Modification Of Lithium-rich Manganese-based Lithium-ion Battery Cathode Materials

Lithium-rich manganese-based cathode materials（LLO）has received much attention in recent years due to its higher capacity performance than Li Co O₂over a wide voltage range of 2.0 to 4.8 V.However,the voltage fade and poor cycling performance of LLOs severely limit their commercialisation.In this paper,Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂（LMNC）cathode materials were selected for the study,and the preparation and modification studies were carried out with the aim of improving the electrochemical performance,and the matching of sulphide solid-state electrolytes,halide solid-state electrolytes and LLO were also explored.The research is as follows:On the one hand,in liquid battery systems,LLO will lose oxygen during cycling leading to performance degradation,while the layered structure of the materials will continue to transform into spinel structure as cycling progresses,resulting in poor electrochemical performance of the cathode materials.Surface treatment is often considered as one of the effective solutions to improve the cycling stability of LLO.Therefore,in this work,a stable rock salt phase structure（RSP）was formed by using phosphate induction to reconstruct the surface of LMNC,in the hope of improving the problems present in the material.Characterization by scanning transmission electron microscopy-high angle annular dark field image（STEM-HAADF）,high-resolution scanning electron microscopy,in situ XRD and in situ EIS revealed that a Ni O-rich RSP interfacial protective layer was formed on the surface of the material by the induction of phosphate,which not only stabilized the layer structure but also enabled the electrode material to achieve excellent electrochemical properties.At 1 C and 5 C rates,the capacity retention of the modified material after 200 cycles reached 71.1%and 81.3%,respectively,compared to only 53.2%and 75.2%for the bare material.The experimental results demonstrate that the protective layer of Ni O rock salt phase formed by phosphate treatment not only inhibits the transformation of the layered structure to spinel structure during cycling,but also reduces the side reactions between the electrolyte and LMNC and facilitates the transport of lithium ions on the surface region of the cathode.On the other hand,all-solid-state lithium batteries with high specific energy can be developed by taking advantage of the excellent properties possessed by LLO.However,the large interfacial impedance exhibited by the battery during cycling is one of the most important reasons limiting the development of all-solid-state batteries.This work focuses on the interfacial problems exposed during the matching of LLO with sulphide solid-state electrolytes（Li Si PSCl）.In order to reduce the impact of interfacial impedance,the LLO is treated using the high electrical conductivity and good mechanical flexibility of the halide solid-state electrolyte（Li₃In Cl₆）with the better compatibility of the oxide cathode material.Meanwhile,Ru@LMNC was synthesized by using sol-gel method to lower the charging voltage and reduce the decomposition effect of high voltage on Li₃In Cl₆under high voltage.The actual results of the all-solid-state battery demonstrate that the first cycle discharge specific capacity at 0.1 C rate reached 209.2 m Ah g^-1compared to 147.3 m Ah g^-1for bare material.In terms of capacity retention,After 1000 cycles at 1 C,it reached51.2%.This compares to 28.3%for bare material.The cathode material modified by Ru doping effectively improved the electrochemical performance of the LLO in the all-solid-state battery system.The above work provides a new idea to explore the development of LLO in liquid and solid-state battery systems.