Structural and Electrochemical Sodium (De)intercalation Properties of Carbon‐Coated NASICON‐Na_3+yV_2−yMn_y(PO₄)₃ Cathodes for Na‐Ion Batteries

Abstract

Sodium-ion batteries are emerging as frontrunner candidates for grid storage application due to inexpensive and Earthabundant sodium precursor. [1] The present Na-ion prototype, which uses layered sodium-ion oxide cathode and hard carbon anode, provides moderate energy density (%150 Wh kg À1 ) compared with its Li-ion counterpart with few hundreds of cycles. [2] Albeit the layered oxides offer high intercalation capacities, they undergo multiple phase transitions during Na (de)intercalation which limit their cycle life, besides other issues such as lower insertion voltage and air instability. [3] Alternatively, polyanionic cathodes offer numerous advantages over their layered oxide counterparts such as rich crystal chemistry, chemical tunability, enhanced structural, chemical and thermal stabilities, and higher sodium-ion mobilities. [4] Among them, NASICON-Na 3 V 2 (PO 4 ) 3 (NVP) offers attractive operating voltage (V 4þ /V 3þ at 3.38 V vs Na þ /Na 0 ) with moderate storage capacity (%100 mAh g À1 ). [5,6] While the micrometer-sized NVP cathode delivers limited capacity (90 mAh g À1 at 1C rate), two major methodologies are utilized to improve its electrochemical performances, namely, 1) synthesizing carbon-coated NASICON-Na 3 V 2 (PO 4 ) 3 nanomaterials [7][8][9][10][11][12][13][14] and 2) tuning chemical composition through chemical doping /substitution. [15][16][17][18][19][20][21] Different alio-and isovalent cationic substitutions in the NVP yielded vanadium-lean multielectron redox cathodes (e.g., Na 3 VFe(PO 4 ) 3 and Na 4 VMn(PO 4 ) 3 ). [21,22] In particular, the V/Mn-based NASICON cathodes offer relatively higher operating voltage, lower cost, and toxicity compared with the NVP. Recently, our group systemically studied the impact of Mn 2þ substitution on the structural and electrochemical properties of micrometer-sized bulk Na 3þy V 2Ày Mn y (PO 4 ) 3 cathodes which were prepared by solid-state route. [23] In the voltage window of 3.8-2.75 V versus Na þ /Na 0 , the y ¼ 0.75 cathode delivered highest capacity of %104 mAh g À1 with good cycling stability (86% of retention after 100 cycles) and better rate performances (91 mAh g À1 at 5C). However, the Mn-rich cathodes displayed severe capacity decay upon extending the cycling window to 4.2-2.75 V versus Na þ /Na 0 due to irreversible structural transformation occurring at higher voltage. [23] The NASICON cathodes with micrometer-sized particles exhibited limited reversibility, cycling stability, and rate

Improved Electrochemical Performance of NASICON Type Na3V2–xCox(PO4)3/C (x = 0–0.15) Cathode for High Rate and Stable Sodium-Ion Batteries

“…A slight decrease observed in c-parameter for NVP-Co10 and NVP-Co15 samples may be attributed to the increase in the population of Na1 sites, resulting in a reduction in electrostatic repulsion between the oxygen layers that are perpendicular to the c-axis of the unit cell. 34,46,47 Similarly, lattice constant a with the tiny variation upon the substitution (8.59 Å) confirms the identical [O 3 NaO 3 (V/Co)O 3 NaO 3 ] column size. 46 The detailed bond lengths for the atoms from the Bond Valence Sum (BVS) calculations and the refined atomic positions and occupancies for all the samples are also presented in Tables S1 and S5 of the Supporting Information.…”

Stabilizing Multi‐Electron NASICON‐Na1.5V0.5Nb1.5(PO4)3 Anode via Structural Modulation for Long‐Life Sodium‐Ion Batteries

“…The synthesis of NVP was carried out according to the literature. [ 57 ] The NVP electrode was prepared by mixing the active material, Super C45 and PVDF in a weight ratio of 70:22:8 with NMP and the slurry was coated on an Al foil. The capacity ratio between anode and cathode was maintained at ≈1.2:1 (mass ratio is ≈1.07:1), so that the cell capacity was limited by the cathode.…”

Tailoring High-Performance Ternary Transition Metal-Based NASICON-Na(9–2x–3y–4z)MnxVyZrz(PO4)3 Cathodes via Combinatorial Chemical Substitutions

“…More interestingly, the systematic substitution of Mn 2+ into Na 3+ x V 2– x Mn x (PO 4 ) 3 series increases the length of solid-solution domains during Na (de)­intercalation, and the intermediate Na 3.75 V 1.25 Mn 0.75 (PO 4 ) 3 also delivers high rate capabilities (89 mAh g –1 at 5C rate) , Further, the V/Mn-based NASICON cathodes were subjected to high-voltage cycling (>3.8 V) to attain higher capacities (∼150 mAh g –1 ), but they suffered serious capacity decay due to irreversible structural degradation. ,− …”