Proton-Reservoir Hydrogel Electrolyte for Long-Term Cycling Zn/PANI Batteries in Wide Temperature Range.

Advanced aqueous batteries are promising for next generation flexible devices owing to the high safety, yet still requiring better cycling stability and high capacities in wide temperature range. Herein, a polymeric acid hydrogel electrolyte (PAGE) with 3 M Zn(ClO4 )2 was fabricated for high performance Zn/polyaniline (PANI) batteries. With PAGE, even at -35 °C the Zn/Zn symmetrical battery can keep stable for more than 1 500 h under 2 mA cm-2 , and the Zn/PANI battery can provide ultra-high stable specific capacity of 79.6 mAh g-1 for more than 70 000 cycles at 15 A g-1 . This can be mainly ascribed to the -SO3 - H+ function group in PAGE. It can generate constant protons and guide the (002) plane formation to accelerate the PANI redox reaction kinetics, increase the specific capacity, and suppress the side reaction and dendrites. This proton-supplying strategy by polymeric acid hydrogel may further propel the development of high performance aqueous batteries.

Guiding Zn Uniform Deposition with Polymer Additives for Long-lasting and Highly Utilized Zn Metal Anodes.

The parasitic side reaction on Zn anode is the key issue which hinders the development of aqueous Zn-based energy storage systems on power-grid applications. Here, a polymer additive (PMCNA) engineered by copolymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) and N-acryloyl glycinamide (NAGA) was employed to regulate the Zn deposition environment for satisfying side reaction inhibition performance during long-term cycling with high Zn utilization. The PMCNA can preferentially adsorb on Zn metal surface to form a uniform protective layer for effective water molecule repelling and side reaction resistance. In addition, the PMCNA can guide Zn nucleation and deposition along 002 plane for further side reaction and dendrite suppression. Consequently, the PMCNA additive can enable the Zn//Zn battery with an ultrahigh depth of discharge (DOD) of 90.0 % for over 420 h, the Zn//active carbon (AC) capacitor with long cycling lifespan, and the Zn//PANI battery with Zn utilization of 51.3 % at low N/P ratio of 2.6.

Alleviating Side Reactions on Zn Anodes for Aqueous Batteries by a Cell Membrane Derived Phosphorylcholine Zwitterionic Protective Layer.

Aqueous zinc (Zn) ion batteries are attractive for next generation batteries with high safety, yet their applications are still hindered by the uncontrollable dendrite formation and side reactions on Zn anode. Here, a polyzwitterion protective layer (PZIL) was engineered by polymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) in carboxymethyl chitosan (CMCS), which renders the following merits: the choline groups of MPC can preferentially adsorb onto Zn metal to avoid side reactions; the charged phosphate groups chelate with Zn2+ to regulate the solvation structure, further improving side reaction inhibition; the Hofmeister effect between ZnSO4 and CMCS can enhance the interfacial contact during electrochemical characterization. Consequently, the symmetrical Zn battery with PZIL can keep stable for more than 1000 hours under the ultra-high current density of 40 mA cm-2 . The PZIL confers the Zn/MnO2 full battery and Zn/active carbon (AC) capacitor with stable cycling performance under high current density.

Immunizing Aqueous Zn Batteries against Dendrite Formation and Side Reactions at Various Temperatures via Electrolyte Additives.

Aqueous Zn-ion batteries own great potential on next generation wearable batteries due to the high safety and low cost. However, the uncontrollable dendrites growth and the negligible subzero temperature performance impede the batteries practical applications. Herein, it is demonstrated that dimethyl sulfoxide (DMSO) is an effective additive in ZnSO4 electrolyte for side reactions and dendrites suppression by regulating the Zn-ion solvation structure and inducing the Zn2+ to form the more electrochemical stable (002) basal plane, via the higher absorption energy of DMSO with Zn2+ and (002) plane. Moreover, the stable reconstructed hydrogen bonds between DMSO and H2 O dramatically lower the freezing point of the electrolyte, which significantly increases the ionic conductivity and cycling performance of the aqueous batteries at subzero temperatures. As a consequence, the symmetrical Zn/Zn cell can be kept stable for more than 2100 h at 20 °C and 1200 h at -20 °C without dendrite and by-products formation. The Zn/MnO2 batteries can perform steadily for more than 3000 cycles at 20 °C and 300 cycles at -20 °C. This work provides a facile and feasible strategy on designing high performance and dendrite free aqueous Zn-ion batteries for various temperatures.

All-Graphitic Multilaminate Mesoporous Membranes by Interlayer-Confined Molecular Assembly.

Layered mesostructured graphene, which combines the intrinsic advantages of planar graphene and mesoporous materials, has become interestingly important for energy storage and conversion applications. Here, an interlayer-confined molecular assembly method is presented for constructing all-graphitic multilaminate membranes (MMG⊂rGO), which are composed of monolayer mesoporous graphene (MMG) sandwiched between reduced graphene oxide (rGO) sheets. Hybrid assembly of iron-oleate complexes and organically modified GO sheets enables the preferential assembly of iron-oleate precursors at the interlayer space of densely stacked GO, driven by the like-pair molecular van der Waals interactions. Confined pyrolysis of iron-oleate complexes at GO interlayers leads to close-packed, carbon-coated Fe3 O4 nanocrystal arrays, which serve as intermediates to template the subsequent formation of MMG⊂rGO membranes. To demonstrate their application potentials, MMG⊂rGO membranes are exploited as dual-functional interlayers to boost the performance of Li-S batteries by concurrently suppressing the shuttle of polysulfides and the growth of Li dendrites. This work showcases the capability of molecular-based hybrid assembly for synthesizing multilayer mesostructured graphene with high packing density and its use in electrochemical energy applications.

Metallic MoS2 for High Performance Energy Storage and Energy Conversion.

Metallic phase 2D molybdenum disulfide (MoS2 ) is an emerging class of materials with remarkably higher electrical conductivity and catalytic activities. The goal of this study is to review the atomic structures and electrochemistry of metallic MoS2 , which is essential for a wide range of existing and new enabling technologies. The scope of this paper ranges from the atomic structure, band structure, electrical and optical properties to fabrication methods, and major emerging applications in electrochemical energy storage and energy conversion. This paper also thoroughly covers the atomic structure-properties-application relationships of metallic MoS2 . Understanding the fundamental properties of these structures is crucial for designing and manufacturing products for emerging applications. Today, a more holistic understanding of the interplay between the structure, chemistry, and performance of metallic MoS2 is advancing actual applications of this material. This new level of understanding also enables a myriad of new and exciting applications, which motivated this review. There are excellent reviews already on the traditional semiconducting MoS2 , and this review, for the first time, focuses on the uniqueness of conducting metallic MoS2 for energy applications and offers brand new materials for clean energy application.

Heavy Metal-Free Tannin from Bark for Sustainable Energy Storage.

A novel renewable cathode made from earth abundant, low-cost materials can contribute to the intermittent storage needs of renewable energy-based society. In this work, we report for the first-time tannin from Nature as a cathode material. Our approach exploits the charge storage mechanism of the redox active quinone moiety. Tannins extracted from tree bark using environmental friendly aqueous solvents have the highest phenol content (5.56 mol g-1) among all the natural phenolic biopolymers, 5000 times higher than lignin. Tannins coupled with a conductive polymer polypyrrole acquire high specific capacitance values of 370 F g-1 at 0.5 A g-1 as well as excellent rate performance of 196 F g-1 at 25 A g-1. Additionally, we employed carbonized wood as an electrode substrate to produce a sustainable electrochemical device with dramatically improved performance compared to conventional devices. The high surface area provided by the well-aligned, cellular porosity of wood-derived substrate combined with the high mobility of ions and electrons in the carbonized cell walls and deposited tannin can achieve an areal capacitance of 4.6 F cm-2 at 1 mA cm-2, which is 1.5 times higher than activated wood carbon.

Highly ordered mesoporous few-layer graphene frameworks enabled by fe3 o4 nanocrystal superlattices.

While great progress has been achieved in the synthesis of ordered mesoporous carbons in the past decade, it still remains a challenge to prepare highly graphitic frameworks with ordered mesoporosity and high surface area. Reported herein is a simple synthetic methodology, based on the conversion of self-assembled superlattices of Fe3 O4 nanocrystals, to fabricate highly ordered mesoporous graphene frameworks (MGFs) with ultrathin pore walls consisting of three to six stacking graphene layers. The MGFs possess face-centered-cubic symmetry with interconnected mesoporosity, tunable pore width, and high surface area. Because of their unique architectures and superior structural durability, the MGFs exhibit excellent cycling stability and rate performance when used as anode materials for lithium-ion batteries, thus retaining a specific capacity of 520 mAh g(-1) at a current density of 300 mA g(-1) after 400 cycles.

Constructing Lysozyme Protective Layer via Conformational Transition for Aqueous Zn Batteries.

The practical applications for aqueous Zn ion batteries (ZIBs) are promising yet still impeded by the severe side reactions on Zn metal. Here, a lysozyme protective layer (LPL) is prepared on Zn metal surface by a simple and facile self-adsorption strategy. The LPL exhibits extremely strong adhesion on Zn metal to provide stable interface during long-term cycling. In addition, the self-adsorption strategy triggered by the hydrophobicity-induced aggregation effect endows the protective layer with a gap-free and compacted morphology which can reject free water for effective side reaction inhibition performance. More importantly, the lysozyme conformation is transformed from α-helix to ß-sheet structure before layer formation, thus abundant functional groups are exposed to interact with Zn2+ for electrical double layer (EDL) modification, desolvation energy decrease, and ion diffusion kinetics acceleration. Consequently, the LPL renders the symmetrical Zn battery with ultra-long cycling performance for more than 1200 h under high Zn depth of discharge (DOD) for 77.7%, and the Zn/Zn0.25V2O5 pouch cell with low N/P ratio of 2.1 at high Zn utilization of 48% for over 300 cycles. This study proposes a facile and low-cost method for constructing a stable protective layer of Zn metal for high Zn utilization aqueous devices.

Modulating the Coordination Environment of Lithium Bonds for High Performance Polymer Electrolyte Batteries.

The new-generation lithium metal batteries require polymer electrolytes with high ionic conductivity and mechanical properties. However, the performance of the polymer electrolytes is severely influenced by the lithium bond formation between the functional groups and lithium ions (Li+), which has barely been considered in the past. Herein, a lithium bond enriched polymer gel (PAEV) is elaborately designed by copolymerizing 4-acryloylmorpholine (ACMO) and 1-vinyl-3-ethyl imidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][TFSI]) in 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) with the presence of LiFSI. The lithium bonds formed between LiFSI and carbonyl groups in PACMO can be regulated by the Li+ coordination number, and further weakened by the hydrogen bonds with [EMIM][TFSI] and poly[VEIM][TFSI], to effectively render the polymer electrolyte with adjustable ionic conductivity and tunable mechanical property. In addition, with the regulated coordination environment of Li+, the LiF and Li3N layer can be uniformly formed on the Li surface to facilitate Li+ nucleation and deposition. As a consequence, the PAEV electrolyte confers the Li/LiFePO4 (LFP) battery with high capacity of 124 mA h g-1 at 1 C under 25 °C, and 152 mA h g-1 under 50 °C. This work can promote the development of high performance polymer electrolyte via lithium bond manipulation.

Antifreezing Hydrogel Electrolyte with Ternary Hydrogen Bonding for High-Performance Zinc-Ion Batteries.

The new-generation flexible aqueous zinc-ion batteries require enhanced mechanical properties and ionic conductivities at low temperature for practical applications. This fundamentally means that it is desired that the hydrogel electrolyte possesses antifreezing merits to resist flexibility loss and performance decrease at subzero temperatures. Herein, a highly flexible polysaccharide hydrogel is realized in situ and is regulated in zinc-ion batteries through the Hofmeister effect with low-concentration Zn(ClO4 )2 salts to satisfy the abovementioned requirements. The chaotropic ClO4 - anions, water, and polymer chains can form ternary and weak hydrogen bonding (HB), which enables the polymer chains to have improved mechanical properties, breaks the HB of water to remarkably decrease the electrolyte freezing point, and reduces the amounts of free water for effective side reactions and dendrite inhibition. Consequently, even at -30 °C, the Zn(ClO4 )2 in situ optimized hydrogel electrolyte features a high ionic conductivity of 7.8 mS cm-1 and excellent flexibility, which enables a Zn/polyaniline (PANI) battery with a reversible capacity of 70 mA h g-1 under 5 A g-1 for 2500 cycles, and renderd the flexible full battery with excellent cycling performances under different bending angles. This work provides a new pathway for designing high-performance antifreezing flexible batteries via the Hofmeister effect.

Regulating the Molecular Interactions in Polymer Binder for High-Performance Lithium-Sulfur Batteries.

Polymer binders have been shown to efficiently conquer the notorious lithium polysulfide (LiPS) shuttle effects in lithium-sulfur (Li-S) batteries for years, but more study is needed. Herein, a water dispersible and molecular interaction regulated polymer binder (PNAVS) for Li-S batteries was elaborately designed by co-polymerizing N-acryloyl glycinamide and 3-(1-vinyl-3-imidazolio)propanesulfonate. We demonstrate that by modulating the multiple interactions between the functional groups through copolymerization the binder was able to coordinate the LiPSs with higher binding energy for shuttle effect alleviation and cycling performance improvement. In addition, the Li+ diffusion coefficient is also optimized in the PNAVS binder, which facilitates acceleration of the redox kinetics during cycling. Consequently, the PNAVS binder renders the Li-S battery with an ultrastable open circuit voltage for more than 3000 h. Even with a high sulfur loading of 11.7 mg cm-2, the battery can still exhibit excellent areal capacity of 12.21 mA h cm-2. As proof of concept, a pouch cell was also demonstrated with the stable cycling performance for 110 cycles. The binder engineering strategy in this work will propel the practical applications of high-performance batteries.

Gel Electrolyte Constructing Zn (002) Deposition Crystal Plane Toward Highly Stable Zn Anode.

Zinc (Zn) metal anode has been widely evaluated in aqueous Zn batteries. Nevertheless, the dendrite formation issue and consecutive side reactions severely impede the practical applications of Zn metal at high current densities. Herein, it is reported that engineering the gel electrolyte with multifunctional charged groups by incorporating a zwitterionic gel poly(3-(1-vinyl-3-imidazolio) propanesulfonate) (PVIPS) can effectively address the abovementioned issues. The charged groups of sulfonate and imidazole in the gel electrolyte can texture the Zn2+ nucleation and deposition plane to (002), which possesses a high activation energy to resist side reactions and induce uniform growth of Zn metal for a dendrite-free structure. In addition, the Zn2+ solvation structure can be manipulated by the charged groups to further eliminate side reactions for high rate performance Zn batteries. Consequently, the polyzwitterionic gel electrolyte enables a stable cycling with a cumulative capacity of 3000 mA h cm-2 at high density of 7.5 mA cm-2 for the symmetrical Zn battery, and a long-term cycling life for more than 1000 cycles at 5 C of Zn/MnO2 full battery. It is envisioned that the design of the gel electrolyte will provide promising feasibility on safe, flexible, and wearable energy storage devices.

Decoupling of Mechanical Strength and Ionic Conductivity in Zwitterionic Elastomer Gel Electrolyte toward Safe Batteries.

Quasi-solid state electrolyte is one of the promising options for next generation batteries due to its superiority on safety and electrochemistry performance. However, the trade-off between the electrolyte swelling ratio and mechanical property of the quasi-solid state electrolyte significantly influences the battery performance. Herein, we design a nonswelling, solvent-adaptive polymer gel composed of oleophobic zwitterion poly(3-(1-vinyl-3-imidazolio)-propanesulfonate) and oleophilic elastomer poly(2-methoxyethyl acrylate) segments to retain high battery performance without sacrificing the mechanical property in lithium batteries. The as-designed gel can not only uptake enough electrolyte for a high ionic conductivity of 1.78 mS cm-1 but also achieve excellent mechanical strength with compression stress at 90% strain (σ0.9) reaching 5.8 MPa after long time soaking for battery safety due to its nonswelling property in ester electrolyte. Moreover, the as-prepared zwitterionic gel is beneficial to electrolyte salt dissociation, which further enhances the ionic conductivity and transference number of batteries. Consequently, the gel electrolyte can cycle for more than 500 h under a high current density of 3 mA cm-2 on dendrite inhibition performance, and when assembled with LiFePO4 as a cathode, the battery demonstrates a reversible specific capacity as high as 70 mAh g-1 under a high current density of 5 C after 300 cycles. The rational designed solvophilic/solvophobic zwitterionic elastomers provide a guidance for engineering quasi-solid state electrolytes of different solvents with broad applications on flexible devices.

3D Printed High-Performance Lithium Metal Microbatteries Enabled by Nanocellulose.

Batteries constructed via 3D printing techniques have inherent advantages including opportunities for miniaturization, autonomous shaping, and controllable structural prototyping. However, 3D-printed lithium metal batteries (LMBs) have not yet been reported due to the difficulties of printing lithium (Li) metal. Here, for the first time, high-performance LMBs are fabricated through a 3D printing technique using cellulose nanofiber (CNF), which is one of the most earth-abundant biopolymers. The unique shear thinning properties of CNF gel enables the printing of a LiFePO4 electrode and stable scaffold for Li. The printability of the CNF gel is also investigated theoretically. Moreover, the porous structure of the CNF scaffold also helps to improve ion accessibility and decreases the local current density of Li anode. Thus, dendrite formation due to uneven Li plating/stripping is suppressed. A multiscale computational approach integrating first-principle density function theory and a phase-field model is performed and reveals that the porous structures have more uniform Li deposition. Consequently, a full cell built with a 3D-printed Li anode and a LiFePO4 cathode exhibits a high capacity of 80 mA h g-1 at a charge/discharge rate of 10 C with capacity retention of 85% even after 3000 cycles.

Stable Metal Anode enabled by Porous Lithium Foam with Superior Ion Accessibility.

Lithium (Li) metal anodes have attracted much interest recently for high-energy battery applications. However, low coulombic efficiency, infinite volume change, and severe dendrite formation limit their reliable implementation over a wide range. Here, an outstanding stability for a Li metal anode is revealed by designing a highly porous and hollow Li foam. This unique structure is capable of tackling many Li metal problems simultaneously: first, it assures uniform electrolyte distribution over the inner and outer electrode's surface; second, it reduces the local current density by providing a larger electroactive surface area; third, it can accommodate volume expansion and dissipate heat efficiently. Moreover, the structure shows superior stability compared to fully Li covered foam with low porosity, and bulky Li foil electrode counterparts. This Li foam exhibits small overpotential (≈25 mV at 4 mA cm-2 ) and high cycling stability for 160 cycles at 4 mA cm-2 . Furthermore, when assembled, the porous Li metal as the anode with LiFePO4 as the cathode for a full cell, the battery has a high-rate performance of 138 mAh g-1 at 0.2 C. The beneficial structure of the Li hollow foam is further studied through density functional theory simulations, which confirms that the porous structure has better charge mobility and more uniform Li deposition.

Ultralight, highly thermally insulating and fire resistant aerogel by encapsulating cellulose nanofibers with two-dimensional MoS2.

Thermally insulating materials, made from earth-abundant and sustainable resources, are highly desirable in the sustainable construction of energy efficient buildings. Cellulose from wood has long been recognized for these characteristics. However, cellulose can be a flammability hazard, and for construction this has been addressed via chemical treatment such as that with halogen and/or phosphorus, which leads to further environmental concerns. Fortunately, the structure of cellulose lends itself well to chemical modification, giving great potential to explore interaction with other compounds. Thus, in this study, cellulose nanofibers (CNFs) were nano-wrapped with ultrathin 1T phase molybdenum disulfide (MoS2) nanosheets via chemical crosslinking, to produce an aerogel. Thermal and combustion characterization revealed highly desirable properties (thermal conductivity k = 28.09 mW m-1 K-1, insulation R value = 5.2, limit oxygen index (LOI) = 34.7%, total heat release = 0.4 MJ m-2). Vertical burning tests also demonstrated excellent fire retardant and self-extinguishing capabilities. Raman spectra further revealed that MoS2 remained unscathed after 30 seconds of burning in a 1300 °C butane flame. Considering the inherently low density of this material, there is significant opportunity for its usage in a number of insulating applications demanding specific fire resistance properties.

Fabrication of three-dimensionally interconnected nanoparticle superlattices and their lithium-ion storage properties.

Three-dimensional superlattices consisting of nanoparticles represent a new class of condensed materials with collective properties arising from coupling interactions between close-packed nanoparticles. Despite recent advances in self-assembly of nanoparticle superlattices, the constituent materials have been limited to those that are attainable as monodisperse nanoparticles. In addition, self-assembled nanoparticle superlattices are generally weakly coupled due to the surface-coating ligands. Here we report the fabrication of three-dimensionally interconnected nanoparticle superlattices with face-centered cubic symmetry without the presynthesis of the constituent nanoparticles. We show that mesoporous carbon frameworks derived from self-assembled supercrystals can be used as a robust matrix for the growth of nanoparticle superlattices with diverse compositions. The resulting interconnected nanoparticle superlattices embedded in a carbon matrix are particularly suitable for energy storage applications. We demonstrate this by incorporating tin oxide nanoparticle superlattices as anode materials for lithium-ion batteries, and the resulting electrochemical performance is attributable to their unique architectures.

Electronically coupled nanocrystal superlattice films by in situ ligand exchange at the liquid-air interface.

The ability to remove long, insulating ligands from nanocrystal (NC) surfaces without deteriorating the structural integrity of NC films is critical to realizing their electronic and optoelectronic applications. Here we report a nondestructive ligand-exchange approach based on in situ chemical treatment of NCs floating at the liquid-air interface, enabling strongly coupled NC superlattice films that can be directly transferred to arbitrary substrates for device applications. Ligand-exchange-induced structural defects such as cracks and degraded NC ordering that are commonly observed using previous methods are largely prevented by performing ligand exchange at the liquid-air interface. The significantly reduced interparticle spacing arising from ligand replacement leads to highly conductive NC superlattice films, the electrical conductivities and carrier mobilities of which are 1 order of magnitude higher than those of the same NC films subject to substrate-supported exchange using previously reported procedures. The in situ, free-floating exchange approach presented here opens the door for electronically coupled NC superlattices that hold great promise for high-performance, flexible electronic and optoelectronic devices.