Lithiation Mechanism and Improved Electrochemical Performance of TiSnSb-Based Negative Electrodes for Lithium-Ion Batteries

Lithium alloying materials are promising candidates to replace the current intercalation-type graphite negative electrode materials in lithium-ion batteries (LIBs) due to their high specific capacity and relatively low cost. Here, we investigate the electrochemical performance of TiSnSb regarding its charge/discharge cycling stability as a negative electrode material in LIB cells. To assess a more practical performance with respect to a limited active lithium content in LIB full-cells, we evaluate the impact of pre-lithiation for TiSnSb with respect to the cycling stability in a NCM111 parallel to TiSnSb cell setup. The observation of the individual electrode potentials reveals comprehensive insights into the ongoing cell chemistry, showing that clear performance improvements can be achieved via pre-lithiation. Furthermore, the lithiation mechanism of TiSnSb is systematically studied via ex situ Li-7 magic-angle spinning (MAS) nuclear magnetic resonance (NMR), ex situ X-ray diffraction, and static ex situ Sn-119 wideband uniform rate smooth truncation Carr-Purcell Meiboom-Gill (CPMG) WCPMG NMR experiments. For comprehensive references regarding the isotropic Li-7 shift of the Li-Sb intermetallic phases, all thermodynamically stable Li-Sb intermetallics of the binary Li-Sb systems have been synthesized and subsequently characterized by Li-7 MAS NMR. Combined, our measurements for lithiated TiSnSb do not give any evidence for the formation of Li-Sn and Li-Sb intermetallics related to crystalline bulk phases (Li7Sn3, Li7Sn2, Li3Sb, and Li2Sb) as has been previously reported. In contrast, unique insights obtained from static ex situ Sn-119 WCPMG NMR and ex situ XRD measurements reveal the formation of ternary Li-Sb-Sn species during lithiation, which can be assigned to the intermetallic phase Li2.8SbSn0.2. Additionally, the Li-7 MAS NMR measurements combined with the observed discharge capacity reveal a second Li species, which we assign to an amorphous Li-Sn phase.