JP6848330B2 - Non-aqueous electrolyte power storage element - Google Patents

Description

The present invention relates to a non-aqueous electrolyte power storage device.

Non-aqueous electrolyte secondary batteries represented 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.

A carbon material such as graphite is widely used as the negative electrode active material of such a non-aqueous electrolyte power storage element. On the other hand, it has been studied to use a material containing silicon as a negative electrode active material other than the carbon material (see Patent Document 1). Since silicon has a larger electric capacity than carbon materials, it is expected as a promising negative electrode active material.

Japanese Unexamined Patent Publication No. 2014-192042

However, silicon has a large expansion and contraction due to charge and discharge. Therefore, the silicon particles become finer and isolated as the charging and discharging are repeated, which has the disadvantage that the rate of decrease in capacity is large. In addition, the decrease in capacity retention rate is also affected by side reactions such as decomposition of non-aqueous electrolytes.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte storage device provided with a negative electrode containing silicon and having a high capacity retention rate. It is to be.

The non-aqueous electrolyte power storage element according to one aspect of the present invention made to solve the above problems includes a negative electrode containing silicon and a non-aqueous electrolyte, and the non-aqueous electrolytes are lithium bis (fluorosulfonylimide) and lithium bis. It is a non-aqueous electrolyte power storage element containing a lithium salt containing a lithium imide salt containing at least one of (trifluoromethanesulfonylimide), a glyme represented by the following formula (1), and a fluorinated ether.
R ¹ − (OCH ₂ CH ₂ ) _{x −} OR ² ··· (1)
(In the formula (1), R ¹ and R ² are independently alkyl groups having 1 to 3 carbon atoms. X is 3 or 4.)

According to the present invention, it is possible to provide a non-aqueous electrolyte storage element having a negative electrode containing silicon and having a high capacity retention rate.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte secondary battery according to an embodiment of the non-aqueous electrolyte power storage device of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous electrolyte secondary batteries according to an embodiment of the non-aqueous electrolyte power storage element of the present invention. FIG. 3A is a graph showing changes in the discharge capacity retention rates of Examples 6 and 7. FIG. 3B is a graph showing changes in the Coulomb efficiency of Examples 6 and 7.

The non-aqueous electrolyte storage element according to one embodiment of the present invention includes a negative electrode containing silicon and a non-aqueous electrolyte, and the non-aqueous electrolyte is at least lithium bis (fluorosulfonylimide) and lithium bis (trifluoromethanesulfonylimide). It is a non-aqueous electrolyte power storage element (hereinafter, also simply referred to as “storage element”) containing a lithium salt containing a lithium imide salt containing one of them, a glime represented by the following formula (1), and a fluorinated ether. ..
R ¹ − (OCH ₂ CH ₂ ) _{x −} OR ² ··· (1)
(In the formula (1), R ¹ and R ² are independently alkyl groups having 1 to 3 carbon atoms. X is 3 or 4.)

The power storage element has a high capacity retention rate while having a negative electrode containing silicon. The reason for this is not clear, but since the non-aqueous electrolyte has the above composition, the decomposition reaction itself of the non-aqueous electrolyte is reduced, and the SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode containing silicon is stabilized. It is presumed that this suppresses the decrease in the reaction region of silicon due to the deposition of decomposition products. It is presumed that the reason why the decomposition reaction of the non-aqueous electrolyte itself is reduced is that lithium ions form a complex with glyme and that the solvent is diluted with fluorinated ether.

The lithium imide salt is not only a lithium imide salt having a structure in which two carbonyl groups are bonded to a nitrogen atom (-CO-N ^- CO-), but also a structure in which two sulfonyl groups are bonded to a nitrogen atom. It means that those having (−SO ₂ −N ⁻ −SO ₂₋ ) are also included.

It is preferable that the lithium salt further contains lithium nitrate. This makes it possible to reduce the irreversible volume, particularly the irreversible volume derived from the side reaction. It is presumed that this is because the collapsed SEI film portion that cannot follow the volume change of silicon can be suitably repaired by lithium nitrate, and the irreversible reaction mainly due to the decomposition of the non-aqueous electrolyte is suppressed extremely effectively. To.

The molar ratio of lithium nitrate to the lithium imide salt is preferably 0.01 or more and 0.15 or less. Thereby, the irreversible volume, particularly the irreversible volume derived from the side reaction, can be further reduced.

The lithium imide salt is preferably lithium bis (fluorosulfonylimide). By using lithium bis (fluorosulfonylimide), the irreversible capacity can be further reduced and the Coulomb efficiency can be increased.

The molar ratio of the lithium salt (lithium salt / grime) to the grime is preferably 1 or more. As a result, the capacity retention rate can be further increased. It is presumed that this is because when the molar ratio of lithium salt to grime is set to 1 or more, all grime forms a complex and free grime does not exist.

The power storage element preferably further includes a positive electrode containing sulfur. Usually, when a positive electrode containing sulfur is used, the reversibility (Coulomb efficiency, etc.) is lowered due to elution of sulfide into a non-aqueous electrolyte. However, according to the power storage element provided with the non-aqueous electrolyte, the reversibility when a positive electrode containing sulfur can be used can also be enhanced.

<Non-aqueous electrolyte power storage element>
The power storage element according to an embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, as an example of the power storage element, a lithium ion secondary battery which is a non-aqueous electrolyte secondary battery will be described. 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 battery container, and the non-aqueous electrolyte (non-aqueous electrolyte solution) is filled in the battery container. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the battery container, a known metal battery container, resin battery container, or the like that is usually used as a battery container for a non-aqueous electrolyte secondary battery can be used.

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

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

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

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

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

The positive electrode active material preferably contains sulfur. That is, the positive electrode active material is preferably sulfur alone or a sulfur compound. Examples of the sulfur compound include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. The positive electrode active material containing sulfur may be a composite of sulfur and a conductive agent (a material having a higher conductivity than sulfur). Examples of this composite include those in which sulfur is supported on a conductive agent or the like as a carrier, and specific examples thereof include a composite of sulfur and porous carbon. Sulfur has advantages such as high theoretical capacity and low cost. On the other hand, when sulfur or a sulfur compound is used as the positive electrode active material, the reversibility is lowered due to elution of sulfide during charging and discharging as described above and a side reaction. Therefore, according to the power storage element provided with a non-aqueous electrolyte in which side reactions are unlikely to occur, the reversibility can be enhanced even when the positive electrode active material contains sulfur.

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

Examples of the binder (binding agent) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyimide, and polyacrylic acid; and ethylene-propylene-diene rubber. (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and other elastomers; polysaccharide polymers and the like.

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

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

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

The negative electrode base material has conductivity. The negative electrode base material can have the same structure as the positive side base material, but as the material, metals such as copper, nickel, stainless steel, nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. .. That is, a copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

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

The negative electrode active material layer contains silicon as a negative electrode active material. Silicon may exist as a simple substance of silicon or as a silicon compound. Examples of the silicon compound include silicon oxides, silicon nitrides, silicon carbides, and metal silicon compounds. Examples of the metallic silicon compound include compounds containing silicon, lithium, aluminum, tin, zinc, nickel, copper, titanium, vanadium, magnesium and the like. Among these, silicon as the negative electrode active material is preferably silicon alone. Further, the negative electrode active material containing silicon is usually in the form of particles.

The negative electrode active material may further contain other negative electrode active materials. As such other negative electrode active materials, known materials capable of occluding and desorbing lithium ions are usually used, and specifically, carbon materials such as graphite and amorphous carbon; Sn, Ge. Such as metal or semi-metal; metal oxide or semi-metal oxide such as Sn oxide and Ge oxide; polyphosphate compound and the like.

The lower limit of the content ratio of silicon (silicon element) in the negative electrode active material may be 1% by mass, 5% by mass, preferably 10% by mass, more preferably 30% by mass, or 50% of the total negative electrode active material. By mass% is more preferable, 90% by mass is more preferable, and 99% by mass is further preferable. In this way, it is possible to increase the capacity by increasing the content ratio of silicon. When silicon is contained in the negative electrode active material in an amount of even 1% by mass, the irreversible capacity derived from the side reaction between silicon and the non-aqueous electrolyte becomes large, and the charge / discharge cycle performance of the power storage element deteriorates. Even in such a case, the effect of the present invention can be effectively exhibited by applying the configuration of the present embodiment. The upper limit of this content ratio may be 100% by mass.

Further, the negative electrode active material layer is a typical non-metal element such as B, N, P, F, Cl, Br, I, or a typical metal such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge. Elements, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W 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. Further, it may be a multi-layer separator in which an inorganic porous layer is laminated on a porous resin film.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains a lithium salt, a grime represented by the following formula (1), and a fluorinated ether.

(Lithium salt)
The lithium salt contains a lithium imide salt. The lithium imide salt contains at least one of lithium bis (fluorosulfonylimide) (LiFSI: LiN (SO ₂ F) ₂ ) and lithium bis (trifluoromethanesulfonylimide) (LiTFSI: LiN (SO ₂ CF ₃ ) ₂ ). .. Of these, LiFSI is preferable as the lithium imide salt. Moreover, it is preferable that all the contained lithium imide salts are lithium sulfonylimide salts.

Further, the lithium imide salt may further contain other lithium imide salts. Examples of other lithium imide salts include lithium fluorinated alkylsulfonylimide salts such _{as LiN (SO 2} C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F _9). However, as the lower limit of the content ratio of LiFSI and LiTFSI to the lithium imide salt, 50% by mass is preferable, 90% by mass is more preferable, and 99% by mass is further preferable. This content ratio may be substantially 100% by mass.

The lithium salt preferably further contains lithium nitrate (LiNO _3). The lower limit of the molar ratio of lithium nitrate to the lithium imide salt (lithium nitrate / lithium imide salt) is preferably 0.01, more preferably 0.05, further preferably 0.08, and even more preferably 0.1. .. On the other hand, the upper limit of this molar ratio may be, for example, 0.3 or 0.2, but 0.15 is preferable, 0.12 is more preferable, and 0.1 is further preferable. By setting the content ratio of lithium nitrate in the above range, the irreversible volume, particularly the irreversible volume derived from the side reaction, can be further reduced.

The lithium salt may further contain a lithium imide salt and other lithium salts other than lithium nitrate. Examples of the other lithium salts include _{inorganic lithium salts such as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , and LiClO ₄ , and organic lithium such as LiC (SO ₂ CF ₃ ) ₃ and LiC (SO ₂ C ₂ F ₅ ) _3. Salt and the like can be mentioned. However, the upper limit of the content ratio of the other lithium salt to the lithium salt is preferably 10% by mass or 1% by mass. It may be preferable that the above other lithium salts are substantially not contained.

(Grime)
The grime is a compound represented by the following formula (1). The grime is contained as a non-aqueous solvent.
R ¹ − (OCH ₂ CH ₂ ) _{x −} OR ² ··· (1)
In formula (1), R ¹ and R ² are independently alkyl groups having 1 to 3 carbon atoms. x is 3 or 4.

^{Examples of the alkyl group having 1 to 3 carbon atoms in R 1} and R ² in the formula (1) include a methyl group, an ethyl group, an n-propyl group and an i-propyl group. As R ¹ and R ² , methyl groups are preferable, respectively. As x in the formula (1), 4 is preferable. That is, tetraethylene glycol dimethyl ether is preferable as the compound represented by the above formula (1). It is considered that by using such a compound, the complex with the formed lithium ion becomes a particularly stable state, and the decomposition reaction of the non-aqueous electrolyte is further reduced.

The content of the grime is not particularly limited. The lower limit of the molar ratio of lithium salt to grime (lithium salt / grime) may be, for example, 0.5, but is preferably 1. The upper limit of the molar ratio of lithium salt to grime can be, for example, 2, preferably 1.5. Moreover, it is preferable that the molar ratio of the lithium salt to this grime is substantially 1. As a result, a better solvation state is formed, and the capacity retention rate can be increased.

(Fluorinated ether)
The fluorinated ether is a compound in which a part or all of hydrogen atoms contained in the ether are replaced with fluorine atoms. The fluorinated ether is also contained as a non-aqueous solvent.

Examples of the fluorinated ether include a compound represented by the following formula (2).
R ^3- O-R ⁴ ... (2)
In formula (2), R ³ is a fluorinated hydrocarbon group having 1 to 8 carbon atoms. R ⁴ is a hydrocarbon group having 1 to 8 carbon atoms or a fluorinated hydrocarbon group having 1 to 8 carbon atoms.

As the R ^3, fluorinated alkyl group, more preferably a fluorinated alkyl group of 1 to 5 carbon atoms, more preferably a fluorinated alkyl group having 1 to 3 carbon atoms.

As the R ^4, preferably a fluorinated hydrocarbon group, more preferably a fluorinated alkyl group, more preferably a fluorinated alkyl group of 1 to 5 carbon atoms, even more preferably from a fluorinated alkyl group having 2 to 4 carbon atoms ..

Specific examples of the fluorinated ether include CF ₃ OCH ₃ , CF ₃ OC ₂ H ₅ , F (CF ₂ ) ₂ OCH ₃ , F (CF ₂ ) ₂ OC ₂ H ₅ , CF ₃ (CF ₂ ) CH _2. O (CF ₂ ) CF ₃ , F (CF ₂ ) ₃ OCH ₃ , F (CF ₂ ) ₃ OC ₂ H ₅ , F (CF ₂ ) ₄ OCH ₃ , F (CF ₂ ) ₄ OC ₂ H ₅ , F (CF 2) CF ₂ ) ₅ OCH ₃ , F (CF ₂ ) ₅ OC ₂ H ₅ , F (CF ₂ ) ₈ OCH ₃ , F (CF ₂ ) ₈ OC ₂ H ₅ , F (CF ₂ ) ₉ OCH ₃ , CF ₃ CH ₂ OCH ₃ , CF ₃ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ OCH ₃ , CF ₃ CF ₂ CH ₂ OCHF ₂ , CF ₃ CF ₂ CH ₂ O (CF ₂ ) ₂ H, CF ₃ CF ₂ CH ₂ O (CF ₂ ) ₂ F, HCF ₂ CH ₂ OCH ₃ , (CF ₃ ) (CF ₂ ) CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ OCH ₂ CH ₃ , H (CF ₂ ) ₂ OCH ₂ CF ₃ , H (CF ₂ ) ₂ CH ₂ OCHF ₂ , H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₃ H, H (CF 2) ₂ ) ₃ CH ₂ O (CF ₂ ) ₂ H, H (CHF) ₂ CH ₂ O (CF ₂ ) ₂ H, (CF ₃ ) ₂ CHOCH ₃ , (CF ₃ ) ₂ CHCF ₂ OCH ₃ , CF ₃ CHFCF ₂ OCH ₃ , CF ₃ CHFCF ₂ OCH ₂ CH ₃ , CF ₃ CHFCF ₂ CH ₂ OCHF ₂ , CF ₃ CHFCF ₂ OCH ₂ (CF ₂ ) ₂ F, CF ₃ CHFCF ₂ OCH ₂ CF ₂ CF ₂ H, H (CF ₂₎ ) ₄ CH ₂ O (CF ₂ ) ₂ H, CH ₃ CH ₂ O (CF ₂ ) ₄ F, F (CF ₂ ) ₄ CH ₂ O (CF ₂ ) ₂ H, H (CF ₂ ) ₂ CH ₂ OCF ₂ CHFCF ₃ , F (CF ₂ ) ₂ CH ₂ OCF ₂ CHFCF ₃ , H (CF ₂ ) ₄ CH ₂ O (CF) ₂ ) H, CF ₃ OCH ₂ (CF ₂ ) ₂ F, CF ₃ CHFCF ₂ OCH ₂ (CF ₂ ) ₃ F, CH ₃ CF ₂ OCH ₂ (CF ₂ ) ₂ F, CH ₃ CF ₂ OCH ₂ (CF ₂₎ ) ₃ F, CH ₃ O (CF ₂ ) ₅ F, F (CF ₂ ) ₃ CH ₂ OCH ₂ (CF ₂ ) ₃ F, F (CF ₂ ) ₂ CH ₂ OCH ₂ (CF ₂ ) ₂ F, H ( CF ₂ ) ₂ CH ₂ OCH ₂ (CF ₂ ) ₂ H, CH ₃ CF ₂ OCH ₂ (CF ₂ ) ₂ H and the like can be mentioned. Among these, H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether: HFE) is preferable.

As the lower limit of the content of the fluorinated ether, the molar ratio of 1 to the lithium salt is preferably 1 and more preferably 1.5. On the other hand, as the upper limit of the molar ratio to this lithium salt, 3 is preferable, 2.5 is more preferable, and 2 is further preferable. Further, as the lower limit of the content of the fluorinated ether, the molar ratio of 1 to the lithium imide salt is preferably 1 and more preferably 1.5. On the other hand, as the upper limit of the molar ratio to the lithium imide salt, 3 is preferable, and 2.5 is more preferable. Further, as the lower limit of the content of the fluorinated ether, the molar ratio is preferably 1 and more preferably 1.5 with respect to the grime. Further, as the upper limit of the molar ratio to this grime, 3 is preferable, 2.5 is more preferable, and 2 is further preferable. By setting the content of the fluorinated ether in the above range, the stability of the SEI formed can be further enhanced, side reactions can be further suppressed, and the like.

(Other ingredients)
The non-aqueous electrolyte may contain components other than the lithium salt, grime and fluorinated ether as long as the effects of the present invention are not impaired. Examples of the other components include electrolyte salts other than lithium salts, non-aqueous solvents other than glime and fluorinated ether, and various additives contained in other general non-aqueous electrolytes for power storage elements. Can be done.

Examples of other electrolyte salts include sodium salt, potassium salt, magnesium salt, onium salt and the like. However, the content of the electrolyte salt other than the lithium salt in the total electrolyte salt is preferably 10 mol% or less, and more preferably 1 mol% or less.

Examples of other non-aqueous solvents include cyclic carbonates, chain carbonates, esters, amides, sulfones, lactones, nitriles and the like. However, the content of the non-aqueous solvent other than the grime and the fluorinated ether in the total non-aqueous solvent is preferably 10 mol% or less, and more preferably 1 mol% or less. Since the non-aqueous solvent is substantially composed of only grime and fluorinated ether, side reactions and the like can be suppressed and the capacity retention rate can be further increased.

The content of the components other than the electrolyte salt and the non-aqueous solvent in the non-aqueous electrolyte is preferably 5% by mass or less, and more preferably 1% by mass or less. By suppressing the content of other components, side reactions and the like can be suppressed, and the capacity retention rate can be further increased.

(Manufacturing method of non-aqueous electrolyte power storage element)
The method for manufacturing the power storage element is not particularly limited, and known methods can be combined. The manufacturing method includes, for example, a step of producing a positive electrode and a negative electrode, a step of preparing a non-aqueous electrolyte, and a step of laminating or winding the positive electrode and the negative electrode via a separator to form an electrode body in which alternating electrodes are superimposed. , A step of accommodating the positive electrode and the negative electrode (electrode body) in the battery container, and a step of injecting the non-aqueous electrolyte into the battery container. The above injection can be performed by a known method. After injection, 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, in the above embodiment, the non-aqueous electrolyte storage element has been described mainly in the form of a lithium ion secondary battery in which the non-aqueous electrolyte secondary battery is 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 secondary battery 1 which is an embodiment of the non-aqueous electrolyte power storage element according to the present invention. The figure is a perspective view of the inside of the battery container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

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 power storage element, a square power storage element (rectangular power storage element), and a flat power storage element. 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 secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

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

[Example 1]
(Preparation of non-aqueous electrolyte)
LiFSI, which is a lithium imide salt, and G4 (tetraethylene glycol dimethyl ether) were mixed at a molar ratio of 1: 1 to obtain a mixed solution. The above mixed solution and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) were mixed to obtain a non-aqueous electrolyte 1. When the mixed solution was mixed with HFE, the mixture was mixed so that the molar ratio of LiFSI, G4, and HFE in the obtained non-aqueous electrolyte 1 was 1: 1: 2.

(Manufacturing of evaluation cell (non-aqueous electrolyte power storage element))
A negative electrode mixture slurry containing silicon, a conductive agent, and a polyacrylic acid binder in a mass ratio of 70:10:20 and using N-methylpyrrolidone (NMP) as a solvent was prepared. This negative electrode mixture slurry was applied to a disk-shaped (14 mm in diameter) nickel mesh-like base material to prepare a working electrode (negative electrode). On the other hand, a disk-shaped (diameter 16 mm, thickness 300 μm) metallic lithium was used as the counter electrode (positive electrode). As a separator, a polyethylene microporous membrane having a diameter of 26 mm was used. Using the obtained working electrode, counter electrode, separator and non-aqueous electrolyte 1, a coin-shaped cell as a non-aqueous electrolyte power storage element was produced. This will be the evaluation cell of Example 1.

[Example 2]
(Preparation of non-aqueous electrolyte)
LiFSI, which is a lithium imide salt, and G4 (tetraethylene glycol dimethyl ether) were mixed at a molar ratio of 1: 1 to obtain a mixed solution 1. On the other hand, lithium nitrate (LiNO ₃ ) and G4 were mixed at a molar ratio of 1: 1 to obtain a mixed solution 2. The above mixed solution 1, mixed solution 2 and HFE were mixed to obtain a non-aqueous electrolyte 2. Incidentally, the mixed solution 1, upon mixing the mixture solution 2 and HFE, the molar ratio of LiFSI and LiNO ₃ in the non-aqueous electrolyte 2 obtained and G4 and the HFE is 1: 0.05: 1.05: the 2 Mixed as such.

(Manufacturing of evaluation cell (non-aqueous electrolyte power storage element))
An evaluation cell as a non-aqueous electrolyte power storage element was produced in the same manner as in Example 1 except that the non-aqueous electrolyte 2 was used instead of the non-aqueous electrolyte 1.

[Examples 3 to 5]
As a non-aqueous electrolyte power storage element, as in Example 2, except that the type of lithium imide salt used _{and the molar ratio of the lithium imide salt to LiNO 3, G4 and HFE were as shown in Table 1.} The evaluation cell of was prepared.

[Comparative Example 1]
An evaluation cell as a non-aqueous electrolyte power storage device was prepared in the same manner as in Example 1 except that a non-aqueous electrolyte in which LiFSI was dissolved in 1,2-dimethoxyethane (DME) at a concentration of 1 M was used.

[Comparative Example 2]
An evaluation cell as a non-aqueous electrolyte power storage device was prepared in the same manner as in Example 1 except that a non-aqueous electrolyte in which LiFSI was dissolved in 1,2-dimethoxyethane (DME) at a concentration of 5 M was used.

[Comparative Example 3]
In the same manner as in Example 1 except that a non-aqueous electrolyte in _{which LiPF 6} was dissolved at a concentration of 1 M in a mixed solvent of EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DMC (dimethyl carbonate) was used. An evaluation cell as a non-aqueous electrolyte power storage element was prepared.

[Evaluation]
The obtained evaluation cell was subjected to a charge / discharge test in a constant temperature bath set at 25 ° C. Charging was constant current constant voltage (CCCV) charging, and the final charging potential was 0.02 V (vs. Li / Li ⁺ ). The charging termination condition was set until the total charging time was 20 hours or the charging current was 0.02C. The discharge was a constant current (CC) discharge, and the discharge end potential was 1.2 V (vs. Li ^/ Li +). The constant current values for charging and discharging were 0.1 C, with 4200 mAh / g, which is the theoretical capacity of silicon, as 1 C. In each cycle, a rest period of 10 minutes was set after charging and discharging. This cycle was carried out for 10 cycles. The reduction reaction in which lithium ions or the like are occluded in the negative electrode active material is referred to as “charging”, and the oxidation reaction in which lithium ions or the like are released from the negative electrode active material is referred to as “discharge”.

For each evaluation cell, the capacity retention rate at the 10th cycle, the Coulomb efficiency at the 10th cycle, the cumulative irreversible capacity derived from the side reaction, and the cumulative irreversible capacity derived from the isolation of silicon were calculated. The capacity retention rate at the 10th cycle was determined by dividing the discharge capacity at the 10th cycle by the discharge capacity at the 1st cycle. The Coulomb efficiency at the 10th cycle was determined by dividing the discharge capacity at the 10th cycle by the amount of electricity charged at the 10th cycle. The cumulative irreversible volume derived from the side reaction and the cumulative irreversible volume derived from the isolation of silicon were determined by the following methods. These values are shown in Table 1.

The irreversible capacity derived from the side reaction during charging in the second cycle is obtained by subtracting the discharge capacity in the first cycle from the amount of electricity charged in the second cycle. The accumulated value of the irreversible volume derived from the side reaction at the nth cycle (n ≧ 2) thus obtained was calculated as the cumulative irreversible volume derived from the side reaction. Assuming that the irreversible capacity in the charge / discharge reaction of silicon is the sum of the irreversible capacity derived from the side reaction and the irreversible capacity derived from the isolation of silicon, it is derived from the isolation of silicon generated during the discharge of the nth cycle. The irreversible volume is obtained by subtracting the irreversible volume derived from the side reaction at the nth cycle from the irreversible volume at the nth cycle. Therefore, the cumulative irreversible volume derived from the isolation of silicon was calculated by reducing the cumulative irreversible volume derived from the side reaction from the cumulative value of the irreversible volume up to the 10th cycle.

As shown in Table 1, it can be seen that Examples 1 to 5 have a higher capacity retention rate than Comparative Examples 1 to 3. It can also be seen that by using LiFSI as the lithium imide salt, the Coulomb efficiency at the 10th cycle is increased and the cumulative irreversible capacity is reduced. Furthermore, it can be seen that the irreversible volume, particularly the irreversible volume derived from the side reaction, is further reduced by containing lithium nitrate.

[Example 6]
Magnesium oxide (MgO) was extracted by carbonizing magnesium citrate at 900 ° C. in an argon atmosphere for 1 hour and then immersing it in a 1 mol / l sulfuric acid aqueous solution. The residue was washed and dried to give porous carbon. The porous carbon and sulfur were mixed at a mass ratio of 30:70. This mixture was sealed in a closed container under an argon atmosphere, heated to 150 ° C. at a heating rate of 5 ° C./min, held for 5 hours, and then allowed to cool to 80 ° C. Then, the temperature was raised again to 300 ° C. at a heating rate of 5 ° C./min and heat treatment was performed to hold the temperature for 2 hours to obtain a carbon-sulfur composite (hereinafter, also referred to as “SPC composite”).
A positive electrode mixture slurry containing SPC composite as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder at a mass ratio of 85: 5:10, and N-methylpyrrolidone (NMP) as a solvent. Was produced. The obtained positive electrode mixture slurry was applied to a disk-shaped (diameter 12 mm) nickel mesh base material to prepare a positive electrode.
^{The coin-shaped cell of Example 1 was charged to 0.02 V (vs. Li / Li +} ) with a charge electricity amount of 0.1 C to precharge the negative electrode containing silicon. After charging, the coin-shaped cell was disassembled in an argon box having a dew point of −80 ° C., and the negative electrode in a charged state was taken out.
An evaluation cell of Example 6 which is a Si—S secondary battery was produced in the same manner as in Example 1 except that the positive electrode and the negative electrode were used.

[Example 7]
A Si—S secondary battery was produced in the same manner as in Example 6 except that a non-aqueous electrolyte containing LiTFSI was used instead of LiFSI.

[Evaluation]
Using the obtained Si—S secondary batteries (evaluation cells) of Examples 6 and 7, a 20-cycle charge / discharge test was performed according to the method described above. FIG. 3A shows the transition of the capacity retention rate in the evaluation cells of Examples 6 and 7. FIG. 3B shows the transition of the Coulomb efficiency in the evaluation cells of Examples 6 and 7. Each capacity retention rate in FIG. 3A is a value obtained by dividing the discharge capacity in the nth cycle by the capacity in the first cycle.

As can be seen from FIGS. 3 (a) and 3 (b), the Si—S secondary battery of Example 6 using LiFSI is compared with the Si—S secondary battery of Example 7 using LiTFSI. Has a high capacity retention rate. It is presumed that this is because LiFSI reduces the irreversible capacitance of the Si negative electrode and improves the reversibility of the S positive electrode.

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

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

Claims (5)

Equipped with a negative electrode containing silicon and a non-aqueous electrolyte,
The above non-aqueous electrolyte
A lithium salt containing a lithium imide salt containing at least one of lithium bis (fluorosulfonylimide) and lithium bis (trifluoromethanesulfonylimide), and
It contains a non-aqueous solvent containing grime and fluorinated ether represented by the following formula (1) .
The lithium salt further contains lithium nitrate,
The glymes and the content of other non-aqueous solvent other than the fluorinated ether is 1 mol% or less der Ru nonaqueous electricity storage device in the non-aqueous solvent.
R ¹ − (OCH ₂ CH ₂ ) _{x −} OR ² ··· (1)
(In the formula (1), R ¹ and R ² are independently alkyl groups having 1 to 3 carbon atoms. X is 3 or 4.) The molar ratio of lithium nitrate with respect to the lithium imide salt, nonaqueous electricity storage device according to claim 1 is 0.01 to 0.15. The non-aqueous electrolyte storage element according to claim 1 or 2 , wherein the lithium imide salt is lithium bis (fluorosulfonylimide). The non-aqueous electrolyte power storage element according to any one of claims 1 to 3 , wherein the molar ratio of the lithium salt to the grime is 1 or more. The non-aqueous electrolyte power storage element according to any one of claims 1 to 4, further comprising a positive electrode containing sulfur.

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