Rechargeable lithium-ion batteries (LIBs) are recognized as the most important power supply for portable electronic devices, electric vehicle and hybrid electric vehicle. There is a continuing demand for advanced LIBs with longer life spans and higher capacity. Graphite based anode materials are now widely employed in LIBs due to their excellent cycling stability and good conductivity. However, the theoretical capacity of graphite is as low as 372 mA·h·g^-1 that is hard to meet the ever-increasing demand of high energy density LIBs. Recent years, Si based anode materials have attracted enormous attention due to its high reversible capacity (3579 mA·h·g^-1). However, the main challenge facing Si is the huge volume change during lithiation/delithiation process. It is well accepted that nanostructured Si could effectively release the strain stress caused by volume variation, thus maintaining the conductive and structural integrity of the electrode. But, the high surface area of nanostructured anode materials would result in serious side reactions between electrode materials and electrolyte, which would consume a lot of Li⁺, and leading to low coulombic efficiency. Very recently, preparation of nano-Si/graphite composite as anode for LIBs has been demonstrated as a promising high-capacity anode. The Si/graphite anode is able to take full advantages of the properties of these two materials such as the high specific capacity of nano-sized Si, mechanical flexibility and good conductivity of graphite. These beneficial features make Si/graphite hybrid composite as an ideal anode candidate for high-performance LIBs. To date, a lot of fabricating strategies have been reported to prepare Si/graphite composite. The keys and interests are focused on how to make the nanosized Si and graphite particles distributed uniformly, and how to construct a stable framework with three-dimensional conductive network. An overview of the methodologies proposed in the last decade for combining nanosized Si and graphite is summarized, which are composed of a series of technological means. Here, these methodologies are classified in three categories on basis of the composite step, including solid-state approach, liquid-phase mixture method, and chemical vapor deposition process.

The Pt tube-in-tube arrays (TTAs) were designed and synthesized by ZnO template-assisted electrodeposition. As a robust integrated 3D electrocatalyst with high utilization rate and fast transport of electroactive species, the Pt TTAs exhibit a high electrochemically active surface area (ECSA) of 64.9 m²/gPt. Compared with Pt NTAs and commercial Pt/C catalyst, the Pt TTAs exhibit much improved electrocatalytic activity and durability for methanol oxidation. In addition, the Pt TTAs as electrocatalysts exhibit superior CO poisoning tolerance. This work shows the significant progress of Pt-based electrocatalysts with high-performance for direct methanol fuel cells.

Supercapacitors have been regarded as one of the next-generation energy storage devices because of the high power density, excellent cycling performance, long lifespan and easy maintenance. However, its relatively low specific energy hinders its application in the future. Recently, Na-ion based aqueous hybrid supercapacitors have attracted worldwide attention due to its high energy density, environment friendly and low cost. In our work, the Na-ion aqueous hybrid supercapacitor is constructed with NaTi₂(PO₄)₃/C and commercial activated carbon as electrode materials. NaTi₂(PO₄)₃/C nanoparticles with the size of about 40 nm were synthesized by high-temperature solid state reaction method using the NaTi₂(PO₄)₃/C precursor that was prepared through the solution method with Ti(C₄H₉O)₄, NH₄H₂PO₄, Na₂CO₃ as the raw materials, and citric acid as the carbon source. The electrochemical tests were performed using 1 mol·L^-1 Na₂SO₄ solution as the electrolyte. The carbon-coated NaTi₂(PO₄)₃ electrode delivers the discharge capacity of 122 mAh·g^-1 and shows an excellent cycling stability with the retention of 60% of the initial capacity after 1000 cycles at a 10C rate. The supercapacitor was consisted of NaTi₂(PO₄)₃/C anode, AC cathode and 1 mol·L^-1 Na₂SO₄ electrolyte. And the weight ratio of active materials in cathode and anode was 2.2. Cyclic voltammetry, galvanostatic test were employed to study the electrochemical properties of the supercapacitor. The as-fabricated device was then cycled between 0.15~1.4 V with different current density. Our results show the power density of 121.15 W·kg^-1 with specific energy of 18.71 Wh·kg^-1 at the current density of 0.5 A·g^-1. Moreover, the specific energy and power density goes to 14.13 Wh·kg^-1 and 2.42 kW·kg^-1 at a higher current density of 10 A·g^-1. More importantly, the device showed an excellent cycling stability with the retention of 76% after 1000 cycles at a current density of 1 A·g^-1. This research shows the designed hybrid supercapacitor has the potential to be used as auxiliary high-power energy storage device for the practical applications.

Compared with the widely-used lithium-ion battery (LIB), sodium-ion battery (SIB) is a promising energy storage device for large scale energy storage systems due to the low cost and environmental benignity of sodium. However, its practical use is restricted by the lack of suitable anode and cathode materials, especially the applicable anode materials with high performance. SIBs have similar working mechanism to LIBs, and thus, carbon materials are the most promising anode materials for SIBs. But the storage behaviors of Na⁺ and Li⁺ in carbon-based anodes are quite different. Graphite, which is used as the anode of commercial LIBs, hardly accommodates sodium ions. Thus, many researchers investigated sodium ion storage in disordered carbons, especially the hard carbons. Hard carbon is composed of disordered turbostratic nanodomains (TNs) and the pores formed between these domains. The edge/defect sites on the carbon surface, e.g., carbenes, vacancies, and dangling bonds on the edges of TNs, the interlayer space in TNs, and the pores can host the sodium ions. High porosity is normally needed to reach a high capacity and rate capability. But this leads to large irreversible reactions, and thus, a low initial Coulombic efficiency and poor cyclic stability. In this paper, sodium ion storage behaviors in different carbon structures are discussed and the design principles and research advances of carbon-based anode materials are reviewed. Particularly, the commercial carbon molecular sieve (CMS) is highlighted as a promising anode material for the practical use of SIBs. Finally, the future development of carbon anodes for SIB is commented and prospected.

Nowadays, the clean energy is of special concern researches owing to the unavoidable environmental pollutions. To satisfy the demand of sustainable development strategy, it is necessary to develop high-efficient and portable energy storage and conversion devices. Lithium ion batteries (LIBs) are considered as most promising electrochemical energy storage system in this era and are anticipated to power the mentioned applications. Herein, a facile and effective route has been developed for synthesis of CoO/reduced graphite oxide (RGO) composites as LIB anodes. In the synthesis, the GO prepared by the modified Hummers' method was dissolved into deionized water, and then mixed with Co(NO₃)₂ solution. Subsequently, the obtained homogeneous solution was transferred into 100 mL Teflon-lined stainless-steel autoclave. The sealed autoclave was putted into an oven at 160℃ for 6 h. After cooled down to room temperature, the precursor of depositions were filtered, washed with deionized water and dried at 80℃. Finally, the precursor was thermal treated at 500℃ for 2 h in a tube furnace under nitrogen ambient to obtain the final product of CoO/RGO composites. The synthetic composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns proved that the composites were composed of CoO and graphene. SEM images indicated the CoO nanoparticles grown on the graphene nanosheets uniformly. The CoO nanoparticles loaded on the surface of graphene nanosheets could prevent the aggregation of graphene. Meanwhile, the graphene nanosheets could combine with each other to form a large 3D electron conductive network, which can promote the electrical conductivity of the composite. The LIB was assembled in glove-box, in which the composite electrode and metal lithium plate were used as the anode and the cathode, respectively. The electrochemical test results imply that the initial discharge specific capacity could be up to 1312.6 mAh·g^-1 at a current density of 100 mA·g^-1. Notably, the discharge specific capacity is still about 557.4 mAh·g^-1 after 300 cycles at a high current density of 10000 mA·g^-1. It is demonstrated that the composite exhibits high specific capacity, excellent rate capability and well cyclic stability. The 3D network could be used as a stable framework to accommodate the volume change of active material during Li⁺ insertion/extraction, which play important role for the superior electrochemical performance.

Due to the ultrahigh theoretical energy density, lithium-air battery is proposed as the next generation electrochemical
energy storage devices. The improvement of lithium-air battery’s electrochemical performances and its application
largely rely on highly efficient and stable electrodes. In this review, the development and design of air cathode, modification
and protection of lithium anode and assembly of new type lithium-air batteries were summarized.

A honeycomb-like metallic catalyst (Pt-Ni-P/Ti) supported on a Ti sheet was prepared by electrodeposition-displacement method. The Ni-P amorphous alloy was first electrodeposited on the Ti substrate, and then replaced by displacement of Ni in amorphous Ni-P with H₂PtCl₆. The morphology and methanol oxidation performance of the prepared catalyst were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), anodic linear sweep voltammetry (LSV), cyclic voltammetry (CV), and the anodic stripping of a pre-adsorbed CO monolayer. The SEM results show that the Pt-Ni-P nanoparticles obtained by displacement of Ni in amorphous Ni-P with H₂PtCl₆ had a honeycomb-like porous structure, while the Pt-Ni nanoparticles had a wheat-like structure. The formation of the honeycomb-like porous structure can be explained by the so-called "out-situ dissolution-deposition mechanism", in which the metallic Ni in Ni-P/Ti electrode preferentially dissolve to form pore structure and release electron. The released electrons can be captured by the PtCl₆^2- ion adsorbed on the surface of Ni-P and reduced on the surface of Ni-P to form Pt shell, thereby forming a honeycomb-like pore structure. For the Pt-Ni/Ti electrode, the formation of wheat-like structure Pt-Ni nanoparticles can be explained by a so-called "in-situ dissolution-deposition mechanism", in which the Pt replacement reaction can only occur at the surface of Ni, and the replacement Pt monolayer can prevent the further chemical substitution of Pt on Ni, thereby forming a wheat-like structure. The electrochemical test results show that the methanol oxidation and CO oxidation onset potential on Pt-Ni-P/Ti electrode in alkaline solution is more negative than that on Pt-Ni/Ti electrode, indicating that P incorporation can significantly enhance the methanol oxidation activity and CO-tolerance. Moreover, the unique honeycomb-like porous structure is beneficial to the fast mass transportation during the catalytic reaction. The combination of compositionally and geometrically favorable factors provides a new avenue to design new electrocatalysts with excellent methanol oxidation activity and CO-tolerance.

Rechargeable magnesium (Mg) batteries have attracted research attention as one promising alternative for energy storage because of abundant raw materials. However, the strong electrostatic interaction between bivalent Mg-ions and host lattices often cause sluggish solid state diffusion of Mg-ion within the local crystal structure and consequently prevent reversible insertion/extraction of Mg-ion. Thus much more effort has been paid to develop suitable electrode materials with Mg-ion storage capability. This paper reports the synthesis of Sn nanoparticles/reduced-graphene-oxide nanosheet hybrid nanocomposite (Sn/rGO), by simple hydrothermal method and subsequent thermal treatment. Transmission electron microscopy (TEM) clearly shows that in the as-synthesized Sn/rGO powder Sn nanoparticles are well crystallized, and X-ray diffraction (XRD) pattern was consistent well with tetragonal Sn. Thermogravimetric analysis (TG) suggested that the mass percentage of Sn is ca. 82.3 wt% in the Sn/rGO nanocomposite, very close to the design ratio of ca. 83.4 wt%. As Mg-ion battery anode, the Sn/rGO electrode material exhibit a high initial discharge specific capacity (545.4 mAh·g^-1 at 15 mA·g^-1), good reversible ability and rate performance. The impressive electrochemical property could be attributed to the unique structure of Sn/rGO, in which the three-dimensional (3D) conducting network of rGO can effectively prevent the aggregation of Sn nanoparticles and alleviate the serious volume variation of Sn during repeated discharging/charging process, as well as facilitate the fast access of electrons and Mg-ion to improve kinetics for Mg-ion insertion/extraction. Ex situ XRD and SEM characterization were performed to investigate the electrochemical evolution of Sn/rGO electrode at different discharging/charging states. It is found that upon magnesiation crystalline Mg₂Sn appears and subsequently disappears during de-magnesiation process, which indicates the good electrochemical activity of Sn nanoparticles in Sn/rGO hybrid nanocomposite for magnesium storage. Our result will open new avenue to develop high-efficient magnesium storage material for rechargeable Mg batteries.

Lithium/sulfur (Li-S) batteries have recently attracted intensive research interests due to their high theoretical specific energy of 2600 W·h·kg^-1. However, the poor electronic conductivity of sulfur and the high solubility of polysulfides in organic electrolytes lead to poor cycling stability and rate capability. Herein, we report a three-dimensional (3D) nanocomposite network made from nitrogen-doped carbon nanoribbon (NCNB) and nitrogen-doped graphene (NG), which has a high electronic conductivity and can serve as a conductive matrix and a sulfur immobilizer for the sulfur cathode. The NCNB is prepared by thermal nitridation of a unique 3D phenolic resin (PHF) isolated from the polycondensation reaction of 1,4-hydroquinone and formaldehyde. The N content of NCNB-NG can reach as high as 9.7 wt%. Although three types of N bonding geometries, including pyridinic N, pyrrolic N, and graphitic N, are identified in the NCNB-NG composites, we found the pyridinic N is dominant, which facilitates the trapping of intermediate lithium polysulfides. The sulfur was loaded on NCNB-NG by using a Na₂S₂O₃ solution as sulfur source. The scanning electron microscope (SEM) images show that almost no large S particle can be observed in the as-prepared S@NCNB-NG nanocomposites, suggesting a uniform coating of S on the NCNB-NG networks. The transmission electron microscopic (TEM) images and the elemental mapping by Energy-Dispersive X-ray (EDX) analysis also show that nano-sized S particles are uniformly distributed on the NCNB-NG matrix. The as-obtained S@NCNB-NG cathode can deliver a high specific capacity of 1338 mA·h·g^-1 at 0.05 C with about 80% S utilization. It also exhibits excellent rate capability and good cycle stability with a retained specific capacity of 556 mA·h·g^-1 after 300th cycles. These performances are much higher than the control samples using the S@NCNB and the S@PHF nanocomposites as cathodes. The improved performance can be attributed to the unique microstructure and the improved electronic conductivity of the NCNB-NG matrix.

Lithium-ion batteries have dominated the electronic and portable device market, since its commercialization in 1990s. However, the cost gets boosted because of the shortage and uneven distribution of lithium. Due to the advantage of cost compared with lithium-ion batteries, sodium-ion batteries are considered as the potential candidates for large scale energy storage systems. Cu based tunnel type materials were first synthesized through simple solid state reaction, with Na₂CO₃, CuO, Fe₂O₃, MnO₂ and TiO₂ as starting materials. These raw materials were weighed and grounded in an agate mortar, followed by heat treatment at 950℃ for 24 h in air. The obtained samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance test. The XRD results demonstrate the tunnel structure was formed with space group pbam (the same with Na_0.44MnO₂) for each compound. SEM observation manifests that the distribution of particle size is from several hundred of nanometers to several micrometers. The specifically designed compound with Mn substitution (Na_0.66Cu_0.17Mn_0.33Ti_0.50O₂) can deliver 90 mAh/g cycled between 1.5~4.1 V. Good cycling stability was verified for this compound, of which 90% of its capacity maintained after 50 cycles at 0.1C rate. Moreover, the rate capability is also good and 74% of its capacity remained when cycled at 1C rate. Charge transfer mechanism was studied by X-ray photoelectron spectroscopy (XPS), and the electroactivity of Cu³⁺/Cu²⁺ in this tunnel structure was proved. In addition, we also performed in-situ XRD in order to examine the structure change during sodium extraction and intercalation. Only solid solution reaction took place during the test with shift of peaks or change of the peaks' intensity, however without the appearance of new peaks or disappearance of existed peaks. Here we report, for the first time, the electroactivity of Cu³⁺/Cu²⁺ in tunnel type structure. Our results provide new insights in designing tunnel type compound as cathode material for sodium-ion batteries.

As the demand to energy storage devices for portable electronics and electric vehicles increase, lithium-sulfur (Li-S) batteries have attracted much attention for its extremely high energy density. However, the low coulombic efficiency, rapid fading capacity, and poor cycle performance of lithium anode hinder the demonstration of practical Li-S cells. The advanced functional separator/interlayer system have been proposed and verified to retard the shuttle of polysulfides and extend the cycling life of a Li-S cell. In this review, the progress on multifunctional separators/interlayers for lithium sulfur batteries are summarized, including permselective separator inhibiting polysulfide shuttles, separator with low interfacial resistance, and composite electrolyte stabilizing anode and retarding the formation of Li dendrites. New insights into challenge and opportunities of multifunctional separator/interlayer system are also prospected.

Lithium rich material xLi₃NbO₄·(1-x) LiMnO₂ (0 < x < 1) was successfully synthesized by solid state method. Stoichiometric amounts of Li₂CO₃, Mn₂O₃ and Nb₂O₅ were mixed by ball milling, and the mixture was calcinated at 900℃ for 5 h under Ar atmosphere. X-ray diffraction (XRD) results indicate that the samples with 0.25 < x < 0.67 can be indexed as a cubic structure with Fm-3m space group. Electrochemical results show that the samples of x=0.25 and 0.43 have better electrochemical performance, both delivering 216 mAh·g^-1 in the initial cycle between 2 V and 4.8 V. Although voltage decay is an intrinsic drawback of lithium excess materials, the sample of x=0.43 decays slower. We speculate that Li₃NbO₄ helps stabilizing the crystal structure. Ex-situ XPS and XAS studies show that the charging process can be divided into two stages. In the first stage, below 4.3 V, Mn³⁺ is oxidized to Mn⁴⁺, in the second stage, O^2- is oxidized. The reversible oxidation of O^2- is the origin of the achievement of large reversible capacity. Co³⁺ doped material 0.43Li₃NbO₄·0.57LiMn_1-yCo_yO₂ (y=0.25; 0.5) was also synthesized by the same procedure. The structure of the doped material maintains the cubic structure with smaller lattice constant and the variation of lattice constant is in proportion to the amount of Co³⁺. Galvanostatic charge and discharge tests show that 0.43Li₃NbO₄·0.57LiMn_0.75Co_0.25O₂ also delivers a large capacity of 215 mAh·g^-1 in the first cycle between 2 V and 4.8 V, but the voltage plateau in the charging process decreased from 4.3 V to 4.1 V, it can be attributed to the weak dissociation energy of Mn-O bond and the overlap of Co^3+/4+ 3d and O^2- 2p energy band. The electrochemical impedance spectroscopy results show that a moderate amount of Co³⁺ doped into the material decreases the charge transfer resistance. After doped with Co³⁺, the rate capability is improved.

Recycling use is one of the energy and resource saving strategies to dispose depleted batteries, especially primary lithium batteries that employ electrode materials based on expensive and low-abundance elements. In this study, we report in detail the recycling use of discharged Li-AgVO₃ primary battery for rechargeable Li-O₂ battery. We demonstrate that the discharged Li-AgVO₃ cell, in which metallic silver nanoparticles in-situ generated in the vanadium oxide nanowires cathode efficiently catalyze the oxygen reduction/evolution reactions (ORR/OER), can be resumed as rechargeable Li-O₂ cells when they are exposed at O₂ atmosphere. By controlling the discharge depths, we obtained different cathodes that were composed of vanadium oxide nanowires and silver nanoparticles. As the electrode was discharged to a lower voltage, more silver nanoparticles with larger particle size were distributed on the surface of vanadium oxides, as a result of the sequential reduction of Ag⁺ to Ag⁰ and V⁵⁺ to V⁴⁺. Specifically, the average size of formed Ag nanoparticles was 15 nm and 70 nm at ceased discharge voltage of 2.9 V and 2.0 V, respectively, while the formation of V⁴⁺ was observed at discharge voltage lower than 2.3 V. Electrochemical tests indicated that the Li-O₂ cells assembled with the AgVO₃ cathode discharged to 2.3 V (AgVO₃-2.3) exhibited the highest specific capacity (9000 mAh·g_carbon^-1), the lowest overpotential and robust cycling performance (up to 95 cycles at the current density of 300 mA·g_carbon^-1). The remarkable electrochemical performance of the Li-O₂ battery with the AgVO₃-2.3 cathode is attributed to the optimization of amount, size and distribution of generated silver nanoparticles that contribute to high electronic conductivity and abundant active sites for the ORR/OER. A combined analysis of electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed that the AgVO₃-2.3 cathode enables the reversible formation and decomposition of Li₂O₂ with lower charge transfer resistance on discharge and charge. The results presented here would provide new insight into the promising recycling application of depleted primary Li-AgVO₃ batteries in rechargeable high-capacity Li-O₂ batteries.

One of the major technical barriers to the commercialization of proton exchange membrane fuel cells is the high cost of Pt-based oxygen reduction reaction (ORR) electrocatalysts. In this paper, the ORR catalytic performance and the possible mechanism on (5,5) germanium nanotube (GeNT) were studied by density functional theory methods using DZP basis set. The results indicate that the ORR on the GeNT may undergo three mechanisms including O₂ dissociation, OOH dissociation and H₂O₂ dissociation. For any of the above mechanism, the whole process could easily take place on the GeNT with a complete 4e^- ORR pathway. The adsorption properties of the ORR intermediates, especially for O and OH, are also very important for evaluating the catalytic performance. The calculated adsorption energies of the above species are -4.33 and -2.21 eV respectively, much close to those on the Pt. Furthermore, the adsorption energy of H₂O on the GeNT is only -0.05 eV, much weaker than the O₂ binding, indicating the catalytic cycle of ORR could repeat most easily on the GeNT. Therefore, both the reaction energies of the ORR steps and the adsorption energies of ORR intermediates show that the current GeNT model has the catalytic performance similar to that of precious Pt catalyst. Furthermore, the solvent effect was also studied by using three-water-molecule clusters as the real solvent. The obtained results indicate that the solvent effect could affect the geometrical structure of some adsorbed ORR intermediates, such as atomic O. This would lead to the decrease of the heat loss during the O₂ dissociation mechanism. The decreased heat loss would accelerate the following electron transfer steps, due to the fact that an effective electrocatalyst must make the energy loss as small as possible for non-electron-transfer step, in which case the cathode electrocatalyst would deliver all the Gibbs energy of the ORR as electrical work. With solvation, the heat loss is slightly increased from ^*O₂ to ^*OOH, and decreased from ^*OOH to ^*OH in the H₂O₂ dissociation mechanism, which are also more favorable for ORR.

Sodium ion batteries (SIBs) as a new chemical power source have recently attracted a great attention for large-scale energy storage owing to the abundance and low cost of sodium resources. In order to achieve advanced SIBs with high specific energy, long cycling lifetime and fast charge/discharge ability, efforts have been devoted to developing advanced electrode materials with large specific capacity, robust cycling stability and good rate capability, as well as functional electrolytes with high ion-conductivity and wide electrochemical window. Promising cathode materials include high-capacity layered oxides, high-potential fluorophosphates and long-lifetime phosphates. Available anode materials consist of highly stable Ti-based layered oxides and carbon materials, high-capacity elemental metals/non-metals and low-cost metal-based compounds. Effective electrolytes involve ester-based electrolytes and ether-based electrolytes. This review summarizes the recent advance of electrode materials and electrolytes for SIBs, mainly focusing on their electrochemical properties, existing challenges and resolution strategies.