Item:OSW7d5ef82cc31c49dd99a0df7439fe21dd: Difference between revisions

=== Challenges in Metal-Ion Battery Chemistry ===

So first of all, as you know, metal-ion battery chemistry has in fact a series of challenges, because we have the materials that the crystallochemists develop that will be involved in an electrode with carbon additive binders on the current collectors, but then this one will be integrated in a battery, and this battery will deliver a capacity over a number of cycles. So it can be, of course, the autonomy for a car, for instance, but depending on the use of this battery, of course, we will have more or less fast ageing, depending on the temperature, depending on the C-rate of charge and so on. So we have a lot of reactions that can occur in a battery as illustrated here. I will not go into detail, but what we have to retain is a battery is a metastable system and, I would say, the material by itself, so here the positive electrodes, but also with this interaction with the electrolyte, the electrolyte itself being also metastable.

So of course the batteries are made of two electrodes and an electrolyte, and you have different scales you can look at, here I would say the electrode, here the material, and in our case we are more focused, I would say today, on this scale here, the crystal structures and the atomic and electronic structures of the materials, of course in interactions of the electrodes with the electrolytes.

And at first the motivation was really to go towards, I would say, longer life, more safety for all these materials here, moving from lithium cobalt oxide to NCA, nickel cobalt aluminium, and NMC, nickel manganese cobalt. And in that case, we were really playing with the cationic redox. Now in order to answer to more and more demanding applications in energy, we are also moving to other chemistries, such as lithium-rich layered oxides, rock-salt type structures and high-voltage spinel. And in that case, here for the lithium-rich and layered oxides, we are even jumping in structures, compositions where we have cationic redox and in addition, anionic redox.

And then I will move to sodium-ion technology.

And we had demonstrated also at that time a very long cycling for this material. So stability upon cycling. So just a few slides on this technology that I obtained with the courtesy of Tiamat. So for this technology, you can really do a fast charging, high-power density and superior safety of this material.

So in order to show you that solid-state chemists are also, I would say, a force of proposition for new materials again for this sodium-ion technology.

So then I wanted to conclude this part by highlighting that it's only the characterization in depth of the materials, I would say from the local to the long-run structures and knowledge of defect that allows you to understand the materials. We have also a lot of non-equilibrium phase and mechanisms that are observed. And so for that we need the development of in situ cells and we are really still able to identify original mechanisms, new families of materials of interest for sodium-ion batteries. And I will conclude my talk by giving two perspectives to say that very recently, we have studied all these mixed anion chemistries, here with phosphate, tavorite structures as you can see here for lithium, NVPF structures for sodium and KTP-type structures for potassium-ion batteries.

And I will finish this really by mentioning also that it's worth, of course, to consider, I would say, much more abundant materials such as iron polyanionic materials, and especially here I focus on sulphate and sulphate phosphate materials. We found new phases recently and, of course, the challenge here is really to stabilise these materials and to optimise these materials in order to have very good performances. But they are very interesting, because here we have sodium, iron and sulphur or phosphate systems, so only abundant elements.