Energy Storage and materials

Current (symbol, definition, Units, equation)

I, charge per second, Amps (A) or Coulomb/Sec C/s, I= dQ/dt

Resistance (symbol, definition, Units, equation)

R, Opposes or restricts the flow of current or ions, contributes to losses in the battery. (ohm (Ω)), V=IR, R=V/I

Power (symbol, definition, Units, equation)

P, energy delivered/time, watt (W), joule per second (J/s), P=IV

Bulk electrolyte conductivity (symbol, definition, Units, equation)

(σ bulk), the ability for ions to move through an electrolyte, mS/cm, σeff = σbulk x ε/τ²

effective ionic conductivity (symbol, definition, Units, equation)

(σeff), the ability for ions to move through an electrolyte once it is filled into a porous separator or a composite electrode, ms/cm, σeff = σbulk x ε/τ²

Discharge or C-rate (Meaning, and symbol)

_C, how fast the battery can release charge over a period of time, 1C means discharged over 1 hour.

Typically shows up as the X axis of a ragone plot

Tortuosity

(τ), applies to ion transport. it is the ratio of the length of the path the ion takes to its destination / the distance to the destination.

LCO (LiCoO_2) (which electrode, specific capacity, voltage range, phase)

(CAM, ~140-160mAh/g, 3.8-4.2V, single phase (sloping))

NMC (LiNiMnCoO_2) (which electrode, specific capacity, voltage range, phase)

(CAM, ~160-200mAh/g, 3.6-4.2V, single phase (sloping))

NCA ({LiNiCoAlO_2) (which electrode, specific capacity, voltage range, phase)

(CAM, ≥ 200mAh/g, ~3.6-4.2V, Single phase (sloped))

LMO (LiMn_2O_4) (which electrode, specific capacity, voltage range, phase)

(CAM, ~130mAh/g, ~4V, 2 phase (flat))

LFP (LiFePO_4) (which electrode, specific capacity, voltage range, phase)

(CAM, ~160-170mAh/g, ~3.4V, 2 phase (flat curve))

Sulfur (Li-S) (which electrode, specific capacity, voltage range, phase)

(CAM, ~1,675mAh/g, 2V, 2 phase (flat))

Ordered Graphite (LiC_6) (which electrode, specific capacity, voltage range, phase)

(Anode, ~372mAh/g, .2V, Multi phase, 2-phase (flat and stepwise))

Disordered Carbon

(Anode, ~186mAh/g, ~0-1V, 1-phase(sloped))

Silicon Alloys (Li_15Si_4/Li_22Si_5) (which electrode, specific capacity, voltage range, phase)

(Anode, ~3,000mAh/g, .2-.4V, Multi phase)

Lithium Titanate (LTO, Li_4Ti_5O_12) (which electrode, specific capacity, voltage range, phase)

(Anode, ~140mAh/g, 1.4-1.6V, 2-phase (flat))

What are the X and Y axes on a standard Ragone plot, and what type of scale is used?

Y-Axis: Specific Energy (Wh/kg). X-Axis: Specific Power (W/kg). It uses a Log-Log scale to cover multiple orders of magnitude.

What do diagonal contour lines running across a Ragone plot represent?

Lines of constant discharge time (t=Energy/Power)

Why does total usable energy drop on a Ragone plot when power demand increases?

Higher current (I) increases internal Ohmic (I x R_cell) and mass transport polarization losses (Delta E_iR), dissipating usable energy as heat (P_heat) = I^2 x R_cell).

What do the anodic and cathodic current peaks represent on a Cyclic Voltammogram?

• Anodic Peak (Top / Positive Current): Oxidation reaction (extracting Li+ / charging).

• Cathodic Peak (Bottom / Negative Current): Reduction reaction (inserting Li+ / discharging).

What does an increase in peak separation (Delta V_peak) indicate on a CV plot as scan rate increases?

Significant overpotential losses caused by high internal resistance (iR drop) or slow interfacial kinetics.

How is CV used to determine the electrochemical stability window of a liquid electrolyte?

By sweeping voltage across inert electrodes until a sudden exponential current spike occurs, signaling electrolyte breakdown/decomposition.

What is plotted on the X-axis and Y-axis of a Cyclic Voltammogram (CV)?

• X-Axis: Applied Potential (V or E, in Volts vs. Li/Li+) the controlled independent variable linearly swept at a set scan rate (v= dE/dt).

• Y-Axis: Measured Current (I, in mA, A/g, or mA/cm²) the dependent response measured by the potentiostat.

What is plotted on the X and Y axes of a Cycle Life plot?

Discharge Capacity (Ah, mAh/g) or Capacity Retention (%). X-Axis: Cycle Number (integer count of full charge-discharge cycles)

Why does cycling a cell between 20% and 80% SOC significantly extend its cycle life?

Avoiding high voltages (100% SOC) prevents high-potential electrolyte oxidation and slows down SEI on the electrodes