In situ prepared reduced graphene oxide/CoO nanowires mutually-supporting porous structure with enhanced lithium storage performance

Consecutive engineering of anodic graphene supported cobalt monoxide composite and cathodic nanosized lithium cobalt oxide materials with improved lithium-ion storage performances

Downsizing the electrochemically active materials in both cathodic and anodic electrodes commonly brings about enhanced lithium-ion storage performances. It is particularly meaningful to explore simplified and effective strategies for exploiting nanosized electrode materials in the advanced lithium-ion batteries. In this work, the spontaneous reaction between few-layered graphene oxide (GO) and metallic cobalt (Co) foils in mild hydrothermal condition is for the first time employed to synthesize a reduced graphene oxide (RGO) supported nanosized cobalt monoxide (CoO) anode material (CoO@RGO). Furthermore, the CoO@RGO sample is converted to nanosized lithium cobalt oxide cathode material (LiCoO2, LCO) by taking the advantages of the self-templated effect. As a result, both the CoO@RGO anode and the LCO cathode exhibit inspiring lithium-ion storage properties. In half-cells, the CoO@RGO sample maintains a reversible capacity of 740.6 mAh·g-1 after 300 cycles at the current density of 1000 mA·g-1 while the LCO sample delivers a reversible capacity of 109.1 mAh·g-1 after 100 cycles at the current density of 100 mA·g-1. In the CoO@RGO//LCO full-cells, the CoO@RGO sample delivers a reversible capacity of 553.9 mAh·g-1 after 50 cycles at the current density of 200 mA·g-1. The reasons for superior electrochemical behaviors of the samples have been revealed, and the strategy in this work can be considered to be straightforward and effective for engineering both anode and cathode materials for lithium-ion batteries.

Hollow Porous CoO@Reduced Graphene Oxide Self-Supporting Flexible Membrane for High Performance Lithium-Ion Storage

We report an environment-friendly preparation method of rGO-based flexible self-supporting membrane electrodes, combining Co-MOF with graphene oxide and quickly preparing a hollow CoO@rGO flexible self-supporting membrane composite with a porous structure. This unique hollow porous structure can shorten the ion transport path and provide more active sites for lithium ions. The high conductivity of reduced graphene oxide further facilitates the rapid charge transfer and provides sufficient buffer space for the hollow Co-MOF nanocubes during the charging process. We evaluated its electrochemical performance in a coin cell, which showed good rate capability and cycling stability. The CoO@rGO flexible electrode maintains a high specific capacity of 1103 mAh g^-1 after 600 cycles at 1.0 A g^-1. The high capacity of prepared material is attributed to the synergistic effect of the hollow porous structure and the 3D reduced graphene oxide network. This would be considered a promising new strategy for synthesizing hollow porous-structured rGO-based self-supported flexible electrodes.

Fe/Co/N-C/graphene derived from Fe/ZIF-67/graphene oxide three dimensional frameworks as a remarkably efficient and stable catalyst for the oxygen reduction reaction

The development of non-noble metal catalysts with high-performance, long stability and low-cost is of great importance for fuel cells, to promote the oxygen reduction reaction (ORR). Herein, Fe/Co/N-C/graphene composites were easily prepared by using Fe/ZIF-67 loaded on graphene oxide (GO). The Fe/Co/porous carbon nanoparticles were uniformly dispersed on graphene with high specific surface area and large porosity, which endow high nitrogen doping and many more active sites with better ORR performance than the commercial 20 wt% Pt/C. Therefore, Fe/Co/N-C/graphene composites exhibited excellent ORR activity in alkaline media, with higher initial potential (0.91 V) and four electron process. They also showed remarkable long-term catalytic stability with 96.5% current retention after 12 000 s, and outstanding methanol resistance, compared with that of 20 wt% Pt/C catalysts. This work provides an effective strategy for the preparation of non-noble metal-based catalysts, which could have significant potential applications, such as in lithium-air batteries and water-splitting devices.

High lithium storage performance of CoO with a distinctive dual-carbon-confined nanoarchitecture

Herein, a distinctive dual-carbon-confined nanoarchitecture, composed of an inner highly conductive, robust carbon nanotube (CNT) support and outer well-designed porous carbon (PC) coating, was demonstrated to efficiently improve the electrochemical properties of CoO nanoparticles for the first time, and the CoO nanoparticles were confined between the CNTs and porous carbon. The well-designed porous carbon coating showed significant superiority compared to common non-porous carbon coatings, due to its distinctive characteristics such as high flexibility, rich free space and open tunnel-like structure. Therefore, the synergistic effects of the CNT core and the porous carbon sheath endowed the CoO-based composite (CNTs@CoO@PC) with improved electrochemical reaction kinetics, large pseudocapacitive contribution and superior structural stability. As a result, the CNTs@CoO@PC showed outstanding performance with 1090, 571 and 242 mA h g^-1 at 200, 1000 and 5000 mA g^-1 after 300, 600 and 1000 cycles, respectively. Furthermore, this strategy may be used to improve other metal oxide anode materials for lithium storage.

Supercritical CO2 Assisted Solvothermal Preparation of CoO/Graphene Nanocomposites for High Performance Lithium-Ion Batteries

Supercritical CO2 (scCO2) is often used to prepare graphene/metal oxide nanocomposite anodes for high performance lithium-ion batteries (LIBs) by the assisted solvothermal method due to its low viscosity, high diffusion, zero surface tension and good surface wettability. However, the formation mechanism of metal oxides and the combination mechanism between metal oxides and graphene in this system are superficial. In this work, a cobalt monoxide/graphene (CoO/G) nanocomposite is fabricated via the scCO2 assisted solvothermal method followed by thermal treatment. We elucidate the mechanism that amorphous intermediates obtain by the scCO2 assisted solvothermal method, and then ultrafine CoO nanoparticles are crystallized during the heat treatment. In addition, scCO2 can promote CoO to be tightly fixed on the surface of graphene nanosheets by interfacial chemical bonds, which can effectively improve its cycle stability and rate performance. As expected, the CoO/G composites exhibit higher specific capacity (961 mAh g-1 at 100 mA g-1), excellent cyclic stability and rate capability (617 mAh g-1 after 500 cycles at 1000 mA g-1) when applied as an anode of LIB.

Prelithiation: A Crucial Strategy for Boosting the Practical Application of Next-Generation Lithium Ion Battery

With the urgent market demand for high-energy-density batteries, the alloy-type or conversion-type anodes with high specific capacity have gained increasing attention to replace current low-specific-capacity graphite-based anodes. However, alloy-type and conversion-type anodes have large initial irreversible capacity compared with graphite-based anodes, which consume most of the Li⁺ in the corresponding cathode and severely reduces the energy density of full cells. Therefore, for the practical application of these high-capacity anodes, it is urgent to develop a commercially available prelithiation technique to compensate for their large initial irreversible capacity. At present, various prelithiation methods for compensating the initial irreversible capacity of the anode have been reported, but due to their respective shortcomings, large-scale commercial applications have not yet been achieved. In this review, we have systematically summarized and analyzed the advantages and challenges of various prelithiation methods, providing enlightenment for the further development of each prelithiation strategy toward commercialization and thus facilitating the practical application of high-specific-capacity anodes in the next-generation high-energy-density lithium-ion batteries.

Engineering Hierarchical CoO Nanospheres Wrapped by Graphene via Controllable Sulfur Doping for Superior Li Ion Storage

The inferior conductivity and large volume expansion impair the widespread applications of metal oxide-based anode materials for lithium-ion batteries. To address these issues, herein an efficient strategy of structural engineering is proposed to improve lithium storage performance of hierarchical CoO nanospheres wrapped by graphene via controllable S-doping (CoOS_0.1   @ G). S-doping promotes the Li⁺ diffusion kinetics of CoO by expanding the interplanar spacing of CoO, lowering the activation energy, and improving the pseudocapacitance contribution. Meanwhile, the electronic structure of CoO is adjusted by S-doping as confirmed by density functional theory calculations, thus enhancing the conductivity. Finite element analysis reveals that the produced Li₂ S during lithiation improves the structural stability of the S-doped electrode, which is further confirmed by experimental observation. As expected, CoOS_0.1   @ G exhibits excellent lithium storage performance with an initial discharge capacity of 1974 mAh g^-1 at 100 mA g^-1 , and high discharge capacity of 1573 mAh g^-1 after 400 cycles at 500 mA g^-1 . It is believed that the insights into the structural doping enlighten research to explore other metal oxides for fast and stable Li ion storage.

Insight into the Superior Lithium Storage Properties of Ultrafine CoO Nanoparticles Confined in a 3 D Bimodal Ordered Mesoporous Carbon CMK-9 Anode

Ultrafine CoO particles immobilized into the mesopores of three-dimensional cubic bimodal ordered mesoporous carbon CMK-9 is successfully prepared by using a combination of nanocasting and wet-impregnation methods. It is found that the cubic bimodal interconnected mesoporous framework of CMK-9 plays a crucial role in achieving the excellent electrochemical performances by assisting the rapid mass and charge transfer. Among the prepared nanocomposites, CoO(10)@CMK-9 delivers a discharge capacity of 830 mAh g^-1 after 200 cycles at a current density of 100 mA g^-1 in lithium-ion batteries. At a higher current density of 1000 mA g^-1 , the anode presents an outstanding discharge capacity of 636 mAh g^-1 after 200 cycles. In sodium-ion batteries, the anode provides a discharge capacity of 296 mAh g^-1 after 250 cycles at a current density of 100 mA g^-1 . The remarkable performances of CoO(10)@CMK-9 demonstrate the promising potentials of the nanocomposite as the anode for rechargeable batteries.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

Cobalt Hydroxide Carbonate/Reduced Graphene Oxide Anodes Enabled by a Confined Step-by-Step Electrochemical Catalytic Conversion Process for High Lithium Storage Capacity and Excellent Cyclability with a Low Variance Coefficient

Transition metal carbonates/hydroxides have attracted much attention as appealing anode materials due to their considerable reversible electrochemical catalytic conversion capacity. However, their serious positive or negative trends with cycles caused by the electrochemical catalytic conversion seriously affect their practical applications. Herein, novel one-dimensional cobalt hydroxide carbonate (CHC) nanomaterials are tightly anchored on reduced graphene oxide (RGO) sheets via a facile one-pot hydrothermal synthesis, forming surface-confined domains to further restrict the electrochemical catalytic conversion process. The analysis on the cycled electrodes at varied potentials confirms that the added capacity of CHC arises from the step-by-step reversible reactions of Li₂CO₃ and LiOH under the electrochemical catalysis of Co metal generated by the conversion reaction of CHC. The reversible reaction of Li₂CO₃ is followed closely by that of LiOH in the discharge process, while the order is opposite in the charge process. Such a step-by-step electrochemical catalytic conversion process could confine each other to accommodate the volume change and avoid side reactions. The confined effect is further enhanced by limiting the width and length of the CHC, which are determined by regulating the nucleation and growth of CHC on the surface of RGO, leading to an extraordinary cyclability. The optimized CHC/RGO hybrid maintains a high reversible capacity of 1110 mA h g^-1 after 100 cycles at 0.1 A g^-1, which is much higher than the theoretical value of CHC (506 mA h g^-1) on the basis of the recognized conversion reaction. Furthermore, it keeps high reversible capacities of 755 and 506 mA h g^-1 after 200 cycles at 1 and 2 A g^-1, respectively, exhibiting a high-rate cyclability with the lowest coefficient of variance of 9.4% among the reported ones. The confined step-by-step electrochemical catalytic conversion process facilitates high lithium storage capacity and satisfactory cyclability with a pretty low variance coefficient.

Fabrication and understanding of Cu3Si-Si@carbon@graphene nanocomposites as high-performance anodes for lithium-ion batteries

Besides silicon's low electronic conductivity, another critical issue for using silicon as the anode for lithium-ion batteries (LIBs) is the dramatic volume variation (>300%) during lithiation/delithiation processes, which can lead to rapid capacity fading and poor rate capability, thereby hampering silicon's practical applications in batteries. To mitigate these issues, herein, we report our findings on the design and understanding of a self-supported Cu₃Si-Si@carbon@graphene (Cu₃Si-SCG) nanocomposite anode. The nanocomposite is composed of Cu₃Si-Si core and carbon shell with core/shell particles uniformly encapsulated by graphene nanosheets anchored directly on a Cu foil. In this design, the carbon shell, the highly elastic graphene nanosheet, and the formed conductive and inactive Cu₃Si phase in Si serve as buffer media to suppress volume variation of Si during lithiation/delithiation processes and to facilitate the formation of a stable solid electrolyte interface (SEI) layer as well as to enable good transport kinetics. Chemomechanical simulation results quantitatively coincide with the in situ TEM observations of volume expansion and provide process details not seen in experiments. The optimized Cu₃Si-SCG nanocomposite anode exhibits good rate performance and delivers reversible capacity of 483 mA h g^-1 (based on the total weight of Cu₃Si-SCG) after 500 cycles with capacity retention of about 80% at high current density of 4 A g^-1, rendering the nanocomposite a desirable anode candidate for high-performance LIBs.

Tin Nanoparticles Encapsulated Carbon Nanoboxes as High-Performance Anode for Lithium-Ion Batteries

One of the crucial challenges for applying Sn as an anode of lithium-ion batteries (LIBs) is the dramatic volume change during lithiation/delithiation process, which causes a rapid capacity fading and then deteriorated battery performance. To address this issue, herein, we report the design and fabrication of Sn encapsulated carbon nanoboxes (denoted as Sn@C) with yolk@shell architectures. In this design, the carbon shell can facilitate the good transport kinetics whereas the hollow space between Sn and carbon shell can accommodate the volume variation during repeated charge/discharge process. Accordingly, this composite electrode exhibits a high reversible capacity of 675 mAh g⁻¹ at a current density of 0.8 A g⁻¹ after 500 cycles and preserves as high as 366 mAh g⁻¹ at a higher current density of 3 A g⁻¹ even after 930 cycles. The enhanced electrochemical performance can be ascribed to the crystal size reduction of Sn cores and the formation of polymeric gel-like layer outside the electrode surface after long-term cycles, resulting in improved capacity and enhanced rate performance.

Effect of carbon fiber addition on the electromagnetic shielding properties of carbon fiber/polyacrylamide/wood based fiberboards

Carbon fiber (CF) reinforced polyacrylamide/wood fiber composite boards are fabricated by mechanical grind-assisted hot-pressing, and are used for electromagnetic interference (EMI) shielding. CF with an average diameter of 150 nm is distributed on wood fiber, which is then encased by polyacrylamide. The CF/polyacrylamide/wood fiber (CPW) composite exhibits an optimal EMI shielding effectiveness (SE) of 41.03 dB compared to that of polyacrylamide/wood fiber composite (0.41 dB), which meets the requirements of commercial merchandise. Meanwhile, the CPW composite also shows high mechanical strength. The maximum modulus of rupture (MOR) and modulus of elasticity (MOE) of CPW composites are 39.52 MPa and 5823.15 MPa, respectively. The MOR and MOE of CPW composites increased by 38% and 96%, respectively, compared to that of polyacrylamide/wood fiber composite (28.64 and 2967.35 MPa).

Nanosized CoO Loaded on Copper Foam for High-Performance, Binder-Free Lithium-Ion Batteries

The synthesis of nanosized CoO anodes with unique morphologies via a hydrothermal method is investigated. By adjusting the pH values of reaction solutions, nanoflakes (CoO-NFs) and nanoflowers (CoO-FLs) are successfully located on copper foam. Compared with CoO-FLs, CoO-NFs as anodes for lithium ion batteries present ameliorated lithium storage properties, such as good rate capability, excellent cycling stability, and large reversible capacity. The initial discharge capacity is 1470 mA h g⁻¹, while the reversible capacity is maintained at 1776 m Ah g⁻¹ after 80 cycles at a current density of 100 mA h g⁻¹. The excellent electrochemical performance is ascribed to enough free space and enhanced conductivity, which play crucial roles in facilitating electron transport during repetitive Li⁺ intercalation and extraction reaction as well as buffering the volume expansion.

Controlling the Sn-C bonds content in SnO2@CNTs composite to form in situ pulverized structure for enhanced electrochemical kinetics

The Sn-C bonding content between the SnO₂ and CNTs interface was controlled by the hydrothermal method and subsequent heat treatment. Electrochemical analysis found that the SnO₂@CNTs with high Sn-C bonding content exhibited much higher capacity contribution from alloying and conversion reaction compared with the low content of Sn-C bonding even after 200 cycles. The high Sn-C bonding content enabled the SnO₂ nanoparticles to stabilize on the CNTs surface, realizing an in situ pulverization process of SnO₂. The in situ pulverized structure was beneficial to maintain the close electrochemical contact of the working electrode during the long-term cycling and provide ultrafast transfer paths for lithium ions and electrons, which promoted the alloying and conversion reaction kinetics greatly. Therefore, the SnO₂@CNTs composite with high Sn-C bonding content displayed highly reversible alloying and conversion reaction. It is believed that the composite could be used as a reference for design chemically bonded metal oxide/carbon composite anode materials in lithium-ion batteries.

Cobalt Oxide Porous Nanofibers Directly Grown on Conductive Substrate as a Binder/Additive-Free Lithium-Ion Battery Anode with High Capacity

In order to reduce the amount of inactive materials, such as binders and carbon additives in battery electrode, porous cobalt monoxide nanofibers were directly grown on conductive substrate as a binder/additive-free lithium-ion battery anode. This electrode exhibited very high specific discharging/charging capacities at various rates and good cycling stability. It was promising as high capacity anode materials for lithium-ion battery.

A Strategy for Synthesis of Nanosheets Consisting of Alternating Spinel Li4Ti5O12 and Rutile TiO2 Lamellas for High-Rate Anodes of Lithium-Ion Batteries

Ultrathin dual phase nanosheets consisting of alternating spinel Li₄Ti₅O₁₂ (LTO) and rutile TiO₂ (RT) lamellas are synthesized through a facile and scalable hydrothermal method, and the formation mechanism is explored. The thickness of constituent lamellas can be controlled exactly by adjusting the mole ratio of Li:Ti in the original reactants. Alternating insertion of the RT lamellas significantly improves the electrochemical performance of LTO nanosheets, especially at high charge/discharge rates. As anodes in lithium-ion batteries (LIBs), the dual phase nanosheet electrode with the optimized phase ratio can deliver stable discharge capacities of 178.5, 154.9, 148.4, 142.3, 138.2, and 131.4 mA h g^-1 at current densities of 1, 10, 20, 30, 40, and 50 C, respectively. Meanwhile, they inherit the excellent cyclic stability of pure spinel LTO and exhibit a capacity retention of 93.1% even after 500 cycles at 50 C. Our results indicate that the alternating nanoscaled lamella structure is a good alternative to facilitate the transfer of both the Li ions and electrons into the spinel LTO, giving rise to an excellent cyclability and fast rate performance. Therefore, the newly prepared carbon-free LTO-RT nanosheets with high safety provide a new opportunity to develop high-power anodes for LIBs.