Lithium-ion batteries – safety of use

Introduction

Lithium-ion batteries have become a standard in most types of consumer electronics. Due to their numerous advantages, including high energy density and lack of memory effect, they are commonly used in all kinds of portable devices, such as laptops or mobile phones. However, there are certain risks associated with their usage, therefore, they require compliance with several safety rules.

Safety rules

The most important factor for a Li-ion battery to work properly is temperature. Batteries can swell, catch fire, or even explode if overheated. Therefore, they should not be stored in places exposed to heat, such as a vehicle on sunny days, near heaters, stoves and radiators. Short-circuiting or overloading the battery can also cause permanent damage and pose an ignition hazard. Moreover, batteries should not be opened or exposed to any kind of mechanical damage. It is also necessary to keep proper charging and discharging conditions, otherwise the battery can be damaged or its life shortened. It is recommended to use special protection circuits (PCMs) which protect the battery against overcharging, over-discharging and current overload. Batteries with appropriate protection and used according to above mentioned safety rules do not pose any danger.

Charging

Lithium-ion batteries should operate within a certain voltage range – they are not immune to overcharging or over-discharging. Consequently, this imposes certain requirements on battery chargers.

The charging process should be accomplished in two stages:

1) CC (constant-current) – charging with a constant current specific to the cell, until it reaches its maximum voltage. The recommended and maximum charging current should be specified by the manufacturer.

2) CV (constant-voltage) – maintaining a constant charging voltage (usually 4.2V per cell) until the current drops below a certain threshold (2% – 10% of the initial charging current).

Charging current should be based on information specified in the battery datasheet. Higher current allows for faster charging, but can also shorten the battery life, or cause excessive heating. In case of battery packs with cells connected in series, a balancing circuit (BMS) should be used to keep voltage in each cell equal.

Usage tips

Li-Ion batteries should not be discharged below a certain level (approx. 2.5V per cell), as irreversible chemical reactions take place, causing permanent damage to the cells. Long-term storage of discharged batteries may shorten their life, therefore, they should be recharged as soon as possible after being discharged. In case of a long break in use, they should be discharged to nominal voltage (about 40% of maximum capacity) – this allows to extend their life. It is also important to consider appropriate storage conditions, including nominal temperature and humidity.

Recycling

As with other types of cells, Li-ion batteries are subject to a special disposal process. Under no circumstances should they be disposed of with regular waste. The substances they contain should be recycled, in order to reuse them and reduce environmental impact.

Used or defective batteries should be properly stored after disassembly. The cells must be protected against damage and their terminals against shorting together. Then the batteries should be handed over to the appropriate collection point or waste disposal centre for recycling.

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