Energy Storage: Types, Reactions, and Battery Materials

Posted on Feb 22, 2025 in Chemistry

Main Types of Energy Storage

  • Electrochemical: Fuel Cell
  • Electrical: Capacitor
  • Mechanical: Flywheel
  • Thermal: Molten Salt
  • Chemical: Hydrogen
  • Biological: Starch

Gibbs Free Energy

G = Gproducts – Greactants

Voltage: E = -ΔGr / zF

Temperature Dependence: G = H – TΔS

Main Reactions in Batteries

  1. Reconstitution (Major Change)
    • Formation Reaction
    • Displacement
  2. Insertion (Small Change): xA + BC = AxBC

Important Practical Parameters in Batteries

  1. Specific Energy
  2. Energy Density
  3. Operating Voltage
  4. Energy Quality
  5. Charge Capacity

Liquid Electrolytes

Propylene Carbonate, Ethylene Carbonate, Dimethyl Carbonate, Diethyl Carbonate

Li Salts

  • LiClO4
  • LiPF6

Ion Conductivity Trend: Polymer < Liquid < Solid

Advantages of Polymer Electrolytes

  1. Can act as both electrolyte and separator.
  2. Eliminate dendrite growth.
  3. More stable than liquid electrolytes.
  4. Enhanced safety.
  5. Thin films are possible.

General Requirements for Polymer Electrolytes in Li-ion Batteries

  1. Ionic Conductivity: Must be able to achieve large discharge current densities.
  2. Transference Number: Ratio of electric current that is transferred through the movement of Li+ ions.
  3. Thermal and Electrochemical Stability: Must be stable from 0V to 4.5V to work with Li and cathode materials.
  4. Mechanical Properties: Must be easy to manufacture.

Short and Long-Term Nano Battery Targets

  1. Doubling energy density.
  2. 3D nano designs.
  3. High ionic conductivity.
  4. Electrolytes with improved stability.
  5. Assessment of SEI issues.
  6. Shelf life.

How to Determine Ionic Conductivity of a Polymer

  1. Mix polymer electrolytes.
  2. Sandwich the polymer film between two stainless steel disks.
  3. Measure complex impedance.

Models and Equations of Li Conductivity

  • Continuum-Based Models
    • Free Volume Model
    • VTF Model
  • Discrete Models
    • Molecular Dynamics
    • Monte Carlo Simulations

Parameters that Can Affect Ion Conductivity in Polymer Electrolytes

  1. Polymer Host
  2. Li Salt
  3. Filler
  4. Plasticizer
  5. Fabrication Process
  6. Testing Conditions

What is SEI?

During the first charging, electrolytes undergo a chemical reaction that produces a decomposition product. This forms a passive layer (Solid Electrolyte Interphase or SEI) that blocks electron transport while allowing Li+ ions to pass through.

Issues with SEI

Irreversible decomposition of organic solvents greatly affects electrode behavior, potentially causing a battery shortage.

Problems with Rechargeability

  1. Decomposition at unwanted locations.
  2. Shape change.
  3. Dendrites.
  4. Filamentary growth.
  5. Thermal runaway.

Criteria for Cathode Material

  1. High lithium potential.
  2. Insertion must be reversible.
  3. Maximize cell capacity.
  4. Must be stable.

Cathode Classification

  1. Face-Centered
    • Layered Structure (layers to support reversible extraction)
    • Spinel (insertion of Li+)
  2. Hexagonal Array
    • NASICON
    • Olivine

Types of Conventional Capacitors

Variable Trimmer, Film, Mica, Ceramic, Oil or Liquid, Electrolyte

How Does a Fuel Cell Work?

It converts chemical energy from a fuel into electrical energy. Common materials include hydrogen fuel, platinum powder for the anode catalyst, and nickel for the cathode catalyst.

What is Flywheel Energy Storage (FES)?

It works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. Components include:

  1. Steel/carbon fiber composite rotor.
  2. Support bearings (magnetic to reduce friction).
  3. Generator unit.
  4. Vacuum chamber.

Main Types of Polarization

  • Electronic: Stretching of electron clouds.
  • Ionic: Displacement of the relative position of ions.
  • Orientation: Spatial orientation of permanent dipoles.