WO2022195358A1

WO2022195358A1 - Method of sensing temperature of electrochromic devices without a dedicated temperature sensor

Info

Publication number: WO2022195358A1
Application number: PCT/IB2022/000175
Authority: WO
Inventors: Adrian Winoto; Andrew Loxley; Guillermo Garcia; Lyle Kaplan-Reinig
Original assignee: Heliotrope Europe S.L.
Priority date: 2021-03-17
Filing date: 2022-03-15
Publication date: 2022-09-22

Abstract

A method of operating an electrochromic device (EC device) includes using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device, and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

Description

METHOD OF SENSING TEMPERATURE OF ELECTROCHROMIC DEVICES WITHOUT A DEDICATED TEMPERATURE SENSOR

FIELD

[0001] The present invention is generally directed to electrochromic devices, and more particularly to determining a temperature of an electrochromic device without using a dedicated temperature sensor.

BACKGROUND

[0002] An electrochromic (EC) window undergoes a reversible change in optical properties when driven by an applied potential. Some EC devices may include a working electrode, a solid state electrolyte, and a counter electrode sandwiched between two transparent conductor layers and outer glass layers.

SUMMARY

[0003] According to one embodiment of the present disclosure, a method of operating an electrochromic device (EC device) includes using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device, and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

[0004] According to one embodiment of the present disclosure, a method of operating an electrochromic device (EC device) includes using at least one electrochemical property of the EC device to determine a temperature of the EC device.

[0005] According to another embodiment of the present disclosure, an electrochromic system includes an electrochromic device and a controller. The electrochromic device (EC device) includes a working electrode, a counter electrode, an electrolyte located between the working electrode and the counter electrode. The controller includes a processor configured with processor-executable instructions to perform operations comprising using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device, and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a schematic representation of an electrochromic device according to various embodiments.

[0007] FIG. 2 is a block diagram of a controller for an electrochromic device according to various embodiments.

[0008] FIG. 3A is a plot of temperature versus open circuit voltage according to various embodiments.

[0009] FIG. 3B is a plot of dq/dV versus voltage at three temperatures for bright and dark sweeps of an electrochromic device according to various embodiments.

[0010] FIG. 4A is plot of dq/dV versus temperature at a first voltage for an electrochromic device according to various embodiments.

[0011] FIG. 4B is plot of dq/dV versus temperature at a second voltage for an electrochromic device according to various embodiments.

[0012] FIG. 5 is a plot of imaginary impedance versus real resistance at three temperatures according to various embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] Electrochromic devices may be exposed to a wide range of temperatures when deployed. For example, electrochromic glass installed on the outside of buildings may be exposed to a wide range of temperatures and weather conditions, ranging from extreme heat to extreme cold. Electrochromic devices may have a temperature range in which they operate normally. If the electrochromic device is exposed to temperatures outside normal operating temperatures, the operation of the electrochromic device may be compromised. For example, the ionic conductivity of the electrolytes in the electrochromic device may be affected by temperature, which may affect the switching time of the electrochromic device. Specifically, as the temperature of the electrochromic device decreases, the ionic conductivity may decrease, which increases the switching time.

[0014] Furthermore, the present inventors realized that at elevated temperatures, current spikes may damage the EC device. Therefore, voltage should be capped at elevated temperatures to avoid damaging current spikes. In contrast, at lower temperatures, damaging current spikes may be avoided without capping the voltage. Therefore, the magnitude of the current and/or voltage which is applied to switch the state of the EC device from the bright state to the dark state or from the dark state to the bright state depends on the temperature of the EC device. Thus, the temperature of the EC device should be taken into account when selecting the magnitude of the current and/or voltage which is applied to switch the state of the EC device. However, adding a dedicated temperature sensor to the EC device increases the cost and complexity of the EC device.

[0015] Various embodiments described herein use at least one electrochemical property of the EC device to determine the temperature (or a proxy value for the temperature) of the EC device. The at least one electrochemical property which may be used to determine the temperature of the EC device or act as a proxy for the temperature of the EC device includes the charge (e.g., state of charge) of the EC device or a derivative of the charge, such as the rate of charge transfer with voltage of the EC device (e.g., dq/dV, where q is charge, V is the cell / device voltage and “d” is the symbol for “derivative”), as will be described in more detail below. [0016] In one embodiment, the dedicated temperature sensor may be omitted (i.e., absent) from the EC device. Examples of dedicated temperature sensors which may be omitted from the EC device include thermistors (e.g., negative temperature coefficient (NTC) thermistors), thermocouples, resistance temperature detectors (RTDs), semiconductor-based temperature sensors (e.g., semiconductor integrated circuits specifically configured to measure temperature), optical temperature detectors (e.g., pyrometers), or various other thermometers.

[0017] The temperature or a proxy value for the temperature of the EC device that is determined from at least one electrochemical property of the EC device may be used to perform an additional step which is a function of the temperature of the EC device. In one embodiment, the additional step may comprise using the EC device controller to select safe magnitudes of the EC device switching current and/or switching voltage at the given temperature or its proxy value. The additional step may further comprise applying the selected safe magnitude of the at least one of switching current or switching voltage to the EC device to switch the EC device from a darker state (i.e., the dark state) to a brighter state (i.e., the bright state having a higher transmissivity of radiation, such as visible light, than the dark state), and/or to switch the EC device from the brighter state to the darker state.

[0018] In another embodiment, the additional step may comprise converting the determined temperature or the proxy value to temperature data which is used to manage the building or vehicle (e.g., ground based vehicle (such as automobile, mass transit vehicle, train, tmck, etc.,) boat, airplane, etc.) in which the EC device is located. For example, the temperature data may be used to control the temperature of the building (e.g., by controlling the building HVAC system) or vehicle (e.g., by controlling the vehicle heating or air conditioning system).

[0019] In another embodiment the additional step may comprise heating the EC device based on the determined temperature or its proxy value. Specifically, if the determined temperature or its proxy value indicates that the EC device is below a predetermined temperature value, then the controller may apply a heating current to the transparent conductors of the electrochromic device based on the determined temperature or its proxy value. When the heating current is applied to the transparent conductors, the resistivity of the transparent conductors causes the transparent conductor, and therefore the electrolyte of the electrochromic device to heat up. This allows the controller to warm up the electrochromic device. In addition, less lithium salt and ionic liquid components may be used in the electrolyte because the controller maintains the temperature above the minimum temperature. These compounds are relatively expensive, so a system that controls the heat of the electrochromic device may reduce the cost of manufacturing the electrochromic device. Application of the heating current to the electrodes may affect the inter-electrode voltage between the working electrode and the counter electrode. The controller may also control the working current applied between the electrodes of the electrochromic device to maintain the inter-electrode voltage at a desired level. This allows the controller to maintain normal operation by controlling the inter-electrode voltage so that is it not affected by the heating current, as described in U.S. Application Publication Number 2019/0361311 Al, published on November 28, 2019, and incorporated herein by reference in its entirety.

[0020] FIG. 1 illustrates one embodiment of an EC device which may be used as a temperature sensor. It should be noted that such electrochromic devices may be oriented upside down or sideways from the orientations illustrated in FIG. 1. Furthermore, the thickness of the layers and/or size of the components of the device in FIG. 1 are not drawn to scale or in actual proportion to one another other, but rather are shown as representations.

[0021] In FIG. 1, an embodiment electrochromic device 100 may include a first transparent conductor layer 102a, a working electrode 104, a solid state electrolyte 106, a counter electrode 108, and a second transparent conductor layer 102b. Some embodiment electrochromic devices may also include one or more optically transparent layers, such as a transparent layer 110a positioned in front of the first transparent conductor layer 102a and/or a transparent layer 110b positioned behind the second transparent conductor layer 102b. The transparent layers 110a, 110b may be formed of transparent materials, such as plastic or glass.

[0022] The first and second transparent conductor layers 102a, 102b may be formed from transparent conducting films fabricated using inorganic and/or organic materials. For example, the transparent conductor layers 102a, 102b may include inorganic films of transparent conducting oxide (TCO) materials, such as indium tin oxide (ITO) or fluorine doped tin oxide (FTO). In other examples, organic films in transparent conductor layers 102a, 102b may include graphene and/or various polymers.

[0023] In the various embodiments, the working electrode 104 may include nanostructures 112 of a doped or undoped transition metal oxide bronze, and optionally nanostructures 113 of a transparent conducting oxide (TCO) composition shown schematically as circles and hexagons for illustration purposes only. As discussed above, the thickness of the layers of the device 100, including and the shape, size and scale of nanostmctures is not drawn to scale or in actual proportion to each other, but is represented for clarity. In the various embodiments, nanostmctures 112, 113 may be embedded in an optically transparent matrix material or provided as a packed or loose layer of nanostmctures exposed to the electrolyte.

[0024] In the various embodiments, the doped transition metal oxide bronze of nanostmctures 112 may be a ternary composition of the type AxMzOy, where M represents a transition metal ion species in at least one transition metal oxide, and A represents at least one dopant. Transition metal oxides that may be used in the various embodiments include, but are not limited to any transition metal oxide which can be reduced and has multiple oxidation states, such as niobium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, titanium oxide and mixtures of two or more thereof. In one example, the nanostmctured transition metal oxide bronze may include a plurality of tungsten oxide (WO3 ₁) nanoparticles, where 0 < x < 1, such as 0 < x < 0.8, or lithium tungsten oxide nanoparticles.

[0025] In various embodiments, nanostmctures 113 may optionally be mixed with the doped transition metal oxide bronze nanostmctures 112 in the working electrode 104. In the various embodiments, the nanostructures 113 may include at least one TCO composition, which prevents UV radiation from reaching the electrolyte and generating electrons. In an example embodiment, the nanostructures 113 may include an indium tin oxide (ITO) composition, which may be a solid solution of around 60- 95 wt% (e.g., 85-90 wt%) indium(III) oxide (Ih2q3) and around 5-40 wt% (e.g., 10- 15 wt%) tin(IV) oxide (SnC ). In another example embodiment, the nanostructures 113 may include an aluminum-doped zinc oxide (AZO) composition, which may be a solid solution of around 99 wt% zinc oxide (ZnO) and around 2 wt% aluminum(III) oxide (AI2O3). Additional or alternative TCO compositions that may be used to form nanostructures 113 in the various embodiments include, but are not limited to, indium oxide, zinc oxide and other doped zinc oxides such as gallium-doped zinc oxide and indium-doped zinc oxide.

[0026] The nanostructures 112 and optional nanostructure 113 of the working electrode may modulate transmittance of visible radiation as a function of applied voltage and/or current by operating in two different modes. For example, a first mode may be a highly solar transparent (“bright”) mode in which the working electrode 104 is transparent to NIR radiation and visible light radiation. A second mode may be a visible blocking (“dark”) mode in which the working electrode 104 absorbs radiation in the visible spectral region and at least a portion of the NIR spectral region. In an example, application of a first voltage having a negative bias may cause the electrochromic device to operate in the dark mode, blocking transmittance of visible and NIR radiation at wavelengths of around 780-2500 nm. In another example, application of a second voltage having a positive bias may cause the electrochromic device to operate in the bright mode, allowing transmittance of radiation in both the visible and NIR spectral regions. In various embodiments, the applied voltage may be between -2V and 2V. For example, the first voltage may be -2V, and the second voltage may be 2V.

[0027] Optionally, the nanostmctures 112 and/or 113 may be embedded in a matrix and/or capped by a capping layer. For example, the capping layer may comprise a metal oxide material, such as niobium oxide or lithium niobate, and the matrix may comprise an ionically conductive and electrically insulating lithium rich antiperovskite (LiRAP) material, as described in U.S. Patent Number 10,698,287 B2, incorporated herein by reference in its entirety. The LiRAP material may have a formula L1₃OX, where X is F, Cl, Br, I, or any combination thereof. For example, the LiRAP material may comprise L1₃OI.

[0028] In various embodiments, the solid state electrolyte 106 may include at least a polymer material and an optional plasticizer material. The term “solid state,” as used herein with respect to the electrolyte 106, refers to a polymer-gel and/or any other non-liquid material. In some embodiments, the solid state electrolyte 106 may further include a salt containing, for example, an ion species selected from the group of lanthanides (e.g., cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium), alkali metals (e.g., lithium, sodium, potassium, rubidium, and cesium), and alkali earth metals (e.g., beryllium, magnesium, calcium, strontium, and barium). In an example embodiment, such salt in the solid state electrolyte 106 may contain a lithium and/or sodium ions. Polymers that may be part of the electrolyte 106 may include, but are not limited to, poly(methyl methacrylate) (PMMA), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB), poly(ethylene oxide) (PEO), polyurethane acrylate, fluorinated co-polymers such as poly(vinylidene fluoride -co-hexafluoropropylene), poly(acrylonitrile) (PAN), poly(vinyl alcohol) (PVA), etc. Plasticizers that may be part of the polymer electrolyte formulation include, but are not limited to, glymes (tetraglyme, triglyme, diglyme etc.), propylene carbonate, ethylene carbonate, ionic liquids (l-ethyl-3-methylimidazolium tetrafluoroborate, 1 -butyl-3 -me thy limidazolium hexafluorophosphate, l-butyl-3- methylimidazolium bis(trifluoromethane sulfonyl) imide, 1 -butyl- 1-methyl- pyrrolidinium bis(trifluoromethane sulfonyl)imide, etc.), N,N-dimethylacetamide, and mixtures thereof.

[0029] The counter electrode 108 of the various embodiments should be capable of storing enough charge to sufficiently balance the charge needed to cause visible tinting to the nanostructured transition metal oxide bronze in the working electrode 104. In various embodiments, the counter electrode 108 may be formed as a conventional, single component film, a nanostmctured film, or a nanocomposite layer.

[0030] In some embodiments, the counter electrode 108 may be formed from at least one passive material that is optically transparent to both visible and NIR radiation during the applied biases. Examples of such passive counter electrode materials may include CeCh, CeVCh, T1O₂, indium tin oxide, indium oxide, tin oxide, manganese or antimony doped tin oxide, aluminum doped zinc oxide, zinc oxide, gallium zinc oxide, indium gallium zinc oxide, molybdenum doped indium oxide, FeiCb, and/or V₂O_5. In other embodiments the counter electrode 108 may be formed from at least one complementary material, which may be transparent to NIR radiation but which may be oxidized in response to application of a bias, thereby causing absorption of visible light radiation. Examples of such complementary counter electrode materials may include (¾03, MnCE, FeCh, C0O2, N1O2, RhCh, or IrCh. The counter electrode materials may include a mixture or discrete sublayers of one or more passive materials and/or one or more complementary materials described above.

[0031] Optionally, the counter electrode 108 may include nanostructures of one or more passive materials and/or one or more complementary materials described above embedded in a matrix and/or capped by a capping layer. For example, the capping layer may comprise a metal oxide material, such as niobium oxide or lithium niobate, and the matrix may comprise the FiRAP material.

[0032] FIG. 2 illustrates a block diagram of a controller 200 for an electrochromic device according to various embodiments. The controller 200 may include a central processing unit (CPU) 202 and memory 204. The CPU 202 may be a low power processor that processes software instructions for operating and controlling an electrochromic device. The memory 204 may include volatile and non-volatile memory such as RAM, ROM, and FFASH memory. The memory 204 may store various programs and applications for controlling the operation and temperature of the electrochromic device. [0033] The controller 200 may include one or more input/output ports 208 for interfacing with the electrochromic device and other devices. The controller 200 may also include a network interface 206 for communicating with a wider network (e.g., a WAN). The network interface 206 may support wired and/or wireless connections to the network (e.g., a ZigBee® wireless module). The controller 200 may include a bus 210 that connects the various components of the controller 200 together. The controller 200 may also include various other components not illustrated in FIG. 2, such as a battery or other power source (e.g., electrical connection to a power grid) and a universal asynchronous receiver/transmitter (UART).

[0034] According to embodiments of the present disclosure, the EC device operates as a temperature sensor to determine its temperature or its proxy value. In embodiments, the electrochromic device may include a counter electrode 108 and an electrochromic working electrode 104 separated by an electrolyte 106. For example, the EC device 100 of described above with respect to FIG. 1 may be used. Alternatively, any other suitable EC device may be used. The EC device may be located in an electrochromic system containing the EC device and a controller, such as the controller 200 described above with respect to FIG. 2.

[0035] Depending on the applied voltage potential and direction, at least the working electrode of the EC device will undergo an oxidation or reduction reaction. In one embodiment, during a bright sweep (i.e., EC device going from the dark state to the bright state), a positive voltage of IV to 5V, such as 2V to 3V may be applied and the EC device, and the EC device may undergo an oxidation reaction. In another embodiment, during a dark sweep (i.e., EC device going from the bright state to the dark state), a negative voltage of - IV to -5V, such as -2V to -3V may be applied and the EC device, and the EC device may undergo a reduction reaction. Other voltages and reactions may be used depending on the materials of the EC device.

[0036] The present inventors realized that the open circuit voltage of the EC device is a function of temperature. As shown in FIG. 3A, the open circuit voltage (in arbitrary units, “AU”) increases with higher temperature and decreases with lower temperature. Thus, in one embodiment, the value of the measured open circuit voltage value may be used as a proxy for the temperature of the EC device.

[0037] The present inventors also realized that in both the oxidation and reduction processes, the rate of charge transfer with voltage (dq/dV) has a distinct signature based on the reaction. With temperature, the overall general shape of dq/dV curve is the same, but some parts of the curve change with temperature. There are areas of the curve that have more pronounced sensitivity to temperature, and these areas are used to determine a strong correlation with temperature of the EC device.

[0038] FIG. 3B is a plot of dq/dV versus measured voltage at three temperatures for bright and dark sweeps of the EC device according to various embodiments. The top part of FIG. 3B corresponds to the bright sweep, and the bottom part of FIG. 3B corresponds to the dark sweep. A given dq/dV value corresponds to different measured voltage values at different temperatures. For example, a difference in the measured voltage (“Delta V”) at a given dq/dV value for temperatures between -20 and +85 degrees Celsius may be about 500 to 600 mV in the dark sweep. Thus, in this embodiment, the value of the measured voltage at a given dq/dV value may be used as a proxy for the temperature.

[0039] FIGS. 4A and 4B are plots of dq/dV versus temperature at different measured voltages for the EC device according to various embodiments. The controller 200 may perform the above described at least one additional step based on the determined value of dq/dV and/or the measured voltage using a look up table which correlates the dq/dV value and/or measured voltage with the particular additional step action. Alternatively, the temperature of the EC device may be determined (e.g., as temperature data) from a look up table of dq/dV and measured voltage values versus temperature and/or from a plot similar to FIGS. 4 A or 4B. The controller 200 may perform the at least one additional step based on the determined value of temperature or its proxy value using a look up table which correlates the temperature with the particular additional step action. [0040] In summary, the EC device 100 may include a controller 200 that controls the operation and functionality of the EC device. During operation, the controller can apply a voltage and current with a specific recipe. The controller may also sense the voltage and current that is not controlled, e.g., open circuit voltage. The open circuit voltage of the EC device determines the state of charge of the EC device. In one embodiment, the measured open circuit voltage value may be used as a proxy for the temperature of the EC device, as shown in FIG. 3A. In another embodiment, when a constant current pulse is applied to the EC, then a constant voltage at this state of charge is measured to generate a signature redox curve, as described above. By taking the first derivative of the redox curve, a dq/dV versus measured voltage curve is generated, as shown for example in FIG 3B. In some sections of the dq/dV curve, there is a correlation between the dq/dV value and temperature. Thus, by knowing the state of charge and generating a redox curve, the dq/dV value may be correlated with a specific temperature of the EC device.

[0041] The present inventors also realized that the imaginary impedance of the EC device is also function of temperature. As shown in FIG. 5, the imaginary impedance decreases with higher temperature and increases with lower temperature. The initial peak and the initial valley (i.e., the minimum value after the initial peak) values of the imaginary impedance also shift to a lower real resistance value with decreasing temperature. Thus, in one embodiment, the real resistance and the imaginary impedance of the EC device may be measured (e.g., using electrochemical impedance spectroscopy or other measurement techniques) and/or calculated from other measured EC device variables. The value of the imaginary impedance of the EC device (e.g., as a function of the real resistance of the EC device) determined may be used as a proxy for the temperature of the EC device and/or the actual temperature of the EC device may be calculated from the determined imaginary impedance.

[0042] In one embodiment, a method of operating the EC device comprises using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device, and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

[0043] In one embodiment, the at least one electrochemical property of the EC device comprises an open circuit voltage of the EC device. In another embodiment, the at least one electrochemical property of the EC device comprises an imaginary impedance of the EC device.

[0044] In another embodiment, the at least one electrochemical property of the EC device comprises a state of charge of the EC device or a derivative of the state of charge. For example, the at least one electrochemical property of the EC device may comprises a rate of charge transfer with voltage (dq/dV) value, such as the dq/dV value as a function of measured voltage of the EC device.

[0045] In one embodiment, the temperature of the EC device or its proxy value may be determined as follows using look up tables and a constant current pulse. A first look up table correlating a state of charge of the EC device as a function of open circuit voltage (OCV) of the EC device may be stored in the controller 200 or in a separate computer or database which is in communication with the controller 200. A plurality of second look up tables for each value of the state of charge from the first look up table may be stored in the controller 200 or in a separate computer or database which is in communication with the controller 200. Each second look up table correlates dq/dV as the function of the measured voltage of the EC device for each value of the state of charge from the first look up table.

[0046] The first look up table may be generated by measuring state of charge of the EC devices at OCV. The second tables may be generated by measuring charge and voltage of the EC device while applying a constant current pulse to the EC device at different state of charges. The constant current pulse may comprise at least one dark sweep and/or a bright sweep current pulse. A slope graph is then generated from the measured data to generate the dq/dV versus voltage look up table for each state of charge value in the first look up table. [0047] The controller 200 may then perform the following functions using the look up tables: measuring the OCV of the EC device, determining the state of charge of the EC device from the first look up table based on the measured OCV, selecting a corresponding one of the plurality of the second look up tables which corresponds to the determined state of charge, applying a constant current pulse to the EC device, measuring a voltage of the EC device after applying the constant current pulse, and determining the dq/dV value from the selected second look up table based on the measured voltage. The voltage measured after applying the constant current pulse may be measured after the initiation of the constant current pulse but before the termination of the constant current pulse (i.e., during the application of the constant current pulse), and/or after the termination of the constant current pulse. The measured voltage may be a difference between the measured voltage prior to the current pulse and the measured voltage during or after applying the current pulse. The constant current pulse may comprise at least one dark sweep and/or a bright sweep current pulses. For example, a dark sweep current pulse may be applied for 0.3 to 20 seconds, such as 0.5 to 10 seconds. The magnitude of the constant current pulse may be 30 mA to 90 mA, such as 45 mA to 75 mA.

[0048] As described above, in one embodiment, the determined dq/dV value at the measured voltage or the measured voltage at the determined dq/dV value comprises the proxy value for the temperature. In another embodiment, the controller or a separate computer may also determine the temperature of the EC device based on at least one of the determined dq/dV value and the measured voltage, as described above.

[0049] In one embodiment, the EC device lacks a dedicated temperature sensor, such that the determined temperature or the proxy value for the temperature is determined without using a dedicated temperature sensor.

[0050] In one embodiment, the above described additional step comprises selecting a safe magnitude of at least one of switching current or switching voltage at the determined temperature or the proxy value for the temperature. The additional step further comprises applying the safe magnitude of the at least one of switching current or switching voltage to the EC device to switch the EC device from a darker state to a brighter state (i.e., bright sweep) or to switch the EC device from the brighter state to the darker state (i.e., dark sweep).

[0051] In another embodiment, the additional step comprises converting the determined temperature or the proxy value for the temperature to temperature data, and using the temperature data to control a temperature of a building or a vehicle in which the EC device is located.

[0052] In yet another embodiment, the additional step may include heating the EC device based on the determined temperature or the proxy value for the temperature. The EC device may heated by applying a heating current to the EC device if the determined temperature or the proxy value for the temperature is below a predetermined temperature value. Alternatively, the EC device may be heated by raising the temperature of the building or vehicle in which the EC device is located using the building HVAC system or the vehicle temperature control system (e.g., air vents of an automobile, etc.).

[0053] The advantage of using the EC device as a temperature sensor is that dedicated external temperature sensors may be omitted from the EC system. This reduces the total cost of the EC system. Also, the absence of a dedicated temperature sensor means that there is no need for the dedicated sensor to communicate with the window and/or the controller computer, improving data privacy. By using the EC device itself to sense temperature or its proxy value, the device may be operated within its optimum (e.g., safe) conditions, allowing for a more durable and longer lasting EC device.

[0054] The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The description was chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

Claims

1. A method of operating an electrochromic device (EC device) comprising: using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device; and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

2. The method of claim 1, wherein the at least one electrochemical property of the EC device comprises an open circuit voltage of the EC device.

3. The method of claim 1, wherein the at least one electrochemical property of the EC device comprises a state of charge of the EC device or a derivative of the state of charge.

4. The method of claim 1, wherein the at least one electrochemical property of the EC device comprises a rate of charge transfer with voltage (dq/dV) value as a function of a measured voltage of the EC device.

5. The method of claim 4, further comprising: providing a first look up table correlating a state of charge of the EC device as a function of open circuit voltage (OCV) of the EC device; providing a plurality of second look up tables for each value of the state of charge from the first look up table, wherein each second look up table correlates dq/dV as the function of the voltage of the EC device for each value of the state of charge from the first look up table; measuring the OCV of the EC device; determining the state of charge of the EC device from the first look up table based on the measured OCV ; selecting a corresponding one of the plurality of the second look up tables which corresponds to the determined state of charge; applying a constant current pulse to the EC device; measuring the voltage of the EC device after applying the constant current pulse; and determining the dq/dV value from the selected second look up table based on the measured voltage.

6. The method of claim 5, wherein the determined dq/dV value at the measured voltage or the measured voltage at the determined dq/dV value comprises the proxy value for the temperature.

7. The method of claim 5, further comprising determining the temperature of the EC device based on at least one of the determined dq/dV value and the measured voltage.

8. The method of claim 1, wherein the at least one electrochemical property of the EC device comprises an imaginary impedance of the EC device.

9. The method of claim 1, wherein: the EC device comprises a working electrode, a counter electrode, and an electrolyte located between the working electrode and the counter electrode; and the EC device lacks a dedicated temperature sensor, such that the determined temperature or the proxy value for the temperature is determined without using a dedicated temperature sensor.

10. The method of claim 1, wherein the additional step comprises selecting a safe magnitude of at least one of switching current or switching voltage at the determined temperature or the proxy value for the temperature, and applying the safe magnitude of the at least one of switching current or switching voltage to the EC device to switch the EC device from a darker state to a brighter state or to switch the EC device from the brighter state to the darker state.

11. The method of claim 1, wherein the additional step comprises converting the determined temperature or the proxy value for the temperature to temperature data, and using the temperature data to control a temperature of a building or a vehicle in which the EC device is located.

12. The method of claim 1, wherein the additional step comprises heating the EC device based on the determined temperature or the proxy value for the temperature.

13. The method of claim 12, wherein the EC device is heated by applying a heating current to the EC device if the determined temperature or the proxy value for the temperature is below a predetermined temperature value.

14. An electrochromic system, comprising: an electrochromic device (EC device), comprising: a working electrode; a counter electrode; and an electrolyte located between the working electrode and the counter electrode; and a controller comprising a processor configured with processor-executable instmctions to perform operations comprising: using at least one electrochemical property of the EC device to determine a temperature of the EC device or a proxy value for the temperature of the EC device; and performing an additional step which is a function of the temperature of the EC device based on the determined temperature or the proxy value for the temperature of the EC device.

15. The electrochromic system of claim 14, wherein the at least one electrochemical property of the EC device comprises an open circuit voltage of the EC device or an imaginary impedance of the EC device.

16. The electrochromic system of claim 14, wherein the at least one electrochemical property of the EC device comprises a rate of charge transfer with voltage (dq/dV) value as a function of a measured voltage of the EC device.

17. The electrochromic system of claim 16, wherein the processor is configured with processor-executable instructions to perform additional operations comprising: measuring an open circuit voltage (OCV) of the EC device; determining a state of charge of the EC device from a first look up table based on the measured OCV, wherein the first look up table correlates the state of charge of the EC device as a function of open circuit voltage (OCV) of the EC device; selecting a corresponding one of a plurality of second look up tables which corresponds to the determined state of charge, wherein each of the plurality of the second look up tables correlates dq/dV as the function of a measured voltage of the EC device for a respective value of the state of charge in the first look up table; applying a constant current pulse to the EC device; measuring a voltage of the EC device after applying the constant current pulse; and determining the dq/dV value from the selected second look up table based on the measured voltage.

18. The electrochromic system of claim 17, wherein the determined dq/dV value at the measured voltage or the measured voltage at the determined dq/dV value comprises the proxy value for the temperature.

19. The electrochromic system of claim 17, further comprising determining the temperature of the EC device based on at least one of the determined dq/dV value and the measured voltage.

20. The electrochromic system of claim 14, wherein the EC system lacks a dedicated temperature sensor.

21. A method of operating an electrochromic device (EC device) comprising using at least one electrochemical property of the EC device to determine a temperature of the EC device.