ABOUT Lithium BATTERIES

Lithium BATTERIES

The International Air Transport Association (IATA) in their "IATA Lithium Battery Guidance Document – 2017" states that the term "lithium battery" refers to a family of batteries with different chemistries, comprising many types of cathodes and electrolytes. They separate these batteries into:  Lithium metal batteries and Lithium-ion batteries.  Lithium metal batteries are also call primary or non-rechargeable batteries and Lithium-ion batteries are usually called secondary or rechargeable batteries.

LITHIUM BATTERIES and lithium cells

The UN Manual of Tests and Criteria, defines technically a battery and a cell as follows:
A Lithium Battery means two or more cells which are electrically connected together and fitted with devices necessary for use.
Cell means a single encased electrochemical unit (one positive and one negative electrode) which exhibits a voltage differential across its two terminals.

Lithium Thionyl Chloride CELL

Lithium Thionyl Chloride cell (Li-SOCl2) falls into the category of Lithium metal cells or primary (non-rechargeable) . It is the most common cell used in the downhole industry with a stable operating voltage of 3.67V, high energy  capability,  wide operating temperature range and robust construction for high shock and vibration tolerance.

Lithium Thionyl Chloride components

  • Lithium metal anode (-): Lithium has the highest standard potential and electrochemical equivalence among metals. This make it an outstanding option to be used as anode (Electrode that gives up electrons) in high performance batteries. It also has better mechanical characteristics and lower reactivity when compared to other alkali metals.
  • Carbon cathode (+): The porous carbon cathode made of Teflon-bonded acetylene blacks that occupies most of the battery volume  absorbs the electrons during discharge but it is the Thionyl chloride that acts as the active cathode material as well as electrolyte solvent
  • Electrolyte: It is the activator  or electrical conductor that cause electrons to accumulate in the negative terminal or anode and flow when it is connected to the positive terminal, or cathode.  In the case of  Lithium Thionyl Chloride cells.  Thionyl Chloride is use as an electrolyte (and as mention before also acts as an active cathode).  Other lithium batteries may use Sulphuryl chloride  or polar organic liquids.
  • Separator: Separator acts as an insulator for electrons. It  electrically isolates the electrodes but allows the movement of ions. In lithium cells the essential function of battery separator is to prevent short-circuit, while enabling ionic transport between the positive and negative electrodes. The most commonly used separator for Lithium Thionyl Chloride cells is glass fiber, glass mat or filter paper, but  microporous polypropylene membranes are use in other type of primary  lithium batteries. The separator  has the shape of a metallic cylinder and is included in the carbon cathode.

Lithium Thionyl Chloride discharge rate:

Lithium batteries are design to provide a  specific discharge rate for a optimum service life or to provide the opposite that is a high-rate  performance  at the expense of service life.
  • Low rate DESIGN:
Also known as the bobbin design. Lithium metal anode in shaped in the form of a foil placed against the inside wall of cell case. This design deliverers a low current, provide long life to cell and the possibility of accidents handling these cells is very low.
  • moderate rate:
This design for lithium cells has a double anode  layer. The purpose with this type of construction is to increase the anode surface. This design provides similar safety labels to Low Rate Batteries at a higher discharge rate.
  • High rate:
Cells with this design provides the highest power and discharge rate among all the 3 designs due to a bigger anode-cathode surface area. In this design the anode is wound following a spirally shape structure.