Assessment on the Use of High Capacity “Sn4_{4}P3_{3}”/NHC Composite Electrodes for Sodium-Ion Batteries with Ether and Carbonate Electrolytes

This work reports the facile synthesis of a Sn–P composite combined with nitrogen doped hard carbon (NHC) obtained by ball-milling and its use as electrode material for sodium ion batteries (SIBs). The “Sn$_{4}$P$_{3}$”/NHC electrode (with nominal composition “Sn$_{4}$P$_{3}$”:NHC = 75:25 wt%) when coupled with a diglyme-based electrolyte rather than the most commonly employed carbonate-based systems, exhibits a reversible capacity of 550 mAh g$_{electrode}$$^{−1}$ at 50 mA g$^{−1}$ and 440 mAh g$_{electrode}$$^{−1}$ over 500 cycles (83% capacity retention). Morphology and solid electrolyte interphase formation of cycled “Sn$_{4}$P$_{3}$”/NHC electrodes is studied via electron microscopy and X-ray photoelectron spectroscopy. The expansion of the electrode upon sodiation (300 mAh g$_{electrode}$$^{−1}$) is only about 12–14% as determined by in situ electrochemical dilatometry, giving a reasonable explanation for the excellent cycle life despite the conversion-type storage mechanism. In situ X-ray diffraction shows that the discharge product is Na$_{15}$Sn$_{4}$. The formation of mostly amorphous Na$_{3}$P is derived from the overall (electro)chemical reactions. Upon charge the formation of Sn is observed while amorphous P is derived, which are reversibly alloying with Na in the subsequent cycles. However, the formation of Sn$_{4}$P$_{3}$ can be certainly excluded

Tin Graphite Composite as a High Capacity Anode for All Solid State Li Ion Batteries

The use of composites instead of pure metals as negative electrodes is an alternative strategy for making all solid state lithium ion batteries Li SSBs more viable. This study reports on the properties of a composite electrode Sn Graphite consisting of nanosized Sn 17 wt and graphite 83 wt . The theoretical capacity of this material is 478 mAh g Sn Graphite 1. When mixed with Li3PS4 LPS as a solid electrolyte SE , an areal capacity of 1.75 mAh cm 2 active mass loading of 3.8 mg cm 2 is obtained, which can be increased up to 3.0 mAh cm 2 for 7.6 mg cm 2 . At 0.02 mA cm 2 , the Sn Graphite electrode delivers a gravimetric capacity of 470 mAh g Sn Graphite 1, i.e., close to its theoretical value. At 0.1 mA cm 2 , the capacity is 330 mAh g 1 second cycle but drops to 84 mAh g 1 after 100 cycles. Solid state nuclear magnetic resonance spectroscopy ssNMR and X ray photoelectron spectroscopy XPS are used to investigate the stability of the solid electrolyte for this cell configuration. Optimization of the electrode is explored by varying the electrode loading between 3.8 and 7.6 mg cm 2 and the SE content between 0 and 65 . For electrodes without any SE, gravimetric capacities mAh g Sn Graphite 1 and areal capacities mAh cm 2 are lower compared to electrodes with SE; however, their volumetric capacity is higher. This emphasizes the need to optimize the composition of electrodes for SSB

Frequency response of electrolyte-gated graphene electrodes and transistors

The interface between graphene and aqueous electrolytes is of high importance for applications of graphene in the field of biosensors and bioelectronics. The graphene/electrolyte interface is governed by the low density of states of graphene that limits the capacitance near the Dirac point in graphene and the sheet resistance. While several reports have focused on studying the capacitance of graphene as a function of the gate voltage, the frequency response of graphene electrodes and electrolyte-gated transistors has not been discussed so far. Here, we report on the impedance characterization of single layer graphene electrodes and transistors, showing that due to the relatively high sheet resistance of graphene, the frequency response is governed by the distribution of resistive and capacitive circuit elements along the graphene/electrolyte interface. Based on an analytical solution for the impedance of the distributed circuit elements, we model the graphene/electrolyte interface both for the electrode and the transistor configurations. Using this model, we can extract the relevant material and device parameters such as the voltage-dependent intrinsic sheet and series resistances as well as the interfacial capacitance. The model also provides information about the frequency threshold of electrolyte-gated graphene transistors, above which the device exhibits a non-resistive response, offering an important insight into the suitable frequency range of operation of electrolyte-gated graphene devices