BTRexpert

Lead-acid batteries (LABs), are the oldest type of rechargeable battery still widely used today. Known for their low cost, robustness, and high surge current capabilities, LABs are a critical component in energy storage, automotive applications, and backup power systems. With growing attention to environmental sustainability, the recycling and clean recovery of LABs have become equally important.

Chemistry of Lead-Acid Batteries

1. Electrochemical Reactions

   Lead-acid batteries operate based on the reversible electrochemical reaction between lead (Pb), lead dioxide (PbO₂), and sulfuric acid (H₂SO₄):

   • Discharge Reaction: PbO₂​ + Pb + 2H₂SO₄​ → 2PbSO₄​ + 2H₂O
   • Charge Reaction: 2PbSO₄​ + H₂O → PbO₂ + Pb + 2H₂SO₄​
2. Components
   • Positive Electrode (cathode during discharge): Lead dioxide (PbO₂)
   • Negative Electrode (anode during discharge): Sponge lead (Pb)
   • Electrolyte: Dilute sulfuric acid (H₂SO₄)
   • Separator: Microporous material preventing short circuit

Types of Lead-Acid Batteries

Flooded (Vented) Lead-Acid Batteries

• Traditional design with liquid electrolyte
• Requires periodic maintenance and water refilling
Subtypes:
• Starting, Lighting, and Ignition (SLI) Batteries: High-current bursts for engine starting, supports vehicle electrical systems, used in cars, motorcycles, and trucks
• Industrial Batteries: Stationary Batteries used in UPS, telecom, emergency lighting, substations, and Traction Batteries Used in forklifts, pallet trucks, electric buses

Valve-Regulated Lead-Acid (VRLA) Batteries

• Sealed, maintenance-free, and spill-proof
• Electrolyte immobilized (absorbed or gelled)
• Pressure relief valves ensure safe operation
Subtypes:
• Absorbed Glass Mat (AGM): Used in start-stop systems, UPS, motorcycles
• Gel Cell: Suitable for solar systems, wheelchairs, marine use

Structural Design and Construction

• Plates: Lead alloy grids with active material
• Separators: Prevent short circuits
• Container: Usually polypropylene
• VRLA Valves:Control internal pressure and gas release

Cycling Technology and Performance

1. Charge and Discharge Cycles
   • Standard cycle life ranges from 500–1000 cycles
   • VRLA batteries often have better deep discharge performance
   • Charge efficiency: ~70–85% depending on type and depth of discharge (DoD)
2. Sulfation
   • Reversible formation of PbSO₄ crystals during discharge
   • Chronic sulfation reduces capacity—mitigated by periodic equalization or carbon additives
3. Recycling Enhancements:
   • Advanced designs incorporate additives like barium sulfate or carbon
   • Use of refined secondary lead improves cycling consistency

Applications

1. Automotive: Starter batteries (SLI), Electric vehicles (limited by weight and energy density)
2. Energy Storage: Solar PV and off-grid systems, Uninterruptible Power Supplies (UPS)
3. Industrial: Forklifts, telecom towers, and emergency systems

Recycling and Environmental Aspects

Lead-acid batteries are over 95% recyclable, making them one of the most recycled consumer products globally.

1. Standard Recycling Process
   • Breaking and Separation
   • Desulfurization and Paste Processing
   • Smelting and Refining
   • Lead Recovery
2. Emerging Recycling Technologies
   • Hydrometallurgy: Uses leaching and precipitation
   • Electrohydrometallurgy: Electrolysis in alkaline/acidic solutions
   • Vacuum Reduction: Pb-Sb alloy separation
   • Electrowinning: Direct recovery from leachate
   • Alkaline Conversion: For cleaner lead oxide production

Lithium-ion batteries (LIBs) have revolutionized modern electronics and transportation since their commercialization in the 1990s. Powering everything from smartphones to electric vehicles (EVs), they offer high energy density, long cycle life, and low self-discharge. As demand for clean energy grows, LIBs play a central role in electrification and grid stabilization. However, sustainability, supply chain pressure, and end-of-life (EoL) challenges now drive innovation in recycling and materials recovery.

Chemistry of Lithium-Ion Batteries

1. Electrochemical Reactions

   LIBs operate by intercalating lithium ions between a cathode and an anode through an electrolyte. The core reaction during discharge is:

   • Cathode (e.g., LiCoO₂): LiCoO₂ → Li_1−xCoO₂ + xLi⁺ + xe⁻
   • Anode (graphite): xLi⁺ + xe⁻ + C₆ → Li_xC₆

   During charging, the reaction reverses.

2. Components
   • Cathode: LiCoO₂, NMC, LFP, LMO, or NCA
   • Anode: Graphite, silicon-carbon composites
   • Electrolyte: LiPF₆ in organic solvents
   • Microporous polymer films
   • Current Collectors: Copper (anode), aluminum (cathode)

Types of Lithium-Ion Batteries

Type	Cathode	Characteristics	Applications
Lithium Cobalt Oxide-LCO	LiCoO2	High energy density	Smartphones, laptops, cameras
Lithium Nickel Manganese Cobalt Oxide-NMC	LiNiMnCoO2	Balanced performance (Energy density, power, cost, safety)	Electric and hybrid vehicles
Lithium Nickel Cobalt Aluminum Oxide-NCA	LiNiCoAlO2	High energy, long cycle life, high specific energy	High-performance EVs (e.g., Tesla)
Lithium Titanate-LTO	Li4Ti3O12	Fast charging, long cycle life, superior safety	Electric buses, military equipment, grid storage systems
Lithium Iron Phosphate-LFP	LiFePO4	Safe, long life, excellent thermal stability	Electric buses, Stationary energy storage,Industrial EVs

Battery Structure

1. Cell Designs
   • Cylindrical
   • Prismatic
   • Pouch cell
2. Electrode Configuration
   • Coated foil electrodes wound or stacked
   • Electrolyte-soaked separator sandwiched in between
   • Encased in sealed housing with safety vents

Cycling Technology

1. Lifecycle and Degradation
   • LIBs typically endure 500–2000+ cycles
   • Aging due to: SEI growth, lithium plating, electrode cracking,electrolyte decomposition
2. Battery Management Systems (BMS)
   • Monitor voltage, temperature, and SOC
   • Prevent overcharge/discharge
   • Enable thermal safety
3. Second-Life Applications
   • Reuse in grid storage, telecom, or off-grid systems

Applications of Lithium-Ion Batteries

1. Consumer Electronics: Phones, laptops, wearables, focus on compact, high energy density
2. Electric Vehicles: Passenger cars, buses, e-bikes, growth driven by climate policies and falling costs
3. Energy Storage Systems (ESS): Utility-scale storage, solar backup, load balancing, LFP and NMC chemistries dominate here
4. Industrial & Aerospace: Power tools, medical devices, drones, satellites

Recycling Technologies

1. Recycling Drivers
   • Environmental hazards (Co, Ni leaching)
   • Resource scarcity
   • Regulatory pressure
2. Conventional Recycling Processes
   • Pyrometallurgy
   • Hydrometallurgy
   • Direct Recycling
3. Emerging Techniques
   • Bioleaching: using bacteria like Acidithiobacillus ferrooxidans
   • Deep Eutectic Solvents (DES): for green extraction
   • Ultrasonic Separation & Cleaning

Nickel-based rechargeable batteries have been central to energy storage for several decades. Among them, Nickel-Cadmium (NiCd) and Nickel-Metal Hydride (NiMH) batteries stand out for their robust performance, wide temperature range, and proven reliability. With the growing push toward sustainable energy and electrification, these batteries remain relevant — especially in hybrid vehicles, power tools, and backup systems.

However, the toxicity of cadmium and the increasing demand for rare earth elements have intensified interest in efficient recycling and material recovery, particularly for spent NiMH batteries

Types of Nickel-Based Batteries

Nickel-Cadmium (NiCd)

• High discharge rates
• Excellent performance in extreme temperatures
• Strong mechanical durability
• Tolerance to abusive charging
• Environmental toxicity due to cadmium

Nickel-Metal Hydride (NiMH)

• Designed as an environmentally safer alternative to NiCd
• Higher energy density
• No cadmium = safer for the environment
• Better specific energy and capacity retention
• Popular in hybrid electric vehicles (HEVs)

Chemistry of Ni-Based Batteries

1. NiCd Battery Chemistry

   NiCd batteries operate through redox reactions between nickel(III) oxide hydroxide and cadmium:

   • Cd(OH)₂ ​+ 2Ni(OH)₂ ​→ Cd + 2NiO(OH) + 2H₂​O
   • Cd + 2NiO(OH) + 2H₂​O → Cd(OH)₂ + 2Ni(OH)₂​

   NiMH Battery Chemistry

   NiMH batteries use a hydride-forming metal alloy (AB₅ or AB₂ types) as the anode and nickel oxyhydroxide (NiOOH) as the cathode:

   • Anode (Negative):
     MH ↔ M + H⁺ + e^-
   • Cathode (Positive):
     Ni(OH)₂ ​+ OH^- ↔ NiO(OH) + H₂​O + e^-
   • Overall:
     MH + NiO(OH) ↔ M + Ni(OH)₂​

Structure and Cell Design

1. Electrode Components
   • Anode: Hydrogen-absorbing alloy (e.g., LaNi₅, ZrTiNi)
   • Cathode: Nickel hydroxide paste on nickel foam
   • Electrolyte: Aqueous KOH solution
   • Separator: Microporous polymer to prevent short-circuits
2. Cell Formats
   • Cylindrical, prismatic, and button cells
   • Usually sealed, vented for pressure control

Cycling Technology

1. Cycling Technology
   • NiCd: ~1000 cycles
   • NiMH: ~500–1000 cycles
   • Full and trickle charge modes available
   • Fast charging via delta-V control

Applications

1. Consumer Electronics: Cordless phones, cameras, toys (historically NiCd, now NiMH)
2. Power Tools: Durable, high discharge rate required
3. Automotive: NiMH batteries are still used in HEVs
4. Aerospace & Military: NiCd batteries valued for reliability under extreme conditions

Recycling Technologies

Recycling is vital due to: the value of Ni, Co, La, Ce, Nd, Pr, and the environmental concerns (especially Cd).

1. Mechanical Pre-Treatment
   • Discharging and dismantling
   • Grinding and sieving to isolate active material
2. Pyrometallurgy
   • High-temperature smelting for Co and Ni recovery
   • Loss of REEs and hydrogen storage alloys
3. Hydrometallurgy
   • Acid/alkaline leaching of metals
   • Solvent extraction, precipitation, electro-winning