The current research trend is aimed at developing "high-performance" rechargeable batteries, i.e. maximizing power density and energy density, both in terms of the volume of the battery of of its weight. It is obvious that this will drive up the price massively. But what we really need is the exact opposite, namely "low-performance" accumulators with the lowest possible price.
The good old lead-sulfuric acid battery, which has been doing its job reliably for many decades as the starter battery of many millions of cars, is quoted at just 119 €/kWh, and this with reference to a manufacturer in the upper price range. See for example: https://home.uni-leipzig.de/energy/energie-grundlagen/10.html
With a simple short internet search, I find 12V·360Ah=3120Wh for only 237,90€.
This namely accumulator is ready for ordering on the Internet, and it is cheaper by a factor of FIVE than the cheapest "high-performance" lithium-ion batteries. The disadvantage of such a battery is the lifetime, which is given between 500 and 2000 cycles. If we assume an average of 1000 cycles, we get an energy storage price of 7.6 cents per kWh, and thus a value that is not significantly better than for "high-performance" lithium-ion batteries due to the limited lifetime.
What we need, is materials research to optimize electrodes, with top priority given to the following criteria:
-> low-cost electrodes
-> low-cost electrolyte
-> long service life
-> environmentally friendly use (no disposal problems)
How simple alternatives can be imagined, is shown by saltwater accumulators, of which the inventor predicts a lifetime of 3000 ... 5000 cycles.
There are practically no limits to our very creativity – resulting in a research and development program, of which the aims are completely different from the today's standard industrial research direction: Our search is NOT for the most expensive high-tech solution, but for the cheapest low-tech solution with a long service life.
With the electrochemical voltage series in mind, a whole series of potential anode, cathode and electrolyte materials can be tried empirically, in order to find the most cost-effective and durable battery possible. In the end, the development work will be based mainly on empiricism. https://de.wikipedia.org/wiki/Elektrochemische_Spannungsreihe