JP6922242B2 - Manufacturing method of non-aqueous electrolyte storage element and non-aqueous electrolyte storage element - Google Patents

Description

The present invention relates to a non-aqueous electrolyte storage element and a method for manufacturing a 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 and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has 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 non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

Generally, the non-aqueous electrolyte of the non-aqueous electrolyte power storage element includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. In this non-aqueous electrolyte, various additives and solvents are selected and used in order to improve the performance. For example, a secondary battery using a non-aqueous electrolyte containing a fluorinated carbonate such as fluorinated ethylene carbonate is known (see Patent Documents 1 and 2).

JP-A-2008-243810 International Publication No. 2013/100081

One of the performances required for such a non-aqueous electrolyte power storage element is charge / discharge cycle performance. In particular, the non-aqueous electrolyte power storage element has a disadvantage that the charge / discharge cycle capacity retention rate decreases when it is operated at a high voltage. This decrease in volume retention is triggered by oxidative decomposition of a non-aqueous solvent, and the decrease in volume retention is particularly large when a non-aqueous solvent containing ethylene carbonate (EC), which is a high dielectric constant solvent, is used. ..

On the other hand, since the fluorinated carbonate is excellent in oxidation resistance, it is said that the capacity retention rate is improved by using the fluorinated carbonate. In order to obtain the effect of improving the charge / discharge cycle performance by the fluorinated carbonate, it is necessary to contain a certain amount of the fluorinated carbonate. However, when a large amount of fluorinated carbonate is contained, there is an inconvenience that the charge / discharge cycle performance in a low temperature environment is deteriorated due to the low dielectric constant of the fluorinated carbonate and the like.

The present invention has been made based on the above circumstances, and an object of the present invention is a non-aqueous electrolyte power storage element having a high capacity retention rate in a high voltage charge / discharge cycle in a high temperature and low temperature environment, and such a non-aqueous electrolyte storage element. The present invention is to provide a method for manufacturing a non-aqueous electrolyte power storage element.

One aspect of the present invention 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 a fluorinated carbonate, and is described by X-ray photoelectron spectroscopy (XPS). In the spectrum of the positive electrode mixture, the peak position of P2p is 135 eV or less, and the content of the fluorinated carbonate with respect to the non-aqueous electrolyte is 15% by mass or less.

Another aspect of the present invention is to prepare a positive electrode using a positive electrode mixture paste containing an oxo acid of phosphorus, and to contain a fluorinated carbonate, wherein the content of the fluorinated carbonate is 15% by mass or less. It is a method for manufacturing a non-aqueous electrolyte power storage element, which comprises injecting a water electrolyte into a container.

According to the present invention, it is possible to provide a non-aqueous electrolyte storage element having a high capacity retention rate in a high voltage charge / discharge cycle in a high temperature and low temperature environment, and a method for manufacturing such a non-aqueous electrolyte storage element.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte power storage element 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 power storage elements according to an embodiment of the present invention.

The non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode having a positive electrode mixture containing a phosphorus atom and a non-aqueous electrolyte containing a fluorinated carbonate, and the positive electrode mixture according to X-ray photoelectron spectroscopy. In the spectrum, the peak position of P2p is 135 eV or less, and the content of the fluorinated carbonate with respect to the non-aqueous electrolyte is 15% by mass or less.

The non-aqueous electrolyte power storage element has a high capacity retention rate in a high voltage charge / discharge cycle in a high temperature and low temperature environment. The reason for this is not clear, but the following reasons can be inferred. One of the causes of the decrease in the capacity retention rate is that the surface of the positive electrode is invaded by a small amount of hydrogen fluoride (HF) existing in the vicinity of the positive electrode. Due to this erosion, the positive electrode active material component is eluted from the positive electrode surface and diffused to the negative electrode side, and the positive electrode active material component is deposited on the negative electrode. As a result, the irreversible capacitance and resistance of the negative electrode gradually increase, and the charge / discharge cycle capacity retention rate is said to decrease. Further, it is presumed that the trace amount of HF is generated by decomposition of the electrolyte salt containing a fluorine atom in the vicinity of the positive electrode. On the other hand, in the non-aqueous electrolyte power storage element according to the embodiment of the present invention, the peak position of P2p in the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy appears at 135 eV or less. Such a peak is a peak of a phosphorus atom derived from an oxo acid of phosphorus such as phosphonic acid. That is, the above peak indicates that phosphorus atoms derived from phosphorus oxoacid are present on the surface of the positive electrode mixture, and it is presumed that these phosphorus atoms form a film on the surface of the positive electrode mixture. In the non-aqueous electrolyte power storage element, such a coating suppresses the decomposition reaction of the electrolyte salt containing a fluorine atom on the surface of the positive electrode mixture and suppresses the elution of the positive electrode active material component, resulting in high temperature and low temperature environments. The capacity retention rate in the high voltage charge / discharge cycle below can be increased. Further, in the non-aqueous electrolyte storage element, since the non-aqueous electrolyte contains fluorinated carbonate having high oxidation resistance, side reactions (oxidative decomposition of non-aqueous solvent, etc.) that may occur during charging / discharging of the non-aqueous electrolyte storage element Etc.) can be suppressed, so that the capacity retention rate can be further increased. On the other hand, since the content of this fluorinated carbonate is suppressed to 15% by mass or less, it is possible to have a good capacity retention rate even in a low temperature environment.

The sample used for measuring the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy is prepared by the following method. The non-aqueous electrolyte power storage element is discharged to the discharge end voltage at the time of normal use with a current of 0.1 C to bring it into a discharge end state. Here, "during normal use" means a case where the power storage element is used by adopting the discharge conditions recommended or specified for the power storage element. The power storage element in the end-discharged state is disassembled, the positive electrode is taken out, the electrodes are thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut out to a predetermined size (for example, 2 × 2 cm) and used as a sample for XPS spectrum measurement. The work from disassembly of the non-aqueous electrolyte power storage element to XPS measurement is performed in an argon atmosphere with a dew point of -60 ° C. or lower. The equipment used and the measurement conditions in the XPS spectrum of the positive electrode mixture are as follows.
Equipment: "AXIS NOVA" from KRATOS ANALYTICAL
X-ray source: Monochromatic AlKα
Acceleration voltage: 15kV
Analytical area: 700 μm x 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 number: P2p = 15 times, C1s = 8 times

Further, the peak position and the peak height in the above spectrum are values obtained as follows. First, the peak of sp2 carbon in C1s is set to 284.8 eV, and all the obtained spectra are corrected. Next, the spectrum is leveled by removing the background using the linear method. In the spectrum after the leveling process, the value having the highest peak intensity is defined as the peak height. Further, the binding energy indicating this peak height is set as the peak position.

The non-aqueous electrolyte preferably contains ethylene carbonate (EC). When EC is used, the capacity retention rate in the high voltage charge / discharge cycle tends to decrease as described above. However, according to the non-aqueous electrolyte power storage element, even when EC is contained in the non-aqueous electrolyte, it has a high capacity retention rate in a high voltage charge / discharge cycle under high temperature and low temperature environments, and therefore EC is used as a solvent. It can be used effectively.

It is preferable that the charge termination potential of the positive electrode in the non-aqueous electrolyte power storage element during normal use is 4.35 V (vs. Li / Li ^{+) or more.} Since the non-aqueous electrolyte power storage element has a high capacity retention rate in a high voltage charge / discharge cycle under high temperature and low temperature environments, it is used under charging conditions in which the positive electrode potential at the final charge voltage during normal use is relatively high. This effect can be particularly fully exerted in the case of a non-aqueous electrolyte power storage element. Here, the normal use is a case where the non-aqueous electrolyte storage element is used by adopting the charging conditions recommended or specified for the non-aqueous electrolyte storage element, and for the non-aqueous electrolyte storage element. When the charger is prepared, it means the case where the charger is applied to use the non-aqueous electrolyte power storage element. For example, in a non-aqueous electrolyte power storage element using graphite as a negative electrode active material, the positive electrode potential is about 5.1 V (vs. Li ^/ Li +) when the charge termination voltage is 5.0 V, although it depends on the design. be.

The method for producing a non-aqueous electrolyte power storage element according to an embodiment of the present invention includes producing a positive electrode using a positive electrode mixture paste containing an oxo acid of phosphorus, containing a fluorinated carbonate, and containing the above fluorinated carbonate. It is a method for manufacturing a non-aqueous electrolyte power storage element, which comprises injecting a non-aqueous electrolyte having an amount of 15% by mass or less into a container.

According to this manufacturing method, it is possible to manufacture a non-aqueous electrolyte power storage element having a high capacity retention rate in a high voltage charge / discharge cycle in a high temperature and low temperature environment.

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

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the 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 non-aqueous electrolyte 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 a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known aluminum case, resin case or the like which is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture 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 mixture 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 mixture layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. This positive electrode mixture contains a phosphorus atom and, if necessary, an optional component such as a conductive agent, a binder, a thickener, and a filler. It is presumed that the phosphorus atom is present in the coating film that coats the positive electrode active material.

A metal oxide is usually used as the positive electrode active material. Specific positive electrode active materials include, for example _{, a composite oxide represented by Li x} MO _y (M represents at least one transition metal) ( _{Li x} CoO ₂ and Li _{having a layered α-NaFeO type 2} crystal structure). _{Li x} Mn ₂ having a spinel type crystal structure such as _x NiO 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.} O ₄ , 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 (represented) (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 mixture layer, one of these compounds may be used alone, or two or more of these compounds may be mixed and used.

Among the above-mentioned positive electrode active materials, when a positive electrode active material containing at least one of a nickel atom and a manganese atom is used, the effect of the present invention can be more effectively exhibited. As described above, the trace amount of HF present in the non-aqueous electrolyte elutes the components of the positive electrode active material from the positive electrode mixture layer, which affects the capacity retention rate and the like. When the positive electrode active material is a nickel-containing compound or a manganese-containing compound, the above elution is likely to occur, which tends to affect the capacity retention rate and the like. Therefore, by coating such a positive electrode active material with the specific film containing the phosphorus atom, the elution of the nickel-containing compound and the manganese-containing compound can be effectively suppressed.

In the spectrum of the positive electrode mixture layer (positive electrode mixture) by X-ray photoelectron spectroscopy, the peak position of P2p is 135 eV or less, preferably 134.7 eV or less, more preferably 134.4 eV or less, and further 134.2 eV or less. preferable. Further, the peak position is preferably 132 eV or more, more preferably 133 eV or more, further preferably 133.5 eV or more, and even more preferably 134.0 eV or more.

The peak of P2p appearing in the above range is the peak of the phosphorus atom derived from the oxo acid of phosphorus. Such phosphorus atoms are usually present on the surface of the particulate positive electrode active material. With such a phosphorus atom, the decomposition reaction of the electrolyte salt containing a fluorine atom in the vicinity of the positive electrode can be suppressed, and the elution of the positive electrode active material component can be suppressed. The phosphorus atom is preferably present on the surface of the positive electrode active material as a compound containing _{a PO 3} anion, a PO _{4 anion, or a PO x} F _y anion in which a part of the oxygen atom of these anions is replaced with a fluorine atom. .. In the spectrum by X-ray photoelectron spectroscopy, the peak of the phosphorus atom (P2p) of such a compound appears in the range of 133 eV or more and 135 eV or less. Further, the peak position of P2p also depends on the presence of other components, and tends to shift to the higher energy side as compared with the case where these components are not present. However, when the positive electrode mixture is obtained from a positive electrode mixture paste containing a positive electrode active material and phosphorus oxoacid, the peak position of P2p appears in the range of 135 eV or less. Further, in the above spectrum, a peak outside the above range may be present. The peak of P2p appearing in the range where the binding energy is higher than 135 eV is, for example, the peak of the phosphorus atom derived from the fluoride of phosphorus.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the power storage element. 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, and acetylene black is preferable. 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, and glass.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode mixture 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 mixture layer is formed of a so-called negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture forming the negative electrode mixture layer contains optional components such as a conductive agent, a binder, 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 mixture 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 or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide and Sn oxide; polyphosphate compounds; graphite and amorphous. Examples thereof include carbon materials such as carbon (graphitizable carbon or non-graphitizable carbon).

Further, the negative electrode mixture (negative electrode mixture 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.

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

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains a fluorinated carbonate. In addition, the non-aqueous electrolyte further contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

The fluorinated carbonate refers to a compound in which a part or all of hydrogen atoms contained in the carbonate are substituted with fluorine atoms. Examples of the carbonate include chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diphenyl carbonate, ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC). , Vinyl ethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and other cyclic carbonates.

As the fluorinated carbonate, a fluorinated cyclic carbonate is preferable. 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. More preferred. The above-mentioned fluorinated carbonate can be used alone or in combination of two or more.

The upper limit of the content of the fluorinated carbonate in the non-aqueous electrolyte is 15% by mass, preferably 10% by mass, more preferably 5% by mass, still more preferably 3% by mass. By setting the content of the fluorinated carbonate to the above upper limit or less, it is possible to suppress the decrease in the dielectric constant of the non-aqueous electrolyte and to increase the capacity retention rate especially in the high voltage charge / discharge cycle in a low temperature environment. On the other hand, as the lower limit of the content of the fluorinated carbonate, for example, 0.1% by mass is preferable, 0.5% by mass is more preferable, and 1% by mass is further preferable. By setting the content of the fluorinated carbonate to the above lower limit or more, the effect of improving the capacity retention rate by using the fluorinated carbonate can be sufficiently exhibited.

As the non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a secondary battery 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.

Examples of the cyclic carbonate include those exemplified in the description of the fluorinated carbonate, and among these, EC is preferable.

The lower limit of the content of cyclic carbonate in the non-aqueous solvent is preferably 10% by volume, more preferably 20% by volume, and even more preferably 25% by volume. On the other hand, as the upper limit of this content, 70% by volume is preferable, 50% by volume is more preferable, and 40% by volume is further preferable. By setting the content of the cyclic carbonate in the above range, better charge / discharge cycle performance can be exhibited at high and low temperatures.

The above-mentioned chain carbonate has an effect of lowering the viscosity by mixing with a cyclic carbonate such as EC. Examples of the chain carbonate include those exemplified in the description of the fluorinated carbonate, and among these, EMC and DMC are preferable.

When a cyclic carbonate and a chain carbonate are used in combination, the lower limit of the volume ratio of the cyclic carbonate (cyclic carbonate / (cyclic carbonate + chain carbonate)) to the sum of the cyclic carbonate and the chain carbonate is preferably 10% by volume. , 20% by volume is more preferred, and 25% by volume is even more preferred. On the other hand, as the upper limit of this volume ratio, 70% by volume is preferable, 50% by volume is more preferable, and 40% by volume is further preferable.

The lower limit of the total content of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 80% by volume, more preferably 95% by volume, and more preferably 99% by volume or more. The upper limit of this total content may be 100% by volume. In this way, by increasing the total content of cyclic carbonate and chain carbonate in the non-aqueous solvent, the dielectric constants of the non-aqueous solvent and non-aqueous electrolyte become appropriate, and so on, so that the non-aqueous electrolyte storage element is charged and discharged. The cycle performance can be further improved.

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 , LiPF ₂ (C ₂ O ₄ ) ₂ , LiClO ₄ , LiN (SO ₂ F) _{2 , 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 ) Examples thereof include lithium salts having a fluoride hydrocarbon group such as _3.

Among the above electrolyte salts, when an electrolyte salt containing a fluorine atom is used, the effect of the present invention is more exhibited. As described above, the HF in the non-aqueous electrolyte that causes the elution of the positive electrode active material component is generated by the decomposition of the electrolyte salt containing a fluorine atom. In particular, LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiPF ₂ (C ₂ O ₄ ) _2, etc. are prone to generate HF by decomposition. Therefore, when these electrolyte salts are used, the capacity retention rate is likely to decrease due to the elution of the positive electrode active material component. However, even when such an electrolyte salt containing a fluorine atom is used in the non-aqueous electrolyte storage device, it is possible to suppress the generation of HF due to decomposition and suppress the decrease in the capacity retention rate.

The lower limit of the content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 M (mol / L), 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.

Other additives may be added to the non-aqueous electrolyte. However, as the upper limit of the content of the components other than the fluorinated carbonate, the non-aqueous solvent and the electrolyte salt in the non-aqueous electrolyte, 5% by mass may be preferable, and 1% by mass may be more preferable. In some cases, 1% by mass is more preferable.

Further, as the non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte and the like can also be used.

Since the non-aqueous electrolyte secondary battery (storage element) has a high capacity retention rate in a high voltage charge / discharge cycle under high temperature and low temperature environments, it can be used at a high operating voltage. For example, the positive electrode potential at the end-of-charge voltage of the non-aqueous electrolyte power storage element during normal use ^{can be 4.35 V (vs. Li / Li +} ) or more, and 4.4 V (vs. Li / Li +). It can also be the above. On the other hand, the upper limit of the positive electrode potential at the charge voltage at the time of normal use, for example, 5.1V (vs.Li/Li ^+), may be 5.0V (vs.Li/Li ^+).

<Manufacturing method of non-aqueous electrolyte power storage element>
The power storage element is preferably manufactured by the following method. That is, the method for manufacturing a non-aqueous electrolyte power storage device according to an embodiment of the present invention is as follows.
To prepare a positive electrode using a positive electrode mixture paste containing phosphorus oxoacid (positive electrode preparation process),
A non-aqueous electrolyte containing a fluorinated carbonate and having a content of the fluorinated carbonate of 15% by mass or less is injected into a container (non-aqueous electrolyte injection step).

(Positive electrode manufacturing process)
The positive electrode mixture paste usually contains a positive electrode active material and a binder in addition to the oxo acid of phosphorus, and further contains other components if necessary. The positive electrode mixture paste can be obtained by mixing these components. A positive electrode is obtained by applying this positive electrode mixture paste to the surface of the positive electrode base material and drying it.

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 oxo acid include phosphoric acid (H ₃ PO ₄ ), phosphoric acid (H ₃ PO ₃ ), phosphinic acid (H ₃ PO ₂ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), polyphosphoric acid and the like. Can be mentioned. Among these, phosphoric acid and phosphonic acid are preferable, and phosphonic acid is more preferable. With this phosphorus oxo acid, a film containing a phosphorus atom can be formed on the positive electrode mixture (positive electrode active material). Further, the peak position of the phosphorus atom derived from the oxo acid of this phosphorus in the above spectrum appears at 135 eV or less.

The lower limit of the mixing amount of phosphorus oxo acid in the positive electrode mixture paste is preferably 0.05 parts by mass, more preferably 0.2 parts by mass, and 0.3 parts by mass with respect to 100 parts by mass of the positive electrode active material. Is even more preferable, and 0.5 parts by mass is even more preferable. On the other hand, as the upper limit of this mixing amount, 5 parts by mass is preferable, 3 parts by mass is more preferable, and 2 parts by mass is further preferable. By setting the mixing amount of phosphorus oxoacid in the above range, it is possible to form a film containing a sufficient phosphorus atom for the positive electrode active material.

An organic solvent is usually used as the dispersion medium in the positive electrode mixture paste. Examples of this 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. Polar solvents are preferable, and NMP is preferable. More preferred.

The method for applying the positive electrode mixture paste is not particularly limited, and a known method such as roller coating, screen coating, or spin coating can be used.

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

The manufacturing method may include the following steps and the like in addition to the positive electrode manufacturing step and the non-aqueous electrolyte injection step. That is, the manufacturing method includes, for example, a step of manufacturing a negative electrode, a step of laminating or winding a positive electrode and a negative electrode via a separator to form an electrode body on which they are alternately superimposed, and a positive electrode and a negative electrode (electrode body). ) Can be provided in a container (case). Normally, the electrode body is housed in a container, and then the non-aqueous electrolyte is injected into the container, but the order may be reversed. After these steps, a non-aqueous electrolyte secondary battery (non-aqueous electrolyte power storage element) can be obtained by sealing the injection port.

<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 positive electrode of the non-aqueous electrolyte power storage element, the positive electrode mixture does not have to form a clear 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-described embodiment, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Examples of other non-aqueous electrolyte 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 storage element 1 (non-aqueous electrolyte secondary battery) which is an embodiment of the non-aqueous electrolyte storage element according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte power storage element 1 shown in FIG. 1, the electrode body 2 is housed in the container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode mixture and a negative electrode having a negative electrode mixture via 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, a non-aqueous electrolyte is injected into the container 3.

The configuration of the non-aqueous electrolyte 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-mentioned non-aqueous electrolyte 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 power storage elements 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 positive electrode)
N-methylpyrrolidone (NMP) is used as the dispersion medium, Li _1.18 Ni _0.10 Co _0.17 Mn _0.55 O ₂ as the positive electrode active material, acetylene black (AB) as the conductive agent, and binder. Polyvinylidene fluoride (PVDF) was mixed in a mass ratio of 94: 4.5: 1.5 in terms of solid content. _{Phosphonic acid (H 3} PO ₃ ) in an amount of 1% by mass based on the mass of the positive electrode active material was added to this mixture as an additive and then further mixed to obtain a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil having a thickness of 15 μm, which is a positive electrode base material, and dried at 100 ° C. to form a positive electrode mixture on the positive electrode base material. The amount of the positive electrode mixture paste applied was 1.35 g / 100 cm ² in terms of solid content. In this way, a positive electrode was obtained.

(Preparation of negative electrode)
Graphite was used as the negative electrode active material, styrene-butadiene rubber and carboxymethyl cellulose were used as the binder, and water was used as the dispersion medium to prepare a negative electrode mixture paste. The mass ratio of the negative electrode active material to the binder was set to 97: 3. This negative electrode mixture paste was applied to one side of a copper foil having a thickness of 10 μm, which is a negative electrode base material, and dried at 100 ° C. The coating amount of the negative electrode mixture was 1.15 g / 100 cm ² in terms of solid content. In this way, the negative electrode was obtained.

(Preparation of non-aqueous electrolyte)
In a mixed solvent in which EC and EMC are mixed at a volume ratio of 30:70, FEC as an additive at a concentration of 2% by mass and lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt are 1.0 mol / l. To prepare a non-aqueous electrolyte, each of them was dissolved at the concentration of.

(Manufacturing of non-aqueous electrolyte power storage element)
As the separator, a microporous polyolefin membrane coated with an inorganic layer was used. An electrode body was produced by laminating the positive electrode and the negative electrode via the separator. This electrode body was housed in a case made of a metal resin composite film, the non-aqueous electrolyte was injected into the case, and then sealed by heat welding to obtain the non-aqueous electrolyte power storage element (secondary battery) of Example 1.

[Examples 2 to 3 and Comparative Examples 1 to 8]
Except that the types of additives used in the preparation of the positive electrode mixture paste, the non-aqueous solvent used in the preparation of the non-aqueous electrolyte and its volume ratio, and the types and amounts of the additives are as shown in Table 1. In the same manner as in Example 1, each non-aqueous electrolyte power storage element of Examples 2 to 3 and Comparative Examples 1 to 8 was obtained. In addition, "-" in the column of additives in the table indicates that the corresponding additive is not used.

The additives to the non-aqueous electrolyte in Table 1 show the following compounds.
FEC: Fluoroethylene carbonate PRS: 1,3-Propene sultone FMP: Methyl trifluoropropionate VC: Vinylene carbonate LiBOB: LiB (C ₂ O ₄ ) ₂

[evaluation]
(Initial charge / discharge)
Each of the obtained non-aqueous electrolyte power storage elements was initially charged and discharged under the following conditions. After charging at 25 ° C. to 4.50 V with a constant current of 0.1 C (3.2 mA), constant voltage charging (CCCV) was performed at 4.50 V. The charging end condition was until the charging current reached 0.05C. After a 10-minute rest after charging, 0.1 C constant current (CC) discharge was performed up to 2.00 V at 25 ° C.

(XPS measurement)
Each non-aqueous electrolyte storage element in the end-discharged state after the initial charge / discharge was disassembled in an argon atmosphere having a dew point of −60 ° C. or lower, a positive electrode was taken out, washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The obtained positive electrode was sealed in a transfer vessel in an argon atmosphere, and XPS measurement was performed on the surface of the positive electrode mixture of the positive electrode under the above conditions. From the obtained spectrum, the peak position of P2p was determined by the above method. The peak positions of the obtained P2p are shown in Table 1. In addition, "-" in the column of the P2p peak position of the table indicates that the measurement was not performed.

(45 ° C charge / discharge cycle test: capacity retention rate)
After the initial charge and discharge, each non-aqueous electrolyte power storage element is stored in a constant temperature bath at 45 ° C. for 2 hours, charged to 4.35 V with a constant current of 1 C (32 mA), and then at 4.35 V. It was charged at a constant voltage. The charging end condition was until the charging current reached 0.05C. The positive electrode potential at the end of charging was 4.45 V (vs. Li / Li ⁺ ). After a 10-minute rest after charging, the battery was discharged to 2.00 V at a constant current of 1 C (32 mA). These charging and discharging steps were regarded as one cycle, and this cycle was repeated 50 cycles. Charging, discharging and pausing were performed in a constant temperature bath at 45 ° C.

(0 ° C charge / discharge cycle test: capacity retention rate)
After the initial charge and discharge, each non-aqueous electrolyte power storage element is stored in a constant temperature bath at 0 ° C. for 2 hours, charged to 4.35 V with a constant current of 1 C (32 mA), and then at 4.35 V. It was charged at a constant voltage. The charging end condition was until the charging current reached 0.05C. After a 10-minute rest after charging, the battery was discharged to 2.00 V at a constant current of 1 C (32 mA). These charging and discharging steps were regarded as one cycle, and this cycle was repeated 50 cycles. Charging, discharging and pausing were all performed in a constant temperature bath at 0 ° C.

Table 1 shows the discharge capacity at the 50th cycle as the capacity retention rate (%) with respect to the discharge capacity at the first cycle in each of the charge / discharge cycle test at 45 ° C. and the charge / discharge cycle test at 0 ° C.

As shown in Table 1 above, each of the non-aqueous electrolyte power storage elements of Examples 1 to 3 has a capacity retention rate of more than 93% at a high temperature (45 ° C.) and a capacity retention rate of 92. The result is good, exceeding 5%.

On the other hand, in Comparative Example 5 in which 2% by mass of FEC was added to the non-aqueous electrolyte without adding an additive to the positive electrode mixture, the capacity retention rate at high temperature was low. Compared to this Comparative Example 5, it is presumed that the capacity retention rate at high temperature is improved to some extent by increasing the amount of FEC added, but in this case, the capacity retention rate at low temperature is presumed to decrease (comparison). See Example 7). On the contrary, in _{Comparative Example 6 in which H 3} PO ₃ was added to the positive electrode mixture and no additive was added to the non-aqueous electrolyte, the capacity retention rate at low temperature was not sufficient. Further, in Comparative Example 7 in which the amount of FEC added to the non-aqueous electrolyte was 20% by mass, the capacity retention rate was particularly low at low temperatures.

Further, _{Comparative Examples 1 to 4 in which H 3} PO ₃ was added to the positive electrode mixture and various additives such as PRS, FMP, VC or LiBOB were added to the non-aqueous electrolyte, and Li ₃ PO ₄ was added to the positive electrode mixture. Even in Comparative Example 8 in which FEC was added to the non-aqueous electrolyte, an excellent capacity retention rate could not be exhibited in both high temperature and low temperature environments.

That is, the effect of being able to exhibit a high capacity retention rate in high-voltage charge / discharge cycles in both high-temperature and low-temperature environments is that, among the innumerable additives, phosphorus oxoacid is used as the positive electrode mixture. Moreover, it can be said that this is a peculiar effect that occurs only when fluorinated carbonate is used as the non-aqueous electrolyte.

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

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive electrode terminal 4'Positive lead 5 Negative terminal 5'Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (3)

A positive electrode having a positive electrode mixture containing a phosphorus atom and a positive electrode
With a non-aqueous electrolyte containing ethylene carbonate and fluorinated carbonate,
The positive electrode mixture contains a positive electrode active material, and the positive electrode active material contains a composite oxide containing a lithium atom, a cobalt atom, a nickel atom and a manganese atom.
In the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy, the peak position of P2p is 135 eV or less.
A non-aqueous electrolyte power storage device in which the content of the fluorinated carbonate with respect to the non-aqueous electrolyte is 15% by mass or less (provided that the cathode active material is provided with a coating layer containing _{Li 3} PO ₄ on at least a part of the surface. (Excluding non-aqueous electrolyte power storage elements) . The non-aqueous electrolyte power storage element according to claim 1, wherein the charge termination potential of the positive electrode during normal use is 4.35 V (vs. Li / Li ^{+) or more.} And making a positive electrode using lithium atoms, cobalt atoms, positive electrode composite paste containing the positive electrode active material and the phosphorus oxo acid comprising a composite oxide containing nickel atoms and manganese atoms,
A method for producing a non-aqueous electrolyte power storage element, which comprises injecting a non-aqueous electrolyte containing ethylene carbonate and a fluorinated carbonate and having a content of the fluorinated carbonate of 15% by mass or less into a container (provided that the positive electrode active material is used. Except for the method for manufacturing a non-aqueous electrolyte power storage element, which comprises providing a coating layer containing _{Li 3} PO ₄ on at least a part of the surface ).

Images