Metal-Free Polymer-Based Current Collector for High Energy Density Lithium-Metal Batteries.

The energy density of lithium-metal batteries (LMBs) relies substantially on the thickness of the lithium-metal anode. However, a bare, thin lithium foil electrode is vulnerable to fragmentation due to the inhomogeneity of the lithium stripping/plating process, disrupting the electron conduction pathway along the electrode. Accordingly, the current collector is an integral part to prevent the resulting loss of electronic conductivity. However, the common use of a heavy and lithiophobic Cu current collector results in a great anode mass increase and unsatisfactory lithium plating behavior, limiting both the achievable specific energy and the cycle life of LMBs. Herein, a metal-free polymer-based current collector is reported that allows for a substantial mass reduction, while simultaneously extending the cycle life of the lithium-metal anode. The specific mass of the ultra-light, 10 µm thick polymer-based current collector is only 1.03 mg cm-2, which is ≈11% of a 10 µm thick copper foil (8.96 mg cm-2). As a result, LMB cells employing this novel current collector provide a specific energy of 448 Wh kg-1, which is almost 18% higher than that of LMBs using the copper current collector (378 Wh kg-1), and a greatly enhanced cycle life owing to a more homogeneous lithium deposition.

Electrochemical Properties of Al3+/Cl- Doped-0.2Li2MnO3 · 0.8LiNiO2 Cathode Materials for Lithium-Ion Batteries.

Li-rich layered cathode materials, Li1.2Ni0.4-xAlxMn0.6O2.2-y Cly (0 ≤ x ≤ 0.03 and 0 ≤ y ≤ 0.03), were successfully synthesized through coprecipitation, and the effects of Al3+-Cl- co-substitution on their surface morphology, crystal structure, surface chemistry, and electrochemical performance were characterized through XRD, SEM, XPS, TEM, and electrochemical and charge-discharge cycling. Doping the cathodes with Al3+ and Cl- ions enhanced electrochemical performance at room temperature and at a high working temperature of 55 °C. The as-synthesized optimal composition was Li1.2Ni0.37Al0.03Mn0.6O2.17Cl0.03. The discharge capacity demonstrated high cycle retention at 55 °C. XPS analyses revealed that Al3+-Cl- co-substitution enhanced the structural stability of the cathode materials by forming strong Mn-O and Ni-O bonds. Moreover, compared with un-doped cathode materials, the impedance of Al3+-Cl--codoped cathode materials was drastically reduced by 52.2%. The results indicated that Al3+-Cl--codoped Li-excess cathodes deliver a high cycle performance at high temperatures.

Nb-Doped Rutile TiO2 Mesocrystals with Enhanced Lithium Storage Properties for Lithium Ion Battery.

A homogeneous Nb-doped rutile TiO2 mesocrystal material was synthesized successfully through a facile hydrothermal route. The incorporation of Nb5+ not only promotes the crystallization of the building subunits of the rutile TiO2 mesocrystal, but also improves the electrochemical performance at higher current rates. A capacity of 96.3 mAh g-1 at a current density as high as 40 C and an excellent long-term cycling stability with a capacity loss of approximately 0.006 % per cycle at 5 C could be achieved when an appropriate amount of Nb5+ was doped into rutile TiO2 mesocrystal. The reasons for the improvement of rate capability may be attributed to the enhancement of electronic conductivity, Li-ion diffusion kinetics, and the surface storage property for the Nb-doped rutile TiO2 mesocrystal.

Spatial Distributions of Discharged Products of Lithium-Oxygen Batteries Revealed by Synchrotron X-ray Transmission Microscopy.

The discharge products of ether-based Li-O2 cells were grown directly on common carbon-coated TEM grids and observed by oxidation-state-sensitive full field transmission soft X-ray microscopy (TXM). The acquired data have permitted to quantify and localize with spatial resolution the distribution of the oxygen discharge products in these samples (i.e., lithium superoxide, peroxide, and carbonates) and appreciate several compositional, structural, and morphological aspects. Most of the peroxide particles had a toroidal shape, often with a central hole usually open on only one side, and which included significant amounts of superoxide-like phases (LiO2/Li2O2 ratio between 0.2 and 0.5). Smaller particles had smaller or no superoxide content, from which we infer that abundance of soluble LiO2 may have a role in toroid formation. Significant amount of carbonates were found irregularly distributed on the electrode surface, occasionally appearing as small particles and aggregates, and mostly coating lithium peroxide particles. This suggests the formation of a barrier that, similar to the solid electrolyte interface (SEI) critical in Li-ion batteries, requires an appropriate management for a reversible operation.

Spiro-Twisted Benzoxazine Derivatives Bearing Nitrile Group for All-Solid-State Polymer Electrolytes in Lithium Batteries.

In this study, two nitrile-functionalized spiro-twisted benzoxazine monomers, namely 2,2'-((6,6,6',6'-tetramethyl-6,6',7,7'-tetrahydro-2H,2'H-8,8'-spirobi[indeno[5,6-e][1,3]oxazin]-3,3'(4H,4'H)-diyl)bis(4,1-phenylene))diacetonitrile (TSBZBC) and 4,4'-(6,6,6',6'-tetramethyl-6,6',7,7'-tetrahydro-2H,2'H-8,8'-spirobi[indeno[5,6-e][1,3]oxazin]-3,3'(4H,4'H)-diyl)dibenzonitrile (TSBZBN) were successfully developed as cross-linkable precursors. In addition, the incorporation of the nitrile group by covalent bonding onto the crosslinked spiro-twisted molecular chains improve the miscibility of SPE membranes with lithium salts while maintaining good mechanical properties. Owing to the presence of a high fractional free volume of spiro-twisted matrix, the -CN groups would have more space for rotation and vibration to assist lithium migration, especially for the benzyl cyanide-containing SPE. When combined with poly (ethylene oxide) (PEO) electrolytes, a new type of CN-containing semi-interpenetrating polymer networks for solid polymer electrolytes (SPEs) were prepared. The PEO-TSBZBC and PEO-TSBZBN composite SPEs (with 20 wt% crosslinked structure in the polymer) are denoted as the BC20 and BN20, respectively. The BC20 sample exhibited an ionic conductivity (σ) of 3.23 × 10-4 S cm-1 at 80 °C and a Li+ ion transference number of 0.187. The LiFePO4 (LFP)|BC20|Li sample exhibited a satisfactory charge-discharge capacity of 163.6 mAh g-1 at 0.1 C (with approximately 100% coulombic efficiency). Furthermore, the Li|BC20|Li cell was more stable during the Li plating/stripping process than the Li|BN20|Li and Li|PEO|Li samples. The Li|BC20|Li symmetric cell could be cycled continuously for more than 2700 h without short-circuiting. In addition, the specific capacity of the LFP|BC20|Li cell retained 87% of the original value after 50 cycles.

High stability and high performance nitrogen doped carbon containers for lithium-ion batteries.

For a long time, carbon has been an ideal material for various electrochemical energy storage devices and a key component in electrochemical energy storage systems due to its advantages of rich surface states, easy tenability, and good chemical stability. Stable and high-performance carbon materials can support future applications of high specific energy electrodes. Herein and for the first time, we have designed nitrogen-doped carbon hollow containers using oleylamine-coating TiO2 mesocrystals as a precursor with a high specific surface area of 1231 m2 g-1. When applied as an anode for lithium-ion storage, a reversible capacity of 774.5 mA h g-1 is obtained at a rate of 0.5 A g-1 after 200 cycles. Meanwhile, at an even higher rate of 2 A g-1, a capacity of 721.1 mA h g-1 is still achieved after 500 cycles. Moreover, the carbon containers remain structurally intact after a series of cycles. This may be attributed to the nitrogen atoms doped on the carbon surface that can absorb multiple lithium ions and enhance the structural stability. These results provide technical support for the development of high specific energy electrode materials.

Enabling Long-Cycling Life of Si-on-Graphite Composite Anodes via Fabrication of a Multifunctional Polymeric Artificial Solid-Electrolyte Interphase Protective Layer.

The energy density of lithium-ion batteries (LIBs) can be meaningfully increased by utilizing Si-on-graphite composites (Si@Gr) as anode materials, because of several advantages, including higher specific capacity and low cost. However, long cycling stability is a key challenge for commercializing these composites. In this study, to solve this issue, we have developed a multifunctional polymeric artificial solid-electrolyte interphase (A-SEI) protective layer on carbon-coated Si@Gr anode particles (making Si@Gr/C-SCS) to prolong the cycling stability in LIBs. The coating is made of sulfonated chitosan (SCS) that is crosslinked with glutaraldehyde promoting good ionic conduction together with sufficient mechanical strength of the A-SEI. The focused ion beam-scanning electron microscopy and high-resolution transmission electron microscopy images show that the SCS is uniformly coated on the composite particles with thickness in nanometer. The anodes are investigated in Li metal cells Si@Gr/C-SCS||Li metal) and lithium-ion full-cells (LiNi0.6Co0.2Mn0.2O2 (NCM-622)||Si@Gr/C-SCS) to understand the material/electrode intrinsic degradation as well as the impact of the polymer coating on active lithium losses because of the continuous SEI (re)formation. The anode composites exhibit a high capacity reaching over 600 mAh g-1, and even without electrolyte optimization, the Si@Gr/C-SCS illustrates a superior long cycle life performance of up to 1000 cycles (over 67% capacity retention). The excellent long-term cycling stability of the anodes was attributed to the SCS polymer coating acting as the A-SEI. The simple polymer coating process is highly interesting in guiding the preparation of long-cycle-life electrode materials of high-energy LIB cells.

Epoxy-Based Interlocking Membranes for All Solid-State Lithium Ion Batteries: The Effects of Amine Curing Agents on Electrochemical Properties.

In this study, a series of crosslinked membranes were prepared as solid polymer electrolytes (SPEs) for all-solid-state lithium ion batteries (ASSLIBs). An epoxy-containing copolymer (glycidyl methacrylate-co-poly(ethylene glycol) methyl ether methacrylate, PGA) and two amine curing agents, linear Jeffamine ED2003 and hyperbranched polyethyleneimine (PEI), were utilized to prepare SPEs with various crosslinking degrees. The PGA/polyethylene oxide (PEO) blends were cured by ED2003 and PEI to obtain slightly and heavily crosslinked structures, respectively. For further optimizing the interfacial and the electrochemical properties, an interlocking bilayer membrane based on overlapping and subsequent curing of PGA/PEO/ED2003 and PEO/PEI layers was developed. The presence of this amino/epoxy network can inhibit PEO crystallinity and maintain the dimensional stability of membranes. For the slightly crosslinked PGA/PEO/ED2003 membrane, an ionic conductivity of 5.61 × 10-4 S cm-1 and a lithium ion transference number (tLi+) of 0.43 were obtained, along with a specific capacity of 156 mAh g-1 (0.05 C) acquired from an assembled half-cell battery. However, the capacity retention retained only 54% after 100 cycles (0.2 C, 80 °C), possibly because the PEO-based electrolyte was inclined to recrystallize after long term thermal treatment. On the other hand, the highly crosslinked PGA/PEO/PEI membrane exhibited a similar ionic conductivity of 3.44 × 10-4 S cm-1 and a tLi+ of 0.52. Yet, poor interfacial adhesion between the membrane and the cathode brought about a low specific capacity of 48 mAh g-1. For the reinforced interlocking bilayer membrane, an ionic conductivity of 3.24 × 10-4 S cm-1 and a tLi+ of 0.42 could be achieved. Moreover, the capacity retention reached as high as 80% after 100 cycles (0.2 C, 80 °C). This is because the presence of the epoxy-based interlocking bilayer structure can block the pathway of lithium dendrite puncture effectively. We demonstrate that the unique interlocking bilayer structure is capable of offering a new approach to fabricate a robust SPE for ASSLIBs.

An ultrathin ionomer interphase for high efficiency lithium anode in carbonate based electrolyte.

High coulombic efficiency and dendrite suppression in carbonate electrolytes remain challenges to the development of high-energy lithium ion batteries containing lithium metal anodes. Here we demonstrate an ultrathin (≤100 nm) lithium-ion ionomer membrane consisting of lithium-exchanged sulfonated polyether ether ketone embedded with polyhedral oligosilsesquioxane as a coating layer on copper or lithium for achieving efficient and stable lithium plating-stripping cycles in a carbonate-based electrolyte. Operando analyses and theoretical simulation reveal the remarkable ability of the ionomer coating to enable electric field homogenization over a considerably large lithium-plating surface. The membrane coating, serving as an artificial solid-electrolyte interphase filter in minimizing parasitic reactions at the electrolyte-electrode interface, enables dendrite-free lithium plating on copper with outstanding coulombic efficiencies at room and elevated (50 °C) temperatures. The membrane coated copper demonstrates itself as a promising current collector for manufacturing high-quality pre-plated lithium thin-film anode.

Brookite TiO2 mesocrystals with enhanced lithium-ion intercalation properties.

Brookite TiO2 mesocrystals were synthesized for the first time using amorphous titanate used as a precursor, exhibiting a high rate capability when applied as an anode for lithium-ion batteries. An in situ X-ray diffraction test of lithium intercalation into the brookite TiO2 structure was further investigated and revealed a reversible phase transformation.

Hierarchical TiO2-x imbedded with graphene quantum dots for high-performance lithium storage.

Hierarchical TiO2-x imbedded with graphene quantum dots was synthesized through a facile synthetic route and investigated as an anode material for lithium-ion batteries. It delivers a high specific capacity and excellent rate capability (160.1 mA h g-1 at 10 C after 500 cycles).

A dual-functional polymer coating on a lithium anode for suppressing dendrite growth and polysulfide shuttling in Li-S batteries.

A surface coating that simultaneously suppressed Li dendrite growth and polysulfide shuttling on a lithium anode was successfully developed using a polymer blend composed of Nafion® and polyvinylidene difluoride (PVDF). This hierarchically nanostructured composite coating efficiently alleviated the swelling and dissolution problems of cation-selective Nafion® in the electrolyte and provided sufficient mechanical strength to accommodate large volumetric variations in the Li anode during charge-discharge cycles. The Nafion®/PVDF-coated Li anode exhibited substantially enhanced rate performance and cyclability as well as improved Coulombic efficiency for Li-S prototype batteries with a high-S-content cathode.

A dimensionally stable and fast-discharging graphite-silicon composite Li-ion battery anode enabled by electrostatically self-assembled multifunctional polymer-blend coating.

A high-performance graphite-Si composite anode for Li-ion batteries containing Si nanoparticles (NPs) attached onto graphite microparticles was synthesized by adopting a polymer-blend of poly(diallyl dimethyl-ammonium chloride) and poly(sodium 4-styrenesulfonate). The polymer-blend enabled uniform distribution of Si NPs during synthesis and served as a robust artificial solid-electrolyte interphase that substantially enhanced the cycle stability and rate performance of the composite electrode. The electrode exhibited a specific capacity of 450 mA h g(-1), 96% capacity retention at a 10 C-rate, 95% retention after 200 cycles, and the same electrode expansion behavior as a pristine graphite electrode.

A mechanically robust and highly ion-conductive polymer-blend coating for high-power and long-life lithium-ion battery anodes.

A mechanically robust and ion-conductive polymeric coating containing two polymers, polyethylene glycol tert-octylphenyl ether and poly(allyl amine), with four tailored functional groups is developed for graphite and graphite-Si composite anodes. The coating, acting as an artificial solid electrolyte interphase, leads to remarkable enhancement in capacity reversibility and cycling stability, as well as a high-rate performance of the studied anodes.

An unexpected large capacity of ultrafine manganese oxide as a sodium-ion battery anode.

MnO2 is shown for the first time to be electrochemically active as a conversion anode for Na-ion batteries (NIBs). Space-confined ultrafine (UF)-MnO2, with an average crystal size of 4 nm, synthesized using a porous silicon dioxide templated hydrothermal process exhibits a high reversible sodiation capacity of 567 mA h g(-1), in contrast to the negligible activity shown by the aggregates of larger (14 nm) MnO2 nanocrystallites. The remarkably enhanced sodiation activity of the UF-MnO2 is attributable to its greatly reduced crystal size, which facilitates diffusion of Na ions, along with high surface energy arising from extensive heterogeneous interfacial bonding with the SiO2 surrounding. The UF-MnO2 anode exhibits an exceptional rate and cycle performance, exhibiting >70% capacity retention after 500 cycles. In operando synchrotron X-ray absorption near-edge structural analysis reveals combined charge-storage mechanisms involving conversion reaction between Mn(III) and Mn(II) oxides, Mn(III)-O1.5 + Na(+) + e(-)- ↔ 1/2Na2O + Mn(II)-O, and non-Mn-centered redox reactions. The finding suggests a new strategy for "activating" the potential electrochemical electrode materials that appear inactive in the bulk form.

Titanium carbide@polypyrrole core-shell nanoparticles prepared by controlled heterogeneous nucleation for rechargeable batteries.

A unique nanostructure consisting of a TiC nanoparticle core and a conformal polypyrrole shell doped with p-toluene sulfonate has been synthesized by a controlled heterogeneous nucleation process. As an electrode material in a Li-ion containing organic electrolyte, the nanocomposite exhibits remarkable high-rate (up to 400 C-rate) charge-discharge capability and cycling stability even at 50 °C.

Photocatalytic degradation of methyl orange by a multi-layer rotating disk reactor.

INTRODUCTION: Solar wastewater treatment based on photocatalytic reactions is a green process that utilizes renewable energy resources and minimizes secondary pollution. Reactor design plays an important role in promoting treatment efficiency and throughput density (based on unit volume of the reactor). EXPERIMENTAL: A rotating disk reactor that significantly increases the process efficiency has been designed and evaluated for application to photocatalytic decomposition of dye pollutants in aqueous solutions. In this process, a novel multi-layer rotating disk reactor (MLRDR) was presented. Photocatalyst (TiO(2)) particles are immobilized on the surfaces of disks. Within each layer of the reactor, methyl orange aqueous solution is allowed to flow from the center of the disk in a radial direction along the surface of the disk, which is rotating at high speed and is irradiated with UV lamps. The effluent is then directed to the center of another layer that lies underneath. Up to four stacked layers have been tested in this study, and the effects due to the number of the layers and volumetric flow rate on reaction conversion are investigated. RESULTS AND DISCUSSION: The efficiency of this photocatalytic reactor exhibits complex dependence on these parameters. With selected operating conditions, conversions greater than 95% can be achieved within seconds of residence time. Design equations of the reactor have been derived based on fluid dynamics and kinetic models, and the simulation results show promising scale-up potential of the reactor.