O3-type sodium-layered transition-metal oxides, NaNi_0.5Mn_0.5O₂, are one of the most promising cathode materials. However, the application of O3-NaNi_0.5Mn_0.5O₂ cathode material is limited due to the transition metal layer's slip during charge and discharge processes, with multiple irreversible complex phase transitions. In addition, its energy density is limited due to the capacity of O3-NaNi_0.5Mn_0.5O₂ electrode, which is mainly concentrated in the low-voltage region around 3 V, and O3-P3 phase transition easily occurred in this region. This study proposes a precise chemical element substitution strategy for successfully solving these problems Doping with Sn⁴⁺ inhibits the transition metal layer's slip and the irreversible multiphase transformation. Meanwhile, Sn⁴⁺ cannot be hybridized with the O 2p orbital due to the unique outer electronic structure, which lacks a single electron in its d orbital. The O 2p orbital only hybridized with the Ni e_g orbital, increasing the ionic degree of Ni—O bond and Ni's redox potential. Therefore, O3-NaNi_0.5Mn_0.5O₂ can display a high midpoint voltage of 3.28 V. Meanwhile, the electrode material exhibits excellent electrochemical performance and kinetic properties. The controllable redox potential of O3-type cathode material was realized based on molecular orbital hybridization theory to obtain the high-voltage layered oxide cathode materials sodium-ion batteries.

Sodium (Na) metal has been regarded as a promising anode candidate for next-generation batteries with high energy density and power density. The Na metal anode, however, suffers from poor cycling stability and safety hazards associated with Na dendrite growth. To enhance cycling stability, sodium bis(fluorosulfonyl)imide (NaFSI) and sodium trifluoromethanesulfonimide (NaTFSI) were tested as a mixed dual salt in a series of high-concentration electrolytes, with diglyme (G2) as solvent. A NaFSI-NaTFSI high-concentration electrolyte considerably enhanced the cycling stability of Na metal anodes compared with single-salt electrolytes. Electrochemical performance and morphologies of the cycled Na metal anode indicate that the high-concentration dual-salt electrolyte could inhibit corrosion of the current collector and generate stable interfaces on the anodes. Na metal full cells coupled with a Na₃V₂(PO₄)₂F₃ (NVPF) cathode in the optimal dual-salt high-concentration electrolyte have also been realized with stable cycling. This demonstrates the feasibility of this approach for practical applications in sodium metal batteries.

Rechargeable aqueous ammonium-ion batteries using ammonium ions as carriers have many inherent advantages; however, research and exploration of full batteries are still in their infancy. Herein, we developed a 3,4,9,10-perylenetetracarboxylic diimide (PTCDI)//δ-MnO₂ ammonium-ion battery system. The battery uses 0.5 mol/L NH₄Ac as the electrolyte, layered δ-MnO₂ as the cathode material, and PTCDI as the organic anode material, and it can work stably in the voltage range of 0—1.5 V. The layered δ-MnO₂ cathode material was prepared through simple thermal decomposition of KMnO₄ and was characterized by XRD, SEM, TEM, XPS, FTIR, and Raman spectroscopy. Through a proper combination of the PTCDI nanoparticle anode, the capacity retention rate of the full battery remained 92% of the initial capacity after 500 cycles at a current density of 0.5 A/g, and the coulombic efficiency was close to 100%, indicating excellent cycle stability. In addition, the energy storage mechanism of the δ-MnO₂ nanosheet cathode and the ammonium-ion storage dynamics kinetics of the PTCDI organic anode were systematically studied. Ex situ XPS revealed that NH₄⁺ can be reversibly intercalated/deintercalated in the cathode material. The full battery has a relatively high voltage window; thus, it can easily supply power to common electrical appliances, such as small fans and LEDs, and has a good development prospects. In summary, developing novel materials is of great significance to the construction of a new generation of safe and environmentally friendly aqueous ammonium-ion batteries.

Because of their excellent safety and long cycle life, all-vanadium redox flow batteries (VRFBs) hold promise for large-scale energy storage; however, the battery's relatively high-cost limits its commercialization. Increasing the power density of VRFBs is an efficient way to reduce the cost. Flow fields are an important factor in determining power density, and well-designed flow fields can effectively reduce the concentration polarization of VRFBs under high rate discharge, increasing the corresponding power density. Serpentine and interdigitated flow fields are the two most commonly used flow fields in VRFBs at the moment. Conclusions about their contributions to battery performance, however, are debatable. In this paper, we theoretically and experimentally investigate the effect of the specific flow rates and flow field size on the mass transfer and battery performance of VRFBs with serpentine and interdigitated flow fields. The results show that under the same specific flow rate, the electrolyte flow velocity in serpentine flow fields is much higher than in interdigitated flow fields, resulting in better battery performance at low specific flow rates for the former. Increasing the flow rates and size of the flow field can significantly improve the battery performance for both flow fields. However, because the critical flow rate of interdigitated flow fields is greater than that of serpentine flow fields, the performance improvement of the former with the increasing specific flow rates and flow field size is significantly greater than that of the latter, and the performance difference between these two flow fields will gradually decrease or even reverse. This work not only advances our understanding of the flow field structure and mass transfer process in VRFBs but also provides evidence and guidance for the engineering application of the flow fields.

To address the problem of voltage inconsistency in lithium-ion (Li-ion) battery packs, caused by differences in the manufacturing processes of individual cells, an equalization scheme is proposed that can realize multiple equalization types. The scheme consists of an active equalization topology, based on a three-winding transformer, and a corresponding adaptive interleaving control strategy, which can control the flexible transfer of energy between different equalization objects. The circuit can also make real-time adjustments according to battery pack condition, always ensuring the optimal state to achieve fast equalization of the battery pack. Finally, the proposed equalization scheme effectively solves the voltage inconsistency issue and achieves high-speed equalization from simulation.

Combining the conducting polymer polypyrrole (PPy) with layered molybdenum disulfide (MoS₂) has proved to be an effective strategy to obtain a porous network flexible electrode. Various self-standing flexible electrodes with different structural parameters can be synthesized by controlling the preparation conditions. In this study, kinetics of the electrochemical behavior of PPy-MoS₂ electrodes were systematically investigated by analyzing electrochemical impedance spectroscopy and cyclic voltammetry (CV) curves. The Trasatti analysis method was adopted to quantify the charge stored at the inner and outer surfaces during energy storage. Results show that the volumetric capacity of the porous network flexible electrodes varies with thickness. The difference in volumetric capacity derives from the kinetic control on the energy storage reaction. The dominant control in that reaction changes from surface control to diffusion control as the thickness of the flexible electrode increases from 5 to 60 μm. When surface control and diffusion control coexist at similar levels, the porous network flexible electrode yields its maximum capacity (68 mA·h/cm³ at 5 mV/s). Therefore, to maximize storage efficiency, the interaction between active materials and electrolyte ions should be carefully optimized when the porous network film is applied to a flexible electrode.

The use of electrochemical energy storage and conversion technology is a primary method for addressing energy and environmental problems. The key scientific and technological issues of its material development, optimization and design, and system management for industrial-scale applications have received a lot of attention. This paper describes three application cases: lithium-ion batteries, supercapacitors, and proton exchange membrane water electrolysis (PEMWE), as well as the multiphysics models that were developed for each. We discovered and investigated the interactions of transport phenomena, electrochemistry, and current density distributions in the large-format pouch cell based on such experimentally validated models; we introduced "electrostatic image forces" to study the effects of hierarchically porous structures on double layer and pseudocapacitance of the supercapacitor; we considered the transient-state issues in PEMWE engineering, and investigate the effects of two-phase flow transport phenomena on the electrolytic performance. The results show that high C-rate operations and jelly roll materials with low thermal conductivities significantly increase the heterogeneity of internal reactions and current density distributions. It also claims that the volume ratio of micro and mesopores influences the allocation of alternative capacitances in the hierarchical pores and ion transport processes. PEMWE requires materials with high hydrophilia and high liquid saturations in the flow channels to improve electrolytic performance. As a result, the multiphysics models can help with theoretical interpretation and optimization in the areas of material design, process analysis, and system management optimization.

Supercapacitors have been extensively studied as an energy storage device due to their faster charging-discharging rates, higher power density, and longer service life. MXenes with high conductivity, high electrochemical activity, ease of fabrication into film, hydrophilicity, and other characteristics, are widely used in the field of supercapacitors and exhibit excellent energy storage performance. However, the environmental sensitivity and ease of oxidation degradation, which results in the formation of TiO₂ and other compounds that contribute essentially nothing to the capacitance, have significantly hampered the development of high-performance supercapacitors. It is critical to investigate the stability optimization strategy of MXenes colloid and realize the selective regulation of its stability for improving the performance of MXenes in supercapacitors and other potential application fields. Therefore, we summarize the strategies for inhibiting MXenes oxidation, propose an overall scheme of selective stability regulation, and discuss the effect of selective regulation on the performance of supercapacitors, as well as provide suggestions for fabricating high-performance MXenes-based supercapacitors.

Solar energy linked to effective energy storage has the potential to reduce environmental pressure caused by fossil fuel combustion. Concentrated solar power generation combined with phase change heat storage technology offers a promising route to achieve improved energy utilization. In this study, by considering the selection criteria of phase change materials (PCMs) for heat storage, performance aspects of carbon-containing binary system PCMs, especially thermophysical properties, are analyzed. The study found that the binary compounds and solid solutions formed by silicon, boron, aluminum, chromium, iron, and carbon have high melting points. In particular, carbon-containing binary PCMs have broad prospects for application in high-temperature phase change heat storage. Among the carbon-containing binary PCMs, Fe-C binary alloy can meet the heat storage requirements of a high temperature phase change heat storage system (i.e., 1100～1500 ℃). When the alloy is a Fe-C eutectic composition containing 4.3% carbon, the theoretical value of the alloy's phase transformation latent heat is 611 kJ·kg^-1, and its thermal conductivity is approximately (40±16) W·m^-1·K^-1, The phase transition temperature is 1148 ℃, which is suitable for heat storage in a concentrated solar thermal power generation system. The Fe-C binary alloy also has better comprehensive heat storage performance than other alloy components.

Sodium-ion batteries have substantial potential in large-scale energy storage and low-speed electric vehicles owing to their raw material abundance, low cost, safety, and relatively low environmental impact. Recently, sodium vanadium fluorophosphate [Na₃V₂(PO₄)₂F₃, NVPF] has become a focus of research into cathode materials for sodium-ion batteries. Key attributes of NVPF are its stable three-dimensional framework structure, high theoretical capacity (128 mA·h/g), and high working voltage (approximately 3.8 V). However, low electronic conductivity and slow ion diffusion rate resulted in both low actual capacity and unsatisfactory rate performance, which had hindered further development. Therefore, researchers have been able to considerably improve electrochemical performance by optimizing the synthesis process, coating, ion doping, and structural design. Together, these improvements have greatly enhanced the potential for application of NVPF in sodium-ion batteries. Based on a review of recent relevant literature, this paper first introduces the cell characteristics of NVPF. Next, it investigates four Na⁺ extraction/insertion mechanisms (i.e., the solid solution reaction, step-by-step Na⁺ extraction/insertion, three-step Na⁺ extraction/insertion, and two-step Na⁺ extraction/insertion mechanisms). It also briefly summarizes three common synthesis methods (i.e., the high temperature solid-state, hydrothermal, and sol-gel methods) and their advantages and disadvantages. Then, recent progress with enhanced NVPF (modified by coating, ion doping, and optimized structural design) is described in detail. Finally, the practical development of the synthesis and modification of NVPF cathode materials and the NVPF full cell are explored in the context of future real-world applications of NVPF in sodium-ion batteries.

Sodium-ion batteries as a new type of clean and renewable energy technology have attracted more and more attention, and have a distinct advantage especially in the area of large-scale energy storage application. It is expected to partially replace lithium-ion batteries. Phosphorus-based anode materials for sodium-ion batteries have drawn wide attention due to the high theoretical capacity and suitable sodium storage voltage. The poor electrical conductivity and big volume change during cycling processes, however, make their commercialization challenging. To elucidate the research progress of phosphorus-based anode materials for sodium-ion batteries, the sodium storage mechanism, current research status, and modification strategies of red phosphorus, black phosphorus, phosphorene, and metal phosphides as anode materials for sodium-ion batteries have been summarized. Currently, the researches of phosphorus-based sodium-ion battery anodes focus on the combination with conductive carbonaceous materials and the design of materials with confined structure. In addition, protective/conductive coating, elemental substitution/doping, usage of new types of electrolytes, and tuning of electrochemical window can effectively improve the electrochemical performance of phosphorus-based sodium-ion battery anodes. The future research tendency can focus on the preparation of phosphorous-rich materials, the determination of sodium storage mechanism, the usage of advance characterization and theoretical methods, and the study of matched components and full cell.

Aqueous zinc ion batteries (ZIBs) are up-and-coming energy storage systems due to their safety, low cost, and environmental friendliness; hence have vast research potential. Despite rapid improvements in high-performance cathode materials, research on zinc anodes is still lacking. Many strategies focus on improving the zinc anode performance and anode protection to address the inherent shortcomings. In this review, the relevant literature suggests that low Coulomb efficiency (CE) and poor cycling performance are challenges for zinc anode at present, which are due to zinc anode dendrite growth and corrosion phenomena. In this paper, the methods to improve the performance of zinc anode are compared in detail on following aspects: zinc anode alloying treatment, surface structure modification, interfacial protection, electrolyte zinc salt comparison, electrolyte additives, and gel electrolyte, by reviewing recent research on zinc anode design and electrolyte optimization to change the interfacial properties of zinc anode. Finally, we outline the demand for ZIBs research and future strategies for stabilizing the zinc anode interface.

Solid polymer electrolytes (SPEs) has several distinct advantages, including no-leakage, ease of use, and suppression of lithium dendrite growth, all of which are important for improving the cycling life and safety of solid-state lithium metal batteries. Conducting lithium salts, as one of the most essential components of SPEs, could not only act as lithium-ion sources for the transportation of ionic species but also participate in the formation/construction of electrode/SPEs interphases. As a result, the chemical structures of lithium salts are critical for regulating the physical and electrochemical properties of SPEs, as well as their interfacial properties with electrode materials. This work focuses mainly on the research progress of conducting lithium salts, including perfluorinated and partially fluorinated sulfonimide salts, based on our experience in the field of SPEs. Future directions in conducting salt design for SPEs are also discussed.

Benefitting from high gravimetric/volumetric energy density, low cost, and high safety of aluminum anode, rechargeable aluminum ion batteries (AIBs) have become promising next-generation energy-storage battery system. AIBs are comprised of Al anode, cathode materials, and 1-ethyl-3-methylimidazole chloride ([EMIm]Cl)-based ionic liquid electrolyte. Currently, significant progresses have been made in the performance optimization of Al-storage cathodes; however, the practical application of AIBs is limited by electrolyte problems, including high cost, corrosivity, humidity sensitivity, and unstable interface. This review summarizes recent works on AIB electrolyte and the tactics to improve the practicability of AIB electrolyte. From the perspective of cost reduction, modify and optimize the property of low-cost ionic liquid electrolyte and low-temperature molten salt system. In the viewpoint of chemical stability, develop new-type electrolyte systems, such as gel polymer and solid-state electrolyte, which aim at protecting ionic liquids with solid substrate. Exploring low-cost and chemically/electrochemically stable electrolyte is an attractive direction in the field of AIBs. In addition, the modification schemes and existing problems of different electrolytes are comprehensively analyzed and discussed, and the future development of AIB electrolyte is prospected.

Aqueous organic redox flow batteries (AORFBs) represent a promising technology for large-scale storage and efficient utilization of renewable energy. In this paper, we thoroughly review organic electroactive species against four important performance parameters (energy density, power density, efficiency, and cycle life), based on the current status of AORFB research. For the different organic electroactive molecules, we clarify the effects on AORFB performance of solubility, potential, electron number, electrochemical redox kinetics, size, and chemical stability. The development of AORFBs shows favorable prospects relative to lithium iron phosphate batteries, lead carbon batteries, and all-vanadium redox flow batteries. AORFBs with energy density ≥30 Wh/L, maximum discharge power density ≥300 mW/cm², energy efficiency ≥80%, and capacity retention rate ≤0.05%/d can be expected to compete in the long-term energy storage market.

Developing highly efficient oxygen reduction reaction (ORR) electrocatalysts is one of the main techniques to achieve the large-scale application of proton exchange membrane fuel cells (PEMFCs). Noble-metal based catalysts, as robust ORR catalysts, are the most likely candidates for practical application. The large-scale use of noble metal may lead to a high cost of the catalysts. On the other hand, the stabilities of noble-metal catalysts still need further improvements. Confining noble-metal catalysts in physical confinement layer can greatly improve catalytic stability without compromising initial activity, thus prolonging the service life of catalysts. The physical confinement layers can not only inhibit the coalescence of catalysts during high-temperature preparation, but also mitigate the aggregation, detachment and dissolution during electrochemical process. In this review, confined noble-metal ORR catalysts are reviewed, including conducting polymer confined noble-metal catalysts, non-metal-oxide confined noble-metal catalysts, metal-oxides confined catalysts and carbon confined catalysts. Besides, the structure-performance relationship between confinement layers' physical properties and electrocatalytic performance is analyzed. Three main strategies to achieve carbon confinement are emphasized, including 'deposition-conversion' strategy, 'insertion-conversion' strategy and 'one-step pyrolysis' strategy. At last, summary and prospect are given, also some existing challenges are stated.

To counterbalance the reduction of system inertia with increasing renewable generation, the frequency response (FR) service markets in the UK have been reforming to enable procurement from diverse technologies including energy storage systems (ESSs). The Enhanced FR product was introduced in 2016 to allow ESSs to manage the state of energy (SOE) within two envelopes. A two-year weekly auction trial was launched in 2019 to test closer-to-real-time procurement and reduce the financial risk of ESSs by evaluating their performance and payments in each week separately instead of an entire month. In addition, an integrated suite of end-state services has been successively released since 2020 with the phase-out of existing FR services so as to increase the standardisation and transparency of FR markets. The end-end services consisting of Dynamic Containment (DC), Dynamic Moderation (DM) and Dynamic Regulation (DR) deal with different frequency deviation levels and have a limited requirement on full-response duration, which mitigates the barrier to entry for ESSs. The SOE rules are additionally specified to indicate the cases in which ESSs will not be penalised for the under-delivery of DC, DM or DR. Based on the latest technical requirements and procurement/payment mechanisms of DM, this paper simulates the techno-economic operation of a grid-scale lithium-ion battery ESS (BESS) that provides DM to the AC grid while following its operational baselines to restore the SOE. The SOE levels and FR errors of the BESS are calculated to determine its compliance with the SOE rules and under-delivery penalties. Then the DM payment is compared with BESS costs to estimate the net present value at the end of the energy throughput-based lifetime, indicating the profitability of the BESS under the latest energy storage-friendly FR markets. The BESS operating strategy designed here fully considers the specific market mechanisms of end-state FR services, allowing the closer-to-real-time SOE management and meeting the required FR delivery. The specific and novel strategy design and the resulting simulation offer BESS developers with an insight into potential operating scenarios especially at the early stage of end-state FR service markets.