Lithium is the metal with the lowest density, but with the greatest electrochemical potential and energy-to-weight ratio, meaning that it has excellent energy storage capacity. These large energy density and low weight characteristics make it an ideal material to act as a power source for any application where weight is an issue, aircraft applications being a natural candidate.

Experimentation with lithium batteries began in 1912 and the first lithium batteries were sold in the 1970’s. In the nineties, lithium battery technology began to be widely used by a number of industries that were looking for light, powerful and durable batteries.

As it turns out, lithium use in batteries has been one of the major drivers of lithium demand since the rechargeable lithium-ion battery was invented in the early nineties.

Lithium batteries have progressively replaced previous technology batteries – e.g. Nickel-Cadmium, Lead-acid – and can be found in most electronic and autonomous electric systems or equipment. Development and applications are evolving with latest uses including ultra-thin (down to 0.5 mm) and flexible technologies.

The lithium battery market is extremely dynamic and expanding fast, with a growing application as the power source for a wide range of electric vehicles. In fact, no level off is foreseen in the coming years. 

Lithium batteries can take many forms. They can be as tiny as single cell button batteries – for example used as power supply for watches – or multi cells (usually rechargeable) batteries that can act as high power energy sources for electric vehicles, or indeed as back-up power supply on-board aircraft (fig.1).

(fig.1) Types of Lithium batteries: single / multi cells

The term “lithium battery” actually refers to a family of batteries that can be divided into two categories: 

• Lithium-metal, non-rechargeable batteries
  These include coin or cylindrical batteries used in calculators, digital cameras and emergency (back-up) applications for example (fig.2). Lithium-metal batteries have a higher specific energy compared to all other batteries, as well as low weight and a long shelf and operating life.

(fig.2) Lithium-metal batteries

• Lithium-ion / lithium-polymer rechargeable batteries
  Key current applications for this type of batteries are in powering cell phones, laptops or other hand held electronic devices, as well as electric/hybrid cars and power banks (fig.3).
  The advantages of the lithium-ion or lithium-polymer battery are its ability to be recharged in addition to its higher energy density and lighter weight compared to nickel-cadmium and nickel-metal hybrid batteries.
   

(fig.3) Lithium-ion / Lithium-polymer batteries

Although previous battery technologies were not risk-free, lithium based batteries have a larger electrochemical potential; therefore if damaged, mishandled or poorly manufactured, they can suffer stability issues and be subject to what is called a “thermal runaway”. This phenomenon is well recognized now, and it can be mitigated providing awareness and prevention actions are taken.

IIn case of internal degradation or damage, a battery cell rapidly releases its stored energy (potential and chemical) through a very energetic venting reaction, which in turn can generate smoke, flammable gas, heat (up to 600°C and 1500°C locally), fire, explosion, or a spray of flammable electrolyte. The amount of energy released is directly related to the electrochemical energy stored (state of charge) and the type of battery (chemical and design).

Both the primary and secondary types of batteries are capable of self-ignition and thermal run away. And once this process is initiated, it easily can propagate because it generates sufficient heat to induce adjacent batteries into the same thermal runaway state.

Lithium batteries can be both a source of fire through self-ignition and thermal runaway, and a cause of fire by igniting surrounding flammable material.

The phenomenon of thermal runaway in an aircraft environment can be catastrophic. At the least it can range from limited degradation of personal equipment, or minor damage to the overhead storage compartment (fig.4). In the worst situation, thermal runaway in a high density package of lithium batteries can result - and has been implicated - in hull losses.

(fig.7) Consequences of Lithium batteries thermal runaway

By their nature and properties, large numbers of lithium batteries can be found in many places on-board an aircraft (fig.5):

•      In the cabin among the personal electronic devices of crews and passengers
•      In the cockpit as part of tablets used for flight data support
•      In the cargo holds carried as cargo or in passengers baggage
•      In the aircraft design.

(fig.5) Lithium batteries on-board an aircraft

Mitigating the risks posed by lithium batteries and preventing a thermal runaway or a fire starts with securing the batteries that are part of the aircraft design. In this respect, the lithium batteries embedded in the aircraft design are subject to strict development and integration requirements, complying with the highest safety standards. The intrinsic risk of this new generation of lithium based batteries is acknowledged at all levels of the aircraft design phase, as early as from the inception of the product and its systems. It is then mitigated thanks to acceptability justification based on each battery location, and a thorough review of installation, ensuring that no heat source and hazardous material or fluids are in the vicinity.

During an aircraft’s service life, this risk can be mitigated by adhering to common sense precautions, such as using only the OEM parts. The use of counterfeit or non-authorized parts increases the risk of fire and explosion. Consequently, complying with the Airbus Parts Catalogue and exclusively using Airbus or OEM catalogue references for spare batteries is key. 

Similarly, before installing spare batteries in Buyer Furnished Equipment (BFE) or in aircraft, operators should ensure the parts are genuine spare parts, that they have been stored and handled appropriately and present no mark of overheat or damage.

Increased usage of lithium batteries as the power supply of choice has, not surprisingly, led to an increase in the shipping of lithium batteries as air cargo. Today, one of the main risks posed by lithium batteries is related to shipping as freight. The existing ICAO recommendations do not regulate the quantity of lithium batteries that can be shipped as cargo on any single aircraft as a cargo load. The only limitations are associated with what can be loaded into each individual package. It is also worth understanding that these same regulations are not intended to control or contain a fire within that packaging.

Research projects launched in the past years aimed at supporting the development of the new SAE AS6413 packaging standard for air cargo. The effectiveness of the packaging solutions and transport measures are validated through a series of experimental tests, representative of the operating conditions encountered by air transport. In addition, a comprehensive risk assessment method has been developed to support operators in using the solutions and measures in their daily operations (ICAO recommendations adopted by EU regulation).

Today’s cargo fire protection of an aircraft is addressed by: 

• Passive protection (cargo hold linings or protection of essential systems)
• Detection 
• Suppression (use of Halon) or oxygen starvation 
• Preventing hazardous smoke / extinguishing agents into occupied compartments

ICAO is also focussing on establishing appropriate packaging and shipping requirements to ensure safer shipment of lithium-ion batteries. Airbus is also involved in the Civil Aviation Safety Team (CAST) investigating overall approaches from the battery itself to a combination of packaging / container and the aircraft itself.

The importance of correct transport and shipping of lithium batteries therefore becomes key, and the involvement of the shipper and operator is crucial. 

On request of ICAO, SAE has established a standardization working group - SAE G-27, which develops a Performance-Based Package Standard for lithium-ion Cylindrical Cells as a Cargo on Aircraft - AS6413. 

Air transport of lithium batteries is controlled by international and local regulations. If transporting lithium batteries, operators need to first check the latest instructions for the safe transport of dangerous goods by air, be they provided through Airworthiness Authorities or local regulations, and/or the ICAO.

In the end, the responsibility for the safe carriage of dangerous goods (including lithium batteries) lies with the shipper and operator. It is recommended that if carriage of dangerous goods is pursued, then a safety risk assessment of cargo operations should be performed to determine if battery shipments can be handled safely.

With respect to lithium batteries, guidelines for the assessment should consider factors such as:

• The quantity and density of lithium battery shipment
• The type of lithium batteries to be shipped
• Who the supplier/shipper of lithium batteries is and their quality control
• The identification and notification of all shipments of lithium batteries (also Section II lithium batteries)
• Accepting only lithium battery shipments that comply with applicable regulations (ICAO and/or local regulations)
• Overall capability of the aircraft and its systems
• Segregation possibilities of lithium batteries from other flammable/explosive dangerous goods.

Local and/or international regulations provide the applicable set of rules that need to be complied with when transporting lithium batteries. Attention should be given to:

• Training and awareness of employees regarding:
  - The aircraft limitations against a lithium battery fire and existing mitigation means.
  - Regulations, handling procedures, the dangers of mishandling, and methods to identify lithium battery shipments.
• Packaging:
  - Clearly identify shipments of lithium batteries by information on airway bills and other documents.
  - Make sure that the packaging is correctly labelled and identified as dangerous goods according to ICAO technical instructions.
  - Do not ship damaged packages.
• Cargo loading: segregate any lithium battery shipments from other dangerous goods that present a fire hazard (flammable and explosive goods).

Whilst recent discussions have shifted the focus towards the carriage of large quantities of lithium batteries as cargo, due to their proliferation and use in many applications, operators need to also be aware of the risk of carrying lithium batteries in passenger baggage – both checked in, off loaded cabin baggage and also carry-on cabin baggage.

The widespread use of lithium batteries means that hundreds of Portable Electronic Devices (PED) are likely to be carried on a large aircraft, either in hold baggage or as carry-on. Prevention is therefore essential to raise passengers’ awareness of the risks associated with carrying lithium batteries.

Recommendations have been developed with respect to what can or cannot be carried in passenger baggage. IATA regulated and recommended general requirements with regards to carrying and managing what is carried in passenger baggage is that:

• Batteries carried should have been appropriately tested (e.g. should be manufactured by the original manufacturer).
• PEDs containing lithium batteries should be carried in carry-on baggage.
• Spare batteries (i.e. those not contained in a PED), regardless of size, MUST be in carry-on baggage. They are forbidden in checked baggage and should be appropriately protected against short circuit, e.g. by leaving the batteries in its original retail packaging.
• Consider the quantity carried by individuals. Whilst there is no limit on the number of PEDs or spare batteries, below a specified size (normally 100 Watt-hour) that a passenger or crew member may carry, but they must be for personal use.

The key however is making both the ground personnel and the passenger themselves aware of the risks presented by the incorrect carriage of lithium batteries, and making sure that they know the regulations. To increase the awareness of the travelling public, posters and lithium battery pamphlets can be a useful option and are widely used by air carriers and authorities around the world alike. As an example, the FAA has issued Safety Alerts for Operators (SAFO) number 15010, which deals with “Carriage of Spare lithium Batteries in Carry-on and Checked Baggage”.

In May 2025, EASA released  a Safety Information Bulletin SIB No. 2025-03 that provides a set of recommendations for passenger aircraft operators, aerodrome operators and ground handling service providers on actions that should be taken to make passengers aware of the restrictions and conditions applicable to carriage of lithium batteries and PEDs powered by lithium batteries in passenger aircraft.

A key aspect to mitigating the risk is making the owner, namely the passenger, aware of the risks inherent to lithium batteries being used in an aircraft environment. Make sure passengers are aware of what is allowed in the terms of lithium batteries in carry-on baggage, and the requirement for correct storage, but also the impact of a PED getting trapped in the movable seat mechanism.

Due to their small size, PEDs can easily be trapped in seat mechanisms. The subsequent crushing of PEDs during adjustment of the seat can lead to overheat and thermal runaway.

Making passengers aware of this inherent risk can help reduce this scenario. For example, including a note in the pre-flight briefing to ensure that in case a PED is lost, then the seat is not moved until the component is retrieved is an option. Likewise, making cabin and flight crew aware of this potential failure mode is key to quick and efficient action when addressing a fire caused by a PED.

Lithium battery thermal runaways can be caused by design / manufacturing quality / integration shortcomings or by inadequate compliance with a number of basic rules. The following principles should be adhered to in order to minimize the risk of lithium battery fires and explosions: 

• Ensure that lithium cells/batteries shipped comply with international standards.
• Ensure that loads conform with ICAO / IATA labelling, packaging and handling recommendations.
• Ensure compliance to the Airbus Parts Catalogue when replacing aircraft batteries.
• Ensure that ground, flight and cabin crews are trained and passengers are aware of lithium batteries specificities.

Lithium batteries have existed for more than 20 years now and are widely used in all daily applications. This technology is extremely efficient and its range of applications is constantly expanding. Whilst fortunately events involving lithium batteries are rare, and even rarer when occurring in flight, the risk of fire still exists. The specificities of lithium batteries need therefore to be considered in all aspects of aircraft applications and managed correctly.

It is essential to consistently review and adhere to the latest procedures and regulations. ICAO and IATA, along with FAA and EASA, frequently update their documentation and websites to support customers, operators, and stakeholders in staying informed about the evolving challenges related to the air transport of lithium batteries.