Battery Chat with Parri #1: Prof. Arumugam Manthiram

Prof. Arumugam Manthiram, a renowned professor at the University of Texas at Austin, has contributed substantially to the field of energy storage with his research having great impact on the scientific community. In this chat, Prof. Manthiram shares his research path briefly, his perspective on current research performed on high-nickel cathodes, and a glimpse of his future research directions.

Professor Arumugam Manthiram
Professor Arumugam Manthiram

Prof. Arumugam Manthiram currently holds the Cockrell Family Regents Chair in Engineering #5 and is the Director of the Texas Materials Institute.

With over 800 publications and 69k citations, his recent papers in Nature Energy and Nature Communications have been accessed by almost 60,000 people. Working on a wide range of high-nickel cathode materials for Li-ion batteries (among other topics), Prof. Arumugam Manthiram's group recently performed a very interesting comparative study on various high nickel-containing cathode compositions: NMA-89 (89 refers to 89% nickel content) to NMC-89, NCA-89, and Al-Mg co-doped NMC (NMCAM-89).

Parri Adeli: Thanks for taking the time to chat with me. When you were a young scientist, what type of research were you interested in and how did it change throughout the years?

Prof. Arumugam Manthiram: No problem. I did my PhD in India at the Indian Institute of Technology. My PhD was on synthesis and electrical and magnetic properties of molybdenum oxides. When I was doing my PhD in India, one of the examiners for my PhD thesis happened to be the legendary John Goodenough. After finishing my PhD, I worked in India at Madurai Kamaraj University for four years as a lecturer. Then, I proceeded by applying for a postdoc in Goodenough’s group in 1985 at the University of Oxford. Ten months later we went together to the University of Texas at Austin in September 1986. I worked as a postdoc on both batteries and high-temperature superconductors, which at that time was a hot topic. Polyanion cathode work was originally started by me at Oxford in 1985 and two papers came out in 1987 and 1989. Ten years later LiFePO4 came out in 1997. At the time of my postdoctoral fellow work, we didn’t think these polyanions being this useful, because of their very insulating nature. We published the polyanion cathode paper in Journal of Power Sources in 1989. Then, I got a job in Bellcore in New Jersey, but Goodenough said “you are not an industry guy” and persuaded me to stay as a faculty at the University of Texas, and I accepted it. I have stayed at one place in the US, for the past 34 years.

Prof. Arumugam Manthiram giving John B. Goodenough’s Nobel Lecture on Sunday 8 December 2019, at the Aula Magna, Stockholm University
Prof. Arumugam Manthiram giving John B. Goodenough’s Nobel Lecture on Sunday 8 December 2019, at the Aula Magna, Stockholm University

PA: You have been a close friend and colleague of Prof. John Goodenough for the longest time and delivered his Nobel Prize lecture. Could you please share any advice with us that you learned from him? 

AM: John Goodenough is my role model. He is one of the most accomplished scientists, he is very sharp, very smart, with high analytical capabilities. Aside from his many publications, he has helped the society with his research in terms of new materials discovery, for example, for digital computers in the 60s, 70s, and Li-ion batteries as well as solid electrolytes. One good thing I have learned from him is that he sleeps a solid eight hours every day, and sometimes more. That means he can think clearly and that results in good science. If you sleep well and focus when you are at work, at the end of the day you will be more efficient.

PA: Could you please talk a little about your very interesting paper “High‐nickel NMA: A cobalt‐free alternative to NMC and NCA cathodes for lithium‐ion batteries”? Are there any updates on that project that you could share with us?

AM: I love oxides. My PhD was on oxides, and later I worked on oxide cathodes, crystal chemistry, how the atoms arrange and the structure. During my PhD, I didn’t learn much physics. Because I worked with Goodenough who is a physicist, I was exposed to physics and chemistry together, e.g. band structure, redox energy levels, etc.

By combining good crystal chemistry, structural knowledge, and the positions of redox energies of different ions, we have a good understanding of which metal ion will do what in the layered oxide. That’s how we were able to design some cathode compositions. Synthesis condition is very critical. When you increase the nickel content, the synthesis temperature must be lower because Ni3+ is not very stable at high temperature. Cobalt oxide can be heated at 800 to 850 °C with no problem. When you keep on putting nickel, the temperature will go down. For the NMA, good crystal chemistry knowledge, good knowledge of the redox energies of different ions, plus good control of the tank reactor synthesis were helpful. All these together we were able to achieve NMA.

The paper you mentioned has been published, since then we have opened the cells, we have been analyzing those four or five materials to see what the differences are. It’s almost completed and is a subject of another pending paper.

PA: What sparked this study and what is the end goal?

AM: Cobalt is expensive and the overall cost of EVs will go up if we use a lot of batteries with cobalt. Add to that supply chain issues. Cobalt is mined in the Democratic Republic of Congo, there are other issues there, child labor, children getting exposed; all these were concerns to me. All these issues, as well as the cost and supply chain issues for US and Canada, prompted us to first reduce the Co amount and then finally eliminate it completely. We were working with a composition that contained 94% Ni and 6% Co before. We were working on that for three years and have at least five or six published papers on that subject. Slowly, from 94% Ni and 6% Co, we went to Co-free composition. For a very long time, the general belief was that you really need Co and if you remove Co, you cannot get the desired performance. Our group demonstrated that this is not necessarily true, and we can make materials work without Co.

PA: What makes nickel an attractive element for use in battery materials?

AM: The weight of material has to be low for batteries. That means that we must work with 3d transition metals. As you go from left to right, titanium to nickel or copper, the transition metal 3d energy level keeps on going down, so that means you can increase the cell voltage.

The second most important thing is in the 3d transition metal series; Ni is the only one that you can go through two valences, from 2+ to 3+, 3+ to 4+, with no break in the voltage. You still get one continuous, a little bit sloping voltage profile while going through two valence states. That’s amazing. You can do that with vanadium 3+ to 4+, 4+ to 5+ but there will be a break in the voltage. Industry doesn’t like a sudden break in the voltage.

The other advantage of Ni is that its size doesn’t change too much. Ni is way in the right side of the periodic table, therefore the nickel-oxygen bond is very covalent. That means the electron density will be very much delocalized; so you can have good electronic conductivity. If you stay in the left side of the periodic table the issues are that voltage will be lower, electron density will be more localized, and conductivity may be less. Additionally, if you compare Ni and Co, Co can be oxidized only up to 3.5+. You cannot completely charge LCO by removing all the lithium from LCO. You cannot get CoO2, but from LiNiO2, you can remove all the lithium and get NiO2, so Ni4+ can be accessed while Co4+ cannot be accessed.

That’s why when you have Ni, you can have more capacity. When you have Co, you can only have 50% of the capacity.

PA: In your opinion, how will Ni-based cathode materials stack-up to other known and emerging cathode materials and Li-ion technologies such as LFP or rock salt cathodes?

AM: If LFP is made properly, it will work well. Countries like China or India may need the vehicle for short range, then LFP will work for them.  In India, given the extreme temperature fluctuations, good temperature tolerance is required. LFP possesses good temperature tolerance and high rate capabilities. In western countries, e.g. US and Canada, we try to travel long distances. Going from Austin to Dallas, it’s 200 miles, so we need high capacity, high energy density materials. The application and the requirement may be different from people to people and from country to country. For the US, as well as some countries in Europe, energy density is the most dominant factor. Some countries are not very developed, they may have shorter driving distances. It is clear that for countries like US and Canada, the high-Ni cathodes are really wanted because of the high capacity, high energy density and longer driving range. Tesla is already using and will keep using NCA and high Ni. Regarding rock salt cathodes, we still have to see in terms of real cell, how it compares for cyclability and energy density. They have a little bit sloping voltage profile. So, it’s hard to comment on it from a practical perspective at present. But from a basic science perspective, it’s good.

It is clear that for countries like US and Canada, the high-Ni cathodes are really wanted because of the high capacity, high energy density and longer driving range. Tesla is already using and will keep using NCA and high Ni.

PA: What must happen for Ni-based cathode materials to be fully adopted by the Li-ion battery community?

When you have more than 90% Ni, we have three problems, as the nickel content increases; these problems become exponentially challenging. When you go from 70% Ni to 80%, it is harder compared to going from 60% Ni to 70%. 90% to 95% is much harder. 95% to 100% is way harder. The challenges with high nickel are limited 1) cycle life, 2) thermal stability that means safety, and 3) air stability; if you make the material and keep it in air, residual Li will form. Lithium hydroxide and lithium carbonate will form on the surface of a high Ni compound and that is called residual Li in the industry. That creates multiple problems. a) Cyclability will go down. b) Electrode making becomes a headache for the industry because Li carbonate and Li hydroxide on the surface clog the electrode slurry. c) It will also evolve gas. The cell will bulge and that’s a safety hazard. The air stability has lots of consequences so you cannot keep the material in air for long. You must protect it, which costs more money and precaution which is not good for industry. We have to work on that both by bulk doping as well as surface stabilization. I think with all the work being done, the challenges can be worked out as we move forward.

PA: Do you believe in the performance of single crystal NMCs?

AM: The reason cyclability goes down when you have high Ni is that: when you charge it you create Ni4+ -  surface reacts very aggressively with the electrolyte; when it reacts, Ni dissolves, goes though the separator  and deposits on the graphite anode; and that creates problems for the graphite performance and impedance goes up. With single crystal, the major advantage is that you can reduce surface activity; it may also reduce residual lithium. We are making some single crystals in our lab too. We are in the process of making these single crystals with different methods. If there is a way that people can make single crystals without increasing the cost, that will have a lot of potential.   

PA: What is the latest news with TexPower? Where do you see the direction of your research lab in the next five years?

TexPower is a small startup company. They are mainly focusing on scaling up and producing the materials so they can become a demotic supplier. The R&D done at TexPower will be towards that large-scale production capability.

In my lab, I don’t have any restrictions. We will be exploring not just NMA, but also other compositions, while keeping the Ni content high; at the same time, finding out the best cyclability, best air stability and best thermal stability. We are doing lots of exploratory research work in terms of different compositions so we can accomplish good materials. We are also working on single crystal, and we do lots of postmortem analysis after 1000 cycles. We have a lot of analytical capability at UT Austin, such as X-ray photoelectron spectroscopy and High-resolution Transmission Electron Microscopy. We are also following how the impedance changes as we keep on cycling different materials. Our eventual goal in the next few years is: What is the best we can get out of layered oxides in terms of performance? What can we do to overcome their challenges?

We will be focusing on high Ni but aside from that my group is also working on Li-sulfur and Na-sulfur.

PA: How much potential do you see in Li-ion alternative chemistries? Please give your perspective on the Li-ion battery landscape.

AM: Li-ion will still be dominant for a long time even if you have other technologies. Some applications will still use Li-ion because a lot of advantages come with it. Cost is one of the considerations and Li-sulfur will lower the cost, but performance-wise, Li-ion still can have some dominance. Perhaps we can never eliminate Li-ion completely.

A lot of people in the US and Asia are working on Li-S, and progress is continuously being made. One of the problems with the early work was that people used to have a lot of electrolyte, a little bit of sulfur; low loading and coin cell will not tell you everything, so now we are using pouch cells. We also try to have all these parameters under control. Loading at least 5 mg/cm2, less carbon and less liquid electrolyte, the electrolyte to sulfur ratio is less than 5 µl/mg of sulfur. In addition, we are doing anode free cells, meaning at the anode we don’t have any excess metallic lithium.

We are also doing some work with lithiophilic hosts as well. Right now, the problem with Li-S is that with long cyclability, practical energy density is low. For applications that don’t need long life and just need e.g., 200 cycles, Li-S can become potentially viable.

I’ve got a project on multivalent ions, which is on basic science. The problem with multivalent ions, Mg, Ca or Zn, is that if you have closed pack structure, like layered oxide or spinel, it’s very difficult for these ions to move from one site to another site due to electrostatic repulsion. That means you cannot have good rate capability and you cannot utilize the whole material. Then, on top of it, the voltage will be lower, so oxides, closed packed oxides, do not work well. You have to work with open structure materials, which causes lower volumetric energy density too; they may be heavier, and the voltage already will be down with Mg, Ca or Zn. If you want to overcome the diffusion problem, you have to go to more covalent systems like sulfides. You will lose the voltage again. At the end of the day, I do not believe you can get higher energy density than Li-ion or Na-ion with these multivalent ion batteries because of the diffusional challenges, as well as the already intrinsically lower voltages. There may be some cost advantages in some systems, but also there is no good electrolyte available, so there are many, many challenges. It’s very hard for them to compete.

At the end of the day, I do not believe you can get higher energy density than Li-ion or Na-ion with these multivalent ion batteries because of the diffusional challenges, as well as the already intrinsically lower voltages.

PA: Any closing remarks you would like to share with us?

AM: This is a good time for those working on clean energy, including solar, wind, energy storage or even fuel cells, because it’s a critical issue for society; so the scientist and engineers have to work hard and solve some of the challenges that we are facing; for our children and grandchildren to have a better planet and better life as we move forward - because energy is central for everything we do.

PA: Once again, thanks for joining us for this great conversation.

AM: It was nice talking to you.

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