Lithiation and Delithiation Mechanism of Zn ₂ SnO ₄ -Based Conversion-Type Negative Electrodes for Lithium-Ion Batteries

We unravel the lithiation/delithiation mechanism of Zn2SnO4 as a conversion-type negative electrode material in a lithium-ion battery cell by rigorous phase identification via ex situ 7Li magic-angle spinning (MAS) NMR, static 119Sn WCPMG NMR, and operando X-ray diffraction (XRD) techniques. With ongoing lithiation/delithiation, a cascade of LixZn phases is observed, and the 7Li shift for the formed LixZn phases is reported for the first time. Our results show that Zn undergoes an alloying/dealloying-type reaction during electrochemical lithiation/delithiation according to xLi + Zn ↔ LixZn (0 ≤ x ≤ 1). However, considering the Sn alloying/dealloying reaction, the 119Sn WCPMG NMR results indicate that the formed LixSn species differ from those expected for the lithiation of metallic Sn; hence, the alloying/dealloying processes differ from those known for Sn: xLi + Sn ↔ LixSn (0 ≤ x ≤ 4.4), indicating a more complicated conversion mechanism for Zn2SnO4. Furthermore, the 119Sn WCPMG NMR data of the delithiation reaction reveal the formation of amorphous SnO caused by partial oxidation of reformed Sn.