Patent Description:
Electrochemical cells (e.g. batteries) are becoming essential in future electronic and transportation applications. There is significant interest in increasing battery capacity and energy density, reducing the charging time, and increasing the battery lifetime for various mobile applications such as cell phones, laptops, and electric vehicles. One of the major challenges in improving these battery characteristics is the prospect of uncontrolled runaway reactions where current hot spots (due to inhomogeneities in the electrode structure) accelerate undesirable side-reactions or filament formation. Furthermore, any manufacturing defects that result in internal shorts can allow the entire battery capacity to rapidly discharge through the internal short, causing the battery to rapidly heat up and fail catastrophically. In order to design around this potential safety problem, some battery packs include sophisticated thermal and electrical management systems that increase the cost, mass, and volume of the batteries. Even with these sophisticated systems, battery pack designers have no control over current flow within a single cell, which forces them to over-engineer at the battery pack-level. <NPL> disclosesswitching and control of active matrix organic light-emitting devices (AMOLEDs) by printed organic thin-film electrochemical transistors (OETs), including a high-capacitance electrolyte as the gate dielectric layer in the OETs and graded emissive layer (G-EML) OLEO architectures. <NPL> discloses incorporation of electrochemical-gating (EC) in nanowire electronics and a composite solid polymer electrolyte (CSPE) to obtain all-solid-state FETs.

The claimed invention is directed to a system as defined in claim <NUM>.

Embodiments herein relate to systems for controlling the current distribution within an energy device that produces or consumes energy. Current flowing through the energy device either provides energy to the device or provides energy generated by the device to an external load. In various embodiments discussed herein, the current distribution across a surface of the energy device is controlled by a current limiter comprising an array of electrochemical transistors (ECTs) operating under passive or active control. In some embodiments the device is an energy producing device that generates output current controlled by the current limiter. Examples of energy producing devices include a battery cell during discharge, a fuel cell, and a photovoltaic cell. In some embodiments the device is an energy consuming device in which current flowing through the device provides energy to the device. Examples of energy absorbing devices include a battery cell during charging, electroplating and electro-etching cells, and/or other types of electrochemical or photoelectrochemical cells. For simplicity, both energy absorbing and energy producing devices are referred to herein as an "energy device".

<FIG> shows a view of a system <NUM> incorporating a current limiter <NUM> in accordance with some embodiments. The system <NUM> includes at least one current collector electrode <NUM> and a device <NUM> that includes an active region <NUM> configured to produce or consume electrical current. The device <NUM> may include first <NUM> and second <NUM> electrically conductive layers that are electrically coupled to the portion of the device <NUM> that includes the active region <NUM>. As shown in <FIG>, the first electrically conductive layer <NUM> is patterned and is electrically connected to the current limiter <NUM>. Each discrete region <NUM>-<NUM>, <NUM>-<NUM> of the active region <NUM> is associated with one of the patterned regions <NUM>-<NUM>, <NUM>-<NUM> of the patterned electrically conductive layer <NUM>. One or both of the first and second electrically conductive layers <NUM>,<NUM> may be patterned.

A current limiter <NUM> comprising a plurality of ECTs <NUM>-<NUM>, <NUM>-<NUM> is electrically connected between the active region <NUM> of the energy device <NUM> and the current collector electrode <NUM>. The plurality of ECTs <NUM>-<NUM>, <NUM>-<NUM> are arranged in an array such that each ECT <NUM>-<NUM>, <NUM>-<NUM> in the array provides localized current control for the device <NUM>. The array of ECTs <NUM>-<NUM>, <NUM>-<NUM> in the current limiter <NUM> and the patterning of the first electrically conductive layer <NUM> into patterned regions <NUM>-<NUM>, <NUM>-<NUM> may be two dimensional, extending along both the x and y axes as indicated in <FIG>. The ECTs <NUM>-<NUM>, <NUM>-<NUM> can operate as p-type depletion mode electrochemical switches, operating in cut-off mode (negligible current flows through the ECT) when the voltage on the control electrode is above the threshold voltage value and operating in saturation mode (current flows through the ECT) when the voltage at the control electrode is below the threshold voltage value. The ECTs <NUM>-<NUM>, <NUM>-<NUM> can alternatively be n-type, in which case the signs for the cut-off mode will be reversed from those described above. In some embodiments, the ECTs <NUM>-<NUM>, <NUM>-<NUM> can be biased to operate in linear mode to provide localized variable current control.

As discussed in more detail below, each ECT <NUM>-<NUM>, <NUM>-<NUM> in the array operates as an electrochemical transistor having drain and source electrodes with a channel disposed between the drain and the source electrodes. An electrolyte electrically couples a gate electrode to the channel such that an electrical signal at the gate electrode controls electrical conductivity of the channel. The current collector electrode <NUM> serves as a shared drain or source electrode for the ECTs.

<FIG> shows another embodiment of a system <NUM> that incorporates first <NUM> and second <NUM> current limiters. In this embodiment, the first current limiter <NUM> includes an array of first ECTs <NUM>-<NUM>, <NUM>-<NUM> electrically connected between the portion of the device <NUM> that includes the active region <NUM> and the first current collector <NUM>. The second current limiter <NUM> includes an array of second ECTs <NUM>-<NUM>, <NUM>-<NUM> electrically connected between the portion of the device <NUM> that includes the active region <NUM> and the second current collector <NUM>. In the embodiment shown in <FIG>, the first current collector electrode <NUM> is a shared drain or source electrode for the first ECTs <NUM>-<NUM>, <NUM>-<NUM> and the second current collector electrode <NUM> is a shared drain or source electrode for the second ECTs <NUM>-<NUM>, <NUM>-<NUM>.

The device <NUM> includes first <NUM> and second <NUM> electrically conductive layers that are electrically coupled to the active region <NUM>. In the illustrated embodiment of <FIG>, the first and second electrically conductive layers <NUM>, <NUM> are patterned such that each discrete region <NUM>-<NUM>, <NUM>-<NUM> of the active region <NUM> is associated with one of the discrete regions <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> of the patterned electrically conductive layers <NUM>, <NUM>. As shown in <FIG>, the first current limiter <NUM> is disposed between the first current collector layer <NUM> and the spaced apart regions of the first electrically conductive layer <NUM>. The second current limiter <NUM> is disposed between the second current collector layer <NUM> and the spaced apart regions of the second electrically conductive layer <NUM>.

Operation of a system incorporating a current limiter used in conjunction with an energy device as disclosed herein is illustrated with reference to <FIG> shows a system <NUM> as described in <FIG> in which the energy device is a battery cell <NUM>. The battery cell <NUM> may be any type of battery cell, including primary or secondary (rechargeable) types. For example, the battery cell <NUM> may be a lithium ion battery cell, a nickel metal hydride battery cell or a zinc bromide battery cell.

The battery <NUM> includes a positive electrode (cathode during discharge) <NUM>, a negative electrode (anode during discharge) <NUM>, and an electrolyte <NUM> disposed between the positive electrode <NUM> and negative electrode <NUM>. A patterned electrically conductive layer <NUM> is electrically coupled to the positive electrode <NUM>. An electrically conductive layer <NUM> is electrically coupled to the negative electrode <NUM>. In some embodiments, the positive electrode <NUM> and/or negative electrode <NUM> may be substantially continuous layers without substantial physical segregation into smaller layer regions. The battery <NUM> may have relatively large current collection area such that the width, W, of the substantially continuous positive electrode <NUM> and/or negative electrode <NUM> layers are substantially larger than a thickness, T, of the battery <NUM>. The large current collection area facilitates control over discrete regions R1, R2 of the battery <NUM> in which in localized currents C1, C2 flow between the negative electrode <NUM> and the positive electrode <NUM> as indicated by the arrows. In this example, localized current C1 is generated and flows in region R1, and localized current C2 is generated and flows in region R2, wherein the magnitude of the current C1 may or may not be equal to the magnitude of the current C2. Note that in this example, the arrows indicate the direction of the net flow of positive charges, and it is appreciated that the charge carriers can be electrons or ions dissolved in the electrolyte <NUM>.

As illustrated in <FIG>, the first electrically conductive layer <NUM> of the battery <NUM> includes spaced apart contact pads <NUM>-<NUM>, <NUM>-<NUM> that are electrically connected to the positive electrode <NUM> of the battery <NUM> so as to couple each contact pad <NUM>-<NUM>, <NUM>-<NUM> to an associated region R1, R2 of the battery <NUM>. As shown, substantially all, e.g., over <NUM>%, over <NUM>%, or even over <NUM>%, of the localized current C1 from region R1 flows through contact pad <NUM>-<NUM> and substantially all, e.g., over <NUM>%, over <NUM>%, or even over <NUM>%, of the localized current C2 from region R2 flows through contact pad <NUM>-<NUM>.

Note that although discrete contact pads <NUM>-<NUM>, <NUM>-<NUM> are shown in <FIG> as being electrically coupled to the positive electrode <NUM>, in other embodiments, discrete contact pads may be electrically coupled to the negative electrode and not to the positive electrode, or a first set of discrete contact pads may be coupled to the positive electrode and a second set of discrete contact pads may be coupled to the negative electrode (see, e.g., <FIG>).

System <NUM> facilitates distributed control over localized battery currents generated in discrete battery regions R1 to R2 due to the operating states of ECTs <NUM>-<NUM> to <NUM>-<NUM>, respectively. Current C1 flowing through contact pad <NUM>-<NUM> is derived predominantly or exclusively from discrete battery region R1 and localized control over current C1 is achieved by controlling the operating state of ECT <NUM>-<NUM>. For example, the magnitude of localized current C1 in battery region R1 is effectively decreased or increased by controlling the current C1 through transistor <NUM>-<NUM>. The current C1 can be decreased or increased by adjusting a control voltage Vc1 of the ECT <NUM>-<NUM>. Similarly, current C2 flowing through contact pad <NUM>-<NUM> is derived predominantly or exclusively from discrete battery region R2. Localized control over current C2 is achieved by controlling the operating state of ECT <NUM>-<NUM>. For example, current C2 can be decreased or increased by adjusting a control voltage Vc2 of the ECT <NUM>-<NUM>.

<FIG> provides a schematic view of an ECT <NUM>, e.g., an organic ECT (OECT), which may be used for the ECTs <NUM>-<NUM>, <NUM>-<NUM> of the current limiter <NUM> shown in <FIG> and/or for the ECTs <NUM>-<NUM>, <NUM>-<NUM> of the current limiter <NUM> shown in <FIG>, for example. The ECT <NUM> includes gate electrode <NUM>, channel <NUM>, which typically can include a semiconductor film (e.g., a conjugate polymer film), source electrode <NUM>, drain electrode <NUM>, and electrolyte <NUM>. Source electrode <NUM> and drain electrode <NUM> can establish electrical contact to channel <NUM>, while gate electrode <NUM> establishes electrical contact to electrolyte <NUM>. Electrolyte <NUM> can be liquid, gel, or solid. In the most common biasing configuration as shown in <FIG>, a voltage (drain voltage VD) is applied to the drain relative to the source. This can cause a current to flow (drain current), due to electronic charges (usually holes) present in channel <NUM>. When a voltage is applied to the gate (gate voltage VG), charge carriers can be injected into or removed from the channel and charge-compensating ions can be transferred to or from the electrolyte, leading to a change in the electronic charge density and hence the drain current. When the gate voltage is removed and the gate is shorted to the source, the injected charge carriers return to the gate, charge-compensating ions return to the electrolyte, and the drain current goes back to its original value. The terms "drain" and "source" are not meant to imply any particular direction of the flow of positive or negative carriers. The direction of the flow of carriers may be different when a device operates in different modes, e.g., charging or discharging. The terms "drain electrode" or "source electrode" as used herein are arbitrary labels employed for convenience in describing features of the transistors.

PEDOT:PSS (poly(<NUM>,<NUM>-ethylenedioxythiophene) polystyrene sulfonate) can be used as the channel material due to its commercial availability and high electronic and ionic conductivity. PEDOT:PSS is a polymer mixture of two ionomers. One component in this mixture is made up of polystyrene sulfonic acid, which is a sulfonated polystyrene (or PSS). Part of the sulfonic acid groups are deprotonated and carry a negative charge. The other component, PEDOT, is a conjugated polymer and carries positive charges. Because the organic semiconductor PEDOT is doped p-type by the sulfonate anions of the PSS (the dopant), PEDOT:PSS can exhibit a high (hole) conductivity. Hence, in the absence of a gate voltage, the drain current will be high and the transistor will be in the ON state. When a positive voltage is applied to the gate, the PEDOT is electrochemically reduced and ions from the electrolyte (e.g., NaCl in water) compensate the charge of the sulfonate anions. This leads to de-doping of the PEDOT, and the transistor reaches its OFF state.

<FIG> shows the output curves for an ECT with channel dimensions of <NUM> x <NUM> illustrating that at VD = -<NUM> V as VG changes from -<NUM> V to <NUM> V the magnitude of the drain current ID decreases from about <NUM> mA at VG = -<NUM> V to about zero at VG = <NUM> V. <FIG> shows the output curves for the same transistor with the axes swapped and at a different scale to highlight the current limiting behavior of these ECT devices. <FIG> shows the differential resistance (dVD/dID) of the ECT as a function of channel current and gate voltage for the same device as in <FIG> and <FIG>. The cut-off current (the current at which the resistance sharply increases) can be tuned by changing the device dimensions and gate voltage.

According to some embodiments, the current limiter comprises an array of ECTs printed or otherwise deposited onto a current-carrying metal foil. <FIG>, <FIG>, and <FIG> illustrate top, side, and side views, respectively, of a current limiter <NUM> in accordance with some embodiments. <FIG> shows a top view of the current limiter <NUM> along with the patterned electrically conductive layer <NUM> of an energy device. For example, conductive layer <NUM> may correspond to element <NUM> of <FIG>, element <NUM> of <FIG>, or element <NUM> of <FIG>. Although not shown in <FIG>, <FIG>, or <FIG>, the active material of the energy device (see e.g., element <NUM> of <FIG> and elements <NUM>-<NUM> of <FIG>) would be deposited on the patterned electrically conductive layer and the current limiter <NUM> would limit the current through the active material of the energy device.

As best seen in <FIG>, the current limiter <NUM> includes ECTs <NUM>-<NUM>, <NUM>-<NUM> that share a common current collector layer <NUM> in contact with the channel <NUM>-<NUM>, <NUM>-<NUM>. For example, the current collector layer <NUM> may serve as the drain of the ECTs <NUM>-<NUM>, <NUM>-<NUM>. The current collector layer <NUM> can be a current-carrying metal foil which serves to collect current from the energy device. The other electrode in contact with the ECT channel (e.g., the source electrode of the ECT) is a patterned layer comprising conductive pads <NUM>-<NUM>, <NUM>-<NUM> which form discrete spaced apart regions. The pads <NUM>-<NUM>, <NUM>-<NUM> may be disposed on insulator <NUM> such that each pad <NUM>-<NUM>, <NUM>-<NUM> is electrically isolated from other pads <NUM>-<NUM>, <NUM>-<NUM>. Thus, in some configurations the channel <NUM>-<NUM>, <NUM>-<NUM> of each ECT <NUM>-<NUM>, <NUM>-<NUM> is electrically coupled to a respective contact pad <NUM>-<NUM>, <NUM>-<NUM> at one end of the channel <NUM>-<NUM>, <NUM>-<NUM> and to the common current collector layer <NUM> at the other end of the channel <NUM>-<NUM>, <NUM>-<NUM>. The gate electrode <NUM>-<NUM>, <NUM>-<NUM> of the ECT <NUM>-<NUM>, <NUM>-<NUM> shorted to the common current collector layer <NUM> (drain) , according to the claimed invention, or to the pads <NUM>-<NUM>, <NUM>-<NUM> (source), in an embodiment not forming part of the claimed invention. In the claimed invention that includes a gate electrode shorted to either the drain or source electrode, the electrode to which the gate is shorted dictates which direction that the current is limited. The gate <NUM>-<NUM>, <NUM>-<NUM> of the ECT <NUM>-<NUM>, <NUM>-<NUM> is electrically coupled to the electrolyte <NUM>-<NUM>, <NUM>-<NUM> such that the voltage at the gate <NUM>-<NUM>, <NUM>-<NUM> controls the doping level in the channel <NUM>-<NUM>, <NUM>-<NUM> and thus the current flow through the ECT <NUM>-<NUM>, <NUM>-<NUM> as discussed above.

<FIG> illustrates a scenario in which the gate of a first ECT <NUM>-<NUM> is electrically connected to the common current collector layer <NUM> and the gate of a second ECT <NUM>-<NUM> is electrically connected to a contact pad <NUM>-<NUM>. <FIG> represents a possible configuration for the current limiter, however, it will be appreciated that in alternate configurations the gate of each ECT in the array may be electrically connected to the common current collector layer or the gate of each ECT in the array may be connected to a respective contact pad. Furthermore, it will be appreciated that current limiters <NUM>,<NUM> can be present on both sides of the common current collector layer <NUM> as shown in <FIG>. Each of the current limiters <NUM>,<NUM> function in the manner described above, where elements <NUM>-<NUM>,<NUM>-<NUM> correspond to elements <NUM>-<NUM>,<NUM>-<NUM>, elements <NUM>-<NUM>,<NUM>-<NUM> correspond to elements <NUM>-<NUM>,<NUM>-<NUM>, elements <NUM>-<NUM>,<NUM>-<NUM> correspond to elements <NUM>-<NUM>,<NUM>-<NUM>, elements <NUM>-<NUM>,<NUM>-<NUM> correspond to elements <NUM>-<NUM>,<NUM>-<NUM>, and elements <NUM>-<NUM>,<NUM>-<NUM> correspond to elements <NUM>-<NUM>, <NUM>-<NUM>.

In some embodiments, the system may include only one current limiter comprising an ECT array electrically connected through an electrically conductive layer to the negative electrode (anode during discharge) of the battery or other energy device. In some embodiments, the system may include only one current limiter electrically connected through an electrically conductive layer to the positive electrode (cathode) of the energy device. In some embodiments the system may include a first current limiter electrically connected through an electrically conductive layer to the negative electrode of the energy device and a second current limiter electrically connected through an electrically conductive layer to the positive electrode of the energy device. <FIG> illustrate configurations for systems that include one or two current limiters in accordance with various embodiments.

As shown in <FIG>, the current limiter discussed herein can be directly used with existing battery manufacturing process lines in several possible configurations. The ECTs can be deposited at the negative electrode (e.g., anode) of the energy device, the positive electrode (e.g., cathode) of the energy device, or at both the negative and positive electrodes. The gate electrode is shorted to either the common current collector layer , i.e. claimed invention, or the conductive pads in contact with the battery electrodes, i.e. embodiments not forming part of the claimed invention, depending on the ECT carrier type (n-type or p-type) and on which direction the current is to be limited. <FIG> show several possible configurations of systems that include one or two current limiters although additional permutations are possible. For example, <FIG> and <FIG> depict systems <NUM>, <NUM> that include a current limiter at the negative electrode of the energy device to limit the discharge (<FIG>) and charging current (<FIG>), respectively. By limiting the discharge current flowing through the negative electrode of a lithium-ion battery, the rate of self-discharge during an internal short-circuit can be decreased. On the other hand, by limiting the charging current through the negative electrode of a lithium-ion battery, the lithium plating and the formation of lithium dendrites can be suppressed, which decreases the likelihood of an internal short-circuit.

Enhanced design flexibility can be achieved by alternatively or additionally incorporating current limiters at the positive electrode of the energy device as shown in the systems <NUM>, <NUM> depicted in <FIG> and <FIG>. For example, <FIG> depicts a system <NUM> where discharge current through both the positive and negative electrodes is limited, which would further reduce the rate of self-discharge during an internal short-circuit. Alternately, the limiting current directions can oppose each other as shown in the system <NUM> of <FIG>, so the negative electrode limits the charging current while the positive electrode limits the discharging current. Numerous other permutations and combinations of current limiters based on ECTs are possible.

<FIG> show systems <NUM>, <NUM>, <NUM>, <NUM> that include one or two current limiters <NUM>, <NUM>, <NUM> and an energy device <NUM> that is illustrated as a battery. Each current limiter <NUM>, <NUM>, <NUM> includes an array of ECTs, shown as <NUM>-<NUM> and <NUM>-<NUM> or <NUM>-<NUM> and <NUM>-<NUM>, which are p-type in this embodiment but could alternatively be n-type. The battery <NUM> comprises an electrolyte <NUM> disposed between a negative electrode (anode) <NUM> and a positive electrode (cathode) <NUM>. In <FIG> and <FIG>, a substantially continuous electrically conductive layer <NUM> is disposed on the positive electrode <NUM> of the battery <NUM> and a layer <NUM> comprising an array of electrically conductive pads <NUM>-<NUM>, <NUM>-<NUM> is disposed on the negative electrode <NUM>. In <FIG> and <FIG>, a layer <NUM> comprising an array of electrically conductive pads <NUM>-<NUM>, <NUM>-<NUM> is disposed on the positive electrode <NUM> of the battery and a conductive layer <NUM> comprising an array of electrically conductive pads <NUM>-<NUM>, <NUM>-<NUM> is disposed on the negative electrode <NUM>.

<FIG> shows system <NUM> that includes current limiter <NUM> comprising ECTs <NUM>-<NUM>, <NUM>-<NUM>. In the system <NUM> of <FIG>, the current limiter <NUM> controls the discharging current flowing from the common current collector <NUM> to the negative electrode <NUM> (anode) of the battery <NUM>. ECTs <NUM>-<NUM>, <NUM>-<NUM> include a first electrode <NUM>-1d, <NUM>-2d (e.g., a drain electrode), a second electrode <NUM>-<NUM>, <NUM>-<NUM> (e.g., a source electrode), and a control electrode <NUM>-<NUM>, <NUM>-<NUM> (e.g., a gate electrode). The first electrodes <NUM>-1d, <NUM>-2d of each ECT <NUM>-<NUM>, <NUM>-<NUM> are electrically coupled to the common current collector layer <NUM>. The second electrodes <NUM>-<NUM>, <NUM>-<NUM> of each ECT <NUM>-<NUM>, <NUM>-<NUM> are respectively coupled to a corresponding contact pad <NUM>-<NUM>, <NUM>-<NUM> of the battery <NUM> (or other energy device). The contact pads <NUM>-<NUM>, <NUM>-<NUM> electrically connect the second electrodes <NUM>-<NUM>, <NUM>-<NUM> of each ECT <NUM>-<NUM>, <NUM>-<NUM> to the negative electrode <NUM> (anode) of the battery <NUM> (or other energy device). The gate electrodes <NUM>-<NUM>, <NUM>-<NUM> are electrically connected to first electrode <NUM>-1d, <NUM>-2d in this embodiment.

With this arrangement, ECT <NUM>-<NUM> is designed such that it is in the on state when the gate <NUM>-<NUM> is electrically connected to the drain <NUM>-1d. If the magnitude of localized current C1 from the battery <NUM> passing from collection plate <NUM> to contact pad <NUM>-<NUM> is small, the ECT <NUM>-<NUM> operates in the linear regime and acts as a low-resistance resistor. However, if a hot-spot or other undesirable current spike occurs and causes C1 to increase above a designed value, the ECT <NUM>-<NUM> will enter saturation mode and its differential resistance will dramatically increase (see, e.g., <FIG>). This, in turn, causes the localized current C1 to decrease back to acceptable values.

Similarly, ECT <NUM>-<NUM> is designed such that it is in the on state when the gate <NUM>-<NUM> is electrically connected to the drain <NUM>-2d. If the magnitude of localized current C2 from the battery <NUM> passing from collection plate <NUM> to contact pad <NUM>-<NUM> is small, the ECT <NUM>-<NUM> operates in the linear regime and acts as a low-resistance resistor. However, if a hot-spot or other undesirable current spike occurs and causes C2 to increase above a designed value, the ECT <NUM>-<NUM> will enter saturation mode and its differential resistance will dramatically increase (see, e.g., <FIG>). This, in turn, causes the localized current C2 to decrease back to acceptable values.

The current collector <NUM> can be implemented by a metal-containing film or other conductive material, e.g., aluminum, carbon/graphite, copper, gold, silver, indium tin oxide (ITO) or other conductive oxide, etc. that facilitates the combination of localized currents C1 to C2 such that the sum of these currents form the current CDISCHARGE.

<FIG> shows a system <NUM> that includes current limiter <NUM> comprising ECTs <NUM>-<NUM>, <NUM>-<NUM>. In the system <NUM> of <FIG>, the current limiter <NUM> controls the charging current from the negative electrode <NUM> (anode) of the battery <NUM> to the common current collector <NUM>. ECTs <NUM>-<NUM>, <NUM>-<NUM> include a first electrode <NUM>-1d, <NUM>-2d (e.g., a drain electrode), a second electrode <NUM>-<NUM>, <NUM>-<NUM> (e.g., a source electrode), and a gate electrode <NUM>-<NUM>, <NUM>-<NUM>. In current limiter <NUM>, the second electrodes <NUM>-<NUM>, <NUM>-<NUM> of each ECT <NUM>-<NUM>, <NUM>-<NUM> are electrically coupled to the common current collector electrode <NUM>. The first electrodes <NUM>-1d, <NUM>-2d of each ECT <NUM>-<NUM>, <NUM>-<NUM> are respectively coupled to a corresponding contact pad <NUM>-<NUM>, <NUM>-<NUM> of the battery <NUM> (or other energy device). The gate electrodes <NUM>-<NUM>, <NUM>-<NUM> are electrically connected to first electrode <NUM>-1d, <NUM>-2d.

The current collector <NUM> facilitates the combination of localized currents C1 to C2 such that the sum of these currents form the current CCHARGE.

<FIG> shows system <NUM> that includes current limiter <NUM> as in <FIG> and current limiter <NUM>. System <NUM> is arranged such that the energy device <NUM> is disposed between and is electrically connected to the first current limiter <NUM> and the second current limiter <NUM>. In the system <NUM>, the first current limiter <NUM> controls the discharging current from the common current collector <NUM> to the negative electrode <NUM> (anode) of the battery. The second current limiter <NUM> controls the discharging current from the positive electrode <NUM> (cathode) of the battery <NUM> to the common current collector <NUM>.

The second current limiter <NUM> comprises ECTs <NUM>-<NUM>, <NUM>-<NUM>. ECTs <NUM>-<NUM>, <NUM>-<NUM> include a first electrode <NUM>-1d, <NUM>-2d (e.g., a drain electrode), a second electrode <NUM>-<NUM>, <NUM>-<NUM> (e.g., a source electrode), and a gate electrode <NUM>-<NUM>, <NUM>-<NUM>. The second electrodes <NUM>-<NUM>, <NUM>-<NUM> of each ECT <NUM>-<NUM>, <NUM>-<NUM> of the second current limiter <NUM> are electrically connected to the common current collector electrode <NUM>. The first electrodes <NUM>-1d, <NUM>-2d of each ECT <NUM>-<NUM>, <NUM>-<NUM> of the second current limiter <NUM> are respectively coupled to a corresponding contact pad <NUM>-<NUM>, <NUM>-<NUM> of the battery <NUM> (or other energy device). Each gate electrode <NUM>-<NUM>, <NUM>-<NUM> of the ECTs <NUM>-<NUM>, <NUM>-<NUM> of the second current limiter <NUM> is respectively electrically connected to the first electrode <NUM>-<NUM> d, <NUM>-2d of the ECTs <NUM>-<NUM>, <NUM>-<NUM> of the second current limiter <NUM>.

System <NUM> shown in <FIG> includes current limiter <NUM> as in <FIG> and current limiter <NUM> as in <FIG>. In system <NUM> the current limiting directions of the first and second ECT arrays <NUM>, <NUM> oppose each other. System <NUM> is arranged such that the energy device <NUM> is disposed between and is electrically connected to current limiter <NUM> and current limiter <NUM>. In the system <NUM>, the first current limiter <NUM> controls the charging current from the negative electrode <NUM> (anode) of the battery <NUM> to the common current collector <NUM>. The second current limiter <NUM> controls the discharging current from the positive electrode <NUM> (cathode) of the battery <NUM> to common current collector <NUM>.

When a current is drawn from or forced into a battery, the current distributes over each electrode according to the resistance between each point on the current collector and the edge of the batteries. Occasionally, manufacturing defects or other inhomogeneity can lower the resistance to current flow at a particular spot on the current collector leading to a current hot spot. At best, this current hot-spot can lead to decreased cell capacity as the cell is degraded near the current hot spot. At worst, current hot-spots can lead to filament formation and thermal runaway. If a short forms in the battery for any reason, the entire battery capacity can be rapidly discharged through the short, leading to overheating and fire. In a battery cell equipped with a current limiter as disclosed herein, current hot-spots are suppressed by the current-limiting nature of ECTs. Furthermore, in the case of a catastrophic internal short, the ECTs slow the rate of self-discharge through the short, allowing for graceful battery shutdown.

<FIG> is a distributed model for a conventional battery comprising seven subcells or regions. Each battery subcell is modeled by a voltage source <NUM>, series resistance <NUM>, shunt resistance <NUM> (very high for an ideal subcell), and electrode resistances <NUM>. <FIG> depicts a short in subcell <NUM> such that the shunt resistance for subcell <NUM> is very low. Path <NUM> indicates the current flow from subcell <NUM> through the short. Path <NUM> indicates the current flow from adjacent subcell <NUM> through subcell <NUM> due to the short. In a conventional battery, as illustrated in <FIG>, internal shorts can allow the battery capacity to rapidly discharge through the short.

<FIG> is a distributed model for a system comprising a battery and first and second current limiters in accordance with some embodiments. Six subcells of the battery are depicted in <FIG>. Each battery subcell is modeled by a voltage source <NUM>, series resistance <NUM>, shunt resistance <NUM> (very high for an ideal subcell), and electrode resistances <NUM>. Current limiters <NUM>, <NUM> comprising ECTs <NUM>, <NUM> and current collectors represented by resistors <NUM> are disposed at opposite electrodes of the battery. <FIG> depicts a short in subcell <NUM> such that the shunt resistance for subcell <NUM> is very low. Path <NUM> indicates the current flow from subcell <NUM> through the short indicating that the current flow from adjacent subcell <NUM> through subcell <NUM> is controlled by the ECTs <NUM>, <NUM> of subcells <NUM> and <NUM>. By adding ECTs to limit the current flow through any particular region of current collector, the current from other sub-cells that travels through the ECTs is limited, and graceful battery shutdown is possible.

A SPICE simulation was performed using an equivalent circuit model for a system <NUM> comprising current limiter <NUM> and battery <NUM> shown in <FIG>. The simulations indicate that a current limiter comprising ECTs can inhibit current flow from neighboring subcells in the event of a shorted or low resistance battery subcell. <FIG> illustrates the simulated current flowing through the short-circuit as a function of time for batteries without a current-limiter (plot <NUM>), with a current-limiter under internal short-circuiting (plot <NUM>), and with a current-limiter under external short-circuiting (plot <NUM>). <FIG> illustrates the simulated temperature as a function of time for batteries without a current-limiter (plot <NUM>), with a current-limiter under internal short-circuiting (plot <NUM>), and with a current-limiter under external short-circuiting (plot <NUM>). Both the current through the short-circuit and the maximum battery temperature are greatly reduced if one or more ECTs are present to limit the flow of current from adjacent subcells through the short-circuit.

<FIG> shows a portion of the distributed equivalent circuit for the system <NUM> comprising three sub-cells <NUM>, <NUM>, <NUM> (regions) of battery <NUM> disposed between a current limiter <NUM> and current-collector <NUM>. The full distributed equivalent circuit model consists of <NUM> sub-cells, with sub-cells <NUM>, <NUM>, and <NUM> being the <NUM>th, <NUM>th, and <NUM>st sub-cells, respectively. Each subcell represents a battery region of <NUM> in width and <NUM> in length, so the total footprint of the simulated battery is <NUM><NUM>. Each sub-cell of the battery was modeled as a variable-voltage source <NUM> and a <NUM>Ω series resistance <NUM>. Adjacent sub-cells were connected with a <NUM>Ω resistance <NUM>. The variable voltage sources <NUM> start with an output voltage of <NUM> V, with the voltage decreasing as charge is passed. Once <NUM> C of charge is passed through each voltage source <NUM>, the voltage output of the element drops to <NUM> V. This behavior mimics the behavior of batteries, which output less voltage as they become discharged. The series resistance <NUM> represents ionic and kinetic losses during the cell discharge, and the resistance <NUM> represents conduction along the positive electrode material. The sub-cells <NUM>, <NUM>, <NUM> are electrically connected to a common current-collector <NUM>, which is represented by <NUM> mΩ resistors <NUM>. The current limiter <NUM> is comprised of a first pair of ECTs <NUM>-1a/b associated with the battery sub-cell <NUM>, a second pair of ECTs <NUM>-2a/b associated with the battery sub-cell <NUM>, and a third pair of ECTs <NUM>-3a/b associated with the battery sub-cell <NUM>. Each pair of ECTs is connected in series (see, e.g., <FIG>) and functions as described herein. The current limiter <NUM> is disposed between the battery <NUM> and a common current-collector <NUM>, which is represented by <NUM> mΩ resistors <NUM>. A <NUM> mΩ resistor <NUM> represents a short-circuit that can be formed by a dendrite, manufacturing defect, mechanical damage, etc. When wire <NUM> is connected, the short-circuit is an external short-circuit, while in the absence of wire <NUM> the short is an internal short-circuit. The current through the entire distributed circuit was simulated as a function of time with a SPICE simulation, and the heat dissipation in each circuit element was fed into a COMSOL thermal model to estimate the maximum cell temperature as a function of time. This set of simulations was performed with an internal short-circuit (wire <NUM> missing), an external short circuit (wire <NUM> present), and a short-circuit without a current-limiter present (each ECT <NUM>-1a/b, <NUM>-2a/b, <NUM>-3a/b replaced with a wire).

The results of the modeling are represented in graphs 10B and 10C that plot the simulated current that passes through short-circuit <NUM> and the simulated maximum battery temperature as a function of time, respectively. Simulated current passing through the short-circuit <NUM> in the absence of a current-limiter during a short-circuit and maximum battery temperature in the absence of a current-limiter during a short-circuit are represented as solid lines <NUM>, <NUM> in <FIG> and <FIG>, respectively. Simulated current passing through the short-circuit <NUM> in the presence of a current-limiter during an internal short-circuit and simulated maximum battery temperature in the presence of a current-limiter during an internal short-circuit are represented as dotted lines <NUM>, <NUM> in <FIG> and <FIG>, respectively. Simulated current passing through the short-circuit <NUM> in the presence of a current-limiter during an external short-circuit and simulated maximum battery temperature in the presence of a current-limiter during an external short-circuit are represented as dashed lines <NUM>, <NUM> in <FIG> and <FIG>, respectively.

It will be appreciated from the graph of <FIG> that the presence of ECTs <NUM>-1a/b, <NUM>-2a/b, <NUM>-3a/b significantly decreases the current that flows through short-circuit <NUM>. It will also be appreciated from the graph of <FIG> that the presence of ECTs <NUM>-1a/b, <NUM>-2a/b, <NUM>-3a/b significantly decreases the maximum cell temperature that is obtained under both internal and external short-circuit conditions. Furthermore, the output voltage of the battery under moderate current load in the absence of short-circuit <NUM> is negligibly effected by the presence of current-limiter <NUM> (<<NUM> mV decrease).

In some embodiments, the ECTs used in the current limiters discussed herein can be passively controlled (as illustrated, for example, in <FIG>). In some embodiments, the ECTs used in current limiters can be actively controlled as illustrated in <FIG>. <FIG> illustrates a system <NUM> that includes array of ECTs <NUM>-<NUM>, <NUM>-<NUM> that are operably connected between a current collector <NUM> and contact pads <NUM>-<NUM>, <NUM>-<NUM> respectively. Specifically, ECT <NUM>-<NUM> has a first electrode <NUM>-1d (e.g., drain electrode) connected to current collector <NUM>, a second electrode <NUM>-<NUM> (e.g., source electrode) connected to associated contact pad <NUM>-<NUM>, and a control electrode <NUM>-<NUM> (e.g., gate electrode) that receives an associated control signal Vc1. With this arrangement, ECT <NUM>-<NUM> can be turned on, off, or set to an intermediate partially-on state by control voltage Vc1. For example, when control voltage Vc1 is below the threshold voltage of p-type depletion-mode ECT <NUM>-<NUM>, a localized current C1 from the energy device <NUM> passes from contact pad <NUM>-<NUM> to collection plate <NUM>, where current C1 is determined by the control voltage Vc1. For example, in some embodiments, C1 may be proportional to Vc1.

Similarly, ECT <NUM>-<NUM> has a first electrode <NUM>-2d (e.g., drain electrode) connected to current collector <NUM>, a second electrode <NUM>-<NUM> (e.g., source electrode) connected to associated contact pad <NUM>-<NUM>, and a control electrode <NUM>-<NUM> (e.g., gate electrode) that receives an associated control signal Vc2. With this arrangement, ECT <NUM>-<NUM> can be turned on, off, or set to an intermediate partially-on state by control voltage Vc2. For example, when control voltage Vc2 is below the threshold voltage of p-type depletion-mode ECT <NUM>-<NUM>, a localized current C2 from the energy device <NUM> passes from contact pad <NUM>-<NUM> to collection plate <NUM>, where current C2 is determined by the control voltage Vc2. For example, in some embodiments, C2 may be proportional to Vc2.

The current collector can be implemented by a metal or metal-containing film or other conductive material that facilitates the combination of localized currents C1 to C2 such that the sum of these currents form load current CLOAD.

In some embodiments, the current limiter <NUM> may include one or more components <NUM>-<NUM>, <NUM>-<NUM> that control the voltage Vc1, Vc2 at the control electrode <NUM>-<NUM>, <NUM>-<NUM> of the ECTs <NUM>-<NUM>, <NUM>-<NUM>. <FIG> illustrates a current limiter comprising a distributed control system implemented using control subsystems <NUM>-<NUM> and <NUM>-<NUM>. In some implementations the subsystems <NUM>-<NUM>, <NUM>-<NUM> may be or include one or more sensors, such as current sensors and/or temperature sensors, configured to measure localized battery operating parameters in discrete battery regions R1, R2.

<FIG> illustrate current limiters that utilize distributed control circuitry. <FIG> illustrates a current limiter <NUM> having distributed control circuitry <NUM> comprising multiple sensors S1, S2. The current limiter <NUM> comprises an array of ECTs <NUM>-<NUM>, <NUM>-<NUM> that have one electrode electrically coupled directly or indirectly to a common current collector <NUM>. One or more of the ECTs <NUM>-<NUM>, <NUM>-<NUM> is controlled by a sensor. In the illustrated embodiment, the output of sensor S1 provides the control voltage Vc1 for the first ECT <NUM>-<NUM> and the output of sensor S2 provides the control voltage Vc2 for the second ECT <NUM>-<NUM>. The sensors S1 and/or S2 may be configured to sense current, voltage, temperature, strain, chemistry, or any other parameter pertinent to operation of the energy device.

<FIG> illustrates another current limiter <NUM> that includes distributed control circuitry <NUM>. The current limiter <NUM> comprises an array of ECTs <NUM>-<NUM>, <NUM>-<NUM> that have one electrode electrically coupled directly or indirectly to a common current collector <NUM>. Control circuitry <NUM> comprises first circuitry <NUM>-<NUM> that controls the operating state of ECT <NUM>-<NUM> by controlling Vc1 and second circuitry <NUM>-<NUM> that controls the operating state of ECT <NUM>-<NUM> by controlling Vc2. Circuitry <NUM>-<NUM>, <NUM>-<NUM> may comprise one or more sensors S11, S12, S21, S22 coupled to a local controller LC1, LC2 to control the operating states of ECTs <NUM>-<NUM>, <NUM>-<NUM>. Local controllers LC1, LC2 may generate control voltages V c <NUM>, Vc2 based on a variety of information. In some embodiments, the local controllers LC1, LC2 generate control voltages V c <NUM>, Vc2 based at least in part on localized sensor information from one or multiple sensors S11, S12, S21, S22. The local sensor information may indicate operating parameters of the energy device in some embodiments. For example, the sensor information may comprise one or more of temperature, concentration of a chemical substance, concentration of a biological substance, pH, humidity, ion concentration, electrical potential, current, resistance, impedance, capacitance, light intensity, stress, strain, pressure, etc. The sensors may be optical, resistive, or capacitive sensors, for example, and may be mounted on the contact pads, and/or within the interior of the battery or energy device.

In one example configuration, S11 and S21 are current sensors. S11 measures the current through ECT <NUM>-<NUM> and S21 measures the current through ECT <NUM>-<NUM>. Local controller LC1 receives the sensed current value from S11 and compares the sensed current value to a stored current value. If the sensed current value exceeds the stored current value, LC1 adjusts Vc1 such that the current through ECT <NUM>-<NUM> is reduced. Similarly, local controller LC2 receives the sensed current value from S21 and compares the sensed current value to a stored current value. If the sensed current value exceeds the stored current value, LC2 adjusts Vc2 such that the current through ECT <NUM>-<NUM> is reduced.

In some embodiments, local controllers LC1, LC2 may use additional measured or calculated information about the battery, e.g., age of the battery, number of charge and discharge cycles, and/or state of charge of the battery to generate the voltages Vc1, Vc2.

In some embodiments, multiple ECTs of a current limiter, e.g., all the ECTs, are controlled by a central controller as illustrated in <FIG> illustrates a current limiter <NUM> comprising an array of ECTs represented by ECT <NUM>-<NUM> and <NUM>-<NUM>. The operation of ECT <NUM>-<NUM> is controlled by Vc1 at the control electrode of ECT <NUM>-<NUM> and the operation of ECT <NUM>-<NUM> is controlled by Vc2 at the control electrode of ECT <NUM>-<NUM>. The control electrodes of ECT <NUM>-<NUM> and <NUM>-<NUM> are coupled to a central controller which generates voltages Vc1 and Vc2. The central controller may receive sensed information from one or more sensors, S1, S2 as illustrated in <FIG>. The sensed information may indicate operating parameters of the energy device, e.g., current, voltage, temperature, stress, strain, humidity, presence of chemicals or gases, etc..

In one example configuration, S1 and S2 are temperature sensors in thermal contact with localized regions of the energy device. S <NUM> measures the temperature from region R1 and S2 measures the temperature from region R2. The central controller receives the sensed temperature value from S1 and compares the sensed temperature value to a stored temperature value. If the sensed temperature value exceeds the stored temperature value, the central controller adjusts Vc1 such that the current through ECT <NUM>-<NUM> is reduced. Similarly, the central controller receives the sensed temperature value from S2 and compares the sensed temperature value to a stored temperature value. If the sensed temperature value exceeds the stored temperature value, the central controller adjusts Vc2 such that the current through ECT <NUM>-<NUM> is reduced.

In some embodiments, the central or local controller may use additional measured or calculated information about the battery or energy device, e.g., age of the battery, number of charge and discharge cycles, and/or state of charge of the battery to generate the control voltages Vc1, Vc2. For example, if the number of charge/discharge cycles is low, the local or central controller may allow more current to flow through the local regions of the battery. As the number of charge/discharge cycles increases, the local or central controller may decrease the current flowing through the local regions of the battery. In some embodiments, the central or local controller may use the additional measured or calculated information about the battery or energy device alone or in conjunction with sensed battery or energy device operating parameters.

The local controllers and/or central controller may be implemented using discrete circuitry or integrated circuitry. In some embodiments, each of the local controllers and/or the central controller are implemented using a programmable logic array. In some embodiments, each of the local controllers and/or the central controller comprises a microprocessor implementing program steps stored in firmware or software.

<FIG> and <FIG> illustrate another ECT structure that can be used in current limiters as discussed herein. ECT <NUM> can include a current collector <NUM>, a channel <NUM>, a source electrode <NUM>, a drain electrode <NUM>, an electrolyte layer <NUM>, a redox-couple layer <NUM>, and an optional membrane layer <NUM>. Current collector <NUM> can be made of conductive but inert material, such as Au, Ag, Pt, C, Al, etc. Channel <NUM> can be made of conductive polymers with high carrier mobility, such as PEDOT:PSS. Source electrode <NUM> and drain electrode <NUM> can be similar to the source and drain electrodes, respectively, used in the ECT <NUM> illustrated in <FIG>, for example.

Electrolyte layer <NUM> can include various types of electrolytes, such as water with dissolved salt (e.g., NaCl), an organic solvent with dissolved salt, an ionic liquid, a polymer with dissolved salt, a single-ion conducting polymer, a crystalline electrolyte, etc. Alternatively, electrolyte layer <NUM> can include electrolyte in gel or solid form.

Redox-couple layer <NUM> can include one or more redox-couples. A redox-couple can include a reduced species (e.g., Fe<NUM>+) and its corresponding oxidized form (e.g., Fe<NUM>+). Examples of redox-couples included in redox-couple layer <NUM> can include, but are not limited to: Ferricyanide/Ferrocyanide (Fe(CN)<NUM><NUM>-/<NUM>-), Iodide/Triiodide (I-/I<NUM>-), viologen and its derivatives, indigo and its derivatives, Ag/AgCl, Prussian blue, polyaniline, PEDOT, Cu/Cu<NUM>+, ferrocene and its derivatives, etc. In some embodiments, at least two redox-couples can be included in redox-couple layer <NUM>. For example, redox-couple layer <NUM> can include two redox-couples with very different formal potentials, thus allowing for a sharp change in threshold voltage when charges are injected into the gate. Redox-couple layer <NUM> can be in liquid form (e.g., redox-couples dissolved in electrolyte) or solid form. When redox-couple layer <NUM> comprises liquid (e.g., when the redox-couples are dissolved in electrolyte), membrane layer <NUM> can be used to separate the redox-couples from channel <NUM>, thus preventing the redox-couples from reacting with the channel material. More specifically, the membrane should allow carrier movements between electrolyte layer <NUM> and redox-couple layer <NUM>, while preventing redox-couple species from entering electrolyte layer <NUM>. Membrane layer <NUM> can include a porous glass frit, an ion selective membrane, ion-conductive glass, a polymer membrane, an ionically conductive membrane, etc. When redox-couple layer <NUM> includes solid-state redox-couples, membrane layer <NUM> can be optional. Examples of solid-state redox-couples can include, but are limited to: electrochemically active polymers, insoluble organic and inorganic redox couples, and intercalation materials.

The electrochemical potential of channel <NUM> can be a function of the doping level of channel <NUM>. As previously discussed, channel <NUM> can be p-type doped, and the doping level of channel <NUM> at VG = <NUM> V depends on the difference between the electrochemical potentials of the redox process occurring at channel <NUM> and the redox process occurring at redox-couple layer <NUM>. For a particular channel material, the doping level of channel <NUM> can then be adjusted by adjusting the electrochemical potential of redox-couple layer <NUM>. One approach for doing so is to select one or more appropriate redox-couples.

<FIG> presents an energy diagram depicting the energy level of the gate with respect to the energy level of the channel when three different redox-couples are used as gate material, according to one embodiment. In <FIG>, the left side of the drawing shows the electrochemical potential of the gate when three different redox-couples are used as the gate material, with redox-couple <NUM> providing the lowest potential, while redox-couple <NUM> provides the highest. The right side of the drawing shows the electrochemical potential of the channel, which can be a function of the channel doping level. The shading indicates the range of potentials reached during the operation of the transistor, including the "on" and "off' stages. At an arbitrary doping level ρ, the electrochemical potential within the channel (EC) can be expressed as EC = EC(ρ), where ρ is the doping level, as indicated by the solid line. The electrochemical potential within the channel is related to the electrochemical potential within the gate (EG) and the gate voltage (VG) according to the equation EC = EG + VG.

<FIG> also shows that, in order for the channel to reach the arbitrary doping level, different gate voltages are required for the three different gate materials. More specifically, VG1 is required for redox-couple <NUM>, VG2 is required for redox-couple <NUM>, and VG3 is required for redox-couple <NUM>, respectively. From <FIG>, one can also see that, for two different gate materials, the difference in the required gate voltages (δVG) to reach the same doping level can depend on the difference in the electrochemical potentials (δEG) of the two gate voltages. In other words, VG2 - VG1 = EG1 - EG2. For example, using redox-couple Ag/AgAl as a reference, δEG for redox-couple viologen (Viol<NUM>+/<NUM>+) can be -<NUM>. 6V, and δEG for redox-couple ferricyanide/ferrocyanide (Fe(CN)<NUM><NUM>-/<NUM>-) can be <NUM>.

<FIG> shows the transfer functions and threshold voltages of three PEDOT:PSS-based OECTs gated with three different types of redox-couple, according to one embodiment. The left side of the drawing shows the transfer curves for OECTs gated with Ag/AgCl, ferricyanide/ferrocyanide, and viologen. From the drawing, one can see that the transfer curves shift laterally significantly when different gate materials are used. More specifically, compared to the transfer curve of the OECT gated by Ag/AgCl (the center curve), the transfer curve for the OECT gated by viologen shifts to the left (by roughly <NUM> V), and the transfer curve for the OECT gated by ferrocyanide shifts to the right (by roughly <NUM> V). According to the transfer curves, when the gate is unbiased (i.e., VG = <NUM>), the OECT gated by Ag/AgCl is neither completely on nor completely off. However, by selecting a redox-couple with a positive δEG (e.g., ferrocyanide), the OECT can be turned on more at zero gate bias. Similarly, by selecting a redox-couple with a negative δEG (e.g., viologen), the OECT can be turned off at zero gate bias. The ability to turn off the transistor at zero bias makes it possible to make an accumulation mode OECT transistor based on PEDOT:PSS. The operation of an OECT in accumulation mode allows for low power consumption devices with high ON/OFF ratios. This approach to constructing accumulation mode OECT transistors can retain the ease of processing and high carrier mobility of PEDOT:PSS while allowing for lower circuit power consumption and more flexibility in circuit design.

The right side of <FIG> shows the threshold voltages for OECTs gated with different redox-couples as a function of δEG, using Ag/AgCl as reference. The slope of the curve is shown to be roughly <NUM>, meaning that the threshold voltage can be tuned on a one on one ratio by tuning δEG. For example, by selecting a gate material to obtain a δEG of <NUM> V, one can move the threshold voltage (VT) by <NUM> V. Because there is a wide variety of redox-couples to select from, including but not limited to: Fe(CN)<NUM> <NUM>-/<NUM>-, I-/I<NUM>-, viologen and its derivatives, indigo and its derivatives, Ag/AgCl, Prussian blue, polyaniline, PEDOT, Cu/Cu<NUM>+, ferrocene and its derivatives, etc., there can be a wide range of shifting of the threshold voltage. Moreover, one can also modulate the composition ratio within a particular redox-couple to fine-tune δEG, hence VT. For example, using Ag/AgCl as reference, the δEG for redox-couple Fe(CN)<NUM><NUM>-/<NUM>- can be roughly <NUM>. 2V if the redox-couple layer includes the same amount of Fe(CN)<NUM><NUM>- and Fe(CN)<NUM><NUM>-. Note that Fe(CN)<NUM><NUM>- and Fe(CN)<NUM><NUM>- can coexist in an aqueous solution. On the other hand, if one increases the amount of Fe(CN)<NUM><NUM>- by ten-fold, δEG can be decreased by <NUM> mV. Similarly, δEG can be increased by <NUM> mV if the amount of Fe(CN)<NUM><NUM>- is increased by ten-fold. Other ratios between Fe(CN)<NUM><NUM>- and Fe(CN)<NUM><NUM>-can result in different amounts of adjustment of δEG. Similar fine-tuning of δEG can be achieved for other types of redox-couple as well. This way, one can fine tune VT of the PEDOT:PSS OECTs or ECTs prepared with other channel materials.

In addition to tuning the OECT's threshold voltage by selecting different gate materials, in some embodiments, the threshold voltage of an OECT can be tuned dynamically. More specifically, the OECT with a dynamically tunable VT can be gated with a redox-couple with electrochemical potentials that can change under certain conditions. Some redox-couples can have electrochemical potentials that can vary in response to stimuli, such as temperature, heat flow, pressure, humidity, etc. For example, the redox-potential of Fe(CN)<NUM><NUM>-/<NUM>- can be strongly temperature-dependent due to the high entropy change upon electron transfers. This is also known as the thermogalvanic effect. Some redox-couples can have electrochemical potentials that vary in response to changing analyte concentration (e.g., pH level, ion, bio-molecules, gases, etc.) in the environment. For example, the redox-potential of Cu/Cu<NUM>+ can be sensitive to the concentration of Cu<NUM>+ ions in the solution.

<FIG> shows the δEG as a function of temperature for redox-couple Fe(CN)<NUM><NUM>-/<NUM>-, according to one embodiment. One can see that δEG can change by about <NUM> mV when the temperature is increased by roughly <NUM>. Other types of temperature-sensitive redox-couples (e.g., molybdenum and tungsten) can also have a similar effect. The thermogalvanic effect allows for local current control based on local temperature sensing. Thus, in some embodiments, the ECT itself can incorporate sensing for local control of the current through the ECT without requiring an external sensor. For example, current limiters according to some embodiments may incorporate ECTs that have stimuli-responsive gates to change the cut-off current as a function of a sensed parameter such as local temperature, local ion-concentration, or local electrode potential.

Forming a current limiter comprising an array of ECTs as discussed herein is illustrated using the flow diagram of <FIG>. A channel semiconductor layer is deposited <NUM> in a pattern such that multiple discrete regions of the channel semiconductor layer contact a common current collector layer. A solid state electrolyte layer is deposited <NUM> in a pattern of multiple discrete regions such that each discrete region of the solid state electrolyte layer respectively contacts a discrete region of the channel semiconductor layer at first location. A layer of conductive material is deposited <NUM> in a pattern of discrete regions such that each discrete region of the conductive material layer respectively contacts a discrete region of the channel semiconductor layer at a second location. A channel can be formed between the first and second locations of each discrete region of the semiconductor layer. A gate electrode layer is deposited <NUM> in a pattern of discrete regions such that each discrete region of the gate electrode layer respectively contacts a discrete region of the solid state electrolyte layer. Each discrete region of the gate electrode layer may respectively contact a discrete region of the conductive material layer, the current collector layer, or may be electrically connected to a sensor or other control circuitry. For example, in some embodiments, the gate electrodes may be electrically connected to leads or traces that form an electrical connection between the gate electrodes and other components.

Optionally, a second layer of conductive material is deposited in regions that are electrically isolated from the channel semiconductor layer. In this embodiment, the gate electrode layer can be deposited such that each discrete region of the gate electrode layer contacts a discrete region of the solid state electrolyte layer and a discrete region of the conductive material layer or the second conductive material layer or the current collector layer. The second conductive material layer can be used to provide a sensor input to the gate electrode layer, for example.

<FIG> illustrate top down and side views, respectively, of a method for preparing a current limiter comprising an array of ECTs disposed on a current collector layer in a scalable, cost effective process. In some embodiments, these techniques can be achieved by low cost printing and/or coating techniques without photolithography and/or etching steps. <FIG> show top and side views, respectively, after depositing a first insulator layer <NUM> in a striped pattern on the surface of a current collector layer <NUM> leaving strips of the current collector layer <NUM> exposed. <FIG> show top and side views, respectively, after deposition of the semiconductor layer <NUM>, the gate electrode layer <NUM>, and the solid state electrolyte layer <NUM>. A semiconductor channel layer <NUM> is deposited in a pattern of discrete regions such that each discrete region of the semiconductor channel layer <NUM> makes contact with the current collector layer <NUM>. A gate electrode layer <NUM>-a is deposited in a pattern of discrete regions such that each discrete region of the gate electrode layer <NUM>-a makes contact with the current collector layer <NUM>. Alternately, in an embodiment not forming part of the claimed invention, a gate electrode layer <NUM>-b can be deposited in a pattern of discrete regions such that each discrete region of the gate electrode layer <NUM>-b is electrically isolated from the current collector layer <NUM>. A solid state electrolyte layer <NUM> is deposited in a pattern of discrete regions such that each discrete region of the solid state electrolyte layer respectively contacts a discrete region of the gate electrode layer <NUM> and a discrete region of the semiconductor channel layer <NUM>. A second insulator layer <NUM> is deposited in a striped pattern that is offset from the first insulator layer <NUM>, such that portions <NUM> of the semiconductor channel layer <NUM> remain exposed. If gate electrode <NUM>-b was deposited, then the second insulator layer <NUM> is deposited in a pattern that also leaves portions <NUM> of the gate electrode <NUM>-b exposed. <FIG> show top and side views, respectively, after deposition of the second insulator layer <NUM>. An electroless deposition catalyst <NUM> is optionally deposited on the exposed regions <NUM> of the semiconductor channel layer <NUM>, on the second insulator layer <NUM> proximate to the exposed regions <NUM> of the semiconductor channel layer <NUM>, and (if applicable) on the exposed regions <NUM> of the gate electrode <NUM>-b. The subassembly is exposed to an electroless copper or nickel deposition bath to form a layer of electrically conductive material <NUM> patterned into discrete regions wherein each discrete region of electrically conductive material contacts <NUM> is respectively electrically coupled to a discrete region of the semiconductor channel layer <NUM> and (if applicable) a discrete region of gate electrode layer <NUM>-b. Alternately, the electrically conductive material <NUM> can be printed, laminated, evaporated, or sputtered onto the exposed regions <NUM> of the semiconductor channel layer <NUM>, onto the second insulator layer <NUM> proximate to the exposed regions <NUM> of the semiconductor channel layer <NUM>, and (if applicable) onto the exposed regions <NUM> of the gate electrode <NUM>-b. <FIG> show top and side views respectively after the patterned layer <NUM> of electrically conductive material is formed. An energy device having an active region that generates or consumes energy may be formed on the patterned layer <NUM> of electrically conductive material such that the patterned layer <NUM> of electrically conductive material forms the anode or cathode of the energy device.

Embodiments disclosed herein involve one or more arrays of electrochemical transistors that are used as local current limiters within a battery or other active energy producing or consuming device. These current limiters can be passively or actively controlled. The electrochemical transistor arrays can be printed or otherwise patterned onto the metal foils already used as current collectors in batteries to control the flow of current between the current collector and active material, for example. Compared to printed field-effect transistors, the current carried by electrochemical transistors is significantly higher, which enables their use in the current limiting applications discussed herein. The differential resistance of these devices at low currents can be quite low (meaning they do not contribute significantly to the battery or energy device's internal impedance), but at higher currents the differential resistance sharply increases. Furthermore, the current at which the sharp increase in resistance occurs can be tuned by applying different gate voltages. These gate voltages can be actively applied or a similar effect can be achieved by using a 0V gate voltage with gates of differing electrochemical potential (as described with reference to <FIG> of this disclosure.

One embodiment of a current limiter involves an array of ECTs printed or otherwise deposited onto a current-carrying metal foil which forms the current collector for the battery. The ECTs all share a common electrode, which is the current collector for the battery. The other electrode in contact with the ECT channel is a conductive pad that is electrically isolated from the other ECTs. The gate electrode can be shorted to either end of the channel electrode, which dictates which direction of current is limited. Alternately, gate lines can be run to the edge of the array and the gate voltage (e.g., the voltage between the gate and the underlying current collector) can be actively controlled to change the current cut-off as a function of time or location.

These current limiters can be directly used with existing battery manufacturing process lines in several possible configurations. The electrochemical transistors can be deposited on the negative electrode, the positive electrode, or both. Furthermore, the gate electrode can be shorted to either the common current collector, i.e. claimed invention, or the conductive pad in contact with the battery electrolyte i.e. an embodiment not forming part of the claimed invention, depending on which direction of current is to be limited. Furthermore, multiple ECTs can be placed in series to limit the current flow in both directions. By limiting the discharge current flowing through the negative or positive current-collector, the rate of self-discharge during an internal short-circuit can be decreased. On the other hand, by limiting the charging current through the negative electrode, the lithium plating and the formation of lithium dendrites can be suppressed, which decreases the likelihood of an internal short-circuit. Additional design flexibility can be achieved by also incorporating current-limiters on the both electrodes of the battery.

Embodiments include a configuration where discharge current through both the positive and negative electrodes is limited, which would further reduce the rate of self-discharge during an internal short-circuit. Alternately, the limiting current directions can oppose each other as shown in <FIG>, so the negative electrode limits the charging current while the positive electrode limits the discharging current. Numerous other permutations and combinations of current limiters incorporating ECTs are possible.

Current limiters as discussed herein reduce the impact of manufacturing defects or other inhomogeneities in the battery which can lower the resistance to current flow at a particular spot on the current collector leading to a current hot spot. As previously discussed, hot-spots can lead to decreased cell capacity as the cell is degraded near the current hot spot. In extreme scenarios, hot-spots can lead to filament formation and thermal runaway. When shorts form within the battery, the battery capacity may rapidly discharge through the short, leading to overheating and fire. In battery cells equipped with current limiting capability as discussed herein, current hot-spots are suppressed and the rate of self-discharge through a short is slowed.

The current limiters incorporate ECTs and optional control circuitry which can be readily incorporated in existing battery, photovoltaic cell, and fuel cell fabrication processes. The on-current and series resistance of ECTs can be matched to battery control requirements. The technology of the current limiters discussed herein is inexpensive and affords a fine level of spatial control granularity which allows for improvements in other battery and battery-pack components such as separators, battery management systems, less expensive and/or smaller thermal management systems, etc. The current limiters discussed herein can be used to increase charging speed and/or to prolong battery lifetime and/or to reduce uniformity requirements because of feedback. In contrast to thermal shutdown mechanisms, the current limiters comprising ECTs are capable of stopping destructive current flow before it leads to rapid temperature rise.

In some embodiments, the ECTs incorporate stimuli-responsive gates to change the cut-off current as a function of some sensed quantity such as temperature, local ion- concentration, or local electrode potential (state-of-charge).

In some embodiments, multiple ECTs can be connected in series in order to limit the current-flow in both directions. Control structures such as current mirror connections can be used to equalize current through the various cells. More complex printed electronics can also be used to independently control each electrochemical transistor to yield more complex charging and discharging behavior that varies in space and/or time.

<FIG> schematically depicts a current mirror connection that can be used in a current limiter structure in accordance with some embodiments. The first control ECT <NUM> generates a voltage +V at trace <NUM> that sustains a current of I<NUM> through ECT <NUM>. The voltage +V then adjusts the currents through the other ECTs <NUM>, <NUM>, <NUM> to match or mirror I<NUM>. In this way the given or control current can be replicated. If the ECTs <NUM> - <NUM> are respectively connected to multiple energy devices (not shown in <FIG>), the current through the multiple energy devices can be controlled and/or equalized to a common value through the current mirror structure depicted in <FIG>. The common value can be a particular sub cell or a special control circuit. To the extent that the ECT properties match, the current through each of the subcells will match the current through the control device.

<FIG> illustrates a current limiter <NUM> in accordance with some embodiments wherein two ECTs <NUM>, <NUM> are connected in series. Two ECTs <NUM>, <NUM> in series are disposed between a common current collector <NUM> and a contact pad <NUM>. Electrode <NUM>-s of ECT <NUM> is in contact with the isolated contact pad, electrode <NUM>-d of ECT <NUM> is in contact with electrode <NUM>-s of ECT <NUM>, and electrode <NUM>-d of ECT <NUM> is in contact with the common current collector <NUM>. The gate <NUM>-g of ECT <NUM> can be connected to electrode <NUM>-s, <NUM>-d, or to an external control voltage applied with respect to <NUM> or <NUM>-d. The gate <NUM>-g of ECT <NUM> can be connected to electrode <NUM>-s, <NUM>-d, or to an external control voltage applied with respect <NUM> or <NUM>-s.

The ECTs <NUM>, <NUM> (and other ECTs described herein) can be n-type, p-type, accumulation-mode, depletion-mode, and any combination of these types. For example, if ECTs <NUM> and <NUM> are both p-type depletion-mode ECTs, the gate <NUM>-g can be shorted to <NUM>-d and gate <NUM>-g can be shorted to <NUM>-s to achieve current-limiting in both directions. Alternately, a similar effect could be obtained by shorting gate <NUM>-g to <NUM>-s and gate <NUM>-g to <NUM>-d. Furthermore, one of the ECTs <NUM>, <NUM> can be used as a passive current-limiter while the other ECT can be actively controlled. Various permutations and combinations of ECTs will be obvious to a practitioner skilled in the art. The scope of the invention is as set out in the appended set of claims.

Claim 1:
A system (<NUM>), comprising:
at least one current collector layer (<NUM>, <NUM>);
an energy device (<NUM>) that includes an active region (<NUM>) configured to generate or consume electrical current and thereby form a current providing or consuming device, and
a current limiter (<NUM>, <NUM>) comprising a plurality of electrochemical transistors (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) disposed between the active region and the current collector layer, the plurality of electrochemical transistors, ECTs, arranged in an array such that each ECT in the array provides localized current control for the current providing or consuming device, each ECT comprising:
a drain electrode (<NUM>, <NUM>);
a source electrode (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>);
a channel (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) disposed between the drain and the source electrodes;
a gate electrode (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>), wherein the gate electrode is disposed directly on the current collector layer;
an electrolyte that electrically couples the gate electrode to the channel such that an electrical signal at the gate electrode controls electrical conductivity of the channel, wherein the current collector layer is a shared drain or source electrode for the ECTs.