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The hollow Si nanospheres modified by the mechanically robust titanium dioxide (TiO 2 ) shell and the uniform carbon layer are intentionally designed and successfully prepared as the anode active material of high performance lithium-ion batteries. The effects of the robust TiO 2 shell and the uniform carbon layer on the structure and electrochemical performances for the Si@TiO 2 @C nanospheres are studied in detail by X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction and charge/discharge tests. The results show that the hollow structure of the Si core can spontaneously absorb the huge volume expansion stress, the robust TiO 2 shell is used as a compact fence to promote the expansion towards the interior of the Si cavity instead of the exterior in the processes of charge/discharge, and the uniform carbon layer can effectively enhance the electrical conductivity and further control the integrity and stability of the well-wrapped core-shell-shell framework. Typically, the resultant hollow Si@TiO 2 @C nanospheres exhibit a high initial discharge capacity of 2557.1 mAh g −1 with coulombic efficiency of 86.06% as well as a large recuperative discharge capacity of 1270.3 mAh g −1 after 250 cycles at 1 A g −1 with a mean coulombic efficiency of 99.53%. Therefore, the hollow Si@TiO 2 @C nanospheres prepared by one-step sol-gel coating process show outstanding electrochemical properties and are considered as a prospective candidate to the adhibitions of the anode material for new generation power LIBs. [ABSTRACT FROM AUTHOR]

• Compact porous Si@graphene layered structure with improved contact interface and adequate interconnected pores were prepared by a facile hydrothermal method. • The improved Si/graphene contact interface can promote the positive effect of graphene on restraining the volume change and thus enhance the structural stability during repetitive cycling. • The closely wrapping graphene and interconnected pores simultaneously provide adequate paths for fast transfer of electrons and ions, resulting in greatly improved dynamic performance. Si/carbon composites are attractive anode materials for rechargeable Li-ion batteries (RLIBs), which combine the advantages of Si and graphene. Designing special Si/carbon structure with intimate contact interface and abundant void space for fast ion transmission is an effective strategy for enhancing cyclability and rate performance of the electrode materials. Inspired by the structure of fishnet, here we fabricate a binder-free and self-standing Si@porous-graphene (Si@PGN 60) composite with nano silicon particles encapsulated in porous graphene sheets. The obtained Si@PGN 60 sample exhibits many favourable features for high performance Si/carbon anodes, including improved Si/graphene contact interface, and abundant void space for fast ion transmission. Tanks to the unique structure, the resultant Si@PGN 60 anode presents remarkably improved capacity reaching 1839.9 mA h g−1 at 300 mA g−1, and excellent cycling performance (734 mA h g−1 at a high current density of 3000 mA g−1). Here we fabricate a binder-free and self-standing Si@graphene (Si@PGN 60) composite with silicon encapsulated in porous graphene sheets. The obtained Si@PGN exhibits many favourable features for high performance Si/carbon anodes, including improved contact interface between Si and graphene, and abundant void space for fast ion transmission. Tanks to the unique structure, the resultant Si@PGN presents not only remarkably improved capacity reaching 1839.9 mA h g−1 at 300 mA g−1, but also superior rate performance of 734 mA h g−1 at a relatively high current density of 3000 mA g−1. [Display omitted] [ABSTRACT FROM AUTHOR]

With the quick development of electric vehicles and grid energy storage, the demand and production of lithium ion batteries (LIBs) are rapidly increasing, and the problem of lithium resource shortage becomes more and more serious. Both in terms of economic value and environmental protection, the recycling and regeneration of the spent lithium batteries is extremely urgent. Herein, a green and efficient hydrothermal technique for direct regeneration of spent lithium iron phosphate (LiFePO 4 or LFP) was proposed. LFP loses the partial lithium during the long cycle and converts to FePO 4 (FP), therefore, the replacement of the lost lithium is crucial for the regeneration of spent LFP. Herein, the effects of hydrothermal conditions such as reaction temperature, Li+ concentration and reducing agent concentration on the performance of product are systemically studied. Besides, it has been found that the control of hydrothermal condition is conductive to the supplement of Li and the enhancement of electrochemical performance of the product. Under hydrothermal conditions of 200 °C for 3 h, the regenerated LFP shows the optimal electrochemical performance of 165.9, 151.93, 145.92, 133.11 and 114.96 mAh g−1 at 0.1, 0.5, 1, 2, and 5 C, respectively. In addition, the capacity retention is as high as 99.1% after 200 cycles at 1 C. Therefore, this work provides a new idea for the direct regeneration of spent LFP cathode materials. [Display omitted] • Spent LiFePO 4 was repaired by a green and efficient hydrothermal process. • Fe3+ in S-LFP was reduced to Fe2+ by tartaric acid. • Soluble Li+ salt can adequately contact with the spent LFP in hydrothermal process. • The lithium defect in the spent LFP is well repaired. • The repaired materials of R-LFP-700 exhibit excellent electrochemical properties. [ABSTRACT FROM AUTHOR]

Closely wrapped Si@graphene structure with improved contacting interface were synthesized by a facile compression method. The improved contacting interface have greatly enhanced the positive effect of graphene sheets on restraining the volume change of Si nanoparticles and improving the electronic conductivity. The obtained composite sample shows significantly improved electrochemical performance as anode material for Li-ion batteries. [Display omitted] • Closely wrapped Si@graphene structure with improved contact interface was synthesized by a facile compression method. • The improved contact interface has enhanced the effect of graphene on restraining the volume change of Si nanoparticles. • The composite sample shows significantly improved cycling stability and rate performance. Despite their extremely high capacity (4200 mA h g−1), the practical application of silicon anodes is still frustrated by their poor cycling performance, resulting from severe volume changes and pulverization of the electrode material. Introducing graphene in silicon is an ideal approach for addressing these issues. Nevertheless, the large size difference between Si and graphene makes high-quality contact difficult to realize, which severely harms the electrochemical performance of Si/graphene composites. Herein, a unique Si@graphene layer structure (p-Si@GN) with an improved contact interface is fabricated by a facile high-pressure method, in which the surfaces of silicon particles are closely covered by graphene layers, restraining the volume changes from multiple angles. The superior structure of the layered p-Si@GN composite exhibits multiple desired features for high-performance Si-based anodes, such as high Li+ storage capacity resulting from high-capacity Si nanoparticles, outstanding electron conductivity due to the formation of a continuous graphene conductive network, and excellent structural stability due to the enhanced protective function of graphene layers with an improved contact interface. Due to these advantages, the p-Si@GN 40 anode, prepared under 40 MPa pressure, exhibits a significantly improved capacity of 2096.9 mA h g−1 at a current density of 300 mA g−1, an enhanced rate capability of 706.4 mA h g−1 at 3000 mA g−1, and superior cycling performance with a high capacity retention of 82.6 % after 150 cycles. [ABSTRACT FROM AUTHOR]

• Construct carbon protective shell to alleviate huge volume changes of Si. • Robust carbon framework can effectively maintains the structure integrity. • Carbon buffer layer can offer rich e-/ion channels to improve reaction kinetics. • The SCM electrode exhibited excellent electrochemical performance. Si-based anodes have revealed the potential as the next generation of lithium ion battery anode material, whereas the poor conductivity and huge volume changes during (de)lithiation process of silicon still limit their practical application. Herein, the Si/nitrogen doped carbon layer/carbon framework microspheres (SCM) are designed by nano-Si via electro-spray technology as anodes for lithium ion batteries. It has been found that the SCM consists of individual carbon-coated nano-Si primary particles linked by PAN framework, in which the carbon buffer layer can further absorb the stress of volume changes during charge/discharge process, and the carbon framework carbon framework not only provides fast diffusion path of electron, but also effectively reduces the consumption of electrolyte. Therefore, the initial columbic efficiency (ICE) of SCM anode can reach as high as 72%, and the SCM anode also shows a high specific capacity of 1192 mAh g−1 at 0.2 A g−1 and keeps a reversible capacity of 746 mAh g−1 after 200 cycles, demonstrating the as-designed SCM possesses an high ICE and a good electrochemical performance. This strategy provides a significant inspiration for fabricating high-performance Si/C anode materials of lithium-ion battery. [ABSTRACT FROM AUTHOR]

• Four types of Si/G composites with the same components and different combination ways are prepared by simple methods. • Four types of Si/G composites are prepared to study the internal factors affecting the initial coulombic efficiency. • The Si-G@C with large specific surface area still owns the highest initial coulombic efficiency. Investigating the internal factors that affect the initial coulombic efficiency (ICE) of silicon/graphite (Si/G) composites and improving ICE are critical to promote applications of Si/G composites in lithium-ion batteries. Here, four types of Si/G composites are prepared with different specific surface area, Si–G phase interface and charge transfer impedance (R ct) to study the internal factors affecting the ICE of Si/G composites. The experimental results show that the influencing factors on ICE of Si/G composites are not only specific surface area, but also the Si–G phase interface and R ct. During the first lithiation process of Si/G composites, there are some reversible phase (Li x Si, Li x C) and irreversible phase (Li 2 O, Li 2 SiO 4 and organolithium) formed, the ICE of Si/G composites is mainly determined by the irreversible phase. The specific surface area, R ct and Si–G phase interface can affect the reaction kinetics of the materials and the ratio of reversible/irreversible phase content, which ultimately affect the ICE of Si/G composites. A smaller specific surface area and well Si–G phase interface with a low R ct will bring a higher ICE of Si/G composites. This report may provide a new idea for the research of ICE of Si/G composites and promote their practical application. The Si–G, Si–G@C, Si@C–G and Si@C–G@C composites are prepared with different specific surface area, Si–G phase interface and charge transfer impedance (R ct) to study the internal factors affecting the ICE of silicon/graphite composites. The Si–G@C with large specific surface area still owns the highest ICE, due to the well Si–G phase interface and a low R ct , which can affect the reaction kinetics to generate more reversible phase (Li x Si, Li x C) and less irreversible phase (Li 2 O, Li 2 SiO 4 and organolithium). Image, graphical abstract [ABSTRACT FROM AUTHOR]

Oriented construction of high-performance mesoporous TiNb 2 O 7 (m-TNO) is important to the design innovation of anode material for next-generation lithium-ion batteries (LIBs) due to the high capacity and long cyclic life of m-TNO. However, the conductivity enhancement of m-TNO and thus accelerating Li+ transfer is still the key point to realize its practical application in LIBs. In this work, a synergistic strategy based on the single-core/dual-shell m-TNO@TiC@NC hierarchical structure is put forward, which is achieved by using m-TNO as host architecture as well as TiC and N-doped carbon layer (NC) as dual-shell layers. The results show that the m-TNO@TiC@NC hierarchical structure can not only provide an integrated conductive network to improve the conductivity of m-TNO, but also can establish a reinforced structure to maintain the anode stability. Besides, it is found that the m-TNO@TiC@NC composite has a high capacity of 328.6 mAh g−1 at 0.5 C after 200 cycles and a high-rate capacity of 186.4 mAh g−1 at 5 C by galvanostatic discharge-charge tests. Therefore, this kind of special single-core/dual-shell structure design can convincingly enhance the conductivity of m-TNO and facilitate the Li+ transfer rate, thus promoting electrochemical performances of LIBs due to the synergistic effect of dual-shell layers. Image 1 • The m-TNO@TiC@NC composite is achieved by using m-TNO as host architecture as well as TiC and NC as dual-shell layers. • The m-TNO@TiC@NC composite shows the single-core/dual-shell hierarchical structure. • The new-type ceramic material TiC is used as conducting layer. • The m-TNO@TiC@NC composite displays good electrochemical performance. [ABSTRACT FROM AUTHOR]