Batteries are becoming cheaper, safer and greener. This month’s column examines how composition and crystallography of cathodes are critical for the battery’s performance. Alternative chemistries are being actively investigated to make batteries more sustainable. Cobalt, a key component of the cathode, is likely to be substituted by Manganese.
Renewable energy by its nature is intermittent and if it has to grow exponentially in the decades to come, there has to be a concomitant advance in energy storage technology. Batteries have to become cheaper and safer, and also more robust and sustainable. The battery essentially converts electrical energy into chemical energy for storage and reconverts the stored energy to electrical energy on demand. Chemistry and chemical engineering are at the core of design and development of batteries. Understanding ionic transport is the key to improve the performance of battery. Decades ago, battery immediately conjured up lead in our minds; today it is lithium. Though lithium is synonymous with battery today, there are many other components of a battery which play a significant role. Cobalt is one of them. Lithium Cobalt Oxide There are different types of lithium- ion batteries and they are often characterised by their cathodes. The most commonly used cathode is lithium cobalt oxide and it is conventionally referred to by the abbreviation LCO. When the lithium- ion battery is being charged, lithium ions leave the cathode and migrate through a polymeric membrane towards the graphite anode, where they get trapped by a phenomenon known as intercalation. During the discharge cycle, the reverse happens and lithium ions released from the anode travel back towards the cathode where they get similarly intercalated. When positively charged, lithium ions are released from the cathode during the charging cycle, the cathode changes its electrical character. To compensate for this, the cobalt present in the cathode changes its valence from +3 to +4. The valence changes back from +4 to +3, when lithium ions are being intercalated during the discharge cycle. Cobalt thus plays an important role in the functioning of the Li-ion battery. Cobalt’s function of maintaining the cathode’s electro- neutrality can also be achieved by other transitional metals like nickel, aluminum, iron, copper, manganese,which have the ability to change their valence. But cobalt performs this task most efficiently and therein lies its importance to the lithium-ion battery.
Evil Spirit
Cobalt is named after a mischievous mountain-dwelling spirit of German folklore. German miners found an ore which apparently glistened with silver, but refused to yield the precious metal on smelting. Gases released during smelting also caused widespread illness
and even death among the miners. The miners blamed “Kobold”, the impish goblin, for stealing the silver from the ore. More than 500 years later, cobalt continues to trouble our minds, as bulk of it is mined in an unsafe and unethical manner. Almost 60 percent of all
cobalt emanates from Democratic Republic of Congo. The cobalt mining industry in Congo is plagued with corruption, child labour andvarious other forms of human rights abuse. Cobalt from Congo violates all principles of sustainability.
Cobalt-free Chemistry
Of all the different constituents of the lithium-ion battery, cobalt faces the most severe supplycrunch. Cobalt prices have leaped 40 percent in the first quarter of 2021. This is entirely due to the increased demand from EVs. The EV sales increased by 40 percent in 2020 despite the pandemic.Also high cost cobalt would increase the price of EVs and derail plans of their accelerated adoption. Battery makers are looking at alternative cobalt-free chemistries. Launched in early 2020, COBRA (Cobalt-free Batteries for Future Automotive Applications) is a European consortium tasked with the objective of developing a cobalt-free lithium- ion battery by 2024. The first prototypes are expected in early 2022. The battery plans to use Lithium-Nickel-Manganese-Oxide (LNMO) cathode. This cathode has a distinctive architecture known as the spinel – LiNi0.5Mn1.5O4. Manganese is emerging as a key component of the lithium-ion battery and its promise of delivering higher energy density will be eagerly watched.
The Spinel
As the lithium ions enter and exit the cathode while discharging and charging respectively, much like bees flying in and out of the honeycomb, the crystallographic structure of the cathode plays an important role in determining the performance of the battery. The ease with which lithium ions migrate in and out of the cathode determines the charging time and the charge-discharge cycle. It also determines the robustness of the battery and its longevity. One cathode morphology that has caught the fancy if researchers is the spinel. Spinel is a class of minerals, usually,oxides that have a closely packed cubic lattice. The general formula of spinel is AB2O4; A and B are bivalent and trivalent metals respectively and are tetrahedrally and octahedrally coordinated in the lattice. This structure takes the name spinel after the mineral Magnesium Aluminate (MgAl2O4). The spinel structure improves structural and chemical stability against electrochemical cycling and also allows for faster migration of lithium-ions.
Lithium Iron Phosphate
Another strong contender for cobalt-free cathode is lithium iron phosphate (LFP). Unlike LCO, the LFP battery does not overheat during charging and is thus considered safer. The LFP battery is also easier to recycle in the absence of toxic cobalt. Longer lifecycle is another significant advantage of LFP battery over LCO; the difference can be 2 to 10 times. The LFP battery has clear advantages of price, safety and sustainability over LCO. The solitary disadvantage is in size. The energy density of LFP battery is about 40 percent lower than LCO, making it bulkier. This practically rules out its application in EVs. However, it is emerging as an excellent alternative for stationary energy storage. Megapack is a gigantic Li-ion battery having a storage capacity of 3 MWh. Manufactured by Tesla, it is currently the largest energy storage device in the world. Tesla recently made this battery cobalt-free by switching to lithium iron phosphate cathodes.
Circular Battery
While the supply of lithium is comfortable to meet the present demand, International Energy Agency estimates that the demand for lithium from EVs alone will increase 40 times in the next two decades. Unlike lead-acid batteries, only a tiny fraction of lithium-ion batteries are recycled today. If this trend continues, the battery waste from EVs alone will amount to a staggering 10 million tons by 2030. Recycling of lithium-ion batteries is expensive as they are not designed for repair, reuse and recycle. This has to be remedied urgently. The Global Battery Alliance is a consortium of 70 public and private organisations with the objective of creating a sustainable value chain for batteries. A wave of start-ups is surging across Europe and USA to repurpose and recycle old lithiumion batteries. Also, distant on the radar are metal-free, organic batteries that are biodegradable.
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