Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-01-27
2003-02-11
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S221000, C429S223000, C429S224000
Reexamination Certificate
active
06517974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium secondary battery and a method of manufacturing the lithium secondary battery, and more particularly to a lithium secondary battery which prevents the increases in electrode impedance resulting from expansion and contraction of electrode active material due to repeated charging and discharging, and to a method of manufacturing this lithium secondary battery. The present invention also relates to a high energy-density lithium secondary battery having increased sites in which lithium ion can be intercalated and de-intercalated, the increased sites increasing the capacity of positive electrode and negative electrode.
2. Related Background Art
Recently, it has been said that increasing CO
2
gas contained in air exhibits green house effect to cause global warming. Thermal power plants use fossil fuel to convert thermal energy into electric energy. Accordingly, a large amount of CO
2
gas is exhausted, being a barrier in building additional thermal power plants. Therefore, so-called load leveling has been proposed for effective use of electric power generated in the thermal power plants. That is, electric power generated in the night is stored in storage batteries at consumer's homes and the stored electric power is used in the daytime during when electric power consumption increases, thereby leveling load distribution.
For electric vehicles having a feature where substances containing CO
x
, NO
x
, and CH that contaminate air are not exhausted, the development of a high energy-density secondary battery has been demanded. In addition, the development of small size, lighter weight, high performance secondary batteries is urgently demanded which find applications in portable equipment such as book size personal computers, word processors, video cameras, and mobile telephones.
After JOURNAL OF THE ELECTROCHEMICAL SOCIETY 117, 222 (1970) has reported an application of graphite intercalation compound for a negative electrode of a lighter weight, smaller size secondary battery, a rocking chair type secondary battery referred to as a lithium ion battery has been developed and some have been put in practical use. This type of secondary battery uses a carbon material for a negative active material, and an intercalation compound containing lithium ion for positive active material. With this lithium ion battery, the negative electrode is formed of a host material in the form of a carbon material that allows lithium ions as a guest material to be intercalated. The use of such a material suppresses dendrite growth of lithium during the charging of the battery, thereby allowing more number of charging/discharging cycles in the useable life of the battery.
Since the aforementioned lithium ion battery achieves a long-life secondary battery, proposal and research are carried out vigorously in an attempt to apply various carbon materials to the negative electrode. Japanese Patent Application Laid-Open No. 62-122066 proposes a secondary battery using a carbon material where an atomic ratio hydrogen/carbon is less than 0.15, the distance between (002) planes is 0.337 nm or longer, and the crystallite size in c-axis is 15 nm or less. Japanese Patent Application Laid-Open No. 63-217295 proposes a secondary battery using a carbon material where the distance between (002) planes is 0.370 nm or longer, true density is less than 1.70 g/ml, and a peak value of heat generated is 700° C. or higher when subjected to differential thermal analysis in flowing air. There are some research reports on the application of various carbon materials to negative electrode. Carbon fibers are reported in Electrochemical Society Vol. 57, p.614 (1989). Natural graphite is reported in the Proceedings of the 33rd Battery Symposium, Mesofuse microsphere and graphite whisker are reported in the Proceedings of the 34th Battery Symposium, p.77 (1993) and p.77, respectively. Burned furfuryl alcohol resin is reported in the Proceedings of the 58th Conference of the Electrochemical Society of Japan p.158 (1991).
However, with a lithium ion battery which uses a carbon material containing lithium as a negative electrode active material therein, there has been developed no battery whose discharge capacity exceeds the theoretical value of the graphite intercalation compound, the discharge capacity being such that a stable electric power can be drawn from the battery when the battery is used through repeated charging and discharging. That is, the theoretical value is such that a carbon intercalation compound can store one lithium atom for every six carbon atoms. Thus, a lithium ion battery using a carbon material as a negative active material has a long cycle-life but not as large an energy density as a lithium battery that directly uses metal lithium as a negative active material. If the negative electrode of a lithium ion battery formed of a carbon material is to be intercalated with lithium of an amount larger than the theoretical capacity during charging cycle, lithium metal grows in a dendrite pattern on the surface of the negative electrode formed of a carbon material, ultimately causing an internal shorting out between the negative electrode and positive electrode due to repeated charging and discharging cycles. A lithium ion battery with the theoretical capacity of a graphite negative electrode has not a long enough cycle life for practical use.
On the other hand, a high capacity lithium secondary battery that uses metal lithium for negative electrode has been demanded but not put in practical use yet. Because the charging/discharging cycle life is very short. This short cycle life is considered to be primarily due to the fact that metal lithium reacts with impurities such as moisture contained in the electrolyte to form an insulating film on the electrodes and therefore repeated charging and discharging causes lithium to grow in a dendrite pattern, resulting in an internal shorting out between the negative and positive. This leads to the end of the battery life.
If a dendrite pattern of lithium grows to short-circuit negative electrode and positive electrode, the energy stored in the battery is consumed in a short time so that heat is generated and the solvents of the electrolyte are decomposed to generate gas to increase internal pressure, thereby damaging the battery.
In order to alleviate the problem of metal lithium negative electrode that a metal lithium reacts with the moisture and organic solvents contained in the electrolyte, use of a lithium alloy containing lithium and aluminum also has been proposed. However, use of a lithium alloy is not currently in practical use due to the following problems. A lithium alloy is too hard to be wound in a spiral form, and therefore a spiral cylindrical battery cannot be made. The charging/discharging cycle life is not prolonged as much as one expects. A battery using a lithium alloy for negative electrode does not provide as much energy density as a battery using metal lithium.
Japanese Patent Application Laid-Open Nos. 5-190171, 5-47381, 63-114057, and 63-13264 have proposed the use of various forms of lithium for negative electrode. Japanese Patent Application Laid-Open No. 5-234585 proposes the application of metal power on the surface of lithium, the metal powder preventing lithium from producing various kinds of intermetallic compounds. None of the proposals in the aforementioned publications can be a decisive answer that prominently prolongs the life of the negative electrode.
JOURNAL OF APPLIED ELECTROCHEMISTRY 22 (1992) 620 to 627 reports a high energy density lithium secondary battery using an aluminum foil for negative electrode, the lithium secondary battery having an energy density lower than a lithium primary battery. When this lithium secondary battery is subjected to as many charging/discharging cycles as practical, the aluminum foil experiences expansion and contraction repeatedly till the aluminum foil is finally cracked, leading to reduced current collection and dendr
Kawakami Soichiro
Kobayashi Naoya
Yamamoto Tomoya
Cooke Colleen P.
Dunn Tom
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