Directional Flow-Aided Sonochemistry Yields Graphene with Tunable Defects to Provide Fundamental Insight on Sodium Metal Plating Behavior

We report a directional flow-aided sonochemistry exfoliation technique that allows for unparalleled control of graphene structural order and chemical uniformity. Depending on the orientation of the shockwave relative to the flow-aligned graphite flakes, the resultant bilayer and trilayer graphene is nearly defect free (at-edge sonication graphene "AES-G") or is highly defective (in-plane sonication graphene "IPS-G"). AES-G has a Raman G/D band intensity ratio of 14.3 and an XPS-derived O content of 1.3 at. %, while IPS-G has an I_G/D of 1.6 and 6.2 at. % O. AES-G and IPS-G are then employed to understand the role of carbon support structure and chemistry in Na metal plating/stripping for sodium metal battery anodes. The presence of graphene defects and oxygen groups is highly deleterious: In a standard carbonate solution (1 M NaClO₄, 1:1 EC-DEC, 5 vol % FEC), AES-G gives stable cycling at 2 mA/cm² with 100% Coulombic efficiency (CE) (within instrument accuracy) and an area capacity of 1 mAh/cm². Meanwhile IPS-G performs on-par with the baseline Cu support in terms of poor CE, severe mossy metal dendrites, and periodic electrical shorts. We argue that solid electrolyte interface (SEI) stability is the key for stable cycling, with defects of IPS-G being catalytic toward SEI formation. For IPS-G, the SEI layer also shows F-rich "hot spots" due to accelerated decomposition of FEC additive in localized regions.

Catalyst-Free In Situ Carbon Nanotube Growth in Confined Space via High Temperature Gradient

Carbonaceous materials, such as graphite, carbon nanotubes (CNTs), and graphene, are in high demand for a broad range of applications, including batteries, capacitors, and composite materials. Studies on the transformation between different types of carbon, especially from abundant and low-cost carbon to high-end carbon allotropes, have received surging interest. Here, we report that, without a catalyst or an external carbon source, biomass-derived amorphous carbon and defective reduced graphene oxide (RGO) can be quickly transformed into CNTs in highly confined spaces by high temperature Joule heating. Combined with experimental measurements and molecular dynamics simulations, we propose that Joule heating induces a high local temperature at defect sites due to the corresponding high local resistance. The resultant temperature gradient in amorphous carbon or RGO drives the migration of carbon atoms and promotes the growth of CNTs without using a catalyst or external carbon source. Our findings on the growth of CNTs in confined spaces by fast high temperature Joule heating shed light on the controlled transition between different carbon allotropes, which can be extended to the growth of other high aspect ratio nanomaterials.

Rational Design of 1D Partially Graphitized N-Doped Hierarchical Porous Carbon with Uniaxially Packed Carbon Nanotubes for High-Performance Lithium-Ion Batteries

N-doped hierarchical porous carbon with uniaxially packed carbon nanotubes (CNTs) was prepared by copolymer single-nozzle electrospinning, carbonization, and KOH activation. Densely and uniaxially aligned CNTs improve the electrical conductivity and act as a structural scaffold, enhancing the electrochemical performance of the anode. A partially graphitized N-doped carbon shell, which has a rapid ion accessible pore network and abundant redox sites, was designed to expand the redox sites from the surface of the material to the whole material, including the inner part. As an anode, this material exhibited a superior reversible capacity of 1814.3 mA h g^-1 at 50 mA g^-1 and of 850.1 mA h g^-1 at 1000 mA g^-1. Furthermore, the reversible capacity decreased by only 36% after 400 cycles and showed superior rate capability to that of the same material without CNTs, indicating that the CNT acted successfully as a structural scaffold and enhanced the electrical conductivity. This study not only allowed the rational design of the ideal structure of CNT-based carbonaceous anode material, which has both a rapid ion accessible structure and fast electron-transfer path, but also shed light on a potential strategy by which to use CNTs to modify the nitrogen bonding configuration in N-doped carbon for better electrochemical performance.

Fast-Charging and High Volumetric Capacity Anode Based on Co3 O4 /CuO@TiO2 Composites for Lithium-Ion Batteries

This paper presents an investigation of anodic TiO₂ nanotube arrays (TNAs), with a Co₃ O₄ /CuO coating, for lithium-ion batteries (LIBs). The coated TNAs are investigated using various analytical techniques, with the results clearly suggesting that the molar ratio of Co₃ O₄ /CuO in the TiO₂ nanotubes substantially influences its battery performance. In particular, a cobalt/copper molar ratio of 2:1 on the TNAs (Co₂ Cu₁ @TNAs) features the best LIBs anode performance, exhibiting high reversible capacity and enhanced cycling stability. Noticeably, Co₂ Cu₁ @TNAs achieve excellent rate capability even after quite a high current density of 20.0 A g^-1 (≈25 C, where C corresponds to complete discharge in 1 h) and superior volumetric reversible capacity of ≈3330 mA h^-1  cm^-3 . This value is approximately seven times higher than those of a graphite-based anode. This outstanding performance is attributed to the synergistic effects of Co₂ Cu₁ @TNAs: 1) the structural advantage of TNAs, with their large amount of free space to accommodate the large volume expansion during Li⁺ insertion/extraction and 2) the optimized ratio of Co₃ O₄ and CuO in the composite for improved capacity. In addition, no binder or conductive agent is used, which is partly responsible for the overall improved volumetric capacity and electrochemical performance.

WS2-Graphite Dual-Ion Batteries

A novel WS₂-graphite dual-ion battery (DIB) is developed by combining a conventional graphite cathode and a high-capacity few-layer WS₂-flake anode. The WS₂ flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows large-scale and free-material loss production (i.e., volume up to 8 L h^-1 at concentration of 10 g L^-1 and exfoliation yield of 100%) of few-layer WS₂ flakes in dispersion. The WS₂ anodes enable DIBs, based on hexafluorophosphate (PF₆^-) and lithium (Li⁺) ions, to achieve charge-specific capacities of 457, 438, 421, 403, 295, and 169 mAh g^-1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0 A g^-1, respectively, outperforming conventional DIBs. The WS₂-based DIBs operate in the 0 to 4 V cell voltage range, thus extending the operating voltage window of conventional WS₂-based Li-ion batteries (LIBs). These results demonstrate a new route toward the exploitation of WS₂, and possibly other transition-metal dichalcogenides, for the development of next-generation energy-storage devices.

Free-Standing 3D-Sponged Nanofiber Electrodes for Ultrahigh-Rate Energy-Storage Devices

We have designed a self-standing anode built-up from highly conductive 3D-sponged nanofibers, that is, with no current collectors, binders, or additional conductive agents. The small diameter of the fibers combined with an internal spongelike porosity results in short distances for lithium-ion diffusion and 3D pathways that facilitate the electronic conduction. Moreover, functional groups at the fiber surfaces lead to the formation of a stable solid-electrolyte interphase. We demonstrate that this anode enables the operation of Li-cells at specific currents as high as 20 A g^-1 (approx. 50C) with excellent cycling stability and an energy density which is >50% higher than what is obtained with a commercial graphite anode.

Poly(ionic liquid)-Derived N-Doped Carbons with Hierarchical Porosity for Lithium- and Sodium-Ion Batteries

The performance of lithium- and sodium-ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile synthesis of well-defined N-doped porous carbons (NPCs) using a poly(ionic liquid) (PIL) as precursor, and graphene oxide (GO)-stabilized poly(methyl methacrylate) (PMMA) nanoparticles as sacrificial template. The GO-stabilized PMMA nanoparticles are first prepared and then decorated by a thin PIL coating before carbonization. The resulting NPCs reach a satisfactory specific surface area of up to 561 m² g^-1 and a hierarchically meso- and macroporous structure while keeping a nitrogen content of 2.6 wt%. Such NPCs deliver a high reversible charge/discharge capacity of 1013 mA h g^-1 over 200 cycles at 0.4 A g^-1 for lithium-ion batteries, and show a good capacity of 204 mA h g^-1 over 100 cycles at 0.1 A g^-1 for sodium-ion batteries.

Impact of the Acid Treatment on Lignocellulosic Biomass Hard Carbon for Sodium-Ion Battery Anodes

The investigation of phosphoric acid treatment on the performance of hard carbon from a typical lignocellulosic biomass waste (peanut shell) is herein reported. A strong correlation is discovered between the treatment time and the structural properties and electrochemical performance in sodium-ion batteries. Indeed, a prolonged acid treatment enables the use of lower temperatures, that is, lower energy consumption, for the carbonization step as well as improved high-rate performance (122 mAh g^-1 at 10 C).

Revisiting Solid Electrolyte Interphase on the Carbonaceous Electrodes Using Soft X-ray Absorption Spectroscopy

It is widely accepted that solid electrolyte interphase (SEI) layer of carbonaceous material is formed by irreversible decomposition reaction of an electrolyte, and acts as a passivation layer to prevent further decomposition of the electrolyte, ensuring reliable operation of a Li-ion battery. On the other hand, recent studies have reported that some transition metal oxide anode materials undergo reversible decomposition of an organic electrolyte during cycling, which is completely different from carbonaceous anode materials. In this work, we revisit the electrochemical reaction of an electrolyte that produces SEI layer on the surface of carbonaceous anode materials using soft X-ray absorption spectroscopy. We discover that the reversible formation and decomposition of SEI layer are also able to occur on the carbonaceous materials in both Li- and Na-ion battery systems. These new findings on the unexpected behavior of SEI in the carbonaceous anode materials revealed by soft X-ray absorption spectroscopy would be highly helpful in more comprehensive understanding of the interfacial chemistry of carbonaceous anode materials in Li- and Na-ion batteries.

Iron-Catalyzed Graphitic Carbon Materials from Biomass Resources as Anodes for Lithium-Ion Batteries

Graphitized carbon materials from biomass resources were successfully synthesized with an iron catalyst, and their electrochemical performance as anode materials for lithium-ion batteries (LIBs) was investigated. Peak pyrolysis temperatures between 850 and 2000 °C were covered to study the effect of crystallinity and microstructural parameters on the anodic behavior, with a focus on the first-cycle Coulombic efficiency, reversible specific capacity, and rate performance. In terms of capacity, results at the highest temperatures are comparable to those of commercially used synthetic graphite derived from a petroleum coke precursor at higher temperatures, and up to twice as much as that of uncatalyzed biomass-derived carbons. The opportunity to graphitize low-cost biomass resources at moderate temperatures through this one-step environmentally friendly process, and the positive effects on the specific capacity, make it interesting to develop more sustainable graphite-based anodes for LIBs.

Sustainable Waste Tire Derived Carbon Material as a Potential Anode for Lithium-Ion Batteries

The rapidly growing automobile industry increases the accumulation of end-of-life tires each year throughout the world. Waste tires lead to increased environmental issues and lasting resource problems. Recycling hazardous wastes to produce value-added products is becoming essential for the sustainable progress of society. A patented sulfonation process followed by pyrolysis at 1100 °C in a nitrogen atmosphere was used to produce carbon material from these tires and utilized as an anode in lithium-ion batteries. The combustion of the volatiles released in waste tire pyrolysis produces lower fossil CO2 emissions per unit of energy (136.51 gCO2/kW·h) compared to other conventional fossil fuels such as coal or fuel–oil, usually used in power generation. The strategy used in this research may be applied to other rechargeable batteries, supercapacitors, catalysts, and other electrochemical devices. The Raman vibrational spectra observed on these carbons show a graphitic carbon with significant disorder structure. Further, structural studies reveal a unique disordered carbon nanostructure with a higher interlayer distance of 4.5 Å compared to 3.43 Å in the commercial graphite. The carbon material derived from tires was used as an anode in lithium-ion batteries exhibited a reversible capacity of 360 mAh/g at C/3. However, the reversible capacity increased to 432 mAh/g at C/10 when this carbon particle was coated with a thin layer of carbon. A novel strategy of prelithiation applied for improving the first cycle efficiency to 94% is also presented.

Organometallic Precursor-Derived SnO2/Sn-Reduced Graphene Oxide Sandwiched Nanocomposite Anode with Superior Lithium Storage Capacity

Benefiting from the reversible conversion reaction upon delithiation, nanosized SnO₂, with its theoretical capacity of 1494 mA h g^-1, has gained special attention as a promising anode material. Here, we report a self-assembled SnO₂/Sn-reduced graphene oxide (rGO) sandwich nanocomposite developed by organometallic precursor coating and in situ transformation. Ultrafine SnO₂ nanoparticles with an average diameter of 5 nm are sandwiched within the rGO/carbonaceous network, which not only greatly alleviates the volume changes upon lithiation and aggregation of SnO₂ nanoparticles but also facilitates the charge transfer and reaction kinetics of SnO₂ upon lithiation/delithiation. As a result, the SnO₂/Sn-rGO nanocomposite exhibited a superior lithium storage capacity with a reversible capacity of 1307 mA h g^-1 at a current density of 80 mA g^-1 in the potential window of 0.01-2.5 V versus Li⁺/Li and showed a reversible capacity of 767 mA h g^-1 over 200 cycles at a current density of 400 mA g^-1. When cycling at a higher current density of 1600 mA g^-1, the SnO₂/Sn-rGO nanocomposite showed a highly stable capacity of 449 mA g^-1 without obvious decay after 400 cycles.

Binding Energy Referencing for XPS in Alkali Metal-Based Battery Materials Research (II): Application to Complex Composite Electrodes

X-ray photoelectron spectroscopy (XPS) is a key method for studying (electro-)chemical changes in metal-ion battery electrode materials. In a recent publication, we pointed out a conflict in binding energy (BE) scale referencing at alkali metal samples, which is manifested in systematic deviations of the BEs up to several eV due to a specific interaction between the highly reactive alkali metal in contact with non-conducting surrounding species. The consequences of this phenomenon for XPS data interpretation are discussed in the present manuscript. Investigations of phenomena at surface-electrolyte interphase regions for a wide range of materials for both lithium and sodium-based applications are explained, ranging from oxide-based cathode materials via alloys and carbon-based anodes including appropriate reference chemicals. Depending on material class and alkaline content, specific solutions are proposed for choosing the correct reference BE to accurately define the BE scale. In conclusion, the different approaches for the use of reference elements, such as aliphatic carbon, implanted noble gas or surface metals, partially lack practicability and can lead to misinterpretation for application in battery materials. Thus, this manuscript provides exemplary alternative solutions.

Waterborne polyurethane as a carbon coating for micrometre-sized silicon-based lithium-ion battery anode material

Waterborne polyurethane (WPU) is first used as a carbon-coating source for micrometre-sized silicon. The remaining nitrogen (N) and oxygen (O) heteroatoms during pyrolysis of the WPU interact with the surface oxide on the silicon (Si) particles via hydrogen bonding (Si-OH⋯N and Si-OH⋯O). The N and O atoms involved in the carbon network can interact with the lithium ions, which is conducive to lithium-ion insertion. A satisfactory performance of the Si@N, O-doped carbon (Si@CNO) anode is gained at 25 and 55°C. The Si@CNO anode shows stable cycling performance (capacity retention of 70.0% over 100 cycles at 25°C and 60.3% over 90 cycles at 55°C with a current density of 500 mA g^-1) and a superior rate capacity of 864.1 mA h g^-1 at 1000 mA g^-1 (25°C). The improved electrochemical performance of the Si@CNO electrode is attributed to the enhanced electrical conductivity and structural stability.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of M_x V_y O_x+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm^-2 (which equals to 1676.8 mAh g^-1 ) at a current density of 200 mA g^-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm^-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.

Nanoscale Electrical Degradation of Silicon-Carbon Composite Anode Materials for Lithium-Ion Batteries

High-performance lithium-ion batteries (LIBs) are in increasing demand for a variety of applications in rapidly growing energy-related fields including electric vehicles. To develop high-performance LIBs, it is necessary to comprehensively understand the degradation mechanism of the LIB electrodes. From this viewpoint, it is crucial to investigate how the electrical properties of LIB electrodes change under charging and discharging. Here, we probe the local electrical properties of LIB electrodes with nanoscale resolution by scanning spreading resistance microscopy (SSRM). Via quantitative and comparative SSRM measurements on pristine and degraded LIB anodes of Si-C composites blended with graphite (Gr) particles, the electrical degradation of the LIB anodes is visualized. The electrical conductivity of the Si-C composite particles considerably degraded over 300 cycles of charging and discharging, whereas the Gr particles maintained their conductivity.

Stable Metal Anode enabled by Porous Lithium Foam with Superior Ion Accessibility

Lithium (Li) metal anodes have attracted much interest recently for high-energy battery applications. However, low coulombic efficiency, infinite volume change, and severe dendrite formation limit their reliable implementation over a wide range. Here, an outstanding stability for a Li metal anode is revealed by designing a highly porous and hollow Li foam. This unique structure is capable of tackling many Li metal problems simultaneously: first, it assures uniform electrolyte distribution over the inner and outer electrode's surface; second, it reduces the local current density by providing a larger electroactive surface area; third, it can accommodate volume expansion and dissipate heat efficiently. Moreover, the structure shows superior stability compared to fully Li covered foam with low porosity, and bulky Li foil electrode counterparts. This Li foam exhibits small overpotential (≈25 mV at 4 mA cm^-2 ) and high cycling stability for 160 cycles at 4 mA cm^-2 . Furthermore, when assembled, the porous Li metal as the anode with LiFePO₄ as the cathode for a full cell, the battery has a high-rate performance of 138 mAh g^-1 at 0.2 C. The beneficial structure of the Li hollow foam is further studied through density functional theory simulations, which confirms that the porous structure has better charge mobility and more uniform Li deposition.

Stabilization of planar tetra-coordinate silicon in a 2D-layered extended system and design of a high-capacity anode material for Li-ion batteries

Stabilization of planar tetra-coordinate silicon (ptSi) was achieved in compounds and 2D-layered extended systems, in which single molecular ptSi in C₁₂H₈Si captures four additional electrons to maintain a stable planar structure while the extending conjugate interactions are responsible for the stabilization of ptSi in the 2D sheet. Based on the ptSi SiC₁₂ building block, a SiC₈ siligraphene 2D sheet was constructed, and each of its ptSi could accommodate six lithium atoms. The electronic and lithium-storage properties of the ptSi 2D network were explored using first-principles calculations and ab initio molecular dynamics (AIMD) simulations. The newly designed 2D SiC₈ sheet has high thermal and dynamic stability, good electronic conductivity, strong lithium-storage ability, a large theoretical capacity of 1297 mA h g^-1, and facile surface diffusion of Li and Li⁺. The predicted relatively high average cell voltages from 2.24 to 2.47 V are fairly stable as the lithium content varies. These unique properties of the 2D SiC₈ sheet with ptSi make it quite appealing as a novel anode material for high-performance Li-ion batteries (LIBs).

30 Years of Lithium-Ion Batteries

Over the past 30 years, significant commercial and academic progress has been made on Li-based battery technologies. From the early Li-metal anode iterations to the current commercial Li-ion batteries (LIBs), the story of the Li-based battery is full of breakthroughs and back tracing steps. This review will discuss the main roles of material science in the development of LIBs. As LIB research progresses and the materials of interest change, different emphases on the different subdisciplines of material science are placed. Early works on LIBs focus more on solid state physics whereas near the end of the 20th century, researchers began to focus more on the morphological aspects (surface coating, porosity, size, and shape) of electrode materials. While it is easy to point out which specific cathode and anode materials are currently good candidates for the next-generation of batteries, it is difficult to explain exactly why those are chosen. In this review, for the reader a complete developmental story of LIB should be clearly drawn, along with an explanation of the reasons responsible for the various technological shifts. The review will end with a statement of caution for the current modern battery research along with a brief discussion on beyond lithium-ion battery chemistries.

Free-standing nitrogen-doped graphene paper for lithium storage application

A flexible free-standing nitrogen-doped graphene paper (N-GP) is fabricated via a facile hydrothermal approach with doping reaction occurring at the solid/gas interface of graphene oxide and ammonia vapor. Ammonia not only facilitates the doping of oxidized graphene paper efficiently with a nitrogen doping level of ca. 6.81%, but also promotes its reduction. The electrochemical properties of N-GP as an anode of lithium ion batteries (LIB) are evaluated and N-GP delivers almost doubled reversible discharge capacity compared to the undoped graphene paper (GP) as well as a good cyclic stability and rate performance. The proposed strategy to realize simultaneous reduction and nitrogen doping of graphene oxide via hydrothermal approach at the solid/gas interface offers a green and facile solution to modify graphene paper with desired electrochemical performances for LIB application.

Understanding Fundamentals and Reaction Mechanisms of Electrode Materials for Na-Ion Batteries

Development of efficient, affordable, and sustainable energy storage technologies has become an area of interest due to the worsening environmental issues and rising technological dependence on Li-ion batteries. Na-ion batteries (NIBs) have been receiving intensive research efforts during the last few years. Owing to their potentially low cost and relatively high energy density, NIBs are promising energy storage devices, especially for stationary applications. A fundamental understanding of electrode properties during electrochemical reactions is important for the development of low cost, high-energy density, and long shelf life NIBs. This Review aims to summarize and discuss reaction mechanisms of the major types of NIB electrode materials reported. By appreciating how the material works and the fundamental flaws it possesses, it is hoped that this Review will assist readers in coming up with innovative solutions for designing better materials for NIBs.

Metallic VO2 monolayer as an anode material for Li, Na, K, Mg or Ca ion storage: a first-principle study

Using density functional theory (DFT), we assess the suitability of monolayer VO2 as promising electrode materials for Li, Na, K, Mg and Ca ion batteries. The metallic VO2 monolayer can offer an intrinsic advantage for the transportation of electrons in materials. The results suggest that VO2 can provide excellent mobility with lower diffusion barriers of 0.043 eV for K, 0.119 eV for Li, 0.098 eV for Na, 0.517 eV for Mg, and 0.306 eV for Ca. The specific capacities of Li, Na and Mg can reach up to 968, 613 and 815 mA h g-1 respectively, which are significantly larger than the corresponding value of graphite. Herein, with high open-circuit voltage the VO2 sheet could be a promising candidate for the anode material in battery applications.

Bimetallic junction mediated synthesis of multilayer graphene edges towards ultrahigh capacity for lithium ion batteries

In this work, we report on a novel strategy to synthesize high-density graphene edges on a vertically-aligned nanorod array substrate based on multiple segmented Ni-Au units. The growth of graphene layers on Ni and Au was performed by chemical vapor deposition (CVD) leading to the effective generation of edge-rich multilayer graphene due to the distinct carbon solubility. The composite material was applied as an anode in a lithium ion battery (LIB) whose discharging capacity was found to closely depend on the total number of Ni-Au junctions within the vertical nanorods. Graphene deposited on the 19-junction composite Ni-(Au-Ni)₉ exhibited an ultrahigh capacity of 86.3 μAh cm^-2 at 50 μA cm^-2 which was much higher than graphene deposited on 1-junction, 2-junction and pure Ni nanorods. This ultrahigh capacity was mainly ascribed to the generation of high-density graphene edges engineered by the bimetallic junction. The proposed strategy opens new appealing routes to synthesize high-density graphene edges using bimetallic junctions, which is promising for increasing the performance of LIBs and other electrochemical energy systems (supercapacitors, fuel cells, etc.).

A Tunable Molten-Salt Route for Scalable Synthesis of Ultrathin Amorphous Carbon Nanosheets as High-Performance Anode Materials for Lithium-Ion Batteries

Amorphous carbon is regarded as a promising alternative to commercial graphite as the lithium-ion battery anode due to its capability to reversibly store more lithium ions. However, the structural disorder with a large number of defects can lead to low electrical conductivity of the amorphous carbon, thus limiting its application for high power output. Herein, ultrathin amorphous carbon nanosheets were prepared from petroleum asphalt through tuning the carbonization temperature in a molten-salt medium. The amorphous nanostructure with expanded carbon interlayer spacing can provide substantial active sites for lithium storage, while the two-dimensional (2D) morphology can facilitate fast electrical conductivity. As a result, the electrodes deliver a high reversible capacity, outstanding rate capability, and superior cycling performance (579 and 396 mAh g^-1 at 2 and 5 A g^-1 after 900 cycles). Furthermore, full cells consisting of the carbon anodes coupled with LiMn₂O₄ cathodes exhibit high specific capacity (608 mAh g^-1 at 50 mA g^-1) and impressive cycling stability with slow capacity loss (0.16% per cycle at 200 mA g^-1). The present study not only paves the way for industrial-scale synthesis of advanced carbon materials for lithium-ion batteries but also deepens the fundamental understanding of the intrinsic mechanism of the molten-salt method.

Towards K-Ion and Na-Ion Batteries as "Beyond Li-Ion"

Li-ion battery commercialized by Sony in 1991 has the highest energy-density among practical rechargeable batteries and is widely used in electronic devices, electric vehicles, and stationary energy storage system in the world. Moreover, the battery market is rapidly growing in the world and further fast-growing is expected. With expansion of the demand and applications, price of lithium and cobalt resources is increasing. We are, therefore, motivated to study Na- and K-ion batteries for stationary energy storage system because of much abundant Na and K resources and the wide distribution in the world. In this account, we review developments of Na- and K-ion batteries with mainly introducing our previous and present researches in comparison to that of Li-ion battery.

Flexible anode materials for lithium-ion batteries derived from waste biomass-based carbon nanofibers: I. Effect of carbonization temperature

Carbon nanofibers (CNFs) with excellent electrochemical performance represent a novel class of carbon nanostructures for boosting electrochemical applications, especially sustainable electrochemical energy conversion and storage applications. This work builds on an earlier study where the CNFs were prepared from a waste biomass (walnut shells) using a relatively simple procedure of liquefying the biomass, and electrospinning and carbonizing the fibrils. We further improved the mass ratio of the liquefying process and investigated the effects of the high temperature carbonization process at 1000, 1500 and 2000 °C, and comprehensively characterized the morphology, structural properties, and specific surface area of walnut shell-derived CNFs; and their electrochemical performance was also investigated as electrode materials in Li-ion batteries. Results demonstrated that the CNF anode obtained at 1000 °C exhibits a high specific capacity up to 271.7 mA h g-1 at 30 mA g-1, good rate capacity (131.3 and 102.2 mA h g-1 at 1 A g-1 and 2 A g-1, respectively), and excellent cycling performance (above 200 mA h g-1 specific capacity without any capacity decay after 200 cycles at 100 mA g-1). The present work demonstrates the great potential for converting low-cost biomass to high-value carbon materials for applications in energy storage.

Capacity Fading Mechanism of the Commercial 18650 LiFePO4-Based Lithium-Ion Batteries: An in Situ Time-Resolved High-Energy Synchrotron XRD Study

In situ high-energy synchrotron XRD studies were carried out on commercial 18650 LiFePO₄ cells at different cycles to track and investigate the dynamic, chemical, and structural changes in the course of long-term cycling to elucidate the capacity fading mechanism. The results indicate that the crystalline structural deterioration of the LiFePO₄ cathode and the graphite anode is unlikely to happen before capacity fades below 80% of the initial capacity. Rather, the loss of the active lithium source is the primary cause for the capacity fade, which leads to the appearance of inactive FePO₄ that is proportional to the absence of the lithium source. Our in situ HESXRD studies further show that the lithium-ion insertion and deinsertion behavior of LiFePO₄ continuously changed with cycling. For a fresh cell, the LiFePO₄ experienced a dual-phase solid-solution behavior, whereas with increasing cycle numbers, the dynamic change, which is characteristic of the continuous decay of solid solution behavior, is obvious. The unpredicted dynamic change may result from the morphology evolution of LiFePO₄ particles and the loss of the lithium source, which may be the cause of the decreased rate capability of LiFePO₄ cells after long-term cycling.

Neutron vibrational spectroscopic studies of novel tire-derived carbon materials

Sulfonated tire-derived carbons have been demonstrated to be high value-added carbon products of tire recycling in several energy storage system applications including lithium, sodium, potassium ion batteries and supercapacitors. In this communication, we compared different temperature pyrolyzed sulfonated tire-derived carbons with commercial graphite and unmodified/non-functionalized tire-derived carbon by studying the surface chemistry and properties, vibrational spectroscopy of the molecular structure, chemical bonding such as C-H bonding, and intermolecular interactions of the carbon materials. The nitrogen adsorption-desorption studies revealed the tailored micro and meso pore size distribution of the carbon during the sulfonation process. XPS and neutron vibrational spectra showed that the sulfonation of the initial raw tire powders could remove the aliphatic hydrogen containing groups ([double bond splayed left]CH₂ and -CH₃ groups) and reduce the number of heteroatoms that connect to carbon. The absence of these functional groups could effectively improve the first cycle efficiency of the material in rechargeable batteries. Meanwhile, the introduced -SO₃H functional group helped in producing terminal H at the edge of the sp² bonded graphite-like layers. This study reveals the influence of the sulfonation process on the recovered hard carbon from used tires and provides a pathway to develop and improve advanced energy storage materials.

A Single-Step Hydrothermal Route to 3D Hierarchical Cu2 O/CuO/rGO Nanosheets as High-Performance Anode of Lithium-Ion Batteries

As anodes of Li-ion batteries, copper oxides (CuO) have a high theoretical specific capacity (674 mA h g^-1 ) but own poor cyclic stability owing to the large volume expansion and low conductivity in charges/discharges. Incorporating reduced graphene oxide (rGO) into CuO anodes with conventional methods fails to build robust interaction between rGO and CuO to efficiently improve the overall anode performance. Here, Cu₂ O/CuO/reduced graphene oxides (Cu₂ O/CuO/rGO) with a 3D hierarchical nanostructure are synthesized with a facile, single-step hydrothermal method. The Cu₂ O/CuO/rGO anode exhibits remarkable cyclic and high-rate performances, and particularly the anode with 25 wt% rGO owns the best performance among all samples, delivering a record capacity of 550 mA h g^-1 at 0.5 C after 100 cycles. The pronounced performances are attributed to the highly efficient charge transfer in CuO nanosheets encapsulated in rGO network and the mitigated volume expansion of the anode owing to its robust 3D hierarchical nanostructure.

Low Li+ Insertion Barrier Carbon for High Energy Efficient Lithium-Ion Capacitor

Lithium-ion capacitor (LIC) is an attractive energy-storage device (ESD) that promises high energy density at moderate power density. However, the key challenge in its design is the low energy efficient negative electrode, which barred the realization of such research system in fulfilling the current ESD technological inadequacy due to its poor overall energy efficiency. Large voltage hysteresis is the main issue behind high energy density alloying/conversion-type materials, which reduces the electrode energy efficiency. Insertion-type material though averted in most research due to the low capacity remains to be highly favorable in commercial application due to its lower voltage hysteresis. To further reduce voltage hysteresis and increase capacity, amorphous carbon with wider interlayer spacing has been demonstrated in the simulation result to significantly reduce Li⁺ insertion barrier. Hence, by employing such amorphous carbon, together with disordered carbon positive electrode, a high energy efficient LIC with round-trip energy efficiency of 84.3% with a maximum energy density of 133 Wh kg^-1 at low power density of 210 W kg^-1 can be achieved.

Carbon with Expanded and Well-Developed Graphene Planes Derived Directly from Condensed Lignin as a High-Performance Anode for Sodium-Ion Batteries

In this study, we demonstrate that lignin, which constitutes 30-40 wt % of the terrestrial lignocellulosic biomass and is produced from second generation biofuel plants as a cheap byproduct, is an excellent precursor material for sodium-ion battery (NIB) anodes. Because it is rich in aromatic monomers that are highly cross-linked by ether and condensed bonds, the lignin material carbonized at 1300 °C (C-1300) in this study has small graphitic domains with well-developed graphene layers, a large interlayer spacing (0.403 nm), and a high micropore surface area (207.5 m² g^-1). When tested as an anode in an NIB, C-1300 exhibited an initial Coulombic efficiency of 68% and a high reversible capacity of 297 mA h g^-1 at 50 mA g^-1 after 50 cycles. The high capacity of 199 mA h g^-1 at less than 0.1 V with a flat voltage profile and an extremely low charge-discharge voltage hysteresis (<0.03 V) make C-1300 a promising energy-dense electrode material. In addition, C-1300 exhibited an excellent high-rate performance of 116 mA h g^-1 at 2.5 A g^-1 and showed stable cycling retention (0.2% capacity decay per cycle after 500 cycles). By comparing the properties of the lignin-derived carbon with oak sawdust-derived and sugar-derived carbons and a low-temperature carbonized sample (900 °C), the reasons for the excellent performance of C-1300 were determined to result from facilitated Na⁺-ion transport to the graphitic layer and the microporous regions that penetrate through the less defective and enlarged interlayer spacings.

A 3D MoOx/carbon composite array as a binder-free anode in lithium-ion batteries

A 3D aligned MoO_x/carbon composite anode displays good cycle capacity in binder free lithium ion battery applications.

Mesopore-dominant nitrogen-doped carbon with a large defect degree and high conductivity via inherent hydroxyapatite-induced self-activation for lithium-ion batteries

In this study, N-doped mesopore-dominant carbon (NMC) materials were prepared using bio-waste tortoise shells as a carbon source via a one-step self-activation process. With intrinsic hydroxyapatites (HAPs) as natural templates to fulfill the synchronous carbonization and activation of the precursor, this highly efficient and time-saving method provides N-doped carbon materials that represent a large mesopore volume proportion of 74.59%, a high conductivity of 4382 m S⁻¹, as well as larger defects, as demonstrated by Raman and XRD studies. These features make the NMC exhibit a high reversible lithium-storage capacity of 970 mA h g⁻¹ at 0.1 A g⁻¹, a strong rate capability of 818 mA h g⁻¹ at 2 A g⁻¹, and a good capacity of 831 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. This study provides a highly efficient and feasible method to prepare renewable biomass-derived carbons as advanced electrode materials for the application of energy storage.

A hydroxyapatite-induced self-activation method has been used to prepare nitrogen-doped mesopore-dominant carbon. The carbon has abundant macro/mesopores, high conductivity, and favorable defects and exhibited high-performance in LIBs.

Ionic liquids and derived materials for lithium and sodium batteries

A comprehensive review of various applications of ionic liquids and derived materials in lithium and sodium batteries with an emphasis on recent advances.

Wearable energy sources based on 2D materials

This review provides the most recent advances in wearable energy sources based on 2D materials, and highlights the crucial roles 2D materials play in the wearable energy sources.

First-principles study of dual-doped graphene: towards promising anode materials for Li/Na-ion batteries

The interaction of Li/Na with various DDG is studied with the help of DFT. Among them, the Be–B DDG systems exhibit exceptional properties, such as large storage capacities, excellent OCVs, good electronic conductivities, and minor changes in their planes. These properties show that Be–B DDG can serve as promising anode materials for LIBs/SIBs.