Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Reexamination Certificate
2001-02-28
2004-01-20
Tsang-Foster, Susy (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
C429S152000, C429S162000, C429S231950, C029S623400, C029S623500
Reexamination Certificate
active
06680141
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a lithium battery comprising at least:
a negative electrode comprising negative electrode material and a negative current collector;
a positive electrode comprising positive electrode material and a positive current collector; and
a separator separating the negative electrode and the positive electrode, at least the negative electrode material and the positive electrode material being provided with a pattern of holes which accommodate a polymeric material which sticks and presses the negative electrode, the positive electrode and the separator together.
The invention also relates to a method of manufacturing a lithium battery comprising a stack of a negative electrode, a separator, and a positive electrode, which method comprises the steps of applying negative electrode material on a negative current collector so as to form the negative electrode, applying positive electrode material on a positive current collector so as to form the positive electrode, and arranging a separator between the negative and the positive electrode.
BACKGROUND OF THE INVENTION
The growing market for lightweight, portable cordless consumer products, such as CD-players, mobile telephones, laptop computers, and video cameras has led to an increased demand for high-density batteries. Specifically, very thin and flexible batteries are required. In order to provide an acceptable portability, the batteries contained in said consumer products should provide the necessary amount of energy at the smallest possible weight and volume. However, the thinner the battery, the more difficult the application of a pressure needed to maintain a sufficient contact between the respective components of the battery.
A battery according to the preamble is known from the International patent application with publication number 00/04601.
Said battery has a thin and flexible shape and at the same time provides a very high energy density. Moreover, the contact between the electrodes and the separator is obtained and maintained in a very efficient way. The battery can be packed in a thinwalled canister, as the walls of said canister are not needed for maintaining a sufficient pressure on the respective components of the battery.
Lithium is a very advantageous material for use in batteries in which a high energy density is required. Lithium is the lightest of all metals, which promises an extremely high theoretical energy density of metallic lithium. Lithium is a leading contender in the field of negative battery electrode materials, since it has a large negative thermodynamic potential. Moreover, the use of lithium has no negative environmental consequences. Thus, lithium batteries are very promising, especially where weight is an important factor.
The holes in the electrode material are macroscopic holes having a diameter of, for example 1 mm. In a typical example, the pattern of holes forms a rectangular two-dimensional array with a mutual hole distance of 5 mm. The dimensions of the holes and the pattern are chosen in such a way that the active surface area of the electrodes amounts preferably to at least 90%.
The holes may be made by punching or laser cutting. The electrode material may also be directly provided with holes by means of a suitable application method, for example by means of patternwise screen printing of a paste comprising the active electrode material onto the current collector.
In the above embodiment, where only the negative electrode material and the positive electrode material are provided with a pattern of holes, the polymeric material fills said holes and simultaneously contacts the current collectors as well as the separator. The polymeric material in each of the holes acts as a plug or rivet and sticks to the separator, the electrode material, and the current collector, causing these layers to be bonded together.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a battery according to the preamble which is even easier to manufacture and in which the components are aligned in a very precise manner. Moreover, it is an object of the invention to provide a method of manufacturing such a battery.
These objects are achieved in a battery as specified in the preamble, which is characterized in that at least the negative electrode and the positive electrode are provided with a pattern which can be used for the purpose of aligning the electrodes.
Providing the negative electrode and the positive electrode with such a pattern facilitates the alignment of the negative electrode with respect to the positive electrode and vice versa. The result thereof is a lithium battery according to the preamble with a very precise alignment of the respective layers.
Preferably, at least the negative electrode and the positive electrode are provided with one or more alignment holes, which advantageously differ from the pattern of holes present.
Such alignment holes can cooperate with alignment pins or similar aids, present in the device by which the battery is manufactured, in order to align the respective layers. The alignment holes may differ in size and shape from the holes already present in the respective layers.
In a particular embodiment, the pattern is provided outside the area of active material of the battery.
By providing a pattern outside the area of active material of the battery, the active surface is not further reduced. The pattern may, for example, comprise a portion of a current collector projecting outside the area of active material. In an alternative embodiment, the pattern is formed in such projecting portion.
In a particular embodiment, the current collectors are provided with a pattern of holes substantially overlapping the holes in the electrode materials, the holes of both patterns being filled with the polymeric material.
In this embodiment the holes in the electrode materials coincide with the holes in the current collector. A polymeric material can be introduced from the side of the electrodes opposite the separator, for example by melting a polymeric foil and pressing it into the electrodes. Such a melting polymer penetrates the holes, solidifies, and forms a continuous plug.
A preferred embodiment of the battery is characterized in that the separator is provided with a pattern of holes substantially overlapping the holes in the electrode materials, and in that the holes of the patterns are filled with the polymeric material.
The holes in the electrode material and the current collectors coincide with the holes in the separator. The polymeric material introduced into the holes forms a kind of rivets, which provide a bond between the electrodes and the separator.
The lithium battery consists of a positive and a negative electrode which are separated by a polymeric film to prevent electronic contact in an electrolyte. For example, a transition metal oxide, such as manganese oxide, may be used as the positive electrode, and metallic lithium as the negative electrode. The electrolyte may be a lithium salt in a non-aqueous organic solvent with good ionic conductivity and negligible electrical conductivity. During discharging of the battery, lithium ions are transported from the negative electrode towards the positive electrode. During charging, the lithium ions are transported towards and deposited on the negative electrode.
When the above lithium battery with lithium metal for the negative electrode is used as a secondary battery, i.e. a rechargeable battery, the problem of short-circuits in the battery is encountered, caused by the repetition of the charge/discharge cycles. During the charge/discharge cycles lithium metal is dissolved and deposited, which creates the possibility of the growth of lithium metal dendrites on the surface of the negative electrode. Said growing dendrites may penetrate the separator between the negative and the positive electrode and can come into contact with the positive electrode, resulting in a short-circuit.
The use of a lithium metal alloy, such as Li—Al, for the negative electrode, instead of lithium m
Bordes Bente Adriaan
Brink Jan
Feil Hans
Hack Martinus Jacobus Johannes
Hikmet Rifat Ata Mustafa
Halajian Dicran
Tsang-Foster Susy
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