Cycling Stability of Layered Potassium Manganese Oxide in Nonaqueous Potassium Cells

Abstract

Potassium-ion batteries have emerged as an alternative to lithium-ion batteries as energy storage systems. In particular, K x MnO2 has attracted considerable attention as a cathode material because of its high theoretical capacity and low cost. In this study, partial substitution of Mn in P3-type K0.5MnO2 with divalent Ni is performed, resulting in a first discharge capacity of approximately 121 mAh (g-oxide)−1 with 82% retention for 100 cycles. Operando synchrotron X-ray diffraction analysis reveals the occurrence of phase transition from P3 to O3 on charge and O3–P3–P′3 transition on discharge at the first cycle, where P′3 is a new distorted form of the P3 phase, accompanied by reversible Mn4+/3+ and Ni3+/2+ redox pairs, as evidenced by X-ray absorption spectroscopy. The reduced variation in the lattice parameters during de/potassiation for P3-K0.5[Ni0.1Mn0.9]­O2 relative to P3-K0.5MnO2 is suggested as a possible reason for the enhanced electrochemical performance of K0.5[Ni0.1Mn0.9]­O2. These results open the possibility of using inexpensive and high-capacity Mn-based cathode active materials for potassium-ion batteries.

An Exploratory Investigation of Spinel LiMn1.5Ni0.5O4 as Cathode Material for Potassium‐Ion Battery

“…Such value overpasses the capacity retention observed for the non-substituted K 0.3 MnO 2 , [14] K 0.45 MnO 2 [15] and K 0.5 MnO 2 [16] materials, limited to retention capacities in the range 40-66 %. [14][15][16]19] On the other hand, the present capacity retention compares well with some results reported for Co and Ni-substituted manganese oxides. For instance, a value of around 80 % after 100 cycles is reached for Fe, Ni and Co-substituted oxides such as K 0.7 Fe 0.5 Mn 0.5 O 2 , [17] K 0.5 Ni 0.1 Mn 0.9 O 2 [19] and K 0.54 Co 0.5 Mn 0.5 O 2 .…”

“…The reversible capacity value of 90 mAh g À 1 displayed by KMNO is comparable to the values of~100 mAh g À 1 usually reported for layered manganese oxides investigated as cathode materials for KIBs. [14][15][16][17][18][19][20][21] Interestingly, the mid-discharge potential value of~3.10 V is~0.3 V higher than that observed for λ-MO. The consecutive charge is nearly symmetric, showing a wide sloping region followed by a quasi-voltage plateau at 4.40 V. A good efficiency of the potassium extraction/insertion reaction is observed for this second cycle.…”

“…This steady electrochemical fingerprint obtained from the second cycle ( Figure 5b) exhibits close resemblance with the typical profile reported for K x MnO 2 structures in K-containing electrolyte, characterized by a smooth variation in the 4 V-1.5 V or 4.2 V-1.5 V voltage ranges. [14][15][16][17][18][19][20][21] Such observations suggest the occurrence of a major structural change during the first discharge of KMNO and KMO, corresponding to a spinel to layered phase transformation. Furthermore, comparison of the discharge-charge profiles displayed by KMO ( Figure 4b) and KMNO (Figure 5b) reveals the existence of an additional insertion/extraction step at 4.1/4.4 V for KMNO ( Figure S3).…”

“…Up until now, very few promising KIB cathode materials have been successfully reported. Three main categories of compounds have been explored: polyanionic compounds such as KVPO 4 F [10] and K 3 V 2 (PO 4 ) 3 , [11] hexacyanometalates such as Prussian blue KFe 2 (CN) 6 , [12] Prussian blue analogs [13] and layered oxides such as K 0.3 MnO 2 , [14,15] K 0.45 MnO 2 , [15] K 0.5 MnO 2 , [16] K 0.7 Fe 0.5 Mn 0.5 O 2 nanowires, [17] K 0.45 Mg 0.1 Mn 0.9 O 2 , [18] K 0.5 Ni 0.1 Mn 0.9 O 2 , [19] K 0.67 Mn 0.83 Ni 0.17 O 2 , [20] K 0.54 Co 0.5 Mn 0.5 O 2 , [21] K x CoO 2 , [22,23] K 0.5 V 2 O 5 [24] or Na 0.9 Cr 0.9 Ru 0.1 O 2 . [25] Specific capacities between 90-120 mAh g À 1 have been reported for Mn-based layered oxides, depending on the structure, the chemical composition and the voltage range.…”

“…[25] Specific capacities between 90-120 mAh g À 1 have been reported for Mn-based layered oxides, depending on the structure, the chemical composition and the voltage range. [14][15][16][17][18][19][20][21] An outstanding discharge capacity of 178 mAh g À 1 is achieved for K 0.7 Fe 0.5 Mn 0.5 O 2 nanowires, due to the contribution of the two redox systems Fe 4 + /Fe 3 + and Mn 4 + /Mn 3 + , even when the nature of the mechanism is not discussed. [17] Besides these cathode materials, a compound of interest is the 3D phase λ-MnO 2 (λ-MO) with the spinel structure, first isolated by Hunter et al [26] While previous studies have investigated the sodium insertion properties into chemically [27] or electrochemically prepared λ-MO, [28] potassium insertion in such spinel framework has not been reported yet.…”