Precision micro-hole for extended life batteries
Various embodiments of the invention provide an enclosure for a metal-air battery assembly for an extended wear hearing aid. The enclosure includes a diffusion control element having a dimensional property configured for controlling oxygen and moisture diffusion into the metal-air battery assembly to maintain a minimum battery voltage when the hearing aid is operating and worn in an ear canal of a user over an extended period. In an embodiment, the enclosure can comprise a shell with a base end having an opening therein forming a cavity within the shell and a base cap for covering the opening of the base end. A diffusion element is disposed on the base cap. In an embodiment, the diffusion element comprises a laser drilled precision micro hole having an aspect ratio of least about four and a diameter in the range of about 10 to 15 microns.
1. A metal-air battery for an extended wear hearing aid, the battery comprising:
an air cathode assembly;
an anode assembly coupled to the air cathode assembly; and
an enclosure enclosing the air cathode assembly and anode assembly, the enclosure including a diffusion control element having a dimensional property configured for controlling oxygen and moisture diffusion into the metal-air battery to maintain a minimum battery voltage when the hearing aid is operating and worn in an ear canal of a user over an extended period, wherein the enclosure comprises a metal shell having at least one hole and wherein the diffusion control element comprises a polymer layer having a precision micro-hole formed therein and being arranged in series with the hole in the shell to control oxygen and moisture diffusion to the battery.
2. The battery of claim 1 , wherein the shell of the enclosure comprises a base end having an opening therein forming a cavity within the shell and a base cap for covering the opening of the base end.
3. The battery of claim 2 , wherein the at least one hole in the shell is disposed in the base cap and the polymer layer is laminated to the base cap with the micro-hole aligned with the hole in the cap.
4. The battery of claim 1 , wherein the minimum battery voltage is in a range from about 1 volt to 1.3 Volts.
5. The battery of claim 1 , wherein a current drain at which the minimum voltage is maintained is in range from about 40 A to 175 A.
6. The battery of claim 5 , wherein a current drain at which the minimum voltage is maintained is in range from about 40 A to 90 A.
7. The battery of claim 1 , wherein the diffusion control element is configured to control moisture diffusion into the battery to maintain a battery electrolyte concentration within a range sufficient to allow the battery to power the hearing aid.
8. The battery of claim 1 , wherein at least a portion of the micro-hole is curved or non-linear.
9. The battery of claim 1 , wherein the micro-hole is laser drilled.
10. The battery of claim 1 , wherein the micro-hole has a length to diameter ratio such that the gas ingress into the battery is substantially diffusion controlled.
11. The battery of claim 10 , wherein the micro-hole has a length to diameter ratio of at least about 4.
12. The battery of claim 1 , wherein the precision micro-hole in the polymer layer has a diameter not greater than about 15 microns.
13. The battery of claim 1 , wherein the polymer layer has a plurality of precision micro-holes.
14. The battery of claim 1 , wherein the polymer layer and the metal shell comprise a metallized polymer.