Electrochemical cells, which we commonly call batteries, have been a part of our daily lives since most of us were born. From their invention in 1800 by Alessadro Volta, batteries operate on the principle that ions can flow in a chemical reaction from one type of metal, called a cathode, through a salt solution to another metal, called an anode. When these metals are connected with a metal wire, electrons flow from anode to cathode. In short, batteries store and discharge electrical energy, enabling us (among other activities) to change television channels without leaving our sofas.
The chief problem with battery cells is that they eventually reach a state of equilibrium and can no longer hold an electrical charge. Open a certain “catch-all” drawer in most American households and you’ll likely find a graveyard of spent batteries.
For that we have rechargeable battery cells. A common rechargeable battery is the lead-acid battery, which you’ll find in automobiles and other vehicles. These batteries exhibit a very low energy-to-weight ratio, but have a large power-to-weight ratio. They are great for a short burst of high electrical current to, say, start your car, but impossible (and dangerous) to carry around to make a 20-second call on your mobile phone.
A fully discharged lead-acid battery contains two cells of lead sulfate (PbSO4) in a sulfuric acid electrolyte solution. Charging the battery by applying an electrical current to the two electrodes, creates a positively charged lead dioxide plate and a negative plate of lead. Hook these cells up on your automobile starter, and your family vacation is off to a successful start.
The principle of a rechargeable battery is that you need to apply an electrical current to reverse the chemical process that creates electricity. Over the years, various electrode and electrolyte materials have been used in rechargeable batteries, particularly nickel oxide hydroxide and metallic cadmium (NiCd), nickel-metal hydride (NiMH), and silver-zinc (AgZn).
Now the most popular rechargeable, the lithium-ion battery, has several advantages and some famous problems. Lightweight with unmatched volumetric energy density, these batteries can power whole automobiles down to small electronic devices. In our series of application notes reviewing current analysis of materials that can potentially improve lithium-ion batteries using Raman Spectroscopy, we start with the analysis of candidate materials for battery cathodes.
Read Raman Analysis of Lithium-Ion Battery Components – Part I: Cathodes for more information.