LITHIUM-ION AND LITHIUM POLYMER BATTERIES MANUFACTURING

Electrochemical storage systems will increasingly gain in importance in the future. This is true for the energy supply of computers and mobile phones that are becoming more and more sophisticated and smaller. It is also true for power tools and electric vehicles as well as, on a larger scale, for stationary storage of renewable energy.

Lithium-ion battery packs are complex systems of interrelated components and subsystems but can be relatively easily understood by most people because the pack is the thing that we can touch, hold, and feel. But understanding the lithium-ion chemistries and the physics and chemical reactions that occur inside those battery cells requires gaining an understanding of an even more complex set of systems and interrelationships that are really well understood only by those few chemists, researchers, and cell engineers who work with them on a daily basis. And there is even a lot that they do not under- stand about some of the reactions that take place inside the cell. However, even without having done advanced research in chemistry it is possible to achieve a good basic understanding of how these different chemistries work, what the more complex reaction mean, and what happens inside a lithium-ion cell when you use energy from it.

The word “battery” comes from the Old French word baterie, meaning “action of beating,” relating to a group of cannons in battle. In the endeavor to find an energy storage device, scientists in the 1700s adopted the term “battery” to represent multiple electrochemical cells connected together.

The battery consists of two electrodes that are isolated by a separator and soaked in electrolyte to promote the movement of ions. New active materials are being tried, each offering unique attributes but none delivering an ultimate solution.

Improvements have been slow. Whereas Moore’s Law* doubled the number of transistors in an integrated circuit every two years, capacity gain of lithium-ion (Li-ion) has been about 8 percent per year in the decades following its introduction in 1991.

A lithium-ion battery (sometimes Li-ion battery or LIB) is a member of a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the constituent components of a lithium-ion battery cell.

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, small memory effect, and only a slow loss of charge when not in use. Beyond consumer electronics, LIBs are also growing in popularity for military, battery electric vehicle and aerospace applications. For example, lithium-ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolyte, the trend is to use lightweight lithium-ion battery packs that can provide the same voltage as lead-acid batteries, so no modification to the vehicle’s drive system is required.

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO2), which offers high energy density, but presents safety risks, especially whe damaged. Lithium iron phosphate (LiFePO4), lithium manganese oxide (LMnO or LMO) and lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) offer lower energy density, but longer lives and inherent safety. Such batteries are widely used for electric tools, medical equipment and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (LiNiCoAlO2 or NCA) and lithium titanate (Li4Ti5O12 or LTO) are specialty designs aimed at particular niche roles. The new lithium sulphur batteries promise the highest performance to weight ratio.

Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also kept pressurized. Because of this the testing standards for these batteries are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests. This is in response to reported accidents and failures, and there have been battery-related recalls by some companies.

Although the word “battery” is a common term to describe an electrochemical storage system, international industry standards differentiate between a “cell” and a “battery”. A “cell” is a basic electrochemical unit that contains the basic components, such as electrodes, separator, and electrolyte. In the case of lithium-ion cells, this is the single cylindrical, prismatic or pouch unit that provides an average potential difference at its terminals of 3.7 V for LiCoO2 and 3.3 V for LiFePO4. A “battery” or “battery pack” is a collection of cells or cell assemblies which are ready for use, as it contains an appropriate housing, electrical interconnections, and possibly electronics to control and protect the cells from failure.

In this regard, the simplest “battery” is a single cell with perhaps a small electronic circuit for protection.

In many cases, distinguishing between “cell” and “battery” is not important. However, this should be done when dealing with specific applications, for example, battery electric vehicles, where “battery” may indicate a high voltage system of 400 V, and not a single cell.

The term “module” is often used as an intermediate topology, with the understanding that a battery pack is made of modules, and modules are composed of individual cells. Lithium batteries were proposed by M. S. Whittingham, now at Binghamton University, while working for Exxon in the 1970s.[16]Whittingham used titanium(IV) sulfide and lithium metal as the electrodes. However, this rechargeable lithium battery could never be made practical. Titanium disulfide was a poor choice, since it has to be synthesized under completely sealed conditions. This is extremely expensive (~$1000 per kilo for titanium disulfide raw material in 1970s). When exposed to air, titanium disulphide reacts to form hydrogen sulphide compounds, which have an unpleasant odour. For this, and other reasons, Exxon discontinued development of Whittingham’s lithium-titanium disulfide battery.