Prior to 1990, Nickel Cadmium (NiCd) and Lead Acid (PbA) technologies dominated the rechargeable battery market. During the 1990's, Nickel Metal Hydride (NiMH) and Lithium Ion (Li-Ion) rechargeable batteries emerged and today hold high volume positions in various markets alongside NiCd and PbA. Each with strengths and weaknesses, the collective issues of all rechargeable battery technologies revolve around life (cycle and calendar), safety, recharge time, power delivery, extreme temperature performance, and environmental friendliness.
A tremendous amount of activity is directed at developing battery technologies that address these issues. For all battery technologies, the ability to achieve high performance in each area of criteria are directly determined by how the battery is constructed; specifically, the types of electrodes and electrolytes used.
All batteries produce energy from electrochemical reactions. Batteries are comprised of several components, but primarily consist of the following:
- A positive electrode (the cathode) and a negative electrode (the anode)
- An ionic electrolyte: a solution that contains and aids the movement of ions (charged particles) back and forth between the two electrodes
- A porous separator (ensures the two electrodes do not touch but allows ions to travel back and forth between the electrodes)
When a battery is charged, electrons travel from the positive electrode to the negative electrode. On discharge, these electrons return to the positive electrode releasing energy in the process.