Freely-Rotatable Multidentate Molecular Anchor Enables Self-Adaptive Aqueous Binders for Lithium-Ion Batteries.

The rational design and synthesis of reliable binders is a big challenge to efficiently mitigate the severe volume change of silicon‐based anodes for lithium ion batteries. Herein, we report a multidentate molecular anchoring strategy to construct a novel self‐adaptive aqueous binder. This binder composes of robust 3D dynamic networks derived from the crosslinking of the freely‐rotatable multidentate molecular anchor (2,2‐bis(hydroxymethyl)butyric acid, BHB) and polyacrylic acid (PAA) via dynamic hydrogen‐mediated self‐assembly, which effectively imparts the fabrication of high‐strength Si/C anodes and achieves high areal capacities (6.13 mAh cm−2) under a high mass loading of 13 mg cm−2. Furthermore, the dynamic and reversible adhesion and the efficient “net‐to‐point” bonding characteristic contribute to enhance structural and interfacial stability in the NCM811/Si/C full cells. Consequently, the cells demonstrate superior cyclability and electrochemical performance. Notably, this multidentate molecular anchoring strategy can be further extended to develop other BHB‐derived self‐adaptive binders (i.e., BHB/PVA and BHB/CMC) for the purpose of dynamic structure regulation. This work provides valuable insights into the judicious modulation of aqueous binders from the perspective of molecular chemistry and product engineering, paving the pathway for the design of auqeous binders for ultra‐high‐energy Si‐based lithium‐ion batteries.

With the ever-increasing demand for energy storage, lithium ion battery has been an attractive technology that has revolutionized the portable electronic industry [1]. With its large scale applications, such as in hybrid electric vehicles (HEV’s), and plug-in HEVs, there is great interest in developing multifunctional hybrid nanostructured electrode materials for high performance Li-ion batteries [2,3]. Novel architectures of hybrid nanomaterials as both electrodes and electrolytes, have been shown to improve the device performances. New electrode materials with high electrical conductivity and large surface area, resulting in improved electrochemical performances are highly desirable. Though metal oxides with high specific capacity have been extensively studied as advanced Li-ion battery anodes, their structural instability under lithium insertion has been of great concern [4]. Hence, several approaches have been undertaken to improve the electrochemical performance of metal oxides as efficient Li-ion battery anodes. One of the strategies to increase the conductivity is by incorporating the anode material on the conducting carbonaceous matrix including mesoporous carbon, amorphous carbon, carbon nanotubes and graphenes [5].Here, we report the synthesis of Nb2O5 and TiNb2O7 -anchored graphene hybrid nanocomposites through simple hydrothermal method and its electrochemical performance studies as advanced anodes for lithium ion battery. The nanocomposite electrodes have been characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Thermo Gravimetric Analysis (TGA). Using these hybrid nanostructures as positive electrodes in 1 M LiPF6–EC/DMC electrolyte vs. Li metal negative electrodes, Cyclic voltammetry and Galvanostatic charge-discharge cycling measurements have been performed.The self-supported nanostructured electrodes, with graphene as support with homogenously anchored orthorhombic Nb2O5 (T-Nb2O5) and monoclinic TiNb2O7 nanoparticles, exhibited excellent electrochemical performance with high reversible capacity and enhanced rate capability, arising from the synergistic effect of Nb2O5 nanocrystals anchored onto conducting graphene layers. While the presence of three-dimensional structure in Nb2O5 and TiNb2O7 provides open channels and vacant sites for lithium intercalation, presence of conducting graphene sheets improve the kinetics of lithium ion and electron transport, leading to improved battery performances. The hybrid nanocomposite electrodes showed exceptional power capability, with ~80% of the total capacity sustained at 16C rate (Figure 2). We believe these hybrid nanocomposites, with superior electrochemical performance, can be used as efficient anode for high performance lithium ion battery. Figure 1. SEM images of (a) Nb2O5 nanocrystals (b) Nb2O5/graphene (c) TiNb2O7 and (d) TiNb2O7/graphene nanocompositeFigure 2. (a) Galvanostatic cycling of TiNb2O7/graphene nanocomposite electrode, (b) Rate capability of Nb2O5/graphene nanocomposite electrode. References J.-M. Tarascon and M Armand, Nature. 414, 359, (2001).P. G. Bruce, B. Scrosati and J.-M. Tarascon, Angew. Chem. Int. Ed. 47, 2930 (2008)A.L.M. Reddy, S. Gowda, M.M. Shaijumon and P.M. Ajayan, Adv. Mater. 24, 5045-5064 (2012)P. Poizot , S. Laruelle , S. Grugeon , L. Dupont , J.-M. Tarascon , Nature, 407, 496 (2000).Z.-S. Wu, W. Ren, L. Xu, F. Li, H.-M. Cheng, ACS Nano 5, 5463-5471 (2011)

The relatively low coulombic efficiency (CE), especially the high initial capacity loss (ICL), and short cycle life are two major obstacles limit the wide adoption of Si-based materials as anodes of commercial lithium-ion batteries (LIBs). In this work, we introduced an aqueous binary binder composed of polyacrylic acid (PAA) and a water-soluble polymer to a Si-based electrode. Used as anodes of LIBs, the Si-based electrodes with the binary binder exhibited lower ICL and longer cycle life than those with PAA binder. The improved battery performance is ascribed to the unique electrode structure with the binary binder. The analysis from Fourier-transform infrared spectroscopy (FTIR) reveals that the intermolecular hydrogen bonds has been formed between PAA and the new polymer. The formation of hydrogen bonds could affect the properties of slurry for electrode coating and the structure of dried electrodes. Compared to the PAA binder, the new binary binder increases the viscosity of aqueous slurries at low shear rates and prompts the shear thinning, which benefit the preparation of slurries with high stability. Observations from the electron microscopy reveal that a relative porous structure was generated in the electrodes with the binary binder, compared with those with PAA binder. The porous structure could not only facilitate the electrolyte transport, but also accommodate the large volume expansion of Si during the charge/discharge processes. In addition, a thin solid-electrolyte-interface (SEI) film was found at the surface of cycled electrodes with the binary binder.Key words: aqueous binder coulombic efficiency Si-based anode lithium-ion battery

Banana peel pseudographite (BPPG) offers superb dual functionality for sodium ion battery (NIB) and lithium ion battery (LIB) anodes. The materials possess low surface areas (19 - 217 m2 g-1) and a relatively high electrode packing density (0.75 g cm-3 vs. ~ 1 g cm-3 for graphite). Tested against Na, BPPG delivers a gravimetric (and volumetric) capacity of 355 mAhg-1 (by active material ~ 700 mAh cm-3, by electrode volume ~ 270 mAh cm-3) after 10 cycles at 50 mAg-1. A nearly flat ~ 200 mAhg-1 plateau that is below 0.1 V, and a minimal charge/discharge voltage hysteresis, makes BPPG a direct electrochemical analogue to graphite but with Na. A charge capacity of 221 mAhg-1 at 500 mAg-1 is degraded by 7% after 600 cycles, while a capacity of 336 mAhg-1 at 100 mAg-1 is degraded by 11% after 300 cycles, in both cases with ~ 100% cycling coulombic efficiency. For LIB applications BPPG offers a gravimetric (volumetric) capacity of 1090 mAhg-1 (by material ~ 2200 mAh cm-3, by electrode ~ 900 mAh cm-3) at 50 mAg-1. The reason that BPPG works so well for both NIBs and LIBs is that it uniquely contains three essential features: a) dilated intergraphene spacing for Na intercalation at low voltages; b) highly accessible near-surface nanopores for Li metal filling at low voltages; and c) substantial defect content in the graphene planes for Li adsorption at higher voltages. The < 0.1 V charge storage mechanism is fundamentally different for Na versus for Li. A combination of XRD and XPS demonstrates highly reversible Na intercalation rather than metal underpotential deposition. By contrast, the same analysis proves the presence of metallic Li in the pores, with intercalation being much less pronounced.

Further enhancements regarding the energy density and specific power of lithium ion batteries are absolutely necessary in order to satisfy the increasing requirements for automotive applications e.g. extended driving ranges. One way to realize such improvements, depicts the replacement of commonly used carbon-based anode materials with high capacity anodes.1 In this regard silicon (Si) containing composites are considered promising candidates for the replacement of carbonaceous anode materials due to the significantly higher specific capacity of Si. However, the use of Si is still hindered by several challenges that have to be overcome for a successful application. One major issue of Si-based anode materials is the strong capacity decay due to the huge volume changes (~ 300%) of Si during the lithiation/de-lithiation process, leading to an recurring solid electrolyte interphase (SEI) reformation, which results in the ongoing consumption of active lithium from the cathode.2 One concept to alleviate the detrimental effects previously mentioned and to boost the performance of such anode materials, comprises the combination of Si with a matrix material. The general idea behind this approach is to combine Si with a second phase that enhances the mechanical stability and can buffer the volumetric changes of Si and thus, enables the formation of a stable SEI.3,4 In this study, we present a silicon iron (Fe) composite that contains two phases, a crystalline Si phase and a second, intermetallic FexSiy-phase. The applied synthesis route yields materials that combine a porous structure with the aforementioned matrix approach. This composite design is believed to have a beneficial effect on the capacity retention during cycling since it may buffers the volumetric changes of the Si and simultaneously provides extra space for the volume changes. The applied synthesis route contains a ball-milling and washing step, and subsequently the addition of a thin carbon coating. The composites, synthesized this way, are investigated via scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction and thermogravimetric analysis in order to characterize their structure, morphology and composition. Moreover, electrochemical studies on the long-term cycling and rate performance with regard to the application as anodes in lithium ion batteries are conducted. Thereby, this work focuses on the influence of a high temperature treatment, as well as the influence of the Fe to Si ratio on the electrochemical performance. Furthermore, the role of the stabilizing FexSiy matrix phase in the composite is investigated regarding the question whether this phase is inactive towards lithiation or if it contributes to the lithiation/de-lithiation capacity of the composite. References 1 Placke, T.; Kloepsch, R.; Dühnen, S.; Winter, M. Lithium ion, lithium metal, and alternative rechargeable battery technologies: The odyssey for high energy density. Journal of Solid State Electrochemistry 2017, 21, 1939-1964. 2 Wu, H.; Cui, Y. Designing nanostructured Si anodes for high energy lithium ion batteries. Nano Today 2012, 7, 414–429. 3 Besenhard, J. O.; Yang, J.; Winter, M. Will advanced lithium-alloy anodes have a chance in lithium-ion batteries? Journal of Power Sources 1997, 68, 87–90. 4 Park, C.-M.; Kim, J.-H.; Kim, H.; Sohn, H.-J. Li-alloy based anode materials for Li secondary batteries. Chemical Society reviews 2010, 39, 3115–3141.

Due to the urgent demand for lithium-ion batteries (LIBs) with a high energy density, silicon (Si) possessing an ultrahigh capacity has aroused wide attention. However, its practical application is seriously hindered by enormous volume changes of the Si anode during cycling. Developing novel binders suitable for the Si anode has proven to be an effective strategy to improve its electrochemical performance. Herein, we constructed a three-dimensional network binder, in which the polyacrylic acid (PAA) long chains are cross-linked with one kind of amino acid, lysine (Lys). The abundant polar groups in PAA/Lys enable it to tightly adhere to the Si particles via hydrogen bonds, and the cross-linked structure prevents irreversible slipping of the PAA chains upon volume variation of the particles. The Si used was obtained from a sustainable route by recycling photovoltaic waste silicon. With high elasticity and strong adhesion, the PAA/Lys binder can effectively keep the structural integrity of the Si electrode and improve its electrochemical performance. The Si electrode using the PAA/Lys binder exhibits a good cycling stability (1008 mAh g-1 at 2 A g-1 after 250 cycles). Even with a high mass loading of 3.03 mg cm-2, the Si anode can remain stable for 100 cycles at a high fixed areal capacity of 3.03 mAh cm-2. This work gives a practical method to make stable Si electrodes using sustainable Si source and environmentally friendly amino acid-based binders.

The electrochemical performance of silicon-based anodes in lithium-ion batteries is largely determined by the ongoing decomposition of electrolyte compounds at the silicon particle surface and the subsequent formation of a solid-electrolyte-interphase (SEI).1 Yet, the significant extent of electrolyte decomposition products which accumulate in the anodes as a result of the severe morphological changes of the silicon particles upon cycling requires to rethink the concept of a conformal SEI layer as it was proposed for state-of-the-art graphite anodes.2,3 Based on previous studies,4,5 our current characterization is concerned with the relation of the morphological changes and the resulting electrochemical performance of practical silicon-graphite electrodes. Hence, we apply ex-situ neutron depth profiling (NDP) to monitor the distribution of the lithium-containing electrolyte decomposition products across the thickness of silicon-graphite electrodes as a function of the cycle number. In contrast to conventional analytical techniques, NDP is a non-destructive method with a very high sensitivity to lithium, which allows to determine lithium concentration gradients across the thickness of the entire electrode.6 For our investigation, we prepared silicon-graphite (SiG) electrodes with a practical areal capacity of ~1.8 mAh cm-2 (initial thickness: ~19 µm), consisting of 35 wt% nanometer-sized silicon (~200 nm diameter) and 45 wt% graphite (~20 µm diameter). Vapor grown carbon fibers and lithiated poly(acrylic acid) binder accounted for the remaining 20 wt%.4 Utilizing SiG//LiFePO4 coin-cells with a capacitively oversized positive electrode (~3.5 mAh cm-2) and a relatively stable reference potential of ~3.45 V vs. Li/Li+, the silicon-graphite electrodes were aged by galvanostatic charge-discharge cycling at C/2 (~0.9 mA cm-2) up to 140 cycles. In the next step, we fully delithiated the active materials in the electrodes by applying a very slow C-rate of C/50 (~0.04 mA cm-2) and a high delithiation cutoff potential of ~2.0 V vs. Li/Li+. As a result, any residual lithium in these electrodes either originates from lithium-containing electrolyte decomposition products or the LiPAA binder. Based on the NDP spectra of the silicon-graphite electrodes after a different number of cycles, we demonstrate that the irreversible capacity obtained from charge-discharge cycling is directly proportional to the total amount of lithium-containing electrolyte decomposition products that accumulated in the electrodes during the same period. Further, we show that this accumulation is also reflected by the increase of the entire mass loading (coating + SEI) and the significant swelling of the electrodes (+140% in the delithiated state), thus following the two major degradation phenomena of silicon-graphite electrodes, which we discussed in our previous publication.4 In addition, we support our analysis by complementing the NDP spectra with high-resolution cross-sectional scanning electron microscopy (SEM) images of the silicon-graphite electrodes after different numbers of cycles. Finally, we analyze the energy loss of the 3H particles emitted by the nuclear reaction of 6Li with thermal neutrons as a function of the electrode depth, determining the evolution of the lithium concentration gradients across the thickness of the electrodes and discussing the implications on the utilization of the active materials near the separator/anode and the anode/current collector interface. Our analysis allows to shape a refined explanation of the accumulation of electrolyte decomposition products in silicon-graphite electrodes and its implication both on the changes in electrode morphology and the resulting electrochemical performance.

Silicon-carbon (Si/C) composites hold great promise as substitutes for conventional graphite anodes in high-specific-energy lithium-ion batteries (LIBs). However, their performance is hindered by silicon's substantial volume expansion during cycling, which can lead to electrode degradation. Traditional poly(acrylic acid) (PAA) binders often struggle to maintain electrode integrity under these conditions. To address this challenge, polyether modified polyurethane acrylic (PUMA) is used as physicochemical cocrosslinking polymer. PUMA offers superior mechanical properties, elasticity, and interfacial stability, enabling it to effectively accommodate silicon's volume changes and prevent electrode fracture. Through a simple preparation process, we used PUMA as a slurry additive in combination with PAA to form a functional composite binder, facilitating the construction of a stable and robust SEI film. This is conducive to alleviating the volume expansion of silicon and ensuring the cycling stability of the electrode. In Si/C450 half-cells, electrodes enhanced by our binder show a remarkable longevity, maintaining 97.26% of their capacity post 200 cycles at 0.5 C. The full cells Si/C450||NCM811 display a notable performance, achieving a capacity retention of 82.10% after 100 cycles at 0.2 C. These findings underscore the potential of our innovative binder design in enhancing the efficacy of silicon-based anodes in high-energy LIBs.

Na2SnO3 as a novel anode for high performance lithium storage and its electrochemical reaction mechanism

With the ever-increasing demand for energy storage, lithium ion battery has been an attractive technology, which has revolutionized the portable electronic industry and has recently become popular in the electric vehicle market, due to their superior energy density [1]. Innovative materials chemistry has been the key to various advancements in lithium rechargeable battery [2]. Various transition metal oxides have been widely studied as electrode materials for rechargeable lithium-ion batteries because of their high theoretical capacity, safety, environmental benignity and low cost [3]. Recently, there is great interest in developing graphene-based nanocomposites as high performance electrodes, owing to the multifunctional attributes of such electrodes [4]. Such materials designs are expected to offer marked improvements in energy and power densities. Here, we present the synthesis of Nb2O5 anchored graphene hybrid nanocomposites through simple hydrothermal method and their application as high performance anodes for lithium ion battery. Self-supported nanostructured electrode with graphene as support and with homogenously anchored Nb2O5 nanoparticles has been obtained as shown in Figure 1a. Nanostructured hybrid electrodes have been characterized by X-ray diffraction (XRD), Scanning and Transmission Electron Microscopy (SEM/TEM). Cyclic voltammetry and Galvanostatic charge-discharge cycling measurements have been performed using hybrid nanocomposites as positive electrodes in 1 M LiPF6 –EC/DMC electrolyte vs.Li metal negative electrodes. Electrochemical studies of these hybrid electrodes show improved reversible capacities and power capabilities.Conducting graphene sheets improves the kinetics of the lithium ion and electron transport, and conductivity of the metal oxide by the enhanced particle-particle contact and buffering action during lithiation. Synergistic effect of both Nb2O5 nanocrystals anchored onto conducting graphene layers showed reversible capacity of 192 mAhg-1 up to 50 cycles with C/10 rate, indicating two electron transfer process in LixNb2O5 (Figure 1b). Nb2O5anchored graphene sheets with superior electrochemical performance of high reversible capacity, enhanced rate capability, including an improved electronic and ionic conductivity, can be ideal anodes for high performance lithium ion battery. Figure1: (a) TEM image of Nb2O5-anchored graphene nanocomposites; (b) Charge-discharge galvanostatic curves for Nb2O5-anchored graphene electrtodes cycled at a rate of C/10 versus Li and using a charge cut off voltage of 1 V. References J. -M. Tarascon, M. Armand, Nature, 414 (2001), 359.P. G. Bruce, B. Scrosati, J. -M. Tarascon, Angewandte Chemie International Edition, 47, (2008), 2930.P. Poizot, S. Laruelle, S. Grugeon, L. Dupont & J-M. Tarascon, Nature 407, (2000), 496.Z.-S. Wu, W. Ren, L. Xu, F. Li, H.-M. Cheng, ACS Nano 5, (2011), 5463.

This study reports the synthesis of a few-layered graphene (GF) thin film on Ni foam by chemical vapor deposition (CVD) technique and investigation of its electrochemical performance as a negative electrode for lithium-ion batteries (LIBs). A standard deposition procedure with a methane precursor was employed to prepare the GF films. The SEM studies revealed the formation of a dark uniform film on the surface of Ni foam’s wires upon the CVD deposition. The film consisted of numerous GF sheets replicating the shape of the Ni grain boundaries over the Ni wire surface. The Raman spectroscopy of the prepared films on the Ni foam confirmed that the samples are a few-layered GF with high quality and purity. In order to evaluate the potential of the use of the prepared materials as an anode in LIBs, their electrochemical performance was studied in coin-type lithium half-cells using cyclic voltammetry (CV) and galvanostatic cycling. The results of CV showed that both graphene and native oxide layer (NiO) on nickel foam exhibit electrochemical activity with respect to lithium ions. Galvanostatic cycling revealed that both GF and NiO contribute to the overall capacity, which increases upon cycling with a stable Coulombic efficiency of around 99%. The designed 3D GF coated NiO/Ni anode demonstrated a gradual increase of its areal charge capacity from 65 μAh cm-2 at the initial cycle to 250 μAh cm-2 at the final 250th cycle.

High lithium anodic performance of reduced Sn particles on Co metal-organic frameworks for lithium-ion batteries with a long-cycle life

The electrochemical behavior of silicon-based anodes in lithium-ion batteries can be largely influenced by the cut-off potentials. Due to the strongly sloped voltage profile of silicon, changes in the cut-off potentials highly impact the degree of lithiation, and thus the associated volume expansion of the Li-Si alloy.1 While the lithiation cut-off potential of silicon has been addressed in several studies by the groups of Obrovac and Dahn, who highlighted the relevance of the crystalline Li15Si4 phase that forms at potentials below 0.07 V vs. Li/Li+, the de-lithiation cut-off potential of silicon is less understood.2–4 Recently, Klett et al. discussed the beneficial effect of a limited delithiation cut-off potential on the capacity retention of NCM523/silicon-graphite full-cells.5 In the present study, we evaluate the impact of the delithiation cut-off potential on the silicon particle degradation. Building up on previous studies,5,6 our characterization is concerned with the underlying morphological changes the silicon particles undergo during repeated cycling, which ultimately affect the entire electrode integrity. To test this hypothesis, silicon-graphite composite electrodes with a practical areal capacity of ~1.8 mAh cm-2 were prepared, consisting of 35 wt% nanometer-sized silicon (~200 nm) and 45 wt% graphite (~20 µm). Vapor grown carbon fibers and lithiated poly(acrylic acid) binder accounted for the remaining 20 wt%. Utilizing SiG//LiFePO4 Swagelok T-cells with a capacitively oversized positive electrode (~3.5 mAh cm-2) and a stable reference potential of ~3.45 V vs. Li/Li+, three cut-off conditions of the silicon-graphite electrodes, shown in Figure 1, were investigated. First, the silicon-graphite electrodes were fully lithiated to 0.01 V vs. Li/Li+ and completely delithiated to 1.25 V vs. Li/Li+ (brown curve). Second, we limited either the lithiation cut-off potential to 0.05 V vs. Li/Li+ (red curve) or, alternatively, the delithiation cut-off potential to 0.65 V vs. Li/Li+ (blue curve), with the latter two resulting in a capacity utilization of ~80%. By differential capacity analysis of selected galvano-static cycles we demonstrate that silicon-graphite electrodes with a limited delithiation cut-off potential of 0.65 V vs. Li/Li+ show less overpotential growth and significant improvement in capacity retention upon cycling. These observations are further supported by impedance spectroscopy at different states-of-charge using a gold-wire reference electrode to obtain individual impedance spectra from the positive and the negative electrode.7 Figure 1 . Voltage profiles of silicon-graphite electrodes (5th cycles) operated at different cut-off conditions. The data were obtained from SiG//LiFePO4 Swagelok-T cells with a gold-wire reference electrode that was sandwiched between two glass fiber separators soaked with an electrolyte of LP57 + 5 wt% FEC. Areal SiG capacity: ~1.8 mAh cm-2. The electrochemical results are complemented by transmission and scanning electron microscopy of the silicon particles and composite electrodes. The structural analysis indicates that the repeated delithiation of silicon particles to highly oxidative potentials (1.25 V vs. Li/Li+) causes dealloying reactions, which result in a roughening of the particle surface and the formation of highly porous structures, leading to significantly increased irreversible capacity losses and electrode polarization. Finally, a comparison of the different cut-off conditions and a proposal for an improved cycling protocol for silicon-graphite electrodes are discussed.

With the increased demand for developing energy storage technologies, lithium-ion batteries have been considered as one of the most promising candidates due to its high energy density, excellent cyclic performance, and environmental benignity. Indeed, extensive applications of lithium-ion batteries are witnessed in the market, for example, in portable electronic equipment. However, the commercialized graphite anodes for lithium-ion batteries exhibiting low theoretical specific capacity is far from meeting the tremendous demands created by the fast-growing market. Therefore, enormous efforts have been devoted to developing desirable electrode materials with better recyclability and advanced capacity for next-generation lithium-ion batteries. Although alloy anode materials like silicon have the highest gravimetric and volumetric capacity, its huge volume change and low electron and ions conductivity still hinder the broad application in other fields, such as large-scale energy storage systems. Similar challenges also impede the wide implementation of conversion materials in Li-ion batteries. This work is focused on employing different highly conductive materials to improve the electrical conductivity of the entire electrode. At the same time, the formation of the conductive framework is beneficial to accommodate the substantial volume change of the active materials. In Chapter 3, copper nanowires and multi-wall carbon nanotubes coated on the surface of Cu foils built a porous substrate to support the active materials. Silicon was deposited on the porous substrate by the template of copper nanowires and multi-wall carbon nanotubes. The formation of copper nanowires/silicon and multi-wall carbon nanotubes/silicon core-shell structures intrinsically reduces the volume expansion of active materials. Meanwhile, the poles created by the intertwined copper nanowires and multi-wall carbon nanotubes further accommodate the stress from volume change. In addition, the copper nanowires/silicon and multi-wall carbon nanotubes/silicon core-shell structure provide the highly efficient electrons and Li+ diffusion pathways. As a result, we have demonstrated that multi-wall carbon nanotubes/copper nanowires/silicon delivers a high specific capacity of 1845 mAh g-1 in a half cell at a current density of 3.5 A g-1 after 180 cycles with a capacity retention of 85.1 %. In Chapter 4, a free-standing silicon-based anode was developed by preparing a three-dimensional copper nanowires/silicon nanoparticles@carbon composite using freeze-drying. Silicon nanoparticles were uniformly attached along with the copper nanowires, which was reinforced by the carbon coatings. The three-dimensional conductive structure allows the silicon nanoparticles to distribute evenly as well as enhance the electrical and ionic conductivity of the whole electrode. Similarly, considerable interspace produced by the three-dimensional structure can relieve the stress produced by the vast volume expansion of silicon nanoparticles, which is also restricted by the carbon coating layers during the charge and discharge processes. Moreover, the outer layers strengthen the stability of the three-dimensional framework and the contact between the copper nanowires and silicon nanoparticles. The electrochemical performance of copper nanowires/silicon nanoparticles@carbon composite electrode has been measured, which exhibits excellent cycling performance. In Chapter 5, a new highly conductive material, MXene nanosheets, was introduced to promote the electrochemical performance in lithium-ion batteries. In this chapter, the cobalt oxides were chosen as the active material for its controllable and facile synthesis methods. Meanwhile, cobalt oxides, one of the conversion materials as anodes for lithium-ion batteries, face similar issues with silicon. Therefore, an anode involving cobalt oxides nanoparticles mixed with MXene nanosheets on Ni foams has been developed. Small-size cobalt oxides nanoparticles were uniformly distributed within the MXene nanosheets leading to high lithium ions and electrons transmission efficiency, as well as preventing restacking of MXene nanosheets and colossal volume change of the cobalt oxides nanoparticles. As shown in Chapter 5, cobalt oxides /MXene composite electrode remains a stable capacity of 307 mAh g-1 after 1000 cycles when the current density approaches 5 C, which indicates the enormous potential of cobalt oxides/MXene composite as an anode for the high-performance lithium-ion batteries.

Gas-liquid interfacial assembly and electrochemical properties of 3D highly dispersed α-Fe2O3@graphene aerogel composites with a hierarchical structure for applications in anodes of lithium ion batteries