Poly(2,5-dihydroxy-1,4-benzoquinonyl sulfide) (PDBS) as a cathode material for lithium ion batteries

An organic cathode material, poly(2,5-dihydroxyl-1,4-benzoquinonyl sulfide) (PDBS), has been synthesized and assessed as a cathode material for lithium ion batteries. The prepared polymer material is characterized by (13)C solid state NMR, FTIR, XPS and elemental analysis techniques. The (13)C solid state NMR, FTIR and XPS results indicate that the chlorine of chloranilic acid (CLA) is successfully substituted by sulfur after a sulfurization reaction. Elemental analysis shows that the prepared polymer is mainly composed of dimer and trimer. The electrochemical measurements show that the initial discharge capacity of PDBS is up to 350 mAh g(-1), and 184 mAh g(-1) still remains after 100 cycles at the current density of 15 mA g(-1) in the voltage range of 1.5-3.6 V. The PDBS also shows high cycling stability, good rate capability and discharge/ charge coulombic efficiency of higher than 98%, except for in the initial cycles. The good cycling stabilities and the high coulombic efficiency of the material are ascribed to the stable thioether bonds for stabilizing the framework of the polymer and the highly reversible carbonyl groups for energy storage.National Natural Science Foundation of China[20873115]; National Basic Research Program of China (973 program)[2007CB209702

Quasi-Solid-State Ion-Conducting Arrays Composite Electrolytes with Fast Ion Transport Vertical-Aligned Interfaces for All-Weather Practical Lithium-Metal Batteries

The rapid improvement in the gel polymer electrolytes (GPEs) with high ionic conductivity brought it closer to practical applications in solid-state Li-metal batteries. The combination of solvent and polymer enables quasi-liquid fast ion transport in the GPEs. However, different ion transport capacity between solvent and polymer will cause local nonuniform Li$^+$ distribution, leading to severe dendrite growth. In addition, the poor thermal stability of the solvent also limits the operating-temperature window of the electrolytes. Optimizing the ion transport environment and enhancing the thermal stability are two major challenges that hinder the application of GPEs. Here, a strategy by introducing ion-conducting arrays (ICA) is created by vertical-aligned montmorillonite into GPE. Rapid ion transport on the ICA was demonstrated by $^6$Li solid-state nuclear magnetic resonance and synchrotron X-ray diffraction, combined with computer simulations to visualize the transport process. Compared with conventional randomly dispersed fillers, ICA provides continuous interfaces to regulate the ion transport environment and enhances the tolerance of GPEs to extreme temperatures. Therefore, GPE/ICA exhibits high room-temperature ionic conductivity (1.08 mS cm$^{−1}$) and long-term stable Li deposition/stripping cycles (> 1000 h). As a final proof, Li||GPE/ICA||LiFePO$_4$ cells exhibit excellent cycle performance at wide temperature range (from 0 to 60 °C), which shows a promising path toward all-weather practical solid-state batteries

Quantitatively analyzing the failure processes of rechargeable Li metal batteries.

Practical use of lithium (Li) metal for high–energy density lithium metal batteries has been prevented by the continuous formation of Li dendrites, electrochemically isolated Li metal, and the irreversible formation of solid electrolyte interphases (SEIs). Differentiating and quantifying these inactive Li species are key to understand the failure mode. Here, using operando nuclear magnetic resonance (NMR) spectroscopy together with ex situ titration gas chromatography (TGC) and mass spectrometry titration (MST) techniques, we established a solid foundation for quantifying the evolution of dead Li metal and SEI separately. The existence of LiH is identified, which causes deviation in the quantification results of dead Li metal obtained by these three techniques. The formation of inactive Li under various operating conditions has been studied quantitatively, which revealed a general “two-stage” failure process for the Li metal. The combined techniques presented here establish a benchmark to unravel the complex failure mechanism of Li metal

Promoting long-term cycling performance of high-voltage Li2CoPO4F by the stabilization of electrode/electrolyte interface

National Basic Research Program of China (973 program) [2011CB935903]; National Natural Science Foundation of China [21233004, 21021002]High-voltage Li2CoPO4F (similar to 5 V vs. Li/Li+) with double-layer surface coating has been successfully prepared for the first time. The Li3PO4-coated Li2CoPO4F shows a high reversible capacity of 154 mA h g(-1) (energy density up to 700W h kg(-1)) at 1 C current rate, and excellent rate capability (141 mA h g(-1) at 20 C). XRD and MAS NMR results show that Li2CoPO4F can be indexed as an orthorhombic structure with space group Pnma and coexists with Li3PO4. The XPS depth profiles and TEM analysis reveal that the as-prepared material has a double-layer surface coating, with a carbon outer layer and a Li3PO4 inner layer, which greatly enhances the transfer kinetics of the lithium ions and electrons in the material and stabilizes the electrode/electrolyte interface. Using LiBOB as an electrolyte additive is another way to further stabilize the electrode/electrolyte interface, and the LiBOB has a synergistic effect with the Li3PO4 coating layer. In this way, the Li2CoPO4F cathode material exhibits excellent long-term cycling stability, with 83.8% capacity retention after 150 cycles. The excellent cycling performance is attributed to the LiBOB electrolyte additive and the Li3PO4 coating layer, both of which play an important role in stabilizing the charge transfer resistance of Li2CoPO4F upon cycling

Promoting long-term cycling performance of high-voltage Li 2CoPO4F by the stabilization of electrode/electrolyte interface

High-voltage Li2CoPO4F (～5 V vs. Li/Li +) with double-layer surface coating has been successfully prepared for the first time. The Li3PO4-coated Li 2CoPO4F shows a high reversible capacity of 154 mA h g-1 (energy density up to 700 W h kg-1) at 1 C current rate, and excellent rate capability (141 mA h g-1 at 20 C). XRD and MAS NMR results show that Li2CoPO4F can be indexed as an orthorhombic structure with space group Pnma and coexists with Li 3PO4. The XPS depth profiles and TEM analysis reveal that the as-prepared material has a double-layer surface coating, with a carbon outer layer and a Li3PO4 inner layer, which greatly enhances the transfer kinetics of the lithium ions and electrons in the material and stabilizes the electrode/electrolyte interface. Using LiBOB as an electrolyte additive is another way to further stabilize the electrode/electrolyte interface, and the LiBOB has a synergistic effect with the Li3PO 4 coating layer. In this way, the Li2CoPO4F cathode material exhibits excellent long-term cycling stability, with 83.8% capacity retention after 150 cycles. The excellent cycling performance is attributed to the LiBOB electrolyte additive and the Li3PO 4 coating layer, both of which play an important role in stabilizing the charge transfer resistance of Li2CoPO4F upon cycling. ? 2014 The Royal Society of Chemistry

P2-Na0.67 Alx Mn1-x O2 : Cost-Effective, Stable and High-Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility.

Sodium layered P2-stacking Na0.67 MnO2 materials have shown great promise for sodium-ion batteries. However, the undesired Jahn-Teller effect of the Mn4+ /Mn3+ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition-metal layers to decrease the number of Mn3+ , we obtain the low cost pure P2-type Na0.67 Alx Mn1-x O2 (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al-doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid-state NMR techniques. Our results reveal that Al-doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na+ layer thus producing a remarkable rate capability of 96 mAh g-1 at 1200 mA g-1

Unraveling (electro)-chemical stability and interfacial reactions of Li 10 SnP 2 S 12 in all-solid-state Li batteries

Abstract(#br)Li 10 SnP 2 S 12 (LSPS) with high ionic conductivity and moderate price is a promising solid electrolyte for all-solid-state batteries. However, the instability of LSPS and LSPS/electrodes interfaces would cause poor cycle performance issues in the LSPS-based all-solid-state batteries, which have not been well understood. Herein, we address and unravel the decomposition products of LSPS and their Li + transfer characteristics, especially on the surface of LSPS/electrodes by using solid-state nuclear magnetic resonance (ss NMR) spectroscopy coupled with X-ray photoelectron spectroscopy (XPS). The results reveal that the high mechanical energy during ball-milling process leads to the decomposition of LSPS into Li 4 SnS 4 and Li 3 PS 4 . During charge/discharge cycling, specific capacity fading of batteries originates from the formation of new interfacial layer at LSPS/Acetylene black cathode and LSPS/Li metal anode interfaces. Furthermore, our results demonstrate that the rough and porous morphology of the interface formed after cycling, rather than the decomposition products, is the critical factor which results in the increases of the interfacial resistance at LSPS/Li interface and serious formation of Li dendrite. Our results highlight the significant roles of (electro)chemical and interfacial stability of sulfide solid electrolyte in the development of all-solid-state batteries

Additives synergy for stable interface formation on rechargeable lithium metal anodes

Abstract(#br)The attention towards lithium (Li) metal anodes has been rekindled in recent years as it would boost the energy-density of Li batteries. However, notorious safety issues and cycling instability severely hinder their commercialization, especially when cycled in traditional carbonic ester electrolytes that exhibit a wide voltage window and are compatible with most of the cathode materials. Herein, lithium difluorophosphate (LiDFP) and vinylene carbonate (VC) are combined, and demonstrated to be synergistic in constructing in situ a mechanically stable and highly Li-ion conducting surface film on the Li metal anode. This results in uniform and compact Li deposition largely suppressing the formation of Li dendrites, dead lithium and irreversible Li-species as revealed by operando neutron depth profiling (NDP). This enables long-term cycling stability and enhancement of the Coulombic efficiency for rechargeable Li metal anodes. By combining solid state nuclear magnetic resonance (SSNMR) and spectroscopic studies, it is demonstrated that VC slows down the LiDFP reduction, yet promoting the breaking of the P–F bonds, which leads to a protective film. This film is rich in LiF–Li 3 PO 4 inorganic compounds, distributed homogeneously, that is embedded in a matrix of P–O–C species and macromolecular organic compounds like lithium ethylene dicarbonate. This composition is responsible for the improved ionic conductivity and mechanical stability of the protective film during extended cycles. The detailed insight in the additives interaction provides new opportunities for the design of rational surface films necessary for realizing high-performance lithium metal batteries

Evolutionary trajectory of the replication mode of bacterial replicons

As typical bacterial replicons, circular chromosomes replicate bidirectionally and circular plasmids replicate either bidirectionally or unidirectionally. Whereas the finding of chromids (plasmid-derived chromosomes) in multiple bacterial lineages provides circumstantial evidence that chromosomes likely evolved from plasmids, all experimentally assayed chromids were shown to use bidirectional replication. Here, we employed a model system, the marine bacterial genus Pseudoalteromonas, members of which consistently carry a chromosome and a chromid. We provide experimental and bioinformatic evidence that while chromids in a few strains replicate bidirectionally, most replicate unidirectionally. This is the first experimental demonstration of the unidirectional replication mode in bacterial chromids. Phylogenomic and comparative genomic analyses showed that the bidirectional replication evolved only once from a unidirectional ancestor and that this transition was associated with insertions of exogenous DNA and relocation of the replication terminus region (ter2) from near the origin site (ori2) to a position roughly opposite it. This process enables a plasmid-derived chromosome to increase its size and expand the bacterium’s metabolic versatility while keeping its replication synchronized with that of the main chromosome. A major implication of our study is that the uni- and bidirectionally replicating chromids may represent two stages on the evolutionary trajectory from unidirectionally replicating plasmids to bidirectionally replicating chromosomes in bacteria. Further bioinformatic analyses predicted unidirectionally replicating chromids in several unrelated bacterial phyla, suggesting that evolution from unidirectionally to bidirectionally replicating replicons occurred multiple times in bacteria

High-Power-Density, High-Energy-Density Fluorinated Graphene for Primary Lithium Batteries

Li/CFx is one of the highest-energy-density primary batteries; however, poor rate capability hinders its practical applications in high-power devices. Here we report a preparation of fluorinated graphene (GFx) with superior performance through a direct gas fluorination method. We find that the so-called “semi-ionic” C-F bond content in all C-F bonds presents a more critical impact on rate performance of the GFx in comparison with sp2 C content in the GFx, morphology, structure, and specific surface area of the materials. The rate capability remains excellent before the semi-ionic C-F bond proportion in the GFx decreases. Thus, by optimizing semi-ionic C-F content in our GFx, we obtain the optimal x of 0.8, with which the GF0.8 exhibits a very high energy density of 1,073 Wh kg−1 and an excellent power density of 21,460 W kg−1 at a high current density of 10 A g−1. More importantly, our approach opens a new avenue to obtain fluorinated carbon with high energy densities without compromising high power densities