Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1985-12-05
1987-05-26
Walton, Donald L.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429218, 423595, H01M 448, H01M 1040
Patent
active
046685944
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a rechargeable electrochemical apparatus using non-aqueous electrolyte, more particularly, a secondary battery using non-aqueous electrolyte, and a positive electrode of said battery.
BACKGROUND OF THE INVENTION
Hitherto, active developments have been made on non-aqueous electrolytic secondary batteries using an alkali metal, for example lithium, sodium and the like, as a negative electrode, in which a positive active material is an interlayer compound, such as titanium disulfide, and an electrolyte is an organic one made by dissolving lithium perchlorate in an organic solvent such as propylene carbonate. The special features of these secondary batteries are high cell voltage and high energy density caused by using the alkali metal as the negative electrode.
However, the secondary batteries of this sort show short life of frequency (cycles) of charging and discharging when metallic lithium is used as the negative electrode. The charge and discharge efficiency also become low in making charge and discharge. It is believed that these defects are mostly brought about from a decline of the negative electrode. In other words, the lithium negative electrode is mainly prepared by attaching a lithium plate to a screen type current collecting substrate under pressure, and the electrode dissolves in the electrolyte as the lithium ion during discharging. However, it is difficult to change the dissolved lithium ion in the original lithium plate form as it was. The dissolved lithium ion may be actually deposited in a dendrite lithium form which easily breaks at the root and drops away, and it may also be deposited in a small spherical lithium which goes away from the current collecting substrate, which makes the battery impossible to charge and discharge. It may frequently happen that the dendrite lithium grows through a separator for dividing the positive and negative electrodes and connects with the positive electrode to result in short circuit which nullifies the function of the battery.
There have been proposed many improvements to overcome the above problems. Recently, the issue of charge and discharge efficiency of the negative electrode has considerably been improved due to the appearance of excellent lithium occluded alloys. It, in turn, has become more important to develop the materials having the excellent performance as positive active material rather than the negative electrode. As the positive electrode materials, a number of active materials have so far been proposed, among which for example titanium disulfide (TiS.sub.2), niobium selenide (NbSe.sub.2), vanadium oxides, such as V.sub.2 O.sub.5, V.sub.6 O.sub.13 and the like, tungsten oxide (WO.sub.3), molybdenum oxide (MoO.sub.3), chromium oxide (Cr.sub.3 O.sub.8), copper vanadate (Cu.sub.2 V.sub.2 O.sub.7), etc have been studied as positive active materials having high possibility. Generally, the performances required for the positive active materials to be used for the lithium secondary battery are the so-called high energy density with large electric capacity for discharge and high discharge voltage, voltage flatness thereof and cycle life. However, the above possible positive active materials do not entirely satisfy the above requirements. For example, TiS.sub.2 and NbSe.sub.2 show low discharge voltage, V.sub.2 O.sub.5 shows stepwise variation of voltage is discharge which exhibits no flatness, WO.sub.3 has small electric capacity, MoO.sub.3 shows low discharge voltage, Cr.sub.3 O.sub.8 provides a high voltage but has problems in its cycle life, and Cu.sub.2 V.sub.2 O.sub.7 involves a problem in cycle life. J. Electrochemical. Soc. vol. 128 No. 12 to K. M. Abraham, J. L. Goldman, and M. D. Dempsey 2493-2501 (1981) reports the result of studying oxides of Cr or V as a positive active material. The report by Abraham et al relates to V.sub.6 O.sub.13. V.sub.6 O.sub.13 is usually prepared by mixing V.sub.2 O.sub.5 and metallic vanadium and heating at 650.degree. C. The report by Abraham et al al
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Matsui Tooru
Nankai Shiro
Toyoguchi Yoshinori
Yamaura Junichi
Matsushita Electric - Industrial Co., Ltd.
Walton Donald L.
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