The positive and negative plates of a lead-acid battery in a charged state are lead dioxide & sponge lead respectively.
In fact, both positive & negative plates are constructed using an alloy of lead grids on which active material viz. lead sulphate is applied by pasting in the case of pasted plate batteries.
In the case of the tubular positive plate, lead-acid batteries the negative plates are made by pasting lead sulphate to mesh type negative lead grids whereas positive plates are made by filling lead sub oxide in a spine grid encased with a tubular bag. This filled positive plate is pickled by dipping in a dilute solution of sulphuric acid so that the active material lead sub oxide reacts with sulphuric acid & becomes lead sulphate.
The active material of both the plates viz. lead sulfate is then formed using a rectifier. The rectifier charges the positive & negative plates which are placed in jars containing sulphuric acid. During this process of charging a redox reaction changes the lead sulfate of positive by oxidation to lead dioxide and changes the lead sulfate of negative by reduction to spongy lead.
A lead-acid battery is a secondary battery. The chemical reactions taking place during charge & discharge are reversible. These rechargeable batteries can be used for a certain number of cycles as defined by the manufacturer.
Thus these lead-acid batteries have both positive & negative plates which are lead sulfate when in discharged state and are lead dioxide as positive plates and sponge lead as negative plates when the batteries are in a fully charged state.
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Ramesh Natarajan Kailad
UNIK Techno Systems Pvt Ltd