Patent Application
20180287118
The present disclosure relates to a technique for a nonaqueous electrolyte secondary battery.
In recent years, a nonaqueous electrolyte secondary battery using, as a positive electrode active material, a Ni-, Co-, Mn- and Li-containing transition metal oxide has been known as a battery having a high energy density and high thermal stability (see, for example, Patent Literature 1).
In a nonaqueous electrolyte secondary battery, if a battery temperature excessively increases due to, for example, some external factor, a solvent or the like of a nonaqueous electrolyte is electrolyzed to generate a gas, which may increase the internal pressure of the battery in some cases. Therefore, the nonaqueous electrolyte secondary battery is generally provided with a current interrupt device (CID) for interrupting a charging current when the internal pressure of the battery exceeds a prescribed value or a pressure relief valve for lowering the internal pressure of a package, and thus, the safety of the battery is attained (see, for example, Patent Literature 2).
Patent Literature 1: Japanese Patent Laid-Open Publication No. 2007-095443
Patent Literature 2: Japanese Patent Laid-Open Publication No. 2008-034391
In case of a conventional pressure relief valve, the temperature of the battery may increase in some cases even after the pressure relief valve is actuated. As a result, in a battery module including a combination of a plurality of batteries, it is apprehended that other batteries adjacent to the battery having a high temperature may be harmfully affected.
An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery capable of inhibiting excessive temperature increase of the battery after a pressure relief valve is actuated.
A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, a nonaqueous electrolyte containing a nonaqueous solvent, a package housing the positive electrode, the negative electrode and the nonaqueous electrolyte, and a pressure relief valve actuated at a battery temperature of 145° C. or less for lowering an internal pressure of the package when the battery temperature increases.
According to the nonaqueous electrolyte secondary battery of the one aspect of the present disclosure, excessive temperature increase of the battery can be inhibited after the pressure relief valve is actuated.
(Finding Corresponding to Base of Present Disclosure)
A conventional pressure relief valve is designed mainly in consideration of an internal pressure of a package (an internal pressure of a battery) with no consideration given to a battery temperature. The present inventors earnestly examined the relationship between a battery temperature at the time when a pressure relief valve is actuated and increase in the battery temperature occurring after it is actuated, and as a result, have found that if the battery temperature is high at the time when the pressure relief valve is actuated, the battery temperature also increases after it is actuated and reaches a high temperature. Based on this finding, the present inventors have conceived the following aspect of the present invention.
A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode, a negative electrode, a nonaqueous electrolyte containing a nonaqueous solvent, a package housing the positive electrode, the negative electrode and the nonaqueous electrolyte, and a pressure relief valve actuated at a battery temperature of 145° C. or less for lowering a pressure within the package when the battery temperature increases. According to the one aspect of the present disclosure, the pressure relief valve is actuated before the battery temperature exceeds 145° C. at the time of increase in the battery temperature, so as to lower the battery temperature when the pressure within the package is released, and therefore, temperature increase caused by, for example, self-heating occurring due to a chemical reaction caused in the battery is suppressed so that excessive temperature increase of the battery can be inhibited.
Hereinafter, an example of a nonaqueous electrolyte secondary battery according to the one aspect of the present disclosure will be described. A drawing referred to in the description of an embodiment is illustrated merely schematically, and a dimensional proportion and the like of constituting elements illustrated in the drawing may be different from actual ones in some cases.
The package of the nonaqueous electrolyte secondary battery 30 of
In the nonaqueous electrolyte secondary battery 30 of
The sealing plate 19 of
The positive electrode 1 is connected to the filter 6 via a positive electrode lead 8, and the terminal plate 11 serves as an external terminal of the positive electrode 1. On the other hand, the negative electrode 2 is connected to a bottom of the battery case 5 via a negative electrode lead 9, and the battery case 5 serves as an external terminal of the negative electrode 2. In the battery 30 of
The current cut-off valve 14 of
The pressure relief valve 13 of
An actuation temperature of the pressure relief valve 13 is 145° C. or less, preferably 140° C. or less, and more preferably 130° C. or less. The pressure relief valve 13 is preferably actuated at 100° C. or more. In other words, when the battery temperature increases due to abnormality or the like of the overcharge or the like, the pressure relief valve 13 is actuated before the battery temperature exceeds 145° C. (at 145° C. or less), preferably before it exceeds 140° C. (at 140° C. or less), and more preferably in a temperature region of 130° C. or less (for example, in such a manner that it is opened by an internal pressure of the package increased by the battery temperature), and thus, the gas inside the package is released to lower the internal pressure.
When the actuation temperature of the pressure relief valve 13 is 145° C. or less, excessive temperature increase of the battery otherwise caused after the pressure relief valve is actuated 13 can be inhibited. Incidentally, from the viewpoint of a temperature range for use of the battery and the like, the actuation temperature of the pressure relief valve 13 is set preferably to 100° C. or more.
The actuation temperature of the pressure relief valve 13 can be controlled by adjusting, for example, the thickness or the groove depth of the pressure relief valve. Specifically, when pressure resistance of the pressure relief valve is lowered by reducing the thickness of the pressure relief valve or making the groove deep, the actuation temperature can be lowered. In battery design, however, not only there is a limit in the adjustment of the thickness of the pressure relief valve and the groove depth but also a valve actuation temperature is varied depending on another design parameter, and therefore, it may be difficult to control the actuation temperature of the pressure relief valve 13 to 145° C. or less in some cases by using merely these parameters. Therefore, the battery is designed preferably based on the following parameters:
a=Remaining space ratio obtained by expression (2)/Pressure resistance of pressure relief valve (kgf/cm2) Expression (1)
Remaining space ratio=Space remaining within battery (cm3)/Rated capacity (Ah) of nonaqueous electrolyte secondary battery Expression (2)
The pressure resistance of the pressure relief valve of expression (1) corresponds to the internal pressure of the package at the time when the pressure relief valve 13 is actuated (for example, at the time of the valve opening), and is a value measured under hydrostatic pressure. The space remaining within the battery of expression (2) is a value obtained by subtracting, from the internal volume of the package, volumes of all the components, such as the electrode body 4, housed in the package, and is measured according to Archimedes' principle.
In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing a Ni-, Co-, Al- and Li-containing transition metal oxide, the value “a” obtained by expression (1) is preferably 6.5 or less, more preferably 6 or less, and further preferably 5.0 or more and 5.8 or less. When the value “a” obtained by expression (1) is 6.5 or less, the actuation temperature of the pressure relief valve 13 can be easily controlled to 145° C. or less. Incidentally, in the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Al- and Li-containing transition metal oxide, the rated capacity of the nonaqueous electrolyte secondary battery of expression (2) is a battery capacity obtained when the battery is discharged at 0.2 C in a voltage range of 2.5 V to 4.2 V.
In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing a Ni-, Co-, Mn- and Li-containing transition metal oxide, the value “a” obtained by expression (1) is preferably 9.5 or less, and more preferably 9.2 or less. When the value “a” obtained by expression (1) is 9.5 or less, the actuation temperature of the pressure relief valve 13 can be easily controlled to 145° C. or less. Incidentally, in the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Mn- and Li-containing transition metal oxide, the rated capacity of the nonaqueous electrolyte secondary battery of expression (2) is a battery capacity obtained when the battery is discharged at 0.2 C in a voltage range of 3.0 V to 4.1 V.
The pressure resistance of the pressure relief valve is preferably in a range of 20 kgf/cm2 or more and 38 kgf/cm2 or less, and more preferably in a range of 24 kgf/cm2 or more and 34 kgf/cm2 or less from the viewpoint of avoiding damage of the pressure relief valve 13 caused by impact, vibration or the like.
The remaining space ratio obtained by expression (2) is preferably in a range of 0.120 or more and 0.330 or less from the viewpoint of the rated capacity, the amount of the electrolyte solution and the like. In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Al- and Li-containing transition metal oxide, the remaining space ratio obtained by expression (2) is more preferably in a range of 0.160 or more and 0.230 or less. In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Mn- and Li-containing transition metal oxide, the remaining space ratio obtained by expression (2) is more preferably in a range of 0.220 or more and 0.320 or less.
The space remaining within the battery is determined in accordance with the size of the electrode body 4, the injection volume of the nonaqueous electrolyte, the internal volume of the package and the like. The space remaining within the battery may be appropriately set so that a desired remaining space ratio can be obtained, and is preferably in a range of 0.5 cm3 or more and 1.3 cm3 or less from the viewpoint of the amount of the electrolyte solution and the like. In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Al- and Li-containing transition metal oxide, the space remaining within the battery is more preferably in a range of 0.7 cm3 or more and 1.0 cm3 or less. In the nonaqueous electrolyte secondary battery 30 using the positive electrode active material containing the Ni-, Co-, Mn- and Li-containing transition metal oxide, the space remaining within the battery is more preferably in a range of 0.9 cm3 or more and 1.2 cm3 or less.
The positive electrode 1 is made of a positive electrode collector of, for example, a metal foil or the like, and a positive electrode active material layer formed on the positive electrode collector. As the positive electrode collector, a foil of a metal stable in a range of a positive electrode potential, such as aluminum, or a film or the like having the metal as a surface layer can be used.
The positive electrode active material layer contains the positive electrode active material, and in addition, suitably contains a conductive material and a binder. The positive electrode active material is not limited to single use of a Ni-, Co-, Mn- and Li-containing transition metal oxide, but a different positive electrode material may be used together. An example of the different positive electrode material includes lithium cobalt oxide capable of insertion and extraction of lithium ions with a stable crystal structure kept. Besides, particle surfaces of the positive electrode active material may be covered with fine particles of an oxide such as aluminum oxide (Al2O3) or an inorganic compound such as a phosphoric acid compound or a boric acid compound.
The positive electrode active material preferably contains a lithium-containing transition metal oxide represented by general formula, LixNi1-yMyO2 (wherein 0<x<1.1, y≤0.7, and M represents an element excluding Li and Ni). An example of M includes at least one element out of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, Zr and W. From the viewpoint of stability in the crystal structure and the like, at least one element out of Co and Al is preferably contained. The composition ratio y is preferably 0.4 or more and 0.7 or less, and more preferably 0.45 or more and 0.6 or less.
When a Ni-, Co-, Mn- and Li-containing transition metal oxide represented by general formula, LixNi1-yCoβMnγMδO2 (wherein M represents an element excluding Li, Ni, Co and Mn) is used as the positive electrode active material, a sum of β, γ and β is y. In other words, y=β+γ+δ. The composition ratio β is preferably 0.1 or more and 0.4 or less, and more preferably 0.15 or more and 0.3 or less. The composition ratio y is preferably 0.2 or more and 0.4 or less, and more preferably 0.2 or more and 0.35 or less. The composition ratio δ is preferably 0 or more and 0.1 or less, and more preferably 0.001 or more and 0.015 or less.
The positive electrode active material preferably contains one element selected from Zr and W. The Zr and W contained in the positive electrode active material may be present, for example, in a solid solution state in the Li-containing transition metal oxide or the like, or a compound of Zr and W may be present in an adhering state to particle surfaces of the Li-containing transition metal oxide or the like. In either state, a content of the Zr and W in the positive electrode active material is preferably in a range of 0.1% by mole or more and 1.5% by mole or less, and more preferably in a range of 0.2% by mole or more and 0.7% by mole or less. When the content of the Zr and W satisfies the above-described range, the thermal stability is improved as compared with a case where it is out of the range, and therefore, for example, the actuation temperature of the pressure relief valve can be easily controlled to 140° C. or less. The content of the Zr and W in the positive electrode active material is a value obtained by dissolving the positive electrode active material in hydrochloric acid, and measuring the amount of Zr and W in the thus obtained solution by ICP atomic emission spectroscopy.
In general, a lithium-containing transition metal oxide containing Ni is rather poor in the thermal stability in a charged state as compared with a lithium-containing transition metal oxide principally containing Mn, Fe or Co, and hence, the battery temperature is easily increased. In the present embodiment, however, even when a lithium-containing transition metal oxide thus having lower thermal stability is used, the excessive temperature increase of the battery can be effectively inhibited.
The conductive material is used for improving electrical conductivity of the positive electrode active material layer. Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black and graphite. One of these may be singly used, or two or more of these may be used in combination.
The binder is used for keeping a good contact state between the positive electrode active material and the conductive material, and for improving a binding property of the positive electrode active material or the like to the surface of the positive electrode collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and modified products of these. The binder may be used together with a thickener such as carboxymethylcellulose (CMC) or polyethylene oxide (PEO). One of these may be singly used, or two or more of these may be used in combination.
The negative electrode 2 includes a negative electrode collector of, for example a metal foil or the like, and a negative electrode active material layer formed on the negative electrode collector. As the negative electrode collector, a foil of a metal stable in a range of a negative electrode potential, such as copper, or a film or the like having, as a surface layer, a metal stable in the range of the negative electrode potential, such as copper, can be used. The negative electrode active material layer suitably contains a binder in addition to a negative electrode active material capable of absorption/desorption of lithium ions. As the binder, PTFE or the like can be used in the same manner as in the positive electrode, and a styrene-butadiene copolymer (SBR) or a modified product thereof is preferably used. The binder may be used together with a thickener such as CMC.
As the negative electrode active material, for example, natural graphite, artificial graphite, lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, a lithium alloy, carbon and silicon in which lithium is previously absorbed, and an alloy or a mixture of any of these can be used.
As the separator 3, for example, a porous sheet having ion permeability and an insulating property is used. Specific examples of the porous sheet include a microporous thin film, woven fabric and nonwoven fabric. A material of the separator preferably contains, for example, a polyolefin such as polyethylene or polypropylene.
The nonaqueous electrolyte contains the nonaqueous solvent, and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous solvent contains a fluorine-containing organic compound, and a content of the fluorine-containing organic compound is preferably 5% by volume or more and 15% by volume or less, and more preferably 10% by volume or more and 15% by volume or less with respect to a total volume of the nonaqueous solvent. When the content of the fluorine-containing organic compound is 5% by volume or more and 15% by volume or less, the actuation temperature of the pressure relief valve 13 can be easily controlled to 145° C. or less. Incidentally, when the content of the fluorine-containing organic compound is less than 5% by volume, a gas is difficult to generate simultaneously with the increase in the battery temperature as compared with a case where the content satisfies the above-described range, and the actuation temperature of the pressure relief valve 13 may be difficult to control to 145° C. or less in some cases. Alternatively, when the fluorine-containing organic compound exceeds 15% by volume, an amount of a decomposition product of the fluorine-containing organic compound produced at a high temperature increases as compared with the case where the content satisfies the above-described range, and battery performance may be degraded in some cases.
Examples of the fluorine-containing organic compound include a fluorinated cyclic carbonate, a fluorinated open-chain carbonate and a fluorinated open-chain ester.
Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate (FEC), 4,5-difluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-4-methyl-1,3-dioxolan-2-one, 4-trifluoromethyl-1,3-dioxolan-2-one and 4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one (DFBC). Among these, FEC is preferred, for example, from the viewpoint that an amount of hydrofluoric acid generated at a high temperature can be suppressed.
Examples of the fluorinated open-chain carbonate include short open-chain carbonates, such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and methyl isopropyl carbonate, in which part of the hydrogen atoms is substituted by fluorine atoms. Among these, fluorinated ethyl methyl carbonate (FEMC) is preferred, for example, from the viewpoint that the amount of hydrofluoric acid generated at a high temperature is suppressed, and in particular, 2,2,2-trifluoroethyl methyl carbonate is particularly preferred.
Examples of the fluorinated open-chain ester include short open-chain carboxylates, such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate and ethyl propionate, in which part or all of the hydrogen atoms is substituted by fluorine atoms. More specific examples include ethyl 2,2,2-trifluoroacetate, methyl 3,3,3-trifluoropropionate (FMP) and methyl pentafluoropropionate, and for example, from the viewpoint that the amount of hydrofluoric acid generated at a high temperature is suppressed, FMP is preferred.
The nonaqueous solvent may contain, for example, a non-fluorinated solvent in addition to the fluorinated open-chain carbonate and the fluorinate open-chain ester. As the non-fluorinated solvent, any of cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, open-chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, compounds containing esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone, a compound containing a sulfone group such as propane sultone, compounds containing ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1,4-dioxane and 2-methyl tetrahydrofuran, compounds containing nitriles such as butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2,3-propanetricarbonitrile and 1,3,5-pentanetricarbonitrile, and a compound containing an amide such as dimethylformamide can be used.
The electrolyte salt contained in the nonaqueous electrolyte is preferably a lithium salt. As the lithium salt, any of those generally used as supporting salts in conventional nonaqueous electrolyte secondary batteries can be used. Specific examples include LiPF6, LiBF4, LiAsF6, LiClO4, LiCF3SO3, LiN(FSO2)2, LiN(C1F2l+1SO2)(CmF2m+1SO2) (wherein l and m are integers of 1 or more), LiC(CpF2p+1SO2)(CqF2q+1SO2)(CrF2r+1SO2) (wherein p, q and r are integers of 1 or more), Li[B(C2O4)2] (lithium bis(oxalato)borate (LiBOB)), Li[B(C2O4)F2], Li[P(C2O4)F4] and Li[P(C2O4)2F2]. One of these lithium salts may be singly used, or two or more of these may be used in combination.
Hereinafter, the present disclosure will be further described with reference to Examples, but the present disclosure is not limited to these Examples.
[Preparation of Positive Electrode]
A mixture containing 100% by mass of LiNi0.82CO0.15Al0.03O2, 1.0% by mass of acetylene black and 0.9% by mass of polyvinylidene fluoride was obtained, and the mixture was kneaded with N-methyl-2-pyrrolidone to obtain a slurry. Thereafter, the slurry was applied on an aluminum foil collector used as a positive electrode collector, and the resultant was dried and then rolled out to prepare a positive electrode.
[Preparation of Negative Electrode]
A mixture containing 100% by mass of graphite, 1% by mass of a carboxymethylcellulose sodium salt and 1% by mass of a styrene-butadiene copolymer was obtained, and the mixture was kneaded with water to obtain a slurry. Thereafter, the slurry was applied on a copper foil collector used as a negative electrode collector, and the resultant was dried and then rolled out to prepare a negative electrode.
[Preparation of Nonaqueous Electrolyte]
A mixed solvent was adjusted to contain 10% by volume of fluoroethylene carbonate (FEC), 5% by volume of ethylene carbonate (EC), 5% by volume of propylene carbonate (PC), 40% by volume of ethyl methyl carbonate (EMC) and 40% by volume of dimethyl carbonate (DMC), and to the resultant solvent, LiPF6 was added to a concentration of 1.2 mol/l to prepare a nonaqueous electrolyte.
[Preparation of Battery]
An aluminum positive electrode lead was welded to the positive electrode, and a nickel negative electrode lead was welded to the negative electrode. Thereafter, the positive electrode, the negative electrode and a separator were rolled up to obtain a rolled electrode body. Insulating plates were disposed on upper and lower surfaces of the thus obtained rolled electrode body, the electrode body was inserted into a battery can in a bottomed cylindrical shape, and the positive electrode lead and the negative electrode lead were respectively welded to a sealing body and the battery can. Subsequently, the nonaqueous electrolyte was injected into the battery can, the sealing body was fixed by caulking using an insulating gasket, and thus, a cylindrical lithium ion secondary battery was prepared. The sealing body was provided with a pressure relief valve and a current cut-off valve as illustrated in
In the battery A1, the remaining space ratio obtained by expression (1) was 0.192, and the value “a” obtained by expression (2) was 5.57.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC), 10% by volume of ethyl methyl carbonate (EMC) and 75% by volume of dimethyl carbonate (DMC). The resultant was designated as a battery A2. The remaining space ratio and the value “a” of the battery A2 were the same as those of the battery A1.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC), 45% by volume of ethyl methyl carbonate (EMC) and 40% by volume of dimethyl carbonate (DMC). The resultant was designated as a battery A3. The remaining space ratio and the value “a” of the battery A3 were the same as those of the battery A1.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC), 45% by volume of ethyl methyl carbonate (EMC) and 40% by volume of dimethyl carbonate (DMC) and that LiPF6 was added to the resultant solvent to a concentration of 1.4 mol/l. The resultant was designated as a battery A4. The remaining space ratio and the value “a” of the battery A4 were the same as those of the battery A1.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC), 65% by volume of ethyl methyl carbonate (EMC) and 20% by volume of dimethyl carbonate (DMC). The resultant was designated as a battery A5. The remaining space ratio and the value “a” of the battery A5 were the same as those of the battery A1.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC) and 85% by volume of ethyl methyl carbonate (EMC). The resultant was designated as a battery A6. The remaining space ratio and the value “a” of the battery A6 were the same as those of the battery A1.
A battery was prepared in the same manner as in Experimental Example 1 except that the space remaining within the battery was set to 0.98 cm3, and that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC) and 85% by volume of ethyl methyl carbonate (EMC). The resultant was designated as a battery A7. The space remaining within the battery was 0.98 cm3, the remaining space ratio obtained by expression (1) was 0.224, and the value “a” obtained by expression (2) was 6.50.
A battery was prepared in the same manner as in Experimental Example 7 except that a mixed solvent was adjusted to contain 7.5% by volume of fluoroethylene carbonate (FEC), 12.5% by volume of ethylene carbonate (EC) and 80% by volume of ethyl methyl carbonate (EMC). The resultant was designated as a battery A8. The remaining space ratio and the value “a” of the battery A8 were the same as those of the battery A7.
A battery was prepared in the same manner as in Experimental Example 7 except that a mixed solvent was adjusted to contain 5% by volume of fluoroethylene carbonate (FEC), 15% by volume of ethylene carbonate (EC) and 80% by volume of ethyl methyl carbonate (EMC). The resultant was designated as a battery A9. The remaining space ratio and the value “a” of the battery A9 were the same as those of the battery A7.
A battery was prepared in the same manner as in Experimental Example 1 except that a mixed solvent was adjusted to contain 20% by volume of ethylene carbonate (EC), 5% by volume of ethyl methyl carbonate (EMC) and 75% by volume of dimethyl carbonate (DMC) and that LiPF6 was added to the resultant solvent to a concentration of 1.4 mol/l. The resultant was designated as a battery A10. The space remaining within the battery was 1.05 cm3, the remaining space ratio obtained by expression (1) was 0.24, and the value “a” obtained by expression (2) was 6.96.
<ARC (Accelerating Rate Calorimeter) Test>
Each of the batteries A1 to A10 was charged with a constant current of 1000 mA to 4.1 V, and then subjected to ARC test under the following conditions. In the ARC test, an ARC test apparatus manufactured by Thermal Hazard Technology was used with a measurement start temperature set to 80° C., a measurement end temperature set to 200° C., an increment of the measurement temperature set to 10° C., and measurement sensitivity set to 0.02° C./min.
In the ARC test, a temperature sensor was disposed to be in contact with the package of the battery, and the battery temperature was measured from the start of the test (the start of temperature increase) until the battery temperature reached 200° C. The results are shown in
In the batteries A1 to A9, the pressure relief valves were actuated at a temperature of 145° C. or less. The batteries A1 to A9 had larger values of the 180° C. reaching time delay rate than the battery A10 with the pressure relief valve that was actuated at the battery temperature in the vicinity of 180° C. In other words, it can be said that when a pressure relief valve actuated at a battery temperature of 145° C. or less is used, excessive heat generation of the battery after it is actuated can be inhibited. Besides, when the value “a” obtained by expression (2) is preferably 6.5 or less and more preferably 6 or less, and the content of the fluorine-containing organic compound in the nonaqueous electrolyte is preferably 5% by volume or more and 15% by volume or less, and more preferably 10% by volume or more and 15% by volume or less, the actuation temperature of the pressure relief valve can be easily controlled to 145° C. or less, and preferably 140° C. or less.
Besides, in the batteries A1 to A6, the pressure relief valves were actuated at a temperature of 130° C. or less. The batteries A1 to A6 had higher 180° C. reaching time delay rates than the batteries A7 to A10 in which the actuation temperatures of the pressure relief valves were higher than 130° C. In other words, when a pressure relief valve actuated at a battery temperature of 130° C. or less is used, the excessive heat generation of the battery after it is actuated can be further inhibited.
A battery A11 described below was prepared in the same manner as in Experimental Example 1 except for a positive electrode and a nonaqueous electrolyte. The positive electrode and the nonaqueous electrolyte used in the battery A11 is described below.
[Preparation of Positive Electrode]
A mixture containing 96% by mass of LiNi0.5Co0.2Mn0.3O2, 2.5% by mass of acetylene black and 2.5% by mass of polyvinylidene fluoride was obtained, and the mixture was kneaded with N-methyl-2-pyrrolidone to obtain a slurry. Thereafter, the slurry was applied on an aluminum foil collector used as a positive electrode collector, and the resultant was dried and then rolled out to prepare a positive electrode.
[Preparation of Nonaqueous Electrolyte]
A nonaqueous electrolyte was prepared by adjusting a solvent to contain 10% by volume of fluoroethylene carbonate (FEC), 10% by volume of ethylene carbonate (EC), 5% by volume of propylene carbonate (PC), 40% by volume of ethyl methyl carbonate (EMC) and 35% by volume of dimethyl carbonate (DMC), and adding LiPF6 to the resultant solvent to a concentration of 1.4 mol/l.
A rated capacity of the battery A11 was 3500 mAh, and the space remaining within the battery was 1.1 cm3.
In the battery A11, the remaining space ratio obtained by expression (2) was 0.316, and the value “a” obtained by expression (1) was 9.16.
A battery was prepared in the same manner as in Experimental Example 11 except that a mixed solvent was adjusted to contain 15% by volume of fluoroethylene carbonate (FEC), 5% by volume of propylene carbonate (PC), 10% by volume of ethyl methyl carbonate (EMC) and 70% by volume of dimethyl carbonate (DMC). The resultant was designated as a battery A12. The remaining space ratio and the value “a” of the battery A12 were the same as those of the battery A11.
A battery was prepared in the same manner as in Experimental Example 11 except that a positive electrode active material in which Zr was contained as a solid solution in LiNi0.5Co Mn0.30O2 was used. A content of Zr in the positive electrode active material used in this experimental example was 0.5% by mole. The resultant was designated as a battery A13. The remaining space ratio and the value “a” of the battery A13 were the same as those of the battery A11.
A battery was prepared in the same manner as in Experimental Example 11 except that the remaining space ratio was changed. The resultant was designated as a battery A14. The remaining space ratio obtained by expression (2) was 0.324, and the value “a” obtained by expression (1) was 9.39.
Each of the batteries A11 to A14 was charged with a constant current of 840 mA to 4.1 V, and then subjected to the ARC test under the above conditions.
In each of the batteries A11 to A14, the battery temperature increased as the temperature increase in the ARC test was started, and an inflection point at which the battery temperature once decreased was observed at a temperature of 145° C. or less. Besides, in the battery A14, an inflection point was observed at a temperature exceeding 140° C. The results of the actuation temperatures of the pressure relief valves of the batteries A11 to A14 are shown altogether in Table 2.
In the batteries A11 to A14, the pressure relief valves were actuated at a temperature of 145° C. or less. They had larger values of the 180° C. reaching time delay rate than the battery A10 with the pressure relief valve that was actuated at a temperature in the vicinity of 180° C. In other words, it can be said that when a pressure relief valve actuated at a battery temperature of 145° C. or less is used, excessive heat generation of the battery after it is actuated can be inhibited. Besides, when the value “a” obtained by expression (2) is 9.5 or less, the actuation temperature of the pressure relief valve can be easily controlled to 145° C. or less.
Besides, in the batteries A11 to A13, the pressure relief valves were actuated at a temperature of 140° C. or less. They had larger values of the 180° C. reaching time delay rate than the battery A14 with the pressure relief valve that was actuated at a temperature higher than 140° C. In other words, it can be said that when a pressure relief valve actuated at a battery temperature of 140° C. or less is used, excessive heat generation of the battery after it is actuated can be inhibited. Besides, when the value “a” obtained by expression (2) is 9.2 or less, the actuation temperature of the pressure relief valve can be easily controlled to 140° C. or less.
The present disclosure is applicable to a nonaqueous electrolyte secondary battery.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-253569 | Dec 2015 | JP | national |
| 2016-064182 | Mar 2016 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2016/005123 | Dec 2016 | US |
| Child | 15997984 | US |
