More on lithium batteries
Last winter I've complained that it isn't known how Li-ion batteries work on a molecular level, although we daily use them in our laptops and phones
http://shkrobius.livejournal.com/398842.html
That's scandal. That's outrage.
So I decided to find out - and I did!
It turns out that radical chemistry works in such a way that ethylene carbonate (the "magic" electrolyte, see the post), which is reduced on graphite electrode, can polymerize yielding a 3D cross-linked polymer network, like a net, whereas propylene carbonate makes a disconnected network, like a bowl of spaghetti, so electrolyte molecules keep diffusing through it and intercalating between graphene sheets, eventually destroying the electrode.
The reason it took 25 years to find out was that everyone got this chemistry either completely or mostly incorrect... Einstein famously said that imagination is more important than knowledge - sorry, not in chemistry. It was all speculative; no one made direct observations of reaction intermediates postulated in the many models proposed. When computational chemists got involved, their theories (surprise, surprise) provided support for these hand waving models. These folk "knew" what they needed to obtain - and they tweaked their models until they got it: the models are complex; there are lot of knobs to tweak. Incredibly, even on rare occasion when they got it right they dismissed their own results, ascribing discrepancies to model imperfections... People were fooling themselves and each other into believing their own imagination. In chemistry (biology, too), imagining things is cheap, testing theories and making things is hard.
I wonder how it will be received; we are stepping on a lot of toes.
It is all here
http://pubs.acs.org/doi/abs/10.1021/jp406274e
http://pubs.acs.org/doi/abs/10.1021/jp406273p
http://shkrobius.livejournal.com/398842.html
That's scandal. That's outrage.
So I decided to find out - and I did!
It turns out that radical chemistry works in such a way that ethylene carbonate (the "magic" electrolyte, see the post), which is reduced on graphite electrode, can polymerize yielding a 3D cross-linked polymer network, like a net, whereas propylene carbonate makes a disconnected network, like a bowl of spaghetti, so electrolyte molecules keep diffusing through it and intercalating between graphene sheets, eventually destroying the electrode.
The reason it took 25 years to find out was that everyone got this chemistry either completely or mostly incorrect... Einstein famously said that imagination is more important than knowledge - sorry, not in chemistry. It was all speculative; no one made direct observations of reaction intermediates postulated in the many models proposed. When computational chemists got involved, their theories (surprise, surprise) provided support for these hand waving models. These folk "knew" what they needed to obtain - and they tweaked their models until they got it: the models are complex; there are lot of knobs to tweak. Incredibly, even on rare occasion when they got it right they dismissed their own results, ascribing discrepancies to model imperfections... People were fooling themselves and each other into believing their own imagination. In chemistry (biology, too), imagining things is cheap, testing theories and making things is hard.
I wonder how it will be received; we are stepping on a lot of toes.
It is all here
http://pubs.acs.org/doi/abs/10.1021/jp406274e
http://pubs.acs.org/doi/abs/10.1021/jp406273p