Lower Diffusion‐Induced Stress in Nano‐Crystallites of P2‐Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ Novel Cathode for High Energy Na‐ion Batteries

Abstract

ion battery research has been evolving as an indigenous solution to electrochemical energy storage applications. [1][2][3][4] This is in light of the high availability and inexpensiveness of Na resources, sustainability, and redox chemistry similar to lithium-ion batteries. [5] Amidst the various cathode materials being explored for Na-ion batteries, the P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is a preeminent one, [6] owing to the environmental friendliness, [7] facile synthesis, [8] superior specific capacity (theoretical capacity, 173 m Ah g −1 ), [9] higher operating voltage (ideally ≈3.7 V), [10] higher energy density, [11,12] open prismatic framework for sodium-ion diffusion with a low diffusion barrier, [13] good structural integrity [14] cobalt free composition, and air-moisture insensitiveness. [12,15] Challenges that inhibit the peak utilization of the P2 type Na x Ni 1/3 Mn 2/3 O 2 (0 ≤ x ≤ 2/3) cathode for sodium-ion battery are; rapid capacity decay when operated at a higher voltage (>4.2 V), [16,17] large volume change in the structure due to a phase transition from P2 to O2 type, inducing particle cracks and exfoliation. [18] The phase transition from P2 to O2 type is thermodynamically favorable when x < 1/3, where the stacking fault of the O2-type structure co-exists with the P2-type. [19] However, the incapability of the O2-type structure to convert back to P2-type causes an irreversible capacity loss. [20,21] The P2-O2 phase transition during desodiation also causes severe volume change (≈23%). This is due to the lower formation energy density of the O2 type than the P2 type phase at higher voltage, inducing exfoliation and cracking in the crystal. [22] Various strategies such as limiting the cut-off potential have been employed, [23] but the operating voltage, capacity, and energy density were sacrificed. [23,24] Efforts have also been devoted to improving the charge capacity by synthesizing high sodium content P2-type layered oxide cathode materials. It helps in avoiding the structural transition by ensuring electrostatic repulsions between the transition metal oxide slabs. [25] Simultaneous surface coating and Ni doping to subdue the Mn-ions dissolution and the orthorhombic distortion, thereby enhancing the structural stability have also been adopted. [26] P2-type Na 2/3 Ni 1/3 Mn 1/2 Ti 1/6 O 2 (NMTNO) cathode is a preeminent electrode material for Na-ion batteries owing to its open prismatic framework, air-moisture stability, inexpensiveness, appealing capacity, environmental benignity, and Co-free composition. However, the poor cycling stability, sluggish Na-ion kinetics induced in bulk-sized cathode particles, cracking, and exfoliation in the crystallites remain a setback. To outmaneuver these, a designing strategy of a mechanically robust, hexagonal nano-crystallites of P2-type Na 2/3 Ni 1/3 Mn 1/2 Ti 1/6 O 2 (NMTNO nano ) electrode via quick, energy-efficient, and low-cost microwave-irradiated synthesis is proposed. For the first time, employing a unified experimental and theoretical approach w...

The effect of configurational entropy on acoustic emission of P2-type layered oxide cathodes for sodium-ion batteries

“…For both 3-and 7-NTMO 2 , figures 5(a)-(h) and S7 show images collected from the cathodes before and after cycling (1, 5 and 50 cycles). In cycled electrodes, not only the formation of intragranular crack planes, visible as parallel lines, can be observed, but also the expansive delamination and exfoliation of cracked (single-crystalline) particles in absence of other, directly adjacent particles, as also reported in the literature [11,12,17,69,70]. However, when such particles are present, signs of deagglomeration and formation of intergranular voids are increasingly apparent.…”

“…Figure S6 shows additional top-view SEM images of particles at the end of discharge after both one and five cycles, demonstrating that cracks do not disappear after resodiation and return to the initial unit cell volume, while the occurrence of intragranular cracks and associated phenomena, such as delamination, exfoliation and electrochemical creep [17,[68][69][70], increases with the number of cycles. Top-view imaging relies on particles on the electrode surface after assembly and the study of deagglomeration is complicated by loss of such particles from the surface.…”

Sodium Stoichiometry Tuning of the Biphasic‐NaxMnO2 Cathode for High‐Performance Sodium‐Ion Batteries

“…[ 8–12 ] However, owing to the large radius of Na + , it is full of challenges to construct suitable structure that facilitates rapid Na + diffusion and maintains robust stability. [ 13–20 ]…”

“…[8][9][10][11][12] However, owing to the large radius of Na + , it is full of challenges to construct suitable structure that facilitates rapid Na + diffusion and maintains robust stability. [13][14][15][16][17][18][19][20] The manganese oxides (Na x MnO 2 ) have gained numerous investigations owing to their environmental friendliness, abundant resource and low cost. [21,22] The various compositions/crystal structures show reversible Na + insertion/extraction performance.…”

Optimization Strategies Toward Functional Sodium‐Ion Batteries

“…c) Galvanostatic charge-discharge curves of NMTO nano at 0.1 C, potential range 2.5-4.3 V. d) Rate performance and e) cycling stability of NMTO nano and NMTO micro . d) Reproduced with permission [50]. Copyright 2023, John Wiley & Sons.…”