Graphitic Carbon Anode Research Articles

Tailoring the Li+ Intercalation Energy of Carbon Nanocage Anodes Via Atomic Al-Doping for High-Performance Lithium-Ion Batteries.

Graphitic carbon materials are widely used in lithium-ion batteries (LIBs) due to their stability and high conductivity. However, graphite anodes have low specific capacity and degrade over time, limiting their application. To meet advanced energy storage needs, high-performance graphitic carbon materials are required. Enhancing the electrochemical performance of carbon materials can be achieved through boron and nitrogen doping and incorporating 3D structures such as carbon nanocages (CNCs). In this study, aluminum (Al) is introduced into CNC lattices via chemical vapor deposition (CVD). The hollow structure of CNCs enables fast electrolyte penetration. Density functional theory (DFT) calculations show that Al doping lowers the intercalation energy of Li+. The Al-boron (B)-nitrogen (N-doped CNC (AlBN-CNC) anode demonstrates an ultrahigh rate capacity (≈300 mAhg-1 at 10 Ag-1) and a prolonged fast-charging lifespan (862.82 mAhg-1 at 5 Ag-1 after 1000 cycles), surpassing the N-doped or BN-doped CNCs. Al doping improves charging kinetics and structural stability. Surprisingly, AlBN-CNCs exhibit increased capacity upon cycling due to enlarged graphitic interlayer spacing. Characterization of graphitic nanostructures confirms that Al doping effectively tailors and enhances their electrochemical properties, providing a new strategy for high-capacity, fast-charging graphitic carbon anode materials for next-generation LIBs.

Revealing sodium storage mechanism of graphitic carbons with various dimensions by a new strategy

Two kinds of graphitic carbon materials without closed pores were obtained by a new strategy in an effort to thoroughly characterize the sodium storage mechanism in the graphitic carbon anodes of sodium-ion batteries. In the first strategy, the interlayer distance is constant, but the defect concentration varies, while in the second strategy, the defect concentration is constant, but the interlayer distance varies and the graphitic crystallites are of different sizes. In situ X-ray diffraction (XRD) analysis was employed to detect the intercalation/de-intercalation process of Na+ ions in these graphitic carbon materials. The results showed that Na+ intercalation in the interlayer space proceeds in two stages at 1.0–0.5 V and 0.5–0 V, contributing to both sloping and plateau capacity profiles. Moreover, the size of the graphene layers in the graphitic crystallites exerts an effect on the slope and plateau capacities in addition to the interlayer distance and defect concentration. Furthermore, the rate performance of a graphitic anode is mainly determined by the defect content, polar groups, and surface area, rather than the interlayer distance. This is due to the influence of defects and polar groups on the diffusion coefficients of Na+ in the insertion/extraction process in the interlayer space and in the Na+ adsorption/desorption process. This work provides new insight for the design of hard carbon anode materials for high-energy-density sodium-ion batteries.

Battery Materials: In-Situ Analysis with the Scanning Electron Microscope

The concept of decarbonisation has been gradually gaining ground. As a result, emphasis has been given to green energy technology in an attempt to offset the need for fossil fuels. The alternative to fossil fuels could be batteries. Not only can batteries be used for stationary energy storage but also for powering electric vehicles. However, more is increasingly required from batteries: they have to store more energy, perform reliably and function for longer, often under extreme conditions depending on the latitude. Among the different battery technologies that have been developed over the years, lithium ion batteries stand out. The main reason is their superior energy and power density, which can support demanding applications such as electromobility. The drive to make batteries more efficient and able to hold more energy, and eventually deliver more power requires in-depth analysis of materials; in order to understand what promotes or undermines materials performance, what leads to failure, and ultimately, the knowledge to design materials for the next generation of batteries.The scanning electron microscope is a powerful tool supporting in situ analysis of materials. In the short-term, as far as cathode precursor powders are concerned, costs are reduced by early detection of impurities and contamination. In the long-term, the battery quality and performance are safeguarded as failure caused by the presence of contaminants is minimised (contamination particles cause short-circuits by penetrating through the battery components). Scanning electron microscope(SEM)-based quality assurance/quality control of battery powders is routinely done with energy dispersive spectroscopy (EDS) and comes with the advantage of high throughput and minimum instrument down time.Battery materials analysis often focuses on formulation testing. That can be either at the industrial level (enquiring if the result is the intended) or R&D level, that is, experimenting with different recipes to single out the optimal one(s). One of the aspects that can be checked using SEM-based analytical techniques is the composition and distribution of coatings and dopants on the powder particle surface. The addition of coatings (Figure 1A) and dopants (Figure 1B) is crucial to ensuring battery performance. They act as performance enhancers (coatings) and dendrite formation suppressants (dopants). These can be detected and mapped in high resolution with SEM-EDS and they can be analysed more accurately with SEM-WDS. At a later stage, the same techniques can be applied to analyse black mass, the material coming from shredded, spent batteries.Given that the atomic numbers (Z) of the elements comprising the battery powders are often close, there is a limit to the information that an electron image can provide due to the closeness of the grey levels. However, there is need to characterise the internal structure of precursor cathode powders as well as other properties such as shape, size, grain boundaries and texture. SEM-EBSD can bypass this issue and can provide information about the particle internal structure by utilising backscattered electrons. The internal structure information of the particles can be used to study cracking development and propagation. A useful tool for battery components post-mortem analysis. The incorporation the Raman-in-SEM, RISE system provides an additional dimension to battery analysis, meaning we can access a wealth of molecular information. Raman spectroscopy can be employed to aid with the analysis of lithium-containing cathode materials in addition to investigating graphitic carbon anode materials.The primary benefit of the SEM-based techniques briefly discussed here is that they can all be applied in the same SEM chamber, in situ, allowing for data to be obtained under the same conditions as part of the same experiment/workflow, promoting, thus, efficiency and throughput – even more so for beam and/or air sensitive samples, saving time required for sample (re)preparation. Another practical benefit is straightforward data correlation which is facilitated when the exact same sample locations have been analysed. Figure 1

Advancements and Prospects of Graphite Anode for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) have recently attracted considerable attention owing to their resource abundance, low cost and environmental friendliness. Graphite as a mature commercial anode material for lithium-ion batteries, has been proved as a promising anode candidate for KIBs by reversible forming potassium-graphite intercalation compounds. However, large volume expansion and sluggish K+ kinetics caused by the incompatibility between large radius of K+ and the small interlayer spacing of graphite, result in the poor cycle stability and rate performances, hindering its practical application. Extensive research efforts have focused on improving the potassium storage performance of graphite anodes. This review provides an overview of recent advances in addressing these challenges and optimizing the electrochemical performance of graphite anodes for KIBs. Various strategies to improve the electrochemical performance of graphite and graphitic carbon anodes, such as microcrystalline regulation, heteroatom doping, morphological adjustment, and coating modification, are discussed, while the critical issues and challenges associated with graphite anodes and the prospects for their advancement in KIBs are highlighted. The review offers valuable guidelines for rational structural design and promotes the commercial development of high-performance graphite anode materials for KIBs.

Pre-oxidation and catalytic carbonization strategies of hemp-derived multifunctional carbon for lithium-ion batteries/hybrid supercapacitors with high energy density and outstanding cyclability

Biomass-derived carbons (biochar) materials have attracted enormous attention owing to their fabulous performances, inherent structural advantages and cost-effectiveness. Herein, two kinds of biochar electrode materials of porous carbon cathode (KCT-800) and graphitic carbon anode (K-1300) were respectively prepared from a single waste biomass hemp stem core. KCT-800 with uniform 3D hierarchical porous structure and abundant adsorption sites was fabricated via mild pre-oxidation of KNO3 and catalytic carbonization of potassium citrate, delivers a reversible capacity 105 mAh g−1 at 100 mA g−1 without obvious capacity degradation after 6000 cycles under 5 A g−1. In addition, K-1300 sheet-like graphitic carbon anode material was also prepared via simple pre-oxidation and high temperature calcination at 1300 °C, which exhibits a reversible capacity 463 mAh g−1 at 0.2 A g−1 because of the N/O Co-doping natural heteroatom and enhanced the pseudo-capacitance. Furthermore, the Li-ion hybrid supercapacitors were assembled by KCT-800 cathode and K-1300 anode delivers a stunning energy density of 222 Wh kg−1 at 246 W kg−1 with a superior capacity retention of 90 % after 4000 cycles. This strategy not only provides a facile and environmental benign method to prepare biomass-derived carbon materials, but also offers new insights on bio-sources multi-functional energy storage materials.

3D Porous Oxygen-Doped and Nitrogen-Doped Graphitic Carbons Derived from Metal Azolate Frameworks as Cathode and Anode Materials for High-Performance Dual-Carbon Sodium-Ion Hybrid Capacitors.

Sodium-ion hybrid capacitors (SIHCs) in principle can utilize the advantages of batteries and supercapacitors and satisfy the cost demand of large-scale energy storage systems, but the sluggish kinetics and low capacities of its anode and cathode are yet to be overcome. Here, a strategy is reported to realize high-performance dual-carbon SIHCs using 3D porous graphitic carbon cathode and anode materials derived from metal-azolate framework-6s (MAF-6s). First, MAF-6s, with or without urea loading, are pyrolyzed to synthesize MAF-derived carbons (MDCs). Then, cathode materials are synthesized via the controlled KOH-assisted pyrolysis of MDCs (K-MDCs). K-MDCs, 3D graphitic carbons, resulting in a record-high surface area (5214m2 g-1 ) being ≈four-fold higher than pristine MAF-6, oxygen-doped sites for high capacity, rich mesopores affording fast ion transport, and high capacity retention over 5000 charge/discharge cycles. Moreover, 3D porous MDC anode materials are synthesized from N-containing MAF-6 and exhibited to allow cycle stability over 5000 cycles. Furthermore, dual-carbon MDC//K-MDC SIHCs with different loadings (3 to 6mgcm-2 ) are demonstrated to achieve high energy densities exceeding those of sodium-ion batteries and supercapacitors. Additionally, it allows an ultrafast-chargeable high power density of 20000Wkg-1 and robust cycle stability overcoming those of a typical battery.

Engineering stable carbon sponge with moderate interlayer spacing and porous architecture for rapid K+-intercalation

The practical application of graphitic carbon materials in potassium-ion batteries (PIBs) is severely hindered by slow K+-intercalation kinetics and severe volume changes during (de)potassiation process. It is challenging but necessary to achieve satisfactory carbon anode with good structural stability and rapid K+-intercalation rate at low potential. Herein, we theoretically investigated the relationship between K intercalation behavior and carbon interlayer spacing by density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD) simulation, and proposed that kinetics of K intercalation improves gradually with the expanding of interlayer spacing. We accordingly constructed a free-standing carbon sponge material with moderate interlayer spacing and porous hollow structure, which achieves synergistically boosting K+-intercalation rate at low potential and enhancing structural stability. As a result, the porous hollow carbon sponge provides rapid K+-intercalation rate at high current density and accommodate volume variety to ensure excellent structural stability during the long-term (de)potassiation process (over 1000 cycles). Moreover, the full cell is successfully assembled with outstanding cycling performance (over 500 cycles) and high voltage output (2.0–3.7 V). This work provides a novel strategy for developing high-performance graphitic carbon anode with rapid K+-intercalation rate and high structural stability for PIBs.

Mechanistic Insight into Ultrafast Kinetics of Sodium Cointercalation in Few-Layer Graphitic Carbon.

Fast-charging sodium ion batteries remain deeply challenged by the lack of suitable carbonaceous anodes that exhibit intercalation plateau with fast kinetics. Here we develop a few-layer graphitic carbon with nanoscale architecture, which enables shortened Na+ ion diffusion path and fast formation of fully intercalated phase at the same time. Combined in situ Raman and electrochemical test reveal that this graphitic carbon with highly crystalline few layers follows surface-controlled intercalation rather than typical diffusion-controlled kinetics observed in natural graphite. As a result, a few-layer graphitic carbon anode maintains the reversible capacity of 106 mAh g-1 at 10 A g-1 and achieves 87% capacity retention even after 10 000 cycles at 1 A g-1. This work provides new insight on the Na storage mechanism in fast-charging graphitic carbon as well as the design of carbon anodes for high-rate sodium ion batteries.

Epitaxial growth of an atom-thin layer on a LiNi0.5Mn1.5O4 cathode for stable Li-ion battery cycling

Transition metal dissolution in cathode active material for Li-based batteries is a critical aspect that limits the cycle life of these devices. Although several approaches have been proposed to tackle this issue, this detrimental process is not yet overcome. Here, benefitting from the knowledge developed in the semiconductor research field, we apply an epitaxial method to construct an atomic wetting layer of LaTMO3 (TM = Ni, Mn) on a LiNi0.5Mn1.5O4 cathode material. Experimental measurements and theoretical analyses confirm a Stranski–Krastanov growth, where the strained wetting layer forms under thermodynamic equilibrium, and it is self-limited to monoatomic thickness due to the competition between the surface energy and the elastic energy. Being atomically thin and crystallographically connected to the spinel host lattices, the LaTMO3 wetting layer offers long-term suppression of the transition metal dissolution from the cathode without impacting its dynamics. As a result, the epitaxially-engineered cathode material enables improved cycling stability (a capacity retention of about 77% after 1000 cycles at 290 mA g−1) when tested in combination with a graphitic carbon anode and a LiPF6-based non-aqueous electrolyte solution.

Regulation of dual-ion batteries via the defects design in carbon electrode based on the different storage behaviors of PF6− and Li+

Dual-ion batteries (DIBs) have aroused much attention due to their high energy density, low cost, and environmental friendliness compared to conventional alkali metal-ion batteries. However, there are still two severe challenges to confront, including structural collapse for the graphitic carbon cathode due to the intercalation of anions with large size and limited specific capacity of cations intercalation for the graphitic carbon anode, rendering poor rate performance, unsatisfactory cyclability, and insufficient energy density. Herein, a simple design is proposed to prepare cathode and anode materials for PF6− and Li+ intercalation in one synthesis system by regulating boron content in the complex of amino acid with iron (III). The graphitic mesoporous carbon cathode with minimal defect sites shows a superior rate performance and cycling stability for PF6− intercalation. The boron-doped porous carbon anode shows a high capacity of up to 606 mAh g−1 for Li + storage by introducing abundant defects. The DIB assembled by the above cathode and anode can exhibit a maximum energy density of 130 Wh kg−1 at a power density of 580 W kg−1 and an energy density of 74 Wh kg−1 at an ultrahigh power density of 29000 W kg−1.

A new cyclic carbonate enables high power/ low temperature lithium-ion batteries

The modern lithium-ion battery (LIB) configuration was enabled by the “magic chemistry” between ethylene carbonate (EC) and graphitic carbon anode. Despite the constant changes of cathode chemistries with improved energy densities, EC-graphite combination remained static during the last three decades. While the interphase generated by EC protects the fragile graphitic structure, the intrinsic disadvantages of EC (high viscosity, high melting point, excessive interphase growth) lead to mediocre power density and poor performances of LIB at sub-zero temperatures, where lithium depositions form upon charging. Such performance compromises arise from the fundamental dilemma between requiring effective interphase protection and high impedance from excessive growth of interphase. In this work, we designed and synthesized a “double EC” molecule as electrolyte additive to resolve the above dilemma. Erythritol bis(carbonate) (EBC) possesses lower LUMO energy level than EC and hence tends to decompose prior to EC reduction, but its weak solvation toward Li+ restricts the extent of its reduction, thus minimizing the interphase thickness and the corresponding impedances. Electrolytes containing EBC enables both the charging and discharging of ampere-size LIB pouch cells at sub-zero temperatures from 0 to -20℃, demonstrating that the key approach to improve low temperature performances lies in how to tailor interphasial chemistry rather than the bulk electrolyte composition.

Accordion‐Like Carbon with High Nitrogen Doping for Fast and Stable K Ion Storage

AbstractPotassium ion battery (PIB) is a potential candidate for future large‐scale energy storage. A key challenge is that the (de)potassiation stability of graphitic carbon anodes is hampered by the limited (002) interlayer spacing. Amorphous carbon with a hierarchical structure can buffer the volume change during repeated (de)potassiation and enable stable cycling. Herein, a direct pyrolysis approach is demonstrated to synthesize a highly nitrogen‐doped (26.7 at.%) accordion‐like carbon anode composed of thin carbon nanosheets and a turbostratic crystalline structure. The hierarchical structure of accordion‐like carbon is endowed by a self‐assembly process during pyrolysis carbonization. The hierarchical nitrogen‐doped accordion structure enables a high reversible capacity of 346 mAh g−1 and superior cycling stability. This work constitutes a general synthesis methodology that can be used to prepare hierarchical carbon anodes for advanced PIBs.

Boosting the potassium storage performance of carbon anode via integration of adsorption-intercalation hybrid mechanisms

Abstract Graphitic carbon has been drawn extensive attention as an anode for Potassium-ion battery (KIB) because it is favorable for K-intercalation. However, the application of graphitic carbon anode for KIB is prevented by the poor cyclability and poor rate capability, resulting from the huge volume expansion and structural collapse after repeat charge/discharge. Herein, by advantageous functional integration of adsorption-intercalation potassium storage mechanisms, we design flexible nitrogen (N) and oxygen (O) dual-doped carbon coated graphene foam films (denoted as NOC@GF) that realizes unprecedented electrochemical performance for KIBs. Such advanced architecture can release the respective advantages of graphitic carbon with high electrical conductivity stability and favorable of K-intercalation, and amorphous heteroatoms doping carbon layers with abundant active sites for potassium adsorption storage. It delivers high reversible capacity (319 mA h/g at 0.1 A/g with a capacity retention of 94.9% after 550 cycles), long cycling stability (281 mA h/g at 1 A/g with a capacity retention of 98.1% after 5500 cycles), and excellent rate capability (123 mA h/g at 5.0 A/g). And density functional theory (DFT) calculations prove that N and O doping sites are benefit to facilitating K ion adsorption and the graphitic carbon promotes K-ion intercalation storage.

Graphitic Carbon Materials for Advanced Sodium‐Ion Batteries

AbstractLithium‐ion batteries (LIBs) have dominated the energy storage market for more than two decades; however, the quest for lower‐cost battery alternatives is rapidly expanding, especially for large‐scale applications. Sodium‐ion batteries (SIBs) have recently experienced an impressive resurgence owing to the earth's abundance of sodium resources and the similar electrochemistry of SIBs and the well‐established LIBs. Nonetheless, whereas cost‐effective and reliable graphite anodes have served as a cornerstone in current LIB technology, one of the major limitations of SIBs has been the inability to exploit graphite as an electrode because of its negligible sodium storage capability. Recently, however, clear progress has been made in preparing high‐performance graphitic carbon anodes for SIBs with new findings on the mechanisms of sodium storage. Herein, this paper aims to review the progress made in understanding the sodium storage mechanisms in graphitic carbon materials and comprehensively summarize the start‐of‐the‐art achievements by surveying the correlations among the type of graphitic material, microstructure, sodium storage mechanisms, and electrochemical performance in SIBs. In addition, perspectives related to practical applications, including the electrolyte, coulombic efficiency, and applicability in sodium‐ion full cells, are also presented.

3D ordered carbon/SnO2 hybrid nanostructures for energy storage applications

Increasing the specific capacity and cycle life of graphitic carbon anodes is crucial for realizing high-performance lithium ion batteries. Herein, we introduce a new class of graphitic carbon anodes comprising highly ordered three-dimensional nanostructures decorated with SnO2 nanoparticles. The inch-scale, nanostructured graphitic carbon matrices are prepared by supported pyrolysis of epoxy templates patterned by advanced optical lithography. During the subsequent decoration process, the SnO2 nanoparticles are densely formed on the matrix without agglomeration since the periodic nanostructured matrix provides a homogeneous site for nucleation and growth. The surface coverage of the decorated SnO2 nanoparticles and the mass relative to the graphitic carbon are >80% and ∼50 wt%, respectively. The resulting nanostructured C/SnO2 composite monoliths can be assembled solely into LIB coin cells without the aid of binders and conducting agents. The achieved specific capacity and retention are 692 mAh g−1 and 87.31% (at 70th cycle), respectively, which is superior to those of nanostructured carbon anodes prepared in a similar way.

Uniformly expanded interlayer distance to enhance the rate performance of soft carbon for lithium-ion batteries

Various carbons with novel structure attract tremendous interests as anode materials for high-rate batteries due to their rapid lithium-ion transfer; practically, they often deliver low initial cycle coulombic efficiency and serious decay for the large surface area. Here, we report a new soft carbon (SC) electrode prepared by using single and simple carbon sources. The carbon possesses a relatively uniform interlayer distance of 0.37 nm (equal to the interlayer distance of LiC6). Taken as a high-rate anode, SC delivers a remarkable discharge capacity of 169 mAh g−1 at a current density of 20 C (1 C = 372 mAh g−1) after 1000 cycles, which is tenfold higher compared to those of commercial graphitic carbon anodes. In the case of low surface area, the achievement is attributed to rapid ion transport and intercalation in proper interlayer distance causing slight change, which result in high-rate and stability property.

Spontaneous repairing liquid metal/Si nanocomposite as a smart conductive-additive-free anode for lithium-ion battery

Silicon is a promising candidate for negative electrodes due to its high theoretical specific capacity (~ 3579 mA h g−1) and low lithiation potential (~ 0.40 V vs. Li). However, its practical applications in battery have been inhibited by the large volume change (~ 400%) induced by Li+-insertion into Si lattices. Here, we attempt to resolve this issue at a fundamental level, and report for the first time a novel liquid metal (LM)-mediated spontaneous repairing conductive-additive-free Si anode for Li-ion battery. The fluidity of LM ensures the eternal contact between Si and the conducting-network during its repeated electrochemical reactions. The as-prepared nano-composite of LM/Si leads to superior performances as characterized by high capacity utilization (2300 mA h g−1 at 500 mA g−1), long-term stability (968 mA h g−1 after 1500 charge-discharge cycles at 8 A g−1 with 81.3% retention), high rate capability (360 mA h g−1 at 20 A g−1, equivalence of 55 C, or full charge/discharge in 65 s), and, in particular, an extra-ordinarily high initial coulombic efficiency (95.92%), which is not only the highest reported for Si to the best of our knowledge, but also higher than the mature graphitic carbon anodes. The unique approach described in this work not only resolves the basic stress challenges faced by the promising but often problematic alloy-type materials; in broader context it also provides a universal inspiration to all electrode materials whose electric properties suffer from extreme mechanic upheavals induced by the electrochemical strains during the cell reactions.

Iodine and Nitrogen-Codoped Carbon Microspheres for Ultrahigh Volumetric Capacity of Li-Ion Batteries

Because of its high density, a carbon microsphere is a good candidate for ultrahigh volumetric capacity electrode materials. We find that the synergistic effects of nitrogen and iodine element can tremendously improve the carbon electrode capacity. Here, we present a high volumetric capacity anode consisting of iodine and nitrogen codoping carbon microspheres synthesized by a low-temperature solvothermal route. A reversible capacity of 1418 mAh cm–3, which is much larger than that of commercial graphitic carbon anode, is achieved at a current density of 0.05 mA cm–2 by using these carbon microspheres as anode material. After 100 charge–discharge cycles at 0.1 mA cm–2 and 500 charge–discharge cycles at 1 mA cm–2, carbon microspheres retained volumetric capacities of 1335 and 1090 mAh cm–3, respectively

Exploiting Anti-T-shaped Graphene Architecture to Form Low Tortuosity, Sieve-like Interfaces for High-Performance Anodes for Li-Based Cells

Graphitic carbon anodes have long been used in Li ion batteries due to their combination of attractive properties, such as low cost, high gravimetric energy density, and good rate capability. However, one significant challenge is controlling, and optimizing, the nature and formation of the solid electrolyte interphase (SEI). Here it is demonstrated that carbon coating via chemical vapor deposition (CVD) facilitates high electrochemical performance of carbon anodes. We examine and characterize the substrate/vertical graphene interface (multilayer graphene nanowalls coated onto carbon paper via plasma enhanced CVD), revealing that these low-tortuosity and high-selection graphene nanowalls act as fast Li ion transport channels. Moreover, we determine that the hitherto neglected parallel layer acts as a protective surface at the interface, enhancing the anode performance. In summary, these findings not only clarify the synergistic role of the parallel functional interface when combined with vertical graphene nanowalls but also have facilitated the development of design principles for future high rate, high performance batteries.

Morphology, composition and electrochemistry of a nano-porous silicon versus bulk silicon anode for lithium-ion batteries

The volumetric energy density of today’s lithium-ion batteries is limited mostly by the graphitic carbon anode. Silicon is a promising replacement but its excessive volume expansion on lithiation limits its long-term cyclability performance. A nano-sized aluminium containing silicon, leached in acid, with a porous structure is shown to maintain its capacity higher than pure bulk silicon or nano-sized silicon by over 700 mAh/g. The capacity of leached silicon is maintained at 1400 mAh/g for more than 60 cycles. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nuclear magnetic resonance spectroscopy have been used to correlate the electrochemical performance with the materials' morphology and composition.