FIELD

Embodiments described herein relate to battery charging systems, and more particularly, to systems and methods for determining and controlling expansion of rechargeable batteries over time.

BACKGROUND

Portable electronic devices may include one or more batteries that may require recharging from time to time. Such devices may include electric vehicles, cell phones, smart phones, tablet computers, laptop computers, wearable devices, navigation devices, sports devices, health analysis devices, medical data devices, location tracking devices, accessory devices, home appliances, peripheral input devices, remote control devices, and so on. As a result of high packing density, high energy density, long cycle life, and ease of mass production, portable electronic devices typically include one or more lithium-polymer or lithium-ion batteries.

Over the operational life of a lithium-polymer rechargeable battery, the internal resistance of the rechargeable battery may increase as a result of oxidation, lithium dendrite growth, cathodic gas evolution, and/or cathodic degradation, due at least in part to repeated charging and discharging of the rechargeable battery. As a result, the power output capacity of the rechargeable battery may decrease over time, undesirably limiting the useful life of the rechargeable battery and/or the portable electronic device. In other examples, non-optimal charging conditions can also effect an increase in internal resistance of the rechargeable battery. For example, the internal resistance of the battery may increase as a result of charging at high voltage, delayed transition from constant current to constant voltage charging, and/or charging or discharging at a high temperature. In many examples, the internal resistance of the rechargeable battery may correlate or correspond to target charge capacity, rechargeable battery health, and/or rechargeable battery age.

In addition, lithium-polymer batteries may physically expand or swell during charging of the rechargeable battery. For example, the anode material can expand substantially over repeated charging cycles or even during a single charging cycle. In other cases, gas emissions from a charged cathode can, over time, result in an expanded rechargeable battery. Over time, the rechargeable battery can expand beyond its allotted volume within the portable electronic device, damaging components and/or portions the portable electronic device. In these cases, a user of a portable electronic device may be entirely unaware of the expansion of the rechargeable battery until conspicuous physical damage occurs.

Accordingly, there may be a present need for a method and system for detecting, arresting, mitigating, and compensating for rechargeable battery expansion.

SUMMARY

Embodiments descried herein may relate to, include, or take the form of methods and systems for detecting and compensating for rechargeable battery expansion over time.

For example, certain embodiments described herein may take the form of an electronic device including at least a housing, a rechargeable battery within the housing, a processing unit configured to control the electrical input received from a power source coupled to the rechargeable battery, and an expansion detector electrically coupled to the processing unit. In these embodiments, the expansion detector can send an expansion signal to the processing unit upon determining that the rechargeable battery has expanded, and in response to receiving the expansion signal, the processing unit can modify one or more characteristics of the electrical input. For example, the processing unit may modify the output voltage, current, or scheduling of the electrical input.

In certain embodiments, the expansion detector may be any suitable sensor or detector configured to detect dimensional expansion of the rechargeable battery. For example, in certain embodiments the expansion detector may be a capacitive sensor. The capacitive sensor can measure for changes in capacitance between two or more electrically conductive surfaces. In certain embodiments, at least one of the surfaces may be a surface of the rechargeable battery. In one example, a second surface may be a surface of the housing of the electronic device. Upon expansion of the rechargeable battery, the distance between the first and second surface may change and according, the capacitance between the first and second surface can change. In this manner, the capacitive sensor may determine that the rechargeable battery has expanded.

In other examples the capacitive sensor can be positioned elsewhere to detect a dimensional expansion of the rechargeable battery. For example, one electrically conductive plate may be positioned on a top surface of the rechargeable battery and another electrically conductive plate may be positioned on a bottom surface of the rechargeable battery. In further examples, one electrically conductive plate may be positioned within the rechargeable battery and another electrically conductive plate may be positioned outside the rechargeable battery. In other examples, the capacitive sensor may be pixelized in order to determine expansion of the rechargeable battery at more than one location.

Other embodiments may include a configuration in which the expansion detector includes a strain sensor coupled to an external surface of the rechargeable battery, a resistance sensor coupled to an external surface of the rechargeable battery, an acoustic resonance sensor, a photo interrupter positioned across the rechargeable battery, a contact switch, or a pressure sensor. Each of these example expansion detectors may send an expansion signal to the processing unit upon determining that the rechargeable battery has expanded beyond a selected threshold.

Other embodiments described herein may relate to, include, or take the form of a rechargeable battery within the housing of a portable electronic device, the rechargeable battery including at least a rechargeable battery module, a pouch containing the rechargeable battery module, and a rechargeable battery expansion detector electrically coupled to a processing unit associated with the portable electronic device. In these embodiments, the expansion detector can send an expansion signal to the processing unit upon determining that the rechargeable battery has expanded, and in response to receiving the expansion signal, the processing unit can modify one or more characteristics of the electrical input, such as the output voltage, current, or scheduling of the electrical input.

These embodiments may include a configuration in which the expansion detector includes a capacitive sensor, a strain sensor coupled to an external surface of the rechargeable battery, a resistance sensor coupled to an external surface of the rechargeable battery, an acoustic resonance sensor, a photo interrupter positioned across the rechargeable battery, a contact switch, or a pressure sensor. Each of these example expansion detectors may send an expansion signal to the processing unit upon determining that the rechargeable battery has expanded beyond a selected threshold.

Certain embodiments described herein may also relate to, include, or take the form of a method for adjusting power output from a power supply configured to charge a rechargeable battery, the method including at least the operations of determining whether the rechargeable battery has expanded beyond a selected threshold, and changing one or more power output characteristics of the power supply in response to determining that the selected threshold may be exceeded. For example, the output voltage, current, or scheduling of the electrical input and/or power source may be changed in response to determining that the rechargeable battery has expanded.

Additional embodiments described herein may also relate to, include, or take the form of a method for adjusting power output from a power supply configured to charge a rechargeable battery, the method including at least the operations of determining whether the output power presents a risk of rechargeable battery expansion, determining whether the risk of rechargeable battery expansion exceeds a selected threshold, and changing one or more power output characteristics of the power supply in response to determining that the selected threshold may be exceeded. For example, the output voltage, current, or scheduling of the electrical input and/or power source may be changed in response to determining that the rechargeable battery has expanded.

These embodiments may determine an increased risk of rechargeable battery expansion by, for example, determining whether the age of the rechargeable battery exceeds a selected age, determining whether the charge/discharge cycle count of the rechargeable battery exceeds a selected maximum, determining whether the temperature of the rechargeable battery exceeds a selected temperature threshold, determining whether the rate of expansion exceeds a selected rate threshold, or determining whether the internal resistance of the rechargeable battery exceeds a selected resistances threshold.

