Facile Synthesis and Electrochemical Investigation of Li₉V₃(P₂O₇)₃(PO₄)₂as High Voltage Cathode for Li-Ion Batteries

Abstract

We report about a cost-effective synthesis approach for obtaining layered lithium vanadium monodiphosphate Li 9 V 3 (P 2 O 7 ) 3 (PO 4 ) 2 (LVPP) as cathode material for lithium-ion batteries. This polyanionic cathode framework can exchange more than one electron per transition metal at high potentials versus lithium. The influence of crystallite size, carbon coating and working potential window on the electrochemical performance of Li 9 V 3 (P 2 O 7 ) 3 (PO 4 ) 2 is reported. The extraction of nearly 5 Li + ions during the first cycle between 2 and 4.8 V is reached for LVPP with crystallite size of 40 nm and 4.4% carbon coating. A stable reversible specific capacity of 115 mA h g −1 is achieved when cycled between 2 and 4. The demand for new electrode materials for lithium-ion batteries is ever-growing as the applications that require high energy and high power is on the rise. An ideal cathode material for lithium-ion batteries should have versatile properties such as high specific capacity, high redox potential, fast kinetics, long cycle life, low cost, environment compatibility and thermal safety. Until now, lithium iron phosphate (LFP) appears to be the favorite for electro mobility and energy storage applications.1 Despite its intrinsic advantages, especially in terms of safety, LFP suffers from low practically available energy density. With respect to the currently used cathode materials, higher specific energy is achievable through either operating at higher voltage or by enhancing the specific capacity of the active material.After the encounter of monoclinic Li 3 V 2 (PO 4 ) 3 (LVP) which has higher specific energy than LFP, vanadium phosphates and oxy phosphates have been gaining considerable attention as alternative cathode material for lithium-ion batteries.2-6 For instance, monoclinic Li 3 V 2 (PO 4 ) 3 can theoretically deliver a capacity of 197 mA h g −1 when all the three Li ions are extracted at an average potential of 4.1 V. 7,8 As suggested by Goodenough and his coworkers, the above described material operates at a higher potential compared to their iron equivalent due to the inductive effect between vanadium and the phosphate groups.2 This results in increased specific energy. However, monoclinic LVP suffers from sharp drop in electronic conductivity and structural instability with deep de-lithiation at high potentials.8 This makes the extraction of the third lithium unfeasible, thus limiting the specific capacity to 131 mA h g −1 . On further exploration, a new class of lithium-rich phosphate, with composition Li 9 M 3 (P 2 O 7 ) 3( PO 4 ) 2 (M = Fe, Al, Cr, Ga) was identified and firstly reported in 1998 by S. Poisson et al. in his studies on A 2 O-M 2 O 3 -P 2 O 5 (A = Li, Na; M = Fe, Al, Cr, Ga) glasses.9 Since then, various research groups have investigated Li 9 M 3 (P 2 O 7 ) 3( PO 4 ) 2 (M = Fe, Ga, Cr) structures and their properties for various applications. [10][11][12][13] The potential application of the vanadium-based lithium monodiphosphate Li 9 V 3 (P 2 O 7 ) 3 (PO 4 ) 2 (LVPP) ...

Kinetics and Structural Investigation of Layered Li9V3(P2O7)3(PO4)2 as a Cathode Material for Li‐Ion Batteries

“…As expected, in this potential range the third voltage plateau is observed at 4.65 V, and the voltage profile is not retained after the first electrochemical charge. High polarization, significant changes in the voltage profiles and rapid capacity fading are observed upon cycling, in agreement with previously reported results ,. This electrochemical behavior can be ascribed to different reasons, including irreversible structural changes induced by deep de‐lithiation.…”

“…The galvanostatic charge/discharge profiles of M‐LVPP and N‐LVPP at room temperature have been already reported in our previous paper . Improved discharge capacity and high rate capability were obtained for electrodes based on N‐LVPP.…”

“…It is known that higher amount of Li ions can be extracted from LVPP by increasing the upper cut off potential to 4.8 V. We have recently reported that a further voltage plateau occurs during the first charge at 4.65 V contributing to the overall capacity . However, this high voltage plateau disappears after the first cycle.…”

“…Detailed DFT‐based theoretical studies on LVPP, have been carried out by Ceder and his coworkers . Similar to LVP, LVPP can also be cycled within different potential windows, such as 2–4.6 and 2–4.8 V. We recently reported that controlling the growth of crystallites during synthesis can effectively improve cycling stability and rate capability of LVPP . However, open questions on the transport properties within the lattice, changes in the structure and phase transformation during delithiation / lithiation, need to be addressed in order to further improve the electrochemical performance of LVPP.…”

Defects, Dopants and Lithium Mobility in Li 9 V 3 (P 2 O 7 ) 3 (PO 4 ) 2

“…Recently, Balasubramaniam et al . 25 have reported a cost effective way of synthesis and discussed the influence of crystallite size and carbon coating on the electrochemical performance. Jain et al .…”