Patent Application
20170301893
The present embodiments relate to thin film encapsulation (TFE) technology used to protect active devices and, more particularly, to an energy storage device with a wraparound encapsulant.
Thin film encapsulation (TFE) technology is often employed in devices where the devices are primarily electrical devices or electro-optical devices, such as Organic Light Emitting Diodes (OLED). Other than possibly experiencing a generally small global thermal expansion from heat generation during device operation, the electrical devices and electro-optical devices do not exhibit volume changes during operation since just electrons and photons are transported within the devices during operation. Such global effects due to global thermal expansion of a device may affect in a similar fashion every component of a given device including the TFE, and thus, may not lead to significant internal stress. In this manner, the functionality of the TFE in a purely electrical device or electro-optic device is not generally susceptible to stresses from non-uniform expansion during operation.
Notably, in an electrochemical device (“chemical” portion), matter such as elements, ions, or other chemical species having a physical volume (the physical volume of electrons may be considered to be approximately zero) are transported within the device during operation with physical volume move. For known electrochemical devices, e.g., thin film batteries (TFB) based upon lithium (Li), Li is transported from one side to the other side of a battery as electrons are transported in an external circuit connected to the TFB, where the electrons move in an opposite direction to the chemical and elements. One particular example of the volume change experienced by a Li TFB occurs when charging a thin film battery having a lithium cobalt oxide (LiCoO2) cathode (˜15 μm to 17 μm thick LiCoO2). An amount of Li equivalent to several micrometers thick layer, such as 6 micrometers, may be transported to the anode when loading is approximately 1 mAhr/cm2. When Li returns to the cathode side in a discharge process, a comparable volume reduction may result on the anode side (assuming 100% efficiency). The cathode side may also undergo a volume change in an opposite manner, although such changes are generally smaller as compared to the anode side.
As such, known TFE approaches are lacking the ability to accommodate such volume change in a robust manner, to ensure the TFE continues to provide protection of the electrochemical device during repeated cycling of the device.
With respect to these and other considerations the present disclosure is provided.
In view of the foregoing, approaches herein provide encapsulation of a micro battery cell of a cell matrix. The micro battery cell includes an active device (e.g., a thin film energy storage device) formed atop a first side of a substrate, and an encapsulant formed over the active device, wherein the encapsulant adheres to the active device and to a second side of the substrate. In some approaches, the encapsulant penetrates a plurality of openings provided through the substrate, thus allowing the encapsulant to form along the second side of the substrate to fully envelope and seal the micro battery cell.
An exemplary energy storage device in accordance with the present disclosure may include a thin film device formed on a first side of a substrate, and an encapsulant formed over the thin film device, wherein the encapsulant covers the thin film device and a second side of the substrate.
An exemplary micro battery cell in accordance with the present disclosure may include an active device coupled to a first side of a substrate, and an encapsulant formed over the active device, wherein the encapsulant adheres to the active device and to a second side of the substrate.
An exemplary method for forming an energy storage device in accordance with the present disclosure may include providing a thin film device on a first side of a substrate, forming a plurality of openings through the substrate, and forming a thin film encapsulant over the thin film device, wherein the thin film encapsulant is formed along a surface defining one or more of the plurality of openings, and wherein the thin film encapsulant adheres to the thin film device and covers a second side of the substrate.
The accompanying drawings illustrate exemplary approaches of the disclosed embodiments so far devised for the practical application of the principles thereof, wherein:
The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict exemplary embodiments of the disclosure, and therefore are not be considered as limiting in scope. In the drawings, like numbering represents like elements.
Furthermore, certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines otherwise visible in a “true” cross-sectional view, for illustrative clarity. Furthermore, for clarity, some reference numbers may be omitted in certain drawings.
One or more approaches in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, where embodiments of devices and methods are shown. The approaches may be embodied in many different forms and are not to be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so this disclosure will be thorough and complete, and will fully convey the scope of the devices and methods to those skilled in the art.
For the sake of convenience and clarity, terms such as “top,” “bottom,” “upper,” “lower,” “vertical,” “horizontal,” “lateral,” and “longitudinal” will be used herein to describe the relative placement and orientation of these components and their constituent parts, each with respect to the geometry and orientation of the energy storage device as appearing in the figures. The terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.
As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” is to be understood as including plural elements or operations, until such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended as limiting. Additional embodiments may also incorporating the recited features.
As further described herein, the present disclosure relates to thin film encapsulation (TFE) technology used to minimize ambient exposure of active devices, for example, during the fabrication and manufacturing of thin film solid state batteries (TFB) using a maskless patterning process. By improving robustness of the encapsulant(s) battery cell, volume expansion caused by moisture contamination may be mitigated. Specifically, provided herein is a micro battery cell including an active device formed on one or more sides of a substrate. An encapsulant may be formed over the active device, wherein the encapsulant adheres to the active device and to a second side of the substrate. In cases where a second active device is provided on the second side of the substrate, the encapsulant further adheres to and covers the second active device. In some approaches, the encapsulant penetrates a plurality of openings provided through the substrate, thus allowing the encapsulant to extend along the second side of the substrate and fully encapsulate the micro battery cell. As a result, the cohesion force of the wrap around encapsulant may accommodate cell volume expansion and swelling, and may maintain good surface adhesion to other cell stack materials. In some approaches, a vapor or a liquid phase coating technique may be used to form the wraparound encapsulant.
Turning now to
As shown, a plurality of openings 120 may be formed through the substrate 112, for example, along an outer perimeter of the micro battery cell 100 as delineated by broken lines 122, 123, 124, and 125. As will be described in greater detail below, the plurality of openings 120 allow a subsequently formed encapsulant to penetrate through the substrate 112 and wrap along a second side 126 (e.g., a bottom surface) of the substrate 112. In some embodiments, each of the openings 120 has a generally rectangular shape, and extends just partially along the perimeter of the micro battery cell 100 so as to leave remaining a plurality of corner sections 128 for structural support of the substrate 112. The plurality of corner sections 128 hold the micro battery cell 100 in place in the matrix 110, and may later be severed, thus allowing a thin-film storage device of the micro battery cell 100 to be excised.
In some embodiments, the substrate 112 serves as a support for an energy storage device, such as a thin film battery, and is made from a material suitably impermeable to environmental elements. The substrate 112 has a relatively smooth processing surface for forming thin films thereupon, and also has adequate mechanical strength to support the deposited thin films at fabrication temperatures and at battery operational temperatures. For example, the substrate 112 may be an insulator, semiconductor, or a conductor, depending upon the intended electrical properties of the exterior surfaces. More specifically, the substrate 112 may be made from a ceramic, metal, or glass, for example, aluminum oxide, silicate glass, or even aluminum or steel, depending on the application.
In one embodiment, the substrate 112 may include mica, a layered silicate having a muscovite structure and a stoichiometry of KAl3Si3O10(OH)2. Mica has a six-sided planar monoclinic crystalline structure with good cleavage properties along the direction of the large planar surfaces. Because of the crystal structure of mica, the substrate 112 may be split into thin foils along its basal lateral cleavage planes to provide thin substrates having surfaces smoother than most chemically or mechanically polished surfaces.
Turning now to
In some embodiments, the thin film device 130 may include the substrate 112 and a source region disposed on the substrate 102. The source region may represent a cathode of the thin film device 130, wherein the source region may act as a source of a diffusant such as lithium, and wherein the diffusant may reversibly diffuse to and from the source region. The thin film device 130 may also include an intermediate region (not specifically shown) disposed on the source region, and a selective expansion region disposed on the intermediate region. The selective expansion region may be an anode region of the thin film device 130. In some embodiments, the thin films of each layer of the thin film device 130 may be formed by thin film fabrication processes, such as physical or chemical vapor deposition methods (PVD or CVD), oxidation, nitridation or electro-plating.
Although not shown, in some embodiments, an electrolyte layer may be provided between the anode and the cathode of the thin film device 130. In some embodiments, the electrolyte layer may be, for example, an amorphous lithium phosphorus oxynitride film, referred to as a LiPON film. In one non-limiting embodiment, the LiPON film is of the form LixPOyNz. In one approach, the electrolyte layer has a thickness of from approximately 0.1 microns to 5 microns. The electrolyte thickness is suitably large to provide adequate protection from shorting of the cathode and the anode, and suitably small to reduce ionic pathways to minimize electrical resistance and reduce stress.
In some embodiments, the anode and the cathode of the thin film device each include an electrochemically active material, such as amorphous vanadium pentoxide V2O5, or one of several crystalline compounds, such as TiS2, LiMnO2, LiMn2O2, LiMn2O4, LiCoO2 and LiNiO2. In one non-limiting embodiment, the anode is made from Li and the cathode is made from LiCoO2. A suitable thickness for the anode or cathode may be from approximately 0.1 microns to 50 microns.
The thin film device 130 may also include one or more adhesion layers (not shown) deposited on the substrate 112 or the surfaces of any of the other layers of the thin film device 130, to improve adhesion of overlying layers. The adhesion layer may comprise a metal such as, for example, titanium, cobalt, aluminum, or other metals. In some embodiments, the adhesion layer may be a ceramic material such as, for example, LiCoOx, having a stoichiometry of LiCoO2.
Turning now to
The encapsulant 140 may be a soft and pliable, physical volume accommodating layer capable of conforming to the geometries of the micro battery cell 100, as well as accommodating volume changes of the layers of the thin film device 130. In one embodiment, the encapsulant 140 is made from a polymer material having good sealing properties to protect the sensitive battery components of the thin film device 130 from the external environment. For example, the polymer material of the encapsulant 140 may be selected to provide a good moisture barrier, and have an adequately low water permeability rate to allow the layers of the thin film device 130 to survive in humid external environments.
In exemplary embodiments, the encapsulant 140 may include a parylene vapor condensation coating applied simultaneously to the first and second sides 132, 126 of the substrate 112. Alternatively, the encapsulant may include dip coated polymers or dielectric materials applied simultaneously to the first and second sides 132, 126 of the substrate 112, sprayed on or powder coated polymers or dielectric coatings, or CVD dielectric coatings. The encapsulant 140 may be formed using a vapor or a liquid phase coating technique to provide the intended wraparound encapsulation. This has the advantage of using the inherent cohesive strength of the encapsulant 140 to hold the encapsulant 140 in place when the thin film device 130 swells, for example, when charged.
In various embodiments, the encapsulant 140 may have varied dimensions in order to accommodate changes in volume or thickness of different materials in expansion regions. For example, in the case the anode or a portion of the anode of the thin film device 130 constitutes a selective expansion region, the encapsulant 140 may expand or contract in thickness to accommodate the increase or decrease in anode thickness, resulting in less stress, less mechanical failure, and better protection of the layers of the thin film device 130.
In other embodiments, the encapsulant 140 may be a thermoset or thermoplastic polymer undergoing a chemical change during processing to become “set” to form a hard solid material. The thermoset polymer can be a highly cross-linked polymer having a three-dimensional network of polymer chains. Thermoset polymer materials undergo a chemical as well as a phase change when heated. Due to their tightly cross-linked structure, thermoset polymers may be less flexible than most thermoplastic polymers.
In still other embodiments, the encapsulant 140 may be a thermoplastic polymer, such as a melt processable material remaining malleable at high temperatures. The thermoplastic polymer is selected to soften at temperatures of from approximately 65° C. to 200° C. to allow molding the polymer material around the battery cell without thermally degrading the battery cell. A suitable thermoplastic polymer includes, for example, polyvinylidene chloride (PVDC).
Turning now to
As shown in
The second layer 243 of the encapsulant 240 may include a parylene polymer layer, dip coated polymers or dielectric layers/materials, sprayed on or powder coated polymers or dielectric coatings, or CVD dielectric coatings. The second layer 243 of the encapsulant 240 may be formed using a vapor or a liquid phase coating technique to provide the intended wraparound encapsulation. This has the advantage of using the inherent cohesive strength of the second layer 243 of the encapsulant 240 to hold the encapsulant 240 in place in the case the thin film device 230 expands. In various embodiments, the first layer 241 and the second layer 243 of the encapsulant 240 may be the same or different materials.
Turning now to
In this embodiment, the thin film device 330 may be formed atop the substrate 312 prior to subsequent formation of a plurality of openings 320 through the substrate 312, as shown in
Turning to
Turning to
In view of the foregoing, at least the following advantages are achieved by the embodiments disclosed herein. A first advantage is the improvement in encapsulation anchoring to the substrate and the reduction of encapsulant delamination responsible for the premature introduction of unwanted moisture and gas penetration to a thin film device contained therein. A second advantage includes the use of the encapsulant's self-cohesive strength to hold the encapsulation film layer(s) in place in the event the micro battery cell stack swells, for example, when charged.
While certain embodiments of the disclosure have been described herein, the disclosure is not limited thereto, as the disclosure is as broad in scope as the art will allow and the specification may be read likewise. Therefore, the above description is not to be construed as limiting. Instead, the above description is merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.
This application claims priority to U.S. provisional patent application 62/322,415, filed Apr. 14, 2016, entitled Volume Change Accommodating TFE Materials, and incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62322415 | Apr 2016 | US |
