A Cobalt‐Free Li(Li_0.16Ni_0.19Fe_0.18Mn_0.46)O₂ Cathode for Lithium‐Ion Batteries with Anionic Redox Reactions

Abstract

Lithium‐rich, Mn‐based layered oxides Li2MnO3‐LiMO2 (M=Ni, Co) have been considered as promising cathode candidates owing to their high capacity. However, the resources shortage and high price of cobalt make it imperious to substitute cobalt with other high‐abundance elements. Here, we synthesized a low‐cost, cobalt‐free, Fe‐substituted oxide material, Li(Li0.16Ni0.19Fe0.18Mn0.46)O2. It exhibited a high reversible capacity of 169.2 mAh g−1 after 100 cycles and maintained an extraordinarily high discharge potential during cycling. X‐ray photoelectron spectroscopy and DFT calculations revealed that super iron FeIV exists in the delithiated state, and oxygen participates in the redox reaction in addition to the Ni2+/Ni4+ and Fe3+/Fe4+ redox couples. The anionic oxidation preferentially occurred on oxygen with a Li−O−Li configuration and with oxidized Fe and Ni coordination.

A Cobalt‐Free Li(Li0.17Ni0.17Fe0.17Mn0.49)O2 Cathode with More Oxygen‐Involving Charge Compensation for Lithium‐Ion Batteries

“…Calculated geometrical parameters, O-O layer spacing d,v olumec hangesb efore and after delithiation DV,enthalpychanges DH Li ,d istortione nergies E d ,a nd average redox potentials V ave of LNFMO. This is consistentw ith our experimental result for LNFMO, which has ah igh discharge potential (> 3.63 Vv s. Li/ Li + )a tf irst discharge and retains 3.44 Va fter 50 cycles, [43] which implies suppressed potentialf ading. Figure 2d shows the enthalpy changes ¾H O of LNFMO and LNCMO obtainedb ye valuating release of the most-active O4.…”

“…This indicates that Fe substitution can restraino xygen release to ac ertain extent,t hough TMÀOb onds in LNFMO are little weaker than those of LNCMO (Table 2S). This is consistentw ith our experimental result for LNFMO, which has ah igh discharge potential (> 3.63 Vv s. Li/ Li + )a tf irst discharge and retains 3.44 Va fter 50 cycles, [43] which implies suppressed potentialf ading. Release of Oi ons starts at x > 18 in LNFMO and the capacity at x = 18 is approximately 250 mAh g À1 .O nthe basis of the following discussion of the redox processes of TM and O, Or edox processes contribute 22 %t ot he capacity of 250 mAh g À1 ,t hat is, 0. configuration.…”

“…These redox processes of Ni, Fe, and Oi nL NFMO are consistent with the experimental XPS data ( Figure 4S, for detailed results see our previous work [43] ). XPS shows that Ni and Fe in the pristinem aterial are in lower oxidation states (+ 2s tates for Ni and + 3s tates for Fe).…”

“…XPS shows that Ni and Fe in the pristinem aterial are in lower oxidation states (+ 2s tates for Ni and + 3s tates for Fe). Figure 4s hows the delithiation potentiala safunction of x in Li 28Àx Ni 4 Fe 4 Mn 12 O 48 .A ccordingt oe xperiment results, [43] the first charge curve of LNFMO can be divided into two regions. Both Ni and Fe are oxidized to the + 4s tate.…”

“…[43] It has potentialt oachieve higher-energy-density cathode materials, as oxygen oxidation is involved besides Ni 2 + /Ni 3 + /Ni 4 + redox couples during the initial charging, followed by Fe 3 + /Fe 4 + .T he oxidation process is related to the redox competition of TM and O, and Oi nt he Li-O-Li configurationi sp referably oxidized. [43] It has potentialt oachieve higher-energy-density cathode materials, as oxygen oxidation is involved besides Ni 2 + /Ni 3 + /Ni 4 + redox couples during the initial charging, followed by Fe 3 + /Fe 4 + .T he oxidation process is related to the redox competition of TM and O, and Oi nt he Li-O-Li configurationi sp referably oxidized.…”