Patent Application
20160181615
The present invention relates to solid-state batteries. More particularly, this invention relates to solid-state lithium batteries with electrodes that are infused with an ionically-conductive material and methods for forming such batteries.
In an attempt to be more energy efficient as a society, and accommodate more mobile applications, there is a need for improved power sources, such as batteries. Generally, it is desirable to develop safer batteries (e.g., without any flammable liquid) with higher energy densities, longer cycle life, reduced self-discharge, higher power capability, faster charge/discharge rates, wider operating temperature ranges, and lower manufacturing costs. Ideally, these batteries would also be very small (e.g., thin form factor and be scalable to micron-size) and would be capable of being easily integrated with modern printed circuit boards and integrated circuits.
One possible solution for these batteries is solid-state lithium batteries. However, current implementations of solid-state batteries suffer from low manufacturing yield, high manufacturing costs, and low energy density.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale.
The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims, and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
The term “horizontal” as used herein will be understood to be defined as a plane parallel to the plane or surface of the substrate, regardless of the orientation of the substrate. The term “vertical” will refer to a direction perpendicular to the horizontal as previously defined. Terms such as “above”, “below”, “bottom”, “top”, “side” (e.g. sidewall), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane. The term “on” means there is direct contact between the elements. The term “above” will allow for intervening elements.
In some embodiments, methods are provided for forming solid-state batteries in such a way as to improve performance and/or reduce manufacturing costs. In some embodiments, in order to, for example, increase throughput (i.e., reduce manufacturing time/costs) and increase energy density, the solid-state battery is formed on a thin, conductive substrate, such as aluminum, copper, steel (carbon or stainless), or a cladded foil. A layer stack is formed between the substrate and the cathode current collector. The layer stack includes a diffusion barrier layer and perhaps at least one adhesion layer. The diffusion barrier layer may be made of chromium, molybdenum, a conductive metal nitride, a conductive metal oxynitride, and/or a conductive metal oxide. The adhesion layer may be made of titanium or chromium. In some embodiments, two adhesion layers are included, on opposing sides of the diffusion barrier layer. The cathode current collector may be formed on the upper most layer of the stack.
In some embodiments, in order to, for example, increase the interfacial area between the various components/layers of the battery (e.g., to increase external cell capacity and energy density, as well as provide stress relief to prevent adhesion failure and delamination, at least one of the components/layers (e.g., the substrate and/or any of the layers) is provided with a surface roughness (or topographical roughening). The surface roughness may be provided by performing an etching process (e.g., wet or dry) to the substrate (e.g., metal foil or ceramic) before the other components/layers are formed, or by etching one of the functional layers after it is deposited (e.g., the cathode current collector). In some embodiments, the surface roughness is introduced by including an additional layer in the device, such as a transparent conductive oxide, which may then be etched. In some embodiments, the surface roughness is created by forming one of the layers with particles of various size dispersed therein (e.g., a sol-gel formulation). The surface roughness may also be created on the substrate by forming the substrate via casting/firing (e.g., ceramic substrates, such as aluminum oxide), for example, by stamping or laser ablating the substrate after it is formed or by casting the substrate on a textured surface.
In some embodiments, in order to, for example, reduce manufacturing costs, the cathode current collector is made of a material that is less expensive than the materials typically used (e.g., gold or platinum). General examples include conductive metal oxides, conductive metal nitrides, conductive metal carbides, either crystalline or amorphous. Specific examples include fluorine-doped tin oxide, titanium nitride, tantalum nitride, indium tin oxide, and indium zinc oxide.
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However, it should be understood that in some embodiments, the second component 502 is formed in such a way that the texture formations 506 are present on the upper surface 504 thereof (i.e., no additional texturing process is required). For example, in some embodiments, the second component 502 is made of a transparent conductive oxide and is formed using a CVD process. As will be appreciated by one skilled in the art, the CVD process may be controlled such that the transparent conductive oxide is deposited in a textured manner. As another example, in some embodiments, the upper surface of the first component 500 is textured, or patterned, such that the upper surface 504 of the second component 502 is contoured or textured in a similar manner. Such a method may be used, for example, in some embodiments in which the second component 502 is a substrate (e.g., substrate 100) which is formed using a sol-gel and/or fire-casting process (e.g., made of a ceramic material, such as aluminum oxide). As a further example, in some embodiments in which the second component 502 is formed using a sol-gel process, the formulation used may include particles of various sizes, which results in the upper surface 504 being textured.
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The various layers (or components) in the battery stack 808 may be formed sequentially (i.e., from bottom to top) above the substrate 802 using, for example, PVD and/or reactive sputtering processing, or any other processes (e.g., plating, sol-gel processes, etc.) that are suitable depending on the material(s), thicknesses, etc. Although the components may be described as being formed “above” the previous component (or the substrate), it should be understood that in some embodiments, each layer is formed directly on (and adjacent to) the previously provided/formed component. In some embodiments, additional components (or layers) may be included between the components shown in
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The cathode (or first electrode) 814 is formed above the cathode current collector 812. In some embodiments, the cathode 814 includes lithium and cobalt (e.g., lithium-cobalt oxide) and has a thickness of, for example, greater than about 4 μm (e.g., even greater than 10 μm), such as between about 5 μm and about 15 μm. The cathode 814 may be formed using, for example, PVD (e.g., sputtering), a sol-gel process, screen printing, tape casting, electrophoretic deposition, or any other suitable method. In the embodiment shown in
After the material of the cathode 814 is deposited, a sintering process may be performed, for example, to increase the density of the material. This annealing may also be required in order to adjust the crystallographic orientation of the material of the cathode for optimal performance. The heating process may be performed in the same processing chamber in which the cathode 814 (and perhaps other components of the battery 800) is formed (i.e., “in situ”). Alternatively, the heating process may be performed in a different processing chamber than that used to form the cathode 814 (i.e., “ex situ”). In some embodiments, the cathode 814 is heated to a temperature of, for example, greater than about 600° C. (e.g., between about 600° C. and about 800° C.) during the heating process. The heating process may be performed in a gaseous environment including sources of oxygen, nitrogen, argon, and/or hydrogen (e.g., 80% nitrogen, 20% oxygen, air/atmosphere, etc.) with either ambient humidity, or no humidity. In some embodiments, the heating process is performed for a duration of, for example, greater than 30 minutes (e.g., 30-60 minutes). The heating process may utilize a temperature ramp rate of, for example, between about 5° C. and about 10° C. per minute (e.g., starting from room temperature).
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The anode (or second electrode) 818 is formed above the electrolyte 816. In some embodiments, the anode 818 includes (or is made of) lithium metal, and perhaps silicon, and/or carbon as well. The anode 818 may have a thickness of, for example, between 1.0 μm and 5.0 μm. In the depicted embodiment, the anode 818 is formed such that it covers an end of the electrolyte 816 opposite an exposed end of the cathode current collector 812.
The anode (or second) current collector 820 is formed above the anode 818. In some embodiments, the anode current collector 820 includes (or is made of) a conductive material that is thermodynamically and (electro-)chemically stable with the material (e.g., lithium metal) of the anode 818. Suitable materials include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, lanthanum, hafnium, molybdenum, tantalum, tungsten, titanium nitride, or a combination thereof (e.g., a bi-layer, tri-layer, multi-layer, sandwich, composite or alloy). The anode current collector 820 may have a thickness of, for example, between about 0.1 μm and about 3 μm. In the depicted embodiment, the anode current collector 820 is formed such that it covers both ends of the anode 818 and a portion thereof is formed directly on an exposed portion of the substrate 802. It should be noted that in some embodiments the anode current collector 820 may not be formed above the anode 818. In some embodiments, the anode current collector 820 may be formed above the substrate 802 and be partially covered by (and in contact with) the anode 818, but not the cathode 814 or the cathode current collector 812.
The protective layer 822 is formed over the anode current collector 820. In some embodiments, the protective layer 822 includes (or is made of) a nitride, such as aluminum nitride or silicon nitride. In some embodiments, the protective layer 822 includes parylene (e.g., as a single layer, or part of an alternating multi-layer stack also including, for example, a nitride, oxide, or oxynitride). The protective layer 822 may have a thickness of, for example, between about 1 μm and about 30 μm. As is shown in
During operation of the battery 800, when the battery 800 is allowed to discharge, lithium ions (i.e., Li+) migrate from the anode 818 to the cathode 814 by diffusing through the electrolyte 816. When the anode and cathode reactions are reversible, as for an intercalation compound or alloy, such as lithium-cobalt oxide, the battery 800 may be recharged by reversing the current. The difference in the electrochemical potential of the lithium determines the cell voltage. Electrical connections are made to the battery 800, for both discharging and charging, through the current collectors 812 and 820.
In some embodiments, the use of the layer stack between the substrate and the current collector (e.g., the cathode current collector) described above may prevent diffusion of material (e.g., iron and nickel) from the substrate (e.g., electrically conductive substrates) into the active components of the battery (e.g., the cathode), while also preventing diffusion of material (e.g., lithium and cobalt) from the active components into the substrate, particularly during the annealing of the cathode. As a result, the capacity, voltage, and cycle life of the batteries may be improved.
In some embodiments, the texturing of the surfaces between the components of the battery increases the interfacial area between the components. As a result, the capacity, energy density, and power of the batteries may be increased in a low-cost manner, using conventional solid-state battery materials. Additionally, the texturing may provide stress relief to prevent adhesion failure and/or delamination, particularly when relatively thick layers are used, which may allow wider manufacturing process windows to be used and lead to longer battery life. The texturing may also improve the battery with respect to adhesion between components/layers, nucleation, ion or electron conductivity (impedance/resistance) across the interfaces, durability, cyclability, as well as remove contaminants. In some embodiments, the manufacturing costs of the batteries may be reduced due to the use of relatively inexpensive materials in the cathode current collector (e.g., conductive metal oxides, conductive metal nitrides, conductive metal carbides, etc.).
At block 904, a diffusion barrier layer is formed above the substrate. In some embodiments, the diffusion barrier layer includes an electrically conductive material and has a thickness of, for example, between about 100 nm and about 1000 nm. In some embodiments, the diffusion barrier layer includes tantalum, titanium, chromium, molybdenum, zinc, tin, cadmium, or a combination thereof. Other suitable examples include conductive metal nitrides, such as tantalum nitride or titanium nitride, conductive metal oxynitrides, such as titanium oxynitride, and conductive metal oxides, such as doped zinc oxide, doped tin oxide, doped cadmium oxide.
At block 906, at least one adhesion layer is formed above the substrate. In some embodiments, one adhesion layer is formed between the substrate and the diffusion barrier layer, and another adhesion layer is formed above the diffusion barrier layer. The adhesion layer(s) may be made of an electrically conductive material, such as titanium, chromium, or a combination thereof and have a thickness of, for example, between about 1 nm and about 50 nm.
At block 908, a first current collector is formed above the diffusion barrier layer and the adhesion layer(s). In some embodiments, the first current collector includes an electrically conductive material. In some embodiments, the first current collector includes a noble metal, such as gold, platinum, cobalt, palladium, or a combination thereof. In some embodiments, the current collector includes a relatively low-cost material, such as a conductive metal oxide, a conductive metal nitride, a conductive metal carbide, or a combination thereof. Examples include fluorine-doped tin oxide, titanium nitride, tantalum nitride, ITO, and indium zinc oxide. The first current collector may have a thickness of, for example, between about 100 nm and about 300 nm.
At block 910, a first electrode (e.g., a cathode) is formed above the first current collector. In some embodiments, the first electrode includes lithium and cobalt (e.g., lithium-cobalt oxide) and has a thickness of, for example, between about 5 μm and about 15 μm, such as about 10 μm (or more).
At block 912, an electrolyte is formed above the first electrode. The electrolyte may be a solid electrolyte formed, or deposited, using a PVD process. In some embodiments, the electrolyte includes LiPON and has a thickness of, for example, between about 1 μm and about 2 μm. At block 914, a second electrode (e.g., an anode) is formed above the electrolyte. The second electrode may include lithium metal and have a thickness of, for example, between 1 μm and 5 μm.
At block 916, a second current collector (e.g., an anode current collector) is formed above the second electrode. In some embodiments, the second current collector includes scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, lanthanum, hafnium, molybdenum, tantalum, tungsten, titanium nitride, or a combination thereof. The second current collector may have a thickness of, for example, between about 0.1 μm and about 3+ μm.
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Thus, in some embodiments, methods for forming a solid-state battery are provided. A substrate is provided. A diffusion barrier layer is formed above the substrate. The diffusion barrier layer includes at least one of tantalum, titanium, chromium, molybdenum, zinc, tin, cadmium, or a combination thereof. At least one adhesion layer is formed above the substrate. The at least one adhesion layer is made of a material different than that of the diffusion barrier layer and includes at least one of titanium, chromium, or a combination thereof. A first current collector is formed above the diffusion barrier layer and the at least one adhesion layer. A first electrode is formed above the first current collector. An electrolyte is formed above the first electrode. A second electrode is formed above the electrolyte. A second current collector is formed above the second electrode.
In some embodiments, methods for forming a solid-state battery are provided. A substrate is provided. The substrate includes an electrically conductive material. A first adhesion layer is formed above the substrate. The first adhesion layer includes at least one of titanium, chromium, or a combination thereof. A diffusion barrier layer is formed above the first adhesion layer. The diffusion barrier layer includes at least one of tantalum, titanium, chromium, molybdenum, zinc, tin, cadmium, or a combination thereof. A second adhesion layer is formed above the diffusion barrier layer. The second adhesion layer includes at least one of titanium, chromium, or a combination thereof. The first adhesion layer and the second adhesion layer are each made of a material different than that of the diffusion barrier layer. A first current collector is formed above the second adhesion layer. A first electrode is formed above the first current collector. An electrolyte is formed above the first electrode. A second electrode is formed above the electrolyte. A second current collector is formed above the second electrode.
In some embodiments, solid-state batteries are provided. The solid-state batteries include a substrate. A diffusion barrier layer is formed above the substrate. The diffusion barrier layer includes at least one of tantalum, titanium, chromium, molybdenum, zinc, tin, cadmium, or a combination thereof. At least one adhesion layer is formed above the substrate. The at least one adhesion layer is made of a material different than that of the diffusion barrier layer and includes at least one of titanium, chromium, or a combination thereof. A first current collector is formed above the diffusion barrier layer and the at least one adhesion layer. A first electrode is formed above the first current collector. An electrolyte is formed above the first electrode. A second electrode is formed above the electrolyte. A second current collector is formed above the second electrode.
Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.
