# Question about reversible chemistries in anode and cathodes

I've been reading a lot about cathode and anode chemistries recently involving Li-ion cells and solid state chemistries. What makes a decent anode seems to make sense as it is a lower potential area that can accept a lot of lithium ions without being damaged (high cycle life). However, what makes a good cathode still isn't as straight forward to me. It seems the ionization energy of the metal oxides are really important towards power density, but I don't really understand why metal oxides are used.

My guess is something like this: Ionizations of metal oxides leave positive metal ions transitions such as $$\ce{Ni^2+}$$ -> $$\ce{Ni^3+}$$, $$\ce{Cu^2+}$$ -> $$\ce{Cu^3+}$$, and $$\ce{Mg^2+}$$ -> $$\ce{Mg^4+}$$ . Lithium is also positively charged so you are creating a lot of potential energy by shoving lithium into these metal ion locations. Since this is very high energy lithium will spontaneously flow out of the matrix if allowed and maintain good stability with the lost lithium due to the ionization of the metals in the oxide. Good anode materials like lithium metal and crystalline silicon can absorb a lot of lithium, but they would not have a high potential energy for discharge making them unsuited for being a cathode material. Is this why metal oxides are used? Why are metal oxides so good at this? What exactly prevents the lithium ions from just flowing to the anode when not under load?