JP6919202B2 - Manufacturing method of non-aqueous electrolyte, power storage element and power storage element - Google Patents

Description

The present invention relates to a non-aqueous electrolyte, a power storage element, and a method for manufacturing the power storage element.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as power storage elements other than non-aqueous electrolyte secondary batteries.

Generally, the non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and other components are added as necessary. As the non-aqueous solvent, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are used. The non-aqueous solvent used for such a non-aqueous electrolyte is used in combination with other non-aqueous solvents for the purpose of improving performance and the like. Specifically, a non-aqueous electrolyte to which fluorinated ether is added in order to improve charge / discharge cycle performance has been proposed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 8-37024

However, the above-mentioned conventional non-aqueous electrolyte does not have sufficient charge / discharge cycle performance in a low temperature environment, and there is a demand for a non-aqueous electrolyte power storage element having higher charge / discharge cycle performance even in a low temperature environment.

The present invention has been made based on the above circumstances, and an object of the present invention is a non-aqueous electrolyte which can increase the capacity retention rate in a charge / discharge cycle even at high temperature and low temperature, and this non-aqueous electrolyte. It is an object of the present invention to provide a power storage element comprising the above, and a method for manufacturing the power storage element.

One aspect of the present invention made to solve the above problems is that at least one of the groups containing a fluorinated cyclic carbonate and a fluorinated ether and bonded to an oxygen atom of the fluorinated ether is methyl fluorinated. A non-aqueous electrolyte which is a group, an ethyl fluorinated group or an isopropyl fluorinated group, and the fluorinated ether has a fluorination rate of 0.6 or less. Here, the fluorination rate refers to the ratio of the number of fluorine atoms to the total number of fluorine atoms and hydrogen atoms contained in the molecule.

Another aspect of the present invention is a power storage element including the non-aqueous electrolyte.

Another aspect of the present invention is a method for manufacturing a power storage element using the non-aqueous electrolyte.

According to the present invention, it is possible to provide a non-aqueous electrolyte capable of increasing the capacity retention rate in a charge / discharge cycle even in a low temperature environment, a power storage element provided with the non-water electrolyte, and a method for manufacturing the power storage element.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous electrolyte secondary batteries according to an embodiment of the present invention.

One aspect of the present invention contains a fluorinated cyclic carbonate and a fluorinated ether, and at least one of the groups bonded to the oxygen atom of the fluorinated ether is a fluorinated methyl group, a fluorinated ethyl group, or fluorinated. It is a non-aqueous electrolyte having an isopropyl group and having a fluorination rate of 0.6 or less for the fluorinated ether.

According to the non-aqueous electrolyte, the capacity retention rate in the charge / discharge cycle can be increased even in a low temperature environment. The reason for this effect is not clear, but it is thought to be as follows. When the non-aqueous electrolyte contains a fluorinated cyclic carbonate, the charge / discharge cycle performance in a high temperature environment is improved. However, the non-aqueous electrolyte containing the fluorinated cyclic carbonate increases the resistance in the low temperature environment by forming a film on the positive electrode or the negative electrode and increasing the viscosity of the non-aqueous electrolyte in the low temperature environment. By containing a specific fluorinated ether in the non-aqueous electrolyte, the resistance of the coating film formed on the positive electrode or the negative electrode can be reduced, or the increase in viscosity of the non-aqueous electrolyte can be suppressed, and in a low temperature environment. Since the resistance can be lowered, it is presumed that the charge / discharge cycle capacity retention rate is less likely to decrease even in a low temperature environment. Further, it is presumed that by including the fluorinated cyclic carbonate in the non-aqueous electrolyte, the continuous reductive decomposition of the fluorinated ether can be suppressed and the above effect can be obtained.

The upper limit of the number of carbon atoms of the fluorinated ether is preferably 4. 2 is preferable as the lower limit of the number of carbon atoms. By setting the carbon number of the fluorinated ether in the above range, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

The specific gravity of the fluorinated ether is preferably 1.40 or less. As the specific gravity of the fluorinated ether, a value of 20 ° C. is adopted. By setting the specific gravity of the fluorinated ether in the above range, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

It is preferable that any of the above groups is a methyl group, an ethyl group, a propyl group or an isopropyl group. When any of the above groups is a methyl group, an ethyl group, a propyl group or an isopropyl group, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

Another aspect of the present invention is a power storage element including the non-aqueous electrolyte. Since the power storage element includes the non-aqueous electrolyte, the capacity retention rate in the charge / discharge cycle can be increased even in a low temperature environment.

Another aspect of the present invention is a method for manufacturing a power storage element using the non-aqueous electrolyte. According to the method for manufacturing the power storage element, since the non-aqueous electrolyte is used, it is possible to obtain a power storage element capable of increasing the capacity retention rate in the charge / discharge cycle even in a low temperature environment.

<Non-aqueous electrolyte>
The non-aqueous electrolyte according to the embodiment of the present invention contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid. That is, the non-aqueous electrolyte is not limited to a liquid electrolyte, but also includes a solid electrolyte, a gel electrolyte, and the like.

(Non-aqueous solvent)
The non-aqueous solvent contains a fluorinated cyclic carbonate and a fluorinated ether. At least one of the groups bonded to the oxygen atom of the fluorinated ether is a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group, and the fluorination rate of the fluorinated ether is 0.6 or less. It is a water electrolyte.

(Fluorinated cyclic carbonate)
The fluorinated cyclic carbonate refers to a compound in which a part or all of hydrogen atoms contained in a cyclic carbonate such as ethylene carbonate, propylene carbonate, and butylene carbonate are substituted with a fluorine atom.

Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonate such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonate, and fluorinated butylene carbonate, but fluorinated ethylene carbonate is preferable, and FEC is preferable. Is more preferable. The above-mentioned fluorinated cyclic carbonate can be used alone or in combination of two or more.

The content of the fluorinated cyclic carbonate in the non-aqueous solvent is not particularly limited, but the lower limit thereof is preferably 5% by volume, more preferably 8% by volume. On the other hand, as the upper limit of this content, 25% by volume is preferable, 20% by volume is more preferable, and 15% by volume is further preferable. By setting the content of the fluorinated cyclic carbonate to the above lower limit or more and the above upper limit or less, the effect of increasing the capacity retention rate in the charge / discharge cycle can be more sufficiently exhibited even at high temperature and low temperature.

(Fluorinated ether)
The fluorinated ether refers to a compound in which a part or all of the hydrogen atoms of the hydrocarbon group of the ether are replaced with fluorine atoms.

In the fluorinated ether, at least one of the groups bonded to the oxygen atom of the fluorinated ether is a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group. Since at least one of the groups bonded to the oxygen atom of the fluorinated ether is a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group, the capacity is maintained in the charge / discharge cycle even at high temperature and low temperature. The rate can be increased. Specifically, both of the groups bonded to the oxygen atom of the fluorinated ether may be a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group, while binding to the oxygen atom of the fluorinated ether. Only one of the groups may be a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group.

The upper limit of the fluorination rate of the fluorinated ether is 0.6. Here, the fluorination rate refers to the ratio of the number of fluorine atoms to the total number of fluorine atoms and hydrogen atoms contained in the molecule. On the other hand, as the lower limit of the fluorination rate of the fluorinated ether, 0.3 is preferable, and 0.4 is more preferable. When the fluorination rate of the fluorinated ether is within the above range, the capacity retention rate in the charge / discharge cycle can be increased even at high temperature and low temperature.

As the upper limit of the number of carbon atoms of the fluorinated ether, 8 is preferable, 6 is more preferable, and 4 is further preferable. As the lower limit of the number of carbon atoms, 2 is preferable, and 3 is more preferable. By setting the carbon number of the fluorinated ether in the above range, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

The specific gravity of the fluorinated ether is preferably 1.40 or less. As the specific gravity of the fluorinated ether, a value of 20 ° C. is adopted. By setting the specific gravity of the fluorinated ether in the above range, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

Any of the above groups is preferably a methyl group, an ethyl group, a propyl group or an isopropyl group, and more preferably a methyl group or an ethyl group. When any of the above groups is these groups, the capacity retention rate in the charge / discharge cycle of the power storage element can be further increased.

Examples of the fluorinated ether include ethyl-1,1,2,2-tetrafluoroethyl ether (fluorination rate: 0.4, carbon number: 4, specific gravity: 1.21) and hexafluoroisopropylmethyl ether (1). , 1,1,3,3,3-hexafluoro-2-methoxypropane) (fluorination rate: 0.6, carbon number: 4, specific gravity: 1.39), trifluoroethyl methyl ether (fluorination rate: 0.4, carbon number: 3, specific gravity: 1.16), methyl-1,1,2,2-tetrafluoroethyl ether (fluorination rate: 0.5, carbon number: 3, specific gravity: 1.30) Among these, ethyl-1,1,2,2-tetrafluoroethyl ether and hexafluoroisopropylmethyl ether are preferable. The above-mentioned fluorinated ether can be used alone or in combination of two or more.

The content of the fluorinated ether in the non-aqueous solvent is not particularly limited, but the lower limit thereof is preferably 10% by volume, more preferably 15% by volume. On the other hand, as the upper limit of this content, 40% by volume is preferable, 35% by volume is more preferable, and 32% by volume is further preferable. By setting the content of the fluorinated ether to the above lower limit or more and the above upper limit or less, the effect of increasing the capacity retention rate in the charge / discharge cycle can be more sufficiently exhibited even at high temperature and low temperature.

(Other non-aqueous solvents)
As the other non-aqueous solvent other than the fluorinated cyclic carbonate and the fluorinated ether, a known non-aqueous solvent usually used as a non-aqueous solvent in the non-aqueous electrolyte of a general power storage element can be used. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles and the like. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the chain carbonate to the cyclic carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but may be, for example, 1: 2 or more and 1:10 or less. preferable.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene. Examples thereof include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and among these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate and the like, and among these, EMC is preferable.

(Electrolyte salt)
As the electrolyte salt, a known electrolyte salt usually used as an electrolyte salt in a non-aqueous electrolyte of a general power storage element can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, but lithium salt is preferable.

Examples of the lithium salt include _{inorganic lithium salts such as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiB (C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ). , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ , a lithium salt having a fluorinated hydrocarbon group, and the like can be mentioned. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The lower limit of the content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 M, more preferably 0.3 M, further preferably 0.5 M, and particularly preferably 0.7 M. On the other hand, the upper limit is not particularly limited, but 2.5M is preferable, 2M is more preferable, and 1.5M is further preferable.

The non-aqueous electrolyte may contain components other than the non-aqueous solvent and the electrolyte salt as long as the effects of the present invention are not impaired. Examples of the other components include various additives contained in the non-aqueous electrolyte of a general power storage device. However, the content of these other components may be preferably 5% by mass or less, and more preferably 1% by mass or less.

The non-aqueous electrolyte can be obtained by adding and dissolving the electrolyte salt to the non-aqueous solvent.

<Power storage element>
The power storage element according to an embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example of the power storage element. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a case, and the case is filled with the non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte described above is used as the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known metal case or the like which is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

According to the non-aqueous electrolyte secondary battery (storage element), since the non-aqueous electrolyte is used, the capacity retention rate in the charge / discharge cycle can be increased even at high temperature and low temperature.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer arranged directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. As the material of the base material, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, as a form of forming the positive electrode base material, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles. Incidentally, to have a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, and "non-conductive" means that the volume resistivity is 10 ⁷ Ω · cm greater.

The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. Further, the positive electrode mixture forming the positive electrode active material layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary.

Examples of the positive electrode active material include _{composite oxides represented by Li x} MO _y (M represents at least one kind of transition metal) ( _{Li x} CoO ₂ and Li _x NiO _{having a layered α-NaFeO type 2} crystal structure). ₂ , Li _x MnO ₃ , Li _x Ni _α Co _(1-α) O ₂ , Li _x Ni _α Mn _β Co _(1-α-β) O _{2, etc., Li x} Mn ₂ O ₄ having a spinel type crystal structure , Li _x Ni _α Mn _(2-α) O ₄ etc.), Li _w Me _x (XO _y ) _z (Me represents at least one kind of transition metal, and X represents, for example, P, Si, B, V, etc.) Examples thereof include polyanionic compounds represented by (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li _{2 MnSiO 4} , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of these compounds may be mixed and used.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the battery performance. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and Ketjen black, metals, conductive ceramics, and the like. Examples of the shape of the conductive agent include powder and fibrous.

Examples of the binder (binding agent) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), Elastomers such as sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and thermoplastic polymers can be mentioned.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group by methylation or the like in advance.

The filler is not particularly limited as long as it does not adversely affect the battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, carbon and the like.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer arranged directly on the negative electrode base material or via an intermediate layer. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.

The negative electrode base material may have the same structure as the positive electrode base material, but as the material, a metal such as copper, nickel, stainless steel, nickel-plated steel or an alloy thereof is used, and copper or a copper alloy is used. preferable. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode active material layer is formed from a so-called negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary. As the optional components such as the conductive agent, the binder, the thickener, and the filler, the same ones as those of the positive electrode active material layer can be used.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is usually used. Specific negative electrode active materials include, for example, metals such as Si and Sn, or semimetals;
Metal oxides such as Si oxides and Sn oxides or metalloid oxides;
Polyphosphoric acid compound;
Carbon materials such as graphite (graphite) and amorphous carbon (graphitizable carbon or non-graphitizable carbon);
Examples thereof include lithium metal composite oxides such as lithium titanate.

Further, the negative electrode mixture (negative electrode active material layer) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and the like may be contained.

(Separator)
As the material of the separator, for example, a woven fabric, a non-woven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the main component of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. Moreover, you may combine these resins.

<Manufacturing method of power storage element>
The method for manufacturing a power storage element according to an embodiment of the present invention is a method for manufacturing a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the non-aqueous electrolyte is used as the non-aqueous electrolyte. The manufacturing method includes, for example, a step of accommodating a positive electrode and a negative electrode (electrode body) in a case and a step of injecting the non-aqueous electrolyte into the case.

The above injection can be performed by a known method. After injection, a non-aqueous electrolyte secondary battery can be obtained by sealing the injection port. Details of each element constituting the non-aqueous electrolyte secondary battery obtained by the production method are as described above. According to the manufacturing method, by using the non-aqueous electrolyte, the capacity retention rate in the charge / discharge cycle can be increased even at high temperature and low temperature.

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. For example, it is not necessary to provide an intermediate layer in the positive electrode or the negative electrode. Further, in the above embodiment, the embodiment in which the power storage element is a non-aqueous electrolyte secondary battery has been mainly described, but other power storage elements may be used. Examples of other power storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte secondary battery 1 which is an embodiment of a power storage element according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'. Further, the non-aqueous electrolyte according to the embodiment of the present invention is injected into the battery container 3.

The configuration of the power storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above power storage elements. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
(Preparation of non-aqueous electrolyte)
_{LiPF 6} is dissolved at a concentration of 1.2 M in a solvent in which FEC, PC, EMC and ethyl-1,1,2,2-tetrafluoroethyl ether (ETFEE) are mixed at a volume ratio of 10:10:50:30. The non-aqueous electrolyte of Example 1 was obtained.

(Manufacturing of power storage element)
_{A positive electrode plate having LiNi 1/3} Co _1/3 Mn _1/3 O ₂ having an α-NaFeO _{type 2} crystal structure as a positive electrode active material was prepared. In addition, a negative electrode plate using graphite as a negative electrode active material was produced. Next, the positive electrode plate and the negative electrode plate were laminated via a separator made of a polyethylene microporous membrane, and wound into a flat shape to prepare an electrode body. This electrode body was housed in a square electric tank can made of aluminum, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the container (square battery can), the container was sealed to obtain a power storage element (square lithium ion secondary battery with a design capacity of 900 mAh).

[Example 2, Comparative Example 1 to Comparative Example 8]
The non-aqueous electrolytes of Example 2 and Comparative Examples 1 to 8 and the power storage device are the same as in Example 1 except that the types and contents of the compounds used are as shown in Tables 1 and 2. Got
In addition to the above ETFEE, the compounds used as non-aqueous electrolytes are as follows.
HFIPME: Hexafluoroisopropylmethyl ether TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether EHFPE: Ethyl-1,1,2,3,3,3-hexa Fluoropropyl ether HFPME: 1,1,2,3,3,3-hexafluoropropylmethyl ether TFETFEE: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether The following “-” In Table 1 indicates that the corresponding component was not used.

[evaluation]
(Charge / discharge cycle test: Capacity retention rate)
(1) Measurement of Discharge Capacity in Initial Charge / Discharge Step Each of the obtained non-aqueous electrolyte power storage elements was subjected to a two-cycle initial charge / discharge step at a temperature of 25 ° C. All voltage controls were performed with respect to the voltage between the positive and negative terminals. Charging in the first cycle is constant current constant voltage charging with a charging current of 0.2C, charge termination voltage of 4.3V, and total charging time of 8 hours, and discharge is constant of discharge current of 0.2C and discharge termination voltage of 2.75V. It was a current discharge. The charging in the second cycle is a constant current constant voltage charge with a charging current of 1.0 C, a charge end voltage of 4.3 V, and a total charge time of 3 hours, and the discharge is a constant discharge current of 1.0 C and a discharge end voltage of 2.75 V. It was a current discharge. A 10 minute rest period was set after charging and discharging in all cycles. The discharge capacity of the second cycle was defined as the initial discharge capacity.

(2) Measurement of discharge capacity after 150 cycles at 0 ° C. After storing each non-aqueous electrolyte power storage element in a constant temperature bath at 0 ° C. for 5 hours, the charging current is 1C, the final charging voltage is 4.3V, and the total charging time is 3 hours. Constant current and constant voltage charging was performed. Next, a 10-minute rest was provided after charging. Then, a constant current discharge with a discharge current of 1C and a discharge end voltage of 2.75V was performed, and then a 10-minute pause was provided. These charging and discharging steps were regarded as one cycle, and this cycle was repeated for 150 cycles. Charging, discharging and pausing were all performed in a constant temperature bath at 0 ° C. For each non-aqueous electrolyte power storage element after the charge / discharge cycle test, the discharge capacity after the charge / discharge cycle test was measured in the same manner as in the second cycle of the initial charge / discharge step. The discharge capacity after 150 cycles at 0 ° C. with respect to the initial discharge capacity is shown in Tables 1 and 2 below as the capacity retention rate (%). In Table 2, the * mark in Comparative Example 8 indicates the value of the capacity retention rate (%) after 100 cycles.

(3) Measurement of discharge capacity after 200 cycles at 45 ° C. After storing each non-aqueous electrolyte power storage element in a constant temperature bath at 45 ° C. for 5 hours, the charging current is 1C, the final charging voltage is 4.3V, and the total charging time is 3 hours. Constant current and constant voltage charging was performed. Next, a 10-minute rest was provided after charging. Then, a constant current discharge with a discharge current of 1C and a discharge end voltage of 2.75V was performed, and then a 10-minute pause was provided. These charging and discharging steps were regarded as one cycle, and this cycle was repeated for 200 cycles. Charging, discharging and pausing were performed in a constant temperature bath at 45 ° C. For each non-aqueous electrolyte power storage element after the charge / discharge cycle test, the discharge capacity after the cycle test was measured in the same manner as in the second cycle of the initial charge / discharge step. The discharge capacity after 200 cycles at 45 ° C. with respect to the initial discharge capacity is shown in Table 1 below as the capacity retention rate (%).

As shown in Table 1 above, in Examples 1 to 2 provided with the non-aqueous electrolyte of the present invention containing a fluorinated cyclic carbonate and a specific fluorinated ether, the specific fluorinated ether is contained. The capacity retention rate at 0 ° C. was superior to that of Comparative Examples 1 to 5 which did not or contained a fluorinated ether other than the specific fluorinated ether. The viscosity of ethyl-1,1,2,2-tetrafluoroethyl ether used in Examples 1 and 2 is 0.486 mPa · s, and the viscosity of hexafluoroisopropyl methyl ether is 0.498 mPa · s. Therefore, it is considered that a fluorinated ether having a relatively low viscosity is preferable.

As shown in Table 1 above, in Examples 1 to 2 provided with the non-aqueous electrolyte of the present invention containing a fluorinated cyclic carbonate and a specific fluorinated ether, the capacity retention rate at 0 ° C. was excellent. The reason can be considered as follows. That is, by containing the fluorinated cyclic carbonate and the above-mentioned specific fluorinated ether, the resistance of the coating film formed on the positive electrode or the negative electrode is reduced, or the viscosity of the non-aqueous electrolyte is reduced, and in a low temperature environment. It is probable that the resistance was kept low.

Further, as shown in Table 2 above, in Comparative Example 6 which does not contain the fluorinated cyclic carbonate and the specific fluorinated ether as the non-aqueous solvent and contains only PC and EMC, the charge / discharge cycle test cannot be performed. there were. Further, in Comparative Example 7 and Comparative Example 8 in which a non-aqueous solvent containing EC was used instead of PC, when the fluorinated cyclic carbonate was not contained, the temperature was 0 ° C. even if the specific fluorinated ether was contained. It was shown that the capacity retention rate did not improve, but rather decreased significantly.

The present invention can be applied to a non-aqueous electrolyte power storage element such as a non-aqueous electrolyte secondary battery used as a power source for a personal computer, an electronic device such as a communication terminal, an automobile, and a non-aqueous electrolyte provided therein.

(Explanation of code)
1 Non-aqueous electrolyte secondary battery 2 Electrode body 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (6)

Fluorinated cyclic carbonate and
Contains fluorinated ether and
The group bonded to the oxygen atom of the fluorinated ether is either a fluorinated methyl group, a fluorinated ethyl group, a fluorinated isopropyl group, a methyl group, an ethyl group, a propyl group or an isopropyl group.
At least one of the above groups is a fluorinated methyl group, a fluorinated ethyl group or a fluorinated isopropyl group.
Aqueous electrolyte off Tsu fluorinated ratio of the fluorinated ether is 0.6 or less (. Except those falling below (A) ~ (D)) .
(A) Hexa having a concentration of 1.30 mol / L in a mixed solvent of fluoroethylene carbonate, dimethyl carbonate and 1,1,2,2-tetrafluoroethylethyl ether having a volume ratio of 15:45:40 and the above mixed solvent. Those containing lithium fluorophosphate (B) In a mixed solvent of fluoroethylene carbonate, dimethyl carbonate and 1,1,2,2-tetrafluoroethylmethyl ether having a volume ratio of 15:45:40 and the above mixed solvent. Solvent containing lithium hexafluorophosphate having a concentration of 1.30 mol / L (C) Fluoroethylene carbonate, ethylene carbonate, ethylmethyl carbonate, diethyl carbonate and 2, having a volume ratio of 5:20:32:33:10 A mixed solvent of 2-difluoroethyl-1,1,2,2-tetrafluoroethyl ether, lithium hexafluorophosphate having a concentration of 1 mol / L in the mixed solvent, and 1% by weight of tris (trimethylsilyl) phosphate. (D) A mixed solvent of fluoroethylene carbonate and 2,2-difluoroethyl-1,1,2,2-tetrafluoroethyl ether having a volume ratio of 30:60 and a concentration of 1 mol / in the above mixed solvent. Containing L lithium hexafluorophosphate and 3% by weight N, O-bis (trimethylsilyl) acetamide The non-aqueous electrolyte according to claim 1, wherein the fluorinated ether has 4 or less carbon atoms. The non-aqueous electrolyte according to claim 1 or 2, wherein the fluorinated ether has a specific gravity of 1.40 or less at 20 ° C. The non-aqueous electrolyte according to claim 1, claim 2 or claim 3, wherein any of the above groups is a methyl group, an ethyl group, a propyl group or an isopropyl group. A power storage element comprising the non-aqueous electrolyte according to any one of claims 1 to 4. A method for manufacturing a power storage element using the non-aqueous electrolyte according to any one of claims 1 to 4.

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