Rechargeable Li-metal batteries using high-voltage cathodes can deliver the highest possible energy densities among all electrochemistries. However, the notorious reactivity of metallic lithium as well as the catalytic nature of high-voltage cathode materials largely prevents their practical application. Here, we report a non-flammable fluorinated electrolyte that supports the most aggressive and high-voltage cathodes in a Li-metal battery. Our battery shows high cycling stability, as evidenced by the efficiencies for Li-metal plating/stripping (99.2%) for a 5 V cathode LiCoPO (~99.81%) and a Ni-rich LiNiMnCoO cathode (~99.93%). At a loading of 2.0 mAh cm, our full cells retain ~93% of their original capacities after 1,000 cycles. Surface analyses and quantum chemistry calculations show that stabilization of these aggressive chemistries at extreme potentials is due to the formation of a several-nanometre-thick fluorinated interphase.

Sodium ion batteries (SIBs) have been considered as a top alternative to lithium ion batteries due to the earth abundance and low cost of sodium compared with lithium. Among all proposed anode materials for SIBs, red phosphorus (P) is a very promising candidate because it has the highest theoretical capacity (∼2600 mAh/g). In this study, a red P-single-walled carbon nanotube (denoted as red P-SWCNT) composite, in which red P is uniformly distributed between tangled SWCNTs bundles, is fabricated by a modified vaporization-condensation method. Benefiting from the nondestructive preparation process, the highly conductive and mechanically strong SWCNT network is preserved, which enhances the conductivity of the composite and stabilizes the solid electrolyte interphase. As a result, the red P-SWCNT composite presents a high overall sodium storage capacity (∼700 mAh/gcomposite at 50 mA/gcomposite), fast rate capability (∼300 mAh/gcomposite at 2000 mA/gcomposite), and stable long-term cycling performance with 80% capacity retention after 2000 sodiation-desodiation cycles. The red P-SWCNT composite fabricated by the vaporization-condensation method significantly extends the cycling stability of P/carbon composite from current ∼100 cycles to ∼2000 cycles.

The lithium metal anode is considered as the ultimate choice for high-energy-density batteries. However, the organic-dominated solid electrolyte interphase (SEI) formed in carbonate electrolytes has a low interface energy against metallic Li as well as a high resistance, resulting in a low Li plating/stripping Coulombic efficiency (CE) of less than 99.0% and severe Li dendrite growth. Herein, inorganic-enhanced LiF-Li3N SEI is designed in commercial 1 M LiPF6/EC-DMC electrolytes by introducing lithium nitrate (LiNO3) and fluoroethylene carbonate (FEC) through a small amount of sulfolane (SL) as a carrier solvent owing to the high solubility of SL for both carbonate solvents and LiNO3. The comprehensive characterizations and simulations demonstrate that the synergistic interaction of LiNO3 and FEC additives alters the solvation structure of 1 M LiPF6/EC-DMC electrolytes and forms additive-derived LiF-Li3N SEI, which increases the average Li CE up to 99.6% in 100 cycles. The designed carbonate electrolyte enables the Li/LiNi0.80Co0.15Al0.05O2 (NCA) cell with a lean lithium metal anode (∼50 μm) to achieve an average CE of 99.7% and a high capacity retention of 90.8% after 150 cycles. This work offers a simple and economical strategy to realize high-performance lithium metal batteries in commercial carbonate electrolytes.

In ballistic thermal conduction, the wave characteristics of phonons allow the transmission of energy without dissipation. However, the observation of ballistic heat transport at room temperature is challenging because of the short phonon mean free path. Here we show that ballistic thermal conduction persisting over 8.3 µm can be observed in SiGe nanowires with low thermal conductivity for a wide range of structural variations and alloy concentrations. We find that an unexpectedly low percentage (∼0.04%) of phonons carry out the heat conduction process in SiGe nanowires, and that the ballistic phonons display properties including non-additive thermal resistances in series, unconventional contact thermal resistance, and unusual robustness against external perturbations. These results, obtained in a model semiconductor, could enable wave-engineering of phonons and help to realize heat waveguides, terahertz phononic crystals and quantum phononic/thermoelectric devices ready to be integrated into existing silicon-based electronics.

The continuous pulverization of alloy anodes during repeated sodiation/desodiation cycles is the major reason for the faster capacity decay. However, if these elements can form a compound (such as Sn 4 P 3 ) after each Na extraction, the pulverization of these elements can be partially repaired and the accumulation of pulverization can be terminated. Therefore, we can use the reversible conversion reaction (Sn 4 P 3 + 9Na ↔ 3Na 3 P + 4Sn) to terminate the continuous pulverization and aggregation of Sn in alloy reaction (4Sn + 15Na ↔ Na 15 Sn 4 ) in the sodiation/desodiation cycles. Therefore, the pulverization of Sn and P during alloy process can be partially self-healed (recovered) by the conversion reaction process. The drastic enhancement in cycle stability of Sn 4 P 3 /C composites compared to individual Sn and P anodes has been reported, [ 6,22 ] where the reversible conversion reaction of Sn 4 P 3 during sodiation/desodiation has been identifi ed. [ 6 ] The reversible conversion reaction can only self-heal the pulverization and aggregation induced in followed alloy reaction by recombining the cracked Sn and P back to P-Sn compounds in each cycle to avoid the crack propagation and Sn and P aggregation, thus improving the cycle stability of alloy reaction anodes to the cycling life of conversion reaction anodes with much high capacity.

CdSe quantum dots have been encapped with aromatic ligands: a-toluenethiol, thiophenol, and p-hydroxythiophenol to enhance the photoluminescence (PL) quenching and photoelectric properties of the quantum dots. The aromatic ligand capped CdSe quantum dots are prepared through ligand exchange with trioctylphosphine oxide (TOPO) capped CdSe quantum dots. The XPS surface chemistry analysis and elemental analysis has confirmed the success of ligand exchange from TOPO to aromatic ligands. Both XRD and HRTEM-SAED studies indicate the crystalline structure of CdSe quantum dots not only remains but is also improved by the ligand exchange of TOPO with thiol molecules. Time resolved PL decay measurements indicate thiophenol and p-hydroxythiophenol ligands effectively quench the emission and have much shorter PL lifetimes than that of TOPO and that of a-toluenethiol. Thus, both thiophenol and p-hydroxythiophenol can act as an effective acceptor for photogenerated holes through aromatic p-electrons. Thiophenol also exhibits good charge transport behavior showing a 10-fold increase in short circuit current density (I sc ) as compared with TOPO in the photocurrent study of fabricated photovoltaic devices.

exceptional battery performance is still a significant challenge at high temperatures due to the structural degradation caused by the fast transfer of alkali-ions. [4] Therefore, Li-ion batteries have been intensively investigated as high temperature batteries owing to the smallest ion size of Li among the alkali-ions. [4,5] Nevertheless, the scarcity and unevenly global distribution of Li resource is an obstacle for the further development of Li-ion batteries. [3,6] One promising strategy to replace Li-ion batteries is developing hightemperature K-ion batteries (KIBs), which have distinguished advantages among alkali-ion batteries, e.g., the significantly more abundance of K than Li (2.09 vs 0.0017 wt% in the Earth crust) and lower redox potential of K + /K than Na + /Na (−2.93 vs −2.71 V). [3,6,7] All these merits ensure KIBs provide clean energy with low cost and high energy density. However, the larger ion size of K + than Li + and Na + results in a significant structural deterioration for the conversion and intercalation electrodes. The conversion electrodes suffer from a large volume change that is tremendously significant in KIBs, [4,8,9] while the capacity of the intercalation electrodes is very low. [10,11] As reported by Amine's group, stabilizing the material surface is the key factor for cycling Li-ion batteries at high temperatures such as 55 °C. [12] Thus, it is extremely challenging for KIB electrodes to withstand a temperature above 55 °C, due to the less stable solid electrolyte interphase (SEI) compared to the Li counterpart. [13] Herein, we designed an organic anode that stores K-ions through surface reaction for high-temperature KIBs beyond the current operating temperature of 55 °C with high rate capability and long cycle life. Azobenzene-4,4′-dicarboxylic acid potassium salts (ADAPTS) with a redox center of azo group (NN) is selected to reversibly react with K + , as shown in Figure 1a. Different from the conversion and intercalation reactions, ADAPTS with surface reaction can largely retain the structural stability during the reversible electrochemical reactions between azo group and K + even at a high temperature. Furthermore, organic compounds are ideal electrode materials for clean energy applications since they are inexpensive and sustainable. [14,15] At the ambient temperature, the ADAPTS anode delivers a reversible capacity of 109 mAh g −1 at 0.1C for 100 cycles and a long-term cycle life of 1000 cycles is achievedThe wide applications of rechargeable batteries require state-of-the-art batteries that are sustainable (abundant resource), tolerant to hightemperature operations, and excellent in delivering high capacity and longterm cycling life. Due to the scarcity and uneven distribution of lithium, it is urgent to develop alternative rechargeable batteries. Herein, an organic compound, azobenzene-4,4′-dicarboxylic acid potassium salts (ADAPTS) is developed, with an azo group as the redox center for high performance potassium-ion batteries (KIBs). The extended π-conjugated structure i...

Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1. However, poor electrochemical reversibility due to repeated breaking/reformation of metal fluoride bonds poses a grand challenge for its practical application. Here we report that both a high reversibility over 1000 cycles and a high capacity of 420 mAh g−1 can be realized by concerted doping of cobalt and oxygen into iron fluoride. In the doped nanorods, an energy density of ~1000 Wh kg−1 with a decay rate of 0.03% per cycle is achieved. The anion’s and cation’s co-substitutions thermodynamically reduce conversion reaction potential and shift the reaction from less-reversible intercalation-conversion reaction in iron fluoride to a highly reversible intercalation-extrusion reaction in doped material. The co-substitution strategy to tune the thermodynamic features of the reactions could be extended to other high energy conversion materials for improved performance.