CHARACTERIZATION AND ELECTROCHEMICAL PERFORMANCE OF MESOPOROUS TIN PHOSPHATE BASED ANODE FOR LITHIUM-ION CELLS

The growth in demand for extra power in rechargeable batteries has encouraged
intense research to develop new materials with even higher capacities. The main focus
of this work is to investigate the electrochemical characteristics of mesoporous tin
phosphate as alternative anode host material for Li-ion batteries. Mesoporous tin
phosphate was synthesized based on a surfactant templating method, where an anionic
surfactant, sodium dodecyl sulfate, was used as the structure directing agent and tin
(IV) chloride (SnCl4) as the inorganic source. The synthesized powder was
characterized by means of thermal, X-ray diffraction (XRD), nitrogen gas sorption
and scanning electron microscope (FE-SEM) techniques. The surfactant synthesized
tin phosphate (SnP2O7) calcined from 200-400°C exhibited amorphous, mesoporous
characteristics. Average pore size distribution obtained for the mesoporous SnP2O7
was around 10-18 nm. The electrochemical behaviour of the synthesized tin
phosphate anode was studied using a combination of electrochemical analysis from
cyclic voltammogram and differential capacity plots. The mesoporous SnP2O7 anode
exhibited electrochemical reactions with lithium within the potential range of 0-2 V
vs. Li+/Li as indicated by cyclic voltammetry analysis. These reactions consist of the
irreversible reaction to form lithium phosphate matrix phases and the reversible
reaction of lithium insertion and extraction upon subsequent charging and
discharging. The formation of the irreversible lithium phosphate phase leads to
substantial losses of more than 50% in lithium ion storage capacity upon the first
discharge cycle. The mesoporous SnP2O7 anodes performed averagely better in terms
of delivering higher discharge capacity when compared to that of the non-mesoporos
SnP2O7 anodes. A narrower cutoff operating voltage range within 0-1.2 V exhibited
better galvanostatic cycling performance of the mesoporous SnP2O7 calcined at 400°C
for 2 hours. This anode delivered a reversible discharge capacity (lithium ion storage
capacity) of 780 mAh/g upon the second cycle and retained 134 mAh/g upon the
fiftieth cycle. The mesoporous structure helps to absorb some volume change of the
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tin particles during lithium alloying and de-alloying process thus improving
cyclability.