Cathode For Li-S Batteries Research Articles

Toward a remarkable Li-S battery via 3D printing

We demonstrate the successful application of 3D printing (additive manufacturing) to construct high energy density and power density sulfur/carbon cathodes for Li-S batteries. A self-standing 3D-printed sulfur/carbon cathode with high sulfur loading based on a low-cost commercial carbon black was fabricated via a facile robocasting 3D printing process. The 3D-printed sulfur/carbon cathode shows excellent electrochemical performance in terms of capacity, cycling stability, and rate retention by facilitating Li+/e- transport at the macro-, micro-, and nano-scale in Li-S batteries. Meanwhile, the areal loading of the sulfur/carbon cathode can be easily controlled by the number of stacking layers during 3D printing process. The Li-S batteries assembled with the 3D-printed sulfur/carbon cathodes with a sulfur-loading of 3 mg cm−2 deliver a stable capacity of 564 mA h g−1 within 200 cycles at 3 C. Moreover, cathodes with a sulfur-loading of 5.5 mg cm−2 show large initial specific discharge capacities of 1009 mA h g−1 and 912 mA h g−1, and high capacity retentions of 87% and 85% after 200 cycles at rates as high as 1 C and 2 C (equaling to high areal current densities of 9.2 mA cm−2 and 18.4 mA cm−2), respectively.

Discrete Hollow Carbon Spheres Derived from Pyrolytic Copolymer Microspheres for Li-S Batteries

Discrete hollow carbon spheres (HCSs) with a high surface-to-volume ratio and distinct conducting shell have attracted immense attention as electrode materials for batteries and supercapacitors. In this study, we developed a novel and scalable method to synthesize well-defined HCSs. The HCSs were prepared using a pyrolytic soft template of styrene/acrylic acid copolymer microspheres. Sulfur could be effectively confined inside the pores of the uniform-sized HCSs (average diameter = 320 nm, shell thickness = 40–50 nm) to produce a S/HCS-65-IM (S content = 65 wt%) Li-S cathode using a modified sulfur-loading method involving solution impregnation followed by melt-diffusion (IM). S/HCS-65-IM delivered much higher capacity and greater cycling stability over 200 cycles and showed much lower impedance build up than S/HCS-65-PM prepared via the conventional melt-diffusion of a physical mixture of sulfur powder and HCSs. The sulfur utilization of S/HCS-65-IM was further improved by more than 20% by suppressing its lithium-polysulfide shuttle effect using a carbon-coated separator (CCS). The S/HCS-65-IM cathode (with CCS) also exhibited excellent cycling stability (capacity retention of >81% after 200 cycles at 0.5 C) and high rate capability with a reduced interfacial charge transfer resistance, suggesting that S/HCS-65-IM (with CCS) is a promising cathode for Li-S batteries.

Active material infusion strategy dependent electrochemical performance of Se-S mixed cathode in Li-S batteries

Nitrogen containing mesoporous carbon spheres act as a host for Se-S mixed cathode in Li-sulfur batteries. We prepare 50 and 60 wt% of active material (Se-S) containing carbon spheres using a single and two step infusion method individually. Loading of 60 wt% Se-S mixed active material in carbon spheres using a two step infusion method exhibits crystalline nature, whereas single step infusion method yields amorphous product. Interestingly, Se and S involve in the electrochemical reaction with Li. Among the products, 60 wt% Se-S loaded carbon spheres from a two step infusion method effectively suppresses the active material against shuttling and retains about 528 and 387 mAh/g of capacity at C/10 and 1C rate respectively due to the better electronic conductivity and polar nature of ∼5% nitrogen present in the carbon sphere. Further, Se-S@carbon sphere cathode demonstrates better electrochemical performance than S or Se@carbon sphere cathodes. The study deals with the effect of mixed active material loaded carbon spheres and the role of infusion method in improving the electrochemical behaviour of Li-S system both individually and in synergy.

Tailoring the structure of clew-like carbon skeleton with 2D Co-MOF for advanced Li-S cells

Metal organic frameworks (MOF)-derived carbon materials can realize self-doping of heteroatoms in situ, which can effectively improve the electrocatalytic activity of electrode material, those are therefore considered as ideal cathode materials for Li-S battery. In this context, the clews of polymer nanobelts (CsPNBs) are regarded as sacrificial template materials, and Co-based metal-organic frameworks (Co-MOF) are in-situ growth on the surface of CsPNBs, after carbonization and activation, the Co-doped hybrid materials are obtained. The physicochemical properties of these hybrid materials can be changed by adjusting activation time and by adding some amount of CsPNBs. When evaluated as a cathode for Li-S batteries, the hybrid nano-architecture exhibits high initial capacities of 1300.69 and 1020.6 mAh g−1 at 0.1 and 0.5C, respectively. The enhanced electrochemical performance of the electrode is closely related to the accessible pore structures optimization as well as Co-doping has cobalt and oxygen-containing groups on the surface of the matrix material. With the help of those advantages, the areal mass loading of the electrodes is improved. Overall, a rarely demonstrated study that involves the correlation between structure and performance of the MOF-derived hybrid materials is systematically elucidated in this work. This research study is crucial to the precise tailoring of the growth for the MOF-derived carbon superstructure to meet their demanding challenge as the electrode materials.

A novel wheel-confined composite as cathode in Li-S batteries with high capacity retention

High energy density Li-S battery has attracted broad attention; however the capacity retention is still non-ideal. The major challenge is to find a way to effectively prevent the shuttle effect of the lithium polysulfides during charging/discharging. Here, we present a novel wheel-confined composite consisting of MnO2 nano-rod as wedge and SnO2 sphere as the skeleton filled with sulfur, which was synthesized using a facile chemical method. The battery with the S@MnO2@SnO2 composite as cathode exhibits a capacity as high as 1323 mAh g−1 at 0.1 C and a high capacity retention of only 0.03% decay per cycle over 500 cycles, which indicates a greatly reduced shuttle effect in Li-S batteries. The battery also shows good rate-performance and low-temperature properties. In addition, the I-V measurements and the first-principle calculations have demonstrated an enhanced electron transfer through the composite.

Nitrogen Doped Carbon Nanosheets Encapsulated in situ Generated Sulfur Enable High Capacity and Superior Rate Cathode for Li-S Batteries.

Lithium-sulfur batteries (LSBs), with large specific capacity (1,675 mAh g−1), are regarded as the most likely alternative to the traditional Lithium-ion batteries. However, the intrinsical insulation and dramatic volume change of sulfur, as well as serious shuttle effect of polysulfides hinder their practical implementation. Herein, we develop three-dimensional micron flowers assembled by nitrogen doped carbon (NC) nanosheets with sulfur encapsulated (S@NC-NSs) as a promising cathode for Li-S to overcome the forementioned obstacles. The in situ generated S layer adheres to the inner surface of the hollow and micro-porous NC shell with fruitful O/N containing groups endowing both efficient physical trapping and chemical anchoring of polysulfides. Meanwhile, such a novel carbon shell helps to bear dramatic volume change and provides a fast way for electron transfer during cycling. Consequently, the S@NC-NSs demonstrate a high capacity (1,238 mAh g−1 at 0.2 C; 1.0 C = 1,675 mA g−1), superior rate performance with a capacity retention of 57.8% when the current density increases 25 times from 0.2 to 5.0 C, as well as outstanding cycling performance with an ultralow capacity fading of only 0.064% after 200 cycles at a high current density of 5.0 C.

The hierarchical porous structure of carbon aerogels as matrix in cathode materials for Li-S batteries

For Li-S batteries, commercial application was hindered by the insulating nature of S and the solubility of polysulfide. Porous carbon materials had proven themselves to be an ideal immobilizer host for S impregnation. Herein, carbon aerogels (CAs) with tunable pore microstructure were synthesized from resorcinol-formaldehyde reaction with increasing catalyst concentration and pyrolysis under high temperature. The results demonstrated that the catalyst concentration played a key role in tuning the porous microstructure of the CAs. In addition, potassium hydroxide (KOH) was introduced to activate the obtained CAs. The activated carbon aerogels (A-CAs) with hierarchical porous structure exhibited the highest specific surface area (1837.4 m2 g−1) and the largest total pore volume (2.276 cm3 g−1), which combined the advantages of both mesoporous and microporous. The effects of porous microstructure, specific surface area, and pore volume of the CAs and A-CAs on S incorporation were studied. The S/A-CAs exhibited significantly improved reversible capacity (1260 mAh g−1 at a rate of 0.1 C), enhanced high-rate property, and excellent cycling performance (229 mAh g−1 after 500 cycles at 1 C) as a cathode for Li-S batteries.

Composite of Vn/Carbon Nanofibers As a Protective Layer on Cathode for High Performance Li-S Batteries

With increasing demand for large scale energy storage systems (ESS), Li-S battery is regarded as a potential candidate for ESS, due to its high theoretical energy density and natural abundance of the cathode material. However, for conventional Li-S batteries, sulfur cathode has suffered from many issues such as low intrinsic electrical conductivity and instability leading to the insufficient utilization of sulfur. In particular, the dissolution of polysulfide intermediates into electrolyte results in the rapid capacity fading of the batteries. Therefore, for the development of the highly efficient Li-S battery, it is essential to improve the conductivity of the sulfur based cathode and maintain/reuse the soluble polysulfide within the cathode structure. To address these issues, some researchers used protective layer composed of carbon, metal oxides or polymers on the sulfur cathode. According to previous studies, carbon based materials as a protective layer on cathode reduced the charge transfer resistance of the sulfur cathodes by acting as an upper conducting network and localized the soluble polysulfides during cycling. This strategy is regarded as a simple and effective solution to make high capacity rechargeable Li-S batteries. In addition, other group demonstrated that Pt as an electrocatalyst could help to convert polysulfide deposits back into soluble long-chain polysulfide, and hence enhanced reaction kinetics and retained high Coulombic efficiency. Catalytic role of vanadium nitride, VN resembles that of more precious Pt. VN has desirable advantages for a sulfur cathode: (1) strong chemical adsorption of polysulfides on it, leading to suppressing the shuttle effect, (2) its high electrical conductivity, and (3) good catalytic activity for enhancing red-ox reaction kinetics. In the present work, we fabricated a composite of VN/carbon nanofibers (VN/CNFs), as a protective sulfur electrode on cathode for Li-S cell, using electrospinning method. The morphology and chemical composition of electrospun VN/CNFs were characterized by SEM, TEM, and XPS, respectively. The Li-S cell with VN/CNFs protective layer exhibited excellent electrochemical performance in terms of specific capacity, cyclability, and rate capability. Owing to the strong and synergic polysulfides anchoring effect of the VN/CNFs, a high initial discharge capacity of 1,480 mAh g-1 and a Coulombic efficiency of ~98% were measured at a rate of C/2, when used in Li-S cell. Further, the Li-S cell exhibited a long-term cyclability: 82% capacity retention even after 200 cycles. Figure 1

Investigating LiNi1/3Mn1/3Co1/3O2 Polarization Resistances in Function of Temperature and Voltage at Different Stages of Lifetime

LiNi1-x-yMnxCoyO2 cathodes (NMCs) are currently employed or evaluated for EVs, due to their high theoretical capacities and operating voltage [1]. In view of EVs’ stringent requirements in terms of performance and lifetime, NMCs have been tested in several cycling protocols, simulating real-life applications, or moving towards more energy-dense devices (high voltage operation). In such protocols, NMCs have displayed different failure mechanisms, often consisting in an overall increased resistance towards polarization. However, hindrances towards polarization are already present in NMCs at beginning-of-life (BOL). Such resistances are voltage (x Li+)-dependent [2], while the impact of temperature is less investigated. Although some of these resistances have been recently addressed in literature (namely, the discussion over the so-called “Irreversible Capacity Loss” [3], which is actually a kinetic limitation [4]), a comprehensive explanation of NMCs’ voltage characteristics at BOL is still missing. This furthermore complicates the understanding of NMCs’ electrochemical response after prolonged cycling, which is necessary for designing optimized cycling protocols. LiNi1/3Mn1/3Co1/3O2 (NMC333) is chosen as representative of the NMCs series, as far as electrochemical [5], structural and electronic [1] properties are concerned. NMC333’s voltage characteristics at BOL and end-of-life (EOL) are investigated in terms of temperature, voltage (x Li+) and applied polarization, and compared with known structural and electronic transitions in the crystal, also x Li+-dependent. Lab-scaled pouch cells in half-cell configuration (NMC333/Li) are tested between +3.6 V and +4.6 V vs. Li. NMC333 electrodes used are either pristine, or harvested from cells cycled at high voltage (+4.6 V vs. Li upper voltage cut-off) and different temperature (10, 25 and 40 °C). Through this protocol, it is possible to decouple temperature- and voltage- related effects on NMC333’s degradation. NMC333’s electrochemistry is investigated both at steady state, by means of OCP curves, and under moderate polarization, by means of Constant Current (CC) cycling at C/10 and Slow Rate Cyclic Voltammetry (SRCV). In Figure 1, CC and SRCV of NMC333 at BOL are reported at different temperatures. Structural and electronic transitions in NMC333 are associated with a different electrochemical behavior below and above +3.8 V vs. Li. Specifically, while at higher voltages an apparent capacitive behavior is displayed, a resistance towards polarization can be identified below +3.8 V vs. Li for both CC and SRCV. Such resistance occurs during charge and discharge, although a T-dependent asymmetry emerges in SRCV between anodic and cathodic scan (namely, a shifting peak onset and an additional shoulder in the anodic peak). By the comparison between CC and SRCV, which are performed at different cycling rates, further insights into the causes of these hindrances can be gathered. A discussion on the resistances towards polarization displayed by NMC333 at different stages of lifetime will bring further insight into its thermodynamic and dynamic voltage characteristics, and their evolution in function of different cycling conditions and operation over time. These notions will be helpful for modelling NMCs, by knowing which phenomena and variables must be taken into account when fitting/predicting performance and lifetime. Additionally, such information will allow for more conscious design of cycling protocols, apt to achieve optimized performance and lifetime of NMCs-containing Li ion batteries. [1] J. Xu, F. Lin, M. M. Doeff, W. Tong, “A review on Ni-based layered oxides for rechargeable Li-ion batteries”, J. Mater. Chem. A 5 (2017), 874 – 901. [2] J. Kasnatscheew, U. Rodehorst, B. Streipert, S. Wiemer-Meyers, R. Jakelski, R. Wagner, I. Cekic Laskovic, M. Winter, “Learning from overpotentials in lithium ion batteries: a case study on the LiNi1/3Mn1/3Co1/3O2 (NMC) cathode”, Journal of the Electrochemical Society 163(14) (20016), A2943 – A2950. [3] S. Kang, W. Yoon, K. Nam, X. Yang, D. P. Abraham, ”Investigating the first-cycle irreversibility of lithium metal oxide cathodes for Li batteries”, J. Mater. Sci. 43 (2008), 4701 – 4706. [4] J. Kasnatscheew, M. Evertz, B. Streipert, R. Wagner, R. Klöpsch, B. Vortmann, H. Hahn, S. Nowak, M. Amereller, A. C. Gentschev, P. Lamp, M. Winter, ”The truth about the 1st cycle coulombic efficiency of LiNi1/3Mn1/3Co1/3O2 (NMC) cathodes”, Phys. Chem. Chem. Phys. 18 (2016), 3956 – 3965. [5] Z. Wu, S. Ji, Z. Hu, J. Zheng, S. Xiao, Y. Lin, K. Xu, K. Amine, F. Pan, “Pre-lithiation of Li(Ni1-x-yMnxCoy)O2 materials enabling enhancement of performance for Li ion battery”, ACS Appl. Mater. Interfaces 8 (2016), 15361 – 15368. Figure 1

Using ethylenediamine to prepare three dimensional nitrogen-doped graphene aerogel/sulfur composite for lithium‑sulfur batteries

Three-dimensional nitrogen-doped graphene aerogel/sulfur (NGA/S) composites are studied for use as cathode materials in Li-S batteries. The NGA/S composites are fabricated using ethylenediamine (EDA) as a nitrogen source and 3D graphene structural modifier through a combination of one-pot hydrothermal and heat melt-diffusion methods. The as-prepared NGA/S composites present a porous 3D interconnected network structure with a high sulfur loading of 77.3 wt%. The electrode with NGA/S as cathode delivers a high initial discharge capacity of 1258 mAh g−1 at a current rate of 0.1 C and maintains a stable capacity of 1077 mAh g−1 after 75 cycles. This high battery capacity and good cycle stability is primarily attributed to the flexible porous 3D structure and N-doping in graphene for this NGA/S structural design which can provide higher sulfur loading, faster charge transfer pathway and better immobilization of lithium polysulfides. The present study demonstrates that the 3D NGA/S composite is a promising material for application as the cathode in Li-S batteries.

Nano potassium phosphotungstate spheres/sulfur composites as cathode for Li-S batteries

Herein, a new strategy of using polyoxometalates (K3PW12O40) to stabilize sulfur was introduced for the first time for Li-S batteries. The as prepared K3PW12O40 spheres/S electrode shows a initial discharge capacity of 1281.0 mAh g−1 with a good cycling stability at a rate of 0.1 C. In particular, the K3PW12O40/S electrode exhibits an initial specific capacity of 810.0 mAh g−1 at a high current rate of 2 C, and remains 560.4 mAh g−1 after 250 cycles. The excellent performances are attributed to the significant roles that K3PW12O40 host played during the charge/discharge process.

A robust sulfur host with dual lithium polysulfide immobilization mechanism for long cycle life and high capacity Li-S batteries

Beyond the physical lithium polysulfide (Li2Sx) entrapment of various 3D porous sulfur hosts, the importance of chemical interactions between sulfur host and Li2Sx on performance of Li-S batteries has recently been highlighted. However, most of these studies focus mainly on one type of chemical interaction and effective suppression of Li2Sx migration is still lacking. Here, we report a uniquely designed sulfur host that can immobilize Li2Sx through a dual chemisorption mechanism. The new sulfur host is consisted of an MXene matrix and polydopamine (PDA) overcoat, where Mxene forms a strong Ti–S bonding by the Lewis acid-base mechanism while PDA withholds Li2Sx through the polar-polar interaction. Benefited from the double chemisorption, the new cathode with a high sulfur loading of 5 mg cm−2 has been demonstrated with an initial capacity of 1001 mA h g−1 at a capacity retention of 65% over 1000 cycles at 0.2 C. Overall, this study not only presents a unique chemical mechanism to entrap Li2Sx, but also provides a new way to rationally design a practical sulfur cathode for high-performance Li-S batteries.

Binary Hierarchical Porous Graphene/Pyrolytic Carbon Nanocomposite Matrix Loaded with Sulfur as a High-Performance Li-S Battery Cathode.

A N,O-codoped hierarchical porous nanocomposite consisting of binary reduced graphene oxide and pyrolytic carbon (rGO/PC) from chitosan is fabricated. The optimized rGO/PC possesses micropores with size distribution concentrated around 1.1 nm and plenty of meso/macropores. The Brunauer-Emmett-Teller specific surface area is 480.8 m2 g-1, and it possesses impressively large pore volume of 2.14 cm3 g-1. On the basis of the synergistic effects of the following main factors: (i) the confined space effect in the hierarchical porous binary carbonaceous matrix; (ii) the anchor effects by strong chemical bonds with codoped N and O atoms; and (iii) the good flexibility and conductivity of rGO, the rGO/PC/S holding 75 wt % S exhibits high performance as Li-S battery cathode. Specific capacity of 1625 mA h g-1 can be delivered at 0.1 C (1 C = 1675 mA g-1), whereas 848 mA h g-1 can be maintained after 300 cycles at 1 C. Even at high rate of 5 C, 412 mA h g-1 can be restrained after 1000 cycles.

Π-π Interaction Enabling Highly Stable Li-Organic Batteries with Graphene Oxide – Based Separators

CuTCNQ is a novel high capacity electrode material with three electrons transfer reaction. The main challenge of its practical application is the dissolution of the intermediate , which is similiar to the sulfur cathode in Li-S batteries. Here, we utilize graphene oxide (GO) coated separator to trap the dissolved aromatic active mateirals through charge transfer reaction by π-π interaction. Consequently, the CuTCNQ battery with GO separator is able to achieve a capacity of 252. mAh g-1 and show a high capacity retention of 81.3% over 100 cycles. Even at a higher current of 500 mA g-1, the cell still exhibits an outstanding cycle performance, delivering a capacity of 119.1 mAh g-1 with 75.8% capacity retention over 350 cycles. Not only for Li-organic battery, GO separator can also serve as a promising alternative separator in organic electrolyte based redox flow batteries. Figure 1

Cathode Nanostructuring and Separator Modification for High-Performance Lithium-Sulfur Batteries

Battery technologies involving Li-S chemistry are promising approaches to realize inexpensive and high energy density storage for sustainable energy applications. However, current Li-S batteries still suffer from short life-time due to active material loss through the soluble polysulfide molecules shuttling between battery cathode and anode.[1] We present herein our recent advances in the understanding of the electrochemical reactions at Li-S battery cathode and addressing the shuttle effect by polysulfide trapping. Specifically, an in-operando characterization technique based on optical microscopy is developed to intuitively visualize the selective deposition of sulfur and Li2S in battery cathodes, and the critical roles of current collectors and additives, including different metals and semiconductors, are demonstrated. Accordingly, innovative cathode architectures are designed to control the oriented deposition and diffusion of sulfur-containing species. In particular, an ultrathin and compact blocking layer of 2D MoS2 and WS2 nanoflakes, with a thickness of ca. 15 nm, are deposited on separator through a solution based self-assembly method,[2] which effectively adsorb polysulfide molecules and thus suppress their diffusion to the battery anode. In addition, Li2S-metal composites and polymer-metal hybrid networks are fabricated as hosts for sulfur cathodes to enable rapid battery charge-discharge processes given the large active surface area and better control of charge (or discharge) product deposition.[3] Combining these two strategies, we report greatly enhanced specific capacity (over 1200 mAh g-1) and cyclability (over 500 cycles) for the nanostructured sulfur cathodes compared to the conventional carbon-sulfur based cathode, and the routes to further improving high-energy and long-life Li-S battery are discussed. [1] Seh, Z. W.; Sun, Y.; Zhang, Q.; Cui, Y. Chem. Soc. Rev. 2016, 45, 5605. [2] Yu, X.; Prévot, M. S.; Guijarro, N.; Sivula, K. Nat. Commun. 2015, 6, 7596. [3] Zhou, G. M.; Sun, J.; Jin, Y.; Chen, W.; Zu, C. X.; Zhang, R. F.; Qiu, Y. C.; Zhao, J.; Zhuo, D.; Liu, Y. Y.; Tao, X. Y.; Liu, W.; Yan, K.; Lee, H. R.; Cui, Y. Adv. Mater. 2017, 29, 1603366

Electrochemical Characterization of High-Performance Sulfur Composites as Cathodes for Li-S Batteries with Application in Automotive Industry

Lithium-sulfur batteries are based on principle of conversion and their properties are very promising for their high theoretical energy density and low cost. However, current electrodes and materials used in Li-S batteries suffer from irreversible electrochemical reaction of polysulfides, low conductivity and stability. Here we summarize preparation and characterization of sulfur samples with polymer additive polypyrrole/polyethylene glycol to improve conductivity and stability of Li-S batteries. We also discuss very simple preparation technique of polypyrrole suitable also for industrial production. The electrochemical properties of sulfur-carbon-polypyrrole (S-C-PPy) composites were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge measurements. Properties of resulting composite samples (especially conductivity) are strongly affected by the preparation technique and conditions. Insulating polymer PEG was used to improve the polymeric structure and mechanical robustness of PPy chain. Porosity of composite sample increase with increasing amount of PPy. On the other hand conductivity is reduced with increased porosity. Electrochemical measurements confirmed that addition of PEG can improve conductivity also in the presence of higher amounts of PPy in the sample. PPy-PEG composite polymer decrease particle to particle contact resistance. Co-polymer coating consisting of PPy-PEG significantly decreases the charge transfer resistance of prepared samples what was confirmed by impedance measurements.

Quantitative characterization of the ionic mobility and concentration in Li-battery cathodes via low frequency electrochemical strain microscopy.

Electrochemical strain microscopy (ESM) can provide useful information on the ionic processes in materials at the local scale. This is especially important for ever growing applications of Li-batteries whose performance is limited by the intrinsic and extrinsic degradation. However, the ESM method used so far has been only qualitative due to multiple contributions to the apparent ESM signal. In this work, we provide a viable approach for the local probing of ionic concentration and diffusion coefficients based on the frequency dependence of the ESM signal. A theoretical basis considering the dynamic behavior of ion migration and relaxation and change of ion concentration profiles under the action of the electric field of the ESM tip is developed. We argue that several parasitic contributions to the ESM signal discussed in the literature can be thus eliminated. The analysis of ESM images using the proposed approach allows a quantitative mapping of the ionic diffusion coefficients and concentration in ionic conductors. The results are validated on Li-battery cathodes (LiMn2O4) extracted from commercial Li-batteries and can provide novel possibilities for their development and further insight into the mechanisms of their degradation.

Porous three-dimensional reduced graphene oxide for high-performance lithium-sulfur batteries

Porous three-dimensional reduced graphene oxide (3D-RGO) was successfully synthesized. After being loaded with sulfur, the as-obtained 3D-S-RGO composite was used as a cathode for Li-S batteries. Due to its unique 3D-structured porous carbon layers with a high surface area, a high sulfur loading (75.8%) was achieved. More importantly, its 3D structure can also serve as a polysulfide storeroom to relieve the shuttle effect. Therefore, compared with regular sulfur-loaded reduced graphene oxide (S-RGO), the 3D-S-RGO cathode exhibits a greatly improved discharge capacity and cycling stability. The 3D-S-RGO cathode delivers an initial discharge capacity of 1140 mAh g−1 at 0.2 C and remains at 790 mAh g−1 after 200 cycles. This study shows that the 3D structure is essential for improving the performance of graphene-based cathodes in Li-S batteries.

Process optimization for producing hierarchical porous bamboo-derived carbon materials with ultrahigh specific surface area for lithium-sulfur batteries

Bamboo derived porous carbon materials, as inexpensive and environmentally friendly, microporous material sources, have been attracting enthusiastic attention for energy storage applications. In this work three different processes were employed to prepare three types of bamboo derived porous carbon materials. Among them, the sample prepared via a one-step activation method delivered the largest total pore volume (1.146 cm3 g−1) and the largest specific surface area (1824.4 m2 g−1) owning to a hierarchical porous structure. After the sample was used to encapsulate sulfur (S) to prepare carbon/S composite as cathodes for Li-S batteries. The composite loaded with 58.5 wt% S exhibited a high initial capacity of 1453 mAh g−1 at a rate of 0.1 C (1 C = 1675 mA g−1). A reversible capacity of 255 mAh g−1 was maintained after 500 cycles at 1 C with a capacity decay rate of only 0.0016% per cycle. This suggests that the bamboo derived porous carbon could be a promising conductive carbon matrix for carbon/S composite cathodes in Li–S batteries.

Atomic Sulfur Anchored on Silicene, Phosphorene, and Borophene for Excellent Cycle Performance of Li-S Batteries.

Dissolution of intermediate lithium polysulfides (LiPS) is an inevitable obstacle for the solid sulfur-based cathode in Li-S batteries. For the first time, herein, atomic sulfur is incorporated into silicene, phosphorene, and borophene to intrinsically eliminate the dissolution of LiPS. The small molecular sulfur species are anchored on the silicene surface with stronger Si-S interaction than the P-S and B-S ones. Meanwhile, a high atomic sulfur coverage (63.1 wt %) is achieved in silicene and concomitantly stabilizes the silicene layer. For the S3-covered silicene, a high theoretical capacity of 857 mA h g-1 is achieved with slight dissolution of LiPS originated from the loss of interior S atoms that are not directly bound with silicene surface. By realizing the elemental S2 coverage on silicene with large surface area, the Li+ ions can react fast with the S2 species, leading to a high theoretical capacity of 891 mA h g-1 without dissolution and migration of the intermediate LiPS. Most interestingly, the discharge products of atomic layer of lithium sulfides on silicene surface exhibit completely different behaviors from the traditional discharge products of solid Li2S, which can function as effective adsorption and activation sites for the conversion of LiPS from long chain to short chain by accelerated redox reaction. The present study gains some key insights into how the atomic sulfur contributes to the intrinsic shuttle inhibition and offers a feasible way to design the atomic sulfur-based cathode materials of Li-S batteries with better electrochemical performance.