JP7155719B2 - Nonaqueous electrolyte storage element and method for manufacturing nonaqueous electrolyte storage element - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers, communication terminals, and automobiles because of their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is configured to be charged and discharged by Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

Lithium hexafluorophosphate (LiPF ₆ ) is widely used as an electrolyte salt for non-aqueous electrolytes. However, it is known that LiPF ₆ easily reacts with trace amounts of water contained in non-aqueous electrolyte storage elements, and the resultant hydrogen fluoride (HF) reduces the charge/discharge performance of non-aqueous electrolyte storage elements. . On the other hand, imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI) are also known as a kind of electrolyte salts used in non-aqueous electrolytes. The imide salt has a higher dissociation property between cations and anions than LiPF ₆ . Therefore, the non-aqueous electrolyte storage element to which this is applied is expected to have good high-rate discharge performance and the like in a low-temperature environment. However, when an imide salt is used as an electrolyte salt, it is used as a positive electrode base material or the like for a non-aqueous electrolyte storage element by charging and discharging at a positive electrode operating potential of 4.0 V (vs. Li/Li ⁺ ) or more. It is known that oxidation corrosion of aluminum occurs and charge/discharge performance deteriorates. On the other hand, it has been reported that by using a high concentration of imide salt, it is possible to suppress oxidation corrosion of aluminum during charging and discharging when the working potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or more. (See patent document 1, non-patent document 1 abstract). Regarding the specific concentration of the imide salt at which this inhibitory effect is obtained, for example, paragraph [0012] of Patent Document 1 states, "When the voltage is 4.5 V, corrosion is confirmed at LiFSI of 1.5 mol/L or more. First, it was found that when the voltage is as high as 4.9 V, corrosion is not confirmed if LiFSI is 4 mol/L."

JP 2015-79636 A

Jianhui Wang et al., “Superconcentrated electronics for a high-voltage lithium-ion battery,” Nature Communications, 2016, 7:12032 doi:10.1038/ncomms12032

LiN(SO ₂ F) ₂ (LiFSI), LiN(C ₂ F ₅ SO ₂ ) ₂ (LiBETI), and LiN(CF ₃ SO ₂ ) ₂ (LiTFSI) as electrolyte salts in the non-aqueous electrolyte storage element as described above. When an imide salt such as imide salt is used at a general concentration of around 1 mol/kg, oxidation corrosion of aluminum tends to occur when the positive electrode develops an operating potential of 4.0 V (vs. Li/Li ⁺ ) or more. . Oxidation corrosion of aluminum is not preferable because the charge/discharge performance of the non-aqueous electrolyte power storage element is greatly reduced during charging/discharging. On the other hand, by using a nonaqueous electrolyte containing a high concentration of imide salt, oxidation corrosion of aluminum can be suppressed, but in this case, the viscosity of the nonaqueous electrolyte increases and the ionic conductivity also decreases. An increase in the viscosity of the non-aqueous electrolyte is one of the advantages of using an imide salt, and is not preferable because it can degrade the high-rate discharge performance, etc. in a low-temperature environment of a non-aqueous electrolyte storage element to which the imide salt is applied.

The present invention has been made based on the circumstances as described above, and an object of the present invention is to provide a non-aqueous electrolyte storage element having good high-rate discharge performance in a low-temperature environment, and such a non-aqueous electrolyte storage element. is to provide a manufacturing method of

One aspect of the present invention, which has been made to solve the above problems, includes a positive electrode having a positive electrode mixture containing a phosphorus atom, and a non-aqueous electrolyte containing an imide salt and a fluorinated ether, and X-rays of the positive electrode mixture In the photoelectron spectroscopy spectrum, the peak attributed to P2p is present at a position of 135 eV or less.

Another aspect of the present invention is to prepare a positive electrode having a positive electrode mixture prepared by applying a positive electrode mixture paste containing an oxoacid of phosphorus, and a non-aqueous electrolyte containing an imide salt and a fluorinated ether. and injecting into a container.

ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte electrical storage element which has favorable high rate discharge performance in a low-temperature environment, and the manufacturing method of such a nonaqueous electrolyte electrical storage element can be provided.

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

A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode having a positive electrode mixture containing phosphorus atoms, and a non-aqueous electrolyte containing an imide salt and a fluorinated ether, and X-ray photoelectrons of the positive electrode mixture It is a non-aqueous electrolyte power storage element in which a peak attributed to P2p exists at a position of 135 eV or less in a spectroscopic spectrum.

According to the non-aqueous electrolyte storage element, even if the imide salt in the non-aqueous electrolyte does not have a high concentration, oxidation corrosion of aluminum can be suppressed, and good high-rate discharge performance can be obtained in a low-temperature environment. Although the reason why the above effect is produced in the non-aqueous electrolyte storage element is not clear, the following reason is presumed. When a positive electrode mixture is formed from a positive electrode mixture paste containing a phosphorus oxoacid, on the surface of the positive electrode mixture and on the surface of aluminum as a positive electrode base material, etc., there is an X-ray photoelectron spectroscopy spectrum derived from this phosphorus oxoacid. , P2p at positions below 135 eV. It is presumed that this film suppresses oxidation corrosion of aluminum as a positive electrode base material and the like, so that good high-rate discharge performance in a low-temperature environment of the non-aqueous electrolyte storage element can be obtained. Further, one of the causes of deterioration in charge/discharge performance of a non-aqueous electrolyte storage element using LiPF ₆ as an electrolyte salt is corrosion of the surface of the positive electrode due to a minute amount of HF present in the vicinity of the positive electrode. Due to this corrosion, the positive electrode active material components are eluted from the surface of the positive electrode and diffused to the negative electrode side, and the positive electrode active material components are deposited on the negative electrode. It is said that this causes the irreversible capacity and resistance of the negative electrode to gradually increase and the charge/discharge performance to deteriorate. The trace amount of HF is presumed to be generated by decomposition of LiPF ₆ in the vicinity of the positive electrode. On the other hand, in the non-aqueous electrolyte power storage device according to one embodiment of the present invention, the peak attributed to P2p in the X-ray photoelectron spectroscopy spectrum derived from the oxoacid of phosphorus formed on the surface of the positive electrode mixture is 135 eV. The film containing the components present in the following positions suppresses the decomposition reaction of the electrolyte salt on the surface of the positive electrode mixture, suppresses the elution of the positive electrode active material components, and as a result, achieves good high-rate discharge performance in low-temperature environments. is assumed to be obtained. Furthermore, in the non-aqueous electrolyte storage element, the non-aqueous electrolyte contains fluorinated ether, which has high oxidation resistance and relatively low viscosity. In addition to suppressing reactions (oxidative decomposition of non-aqueous solvents, etc.), it is also possible to suppress increases in the viscosity of non-aqueous electrolytes and decreases in ionic conductivity. Better high rate discharge performance can be obtained under Although the reason is not clear, the effect of obtaining good high-rate discharge performance in a low-temperature environment of the non-aqueous electrolyte storage element is that the non-aqueous electrolyte contains an imide salt and a fluorinated ether, and X This is a peculiar effect that occurs only when using a positive electrode having a positive electrode mixture in which a peak attributed to P2p exists at a position of 135 eV or less in a line photoelectron spectroscopy spectrum. Further, according to the non-aqueous electrolyte storage element, it is possible to suppress oxidation corrosion of aluminum as a positive electrode base material and the like without increasing the concentration of the imide salt as described above. For this reason, the non-aqueous electrolyte storage element can improve the unfavorable points of the conventional non-aqueous electrolyte storage element using a high-concentration imide salt, such as an increase in the viscosity of the non-aqueous electrolyte and a decrease in the ionic conductivity. It can also be suitably used as a design in which the concentration range of salt is not high.

A sample (positive electrode mixture) used for measurement of X-ray photoelectron spectroscopy is prepared by the following method. The non-aqueous electrolyte storage element is discharged with a current of 0.1 C to the final discharge voltage in normal use, and is brought into a completely discharged state. The fully discharged electric storage device is disassembled, the positive electrode is taken out, the positive electrode is thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut into a predetermined size (for example, 2×2 cm), and this is used as a sample for measurement of X-ray photoelectron spectroscopy. The work from the dismantling of the non-aqueous electrolyte storage element to the preparation of the sample for the measurement of the X-ray photoelectron spectroscopy spectrum is performed in an argon atmosphere with a dew point of -60 ° C. or less, and the prepared sample is enclosed in a transfer vessel and the dew point is -60. C. or below, and introduced into a sample chamber of an X-ray photoelectron spectroscopy spectrometer. The apparatus and measurement conditions used in the measurement of X-ray photoelectron spectroscopy are as follows.
Equipment: KRATOS ANALYTICAL "AXIS NOVA"
X-ray source: monochromatic AlKα
Accelerating voltage: 15 kV
Analysis area: 700 μm × 300 μm
Measurement range: P2p=145-128eV, C1s=300-272eV
Measurement interval: 0.1 eV
Measurement time: P2p = 72.3 seconds/time, C1s = 70.0 seconds/time Accumulation times: P2p = 15 times, C1s = 8 times Further, the peak positions in the above spectrum are obtained as follows. and First, the position of the C1s peak attributed to sp2 carbon is set to 284.8 eV, and the binding energies of all obtained spectra are corrected. A smoothing process is then performed on the corrected spectrum by removing the background using the linear method. In the spectrum after the flattening process, the binding energy showing the highest intensity of the peak attributed to P2p is taken as the position of the peak attributed to P2p.

In the non-aqueous electrolyte storage element, the non-aqueous electrolyte preferably further contains a fluorinated cyclic carbonate.

In the non-aqueous electrolyte storage element, by further containing a fluorinated cyclic carbonate with high oxidation resistance in the non-aqueous electrolyte, side reactions that may occur during charging and discharging of the non-aqueous electrolyte storage element (oxidative decomposition of non-aqueous solvents, etc.) etc.) can be suppressed. Therefore, by including a fluorinated cyclic carbonate and a fluorinated ether at the same time, better high-rate discharge performance can be obtained in a low-temperature environment.

A method for producing a non-aqueous electrolyte storage element according to an embodiment of the present invention comprises preparing a positive electrode having a positive electrode mixture prepared by applying a positive electrode mixture paste containing an oxoacid of phosphorus, an imide salt and A method for manufacturing a non-aqueous electrolyte storage element using a non-aqueous electrolyte containing a fluorinated ether.

By using a positive electrode mixture paste containing a phosphorus oxoacid, a positive electrode mixture in which a peak attributed to P2p exists at a position of 135 eV or less in an X-ray photoelectron spectroscopy spectrum can be obtained. Therefore, according to the production method, even if the concentration range of the imide salt is not high, it is possible to produce a non-aqueous electrolyte storage element having good high-rate discharge performance in a low-temperature environment.

Hereinafter, a non-aqueous electrolyte storage element and a method for manufacturing the non-aqueous electrolyte storage element according to one embodiment of the present invention will be described in detail.

<Non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery will be described below as an example of the non-aqueous electrolyte storage element. The positive electrode and the negative electrode generally form an electrode body alternately stacked by lamination or winding with a separator interposed therebetween. This electrode assembly is housed in a container, and the container is filled with the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. As the container, known metal containers, resin containers, and the like, which are usually used as containers for non-aqueous electrolyte secondary batteries, can be used.

(positive electrode)
The positive electrode has a positive electrode substrate and a positive electrode material mixture layer disposed directly on the positive electrode substrate or via an intermediate layer.

The said positive electrode base material has electroconductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance between high conductivity and cost. In addition, when the positive electrode base material is aluminum or an aluminum alloy, it suppresses deterioration of the charge and discharge performance of the non-aqueous electrolyte storage element, which is presumed to be mainly caused by oxidation corrosion of aluminum, and provides good performance in a low temperature environment. It is possible to more fully enjoy the effect of having high rate discharge performance. Forms of formation of the positive electrode substrate include foil, deposited film, and the like, and foil is preferable from the viewpoint of cost. In other words, aluminum foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode mixture layer. The structure of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles. The term “conductivity” means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω·cm or less. means that the volume resistivity is greater than 10 ⁷ Ω·cm.

The positive electrode mixture layer is a layer formed from a positive electrode mixture. This positive electrode mixture contains a positive electrode active material and phosphorus atoms, and optionally other optional components such as a conductive agent, a binder, a thickener, a filler, and a dispersant. In the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture, a peak attributed to P2p exists at a position of 135 eV or less. The positive electrode mixture layer is usually formed on the surface of the positive electrode substrate by coating and drying a positive electrode mixture paste containing a positive electrode active material, phosphorus oxoacid, and the like. However, part or all of the phosphorus oxoacid may be denatured in the non-aqueous electrolyte storage element. Also, the phosphorus atoms are presumed to exist in the film formed on the surface of the positive electrode mixture. That is, the presence of the phosphorus atoms derived from the oxoacid of phosphorus in the film formed on the surface of the positive electrode mixture causes the peak attributed to P2p to be 135 eV or less in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture. It is presumed that it will exist in the position.

Examples of the positive electrode active material include lithium-transition metal composite oxides and polyanion compounds. Lithium transition metal composite oxides include, for example, composite oxides represented by Li _x MO _y (M represents at least one transition metal) ₍ Li _x CoO ₂ , Li _{xNiO2 , LixMnO3} , _LixNiαCo (1- _{α ) O2} , _{LixNiαCoβAl} (1- _α - _{β ) O2} , _{LixNiαMnβCo ( 1 - α Li x Mn 2 O 4 , Li x Ni α Mn ( _ 2-α)} O ₄ etc.). As the _polyanion compound, a _{polyanion compound ( LiFePO4} , _LiMnPO4 , _LiNiPO4 , _{LiCoPO4 , Li3V2 ( PO4} ) ₃ , _{Li2MnSiO4 , Li2CoPO4F} , etc.). Elements or polyanions in these compounds may be partially substituted with other elements or anionic species. In the positive electrode mixture layer, one kind of these compounds may be used alone, or two or more kinds may be mixed and used.

The positive electrode active material preferably contains a positive electrode potential that can be nobler than 4.0 V (vs. Li/Li ⁺ ) at the end-of-charge voltage during normal use of the non-aqueous electrolyte storage element. A lithium-transition metal composite oxide is preferable as such a positive electrode active material. The non-aqueous electrolyte storage element has good high-rate discharge performance in a low-temperature environment even in use where the maximum potential of the positive electrode reaches 4.0 V (vs. Li/Li ⁺ ). Therefore, by using a positive electrode active material that can have a positive electrode working potential of 4.0 V (vs. Li/Li ⁺ ) or more, the energy density is increased, and a non-aqueous electrolyte having good high-rate discharge performance in a low-temperature environment. A power storage element can be used. Here, the term "during normal use" refers to the case where the non-aqueous electrolyte storage element is used under the charging/discharging conditions recommended or specified for the non-aqueous electrolyte storage element. Regarding charging conditions, when a charger for the non-aqueous electrolyte storage element is prepared, the case where the non-aqueous electrolyte storage element is used by applying the charger is referred to as normal use.

The lower limit of the content of the lithium-transition metal composite oxide in the total positive electrode active material is preferably 50% by mass, more preferably 90% by mass, and even more preferably 99% by mass. The positive electrode active material may be substantially composed of only the lithium-transition metal composite oxide. By increasing the content of the lithium-transition metal composite oxide in this way, it is possible to further increase the energy density while maintaining favorable high-rate discharge performance in a low-temperature environment.

The positive electrode active material more preferably contains a positive electrode active material that can have a positive electrode operating potential of 4.4 V (vs. Li/Li ⁺ ) or more at the end-of-charge voltage during normal use of the non-aqueous electrolyte storage element. A positive electrode active material that can have a positive electrode operating potential of 4.4 V (vs. Li/Li ⁺ ) or higher at the end of charge voltage during normal use is a positive electrode active material that is reversible at a potential of 4.4 V (vs. Li/Li ⁺ ) or higher. It may be a positive electrode active material capable of intercalating and deintercalating lithium ions. As such a positive electrode active material, for example, Li _1+x (Ni _α Mn _β Co _(1-α-β) ) _1-x O ₂ ( ₀ <x< 1, 0≦α<0.5, 0.5<β≦1, 0≦1-α-β<0.5) and Li _x Ni _α Mn _(2-α) O ₄ having a spinel crystal structure Examples include LiNi _0.5 Mn _1.5 O ₄ , and examples of polyanion compounds such as LiNiPO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ F and Li ₂ MnSiO ₄ .

The content of the positive electrode active material in the positive electrode mixture layer can be, for example, 80% by mass or more and 98% by mass or less, preferably 90% by mass or more.

In the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture, the upper limit of the position of the peak attributed to P2p is preferably 134 eV. On the other hand, the lower limit of the position of this peak may be 130 eV or 132 eV.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the electric storage element. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, carbon black such as ketjen black, metals, conductive ceramics, and the like, with acetylene black being preferred. The shape of the conductive agent may be powdery, fibrous, or the like.

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

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

The filler is not particularly limited as long as it does not adversely affect the performance of the electric storage device. Main components of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

(negative electrode)
The negative electrode has a negative electrode substrate and a negative electrode mixture layer that is disposed directly on the negative electrode substrate or via an intermediate layer. The intermediate layer can have the same structure as the intermediate layer of the positive electrode.

The negative electrode substrate can have the same structure as the positive electrode substrate, but as a 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 substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode mixture layer is formed from a negative electrode mixture containing a negative electrode active material. Moreover, the negative electrode mixture forming the negative electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, a filler, and a dispersant, if necessary. Optional components such as a conductive agent, a binder, a thickener, a filler, and a dispersant may be the same as those used for the positive electrode mixture layer.

As the negative electrode active material, a material capable of intercalating and deintercalating lithium ions and the like is usually used. Specific negative electrode active materials include, for example, metals or semimetals such as Si and Sn; metal oxides such as Si oxides and Sn oxides or semimetal oxides; polyphosphate compounds; Examples thereof include carbon materials such as carbon (easily graphitizable carbon or non-graphitizable carbon).

Furthermore, the negative electrode mixture (negative electrode mixture layer) includes typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge. and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W.

(separator)
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferred from the viewpoint of strength, and a non-woven fabric is preferred from the viewpoint of 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, aramid, and the like are preferable from the viewpoint of oxidative decomposition resistance. Also, these resins may be combined.

An inorganic insulator layer may be provided between the separator and the electrode (usually the positive electrode). This inorganic insulating layer is a porous layer that is also called a heat-resistant layer. A separator having an inorganic insulating layer formed on one or both surfaces of a porous resin film can also be used. The inorganic insulator layer is usually composed of inorganic insulator particles and a binder, and may contain other components. As the inorganic insulating particles, Al ₂ O ₃ , SiO ₂ , aluminosilicate and the like are preferable.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains an imide salt and a non-aqueous solvent containing a fluorinated ether in which the imide salt is dissolved. In addition, the non-aqueous electrolyte is not limited to liquid. That is, the above-mentioned non-aqueous electrolyte includes solid and gel electrolytes.

(Imide salt)
Examples of the imide salt include lithium imide salt, sodium imide salt, potassium imide salt and the like, and lithium imide salt is preferred.

LiN(SO ₂ F) ₂ (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(CF ₃ SO ₂ ) ₂ (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiN(C ₂ F ₅ SO ₂ ) ₂ (lithium bis(pentafluoroethanesulfonyl)imide: LiBETI), LiN(C ₄ F ₉ SO ₂ ) ₂ (lithium bis(nonafluorobutanesulfonyl) imide), FSO ₂ --N--SO _{2 -C4F9Li} , _CF3 -SO2 _- N _- SO2 _{- C4F9Li} , _{CF3 -} SO2 _- N _- SO2 _- N _{- SO2CF3Li2} , _{CF3 -} SO2- N-SO2-CF2-SO2 _- N-SO2 _{- CF3Li2 , CF3 -} SO2 _- N _- SO2 _- CF2 _{- SO3Li2} , _{CF3 -} SO2 _- N _- SO2 Lithium sulfonylimide salts such as —CF ₂ —SO ₂ —C(—SO ₂ CF ₃ ) ₂ Li ₂ ; Lithium phosphonylimide salts such as LiN(POF ₂ ) ₂ (lithium bis(difluorophosphonyl)imide: LiDFPI) etc. can be mentioned. Lithium imide salts can be used alone or in combination of two or more.

The lithium imide salt preferably has a fluorine atom, and specifically preferably has, for example, a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, or the like. Among the lithium imide salts, lithium sulfonyl imide salts are preferred, LiFSI, LiTFSI and LiBETI are more preferred, and LiFSI is even more preferred. These imide salts are imide salts that relatively easily cause oxidation corrosion of aluminum during charging and discharging when the operating potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or higher. Therefore, when such an imide salt is used, oxidation corrosion of aluminum is suppressed during charging and discharging when the working potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or higher, and the low-temperature environment of the non-aqueous electrolyte storage element The advantage of the present invention, having good high rate discharge performance under low temperature conditions, is obtained particularly effectively.

In the non-aqueous electrolyte storage element, the content of the imide salt in the non-aqueous electrolyte is not particularly limited, but the lower limit of the content of the imide salt in the non-aqueous electrolyte is, for example, 0.5 mol dm ^-3 . Preferably, 0.8 mol dm ^-3 is more preferred. By making the content of the imide salt equal to or higher than the above lower limit, the charge/discharge performance can be enhanced. On the other hand, the upper limit of this content is preferably 2 mol dm ^-3 , more preferably 1.4 mol dm ^-3 , still more preferably 1.2 mol dm ^-3 , and even more preferably 1.1 mol dm ^-3 . By setting the content of the imide salt to the above upper limit or less, it is expected that particularly good high-rate discharge performance in a low-temperature environment of the non-aqueous electrolyte storage element can be obtained. According to the non-aqueous electrolyte storage element, even if the imide salt is used in a concentration range that is not such a high concentration, the working potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or more. Oxidative corrosion is suppressed. Therefore, in the non-aqueous electrolyte storage element, there is no need to use the imide salt at a high concentration. Moreover, the viscosity of the non-aqueous electrolyte usually increases when the imide salt is used at a high concentration. On the other hand, in the non-aqueous electrolyte storage element, by setting the concentration of the imide salt in the non-aqueous electrolyte to a concentration range that is not as high as the above range, the increase in the viscosity of the non-aqueous electrolyte can be suppressed. It is expected that good high-rate discharge performance and the like can be obtained in a low-temperature environment of non-aqueous electrolyte storage devices.

(other electrolyte salts)
The non-aqueous electrolyte may or may not contain an electrolyte salt other than the imide salt. Examples of such electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts other than imide salts. When an electrolyte salt other than an imide salt is contained, the upper limit of the content of the electrolyte salt other than the imide salt in the non-aqueous electrolyte may be preferably 1 mol dm ^-3 , and more preferably 0.1 mol dm ^-3 . Sometimes preferred, sometimes 0.01 mol dm ⁻³ is even more preferred. By setting the content of the electrolyte salt other than the imide salt to the above upper limit or less, it is possible to obtain particularly good high-rate discharge performance of the non-aqueous electrolyte storage element in a low-temperature environment.

In addition, when LiPF ₆ is used as another electrolyte salt, the peak attributed to P2p derived from LiPF ₆ in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture is at a position exceeding 135 eV (usually, more than 135 eV and 138 eV or less range). Therefore, the peak attributed to P2p derived from LiPF ₆ can be distinguished from the peak attributed to P2p derived from the oxoacid of phosphorus due to the difference in peak positions.

(Non-aqueous solvent)
The non-aqueous solvent contains at least a fluorinated ether.

(fluorinated ether)
Examples of the fluorinated ether include 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether (TFEE), 1,1,2,2-tetrafluoroethyl-ethyl ether, 1,1 , 2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl Ether, 1,1,2,2-tetrafluoropropyl-1,1,2,3,3,3-hexafluoropropyl ether and the like can be mentioned. One or more of the fluorinated ethers may be used. The fluorinated ether is required to have a low viscosity and not too low solubility of the electrolyte salt. Therefore, it is preferable that the proportion of fluorine atoms contained in the molecule is not too high, and that the molecular weight is not too high. From this point of view, 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether (TFEE) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetra Fluoropropyl ether (HFE) is preferred and 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether (TFEE) is particularly preferred.

The content of the fluorinated ether is not particularly limited, but the lower limit of the content of the fluorinated ether in the total non-aqueous solvent is preferably 10% by volume, more preferably 15% by volume, and even more preferably 20% by volume. On the other hand, the upper limit of the content of the fluorinated ether is preferably 95% by volume, more preferably 90% by volume, still more preferably 80% by volume, and even more preferably 60% by volume. By setting the total content of the fluorinated ether to the above lower limit or more in this way, the low temperature of the non-aqueous electrolyte storage element during charge and discharge when the working potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or more Good high-rate discharge performance under environmental conditions can be obtained. On the other hand, by setting the content of the fluorinated ether to the above upper limit or less, the viscosity of the nonaqueous electrolyte, the conductivity of lithium ions, and the like can be optimized.

(fluorinated cyclic carbonate)
The non-aqueous solvent preferably further contains a fluorinated cyclic carbonate. Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluoromethylethylene carbonate, trifluoroethylethylene carbonate, and the like. One or more of the fluorinated cyclic carbonates may be used. The fluorinated carbonate can suppress side reactions that can occur during charging and discharging, particularly at a potential of 4.0 V (vs. Li/Li ⁺ ) or higher. can obtain particularly good high-rate discharge performance. From this point of view, fluoroethylene carbonate (FEC) is preferred.

The content of the fluorinated cyclic carbonate is not particularly limited, but the lower limit of the content of the fluorinated cyclic carbonate in the total non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and further 20% by volume. preferable. On the other hand, the upper limit is preferably 70% by volume, more preferably 50% by volume, and even more preferably 30% by volume. By making the content of the fluorinated cyclic carbonate equal to or higher than the above lower limit in this manner, it is possible to more effectively suppress side reactions that may occur during charging and discharging of the non-aqueous electrolyte power storage element. On the other hand, by setting the content of the fluorinated cyclic carbonate to the upper limit or less, the viscosity of the non-aqueous electrolyte, the conductivity of lithium ions, and the like can be optimized.

(Other non-aqueous solvents)
In addition to the fluorinated ether and the fluorinated cyclic carbonate, other non-aqueous solvents that can be used include known non-aqueous solvents that are commonly used as non-aqueous solvents for general non-aqueous electrolytes for electric storage elements. Examples of the nonaqueous solvent include carbonates (cyclic carbonates and chain carbonates), esters, ethers, amides, sulfones, lactones, nitriles, and the like. Among these, it is preferable to use at least carbonate. The carbonate may be a cyclic carbonate or a chain carbonate. Further, the carbonate may be a carbonate having no substituent or a carbonate having a substituent. A hydroxyl group, a halogen atom, etc. can be mentioned as this substituent. One or more of the above carbonates can be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, and the like.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate (TFEMC), bis(trifluoroethyl) carbonate (FDEC), and the like. can be mentioned.

The carbonate is required to have a low viscosity and not have too low an electrolyte salt solubility. Therefore, a chain carbonate having a low viscosity is preferable, a carbonate having a molecular weight not too large is also preferable, and a carbonate having no substituent is also preferable. From this point of view, diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) are preferred.

Cyclic carbonates including the above-mentioned fluorinated cyclic carbonates and chain carbonates can be used in combination, and each can be used alone or in combination of two or more. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate not including the fluorinated cyclic carbonate and the chain carbonate (cyclic carbonate:chain carbonate) is not particularly limited, but is, for example, 5:95. 50:50 or less. The content of the carbonate is not particularly limited, but the lower limit of the content of the cyclic carbonate including the fluorinated cyclic carbonate in the total non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume. , 20% by volume is more preferred. On the other hand, the upper limit is preferably 70% by volume, more preferably 50% by volume, and even more preferably 40% by volume. Furthermore, the lower limit of the content of chain carbonate in the total non-aqueous solvent is preferably 20% by volume, more preferably 40% by volume. On the other hand, the upper limit is preferably 85% by volume, more preferably 80% by volume.

Other additives may be added to the non-aqueous electrolyte. However, the upper limit of the content of components other than the electrolyte salt containing the imide salt and the non-aqueous solvent containing the fluorinated ether in the non-aqueous electrolyte may be preferably 5% by mass, and more preferably 1% by mass. In some cases, 0.1% by weight is more preferred.

(Operating voltage of non-aqueous electrolyte storage element)
In the non-aqueous electrolyte storage element, the lower limit of the maximum potential of the positive electrode may be, for example, 4.0 V (vs. Li/Li ⁺ ), or 4.2 V (vs. Li/Li ⁺ ). may be 4.4 V (vs. Li/Li ⁺ ), may be 4.5 V (vs. Li/Li ⁺ ), and may be 4.6 V (vs. Li/Li ⁺ ) It may be 4.7 V (vs. Li/Li ⁺ ). In addition, the upper limit of the maximum attainable potential of the positive electrode may be, for example, 5.4 V (vs. Li/Li ⁺ ) or 5.0 V (vs. Li/Li ⁺ ). The non-aqueous electrolyte storage element is generally susceptible to oxidation corrosion of aluminum when an imide salt is used, and the maximum potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or more. In this case, the positive electrode can be used at an operating potential of 4.0 V (vs. Li/Li ⁺ ) or higher because the deterioration of the high-rate discharge performance of the non-aqueous electrolyte storage element in a low-temperature environment is suppressed. Since the maximum potential of the positive electrode is thus high, the energy density of the non-aqueous electrolyte storage element can be increased.

The maximum attainable potential of the positive electrode is preferably the positive electrode potential at the end-of-charge voltage of the non-aqueous electrolyte storage element during normal use. In general, when the potential of the positive electrode frequently rises to a high potential due to repeated charging and discharging, the high-rate discharge performance tends to deteriorate in a low-temperature environment. Therefore, when the maximum potential of the positive electrode frequently reaches, for example, 4.4 V (vs. Li/Li ⁺ ) or more due to repeated charging and discharging, the effect of the non-aqueous electrolyte storage element is more pronounced.

<Method for producing non-aqueous electrolyte storage element>
The non-aqueous electrolyte storage element is preferably produced by the following method. That is, a method for manufacturing a non-aqueous electrolyte storage element according to an embodiment of the present invention includes manufacturing a positive electrode having a positive electrode mixture prepared by applying a positive electrode mixture paste containing an oxoacid of phosphorus (positive electrode preparation step) and injecting a nonaqueous electrolyte containing an imide salt and a fluorinated ether into a container (nonaqueous electrolyte injection step).

(Positive electrode manufacturing process)
The positive electrode material mixture paste usually contains a positive electrode active material and a binder in addition to the oxoacid of phosphorus, and further contains other components as necessary. A positive electrode mixture paste can be obtained by mixing these components. This positive electrode mixture paste is applied to the surface of the positive electrode substrate and dried to obtain a positive electrode in which the peak attributed to P2p exists at a position of 135 eV or less in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture.

The phosphorus oxoacid refers to a compound having a structure in which a hydroxyl group (--OH) and an oxy group (=O) are bonded to a phosphorus atom. Examples of the phosphorus oxoacid include phosphoric acid (H ₃ PO ₄ ), phosphonic acid (H ₃ PO ₃ ), phosphinic acid (H ₃ PO ₂ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), polyphosphoric acid, and the like. mentioned. Among these, phosphoric acid and phosphonic acid are preferred, and phosphonic acid is more preferred. This phosphorus oxoacid forms a film containing phosphorus atoms on the positive electrode.

The lower limit of the content (addition amount) of the phosphorus oxoacid in the positive electrode mixture paste is preferably 0.05 parts by mass, more preferably 0.1 parts by mass, and 0 .3 parts by weight is more preferred. On the other hand, the upper limit of this content is preferably 5 parts by mass, more preferably 3 parts by mass, and even more preferably 2 parts by mass. By setting the content of the oxoacid of phosphorus within the above range, it is possible to obtain particularly good high-rate discharge performance in a low-temperature environment.

An organic solvent is usually used as a dispersion medium for the positive electrode mixture paste. Examples of the organic solvent include polar solvents such as N-methyl-2-pyrrolidone (NMP), acetone and ethanol, and non-polar solvents such as xylene, toluene and cyclohexane.

The method of applying the positive electrode material mixture paste is not particularly limited, and can be performed by known methods such as roller coating, screen coating, and spin coating.

(Non-aqueous electrolyte injection step)
The non-aqueous electrolyte injection step can be performed by a known method. That is, a non-aqueous electrolyte having a desired composition is prepared, and the prepared non-aqueous electrolyte is poured into a container.

The manufacturing method may include the following steps, etc., in addition to the positive electrode preparation step and the non-aqueous electrolyte injection step. That is, the manufacturing method includes, for example, a step of producing a negative electrode, a step of forming an alternately stacked electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween, and a positive electrode and a negative electrode (electrode body ) into a container. Usually, the non-aqueous electrolyte is injected into the container after the electrode assembly is placed in the container, but this order may be reversed. After these steps, a non-aqueous electrolyte storage element can be obtained by sealing the injection port.

<Other embodiments>
The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved modes in addition to the above-described modes. For example, the intermediate layer may not be provided in the positive electrode or negative electrode. Moreover, in the positive electrode of the non-aqueous electrolyte storage element, the positive electrode mixture does not have to form a distinct layer. For example, the positive electrode may have a structure in which a positive electrode mixture is supported on a mesh-shaped positive electrode base material.

Further, in the above embodiments, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic diagram of a rectangular non-aqueous electrolyte storage element 1 that is an embodiment of the non-aqueous electrolyte storage element according to the present invention. In addition, the same figure is taken as the figure which saw through the inside of a container. In the non-aqueous electrolyte storage element 1 shown in FIG. 1, the electrode body 2 is accommodated in the container 3 . The electrode body 2 is formed by winding a positive electrode containing a positive electrode mixture and a negative electrode containing a negative electrode mixture with a separator interposed therebetween. The positive electrode is electrically connected to a positive terminal 4 via a positive lead 4', and the negative electrode is electrically connected to a negative terminal 5 via a negative lead 5'. Further, the container 3 is filled with a non-aqueous electrolyte.

The configuration of the non-aqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries (rectangular batteries), flat batteries, and the like. The present invention can also be implemented as a power storage device including a plurality of non-aqueous electrolyte power storage elements described above. One embodiment of a 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 nonaqueous electrolyte power storage elements 1 . The power storage device 30 can be mounted as a power supply for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

(Preparation of positive electrode P1)
As a positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO ₂ structure and represented by Li ₁₊ αMe ₁ -αO ₂ (Me is a transition metal including Mn, 0.1<α<0 .2, the molar ratio of Mn to Me (Mn/Me is 0.5<Mn/Me). N-methylpyrrolidone (NMP) was used as a dispersion medium, and the positive electrode active material, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and phosphonic acid (H ₃ PO ₃ ) were added as solids. They were mixed at a mass ratio of 93.5:4.5:1.5:0.5 in conversion to obtain a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil serving as a positive electrode substrate and dried to form a positive electrode mixture layer on the positive electrode substrate. Also, the positive electrode material mixture paste was applied to the opposite side of the aluminum foil in the same manner and dried. The positive electrode mixture layer formed on the opposite side was peeled off after drying. Thus, the positive electrode P1 was obtained.

(Preparation of positive electrode P2)
A positive electrode P2 was obtained in the same manner as in the above “preparation of positive electrode P1” except that phosphonic acid was not mixed in the positive electrode mixture paste.

(Preparation of negative electrode)
A negative electrode was produced using graphite as a negative electrode active material.

[Example 1]
(Preparation of non-aqueous electrolyte)
1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether (TFEE), which is a fluorinated ether, and fluoroethylene carbonate (FEC), which is a fluorinated cyclic carbonate, and other solvents substituted Lithium bis(fluorosulfonyl)imide (LiFSI) was added as an electrolyte salt to a mixed solvent obtained by mixing ethyl methyl carbonate (EMC), which is a chain carbonate having no group, at a volume ratio of 60:20:20. A non-aqueous electrolyte was prepared by dissolving at a concentration of 0 mol dm ⁻³ .

(Preparation of non-aqueous electrolyte storage element)
An electrode assembly was produced by laminating the positive electrode P1 and the negative electrode via a separator, which is a polyolefin microporous film. This electrode body is housed in a container made of a metal-resin composite film, the non-aqueous electrolyte is injected into the interior, and the opening is sealed by heat welding. battery).

[Examples 2-3, Comparative Examples 1-7]
In the same manner as in Example 1, except that the types of the positive electrode and electrolyte salt, and the type and mixing volume ratio of the solvent were as shown in Table 1, each non-metallic material of Examples 2-3 and Comparative Examples 1-7 was prepared. A water electrolyte storage device was obtained.

In addition, the solvent in a table|surface shows the following compounds.

FEC: fluoroethylene carbonate TFEE: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether EMC: ethyl methyl carbonate EC: ethylene carbonate TFEMC: trifluoroethyl methyl carbonate

[Battery evaluation]
(initial charge/discharge)
The obtained non-aqueous electrolyte storage elements of Examples 1 to 3 and Comparative Examples 1 to 7 were initially charged and discharged under the following conditions. After charging at a constant current of 0.1C to 4.5V at 25°C, the battery was charged at a constant voltage of 4.5V. The charging termination condition was until the charging current reached 0.05C. After a rest period of 10 minutes was provided after charging, the battery was discharged at a constant current of 0.1 C to 2.0 V at 25°C.

(X-ray photoelectron spectroscopy)
Each non-aqueous electrolyte storage element in a completely discharged state after the initial charge and discharge is dismantled in an argon atmosphere with a dew point of −60° C. or less, the positive electrode is taken out, the positive electrode is washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. did. The obtained positive electrode was sealed in a transfer vessel in an argon atmosphere, introduced into a sample chamber of an X-ray photoelectron spectroscopy spectrum measuring device, and subjected to X-ray photoelectron spectroscopy measurement of the surface of the positive electrode mixture of the positive electrode under the conditions described above. rice field. From the obtained spectrum, the peak position attributed to P2p was determined by the method described above. In the positive electrode mixtures (P1) of Examples 1 to 3 and Comparative Examples 3 to 6 in which phosphonic acid was used in the positive electrode mixture paste, the peak attributed to P2p was present between 133 and 134 eV. In the positive electrode mixtures (P2) of Comparative Examples 1, 2 and 7 in which phosphonic acid was not used in the positive electrode mixture paste, no peak attributed to P2p was observed in the range of 135 eV or less. In the positive electrode mixtures of Comparative Examples 5 to 7 using LiPF ₆ as the electrolyte salt, a peak attributed to P2p derived from LiPF ₆ was confirmed at 136 eV.

(Low temperature high rate discharge test)
Each non-aqueous electrolyte storage element after the initial charge/discharge was stored in a constant temperature bath at 25° C. for 2 hours, charged to 4.5 V at a constant current of 0.1 C, and then charged at a constant current of 4.5 V. charged with voltage. The charging termination condition was until the charging current reached 0.05C. The positive electrode potential (=maximum attainable potential of the positive electrode) at the end of charging was 4.6 V (vs. Li/Li ⁺ ). After a rest period of 10 minutes was provided after charging, the battery was discharged to 2.0 V at a constant discharge current of 2.0C. The discharge capacity at this time is defined as "25°C 2C capacity". Further, after a rest period of 10 minutes was provided after the discharge, the battery was discharged to 2.0V at a constant current of 0.1C. A rest period of 10 minutes was provided after discharge. Subsequently, the batteries were charged to 4.5V at a constant current of 0.1C, and then charged at a constant voltage of 4.5V. The charging termination condition was until the charging current reached 0.05C. Each non-aqueous electrolyte storage element after charging was stored in a constant temperature bath at 0° C. for 5 hours, and then discharged to 2.0 V at a constant current of 2.0 C. The discharge capacity at this time is defined as "0° C. 2C capacity". Further, after discharging, the battery was stored in a constant temperature bath at 25° C. for 5 hours, and then discharged to 2.0 V at a constant current of 0.1 C. A rest period of 10 minutes was provided after discharge.

(Evaluation of low-temperature high-rate discharge performance)
For each non-aqueous electrolyte storage element, the ratio of "0° C. 2C capacity" to the above "25° C. 2C capacity" is calculated and defined as "0° C./25° C. ratio" (%). This is shown in Table 1 as low-temperature high-rate discharge performance.

As can be seen from the comparison between Example 1 and Comparative Example 1 in Table 1 above, in the non-aqueous electrolyte storage element in which the non-aqueous electrolyte contains an imide salt as an electrolyte salt and a fluorinated ether as a non-aqueous solvent, By using the positive electrode P1 in which the peak attributed to P2p exists at a position of 135 eV or less in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture, the positive electrode P2 in which the peak attributed to P2p does not exist at a position of 135 eV or less was used. It can be seen that the 0° C./25° C. ratio is higher than in the case of the non-aqueous electrolyte storage element, and that good high-rate discharge performance can be obtained in a low-temperature environment. Note that, in Example 1, the 25° C. 2C capacity was equivalent to that of Comparative Example 1, and the 0° C. 2C capacity was larger, so the 0° C./25° C. ratio was higher. This is because oxidation corrosion of aluminum, which is likely to occur during charging and discharging when the working potential of the positive electrode is 4.0 V (vs. Li/Li ⁺ ) or more when an imide salt is used as the electrolyte salt, is caused by the positive electrode mixture. The charging and discharging of the non-aqueous electrolyte storage element is suppressed by the formed film derived from the oxoacid of phosphorus, and the inclusion of a fluorinated ether that has high oxidation resistance and relatively low viscosity as a non-aqueous solvent. It is considered that this effect is achieved by suppressing side reactions (such as oxidative decomposition of non-aqueous solvents, etc.) that may sometimes occur, and by suppressing increases in viscosity and decreases in ionic conductivity of non-aqueous electrolytes.

Further, as can be seen from the comparison between Comparative Examples 2 and 3, in the non-aqueous electrolyte storage element in which the non-aqueous electrolyte contains an imide salt as an electrolyte salt, even if the non-aqueous solvent does not contain a fluorinated ether, , It can be seen that the 0 ° C./25 ° C. ratio tends to increase by using the positive electrode P1 in which the peak attributed to P2p exists at a position of 135 eV or less in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture. It can be seen that in Example 1, which contains a fluorinated ether as the water solvent, even better high-rate discharge performance can be obtained in a low-temperature environment. That is, the effect of obtaining good high-rate discharge performance in a low-temperature environment by applying an imide salt is more pronounced by applying a fluorinated ether that has high oxidation resistance and relatively low viscosity as a non-aqueous solvent. It can be said that it is an effect that occurs in

On the other hand, as can be seen from the comparison between Comparative Examples 4 and 5, when the non-aqueous electrolyte does not contain a fluorinated ether, the peak attributed to P2p in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture is 135 eV or less. Even if the electrolyte salt of the non-aqueous electrolyte is changed from LiPF ₆ to imide salt, the 0° C./25° C. ratio is the same or less, and in the low-temperature environment of the non-aqueous electrolyte storage element It can be seen that good high-rate discharge performance cannot be obtained. Here, Comparative Examples 4 and 5 are not fluorinated ethers with high oxidation resistance and relatively low viscosity in non-aqueous solvents, but fluorinated linear carbonates with high oxidation resistance but relatively high viscosity. It is considered that good high-rate discharge performance in a low-temperature environment of the non-aqueous electrolyte storage element was not obtained because TFEMC was used. Thus, a positive electrode in which the peak attributed to P2p in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture exists at a position of 135 eV or less, contains an imide salt as an electrolyte salt, and a fluorinated ether as a non-aqueous solvent. The effect that a non-aqueous electrolyte storage device using a non-aqueous electrolyte has good high-rate discharge performance in a low-temperature environment is a peculiarity that was completely unpredictable from conventional knowledge that occurs only when these are combined. It can be said that it is a good effect.

Furthermore, as can be seen from the comparison between Comparative Examples 6 and 7, when LiPF ₆ was used as the electrolyte salt, the fluorinated ether was included as the non-aqueous solvent, and the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture showed P2p. The 0° C./25° C. ratio is the same even when the positive electrode P1 whose attributed peak exists at a position of 135 eV or less is used, and good high-rate discharge performance in a low-temperature environment of the non-aqueous electrolyte storage element can be obtained. I know not. From the above, the effect of the present invention that good high-rate discharge performance in a low-temperature environment of a non-aqueous electrolyte storage element can be obtained is that the imide salt as the electrolyte salt, the fluorinated ether as the non-aqueous solvent, It is a peculiar effect that occurs only when combined with the positive electrode P1, in which the peak attributed to P2p exists at a position of 135 eV or less in the X-ray photoelectron spectroscopy spectrum of the positive electrode mixture. It can be said that this effect is more pronounced when combined with

As shown in other Examples 2 and 3, the peak attributed to P2p in the X-ray photoelectron spectroscopy spectrum of the non-aqueous electrolyte containing the imide salt and the fluorinated ether and the positive electrode mixture is at a position of 135 eV or less. By using the positive electrode P1 present in the non-aqueous electrolyte storage element, the effect of obtaining good high-rate discharge performance in a low-temperature environment is caused by the non-aqueous electrolyte containing an imide salt and a fluorinated ether. Although it is exhibited regardless of the composition of the non-aqueous solvent, as can be seen from the comparison between Example 2 and Example 3, it can be said that it is exhibited more effectively by including the fluorinated cyclic carbonate at the same time as the fluorinated ether. .

INDUSTRIAL APPLICABILITY The present invention can be applied to electronic devices such as personal computers and communication terminals, and non-aqueous electrolyte storage elements used as power sources for automobiles and the like.

1 non-aqueous electrolyte storage element 2 electrode body 3 container 4 positive electrode terminal 4' positive electrode lead 5 negative electrode terminal 5' negative electrode lead 20 storage unit 30 storage device

Claims (2)

preparing a positive electrode having a positive electrode mixture prepared by applying a positive electrode mixture paste containing an oxoacid of phosphorus;
Injecting a non-aqueous electrolyte containing an imide salt and a fluorinated ether (excluding those having an imide salt content of 5.0% by mass or less in the non-aqueous electrolyte) into a container. manufacturing method. A non-aqueous electrolyte storage element obtained by the method for manufacturing a non-aqueous electrolyte storage element according to claim 1 .

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