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Li-metal battery systems are attractive for next-generation high-energy batteries due to their high theoretical specific capacity and Li-metal's low redox potential. Anode-free Li-metal batteries (AFLBs) have a higher energy density than conventional Li-metal batteries because the anode material is absent in the pristine state. An additional advantage is that the battery production costs are relatively low due to simplified anode coating processing, which makes AFLBs favorable for large-scale industrial production. Despite these advantages, commercializing AFLBs remains challenging because of the high reactivity of Li-metal and dendrite-growth issues at the anode side. The chemical and physical properties of solid-electrolyte interphase (SEI) formed at Li-metal anodes determine the Li-ion transport kinetics, Li-metal deposition behavior, and overall cycling performance. The key to resolving these issues is to grow a homogeneous Li-metal and design a stable SEI. Many approaches, such as electrolyte optimization and artificial layers design, have been developed to guide a uniform Li-metal growth and form a stable SEI, facilitating rapid Li-ion transport and suppressing Li-dendrite growth and other undesirable side reactions. An overview of these discoveries and developments in Li-growth and SEI engineering and insights into the intrinsic mechanisms of battery performance, presented in this review, is, therefore, of great interest to the battery research community.

Quasi-solid-state silver-zinc (Ag-Zn) batteries, featuring high energy density, stable voltage output, and outstanding safety, have been considered as promising power source for wearable electronics, while they suffer from poor areal capacity and insufficient rechargeability caused by low surface area and structural deterioration of cathode. In this work, we address these problems through redesigning the cathode with core-shell AgCl/carbon fiber structure decorated with MXene nanosheets. Benefiting from the unique structure with high surface area, the capacity is over two times higher than that with irregular morphology, and undesired Ag migration is suppressed owing to MXene protective layer, leading to enhanced structural integrity and ultralong cycle life. Theoretical calculations and experimental result reveal that a heterostructure is formed between MXene and Zn-coated AgCl, stabilizing the cathode structure. The battery demonstrates high capacity of 2.97 mAh cm−2 and impressive cyclability, maintaining 78% of initial capacity after 400 cycles at 4 mA cm−2, with nearly 100% coulombic efficiency. Moreover, robust mechanical flexibility is demonstrated in the separator-free batteries, and they can operate when twisted, cut, put on fire, and sealed in ice, suggesting the viability for practical application scenarios. This work offers pivotal guidance to construct stable electrodes and advanced batteries for powering electronics.

Simultaneously realizing the cathode and anode protection is critical for developing practical lithium sulfur (Li-S) batteries. Currently, many efforts have been devoted to solving problems related to either shuttle effect on sulfur cathode or dendrite growth on lithium anode. However, dual side protection is rarely reported. Herein, we rationally designed and synthesized yolk-shell nitrogen doped carbon frameworks embedded with heterostructures ZnSe-CoSe2 (ZnSe-CoSe2@NC), working as “two-in-one” hosts for both the sulfur cathode and lithium anode protection. As an anode host, the in situ formed Li2Se phase contributes to the Li+ transfer. Co and Zn guides a homogenous growth of Li within the 3D framework, thus effectively suppressing Li dendrite growth. Meanwhile, the heterostructure ZnSe-CoSe2 endows the cathode host with superior electronic conductivity, strong polysulfide chemisorption and efficient catalytic activity for polysulfide redox when compared with single metal selenides. Combined with these advantages, this Li-S full cell exhibits ultralong cycle life over 1000 cycles at 2 C. Even with a high sulfur loading (6.08 mg cm−2) and lean electrolyte (4.1 µL mg−1), the full cell achieves a high areal capacity of 4.16 mA h cm−2 after 100 cycles at 0.2 C. This work not only provides a new approach for the structure design of Li-S full battery, but also improves the utilization of active electrode materials.

Electrolyte solutions function as ionic conductors in Li-ion batteries and inevitably induce concentration gradients during battery operation. It is shown that in addition to these concentration gradients, very specific Li+ concentration waves in the electrolyte are formed in graphite-based porous electrode/Li cells. This phenomenon has been investigated by both simulations and experiments. From the simulations, it has been concluded that the occurring Li+ concentration waves in the electrolyte vary with position and time. Such waves originate from the fluctuations of the reaction distribution inside the porous electrode and depend on both the thermodynamics (open-circuit voltage, OCV) and kinetics (charge transfer reaction heterogeneity). Li+ concentration waves occurring inside the separator region are directly related to the battery output voltage at low current applications. A four-electrode device is used to validate the electrolyte concentration waves experimentally. The electric potential differences between the reference electrodes and counter electrode show regular fluctuations, demonstrating the existence of concentration waves in the electrolyte. The simultaneous appearance of the fluctuations in the potential differences and the transitions from plateaus to slopes in the battery output voltage illustrates the dependency of Li+ concentration waves on the thermodynamics and kinetics of the electrochemical reactions.

MXenes (two dimensional (2D) transition metal (TM) carbides (TMCs), TM nitrides (TMNs), and TM carbonitrides (TMCNs) are emerged as future biggest 2D materials (2DMs) family with novel applications in different nanotechnological research in academic as well as industrial level. MXenes NMs have the potential to be classified as a “wonder material” in the category of 2D nanomaterials (NMs). MXenes were studied and synthesized for over a decade since their first discovery in 2011, and till now more than 50 members are experimentally studied and more than 100 are theoretically investigated. Synthesis techniques are not restricted to the first introduced top-down HF based etching method but new innovative synthesis methods, such as, water (H2O)-free etching, molten salts etching and bottom-up method, like Chemical vapor deposition (CVD) method etc were also studied, providing multifunctional surface chemistry based MXenes NMs with novel configuration, and desirable characteristics. MXenes are used as important components in a number of flexible energy storage devices (FESDs), for instance secondary batteries, supercapacitors (SCs), Micro-SCs (MSCs) and Micro-batteries (MBs), etc due to their distinctive layered structures, high electrochemical performance and fascinating functional capabilities. In this review, we first will discuss in detail the MXenes NMs synthesis methods, secondly selected properties, and third their applications in various FESDs. After that, we will summarize and discuss the most present problems associated with MXenes NMs synthesis and their applications in FESDs, and possible solutions to those problems. Finally we will discuss the presents interesting vision for the future progress of the MXenes-based NMs in wearable and FESDs, their limitations, and suggestions.

With the growing demand for high-energy-density lithium-ion batteries, layered lithium-rich cathode materials with high specific capacity and low cost have been widely regarded as one of the most attractive candidates for next-generation lithium-ion batteries. However, issues such as voltage decay, capacity loss and sluggish reaction kinetics have hindered their further commercialization for decades. Intensive investigations have been devoted to developing high-performance lithium-rich cathode materials, highlighting the importance of improvement strategies as a potential approach. Herein, we summarize various strategies for improving performances of layered lithium-rich cathode materials for next-generation high-energy-density lithium-ion batteries. These include surface engineering, elemental doping, composition optimization, structure engineering and electrolyte additives, with emphasis on the effect and functional mechanism of corresponding techniques. In the subsequent section, we illustrate opportunities and challenges for designing high-performance lithium-rich cathode materials and bridging the gap between the laboratory and practical applications.

© 2019 Elsevier B.V. Construction of three-dimensional (3D) composite lithium metal anodes (LMAs) based on Li melt-infusion into a 3D porous scaffold has been demonstrated to be effective for solving the issue of the considerable relative volume change of LMAs during Li plating/stripping. However, little attention has been paid to controllable regulation of the structure and interface of 3D composite LMAs. In this study, 3D composite LMAs, namely Li–AuLi3@CF electrodes, are firstly fabricated by infusion of molten Li into carbon fiber (CF) paper modified with nanoporous gold (NPG) which is converted to AuLi3 after infusion. We herein demonstrate a synergistic structure and interface engineering strategy realized by a simple and effective pre-stripping protocol to initially expose a portion of the 3D AuLi3@CF scaffold to create “PS-Li-AuLi3@CF” electrodes, which greatly boosted the electrochemical performance. Symmetrical Li|Li cells with PS-Li-AuLi3@CF electrodes show an overpotential of 111 ​mV after cycling at a current density of 0.5 ​mA ​cm−2 for 1800 ​h. Additionally, Li|LiFePO4 (LFP) and Li|sulfurized polyacrylonitrile (SPAN) full cells with PS-Li-AuLi3@CF electrodes exhibit a high capacity retention of 96.1% with a Coulombic efficiency (CE) of 99.2% after 1000 cycles at 5C, and a capacity retention of 70.6% with a CE of 99.8% after 1000 cycles at 2C, respectively. This work provides a simple and highly effective method for engineering the structure and interface of 3D composite LMAs to boost their electrochemical performance for high-energy-density rechargeable lithium metal batteries (LMBs).

© 2019 Lithium nitrate (LiNO3) has been widely applied as an additive to effectively protect lithium (Li) metal anode via enhancing the interfacial stability. However, few researches have been carried out to protect Li metal anode with LiNO3 in carbonate electrolyte, because of its sparingly solubility. Herein, we propose a concept of sustainably and controllably releasing NO3− in carbonate electrolyte by intercalating superfluous LiNO3 particles between bi-layer polypropylene (PP) membranes (PP/LiNO3/PP). The sandwiched biscuit-like configuration prevents the direct attachment of non-conducting LiNO3 to active materials, facilitating the battery operation. Moreover, this construction is conductive to form uniform and stable solid electrolyte interphase (SEI) in virtue of Li–N compounds on Li metal by slow but continuous releasing of NO3− from LiNO3 particles. Li metal anode with the PP/LiNO3/PP configuration showed a high Coulombic efficiency of over 95.3% after 550 cycles at a current density of 1 mA cm−2. When paired with LiNi0.80Co0.10Al0.10O cathode, the Li metal full cell with the intercalated LiNO3 particles could deliver a discharge capacity of 103.8 mAh g−1 at the 500th cycle at 1C current density, which is far superior to the performance of the cell without LiNO3 additive. More profoundly, the PP/LiNO3/PP configuration is also applicable to the commercialized anode such as Silicon-Graphite to improve the electrochemical performance prominently. This strategy is not only a facile and efficient way in protecting Li metal anode, but also a universal method enabling the additives with sparingly solubility to be widely used in modern energy industries.

© 2020 Elsevier B.V. Sodium iron hexacyanoferrate (NaFeHCF) has been considered as a potential cathode for sodium-ion batteries owing to its low-cost and easily prepared procedure. However, it is still challenging to achieve long cyclic stability and superior rate capability, and the sodium storage mechanism of sodium-rich NaFeHCF is still elusive. Herein, a sodium-rich NaFeHCF with rhombohedral structure is presented with excellent electrochemical performances within 2.0–4.2 ​V. The specific capacity of ~115 ​mA ​h ​g−1 is obtained by utilizing two plateaus around 2.9 and 4.06 ​V, respectively. Remarkable rate performance from 10 to 4000 ​mA ​g−1 and 1000 cycles with high capacity retention is achieved as well. Synchrotron powder X-ray diffraction (PXRD) and structural refinement reveals that sodium-ions occupy three different sites (interstitial, face and edge) in rhombohedral unit cell, which contribute different capacities on different plateaus during Na+ extractions. Moreover, the rhombohedral structure is well-maintained after long-term Na+ extractions/insertions and reversible phase transitions with small volume variation are observed through in-situ synchrotron PXRD. The kinetic properties of Na+ in rhombohedral unit cell are identified by ab-initio molecular dynamics method and density functional theory calculations, which indicate that Na+ transport on three-dimensional diffusion paths, thus enabling the outstanding rate performance of NaFeHCF.

© 2019 Safe and high-energy-density all solid-state lithium metal batteries (ASSLMBs) are great in demand for future electrical vehicle and grid energy storage. The compatibility of electrode-electrolyte interface is a critical factor influencing the electrochemical performance of ASSLMBs. Herein, we propose a plastic super-conductive carrier to deter untoward reaction between Li anode and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) electrolyte by in-situ solidifying succinonitrile-based plastic interlayer with Li6.4La3Zr2Al0.24O12 (LLZAO) nanowires (l-SN). The method of in-situ solidification promises the low interfacial resistance. The l-SN interlayer can not only act as a physical obstacle to isolate LAGP pellet from Li metal, but also provide three-dimensional ion channels to regulate the transfer of Li ions, delivering an uniform Li ion distribution for dendrite-free Li deposition. The Li|l-SN|LAGP|l-SN|Li symmetric cell can stably cycle for 240 h without short circuit at room temperature (R.T). This approach enables a high specific capacity of 152.5 mAh g−1 at 0.1C for Li|l-SN|LAGP|l-SN|LiFePO4 cells at R.T. Furthermore, the integrated ASSLMBs show excellent cyclic stability at 40 °C with an initial discharge capacity of 168.4 mAh g−1 at 0.5C and retention of 93.17% after 100 cycles. The super-ionic property at the interface makes excellent rate performance of ASSLMBs at 40 °C. This strategy is facile and efficient in promising safe and outstanding ASSLMBs and also has some referential values for other unstable electrolyte interface beyond LAGP.

© 2020 Elsevier B.V. Recently, flexible lithium metal batteries (LMBs) are considered as a promising power source for next-generation flexible and wearable electronic devices due to their high energy densities. However, the usage of metallic Li anodes inevitably causes safety risk due to the growth of Li dendrites. In this review, we summarized the recent research progresses on flexible LMBs, with specific emphasis on the design of composite Li metal anodes and solid-state electrolytes with high flexibility and safety. We begin with a brief introduction of flexible LMBs and the associated anodes and electrolytes. Then, the preparation of flexible composite Li metal anodes has been described in detail, with the evolution from the conventional electrodeposition method to thermal infusion and mechanical rolling methods. For solid-state electrolytes, the advanced progress on shapeable ceramic, polymer, and hybrid electrolytes have been introduced. We also presented comprehensive summaries on high-energy-density flexible LMBs, including flexible lithium-sulfur batteries and lithium-oxygen batteries. Finally, we proposed the future trends, challenges, and prospects toward the practical applications of advanced flexible LMBs.

Vanadium-based mixed oxides are promising for high-energy-density lithium-ion batteries (LIBs) due to their abundant oxidation states, complex chemical compositions and synergistic effects, but the large volume change upon lithiation/delithiation limits the electrochemical properties. Two-dimensional nanostructures have great potential in the development of electrode materials by promoting the ion transport and alleviating the volume change. Herein, porous MoV2O8 nanosheets are synthesized via a solvothermal process followed by thermal treatment without using any surfactants. Benefiting from the nanosheet structure with large surface area and abundant pores, the MoV2O8 electrode exhibits impressive lithium storage properties with superior rate performance and prolonged cyclability. Superior reversible capacities of 1396 and 570 mA h g–1 can be maintained after 120 cycles at 200 mA g–1 and after 1000 cycles at 10 A g–1, respectively. Furthermore, the lithium storage mechanism of the MoV2O8 nanosheets was investigated by in-situ X-ray diffraction, ex-situ X-ray diffraction and X-ray photoelectron spectroscopy measurements, which confirms the synergistic effects of Mo and V upon lithiation/delithiation. In addition, a full cell consisting of the MoV2O8 nanosheets and commercial LiFePO4 exhibited good electrochemical performance, demonstrating the great potential of the MoV2O8 nanosheets as an anode material for LIBs.

The oil from waste coffee possesses the potential as a feedstock for biodiesel production. In this study, waste coffee grounds were collected from Turkey. Then the oil was extracted from waste coffee grounds using N-hexane. The two-step acid-base catalyst transesterification process was used to produce biodiesel as the acid value of the crude oil was found higher (15.4 mgKOH/g).This was followed by an investigation of some physical and chemical properties. It was found that the properties of waste coffee biodiesel fell within the limit of ASTM standards. So the studied physicochemical properties of the waste coffee biodiesel suggest that this fuel can be used as a fuel in diesel engines.

© 2019 The Authors. Published by Elsevier Ltd. Global energy demand has risen sharply over the years with developing countries recording the greatest share in this trend. Biomass as an energy resource is mostly available locally and can easily be converted into secondary energy without huge capital investments. Nowadays, Bangladesh shares a percentage of renewable energy only 3% of total energy ratio, Bangladesh has already taken a master plan in the renewable energy sector. Whereas installed electricity generation installed capacity of Bangladesh rapidly increased to 13265 MW with captive generation capacity which is insufficient for fulfilling the demand of electricity of the nations. One-third of the power production of Bangladesh depends on expensive imported fossil fuel energy resources and 65% of power generation depends on a natural gas reserve of the country, though one day the reserve of current gas will be diminished. Moreover, inadequate electricity production leads the country in a un-industrialization. The present and future crucial energy crisis situation adapted by installing renewable power into electricity production. The current renewable energy agenda of Bangladeshi government force the specialization of renewable energy generation budget by decreasing global pollution with saving movement of biomass, solar, hydro, wind, and tidal power sector. This paper presents the currents national energy scenario of Bangladesh. According to this, the greater potentiality of renewable energy resources is also reviewed and presented in this paper.

© 2019 The Authors. Published by Elsevier Ltd. Household waste generation has become a serious environmental issue in recent years. However, some technologies are available to convert household domestic waste into energy. One of such techniques is the biogas generation using household waste. The biogas generation technique is not a new method of energy generation, but its production efficiency is questionable. Biogas yield from domestic waste are influenced by pH level, temperature, HRT and C/N ratio. Moisture and the temperature levels in the biogas generation systems are very critical to its production efficiency, especially this is highly affected in the colder weather condition. Solar assisted biogas plant may provide better production efficiency compared to the traditionally designed biogas plant. In this paper, the scopes and opportunities of solar assisted biogas generation are reviewed. Possible benefits and challenges associated with the solar assisted biogas generation are highlighted.

© 2019 The Authors. Published by Elsevier Ltd. Increasing global energy demand at a rate faster than the population growth has led the researcher to look for alternative fuel. Amongst the options, biodiesel is an environmentally sustainable substitute of diesel fuel being renewable, biodegradable and have similar properties of fossil diesel. Among the biodiesel sources, microalgae is a potential third generation biodiesel feedstock which can be produced throughout the year and its oil yield is higher than any other crops. This paper reviews recent development in microalgae biodiesel in terms of its oil extraction technics, challenges of oil extraction, production of biodiesel from microalgae oil and its fuel properties. Finally, the paper discusses the performance and combustion analysis of diesel engine fuelled with microalgae biodiesel. This paper provides a clear understanding of the potential use of microalgae biodiesel as an alternative source to fossil diesel for diesel engines.

© 2018 Multivalent ion storage mechanism is applied to construct high-performance aqueous zinc-ion hybrid supercapacitors (ZHSs). The constructed MnO2 nanorods//activated carbon (AC) ZHSs with ZnSO4 aqueous electrolyte are significantly different from the common MnO2//AC asymmetric supercapacitors with Na2SO4 electrolyte in electrochemical behaviors and energy storage mechanism. The ZHSs show the maximum specific capacity of 54.1 mA h g−1 and maximum energy density of 34.8 W h kg−1 at the optimal mass ratio of AC to MnO2. The ZHSs are capable of being charged/discharged rapidly within only 2–17 s, delivering a large power of 3.3–13.0 kW kg−1. Reversible insertion/extraction of Zn2+ into/from MnO2 nanorods and ion adsorption/desorption on AC particle surface, as well as partially reversible formation/dissolution of Zn4(OH)6SO4·nH2O participates on both electrodes, are established as the energy storage mechanism of the ZHSs. Electrochemical performance of the ZHSs can be further optimized through electrolyte composition regulation. Addition of Mn2+ cations into ZnSO4 electrolyte leads to significantly enhanced energy density (58.6 W h kg−1) of the ZHSs, while anion replacement of SO42- by CF3SO3- suppresses manganese dissolution and Zn4(OH)6SO4·nH2O formation, thus resulting in good cycling stability with 93.4% capacity retention over 5000 charge/discharge cycles. Overall, the ZHSs based on multivalent ion storage are promising to be applied as high-performance, extremely safe and eco-friendly energy storage devices for wearable/portable electronics and hybrid electric vehicles.