Batteries have come a long way since the voltaic cell. Alessandro Volta would be surprised at the newfangled inventions that go by the name battery. One of the biggest changes is the emergence of the rechargeable battery. Both lithium-ion and nickel-cadmium batteries are rechargeable.
Dateline and Materials Used
Nickel-cadmium (NiCd) is one of the oldest rechargeable batteries; lithium ion is among the newest technologies. NiCd uses cadmium for the anode (negative terminal), nickel oxyhydroxide for the electrode (positive terminal) and aqueous potassium hydroxide as the electrolyte. The lithium-ion (li-ion) uses graphite as the anode and lithium oxide for the cathode. The electrolyte is generally a lithium salt.
Energy density in a battery refers to the amount of energy that the battery can contain. Its unit of measure is Wh/kg (Watt hours per kilogram). A lithium-ion battery has greater energy density. A NiCd battery provides about 60 Wh/kg. Lithium-ion batteries come in three chemistries. The lithium-ion manganese and lithium-ion phosphate batteries provide around 110 Wh/kg. The lithium-ion cobalt battery tops the chart at 160 Wh/kg.
Power Density and Voltage
Power density refers not to the run-time but to bursts of power that the battery is capable of. The best combination provides good energy density and power density. Lithium-ion batteries have better power density than nickel-cadmium batteries. The NiCd rates at 1.25 volts. The lithium-ion cell has an initial voltage of 3.6 volts. It also has about twice the capacity of a NiCd battery.
Properly maintained, the nickel-cadmium battery gives about a thousand charge/discharge cycles--the number of times you can recharge the battery. The lithium-ion battery gives between 300 to 500 charge/discharge cycles.
When you recharge a battery without fully discharging it, a temporary loss of cell capacity can occur. This is the dreaded "memory effect" that has haunted NiCd batteries. The cadmium crystallizes, thus reducing the area exposed to the electrolyte. Lowered performance results. The lithium-ion battery displays no memory effect.
Fully discharge the nickel-cadmium battery before recharging. A full discharge, remember, is not bringing it to zero volts, but to the 1-volt level. The lithium-ion battery does not need periodic discharge. Prime (slow-charge) new NiCd batteries. Li-ion batteries do not need to be primed before use. Store unused batteries in a cool, dry place. If you are putting away the batteries, partially charge them, and fully charge before use.
Cost and Disposability
The lithium-ion battery costs about 40 percent more to manufacture. This is because it has an extra protection circuit to monitor the voltage and current. The cadmium in the NiCd is toxic. The federal government classifies it as hazardous waste. The li-ion is nonhazardous waste.