Patent Application
20170040605
Batteries that include lithium metal have a higher theoretical energy density as compared to other batteries that include alkaline or nickel-metal-hydride materials. However, lithium-containing batteries have not realized their full potential due to various challenges such as poor cycle performance and safety concerns. Accordingly, a need exists to reduce loss of Li-metal due to irreversible surface reactions during charge/discharge, reduce dendritic growth at the anode/current collector interface during charging, and reduce surface expansion/contraction due to non-uniform plating of lithium.
A battery may include a substrate, a cathode, and an electrolyte. The substrate may micro-porous. That is, a surface of the substrate may include a plurality of pores, which may include voids, channels, spaces, and/or surface texture. The substrate may be configured to house lithium metal. During charge and discharge cycles, the lithium metal may be exchanged between the lithium-containing substrate and the cathode via the electrolyte. In such a scenario, the substrate may act as a lithium-containing anode as well as an anode current collector.
In a first aspect, a battery is provided. The battery includes a substrate, a cathode, and an electrolyte. The substrate includes a first surface having a plurality of pores. The plurality of pores is configured to house lithium metal. The electrolyte is disposed between the first surface of the substrate and the cathode and is configured to reversibly transport lithium ions via diffusion between the plurality of pores and the cathode.
In a second aspect, a method of manufacturing a battery is provided. The method includes forming a substrate having a first surface, the first surface having a plurality of pores. The plurality of pores is configured to house lithium metal. The method also includes incorporating lithium metal into at least a portion of the plurality of pores. The method further includes forming an electrolyte disposed between the first surface of the substrate and a cathode. The electrolyte is configured to reversibly transport lithium ions via diffusion between the substrate and the cathode. The method yet further includes forming the cathode.
Other aspects, embodiments, and implementations will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.
The present disclosure describes a battery having a micro-porous current collector or substrate that is configured to incorporate lithium metal within its pores. As such, in some cases, a specific anode material (such as graphite or silicon) may not be needed. That is, the micro-porous substrate may serve joint functions as an anode (e.g. a reservoir of lithium metal) and as a high-conductivity current collector.
The micro-porous substrate may improve exchange of Li-metal near the anode/collector interface. That is, the porous substrate structure may increase the volume within which lithium may be incorporated in the current collector. As a possible result, battery performance may be improved due to higher lithium diffusion rates, especially over the cycle life of the battery. Accordingly, the disclosure may enable lithium ion batteries to provide higher efficiency, higher power density, and/or better cycle life.
In an example embodiment, the micro-porous substrate is a metal, such as copper or nickel. For instance, the metal may be electrochemically stable with lithium. Additionally or alternatively, the micro-porous substrate may include another electrically-conductive material. For example, the electrically-conductive material may include a conductive polymer or carbon nanotubes. Other porous, electrically-conductive materials are contemplated herein. In some embodiments, the micro-porous portion of the substrate may be 20-30 microns thick. However, other thicknesses are possible.
The pores within the substrate may be spherical in shape, although other shapes are possible. For example, the pores may be cylindrical, random, pseudo-random, or another shape. The pores may have a regular or irregular spacing. The pores may be arranged in an array, such as in a hexagonal close-pack, square, linear, or another array arrangement. For example, a plurality of spherical pores may be arranged in a square lattice with a center-to-center spacing of approximately 100 microns. The square lattice may be repeated as a plurality of stacked layers of pores within the micro-porous substrate.
In some embodiments, the porous substrate may be sponge-like. Additionally or alternatively, the substrate may include a micro-porous portion and a solid, non-porous portion. In an example embodiment, the micro-porous substrate may include a mesh material. In other embodiments, the entire substrate may be micro-porous.
Lithium may be introduced into the micro-porous substrate via a pre-lithiation process. The pre-lithiation process may include various ways to incorporate lithium metal into the micro-porous substrate. In an example embodiment, lithium may be electroplated into the pores using an electrochemical plating process. In such a scenario, the micro-porous substrate may be introduced into a plating bath. The plating bath may include a liquid solution that includes lithium metal and/or lithium-containing compounds. The lithium may be plated into the pores of the micro-porous substrate via standard electroplating or electroless plating.
In an alternative embodiment, pre-lithiation may include evaporation of lithium into the micro-porous substrate. Yet further, pre-lithiation may include solid lithium metallic particle (SLMP) deposition onto the micro-porous substrate. Other ways of introducing lithium into the pores of the micro-porous substrate are contemplate herein.
The micro-porous substrate may be formed using a variety of manufacturing methods. For example, the substrate material, which may be a metal such as copper or nickel, may be oxidized in a heated oxygen environment, such as an oxidation tube furnace. Following oxidation, the pores in the substrate material may be etched via wet or dry etching. In an example embodiment, the oxidized substrate may be etched using hydrofluoric (HF) acid and/or sulfuric acid. Alternatively, the oxidized substrate may be dry etched using, for example, a reactive ion etch (RIE) system.
In some manufacturing processes, an oxidation step need not be used. For example, the substrate may include a plurality of defects, which may be original to the substrate or artificially added to the substrate. In such a scenario, the porous substrate may be formed by etching, e.g. a wet chemical etch.
While the above examples include “top-down” methods for forming the micro-porous substrate (e.g. by removing bulk metal material), “bottom-up” methods are also possible within the scope of this disclosure. Namely, additional or alternative manufacturing processes may include forming the micro-porous substrate with additive material deposition. For example, the micro-porous structure may be formed using a 3-D printer, seeded and/or pre-patterned electroplating, patterned metal evaporation, focused ion beam (FIB), electrospinning, or other additive material deposition techniques.
It is understood that many other manufacturing processes are operable to provide metal materials having holes, pores, texture, or other physical patterning. All such manufacturing processes are contemplated herein.
The batteries and manufacturing methods described herein may be applied to a variety of battery chemistries and battery types. For example, the battery may be a thin film-type battery or a jelly roll-type battery. Furthermore, the anode may include lithium metal and the cathode may include lithium cobalt oxide (LiCoO2 or LCO).
In an example embodiment, a substrate 114 may include a plurality of cylindrically-shaped pores 116. A cylindrically-shaped pore 110 may have a pore diameter 111 of 1-10 microns; however other pore diameters are possible. In such a scenario, the cylindrically-shaped pore 110 may have a height equal to a substrate thickness 117. In other embodiments, the height of the cylindrically-shaped pore 100 may be less than the substrate thickness 117. The substrate thickness 117 may be 10-60 microns; however other substrate thicknesses are possible. The cylindrically-shaped pores 116 may be separated by a center-to-center pore spacing 118 of 10-200 microns.
In another example embodiment, a substrate 124 may include a plurality of spherically-shaped or hemispherically-shaped pores 126. A hemispherically-shaped pore 120 may have a pore diameter of 1-10 microns; however other pore diameters are possible.
In yet another example embodiment, a substrate 134 may include a plurality of cone-shaped pores 136. A cone-shaped pore 130 may have a pore diameter of 1-10 microns at its widest point; however other pore diameters are possible.
In a further example embodiment, a substrate 144 may include a plurality of square- or rectangular-shaped pores 146. A square- or rectangular shaped pore 140 may have a pore side length of 1-10 microns.
The pore shapes described herein may be arranged in a variety of regular or irregular arrangements. For example, the pores may be arranged in a hexagonal close-packed configuration along a surface of the substrate. Alternatively, the pores may be arranged in a square lattice or another regular arrangement. Additionally or alternatively, the pores may be arranged in a random configuration along the surface of the substrate.
While
A cross-sectional view 210 along line A-A′ illustrates the substrate 202 as having a plurality of pores. For example, the pores may have a circular cross-section 212 and/or an elliptical cross-section 214. In some embodiments, the plurality of pores in the substrate 202 may be similar to a sponge, coral, steel wool, mesh, or another type of porous material.
The battery 300 may further include a separator 308 and a cathode 310. The separator 308 may include a material configured to maintain a physical separation between the substrate 302 and cathode 310. For example, the separator 308 may be a fibrous or polymeric membrane. Furthermore, the battery 300 may include an electrolyte 312, which may be present in and/or around the separator 308.
The cathode 310 may include a material such as lithium cobalt oxide (LiCoO2, or LCO). Additionally or alternatively, the cathode 310 may include lithium manganese oxide (LiMn2O4, or LMO), lithium nickel manganese cobalt oxide (LiNixMnyCozO2, or NMC), or lithium iron phosphate (LiFePO4). Other cathode materials are possible. Furthermore, the cathode may be coated with aluminum oxide and/or another ceramic material, which may allow the battery to operate at higher voltages and/or provide other performance advantages.
In example embodiments, LCO may be deposited using RF sputtering or PVD, however other deposition techniques may be used to form the cathode 310. The deposition of the cathode 310 may occur as a blanket over the entire substrate. A subtractive process of masking and etching may remove cathode material where unwanted. Alternatively, the deposition of the cathode 310 may be masked using a photolithography-defined resist mask.
In some embodiments, the battery 300 may include a cathode current collector (not illustrated). For example, the cathode current collector may include a material that functions as an electrical conductor. Furthermore, the cathode current collector may be configured to be block lithium ions and various oxidation products (H2O, O2, N2, etc.). In other words, the cathode current collector may include materials that have minimal reactivity with lithium. For example, the cathode current collector may include one or more of: Au, Ag, Al, Cu, Co, Ni, Pd, Zn, and Pt. Alloys of such materials are also contemplated herein. In some embodiments, an adhesion layer material, such as Ti may be utilized. In other words, the cathode current collector may include multiple layers, e.g. TiPtAu. Other materials are possible to form the cathode current collector. For example, the cathode current collector may be formed from carbon nanotubes and/or metal nanowires.
The cathode current collector may be deposited using RF or DC sputtering of source targets. Alternatively, PVD, electron beam-induced deposition or focused ion beam deposition may be utilized to form the cathode current collector.
The electrolyte 312 may be disposed between the cathode 310 and the substrate 302. The electrolyte 312 may include a material such as lithium phosphorous oxynitride (LiPON). Additionally or alternatively, the electrolyte 312 may include a flexible polymer electrolyte material. Yet further, the electrolyte 312 may include a liquid electrolyte, such as a solution including a lithium salt such as LiPF6 or LiBF4 and an organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), and/or diethyl carbonate (DEC). Other electrolyte materials are possible.
Generally, the electrolyte 312 may be configured to permit lithium ion conduction between the substrate 302 and the cathode 310. Namely, electrolyte 312 may be configured to reversibly transport lithium ions via diffusion between the plurality of pores 304 in the substrate 302 and the cathode 310. In an example embodiment, the LiPON material may allow lithium ion transport while preventing a short circuit between the substrate 302 and the cathode 310.
In an example embodiment, the cathode 310 and the substrate 302 may be electrically coupled to a circuit 320. That is, the battery 300 may generally provide power to the circuit 320. In some cases, circuit 320 may provide power to battery 300 so as to recharge it.
It should be understood that
The blocks of method 400 may be carried out to form or compose the elements of battery 300 as illustrated and described in reference to
Method 400 may describe a method of manufacturing a battery. Block 402 includes forming a substrate having a first surface, the first surface having a plurality of pores. The substrate may include the porous substrates as illustrated and described in reference to
The plurality of pores is configured to house lithium metal. For example, the plurality of pores may be arranged so as to reversibly exchange lithium metal with a cathode via an electrolyte in a battery configuration. Furthermore, the substrate material may include a material that is chemically and/or electrochemically stable in the presence of lithium metal. As described herein, the substrate may include an electrically-conductive material such as copper and/or nickel.
The plurality of pores may be formed via additive and/or subtractive fabrication processes. For example, the substrate material may be optionally oxidized via an oxidation furnace. Thereafter, the pores may be etched using wet chemical etch (e.g. hydrofluoric acid, HF) and/or a dry plasma etch (carbon tetrafluoride, CF4) processes. In some embodiments, one or more lithography steps may be included to mask/protect some areas of the substrate during etch. Additionally or alternatively, the substrate may be embossed, imprinted, or otherwise modified to form the plurality of pores.
In another example embodiment, the porous portion of the substrate may be formed by adding substrate material around the pore volumes. For instance, at least the porous portion of the substrate may be formed via 3D printing, evaporation, or electroplating. Again, one or more lithography steps may be included, for example, to form the pore volumes. Additionally or alternatively, the substrate may be evaporated or electroplated into a diblock copolymer mold. The mold may thereafter be removed via subsequent copolymer etching and/or dissolving.
It is understood that many other fabrication techniques exist to form a porous portion in a metal, such as copper or nickel. All such other fabrication techniques are contemplated herein.
As described elsewhere herein, the plurality of pores may include a multi-layer, square lattice arrangement of pores. In such a scenario, the pores may have a center-to-center spacing of 100 microns. In some embodiments, the pores may have pore diameters between 1-10 microns.
Various pore configurations and arrangements are possible. For example, the plurality of pores may be disposed in a square lattice, a hexagonal close-packed lattice, or a pseudo-random, sponge-like arrangement. In yet further embodiments, the substrate may include a mesh structure.
Block 404 includes incorporating lithium metal into at least a portion of the plurality of pores. In an example embodiment, a lithium metal may be introduced into the pores of the substrate in a pre-lithiation process. The pre-lithiation process may be provided in various ways. For example, lithium metal may be electroplated into the pores via an electrochemical process. Namely, the substrate may be immersed in a lithium-containing solution. In such a scenario, an electrical field may be created between the solution and the substrate. Lithium metal may dissociate from the solution and become incorporated into the pores of the substrate.
Alternatively or additionally, lithium metal may be evaporated into the pores. For example, a lithium metal target may be a source for a RF sputtering, electron beam, thermal, or plasma-based evaporation system.
As another alternative, lithium metal may be deposited onto the substrate via a stabilized lithium metal powder (SLMP). In an example embodiment, the SLMP may be sprayed or otherwise deposited onto the first surface of the substrate. Further processing steps, such as physical pressure and/or heating/sintering may be provided. Other ways of incorporating lithium metal into the pores of the substrate are contemplated herein.
In some embodiments, a substrate pretreatment step may be provided before the incorporation of lithium into the plurality of pores. For example, the substrate may be cleaned with an organic solvent and/or a wet chemical (e.g. HF) etch. Other substrate preparation or cleaning processes are possible.
Block 406 includes forming an electrolyte disposed between the first surface of the substrate and a cathode. The electrolyte is configured to reversibly transport lithium ions via diffusion between the substrate and the cathode. In an example embodiment, the electrolyte includes a liquid electrolyte, such as a lithium salt (e.g. LiPF6 or LiBF4) dissolved in an organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), and/or diethyl carbonate (DEC).
In another example embodiment, the electrolyte may include a liquid solvent having a high-concentration of ether. In such a scenario, the electrolyte may further include lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt. Other electrolyte materials are possible.
In some embodiments, a separator material may be interposed between the first surface of the substrate and the cathode. The separator may provide a physical barrier to prevent an electrical short between the substrate and the cathode. In such a scenario, the separator may be electrically-insulating and may be permeable so as to allow diffusion of lithium ions through it.
Block 408 includes forming the cathode. The cathode may be cathode 310 as illustrated and described in reference to
The support 601 may include a variety of materials. For example, support 601 may include one or more of: a silicon wafer, a plastic, a polymer, paper, fabric, glass, or a ceramic material. Other materials for support 601 are contemplated herein. Generally, support 601 may include any solid or flexible material that is sufficiently insulating so as to prevent a short circuit between the substrate 602 and the cathode 610.
The spacer 607 may include an insulating material that may be operable to prevent a short circuit between the substrate 602 and the cathode 610. The spacer 607 may include silicon carbide, silicon dioxide, or another insulating material that is non-reactive with lithium.
In some embodiments, electrolyte 608 may include a solid electrolyte. For example, electrolyte 608 may include Li2+2xZn1−xGeO4 (LISICON). In an alternative embodiment, the electrolyte 608 may include lithium phosphorous oxynitride (LiPON). In some embodiments, the electrolyte 608 may be deposited by RF magnetron sputtering or PVD. For example, PVD of electrolyte 608 may include exposing a target of lithium phosphate to plasma in a nitrogen environment. Alternatively or additionally, the electrolyte 608 may include a different material. The electrolyte 608 may have a layer thickness between 10-30 microns; however other electrolyte layer thicknesses are possible.
The electrolyte 608 may be able to conform to a shape of the underlying layers. In some embodiments, the electrolyte 608 may optionally include a gel and/or liquid electrolyte. In such scenarios, the battery may include a further insulating separator material that may incorporate the gel or liquid electrolyte.
In an example embodiment, the battery may be configured in a stacked arrangement. That is, instances of battery illustrated in
It is understood that other battery elements may be included in some or all of the embodiments described herein. For example, embodiments may include a cathode current collector and/or a substrate current collector. Such current collectors may include a metal and may be 200-1000 nanometers thick. Other materials and thicknesses are possible.
While some embodiments described herein may include additive deposition techniques (e.g. blanket deposition, shadow-masked deposition, selective deposition, etc.), subtractive patterning techniques are additionally or alternatively possible. Subtractive patterning may include material removal after deposition onto the substrate or other elements of the battery. In an example embodiment, a blanket deposition of material may be followed by a photolithography process (or other type of lithography technique) to define an etch mask. The etch mask may include photoresist and/or another material such as silicon dioxide (SiO2) or another suitable masking material.
The subtractive patterning process may include an etching process. The etch process may utilize physical and/or chemical etching of the battery materials. Possible etching techniques may include reactive ion etching, wet chemical etching, laser scribing, electron cyclotron resonance (ECR-RIE) etching, or another etching technique.
In an example embodiment, selective removal of a portion of any of a current collector, electrolyte, substrate, or cathode may include laser-scribing the respective portion of the collector, electrolyte, substrate, and cathode. That is, a blanket layer of the current collector, electrolyte, substrate, and/or cathode material may be deposited. Subsequently, a laser scribe may remove portions of the respective materials. The laser scribe may include a high-power laser configured to ablate or otherwise remove material from a surface. The laser light may be directed by an optical system according to a predetermined scribing pattern or mask pattern. Each of the current collector, electrolyte, substrate, and cathode may have an associated mask pattern to define the material to remove (and preserve) via laser scribing.
In some embodiments, material liftoff processes may be used. In such a scenario, a sacrificial mask or liftoff layer may be patterned on the substrate before material deposition. After material deposition, a chemical process may be used to remove the sacrificial liftoff layer and battery materials that may have deposited on the sacrificial liftoff layer. In an example embodiment, a sacrificial liftoff layer may be formed using a negative photoresist with a reentrant profile. That is, the patterned edges of the photoresist may have a cross-sectional profile that curves inwards towards the main volume of photoresist. Materials may be deposited to form, for instance, the anode and cathode current collectors. Thus, material may be directly deposited onto the substrate in areas where there is no photoresist. Additionally, the material may be deposited onto the patterned photoresist. Subsequently, the photoresist may be removed using a chemical, such as acetone. In such a fashion, the current collector material may be “lifted off” from areas where the patterned photoresist had been. Other methods of sacrificial material removal are contemplated herein.
The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an illustrative embodiment may include elements that are not illustrated in the Figures.
While various examples and embodiments have been disclosed, other examples and embodiments will be apparent to those skilled in the art. The various disclosed examples and embodiments are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
