- Q1.) Discharge
- Ans.) Electrons flow from anode
through the external load to the cathode. To complete the circuit
ions pass through the electrolyte between anode and cathode.
- Q2.) Charge
- Ans) The recharge process reverses the
flow of electrons and the anode and cathode roles. Whereas the
terminal which under discharge was oxidized, it is now reduced, and
the terminal which under discharge was reduced is now oxidized. The
circuit is completed by transfer of ions through the electrolyte. In
a primary battery once discharged, the process cannot be reversed
and it is discarded, in a secondary battery or storage battery a
recharge process can be used to renew the unit
Electrochemical principals and reactions:/ performance
- Ans.) Several factors affect the
conversion efficiency of a cell. The activation polarization, the
concentration polarization, and internal impedance or IR loss¡¤.
The total internal impedance of a cell is the sum of the ionic
resistance of the electrolyte and the resistances of current
carrying components. When operated at low current discharge rates,
the polarization and IR losses are at minimum, thus the output
voltage is near the open circuit no load voltage and can deliver
most of its available energy. With higher currents, the IR losses
increase, lowering the output voltage at the terminals and the
discharge slope is a steeper decline. A common way to specify the
charge and discharge current of a battery is the C rate. It denotes
the rate of total battery capacity. It is calculated by dividing the
charge or discharge current by the total numerical battery capacity
¡£Ampere-hours, Ah¡¤. For example a 30Ah
battery is discharged with a current of 6A. The C rate is equal to
6A / 30Ahr=0.2C rate, also expressed fractionally as a C/5 rate.
- Ans.) A battery life will be less at
lower temperatures. As the temperature is lowered the
electro-chemical activity lessens and the internal resistance
increases. This does not mean that the higher the temperature, the
longer life is achieved. Depending upon the type of battery, too
high a temperature will cause chemical deterioration and loss of
capacity. The main thing to remember is to keep batteries cool
during storage and warm ¡£never hot¡¤
during operation. Consult the manufacturers specifications for
recommendations and limits.
- Q5.) Battery age
- Ans.) Things that influence the life
of a battery include the cell design, the electro-chemical process,
temperature, and time. During storage, some battery types develop
protective films or coatings on the active material. Once placed
into service, these cells may experience what is called
"voltage delay", a lower voltage output temporarily until
the film is broken through by the electro-chemical reaction. The
films can greatly extend the shelf life of the cell.
- Q6.) Battery capacity
- Ans.) The capacity of a battery is
expressed in units of electric charge, coulombs or ampere-hours.
- Q7.)What the maximum
discharge current of Li-ion battery?
- Ans.) About 2C for continuous
discharge and 3C for instantaneous discharge. But these numbers can
be changed by re-designing the battery. For example, by sacrificing
about 25% capacity we can increase the maximum discharge rate to 6C.
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