Lithium Batteries as a Power Source for Wearable Products

A power source for wearable products must meet many requirements.  Its charge and discharge circuit design must meet the technical specifications for manufacturability, EMC, EMI, and other certifications. The wearable battery must also require a certain level of cost advantage, quality, and technology.  These many requirements make lithium batteries appealing as a power source, which is why they are widely used in wearable products.

A lithium-ion (Li-ion) polymer battery has a power supply voltage of about 3.7V. The lithium-containing oxide is used as the positive electrode, and the layered carbon is used to replace the metal lithium of the traditional lithium primary battery as the negative electrode.

There are so many advantages to using lithium batteries in wearable products. First, the output voltage ranges from 3V to 4.2V. Second, it has a wide operating temperature range of -20℃ to 60 ℃ and a charging temperature range of 0℃ to 50 ℃. Lithium batteries also have a long cycle life that can generally reach more than 500 cycles, even 1,000 cycles.  Lithium Iron Phosphate batteries can reach more than 2,000 times.  Other benefits include no memory effect, low self-discharge rate during storage, and full-charge Li-ion storage at room temperature. After 1 month, the self-discharge rate can come out to about 5-10%.

Lithium Polymer batteries also do not consist of substances harmful to the environment, and they can be made into various special shape batteries.  Every shape is possible, such as the following: Rectangle battery● Ultra Thin Battery●Curved Battery●Round Lipo Battery●Triangle Battery●Hexagon Battery●Ultra Narrow Battery●C Shape Battery●D Shape Battery●Polygonal Battery

These shapes can range anywhere from round to curved, which helps in the development of the numerous consumer electronics out today.

These benefits are a stark contrast to the lithium batteries that were used in mobile phones a year ago since they needed to be charged and discharged three times.

However, nothing’s perfect, and Li-ion batteries are no exception. There can be some weaknesses, such as poor compatibility with ordinary batteries; inconvenient replacement with ordinary, dry batteries; and swelling after repeated charging and discharging. The structural design must also reserve a certain amount of expansion space for the battery. There must be special protection circuits to prevent overcharge, over-discharge, and overcurrent as well.

There are further benefits to using lithium batteries as a power source:

In addition to adding protection circuits to prevent overcharge, over-discharge, and overload, Lithium polymer batteries have vent holes, which help in avoiding the destruction of cells.  These vent holes are thin holes on the surface of the battery case. When a cell short circuits, a large amount of gas generates inside a battery in a short period of time.  With the pressure rapidly increasing, there is a threat of explosion, but the vent holes prevent the internal pressure of a battery from rising too high, thus circumventing an explosion.

Furthermore, the separator inside a Lithium Polymer battery has high puncture resistance and prevents internal short circuits.  On top of that, the separator will melt when the internal temperature of a battery rises too high, and it will prevent an explosion.  When the internal temperature of a battery reaches above 130℃, the mesh pores of the separator will be closed to prevent the passage of Lithium ions and increase the internal resistance to 2kΩ,  thereby protecting the battery. Once the air vent and diaphragm are activated, the battery will be permanently disabled.

A general Lithium battery’s circuit board will protect the battery from overcharge, over-discharge, and overload. Several key pins, such as the DO, CO, and VM, generate different levels in different situations. They control whether the N-channel MOS transistor is turned on or not, and they generate appropriate changes so that the battery is protected. There are also Lithium battery chips that form an integrated IC.

It is for these many reasons that Lithium batteries are commonly used in wearable products.

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