system
Given the following post, respond as if you're commenting on Reddit:
human
What is holding us back in making more efficient batteries, to store e.g. solar generated electricity?

I'm reading a lot of places that what really hinders renewable energy sources from reaching its peak is that we're unable to store energy properly. Could someone elaborate a bit on that?

Secondly, given that the statement is true, why can't we use rechargeable batteries, e.g. lithium batteries, to store the energy produced? Wouldn't a solution to this make solar power a lot more attractive than what it already is, since you would be able to store daytime generated electricity?
gpt
We are using batteries to store excess renewable energy.  Just not the kind of battery you're familiar with.  There's something called a flow battery, explicitly designed for grid-scale energy storage.   Many companies are racing to commercialize their products to handle the burgeoning demand for renewable storage, using many different chemistries that are quite different from consumer batteries.  The main idea of a flow battery is to decouple energy and power.  Power is the instantaneous voltage times current, while energy is power over a duration of time.  A lithium ion battery has a fixed relationship due to the need for the lithium ions to be within a certain distance of the electrodes.  This means in order to increase capacity, you have to increase everything that goes into the battery as well.  A flow battery uses external storage tanks of electrolyte that can be of arbitrary size that is independent of the electrode area.  The electrode area determines the power, but the size of the tanks determine the total energy capacity.  Need more capacity?  Just add more tanks.  

This tech has its own set of challenges, however, and they're not trivial.  The main problems stem from electrolyte crossover through the separator membrane,  efficiency degradation, and cost of the electrolyte.  There are literally dozens of different chemical schemes being explored right now with the aim of addressing these points.  Bets are on as to which tech will win out.  Chances are, however, you the end user will never purchase such a system.  They're designed for utilities to incorporate.