Modifying Li@Mn₆ Superstructure Units by Al Substitution to Enhance the Long‐Cycle Performance of Co‐Free Li‐Rich Cathode

Abstract

As one of the most promising cathodes for Li‐ion batteries, Li‐rich layered oxides suffer from low Coulombic efficiency, severe capacity fading, and voltage decay, which are related to the aggregated Li@Mn6 superstructure units. Herein, a Co‐free Li‐rich oxide Li[Li1/4Mn1/2Ni1/6Al1/12]O2 through Al substitution of Co in Li[Li1/4Mn1/2Ni1/6Co1/12]O2, is designed. Combining the average structural refinement with the detailed local structural/chemical analysis, it is found that the introduced Al ions occupy the Mn sites in Li@Mn6 superstructure units, which further induces the partial replacement of the central Li ions in Li@Mn6 units by Ni2+. The modified superstructure units stabilize the anionic framework and suppress structural degradation during long‐term cycling. A superior cyclability (a capacity retention of 91.4% after 500 cycles at 1 C) is achieved. This work not only deepens the understanding into the mechanism of Al substitution, but also provides a novel route to design high‐performance Li‐rich cathodes by modifying the local functional units.

Inhibiting Mn Migration by Sb‐Pinning Transition Metal Layers in Lithium‐Rich Cathode Material for Stable High‐Capacity Properties

“…[ 34,35 ] At the same time, the crystal structure model with atomic arrangement features also can be observed in Figure 1d. [ 36 ] As shown in Figure 1e, through modulation of Sb, the distance between Mn and O becomes larger, realizing the decrease of energy level of Mn 3d and O 2p orbitals, beneficial to restrain the over redox of anions and cations. Additionally, Figure S4, Supporting Information, reveals that the parallelogram circled belonging to SLNMO C2/m [100] zone axis also has an enlarged side length, which further confirms the consistency of the conclusion.…”

Approaching a stable oxygen redox reaction in lithium-rich cathode materials: structural perspectives from mechanism to optimization

“…During cycles, more and more TM ions are trapped in the Li layer, resulting in permanent voltage decay and even spinel phase transition. 7,165 Hence, they believe that the fundamental factor of voltage decay in Li-rich materials is not the TM ion migration, but the irreversibility of TM ions in the Li layer returning to the TM layer. Based on this, the O2-LLO was designed to build an energy barrier between the V tet and Li oct sites to prevent the permanent retention of TM ions in the Li layer and realize the reversible back-intercalation of TM ions.…”

Restraining the Octahedron Collapse in Lithium and Manganese Rich NCM Cathode toward Suppressing Structure Transformation

“…[ 1,2 ] Compared with the advanced anode, the energy density of LIBs is more largely determined by discharge capacity and voltage of the cathode. [ 3–5 ] Lithium and manganese rich nickel cobalt manganese oxide (LMRNCM), x Li 2 MnO 3 ·(1‐ x )LiTMO 2 (TM (transition metal) = Mn, Ni, Co), has been considered as an attractive next‐generation cathode candidate owing to its high energy density (≈1000 Wh kg −1 ) and low cost. [ 6 ]…”

“…The less spinel-like phase in LMRNCM-PAN particle directly proves that the irreversible migration of TM ions is effectively suppressed by coordination bond interaction. [3,48] After 150 cycles, the spinel-like phase in the LMRNCM-PVDF is observed in the HRTEM images (Figure S14, Supporting Information). By contrast, although the spots of the spinel-like phase become brighter in FFT of the LMRNCM-PAN particle selected area, the spots of layered structure still can be observed.…”

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Compared with the advanced anode, the energy density of LIBs is more largely determined by discharge capacity and voltage of the cathode. [3][4][5] Lithium and manganese rich nickel cobalt manganese oxide (LMRNCM), xLi 2 MnO 3 •(1-x)LiTMO 2 (TM (transition metal) = Mn, Ni, Co), has been considered as an attractive next-generation cathode candidate owing to its high energy density (≈1000 Wh kg −1 ) and low cost. [6] According to the charge compensation mechanism and the energy level theory, when the Li + extraction voltage is lower than 4.4 V, the TM ions of high electron energy level is mainly oxidized to maintain electrical neutrality.

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