Regulating cathode surface hydroxyl chemistry enables superior potassium storage.

Potassium vanadium fluorophosphate (KVPO4F) is regarded as a promising cathode candidate for potassium-ion batteries due to its high working voltage and satisfactory theoretical capacity. However, the usage of electrochemically inactive binders and redundant current collectors typically results in inferior electrochemical performance and low energy density, thus implying the important role of rational electrode structure design. Herein, we have reported a scalable and cost-effective synthesis of a cellulose-derived KVPO4F self-supporting electrode, which features a special surface hydroxyl chemistry, three-dimensional porous and conductive framework, as well as super flexible and stable architecture. The cellulose not only serves as a flexible substrate, a pore-forming agent, and a versatile binder for KVPO4F/conductive carbon but also enhances the K-ion migration ability. Benefiting from the special hydroxyl chemistry-induced storage mechanism and electrode structural stability, the flexible freestanding KVPO4F cathode exhibits high-rate performance (53.0% capacity retention with current densities increased 50-fold, from 0.2 C to 10 C) and impressive cycling stability (capacity retention up to 74.9% can be achieved over 1,000 cycles at a rate of 5 C). Such electrode design and surface engineering strategies, along with a deeper understanding of potassium storage mechanisms, provide invaluable guidance for better electrode design to boost the performance of potassium-ion energy storage systems.

Novel Structural Design and Adsorption/Insertion Coordinating Quasi-Metallic Na Storage Mechanism toward High-performance Hard Carbon Anode Derived from Carboxymethyl Cellulose.

Hard Carbon have become the most promising anode candidates for sodium-ion batteries, but the poor rate performance and cycle life remain key issues. In this work, N-doped hard carbon with abundant defects and expanded interlayer spacing is constructed by using carboxymethyl cellulose sodium as precursor with the assistance of graphitic carbon nitride. The formation of N-doped nanosheet structure is realized by the CN• or CC• radicals generated through the conversion of nitrile intermediates in the pyrolysis process. This greatly enhances the rate capability (192.8 mAh g-1 at 5.0 A g-1 ) and ultra-long cycle stability (233.3 mAh g-1 after 2000 cycles at 0.5 A g-1 ). In situ Raman spectroscopy, ex situ X-ray diffraction and X-ray photoelectron spectroscopy analysis in combination with comprehensive electrochemical characterizations, reveal that the interlayer insertion coordinated quasi-metallic sodium storage in the low potential plateau region and adsorption storage in the high potential sloping region. The first-principles density functional theory calculations further demonstrate strong coordination effect on nitrogen defect sites to capture sodium, especially with pyrrolic N, uncovering the formation mechanism of quasi-metallic bond in the sodium storage. This work provides new insights into the sodium storage mechanism of high-performance carbonaceous materials, and offers new opportunities for better design of hard carbon anode.

Boron-Catalyzed Graphitization Carbon Layer Enabling LiMn0.8 Fe0.2 PO4 Cathode Superior Kinetics and Li-Storage Properties.

The poor electrode kinetics and low conductivity of the LiMn0.8 Fe0.2 PO4 cathode seriously impede its practical application. Here, an effective strategy of boron-catalyzed graphitization carbon coating layer is proposed to stabilize the nanostructure and improve the kinetic properties and Li-storage capability of LiMn0.8 Fe0.2 PO4 nanocrystals for rechargeable lithium-ion batteries. The graphite-like BC3 is derived from B-catalyzed graphitization coating layers, which can not only effectively maintain the dynamic stability of the LiMn0.8 Fe0.2 PO4 nanostructure during cycling, but also plays an important role in enhancing the conductivity and Li+ migration kinetics of LiMn0.8 Fe0.2 PO4 @B-C. The optimized LiMn0.8 Fe0.2 PO4 @B-C exhibits the fastest intercalation/deintercalation kinetics, highest electrical conductivity (8.41 × 10-2 S cm-1 ), Li+ diffusion coefficient (6.17 × 10-12 cm2 s-1 ), and Li-storage performance among three comparison samples (B-C0, B-C6, and B-C9). The highly reversible properties and structural stability of LiMn0.8 Fe0.2 PO4 @B-C are further proved by operando XRD analysis. The B-catalyzed graphitization carbon coating strategy is expected to be an effective pathway to overcome the inherent drawbacks of the high-energy density LiMn0.8 Fe0.2 PO4 cathode and to improve other cathode materials with low-conductivity and poor electrode kinetics for rechargeable second batteries.

Synergistic Effect, Structural and Morphology Evolution, and Doping Mechanism of Spherical Br-Doped Na3 V2 (PO4 )2 F3 /C toward Enhanced Sodium Storage.

Na3 V2 (PO4 )2 F3 has attracted wide attention due to its high voltage platform, and stable crystal structure. However, its application is limited by the low electronic conductivity and the ease formation of impurity. In this paper, the spherical Br-doped Na3 V2 (PO4 )2 F3 /C is successfully obtained by a one-step spray drying technology. The hard template polytetrafluoroethylene (PTFE) supplements the loss of fluorine, forming porous structure that accelerates the infiltration of electrolyte. The soft template cetyltrimethylammonium bromide (CTAB) enables doping of bromine and can also control the fluorine content, meanwhile, the self-assembly effect strengthens the structure and refines the size of spherical particles. The loss, compensation, and regulation mechanism of fluorine are investigated. The Br-doped Na3 V2 (PO4 )2 F3 /C sphere exhibits superior rate capability with the capacities of 116.1, 105.1, and 95.2 mAh g-1 at 1, 10, and 30 C, and excellent cyclic performance with 98.3% capacity retention after 1000 cycles at 10 C. The density functional theory (DFT) calculation shows weakened charge localization and enhanced conductivity, meanwhile the diffusion energy barrier of sodium ions is reduced with Br doping. This paper proposes a strategy to construct fluorine-containing polyanions cathode, which enables the precise regulation of structure and morphology, thus leading to superior electrochemical performance.

Insights into the sodium storage mechanism of Bi2Te3 nanosheets as superior anodes for sodium-ion batteries.

Although bismuth-based anode materials for sodium-ion batteries (SIBs) have attracted wide attention, their large volume variation hinders their actual applications, especially in Bi2Te3 systems. In this study, Bi2Te3 nanosheets (BT-Ns) are fabricated by a novel strategy via a solvent reductive reaction. The elements Bi and Te are spontaneously grown into ultrathin nanosheets because the hexagonal crystal of Bi2Te3 has a strong tendency to grow horizontally. The crystal structure of the BT-Ns is well developed and the thickness is about 1.42 nm, which can not only offer more active sites but also promote electrical conductivity and the diffusion of Na ions and electrons. It exhibits excellent rate and long-term cyclic performance, delivering 364.0 mA h g-1 at 5 A g-1 after 1200 cycles. The high rate and long-term cyclic performance of the Bi2Te3 anodes is attributed to the facile design of the 2D nanosheet structure, presenting an effective strategy to construct anodes for SIBs. The sodium storage mechanism of Bi2Te3 follows a three-step crystallographic phase change of Bi2Te3, discovered by an in situ X-ray diffraction analysis. The applicability of BT-N anodes in full cells via pairing with Na3V2(PO4)3 cathodes delivers excellent performance (energy density of 107.2 W h kg-1) and satisfactory practical applied prospects.

Construction and Theoretical Calculation of an Ultra-High-Performance LiVPO4F/C Cathode by B-Doped Pyrolytic Carbon from Poly(vinylidene Fluoride).

B-doped pyrolytic carbon from poly(vinylidene fluoride) (PVDF) was used to enhance the performance of a LiVPO4F/C cathode, which is much cheaper than carbon nanotubes and graphene. The carbon layer in LVPF/C-B3 becomes more and more regular compared with the undoped sample. The electronic conductivity, diffusion coefficient, and rate and cycle performance of the B-doped cathode are greatly improved. The capacities of LVPF/C-B3 at 0.2C, 5C, and 15C are 148.1, 132.9, and 125.6 mAh·g-1, which may be the best reported magnitude. The crystallite structure of LiVPO4F/C is well maintained after 300 charge and discharge cycles. The carbonization process of PVDF is greatly accelerated. These improvements are attributed to the changes in chemical and electronic structures. The generation of BC2O and BCO2 results in many defective active sites, and BC3 promotes the growth of a six-membered carbon ring. According to the first-principles approach based on density functional theory, the state density around the Fermi level of the B-doped pyrolytic carbon is increased. The electronic structure of pyrolytic carbon is transformed from a P-type semiconductor to a metal-like structure through the generation of pyridinic-like and graphitic-like B. Therefore, the electronic conductivity of LiVPO4F/C is increased.

Effect of Environmental Temperature on the Content of Impurity Li3V2(PO4)3/C in LiVPO4F/C Cathode for Lithium-ion Batteries.

Previous studies have shown that the impurity Li3V2(PO4)3 in LiVPO4F will adversely affect its electrochemical performance. In this work, we show that the crystalline composition of LiVPO4F/C is mainly influenced by the environmental temperature. The content of Li3V2(PO4)3 formed in LiVPO4F/C is 0, 11.84 and 18.75% at environmental temperatures of 10, 20, and 30°C, respectively. For the sample LVPF-30C, the SEM pattern shows a kind of alveolate microstructure and the result of selected area electron diffraction shows two sets of patterns. The LiVPO4F/C cathode without impurity phase Li3V2(PO4)3 was prepared at 10°C. The selected area electron diffraction result proves that the lattice pattern of LiVPO4F is a regular parallelogram. Electrochemical tests show that only one flat plateau around 4.2 V appears in the charge/discharge curve, and the reversible capacity is 140.4 mAh·g-1 at 0.1 C, and 116.3 mAh·g-1 at 5 C. From these analyses, it is reasonable to speculate that synthesizing LiVPO4F/C at a low environmental temperature is a practical strategy to obtain pure crystalline phase and good electrochemical performance.

Chemical reaction characteristics, structural transformation and electrochemical performances of new cathode LiVPO4F/C synthesized by a novel one-step method for lithium ion batteries.

A new cathode LiVPO4F/C with a high working voltage of around 4.2 V was synthesized by a novel one-step method. The color of the solution turns green, which implies that V2O5 is successfully reduced to V3+. The reaction thermodynamics indicates that LiVPO4F/C is formed when the sintering temperature is higher than 650 °C, while the accompanying impurity phase Li3V2(PO4)3/C is also generated. The reaction kinetics proves that the reaction is third order and the activated energy is 208.9 kJ mol-1. X-ray photoelectron spectra imply that the components of LiVPO4F/C prepared at 800 °C (LVPF800) are in their appropriate valence. LVPF800 is composed of micron secondary particles aggregating from nano subglobose. The structural transformation shows that the V : P : F ratio in LVPF800 is close to 1 : 1 : 1. The reason behind generation of impurity Li3V2(PO4)3 at a high temperature of 850 °C is demonstrated directly, which is mainly due to the volatilization of VF3. The electrochemical performances of the cathode are related to the crystallite content of LiVPO4F/C and Li3V2(PO4)3/C. The specific capacities at 0.2 and 5C of LVPF800 are as high as 139.3 and 116.5 mA h g-1. Electrochemical analysis reveals that LVPF800 possesses an excellent reversibility in the extraction and insertion process and minimum charge transfer resistance.

[Analysis of cell morphology and immunophenotypic characteristics in 47 cases of multiple myeloma].

OBJECTIVE: This study was to investigate the cell morphology and cell immune phenotypic characteristics in patients with multiple myeloma (MM). METHODS: The flow cytometry with multiparametric direct immunofluorescence technique, and CD45/SSC and CD38(+)(+)/CD138(+) gating were used to measure cell markers CD138, CD38, CD56, CD117, CD3, CD13, CD33, CD19, CD7, CD20, CD22, CD34, CD28 in 47 MM patients. At the same time the morphology examination of bone marrow cells was performed. RESULTS: The suspicious myeloma cell ratio in MM patients was 9.42%-74.25% detected by flow cytometry, moreover, the myeloma cell ratio detected by morphology examination was 11.0%-80.6%, there was a good correlation between the two detection methods (r(2) = 0.54, P < 0.001). The ratio of antigen positive expression was as follows: 74.46% for CD138, 100% for CD38, 57.44% for CD56, 40.42% for CD117, 6.38% for CD13, 19.15% for CD33, 8.51% for CD20, 27.66% for CD28, 2.12% for CD22, 4.25% for CD34, 0% for CD3, 0% for CD19, 0% for CD7. CONCLUSIONS: CD45/SSC and CD38(+)/CD138(+) gating technique can accurately gate multiple myeloma cell sets which need analysis, the majority of myeloma cells expreses CD138, CD38, CD56 antigens. The immunophenotypic analysis combined with the cell morphology examination more contribute to the diagnosis and differential diagnosis of multiple myeloma.