Patent Application
20170301895
The present embodiments relate to thin film encapsulation (TFE) technology used to protect active devices and, more particularly, to an energy storage device with an anchored encapsulant.
Thin film encapsulation (TFE) technology is often employed in devices where the devices are purely 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 the device operation, these 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 charge carriers.
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 (assuming 100% dense Li), 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, though such changes are generally smaller as compared to the anode side.
During a battery cell charge and discharge cycle, the encapsulation layer may lift along cell edges due to a combination of laser edge cutting heat affect zone (HAZ) and poor encapsulation layer adhesion along the cell edges. Such cell edge delamination leads to the premature introduction of unwanted moisture and gas penetration, resulting in an adverse impact to the battery cell performance. Furthermore, the encapsulation layer cell edge moisture blocking lateral width design rule is constrained to maximize cell area for higher cell capacity. This leaves minimal cell edge surface area available for lateral encapsulation protection and, as a result, the moisture penetration lateral pathway is short.
With respect to these and other considerations the present disclosure is provided.
In view of the foregoing, approaches herein provide improved encapsulation of an energy storage device. In one approach, a thin film storage device stack is formed atop a first side of a substrate, and an encapsulant is formed over the thin film storage device stack. Prior to formation of the encapsulant, a recess may be formed in the substrate adjacent the thin film storage device stack, wherein the encapsulant extends into the recess. In some approaches, the recess is provided partially through a depth of the substrate, and has a geometry to promote anchoring of the encapsulant therein.
An exemplary energy storage device in accordance with the present disclosure may include a thin film storage device stack formed atop a first side of a substrate, an encapsulant formed over the thin film storage device stack, and a recess formed in the substrate adjacent the thin film storage device stack, wherein the encapsulant extends into the recess.
An exemplary micro battery in accordance with the present disclosure may include a thin film storage device stack formed atop an upper surface of a substrate, and a thin film encapsulant formed over the substrate, wherein the thin film encapsulant adheres to exposed surfaces of the thin film storage device stack and to the upper surface of the substrate. The micro battery further includes a recess formed in the substrate adjacent the thin film storage device stack, wherein the thin film encapsulant is secured within the recess.
An exemplary method for forming a micro battery cell in accordance with the present disclosure may include providing a thin film storage device stack atop a first side of a substrate, providing a recess in the substrate adjacent the thin film storage device stack, and forming a thin film encapsulant over the thin film storage device stack, wherein the thin film encapsulant is formed within the recess formed in the substrate.
The accompanying drawings illustrate exemplary approaches of the disclosed embodiments so far devised for the practical application of the principles thereof, and 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 micro battery 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,” “an embodiment,” or “exemplary embodiment” of the present disclosure are not intended as limiting. Additional embodiments may also incorporate the recited features.
As further described herein, the present disclosure provides techniques for anchoring one or more encapsulation layers around an active region of a micro battery cell by first introducing a cell edge substrate trench or recess prior to starting the encapsulation process. The trench or recess may be a continuous feature or plurality of repeating features provided around the battery cell edge, and can be tailored by design depending on a cell active area (e.g., cell capacity) to actual area utilization ratio trade off. The trench or repeating feature edge(s) can be sharp or sloped depending on a sidewall coating ability of the encapsulant. An optional adhesion promoter substrate surface treatment may be implemented to further enhance the adhesion of the substrate surface to the encapsulant. The encapsulant may be coated and anchored within the recesses to enhance edge adhesion and minimize edge delamination. Furthermore, the cell edge substrate trench or recess provides longer moisture penetration pathway(s) via the encapsulant to help keep moisture from reaching the active region of a micro battery cell, thus improving the battery cell cycle life and charge retention.
Turning now to
The substrate 112 serves as a support for an energy storage device, such as a thin film solid state micro battery, and is made from a material suitably impermeable to environmental elements, has a relatively smooth processing surface to form thin films thereupon. The substrate 112 may also have sufficient 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, such as, for example, aluminum oxide, silicate glass, or even aluminum or steel, depending on the application.
In one embodiment, the substrate 112 comprises mica, a layered silicate typically 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.
As further shown in
The thin film storage device stack 130 may encompass the substrate 112 and a source region disposed on the substrate 112. In various embodiments, the source region may represent a cathode of the thin film storage device stack 130, wherein the source region acts 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 storage device stack 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, for example, of the thin film storage device stack 130. In some embodiments, the thin films of each layer of the thin film storage device stack 130 may be formed by thin film fabrication processes, such as for example, 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 storage device stack 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 approximately 5 microns. The electrolyte thickness is suitably large to provide sufficient 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 storage device stack 130 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 approximately 50 microns.
The thin film storage device stack 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 storage device stack 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, AlOx, having a stoichiometry of A2O3.
Turning to
In various embodiments, the encapsulant 140 is a thin film encapsulant including pliable, physical volume accommodating layers capable of conforming to the geometries of the micro battery cell 100, including the recess 102. In one embodiment, the encapsulant 140 may be made from a polymer material having good sealing properties to protect the sensitive battery components of the thin film storage device stack 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 a sufficiently low water permeability rate to allow the layers of the thin film storage device stack 130 to survive in humid external environments.
In exemplary embodiments, the encapsulant 140 may include parylene, dip or spin coated polymers or dielectric materials, sprayed on polymers or dielectric coatings, or CVD dielectric coatings. In one embodiment, the encapsulant 140 may be a dyadic thin film encapsulant, wherein the dyad may include polymer and dielectric, or polymer and metal layers. The encapsulant 140 may be formed using a vapor or a liquid phase coating technique to allow the encapsulant 140 to form within each of the recesses 102. This has the advantage of using the inherent cohesive strength of the encapsulant 140 to hold the encapsulant 140 in place within the recesses 102 should the thin film storage device stack 130 swell, for example, when charged.
In various embodiments, the encapsulant 140 may have a varied dimension 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 storage device stack 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 storage device stack 130.
In other embodiments, the encapsulant 140 may be a thermoset or thermoplastic polymer capable of 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 melt processable thermoplastic polymer (e.g., a polymer formed when in a melted or viscous phase) malleable at high temperatures. The thermoplastic polymer is selected to soften at temperatures of from approximately 65° C. to approximately 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
The first layer 241 of the encapsulant 240 may be a polymer having good sealing properties to protect the sensitive battery components of the thin film storage device stack 230 from the external environment. In various embodiments, the first layer 241 of the encapsulant 240 may be sprayed on or spin coated polymers and/or dielectric coatings, or CVD dielectric coatings.
As shown in
In various embodiments, the second layer 243 of the encapsulant 240 may include parylene, dip coated or spin coated polymers or dielectric materials, sprayed on 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 form the second layer 243 of the encapsulant within the recesses 202. 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 within the recesses 202 should the thin film storage device stack 230 expand. In various embodiments, the first layer 241 and the second layer 243 of the encapsulant 240 may be different or the same material(s).
Turning now to
As further shown, the anchoring recesses 302 are joined together by a trench 303 formed partially through the substrate 312. In various embodiments, the trench 303 may have a different shape, and/or extend to a different depth, than the plurality of anchoring recesses 302. For example, the plurality of anchoring recesses 302 may extend fully through the substrate 312, yet the trench 303 is formed just partially into the substrate 312. The trench 303 may provide further anchoring of an encapsulant formed over the thin film storage device stack 330, as well as a continuous path around the thin film storage device stack 330 for oxidant/moisture permeation.
In the embodiment shown in
In the embodiment shown in
Turning now to
In the embodiment demonstrated in
In view of the foregoing, at least the following advantages are achieved by the embodiments disclosed herein. A first advantage is the reduction of encapsulant delamination responsible for the premature introduction of unwanted moisture and gas penetration using a set of encapsulant anchoring recesses. 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. A third advantage includes providing an extended lateral moisture penetration pathway via the trench or recesses for improving the battery cell cycle life and charge retention. A fourth advantage includes an increased edge contact surface area using the trench or recesses, further aiding to adhesion of the encapsulant.
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 No. 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 |
