Potential High Energy Density Research Articles

Cryo-TEM studies of binder free high performance FeF2 cathode based full cells enabled by surface engineering

Iron-based fluorides (IBFs, typically FeF3 and FeF2) are potential next generation high energy density cathodes for lithium-ion batteries (LIBs) due to their high specific capacity, cost effectiveness and crustal abundance. However, IBFs decompose electrolyte violently which impedes their practical implementation in LIBs. Herein we report a strategy to embed FeF2 nanoparticles in an interconnected cyclic polyacrylonitrile (cPAN) network to passivate the cathode/electrolyte interface. Moreover, cPAN affords strong adhesion to both the FeF2 nanoparticles and the current collector, essentially acting as a binder that is superior to polyvinylidene fluoride (PVDF). Cryo-transmission electron microscopy reveals that the amorphous cPAN was uniformly coated on the FeF2 surface with a thickness of 5 nm, acting as an effective (cathode electrolyte interphase) CEI layer that inhibited the growth of excessive CEI, thus achieved stable cycling in lean electrolyte. When paired with the high capacity SiO/C anode, the FeF2-cPAN|SiO/C full cell delivered a capacity of 400 mAh/g after 100 cycles at 0.5C. Density functional theory (DFT) calculation indicates that the cPAN is inert to the electrolyte, thus suppresses the catastrophic electrolyte decomposition caused by FeF2. DFT further suggests that the existence of vacancies on the carbon surface will cause H transfer reaction of the solvent, leading to the degradation of the electrolyte. This study provides a viable technology to enable high energy density FeF2 cathode-based LIBs for energy storage applications.

Novel high-pressure phases of nitrogen-rich Y-N compounds.

Five new high-pressure phases (I4̄3d-Y4N3, R3c-Y2N3, P1̄-II-YN4, P1̄-YN6, and P31c-YN8) are proposed by the crystal structure prediction. A series of polynitrogen forms were achieved in the nitrogen-rich Y-N compounds, including diatomic N2, an isolated N8 chain, an infinite N chain with an N6 unit, and an infinite N layer with bent N18 rings. The high energy densities of P1̄-II-YN4 (1.98 kJ g-1), P1̄-YN6 (2.35 kJ g-1), and P31c-YN8 (3.77 kJ g-1) make them potential high energy density materials. More importantly, P1̄-II-YN4, P1̄-YN6, and P31c-YN8 exhibit excellent explosive performance, with detonation pressures 4-8 times that of TNT (19 GPa) and detonation velocities 1-2 times that of TNT (6.90 km s-1). The electronic structure and bonding properties show that the high stability of Y-N compounds originates from the strong N-N covalent bond and the weak Y-N ionic bond interaction. The increase in the transferred charge quantity as the pressure decreased is more conducive to stabilizing the polymeric nitrogen structure, which leads to the metastable properties of P1̄-II-YN4 and P1̄-YN6 under ambient conditions. Finally, the infrared (IR) spectra of P1̄-II-YN4, P1̄-YN6, and P31c-YN8 are calculated to provide a reference in experimental synthesis.

Synthesis, Characterization and DFT Study of a New Family of High-Energy Compounds Based on s-Triazine, Carborane and Tetrazoles.

An efficient one-pot synthesis of carborane-containing high-energy compounds was developed via the exploration of carbon-halogen bond functionalization strategies in commercially available 2,4,6-trichloro-1,3,5-triazine. The synthetic pathway first included the substitution of two chlorine atoms in s-triazine with 5-R-tetrazoles (R = H, Me, Et) units to form disubstituted tetrazolyl 1,3,5-triazines followed by the sequential substitution of the remaining chlorine atom in 1,3,5-triazine with carborane N- or S-nucleophiles. All new compounds were characterized by IR- and NMR spectroscopy. The structure of four new compounds was confirmed by single crystal X-ray diffraction analysis. The density functional theory method (DFT B3LYP/6-311 + G*) was used to study the geometrical structures, enthalpies of formation (EOFs), energetic properties and highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energies and the detonation properties of synthesized compounds. The DFT calculation revealed compounds processing the maximum value of the detonation velocity or the maximum value of the detonation pressure. Theoretical terahertz frequencies for potential high-energy density materials (HEDMs) were computed, which allow the opportunity for the remote detection of these compounds.

Improving performances of oxide solid electrolytes by a magnetic field for all-solid-state lithium-metal batteries

All-solid-state lithium-metal batteries have been regarded as the next-generation energy storage due to the potential high safety and high energy density. However, for oxide solid electrolytes (SEs), the relatively low ionic conductivities and the growth of lithium dendrite leading to safety issues limit their commercialization. Here, we systematically investigate the influences of external magnetic field on electrochemical performances of oxide SEs. It reveals that the magnetic field can improve ionic conductivity of SEs and the cycle performance in Li symmetric cells. The enhanced performance is because the magnetohydrodynamics effect can promote diffusion in SEs and homogenize distribution of lithium deposition to avoid the propagation of lithium dendrite. This strategy can be extent to other types of SEs or various energy applications.

Polymer hydrogel based quasi-solid-state sodium-ion supercapacitor with 2.5 V wide operating potential window and high energy density

The present work reports a quasi-solid state sodium ion-based asymmetric supercapacitor (ASC) device with nitrogen-doped reduced graphene oxide (NrGO) and boron-doped reduced graphene oxide (BrGO) electrodes. The choice of NrGO (BrGO) for the cathode (anode) is accomplished through a computational investigation of electrode quantum capacitances based on density functional theory (DFT). Nanocellulose is used as an electrode binder due to its biodegradability, enhanced wettability, good ion permeability, and low cost. The NaClO4-PVA based hydrogel membrane is the separator-less quasi-solid state gel electrolyte in the fabricated device. The specific capacitance of the NrGO || BrGO ASC device is obtained as 251.2 F g−1, at a current density of 1 A g−1 with a wide potential window of 2.5 V which is better than the previous reports. This device offers a better performance in comparison to the rGO||rGO, NrGO||NrGO and BrGO||BrGO symmetric supercapacitor (SSC) devices due to the synergistic effect of non-faradic capacitance and pseudocapacitance. The ASC device shows an energy density of 54.5 Wh kg−1 at a power density of 1.25 kW kg−1 and significant capacitance retention of 84.8% after 10,000 cycles at a high current density of 15 A g−1.

Polymerization of nitrogen in two theoretically predicted high-energy compounds ScN6 and ScN7 under modest pressure

Materials under high pressure usually exhibit unique chemical and physical properties. Polynitrogen compounds have received widespread attention as potential high energy density materials. This paper uses CALYPSO crystal structure prediction method to study the structures of ScN6 and ScN7 in 0–100 GPa. Theoretical calculations show that ScN6 is thermodynamically stable above 80 GPa, while ScN7 is thermodynamically stable from 30 GPa to 90 GPa. Furthermore, ScN7 is metastable under ambient conditions, demonstrating that it can be quenched to ambient conditions after high pressure synthesis. The P -ScN6 is a three-dimensional extended fold multi-nitrogen network, and the P -ScN7 contains a five-membered ring and a curved N4 molecular unit. Both P -ScN6 and P -ScN7 contain a lot of N–N single bonds and N=N double bonds. The energy densities of P -ScN6 and P -ScN7 are 3.97 kJ g−1 and 3.12 kJ g−1, respectively. The detonation velocity and detonation pressure of the P -ScN6 phase and P -ScN7 phase are also higher than that of TNT. Excellent energy storage properties and detonation performance show that they can be used as potential high-energy materials. These results opened up a new way for the synthesis of nitrogen-rich compounds.

Density functional theory investigation of triazole substituted nitro borazine derivatives as high energy density material

This work involves Density Functional Theory (DFT) investigation for prediction of nitrogen enriched boron based heterocyclic molecules for potential application as high energy density materials (HEDMs). The development of environment benign energetic materials as propellants, explosives, construction, military purposes and safety equipments are of immense interest. Boron based heterocyclic molecules with high nitrogen content have remarkable explosive properties. They are safe to the environment as their decomposition produces safe nitrogen gas instead of toxic hydrocarbons. In this work we have performed DFT calculations of thermodynamic properties and explosive characteristics of triazole substituted nitro borazine derivatives to assess their role as possible HEDMs. Effects of substitution of triazole group along boron atom and nitrogen atom have been investigated. Energetic properties that are important in deciding the explosive characteristics have been computed. Calculation of heat of formation through isodesmic reaction, detonation properties, heat of combustion etc. has been carried out. Further, crystal density, chemical stability and impact sensitivity have been analyzed. The designed molecules have nitrogen content of more than 48% and density in the range of 1.74–1.78 g/cm3. Impact sensitivity of the molecules indicates them as highly insensitive towards impact. Computed results in our investigation suggests that substitution of triazole ring along boron atom of the nitro borazine derivatives could be a potential high energy density material.

Synthesis of KVPO4F/Carbon Porous Single Crystalline Nanoplates for High-Rate Potassium-Ion Batteries.

With high theoretical capacity and operating voltage, KVPO4F is a potential high energy density cathode material for potassium-ion batteries. However, its performance is usually limited by F loss, poor electronic conductivity, and unsteady electrode/electrolyte interface. Herein, a simple one-step sintering process is developed, where vanadium-oxalate-phosphite/phosphate frameworks and fluorinated polymer are used to synthesize carbon-coated KVPO4F nanoplates. It is found that the V-F-C bond generated by fluorinated-polymer-derived carbon at the interface of KVPO4F/C nanoplates diminishes the F loss, as well as enhances K-ions migration ability and the electronic conductivity of KVPO4F. The as-synthesized KVPO4F/C cathode delivers a reversible capacity of 106.5 mAh g-1 at 0.2 C, a high working voltage of 4.28 V, and a rate capability with capacity of 73.8 mAh g-1 at the ultrahigh current density of 100 C. In addition, a KVPO4F/C//soft carbon full cell exhibits a high energy density of 235.5 Wh kg-1.

Ensemble learning directed classification and regression of hydrocarbon fuels

Predicting the properties of fuels based on their structures is essential to develop next generation fuels for various applications, e.g., aircraft, rocket, and missile. In this study, an ensemble learning assisted method has been developed for accurate and quick prediction of fuel properties based on their structures. Two descriptors of hydrocarbon molecules, continuous operable molecular entry specification (COMES) and Coulomb matrix (CM), are compared as the input of the learning model. The optimized stacking of various base learners, including Boosting, Bagging, NeuralNetwork, Trees, Voting, Linear, Neighbors and Kernel, have been achieved for efficient screening of potential high energy density fuels (HEDFs) and accurate prediction of fuel properties. Hydrocarbon molecules are efficiently classified into HEDFs and non-HEDFs based on their structures by the stacking model of ensemble learning, which exhibits superior generalization performance to the single learner. The properties of these potential HEDFs are accurately predicted by another stacking model, including density, heat value, freezing point, boiling point, flash point, and specific impulse. Both underfitting and overfitting have been effectively restricted by the COMES descriptor and the ensemble-learning model. Based on efficient classification and regression realized by our method, the discovery of new hydrocarbon fuels with specific criteria will be accelerated.

Solid Polymer Electrolyte Reinforced with a Li1.3Al0.3Ti1.7(PO4)3-Coated Separator for All-Solid-State Lithium Batteries.

Poly(ethylene oxide) (PEO)-based solid-state lithium batteries (SSLBs), accompanied by potential high energy density and reliable safety, have attracted wide attention. However, PEO-based solid-state electrolytes (SSEs) are hard to scale up due to their low oxidation stability, low ionic conductivity at room temperature, and relatively poor mechanical properties. Here, a PEO-based ceramic-polymer (PCP) composite SSE is designed. The porous Li1.3Al0.3Ti1.7(PO4)3 (LATP)-coated polyethylene (PE) separator is filled with PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution, which possesses both a robust mechanical property and processable flexibility. The results show the PCP membrane effectively suppresses the growth of lithium (Li) dendrites identified by a flat Li deposition. It is attributed to the robustness of the PCP membrane itself and the formation of a mixed ionic/electronic conducting interphase (MCI) intertwined with a solid electrolyte interface (SEI) between the PCP membrane and the Li anode. The MCI-SEI intertwined mixed phase facilitates the homogeneous Li deposition and enhances the cycle stability of the electrolyte/anode interface. Hence, the PCP membrane effectively prevents short-circuiting and shows a good cycling stability of more than 2000 h in a Li/PCP/Li symmetric cell with a current density of 0.2 mA cm-2 at 60 °C. Moreover, the Li/PCP/LiFePO4 all-solid-state battery shows a stable cycling performance with 160 mAh g-1 at 0.2C after 200 cycles at 60 °C. The results show the purposed PCP membrane based on a LATP-coated PE separator is easy to be fabricated and could be practical for many applications.

(Battery Division Postdoctoral Associate Research Award Address Sponsored by MTI Corporation and the Jiang Family Foundation) Advances in Understanding the Rechargeable Zinc-air Batteries Chemistry

As a possible post lithium-ion battery technology, metal-air batteries have revived interest recently. Among the different types of metal-air batteries, rechargeable zinc-air battery (ZAB) is a promising electrochemical energy storage device with the advantages of potential low cost, high safety, environmental friendliness and high energy density. However, current ZAB still suffer from the strongly alkaline electrolyte, which is chemically unstable towards the active cathode material (ambient air) and to a large extent causes electrochemical irreversibility at the Zn metal anode. Zn metal in alkaline environment suffers from formation of high surface area dendrites, well known from Li metal anodes, non-uniform electrodeposition/-dissolution, and persistent corrosion that consumes electrolyte. On the cathode side, the reaction between alkaline electrolytes and CO2 in air produces insoluble carbonate salts, which irreversibly consumes electrolyte, and also physically clogs and chemically deactivates the porous air cathode. Since the redox reaction of O2 occurs via a sluggish 4e-(electron) oxygen reduction reaction (ORR) in conventional alkaline electrolytes, bi-functional catalysts have to be used on the cathode.Herein, specific attention is given to the obstacles caused by the conventional alkaline electrolytes with the focus on the fundamental understanding in battery chemistry. Recently, we demonstrated a previous-unknown reversible zinc peroxide (ZnO2)/O2 chemistry for the rechargeable ZAB.[1] By comparing the hydrophobicity of anions of Zn salts, we selected the hydrophobic trifluoromethanesulfonate (OTf-) anion with a large size as a constituent of the electrolyte solute. Comprehensive characterization and simulations identified the critical role of hydrophobic OTf- anions in dictating the electrochemical double layer structure that favors the formation of ZnO2 and suppression of H2O-involved reactions. Leveraging the high reversibility of both air cathode and Zn metal anode in the Zn(OTf)2 electrolyte, the Zn-air full cell demonstrated excellent cycling performance in ambient air despite a simple cell structure. Such tailoring of interfacial structures via electrolyte properties provides a solution to the electrochemical irreversibility that has been plaguing not only alkaline ZABs, but essentially all metal-air batteries for centuries, especially those with promising high theoretical energy densities using materials with abundance, but being only feasible in alkaline electrolytes as either primary or mechanically rechargeable batteries.Keywords: Energy Storage, Zn-air batteries, Electrolytes, Battery ChemistryReferences [1] Wei Sun, Fei Wang, Bao Zhang, Mengyi Zhang, Verena Küpers, Xiao Ji, Claudia Theile, Peter Bieker, Kang Xu, Chunsheng Wang, Martin Winter, A rechargeable zinc-air battery based on zinc peroxide chemistry, Science 371, (2021) 46-51.

Design and properties of a new family of wing-like and propeller-like multi-tetrazole molecules as potential high-energy density compounds.

Density functional theory (DFT) methods were employed to design a new family of wing-like and propeller-like multi-tetrazole molecules based on the combination of N-center multi-tetrazole and various energetic groups. The optimized geometry, electronic properties, and thermodynamics were calculated for investigating the molecular stability and chemical reactivity. Their energetic parameters including density, heats of formation, detonation properties, and impact sensitivity were extensively evaluated, and the effects of energetic groups were investigated as well. These newly designed wing-like and propeller-like multi-tetrazole molecules exhibit acceptable oxygen balance, moderate impact sensitivities, high density, excellent heats of formation, and good detonation performance. Especially, B3, B4, B5, and B6 are very helpful for enhancing their detonation performance (D ≥ 9500m·s-1, P ≥ 41 GPa) are promising candidates for new environmentally friendly HEDMs.

Interface Improvement of Li6.4La3Zr1.6Ta0.6O12@La2Sn2O7 and Cathode Transfer Printing Technology with Splendid Electrochemical Performance for Solid-State Lithium Batteries.

All-solid-state lithium batteries (ASSLBs) are regarded as the next-generation energy storage devices due to their superior safety and potential high energy density. In ASSLBs, a composite solid electrolyte is the most competitive candidate. The interface between the cathode and composite electrolyte and the interface between ceramic and polymers are important factors affecting the performance of solid-state batteries. The interface between the superionic conductor and polymer electrolyte (polyvinylidene fluoride) was modified by in situ synthesis of a pyrochlore-type La2Sn2O7 (LSO) ceramic layer on the surface of Li6.4La3Zr1.4Ta0.6O12 (LLZTO). The synthesis of LSO consumes La in LLZTO, increases the concentration of lithium ions in LLZTO, and significantly improves the conductivity of the composite electrolyte (LLZTO@LSO-CSE). Compared with the pristine sample (3.15 × 10-5 S cm-1), the conductivity of LLZTO@0.9%LSO-CSE was improved by an order of magnitude (as high as 1.30 × 10-4 S cm-1). At the same time, the lithium-ion transference number of LLZTO@0.9%LSO-CSE and LLZTO@1.5%LSO-CSE was 0.42 and 0.44, respectively (LLZTO@0%LSO-CSE was 0.36). Meanwhile, the pyrochlore structure of LSO has the characteristics of fast energy storage and conversion, so the full cell LiFePO4|LLZTO@LSO-CSE|Li showed superior rate capability and cycling stability. As anticipated, the discharge capacities of LiFePO4|LLZTO@0.9%LSO-CSE|Li were 141.4 mA h g-1 (1 C) and 128.1 mA h g-1 (2 C), respectively. However, the discharge capacities of pristine batteries without LLZTO modification were 122.5 mA h g-1 (1 C) and 88.7 mA h g-1 (2 C). After 400 cycles, the discharge capacity of the LiFePO4|LLZTO@0.9%LSO-CSE|Li remained at 110.6 mA h g-1, the Coulomb efficiency was 99.4%, and the capacity retention rate was 72% compared to 75.5 mA h g-1, 98, and 49% for the pristine one, respectively. In addition, the transfer printing (TP) technology was used to improve the interface between the cathode and the solid-state electrolyte, which immensely increased the energy density (without aluminum foil). Compared with the original interface impedance of 379 Ω, the interface impedance was significantly reduced to 213 Ω. This uniquely developed LLZTO@LSO-CSE combined with the TP technology can provide an effective approach for the development of all-solid-state batteries.

New Potential High Energy Density Compounds: 7-Amino-6-nitro-[1,2,5]oxadiazolo[3,4-b]pyridine-1-oxide Derivatives

New Potential High Energy Density Compounds: 7-Amino-6-nitro-[1,2,5]oxadiazolo[3,4-b]pyridine-1-oxide Derivatives

Design of C-H-N-O based new hetero-cyclic high energy density molecules: a theoretical survey

Theoretical study of C-H-N-O based new high energy density molecules is modeled with well-known FOX-7 (1, 1 - dinitro 2, 2 - diamino ethylene) moiety. We have designed some new hetero-cyclic molecules which can serve as a potential high energy density molecule. We have reported the optimized structures, frequency calculations, thermal stability, impact sensitivity, natural bond orbital analysis and detonation properties of these molecules. A thorough analysis has been performed with the crystal density, the energy of activation for nitro (C-NO2) to nitrito (C-ONO) conversion and the C-NO2 bond dissociation energy of these molecules. Atoms in molecules (AIM) analysis has been done in order to get the stability of the weakest C-NO2 bond and the covalent character of the bonds. The electronic structure calculation has been performed at the B3LYP level of theory with aug-cc-pVDZ basis set by using G16 quantum chemistry package. These designed molecules have found to possess superior detonation properties than FOX-7 molecule and thus suggest for laboratory synthesis by expert experimentalists.

Solid-state electrolytes: Advances and perspectives

All-solid-state Li batteries (ASSLiBs) that use solid-state electrolytes (SSEs) to replace liquid organic electrolytes are considered as promising next-generation energy storage devices because of their wide electrochemical potential windows, high safety, and high energy density. Therefore, ASSLiBs have attracted a lot of attention in recent years. In this review, we focus on the main challenges on the synthesis and the electrochemical properties of the SSEs including (i) crystal structures and modification of kinetics of Li-ion migration through doping technology, (ii) synthesis technologies and its effect on the electrochemical performances of the SSEs, and (iii) ambient condition stability and degration of SSEs. Finally, perspectives of future researches on the SSEs are presented.

Revealing the structure design of alloyed based electrodes for alkali metal ion batteries with in situ TEM

With the guidance of in situ TEM, the high energy density alloyed based anode materials can be realized optimization structure design, thus obtaining excellent electrochemical performances in storing metal ions. Alloyed based anode materials with high theoretical specific capacity and low reaction potential are considered to be highly potential high-energy density anode materials for alkali metal ion batteries (AMIBs). Thus, the design of alloyed based materials with high electrochemical performance has attracted great attention. Among the numerous characterization methods for guiding electrode materials design, in situ transmission electron microscopy (TEM) gradually plays an irreplaceable role due to its high temporal and spatial resolution in directly observing the change of morphology, crystal structure and element evolutions. Herein, we reviewed the two current research hotspots and mainly focused on the structure design of alloyed based electrode material under the guidance of in situ TEM. Specifically, various nanostructure designs of alloyed based electrode materials with guidance of in situ TEM were employed to solve the key scientific issues of the violent volume change during alloying/dealloying processes for enhanced electrochemical performances. Mainly through introducing buffer space in the electrode material to reduce volume change to improve structural stability, including porous structure (0D), nanotube structure (1D), simple hollow structure, yolk-shell structure and some hybrid hollow structures (3D). Furthermore, the direct guidance of in situ TEM is expected for creating new opportunities to next-generation electrode material design for AMIBs.

Recent Advances and Perspectives on Calcium-Ion Storage: Key Materials and Devices.

The urgent demand for cost-effective energy storage devices for large-scale applications has led to the development of several beyond-lithium energy storage systems (EESs). Among them, calcium-ion batteries (CIBs) are attractive due to abundant calcium resources, excellent volumetric and gravimetric capacities of Ca metal anode, and potential high energy density coming from the multivalent feature of Ca-ion. Therefore, the exploration of CIBs electrode materials and the construction of CIBs devices are gaining increasing research interest. Relevant publications cover a wide range of materials by both theoretical and experimental investigations, whereas the performances of rocking-chair CIBs have been unsatisfactory. Meanwhile, multi-ion strategies using more than one ion as the charge carrier have been demonstrated to be feasible and promising options in realizing room temperature CIBs. The summary and reflection of previous studies would provide useful information for future exploration and optimization. In this circumstance, this paper overviews the reported CIBs electrode materials, including both anode and cathode, and presents the latest progress of multi-ion strategies in CIBs. Fundamental challenges, potential solutions, and opportunities are accordingly proposed, mimicking other more mature EESs. This review may promote the development of electrode materials and accelerate the construction of low-cost and high-performance CIBs.

Analysis of Li Deposition/Dissolution Behavior on the Interphase between Li Metal Anode and Glyme-Based Electrolytes for Li-Air Batteries

In recent years, rechargeable Li-air batteries (LAB) have attracted much attention because of their potential high energy density over 5 times larger than that of the conventional Li-ion batteries [1]. However, there are many problems still to be solved for all the cell components: the cathode, anode and electrolyte solution. As for the anode, Li dendrite growth during discharge/charge cycles should be suppressed to stabilize the cycle life of the LAB. In order to improve the reversibility of the Li electrode, we have been evaluating tetraglyme (G4)-based electrolyte solutions by using a Li|Li symmetric cell [2]. We confirmed that a 1.0 M LiNO3/G4 electrolyte solution containing O2 formed a Li2O protective layer on the Li surface effectively, which suppressed the formation of Li dendrite at the current density of 0.2 mA cm-2. In this study, high rate tests up to 2.0 mA cm-2 above our target of 0.4 mA cm-2 were applied to verify and analyze the reversibility of Li electrode reaction.LiN(SO2CF3)2 (LiTFSI, 99.9%, KISHIDA) and LiNO3 (99.9% purity, Wako) were vacuum- dried at 110 °C and dissolved in tetraglyme (G4, Japan Advanced Chemicals, H2O < 30 ppm) solvent to prepare 1.0 M glyme electrolyte solution of each electrolyte salt. Li|Li symmetric cells with 1.0 M LiNO3/G4 or 1.0 M LiTFSI/G4 electrolyte solution were assembled in an Ar-filled glove box to be used for Li dissolution/deposition tests in an isothermal chamber set at 30°C at a constant current from 0.2 to 2.0 mA cm-2. The surface of the Li electrodes after the dissolution/deposition test and its cross-section were observed by SEM-EDS and analyzed by elementary analysis. In addition, the outermost surface was analysed by using XPS.The flatness of the polarization curve for dissolution/deposition tests in the 1.0 M LiNO3/G4 electrolyte suggests that Li dendrite growth and electrolyte decomposition are suppressed at an applied current of 0.6 mA cm-2 or less. Fig. 1 shows the SEM image of the Li electrode surface after the dissolution/deposition test. Although no large dendrites were observed in the LiNO3/G4 electrolyte, the entire surface was covered with fine Li dendrites of about 100 nm in diameter and about 800 nm long in the LiTFSI one (Fig. 1a & c). In addition, the cross-sectional SEM image of the Li surface tested in the LiNO3/G4 electrolyte shows some pits, while that in the LiTFSI/G4 electrolyte solution exhibits bulky decomposition product layer of about 20 μm thick accompanying a larger crevices (Fig. 1b & d).C 1s spectra of XPS showed a dominant signal assigned to Li2CO3 on the electrodes tested at higher rates, which suggested the formation of the protective layer of Li2CO3 and Li2O. Moreover, weak signals such as C-C and C-O detected on the Li surface in LiNO3/G4 electrolyte solution suggested the suppressed degradation. The details of the mechanism will be discussed on our presentation.This study was supported by JST “Next Generation Batteries Area in Advanced Low Carbon Technology Research and Development Program (ALCA)” from MEXT, Japan.[1] P. G. Bruce, S. A. Freunber, L. J. Hardwick, J-M. Tarascon, Nature materials, 11, 19 (2012).[2] M. Saito, S. Yamada, T. Fujinami, S. Kosaka, Y. Tachikawa, K. Ito, Y. Kubo, ECS Trans., 75(22), 53 (2017). Figure 1

First principles investigation of electron correlation and Lifshitz transition within iron polynitrides

Metal poly-nitrogen compounds are gaining great interests as potential high energy density materials. Several iron polynitrides have been recently synthesized and investigated under high pressure (2018 Nature Communications 9 2756). In this work the electron correlations within these iron poly-nitrogen compounds were self-consistently determined, benchmarked with those obtained from linear response approach. Along with the increase of the concentration of nitrogen, the Coulomb interaction strengths show a monotonic decrease, where FeN and FeN2 are antiferromagnetic and the others are ferromagnetic. Then the electron correlation is studied along with the pressure, where the electrons are more delocalized as pressure becomes higher. One electronic topological transition was found for FeN2, owing to a breaking of symmetry of spin and a transition of magnetism induced by a structural change. The band structure, densities of states, Fermi surface and absorption spectra were calculated and discussed.