JPS63121269A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To prevent the reaction between electro-deposited lithium and an electrolyte and improve the charge/discharge cycle characteristic by adding specific third sulfonium salt to the electrolyte. CONSTITUTION:0.001-0.3 mol/1 of third sulfonium salt shown by formula (I) is added to an electrolyte, thereby the anion portion of the third sulfonium salt, i.e., portion having a large X<-> portion, is dissolved in the electrolyte and dissociated into third sulfonium cation and anion, and a barrier layer is formed on the surface of electro-deposited lithium to prevent the reaction between the electro-deposited lithium and the electrolyte. Thereby, the charge/discharge cycle characteristic is improved. R1-, R2-, R3-are selected among a group of CH3-, C2H5-, i-C3H7-, n-C3H7-, n-C4H9-, n-C6H13-, C6H5-, p-CH3C6H5-, p-FC6H5, and X<-> is selected among a group of halogen group, NO3<->, ClO4<->, methyl ben zene sulfate, trifluoro benzene sulfate, PF6<->, AsF6<->.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lithium secondary battery, and more particularly to improvements in its electrolyte.

[Conventional technology]

Conventionally, lithium secondary batteries have used fully bent lithium for the negative electrode, but there has been a problem that the negative electrode deteriorates due to repeated charging and discharging cycles. This is because lithium is deposited in a dendrite shape during charging, and the electrodeposited lithium deposited in a dendrite shape is very active and reacts with the components in the electrolyte, causing it to form on the surface of the negative electrode! form a b-state membrane,
Alternatively, the above dendrite-like lithium grows due to repeated charging and discharging, breaks off from its base and falls off, and cannot be used for charging and discharging reactions.In addition, the dendrite-like lithium that grows due to repeated charging and discharging becomes a positive electrode. Another problem occurred in that the battery penetrated the separator separating the negative electrode and came into contact with the positive electrode, causing an internal short circuit and causing the battery to lose its function.

Therefore, it has been proposed to prevent deterioration of the negative electrode and improve charge/discharge cycle characteristics by using a lithium-aluminum alloy for the negative electrode (for example, US Pat. No. 4,002,492).

The above-mentioned proposal to use a lithium-aluminum alloy for the negative electrode utilizes an electrochemical alloying reaction between lithium and aluminum to diffuse lithium into the aluminum and cause the electrodeposited lithium to interact with the electrolyte. This is an attempt to improve charge/discharge cycle characteristics by suppressing reactions and dendrite growth, but the electrochemical alloying reaction between lithium and aluminum during charging is not fast enough, A satisfactory improvement in charge/discharge cycle characteristics was not necessarily achieved.

In addition, various proposals have been made to add additives to the electrolyte to improve charge/discharge cycle characteristics, but as shown below, these have not been as effective as expected.For example, U.S. Patent No. 4,374.910 proposes adding 2-methoxyethanol, 2-methyltetrahydrofuran, etc. to the electrolytic solution.
trochimica+Acta,, Vol.

22, pp. 75-83 (1977) proposed adding nitromethane or S02 to the electrolyte, and JP-A-58-87777 proposed adding ethylenediamine or its derivatives to the electrolyte. ing.

In all of these, additives react with lithium to form an ion-conductive film on the surface of the negative electrode, and this film aims to improve charge-discharge cycle characteristics by avoiding direct contact between lithium and the electrolyte. However, when charge/discharge cycles are repeated, lithium turns into powder and the reaction area of the negative electrode expands, but based on the additives mentioned above (film formation cannot follow this, and eventually the active electrodeposited lithium Due to direct contact with the electrolyte, a reaction between the electrodeposited lithium and the electrolyte occurred, resulting in deterioration of the negative electrode, and the expected improvement in charge/discharge cycle characteristics could not be achieved.

In addition, when S02 is added and the positive electrode active material is titanium disulfide (TiS2), S02 reacts with titanium disulfide to form a passive film on the surface of the positive electrode active material, making it impossible for titanium disulfide to discharge. There was also the problem of it disappearing.

[Problem that the invention seeks to solve]

The purpose of this invention is to solve the problem that the charge/discharge cycle characteristics of the conventional products mentioned above were insufficient, and to provide a lithium secondary battery with excellent charge/discharge cycle characteristics by increasing the reversibility of lithium. .

[Means to solve the problem]

The present invention prevents the reaction between electrodeposited lithium and the electrolytic solution by adding a tertiary sulfonium salt represented by the general formula (1) described in detail later to the electrolytic solution, thereby improving charge-discharge cycle characteristics. It is something.

That is, when a tertiary sulfonium salt is added to the electrolyte,
This tertiary sulfonium salt dissociates in the electrolyte, and tertiary sulfonium cations become present in the electrolyte, and these tertiary sulfonium cations form an ionic barrier layer on the lithium surface of the negative electrode during charging. And this third
It is believed that the sulfonium cation barrier layer prevents the electrolyte solvent in which lithium ions are solvated from reacting with the electrodeposited lithium. Since this barrier layer is formed on the surface of the electrodeposited lithium by the tertiary sulfonium cations present in the electrolytic solution almost simultaneously with the formation of the electrodeposited lithium, repeated charging and discharging cycles may cause the lithium surface of the negative electrode to become uneven or Even if the form of the lithium surface of the negative electrode changes, such as by powdering and increasing the surface area, regardless of the form of the negative electrode,
A barrier layer of tertiary sulfonium cations is formed almost simultaneously with the formation of electrodeposited lithium, and prevents the reaction between the electrodeposited lithium and the electrolyte, thereby increasing the reversibility of charging and discharging lithium and improving battery charging. Discharge cycle characteristics are improved.

The tertiary sulfonium salt added to the electrolyte in the present invention is represented by the following general formula (1).

(In the formula, R1-1R2-1R3- is CH3-5C2R5
-1i -C3R7-1n-C3H7-1n-C4R9
-% n-c5 HI3-% C6R5-SP-CH3
selected from the group consisting of C5R5- and P-FC6H5-, R1-1R2-1R3- may be the same or different, X- is Cl-1Br-
1! -1SCN", BF4-, B (C6R5)4
-1B-CP-FCs Hc, ) 4- , B (P
-FCs R5)3 CH3- and 5bF6-) The tertiary sulfonium salt represented by the above general formula (1) has an anion moiety, that is, an It is soluble in the solvent, and therefore in the electrolyte, and immediately dissociates into a tertiary sulfonium cation and anion, and the tertiary sulfonium cation forms a barrier layer on the electrodeposited lithium surface as described above and is then electrodeposited. Prevents the reaction between lithium and electrolyte and improves charge/discharge cycle characteristics.-
On the other hand, the tertiary sulfonium salts represented by the above general formula (1) with a small portion of
The lithium ions (Li+) of the electrolyte and the tertiary sulfonium cations undergo ion exchange, and some of them dissociate and dissolve, and the tertiary sulfonium cations form a barrier layer on the electrodeposited lithium surface as described above. The formation prevents the reaction between the electrodeposited lithium and the electrolyte, increasing the reversibility of lithium and improving the charge-discharge cycle characteristics.

As mentioned above, in the tertiary sulfonium salt represented by general formula (I), it can be used even if the X portion is small, but from the viewpoint of solubility, it is preferable that the X portion is large. anion of the electrolyte used in
For example, PF6-1AsF6-1SbF6-1BF4-5
C104-1B (C6R5)4'''' etc. are preferred.

On the other hand, typical hydrocarbon groups or octoday-substituted hydrocarbon group moieties represented by R1, R2, R3, etc. include, for example, tri-n-butyl, triphenyl, ethyldiphenyl, n-butyldiphenyl, -Propyldiphenyl! -propyldiphenyl, n-hexyldiphenyl, tri-n-propyl and the like.

The amount of the tertiary sulfonium salt represented by the general formula (1) is preferably 0.001 gaol/1 or more, preferably 0.01 mol/1 or more, which is the amount of the tertiary sulfonium salt added. is 0.001 mol/
This is because if the amount is less than E, the barrier effect of the tertiary sulfonium cation will not be sufficiently exhibited.

On the other hand, the upper limit of the amount of the tertiary sulfonium salt represented by general formula (1) varies depending on whether lithium is used for the negative electrode or a lithium alloy is used for the negative electrode. The amount of the tertiary sulfonium salt represented by formula (I) is 0.0O1 to 0.3 mol.
/ It is preferable, and when using a lithium alloy for the negative electrode, the amount of the tertiary sulfonium salt represented by the general formula (-) is 0.001 to 0.8 mol/
It is preferable to set it in the range of 1. This is because when the amount of the tertiary sulfonium salt represented by the general formula (1) added to the electrolytic solution increases, the density of the barrier layer formed by the tertiary sulfonium salt increases, reducing the electrodeposition area during charging. This is because increased local current density - dendrite growth - tends to cause soft shorting.

In the battery of the present invention, lithium or a lithium alloy is used for the negative electrode. Examples of lithium alloys include lithium-aluminum, lithium-lead, lithium-gallium, lithium-indium, lithium-gallium-indium, lithium-magnesium, lithium-zinc,
Lithium alloys such as lithium-bismuth and lithium alloys made by adding small amounts of other metals to these lithium alloys are used.

Examples of the lithium ion conductive organic non-aqueous electrolyte include 1.2-dimethoxyethane, 1.2-jethoxyethane, ethylene carbonate, propylene carbonate, T
For example, LiClO4,
LiPF6, LiSb6, LiSbF6, l, 1BF4
, LiB (Cs Hs) 4 or the like is used. Also,
In order to stabilize the electrolyte such as LiPF6 in the electrolytic solution, it is also preferably employed to add a stabilizer such as hexamethylphosphoric triamide to the electrolytic solution.

As the positive electrode active material, for example, titanium disulfide (T
i32), molybdenum disulfide (MQS2), molybdenum trisulfide (MO33), iron disulfide (Fes2), zirconium sulfide (ZrS2), niobium disulfide (NbS2), nickel phosphorous trisulfide (NiPS3), vanadium selenide (VSe2) ) and other transition metal chalcogen compounds are used.

In particular, titanium disulfide has a layered crystal structure, and the diffusion constant of lithium ions inside it is large. When titanium disulfide is used as a positive electrode active material, the charge/discharge reaction on the positive electrode side proceeds smoothly, and the lithium is reversible. It is preferred because it has good properties.

〔Example〕

Next, the present invention will be explained in more detail by giving examples.

Example 1 The following negative electrode, positive electrode, and electrolyte were used as power generation elements, and the structure shown in Fig. 1 had a diameter of 20.0 s+m and a height of 1.6 m.
An m- button type lithium secondary battery was manufactured.

The negative electrode is made of a lithium-aluminum alloy, and this lithium-aluminum alloy has a thickness of 0.1 mm.

Diameter 8. Two lithium plates with a thickness of 0.3 mm and a diameter of 8. One lithium plate, the aluminum plate, and the other lithium plate are placed in the negative electrode can in this order, and then the battery is assembled according to a conventional method, and the lithium and aluminum are combined in the presence of an electrolyte. The theoretical amount of electricity of lithium in this negative electrode is approximately 2
It is 2mAh.

The positive electrode uses titanium disulfide as the positive electrode active material, and is a pellet-shaped material made by pressure-molding a mixture of 100 parts by weight of titanium disulfide powder and 5 parts by weight of polytetrafluoroethylene powder. The theoretical amount of electricity of the positive electrode is about 8 mAh.

The electrolyte contains 1.0% of LiPF5 in a mixed solvent consisting of 60% by volume of 4-methyl-1,3-dioxolane, 34.8% by volume of 1,2-dimethoxyethane, and 5.2% by volume of hexamethylphosphoric triamide. mol/1 dissolved organic non-aqueous electrolyte [Hereafter, the composition of this electrolyte will be referred to as IM
LiPF5/4-Me-Diox:DME:HM P
A' (expressed as 60: 34.8: 5.2'/1%]), and when assembling the battery, add 0.05 mol/l of butyl diphenylsulfonium hexafluorophosphate to this electrolyte. Added.

In FIG. 1, numeral 1 denotes a negative electrode, and as described above, this negative electrode l is made of a lithium-aluminum alloy or alloyed with lithium and aluminum in the battery. 2
is a positive electrode, and as described above, this positive electrode 2 is made of a molding mixture containing titanium disulfide as an active material.

3 is a separator made of a microporous polypropylene film, and 4 is an electrolyte absorber made of a polypropylene nonwoven fabric. As mentioned above, the electrolyte to which n-butyl diphenylsulfonium hexafluorophosphate is added is mainly absorbed by this electrolyte absorber. 4. It is impregnated and held within the separator 3 and the positive electrode 2. 5 is a negative electrode can made of stainless steel W4 with nickel plating on the surface, and 6 is a negative electrode can 5.
The current collector on the negative electrode side is made of a stainless steel mesh spot-welded to the inner surface of the electrode. 7 is a positive electrode can, and like the negative electrode can 5, this positive electrode can 7 is made of stainless steel and has a nickel plated surface. 8 is stainless steel! ! ! This is a current collector on the positive electrode side made of a mesh, and is disposed on one surface of the positive electrode 2 when the positive electrode 2 is press-molded. Further, 9 is an annular gasket made of polypropylene, and 10 is a spacer made of polypropylene.

Example 2 Electrolyte solution with the same composition as Example 1 [Composition: IM LtPFs
/4-Me-Diox: DME: HMPA (
60:34.8 : 5.2 y, %)] to] tree n
-butylsulfonium hexafluorophosphate at 0.
08! A button-type lithium secondary battery having the same structure as in Example 1 was produced except that 1.0/1 was added.

Comparative Example 1 Electrolyte solution with the same composition as Example 1 [Composition: IMLiP Fs
/ 4-Me-Diox: DME: HMPA (
60:34.8 F 5.2″/, %)] was used as it was without adding n-butyldiphenylsulfonium hexafluorophosphate as in Example 1. Same configuration as Example 1. A button-shaped lithium secondary battery was fabricated.

The batteries of Examples 1 and 2 and the battery of Comparative Example 1 were repeatedly charged and discharged at a discharging current of 2.5 mA, a charging current of 0.5 mA, an end-of-discharge voltage of 1.5 V, and an end-of-charge voltage of 2.2 ■. The number of cycles that could be discharged was investigated, and the results are shown in Table 1.

Table 1 As shown in Table 1, I M L i P F s
/ 4-Me-Diox; DME: HMPA
(60:34.8:5.2'JC%) system electrolyte, Example 1 in which n-butyldiphenylsulfonium hexafluorophosphate was added or tri-n-butylsulfonium hexafluorophosphate In Example 2, in which these were added, the number of cycles that could be discharged to 3 mAh was greater than in Comparative Example 1, in which they were not added, and the charge-discharge cycle characteristics were excellent.

Example 3 LiAsF6 was added to a mixed solvent consisting of 60% by volume of 4-methyl-1,3-dioxolane, 34.8% by volume of 1,2-dimethoxyethane and 5.2% by volume of hexamethylphosphoric triamide as an electrolyte. e+ol/l melted organic non-aqueous electrolyte [hereinafter, the composition of this electrolyte will be referred to as LM
LiAs・F6/4-Me-Diox:DME:H
MPA (expressed as 80:34.8!5.2
A button-type lithium secondary battery having the same configuration as in Example 1 except that 1/1 was added was produced.

Example 4 Electrolyte solution with the same composition as Example 3 [Composition: IM LiA s
Fs/4-Me-Diox: DME: HM
PA (60: 34.8: 5.2″g%)]
A button-shaped lithium secondary battery having the same structure as in Example 3 was produced, except that 0.1 mol/1 tri-n-butylsulfonium hexafluoroarsenate was added.

Comparative Example 2 Electrolyte solution with the same composition as Example 3 [Composition: IM LiA s
Fs/4-Me-Diox: DME + HM
PA (60: 34.8: 5.2'/, %)]
A button-type lithium secondary battery having the same structure as in Example 3 was produced, except that n-butyldiphenylsulfonium hexafluoroarsenate was used as it was without adding n-butyldiphenylsulfonium hexafluoroarsenate.

The batteries of Examples 3 and 4 and the battery of Comparative Example 2 were repeatedly charged and discharged under the same conditions as the battery of Example 1, and the number of cycles capable of discharging 3 mAh was determined. The results are shown in Table 2.

Table 2 As shown in Table 2, I M L i A s F
s/4-Me-Diox: DME: HMPA
(60:34.8:5.2X%) system electrolyte, Example 3 where n-butyl diphenylsulfonium hexafluoroarsenate was added
Example 4, in which -butylsulfonium hexafluoroarsenate was added, had a greater number of cycles capable of 3 mAh discharge, and had excellent charge-discharge cycle characteristics, compared to Comparative Example 2, in which it was not added.

Example 5 As an electrolyte, 60% by volume of propylene carbonate and 1
, 2-dimethoxyethane, 1.0 sol/1 dissolved in a mixed solvent consisting of 40% by volume of an organic non-aqueous electrolyte (hereinafter, the composition of this electrolyte will be referred to as IMLtAsrFs).
/PC:DME (60:40″y,%)]
n-butyldiphenylsulfonium hexafluoroarsenate was added to the electrolyte at 0.04 ana17
A button-type lithium secondary battery having the same structure as in Example 1 except that 1 was added was produced.

Comparative Example 3 Electrolyte solution with the same composition as Example 5 [Composition: IM LiAs
A button having the same structure as in Example 5, except that Fs/PC:DME (60:40y,%)] was used as it was without adding n-butyl diphenylsulfonium hexafluoroarsenate. A type lithium secondary battery was manufactured.

The battery of Example 5 and the battery of Comparative Example 3 were repeatedly charged and discharged under the same conditions as the battery of Example 1.
The number of cycles that could be discharged was investigated, and the results are shown in Table 3.

Table 3 As shown in Table 3, IM LiAsF5/Pc:
In the case of using a DMF, (60:40'yI%) based electrolyte, Example 5 in which n-butyldiphenylsulfonium hexafluoroarsenate was added was obtained by adding the above n-butyldiphenylsulfonium hexafluoroarsenate. 3mAh compared to Comparative Example 3 which did not
The number of dischargeable cycles was large, and the charge/discharge cycle characteristics were excellent.

Example 6 An AA-sized spiral lithium secondary battery having the structure shown in FIG. 2 was manufactured using the following negative electrode, positive electrode, and electrolyte as power generation elements.

A lithium sheet with a thickness of 0.2 mm, a width of 40 nm, and a length of 80 mm was used for the negative electrode, and titanium disulfide powder 10 was used for the positive electrode.
A mixture powder of 0 parts by weight and 10 parts by weight of polytetrafluoroethylene powder was prepared using a current collector made of a stainless steel mesh with 60 meshes as a core material, and the thickness was 0.3 mar.
A sheet formed into a sheet having a length of 100 m11+ and a width of 35 II11 was used.

The electrolytic solution had the same composition as in Example 1 [composition: lMLiPF6/4-Me-Di
ox: DME: HMPA (60:34.8:5
．． 2"jCt%)] and added 0.2" of n-propyldiphenylsulfonium hexafluorophosphate to it.
02 mol/it 7F1 and this n-propyldiphenylsulfonium hexafluorophosphate was added, and a spiral lithium secondary battery having the structure shown in FIG. 2 was prepared using the negative electrode and positive electrode as power generation elements. Created.

In FIG. 2, reference numeral 11 denotes a negative electrode formed by spirally winding the lithium sheet, and when winding the lithium sheet spirally, a winding core 22 with a lead wire 23 is attached.
350 mesh stainless steel with spot welded to one end! The lithium sheet was crimped onto a current collector (not shown) on the negative electrode side made of a mesh, and inserted into a cylindrical separator (3) made of a microporous polypropylene film.

Reference numeral 12 denotes a positive electrode, and the positive electrode 12 is a positive electrode mixture sheet made of titanium disulfide as an active material, as described above, which is spirally wound. The end of the current collector (not shown), which is the core material of
In other words, a current collecting foil 24 made of stainless steel with a thickness of 20 μm is spot welded to the end (not the winding start side), and the positive electrode mixture sheet is collected on the electrolyte absorber 14 made of a cylindrical polypropylene nonwoven fabric. It is inserted so that the electric foil 24 is exposed.

Then, the negative electrode side member and the positive electrode side member are overlapped,
The negative electrode 11 and the positive electrode 12 are housed in the battery container 15 in a spiral shape by winding the electrodes in a spiral shape around the winding core 22 to create a so-called vortex electrode.

Note that, in FIG. 2, hunting of the separator 13 and the electrolyte absorber 14 is omitted to avoid complication.

The battery container 15 is made of 6m stainless steel, and the reference numeral 16 is an electrolytic solution to which the above-mentioned 1-propyl diphenyl sulfonium hexafluorophosphate is added. , 17 is the bottom insulation material,
Reference numeral 18 denotes an upper insulating material, which is made of a polypropylene nonwoven fabric, and the upper part of the lead wire 23 vertically penetrates approximately the center of the upper insulating material 18.

Reference numeral 19 denotes a battery lid, and this battery i19 is annular and made of stainless steel, and the rising edge of the outer periphery is welded to the open end of the battery container 5. The inner peripheral side of the battery M19 is collected via a glass seal 20. An Ii#A child 21 is provided.

The current collector terminal 21 is a stainless steel pipe with the upper end sealed, and is shaped like a pipe when the battery is assembled, and the electrolyte is injected into the battery from the pipe attached to the battery i19 using a vacuum impregnation method. , after the electrolyte is injected, the upper end of the pipe is inserted into the pipe with a nickel lead wire 2
It is welded together with the upper end of 3 and sealed.

The winding core 22 is made of a nickel rod with a diameter of 1.5 mm.
As mentioned above, one end of a current collector (not shown) made of a stainless steel mesh onto which a lithium sheet is crimped is welded to the winding core 22 in the production of the spiral electrode.
Therefore, the winding core 22 also functions as a current collector on the negative electrode side, and the current collecting terminal 21 attached to the center of the battery lid 19 is connected to the winding core 22 via the lead wire 23. Works as a negative terminal.

On the other hand, a current collector foil 24 welded to the end of the current collector on the positive electrode side is in contact with the inner surface of the battery container 15.
Reference numeral 5 also serves as a positive terminal, and the battery cover 19 also functions as a positive terminal by being welded to the battery container 15. Then, the glass seal 20 is attached to the battery cover 1.
9 and the current collecting terminal 21 are sealed and insulated between them.

Example 7 Electrolyte solution with the same composition as Example 6 [Composition: IMLiPFs/
4-Me-Diox: DME: HMPA (6
A spiral lithium dihydride having the same structure as Example 6 except that 0.01 mO1/! of ruhexyldiphenylsulfonium hexafluorophosphate was added to The next battery was fabricated.

Comparative Example 4 Electrolyte with the same composition as Example 6 [Composition: IMLtP F6/
4-Me-Diox: DME: HMPA (6
0:34.8:5.2''/, %)] was used as it was without adding n-propyldiphenylsulfonium hexafluorophosphate as in Example 6. A spiral lithium secondary battery consisting of the following configuration was fabricated.

The batteries of Examples 6 and 7 and the battery of Comparative Example 4 were used at a discharge current of 100 mA, a charging current of 50 mA, and a discharge end voltage of 1.5.
The battery was repeatedly charged and discharged under the conditions of 266 cm and a charge end voltage of 266 cm, and the number of cycles capable of discharging 100 mAh was determined, and the results are shown in Table 4.

Table 4 As shown in Table 4, I M L i P F s
/ 4-Me-ro 1ox: DME: HMP
A (60:34.8:5.2''g%) system electrolyte is used in a spiral lithium secondary battery that uses lithium as the negative electrode, but gerbropyldiphenylsulfonium hexafluorophosphate is used in the electrolyte. Example 6 with the addition of hexafluorophosphate and Example 7 with the addition of ruhexyldiphenylsulfonium hexafluorophosphate had a higher number of 100mAh discharge cycles than Comparative Example 4 without these additions, and the charge/discharge rate was It had excellent cycle characteristics.

Example 8 Electrolyte solution with the same composition as Example 3 [Composition: IM LiA s
Fs/4 Me-Diox: DME: H
MPA (60: 34.8: 5.2 y, %)] was a spiral shape having the same structure as in Example 6, except that 0.02 mol/1 of n-propyldiphenylsulfonium hexafluoroarsenate was added. A lithium secondary battery was manufactured.

Example 9 Electrolyte solution with the same composition as Example 8 (composition: IM t, tAs
Fs/4 Me-Diox: DME: H
MPA (60: 34.8: 5.2'jC%)
] 0.01 mol/j of N-hexyldiphenylsulfonium hexafluoroarsenate! A spirally wound lithium secondary battery having the same structure as in Example 8 except for the addition of the above ingredients was produced.

Comparative Example 5 Electrolyte solution with the same composition as Example 8 [Composition: IM LiAs
Fs/4-Me-Diox: DME: HMP
A (60734,8F 5.2''y, %)] was prepared in the same manner as in Example 8, except that garbrovir diphenylsulfonium hexafluoroaltriumate was used as it was without adding garbrovir diphenylsulfonium hexafluoroaltriumate. A spiral-shaped lithium secondary battery was fabricated.

The batteries of Examples 8 and 9 and the battery of Comparative Example 5 were repeatedly charged and discharged under the same conditions as the battery of Example 6, and
The number of cycles that allowed Ah discharge was investigated, and the results are shown in Table 5.

Table 5 As shown in Table 5, I M L i A s F
s/4-Me-Diox: DME: HMPA
(60:34.8:5.2X%) system electrolyte,
Even in spiral type lithium secondary batteries using lithium as the negative electrode, Example 8 in which n-propyldiphenylsulfonium hexafluoroarsenate was added to the electrolyte and Example 8 in which n-hexyldiphenylsulfonium hexafluoroarsenate was added Compared to Comparative Example 5 in which these were not added, Sample No. 9 had a larger number of cycles capable of discharging at 100 mAh and had excellent charge/discharge cycle characteristics.

〔Effect of the invention〕

As explained above, in the present invention, by adding a tertiary sulfonium salt represented by 2N) to the electrolyte, it was possible to provide a lithium secondary battery with excellent charge/discharge cycle characteristics.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a button-shaped lithium secondary battery according to the present invention, and FIG. 2 is a cross-sectional view showing an example of a spiral-shaped lithium secondary battery according to the present invention. 1.11... Negative electrode, 2.12... Positive electrode, 3.1
3... Separator, 4,14... Electrolyte absorber,
16... Electrolyte 1st Figure 1... Negative electrode 2... Positive electrode 3... Separator 2nd figure

Claims (4)

[Claims] (1) In a lithium secondary battery comprising a positive electrode, a lithium ion conductive organic nonaqueous electrolyte, and a negative electrode made of lithium or a lithium alloy, the electrolyte has the general formula (I
) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R_1-, R_2-, R_3- are CH_3-,
C_2H_5-, i-C_3H_7-, n-C_3H_
7-, n-C_4H_9-, n-C_6H_1_3-,
C_6H_5-, p-CH_3C_6H_5- and p
-FC_6H_5-, R
_1-, R_2-, and R_3- may be the same or different. X^- is Cl^-, Br^-,
I^-, NO_3^-, ClO_4^-, ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲There are mathematical formulas, chemical formulas, tables, etc.▼, PF_6^-, A_5F_6^-, SCN^-,
BF_4^-, B(C_6H_5)_4^-, B(p-
FC_6H_5)_4^-, B(p-FC_6H_5)
A lithium secondary battery comprising a tertiary sulfonium salt selected from the group consisting of _3CH_3^- and SbF_6^-. (2) The negative electrode is composed of lithium, and the amount of the tertiary sulfonium salt represented by the general formula (I) added to the electrolyte is 0.00.
The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a content of 1 to 0.3 mol/l. (3) The negative electrode is composed of a lithium alloy, and the amount of the tertiary sulfonium salt represented by the general formula (I) added to the electrolyte is 0.
The lithium secondary battery according to claim 1, which has a content of 0.001 to 0.8 mol/l. (4) The lithium secondary battery according to claim 1, 2, or 3, wherein the positive electrode active material is titanium disulfide.