Binding Li₃PO₄ to Spinel LiNi_0.5Mn_1.5O₄ via a Surface Co‐Containing Bridging Layer to Improve the Electrochemical Performance

Abstract

Coating the surface of cathode materials with Li3PO4 to improve the cycling performance is commonly practiced; however, obtaining an effective and uniform coating of Li3PO4 on cathode materials is extremely difficult due to the lack of strong bonds between them. Herein, this issue is solved by coating the surface of LiNi0.5Mn1.5O4 with Li3PO4 via a novel hydrothermal method. It is shown that a uniform Li3PO4 surface coating can only be obtained by introducing a small amount of additional metal ions, such as Co, in the starting solution. X‐ray photoelectron microscopy combined with scanning transmission electron microscopy reveals that the Co ions diffuse into the 16c sites of the surface of the spinel LiNi0.5Mn1.5O4 structure, making the surface layer act as a bridging layer that connects olivine Li3PO4 with bulk spinel LiNi0.5Mn1.5O4. The high‐voltage LiNi0.5Mn1.5O4 half‐cell with the optimal Li3PO4 coating shows a discharge capacity retention of 95.8% after 50 cycles at 55 °C, compared with the only 81.1% discharge capacity retention of the bare counterpart.

Lithium-Ion Conductivity Epitaxial Layer Contributing to the Structure and Cycling Stability of LiMn2O4 Cathodes

“…Nevertheless, the structural incompatibility between the rhombohedral Li 3 PO 4 and the material structures makes it difficult for rhombohedral Li 3 PO 4 to bond to the surface of the spinel cathode material making it difficult to combine them; these coating processes tend to form an uneven modification and poor crystallographic layer . Recently, Wu et al reported that the introduction of Co/Fe as a bridging ion in the process of spinel coating can effectively induce a uniform coating of structurally incompatible Li 3 PO 4 on the surface of the spinel cathode structure, exhibiting superior high-temperature capacity retention to that of the bare LMO electrode. , To study the reaction of the electrode/electrolyte interface, a pulsed laser deposition method was used to prepare Li 3 PO 4 epitaxial film-coated LMO, which effectively improved the electrode structure and surface stability and the electrochemical properties of the thin-film electrode. , Li et al suggest that using ball milling and high-temperature heating to coat the LiMn 2 O 4 surface with a nano-Li 3 PO 4 layer to improve the high-temperature performance of the materials, the electrode exhibited a 19.4% increase in capacity retention after 100 cycles at 55 °C . Previous works have suggested that if the coating material is loosely bonded with the cathode surface, the improvement in cycling performance is limited, especially at high-temperature conditions.…”