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Down To Earth Magazine July 2022 (Part 1): Fire in Electric Vehicles!


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Fire in Electric Vehicles: Introduction

  • On March 28, the Union Ministry of Road Transport and Highways ordered a probe into the circumstances that led to the fire incidents.
  • The findings, submitted by the Centre for Fire Explosives and Environment Agency (CFEEA) in May, point at unsafe battery cells and faulty pack design.


Fire in Electric Vehicles: What Kind of Batteries do we use?

  • The EV battery pack comprises multiple battery cells and a battery management system (BMS).
  • The cells have four essential components—cathode, anode, separator and electrolyte. Battery cells operate by discharging lithium ions from the anode to the cathode through the electrolyte.
  • Most lithium-ion batteries use anodes made of graphite, which receives lithium ions as the battery charges, and releases them as it discharges.
    The maximum amount of lithium that can be collected on the anode measures the battery’s capacity, defining the distance a vehicle can be driven on a single charge.
  • Information such as the C-rate or charging speed and other factors related to battery health is controlled by
    BMS, which is an integral part of the battery.
  • India does not manufacture either BMS or battery cells.
  • Some companies assemble BMS with imported components while others buy them off the shelf and integrate them with battery cells.
  • About 90 per cent of fires in lithium-ion batteries are caused by an internal short circuit—indicating a failure in the battery pack to manage its components, as well as the inability of a cell to maintain its integrity.


Fire in Electric Vehicles: Who is to blame?

The Fire Explosives and Environment Agency submitted its findings on incidents of electric vehicle (EV) fires to the government in May.

The findings say: 

  • EV two-wheeler companies may have used “lower-grade materials to cut costs” despite submitting A-grade cells for testing, taking advantage of the loosely framed rules.
  • The cells had problems with thermal and battery management systems.
  • The problems with the batteries were specific to each company and the report noted negligence on the part of testing agencies such as the automotive Research Association of India.


Fire in Electric Vehicles: The Battery Cooling System

  • The battery has a thermal management system to contain the heat or fire and software to control it and to communicate with the driver about it. Thermal management in batteries can be active and/or passive.
  • Most electric four-wheelers have an active thermal management system which involves liquid cooling of the battery. They also use passive cooling methods with phase change material (pcm), a wax-like material that melts when the temperature rises in the cell. The liquid thus formed has the ability to absorb some of the heat, but has limited capacity to stop a fire. A combination of active and passive cooling systems offer electric four-wheelers a more efficient way to avoid fires.
  • But e-scooters, which have a 2-3 kWh battery, are constrained for space within the battery cavity and cannot accommodate an active cooling system. The batteries are typically air cooled and have pcms incorporated in the pack. A number of the e-scooter fires included white smoke. That is vapourised pcm being “vented” by the battery.


Why Battery Catches Fire?

The electric vehicle battery comprises multiple battery cells and a battery management system. The cells have four
components—cathode, anode, separator and electrolyte. The cell operates by discharging lithium ions from the
anode to the cathode through the electrolyte. The following are the most common ways a battery catches fire:

Rupture in solid electrolyte interface

The graphite anode has a thin layer called the solid electrolyte interface to protect the graphite from reacting with the electrolyte. Irregularity in its formation can run the risk of a rupture in the event of an external force, even movement on an uneven road. As the electrolyte is flammable, such a rupture can cause fire.

Oxygen-generating compounds

Batteries in e-scooters use a cathode chemistry called lithium nickel manganese cobalt oxide (NMC). Such oxide layered compounds have a tendency to generate large amounts of oxygen at temperatures above 200˚Celsius. If there is a hot spot within the battery, the oxygen will help build a fire.

Combustion caused by dendrites during charging

Dendrites are thin, hair-like structures that form on the anode due to overcharging. After the graphite is fully charged, the lithium ions continue to pile on the graphite and can grow long enough to break through the separator, coming into contact with the cathode, causing a short circuit.

Fault in battery management system

A battery management system (BMS) can stall an overcharging event to prevent a fire. A faulty BMS is believed to be one of the reasons behind the explosions of mobile phones a few years ago. Ever since, lithium ion batteries are programmed to charge up not beyond 80 per cent

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