Electric vehicles are complex systems that include various advanced electronic components and subsystems, each performing functions vital to their operation. In this article, we will focus on EV batteries and their charging systems, analyzing their main characteristics and the most critical aspects of their design.

EV batteries

Batteries serve as the primary source of power for the electric motor, typically a three-phase motor operating on alternating current (AC). The motor is controlled by an inverter, which, powered by the electrical bus connected to the batteries, generates the signals (waveforms with variable voltage and frequency) required to control the motor’s speed and torque.

It is essential to note that some advanced EVs, including the Tesla Model 3 Dual Motor, feature two motors, connected to the front and rear axles (eAxles). While this increases the safety and performance of the vehicle in the most difficult traction conditions, it also increases the power requirements that the batteries must meet.

EV batteries primarily use Li-ion technology, but there are several alternatives that could provide advantages. (Source: Adobe Stock)

Li-ion technology

Most batteries used in EVs today are based on lithium-ion (Li-ion) technology. This technology offers high energy density, the ability to store charge for long periods, and reduced weight and size compared with other technologies, such as traditional lead-acid batteries.

Using fast-charging systems, which are increasingly common in public infrastructure for charging EVs, these batteries can reach 80% of their total charge capacity in less than 30 minutes. However, Li-ion cells have some limitations related to their chemical structure that must be considered.

Charging Li-ion batteries too quickly, especially with high currents, causes cell degradation and therefore a reduction in their capacity. Overcharging the cells can lead to a particular condition known as thermal runaway, in which the battery can reach very high temperatures, generating short-circuits, flames, and even explosions.

To ensure safety, it is therefore necessary to find the right balance between charging time and battery lifespan. The battery management system (BMS), another essential component of EVs, serves to control the state of charge and state of discharge of the battery, as well as the state of health of the individual cells, balancing the charge between them to ensure uniform use. It also provides protection in case of overtemperature or other hazardous conditions.

For example, Marelli has introduced an innovative BMS for automotive applications (Figure 1) that uses electrochemical impedance spectroscopy (EIS) to detect cell degradation in advance, thereby extending battery life and maintaining capacity and performance. The system developed by Marelli performs low-frequency impedance measurements during cell charge/discharge cycles, enabling accurate estimation of cell life remaining and preventing thermal runaway phenomena.

Figure 1: Marelli’s BMS based on EIS (Source: Marelli Holdings Co. Ltd.)

Currently, most EVs use two versions of Li-ion technology: nickel, manganese, and cobalt, and lithium-iron phosphate. The former offers a longer range and shorter charging times but requires the use of rare metals and complex manufacturing systems. The latter uses readily available materials and is inexpensive to produce but results in a heavier battery pack and slower charging at low temperatures.

Alternatives to Li-ion technology

Solid-state batteries use a solid electrolyte instead of the liquid electrolyte used in common Li-ion batteries. This could provide some important advantages, including higher energy density (for the same capacity, less space is required), faster charging, and greater safety (a solid electrolyte is less prone to catching fire).

Solid-state batteries are currently being studied by major automotive and battery manufacturers, and the time for commercialization and widespread adoption is approaching. Stellantis and Factorial Energy have announced that they have achieved an important milestone in this direction, namely the validation of solid-state batteries for automotive use with an energy density of 375 kW/kg.

The batteries, based on Factorial’s proprietary FEST technology (Figure 2), can operate in a temperature range from −30°C to 45°C and allow fast charging from 15% to 90% in 18 minutes. Stellantis has said that it will install Factorial batteries in a demonstration fleet of vehicles in 2026.

Figure 2: Factorial’s FEST solid-state batteries with an energy density of 375 kW/kg have passed the validation phase. (Source: Stellantis N.V.)

Sodium-ion batteries work in a similar way to Li-ion batteries but use sodium ions (Na+) instead of lithium ions (Li+) as charge carriers. Sodium is a very abundant material in nature, as it is found in saltwater and the earth’s crust.

Battery manufacturer CATL has claimed the first mass production of a sodium-ion battery. The new Naxtra sodium-ion battery is available in two versions: the passenger EV battery and the 24-V heavy-duty truck battery. Capable of operating from −40°C to 70°C, the passenger EV version retains 90% of its usable power at −40°C and offers an energy density of 175 Wh/kg, the highest value achieved by a sodium-ion battery, according to the company. Naxtra can withstand up to 10,000 charge/discharge cycles, offering a range of 500 km.

Lithium-sulfur batteries (Li-S) use sulfur, which has a higher energy capacity than lithium and is an abundant material, as the cathode material. While offering a potential increase in energy density, these batteries have a shorter lifespan than Li-ion technology.

California-based company Lyten has developed compact, lightweight Li-S batteries made entirely from U.S.-sourced materials. These batteries power drones in defense applications and provide over three hours of flight time.

Battery recycling

Current EV batteries are guaranteed by vehicle manufacturers to last between 10 and 12 years, or between 100,000 and 150,000 miles. However, once this limit is reached, the batteries still retain a significant charge capacity and can have a second life when used in less critical applications, such as battery energy storage systems (BESSes), in which space and weight are less pressing requirements than in EVs.

For example, the PIONEER (airPort sustaInability secONd lifE battEry stoRage) project at Aeroporti di Roma (ADR) Fiumicino Airport will use batteries from decommissioned Nissan and Stellantis EVs to build a BESS capable of providing 10 MWh of energy. The project, co-financed by the European Union, involves collaboration between ADR, Enel (Italy’s largest energy company), the German research institute Fraunhofer, and the Italian company Loccioni, which is responsible for integrating the batteries into the BESS.

EV charging

EVs can be charged at different power and current levels using specific EV supply equipment (charger or EVSE). The technical characteristics of the three charging levels are summarized in Table 1.

Level 1 charging uses a standard, 120-VAC household outlet. It is the slowest charging method, making it best for overnight charging if you don’t drive long distances daily or as a convenient backup option.

Level 2 charging plugs into a common, 240-VAC outlet, providing a good balance between speed and affordability. It is widely used in home chargers, workplaces, and public charging stations.

Level 3 DCFC delivers direct current directly to your EV’s battery, bypassing the car’s internal charger. This is the fastest available charging method, typically found at public stations, along major roadways, and for commercial use. To protect your vehicle’s battery, charging speeds usually slow down once the battery reaches about 80% capacity.

The block diagram of a general EV charger is shown in Figure 3. The AC input filter helps protect the device from noise and interference affecting the AC power line (e.g., the grid). The rectifier and PFC stage rectifies the input AC voltage and performs power-factor correction to achieve a nearly one power factor (this ensures the maximum efficiency). The isolated DC/DC stage provides galvanic isolation between the input (AC voltage) and output (EV batteries). The output filter reduces noise and distortion caused by the charging process at the DC output stage.

Figure 3: Block diagram of a basic EV charger (Source: Stefano Lovati)

The power stage, highlighted in Figure 3, is important for maximizing the charger’s efficiency, reducing power losses. Wide-bandgap components, such as silicon carbide (SiC) and gallium nitride (GaN), are increasingly being used in the power stage due to their superior electrical properties over silicon. This is particularly important for DCFC charging stations, in which the output voltage ranges from 400 V to 800 V and above. A DCFC system can also integrate bidirectional power switches in the power conversion stage, thus allowing the EV’s battery to discharge, transferring power to the grid.

Development tools

Chipmakers are also contributing to the development of charging stations with development platforms and reference designs.

One example is NXP Semiconductors’ EasyEVSE development platform, aimed at simplifying the design of charging stations. It comprises software, boards, wires, design files, and full instructions for rapidly simulating a charging control session between a charging station and an EV.

Allowing for bidirectional power transfer, the board is built around the i.MX 93 application processor and contains a Murata module with the NXP IW612 chipset, which supports Wi-Fi 6 and Bluetooth Low Energy 5.2. The solution includes Yocto and the Linux operating system.

Another example is onsemi’s SEC-25KW-SIC-PIM-GEVK reference design for a 25-kW fast DC EV charger using a SiC power integrated module. This full SiC system consists of PFC and DC/DC stages with several 1,200-V half-bridge SiC modules. Their low R_DS(on) and low parasitic inductance greatly reduce conduction and switching losses.

The power stage controller is based on the Zynq-7000 SoC, which includes an integrated FPGA and an Arm processor. To charge 400-V or 800-V EV batteries, the system offers a maximum of 25 kW over a 200- to 1,000-V output voltage at 96% all-time efficiency. At PCIM 2025, onsemi unveiled a 100-kW SiC-based EV charging brick, which supports bidirectional power transfer and megawatt charging.

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