Improving the oxygen redox reversibility of Li-rich battery cathode materials via Coulombic repulsive interactions strategy

Abstract

The oxygen redox reaction in lithium-rich layered oxide battery cathode materials generates extra capacity at high cell voltages (i.e., >4.5 V). However, the irreversible oxygen release causes transition metal (TM) dissolution, migration and cell voltage decay. To circumvent these issues, we introduce a strategy for tuning the Coulombic interactions in a model Li-rich positive electrode active material, i.e., Li1.2Mn0.6Ni0.2O2. In particular, we tune the Coulombic repulsive interactions to obtain an adaptable crystal structure that enables the reversible distortion of TMO6 octahedron and mitigates TM dissolution and migration. Moreover, this strategy hinders the irreversible release of oxygen and other parasitic reactions (e.g., electrolyte decomposition) commonly occurring at high voltages. When tested in non-aqueous coin cell configuration, the modified Li-rich cathode material, combined with a Li metal anode, enables a stable cell discharge capacity of about 240 mAh g−1 for 120 cycles at 50 mA g−1 and a slower voltage decay compared to the unmodified Li1.2Mn0.6Ni0.2O2.

Oxygen-redox activity in non-Li-excess W-doped LiNiO2 cathode

“…Interestingly, this energy loss feature is highly comparable, if not identical, to that previously reported for all charged Li-excess and certain layered Na cathode materials. [13][14][15][16]18,64]. Ref.…”

“…[16] Based on this, it is reasonable to assume that molecular O2 is formed in the bulk of WLNO charged to 4.7 V, and the origin of the RIXS feature should be the same as that reported in Li1.2Mn0.54Ni0.13Co0.13O2 and other charged O-redox cathodes. [13][14][15][16]18,64] However, rationalising the formation of trapped bulk molecular O2 in the non-Li-excess WLNO cathode using the same reasoning as in Li-excess cathodes is not straightforward.…”

“…[11,12] Recent high-resolution RIXS (hr-RIXS) studies have ascribed the 'excess' capacity during charging to O 2− oxidation within the bulk as trapped molecular O2 (while ruling out other O-O dimer species) inside nano-sized pores (vacancies) formed through in-plane TM migration. [13,14] At the surface, the O 2− oxidization leads to irreversible O2 loss. The bulk O 2− →O2 oxidation phenomenon has been extended to other Liexcess systems [15,16] as well as Na intercalation compounds.…”

Controlled Cationic Disordering Eliminates Irreversible Anionic Redox for High-Energy-Density Lithium Battery

“…Numerous strategies have been proposed to inhibit irreversible oxygen evolution of LLO cathodes, such as oxygen vacancy injection [24][25][26] , spinel coating/integration [27][28][29] , anion doping 30,31 , etc.…”

“…The essence of those methods is to reduce the activity of lattice oxygen, which improves the chargedischarge reversibility but inevitably suppresses the oxygen redox thus sacrificing the energy density [24][25][26][27][28][29][30][31] . In addition, considerable efforts have also been made via regulating the structure of LLO materials [32][33][34] , yet they often demand complicated processes that will increase the manufacturing cost.…”