LITHIUM-ION BATTERIES MANUFACTURING UNIT

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 aneven 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.

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 becomingmore and more sophisticated and smaller. It is also true for power tools andelectric vehicles as well as, on a larger scale, for stationary storage of renewableenergy.

The word “battery” comes from the Old French word batteries, 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 familyof rechargeable battery types in which lithium ions move from the negative electrode tothe positive electrode during discharge and back when charging. Li-ion batteries usean intercalated lithium compound as one electrode material, compared tothe metallic lithium used in a non-rechargeable lithium battery. The electrolyte, whichallows for ionic movement, and the two electrodes are the constituent components of alithium-ion battery cell.

Lithium-ion batteries are common in consumer electronics. They are one of the mostpopular types of rechargeable batteries for portable electronics, with a high energydensity, small memory effect, and only a slow loss of charge when not in use. Beyondconsumer electronics, LIBs are also growing in popularity for military, battery electricvehicle and aerospace applications. For example, lithium-ion batteries are becoming acommon replacement for the lead acid batteries that have been used historically for golfcarts and utility vehicles. Instead of heavy lead plates and acid electrolyte, the trend is touse lightweight lithium-ion battery packs that can provide the same voltage as lead-acidbatteries, 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 energydensity, but longer lives and inherent safety. Such batteries are widely used for electrictools, medical equipment and other roles.

NMC in particular is a leading contender forautomotive applications. Lithium nickel cobalt aluminum oxide (LiNiCoAlO2 or NCA)and lithium titanate (Li4Ti5O12 or LTO) are specialty designs aimed at particular nicheroles. The new lithium sulphur batteries promise the highest performance to weightratio.

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

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 basiccomponents, such as electrodes, separator, and electrolyte. In the case of lithium-ioncells, this is the single cylindrical, prismatic or pouch unit, that provides an averagepotential 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 readyfor use, as it contains an appropriate housing, electrical interconnections, and possiblyelectronics to control and protect the cells from failure.

In this regard, thesimplest “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 singlecell.

The term “module” is often used as an intermediate topology, with the understandingthat 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, whileworking for Exxon in the 1970s.[16]Whittingham used titanium(IV) sulfide and lithiummetal as the electrodes.

However, this rechargeable lithium battery could never be madepractical. Titanium disulfide was a poor choice, since it has to be synthesized undercompletely sealed conditions. This is extremely expensive (~$1000 per kilo for titaniumdisulfide raw material in 1970s). When exposed to air, titanium disulphide reacts to formhydrogen sulphide compounds, which have an unpleasant odour. For this, and otherreasons, Exxon discontinued development of Whittingham’s lithium-titanium disulfide battery.

Batteries with metallic lithium electrodes presented safety issues,as lithium is a highly reactive element; it burns in normal atmospheric conditions becauseof the presence of water and oxygen. As a result, research moved to developbatteries where, instead of metallic lithium, only lithium compounds are present, beingcapable of accepting and releasing lithium ions.