A Li-rich layered-spinel cathode material for high capacity and high rate lithium-ion batteries fabricated via a gas-sol
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Published online 8 September 2020 | https://doi.org/10.1007/s40843-020-1433-4
A Li-rich layered-spinel cathode material for high capacity and high rate lithium-ion batteries fabricated via a gas-solid reaction 1,3†
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Lingqun Xu , Zhenhe Sun , Yu Zhu , Yu Han , Manman Wu , Yanfeng Ma , Yi Huang , 2,3* 2,3* Hongtao Zhang and Yongsheng Chen ABSTRACT Lithium-rich layered oxide (LLO) cathode materials have drawn extensive attention due to their ultrahigh specific capacity and energy density. However, their commercialization is still restricted by their low initial coulombic efficiency, slow intrinsic kinetics and structural instability. Herein, a facile surface treatment strategy via gaseous phosphine was designed to improve the rate performance and capacity stability of LLOs. During the solid-gas reaction, phosphine reacted with active oxygen at the surface of LLOs due to its reductivity, forming oxygen vacancies and spinel phase at the surface region. As a result, Li ion conductivity and structural stability were greatly enhanced. The phosphinetreated LLOs (LLO@P) showed a layered-spinel hybrid structure and delivered an outstanding rate performance of −1 156.7 mA h g at 10 C and a high capacity retention of 74% after 300 cycles at 5 C. Keywords: cathode materials, li-rich, layered-spinel structure, high rate performance, phosphine
INTRODUCTION Lithium-ion batteries (LIBs) are considered to be one of the most promising energy storage devices for electric vehicles due to their high energy density and long life span [1,2]. However, further improvement in energy density is necessary for their applications in electric vehicles and storage systems [3–5]. The practical capacity of cathode materials is the key factor influencing the energy density of LIBs [6]. Li-rich layered oxide (LLO) cathode materials have been brought into focus due to their ultrahigh specific capacity and energy density (Fig. S1) [6–9].
However, there are still some challenges which restrict the industrialization and commercial applications of LLOs [10,11], including poor kinetics, inferior structural stability and low initial coulombic efficiency [12–14]. LLOs consist of rhombohedral LiMO2 (M = Mn, Ni or Co) phase and monoclinic Li2MnO3 phase [15,16]. The special oxygen anion redox process provides LLOs with a −1 high specific capacity of over 300 mA h g [1]. However, oxygen is easily and irreversibly extracted from the crystal structure during the active processes of Li2MnO3, which simultaneously destroys the crystal structure of LLOs and leads to large irreversible specific capacity as well as low initial coulombic efficiency [17–19]. Furthermore, the released oxygen can react with electrolyte and generate various byproducts, which accelerates the accumulation of inert components and increases the internal impedance [1,20,21]. Besides, LLOs show poor kinetics due to the introduction of Li2MnO3 component with inferior ion and electron conductivities [13]. As a result, the rate performance and cycle stability of LLOs need to be
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