K0.54[Co0.5Mn0.5]O2: New cathode with high power capability for potassium-ion batteries

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

“…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 clearly indicates the participation of Ni ions in the redox reactions. It is noteworthy such high voltage plateau was not observed in the case of the Ni-substituted K 0.5 Ni 0.1 Mn 0.9 O 2 oxide, [21] for which Ni 3 + /Ni 2 + and Mn 4 + /Mn 3 + redox processes were involved below 4 V. Hence, the occurrence of the Ni 4 + / Ni 3 + transition at a higher voltage of 4.1/4.4 V can be safely proposed for KMNO. This high voltage step involves a faradaic yield of � 30 mAh g À 1 , which indicates that 0.1e À would contribute to the Ni 4 + /Ni 3 + redox reaction while the remaining 0.2e À would be implied in the Mn 4 + /Mn 3 + transition occurring at lower voltage (from 3.5 V to 2 V).…”

“…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.…”