Patent Application
20230361395
The present invention relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to an electrical power source, for example, a primary or a secondary electrochemical cell. While there are no limits to the shape of the electrical power source, it preferably has a total size or volume that is less than 0.5 cc. Such so-called miniature-sized electrical power sources enable numerous new and improved medical device therapies. Miniature electrical power sources are defined as those having a size or total volume that is less than 0.5 cc.
The present invention offers a solution to current implantable electrical power source size limitations by diffusion bonding opposed shaped titanium members to an intermediate ceramic ring to form an open-ended container. The anode covered by a separator is housed inside the container. Separately, the cathode is contacted to the inner surface of a titanium lid with a laterally off-set via in the lid serving as an electrolyte fill port. The open end of the container is then closed by welding the lid to the container to complete the power source casing. After an activating electrolyte is filled into the casing through the fill port, the port is closed. This construction electrically isolates the opposite polarity anode and cathode from each other by the intermediate ceramic ring. That way, the titanium members separated by the intermediate ceramic ring serve as opposite polarity terminals for the electrical power source.
One approach that has been widely used to make miniature electrochemical cells is referred to as a thin film technology where opposite polarity electrode active materials deposited onto a respective current collector by physical vapor deposition (PVD) are activated with a solid electrolyte. This is an attractive approach since there is no manual handling of miniature parts and the manufacturing process is well suited to automated production using a pick-and-place semiconductor-type approach.
However, one drawback of thin film electrochemical cells is that the electrodes are non-porous, which means that the reaction rate is limited by solid-state diffusion of ions through the active layers. Solid-state diffusion limits the active electrode thickness to a range of about 10 microns to about 20 microns, which equates to typical capacities of about 75 to about 100 pAh/cm2. This capacity range means that there is generally not enough space available in many medical and non-medical devices to provide sufficient capacity to power the device.
Alternate approaches developed by Greatbatch Ltd., Clarence, New York, are the hermetic coin cells shown in U.S. Pub. Nos. 2022/0085473 to Arellano et al. and 2022/0166095 to Dianetti et al. The electrochemical cell configurations described in these publications can provide capacities of about 2,000 pAh/cm2, or more. However, even that much capacity may not be enough for some medical device applications. A significant drawback is that the space inside the casing that is available for the electrodes is reduced by a glass-to-metal seal, which results in an effective wall thickness of about 625 μm around the casing circumference. According to the present invention, in order to increase the cell's capacity to greater than about 4000 PAh/cm2, it is desired to minimize the wall thickness to about 100 μm around the casing circumference.
Further, the glass-to-metal seal of the cell designs described in the '473 and '095 publications is most reliable in a cylindrical shape. However, in order to maximize utilization of space within the medical device being powered by the miniature electrical power source of the present invention, it is desired to have a design that can be made in any shape including those that are not cylindrical.
Finally, the cell designs described in the '473 and '095 publications require precision machining and assembly of the individual parts that are assembled into the cells. For scale-up to very high volumes, an array-type approach using host titanium and ceramic sheets is desired where parts for multiple power sources are handled and produced simultaneously.
A significant benefit attributed to manufacturing an electrical power source according to the present invention is that a plurality of power sources are manufactured in a batch process using three host titanium sheets and one ceramic host sheet. The host titanium sheets are designated the host titanium base sheet, the host titanium top sheet, and the host titanium third or lid sheet. The host base, top and lid sheets each have a thickness that ranges from about 200 μm to 1 mm but are desirably only as thick as necessary to provide the required mechanical strength for the power source. The ceramic host sheet has a thickness that ranges from about 100 μm to about 150 μm.
The manufacturing process begins by cutting or milling a plurality of recesses part-way into the thickness of the host titanium base sheet. Separately, a plurality of openings are cut through the ceramic host sheet and through the host titanium top sheet. The openings in the host ceramic sheet and the host titanium top sheet are made using a milling machine that traces out the periphery of the inside diameter of a ring by making a circle having an outside diameter that is equal to the inside diameter of the to-be-built casing.
Both sides of the ceramic host sheet are coated with a titanium layer, preferably using a physical vapor deposition (PVD) process. The thusly processed ceramic host sheet is mounted on top of the host titanium base sheet and the host titanium top sheet is then mounted on top of the ceramic host sheet with the respective openings in the top host sheet and in the ceramic host sheet being in registry with each other and with the plurality of recesses in the base host sheet. The titanium base and top host sheets are then diffusion bonded to the intermediate ceramic host sheet. This is done by subjecting the host sheet stack to a pressure ranging from about 1 MPa to about 5 MPa at a temperature ranging from about 850° C. to about 950° C. for up to about 2 hours. This forms a plurality of open-ended containers in the bonded stack.
In a separate manufacturing line, anodes for a primary electrochemical cell are cut or punched from a sheet of lithium or a lithium alloy. Graphite, silicon, lithium titanium oxide are exemplary anode materials for a secondary electrical power source. For a secondary system, the desired anode active material is mixed in a solvent with a conductive carbon and a polymeric binder constituent to make an anode active slurry or paste that is formed into a sheet by tape casting, extruding, or coating using any method. Secondary anodes are then cut or punched from this sheet and, after drying, the resulting anodes are pressed to a final porosity of about 20% to about 40%. In either a primary or a secondary system, the thickness of the anode active material preferably ranges from about 50 μm to about 500 μm. Individual anodes are then adhered to the base host sheet, nested in one of the shaped recesses, using a conductive carbonaceous paste composed of carbon black and a polymeric binder.
Next, separators cut from a sheet to the desired shape are placed into the open-ended container on top of the anode. Then, after the host titanium base and top sheets are bonded to the intermediate ceramic host sheet and an anode covered by a separator is nested in each of the open-ended containers, a laser is used to cut through the bonded sheets to singulate open-ended containers having the desired shape, whether cylindrical or non-cylindrical, of a power source for a medical device.
Separately, a plurality of spaced-apart cathodes, each having a thickness that ranges from about 50 μm to about 500 μm, are adhered to the host titanium lid sheet using a conductive carbonaceous paste. Examples of cathode active materials for secondary electrochemical cells include lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, among others. For primary cells, silver vanadium oxide, carbon monofluoride (CFx) or manganese dioxide are preferred. The desired cathode active material is preferably combined with a polymeric binder and a conductive carbon. The electrode sheets from which the cathodes are cut or punched are formed by making a slurry of the electrode constituents in a solvent and then tape casting, extruding, or coating using any method. After drying, the resulting cathodes are pressed to a final porosity of about 20% to about 40%. A plurality of plate-shaped titanium lids are then cut from the lid host sheet. The lids are sized to close the previously described open-ended container and have a thickness that ranges from about 100 μm to about 200 μm.
Each lid also has an electrolyte fill port that is laterally off-set from the adhered cathode. The fill port is formed by laser or mechanical milling a respective plurality of openings into the lid host sheet in alignment with each casing that will subsequently be singulated from the stacked assembly of the host titanium base and top sheets and the intermediate host ceramic sheet. Lids cut from the third host titanium sheet are then welded to the open end of a container to form a casing, each housing an electrode assembly.
A suitable activating electrolyte is a non-aqueous solution containing a lithium salt dissolved in a mixture of solvents including at least one low viscosity solvent and at least one high permittivity solvent. Then, after filling each casing with electrolyte, the fill port is close-welded by melting the titanium material of the lid surrounding the port using a laser. Alternately, a metallic plug is inserted into the fill port and welded to the titanium lid.
If desired, a gold conductive pad for each power source is supported on a titanium adhesion layer contacted to an outer surface of both the host titanium top and base sheets. The gold conductive pads are preferably deposited using PVD or chemical vapor deposition (CVD) methods known in the art.
Depending on their chemistry, the electrical power sources are then subjected to an appropriate electrical test. In one example, a carbon/lithium nickel manganese cobalt oxide secondary cell having a diameter of 2.5 mm and a height of 0.7 mm is charged to 4.2 V. The cell is aged on open circuit voltage (OCV) for 2 to 3 weeks before several charge/discharge cycles between 4.2 V and 3.0 V are performed at a C/5 rate. The cell capacity is about 300 pAh.
Individual electrical power sources singulated from the stacked and weld-connected top, intermediate, and base host sheets closed by a lid according to the present invention have a diameter of about 2.5 mm and a height of about a 0.7 mm. The resulting wall thickness is about 100 μm, which is substantially less than the 625 μm seal of the prior art cells described in the previously discussed U.S. Pub. Nos. 2022/0085473 to Arellano et al. and 2022/0166095 to Dianetti et al. The efficient packaging of the present invention electrical power sources results in a delivered capacity of about 300 pAh, or more.
These and other aspects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following detailed description and to the appended drawings.
As described in this specification, a high-purity fused silica wafer is commercially available from numerous manufacturers. A suitable high-purity fused silica wafer has a thickness that ranges from about 100 μm to about 4 mm. One source is Corning, Incorporated, Corning, New York under the designations 7979, 7980 and 8655, designation 7980 being preferred.
As described in this specification, the term “plurality” means more than two up to a large number.
As described in this specification, the term “diffusion bonding” is a solid-state welding technique used to join similar metals together, for example, separate titanium members. Diffusion bonding operates on the principle of solid-state diffusion, wherein the atoms of two solid, metallic surfaces intersperse themselves over time. This is typically accomplished at an elevated temperature, which is approximately 50% to 75% of the absolute melting temperature of the materials. Diffusion bonding is usually implemented by applying high pressure, in conjunction with necessarily high temperature, to the materials to be welded.
Turning now to the drawings,
The electrical power source 10 has a casing 12 housing an electrode assembly comprising a separator 14 that is positioned intermediate an anode active material 16 and an opposite polarity cathode active material 18. The casing 12 is manufactures from an intermediate ceramic ring 20 that is diffusion bonded to both a titanium tray-shaped base plate 22 and a titanium top ring 24. A titanium lid 26 is welded to the titanium ring 24 to close the casing 12. The titanium lid 26 has an opening that serves as an electrolyte fill port 28 for activating the electrode assembly with an electrolyte. After electrolyte is filled into the casing, the fill port 28 is hermetically sealed.
As previously described in the Summary of the Invention section of this specification, in a high-volume manufacturing process the intermediate ceramic ring 20, the titanium base tray 22, the titanium top ring 24 and the titanium lid 26 are contained in respective ceramic and host titanium sheets. However, with initial reference to
In greater detail as shown in
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The next step in manufacturing the exemplary electrical power source 10 is to coat the upper and lower ring-shaped edges 20B, 20C of the ceramic ring 20 with a titanium layer, preferably using a physical vapor deposition (PVD) process. The PVD coated titanium layers range from about 0.1 μm to about 5 μm thick. The thusly processed ceramic ring 20 in mounted on top of the upper ring-shaped rim 22C of the titanium base tray 22. The lower ring-shaped edge 24C of the titanium top ring 24 is then contacted to the upper ring-shaped edge 20B of the ceramic ring. In this alignment, the respective openings in the titanium top ring 24 and the ceramic ring 20 are in registry with each other and with the recess 22D in the titanium base tray 22. The titanium base tray 22 and the titanium top ring 24 are then diffusion bonded to the intermediate ceramic ring 20. This is done by subjecting the stack to a pressure ranging from about 1 MPa to about 5 MPa at a temperature ranging from about 850° C. to about 950° C. for up to about 2 hours. This treatment causes the titanium materials of the titanium base tray 22 and of the titanium top ring 24 to chemically bond to the PVD deposited titanium layers contacting the opposed ring-shaped edges 20B, 20C of the ceramic ring 20. An open-ended container results from the bonded stack.
Referring back to
In the case of a primary electrical power source 10, lithium is an exemplary anode active material. Other suitable anode active materials for a primary electrochemical cell include lithium alloys and intermetallic compounds including, for example, Li—Si, Li—Sn, Li—Al, Li—B and Li—Si—B alloys, and mixtures and oxides thereof. Anodes for a primary electrical power source 10 are cut or punched from a sheet of lithium or lithium alloy. Carbon, graphite, silicon, and lithium titanium oxide (Li4Ti5O12) are exemplary anode materials for a secondary electrical power source. In the event that the anode active material is not lithium, the active material is preferably combined with a conductive carbon and a polymeric binder, such as PVDF, carboxymethyl cellulose, or styrene-butadiene rubber.
Anodes for a secondary power source are cut or punched from sheets that are formed as a slurry of the anode active material mixed with the conductive carbon and polymeric binder constituents in a solvent to make an anode active slurry or paste that is then tape cast, extruded, or coated by any method. After drying, the resulting porous secondary anodes are pressed to a final porosity of about 20% to about 40%. In that manner, the titanium base tray 22 serves as a negative-polarity terminal electrically connected to the anode active material 16 through the carbonaceous paste current collector 30.
In a similar manner, a thin layer of a conductive carbonaceous paste 32 serving as a cathode current collector is contacted to the lower planar surface 26B of the titanium lid 26. The carbonaceous paste 32 is preferably composed of carbon black and a polymeric binder and has a thickness that ranges from about 0.1 μm to about 3 μm.
A cathode active material 18 is then contacted to the carbonaceous paste 32. The cathode active material 18 preferably extends to the peripheral edge of the carbonaceous paste 32 and is deposited to a thickness that ranges from about 25 μm to about 5,000 μm, more preferably to a thickness of about 50 μm to about 500 μm. Lithiated metal oxide-based materials, for example LiCoO2, LiMnO2, LiMn2O4, LiFePO4, lithium nickel manganese cobalt oxide (LiNiaMnbCo1-a-bO2), lithium nickel cobalt aluminum oxide are suitable cathode active materials for a secondary electrochemical cell. For a primary electrochemical system, Ag2V4O11, CFx and manganese dioxide are preferred.
Cathodes for a primary or secondary power source are cut or punched from sheets that are formed as a slurry of the cathode active material mixed with the conductive carbon and polymeric binder constituents in a solvent to make a cathode active slurry or paste that is then tape cast, extruded, or coated by any method. After drying, the resulting porous cathodes are pressed to a final porosity of about 20% to about 40%.
A separator 14 is cut from a sheet to a size to rest on top of the anode active material 16 and fit into the inside diameter of the intermediate ceramic ring 20. The separator 14 can extend to the ceramic ring 20, but that is not necessary. It is only required that the separator 14 is large enough to prevent the anode active material 16 from physically contacting the cathode active material 18. An exemplary separator 14 is comprised of a porous polymeric material such as polyethylene or a polyethylene/polypropylene composite.
To complete the electrode assembly, the lid 26 supporting the conductive carbonaceous paste 32 and the cathode active material 18 is placed on the upper ring-shaped edge 24B of the titanium top ring 24. The lid 26 is then laser welded to the titanium ring 24 to close the casing 12. In that manner, the lid 26 connected to the top ring 24 serve as a positive-polarity terminal electrically connected to the cathode active material 18 through the carbonaceous paste 32.
To help improve electrical connectivity of the power source 10 to a load (not shown), a negative polarity biocompatible conductive pad 34 is supported on a titanium adhesion layer (not shown) contacted to the outer surface of the base wall 22B of the titanium base tray 22. Similarly, a positive polarity biocompatible conductive pad 36 is supported on a titanium adhesion layer (not shown) contacted to the upper planar surface 26A of the titanium lid 26. The conductive pads 34, 36 are preferably made of gold that is deposited on the titanium tray 22 and lid 26 using PVD or chemical vapor deposition (CVD) methods known in the art.
The fill port 28 in the lid 26 is spaced laterally from the carbonaceous paste 32. This positioning provides a space or gap between the lower planar surface 26B of the lid 26 and the cathode active material 18 so that electrolyte (not shown) can flow into the interior of the casing 12 to activate the electrode assembly. A suitable electrolyte is a non-aqueous solution containing a lithium salt selected from LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, LiO2, LiAlCl4, LiGaCl4, LiC(SO2CF3)3, LiN(SO2CF3)2, LiSCN, LiO3SCF3, LiC6FSO3, LiO2CCF3, LiSO6F, LiB(C6H5)4, LiCF3SO3, and mixtures thereof, dissolved in a mixture of solvents including ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dimethoxyethane, gamma-butyrolactone and propylene carbonate, plus various additives as required.
Preferably, the fill port 28 is closed by directing a laser beam at the titanium lid 26, or by press-fitting a closure plug (not shown) into the port 28, followed by weld the plug to the lid.
After electrolyte filling, the electrical power sources 10 of the present invention, whether of a primary or a secondary chemistry, are subjected to an appropriate electrical test. In one exemplary secondary electrochemical cell, a carbon/lithium nickel manganese cobalt oxide couple with a 2.5 mm diameter and a 0.7 mm height is charged to 4.2 V. The cell is then aged on open-circuit voltage (OCV) for 2 to 3 weeks before several charge/discharge cycles between 4.2 and 3.0 V are performed at a C/5 rate.
Exemplary electrical power sources according to the present invention have a diameter of about 2.5 mm and a height of about 0.7 mm. The wall thickness of the ceramic ring 20, the titanium top ring 24 and the annular sidewall 22A of the titanium base tray 22 are about 100 μm while the lid 26 and the base wall 22B of the titanium base tray 22 have thicknesses that are <100 μm, but in some electrical power sources can be as thick as about 4 mm. Thus, the efficient packaging of the miniature-sized electrical power sources according to the present invention results in a delivered capacity of about 300 pAh, or more.
Referring now to
It is appreciated that various modifications to the inventive concepts described herein may be apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined by the hereinafter appended claims.
This application claims priority to U.S. Provisional Application Ser. No. 63/338,922, filed on May 6, 2022.
| Number | Date | Country | |
|---|---|---|---|
| 63338922 | May 2022 | US |
