Ti‐Based Surface Integrated Layer and Bulk Doping for Stable Voltage and Long Life of Li‐Rich Layered Cathodes

Abstract

High-energy-density lithium-rich layered oxides (LLOs) hold the greatest promise to address the range anxiety of electric vehicles. Their application, however, has been prevented by fast voltage decay and capacity fading for years, which mainly originate from irreversible transition-metal migration and undesirable cathode-electrolyte interfacial reactions. Herein, a Ti-based surface integrated layer and bulk doping, which greatly improve the voltage and capacity stability of LLOs is synchronously constructed. More importantly, STEM and Raman results demonstrate that continuous and uniform surface Ti-based integrated layer is a spinel-like rocksalt structure with Fd-3m space group, which is built through by several the replacement of Li ions in surface several atomic layers by Ti ions. After 500 cycles, Ti-150 sample delivers a capacity retention of 85%, and its voltage decay rate from the 30th to the 500th cycle is only ≈0.72 mV/cycle. Spectral results and DFT calculations suggest that bulk Ti-doping mitigates the migration of Mn and Ni ions in the bulk, while Ti-based integrated layer significantly suppresses surface structure evolution and interfacial reactions by impeding the generation of surface Li vacancies during Li extraction as well as preventing direct contact between electrolyte and active materials.

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

“…The charge from the metal band to the unhybridized oxygen state has to overcome greater obstacles, thereby promoting reversible oxygen redox. [21,58] Furthermore, the changes in bond length were acquired in the optimized crystal structure model, in which the MnO bond in SbLi 2 MnO 3 was extended from 1.949 to 1.952 or 1.994 Å under Sb regulation, confirming the analysis of STEM characterization, reflecting the decline of Mn 3d hybrid orbital energy level. [28] Elongated MnO bond enhances the ionization and charge transfer gap of LNMO, which favors effective oxygen oxidation and inhibits the formation of molecular oxygen.…”

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

“…The structural phase transformation of LLO due to the TM migration during cycling is closely related to the participation of lattice oxygen redox in charge compensation reactions. 4,97,98 The irreversible OR reaction induces the release of lattice oxygen, which weakens the binding force of TMs. 84,99 During the charging and delithiation process, the migration energy barrier of manganese ions decreases owing to the continuous formation of lithium and oxygen vacancies, and manganese ions tend to migrate to the lithium layer to form a defect-like spinel structure.…”

“…3 Despite the great prospects, the practical uses of LLOs are hindered by inherent drawbacks such as severe voltage decay, low coulombic efficiency, irreversible capacity loss, and so on, while most of them could be attributed to the irreversible oxygen redox (OR) reaction upon charge-discharge processes. 4,5 Typically, the OR chemistry refers to oxidation or reduction of oxygen under high chemical potential (e.g., vs. O 2 , H 2 /H + or AM/ AM + , AM ¼ alkali metal). 6 For the LLO cathodes in particular, the OR reaction mainly occurs at voltages higher than 4.0 V (vs. Li/Li + ), offering substantial capacity but meanwhile bringing about a host of irreversible charge-discharge behaviors.…”

Improving the Electrochemical Performance of a Lithium-Rich Layered Cathode with an In Situ Transformed Layered@Spinel@Spinel Heterostructure

“…Based on the above analysis, the key issue to improve lithium-rich layered oxide performance is to inhibit the phase transition and the irreversible release of lattice oxygen during the initial cycle. A great many modification studies have been carried out to improve the electrochemical performance of lithium-rich layered oxides. ,, To overcome these problems, many approaches have been investigated, such as material pretreatment, − cationic doping, − anion doping, − surface coating, − and core–shell structure. − In all the above strategies, the core–shell structure has been extensively studied because of the fact that no inactive component is introduced and the synergistic effect between the core component and the shell component is beneficial to improve the performance of the electrode. On the one hand, shell components can protect the host material from electrolyte corrosion and reduce the interfacial side reactions.…”