This report summarizes the results regarding the development of nano-composite materials based on oxidized MAX phase Ti3Al1-xSnxC2 to be used as anodes in lithium (LIB) and sodium ion (NIB) batteries. To conclude the testing carried out during the previous three-years RdS plan, the storage capacity of nano-composites based on SnO2 and MXenes (SnO2@MX),that have shown low stability in NIB system, have also been tested as anode for LIB.

For the first class of compounds, the experimental activity was aimed at: i) improving the characterization of formulations with Sn=0.4 and 0.7 to understand the mechanisms of formation of Ti and Sn oxides on the surface of the MAX phase grains.

The target is to correlate their chemi-physical properties with the electrochemical storage performance; ii) verifying the reproducibility of the synthesis via spark plasma sintering (SPS) of the MAX phase Ti3Al1-xSnxC2 with x ≤0.7 and verify the storage performance as anodes Vs Li and Na; iii) extending the MAX phase formulation range, verifying the possibility to synthesize Ti3SnC2 samples via SPS; iv) further extending the experimental matrix of the oxidation condition for the powder of MAX phase Ti3Al1-xSnxC2 with x ≤1 to complete the correlation study between the morphology/nano-structuring of the oxides induced by thermal treatments in air and the storage performance as LIB and NIB anodes.

The results achieved by testing nano-composites derived from the oxidation of Ti3Al1-xSnxC2 with x ≤1 have consolidated and improved the preliminary results obtained in the previous RdS activities: tests in half-cells have shown maximum specific capacity values close to 120-130 mAh /g vs Na and 350 mAh/g vs Li. In the case of sodium, preliminary tests to improve the electrical conductivity of the MAX phase powders with carbon coatings have pushed the maximum capacity up to ≈170 mAh/g. Regarding the use as anodes in LIB, the developed materials have shown performance similar to graphite for low charging rate and better capacity values for fast recharges.

Good results have also been achieved in the synthesis of Ti3SnC2 via SPS, produced in RSE with a purity comparable to the best samples described in the literature (≈70-75%). Furtherly, the RSE activity was the first to verify the technical feasibility of the synthesis of this MAX phase formulation using SPS.

Regarding the SnO2@MX nano-composite, after the electrochemical test as anode per NIBs in the past RdS three-year program, studies as anode for LIB have been carried out investigating the different mechanisms involved to reach the impressive values of specific capacity achieved, 450 mAh /g for currents of 2 A/g.

The Report is available on the Italian site