Surface Structure Evolution and its Impact on the Electrochemical Performances of Aqueous‐Processed High‐Voltage Spinel LiNi_0.5Mn_1.5O₄ Cathodes in Lithium‐Ion Batteries

Abstract

LiNi0.5Mn1.5O4 (LNMO) is a promising cathode in lithium‐ion batteries (LIBs) due to its high operating voltage and open Li+ diffusion framework. However, the instability of the electrode–electrolyte interface and the negative environmental impact of electrode fabrication processes limit its practical application. Therefore, switching electrode processing conditions to aqueous and understanding the accompanying surface structural evolution are imperative. Here, water‐treated, poly(acrylic acid) (PAA)‐treated, and H3PO4‐treated LNMO, labeled as W‐LNMO, A‐LNMO, and H‐LNMO, are studied systematically. W‐LNMO shows a high concentration of Mn3+ induced by Li loss while a conformal PAA layer formed on A‐LNMO reduces this phenomenon. H‐LNMO displays a second MnPO4∙H2O phase. Upon cycling, a fast capacity decay is observed in W‐LNMO while an extra plateau at ≈2.7 V appears in the initial charging, corresponding to a two‐phase transition. A surface reconstruction layer from a spinel to a rock‐salt phase with a reductive Mn2+ segregation is observed in W‐LNMO after 105 cycles. The PAA layer persists on A‐LNMO and alleviates the capacity decay. H‐LNMO delivers a relatively low capacity due to the formation of a MnPO4∙H2O phase. This study provides new insights into manipulating the surface chemistry of LNMO cathodes to enable aqueous, large‐scale processingin LIBs.

Unraveling the Role of Surficial Oxygen Vacancies in Stabilizing Li‐Rich Layered Oxides

“…The first charge/discharge profiles of LRH‐114 and LR‐114 in Figure 3 a show similar discharge capacities of around 300 mA h g −1 at 0.1 C (1 C = 250 mA g −1 ). Notably, the small discharge plateau at around 2.6 V for LRH‐114 is related to the spinel phase, [ 21 ] which is confirmed by the corresponding d Q /d V curve (Figure 3b). LRH‐114 exhibits better rate performance (Figure S9, Supporting Information), and the larger Li + diffusion coefficients ( D Li + ) derived from the GITT data (Figure S10, Supporting Information).…”

Improved Electrochemical Performance of Spinel LiNi0.5Mn1.5O4 Cathode Materials with a Dual Structure Triggered by LiF at Low Calcination Temperature

“…X-ray photoelectron spectroscopy (XPS) analysis was carried out to further understand the surface chemical composition and the chemical valence states of the as-prepared samples, and Figure shows the corresponding results. The high-resolution F 1s spectrum (Figure a) could be deconvoluted into three peaks, the binding energy of C–F at 688.0 eV (binding with applied carbon sources for XPS testing), the binding energy of Li–F at 685.0 eV, and the binding energy of TM-F around 684.0–685.0 eV. − The higher the LiF content added to LNMO, the higher the Li–F remaining on the surface of the LNMO particles. More interestingly, the ratio of TM-F bond intensity in the coating layer for LNMO-1.3LiF is larger than that of LNMO-2.6LiF, indicating that the surface chemical compositions of the coating layer will have an important role in the electrochemical performance of the as-prepared cathode materials.…”

Facet Dependence and Vacancy-Controlled Reversibility of the Spinel-to-Rocksalt Phase Transformation at Co3O4 Surfaces

“…For example, in Li-ion batteries using spinel oxide cathodes, irreversible S−R transformation was reported to block Li-ion transport and hence leads to capacity fading. 11,12 Nevertheless, for the oxygen evolution reaction (OER) of water splitting, a limiting reaction for green hydrogen production, 7 the S−R transformation could play an important role in promoting the catalytic activity of spinel oxide electrocatalysts. A typical example is the Co 3 O 4 spinel oxide, which represents one of the most active electrocatalysts for the OER.…”

“…Under the electrochemical conditions, it is shown that the spinel oxide surface may transform to a rocksalt phase, where the metal cations migrate from the tetrahedral sites to empty octahedral sites. − This spinel-to-rocksalt (S–R) transformation was reported to significantly affect their electrochemical performance and degradation depending on its different reversibility under different conditions. For example, in Li-ion batteries using spinel oxide cathodes, irreversible S–R transformation was reported to block Li-ion transport and hence leads to capacity fading. , Nevertheless, for the oxygen evolution reaction (OER) of water splitting, a limiting reaction for green hydrogen production, the S–R transformation could play an important role in promoting the catalytic activity of spinel oxide electrocatalysts. A typical example is the Co 3 O 4 spinel oxide, which represents one of the most active electrocatalysts for the OER.…”