Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1999-09-01
2003-02-18
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S163000, C429S179000, C429S175000, C429S180000, C429S185000, C429S231950
Reexamination Certificate
active
06521374
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to lithium secondary cells, i.e., to improvements in lithium secondary cells wherein the negative electrode is made chiefly from metallic lithium, lithium alloy and/or a carbon material or oxide material capable of absorbing and desorbing lithium, and the positive electrode is prepared mainly from a positive electrode material typical of which is a metallic oxide. More particularly the invention relates to improvements in the positive electrode terminal and the negative electrode terminal for delivering current from an electrode unit serving as the electricity generating element to an external circuit.
BACKGROUND OF THE INVENTION
The negative electrode materials heretofore proposed for use in lithium secondary cells include graphite, coke and like carbon materials, metallic lithium, lithium alloys and tin oxides. Among these, carbon materials are already in use for negative electrodes to provide lithium secondary cells. Graphite is one of the materials which are generally used for negative electrodes because graphite exhibits a discharge potential in close proximity to the potential of metallic lithium to afford lithium secondary cells of high energy density.
For example, JP-A No. 92335/1997 discloses one of lithium secondary cells wherein such materials are used for the negative electrode. The proposed cell has a negative electrode prepared from a carbon material and a negative electrode output terminal made from pure copper. Pure copper remains stable at the negative electrode potential during the charging and discharging of the lithium secondary cell and is therefore used for the negative electrode output terminal. Besides pure copper, titanium, nickel, stainless steel, etc. appear useful as potentially stable materials, whereas pure copper is thought suitable in view of ease of working.
However, pure copper is susceptible to oxidation and liable to form an oxide film at the portion of the cell exposed to the atmosphere, so that when used for the negative electrode terminal, pure copper has the problem of giving increased contact resistance at the connection to an external circuit, causing faulty contact to result in a discharge voltage drop.
On the other hand, pure aluminum is used for the positive electrode terminal of such a lithium secondary cell (see, for example, JP-A No. 92335/1997) since pure aluminum is also stable at the positive electrode potential during the charging and discharging of the cell. Although titanium, stainless steel, etc. appear useful as potentially stable materials besides pure aluminum, pure aluminum is considered to be suitable from the viewpoint of easy of working, conductivity and material cost.
Pure aluminum is nevertheless prone to form an oxide film, so that when used for the positive electrode terminal, this metal has the problem of offering greater contact resistance at the connection to an external circuit, giving rise to faulty contact or causing a discharge voltage drop as in the case of the negative electrode terminal.
Moreover, the positive or negative electrode terminal is not always satisfactory in mechanical strength and is not always suitable to tighten up with sufficiently great torque when a lead is to be attached thereto for connection to an external power source. This entails the problem that the terminal mount portion will not be sealed off effectively.
SUMMARY OF THE INVENTION
An object of the present invention, which is to overcome these problems, is to propose improved positive electrode terminal and negative electrode terminal, and an improved electrode terminal for a positive or negative electrode, for use in delivering the electric energy produced by an electricity generating element to an external device, and to further provide a lithium secondary cell having the positive electrode terminal and/or the negative electrode terminal.
Another object of the invention is to use the positive electrode terminal and/or the negative electrode terminal to assure the terminal or terminals of an enhanced mechanical strength in fabricating the cell and thereby improve the reliability of electrical connection of the cell to an external circuit and give an improved sealing effect to the terminal mount portion or portions. The formation of oxide film on the surfaces of the positive and negative electrode terminals is inhibited, enabling the terminals to retain high conductivity to suppress the discharge voltage drop of the cell.
To fulfill the above objects, the present invention provides a lithium secondary cell which comprises an battery can
3
, a positive electrode terminal
51
, a negative electrode terminal
81
, an electrode unit
4
and an insulating member
53
, the battery can
3
having the electrode unit
4
housed therein, the electrode unit
4
having a positive electrode and a negative electrode which are electrically connected to the positive electrode terminal
51
and the negative electrode terminal
81
, respectively, the electrode terminals
51
and
81
being insulated from each other by the insulating member
53
. The lithium secondary cell is characterized in that the positive electrode terminal
51
is formed from an aluminum alloy containing at least 1.0 wt. % of a different metal as an additive element.
With the lithium secondary cell of the invention, the positive electrode terminal
51
has a remarkably improved strength and can therefore be tightened up with sufficiently great torque.
Stated more specifically, the different metal in the aluminum alloy can be at least one element selected from the group consisting of Mg, Si, Fe, Cu, Mn, Zn, Cr and B.
When the aluminum alloy contains at least 0.30 wt. % to not greater than 0.85 wt. % of Mg, reduced electric resistance will result, giving the cell an increased power density.
Reduced electric resistance and an increased cell power density are available alternatively when the aluminum alloy contains at least 0.25 wt. % to not greater than 0.75 wt. % of Si.
Further stated more specifically, the aluminum alloy has the composition of A6101 prescribed in JIS, i.e., a composition comprising 0.35 to 0.8 wt. % of Mg, 0.30 to 0.7 wt. % of Si, 0.50 wt. % of Fe, 0.10 wt. % of Cu, 0.03 wt. % of Mn, 0.10 wt. % of Zn, 0.03 wt. % of Cr, 0.06 wt. % of B and the balance Al.
The cell can be so constructed that the battery can
3
and the positive electrode terminal
51
are insulated from each other by the insulating member
53
. Further the battery can
3
and the negative electrode terminal
81
can be insulated from each other by the insulating member
53
. Additionally, the battery can
3
and the positive electrode terminal
51
, as well as the battery can
3
and the negative electrode terminal
81
, may be insulated from each other by the insulating member
53
.
The present invention provides another lithium secondary cell which comprises an battery can
3
, a positive electrode terminal
51
, a negative electrode terminal
81
, an electrode unit
4
and an insulating member
53
, the battery can
3
having the electrode unit
4
housed therein, the electrode unit
4
having a positive electrode and a negative electrode which are electrically connected to the positive electrode terminal
51
and the negative electrode terminal
81
, respectively, the electrode terminals
51
and
81
being insulated from each other by the insulating member
53
. The lithium secondary cell is characterized in that the negative electrode terminal
81
is formed by plating a substrate of copper with nickel.
Most suitably, the substrate of the negative electrode terminal
81
is made of oxygen-free copper.
The present invention provides another lithium secondary cell which comprises an battery can
3
, an electrode terminal
511
, an electrode unit
4
and an insulating member
53
, the battery can
3
having the electrode unit
4
housed therein, the electrode unit
4
having two electrodes electrically connected to the electrode terminal
511
and the battery can
3
, respectively, the electrode terminal
511
and the battery can
3
be
Fujiwara Kazuyasu
Nakanishi Naoya
Nohma Toshiyuki
Satoh Kouichi
Yonezu Ikuo
Kubovcik & Kubovcik
Sanyo Electric Co,. Ltd.
Weiner Laura
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