P2-type Na_2/3Ni_1/3Mn_2/3O₂ Cathode Material with Excellent Rate and Cycling Performance for Sodium-Ion Batteries

Abstract

P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is an air-stable cathode material for sodium-ion batteries. However, it suffers irreversible P2-O2 phase transition in 4.2-V plateau and shows poor cycling stability and rate capability within this plateau. To evaluate the practicability of this material in 2.3-4.1 V voltage range, single-crystal micro-sized P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 with high rate capability and cycling stability is synthesized via polyvinylpyrrolidone (PVP)-combustion method. The electrochemical performance is evaluated by galvanostatic charge-discharge tests. The kinetics of Na + intercalation/ deintercalation is studied detailly with potential intermittent titration technique (PITT), galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). The discharge capacity at 0.1 C in 2.3-4.1 V is 87.6 mAh g-1. It can deliver 91.5% capacity at 40 C rate and keep 89% after 650 cycles at 5C. The calculated theoretical energy density of full cell with hard carbon anode is 210 Wh kg-1. The moderate energy density associated with high power density and long cycle life is acceptable for load adjustment of new-energy power, showing the prospect of practical application.

Negligible voltage hysteresis with strong anionic redox in conventional battery electrode

“…Additionally, the excellent rate performance and cycling stability of our material indicating an optimum configuration of the ORR on its kinetics. 33 This is the first time that strong and reversible (96%) ORR is conclusively confirmed with highly reversible electrochemical profile in both the voltages and profile lineshape, which were previously considered inherent to only cationic redox reactions.…”

“…Sample preparation and electrochemical profile have been discussed in previous works. 33 It is very important to note that these electrode displays excellent rate capability and cycling stability with highly reversible charge-discharge profile, indicating decent kinetics in NNMO system. 33 The voltage hysteresis of 4.2-V plateau is only about 0.1 V at 0.1 C (16 mA g -1 ), which is comparable with traditional cathode materials, e. g. LiCoO2.…”

“…33 It is very important to note that these electrode displays excellent rate capability and cycling stability with highly reversible charge-discharge profile, indicating decent kinetics in NNMO system. 33 The voltage hysteresis of 4.2-V plateau is only about 0.1 V at 0.1 C (16 mA g -1 ), which is comparable with traditional cathode materials, e. g. LiCoO2. 21 The Ni redox reaction could be quantitatively analyzed by fitting the Ni-L TFY spectra using a linear combination of the Ni 2+/3+/4+ standard TFY spectra from calculations.…”

“…1a). Additionally, this material is highly air stable with great practical potentials 32 , as well as excellent rate performance indicating facile kinetics 33 . The critical question here is whether the highly stable and high-rate properties stems from the typical cationic redox mechanism, or ORR could also offer such a good electrochemical performance with facile kinetics.…”

Redox Mechanism in Na-Ion Battery Cathodes Probed by Advanced Soft X-Ray Spectroscopy

“…Secondly, unlike other NIB electrodes, this compound presents a highly reversible electrochemical profile with well-defined plateaus close to each other during initial cycling, leading to a relatively high Columbic efficiency. Thirdly, the compound is highly air-stable and has an excellent rate and cycling performance, indicating great practical potentials and facile kinetics (Mao et al, 2019 ).…”