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The present study investigates on the effect of excessive Ni doping, secondary heat-treatment and their influence on the structural and electrochemical properties of LiMn1.3Ni0.7Oy spinel samples prepared by a two-step solid state synthesis. X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), electrochemical studies and in-situ synchrotron XRD (SXRD) results acquired during electrochemical lithiation indicates that the concentration of Mn3+ and the corresponding ordering of the spinel composition can be controlled by excessive nickel doping and secondary annealing (at 700°C). Moreover, the above characterizations also confirmed long-range cation ordering (P4332) in addition to minor contributions from the Mn3+ content in the secondary annealed spinel (LiMn1.3Ni0.7Oy). More importantly, the combined effect of extended Ni-doping and secondary heat-treatment is clearly reflected as an enhancement in the rate performances of LiMn1.3Ni0.7Oy spinel cathode at elevated current rates (discharge capacity of around 88 and 61 mAh/g at 0.457 and 0.914 A/g current densities). [ABSTRACT FROM AUTHOR]

Mono-dispersed and densely packed, LiFePO4 cathodes with high rate performance versus lithium were synthesized using a two-step polyol process. The particle-size distribution and packing density of LiFePO4 nanoparticles were fine-tuned via separation of the nucleation and particle growth processes in the polyol medium by varying reaction time and temperature. Precisely, the LiFePO4 samples were synthesized by heating the reaction mixtures at 200°C for various reaction times (0, 1, 3 and 6 h) to facilitate nucleation and thereafter the solution temperature was raised and maintained at 320°C to facilitate the crystal growth process. XRD studies confirmed the formation of olivine phase in all the samples. The FE-SEM, FE-TEM and particle-size distribution studies illustrate that the particle-size of olivine nanocrystals may be tuned to approximately 200 nm by controlling the aging time at 200°C or in other words separating the nucleation and crystal growth process. The olivine cathodes synthesized by maintaining 3-6 h aging time demonstrate improved discharge capacities and cycle performances in comparison to those of the remaining samples. In particular, the 6 h olivine cathode registered average discharge capacities of 130, 87 and 64 mAh/g at 5 C, 10 C and 15.7 C current rates respectively. [ABSTRACT FROM AUTHOR]

Abstract: Urea-assisted auto-combustion synthesis was used for the easy and scalable preparation of TiO2 nanoparticles for use as anodes in lithium-ion batteries. The prepared TiO2 powder was annealed at 300°C, 400°C, 500°C and 600°C to optimize the system and assess the effects of particle size on electrochemical properties. X-ray diffraction patterns confirmed that pure anatase phase TiO2 formed at up to 500°C, above which mixed phases of anatase and rutile emerged. Field-emission transmission electron microscopy showed that spherical particles of 8–25nm were formed. The electrochemical performances of annealed TiO2 samples were tested by charging/discharging, C-rate measurement and electrochemical impedance spectroscopy. It was clearly found that the crystal particle size has a striking impact on the Li insertion behavior and lithium storage capability. TiO2 nanoparticles electrode annealed at lower temperature 300°C showed high rate capability, excellent capacity retention and high electrical conductivity due to its very small particles and nonideal crystal lattices. [Copyright &y& Elsevier]

Abstract: We report on the solvothermal preparation of pure Li4Ti5O12 and Li4Ti5O12/graphene (15 wt% and 30 wt%) nanocomposites anode for high-performance lithium-ion batteries. Structure and morphology studies of the nanocomposites by X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy reveal Li4Ti5O12 nanoparticles embedded onto the graphene nanosheets. On comparison to pure spinel Li4Ti5O12, the electrochemical performances of the Li4Ti5O12/graphene nanocomposites indicate higher capacities and enhanced cycle performances within the voltage domain of 1.0–2.5 V, under current rates as high as 10.4 C. The production of phase pure Li4Ti5O12 nanoparticles ensures the short ion-diffusion paths while the presence of graphene facilitates improved structural network and hence enhanced electronic transport in the prepared nanocomposites. These factors eventually amount to impressive electrochemical properties. [Copyright &y& Elsevier]

Nanocrystalline LiFePO4/C has been synthesized under a very short period of time (90 sec) using a polyol-assisted microwave heating synthesis technique. The X-ray diffraction (XRD) data indicates that the rapidly synthesized materials correspond to phase pure olivine. Post-annealing of the as-prepared sample at 600 °C in argon atmosphere yields highly crystalline LiFePO4/C. The morphology of the samples studied using scanning electron microscopy (SEM) reveals the presence of secondary particles formed from aggregation of primary particles in the range of 30-50 nm. Transmission electron microscopy (TEM) images reveal a thin carbon layer coating on the surface of the primary particle. The charge/discharge studies indicate that the as-prepared and annealed LiFePO4/C samples delivered initial discharge capacities of 126 and 160 mA h g-1, respectively, with good capacity retentions at 0.05 mA cm-2 current densities. The post-annealing process indeed improves the crystallinity of the LiFePO4 nanocrystals, which enhances the electrode performance of LiFePO4/C.