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New High Capacity Cathode Materials for Rechargeable Li-ion Batteries: Vanadate-Borate Glasses

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ABSTRACT

V2O5 based materials are attractive cathode alternatives due to the many oxidation state switches of vanadium bringing about a high theoretical specific capacity. However, significant capacity losses are eminent for crystalline V2O5 phases related to the irreversible phase transformations and/or vanadium dissolution starting from the first discharge cycle. These problems can be circumvented if amorphous or glassy vanadium oxide phases are employed. Here, we demonstrate vanadate-borate glasses as high capacity cathode materials for rechargeable Li-ion batteries for the first time. The composite electrodes of V2O5 – LiBO2 glass with reduced graphite oxide (RGO) deliver specific energies around 1000 Wh/kg and retain high specific capacities in the range of ~ 300 mAh/g for the first 100 cycles. V2O5 – LiBO2 glasses are considered as promising cathode materials for rechargeable Li-ion batteries fabricated through rather simple and cost-efficient methods.

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(a) The first ten charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite in a potential window of 1.5–4.0 V at 50 mA/g rate, (b) the rate capability of the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50, 100, 200 and 400 mA/g rates (at room temperature), (c) discharge capacity vs. cycle number for the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50 and 100 mA/g rates.
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f4: (a) The first ten charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite in a potential window of 1.5–4.0 V at 50 mA/g rate, (b) the rate capability of the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50, 100, 200 and 400 mA/g rates (at room temperature), (c) discharge capacity vs. cycle number for the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50 and 100 mA/g rates.

Mentions: The cells with a cathode composition of ~ 74 wt-% active material, ~ 16 wt-% conductive carbon originating from the RGO (no additional carbon black) and ~ 10 wt-% PVDF were cycled between 1.5 V and 4.0 V at a rate of 50 mA/g. Similar to the plain glass material, the reported specific capacities for the composite electrode material are calculated based on the active mass of V2O5 – LiBO2 glass; not exclusively on the mass of V2O5, and RGO is considered as an inactive part in the potential window of our interest, as well. The first ten galvanostatic charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite are shown in Fig. 4a. The first discharge capacity has been raised to ~ 405 mAh/g for the composite electrode. This capacity corresponds to the insertion of ~ 3.4 Li per formula unit of V2O5 – LiBO2 glass. A high capacity of ~ 390 mAh/g is reached in the subsequent charge proving that the RGO/V2O5 – LiBO2 glass composite also does not suffer from the large irreversible capacity loss associated with the phase transformations of crystalline V2O5. Remarkably, this initial charge capacity is largely preserved in the range of ~ 300 mAh/g within the first 100 cycles (Fig. 4c). If the cell is charged to 4.5 V first, the glass material can be also delithiated resulting a first charge capacity of ~ 20–25 mAh/g, however, the cycling stability is found to be rather poor in the large potential window (Figure S12 & S13). The electrochemical activity in the first charge also indicates the presence of the partially reduction of V5+ species to V4+ species in the glass material. Based on the obtained first charge capacity, the formation of Li0.3V2O5 phases above the glass transition, XPS and magnetic measurements (Fig. S9, S10 and S11), the averaged oxidation state for vanadium in the glassy electrode materials can be given as ~ 4.8–4.9 +. The sloping characteristic of the galvanostatic charge/discharge curves again indicates a homogeneous phase process. The rate capability for the RGO/V2O5 – LiBO2 glass composite has been enhanced as well. Fig. 4b shows the rate capability within first 50 galvanostatic cycles between 1.5 V and 4.0 V. For rates of 50, 100, 200 and 400 mA/g, average discharge capacities are ~ 388, 355, 329 and 299 mAh/g, respectively. When the rate is changed back from 400 mA/g to 50 mA/g, the discharge capacity recovers from 298 mAh/g to ~ 370 mAh/g at the 42nd cycle. The specific energy is ~ 900 Whkg−1 with an average discharge voltage of ~ 2.4 V at this cycle. The favorable response of the electrochemical system to higher charge/discharge rates demonstrates the improvements arising from the composite electrode. The capacity delivered at the highest rate (400 mA/g) is more than doubled compared to the amount obtained for the V2O5 – LiBO2 glass electrode without RGO. The improvement made with ball-milling and conductive coating is encouraging as it shows that the problem is mainly stemming from the kinetic problems associated with the larger glass particles. Clearly, further optimization of the electrochemical performance can be expected by improving the composite characteristics.


New High Capacity Cathode Materials for Rechargeable Li-ion Batteries: Vanadate-Borate Glasses
(a) The first ten charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite in a potential window of 1.5–4.0 V at 50 mA/g rate, (b) the rate capability of the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50, 100, 200 and 400 mA/g rates (at room temperature), (c) discharge capacity vs. cycle number for the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50 and 100 mA/g rates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382707&req=5

f4: (a) The first ten charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite in a potential window of 1.5–4.0 V at 50 mA/g rate, (b) the rate capability of the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50, 100, 200 and 400 mA/g rates (at room temperature), (c) discharge capacity vs. cycle number for the RGO/V2O5 – LiBO2 glass composite within 1.5–4.0 V at 50 and 100 mA/g rates.
Mentions: The cells with a cathode composition of ~ 74 wt-% active material, ~ 16 wt-% conductive carbon originating from the RGO (no additional carbon black) and ~ 10 wt-% PVDF were cycled between 1.5 V and 4.0 V at a rate of 50 mA/g. Similar to the plain glass material, the reported specific capacities for the composite electrode material are calculated based on the active mass of V2O5 – LiBO2 glass; not exclusively on the mass of V2O5, and RGO is considered as an inactive part in the potential window of our interest, as well. The first ten galvanostatic charge/discharge curves of the RGO/V2O5 – LiBO2 glass composite are shown in Fig. 4a. The first discharge capacity has been raised to ~ 405 mAh/g for the composite electrode. This capacity corresponds to the insertion of ~ 3.4 Li per formula unit of V2O5 – LiBO2 glass. A high capacity of ~ 390 mAh/g is reached in the subsequent charge proving that the RGO/V2O5 – LiBO2 glass composite also does not suffer from the large irreversible capacity loss associated with the phase transformations of crystalline V2O5. Remarkably, this initial charge capacity is largely preserved in the range of ~ 300 mAh/g within the first 100 cycles (Fig. 4c). If the cell is charged to 4.5 V first, the glass material can be also delithiated resulting a first charge capacity of ~ 20–25 mAh/g, however, the cycling stability is found to be rather poor in the large potential window (Figure S12 & S13). The electrochemical activity in the first charge also indicates the presence of the partially reduction of V5+ species to V4+ species in the glass material. Based on the obtained first charge capacity, the formation of Li0.3V2O5 phases above the glass transition, XPS and magnetic measurements (Fig. S9, S10 and S11), the averaged oxidation state for vanadium in the glassy electrode materials can be given as ~ 4.8–4.9 +. The sloping characteristic of the galvanostatic charge/discharge curves again indicates a homogeneous phase process. The rate capability for the RGO/V2O5 – LiBO2 glass composite has been enhanced as well. Fig. 4b shows the rate capability within first 50 galvanostatic cycles between 1.5 V and 4.0 V. For rates of 50, 100, 200 and 400 mA/g, average discharge capacities are ~ 388, 355, 329 and 299 mAh/g, respectively. When the rate is changed back from 400 mA/g to 50 mA/g, the discharge capacity recovers from 298 mAh/g to ~ 370 mAh/g at the 42nd cycle. The specific energy is ~ 900 Whkg−1 with an average discharge voltage of ~ 2.4 V at this cycle. The favorable response of the electrochemical system to higher charge/discharge rates demonstrates the improvements arising from the composite electrode. The capacity delivered at the highest rate (400 mA/g) is more than doubled compared to the amount obtained for the V2O5 – LiBO2 glass electrode without RGO. The improvement made with ball-milling and conductive coating is encouraging as it shows that the problem is mainly stemming from the kinetic problems associated with the larger glass particles. Clearly, further optimization of the electrochemical performance can be expected by improving the composite characteristics.

View Article: PubMed Central - PubMed

ABSTRACT

V2O5 based materials are attractive cathode alternatives due to the many oxidation state switches of vanadium bringing about a high theoretical specific capacity. However, significant capacity losses are eminent for crystalline V2O5 phases related to the irreversible phase transformations and/or vanadium dissolution starting from the first discharge cycle. These problems can be circumvented if amorphous or glassy vanadium oxide phases are employed. Here, we demonstrate vanadate-borate glasses as high capacity cathode materials for rechargeable Li-ion batteries for the first time. The composite electrodes of V2O5 – LiBO2 glass with reduced graphite oxide (RGO) deliver specific energies around 1000 Wh/kg and retain high specific capacities in the range of ~ 300 mAh/g for the first 100 cycles. V2O5 – LiBO2 glasses are considered as promising cathode materials for rechargeable Li-ion batteries fabricated through rather simple and cost-efficient methods.

No MeSH data available.


Related in: MedlinePlus