Vapor-phase atomic-controllable growth of amorphous Li2S for high-performance lithium-sulfur batteries

Amorphous Materials for Lithium-Ion and Post-Lithium-Ion Batteries

Lithium-ion and post-lithium-ion batteries are important components for building sustainable energy systems. They usually consist of a cathode, an anode, an electrolyte, and a separator. Recently, the use of solid-state materials as electrolytes has received extensive attention. The solid-state electrolyte materials (as well as the electrode materials) have traditionally been overwhelmingly crystalline materials, but amorphous (disordered) materials are gradually emerging as important alternatives because they can increase the number of ion storage sites and diffusion channels, enhance solid-state ion diffusion, tolerate more severe volume changes, and improve reaction activity. To develop superior amorphous battery materials, researchers have conducted a variety of experiments and theoretical simulations. This review highlights the recent advances in using amorphous materials (AMs) for fabricating lithium-ion and post-lithium-ion batteries, focusing on the correlation between material structure and properties (e.g., electrochemical, mechanical, chemical, and thermal ones).  We  review both the conventional and the emerging characterization methods for analyzing AMs and present the roles of disorder in influencing the performances of various batteries such as those based on lithium, sodium, potassium, and zinc. Finally,  we  describe the challenges and perspectives for commercializing rechargeable AMs-based batteries.

Synthesis of Deliquescent Lithium Sulfide in Air

In the field of lithium-sulfur batteries (LSBs) and all-solid-state batteries, lithium sulfide (Li2S) is a critical raw material. However, its practical application is greatly hindered by its high price due to its deliquescent property and production at high temperatures (above 700 °C) with carbon emission. Hereby, we report a new method of preparing Li2S, in air and at low temperatures (∼200 °C), which presents enriched and surprising chemistry. The synthesis relies on the solid-state reaction between inexpensive and air-stable raw materials of lithium hydroxide (LiOH) and sulfur (S), where lithium sulfite (Li2SO3), lithium thiosulfate (Li2S2O3), and water are three major byproducts. About 57% of lithium from LiOH is converted into Li2S, corresponding to a material cost of ∼$64.9/kg_Li2S, less than 10% of the commercial price. The success of conducting this water-producing reaction in air lies in three-fold: (1) Li2S is stable with oxygen below 220 °C; (2) the use of excess S can prevent Li2S from water attack, by forming lithium polysulfides (Li2Sn); and (3) the byproduct water can be expelled out of the reaction system by the carrier gas and also absorbed by LiOH to form LiOH·H2O. Two interesting and beneficial phenomena, i.e., the anti-hydrolysis of Li2Sn and the decomposition of Li2S2O3 to recover Li2S, are explained with density functional theory computations. Furthermore, our homemade Li2S (h-Li2S) is at least comparable with the commercial Li2S (c-Li2S), when being tested as cathode materials for LSBs.

High-Precision Regulation of Nano-Grating Linewidth Based on ALD

A nano-grating standard with accurate linewidth can not only calibrate the magnification of nano-measurement instruments, but can also enable comparison of linewidths. Unfortunately, it is still a challenging task to control the linewidth of nano-grating standards. Accordingly, in this paper, atomic layer deposition (ALD) was used to regulate the linewidth of the one-dimensional grating standards with a pitch of 1000 nm, fabricated by electron beam lithography (EBL). The standards were measured using an atomic force microscope (AFM) before and after ALD, and the linewidth and pitch of the grating were calculated through the gravity center method. The obtained results prove that the width of a single grating line in the standard can be regulated with great uniformity by precisely utilizing ALD. Meanwhile, the proposed method does not affect the pitch of grating, and the measurement uncertainty of standards is less than 0.16% of the pitch, thereby demonstrating a high surface quality and calibration reliability of the standards, and realizing the integration of linewidth and pitch calibration functions. Moreover, the precise and controllable fabrication method of the micro-nano periodic structure based on ALD technology has many potential applications in the fields of optoelectronic devices and biosensors.

Approaches to Combat the Polysulfide Shuttle Phenomenon in Li–S Battery Technology

Lithium–sulfur battery (LSB) technology has tremendous prospects to substitute lithium-ion battery (LIB) technology due to its high energy density. However, the escaping of polysulfide intermediates (produced during the redox reaction process) from the cathode structure is the primary reason for rapid capacity fading. Suppressing the polysulfide shuttle (PSS) is a viable solution for this technology to move closer to commercialization and supersede the established LIB technology. In this review, we have analyzed the challenges faced by LSBs and outlined current methods and materials used to address these problems. We conclude that in order to further pioneer LSBs, it is necessary to address these essential features of the sulfur cathode: superior electrical conductivity to ensure faster redox reaction kinetics and high discharge capacity, high pore volume of the cathode host to maximize sulfur loading/utilization, and polar PSS-resistive materials to anchor and suppress the migration of polysulfides, which can be developed with the use of nanofabrication and combinations of the PSS-suppressive qualities of each component. With these factors addressed, our world will be able to forge ahead with the development of LSBs on a larger scale—for the efficiency of energy systems in technology advancement and potential benefits to outweigh the costs and performance decay.

Green synthesis of the battery material lithium sulfide via metathetic reactions

We report a synthesis of lithium sulfide, the cost-determining material for making sulphide solid electrolytes (SSEs), via spontaneous metathesis reactions between lithium salts (halides and nitrate) and sodium sulfide. This innovative method is economical, scalable and green. It will pave the way to developing practical SSE-based solid-state lithium batteries.

Atomic layer deposition of lithium zirconium oxides for the improved performance of lithium-ion batteries

Recently there has been increasing interest to develop lithium-containing films as solid-state electrolytes or surface coatings for lithium-ion batteries (LIBs) and related systems. In this study, we for the first time investigated the thin film growth of lithium zirconium oxides (Li_xZr_yO or LZOs) through combining two individual atomic layer deposition (ALD) processes of ZrO₂ and LiOH, i.e., sub-ALD of ZrO₂ and LiOH. We revealed that the hygroscopic nature of the LiOH component has a big impact on the growth of LZOs. We found that an increased temperature to 225 °C was more effective than an elongated purge to mitigate the adverse effects of physisorbed H₂O. We further discovered that, during the resultant LZO super-ALD processes, the growth of sub-ALD LiOH has been promoted while the growth of sub-ALD ZrO₂ has been inhibited. In this study, a suite of instruments has been applied to characterize the LZO super-ALD processes and the resultant LZO films, including in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), atomic force microscopy (AFM), synchrotron-based X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Furthermore, we applied the resulting LZO films over LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) cathodes in LIBs and demonstrated that the LZO coating films could evidently improve the lithium-ion insertion and extraction rates of the NMC622 electrodes up to 3.4 and 2.6 times, respectively. The LZO-coated NMC622 cathodes exhibited much better performance than the uncoated NMC622 ones.

Atomic and Molecular Layer Deposition of Alkali Metal Based Thin Films

Atomic layer deposition (ALD) is the fastest growing thin-film technology in microelectronics, but it is also recognized as a promising fabrication strategy for various alkali-metal-based thin films in emerging energy technologies, the spearhead application being the Li-ion battery. Since the pioneering work in 2009 for Li-containing thin films, the field has been rapidly growing and also widened from lithium to other alkali metals. Moreover, alkali-metal-based metal-organic thin films have been successfully grown by combining molecular layer deposition (MLD) cycles of the organic molecules with the ALD cycles of the alkali metal precursor. The current literature describes already around 100 ALD and ALD/MLD processes for alkali-metal-bearing materials. Interestingly, some of these materials cannot even be made by any other synthesis route. In this review, our intention is to present the current state of research in the field by (i) summarizing the ALD and ALD/MLD processes so far developed for the different alkali metals, (ii) highlighting the most intriguing thin-film materials obtained thereof, and (iii) addressing both the advantages and limitations of ALD and MLD in the application space of these materials. Finally, (iv) a brief outlook for the future perspectives and challenges of the field is given.

Enhanced ion transport in Li2O and Li2S films

Films of Li₂O and Li₂S grown by sputter deposition exhibit Li⁺ conductivity values at room temperature which are enhanced by 3-4 orders of magnitude relative to bulk samples. Possible mechanisms are discussed. The results may help explain the ion transport pathway through passivation layers containing these chalcogenides in batteries.

Recent progress and future prospects of atomic layer deposition to prepare/modify solid-state electrolytes and interfaces between electrodes for next-generation lithium batteries

Lithium ion batteries (LIBs) are encouraging electrochemical devices with remarkable properties including a high energy/power density, fast charging capability, and low self-discharge rate. Further increase in energy density as well as safe usage is needed for next-generation LIBs in electric transportation vehicles. Solid-state electrolytes (SSEs) are very promising for high-performance LIBs since they enable improved safety along with increased energy density compared to flammable liquid organic electrolytes. However, utilizing SSEs with a Li metal anode is very challenging due to the possibility of undesired side reactions and the formation of an unstable solid-electrolyte interphase. Therefore, it is critical to enhance the stability of SSEs against the Li anode. One feasible approach is to form a thin and conductive interlayer between the Li anode and solid-state electrolyte. Atomic layer deposition (ALD) is a unique technique for conformal coating of complex 3D structures with finely controlled film thickness (at the atomic scale). ALD coating on the surface of SSEs can be adopted for engineering solid-electrolyte interfaces with desired attributes and improved stability. In this review paper, we have discussed recent progress in implementing the ALD technique for depositing thin layers on various SSE configurations including lithium phosphorus oxynitride (LiPON), garnets, oxides, perovskites, sulphides, Li₃BO₃-Li₂CO₃ (LBCO), and sodium super ionic conductors (NASICON). We have also highlighted the major areas for future research and development in the field. We believe that this review will be very helpful for directing future research on implementing ALD for synthesizing stable and high-performance SSEs with an engineered solid-electrolyte interface for next-generation electrochemical devices (e.g., Li-ion batteries, supercapacitors, and flow batteries).

Reaction mechanism of atomic layer deposition of aluminum sulfide using trimethylaluminum and hydrogen sulfide

Atomic layer deposition (ALD) is a nanopreparation technique for materials and is widely used in the fields of microelectronics, energy and catalysis. ALD methods for metal sulfides, such as Al2S3 and Li2S, have been developed for lithium-ion batteries and solid-state electrolytes. In this work, using density functional theory calculations, the possible reaction pathways of the ALD of Al2S3 using trimethylaluminum (TMA) and H2S were investigated at the M06-2X/6-311G(d, p) level. Al2S3 ALD can be divided into two consecutive and complementary half-reactions involving TMA and H2S, respectively. In the TMA half-reaction, the methyl group can be eliminated through the reaction with the sulfhydryl group on the surface. This process is a ligand exchange reaction between the methyl and sulfhydryl groups via a four-membered ring transition state. TMA half-reaction with the sulfhydrylated surface is more difficult than that with the hydroxylated surface. When the temperature increases, the reaction requires more energy, owing to the contribution of the entropy. In the H2S half-reaction, the methyl group on the surface can further react with the H2S precursor via a four-membered ring transition state. The orientation of H2S and more molecules have minimal effect on the H2S half-reaction. The reaction involving H2S through a six-membered ring transition state is unfavorable. In addition, the methyl and sulfhydryl groups on the surface can both react with the adjacent sulfhydryl group on the subsurface to form and release CH4 or H2S in the two half-reactions. Furthermore, sulfhydryl elimination occurs more easily than methyl elimination on the surface. These findings for the TMA and H2S half-reactions of Al2S3 ALD may be used for studying precursor chemistry and improvements in the preparation of other metal sulfides for emerging applications.

Understanding KOtBu in atomic layer deposition - in situ mechanistic studies of the KNbO3 growth process

Functional coatings based on alkali metals have become increasingly attractive in the current shift towards sustainable technologies. While lithium-based compounds have a natural impact on batteries, other alkali metal compounds are important as replacements for toxic materials in a range of electronic devices. This is especially true for potassium, being a major component in e.g. KxNa1-xNbO3 (KNN) and KTaxNb1-xO3 (KTN), with hope to replace Pb(ZrxTi1-x)O3 (PZT) in piezo-/ferroelectric and electrooptic devices. ALD facilitates functional conformal coatings at deposition temperatures far below what is reported using other techniques and with excellent compositional control. The ALD growth of potassium-containing films using KOtBu has, however, been unpredictable. Untraditional response to the pulse composition and precursor dose, severe reproducibility issues, and very high growth per cycle are some of the puzzling features of these processes. In this article, we shed light on the growth behavior of KOtBu in ALD by in situ quartz crystal microbalance and Fourier transform infrared spectroscopy studies. We study the precursor's behavior in the technologically interesting KNbO3-process, showing how the potassium precursor strongly affects the growth of other cation precursors. We show that the strong hygroscopic nature of the intermediary potassium species has far-reaching implications throughout the growth. This helps not only to enhance the understanding of alkali metal containing compounds' growth in ALD, but also to provide the means to control the growth of novel sustainable technological materials.

Li2S growth on graphene: Impact on the electrochemical performance of Li-S batteries

Lithium-sulfur batteries show remarkable potential for energy storage applications due to their high-specific capacity and the low cost of active materials, especially sulfur. However, whereas there is a consensus about the use of lithium metal as the negative electrode, there is not a clear and widely accepted architectural design for the positive electrode of sulfur batteries. The difficulties arise when trying to find a balance between high-surface-area architectures and practical utilization of the sulfur content. Intensive understanding of the interfacial mechanisms becomes then crucial to design optimized carbon-hosted sulfur architectures with enhanced electrochemical performance. In this work, we use density functional theory (DFT)-based first principles calculations to describe and characterize the growing mechanisms of Li₂S active material on graphene, taken as an example of a nonencapsulated carbon host for the positive electrode of Li-S batteries. We first unravel the two growing mechanisms of Li₂S supported nanostructures, which explain recent experimental findings on real-time monitoring of interfacial deposition of lithium sulfides during discharge, obtained by means of in situ atomic force microscopy. Then, using a combination of mathematical tools and DFT calculations, we obtain the first cycle voltage plot, explaining the three different regions observed that ultimately lead to the formation of high-order polysulfides upon charge. Finally, we show how the different Li₂S supported nanostructures can be characterized in X-ray photoelectron spectroscopy measurements. Altogether, this work provides useful insights for the rational design of new carbon-hosted sulfur architectures with optimized characteristics for the positive electrode of lithium-sulfur batteries.

Cationic and anionic redox in lithium-ion based batteries

This review will present the current understanding, experimental evidence and future direction of anionic and cationic redox for Li-ion batteries.

Revealing the Reaction Mechanism of Sodium Selenide Confined within a Single-Walled Carbon Nanotube: Implications for Na-Se Batteries

The sodium-selenium (Na-Se) battery is a competitive candidate as the practical next-generation energy storage device. A Na₁₆Se₈ cluster confined within a (10, 10) single-walled carbon nanotube is constructed to reveal the nanoconfinement effect on the reaction mechanism of the Na-Se battery cathode. It is found that the nanoconfinement can enhance the electronic conductivity of Na _x≥12Se₈ nanostructures because itinerant electrons appear under this condition. During desodiation, polyselenide chains grow longer and the intermediate products become insulators for transferring electrons. However, hole polarons have the potential to act as charge carriers in Na _x≤10Se₈ nanostructures. The open-circuit voltage profile is plotted, and the voltage window is 1.67 ≤ U ≤ 1 V. After the first charge cycle, the cathode cannot discharge to Na₁₆Se₈, but the reversible specific capacity can still arrive at 302 mA h/g of the cathode composite.

Li2 S- or S-Based Lithium-Ion Batteries

While members of the Li-S battery research community are becoming more conscious of the practical testing parameters, the widespread commercialization of S-based batteries is still far from realization. Particularly, the metallic Li used as the anode poses potential safety and cycle stability concerns. Alternatively, other S-battery configurations without a Li anode, i.e., lithium-ion, Li₂ S, or S batteries, do not suffer from the same safety concerns and can possibly serve as better methods to bring room-temperature S-based battery technologies to industry. However, whether Li₂ S or S will be used as the initiating cathode material remains unclear as each offers their own unique advantages and disadvantages. Here, both S and Li₂ S as cathodes are briefly discussed and the key benefits of Li₂ S are highlighted.

Synthesis of Thin-Film Metal Pyrites by an Atomic Layer Deposition Approach

Late 3d transition metal disulfides (MS₂ , M=Fe, Co, Ni, Cu, Zn) can crystallize in an interesting cubic-pyrite structure, in which all the metal cations are in a low-spin electronic configuration with progressive increase of the e_g electrons for M=Fe-Zn. These metal pyrite compounds exhibit very diverse and intriguing electrical and magnetic properties, which have stimulated considerable attention for various applications, especially in cutting-edge energy conversion and storage technologies. The synthesis of the metal pyrites is certainly very important, because highly controllable, reproducible, and reliable synthesis methods are virtually essential for both fundamental materials research and practical engineering. In this Concept, a new approach of (plasma-assisted) atomic layer deposition (ALD) to synthesize the thin-film metal pyrites (FeS₂ , CoS₂ , NiS₂ ) is introduced. The ALD synthesis approach allows for atomic-precision control over film composition and thickness, excellent film uniformity and conformality, and superior process reproducibility, and therefore it is of high promise for uniformly conformal metal pyrite thin-film coatings on complex 3D structures in general. Details and implications of this ALD approach are discussed in this Concept, mainly from a conceptual perspective, and it is envisioned that, with this new ALD synthesis approach, a significant amount of new studies will be enabled on both the fundamentals, and novel applications of the metal pyrite materials.

Metal Fluorides as Lithium-Ion Battery Materials: An Atomic Layer Deposition Perspective

Lithium-ion batteries are the enabling technology for a variety of modern day devices, including cell phones, laptops and electric vehicles. To answer the energy and voltage demands of future applications, further materials engineering of the battery components is necessary. To that end, metal fluorides could provide interesting new conversion cathode and solid electrolyte materials for future batteries. To be applicable in thin film batteries, metal fluorides should be deposited with a method providing a high level of control over uniformity and conformality on various substrate materials and geometries. Atomic layer deposition (ALD), a method widely used in microelectronics, offers unrivalled film uniformity and conformality, in conjunction with strict control of film composition. In this review, the basics of lithium-ion batteries are shortly introduced, followed by a discussion of metal fluorides as potential lithium-ion battery materials. The basics of ALD are then covered, followed by a review of some conventional lithium-ion battery materials that have been deposited by ALD. Finally, metal fluoride ALD processes reported in the literature are comprehensively reviewed. It is clear that more research on the ALD of fluorides is needed, especially transition metal fluorides, to expand the number of potential battery materials available.

An Ultrahigh Capacity Graphite/Li2S Battery with Holey-Li2S Nanoarchitectures

The pairing of high-capacity Li2S cathode (1166 mAh g-1) and lithium-free anode (LFA) provides an unparalleled potential in developing safe and energy-dense next-generation secondary batteries. However, the low utilization of the Li2S cathode and the lack of electrolytes compatible to both electrodes are impeding the development. Here, a novel graphite/Li2S battery system, which features a self-assembled, holey-Li2S nanoarchitecture and a stable solid electrolyte interface (SEI) on the graphite electrode, is reported. The holey structure on Li2S is beneficial in decomposing Li2S at the first charging process due to the enhanced Li ion extraction and transfer from the Li2S to the electrolyte. In addition, the concentrated dioxolane (DOL)-rich electrolyte designed lowers the irreversible capacity loss for SEI formation. By using the combined strategies, the graphite/holey-Li2S battery delivers an ultrahigh discharge capacity of 810 mAh g-1 at 0.1 C (based on the mass of Li2S) and of 714 mAh g-1 at 0.2 C. Moreover, it exhibits a reversible capacity of 300 mAh g-1 after a record lifecycle of 600 cycles at 1 C. These results suggest the great potential of the designed LFA/holey-Li2S batteries for practical use.

In Situ Electrochemically Derived Amorphous-Li2 S for High Performance Li2 S/Graphite Full Cell

High-capacity Li₂ S cathode (1166 mAh g^-1 ) is regarded as a promising candidate for the next-generation lithium ion batteries. However, its high potential barrier upon the initial activation process leads to a low utilization of Li₂ S. In this work, a Li₂ S/graphite full cell with the zero activation potential barrier is achieved through an in situ electrochemical conversion of Li₂ S₈ catholyte into the amorphous Li₂ S. Theoretical calculations indicate that the zero activation potential for amorphous Li₂ S can be ascribed to its lower Li extraction energy than that of the crystalline Li₂ S. The constructed Li₂ S/graphite full cell delivers a high discharge capacity of 1006 mAh g^-1 , indicating a high utilization of the amorphous Li₂ S as a cathode. Moreover, a long cycle life with 500 cycles for this Li₂ S/graphite full cell is realized. This in situ electrochemical conversion strategy designed here is inspired for developing high energy Li₂ S-based full cells in future.

Revealing reaction mechanisms of nanoconfined Li2S: implications for lithium–sulfur batteries

Using Li₂S as an active material and designing nanostructured cathode hosts are considered as promising strategies to improve the performance of lithium–sulfur (Li–S) batteries.

Recent Progresses and Development of Advanced Atomic Layer Deposition towards High-Performance Li-Ion Batteries

Electrode materials and electrolytes play a vital role in device-level performance of rechargeable Li-ion batteries (LIBs). However, electrode structure/component degeneration and electrode-electrolyte sur-/interface evolution are identified as the most crucial obstacles in practical applications. Thanks to its congenital advantages, atomic layer deposition (ALD) methodology has attracted enormous attention in advanced LIBs. This review mainly focuses upon the up-to-date progress and development of the ALD in high-performance LIBs. The significant roles of the ALD in rational design and fabrication of multi-dimensional nanostructured electrode materials, and finely tailoring electrode-electrolyte sur-/interfaces are comprehensively highlighted. Furthermore, we clearly envision that this contribution will motivate more extensive and insightful studies in the ALD to considerably improve Li-storage behaviors. Future trends and prospects to further develop advanced ALD nanotechnology in next-generation LIBs were also presented.

Atomic and molecular layer deposition: off the beaten track

ALD archetype and deviations from it.

Insulator-to-metal transition of lithium–sulfur battery

Li₂S is a promising battery material due to the high theoretical capacity and high energy density.

Recent Development of Advanced Electrode Materials by Atomic Layer Deposition for Electrochemical Energy Storage

Electrode materials play a decisive role in almost all electrochemical energy storage devices, determining their overall performance. Proper selection, design and fabrication of electrode materials have thus been regarded as one of the most critical steps in achieving high electrochemical energy storage performance. As an advanced nanotechnology for thin films and surfaces with conformal interfacial features and well controllable deposition thickness, atomic layer deposition (ALD) has been successfully developed for deposition and surface modification of electrode materials, where there are considerable issues of interfacial and surface chemistry at atomic and nanometer scale. In addition, ALD has shown great potential in construction of novel nanostructured active materials that otherwise can be hardly obtained by other processing techniques, such as those solution-based processing and chemical vapor deposition (CVD) techniques. This review focuses on the recent development of ALD for the design and delivery of advanced electrode materials in electrochemical energy storage devices, where typical examples will be highlighted and analyzed, and the merits and challenges of ALD for applications in energy storage will also be discussed.

Graphene-Li2S-Carbon Nanocomposite for Lithium-Sulfur Batteries

Lithium sulfide (Li2S) with a high theoretical specific capacity of 1166mAh g(-1) is a promising cathode material for next-generation Li-S batteries with high specific energy. However, low conductivity of Li2S and polysulfide dissolution during cycling are known to limit the rate performance and cycle life of these batteries. Here, we report on the successful development and application of a nanocomposite cathode comprising graphene covered by Li2S nanoparticles and protected from undesirable interactions with electrolytes. We used a modification of our previously reported low cost, scalable, and high-throughput solution-based method to deposit Li2S on graphene. A dropwise infiltration allowed us to keep the size of the heterogeneously nucleated Li2S particles smaller and more uniform than what we previously achieved. This, in turn, increased capacity utilization and contributed to improved rate performance and stability. The use of a highly conductive graphene backbone further increased cell rate performance. A synergetic combination of a protective layer vapor-deposited on the material during synthesis and in situ formed protective surface layer allowed us to retain ∼97% of the initial capacity of ∼1040 mAh gs(-1) at C/2 after over 700 cycles in the assembled cells. The achieved combination of high rate performance and ultrahigh stability is very promising.

Facile Synthesis of Lithium Sulfide Nanocrystals for Use in Advanced Rechargeable Batteries

This work reports a new method of synthesizing anhydrous lithium sulfide (Li2S) nanocrystals and demonstrates their potential as cathode materials for advanced rechargeable batteries. Li2S is synthesized by reacting hydrogen sulfide (H2S) with lithium naphthalenide (Li-NAP), a thermodynamically spontaneous reaction that proceeds to completion rapidly at ambient temperature and pressure. The process completely removes H2S, a major industrial waste, while cogenerating 1,4-dihydronaphthalene, itself a value-added chemical that can be used as liquid fuel. The phase purity, morphology, and homogeneity of the resulting nanopowders were confirmed by X-ray diffraction and scanning electron microscopy. The synthesized Li2S nanoparticles (100 nm) were assembled into cathodes, and their performance was compared to that of cathodes fabricated using commercial Li2S micropowders (1-5 μm). Electrochemical analyses demonstrated that the synthesized Li2S were superior in terms of (dis)charge capacity, cycling stability, output voltage, and voltage efficiency.

Bottom-up, hard template and scalable approaches toward designing nanostructured Li2S for high performance lithium sulfur batteries

Li2S with a high theoretical capacity of 1166 mA h g(-1) and the capability to pair with lithium free anodes has drawn much attention for lithium sulfur (Li-S) battery applications. However, the fast battery decay and the low capacity retention due to dissolution of intermediate polysulfides in electrolytes limit its development. Designing a nanosized and nanostructured host for Li2S through facile techniques is one of the ways to alleviate the dissolution and improve Li-S battery performance; nevertheless, it is technically difficult to synthesize nanosized and nanostructured hosts for Li2S because Li2S is highly sensitive to moisture and oxygen. Herein, a novel technique, i.e., a bottom-up, hard template and scalable method, is proposed to engineer nanoLi2S composites with core-shell structures as cathodes of Li-S batteries. The size of the as-prepared nanostructured Li2S is around 100 nm. With the assistance of FETEM, HRTEM and EFTEM elemental mapping, an excellent core-shell structure has been confirmed and the outside carbon shell has a thickness of 20-50 nm, effectively retarding polysulfide outflow and dissolution. A high initial capacity of 915 mA h g(-1) at 0.2 C has been achieved upon electrochemical cycling and the battery still has exceptional capacity retention after prolonged 200 cycles with a limited decay of 0.18% per cycle. Also, at 0.5 C the electrode exhibits 60% capacity retention with a long life of 300 cycles. We attribute these good performances to the nano-architecture constructed by the novel and facile method.

Li2S Nanocrystals Confined in Free-Standing Carbon Paper for High Performance Lithium-Sulfur Batteries

Lithium sulfide (Li2S) with a high theoretical capacity of 1166 mAh g(-1) is a promising cathode material for Li-S batteries as it allows for the use of lithium-free anodes. However, a large overpotential (~1 V) is usually needed to activate microsized Li2S particles due to their low electronic and ionic conductivities. Here, nano-Li2S/carbon paper electrodes are developed via a simple Li2S solution filtration method. Li2S nanocrystals with a size less than 10 nm are formed uniformly in the pores of carbon paper network. These electrodes show an unprecedented low potential difference (0.1 V) in the first and following charges, also show high discharge capacities, good rate capability, and excellent cycling performance. More specifically, the nano-Li2S/carbon nanotube paper electrodes show a reversible capacity of 634 mAh g(-1) with a capacity retention of 92.4% at 1C rate from the 4th to 100th cycle, corresponding to a low capacity fading rate of 0.078% per cycle. These results demonstrate a facile and scalable electrode fabrication process for making high performance nano-Li2S/carbon paper electrodes, and the superior performance makes them promising for use with lithium metal-free anodes in rechargeable Li-S batteries for practical applications.

Atomic layer deposition of metal sulfide materials

CONSPECTUS: The field of nanoscience is delivering increasingly intricate yet elegant geometric structures incorporating an ever-expanding palette of materials. Atomic layer deposition (ALD) is a powerful driver of this field, providing exceptionally conformal coatings spanning the periodic table and atomic-scale precision independent of substrate geometry. This versatility is intrinsic to ALD and results from sequential and self-limiting surface reactions. This characteristic facilitates digital synthesis, in which the film grows linearly with the number of reaction cycles. While the majority of ALD processes identified to date produce metal oxides, novel applications in areas such as energy storage, catalysis, and nanophotonics are motivating interest in sulfide materials. Recent progress in ALD of sulfides has expanded the diversity of accessible materials as well as a more complete understanding of the unique chalcogenide surface chemistry. ALD of sulfide materials typically uses metalorganic precursors and hydrogen sulfide (H2S). As in oxide ALD, the precursor chemistry is critical to controlling both the film growth and properties including roughness, crystallinity, and impurity levels. By modification of the precursor sequence, multicomponent sulfides have been deposited, although challenges remain because of the higher propensity for cation exchange reactions, greater diffusion rates, and unintentional annealing of this more labile class of materials. A deeper understanding of these surface chemical reactions has been achieved through a combination of in situ studies and quantum-chemical calculations. As this understanding matures, so does our ability to deterministically tailor film properties to new applications and more sophisticated devices. This Account highlights the attributes of ALD chemistry that are unique to metal sulfides and surveys recent applications of these materials in photovoltaics, energy storage, and photonics. Within each application space, the benefits and challenges of novel ALD processes are emphasized and common trends are summarized. We conclude with a perspective on potential future directions for metal chalcogenide ALD as well as untapped opportunities. Finally, we consider challenges that must be addressed prior to implementing ALD metal sulfides into future device architectures.