CHAPTER 7 Lithium-Ion and Other Cell Chemistries In this chapter, we will develop a basic understanding of the types of chemistries, form factors, and their benefits and challenges for many of the cells that are being used in energy storage systems (ESSs) today. We briefly review some of the other chemistries that are or have been used in various applications including lead acid, nickel metal hydride (NiMh), nickel metal chloride, sodium sulfur, sodium chloride and others. However, the main focus will be on the many different lithium-ion chemistries that are either in use today or are being developed for future applications. Batteries are typically classified into one of two categories:
either primary or secondary. The general difference is whether the batteries are rechargeable or not. Primary batteries are not rechargeable; they are single-use batteries and must be discarded after they have been dis- charged. Examples of these are the simple alkaline batteries that are used in many household devices. Secondary batteries are rechargeable, multiuse batteries that can be charged over again. The amount of life, or use, in a rechargeable battery is dependent on the chemistry and operating profile. Some cells can be charged and discharged hundreds of times; others can be charged and discharged thousands of times.
Before we begin to break down the definition of what a battery is, we should get a basic under- standing of the different components that make up a battery cell. While this is somewhat simpli- fied, there are essentially five main components that make up a battery. The cathode is the “positive” half of the battery cell, which is made up of a substrate of some sort that is coated with the active material. In lithium-ion batteries, the substrate is often a very thin film of aluminum. The anode is the “negative” half of the battery cell and is usually made up of a thin copper substrate that is coated with the active anode material.
Between these two halves is a “separator” material that prevents the two halves from touching and creating a short circuit. These three components are assembled together to form the electrodes and are either wound or stacked to form what is referred to as a jellyroll. The fourth component of a lithium-ion battery is the enclosure, which is most often a can or pouch, in which the jellyroll is inserted. This may take the form of a metal can, a plastic housing, or a polymer type “pouch.” Once this is done, the fifth element is added to the mix—an electrolyte. The electrolyte is the medium that allows the ions to pass back and forth within the cell.
There are many other bits and pieces that may be included in a battery cell, such as a current interrupt device (CID) or a positive thermal coefficient (PTC) which is a resettable thermal fuse. But these are not included in all cell types or chemistries. The next thing that we should do is to clearly define what a battery is and how it differs from other types of energy storage. Most simply, a battery is an electrochemical means of storing The Handbook of Lithium-Ion Battery Pack Design. http://dx.doi.org/10.1016/B978-0-12-801456-1.00007-5 Copyright © 2015 Elsevier Inc. All rights reserved. 65