Batteries: What are the options?

As the world increasingly turns to renewable energy sources and grid-scale energy storage, an understanding of the various battery technologies available is beneficial. Each type of battery offers unique characteristics that make it suitable for specific applications, from grid stabilisation to backup power systems. In this post, we'll explore the main types of stationary batteries, their underlying chemistry, typical applications, and the pros and cons of each technology. 

Before looking at individual battery types, however, a general note may be useful. All batteries are electrochemical devices and, as such, they are inescapably subject to the laws that govern the rate of chemical reactions. In particular, all batteries are affected by temperature. High temperatures will lead to shorter battery life, while low temperatures will reduce capacity and performance. Batteries that are required to operate in either unusually hot or cold conditions must, therefore, be chosen and sized with particular care.

 

Lead-acid batteries

Lead-acid batteries are one of the oldest and best established rechargeable battery technologies. They have been used for over a century in a wide range of applications, from automotive starting to uninterruptible power supplies and off-grid energy storage.

Chemistry

Lead-acid batteries consist of lead dioxide (PbO2) positive plates and sponge lead (Pb) negative plates, immersed in a sulphuric acid (H2SO4) electrolyte.

Types

1. Vented Lead Acid (VLA): Also known as flooded lead-acid batteries, these require regular water top-ups.
2. Valve Regulated Lead Acid (VRLA): Sealed batteries, including absorbent glass mat and gel types. These require regular testing as they work in an electrolyte-starved mode.

Typical applications

• Backup power for telecommunications and data centres
• Off-grid and grid-tied renewable energy systems
• Uninterruptible Power Supplies (UPS)
• Electric vehicle charging stations
• Petrol and diesel vehicle starting

Pros

• Well-established technology with a long history: This means there's a wealth of knowledge and experience in their use and maintenance.
• Low initial cost: Lead-acid batteries are often the most economical choice for short-term energy storage needs.
• Highly recyclable: Nearly 100% of a lead-acid battery can be recycled, making them an environmentally responsible choice.
• Reliable and tolerant to overcharging: When properly managed, lead-acid batteries can withstand occasional overcharging without significant damage.

Cons

• Lower energy density compared to newer technologies: They require more space to store the same amount of energy as more advanced battery types.
• Shorter cycle life, especially if deeply discharged: Regular deep discharges can significantly reduce the lifespan of lead-acid batteries.

 

Lithium-Ion Batteries

Due to their high energy density and efficiency, lithium-ion batteries have revolutionised energy storage. They've become increasingly popular in grid-scale energy storage, electric vehicles and portable electronics.

Chemistry

Lithium-ion batteries use a lithium compound as the positive electrode and typically graphite as the negative electrode. The electrolyte is a lithium salt in an organic solvent.

Types

1. Lithium Nickel Manganese Cobalt Oxide: Offers a good balance of energy density and power.
2. Lithium Iron Phosphate: Known for its safety and long cycle life.
3. Lithium Nickel Cobalt Aluminium Oxide: Provides high energy density.
4. Lithium Manganese Oxide: Offers good thermal stability and safety.

Typical applications

• Grid-scale energy storage and grid stabilisation
• Electric vehicles and hybrid electric vehicles
• Residential and commercial energy storage systems
• Portable electronics and power tools

Pros

• High energy density: This allows for more compact and lightweight energy storage solutions, which is crucial for applications like electric vehicles.
• Long cycle life: Many lithium-ion batteries can withstand thousands of charge-discharge cycles, making them cost-effective in the long run.
• Low self-discharge rate: They can hold their charge for longer periods when not in use, making them suitable for intermittent use applications.
• No memory effect: Unlike some older battery technologies, lithium-ion batteries don't need to be fully discharged before recharging.
• Fast charging capability: This is particularly beneficial for applications requiring quick turnaround times, such as electric vehicles.

Cons

• Higher initial cost: Although prices are decreasing, lithium-ion batteries are still more expensive upfront than lead-acid batteries.
• Potential safety concerns (thermal runaway): In rare cases, lithium-ion batteries can overheat and catch fire.
• Require sophisticated battery management systems: To prevent overcharging, over-discharging, overheating and to balance cells, complex control systems are needed.
• Performance degrades at high temperatures: Exposure to high temperatures can accelerate capacity loss and reduce the battery's overall lifespan.

 

Flow Batteries

Flow batteries are a unique type of rechargeable battery where the energy is stored in a liquid electrolyte. They offer the advantage of decoupling power and energy capacity, making them highly scalable for large-scale energy storage applications.

Chemistry

The most common type is the Vanadium Redox Flow Battery (VRFB), which uses vanadium ions in different oxidation states. Other chemistries include zinc-bromine and iron-chromium.

Typical Applications

• Large-scale grid energy storage
• Renewable energy integration
• Microgrid and off-grid systems
• Industrial and commercial energy management

Pros

• Long cycle life: Flow batteries can typically withstand tens of thousands of charge-discharge cycles without significant degradation.
• Can be fully discharged without damage: Unlike many other battery types, flow batteries are not harmed by complete discharge.
• Easily scalable by increasing tank size: The energy capacity can be increased simply by using larger electrolyte tanks, without changing the power components.
• Lower fire risk than lithium-ion: The aqueous electrolytes used in most flow batteries are non-flammable, reducing safety concerns.

Cons

• Lower energy density: Flow batteries require more space than technologies like lithium-ion to store the same amount of energy.
• Complex system: The need for large electrolyte tanks makes flow batteries more mechanically complex than solid-state batteries.
• Higher initial costs: The complexity of flow battery systems often results in higher upfront costs, although their long lifespan can offset this.
• Potential for electrolyte leakage: Proper containment and maintenance are crucial to prevent environmental contamination from electrolyte leaks.

 

Sodium-Ion Batteries

Sodium-ion batteries are an emerging technology that offers a potentially more sustainable alternative to lithium-ion batteries. They use abundant, low-cost materials and could significantly improve future energy storage applications.

Chemistry

Similar to lithium-ion but uses sodium ions instead of lithium ions for charge transfer. The cathode is typically a layered metal oxide, while the anode is often hard carbon.

Typical Applications

• Grid-scale energy storage
• Residential and commercial energy storage
• Electric vehicles
• Portable electronics (in development)

Pros

• More abundant and cheaper raw materials: Sodium is much more plentiful than lithium, potentially leading to lower costs and more sustainable production.
• Potentially more environmentally friendly: The materials used in sodium-ion batteries are generally less toxic and easier to recycle than those in lithium-ion batteries.
• Can be fully discharged for safer transport: Unlike lithium-ion batteries, sodium-ion batteries can be completely discharged, simplifying shipping and storage logistics.

Cons

• Lower energy density compared to lithium-ion: Sodium-ion batteries may not be suitable for applications where weight and size are critical factors.
• Technology still in early stages of commercialisation: As a newer technology, sodium-ion batteries have yet to prove their long-term reliability and performance in real-world applications.
• Limited track record in large-scale applications: The lack of extensive field data makes it challenging to predict long-term performance and potential issues.

 

Nickel-Based Batteries

While less common in new installations, nickel-based batteries still find use in some stationary applications. They offer reliable performance and can handle harsh environmental conditions.

Chemistry

Nickel-based batteries use nickel oxyhydroxide (NiOOH) as the positive electrode. The negative electrode and electrolyte differ between types. During discharge, the nickel oxyhydroxide electrode is reduced to nickel hydroxide, while the negative electrode is oxidised. This process is reversed during charging.

Types

1. Nickel-Cadmium (NiCd): Known for their durability.
2. Nickel-Metal Hydride (NiMH): Offers higher energy density than NiCd without the use of toxic cadmium.

Typical Applications

• Industrial backup power systems
• Railway signalling
• Aircraft starting and emergency power
• Remote telecommunications systems

Pros

• Robust and durable: Nickel-based batteries can withstand harsh conditions, including physical stress.
• Good cycle life: When properly maintained, nickel-based batteries can last for many years and thousands of cycles.

Cons

• Lower energy density than lithium-ion: This makes them less suitable for applications where space and weight are at a premium.
• Memory effect (especially in NiCd): Partial discharge cycles can lead to a loss of usable capacity, requiring periodic full discharge cycles.
• Environmental concerns with cadmium in NiCd batteries: The toxic nature of cadmium has led to restrictions on NiCd battery use in many regions.

 

The Importance of Proper Testing

Each of these battery technologies requires a specific testing regime to ensure optimal performance, safety and longevity. Testing methods and frequency vary significantly between different battery types. For example:

• Lead-acid batteries often require regular specific-gravity measurements, capacity testing and ohmic testing to assess their state of health.
• Lithium-ion batteries benefit from sophisticated state-of-health monitoring and impedance testing to detect early signs of degradation.
• Flow batteries may need electrolyte composition analysis in addition to standard electrical tests to ensure optimal performance.

Proper testing is essential not only for maintaining battery performance but also for ensuring the safety and reliability of energy storage systems. Regular testing can help identify potential issues before they lead to failures, optimise battery management strategies, and extend the overall lifespan of the energy storage system.

 

Conclusion

Stationary batteries are diverse, with each technology offering unique advantages and challenges. As we continue to advance our energy storage capabilities, it's likely we'll see further innovations and improvements in battery technology.

Understanding the characteristics of different battery types is central to selecting the right technology for specific applications. Equally important is implementing appropriate testing and maintenance regimes to ensure these batteries perform optimally throughout their lifecycle.

In our upcoming post, we'll explore the intricacies of testing different battery technologies and how Megger's solutions can help ensure the reliability and longevity of energy storage systems.