BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to an electrochemical cell that preferably has a total size or volume that is less than 0.5 cc. Such so-called miniaturized electrochemical cells enable numerous new and improved medical device therapies. Miniature electrochemical cells are defined as those having a size or total volume that is less than 0.5 cc.

2. Prior Art

Electrochemical cells must have two opposite polarity terminals that are electrically isolated from each other. In use, the terminals are connected to a load, such as the circuitry of an implantable medical device to power the medical device. In that respect, an electrochemical cell which is sufficiently hermetic to prevent ingress of moisture and egress of electrolyte so that it can operate for ten years or more requires robust sealing methodologies while still providing adequate electrical isolation between the opposite polarity terminals. However, conventional sealing techniques are often not practical when cell size drops below 0.5 cc. That is because the seals themselves take up a major portion of the overall cell volume.

For that reason, the present invention provides a casing construction that is suitable for use with both hermetically sealed primary and secondary or re-chargeable electrochemical cells. While useful with cells of virtually any size, the present hermetic casing is particularly well suited for cells having a total volume or size that is less than 0.5 cc.

SUMMARY OF THE INVENTION

The present invention describes an electrochemical cell that is enabled by a casing construction which is readily adapted to miniature cell designs. However, while the present casing is adapted for miniature electrochemical systems, the casing design is also applicable to cells that are not classified as “miniature”. A miniature electrochemical cell is defined as one having a total volume that is less than 0.5 cc.

A known problem with conventional miniature electrochemical cell designs is the need for the materials from which the cell is constructed to be both chemically compatible with each other and not susceptible to undesirable corrosion reactions. A miniature electrochemical cell according to the present invention uses an electrically conductive metal-containing paste that is filled into a via hole extending through a cup-shaped, open-ended ceramic container. The via hole is formed (drilled, punched or cut) with the ceramic container being in a green state. The open-ended ceramic container is then sintered to transform the metal-containing paste into a solid electrically conductive pathway extending through the sintered ceramic container.

Next, an anode current collector is deposited on an inner surface of the open-ended ceramic container in contact with the electrically conductive pathway. In addition to providing electrical conduction from the to-be-deposited anode active layer to the electrically conductive material residing in the via hole, the anode current collector protects the metallic electrically conductive material from corrosive reactions with other battery components while exhibiting good adhesion to the ceramic container or, should there be one, to an adhesion layer, for example an adhesion layer of titanium, on an inner surface of the ceramic container. An exemplary anode current collector according to the present invention is from about 0.1 microns to about 50 microns thick and is comprised of a metallic layer deposited on the inner surface of the ceramic container using a physical vapor deposition (PVD) process, for example sputtering deposition or evaporation deposition, so that the deposited metal serving as the current collector covers the via hole. Exemplary current collector materials include nickel, titanium, copper, and Ti/NiV composites.

An anode active material is deposited on the current collector opposite the electrically conductive pathway. The anode active material is pressed into a pellet, spray-coated, or printed and has a shape that encases the anode current collector to contact the inner surface of the ceramic container. That way, the anode active material is in electrical continuity with the electrically conductive pathway through the current collector. The electrically conductive pathway serves as the negative terminal for the electrochemical cell.

A separator is supported on the anode active material opposite the electrically conductive material in the anode via hole. A cathode active material contacts the separator opposite the anode active material. Just before the open end of the ceramic container is closed with an electrically conductive cover plate or lid, a nonaqueous electrolyte is filled into the container. The electrolyte serves to activate the electrode assembly comprising the anode and cathode active materials prevented from direct physical contact with each other by the intermediate separator.

An intermediate ring-shaped gold pre-form resides between the electrically conductive lid and the upper edge of an annular sidewall comprising the open-ended ceramic container. Alternatively, a physical vapor deposition (PVD) process is used to coat gold onto the upper edge of the annular sidewall or onto an inner surface of the titanium lid. Preferably, the upper annular edge of the container is metallized prior to contacting the gold to the container. Then, an ultra-sonic welding process or a laser welding process is used to melt and seal the gold to the metal lid and to the ceramic container, thereby closing the open end of the container. An important aspect of the present miniature electrochemical cell is that the cathode active material directly contacts an inner surface of the lid. That way, the lid serves as the positive terminal for the electrochemical cell.

Thus, the present invention describes a miniature electrochemical cell activated with a nonaqueous electrolyte. The anode or negative terminal is comprised of a metal-containing material residing in and hermetically bonded or sealed to an anode via hole extending through the cup-shaped ceramic container. The hermetic bond is formed by co-firing a metal-containing paste filled into the via hole extending through a green ceramic body comprising the ceramic container. The metal-containing material is preferably substantially pure platinum, or a platinum/ceramic composite and the open-ended ceramic container is comprised of 3% YSZ or alumina. The metal lid is sized and shaped (configured) to close the open end of the ceramic container to thereby provide the cell casing. The cathode active material contacts the lid and the separator opposite the anode active material.

Alternatively, the metal-containing material in the anode via hole is gold, which is formed by brazing gold into a via hole formed (drilling, punching, cutting, machining, and waterjet cutting) through the pre-sintered ceramic container. Prior to sintering the green-state ceramic container, the via hole is coated with titanium or titanium and niobium to facilitate gold wetting of the via hole wall.

The present electrochemical cell is not limited to any one chemistry and can be of an alkaline cell, a primary lithium cell, a rechargeable lithium cell, a Ni/cadmium cell, a Ni/metal hydride cell, a supercapacitor, a thin film solid-state cell, and the like. Preferably, the cell is a lithium-ion electrochemical cell comprising a carbon-based or Li4Ti5O12-based anode and a lithiated metal oxide-based cathode, such as of LiCoO2or lithium nickel manganese cobalt oxide (LiNiaMnbCo1-a-bO2). In an alternate embodiment, the cell is of a primary chemistry having a lithium anode and a metal oxide cathode, for example a silver vanadium oxide cathode active material. Fluorinate carbon (CFx) is another suitable cathode active material.

These and other aspects of the present invention will become increasingly more apparent to those of ordinary skill in the art by reference to the following description and the appended drawings.

