Why are lithium cells so much more powerful than alkaline, NiMH, NiCd, etc?

Question

And yet, they are so much lighter. In this case bigger and heavier is most certainly not better.

Answer 1

MAKE this clear:
bigger and heavier the better doesnot apply IN THIS CASE.

The more difference there is in electrode potential the more volts u get.

Li-ion batteries are lighter than other equivalent secondary batteries — often much lighter. The energy is stored in these batteries through the movement of lithium ions. Lithium is the third lightest element, giving a substantial saving in weight compared to batteries using much heavier metals. However, the bulk of the electrodes are effectively "housing" for the ions and add weight, and in addition "dead weight" from the electrolyte, current collectors, casing, electronics and conductivity additives reduce the charge per unit mass to little more than that of other rechargeable batteries. The forte of the Li-ion chemistry is the high open circuit voltage in comparison to aqueous batteries (such as lead acid, nickel metal hydride and nickel cadmium).

Li-ion batteries do not suffer from the memory effect. They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in nickel metal hydride batteries and 20% per month in nickel cadmium batteries

According to one manufacturer, Li-Ion cells (and, accordingly, "dumb" Li-Ion batteries) do not have any self-discharge in the usual meaning of this word. What looks like a self-discharge in these batteries is a permanent loss of capacity, described in more detail below. On the other hand, smart Li-Ion batteries do self-discharge, due to the small constant drain of the built-in voltage monitoring circuit. This drain is the most important source of self-discharge in these batteries.