3.1 Lead-acid battery chemistry, design, and applications
3 min read•august 7, 2024
Lead-acid batteries are the oldest rechargeable battery technology, still widely used today. They come in two main types: flooded cell and (VRLA). Each has unique characteristics, making them suitable for different applications.
Lead-acid batteries have low energy density but are reliable and cost-effective. They're commonly used in automotive, UPS systems, and deep cycle applications. Understanding their chemistry, design, and performance is crucial for optimizing their use in various energy storage scenarios.
Lead-Acid Battery Types and Design
Flooded Cell and VRLA Batteries
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- Flooded cell lead-acid batteries contain liquid that can move freely within the battery case
- Require regular maintenance, including topping up the electrolyte level with distilled water
- Prone to spillage if not handled properly (stationary applications)
- Valve-regulated lead-acid (VRLA) batteries have a sealed design with a pressure relief valve
- Electrolyte is immobilized in a gel or absorbed in a glass mat (AGM)
- Maintenance-free and spill-proof, making them suitable for portable applications (UPS systems, wheelchairs)
- Higher cost compared to flooded cell batteries
Deep Cycle and Plate Design
- batteries are designed for repeated deep discharges (up to 80% depth of discharge)
- Thicker plates and higher active material density compared to starter batteries
- Used in applications requiring long-term energy storage (solar power systems, golf carts)
- Plate design affects battery performance and longevity
- Flat plates are simple and cost-effective but have limited surface area
- Tubular plates have higher surface area and improved but are more expensive to manufacture
- Grid alloys, such as lead-calcium and lead-antimony, influence battery characteristics
- Lead-calcium alloys reduce water loss and self-discharge but have lower cycle life
- Lead-antimony alloys improve deep cycling performance but increase water loss and maintenance requirements
Lead-Acid Battery Performance Characteristics
Energy Density and Self-Discharge
- of lead-acid batteries ranges from 30-50 Wh/kg
- Lower than other rechargeable battery technologies (Li-ion, NiMH)
- Limits their use in weight-sensitive applications (portable devices)
- Energy density of lead-acid batteries is approximately 60-110 Wh/L
- Requires larger battery sizes for high-energy applications (electric vehicles)
- of lead-acid batteries is relatively low, typically 3-5% per month at room temperature
- Increases with rising temperature and battery age
- Regular charging is necessary to maintain full capacity
Charge-Discharge Cycle and Sulfation
- of lead-acid batteries is around 70-80%
- Energy losses occur due to internal resistance and heat generation
- Proper charging algorithms (constant current-constant voltage) can optimize efficiency
- is a common failure mode in lead-acid batteries
- Occurs when lead sulfate crystals grow and accumulate on the plates during prolonged periods of low charge
- Reduces battery capacity and increases internal resistance
- Regular charging and occasional equalization charges can help prevent sulfation
Lead-Acid Battery Applications
Automotive and UPS Systems
- Automotive applications are the most common use for lead-acid batteries
- Starting, lighting, and ignition (SLI) batteries provide high current for engine starting
- Deep cycle batteries power electric vehicles (forklifts, golf carts)
- Low cost and reliable performance make them the preferred choice for vehicles
- Uninterruptible power supply (UPS) systems rely on lead-acid batteries for backup power
- Provide continuous power during utility outages to critical loads (data centers, hospitals)
- VRLA batteries are commonly used due to their maintenance-free and spill-proof design
- Long service life and high reliability are essential for UPS applications
Lead-Acid Battery Electrolyte
Electrolyte Composition and Concentration
- The electrolyte in lead-acid batteries is a mixture of sulfuric acid (H2SO4) and water
- Sulfuric acid is the active component that participates in the electrochemical reactions
- Water acts as a solvent and helps in ionic conductivity
- Electrolyte concentration, measured in terms of specific gravity, varies during charge and discharge
- Fully charged battery has a specific gravity of around 1.28
- Specific gravity decreases during discharge as sulfuric acid is consumed
- Electrolyte concentration affects battery performance and freezing point
- Higher concentration improves capacity but increases the risk of sulfation and decreases the freezing point
- Lower concentration reduces capacity but improves low-temperature performance
- Proper electrolyte maintenance, including regular specific gravity checks and adjustments, is crucial for optimal battery performance and longevity
Key Terms to Review (19)
Anode: The anode is the electrode in an electrochemical cell where oxidation occurs, meaning it is where electrons are released. This process is essential in both galvanic and electrolytic cells, as it plays a critical role in generating electric current and facilitating chemical reactions. Understanding the function of the anode helps in grasping the overall operation of various types of batteries and energy storage systems.
Cathode: The cathode is the electrode in a cell where reduction occurs, meaning it gains electrons during a redox reaction. In the context of batteries, the cathode plays a critical role in energy storage and release, influencing the overall performance and efficiency of various battery technologies.
Charge-Discharge Cycle Efficiency: Charge-discharge cycle efficiency refers to the ratio of the energy output of a battery during discharging to the energy input during charging, expressed as a percentage. This metric is crucial in evaluating the performance of lead-acid batteries, as it directly impacts their usability and lifespan in various applications, such as automotive and stationary storage systems. High efficiency indicates that a battery can effectively convert and store energy, while low efficiency suggests energy losses that can occur during the chemical reactions involved in charging and discharging.
Cycle life: Cycle life refers to the number of charge and discharge cycles a battery can undergo before its capacity falls to a specified percentage of its original capacity, often around 80%. It serves as a crucial performance indicator for assessing the longevity and efficiency of energy storage systems, influencing design choices and applications across various battery technologies.
Deep cycle lead-acid: Deep cycle lead-acid batteries are a type of rechargeable battery designed to provide a steady amount of current over an extended period, making them ideal for applications that require prolonged energy discharge. Unlike traditional lead-acid batteries, which are designed for short bursts of power, deep cycle lead-acid batteries can be deeply discharged and recharged many times without significant damage. This characteristic makes them particularly suitable for renewable energy systems, electric vehicles, and backup power applications.
Electrolyte: An electrolyte is a substance that conducts electricity when dissolved in water or melted, due to the presence of free ions. In the context of energy storage, electrolytes play a crucial role in facilitating the movement of ions between the anode and cathode, which is essential for redox reactions and overall battery performance.
Equalization Charging: Equalization charging is a controlled overcharge process applied to lead-acid batteries, aimed at balancing the charge across individual cells. This technique helps to ensure that all cells reach the same voltage level, thereby maximizing the battery's capacity and lifespan. It is especially important for lead-acid batteries, which can develop imbalances due to varying rates of charge and discharge in different cells.
Float Charging: Float charging is a method of battery charging that maintains a lead-acid battery at a specific voltage level to keep it fully charged without overcharging. This technique is crucial in applications where the battery must be kept in a ready state for immediate use, ensuring reliability and longevity. Float charging helps to prevent sulfation, a common issue that can reduce battery performance and lifespan.
Flooded lead-acid: Flooded lead-acid refers to a type of lead-acid battery where the electrolyte is in liquid form, fully submerging the lead plates. This design allows for effective electrochemical reactions during charging and discharging processes, enabling the battery to deliver reliable energy storage. Flooded lead-acid batteries are commonly used in various applications, including automotive, renewable energy systems, and backup power supplies, due to their robustness and relatively low cost.
Grid Design: Grid design refers to the strategic arrangement and integration of energy sources, storage systems, and distribution networks to optimize the delivery and reliability of electricity. It encompasses the planning and development of power systems that include various technologies, such as lead-acid batteries, which play a crucial role in stabilizing and supporting the electrical grid, particularly in applications requiring reliable energy storage solutions.
Lead Contamination: Lead contamination refers to the presence of lead, a toxic heavy metal, in the environment that poses health risks to humans and ecosystems. In the context of lead-acid batteries, this contamination can occur through the improper disposal of batteries or leaks from damaged units, leading to soil and water pollution. Understanding lead contamination is essential for mitigating its environmental impact and ensuring safe handling and recycling practices for lead-acid batteries.
Plate construction: Plate construction refers to the specific design and assembly of the electrodes within lead-acid batteries, which are crucial for their electrochemical performance. The plates are typically made of lead or lead dioxide and are designed to maximize surface area for efficient chemical reactions while ensuring mechanical stability and electrical conductivity. Understanding plate construction is vital as it directly impacts the battery's capacity, efficiency, lifespan, and overall performance in various applications.
Recycling Processes: Recycling processes involve the collection, treatment, and reprocessing of materials to reclaim valuable resources and reduce waste. In the context of lead-acid batteries, these processes are critical for recovering lead, sulfuric acid, and other components, ensuring environmental safety and promoting sustainability. Effective recycling not only minimizes the environmental impact of battery disposal but also contributes to the circular economy by making it possible to reuse materials in new battery production or other applications.
SAE J537: SAE J537 is a standard established by the Society of Automotive Engineers that outlines the specifications for lead-acid storage batteries used in automotive applications. This standard covers various aspects such as performance testing, physical dimensions, and design requirements, ensuring consistency and safety across different battery manufacturers and models. Understanding this standard is crucial for evaluating lead-acid batteries' chemistry, design, and real-world applications in vehicles and other energy storage systems.
Self-discharge rate: The self-discharge rate is the measure of how quickly a stored energy device loses its charge over time when not in use. This phenomenon occurs due to internal chemical reactions and other factors that lead to energy loss, impacting the overall efficiency and performance of various energy storage technologies.
Specific Energy: Specific energy is defined as the amount of energy stored per unit mass of a system, typically expressed in watt-hours per kilogram (Wh/kg). This term is crucial when evaluating different energy storage systems, as it helps determine their efficiency and performance in applications such as transportation and grid storage. A higher specific energy indicates that a technology can store more energy without increasing its weight, which is particularly important for mobile applications like electric vehicles and portable devices.
Sulfation: Sulfation refers to the process where lead sulfate crystals form on the plates of a lead-acid battery during discharge and can hinder its performance and longevity. This process occurs when the battery is not fully charged, causing lead sulfate to accumulate, which can eventually result in decreased capacity and failure of the battery. Understanding sulfation is crucial for maintaining the efficiency and lifespan of lead-acid batteries, as it directly impacts their ability to store and deliver energy effectively.
UL 1989: UL 1989 is a safety standard developed by Underwriters Laboratories that establishes requirements for the performance and testing of lead-acid batteries used in stationary applications. This standard is significant because it ensures that batteries meet certain safety and performance criteria, which is crucial for reliable energy storage solutions in various applications, including uninterruptible power supplies (UPS) and renewable energy systems.
Valve-regulated lead-acid: Valve-regulated lead-acid (VRLA) batteries are a type of lead-acid battery designed to operate in a sealed environment, which minimizes electrolyte loss and allows for safer operation. These batteries utilize a one-way valve to release excess gas buildup during charging, preventing over-pressurization while maintaining the integrity of the electrolyte. This design feature makes VRLA batteries particularly suited for applications where maintenance and safety are crucial, such as in telecommunications and backup power systems.