A stable tunnel-type NaGe3/2Mn1/2O4 anode for Na-ion batteries

Tunnel-type NaGe_3/2Mn_1/2O₄ was fabricated for anode of sodium ion batteries, delivering a discharge capacity of 200.32 mAh g⁻¹ and an ultra-low potential platform compared with that of pure Na₄Ge₉O₂₀ (NGO). The results of X-ray photoelectron spectroscopy (XPS) demonstrate that Ge redox occurs, and partial substitution of Mn effectively improves the Na-storage properties compared to those of NGO.

We investigated tunnel-type NaGe_3/2Mn_1/2O₄; the main structure is Na₄Ge₉O₂₀. NaGe_3/2Mn_1/2O₄ electrodes as anodes for sodium ions batteries deliver a discharge capacity of 200.32 mAh g⁻¹ and satisfactory capacity retention after 50 cycles.

In terms of the high abundance and ready availability of sodium, sodium-ion batteries (SIBs) have been generally regarded as a better alternative to lithium-ion batteries for power stations.^1–4 Hard carbon is widely recognized as one of the most attractive and ideal anode materials for SIBs.^5,6 However, the potential required for sodium ions to insert into hard carbon is very close to that for sodium plating, resulting in sodium dendrites, which raise safety concerns.^7,8 Moreover, the reaction of electrode materials with sodium through alloying or conversion mechanisms always results in serious volume changes in the process of sodium insertion and extraction.⁹ Therefore, insertion-type transition-metal oxides as anodes have attracted much attention owing to their suitable operating potentials and minor volume expansion.^10,11 Recently, embedded titanium/vanadium/molybdenum based oxides with layered structures have been studied as anode materials for SIBs,¹² such as layered Na₂Ti₃O₇,¹³ tunnel Na₂Ti₆O₁₃ (ref. 14) and spinel Li₄Ti₅O₁₂.¹⁵ In addition, post-spinel structured materials have been proposed, which show ultra-stable cycle performances via highly reversible sodium-ion insertion/desertion through large-size tunnels. Recently, in Zhou''s group, NaVSnO₄ (ref. 16) and NaV_1.25Ti_0.75O₄ (ref. 17) have been prepared and they have been shown to possess robust cycle lifetimes (more than 10 000 cycles) and discharge plateaus of 0.84 V and 0.7 V, respectively. Meanwhile, in our group, Na_0.76Mn_0.48Ti_0.44O₂ has been developed, which holds an initial discharge capacity of 103.4 mAh g⁻¹, shows a superb rate capability and retains 74.9% capacity after 600 cycles.¹⁸ The large radius of the redox active metal center could optimize the tunnel size and thus boosting the electrochemical performance. It is also a big challenge to find further suitable active centers for insertion-type transition metal oxides as anodes of SIBs. Besides, a host of published reports have said that germanium-based materials can be used as alloy anodes for SIBs with highly reversible sodium storage properties and satisfactory ionic/electronic conductivity.¹⁹ However, it is unclear to us whether Ge could act as an active center in a transition-metal oxide anodes.In this work, we fabricated a tunnel-type NaGe_3/2Mn_1/2O₄ (NGMO) material. When used as the anode of SIBs, it delivers a sustained discharge capacity of 200.32 mAh g⁻¹. Compared with NaVSnO₄ (ref. 16) and NaV_1.25Ti_0.75O₄,¹⁷ NGMO delivers a lower safety voltage of 0.36 V. Pure Na₄Ge₉O₂₀ (NGO) as a comparative sample, only exhibits a capacity of 24.8 mAh g⁻¹, which is far inferior to that of NGMO. During discharge and charge process, reversible redox reactions around Ge center occur, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The introduction of Mn in the NGMO improves the reversibility of the Ge redox performance.The structure of NGMO was carefully characterized by XRD, and Rietveld refinement was performed as depicted in Fig. 1. The main Bragg peaks of NGMO could be assigned to space groups of P1(2) and I4₁/a(88), which were fitted to give lattice parameters of a = 10.56/15.04 Å, b = 11.18/15.04 Å, and c = 9.22/7.39 Å, and a volume of 811.2/1672.2 ų, respectively. Na₄Ge₉O₂₀ has a typical tunnel structure, which consists of polymerized Ge/MnO₄ tetrahedra connected with Ge/MnO₆ octahedra. Four Ge/MnO₆ octahedra are connected together by sharing edges to form a tetrameric (Ge/Mn)₄O₁₆ cluster. Each cluster is connected to six GeO₄ tetrahedra, and adjacent clusters are connected by GeO₄ tetrahedra. Na atoms are located in the channels and have elongated Na–O bonds.¹⁹ This highly stable crystal structure can effectively accelerate the migration of sodium ions.²⁰Fig. 2 shows the low and high magnification scanning electron microscopy (SEM) images of NGMO, which is composed of particles of different sizes from 1 to 3 μm; the larger particles are the result of sintering at high temperature. SEM images of NGO with different magnifications are given in Fig. S1,^† and show that the average particle size of NGO is 1 μm.Open in a separate windowFig. 1The Rietveld refinement spectra of NGMO.Open in a separate windowFig. 2(a) and (b) SEM images of NGMO at different magnifications.The morphology and fine structure were studied by transmission electron microscopy (TEM). Fig. 3a and b show the low magnification TEM images. It can be seen from the images that NGMO has an irregular sheet-like morphology with particle sizes from 250 nm to 2 μm. As shown in Fig. 3c, the lattice spacing of the (200) plane is 4.55 Å. In the SAED pattern of Fig. 3d, the red line corresponds to the (020) plane in NGMO, and the lattice spacing is 13.100 Å. These results clearly demonstrate that NGMO exhibits good crystallinity. The corresponding energy dispersive X-ray spectroscopy (EDS) results, and Raman and infrared spectra (IR) are provided in Table S1 and Fig. S2.^† The results indicate that the atomic ratio of Na : Ge : Mn is close to 1 : 1.5 : 0.5 and that there is little sodium loss. The Raman and IR peaks in the high frequency region are attributed to stretching vibrations of Ge–O–Ge and the peaks between 600 and 400 cm⁻¹ are attributed to the bending vibrations of Ge–O–Ge in NGMO.Open in a separate windowFig. 3(a) and (b) Low resolution TEM images, (c) a HRTEM image and (d) a SAED image of NGMO.Galvanostatic electrochemical measurements were evaluated in a voltage range of 0.05–2.0 V, with the current density of 20 mA g⁻¹. Fig. 4a and b show the discharge and charge profiles of NGMO and NGO, respectively. Because of the formation of a solid electrolyte interface (SEI) layer in the initial cycle, the electrochemical behaviour tends stabilize in the second cycle, so voltage profiles are given from the second cycle; the first cycles of the discharge–charge curves of NGMO and NGO materials are given in Fig. S3.^† It can be seen intuitively that both NGMO and NGO have low voltage platforms, while NGMO has the smaller polarization. In Fig. 4a, we notice a reversible voltage profile in the second cycle with discharge capacity of 200.32 mAh g⁻¹ for NGMO. Only NGMO has a flat potential platform and delivers an ultra-low plateau potential. It can be seen from Fig. 4b that NGO shows a capacity of 24.8 mAh g⁻¹, obvious polarization at the 20^th cycle and increased capacity due to the surface side-effect. Fig. 4c indicates that the capacity retention of the NGMO electrode after 50 cycles is 86.2%, which is superior to that of NGO; the coulombic efficiency of NGMO is also provided in Fig. S4.^† To further understand the redox reactions along with the discharge/charge process in NGMO, Fig. 4d displays the differential capacity versus voltage (dQ/dV) curve. The clear anodic peak at 0.33 V and cathodic peak at 0.81 V correspond well with the redox reactions of NGMO.Open in a separate windowFig. 4Electrochemical performance: (a) and (b) voltage profiles of NGMO and NGO, respectively; (c) cycling performance; (d) dQ/dV profile of NGMO. The current density was controlled at 20 mA g⁻¹ over a voltage range of 0.05–2.0 V.The electrochemical impedance spectra (EIS) of fresh and cycled electrodes of NGMO and NGO, with a frequency range of 0.01 Hz to 100 kHz, are shown in Fig. 5. From Fig. 5a, it is obvious that the charge-transfer resistance of the fresh NGMO electrode is lower than that of NGO. This indicates that the migration of charges in the NGMO material occurs more easily than in NGO, which also facilitates the shifting of ions on the surface and inside of the electrodes of NGMO. In Fig. 5b, NGMO electrode in its 10^th cycle exhibits a smaller charge-transfer resistance than both NGO and the NGMO fresh electrode, indicating that the surface of NGMO more readily forms a stable SEI film.¹⁸ The EIS results were fitted by the model shown in Fig. S5.^† The fitting results are provided in Table S2.^† The resistances of the fresh and cycled electrodes of NGMO and NGO are composed of an internal resistance (R_s), the resistance of the surface film (SEI) (R_f; a small semicircle in the high frequency region), the resistance of the charge transfer (R_ct; another opposite semicircle in the middle frequency region), and the Warburg resistance (W; an oblique line in the low frequency region).²¹ Both the fresh and cycled electrodes of NGMO deliver lower charge transfer resistance than NGO. Meanwhile, the transfer resistance of the cycled NGMO electrode is lower than that of the fresh electrode and its slope at low frequency is higher than that of the fresh one (Table S2^†). All these results show that NGMO has lower resistance and better electronic/ionic conductivity than NGO.Open in a separate windowFig. 5Nyquist plots of (a) fresh NGMO and NGO electrodes, and (b) NGMO and NGO electrodes after ten cycles.The evolution of the chemical valence states of the 150-times discharged electrodes were observed by XPS and SEM as provided in Fig. S6.^† It is generally clear that the electrode surface was covered with a thick SEI layer after discharging. Ar plasma etching was used to obtain the internal information. The Ge 3d core-level of the discharged NGMO electrode with and without etching is shown in Fig. S7.^† Before etching, the peaks of the Ge 3d core-level could be fitted to Ge¹⁺ and Ge²⁺.²² After etching, (Fig. S7c^†), the peaks at 30.8 eV and 30.2 eV were also associated with Ge¹⁺ and Ge²⁺, respectively. This result indicates that the valence of Ge decreases as a whole and that there is no obvious difference between the etched and non-etched samples. The reversible redox reactions of Ge remain stable even after cycling. Meanwhile, the Mn 2p core-level spectra are shown in Fig. S7d–f.^† For the Mn 2p core level, owing to the spin orbit coupling, the valence states of Mn comprise two couples including Mn³⁺ and Mn²⁺ (Fig. S7e and f^†). The binding energies of Mn³⁺ are 642.37 eV and 654.04 eV, and the binding energies of Mn²⁺ are 640.71 eV and 652.18 eV. Similarly, after discharging, the binding energies of Mn³⁺ are 642.40 eV and 654.06 eV, and those for Mn²⁺ are 640.69 eV and 652.20 eV, indicating that there are no changes in Mn binding energies before and after etching. This is in good agreement with results in previous reports.^23,24 All results also show that a thin SEI layer has been formed, favoring ions transfer on the repeatedly cycled electrode. It can be seen from the refined XRD results that NGMO consists of Ge⁴⁺, Mn²⁺ and Mn³⁺, and combined with XPS analysis, the results show that the valence states of Mn does not change for the discharged NGMO electrode. Ge displays electrochemical activity in NGMO, and Mn exhibits good chemical stability in the framework.     

Nucleation density and pore size tunable growth of ZnO nanowalls by a facile solution approach: growth mechanism and NO2 gas sensing properties

Nanowalls are novel nanostructures whose 3D porous network morphology holds great potential for applications as gas sensors. The realization of such a nanowall-based gas sensor depends directly on the comprehensive understanding of the growth mechanism of the nanowalls. We induced nucleation density and pore size evolution by increasing the dipping and growth times. The investigation indicates that the 3D porous ZnO nanowalls consist of a seed layer of ZnO nanoparticles and a growth layer of the vertically grown ZnO nanosheets. The seed layer nucleation density dominance is driven by the dipping time. The pore size and the height of the as-grown ZnO nanowalls are determined by varying the growth time. Possible growth mechanisms governing the physical characteristics of the synthesized ZnO nanostructures in the solution process are proposed and discussed. The gas sensor that was fabricated from the ZnO nanowall structure exhibited strong dependence on the microstructure, which was mainly determined by the preparation conditions.

Nanowalls are novel nanostructures whose 3D porous network morphology holds great potential for applications as gas sensors.     

The effects of deposition time and current density on the electrochemical performance of flexible and high-performance MnO2@PFG composite electrodes

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG). The paper fiber between graphene sheets could be used as a flexible substrate for MnO₂ nanoparticles, and the microscopic morphologies and electrochemical performances of the MnO₂@PFG electrodes were tuned via regulating the deposition current densities and deposition times. 3D graphene on PFG served as a highly conductive backbone with a high surface area for the deposition of the MnO₂ nanoparticles, which provided high accessibility to electrolyte ions for shortening the diffusion paths. The MnO₂-10-600 s@PFG composite electrode achieved a maximum specific capacitance of 878.6 mF cm⁻² with an MnO₂ loading mass of 3.62 mg cm⁻² (specific capacitance of 187.7 F g⁻¹) at a current density of 0.5 mA cm⁻² in a 1 M NaSO₄ aqueous solution. Additionally, the MnO₂-10-600 s@PFG composite material with the most favorable composite ratio exhibited the highest energy density of 61.01 mW h cm⁻², maximum power density of 1249.78 mW cm⁻², excellent capacitance retention with no more than 7% capacitance loss after 10 000 cycles and good mechanical flexibility (about 91.06% of its original capacitance after 500 bending times). By combining the electric double layer capacitance of graphene networks with the pseudocapacitance of the MnO₂ nanostructures, the flexible electrode showed much enhanced electrochemical capacitance behaviors with robust tolerance to mechanical deformation; thus, it is promising for being woven into textiles for wearable electronics.

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG).     

A preparation of β-glucans and anthocyanins (LoGiCarb™) lowers the in vitro digestibility and in vivo glycemic index of white rice

The effect of a proprietary blend of β-glucan, anthocyanins and resistant dextrin (LoGICarb™) on the (1) in vitro digestibility and (2) in vivo glycemic response of humans to white rice, were carried out. The amounts of glucose released, rapidly digestible starch, and predicted glycemic index of white rice were significantly reduced, with addition of LoGICarb™. The mean glycemic index (GI) value of white rice, were also reduced from 72 to 55.0 ± 4.52, in 14 test subjects. These effects were due to the combination of anthocyanins and β-glucans in one sachet of LoGICarb™. The anthocyanins could bind α-amylase, reducing the amount of available enzymes for starch digestion, thus slowing down starch digestion in white rice. In addition, β-glucans helped increase the viscosity of meal bolus. This is the first study that demonstrated addition of plant-based extracts could significantly decrease the digestibility and GI value of cooked white rice.

A blend of β-glucans and anthocyanins lowers the digestibility and glycemic index of white rice.     

Apelin-36通过中枢途径对大鼠摄食、胃肠运动调节作用的研究

目的探讨Apelin-36对大鼠摄食行为、胃肠运动的影响以及可能的途径。 方法健康成年雄性SD大鼠共88只。采用随机数字表法从中随机选取32只大鼠,侧脑室埋管并注射生理盐水或Apelin-36(10 nmol/L) 3 μl、6 μl、9 μl,每组8只,测定48 h摄食量。采用随机数字表法选取16只大鼠侧脑室埋管并注射生理盐水或Apelin-36(10 nmol/L) 9 μl,每组8只,计算胃排空率。采用随机数字表法选取16只大鼠,麻醉后在十二指肠降部放置水囊,连接压力感受器,在体检测侧脑室注射生理盐水或Apelin-36后十二指肠运动变化情况,每组8只。随机数字表法选取16只大鼠,在体检测结肠的运动变化情况,每组8只。另外,随机数字表法选取8只大鼠,剖离胃体、十二指肠、结肠平滑肌条,离体条件下检测生理盐水或Apelin-36对平滑肌运动的影响。 结果48 h累计单位体重摄食结果显示,Apelin-36 3 μl、6 μl、9 μl组摄食量分别为(147.75±33.06)g/Kg、(127.69±23.94)g/Kg、(99.91±18.48)g/Kg,少于生理盐水组[(160.84±28.51)g/kg],并依次递减,差异有统计学意义(F＝7.99,P<0.01),Apelin-36 9 μl组摄食量较生理盐水组、Apelin-36 3 μl组降低,均差异有统计学意义(t＝6.49, 5.10;均P<0.01);Apelin-36 9 μl组黑夜(24 h)累计单位摄食量[(45.08±11.86)g/Kg],明显少于生理盐水组[(70.77±23.23)g/Kg](t＝4.44,P<0.05)。侧脑室注射Apelin-36后大鼠胃排空率为(68.10±6.03)%,较生理盐水组[(79.21±7.94)%]降低,差异有统计学意义(t＝3.15,P<0.01)。侧脑室注射Apelin-36后十二指肠降部平滑肌运动幅度降低至(0.29±0.08)g,明显低于生理盐水组[(0.81±0.16)g](t＝8.36,P<0.01);而远端结肠的运动幅度[(0.20±0.09)g],较生理盐水组[(0.22±0.08)g]差异无统计学意义(t＝0.31,P>0.05)。离体条件下Apelin-36对胃体[(0.19±0.06)g]、十二指肠[(0.09±0.02)g]、结肠平滑肌运动[(0.07±0.01)g]均无显著影响,与生理盐水组[(0.19±0.06)g、(0.08±0.01)g、(0.06±0.02)g]比较,均差异无统计学意义(t＝0.13, 0.22, 0.41;均P>0.05)。 结论侧脑室注射Apelin-36可减少摄食,抑制胃排空、十二指肠运动,但离体条件下Apelin-36对胃肠道平滑肌运动无直接影响。     

可逆性胼胝体压部病变综合征2例报道并文献复习

目的:探讨可逆性胼胝体压部病变综合征(RESLES)影像学表现和临床特征。方法:回顾性研究本院2例核磁共振扫描表现为胼胝体压部可逆性病变的影像学特征和临床表现。结果:2例患者均显示为胼胝体压部局限性、可逆性病灶,T1WI上表现为胼胝体压部圆形或类椭圆形的孤立性稍低信号,T2WI表现为高信号,FLAIR为高信号,DWI表现为高信号,对应部位ADC信号减低,增强扫描病灶未见明显强化,灶周未见明显水肿及占位效应。其中1例有上呼吸道感染病史,另1例伴有低热、后出现癫痫发作;2例患者均有低钠血症。2例患者均经抗病毒、抗炎对症治疗后复查头颅MR,其中1例14天后复查发现胼胝体压部病灶完全消失,临床症状完全缓解;另1例7天后复查头颅MR,病灶较第一次有所增大,随后患者出院并未返院复查。结论:可逆性胼胝体压部病变综合征病因复杂,临床表现多种多样,头颅MR病灶可逆,具有自限性,预后较好。     

Interobserver agreement for contrast-enhanced ultrasound of liver imaging reporting and data system: A systematic review and meta-analysis

BACKGROUNDHepatocellular carcinoma is the most common primary liver malignancy. From the results of previous studies, Liver Imaging Reporting and Data System (LI-RADS) on contrast-enhanced ultrasound (CEUS) has shown satisfactory diagnostic value. However, a unified conclusion on the interobserver stability of this innovative ultrasound imaging has not been determined. The present meta-analysis examined the interobserver agreement of CEUS LI-RADS to provide some reference for subsequent related research.AIMTo evaluate the interobserver agreement of LI-RADS on CEUS and analyze the sources of heterogeneity between studies.METHODSRelevant papers on the subject of interobserver agreement on CEUS LI-RADS published before March 1, 2020 in China and other countries were analyzed. The studies were filtered, and the diagnostic criteria were evaluated. The selected references were analyzed using the “meta” and “metafor” packages of R software version 3.6.2.RESULTSEight studies were ultimately included in the present analysis. Meta-analysis results revealed that the summary Kappa value of included studies was 0.76 [95% confidence interval, 0.67-0.83], which shows substantial agreement. Higgins I² statistics also confirmed the substantial heterogeneity (I² = 91.30%, 95% confidence interval, 85.3%-94.9%, P < 0.01). Meta-regression identified the variables, including the method of patient enrollment, method of consistency testing, and patient race, which explained the substantial study heterogeneity.CONCLUSIONCEUS LI-RADS demonstrated overall substantial interobserver agreement, but heterogeneous results between studies were also obvious. Further clinical investigations should consider a modified recommendation about the experimental design.     

The comprehensive analysis of clinical trials registration for IgA nephropathy therapy on ClinicalTrials.gov

ObjectivesIgA Nephropathy (IgAN) is common chronic kidney disease with a high incidence. This study aims to analyze comprehensively therapeutic clinical trials for IgAN registered on ClinicalTrials.gov.MethodsTherapeutic trials for IgAN registered on ClinicalTrials.gov. up to 15 August 2021 were obtained. The general characteristics, features of experimental design, treatment strategies, and some main inclusion criteria and outcome measures were accessed.ResultsA total of 104 therapeutic clinical trials for IgAN were extracted on ClinicalTrials.gov up to 15 August 2021. Most of these trials explored the treatment for primary IgAN confirmed by renal biopsy in adults. Only 9% of all selected trials had results. Forty-five percent of trials recruited 50 or fewer participants, and 73% were adults or older adults. 99% of trials were interventional studies, and of all the interventional trials, 70% of trials were randomized, and 68% exercised a parallel assignment of intervention model. Immunosuppression was the most studied for the treatment of IgAN. Moreover, many novel agents had been increasingly studied in recent years. Furthermore, the inclusion criteria and primary outcome measures in these trials were diverse, and the level of proteinuria and change of proteinuria levels were the most used as inclusion criteria and primary outcome, respectively.ConclusionsThe majority of therapeutic trials for IgAN were randomized, none masking and parallel-assignment interventional studies, primarily recruiting adult patients as research subjects. These trials had relatively small sample sizes and short observation. Thus, more large-scale, multicenter, and randomized controlled trials are still needed to improve the management for IgAN.