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17 October 2014
Lithium-Based Batteries : An Engineering Marvel Part 2
The basic architecture of the Li-ion battery is same as the Nickel and Lead based versions. It employs a positive electrode called the cathode, an anode which acts as a negative electrode and an electrolyte for conduction between the two electrodes. The cathode generally is made up of metal-oxide and the anode is made of porous carbon material. During charging the Li-ions flow from cathode to anode while during the discharge the ions follow in the opposite direction.
Basically during discharge the anode experiences oxidation i.e. it loses electrons from material and the cathode gains these electrons and gets reduced. Lithium based batteries are available in many different varieties and though they all have the Li-ion principal in common their performance can vary greatly based on material chosen for the cathode. Some commonly used cathode materials in Lithium-based batteries are Lithium Manganese Oxide, Lithium-Iron Phosphate and Lithium Cobalt Oxide etc. In the original Li-ion battery marketed by Sony the anode was made of coke. Since the year 1997 most manufacturers have changed to graphite based anode because it offers a much flatter and stable discharge curve. Graphite is known to store Li-ion very well and hence offers long time stability. Due to these properties it is the most popular Anode material followed by soft and hard carbons. New age materials like carbon nano tubes still haven’t found extended commercial use.
Advances in Anode technology are also being made and a new material being tried out is silicon based alloy. Silicon achieves about a 30 % gain in specific energy with reduced load currents and a reduced life cycle. Also there has been research done on using lithium titanate as anode material and it shows good load capacities and great low temperature performance though the specific energy levels are low.
Manufacturers can opt to mix and match anode and cathode materials to obtained desired cell attributes. But promoting one attribute can compromise the integrity of the other. Manufactures have to balance out these aspects to provide customers with the best products. Safety and longevity should not be compromised just to achieve low cost and high levels of specific energy. The competition to developan ideal battery is extremely intense in our present day. And hence there is a lot of research being done on optimizing all aspects of Lithium-based batteries.
Li-ion batteries generally provide high energy density and low self-discharge. The Li-ion battery doesn’t require a periodic discharge due to the absence of memory. The batteries themselves are extremely low maintenance. There are also certain limitations associated with Lithium based batteries. It requires a special circuit built into it to limit current and voltage. Even the Li-ion battery is subject to aging and holds no advantage over other chemistries in this regard. Also there may be certain transportation regulations imposed upon their shipping when done in large quantities.
All in all the Li-ion or Lithium-based battery is a marvel of engineering and offers an excellent source of concentrated energy. It is easily rechargeable and now is more or less a household item with its extensive use in mobile phones, tablets and other portable devices. The high levels of specific energy, slow discharge and high nominal voltage levels have promoted its usage in other industries such as the automobile sector. Advances are being made almost every month in Lithium-based battery technology which will slowly make their way to the customer in due course.
