Abusive tests on Li-ion batteries

Friday 19 August 2022

Nowadays, lithium-ion batteries are central to our daily lives. Marketed in 1991 by Sony, they are now found in our smartphones, laptops, tablets, electronic cigarettes, and in all EDPMs, these new motorized modes of transport such as the bicycle and the electric scooter, the hoverboard, monowheel, etc.

However, the news reminds us from time to time of their dangerousness; Although they are rare, fires caused by Li-ion batteries remain spectacular (devices that melt, explosions, etc.), especially since they can cost human lives.

In this article, we are going to come back to the operation of Li-ion batteries, to ask ourselves if it is possible to seek ever greater security. We will also tell you what to do in the event of a fire in your electronic devices due to a defective Li-ion battery.

 

How does a Li-ion battery work?

A lithium-ion battery is made up of several individual cells connected to each other. It provides energy through the movement of ions.

Each battery is based on three elements: a positive electrode (cathode), a negative electrode (anode) and an electronic liquid layer between the two (electrolyte).

Rather, the cathode contains metallic lithium, such as cobalt and lithium dioxide, while the anode contains lithium carbon dioxide.

The use of these materials allows intercalation: This is the insertion of a molecule between two other molecules. Thus, the lithium ions can easily insert themselves into the electrodes or withdraw from them.

During charging, when current is supplied to the battery, positive lithium ions move from the anode to the cathode, passing through the electrolyte, causing the cathode to release electrons.

Conversely, when the device discharges, the positive ions leave the cathode, and the electrons undertake the opposite path, and therefore, deliver electricity.

The electrolyte used to insulate the two electrodes (anode and cathode) is highly flammable. It consists of an organic solvent and a conductive salt. Therefore manufacturers of lithium-ion batteries incorporate a separator (plastic material that coats the electrolyte). This prevents the electrodes from touching each other.

 

Why are lithium batteries well suited to mobile technologies?

Lithium-ion batteries have the highest charge density of all battery types. On the one hand, lithium is the lightest of all metals. It is also the most electro positive chemical element: electro positivity corresponds to the ability of an element to share electrons to produce positive ions. Lithium loses electrons very easily. Thus, it can naturally produce a lot of energy.

 

What are the dangers of a Lithium-ion battery?

During charging, small metallic deposits called “dendrites” may form on the anode. The lithium ions do not fit correctly into the negative electrode and form these dendrites which can cause a short circuit, by creating a conductive bridge between the two electrodes. Hence the need for a separator thick enough to avoid short circuits, which cause thermal runaway.

 

Thermal Runaway

The temperature inside a battery is determined by the balance between the heat generated and that dissipated by it. Strong thermal energy leads to evaporation of the electrolyte, thereby creating additional heat and combustible gases. When the pressure exceeds a certain threshold, the inflammable gases present in the electrolyte (fluorine, phosphorus, heavy metals, etc.) are released and form an inflammable mixture with the air: flames appear outside the battery.

 

Main causes of Li-ion battery fires

• Overload: an electrical overload can occur here for several reasons, for example with the use of an unsuitable charger. It is recommended to always use the original charger of the device.
• Deep discharge: Recharging after prolonged storage at exceptionally low voltage can cause the cells to catch fire. If lithium-ion batteries are not used for a long time, they can discharge completely. If an attempt is then made to recharge the fully drained batteries, the energy supplied can no longer be converted correctly due to the lack of electrolyte fluid or its deterioration (for example by cold, heat, etc.). This may cause a short circuit or fire.
• Excessive temperature: above a certain temperature (75 to 100°C), a chain reaction occurs for all lithium-ion battery technologies.
• Mechanical damage: When handling your devices containing lithium-ion batteries, there is always a risk of damage (falling on hard ground, etc.). A shock can tear or damage the separator. The two electrodes can then come into contact and cause a short circuit.
• Fire: A fire external to the Li-ion battery can cause the temperature of the cells to rise and bring it to the threshold for triggering thermal runaway. We recommend for greater safety a design of the battery with non-flammable materials and validation by fire test of the automotive regulations UN R100 revision 2/3.

 

What safety devices are used in a Li-ion battery?

There are several protection systems on lithium batteries. They are located at two levels: the lithium cells (including the fuses) and the BMS (Battery Management System), the circuit which manages the charge and the discharge of the cells.

BMS

The BMS is an electronic card which directs the charge, and normally the discharge, of the cells and provides information on certain operating parameters (discharge intensity, minimum voltage, etc.). The BMS constantly monitors the lithium battery and isolates it in the event of a problem.

Behind the term BMS can hide functionality and battery controls. Some less fussy manufacturers do not hesitate to equip the batteries with BMS cards which are far too simple, and which only resolve the anomalies linked to the charge (and not the discharge), and do not control all the internal parameters of the battery. Lithium ions.

Here are some parameters that can be controlled by the BMS:

• Measurements of battery current, temperature, and state of charge: these measurements make it possible to limit the risks due to overcharging and to solve problems linked to the appearance of dendrites
• Temperature measurements and threshold detection: correct operation of the BMS causes the battery to be disconnected from the application in the event of excessive temperature.

 

How to fight against a lithium-ion battery fire?

The new generations of lithium batteries are more efficient (fast charging, greater autonomy) but they are also more strongly subjected to heat during their use, which can cause thermal runaway and, as we have seen, cause fires.

Unusual or abusive conditions of use (overload, short-circuit, presence of an external heat source, etc.) can therefore cause sudden increases in temperature that can lead to fires, explosions, or the release of toxic products.

The types of lithium batteries are quite varied and the ease with which they pack and die out are different depending on their nature.

Good to know: the more the battery is charged, the stronger the power of the fire will be.

When the fire takes place outside, the damage is limited, and the solution is simple: let it burn (while alerting the firefighters).

Attempts to put out fires with conventional inert agents are usually doomed to failure, because Lithium-ion batteries themselves produce the oxygen that feeds the fire.

One of the characteristics of a Li-ion battery thermal runaway is the possibility of re-ignition after a delay that can exceed 24 hours, which is why it is essential to cool the device.

There are several solutions, including:

• Extinguishing with water (note that a large release of toxic fumes is to be expected.): Since lithium is very reactive, some advice against bringing it into contact with water. Water on a lithium battery fire can have the effect of fanning the flames and making it much more difficult to extinguish. However, recent research has shown that larger amounts of water are able to effectively contain and fight lithium fires. Large batteries, for example those in electric cars, pose a huge challenge for firefighters when they catch fire.
• Sand: it is also often mentioned to stifle the supply of oxygen and stop the fire
• The most effective solution would be the use of the powder extinguishing agent (D) designed to stop fires on metals. The operator must have SCBA equipment (Self-Contained Breathing Apparatus) and body protection.
• New extinguishers are appearing for lithium-based fires. The principle is to have a material that is fluid enough to coat each cell, cool it and asphyxiate it.
• There are also extinguishing granules

To reduce or slow down the risk of fire spreading or the escape of toxic gases, there are special fireproof bags called “Lipo safe bags” for charging and storing lithium-based batteries.

 

How to reduce the risks?

 At the level of lithium-ion battery manufacturers

Lithium-ion battery manufacturers should never compromise on safety. It is a question of not neglecting the thickness of the separators, however, for the moment, the only way to improve the autonomy of a battery is to increase the thickness of the electrodes (anode and cathode), while decreasing that of the separator, to keep a constant volume.

Likewise, these manufacturers must include high quality cells and BMS in their Li-ion batteries, and not seek indefinitely to reduce the charging time: indeed, the only way to achieve this is to increase a little the greater the intensity of the electric current delivered when. Charge, and therefore increase the risk of short circuit caused by the formation of dendrites.

 

How to reduce the risks as user of these batteries?

Lithium-ion battery manufacturers should never compromise on safety. It is a question of not neglecting the thickness of the separators, however, for the moment, the only way to improve the autonomy of a battery is to increase the thickness of the electrodes (anode and cathode), while decreasing that of the separator, to keep a constant volume.

Likewise, these manufacturers must include high quality cells and BMS in their Li-ion batteries, and not seek indefinitely to reduce the charging time: indeed, the only way to achieve this is to increase a little the greater the intensity of the electric current delivered when. Charge, and therefore increase the risk of short circuit caused by the formation of dendrites.

 

Abusive tests on Li-ion batteries: CREPIM's missions

CREPIM: Material & Fire Test Expert  - CREPIM tests the reaction to fire and resistance of lithium-ion batteries. We perform abusive testing for overload, thermal runaway, internal and external short circuit, and fuel stimulated fire.

 For EV charging stations:

Europe

• Casing (Standard IEC 61851-1)
  • EN 60695-2-10/11/12 (Glow Wire Flammability index GWFI @ 650°C)
• Sockets and other dielectrics (Standard IEC 62196-1)
  • EN 60695-2-10/11/12 (Glow Wire Flammability index GWFI @ 650°C or 850°C depending of the final application)

USA

• Casing (Standard UL 2594 & 2202)
  • ASTM E 162 
  • UL 94 5V

• Sockets and other dielectrics (Standard UL 2251)
  • UL 94 HB

 

 For EV & static accumulators - Europe & USA

• E-mobility
  • UNECE R100 & R136
• Static accumulators
  • UL 2580, UL 1973, NF EN 62619 – ask for me details or standards
• Other abusive tests: EN 50604-1; ISO 12405, SAE J2464