One‐Step Sintering Synthesis Achieving Multiple Structure Modulations for High‐Voltage LiCoO₂

Abstract

The structure instability issues of the highly delithiated LiCoO2 have significantly hindered its high‐voltage applications (≥4.55 V vs Li/Li+). Herein, for the first time, multiple modifications of Li0.9Mg0.05CoO2 (L0.9M0.05CO) via a simple one‐step sintering synthesis are reported. A combination of the bulk Li/Co antisites, a Mg‐pillar enriched surface, and a thin MgO coating layer is achieved to maintain both the bulk and surface structural stability of L0.9M0.05CO upon cycling at an upper cut‐off voltage of 4.6 V. The bulk Li/Co antisites are discovered to enhance the H1‐3 phase evolution reversibility, the Mg pillars that substitute the Li sites effectively reinforces the surface structure, and the thin MgO coating layer can effectively prevent the cathode from severe side reactions. Benefiting from the reduced but reversible H1‐3 phase transition and the reinforced surface structure, L0.9M0.05CO shows an excellent cycle stability. This work provides a new structure modulation route for developing high‐voltage LiCoO2 cathodes.

Structural Understanding for High‐Voltage Stabilization of Lithium Cobalt Oxide

“…We recently advanced this study and discovered that Mg doping also induces bulk Li/Co antisites and a surface Mg─O layer, thereby preserving the stability of both the bulk and surface structure. [90] Furthermore, Liu et al achieved LMCO and LCMO with the same 4% doping amount and confirmed the superior structural stability of LMCO, which is due to the above Mg-pillaring benefits plus alleviated CoO 6 distortion and structural stress. [91] Al as an LCO dopant also has various merits, such as 1) good lattice solubility due to similar ionic radius (0.535 Å) and same +3 valence as Co 3+ and presence of isostructural 𝜆-LiAlO 2 , 2) excellent structural stabilization by stronger Al─O bonding (bond energy: 511 ± 3 kJ mol −1 ) than Co─O (bond energy: 384.5 ± 13.4 kJ mol −1 ) and invariable valence, [92] and 3) improved operating voltage and thermal stability.…”

“…We recently advanced this study and discovered that Mg doping also induces bulk Li/Co antisites and a surface Mg─O layer, thereby preserving the stability of both the bulk and surface structure. [ 90 ] Furthermore, Liu et al. achieved LMCO and LCMO with the same 4% doping amount and confirmed the superior structural stability of LMCO, which is due to the above Mg‐pillaring benefits plus alleviated CoO 6 distortion and structural stress.…”

Fundamentals, status and challenges of direct recycling technologies for lithium ion batteries

“…The lithium and cobalt contained in LCO are facing a supply crisis; so the development of a recycling technology for the material is of the utmost importance. 95 LCO crystals are hexagonal and have an O3-type layer structure (space group: R 3̄ m ). During charging, it gradually undergoes a phase transition from H1 to H2, M1, H3, M2 and O1 phases with the continuous deintercalation of Li + (Fig.…”

Revealing the Grain-Boundary-Cracking Induced Capacity Decay of a High-Voltage LiCoO2 at 4.6 V

“…Based on this basis, we have developed some facile methods to reinforce the surface structure of LCO, including reconstructing an Al/F enriched and spinel reinforced surface to reduce the side reaction, and promoting the surface electric conductivity of LCO by over one magnitude via constructing a disordered rock-salt phase in the surface region . Besides, we also have developed a one-step sintering synthesis to achieve a combination of bulk Li/Co antisites, Mg-pillar enriched surface, and thin Mg–O coating layer for enhanced structure stability in both the bulk and surface region …”