Silicon is one of the most attractive anode materials for lithium ion batteries on account of its low discharge potential and the highest theoretical capacity for lithium storage. However, the large volume effect, poor electronic conductivity and incompatibility with the conventional electrolyte hinder its commercial applications. So far, strategies to overcome these hinders include designing the composition and microstructure of silicon active materials to suppress the volume change and improve the conductivity, developing new binders and electrolyte additives and exploring new current collectors and suitable electrode structures. There are mainly two methods to improve the silicon active materials. One is to decrease the scale of active Si domain to nanoscale, the other is to fabricate the composite structures. This paper summarizes the recent progress in silicon based composite materials, including Si-nonmetal composites and Si-metal composites, as well as some researches of our group, and discusses the technological bottlenecks and development trends.

It has been 20 years since lithium ion battery appeared as a commercial product. Different kinds of new electrode materials are urgently needed to meet the demands of the society. In this review, some knowledge about lithium ion battery is first given. Then we focus on several new positive/negative electrode materials reported up to date. When they were used as lithium ion battery electrode materials, how they are synthesized, the main improvement methods and their electrochemical performance will be presented. Finally, we give a short summary of the advantages/disadvantages of these new electrode materials. Furthermore, an outlook for the potential applications of lithium ion batteries in the future is proposed.

The cathode (positive electrode) is the single (or major) donor of lithium ions in current lithium ion batteries. It is becoming the bottleneck to the increase of energy density and the decrease of cost of lithium ion batteries. This review presents the research progress in our laboratory in surface modification and structural designing of cathode materials after a brief introduction to the structures, the performance features and the main problems of some typical cathode materials.

Radical polymers are aliphatic or nonconjugated polymers bearing organic redox radicals as pendant groups on their structural unit. These radical sites populated in large densities allow the electrochemical redox reaction taking place through the polymer layer by redox gradient-driven electron transport and behave as electroactive centers. Since radical polymer can be designed with a large population of redox radicals and electron exchange between the radical sites are usually very fast, they are considered as a new class of charge storage and transport materials with the possibility to provide high electrical storage capacity and high charge-discharge rate capability. Particularly, these polymers are completely organic with the advantage of being fully substainable, they are ideal for the displacement of inorganic materials in diverse applications such as electrochemical supercapacitors, photovoltaic cells and rechargeable batteries.This paper is intended to review the structural characteristics, electrochemical reaction mechanisms and current development status of the radical polymers as electode-active materials, with focus on the technological challenges and ongoing research strategies of these novel electrode materials as used for construction of high capacity and high rate rechargeable batteries. Also, the problems in the development of radical polymer electrodes are discussed.

Li₄Ti₅O₁₂ spinel has advantages of superior cycling performance, long and stable voltage plateau, enhanced safety, low cost, environmental friendliness, and can be easily prepared. It has been widely studied in lithium ion batteries. In this paper, the recent progress in synthesis study of Li₄Ti₅O₁₂ is systematically reviewed based on the latest literature. Some important synthesis methods such as solid state, sol-gel, molten salt, combustion, spray drying and hydro/solvothermal synthesis are summarized. Improvements to improve the conductivity of Li₄Ti₅O₁₂ by doping and surface modification are also elaborated in this paper. The problems that should be resolved and the further perspectives are pointed out.

Silicon-based materials are promising anode materials for lithium-ion batteries (LIBs) due to their high-energy capacity. However, the commercialization of silicon-based materials as the anode of LIBs has been hindered by the huge volume change, poor cycle life and low initial coulombic efficiency during the charge/discharge process. This article reviews the change of both the crystal structure and the surface/interface of Si-based material during the intercalation/deintercalation of lithium, and the methods improving the electrochemical performance. In addition, the prospects of silicon-based materials as the anode of LIBs are also discussed.

Li-ion battery (LIB) has been considered as a preferred power source for electric vehicles and energy storage devices due to its high energy density and high rate capability. However, the safety concern severely hinders the developments and applications of large capacity or high power LIBs in these fields. To solve this problem,mang efforts have been focused on the development of internal and self-activating safety mechanisms for LIBs in recent years. This paper is intended to review the recent progresses in this field, including polymerizable electrolyte additives, redox shuttle, potential-sensitive separator, and temperature-sensitive electrode. The problems and further orientation in this research area are discussed after a brief introduction to their working mechanisms and research status.

This review summarizes the research in nanosized thin film electrode materials for ion batteries and our progress in this field. Nanosized thin film electrode materials are introduced by dividing into nanoparticle-materials and nanostructure-materials. For nanoparticle materials, besides introducing traditional thin film electrode materials like lithium-metal oxide (LiMO₂, LiMn₂O₄, etc.) and lithium-metal polyanion (LiFePO₄, etc.), we emphasize a series of novel thin film electrodes with new electrochemical reaction mechanisms based on nanometer-size effects, including binary metal compound (MX), composite materials contained lithium (M-LiX) and polynary composite system (MXY, M₁X-Y, M₁X-M₂Y). The investigations of these new kinds of electrode materials will open new opportunity for the development of lithium ion battery. For nanostructured materials, we focuse on three-dimensional (3D) structured electrode and carbon micro-net films electrode. These studies lay the foundations for future 3D microbatteries.

Lithium-ion batteries (LIBs) are one of the important electrochemical power sources for low- or zero-emission hybrid electrical and electrical vehicles, energy-efficient cargo ships and locomotives, and aerospace in the modern society. The difficulties in mastering the electrode/electrolyte interface have slowed down the progress of LIBs. Interfacial processes of lithium ion batteries include mainly insertion/extraction of lithium ion, solvation/desolvation of lithium with solvents, formation and variation of solid electrolyte interphase (SEI) layer, and decomposition of electrolyte. Interfacial processes directly affect the efficiency of electrochemical energy conversion and storage, such as the cycling ability, the lifetime and the reversible capacity, as well as the safety issue of lithium ion batteries. The characterization of the interface processes at a molecular level by FTIR spectroscopy is one of the key subjects, as it is helpful for the improvement the performance of lithium ion batteries and development of non-aqueous theory. Recent progresses about the application of FTIR spectroscopy in lithium ion batteries are reviewed. This review put emphasis on: (a) the characterization of chemical composition and variation of SEI layer on cycled or aged electrode materials by ex situ FTIR spectroscopy, and (b) the investigation of decomposition of electrolyte, formation of SEI layer and the insertion/extraction of lithium ion by both in-situ FTIR reflection spectroscopy and in situ FTIR transmission spectroscopy.

Electrolyte is considered as one of the key materials to decide the performance of Li-ion batteries. Novel boron-based lithium salts have attracted people’s interests because of its varieties and environmental-friendly property. Lithium bis(oxalato)borate (LiBOB), as one of boron-based lithium salts, is believed to be a candidate for commercial LiPF₆ due to its good film-forming property and high thermal stability. In the paper, the new development of boron-based lithium salts is introduced, and LiBOB is also evaluated as lithium salt of electrolyte for Li-ion battery. The main influencing factors of LiBOB-based electrolyte are summarized. Especially, it has focused on the compatibility of LiBOB-based electrolyte with anode and metal oxide cathode. The application of LiBOB-based polymer electrolyte and LiBOB plastic chip electrolyte are introduced.

In recent years, ionic liquids have attracted considerable interest in batteries because of their unusual properties, such as high thermal stability, high ionic conductivity, wide electrochemical window, negligible vapor pressure and nonflammability, etc. In this paper, the recent research advances of key technologies on the application of ionic liquids in batteries are reviewed, especially on the results of our research team focus on ionic liquid-based functional electrolytes for lithium secondary battery, supercapacitor and fuel cell. Furthermore, the current problems as well as the corresponding research directions are discussed, and the possible application prospects are also proposed.

Most low-power electronic and microelectromechanical system (MEMS) devices designed today use conventionally macroscopic external power supplies. This places limits on the functionality of these microdevices in many applications. An alternative solution is to design power sources at a microscale, which can be integrated together with these microdevices on the same chips. We mainly review the work done in our group on developing and studying of solid state microscale lithium ion batteries compatible with microelectronics with respect to the material system employed, the solid state electrolyte-cathode interface, the batteries’ microfabrication process and performance.

With the rapid development of lithium ion batteries with higher energy density, higher power density and high security, the research of new functional electrolytes has attracted considerable attention in novel materials field for lithium ion batteries. In this paper, the recent research advances of key technologies on the application of lithium salts and additive functional electrolytes in lithium ion batteries are reviewed, especially on the results of our research team focusing on new functional electrolytes based on lithium organic borate salt, such as lithium bis(oxalato)borate and lithium oxalyldifluoroborate , and sulfite additives for the purpose of improving security, temperature adaptability and the compatibility between electrolytes and electrodes of lithium ion batteries. These electrolytes exhibit high thermal stability and good electrochemical properties. Moreover, lithium organic borate salt and sulfite have been investigated as new solid electrolyte interphase (SEI) film-forming materials. The formation of a stable passivating film on the graphite surface is believed to be the reason for the improved cell performance, including cycle life, self-discharge, coulombic efficiency and irreversible capacity. Furthermore, current problems as well as the corresponding research directions are discussed, and the possible application prospects are also proposed.

The rechargeable lithium-ion battery has been extensively used in mobile communication and portable instruments due to its many advantages, such as high volumetric and gravimetric energy density and low self-discharge rate. In addition, it is the most promising candidate as the power source for (hybrid) electric vehicles and stationary energy storage. The properties of electrode/electrolyte interfaces play an important role in the electrochemical performance of the electrode material and a battery, such as the capacities, irreversible charge “loss”, rate capability and cyclability. In present paper, the methods to investigate the properties of electrode/electrolyte interfaces, for example, traditional electrochemical methods, microscopy methods, spectroscopic methods, electrochemical quartz crystal microgravimetry (EQCM) are summarized. The principles, advantages and disadvantages of these methods and their applications in investigating the properties of electrode/electrolyte interfaces, especially the progress in the combination of these methods to investigate the properties of electrode/electrolyte interfaces, are introduced in detail, and these methods will be considerable to study the new materials or the traditional materials for lithium-ion batteries in the future.

Application of lithium ion battery (LIB) has been widely extended as its energy density is improved and its cost is reduced. Especially in recent years, significant attention has been paid to application of LIB in electric vehicles and energy storage. However, safety performance of LIB is considered as one of the major barriers which impede the expansion of these application fields. Since safety performance of LIB is fundamentally determined by thermal stability of materials for lithium-ion battery, this paper reviews recent research progress in this field. Among all of the safety tests, overcharge, hot box, nail penetration, crush and internal short are usually considered to be critical ones. This paper discusses major factors influencing these safety tests based on research results obtained in the authors'group. This paper also summarizes state-of-the-art approaches to improve safety performance of LIB in terms of battery materials, cell design and manufacturing.

Recently, Li excess (or Li-rich) layered ordered/disordered materials for Li-ion battery exhibited amazing electrochemical performances and thus received extensive attention. They all can be formulated as Li_1+xM_1－xO₂ (M can be one or multi-metal ions, x≥0). However, the complexity of composition and structure in most of Li_1+xM_1－xO₂ compounds (M usually represents multi-metal ions such as M= Ni_1-x-yCo_xMn_y and materials can present different interlayer/intralayer cations ordering in structure) and variability of valence in some metal ions ( different valences in some metals ions such as Ni and Mn may form depending on conditions) easily make readers confused in understanding nature of those materials. The clear interpretation of those materials' nature in references is still not enough at present and even some materials were misinterpreted in some references. In this review, on the basis of their structure, the nature of Li excess (or Li-rich) layered ordered/disordered materials was firstly described precisely according to LiAO₂-Li₂BO₃ solid solution. In combination with our research results, it was further discussed how to utilize phase diagram to assist readers to understand those complicated Li_1+xM_1－xO₂ materials and further design new compounds. Some recent important progress on these materials was also commented.

Solid oxide fuel cells (SOFCs) are a type of electrochemical energy conversion devices with high efficiencies and low emissions. The practical application of SOFCs technology would have a great environmental benignity and be beneficial for a sustainable development of the world. The decrease of operation temperature can accelerate the commercialization of SOFCs technology, the key is the development of high performance of cathodes operated at low temperature. In this paper, we mainly have a comprehensive introduction on the progress in developing of novel cathodes for reduced temperature SOFCs, including perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ, double perovskite-type LnBaCo₂O_5+δ, other perovskite-type cobalt-based mixed conducting electrodes, non-cobalt-related mixed conducting oxide electrodes, precious metal modified oxide electrodes and nano-structured composite electrodes prepared by infiltration, and specific cathodes for proton-conducting SOFCs. More attentions are paid to the development in our lab within the last five years. The development trend of cathode in SOFCs is proposed.

Solid oxide fuel cells (SOFCs) are an novel energy conversion device, which has been extensively used for its high energy efficiency, high stability, fuel flexibility, and low pollution emission. Lowering down its operating temperature is important for commercialization. More attentions are therefore paid on how to decrease the operating temperature from traditional 800—1 000℃ to 600℃ or below. The paper summarizes the development of the electrolytes, cathodes, and anodes for SOFCs operated below 600℃. Choosing alternative ceria-based oxides with high ionic conductivity at low temperature, decreasing the electrolyte thickness, and constructing bilayered electrolytes with additional electronic blocking layer to enhance the open circuit voltage are all effective approaches for the improving electrolytes. While for the electrodes, novel materials are developed to increase the catalytic activity at low temperature. Moreover, ion-impregnation method is applied to optimize the microstructure of electrodes. Thus the triple phase boundary and active site has been enhanced, resulting in decreased electrode resistance and direct utilization of hydrocarbon without carbon deposition. In addition, new types of low temperature SOFCs such as single chamber SOFCs and micro SOFCs are also presented, which might have significant impact on the development of low temperature SOFCs.

Inorganic proton conductor is a kind of important functional material for many potential electrochemical applications such as fuel cell, hydrogen sensor, electrolytic preparation and separation and purification of hydrogen, hydrogen pump, steam pump, removal of nitrogen oxide, hydrogenation and dehydrogenation of some organic compounds, recover of hydrogen isotopes from nuclear fusion reactor, and ammonia synthesis at atmospheric pressure, etc. In this paper, the recent progress of inorganic proton conductors is reviewed, mainly including typical inorganic proton conductors, their defect chemistry and proton transport mechanism, possible applications, some issues, and expectations for the future.

Single chamber solid oxide fuel cell (SC-SOFC) is different from the conventional solid oxide fuel cell with dual gas chamber structure. Both cathode and anode of SC-SOFC are exposed to the only one gas chamber. Mixed gas containing fuel and oxidant is fed during operation and it can generate electric energy by the selectively catalytic activities of cathode and anode. SC-SOFC has many particular advatages, such as more simple structure, eliminating the need for sealing and easy stacking etc. In this paper, the recent research advances of SC-SOFC are reviewed, including brief introduction of operational principle of SC-SOFC, the selection of key materials for SC-SOFC, the discussion of main influencing factors on SC-SOFC, as well as the design and test of micro-stack (battery) system. The investigation results on SC-SOFC of our research group are highlighted, including composite cathode, oxide anode with Ni modification, and some novel designs for SC-SOFC micro stacks, such as star-type and array-type stacks, and so on. Finally, an outlook about the potential applications of SC-SOFC is given according to the analysis of its merits and drawbacks.

In this review, various kinds of key materials of solid oxide fuel cells (SOFCs) are summarized such as the electrolyte, cathode, and anode materials. Their functions, requirements, and development tendency are discussed. Different key materials are compared in order to find the way of improving their performance. In addition, the development of the SOFC stacks in Shanghai Institute of Ceramic is also introduced. The Researchers have solved the problem of high temperature sealing and succeeded in thermal cycling; as for the interconnector, they have successfully designed the structures for gas flowing and sealing, and solved the key problems of plasma spraying for the alloy protecting layer; they have also developed the test devices for the 1 000W and 5 000W SOFC stacks. The highest power obtained was more than 800W; the longest operation time was over 1 400h with the degradation rate being less than 3%/1 000h.

The manufacturing of solid oxide fuel cell (SOFC) and its main components at low temperature are very important to optimise the performance of material, cell and lower the cost. The cubic full dense yttria stabilized zirconia (YSZ) electrolyte, one of the most popular electrolyte in SOFC, is obtained by three-step sintering process at 1 200—1 300℃ from nano powders, which needs to be dense at 1 400—1 450℃ by traditional sintering process. The scandia stabilized zirconia (ScSZ) and gadolinia doped ceria (GDC) electrolytes are sintered to be full dense respectively at low temperature of 900℃ and 800℃ from 3nm powders of ScSZ and by sintering additives, which, now, are widely used in SOFC process. The low temperature process of SOFC would be benefit to put forward SOFC commercial ization in the market.

Reversible solid oxide cells based on proton conducting electrolytes (H-RSOC) are regarded as efficient energy conversion devices for practical application of renewable energy, such as solar energy and wind energy to smooth out their fluctuation and intermittence. In this paper, the requirements and development of electrode and electrolyte materials for H-RSOC are briefly reviewed, and especially, the reaction mechanisms of air electrode with respect to their demand on air electrode materials are summarized. Working in solid oxide fuel cells (SOFC) mode, the migration of protons to triple phase boundaries (TPBs) and the surface diffusion of oxygen ions to TPBs are supposed to be the rate limiting steps, which favors the composite consisting of oxygen ion-electron mixed conductors and proton conductors as air electrode. While in solid oxide electrolysis cells (SOEC) mode, the transferring of protons decomposed from water to TPBs and the protons at TPBs transferring to the electrolyte are deemed as the rate limiting steps, and novel proton-electron mixed conductor might be the best choice of such air electrode. That’s because that the proton transfer in such proton-electron mixed conducting air electrode would be greatly improved for their high volume ratio (~60%) and for their greatly enlarged electro active sites, which expands from traditional TPBs in composite electrodes to the interface of gas phase/ mixed conducting air electrode.

Proton exchange membrane fuel cell (PEMFC), which is the closest to commercialization in all the five types of fuel cells, is one of the most promising power sources as the future electric vehicle engine and has rapid progress in the past two decades. To date, the biggest obstacles in the way of PEMFC’s commercialization are cost and lifetime, which must be solved by searching and developing novel materials. These areas have already become the keystones and hotspots in PEMFC’s research and development. In this paper, recent years’ developments on the key materials of PEMFC are reviewed. Firstly, the development in proton exchange membrane is introduced including the directions of fluorinated membrane, non-fluorinated membrane, high temperature membrane, inorganic ceramic membrane and so on. Secondly, the recent progress in platinum based and non-platinum electrocatalyst used in PEMFC is introduced; thirdly, the research results of the characteristics and materials of the gas diffusion layer in PEMFC is introduced. In the last, bipolar plates materials and their machining methods of graphite, metal and composite materials for PEMFC are reviewed. The authors also comment the state-of-the-art development of each material, and provide outlook of the future develop directions of the PEMFC materials.

In order to improve catalytic activity and stability, alloying Pt with a non-noble metal has proved to be a successful strategy for the development of new electrocatalysts for low temperature fuel cell. An alloy is a mixture containing two or more metallic elements or metallic and nonmetallic elements usually fused together or dissolving into each other when molten. Solid solution is the alloy when two metals (or nonmetallic) are completely soluble in liquid state and also completely soluble in solid state. Usually, the atomic positions and stoichiometric of the solid solution are uncertain, for example, commercial electrocatalyst PtRu alloy. Intermetallic compound is a compound of two or more metallic elements or metallic and nonmetallic elements. Usually, the atomic positions and stoichiometric of the intermetallic compound are fixed. Pt-based intermetallic compounds have been paid more and more attentions by researchers due to its many excellent properties. In this review paper, we present the recent progress of Pt-based intermetallic compounds used in low temperature fuel cell. The synthesis method and some Pt-based intermetallic compounds are present. The future development of this research field is prospected.

Direct methanol fuel cells (DMFCs) are known as the most promising green power source, have acknowledged special superiorities and already obtained primary effects on commercialization. In this article, based on membrane electrode assembly (MEA), which is the key component of a DMFC, the preparation and optimization progress of catalyst, proton exchange membrane (PEM), the preparation of MEA, as well as the current reseach situation of activation technology for MEA are detailed combined with our experimental work. The process of multi-step activation, the method of MEA regeneration and the test technology of the current fraction of CO₂ are presented and the catalyst nucleation mechanism, PEM mass transfer mechanism and the benefit of methanol penetrating are discussed, as well. Moreover, future work is forecasted. Based on the macromolecule polymer molding theory, a new thought is proposed in this paper that the catalyst slurry is directly sprayed on PEM to form the three-dimensional network structure, which will realize the gradient catalysis functionality and improve the preparation of catalyst layer of MEA. Finally, this article also describes the flow field design, performance testing and system control and other aspects of research status.

The lithium/sulfur redox couple has almost the highest specific-energy density of 2 600Wh/Kg among all the redox couples enabling for chargeable batteries and has a specific capacity of 1 675mAh/g, assuming complete reaction of lithium and sulfur to the product Li₂S. Fruitful results were made with the purpose of enhancing the reversibility of the lithium sulfur battery and the utilization of sulfur in the cathode over the past twenty years. In this paper, the effects of the factors on the capacity fading of the lithium sulfur battery are studied. New method and technical development of lithium sulfur battery reported in recent years are reviewed, mainly including the development of the cathode materials, adhesive agents, electrolyte and anode of the battery. The further tendencies of lithium sulfur battery are also represented.

Lithium-sulfur battery has been receiving more attention due to its high theoretical energy density of 2 600Wh/kg. However, there are still some serious problems for sulfur cathode in organic electrolyte, including the lower utilization and poor cycle performance of sulfur active material, which becomes a big barrier for the research and development of lithium-sulfur battery. This review introduces the recent research process of sulfur-carbon composite cathode based on various porous carbon to support elemental sulfur. The larger surface area and developed porosity of porous carbon are beneficial for the homogeneous dispersion of elemental sulfur, and the strong adsorbability arising from the micropores or mesopores can successfully restrain the solubility and loss of lithium polysulfides, thus leading to the improved electrochemical performance of the composite cathodes. Accordingly, this article mainly illustrates the electrochemical capacity and cycle stability of the composites arising from the various pore size of porous carbon. By comparing, it is suggested that hierarchical porous carbon with highly developed micropores and mesopores is the most promising carrier to loading elemental sulfur, as it can ensure both the excellent electrochemical cycle stability and larger electrochemical capacity of the sulfur cathode.

Lithium sulfur battery is a high capacity energy storage system with very bright future, and it is considered as the next generation portable energy supply device for electronic vehicle (EV) and hybrid vehicle (HEV). Through decades of research and development,people understand this system stepwisely. The electrochemistry of sulfur cathode is very complex and hard to be examined,which is the key point to develop lithium sulfur battery. Although there are many unknown mechanisms in the electrochemical process of charge/discharge of the lithium sulfur battery, some achievements have been made on the development of cathode materials which provide various sources to study. Sulfur is an insulating molecular crystal, carbon is added as the additive reagent to improve the electric conductivity in the cathode, sulfur/carbon composite is common as cathode active material in lithium sulfur battery. Ethers and polymers are employed as the components of the electrolytes to coordinate with sulfur cathode. This paper reviews the achievements on lithium sulfur battery in the past decade from the respects of lithium sulfur battery system, cathode materials, electrolytes, cathode structure and new systems based on lithium sulfur battery. The weaknesses are revealed and the future is prospected.

Lithium sulfur battery is a promising energy storage system due to its high specific energy density, low cost and environmental friendliness. But poor cycle performance has hindered its practical application.In this paper, the developing levels of lithium sulfur battery are introduced concisely. The important progress on the cathode materials, electrolytes, lithium anode and new battery composition of this battery system are reviewed. Furthermore, some investigation results in recent 5 years in this field of Chemical Defense Institute are mainly introduced. Firstly, two kinds of cathode materials, conducting polymer sulfides and mesoporous carbon/sulfur composites were prepared which improved the sulfur utilization and cycle performance. Compared with conducting polymer sulfides, mesoporous carbon/sulfur composites can embody more sulfur, so were preferable to high energy batteries. Secondly, an electrochemically stable binder, gelatin binder also functioned as a highly adhesive agent and an effective disperser was applied in lithium sulfur batteries. A novel porous sulfur cathode with the gelatin binder was prepared by using a freeze-drying mathod. Thirdly, a suitable electrolyte composition were investigated. Fourthly, the interface performance of lithium anode in lithium sulfur battery were studied. Integrating these technologies, the prototype polymer battery was assembled. It presented the energy density of more than 300Wh/kg, and showed about 60% remaining capacity after 100 cycles at 100% DOD. Finally, the prospects of the future research on lithium sulfur batteries are proposed.

Flexible dye-sensitized solar cell has attracted much attention due to its advantages of low cost and easy production.Flexible dye-sensitized solar cell comprised of a nanocrystalline TiO₂ film electrode based on Ti-metal substrate and a counter-electrode based on plastic substrate is investigated. In order to improve the photovoltaic performance, the different methods including electrophoretic deposition under low DC field, electrochemical anodization by DC and pulse voltages and screen printing in cooperation with high-temperature sintering were employed to prepare Ti substrate based nanocrystalline TiO₂ film electrodes and TiO₂ nanotube film electrodes, and low-temperature methods of electrochemical deposition and chemical reduction were used to prepare Pt and carbon counter-electrodes on the plastic substrate. The mechanism and characters of these methods and the techniques of optimization were analyzed and discussed. The performance of the nanocrystalline TiO₂ film electrodes and counter-electrodes prepared by different methods were measured and evaluated by their photovoltaic behavior measurements. Flexible dye-sensitized solar cells with Ti substrate based TiO₂ photoelectrodes and plastic substrate based Pt counter-electrodes prepared by different methods were fabricated. The maximal light to electricity conversion efficiency of 6.74% was achieved.

Dye-sensitized solar cells (DSCs) are promising alternative to conventional Si-based solar cells due to their low cost, easy fabrication and relatively high conversion efficiency. In the DSC, the electrolyte plays an important role in the regeneration of dye molecules and the charge transportation. Although the DSCs based on the liquid electrolyte can present much better photovoltaic performance, the disadvantages of the liquid electrolytes ( i.e. volatility and easy leakage) are supposed to reduce the long-term stability. Therefore, the development of (quasi) solid-state electrolytes is necessary and imperative. In this paper, the recent progress on the solid-state electrolytes and the prospects are given.

Dye-sensitized solar cells (DSSCs) are one of the main development trends of solar cells. Dye sensitizer, which greatly affects the photoelectronic efficiency of solar cells, is all along an important research focus in the field of cell materials. The sensitizers used in DSSC are mainly divided into two types: metal complex dye and organic dye according to research results during recent twenty years. On the basis of different structures, the metal complex sensitizers utilized in DSSC can be classified into polypyridyl complex sensitizers of ruthenium and other metal such as osmium and platinum, metal porphyrin and phthalocyanine sensitizers, and their photoelectric conversion properties are reviewed in detail. Organic dye sensitizers with general structure of “donor (D)-π conjugation bridge-acceptor (A)” are widely used in DSSC because of their high molar extinction coefficient and low cost. The relations of photoelectric conversion properties with structures of organic dye sensitizers including oligoene dye, coumarin dye, carbazole dye, indoline dye, fluorene dye and triphenylamine dye are reviewed in detail.

In this paper a short introduction to the latest development on hybrid supercapacitors based on intercalation compounds is presented, and the up-to-date research results of our laboratory on the influence of aqueous electrolytes, electrode materials (activated carbons, MnO₂, V₂O₅, LiCoO₂, LiMn₂O₄, Na_xMnO₂ and K_xMnO₂) and some supercapacitors are mainly expounded. It should be noted that the hybrid supercapacitors based on intercalation compounds containing alkali metal elements presents great promise for applications due to the following reasons: (1) the electrolytes are different from those of other supercapacitors and they do not need to provide anions and cations for positive and negative electrodes, (2) the electrode materials have high capacitance, high power density and excellent cycling behavior. For example, in the case of amorphous nano MnO₂, after 23 000 full cycles, the capacitance retention is above 94%. As to the hybrid supercapacitor of AC//LiMn₂O₄ nanorod, its energy density based on the active electrode materials can be above 50Wh/kg with excellent power characteristics. Finally, some future directions are pointed out especially some non-carbon based negative electrode materials with capacitive and redox behaviors.

Compared with conventional secondary batteries, electrochemical supercapacitors exhibit the long cycling life and high power density, but with low energy density. In order to improve the energy density of supercapacitor, the most promising approaches are either to use an electrode material with large specific capacitance or increase its working voltage by utilizing a hybrid supercapacitor system which consist an activated carbon electrode and a battery elelctrode material (pseudo-capacitor material). The present paper introduces the development of the hybrid supercapacitor and the recent research on the electrode materials for hybrid supercapacitor. Many studies have been undertaken for the various hybrid supercapacitor systems to obtain higher energy density, coupling redox-active material electrodes with activated carbon electrode, such as activated carbon/NiOOH (FeOOH), activated carbon/graphite, activated carbon/metal oxides and activated carbon/polymer hybrid supercapacitors. Recently, Li-ion intercalated compounds Li₄Ti₅O₁₂ and lithium-ion battery carbon materials are attracting much attention as positive electrode with a negative activated carbon electrode. At the same time, many researches focus on the various hybrid capacitor systems consisting of negative activated carbon electrode and positive aqueous Lithium-ion battery materials electrode, such as LiMn₂O₄, LiCoO₂, LiTi₂(PO₄)₃ and LiCo_1/3Ni_1/3Mn_1/3O₂.These hybrid supercapacitors are improved in energy density and also with the working voltage increased, comparing with the traditional activated carbon/activated carbon electrochemical double-layer capacitor. In the paper, the research situation and development tend of several kinds of hybrid systems and the currently studied relative materials are also introduced.

Carbon materials play crucial roles in supercapacitors and the research in this field is very active in recent years. Various carbon materials such as activated carbons, activated carbon fibers, carbon aerogels, carbon nanotubes, glassy carbons, template carbons, carbide-derived carbons and grphene have been widely investigated as electrode materials for supercapacitors. In this paper, recent works of our group on research of carbon materials for supercapacitors are summarized, including activated carbon prepared by chemical activation, nano CaCO₃ templated mesoporous carbon, carbon nanotube array electrode and carbon with heteroatoms. The further research directions are also discussed.