Li-sulfur Batteries Research Articles

3D-hybrid material design with electron/lithium-ion dual-conductivity for high-performance Li-sulfur batteries

We report a novel 3D-hybrid cathode material with three-dimensional (3D) N-GO/CNT framework to load sulfur (77.6 wt %), and sulfonated polyaniline (SPANI) of coating layer. Used as a cathode material, it possesses a high capacity (1196 mAh g−1@0.3 A g−1@1.6 mg cm−2), excellent charging-discharging rate (680 mAh g−1@7.5 A g−1) and long-life performance (maintaining 71.1% capacity over 450 cycles), which is mainly attributed to the benefits of excellent electronic/Li-ionic dual-conductivity and confinement effect of the 3D-hybrid N-GO/CNT framework coated by self-doping conducting polymer SPANI. Thus, a 3D sulfur cathode modified with electronic/Li-ionic dual-conduction network can significantly enhance the electrochemical performance and stability, and this novel type of material is very promising for commercial applications that require high energy and power density, long life, and excellent abuse tolerance.

Understanding the Effect of Additives in Li-ion and Li-Sulfur Batteries by Operando ec- (S)TEM

Understanding the Effect of Additives in Li-ion and Li-Sulfur Batteries by <i>Operando ec-</i> (S)TEM

Nanostructured Li Metal Anode to Inhibit Dendrite Growth in Safe Li-Metal Batteries

Li metal is considered as the “Holy Grail” of energy storage systems due to its extremely high theoretical specific capacity (3860 mAh g−1), low gravimetric density (0.59 g cm−3), and lowest negative redox potential (−3.040 V vs. standard hydrogen electrode). The bright prospects give rise to worldwide interests in the metallic Li for the next generation energy storage systems, including highly considered rechargeable metallic Li batteries such as Li-O2 and Li-sulfur (Li–S) batteries. However, the formation of Li dendrites induced by inhomogeneous distribution of current density on the Li metal anode and the concentration gradient of Li ions at the electrolyte/electrode interface is a crucial issue that hinders the practical demonstration of high-energy-density metallic Li batteries. A unique nanostructured anode with Li metal distributed in fibrous Li7B6 matrix is proposed as a promising anode to prevent the dendrite growth. The nanostructured anode is with a large specific area, thus rendering a low current density on the Li metal anode. The dendrite growth is effectively inhibited via decreasing the growth velocity of Li deposits and then limiting the final size of deposited Li on the nanostructured matrix, thus leading to the dendrite-free morphology at macroscale. The concentration gradient of Li ions near the anode surface are sharply reduced, because the 3D Li7B6 fibrous structure provides quantities of free space to accommodate electrolyte. To improve the Coulombic efficiency of Li depositing/dissolution, a dual-phase Li metal anode containing polysulfide-induced SEI and nanostructured graphene framework was investigated for Li-S batteries. Free-standing graphene foam provides several promising features as underneath layer for Li anode, including (1) relative larger surface area than 2D substrates to lower the real specific surface current density and the possibility of dendrite growth, (2) interconnected framework to support and recycle dead Li, and (3) good flexibility to sustain the volume fluctuation during repeated incorporation/extraction of Li. The synergy between the LiNO3 and polysulfides provides the feasibility to the formation of robust SEI in an ether-based electrolyte. The efficient in-situ formed SEI-coated graphene structure allows stable Li metal anode with the cycling Coulombic efficiency of ∼97 % with high safety and efficiency performance, which is with a low resistance of 19.65 Ω (29.10 Ω for Cu foil based Li metal anode) and high ion conductivity of 5.42×10-2 mS cm-1 (2.33×10-2 mS cm-1 for Cu foil based Li metal anode). These results indicated that interfacial engineering of nanostructured electrode were a promising strategy to handle the intrinsic problems of Li metal anodes, thus shed a new light toward LMBs, such as Li-S and Li-O2 batteries with high energy density. Reference [1] X. B. Cheng, H. J. Peng, J. Q. Huang, F. Wei, Q. Zhang, Small 2014, 10, 4257[2] X. B. Cheng, H. J. Peng, J. Q. Huang, R. Zhang, C. Z. Zhao, Q. Zhang, ACS Nano 2015, 9, 6373[3] R. Zhang, X.B. Cheng, C.Z. Zhao, H.J. Peng, J.L. Shi, J.Q. Huang, J.F. Wang, F. Wei, Q. Zhang. Adv Mater 2016, 28, 2155.[4] X.B. Cheng, T.Z. Hou, R. Zhang, H.J. Peng, C.Z. Zhao, J.Q. Huang, Q. Zhang Q Adv Mater 2016, 28, 2888

Challenges and Issues Facing Lithium Metal for Solid State Rechargeable Batteries

Research on lithium metal combined with polymer electrolyte in lithium rechargeable batteries was started in 1979. Since that time, lithium battery research has expanded worldwide. Several new polymers, solid electrolytes and ionic liquids with improved conductivity were identified. These advances resulted from a better understanding of the major parameters controlling ion migration, such as favorable polymer structure, phase diagrams between solvating polymers and lithium salts, and the development of new lithium counter-anions. In spite of the progress so far, the quest for a highly conductive dry polymer at room temperature is still not available. However, effort is continuing, and all-lithium polymer battery (LPB) developers presently face the challenge of whether to heat the polymer electrolyte to enable high-power performance, as required for electric vehicles and energy storage. LPB developers have explored both the high-temperature and low-temperature options. The commercial use of lithium metal/polymer batteries has been delayed because of the adverse effects of dendrites on the surface of the lithium electrodes, and the difficulty in finding a polymer that has both the mechanical strength and ionic conductivity required in a solid electrolyte. However, recent strategies have emerged to overcome these difficulties, and now these batteries are currently an option for different applications, including electric cars.In this presentation, we review these strategies and discuss the different promising routes that should result in further progress on lithium metal/polymer batteries in the near future. This presentation also discusses the challenges and opportunities in developing thin lithium negative electrodes with stable SEI layers for three battery technologies using: All solid-state Li-sulfur batteries Rechargeable lithium batteries containing dry polymer and ionic liquid-polymer electrolytes 3. Li-air batteries. In addition, we will discuss the safety of lithium, dendrite mechanism, interface phenomena, side reactions, protection of lithium metal, and lithium alloys that are relevant to lithium batteries. Acknowledgement: The author thanks the SCE IREQ and LTE Shawinigan teams for helpful discussion.

Li+ Local Structure in Li–Tetraglyme Solvate Ionic Liquid Revealed by Neutron Total Scattering Experiments with the 6/7Li Isotopic Substitution Technique

Equimolar mixtures of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraglyme (G4: CH3O-(CH2CH2O)4-CH3) yield the solvate (or chelate) ionic liquid [Li(G4)][TFSA], which is a homogeneous transparent solution at room temperature. Solvate ionic liquids (SILs) are currently attracting increasing research interest, especially as new electrolytes for Li-sulfur batteries. Here, we performed neutron total scattering experiments with (6/7)Li isotopic substitution to reveal the Li(+) solvation/local structure in [Li(G4)][TFSA] SILs. The experimental interference function and radial distribution function around Li(+) agree well with predictions from ab initio calculations and MD simulations. The model solvation/local structure was optimized with nonlinear least-squares analysis to yield structural parameters. The refined Li(+) solvation/local structure in the [Li(G4)][TFSA] SIL shows that lithium cations are not coordinated to all five oxygen atoms of the G4 molecule (deficient five-coordination) but only to four of them (actual four-coordination). The solvate cation is thus considerably distorted, which can be ascribed to the limited phase space of the ethylene oxide chain and competition for coordination sites from the TFSA anion.

Understanding the Effect of Additives in Li-Sulfur Batteries by Operando ec- (S)TEM

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Graphene‐Based Nanocomposites for Energy Storage

Since the first report of using micromechanical cleavage method to produce graphene sheets in 2004, graphene/graphene‐based nanocomposites have attracted wide attention both for fundamental aspects as well as applications in advanced energy storage and conversion systems. In comparison to other materials, graphene‐based nanostructured materials have unique 2D structure, high electronic mobility, exceptional electronic and thermal conductivities, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. Therefore, they are considered as attractive materials for hydrogen (H2) storage and high‐performance electrochemical energy storage devices, such as supercapacitors, rechargeable lithium (Li)‐ion batteries, Li–sulfur batteries, Li–air batteries, sodium (Na)‐ion batteries, Na–air batteries, zinc (Zn)–air batteries, and vanadium redox flow batteries (VRFB), etc., as they can improve the efficiency, capacity, gravimetric energy/power densities, and cycle life of these energy storage devices. In this article, recent progress reported on the synthesis and fabrication of graphene nanocomposite materials for applications in these aforementioned various energy storage systems is reviewed. Importantly, the prospects and future challenges in both scalable manufacturing and more energy storage‐related applications are discussed.

Sulfide Electrolytes: Study of Local Li-Ion Dynamics in Li3PS4 Using Li(7) NMR Relaxometry

The attractive long-term stability and safety of so-called all-solid-state batteries has given new impetus to developing powerful solid Li+ electrolytes. Post Li-ion batteries equipped with solid electrolytes may also be very attractive for hybrid electric vehicles as these systems are expected to withstand high operation temperatures. Moreover, they may serve as attractive components in Li-oxygen and Li-sulfur batteries. In addition to the various oxides and phosphates studied so far, see, e.g., refs. [1,2], sulfide-based materials have attracted particular attention due to their very high ionic conductivities [3,4]. Li3PS4 represents such a promising candidate, since its achievable Li-ion conductivity is comparable to that of liquid electrolytes. Phase-pure Li3PS4 was prepared by joint high-energy ball-milling of Li2S and P2S5 for 35 hours and subsequent heat treatment at 260 °C for 17 hours. X-ray diffraction analysis corroborated the phase purity of the sample prepared. To study the elementary steps of ion hopping in Li3PS4 7Li solid-state nuclear magnetic resonance (NMR) spectroscopy was employed. In particular, we used temperature-variable relaxometry measurements carried out in both the laboratory and rotating frame of reference to shed light on local as well as long-range ion dynamics. Line shape measurements revealed fast Li-ion exchange able to completely average homonuclear dipole-dipole interactions at temperatures much below ambient. This perfectly agrees with a recent NMR study focusing on field gradient experiments [5]. Moreover, it is in line with our spin-lattice relaxation (SLR) measurements performed at low temperatures: From the low temperature flank of the diffusion-induced SLR rates an activation energy as low as 0.1 eV was determined. Such a low value indicates fast, localized Li jumps present in Li3PS4. The high Li+ diffusivity also manifests itself in the appearance of an SLR spin-lock NMR rate peak that shows up well below room temperature. [1] H. Buschmann, J. Dölle, S. Berendts, A. Kuhn, P. Bottke, M. Wilkening, P. Heitjans, A. Senyshyn, H. Ehrenberg, A. Lottnyk, V. Duppel, L. Kienle, J. Janek, Phys. Chem. Chem. Phys. 13 (2011) 19378 [2] V. Epp, Q. Ma, E.-M. Hammer, F. Tietz, M. Wilkening, Phys. Chem. Chem. Phys., 17 (2015) 32115 [3] M. Tatsumisago, M. Nagao, A. Hayashi, J. Asian Ceram. Soc., 1 (2013) 17 [4] V. Epp, O. Gün, H.-J. Deiseroth, M. Wilkening, J. Phys. Chem. Lett., 4 (2013) 2118 [5] K. Hayamizu, Y. Aihara, T. Watanabe, T. Yamada, S. Ito, N. Machida, Solid State Ion., DOI: 10.1016/j.ssi.2015.06.016

Investigating Olivine Cathode for Rechargeable Magnesium Battery with Theoretical and Experiment Approach

Lithium ion batteries (LIBs) are quickly becoming the mainstream power sources for environmentally friendly vehicles such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV) and electric vehicles (EV) due to their high energy density. On the other hand, a battery system with even higher energy density is required for the long-range PHV and EV applications, and therefore, post lithium ion batteries (PLIB) such as Li-sulfur batteries and Li-air batteries have been getting more attention in recent years. Rechargeable magnesium batteries are also a candidate for the PLIB thank to the natural abundance of magnesium and the absence of dendrite formation when magnesium metal is used as the anode. In addition, the magnesium batteries are expected to have high energy density because of its divalent nature. However, there is not much progress on the development of novel cathodes since an innovation of Chevrel phase materials such as MgxMo6S8. The difficulty lies in the strong polarization character of the small and divalent Mg2+ and consequently the intercalation and diffusion of Mg2+ ions is somewhat difficult and complicated. Because of the so-called “diagonal relationship” in the periodic table stating the chemical similarity between lithium and magnesium, significant amount of efforts have been attempted to use compounds analogous to classical Li-ion battery cathode as Mg-intercalation hosts. As olivine LiFePO4 is one of the commercialized Li-ion battery cathode, it is of great interest to examine the performance of olivine compounds as Mg battery cathode. In this work, a comprehensive study about the performance of olivine FePO4 as Mg battery cathode is performed. With a combined theoretical and experimental approach we show that the intercalation of magnesium does not occur in the electrochemical operations. On the contrary to the common belief that the intercalation of magnesium is critically determined by the mobility of Mg2+ ions in the lattice, we demonstrate that the failure of FePO4 cathode is due to the formation of amorphous layer in the electrochemical process that passivates the active particle, similar to the phenomenon that we reported before for α-MnO2 cathode. Our research provides new insight for the magnesiation mechanism of a classical cathode and elucidate several directions towards future rechargeable Mg battery.

Nanostructured Anode to Inhibit Dendrite Growth in Li Metal Batteries

Li metal is considered as the “Holy Grail” of energy storage systems due to its extremely high theoretical specific capacity (3860 mAh g−1), low gravimetric density (0.59 g cm−3), and lowest negative redox potential (−3.040 V vs. standard hydrogen electrode). The bright prospects give rise to worldwide interests in the metallic Li for the next generation energy storage systems, including highly considered rechargeable metallic Li batteries such as Li-O2 and Li-sulfur (Li–S) batteries. However, the formation of Li dendrites induced by inhomogeneous distribution of current density on the Li metal anode and the concentration gradient of Li ions at the electrolyte/electrode interface is a crucial issue that hinders the practical demonstration of high-energy-density metallic Li batteries. A unique nanostructured anode with Li metal distributed in fibrous Li7B6 matrix is proposed as a promising anode to prevent the dendrite growth. The nanostructured anode is with a large specific area, thus rendering a low current density on the Li metal anode. The dendrite growth is effectively inhibited via decreasing the growth velocity of Li deposits and then limiting the final size of deposited Li on the nanostructured matrix, thus leading to the dendrite-free morphology at macroscale. The concentration gradient of Li ions near the anode surface are sharply reduced, because the 3D Li7B6 fibrous structure provides quantities of free space to accommodate electrolyte. To improve the Coulombic efficiency of Li depositing/dissolution, a dual-phase Li metal anode containing polysulfide-induced SEI and nanostructured graphene framework was investigated for Li-S batteries. Free-standing graphene foam provides several promising features as underneath layer for Li anode, including (1) relative larger surface area than 2D substrates to lower the real specific surface current density and the possibility of dendrite growth, (2) interconnected framework to support and recycle dead Li, and (3) good flexibility to sustain the volume fluctuation during repeated incorporation/extraction of Li. The synergy between the LiNO3 and polysulfides provides the feasibility to the formation of robust SEI in an ether-based electrolyte. The efficient in-situ formed SEI-coated graphene structure allows stable Li metal anode with the cycling Coulombic efficiency of ∼97 % with high safety and efficiency performance, which is with a low resistance of 19.65 Ω (29.10 Ω for Cu foil based Li metal anode) and high ion conductivity of 5.42×10-2 mS cm-1 (2.33×10-2 mS cm-1 for Cu foil based Li metal anode). These results indicated that interfacial engineering of nanostructured electrode were a promising strategy to handle the intrinsic problems of Li metal anodes, thus shed a new light toward LMBs, such as Li-S and Li-O2 batteries with high energy density. Reference [1] X. B. Cheng, H. J. Peng, J. Q. Huang, F. Wei, Q. Zhang, Small 2014, 10, 4257 [2] X. B. Cheng, H. J. Peng, J. Q. Huang, R. Zhang, C. Z. Zhao, Q. Zhang, ACS Nano 2015, 9, 6373

Approaching High-Performance Li-Sulfur Batteries By Surface Modification Using Atomic Layer Deposition

Approaching High-Performance Li-Sulfur Batteries by Surface Modification Using Atomic Layer Deposition Xiangbo Meng†#, Yuzi Liu‡, Joseph A. Libera†, Kevin R. Zavadil§ and Jeffrey W. Elam†* † Energy Systems Division, ‡ Center for Nanoscale Materials, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL, USA 60439 § Materials Science and Engineering, Sandia National Laboratories, Albuquerque, NM, USA 87185 # Presenting author: xmeng@anl.gov; * Corresponding author: jelam@anl.govElectrical energy storage (EES) is critical for the widescale implementation of renewable clean energies. With the commercialization of lithium-ion batteries (LIBs) in portable electronics, new battery technologies are being intensively investigated in order to provide higher energy density for other applications such as electrical vehicles. Lithium-sulfur (Li-S) batteries are very intriguing, given their high theoretical specific energy density of 2567 Wh/kg. However, Li-S batteries suffer from a number of major hurdles in practice, such as the insulating S and Li2S, soluble polysufides (Li2Sx, x≥4), and lithium dendrite growth. Although a huge amount of research effort has been invested to date, a lack of viable technologies exists to create high performance for practical applications. In our recent studies, both S cathodes and lithium metal anodes were modified via atomic layer deposition (ALD). Our research disclosed that uniform and conformal ALD coatings are very beneficial for Li-S batteries to approach high performance. Specifically, effects of ALD coating were exhibited in: (1) depressing the shuttle effect of polysulfides and (2) inhibiting lithium dendrite growth. As a result, the ALD-modified Li-S batteries showed improved Coulombic efficiency, much longer cycling lifetime, and enhanced safety. In our studies, different ALD coatings were investigated, including Al2O3 and LixAlyS. This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES). Electron microscopy was performed at Center for Nanoscale Materials at Argonne National Laboratory.

(Invited) Catholyte-Based High Capacity Li-Sulfur Batteries

There is currently a considerable interest in the development of high capacity energy storage technologies. It is driven by the need in transport applications, such as electric vehicles (EV) where a capacity to go more than 500 km on one charge would be a desirable goal, as well as by renewable energy applications based on intermittent sources. The state-of-the-art for commercial rechargeable energy storage systems is the lithium ion battery (LIB) which has revolutionized the market for portable electronics. However, neither their capacity nor their price is currently matching the needs from the automotive or the renewable energy sectors. In addition, there is a need to improve the sustainability of the battery when considering mass implementation of large-scale energy storage systems. Li-Sulfur (LiS) technology has great potential for large-scale energy storage applications due to the very high theoretical specific capacity (1675 mAh g-1) and high energy density (2500 Wh kg-1) [1]. In addition the technology has potential for being a sustainable solution due to the abundance, low price and low toxicity of sulfur. However, a much lower practical capacity, limited cyclability, and low rate capability prevent commercialization of the technology. The origin of many of the problems can be traced to the intrinsic electrochemical process of the Li-Sulfur cell. During discharge sulfur is converted to Li2S through a series of steps involving the creation of lithium polysulfides (Li2Sx, 2<x≤8). A major issue is that these polysulfides have a relatively large solubility in standard electrolytes. In addition, the dissolved polysulfides cause degradation of the anode through shuttle reactions when they migrate through the electrolyte, forming insoluble layers on the anode surface. This leads to active material loss during the discharge-charge process gradually reducing the capacity and decreased Coulombic efficiency of the cell [7-10]. In addition, conducting material has to be added to sulfur (more than 30 wt%) when forming the cathode since sulfur has low electronic conductivity Consequently, the amount of active material in the cathode is further decreased, as is consequently the practical energy density of the cell. The problems in the Li-Sulfur battery can be addressed by new materials concepts for both the electrolyte and the cathode. For the development of the electrolyte promising approaches include moving away from organic solvents, improving both performance and safety, and the use of polymer gel or solid polymer electrolytes or ceramic electrolytes [2]. It has also been shown that by deliberately adding polysulfides to the electrolyte a more stable cycling, high capacity and good utilization of active material can be obtained [3]. To mitigate the polysulfide dissolution, and improve the conductivity of the cathode at the same time, nanostructured porous-carbon/sulfur composites have been applied [1]. Even though these approaches have proven rather successful in preventing polysulfide dissolution the practical energy density of these cells remain limited due to rather low active material (sulfur) loading. In this contribution we present different approaches towards Li-Sulfur cells with improved stability, safety, and high energy density. These include both new electrolyte and cathode solutions [2]. In particular we will discuss the application of the catholyte concept, where the active material is dissolved in the electrolyte. We show that by using a nanostructured porous-carbon cathode we can obtain a very high practical energy density, high sulfur utilization, and stable cycling. We also discuss the role of the presence of polysulfides in the electrolyte for the stabilization of the Li-metal anode in this cell [4].

Structured Anode to Inhibit Dendrite Growth in Li Metal Batteries

Li metal is considered as the “Holy Grail” of energy storage systems due to its extremely high theoretical specific capacity (3860 mAh g−1), low gravimetric density (0.59 g cm−3), and lowest negative redox potential (−3.040 V vs. standard hydrogen electrode). The bright prospects give rise to worldwide interests in the metallic Li for the next generation energy storage systems, including highly considered rechargeable metallic Li batteries such as Li-O2 and Li-sulfur (Li–S) batteries. However, the formation of Li dendrites induced by inhomogeneous distribution of current density on the Li metal anode and the concentration gradient of Li ions at the electrolyte/electrode interface is a crucial issue that hinders the practical demonstration of high-energy-density metallic Li batteries. A unique nanostructured anode with Li metal distributed in fibrous Li7B6 matrix is proposed as a promising anode to prevent the dendrite growth. The nanostructured anode is with a large specific area, thus rendering a low current density on the Li metal anode. The dendrite growth is effectively inhibited via decreasing the growth velocity of Li deposits and then limiting the final size of deposited Li on the nanostructured matrix, thus leading to the dendrite-free morphology at macroscale. The concentration gradient of Li ions near the anode surface are sharply reduced, because the 3D Li7B6 fibrous structure provides quantities of free space to accommodate electrolyte. To improve the Coulombic efficiency of Li depositing/dissolution, a dual-phase Li metal anode containing polysulfide-induced SEI and nanostructured graphene framework was investigated for Li-S batteries. Free-standing graphene foam provides several promising features as underneath layer for Li anode, including (1) relative larger surface area than 2D substrates to lower the real specific surface current density and the possibility of dendrite growth, (2) interconnected framework to support and recycle dead Li, and (3) good flexibility to sustain the volume fluctuation during repeated incorporation/extraction of Li. The synergy between the LiNO3 and polysulfides provides the feasibility to the formation of robust SEI in an ether-based electrolyte. The efficient in-situ formed SEI-coated graphene structure allows stable Li metal anode with the cycling Coulombic efficiency of ∼97 % with high safety and efficiency performance, which is with a low resistance of 19.65 Ω (29.10 Ω for Cu foil based Li metal anode) and high ion conductivity of 5.42×10-2 mS cm-1 (2.33×10-2 mS cm-1 for Cu foil based Li metal anode). These results indicated that interfacial engineering of nanostructured electrode were a promising strategy to handle the intrinsic problems of Li metal anodes, thus shed a new light toward LMBs, such as Li-S and Li-O2 batteries with high energy density. Reference [1] X. B. Cheng, H. J. Peng, J. Q. Huang, F. Wei, Q. Zhang, Small 2014, 10, 4257 [2] X. B. Cheng, H. J. Peng, J. Q. Huang, R. Zhang, C. Z. Zhao, Q. Zhang, ACS Nano 2015, 9, 6373

Tunable Large Mesopores in Carbon Nanofiber Interlayers for High-Rate Lithium Sulfur Batteries

Lithium sulfur battery interlayers were made from mesoporous carbon nanofibers with large tunable mesopores (17–50+ nm). The nanofibers were prepared by blending and electrospinning two immiscible polymers, polyacrylonitrile (PAN) and cellulose diacetate (CDA) with dimethylformamide as the solvent. Humidity control during the electrospinning process made adjustments to the size of the meso- scaled phase separation domains of the sacrificial CDA. The resultant fiber mat was carbonized and activated in air to create micropores in mesoporous carbon nanofibers (MPCNF). The pore characteristics of the activated MPCNFs were examined and then tested as interlayers in Li-sulfur batteries. First, a fundamental study was conducted regarding the effectiveness of the interlayer versus its own weight and the overall sulfur composition along with a characterization of the pore filling and impedance. Secondly, the effect of micropores and three different pore widths of large mesopores in interlayers on battery performance was studied which revealed that the largest mesopores played a critical role in improving rate capability. Cells with MPCNF interlayers with 50+ nm pores and 70:30 sulfur:Super P composite cathodes had a discharge capacity of over ∼ 1100 mAh g−1 sulfur for 100 cycles at 0.5C and exhibited improved high charge rate capabilities with 850mAh g−1 at 3C.

Applications of Dendrimer-Based Nano-Architectures in Lithium-Air and Lithium-Sulfur Batteries

Dendritic branched polymers, particularly the well studied, most commonly synthesized and commercially available polyamidoamine (PAMAM) dendrimers have a high degree of surface functionalities, high surface-area, large molecular weights, and ample well-defined interior space. PAMAM dendrimers are particularly attractive candidates as templates for the synthesis of catalyst metal nanoparticles due to a high density of interior tertiary amines, which are able to complex with metal ions and variable surface groups to tailor their solubility. These remarkable physico-chemical properties of dendrimers enable them to be applied in next-generation energy storage technologies. Amongst all sustainable rechargeable Li-batteries, Li-air (Li-O2) and Li-sulfur (Li-S) batteries are the most promising with very high theoretical specific energy densities (11,140 Wh/kg and 2,600 Wh/kg respectively). However, several fundamental issues hinder their commercialization; for example, slow kinetics of the oxygen evolution reaction (OER) during charging results in low round-trip efficiency of the Li-O2 battery. High voltage required during the OER process leads to degradation of non-aqueous electrolytes and carbon-based air electrodes resulting in rapid capacity fade and further increasing the discharge-charge voltage. In Li-S batteries, the charge/discharge reaction creates highly soluble polysulfide intermediates in electrolytes, causing irreversible loss of active sulfur and low cycling efficiency. Furthermore, most research focus has been on improving the cycle life of the batteries by using thin electrodes (<2 mg/cm2 of active sulfur loading). However, for practical applications, it is imperative to validate the different approaches on fabricating electrodes at a relevant scale. Here, we will discuss a fundamental understanding of branched polymers as advanced energy storage materials expanding their applications to sustainable high-energy density storage and conversion systems such as those mentioned above. We have recently showed that PAMAM dendrimers can be used as hosts to encapsulate monodispersed ruthenium oxide (RuO2) nanoparticles, and employed as catalysts in the air electrode for Li-O2 batteries. The dendrimers stabilized the RuO2 nanoparticles while ensuring the availability of the entire nanoparticle surface for catalysis, thus reducing the amount of noble metal catalysts used in these systems by almost ten times than the state-of-the-art, without sacrificing their catalytic efficiency. We will further discuss the formation of highly catalytically efficient sub-nanometer clusters of Ru atoms using dendrimers as templates, i.e. dendrimer-based superatoms, in organic solvents. Additionally, we also explored the application of chemically modified PAMAM dendrimers with high electronic conductivity in Li-S batteries. These modified dendrimers showed a better cycling stability compared with hyperbranched polymers used as cathode materials. While challenges exist in the properties of the cathode materials themselves, the binder in the electrode is also critical in bonding the active materials together as well as maintaining a good electrical contact with the current collector. We have been able to obtain high loading (> 4 mg/cm2) of active sulfur using dendrimer-based functional binders with various surface functionalities. Here, we will discuss the structure-function relationships of dendrimer-based binders and cathode materials in enhancing the performance of high areal capacity Li-S batteries. Detailed characterizations of these novel nano-architectures will be discussed to understand how their structure and chemistry influence the electrochemical performance of the aforementioned energy systems. By using novel dendrimer chemistry and assembly, our research provides new clues to embody the nanoscale properties of soft and porous dendritic nanostructures for improving the state‐of‐the‐art of sustainable, high energy density battery technology applications.

A Novel Conceptual Mg Battery with High Rate Capability

Lithium ion batteries (LIBs) are quickly becoming the mainstream power sources for environmentally friendly vehicles such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV) and electric vehicles (EV) due to their high energy density. On the other hand, a battery system with even higher energy density is required for the long-range PHV and EV applications, and therefore, post lithium ion batteries (PLIB) such as Li-sulfur batteries and Li-air batteries have been getting more attention in recent years. Rechargeable magnesium batteries are also a candidate for the PLIB thank to the natural abundance of magnesium and the absence of dendrite formation when magnesium metal is used as the anode. In addition, the magnesium batteries are expected to have high energy density because of its divalent nature. However, there is not much progress on the development of novel cathodes since an innovation of Chevrel phase materials such as MgxMo3S4. The difficulty lies in the strong polarization character of the small and divalent Mg2+ and consequently the intercalation and diffusion of Mg2+ ions is somewhat difficult and complicated. Here, we report an interesting approach to find another redox reaction on the cathode side that replaces the classic intercalation reaction and balances the electron transfer. The charge transfer is achieved through the simultaneous transport of dual ions in the electrolyte during the electrochemical cycling. Reversibility on the interesting chemistry was confirmed by multiple techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy, Scanning electron microscopy and so on. Figure 1 shows one of the conceptual Mg batteries comprising a Mg metal anode, a AgCl cathode and a Grignard-based electrolyte. As can be seen, fairly flat discharge-charge curves are repeatedly observed. Also, even at a rate of 10 C, the cell works very well and maintains over 100 mAh/g which is over 50 % of the capacity observed at 0.1 C. The significant change in cathode material design gave us a new finding of an impressive Mg battery with high rate capability. Figure 1

A Dual-Phase Cathode and a Si/SiOx Anode for Li-Sulfur Batteries

The lithium-sulfur battery is one of the most promising high-energy-density electrochemical energy storage systems for emerging applications such as power storage systems for renewable energy plants and the powering of sustainable electric vehicles.1 The natural abundance and low cost of sulfur, coupled with the high theoretical energy density of sulfur-based cathodes, namely, 1675 mAh g-1 and 3500 Wh kg-1, are the major advantages of this sulfur battery.2 However, the insulating nature of sulfur, leads to low active material utilization, and sulfur electrodes have low stability, arising from the formation of soluble lithium polysulfide during cell operation; these problems, have so far limited the commercialization of this battery.3 There has been consistent progress recently toward optimizing the sulfur electrode.4 Recently, several research groups have reported that the addition of lithium polysulfide to the electrolyte could improve the performance of the Li/S battery in terms of cycle performance and energy density.5 Another major concern regarding the lithium-sulfur battery system is its use of a lithium metal anode, which is well known to have some critical problems including chemical reactivity in commonly used organic electrolytes and dendritic growth of lithium during cycling, leading to poor cycle performance and safety problems. In addition, when coupled with a sulfur cathode, the lithium metal anode reacts with lithium polysulfide to form an insoluble Li2S phase on the lithium surface, leading to the loss of lithium metal and eventually causing poor cycle performance of the system. It should be also noted that an excess amount of lithium metal is needed to construct the full cell to secure its long cycle life, which might lead to degradation of both the energy density and the safety of the full cell. Herein, we demonstrated a lithium-ion sulfur cell configuration using a newly designed dual-type sulfur cathode and a lithiate Si/SiOx nanosphere anode with optimized liquid electrolyte. Our dual-type sulfur cathode system delivered maximum capacity on the order of 1,300 mAh g-1as referred to the mass of the overall sulfur content; that is to say, the mass of sulfur both in the solid cathode and in the dissolved lithium polysulfide. The lithiated Si/SiOx nanosphere anode used showed highly stable cycling behavior over 100 cycles, with a capacity as high as 800 mAh g-1and cycling efficiency approaching 100%. The full lithium-ion sulfur cell presented herein delivered a capacity on the order of about 750mAhg-1. We believe that these results might advance the practical development of the lithium-ion sulfur battery, particularly for use in emerging markets including electric vehicles and large-scale power storage systems for use with renewable energy systems.

Effect of Metal Nanoparticles on the Polysulfide Conversion Reactions in Rechargeable Li-Sulfur Batteries

Rechargeable lithium-sulfur (Li-S) batteries have emerged as the most promising electrochemical energy storage systems due to their high energy density, wide range of temperature operation, cost effectiveness, and eco-friendly in nature. Nevertheless, the drawbacks associated with the Li-S batteries such as insulating nature of sulfur species, corrosive nature of predeposited polysulfides at electrodes during discharge-charge processes, and formation of thick SEI layer still need to be circumvented. One of the promising ways to alleviate these problems is to use highly porous, conductive, and active species which can improve the kinetics of polysulfide conversion reactions and diffusion processes. In this context, we have investigated electronically conductive species incorporated graphene, specifically Metal/graphene hybrids (metal = Pt, Ni, and Co) as cathode in Li-S batteries and performed systematic studies to understand the electrochemical behavior of polysulfides during discharge-charge processes. Metal/graphene hybrids were prepared through wet chemical routes and employed them as electrodes for the conversion of polysulfides in Li-S batteries. Structural and morphological techniques depicted phase purity of the materials and well-dispersed metallic nanocrystallites with an average size of 5 nm on the graphene sheets. Electrochemical studies were carried out by assembling Li/sulfur cells inside glove box using a porous metal/graphene as electrodes cathode, 0.6M Li2S8-1M LiTFSI in TEGDME as electrolyte, and metallic lithium as anode. Galvanostatic discharge-charge tests indicated a two-fold increment in the Li-S battery performance with metal/graphene compared to pure graphene. A high discharge capacity of 750 mAh/g at C-rates of C/10 has been observed with Pt/graphene. The studies on metal/graphene based Li-S battery revealed pivotal role of metallic nanoparticles in enhancing the polysulfide conversion processes. # - Corresponding Author - leela.arava@wayne.edu

Solvent Activity in Electrolyte Solutions Controls Electrochemical Reactions in Li-Ion and Li-Sulfur Batteries

Solvent–ion and ion–ion interactions have significant effects on the physicochemical properties of electrolyte solutions for lithium batteries. The solvation structure of Li+ and formation of ion pairs in electrolyte solutions composed of triglyme (G3) and a hydrofluoroether (HFE) containing 1 mol dm–3 Li[TFSA] (TFSA: bis(trifluoromethanesulfonyl)amide) were analyzed using pulsed-field gradient spin–echo (PGSE) NMR and Raman spectroscopy. It was found that Li+ is preferentially solvated by G3 and forms a [Li(G3)]+ complex cation in the electrolytes. The HFE scarcely participates in the solvation because of low donor ability and relatively low permittivity. The dissociativity of Li[TFSA] decreased as the molar ratio of G3/Li[TFSA] in the solution decreased. The activity of G3 in the electrolyte diminishes negligibly as the molar ratio approaches unity because G3 is involved in 1:1 complexation with Li+ ions. The negligible activity of G3 in the electrolyte solutions has significant effects on the electroch...

Free-standing graphene-based porous carbon films with three-dimensional hierarchical architecture for advanced flexible Li–sulfur batteries

A novel free-standing cathode film consisting of hierarchically porous carbon-encapsulated sulfur has been designed and fabricated for Li–sulfur batteries.