Growth mechanisms for spherical Ni_(0.815)Co_(0.15)Al_(0.035)(OH)_(2) precursors prepared via the ammonia complexation precipitation method

The microstructures of precursors strongly affect the electrochemical performance of Ni-rich layerstructured cathode materials.In this study,the growth behaviour of Ni_(0.815)Co_(0.15)Al_(0.035)(OH)_2(NCA) prepared via the ammonia complexation precipitation method in a 50-L-volume continuously stirred tank reactor(CSTR) is studied in detail.The growth of Ni(OH)2-based hydroxide can be divided into a nucleation process,an agglomeration growth process,a process in which multiple growth mechanisms coexist,and an interface growth process over time,while the inner structure of the CSTR can be divided into a nucleation zone,a complex dissolution zone,a growth zone,and a maturation zone.The concentration of ammonium ions affects the growth habit of the primary crystal significantly due to its specific adsorption on the electronegative crystal plane.When the ammonia concentration is <1.5 mol L^(-1) at 60℃ at pH=11.5,the precursors grow preferentially along the(1 0 1) crystal plane,whereas they grow preferentially along the(0 0 1) crystal plane when the concentration is >2.0 mol L^(-1).The LiNi_(0.815)Co_(0.15)Al_(0.035)O_2 materials inherit the grain structure of the precursor.Materials prepared from precursors with(1 0 1)preferential primary particles show a higher specific capacity and better rate performance than those that were prepared from(0 0 1) preferential primary particles,but the latter realize a better cycling performance than the former.

Preparation of Spherical FePO4 by Chemical Co-precipitation Combined with Spray-Drying

Well-shaped spherical agglomerates of FePO4 particles were prepared by a novel method:chemical co-precipitation combined with spray-drying.Tap density analysis,Brunauer-Emmett-Teller analysis,characterizations of X-ray diffraction,scanning electron microscopy,and transmission electron microscopy confirmed that the micron-sized spherical agglomerates with high specific surface area and high tap density were composed of the uniform nano-sized particles.The effects of pH and reaction time on the morphology of the FePO4 particles were investigated by experimental and theoretical analyses.The analyses revealed that amorphous FePO4 was responsible for forming a well-shaped spherical agglomerate,and the ideal spherical particles were obtained at pH 3.The reaction time also played a significant role in controlling the size and surface morphology of the FePO4 particles,and smooth spherical FePO4 particles were obtained at a reaction time of 6 h.By this novel method,poly-porous spherical iron phosphate particles were prepared,which can be used with high efficiency in some special fields,especially as a precursor for synthesizing LiFePO4 and catalysts.

MORPHOLOGICAL AND MICROSTRUCTURAL CHANGES DURING THE HEATING OF SPHERICAL CALCIUM ORTHOPHOSPHATE AGGLOMERATES PREPARED BY SPRAY PYROLYSIS

The microstructural changes taking place during heating of calcium orthophosphate (Ca3(PO4)2) agglom- erates were examined in this study. The starting powder was prepared by the spray-pyrolysis of calcium phosphate (Ca/P ratio=1.50) solution containing 1.8 mol·L-1 Ca(NO3)2, 1.2 mol·L-1 (NH4)2HPO4 and concentrated HNO3 at 600 C, using an o air-liquid nozzle. The spray-pyrolyzed powder was found to be composed of dense spherical agglomerates with a mean diameter of 1.3 μm. This powder was further heat-treated at a temperature between 800 and 1400 C for 10 min. When o the spray-pyrolyzed powder was heated up to 900 C, only β-Ca3(PO4)2 was detected, and the mean pore size of the o spherical agglomerates increased via the (i) elimination of residual water and nitrates, (ii) rearrangement of primary par- ticles within the agglomerates, (iii) coalescence of small pores (below 0.1 μm), and (iv) coalescence of agglomerates with diameters below 1 μm into the larger agglomerates. Among the heat-treated powders, pore sizes within the spherical agglomerates were observed to be the largest (mean diameter: 1.8 μm) for the powder heat-treated at 900 C for 10 min. o With an increase in heat-treatment temperature up to 1000 C, the spherical agglomerates were composed of dense o shells. Upon further heating up to 1400 C, the hollow spherical agglomerates collapsed as a result of sintering via the o phase transformation from β- to α-Ca3(PO4)2 (1150 C), thus leading to the formation of a three-dimensional porous net- o work.

Research on optical fiber magnetic field sensors based on multi-mode fiber and spherical structure

A magnetic field sensor with a magnetic fluid(MF)-coated intermodal interferometer is proposed and experimentally demonstrated. The interferometer is formed by sandwiching a segment of single mode fiber(SMF) between a segment of multi-mode fiber(MMF) and a spherical structure. It can be considered as a cascade of the traditional SMF-MMF-SMF structure and MMF-SMF-sphere structure. The transmission spectral characteristics change with the variation of applied magnetic field. The experimental results exhibit that the magnetic field sensitivities for wavelength and transmission loss are 0.047 nm/m T and 0.215 d B/m T for the interference dip around 1 535.36 nm. For the interference dip around 1548.41 nm,the sensitivities are 0.077 nm/m T and 0.243 d B/m T. Simultaneous measurement can be realized according to the different spectral responses.

Suppression of voltage decay through adjusting tap density of lithium-rich layered oxides for lithium ion battery

The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low cost.In this work,the relationship between voltage decay and tap density of LLOs has been focused.The voltage decay can be significantly suppressed with the increasing tap density as well as the homogenization of the primary or secondary particle size of agglomerated spherical LLOs.Experimental results have shown that an extreme small voltage decay of 0.98 m V cycle^(-1)can be obtained through adjusting the tap density of agglomerated spherical LLOs to 1.99 g cm^(-3),in which the size of primary and secondary particles are uniform.Our work offers a new insight towards the voltage decay and capacity fading of LLOs through precursor preparation process,promoting their application in the real battery in the future.