WO1996031892A1 - Thermal sensing device comprising a capacitor with dielectric layer of space charge polarization material - Google Patents

Thermal sensing device comprising a capacitor with dielectric layer of space charge polarization material Download PDF

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Publication number
WO1996031892A1
WO1996031892A1 PCT/US1996/004292 US9604292W WO9631892A1 WO 1996031892 A1 WO1996031892 A1 WO 1996031892A1 US 9604292 W US9604292 W US 9604292W WO 9631892 A1 WO9631892 A1 WO 9631892A1
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Prior art keywords
space
charge polarization
sensing device
capacitor
thermal sensing
Prior art date
Application number
PCT/US1996/004292
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French (fr)
Inventor
Hitendra K. Patel
Original Assignee
Motorola Inc.
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Publication date
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Publication of WO1996031892A1 publication Critical patent/WO1996031892A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/018—Dielectrics
    • H01G4/06—Solid dielectrics
    • H01G4/08—Inorganic dielectrics
    • H01G4/10—Metal-oxide dielectrics
    • H01G4/105—Glass dielectric
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H01M10/486—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for measuring temperature
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007—Regulation of charging or discharging current or voltage
    • H02J7/007188—Regulation of charging or discharging current or voltage the charge cycle being controlled or terminated in response to non-electric parameters
    • H02J7/007192—Regulation of charging or discharging current or voltage the charge cycle being controlled or terminated in response to non-electric parameters in response to temperature
    • H02J7/007194—Regulation of charging or discharging current or voltage the charge cycle being controlled or terminated in response to non-electric parameters in response to temperature of the battery
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/14—Cells with non-aqueous electrolyte
    • H01M6/18—Cells with non-aqueous electrolyte with solid electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This invention relates in general to thermal sensing devices, and more particularly, to thermal sensing devices based on capacitive measurements.
  • Thermal sensors have been employed in a wide variety of applications.
  • a thermal sensor is used to determine whether a battery being charged in a charging unit has exceeded a safe temperature.
  • Temperature sensors have assumed a variety of forms and designs which vary in cost, size, complexity and flexibility. For electronic device application, it is desirable to minimize cost, size and complexity while maximizing the potential use for such thermal devices.
  • temperature exceeding a target value causes an activity, such as a current flow, or voltage change, to occur in a particular device within the sensing circuit, thus enabling the sensing circuit to detect the temperature change.
  • a bipolar transistor which has a base to emitter voltage that decreases relative to the ambient temperature.
  • Patent No. 5,359,263 issued to Giordano, et al, on October 25, 1994, for an Integrated Circuit Thermal Sensor.
  • Thermal sensors have also been developed based on the characteristics of ferroelectric materials.
  • a ferroelectric material In a ferroelectric material, an electrical signal can be generated in response to a physical stimulus.
  • a pyroelectric material possesses ferroelectric characteristics.
  • an electrical signal In a pyroelectric material, an electrical signal can be generated in response to a change in temperature for the material. The electrical signal results from changes in polarization requiring a redistribution of surface charges within the material.
  • ferroelectric space-charge polarization for capacitive purposes.
  • ferroelectric capacitors are used in non-volatile, non- destructive memory devices.
  • internal polarization and space-charge regions are used in combination with an applied electric field to define distinguishable states which may be used to store information.
  • One such method is described in U.S. Patent No. 5,140,548 issued to Brennan on August 18, 1992 for a Ferroelectric Space Charge Capacitor Memory.
  • the capacitor described therein includes a ferroelectric dielectric medium disposed between a pair of spaced electrodes. Space charge polarization is due to ions in motion in a response to an electric field within the dielectric which results in the formation of space-charge regions adjacent to the electrodes which accumulates charges of a particular polarity.
  • Thermal sensing circuits have employed a variety of designs to detect specific changes of temperature. Such sensing circuits typically rely on a device that changes electrical characteristics in response to a physical impetus. However, many prior art devices have a narrow range of temperature that can be detected thereby limiting such devices to two- state applications. Moreover, many prior art thermal sensing devices have limited temperature resolution without additional complex circuitry. A need exists to provide a thermal sensing device which has broader flexibility in temperature detection which can be implemented using a simple configuration.
  • FIG. 1 is a block diagram of a battery charging system employing a space-charge polarization capacitor as a thermal sensing device, in accordance with the present invention.
  • FIG. 2 is a side view of the space-charge polarization capacitor of FIG. 1, in accordance with the present invention.
  • FIG. 3 is a graph of dielectric constant measurements over a wide frequency and temperature range for a lithium conducting boron sulfide glass used as a dielectric in a space-charge polarization capacitor, in accordance with the present invention.
  • FIG. 4 is a graph of the data of FIG. 3 normalized for a particular frequency, in accordance with the present invention.
  • FIG. 5 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium sulfide and silicon sulfide, in accordance with the present invention.
  • FIG. 6 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium iodide, lithium sulfide, and silicon sulfide, in accordance with the present invention.
  • FIG. 7 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium chloroborate, in accordance with the present invention.
  • the present invention provides for a thermal sensing device which uses a space-charge polarized dielectric material characterized according temperature and frequency dependent behavior.
  • a glass electrolyte dielectric material is used to form a capacitor, and the capacitor operated in a transition region where large changes in capacitance occur due to linear changes in temperature and frequency.
  • the dielectric material is preferably characterized by the transition region between low and high frequency capacitance.
  • the battery charging system 100 includes a battery charger 114 and a battery pack 112.
  • the battery pack 112 includes a pair of battery cells 118 and a pair of battery contacts 120, 122, to electrically couple the battery pack 116 to either the battery charger 114 or to a device (not shown) to be powered by the battery pack 116.
  • the battery pack further incorporates a thermal sensing device 110, including a space-charge polarization capacitor 112, and a third contact 124 to allow the thermal sensing device 110 to communicate with the battery charger 114.
  • the battery charger 114 includes a power or charging current source 126 electrically coupled to a microcontroller 128, via a control line 130.
  • the battery charger 114 further includes electrical contacts 132, 134 to make an electrical connection with the battery pack 116.
  • a first battery charger contact 132 is electrically coupled to the power supply 126 via a first electrical line 136
  • a second battery charger contact 134 is electrically coupled to the power supply 126 via a second electrical line 138.
  • a thermal sensor contact 140 on the battery charger 114 electrically couples the thermal sensing device 110 of the battery pack 116 through a corresponding thermal sensor contact 124.
  • An oscillator 142 is electrically disposed between the microcontroller 124 and the thermal sensor contact 140 of the battery charger 114.
  • the microcontroller 128 controls the oscillator 142 to determine the capacitance of the thermal sensing device 110. This capacitance is used together with a reference table or process (not shown) to make a determination relating to the temperature or thermal status of the battery pack 116.
  • the thermal sensing device 110 is thermally coupled to the battery cells 118 in the battery pack 116 in order to optimize the heat transfer from the cells 118, and hence thermal detection.
  • the capacitance of the thermal sensing device 110 changes in a manner described in greater detail below.
  • the microcontroller 128, via the oscillator, relates a capacitance change to a temperature change. In this manner, it is possible to determine when the temperature of the battery cells 118 or battery pack 116 is such that continued charging would degrade the performance or characteristics of the battery pack 116, or result in battery failure. Charging of the cells 118 may thus be terminated when a preselected capacitance is reached.
  • FIG. 2 is a side view of the space-charge polarization capacitor 112 used in the thermal sensing device 110 of FIG. 1, in accordance with the present invention.
  • the capacitor 112 is a parallel plate capacitor comprising a fast ion conducting glass material 205 as a dielectric layer, and a conducting material, such as gold 201, disposed on either side of the glass material 205 as electrodes to complete the parallel plate capacitor 112.
  • the dielectric material 205 is preferably an electrolyte which exhibits space-charge polarization behavior in response to an electric field.
  • space-charge polarization is due to ion motion within a dielectric wherein the ions are impeded at the interface between an electrically conducting surface and the dielectric, due to intrinsic barriers within the dielectric.
  • This behavior is both temperature and frequency dependent.
  • Materials exhibiting this behavior include the following: a) electrolytes such as potassium hydroxide or sulfuric acid in aqueous solutions; b) sodium ions in ⁇ alumina; c) silver, lithium and sodium ions in a fast conducting glass; d) silver in RbAg4l5; and e) lithium ions or other salts in a non-aqueous liquid, gel, or polymer solid.
  • the make up of the dielectric material can be adjusted to increase the concentration of the ions, and therefore its ionic conductivity.
  • the response rate of the dielectric material to an electric field is related to the ionic conductivity.
  • the dielectric response for the space-charge polarization is described by a first equation:
  • ⁇ is the dielectric constant and is proportional to the capacitance
  • ⁇ hf is a high frequency value for the dielectric constant
  • ⁇ space is the low frequency contribution of space charged polarization to the dielectric constant
  • ⁇ is a signal frequency in radians
  • ⁇ is the relaxation time of the polarization mechanism.
  • the dielectric spectrum is divided into the following regions:
  • transition region ⁇ ⁇ 1; 3. high frequency / low temperature plateau: ⁇ » 1; ⁇ ' - ⁇ hf-
  • the transition region between the low and high frequency capacitance is due to a relaxation of the space-charge polarization mechanism.
  • the time the field is in one direction decreases. Consequently, the time required for an ion to move in one direction and be impeded by a barrier begins to match the time that the field is in that direction.
  • the faster ions will run into a barrier and store charge for a short time, but the slower ions will only have time to run into a barrier and change directions as the field changes and hence not store a charge. This will result in a decrease in capacitance.
  • space-charge polarization is non-existent because the field changes too rapidly for the ions to accumulate at any interface or barrier.
  • the temperature dependent dielectric response of the dielectric material can be characterized by a second equation:
  • ⁇ o is the high temperature polarization relaxation time limit, i.e., the average for an ion to run into a physical barrier as temperature goes to infinity
  • ⁇ is an activation energy value for ion mobility
  • T is temperature in Kelvin
  • k is the Boltzman constant
  • capacitors such as thir. film capacitors, are made of dielectric material, which exhibit the dielectric response described by the equation for ⁇ ', can be used as thermal sensors. Particularly, in the region of the spectrum where ⁇ o is approximately 1, large changes in capacitance occur due to linear changes in temperature and frequency.
  • the capacitors are formed from fast ion conducting glass material.
  • the capacitor is made of a glass electrolyte having a composition selected from a first ternary system of boron sulfide, lithium sulfide, and lithium iodide.
  • the glass electrolyte had a composition of seventy percent lithium sulfide and thirty percent boron sulfide (0.70 Li2S + 0.30 B2S3).
  • the glass electrolyte was made using the following steps: 1) batching the appropriate composition; 2) placing the composition in a graphite crucible and melting the composition in a melting furnace; 3) casting the melted composition into a disk of approximately 2 centimeters in diameter and 0.1 millimeters in thickness; and 4) placing this disk in a preheated stainless steel mold having a temperature of approximately 300 degrees Celsius (°C).
  • a capacitor was made using the glass electrolyte as a dielectric material by sputtering each face of the disk through a mask with gold electrodes. Capacitance measurements on devices with glass and polymer electrolytes were taken over a wide temperature range of -100 °C to 200 °C, and a frequency range of 0.1 hertz to 1 megahertz.
  • FIG. 3 is a graph 300 of dielectric constant measurements over a wide frequency and temperature range for the lithium conducting boron sulfide glass used as a dielectric in a space-charge polarization capacitor, in accordance with the present invention.
  • the data show the approximate frequency and temperature dependence of the dielectric constant described by the second equation. At low frequency, the dielectric constant is dominated by space-charge polarization. As frequency increases, the space-charge polarization mechanism contribution begins to decrease and the measured dielectric constant begins to decrease. At a high frequency, space-charge polarization is negligible and the measured dielectric constant is due to higher frequency polarization mechanisms.
  • the temperature dependence of the dielectric constant is shown by the isothermal (constant temperature) spectra shifting of the curves or plots to the right with increasing temperature.
  • FIG. 4 is a graph 400 showing the data of FIG. 3 normalized for a particular frequency. The isothermal curves are superpositioned on each other which shows that the shape of the spectrum is temperature and frequency independent. This result is consistent with the second equation. Note the transition region 410 where ⁇ o is approximately 1.
  • the capacitor 112 was formed from a dielectric material selected from a second ternary system of silicon sulfide, lithium sulfide, and lithium iodide.
  • the glass electrolyte had a composition of substantially equal amounts of lithium sulfide and silicon sulfide (0.50 Li2S + 0.499 SiS2).
  • FIG. 5 shows a graph 500 comparing capacitance to temperature of this particular composition at various frequencies. The capacitance curves vary by orders of magnitude for linear changes in temperature. These capacitance versus temperature profiles may vary depending on the frequency, composition and thickness of the dielectric. The width of the transition region can be controlled by increasing or decreasing of the contribution of ionic sites in the dielectric through materials processing.
  • the temperature sensing device can be fabricated as a solid state device that has a wide temperature range of operation when compared to polymeric or liquid devices.
  • the graph 500 was generated by plotting capacitance values for different isotherms (temperature) at a fixed frequency from data in plots similar to those shown in FIG. 3.
  • a set of iso-frequency (constant frequency) data forms a S-type curve where the capacitance increases with temperature. Iso-frequency curves are shifted to the right as the frequency increases.
  • the graph 500 shows that the capacitor is most suited for sub-ambient temperature sensing if frequencies of less than 10 kilohertz are used. For higher probe frequencies, higher temperature ranges may be sensed.
  • the capacitor 112 was formed from a dielectric material of the second ternary system, and having a composition of lithium iodide, lithium sulfide, and silicon sulfide (0.1 Lil + 0.9 (Li2S + SiS2)).
  • FIG. 6 shows a capacitance versus temperature graph or plot 600 for this particular composition. This graph shows similar results to those of FIG. 5 except that the curves are less S-like. The change in the shape of the curve is due to the addition of Lil to the glass. This result shows that the shape of the curve can be changed by manipulating the chemistry and changing the distribution of ion-sites.
  • graph 600 the transition between the low temperature to high temperature capacitance is broad compared to the graph of FIG. 5.
  • the capacitor 112 comprised a glass composition from a third ternary system of lithium oxide, lithium chloride, and boron oxide.
  • the a dielectric material of the capacitor has a composition of lithium chloroborate (0.27Li2 ⁇ + 0.05( LiCl)2 + 0.67 B2O3).
  • FIG. 7 shows a capacitance versus temperature plot 700 for this particular composition.
  • the ionic conductivity of this glass composition is approximately three orders of magnitude less than the previously sited examples. Higher temperatures are therefore needed to make ions in this glass more mobile and hence contribute to space-charge polarization.
  • the sensing temperature range is between 20 - 160 °C for frequencies less than 1 kilohertz.
  • the present invention offers significant benefits over the prior art.
  • the use of ion conducting glasses as capacitors, particularly for thermal sensing applications, is particularly significant.
  • Glass space-charge polarization capacitors are extremely sensitive to temperature resulting in a large signal-to-noise response. These capacitors can be designed to sense temperature over a narrow range, for a switch-like behavior, or wide temperature range.
  • the temperature sensing region can be selected by varying the ionic conductivity in the glass.
  • Inorganic glasses typically are stable at higher temperatures than polymer sensors. Consequently, temperature sensors from these capacitors are stable in elevated and caustic environments.
  • the processing costs of these types of capacitors are low because starting materials are commonly available in an inexpensive form.

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Abstract

A thermal sensing device (110) includes a capacitor (112) having a dielectric layer (205) having a space-charge polarization dielectric material. The dielectric layer (205) is preferably formed from ion conducting glass.

Description

THERMAL SENSING DEVICE COMPRISING A CAPACITOR WITH DIELECTRIC LA OF SPACE CHARGE POLARIZATION MATERIAL
Technical Field
This invention relates in general to thermal sensing devices, and more particularly, to thermal sensing devices based on capacitive measurements.
Background of the Invention
Thermal sensors have been employed in a wide variety of applications. In one example, a thermal sensor is used to determine whether a battery being charged in a charging unit has exceeded a safe temperature. Temperature sensors have assumed a variety of forms and designs which vary in cost, size, complexity and flexibility. For electronic device application, it is desirable to minimize cost, size and complexity while maximizing the potential use for such thermal devices. In a typical prior art thermal sensing circuit, temperature exceeding a target value causes an activity, such as a current flow, or voltage change, to occur in a particular device within the sensing circuit, thus enabling the sensing circuit to detect the temperature change. Here, it is common to use a bipolar transistor which has a base to emitter voltage that decreases relative to the ambient temperature. One such example is presented in U.S. Patent No. 5,359,263 issued to Giordano, et al, on October 25, 1994, for an Integrated Circuit Thermal Sensor. Thermal sensors have also been developed based on the characteristics of ferroelectric materials. In a ferroelectric material, an electrical signal can be generated in response to a physical stimulus. A pyroelectric material possesses ferroelectric characteristics. In a pyroelectric material, an electrical signal can be generated in response to a change in temperature for the material. The electrical signal results from changes in polarization requiring a redistribution of surface charges within the material. A publication to Brown, from Atochem Sensor Ltd., dated December 14, 1990, describes a thermal detector taken advantage of the pyroelectric characteristic of polyvinylidene fluoride copolymers. Another type of ferroelectric material known in the art uses ferroelectric space-charge polarization for capacitive purposes. For example, such ferroelectric capacitors are used in non-volatile, non- destructive memory devices. In such devices, internal polarization and space-charge regions are used in combination with an applied electric field to define distinguishable states which may be used to store information. One such method is described in U.S. Patent No. 5,140,548 issued to Brennan on August 18, 1992 for a Ferroelectric Space Charge Capacitor Memory. The capacitor described therein includes a ferroelectric dielectric medium disposed between a pair of spaced electrodes. Space charge polarization is due to ions in motion in a response to an electric field within the dielectric which results in the formation of space-charge regions adjacent to the electrodes which accumulates charges of a particular polarity.
Thermal sensing circuits have employed a variety of designs to detect specific changes of temperature. Such sensing circuits typically rely on a device that changes electrical characteristics in response to a physical impetus. However, many prior art devices have a narrow range of temperature that can be detected thereby limiting such devices to two- state applications. Moreover, many prior art thermal sensing devices have limited temperature resolution without additional complex circuitry. A need exists to provide a thermal sensing device which has broader flexibility in temperature detection which can be implemented using a simple configuration.
Brief Description of the Drawings
FIG. 1 is a block diagram of a battery charging system employing a space-charge polarization capacitor as a thermal sensing device, in accordance with the present invention.
FIG. 2 is a side view of the space-charge polarization capacitor of FIG. 1, in accordance with the present invention.
FIG. 3 is a graph of dielectric constant measurements over a wide frequency and temperature range for a lithium conducting boron sulfide glass used as a dielectric in a space-charge polarization capacitor, in accordance with the present invention.
FIG. 4 is a graph of the data of FIG. 3 normalized for a particular frequency, in accordance with the present invention. FIG. 5 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium sulfide and silicon sulfide, in accordance with the present invention.
FIG. 6 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium iodide, lithium sulfide, and silicon sulfide, in accordance with the present invention.
FIG. 7 is a graph showing the capacitance versus temperature measurements at various frequencies for a dielectric material including lithium chloroborate, in accordance with the present invention.
Detailed Description of the Preferred Embodiment
While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.
Generally, the present invention provides for a thermal sensing device which uses a space-charge polarized dielectric material characterized according temperature and frequency dependent behavior. Preferably, a glass electrolyte dielectric material is used to form a capacitor, and the capacitor operated in a transition region where large changes in capacitance occur due to linear changes in temperature and frequency. When the space-charge polarization capacitor is used as a thermal sensing device, the dielectric material is preferably characterized by the transition region between low and high frequency capacitance.
Referring to FIG. 1, a block diagram of a battery charging system 100 is shown, in accordance with the present invention. The battery charging system 100 includes a battery charger 114 and a battery pack 112. The battery pack 112 includes a pair of battery cells 118 and a pair of battery contacts 120, 122, to electrically couple the battery pack 116 to either the battery charger 114 or to a device (not shown) to be powered by the battery pack 116. The battery pack further incorporates a thermal sensing device 110, including a space-charge polarization capacitor 112, and a third contact 124 to allow the thermal sensing device 110 to communicate with the battery charger 114. The battery charger 114 includes a power or charging current source 126 electrically coupled to a microcontroller 128, via a control line 130. The battery charger 114 further includes electrical contacts 132, 134 to make an electrical connection with the battery pack 116. A first battery charger contact 132 is electrically coupled to the power supply 126 via a first electrical line 136, and a second battery charger contact 134 is electrically coupled to the power supply 126 via a second electrical line 138. A thermal sensor contact 140 on the battery charger 114 electrically couples the thermal sensing device 110 of the battery pack 116 through a corresponding thermal sensor contact 124. An oscillator 142 is electrically disposed between the microcontroller 124 and the thermal sensor contact 140 of the battery charger 114. The microcontroller 128 controls the oscillator 142 to determine the capacitance of the thermal sensing device 110. This capacitance is used together with a reference table or process (not shown) to make a determination relating to the temperature or thermal status of the battery pack 116.
Preferably the thermal sensing device 110 is thermally coupled to the battery cells 118 in the battery pack 116 in order to optimize the heat transfer from the cells 118, and hence thermal detection. As the cells 118 generate heat, the capacitance of the thermal sensing device 110 changes in a manner described in greater detail below. The microcontroller 128, via the oscillator, relates a capacitance change to a temperature change. In this manner, it is possible to determine when the temperature of the battery cells 118 or battery pack 116 is such that continued charging would degrade the performance or characteristics of the battery pack 116, or result in battery failure. Charging of the cells 118 may thus be terminated when a preselected capacitance is reached.
FIG. 2 is a side view of the space-charge polarization capacitor 112 used in the thermal sensing device 110 of FIG. 1, in accordance with the present invention. The capacitor 112 is a parallel plate capacitor comprising a fast ion conducting glass material 205 as a dielectric layer, and a conducting material, such as gold 201, disposed on either side of the glass material 205 as electrodes to complete the parallel plate capacitor 112. The dielectric material 205 is preferably an electrolyte which exhibits space-charge polarization behavior in response to an electric field. Generally, space-charge polarization is due to ion motion within a dielectric wherein the ions are impeded at the interface between an electrically conducting surface and the dielectric, due to intrinsic barriers within the dielectric. This behavior is both temperature and frequency dependent. Materials exhibiting this behavior include the following: a) electrolytes such as potassium hydroxide or sulfuric acid in aqueous solutions; b) sodium ions in β alumina; c) silver, lithium and sodium ions in a fast conducting glass; d) silver in RbAg4l5; and e) lithium ions or other salts in a non-aqueous liquid, gel, or polymer solid. The make up of the dielectric material can be adjusted to increase the concentration of the ions, and therefore its ionic conductivity. The response rate of the dielectric material to an electric field is related to the ionic conductivity. The dielectric response for the space-charge polarization is described by a first equation:
Figure imgf000007_0001
where ε is the dielectric constant and is proportional to the capacitance; εhf is a high frequency value for the dielectric constant, εspace is the low frequency contribution of space charged polarization to the dielectric constant; ω is a signal frequency in radians, and τ is the relaxation time of the polarization mechanism.
The dielectric spectrum is divided into the following regions:
1. low frequency / high temperature plateau: ωτ « 1; ε' ~ εspace
2. transition region: ωτ ~ 1; 3. high frequency / low temperature plateau: ωτ » 1; ε' - εhf-
The transition region between the low and high frequency capacitance is due to a relaxation of the space-charge polarization mechanism. As the electric field increases, the time the field is in one direction decreases. Consequently, the time required for an ion to move in one direction and be impeded by a barrier begins to match the time that the field is in that direction. At this frequency, the faster ions will run into a barrier and store charge for a short time, but the slower ions will only have time to run into a barrier and change directions as the field changes and hence not store a charge. This will result in a decrease in capacitance. In the third region, space-charge polarization is non-existent because the field changes too rapidly for the ions to accumulate at any interface or barrier. The temperature dependent dielectric response of the dielectric material can be characterized by a second equation:
Figure imgf000008_0001
where τo is the high temperature polarization relaxation time limit, i.e., the average for an ion to run into a physical barrier as temperature goes to infinity, ΔΕ is an activation energy value for ion mobility, T is temperature in Kelvin, and k is the Boltzman constant.
According to the present invention, capacitors, such as thir. film capacitors, are made of dielectric material, which exhibit the dielectric response described by the equation for ε', can be used as thermal sensors. Particularly, in the region of the spectrum where ωτo is approximately 1, large changes in capacitance occur due to linear changes in temperature and frequency. Preferably, the capacitors are formed from fast ion conducting glass material.
In one example, the capacitor is made of a glass electrolyte having a composition selected from a first ternary system of boron sulfide, lithium sulfide, and lithium iodide. Particularly, the glass electrolyte had a composition of seventy percent lithium sulfide and thirty percent boron sulfide (0.70 Li2S + 0.30 B2S3). The glass electrolyte was made using the following steps: 1) batching the appropriate composition; 2) placing the composition in a graphite crucible and melting the composition in a melting furnace; 3) casting the melted composition into a disk of approximately 2 centimeters in diameter and 0.1 millimeters in thickness; and 4) placing this disk in a preheated stainless steel mold having a temperature of approximately 300 degrees Celsius (°C). A capacitor was made using the glass electrolyte as a dielectric material by sputtering each face of the disk through a mask with gold electrodes. Capacitance measurements on devices with glass and polymer electrolytes were taken over a wide temperature range of -100 °C to 200 °C, and a frequency range of 0.1 hertz to 1 megahertz.
FIG. 3 is a graph 300 of dielectric constant measurements over a wide frequency and temperature range for the lithium conducting boron sulfide glass used as a dielectric in a space-charge polarization capacitor, in accordance with the present invention. The data show the approximate frequency and temperature dependence of the dielectric constant described by the second equation. At low frequency, the dielectric constant is dominated by space-charge polarization. As frequency increases, the space-charge polarization mechanism contribution begins to decrease and the measured dielectric constant begins to decrease. At a high frequency, space-charge polarization is negligible and the measured dielectric constant is due to higher frequency polarization mechanisms. The temperature dependence of the dielectric constant is shown by the isothermal (constant temperature) spectra shifting of the curves or plots to the right with increasing temperature.
FIG. 4 is a graph 400 showing the data of FIG. 3 normalized for a particular frequency. The isothermal curves are superpositioned on each other which shows that the shape of the spectrum is temperature and frequency independent. This result is consistent with the second equation. Note the transition region 410 where ωτo is approximately 1.
In a second example, the capacitor 112 was formed from a dielectric material selected from a second ternary system of silicon sulfide, lithium sulfide, and lithium iodide. Particularly, the glass electrolyte had a composition of substantially equal amounts of lithium sulfide and silicon sulfide (0.50 Li2S + 0.499 SiS2). FIG. 5 shows a graph 500 comparing capacitance to temperature of this particular composition at various frequencies. The capacitance curves vary by orders of magnitude for linear changes in temperature. These capacitance versus temperature profiles may vary depending on the frequency, composition and thickness of the dielectric. The width of the transition region can be controlled by increasing or decreasing of the contribution of ionic sites in the dielectric through materials processing. In the case of glass electrolytes, the temperature sensing device can be fabricated as a solid state device that has a wide temperature range of operation when compared to polymeric or liquid devices. The graph 500 was generated by plotting capacitance values for different isotherms (temperature) at a fixed frequency from data in plots similar to those shown in FIG. 3. A set of iso-frequency (constant frequency) data forms a S-type curve where the capacitance increases with temperature. Iso-frequency curves are shifted to the right as the frequency increases. The graph 500 shows that the capacitor is most suited for sub-ambient temperature sensing if frequencies of less than 10 kilohertz are used. For higher probe frequencies, higher temperature ranges may be sensed. In a third example, the capacitor 112 was formed from a dielectric material of the second ternary system, and having a composition of lithium iodide, lithium sulfide, and silicon sulfide (0.1 Lil + 0.9 (Li2S + SiS2)). FIG. 6 shows a capacitance versus temperature graph or plot 600 for this particular composition. This graph shows similar results to those of FIG. 5 except that the curves are less S-like. The change in the shape of the curve is due to the addition of Lil to the glass. This result shows that the shape of the curve can be changed by manipulating the chemistry and changing the distribution of ion-sites. In graph 600, the transition between the low temperature to high temperature capacitance is broad compared to the graph of FIG. 5.
In a fourth example, the capacitor 112 comprised a glass composition from a third ternary system of lithium oxide, lithium chloride, and boron oxide. Particularly, the a dielectric material of the capacitor has a composition of lithium chloroborate (0.27Li2θ + 0.05( LiCl)2 + 0.67 B2O3). FIG. 7 shows a capacitance versus temperature plot 700 for this particular composition. The ionic conductivity of this glass composition is approximately three orders of magnitude less than the previously sited examples. Higher temperatures are therefore needed to make ions in this glass more mobile and hence contribute to space-charge polarization. The sensing temperature range is between 20 - 160 °C for frequencies less than 1 kilohertz. This example shows that if restrictions on the temperature range and probe frequency are imposed, then glasses with an appropriate ionic conductivity can be engineered to meet particular restrictions. This glass composition yields a very useful combination of measurable temperature range and low probe frequency for applications requiring temperature sensing between ambient and 100 °C.
The present invention offers significant benefits over the prior art. The use of ion conducting glasses as capacitors, particularly for thermal sensing applications, is particularly significant. Glass space-charge polarization capacitors are extremely sensitive to temperature resulting in a large signal-to-noise response. These capacitors can be designed to sense temperature over a narrow range, for a switch-like behavior, or wide temperature range. The temperature sensing region can be selected by varying the ionic conductivity in the glass. Inorganic glasses typically are stable at higher temperatures than polymer sensors. Consequently, temperature sensors from these capacitors are stable in elevated and caustic environments. Moreover, the processing costs of these types of capacitors are low because starting materials are commonly available in an inexpensive form.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
What is claimed is:

Claims

Claims
1. A thermal sensing device comprising a capacitor having a dielectric layer, the dielectric layer comprising a space-charge polarization material.
2. The thermal sensing device of claim 1, wherein the space- charge polarization material comprises a fast ion conducting material.
3. The thermal sensing device of claim 1, wherein the space- charge polarization material comprises an electrolyte.
4. The thermal sensing device of claim 3, wherein the electrolyte comprises an ion conducting glass.
5. The thermal sensing device of claim 4, wherein the ion conducting glass comprises a composition from a ternary system of lithium sulfide, lithium iodide and boron sulfide.
6. The thermal sensing device of claim 4, wherein the ion conducting glass comprises a composition from a ternary system of lithium sulfide, lithium iodide and silicon sulfide.
7. The thermal sensing device of claim 4, wherein the ion conducting glass comprises a composition from a ternary system of lithium oxide, lithium chloride, and boron oxide.
8. The thermal sensing device of claim 1, wherein the space- charge polarization material has a dielectric response ε' characterized by:
Figure imgf000013_0001
where hf is a dielectric constant value for the space-charge polarization material at a high frequency, εSpace is a dielectric constant for the space-charge polarization material attributable at a low frequency to space charge polarization, ω is a signal frequency in radians, τo is a high temperature polarization relaxation time limit, ΔΕ is an activation energy value, T is temperature in Kelvin, and k is Boltzman's constant.
9. The thermal sensing device of claim 8, wherein ωτo is approximately 1.
10. A battery charging apparatus, comprising: a battery cell; a battery charger; and a thermal sensing device disposed between the battery cell and the battery charger, the thermal sensing device comprising a capacitor, the capacitor having a dielectric layer comprising glass material, the glass material having space-charge polarization.
11. The battery charging apparatus of claim 10, wherein the glass material is characterized by a transition region between low and high frequency capacitance.
12. A capacitor having a dielectric layer comprising a space- charge polarization glass material.
13. The capacitor of claim 12, wherein the space-charge polarization glass material comprises a composition from a ternary system of lithium sulfide, lithium iodide and boron sulfide.
14. The capacitor of claim 12, wherein the space-charge polarization glass material comprises a composition from a ternary system of lithium sulfide, lithium iodide and silicon sulfide.
15. The capacitor of claim 12, wherein the space-charge polarization glass material comprises a composition from a ternary system of lithium oxide, lithium chloride, and boron oxide.
16. The capacitor of claim 12, wherein the space-charge polarization glass material has a dielectric response ε' characterized by:
Figure imgf000015_0001
where εhf is a dielectric constant value for the space-charge polarization glass material at a high frequency, εSpace a dielectric constant for the space-charge polarization glass material attributable at a low frequency to space-charge polarization, ω is a signal frequency in radians, τo is a polarization relaxation time, ΔΕ is an activation energy value, T is temperature in Kelvin, and k is Boltzman's constant.
17. The capacitor of claim 16, wherein ωτo is approximately 1.
PCT/US1996/004292 1995-04-03 1996-04-02 Thermal sensing device comprising a capacitor with dielectric layer of space charge polarization material WO1996031892A1 (en)

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WO2018114226A1 (en) * 2016-12-20 2018-06-28 Bayerische Motoren Werke Aktiengesellschaft High-voltage battery for a motor vehicle, in particular a car

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US4712055A (en) * 1987-04-01 1987-12-08 The Singer Company Battery charger circuit
JPH05306118A (en) * 1992-05-07 1993-11-19 Matsushita Electric Ind Co Ltd Amorphous lithium ion conductive solid electrolyte and its synthesizing method

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US4712055A (en) * 1987-04-01 1987-12-08 The Singer Company Battery charger circuit
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Publication number Priority date Publication date Assignee Title
EP0966090A3 (en) * 1998-06-17 2003-04-23 Black & Decker Inc. Method & apparatus for charging batteries
WO2018114226A1 (en) * 2016-12-20 2018-06-28 Bayerische Motoren Werke Aktiengesellschaft High-voltage battery for a motor vehicle, in particular a car

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