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The thermal stability of the polyethylene (PE) separator is of utmost importance for the safety of lithium-ion batteries. Although the surface coating of PE separator with oxide nanoparticles can improve thermal stability, some serious problems still exist, such as micropore blockage, easy detaching, and introduction of excessive inert substances, which negatively affects the power density, energy density, and safety performance of the battery. In this paper, TiO2 nanorods are used to modify the surface of the PE separator, and multiple analytical techniques (e.g., SEM, DSC, EIS, and LSV) are utilized to investigate the effect of coating amount on the physicochemical properties of the PE separator. The results show that the thermal stability, mechanical properties, and electrochemical properties of the PE separator can be effectively improved via surface coating with TiO2 nanorods, but the degree of improvement is not directly proportional to the coating amount due to the fact that the forces inhibiting micropore deformation (mechanical stretching or thermal contraction) are derived from the interaction of TiO2 nanorods directly "bridging" with the microporous skeleton rather than those indirectly "glued" with the microporous skeleton. Conversely, the introduction of excessive inert coating material could reduce the ionic conductivity, increase the interfacial impedance, and lower the energy density of the battery. The experimental results show that the ceramic separator with a coating amount of ~0.6 mg/cm2 TiO2 nanorods has well-balanced performances: its thermal shrinkage rate is 4.5%, the capacity retention assembled with this separator was 57.1% under 7 C/0.2 C and 82.6% after 100 cycles, respectively. This research may provide a novel approach to overcoming the common disadvantages of current surface-coated separators. [ABSTRACT FROM AUTHOR]

The spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) material is considered as a promising cathode in high-voltage lithium-ion batteries due to its advantageous voltage and capacity. Previous results indicate that the electrodes constructed by LNMO with the same compositions while differing in the crystallite geometries always exhibit various electrochemical performances. Here, to probe the relationships between the crystalline geometry of the obtained cathodes and their electrochemical properties, we synthesized different facet-exposed LNMOs with the same compositions using a template method. We demonstrate that the crystallite geometries of the hydroxide precursors can be tuned easily via varying the synthesize parameters, while the tuned precursors can be employed as the templates during the final product preparation. LNMOs enclosed by single {111} facets (LNMO-OH) and both {110} and {100} facets (LNMO-HP) are obtained and employed to elucidate the particle geometry-dependent electrochemical properties. Despite better rate capabilities exhibited for LNMO-HP because of the higher lithium diffusion coefficients along these crystal orientations, inferior cycling performance is released compared with its LNMO-OH counterpart. These insights can provide informative guidance in particle geometry-dependent material construction, thus helpful in realizing high-performance LNMO cathode. • Different facet-exposed LNMOs with the same compositions were synthesized. • The crystallite geometries of the hydroxide precursors can be tuned easily via varying the synthesize parameters. • Facet-exposed LNMOs exhibit various electrochemical properties. • Working mechanism of different LNMOs was investigated. [ABSTRACT FROM AUTHOR]

Abstract A LiNi 0.5 Mn 1.5 O 4 material with nanoplate morphology and ordered spinel phase is synthesized via co-precipitation method. From the results of XRD, FT-IR, SEM and TEM analysis, it can be seen that the LiNi 0.5 Mn 1.5 O 4 sample possess a crystal structures of the space groups of P4 3 32 and plate-like morphology exposed {100} and {110} surfaces. The electrochemical tests show that it exhibits an acceptable rate capability, however, the cycling property, especially the stored performance is unsatisfactory. The following electrochemical impedance spectroscopy, SEM and ICP characterizations reveal the relationship between the surfaces and their electrochemical properties: during cycling or storing process, a charge transfer between Ni and Mn is taken place on the {100} and {110} surfaces, resulting in declines in the valence of Mn(IV). Then, the Mn could dissolve from spinel electrode surfaces into electrolyte undergoing a disproportionation reaction of Mn3+. Last, these results lead to the capacity retention and voltage platform continues to deteriorate. Highlights • Ordered LNMO nanoplates exposing {100} and {110} crystal planes were synthesized. • Ordered LNMO nanoplates exhibited an acceptable rate capability. • Ordered LNMO nanoplates showed an unsatisfactory cycling and stored performance. • A charge transfer between Ni and Mn was taken place on the {100} and {110} surfaces • Serious Mn dissolution occur on the {100} and {110} surfaces. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have synthesized the layered LiNi0.5Mn0.5O2−xF x (0⩽ x ⩽0.04) by hydroxide co-precipitation method. [•] The structure, morphology and electrochemical performance of LiNi0.5Mn0.5O2 are influenced by F doping effect. [•] The cations mixing of pure LiNi0.5Mn0.5O2 decreases and Li+ diffusion coefficient increases with doping F. [•] The reversible capacity of LiNi0.5Mn0.5O1.96F0.04 is 155.0mAhg−1 after 50 cycles at 0.2 C, 0.5 C and 1.0 C ratios between 2.8 and 4.6V. [ABSTRACT FROM AUTHOR]