WO2015103285A1

WO2015103285A1 - Architectural active materials for lead acid batteries

Info

Publication number: WO2015103285A1
Application number: PCT/US2014/072791
Authority: WO
Inventors: Collin Mui; Daniel MOOMAW
Original assignee: Gridtential Energy, Inc.
Priority date: 2013-12-30
Filing date: 2014-12-30
Publication date: 2015-07-09

Abstract

Apparatus and techniques are described herein, such as can be used to form or provide a portion of a battery electrode assembly. For example, one or more material layers having a controlled porosity or density can be deposited on a semiconductor substrate, such as upon a silicide layer formed on or within the semiconductor substrate. Such deposition can include electrodeposition or electrophoretic deposition of an active material layer to provide a current collector, for example.

Description

ARCHITECTURAL ACTIVE MATERIALS

FOR LEAD ACID BATTERIES

CLAIM OF PRIORITY

This application claims the benefit of priority of Mui et al., U.S. Provisional Patent Application Serial Number 61/921,783, titled "ARCHITECTURAL ACTIVE MATERIALS FOR LEAD ACID BATTERIES," filed on December 30, 2013 (Attorney Docket No.

3601.004PRV), which is hereby incorporated by reference herein in its entirety.

BACKGROUND

The lead acid battery, with a worldwide market of ~ $40B in 2012, is a widely-used energy storage technology due generally to its simplicity, robustness, and low cost. In addition to lead acid battery use in applications as automotive starter batteries, such batteries are also widely used in traction applications such as wheelchairs, golf carts, and forklifts, as well as mid-size stationary installations targeted for residences, offices, and communities.

The active electrochemical materials in a lead acid battery are lead dioxide (Pb0₂) in a positive plate, lead (Pb) in a negative plate, and a sulfuric acid (H2SO4) electrolyte. The active materials are generally provided in the form of pastes including litharge (PbO) and red lead (Pb₃0₄) particles, sulfuric acid (H2SO4), as well as additives specific for the positive and negative plates. Generally-available lead acid battery electrodes are constructed by a sequence of paste, cure, and formation steps where the active materials are pasted and spread onto the current collector; cured and dried to become a cohesive porous structure; soaked in H2SO4; and formed electrochemically in a manner that nominal storage capabilities are achieved during battery operation.

OVERVIEW

Despite numerous desirable characteristics, generally-available lead acid batteries have several disadvantages, including low energy density and poor cycling life, especially at high discharge current. Although the low energy density of generally-available lead acid batteries can be attributed to high density of lead current collectors and active materials, a poor cycling life at fast discharge rates can be related to the properties of the active materials.

First, generally-available active material pastes include discrete particles held together by the surface tension of the liquid in the paste. Adhesive and cohesive forces of the active materials are weak even after the paste and cure processes. When the battery is discharged, PbC and Pb can react with H2SO4 to form PbS0₄. Because the density of PbS0₄ is lower than that of PbC>2 and Pb, the active materials generally expand during the discharge process. The electrochemical reactions are reversed and the active materials shrink during the charge process.

After many charge-discharge cycles, repeated expansion and shrinkage of the active materials results in increased stress in the material layers. Exacerbated by weak adhesion and cohesion, active material particles eventually detach and shed off from the current collector, which can lead to capacity fade and short cycle life.

Second, the particles in generally-available pastes may form a porous network of active materials on the current collector. However, the porosity of the active material layer generally depends on the particle size and the packing density of the paste. Thus, the porosity of the active material can be generally constant throughout the layer. During charge and discharge, electrolyte diffuses into the paste and reacts with the active materials, and the reaction products diffuse out to the electrolyte reservoir. The rate of electrolyte diffusion generally limits the rate of charge and discharge.

A charge or discharge rate-limiting aspect can be evident especially for thick active material layers. At high charge and discharge rates, electrolyte cannot diffuse deep into the active material layer. Accordingly, in such an example, charge and discharge currents are supplied by the electrochemical reactions at the top of the active layer near the material- electrolyte interface. The material near the surface of the paste layer can undergo electrochemical reaction to a greater extent, which can result in more pronounced material expansion and shrinkage. Such increased material stress can accelerate particle shedding and dislodging from the porous paste network, which can further degrade cycle life at high charge and discharge rates.

Accordingly, the present inventors have recognized, among other things, that it is desirable to have active material layers that adhere strongly to the current collector and are highly porous with strong cohesive forces within. Furthermore, the present inventors have also recognized, that the porosity of the active material layer can be controlled to vary across a thickness of the active material layer, (e.g., having a greater porosity such as near the electrolyte interface but having a lesser porosity or greater density near the current collector, or vice versa). In this manner, for example, diffusion characteristics can be controlled within a porous layer, such as reduce stress in the active material from repeated cycling. This can improve the cycling performance, such as particularly at high charge or discharge rates. In an example, an active material having a controlled porosity across a thickness of an active material layer can be referred to as an "architectural" porous active material layer, and such an architectural porous active material layer can be included as a portion of a battery assembly, such as a portion of a battery plate assembly. Such an architectural porous active material can be held together by strong cohesive chemical bonding, and can provide adhesion to the current collector. For example, a thin layer of metal silicide can be first formed on a surface of a current collector as a contact or adhesion layer. The metal silicide surface can be wet-cleaned to etch off surface silicon and metal oxides, such as prior to active material deposition.

Electrodeposition can be used to deposit lead (Pb) or lead dioxide (PbC ) onto the current collector, such as upon one or more silicide layers. Such electrodeposition and cleaning need not be separate steps. For example, a plating bath can formulated or otherwise established such that the metal silicide surface is cleaned in-situ during the initial nucleation stage of the deposition process, such that the Pb or PbC layer can adhere strongly to the surface. In one approach, a technique of hydrogen co-deposition can be used to deposit a porous Pb layer as the active material. In another approach, a porous layer deposition can be achieved by electrodeposition through a template mask. Generally, in electrodeposition, the atoms in the deposited layer are chemically bonded, resulting in strong cohesive forces within the active material layer. Because the porosity of the active material layer can be determined by the relative rates of electrodeposition and hydrogen evolution, the porosity of the active material layer can be modulated, such as by controlling electrodeposition parameters such as one or more of a plating bath composition, a plating current density, or a plating bath agitation, for example.

An architectural active material layer can be established by depositing a dense layer at the surface of the current collector with a low current density, followed by gradual increase of the current density to promote porosity near the top of the layer. In another approach, such as including masked deposition, the porosity of the active material layer can be determined (and controlled) such as using a controlled porosity of the template mask. A porosity profile can exist in the mask to deposit an active material layer with a specific porosity profile. The resulting architectural active material layer can be incorporated into a high-performance battery, such as a lead acid battery.

This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and IB illustrate generally a section view of an example 100 including a monopolar battery plate 120A in FIG. 1A and a corresponding monopolar battery architecture in FIG. IB.

FIGS. 2A and 2B illustrate generally a section view of an example including a bipolar battery plate 121A and a corresponding bipolar battery architecture.

FIG. 3 illustrates generally a section view of an example including a porous active material that can include a controlled porosity with respect to depth.

FIG. 4A includes an illustrative example of a scanning electron micrograph (SEM) image illustrating generally Pb/NiSi/Substrate interfaces, such as can be included as a portion of a battery plate assembly.

FIG. 4B includes an illustrative example of a scanning electron micrograph (SEM) image illustrating generally Pb02/NiSi/substrate interfaces, such as can be included as a portion of a battery plate assembly.

FIG. 5A illustrates generally a technique that can include a co-deposition approach for providing a porous active material layer.

FIG. 5B illustrates generally a technique that can include using a mask for providing a porous active material layer.

FIGS. 6A and 6B include illustrative examples of a scanning electron micrograph (SEM) image illustrating generally porous active material layers having different specified porosity profiles with respect to depth.

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

DETAILED DESCRIPTION FIGS. 1A and IB illustrate generally a section view of an example 100 including a monopolar battery plate 120A in FIG. 1A and a corresponding monopolar battery architecture in FIG. IB. In a monopolar configuration, a current collector generally includes an active material of a single polarity (e.g., positive or negative) applied to both (e.g. opposite) sides of the current collector, such as including application of the active material in paste form. For example, in FIG. 1A, a conductive silicon wafer 104 can provide a substrate for the battery plate 120A assembly, such as to provide the current collector. The conductive silicon wafer 104 can include an ohmic contact layer 106A, such as a metal silicide, to enhance conduction between an active material 1 12A and the conductive silicon wafer 104. Such a silicide can include a metal species such as nickel, cobalt, titanium, tantalum, tungsten, molybdenum, or combinations thereof. In an example, an adhesion layer 108A can also be included, such as to one or more of promote adhesion or to provide compatibility with an electrolyte in the electrolyte region 1 16A. Other configurations can be used, such as including multiple film layers to provide one or more of the ohmic contact layer 106A or adhesion layer 108A.

The active material 1 12A can be provided in paste form, such as cured during fabrication. One or more separators such as a separator 1 14A can be used to create a cavity or preserve a region 1 16A for electrolyte. In an example, the electrolyte can be a liquid or gel, or can be included such as impregnating another material, to provide a combination of electrolyte and separator. In the example of FIGS. 1A and IB, a housing 122 can be provided, and can (but need not) fluidically isolate the electrolyte region 1 16A from other electrolyte regions between other plates.

In an example of a monopolar plate 120A, the second surface of the battery plate

120A can include a second ohmic contact layer 106B, a second adhesion layer 108A, and a second active material 1 12B, such as generally including the same materials as the layers on the first surface of the silicon wafer 104. For example, the second active material 1 12B can include the same active material and polarity as the first active material 1 12A. The first and second active materials 1 12A and 1 12B can be formed or can include materials such as having a controlled porosity that varies with respect to depth, such as described in other examples elsewhere herein.

A positive-negative pair can be formed such as including the first plate 120A having a first polarity active material and a second plate 120B having an opposite second polarity active material, to form an electrochemical cell in the electrolyte 1 14, such as shown illustratively in FIG IB. In a lead-acid example, such a single cell voltage can be around 2. IV. A number of cells can be arranged electrically in parallel configuration as a stack 132A. Individual stacks 132A through 132N can be connected in series to assemble a battery pack 102 such that the voltage can be represented as Ns*Vcell, where Ns can represent the number of stacks and Vcell can represent the cell voltage.

In FIG. IB, a first terminal 130A can provide a first polarity, and a second terminal 13 OB can provide an opposite second polarity. The first and second terminals can be coupled to the first stack 132A and last stack 132N, respectively, and the stacks can be coupled together serially using a first bus 124A through an "Nth" bus 124N. By contrast to FIG. IB, a battery architecture using a bipolar plate configuration can offer design simplicity.

Respective positive and negative active materials can be applied, such as through pasting, onto opposite sides of the current collector to form a bipolar plate.

FIGS. 2A and 2B illustrate generally a section view of an example including a bipolar battery plate 121 A and a corresponding bipolar battery architecture. Similar to the example of FIG. 1A, a first bipolar battery plate 121A can include a conductive silicon wafer 104 as a current collector. The bipolar battery plate 121 A can include one or more of an ohmic contact layer 106A and an adhesion layer 108A located at or near a first surface of the conductive silicon wafer 104. An active material 1 12A can include a first polarity. A second ohmic contact layer 106B can be included on a second surface of the conductive silicon wafer 104 opposite the first surface. The second ohmic contact layer 106B can include the same material as the first ohmic contact layer 106A or a different material, such as to provide an electrode for connection to other portions of a battery assembly, to provide a corrosion- resistant layer, or to provide a mirror image configuration having a stack-up similar to the first surface of the conductive silicon wafer 104. A second adhesion layer 108B can also be included. A second active material 112B can be included, such as having a polarity opposite the first active material 1 12A. As in the example of FIG. 1A, a first electrolyte region 1 16A can separate the battery plate 121A from an adjacent battery plate 121C, and a second electrolyte region 1 16B can separate the battery plate 121A from another adjacent battery plate 12 IB. The electrolyte regions 1 16A and 1 16B can include a separator, such as assist in maintaining a specified separation between the battery plates. The electrolyte regions 1 16A and 1 16B are generally fluidically isolated from each other so that conduction occurs serially through a bulk of the conductive silicon wafer 104. The first and second active material layers 1 12A and 112B can be formed or can include materials such as having a controlled porosity that varies as a function of depth, as described in other examples herein.

FIG. 2B illustrates generally an example that can include a battery pack 202 having one or more bipolar battery plates, such as bipolar plates 121A, 121B, and 121C. Such bipolar plates can be sandwiched with electrolyte in regions 1 16A and 1 16B, for example, to form sealed cells. In an example, an electrolyte in region 1 16A can be one or more of fluidically isolated or hermetically sealed so that electrolyte cannot bypass the bipolar plate 121 A to an adjacent region such as the electrolyte region 1 16B, or to suppress or inhibit leakage of electrolyte from the pack 202. As shown illustratively in FIG. 2B, cells can be disposed in a series configuration. The cells can be aligned to form a stack 131 A.

In a bipolar architecture, a current collector (e.g., a silicon wafer 104 such as included as a portion of the bipolar plate 121A) can be shared between the negative electrode of one cell and a positive electrode of the next. A first bus 124A can connect to a first electrode in each stack 131 A through 13 IN, and a second bus 124B can connect to an opposite electrode in each stack 131 A through 13 IN. By contrast with FIG. IB, the stacks 131 A through 13 IN can each provide serial connections through the bulk of the conductive silicon wafers as shown by the arrows. In this manner, a total number of interconnect buses external to the stack 131 A through 13 IN can be reduced as compared to an architecture using monopolar plates.

Other configurations of interconnecting one or more stacks 131 A through 13 IN can be used. For example, bipolar stacks 131 A through 13 IN can be connected in parallel for lower voltage applications, such as to assemble a lower voltage battery pack. Alternatively, a single bipolar stack with many cells can form a higher-voltage pack. In either case, the voltage of the battery pack can be (Np-l)*Vcell, where Np can represent the number of current collector plates in each stack, and Vcell can represent the cell voltage.

FIG. 3 illustrates generally a section view of an example of a battery plate 321 including porous electrochemically-active material layers 312A and 312B that can include a controlled porosity that varies across a thickness of the layers 312A and 312B, and such a controlled porosity can be referred to as an "architectural" porous active material layer.

The present inventors have recognized, among other things, that a battery assembly can include using a plate assembly having active material layers having a controlled porosity, such as can be controlled to vary across a thickness of the active material layer. A battery plate having one or more such porous active material layers can be included as a portion of a battery assembly, such as a lead acid battery assembly. Such active material layers can be fabricated to provide desirable characteristics including good adhesion to a current collector 304, strong cohesion within the layer, and high porosity, such as having a modulated porosity throughout the layer.

In the illustrative example of FIG. 3, of an architectural porous active material layer is shown schematically, such as for use as a bipolar battery plate 321. Fabrication of the battery plate 321 can include formation of one or more thin film layers. The thin film layers can be electrochemically inactive, such as comprising one or more of layer 306A or layer 306B. Such layers 306A or 306B can be included to facilitate an ohmic contact between the current collector 304 (e.g., a rigid semiconductor substrate such as can include a silicon wafer) and the active material layers 312A or 312B. The layers 306A or 306B can also facilitate adhesion of the active material layers 312A or 312B to the plate assembly 321.

In an example, one or more of the layers 306A or 306B can include a metal silicide as one or more of a contact or adhesion layer on the current collector 304. The metal silicide surface can be cleaned (e.g., initially cleaned) to remove silicon or metal oxides on its surface. Lead (Pb) electrodeposition can be performed with a plating batch containing lead(II) tetrafluoroborate [Pb(BF₄)₂] to deposit a thin layer of Pb at the metal silicide surface, such as after cleaning.

In order to deposit a porous Pb active material layer with modulated porosity (e.g., having a controlled porosity profile with respect to depth or across a thickness of the active material layer), one or more deposition process parameters such as voltage, current density, or electrolyte agitation, can be controlled during the plating process. Because the Pb atoms in the electrodeposited layer are chemically bonded to one another, the porous Pb active material can provide desirable cohesion.

In an illustrative example, the current collector 304 can be fabricated such as including a rigid silicon wafer. A metal silicide can be formed on a surface of the silicon wafer, such as by depositing a metal layer with physical vapor deposition (PVD), followed by heating the substrate to high temperatures (e.g., an annealing process). A thickness of the PVD-deposited metal silicide layer (such as comprising one or more of the layers 306A or 306B) can be between about 20 to about 100 nanometers, in an illustrative example.

In an illustrative example, nickel silicide (NiSi) can be formed on silicon by annealing nickel (Ni) to about 450 to about 550 degrees Celsius (°C). In another illustrative example, titanium disilicide (C54-phase TiSi₂) can be formed on the silicon surface by annealing PVD- deposited titanium (Ti) to about 800 to about 900 °C. Both NiSi and C54 TiSi₂ can provide low-resistivity ohmic contacts with a silicon current collector 304. In addition, metal silicides can act as good adhesion layers, such as for electrodeposition of other layers, such as a thin layer 309A or 309B of lead.

The metal silicide surface can be cleaned prior to electrodeposition. For example, a sequence of wet-clean operations can be performed to remove metal and silicon oxides, as well as organic and inorganic contaminants on the surface. In an illustrative example, a cleaning sequence for NiSi can include three different solvents. For example, the current collector can be ultra-sonicated in buffered oxide etch (BOE) solution, deionized water, and ethanol. The cleaning time for each step can be about 1 to about 3 minutes, in an illustrative example. The current collector can be dried with nitrogen (e.g., using a nitrogen gun). Other generally-available semiconductor wet-clean procedures or apparatus can be used, such as to remove contaminants on a metal silicide surface.

In an illustrative example, a plating chemistry based on lead (II) tetrafluoroborate [Pb(BF₄)2] can be used, such as to electrodeposit a thin layer of lead (Pb), such as comprising one or more of the layers 309A or 309B in FIG. 3, on a cleaned metal silicide surface, such as can include one or more of the layers 306A or 306B, respectively. In one approach, a

Pb(BF₄)2 plating chemistry can be used with the addition of fluoroboric acid (HBF₄) and boric acid [B(OH)3] . However, an aqueous solution of Pb(BF4)2 with no HBF₄ or B(OH)3 can be instead be used to deposit a thin Pb layer with strong adhesion onto an NiSi surface. For example, FIG. 4A includes an illustrative example of a scanning electron micrograph (SEM) image 421 A illustrating generally Pb/NiSi/Substrate interfaces, such as can be included as a portion of a battery plate assembly. A NiSi layer 406A can be formed on a rigid silicon substrate 404. A lead layer 412A can then be deposited on the NiSi surface. The NiSi layer 406A can be provide ohmic contact between the lead layer 412A and the substrate 404, and can promote adhesion of the lead layer 412A to the substrate 404.

In an illustrative example, a plating bath concentration can range from 0.1 M to 1.0

M, and a plating current density can be established having about 10 to about 100 milliamps per square centimeter (mA/cm²). A lower current density can be used for the deposition of a dense layer at the metal silicide interface, such that the metal silicide is protected from electrolyte corrosion of a negative plate, in the example of a lead acid battery.

To protect the metal silicide in a positive plate, a thin layer of lead dioxide (PbC ) or tin dioxide (SnC ) can be used. In an example, PbC>2 can be deposited on the metal silicide with lead (II) tetrafluoroborate [Pb(BF₄)2] or lead (II) nitrate [Pb(N0₃)2] plating chemistry and process parameters similar to those for Pb electrodeposition, except that the current is reversed. FIG. 4B includes an illustrative example of a scanning electron micrograph (SEM) image 42 IB illustrating generally PbC /NiSi/substrate interfaces, such as can be included as a portion of a battery plate assembly. A NiSi layer 406B can be formed on the rigid silicon substrate 404, such as upon a surface of the substrate 404 opposite the layers shown in the example 421A of the FIG 4A. A lead dioxide layer 412B can then be formed on the NiSi surface. The NiSi layer 406B can be provide ohmic contact between the lead dioxide layer 412B and the substrate 404, and can promote adhesion of the lead dioxide layer 412B to the substrate 404. In another example, SnC>2 can be deposited, such as using physical vapor deposition (PVD) or electrodeposition on the metal silicide surface, for example.

FIG. 5A illustrates generally a technique that can include a co-deposition approach for providing a porous active material layer 512D. At 540, a thin layer of lead 512A can be deposited upon a substrate 504, such as upon one or more electrochemically-inactive thin film layers upon the substrate 504 (e.g., upon a silicide layer). At 550, electrodeposition can be initiated or can proceed including evolution of hydrogen at or just below the surface of the material 512B being deposited. Various process parameters can be modulated during deposition, as described elsewhere herein, such as to vary the porosity of the material layer across the material layer thickness, to provide an electrochemically-active material layer 512C having a controlled porosity profile.

In an illustrative, of porous lead active material layer (e.g., layers 312A or 312B as shown in FIG. 3 or layer 512D as shown in FIG. 5A) for a negative plate can be achieved through hydrogen co-deposition as shown in FIG. 5A, in which the electrochemical reactions of material deposition can occur concurrently with hydrogen evolution at the surface of the material deposited. The hydrogen bubbles act can as an in-situ template around which electrodeposition of lead active material occurs. The resulting active material layer can therefore be highly porous. In hydrogen co-deposition, the porosity of the material can be controlled by the relative rates of material deposition and hydrogen evolution, which in turn can be controlled by one or more process parameters such as plating bath composition, voltage and current density, or agitation during the deposition, for example.

In general, low concentrations and high current density favors bubble formation and therefore high porosities. For porous lead electrodeposition on metal silicides, lead (II) tetrafluoroborate [Pb(BF₄)₂], lead (II) methanesulfonate [Pb(CH₃S0₃)₂], or lead (II) perchlorate [Pb(C10₄)2] can be used as the plating bath, such as having concentration ranges from about 0.01 M to about 0.25 M. The current density for hydrogen evolution can be from about 0.1 to about 1.0 A/cm², according to an illustrative example. An un-agitated plating bath can be used for porous material deposition, but agitation can also be used to control porosity.

A porosity of the electrodeposited lead (Pb) can be modulated (e.g., controlled), such as by changing the process parameters during the deposition. In one illustrative example, a lower current density can be used to deposit a less porous layer at the bottom (e.g., a portion nearest the substrate), followed by increasing the current density to deposit a more porous layer on the top (e.g., a portion distal to the substrate) of the active material layer. In another illustrative example, electrodeposition can include using an agitated bath to deposit a less porous layer at the bottom, then bath agitation can be reduced or suppressed, as deposition progresses, such that a more porous layer is deposited at the top (e.g., as shown illustratively in FIG. 6A). Such variation of process parameters can be controlled or varied substantially continuously during deposition, or such parameters can be varied in a step-wise manner during deposition, for example.

In an illustrative example, lead dioxide (PbC ) active material layers for the positive plate of a lead acid battery can be deposited electrochemically at the anode of an electrolytic cell. The plating bath chemistry can include lead (II) tetrafluoroborate [Pb(BF₄)2] , lead (II) methanesulfonate [Pb(CH₃S0₃)₂], lead (II) nitrate [Pb(N0₃)₂], or lead (II) perchlorate

[Pb(C10₄)2] . Similar to lead electrodeposition, the particle size and the porosity of the resulting PbC>2 active material layer can be modulated by controlling deposition parameters such as plating bath concentration, current density, and bath agitation (e.g., as shown illustratively in FIGS . 6A and 6B) .

FIG. 5B illustrates generally a technique that can include using a mask for providing a porous active material layer. At 570, a mask 585 can be deposited, formed, or placed upon the substrate 504. At 580, an electrochemically-active material layer 512E can be formed, such a deposited upon the substrate 504. The template 585 can establish locations where voids or pores will be formed when the mask 585 is "lifted off or otherwise removed. For example, at 590, upon removal of the mask (e.g., "template removal"), such as can include a wet etching process, the electrochemically-active material layer 512F remains and includes pores or voids.

A porosity of the lead dioxide (PbC ) active material layer can be controlled at least in part using electrodeposition through a template mask. For example, a high surface area metal or metal oxide mesh can be used as a mask. In another approach, a polymer membrane can be used as the mask. After PbC>2 electrodeposition, the mask can be removed, such as by using wet etching techniques.

In another example, porous PbC>2 can be deposited by electrophoretic deposition. In electrophoretic deposition, PbC>2 particles can be dispersed into an organic solvent. Then, a potential can be applied at the current collector and deposition of PbC particles can occur by electrophoretic forces. In electrophoretic deposition, a porosity of the active material layer can be determined at least in part by an initial particle size distribution. FIGS. 6A and 6B include illustrative examples 621 A and 62 IB of scanning electron micrograph (SEM) images illustrating generally porous active material layers having different specified porosity profiles with respect to depth. In FIG. 6A, an active material layer 612A includes a relatively less porous structure nearby an interface with a substrate 604, as compared to a relatively more porous structure in a region distal to the interface, illustrating generally that such a porous structure varies across a thickness of the active material layer 612A. In FIG. 6B, an active material layer 612B includes a relatively more porous structure nearby an interface with the substrate 604, as compared to a relatively less porous structure in a region distal to the interface.

Various Notes & Examples

Example 1 can include or use subject matter (such as an apparatus, a method, a means for performing acts, or a device readable medium including instructions that, when performed by the device, can cause the device to perform acts), such as can include or use a battery plate comprising a rigid semiconductor substrate and a first electrochemically-active material layer located upon the rigid semiconductor substrate, the first electrochemically-active layer comprising a porous medium including a porosity that varies across a thickness of the first electrochemically-active material layer.

Example 2 can include, or can optionally be combined with the subject matter of Example 1, to optionally include a second electrochemically-active material layer located on a surface of the rigid semiconductor substrate opposite the first electrochemically-active material layer.

Example 3 can include, or can optionally be combined with the subject matter of Example 2, to optionally include a polarity of the second electrochemically-active material layer opposite the polarity of the first electrochemically-active material layer to provide a bipolar battery plate.

Example 4 can include, or can optionally be combined with the subject matter of one or any combination of Examples 2 or 3 to optionally include a

second electrochemically-active material layer comprising a porosity that varies across a thickness of the second electrochemically-active material layer.

Example 5 can include, or can optionally be combined with the subject matter of one or any combination of Examples 2 through 4 to optionally include a rigid semiconductor substrate comprising a silicon wafer, the first electrochemically-active material layer comprising lead, and the second electrochemically-active material layer comprising a compound including lead and oxygen.

Example 6 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 5 to optionally include one or more thin film layers for ohmic contact and adhesion formed between the current collector and the first electrochemically-active material layer.

Example 7 can include, or can optionally be combined with the subject matter of Example 6, to optionally include one or more thin film layers including an electrochemically- inactive layer comprising one or more of a metal, a metal silicide, a metal nitride, or a metal oxide.

Example 8 can include, or can optionally be combined with the subject matter of Example 7, to optionally include a metal included in one or more of the metal, the metal silicide, the metal nitride, or the metal oxide comprising one or more of molybdenum, nickel, tantalum, tin, titanium, or tungsten.

Example 9 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 8 to include, subject matter (such as an apparatus, a method, a means for performing acts, or a machine readable medium including instructions that, when performed by the machine, that can cause the machine to perform acts), such as can include

forming a battery plate, including forming one or more electrochemically-inactive thin film layers upon a rigid semiconductor substrate, and forming a first electrochemically-active material layer upon one of the one or more electrochemically-inactive thin film layers, the forming the first electrochemically-active material layer including varying a porosity of the electrochemically-active material layer across a thickness of the electrochemically-active material layer.

Example 10 can include, or can optionally be combined with the subject matter of Example 9 to optionally include forming the one or more electrochemically-inactive thin film layers including using physical vapor deposition and annealing.

Example 1 1 can include, or can optionally be combined with the subject matter of one or any combination of Examples 9 or 10 to optionally include forming a thin layer of lead upon the one or more electrochemically-inactive thin film layers.

Example 12 can include, or can optionally be combined with the subject matter of Example 11 , to optionally include forming the thin layer of lead including electrodepositing the lead using a plating solution comprising lead (II) tetrafluoroborate. Example 13 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 1 or 12 to optionally include forming the thin layer of lead including electrodepositing the lead using a plating solution comprising lead (II). Example 14 can include, or can optionally be combined with the subject matter of one or any combination of Examples 9 through 13 to optionally include cleaning a surface of the one or more electrochemically-inactive thin film layers to facilitate adhesion of the first electrochemically-active material on the battery plate.

Example 15 can include, or can optionally be combined with the subject matter of one or any combination of Examples 9 through 14 to optionally include forming the first electrochemically-active material layer using electrodeposition.

Example 16 can include, or can optionally be combined with the subject matter of Example 15, to optionally electrodeposition comprising forming a lead layer using a plating solution comprising one of lead (II) methanesulfonate, lead (II) perchlorate, or lead (II) tetrafluoroborate.

Example 17 can include, or can optionally be combined with the subject matter of Example 15 to optionally include electrodeposition including forming a lead dioxide layer using a plating solution comprising one of lead (II) methanesulfonate, lead (II) perchlorate, or lead (II) tetrafluoroborate.

Example 18 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 through 17 to optionally include a concentration of an electrodeposition plating solution selected from a range of about 0.01 M to about 0.25 M and a current density used for electrodeposition selected from a range of about 0.1 to about 1.0 A/cm².

Example 19 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 through 18 to optionally include one or more electrodeposition process parameters, including one or more of a current density, or a solution agitation, modulated during the deposition process to vary the porosity of the first electrochemically-active material layer across the thickness of the first electrochemically- active material layer.

Example 20 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 through 19 to optionally include electrodeposition performed using a template mask to vary the porosity of the first electrochemically-active material layer across the thickness of the first electrochemically-active material layer. Example 21 can include, or can optionally be combined with the subject matter of Example 20 to optionally include removing the mask after electrodeposition.

Example 22 can include, or can optionally be combined with the subject matter of one or any combination of Examples 9 through 21 to optionally include depositing the first electrochemically-active material layer using electrophoretic deposition of lead dioxide.

Example 23 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 22 to include, subject matter (such as an apparatus, a method, a means for performing acts, or a machine readable medium including instructions that, when performed by the machine, that can cause the machine to perform acts), such as can a battery assembly, comprising a housing and a bipolar battery plate. The bipolar battery plate can include a rigid semiconductor substrate, a first electrochemically- active material layer located upon the rigid semiconductor substrate, the first

electrochemically-active layer comprising a porous medium including a porosity that varies across a thickness of the first electrochemically-active material layer, a second

electrochemically-active material layer located on a surface of the rigid semiconductor substrate opposite the first electrochemically-active material layer, and one or more thin film layers including an electrochemically-inactive layer comprising one or more of a metal, a metal silicide, a metal nitride, or a metal oxide. In Example 23, a polarity of the second electrochemically-active material layer is opposite the polarity of the first electrochemically- active material layer to provide the bipolar battery plate.

Example 24 can include, or can optionally be combined with the subject matter of Example 23 to optionally include a thin layer of lead upon the one or more electrochemically- inactive thin film layers, and the first electrochemically-active material layer is located upon the thin layer of lead.

Example 25 can include, or can optionally be combined with the subject matter of one or any combination of Examples 23 or 24 to optionally include

the rigid semiconductor substrate comprising a silicon wafer, the first electrochemically- active material layer comprising lead, and the second electrochemically-active material layer comprising a compound including lead and oxygen.

Example 26 can include, or can optionally be combined with any portion or combination of any portions of any one or more of Examples 1 through 25 to include, subject matter that can include means for performing any one or more of the functions of Examples 1 through 25, or a machine-readable medium including instructions that, when performed by a machine, cause the machine to perform any one or more of the functions of Examples 1 through 25.

Each of these non-limiting examples can stand on its own, or can be combined in various permutations or combinations with one or more of the other examples.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as "examples." Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls.

In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In this document, the terms "including" and "in which" are used as the plain- English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or nonvolatile tangible computer-readable media, such as during execution or at other times.

Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

THE CLAIMED INVENTION IS:

1. A battery plate comprising:

a rigid semiconductor substrate; and

a first electrochemically-active material layer located upon the rigid semiconductor substrate, the first electrochemically-active layer comprising a porous medium including a porosity that varies across a thickness of the first electrochemically-active material layer.

2. The battery plate of claim 1, comprising a second electrochemically-active material layer located on a surface of the rigid semiconductor substrate opposite the first

electrochemically-active material layer.

3. The battery plate of claim 2, wherein a polarity of the second electrochemically-active material layer is opposite the polarity of the first electrochemically-active material layer to provide a bipolar battery plate.

4. The battery plate of claim 3, wherein the second electrochemically-active material layer comprises a porosity that varies across a thickness of the second electrochemically- active material layer.

5. The battery plate of claim 3, wherein the rigid semiconductor substrate comprises a silicon wafer;

wherein the first electrochemically-active material layer comprises lead; and wherein the second electrochemically-active material layer comprises a compound including lead and oxygen.

6. The battery plate of claim 1, comprising one or more thin film layers for ohmic contact and adhesion formed between the current collector and the first electrochemically- active material layer.

7. The battery plate as in claim 6, wherein the one or more thin film layers includes an electrochemically-inactive layer comprising one or more of a metal, a metal silicide, a metal nitride, or a metal oxide.

8. The battery plate of claim 7, wherein the metal included in one or more of the metal, the metal silicide, the metal nitride, or the metal oxide includes one or more of molybdenum, nickel, tantalum, tin, titanium, or tungsten.

9. A method for forming a battery plate, comprising:

forming one or more electrochemically- inactive thin film layers upon a rigid semiconductor substrate; and

forming a first electrochemically-active material layer upon one of the one or more electrochemically-inactive thin film layers, wherein the forming the first electrochemically- active material layer includes varying a porosity of the electrochemically-active material layer across a thickness of the electrochemically-active material layer.

10. The method of claim 9, wherein forming the one or more electrochemically-inactive thin film layers includes using physical vapor deposition and annealing.

11. The method of claim 9, comprising forming a thin layer of lead upon the one or more electrochemically-inactive thin film layers.

12. The method of claim 1 1 , wherein forming the thin layer of lead includes

electrodepositing the lead using a plating solution comprising lead (II) tetrafluoroborate.

13. The method of claim 1 1, wherein forming the thin layer of lead includes

electrodepositing the lead using a plating solution comprising lead (II).

14. The method of claim 9, comprising cleaning a surface of the one or more

electrochemically-inactive thin film layers to facilitate adhesion of the first

electrochemically-active material on the battery plate.

15. The method of claim 9, wherein the forming the first electrochemically-active material layer includes using electrodeposition.

16. The method of claim 15, wherein the electrodeposition includes forming a lead layer using a plating solution comprising one of lead (II) methanesulfonate, lead (II) perchlorate, or lead (II) tetrafluoroborate.

17. The method of claim 15, wherein the electrodeposition includes forming a lead dioxide layer using a plating solution comprising one of lead (II) methanesulfonate, lead (II) perchlorate, or lead (II) tetrafluoroborate.

18. The method of claim 15, wherein a concentration of an electrodeposition plating solution is selected from a range of about 0.01 M to about 0.25 M; and

wherein a current density used for electrodeposition is selected from a range of about 0.1 to about 1.0 A/cm².

19. The method of claim 15, wherein one or more electrodeposition process parameters, including one or more of a current density, or a solution agitation, are modulated during the deposition process to vary the porosity of the first electrochemically-active material layer across the thickness of the first electrochemically-active material layer.

20. The method of claim 15, wherein the electrodeposition is performed using a template mask to vary the porosity of the first electrochemically-active material layer across the thickness of the first electrochemically-active material layer.

21. The method of claim 20, wherein the mask is removed after electrodeposition.

22. The method of claim 9, comprising depositing the first electrochemically-active material layer using electrophoretic deposition of lead dioxide.

23. A battery assembly, comprising:

a housing; and

a bipolar battery plate including:

a rigid semiconductor substrate;

a first electrochemically-active material layer located upon the rigid semiconductor substrate, the first electrochemically-active layer comprising a porous medium including a porosity that varies across a thickness of the first

electrochemically-active material layer; a second electrochemically-active material layer located on a surface of the rigid semiconductor substrate opposite the first electrochemically-active material layer; and

one or more thin film layers including an electrochemically-inactive layer comprising one or more of a metal, a metal silicide, a metal nitride, or a metal oxide; wherein a polarity of the second electrochemically-active material layer is opposite the polarity of the first electrochemically-active material layer to provide the bipolar battery plate.

24. The battery assembly of claim 24, comprising a thin layer of lead upon the one or more electrochemically-inactive thin film layers;

wherein the first electrochemically-active material layer is located upon the thin layer of lead.

25. The battery assembly of claim 23, wherein the rigid semiconductor substrate comprises a silicon wafer;