Week 1 Understanding Different Battery Chemistry

Aim :

1.Prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells.Give your detailed explanation on it

2.Compare the differences between each type of Li+ion batteries based on their characteristics

Solution :

Construction of Battery :

Lead acid batteries used in the RV and Marine Industries usually consist of two 6-volt batteries in series, or a single 12-volt battery. These batteries are constructed of several single cells connected in series each cell produces approximately 2.1 volts. A six-volt battery has three single cells, which when fully charged produce an output voltage of 6.3 volts.

A battery cell consists of two lead plates a positive plate covered with a paste of lead dioxide and a negative made of sponge lead, with an insulating material (separator) in between. The plates are enclosed in a plastic battery case and then submersed in an electrolyte consisting of water and sulfuric acid

Anode : It is the electrode through which the conventional current enters into a polarized electrical device .

Cathode : It is the electrode through which the conventional current leaves into a polarized electrical device .

In figure # 3, above a fully charged battery is connected to a load (light bulb) and the chemical reaction between sulfuric acid and the lead plates produces the electricity to light the bulb. This chemical reaction also begins to coat both positive and negative plates with a substance called lead sulfate also known as sulfation (shown as a yellow build-up on plates). This build-up of lead sulfate is normal during a discharge cycle. As the battery continues to discharge, lead sulfate coats more and more of the plates and battery voltage begins to decrease from fully charged state of 12.6-volts (figure # 4).

In figure # 5 the battery is now fully discharged, the plates are almost completely covered with lead sulfate (sulfation) and voltage has dropped to 10.5-volts.

Lead sulfate (sulfation) now coats most of the battery plates. Lead sulfate is a soft material, which can is reconverted back into lead and sulfuric acid, provided the discharged battery is immediately connected to a battery charger. If a lead acid battery is not immediately recharged, the lead sulfate will begin to form hard crystals, which can not be reconverted by a standard fixed voltage (13.6 volts) battery converter/charger.

Types of Batteries and their chemical reactions :

A Primary Battery is one of the simple and convenient sources of power for several portable electronic and electrical devices like lights, cameras, watches, toys, radios etc. As they cannot be recharged electrically, they are of “use it and when discharged, discard it” type.

Usually, primary batteries are inexpensive, light weight, small and very convenient to use with relatively no or less maintenance. Majority of the primary batteries that are used in domestic applications are single cell type and usually come in cylindrical configuration (although, it is very easy to produce them in different shapes and sizes).

A Secondary Battery is also called as Rechargeable Battery as they can be electrically recharged after discharge. The chemical status of the electrochemical cells can be “recharged” to their original status by passing a current through the cells in the opposite direction of their discharge.

There are some other types of Secondary Batteries but the four major types are:

• Lead – Acid Batteries
• Nickel – Cadmium Batteries
• Nickel – Metal Hydride Batteries
• Lithium – Ion Batteries

Lead – Acid Batteries

The lead-acid batteries are by far the most popular and most used rechargeable batteries. They have been a successful product for more than a century. Lead-acid batteries are available in several different configurations like small sealed cells with capacity of 1 Ah to large cells with capacity of 12,000 Ah.

As the name implies, these batteries have some lead in them. In fact, both electrodes (the conductors through which electricity enters or leaves the battery) contain some lead—the anode (positively changed electrode) is made of lead metal (Pb) and the cathode (the negatively charged electrode) is lead dioxide (PbO₂). The electrodes are placed within an electrolyte solution of sulphuric acid (H₂SO₄), which is made up of hydrogen ions (H⁺) and bisulphate ions (HSO₄).

The lead at the anode reacts with the bisulphate from the electrolyte, freeing up some electrons, and producing lead sulphate, which forms crystals upon the anode, and hydrogen ions which go into the electrolyte. The electrons travel over to the cathode via an external circuit, where they, along with bisulphate and hydrogen ions from the electrolyte, react with the lead dioxide cathode. This also produces lead sulphate, which again forms crystals, this time on the cathode.

As the battery charges, the chemical reactions described above that produce the electricity are forced backwards. The lead sulphate coatings are dissolved and forced back into the electrolyte as Pb2+ and SO₄^2- ions. The Pb²⁺ ions then pick up two electrons and are re-plated onto the anode as neutral Pb.

During discharge, the reaction at the anode is the creation of lead sulphate, along with some hydrogen and electrons, as lead reacts with sulphate from the electrolyte solution:

At the cathode, lead oxide also reacts with sulphate from the electrolyte, producing lead sulphate, along with some water:

The total reaction is:

NICKEL-CADMIUM

Although they’re now distinctly old news, nickel-cadmium (NiCad) batteries were the first rechargeable batteries used in power tools, torches and other portable devices. These were the guys in our mobile phones before lithium-ion batteries booted them out

The anode is made from cadmium (Cd) and their cathodes are nickel oxide hydroxide (NiO(OH)₂), usually with an electrolyte of potassium hydroxide (KOH).

Nickel oxide hydroxide makes a very good electrode, as it can be produced to have a large surface area, and this increases the active area available for the reaction. Also, it doesn’t react with the electrolyte during the reaction, which keeps the electrolyte solution nice and pure and helps the cell last a (relatively) long time before pesky side-reactions make it degrade.

During discharge, cadmium is oxidised at the anode:

Cd+2OH−→Cd(OH)2+2e−Cd+2OH−→Cd(OH)2+2e−

The nickel hydroxide cathode is reduced:

NiO(OH)+H2O+e−→Ni(OH)2+OH−NiO(OH)+H2O+e−→Ni(OH)2+OH−

The entire reaction during battery discharge is:

2NiO(OH)+Cd+2H2O→2Ni(OH)2+Cd(OH)2

NICKEL-METAL HYDRIDE (NiMH)

hese problems with NiCad batteries led to the cadmium anode being replaced with a hydrogen-absorbing intermetallic alloy (a combination of metals with a defined crystal structure) that can gobble up to 7 per cent hydrogen by weight. Essentially, the anode is the hydrogen; the metal alloy merely serves as a storage vessel for it.

The most common combination of metals for this alloy are ones with a strong hydride-forming capability, along with a weak hydride-forming metal.

Another consideration when putting together the metal alloy is that when some metals absorb hydrogen, the reaction gives off heat—it’s exothermic. Others absorb heat in an endothermic reaction. We don’t really want a battery that either produces or sucks in heat as it discharges, so, along with the strong–weak hydride forming combination the alloy is also made from, we need a combination of exothermic and endothermic metals.

Most commonly, the electrode will be a combination of a rare earth element such as lanthanum (La), cerium (Ce) neodymium (Nd) or praseodymium (Pr), mixed with nickel (Ni), cobalt (Co), manganese (Mn) or aluminium (Al).

The electrons that produce the battery’s electric current come from the oxidation of hydrogen atoms, which turn into protons. These protons react with hydroxide ions (OH^-) from the electrolyte to make water. The metal alloy that forms the anode along with the hydrogen does not take part in the chemical reaction that drives the cell; it’s basically a bystander that just provides a home for the all-important hydride ions.