JP4701599B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

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

  In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable devices and personal digital assistants, etc., the batteries used as the power source are compact, lightweight, high energy density, and repeatedly charged for a long time. There is a strong demand for the development of secondary batteries capable of discharging. Among them, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are the most promising and active as secondary batteries that satisfy these needs compared to lead batteries and nickel cadmium batteries that use aqueous electrolytes. Research has been conducted.

The positive electrode active material of the nonaqueous electrolyte secondary battery includes general formula Li _x such as titanium disulfide, vanadium pentoxide and molybdenum trioxide, lithium cobalt composite oxide, lithium nickel composite oxide and spinel type manganese oxide. Various compounds represented by MO ₂ (where M is one or more transition metals) have been studied. Among them, lithium cobalt composite oxide, lithium nickel composite oxide, spinel-type lithium manganese oxide, etc. are charged and discharged at an extremely noble potential of 4 V (vs Li / Li ⁺ ) or higher. A battery having a high discharge voltage can be realized.

  Various negative electrode active materials for non-aqueous electrolyte secondary batteries, such as metallic lithium, lithium alloys, and carbon materials capable of occluding / releasing lithium, have been studied. There is an advantage that a battery having a long life can be obtained and safety is high.

For the electrolyte of a non-aqueous electrolyte secondary battery, a supporting salt such as LiPF ₆ or LiBF ₄ is generally mixed with a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate. A dissolved electrolyte is used.

  Non-aqueous electrolyte secondary batteries have a high energy density and use flammable organic solvents, so if they are used abnormally, an internal short circuit is caused or they are overcharged. In some cases, the battery temperature rapidly rises due to the decomposition of the battery member, the safety valve is opened, and an organic solvent or other decomposition gas is ejected or smoke may be generated.

  Therefore, a technique for improving the safety of the battery without impairing the battery performance has been sought. For example, in order to ensure the safety of the battery at an internal short circuit or high temperature, the hole is closed by melting at a high temperature. Technologies such as a shutdown separator and a PTC element whose resistance increases with increasing temperature are used.

  In addition, a method of adding a low molecular weight compound having polymerization reactivity during overcharge to a nonaqueous electrolyte has been proposed, and a method for adding a low molecular weight compound having polymerization reactivity during overcharge to a nonaqueous electrolyte. Are described for compounds such as biphenyl in Patent Document 1, Patent Document 2 and Patent Document 3, for example.

  These include aromatic compounds such as biphenyl that undergo a polymerization reaction at the positive electrode during overcharge to increase the internal resistance and suppress the charge reaction, or form a conductive polymer during polymerization to cause an internal short circuit. Various effects such as preventing overcharging or generating gas during polymerization to activate the internal electric circuit breaker are described.

  Furthermore, Patent Document 4 describes an alkylbenzene derivative or a cycloalkylbenzene derivative having a similar structure, and describes that the safety of the battery during overcharge is improved.

  Patent Document 5 describes a method for improving battery safety by using a non-aqueous electrolyte containing a phosphazene compound as a solvent having excellent self-extinguishing properties or flame retardancy.

JP-A-9-106835 JP-A-9-171840 JP-A-10-32258 Japanese Patent No. 3113652 JP, 2001-338682, A The reasons for using a nonaqueous electrolyte containing a phosphazene compound as described above are as follows. In non-aqueous electrolytes mainly composed of aprotic organic solvents used in non-aqueous electrolyte secondary batteries, if the battery temperature rises abnormally and the electrolyte is vaporized or decomposed, The reaction may cause the safety valve to open and produce smoke.

  As a countermeasure for this, for example, by containing a phosphazene compound in these conventional non-aqueous electrolytes, the above-mentioned non-aqueous electrolyte is decomposed by the action of nitrogen gas released by decomposition of the phosphazene compound, or halogen gas when halogen is contained. It is expected that the water electrolyte exhibits self-extinguishing properties or flame retardancy and prevents the opening of the safety valve and smoke generation as described above.

  In addition, phosphorus contained in the structure of the phosphazene compound has an action of suppressing chain decomposition of the polymer material constituting the battery, and is therefore said to be able to effectively impart self-digestibility and flame retardancy. .

  A non-aqueous electrolyte containing a phosphazene compound is flame retardant or non-flammable, and it is expected that the safety of the battery will be improved by using this. However, only this compound is used as a solvent for the non-aqueous electrolyte. When used, battery performance such as discharge characteristics cannot be maintained, and therefore, it has been proposed to use it mixed with a conventional non-aqueous electrolyte such as a cyclic carbonate or a chain carbonate in which a supporting salt is dissolved.

  In this way, by mixing and using a phosphazene compound and a conventional non-aqueous electrolyte, the flammability of the electrolyte is suppressed, the opening of the safety valve of the battery and the generation of smoke can be suppressed, and good discharge performance is achieved. Expected to get.

  In other words, aromatic compounds such as biphenyl undergo a polymerization reaction on the positive electrode during overcharge, resulting in an increase in internal resistance, protection of overcharge due to a mild internal short circuit, operation of an internal current interruption device due to gas generation, etc. The phosphazene compound imparts flame retardancy to the non-aqueous electrolyte by the action of phosphorus and, when a halogen is included in the structure, by the action of phosphorus. By suppressing it, it was said that the effect of improving the safety of the battery was obtained.

  However, when an aromatic compound is added to the non-aqueous electrolyte to improve safety during overcharging, hydrogen gas is the main component due to decomposition of the aromatic compound when the battery is placed in an overcharged state. In the case of a battery of mainly rectangular or long cylindrical shape, deformation of the battery case occurs easily, which causes deformation of the electrode group in the battery case, This causes a short circuit between the electrode plates.

  Further, when the amount of the aromatic compound added is increased in order to increase the effect of the additive, the discharge characteristics such as the discharge capacity may be deteriorated, or the battery may swell when left at high temperature.

  In addition, when the phosphazene compound is mixed in the non-aqueous electrolyte, there is an effect of making the non-aqueous electrolyte incombustible and non-combustible, but the phosphazene compound itself is decomposed at the positive and negative electrodes during overcharge to charge the active material. Since there is no overcharge prevention action such as lowering the level, in overcharge with a large current, the charge reaction of the positive and negative electrodes proceeds, and the electrolyte solution is finally decomposed. As a result, the internal pressure increased, the safety valve was opened, and gas was blown out to break.

  Thus, even when using phosphazene that imparts flame retardancy and incombustibility to the non-aqueous electrolyte, if the charging of the active material proceeds as in overcharging, the thermal stability decreases and the decomposition of the solvent proceeds. Thus, the safety of the battery could not be sufficiently improved. Moreover, when the mixing amount of the phosphazene compound is increased for the purpose of imparting flame retardancy and nonflammability to the nonaqueous electrolyte, there are problems such as deterioration of discharge characteristics such as discharge capacity.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the safety during overcharge can be drastically improved by including an aromatic compound and a phosphazene compound in the non-aqueous electrolyte. I found it.

The invention according to claim 1 relates to a non-aqueous electrolyte secondary battery, wherein the non- aqueous electrolyte includes a positive electrode that absorbs and releases lithium, a negative electrode, and a non-aqueous electrolyte. And 0.5 wt% or more and 6.0 wt% or less of at least one aromatic compound selected from a biphenyl derivative, a naphthalene derivative and a benzene derivative with respect to the total weight of the non-aqueous electrolyte, and the phosphazene compound It is characterized by being contained in an amount of 0.5 wt% to 30 wt% .

According to a second aspect of the present invention, in the nonaqueous electrolyte secondary battery according to the first aspect, the nonaqueous electrolyte contains 1.0 wt% or more and 4.0 wt% of the aromatic compound with respect to the total weight of the nonaqueous electrolyte. %, And the phosphazene compound is contained in an amount of 1.0 wt% to 20 wt% .

  According to the first aspect of the present invention, a nonaqueous electrolyte secondary battery excellent in safety during overcharge can be obtained by including an aromatic compound and a phosphazene compound in the nonaqueous electrolyte.

  Further, according to the invention of claim 2, by setting the addition amount of the aromatic compound to 1 to 4 wt% and the addition amount of the phosphazene compound to the range of 1 to 20 wt%, these compounds are contained in the non-aqueous electrolyte. To obtain a non-aqueous electrolyte secondary battery with significantly improved safety during overcharge without the deterioration of discharge characteristics such as discharge capacity and the increase of battery swelling when left at high temperatures. Can do.

  As the aromatic compound used in the present invention, those having an oxidation potential at a potential nobler than the potential of the positive electrode at the time of full charge of a normally used battery are preferable in use, for example, biphenyl, halogenated biphenyl, alkylbiphenyl. And the like, naphthene derivatives such as halogenated naphthalene, benzene derivatives such as halogenated benzene, alkylbenzene, cycloalkylbenzene, and anisole are preferably used.

  Moreover, as an example of a phosphazene compound, the chain | strand-shaped phosphazene derivative shown by Chemical formula 1 and the cyclic phosphazene derivative shown by Chemical formula 2 are used suitably, These can be used individually or in mixture.

  In a non-aqueous electrolyte secondary battery, when the non-aqueous electrolyte contains only an aromatic compound, the aromatic compound is polymerized on the positive electrode during overcharge to lower the charge level of the active material, and the thermal stability of the active material is improved. . However, the generated hydrogen gas increases the internal pressure of the battery and causes the battery to swell, causing the power generation element composed of the positive electrode plate, the negative electrode plate, and the separator to deform, causing an internal short circuit inside the battery, resulting in damage to the battery. it is conceivable that.

  On the other hand, when the non-aqueous electrolyte contains only the phosphazene compound, there is an effect of suppressing the decomposition of the organic solvent at a high temperature, and the non-aqueous electrolyte is imparted with flame retardancy and non-flammability, but the positive and negative electrode active materials are charged. It is considered that the reaction proceeds and the thermal stability of the positive and negative electrodes is lowered, and the organic solvent is finally rapidly decomposed at the end of the overcharge, thereby generating heat and increasing the internal pressure of the battery, resulting in damage to the battery.

  Therefore, when the non-aqueous electrolyte contains an aromatic compound and a phosphazene compound at the same time, the charging reaction of the active material is suppressed by the action accompanying the polymerization of the aromatic compound during overcharge, and the thermal stability of the active material is improved. In addition, it is presumed that the occurrence of an internal short circuit can be prevented by suppressing gas generation due to decomposition of the organic solvent by the phosphazene compound and suppressing swelling of the battery.

  However, when the content of the aromatic compound relative to the total weight of the electrolyte is less than 1 wt%, the action of suppressing the charge reaction of the active material is reduced, and when the content of the phosphazene compound is less than 1 wt%, the organic solvent It is considered that the function of suppressing the gas generation due to decomposition of the water becomes small.

  Further, when the content of the aromatic compound with respect to the total weight of the electrolyte exceeds 4 wt%, it is easily oxidized at the positive electrode when left at a high temperature of 80 ° C., and the swelling of the battery increases, and the content of the phosphazene compound is 20 wt. In the case of exceeding%, it is considered that the polarization during charge / discharge increases due to a decrease in the ionic conductivity of the electrolyte itself, and the discharge capacity greatly decreases.

  Therefore, in this invention, it is preferable to contain 1 wt%-4 wt% of aromatic compounds, and 1-20 wt% of phosphazene derivatives with respect to electrolyte total weight.

  R in the chain phosphazene derivative represented by Chemical Formula 1 is not particularly limited as long as it is a monovalent substituent. Examples of the monovalent substituent include a hydrogen atom, a halogen, an alkoxy group, an alkyl group, a carboxyl group, and an acyl. Groups, aryl groups, functional groups containing sulfur, phosphorus, nitrogen and the like, and n is 3-15.

  Here, preferable examples of the halogen element include fluorine, chlorine, bromine and the like. R may be all the same type of substituents, and some of them may be different types of substituents.

  Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, butoxy group, and alkoxy-substituted alkoxy groups such as methoxyethoxy group and methoxyethoxyethoxy group, as well as phenoxy groups and substituted phenoxy groups. . Also. Hydrogen in the alkoxy group may be substituted with a halogen element such as fluorine.

  Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group and the like. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group.

  The monovalent substituent further preferably contains a halogen element. The more the number of substituents containing halogen elements in the molecular structure of the phosphazene derivative, the lower the flammability of the electrolyte solution.

  As the non-aqueous electrolyte, either an electrolytic solution or a solid electrolyte can be used. In the case of using an electrolytic solution, as an electrolytic solution solvent, ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, sulfolane, 1,2-dimethoxyethane, 1,2-di- Ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, dimethyl carbonate, diethyl carbonate, Non-ethyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, dibutyl carbonate, vinylene carbonate, N-methyloxazolidinone, N-ethyloxazolidinone, etc. The solvent, alone or can be used mixed solvents thereof.

The nonaqueous electrolyte is used by dissolving the supporting salt in these nonaqueous solvents. Examples of the supporting salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN (SO ₂ CF ₃ ). ₂ , salts such as LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , LiN (COCF ₂ CF ₃ ) ₂ and LiPF ₃ (CF ₂ CF ₃ ) ₃ or mixtures thereof may be used. it can.

  In the case of using a solid electrolyte, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and an electrolyte solution may be further contained in the polymer solid electrolyte. Moreover, when using a gel-like polymer solid electrolyte, the electrolyte solution which comprises gel and the electrolyte solution contained in the pore etc. may differ. When such a polymer solid electrolyte is used, the aromatic compound and the phosphazene compound of the present invention may be contained in the electrolytic solution.

As the positive electrode active material, a composite oxide represented by a composition formula Li _x MO ₂ , Li _y M ₂ O 4 (where M is one or more transition metals, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2). A metal chalcogenide or metal oxide having a tunnel structure or a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiCo _x Ni _1-x O ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS. ₂ etc. are mentioned. Examples of the organic compound include conductive polymers such as polyaniline. Furthermore, the above various active materials may be mixed and used regardless of whether they are inorganic compounds or organic compounds.

Further, as the negative electrode material compound, Al, Si, Pb, Sn, Zn, Cd, etc. and lithium alloys, LiFe ₂ O ₃ , WO ₂ , MoO ₂ , SiO, CuO, etc. metal oxides, graphite, carbon A carbonaceous material such as Li ₃ N, lithium nitride such as Li ₃ N, or metallic lithium, or a mixture thereof may be used.

  Moreover, as a separator of the nonaqueous electrolyte battery according to the present invention, a woven fabric, a non-woven fabric, a synthetic resin microporous membrane, or the like can be used, and a synthetic resin microporous membrane can be particularly preferably used. Among these, polyolefin microporous membranes such as polyethylene and polypropylene microporous membranes, or microporous membranes composed of these are preferably used in terms of thickness, membrane strength, membrane resistance, and the like.

  Furthermore, a separator can also be used by using a solid electrolyte such as a polymer solid electrolyte. Further, a synthetic resin microporous membrane and a polymer solid electrolyte may be used in combination. In this case, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and the polymer solid electrolyte may further contain an electrolytic solution.

  In addition, the shape of the battery is not particularly limited, and can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a rectangular shape, a long cylindrical shape, a coin shape, a button shape, a sheet shape, and a cylindrical battery, The effect is particularly great in batteries such as a rectangular shape, a long cylindrical shape, a coin shape, a button shape, and a sheet shape, in which the battery case is easily deformed due to an increase in the battery internal pressure.

  Hereinafter, specific embodiments to which the present invention is applied will be described. However, the present invention is not limited to the embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. .

[Example 1]
FIG. 1 is a schematic cross-sectional view of a prismatic nonaqueous electrolyte secondary battery of the present example. In this rectangular nonaqueous electrolyte secondary battery 1, a positive electrode 3 formed by applying a positive electrode mixture to an aluminum current collector and a negative electrode 4 formed by applying a negative electrode mixture to a copper current collector are interposed via a separator 5. The wound flat flat electrode group 2 and the non-aqueous electrolyte are housed in a battery case 6 and have a width of 30 mm × a height of 48 mm × a thickness of 4.0 mm.

  A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, a negative electrode terminal 9 is connected to the negative electrode 4 via a negative electrode lead 11, and a positive electrode 3 is connected to the battery lid via a positive electrode lead 10. Has been.

  The positive electrode plate is a positive electrode mixture formed by mixing 5% by weight of polyvinylidene fluoride as a binder, 4% by weight of acetylene black as a conductive agent, and 87% by weight of a positive electrode active material as a lithium cobalt composite oxide. N-methylpyrrolidone was added to prepare a paste, which was then applied on both sides of a 15 μm thick aluminum foil current collector and dried.

  A negative electrode plate was prepared by adding 95% by weight of graphite (graphite), 2% by weight of carboxymethyl cellulose and 3% by weight of styrene butadiene rubber to a paste form by adding appropriate moisture, and then preparing a 10 μm thick copper foil current collector on both sides. It was manufactured by coating and drying.

A polyethylene microporous membrane is used for the separator, and the electrolyte is an aromatic compound represented by Chemical Formula 3 in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3: 7 (volume ratio). One of the compounds, cyclohexylbenzene (CHB), was dissolved so as to be 0.5 wt% with respect to the total amount of the electrolytic solution. Moreover, in the phosphazene compound of Chemical Formula 2, n = 3, 5 of 6 Rs are F, and 1 is an ethoxy group, and ethoxypentafluorocyclotriphosphazene (ECP) represented by Chemical Formula 4 is added to the total amount of the electrolytic solution. On the other hand, a non-aqueous electrolyte solution was used which was dissolved so as to be 0.5 wt%, and further LiPF ₆ was dissolved so as to be 1 mol / L after adjustment.

  Twelve cells of the nonaqueous electrolyte secondary battery of Example 1 were produced by the above configuration and procedure.

[Examples 2 to 25 and Comparative Examples 1 to 11]
As for the 35 types of batteries of Examples 2 to 25 and Comparative Examples 1 to 11, as shown in Table 1, except that the amounts of CHB and ECP contained in the electrolyte were changed, they were exactly the same as Example 1. A non-aqueous electrolyte secondary battery was prepared for each 12 cells.

  Table 1 shows the amounts of CHB and ECP contained in the electrolyte (% by weight with respect to the total amount of the electrolytic solution) in the batteries of Examples 1 to 25 and Comparative Examples 1 to 11.

  The initial discharge capacity at 25 ° C. was measured for the prismatic nonaqueous electrolyte secondary batteries of Examples 1 to 25 and Comparative Examples 1 to 11 produced as described above. In addition, after discharging for 2.5 hours with a constant current-constant voltage charge with a charge current of 650 mA and a charge voltage of 4.20 V at 25 ° C., the discharge capacity is discharged under conditions of a discharge current of 650 mA and a final voltage of 2.8 V. Was measured.

Of the 12 cells after the initial discharge capacity confirmation test, 3 cells were subjected to a high temperature storage test. The high temperature storage test was performed by charging the battery under the charging conditions during the initial discharge capacity confirmation test, leaving the charged battery in a constant temperature bath at 80 ° C. for 48 hours, and measuring the battery thickness after cooling.
9 out of 12 cells after the initial discharge capacity confirmation test was overcharged by charging for 3 hours with a constant current-constant voltage charge of 1A and charge voltage of 12V, and the batteries after the test were damaged. The presence or absence was confirmed.

  Table 2 shows the test results of the batteries of Examples 1 to 25 and Comparative Examples 1 to 11. In Table 2, “Discharge capacity” indicates the average value of the initial discharge capacity of each battery, “Battery thickness” indicates the average value of the battery thickness of each battery after the high-temperature storage test, and “Number of breaks” indicates an excessive value. The number of cells damaged in 9 cells in the charge test result is shown.

  From Table 4, the batteries of Examples 1 to 25 containing CHB and ECP at the same time in the nonaqueous electrolyte were compared with the batteries of Comparative Examples 1 to 11 each containing CHB and ECP alone in the nonaqueous electrolyte. As a result, the number of breaks in the overcharge test decreased, and good safety during overcharge could be ensured.

Further, the batteries of Examples 7 ～9,12～14,17～19 and 22 to 24 of 1 wt% to 4 wt% and ECP a CHB in the nonaqueous electrolyte containing a 1 wt% 20 wt% at the same time, examples Compared with 6 , 10, 11, 15, 16, 20, 21, and 25 batteries, it suppresses battery swelling when left at high temperatures without reducing the discharge capacity, and provides high safety during overcharge. I found out that

  Although the reason why such a result was obtained has not been clarified, when CHB, which is an aromatic compound, is used alone, the additive itself polymerizes on the positive electrode during overcharge, thereby reducing the charge level of the active material. Lowering the temperature improves the thermal stability of the active material, but the generated hydrogen gas increases the internal pressure of the battery, causing the battery to swell, causing the element to deform and causing an internal short circuit, resulting in damage to the battery. It is thought that it reached. Further, when the addition amount is as large as 6 wt%, it is considered that the battery is oxidized and easily polymerized when left at a high temperature of 80 ° C., and the swelling of the battery is increased.

  In addition, when EPZ is used alone, it has an effect of suppressing decomposition of the organic solvent at a high temperature by addition to the non-aqueous electrolyte, and imparts flame retardancy and non-flammability to the non-aqueous electrolyte. Charging reaction of the active material progresses, and the thermal stability of the positive and negative electrodes decreases. Finally, the organic solvent suddenly decomposes at the end of overcharging, resulting in heat generation and increase in battery internal pressure, leading to damage to the battery. It is considered a thing. Further, when the addition amount is increased to 40 wt%, it is considered that the polarization during charge / discharge increases due to the decrease in the ionic conductivity of the electrolyte itself, and the discharge capacity greatly decreases.

  On the other hand, when a non-aqueous electrolyte containing 1 wt% to 4 wt% of CHB, which is an aromatic compound, and 1 to 20 wt% of a phosphazene derivative ECP containing a halogen is used, the action accompanying polymerization of the aromatic compound during overcharge In addition to suppressing the charging reaction of the active material to improve the thermal stability of the active material, the generation of internal short circuit was prevented by suppressing the gas generation due to the decomposition of the organic solvent by ECP and suppressing the swelling of the battery Can be considered.

[Examples 26 to 45 and Comparative Examples 12 to 16]
For the 25 types of batteries of Examples 26 to 45 and Comparative Examples 12 to 16, as shown in Table 3, biphenyl (BPh) represented by Chemical Formula 5 was used as an aromatic compound to be included in the electrolyte. Were made in the same manner as in Example 1 to produce 12 nonaqueous electrolyte secondary batteries.

  For the 25 types of batteries of Examples 26 to 45 and Comparative Examples 12 to 16, the initial discharge capacity, the battery thickness after the high temperature standing test, and the number of breaks in the overcharge test were determined under the same test conditions as in Example 1. The “discharge capacity”, “battery thickness”, and “number of breaks” in Table 4 have the same contents as in Table 2.

  The results in Table 4 are almost the same as the trends obtained in Table 2, and it was found that substantially the same effect can be obtained even when the type of aromatic compound is changed.

[Examples 46 to 65]
For the 20 types of batteries of Examples 46 to 65, as shown in Table 5, except that pentafluorophenoxycyclotriphosphazene (PCP) represented by Chemical Formula 6 was used as the phosphazene compound to be included in the electrolyte. In exactly the same manner as in Example 1, 12 nonaqueous electrolyte secondary batteries were produced. For comparison, Table 5 also shows the batteries of Comparative Examples 7 to 11.

  For the 20 types of batteries of Examples 46 to 65, under the same test conditions as in Example 1, the initial discharge capacity, the battery thickness after the high-temperature storage test, and the number of breaks in the overcharge test were determined. The “discharge capacity”, “battery thickness”, and “number of breaks” in Table 4 have the same contents as in Table 2. For comparison, Table 6 also shows the battery data of Comparative Examples 7-11.

  The results in Table 6 are almost the same as the trends obtained in Table 2 and Table 4, and it was found that substantially the same effect can be obtained when the type of phosphazene compound is changed.

  Further, in the examples and comparative examples, the electrolyte solvent is described for the EC: EMC system. However, when the ratio of the cyclic carbonate and the chain carbonate is changed, or when the concentration of the electrolyte salt is changed, the chain solvent is used. The same tendency is observed when dimethyl carbonate or diethyl carbonate is used as the carbonate, and the same tendency is also obtained when propylene carbonate or gamma butyrolactone is partially used instead of cyclic and chain carbonates. It was.

  The same effect can be obtained when biphenyl derivatives such as 2-fluorobiphenyl, 4-fluorobiphenyl, and methylbiphenyl are used as aromatic compounds, or when cycloalkylbenzene derivatives and naphthalene derivatives are used as phosphazene derivatives. The same tendency was obtained when the type and number of substituents were changed or when chain phosphazene was used.

The figure which shows the cross-section of the square battery of the Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Square type nonaqueous electrolyte secondary battery 2 Winding type electrode group 3 Positive electrode 4 Negative electrode 5 Separator 6 Battery case 7 Battery cover 8 Safety valve 9 Positive electrode terminal 10 Positive electrode lead 11 Negative electrode lead

Claims (2)

In a non-aqueous electrolyte secondary battery comprising a positive electrode that absorbs and releases lithium, a negative electrode, and a non-aqueous electrolyte, the non-aqueous electrolyte includes a biphenyl derivative and a naphthalene derivative with respect to the total weight of the non-aqueous electrolyte. And at least one aromatic compound selected from benzene derivatives is contained in an amount of 0.5 wt% to 6.0 wt%, and a phosphazene compound is contained in an amount of 0.5 wt% to 30 wt%. Electrolyte secondary battery. The non-aqueous electrolyte contains 1.0 to 4.0 wt% of the aromatic compound and 1.0 to 20 wt% of the phosphazene compound with respect to the total weight of the non-aqueous electrolyte. the non-aqueous electrolyte secondary battery according to claim 1, characterized in that it is.

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