Surface Design with Cation and Anion Dual Gradient Stabilizes High‐Voltage LiCoO₂

Abstract

energy density among the reported cathode materials, thus dominates the current battery market for electronics. [3,4] The practical reversible capacity of LCO is only ≈160 mA h g −1 with a cutoff voltage of 4.35 V, far below the theoretical capacity (274 mA h g −1 ), thus there is still a large space for expanding the capacity. [5,6] Further increasing the charging cutoff voltage is the most effective approach to extract more Li + from the LCO framework. [7,8] For example, La-and Al-co-doped LCO offered an initial capacity of ≈190 mA h g −1 with a cut-off voltage of 4.5 V and retained 96% capacity after 50 cycles, [9] and Ti-Mg-Al co-doped LCO offered an initial capacity of 202 mA h g −1 with a cut-off voltage of 4.6 V and retained 86% capacity after 100 cycles. [10] However, the origin of structural stability by these trace doping remains unclear, which restricts the further development of high-voltage LCO.Our recent work revealed the structural differences between regular LCO and high-voltage LCO at the atomic level, and correlated the curvature of the Co-O layers near the surface with structural instability. [11] Li's group reported a hybrid Co cation and O anion redox occurred at a high voltage of 4.6 V. [12] As shown in Scheme 1a, the generated Co 4+ and O − species at high potentials would induce the severe surface side reactions, including the catalytic decomposition of the carbonate-based electrolyte, and the lattice O loss in the form of CO 2 . Such O loss would lead to the irreversible Co migration, formation of dense Co 3 O 4 spinel phase at the surface that would block Li + diffusion, [13] and lattice distortion in the bulk evolving into microcracks upon cycling. [14] Aiming to effectively resolve these critical issues, surface engineering is proved to be a direct and efficient strategy. [15] Lu's group reported the ternary lithium, aluminum, fluorine-modified LCO with improved cycling stability when operating at 4.6 V. [16] However, the active material was covered with a large amount of Al 2 O 3 and LiAlO 2 particles rather than a uniform coating layer, and it was still susceptible to HF attack from the electrolyte, thus the interfacial stability and structural integrity deteriorated upon longterm cycling. LCO with modified surface by electrochemically stable solid electrolyte Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 was prepared through mechanical mixing followed by a high-temperature annealing process to mitigate the catalytic effect of surficial Co 4+ species at LiCoO 2 (LCO) is the most successful cathode material for commercial lithium-ion batteries. Cycling LCO to high potentials up to 4.5 V or even 4.6 V can significantly elevate the capacity but cause structural degradation due to the serious surface side reaction between the highly oxidized Co 4+ and O − species with organic electrolytes. To tackle this concern, a new strategy, constructing cation and anion dual gradients at the surface of LCO (DG-LCO), is proposed. Specifically, the electrochemically inactive cation and anion are selected to substitu...

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“…1d). Referring to the previous papers, 24,25 we chose the EDS mapping image to visualize the elemental gradient. The four regions reveal a similar gradient distribution of Na and S (Fig.…”

High‐Entropy Surface Complex Stabilized LiCoO2 Cathode

“…Foreign element doping has been verified to be an effect method to limit the oxygen evolution and improve the stability of LCO. [20,22,23] Intriguingly, in some doping cases, segregation of the alien dopants can be observed on particle surface. [24,25] For examples, a highly soluble Ni and Al can segregate on the surface of LCO [20] and LiNi 0.94 Co 0.06 O 2 , [26] respectively.…”

Temperature-Driven Anisotropic Mg2+ Doping for a Pillared LiCoO2 Interlayer Surface in High-Voltage Applications

“…11,21−26 This method offers an effective type of surface-coating layer that can undergo a certain degree of expansion and contraction with the LCO bulk phase, thereby preventing the surface-coating layer from being damaged by the volume change of LCO. 23,24,27,28 Therefore, surface lattice coherent interface engineering is a significant development in improving the cycling stability of LCO under high voltage.…”

“…However, LCO is prone to layer-by-layer cleavage in the c -axis direction due to anisotropic volume change between the c -axis and a -axis directions, which can potentially rupture the surface-coating layer during battery cycling . To address these issues, researchers have developed lattice coherent interface engineering. ,− This method offers an effective type of surface-coating layer that can undergo a certain degree of expansion and contraction with the LCO bulk phase, thereby preventing the surface-coating layer from being damaged by the volume change of LCO. ,,, Therefore, surface lattice coherent interface engineering is a significant development in improving the cycling stability of LCO under high voltage.…”