Fragen

+high specific power [W/kg]

+high power density [W/m³]

+longer lifetime

+maintenance free

+efficiency typ. >96% (Supercap)

-self discharge

-low specific energy [J/kg]

-low energy density [J/m³]

-high cost

+high power density [W/m³]

+very high cycle life

+uncritical deep discharge

+precise SoC determination

+No capacity fade over time

-self discharge (air-resistance, friction…)

-low energy density [J/m³]

-manufacturing cost

-long efficiency chain

-additional systems needed (cooling, vacuum, power electronics..)

+high specific energy [J/kg]

+high energy density [J/m³]

+low cost

+low energy factor

-cyclic ageing (electromagnetic processes)

-average specific power [W/kg]

primary batteries: one time use (not rechargeable), energy density 150-300 Wh/kg, can be used with high C-rates (therm. run has to be taken care of!)

secondary batteries: multiple use (rechargeable), energy density to a maximum of 150Wh/kg, if battery is used sparely (schonend) the lifetime is longer

acqueous systems (NiCd, lead, NiMH): 1.0V to max 2.2V

non acqueous system (Li-Ion): 2.7V to 3.6V

Capacitor:

10°C or 100mV less doubles the lifetime

low impact on the capacitance

Battery:

low temperature -> inner resistance rises -> voltage drops

high temperature -> electrochemical processes happen more easily -> voltage rises

self discharge doubles every 10K

Flywheel:

Due friction in e.g. bearings (Lager) cooling is needed -> otherwise the machine could stop

No direct impact of ability to store energy (low/high ambient temperature)

Above 2.2V, non-aqueous electrolytes must be used because the aqueous electrolyte decomposes.

Lead acid battery (30 - 50 Wh/kg)

NiCd (50 Wh/kg)

NiMH (90Wh/kg)

LiFePO4 (110 Wh/kg)

Lithium-NMC (Nickel, Mangan, Cobalt) (130 Wh/kg)

Lead: Can not be discharged completely, ~2V per cell, high currents, lifespan of some years

NiCd: Cd (Cadmium) is a toxic metal

LiFePO4: less security measures needed, later thermal runaway (> 200°C)

LiNMC: high energy density, earlier thermal runaway (< 160°C)

high temperature can cause electrolyse decomposition or dendrite forming. The decomposition can produce toxic gases and the dendrite can cause a short circuit. Both conditions make the situation worse, resulting in an further increase of temperature which might end in a fire or explosions -> Chain reaction

Li-based batteries with non-organic electrolytes have a better thermic stability. Solid-state batteries are even better in this regard, as no electrolyse decomposition can happen.

Battery:

blue: Cathode

red: Anode

Capacitor:

+Higher efficiency

+can boost and step down a voltage

+stable output voltage, even if input voltage varies

-complex circuit

-higher cost

-ripple in output voltage

-high switching frequencies can cause EMI

light: solar cells

mechanical vibrations: piezoelectric materials

ambienttemperature differences: Peltier-Element

Wind (kinetic energy): micro wind turbines

radio frequencies: antenna’s

if one cell is damaged, the whole system is affected and in the worst case does not work anymore. Different cells might have different self-discharge-rates and different cell capacitances, which can cause a higher stress on other cells.

A batterymanagement system (BMS) can be used. It balances the cells with passive components (resistors, diodes..) or active circuits (charge pump…)

to observe the dynamical behaviour

simulations to find possible optimizations

Model can be used for controller design or prediction-purposes if possible

Battery:

Condensator:

Two electrodes, mechanically seperated by a separator which are electrically connected via the electrolyte. The electrolyte is a mixture of positive and negative Ions in a solvent e.g. water. In the boundary layer where the liquid touches the surface the so called double layer effect takes place.

Double layer capacitance occurs at the interface between an electrode and an electrolyte.

When a conductive electrode is placed in an ionic solution, opposite charges accumulate on both sides of the interface:

• Electrons (or holes) on the electrode surface

• Ions of opposite charge in the electrolyte near the surface

These two layers of charge form an electric double layer, which behaves like a capacitor — storing charge electrostatically.

Very small d -> high capacitance value and electric field strength

if field strength too high -> relative dielectric conductivity decreases

Pseudocapacitance arises from fast, reversible redox (faradaic) reactions at the electrode surface, rather than purely electrostatic charge storage.

In this process, ions from the electrolyte chemically adsorb onto or intercalate into the electrode material, transferring charge through electron exchange.

It behaves like a capacitor because the current–voltage relationship remains nearly linear, but it involves faradaic charge transfer, unlike the non-faradaic double layer capacitance.

Basic principle:

• It consists of two half-cells, each with a metal electrode in a solution of its ions.

• Oxidation occurs at the anode (electrons are released).

• Reduction occurs at the cathode (electrons are gained).

• The electrons flow through an external circuit from anode → cathode, producing electric current.

• A salt bridge or porous membrane allows ion flow to maintain charge balance.

Example: In a Zn–Cu cell:

Chemical reactions that involve the transfer of electrons between substances (A and B, e.g. copper and zinc).

In simple terms:

• Oxidation = loss of electrons

• Reduction = gain of electrons

When these two processes occur together in a system (an electrochemical cell), they create an electric current or are driven by one

Working principle:

It operates based on the reversible movement of lithium ions (Li⁺) between the cathode (LiFePO₄) and the anode (graphite, C) during charging and discharging.

Discharge:

• Lithium atoms in graphite are oxidized, releasing electrons and Li⁺ ions

• Li⁺ ions move through the electrolyte to the cathode, where they combine with FePO₄ and incoming electrons to form LiFePO₄.

• if fully discharged, Li is on cathode side

Charging:

• The process is reversed using external electrical energy.

• Li⁺ ions move back from the cathode (LiFePO₄) to the anode (graphite), and electrons return through the external circuit.

A lead-acid battery has:

• Anode (negative plate): Lead (Pb)

• Cathode (positive plate): Lead dioxide (PbO₂)

• Electrolyte: Dilute sulfuric acid (H₂SO₄)

Discharge:

• Anode (oxidation -> release electrons), Cathode (reduction -> accept electrons)

• Both plates become lead sulfate (PbSO₄), and the sulfuric acid concentration decreases as water forms

Charging:

An external power source reverses the reactions.

• At the anode: PbSO₄ is converted back to Pb.

• At the cathode: PbSO₄ is converted back to PbO₂.

• The electrolyte (H₂SO₄) is restored.

• When energy is supplied (from an engine or motor), the flywheel accelerates, storing energy as rotational kinetic energy:

  E = 1/2 * I * ω

  where I = moment of inertia and ω = angular velocity.

• When energy is required, the flywheel slows down, releasing the stored energy back to the system

windage losses -> evacuation of rotational chamber needed (depending on speed up to 100W lost in evacuated chamber!)

efficiency of electrical machine -> high efficiency needed > 95%

bearings -> friction losses due roatation (if magnetic bearings -> no friction, but supply voltage needed!)

auxilliary systems -> pump, cooling systems, radiators, power electronics…

The Warburg Impedance models diffusion processes in a battery.

The C-rate is a measure of the “load” of an energyy storage.

Unit [1/h]

10 C discharge -> empty in 6 min

0.1 C charge -> charged in 10h

It does not hold information about weight/size.