When you switch from diesel engine to a full electric powertrain, it is no more possible to only think in terms of power.

You have to also specify the working time during which you want your power to be available:

For on-time smaller than 100 ms, chemical capacitors are well adapted;
Ultracapacitors are well adapted for an-time of some seconds (max 5 to 10 s)
For on-time ranging from 10 s to 1 mn, high power lithium-ion batteries are often the most cost effective solution. New technologies are under development for this particular application (LiCap, which are a mix of ultracapacitors and lithium-ion technology) but they are still too expensive to be developed in high volume and low price.
From several minutes to several hours (<12h depending on the application), the electrochemical accumulator are well adapted and the lithium-ion battery is the most performing one. For longer continuous operation, a diesel genset or a fuel cell can be a good solution.

To answer the needs of a specific application, the storage system must be capable of always delivering the requested power and energy to fulfill the requested duty cycle. The two main criteria to size an electrical energy storage are then the maximal power and the energy to deliver. The time criteria explained here above is included in the capacity to deliver energy since energy is the integral of power for a dedicated time.

The Ragone plat helps to compare the different energy storage technologies by their power and energy characteristics (see Figure 2).

Figure 2 : Diagramme de Ragone pour différentes technologies de stockage (source : Research Gare, Giuseppe Graber, Università degli Studi di Salerno)

One shall note the very wide range of usage covered by lithium-ion technology: a power density reaching the best ultrapacacitors and the best energy density among batteries. We will see in the next WATTALPS TechLetter that the term lithium-ion covers a high number of technologies and designs, each of which addressing a specific case. There is indeed not one technology to cover all the applications and the choice of the appropriate technology is always a matter of compromise between power, energy, safety, cost, life and resistance to environmental constraints (especially temperature).

A lot of projects have mixed different types of storage to try and benefit from the energy density of the best lithium-ion technology while keeping the high power and cycle life of a ultracapacitor. Very few of these projects have been taken to series production due to a high cost and added complexity. Some automotive starter batteries use lead acid technology combined with ultracapacitors but this solution tend to be replaced by high power lithium batteries (see http://uyilo.org.za/uyilo/media/Store/documents/2-2-Schweiger-12-V-Lithium-Ion-Starter-Batteries.pdf ).

Very regularly, new scientific advances claim the discover of new revolutionary materials to significantly increase battery performances (charge in 5 mn, outstanding life, energy multiplied by 10…). One has to look at these discoveries for what they are : scientific progress. As illustrated on the graph, the evolution of battery technology is slow. As an example, the best technology of today has been firstly commercialized in 1991 and the concept was invented in 1978 (source : Jean-Marie Tarascon, Collège de France).

To go a bit further:

Battery history and lithium-ion technology – easy – http://gvallver.perso.univ-pau.fr/doc/BatterieLiion.pdf

To go even further :

Battery history and lithium-ion technology – scientist – https://www.college-de-france.fr/media/jean-marie-tarascon/UPL51353_courshistoirefinal_Tarascon.pdf (especially from page 28 for lithium-ion technology).