Traditional Graphite Anode Research Articles

Dual-network nanoporous NiFe2O4/NiO composites for high performance Li-ion battery anodes

The electrochemical properties of traditional graphite anodes cannot meet the current market requirements, which restrict the commercial applications of lithium-ion batteries (LIBs). Herein, we report a facile one-step dealloying strategy to fabricate dual-network nanoporous NiFe2O4/NiO composites. The composite presents excellent electrochemical performance, delivering a high reversible capacity of 1618 mAh g−1 at 200 mA g−1 for 100 cycles followed at 500 mA g−1 for 250 cycles. Even at 1000 mA g−1, a specific capacity of 416 mAh g−1 can be retained after 2000 cycles. The good electrochemical performance ascribes to the synergistic effect of two kinds of active materials (NiFe2O4 and NiO) and the unique dual-network porous structure, in which the plenty of pores can accommodate the volume change during the charge/discharge cycling while a mass of mesopores on the skeletons shorten the diffusion distances of ions and electrons. The employed strategy opens a door for the novel structural design of dealloyed anode materials, which may facilitate the further development of the dealloying technique for various application fields.

Phosphoric acid induced homogeneous crosslinked phosphorus doped porous Si nanoparticles with superior lithium storage performance

The high volume expansion and low electrical conductivity issues severely limit practical application of Si-based materials for Li ion batteries (LIBs). Here we prepare the homogeneous crosslinked phosphorus (P) doped porous Si nanoparticles (P doped pSi) via magnesiothermic reduction of P contained nanosize SiO2 (P-SiO2). Phosphoric acid (H3PO4) acts as a bifunctional additive to reduce particle size of SiO2 and achieve P doping of porous Si. The employment of this modified nanosize SiO2 as precursor effectively alleviates the agglomeration of Si grains. Besides, the P doping characteristic is quite effective to promote the charge transfer performance of Si anode. Finally, P doped pSi anode displays superior cycle capacity and rate capability in half cells with 1761 mAh g−1 at 0.5 A g−1 after 80 cycles and 700 mAh g−1 at 5 A g−1 even after 400 cycles. Furthermore, the electrochemical performance of P doped pSi//LiFePO4 full cell is also evaluated. All the results indicate that P doped pSi is an excellent competitor to replace traditional graphite anode for LIBs.

Novel silane-treated polyacrylonitrile as a promising negative electrode binder for LIBs

With the rapid increment of the electric vehicle market, silicon has attracted tremendous attention as a promising anode material for lithium-ion batteries (LIB) due to its tenfold higher gravimetrical energy density compared with a traditional graphite anode. To eliminate the well-known poor cycle life issue originated from the large volume expansion of the silicon-based electrode, the development of novel polymeric binder is essential. Herein, we synthesized a novel silane-treated polyacrylonitrile (Si-PAN) as an anode binder using facile azide-nitrile click reaction. Incorporation of silane to the cyclized-PAN structure enhances affinity between the electrode components and a current collector because it has organic and inorganic moiety simultaneously in polymeric backbone. This work implements a Si-alloy (Si70Ni20Cu10) based electrode with improved capacity retention through the optimization of silane amount and thermal treatment condition. Namely, the electrode composing Si-treated PAN-2.0 binder and Si-alloy, after being thermally treated at 450 °C shows stable discharge capacity of 760 mA h g−1 upon 50 cycles, resulting in 46% capacity retention improvement against pristine PAN binder (at 450 °C). New binder demonstrates a great potential to improve the electrochemical properties of next-generation electrode materials for energy storage systems.

The critical role of carbon in marrying silicon and graphite anodes for high‐energy lithium‐ion batteries

AbstractIncreasing the energy density of conventional lithium‐ion batteries (LIBs) is important for satisfying the demands of electric vehicles and advanced electronics. Silicon is considered as one of the most‐promising anodes to replace the traditional graphite anode for the realization of high‐energy LIBs due to its extremely high theoretical capacity, although its severe volume changes during lithiation/delithiation have led to a big challenge for practical application. In contrast, the co‐utilization of Si and graphite has been well recognized as one of the preferred strategies for commercialization in the near future. In this review, we focus on different carbonaceous additives, such as carbon nanotubes, reduced graphene oxide, and pyrolyzed carbon derived from precursors such as pitch, sugars, heteroatom polymers, and so forth, which play an important role in constructing micrometer‐sized hierarchical structures of silicon/graphite/carbon (Si/G/C) composites and tailoring the morphology and surface with good structural stability, good adhesion, high electrical conductivity, high tap density, and good interface chemistry to achieve high capacity and long cycling stability simultaneously. We first discuss the importance and challenge of the co‐utilization of Si and graphite. Then, we carefully review and compare the improved effects of various types of carbonaceous materials and their associated structures on the electrochemical performance of Si/G/C composites. We also review the diverse synthesis techniques and treatment methods, which are also significant factors for optimizing Si/G/C composites. Finally, we provide a pertinent evaluation of these forms of carbon according to their suitability for commercialization. We also make far‐ranging suggestions with regard to the selection of proper carbonaceous materials and the design of Si/G/C composites for further development.

Stabilizing Silicon Anode Chemistry for Long Cycle and Calendar Life Electrodes

Replacing traditional graphite anode by Si anode can greatly improve the energy density of lithium-ion batteries. However, the large volume expansion and the formation of highly reactive lithium silicides during charging cause the continuous lithium and electrolyte consumption as well as the fast decay of Si anodes. In this work, by formulating new electrolytes and additives, we demonstrate lifetime stabilization of the anode chemistry during the initial lithiation process. Using solid-state nuclear magnetic resonance spectroscopy, we show that stabilization suppresses the detrimental chemical reactions between the lithium silicides and common electrolyte solvents as well as binders. Formulated electrolytes were tested in commercially relevant electrodes, which show higher capacity, superior cyclability, and higher coulombic efficiencies in both half-cell and full-cell configurations when compared with standard electrolytes. We show an improvement in capacity retention from ~25% after 270 cycles to ~60% and a consistent 0.2%+ improvement in coulombic efficiencies in full cells when compared to state of the art baselines with silicon anodes. Post-electrochemistry characterizations demonstrate the mechanistic details silicon anion stabilization. This study opens a new and simple way to stabilize silicon anodes to enable widespread application of Si anodes for lithium-ion batteries.

High lithium anodic performance of flower-like carbon nanoflakes derived from MOF based on double ligands

Carbon-based anode materials with unique structure, high electrical conductivity, high Li storage performance and excellent cycling stability are promising alternatives to traditional graphite anode materials in lithium-ion batteries (LIBs). Here we report a flower-like carbon material with hierarchical structure that is prepared by carbonization of a flower-like Zn-based metal-organic framework (MOF). The 2D layered MOF network precursor, namely [Zn(BDC)(MelM)·(DMF)] (BDC = benzene dicarboxylic acid, MelM = 2-Methylimidazole), is constructed using two ligands under solvothermal conditions. As an anode material for LIBs, these carbon nanoflakes exhibit remarkable electrochemical performance (capacity, cyclability, and rate capability); the capacity of 902.5 mAh g−1 was retained after 200 cycles at a current density of 100 mA g−1. The remarkable performance results from the unique morphology of carbon nanoflakes which is beneficial for infiltration of electrolyte and the transportation of Li ions.

Using Mixed Salt Electrolytes to Stabilize Silicon Anodes for Lithium-Ion Batteries via in Situ Formation of Li-M-Si Ternaries (M = Mg, Zn, Al, Ca).

Replacing traditional graphite anode by Si anode can greatly improve the energy density of lithium-ion batteries. However, the large volume expansion and the formation of highly reactive lithium silicides during charging cause the continuous lithium and electrolyte consumption as well as the fast decay of Si anodes. In this work, by adding 0.1 M M(TFSI)x (M = Mg, Zn, Al and Ca) as a second salt into the electrolyte, we stabilize the anode chemistry through the in situ formation of Li-M-Si ternary phases during the charging process. First, lithium silicides and magnesium lithium silicides were synthesized as model compounds to investigate the influence of metal doping on the reactivity of lithiated Si. Using solid-state nuclear magnetic resonance spectroscopy, we show that Mg doping can dramatically suppress the chemical reactions between the lithium silicide compounds and common electrolyte solvents. New mixed salt electrolytes were prepared containing M(TFSI)x as a second salt to LiPF6 and tested in commercially relevant electrodes, which show higher capacity, superior cyclability, and higher Coulombic efficiencies in both half-cell and full-cell configurations (except for Zn) when compared with standard electrolytes. Post-electrochemistry characterizations demonstrate that adding M salts leads to the co-insertion of M cations along with Li into Si during the lithiation process, stabilizing silicon anions by forming more stable Li-M-Si ternaries, which fundamentally changes the traditional Li-Si binary chemistry while minimally affecting silicon electrochemical profiles and theoretical capacities. This study opens a new and simple way to stabilize silicon anodes to enable widespread application of Si anodes for lithium-ion batteries.

A novel itaconic acid-graphite composite anode for enhanced lithium storage in lithium ion batteries

An itaconic acid-graphite composite anode is prepared for lithium ion batteries. The composite anode exhibits much improved electrochemical performances compared to the traditional graphite anode. A high specific capacity of 571 mAh g−1 can be obtained at 25 mA g−1 in the voltage range of 0.01–3.0 V vs. Li/Li+, and retained 96.8% at 10 A g−1. After cycled 200 cycles at 100 mA g−1 charge/200 mA g−1 discharge, a reversible capacity of 693 mAh g−1 still can be achieved. At 0.01–1.5 V vs. Li/Li+, it still delivers a specific capacity of 460 mAh g−1, higher than the theoretical capacity of graphite (372 mAh g−1). The reversible lithiation/delithiation process of both itaconic acid and graphite contribute the high capacity. The excellent rate performances are related to the buffering of the itaconic acid matrix combining its superior lithium storage capability. And the stable solid electrolyte interphase formed on the electrode during electrochemical cycling is the main factor for the stable cycle.

Hydrothermal synthesis and energy storage performance of ultrafine Ce2Sn2O7 nanocubes

Ultrafine cube-shape Ce2Sn2O7 nanoparticles crystallized in pure pyrochlore phase with a size of about 10 nm have been successfully synthesized by a facile hydrothermal method. Conditional experiments have been conducted to optimize the processing parameters including temperature, pH, reaction duration, precipitator types to obtain phase-pure Ce2Sn2O7. The crystal structure, morphology and sizes and specific surface area have been characterized by X-ray diffractometer (XRD), Raman spectrum, transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and Brunauer-Emmett-Teller (BET). The as-synthesized Ce2Sn2O7 ultrafine nanocubes have been evaluated as electrode materials for pseudo-capacitors and lithium ion batteries. When testing as supercapacitors, a high specific capacitance of 222 F/g at 0.1 A/g and a good cycling stability with a capacitance retention of higher than 86% after 5000 cycle have been achieved. When targeted for anode material for lithium ion batteries, the nanocubes deliver a high specific reversible capacity of more than 900 mA∙h/g at 0.05C rate. The rate capability and cycling performance is also very promising as compared with the traditional graphite anode.

(Invited) Si Materials for Li-ion Battery Negative Electrode Applications

Silicon is an attractive candidate for lithium-ion batteries negative electrode materials because it delivers 10 times greater theoretical (~4200 mAh/g) specific capacity than that of traditional graphite anode (~370 mAh/g). However, the widespread application of silicon materials has remained to be a significant challenge, originating from large volume changes during lithium insertion and extraction processes and excessive surface reaction with electrolyte. This large volume change causes cracking and pulverization of silicon, leading to loss of the electrical contact in the electrode. The Si volume change coupled with excessive electrolyte surface reaction, leads to drastic capacity fading. To address the large volume change, new electrode fabrication approaches have been developed such as nano-Si materials assembly and new binder development. New functional binders with electronic conductivity, adhesive functional groups, and crosslinking functional groups are the recent research focuses. To address the excessive surface reactions of Si with electrolyte, electrolyte additives of different chemistry has been developed and tested. Fluorocarbon additives such as FEC have demonstrated as an effective SEI formation additive for Si materials. Electrolyte additives for Si materials has been a very active area of research. Electrolyte additives with due functionalities have attract major interest lately. Si particle coatings such carbon coating as an electric conductive medium and electrolyte insulating buffering layer have been widely used to encapsulate the silicon particles and prevent electrolyte reaction. There are many different carbon precursors for performing the carbon coating, which produce carbon coatings with different chemical and morphological carbon coatings. The Si materials with highly graphitized and dense coating is able to not only deliver higher gravimetric capacity and stable cycling compared to that of the Si with disordered carbon coating, but also alter the Si materials bulk transformation. A comprehensive discussion of the Si materials coating, electrode design and electrolyte additives and its electrochemical performance will be presented.

MoS2/Reduced Graphene Oxide Aerogel Composite for Lithium Ion Battery Anodes

As well known, the increasing consumption of fossil fuel and the consequent environment problems, energy storage has become a global concern. The rechargeable batteries with high capacity, low cost and long cycling life is highly desired for large-scale applications in the future. 1 In the past decade, rechargeable lithium ion batteries (LIBs) have attracted considerable attention for their various advantages, such as high specific capacity, high voltage, long cycle life, and low self-discharge. These features make LIBs to be ideal power source for portable electronic devise and electric vehicles (EVs). 2Nevertheless, LIBs are encountering the next-level energy storage demand on further increase of energy density, operation safety and cycle life for EVs and smart grid energy technologies. 1 One hinder is the low specific capacity of the traditional graphite anode materials. Great efforts have been made to develop suitable anode materials with both high capacity and safety. Recently, transition metal sulfides have emerged as promising electrode materials for LIBs because of their high specific capacity, low cost, and other unique properties. Particularly, molybdenum disulfide (MoS2), a representative 2D material which delivers a similar structure to graphene, has been actively investigated owing to its high specific capacity (669 mAh g-1) from the four-electron transfer reaction, MoS2+4Li+4e→Mo+2Li2S. However, MoS2 still suffers from the inherent low electrical conductivity and large inherent volume change, which will result in poor cycling stability and rate property. 3 To address these drawbacks, one of the most effective strategies is to combine MoS2 with conductive carbon-based materials, such as porous carbon, carbon nanotubes and graphene. 4 Herein, the MoS2 nanosheets has been successfully grown on reduced graphene oxide (r-GO) aerogel with a one-pot hydrothermal method. The prepared MoS2 nanosheets show a strong interaction with the r-GO aerogel substrate which could provide strong combination and facile electron transport between the MoS2 and r-GO substrate. The unique structure of the composite which could remain the high capacity of the MoS2 and the high conductivity of the r-GO aerogel. This synergy effects makes the MoS2/r-GO composite exhibits excellent lithium storage performance with high capacity (950 mAh g-1 at 0.05 A g-1), good cyclic stability ( about 600 mAh g-1 at 200 cycles). Figure captions Figure 1. (a) Charge-discharge profiles of MoS2/r-GO composites. (b) Cycling performances at the current density of 0.05 A g-1 and 100 mA g-1. References Zhang, Z.; Zhao, H.; Teng, Y.; Chang, X.; Xia, Q.; Li, Z.; Fang, J.; Du, Z.; Świerczek, K., Carbon-Sheathed MoS2 Nanothorns Epitaxially Grown on CNTs: Electrochemical Application for Highly Stable and Ultrafast Lithium Storage. Advanced Energy Materials 2017, 8 (7), 1700174.Qin, W.; Li, Y.; Teng, Y.; Qin, T., Hydrogen bond-assisted synthesis of MoS2/reduced graphene oxide composite with excellent electrochemical performances for lithium and sodium storage. Journal of Colloid and Interface Science 2018, 512, 826-833.Zhang, X. Q.; Li, X. N.; Liang, J. W.; Zhu, Y. C.; Qian, Y. T., Synthesis of MoS2@C Nanotubes Via the Kirkendall Effect with Enhanced Electrochemical Performance for Lithium Ion and Sodium Ion Batteries. Small 2016, 12 (18), 2484-2491.Xia, S.; Wang, Y.; Liu, Y.; Wu, C.; Wu, M.; Zhang, H., Ultrathin MoS2 nanosheets tightly anchoring onto nitrogen-doped graphene for enhanced lithium storage properties. Chemical Engineering Journal 2018, 332, 431-439. Figure 1

Title Confined Sn Nanoparticles into 3D Porous Carbon Skeleton for High Performance Lithium Storage

AbstractSn‐based materials, one of the most promising alternatives, hold higher theoretical capacity (994 mA h g−1) than traditional graphite anodes and attract great attention in lithium‐ion batteries (LIBs). In this work, an in‐situ formed sodium chloride (NaCl) is employed as the template to support the formation of a three‐dimensional (3D) hierarchical porous carbon skeleton. The 3D porous materials, which specific surface area reach 221.1 m2/g, can shorten the ions transport path and increase the contact between the electrode and the electrolyte. Meanwhile, the Sn nanoparticles are restricted in the carbon matrix, which can effectively enhance the conductivity and solve some major problems of the volume fluctuation, particle aggregation and electrode pulverization. Consequently, the 3D porous carbon skeleton/Sn (3D‐PCSS) composites exhibit a high capacity (1046.7 mA h g−1 at 50 mA g−1 after 60 cycles), long cycle life (490 mA h g−1 after 600 cycles at 1000 mA g−1) and excellent rate performance. Moreover, a new method to improve energy storage properties in LIBs will be involved‐confining Sn nanoparticles in hierarchically porous 3D carbon skeleton.

Discovery of Calcium‐Metal Alloy Anodes for Reversible Ca‐Ion Batteries

AbstractCa‐ion batteries (CIBs) show promise to achieve the high energy density required by emerging applications like electric vehicles because of their potentially improved capacities and high operating voltages. The development of CIBs is hindered by the failure of traditional graphite and calcium metal anodes due to the intercalation difficulty and the lack of efficient electrolytes. Recently, a high voltage (4.45 V) CIB cell using Sn as the anode has been reported to achieve a remarkable cyclability (>300 cycles). The calciation of Sn is observed to end at Ca7Sn6, which is surprising, since higher Ca‐content compounds are known (e.g., Ca2Sn). Here, the Sn electrochemical calciation reaction process is investigated computationally and the reaction driving force as a function of Ca content is explored using density functional theory (DFT) calculations. This exploration allows the identification of threshold voltages which govern the limits of the calciation process. This information is then used to design a four‐step screening strategy and high‐throughput DFT is utilized to search for anode materials with higher properties. Many metalloids (Si, Sb, Ge), (post‐)transition metals (Al, Pb, Cu, Cd, CdCu2) are predicted to be promising inexpensive anode candidates and warrant further experimental investigations.

Enhanced electrochemical performance by size-dependent SEI layer reactivation of NiCo2O4 anodes for lithium ion batteries

Under over-increasing demand of advanced lithium-ion batteries (LIBs) for long-range electric vehicles (EVs), high-capacity transition metal oxide (TMO) negative electrodes for LIBs are thought as potential substitutes of traditional graphite anodes. A major barrier for TMO anodes is volumetric expansion during lithiation processes, leading to active material pulverization and falling off current collectors, which seriously deteriorates capacity retention. Herein, apart from conventional mechanical degradation, another capacity fading mechanism is revealed. Furthermore, the understanding is supported by an interesting cycling property. Firstly, NiCo2O4 with designed morphologies of nanoplates and microspheres are studied for the initial (de)lithiation and prolonged cycles. The morphology changes indicate solid electrolyte interphase (SEI) layer accumulating on the surface of electrodes and impeding the contact and reactions between lithium and active materials with a result of severe capacity loss. It can be understood as SEI layer insulating NiCo2O4, and if SEI film appropriately changes, high capacities can recovery. This conjecture is confirmed by following research of NiCo2O4 nanoparticles with amazing cycling performance prepared by a facile water-bath method. As LIB anodes, NiCo2O4 nanoparticles exhibit capacities of 1144 mAh g−1 at the initial discharging, 230 mAh g−1 at the 100th cycle and 661 mAh g−1 at the 500th cycle. The corresponding coulombic efficiency is of 73.1%, 98.4% and 99.5%, respectively. By TEM characterization in combination with electrochemical analysis, size-dependent SEI layer reactivation (from thick and unstable to thin and stable) is a key role on the dramatic capacity recovery.

Nanoflake δ-MnO2 deposited on carbon nanotubes-graphene-Ni foam scaffolds as self-standing three-dimensional porous anodes for high-rate-performance lithium-ion batteries

The electrification of transportation necessitates the growth of high-power-density lithium ion batteries. However, traditional graphite anodes in lithium ion batteries perform poorly especially when charged or discharged under high current density. In this work, we deposit nanoflake δ-MnO2 on the carbon nanotubes-Graphene-Nickel foam compound matrix and apply it as a self-standing anode without binder or conductive agent. This composite buffers volume change, enables more electrochemical active sites, boosts the conductivity of electrode materials and facilitates lithium-ion diffusion. The resulting lithium ion batteries with the composite anodes show improved cycle life and enhanced rate performance, yielding a high specific capacity of 1250 mAh g−1 for 350 cycles at 0.4 A g−1 and 490 mAh g−1 over 700 cycles at 4.0 A g−1.

Recent Progresses and Prospects of Cathode Materials for Non-aqueous Potassium-Ion Batteries

Rechargeable potassium-ion batteries (KIBs) are potential alternatives to lithium-ion batteries for application in large-scale energy storage systems due to their inexpensive and highly abundant resources. Recently, various anode materials have been investigated for use in KIBs, especially the traditional graphite anodes which have already been successfully applied in KIBs. In contrast, the appropriate cathode materials which are able to accommodate large K ions are urgently needed. In this review, a comprehensive summary of the latest advancements in cathode materials for non-aqueous KIBs in terms of capacity, cycle life and energy density will be presented, as well as K-storage mechanisms. In addition, various strategies to improve K-storage performance will be provided through combining insights from the study of material structures and properties and thus bring low-cost non-aqueous KIBs a step closer to application in sustainable large-scale energy storage systems.

Sila raises $70 million for silicon anodes

Sila Nanotechnologies, a start-up based in Alameda, Calif., has raised $70 million in its fourth round of venture funding from Sutter Hill Ventures; Next47, a venture firm backed by Siemens; and Amperex Technology, a Chinese battery maker. Sila is working to commercialize lithium-ion battery anodes made primarily of silicon. Researchers have long known that replacing traditional graphite anodes with ones made with silicon can greatly increase the energy density of lithium-ion batteries. But the trick is formulating the material to prevent its bad habit of swelling. Lithium-ion battery anodes store lithium that settles there when batteries are charged. Graphite is a cheap, durable anode material; however, it has limited storage capacity. “Batteries are a key component in the future of mobility and electrification, but the current technology can’t keep up,” says Next47 partner T.J. Rylander. Silicon can store much more lithium, but the resulting swelling ends up degrading the battery.

Complete hollow ZnFe2O4 nanospheres with huge internal space synthesized by a simple solvothermal method as anode for lithium ion batteries

Complete hollow ZnFe2O4 nanospheres with well crystallization and uniform dispersion were successfully synthesized via a facile solvothermal method. The obtained ZnFe2O4 material displays a complete hollow sphere structure with a huge interspace diameter of 180 nm. When used as anodes for lithium ion battery, the as-prepared sample exhibits high initial discharge/charge capacities of 1321.4/976.8 mA h·g−1 at 100 mA·g−1, with an initial Coulombic efficiency reaching as high as 73.9%. Surprisingly, the specific capacity of ZnFe2O4 electrodes experiences a process of decrease in initial 20 cycles and stable increase in subsequent 100 cycles, with a considerable discharge capacity of 1101.3 mA h·g−1 at 200 mA·g−1 after 120 cycles. Even at a high rate of 1600 mA·g−1, the capability for electrodes still maintains at 703.6 mA h·g−1, much larger than traditional commercialized graphite anode (372 mA h·g−1). Such remarkable electrochemical properties of the only ZnFe2O4 material are even superior than those complex and expensive ZnFe2O4-based composites reported previously. It is believed that zinc ferrite nanosphere material with high reversible capacity, favorable cycling stability and good rate capability holds promise for becoming an alternative anode of lithium-ion batteries.

Controlled Synthesis of Mos­2 Microparticles for Lithium Ion Batteries

Introduction – MoS2 is promising as alternative to traditional graphite anodes. MoS2 possesses a low redox potential relative to lithium and approximately 3x the theoretical capacity of graphite, making it an ideal candidate for lithium ion battery anodes [1, 2]. To achieve high storage capacities and stable capacities over many charge/discharge cycles, high electrochemically active surface areas and access to layer edge intercalation sites is required. Controlled growth of MoS2 microspheres, whose robust morphology should provide a stable structure and abundant access to intercalation sites also allows for the control of particle surface area to volume ratios, a key component to determining electrochemical activity of the anode particles. In this work, experimental parameters such as precursor materials, temperature and pressure are varied for the hydrothermal synthesis of MoS2 microparticles, giving control over particle morphology and size. The influence of surface area to volume ratios are then examined with respect to material stability and capacity. Fabrication procedures and preliminary results are shown in the following sections.Fabrication procedures – Synthesis of MoS2 microspheres is accomplished by a hydrothermal procedure under high pressure. In a typical procedure hexammonium heptamolybdate tetrahydrate and thiourea are vigorously in a solution of deionized water. The solution is then transferred to a Teflon lined autoclave reactor vessel and heated to 220 °C for an extended period of time. The resulting black MoS2 precipitate is collected by centrifugation and washed with ethanol and deionized water several times to remove impurities. Lingering solvent is then removed by drying the material at low temperatures in atmosphere overnight.Preliminary results – X-ray diffraction spectra of MoS2 microspheres taken at different reaction times are shown in Figure 1(a). Material crystallinity is observed to be dependent on reaction time. An SEM image typical of the fabricated MoS2 microspheres is shown in Figure 1(b), showing that the microspheres are composed of conglomerations of MoS2 sheets. Figure 1(c) shows particle size distributions of the three reaction times. All resulted in two size distributions per reaction time, with an increase in reaction time yielding an increase in both particle size distributions. Figure 1(d) shows surface area to volume ratios (S.V.R.) of the measured particle size distributions plotted against the S.V.R. function for a sphere.References – [1] T. Stephenson, Z. Li, B. Olsen, D. Mitlin, Energy & Environmental Science, 7 (2014) 209-231. [2] N. Yabuuchi, K. Kubota, Y. Aoki, S. Komaba, The Journal of Physical Chemistry C, 120. Figure 1

Expanding Interlayer Spacing of Hard Carbon by Natural K+ Doping to Boost Na-Ion Storage.

Heteroatom-doped carbon is an attractive material for anodes in lithium-/sodium-ion batteries as a replacement for traditional graphite anodes. However, the complex fabrication process and high cost limit practical applications of these carbon materials. Here, we report a low-cost, natural potassium-doped carbon material, which is directly carbonized from the coconut endocarp-a kind of high potassium-containing biomass material. The obtained carbon structure features an expanded d(002)-spacing (0.4 nm) originating from the superhigh potassium content (6654 mg kg-1). Because of the improvement on charge transfer kinetics and electrical properties, the potassium-doped carbon anode exhibits promising electrochemical performance in sodium-ion batteries, including high initial reversible capacity (314 mAh g-1) and good cycle stability (289 mAh g-1 after 200 cycles). Additionally, this work opens up a new approach for the design of heteroatom-doped carbon materials from the viewpoint of being naturally environmental friendly.