WO2010035197A1

WO2010035197A1 - Flexible all solid state battery with enhanced deposition freedom

Info

Publication number: WO2010035197A1
Application number: PCT/IB2009/054105
Authority: WO
Inventors: Rogier Adrianus Henrica Niessen; Petrus Henricus Laurentius Notten; Ronald Dekker
Original assignee: Koninklijke Philips Electronics, N.V.; U.S. Philips Corporation
Priority date: 2008-09-26
Filing date: 2009-09-18
Publication date: 2010-04-01
Also published as: TW201031042A

Abstract

A flexible battery and method for fabricating a flexible battery includes forming (602) at least one battery stack layer on a stop layer (604) formed on a first substrate. The first substrate is capable of withstanding processing temperatures above 400 degrees C. The at least one battery stack layer is transferred (606) to a flexible substrate by a substrate transfer process. The first substrate is removed (610) down to the stop layer.

Description

FLEXIBLE ALL SOLID STATE BATTERY WITH ENHANCED DEPOSITION FREEDOM

This application claims priority to Provisional Application Serial No. 61/100,282, filed on September 26, 2008, incorporated herein by reference in its entirety.

Related applications are EP08105538.6 (Sputter Deposition of Multilayers in 3D for Example for All Solid State Batteries), filed October 9, 2008 by NXP B. V., EP08165425.3 (Ultra-Flexible All Solid State Batteries), filed September 29, 2008 by NXP B. V. and IB2007/053312 (WO2008023322A2, Electrochemical Energy Source, and Method for Manufacturing of such an Electrochemical Energy Source) , filed August 20, 2007 by Koninklijke Philips Electronics N.V.

This disclosure relates to solid state batteries and, more particularly, to methods for fabricating batteries with deposited materials and batteries so made.

Presently, planar thin film all solid-state batteries are being developed by a number of companies and institutes. These generally utilize rigid and thick substrates like glass or mica. In order to enlarge the applicability of these planar systems, thin film batteries are now deposited onto thick (somewhat) flexible substrates such as polyimide, Kapton™, PEEK™, and other polymers. This provides the thin film batteries with a certain degree of flexibility (e.g., the ability to flex).

Future small-scale electronic devices and applications will employ many types of (integrated) power sources. Currently, 3D integrated all-solid-state rechargeable batteries are being developed. Novel concepts (3D integration) of all-solid-state rechargeable thin film Li- ion batteries were previously described in commonly assigned patent publications WO2005/O27245A2 and US Publication No. 2008/0148555A1 to F. Roozeboom et al, both incorporated herein by reference. These state-of-the-art power sources can be advantageously used in many applications ranging from medical implantables (brain/nerve/muscle stimulation, implantable drug delivery) , (bio) sensors and autonomous devices (networked sensor nodes) .

Presently known (somewhat) bendable thin film solid- state batteries employ rather thick polymer substrates such as polyimide, Kapton™ or PEEK™. However, this limits the maximum processing temperature to about 350 - 400 ⁰C. Additionally, in known thin film battery manufacturing, a fixed deposition order exists that is based on the chemical compatibility of the actual battery materials used (e.g., current collectors, anode, electrolyte, cathode, packaging) . This order is either: i) substrate, cathode current collector, cathode, electrolyte, anode, anode current collector; or ii) substrate, anode current collector, anode, electrolyte, cathode, cathode current collector. This order results in a low degree of freedom with respect to the variety of materials that can be employed in the complete processing scheme of thin film batteries. Moreover, the substrates generally used are quite thick (e.g., > 100 um) and are therefore merely considered (somewhat) bendable and certainly not fully flexible or foldable .

The present invention described herein aims to solve at least the above mentioned problems. One way to solve the drawbacks of the prior art is by using a substrate transfer step at a certain point in the complete manufacturing process of a thin film solid-state battery. The battery structure may be advantageously designed to accommodate such a step. The process itself also permits the manufacture of new and highly desirable battery structures.

In accordance with the present principles, a maximum processing temperature of the actual battery stack is decoupled from that of the final substrate to which the structure (battery) is transferred. This means that the maximum processing temperature is limited only by the initial substrate used and can thus be well over 800⁰C in the case of, e.g., quartz. This additional freedom in the temperature budget results in a wider range of material selection and thus superior battery performance, as compared to prior art deposition on a polymer substrate. In addition, fully flexible solid-state batteries are obtained.

As a structure (the battery) can be transferred to a second substrate at any stage in the manufacturing process of the complete thin film battery, a partially formed or deposited battery may be transferred, including, e.g., only the cathode/electrolyte stack, or the anode/electrolyte stack. The result is that the remaining part of the battery can be deposited at a later stage, breaking or altering the generally-used deposition order in thin film battery manufacturing. This additional benefit may be especially advantageous in the optimization of the individual battery layers .

The thickness and material of the substrate to which the structure (the battery) is being transferred can be chosen at will. Very thin foils of polymers (e.g., about 10 microns of polyimide, even less in some cases) can result in fully flexible devices. This lies in the fact that upon applying this flexible second substrate, the rigidity/mechanical stability needed for handling the device (in processing) is still provided by the initial (i.e., the first) substrate.

A method for fabricating a flexible battery includes forming at least one battery stack layer on a first substrate capable of withstanding processing temperatures above 400 degrees Centigrade. The at least one battery stack layer is transferred to a flexible substrate by a substrate transfer process. Another method for fabricating a flexible battery includes forming at least one battery stack layer on a stop layer formed on a first substrate. The first substrate is capable of withstanding processing temperatures above 400 degrees C. The at least one battery stack layer is transferred to a flexible substrate by a substrate transfer process. The first substrate is removed down to the stop layer .

These and other objects, features and advantages of the present disclosure will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings .

This disclosure will present in detail the following description of preferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a solid state battery stack in accordance with one illustrative embodiment;

FIG. 2 is a cross-sectional view of a solid state battery stack fabricated in accordance with a prior art deposition process;

FIG. 3 is a cross-sectional view of a solid state battery stack process using substrate transfer technology (STT) in accordance with one illustrative embodiment;

FIGS. 4A-4G are cross-sectional views showing an illustrative substrate transfer technology (STT) process in accordance with one embodiment;

FIG. 5 is a cross-sectional view of a solid state battery stack process with the ability for processing before the transfer and after the transfer in accordance with one illustrative embodiment; and

FIG. 6 is a block/flow diagram showing a method for fabricating a flexible solid state battery stack using substrate transfer technology (STT) in accordance with one illustrative embodiment.

The present disclosure describes a flexible, all solid state battery and a method of manufacturing a flexible, all solid state battery. All or part of the battery structure is deposited on a substrate with a high maximum processing temperature. After high temperature processing, the battery stack is transferred using substrate transfer technology ("STT") to a substrate (e.g., a flexible substrate) that needs a lower maximum processing temperature. The present principles permit high annealing temperatures to be used on the initial substrate and permit the altering of the deposition order of the individual layers of the battery. A fully shapeable or flexible power source is achieved.

The present embodiments include the manufacturing of a fully flexible all solid-state battery with substantially enhanced deposition freedom. Currently, all-solid-state rechargeable batteries are thoroughly investigated as the future power source for small-scale electronic applications, e.g., implantable devices. Currently, more applications arise where a fully shapable or flexible power source is desired. This is especially advantageous in, e.g., in-vivo applications like cochlear or retinal implants. For this, a substrate transfer step is used to manufacture a fully flexible all solid-state power source.

Moreover, the utilization of this substrate transfer step provides significant advantages over prior art methods of manufacturing flexible solid-state batteries. First, high anneal temperatures can be employed (e.g., greater than 800⁰C or beyond) depending on the actually used initial substrate, which is not possible when using polymer substrates (e.g., maximum temperature is between about 350-400⁰C) . The present methods can be highly beneficial in obtaining the proper crystallographic phases. Secondly, at any stage during the deposition of the battery stack, a substrate transfer step can be utilized. This results in the deposition order of the individual layers of the battery being altered as needed, providing additional freedom in processing of the battery stack.

In one particularly useful embodiment, a silicon substrate is described for a first substrate, and in particular, a silicon on insulator (SOI) substrate is provided. However, it should be understood that other substrate materials may be employed, including but not limited to ceramics, glass, quartz, Gallium Arsenide, Germanium or the like. It should be further understood that the other layers described herein may include other suitable materials not explicitly described herein. Such materials may be selected depending on their performance in a solid-state battery, and their crystallographic phases which depend on anneal temperatures enabled by the initial substrate.

It should be understood that the present invention will be described in terms of batteries; however, the teachings of the present invention are much broader and are applicable to any devices that can benefit from transferring deposited layers from one substrate to another (e.g., electrochromic devices) . Embodiments described herein are preferably located or patterned using lithography etching and hence are located in accordance with the applicable accuracy of the lithographic process selected. It should also be noted that photolithographic processing is preferred but is merely illustrative. Other processing techniques may also be employed.

It should further be understood that the illustrative example of batteries may be adapted to include additional electronic components and supporting layers (e.g., current collector layers, etc.). These components may be formed integrally with the battery or mounted with the battery on a substrate carrier with other components. The elements depicted in the FIGS, may be implemented in various combinations of hardware and provide functions which may be combined in a single element or multiple elements .

Referring now to the drawings in which like numerals represent the same or similar elements and initially to FIG. 1, a battery stack 50 is illustratively shown in accordance with an illustrative embodiment. A first step would be to deposit a bottom current collector stack 52 comprising a multi-laminate of, e.g., SiO₂/TiO₂/Ti/Pt . Hereafter, a cathode 54, solid electrolyte 56, anode 58 (plus current collector 60) and a capping layer 62 can then be deposited in succession. In this multi-laminate, a Siθ2/TiU2 layer 67 of stack 52 can be very effectively used as an etch stop, which is employed to protect a layer 66 during back-etching/grinding of the silicon substrate 64. In a back-etch of an initial silicon substrate 64, Ti/Pt layer 66 remains in the cathode current collector stack 52 and acts as the actual cathode current collector for the battery, which will be formed. As long as a proper etch- stop or cleave layer is provided for the base substrate 64 for processing of the full solid-state battery, a transfer step disclosed herein can be utilized.

Aside from the final product being fully flexible in case the battery has been transferred to a thin polyimide or the like (for example, a parylene polymer may be employed, which is also biocompatible) substrate and the fact that processing of the battery itself is done on a highly temperature resistant substrate, substantial additional freedom with respect to the maximum processing temperature is provided.

Referring to FIG. 2, a prior art example is shown of a planar thin film battery 80 deposited onto a polyimide substrate. The battery includes a polyimide initial substrate 88 onto which an anode is deposited followed by, in succession, an electrolyte layer 84 and a cathode layer 82. The anode layer 86 and the cathode layer 82 may be switched. As the maximum processing temperature in this case is only 350 - 400⁰C, the active materials in the battery have to be chosen carefully and within a small and confined group. One can in fact only use low-temperature electrode materials, such as vanadium oxides, tungsten oxides, or molybdenum oxides and low-temperature (or room temperature deposited) solid electrolytes like LIPON, which is a known material. In the prior art, batteries are known to comprise a V₂O₅ cathode 82, LIPON electrolyte 84 and a Li₈V₂O₅ anode 86. Manufacturing of these types of batteries is difficult as the anode 86 needs to be lithiated prior to the electrolyte deposition of layer 84, which is a difficult step involving evaporation and subsequent solid-state reaction of metallic lithium. Even in the reversed stack, where the anode is deposited last, lithiation via, e.g., evaporation of metallic lithium is very sensitive.

In another prior art example (not shown here) , a battery comprises a LIi_-3V₂O₅ cathode and LIPON electrolyte, and the anode is in-situ plated onto a current collector. Again, lithiation needs to be performed which is highly impractical. Moreover and more importantly, all active layers remain amorphous, due to the low maximum processing temperature. This results in a battery stack that can only be effectively utilized at a (very) low discharge rate.

Referring to FIG. 3, processing steps for a thin film battery 100 are shown. A substrate transfer technology (STT) 101 is employed in accordance with the present principles. As an initial substrate 102 is capable of withstanding high temperatures, e.g., silicon, the maximum processing temperature is substantially higher (> 800 ⁰C) . As a result, electrochemically superior cathode materials can be chosen for a cathode 104, such as, e.g., a LiCoO₂. To crystallize this cathode a temperature of 600 - 800 ⁰C is needed. Additionally, high(er) temperature electrolytes and anodes can be utilized for an electrolyte layer 106 and anode 108. For example, a Garnet-structure solid electrolyte including (but not limited to) Li₅La₃M₂Oi₂ (M = Nb, Ta, Bi) and Li₆ALa₂M₂Oi₂ (A = Ca, Sr, Ba; M= Nb, Ta, Bi) (600-800 ⁰C) and a Li₄Ti₅Oi₂ anode (500-600 ⁰C) may be employed. Improved performance is achieved by achieving crystalline forms of these materials. Other materials for the battery stack layers and the initial substrate are also contemplated.

After full processing the complete battery stack can be transferred onto a flexible substrate 110, e.g., a polyimide substrate, that permits 350 - 400 ⁰C for additional post-processing. This makes these batteries inherently stable under all solder-reflow processes. The flexible substrate 110 may have dimensions (e.g., 10 microns or less, although larger dimensions are contemplated as well) to permit the battery 100 to be flexible and even bendable, in addition to providing superior performance due to enhanced material selection and material phase (e.g., crystal structure) .

A solid-state battery stack 100 is manufactured on a flexible substrate using novel manufacturing methods, e.g., using Substrate Transfer Technology (STT) 101. In this case, larger freedom in the temperature budget is achieved and highly crystalline active materials can be employed, giving superior battery performance. Note that FIG. 3 selectively omits less important layers of the battery structure for simplicity. The STT process 101 provides advantages over the prior art manufacturing techniques which directly deposit the battery stack onto a polyimide substrate.

Referring to FIGS. 4A-4G, a process-flow of an illustrative substrate transfer technology (STT) process is shown in accordance with one embodiment. It should be understood that other process steps and process components (e.g., layers, etc.) may be employed to achieve the STT process. Using STT, a battery 412, which is originally processed onto a silicon oxide layer 414 of a SOI substrate 416, can be transferred to another substrate of choice. The battery 412 as represented in FIGS. 4A-4G may be a stack of layers that are to be transferred from a first substrate 416 to a second substrate 418. When a very thin and flexible polymer (418), like polyimide, etc., is used in this transfer, the resulting battery 412 is highly flexible.

A SOI substrate includes a SiO₂ layer or other etch stop layer 414 thereon, and battery 412 is formed thereon in FIG. 4A. In FIG. 4B, a polyimide or other flexible layer 418 is applied and removed from wafer edges (see FIG. 4D) . In FIG. 4C, a plasma enhanced chemical vapor deposition (PECVD) process forms a separator oxide 420 over the edges and polyimide 418. Other layers and processes may also be employed. In FIG. 4D, a primer solution 422 is applied to wafer edges to provide adhesion for transference of the battery 412 to another substrate.

In FIG. 4E, the separator oxide 420 is adhered to a glass carrier 426 using an adhesive layer 424. The silicon substrate 416 is removed from the assembly, by e.g., grinding, cleaving, wet etching and/or dry etching (like reactive ion etching, sputter etching) stopping in layer 414. The battery

412 along with the polyimide 418 and separator oxide 420 are lifted from the glass carrier 426. The glass carrier 426 is then recycled and employed again.

It should be noted that, for the present invention, a base substrate does not have to be a Silicon-On-Insulator

(SOI) wafer. The high cost of SOI substrate wafers makes this type of substrate less desirable, although still useable in accordance with the present invention. A desirable attribute of the present invention is that essentially any substrate can be used as long as a proper etch-stop or other stop layer

(polish stop, cleave layer, etc.), equivalent to the SiO₂ layer 414 in the SOI wafer 416, is provided during the course of manufacturing of the complete battery device. (The layer should, however, be preferably placed between the substrate 416 and actual battery stack 412) . For example, one may start processing the battery on top of a standard silicon (monitor) wafer, which is rather inexpensive.

Referring to FIG. 5, another process sequence is shown for employing a second flexible substrate in accordance with the present principles. Transfer to a second (flexible) substrate 510 provides additional advantages. For example, a battery can be transferred after only part of the battery has been deposited. Instead of adhering to a standard deposition order (cathode current collector, cathode, electrolyte, anode and anode current collector) , a solid electrolyte 506 has been deposited directly onto an initial substrate 502, followed by an anode 508 and an anode current collector (not shown) . After transferring a partial battery stack by substrate transfer 520 to a flexible substrate 510, a cathode 512 and a cathode current collector (not shown) can easily be deposited. In this way, more processing freedom is provided and a beneficial process is provided when trying to engineer/optimize individual active layers of the battery stack.

The transfer of a partial battery stack

(electrolyte/anode part) from a rigid, thick substrate (e.g., silicon) to a flexible substrate 510 (e.g., polyimide) provides processing on top of the electrolyte layer 506. The cathode 512 is deposited last, which completes the full stack. Note that for the sake of clarity only selected layers are shown .

The disclosed concept can be advantageously used in planar 2D integrated all-solid-state rechargeable batteries, as well as in 3D integrated all-solid-state rechargeable batteries and non-rechargeable (primary) batteries. Additionally, it can be utilized for the manufacturing of electronic devices. The present embodiments disclose the manufacturing of a fully flexible thin film solid-state battery. This improved (integrated) power source can be advantageously used in small high power electronics applications. The list of possible uses includes, among others, implantables, hearing aids, autonomous network device, and nerve and muscle stimulation devices and others.

Referring to FIG. 6, a method for fabricating a flexible solid-state battery is illustratively shown in accordance with one embodiment. In block 602, at least one battery stack layer is formed on a first or initial substrate. In one embodiment, the battery stack layer includes a first electrode layer, an electrolyte layer and perhaps a second electrode layer formed on an initial substrate capable of withstanding processing temperatures above 400 degrees Centigrade (C) . The processing temperatures may include deposition temperatures, anneal temperatures, cure temperatures, etc. The temperature may advantageously be greater than 400 degrees C, and may be more 600 degrees C or even more than 800 degrees C.

The first electrode layer may include a cathode layer or an anode layer. In one embodiment, the battery stack layer may include an anode comprising Li₄Ti₅Oi₂, a cathode comprising LiCoO₂ and an electrolyte comprising Li₅La₂Ta₃Oi₂. These materials (or other materials) preferably form a crystalline phase since a much greater thermal budget is available .

Other layers may be included or substituted, e.g., a cathode and an electrolyte layer may be included or an anode and electrolyte layer may be included. Such layers may include supporting layers and, in particular cathode, and/or anode collecting layers may be included. In a particularly useful embodiment, an etch stop layer is provided between the initial substrate and the battery stack in block 604.

In block 606, the battery stack layer (e.g., the first electrode layer and the electrolyte layer) is transferred to a flexible substrate by a substrate transfer process. This includes adhering the battery stack to a flexible substrate or depositing the flexible substrate on the battery stack in block 608.

The initial substrate is removed in block 610. This may include at least one of wet etching, dry etching, grinding, polishing and cleaving the initial substrate down to the etch stop layer. Post processing may be performed on the flexible battery in block 612. This may include depositing additional layers (e.g., anode or cathode on the battery stack), shaping operations, etching, etc.

In interpreting the appended claims, it should be understood that: a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; c) any reference signs in the claims do not limit their scope; d) several "means" may be represented by the same item or hardware or software implemented structure or function; and e) no specific sequence of acts is intended to be required unless specifically indicated.

Having described preferred embodiments (which are intended to be illustrative and not limiting) , it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the disclosure disclosed which are within the scope and spirit of the embodiments disclosed herein as outlined by the appended claims. Having thus described the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.

Claims

CLAIMS :

1. A method for fabricating a flexible battery, comprising: forming (602) at least one battery stack layer on a stop layer (604) formed on a first substrate, the first substrate being capable of withstanding processing temperatures above 400 degrees C; transferring (606) the at least one battery stack layer to a flexible substrate by a substrate transfer process; and removing (610) the first substrate from the stop layer .

2. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming the at least one battery stack layer at a temperature above 400 degrees C.

3. The method as recited in claim 2, wherein the temperature is above 600 degrees C.

4. The method as recited in claim 1, wherein the forming (602) at least one battery stack layer includes forming at least one of a cathode layer, an electrolyte layer and an anode layer on the stop layer.

5. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming an electrolyte layer and a cathode layer and transferring includes transferring (606) the electrolyte layer and the cathode layer to the flexible substrate.

6. The method as recited in claim 5, further comprising depositing (612) an anode on the electrolyte layer.

7. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming an electrolyte layer and an anode layer and transferring includes transferring (606) the electrolyte layer and the anode layer to the flexible substrate.

8. The method as recited in claim 7, further comprising depositing (612) a cathode on the electrolyte layer .

9. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming a crystalline phase in at least one of an electrolyte layer, an anode layer and a cathode layer.

10. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming an anode comprising Li₄Ti5θi₂.

11. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming a cathode comprising LiCoC>2.

12. The method as recited in claim 1, wherein forming (602) at least one battery stack layer includes forming an electrolyte comprising a Garnet-structured solid electrolyte including at least one of Li₅La₃M₂Oi₂ (M = Nb, Ta, Bi) and Li₆ALa₂M₂Oi₂ (A = Ca, Sr, Ba; M= Nb, Ta, Bi) .

13. The method as recited in claim 1, wherein the flexible substrate includes one of polyimide and parylene material having a thickness of 10 microns or less.

14. A method for fabricating a flexible solid-state battery, comprising: forming (602) a battery stack having a first electrode layer and an electrolyte layer on a stop layer (604) of an initial substrate, the initial substrate capable of withstanding processing temperatures above 400 degrees C; processing (602) the battery stack at a temperature in excess of 400 degrees C; transferring (606) the first electrode layer and an electrolyte layer to a flexible substrate by a substrate transfer process; and removing (610) the initial substrate down to the stop layer.

15. The method as recited in claim 14, wherein forming (602) includes forming one of the first electrode layer and the electrolyte layer at a temperature above 400 degrees C.

16. The method as recited in claim 15, wherein the temperature is above 600 degrees C.

17. The method as recited in claim 14, wherein the first electrode layer includes one of a cathode layer and an anode layer.

18. The method as recited in claim 14, wherein forming (602) includes forming a crystalline phase in at least one of the electrolyte layer and the first electrode layer.

19. The method as recited in claim 14, wherein the first electrode layer includes an anode comprising Li₄Ti₅Oi₂.

20. The method as recited in claim 14, wherein the first electrode layer includes a cathode comprising LiCoO₂.

21. The method as recited in claim 14, wherein forming includes forming an electrolyte comprising a Garnet- structured solid electrolyte including at least one of Li₅La₃M₂Oi₂ (M = Nb, Ta, Bi) and Li₆ALa₂M₂Oi₂ (A = Ca, Sr, Ba; M= Nb, Ta, Bi) .

22. The method as recited in claim 14, wherein removing (610) the initial substrate includes at least one of wet etching, dry etching, polishing and cleaving.

23. The method as recited in claim 14, wherein the stop layer includes an etch stop layer, and removing (610) the initial substrate includes etching the initial substrate to the etch stop layer.

24. A flexible battery, comprising: a battery stack (100) including at least one layer formed by processing temperatures above 400 degrees C; a flexible substrate (110) adhered to the battery stack.

25. The flexible battery as recited in claim 24, wherein the battery stack layer includes at least one of a cathode layer (104), an electrolyte layer (106) and an anode layer (108) .

26. The flexible battery as recited in claim 25, wherein the battery stack layer includes a crystalline phase in the at least one of an electrolyte layer (106), an anode layer (108) and a cathode layer (104) .

27. The flexible battery as recited in claim 24, wherein the battery stack layer includes an anode (108) comprising Li₄Ti₅Oi₂.

28. The flexible battery as recited in claim 24, wherein the battery stack layer includes a cathode (104) comprising LiCoO₂.

29. The flexible battery as recited in claim 24, wherein the battery stack layer includes an electrolyte (106) comprising a Garnet-structured solid electrolyte including at least one of Li₅La₃M₂Oi₂ (M = Nb, Ta, Bi) and Li₆ALa₂M₂Oi₂ (A = Ca, Sr, Ba; M= Nb, Ta, Bi) .

30. The flexible battery as recited in claim 24, wherein the flexible substrate (110) includes one of polyimide and parylene material having a thickness of 10 microns or less .