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From in situ transmission electron microscopy (TEM) observations, we present direct evidence of lithium-assisted welding between physically contacted silicon nanowires (SiNWs) induced by electrochemical lithiation and delithiation. This electrochemical weld between two SiNWs demonstrates facile transport of lithium ions and electrons across the interface. From our in situ observations, we estimate the shear strength of the welded region after delithiation to be approximately 200 MPa, indicating that a strong bond is formed at the junction of two SiNWs. This welding phenomenon could help address the issue of capacity fade in nanostructured silicon battery electrodes, which is typically caused by fracture and detachment of active materials from the current collector. The process could provide for more robust battery performance either through self-healing of fractured components that remain in contact or through the formation of a multiconnected network architecture., (© 2012 American Chemical Society)

P2‐type layered oxides suffer from an ordered Na+/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na+ extraction/insertion. The deficient sodium in the P2‐type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na+ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2‐type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau‐free P2‐type cathode‐Na0.85Li0.12Ni0.22Mn0.66O2 (P2‐NLNMO) was developed. The complete solid‐solution reaction over a wide voltage range ensures both fast Na+ mobility (10−11 to 10−10 cm2 s−1) and small volume variation (1.7 %). The high sodium content P2‐NLNMO exhibits a higher reversible capacity of 123.4 mA h g−1, superior rate capability of 79.3 mA h g−1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid‐solution reaction are critical to realizing high‐performance P2‐type cathodes for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: The effect of H2O in electrolytes and in electrode lattices on the thermodynamics and kinetics of reversible multivalent‐ion intercalation chemistry based on a model platform of layered VOPO4 has been investigated. The presence of H2O at the electrolyte/electrode interface plays a key role in assisting Zn2+ diffusion from electrolyte to the surface, while H2O in the lattice structure alters the working potential. More importantly, a dynamic equilibrium between bulk electrode and electrolyte is eventually reached for H2O transport during the charge/discharge cycles, with the water activity serving as the key parameter determining the direction of water movement and the cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: Organic electrode materials are promising for green and sustainable lithium‐ion batteries. However, the high solubility of organic materials in the liquid electrolyte results in the shuttle reaction and fast capacity decay. Herein, azo compounds are firstly applied in all‐solid‐state lithium batteries (ASSLB) to suppress the dissolution challenge. Due to the high compatibility of azobenzene (AB) based compounds to Li3PS4 (LPS) solid electrolyte, the LPS solid electrolyte is used to prevent the dissolution and shuttle reaction of AB. To maintain the low interface resistance during the large volume change upon cycling, a carboxylate group is added into AB to provide 4‐(phenylazo) benzoic acid lithium salt (PBALS), which could bond with LPS solid electrolyte via the ionic bonding between oxygen in PBALS and lithium ion in LPS. The ionic bonding between the active material and solid electrolyte stabilizes the contact interface and enables the stable cycle life of PBALS in ASSLB. [ABSTRACT FROM AUTHOR]

Abstract: Electrolytes that are able to reversibly deposit/strip Mg are crucial for rechargeable Mg batteries. The most studied complex electrolytes based on Lewis acid‐base chemistry are expensive, difficult to be synthesized, and show limited anodic stability. Conventional electrolytes using simple salts such as Mg(TFSI)2 can be readily synthesized, but Mg deposition/stripping in these simple salt electrolytes is accompanied by a large overpotential due to the formation of a surface layer on the Mg metal with a low Mg ion conductivity. Here the overpotential for Mg deposition/stripping in a simple salt, Mg(TFSI)2‐1,2‐dimethoxyethane (DME), electrolyte is significantly reduced by adding a small concentration of iodine (≤50 × 10−3 m) as an additive. Mechanism studies demonstrate that an Mg ion conductive solid MgI2 layer is formed on the surface of the Mg metal and acts as a solid electrolyte interface. With the Mg(TFSI)2‐DME‐I2 electrolyte, a very small voltage hysteresis is achieved in an Mg‐S full cell. [ABSTRACT FROM AUTHOR]

The redox chemistry of magnesium and its application in rechargeable Mg batteries has received increasing attention owing to the unique benefits of Mg metal electrodes, namely high reversibility without dendrite formation, low reduction potentials, and high specific capacities. The Mg/S couple is of particular interest owing to its high energy density and low cost. Previous reports have confirmed the feasibility of a rechargeable Mg/S battery; however, only limited cycling stability was achieved, and the complicated procedure for the preparation of the electrolytes has significantly compromised the benefits of Mg/S chemistry and hindered the development of Mg/S batteries. Herein, we report the development of the first rechargeable Mg/S battery with a MgTFSI2/MgCl2/DME electrolyte (DME=1,2-dimethoxyethane, TFSI=bis(trifluoromethanesulfonyl)imide) and realize the best cycling stability among all reported Mg/S batteries by suppressing polysulfide dissolution. Mechanistic studies show that the battery works via S0/MgS x redox processes and that the large voltage hysteresis is mainly due to the Mg anode overpotential. [ABSTRACT FROM AUTHOR]

Safety and the polysulfide shuttle reaction are two major challenges for liquid electrolyte lithium-sulfur (Li-S) batteries. Although use of solid-state electrolytes can overcome these two challenges, it also brings new challenges by increasing the interface resistance and stress/strain. In this work, the interface resistance and stress/strain of sulfur cathodes are significantly reduced by conformal coating ≈2 nm sulfur (S) onto reduced graphene oxide (rGO). An Li-S full cell consisting of an rGO@S-Li10GeP2S12-acetylene black (AB) composite cathode is evaluated. At 60 °C, the all-solid-state Li-S cell demonstrates a similar electrochemical performance as in liquid organic electrolyte, with high rate capacities of 1525.6, 1384.5, 1336.3, 903.2, 502.6, and 204.7 mA h g−1 at 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 C, respectively. It can maintain a high and reversible capacity of 830 mA h g−1 at 1.0 C for 750 cycles. The uniform distribution of the rGO@S nanocomposite in the Li10GeP2S12-AB matrix generates uniform volume changes during lithiation/delithiation, significantly reducing the stress/strain, thus extending the cycle life. Minimization of the stress/strain of solid cells is the key for a long cycle life of all-solid-state Li-S batteries. [ABSTRACT FROM AUTHOR]

Bipolar materials, which work as both the cathode and anode material in aqueous sodium-ion batteries, have advantages over aqueous electrolytes such as the low cost of sodium and high convenience of the material processing. However, the available materials are greatly limited. Herein, Prussian blue FeFe(CN)6 nanocubes were successfully synthesized by using a modified co-precipitation method. Owing to the well-separated redox reactions, fair cycling stability and rate capability of FeFe(CN)6, it could be developed as a bipolar material in an aqueous sodium-ion battery. The as-obtained full battery exhibits good cycling stability and rate capability. It was able to deliver a capacity of 32 mAhg-1 at 20 C, 76% of the capacity at 2 C. After 200 cycles at 2 C, 97% of the initial capacity was maintained for this battery, which suggests good cycling stability. [ABSTRACT FROM AUTHOR]

Every year a large amount of ammonia is mechanically compressed with a low efficiency (∼65%) as an environmentally friendly chemical for fuel storage, transportation, food preservation and air conditioning. Electrochemical compression with a high efficiency (93%) offers an opportunity for substantial energy savings. But ammonia is never considered electrochemically compressible because of the known decomposition at high applied potentials. The concept of using a carrier gas to co-compress ammonia was proposed but never experimentally validated. Here for the first time, we realized electrochemical compression of ammonia by using a proton exchange membrane as an NH4+ conductor and hydrogen as a carrier to avoid decomposition. The ammonia transfer mechanism and kinetics in a Nafion membrane was investigated and verified using electro-analytical methods, and the continuous electrochemical ammonia compression at a constant voltage of 200 mV with a stable current density for 7 hours has been demonstrated. NH4+ transports in the Nafion membrane by hopping and vehicular mechanisms with a high NH4+ conductivity of 4 × 10−2 S cm−1 at 50% RH and 70 °C, and a constant transfer ratio of 2 between NH3 and H2 ensure a stable and high compression rate. [ABSTRACT FROM AUTHOR]

Advanced electrode materials have been intensively explored for next-generation lithium-ion batteries (LIBs), and great progresses have been achieved for many potential candidates at the lab-scale. To realize the commercialization of these materials, industrially-viable synthetic approaches are urgently needed. Spray pyrolysis (SP), which is highly scalable and compatible with on-line continuous production processes, offers great fidelity in synthesis of electrode materials with complex architectures and chemistries. In this review, motivated by the rapid advancement of the given technology in the battery area, we have summarized the recent progress on SP for preparing a great variety of anode and cathode materials of LIBs with emphasis on their unique structures generated by SP and how the structures enhanced the electrochemical performance of various electrode materials. Considering the emerging popularity of sodium-ion batteries (SIBs), recent electrode materials for SIBs produced by SP will also be discussed. Finally, the powerfulness and limitation along with future research efforts of SP on preparing electrode materials are concisely provided. Given current worldwide interests on LIBs and SIBs, we hope this review will greatly stimulate the collaborative efforts among different communities to optimize existing approaches and to develop innovative processes for preparing electrode materials. [ABSTRACT FROM AUTHOR]

The polysulfide shuttle reaction has severely limited practical applications of Li-S batteries. Recently, functional materials that can chemically adsorb polysulfide show significant enhancement in cycling stability and Coulombic efficiency. However, the mechanism of the chemisorption and the control factors governing the chemisorption are still not fully understood. Here, it is demonstrated for the first time that the surface acidity of the host material plays a crucial role in the chemisorption of polysulfide. By tailoring the surface acidity of TiO2 via heteroatom doping, the polysulfide-TiO2 interaction can be fortified and thus significantly the capacity fading be reduced to 0.04% per cycle. The discovery presented here sheds light on the mechanism of this interfacial phenomenon, and opens a new avenue that can lead to a practical sulfur/host composite cathode. [ABSTRACT FROM AUTHOR]

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite-free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg−1) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x. Herein, we demonstrate the first reversible Al/S battery in ionic-liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid-state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid-state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system. [ABSTRACT FROM AUTHOR]

Sulfur intercalated expanded graphite for Li‐S battery cathodes is synthesized by in situ one‐step sulfur reduction and intercalation of graphite oxide (GO). The unique structural reduced graphene oxide (RGO)/S nanocomposite cathodes exhibit high capacity, super rate capability, and long cycle stability. The exceptional electrochemical properties of the RGO/S composites plus their simple fabrication make this class of materials attrac­tive for further investigation in Li‐S batteries applications. [ABSTRACT FROM AUTHOR]

Abstract: Well dispersed chestnut-like Cd2Ge2O6 (CGO) and Cd2Ge2O6/reduced graphene oxide (CGO/RGO) nanocomposites are successfully prepared via a facile one-pot hydrothermal method and characterized as novel lithium storage materials for the first time. Electrochemical characterization of lithiation/delithiation of the CGO/RGO nanocomposites reveals a large capacity of 943mAhg−1 for the first cycle and a capacity retention of 721mAhg−1 even after 100 cycles. The superior electrochemical performance of the CGO/RGO nanocomposites electrode compared to the pure CGO electrode can be attributed to the well dispersed RGO which enhances the electronic conductivity and accommodate the volume change during the lithium storage process. [Copyright &y& Elsevier]

The electrochemical properties of a solid polymer electrolyte consisting of a diblock copolymer and lithium bis(oxalato)borate, LiBC4O8 (LiBOB) salt, is reported. The spherical microphase-separated diblock copolymer is composed of a majority poly(ethylene oxide) (PEO) block and a minority random copolymer block of methyl methacrylate (MMA) and lithium salt of methacrylic acid (MAALi), PEO-b-(PMMA-ran-PMAALi). Salt-optimized electrolyte membranes of the diblock copolymer and LiBOB salt exhibited an average lithium-ion transference number (TLi+) value of 0.9 at room temperature (21-23°C). The solid-state flexible, translucent polymer electrolyte shows a wide electrochemical stability window and excellent interface properties with the lithium metal electrode. The combination of these properties makes these block copolymer membranes viable electrolyte candidates for flexible lithium-ion batteries. [ABSTRACT FROM AUTHOR]

A disk pressed from commercial SnO2 powder, sandwiched between two nickel screen current collectors, was used as a lithium-ion secondary anode. Its electrochemical lithium insertion–extraction behavior was investigated by galvanostatic charge–discharge and galvanostatic intermittent titration (GITT) using a microcurrent on one current collector. The trans-electrode voltage was measured to monitor the transmissive resistance across the SnO2 electrode during the discharge–charge process. Special electrochemical impedance spectroscopy (EIS) protocols were used to investigate the kinetic and transmissive impedances during initial lithium insertion. Protocol B or C EIS, described in the text, give the local transmissive impedance near the operating current collector, while Protocol B′ or C′ give the local transmissive impedance near the other current collector. The use of special EIS protocols showed that the inner transmissive impedance near the operating current collector side is higher than that near the other current collector. [Copyright &y& Elsevier]

Electrochemical impedance spectroscopy (EIS) and in-situ intrinsic resistance measurements were applied to sandwiched disk graphite electrodes to investigate the mechanism of formation of irreversible capacity during initial galvanostatic or potentiostatic lithium intercalation into graphite in four different electrolyte formulations. The stability of the solid ∣ electrolyte interphase (SEI) film formed during pre-cycling eight times between 1.5 and 0.2 V versus Li ∣ Li+ in 1.0 M LiPF6+ethylene carbonate (EC) based electrolytes was studied using EIS and in-situ intrinsic resistance measurements during subsequent cycling in the same electrolyte between 0.4 and 0.0 V, and in 1 M LiPF6–propylene carbonate (PC) between 0.4 and 0.0 V. The purpose of the first set of results was to investigate the effect of the volume change resulting from stage transformation during Li intercalation–deintercalation on the stability of the previously formed SEI film. The second measurements were taken to study the reaction of the corresponding film in PC electrolyte. Results show that the two potential plateaus at around 0.9 and 0.6 V in the first galvanostic charge largely correspond to solvated Li intercalation into graphite with some contribution from the formation of the SEI film. In EC-containing mixtures, this solvent has little influence on co-intercalation at 0.9 V, but can effectively inhibit the process at 0.6 V. Potentiostatic charging at 0.2 or 0.7 V accelerates co-intercalation. Although the SEI film formed during cycling in EC-containing electrolytes can inhibit PC co-intercalation during subsequent cycles in the presence of this solvent, a new layer of different SEI film may also form. [Copyright &y& Elsevier]

Jahn-Teller distorted Mn(III) (t 2g 3e g 1) ions play a key role in the performance of manganese-based layered oxides. Here we show that there is an obvious relationship between the Jahn-Teller distortion of a trivalent manganese and the electrochemistry in a pair of Na isomer, namely orthorhombic and hexagonal P2-type Na 2/3 Mn 0.9 Ti 0.1 O 2 having the same composition. It is found that more reversible phase transformations, higher working voltage and faster Na diffusion correlated with Jahn-Teller effect are found for distorted P′2-Na 2/3 Mn 0.9 Ti 0.1 O 2 upon Na+ ions extraction/insertion. Such Jahn-Teller distorted Mn assisted Na migration enables that the orthorhombic Na 2/3 Mn 0.9 Ti 0.1 O 2 delivers a high specific capacity of 204.0 mA h g−1 with a 2.7 V average working voltage, reaching 550 Wh Kg−1 with both better cycle stability (a capacity retention of 82.3% after 100 cycles) and enhanced rate capability (97.8 mA h g−1 cycled at 10C) in Na cell in contrast with undistorted Na 2/3 Mn 0.9 Ti 0.1 O 2. This strategy for understanding the Jahn-Teller effect of P2-type compounds at orbital energy level grasps new insight into designing high energy density positive electrode materials for Na-ion batteries. A pair of sodium isomer with stoichiometric Na 2/3 Mn 0.9 Ti 0.1 O 2 composition are reported as high-energy cathode for Na-ion batteries. The orthorhombic phase demonstrates more reversible phase transformations, higher working voltage and faster Na diffusion correlated with Jahn-Teller effect than hexagonal one upon Na+ ions extraction/insertion. Image 1 • A pair of sodium isomer with different Jahn-Teller distortion are reported as high-energy cathode for Na-ion batteries. • The orthorhombic Na 2/3 Mn 0.9 Ti 0.1 O 2 delivers a high specific capacity of 204.0 mA h g−1 with a 2.7 V average working voltage, reaching 550 Wh Kg−1. • The orthorhombic phase demonstrates more reversible phase transformations, higher working voltage and faster Na diffusion than hexagonal one. [ABSTRACT FROM AUTHOR]

The demand for high energy Na-ion batteries has promoted intensive research on high energy oxygen redox chemistry in layered transition metal oxide cathodes. However, most layered cathodes with oxygen redox might suffer from irreversible electrochemical reaction, fast capacity decay and underlying O 2 release. Herein, we report that copper element with a strong electronegativaty can stablize Na-deficient P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 phase to achieve both cationic and anionic redox chemistry. Hard and soft X-ray absorption spectra demonstrate that all Mn3+/Mn4+, Cu2+/Cu3+ and O2−/(O 2)n− participate in the redox reaction upon Na+ ions extraction and insertion. Density functional theory (DFT) calculations confirm that the strong covalency between copper and oxygen ensures the cationic and anionic redox activity in P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 phase. The P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 cathode could deliver stable cycling life with 87.9% capacity retention at 1C during 100 cycles, as well as high rate performance (70.3 mA h g−1 cycled at 10C). Our findings not only provide a promising guidelines to enhance the electrochemical performance of layered oxides based on anionic redox activity, but also explore the potential science behind oxygen redox process. A new Na-deficient P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 phase that shows both cationic and anionic activity using a strong electronegative copper element. The existence of strong covalency between copper and oxygen promises cationic and anionic redox chemistry upon solid-solution Na+ ions extraction and insertion process. As a result, this phase could deliver stable cycling life in both Na-half cells and full Na-ion cells. Image 1 • A new Na-deficient P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 phase that shows both cationic and anionic activity. • The existence of strong covalency between Cu 3d and O 2p orbitals promises cationic and anionic redox chemistry. • This new Na-deficient P2-Na 2/3 Mn 0.72 Cu 0.22 Mg 0.06 O 2 phase could deliver stable cycling life in both half and full Na-ion cells. [ABSTRACT FROM AUTHOR]

Nano-silicon-based disordered carbon composites prepared by mechanical milling and pyrolysis have been examined as anodes of a lithium ion cell. Electrochemical measurements show that the charge–discharge capacity of disordered carbon composites incorporating both silicon-polyparaphenylene (Si-PPP) and silicon-polyvinyl chloride (Si-PVC) with differing silicon contents, decreases with increasing pyrolysis temperature. Si-PVC-based materials have a better cycle life than those based on Si-PPP at the same silicon content. [Copyright &y& Elsevier]

In this study, a new metal hydride heat pump system driven by an electrochemical compressor was proposed. The system uses the electrochemical compressor to generate absorption heating and desorption cooling in two identical LaNi 5 reactors operating at different pressure levels. A thermodynamic model was developed to predict the system performance in terms of various parameters. Modeling shows EC compression efficiency has a great impact on system performance. The system is suitable for cooling application less than 200 W where mechanical compressors are the most inefficient. The high compression efficiency of electrochemical compressor could potentially make the cooling system more competitive than existing metal hydride heat pump systems. [ABSTRACT FROM AUTHOR]

Carbonaceous materials have greatpotential for applications asanodes of alkali-metal ion batteries, such as Na-ion batteries andK-ion batteries (NIB and KIBs). We conduct an in situ study of theelectrochemically driven sodiation and potassiation of individualcarbon nanofibers (CNFs) by transmission electron microscopy (TEM).The CNFs are hollow and consist of a bilayer wall with an outer layerof disordered-carbon (d-C) enclosing an inner layerof crystalline-carbon (c-C). The d-C exhibits about three times volume expansion of the c-C after full sodiation or potassiation, thus suggesting a much higherstorage capacity of Na or K ions in d-C than c-C. For the bilayer CNF-based electrode, a steady sodiumcapacity of 245 mAh/g is measured with a Coulombic efficiency approaching98% after a few initial cycles. The in situ TEM experiments also revealthe mechanical degradation of CNFs through formation of longitudinalcracks near the c-C/d-C interfaceduring sodiation and potassiation. Geometrical changes of the tubeare explained by a chemomechanical model using the anisotropic sodiation/potassiationstrains in c-C and d-C. Our resultsprovide mechanistic insights into the electrochemical reaction, microstructureevolution and mechanical degradation of carbon-based anodes duringsodiation and potassiation, shedding light onto the development ofcarbon-based electrodes for NIBs and KIBs. [ABSTRACT FROM AUTHOR]

Abstract: The effects of carbonization process and carbon nanofiber/nanotube additives on the cycling stability of silicon–carbon composite anodes were investigated by monitoring the impedance evolution during charge/discharge cycles with electrochemical impedance spectroscopy (EIS). Three types of Si–C anodes were investigated: the first type consisted of Si nanoparticles incorporated into a network of carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWNTs), with annealed polymer binder. The second type of Si–C anodes was prepared by further heat treatment of the first Si–C anodes to carbonize the polymer binder. The third Si–C anode was as same as the second one except no CNFs and MWNTs being added. Impedance analysis revealed that the carbonization process stabilized the Si–C anode structure and decreased the charge transfer resistance, thus improving the cycling stability. On the other hand, although the MWNTs/CNFs additives could enhance the electronic conductivity of the Si–C anodes, the induced inhomogeneous structure decreased the integrity of the electrode, resulting in a poor long term cycling stability. [Copyright &y& Elsevier]