How to work a Lithium ion battery ?

A portable powersupply has become the lifeline of the modern technological world, especially the lithium-ion battery. Imagine a world where all cars are driven by induction motors and notinternal combustion engines. Induction motors are superior to IC engines in almost all engineering aspects, as well as being more robust and cheaper.

Another huge disadvantage of IC engines is that they only produce usable torque in a narrow band of engine RPM. Considering all of these factors, induction motors are definitely the perfect choice for an automobile. However, the power supplyfor an induction motor is the real bottleneck in achieving a major induction motor revolution in the automobile industry.

Construction of lithium-ion battery :-

Let's explore how Tesla, with the help of lithium-ion cells, solved this issue and why lithium-ion cells are going to become even better in the future. Let's take a lithium-ion cell out from the battery pack and break it down. different layers of chemical compounds inside it. Tesla's lithium-ion battery works on an interesting concept associated with metals called the electrochemical potential. Electrochemical potential is the tendency of a metal to lose electrons.

History of lithium-ion battery :-

In fact, the very first cell,developed by Alessandro Volta more than 200 years ago, was based on the concept of electrochemical potential. A general electrochemical series is shown here. According to these values,lithium has the highest tendency to lose electrons and fluorine has the least tendency to lose electrons. Volta took two metals with different electrochemical potentials, in this case, zinc and silver, and created an external flow of electricity. Sony made the first commercial model of a lithium-ion battery in 1991. It was again based on the same concept of electrochemical potential.

Basic working principle of lithium-ion battery :-

Lithium, which has the highest tendency to lose electrons, was used in lithium-ion cells. Lithium has only one electron in its outer shell and always wants to lose this electron. Due to this reason, pure lithiumis a highly reactive metal. It even reacts with water and air. The trick of a lithium-ionbattery operation is the fact that lithium, in its pure form, is a reactive metal. But when lithium is part of a metal oxide, it is quite stable.

Assume that somehow we have separated a lithium atom from this metal oxide. This lithium atom is highly unstable and will instantly form alithium-ion and an electron. However, lithium, as a part of metal oxide, is much more stable than this state. If you can provide two different paths for the electron and lithium-ion flow between the lithium and the metal oxide, the lithium atom will automatically reach the metal oxide part. During this process, wehave produced electricity from the electron flow through the one path. From these discussions, it is clear that we can produce electricity from this lithium metal oxide, if we firstly separate out lithium atoms from the lithium metaloxide, and secondly, guide the electrons lost from such lithium atoms through an external circuit.

Let's how lithium-ion cells achieve these two objectives. A practical lithium-ion cell also uses an electrolyte and graphite. Graphite has a layered structure. These layers are loosely bonded so that the separated lithium-ions can be stored very easily there. The electrolyte between the graphite and the metal oxide acts as a guard which allows only lithium-ions through. Now what happens when you connect a power source across this arrangement. The positive side of the power source will obviously attract and remove electrons from the lithium atoms of the metal oxide. These electrons flow through the external circuit as they cannot flow through the electrolyte and reach the graphite layer. In the mean time, the positively charged lithium-ions will be attracted towards the negative terminal and will flow through the electrolyte. lithium-ions also reachthe graphite layer space and get trapped there. Once all the lithium atomsreach the graphite sheet, the cell is fully charged. Thus we have achieved the first objective which is the lithium-ionsand electrons detached from the metal oxide.

As we discussed, thisis an unstable state, as if being perched on top of a hill. As soon as the power source is removed, and a load is connected, thelithium-ions want to go back to their stable state asa part of the metal oxide. Due to this tendency, the lithium-ions move through the electrolyte and electrons via the load, just like sliding down a hill. Thus we get an electrical current through the load. Please note that the graphite does not have a role in the chemical reaction of the lithium-ion cells. Graphite is just a storage medium for lithium-ions. If the internal temperature of the cell rises due to some abnormal condition, the liquid electrolyte will dry up and there will be a shortcircuit between the anode and cathode and this can lead to a fire or an explosion. To avoid such a situation,an insulating layer, called the separator, is placed between the electrodes.

The separator is permeable for the lithium-ions because of its micro porosity. In a practical cell, the graphite and metal oxide are coated on to copper and aluminum foils. The foils act as current collectors here and the positive and negative tabs can be easy taken out from the current collectors. An organic salt of lithiumacts as the electrolyte and it is coated on to the separator sheet. All these three sheets are wound onto the cylinder around a central steel core, thus making the cell more compact. A standard lithium-ion cell has a voltage of between three and 4.2 volts. Many such lithium-ion cell connected in series and in a parallel fashion to form a module. 16 such modules are connected in series to form a battery pack in the Tesla car.

Disadvantages of lithium-ion battery

1. Lithium-ion cells produce a lot of heat during the operation and the high temperature will decay the cells' performance.
2. More costly for maintenance.
3. A battery management system is used to manage the temperature,state of charge, voltage protection andcell health monitoring of such a huge number of cells.

Glycol-based cooling technology is used in the Tesla battery pack. The BMS (Battery management system) adjusts to the glycol flow rate to maintain the optimum battery temperature. Voltage protection is another crucial job of the BMS.

For example, suppose three cells, during charging a higher capacity cell will be charged more than the rest. To solve this problem, the BMS uses some thing called cell balancing. In cell balancing, all the cells are allowed to charge and discharge equally,thus protecting them from over and under voltage. This is where Tesla score sovereign Nissan battery technology.

The Nissan Leaf has a huge battery cooling issue due to the big size of its cells and the absence of an active cooling method. The small multiple cell design has one more advantage. During high power demand situations, the discharge strain will be divided equally among each of the cells. Instead of many small cells if we had used a single giant cell, it would have been putunder a lot of strain, and eventually it would suffer premature death. By using many small cylindrical cells, the manufacturing technology of which is already well established, Tesla clearly made a winning decision. There is a magical phenomenon which happens within lithium-ion cells during their very first charge that saves the lithium-ion cells from sudden death. Let's see what it is.

The electrons in the graphite layer are a major problem. The electrolyte will be degraded if the electrons comeinto contact with it. However, the electrons never come into contact with the electrolyte due to an accidental discovery, the solid electrolyte interface. When you charge the cell for the first time, as explained above, the lithium-ions move through the electrolyte. Here, in this journey, solvent molecules in the electrolyte cover the lithium-ions. When they reach the graphite, the lithium-ions, along with the solvent molecules, react with the graphite and form a layer there called the SEI layer. The formation of this SEI layeris a blessing in disguise. It prevents any direct contact between the electrons and the electrolyte, thus saving the electrolyte from degradation. In this overall process of theformation of the SEI layer, it will consume 5% of the lithium. The remaining 95% ofthe lithium contributes to the main working of the battery. Even though the SEI layerwas an accidental discovery, with over two decades ofresearch and development, scientists have optimizedthe thickness and chemistry of the SEI layer for maximum cell performance. It is amazing to find outthat those electronic gadgets we used around two decades back did not use lithium-ion batteries.

With its amazing speed of growth, the lithium-ion battery market is expected to become a $90 billion annual industry within a few years. The currently achieved numberof charge discharge cycles of a lithium-ion battery is around 3,000. Great minds across the globeare putting their best efforts into increasing this to 10,000 cycles. That means you would not have to worry about replacing the battery in your car for 25 years. Millions of dollars have already been invested in research into replacing the storage medium graphite with silicon. If this is successful, the energy density of the lithium-ion cell will then increase by more than five times.

About Admin MC3

This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.