Reversible Conversion Reactions and Small First Cycle Irreversible Capacity Loss in Metal Sulfide‐Based Electrodes Enabled by Solid Electrolytes

Abstract

Solid-state batteries can potentially enable new classes of electrode materials which are unstable against liquid electrolytes. Here, SnS nanocrystals, synthesized by a wet chemical method, are used to fabricate a Li-ion electrode, and the electrochemical properties of this electrode are examined in both solid and liquid electrolyte designs. The SnS-based solid-state cell delivers a capacity of 629 mA h g -1 after 100 cycles and exhibits an unprecedentedly small irreversible capacity in the first cycle (8.2 %), while the SnS-based liquid cell shows a rapid capacity decay and large first cycle irreversible capacity (44.6 %). Cyclic voltammetry (CV) experiments show significant solid electrolyte interphase (SEI) formation in the liquid cell during the first discharge while SEI formation by electrolyte reduction in the solid-state cell appears negligible. Along with CV, x-ray photoelectron spectroscopy(XPS) and energy dispersive spectroscopy (EDS) are used to investigate the differences between the solid-state and liquid cells. The reaction chemistry of SnS in solid-state cells is also studied in detail by ex situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The overarching findings are that use of solid electrolyte suppresses materials degradation and electrolyte reduction which leads to a small first cycle irreversible capacity and stable cycling.

Good Solid‐State Electrolytes Have Low, Glass‐Like Thermal Conductivity

“…[16,17] Amorphous Li 2 S-P 2 S 5 was prepared using high energy ball milling following a procedure described previously. [18] No posttreatment was used for this sample.…”

Recent Tactics and Advances in the Application of Metal Sulfides as High‐Performance Anode Materials for Rechargeable Sodium‐Ion Batteries

“…[ 53,54 ] The current studies on the conversion reactions focus on the initial structural irreversibility and improvement on polarization kinetics to increase the anode performance stability. [ 55–57 ] The majority of these studies verified the importance of promoting the interfacial and superficial charge transfer to facilitate the Na‐ion transport and process reversibility. On the other hand, studies in identifying the possibility of the occurrence of conversion and alloying reactions in TMS materials were studied as well; the obtained results served as a guideline for developing suitable material design and enhancement methodologies.…”

High-Capacity Anode Materials for All-Solid-State Lithium Batteries

“…SnS nanoparticles were fabricated by heating an oleylamine solution with sulfur and SnCl 2 at 230 • C for 2 h, and the charge-discharge properties of the SnS were tested both in liquid and solid electrolytes (77.5Li 2 S•22.5P 2 S 5 glass) (Kim et al, 2019a). Although the first discharge capacity in the liquid electrolyte (1,123 mAh g −1 ) was higher than that in the solid electrolyte (802 mAh g −1 ), the capacity decayed to 148 mAh g −1 after 50 cycles, while 85.6% of the discharge capacity at the second cycle was maintained for 100 cycles using the solid electrolyte (Kim et al, 2019a). The origin of the better properties in the solid-state cell can be explained by the reversibility of the conversion reaction.…”

“…The discharge reaction of SnS consists of the conversion reaction of SnS + 2Li + + 2e − → Li 2 S + Sn followed by the alloying reaction of Sn. In the solid-state cell, the products of the conversion reaction (Li 2 S) would reversely react with the Sn during the subsequent reconversion reaction while Li 2 S was dissolved in the carbonate-based liquid electrolytes (Kim et al, 2019a). Hence, it is expected that the use of the solid electrolytes leads to a wider material selectivity of the anode materials.…”

“…Although the material developments of high-capacity anodes have also been actively studied in liquid electrolytes, the material selectivity of the solid electrolytes will also be the key for the construction of the allsolid-state LIBs with Si and Sn. Although the Li 2 S-P 2 S 5 systems are not thermodynamically stable with Li-Sn, the stable SEI formation would result in the excellent cycling properties of SnS with 77.5Li 2 S•22.5P 2 S 5 glass (Kim et al, 2019a). It seems that the solid electrolytes with their favorable mechanical properties are required for the stable cycling of anodes by buffering the volume change of the active materials in a solid electrolyte layer.…”