Abstract

AbstractLithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solid‐state batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodium‐ion batteries. Copper thiophosphate (Cu3PS4) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na+/Na is studied in half cells using different electrolytes with 1 m NaPF6 in diglyme showing the best result. Cu3PS4 shows highly reversible charge storage with capacities of about 580 mAh g−1 for more than 200 cycles @120 mA g−1 and about 450 mAh g−1 for 1400 cycles @1 A g−1. The redox behavior is studied by operando X‐ray diffraction and X‐ray photoelectron spectroscopy. During initial sodiation, Cu3PS4 undergoes a conversion reaction including the formation of Cu and Na2S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu3PS4 for lithium storage is smaller, leading to about 170 mAh g−1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.

Highlights

  • Lithium and sodium thiophosphates have recently attracted attention because of their potential use as solid electrolytes in solidfrom the rich chemistry of layered oxides, polyanion compounds and Prussian blue analogues, which allows tuning of the state batteries

  • 6.39 Å were measured for the interplanar distance of the (100) lattice plane, which is in good agreement with the length of the b-axis of the Cu3PS4 unit cell

  • A signal for PS43− has been reported at 161.5 eV for Li3PS4,[35a] at 163.7 eV for crystalline Ag3PS4 and at 162.1 eV for amorphous Ag3PS4.[35b]. The small deviations between the different thiophosphates are due to the different cations

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Summary

Introduction

Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solidfrom the rich chemistry of layered oxides, polyanion compounds and Prussian blue analogues, which allows tuning of the state batteries. These compounds, exhibit only limited stability in electrode properties.[3] To reduce cost, compractice as they react with the electrodes. The standard material in lithium-ion batteries, can only be applied using solvent cointercalation phenomena in ether electrolytes.[5] The capacity, is limited to around 110 mAh g−1 so far and the electrode undergoes large volume changes during cycling.[6] Higher capacities can be achieved in disordered carbons,[7] but. The progress in the field is frequently summarized in litera- metalloids, only Sn, Sb, and Pb show high storage capacities.[1e,9]

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