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Secondary batteries:

Secondary (rechargeable) batteries can be recharged by applying a reverse current, as the electrochemical reaction is reversible. The original active materials at the two electrodes can be reconstituted chemically and structurally by the application of an electrical potential between the electrodes to “inject” energy. These batteries can be discharged and recharged many times.

Applications:

These fall into two categories:

(a) The battery is used as an energy storage device. It is constantly connected to an energy source and charged by it. It can then release the stored energy whenever needed, e.g. in

  • Car battery used to start engine
  • Aircraft systems
  • Standby power resources
  • Emergency no-fail systems

(b) The battery is used as a primary battery would be but is then recharged instead of being disposed of, e.g. in

  • Electric vehicles
  • Mobile phones
  • Cameras
  • Power tools
  • Toys
  • Portable computers

Advantages:

  • High power density
  • High discharge rate
  • Good low temperature performance

Disadvantages:

  • Lower Energy density
  • Poorer charge retention
  • Safety issues
  • Lack of standards
  • High initial costs

 

The table below demonstrates the properties of various rechargeable batteries:

System Nominal Cell Voltage (V) Capacity (Wh/kg) Advantages Disadvantages Applications
2.00
35
Low cost; good high and low-temperature operation
Low cycle life; low energy density; poor charge retention
Cars; lawn mowers; aircraft
Ni/Cd
1.20
30
Good physical durability; good charge retention; good cycle life
High cost; memory effect
Aircraft; emergency power applications
Ni/Fe
1.20
60
Good physical durability; long cycling and standing life
Low power and energy density; high self discharge; high cost
Stationary applications; fork lift trucks
Ni/Zn
1.60
27
High energy density; low cost; good low-temperature performance
Poor cycle life
Electric scooters/bikes; military vehicles
Zn/AgO
1.50
90
Highest energy density; low self discharge; high discharge rate
High cost; low cycle life; low performance at low temperatures
Military equipment eg torpedo propulsion, submarines
Cd/AgO
1.20
55
High energy density; low self discharge; Good cycle life
High cost; low performance at low temperatures
Portable power tools; satellites
Ni/H2
1.40
55
High energy density; good cycle life; can tolerate over charge
High initial cost; self discharge proportional to H2 pressure
Aerospace
Ag/H2
1.40
80
High energy density; good cycle life
High cost - limited to military and aerospace applications
Aerospace
up to 4.2
135
High specific energy; good shelf life; moldable; non-volatile
High cost; expensive control methods needed for charge/discharge
Mobile phones

 

 


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