Nanomaterials have some disadvantages in application as Li ion battery materials, such as low density, poor electronic conductivity and high risk of surface side reactions. In recent years, materials with core-shell nanostructures, which was initially a common concept in semiconductors, have been introduced to the field of Li ion batteries in order to overcome the disadvantages of nanomaterials, and increase their general performances in Li ion batteries. Many efforts have been made to exploit core-shell Li ion battery materials, including cathode materials, such as lithium transition metal oxides with varied core and shell compositions, and lithium transition metal phosphates with carbon shells; and anode materials, such as metals, alloys, Si and transition metal oxides with carbon shells. More recently, graphene has also been proposed as a shell material. All these core-shell nanostructured materials presented enhanced electrochemical capacity and cyclic stability. In this review, we summarize the preparation, electrochemical performances, and structural stability of core-shell nanostructured materials for lithium ion batteries, and we also discuss the problems and prospects of this kind of materials.

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The conversion reaction mechanism has widely been accepted in interpreting and evaluating the lithium storage capability of transition metal oxides (MOs). However, this mechanism cannot well explain the phenomenon of the extra capacity which exists in almost all MO materials and attracts much attention.Up to now, the extra capacity phenomenon has generally been ascribed to the reversible conversion of polymeric gel-like films. However, the essential role of metal nanoparticles in this process has not been systematically investigated. To further illustrate the role of metal nanoparticles for the extra capacity, Fe 3 O 4 @C and Fe@C monodispersed hierarchical core-shell microspheres were designed and adopted as the case study. Naturally Fe 3 O 4 @C composites exhibited a large Li storage capacity beyond its theoretical value. However, Fe@C microspheres, which are usually regarded to be inert for lithium storage, still presented a certain electrochemical capacity. Fe nanoparticles might serve as electrocatalysts for the reversible conversion of some components of solid electrolyte interface films, and bring extra capacity to Fe 3 O 4 and electrochemical capacity to Fe. This study can enlighten us for the exploiting of advanced active materials and electrolytes for Li ion batteries, and new energy storage devices.Fe@C composites, XRD and EDS of Fe@C composites, CV curves and cycling performances of FeCO 3 and FeOOH, extra capacity of MOs, CV analysis of Fe-based inorganic compounds and metal-nanoparticle-related materials, TEM images and cycling performance of M/C nanosheets, and HRTEM images of Fe@C composites aer the initial charge. See

Core double-shell Si@SiO(2)@C nanocomposites were prepared through a facile route. SiO(2) and carbon double shells effectively accommodated the volume swing of Si during repeated cycles and enhanced the electronic network between nanoparticles.