The Surprising Role of Lead-Acid and NiMH Batteries in Electric Cars

Batteries have come a long way since the 19th century when the lead-acid battery became the first rechargeable battery known to mankind. Over time, advancements led to the development of the nickel-metal cadmium (NiCd) battery, followed by nickel-metal hydride (NiMH), and eventually, the lithium-ion battery. While lead-acid batteries are no longer the primary choice for electric vehicles (EVs) due to their limitations, NiMH batteries continue to find a place in hybrid and all-electric vehicles. Let’s delve into the construction, working, and role of these two battery technologies in today’s automotive landscape. 

Lead-Acid Batteries: The Pioneer of Rechargeable Technology 

What Are Lead-Acid Batteries Used For? 

Lead-acid batteries are widely used in internal combustion engine (IC) cars to start the engine and provide intermittent electricity. They are known for their reliability, safety, and affordability, making them ideal for applications that don’t demand sustained power delivery. 

Construction and Working 

1. Electrodes and Electrolyte: A lead-acid battery comprises two electrodes: 

• Anode: Lead peroxide (rigid structure). 
• Cathode: Pure lead (spongy structure). 

These electrodes are immersed in a sulfuric acid solution, which serves as the electrolyte. 

2. Separators: To prevent short circuits, separators made from materials like rubber or glass are placed between the electrodes. 

How It Works 

1. Discharge Phase: 

• The sulfuric acid breaks down into positively charged hydrogen ions and negatively charged sulfate ions. 
• Hydrogen ions move to the lead peroxide (anode), gaining electrons and leaving the anode positively charged. 
• Sulfate ions move to the lead (cathode), transferring electrons and leaving it negatively charged. 
• This charge imbalance generates an electric current as electrons flow from the cathode to the anode. 

2. Recharge Phase: 

• During recharging, the process reverses, restoring the original chemical composition of the electrodes and electrolyte. 

Types of Lead-Acid Batteries 

Flooded Lead-Acid Batteries: 

• The electrolyte is in liquid form, and gases produced during reactions are vented out. 
• These batteries require regular maintenance, including topping up with distilled water. 

Sealed Lead-Acid Batteries (VRLA): 

• The electrolyte is gel-like to prevent leakage. 
• Oxygen and hydrogen gases recombine to form water, reducing the need for maintenance. 
• A valve allows excess hydrogen to escape, ensuring safety. 

Limitations 

• Poor performance in cold temperatures. 
• Low energy density and shorter lifespan. 
• Limited range, making them unsuitable for modern EV requirements. 

Nickel-Metal Hydride Batteries: The Resilient Alternative 

Why NiMH Batteries? 

Despite the rise of lithium-ion batteries, NiMH batteries are still favored for their ability to withstand extreme temperatures. They are commonly found in hybrid vehicles like the Toyota Prius and even some all-electric models. 

Construction and Working 

Components: 

• Anode: Metal hydride. 
• Cathode: Nickel. 
• Electrolyte: Potassium hydroxide. 

Working: 

• During discharge, electrons flow from the anode to the cathode through an external circuit, creating an electric current. 
• During recharge, the process reverses, restoring the battery’s charge. 

Advantages Over Lead-Acid Batteries 

• Better performance across a wider range of temperatures. 
• Higher energy density and longer lifespan. 
• Improved efficiency and reduced environmental impact. 

Why These Batteries Are Still Relevant 

While lithium-ion batteries dominate the EV industry due to their superior energy density and efficiency, lead-acid and NiMH batteries continue to play crucial roles in specific applications: 

• Lead-Acid Batteries: Still widely used in IC engine cars and backup power systems. 
• NiMH Batteries: Preferred in hybrids and certain EVs for their durability and resilience in extreme weather. 

The Road Ahead for Battery Technologies 

Lead-acid and NiMH batteries may be considered legacy technologies, but they’ve laid the foundation for the advanced batteries we see today. Their continued presence in the automotive industry highlights their adaptability and relevance in meeting specific needs. As battery technologies evolve, these pioneers remain integral to understanding and innovating the future of energy storage. 

By appreciating the history and mechanics of these batteries, we gain valuable insights into the evolution of energy storage and its role in powering our world. 

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