What is The Difference in Service Life Between Lead-acid Batteries and Lithium Ion Batteries?

Batteries have evolved a great deal. Today, there is a wide range of battery chemistries designed to meet specific users’ needs.

Lead-acid and lithium-ion are the two leading rechargeable battery technologies with li-ion slowly taking on more responsibilities. Today, we look at the principle of these batteries and how they influence customer experience.

The Principle of Lead-acid Battery and Lithium-ion Battery

The first difference between lead-acid and lithium-ion batteries is their working principle. Here is an overview of what each battery offers:

The Principle of Lead-acid Battery

A lead-acid battery is one of the oldest types of rechargeable batteries. Its basic principle revolves around the electrochemical reaction between lead, lead dioxide, and sulfuric acid. In its discharged state, the battery contains a positive plate made of lead dioxide and a negative plate made of sponge lead, both immersed in an electrolyte solution of diluted sulfuric acid. 

When the battery is being charged, the lead dioxide (at the positive plate) and the sponge lead (at the negative plate) react with the sulfuric acid in the electrolyte, leading to the formation of lead sulfate and water. During discharge, the process is reversed. The lead sulfate and water are converted back to lead dioxide, sponge lead, and sulfuric acid, releasing electrical energy in the process. 

This conversion between chemical energy and electrical energy is what powers devices connected to the battery. Over time, the repetitive formation of lead sulfate during the charging cycle can lead to the creation of stable lead sulfate crystals, a process called sulfation, which diminishes the capacity and lifespan of the battery.

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The Principle of Lithium-ion Battery

Lithium-ion batteries, often found in portable electronics and electric vehicles, operate based on the movement of lithium ions between the positive and negative electrodes. In its simplest form, a lithium-ion battery consists of a positive electrode (cathode) made of a lithium metal oxide, a negative electrode (anode) made of carbon (often graphite), and an electrolyte that allows for the movement of lithium ions. 

During the discharging phase, lithium ions move from the anode to the cathode, releasing energy in the process. Electrons are simultaneously released from the anode and travel through the external circuit, providing power to the connected device, before re-entering the battery at the cathode.

When charging, the process is reversed: lithium ions move from the cathode back to the anode. A separator within the battery ensures that the positive and negative electrodes remain apart, preventing short-circuiting. One of the key advantages of lithium-ion batteries is their ability to store a significant amount of energy in a relatively small and light package, making them particularly suited for modern electronic devices and transportation needs.

Influencing Factors of Battery Life

When buying a battery, it’s crucial to find one that offers the most life. You want something that can serve you for a long time. However, there are certain factors that will determine how long  the battery will last. They include:

Depth of Discharge (DoD): Battery life is often related to how deeply a battery is discharged on each cycle. Shallow discharges (using only a small portion of a battery's capacity) can result in a greater number of total life cycles compared to deep discharges.

Charge Cycles: A charge cycle refers to the process of charging a battery from 0% to 100%. Batteries have a finite number of charge cycles before their capacity diminishes below a certain threshold (commonly 80% of original capacity).

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Charging Rate: Charging a battery too quickly can generate excessive heat, which can damage the battery's internal components, reducing its overall lifespan.

Temperature: Extreme temperatures, both hot and cold, can negatively affect a battery's performance and longevity. Batteries tend to degrade faster at high temperatures, while very cold temperatures can reduce their capacity.

Overcharging: Keeping a battery at full charge for extended periods can strain and degrade the battery, especially if it remains connected to a charger that keeps topping it up.

Storage Conditions: Storing a battery in a partly charged state (around 50% to 60%) in a cool, dry place is ideal. Prolonged storage at full discharge or full charge can degrade battery health.

Physical Damage: Dropping a battery or subjecting it to physical shocks can damage its internal components, potentially leading to reduced life or even failure.

Internal Resistance: Over time, a battery's internal resistance can increase due to chemical reactions within the battery. Higher resistance means the battery has to work harder, which can lead to faster degradation.

Battery Management System (BMS): Modern batteries, especially lithium-ion types, often come with a BMS that monitors and manages the battery's charge, discharge, and temperature. A good BMS can significantly influence and extend a battery's lifespan by ensuring optimal operating conditions.

In short, the lifespan of a battery is determined by a combination of factors related to its design, use, and environment. Understanding and managing these factors can help users optimize the longevity and performance of their batteries.

Cycle Life of Lead-acid Batteries and Lithium-ion Batteries

Life cycle is another big parameter determining the how batteries work. Consider the following:

Lead-acid Batteries

The cycle life of lead-acid batteries largely depends on their design and depth of discharge (DoD). Typically, starting, lighting, and ignition (SLI) lead-acid batteries, which are frequently found in cars and vehicles, have a cycle life of about 200-300 cycles to 50% DoD. 

This means they can be discharged to half their capacity this many times before their overall capacity diminishes significantly. On the other hand, deep-cycle lead-acid batteries, designed for applications where a deep discharge is needed like in solar energy storage or marine use, fare better with a cycle life ranging from 500 to 1,000 cycles to 50% DoD. 

Some high-quality deep-cycle lead-acid batteries can even exceed this range. It's worth noting that repeatedly discharging these batteries beyond their recommended DoD can significantly reduce their cycle life.

Lithium-ion Batteries

Lithium-ion batteries are known for their extended cycle lives compared to many other battery types. On average, a lithium-ion battery has a cycle life of 1,000 to 5,000 cycles to 80% DoD. 

This means they retain at least 80% of their original capacity even after thousands of charge and discharge cycles. However, the exact number can vary based on the specific lithium-ion chemistry and the battery's design. 

For instance, Lithium Iron Phosphate (LiFePO4) batteries tend to have a higher cycle life than other common lithium-ion chemistries. Proper management, like avoiding full discharges and extreme charging rates, can further enhance the cycle life of lithium-ion batteries.

Conclusion 

While both lead-acid and lithium-ion batteries have their own merits and applications, lithium-ion batteries typically offer a longer cycle life. This longer cycle life, combined with their higher energy density and declining cost, has led to their widespread adoption in a variety of modern applications, including smartphones, laptops, and electric vehicles.