Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge–discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Wh l−1 at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology.

Flexible lithium-ion batteries are critical for the next-generation electronics. However, during the practical application, they may break under deformations such as twisting and cutting, causing their failure to work or even serious safety problems. A new family of all-solid-state and flexible aqueous lithium ion batteries that can self-heal after breaking has been created by designing aligned carbon nanotube sheets loaded with LiMn O and LiTi (PO ) nanoparticles on a self-healing polymer substrate as electrodes, and a new kind of lithium sulfate/sodium carboxymethylcellulose serves as both gel electrolyte and separator. The specific capacity, rate capability, and cycling performance can be well maintained after repeated cutting and self-healing. These self-healing batteries are demonstrated to be promising for wearable devices.

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Improving one property without sacrificing others is challenging for lithium-ion batteries due to the trade-off nature among key parameters. Here we report a chemical vapor deposition process to grow a graphene–silica assembly, called a graphene ball. Its hierarchical three-dimensional structure with the silicon oxide nanoparticle center allows even 1 wt% graphene ball to be uniformly coated onto a nickel-rich layered cathode via scalable Nobilta milling. The graphene-ball coating improves cycle life and fast charging capability by suppressing detrimental side reactions and providing efficient conductive pathways. The graphene ball itself also serves as an anode material with a high specific capacity of 716.2 mAh g−1. A full-cell incorporating graphene balls increases the volumetric energy density by 27.6% compared to a control cell without graphene balls, showing the possibility of achieving 800 Wh L−1 in a commercial cell setting, along with a high cyclability of 78.6% capacity retention after 500 cycles at 5C and 60 °C.

material has an ultra-high specifi c capacity but it suffers from a severe degradation during charge and discharge processes. Flexible LIBs mainly from carbon-based fl exible electrodes have been widely explored such as nanoporous CNTs, [ 31 ] graphene papers, [ 32 ] electrospun porous carbon nanofi bers, [ 33 ] and hollow CNT/carbon nanofi ber composite material. [ 34 ] However, the high contact resistance within the randomly dispersed CNTs or graphene sheets limits the full expression of their advantages. As a result, superior fl exible electrodes are still under pressing demands to enhance the overall performance of fl exible LIBs.In this Communication, a new family of aligned N-doped core-sheath carbon nanotube (N-CNT) fi lms has been synthesized and developed as fl exible and effective anodes of LIBs. The N-CNT fi lm is synthesized from a template of aligned CNT sheet by chemical vapor deposition ( Figure 1 a). Typically, N-doped graphene layers are coaxially grown around bare CNTs in the sheet, and the N-doped sheath can be well controlled by varying the growth time. These N-CNT fi lms exhibit high tensile strength of 690 MPa and electrical conductivity of 410 S cm −1 . In particular, the N-doped graphene layer favors the intercalation of lithium ions, so they can be used as new electrodes for highperformance LIBs. They display a high capacity of 390 mAh g −1 that retains 97% after 200 cycles at a high rate of 4C.To prepare the N-CNT fi lm, aligned CNT sheets that had been drawn out of the spinnable CNT array were stacked along the CNT length on a heat-resisted ceramic framework. It was then transferred to a tube furnace to regrow the nitrogen-doped graphene layers on the outer surfaces of CNTs using acetonitrile as both nitrogen and carbon sources. At high temperature of 1060 °C, acetonitrile decomposed into C-and N-containing fragments, which were attached onto the surface of the template CNT and reformed as new graphene sheets along with the radial direction. Due to the defects introduced by the N-doping, the new grown layers were less uniform compared with original CNT walls ( Figure S1, Supporting Information). The thickness of nitrogen-doped graphene was controlled by varying the reaction time (Figure 1 b). The N-CNT fi lms were compared for the reaction time of 10, 30, 60, and 90 min by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)

Because of the higher specific capacity, nickel-rich layered cathode material has received much attention from the lithium-ion battery community. However, its cycle life is desired to improve further for practical applications, and unstable interface with electrolyte is one of the main capacity fading mechanisms. Here, we report a facile chemical vapor deposition process involving mixed gases of CO 2 and CH 4 , which yields thin and conformal artificial solid-electrolyte-interphase (SEI) layer consisting of alkyl lithium carbonate (LiCO 3 R) and lithium carbonate (Li 2 CO 3 ) on nickel-rich active cathode powder. The coating layer protects from side reactions and improves the cycle life and efficiency significantly. Remarkably, the coating process is self-terminated after the thickness reaches ∼10 nm, leading to the coating layer to account for only 0.48 wt %, because of the growing binding energy between the gas mixture and the surface products. The self-termination is characterized by various analytical tools and is well-explained by density functional theory calculations. The current gas phase coating process should be applicable to other battery materials that suffer from continuous side reactions with electrolyte.

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