Center-iodized graphene as an advanced anode material to significantly boost the performance of lithium-ion batteries

Influence of Lattice Defects on Trans-Oligoene Substructure Formation in Graphene

The photochemical reaction of iodine and graphene induces strong new Raman modes due to the formation of trans-oligoene substructures in graphene domains. This unique reactivity was demonstrated before on defect-free graphene, however leaving the influence of e. g. carbon vacancies, unexplored. Here, we investigate the photochemical reaction applied on graphene with varying average distances of lattice defects and statistically analyze the characteristic Raman modes which develop with the iodination reaction. We show that the iodination reaction does not lead to Raman-active defects and thus, the newly formed trans-oligoene substructures do not contribute to the D-mode of graphene. A statistical analysis reveals the correlation between the average distance of lattice defects and the intensity of the v1-mode. For defective graphene with average defect distances below ~1 nm no new Raman modes evolve, which is the lower limit of the substructure size probed at 532 nm and explains why this observation was not possible before using common graphene oxide as graphene source.

High-performance expanded graphite regenerated from spent lithium-ion batteries by integrated oxidation and purification method

Currently, the recycling of spent lithium-ion batteries (LIBs) has mainly been focused on the extraction of precious metals, such as lithium, cobalt and nickel from cathodes, while the waste graphite anode has been overlooked due to its low-cost production and abundant resources reserve. However, there are enormous potential value and pollution risk in the view of graphite recycling. Thus, we propose an original method to prepare expanded graphite (EG) as new anode material generated from waste graphite in LIBs which integrates the oxidation and purification in one-step. By regulating the oxidizability of potassium hypermanganate in the sulfur-phosphorus mixed acid system, the expansion of graphite and removal of impurities are realized simultaneously and thoroughly. As anticipated, the shortening of preparation process and purification procedure can also reduce the generation of polluting substances and production cost. It displays excellent electrochemical performance (reversible capacity of 435.8 mAh·g-1 at 0.1C and long-term cycling property of 370 mAh·g-1 at 1C after 1000 cycles), which is even higher than that of pristine commercial graphite. This delicate strategy of high-performance expanded graphite recycling achieves the integration of purification and value-added processes, providing the instructive guide to regenerate industrial-grade anode materials for the increasing LIBs demand in the future.

On the Road to the Frontiers of Lithium-Ion Batteries: A Review and Outlook of Graphene Anodes

Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started with and then the approaches to improve its electrochemical performance are comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggregation, fast electrons/ions transportation, and optimal solid electrolyte interphase are discussed, demonstrating the close connection between the surface structure and electrochemical activity of graphene. Second, graphene derivatives anodes prepared by heteroatom doping and covalent functionalization are outlined, which show great advantages in boosting the Li storage performances because of the additionally introduced defect/active sites for further Li accommodation. Furthermore, binder-free and free-standing graphene electrodes are presented, exhibiting great prospects for high-energy-density and flexible LIBs. Finally, the remaining challenges and future opportunities of practically available graphene anodes for advanced LIBs are highlighted.

Turbostratic Lattice and Electronegativity Modification Jointly Enabled an Ultra-High-Rate and Long-Lived Carbon Anode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are considered as a promising technology alternative to lithium-ion batteries due to more abundance of potassium than lithium and a lower redox potential of K/K⁺ than that of Na/Na⁺. The critical limitation in PIBs is the electrode with poor rate capability and cycling stability induced by the sluggish reaction kinetics and large volume change during potassiation and depotassiation. In this work, we report a turbostratic lattice iodine-doped carbon (TLIC) nanosheet as an advanced innovative anode for PIBs displaying fast charge/discharge and electrode stability. The turbostratic lattice caused by doping of large-sized iodine and the unique charge transfer between iodine/carbon atoms creates more active sites and a shorter transport distance for K ions, improves the electrochemical activity, promotes rapid ion diffusion, and enhances pseudocapacitive behavior. The TLIC exhibits a high capacity of 433.5 mAh g^-1 at 50 mA g^-1, an ultrahigh rate capability of 162.1 mAh g^-1 at 20 A g^-1, and an excellent capacity retention of ∼96% (206 mAh g^-1) after 4000 cycles. The combination of turbostratic lattice and pseudocapactive storage is an effective approach to designing carbon electrodes with the transformational performance of high capacity, rate performance, and long lifetime for practical applications of PIBs.

Green approach for the synthesis of monolayer reduced graphene oxide: one-step protocol with simultaneous iodination and reduction

A schematic representation of iodinated GO and RGO formation in a single step.

Facile method to produce sub-1 nm pore-rich carbon from biomass wastes for high performance supercapacitors

Sub-1 nm pores can lead to an anomalous increase in the supercapacitive performance [1], but it still faces great challenges from its relatively low sub-1 nm pore content, complicated preparation process, low yield and high cost. Here we successfully prepared a sub-1 nm pore-rich carbon from biomass wastes using a facile method by pre-treating walnut shell powder at 380 ℃ in air for different times to delicately tailor carbon defects, followed by KOH activation at 700 ℃. The as-prepared optimal material delivers the highest sub-1 nm pore content (V_{sub-1 nm} = 0.57 cm³ g^-1, V_{sub-1 nm}/V_t = 58.4 %) among all reported porous carbons. A supercapacitor made from the material accomplishes an ultrahigh specific capacitance of 298.7F g^-1 at 1 A g^-1 in a two-electrode device, excellent rate capability (78.8 % retention from 1 to 10 A g^-1) and long-cyclic life (94 % retention after 10,000 cycles at 10 A g^-1) in KOH. Even in Et₄NBF₄ electrolyte that is often used in commercial supercapacitors, a high energy density of 82.8 Wh kg^-1 at 7 kW kg^-1 and excellent cycling performance (90 % retention after 10,000 cycles at 5 A g^-1) can be achieved, ranking the best among all reported carbon-based electrical double layer capacitors tested in the same electrolyte. More importantly, it drives a light-emitting-diode (LED) to operate for as long as 20 min, vividly demonstrating the great potential of sub-1 nm pore-rich carbon-based high performance supercapacitors in practical applications.

Cobalt-promoted fabrication of 3D carbon with a nanotube-sheet mutual support structure: scalable preparation of a high-performance anode material for Li-ion batteries

Currently, the design of carbon-based composite as a high-performance anode material for lithium-ion batteries (LIBs) presents challenges for commercial application. Herein, we developed a three-dimensional carbon-based material with a nanotube-sheet mutual support structure (MS-CNTS) engineered by the catalytic effect of Co species. The present work highlights a concise 'solvent-free' synthetic method allowing for large-scale output, which is potentially available for low cost commercial use. With the readily available acetylacetonate and cobalt (II) acetylacetonate as starting chemicals, this nanostructured carbonaceous material is fabricated with aldol condensation to construct a Co-contained carbon-link network polymer precursor followed by annealing under argon. It is composed of brim-curled graphene-like carbon nanosheets and carbon nanotubes, which support each other's structures to effectively avoid agglomeration. Therefore, it enables high performance in LIBs. In spite of the trace amount of cobalt, the carbon-based MS-CNTS anode delivers a high charge capacity of 1028 mAh g-1 at 0.1 A g-1, high rate capacity of 495 mAh g-1 at 2 A g-1, and ultra-long cycling life with a very low capacity decay of 0.008% per cycle over 1000 cycles at 0.5 A g-1, accompanied by 100% Coulombic efficiency. From full cell measurements, we further confirm the considerable promise of MS-CNTS as anodes with a long cycling life.

F-Doping effects on carbon-coated Li3V2(PO4)3 as a cathode for high performance lithium rechargeable batteries: combined experimental and DFT studies

F-Doping effects on polyaniline-derived carbon coated Li3V2(PO4)3 (Li3V2(PO4)3-xFx@C) as a cathode for high performance Li rechargeable batteries are systematically investigated with a combined experimental and DFT theoretical calculation approach. The results clearly indicate that the doping amount has a significant impact on the rate capability and long cycle life. The optimal material (Li3V2(PO4)2.88F0.12@C) delivers 123.16 mA h g-1@2C, which is close to the theoretical value (133 mA h g-1), while showing a greatly improved cycle stability. Rietveld refinements show that the F- doping does not obey Vegard's Law, which may be attributed to the generated lower valence of V ions. AC impedance spectroscopy shows that the F-doping can achieve faster interfacial charge transfer for higher reaction reversibility. DFT calculations confirm that the lower V2+ (t2g↑)3 does exist in Li3V2(PO4)2.88F0.12, and the mean nearest neighbor Li-O bond length also increases for faster electrochemical kinetics, and further reveal that there is a tendency for a transition from the insulator to the n-type semiconductor due to the F dopant. The combined experimental and calculated results suggest that F-doping indeed greatly facilitates the charge transfer rate of the Li+ insertion/de-insertion process for better reversibility and enhances the Li+ diffusion rate to access the reaction sites, thus resulting in high rate capacity and cycling stability. This work not only offers a facile and effective approach to synthesize high performance Li-ion battery material for very promising practical applications, but also discloses scientific insights on element coating and doping to guide the electrode material design for fast electrode kinetics in energy storage devices.

Rationally designed hierarchical porous CNFs/Co3O4 nanofiber-based anode for realizing high lithium ion storage

To achieve a high power density of lithium-ion batteries, it is essential to develop anode materials with high capacity and excellent stability. Cobalt oxide (Co₃O₄) is a prospective anode material on account of its high energy density. However, the poor electrical conductivity and volumetric changes of the active material induce a dramatic decrease in capacity during cycling. Herein, a hierarchical porous hybrid nanofiber of ZIF-derived Co₃O₄ and continuous carbon nanofibers (CNFs) is rationally constructed and utilized as an anode material for lithium-ion batteries. The PAN/ZIF-67 heterostructure composite nanofibers were first synthesized using electrospinning technology followed by the in situ growth method, and then the CNFs/Co₃O₄ nanofibers were obtained by subsequent multi-step thermal treatment. The continuous porous conductive carbon backbone not only effectively provides a channel to expedite lithium ion diffusion and electrode transfer, but also accommodates volume change of Co₃O₄ during the charge–discharge cycling process. The electrode exhibits a high discharge capacity of 1352 mA h g⁻¹ after 500 cycles at a constant current density of 0.2 A g⁻¹. Additionally, the composites deliver a discharge capacity of 661 mA h g⁻¹ with a small capacity decay of 0.078% per cycle at a high current density of 2 A g⁻¹ after 500 cycles. This hierarchical porous structural design presents an effective strategy to develop a hybrid nanofiber for improving lithium ion storage.

Hierarchical porous CNFs/Co₃O₄ nanofiber is rationally designed and constructed as an anode for achieving high capacity and stable lithium ion batteries.