Batteries: Nanoscience As A Possible Solution To Lithium Scarcity

Although the earliest systematic discussion on modern nanoscience is considered to be a fascinating speech given by physicist Richard Feynman during a meeting at the California Institute of Technology (Caltech) on 29 December 1959, nanoscale materials were already in use for centuries.

Alternate-sized gold and silver particles created colours in the stained glass windows of medieval churches hundreds of years ago. The artists back then just didn’t know that the process they used to create these beautiful works of art actually led to changes in the composition of the materials they were working with.

Nanotechnology is science conducted at the nanoscale, which is about 1 to 100 nanometres. One nanometer is a billionth of a metre. Here are a few illustrative examples from this small span:

● There are 25,400,000 nanometres in an inch.

● A sheet of newspaper is about 100,000 nanometres thick.

● On a comparative scale, if a marble were a nanometre, then one metre would be the size of the Earth.

The size distribution, the specific surface features, the unique physical, chemical, mechanical, and optical properties, and the quantum effects of the matter at nanoscale differ significantly from what they are at their macro levels.

When particle size is made to be nanoscale, properties such as melting point, fluorescence, electrical conductivity, magnetic permeability, and chemical reactivity change as a function of the size of the particle.

For instance, nanoscale gold particles are not in the yellow colour with which we are familiar; nanoscale gold can appear red or purple. At the nanoscale, the motion of the gold’s electrons is confined. Because this movement is restricted, gold nanoparticles react differently with light compared to larger-scale gold particles.

Given their unique properties, nanomaterials are used in a variety of applications, from treating cancers to highly efficient solar cells, from smart, wrinkle-free textile fabrics to faster and more efficient electronic chips and in fighting air and water pollution.

Battery Chemistry

With this background on nanotechnology, let us now understand the basics of battery chemistry, its importance in the light of the electric vehicle (EV) buzz, the consequent “lithium rush,” and the challenges therein.

A battery is a device that converts chemical energy into electrical energy. What happens inside the battery is an electrochemical reaction that can be reversible in nature.

A rechargeable lithium-ion battery is the most widely used battery that finds application in most of our electronic equipment. Examples are mobile phones, laptops, and the Tesla Model S.

The power-generating compartment (also called a “cell”) essentially has three components: a positive electrode (connected to the battery’s positive terminal, typically lithium-cobalt oxide, LiCoO2), a negative electrode (connected to the battery’s negative terminal, typically made from carbon), and an electrolyte (a chemical medium through which ions are transported and an electrochemical reaction ensues).

Charging or Discharging of a Lithium-ion Battery

When connected to an external electric power source, that is, while being charged, positive electrode, the lithium-cobalt oxide gives up some of its lithium ions, which move through the electrolyte to the negative electrode (generally graphite, a form of carbon) and remain there.

As shown in the figure, lithium ions settle in between the layers of graphene (sheets of carbon one atom thick) of graphite electrode. When all the available space is filled and no further lithium ions can be accommodated, the battery is said to be fully charged.

When the device is unplugged and being run on battery, that is, while getting discharged, these lithium ions resting in between the graphene layers are transported back to their original state. Electrons flow from the negative electrode to the positive electrode through the outer circuit powering your mobile phone or laptop.

When all the ions move back, the battery is fully discharged (the point of 0 per cent battery on your mobile phones).

Why Go After Lithium?

Lithium is the lightest metal and the least-dense solid element. The element's high electrochemical potential makes it a valuable component of high-energy-density rechargeable lithium-ion batteries.

Lithium-ion batteries have no memory effect, a detrimental process where repeated partial discharge or charge cycles can cause a battery to ‘remember’ a lower capacity.

But, most importantly, because lithium is the smallest of all metals (in terms of its atomic size), it’s easy for it to shuttle in and out of those graphene layers (a process called ‘intercalation’).

However, lithium is not abundantly available to sustainably meet the ever-increasing demand, especially when we are at the cusp of a transition to EVs.

Moreover, that the majority of lithium supply chains are concentrated in China is not good news for India, which aspires to become atmanirbhar (self-reliant) and meet its EV goals while confronting China along its border.

A possible solution, therefore, is replacing lithium with sodium, which is the second-lightest and the next smallest metal after lithium with similar voltages and packing technology. Moreover, processing and obtaining usable sodium costs $150 per tonne compared to $5,000 per tonne for lithium.

However, on account of having a bigger atomic size, the dwelling space for sodium ions amidst the graphene layers comes down, minimising the ease of intercalation and battery efficiency.

This is where nanochemistry can possibly come into play.

Carbon nanomaterial (nanofibers or nanoparticles), also referred to as hard carbon because of its very high surface area-to-volume ratio (a unique physical property at that size), has an inherent advantage of increased porosity and ‘d spacing’ (spacing between two consecutive layers of carbon).

As shown in the figure below, sodium ions can sit not just in between the two-dimensional carbon sheets but also in the ‘pore spaces’ of the hard carbon matter.

As part of my final-year engineering project at the National Institute of Technology, Warangal, we synthesised carbon nanofibers using electrospinning technology and tried microwave-assisted ‘exfoliation’ to further increase the porosity and d-spacing.

Electrospinning, a fascinating fibre fabrication technique, uses electric force to draw charged threads of polymer solutions or polymer melts up to fibre diameters in the order of some hundred nanometres.

The fibre mat thus obtained was subjected to pyrolysis (heating in the absence of oxygen at high temperatures) followed by exfoliation to test if it increased the porosity and d-spacing.

Our objective was to enhance the ease of intercalation and the number of sodium ions that can be accommodated in the negative electrode, thereby enhancing battery efficiency and capacity.

Atmanirbharta in Nanotechnology

India should look to tap into the potential of nanotechnology. Its impact can be felt across a variety of areas.

As Arindam Ghosh and Yamuna Krishnan write, self-reliance in nanotechnology can make good use of the natural and human resources India has and also help make the country self-reliant in sectors like defence.

This article has been published as part of Swasti 22, the Swarajya Science and Technology Initiative 2022. Read other Swasti 22 submissions.