Rational design of bimetallic oxide anodes for superior Li+ storage

Abstract

The rapid advancement of scientific technology leads to a growing need for energy storage equipment in modern society. Lithium-ion batteries (LIBs) are extensively utilized in portable electronics, handy electric tools, medical electronics, and other industries due to their exceptional features such as high energy density, high power density, long lifespan, low self-discharge rate, wide operating temperature range and environmentally-friendly nature. However, the recent rapid development of mobile electronics and electric vehicles requires energy storage devices with even higher energy and power densities. To achieve this goal, it is essential to develop advanced electrode materials featuring high capacity, high rate capability, and long cycle life. The design of high-performance anode materials is an important aspect of constructing the ideal LIB devices. Besides the commercialized graphite, many metal oxides can also act as anode in the LIBs. In detail, the oxides that served as LIB anodes can be classified into intercalation-type, conversion-type and conversion-alloying-type anodes based on their Li⁺ storage mechanisms. Due to their robust metal-oxygen bonds, intercalation-type anodes, such as d⁰ metal oxides, exhibit stable cycling performance and high-rate capability. However, the limited valence change of intercalation-type metal ions often results in low theoretical capacities. In comparison, conversion-alloying type anodes, exemplified by p-block metal oxides, offer high theoretical capacities and low Li⁺ extraction potential, making them suitable for high-energy-density LIBs. Nevertheless, the Li⁺ intercalation process induces severe phase agglomeration and volume expansion, leading to rapid capacity decay and poor rate capability. Therefore, these drawbacks severely limit the wild utilization s of metal oxide anodes in commercialized LIBs. Recently, substantial efforts have been made to design novel bimetallic oxide anodes. Among these anodes, the incorporation of intercalation-type or conversion-type motifs into conversion-alloying-type metal oxides enables the creation of bimetallic oxide anodes with optimized electronic and ionic conductivities. This approach has the potential to combine the advantages of high capacity, high-rate capability, and long cycle life in a single system. To uncover the underlying Li⁺ storage mechanisms, this review analyzes the bond situations and electronic structures of various metal oxides. Additionally, it introduces a new graphic representation of the Li⁺-ion charge/discharge process using density of states (DOS) graphs. The multi-step lithium storage mechanisms in bimetallic oxide anodes are also discussed. Drawing on recent progress in the field, this review provides fundamental academic insights and practical perspectives for the development of high-capacity, high-rate, and robust bimetallic compound anodes.