The electric vehicles story is taking off rather nicely in India. Last year, electric two-wheeler sales increased to 2.3 lakh units from 41,050 in 2020-21; for electric three-wheelers the figure was about 1.78 lakh from 88,391; and for electric four-wheelers it was 19,520 units (4,588). However, the dampener to this heartening data is in the form of safety concerns, after a couple of electric bikes caught fire. A prospective EV buyer might be excused for dithering at the doorstep of the showroom.
Podcast | How solid-state batteries can stop EVs from catching fire
Nevertheless, EV batteries catching fire may soon be history. The world is moving towards ‘solid-state batteries’, which, as the name suggests, have only solid components. In contrast, today’s lithium ion (Li-ion) batteries have liquid electrolytes — the medium in which positive ions move from the anode to the cathode.
Typically, in Li-ion batteries the liquid electrolytes are organic solvents, which are highly flammable, says MM Shaijumon, Associate Professor at the Indian Institute of Science Education and Research (IISER), Thiruvananthapuram. If current distribution is uneven, filament-like structures called dendrites can form, connecting the two electrodes and causing a short-circuit.
“The dendrites connect the anode and cathode through the separator, providing a low-resistance path for electron transport, resulting in high self-discharge currents to ignite the flammable electrolyte and leading to explosions,” says Ramaswamy Murugan, professor of Physics, Pondicherry University, in a recent article in the Journal of The Electrochemical Society. “Therefore, dendrite growth is one of the most highlighted issues since it affects the safety of a battery,” the paper says.
Efficiency first
In contrast, batteries with solid electrolytes do not have the danger of dendrite growth. The move to solid-state batteries, though, is primarily driven by the ‘efficiency’ factor rather than ‘safety’.
A better battery is one that can pack more energy. Scientists say solid-state batteries can have an energy density of 350 watt-hour per kg, as opposed to 100-260 Whr/kg of the conventional lithium-ion batteries. “The absence of a liquid electrolyte in all-solid-state lithium batteries simplifies the packaging and reduces dead weight in the battery, resulting in improved energy density,” says Murugan.
Shaijumon notes that solid-state electrolytes are typically less reactive than today’s liquid or gel-type electrolytes; they will last longer.
Banding together
Now, the good news against this backdrop is, the government of India recently announced a major push towards solid-state battery research. A consortium of 15 institutions, including the IITs of Bombay, Roorkie, Kanpur, Kharagpur, has been set up, with IISER as the lead centre. This initiative of the Department of Science and Technology is one of three that constitute the ‘Integrated Clean Energy Material Acceleration Platform’. The consortium “aims to accelerate the development of solid-state battery technology using AI [artificial intelligence] and ML [machine learning], through automated processes,” says a government press release. Each of the partner institutions has a specific role — for example, IIT Roorkie would work on the electrolyte and device testing.
In a conversation with Quantum, Shaijumon observed that the development of solid-state batteries is a question of engineering — the science itself is settled. The major challenges arise out of the basic differences in the electrochemical, mechanical and electrical properties of the solid electrolytes, compared with the conventional liquid electrolytes, he said.
Yogesh Sharma of IIT Roorkie, who is the lead principal investigator for this project, explained to Quantum that the fundamental challenge with solid electrolytes is the “interface with the electrodes”. In a cell (a battery is a combination of cells), there are two electrodes — the anode, which is the electron giver, and the cathode, which is the electron acceptor. The electrons move from the anode to the cathode via an external circuit — that ‘flow’ is electricity. The atoms that have lost electrons, to become positively charged ions, also move from the anode to the cathode, but through the electrolyte. If the electrolyte is a liquid, it would percolate into the electrodes and the ion transfer would be easy. If it is a solid, the ion transfer would be limited to the regions where the electrolyte and electrodes are in contact. So, the principal challenge is to get ‘good ionic conductivity’ even while using a solid electrolyte. The consortium would be looking at the compatibility of different solid electrolyte candidates with the electrodes, Sharma said, adding that research aims to develop “nano-structured electrolytes”.
Further, a big question is whether the existing infrastructure for lithium-ion battery production could be exploited for making solid-state batteries.
Help from AI
If the advantages of the solid-state battery are so obvious, then what is holding back its quick adoption? Well, it is still work-in-progress. Shaijumon says that “significant efforts” are needed before solid-states batteries can become a commercial reality. “For example, the slot-die method cannot be employed, due to the brittle nature of the inorganic solid electrolyte,” he points out. Bulk production needs innovative manufacturing techniques.
That is exactly what the 15-member consortium is working on. Looking at different electrolytes and analysing the appropriateness of each of their properties is a humungous task — that is where AI comes in. Phosphates and oxides of lithium (lithium aluminium germanium phosphate or LAGP; and lithium lanthanum zirconium oxide or LLZO, which is a garnet material) are the most studied solid electrolyte materials.
The aim of the consortium is to come up with a device — a solid-state battery fit to be commercialised. “Solid-state batteries combine the performance of conventional lithium-ion/lithium polymer systems with higher safety for usage and flexibility in form-factor, to target versatile applications,” says Chandramouli Subramaniam of IIT Bombay. “Such a project, taken up in a consortium mode, will bring together varied expertise to deliver the holy grail of energy storage in a time-bound and cost-effective manner.”
Both Shaijumon and Sharma have described the effort as “challenging”. It would take about three years, but when the device is developed, India would have a home-grown, low-cost battery technology guaranteed to transport people safely.