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Electric Vehicles Batteries: Requirements and Challenges

A robust electric vehicle performance demands a long life cycle, higher power density, and a cost-effective battery. In this regard, Li-ion batteries stand out due to their superior energy and power density and long life cycle, and they are being used in practically all-electric cars.

However, lithium-ion batteries have several issues such as being vulnerable to overheating and thermal imbalance, affecting electric vehicle performance and safety. Installing an appropriate battery management system is necessary to take full advantage of the electric vehicle.

What is a Battery Management System?

A battery management system (BMS) is an electronic structure that controls the charging and discharging of the battery, is responsible for the safety of its operation, monitors the state of the battery, and evaluates secondary performance data.

Role of BMS in the Performance of Electric Vehicles

The BMS provides individual control of the voltage and resistance of each cell, determines the loss of capacity due to imbalance, and ensures safe connection/disconnection of the load.

The functionality of BMS improves the operating mode and service life of EV batteries.

The BMS monitors and regulates the safety circuitry of the electric vehicle. When problematic conditions such as overvoltage or overheating are detected, the BMS alerts the user and initiates the predetermined corrective procedure. In addition to these activities, the BMS monitors electric vehicle temperature to optimize energy use and communicates with specific components and operators.

Without a BMS, an electric vehicle's energy management will be unpredictable, leaving it vulnerable to various safety hazards that could result in catastrophic failures such as a short circuit or thermal meltdown of the battery. Therefore, the BMS is vital for an electric vehicle's safety and efficient power management.

How Does a BMS Increase the Performance of EVs?

The BMS is primarily responsible for monitoring the battery's parameters. The analog front end collects data to determine the battery's state of health (SOH), state of charge (SOC), and cell balancing. This improves the performance of an electric vehicle.

The BMS performs the following functions to ensure the safe and efficient operation of electric vehicles.

Cell balancing

Due to inconsistency among the battery cells, a small voltage imbalance is always present. The cell balancing circuit in BMS ensures the same level of discharge and charge of each cell so that some cells are not overloaded and destroyed. Balancing the charge and discharge of individual cells increases the overall performance, operation, and safety of the electric vehicle.

State of charge

The state of charge (SOC) of an EV battery's cell denotes the usable capacity as a percentage of the rated capacity.

SOC evaluation helps in the determination of the battery's energy availability and its lifespan. There are three methods of determining SOC: coulomb counting, direct measurement, and a combination of these two techniques.

State of health

State of health (SOH) measures the battery's general condition and ability to achieve the stated performance relative to a new battery. The SOH of the cell could be determined using any parameter, such as cell conductance or impedance that alters considerably with time.

Communication

The BMS also facilitates communication of information to the driver, for example, by triggering an alarm or reporting the state of charge, as well as to other onboard equipment, for example, to request changes in vehicle operation in response to the condition of the battery. BMS can also be used to monitor diagnostics and performance of the electric vehicle or set system parameters.

Future Developments of Battery Management Systems

Wireless battery management system

New EV battery management systems are being developed in response to consumer and societal demands for better performance. The development of wireless BMS is one area that offers significant improvements to the cost and performance of EVs.

A wireless BMS helps reduce its size and weight, increasing the driving range and vehicle economy, and making the electric vehicle less expensive to manufacture and operate.

Improved BMS for fast charging EV batteries

Fast charging is a quickly emerging and urgently required innovation for electric vehicles, particularly buses and vehicles that must operate continuously. An electric vehicle (EV) can take many hours to fully charge using conventional AC charging, while fast charging can accomplish this in under 20 minutes.

Fast charging EV batteries necessitate more advanced battery management and accurate assessments of conditions inside battery cells to avoid overcharging and overheating.

The Demand for Battery Management Systems

With the increase in electric vehicle production, the demand for BMSs has also increased. Despite the pandemic, approximately 10 million EVs were on the road in 2020, representing 4.6 percent of all vehicles sold worldwide. As the popularity of electric vehicles is increasing, so will the demand for performance and cost comparable to traditional vehicles.

EV battery management systems will play a crucial role in delivering affordable, comparable performance, allowing society to benefit from electric vehicles on a large scale by enhancing their safety, reliability, and efficiency.