Impact of composite structure and morphology on electronic and ionic conductivity of carbon contained LiCoO2 cathode

Cathodes in lithium ion batteries consist of an ionic conductor, an electronic conductor and a binder in order to make a composite that is both electronically and ionically conductive. The carbon coating on the cathode material plays a critical role for the electrochemical properties of lithium ion batteries due to the increased electronic conductivity. We explain the relationship between the electrochemical properties and the characteristics of composites prepared using the ball-milling process in this report. We investigated two types of carbonaceous materials (graphite and carbon black) in LiCoO₂ electrodes. These selected carbon materials have different characteristics and structure upon ball-milling with LiCoO₂. The composite prepared by ball-milling for 5 min leads to better mixing of carbon and LiCoO₂, an intimate contact of carbon on LiCoO₂, a higher lithium ion diffusion (DLi) than non ball-milled and longer ball-milled composites. On the other hand, a longer time of ball-milling (30 and 60 min) decreases the electronic and ionic conductivity due to an increase of disordered structure of carbon and a thick and dense carbon coating layer on LiCoO₂ particles, preventing the diffusion of lithium ions, respectively

Nickel hydroxide/chemical vapor deposition-grown graphene/nickel hydroxide/nickel foam hybrid electrode for high performance supercapacitors

Rational design of electrode structures has been recognized as an effective strategy to improve the electrochemical performance of electrode materials. Herein, we demonstrate an integrated electrode in which nickel hydroxide (Ni(OH)2) nanosheets are deposited on both sides of chemical vapor deposition-grown graphene on Ni foam, which not only effectively optimizes electrical conductivity of Ni(OH)2, but also accommodates the structural deformation assciated with the large volume change upon cycling. The synthesized Ni(OH)2/graphene/Ni(OH)2/Ni foam electrode exhibits a high specific capacity of 991 C g−1 at a current density of 1 A g−1, which is higher than the theoretical specific capacity of additive sum of Ni(OH)2 and graphene, and retains 95.4% of the initial capacity after 5000 cycles. A hybrid supercapacitor is constructed by using Ni(OH)2/graphene/Ni(OH)2/Ni foam as the positive electrode and activated carbon on Ni foam as the negative electrode, which achieves a maximum energy density of 49.5 W h kg−1 at a power density of 750 W kg−1, and excellent cycling lifespans with 89.3% retention after 10000 cycles at 10 A g−1

Phosphorous-containing oxygen-deficient cobalt molybdate as an advanced electrode material for supercapacitors

The intrinsically poor electrical conductivity and insufficient number of electrochemically active sites of transition-metal oxides hamper their wide application in high-performance supercapacitors. Herein, we demonstrate an effective strategy of creating phosphorus-containing cobalt molybdate (CoMoO4) with oxygen vacancies (P-CoMoO4-x) on nickel foam for use as a supercapacitor electrode. Experimental analyses and theoretical calculations reveal that the electronic structure of P-CoMoO4-x can be efficiently modulated by incorporating P heteroatoms and O vacancies, thereby simultaneously reducing the energy band gap and increasing electrical conductivity. Moreover, incorporating P into P-CoMoO4-x weakens the Co-O bond energy and induces the low oxidation states of molybdenum species, facilitating surface redox chemistry and improving electrochemical performance. Accordingly, the optimized P-CoMoO4-x electrode exhibits a high specific capacity of 1368 C g−1 at a current density of 2 A g−1, and it retains 95.3% of the initial capacity after 5000 cycles at a high current density of 10 A g−1. An asymmetric supercapacitor assembled with the optimized P-CoMoO4-x as positive electrode and activated carbon as negative electrode delivers a high energy density of 58 W h kg−1 at a power density of 850 W kg−1 as well as achieves excellent cycling lifespan

Phosphorus-mediated MoS2 nanowires as a high-performance electrode material for quasi-solid-state sodium-ion intercalation supercapacitors

Molybdenum disulfide (MoS2) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na+-ion charge storage kinetics of MoS2 for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na+ ion is lowered by a facile phosphorus-doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na-vacancy diffusion on P-doped MoS2 (0.11 eV) is considerably lower than that on pure MoS2 (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P-doping. Moreover, the Na-vacancy diffusion coefficient of the P-doped MoS2 at room temperatures can be enhanced substantially by approximately two orders of magnitude (10−6–10−4 cm2 s−1) compared with pure MoS2. Finally, the quasi-solid-state asymmetrical supercapacitor assembled with P-doped MoS2 and MnO2, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg−1 at 850 W kg−1 and excellent cycling stability with 93.4% capacitance retention after 5000 cycles at 8 A g−1

Gene silencing of <i>Sugar-dependent 1</i> (JcSDP1), encoding a patatin-domain triacylglycerol lipase, enhances seed oil accumulation in <i>Jatropha curcas</i>

BACKGROUND: Triacylglycerols (TAGs) are the most abundant form of storage oil in plants. They consist of three fatty acid chains (usually C16 or C18) covalently linked to glycerol. SDP1 is a specific lipase for the first step of TAG catabolism in Arabidopsis seeds. Arabidopsis mutants deficient in SDP1 accumulate high levels of oils, probably due to blockage in TAG degradation. We applied this knowledge from the model plant, Arabidopsis thaliana, to engineer increased seed oil content in the biodiesel plant Jatropha curcas using RNA interference (RNAi) technology. RESULTS: As Jatropha is a biodiesel crop, any significant increase in its seed oil content would be an important agronomic trait. Using A. thaliana as a model plant, we found that a deficiency of SDP1 led to higher TAG accumulation and a larger number of oil bodies in seeds compared with wild type (Columbia-0; Col-0). We cloned Jatropha JcSDP1, and verified its function by complementation of the Arabidopsis sdp1-5 mutant. Taking advantage of the observation with Arabidopsis, we used RNAi technology to generate JcSDP1 deficiency in transgenic Jatropha. We found that Jatropha JcSDP1-RNAi plants accumulated 13 to 30% higher total seed storage lipid, along with a 7% compensatory decrease in protein content, compared with control (CK; 35S:GFP) plants. Free fatty acid (FFA) content in seeds was reduced from 27% in control plants to 8.5% in JcSDP1-RNAi plants. CONCLUSION: Here, we showed that SDP1 deficiency enhances seed oil accumulation in Arabidopsis. Based on this result, we generated SDP1-deficient transgenic Jatropha plants using by RNAi technology with a native JcSDP1 promoter to silence endogenous JcSDP1 expression. Seeds of Jatropha JcSDP1-RNAi plants accumulated up to 30% higher total lipid and had reduced FFA content compared with control (CK; 35S:GFP) plants. Our strategy of improving an important agronomic trait of Jatropha can be extended to other oil crops to yield higher seed oil

Eco-friendly synthesis of self-supported N-doped Sb2S3-carbon fibers with high atom utilization and zero discharge for commercial full lithium-ion batteries

Antimony trisulfide (Sb2S3) is a prospective electrode material for lithium-ion batteries (LIBs) because of its thermal stability, low price, and high specific capacity. However, the commercialization of Sb2S3 as an anode material is greatly hindered by its poor electronic conductivity and massive volume variation during charge/discharge cycles. Moreover, growing demand in reducing greenhouse gas emission requires the material preparation process to be pollution free and highly energy efficient. Herein, we introduce, for the first time, an eco-friendly and highly efficient one-step annealing method to construct a three-dimensional (3D) flexible conductive network and buffer matrix for N-doped Sb2S3-carbon fibers (NSSCs) as a high-performance anode. It is assembled by mixing sulfur and antimony in the atomicity level with a stoichiometric ratio as the electrospinning precursor and then annealed in a sealed quartz tube to assure the high atom utilization of nitrogen and sulfur. Benefiting from the 3D structure and compositional advantages, the NSSC electrode with improved conductivity and carbon buffer matrix exhibits superior Li-storage performance. As a result, this work not only promotes the commercialization of antimony trisulfide but also points out a general eco-friendly method, which can be widely applied to synthesize a variety of flexible metal sulfides and metal nitrides with high atom utilization and zero discharge

Epitaxial Growth of Two-dimensional Insulator Monolayer Honeycomb BeO

The emergence of two-dimensional (2D) materials launched a fascinating frontier of flatland electronics. Most crystalline atomic layer materials are based on layered van der Waals materials with weak interlayer bonding, which naturally leads to thermodynamically stable monolayers. We report the synthesis of a 2D insulator comprised of a single atomic sheet of honeycomb structure BeO (h-BeO), although its bulk counterpart has a wurtzite structure. The h-BeO is grown by molecular beam epitaxy (MBE) on Ag(111) thin films that are conveniently grown on Si(111) wafers. Using scanning tunneling microscopy and spectroscopy (STM/S), the honeycomb BeO lattice constant is determined to be 2.65 angstrom with an insulating band gap of 6 eV. Our low energy electron diffraction (LEED) measurements indicate that the h-BeO forms a continuous layer with good crystallinity at the millimeter scale. Moir\'e pattern analysis shows the BeO honeycomb structure maintains long range phase coherence in atomic registry even across Ag steps. We find that the interaction between the h-BeO layer and the Ag(111) substrate is weak by using STS and complimentary density functional theory calculations. We not only demonstrate the feasibility of growing h-BeO monolayers by MBE, but also illustrate that the large-scale growth, weak substrate interactions, and long-range crystallinity make h-BeO an attractive candidate for future technological applications. More significantly, the ability to create a stable single crystalline atomic sheet without a bulk layered counterpart is an intriguing approach to tailoring novel 2D electronic materials.Comment: 25 pages, 7 figures, submitted to ACS Nano, equal contribution by Hui Zhang and Madisen Holbroo

Heteroatomic interface engineering of MOF-derived metal-embedded P- and N-codoped Zn node porous polyhedral carbon with enhanced sodium-ion storage

Amorphous-ordered mesoporous carbon materials are regarded as the most promising anode candidate for sodium-ion batteries (SIBs) owing to their eco-friendliness, abundance, thermal stability, and low price. However, poor rate, low initial Coulombic efficiency, and poor cycling performance have been the major challenges of SIBs. Herein, we successfully constructed a robust phosphorus and nitrogen-codoped Zn node porous polyhedral carbon polyhedron (P-N-Zn-C). The as-prepared P-N-Zn-C anode delivers outstanding electrochemical performance and ultrahigh stability and has achieved a remarkable capacity of 460 mA h g-1 at 100 mA g-1, long-term cycling stability of up to 100 cycles, and an excellent rate performance even at a current density of up to 1000 mA g-1. The remarkable performance can be ascribed to the enlarged interlayer distances of carbon and the existence of Zn node, which facilitate the insertion-extraction of Na ions. The first-principles density functional theory calculations revealed that the presence of P, N, and Zn could reduce the band gaps between the valence and conduction bands and accelerate the electron transfer reaction rate. This study underscores the potential importance of heteroatom doping as an effective strategy for improving the performance of carbon electrode materials

New insight into the effect of fluorine doping and oxygen vacancies on electrochemical performance of Co2MnO4 for flexible quasi-solid-state asymmetric supercapacitors

Anion doping and oxygen-defect creation have been extensively employed to modify the electronic properties and increase concentration of electrochemically active sites of electrode materials for electrical energy storage technologies; however, comprehensive study of the roles of anion doping and oxygen vacancy on the enhancement of electrochemical performance is not clear. Herein, we provide new insight into the effect of fluorine dopant and oxygen vacancy on electrochemical performance of fluorine-doped oxygen-deficient Co2MnO4 (F-Co2MnO4-x) nanowires grown on carbon fiber (CF) as advanced electrode materials for supercapacitor. An experimental and theoretical study reveals that the structural and electronic properties in F-Co2MnO4-x is effectively tuned by introducing F dopants and oxygen vacancies, synergistically increasing electrical conductivity and providing rich Faradaic redox chemistry. The resultant F-Co2MnO4-x achieves a high specific capacity of 269 mA h g−1 at 1 A g−1, and superior cyclic stability with 93.2% capacity retention after 5000 cycles at 15 A g−1. A flexible quasi-solid-state asymmetric supercapacitor (ASC) is constructed with F-Co2MnO4-x/CF as the positive electrode and Fe2O3/CF as the negative electrode. The ASC device exhibits a high energy density of 64.4 W h kg−1 at a power density of 800 W kg−1. Significantly, the device yields 89.9% capacitance retention after 2000 bending tests at a bending angle ranging from 0 to 30°, demonstrating the high integration of excellent mechanical flexibility and cycling stability