CA1317631C

CA1317631C - Non-aqueous electrolyte cell

Info

Publication number: CA1317631C
Application number: CA000616388A
Authority: CA
Inventors: Nobuhiro Furukawa; Masatoshi Takahashi
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1988-07-01
Filing date: 1992-05-26
Publication date: 1993-05-11
Anticipated expiration: 2008-11-08
Also published as: DE3855872D1; EP0349675A3; EP0349675A2; CA1317632C; CA1317633C; CA1308778C; DE3855872T2; EP0349675B1; US5112704A

Abstract

ABSTRACT OF THE DISCLOSURE
A non-aqueous electrolyte cell having a positive electrode, a negative electrode and an electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfonate. The organic solvent comprises an organic solvent mixture of at least two high boiling point solvents including at least one cyclic carbonates. The negative electrode comprises a lithium alloy. The electrolyte includes a reaction inhibitor added thereto for inhibiting reaction between the cell can and the electrolyte.
Further, the lithium trifluoromethanesulfonate is heated, dried and dehydrated in a vacuum at 80-150°C.

Description

~" 1317631 NON-AQUEOUS 8L~CTROLYTE C~LL

(1) Field of the Invention The present invention in this divisional application and in the parent Canadian patent application serial number 582,548, filed November 8, 1988 relates to a non-aqueous electrolyte cell comprising a positive electrode, a negative electrode, and an electrolyte consisting of a solute and an organic solvent, all contained in a cell can, in which lithium trifluoromethanesulfonate is employed as the solute.
(2) Description of the Prior Art A non-aqueous electrolyte cell in which the negative electrode has lithium, sodium or an alloy thereof as an active material provides the advantages of high energy density and low self-discharge rate. However, this type of cell is inferior in low temperature discharge characteristics and has room for improvement in this respect.
In view of the above situation, proposals have been made to improve the low temperature discharge characteristics of the lithium cell by using lithium trifluoromethanesulfonate (LiCF3So3) as the solute, which is ~highly soluble ln a non-aqueous~solvent and does not cause deposltion of lithium salt on the negative electrode during 25 ~ low temperature discharge.
Where lithium trifluoromethanesulfonate is used : :: ` ~ :

: :

`'` :-as the solute, initial low temperature discharge characteristics are improved but there is a problem of deterioration in low temperature discharge characteristics after a long storage period. The deterioration takes place for the following reasons:
(1) When this type of cell is stored for a long period, a reaction occurs between fluorine ionized from lithium trifluoromethanesulfonate and the lithium whlch is the active material of the negative electrode. As a result, a layer of lithium fluoride which is a passive substance is formed on the negative electrode surface, thereby increasing internal resistance of the electrode.
~2) A cell can becomes corroded during the storage period due to fluorine ionized from lithium trifluoromethanesulfonate, and metallic ions formed by the corrosion deposit on the negative electrode surface, thereby increasing internal resistance of the electrode.
~ Meanwhile, the followlng cells have heen proposed:
(1) Cells in which the electrolyte includes a ;solvent ~mixture o~f propyl~ene~carbonate and 1,2-d1methoxyethane (U.S. Patents Nos. 4,279,972 and 4,482,613); a cell in which the electrolyte includes a solvent mixture of propylene carbonate, 1,2-~; - 2 -: ` :

~ ' ~ . .

` 1317631 dimethoxyethane and 1,3-dioxolane (V.S. Patent No.
4,129,691); a cell in which the electrolyte includes a solvent consisting of dimethylformamide (U.S. Patent No. 4,142,028); a cell in which the electrolyte includes a solvent mixture of propylene carbonate and tetrahydrofuran ~Japanese Patent Publication Kokai No.
60-243972); and a cell in which the electrolyte includes a solute consisting of lithium perchlorate and a solvent mixture of propylene carbonate and 1,2-dimethoxyethane (Japanese Patent Publication Kokai No.60-86771).
(2) A cell having a can formed of stainless steel, and in particular ferritic stainless steel containing almost no nickel.
However, the cells listed in paragraph ~1~ above do not provide sufficient improvement in the low temperature discharge characteristics after storage yet.
The cell in paragraph (2) fails to solve the problem of metal corrosion to the full extent.
Thus the cells proposed heretofore do not provide sufficient improvement in the low temperature dlscharge characterlstics after~storage~

~SUMMARY OF THE INVENTION
A primary object of the present lnvention, : ~

' ~``` 1317631 therefore, is to provide a non-aqueous electrolyte cell having excellent low temperature discharge characteristics after a long storage period.
Another object of the invention is to provide a non-aqueous electrolyte cell having excellent hiqh rate discharge characteristics after a long storage period.
These objects are fulfilled, according to the present invention by a non-aqueous electrolyte cell having a positive electrode, a negative electrode and an electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfo-nate, wherein the organic solvent comprises an organic solvent mixture of at least two high boiling point solvents including at least one cyclic carbonates~
The above objects are fulfilled also by a non-aqueous electrolyte cell having a positive electrode, a negative electrode and an electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfonate, wherein the negative electrode comprises a Iithium~alloy.
: Furthér, the ob~ects of~the present invention are ful~:illed by a non-aque~us electrolyte cell having a po~sitive electrode, a negative electrode and an ~ 4 _ ::: : ::

.

electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfonate, wherein the electrolyte includes a reaction inhibitor added thereto for inhibiting reaction between the cell can and the electrolyte.
Still further, the objects of the invention are fulfilled by a non-aqueous electrolyte cell having a positive electrode, a negative electrode and an electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfonate, wherein the lithium trifluoromethanesulfonate is heated, dried and dehydrated in a vacuum at 80-150C.
The organic solvent mixture may comprise ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane.
Further, the organic solvent mixture may comprise ethylene carbonate, r-butyrolactone and 1,2-dimethoxyethane~
The organic solvent mixture may ~comprisepropylene carbonate, sulfolane and tetrahydrofuran.
he organic solvent may~ include at least two cyclic~carbonates.
~ The lithium al;loy may be selected from the group consisting of li~thium-alumlnum alloy, lithium-indium :: ~: : . : : ~

_ 5 : ~

.
' ~ ~

^~` 1317631 alloy,lithium-tin alloy, lithium-lead alloy, lithium-bismuth alloy, lithium-gallium alloy, lithium-strontium alloy, lithium-silicon alloy, lithium-zinc alloy, lithium-cadmium alloy, lithium-calcium alloy and lithium-barium alloy.
The reaction inhibi tor may be selected from the group consisting of lithium nitrate, triethyl phosphate, tri-n-butyl phosphate, NNN'N'-tetramethyl ethylenediamine, 1,2-diphenyl ethylenediamine, diethyldlthiocarbamin, triethyle phosphate, ammonium hypophosphite, and urea orthophosphite.
The foregoing objects of the present invention are fulfilled for the following reasons:
(1) Where the organic solvent comprises an organic solvent mixture of at least two high boiling point solvents including at least one cyclic carbonates, films of lithium carbonate are formed on surfaces of the negative electrode, and these films suppress reaction between the negative electrode and the electrolyte. Consequently, the negative electrode surfaces remain free from formatlon of passive films of~lithium fluoride, thereby suppressing an increase ~in the internal resistance of the electrode. As a ; ;result, the low temperature dlscharge characteristics after a long period of storage are improved.
The above organlc solvent m~ixture is also - 6 _ ~:
;:
.~., .,., .. ~, . .. .

effective to prevent lowering of the conductivity, whereby the cell has excellent high rate discharge characteristics after a long storage period.
Where the electrolyte includes two cyclic carbonates, a solvent of high conductivity and high viscosity and a solvent of low conductivity and low viscosity may be mixed in a suitable ratio to realize optimal conductivity and viscosity levels for high rate discharge~ This further improves the high rate discharge characteristics after storage.
(2) Where the negative electrode comprises a lithium alloy which is lower in activity than lithium used alone, reaction between fluorine ions from lithium trifluoromethanesulfonate and lithium in the lithium alloy is suppressed even when the cell is stored for a long period. Thus, there is little possibility of passive films being formed on the negative electrode surfaces, whereby low temperature discharge characteristics after a long storage period are improved.
~ ~3) Where the electrolyte includes a reaction ; ~inhibitor (specificall7, a~phosphorus compound or a ; nitrogen compound) added thereto for inhibiting reactlon between the cell can and the electrolyte, corrosion of the cell can is suppressed during storage even if lithium trifluoromethanesulfonate is used as , :

the solute. Thus, the cell is superior in not only initial but post-storage low temperature discharge characteristics.
Other objects, features and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig~ 1 is a sectional view of a non-aqueous electrolyte cell according to the present invention, Fig. 2 is a graph showing lnitial low temperature discharge characteristics of Cell A according to the invention, Comparative Cell V1 and Comparative Cell V2, Fig. 3 is a graph showing post-storage low temperature discharge characteristics of Cells A, V1 and V2, Fig, 4 is a graph showing initial high rate discharge characteristics of Cells A, V1 and V2, : Fig. 5 is a graph ~howing high rate discharge ~ characteristics after stora~e of Cells A~ V1 and V2, : Fig. 6 is a: gxaph showing :showing initial low : ;~ temperature dlscharge ~characte~ristics of Cell B
; according to the lnvention, Comparative Cell V1 and : Compaxative Cell V3, ~25 ~ : Fig. 7 is a graph showi:~g post-storage low ~: :
:::: ~ :
8 _ : ': ~ :
..

- ' ~ '' :

~ ~`` t317631 temperature discharge characteristics of Cells B, V1 and V3, Fig. 8 is a graph showing initial high rate discharge characteristics of Cells B, Y1 and V3, Fig. 9 is a graph showing post-storage high rate discharge characteristics of Cells ~, Vl and V3, Fig. 10 is a graph showing showing initial low temperatuxe discharge characteristics of Cell C
according to the invention, Comparative Cell W1 and Comparative Cell W2, Fig. 11 is a graph showing post-storage low temperature discharge characteristics of Cells C, W1 and W2, Fig, 12 is a graph showing initial high rate discharge characteristics of Cells C, W1 and W2, Fig. 13 is a graph showing post-storage high rate discharge characteristics of Cells C, W1 and W2, Fig. 14 is a graph showing initial high rate discharge characteristics of Cells A, D1 and D2 according to the invention and Comparative Cells V1, V2 and X1, FigO 15 is a graph showing post-storage high rate discharge characterlstics of:~Cells A, D1, D2, V1, V2 and X1, 25~ Figs. 16 through 18 are graphs showing relationship~ between mixing ratio and discharge :' : :
_ g _ , ~' "" 1317631 capacity in solvent mixtures of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane, Fig. 19 is a graph showing initial low temperature discharge characteristics of Cells E1-E3 according to the invention and Comparative Cell Y, Fig. 20 is a graph showing post-storage low temperature discharge characteristics of Cells E1-E3 and Y, Fig. 21 is a graph showing relationship between discharge capacity and the amount of aluminum added to lithium-aluminum alloy, Fig. 22 is a graph showing relationship between discharge capacity and t:he amount of indium added to indium-aluminum alloy, Fig. 23 is a graph showing initial low temperature discharge characteristics of Cells F1-F3 according to the invention and Comparative Cell Z, Fig. 24 is a graph showlng post-storage low temperature discharge characteristics of Cells F1-F3 and Z, Fig~ 25 lS a gxaph showing initial low temperature discharge characteristics of Cells F1 and G~according to the invention, Fig. 26 is a graph showing post-storage low temperature discharge characteristics of Cells F1 and G, .

.

Fig. 27 is a graph showing initial low temperature discharge characteristics of Cells G and H
according to the invention, Figl 28 is a graph showing post-storage low temperature discharge characteristics of Cells G and H, Fig. 29 is a graph showing initial low temperature discharqe characteristics of Cells I1 according to the invention and Comparative Cells U1-10 U~, Fig9 30 is a graph showing post-storage low temperature discharge characteristics of Cells I1 and U1-U3, ~ Fig. 31 is a graph showing relationship between drying temperature of lithium trifluoromethanesulfo-nate and discharge capacity of a cell using lithium trifluoromethanesulfonate, FigO 32 is a graph showing initiaI low temperature discharge characteristics of Cells I2 according to the invention and Comparative Cells U4 : :and US, and Plg. 33~is a graph~showing post-storage low temperature discharge~characteristics of Cells I1, U4 and~ V5. ::
:
: : :
:: : :
`~ ~ 25 DETAI1ED DESCRIPTION OF THE PREFERRED EMBODIMENTS

:~ :

. ':

r~
t317631 FIRST_EMBODIMENT
~Example) An embodiment of the present invention will be described with reference to a flat type non-aqueous electrolyte cell as shown in Fig. 1.
The cell comprises a negative electrode 2 formed of lithium metal and pressed upon an inside surface of a negative collector 7. The negative collector 7 is secured to a bottom inside surface of a negative can 5 formed of ferritic stainless steel (SUS 430) and having an approximately U-shaped section~ The negative can 5 is peripherally secured in an insulating packing 8 formed of polypropylene, while a positive can 4 formed of stainless steel and having an approximately U-shaped section oriented opposite to the negative can 5 is secured peripherally of the insulating packing 8. A positive collector 6 is secured to a bottom inside surface of the positive can 4, and a positive electrode 1 is secured to an inside surface of the positive collector S. A separator 3 ~ impregnated with an electrolyte is disposed between : the positive electrode 1 and the negative electrode 2~
: The~positive el~ectrode 1 employs manganese dloxide heat-treated:~in~a~temperature range of 350-430C to act as an active~material. This manganese di~oxide: was ~ixed with carbon powder acting as a ~: :

``` 1317631 conductive agent and fluororesin powder acting as a binding agent in the ratio by weight of 85:10:5. The mixture was molded under pressure, and then heat-treated at 250-350C, thereby resulting in the positive electrode 1. The negative electrode 2 was produced by punching a piece having a selected size out of a rolled plate of lithium.
The electrolyte comprises 1 moltlit. of lithium trifluoromethanesulfonate (LiCF3SO3~ dissolved in a solvent mixture of ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 2:2:6. This electrolyte contains no additive. The cell is 20mm in diameter and 2.5mm in thickness, and has a capacity of 130mA~.
The cell manufactured as above is hereinafter called Cell A.
~Comparative Example I) A cell was manufactured, for comparison purposes, in the same way as above excepting that the electrolyte here comprised a solvent including ethylene carbonate and 1,2-dimethoxyethane mixed in the~ratio of 4:6~ ~
: This cell is hereinafter called Cell V1.
~(Comparative Example~II) Another cell was manufactured in the same way as above excepting that the electrolyta here comprised a .

:

' ~'~ 1317631 solvent including butylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 4:6.
This cell is hereinafter called Cell V2.
Table 1 below shows particulars of the various components of Cells A, V1 and V2.
Table 1 . , _ . _ _ . _ _ Cell _ A _ V2 P. Electrode MnO2 MnO2 _ 2 _ N. Electrode Li Li Li . -- :-_ _- _ . -- _ El ectrolyte Solvent EC~BC+DME EC~DME BC+DME
._ _.. _ . _ Solute LiCF3so3 LiCF3so3 LicF3so3 Ad ditive None None None (~xperiment I) 15Initial and post-storage low temperature discharge characteristics of Cells A of the present invention and Comparative Cells V1 and V2 were checked, and the results are shown in Figs. 2 and 3 Fig~ 2 shows low temperature discharge characteristics observed when the cells were discharged at a temperature of -20C and with a load of 3KQ
mmediately aEter assembly. Fig. 3 shows low temperature discharge characteristics observed when : the cells:were discharged at the:temperature of -20C

:` :
~ ~ 25 :and with the load of 3KQ after storing the cells for :
:::

:' ', ~

~317631 three months at a temperature of 60C (which corresponds to storage for 4 and half years at room temperature) following their assembly.
As seen from FigsO 2 and 3, Cell A of the present invention is superior to Comparative Cells V1 and V2 in both initial and post-storage low temperature discharge characteristics.
~Experiment II) Initial and post-storage high rate discharge characteristics of Cells A, V1 and V2 were checked, and the results are shown ln Figs. 4 and 5. Fig. 4 shows high rate discharge characteristics observed when the cells were discharged at a temperature of 25C and with a load of 300Q immediately after assembly. Fig. S shows high rate discharge characteristics observed when the cells were discharged at the temperature of 25C and with the load of 300~ after storing the cells for three months at the temperature of 60C following their assembly.
As seen from Figs. 4 and 5, Cell A of the prese~t invention is superior to Comparative Cells V1 and V2 in both inltial and post-st~rage hlgh rate discharge characteristics.
SECOND EMBODIMENT
25 (~Example : : : : : :
~ A cell was manufactured in the same way as the :: ::
. : ~ : , - 1 5 _ : ~: :
.: :

example in the first embodiment excepting that the electrolyte used here comprised a solvent including ethylene carbonate, r-butyrolactone and 1,2-dimethoxyethane mixed in the ratio of 2:2:6.
The cell manufactured as above is hereinafter called Cell B.
(Comparative Example I) Comparative Cell V1 used in the first embodiment is also used here.
(Comparative Example II) A cell was manufactured in the same way as the example in the first embodiment excepting that the electrolyte here comprised a solvent including r-butyrolactone and 1,2-dimethoxyethane mixed in the ratio of 4:6.
This cell is hereinafter called Cell V3.
Table 2 below shows particulars of the various components of Cells B, V1 and V3.
Table 2 . . ._ ---_ Cell B V1 V3 . _ _ ._ .. . _ _ ~ P. Electrode MnO2 MnO2 MnO2 ~ ._ . _. _ N. Electrode Li Li Li : . = . . _ . --- --~ -- ~
: ~ El ctrolyte . ~
Solvellt EC+y-BL+D~E EC~DME y-BL~DME
SoIute LiCF3~iCP3503 LiC~3so3 - -- - - - - -~
Ad itive None None None : ~: : ~ : _ : ~ .

lExperiment I) Initial and post-storage low temperature discharge characteristics of Cells B of the present invention and Comparative Cells V1 and V3 were checked S in the same manner as in Experiment I for the first embodi~ent, and the results are shown in Figs. 6 and 7.
As seen from Figs. 6 and 7, Comparative Cell V1 is inferior in initial as well as post-storage characteristics, whereas comparative Cell V3 has superior initial characteristics but very poor post-storage characteristics. By contrast, Cell B of the present invention has proved superior in both initial and post-storage characteristics.
(Experiment II) Initial and post-storage high rate discharge characteristics of Cells B, V1 and V3 were ahecked in the same manner as in Experiment II for the first embodiment, and the results are shown in Figs. 8 and ; : 20 9.
: As seen from Figs. 8 and 9, Comparative Cell V1 : : is inferior in both inltial~ and post-storage characteristics~, whereas comparative Cell V3 has ~ superior initial characteristics:but very poor post-:~ 25 : sto~rage characteristics~ By~contrast, Cell B of the present invention has proved superior in both initial , ~
::
:: :

' : ' '^ ~^' ', " , ' ' ' , , .

I ~ 1 763 1 and post-storage characteristics.
THIRD EMBODIMENT
(Example) A cell was manufactured in the same way as the S example in the first embodiment excepting that the electrolyte used here comprised a solvent including propylene carbonate, sulfolane and tetrahydrofuran mixed in the ratio of 2:2:6.
The cell manufactured as above is hereinafter called Cell C, (Comparative Example I) A cell was manufactured in the same way as the example in the first embodiment excepting that the electrolyte here comprised a solvent including propylene carbonate and tetrahydrofuran mixed in the ratio of 4:6.
This cell is hereinafter called Cell W1.
~Comparative Example II) A cell was manufactured in the same way as the example in the ~irst embodiment excepting that the : : electrolyte here comprised a solvent including : :: sulfolane and tetrahydrofuran mixed in the ratio of : : ~ 4:6.:
~ This cell is hereinafter:called Cèll W2.
: ~ Z5~: Table 3 below shows particulars of the various ;: components of Cells C,~ W1 and W2.

1 ~ : ' ~ .

'" ' ~' ~ ' .
',, ' ' , 13~7631 Table 3 _ _ _ _ _ Cell C W1 W2 _ __ P. ElectrodeMnO2 MnO2 MnO2 _ _ _ N. ElectrodeLi Li Li ~ _ ~ ---Ele~ :trolyte Solvent PC+SL~THF PC+THF SL~THF
_ _ Solute LiCF3S03 LiCF3so3 LiCF3So3 Add Ltive None None None (Experiment I) Initial and post-storage low temperature dischaxge characteristics of Cells C of the present invention and Comparative Cells W1 and W2 were checked in the same manner as in Experiment I for the first embodiment, and the results are shown in Figs. 10 and 15 11.
As seen from Figs. 10 and 11, Comparative Cell W1 is inferior in initial and post-storage characteristics, whereas comparative Cell W2 has superior initial characteristics but very poor post-storage characteristics. By contrast, Cell C of thepresent invention has proved superior in both initial and post-storage characteristics.

~ :
Experiment II~ ~

Ini~tial and; post-storage high rate discharge characteristlcs of Cells C~ W1 and W2 were checked in ; - 1 9 ' :: ::

- . .

.: .- . . ~ : .
,:
.
.

13~ 7631 the saMe manner as in Experiment II for the first embodiment, and the results are shown in Figs. 12 and 13.
As seen from Figs. 12 and 13, Comparative Cell W1 is inferior in both initial and post-storage characteristics, whereas comparative Cell W2 has superior initial characteristics but very poor post-storage characteristics. By contrast, Cell C of the present invention has proved superior in both initial and post-storage characteristics.
FOURTH EMBODIMENT
Examples I and II) Cells were manufactured in the same way as the example in the first embodiment excepting that the electrolytes used here comprised a solvent including ethylene carbonate, propylane carbonate and 1,2-dimethoxyethane mixed in the ratio of 2:2:6, and a solvent including ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 2:2:6, respectively.
These cells manufactured as above are hereinafter ~ called Cells D1 and D2.
; ~ ~(Comparative Example~
A cell was manufactured in the same way as the example in the first embodiment excepting that the electro}yte here comprised a solvent including `~` t317631 propylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 4:6.
This cell is hereinafter called Cell X1.
(Experiment I) Initial and post-storage high rate discharge characteristics of Cells D1, D2 and A of the present invention and Comparative Cells X1, V1 and V2 were checked in the same manner as in Experiment II for the first embodiment, and the results are shown in Figs.
14 and 15.
As seen from Figs. 14 and 15~ Cells D1, D2 and A
are superior to Comparative Cells X1, V1 and V2 in both initial and post-storage high rate discharge characteristics. Further, Cells D1~ D2 and A of the 15 present invention are superior also to Cells B and C~
This is due to the fact that, in the case of electrolyte including two cyclic carbonates, the conductivity and viscosity of the electrolyte can be set to levels well suited for hiqh rate discharge characteristics.
: (Experiment II) : ~ The solvent mixtures of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane were ; ~ checked with respect to the relatibnship between the :25 ~mixing:ratio and discharge capacity, and the results :; are shown in Figs. 15~through 18. The cells were - 21 - :
:
: .
, .,.,. ~ , , .
, ~' ' `

`~
~317631 discharged at a temperature of 25C and ~"ith a resistance of 300~.
As seen from Figs. 16 through 18, it is desirable that the cyclic carbonates are mixed in the solvent in 5-30 vol %.
FIFTH EMBODIMENT
(Example I) A cell was manufactured in the same way as the example in the first embodiment excepting that the ~0 electroly,te used here comprised a~solvent including propylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 4:6, and that the negative electrode 2 comprised lithium-aluminum alloy.
The negative electrode 2 was prepared by punchinq a piece having a selected size out of lithium-aluminum alloy including 2% by weight of aluminum.
The cell manufactured as above is hereinafter called Cell E1.
(Example II) A cell was manufactured in the same way as Example I above exceptlng that the negative electrode 2 comprised lithium-i~ndium alloy including 2~ by weight of indium.
This cell is hereinafter called Cell E2.
:
; 25 (Example III~ ~
A cell was manufactured in the same way as - 22 - ~

Example I above excepting that the negative electrode 2 comprised lithium-tin alloy including 2% by weight of tin.
This cell is hereina~ter called Cell E3.
(Comparative Example) A cell was manufactured, for comparative purposes, in the same way as Example I above excepting that the negative electrode 2 comprised lithium a~one.
This cell is hereinafter called Cell Y.
Table 4 below shows particulars of the various : components of Cells E1-E3 and Y.
Table 4 ¦ Cell _ . _ ,,, E2 L E3 .
l P. Electrode MnO2 MnO2 MnO2 MnO2 N. Electrode Li-Al Li-In Li-Sn Li I
Electrolyte . . _ ¦ Solvent PC+DME PC+DME PC~DME PC+DME
¦ Solute LiCF3503 LiCF3S03 LiCF3so3 LicF3so3 Additive - None I None None None (Experiment I~
Initial and post-stora~e~ low temperature : dlscharge characteristlcs o:f Cells E1-E3 of the present inventlon and~Comparative Cell Y were checked n the same manner,as in Experiment I for the first ~émbodiment, and the results are shown in Figs. 19 and :: ' `

" .

20.
As seen from Figs. 19 and 20, Cells E1-E3 and Y
are similax in initial low temperature discharge characteristics~ but Cells E1-E3 are superior to Cell Y in post-storage low temperature discharqe characteristicsf Cell E1 being the best of all.
(Experiment II) The internal resistance of these cells were measured before and after storage at high temperature.
The results are shown in Table 5 below.
Table 5 . .._ ._ .. .
Internal Resistance _ Before Storage After Storage Cell E1 10-12 Q 13-16 Q

Cell E2 10-12 ~ 14-16Q

Cell E3 10-12 ~ 14-1S Q

Cell Y 10-12Q 25-35 ~
. .. ~ . _ It will be seen from Table 5 that the inte nal ~ resistance of Cells E1-E3 increased only slightly in contrast with that of Cell Y which shows a substantial increase after storage.
(Experiment III~
The rela~ionship between~the;amount of aluminum in~the lithium-a1uminum alloy and~the cmll capacity 25 ~was checked immediately~after assembly of the cells and~after storiny ~the cells~at~60C for three months, .

` - 24 -:
::

- : . ' and the results are shown in Fig. 21. The cells were discharged at a temperature of -20C and with a load of 3K ~ .
As seen from Fig. 21, the cells have a discharge capacity exceeding 100mAH after storage where aluminum is added in 0.01-20% by weight. It is thus desirable that aluminum is added in 0.01-20% by weight.
This means that aluminum produces little effect if added in less than 0.01% by weight, and lowers the cell capacity if added in an amount exceeding 20% by weight.
The relationship between the amount of indium in the lithium-indium alloy and the cell capacity was checked under the same conditions, and the results are shown in Fig. 22.
It will be seen that, here again, indium should preferably be added in 0.01-20% by weight.
In the fifth embodiment, the negative electrode comprises lithium-aluminum alloy, lithium-indium alloy or lithium-tin alloy. The material used for the .
negative electrode is not limited to these alloys.
Sim1lar effects may be~ pr~oduced where~the negative electrode comprises lithiu~m-lead alloy, lithium-blsmuth alloy, lith~ium~-galllum alloy, lithium-25 ~ strontium alloy, lithium-silicon alloy, lithium-zinc alloy, lithlum-cadmium alloy, lithium-calcium alloy or .

, lithium-barium alloy.
SIXTH EMBODIMENT
(Example I) A cell was manufactured in the same way as the example in the first embodiment excepting that the electrolyte used here comprised a solvent including propylene carbonate and 1,2-dimethoxyethane mixed in the ratio of 4:6, with lithium nitrate ~LiN03) dissolved in the electrolyte in 1g/lit.
The cell manufactured as above is hereinafter called Cell F1.
~Example II) A cell was manufactured in the same way as Example I above excepting that triethyl phosphate was added in 0.1g/lit. to the electrolyte.
This cell is hereinafter called Cell F2.
(Example III) A cell was manufactured in the same way as Example I above excepting that tri-n-butyl phosphate was added in 001g/lit. to the electrolyte.
This cell is hereinafter called Cell F3.
tComParatlve Example) ~ -A cell was manufactured in the same way as Example I above excepting that no additive is included in the electrolyte.
This cell is hereinafter ca}led Cell Z, : : : ~
~ 26 - ~

:

~ . .
.

1 3 1 763 ~

Table 6 below shows particulars of the various components of Cells F1-F3 and Z.

Table 6 _ _ _ ._ Cell F1 F2 F3 ~ Z
-- _ . . .. _ _ 5 P. Electrode MnO2 MnO2 MnO2 MnO2 . __ . _ . . . . _ . _ N. Electrode Li Li Li Li _ . _ ~ . _ _-El ~ctrolyte . , .

Solvent PC+DME PC+DME PC~DME PC+DME
_ . _ Solute LiCF3so3 LiCF3so3 LiCF3so3 \ LicF3so3 10 ~d ~itive LiNO3 triethyl tri-n-butyi\ None ~ . phosphate I phosphate (Experiment I) Initial and post-storage low temperature discharge characteristics of Cells F1-F3 of the present invention and Comparative Cell Z were checked in the same manner as in Experiment I for the first embodiment, and the results are shown in Figs. 23 and 24.
As seen from Figs. 23 and 24, Cells F1-F3 and Z
are similar in initial low~ temperature discharge characteristics, but Cells F1-F3 are superior to Cell : :
Z in pos~t-storage low temperature discharge :
: : characteristlcs, Cell F1 belng the best of all~

(Experiment II) ~ ~ The internal impedance of these cells were measured with 1RHz frequency after storage at high ~ :
: - 27 -:: :

. .,, .,, ~ .

temperature. The results are sho~Jn in Table 7 below.

Table 7 . _ . ..
Internal Resistance _ .
Before Storage After Storage __ _ _ . _ ... _ __ 5 Cell F1 10-12 ~ 13-15Q

Cell F2 10-12 ~ 14-15 ~

Cell F3 10-12 Q 14-15 Q

Cell Z 10-12 Q 25-35 Q
. _ It will be seen from Table 7 that the internal lmpedance of Cells F1-F3 increased only slightly in contrast with that of Cell Z which showed a substantial increase after storaqe.
The cells were disassembled after the storage.
It was found that Cell Z had the lithium surface of the negative electrode discolored black but Cells F1-F3 showed no such phenomenon~
Further, the cell cans were observed through a metallurgical microscope after the storage. Cell Z
showed considerable pitting~corrosion of the can but ; 20 Cells F1-F3 were free from corrosion.
These results point to the fact that, in the case of Comparatlve Cell Z, re-~depositlon took place as a , result of the corrosi~on~of the c811 can during the storage, thereby loweri~ng t~he~ post-storage low 25~ temperature dlscharge characterlstics. In the case of 28 ~

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~ : :'' , Cells F1-F3 of the present invention having the electrolyte added with lithium nitrate, triethyl phosphate or tri-n-butyl phosphate, it is believed that the corrosion of the can is suppressed thereby to prevent lowering of the post-storage low temperature discharge characteristics.
SEVENTH EMBODIMENT
A cell was manufactured in the same way as Example I in the sixth embodiment excepting that the negative electrode comprised lithium-aluminum alloy tAl: 2~ by weight).
This cell is hereinafter called Cell G.
5Experiment I) Initial and post-storage low temperature discharge characteristics of Cells G and F1 of the present invention were checked in the same manner as in Experiment I for the first embodiment, and the results are shown in Figs. 25 and 26.
As seen from Figs. 25 and 26, both cells are similar in initial low temperature discharge characteristics, but Cell G has proved an improvement ~upon Cell F1 in post-storage~characteristics.
EIGHTB EMBODIMENT ~
A cell was manuf~actured~in the same way as ~Example I in the~sixth embodiment excepting that the ; negative Plectrode 2 comprised lithium-aluminum alloy - 29 - ~

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13~7631 ~Al: 2~ by weight), and the electrolyte comprised an organic solvent mixture of ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane.
The cell manufactured as above is hereinafter called Cell H.
(Experiment3 Initial and post-storage low temperature discharge characteristics of Cells H and G of the present invention were checked in the same manner as in Experiment I for the first embodiment, and the results are shown in Figs. 27 and 28.
As seen from Figs. 27 and 28, Cell H is an improvement upon Cell G in both initial and post-storage low temperature discharge characteristics.
15In the sixth to eighth embodiments, lithium nitrate, triethyl phosphate and tri-n-butyl phosphate are used as additives. The additives are not limited to these substances, but simllar effects are produced by using other nitrogen compounds (NNN'N'-tetramethyl ~ ethylenediamine, 1,2-diphenyl ethylenediamine, di-ethyldithiocarbamin~, and other phosphoric compounds ~ (triet~yle phosphate, ammonlum hypophosphite, urea ; ~ ~ orthophosphite).
~ Ninth Embodiment ; ~ 25 ~ ~ A cell was manufactured in t~he same way as the example in the first embodiment excepting that the :

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electrolyte comprised a solute consisting of lithium trifluoromethanesulfonate (LiCF3SO3) heated, dried and dehydrated at 120C in a vacuum (not exceeding 5mmHg) for 12 hours, and a solvent mixture of propylene carbonate and 1,2-dimethoxyethane. Lithium trifluoro-methanesulfonate was dissolved in 1 mole/lit. in the solvent mixture.
This cell is hereinafter called Cell I1.
(Comparative Examples I-III) Three cells were manufactured, for comparison purposes, in the same way as Example I in the seventh embodiment excepting that the electrolyte comprised solutes consisting of lithium trifluoromethanesulfo-nate dried at 25C in a vacuum for 12 hours, lithium trifluoromethanesulfonate dried at 50C in a vacuum for 12 hours, and lithium trifluoromethanesulfonate dried at 200C in a vacuum for 12 hours, respectively.
These cells are hereinafter called Cells U1, U2 and U3.
~(Experiment I) Initial and post-storage low temperature ; ~ dlscharge characteristics of Cells I1 of~the present invent1on and~Comparatlve~Cells~U1-U3 were checked in ;the~same manner~as~ln~Experlment I for the first 2~5~ ~embod~ment; and~the results are~shown in Figs. 29 and 30. ~

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, t31~631 As seen from Fig. 29, Cell U3 has poor initial low temperature discharge characteristics. This is considered due to thermal decomposition of lithium trifluoromethanesulfonate occurring when dried at 200C.
Further, as seen from Fig. 30, not only Cell U3 but Cells U1 and U2 have poor post-storagP low temperature discharge characteristics. This is considered due to insufficient removal of moisture during the drying treatment of lithium trifluoro-methanesulfonate, and a reaction occurring during the storage between the water and the lithium of the negative electrode.
By contrast, Cell I1 of the present invention shows excellent initial and post-storage low temperature discharge characteristics.
(Experiment II) The relationship between the lithium trifluoro-methanesulfonate drying temperatures in a vacuum 5all ~for 12 hours) and the discharge capacity of the cells :
after storing the cells at~60C for three months was checked by discharging the eells at -20C with a resistance of 3K~. The resu1ts are~shown in Fig. 31.
As seen from~Fig~31,~excell~nt post-storage low 25~ temperature discharge characterlstics are obtained where lithium trifluoromethanesulfonate is dried at , . ' ' ,; , 80-150C.
This is believed due to the fact that, where lithium trifluoromethanesulfonate heated and dried at 80-150C is used in cells, lithium trifluoromethane-sulfonate does not become decomposed and its moistureis removed sufficiently.
(Example II) A cell was manufactured in the same way as Example I above excepting that the non-aqueous electrolyte comprised a solvent mixture of ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane, with lithium nitrate added in 1q/lit. to the electrolyte. Lithium trifluoromethanesulfonate was dissolved in 1 mole/lit. in the solvent mixture.
This cell is hereinafter called Cell I2.
(Comparative Examples IV and V) Cells were manufactured, for comparison purposed, in the same way as Example II above excepting that the non-aqueous electrolyte comprised solutes consisting of lithium trifluoromethanesulfonate dried at room temperature in a vacuum for~12 hours, and lithium trifluoromethanesulfonate dried at 200C in a vacuum for 12 hours, respectively.
These cells are hereinafter called Cells U4 and U5.
(Exp riment III) 1~17631 Initial and post-storage low temperature discharge characteristics of Cells I2 of the present invention and Comparative Cells U4 and U5 were checked in the same manner as in Experiment I for the first embodiment, and the results are shown in Figs. 32 and 33.
As seen from Figs. 32 and 33, Cell U5 has poor initial and post-storage low temperature discharge characteristics, while Cell U4 has poor post-storage low temperature discharge characteristics.
By contrast, Cell I2 of the present invention shows excellent initial and post-storage low temperature discharge characteristics.
Further, Cell I2 shows slightly better post-storage low temperature discharge characteristics than Cell I1. This is due to the fact that the two cyclic carbonates included in the soIvent of the electrolyte suppress formation of passive films on the negative electrode surface, and Iithium nitrate included in the electrolyte suppresses corrosion of the cell cans In the first to ninth embodiments descr;bed a~bove, the positive electrode~ comprises manganese dioxide.~ However, this is~not llmitative, and similar effects may be produced~ by~ positive electrodes comprising other oxides (modiied MnO2~ densified MnO~, MnO2 containlng~lithium, MoO3, CuO, CrOx, V2O

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etcO), sulfides (FeS, TiS2, MoS2, etc.) and halides ((CF)n, etc.).

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A non-aqueous electrolyte cell having a positive electrode, a negative electrode and an electrolyte contained in a cell can, the electrolyte including a solute and an organic solvent, the solute comprising lithium trifluoromethanesulfonate, wherein said lithium trifluoromethanesulfonate is heated, dried and dehydrated in a vacuum at 80-150°C.

2. A cell as claimed in claim 1, wherein said organic solvent comprises a mixture of at least two high boiling point solvents including at least one cyclic carbonate.

3. A cell as claimed in claim 2, wherein said organic solvent mixture comprises two cyclic carbonates.

4. A cell as claimed in claim 2, wherein said organic solvent mixture comprises ethylene carbonate, butylene carbonate and 1,2-dimethoxyethane.