During the past four decades, Solid State Ionics (SSI) field has attracted numerous researchers and engineers to cultivate new technologies which plays important roles in the development of sustainable energy utilization and clean transportation tools. The commercialization of lithium ion battery, sodium sulfur battery, sodium chloride battery, solid oxygen sensors have illustrated the success of SSI’s theories and technologies. The discovery and successful applications of ionic or mixed conductive materials, such as LiCoO2 and LiFePO4 as active materials of lithium ion battery cathode, Na-β/β″-Al2O3 ceramics as solid electrolytes and separators for sodium based batteries, ZrO2 as electrolytes for SOFC and oxygen sensors, and the newly developed Li10GeP2S12[1] and Li7La3Zr2O12[2] as lithium ion conductor, laid a solid foundation for the development of SSI technologies.
　　Recently, rechargeable lithium metal anode based batteries have become hot research topics in the field of SSI due to their extremely high specific capacity suitable for future generation of power sources in portable electronic devices, electric vehicles and energy storage systems. Among all the Li anode based batteries, Li-S and Li-air battery systems are the two most attractive candidates because of the low cost and abundance of sulfur and air as cathode active materials, especially the characteristics of easy access of active O2 from the surrounding air for Li-air batteries.
　　Breakthroughs have been made recently with these batteries. SION Power’s Li-S cells reached the highest practical specific energy as high as 350 Wh/kg, with a pack of 576 cells engineering the QinetiQ Zephyr Unmanned Aerial Vehicle (UAV) more than 336 h (14 d) of continuous flight, significantly surpassing the previous official record[3]. Their energy densities are higher than 500 Wh/kg for more than 500 cycles[3] and commercialization in the near future[4] are expected. Many Chinese institutions successfully prepared soft package lithium sulfur batteries[5]. The highest specific capacity of sulfur electrode over 900 mAh/g at 2C rate was realized by the Shanghai Institute of Ceramics, Chinese Academy of Sciences. Important advances in Li-air batteries were also made by designing carbon free air electrode [6,7] and by the aid of LATP solid lithium electrolyte lately[8]. However, the development of the rechargeable high energy lithium metal batteries are still hindered by the high reactivity of lithium metal with liquid electrolytes and the occurrence of dendrite growth during charge and discharge cycles. Moreover, the cycling stability of the batteries are still far away from the standard of practical applications of electric vehicle and electronic devices. Owing to the intrinsic highly resistive feature of the cathode materials, sulfur and lithium containing resultants with oxygen, structural and compositional designs of the cathode, the protection of lithium metal anode, and the control of the electrode/electrolyte interface are urgent matter to develop practical rechargeable lithium batteries.
　　SSI has been tackling the vital technical problems of high performance devices with solid ionic and mixed conductors as their key materials, which has great potential contribution to future energy and environmental needs of our society.

Sodium ion batteries are now actively developed as a new generation of electric energy storage technology because of their advantages of resource abundance and low cost. Particularly for large scale stationary electric storage, aqueous Na-ion batteries display better safety, lower cost and better environmental compatibility, providing a great prospect for widespread applications. However, there exist a number of difficulties in the development of Na-storage materials and aqueous Na-ion technology. To solve these problems, this review analyzes the different chemistry of the Na-storage materials and their electrochemical reactions in aqueous electrolytes, and discusses the recent development of Na+ host materials and aqueous Na-ion batteries. In addition, based on our experience and understanding, possible strategies are proposed for further development of low cost and pollution-free materials for aqueous Na-ion batteries.

Glassy electrolytes have broad prospects for the application in all solid-state lithium ion batteries since they have isotropic conductivity and higher lithium ionic conductivity compared with ceramic electrolytes. In recent years, numerous groups have attempted to improve the lithium ionic conductivity, chemical and electrochemical stability of glassy electrolytes through nitrogen-incorporation by radio-frequency magnetron sputtering, preparing mixed former glasses and glass-ceramics by special technologies. In present review, conductive characteristics and mechanism in various glassy electrolytes are introduced. The micro-mechanisms of mixed former effect in several typical glassy electrolytes are discussed emphatically. The mixed former effect produces the non-bridge oxygen providing lithium-ion with the vacant place to move into or out, as well as expanding the lithium-ion conduction pathway to enhance ionic mobility in the network. The effect is brought about by the phase separation in micro structure of glassy electrolytes, which can be described as the isolation of continuous Li-rich phase with high ionic conductivity and isolated Li-poor phase with low ionic conductivity in micro structure. Finally, the premise conditions of mixed former effect occurring to a ternary glassy are summarized. Further study on conductive mechanisms of glassy electrolytes has important guiding significance for theory in developing glassy electrolytes with good chemical and electrochemical performances.

Lithium-sulfur battery, fabricated with metal lithium as anode and sulfur as cathode, has received more attention as the most promising high energy power sources due to its high theoretical energy density (2600 Wh/kg). However, there are some serious and unavoidable problems for lithium-sulfur battery based on the dissolution-deposition processes in organic electrolyte, including serious structure change of metallic lithium anode, the lower utilization and poor cycle performance of active materials, which become a big barrier for the research and development of lithium-sulfur battery. The current status, problems and challenges of lithium-sulfur battery are summarized, including the sulfur-based cathode composites, electrolyte and lithium anode.

Nano-structure could effectively enhance the electro-chemical properties of solid oxide fuel cell cathodes and the output power of single cells, which has a good application prospect. This article mainly focuses on the literatures reported about the long term stability of nano-structure cathode and electrode stability theoretical models. Nano-structure cathode has excellent stability at relatively low temperatures. Isothermal grain growth of nano-particles is self-limited because of the size effect. And nano-structure could significantly reduce the micro-strain induced by the misfit between electrolyte and electrocatalyst, which can keep the two phase in good contact. In addition, nano-structure can also weaken the interface break between two-phase particles in thermal cycle process. The performance of La_0.8Sr_0.2MnO_3-δ and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ nano-structure cathodes increases by 2.3-78 times compared with traditional composites, and maintains a stable power output in 1000 h.

Silicon and graphite with polyvinylidene fluoride as the matrix was pyrolyzed to obtain the Si/C/graphite composite anode with the stable and excellent electrochemical performance. The morphology of the composite was characterized by transmission electron microscope (TEM). The result showed that the composite had core-shell structure in which silicon particles were wrapped by the amorphous carbon. The effects of the silicon particle size and the graphite content on the electrode electrochemical performance were investigated systematically. It reveals that the fine size of silicon particles is beneficial to obtain a stable electrochemical performance. The appropriate content ratio of graphite and silicon is necessary to increase the reversible capacity of the composite. When the mass ratio of silicon to graphite is 1:1 and the silicon particle size is 50 nm, the Si/C/graphite composite presents the first discharge specific capacity of about 1741.6 mAh/g and the first coulombic efficiency of 72.4%. The reversible specific capacity still remains 820 mAh/g after 60 cycles. It demonstrates that the carbon-coating structure can be obtained by pyrolyzing the organic matter which will improve the electrochemical performance of the silicon-based anodes effectively.

Mn_xV₂O₅ (x=0~0.06) was prepared by hydrothermal method with H₂O₂ and V₂O₅ as precursors and Mn²⁺ added directly in the sol preparation process. Structures and morphologies of the materials were characterized by X-ray diffraction (XRD), X-ray Photoelectron Spectroscope (XPS) and scanning electron microscope (SEM). The results indicate that the V₂O₅ is well crystallized as an orthorhombic structure without any detectable impurity phase with the doping of Mn²⁺. The doping Mn²⁺ is situated between anionic sheets of VO₆ chain in the V₂O₅ and the morphology of V₂O₅ changes from nanorods to nanobelts cluster. The electrochemical behavior of the Mn_xV₂O₅ acted as cathode materials is studied by charge-discharge test and electrochemical impedance spectra (EIS) test through a three electrode system. The results indicate that the efficiency of the first charge-discharge of the material enhances to 90% with the Mn²⁺ doping. The discharge capacity of the Mn_0.01V₂O₅ is up to 192.2 mAh/g after 90 charge-discharge cycles at 0.2C rate. The doping Mn²⁺ performs efficiently in ionic conductivity of V₂O₅ electrode material, and the ionic conductivity of Mn_0.02V₂O₅ is enhanced from 6.27×10^-4 S/cm to 1.58×10^-3 S/cm.

Silicon nanowire arrays were fabricated by metal-assisted chemical etching of single crystal silicon wafer. Then the silicon nanowire powder was obtained via ultrasonicating from silicon wafer and utilized as the anode electrode material of lithium ion battery. The effects of Ag catalyst deposition process and the subsequent anisotropic chemical etching on the formation of silicon nanowires were systematically investigated. The redistribution of Ag particles was found during the chemical etching. The large-area silicon nanowire arrays with proper length-diameter ratio were obtained by optimizing the concentration of AgNO₃, HF and H₂O₂ solution. The silicon nanowires exhibited the classical alloy-reaction plateaus of silicon and the specific capacity above 1800 mAh/g prior to the sixth cycle.

An effective method of using cellulosic substances (filter paper) as template was employed to prepare SnO₂ nanotubular materials examined as anode for Li-ion battery. According to XRD, SEM, TEM and HR-TEM analysis, the synthesized nanotubular materials retained morphological hierarchy of the filter paper, and each nanotube was composed of nano-sized SnO₂ ranged from 5 nm to 15 nm. At the same time, the N₂ adsorption/desorption tests show that the materials are mesoporous structure. It exhibits a stable reversible capacity of 580 mAh/g at constant current density of 100 mA/g, and the reversible capacity remains at 550 mAh/g after 60 cycles, showing a high reversible capacity and stable cycle performance as anode for Li-ion battery.

Pt-Fe alloy for proton exchange membrane fuel cell (PEMFC) cathode catalyst was prepared on the porous carbon cloth by electrodeposition under the constant voltage. The reduction potential was determined by cyclic voltammetry (CV). The physical and electrochemical performances of catalysts were characterized by X-ray difffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), energy dispersive spectrograph (EDS), cyclic voltammetry (CV), single cell polarization test and in-situ electrochemical impedance spectroscopy (EIS) technique. The results show that the highly-dispersed Pt-Fe alloy catalyst is obtained by electrodeposition at 0.075 V. The electrodeposition time has remarkable effect on the compositions of Pt-Fe alloy. The ratio of Pt to Fe increases with the co-deposition time. Fe can sufficiently improve the catalytic activity of Pt for oxygen reduction reaction (ORR). Pt-Fe alloy catalyst electrodeposited for 30 min shows better catalytic activity for ORR than pure Pt catalyst.

The Ba_1-xSr_xCo_0.7Fe_0.2Nb_0.1O_3-δ(x=0, 0.1, 0.2, 0.3, 0.4) oxides were synthesized by the conventional solid state reaction process and investigated as a cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). All prepared Ba_1-xSr_xCo_0.7Fe_0.2Nb_0.1O_3-δ(x=0-0.4) powders were sintered at 1000 ℃. X-ray diffraction patterns indicate that all samples have a single phase of cubic perovskite structure. The morphologies of the symmetric cell were characterized by a scanning electron microscope (SEM). The cathode exhibits fine uniform microstructure with appropriate porosity, and shows good bonding and continuous contact with the dense Ce_0.85Sm_0.15O_1.925(SDC) electrolyte pellet. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures show that a cathode Ba_0.8Sr_0.2Co_0.7Fe_0.2Nb_0.1O_3-δ exhibits the best electrochemical performance. The maximum power density of single cell with Ba_0.8Sr_0.2Co_0.7Fe_0.2Nb_0.1O_3-δ cathode, Ni_0.9Cu_0.1-SDC anode and SDC electrolyte is 155 mW/cm² at 600℃. The encouraging results suggest that Ba_0.8Sr_0.2Co_0.7Fe_0.2Nb_0.1O_3-δ is a very promising cathode material for IT-SOFCs.

A Ti/TiO₂-MnO composite electrode was prepared by anodizing, chemical dipping and annealing. The crystalline structure and the microscopic morphology of the sample were characterized by XRD and SEM. The results show that the pore diameters of the Ti/TiO₂ nanotube arrays (NTAs) range from 60 nm to 95 nm, and their lengths range from 350 nm to 820 nm. Ti/TiO₂ nanotube array obtained through anodizing at ambient temperature is amorphous. However, it transforms from amorphous to anatase after annealing at 500℃. Only MnO is found after the sample is immersed in MnSO₄ solution. A button supercapacitor device is assembled and its cyclic voltammetry curves are determined. It shows that its cyclic voltammetry curves have a pair of redox peaks, which corresponds to the calation/intercalation process of H⁺ in NTAs. The intercalation/calation process of H⁺ is controlled by diffusion. The CV response current of Ti/TiO₂-MnO electrode decreases as TiO₂ transforms from amorphous structure to anatase and MnO deposites in NTAs.

The effect of SnO₂ nanocrystalline coatings on the performance of dye-sensitized solar cells (DSSC) based on TiO₂-nanoparticle photoanode was studied. The TiO₂-nanoparticle photoanode was prepared by screen-printing technique, and the SnO₂ nanocrystalline films were coated on TiO₂ nanoparticles by soaking TiO₂ photoanodes in SnO₂ solution with different concentrations or different time. SEM images indicate SnO₂ nanocrystalline films have smaller surface grains than the TiO₂ nanocrystalline films. The electrical properties of the films indicate that SnO₂ thin films growing on the TiO₂ films by soaking TiO₂ films in 0.4 mol /L SnO₂ solution for 50 min play a positive role on the structure and performance of the TiO₂ films, and the conversion efficiency of the solar cell with TiO₂/SnO₂ photoanode is about 7% higher than that of TiO₂ films.

Theoretical studies on the structures, stabilities and electronic properties of Si_nLi (n=1-10) clusters were carried out by the density functional theory (DFT). The results show that lithium atom prefers to stay at the surface of cluster and likes to be adsorbed on the bridge site. The binding energies indicate that the stabilities of Si_nLi clusters can be enhanced by adsorption of lithium atom. Additionally, lithium atom binding energies show that the interaction between lithium atom and silicon cluster increases as decreasing the cluster size, which is an important factor for the amorphization process upon lithiation of the silicon based anode materials for Li-ion batteries. The ionization potential, electron affinity potential, chemical potential and energy gap of the Si_nLi clusters all indicate that Si₄Li and Si₇Li are easier to lose α electron to form cationic clusters.

Reconstruction and characterization of the porous composite electrode via experimental and numerical approaches are the basis and prerequisite of pore-scale modeling. The Monte Carlo approach was employed to reconstruct the LiCoO₂ cathode of a Li-ion battery. The reconstructed electrode resolves sub-micrometer microstructure, thus evidently distinguishing the three individual phases: LiCoO₂ as active material, pores (electrolyte), and additives. An extensive characterization was subsequently performed to calculate some important structural parameters and transport properties, including the geometrical connectivity and the specific surface area, etc. Particularly, a self-developed D3Q15 LB (Lattice Boltzmann) model was used to calculate the effective thermal (or electric) conductivity and the effective species diffusivity in electrolyte (or solid) phase, and the tortuosity of an individual phase. The reconstructed 3D microstructure is consistent with the real cathode microstructure concerning several important statistical features including porosity, volume fraction of each phase, and two-point correlation functions etc. LB model predictions indicate that the effective transport coefficients are closely related to the micro-morphology in electrodes.

Olivine-structured LiMn_0.8Fe_0.2PO₄/C solid solution was successfully prepared by a Sol-Gel approach combined with a high-temperature solid-state reaction, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results revealed that LiMn_0.8Fe_0.2PO₄ nanoparticles were evenly dispersed in the in-situ formed carbon conductive network. When the nanocomposite served as a cathode material for lithium-ion batteries (LIBs), except a short plateau (~3.5 V vs Li⁺/Li) ascribed to Fe³⁺/Fe²⁺ couples in the charging/discharging profile, the long plateau at higher voltage (~4.1 V vs Li⁺/Li) is corresponding to the redox reaction of Mn during the Li+ extraction/insertion in the LiMn_0.8Fe_0.2PO₄ lattice, and this high voltage plateau can significantly enhance the energy density of relevant LIBs. In addition, the chemical diffusion behavior of lithium in the LiMn_0.8Fe_0.2PO₄/C electrode was investigated in detail using galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscope (EIS), and the chemical diffusion coefficients of lithium, D_Li, obtained by GITT and EIS were 5×10^-15 -1×10^-14 cm²/s and 1.27×10^-13- 2.11×10^-13 cm²/s, respectively. The results indicate that the value of D_Li increases with elevated test temperature, and it can be inferred that the electrochemical properties of such materials can be improved by raising the working temperature.

NASICON-structured Na₃Zr₂Si₂PO₁₂ was synthesized by a Sol-Gel approach. Phase-pure samples were successfully sintered at 1050℃ when adding 10% excessive Na and P in the precursors, while a small amount of ZrO₂ impurity was detected without adding excessive phosphorus. Electrochemical impedance spectrum tests indicate that the ionic conductivity of the former is as high as 5.4×10^-4 S/cm at room temperature, which is higher than that of samples prepared from the precursors without adding excessive phosphorus (3.7×10^-4 S/cm). Further analysis reveals that the evaporation of phosphorus at high temperature would cause the formation of ZrO₂ impurity in the samples, leading to a lower ionic conductivity. Compared with solid state reaction approach, samples with enhanced ionic conductivity can be obtained at a rather lower temperature by Sol-Gel synthesis.

The lithium-rich cathode materials Li[Li_0.2Co_0.13Ni_0.13Mn_0.51Al_0.03]O₂ doped with 3% Al³⁺ were synthesized by a polymer-pyrolysis method. The structure and morphology of the as-prepared material were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM). The structural analyses exhibit that the Al³⁺-doped sample maintains the layered structure of the Li-rich oxide material and no impurity is detected in XRD patterns. The charge-discharge tests show that the Al³⁺-doped sample has a high charge/discharge capacity of 349.1/303.8 mAh/g (initial coulombic efficiency of 87%) at current density of 30 mA/g. Additionally, Al³⁺-doped sample also exhibits excellent cyclability with 91.7% capacity retention over 100 cycles. The results demonstrate that Al³⁺ doping is favorable to maintain the structural stability of the layered structure during the electrochemical lithium insertion/extraction, so as to provide a promising route to develop cathode materials with high capacity and stability.

The structure and electrochemical performance of Al₂O₃-coated LiFePO4 cathode materials were investigated. A nano Al₂O₃ coating on the surface of commercial LiFePO₄/C particles (Aleees Inc.) was prepared by using the Sol-Gel method. The effect of the amount of Al₂O₃ coating on the electrochemical performance and structural stability of LiFePO₄ electrodes at room temperature (25℃) and elevated temperatures (55℃) was studied. The results show that 2wt% Al₂O₃ coating can effectively enhance the cycling capacity, alleviate capacity fading at high temperature and reduce cell impedance. It is largely attributed to Al₂O₃ coating, which plays a regulatory role of lithium-ion inserting the lattice and preventing direct contact between the cathode material and the electrolyte, and improves the structural stability of LiFePO₄ during cycles.

Pure CaCu₃Ti₄O₁₂ (CCTO) thin film and NiO-doped CaCu_3-xNi_xTi₄O₁₂ (CCNTO) thin film with x=0.10, 0.20 and 0.30 were prepared by Sol-Gel method. The effects of NiO on the dielectric properties and microstructure revolution of CCTO were studied. The crystalline structure and the surface morphology of the films were markedly influenced by NiO content. AFM images of the CaCu_3-xNi_xTi₄O₁₂ samples showed that the grain size of Ni-doped CCTO was smaller than the grain size of CCTO without Ni doping. For the CCNTO thin film(x=0.2), the lowest leakage current was obtained and the minimum value reached 0.564 mA. Meanwhile, the highest threshold voltage and nonlinear coefficient were 81 V/mm and 1.9, respectively. The dielectric constant increased when the doping content of Ni reached a certain level. Besides, the dielectric loss was decreased firstly, and then increased.