Electromigration Separation of Lithium Isotopes: The Effect of Electrode Solutions

Both lithium-6 and lithium-7 with high abundance are indispensable materials in nuclear industry. Here, an aqueous solution│organic solution│aqueous solution system was fabricated to separate lithium isotopes. The effects of species and concentration of electrolytes in the electrode solutions on the lithium ions migration and lithium isotope separation with different voltages and migration time was studied. It was found that lithium-7 was enriched in aqueous solutions on both sides at 0 V and 2 V, while lithium-7 was enriched in anode solution and lithium-6 was enriched in cathode solution at 16 V. The weakening stability of the chelate consisted of crown ether and lithium ion with increasing voltage was believed to the possible reason. Meanwhile, the variation of electrolyte in electrode solution led to notable changes in migration ratio of lithium ions and lithium isotope separation effect, which can be attributed to the different degree of both ionization and hydrolysis for various electrolytes in aqueous solutions and the different ability of H+ and NH4+ to replace Li+ of chelate in organic solutions. This work is of great significance for the selection of electrode solutions in electromigration separation of lithium isotopes and even other electrochemical systems.

LLCZN/PEO/LiPF6 Composite Solid-State Electrolyte for Safe Energy Storage Application

All-solid-state batteries (ASSBs) are gaining traction in the arena of energy storage due to their promising results in producing high energy density and long cycle life coupled with their capability of being safe. The key challenges facing ASSBs are low conductivity and slow charge transfer kinetics at the interface between the electrode and the solid electrolyte. Garnet solid-state electrolyte has shown promising results in improving the ion conductivity but still suffers from poor capacity retention and rate performance due to the interfacial resistance between the electrodes. To improve the interfacial resistance, we prepared a composite consisting of Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) garnet material as the ceramic, polyethylene oxide (PEO) as the polymer, and lithium hexafluorophosphate (LiPF6) as the salt. These compounds are mixed in a stoichiometric ratio and developed into a very thin disc-shaped solid electrolyte. The LLCZN provides a lithium-ion transport path to enhance the lithium-ion conduction during charging and discharging cycles, while the LiPF6 contributes more lithium ions via the transport path. The PEO matrix in the composite material aids in bonding the compounds together and creating a large contact area, thereby reducing the issue of large interfacial resistance. FESEM images show the porous nature of the electrolyte which promotes the movement of lithium ions through the electrolyte. The fabricated LLCZN/PEO/LiPF6 solid-state electrolyte shows outstanding electrochemical stability that remains at 130 mAh g−1 up to 150 charging and discharging cycles at 0.05 mA cm−2 current. All the specific capacities were calculated based on the mass of the cathode material (LiCoO2). In addition, the coin cell retains 85% discharge capacity up to 150 cycles with a Coulombic efficiency of approximately 98% and energy efficiency of 90% during the entire cycling process.

Facile Synthesis of Multi-channel Surface Modified Amorphous Iron Oxide Nanospheres as a High-performance Anode Material for Lithium-ion Batteries

The application of iron oxide as anode of lithium-ion batteries is hindered by its poor cycle stability, low rate performance and large voltage hysteresis. To address these problems, multi-channel surface modified amorphous Fe2O3 nanospheres were synthesized by using a facile hydrothermal method, which exhibited outstanding electrochemical performances. According to crystalline state and microstructure, it was found that surface structure of the amorphous Fe2O3 nanospheres can be controlled by adjusting the reaction time, due to the synergistic effect of ripening and hydrogen ion etching. Owing to the isotropic nature and the absence of grain boundaries, the amorphous Fe2O3 nanospheres could withstand high strains during the intercalation of lithium ions. Meanwhile, the multi-channel surface structure can not only increase the contact area between Fe2O3 nanospheres and electrolyte, but also reserve space for volume expansion after lithium storage, thereby effectively alleviating the volume change during the intercalation-deintercalation of lithium ions. As confirmed by the Galvanostatic intermittent titration analysis results, the amorphous Fe2O3 electrode had higher Li+ diffusion coefficient than the crystalline counterpart. As a result, the multi-channel surface modified amorphous Fe2O3 electrode exhibited higher specific capacity, more stable cycle performance and narrower voltage hysteresis. It is believed that amorphous metal oxides have great potential as high-performance anode of next-generation lithium-ion batteries.

Synthesis of MnO-Sn cubes embedding in nitrogen-doped carbon nanofibers with high lithium-ion storage performance

In this paper, a carbon nanofiber (CNF) hybrid nanomaterial composed of MnO-Sn cubes embedding in nitrogen-doped CNF (MnO-Sn@CNF) is synthesized through electrospinning and post-thermal reduction processes. It exhibits good electrochemical lithium-ion storage performance as anode, such as high reversible capacity, outstanding cycle performance (754 mAh g-1 at 1 A/g after 1000 cycles), and good rate capability (447 mAh g-1 at 5A/g). The excellent electrochemical properties are derived from unique nanostructure design. MnO-Sn@CNF has a three-dimensional (3D) conductive network with a stable core-shell structure, which improves the electrical conductivity and mechanical stability of the materials. In addition, the mesopores on the surface of carbon fibers can shorten the diffusion distance of lithium ions and promote the combination of active sites of the material with lithium ions. The internal MnO and Sn form a heterostructure, which enhances the stability of the physical structure of the electrode material. This material design method provides a reference strategy for the development of high-performance lithium-ion batteries anode.

Second Harmonic Generation in Lithiated Silicon Nanowires: Derivations and Computational Methods

This research will examine the computational methods to calculate the nonlinear optical process of second harmonic generation (SHG) that will be hypothesized to be present during lithium ion insertion into silicon nanowires. First it will be determined whether the medium in which SHG is conveyed is non-centrosymmetric or whether the medium is inversion symmetric where SHG as a part of the second-order nonlinear optical phenomenon does not exist. It will be demonstrated that the main interaction that determines SHG is multiphoton absorption on lithium ions. The quantum harmonic oscillator (QHO) is used as the background that generates coherent states for electrons and photons that transverse the length of the silicon nanowire. The matrix elements of the Hamiltonian which represents the energy of the system will be used to calculate the probability density of second-order nonlinear optical interactions which includes collectively SHG, sum-frequency generation (SFG) and difference-frequency generation (DFG). As a result, it will be seen that at varies concentrations of lithium ions (Li+) within the crystallized silicon (c-Si) matrix the second-order nonlinear optical process has probabilities substantial enough to create second harmonic generation that could possibly be used for such applications as second harmonic imaging microscopy.