Facile Synthesis of Sustainable Activated Biochars with Different Pore Structures as Efficient Additive-Carbon-Free Anodes for Lithium- and Sodium-Ion Batteries

The present work elucidates facile one-pot synthesis from biomass forestry waste (Norway spruce bark) and its chemical activation yielding high specific surface area (SBET) biochars as efficient lithium-and sodium-ion storage anodes. The chemically activated biochar using ZnCl2 (Biochar-1) produced a highly mesoporous carbon containing 96.1% mesopores in its structure as compared to only 56.1% mesoporosity from KOH-activated biochars (Biochar-2). The latter exhibited a lower degree of graphitization with disordered and defective carbon structures, while the former presented more formation of ordered graphite sheets in its structure as analyzed from Raman spectra. In addition, both biochars presented a high degree of functionalities on their surfaces but Biochar-1 presented a pyridinic-nitrogen group, which helps improve its electrochemical response. When tested electrochemically, Biochar-1 showed an excellent rate capability and the longest capacity retentions of 370 mA h g-1 at 100 mA g-1 (100 cycles), 332.4 mA h g-1 at 500 mA g-1 (1000 cycles), and 319 mA h g-1 at 1000 mA g-1 after 5000 cycles, rendering as an alternative biomass anode for lithium-ion batteries (LIBs). Moreover, as a negative electrode in sodium-ion batteries, Biochar-1 delivered discharge capacities of 147.7 mA h g-1 at 50 mA g-1 (140 cycles) and 126 mA h g-1 at 100 mA g-1 after 440 cycles

Development of Advanced Electrodes and Electrolyte for the Lithium Battery

Lithium-ion batteries (LIBs) have become an essential commodity ever since their commercialization in the 1990s to power portable electronic devices such as laptop computers, mobile phones, etc. This is mainly due to the LIB‘s ability to store and deliver high energy and power densities more competitively than or equivalently to the fast depleting, non-recyclable fossil fuels. Nevertheless, they require a paradigm shift to make them suitable for powering plug-in electric vehicles and as an alternative to power grids to minimize the energy loss by transmission. The present state-of-the-art LIB containing ‘graphite’ anode and ‘layered LiCoO2’ cathode, with Li-ions mobilized by organic electrolyte, has limited energy density, however, and raises serious safety issues. So, the demand for high energy density and power density anode and cathode materials with a solid electrolyte layer sandwiched between them could be an ideal engineering design for future safe plug-in electric vehicles. To date, layered graphite has been widely used as an anode material in LIBs ever since its launch in the 1990s, but its limited theoretical capacity of 372 mA h g-1 and the very low diffusion coefficient of lithium in graphite (10-9 to 10-7 cm2 s-1) restrict its use in high energy applications such as plug-in electric vehicles. Therefore, the anode of the battery is the key component in a rechargeable battery with such high energy density. Alternatively, metallic lithium would be an ideal anode, but it has safety problems resulting from anode dendrite formation. This growth from the metallic-lithium anode, when it is used in conjunction with an organic-liquid electrolyte, has resulted in the development of \u27conversion-reaction\u27 based non-layered compounds (such as transition metal oxides, nitrides, fluorides, sulphides, phosphides, and even hydrides), as they offer numerous advantages, including multiple electron transfer, the ability to tune the redox centre based on anions of transition metal compounds, and most importantly, their capability to recover their original phase upon reversing the polarity. This reaction results in fast capacity fade, however, due to the stress induced by accommodating the volume changes during cycling and the sluggish reaction kinetics upon charge transfer, while the intrinsic structural changes could damage the electrode when it is cycled at high current densities. Enormous efforts were made in past decades to circumvent these disadvantages by tuning their morphologies and particle size, but even so, fabricating a durable conversion electrode exhibiting superior reversible energy and power densities remains a great challenge. The use of blended nanostructures, wherein nanostructured active electrode materials are chemically or non-covalently bonded to conductive materials, has proved to be an effective method for achieving high performing electrode materials for LIBs by improving their electrical conductivity and electron transfer. Although the results have been encouraging, there are still issues that haunt the electrochemical performance of these composites. This is mainly due to the random/improper distribution of active materials (AM) with uneven particle sizes over carbonaceous materials, leading to poor synergy with no change in electrical conductivity and, therefore, no effect on their overall electrochemical performance. There are also limits to the high loading of AM into the composites. As the composites have had a high weight ratio of carbonaceous materials to AM, the operating voltage was reduced to a level similar to that of traditional graphite, further impeding understanding of the AM mechanism of energy storage and its contributions towards overall electrochemical performance. Therefore, in this thesis, the work is built on a strategy that could transform bulk AM into well-defined two-dimensional (2D) nanostructured AM to increase the edge density of its inert basal planes for use as the sole active anode material, followed by construction of electrodes with a three-dimensional (3D) architecture consisting of 2D nanostructured AM sandwiched between low/negligible quantities (≤20 wt.%) of conductive reduced graphene oxide (rGO) for long-term stable lithium storage

Enhanced capacity and cycle life of nitrogen-doped activated charcoal anode for the lithium ion battery: a solvent-free approach

Herein, we investigated the electrochemical performance of nitrogen-doped commercial activated charcoal (R-AC) for lithium-ion batteries (LIBs). With this aim, nitrogen was doped into R-AC via a solvent-free approach, which involved annealing R-AC under N2 and NH3 atmospheres at 800 °C, and the product was tested as an anode for LIBs. The sample annealed under an NH3 atmosphere (NH-AC) had a nitrogen doping level of 4.7 at% with a specific surface area of 894.5 m2 g−1 and a reduced O/C ratio of 0.31 in comparison to the sample annealed under an N2 atmosphere (N-AC) and R-AC. Raman spectroscopy detected disorder/defects owing to the introduction of various C-N-C terminal bonds on the surface of R-AC, which significantly improved the electrical conductivity of both N-AC and NH-AC. Therefore, endowed with these physicochemical properties, NH-AC delivered a high specific capacity of 736.4 mA h g−1 at 50 mA g−1 (up to 150 cycles) and 524 mA h g−1 at 200 mA g−1 even after 500 cycles, which indicates much better performance in comparison to those of R-AC, N-AC and commercial graphite. This remarkable electrochemical performance of NH-AC can be attributed to the synergistic effect of its large specific surface area, disordered graphitic structure, and low charge transfer resistance, which enable it to act as an anode for high-performance LIBs

Few Atomic Layered Lithium Cathode Materials to Achieve Ultrahigh Rate Capability in Lithium-Ion Batteries

The most promising cathode materials, including LiCoO2 (layered), LiMn2O4 (spinel), and LiFePO4 (olivine), have been the focus of intense research to develop rechargeable lithium-ion batteries (LIBs) for portable electronic devices. Sluggish lithium diffusion, however, and unsatisfactory long-term cycling performance still limit the development of present LIBs for several applications, such as plug-in/hybrid electric vehicles. Motivated by the suc-cess of graphene and novel 2D materials with unique physical and chemical properties, herein, a simple shear-assisted mechanical exfoliation method to synthesize few-layered nanosheets of LiCoO2, LiMn2O4, and LiFePO4 is used. Importantly, these as-prepared nanosheets with preferred orientations and optimized stable structures exhibit excellent C-rate capability and long-term cycling performance with much reduced volume expansion during cycling. In particular, the zero-strain insertion phenomenon could be achieved in 2-3 such layers of LiCoO2 electrode materials, which could open up a new way to the further development of next-generation long-life and high-rate batteries

Unlocking the potential of amorphous red phosphorus films as a long-term stable negative electrode for lithium batteries

Amorphous red phosphorus films (NS-RP) synthesized by a high energy sonication technique delivered a reversible capacity of 2137 mA h g-1 when used as a sole active lithium battery anode. After incorporation of reduced graphene oxide in NS-RP, the hybrid delivered a reversible capacity of 706 mA h g-1, even after 200 cycles

A microwave autoclave synthesized MnO2/graphene composite as a cathode material for lithium-oxygen batteries

Graphene sheets (GNS) have been synthesized using a fast and effective microwave autoclave method in which the MnO2 nanoflakes are coated on the GNS in situ to form a composite material. The structures, compositions, and morphologies of the samples were characterized by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and electron microscopy. Application of the catalyst cathodes in Li-O2 batteries was also investigated. Compared with GNS cathode, dramatic improvements in the catalytic performance of the composite cathode have been obtained. This superior performance is attributed to the synergistic benefits from the GNS with three-dimensional structure and the MnO2 nanoflakes that cover them. The GNS not only increase the electrical conductivity of the composite cathode but also offer enough space for the tri-phase reaction and to buffer the volume changes during cycling. Due to their intrinsically high catalytic activity, the MnO2 nanoflakes could efficiently boost the oxygen reduction reaction and oxygen evolution reaction, improving the electrocatalytic performance of the MnO2/GNS composite as cathode for Li-O2 batteries

Electrochemical performance enhancement in MnCo2O4 nanoflake/graphene nanoplatelets composite

The synthesis and characterization of MnCo2O4 nanoflake/graphene nanoplatelets composite is reported here for high performance supercapacitor electrode applications. The MnCo2O4 nanoflakes with different morphologies were synthesized successfully via a hydrothermal technique by changing the amount of NH4F. The MnCo2O4 nanoflakes in combination with the graphene nanoplatelets was deposited on Ni foam using an electrophoretic deposition technique. The as prepared composite electrode showed superior performance in terms of specific capacitance and cycling stability, as compared to the pristine MnCo2O4 system, due to the enhanced electronic conductivity resulted from bond formation between carbon and MnCo2O4. A high specific capacitance of ∼1268 F g−1 was observed at 1 mV s−1 scan rate. Noteworthy cycling stability was observed even at the end of 10,000 cycles of consecutive charging and discharging at a current density of 7.81Ag−1

Self-assembled porous carbon microparticles derived from halloysite clay as a lithium battery anode

A naturally available clay mineral, halloysite, is used as a templating agent for the preparation of porous carbon microparticles (PCMs); these PCMs have been investigated as a candidate for lithium-ion battery (LIB) anodes. The PCMs are obtained with furfuryl alcohol as the carbon precursor; we also propose a possible mechanism for their self-assembled structure. This structure exhibits a Brunauer-Emmett-Teller surface area of 329 m2 g-1, which is higher than that of halloysite (50 m2 g-1). Even after 300 cycles, the PCMs exhibited a stable reversible discharge capacity of 600 mA h g-1 when tested at 100 mA g-1. Furthermore, the presence of porous structure in PCM electrode provides surface controlled reaction, contributing pseudocapacitance (58.5%) to the total charge storage capacity

Tuning the morphology of Co3O4 on Ni foam for supercapacitor application

In this work, NH4F was used as a vital additive to control the morphology of Co3O4 precursors on Ni foam in a conventional hydrothermal reaction, and then, via thermal decomposition, to obtain Co3O4 material. The amount of NH4F plays a pivotal role in the formed morphology of the Co3O4 precursors, and four morphologies of Co3O4 were obtained through close control of the amount of additive: nanowires, thin nanowire-clusters, thick nanowire-clusters, and fan-like bulks. The morphological evolution process of the Co3O4 precursors has been investigated according to their intermediates at different reaction stages, and some novel growth mechanisms are proposed: (1) the amount of NH4F in the solution system affects the chemical composition of the precursors; (2) with an increasing amount of NH4F in the solution system, the morphology will tend to form more ordered states and more distinct hierarchical structures; (3) with an increasing amount of NH4F in the solution system, the growth of products will tend to form denser structures; (4) the amount of NH4F in the solution system will affect the mass loading of products. The four different morphologies of Co3O4 were tested as free-standing electrode materials for supercapacitor application. Co3O4 with the thin-nanowire-cluster morphology exhibits the best electrochemical performance: the specific area capacitance is 1.92 F cm-2 at the current density of 5 mA cm-2 and goes up to 2.88 F cm-2 after 3000 charge-discharge cycles, while the rate capability is 72.91% at the current density of 30 mA cm-2

Long stable cycling of fluorine-doped nickel-rich layered cathodes for lithium batteries

Theoretically, layered Ni-rich metal oxides are capable of delivering 200 mA h g−1. However, their performances deteriorate due to an irreversible surface reaction with the electrolyte, which could be overcome by the partial substitution of fluorine for oxygen. Herein, a fluorine-doped, Ni-rich metal oxide with the composition LiNi0.7Co0.15Mn0.15O1.95F0.05 exhibited a capacity of 170 mA h g−1 after 100 cycles when tested against lithium