B. Das

Synthesis of porous-CoN nanoparticles and their application as a high capacity anode for lithium-ion batteries

CoN nanoparticles are prepared by nitridation of Co3O4 in the presence of NH3 + N2 atmosphere and characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HR-TEM) along with selective area electron diffraction (SAED) and BET surface area techniques. The Li-cycling performance of porous-CoN nanoparticles is evaluated by galvanostatic cycling and cyclic voltammetry (CV) in cells with Li-metal as the counter electrode in the voltage range of 0.005–3.0 V at ambient temperature. When cycled at 250 mA g−1 (0.31 C; 1C = 800 mA g−1), a first-cycle reversible capacity of 780 (±5) mA h g−1 (2.13 moles of Li) is noticed. During cycling, an increase in reversible capacity is observed from 710 (±5) mA h g−1 (1.93 moles of Li) at the 5th cycle to 790 (±5) mA h g−1 (2.15 moles of Li) at the 25th cycle. After this, capacity-fading is noticed and reaches 660 (±5) mA h g−1 (1.8 moles of Li) at the end of the 60th cycle. The capacity-fading is 16% in the range of 25–60 cycles. Excellent rate capability is shown when the cell is cycled at 1.25 C (up to 60 cycles). The coloumbic efficiency is found to be >96% in the range of 10–60 cycles. From CV, the average charge and discharge potentials are; 2.2 and 0.87 V, respectively. The Li-cycling behavior of porous-CoN nanoparticles is discussed based on the observed capacity, ex situ XRD, HR-TEM and SAED data. The results show that porous-CoN nanoparticles are a prospective anode material for Li-ion batteries.

Nano-phase tin hollandites, K2(M2Sn6)O16 (M = Co, In) as anodes for Li-ion batteries

The nano-phase tin hollandites, K2(M2Sn6)O16 (M = Co, In) of particle size <10 nm are prepared by high energy ball-milling of pre-synthesized compounds and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-cycling behavior of M = Co (nano-(K–Co)) and M = In (nano-(K–In)) is evaluated by galvanostatic cycling and cyclic voltammetry (CV) with Li-metal as counter electrode in the voltage range, 0.005–0.8 V (or 1.0 V). When cycled at 60 mA g−1 (0.12 C) in the voltage range, 0.005–0.8 V, a stable capacity of 500 (±5) mA h g−1 up to 60 cycles is noticed for nano-(K–Co), whereas nano-(K–In) showed an initial capacity of 570 (±5) mA h g−1, which dropped to 485 (±5) mA h g−1 (15% loss) at the end of 60 cycles. At 1 C-rate, the nano-(K–Co) showed a capacity of 410 (±5) mA h g−1 stable up to at least 100 cycles. Under similar cyclic conditions, the heat-treated electrode (300 °C, 12 h, Ar) of nano-(K–In) showed a significant improvement and gave a stable capacity of 570 (±5) mA h g−1 in the range of 5–50 cycles. The Coulombic efficiencies in both the compounds increased to 96–98% in the range of 10–60 cycles. For both the nano-phases, the average discharge potential is 0.13 V and average charge potential is 0.5 V vs.Li, as determined by the galvanostatic and CV data. Electrochemical impedance spectroscopy (EIS) data on nano-(K–Co) as a function of voltage are presented and discussed. The apparent Li-diffusion co-efficient (DLi+), estimated from EIS data, is 2.0–2.6 (±0.2) × 10−14 cm2s−1 between 0.25 and 0.45 V during the first-cycle. The observed Li-cycling data have been interpreted in terms of the alloying–de-alloying reaction of Sn in the nano-composite, ‘Sn–K2O–Co/In–Li2O’.

Synthesis and Li-storage behavior of CrN nanoparticles

Bulk CrN nanoparticles are prepared by the thermal decomposition of a Cr–urea complex in a flowing NH3 + N2 atmosphere and characterized by X-ray diffraction (XRD) and high resolution-transmission electron microscopy (HR-TEM) along with selective area electron diffraction (SAED) techniques. The Li-cycling performance of bulk CrN is evaluated by galvanostatic cycling and cyclic voltammetry on the cells with Li metal as counter electrode in the voltage range of 0.005–3.0 (3.5) V at ambient temperature. When cycled at 60 mA g−1 (0.1 C) up to 3.0 V, the composition 55:30:15 (active material:carbon:binder) showed a first-cycle reversible capacity of 635 (±10) mA h g−1 (1.6 moles of Li). The reversible capacity of 500 (±10) mA h g−1 (1.23 moles of Li) is stable between 10 and 80 cycles. At 0.5 C, it showed a stable capacity of 350 (±10) mA h g−1 for 40 cycles and the original capacity is regained when cycled at 0.1 C rate after 160 cycles. The coulombic efficiency is found to be >96% in the range of 20–80 cycles. The low impedance at the discharge potential <1.3 V and high impedance at charge potential 3.0 V evaluated from the impedance spectra (EIS) showed the decomposition and formation of CrN during the 1st cycle. The apparent DLi+ obtained from EIS is in the range, 0.73–3.6 (±0.1) × 10−14 cm2 s−1 during the first-cycle.

A disc-like Mo-metal cluster compound, Co2Mo3O8, as a high capacity anode for lithium ion batteries

The disc-like Mo-metal cluster compound, Co2Mo3O8 has been prepared by a one-step carbothermal reduction method from CoMoO4 and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), Fourier transform-infrared (FT-IR) and micro-Raman spectroscopy at room temperature. The Li-cycling behaviour was investigated by galvanostatic cycling and cyclic voltammetry (CV) in the voltage range of 0.005–3.0 V vs. Li at room temperature. It is inferred that the as prepared Co2Mo3O8 delivered a high first cycle reversible capacity of 900 (±5) mA h g−1 (17.9 moles of Li). The compound showed slow capacity degradation upon cycling and reached 425 (±5) mA h g−1 (8.5 Li) at the end of the 40th cycle. The ball milled Co2Mo3O8 (Co2Mo3O8-B) showed similar cycling behaviour and a reversible capacity of 400 (±5) mA h g−1 (7.8 Li) was observed at the end of the 30th cycle. Interestingly, the heat-treated Co2Mo3O8 (Co2Mo3O8-H) showed improved Li-storage behaviour when cycled under similar conditions. It showed almost a stable capacity of 790 (±5) mA h g−1 (15.7 Li) at the end of 60th cycle. All the compounds showed excellent coulombic efficiency in the range of 97–99%. The electrochemical impedance spectroscopy (EIS) measurement is performed on a Li/Co2Mo3O8 system at selected voltages during first discharge and charge cycling. The possible reaction mechanism is proposed based on CV, ex situ XRD, ex situ TEM and electrochemical impedance spectroscopy (EIS) data on the Li/Co2Mo3O8 system.