Protection devices for lithium-ion Li-ion batteries, protection schemes for voltage, against deep discharge, temperature, threshold pressure level inside the case.

Commercial lithium-ion batteries have the most advanced protection among all types of batteries. This level of protection for lithium-ion Li-ion batteries is due to the fact that, being connected to any electronic device, they are constantly in the hands of a person.

Protection devices for lithium-ion Li-ion batteries, protection schemes for voltage, against deep discharge, temperature, threshold pressure level inside the housing.

Usually, a key on a field effect transistor is used in the protection circuit of lithium-ion Li-ion batteries. When it reaches a voltage of 4.30 V on the battery element, it opens and thereby stops the charging process. In addition, the existing thermal fuse when the battery is heated to 90 degrees disconnects its load circuit. Thus providing her thermal protection.

But that is not all! Each element has a switch that trips when a threshold pressure level is reached inside its body, equal to 1034 kPa (10.5 kg / m2), and breaks the load circuit. There is also a deep discharge protection circuit that monitors the battery voltage and breaks the load circuit if it drops to 2.5 V per cell.

Protection devices for lithium-ion Li-ion batteries, protection schemes for voltage, against deep discharge, temperature, threshold pressure level inside the case.

The internal resistance of the protection circuit of lithium-ion Li-ion batteries of the mobile phone in the on state is 50-100 mOhm (0.05-0.1 Ohm). Structurally, it consists of two keys connected in series. One of them is triggered when the upper threshold is reached, and the other – the lower threshold of voltage on the battery.

The total resistance of these keys actually provides a doubling of its internal resistance. Especially if it consists of only one element. Mobile phone batteries must provide high load currents. This is possible with the lowest possible internal resistance of lithium-ion Li-ion batteries. Thus, the protection circuit is an obstacle limiting its operating current.

Lithium-ion Li-ion batteries without protection circuits.

In some types of lithium-ion Li-ion batteries using manganese in their chemical composition and consisting of 1-2 elements, the protection scheme is not used. Instead, they have only one fuse. And such batteries are safe due to their small size and low capacity. In addition, manganese is quite tolerant of violations of the operating rules of lithium-ion Li-ion batteries. The lack of a protection circuit reduces the cost of lithium-ion batteries, but introduces new problems.

Problems in the absence of protection schemes in lithium-ion Li-ion batteries.

In particular, mobile phone users can use abnormal chargers to recharge their batteries. With such inexpensive chargers designed to recharge from a household network or from the car’s on-board network, you can be sure that if there is a protection circuit in the battery, it will turn it off when the voltage reaches the end of the charge.

If there is no protection circuit, recharge of lithium-ion Li-ion batteries will occur. And, as often happens, their irreversible failure. This process is usually accompanied by increased heating and bloating of the battery case. Of course, such situations cannot be allowed. In addition, if the battery fails due to the use of an abnormal charger, it cannot be replaced under warranty..

Lithium-ion batteries with cobalt electrodes, for example, require complete protection. A discharge of static electricity or a malfunction of the charger may result in failure of the battery protection circuit. This means that as a result, the solid-state key of the protection circuit is constantly on, and the user does not suspect this.

In this case, the battery may function normally, but it will not meet the safety requirements. During the charge, overheating and bloating of the housing may occur. And in some cases, the release of gases with ignition (“ventilation with a flame”) with all the ensuing consequences. Short circuiting the terminals of lithium-ion Li-ion batteries is also dangerous.

Explosion hazard lithium-ion Li-ion batteries.

Manufacturers of lithium-ion Li-ion batteries in their technical specifications try not to mention their explosion hazard. Instead, they use the term “flame ventilation”. And although this reaction proceeds more slowly than the explosion, it is so intense that it leads to a strong shock at a short distance from the battery. And it may damage the electronic device that is powered by this battery.

Most manufacturers of lithium-ion batteries do not sell them separately as battery cells. Instead, they produce and sell lithium-ion batteries with built-in protection circuits..

Because they understand the danger posed by their inept use, and in the interests of the consumer, they try to minimize the possible negative consequences that may arise during their operation. Strict certification of company products also serves the same purposes. Prior to the emergence of new types of lithium-ion Li-ion batteries on the market.

Based on the book Battery.
Khrustalev D.A..

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