From the first intercalating cathode (TiS2) to discovery of LiCoO2

Hello everyone, are you ready for an exciting journey to Li-ion batteries? Let’s start! 

As you know before Li-ion batteries, we used to use aqueous electrolytes. This limits the operation voltage, basically we cannot cycle the electrodes above 2 V. To cycle the electrodes at higher voltage, researchers suggested to use non-aqueous electrolytes in rechargeable batteries. By non-aqueous electrolytes, the battery safety improved because there is no water evaporation/moisture issue anymore.

In 1970s, for the first time, layered TiS₂ cathode was used as an intercalating electrode with Li metal anode and non-aqueous electrolyte. Layered cathode brought good reversibility during charge-discharge of the battery. Li ions (Li⁺) could flow from anode to cathode and intercalate into cathode 2D layers, which was accompanied by reduction of Ti⁺⁴ to Ti³⁺ ions. However, researchers realized that operating voltage is still low (<2.5 V). But why? The reason was behind the Density of States (DOS) theory.

Now, we need to know what the DOS is. If we define DOS; it is a way to show electronic configuration of molecular orbitals. If we consider the case in TiS₂ – Li system, DOS demonstrates that we have overlapping between bands. Here, transition metal (Ti ^3+/4+) 3d band is overlapping the S^2- 3p band. For example, Fig. 1 displays that Co^2+/3+ 3d band is overlapping with S^2- 3p band. The overlapping causes introduction of holes or formation of molecular ions (S₂^2-).

Later, Goodenough’s (still is not good enough to be awarded by Nobel Prize (!), why??) groups tried to find a solution to this problem. What they did is use of oxide based cathodes instead of sulphide based one. This is so reasonable that the gap between transition metal (Co) 3d band and O^2- 2p band will be higher, so no more overlapping problem. This is much obvious in Co^2+/3+ case that there is no overlapping. This research also opened a new road to layer-oxides world by discovery of LiCoO₂ (LCO), which will be explained in the next chapter.

Reference: “Handbook of Battery Materials” but the story and the way of describing the information belongs to me. (no cheating/no coping)

If Lithium was a girl..

This is me: I am lithium, but they call me Li.

 I am valuable and expensive, like silver and gold becuase people need me in any field, such as energy storage, medicine and metallugy. Therefore, I am a little bit prima donna,, ahh everyone likes me what should I do!! :)

I am a fit girl, not so dense,, I can produce sufficient energy even I have a very low density, so all boys like me! I am the only one! :)

You should know I am a really shiny, soft and sensitive girl, I can react easily with water and tend to produce hydroxides. I even like air and produce my oxides, nitrates and carbonates. I cannot stay alone!! Ohh I like everyone!! OMG I am so nice!! :)



My energy (activation) is such high, you cannot take the electrons from me! If you do this, I become super angry and release a lot of heat!



I have a question for you: Why am I so sensitive (reactive)? In fact, I am on the upper left side of the periodic table, and generally metallic properties increase down the group (not up the group). It is a little bit strange, isn't it? Do you have an idea? Mmm, I am mysterious, right? :)

If you wanna know more about me, why not stay in touch?? Lets follow my blog! 

See you my crazy scientist!! Do you believe you can find my best friend, high voltage electrolyte for your high performance batteries? Oh keep doing research. I think, one day you will find something... but I am sure today is not that day.. Oh do not be sad, you know this is research... But I believe, we can learn anything from Google unckle if we know how to do search. 

Ok, see you next time,, I need some beauty nap. Omg I talked a lot, I seriously need to sleep! Kiss!!