Bilayer-graphene-coated Si nanoparticles as advanced anodes for high-rate lithium-ion batteries

Ultrathin Carbon Sheet Obtained by Self-Template Method toward Highly Effective Charge Transfer for Si-Based Anodes

A dynamic and stable charge transfer process is the key to exerting lithium storage characteristics of the silicon anode with a large volume change. In this work, the composite with an ultrathin carbon sheet skeleton is prepared by freeze-drying and a copyrolysis process after uniformly mixing citric acid and hydroxylated Si NPs, which is different from traditional conformal carbon coating derived from citric acid. A flexible carbon sheet reduces internal particle (Si-OH@NC) slip and cooperates with interfacial Si-O-C bonding to buffer machinal stress in the electrode during cycling. More importantly, the carbon sheet network increases the point-to-surface contact area between the active material and the conductive agent, ensures continuous electrical connection from the current collector to the active material, and promotes a rapid and stable electron transfer process. Besides, the N-doped C structure with remarkable nucleophilicity guarantees fast ion transport, which is confirmed by theoretical calculation. In this way, the reaction reversibility of the Si-based electrode is further realized during cycles. As a result, the electrode delivers excellent cycle performance (reversible capacity of 1001.9 mAh g-1 at 1 A g-1 after 500 cycles) and rate performance (capacity retention of 86.8 and 65.8% at 1 and 3 A g-1, respectively, compared to 0.2 A g-1). The idea of constructing a highly efficient electrode conductive network through a doped-carbon sheet network is also applicable to other active materials with huge volume changes during lithium storage.

Interface Engineering Enables Wide-Temperature Li-Ion Storage in Commercial Silicon-Based Anodes

Silicon-based materials have been considered potential anode materials for next-generation lithium-ion batteries based on their high theoretical capacity and low working voltage. However, side reactions at the Si/electrolyte interface bring annoying issues like low Coulombic efficiency, sluggish ionic transport, and inferior temperature compatibility. In this work, the surface Al2 O3 coating layer is proposed as an artificial solid electrolyte interphase (SEI), which can serve as a physical barrier against the invasion of byproducts like HF(Hydrogen Fluoride) from the decomposition of electrolyte, and acts as a fast Li-ion transport pathway. Besides, the intrinsically high mechanical strength can effectively inhibit the volume expansion of the silicon particles, thus promoting the cyclability. The as-assembled battery cell with the Al2 O3 -coated Si-C anode exhibits a high initial Coulombic efficiency of 80% at RT and a capacity retention ratio up to ≈81.9% after 100 cycles, which is much higher than that of the pristine Si-C anode (≈74.8%). Besides, the expansion rate can also be decreased from 103% to 50%. Moreover, the Al2 O3 -coated Si-C anode also extends the working temperature from room temperature to 0 °C-60 °C. Overall, this work provides an efficient strategy for regulating the interface reactions of Si-based anode and pushes forward the practical applications at real conditions.

Preparation of Buffered Nano-Submicron Hierarchical Structure Hollow SiOx @C Anodes for Lithium-Ion Battery Materials with Carboxymethyl Chitosan

Silicon-based materials are among the most promising anode materials for next-generation lithium-ion batteries. However, the volume expansion and poor conductivity of silicon-based materials during the charge and discharge process seriously hinder their practical application in the field of anodes. Here, we choose carboxymethyl chitosan (CMCS) as the carbon source coating and binding on the surface of nano silicon and hollow silicon dioxide (H-SiO2 ) to form a hierarchical buffered structure of nano-hollow SiOx @C. The hollow H-SiO2 can alleviate the volume expansion of nano silicon during the lithiation process under continuous cycling. Meanwhile, the carbon layer carbonized by CMCS containing N-doping further regulates the silicon's expansion and improves the conductivity of the active materials. The as- prepared SiOx @C material exhibits an initial discharge capacity of 985.4 mAh g-1 with the decay rate of 0.27 % per cycle in 150 cycles under the current density of 0.2 A g-1 . It is proved that the hierarchical buffer structure nano-hollow SiOx @C anode material has practical application potential.

Toward the Improvement of Silicon-Based Composite Electrodes via an In-Situ Si@C-Graphene Composite Synthesis for Li-Ion Battery Applications

Using Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g^-1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways.

High-ICE and High-Capacity Retention Silicon-Based Anode for Lithium-Ion Battery

Silicon-based anodes are promising to replace graphite-based anodes for high-capacity lithium-ion batteries (LIB). However, the charge–discharge cycling suffers from internal stresses created by large volume changes of silicon, which form silicon-lithium compounds, and excessive consumption of lithium by irreversible formation of lithium-containing compounds. Consumption of lithium by the initial conditioning of the anode, as indicated by low initial coulombic efficiency (ICE), and subsequently continuous formation of solid-electrolyte-phase (SEI) on the freshly exposed silicon surface, are among the main issues. A high-performance, silicon-based, high-capacity anode exhibiting 88.8% ICE and the retention of 2 mAh/cm² areal capacity after 200 discharge–charge cycles at the rate of 1 A/g is reported. The anode is made on a copper foil using a mixture of 70%:10%:20% by weight ratio of silicon flakes of 100 × 800 × 800 nm in size, Super P conductivity enhancement additive, and an equal-weight mixture of CMC and SBR binders. Pyrolysis of fabricated anodes at 700 °C in argon environment for 1 h was applied to convert the binders into a porous graphitic carbon structure that encapsulates individual silicon flakes. The porous anode has a mechanically strong and electrically conductive graphitic carbon structure formed by the pyrolyzed binders, which protect individual silicon flakes from excessive reactions with the electrolyte and help keep small pieces of broken silicon flakes together within the carbon structure. The selection and amount of conductivity enhancement additives are shown to be critical to the achievement of both high-ICE and high-capacity retention after long cycling. The Super P conductivity enhancement additive exhibits a smaller effective surface area where SEI forms compared to KB, and thus leads to the best combination of both high-ICE and high-capacity retention. A silicon-based anode exhibiting high capacity, high ICE, and a long cycling life has been achieved by the facile and promising one-step fabrication process.

Enhanced Electrochemical Performance Promoted by Tin in Silica Anode Materials for Stable and High-Capacity Lithium-Ion Batteries

Although the silicon oxide (SiO2) as an anode material shows potential and promise for lithium-ion batteries (LIBs), owing to its high capacity, low cost, abundance, and safety, severe capacity decay and sluggish charge transfer during the discharge-charge process has caused a serious challenge for available applications. Herein, a novel 3D porous silicon oxide@Pourous Carbon@Tin (SiO2@Pc@Sn) composite anode material was firstly designed and synthesized by freeze-drying and thermal-melting self-assembly, in which SiO2 microparticles were encapsulated in the porous carbon as well as Sn nanoballs being uniformly dispersed in the SiO2@Pc-like sesame seeds, effectively constructing a robust and conductive 3D porous Jujube cake-like architecture that is beneficial for fast ion transfer and high structural stability. Such a SiO2@Pc@Sn micro-nano hierarchical structure as a LIBs anode exhibits a large reversible specific capacity ~520 mAh·g-1, initial coulombic efficiency (ICE) ~52%, outstanding rate capability, and excellent cycling stability over 100 cycles. Furthermore, the phase evolution and underlying electrochemical mechanism during the charge-discharge process were further uncovered by cyclic voltammetry (CV) investigation.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.