Investigation of NaTiOPO4 as Anode for Sodium-Ion Batteries: A Solid Electrolyte Interphase Free Material?

Tavorite NaTiOPO4 (NaTP) is here explored as a possible solid electrolyte interphase (SEI) free anode material for Na-ion batteries (NIBs). The operation voltage is found around 1.4 V vs Na+/Na with a very low polarization (around 0.02 V) and an efficiency of ∼95% after 100 cycles in half-cells. Operando X-ray diffraction measurements have unveiled that insertion and deinsertion of Na ions occurs via a symmetric mechanism involving biphasic and solid solution reactions. The evolution of the SEI formation at different voltage values upon electrochemical cycling has been analyzed by means of X-ray photoelectron spectroscopy (XPS), and the results show that although not inexistent, a very thin and stable SEI layer is formed that positively contributes to the excellent cycling stability of the material.