Enhancing lithium storage rate and durability in sphalerite GeP by engineering configurational entropy

Abstract

Monoclinic GeP with a layered structure, featuring a large capacity, low plateau, and high initial coulombic efficiency (ICE), has been demonstrated as a promising alternative anode material for Li-ion batteries. However, its semiconductor feature and overutilization of expensive Ge pose a significant obstacle to its further advancement. To further improve electronic and Li-ionic conductivity, and reduce the cost, via a mechanochemical method, we synthesize a cubic GeP-based compound, ZnGeSiP₃, which possesses a triple cation-mixed sphalerite lattice, affording metallic conductivity and rapid Li-ion diffusion, and thereby outperforms monoclinic GeP due to enhanced conformational entropy, as verified through theoretical calculations and experimental analyses. Various characterization techniques, such as operando X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), confirm the reversible storage of Li-ions within ZnGeSiP₃via intercalation and subsequent conversion reactions, yielding a notable reversible capacity of 1638 mA h g⁻¹ with an ICE of 92% at 100 mA g⁻¹. The graphite-modified ZnGeSiP₃ composite exhibits exceptional long-term cycling stability, retaining 981 mA h g⁻¹ after 1600 cycles at 2000 mA g⁻¹, and ultrahigh rate performance, maintaining 568 mA h g⁻¹ at 22 000 mA g⁻¹, surpassing most previously studied anodes. Drawing inspiration from the favorable entropic effects, we synthesize high-entropy cation-mixed sphalerite-structured GeP-based compounds, including CuSnAlZnGeSiP₆, CuSn (or Al)ZnGeSiP₅, and SnAlZnGeSiP₅, as well as quaternary cation-disordered sphalerite-structured GeP-based compounds of Cu (or Sn, or Al)ZnGeSiP₄. Furthermore, we synthesize high-entropy sphalerite-structured GeP-based compounds ZnGeSiPSSe and ZnGeSiP₂Se (or S) with disordered cationic and anionic compositions, effectively addressing the challenge of incompatible multiple anions and cations. The phase formation mechanisms of these sphalerite-structured GeP-based compounds can be attributed to their negative phase formation energies, benefiting from the elevated conformational entropy. Crucially, all the aforementioned sphalerite-structured GeP-based compounds have metallic conductivity and showcase superior electrochemical Li-storage properties, including high capacity, high ICE, small polarization loss, and suitable operating potential. Broadly, the high conformational entropy strategy can serve as a new design paradigm for high-performance and cost-effective anodes for LIBs and beyond.