Is lithium-ion battery safe? How to handle it safer?

The widespread use of lithium-ion batteries in modern society has revolutionized the way we live and work, from powering our mobile devices and electric vehicles to supporting renewable energy systems. These high-performance batteries offer numerous advantages, such as higher energy density, longer cycle life, and lower self-discharge rate, but with increasing demand for high-performance batteries, concerns about their safety have also risen.

The safety of lithium-ion batteries depends on various factors such as the manufacturing process, quality of materials used, and usage conditions. Lithium-ion batteries are known to be prone to thermal runaway, a self-sustaining exothermic reaction that can lead to overheating, fire, and explosion. In this article, we will explore the safety issues of lithium-ion batteries, the factors that contribute to their thermal instability, and the strategies to mitigate the risks.

Basics of lithium-ion batteries

Lithium-ion batteries are rechargeable batteries that use lithium ions as the charge carriers. They consist of two electrodes (anode and cathode) separated by a separator and immersed in an electrolyte. The anode is typically made of graphite, and the cathode can be made of various materials, such as lithium cobalt oxide, lithium manganese oxide, or lithium iron phosphate. When the battery is charged, lithium ions migrate from the cathode to the anode through the electrolyte, where they are intercalated into the graphite structure. During discharge, the process is reversed, and lithium ions move back to the cathode, generating an electrical current.

Having the basic knowledge would help us to understand the safety concerns of lithium-ion batteries as below.

Thermal runaway

Lithium-ion batteries are prone to several safety issues, including overcharging, over-discharging, short-circuiting, and physical damage. However, the most serious safety concern is thermal runaway, which can occur when the battery is subjected to elevated temperatures, mechanical abuse, or internal defects. Thermal runaway is a chain reaction that releases heat, gas, and sometimes flames, which can damage the battery, the device, or even the surroundings.

To prevent thermal runaway, lithium-ion batteries are designed with safety features such as temperature sensors, pressure relief valves, and shutdown mechanisms that can disconnect the battery in case of overheating. However, despite these safety measures, lithium-ion battery incidents can still occur. In 2019, for example, a Tesla Model S caught fire after it crashed into a tree, leading to concerns about the safety of electric vehicles. Similarly, in 2016, Samsung had to recall millions of Galaxy Note 7 smartphones after reports of batteries catching fire.

To address these safety concerns, researchers are working on developing safer lithium-ion batteries by using new materials and designs that can prevent thermal runaway. For example, some researchers are developing solid-state lithium-ion batteries that use solid electrolytes instead of liquid ones, which can reduce the risk of fire.

Overcharging

Overcharging occurs when the battery is charged beyond its capacity or at a rate that is too fast for the battery to handle. Overcharging can cause the formation of metallic lithium, which can grow into dendrites that penetrate the separator and cause a short circuit. This short circuit can lead to a thermal runaway, where the battery releases heat and gas, leading to swelling, deformation, or rupture of the cell. Overcharging can also cause the electrolyte to decompose, releasing flammable gases such as ethylene and propylene, which can ignite and cause a fire.

To mitigate the risk of overcharging, lithium-ion batteries are equipped with protection circuits that monitor the battery voltage and current and cut off the charging when the battery is fully charged or when the voltage exceeds a safe limit. Additionally, chargers should be designed to match the battery's voltage and current requirements and should be certified to meet safety standards, such as UL or CE.

Over-discharging

Over-discharging occurs when the battery is discharged beyond its safe lower limit or when the voltage drops too low. Over-discharging can cause the cathode to undergo irreversible structural changes, leading to a loss of capacity or a reduction in the battery's lifespan. Over-discharging can also cause the anode to become coated with metallic lithium, which can cause a short circuit or a thermal runaway.

To mitigate the risk of over-discharging, lithium-ion batteries are equipped with protection circuits that monitor the battery voltage and cut off the discharging when the voltage drops below a safe limit. Additionally, devices should be designed to avoid over-discharging by implementing software or hardware protection, such as battery management systems (BMS) that optimize the battery usage and prevent over-discharging.

Short-circuiting

Short-circuiting occurs when the positive and negative terminals of the battery come into direct contact, bypassing the separator. This can cause a rapid discharge of energy, leading to overheating, venting, and even explosion.

To avoid short-circuiting, it's important to handle lithium-ion batteries with care and avoid exposing them to conductive materials like metal objects or liquids. When storing or transporting batteries, make sure they are kept in a protective case or container to prevent accidental contact with other objects.

Physical damage

Physical damage to a lithium-ion battery can occur due to impact, puncture, or crushing. This can damage the internal structure of the battery and cause a leakage of the electrolyte, which can be corrosive and pose a safety hazard.

To avoid physical damage, handle batteries with care and avoid dropping or crushing them. When transporting or storing batteries, use a protective case or container to prevent damage.

Additionally, it's important to follow the manufacturer's recommendations for charging and discharging lithium-ion batteries. Overcharging or undercharging can also damage the battery and shorten its lifespan.

In summary, to avoid the impact of the above factors on lithium-ion batteries, it's important to handle batteries with care and follow the manufacturer's recommendations for charging and discharging. Keep batteries away from conductive materials, use a protective case or container when storing or transporting batteries, and avoid overcharging or undercharging the battery.