Is it possible create crystalline solvate of electrons?
At first I would like to advise you reading about electrides, which were mentioned in the comments. Secondly I won't write about electrides because the links given in the comments are much better at explaining them. So I am going to be a little bit abstract with this question. The first problem which you will come through is Coulomb's law:
$$\mathbf F=\frac{1}{4\pi \epsilon_{0}}\frac{Q_{1}Q_{2}}{|\mathbf r|^{2}}\frac{\mathbf r}{|\mathbf r|}$$
If you could somehow prepare even $0.01$ moles of electrons, they would be attracted to the ions which they were separated from very strongly even from kilometers away. The second problem is that electrons can't be simply trapped into any substance because of their wavelike nature and they would tend to "stay" in a localised or in a delocalised state in the molecoules. And here comes the two main things which are preventing such things to exist: 
1. Charge distribution 
If a conducting body is charged, the charge tends to build up on the edges, and in your situation the repulsive force between the electrons would be so huge, they would "kick" each other off on the edges of the pieces of the substance so it would loose it's electrons.An interesting phenomena such substance would have: Let's suppose the substance containing the electrons is a liquid. All the electrons would be located on the surface of the liquid because of the faraday effect.When the surface of the liquid is disturbed waves appear on it's surface. Let's suppose the electrons somehow can't be kicked off from the surface.
Then there would always be electric current in the liquid because the elecrons would always try to get to the most sharp edge on the surface and the liquid would generate extremely complex magnetic fields because of the currents flowing on the surface of the liquid (I am so excited about the idea of such a liquid, I am so sad I have no idea how it would be possible to make it)
2. Quantum mechanics
The band gap determines if a substance is an insulator or a semiconductor or a conductor. And adding more electrons to something doesn't modify the band gaps. Like if I charge a plastic rod with electrons it won't become a conductor. But there is an alternative solution. If you dope the substance it can modify the band gap energy and it can be more conductive but you can't simply trap electrons in something (F-centers are a completely different story). Imagine irradiating carbon nanotubes with electrons. I wouldn't suspect it becoming more conducting .
Anyway the best source for pure electrons is an electron gun 
If you want to deepen your knowledge about the nature of electrons and conductivity I advise you learning some solid-state physics, quantum mechanics and electromagnetism.(None of them is a light weekend program)