Lead-acid batteries and lithium-ion batteries

Let's explore the differences between lithium-ion batteries and lead-acid batteries. Both lead-acid batteries and lithium-ion batteries are very common backup power sources. When choosing which battery is better for your device application, you need to consider multiple factors such as voltage, capacity, number of cycles, etc. due to the different characteristics of the two batteries.

Chemistry and structure
Lithium-ion batteries
The working principle of lithium-ion batteries is based on the reversible electrochemical reaction between two electrodes (anode and cathode) in an electrolyte. The electrode materials used in lithium-ion batteries are usually lithium compounds (for example, lithium cobalt oxide, lithium iron phosphate, etc.), and the electrolyte is a non-aqueous electrolyte (an organic solvent containing lithium salts). The electrodes are usually thin layers on a conductive substrate, which allows for high energy density.

Schematic diagram of lithium battery reactionSchematic diagram of lithium battery reaction
The negative electrode is usually made of graphite. The anode in a lithium-ion battery stores lithium ions (Li⁺) during charging, and lithium ions move from the anode to the cathode during discharge. The positive electrode is also usually made of graphite. The cathode in a lithium-ion battery stores lithium ions (Li⁺) during charging, and lithium ions move from the anode to the cathode during discharge.

During charging, lithium ions move from the cathode through the electrolyte and intercalate (embed) into the anode material. During discharge, the process reverses: lithium ions move from the anode through the electrolyte to the cathode. While the lithium ions migrate through the electrolyte, electrons flow through an external circuit, creating an electric current that can power devices.

Lead-acid batteries
The working principle of lead-acid batteries involves an electrochemical reaction between lead and lead dioxide electrodes in a sulfuric acid electrolyte, providing a reliable source of electrical energy. Due to the characteristics of lead-based chemistry, lead-acid batteries have thick and bulky electrodes.

Schematic diagram of lead-acid battery reaction Schematic diagram of lead-acid battery reaction
Energy density
Lithium-ion batteries generally have a higher energy density than lead-acid batteries. This means that it can store more energy per unit volume or weight, making them lighter and more compact for the same energy capacity.

The volumetric energy density of lithium-ion batteries is significantly higher than that of lead-acid batteries. This means that lithium-ion batteries can store more energy per unit volume, allowing for smaller, more compact battery packs.

The energy density of lead-acid batteries is lower than that of lithium-ion batteries, resulting in larger and heavier batteries for the same energy storage capacity.

Likewise, lithium-ion batteries have a higher gravimetric energy density than lead-acid batteries. This results in a lighter battery pack for a given energy capacity, which is critical in applications where weight is a concern, such as electric vehicles.

Cycle Life
The cycle life of a battery refers to the number of charge and discharge cycles it can undergo before its capacity drops to a specified level.

Lithium-ion batteries typically have a longer cycle life than lead-acid batteries. Depending on the specific chemistry and conditions of use, lithium-ion batteries can withstand hundreds to thousands of charge and discharge cycles.

Lead-acid batteries, while rugged, typically have a shorter cycle life, especially when subjected to deep discharge.

Lithium-ion batteries are suitable for applications that require long cycle life, high energy density, and light weight, such as electric vehicles, portable electronics, and energy storage. Lead-acid batteries remain competitive in applications where cost-effectiveness, reliability, and an existing recycling infrastructure are critical, such as automotive starting batteries and static power backup systems.

Discharge Rate
A battery's discharge rate refers to the rate at which it releases stored energy, usually measured as the C-rate.

Lithium-ion batteries are capable of high discharge rates, typically ranging from 1C to 2C or higher, depending on chemistry and design. Even at high discharge rates, the voltage and capacity of lithium-ion batteries remain relatively stable, which is important for applications that require instantaneous high power output or sustained high power output.

Lead-acid batteries are generally not suitable for high discharge rate applications. Common discharge rates for lead-acid batteries range from 0.05C to 0.2C, depending on the type (such as lead-acid batteries, AGM or gel batteries). Some AGM (absorbed glass blanket) or high-performance lead-acid batteries can handle moderate discharge rates up to 0.5C or slightly higher.

At high discharge rates, lead-acid batteries may experience voltage drop and capacity reduction, while lithium-ion batteries have a stable discharge rate, which gradually decreases to 60% for lead-acid batteries. This limitation makes lead-acid batteries less suitable for applications that require rapid energy release or high power requirements.

Lead-acid batteries are better suited for applications that require moderate discharge rates, such as automotive starting batteries, backup power systems, and static applications. Due to voltage drop and reduced efficiency at high discharge rates, they are less effective in applications that require rapid discharge.

Lithium-ion batteries are superior to lead-acid batteries at high discharge rates. They can deliver significant power output quickly and efficiently, and are suitable for applications that require a large power surge, such as electric vehicles, power tools, and some industrial equipment.

Discharge Voltage
Lithium-ion batteries maintain a relatively stable voltage for most of the discharge cycle, until near the end of capacity. This makes them suitable for applications that require stable voltage and consistent performance.

Lead-acid batteries have a lower nominal voltage per cell than lithium-ion batteries. During discharge, their voltage gradually decreases, especially near the end of capacity. This characteristic is common in applications where the battery voltage range and discharge characteristics are key factors.

In practical applications, understanding these voltage characteristics can help select the appropriate battery type based on voltage requirements, discharge characteristics needs, and overall performance expectations.

Charging Characteristics
Lithium-ion batteries can be charged quickly, and some types of lithium-ion batteries are capable of rapid charging without significant damage. They also have a lower self-discharge rate than lead-acid batteries.

Lead-acid batteries generally charge more slowly than lithium-ion batteries, especially when near full charge. Rapid charging can cause heating and requires careful monitoring.

For example, a 3000 milliamp-hour (mAh) lithium-ion battery charged at 1500 milliamps (1.5A) would theoretically take about 2 hours to fully charge (assuming a 1C charge rate). A 12-volt lead-acid battery with a capacity of 100 ampere-hours (Ah) would take about 10 hours to fully charge at a charge rate of 10 amps (about 0.1C).

Temperature Effects
Lithium-ion batteries perform best in temperatures ranging from 0°C to 45°C (32°F to 113°F). Lead-acid batteries are more tolerant of temperature extremes than lithium-ion batteries. They can operate effectively in the range of -20°C to 50°C (-4°F to 122°F).

Lithium-ion batteries are more sensitive to temperature extremes and require careful thermal management to ensure safety and optimal performance. Cold temperatures (below 0°C) can temporarily reduce the capacity and power output of a battery. Extremely low temperatures can cause the battery to become sluggish, and charging or discharging at very low temperatures can cause irreversible damage.

Lead-acid batteries have a wider operating temperature range and are better able to withstand both high and low temperatures. Although lead-acid batteries are better able to withstand high temperatures, overheating can still accelerate battery aging and increase water loss.

Both battery types require monitoring and adherence to temperature guidelines to ensure safe operation and extended life.

Applications and Uses
Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, which require maximizing energy per unit volume or weight.

Lithium-ion batteries are commonly used in portable electronic devices (e.g., laptops, smartphones), electric vehicles (EVs), and renewable energy storage systems due to their high energy density and low weight.

Lead-acid batteries are traditionally used in automotive starting batteries, backup power systems (UPS), and industrial applications (e.g., forklifts, golf carts) due to their durability, low cost, and suitability for high current output. Despite their lower energy density, lead-acid batteries are competitive in applications where cost-effectiveness, durability, and an existing recycling and disposal infrastructure take precedence over weight and volume.

Maintenance
Lithium-ion batteries generally require less maintenance than lead-acid batteries. They do not require electrolyte checks or periodic equalization charges. Lithium-ion batteries are generally easier to install due to their light weight, compact size, and flexible mounting. They require less structural support and have lower ventilation requirements than lead-acid batteries.

Lead-acid batteries require periodic maintenance, such as checking electrolyte levels, specific gravity, and ensuring proper charging to prevent sulfation. Due to their heavy weight and the release of gases during charging, lead-acid batteries require a sturdy mounting structure and adequate ventilation. In addition, they require specific maintenance visits for periodic inspections and service.

Summary
When choosing between lithium-ion and lead-acid batteries, consider the specific application needs, including power requirements, space constraints, cost considerations, and environmental factors. Each battery type has unique advantages that make it suitable for different industries and applications.