Phylogeography of the widespread plant Ailanthus altissima (Simaroubaceae) in China indicated by three chloroplast DNA regions

Ailanthus altissima (Mill.) Swingle, a temperate tree species, has a wide distribution in China. To infer its refugia and patterns of migration during past climatic changes in China, genetic variations among different populations were studied. Gene sequences of three chloroplast DNA spacer regions, psbA-trnH, trnL-trnF, and trnD-trnT, were obtained from 440 individuals of 44 populations. The distribution of haplotype and the relationships among them were investigated by haplotype network. In addition, the genetic diversity of the sampled regions was inferred, and the biogeographic history was also reconstructed. Twelve haplotypes were identified, among which, five were unique. The phylogenetic analysis and geographical distribution of haplotypes indicate that multiple glacial refugia existed in mainland China during the Quaternary oscillations. Due to the combined effects of contiguous range expansion and allopatric fragmentation, significant genetic structure was not found in this study. Based on biogeographic and demographic analysis, three main dispersal routes were identified for the major haplotypes, whereas others were more likely localized demographic expansion

Layered Lithium-Rich Oxide Nanoparticles Doped with Spinel Phase: Acidic Sucrose-Assistant Synthesis and Excellent Performance as Cathode of Lithium Ion Battery

Nanolayered lithium-rich oxide doped with spinel phase is synthesized by acidic sucrose-assistant sol–gel combustion and evaluated as the cathode of a high-energy-density lithium ion battery. Physical characterizations indicate that the as-synthesized oxide (LR-SN) is composed of uniform and separated nanoparticles of about 200 nm, which are doped with about 7% spinel phase, compared to the large aggregated ones of the product (LR) synthesized under the same condition but without any assistance. Charge/discharge demonstrates that LR-SN exhibits excellent rate capability and cyclic stability: delivering an average discharge capacity of 246 mAh g^–1 at 0.2 C (1C = 250 mA g^–1) and earning a capacity retention of 92% after 100 cycles at 4 C in the lithium anode-based half cell, compared to the 227 mA g^–1 and the 63% of LR, respectively. Even in the graphite anode-based full cell, LR-SN still delivers a capacity of as high as 253 mAh g^–1 at 0.1 C, corresponding to a specific energy density of 801 Wh kg^–1, which are the best among those that have been reported in the literature. The separated nanoparticles of the LR-SN provide large sites for charge transfer, while the spinel phase doped in the nanoparticles facilitates lithium ion diffusion and maintains the stability of the layered structure during cycling

Sodium Intercalation Behavior of Layered Na_<i>x</i>NbS₂ (0 ≤ <i>x</i> ≤ 1)

A layered sulfide, Na_0.5NbS₂ (space group: <i>P</i>6₃/<i>mmc</i>), was synthesized by a conventional solid-state reaction as an electrode material for a Na-ion battery. Galvanostatic Na insertion/extraction was performed to characterize the system Na_<i>x</i>NbS₂ (0 ≤ <i>x</i> ≤ 1.0) operating on the Nb­(IV)/Nb­(III) redox couple. Although the system shows a high specific capacity of 143.6 mAh g^–1, the voltage profile is not suitable with a signature of Na/vacancy ordering at <i>x</i> = 0.5. First-principles calculation was applied to reveal possible structures of Na_<i>x</i>NbS₂ and describe the corresponding electrochemical properties. The calculated Na binding energies and voltages are in good agreement with experimental charge/discharge voltages. We also found a possible atomic arrangement of Na/vacancy ordering in Na_0.5NbS₂. Although layered NaMS₂ systems allow full sodium intercalation, the strong Na⁺–Na⁺ intralayer interaction induces layer gliding and Na⁺-ion ordering that create undesirable steps in the voltage profile

Constructing Unique Cathode Interface by Manipulating Functional Groups of Electrolyte Additive for Graphite/LiNi_0.6Co_0.2Mn_0.2O₂ Cells at High Voltage

A novel electrolyte additive, 1-(2-cyanoethyl) pyrrole (CEP), has been investigated to improve the electrochemical performance of graphite/LiNi_0.6Co_0.2Mn_0.2O₂ cells cycling up to 4.5 V vs Li/Li⁺. The 4.5 V cycling results present that after 50 cycles, up to 4.5 V capacity retention of the graphite/LiNi_0.6Co_0.2Mn_0.2O₂ cell is improved significantly from 27.4 to 81.5% when adding 1% CEP to baseline electrolyte (1 M LiPF₆ in EC/EMC 1:2, by weight). Ex situ characterization results support the mechanism of CEP for enhancing the electrochemical performance. On one hand, the significant enhancement is ascribed to a formed superior cathode interfacial film by preferential oxidation of CEP on the cathode electrode surface suppressing electrolyte decomposition at high voltage. On the other hand, the duo Lewis base functional groups can effectively capture dissociation product PF₅ from LiPF₆ with the presence of an unavoidable trace amount of water or aprotic impurities in the electrolyte. Thus this mitigates the hydrofluoric acid (HF) generation that leads to the reduction of transition-metal dissolution in the electrolyte upon cycling at high voltage. The theoretical modeling suggests that CEP has a mechanism of stabilizing electrolyte via combination of CN: functional group and H₂O. The work presented here also shows nuclear magnetic resonance spectra analysis to prove the capability of CEP reducing HF generation and X-ray photoelectron spectroscopy analysis to observe cathode surface composition

Structural Exfoliation of Layered Cathode under High Voltage and Its Suppression by Interface Film Derived from Electrolyte Additive

Layered cathodes for lithium-ion battery, including LiCo_{1–<i>x</i>–<i>y</i>}Ni_<i>x</i>Mn_<i>y</i>O₂ and <i>x</i>Li₂MnO₃·(1–<i>x</i>)­LiMO₂ (M = Mn, Ni, and Co), are attractive for large-scale applications such as electric vehicles, because they can deliver additional specific capacity when the end of charge voltage is improved to over 4.2 V. However, operation under a high voltage might cause capacity decaying of layered cathodes during cycling. The failure mechanisms that have been given, up to date, include the electrolyte oxidation decomposition, the Ni, Co, or Mn ion dissolution, and the phase transformation. In this work, we report a new mechanism involving the exfoliation of layered cathodes when the cathodes are performed with deep cycling under 4.5 V in the electrolyte consisting of carbonate solvents and LiPF₆ salt. Additionally, an electrolyte additive that can form a cathode interface film is applied to suppress this exfoliation. A representative layered cathode, LiCoO₂, and an interface film-forming additive, dimethyl phenylphosphonite (DMPP), are selected to demonstrate the exfoliation and the protection of layered structure. When evaluated in half-cells, LiCoO₂ exhibits a capacity retention of 24% after 500 cycles in base electrolyte, but this value is improved to 73% in the DMPP-containing electrolyte. LiCoO₂/graphite full cell using DMPP behaves better than the Li/LiCoO₂ half-cell, delivering an initial energy density of 700 Wh kg ^–1 with an energy density retention of 82% after 100 cycles at 0.2 C between 3 and 4.5 V, as compared to 45% for the cell without using DMPP