SODIUM ion advanced batteries for remote controlled robots – SODIUM

To reach such a goal the RS2E and CEA conjointly decided to merge their efforts to promote the technological development and scaling up of our laboratory prototypes and benchmark our present Na-ion chemistry in terms of sustainability, cost, safety and performances. Through such a cooperative approach efforts were devoted to i) the design of new synthesis methods to elaborate highly performing Na-performing electrodes in a shorter time and less costly process, ii) the elaboration of a well-controlled pyrolysis protocol for preparing carbon electrodes with the lowest irreversible capacity and iii) the formulation of a proper Li-based electrolyte with the addition of the right additive for lowering it its degradation. Once this optimization achieved, large size electrodes will be made and 18650 cells will be assembled and tested under various conditions for performances.

Numerous research advances, which were the results of both fundamental studies conducted with state of the art insitu characterization tools, were achieved. Among them we will highlight
1) Optimization of both carbons and alloys-based electrodes with unprecedented performances in terms of capacity and cyclelife.
2) Reduction of the synthesis time of the Na-based polyanionic positive electrode by a factor of 5 while preserving all of its performance in terms of capacity and power rate and up-scaling of this new synthesis protocol to prepare large batch sample (> 1Kg).
3) Confection of a four components electrolytes (3 solvents + one additive) highly resistant against degradation during cycling.
On the basis of the above findings a first set of Na-ion (18650) prototypes were assembled by the CEA and tested for their performances. Energy densities of 70Wh/kg together with excellent capacity retention (<5% decay after 800 cycles) and attractive power rate capabilities were achieved. To the best our knowledge, this is the first time that the Na-ion technology has been benchmarked using 18650 casing.
Overall such rapid technology achievements demonstrate that pilot lines pertaining to the Li-ion production can easily be implemented to produce Na-ion cells, which is a pleasant surprise for the future of this technology. Moreover, the abundance of the materials used together with the easiness of the developed synthesis process gives to this technology sustainability attractiveness.

Owing to an efficient synergy between the different partners, the project had rapidly evolved and we are fully optimistic in meeting the project objectives. Our second year efforts will mainly consist in 1) developing Na-ion modules capable of meeting the performance targets dictated by the type of robot, selected within the scope of this project, and 2) demonstrate the cost-effectiveness, sustainability, and safety aspects of the Na-ion technology with respect to mass storage applications. This calls for the necessity to i) carry-out life cycle analysis costs, and ii) implementing the safety tests cells develop for the Li-ion technology to the Na-ion one. Performances-wise, efforts will aim i) at the materials levels by tuning their composition and morphology and ii) at the electrode level by fine tuning the formulation for a better cell balancing. All of these will improvements will be implemented in cell prototyping.

To be added...

In recent years, lithium batteries have emerged as the best technology to power electric vehicles and are regarded as a serious contender for grid applications. Foreseen feedstock considerations already blow the whistle on lithium resources. Fears of limited lithium supplies at an affordable cost have driven the development of new chemistries and the most appealing alternative is to use sodium (Na) instead of lithium (Li). There are several reasons for this: Na resources are in principle unlimited, evenly distributed worldwide and their cost is extremely low; Na does not alloy with Al enabling the use of cheap Al current collectors; and last but not least Na has similar intercalation chemistry to that of Li. Moreover, sodium technology has already been successfully implemented in today’s commercialized high temperature Na/S cells for MW size electrochemical energy storage and for Na/NiCl2 ZEBRA-type systems for electric vehicles1. In spite of this, the development of Na-ion batteries did not materialize because of preconceived ideas that Na-ion could not compete with Li-ion in terms of i) energy density owing to the fact that Na is heavier than Li and has a higher redox potential and ii) of power rate due the larger ionic radii of Na+.
Over the last four years, by reuniting their efforts through the RS2E structure, members of the present application have decided to challenge such preconceived ideas. Based on both our present understanding of this technology and recent research advances at the electrode/electrolyte level we have reached the confidence that making Na-ion batteries is a realistic target with present cost estimates predicting a 30% reduction per kWh as compared to Li-ion technology2. Moreover, the first laboratory assembled Na-ion cells, based on home developed electrode/electrolyte formulations, do prove the viability of the concept since they are showing impressive power and cycle life capabilities. Being among the pioneers in such resurging interest for Na-ion batteries, we do not want to repeat the Li-ion history for which the concept came from European and American researchers but development and commercialization took place in Japan. For such a reason, we conjointly decided with CEA to promote the technological development and scaling up of our laboratory prototypes and benchmark our present Na-ion chemistry in terms of sustainability, cost, safety and performances, the CEA bringing its expertise in materials scale-up and prototyping. The DESCARTES program provides a timely opportunity as it perfectly coincides with our objectives of promoting Na-ion as a new emerging technology not only for EV’s and grid applications but also as a technology capable of meeting the performance targets (1 Ah, 8 A discharge and 16 A peaks) dictated by the field of robotics in a cost-effective, sustainable and environmental-friendly manner. To reach the project targeted performance, our strategy will be to optimize our present Na-ion system proven to work at the lab scale. Having already structured our benchmarking efforts within the RS2E, one year is a realistic target to demonstrate the potential and originality of our approach, with 2 and 3 years lapse time being fully adequate to reach a workable module pack to be tested on a DGA robot, respectively