Introduction

Electric vehicles (EVs) are revolutionising transportation with their efficiency and eco-friendliness. Have you ever wondered how they run? The answer lies in their beating hearts - the batteries. This article will take you through EV batteries, unravelling their structure, chemistry, and crucial components that keep them running smoothly.

Structure of an EV battery:

At the heart of an EV battery lies the single battery cell, the smallest power unit. These cells are connected in series or parallel to form different battery modules, and multiple modules are then linked in series to create the power battery pack.

A manufacturer chooses between cylindrical, prismatic, pouch, or prismatic with LFP chemistry cells depends on specific application requirements. Each type has its strengths and weaknesses, ranging from power output to cost-effectiveness, making it essential to consider factors such as durability, customizability, and performance for the desired application.

Chemistry of EV battery cells:

A standard battery cell comprises four critical components: anodes (negative electrodes), cathodes (positive electrodes), a diaphragm, electrolytes. These elements are enclosed in a robust casing made of steel or aluminium-plastic.

How Lithium-ion batteries work:

Lithium-ion batteries consist of electrolytes, a solution that transports positively charged ions between the cathode and the anode terminals. Electrolytes enable the transfer of electric charge between terminals, facilitating the conversion of stored energy into usable electrical energy.

A thin layer called a separator, within the electrolyte solution, allows lithium ions to pass through while blocking electrons, maintaining separation between electrodes.

While charging, an external voltage moves lithium-ions from the anode to the cathode through the electrolyte, storing energy. When discharging, stored energy is released as lithium ions move from the cathode back to the anode, powering your EV. Electrolyte can be of two types:

• Liquid state electrolyte
• Solid state electrolyte: The most significant difference in a solid-state battery is the use of a solid electrolyte instead of liquid. The solid electrolyte is typically a lithium-ion conductive ceramic or polymer material.

Lithium-Ion battery electrolytes

The most common electrolyte used in a lithium-ion battery is a lithium salt solution. Some common lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), LiCIO4 in an organic solvent.

Lithium hexafluorophosphate (LiPF6) is commonly used, as it provides stability for lithium ions during charging and discharging.

Ongoing technological advancements like solid ceramic electrolytes and advanced battery management systems and contributing to making lithium-ion batteries safer and more reliable.

The role of Battery Management Systems (BMS):

The Battery Management System (BMS) is the brain behind managing EV batteries. It monitors the battery's state of charge, temperature, and voltage, ensuring its health and performance.

How BMS Works:

1. Monitoring and balancing

The BMS continuously monitors various parameters such as voltage, current, temperature, and state of charge (SOC) of individual cells within the battery pack.

2. State of Charge (SOC) estimation

It estimates the SOC of the battery by tracking the flow of energy in and out of the cells. This helps in providing accurate information about the remaining charge.

3. Safety and protection

The BMS is responsible for ensuring the battery operates within safe limits. If it detects overcharging, over-discharging, or excessive temperature, it can take corrective actions such as disconnecting the battery from the charger or load to prevent damage or safety hazards.

4. Cell balancing

It manages the balance of charge between individual cells. This prevents some cells from overcharging while others remain undercharged, which can lead to reduced capacity and potential safety issues.

5. Thermal management

BMS helps in thermal management by controlling heating and cooling systems to maintain the battery's temperature within an optimal range, improving efficiency and longevity.

6. Communication and reporting

The BMS often communicates with the vehicle's control system and can provide real-time data on the battery's health and performance. This information is critical for both drivers and service technicians.

Looking ahead:

The lithium-ion battery is engineered for long-term use. Like regular devices, EV batteries gradually lose power over time, typically retaining about 80% of their original capacity after eight years of daily use. Regular charging is the key to avoiding potential power disruptions.