Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-04-11
2003-05-27
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S317000, C558S265000, C558S276000
Reexamination Certificate
active
06569572
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a lithium battery utilizing a gel electrolyte, and further to a polyelectrolyte, an electrolyte material, a di(metha)-acrylic ester and a di(metha)-acrylate polymer.
With a recent tendency to design a portable electric device into a compact form, a demand for a lithium battery providing a high energy density has been increasing. It is expected to apply this lithium battery to a large-size battery such as for use in an electric vehicle etc. In studies and developments of the battery, it is indispensable to establish various technologies for increasing a high energy density and battery capacity, and improving a stability.
Incidentally, a battery utilizing the polymeric solid electrolyte provides high reliability and safety owing to its non-leakage property of electrolyte as compared with conventional battery utilizing a liquid electrolyte. In addition, this battery enables thinning of film, simplification of package and decrease in weight. For this reason, a large expectation is placed on the polymeric solid electrolyte. As for the polymeric solid electrolyte, those described in the Published Patent Application (KOKAI) No. 5-25353 and the Published Patent Application (KOKAI) No. 6-223842 are well known. However, the polymeric solid electrolyte is generally composed of a composite of polymeric compound and alkali metal salt, and its ion conduction mechanism is one which utilizes a molecular motion of the polymeric compound. For this reason, the polymeric solid electrolyte has, in general, a small ion conductivity as compared with the liquid electrolyte. The battery using the polymeric solid electrolyte has included such a problem that its charge/discharge current density has been limited as compared with the battery using the liquid electrolyte.
Accordingly, it is desired to develop a polymeric solid electrolyte having a high ion conductivity.
Under such circumstances, as described in the Published Patent Application (KOKAI) No. 63-94563, a polyelectrolyte having a comparatively high ion conductivity can be obtained in such a way that a crosslink polyalkylene oxide is used for the polymeric compound and an organic solvent is contained in the composite of the polymeric compound and the alkali metal salt. Such a polyelectrolyte containing the organic solvent is called as a gel electrolyte and its application to a lithium battery is actively examined at present. On the other hand, gel electrolytes are also examined which utilize polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF) or similar compound of them as the polymeric compound, in place of the crosslink polyalkylene oxide. However, the gel electrolyte using the PAN can not maintain its state of film at high temperature because the polymeric compound is apt to become fluidic with an increase in its temperature, so that it is inferior in its form stability at high temperature. The gel electrolyte using the PVdF is inferior in its liquid electrolyte holding ability because the PVdF presents its slight solubility against the liquid electrolyte. On the contrary, the gel electrolyte using the crosslink polyalkylene oxide as the polymeric compound has a high liquid electrolyte holding ability because the polymeric compound presents its compatibility with the liquid electrolyte, and its form can be maintained over a wide range of temperature because the polymeric compound has a crosslink structure. Namely, the gel electrolyte using the crosslink polyalkylene oxide, when used for the lithium battery, can improve a reliability and safety of battery because the gel electrolyte is superior in the liquid electrolyte holding ability and the form stability.
However, the lithium battery equipped with the gel electrolyte using the crosslink polyalkylene oxide is not superior in its low-temperature property and high-rate property during charging and discharging, and its battery performance is inferior to those of the lithium battery equipped with the gel electrolyte using the PAN and the PVdF. A cause of this problem may be supposed as follows.
In the gel electrolyte, lithium ion preferentially coordinates with the crosslink polyalkylene oxide forming the polymeric compound as compared with an organic solvent such as a generally used cyclic ester carbonate. This is suggested by a fact that an ether-group solvent having a structure similar to the crosslink polyalkylene oxide has a large possibility to preferentially coordinate with the lithium ion because of a large donor number, as compared with the cyclic ester carbonate etc. Then, since the polymeric compound has an extremely low moving ability as compared with the organic solvent, a moving ability of lithium ion in the gel electrolyte is decreased, when the lithium ion preferentially coordinates with the crosslink polyalkylene oxide forming the polymeric compound rather than the organic solvent.
On the contrary, it can be considered that, in the gel electrolyte using the PAN or PVdF as the polymeric compound, the lithium ion is not restricted by the polymeric compound and the decrease in the moving ability of lithium ion is controlled because a lithium salt is slightly soluble or not soluble to the polymeric compound. As described above, however, the gel electrolyte using the PAN includes such a problem that it is inferior in the form stability at high temperature and the gel electrolyte using the PVdF includes such a problem that it is inferior in the liquid electrolyte holding ability.
SUMMARY OF THE INVENTION
A first object of this application is to provide a lithium battery which is able to improve its reliability and safety, and further to improve its low-temperature property and high-rate property during charging and discharging.
A second object of this application is to provide a polyelectrolyte which is superior in its ion conductivity and also in its electrochemical stability.
A third object of this application is to provide an electrolyte material which is able to compose the polyelectrolyte of the above second object.
A fourth object of this application is to provide a di(metha)-acrylic ester and a di(metha)-acrylate polymer forming an useful novel compound.
In order to accomplish the first object, a first invention of this application is characterized by that, in a lithium battery equipped with a positive electrode, a negative electrode and a gel electrolyte, the gel electrolyte is composed of at least an ester-group or ether-group aprotic polar solvent, a lithium salt and a polymeric compound; and this polymeric compound comprises a polymer of at least one compound among those expressed by an equation (I) and an equation (II).
(k: zero or number of 1 or more, m: number of 1 or more, R
1
:C
p
H
2p
, R
2
:C
q
H
2q
, p≠q, p & q: integer of 1 or more, A: CH
2
═CH—CO— or CH
2
═C(CH
3
)—CO—, X: n-valent combination group (n: integer ranging from 1 to 4), r: zero or number of 1 or more, s: number of 1 or more, R
3
: C
t
H
2t
, R
4
: C
u
H
2u
, t≠u, t & u: integer of 1 or more)
According to the lithium battery of this invention, the low-temperature property and high-rate property during charging and discharging can be improved because the gel electrolyte can exert a high lithium ion mobility. A reason of this fact may be considered as follows. The polymer of compound expressed by the equation (I) and the polymer of compound expressed by the equation (II) have structural characteristics inferior in their lithium ion coordination property as compared with the crosslink polyaklylene oxide. These structural characteristics are caused by the number of carbon atom sandwiched by two oxygen atoms. Therefore, in the gel electrolyte of this invention, the lithium ion coordinates to about the same extent with the polymeric compound and the ester-group or ether-group aprotic polar solvent. Consequently, in the gel electrolyte of this invention, a percentage of the lithium ion restricted by the polymeric compound is reduced as compared with a case of the gel electrolyte using the crosslink polyalkylene oxide. Therefore, the
Ishitoku Takeshi
Izuchi Syuichi
Nogi Hidenobu
Ochiai Seijiro
Shindo Masaharu
Crowell & Moring LLP
Kalafut Stephen
Yuasa Corporation
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