Suppression and Mechanism of Voltage Decay in Sb-Doped Lithium-Rich Layered Oxide Cathode Materials.

Voltage decay during cycling is the major problem for lithium-rich layered oxide cathodes. Here, we designed Sb-doped lithium-rich layered oxides prepared by a coprecipitation-solvent thermal method, aiming to alleviate the voltage decay of lithium-rich layered oxides. The midpoint discharge voltage and specific capacity of Li1.20Ni0.133Co0.133Mn0.633Sb0.01O2 (LLMO-Sb1) demonstrate almost no decaying after 100 cycles at 1 C. Moreover, it exhibits a large rate capacity (215 mAh g-1 at 5 C). The suppressed voltage decay and enhanced cycle performance of Sb-doped material are attributed to the high Sb-O bond energy, which can enhance the stability of the layered structure and suppress the layered-to-spinel phase transition. Moreover, Sb doping improves the rate capacity by reducing the energy barrier of lithium ion diffusion. This work opens a gate to prevent the oxidation of superoxo and peroxo, stabilizing the layered structure by selecting an element with a suitable radius and electronegativity.

Role of Residual Li and Oxygen Vacancies in Ni-rich Cathode Materials.

Residual Li and oxygen vacancies in Ni-rich cathode materials have a great influence on electrochemical performance, yet their role is still poorly understood. Herein, by simply adjusting the oxygen flow during the high-temperature sintering process, some Li2O can be carried into the exhaust gas and the contents of residual Li and oxygen vacancies in LiNi0.825Co0.115Mn0.06O2 cathodes can be accurately controlled. Residual Li reduces the surficial Li+ diffusion coefficient, thereby limiting the rate property of the cathode. Oxygen vacancies affect the oxygen release energy in the crystal, and the lowest oxygen release energy is found at an oxygen vacancy concentration of 8.35%, resulting in an unstable structure and thereby poor cycle performance. The Ni-rich cathode with low residual Li and oxygen vacancy contents exhibits superior capacity retention (89.55 and 77.66%) at 2C after 300 cycles between 2.7-4.3 and 2.7-4.5 V. These findings clarify the role of residual Li and oxygen vacancies in Ni-rich cathode materials and provide a simple way to obtain high-performance Ni-rich cathodes for high-energy-density Li-ion batteries.

Promoting the Performance of Li-CO2 Batteries via Constructing Three-Dimensional Interconnected K+ Doped MnO2 Nanowires Networks.

Nowadays, Li-CO2 batteries have attracted enormous interests due to their high energy density for integrated energy storage and conversion devices, superiorities of capturing and converting CO2. Nevertheless, the actual application of Li-CO2 batteries is hindered attributed to excessive overpotential and poor lifespan. In the past decades, catalysts have been employed in the Li-CO2 batteries and been demonstrated to reduce the decomposition potential of the as-formed Li2CO3 during charge process with high efficiency. However, as a representative of promising catalysts, the high costs of noble metals limit the further development, which gives rise to the exploration of catalysts with high efficiency and low cost. In this work, we prepared a K+ doped MnO2 nanowires networks with three-dimensional interconnections (3D KMO NWs) catalyst through a simple hydrothermal method. The interconnected 3D nanowires network catalysts could accelerate the Li ions diffusion, CO2 transfer and the decomposition of discharge products Li2CO3. It is found that high content of K+ doping can promote the diffusion of ions, electrons and CO2 in the MnO2 air cathode, and promote the octahedral effect of MnO6, stabilize the structure of MnO2 hosts, and improve the catalytic activity of CO2. Therefore, it shows a high total discharge capacity of 9,043 mAh g-1, a low overpotential of 1.25 V, and a longer cycle performance.

The exceptionally high thermal conductivity after 'alloying' two-dimensional gallium nitride (GaN) and aluminum nitride (AlN).

Alloying is a widely employed approach for tuning properties of materials, especially for thermal conductivity which plays a key role in the working liability of electronic devices and the energy conversion efficiency of thermoelectric devices. Commonly, the thermal conductivity of an alloy is acknowledged to be the smallest compared to the parent materials. However, the findings in this study bring some different points of view on the modulation of thermal transport by alloying. The thermal transport properties of monolayer GaN, AlN, and their alloys of Ga x Al1-x N are comparatively investigated by solving the Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of Ga0.25Al0.75N alloy (29.57 Wm-1 K-1) and Ga0.5Al0.5N alloy (21.49 Wm-1 K-1) are found exceptionally high to be between AlN (74.42 Wm-1 K-1) and GaN (14.92 Wm-1 K-1), which violates the traditional knowledge that alloying usually lowers thermal conductivity. The mechanism resides in that, the existence of Al atoms reduces the difference in atomic radius and masses of the Ga0.25Al0.75N alloy, which also induces an isolated optical phonon branch around 18 THz. As a result, the scattering phase space of Ga0.25Al0.75N is largely suppressed compared to GaN. The microscopic analysis from the orbital projected electronic density of states and the electron localization function further provides insight that the alloying process weakens the polarization of bonding in Ga0.25Al0.75N alloy and leads to the increased thermal conductivity. The exceptionally high thermal conductivity of the Ga x Al1-x N alloys and the underlying mechanism as revealed in this study would bring valuable insight for the future research of materials with applications in high-performance thermal management.

New Insight into the Confinement Effect of Microporous Carbon in Li/Se Battery Chemistry: A Cathode with Enhanced Conductivity.

Embedding the fragmented selenium into the micropores of carbon host has been regarded as an effective strategy to change the Li-Se chemistry by a solid-solid mechanism, thereby enabling an excellent cycling stability in Li-Se batteries using carbonate electrolyte. However, the effect of spatial confinement by micropores in the electrochemical behavior of carbon/selenium materials remains ambiguous. A comparative study of using both microporous (MiC) and mesoporous carbons (MeC) with narrow pore size distribution as selenium hosts is herein reported. Systematic investigations reveal that the high Se utilization rate and better electrode kinetics of MiC/Se cathode than MeC/Se cathode may originate from both its improved Li+ and electronic conductivities. The small pore size (<1.35 nm) of the carbon matrices not only facilitates the formation of a compact and robust solid-electrolyte interface (SEI) with low interfacial resistance on cathode, but also alters the insulating nature of Li2 Se due to the emergence of itinerant electrons. By comparing the electrochemical behavior of MiC/Se cathode and the matching relationship between the diameter of pores and the dimension of solvent molecules in carbonate, ether, and solvate ionic liquid electrolyte, the key role of SEI film in the operation of C/Se cathode by quasi-solid-solid mechanism is also highlighted.

Bimetal-organic Framework-derived Co9 S8 /ZnS@NC Heterostructures for Superior Lithium-ion Storage.

Heterostructure engineering of electrode materials, which is expected to accelerate the ion/electron transport rates driven by a built-in internal electric field at the heterointerface, offers unprecedented promise in improving their cycling stability and rate performance. Herein, carbon nanotubes with Co9 S8 /ZnS heterostructures embedded in a N-doped carbon framework (Co9 S8 /ZnS@NC) have been rationally designed via an in-situ vapor chemical transformation strategy with the aid of thiophene, which not only acted as carbon source for the growth of carbon nanotubes but also as sulfur source for the sulfurization of metal Zn and Co. Density functional theory (DFT) calculation shows an about 3.24 eV electrostatic potential difference between ZnS and Co9 S8 , which results in a strong electrostatic field across the interface that makes electrons transfer from Co9 S8 to the ZnS side. As expected, a stable cycling performance with reversible capacity of 411.2 mAh g-1 at 1000 mA g-1 after 300 cycles, excellent rate capability (324 mAh g-1 at 2000 A g-1 ) and a high percentage of pseudocapacitance contribution (87.5% at 2.2 mv/s) for lithium-ion batteries (LIBs) are achieved. This work provides a possible strategy for designing multicomponent heterostructural materials for application in energy storage and conversion fields.

Template-Free Synthesis of N-Doped Porous Carbon Materials From Furfuryl Amine-Based Protic Salts.

Nitrogen-doped porous carbon materials (NPCMs) are usually obtained by carbonization of complicated nitrogen-containing polymers in the presence of template or physical/chemical activation of the as-synthesized carbon materials. Herein we reported the facile synthesis of NPCMs by direct carbonization of a series of furfuryl amine (FA)-based protic salts ([FA][X], X = NTf2, HSO4, H2PO4, CF3SO3, BF4, NO3, Cl) without any templates, tedious synthetic steps and other advanced techniques. The thermal decomposition of precursors and structure, elemental composition, surface atomic configuration, and porosity of carbons have been carefully investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), combustion elemental analysis, energy-dispersive spectrometry, and nitrogen isotherm adsorption. Different from the parent amine FA that was evaporated below 130°C and no carbon was finally obtained, it was found that all the prepared protic precursors yield NPCMs. These carbon materials were found to exhibit anion structure- dependent carbon yield, chemical composition, and porous structure. The obtained NPCMs can be further exploited as adsorbents for dye removal and decoloration. Among all NPCMs, [FA][H2PO4]-derived carbon owing to its high surface area and special pore structure exhibits the highest adsorption capacities toward both Methylene blue and Rhodamine B.

Submicron-Sized Nb-Doped Lithium Garnet for High Ionic Conductivity Solid Electrolyte and Performance of Quasi-Solid-State Lithium Battery.

The garnet Li7La3Zr2O12 (LLZO) has been widely investigated because of its high conductivity, wide electrochemical window, and chemical stability with regards to lithium metal. However, the usual preparation process of LLZO requires high-temperature sintering for a long time and a lot of mother powder to compensate for lithium evaporation. In this study submicron Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powder-which has a stable cubic phase and high sintering activity-was prepared using the conventional solid-state reaction and the attrition milling process, and Li stoichiometric LLZNO ceramics were obtained by sintering this powder-which is difficult to control under high sintering temperatures and when sintered for a long time-at a relatively low temperature or for a short amount of time. The particle-size distribution, phase structure, microstructure, distribution of elements, total ionic conductivity, relative density, and activation energy of the submicron LLZNO powder and the LLZNO ceramics were tested and analyzed using laser diffraction particle-size analyzer (LD), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electrochemical Impedance Spectroscopy (EIS), and the Archimedean method. The total ionic conductivity of samples sintered at 1200 °C for 30 min was 5.09 × 10-4 S·cm-1, the activation energy was 0.311 eV, and the relative density was 87.3%. When the samples were sintered at 1150 °C for 60 min the total ionic conductivity was 3.49 × 10-4 S·cm-1, the activation energy was 0.316 eV, and the relative density was 90.4%. At the same time, quasi-solid-state batteries were assembled with LiMn2O4 as the positive electrode and submicron LLZNO powder as the solid-state electrolyte. After 50 cycles, the discharge specific capacity was 105.5 mAh/g and the columbic efficiency was above 95%.

High-Performance Lithium-Rich Layered Oxide Material: Effects of Preparation Methods on Microstructure and Electrochemical Properties.

Lithium-rich layered oxide is one of the most promising candidates for the next-generation cathode materials of high-energy-density lithium ion batteries because of its high discharge capacity. However, it has the disadvantages of uneven composition, voltage decay, and poor rate capacity, which are closely related to the preparation method. Here, 0.5Li2MnO3·0.5LiMn0.8Ni0.1Co0.1O2 was successfully prepared by sol-gel and oxalate co-precipitation methods. A systematic analysis of the materials shows that the 0.5Li2MnO3·0.5LiMn0.8Ni0.1Co0.1O2 prepared by the oxalic acid co-precipitation method had the most stable layered structure and the best electrochemical performance. The initial discharge specific capacity was 261.6 mAh·g-1 at 0.05 C, and the discharge specific capacity was 138 mAh·g-1 at 5 C. The voltage decay was only 210 mV, and the capacity retention was 94.2% after 100 cycles at 1 C. The suppression of voltage decay can be attributed to the high nickel content and uniform element distribution. In addition, tightly packed porous spheres help to reduce lithium ion diffusion energy and improve the stability of the layered structure, thereby improving cycle stability and rate capacity. This conclusion provides a reference for designing high-energy-density lithium-ion batteries.

Effect of Different Composition on Voltage Attenuation of Li-Rich Cathode Material for Lithium-Ion Batteries.

Li-rich layered oxide cathode materials have become one of the most promising cathode materials for high specific energy lithium-ion batteries owning to its high theoretical specific capacity, low cost, high operating voltage and environmental friendliness. Yet they suffer from severe capacity and voltage attenuation during prolong cycling, which blocks their commercial application. To clarify these causes, we synthesize Li1.5Mn0.55Ni0.4Co0.05O2.5 (Li1.2Mn0.44Ni0.32Co0.04O2) with high-nickel-content cathode material by a solid-sate complexation method, and it manifests a lot slower capacity and voltage attenuation during prolong cycling compared to Li1.5Mn0.66Ni0.17Co0.17O2.5 (Li1.2Mn0.54Ni0.13Co0.13O2) and Li1.5Mn0.65Ni0.25Co0.1O2.5 (Li1.2Mn0.52Ni0.2Co0.08O2) cathode materials. The capacity retention at 1 C after 100 cycles reaches to 87.5% and the voltage attenuation after 100 cycles is only 0.460 V. Combining X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), it indicates that increasing the nickel content not only stabilizes the structure but also alleviates the attenuation of capacity and voltage. Therefore, it provides a new idea for designing of Li-rich layered oxide cathode materials that suppress voltage and capacity attenuation.

O-Doping Boosts the Electrochemical Oxygen Reduction Activity of a Single Fe Site in Hydrophilic Carbon with Deep Mesopores.

Carbon-based electrocatalysts with single metal sites hold great potential for mechanism exploration via mimicking molecular catalysts, due to their distinct catalytic sites. In addition to metal atoms, the neighboring nonmetal heteroatoms such as N, S, and O atoms, which are widely detected in carbon-based single-atom catalysts, may also contribute to enhancing the electrochemical activity of single-metal centers. In this work, the boosting effect of O-doping toward the electrochemical oxygen reduction reaction (ORR) was evaluated by both experimental studies and DFT calculations. O-doped carbon-supported single-Fe-site catalysts possessing deep mesopores and desirable hydrophilic surface were achieved by confined carbonization in an inert or reductive atmosphere (SAFe-NDC and SAFe-NDC-H). As compared to the state-of-the-art Pt/C, these catalysts showed superior catalytic activity toward the ORR in terms of half-wave potential, Tafel slope, and long-term stability. In particular, SAFe-NDC-H outperformed its SAFe-NDC counterpart. Considering that these two catalysts possess a comparable porous structure, surface properties, and local electronic structure of a single Fe site, the dopant nonmetal O atoms, specifically, carbonyl group (C═O), are revealed to affect the ORR activity of the single Fe site exclusively. The introduced C═O facilitates the formation of *OOH as well as the reduction of *OH, thereby reducing the catalysts' overpotential.

The Effects of Reversibility of H2-H3 Phase Transition on Ni-Rich Layered Oxide Cathode for High-Energy Lithium-Ion Batteries.

Although LiNi0.8Co0.1Mn0.1O2 is attracting increasing attention on account of its high specific capacity, the moderate cycle lifetime still hinders its large-scale commercialization applications. Herein, the Ti-doped LiNi0.8Co0.1Mn0.1O2 compounds are successfully synthesized. The Li(Ni0.8Co0.1Mn0.1)0.99Ti0.01O2 sample exhibits the best electrochemical performance. Under the voltage range of 2.7-4.3 V, it maintains a reversible capacity of 151.01 mAh·g-1 with the capacity retention of 83.98% after 200 cycles at 1 C. Electrochemical impedance spectroscopy (EIS) and differential capacity profiles during prolonged cycling demonstrate that the Ti doping could enhance both the abilities of electronic transition and Li ion diffusion. More importantly, Ti doping can also improve the reversibility of the H2-H3 phase transitions during charge-discharge cycles, thus improving the electrochemical performance of Ni-rich cathodes.

Understanding the Impact of K-Doping on the Structure and Performance of LiFePO4/C Cathode Materials.

The K-doped Li1-xKxFePO4 (x = 0, 0.005, 0.01, and 0.02) samples were synthesized successfully via a solid-state method, and the electronic structures of the samples were calculated by the first-principles based on density functional theory. Theoretical calculations show that the bandwidth of Li1-xKxFePO4 decreases with the increase in K+ doping, which is consistent with the experimental results. It was demonstrated that Li0.995K0.005FePO4 delivers higher capacity retention with 92.7% after 100 cycles compared with LiFePO4 (86.3%) at 1 C and shows better high-rate performance with capacities of 151.9, 151.8, 149.2, 128.3, and 84.6 mAh·g-1 at current densities of 0.1 C, 0.2 C, 0.5 C, 1 C, and 3 C; the corresponding values for LiFePO4 were 153.2, 136.5, 125.9, 111.5, and 66.0 mAh·g-1. Owing to the expanded Li ion diffusion pathway, EIS analysis showed that the lithium ion diffusion coefficient of LiFePO4 doped with K ion was significantly improved compared to LiFePO4; the values were 1.934×10-13 and 1.658×10-12 cm²·s-1, respectively. Additionally, Li0.995K0.005FePO4 showed a lower charge transfer resistance (300.2 Ω compared to 407.1 Ω of LiFePO4).

Porous Hollow Superlattice NiMn2O4/NiCo2O4 Mesocrystals as a Highly Reversible Anode Material for Lithium-Ion Batteries.

As a promising high-capacity anode material for Li-ion batteries, NiMn2O4 always suffers from the poor intrinsic conductivity and the architectural collapse originating from the volume expansion during cycle. Herein, a combined structure and architecture modulation is proposed to tackle concurrently the two handicaps, via a facile and well-controlled solvothermal approach to synthesize NiMn2O4/NiCo2O4 mesocrystals with superlattice structure and hollow multi-porous architecture. It is demonstrated that the obtained NiCo1.5Mn0.5O4 sample is made up of a new mixed-phase NiMn2O4/NiCo2O4 compound system, with a high charge capacity of 532.2 mAh g-1 with 90.4% capacity retention after 100 cycles at a current density of 1 A g-1. The enhanced electrochemical performance can be attributed to the synergistic effects of the superlattice structure and the hollow multi-porous architecture of the NiMn2O4/NiCo2O4 compound. The superlattice structure can improve ionic conductivity to enhance charge transport kinetics of the bulk material, while the hollow multi-porous architecture can provide enough void spaces to alleviate the architectural change during cycling, and shorten the lithium ions diffusion and electron-transportation distances.

Improved Electrochemical Performance of Surface Coated LiNi0.80Co0.15Al0.05O2 With Polypyrrole.

Nickel-rich ternary layered oxide (LiNi0.80Co0.15Al0.05O2, LNCA) cathodes are favored in many fields such as electric vehicles due to its high specific capacity, low cost, and stable structure. However, LNCA cathode material still has the disadvantages of low initial coulombic efficiency, rate capability and poor cycle performance, which greatly restricts its commercial application. To overcome this barrier, a polypyrrole (PPy) layer with high electrical conductivity is designed to coat on the surface of LNCA cathode material. PPy coating layer on the surface of LNCA successfully is realized by means of liquid-phase chemical oxidation polymerization method, and which has been verified by the scanning electron microscopy (SEM), transmission electron microscope (TEM) and fourier transform infrared spectroscopy (FTIR). PPy-coated LNCA (PL-2) exhibits satisfactory electrochemical performances including high reversible capacity and excellent rate capability. Furthermore, the capability is superior to pristine LNCA. So, it provides a new structure of conductive polymer modified cathode materials with good property through a mild modification method.

High Performance and Structural Stability of K and Cl Co-Doped LiNi0.5Co0.2Mn0.3O2 Cathode Materials in 4.6 Voltage.

The high energy density lithium ion batteries are being pursued because of their extensive application in electric vehicles with a large mileage and storage energy station with a long life. So, increasing the charge voltage becomes a strategy to improve the energy density. But it brings some harmful to the structural stability. In order to find the equilibrium between capacity and structure stability, the K and Cl co-doped LiNi0.5Co0.2Mn0.3O2 (NCM) cathode materials are designed based on defect theory, and prepared by solid state reaction. The structure is investigated by means of X-ray diffraction (XRD), rietveld refinements, scanning electron microscope (SEM), XPS, EDS mapping and transmission electron microscope (TEM). Electrochemical properties are measured through electrochemical impedance spectroscopy (EIS), cyclic voltammogram curves (CV), charge/discharge tests. The results of XRD, EDS mapping, and XPS show that K and Cl are successfully incorporated into the lattice of NCM cathode materials. Rietveld refinements along with TEM analysis manifest K and Cl co-doping can effectively reduce cation mixing and make the layered structure more complete. After 100 cycles at 1 C, the K and Cl co-doped NCM retains a more integrated layered structure compared to the pristine NCM. It indicates the co-doping can effectively strengthen the layer structure and suppress the phase transition to some degree during repeated charge and discharge process. Through CV curves, it can be found that K and Cl co-doping can weaken the electrode polarization and improve the electrochemical performance. Electrochemical tests show that the discharge capacity of Li0.99K0.01(Ni0.5Co0.3Mn0.2)O1.99Cl0.01 (KCl-NCM) are far higher than NCM at 5 C, and capacity retention reaches 78.1% after 100 cycles at 1 C. EIS measurement indicates that doping K and Cl contributes to the better lithium ion diffusion and the lower charge transfer resistance.

Building Honeycomb-Like Hollow Microsphere Architecture in a Bubble Template Reaction for High-Performance Lithium-Rich Layered Oxide Cathode Materials.

In the family of high-performance cathode materials for lithium-ion batteries, lithium-rich layered oxides come out in front because of a high reversible capacity exceeding 250 mAh g-1. However, the long-term energy retention and high energy densities for lithium-rich layered oxide cathode materials require a stable structure with large surface areas. Here we propose a "bubble template" reaction to build "honeycomb-like" hollow microsphere architecture for a Li1.2Mn0.52Ni0.2Co0.08O2 cathode material. Our material is designed with ca. 8-µm-sized secondary particles with hollow and highly exposed porous structures that promise a large flexible volume to achieve superior structure stability and high rate capability. Our preliminary electrochemical experiments show a high capacity of 287 mAh g-1 at 0.1 C and a capacity retention of 96% after 100 cycles at 1.0 C. Furthermore, the rate capability is superior without any other modifications, reaching 197 mAh g-1 at 3.0 C with a capacity retention of 94% after 100 cycles. This approach may shed light on a new material engineering for high-performance cathode materials.

Repeated intracoronary infusion of peripheral blood stem cells with G-CSF in patients with refractory ischemic heart failure--a pilot study.

BACKGROUND: Recent investigations have suggested the clinical efficacy of granulocyte colony-stimulating factor (G-CSF) infusion alone or in combination with a single dose delivery of peripheral blood stem cells (PBSC) infusion in patients with myocardial infarction (MI) and congestive heart failure (HF). The current study tested the feasibility and effect of repeated intracoronary infusions PBSC and the mobilization of G-CSF in patients with refractory HF after MI. METHODS AND RESULTS: Patients with recent large MI and a lower left ventricular ejection fraction (LVEF) were enrolled into one of the following 3 groups: Group R (n=15) received repeated intracoronary infusion of PBSC and one-dose of G-CSF; Group S (n=15) received a single infusion of PBSC and a G-CSF dose; and Group C (n=15) received neither PBSC nor a G-CSF dose. Cardiac performance was evaluated by echocardiography and single photon-emission computed tomography (SPECT). All the patients underwent 12-month follow-up. LVEF in Group R (47.00±4.90%) was significantly higher than that in Group S (44.40±3.87%, P<0.01) and Group C (40.80±3.41%, P<0.01). Similarly, the improvement of myocardial perfusion assessed by SPECT in Group R was more than that in Group S (P=0.012) and Group C (P<0.01). Neither death nor new MI occurred. CONCLUSIONS: Repeated intracoronary infusions of PBSC plus mobilization of G-CSF might be an optional effective strategy for treating patients with refractory HF after recent large MI.