Patent Application
20090010462
Embodiments of the present invention relate to a rechargeable thin film battery system for electrical devices such as hearing aids.
Small and thin batteries have been extensively used as mobile power supplies for portable electronic devices such as mobile phones, PDA's, remote sensors, miniature transmitters; medical devices such as hearing aids, pacemakers, blood-pressure monitoring devices, and implantable medical devices; and other applications such as smart cards and MEMS devices, PCMCIA cards, and CMOS-SRAM memory devices. The batteries should have a sufficient electrical power capacity to power the electronic device reasonable length of time. The power capacity requirement can result in a battery which is quite heavy compared to the weight of the electronic device. Conventional batteries also often use potentially toxic materials that may leak out and are consequently subjected to extensive governmental regulation.
For example, hearing aids are typically powered by small disposable batteries which are zinc-air batteries. These small batteries have sizes ranging from size 675 for behind-the-ear units and cochlear implants with a diameter of 11.60 mm and height of 5.40 mm to even smaller size 5 batteries for hearing aids inserted into the ear canal, which have diameters of 5.75 mm and heights of 2.15 mm. However, these small disposable batteries have to be replaced quite often and the replacement process is difficult to perform and can create environmental problems. One reason why only approximately 20% of hearing impaired Americans use hearing aids is the often daunting task of frequently having to handle extremely small batteries, particularly for elderly patients. There are also substantial environmental issues created from the disposal of millions of zinc-air batteries.
To address this concern, hearing aid manufacturers have recently begun to consider the use of rechargeable batteries for their next generation products, such as NiMH batteries, which are recharged by removing the batteries from the hearing aid and inserting them into recharging units. While this addresses the environmental concerns associated with the disposal of zinc-air batteries, it does not obviate the need for having to frequently remove and reinstall the batteries, which may be as often as daily for high-power digital hearing aids. Aside from inconvenience of daily removal and installation of the batteries, the removal and reinstallation process also increases the likelihood of damaging delicate hearing aid components.
Another approach is to design hearing aids to allow for directly plugging the entire hearing aid into slots in suitably configured chargers. This overcomes the problem of having to remove and reinstall batteries. For example, rechargeable NiMH battery-powered hearing aids are plugged into recharging units after approximately 20 hours of use. However, such units require contacting the outer shell of the hearing aid for recharging, and one problem with this system is that moisture or water enters the hearing and through the exposed contact regions. Behind-the-ear models frequently become wet from perspiration or from rain and hearing aids installed within the ear canal that are not removed while taking a shower can get wet. Furthermore, the charger itself can short out when a wet hearing aid is plugged into the charger.
One solution to the problem of exposed contacts for rechargeable hearing aids is to inductively charge the hearing aid battery by coupling power between an external power source and a coil located internally to the device. However, such inductive chargers have their own set of difficulties, including adequate coupling between the primary inductor in the charger and the secondary inductor in the hearing aid; e.g. see U.S. Pat. No. 6,658,124 (Meadows). However, even with adequate coupling, conventional rechargeable batteries are not a panacea. For example, most rechargeable batteries such as for example nickel cadmium, and others, have a “memory” that relates the amount of stored energy to the number of discharging and charging cycles. For example, if half the energy is used up and a battery is recharged after that period, eventually, only half the energy is left available on the battery.
Another type of rechargeable battery which has also been used for portable devices include a lithium ion batteries. In this battery, the cathode is made from lithium and the electrolyte comprises lithium phosphoric oxide. These batteries provide a somewhat higher energy density and capacity. However, rechargeable batteries such as lithium ion batteries often overheat and rupture when being recharged. The overheated batteries can even catch fire and destroy the surrounding electronic device, or even be a hazard to the user. Consequently, lithium ion batteries and not extensively used, and nickel-metal-hydride (NiMH) batteries are preferred for hearing aids because they have fewer memory effects and are more tolerant of overcharging. The problems of memory and overcharging are particularly acute for hearing aids because a hearing aid may partially discharge a battery during the day and then be placed on a charger overnight. If more than one hearing aid is used, the batteries may be in different states of charge but are charged simultaneously.
Thus, it is desirable to have a power source that does not require frequent replacement or disassembly. It is also desirable to have a rechargeable power source that provides increased electrical energy specific capacity and density. It is further desirable to have a recharging system for the battery that is separable and can recharge the battery without being directly connected to electrical contacts of the battery.
These features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, which illustrate examples of the invention. However, it is to be understood that each of the features can be used in the invention in general, not merely in the context of the particular drawings, and the invention includes any combination of these features, where:
An embodiment of a rechargeable battery assembly comprising a rechargeable battery module 20 to provide power to a portable electronic device, and an external battery charger 24, is shown in
An embodiment of a rechargeable thin film battery 26 suitable for the battery module 20 is shown in
The battery component films 36 can be employed in a number of different arrangements, shapes, and sizes, and they cooperate to form a battery to receive, store, and discharge electrical energy. The battery component films 36 include at least a pair of electrode films with an electrolyte film 38. The electrode films can include one or more of a cathode current collector film 40, a cathode film 42, an anode film 46, and an anode current collector film 48, which are all inter-replaceable. For example, the battery 26 can include (i) a pair of cathode and anode films or a pair of current collector films, (ii) both the anode/cathode films and the current collector films, or (iii) various combinations of these films, for example, a cathode film and an anode and anode current collector film but not a cathode current collector film, and so on. The exemplary versions of the battery 26 illustrated herein are provided to demonstrate features of the battery 26 and to illustrate their processes of fabrication; however, it should be understood that the exemplary battery structures should not be used to limit the scope of the invention, and alternative battery structures as would be apparent to those of ordinary skill in the art are within the scope of the present invention. The battery component films 36 are typically less than 100 microns allowing the thin film batteries to be less than about 1/100th of the thickness of conventional batteries. The battery component films 36 are formed by processes, such as for example, physical and chemical vapor deposition (PVD or CVD), oxidation, nitridation, and electroplating.
In one version, as shown in
The cathode film 42 comprises an electrochemically active material is then formed over the current collector film 40. In one version, the cathode film 42 is composed of lithium metal oxide, such as for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron oxide, or even lithium oxides comprising mixtures of transition metals such as for example, lithium cobalt nickel oxide. Other types of cathode films 42 that may be used comprise amorphous vanadium pentoxide, crystalline V2O5 or TiS2. Typically, the cathode film stack has a thickness of at least about 5 microns, or even at least about 10 microns. In one example, the cathode film 42 comprises crystalline lithium cobalt oxide, which in one version, has the stoichiometric formula of LiCoO2.
An electrolyte film 38 is formed over the cathode film 42. The electrolyte film 38 can be, for example, an amorphous lithium phosphorus oxynitride film, also known as a LiPON film. In one embodiment, the LiPON has the stoichiometric form LixPOyNz in an x:y:z ratio of about 2.9:3.3:0.46. In one version, the electrolyte film 38 has a thickness of from about 0.1 microns to about 5 microns. This thickness is suitably large to provide sufficiently high ionic conductivity and suitably small to reduce ionic pathways to minimize electrical resistance and reduce stress.
An anode film 46 formed over the electrolyte film 38. The anode film 46 can be the same material as the cathode film 42, as already described. A suitable thickness is from about 0.1 microns to about 20 microns. In one version, anode film 46 is made from lithium which is also sufficiently conductive to also serve as the anode current collector film 48, and in this version the anode film 46 and anode current collector film 48 are the same. In another version, the anode current collector film 48 is formed on the anode film 46, and comprises the same material as the cathode current collector film 40 to provide a conducting surface from which electrons may be dissipated or collected from the anode film 46. For example, in one version, the anode current collector film 48 comprises a non-reactive metal such as silver, gold, platinum, in a thicknesses of from about 0.05 microns to about 5 microns.
After the deposition of all the battery component films 36, a protective coating is formed over the battery component films 36 to provide protection against environmental elements. In one example, the protective coating comprises a plurality of polymer and ceramic layers that are superimposed on each other. Portions of the cathode current collector film 40 and anode current collector film 48 that extend out from under a battery cell 60 form a pair of terminals that is used to connect the battery cell 60 of the battery 26 to the external environment.
The embodiment of the rechargeable thin film battery 26 described herein provides a higher energy storage capacity, energy density, and specific energy level, than conventional solid state batteries. The thin film battery 26 is typically less than about 1/100th of the thickness of conventional batteries and can be formed by thin film fabrication processes, such as for example, physical or chemical vapor deposition methods (PVD or CVD), oxidation, nitridation or electroplating. Advantageously, the thin film battery 26 described herein provides significantly higher specific energy capacity and energy density than conventional thin film batteries. The energy density level is the fully charged output energy level per unit volume of the battery. The specific energy level is the fully charged output energy level per unit weight of the battery. Conventional thin film batteries have large sizes and are heavier, and consequently, have maximum energy density levels of 200 to 350 W-hr/l and specific energy levels of 30 to 120 W-hr/L. However, the thin film battery described has an energy density level exceeding 300 W-hr/L.
The rechargeable thin film battery 26 is charged by a receiving induction coil 64 and electrically coupled to a battery control circuit 28 as shown in
In one version, the receiving induction coil 64 comprises a first induction coil 64a having a first central axis oriented along a first direction, and a second induction coil 64b having a second central axis oriented along a second direction that is a different direction than the first direction. As result, the first and second coils 64a,b are positioned in different planes. For example, the second induction coil 64b can have a second central axis that is oriented perpendicular to the first central axis of the first induction coil 64a. This allows the receiving induction coil 64 to receive a voltage even if the coil 64 is misaligned with the transmission induction coil 66 of a battery charger 24. In one version, the first and second induction coils 64a,b each comprise from about 100 to about 1000 turns, each turn comprising an area of between about 1 and about 30 mm2.
The battery control circuit 28 receives electrical power from the receiving induction coil 64 and controls charging and discharging of the battery 26. The battery control circuit 28 can have one or more optional sub-circuits, which can include a rectifier circuit 68, battery protection circuit 70 comprising a battery charging circuit 72 and a battery discharging circuit 74, and a voltage converter circuit 78, which can be a step-down or step-up circuit to suite the voltage output requirements.
The rectifier circuit 68 is coupled to the receiving induction coil 64 and serves to convert the coil's AC current to a DC current for direct charging of the battery 26. The rectifier circuit 68 is capable of converting an AC voltage of between about 3.2 and 21 Volts at a frequency of about 60 Hz or above to a DC voltage of between about 4.5 and 30 volts or even between about 4.5 and 5 volts. The rectifier circuit 68 can comprise a diode bridge rectifier that is connected between a terminal of the receiving induction coil 64 and the load. A capacitor can be provided in parallel with the load so as to smooth the rectified wave form. Alternately, the rectifier circuit 68 can comprises an integrated circuit (IC) chip. In one prospective embodiment the rectifier circuit 68 is integrated with the battery protection circuit 70 as in the case of an integrated control circuit 28.
The battery protection circuit 70 comprises two different sub-circuits, namely a battery charging circuit 72 and a battery discharging circuit 74, and the sub-circuits may be separate circuits or maybe combined into a single operable circuit. The battery charging circuit 72 protects the battery from overcharging by limiting the maximum charging voltage to a value that is below a maximum charging voltage value. In one application, the battery charging circuit 72 limits the maximum charging voltage to the value of less than about 4.2 volts during charging. In addition, the battery charging circuit 72 can also limit the maximum amperage provided to charge the battery. The battery charging circuit 72 prevents over threshold charging voltages, which can damage the battery 26, or cause the battery to heat up to a temperature that is sufficiently high to damage the battery. The battery charging circuit 72 is particularly useful when the rechargeable battery module 20 is misaligned during insertion to a misaligned position which results in a higher voltage being inductively transmitted from an external transmission induction coil 66 to the receiving induction coil 64. Providing a battery charging circuit 72 that is integral with the battery recharging module 20, allows the module 20 to be misaligned on a battery charger without adverse effects.
The battery protection circuit 70 can also include a battery discharging circuit 74 that controls the discharge of current from the battery 26. The battery discharging circuit 74 protects the battery 26 from excessive or over-discharge by shutting of or terminating the discharge voltage from the battery 26 when the battery voltage reaches a predetermined minimum voltage level that is predetermined and is based on the capacity of the battery. For example, the minimum voltage level for a thin film battery 26 as described above can be about 3.4 Volts.
In one exemplary embodiment the charging circuit 72 comprises an adapter charger IC chip 51, such as for example, a MAX8804Y or MAX8804Z integrated circuit (IC) chip available from Maxim Integrated Products, of Sunnyvale, Calif. The adapter charger IC chips 51 are dual-input, stand-alone, constant-current, constant-voltage, thermally regulated linear charger that were developed for lithium ion batteries. The IC chips 51 include a current-sensing circuit, MOS pass element, thermal-regulation circuitry, and over voltage protection. The IC chip 51 is capable of serving as a stand-alone charger to control the charging sequence from the prequalification state through the fast-charge, top-off charge, and full charge indication. As shown in
In one prospective embodiment the battery protection circuit 70 comprises an integrated circuit which serves as both the charging circuit 72 and the discharging circuit 74. Custom integrated battery protection circuits are readily available and one such circuit comprises, for example, an S-8211 C integrated circuit available from Seiko Instruments, Chiba, Japan.
The voltage converter circuit 78 is provided to receive the voltage of the thin film battery 26 and to output a pre-determined voltage value between the output terminals 44a,b. In one embodiment the voltage converter circuit 78 is a step-down circuit that steps the voltage of the thin film battery 26 down to provide a conventional lower voltage between the output terminals. In one embodiment the voltage converter circuit receives a voltage of the thin film battery that is between about 3.3 and 4.3 Volts and outputs a voltage between the output terminals of about 1.2 Volts at a current draw of about 20 mA. A suitable voltage converter circuit 78 comprises, for example, a MAX8581 or MAX8582 step-down converter integrated circuit (IC) chip 79 available from Maxim Integrated Products, Sunnyvale, Calif., USA. The voltage converter IC chips 79 are step-down converters that can receive the battery voltage of between 2.7 and 5.5 V and output an adjustable voltage level that can be set between a low of about 0.4 V up to the voltage of the battery. The MAX8581 and MAX8582 are additionally equipped with thermal shutdown circuitry that will automatically shut down current flow through the chip above about 160° C. As shown in
A rechargeable battery assembly comprises the rechargeable battery module 20 and a battery charger 24. The battery charger 24 receives the rechargeable battery module 20 (or the electronic device containing the module) and provides power to be coupled to the receiving induction coil 64 of the battery module 20 to provide electrical power to recharge the battery 26. The battery charger 24 comprises an external housing 80 enclosing transmission induction coil 66. The transmission induction coil 66 is powered by a voltage transforming circuit 82 which connects to an external power supply 84 to provide an alternating voltage to the transmission induction coil 66. In one embodiment the alternating voltage that is supplied to the transmission induction coil 66 has a frequency of between about 50 kHz and about 5 MHz or even between about 200 kHz and about 2 MHz. The external housing 80 comprises a receiving surface 88 to receive the rechargeable battery module 20. The battery charger 24 can output a power to the recharging battery assembly of up to about 10 Watts when connected to an outside power source comprising an AC power source of about 60 hz and about 120V.
In one embodiment, the charger 24 comprises a flat surface for placement of the rechargeable battery module 20, or an electronic device containing the rechargeable battery module 20, thereon. In this version, the battery charger 24 also has a support bracket 90 surrounding its receiving surface 88 to hold and support the rechargeable battery module 20 (or the electronic device containing the rechargeable battery module 20) to properly orient the module/device for optimal power coupling between the battery charger 24 and the rechargeable battery module 20. A suitable support bracket 90 comprises an internal profile that matches the external shape of the rechargeable battery module 20 or electronic device. In another embodiment the receiving surface 88 is shaped to conform to the enclosure about the rechargeable battery module 20 thereby allowing the module 20 to be firmly seated thereon.
In another embodiment, the battery charger 24 comprises a transmission induction coil 66 that is located inside the charger casing about the shaped receiving surface 88 thereby allowing for partial insertion of the rechargeable battery module 20 or electronic device therein, as shown in
In a further embodiment, as shown for example in
The voltage transforming circuit 82 is provided to convert an AC line voltage to a voltage and current suitable for driving the transmission induction coil 66. In one version, the voltage transforming circuit 82 comprises a transformer.
The rechargeable battery module 20 can be used in a number of different electronic devices. For example, the rechargeable battery module 20 can be used as a mobile power supply for portable electronic devices such as mobile phones, satellite phone, personal digital assistants, remote sensors, miniature transmitters, smart cards, MEMS devices, PCMCIA cards, and CMOS-SRAM memory devices. The rechargeable battery module 20 also has extensive applications for external and implantable medical devices such as hearing aids, pacemakers, blood-pressure monitoring devices, and neural stimulators. The rechargeable battery module 20 is designed to fit any one of these requirements by providing a sufficient electrical power capacity to power the electronic device for a reasonable length of time that can vary with the type of electronic device.
In one application, the rechargeable battery module 20 is used to provide rechargeable power for an external hearing aid. In this version, the rechargeable battery module 20 comprises a thin film rechargeable battery 26 and circuits designed to allow the battery module 20 to provide an electrical power output that is equivalent to the power output provided by non-rechargeable hearing aid batteries such as zinc-air batteries. The rechargeable battery module 20 can also be made to have external dimensions that are the same as conventional hearing aid batteries to allow ready replacement and interchangeability of a hearing aid battery with the rechargeable battery module 20. For example, the rechargeable battery module 20 can be enclosed by a housing 40 which provides a protective enclosure and has output terminals 42a,b for connecting the rechargeable battery module 20 to an external electronic device. A suitable housing 40 comprises a cylindrical metal housing 42 as shown in
In one version, the rechargeable battery module 20 is designed and shaped to replace currently used zinc-air batteries and to provide an operating voltage of about 1.3 V. In this version, the voltage provided by the thin film rechargeable battery 26 has to be stepped down to convert the voltage to value from 4.2 volts to 1.3 volts. This would allow for the direct replacement of non-rechargeable batteries currently used in hearing aids with such battery modules 20. The battery modules 20 can then be inductively recharged without requiring their frequent removal from the hearing aid.
Embodiments of a hearing aid 92 comprising a rechargeable battery module 20 is shown in
The signal processor 100 receives the signal from the microphone 98 and outputs a modified electrical signal to power the speaker 102. The signal processor 100 typically comprises an amplifier to receive an electrical signal from the microphone 98 and output a modified electrical signal. The amplifier is coupled to a computer chip comprising operable analytical code to control the amplifier. The signal processor 100 amplifies components of the signal and can selectively amplify certain frequencies or ranges of frequencies. In several versions the signal processor 100 can be adjusted to selectively amplify certain frequencies or ranges of frequencies that correspond to the individual impairment of the wearer. The signal output of the signal processor 100 is connected to the input of the speaker 102.
The speaker 102 outputs a modified sound signal to the ear of the wearer. The speaker 102 receives the modified electrical signal from the signal processor 100 and outputs a sound signal.
The casing 94 provides a protective enclosure and mounting structure for the components of the hearing aid 92. The shape of the casing 94 is determined depending on the type of hearing aid and requirements of the wearer. For example, the casing 94 can comprise a flat rectangular casing 94a as in for “behind-the-ear” (BTE) hearing aids 92a, as shown for example in
While illustrative embodiments of the rechargeable battery module 20 are described in the present application, it should be understood that other embodiments are also possible. For example, alternative thin film battery designs and configurations can be used within the rechargeable battery module 20. Also, the rechargeable battery module 20 can be packaged with an electronic device to save space while still providing a hermetic seal around the battery. Thus, the scope of the claims should not be limited to the illustrative embodiments described herein.
