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Energy Storage > Midterm Review > Flashcards

Midterm Review Flashcards

1
Q

What are the main types of energy storage and how are they classified?

A

Electrochemical
*Batteries
*Fuel Cells

Electrical
*Capacitors/Supercapacitors

Mechanical
*Springs
*Flywheels

Thermal
*Molten Salt

Chemical
*Hydrogen

Bio
*Starch
*Glycogen

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2
Q

What is a Ragone Plot?

A

Plot that compares the Energy Density [Wh/kg] to the Power Density [W/kg] of various electrochemical devices

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3
Q

How does a conventional capacitor work?

A

Electrical component that stores electric charge/energy in an electric field. It has two conductive plates separated by a dielectric which is an insulating material.

When voltage is applied across the terminals of a capacitor, an electric field develops across the dielectric, causing temporary storage of charge. The amount of charge a capacitor can store depends on its capacitance, which is measured in Farads.

C = e_0e_r*A/d

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4
Q

How does a supercapacitor/double capacitor work?

A

Operates under the same basic principle as a conventional capacitor however they differ significantly in their construction and materials which allows them to offer much higher capacitance and energy density than conventional capacitors.

Supercapacitors consist of two porous electrodes that are soaked in an electrolyte and separated by an ion-permeable membrane (separator). The electrodes in supercapacitors are made from materials with very high surface area, such as activated carbon, carbon nanotubes, or graphene.

**Electric Double Layer Capacitance: when voltage is applied, ions in the electrolyte arrange themselves at the surface of the electrodes in a layer (creating what is known as an electric double layer or Hemholtz layer), but there is no chemical reaction involved.

The separation of charge at the interface between the electrode and the electrolyte stores energy. This is a highly reversible process, allowing supercapacitors to be charged and discharged many times.

MORE:
At the interface between the liquid ionic electrolyte and each electrode, a special phenomenon occurs… The ions in the electrolyte solution line up like a wall and create a liquid electrode.

The SOLID electrode plate, and the newly formed lined up ion wall together create a capacitor with a potential difference across them, hence the “double layer”. This exists on each side of the capacitor.

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5
Q

Supercapacitor Materials: Electrodes

A

Activated Carbon, carbon nanotubes, graphene, metal oxides

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6
Q

Supercapacitor Materials: Electrolytes

A

Aqueous Electrolytes, organic electrolytes, ionic liquids

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7
Q

Supercapacitor Materials: Separators

A

Polymeric membranes (polypropylene (PP), polyethylene (PE), and polyvinylidene fluoride (PVDF)), ion exchange membranes

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8
Q

Supercapacitor Materials: Current Collectors

A

Aluminum foil, nickel foil

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9
Q

How does a LIB work?

A

Composed of anode, cathode, electrolyte, (and a separator if the electrolyte is a liquid/gel)

During Discharge:
ions move out of the anode and travel to the cathode through the electrolyte and separator (the separator allows Li ions to travel through but not free electrons). The free electrons go through the external wire and power the circuit and eventually when most Li ions are moved to the other side they pair with the electrons again and the battery is “dead”.

During Charging:
Ions move back from the cathode to the anode through the separator. Electrons leave the cathode and travel externally through the external wire to the load. Li ions enter the anode.

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10
Q

What are the cons for LIB?

A

Dendrite growth: dendrite growth is the growing of metallic branch-like bridge from one electrode to the other, causing electrical shorting. This mainly occurs when Lithium metal is used as the anode and therefore we dont use Lithium metal as an anode.

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11
Q

LIB Cathode materials

A

Lithium Cobalt Oxide (LiCoO₂)
Lithium Manganese Oxide (LiMn₂O₄)
Lithium Iron Phosphate (LiFePO₄)
Lithium Nickel Manganese Cobalt Oxide (NMC, LiNiMnCoO₂)
Lithium Nickel Cobalt Aluminum Oxide (NCA, LiNiCoAlO₂)

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12
Q

LIB Anode materials

A

Graphite
Lithium Titanate (Li₄Ti₅O₁₂)
Silicon
Silicon Nanowires (SiNWs)
Carbon Nanotubes (CNTs)

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13
Q

LIB Materials: Electrolyte

A

Liquid Electrolytes

Solid Electrolytes

Polymer

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14
Q

LIB Materials: Separator

A

Polyethylene (PE)

Polypropylene (PP)

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15
Q

Gibbs Free Energy Equation

A

G(p,T) = H - TS

Where H is enthalpy
T is temperature
S is entropy

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16
Q

Gibbs Energy Balance: LIB

A

Gr = -zFE

z is charge number (electrons)
E is voltage between electrodes
F is Faraday’s constant = 96,500 Coulombs per mole

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17
Q

Main reactions in LIB

A

1.) Reconstitution
a. Formation
A + B = AB

  b. Displacement
          A + BX = AX + B

2.) Insertion (Intercalation)

           xA + BC = A_xBC
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18
Q

Important practical parameters in LIB

A

Specific Energy - energy per unit weight
Energy Density - energy per unit volume
Operating Voltage
Energy Quality
Charge Capacity
Stored Energy

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19
Q

Why do practical battery parameters not match the calculated theoretical values?

A

Presence of passive components (separator, current collectors, etc.)

Effective utilization of the active components in the chemical reactions are less than optimal (they add to weight but do not contribute to the transduction between electrical and chem. energy)

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20
Q

What are typical organic liquid electrolytes used in LIB’s?

A

Propylene Carbonate (PC), Ethylene Carbonate (EC), Di-Methyl Carbonate (DMC), Diethyl Carbonate (DE)

liquid electrolytes may be a mixture of two or more

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21
Q

What are typical Li Salts used in LIB’s?

A

LiClO4, LiPF6

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22
Q

Examples of Solid Polymers in LIB’s?

A

PolyEthylene Oxide (PEO), PolyVinyliDeneFluoride (PVDF)

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23
Q

Electrolyte Classification

A
  1. Liquid electrolytes
    -Composed of lithium salts (LiPF6, LiClO4)
    -High ionic conductivity, easy to manufacture
    -Generally liquid electrolytes do not use fillers or plasticizers.. Their performance is mainly dictated by the solvent and salt combination
  2. Solid Polymer Electrolytes (SPE’s)
    -Composed of a polymer matrix (polyethylene oxide “PEO”, that holds lithium salts. The polymer itself facilitates ion transport
    -Safe, lightweight, flexible, but lower ionic conductivity at room temp. compared to liquid electrolytes.
    -Plasticizers may be added to improve ionic conductivity and mechanical flexibility by reducing the crystallinity of the polymer
    -Fillers (ceramic nanoparticles) are also used to enhance mechanical strength and ionic conductivity
  3. Gel Polymer Electrolytes (GPE’s)
    -Similar to SPE’s materials but incorporate a liquid component within the polymer matrix to form a gel-like substance. The matrix is still primarily a polymer like PEO, with lithium salts dissolved in it.
    -Combine high ionic conductivity of liquid electrolytes with the mechanical stability of SPE’s
    -Plasticizers are often used to facilitate the dissolution of more liquid within the polymer, enhancing ionic conductivity.
    Fillers can be added to improve mechanical properties and ionic conductivity.
  4. Ceramic Electrolytes
    -Materials: Made from solid ceramic materials (e.g., lithium phosphorus oxynitride or LiPON, garnet-type materials like Li7La3Zr2O12).
    -Characteristics: High ionic conductivity (in some types), excellent thermal stability, and non-flammability.
    -Usage of Fillers/Plasticizers: Not applicable in the traditional sense. Ceramic electrolytes do not typically incorporate plasticizers or polymeric fillers, as they are solid-state materials.
  5. Polymer Nanocomposite Electrolytes
    -Materials: A subset of composite electrolytes that specifically incorporate nanoscale fillers into the polymer matrix.
    -Characteristics: Enhanced mechanical properties and ionic conductivity due to the high surface area and unique interactions at the nanoscale.
    -Usage of Fillers/Plasticizers:
    Nanomaterials (e.g., nano-sized ceramic particles, carbon nanotubes, graphene) are used as fillers to improve conductivity and mechanical strength.
    Plasticizers can be used to enhance the polymer’s flexibility and ionic conductivity.

Summary:
Liquid and Gel Polymer Electrolytes are versatile and have high ionic conductivity but might require measures to enhance safety due to their liquid components.
Solid Polymer and Ceramic Electrolytes offer enhanced safety and stability but often at the cost of lower ionic conductivity, especially at room temperature.
Composite and Polymer Nanocomposite Electrolytes are designed to harness the benefits of both polymers and ceramics, using fillers to enhance conductivity and strength, and sometimes plasticizers to improve flexibility.
Each type of electrolyte has its advantages and trade-offs, and the choice depends on the specific requirements of the battery application, including energy density, power output, operating temperature range, safety, and cost.

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24
Q

What are the two main phases to Gel Polymer Electrolytes?

A

Liquid salt/Plasticizer solution and Solid Polymer Matrix

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25
Q

What are advantages/disadvantages of Polymer electrolytes in LIB’s?

A

Advantages:
-Can act as both electrolyte and separator
-Can eliminate dendrite growth
-Can conform to the varying volume of electrodes during cycling
-Less reactive and thermodynamically more stable towards lithium compared to liquid electrolytes
-Safer
-Flexible (thin films) good for nanoscale batteries

Disadvantages:
Low ion conductivity
Expensive

26
Q

What is the effect of nanofillers in polymer electrolytes in LIB’s?

A

Nanofillers increase ion conductivity of polymer electrolytes by 2-3 orders of magnitude

Fillers play a direct role in salt dissociation and possibly ion mobility

27
Q

What is the effect of plasticizer in polymer electrolytes in LIB’s?

A

Plasticizers have been shown to increase ionic conductivity, but mechanical properties can be compromised.

28
Q

What are general requirements for polymer electrolytes in LIB’s?

A
  1. Ion Conductivity: must be high to achieve large discharge current densities; at minimum it should compete with the values for liquid electrolytes
  2. Transference Number: must be close to unity; a transference number of 0.5, means that only half of the charges are transferred through the movement of lithium ions.
  3. Thermal and Electrochemical Stability: must be thermally stable for a broad operation temperature range; must be electrochemically stable from 0V to 4.5V to be compatible with lithium and cathode materials.
  4. Mechanical Properties: must be adequate for manufacturability and structural stability during operation.
29
Q

What are some short-term and long-term nanobattery targets?

A

-Doubling the energy density of lithium-ion batters using nanomaterials
-Three-dimensional nanobattery designs and enhancing power density
-High ionic conductivity electrolytes especially at low temperatures
-Electrolytes with improved voltage stability
-Assessment of solid electrolyte interface (SEI) issues
-Cost-effective manufacturing
-Longer shelf-life

30
Q

How do you determine LI ion conductivity of a polymer electrolyte?

A

sigma = d/RS

R: Bulk resistance
d: polymer thickness
S: film surface area

  1. Mix polymer electrolyte components
  2. Sandwich polymer film between two stainless steel discs
  3. Measure complex impedance
31
Q

What parameters can affect ion conductivity in polymer nanocomposite electrolytes?

A

Filler type (ceramic nanoparticles, metal oxides, carbon nanotubes, graphene) and surface characteristics

Filler concentration

Polymer-Filler interaction

Ion Transport pathways

Temperature

Electrode-electrolyte interface

32
Q

What is solid electrolyte interphase (SEI)?

A

During the first charging of the Li ion battery, the electrolyte undergoes reduction at the negatively polarized graphite surface

The chemical reaction of electrolyte leads to the formation of a passive layer made of organic and inorganic electrolyte decomposition products

Ideally, the passivation layer prevents further electrolyte decomposition by blocking the electron transport while allowing Li ion transport

This passivation layer is called “solid electrolyte interphase” or SEI

This is important because every SEI parameter such as composition, thickness, morphology, and compactness, can significantly affect battery performance.

33
Q

Issues with SEI

A

Formation Variability: The SEI layer’s composition and thickness can vary, affecting battery performance and lifetime.

Ionic Conductivity: SEI may hinder ion transport, reducing battery efficiency and capacity.

Chemical Stability: Unstable SEI can decompose, affecting battery safety and longevity.

Mechanical Stress: Volume changes during charge-discharge cycles can crack SEI, exposing new electrode surface and leading to capacity loss.

Growth Over Time: Continuous SEI growth consumes lithium and electrolyte, leading to capacity fade.

34
Q

Problems with rechargeability of elemental elctrodes (such as Li metal)?

A

Deposition of unwanted locations
-Li metal would be deposited at current collector and locations other than the electrode (which is where decomposition is desired)

Shape change
-The location of Li electro-deposition (during charging) is not the same as where de-plating (during discharge) took place, thus leading to shape change.

Dendrites
-Local gradient of the element’s chemical potential in the electrolyte adjacent to solid electrode surface
-Surface roughness or protuberance on the electrode grows at a faster rate than the rest of the interface, leading to dendrite growth

Filamentary Growth
-A different phenomenon often mistaken for dendrite formation
-The presence of a reaction product layer upon the growth electrode/electrolyte interface
-The useful layer is referred to as SEI which allows passage of ions
-The harmful layer is when it is ion blocking, and significantly increase the interfacial impedance

Thermal Runaway
-The reactions at the electrode/electrolyte interface are exothermic and cause local heating
-This problem is dramatically increased due to cycling
-It can lead to serious safety issues

35
Q

What are the criteria for the cathode materials in LIB’s?

A
  1. The insertion compound Li_xM_yX_z should have a high lithium chemical potential to maximize the cell voltage
  2. The insertion compound must permit a large amount of lithium, x, to be inserted/extracted, to maximize cell capacity.
    -Combination of high capacity and high cell voltage can maximize energy density (capacity x voltage)
  3. The lithium insertion/extraction process must be reversible
    -No or minimal changes in the host structure over the entire range x of lithium insertion/extraction
    -This leads to good cycle life for the battery
    -This requires that the insertion compound has good structural stability without breaking any M-X bonds
  4. The insertion compound must support mixed conduction. It should have both good electronic conductivity and good lithium ion conductivity
    -This property will minimize polarization losses during charge/discharge process
    -This property will support high current and power densities
  5. The cathode material must be chemically stable without undergoing any reaction with the electrolyte over the entire range of lithium insertion/extraction
  6. The redox energy of the cathode material must lie within the band gap of the electrolyte to prevent unwanted oxidation or reduction of the electrolyte
  7. Commercially, the cathode material must be inexpensive, lightweight and environmentally friendly.
36
Q

How are the dielectric materials classified? What are some characteristics of each type?

A

Classified by either Ferroelectric or Non-ferroelectric

Ferroelectric: Electric polarization is actuated by external electric fields
-Non-polar materials: electric field can only cause elastic displacement of electron clouds, so they exhibit only electronic polarization
-Semi-polar/Nonpolar materials: Electric field will cause both electronic polarization and ionic polarization
-Polar/Dipolar materials: Exhibit all three fundamental tyhpes of polarization: electronic, ionic, and orientational polarization

Non-ferroelectric:
-Permanent electric field
-Named in analogy to a ferromagnetic material that has a permanent magnetic pole
-A ferroelectric material is normally in single crystalline or polycrystalline material which can transition from ordered to disordered phase and vise versa
-Exhibit spontaneous electric polarization over a certain temperature range
-This critical temperature is known as the “Curie Temperature”

37
Q

Three main types of polarization?

A

Electronic, Ionic/Atomic, Orientational

Electronic polarization is the displacement of electrons relative to nuclei in an atom under an electric field, affecting all materials and is instantaneous.

Atomic (Ionic) polarization involves the displacement between positive and negative ions in ionic materials, leading to polarization when exposed to an electric field.

Orientational (Dipolar) polarization occurs in materials with permanent dipoles, which align with an electric field, significant in polymers and biological molecules, and is temperature-dependent.

38
Q

What are the different types of conventional capacitors?

A

Variable/”air capacitors”
Trimmer capacitor
Film capacitor
Mica capacitor
Ceramic capacitor
Oil or liquid dielectric capacitor
Electrolytic capacitor

39
Q

Supercapacitor Schematic (different types)

A

Two main branches are:
Double-Layer Capacitors and Pseudocapacitors

Double layer capacitors store their charge Electrostatically in the Hemholtz Layer and Pseudocapacitors store their charge Electrochemically (Faradaic charge transfer)

Double-Layer Capacitors can further be broken down into Activated Carbons, Carbon Aerogels, and Carbon Nanotubes

Pseudocapacitors can further be broken down into conducting polymers and metal oxides

There are also hybrid capacitors which combine both methods of charge storage; electrostatically and electrochemically

40
Q

What are the different types of thermal energy storage?

A

Molten Salt - Solar Towers

41
Q

What are the different types of mechanical energy storage?

A

Flywheels (E = 1/2*Iw^2)

Hydroelectric (dams and pump-storage systems)

Springs

Compressed air

42
Q

What are the different types of chemical energy storage?

A

Hydrogen Storage:
Physical storage of hydrogen
-Liquid hydrogen
-Gaseous hydrogen
-Cryo-compressed

Chemical storage of hydrogen
-Metal hydrides
-Carbohydrates
-Hydrocarbons
-Ammonia

43
Q

What are the different types of biological energy storage?

A

Biodiesel

Starch

Glycogen

44
Q

What is a fuel cell?

A

Fuel cells are devices that convert chemical energy storage from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. They produce electricity, water, and heat as by-products

45
Q

What are the key components of fuel cells?

A

Anode, cathode, electrolyte.

The anode is where the fuel is oxidized, the cathode is where oxygen reduction takes place, and the electrolyte conducts ions between the two electrodes.

46
Q

The role of hydrogen fuel cells

A

Hydrogen is often used as the fuel in a fuel cell because it has high energy content and produces only water when it reacts with oxygen, making it an environmentally friendly option.

47
Q

What are the chemical reactions in a fuel cell?

A

In a hydrogen fuel cell, hydrogen gas (H2) is oxidized at the anode to produce hydrogen ions (H+) and electrons. The electrons flow through an external circuit to the cathode, where they contribute with oxygen (O2) and hydrogen ions to produce water (H2).

48
Q

How do fuel cells generate electricity?

A

Electricity is generated in fuel cells by the flow of electrons from the anode to the cathode through an external circuit. This flow of electrons provides the electrical power.

49
Q

What are the benefits of Fuel Cells?

A

Fuel cells are efficient, can operate continuously as long as fuel is supplied, produce low to zero emissions, and have a high energy density compared to batteries.

50
Q

What is anode catalyst in a fuel cell?

A

Anode catalyst is a material that breaks down the fuel into electrons and ions. The common anode catalyst is fine platinum powder.

51
Q

What is cathode catalyst in a fuel cell?

A

Cathode catalysts turn ions into the waste chemicals like water or carbon dioxide. The cathode catalyst is made up of nickel.

52
Q

What is a Proton Exchange Membrane Fuel Cell?

A

A PEM fuel cell is a type of fuel cell that uses a solid polymer as an electrolyte and operates at relatively low temperatures. It’s known for its quick start-up time and suitability for applications requiring varying power outputs.

53
Q

How does a PEM fuel cell differ from other fuel cells?

A

PEM fuel cells use a solid polymer electrolyte (membrane), whereas other fuel cells might use liquid electrolytes. This solid membrane only allows protons (positive hydrogen ions) to pass through it, blocking electrons

54
Q

How do electrolytic capacitors work and why do they have polarity in connection?

A

An electrolytic capacitor is nearly the same as a supercapacitor but it isn’t “super”. They key here is that they both use/have electrolyte. The supercapacitor has the hemholtz layer that makes it different.

55
Q

Describe polarization in ferroelectric materials

A

Ferroelectric materials exhibit spontaneous electric polarization over a certain temperature range.

This critical temperature is known as the Curie temperature and defines a phase transition from ordered to disordered.

56
Q

Describe the components of flywheel energy storage (FES) system

A

Rotor (flywheel), bearings, electric motors/generators

57
Q

Most common polymer electrolyte membrane material for fuel cells

A

Nafion

58
Q

Two main types of fuel cells

A

Hydrogen Fuel (Proton Exchange Membrane, PEM)

Solid Oxide

59
Q

General requirements for Polymer Electrolytes

A
  1. Ionic conductivity: must be high
  2. Transference Number: must be close to unity
  3. Thermal and electrochemical stability: must be thermally stable for broad operation temperature range
  4. Mechanical Properties: must be adequate for manufacturability and structural stability
60
Q

What is Curie temperature

A

Critical temperature that defines a phase transition from ordered to disordered phase. This is the temperature at which a ferroelectric material will exhibit spontaneous electric polarization

Energy Storage (2 decks)

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