Carbon-coated Silicon Monoxide Research Articles

A stable full cell having high energy density realized by using a three-dimensional current collector of carbon nanotubes and partial prelithiation of silicon monoxide

The prelithiation of SiO-based negative electrodes is essential for stable and high-energy-density Li secondary batteries. In this study, a new partial prelithiation method by two-stack electrodes was developed using lightweight and high-capacity carbon-coated silicon monoxide (SiO/C) films held in a sponge-like matrix of carbon nanotubes (CNTs). The charge-discharge cycles of a full cell with the partially prelithiated SiO/C-CNT negative electrode (p-LixSiO/C-CNT with SiO/C content of 85 mass%) and LiNi0.8Mn0.1Co0.1O2 (NCM811)-CNT positive electrode (NCM content of 97 mass%) reduced the irreversible capacity, achieving high energy densities per the total mass of the negative and positive electrodes of 542 and 420 W h kgelectrode−1 at the 1st and 300th cycle, respectively, with high areal capacities of 4.6 and 3.1 mA h cm−2 for the negative and positive electrodes. The flexible CNT sponge matrix expanded/shrunk reversibly during lithiation/delithiation and retained its structure, whereas the thin Li metal formed Li dendrites and dead Li after cycling, as demonstrated by scanning electron microscopy. The partial prelithiation method of simply stacking the pristine SiO/C-CNT film with a fully prelithiated film enables the careful control of the degree of prelithiation, contributing to full cells of various chemistries.

Carbon-coated SiO for LIBs with superior capacity and cycle stability

Silicon monoxide (SiO) is suggested as anode for LIBs with excellent theoretical capacity. Unfortunately, the low electrical conductivity and volume expansion limit its practical application. The preparation of SiO@C composites can effectively solve these problems. SiO@C composite materials are constructed with phenolic resin pyrolysis method. Experimental data indicate that SiO@C-20 with carbon content of 20 wt% possesses a high discharge capacity and superior initial coulombic efficiency (74.81 %) compared to others. The superior performance can be attributed mainly to carbon ratio with adjusting phenolic resin.

Stable and high-capacity SiO negative electrode held in reversibly deformable sponge-like matrix of carbon nanotubes

A lightweight, high-capacity negative electrode was developed by suspending carbon-coated silicon monoxide (SiO/C) particles in a sponge-like matrix of carbon nanotubes (CNTs) without using metal foils or polymeric binders. High initial delithiation capacities per electrode (SiO/C + CNT) of >1200 mA h gelectrode−1 and >1100 mA h cmelectrode−3 were achieved with an optimum SiO/C content of 85 mass%. The lithiation/delithiation cycle with capacity control at a 45% SiO utilization ratio achieved a high delithiation capacity of 584 mA h gelectrode−1 for 236 cycles. In addition, the flexible and electrically conductive CNT sponge matrix enabled reversible expansion/shrinkage of the entire electrode during lithiation/delithiation, as evidenced by scanning electron microscopy.

A novel double-coated anode material SiOx/C/Cu2O for lithium ion batteries

Silicon monoxide (SiOx, 0 < x < 2) has been one of the new directions of scientific researchers because of some characteristics, such as higher theoretical specific capacity and lower volume expansion efficiency. However, its disadvantages such as the volume expansion effect and poor conductivity still exist in the process of charge and discharge, which limit its commercialization process. In this paper, cuprous oxide and carbon coated silicon monoxide (SiOx/C/Cu2O) composites were obtained by high temperature heat treatment. In the SiOx/C/Cu2O anodes, carbon can buffer the volume expansion of the lithium intercalation, enhance the conductivity of the material, reduce the contact between the electrolyte and the active substance, Cu2O can further reduce the contact between the electrolyte and the active substance, greatly buffer the change of electrode structure and improve the overall cycling performance. After the rate of 0.5C (1C = 2100 mA g−1) for 500 cycles, the discharge specific capacity is 704.0 mAh g−1, about 350 mAh g−1 higher than SiOx, which shows excellent long-cycle ultra-high stability.

Lithium/Boron Co-doped Micrometer SiOx as Promising Anode Materials for High-Energy-Density Li-Ion Batteries.

The carbon-coated silicon monoxide (SiOx@C) has been considered as one of the most promising high-capacity anodes for the next-generation high-energy-density lithium-ion batteries (LIBs). However, the relatively low initial Coulombic efficiency (ICE) and the still existing huge volume expansion during repeated lithiation/delithiation cycling remain the greatest challenges to its practical application. Here, we developed a lithium and boron (Li/B) co-doping strategy to efficiently enhance the ICE and alleviate the volume expansion or pulverization of SiOx@C anodes. The in situ generated Li silicates (LixSiOy) by Li doping will reduce the active Li loss during the initial cycling and enhance the ICE of SiOx@C anodes. Meanwhile, B doping works to promote the Li+ diffusion and strengthen the internal bonding networks within SiOx@C, enhancing its resistance to cracking and pulverization during cycling. As a result, the enhanced ICE (83.28%), suppressed volume expansion, and greatly improved cycling (85.4% capacity retention after 200 cycles) and rate performance could be achieved for the Li/B co-doped SiOx@C (Li/B-SiOx@C) anodes. Especially, the Li/B-SiOx@C and graphite composite anodes with a capacity of 531.5 mA h g-1 were demonstrated to show an ICE of 90.1% and superior cycling stability (90.1% capacity retention after 250 cycles), which is significant for the practical application of high-energy-density LIBs.

Onion-like Synergetic Multilayer Coating for High-Stability Silicon Monoxide Anode in Lithium-Ion Batteries

Silicon monoxide (SiO) is a potential next-generation high-capacity anode material for lithium-ion batteries. However, SiO undergoes severe volume change during charge and discharge, which leads to mechanical failure and thus fast capacity decay. Nano-structuring has been reported as an effective method to improve cycle stability of SiO by preventing particle pulverization and increasing void content to accommodate the large volume change. Though, nano-particles are difficult to handle and energy-intensive to manufacture in large scale. In addition, the larger surface area facilitates side reactions between active material and electrolyte. Therefore, the use of micron-size materials is desirable. Herein, we engineer a multilayer surface coating on micron-sized (5 µm) carbon-coated SiO particles (SiO@C) to enhance the stability of the electrode during charge and discharge. The layer of carbon on SiO@C enhances its electrical conductivity. The material is treated with ultra-violet irradiation to generate -OH functional groups on its surface. The resulting particles are treated with an organosilane self-assembled monolayer (SAM) with (3-aminopropyl)triethoxysilane (APTES). The powder is then further combined with imide monomers and heat-treated to form a robust chemical bonding between the amine (-NH2) functional group of the SAM and the dianhydride group of the polyimide (PI) on the surface. The resulting SiO@C@UV@NH2@PI composite possesses excellent mechanical stability, where the high-modulus PI layer suppresses volume change, particle pulverization and electrode cracking during charge and discharge. In addition, the PI coating reduces side reactions between the electrolyte and the active material and improves the Coulombic efficiency of the electrode. Our study demonstrates that the SiO@C electrode with the multilayer coating exhibits a stable capacity of 1310.7 mAh g-1 after 100 cycles at 150 mA g-1, and a capacity of 910.3 mAh g-1 (capacity retention 94.2%, with respect to the 2nd cycle) under 1 A g-1 after 300 cycles. In comparison, SiO@C electrode without surface coating gives only a reversible capacity of 247.1 mAh g-1 after 100 cycles, with a 15.1% capacity retention (see Figure 1a). Figure 1b shows a comparison of the thickness change of the two SiO electrodes during charge-discharge, verifying that the multilayer coating can reduce volume expansion. Further characterizations of the surface-coated material to identify the mechanism of the improvement are underway and more data will be presented at the meeting. Figure 1

Insights into the Interfacial Instability between Carbon-Coated SiO Anode and Electrolyte in Lithium-Ion Batteries

Carbon-coated SiO is the most promising alternative to the graphite anode for improving the energy density of currently commercialized lithium-ion batteries but exhibits poor cyclic stability that leaves an unclear mechanism. To address this issue, the surface properties of commercial carbon-coated silicon monoxide are investigated in a 1.0 M LiPF6-dimethyl carbonate electrolyte with and without ethylene carbonate (EC), with a comparison of graphite. Unlike graphite that can work well in the electrolytes with and without EC during initial 30 cycles, carbon-coated SiO suffers a serious capacity decay, especially in the electrolyte without EC. By identifying the samples after various cycles, it is found that a relatively stable interphase that makes graphite work well cannot be built on carbon-coated SiO. The chemical analyses demonstrate that there is a strong interaction between SiO with hydrofluoric acid in the electrolyte, which leads to destruction of the carbon-coating layer and prevents the formation of a protective interphase.

Enhanced electrochemical performance of SiO anode material via nitrogen-doped carbon coating in a facile and green route

Silicon monoxide (SiO) has triggered widespread attention due to its high-energy density and satisfied operating voltage. In this work, the nitrogen-doped carbon-coated SiO (SiO/NC) composite anode material was prepared by a facile and green sintering route. The raw SiO material was modified by using economical and eco-friendly citric acid and melamine as carbon and nitrogen sources. A homogeneous layer of amorphous nitrogen-doped carbon exists in the surface of SiO/NC composite, which is confirmed through XRD, SEM, TEM, EDS, and XPS analysis. The carbon coating in combination with the introduction of nitrogen atoms impels the as-prepared anode material to show better electrochemical performance than raw SiO anode. Specifically, the initial Li-extraction capacity of SiO/NC anode was enhanced to 1280mAhg−1 in contrast to 777mAhg−1 of the raw SiO electrode, and it still maintains 90.5% of capacity after 150cycles at 1000mAg−1. In addition, the SiO/NC anode achieves an excellent rate-capability of 880mAhg−1 at 2000mAg−1, while the non-coated SiO offers only 464mAhg−1. Above all, this synthesis strategy is beneficial to advance the production and applications of SiO anode materials in future LIBs.

SWNT Networks with Polythiophene Carboxylate Links for High-Performance Silicon Monoxide Electrodes

Carboxylated polythiophenes, such as poly[3-(potassium-4-butanoate) thiophene] (PPBT), play a critical role in securely connecting single-walled carbon nanotube (SWNT) electrical networks onto the surface of carbon-coated silicon monoxide (c-SiOx). These connections are a function of the materials’ surface chemistries and resultant physical/chemical bonding through favorable molecular interactions. Specifically, the PPBT π-conjugated backbone and alkyl side chain carboxylate moieties (COO−), respectively, physically interact with the SWNT and c-SiOx carbon layer π-electron-rich surfaces, and chemically bind to surface hydroxyl (−OH) species of the c-SiOx electroactive materials to form a carboxylate bond. This approach effectively captured pulverized particles that form during battery operation and beneficially suppressed the thickness change that electrodes typically undergo. The resultant electrodes exhibited superior electrochemical performance, which was ascribed to stable SEI layer formation, reduced...

Highly Graphitized Carbon Coating on SiO with a π⁻π Stacking Precursor Polymer for High Performance Lithium-Ion Batteries.

A highly graphitized carbon on a silicon monoxide (SiO) surface coating at low temperature, based on polymer precursor π–π stacking, was developed. A novel conductive and electrochemically stable carbon coating was rationally designed to modify the SiO anode materials by controlling the sintering of a conductive polymer, a pyrene-based homopolymer poly (1-pyrenemethyl methacrylate; PPy), which achieved high graphitization of the carbon layers at a low temperature and avoided silicon carbide formation and possible SiO material transformation. When evaluated as the anode of a lithium-ion battery (LIB), the carbon-coated SiO composite delivered a high discharge capacity of 2058.6 mAh/g at 0.05 C of the first formation cycle with an initial Coulombic efficiency (ICE) of 62.2%. After 50 cycles at 0.1 C, this electrode capacity was 1090.2 mAh/g (~82% capacity retention, relative to the capacity of the second cycle at 0.1 °C rate), and a specific capacity of 514.7 mAh/g was attained at 0.3 C after 500 cycles. Furthermore, the coin-type full cell composed of the carbon coated SiO composite anode and the Li[Ni0.5Co0.2Mn0.3O2] cathode attained excellent cycling performance. The results show the potential applications for using a π–π stacking polymer precursor to generate a highly graphitize coating for next-generation high-energy-density LIBs.

Comparative Study on the Electrochemical Performances of SiO Anode Materials with Carbon-Coating and Boron-Doping for Lithium-Ion Batteries

Recently, Silicon monoxide (SiO) has been received much attention as an alternative choice instead of pure Si anode materials. When SiO anode undergoes lithiation processes, Li oxide (Li2O) and Li silicates (Li4SiO4) are mainly formed and that act as a more stable phase than the Li-Si alloys during long cycles. Moreover SiO is thermodynamically unstable at all temperatures, it can be easily transformed into nano-crystalline Si (nc-Si) and SiOx during heat treatment, triggering a disproportionation reaction. The nc-Si acts to increase the reversible capacity and the SiOx matrix plays an important role in accommodating the volume expansion of embedded nc-Si during alloying/de-alloying processes. However, the electrical conductivity of heat-treated SiO remains low because of this material’s intrinsic semiconductor nature and inactive phases. Carbon coating has been regarded as one of the most effective and typical ways to improve the electrochemical properties of SiOx. Dispersed carbon particles provide pathways for electron transfer and decrease the resistance of the electrode, thus resulting in improved conductivity and electrochemical properties of the SiO negative electrode. However, the local capacity fading caused by electrical loss between the active materials and the carbon coating is unavoidable during long cycle test. Moreover, carbon coating requires additional processing with carbon sources. In this study, we introduce a comparative study that consists of boron-doped SiO (HB-SiO) and carbon-coated SiO (HC-SiO) to verify the effective way for improving the electrochemical performances of SiO anode materials. From the electrochemical results, HB-SiO electrode exhibits about 1.6 times higher than that of HC-SiO electrode, having 611 mAh g-1 at 0.5 C rate after 500 cycles. Electrochemical impedance spectroscopy (EIS) measurement reveals that the internal resistance of the HB-SiO electrode is superior to that of HC-SiO electrode.

탄소가 코팅된 일산화규소(SiO) 음극에서 전해질 첨가제로서 Lithium Bis(oxalato)borate의 영향

As an electrolyte additive, the effects of lithium bis(oxalate)borate (LiBOB) on the electrochemical properties of a carbon-coated silicon monoxide (C-coated SiO) negative elec- trode are investigated. The used electrolyte is 1.3 M LiPF6 that is dissolved in ethylene car- bonate (EC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) (5:25:70 v/v/v) with or without 0.5 wt. % LiBOB. In the LiBOB-free electrolyte, the film resistance is not so high

Nitrogen-doped carbon coating for a high-performance SiO anode in lithium-ion batteries

We report a simple process to coat silicon monoxide (SiO) particles with nitrogen-doped carbon layers (NC-SiO) by using a nitrogen-containing ionic liquid. The nitrogen-doping addresses the moderate electric conductivity of SiO particles as large as 20μm and thus enables NC-SiO to exhibit substantially improved specific capacity and rate performance as compared to those of bare carbon-coated SiO (C-SiO) and bare SiO counterparts. Due to the simplicity of the coating procedure, the current approach should be readily applicable to other lithium battery electrodes that suffer from low electronic conductivities.

Capacity variation of carbon-coated silicon monoxide negative electrode for lithium-ion batteries

The capacity variation observed with a carbon-coated silicon monoxide (C-SiO) composite electrode has been explained by the microstructural changes evolved during cycling. In an initial few cycles, the Si domain in SiO is lithiated by alloying reaction, during which cracks form in the Si domain due to volume change. An increase in the contact area between Si and electrolyte solution due to the crack formation, and down-sizing of Si particles facilitate the lithiation reaction, such that the Si domain is lithiated to the most lithium-rich Li–Si phase (Li15Si4). Due to an increase in the degree of lithiation, the reversible capacity steadily increases. A severe volume change that is accompanied by the full lithiation, however, leads to a serious particle crack and pulverization, and surface film deposition on the newly exposed Si surface. All these features lead to a breakdown of electrically conductive network within the electrode layer. As a result, some Si particles are electrically isolated to cause a loss in the reversible capacity.

Electrochemical behavior of carbon-coated silicon monoxide electrode with chromium coating in rechargeable lithium cell

The effects of Cr coating are studied with respect to improving the electrochemical characteristics of carbon-coated silicon monoxide anodes in rechargeable Li cells. The Cr coating is applied by ion beam sputtering. Analyses of the coating are carried out by EDX, SEM, TEM, and EPMA. A coin cell (CR2032) with a carbon-coated SiOx anode coated with Cr and a lithium cobalt oxide (LCO) cathode is assembled in an argon-filled glove box. The charged capacity of the Cr-coated SiOx–C/LCO cell is 1127 mAh g−1 in the 1st cycle at 0.1 C, while that of the uncoated SiOx–C/LCO cell is 956 mAh g−1. In addition, the Cr-coated SiOx–C/LCO cell has a discharged capacity of 733 mAh g−1, which is higher than that of the uncoated cell (635 mAh g−1). Furthermore, the discharge capacity retention ratio (100th:2nd) of the Cr-coated cell is 75% while that of the uncoated cell is 69%. The rate capability of the Cr-coated cell is superior to that of the uncoated cell. Cr has good electrical conductivity, enabling more Li ions to be stored in the Cr-coated cell than in the uncoated cell. Investigations into the improved electrochemical characteristics are carried out through the analyses of impedance, voltage profile, and cycle data.

Electrochemical behavior of a lithium-pre-doped carbon-coated silicon monoxide anode cell

Owing to high energy density, silicon monoxide is an attractive anode material for lithium ion secondary batteries. However, its huge irreversible capacity during initial cycling makes it difficult to use in lithium secondary batteries. A new technique for lithiation in the silicon monoxide has been developed using Li powders. The electrochemical behavior of the lithium powder pre-doped carbon-coated silicon monoxide (OG) anode cell was studied. The cells showed reduced initial irreversibility and enhanced coulombic efficiency. The behavior of the cells was analyzed by X-ray diffraction and electrochemical testing methods.