Three-Dimensional Nitrogen-Doped Carbonaceous Networks Anchored with Cobalt as Separator Modification Layers for Low-Polarization and Long-Lifespan Aluminum-Sulfur Batteries.

Aluminum-sulfur (Al-S) batteries have attracted extensive interest due to their high theoretical energy density, inherent safety, and low cost. However, severe polarization and poor cycling performance significantly limit the development of Al-S batteries. Herein, three-dimensional (3D) nitrogen-doped carbonaceous networks anchored with cobalt (Co@CMel-ZIF) is proposed as a separator modification layer to mitigate these issues, prepared via carbonizations of a mixture of ZIF-7, melamine, and CoCl2. It exhibits a 3D network structure with a moderate surface area and high average pore diameter, which is demonstrated to be effective in adsorbing the aluminum polysulfides and hindering the mobility of polysulfides across the separator for enhanced cyclic stability of Al-S batteries. Meanwhile, Co@CMel-ZIF are characterized by abundant catalytic pyridinic-N and Co-Nx active sites that effectively eliminate the barrier of sulfides' conversion and thereby facilitate the polarization reduction. As a result, Al-S cells based on the separator modified with Co@CMel-ZIF exhibit a low voltage polarization of 0.47 V under the current density of 50 mA g-1 at 20 °C and a high discharge specific capacity of 503 mAh g-1 after 150 cycles. In contrast, the cell employing a bare separator exhibits a polarization of 1.01 V and a discharge capacity of 300 mAh g-1 after 70 cycles under the same conditions. This work demonstrates that modifying the separators is a promising strategy to mitigate the high polarization and poor cyclability of Al-S batteries.

Layered Oxide Cathodes for Sodium-Ion Batteries: Storage Mechanism, Electrochemistry, and Techno-economics.

ConspectusLithium-ion batteries (LIBs) are ubiquitous in all modern portable electronic devices such as mobile phones and laptops as well as for powering hybrid electric vehicles and other large-scale devices. Sodium-ion batteries (NIBs), which possess a similar cell configuration and working mechanism, have already been proven as ideal alternatives for large-scale energy storage systems. The advantages of NIBs are as follows. First, sodium resources are abundantly distributed in the earth's crust. Second, high-performance NIB cathode materials can be fabricated by using solely inexpensive and noncritical transition metals such as manganese and iron, which further reduces the cost of the required raw materials. Recently, the unprecedented demand for lithium and other critical minerals has driven the cost of these primary raw materials (which are utilized in LIBs) to a historic high and thus triggered the commercialization of NIBs.Sodium layered transition metal oxides (NaxTMO2, TM = transition metal/s), such as Mn-based sodium layered oxides, represent an important family of cathode materials with the potential to reduce costs, increase energy density and cycling stability, and improve the safety of NIBs for large-scale energy storage. However, these layered oxides face several key challenges, including irreversible phase transformations during cycling, poor air stability, complex charge-compensation mechanisms, and relatively high cost of the full cell compared to LiFePO4-based LIBs. Our work has focused on the techno-economic analysis, the degradation mechanism of NaxTMO2 upon cycling and air exposure, and the development of effective strategies to improve their electrochemical performances and air stability. Correlating structure-performance relationships and establishing general design strategies of NaxTMO2 must be considered for the commercialization of NIBs.In this Account, we discuss the recent progress in the development of air-stable, electrochemically stable, and cost-effective NaxTMO2. The favorable redox-active cations for NaxTMO2 are emphasized in terms of abundance, cost, supply, and energy density. Different working mechanisms related to NaxTMO2 are summarized, including the electrochemical reversibility, the main structural transformations during the charge and discharge processes, and the charge-compensation mechanisms that accompany the (de)intercalation of Na+ ions, followed by discussions to improve the stability toward ambient air and upon cycling. Then the techno-economics are presented, with an emphasis on cathodes with different chemical compositions, cost breakdown of battery packs, and Na deficiency, factors that are critical to the large-scale implementation. Finally, this Account concludes with an overview of the remaining challenges and new opportunities concerning the practical applications of NaxTMO2, with an emphasis on the cost, large-scale fabrication capability, and electrochemical performance.

Bio-Waste-Derived Hard Carbon Anodes Through a Sustainable and Cost-Effective Synthesis Process for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are postulated as sustainable energy storage devices for light electromobility and stationary applications. The anode of choice in SIBs is hard carbon (HC) due to its electrochemical performance. Among different HC precursors, bio-waste resources have attracted significant attention due to their low-cost, abundance, and sustainability. Many bio-waste materials have been used as HC precursors, but they often require strong acids/bases for pre-/post-treatment for HC development. Here, the morphology, microstructure, and electrochemical performance of HCs synthesized from hazelnut shells subjected to different pre-treatments (i. e., no pre-treatment, acid treatment, and water washing) were compared. The impact on the electrochemical performance of sodium-ion cells and the cost-effectiveness were also investigated. The results revealed that hazelnut shell-derived HCs produced via simple water washing outperformed those obtained via other processing methods in terms of electrochemical performance and cost-ecological effectiveness of a sodium-ion battery pack.

Important Impact of the Slurry Mixing Speed on Water-Processed Li4Ti5O12 Lithium-Ion Anodes in the Presence of H3PO4 as the Processing Additive.

The aqueous processing of lithium transition metal oxides into battery electrodes is attracting a lot of attention as it would allow for avoiding the use of harmful N-methyl-2-pyrrolidone (NMP) from the cell fabrication process and, thus, render it more sustainable. The addition of slurry additives, for instance phosphoric acid (PA), has been proven to be highly effective for overcoming the corresponding challenges such as aluminum current collector corrosion and stabilization of the active material particle. Herein, a comprehensive investigation of the effect of the ball-milling speed on the effectiveness of PA as a slurry additive is reported using Li4Ti5O12 (LTO) as an exemplary lithium transition metal oxide. Interestingly, at elevated ball-milling speeds, rod-shaped lithium phosphate particles are formed, which remain absent at lower ball-milling speeds. A detailed surface characterization by means of SEM, EDX, HRTEM, STEM-EDX, XPS, and EIS revealed that in the latter case, a thin protective phosphate layer is formed on the LTO particles, leading to an improved electrochemical performance. As a result, the corresponding lithium-ion cells comprising LTO anodes and LiNi0.5Mn0.3Co0.2O2 (NMC532) cathodes reveal greater long-term cycling stability and higher capacity retention after more than 800 cycles. This superior performance originates from the less resistive electrode-electrolyte interphase evolving upon cycling, owing to the interface-stabilizing effect of the lithium phosphate coating formed during electrode preparation. The results highlight the importance of commonly neglected─frequently not even reported─electrode preparation parameters.

Zinc-Ion Hybrid Supercapacitors Employing Acetate-Based Water-in-Salt Electrolytes.

Halide-free, water-in-salt electrolytes (WiSEs) composed of potassium acetate (KAc) and zinc acetate (ZnAc2 ) are investigated as electrolytes in zinc-ion hybrid supercapacitors (ZHSs). Molecular dynamics simulations demonstrate that water molecules are mostly non-interacting with each other in the highly concentrated WiSEs, while "bulk-like water" regions are present in the dilute electrolyte. Among the various concentrated electrolytes investigated, the 30 m KAc and 1 m ZnAc2 electrolyte (30K1Zn) grants the best performance in terms of reversibility and stability of Zn plating/stripping while the less concentrated electrolyte cannot suppress corrosion of Zn and hydrogen evolution. The ZHSs utilizing 30K1Zn, in combination with a commercial activated carbon (AC) positive electrode and Zn as the negative electrode, deliver a capacity of 65 mAh g-1 (based on the AC weight) at a current density of 5 A g-1 . They also offer an excellent capacity retention over 10 000 cycles and an impressive coulombic efficiency (≈100%).

Concentrated Electrolytes Enabling Stable Aqueous Ammonium-Ion Batteries.

Rechargeable aqueous batteries are promising devices for large-scale energy-storage applications because of their low-cost, inherent safety, and environmental friendliness. Among them, aqueous ammonium-ion (NH4 + ) batteries (AAIB) are currently emerging owing to the fast diffusion kinetics of NH4 + . Nevertheless, it is still a challenge to obtain stable AAIB with relatively high output potential, considering the instability of many electrode materials in an aqueous environment. Herein, a cell based on a concentrated (5.8 m) aqueous (NH4 )2 SO4 electrolyte, ammonium copper hexacyanoferrate (N-CuHCF) as the positive electrode (cathode), and 3,4,9,10-perylene-bis(dicarboximide) (PTCDI) as the negative electrode (anode) is reported. The solvation structure, electrochemical properties, as well as the electrode-electrolyte interface and interphase are systematically investigated by the combination of theoretical and experimental methods. The results indicate a remarkable cycling performance of the low-cost rocking-chair AAIB, which offers a capacity retention of ≈72% after 1000 cycles and an average output potential of ≈1.0 V.

Elucidating the Role of Microstructure in Thiophosphate Electrolytes - a Combined Experimental and Theoretical Study of ß-Li3 PS4.

Solid-state batteries (SSBs) are promising candidates to significantly exceed the energy densities of today's state-of-the-art technology, lithium-ion batteries (LIBs). To enable this advancement, optimizing the solid electrolyte (SE) is the key. ß-Li3 PS4 (ß-LPS) is the most studied member of the Li2 S-P2 S5 family, offering promising properties for implementation in electric vehicles. In this work, the microstructure of this SE and how it influences the electrochemical performance are systematically investigated. To figure this out, four batches of ß-LPS electrolyte with different particle size, shape, and porosity are investigated in detail. It is found that differences in pellet porosities mostly originate from single-particle intrinsic features and less from interparticle voids. Surprisingly, the ß-LPS electrolyte pellets with the highest porosity and larger particle size not only show the highest ionic conductivity (up to 0.049 mS cm-1 at RT), but also the most stable cycling performance in symmetrical Li cells. This behavior is traced back to the grain boundary resistance. Larger SE particles seem to be more attractive, as their grain boundary contribution is lower than that of denser pellets prepared using smaller ß-LPS particles.

Investigation of a Fluorine-Free Phosphonium-Based Ionic Liquid Electrolyte and Its Compatibility with Lithium Metal.

A novel fluorine-free ionic liquid electrolyte comprising lithium dicyanamide (LiDCA) and trimethyl(isobutyl)phosphonium tricyanomethanide (P111i4TCM) in a 1:9 molar ratio is studied as an electrolyte for lithium metal batteries. At room temperature, it demonstrates high ionic conductivity and viscosity of about 4.5 mS cm-1 and 64.9 mPa s, respectively, as well as a 4 V electrochemical stability window (ESW). Li stripping/plating tests prove the excellent electrolyte compatibility with Li metal, evidenced by the remarkable cycling stability over 800 cycles. The evolution of the Li-electrolyte interface upon cycling was investigated via electrochemical impedance spectroscopy, displaying a relatively low impedance increase after the initial formation cycles. Finally, the solid electrolyte interphase (SEI) formed on Li metal appeared to have a bilayer structure mostly consisting of DCA and TCM reduction products. Additionally, decomposition products of the phosphonium cation were also detected, despite prior studies reporting its stability against Li metal.

Stabilizing the Li1.3 Al0.3 Ti1.7 (PO4 )3 |Li Interface for High Efficiency and Long Lifespan Quasi-Solid-State Lithium Metal Batteries.

To tackle the poor chemical/electrochemical stability of Li1+x Alx Ti2-x (PO4 )3 (LATP) against Li and poor electrode|electrolyte interfacial contact, a thin poly[2,3-bis(2,2,6,6-tetramethylpiperidine-N-oxycarbonyl)norbornene] (PTNB) protection layer is applied with a small amount of ionic liquid electrolyte (ILE). This enables study of the impact of ILEs with modulated composition, such as 0.3 lithium bis(fluoromethanesulfonyl)imide (LiFSI)-0.7 N-butyl-N-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr14 FSI) and 0.3 LiFSI-0.35 Pyr14 FSI-0.35 N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14 TFSI), on the interfacial stability of PTNB@Li||PTNB@Li and PTNB@Li||LiNi0.8 Co0.1 Mn0.1 O2 cells. The addition of Pyr14 TFSI leads to better thermal and electrochemical stability. Furthermore, Pyr14 TFSI facilitates the formation of a more stable Li|hybrid electrolyte interface, as verified by the absence of lithium "pitting corrosion islands" and fibrous dendrites, leading to a substantially extended lithium stripping-plating cycling lifetime (>900 h). Even after 500 cycles (0.5C), PTNB@Li||LiNi0.8 Co0.1 Mn0.1 O2 cells achieve an impressive capacity retention of 89.1 % and an average Coulombic efficiency of 98.6 %. These findings reveal a feasible strategy to enhance the interfacial stability between Li and LATP by selectively mixing different ionic liquids.

Role of the voltage window on the capacity retention of P2-Na2/3[Fe1/2Mn1/2]O2 cathode material for rechargeable sodium-ion batteries.

P2-Na2/3[Fe1/2Mn1/2]O2 layered oxide is a promising high energy density cathode material for sodium-ion batteries. However, one of its drawbacks is the poor long-term stability in the operating voltage window of 1.5-4.25 V vs Na+/Na that prevents its commercialization. In this work, additional light is shed on the origin of capacity fading, which has been analyzed using a combination of experimental techniques and theoretical methods. Electrochemical impedance spectroscopy has been performed on P2-Na2/3[Fe1/2Mn1/2]O2 half-cells operating in two different working voltage windows, one allowing and one preventing the high voltage phase transition occurring in P2-Na2/3[Fe1/2Mn1/2]O2 above 4.0 V vs Na+/Na; so as to unveil the transport properties at different states of charge and correlate them with the existing phases in P2-Na2/3[Fe1/2Mn1/2]O2. Supporting X-ray photoelectron spectroscopy experiments to elucidate the surface properties along with theoretical calculations have concluded that the formed electrode-electrolyte interphase is very thin and stable, mainly composed by inorganic species, and reveal that the structural phase transition at high voltage from P2- to "Z"/OP4-oxygen stacking is associated with a drastic increased in the bulk electronic resistance of P2-Na2/3[Fe1/2Mn1/2]O2 electrodes which is one of the causes of the observed capacity fading.

Enhanced Li+ Transport in Ionic Liquid-Based Electrolytes Aided by Fluorinated Ethers for Highly Efficient Lithium Metal Batteries with Improved Rate Capability.

FSI- -based ionic liquids (ILs) are promising electrolyte candidates for long-life and safe lithium metal batteries (LMBs). However, their practical application is hindered by sluggish Li+ transport at room temperature. Herein, it is shown that additions of bis(2,2,2-trifluoroethyl) ether (BTFE) to LiFSI-Pyr14 FSI ILs can effectively mitigate this shortcoming, while maintaining ILs' high compatibility with lithium metal. Raman spectroscopy and small-angle X-ray scattering indicate that the promoted Li+ transport in the optimized electrolyte, [LiFSI]3 [Pyr14 FSI]4 [BTFE]4 (Li3 Py4 BT4 ), originates from the reduced solution viscosity and increased formation of Li+ -FSI- complexes, which are associated with the low viscosity and non-coordinating character of BTFE. As a result, Li/LiFePO4 (LFP) cells using Li3 Py4 BT4 electrolyte reach 150 mAh g-1 at 1 C rate (1 mA cm-2 ) and a capacity retention of 94.6% after 400 cycles, revealing better characteristics with respect to the cells employing the LiFSI-Pyr14 FSI (operate only a few cycles) and commercial carbonate (80% retention after only 218 cycles) electrolytes. A wide operating temperature (from -10 to 40 °C) of the Li/Li3 Py4 BT4 /LFP cells and a good compatibility of Li3 Py4 BT4 with LiNi0.5 Mn0.3 Co0.2 O2 (NMC532) are demonstrated also. The insight into the enhanced Li+ transport and solid electrolyte interphase characteristics suggests valuable information to develop IL-based electrolytes for LMBs.

Improved Sodiation Additive and Its Nuances in the Performance Enhancement of Sodium-Ion Batteries.

The abundance of the available sodium sources has led to rapid progress in sodium-ion batteries (SIBs), making them potential candidates for immediate replacement of lithium-ion batteries (LIBs). However, commercialization of SIBs has been hampered by their fading efficiency due to the sodium consumed in the formation of solid-electrolyte interphase (SEI) when using hard carbon (HC) anodes. Herein, Na2C3O5 sodium salt is introduced as a highly efficient, cost-effective, and safe cathode sodiation additive. This sustainable sodium salt has an oxidation potential of ∼4.0 V vs Na+/Na°, so it could be practically implemented into SIBs. Moreover, for the first time, we have also revealed by X-ray photoelectron spectroscopy (XPS) that in addition to the compensating Na+ ions spent in the SEI layer, the high specific capacity and capacity retention observed from electrochemical measurements are due to the formation of a thinner and more stable cathode-electrolyte interphase (CEI) on the P2-Na2/3Mn0.8Fe0.1Ti0.1O2 while using such a cathode sodiation additive. Half-cell studies with P2-Na2/3Mn0.8Fe0.1Ti0.1O2 cathodes show a 27% increase in the specific capacity (164 mAh gP2-1) with cathode sodiation additives. Full-cell studies with the HC anode show a 4 times increase in the specific capacity of P2-Na2/3Mn0.8Fe0.1Ti0.1O2. This work provides notable insights into and avenues toward the development of SIBs.

Cathode-Electrolyte Interphase in a LiTFSI/Tetraglyme Electrolyte Promoting the Cyclability of V2O5.

V2O5, one of the earliest intercalation-type cathode materials investigated as a Li+ host, is characterized by an extremely high theoretical capacity (441 mAh g-1). However, the fast capacity fading upon cycling in conventional carbonate-based electrolytes is an unresolved issue. Herein, we show that using a LiTFSI/tetraglyme (1:1 in mole ratio) electrolyte yields a highly enhanced cycling ability of V2O5 (from 20% capacity retention to 80% after 100 cycles at 50 mA g-1 within 1.5-4.0 V vs Li+/Li). The improved performance mostly originates from the V2O5 electrode itself, since refreshing the electrolyte and the lithium electrode of the cycled cells does not help in restoring the V2O5 electrode capacity. Electrochemical impedance spectroscopy (EIS), post-mortem scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) have been employed to investigate the origin of the improved electrochemical behavior. The results demonstrate that the enhanced cyclability is a consequence of a thinner but more stable cathode-electrolyte interphase (CEI) layer formed in LiTFSI/tetraglyme with respect to the one occurring in 1 M LiPF6 in EC/DMC (1:1 in weight ratio, LP30). These results show that the cyclability of V2O5 can be effectively improved by simple electrolyte engineering. At the same time, the uncovered mechanism further reveals the vital role of the CEI on the cyclability of V2O5, which can be helpful for the performance optimization of vanadium-oxide-based batteries.

Operando pH Measurements Decipher H+/Zn2+ Intercalation Chemistry in High-Performance Aqueous Zn/δ-V2O5 Batteries.

Vanadium oxides have been recognized to be among the most promising positive electrode materials for aqueous zinc metal batteries (AZMBs). However, their underlying intercalation mechanisms are still vigorously debated. To shed light on the intercalation mechanisms, high-performance δ-V2O5 is investigated as a model compound. Its structural and electrochemical behaviors in the designed cells with three different electrolytes, i.e., 3 m Zn(CF3SO3)2/water, 0.01 M H2SO4/water, and 1 M Zn(CF3SO3)2/acetonitrile, demonstrate that the conventional structural and elemental characterization methods cannot adequately clarify the separate roles of H+ and Zn2+ intercalations in the Zn(CF3SO3)2/water electrolyte. Thus, an operando pH determination method is developed and used toward Zn/δ-V2O5 AZMBs. This method indicates the intercalation of both H+ and Zn2+ into δ-V2O5 and uncovers an unusual H+/Zn2+-exchange intercalation-deintercalation mechanism. Density functional theory calculations further reveal that the H+/Zn2+ intercalation chemistry is a consequence of the variation of the electrochemical potential of Zn2+ and H+ during the electrochemical intercalation/release.

Toward Stable Electrode/Electrolyte Interface of P2-Layered Oxide for Rechargeable Na-Ion Batteries.

The electrochemical properties of P2-Na2/3Mn0.8Fe0.1Ti0.1O2 layered oxide, which is a promising cathode material for rechargeable Na-ion batteries (NIBs), are evaluated with an optimized in-house ionic liquid (IL)-based electrolyte, and its performance is compared with that using carbonate-based electrolyte. The IL-based system reveals better electrochemical performance at room temperature than the carbonate electrolyte-based one at 0.1C and 1C, especially in terms of cycling stability, with a 97% capacity retention after 100 deep cycles (0.1C). The electrode/electrolyte interface is thoroughly studied in both systems by means of X-ray photoelectron spectroscopy and scanning electron microscopy so as proof that the formed interface is crucial to optimizing the electrochemical performance of NIBs. The carbonate-based system shows a thin, inhomogeneous, and unstable interface layer, while the IL-based one exhibits an even thinner but homogeneous and more stable interface, which may result in safer and longer-lasting NIBs.

Composition and evolution of the solid-electrolyte interphase in Na2Ti3O7 electrodes for Na-ion batteries: XPS and Auger parameter analysis.

Na2Ti3O7 is considered a promising negative electrode for Na-ion batteries; however, poor capacity retention has been reported and the stability of the solid-electrolyte interphase (SEI) could be one of the main actors of this underperformance. The composition and evolution of the SEI in Na2Ti3O7 electrodes is hereby studied by means of X-ray photoelectron spectroscopy (XPS). To overcome typical XPS limitations in the photoelectron energy assignments, the analysis of the Auger parameter is here proposed for the first time in battery materials characterization. We have found that the electrode/electrolyte interface formed upon discharge, mostly composed by carbonates and semicarbonates (Na2CO3, NaCO3R), fluorides (NaF), chlorides (NaCl) and poly(ethylene oxide)s, is unstable upon electrochemical cycling. Additionally, solid state nuclear magnetic resonance (NMR) studies prove the reaction of the polyvinylidene difluoride (PVdF) binder with sodium. The powerful approach used in this work, namely Auger parameter study, enables us to correctly determine the composition of the electrode surface layer without any interference from surface charging or absolute binding energy calibration effects. As a result, the suitability for Na-ion batteries of binders and electrolytes widely used for Li-ion batteries is questioned here.

Structure of H2Ti3O7 and its evolution during sodium insertion as anode for Na ion batteries.

H2Ti3O7 was prepared as a single phase material by ionic exchange from Na2Ti3O7. The complete ionic exchange was confirmed by (1)H and (23)Na solid state Nuclear Magnetic Resonance (NMR). The atomic positions of H2Ti3O7 were obtained from the Rietveld refinement of powder X-ray diffraction (PXRD) and neutron diffraction experimental data, the latter collected at two different wavelengths to precisely determine the hydrogen atomic positions in the structure. All H(+) cations are hydrogen bonded to two adjacent [Ti3O7](2-) layers leading to the gliding of the layers and lattice centring with respect to the parent Na2Ti3O7. In contrast with a previous report where protons were located in two different positions of H2Ti3O7, 3 types of proton positions were found. Two of the three types of proton are bonded to the only oxygen linked to a single titanium atom forming an H-O-H angle close to that of the water molecule. H2Ti3O7 is able to electrochemically insert Na(+). The electrochemical insertion of sodium into H2Ti3O7 starts with a solid solution regime of the C-centred phase. Then, between 0.6 and 1.2 inserted Na(+) the reaction proceeds through a two phase reaction and a plateau at 1.3 V vs. Na(+)/Na is observed in the voltage-composition curve. The second phase resembles the primitive Na2Ti3O7 cell as detected by in situ PXRD. Upon oxidation, from 0.9 to 2.2 V, the PXRD pattern remains mostly unchanged probably due to H(+) removal instead of Na(+), with the capacity quickly fading upon cycling. Conditioning H2Ti3O7 for two cycles at 0.9-2.2 V before cycling in the 0.05-1.6 V range yields similar specific capacity and better retention than the original Na2Ti3O7 in the same voltage range.