Transcript Slide 1
The battery Alkaline batteries We have all heard of alkaline batteries. Did you ever wonder what makes them unique from the rest of the battery community? Here is what goes in them: The alkaline cathode is a mixture of manganese dioxide, graphite and an electrolyte. The mixture is granulated, aged, and then compacted into a pressed tablet assembly. Next, these tablets are inserted into a steel can. The steel can and the mixture thus becomes the cathode of the alkaline battery. An indentation is then made near the top of the can and the sealant is placed just above it. These two steps help safeguard the battery against leakage. As with the zinc chloride battery, the cathode and the anode portions of the alkaline battery must be kept from coming into contact with one another. Therefore, we must insert a paper separator, which is soaked with an electrolyte that promotes ionic (or electrolyte) conductivity once the battery is in use. Alkaline batteries We now insert the anode. In alkaline batteries, the anode is actually a gel made up of mostly zinc powder and several other materials. This gel is inserted into the steel can against the separator paper. With the anode and cathode in place, we now have a usable alkaline battery. However, because it is unsealed, the battery would not have a long shelf life. Therefore, a seal must be used to ensue the high quality and performance of the alkaline battery. The seal is made up of a brass nail, which acts as the current collector, a plastic gasket, a steel washer and a metal end cap. The four items are pre assembled and inserted into the middle of the steel can, up against the indentation which was formed earlier. A top is welded to the other end of the can to provide the positive polarity safety feature. The batteries are then stored, given a second voltage test, and a decorative outer label is applied. Batteries How car batteries are constructed How a Battery is Made Batteries are made of five basic components: • A resilient plastic container. • Positive and negative internal plates made of lead. • Plate separators made of porous synthetic material. • Electrolyte, a dilute solution of sulfuric acid and water, better known as battery acid. • Lead terminals, the connection point between the battery and whatever it powers. Batteries Car battery A paste mixture of lead oxide -- which is powdered lead and other materials -sulfuric acid and water is applied to the grids. Expander material made of powdered sulfates is added to the paste to produce negative plates. Inside the battery, the pasted positive and negative plates must be separated to prevent short circuits. Separators are thin sheets of porous, insulating material used as spacers between the positive and negative plates. Fine pores in the separators allow electrical current to flow between the plates while preventing short circuits. Batteries The car battery In the next step, a positive plate is paired with a negative plate and a separator. This unit is called an element, and there is one element per battery cell, or compartment in the container. Elements are dropped into the cells in the battery case. The cells are connected with a metal that conducts electricity. The lead terminals, or posts, are then welded on. The battery is then filled with electrolyte - or battery acid -- a mixture of sulfuric acid and water, and the cover is attached. The battery is checked for leaks. Batteries Car battery chemistry The reaction that generates the current is: Anode Cathode Overall Batteries Interesting battery facts Some batteries self-discharge. NiMH (nickel metal hydride) and NiCd (nickel cadmium) lose charge more rapidly than alkaline batteries even though they are not used. The term ‘losing charge’ does not mean that batteries lose electrons because charges are conserved. Instead, this means that the battery’s potential to generate current diminishes. When we ‘charge’ batteries, we are not adding electrons, we are converting electrons from a low energy state (in the reacted chemical) to a high energy state (in the original state). Website describing environmentally friendly batteries http://www.greenbatteries.com/ Website comparing alkaline batteries http://www.powerstream.com/BatteryFAQ.html Batteries Comparison Battery type Construction materials and chemistry Advantages/ disadvantages Use NiMH Nickel metal hydride Nickel and a metal that forms a hydride, such as lanthanum Environmentally friendly, fast recharge, can handle fast discharge rates better than alkaline / selfdischarge Cameras and other auto-off electronics NiCd Nickel cadmium Anode: nickelic hydroxide Cathode: cadmium Cadmium is toxic, rechargeable / self-discharge Cameras and other auto-off electronics Alkaline Anode: zinc metal Cathode: manganese oxide Electrolyte: potassium hydroxide Materials are environmentally OK, but these are not rechargeable Flashlights Li metal is not rechargeable, the lithium ion battery is. Pacemakers, defibrillators, watches, meters, cameras, calculators, portable, low-power use Zn + 2OH- —> ZnO + H2O + 2 e2 MnO2 + H2O + 2 e- —>Mn2O3 + 2 OHZn + 2MnO2 —> ZnO + Mn2O3 E=1.5 V Li Lithium / Li ion Anode lithium metal Cathode: thionyl chloride Li —> Li+ + e4Li+ + 4e- + 2SOCl2 —> 4LiCl + SO2 + S 4Li + 2SOCl2 —> 4LiCl + SO2 + S Li ion battery is different