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Batteries/Thin Film 070330
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 (March 2007) Oak Ridge Micro-Energy (OKME) finds success in initial development of new low-voltage prototype battery. OKME reported results of a prototype battery that delivers 74% of its capacity between 2 Volts and 1 Volt.
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Patent Number 6,994,933 B1
Long Life Thin Film Battery and Method Therefore
Inventor: Bates
Asignee: Oak Ridge Micro-Energy, Inc.
Summarized by Donald Georgi

This patent relates to extending the life of thin film primary and rechargeable micro-batteries. The method is to add coatings which are both impenetrable to oxygen and water plus other coatings which are sacrificial in that they chemically combine with oxygen and water to form an oxide or hydroxide which limits migration.

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The cross section of a thin film battery shows the cathode 20, and the anode 24 separated by a solid electrolyte 22. The battery is constructed by vacuum deposition methods on an insulating substrate 12, beginning with the cathode current collector 16 and the anode current collector 18. Next, the cathode 20 is deposited and then the solid electrolyte 22, followed by the anode 24. Coatings 28, of parylene and metallization, allowed oxygen and water penetration which limited battery life to 3 months. +

 The thin film battery is structured according to prior art and employs a common solid electrolyte with the sulfide addition described in a previous Oak Ridge Micro-Energy (Stock symbol, OKME) patent # 6,818,356 B1.

If the oxygen and water can be limited, there is a possibility that thin film batteries can suitably perform for 20 years. Based on scientific principles, it has been determined that the maximum oxygen penetration can be no more than 1.6 micromoles/m2 per day and a maximum of 3.3 micromoles/m2 per day of water.

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The central point of this patent is illustrated in this figure with the protective composite planarization layer/barrier layer added to block the penetration of oxygen and water into the battery components. The purpose of blocking external migration is to keep battery materials pure and thus extend life to 20 years. Also shown is another protective layer 44 added for temporary protection and increased conductivity from anode 24 to the anode current collector 18. +

Past patented processes have defined multilayer paralyne and metallization layers without success because of the pin holes and asperities which provide contaminant pathways.

In this patent, the surface conditions are corrected with  a planarization layer made up of a polymeric film with superior flatness which then allows for metallization, ceramic and/or sacrificial layers to be built up over the battery components to seal it from the contaminants. A number of layer possibilities are described and fundamental coating processes are included.

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A schematic cross section of the battery coating shows the anode 24 protected by a first planarization layer of a monomer oligomer. A metal layer 38 adds isolation as does a ceramic layer 40, followed by a final polymeric layer 42. The thickness of these layers is in the range of 20 nanometers to 5 microns. +

Claims

There are four  fundamental claims:  

Claim 1 describes the method for improving the life of a thin film rechargeable with steps of applying the planarization layer over the anode layer followed by coatings of metal, ceramic and polymeric materials. Claims 2-8 expand on the basic concept by defining a lithium or lithium-ion anode. The polarization material can be acrylates, diacrylates, triacylates and polyolefing which do not contain an organic acid. Polarization flatness is less than 0,005 cm/in. Provision for placing a metallization layer on the anode prior to placing the planarization is allowed as long as it does not alloy with the anode. Adding a coating of lithium-phosphorus oxynitride and/or a sacrificial layer of magnesium is provided for.

Claim 9 is similar to claim 1 except that it describes the structure of the rechargeable battery which is placed on a substrate. A  description of the cathode, electrolyte and anode are covered before the layers of planarization and coatings are added. In claims 10-15 identical coatings descriptions to those of  claims 1-8 are restated.

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Although this cross section is similar to figure 3, there is an addition of another protective layer 44 between the anode and the planarization layer. It consists of a metal conductor which does not alloy with the anode, such as nickel. The layer provides additional temporary protection and improves the anode current path to its current collector. +

Claim 16 describes the thin film rechargeable battery improvements consisting of the planarization and other layers, with claims 17-20 listing details of the layers as previously described.

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Building on the structure of Figure 4, two additional layers, 46 and 48 are added on each side of the planarization layer 36. Layer 46 is electrolyte material, not responsible for ionic transfer. There is apparently no explanation of why the layer is included for performance reasons, but it is interesting to note that the layer is mentioned in claims 6, 14,19 and 21. Again in these claims, no purpose is given, but the specifics of the electrolyte are given in claim 21, describing the chemistry as discussed in the prior OKME patent # 6,818,356 B1. Layer 48 is a sacrificial or getter layer made of magnesium, which will react with oxygen to form an oxide or with water to form a hydroxide, to keep oxygen and water from migrating to the battery components. +

Claim 21 specifically identifies the solid electrolyte as the one using the sulfide ion dopant as described in patent 6,818,356 B1.

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Figure 6 is a side view of the coating process equipment, while Figure 7 is the top view. Chambers 62-68 are deposition chambers separated by gate valves which isolate each chamber for its particular process. Chamber 76 is an anode load chamber used to transfer into the polymer coating chamber 64. Chamber 78 is a spin coating or dip coating or spray chamber for alternate processes to apply the  planarization layer. +

Other Applications?

The patent is very specific about applicability to thin-film batteries. (BD note: but is there any part of it which is applicable to other lithium/Lithium-ion chemistries?)     
          BD