge, the maximum current at which the battery surface temperature was 135 ° C. or lower was defined as the overcharge safe current value. The results are shown in Table 1.

Further, in order to investigate the high temperature storage characteristics of the battery, a storage test was conducted as shown below. Example 1 above
-2 and the batteries of Comparative Examples 1-2 were charged with a constant current of 1 CmA until the battery voltage reached 4.2V, and further charged to 4.2V.
Charged for 2.5 hours at a constant voltage of 3.0V at 1CmA
Was discharged until the discharge capacity was measured. The discharge capacity at this time was defined as the discharge capacity before storage. Then, at 1 CmA, 4.
The battery was charged to 2V and further charged at a constant voltage of 4.2V for 2.5 hours. After charging, place the battery in a 60 ° C constant temperature bath.
After storage for 0 days, the battery was discharged at 3.0 V with 1 CmA and the discharge capacity was measured. The discharge capacity at this time was taken as the discharge capacity after storage, and the self-discharge rate due to storage was determined by the following formula. The results are shown in Table 1.

[0044]

[Table 1]

As is clear from the results shown in Table 1, the batteries of Examples 1 and 2 were Comparative Examples in which the cyclohexylbenzene belonging to the compound (A) having an alkyl group bonded to the benzene ring was not contained in the electrolytic solution. Compared with the battery No. 2, the overcharge safety current is more than 10 times larger, and the safety at overcharge is 10 times.
I was able to increase it more than twice. In addition, the batteries of Examples 1 and 2 have less self-discharge due to high temperature storage and higher temperature storage than the batteries of Comparative Example 1 in which the electrolyte solution did not contain trioctyl phosphate belonging to the phosphoric acid ester (B). The characteristics were also excellent.

On the other hand, the battery of Comparative Example 1, which contained cyclohexylbenzene but did not contain trioctyl phosphate, had a high level of safety during overcharging, but a large amount of self-discharge during high temperature storage. , The high temperature storage characteristics were poor. Also, although trioctyl phosphate was included,
The battery of Comparative Example 2 containing no cyclohexylbenzene showed less self-discharge due to high temperature storage,
It lacked safety when overcharged.

[0047]

As described above, according to the present invention, it is possible to provide a non-aqueous secondary battery having high safety during overcharge and excellent high temperature storage characteristics.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an example of a non-aqueous secondary battery according to the present invention, in which (a) is a plan view thereof and (b) is a partial vertical sectional view thereof.

FIG. 2 is a perspective view of the non-aqueous secondary battery shown in FIG.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 separator 4 battery case 5 insulator 6 electrode stack 7 Positive electrode lead body 8 Negative electrode lead body 9 Lid plate 11 terminals 12 insulator 13 Lead plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fusashi Kita             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F term (reference) 5H029 AJ02 AJ04 AJ12 AK02 AK03                       AL02 AL06 AL07 AL08 AM00                       AM02 AM03 AM04 AM05 AM07                       AM16 BJ02 BJ14 DJ02 DJ08                       DJ16 EJ01 EJ11 EJ12 HJ01                       HJ02

Claims (4)

[Claims] 1. A non-aqueous secondary battery using a non-aqueous electrolytic solution in which a metal oxide is used as a positive electrode active material and a carbon material or a material into which Li can be inserted is used as a negative electrode active material. Containing a compound (A) having an alkyl group bonded to a benzene ring and a phosphoric acid ester (B), wherein the phosphoric acid triester (B) is 0.1% by mass or more with respect to the compound (A).
A non-aqueous secondary battery containing 0 mass% or less. 2. The phosphoric acid ester (B) has the general formula (R ₁
O) ₃ P = O (R ₁ : an alkyl group having 1 or more carbon atoms), a phosphoric acid triester represented by the general formula (R ₂ O) ₂ P (O
H) = O (R ₂ : an alkyl group having 1 or more carbon atoms) and a phosphoric acid diester represented by the general formula (R ₃ O) P (OH)
The non-aqueous secondary battery according to claim 1, wherein the non-aqueous secondary battery is at least one selected from the group consisting of phosphoric acid monoesters represented by ₂ = O (R ₃ : an alkyl group having 1 or more carbon atoms). 3. The non-aqueous electrolyte contains 3% by mass or more and 7% by mass or less of a compound (A) having an alkyl group bonded to a benzene ring, and a phosphoric acid ester (B) with respect to the compound (A). A non-aqueous secondary battery containing 0.1% by mass or more and 5% by mass or less. 4. The non-aqueous secondary battery according to claim 1, wherein the form of the battery is a prismatic battery or a laminated battery.