Elucidating the Reductive Decomposition Mechanism in Sulfide Solid Electrolyte Li4SnS4

The sulfide solid electrolyte Li4SnS4 has garnered considerable interest due to its exceptional moisture durability, which is attributed to its stable hydrated state. However, a major limitation of certain sulfide solid electrolytes, including Li4SnS4, is their low reduction durability, which limits their application in the negative electrodes of all-solid-state batteries and impedes qualitative material development assessments. In this study, we introduced a quantitative and straightforward method for evaluating the reductive decomposition of Li4SnS4 to better understand its degradation mechanism. The configuration of the electrochemical evaluation cell was modified from SUS|Li4SnS4|Li to SUS|Li4SnS4|Li3PS4|Li, allowing for stabilization of the reference potential of the counter electrode. The reductive decomposition potential of Li4SnS4 was quantitatively assessed by using cyclic voltammetry in a two-layer electrochemical evaluation cell. We observed a minor irreversible reduction current below +1.2 V and a pronounced decomposition peak at +1.0 V. Notably, reductive decomposition continued below 0 V, which is typically the onset point for Li electrodeposition. Postreduction, the solid electrolyte was comprehensively analyzed through optical microscopy, X-ray diffraction, and X-ray absorption spectroscopy. These analyzes revealed the following: (i) The SnS44- unit in Li4SnS4 initially decomposes into Li2S and β-Sn with the dissociation of the Sn-S bond; (ii) the resulting β-Sn forms LixSn alloys such as Li0.4Sn; and (iii) the ongoing reductive decomposition reaction is facilitated by the electronic conductivity of these LixSn alloys. These findings offer crucial methodological and mechanistic insights into the development of higher-performance solid electrolyte materials.

Alkali-Ion Intercalation Chemistry and Phase Evolution of Sn4P3

Despite its high theoretical capacities, Sn4P3 anodes in alkali-ion batteries (AIBs) have been plagued by electrode damage and capacity decay during cycling, mainly rooted in the huge volume changes and irreversible phase segregation. However, few reports endeavor to ascertain whether these causes bear relevance to phase evolution upon cycling. Moreover, the phase evolution mechanism for alkali-ion intercalation remains imprecise. Herein, the structural transformations and detailed mechanisms upon various alkali-ion intercalation processes are systematically revealed, utilizing both experimental techniques and theoretical simulations. The results reveal that the energy storage of Sn4P3 occurs in a two-stage process, starting from an insertion process, followed by a transition process. As the cycle proceeds, the final delithiated/desodiated/depotassiated components gradually trap alkali ions (Li+, Na+, and K+), which is attributed to the incomplete electrochemical transition and difficulty in Sn4P3 regeneration due to the kinetic limitations in removing M (M = Li, Na, and K). Furthermore, Sn4P3 anode obeys the "shrinking core mechanism" in potassium-ion batteries (KIBs), wherein a minor fraction of Sn4P3 in the outer layer of the particles is initially involved in the potassiation/depotassiation processes, followed by a gradual participation of the inner parts until the entire particle is involved. It is worth mentioning that K-Sn alloys are not found to exist during the transition process of KIBs; instead, K-Sn-P phases are found, which makes it differ from that in lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs). These findings are expected to deepen the understanding of the reaction mechanism of Sn4P3 and enlighten the material designs for improved performance.

Atomic Welded Dual-Wall Hollow Nanospheres for Three-in-One Hybrid Storage Mechanism of Alkali Metal Ion Batteries

The rational design of hierarchical hollow nanomaterials is of critical significance in energy storage materials. Herein, dual-wall hollow nanospheres (DWHNS) Sn/MoS₂@C are constructed by in situ confined growth and interface engineering. The inner hollow spheres of Sn/MoS₂ are formed by atomic soldering MoS₂ nanosheets with liquid Sn at high temperature. The formation mechanism of the hierarchical structure is explored by the morphology evolutions at different temperatures. The DWHNS Sn/MoS₂@C manifest abundant inner space and high specific surface area, which provides more support sites for Li⁺/Na⁺/K⁺ storage and alleviates the volume effect of tin-based electrode materials to a certain extent. The composite material manifests an outstanding specific capacity and satisfactory reversibility of lithium ion batteries (∼931 mAh g^-1 at 1 A g^-1 after 500 cycles), sodium ion batteries (∼432 mAh g^-1 at 1 A g^-1 after 400 cycles), and potassium ion batteries (∼226 mAh g^-1 at 1 A g^-1 after 300 cycles). Additionally, the morphology evolution and mechanism analysis of DWHNS Sn/MoS₂@C in alkali metal ion batteries are verified by ex situ measurement, which confirms the three-in-one hybrid storage mechanism, i.e., intercalation reaction of carbon shells, conversion reaction of MoS₂, and alloying reaction of tin.

Structural and Electrochemical Properties of Type VIII Ba8Ga16-δSn30+δ Clathrate (δ ≈ 1) during Lithiation

Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host-guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba₈Ga_16-δSn_30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (Li_xBa_0.17Ga_0.33Sn_0.67, x = 2-3) with local structures similar to those in the crystalline binary Li-Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li⁺) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li-Sn or Li-Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.

Stanene-Based Nanosheets for β-Elemene Delivery and Ultrasound-Mediated Combination Cancer Therapy

Ultrasound (US)-mediated sonodynamic therapy (SDT) has emerged as a superior modality for cancer treatment owing to the non-invasiveness and high tissue-penetrating depth. However, developing biocompatible nanomaterial-based sonosensitizers with efficient SDT capability remains challenging. Here, we employed a liquid-phase exfoliation strategy to obtain a new type of two-dimensional (2D) stanene-based nanosheets (SnNSs) with a band gap of 2.3 eV, which is narrower than those of the most extensively studied nano-sonosensitizers, allowing a more efficient US-triggered separation of electron (e^- )-hole (h⁺ ) pairs for reactive oxygen species (ROS) generation. In addition, we discovered that such SnNSs could also serve as robust near-infrared (NIR)-mediated photothermal therapy (PTT) agents owing to their efficient photothermal conversion, and serve as nanocarriers for anticancer drug delivery owing to the inherent 2D layered structure. This study not only presents general nanoplatforms for SDT-enhanced combination cancer therapy, but also highlights the utility of 2D SnNSs to the field of nanomedicine.

Formation of spherical Sn particles by reducing SnO2 film in floating wire-assisted H2/Ar plasma at atmospheric pressure

A green method to synthesize spherical Sn particles by reducing SnO₂ film in atmospheric-pressure H₂/Ar plasma at low temperatures for various applications is presented. The floating wire-assisted remotely-generated plasma with a mixture of 0.05% H₂/Ar gas formed spherical metallic Sn particles by reducing a SnO₂ layer on glass substrate. During the reduction process, H radical density was measured by using vacuum ultraviolet absorption spectroscopy, and plasma properties including electron density and gas temperature were diagnosed by optical emission spectroscopy. The inductively coupled generated plasma with a high electron density of 10¹⁴ cm⁻³, a hydrogen atom density of 10¹⁴ cm⁻³, and a gas temperature of 940 K was obtained at a remote region distance of 150 mm where the SnO₂/glass substrate was placed for plasma treatment. The process has been modeled on the spherical Sn formation based on the reduction of SnO₂ films using H radicals. Depending on the treatment condition, the total reduction area, where spherical Sn particles formed, was enlarged and could reach 300 mm² after 2 min. The substrate temperature affected the expansion rate of the total reduction area and the growth of the Sn spheres.

Converting bimetallic M (M = Ni, Co, or Fe)-Sn nanoparticles into phosphides: a general strategy for the synthesis of ternary metal phosphide nanocrystals

Ternary metal tin phosphides are promising candidates for electrochemical or catalytic applications. Nevertheless, their synthesis, neither as bulk nor nanomaterials is well investigated in the literature. Here, we describe a general synthetic strategy to convert bimetallic M-Sn (M = Ni, Co, and Fe) nanoparticles to ternary metal phosphides by decomposition of tributylphosphine at 300 °C. At high phosphorus concentrations, Ni₃Sn₄ nanoparticles convert to hybrid structured Ni₂SnP and β-Sn. The CoSn₂ and FeSn₂ nanoparticles undergo a phosphorization, too and form hybrid nanocrystals reported here for the first time, containing ternary or binary phosphides. We identified the crystal structure of the nanoparticles via XRD and HRTEM measurements using the diffraction data given for Ni₂SnP in literature. We were able to locate the Ni₂SnP and β-Sn crystal structure within the nanoparticles to demonstrate the phase composition of the nanoparticles. By transferring the synthesis to cobalt and iron, we obtained nanoparticles exhibiting similar hybrid structures and ternary element compositions for Co-Sn-P and binary Fe-P and FeSn₂ compositions. In the last step, we used the given information to propose a conversion mechanism from the binary M-Sn nanoparticles through phosphorization.

SnO2 Model Electrode Cycled in Li-Ion Battery Reveals the Formation of Li2SnO3 and Li8SnO6 Phases through Conversion Reactions

SnO₂ is an attractive negative electrode for Li-ion battery owing to its high specific charge compared to commercial graphite. However, the various intermediate conversion and alloy reactions taking place during lithiation/delithiation, as well as the electrolyte stability, have not been fully elucidated, and many ambiguities remain. An amorphous SnO₂ thin film was investigated for use as a model electrode by a combination of postmortem X-ray photoelectron spectroscopy supported by density functional theory calculations and scanning electron microscopy to shed light on these different processes. The early stages of lithiation reveal the presence of multiple overlapping reactions leading to the formation of Li₂SnO₃ and Sn⁰ phases between 2 and 0.8 V vs Li⁺/Li. Between 0.45 V and 5 mV vs Li⁺/Li Li₈SnO₆, Li₂O and Li _xSn phases are formed. Electrolyte reduction occurs simultaneously in two steps, at 1.4 and 1 V vs Li⁺/Li, corresponding to the decomposition of the LiPF₆ salt and ethylene carbonate/dimethyl carbonate solvents, respectively. Most of the reactions during delithiation are reversible up to 1.5 V vs Li⁺/Li, with the reappearance of Sn⁰ accompanied by the decomposition of Li₂O. Above 1.5 V vs Li⁺/Li, Sn⁰ is partially reoxidized to SnO _x. This process tends to limit the conversion reactions in favor of the alloy reaction, as also confirmed by the long-term cycling samples.

A battery cell for in situ NMR measurements of liquid electrolytes

Development of an in situ battery cell to monitor the liquid electrolyte by means of NMR spectroscopy.