A Novel Si/C Composite Anode Material for High Performance Lithium Ion Battery Using a Cost-Saving Approach

To response the multiply increased demand in portable electronics, hybrid electric vehicles and large scale energy storage over the last decade, Li-ion batteries (LIBs) with higher energy density and power capability have been desired. With respect to the anode of LIB, Silicon have received a great deal of interest as the fully lithiated (ca. Li22Si5) alloy has the highest theoretical capacity of any known material at 4140 mAh/g (3579 mAh/g for Li15Si4at room temperature). Although it is about 10 times higher than that of a conventional graphite anode, a Si-based electrode has yet to find use in commercial application because of its low coulombic efficiency (C.E.) and poor capacity retention. Si is typically known to undergo over 300% of volume expansion on Li insertion, which leads to cracking and crumbling of active particles and the resultant loss of electrical contact between electro-active materials causes rapid capacity fading. Although extensive researches have been reported to alleviate the problems, most of approaches are commercially unviable as they usually involve complicated and prohibitively high cost processes. Hence, a Si anode with sufficient performances and low cost production is highly desired. This study presents a novel cost-saving Si-based anode material with high coulombic efficiency and prolonged cyclability of excellent electrochemical performances using a low-cost synthesis though the attractive route. As a part of our strategy, we attempted to employ a by-product derived from a granular poly-Si mass production system for the feedstock of solar cell application. In such a way, a certain amount of amorphous silicon particles (ASP), the by-product, is derived homogeneously from the nucleation of gas dust in a silane-based gas phase reactor. (Fig. 1 shows HRTEM image and SAD pattern for ASP.) Our pioneering attempt is advantageously characterized by follows: 1) obtained sub-micron sized Si particles are superior to nano-sized Si particles in the battery performance and business value and 2) the production cost is expected to be many times lower than nano-sized Si by utilizing the by-product from an already matured mass production. Further improvement in consideration of commercial feasibility and processing cost is achieved by employing ASP into spherical Si/graphite/carbon composite systems. In Fig. 2, it is seen that spherical ASP/graphite/carbon composite is obtained with the particle size around 7-11 μm. Representative cross-section view demonstrates carbon coated ASP are enclosed by graphite layers; though vacant areas exist sparsely. In the optimized system, the mechanical stress on Si particles induced by huge volume expansion on Li insertion is alleviated and the direct contact between Si and electrolyte is prevented, by which irreversible reaction leading to deterioration of coulombic efficiency is reduced. In this context, we have performed a systematic study on the influence of choice and application method of carbon material which is a critical element in the composites. In such a way, ASP are carbon coated before or during the fabrication process of spherical composites and the achieved advantageous characteristics are summarized as follows: 1) separation of each silicon particles, preventing agglomeration and 2) a strong bonding between Si and graphite for maintaining the electrical contact on charge-discharge, 3) a ductile matrix to buffer the huge stress caused by volume expansion and 4) vacant space inside the composite to accommodate the huge volume changes. It is worth noting that such extraordinary ASP/graphite/carbon composites are manufactured in an inexpensive way as the process consists of only a few steps. The electrochemical characterization demonstrates remarkable performances as the coulombic efficiency at the first cycle reaches up to 90% and the capacity retention after 100cycle is over 92% at 620 mAh/g. Material characterization is performed through several different analytical methods including HRTEM, in-situ solid state lithiation, in-situ dilatometer to support and discuss the unique properties of ASP and the superior performances of our spherical Si/graphite/carbon composite systems.

Charging up Stationary Energy Storage

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh/g), low density (0.59 g/cm3) and the lowest negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode, SHE). Li battery based on Li metal anode is expected to have an order of magnitude higher energy density than today's Li-ion battery. This will enhance energy and power capability of battery devices used in portable electronics, hybrid electric cars, aerospace, telecommunication, military, etc.). The Li metal battery will fulfill the high energy demand that cannot be met through the current Li-ion batteries (e.g. all electric transportation or many other applications which require light weight, high energy density, high power density batteries with small battery footprint and safest). But, to date, uncontrolled dendritic Li growth and limited Coulombic efficiency (CE) during Li deposition/stripping of a bulk Li anode, are the main reason behind low cycle life, which has limited their practical applications. Furthermore, the rate of dendrite growth gets amplified when the cell is cycled at high charge-discharge current density, high charge voltage, and high areal discharge. Increasing anode surface area would reduce the effective charge/discharge current. Additionally, thin films and high surface area Li anodes exhibit high ionic and electronic conductivity contributing to the high efficiency of the current collection required for high capacity battery. Although low CE can be partially compensated by an excess amount of Li (at the expense of lower useable Li energy), fire and other hazards associated with the dendrite growth have limited the development of rechargeable Li metal batteries. Most approaches to dendrite prevention focus on improving the stability and uniformity of the solid-electrolyte interface (SEI) on the bulk Li surface by adjusting electrolyte components and optimizing SEI formation additives. It is very difficult to achieve sufficient passivation on Li electrode due to the thermodynamic instability of Li with electrolytes [1,2]. As an alternative, various mechanical barriers have been proposed to block dendrite penetration [3]. These approaches rely on a strong mechanical barrier provided by an SEI film or a separator to suppress Li dendrite penetration but do not change the fundamental, self-amplifying behavior of the dendrite growth. Also, it is hard to find a mechanical barrier material with required shear modulus (required > 109 Pa) with desired conductivity. In other words, these methods did not prevent Li dendrites from growing during long-term cycling at high charge-discharge current density, high charge voltage, and high areal discharge, or hardly improved the CE and safety in Li deposition/stripping which is not suitable for practical rechargeable Li batteries [1]. We have developed a novel ionic-electronic-mechanical membrane (an artificial SEI), which allows long-term Li cycleability and improved safety by reducing dendrite formation. The new artificial SEI is comprised of three different materials to fulfill the desired SEI criteria such as: (a) facilitate uniform Li ion dispersion and deposition on entire Li surface, (b) desired SEI conductivity (c) mechanical separation of Li and electrolyte and flexibility to contain anode volume change during Li stripping and deposition. The combined effect of the invented SEI result into more than 300% increase in number of cycles and 3-4 times increase in usable Li energy density (i.e. high Coulombic efficiency (CE)) of a wet battery composed of protected Li metal anode, liquid electrolyte (e.g. lithium hexafluoro arsenate, LiAsF6) and Li-ion cathode (e.g. lithium cobalt oxide, LCO) for the advancement of a battery beyond the state-of-the-art Li-ion battery. The added advantage of the invented SEI is improved safety due to suppression of dendrite growth by mechanically strong/flexible SEI and controlled, uniform deposition/stripping of Li from Li anode surface. The protected Li anode may be incorporated into wet cell batteries or solid state batteries having transition metal oxide cathodes (more specifically the state-of-the-art Li-ion cathodes) or Sulfur cathode (Li-S battery) or Oxygen cathode (Li-O2 battery). Moreover, similar methodologies can be applied to other rechargeable metal anodes (Na, Al, Mg, etc.) used in batteries.

With a theoretical specific energy of 2500 W h kg-1 and energy density of 2800 W h L-1, the Li-S battery system is believed to provide the step-up in energy density necessary for lithium-based battery technologies to expand from portable electronics to transportation and grid-storage applications.1 However, the growth of dendrites during repeated Li plating/stripping and the low coulombic efficiency (CE) of these processes have limited application of rechargeable Li metal batteries.2 For example, a 300% excess amount of lithium often used in these batteries would directly result in halving the theoretical specific energy of the Li/S cells. In this presentation, the design of new electrolyte systems which enable high CE of lithium metal plating/stripping and high stability in the sulfur environment will be discussed. Tailoring of electrolyte properties for the lithium negative electrode has proven to be a successful strategy for improving the capacity retention and cycle life of Li-S full cells. This also enables lower electrolyte/sulfur mass ratios to be used and a lower excess of lithium metal; ultimately increasing the energy density of the system. A new class of electrolytes based on a high concentration of selected lithium salts in pure diethylene glycol dimethyl ether (diglyme) solvent provides a CE for lithium plating/stripping of greater than 99% for over 200 cycles and greater than 95% for over 500 cycles (Figure 1). In contrast, lithium metal cycles for less than 40 cycles at high CE in the standard 1 M LiTFSI + 2wt% LiNO3 in DOL:DME electrolyte. To realize the benefits of sulfur cathodes over intercalation cathodes currently using in Li-ion cells, high loading (high capacity) cathodes need to be used. In Figure 2a, a Cu||Li cell is cycled with the new diglyme-based electrolyte to a capacity of 6 mAh/cm2 at a current density of 0.6 mA/cm2 (C/10). Even at this high capacity, lithium is cycling with >99% CE. Lithium symmetrical cells were also cycled at a current density of 0.5 mA/cm2 to 5 mAh/cm2 (Figure 2b). In this case, the increase in polarization was used a metric to determine the practical cycle life of Li metal in the different electrolytes. No polarization is observed for the diglyme-based electrolyte after 2200 hours in the Li||Li cell. The inexpensive sulfur cathode paired with a low excess of lithium metal and the low-cost salt/solvent system may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.

Applications of silicon as a high-performance anode material have been impeded by its low intrinsic conductivity and huge volume expansion (>300%) during lithiation. To address these problems, nano-Si particles along with conductive coatings and engineered voids are often employed, but this results in high-cost anodes. Here, we report a scalable synthesis method that can realize high specific capacity (∼800 mAh g–1), ultrafast charge/discharge (at 8 A g–1 Si), and high initial Coulombic efficiency (∼90%) with long cycle life (1000 cycles) at the same time. To achieve 1000 cycle stability, micron-sized Si particles are subjected to high-energy ball milling to create nanostructured Si building blocks with nano-channel-shaped voids encapsulated inside a nitrogen (N)-doped carbon shell (termed as Si microreactor). The nanochannel voids inside a Si microreactor not only offer the space to accommodate the volume expansion of Si but also provide fast pathways for Li-ion diffusion into the center of the nanostructured Si core and thus ultrafast charge/discharge capability. The porous N-doped carbon shell helps to improve the conductivity while allowing fast Li-ion transport and confining the volume expansion within the Si microreactor. Submicron-sized Si microreactors with a limited specific surface area (35 m2 g–1) afford sufficient electrode/electrolyte interfacial area for fast lithiation/delithiation, leading to the specific capacity ranging from ∼800 to 420 mAh g–1 under ultrafast charging conditions (8 A g–1), but not too much interfacial area for surface side reactions and thus high initial Coulombic efficiency (∼90%). Since Si microreactors with superior electrochemical properties are synthesized via an industrially scalable and eco-friendly method, they have the potential for practical applications in the future.

Rechargeable batteries (e.g., Li-ion) are widely used to power a number of portable electronic devices such as mobile phones and laptops. Li-ion batteries (LIBs) in particular have revolutionized electric vehicle technology, nonetheless, they suffer from poor energy and power densities, which ultimately limit the driving range and increase the cost. Recently, silicon (Si) anode has attracted a considerable attention from battery researchers as an alternative to conventional graphite anode due to its high specific capacitance (4200 mAh g-1) corresponding to Li22Si5. However successful commercialization of Si anodes in battery packs is hindered by the irreversible capacity loss during cycling associated with volume expansion (~300%), finally leading to electrode failure. In recent times, there have been a number of reports claiming high specific capacities for Si composites but they involve complex synthesis steps leading to higher cost. In this poster, we will discuss our approach of making a composite with CNTs and commercial Si using ultrasonication method. Carbon nanotubes (CNTs) have excellent electrical conductivity and mechanical stability. The composite electrodes when assembled into a battery showed excellent electrochemical performance: albeit small losses in coulombic efficiency during initial six cycles, they retained 100% efficiency for more than 150 cycles. This could be attributed to the inclusion of CNTs which form a flexible network around Si particles, and facilitates volume expansion/contraction during reduction/oxidation of the electrode. Such modification of Si anodes can be seamlessly integrated into commercial manufacturing.

A widely applicable strategy to convert fabrics into lithiophilic textile current collector for dendrite-free and high-rate capable lithium metal anode

Silicon has a high potential to replace commercial graphite anodes in lithium-ion batteries (LiBs). It can facilitate achieving excellent energy densities because of its high theoretical specific lithiation capacity (Chan et al. 2008). However, major challenges such as rapid capacity fading and low Coulombic efficiency due to the huge volume change (∼300 %) during cycling have seriously hindered its commercialization (Wu et al. 2013). Although nanostructuring has been successful in minimizing volume expansion issues, the electrochemical performance of nano-sized silicon is still limited due to unstable solid-electrolyte interphase, low coating density and overall poor electrical properties due to the higher interparticle resistance (Liu et al. 2014). To tackle those challenges, here we introduce a new concept of post-synthesis spray drying to produce hierarchically structured micro-agglomerates from silicon/carbon (Si/C) composite nanoaggregates synthesized in the gas phase (Amin et al. 2023; Adil Amin et al.).The resulting agglomerates were characterized i) on the powder level by scanning electron microscopy (Fig. 1a) and N2 sorption, ii) on the dispersion level by rheometry and analytical centrifugation, iii) on the electrode level by atomic force microscopy for structure and iv) via electrochemical testing on half-cells for electrochemical performance (Fig. 1b). These results show that electrodes from Si/C supraparticles with the highest concentration of stabilizer exhibit better redispersion stability and excellent first cycle specific discharge capacity as well as better cycling stability as compared to the Si/C composite nanoaggregates (4 wt.% carbon content). Furthermore, compared to the reference electrodes made of nanoaggregates, the more stable supraparticles (3 wt.% stabilizer) showed the highest first Coulombic efficiency. This is due to the reduction of their surface to volume ratio which helps in forming less volume of solid electrolyte interface.To conclude, our investigation suggests how an established industrial process (gas phase synthesis of nanoparticle in a hot-wall reactor) can be combined with scalable one-step spray drying to get dense active materials for LiBs. This enables to fully utilize the new materials’ potential by the right packaging into optimum electrode structures with high performance and longevity. Furthermore, we are of the opinion that this pioneering method can be utilized as a broadly relevant design principle to enhance other (anode) materials that encounter analogous problems of volume expansion. Publication bibliography Amin, Adil; Özcan, Fatih; Loewenich, Moritz; Kilian, Stefan O.; Wiggers, Hartmut; Segets, Doris; Wassmer, Theresa; Bade, Stefan; Lyubina, Julia: Hierarchically Structured Si/C Agglomerates by Spray-Drying. Patent no. PCT / EP 2022/ 052453.Amin, Adil; Loewenich, Moritz; Kilian, Stefan O.; Wassmer, Theresa; Bade, Stefan; Lyubina, Julia et al. (2023): One-Step Non-Reactive Spray Drying Approach to Produce Silicon/Carbon Composite-Based Hierarchically Structured Supraparticles for Lithium-Ion Battery Anodes. In J. Electrochem. Soc. 170 (2), p. 20523. DOI: 10.1149/1945-7111/acb66b.Chan, Candace K.; Peng, Hailin; Liu, Gao; McIlwrath, Kevin; Zhang, Xiao Feng; Huggins, Robert A.; Cui, Yi (2008): High-performance lithium battery anodes using silicon nanowires. In Nature nanotechnology 3 (1), pp. 31–35. DOI: 10.1038/nnano.2007.411.Liu, Nian; Lu, Zhenda; Zhao, Jie; McDowell, Matthew T.; Lee, Hyun-Wook; Zhao, Wenting; Cui, Yi (2014): A pomegranate-inspired nanoscale design for large-volume-change lithium battery anodes. In Nature nanotechnology 9 (3), pp. 187–192. DOI: 10.1038/nnano.2014.6.Wu, Hui; Yu, Guihua; Pan, Lijia; Liu, Nian; McDowell, Matthew T.; Bao, Zhenan; Cui, Yi (2013): Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. In Nature communications 4, p. 1943. DOI: 10.1038/ncomms2941. Figure 1

Achieving fully reversible conversion in Si anode for lithium-ion batteries by design of pomegranate-like Si@C structure

The replacement of graphite by silicon as the active material in negative electrodes of Li-ion batteries is very attractive since the specific capacity of Si is 10 times higher than that of graphite. However, Si suffers from huge volume variation (up to ~300% vs 10% for C) during its lithiation. This leads to the electrode/particle cracking which induces electrical disconnections in addition to cause an instability of the solid electrolyte interface (SEI), resulting in poor cycle life and low coulombic efficiency. A precise evaluation of the expansion/contraction behavior of the Si-based electrodes upon cycling is thus highly relevant to develop more efficient electrode formulations. For this purpose, a simple and efficient method consists of integrating a contact displacement transducer to the electrochemical cell, which permits a measurement of any thickness change of the working electrode upon its charge and discharge as shown hereafter. In the present study, electrochemical dilatometry experiments are performed on silicon/carbon/carboxymethylcellulose (Si/C/CMC) composite electrodes. It is shown that the pH of the slurry (pH 7 vs. buffered pH 3) and the size of the Si particles (1-5 µm vs. 85 nm) have a major impact on their electrochemical performance (Fig. 1) and their expansion/contraction behavior (Fig. 2a-c). During the first discharge (lithiation), a maximum electrode thickness expansion of ~130% is observed for the pH3-micro Si electrode (Fig. 2b). compared to ~330% for the pH7-micro Si electrode. (Fig. 2a). A lower irreversible expansion is also observed at the end of the 1st cycle (~50% compared to ~180% for the pH7 electrode). It can be explained by the the formation of more cohesive (covalent) bonds between the Si particles and the CMC chains when the electrode is prepared with a slurry buffered at pH 3, increasing the mechanical strength of the composite electrode and its ability to reversibly sustain the volume variations of the silicon particles. 1,2 However,when the 1-5µm Si is replaced by 85 nm Si, a very large and abrupt expansion/contraction of the electrode is observed (up to 500%, see Fig. 2c), resulting in a significant decrease of the electrode cycle life (Fig. 1). It may be related to the higher specific surface area and/or lower surface oxidation state of the nanosized Si powder, inducing a less efficient grafting of the CMC binder at the surface of the Si particles. 3 Additionaldilatometric experiments with oxidized Si nanoparticles and with different CMC amounts will be presented to address this issue. 1. D. Mazouzi, B. Lestriez, L. Roué, D. Guyomard. Silicon composite electrode with high capacity and long cycle life. Electrochem. Solid State Let. 12 (2009) A215-A2182. 2. A. Tranchot, P-X. Thivel, H. Idrissi, L. Roué. Impact of the slurry pH on the expansion/contraction behavior of silicon/carbon/carboxymethylcellulose electrodes for Li-ion batteries. J. Electrochem. Soc., submitted. 3. N. Delpuech, D. Mazouzi, N. Dupré, P. Moreau, M. Cerbelaud, J. S. Bridel, J.-C. Badot, E. De Vito, D. Guyomard, B. Lestriez, and B. Humbert. Critical Role of Silicon Nanoparticles Surface on Lithium Cell Electrochemical Performance Analyzed by FTIR, Raman, EELS, XPS, NMR, and BDS Spectroscopies. J. Phys. Chem. C 118 (2014) 17318−17331. Figure 1

Introduction Lithium ion (Li-ion) batteries have become the standard power source for notebook computers and other portable electronic devices. Current graphite anodes in Li-ion batteries offer numerous advantages including good cycle life at relatively low cost. However, graphite anodes are limited by their theoretical specific capacity of 375 mAh/g for larger storage requirements in some applications such as electric vehicles. One approach to increasing the energy density of Li-ion batteries is to use higher capacity electrodes. Among other promising candidates, aluminum (Al) and tin (Sn), with their relatively high theoretical specific capacity of 993 (at LiAl) and 959 (at Li17Sn4) mAh/g, respectively, may prove to be worthy alternative anode materials. During the alloying/de-alloying process with lithium (Li), aluminum suffers from volumetric expansions of ~100%, forming a LiAl intermetallic alloy. Similarly, tin also experience volumetric expansions, the order of ~300%, possibly through the formation of thermodynamically stable intermetallic phases of Li2Sn5, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, Li17Sn4. This significant volumetric change causes mechanical strain leading to particle pulverization of the active material and believed to be a contributing factor to capacity fade. Fundamental understanding of the lithiation/de-lithiation and associated processes are necessary in order to address the capacity fade and provide strategies to optimize the chemical and structural parameters of the next generation of Li-ion battery electrodes. Here, we demonstrate that in situ NDP (in a custom-designed battery coin cell) is an effective tool for the quantification and visualization of Li transport in real time, under battery charge and discharge operations. The obtained spatial and temporal resolution of Li allows for the direct observation of the transient and non-equilibrium nature of the chemical transformations and reactions occurring during the lithiation and de-lithiation of Li storage materials, providing insights in addressing issues related to transport, materials selection, and structural integrity. Experimental Electrochemical half-cells were constructed with Al foil (0.016 mm thick, 98.5%, Reynolds) and Sn foil (0.0125 mm thick, 97.4%, Goodfellow) as the working electrode in a disk geometry (12 mm in diameter), metallic lithium (Chemetall Foote Corp) disc (12 mm in diameter) as a combined counter and reference electrode, a Celgard® separator (~ 25 mm), and electrolyte (1 M LiBF4 or 1 M LiPF6 in 1:1 ethylene carbonate: dimethyl carbonate from Sigma Aldrich) were assembled in a modified CR2032 coin cells (MTI Corp). Coin cell components were cleaned in acetone (≥ 99.5%) and methanol (≥ 99.8%) in sequence followed by overnight drying at 55 oC under vacuum. The coin cells were crimped using a manual hydraulic crimping machine (MSK-110, MTI Corp) equipped with a CR2032 die at pressures of 1100 – 1200 psi. The coin cells were modified with a 9.5 mm diameter hole on one of the casings to allow the placement of a Kapton® film (7.5 mm thickness). The handling and assembling of materials were performed in an Argon-filled glovebox (mBraun) with continuous detection of H2O < 0.5 ppm and O2< 0.5 ppm. Electrochemical measurements were performed on a Gamry Potentiostat (Reference 600, Gamry Instruments). The mass of the electroactive Al and Sn electrode were determined by weighing. Results and Discussion During the initial charging of the battery, lithium is first driven towards and enriched at the surface of the tin followed by propagation throughout the entire tin material. It was discovered that the highest rate of the lithiation occurred near the surface suggesting that lithiation is not limited by electron transfer. Our data demonstrated that, in fact, the driving force for lithium transport within the Sn electrode is purely diffusion. Based on the NDP data, the ambient diffusion coefficient of lithium in Sn is between 0.8 – 2 x10-7 cm2/second. Our work also suggests that tin does not lithiated in uniform increments and that significant parasitic side-reactions may have contributed to the decreased coulombic efficiency observed. Conclusion The experiments presented here can be replicated for an extensive range of anodes and cathodes, not limited to intermetallic forming materials. This technique can aid in the development of a comprehensive range of materials, architectures for specific purposes (high energy vs. high power applications). For example, this methodology can be used to obtain information concerning Li trapped within localized pockets in the electrode resulting in low coulombic efficiencies; provide understanding of requirements for optimum materials architecture promoting efficient Li transport, which is often the rate limiting step in battery processes, gain insight towards materials properties for high rates of Li transport, and provide a direct experimental verification method for models predicting mass and charge transfer in Li-ion cells, including failure and aging mechanisms. Figure 1

The development of energy storage devices that can efficiently operate at temperatures below 0 °C is necessary for both terrestrial and space-based applications. NASA has previously carried out pioneering work that has enabled Li-ion batteries to operate at temperatures down to -30 °C through the development of new carbonate electrolyte formulations. [1-2] However, secondary batteries that utilize lithium metal anodes instead of conventional graphite anodes could significantly boost energy density and specific energy, but the behavior of lithium electrodes at low temperatures are largely unknown. In this work, we investigate the effect of sub-zero temperatures on electrochemical behavior, morphological evolution, and solid-electrolyte interphase (SEI) formation of Li metal anodes in carbonate and ether solvents. Electrolytes made with solvents such as ethylene carbonate and ethyl methyl carbonate with ester co-solvents (e.g., ethyl propionate) exhibit sufficient conductivity and show effective Li deposition/stripping down to -30 °C, but with relatively low average Coulombic efficiencies (CEs) of ~70 % (similar to the room-temperature CE of ~73 %). The introduction of SEI-stabilizing additives such as fluoroethylene carbonate (FEC) boosts the average Coulombic efficiency across a range of temperatures (CE = ~94 %). Ether-based electrolytes, on the other hand, enable Li deposition/stripping down to -70 °C with high CEs (~95 %). Interestingly, investigation of the Li morphology after cycling revealed that distinct Li morphologies form at different temperatures, which may be related to differences in SEI chemistry and structure. These results provide important new information for engineering Li metal anodes for efficient operation under a variety of conditions.

Lithium-ion (Li-ion) batteries have been ubiquitously utilized in the modernized world in portable electronic, electrical vehicles, and grid-scale energy storage. However, demand satisfaction for traditional Li-ion batteries is becoming difficult due to their limited capacity and energy density. Moreover, there are challenges related to the availability of non-renewable critical materials for Li-ion batteries such as Co, Ni, and graphite, and environmental pollution during battery creation and recycling. Further neglect of these problems will lead to dramatic consequences at which batteries will become a part of the environmental problems but not a solution to these problems as they should be. Therefore, it is highly imperative to explore novel battery systems that show high energy density, low production cost and low environmental pollution during production, use and recycling. One of the most promising candidates is the lithium-sulphur (LiS) battery, which offers various advantages such as high energy density, high theoretical specific capacity, and affordable cost, because of the high availability of elemental sulphur and carbon used in this type of battery. The theoretical gravimetric energy density of LiS batteries is 2567 Wh/kg which is 4.5 times higher than the energy density of conventional Li-ion batteries. Despite the richness of sulphur in the Earth’s crust and its prominent merits in energy density and cost, several problems have restricted the development of LiS batteries for commercialization. The most notorious and intractable problem is the high solubility of the sulphur species (Li2Sx, 3≤x≤8) in common Li-ion battery electrolytes that leads to the so-called lithium polysulfide (LiPS) shuttle effect and loss of battery capacity, Li metal anode corrosion, and low coulombic efficiency during interaction of the LiPS with Li metal anode. The most prospective solution to address the above drawbacks is sulphur incorporation with a porous, high-conductive carbon host that will tolerate sulphur volume expansion, improve the conductivity of the electrode, prevent the shuttle effect, and allow reversible lithium-ion migration during charging and discharging.However, to achieve the excellent operation performances of the porous carbon host its properties should be carefully tuned and the LiPS absorption ability of the carbon host should be improved for example by metal oxide doping. Many different strategies for the creation of the required material were proposed in recent years. Unfortunately, many proposed synthetic methods require a hard template to provide fine control of the pore distribution in the materials, which is a significant drawback as in this case harsh conditions are required for template removal. In addition, the formation of doped carbons with good electrical conductivity often demands high temperatures, simultaneously causing the undesirable reduction of metal cations to their metallic state followed by the aggregation to form nanoparticles, together with the collapse of the carbon matrices. Therefore, it still urgently needs to find a new strategy to produce a porous carbon host for the sulfur with fine porosity and good lithium polysulfide absorption ability, which purpose to accelerate the successful commercialization of this battery technology on the market.In our current work, we are investigating the possibility to synthesize finely dispersed metal oxide catalysts on hollow N-doped porous carbon capsules produced from zeolitic imidazolate framework (ZIF-8). The coating of the ZIF-8 with metal–tannic acid coordination polymer allows to uniformly dispersed metal oxide nanoparticles, such as Fe2O3, MnO, CoO etc., on hollow carbon capsules after the pyrolysis process. Moreover, the carbon produced by ZIF-8 pyrolysis is expected to be both doped with nitrogen and highly porous, which should have a positive effect on the maximum sulfur loading possibility in the carbon host and lithium polysulfide absorption ability. In addition, the used approach for the synthesis of the hollow N-doped porous carbon allows the distribution of multicomponent metal oxide nanoparticles on the surface of the hollow carbon capsules, which may have a synergetic effect and improve the lithium polysulfide absorption ability of the produced materials. The structural, compositional, and morphological properties of the created material are investigated using SEM, EDS, XPS, Raman spectroscopy, FTIR and TGA techniques. The effect of the different metal oxide nanoparticles and their combinations on the lithium polysulfide absorption ability of the synthesized materials are investigated by analysis of the electrochemical performances of the Li-S batteries, where synthesized material was used as the sulfur host during the creation of the Li-S battery cathode.

The reversible electrochemical transformation from lithium (Li) and sulfur (S) into Li2 S through multielectron reactions can be utilized in secondary Li-S batteries with very high energy density. However, both the low Coulombic efficiency and severe capacity degradation limits the full utilization of active sulfur, which hinders the practical applications of Li-S battery system. The present study reports a ternary-layered separator with a macroporous polypropylene (PP) matrix layer, graphene oxide (GO) barrier layer, and Nafion retarding layer as the separator for Li-S batteries with high Coulombic efficiency and superior cyclic stability. In the ternary-layered separator, ultrathin layer of GO (0.0032 mg cm(-2) , estimated to be around 40 layers) blocks the macropores of PP matrix, and a dense ion selective Nafion layer with a very low loading amount of 0.05 mg cm(-2) is attached as a retarding layer to suppress the crossover of sulfur-containing species. The ternary-layered separators are effective in improving the initial capacity and the Coulombic efficiency of Li-S cells from 969 to 1057 mAh g(-1) , and from 80% to over 95% with an LiNO3 -free electrolyte, respectively. The capacity degradation is reduced from 0.34% to 0.18% per cycle within 200 cycles when the PP separator is replaced by the ternary-layered separators. This work provides the rational design strategy for multifunctional separators at cell scale to effective utilizing of active sulfur and retarding of polysulfides, which offers the possibility of high energy density Li-S cells with long cycling life.

Lithium metal, with a high theoretical capacity of 3860 mAh/g and a low electrochemical potential of −3.040 V, is an attractive anode material. However, its application has been hampered by irregular lithium dendrite growth and low coulombic efficiency. To solve these problems, a facile air calcination strategy was used to prepare cake‐like TiO2 nanoparticles with rich pores, which were further coated on one side of the commercial Celgard separator. The nanoscale mesoporous channels on the surface of TiO2 particles can effectively block the growth of lithium dendrites, leading to dense and uniform Li deposition with a high coulombic efficiency. Compared with the blank cell (50 cycles of normal operation), the Li||Cu cell with modified separator can run 100 cycles at 2 mA/cm2 with an average coulombic efficiency of 97.3 %. These results herald a new approach to dendrite‐free lithium anodes by nanostructured ceramic coating on the separator.