Surface-Phase Engineering via Lanthanum Doping Enables Enhanced Electrochemical Performance of Li-Rich Layered Cathode

Abstract

High-capacity Li-rich layered oxides (LLOs) hold giant promise as cathodes for Li-ion batteries but still suffer from cycling instability and voltage decay. The oxygen redox reaction and phase transformation to spinel are major incentives for performance deterioration. Hence, we propose a La-doping strategy to stabilize surface oxygen and reduce spinel phase components. The special La–O bond could exhibit not only an electrovalent characteristic bond but also a relative covalent property, which enhances the stability of lattice oxygen and the reversibility of oxygen redox. The spinel phase composition of surface area could be reduced through La doping, which suppresses capacity fade and voltage decay. Accordingly, the La-doping LLOs with Li and O vacancy defects forming at the surface area exhibit excellent reversible capacity (225 mA h/g at 1 C and 145 mA h/g at 5 C) and rate performance (80.68 and 81.76% capacity retention over 300 cycles at 1 and 5 C). This study could be extended to synthesize other advanced cathode materials for next-generation Li-ion batteries and even be helpful to the R&D of rare-earth utilization.

Ni/Mg Dual Concentration-Gradient Surface Modification to Enhance Structural Stability and Electrochemical Performance of Li-Rich Layered Oxides

“…The intensity, symmetry, and position of the peaks in the CV curves are indicative of polarization and redox kinetics. 40 CV tests with different scanning rates (0.1 0.2, 0.5, 0.8, and 1 mV/s) were performed from 2 to 4.8 V, respectively, as shown in Figure 5a−c. The apparent Li + diffusion coefficient (D Li ) can be calculated according to the Randle−Sevcik equation by fitting the relationship between the scan rate and the peak current (i p ) as follows 13,31 I n AD v C 2.99 10 p Li…”

“…The intensity, symmetry, and position of the peaks in the CV curves are indicative of polarization and redox kinetics . CV tests with different scanning rates (0.1 0.2, 0.5, 0.8, and 1 mV/s) were performed from 2 to 4.8 V, respectively, as shown in Figure a–c.…”

Enhanced Performance of Li‐Rich Manganese Oxide Cathode Synergistically Modificated by F‐Doping and Oleic Acid Treatment

“…As shown in Figure 5i, the peaks at ≈532.5, 531.5, 530.5, and 529.5 eV may origin from oxidized electrolytes, CO 3 2− derivative, oxygen vacancy defects, and lattice oxygen, respectively. [31,36,44] The peak intensities of CO 3 2− and oxidized electrolyte of FOA are significantly lower than those of PR, revealing that the incorporated F element and as-coated carbon layer could reduce the electrolyte corrosion and TM dissolution. Additionally, the oxygen vacancy ratio of FOA sample was higher than that of PR.…”

“…The peak at ≈3.15 V of PR sample during the discharge process is primarily attributed to the transformation from layered phase to spinel phase of LRMOs with extended cycling time, which may produce a partial spinel phase. [ 36 ] This peak of FOA sample can be separated into two peaks that are positioned at 3.42 and 3.66 V, respectively. These peaks overlap each other and form a small rejection plateau.…”

“…This phenomenon shows that our proposed modification strategy could favor the structural stability of LRMOs. [ 36,37 ] In other words, the reduction peak of FOA sample diverges to higher potential, indicating that its polarization is weakened. This characteristic demonstrates that the electron conductivity of FOA might be enhanced.…”