Patent Application
20120058380
This present invention relates to the manufacture of an integrated solid-state electrochemical cell. More particularly, the present invention provides a device and method for fabricating a solid-state thin film battery device. Merely by way of example, the invention has been provided with use of lithium based cells. Additionally, such batteries can be used for a variety of applications such as portable electronics (cell phones, personal digital assistants, music players, video cameras, and the like), power tools, power supplies for military use (communications, lighting, imaging and the like), power supplies for aerospace applications (power for satellites), and power supplies for vehicle applications (hybrid electric vehicles, plug-in hybrid electric vehicles, and fully electric vehicles). The design of such batteries is also applicable to cases in which the battery is not the only power supply in the system, wherein additional power is provided by a fuel cell, other battery, internal combustion (IC) engine or other combustion device, capacitor, solar cell, etc.
Common electro-chemical cells often use liquid electrolytes. Such cells are typically used in many conventional applications. Alternative techniques for manufacturing electro-chemical cells include solid state cells. Such solid state cells are generally in the experimental state, have been difficult to make, and have not been successfully produced in large scale. Although promising, solid state cells have not been achieved due to limitations in cell structures and manufacturing techniques. These and other limitations have been described throughout the present specification and more particularly below.
Solid state batteries have been proven to have several advantages over conventional batteries using liquid electrolytes in lab settings. Safety is the foremost one. A solid state battery is intrinsically more stable than batteries based on liquid electrolyte cells, since it does not contain a liquid that causes undesirable reactions, which can result thermal runaway, and an explosion in the worst case. Solid state batteries can store more energy for the same volume or same mass compared to conventional batteries. Good cycle performance, more than 10,000 cycles, and good high temperature stability also has been reported.
Despite of these outstanding properties of solid state batteries, there are challenges to address in the future to make this type of batteries available in the market. To exploit the compactness and high energy density, packaging of such batteries should be improved. To be used in variety of applications such as consumer electronics or electric vehicle, other than the current application, radio frequency identification (RFID), large area and fast film deposition techniques at low cost should be developed.
From the above, it is seen that techniques for improving solid-state cells are highly desirable.
According to the present invention, techniques related to the manufacture of electrochemical cells are provided. More particularly, the present invention provides a device and method for fabricating a solid state thin film battery device. Merely by way of example, the invention has been provided with use of lithium based cells. Additionally, such batteries can be used for a variety of applications such as portable electronics (cell phones, personal digital assistants, music players, video cameras, and the like), power tools, power supplies for military use (communications, lighting, imaging and the like), power supplies for aerospace applications (power for satellites), and power supplies for vehicle applications (hybrid electric vehicles, plug-in hybrid electric vehicles, and fully electric vehicles). The design of such batteries is also applicable to cases in which the battery is not the only power supply in the system, wherein additional power is provided by a fuel cell, other battery, IC engine or other combustion device, capacitor, solar cell, etc.
In a preferred embodiment, the present method and battery cell uses specific process and design parameters. These parameters can be determined through numerical techniques using selected upper and lower bounds to achieve desirable results for certain applications. As an example, such numerical techniques included those described in a pioneering approach described in U.S. Pat. No. 7,945,344 issued May 17, 2011, which is hereby incorporated by reference, and commonly assigned. In a preferred embodiment, the present battery structure used information from the techniques described in the aforementioned U.S. patent.
In a preferred embodiment, the present invention provides a method and device using a prismatic multilayer structure with post or self terminated current collectors conforming to a viable volume having >20% increase in energy density over 280 Watt-hour/Kilogram, as referenced to conventional battery technology. As used herein, the term prismatic is consistent with a definition known to one of ordinary skill in the art, although there may be some slight variations. In a specific embodiment, the method and device includes a multilayer structure comprised of >100 and <3000 cells in parallel conforming to energy density optimization calculations. Some results of this construction are shown in
In a preferred embodiment, a monolithically integrated thin-film solid-state lithium battery device comprises multiple layers of lithium electrochemical cells. The lithium electrochemical cell is the smallest unit in the thin-film solid-state lithium battery that can provide electron energy and, in a specific embodiment, each cell is characterized by a spatial region of less than 100 centimeter squared. The preferred thickness of each layer in the electrochemical cell is obtained by a numerical method.
In a preferred embodiment, the single lithium electrochemical cell comprises layers deposited by physical vapor deposition processes in the sequence of a cathode barrier, cathode current collector, cathode, electrolyte, anode, anode current collector, and anode barrier overlying a substrate. In a specific embodiment, the substrate layer in the thin-film solid-state electrochemical cell device provides the mechanical support for the following layers. Therefore, its stiffness has to sustain the induced weight and stresses due to the following deposited layers thereon. In an embodiment, thin polymers, especially those like polyethylene terephthalate (PET), are used as substrates that have a thickness of less than 10 microns. In another embodiment, metalized PET, which a very thin layer (e.g., 0.1 microns) of copper is coated above the PET, is used to prevent the oxygen and moisture of the substrate from diffusing into the cathode and cathode current collector. The thickness of the metalized metal on the PET is on the order of Angstroms of a meter.
In a preferred embodiment, the cathode barrier layer between the substrate and cathode current collector of electrochemical cell device is used to inhibit the reaction of lithium with the moisture inside substrate. An oxide, nitride, or phosphate of metal is preferable for this layer. The metal type comes from the Groups 4, 10, 11, 13 and 14 of the periodic table. The thickness of this layer is on the order of 0.1 microns or less. In another preferred embodiment, lithium phosphate (LixPOy where x+y<=7) is used as cathode barrier.
In another preferred embodiment, the cathode and anode current collectors in the electrochemical cell device are necessary to collect and transport the electron current from the cathode and anode toward the external load. The electrical conductivity is on the order of 107 S/m or higher. The cathode and the anode current collector are made of a conductive metal selected from an element in Groups 10, 11, and 13 of the periodic table or wherein the cathode and the anode current collector are made of a copper material with electronic conductivity higher than 107 S/m. The cathode and anode current collectors need to be chemically stable at the voltage at which they are operated. In an embodiment, the thickness of the current collector is between about 0.1 and about 2 microns.
In preferred embodiment, a cathode electrode material comprises an amorphous or crystalline lithiated transition metal oxide and lithiated transition metal phosphate, wherein the metal comes Groups 3 to 12 of the periodic table. Preferably, the cathode electrode material comprises amorphous lithiated vanadium based oxide with electrical conductivity ranging from 10−6 to 10−2 S/m (preferably less than 10−3 S/m), and ionic diffusivity ranging 1×10−16 to 1×10−14 m2/s. The vanadium based oxide overlies the electrically conductive layer, the cathode electrode material being characterized with a layer thickness between about 0.2 and about 2 micrometers. The electrical conductivity can be adjusted by the process condition.
In a specific embodiment, the solid-state glassy electrolyte of this electrochemical cell device comprises amorphous lithiated oxynitride phosphorus with ionic conductivity ranging from 10−5 to 10−4 S/m. The ionic conductivity of glassy electrolyte can be tuned by the nitrogen concentration and evaporation process conditions. This glassy electrolyte material can be configured as an electrolyte overlying the cathode electrode material. This glassy electrolyte material is capable of shuttling lithium ions during a charge process and a discharge process, and is characterized with layer thickness between about 0.1 and about 1 micrometers.
In a specific embodiment, a solid-state layer of negative electrode material configured as an anode in this device is capable of electrochemically inserting lithium into the host lattice or plating of Li-ions during a charge process and a discharge process. This solid-state anode layer can have layer thickness between about 0.2 and about 3 micrometers. The layer thickness of the anode can be several times the size of cathode layer thickness so that it could ensure enough lithium concentration for shuttling back and forth between cathode and anode through electrolyte.
In a preferred embodiment, the anode barrier layer overlies the anode current collector in this device. This anode barrier layer is used to inhibit the reaction of lithium with the moisture external air. An oxide, nitride, or phosphate of metal is preferable for the material used in this layer. Such metals come from Groups 4, 10, 11, 13 and 14 of the periodic table. These metal oxides, metal nitrides, or metal phosphates are easy to evaporate and deposited. In this method and structure, the thickness of this layer is on the order of 0.1 microns or less. In one preferred embodiment, the lithium phosphate (LixPOy where x+y<=7) is used as anode barrier.
Benefits are achieved over conventional techniques. Depending upon the specific embodiment, one or more of these benefits may be achieved. In a preferred embodiment, the present invention provides a suitable solid state battery structure having specific layer thicknesses, compositions, and materials that provide for unexpected results over conventional battery technology. Preferably, the present battery device has the following characteristics:
Depending upon the embodiment, one or more of these benefits may be achieved. Of course, there can be other variations, modifications, and alternatives. The present invention achieves these benefits and others in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
The following diagrams are merely examples, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this process and scope of the appended claims.
According to the present invention, techniques related to the manufacture of electrochemical cells are provided. More particularly, the present invention provides a device and method for fabricating a solid state thin film battery device. Merely by way of example, the invention has been provided with use of lithium based cells, but it would be recognized that other materials such as zinc, silver, copper and nickel could be designed in the same or like fashion. Additionally, such batteries can be used for a variety of applications such as portable electronics (cell phones, personal digital assistants, music players, video cameras, and the like), power tools, power supplies for military use (communications, lighting, imaging and the like), power supplies for aerospace applications (power for satellites), and power supplies for vehicle applications (hybrid electric vehicles, plug-in hybrid electric vehicles, and fully electric vehicles). The design of such batteries is also applicable to cases in which the battery is not the only power supply in the system, wherein additional power is provided by a fuel cell, other battery, IC engine or other combustion device, capacitor, solar cell, etc.
As smartphone and portable electronic device functional capabilities increases, the needs to have longevity of a power supply increases as well. A solid-state lithium battery is one promising candidate to supply energy to a smartphone or other similar portable electronic devices. The solid-state lithium battery comprises multiple layers of much smaller unit of lithium electrochemical cells connected in series or in parallel, depending on the application needs. The current drawback of lithium ion batteries is their short cycle longevity, due to the side reaction of dendrite lithium formed inside the cell to short the positive and negative electrode. In extremely severe situations, the side reaction could cause thermal run away and lead to human injury. Hence, the current development trend of lithium ion batteries is to develop a solid electrolyte to replace the liquid electrolyte, such as the polymer electrolyte to reduce the possibility of lithium dendrite growth during the charge and discharge process, or using proprietary separator to inhibit the dendrite short the positive and negative electrodes.
However, thin-film solid-state lithium battery has the advantage of preventing dendrite growth due to the high stiffness of solid-state layers. Also, because of its thin-film spatial dimension, thin-film solid-state lithium batteries also own a high rate capability. The second set if demands for applications, such as smartphone and portable electronic devices, is longer operational times, smaller volume sizes, and lighter weight. These demands require higher energy density per volume and per mass. Conventional commercial lithium ion batteries comprise porous electrodes, and liquid or polymer electrolytes. Because of it porous electrodes and electrolyte features, the conventional commercial lithium ion battery has a limited capability to be further reduced in its size and weight. Also, the conventional lithium ion battery requires several extra materials that do not contribute to the overall energy of the battery, such as the separator and electrolyte, which increase the volume and mass of the whole battery. Furthermore, those dead weight components and volume reduces the specific energy and volumetric energy density of the lithium ion battery. On the other hand, in this invention, we propose thin-film solid-state lithium battery, which utilizes almost all available spatial volume, and also reduces the dead weight and dead volume materials in order to further increase overall energy of the battery.
This smallest unit in thin-film solid-state lithium batteries is comprised of a substrate 201, cathode barrier 202, cathode current collector 203, cathode 204, electrolyte 205, anode 206, anode current collector 207, anode barrier layer 208 in sequence as illustrated in
Physical vapor deposition (PVD) processes, often called thin-film processes, are atomistic deposition processes in which materials is vaporized from solid or liquid source material in the form of atoms or molecules, transported in the form of a vapor through a vacuum or low pressure gaseous plasma chamber to the substrate where it condenses to form the film layer material. Here, the term “thin film” is applied to layers that have thicknesses on the order of several micrometers or less. PVD processes can be sued to deposit films of elements and alloys as well as compounds using reactive deposition processes. The resulting films can range from single crystal to amorphous, fully dense to less than fully dense, pure to impure, and thin to thick. In order to maximize the energy density of battery device in a specific embodiment, the mathematical model is used to facilitate this. The process flow diagrams are shown in
The substrate layer 201 in the thin-film solid-state electrochemical cell provides the mechanical support for the following layers. Therefore, it must to have the stiffness to sustain the induced weight and stresses due to the following deposited layers latter on. Therefore, typical substrate will be thick and stiff material. However, in this device, we choose thin polymer, especially the polyethylene terephthalate (PET), to be our substrate, in which the substrate thickness is less than 10 microns. Sometimes, in order to prevent the oxygen and moisture from the substrate to diffuse into cathode and cathode current collector, metallized PET, which a very thin layer of copper is coated above the PET, is invented for this purpose, which can reduce the impurity of the cathode and extend its longevity. The thickness of the metalized metal on PET is in the order Angstrom meters.
The cathode barrier layer 202 between the substrate and cathode current collector of the device in a specific embodiment is used to inhibit the reaction of lithium with the moisture inside substrate. Organic materials can be used for this function. An oxide, nitride, or phosphate of metal is preferable for this layer. The metal comes from Groups 4, 10, 11, 13 and 14 of the periodic table. These metal oxides, metal nitrides, or metal phosphates are easy to evaporate and deposit. In a specific embodiment, the thickness of this layer is on the order of 0.1 microns or less. One of promising candidates is the lithium phosphate (LixPOy where x+y<=7).
The cathode 203 and anode current collectors 207 in this device are necessary to collect and transport the electron current from the cathode toward the external load. Hence, it needs to have high electrical conductivity, which is in the order of 107 S/m or higher. The cathode and anode current collectors need to be chemical stable at the voltage where they are operated. The cathode current collector needs to be stable at the range of 1.5 to 5 V vs. lithium, and anode current collector needs to be stable at range 0 to 1V versus lithium. Although the current collector is necessary in the electrochemical cell to transport the electrons, it does not contribute the electronic energy of the cell. Hence, it needs to be thin to reduce the volume and mass; however, it cannot be too thin. The potential drop through the film is depending of the thickness of the film as,
where L is the length of the film, H is the thickness of the film, and is the electrical conductivity of the film. Therefore, the thickness cannot be lower than certain value to minimize the potential drop across the film. In a specific embodiment, the thickness of the current collector is between about 0.1 and about 2 microns.
In this device, a cathode electrode material 204 comprised of amorphous or crystalline lithiated transition metal oxide and lithiated transition metal phosphate, wherein the metal comes from Groups 3 to 12 of the periodic table, preferably amorphous lithiated vanadium based oxide with electrical conductivity ranging from 10−6 to 10−2 S/m (preferably less than 10−3 S/m), and ionic diffusivity ranging 1×10−16 to 1×10−14 m2/s. The vanadium based oxide overlying the electrically conductive layer, the cathode electrode material being characterized with a layer thickness between about 0.2 and about 2 micrometers. The electrical conductivity can be adjusted by the process condition in a specific embodiment.
The solid-state glassy electrolyte 205 of this device comprises amorphous lithiated oxynitride phosphorus with ionic conductivity ranging from 10−5 to 10−4 S/m. The ionic conductivity of glassy electrolyte can be tuned by the nitrogen concentration and evaporation process conditions. This glassy electrolyte material configured as an electrolyte overlying the cathode electrode material, the glassy electrolyte material being capable of shuttling lithium ions during a charge process and a discharge process, the glassy electrode material characterized with layer thickness between about 0.1 and about 1 micrometers.
A solid-state layer of negative electrode material configured as an anode 206 in this device is capable of electrochemically insertion lithium into the host lattice or plating of Li-ions during a charge process and a discharge process. This solid-state anode layer having layer thickness between about 0.2 and about 3 micrometers, which has to been about several times of cathode capacity so that it could ensure enough lithium concentration for shuttling back and forth between cathode and anode through electrolyte.
The anode barrier layer 208 overlies the anode current collector in this device is used to inhibit the reaction of lithium with the moisture external air. Organic materials can be used for this function. An oxide, nitride, or phosphate of metal is preferable for this layer. The metal comes from Groups 4, 10, 11, 13 and 14 of the periodic table. These metal oxides, metal nitrides, or metal phosphates are easy to evaporate and deposit. In this invention, the thickness of this layer is in the order of 0.1 microns or less. One of promising candidates is the lithium phosphate (LixPOy where x+y<=7).
In a specific embodiment, the electrochemical cells are formed by physical vapor deposition techniques in the sequence of barrier-cathode current collector-cathode-electrolyte-anode-anode current collector-anode barrier repeated more than 100 times, but less than 3000 times, and in the sequence of cathode current collector-cathode-electrolyte-anode-anode current collector-anode-electrolyte-cathode-cathode current collector repeatedly more than 2 times of this sequence on top of substrate layer to reduce the number of layers of substrate and increase the volumetric energy density of the solid-state lithium battery. The flow diagram of physical vapor deposition process is shown in
In order to show examples of certain benefits for the embodiments herein, we performed certain experiments in the following examples. Of course, these examples are merely illustrations, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.
The iPhone 4 is very popular smartphone in 2010 and 2011. It supports over 425000 applications, commonly called “Apps,” which are available to purchase and download. However, it is known that the useable time and longevity of battery are the drawbacks of iPhone 4 when compared with other brand name smartphones. In order to elongate the battery useable time, Apple eliminates the use of Adobe Flash to lower the power consumption.
In this example, we demonstrate that the currently designed thin-film solid-state lithium battery can outperform the iPhone 4 current battery such that the iPhone 4's capabilities can be further extended. The conventional iPhone 4 battery is labeled with 5.25 Watt-hours (Wh), and its spatial volume is 11.5 centimeter cubic. Hence, its volumetric energy density is about 4.60×105 Wh/m3 (=460 Wh/L). In this example, we have designed a thin-film solid-state battery with the size of 7.2×3.2×0.5 (cm3). A lithium vanadium based oxide was used as the cathode material, lithium based phosphate oxynitride as electrolyte and barrier, lithium metal as the anode, nickel metal as the current collector, and polyethylene terephthalate (PET) as the substrate. The electrochemical cells are stacked in two different ways as shown in
In this example, the assumptions are listed in Table 1. Two design variables are assigned: the cathode thickness ranging from (0.2 to 2 μm), and cathode electrical conductivity ranging from (10−6 to 10−5 S/m) as shown in Table 2.
[0.2, 2.0] μm
The results are demonstrated in
In this example, we demonstrated the comparison between the battery design in a specific embodiment, with the current existing battery using in the conventional smartphone and mobile computing devices. These conventional smartphone and mobile computing devices are HTC Thunderbolt, HTC Inspire 4G, HTC EVO 4G, T-Mobile myTouch 4G, Motorola Droid X2, T-Mobile G2X, iPhone 4, Motorola Atrix 4G, and Samsung Nexus S 4G. The weight and volume of the batteries used in those device are shown in
In a specific embodiment, the present battery has the volume as the iPhone 4, and its weight ranging from 0.02 to 0.03 kg depending on the design. The design is based on the numerical methods. The smartphones and mobile computing devices are discharged at constant current rate. The volumetric and gravimetric energy densities of these electronic devices are shown in
While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. As an example, the present device has been described in terms of a prismatic battery cell package. However, it would be appreciated that other form factors (e.g., cylinder, button) can also be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.
The present application incorporates by reference, for all purposes, the following issued patent: U.S. Pat. No. 7,945,344, filed Jun. 15, 2009.
