secondary cell

A secondary cell is a battery cell whose reaction can be reversed by applying electricity (rechargeable). A typical secondary cell is capable of hundreds of charging cycles.

Lead-Acid Battery (Storage Battery)

• $\xi =2\mathrm{V}$
• concentration cell

$$\begin{array}{rlrl}\text{Anode:}& & \mathrm{Pb}+\mathrm{HSO}{}_4{}^{-}& \to \mathrm{PbSO}{}_4+\mathrm{H}{}^{+}+2\mathrm{e}{}^{-}\\ \text{Cathode:}& & \mathrm{PbO}{}_2+\mathrm{HSO}{}_4{}^{-}+3\mathrm{H}{}^{+}+2\mathrm{e}{}^{-}& \to \mathrm{PbSO}{}_4+2\mathrm{H}{}_2\mathrm{O}\end{array}$$

A car battery consists of 6 lead-acid battery cells in series, which produces 12 volts. Cars don’t start at lower temperatures since the cell contracts and there is lesser distance between ions, leading to less ionic potential and voltage. A typical car battery last several years. Water needs to be topped off once in a while since electrolysis of water occurs. 35% sulfuric acid by mass.

Nickel-Cadmium (NiCad) Battery

• Home use
• Typically used in cordless electronic devices (shavers)
• $\xi =1.4\mathrm{V}$
• An occasional complete discharge is recommended to maintain battery capacity.

$$\begin{array}{rlrl}\text{Anode:}& & \mathrm{Cd}(\mathrm{s})+2\mathrm{OH}{}^{-}(\mathrm{aq})& \to \mathrm{Cd}(\mathrm{OH}){}_2(\mathrm{s})+2\mathrm{e}{}^{-}\\ \text{Cathode:}& & 2\mathrm{NiO}(\mathrm{OH})(\mathrm{s})+2\mathrm{H}{}_2\mathrm{O}(\mathrm{l})+2\mathrm{e}{}^{-}& \to 2\mathrm{Ni}(\mathrm{OH}){}_2(\mathrm{s})+2\mathrm{OH}{}^{-}(\mathrm{aq})\end{array}$$

Lithium Battery (Li-Ion Cell)

Anode: $\mathrm{Li}{}_x\mathrm{C}{}_6$ Cathode: $\mathrm{Li}{}_y\mathrm{CoO}{}_2$

• reliable and long service time (2-3 years)
• double the capacity of NiCad
• avoid heat exposure (explosion risk)
• complete discharge recommended once in a while