CDOT DEVICE FOR WIRELESS CHARGING

A battery protection device includes a Charge/Discharge Over Temperature (CDOT) device and a wireless charging coil. The CDOT device consists of a first electrode, a second electrode, and a variable resistance material. The first electrode is located on a substrate and has a first collection of fingers. The second electrode is located on the substrate and has a second collection of fingers. The first fingers and the second fingers are disposed in an interdigitated, spaced-apart relationship with one another, resulting in a gap between them that is serpentine and tortuous. The variable resistance material changes its resistance in response to a change in temperature.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to wireless charging and, more particularly, to mechanisms to thermally manage a battery during wireless charging.

BACKGROUND

Mobile devices, such as smartphones and laptop computers, utilize batteries to enable the device to be operable without being plugged into a power source. Many smartphones, for example, include rechargeable batteries, such as lithium-ion batteries. Over time and use, the lithium-ion batteries lose their charge, resulting in loss of function of the smartphone. By plugging the smartphone into the power source, the lithium-ion batteries may be recharged, enabling the smartphone to once again be mobile.

Some batteries can be charged using wireless charging. As one example, a type of induction charging known as the Qi wireless standard allows the battery to be charged in the presence of a magnetic field. The charging device includes an induction coil and the mobile device include a second induction coil. Together, the coils create a magnetic field that sends electric current to charge the battery.

In simplest terms, the battery is designed such that electrons flow between its terminals, supplying current to the mobile device. Batteries operates within a relatively narrow temperature range. If the temperature of the battery goes outside the temperature range, thermal runaway can occur. Thermal runaway is a chemical reaction within the battery cell that produces heat, which can cause the battery cell temperature to rise incredibly fast (within milliseconds). Thermal runaway can thus cause the battery to melt, explode, and even start fires.

While poor battery maintenance such as physical damage, excess heat, or excess cold can be the culprit, thermal runaway can also be caused by charging events, such as overcharging or rapid charging. In the case of wireless charging, the magnetic field produced by the induction coils may generate excess heat, resulting in thermal runaway. Ultimately, these events can damage the components of the battery and limit its life and may even damage the mobile device housing the battery.

It is with respect to these and other considerations that the present improvements may be useful.

SUMMARY

An exemplary embodiment of a battery protection device in accordance with the present disclosure may include a Charge/Discharge Over Temperature (CDOT) device and a wireless charging coil. The CDOT device consists of a first electrode, a second electrode, and a variable resistance material. The first electrode is located on a substrate and has a first collection of fingers. The second electrode is located on the substrate and has a second collection of fingers. The first fingers and the second fingers are disposed in an interdigitated, spaced-apart relationship with one another, resulting in a gap between them that is serpentine and tortuous. The variable resistance material changes its resistance in response to a change in temperature. The wireless charging coil is connected to the CDOT device.

An exemplary embodiment of mobile device in accordance with the present disclosure may include a rechargeable battery, a CDOT device, and a wireless charging coil. The rechargeable battery is controlled by a battery management system. The CDOT device includes a variable resistance material to change its resistance in response to a change in current. The wireless charging coil forms a magnetic field in response to being proximate a second wireless charging coil which is external to the mobile device.

DETAILED DESCRIPTION

A novel circuit protection device, known as a CDOT device, short for Charge/Discharge Over Temperature, is disclosed for use in battery charging applications, such as mobile phones. The CDOT device includes electrodes having interdigitated fingers to form a tortuous, serpentine gap, upon which variable resistance material is deposited. The CDOT device is connected in series with a wireless charging coil inside the mobile phone and protects the wireless charging coil, the battery, and other components in the mobile phone from overtemperature, overcurrent, and overvoltage events, thus mitigating the possibility of thermal runaway in the battery.

For the sake of convenience and clarity, terms such as “top”, “bottom”, “upper”, “lower”, “vertical”, “horizontal”, “lateral”, “transverse”, “radial”, “inner”, “outer”, “left”, and “right” may be used herein to describe the relative placement and orientation of the features and components, each with respect to the geometry and orientation of other features and components appearing in the perspective, exploded perspective, and cross-sectional views provided herein. Said terminology is not intended to be limiting and includes the words specifically mentioned, derivatives therein, and words of similar import.

FIG.1is a representative drawing of a wireless charging system100, according to exemplary embodiments. The wireless charging system100features a mobile device102such as a smartphone, which houses a wireless charging coil104and a battery106, with a Charge/Discharge Over Temperature (CDOT) device108disposed therebetween. The wireless charging coil104operates with a second wireless charging coil within an external charging device (not shown) to charge the battery106. In exemplary embodiments, as shown in further detail below, the CDOT device108is connected to the wireless charging coil104to provide both temperature detection and overcurrent protection, thus mitigating the possibility of thermal runaway of the battery106.

FIGS.2A-2Eare representative drawings of the CDOT device108ofFIG.1, according to exemplary embodiments.FIG.2Ais a perspective view of the CDOT device108whileFIGS.2B-2Eare plan views of the CDOT device or portions thereof. The CDOT device108features a pair of conductors202aand202b(collectively, “conductor(s)202”) disposed between a substrate210and a variable resistance material218. Each conductor202is made up of electrodes and fingers: conductor202aincludes electrode204aand fingers206a-iwhile conductor202bincludes electrode204band fingers208a-j(collectively, “electrode(s)204”, “finger(s)206”, and “finger(s)208”). The conductor202ais electrically connected to the electrode204aand the conductor202bis electrically connected to the electrode204b, with the electrodes204being disposed on the substrate210in a confronting arrangement.

In exemplary embodiments, the fingers206of the electrode204aare disposed in an interdigitated, spaced-apart relationship with the fingers208of the electrode204b, resulting in a serpentine, tortuous gap212therebetween. InFIG.2A, conductor202aincludes nine fingers206a-iand conductor202bincludes ten fingers208a-jwhile InFIGS.2B-2E, both conductors include eight fingers. In exemplary embodiments, the conductors202may have any number of fingers, as the illustrations are not meant to be limiting.

The electrodes204may be disposed on an intermediate substrate (e.g., a segment of FR-4 printed circuit board material), which may in turn be disposed on, and adhered to, the substrate210. In exemplary embodiments, the substrate210is formed of a dielectric material that has an adhesive material on one or both sides, allowing the CDOT device108to be adhered to a surface, such for connection to the wireless charging coil104(FIG.1). In various non-limiting embodiments, the substrate210may be Scotch Tape, polyvinyl chloride (PVC) tape, Mylar, and so on. In exemplary embodiments, the substrate210is a polyethylene terephthalate (PET). The conductors202, which include the electrodes204, the fingers206, and the fingers208, may be formed of elongated segments of flexible, electrically conductive material that may be adhered to, printed on, or otherwise applied to the substrate210. Examples of materials to be used for the conductors202include, but are not limited to, copper mesh, silver epoxy, various types of metal wire or ribbon, conductive ink, and so on. In exemplary embodiments, the conductors202are made of a silver conductive ink.

In exemplary embodiments, the electrodes204are integral, contiguous portions of respective conductors202. In exemplary embodiments, the conductors202and the electrodes204are formed of a flexible material. Confronting ends of the adjacent conductor202amay be cut, printed, or otherwise formed to define the electrode204awith interdigitated fingers206. Similarly, confronting ends of the adjacent conductor202bmay be cut, printed, or otherwise formed to define the electrode204bwith interdigitated fingers208. Electrode204ais shown as being perpendicular to fingers206and electrode204bis shown as being perpendicular to fingers208. Alternatively, the fingers206and208may be otherwise arranged, such as diagonally from their respective electrodes204, meandering in a curve-like configuration, or otherwise extending in a non-perpendicular manner distinct from what is shown inFIGS.2A-2E, to form the tortuous, serpentine gap212therebetween, as the illustration is not meant to be limiting.

The variable resistance material218is indicated as dark sheet disposed upon the electrodes204, the fingers206, and the fingers208. The variable resistance material218is shown as partially transparent inFIGS.2B and2Cand is moved inFIG.2Cto reveal the underlying components in the plan view. The variable resistance material218is generally opaque but is shown as “transparent” so that the other features of the CDOT device108are visible. In exemplary embodiments, the variable resistance material218and the conductors202form a temperature sensing element that also provides overcurrent protection.

In exemplary embodiments, the variable resistance material218is disposed on the fingers206and208to bridge and/or fill the gap212, which also results in the fingers206being connected to the fingers208. In exemplary embodiments, the fingers206and208are spaced a predetermined distance apart to accommodate the prevention of polymer breakdown in the variable resistance material under a high electric field. Additionally, care is ensured that the fingers206and208not exhibit ferro- or antiferro-magnetic properties. In exemplary embodiments, the fingers206and208are made using copper, high conductivity carbon-based materials, such as carbon nanotube, pyrolyzed carbon, graphite, and/or combinations of these materials. This ensures that the CDOT device108does not block, even partially, the transfer of energy to the wireless receiver, that is, the charging coil of the mobile device102(FIG.1). The charging coil of the charging device (seeFIG.7, below) may be referred to as the primary coil while the charging coil of the mobile device is known as the secondary coil.

InFIG.2D, the conductors202and the substrate210are shown, with the variable resistance material218removed; inFIG.2E, only the conductors202are shown. The gap212is called out in various places inFIGS.2A-2Ebut is essentially occupies the entire “white space” within the rectangular structure ofFIG.2E. Looking particularly atFIGS.2D and2E, the fingers206and208alternate with one another and with the gap212, with finger206abeing adjacent to a portion of the gap, which is adjacent to finger208a, which is adjacent to another portion of the gap, which is adjacent to finger206b, which is adjacent to another portion of the gap, which is adjacent to finger208c, which is adjacent to another portion of the gap, and so on. In exemplary embodiments, the variable resistance material218is a polymeric positive temperature coefficient (PPTC) ink material that is disposed atop these alternating fingers and gaps, which fills into and occupies the regions of both the fingers and the gap within the interdigitated structure.

Apertures214aand214b(collectively, “aperture(s)214”) are formed in the substrate210while apertures216aand216b(collectively, “aperture(s)216”) are formed in the conductors202. In exemplary embodiments, the apertures214and216enable alignment of the elements of the CDOT device108prior to assembly. The apertures214and216may also allow the CDOT device108to be secured to the wireless charging coil104, as illustrated inFIGS.3A-3C, below.

In various embodiments, the PPTC material that makes up the variable resistance material218of the CDOT device108has an electrical resistance that increases sharply when the variable resistance material reaches a predefined temperature, known as the “PPTC activation temperature”. In other embodiments, the variable resistance material218is a polymeric negative temperature coefficient (PNTC) material having an electrical resistance that decreases sharply when the variable resistance material reaches a predefined temperature, known as the “PNTC activation temperature”. In a specific, non-limiting embodiment, the variable resistance material218is a PPTC material formed of conductive particles (e.g., conductive ceramic particle) suspended in a polymer resin. In exemplary embodiments, the variable resistance material218is applied to the fingers206and208as a fluidic ink or as a compound that may be subsequently cured to form a solid mass that partially covers and/or envelopes the fingers.

In exemplary embodiments, the variable resistance material218consists of one or more crystalline or semicrystalline polymers with a melting temperature preferably below 70° C., polyurethanes, polyesters, various copolymers of ethylene butyl acetate (EBA), and/or low molecular weight polyethylenes. Where the wireless charging system100features a high-temperature battery, the variable resistance material218consists of polyvinylidene fluoride or polyvinylidene difluoride (PVDF), in some embodiments. Where the wireless charging coil104may be exposed to high temperatures, the conductive part of the variable resistance material218consists preferably of carbon-based particles such as carbon black, carbon nanotubes, and so on, in exemplary embodiments.

The PPTC activation temperature may be different from the PNTC activation temperature. In exemplary embodiments, the PPTC/PNTC material of the variable resistance material218is carefully chosen to ensure that the PPTC/PNTC activation temperature is within a certain temperature range. Thus, the variable resistance material218may be crafted for a specific application in which the PPTC/PNTC activation temperature protects the circuit of the application.

In exemplary embodiments, the CDOT device108is connected in electrical series between the wireless charging coil104and the battery106to provide both temperature sensing and overcurrent protection. As one example, the conductor202awould be connected to the wireless charging coil104and the conductor202bwould be connected to the battery106, thus forming an in-series connection between the two devices.

In some embodiments, the CDOT device108is formed of a thin, flexible material. In other embodiments, the CDOT device108is formed of a not thin, rigid material. In exemplary embodiments, the CDOT device108is made of a material that is transparent to the magnetic field formed by the wireless charging coil104once paired with a similar charging coil disposed within a battery charger. In one embodiment, the CDOT device108is made using diamagnetic material. Materials are said to be diamagnetic if the electrons within the material are paired and thus there are no free electrons within the material. Wood, copper, gold, bismuth, mercury, silver, lead, neon, water, and superconductors are diamagnetic, for example. In exemplary embodiments, the CDOT device108is made using one or more of the following combinations of materials: carbon black, polymers, copper fingers, and diamagnetic ceramic. In exemplary embodiments, the CDOT device108is made using diamagnetic materials that expel magnetic field lines. Further, in exemplary embodiments, conductive particles in the dielectric matrix of the CDOT device108are selected to minimize eddy currents.

In some embodiments, the CDOT device108is flexible to accommodate the geometry of its application. In exemplary embodiments, the CDOT device108features holes or perforations disposed particularly to concentrate magnetic fields and/or steer the magnetic fields in a particular direction. Perforations could be real or virtual by masking parts of the variable resistance material218of the CDOT device108with magnetic materials.

Additionally, in some embodiments, the CDOT device108can be enhanced using flexible metal oxide varistor (MOV) type circuitry to accommodate overvoltage due to field interference lines or changed angles from the magnetic field produced during battery charging, where the ferric shield concentrator could be saturated. The ferric shield concentrator is a ferroelectric material that confines the magnetic field to the vicinity of a receiver antenna.

FIGS.3A-3Care representative drawings of a coupling apparatus300, according to exemplary embodiments.FIG.3Ashows a first configuration;FIG.3Bshows a second configuration, andFIG.3Cshows a third configuration of the coupling apparatus300. The coupling apparatus300consists of the wireless charging coil104and the CDOT device108of the mobile device102fromFIG.1. The wireless charging coil104is a typically tightly wound piece of electrically conductive wire302, such as copper. Together with a similar coil on a charging device, the wireless charging coil104form a transformer that causes a magnetic field having a magnetic flux. The wireless charging coil104is thus a magnet/ferrite concentrator/shield. The resulting magnetic flux density is based on characteristics such as the number of turns of the wire302, the diameter of the electrically conductive wire, the material used for the wire, the distance between the coils, and the current. The wireless charging coil104thus consists of the electrically conductive wire302having two end points304and306.

The CDOT device108may be connected to either end of the conductive wire302. InFIG.3A, the CDOT device108is connected to the end point304, with either the conductor202aor the conductor202bof the CDOT device108(FIGS.2A-2E) being connected to the conductive wire302. InFIG.3B, the CDOT device108is connected to the end point306. Either end point connection,304or306, establishes an in-series connection between the wireless charging coil104and the CDOT device108. InFIGS.3A and3B, the CDOT device108is insignificant in size relative to the charging coil. However, the configuration ofFIG.3Cshows that, whether connected at the end point304or the end point306, the CDOT device108can partially or fully cover the wireless charging coil104, in exemplary embodiments. Once connected to one of the end points304or306, the CDOT device108can assume a variety of different positions relative to the wireless charging coil104.

When the wireless charging coil104is paired with a similar wireless charging coil of a battery charger, the two wireless charging coils operate as a transformer, creating a magnetic field which enables the battery to be charged. Sometimes, the magnetic field saturation gets high enough that the wireless charging coil104gets overheated. Left unmanaged, the overheating can result in thermal runaway within the mobile device102, which can destroy both the battery106and the mobile device. In exemplary embodiments, the CDOT device108disposed in series with the wireless charging coil104provides current limiting and voltage limiting, thus preventing this overheating.

Further, the nature of wireless charging can cause conditions that are unmanageable. When the magnetic field supplied is constant or the magnetic field lines are set by simple geometry, it is possible to design a part that will fit into a rigid design. However, if magnetic field lines can be changed simply due to a change in device placement, which can occur with wireless charging, virtual loops can result, which can cause unintended behavior, such as overheating. The presence of the CDOT device108in series with the wireless charging coil104provides a mechanism to limit current and/or voltage, as needed, to prevent unintended behavior during the wireless charging event.

Further, in exemplary embodiments, the conductors202of the CDOT device108are designed to not exhibit ferro- or antiferro-magnetic properties. Ferromagnetism is the susceptibility to magnetism while antiferromagnetism occurs when the magnetic moments of atoms or molecules within a material, which is related to the spin of electrons, align in a regular pattern with neighboring spins pointing in opposite directions. Both ferromagnetism and antiferromagnetism would prevent the transfer of energy during the wireless charging event.

There are other failure conditions that might arise with the mobile device102that are addressed by the CDOT device108, in exemplary embodiments. Mobile devices generally include transient voltage suppressors (TVS) to protect against overvoltage events. Nevertheless, a transient of ≤100 Vpk can still heat up the mobile device. The presence of the transient throughout the failure condition can also result in unintended heat. During the charging event, current in the wireless charging coil104can increase, which also increases the heat to the mobile device. Other events, like leaving the mobile device in a hot car, can result in device failure. Including the CDOT device108with the wireless charging coil104addresses one or more of these failure conditions, in exemplary embodiments.

FIG.4is a representative diagram of a circuit400used to illustrate the relationship between the components ofFIG.1, according to exemplary embodiments. The wireless charging coil104(shown as an inductor Ls), the CDOT device108(shown as a variable resistor), and the battery106are included in the circuit400. The circuit400also includes two capacitors402(Cs) and404(Cd) and a TVS diode408disposed within a battery management system406. In exemplary embodiments, the battery management system406is an integrated circuit consisting of a rectifier and buck stage and includes the TVS diode408. Like the CDOT device108, the TVS diode408also protects the battery106from high-voltage transients.

Recall fromFIGS.3A and3Bthat the CDOT device108is connected at one end to the wireless charging coil104. In exemplary embodiments, the other end of the CDOT device108is connected to both the capacitor404as well as the battery management system406, specifically, the TVS diode408. In exemplary embodiments, the circuit400, including the CDOT device108, does not significantly alter the inductance of the wireless charging coil104and thus does not significantly change the resonance frequency.

FIGS.5A and5Bare representative drawings of the CDOT device108, according to exemplary embodiments.FIG.5Ais a top view andFIG.5Bis a bottom view of the CDOT device108. In exemplary embodiments, the CDOT device108is rectangular in shape, but can also be formed as a circle, an oval, a triangle, any other polygon-shape, or may be amorphous in shape. The CDOT device108may be custom-shaped to fit the environment in which it is to be used, for example. In the illustrations ofFIGS.5A and5B, the CDOT device is 355 mm×35 mm, 300 to 500 μm thick, with a voltage rating of 60 Vdc, a trip temperature of 60° C., a hold current of 400 mA (@ 25° C.), and a trip current of 450 mA (@ 25° C.). The variable resistance material, the number, shape, and size of the fingers, and other CDOT device components can be adjusted to fit the characteristics of the environment in which the CDOT device is to be used.

FIG.6is a graph600showing the magnetic field in the presence of the CDOT device108, according to exemplary embodiments. The graph600shows that the magnetic field generated by the wireless charging coil104paired with a similar wireless charging coil in a battery charging device is not affected by the presence of the CDOT device108, in exemplary embodiments. The graph600shows that, between 50 kHz and 300 kHZ, there is no change in the magnetic field generated by the wireless charging pair.

FIG.7is a representative drawing of the mobile device paired with a wireless charging device, according to exemplary embodiments. The mobile device102fromFIG.1is shown, including the wireless charging coil104, the battery106, and the CDOT device108, with the CDOT device being disposed between the battery and the wireless charging coil. A wireless charging device702is also shown, which has its own wireless charging coil704. When the mobile device102is placed in proximity to the wireless charging device702the wireless charging coil104and the wireless charging coil704operate like a transformer and generate a magnetic field. This magnetic field is used to charge the battery106. In exemplary embodiments, the CDOT device108connected in series with the wireless charging coil704automatically increases its resistivity in response to an increase in temperature, which slows down the charging operation of the wireless charging device702. Further, in exemplary embodiments, the CDOT device108automatically increases its resistivity in response to an overcurrent or overvoltage condition, which also slows down the charging operation of the wireless charging device702. Once the failure conditions cease, the resistivity of the CDOT device108is decreased, allowing the wireless charging device702to resume full charging of the battery106.

The CDOT device108is thus a PTC or NTC device that increases its resistivity in response to increased temperature, increased current flow, or increased voltage, which protects the mobile device102from undesired heating, which also mitigates the possibility of thermal runaway in the battery106. In addition to mobile devices, the CDOT device108may also be used in industrial chargers or transformers, in some embodiments.

While the present disclosure refers to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claim(s). Accordingly, it is intended that the present disclosure is not limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.