TY - JOUR
T1 - Investigation of Na 3 V 2 (PO 4 ) 2 O 2 F as a sodium ion battery cathode material
T2 - Influences of morphology and voltage window
AU - Xu, Junling
AU - Chen, Jizhang
AU - Tao, Li
AU - Tian, Zhilin
AU - Zhou, Shuang
AU - Zhao, Ni
AU - Wong, Ching Ping
N1 - Publisher Copyright:
© 2019
PY - 2019/6
Y1 - 2019/6
N2 - Na-ion batteries (NIBs) offer a low-cost solution for energy storage applications. However, the cathode materials of NIBs are still limited by their low energy density, exhibiting either small capacity or low operation voltage. In this work we explored a high-voltage cathode material, vanadium fluorophosphate Na 3 V 2 (PO 4 ) 2 O 2 F. We prepared the material in both nano-size and micro-size by a hydrothermal method, adopting ethylene glycol and water as the solvent, respectively. The morphology and physiochemical properties of the nano-sized and micro-sized Na 3 V 2 (PO 4 ) 2 O 2 F are systematically characterized and the battery cycling performances are examined in different voltage windows. Interestingly, we find that the battery capacity and rate capability are highly dependent on the cathode morphology while the cyclability of the electrode is mainly affected by the operation voltage window. The nano-sized Na 3 V 2 (PO 4 ) 2 O 2 F can achieve an energy density of 459 Wh kg −1 with good cyclability within a voltage window of 3–4.5 V while the micro-sized Na 3 V 2 (PO 4 ) 2 O 2 F delivers a much poorer electrochemical performance due to its coarse morphology. By widening the operation voltage window to 1–4.5 V, an energy density of 660 Wh kg −1 can be obtained from the nano-sized Na 3 V 2 (PO 4 ) 2 O 2 F electrode at the initial cycles, but it decreases significantly after tens of cycles. We analyzed the rate capability of Na 3 V 2 (PO 4 ) 2 O 2 F by considering multi Na + ion intercalation reactions and found the large voltage window induced additional Na + ion intercalation reaction occurs through a much slower kinetic process as compared to other reactions activated in the narrower voltage window (e.g., 3–4.5 V). The model of the intercalation reactions as well as the possible reasons of the degraded cycling performance in wide operation voltage windows are discussed based on the battery charging-discharging behavior, electrochemical impedance analysis, ex-situ morphology measurements and previously established material models. The findings validate the potential of Na 3 V 2 (PO 4 ) 2 O 2 F as a high energy density cathode material for NIB, but also call for new crystal structure design of Na 3 V 2 (PO 4 ) 2 O 2 F to achieve high energy density and good cyclability at the same time.
AB - Na-ion batteries (NIBs) offer a low-cost solution for energy storage applications. However, the cathode materials of NIBs are still limited by their low energy density, exhibiting either small capacity or low operation voltage. In this work we explored a high-voltage cathode material, vanadium fluorophosphate Na 3 V 2 (PO 4 ) 2 O 2 F. We prepared the material in both nano-size and micro-size by a hydrothermal method, adopting ethylene glycol and water as the solvent, respectively. The morphology and physiochemical properties of the nano-sized and micro-sized Na 3 V 2 (PO 4 ) 2 O 2 F are systematically characterized and the battery cycling performances are examined in different voltage windows. Interestingly, we find that the battery capacity and rate capability are highly dependent on the cathode morphology while the cyclability of the electrode is mainly affected by the operation voltage window. The nano-sized Na 3 V 2 (PO 4 ) 2 O 2 F can achieve an energy density of 459 Wh kg −1 with good cyclability within a voltage window of 3–4.5 V while the micro-sized Na 3 V 2 (PO 4 ) 2 O 2 F delivers a much poorer electrochemical performance due to its coarse morphology. By widening the operation voltage window to 1–4.5 V, an energy density of 660 Wh kg −1 can be obtained from the nano-sized Na 3 V 2 (PO 4 ) 2 O 2 F electrode at the initial cycles, but it decreases significantly after tens of cycles. We analyzed the rate capability of Na 3 V 2 (PO 4 ) 2 O 2 F by considering multi Na + ion intercalation reactions and found the large voltage window induced additional Na + ion intercalation reaction occurs through a much slower kinetic process as compared to other reactions activated in the narrower voltage window (e.g., 3–4.5 V). The model of the intercalation reactions as well as the possible reasons of the degraded cycling performance in wide operation voltage windows are discussed based on the battery charging-discharging behavior, electrochemical impedance analysis, ex-situ morphology measurements and previously established material models. The findings validate the potential of Na 3 V 2 (PO 4 ) 2 O 2 F as a high energy density cathode material for NIB, but also call for new crystal structure design of Na 3 V 2 (PO 4 ) 2 O 2 F to achieve high energy density and good cyclability at the same time.
KW - Morphology
KW - Na V (PO ) O F
KW - Na-ion battery
KW - Voltage window
UR - http://www.scopus.com/inward/record.url?scp=85063752084&partnerID=8YFLogxK
U2 - 10.1016/j.nanoen.2019.03.063
DO - 10.1016/j.nanoen.2019.03.063
M3 - Article
AN - SCOPUS:85063752084
SN - 2211-2855
VL - 60
SP - 510
EP - 519
JO - Nano Energy
JF - Nano Energy
ER -
