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This is a part of the EV Innovation Intelligence series

Li-ion is the dominant standard for batteries for the e-mobility industry. And most industry experts think that Li-ion chemistry has established a strong foundation that will last at least for a couple of decades.

Or will it?

While some battery chemistries or battery types such as flow batteries could be more suited for stationary storage, there indeed are half a dozen new chemistries vying for a place – and possibly the top place – on the podium.

Solid-state batteries

The candidate most spoken about as having the potential to overtake LiB is the solid-state battery chemistry. Until a couple of years back, it looked as if this will take over a decade to get anywhere near commercial, it now looks that it could be faster.

Technically, solid-state batteries are Li batteries too. The cell architecture and the electrolyte changes. The solid electrolyte allows faster transfer of li-ions between the cathode and Anode, therefore faster charging and strong discharging. Moreover, the solid-state implies less space is taken up. So a solid-state battery cell probably has a smaller size. Therefore SSB has more volumetric energy density than normal Li-ion batteries.

Flow batteries

Flow batteries present interesting possibilities too, and they are already being commercialized, but these are far more suited to stationary storage systems than mobile.

Ultra-capacitors & super-capacitors

There has been a spate of announcements the last few years on startups working around capacitors. Capacitors get charged really fast, though they cannot hold a lot of energy. Many startups are hence working on a hybrid of capacitor/battery combination to leverage the strengths of capacitors and batteries.

Different Li chemistry batteries

Within Li-ion batteries, efforts are ongoing to use a number of different chemistries both at the anode and cathode, though these would technically come under the Li-ion chemistry.

There could be changes at the anodes as well. Graphite has been long used as the primary anode material. Silicon recently has shown the potential to replace graphite while being more efficient in losing electrons and taking in ions. Also, Silicon is the earth’s second most abundant material. And that helps.

  • LTO is one of the safest lithium-ion chemistries and does not involve thermal rundowns. The high current flow implies faster charging of the battery than other Li-ion batteries. A disadvantage of lithium-titanate batteries is that they have a lower inherent voltage (2.4 V), which leads to lower specific energy (about 30–110 Wh/kg) than conventional lithium-ion battery technologies, which have an inherent voltage of 3.7 V, although some lithium-titanate batteries are reported to have an energy density of up to 177 Wh/L.
  • Lithium-sulfur batteries are a little different from normal LiBs, where lithium is used in the anode and sulfur in the cathode. Lithium-sulfur batteries may succeed lithium-ion cells because of their higher energy density and reduced cost due to the use of sulfur] Some Li–S batteries offer specific energies on the order of 500 Wh/kg, significantly better than most lithium-ion batteries. Though Li-S has been around since the 1960s, it is not yet commercialized owing to sulfur as a weak cathode. The sulfur content decreases in time rendering the battery useless in 3-4 years. However, the academic versions of Li-S have been showing promise. One start-up has achieved 470 Wh/kg of specific energy density and is aiming to increase it to 500 Wh/kg while guarding the sulfur.

Metal air batteries

Metal air batteries typically cannot be recharged, though they have higher energy densities than Li-ion batteries. The trick is to figure out how to overcome the no-recharge problem.

In these batteries, the anode metal would have to replace, but these can be recycled and reused. Most metal-air batteries are Zinc and Aluminium which are near infinitely recyclable.

In use cases, Al-air batteries have been shown to attain a range of 1600kms on a single sheet of aluminum. Then the sheet would have to be replaced.

  • Aluminum-air flow batteries for EVs outperform the existing lithium-ion batteries in terms of higher energy density, lower cost, longer cycle life, and higher safety. Aluminum-air flow batteries are primary cells, which means that they cannot be recharged via conventional means. In EVs, they produce electricity by replacing the aluminum plate and electrolyte. Considering the actual energy density of gasoline and aluminum of the same weight, aluminum is superior.

Over the past several years, over 100 villages in Africa and Asia have received power from batteries that use zinc and oxygen, the basis of an energy storage system developed by Arizona-based NantEnergy. Zinc’s abundant supply, fundamental stability, and low cost make it an attractive alternative to lithium, but efforts to make it commercially viable at scale have been few and far between. NantEnergy’s zinc-air battery system replaces a second electrode with one that “breathes air”, using oxygen from the atmosphere to extract power from zinc.

Lead-acid batteries

Lead-acid batteries are not yet dead, even in electric vehicles. While their chances of being in electric vehicles in the future are low, lead-acid batteries are the workhorse of the stationary storage systems and they could find use in parallel with other battery types to compete against Li-ion batteries in stationary storage.

Sodium sulfur batteries

These are molten-salt batteries constructed from liquid sodium and sulfur). Sporting high energy density, these also have high efficiency for charging & discharging, and long cycle life. An added advantage is of course that these are fabricated from inexpensive materials.

So far, however, these batteries have seen to be more suitable for stationary energy storage applications where they are seeing increasing traction.

For instance, in February 2019, Abu Dhabi installed the world’s largest storage battery which makes use of sodium-sulfur battery cells. It is five times larger than the second-largest storage battery at 108 megawatts (MW)/ 648 megawatt-hours (MWh).

Some challenges are present with these batteries, though. There are risks involved with handling both sodium and sulfur due to the volatile nature of both reactants. Liquid sodium coming into contact with water in the atmosphere poses a significant risk due to the highly exothermic reaction, which could become explosive when working at scale.

Graphene-based batteries

Using graphene coatings in Li-ion batteries could increase their energy efficiency and significantly decrease the time to charge. These are expected to have a big future, but the future doesn’t seem to have arrived as of early 2021.

Fluoride batteries

Fluoride batteries have the potential to last eight times longer than lithium batteries, but that’s easier said than done. That’s because fluoride is an anion, or a negatively charged ion, which is the magic behind its high energy density but is also the reason it’s reactive and hard to stabilize. In December 2018, a research team announced that they had hit upon a liquid electrolyte that could stabilize the element and make it usable at room temperature, so things are starting to look good for fluoride batteries.

What are the key drawbacks of the current LiB battery chemistries and how are the emerging battery chem trying to overcome these?

Drawbacks of the current LiB battery chemistries:

  • Requires protection circuit to maintain voltage and current within safe limits 
  • Subject to aging, even if not in use – storage in a cool place at 40% charge reduces the aging effect. 
  • Transportation restrictions – shipment of larger quantities may be subject to regulatory control. (This restriction does not apply to personal carry-on batteries.)
  • Expensive to manufacture – about 40 percent higher in cost than nickel-cadmium.
  • Not fully mature – metals and chemicals are changing on a continuing basis.

It is estimated that there is a new development in battery chemistry almost every 6 months as more OEMs are particular about the technology they require for their vehicles and newer regulations coming into place from different geographies.  Innovation and performance characteristics in batteries aren’t limited to their electrode chemistries alone. Other factors such as coating materials, state of electrolyte, and their structural arrangement in a cell also contribute to the battery’s overall performance.

  • Leclanché is working on a technology that uses lithium iron phosphate (LFP), which has an “olivine” structure, as the cathode, and lithium titanate oxide (LTO), which has a “spinel” structure, as the anode. These structures are better at handling the flow of lithium ions in and out of the material. These cells can be charged 100% in just 9 minutes.
  • Regarding the silicon anode problem – Sila Nano’s approach is to encase silicon atoms inside a nano-sized shell with lots of empty room inside. That way, the SEI is formed on the outside of the shell and the expansion of silicon atoms happens inside it without shattering the SEI after each charge-discharge cycle.
  • Regarding highly volatile electrolytes – Lithium batteries always use flammable liquids as the electrolyte.. One solution is to use solid electrolytes. But that means other compromises. A battery design can easily include a liquid electrolyte that’s in contact with every bit of the electrodes, making it able to efficiently transfer ions. It’s much harder with solids. Imagine dropping a pair of dice into a cup of water. Now imagine dropping those same dice into a cup of sand. Obviously, the water will touch far more surface area of the dice than the sand will. 
  • Alternatives to lithium are quite far from batteries. It is difficult to find anodes for chemistries such as sodium-ion batteries. Employing nanosized or nanostructured forms of the active material has been demonstrated as an effective strategy to overcome this problem, yet it is questionable whether such methods are sufficiently cost-effective to be implemented on an industrial scale. Since the only advantages of SIBs are the low cost of sodium salts and the fact that low-cost Al current collectors can be used on the anode side (because Na, unlike Li, does not alloy with Al), many electrode materials developed to date for SIBs are unsuitable for the use in commercial cells considering the relatively high cost of their preparation.
  • Estimations show that by 2025, 75% of the world’s lithium consumption will be for batteries which still puts it at half of the world’s available lithium resources, so there is a motive that the electric vehicle industry will not be severely affected by lithium scarcity. Moreover, almost every major EV OEM is looking towards battery recycling(which in itself is at an advanced stage where 98% of total constituents can be recovered) to ensure the value chain is not depreciating.

Which are the top battery types other than lithium-ion batteries that have the potential for EVs? What is their current status of development/ commercialization?

  • Magnesium-ion batteries could serve as an alternative to lithium-ion batteries in electric cars and grid storage. Such batteries would use a cathode and an electrolyte similar to that of lithium-ion. However, the anode would be critically different. A typical Mg-ion battery would not make use of graphite, or any sort of intercalation anode, and would directly use magnesium metal.
    • On paper, magnesium-ion offers a tremendous potential energy boost over lithium-ion, possibly as much as two-to-one. In theory, such capabilities would enable automakers to use batteries that are half the size, while offering the same power. However, such advancements face several technical challenges and are still far from the prototype stage.
  • .Lithium–Sulphur – Magnesium-ion batteries could serve as an alternative to lithium-ion batteries in electric cars and grid storage. Such batteries would use a cathode and an electrolyte similar to that of lithium-ion. However, the anode would be critically different. A typical Mg-ion battery would not make use of graphite, or any sort of intercalation anode, and would directly use magnesium metal.
    • On paper, magnesium-ion offers a tremendous potential energy boost over lithium-ion—possibly as much as two-to-one. In theory, such capabilities would enable automakers to use batteries that are half the size, while offering the same power. However, such advancements face several technical challenges and are still far from the prototype stage.
  • Nickel-zinc batteries are cost-effective, safe, non-toxic, eco-friendly batteries that could compete with Li-ion batteries for energy storage. However, the main barrier for commercialization has been the low cycle life of nickel-zinc batteries.
    • Chinese researchers from the Dalian University of Technology have developed a breakthrough technique to improve the performance of Ni-Zn batteries by solving the issue of Zn electrode dissolution, dendrite formation, and performance.
  • Sodium-Metal – Stanford researchers released a paper claiming that their sodium batteries could compete with lithium-ion batteries. The Stanford battery uses sodium, a cheaper, more abundant material than lithium, and is still in the development stage.
    • The cathode of this battery is made up of sodium, and the anode is made from phosphorus, with the addition of a compound derived from rice bran or corn. According to researchers, this chemical combination yields efficiency rates comparable to that of lithium-ion batteries at a lower cost. The main advantage of the sodium battery lies in the fact that sodium is much more abundant than lithium, and it costs $150 per ton versus $15,000 for lithium. 
  • Aluminum-ion and Lithium-ion batteries are very similar, except that the former has an aluminum anode. Aluminum-ion batteries provide increased safety and faster charging time at a lower cost than lithium-ion batteries; however, there are still issues with cyclability and life span. Stanford University is a leading developer of aluminum-ion batteries that incorporate a graphite cathode. The research holds the potential for making cheap, ultra-fast charging, and flexible batteries, with thousands of charge cycles, in addition to being a safe, non-flammable option with a high charge storage capacity.
    • Aluminum-air flow batteries for EVs outperform the existing lithium-ion batteries in terms of higher energy density, lower cost, longer cycle life, and higher safety. Aluminum-air flow batteries are primary cells, which means that they cannot be recharged via conventional means. In EVs, they produce electricity by replacing the aluminum plate and electrolyte. Considering the actual energy density of gasoline and aluminum of the same weight, aluminum is superior.

This is a part of the EV Innovation Intelligence series

Posts in the series

Tesla’s Valuation | EV’s in different countries | Purpose built EVs | Mainstream Fuel Cells | IT in Emobility | EVs versus ICEs | Advent of China in Emobility | Charging vs Swapping | Micromobility & EVs | Electric Aviation | Li-ion alternatives | Million Mile Battery | Battery Startups versus Giants | Sales & Financing Models | Ultrafast Charging a Norm | Heavy Electric Vehicles | Material Sciences in Emobility | Lithium Scarcity | Solar Power in EV Ecosystem | EV Manufacturing Paradigm | Innovations in Motors | EV Startups – a speciality Oil Companies’ Strategies | EV Adoption Paths | Covid-19 affect on the EV Industry |

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