The Elusive Holy Grail of Batteries

None of the various battery types which have been developed so far seem likely to be able to get around all of the difficulties that need to be solved for use in a high performance, mass produced and sell-able EV, not without being inefficient and extremely expensive.

There are similarities to the main problems of the internal combustion engine (ICE) in a vehicle:
It needs to produce torque across a wide range of revs, and power, and low emissions, and low noise levels, and low pollution, and have low weight, and last a long time, and need little servicing, and not be too complex...
Of course the ICE will therefore have severe limitations, or an extreme price and/or extreme servicing requirements, you know the story.

But a specialized ICE, which always runs at it's optimum speed and load, can be much more efficient, simple, free of service requirements and extremely long lasting. The oil in such an engine needs to be perfect for just one set of circumstances; the vibrations can be almost eliminated at the typical constant running speed, parts don't heat up and cool down and fatigue unduly etc., you know that story, too!

Now take the leap and apply this kind of thinking to batteries:

I propose that for a high performance advanced EV it would be beneficial to install several different types of battery in such a way that they support each other synergistically! A "specialist battery' for each of the attributes that are hard to combine into just one battery type!

A) A large, high energy density battery capable of producing a constant base load current.
This battery constantly recharges the other battery types in the system, at the most efficient, constant rate, with minimal losses, allowing for minimal heat production, exceptionally long life, and large energy storage for the weight and volume used. This battery needs to be able to provide a constant current sufficient to maintain vehicle speed at highway speed for long periods without straining or suffering any damage. It does however not need to be able to produce the currents needed to accelerate, go up steep hills or burn tyres. It also does not need to be able to absorb massive amounts of regen breaking energy. These are the jobs of the other parts of the system. It's constant power rating would be similar to the motors constant power rating.

B) The next part of the system could be a smaller battery of a chemistry type that is capable of rapid charge and discharge. It would provide the energy needed during normal acceleration, during fast uphill driving and during faster than normal highway driving for fairly short periods. It must have a high C rating for both charging and discharging and a high cycle life expectancy, because it provides the immediate energy source and energy dump for stop-and-go city traffic including normal (but not emergency) regenerative breaking. This battery does not need to be able to provide the extreme power needed to do a full power acceleration, or absorb the power of an emergency regen breaking maneuver; that's the job of the next part! It's constant power rating would be higher than the motors continuous power rating, but much lower than the motors peak power rating. The capacity can be fairly low.

C) The third part would be a small battery (and/or super-capacitors) with low capacity, but capable of producing and absorbing phenomenal currents during hard acceleration and emergency regenerative breaking.This battery and/or capacitors must be able to absorb the maximum regen currents without getting damaged, and to produce enough power for a single acceleration from zero to top speed, even uphill into a headwind, but this is only needed for a few seconds at a time.

I think we already have suitable battery types for the roles of A), B), and C)!

As long as we try to find the "Holy Grail Battery" that combines all the attributes needed in an EV into just one type of battery, we are reproducing the inefficiency problems of the internal combustion engine as described above. It will likely fail.
There will probably never be a battery that can do it all and still be affordable, recyclable, non-toxic and durable!

Of course, this synergistic battery combination needs a complex battery management system.
But again, I think this could be designed and built by using already existing components.