Last April, the first prototype scooter incorporating the EMIC battery system was unveiled at the Saft Batteries Industrial Battery Technology Center (CTBI) in San Sebastián de los Reyes. Simultaneously, the system was presented in Brussels at an event specifically focused on electric mobility. The leading manufacturers of these types of vehicles have enthusiastically welcomed this invention and have approved the launch of several trials of the system in their vehicles.

The fundamental concept behind this innovation is "true portability." The system essentially involves dividing the vehicle's traction battery into several parts, making each one easily transportable by a single person. For example, the system currently shown in the prototype consists of two battery cartridges that individually provide enough energy to travel approximately 15 km in urban environments, with all the acceleration and power required by the vehicle. With both cartridges installed, the vehicle can travel 30 km. And each cartridge weighs only 2 kg.

Obviously, the amount of energy, or in other words, the number of kilometers we can travel with the vehicle, depends on the weight of the battery. Therefore, battery cartridges of varying energy capacities can be assembled to meet different range requirements for each user. This opens up a wide range of advantages, among which the following stand out:

The electric motorcycle can be sold without batteries, allowing each buyer to choose the battery size that best suits their needs.
The battery cartridges can be recharged at an urban charging station by connecting the vehicle with a standard cable, or they can be recharged individually at home or in the office using desktop chargers by removing them from the motorcycle.
A single motorcycle is sufficient for multi-shift fleet operations. Each shift carries the cartridges corresponding to its range requirements, and these are recharged during the following shift, outside the vehicle, while another set of cartridges provides traction for the next shift.
Cartridges with varying energy capacities can be assembled; for example, cartridges can be manufactured for 15, 30, or 45 km of range. Cartridges of different sizes and weights can be combined within the same vehicle throughout its lifespan to accommodate changes in range requirements.

The currently designed system connects up to four cartridges to the vehicle via a card called a connector. The main functions of this connector card are as follows:

Individualized management of charging and discharging for each cartridge (BMS).
Collective management of battery system performance based on external factors (power requirements, external temperature, etc.).
Continuous monitoring of the system status and transmission of alarms and information to the vehicle.
Protection of the battery system against potential misuse (overvoltage, overheating, etc.).
Data storage for determining battery health and tracking its lifespan.

Simply put, the system's operation is based on the characteristic charge and discharge curve of certain electrochemical systems within the Lithium-ion family, where the battery's state of charge can be relatively easily determined through the open-circuit voltage (see Figure 1). It's important to note that not all Lithium-ion systems are suitable for use with the EMIC system. Those with very flat charge and discharge curves, such as those based on LiFePO4 cathodes, cannot be managed using this system (see Figure 2).

Also noteworthy is the system's algorithmic approach for displaying and managing battery health information. Each electrochemical technology exhibits different behavior characteristics in response to certain signals. Comprehensive studies conducted at our CTBI are enabling us to correlate voltage, temperature, and current measurements—common in these systems—with battery lifespan, a particularly useful parameter for cyclic applications like the one presented in this article.

It goes without saying that, in addition to varying sizes, shapes, and weights, the system's installation flexibility in an electric vehicle is impressive. Being able to divide the battery into different parts (cartridges) allows each to be placed in different positions and locations within the vehicle, balancing, for example, aerodynamic loads, thus enabling multiple solutions. Ultimately, each part will need to be connected via a simple, short-wire cable to the connector board, which will be installed in a secure location inside the motorcycle. Imagine the number of possible configurations that can be designed.
Furthermore, it's important to note that lithium-ion batteries come in different formats depending on their application (Figure 3). Thus, there are high-capacity, low-power battery models, models specifically designed for high charge and discharge currents, models with varying cycle lifespans, and so on, all of which can be configured using the EMIC system. In other words, the EMIC system is not just a battery system for use in electric mobility for small vehicles; it is an invention that opens the door to multiple applications where the battery, as we know it today, is necessary but presents installation and autonomy drawbacks for various reasons.

Finally, I would also like to highlight the ease with which the EMIC system can be integrated into smart grids, thanks to the quantity and quality of information it handles regarding battery status and its ability to communicate, using different protocols, with various devices in complex systems. This opens up a new world for battery management in the grids of the future.

Author:

Joaquín J. Chacón Guadalix, General Manager – Saft Baterías SL.