electrolyte

An electrolyte is a liquid or solution that contains particles able to carry electric charge.

• When a salt, acid, or base dissolves in water, it can split into tiny charged particles called ions. Positive ions and negative ions move through the liquid.
• In a voltaic cell, these moving ions allow the chemical reactions at the two metal electrodes to continue. This helps the cell produce a steady electric current in the outside wire.
• Pure water is a very poor electrolyte because it has very few ions. Saltwater, lemon juice, vinegar, and dilute acids conduct much better because they contain more ions.
• Think of ions as tiny delivery vehicles inside the liquid: they carry charge from one part of the cell to another, while electrons travel through the external wire.
• The electrolyte does not have to be a liquid. Some batteries use a paste or gel electrolyte, but it still needs mobile ions to work.

That is why lemon juice can help make a simple battery work: its acidic liquid provides ions that complete the chemical pathway inside the cell.