Self-terminating, heterogeneous solid-electrolyte interphase enables reversible Li-ether cointercalation in graphite anodes.

Ether solvents are suitable for formulating solid-electrolyte interphase (SEI)-less ion-solvent cointercalation electrolytes in graphite for Na-ion and K-ion batteries. However, ether-based electrolytes have been historically perceived to cause exfoliation of graphite and cell failure in Li-ion batteries. In this study, we develop strategies to achieve reversible Li-solvent cointercalation in graphite through combining appropriate Li salts and ether solvents. Specifically, we design 1M LiBF4 1,2-dimethoxyethane (G1), which enables natural graphite to deliver ~91% initial Coulombic efficiency and >88% capacity retention after 400 cycles. We captured the spatial distribution of LiF at various length scales and quantified its heterogeneity. The electrolyte shows self-terminated reactivity on graphite edge planes and results in a grainy, fluorinated pseudo-SEI. The molecular origin of the pseudo-SEI is elucidated by ab initio molecular dynamics (AIMD) simulations. The operando synchrotron analyses further demonstrate the reversible and monotonous phase transformation of cointercalated graphite. Our findings demonstrate the feasibility of Li cointercalation chemistry in graphite for extreme-condition batteries. The work also paves the foundation for understanding and modulating the interphase generated by ether electrolytes in a broad range of electrodes and batteries.

Diamond formation mechanism in chemical vapor deposition.

It is a key challenge to prepare large-area diamonds by using the methods of high-pressure high-temperature and normal chemical vapor deposition (CVD). The formation mechanism of thermodynamically metastable diamond compared to graphite in low-pressure CVD possibly implies a distinctive way to synthesize large-area diamonds, while it is an intriguing problem due to the limitation of in situ characterization in this complex growth environment. Here, we design a series of short-term growth on the margins of cauliflower-like nanocrystalline diamond particles, allowing us to clearly observe the diamond formation process. The results show that vertical graphene sheets and nanocrystalline diamonds alternatively appear, in which vertical graphene sheets evolve into long ribbons and graphite needles, and they finally transform into diamonds. A transition process from graphite (200) to diamond (110) verifies the transformation, and Ta atoms from hot filaments are found to atomically disperse in the films. First principle calculations confirm that Ta-added H- or O-terminated bilayer graphene spontaneously transforms into diamond. This reveals that in the H, O, and Ta complex atmosphere of the CVD environment, diamond is formed by phase transformation from graphite. This subverts the general knowledge that graphite is etched by hydrogen and sp3 carbon species pile up to form diamond and supplies a way to prepare large-area diamonds based on large-sized graphite under normal pressure. This also provides an angle to understand the growth mechanism of materials with sp2 and sp3 electronic configurations.

All van der Waals Semiconducting PtSe2 Field Effect Transistors with Low Contact Resistance Graphite Electrodes.

Contact resistance is a multifaceted challenge faced by the 2D materials community. Large Schottky barrier heights and gap-state pinning are active obstacles that require an integrated approach to achieve the development of high-performance electronic devices based on 2D materials. In this work, we present semiconducting PtSe2 field effect transistors with all-van-der-Waals electrode and dielectric interfaces. We use graphite contacts, which enable high ION/IOFF ratios up to 109 with currents above 100 µA µm-1 and mobilities of 50 cm2 V-1 s-1 at room temperature and over 400 cm2 V-1 s-1 at 10 K. The devices exhibit high stability with a maximum hysteresis width below 36 mV nm-1. The contact resistance at the graphite-PtSe2 interface is found to be below 700 Ω µm. Our results present PtSe2 as a promising candidate for the realization of high-performance 2D circuits built solely with 2D materials.

Direct Determination of Torsion in Twisted Graphite and MoS2 Interfaces.

The design space of two-dimensional materials is undergoing significant expansion through the stacking of layers in non-equilibrium configurations. However, the lack of quantitative insights into twist dynamics impedes the development of such heterostructures. Herein, we utilize the lateral force sensitivity of an atomic force microscope cantilever and specially designed rotational bearing structures to measure the torque in graphite and MoS2 interfaces. While the extracted torsional energies are virtually zero across all angular misfit configurations, commensurate interfaces of graphite and MoS2 are characterized by values of 0.1533 and 0.6384 N-m/m2, respectively. Furthermore, we measured the adhesion energies of graphite and MoS2 to elucidate the interplay between twist and slide. The adhesion energy dominates over the torsional energy for the graphitic interface, suggesting a tendency to twist prior to superlubric sliding. Conversely, MoS2 displays an increased torsional energy exceeding its adhesion energy. Consequently, our findings demonstrate a fundamental disparity between the sliding-to-twisting dynamics at MoS2 and graphite interfaces.

Large and Pressure-Dependent c-Axis Piezoresistivity of Highly Oriented Pyrolytic Graphite near Zero Pressure.

The c-axis piezoresistivity is a fundamental and important parameter of graphite, but its value near zero pressure has not been well determined. Herein, a new method for studying the c-axis piezoresistivity of van der Waals materials near zero pressure is developed on the basis of in situ scanning electron microscopy and finite element simulation. The c-axis piezoresistivity of microscale highly oriented pyrolytic graphite (HOPG) is found to show a large value of 5.68 × 10-5 kPa-1 near zero pressure and decreases by 2 orders of magnitude to the established value of ∼10-7 kPa-1 when the pressure increases to 200 MPa. By modulating the serial tunneling barrier model on the basis of the stacking faults, we describe the c-axis electrical transport of HOPG under compression. The large c-axis piezoresistivity near zero pressure and its large decrease in magnitude with pressure are attributed to the rapid stiffening of the electromechanical properties under compression.

Probing the range of applicability of structure- and energy-adjusted QM/MM link bonds III: QM/MM MD simulations of solid-state systems at the example of layered carbon structures.

The previously introduced workflow to achieve an energetically and structurally optimized description of frontier bonds in quantum mechanical/molecular mechanics (QM/MM)-type applications was extended into the regime of computational material sciences at the example of a layered carbon model systems. Optimized QM/MM link bond parameters at HSEsol/6-311G(d,p) and self-consistent density functional tight binding (SCC-DFTB) were derived for graphitic systems, enabling detailed investigation of specific structure motifs occurring in graphene-derived structures v i a quantum-chemical calculations. Exemplary molecular dynamics (MD) simulations in the isochoric-isothermic (NVT) ensemble were carried out to study the intercalation of lithium and the properties of the Stone-Thrower-Wales defect. The diffusivity of lithium as well as hydrogen and proton adsorption on a defective graphene surface served as additional example. The results of the QM/MM MD simulations provide detailed insight into the applicability of the employed link-bond strategy when studying intercalation and adsorption properties of graphitic materials.

A Slightly Expanded Graphite Anode with High Capacity Enabled By Stable Lithium-Ion/Metal Hybrid Storage.

Integrating lithium-ion and metal storage mechanisms to improve the capacity of graphite anode holds the potential to boost the energy density of lithium-ion batteries. However, this approach, typically plating lithium metal onto traditional graphite anodes, faces challenges of safety risks of severe lithium dendrite growth and short circuits due to restricted lithium metal accommodation space and unstable lithium plating in commercial carbonate electrolytes. Herein, a slightly expanded spherical graphite anode is developed with a precisely adjustable expanded structure to accommodate metallic lithium, achieving a well-balanced state of high capacity and stable lithium-ion/metal storage in commercial carbonate electrolytes. This structure also enables fast kinetics of both Li intercalation/de-intercalation and plating/stripping. With a total anode capacity of 1.5 times higher (558 mAh g-1) than graphite, the full cell coupled with a high-loading LiNi0.8Co0.1Mn0.1O2 cathode (13 mg cm-2) under a low N/P ratio (≈1.15) achieves long-term cycling stability (75% of capacity after 200 cycles, in contrast to the fast battery failure after 50 cycles with spherical graphite anode). Furthermore, the capacity of the full cell also reaches a low capacity decay rate of 0.05% per cycle at 0.2 C under the low temperature of -20 °C.

Waste to Wealth: One-Step Exfoliating of Spent Graphite to Build a Low-Cost Cathode for Lithium-Sulfur Batteries.

With the booming development of Li-ion batteries (LIBs), the recycling and reusing of spent graphite (SG) from LIBs is becoming increasingly crucial. Meanwhile, developing low-cost and efficient carbon hosts for lithium-sulfur (Li-S) batteries has gained widespread attention in the past decade. Nevertheless, the processing of carbon materials as sulfur hosts is often energy-consuming and complex. Herein, a simple and environmental-friendly strategy is proposed to reuse the SG to prepare graphene/sulfur composite cathode for Li-S batteries. Due to expanded layer spacing and defects of SG, sulfur molecules can strip it into a graphene-type host via ball milling. By optimizing the S/SG ratio and ball milling time, the as-prepared graphene/sulfur composite cathode with 70 wt.% sulfur content exhibits a high capacity of 1000 mAh g-1. With a high sulfur loading of 4.68 mg cm-2, the graphene/sulfur cathode can maintain 526 mAh g-1 after 400 cycles. This work provides a novel waste-to-wealth perspective for recycling spent graphite from LIBs to reuse in Li-S batteries.

Construction of 3D Fibonacci Cauliflower-Like NiCo2S4/Expanded Graphite Heterogeneous Structures for Enhanced Electromagnetic Wave Absorption.

Highly efficient electromagnetic wave (EMW)-absorbing multicomposites can be fabricated by constructing particular structures using suitable components. Expanded graphite (EG) has a 3D, low-density porous structure; however, it suffers from poor impedance matching and EMW absorption properties. Based on this information, in the present study, NiCo2S4 components with different morphologies are successfully loaded onto a 3D EG surface using a facile microwave solvothermal method to achieve a synergistic effect between the different components. The NiCo2S4 content is adjusted to alter the compositional morphology and electromagnetic parameters of the composites to achieve impedance-matching and obtain excellent EMW absorption properties. The heterogeneous interface between EG and NiCo2S4 induces an inhomogeneous spatial charge distribution and enhances interfacial polarization. The defects in the material and oxygen-containing groups induce dipole polarization, which enhances the polarization-relaxation process of the composites. The 3D porous heterostructure of the "Fibonacci cauliflower"-shaped NiCo2S4/EG composites results in an optimal reflection loss of -64.93 dB at a filler rate of only 14 wt.%. Analysis of the synergistic conduction loss and polarization loss mechanisms in carbon-based materials with heterogeneous interfaces has led to the development of excellent EMW absorption materials.

Interphase Engineering Enhanced Electro-chemical Stability of Prelithiated Anode.

Prelithiation is an essential technology to compensate for the initial lithium loss of lithium-ion batteries due to the formation of solid electrolyte interphase (SEI) and irreversible structure change. However, the prelithiated materials/electrodes become more reactive with air and electrolyte resulting in unwanted side reactions and contaminations, which makes it difficult for the practical application of prelithiation technology. To address this problem, herein, interphase engineering through a simple solution treatment after chemical prelithiation is proposed to protect the prelithiated electrode. The used solutions are carefully selected, and the composition and nanostructure of the as-formed artificial SEIs are revealed by cryogenic electron microscopy and X-ray photoelectron spectroscopy. The electrochemical evaluation demonstrates the unique merits of this artificial SEI, especially for the fluorinated interphase, which not only enhances the interfacial ion transport but also increases the tolerance of the prelithiated electrode to the air. The treated graphite electrode shows an initial Coulombic efficiency of 129.4%, a high capacity of 170 mAh g-1 at 3 C, and negligible capacity decay after 200 cycles at 1 C. These findings not only provide a facile, universal, and controllable method to construct an artificial SEI but also enlighten the upgrade of battery fabrication and the alternative use of advanced electrolytes.

A Durable and High-Voltage Mn-Graphite Dual-Ion Battery Using Mn-Based Hybrid Electrolytes.

Rechargeable Mn-metal batteries (MMBs) can attract considerable attention because Mn has the intrinsic merits including high energy density (976 mAh g-1), high air stability, and low toxicity. However, the application of Mn in rechargeable batteries is limited by the lack of proper cathodes for reversible Mn2+ intercalation/de-intercalation, thus leading to low working voltage (<1.8 V) and poor cycling stability (≤200 cycles). Herein, a high-voltage and durable MMB with graphite as the cathode is successfully constructed using a LiPF6-Mn(TFSI)2 hybrid electrolyte, which shows a high discharge voltage of 2.34 V and long-term stability of up to 1000 cycles. Mn(TFSI)2 can reduce the plating/stripping overpotential of Mn ions, while LiPF6 can efficiently improve the conductivity of the electrolyte. Electrochemical in-situ characterization implies the dual-anions intercalation/de-intercalation at the cathode and Mn2+ plating/stripping reaction at the anode. Theoretical calculations unveil the top site of graphite is the energetically favorable for anions intercalation and TFSI- shows the low migration barrier. This work paves an avenue for designing high-performance rechargeable MMBs towards electricity storage.

3D Pathways Enabling Highly-Efficient Lithium Reservoir for Fast-Charging Batteries.

Enhancing the mobility of lithium-ions (Li+) through surface engineering is one of major challenges facing fast-charging lithium-ion batteries (LIBs). In case of demanding charging conditions, the use of a conventional artificial graphite (AG) anode leads to an increase in operating temperature and the formation of lithium dendrites on the anode surface. In this study, a biphasic zeolitic imidazolate framework (ZIF)-AG anode, designed strategically and coated with a mesoporous material, is verified to improve the pathways of Li+ and electrons under a high charging current density. In particular, the graphite surface is treated with a coating of a ZIF-8-derived carbon nanoparticles, which addresses sufficient surface porosity, enabling this material to serve as an electrolyte reservoir and facilitate Li+ intercalation. Moreover, the augmentation in specific surface area proves advantageous in reducing the overpotential for interfacial charge transfer reactions. In practical terms, employing a full-cell with the biphasic ZIF-AG anode results in a shorter charging time and improved cycling performance, demonstrating no evidence of Li plating during 300 cycles under 3.0 C-charging and 1.0 C-discharging. The research endeavors to contribute to the progress of anode materials by enhancing their charging capability, aligning with the increasing requirements of the electric vehicle applications.

Helical Micropillar Processed by One-Step 3D Printing for Solar Thermal Conversion.

Solar thermal utilization has broad applications in a variety of fields. Currently, maximizing the photo-thermal conversion efficiency remains a research hotspot in this field. The exquisite plant structures in nature have greatly inspired human structural design across many domains. In this work, inspired by the photosynthesis of helical grass, a HM type solar absorber made in graphene-based composite sheets is used for solar thermal conversion. The unique design promoted more effective solar energy into thermal energy through multiple reflections and scattering of solar photons. Notably, the Helical Micropillar (HM) is fabricated using a one-step projection 3D printing process based on a special 3D helical beam. As a result, the solar absorber's absorbance value can reach 0.83 in the 400-2500 nm range, and the surface temperature increased by ≈128.3% relative to the original temperature. The temperature rise rate of the solar absorber reached 22.4 °C min-1, demonstrating the significant potential of the HM in practical applications of solar thermal energy collection and utilization.

A Novel Structured Si-Based Composite with 2D Structured Graphite for High-Performance Lithium-Ion Batteries.

Silicon is a promising alternative to graphite anodes for achieving high-energy-density in lithium-ion batteries (LIBs) because of its high theoretical capacity (3579 mAh g-1). However, silicon anode must be developed to address its disadvantages, such as volume expansion and low electronic conductivity. Therefore, the use of silicon as composed with graphite and carbon anode materials is investigated, which requires properties such as a spherical morphology for high density and encapsulation of silicon particles in the composite. Herein, a graphite@silicon@carbon (Gr@Si@C) micro-sized spherical anode composite is synthesized by mechanofusion process. This composite comprises an outer surface, middle layer, and core pore, which are formed by the capillary force arising from 2D structured graphite and pitch properties. This structure effectively addresses the intrinsic issues associated with Si. Gr@Si@C exhibits a high capacity of 1622 mAh g-1 and capacity retention of 72.2% after 100 cycles, with a high areal capacity 4.2 mAh cm-2. When Gr@Si@C is blended with commercial graphite, the composite exhibits high capacity retention and average Coulombic efficiency after cycling. The Gr@Si@C blended electrode exhibits a high energy density of 820 Wh L-1 with ≈16% metallic Si in the electrode (40 wt.% composite), enabling the realization of practical commercial LIBs.

Weakly Solvating Ether-Based Electrolyte Constructing Anion-Derived Solid Electrolyte Interface in Graphite Anode toward High-Stable Potassium-Ion Batteries.

Low-cost graphite has emerged as the most promising anode material for potassium-ion batteries (PIBs). Constructing the inorganic-rich solid electrolyte interface (SEI) on the surface of graphite anode is crucial for achieving superior electrochemical performance of PIBs. However, the compositions of SEI formed by conventional strongly solvating electrolytes are mainly organic, leading to the SEI structure being thick and causing the co-intercalation behavior of ions with the solvent. Herein, a weakly solvating electrolyte is applied to weaken the cation-solvent interaction and alter the cation solvation sheath structures, conducing to the inorganic composition derived from anions also participating in the formation of SEI, together with forming a uniformly shaped SEI with superior mechanical properties, and thus improving the overall performance of PIBs. The electrolyte solvation structure rich in aggregated ion pairs (AGGs) (69%) enables remarkable potassium-ion intercalation behavior at the graphite anode (reversible capacity of 269 mAh g-1) and highly stable plating/stripping of potassium metal anode (96.5%). As a practical device application, the assembled potassium-ion full-battery (PTCDA//Graphite) displays superior cycle stability. The optimizing strategy of cation solvation sheath structures offers a promising approach for developing high-performance electrolytes and beyond.

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Si-Rich Silicon-Graphite Anodes.

Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70 wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200 mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200 mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30% Si electrode, crystalline Si amorphization at potentials <110 mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70% Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

Architecting Sturdy Si/Graphite Composite with Lubricative Graphene Nanoplatelets for High-Density Electrodes.

Densification of the electrode by calendering is essential for achieving high-energy density in lithium-ion batteries. However, Si anode, which is regarded as the most promising high-energy substituent of graphite, is vulnerable to the crack during calendering process due to its intrinsic brittleness. Herein, a distinct strategy to prevent the crack and pulverization of Si nanolayer-embedded Graphite (Si/G) composite with graphene nanoplatelets (GNP) is proposed. The thickly coated GNP layer on Si/G by simple mechanofusion process imparts exceptional mechanical strength and lubricative characteristic to the Si/G composite, preventing the crack and pulverization of Si nanolayer against strong external force during calendering process. Accordingly, GNP coated Si/G (GNP-Si/G) composite demonstrates excellent electrochemical performances including superior cycling stability (15.6% higher capacity retention than P-Si/G after 300 cycles in the full-cell) and rate capability under the industrial testing condition including high electrode density (>1.6 g cm-3) and high areal capacity (>3.5 mAh cm-2). The material design provides a critical insight for practical approach to resolve the fragile properties of Si/G composite during calendering process.

Understanding the Coupling Mechanism of Intercalation and Conversion Hybrid Storage in Lithium-Graphite Anode.

Anodes with high capacity and long lifespan play an important role in the advanced batteries. However, none of the existing anodes can meet these two requirements simultaneously. Lithium (Li)-graphite composite anode presents great potential in balancing these two requirements. Herein, the working mechanism of Li-graphite composite anode is comprehensively investigated. The capacity decay features of the composite anode are different from those of Li ion intercalation in Li ion batteries and Li metal deposition in Li metal batteries. An intercalation and conversion hybrid storage mechanism are proposed by analyzing the capacity decay ratios in the composite anode with different initial specific capacities. The capacity decay models can be divided into four stages including Capacity Retention Stage, Relatively Independent Operation Stage, Intercalation & Conversion Coupling Stage, Pure Li Intercalation Stage. When the specific capacity is between 340 and 450 mAh g-1, its capacity decay ratio is between that of pure intercalation and conversion model. These results intensify the comprehensive understandings on the working principles in Li-graphite composite anode and present novel insights in the design of high-capacity and long-lifespan anode materials for the next-generation batteries.

Introduced Iron-Based Catalysts for Low-Temperature Upcycling Regeneration of Spent Graphite towards Ultra-Fast Lithium Storage Properties.

Spent graphite, as the main component of retired batteries, have attracted plenty of attentions. Although a series of recycling strategies are proposed, they still suffer from high cost of regeneration and large CO2 emission, mainly ascribed to the full-recovery of surface and internal phase at ultra-high temperature. However, the existing of suitable internal defects is conductive to their energy-storage abilities. Herein, with the introduction of Fe-based catalysts, spent graphite is successfully repaired at low temperature with the tailored surface traits, including conductivities, isotropy and so on. As Li-storage anodes, all of samples can display a capacity of 340 mAh g-1 above at 1.0 C after 200 cycles. At high rate 5.0 C, their capacity can be also kept ≈300 mAh g-1, and remained ≈233 mAh g-1 even after 1000 cycles. Assisted by electrochemical and kinetic behaviors, their cycling traits with dynamic surface transformations are detailed explored, including activated/fading mechanism, Li-depositions forming etc. Moreover, the calculated constant time of as-optimized regenerated sample is ≈3.0 × 10-4 s, further revealing the importance of surface designing. Therefore, the work is expected to shed light on their energy-storage behaviors, and offer low-temperature regenerated strategies of spent graphite with high value.

Sustainable Fabrication of Graphene Oxide Cathodes from Graphite of Failed Commercial Li-Ion Batteries for High-Performance Aqueous Zn-Ion Batteries.

The need for revamping spent graphite (SG) from battery waste of commercial lithium-ion batteries and employing it as a source for the synthesis of graphene oxide (GO) is focused. Thus, this work emphasizes the study of GO sheets, synthesized via modified Hummer's method from spent graphite (SG-GO) as cathodes for an aqueous zinc ion battery (AZIB) system, for the first time in literature. For comparison, graphene oxide is also synthesized using commercial graphite powder, its structural and morphological properties are analyzed with SG-GO. The coin cell AZIB device is fabricated for both the GOs and the electrochemical performances revealed that SG-GO portrayed an enhanced charge capacity of 270 mAh g-1 at 0.1 A g-1 in 3 m ZnSO4 in comparison to GO which delivered ≈198 mAh g-1 at the same current density of 0.1 A g-1. The long-run cycling analysis of SG-GO elucidated the capacity retention of 77.3% at 1 A g-1 even after 1000 cycles. Moreover, the performance of SG-GO is inspected in different electrolyte systems and the suitable electrolyte underwent concentration variation studies to figure out the capability of the system in storing Zn2+ ions which is found to be more in 3 M ZnSO4 electrolyte.