Over the decade, the demand for Electric Vehicles (EVs) in India has increased massively in both urban and rural areas (particularly Electric 2-Wheeler & 3-Wheeler). As per the data compiled by the Federation of Automobile Dealers Associations (FADA), this growing trend has led to a jump in electric vehicle retail sales by over three-fold in the last fiscal with two-wheeler offtake leading the segment. In FY 2021-22, total EV retails witnessed a sale of 4,29,217 units from 1,34,821 units in the previous financial year, indicating a growth of over 200%.
This growing demand for electric vehicles has also made people more concerned about the safety and shelf-life of the vehicle’s battery. It is a must for EV batteries to hold a huge amount of energy so that the vehicles can be operated at a fast speed. Maintaining internal temperature within specific limits is essential in this case to ensure the battery cells’ safety and stability. If the temperature exceeds the limit on either end, a chain reaction occurs, known as thermal runaway. This chemical reaction can destroy the battery, and can even ignite a fire.
The reaction inside the battery produces an excessive amount of heat, which drives the temperature incredibly fast (in milliseconds to around 400 degrees Celsius) causing further chemical reactions and creating more heat. The energy stored in the battery is released very suddenly, causing gassing of the battery. In extreme cases, thermal runaway can cause the battery to explode and start fires. In minor cases, it can cause it to melt or damage beyond repair.
There are several circumstances which can cause thermal runaway in a battery. It can be due to an internal short-circuit caused by physical damage to the battery, poor battery maintenance, overcharging a battery beyond its safe maximum voltage or rapid charging caused by excessive current flow. Often thermal runaway is caused when the temperature outside is either low or high, eventually degrading the performance of the battery. It leads to irreversible damage, triggering a chain of reactions.
Currently in India, most EVs are run on Lithium-ion batteries due to their long cycle life, high energy density, and power density. The core temperature of these batteries plays a major role in their high performance. The functioning of these batteries depends on chemical reactions. Excessive cold can also slow or stop chemical reactions.
There are several ways to reduce the risk of thermal runaway in batteries. Here are some best practices and ways to prevent it and protect the electric vehicle batteries:
· Maintaining Operating Temperature: With help of a Smart Battery Management System (BMS).
· Proper Ventilation: Through air or by use of a liquid cooling system to facilitate heat dissipation
· Avoid Abusive Usage of Battery: Avoiding overcharging or undercharging the battery that can impact its performance.
Fortunately, there are new technologies that can make these batteries safer and prevent the initiation of chain reactions. The major three fundamental solutions to increase the safety of a typical EV Battery pack are an efficient thermal management system, advanced BMS hardware/software and the use of special thermal material.
Battery Thermal Management Systems (BTMS) are generally categorized into passive or active systems. A passive cooling system relies on dissipating heat through natural convection and radiation. They have no moving parts and can be adequate if a larger space envelope is available (relative to the size of the battery) or low performance (low charge/discharge rates) is required. The system often relies on increasing the thermal inertia of the system by adding more thermal mass. On the other hand, active cooling systems rely on cooling fluid forced through the battery using a blower or positive displacement pump.
Passive cooling is low cost and energy-efficient, as it does not require any external source of energy for the cooling or heating process. This makes the system economical and helps in reducing the net load on the battery. Hence, passive systems are majorly used in Electric 2-Wheelers.
Lithium-ion batteries mostly include a built-in Battery Management System (BMS), which serves as the control centre for the battery pack and ensures that the battery operates under safe conditions. BMS is critical to the safe operation, and optimal performance of lithium-ion batteries and helps minimize the possibility of thermal runaway. A typical BMS manages cell voltage, cell current, cell temperature, cell charge balancing, charge control, an internal short circuit detection. It also protects the batteries by controlling or balancing their environment.
The use of special materials with excellent thermal conductivity and low thermal resistance inside the battery pack can enhance the thermal management of an EV pack. Special thermal fluids, glue, and adhesive material can be used in between the battery cells or battery pack layers to control the heat dissipation inside the pack.
With the involvement and encouragement of the Government of India, certain standard safety measures for EV batteries have been enforced to improve their quality. With codes and standards being followed as per the designing guidelines, the safety and performance of EV pack designs in India by Original Equipment Manufacturers (OEMs) will further improve. The below standards have been recently published by the Automotive Research Association of India (ARAI) to regulate the safety aspects of an EV battery pack.
With a fool-proof EV pack design having an efficient thermal management system and an Intelligent BMS, an EV pack can be made safe and ready to use without risking human life.
Article by Mr. Hiren Pravin Shah , Executive Director & CEO, Replus, a part of LNJ Bhilwara Group.