Advanced Energy Storage Systems Research Articles

Advanced exergy and exergo-economic analyses of an advanced adiabatic compressed air energy storage system, part 2: Parametric study and optimization

In this study, parametric analysis and multi-objective optimization of the advanced adiabatic compressed air energy storage system (AA-CAES) were performed. Non-dominated Sorting Genetic Algorithm (NSGA-II) method was used in the multi-objective optimization study. In the optimization study, objective functions were determined in the conventional and advanced exergy/exergo-economic analyses concept. In the optimization study in the concept of advanced exergo-economic analyses, a new performance criterion that is not in the literature was determined and the results were confirmed by conventional exergo-economic analyses. In this study, the modified total unit product cost, which is given as the new performance criterion, is defined on the basis of avoidable feed exergy cost rate and avoidable investment cost rate. This shows the potential to be improved in the cost of the system and gives more detailed information than the total unit product cost in conventional exergo-economic analysis. As a result of the optimization study, the total unit product cost and the exergy efficiency of the system were found to be 162.9 $/day and 64.3%, respectively for the conventional exergy/exergo-economic analyses concept. For the advanced exergy/exergo-economic analyses concept, the modified total unit product cost and the modified exergy efficiency of system were found to be 103.5 $/day and 91.9 %. The exergy efficiency and the total unit product cost improved by 16.48 % and 3.55 %, respectively, with the optimization study according to the basic case of the overall system. With the parametric study, the increase in the efficiency of the wind turbine affected the exergy destruction rate more than the other system components. While the effect of the increase in the efficiency of the turbines on the exergy destruction cost rate of the system is greater than the other system components, the system component that most affects the cost rate of the system is the compressors.

Cu2Se@C thin film with three-dimensional braided structure as a cathode material for enhanced Cu2+ storage

In the face of multiple challenges brought by the changes of global climate and environment, developing clean energy and updating green energy storage equipment are important ways to achieve carbon peak and carbon neutrality. Aqueous batteries have become a research hotspot due to their advantages of using the multivalent charge carrier, high ionic conductivity, environmental friendliness and cost effectiveness. In this work, the Cu2Se@C (Cu2Se coated on carbon clothes) thin film with a three-dimensional braided structure is fabricated by a simple electrochemical deposition method for Cu2+ storage for the first time. Compared with the commercial Cu2Se powder, the well-designed Cu2Se@C film shows enhanced specific capacity (640 mAh/g at 0.5 A/g) and rate performance (542 mAh/g at 5 A/g) as well as superior cycling stability (82.7% capacity retention after 1000 cycles at 1 A/g). The Cu2+ storage mechanism of the Cu2Se@C electrode is based on a reversible phase transition process of Cu2Se ↔ Cu2-xSe ↔ CuSe ↔ CuSe2. In kinetic characteristic analysis, the Cu2Se@C electrode demonstrates faster Cu2+ diffusion in discharge process than charge process resulting from the phase transition and the variation of interplanar spacing. This work highlights a facile one-piece design strategy and opens a new gateway for the exploration of advanced aqueous energy storage systems.

Photothermal-assisted scheme design and thermodynamic analysis of advanced adiabatic compressed air energy storage system

The conventional photothermal-assisted scheme adopted by advanced adiabatic compressed air energy storage (AA-CAES) has equal stages of expanders and high-temperature reheaters, and is equipped with a regenerator to waste heat recovery, which is relatively complex and requires high solar heat supply and solar irradiance. In this paper, a novel photothermal-assisted AA-CAES (PT-AA-CAES) with a simpler structure and suitable for low solar irradiance is designed, which adopts 3-stage expansion and 2-stage high-temperature reheat. The thermodynamic model of PT-AA-CAES system is established, and a comprehensive evaluation coefficient combining exergy efficiency and energy storage density is proposed. The numerical results demonstrate that the compressor unit outlet pressure and expansion unit inlet pressure with the optimal comprehensive performance are 10 MPa and 4 MPa. Furthermore, when the solar irradiance is below 690 W/m2, 660 W/m2, and 600 W/m2, the output work, exergy efficiency, and energy storage density of the novel PT-AA-CAES system will surpass those of the conventional PT-AA-CAES system with the same solar heat consumption, and at a solar irradiance of 580 W/m2, the exceeded values are 44.3 kW h, 2.03%, and 0.15 kW h/m3, respectively. These conclusions can assist the AA-CAES system in the selection of unit pressures and photothermal-assisted scheme.

ANALYSIS OF THE FEATURES OF EFFECTIVE IMPLEMENTATION OF SOLAR POWER PLANTS IN LOCAL ENERGY SUPPLY SYSTEMS

It is shown that renewable energy sources (RES) are increasingly dominating the electricity market in many countries, while the amount of electricity generation by solar power plants (SPP) has been growing at a record pace in recent years. It is noted that although the share of RES continues to grow and the photovoltaic industry is developing rapidly, the industry still faces many challenges, in particular, how to continue to reduce the Levelized Cost of Energy (LCOE), improve the efficiency of operation and maintenance, and maintain the stability of the power grid, to ensure system security. The effective implementation of solar generation requires an analysis of the prospects for the development of local electric power systems that include SPP, the development of mechanisms and appropriate regulatory, methodological, technical and organizational support that will contribute to the effective development of solar generation, the construction of modern system (schematic) solutions.
 The analysis of the features of the development of green generation in Poland and Ukraine was carried out, the positive factors that influenced the development of renewable energy sources in Ukraine were determined, which made it possible to form the technical, economic and organizational conditions for the successful development of solar generation, in particular, information was provided on new players in developed energy markets according to the Fourth Energy EU package. The analysis showed that when increasing the efficiency of SPP systems, planning and demand management in the electric network, effective functioning of Energy Smart Community (ESC) become important.
 The basic components of the effective functioning of electric power systems with SPP are highlighted, namely: concepts of configurations of photovoltaic systems, Smart-inverters, Energy Storage System (ESS), formation of Virtual Power Plant (VPP) based on SPP. It is shown that each of the four concepts involves the connection of a series of photovoltaic panels or strings and power electronics devices (DC converters and inverters), which are configured taking into account the peculiarities of the functioning of various structural (schematic) solutions. The advantages of using Smart-inverters as a new technology that can help integrate solar energy and other distributed energy resources into the electrical network are evaluated. Smart inverters are used to help the electrical grid cope with intermittent generation, helping the electrical grid remain stable and maintain voltage and frequency requirements.
 It was determined that in any photovoltaic system, the ESS itself becomes a central component that significantly affects the cost, maintenance requirements, reliability and design of the SPP, and the important parameters of the ESS that affect the operation and performance of the photovoltaic system are the battery maintenance requirements, battery life, available power and efficiency. Trends in the market of advanced energy storage systems for SPPs for the next decade are presented. The functioning of virtual power plants based on SPP, as a network of aggregated distributed energy resources that are remotely connected and work together with flexible electricity consumers, is aimed at maximizing the benefits of participants. The possibilities and trends of SPP development in the near future, which are based on the research of Huawei, are presented.

Exergy analysis and particle swarm optimization of clean energy router based on a solar‐thermal‐assisted advanced adiabatic compressed air energy storage system

AbstractThe clean Energy router based on advanced adiabatic compressed air energy storage (AA‐CAES) has the characteristics of large capacity, high efficiency and zero carbon emission which are an effective mitigation scheme for the integration of renewables and peak‐shaving and a new clean energy technology for storing energy in the world. A novel solar‐thermal‐assisted AA‐CAES (ST‐AA‐CAES) is proposed in this paper, integrating variable thermal energy storage to improve the system electric to electric (E2E) and round‐trip efficiency (RTE). The efficiency and exergy evaluation of ST‐AA‐CAES are carried out to determine the performance of ST‐AA ‐CAES. The results illustrate that E2E, RTE, and exergy efficiency can reach 56.4%, 95.5%, and 55.9%, respectively. Meanwhile, the details of exergy efficiency and destruction of each subsystem are demonstrated. Particle swarm optimization algorithm is applied to analyse the economy of optimally integrated energy systems which has the advantages of high accuracy, convenient implementation and fast convergence. The system can be applied in abundant solar energy resources area with high efficiency and multi‐energy supply capability.

Carbonized bacterial cellulose as free-standing cathode host and protective interlayer for high-performance potassium-sulfur batteries with enhanced kinetics and stable operation

Due to the limited capacity of Lithium (Li)-ion batteries and the scarce reserves of Li, potassium-sulfur battery (KSB) seems to be the most appealing candidate for next-generation advanced energy storage systems owing to the abundance of sulfur as well as potassium in addition to the high capacity offered by sulfur cathodes. However, the development of KSB is in the nascent stage, primarily because of the highly unstable and reactive potassium anode, which needs special consideration for its protection. To overcome this, for the first time to the best of our knowledge, we introduce the free-standing carbonized bacterial cellulose (CBC) not only as an anode-protective interlayer but also as a cathode host. Further, the K2S6 catholyte is used as an active material, enabling the even distribution of active sulfur and high sulfur loading. Benefitting from the superior physicochemical properties of CBC and the introduction of it as a protective interlayer, the KSB, as developed, can be cycled for continuous 500 cycles even at high current rates such as 2 and 5C, respectively. The cell with CBC as a cathode host and an interlayer retained 73% and 62% of initial capacity after 300 and 500 cycles at 1 and 2C, respectively. Potassium striping and plating test show that the CBC interlayer effectively enables uniform nucleation and growth, reducing dendrite formation. The first-principles calculations are also performed to substantiate these advancements in electrochemical performances. This study may pave the way for the practical realization of KSB with stable operation and long cycle life.

Ca/Co-based composites with improved cyclic stability and optical absorption for advanced thermochemical energy storage systems

Thermochemical energy storage (TCES) is a promising technology to overcome solar intermittency and volatility. However, weak solar absorption, poor cyclic stability for calcium carbonates, and cost issues for metal oxides hinder the applicability of these materials for thermochemical energy storage. Herein, an advanced, affordable, and effective TCES system is proposed, and the corresponding calcium carbonate-metal oxide synergistic material is designed with improved solar absorption and cyclic stability. The optimum molar ratio is Ca:Co:Mn:Mg = 100:20:7.5:5 for the synergistic material fabricated by the modified sol–gel method, where Ca element plays the primary role in heat storage, Co element serves as the primary optical performance enhancer and secondary heat storage component, and Mn/Mg elements act as the secondary performance modifiers. The solar absorptivity is boosted to ∼79.3%, and the heat storage density is 1295 kJ/kg after 30 high-temperature cycles, which are 6 times and 2.2 times higher than those of commercial calcium carbonate, respectively. Homogeneous mixing of modifiers at the microscale and stable, well-developed pore structure are critical factors for cyclic stability enhancement. The change of electronic structure on the Fermi level caused by Co/Mn ion doping is the key to optical absorption improvement, and the promoting amplitude exhibits wavelength dependence. This work expands the limited list of currently available TCES materials and the comprehensive description of optical properties offers guidance for future implementation of TCES materials with high solar absorption in specific wavelengths.

Ameliorating Phosphonic-Based Nonflammable Electrolytes Towards Safe and Stable Lithium Metal Batteries.

High-energy-density lithium metal batteries with high safety and stability are urgently needed. Designing the novel nonflammable electrolytes possessing superior interface compatibility and stability is critical to achieve the stable cycling of battery. Herein, the functional additive dimethyl allyl-phosphate and fluoroethylene carbonate were introduced to triethyl phosphate electrolytes to stabilize the deposition of metallic lithium and accommodate the electrode-electrolyte interface. In comparison with traditional carbonate electrolyte, the designed electrolyte shows high thermostability and inflaming retarding characteristics. Meanwhile, the Li||Li symmetrical batteries with designed phosphonic-based electrolytes exhibit a superior cycling stability of 700 h at the condition of 0.2 mA cm-2, 0.2 mAh cm-2. Additionally, the smooth- and dense-deposited morphology was observed on an cycled Li anode surface, demonstrating that the designed electrolytes show better interface compatibility with metallic lithium anodes. The Li||LiNi0.8Co0.1Mn0.1O2 and Li||LiNi0.6Co0.2Mn0.2O2 batteries paired with phosphonic-based electrolytes show better cycling stability after 200 and 450 cycles at the rate of 0.2 C, respectively. Our work provides a new way to ameliorate nonflammable electrolytes in advanced energy storage systems.

Synthesis and analysis of structural, dielectric, and thermistor behaviour of zinc ferrite

This paper discusses the synthesis, dielectric properties, and applications of ZnFe2O4 for the thermistor. A high-temperature solid-state reaction method is used to create the polycrystalline ZnFe2O4 sample. The X-ray diffraction study identified the single spinel Cubic phase formation at room temperature without any impurities. The broadening of the XRD peaks determined structural parameters including crystallite size, microstrain, dislocation density, and percentage crystallinity which confirms the lower number of lattice defects in the ferrite. The dielectric properties of the sample are investigated as a function of temperature over selected frequencies. The high dielectric constant and low dielectric loss of the material suggest that it can be used in advanced energy storage systems. The minimal activation energies in the high-temperature region determined from the slope of the linear fit of the temperature-dependent curve indicate the enhancement of electrical conductivity. Looking into the strong dependence of resistivity on temperature, the thermistor parameters are evaluated using the resistance at different temperatures, which suggests its possible application for a thermistor as well as a temperature sensor. The calculation of different thermistor parameters such as thermistor constant, sensitivity factor, and activation energy confirms a negative temperature coefficient of resistance behavior of the ferrites at different temperatures and frequencies.

Polymer-Grafted Nanoparticles with Variable Grafting Densities for High Energy Density Polymeric Nanocomposite Dielectric Capacitors.

Designing high energy density dielectric capacitors for advanced energy storage systems needs nanocomposite-based dielectric materials, which can utilize the properties of both inorganic and polymeric materials. Polymer-grafted nanoparticle (PGNP)-based nanocomposites alleviate the problems of poor nanocomposite properties by providing synergistic control over nanoparticle and polymer properties. Here, we synthesize "core-shell" barium titanate-poly(methyl methacrylate) (BaTiO3-PMMA) grafted PGNPs using surface-initiated atom transfer polymerization (SI-ATRP) with variable grafting densities of (0.303 to 0.929) chains/nm2 and high molecular masses (97700 g/mL to 130000 g/mol) and observe that low grafted density and high molecular mass based PGNP show high permittivity, high dielectric strength, and hence higher energy densities (≈ 5.2 J/cm3) as compared to the higher grafted density PGNPs, presumably due to their "star-polymer"-like conformations with higher chain-end densities that are known to enhance breakdown. Nonetheless, these energy densities are an order of magnitude higher than their nanocomposite blend counterparts. We expect that these PGNPs can be readily used as commercial dielectric capacitors, and these findings can serve as guiding principles for developing tunable high energy density energy storage devices using PGNP systems.

Bimetallic nanoparticles decorated porous carbon as the host material to enhance the performance of lithium-sulfur batteries

Lithium-sulfur battery (LSB) is one of the most appealing candidates for advanced next-generation electrochemical energy storage systems based on the merits of extraordinary theoretical specific energy density, abundant resources and environmental friendliness of sulfur. However, the ‘‘shuttle effect” of lithium polysulfides (LiPSs) and low utilization of sulfur cathode severely plague the large-scale commercialization of the LSBs. In this work, a novel host material for sulfur cathode, namely porous carbon (PC) decorated with NiCo2O4 nanoparticles (NiCo2O4/PC), was designed and prepared. Among all tested NiCo2O4 nanoparticles with different morphologies, the NiCo2O4 nanoparticles with honeycomb pore shape (C-NiCo2O4) showed excellent performance as sulfur cathode host. Benefiting from the synergistic advantages between PC and C-NiCo2O4 nanoparticles, the C-NiCo2O4/PC host materials showed strong adsorption for LiPSs, promising the alleviation of shuttle effect and promoting the catalytic conversion process of LiPSs. As a result, the LSBs with S@C-NiCo2O4/PC cathode delivered a high specific capacity of 1065.2 mAh g−1 at 0.1C, a stable cycling over 500 cycles with low fading rate of 0.053% per cycle at 0.5C and an enhanced rate capability compared with those of S@C-NiCo2O4 and S@PC cathodes. This work demonstrated the synergistic effect of physical shackle from PC and adsorption-catalysis from NiCo2O4 nanoparticles, which might provide new insights into the optimization of carbonaceous architecture for rationally regulating the polysulfide redox reactions.

Boosting potassium-based dual ion battery with high energy density and long lifespan by red phosphorous

The potassium dual-ion batteries (DIBs) have been attracting a great attention in recent years due to their promising environmental benignancy, high energy density, and long lifespan. The active materials based on conversion reaction mechanism are favorable and widely expected to alleviate the dendrite formation, red phosphorous was thus employed and fabricated into a three-dimensional porous carbon matrix anchored by P–O–C chemical bonding using vaporization–condensation–conversion process. Meanwhile, the elements modified carbon can not only guarantee the electronic conductivity and ions diffusion, but also alleviate the red phosphorous volumetric expansion and detachment. When coupled with graphite, the K-DIBs demonstrate excellent electrochemical performance with a high 213 Wh kg−1 energy density and a promising stability up to 650 cycles. This explored material will provide highly relevant insights for next-generation advanced energy storage systems.

Quantum Energy Storage in 2D Heterointerfaces

AbstractTo address the global energy and environmental crisis, advanced energy storage systems with their superior electrochemical performances have been growing exponentially. The electrochemical properties of the selected electrode materials have a direct impact on the performance of these energy storage technologies. 2D structures are considered promising materials for energy storage systems because of their unique and outstanding electrochemical characteristics. Therefore, hybridization of 2D nanosheets with other low‐dimensional materials can improve storage capacity by modulating and exploiting the synergy between the same. This comprehensive review highlights energy storage devices, their mechanisms, and key problems, with a focus on electrodes made of new generation 2D hybrids. Following that, the strategies that enable face‐to‐point, face‐to‐line, and face‐to‐face heterointerfaces are discussed in details. In addition, a design approach is provided for synergistically coupling 2D with other quantum materials for designing efficient and long‐lasting storage systems. It is anticipated that this review article will serve as helpful motivation for developing excellent energy storage devices with improved electrochemical capability.

Carbonized Bacterial Cellulose-Derived Binder-Free, Flexible, and Free-Standing Cathode Host for High-Performance Stable Potassium–Sulfur Batteries

In search of improved advanced energy storage systems to meet our fast-growing energy demands for large-scale applications, potassium–sulfur batteries (KSBs) provide an essential alternative due to their high specific capacity apart from the low cost and abundance of potassium and sulfur. However, the insulating nature of sulfur, volume changes, and shuttle effect impede the development of these batteries. Further, the binder, carbon additives, and current collector used in the assembly of cells in a conventional approach decrease the energy density of cells. To overcome these challenges, we propose a binder-free and free-standing carbonized bacterial cellulose (CBC) as a cathode host that not only provides a conducting pathway but also has a porous network that is resilient to volume change. To ensure the uniform loading of sulfur, CBC was dipped into the sulfur/carbon disulfide solution, followed by melt diffusion at 160 °C to prepare a sulfur-infused CBC (S-CBC) cathode. This S-CBC cathode with an interconnected fiber network delivers a significantly high reversible capacity of 1311 mA h g–1 at a current density of 50 mA g–1. While connected for long-term cycling, the potassium sulfur cell delivers an initial reversible capacity of 475 mA h g–1 at 100 mA g–1. Once the cell is stabilized after 80 cycles, it maintains a capacity of 123 mA h g–1 with a capacity retention of 86% after 500 cycles. This enhanced electrochemical performance of flexible and free-standing S-CBC cathode is further analyzed using first-principles calculations. Moreover, the efficacy of the S-CBC cathode is also tested under high sulfur loading (1.6 and 2.4 mg cm–2, respectively) for the practical development of KSBs.

“Pore‐Hopping” Ion Transport in Cellulose‐Based Separator Towards High‐Performance Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) have great potential for large‐scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its application. Herein, a cellulose‐based composite separator (CP@PPC) was prepared by immersion curing of cellulose‐based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The “pore‐hopping” ion transport mechanism in CP@PPC opens up extra Na+ migration paths, resulting in a high Na+ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one‐up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems.

"Pore-Hopping" Ion Transport in Cellulose-Based Separator Towards High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have great potential for large-scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its application. Herein, a cellulose-based composite separator (CP@PPC) was prepared by immersion curing of cellulose-based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The "pore-hopping" ion transport mechanism in CP@PPC opens up extra Na+ migration paths, resulting in a high Na+ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one-up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems.

Robust NASICON-type iron-based Na4Fe3(PO4)2(P2O7) cathode for high temperature sodium-ion batteries

Iron-based mixed phosphates sodium ion batteries (SIBs) are promising sustainable storage devices due to the low-costing and non-toxicity characters. Whereas, their real application is seriously restricted by the sluggish Na+ diffusion and inferior intrinsic electronic conductivity. Herein, we propose mesoporous sponge-like structural Na4Fe3(PO4)2(P2O7) (NFPP) in-situ caged in carbon layer and cross-linked graphene nanosheets (NFPP@C@rGO), toward fast charging and highly stable sodium ion half/full cells in a wide temperature range. This rational strategy gives the cathode superior long-lasting cycling stability, specifically, 86.7 % capacity retention is retained at 20 C for over 30,000 cycles, displaying a capacity loss less than 0.00045 % per cycle. Notably, outstanding thermal stability at 60 °C is achieved and no obvious capacity degradation can be observed after cycling for 200 times at 1 C. Furthermore, the impressive electrochemical performances of full cells are determined, ascribed to the improved electronic conductivity and structural stability (e.g. a small volume change of ∼4.1 % during sodium ion insertion/deinsertion), which is confirmed by in-situ X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements. All the results above prove that the NFPP@C@rGO is of high potential for advanced energy storage system based on its low costs, long-lasting cyclability and excellent thermal stability.

Cerium oxide as cathode material for aqueous zinc-ion battery

Zinc-ion battery is regarded as one of the potential alternatives for advanced energy storage system, due to its high discharge capacity, low cost, and environmental benignity. The research and development of new electrode materials and reaction mechanism for zinc-ion battery have attracted most attention. Herein, cerium oxide is systematically investigated as a novel cathode material for aqueous zinc-ion battery. The battery charge and discharge test results show that cerium oxide has a discharge specific capacity comparable to that of manganese oxide cathode material, the discharge specific capacity is stable at 143.8 mAh g−1 after 500 cycles. The cyclic voltammetry curves and charge-discharge curves of cerium oxide are very similar to manganese oxide cathode materials. The results of X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that the performance of cerium oxide as a cathode material for aqueous zinc-ion battery is related to the reaction product of zinc sulfate hydroxide hydrate and manganese ion in the electrolyte. And it is found that the discharge cut-off voltage also plays a crucial role in the discharge capacity of the aqueous zinc-ion battery with manganese ion.

Ultrafine Co-Species Interspersed g-C3N4 Nanosheets and Graphene as an Efficient Polysulfide Barrier to Enable High Performance Li-S Batteries.

Lithium-sulfur (Li-S) batteries are regarded as one of the promising advanced energy storage systems due to their ultrahigh capacity and energy density. However, their practical applications are still hindered by the serious shuttle effect and sluggish reaction kinetics of soluble lithium polysulfides. Herein, g-C3N4 nanosheets and graphene decorated with an ultrafine Co-species nanodot heterostructure (Co@g-C3N4/G) as separator coatings were designed following a facile approach. Such an interlayer can not only enable effective polysulfide affinity through the physical barrier and chemical binding but also simultaneously have a catalytic effect on polysulfide conversion. Because of these superior merits, the Li-S cells assembled with Co@g-C3N4/G-PP separators matched with the S/KB composites (up to ~70 wt% sulfur in the final cathode) exhibit excellent rate capability and good cyclic stability. A high specific capacity of ~860 mAh g-1 at 2.0 C as well as a capacity-fading rate of only ~0.035% per cycle over 350 cycles at 0.5 C can be achieved. This bifunctional separator can even endow a Li-S cell at a low current density to exhibit excellent cycling capability, with a capacity retention rate of ~88.4% at 0.2 C over 250 cycles. Furthermore, a Li-S cell with a Co@g-C3N4/G-PP separator possesses a stable specific capacity of 785 mAh g-1 at 0.2 C after 150 cycles and a superior capacity retention rate of ~84.6% with a high sulfur loading of ~3.0 mg cm-2. This effective polysulfide-confined separator holds good promise for promoting the further development of high-energy-density Li-S batteries.

Oxygen vacancy-modulated zeolitic Li4Ti5O12 microsphere anode for superior lithium-ion battery

Spinel Li4Ti5O12 (LTO) is a promising anode material for state-of-the-art high-power lithium-ion batteries (LIBs) owing to its “zero strain” characteristics during fast charging/discharging, long cycle life, and high rate capability. However, the poor ionic/electronic conductivity and sluggish ionic diffusion coefficient of LTO restrict its practical utility. Porous zeolitic LTO (Z-LTO) microspheres were synthesized herein as anode materials for LIBs using TiO2 and LiOH∙H2O via a hydrothermal method combined with Ar/H2 thermal treatment. The increased concentration of Ti3+ self-doping-derived oxygen vacancies in as-synthesized Z-LTO and porous microspherical Z-LTO aggregates greatly improved the electronic conductivity and structural stability. These features contributed to achieving much higher discharge capacities of ∼210 and ∼180 mAh g−1 at 0.5 C and 1 C rates, respectively, as well as excellent ultra-high rate capability of 45 mAh g–1 at 50 C rate, while still maintaining the outstanding long-life cyclic stability (∼181 mAh g−1 at 5 C rate after 2000 cycles), with 90% capacity retention, compared to commercial LTO (C-LTO). Charge contribution kinetics analysis indicated that the lithium storage mechanisms in Z-LTO, particularly at a high rate, were dominantly diffusion-controlled due to the larger ion-diffusion ability (DLi ≈ 4.18 × 10−8 cm2 s−1). This finding confirms that the generation of surface defects by creating Ti3+/Ti4+ pairs and oxygen vacancy engineering in LTO is an effective approach for enhancing the ion/electron mobility, which can be extended to boost the battery performance of other materials with low ionic conductivities for advanced energy storage systems.