🔋Energy Storage Technologies Unit 3 – Battery Types: Lead-Acid, NiCd, and NiMH

Key Concepts and Definitions

• Battery a device that converts chemical energy into electrical energy through electrochemical reactions
• Anode the negative electrode in a battery where oxidation occurs during discharge
• Cathode the positive electrode in a battery where reduction occurs during discharge
• Electrolyte a substance that conducts ions between the anode and cathode in a battery
  • Can be liquid, gel, or solid
• Capacity the amount of electrical charge a battery can store, measured in ampere-hours (Ah)
• Energy density the amount of energy stored per unit volume or weight of a battery (Wh/L or Wh/kg)
• Cycle life the number of charge-discharge cycles a battery can undergo before its capacity drops below a specified level
• Self-discharge the gradual loss of charge in a battery when not in use due to internal chemical reactions

Historical Development

• Lead-acid batteries invented by French physicist Gaston Planté in 1859, making them the oldest rechargeable battery technology
• Nickel-cadmium (NiCd) batteries developed by Swedish inventor Waldemar Jungner in 1899
  • Improved upon by Thomas Edison in the early 1900s
• Nickel-metal hydride (NiMH) batteries introduced in the 1970s as an alternative to NiCd batteries
  • Became commercially available in 1989
• Environmental concerns over cadmium led to the development of NiMH batteries as a more eco-friendly alternative
• Advancements in materials science and manufacturing processes have improved the performance and affordability of these battery technologies over time

Battery Chemistry Basics

• Batteries convert chemical energy into electrical energy through redox reactions
  • Reduction occurs at the cathode, gaining electrons
  • Oxidation occurs at the anode, losing electrons
• Electrolyte facilitates the movement of ions between the electrodes
  • Maintains charge balance and enables the flow of electric current
• Separator prevents direct contact between the anode and cathode to avoid short-circuiting
  • Allows ions to pass through
• Charge and discharge cycles involve the reversible movement of ions between the electrodes
  • During discharge, ions move from the anode to the cathode
  • During charge, ions move from the cathode to the anode
• Battery chemistry determines key characteristics such as voltage, capacity, energy density, and cycle life

Lead-Acid Batteries

• Consist of a lead dioxide (PbO2) cathode, a spongy lead (Pb) anode, and a sulfuric acid (H2SO4) electrolyte
• During discharge, both electrodes react with sulfuric acid to form lead sulfate (PbSO4), releasing electrons and generating electricity
• Charging reverses the process, converting lead sulfate back into lead dioxide at the cathode and spongy lead at the anode
• Nominal cell voltage of 2.1 V, with a typical battery voltage of 12 V (six cells in series)
• Relatively low energy density (30-50 Wh/kg) but high power density
• Affordable and reliable, with a long history of use in automotive and stationary applications
• Require regular maintenance, such as topping up the electrolyte and preventing sulfation

Nickel-Cadmium (NiCd) Batteries

• Consist of a nickel hydroxide (NiOOH) cathode, a cadmium (Cd) anode, and an alkaline electrolyte (usually potassium hydroxide, KOH)
• During discharge, nickel hydroxide is reduced to nickel hydroxide (Ni(OH)2), and cadmium is oxidized to cadmium hydroxide (Cd(OH)2)
• Charging reverses the process, converting nickel hydroxide back to nickel oxyhydroxide and cadmium hydroxide back to cadmium
• Nominal cell voltage of 1.2 V
• Higher energy density (40-60 Wh/kg) compared to lead-acid batteries
• Robust and reliable, with good low-temperature performance and long cycle life
• Suffer from "memory effect," where the battery's capacity decreases if not fully discharged before recharging
• Cadmium is toxic and environmentally harmful, leading to restrictions on NiCd battery use and disposal

Nickel-Metal Hydride (NiMH) Batteries

• Consist of a nickel hydroxide (NiOOH) cathode, a hydrogen-absorbing alloy anode, and an alkaline electrolyte (usually potassium hydroxide, KOH)
• During discharge, nickel oxyhydroxide is reduced to nickel hydroxide (Ni(OH)2), and the hydrogen-absorbing alloy releases hydrogen ions, which combine with hydroxide ions to form water
• Charging reverses the process, converting nickel hydroxide back to nickel oxyhydroxide and the hydrogen-absorbing alloy absorbing hydrogen
• Nominal cell voltage of 1.2 V, similar to NiCd batteries
• Higher energy density (60-120 Wh/kg) compared to NiCd batteries
• Environmentally friendlier than NiCd batteries due to the absence of toxic cadmium
• Reduced "memory effect" compared to NiCd batteries, but still present to some extent
• Higher self-discharge rate compared to NiCd batteries, leading to shorter shelf life

Comparative Analysis

• Lead-acid batteries have the lowest energy density but are the most affordable and widely used in large-scale applications (automotive, UPS systems)
• NiCd batteries have higher energy density and longer cycle life than lead-acid batteries but are more expensive and environmentally harmful due to cadmium
• NiMH batteries have the highest energy density among the three and are more environmentally friendly than NiCd batteries
  • Suitable for portable electronics and hybrid electric vehicles
• Lead-acid batteries require regular maintenance, while NiCd and NiMH batteries are sealed and maintenance-free
• NiCd batteries have the best low-temperature performance, followed by lead-acid and NiMH batteries
• NiMH batteries have a higher self-discharge rate compared to lead-acid and NiCd batteries

Applications and Use Cases

• Lead-acid batteries widely used in automotive applications (starting, lighting, and ignition), uninterruptible power supplies (UPS), and stationary energy storage systems
• NiCd batteries used in portable power tools, emergency lighting, and aviation due to their robustness and reliability
  • Also used in some industrial applications and older cordless phones
• NiMH batteries popular in portable electronics (laptops, cameras, smartphones), hybrid electric vehicles, and some industrial applications
  • Replaced NiCd batteries in many applications due to higher energy density and reduced environmental impact
• The choice of battery technology depends on factors such as energy density, power density, cycle life, cost, and environmental considerations

Environmental Considerations

• Lead and cadmium are toxic heavy metals that can harm the environment and human health if not properly disposed of or recycled
• NiCd batteries face restrictions and regulations due to the use of cadmium, with many countries implementing battery collection and recycling programs
• NiMH batteries are considered more environmentally friendly than NiCd batteries due to the absence of cadmium
  • Still contain nickel, which can be harmful if not properly handled
• Proper battery disposal and recycling are crucial to minimize environmental impact and recover valuable materials
  • Many countries have established battery collection and recycling infrastructure
• Researchers are working on developing more sustainable and eco-friendly battery technologies to reduce the environmental footprint of energy storage systems

Future Trends and Developments

• Increasing demand for high-performance, cost-effective, and environmentally friendly energy storage solutions
• Research focused on improving energy density, cycle life, and safety of existing battery technologies
  • Nanostructured materials and advanced manufacturing processes show promise
• Development of new battery chemistries and materials, such as lithium-ion, sodium-ion, and solid-state batteries
  • Aim to overcome limitations of current technologies
• Growing emphasis on battery recycling and circular economy approaches to minimize waste and environmental impact
• Integration of battery storage with renewable energy sources (solar, wind) to enable a more sustainable and resilient energy infrastructure
• Advancements in battery management systems (BMS) and smart charging technologies to optimize performance and extend battery life