Transition metal oxides can be broadly classified into two categories depending on the lithium storage mechanism:
The first type: is a traditional lithium intercalation oxide. In the process of lithium deintercalation, it is only accompanied by changes in material structure and composition, and there is no reversible generation and decomposition of Li2O, such as LiO2, MoO2, Nb2O5, and the like. Such materials generally have good reversible deintercalation lithium performance, but have a lower specific capacity and a higher lithium insertion potential.
The second is the conversion reaction that occurs during lithium storage. The transition metal oxide MO (M=Fe, Co, Ni, Cu, etc.), the structure itself is a rock salt structure, cannot provide the insertion and extraction vacancies of lithium ions, and the metal itself cannot form an alloy with lithium. During charge and discharge, the material undergoes a redox reaction accompanied by the formation and decomposition of Li2O.
The reason for this phenomenon is that after the end of the discharge, the nano-sized metal particles are uniformly dispersed in the Li2O matrix, and this dispersion imparts electrochemical activity to Li2O, thereby realizing reversible lithium storage of the metal oxide.
As a new type of lithium storage mechanism, the conversion mechanism is different from the traditional embedding/deintercalation mechanism, which can provide higher capacity and charge and discharge capability. It has become a research hotspot in recent years, but with this, the transition The volume of metal oxide changes greatly during charge and discharge, which tends to cause the active material to escape from the current collector, resulting in a person with too fast capacity degradation, deteriorating cycle performance, and a large irreversible capacity for the first time.
Therefore, as a negative electrode material for lithium ion batteries, transition metal oxides mainly need to solve the problem of reducing the first irreversible capacity and voltage platform of metal oxides and improving their cycle performance.
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