Marcasite (m-FeS2) exhibits higher electronic conductivity than that of pyrite (p-FeS2) because of its lower semiconducting gap (0.4 vs 0.7 eV). Meanwhile, as demonstrates stronger Fe–S bonds and less S–S interactions, the m-FeS2 seems to be a better choice for electrode materials compared to p-FeS2. However, the m-FeS2 has been seldom studied due to its sophisticated synthetic methods until now. Herein, a hierarchical m-FeS2 and carbon nanofibers composite (m-FeS2/CNFs) with grape-cluster structure was designed and successfully prepared by a straightforward hydrothermal method. When evaluated as an electrode material for lithium ion batteries, the m-FeS2/CNFs exhibited superior lithium storage properties with a high reversible capacity of 1399.5 mAh g–1 after 100 cycles at 100 mA g–1 and good rate capability of 782.2 mAh g–1 up to 10 A g–1. The Li-storage mechanism for the lithiation/delithiation processes of m-FeS2/CNFs was systematically investigated by ex situ powder X-ray diffraction patterns and scanning electron microscopy. Interestingly, the hierarchical m-FeS2 microspheres assembled by small FeS2 nanoparticles in the m-FeS2/CNFs composite converted into a mimosa with leaves open shape during Li+ insertion process and vice versa. Accordingly, a “CNFs accelerated decrystallization–recrystallization” mechanism was proposed to explain such morphology variations and the decent electrochemical performance of m-FeS2/CNFs.Keywords: anode materials; carbon nanofibers; FeS2; lithium ion batteries; marcasite;

In this work, a flexible and self-supporting P-doped carbon cloth (FPCC), which is composed of interwoven mesh of hollow microtubules with porous carbon walls, is prepared via a vacuum-sealed doping technology by employing the commercially available cotton cloth as sustainable and scalable raw material. When directly used as binder-free anode for sodium-ion batteries, the as-prepared FPCC delivers superior Na-storage properties in terms of specific capacity up to 242.4 mA h g–1, high initial Coulombic efficiency of ∼72%, excellent rate capabilities (e.g., 123.1 mA h g–1 at a high current of 1 A g–1), and long-term cycle life (e.g., ∼88% capacity retention after even 600 cycles). All these electrochemical data are better than the undoped carbon cloth control, demonstrating the significance of P-doping to enhance the Na-storage properties of cotton-derived carbon anode. Furthermore, the technologies of electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are implemented to disclose the decrease of charge transfer resistance and improvement of Na-migration kinetics, respectively.Keywords: anode; binder free; carbon cloth; flexible; phosphorus doping; sodium ion batteries;

•Ultrafine nano-Si was prepared via a NaCl-assisted magnesiothermic reduction.•Heat scavenger NaCl promotes the formation of silicon nanograins of 5–10 nm.•Raw material is highly cheap and scalable silicate, promising its practicability.•Graphene nanosheets improve the Li-storage properties of nano-Si as anode for LIBs.•Final nano-Si/rGO exhibits high reversible capacity and superior rate capability.Herein, ultrafine nano-Si has been prepared via a NaCl-assisted magnesiothermic reduction with scalable silicate as Si source. In the high-temperature procedures of magnesiothermic reduction, as an effective heat scavenger, adjuvant NaCl promote the formation of interconnected Si nanoparticles with ultra-small size of 5–10 nm. When used as anode materials for lithium-ion batteries, reduced graphene oxide (rGO) plays a significant role in enhancing the electrochemical performance due to its high conductivity and flexibility by forming the nano-Si/rGO composite. The nano-Si/rGO composite exhibits much improved Li-storage properties in terms of superior high-rate capabilities and excellent cycle stability compared to the pure nano-Si as well as the micro-Si prepared from no addition of NaCl. It can deliver a high specific capacity of 1955 mA h g−1 at 100 mA g−1 with high initial columbic efficiency of >80%. In addition, nano-Si/rGO exhibits superior rate capability (891 mA h g−1 at 5 A g−1). The significantly enhanced Li-storage properties could be attributed to the synergistic effects of highly conductive rGO and nanosized Si particles in the nano-Si/rGO. While the former can improve the electrical conductivity, the latter will decrease the Li+ diffusion length, improve the capacity and optimize the cycling stability.

Sodium-ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short-term cycle life, and poor low-temperature performance, which severely hinder their practical applications. Here, a high-voltage cathode composed of Na3V2(PO4)2O2F nano-tetraprisms (NVPF-NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF-NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na+/Na with a specific capacity of 127.8 mA h g−1. The energy density of NVPF-NTP reaches up to 486 W h kg−1, which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X-ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF-NTP shows long-term cycle life, superior low-temperature performance, and outstanding high-rate capabilities. The comparison of Ragone plots further discloses that NVPF-NTP presents the best power performance among the state-of-the-art cathode materials for SIBs. More importantly, when coupled with an Sb-based anode, the fabricated sodium-ion full-cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.

•A series of Al-doped Na2/3Mn1-xAlxO2 cathode materials are prepared for SIBs.•Al doping promotes the formation of layered P2-type crystal structure.•Al doping suppresses the Jahn-Teller effect via decreasing the content of Mn3+.•Accordingly, Na2/3Mn8/9Al1/9O2 at x = 1/9 presents the best electrochemical properties.•GITT and CV at varied scan rates are used to investigate the electrode kinetics.Recently, sodium-ion batteries (SIBs) have been considered as the promising alternative for lithium-ion batteries. Although layered P2-type transition metal oxides are an important class of cathode materials for SIBs, there are still some hurdles for the practical applications, including low specific capacity as well as poor cycling and rate properties. In this study, the electrochemical properties of layered Mn-based oxides have been effectively improved via Al doping, which cannot only promote the formation of layered P2-type structure in the preparation processes but also stabilize the lattice during the successive Na-intercalation/deintercalation due to suppression of the Jahn-Teller distortion of Mn3+. Among the as-prepared series of Na2/3Mn1-xAlxO2 (x = 0, 1/18, 1/9, and 2/9), Na2/3Mn8/9Al1/9O2 with x = 1/9 exhibits the optimal doping effect with the best electrochemical properties, in terms of the highest specific capacity of 162.3 mA h g−1 at 0.1 C, the highest rate capability, and the best cycling stability in comparison to the undoped Na2/3MnO2 and the other two materials with different Al-doped contents. Both cyclic voltammetry at varied scan rates and galvanostatic intermittent titration technique disclose the optimal electrode kinetics (the highest Na-diffusion coefficient) of the best Na2/3Mn8/9Al1/9O2.Download high-res image (308KB)Download full-size image

Although the composite of metal oxide and porous carbon has been confirmed as an effective material to chemically adsorb polysulfides, the low conductivity of the metal oxide results in the need for extra pathways for the diffusion of polysulfides from adsorption sites to redox-active sites. This process results in sluggish reaction kinetics and escaped polysulfides. In this work, a Gerber tree-like interlayer with multiple components was designed to fully mediate the electrochemical conversion of Li–S batteries and shorten the diffusion distance of polysulfides in the composite. The branches of the interlayer contained TiO2 and Co3O4 nanocrystals embedded into N-doped porous carbon, while the fruit was catalytic metal cobalt. The two co-existing chemical adsorbents ensure the restriction of polysulfides through S–Ti–O bonding and Lewis acid–base interaction. Moreover, the metal Co catalyzes the transformation of adsorbed polysulfides into low-order ones, which largely shortens the diffusion pathway, improving the reaction kinetics and preventing the migration of polysulfides. The cell with the interlayer exhibited outstanding electrochemical performance. After 100 cycles, a reversible capacity of 968 mA h g−1 was maintained at 0.1C with a stable capacity retention of 85%. Even at the current rate of 1C, the cell delivered a capacity of 684.5 mA h g−1 after 300 cycles.

Recently, room temperature sodium ion batteries (SIBs) have attracted considerable attention as one of the promising candidates to replace lithium ion batteries. Nevertheless, achieving high capacity and cycling stability remains a great challenge for the electrode materials of SIBs. Compared to the traditional inorganic electrode materials, organic ones should be more attractive because of their easier sodium (Na)-transport accessibility as well as their diversities of organic skeleton and functional groups. In this work, a new carboxyl-based organic, sodium trimesic (Na3TM), is proposed for the first time as an anode material for SIBs, and its Na-storage properties are significantly enhanced by constructing three-dimensional conductive networks of carbon nanotubes (CNT-NWs) in the Na3TM microparticles. In comparison to the pure Na3TM exhibiting almost inactive Na storage, the prepared CNT-NWs@Na3TM composite delivers a reversible capacity of 214.6 mA h g−1 at 0.1 A g−1, and exhibits excellent rate performance with the specific capacities of 149 and 87.5 mA h g−1 at 1 and 10 A g−1, respectively. The CNT-NWs@Na3TM also exhibit good cycling performance. More importantly, the Na-storage mechanism of CNT-NWs@Na3TM was ascertained using several ex situ technologies of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and 23Na solid-state nuclear magnetic resonance spectroscopy. It is discovered that the two Na uptake/release processes were reversible during cycling and contributed to the Na-storage capacity except for the 1st sodiation process with a three Na uptake.

The synergistic design of cathode region was conducted to minimize the shuttle effect of polysulfides and decrease the loading of inactive components in order to acquire high-energy-density lithium–sulfur (Li–S) batteries. The well-designed cathode region presented two special characteristics: one was the intertwined nanofibers interlayer based on ultrafine TiO2 nanocrystal uniformly embedded within N-doping porous carbon; the other was the lightweight and three-dimensional current collector of fibrous cellulose paper coated by reduced graphene oxide. In consequence, the decent reversible capacity of 874.8 mA h g–1 was acquired at 0.1 C with a capacity retention of 91.83% after 100 cycles. Besides, the satisfactory capacity of 670 mA h g–1 was delivered after 300 cycles at 1 C with the small decay rate of only 0.08%. Because of higher capacity and lower loading of inactive component in cathode region, the energy density of cell increased more than five times compared with unmodified cell. Moreover, to further enhance the energy density, the high-sulfur-loading electrode was fabricated. A good areal capacity of 4.27 mA h cm–2 was retained for the cell with the active material of 4 mg cm–2 and the cycle stability was also well-maintained. In addition, due to the flexibility of interlayer and current collector, Li–S full cell (in pouch cell format) was easily curved. Therefore, the synergistic design for cathode region, which combines the flexible and mass-produced interlayer and current collector together, provides an effective access to Li–S batteries with high energy density and flexibility for practical application.Keywords: cathode region; high energy density; lightweight current collector; Li−S batteries; TiO2 interlayer

In this work, the lightweight and scalable organic macromolecule graphitic carbon nitride (g-C3N4) with enriched polysulfide adsorption sites of pyridinic-N was introduced to achieve the effective functionalization of separator at the molecular level. This simple method overcomes the difficulty of low doping content as well as the existence of an uncontrolled form of nitrogen heteroatom in the final product. Besides the conventional pyridinic–N-Li bond formed in the vacancies of g-C3N4, the C–S bond was interestingly observed between g-C3N4 and Li2S, which endowed g-C3N4 with an inherent adsorption capacity for polysulfides. In addition, the microsized g-C3N4 provided the coating layer with good mechanical strength to guarantee its restriction function for polysulfides during long cycling. As a result, an excellent reversible capacity of 840 mA h g–1 was retained at 0.5 C after 400 cycles for a pure sulfur electrode, much better than that of the cell with an innocent carbon-coated separator. Even at a current density of 1 C, the cell still delivered a stable capacity of 732.7 mA h g–1 after 500 cycles. Moreover, when further increasing the sulfur loading to 5 mg cm–2, an excellent specific capacity of 1134.7 mA h g–1 was acquired with the stable cycle stability, ensuring a high areal capacity of 5.11 mA h cm–2. Besides the intrinsic adsorption ability for polysulfides, g-C3N4 is nontoxic and mass produced. Therefore, a scalable separator decorated with g-C3N4 and a commercial sulfur cathode promises high energy density for the practical application of Li–S batteries.

As a promising alternative for lithium ion batteries, room-temperature sodium ion batteries (SIBs) have become one significant research frontier of energy storage devices although there are still many difficulties to be overcome. For the moment, the studies still concentrate on the preparation of new electrode materials for SIBs to meet the applicability. Herein, one new P2–Na2/3Ni1/3Mn5/9Al1/9O2 (NMA) cathode material is successfully prepared via a simple and facile liquid-state method. The prepared NMA is layered transition metal oxide, which can keep stable crystal structure during sodiation/desodiation as demonstrated by the ex situ X-ray diffraction, and its electrochemical properties can be further enhanced by connecting the cake-like NMA microparticles with reduced graphene oxide (RGO) using a ball milling method. Electrochemical tests show that the formed RGO-connected NMA (NMA/RGO) can deliver a higher reversible capacity of up to 138 mAh g–1 at 0.1 C and also exhibit a superior high-rate capabilities and cycling stability in comparison to pure NMA. The much improved properties should be attributed to the reduced particle size and improvement of electrical conductivity and apparent Na+ diffusion due to RGO incorporation, which is comprehensively verified by the electrochemical technologies of galvanostatic intermittent titration technique, electrochemical impedance spectroscopy and cyclic voltammetry at various scan rate as well as ex-situ X-ray diffraction studies.Keywords: cathode; diffusion coefficient; layered transition metal oxide; reduced graphene oxide; sodium ion batteries

Graphene incorporation should be one effective strategy to develop advanced electrode materials for a sodium-ion battery (SIB). Herein, the micro/nanostructural Sb/graphene composite (Sb-O-G) is successfully prepared with the uniform Sb nanospheres (∼100 nm) bound on the graphene via oxygen bonds. It is revealed that the in-situ-constructed oxygen bonds play a significant role on enhancing Na-storage properties, especially the ultrafast charge/discharge capability. The oxygen-bond-enhanced Sb-O-G composite can deliver a high capacity of 220 mAh/g at an ultrahigh current density of 12 A/g, which is obviously superior to the similar Sb/G composite (130 mAh/g at 10 A/g) just without Sb–O–C bonds. It also exhibits the highest Na-storage capacity compared to Sb/G and pure Sb nanoparticles as well as the best cycling performance. More importantly, this Sb-O-G anode achieves ultrafast (120 C) energy storage in SIB full cells, which have already been shown to power a 26-bulb array and calculator. All of these superior performances originate from the structural stability of Sb–O–C bonds during Na uptake/release, which has been verified by ex situ X-ray photoelectron spectroscopies and infrared spectroscopies.Keywords: antimony nanospheres; full cells; graphene; oxygen bonds; sodium-ion batteries

•Dual-carbon enhanced Si-based composite (Si/C/G) was prepared.•It exhibits the best Li-storage properties compared to two single-carbon ones.•Low-cost and abundant Diatomite mineral was employed as Si raw material.•The preparation processes are simple, non-toxic and easy to scale up.Dual-carbon enhanced Si-based composite (Si/C/G) has been prepared via employing the widely distributed, low-cost and environmentally friendly Diatomite mineral as silicon raw material. The preparation processes are very simple, non-toxic and easy to scale up. Electrochemical tests as anode material for lithium ion batteries (LIBs) demonstrate that this Si/C/G composite exhibits much improved Li-storage properties in terms of superior high-rate capabilities and excellent cycle stability compared to the pristine Si material as well as both single-carbon modified composites. Specifically for the Si/C/G composite, it can still deliver a high specific capacity of about 470 mAh g−1 at an ultrahigh current density of 5 A g−1, and exhibit a high capacity of 938 mAh g−1 at 0.1 A g−1 with excellent capacity retention in the following 300 cycles. The significantly enhanced Li-storage properties should be attributed to the co-existence of both highly conductive graphite and amorphous carbon in the Si/C/G composite. While the former can enhance the electrical conductivity of the obtained composite, the latter acts as the adhesives to connect the porous Si particulates and conductive graphite flakes to form robust and stable conductive network.

•Sb/graphene micro/nanocomposite was prepared via a scalable in-situ procedure.•Sb nanoparticles were uniformly embedded into graphene network.•The secondary particulates were in micrometer size benefiting for practical application.•It exhibits much enhanced Na-storage properties compared to ex-situ prepared sample.•It can still deliver a high capacity (112 mAh/g) even at an ultrahigh current density (6 A/g).Metallic antimony (Sb) is one promising candidate as anode material for sodium-ion batteries (SIBs) due to its high theoretical capacity of 660 mAh/g. However, the electrochemical formation of Na3Sb alloy makes it will suffer from tremendous volume variation during Na-uptake/release cycling and hence poor practical Na-storage properties. The incorporation of reduced graphene oxide (rGO) should be one effective strategy to overcome this issue. Herein, it is excitingly discovered that in-situ preparation micro/nanocomposite composed of Sb and rGO has played an effective role on improving Na-storage performance, especially fast energy storage and cycle life. The in-situ-prepared micro/nanocomposite (I-Sb/rGO) can deliver a superior capacity of 112 mAh/g even at an ultrahigh current density of 6 A/g compared to the ex-situ-prepared one (E-Sb/rGO). And it also exhibits outstanding cycle life with a residual capacity of 173 mAh/g after 150 cycles at current density of 0.5 A/g, much higher than that (36 mAh/g) of the ex-situ one. Those enhanced performance can be attributed to the advanced in-situ-prepared process.

Among the transition metal oxides as anode materials for lithium ion batteries (LIBs), the MnO material should be the most promising one due to its many merits mainly relatively low voltage hysteresis. However, it still suffers from inferior rate capabilities and poor cycle life arising from kinetic limitations, drastic volume changes and severe agglomeration of active MnO particulates during cycling. In this paper, by integrating the typical strategies of improving the electrochemical properties of transition metal oxides, we had rationally designed and successfully prepared one superior MnO-based nanohybrid (MnO@C/RGO), in which carbon-coated MnO nanoparticles (MnO@C NPs) were electrically connected by three-dimensional conductive networks composed of flexible graphene nanosheets. Electrochemical tests demonstrated that, the MnO@C/RGO nanohybrid not only showed the best Li storage performance in comparison with the commercial MnO material, MnO@C NPs and carbon nanotube enhanced MnO@C NPs, but also exhibited much improved electrochemical properties compared with most of the previously reported MnO-based materials. The superior electrochemical properties of the MnO@C/RGO nanohybrid included a high specific capacity (up to 847 mA h g−1 at 80 mA g−1), excellent high-rate capabilities (for example, delivering 451 mA h g−1 at a very high current density of 7.6 A g−1) and long cycle life (800 cycles without capacity decay). More importantly, for the first time, we had achieved the discharging/charging of MnO-based materials without capacity increase even after 500 cycles by adjusting the voltage range, making the MnO@C/RGO nanohybrid more possible to be a really practical anode material for LIBs.

In this work, the chemical interaction of cathode and lithium polysulfides (LiPSs), which is a more targeted approach for completely preventing the shuttle of LiPSs in lithium–sulfur (Li–S) batteries, has been established on the electrode level. Through simply posttreating the ordinary sulfur cathode in atmospheric environment just for several minutes, the Au nanoparticles (Au NPs) were well-decorated on/in the surface and pores of the electrode composed of commercial acetylene black (CB) and sulfur powder. The Au NPs can covalently stabilize the sulfur/LiPSs, which is advantageous for restricting the shuttle effect. Moreover, the LiPSs reservoirs of Au NPs with high conductivity can significantly control the deposition of the trapped LiPSs, contributing to the uniform distribution of sulfur species upon charging/discharging. The slight modification of the cathode with <3 wt % Au NPs has favorably prospered the cycle capacity and stability of Li–S batteries. Moreover, this cathode exhibited an excellent anti-self-discharge ability. The slight decoration for the ordinary electrode, which can be easily accessed in the industrial process, provides a facile strategy for improving the performance of commercial carbon-based Li–S batteries toward practical application.Keywords: anti-self-discharge; Au nanoparticles; chemical Au−S interaction; Li−S batteries; postdecorated cathodes

A new cathode material composed of romanechite-structured Na0.31MnO1.9 nanofibers is developed for sodium-ion batteries for the first time. It can deliver a Na-uptake capacity of >100 mA h g−1 with a superior high-rate capability and good cycling performance in the voltage range of 2–4.5 V vs. Na+/Na, and exhibit the unique ability of fast charging with the normal discharge rate.

•A facile and mass-producible strategy was developed to modify the surface of Cu foils with carbon.•The modified carbon is robust and strong.•Overall performances of lithium ion batteries were improved by the surface carbon modification on Cu current collector.•Full-cell systems were used to evaluate the effects of Cu surface modification.We have developed a facile and mass-producible strategy named electric discharge method to successfully improve the surface properties of Cu foils with rough carbon layer. Electrochemical tests in half-cells demonstrate that the coated carbon layer can significantly reduce the polarization resistance and enhance the reversible capacity of graphite anode when utilizing the Cu foils as current collector for lithium ion batteries. More importantly, the developed carbon coated Cu anode current collector can also improve the overall performances of LiFePO4 full cells in terms of enhanced rate capability (from 887.9 to 946.3 mAh at 4C rate), reduced polarization voltage (11.7 mV lower at 4C rate), longer cycle life (about 650 increased cycles if taking 80 % capacity retention as the end of cycle life when used at 1 C rate) as well as improved low-temperature performance (capacity retention: 42.87% vs. 38.85% at -20 °C).

Graphene material prepared by reducing graphene oxide (GO, prepared by the modified Hummers method) has been considered as one of the most promising candidates for electrode materials for supercapacitors due to its mass producibility, high electrical conductivity, large specific surface area, and superior mechanical strength. However, it usually exhibits an unfavorable cycling performance, mainly large capacitance fading in the initial thousands of cycles, as shown but not discussed in some previous reports. In this paper, we not only find a similar phenomenon to a commercial graphene material, but also develop a very simple method to successfully enhance its electrochemical properties in terms of cycle life as well as high-rate performance, leakage current and alternating current impedance. For example, the relatively low capacitance retention of about 89.9% at the initial 1000th cycle was increased up to 99.7% after improvement, the capacitance retention was raised to 73% from 43% at a scan rate of 100 mV s−1 in cyclic voltammetry, and leakage current density was significantly more than halved (from 2.42 mA g−1 to 1.01 mA g−1). Additionally, the reasons for the improvement are also disclosed by analyzing the characterization results of X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. It is found that the optimization of the functional groups of doped nitrogen and oxygen atoms may contribute to the improvement of cycle life and decrease of leakage current density, and the enhanced rate performance can be attributed to the increase of electrical conductivity.

Although a wide variety of biomass, such as human hair, chicken eggshells and ox horns, have been used to prepare carbon electrode materials for energy storage, most of them have very limited production, which restricts their large-scale application. Herein, the very prolific biomass of chitosan is employed as an abundant raw material to successfully prepare one porous N-doped carbon material (PNCM). Structural characterizations demonstrate that this PNCM is hierarchically porous with abundant macro/micropores and 4.19% N-doping. The electrochemical properties of the PNCM as electrode materials for both supercapacitors and lithium ion batteries are also studied. When used in a supercapacitor, the optimized PNCM synthesized at 700 °C can store electrical energy with a specific capacitance of up to 220 F g−1 in 1 mol L−1 H2SO4 electrolyte, exhibit excellent cycle stability with only 1.3% capacitance decay over 11000 cycles, and deliver high power and energy densities in both aqueous and organic electrolytes. In addition to supercapacitors, the PNCM also exhibits excellent Li-storage properties in terms of high specific capacity (above 460 mA h g−1 at 50 mA g−1) and superior cycle stability (without any capacity decay even after 1100 cycles) when used as an anode material for lithium ion batteries.

•One nanosheet organic anode material (Na2C8H4O4) for SIBs is successfully prepared.•The nanosheet Na2C8H4O4 exhibits much improved electrochemical properties in comparison to the bulk one.•The reasons of improvement are disclosed by ex-situ FTIR, SEM and EIS.•One new one-step desodiation mechanism is found in the Na2C8H4O4 nanosheet system.Recently, room temperature sodium ion batteries (SIBs) have been considered as one of the optimal alternatives for lithium ion batteries although there are still many challenges to be solved. At the present stage, the research priorities for SIBs still focus on the development of various electrode materials to meet the applicability. In this communication, we have controllably prepared a superior anode material (disodium terephthalate, Na2C8H4O4) with nanosheet-like morphology, which exhibits much improved electrochemical properties in terms of larger reversible capacity (248 mA h/g vs. 199 mA h/g), higher rate capabilities (for instance, 1.55 times the bulk material at 1250 mA/g) and better cycling performance (105 mA h/g vs. 60 mA h/g after 100 cycles at 250 mA/g) in comparison with the bulk one prepared at the similar system without the addition of polar solvent dimethylformamide. More importantly, it is further disclosed that, these enhanced performances could be mainly due to the new one-step desodiation mechanism and optimized ionic/electronic transfer pathways in the nanosheet system through the analyses of ex-situ infrared spectra, cyclic voltammogram, galvanostatic curves, scanning electron microscope images and electrochemical impedance spectroscopy.

Nowadays one of the principal challenges for the development of lithium-ion batteries (LIBs) is fulfilling the burgeoning demands for high energy and power density with long cycle life. Herein, we demonstrate a two-step route for synthesizing LiV3O8 nanorods with a confined preferential orientation by using VO2(B) nanosheets made in the laboratory as the precursor. The special structures of nanorods endow the LiV3O8 materials with markedly enhanced reversible capacities, high-rate capability and long-term cycling stability as cathodes for lithium storage. The results show that very desirable initial capacities of 161 and 158 mA h g−1 can be achieved for the LiV3O8 nanorods at extremely high rates of 2000 and 3000 mA g−1, with minimal capacity loss of 0.037% and 0.031% per cycle throughout 300 and 500 cycles, respectively. The energetically optimized electron conduction and lithium diffusion kinetics in the electrode process may shed light on the superior electrochemical properties of the LiV3O8 nanorods, primarily benefitting from the small particle size, large surface area and restricted preferential ordering along the (100) plane.

To make alloying anodes be practicability for lithium-ion batteries, graphene-incorporation has been demonstrated as one of the most effective strategies. However, successive lithiation/delithiation would usually lead to the detachment and self-aggregation of active alloying nanoparticles and graphene. Herein, an oxygen-bonds-bridging (Sn–O–C) Sn/graphene (Sn–O–G) micro/nanocomposite, in which Sn particles are in the ultrasmall scale of <3 nm and embedded in graphene-based microspheres, was prepared via an in-situ co-reduction procedure. Electrochemical tests demonstrated that the Sn–O–G exhibited much improved Li-storage properties in terms of high reversible capacity (1246 mA h/g at 50 mA/g), superior high-rate capabilities (220 mA h/g at 16 A/g) and long-term cycle life (410 mA h/g after 2000 cycles at 4 A/g) in comparison to the Sn/graphene (Sn/G) prepared from the similar procedures just without the presence of Sn–O–C bonds. Because of the same morphology, size and microstructures of both Sn-based anodes, it is speculated that such enhanced properties of Sn–O–G should be benefited from the Sn–O–C bonds. In order to answer “Do the bridging oxygen bonds between active Sn nanodots and graphene improve the Li-storage properties?”, several ex-situ technologies were employed to track the physicochemical and electrochemical variation of Sn–O–G electrodes, revealing the reversibility of breaking/re-formation and durability of Sn–O–C bonds during the successive Li-insertion/extraction. Therefore, the answer is “YES”.Download full-size image

A new cathode material composed of romanechite-structured Na0.31MnO1.9 nanofibers is developed for sodium-ion batteries for the first time. It can deliver a Na-uptake capacity of >100 mA h g−1 with a superior high-rate capability and good cycling performance in the voltage range of 2–4.5 V vs. Na+/Na, and exhibit the unique ability of fast charging with the normal discharge rate.

Although the composite of metal oxide and porous carbon has been confirmed as an effective material to chemically adsorb polysulfides, the low conductivity of the metal oxide results in the need for extra pathways for the diffusion of polysulfides from adsorption sites to redox-active sites. This process results in sluggish reaction kinetics and escaped polysulfides. In this work, a Gerber tree-like interlayer with multiple components was designed to fully mediate the electrochemical conversion of Li–S batteries and shorten the diffusion distance of polysulfides in the composite. The branches of the interlayer contained TiO2 and Co3O4 nanocrystals embedded into N-doped porous carbon, while the fruit was catalytic metal cobalt. The two co-existing chemical adsorbents ensure the restriction of polysulfides through S–Ti–O bonding and Lewis acid–base interaction. Moreover, the metal Co catalyzes the transformation of adsorbed polysulfides into low-order ones, which largely shortens the diffusion pathway, improving the reaction kinetics and preventing the migration of polysulfides. The cell with the interlayer exhibited outstanding electrochemical performance. After 100 cycles, a reversible capacity of 968 mA h g−1 was maintained at 0.1C with a stable capacity retention of 85%. Even at the current rate of 1C, the cell delivered a capacity of 684.5 mA h g−1 after 300 cycles.

Among the transition metal oxides as anode materials for lithium ion batteries (LIBs), the MnO material should be the most promising one due to its many merits mainly relatively low voltage hysteresis. However, it still suffers from inferior rate capabilities and poor cycle life arising from kinetic limitations, drastic volume changes and severe agglomeration of active MnO particulates during cycling. In this paper, by integrating the typical strategies of improving the electrochemical properties of transition metal oxides, we had rationally designed and successfully prepared one superior MnO-based nanohybrid (MnO@C/RGO), in which carbon-coated MnO nanoparticles (MnO@C NPs) were electrically connected by three-dimensional conductive networks composed of flexible graphene nanosheets. Electrochemical tests demonstrated that, the MnO@C/RGO nanohybrid not only showed the best Li storage performance in comparison with the commercial MnO material, MnO@C NPs and carbon nanotube enhanced MnO@C NPs, but also exhibited much improved electrochemical properties compared with most of the previously reported MnO-based materials. The superior electrochemical properties of the MnO@C/RGO nanohybrid included a high specific capacity (up to 847 mA h g−1 at 80 mA g−1), excellent high-rate capabilities (for example, delivering 451 mA h g−1 at a very high current density of 7.6 A g−1) and long cycle life (800 cycles without capacity decay). More importantly, for the first time, we had achieved the discharging/charging of MnO-based materials without capacity increase even after 500 cycles by adjusting the voltage range, making the MnO@C/RGO nanohybrid more possible to be a really practical anode material for LIBs.