Polycationic doping of the LATP ceramic electrolyte for Li-ion batteries.

All-solid-state Li-ion batteries (LIBs) with a solid electrolyte instead of a liquid one demonstrate significantly higher safety in contrast with the conventional liquid-based LIBs. An inorganic NASICON-type Li conductor Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising solid electrolyte with an ionic conductivity of up to 10-3 S cm-1 at room temperature. However, LATP gradually degrades in contact with Li metal because of reduction of Ti4+ to Ti3+, resulting in a lower ionic conductivity at the electrolyte-electrode interface. Cation doping is a promising approach to stabilize the LATP structure and mitigate the Ti reduction. Here, we report our findings on the alternative polycationic doping strategy of the LiTi2(PO4)3 (LTP) structure, when a heterovalent cation is added along with Al. In particular, we studied the effect of tetravalent and divalent cation dopants (Zr, Hf, Ca, Mg, Sr) of LATP on the Li-ion conduction and Ti reduction during interaction with lithium metal. The samples were prepared by molten flux and solid-state reaction methods. The structure, morphology, and ion-transport properties of the samples were analyzed. The activation energy of Li-ion migration in all synthesized systems was calculated based on the electrochemical impedance spectroscopy (EIS) data retrieved for a temperature range of 25-100 °C. From the obtained results, the tetravalent doping (Zr4+ and Hf4+) appeared to be a more promissing route to improve the LATP electrolyte than the divalent doping (Mg2+, Ca2+, and Sr2+). The X-ray photoelectron spectroscopy analysis of the samples after their contact with lithium provided the data, which could shed light on the effect of the incorporated dopants onto the Ti reduction.

Annealing Optimization of Lithium Cobalt Oxide Thin Film for Use as a Cathode in Lithium-Ion Microbatteries.

The microbatteries field is an important direction of energy storage systems, requiring the careful miniaturization of existing materials while maintaining their properties. Over recent decades, LiCoO2 has attracted considerable attention as cathode materials for lithium-ion batteries due to its promising electrochemical properties for high-performance batteries. In this work, the thin films of LiCoO2 were obtained by radio-frequency magnetron sputtering of the corresponding target. In order to obtain the desired crystal structure, the parameters such as annealing time, temperature, and heating rate were varied and found to influence the rhombohedral phase formation. The electrochemical performances of the prepared thin films were examined as a function of annealing time, temperature, and heating rate. The LiCoO2 thin film cathode annealed at 550 °C for 1 h 20 min demonstrated the best cycling performance with a discharge specific capacity of around 135 mAh g-1 and volumetric capacity of 50 µAh cm-2µm-1 with a 77% retention at 0.5 C rate.

Onion-Structured Si Anode Constructed with Coating by Li4Ti5O12 and Cyclized-Polyacrylonitrile for Lithium-Ion Batteries.

Low dimensional Si-based materials are very promising anode candidates for the next-generation lithium-ion batteries. However, to satisfy the ever-increasing demand in more powerful energy storage devices, electrodes based on Si materials should display high-power accompanied with low volume change upon operation. Thus far, there were no reports on the Si-based materials which satisfy the stated requirements. Hence, here, we report on modified onion-structured Si nanoparticles (SiNPs) co-coated with Li4Ti5O12 (LTO) and cyclized polyacrylonitrile (cPAN) to bring the synergistic effect enhancing the conductivity, tolerance to volume change and stable performance. Obtained results suggest that the nanoparticles were conformally coated with both materials simultaneously and the thicknesses of the films were in a range of a few nanometers. Electrochemical tests show that the modified SiNPs deliver a high initial capacity of 2443 mAh g-1 and stable capacity retention over 50 cycles with 95% Coulombic efficiency.

The Electrochemical Performances of n-Type Extended Lattice Spaced Si Negative Electrodes for Lithium-Ion Batteries.

The electrochemical performances of lithium-ion batteries with different lattice-spacing Si negative electrodes were investigated. To achieve a homogeneous distribution of impurities in the Si anodes, single crystalline Si wafers with As-dopant were ball-milled to form irregular and agglomerated micro-flakes with an average size of ~10 µm. The structural analysis proved that the As-doped Si negative materials retain the increased lattice constant, thus, keep the existence of the residual tensile stress of around 1.7 GPa compared with undoped Si anode. Electrochemical characterization showed that the As-doped Si anodes have lower discharge capacity, but Coulombic efficiency and capacity retention were improved in contrast with those of the undoped one. This improvement of electrochemical characteristics was attributed to the increased potential barrier on the side of Si anodes, inherited from the electronic and mechanical nature of Si materials doped with As. We believe that this study will guide us the way to optimize the electrochemical performances of LIBs with Si-based anodes.

N-Type Doped Silicon Thin Film on a Porous Cu Current Collector as the Negative Electrode for Li-Ion Batteries.

This work reports the preparation of a three-dimensional Si thin film negative electrode employing a porous Cu current collector. A previously reported copper etching procedure was modified to develop the porous structures inside a 9 µm thick copper foil. Magnetron sputtering was used for the deposition of an n-type doped 400 nm thick amorphous Si thin film. Electrochemical cycling of the prepared anode confirmed the effectiveness of utilizing the approach. The designed Si thin film electrode retained a capacity of around 67 µAh cm-2 (1675 mAh g-1) in 100th cycle. The improved electrochemical performance resulted in an enhancement of both areal capacity and capacity retention in contrast with flat and rough current collectors that were prepared for comparison.