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Lithium-ion batteries: 6 questions you may ask yourself about your heavy vehicles

The impact of temperature on the performance or lifespan of batteries, communication protocols to be used, applicable standards… Using lithium-ion batteries for heavy vehicles raises many questions. Here, our R&D experts answer the 6 most commonly raised questions which merit discussion.

#1 – How do extreme temperatures affect lithium-ion batteries?

Ion mobility in electrolytes increases with temperature. Therefore, intense heat or cold has a significant impact on the conductivity of materials and battery cell performance. When operating below 10°C, or above 30°C, the performance of lithium-ion batteries is impacted.

When in operation, a negative temperature will result in a loss of power delivered to the engine. However, this impact is moderate: the heavy vehicle may be very slightly less responsive but will still remain safe. Additionally, the autonomy of the vehicle may also be affected.

When recharging, extreme temperatures also have an impact: recharging the battery of a heavy vehicle in cold weather requires more time. When the temperature is below zero degrees Celsius, charging should be limited, and special attention paid to avoid metallic lithium deposits on the negative electrode which could prematurely age the cell.

Nevertheless, these cell phenomena, which are well-recognised and quantified, are taken into account during the battery design process. A battery is designed for a particular climatic zone and will be different depending on whether it is to be fitted to a vehicle intended for use in Oslo or Dubai. Manufacturer expertise and knowledge makes it possible to respond precisely to builder specifications.

#2 –Does temperature impact lithium-ion battery life?

The aging of a lithium-ion battery is inevitable, and results in a loss of capacity and an increase in internal resistance (loss of power). Aging is initially gradual until the battery capacity reaches 80% (the battery is then considered “end of life” for use in the mobility sector). Beyond this threshold, it can accelerate to “sudden death.” However, the speed of decline can vary, in particular when the battery is subjected to extreme temperatures.

️ 🌡The higher the temperature, the faster the cells age, the heat causing parasitic chemical reactions that degrade the materials.

❄️At very low temperatures, the faster the charge; this results in the intensification of the lithium deposit phenomenon, and consequently, battery damage.

The manufacturer can reduce heat-related aging by taking into account its design and the sizing of the cooling system. It can also search for the best compromise between performance and ideal durability depending on the intended use, and even look at load regulation according to temperature. Everything is a question of balance and optimisation according to the conditions of use and needs.

As a result, Forsee Power offers a wide range of batteries. These can adapt to different uses and will consider the methods used to integrate them into the vehicle: the constraints and the temperature will be different depending on whether the battery is to be placed on the roof or in the chassis.

#3 – What is the usable range of the battery, and how does SOC affect battery life?

The SOC – the state of charge of a battery – is not a physical value, but rather a ratio between the residual capacity available and the nominal capacity of the battery. This is expressed as a percentage.

In theory, the maximum operating range is from 0 to 100% of the onboard capacity. However, using the battery within this full range will accelerate the aging process. Here again, balance is key. The aim is optimisation between performance and battery life: to extend the life of a battery, and therefore optimise its TCO, it is necessary to operate within ideal parameters as indicated by the manufacturer. This is usually between 20% and 90%.

The definition of this operating range is also a question of the manufacturer’s strategy, depending on the type of performance they wish to optimise: this could be the quantity of energy available or the quantity of power available.

For example, on a heavy urban electric vehicle, the objective is to ensure 12 hours of driving per day. On a hybrid vehicle, a more restricted range will be defined, to favour power.

#4 –What are the functional safety standards respected by lithium-ion battery manufacturers?

The functional safety of batteries is covered by several standards:

  • the ISO 61508 standard for industrial applications
  • ISO 26262 for road vehicles
  • EN 50128 in the railway world

Each manufacturer can decide which standards they want to meet.

To guarantee an optimal level of security for its customers, Forsee Power has chosen to develop its offer in accordance with these 3 standards, but also by considering the cybersecurity of heavy vehicles governed by the ISO 21434 standard.

#5 – What are the qualification standards applicable to lithium-ion batteries?

The communication protocol allows the various elements of a battery system to exchange information between themselves, but also with the vehicle, or even the cloud.

The right choice is therefore paramount. The chosen protocol should be:

  • efficient enough to allow the exchange of a sufficient volume of data, at the required speed (with the development of on-board electronics, the quantity of data exchanged is constantly increasing);
  • recognised and shared by the different systems required to communicate.

Therefore, when an industrialist develops a new protocol, it must present real advantages in order to be adopted by a maximum number of players and stand out in the marketplace.

Today, the most widely used protocol, and that chosen by Forsee Power, is the CAN FD protocol (CAN with Flexible Data Rate). This was developed about ten years ago. It is an evolution of the CAN protocol with increased bandwidth.

New developments are inevitable, and Forsee Power’s R&D experts are constantly monitoring to assess any new technology likely to bring real benefits to batteries.

As a result, Forsee Power offers a wide range of batteries. These can adapt to different uses and will consider the methods used to integrate them into the vehicle: the constraints and the temperature will be different depending on whether the battery is to be placed on the roof or in the chassis.

#6 –What are the qualification standards applicable to lithium-ion batteries?

Standards are defined for the approval of batteries, and in particular to certify their safety, especially for vehicles being used to transport passengers.

Forsee Power has thus chosen to obtain ECE R100 (European certification for electric road vehicles) certification (as defined by the European Commission).

This certification includes 9 tests (vibration test, thermal shock cycling test, mechanical shock test, mechanical integrity test (crush test), fire resistance test, external short circuit safety test, overcharge protection test, over-discharge protection test, and over-temperature protection test). These tests are very demanding.