Week 5 Challenge

Aim/Objective: 

• Aggressive driver and the Power/energy source choice.
• Cell voltage Vs. Energy density of various ESS.
• Cell voltage Vs. Power density of various ESS.
• Negative electrode in battery.

Question 1:

Consider a scenario where an aggressive driver is accelerating very rapidly and braking harshly in a city driving. Is battery better a choice to supply power than UC in this scenario?

1. True
2. False

Why?

The statement above is false. The drivers driving pattern can be conclude here as short power transients. Driver is accelerating and we all know how the power demand  shoots up at the time of acceleration though for a short time. You can see in the graph below. Pa here represents the acceleration power. This power is only needed when we are accelerating. It is still dominant amongst all even though we need this power for short time only

Battery can supply this demand but the cost of manufacturing such batteries is extremely high. On the other hand Ultracapacitor holds very high power which it releases on demand and it can get charge quickly too. This quality of having high power density makes the Ultracapacitor a perfect choice of power source for such transient power demands.

Question 2 & 3 :

Consider the following components.

• Lead acid battery
• Nickel cadmium battery
• Nickel Metal hydride battery
• Lithium ion (specify chemistry) battery
• Ultra Capacitor

Create a plot with energy density on the X Axis and cell voltage on the Y axis.  

Comment on the capabilities of these batteries based on the plot created.

Create a plot with power density on the X axis and cell voltage on the Y axis.

A plot of Energy density Vs. cell voltage is shown below:

 

Ultracapacitor: It can be seen that UC can't be used for high energy demanding applications. Its voltage is greater than that of Lead acid NiCd and NiMH. They are widely used in Electric or hybrid vehicles - to provide a quick burst of acceleration over short distances, or to start the main motor.

NiMH & NiCd: Nickel metal hydride and Nickel cadmium have almost similar cell voltage value but energy density of NiMH is very high than NiCd. NiMH batteries are highly recommend in applications that call for long duration but not a high amp load. Nicd are best suitable for portable power application.

Lead-acid: LA batteries has low energy density as compared to NiMH and NiCd but cell voltage value is high. Lead–acid batteries are used in emergency lighting and to power sump pumps in case of power failure. They were the first choice of energy in BEV. But now they have been replaced by other batteries cause they require frequent maintenance.

Lithium-ion: There are many types of lithium ion battery. They are mainly classified on the basis of cathode material used cause anode remains same in all the cases. In plot we have shown the average energy density of it. Now li-ion is widely used in EVs, mobile phones and many more applications. They rule the above plot, cause they have high energy density and high cell voltage as well amongst all. 

A plot of Power density Vs. cell voltage is shown below:

Suprisingly there is very less data available related to the power densities of above shown ESS. Genearlly the values lies between a certain range but the plot shown above represents the avrage value. Clearly ultracapacitor is the king here.

Question 4:

Consider the following scenario:

A battery has just been manufactured in the battery and has been connected to a charger for the first time. The electrode marked as (1) in the picture below is the negative electrode.

1. True
2. False

The statement above is true. Because during charging process the positive electrode (cathode) loses the electron and this electron travels to the anode as a reverse voltage is apllied to the battery. We shold remember that in almost all the electronics devices cathode is -ive and anode is +ive but battery being the active material has cathode termed as +ive and anode as negative. Thats why behaviour of electrodes in batteries is explained in two ways i.e while charging and discharging. Below fig represents what has been theoretically said.