Mechanochemically synthesized conversion electrodes and their application in sodium and lithium ion batteries with diglyme electrolytes

The strongly limited abundance of lithium (Li) and also that of other elements contained in a Li-ion battery (LIB) leads to the need of low-cost and more abundant alternatives. Sodium-ion batteries (SIBs) are a promising alternative as sodium (Na) cells show similar properties to the Li analogues in many cases and allow the use of more environmentally friendly and/or more abundant electrode materials. In comparison to the well-known and commercially used intercalation type electrodes, conversion electrodes enable the transfer of several electrons per formula unit of an electrode material and hence provide higher specific capacities. Conversion electrodes may be classified into alloys and transition metal compounds, both being studied within this dissertation. The first publication (doi: 10.1002/ente.201900389) in this cumulative thesis deals about the influence of the ball milling time onto the electrochemical performance for an SnSb/C intermetallic phase and Sn+Sb/C mixture as an example for alloy electrodes. Herein, it is found that longer milling leads to a more stable composite formation with carbon in order to enhance the cycle life for Sn+Sb and SnSb by galvanostatic cycling and in situ dilatometry studies. In the second publication (doi: 10.1016/j.powera.2020.100031) Cu3P is studied as a transition metal compound electrode, which is found to show a better electrochemical performance for the use of an ether electrolyte in comparison to carbonate electrolytes for both, LIBs and NIBs. In the last publication, (doi: 10.1002/adfm.201910583) a thiophosphate (Cu3PS4) was considered as an electrode material for the first time for NIBs which shows a by sulfur dominated redox activity with capacities of about 450 mAh g−1 after 1400 cycles @1 A g−1 in a voltage window between 0.01 and 2.5 V vs. Na+/Na. The results of this dissertation improve the understanding of using alloy and transition metal compound based conversion electrodes in diglyme electrolytes.