Carbon coating may expedite the fracture of carbon-coated silicon core-shell nanoparticles during lithiation

Fracture Resistant CrSi2-Doped Silicon Nanoparticle Anodes for Fast-Charge Lithium-Ion Batteries

Lithium-ion batteries (LIBs) has been developed over the last three decades. Increased amount of silicon (Si) is added into graphite anode to increase the energy density of LIBs. However, the amount of Si is limited, due to its structural instability and poor electronic conductivity so a novel approach is needed to overcome these issues. In this work, the synthesized chromium silicide (CrSi2) doped Si nanoparticle anode material achieves an initial capacity of 1729.3 mAh g-1 at 0.2C and retains 1085 mAh g-1 after 500 cycles. The new anode also shows fast charge capability due to the enhanced electronic conductivity provided by CrSi2 dopant, delivering a capacity of 815.9 mAh g-1 at 1C after 1000 cycles with a capacity degradation rate of <0.05% per cycle. An in situ transmission electron microscopy is used to study the structural stability of the CrSi2-doped Si, indicating that the high control of CrSi2 dopant prevents the fracture of Si during lithiation and results in long cycle life. Molecular dynamics simulation shows that CrSi2 doping optimizes the crack propagation path and dissipates the fracture energy. In this work a comprehensive information is provided to study the function of metal ion doping in electrode materials.

Elastic Buffering Layer on CuS Enabling High-Rate and Long-Life Sodium-Ion Storage

The latest view suggests the inactive core, surface pulverization, and polysulfide shuttling effect of metal sulfides are responsible for their low capacity and poor cycling performance in sodium-ion batteries (SIBs). Whereas overcoming the above problems based on conventional nanoengineering is not efficient enough. In this work, erythrocyte-like CuS microspheres with an elastic buffering layer of ultrathin polyaniline (PANI) were synthesized through one-step self-assembly growth, followed by in situ polymerization of aniline. When CuS@PANI is used as anode electrode in SIBs, it delivers high capacity, ultrahigh rate capability (500 mAh g^-1 at 0.1 A g^-1, and 214.5 mAh g^-1 at 40 A g^-1), and superior cycling life of over 7500 cycles at 20 A g^-1. A series of in/ex situ characterization techniques were applied to investigate the structural evolution and sodium-ion storage mechanism. The PANI swollen with electrolyte can stabilize solid electrolyte interface layer, benefit the ion transport/charge transfer at the PANI/electrolyte interface, and restrain the size growth of Cu particles in confined space. Moreover, finite element analyses and density functional simulations confirm that the PANI film effectively buffers the volume expansion, suppresses the surface pulverization, and traps the polysulfide.

Strategies for Controlling or Releasing the Influence Due to the Volume Expansion of Silicon inside Si-C Composite Anode for High-Performance Lithium-Ion Batteries

Currently, silicon is considered among the foremost promising anode materials, due to its high capacity, abundant reserves, environmental friendliness, and low working potential. However, the huge volume changes in silicon anode materials can pulverize the material particles and result in the shedding of active materials and the continual rupturing of the solid electrolyte interface film, leading to a short cycle life and rapid capacity decay. Therefore, the practical application of silicon anode materials is hindered. However, carbon recombination may remedy this defect. In silicon/carbon composite anode materials, silicon provides ultra-high capacity, and carbon is used as a buffer, to relieve the volume expansion of silicon; thus, increasing the use of silicon-based anode materials. To ensure the future utilization of silicon as an anode material in lithium-ion batteries, this review considers the dampening effect on the volume expansion of silicon particles by the formation of carbon layers, cavities, and chemical bonds. Silicon-carbon composites are classified herein as coated core-shell structure, hollow core-shell structure, porous structure, and embedded structure. The above structures can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability, with the potential for performance enhancement. Finally, a perspective on future studies on Si-C anodes is suggested. In the future, the rational design of high-capacity Si-C anodes for better lithium-ion batteries will narrow the gap between theoretical research and practical applications.

Encapsulation of core–satellite silicon in carbon for rational balance of the void space and capacity

A novel core–satellite architecture with an elaborate structural design for rational balance of the void space and capacity.

Stress-Affected Lithiation Reactions in Elasto-Viscoplastic Si Particles with Hyperelastic Polymer Coatings: A Nonlinear Chemo-Mechanical Finite-Element Study

Stress-affected two-phase lithiation reactions in spherical elasto-viscoplastic Si particles for Li-ion batteries are studied here to determine the effects of a hyperelastic polymer coating on particle stresses, reaction front velocity, and degree of lithiation. The problem is modelled using finite-strain chemo-mechanical equations that couple stress, with Li-ion diffusion and reaction front velocity, and are solved using the finite-element (FE) approach, taking advantage of spherical symmetry of the problem. FE simulations and the sensitivity analysis reveal: (1) coating thickness is the most influential design parameter that affects the velocity of the reaction front, and (2) increasing values of the coating shear and bulk moduli, and the coating thickness reduce tensile circumferential stresses at the edge of the particle. The latter minimises the risk of particle cracking in the opening mode, but it can also accelerate the arrest of the reaction front, and thus reduce the particle lithiation degree in Li-ion battery anodes.

Hierarchical Graphene-Scaffolded Silicon/Graphite Composites as High Performance Anodes for Lithium-Ion Batteries

To better couple with commercial cathodes, such as LiCoO₂ and LiFePO₄ , graphite-based composites containing a small proportion of silicon are recognized as promising anodes for practical application in lithium-ion batteries (LIBs). However, the prepared Si/C composite still suffers from either rapid capacity fading or the high cost up to now. Here, the facile preparation of hierarchical graphene-scaffolded silicon/graphite composite is reported. In this designed 3D structure, Si nanoparticles are homogeneously dispersed on commercial graphites and then uniformly encapsulated in the hierarchical graphene scaffold. This hierarchical structure is also well characterized by the synchrotron X-ray computed nanotomography technique. When evaluated as anodes for LIBs, the hierarchical composite, with the Si weight ratio of 5 wt%, exhibits a reversible capacity of 559 mA h g^-1 at 75 mA g^-1 , suggesting an unprecedented utilization of Si up to 95%. Even at 372 mA g^-1 , the composite can still maintain a high capacity retention of 90% after 100 cycles. Coupled with the LiFePO₄ cathode, the full cell shows the high capacity of 114 mA h g^-1 at 170 mA g^-1 . The excellent Li-storage properties can be ascribed to the unique designed hierarchical structure.

Multiscale Engineered Si/SiO x Nanocomposite Electrodes for Lithium-Ion Batteries Using Layer-by-Layer Spray Deposition

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO _x nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO _x helps to accommodate the volume changes of the Si. Here, we demonstrate a new electrode architecture for further advancing the performance of Si/SiO _x nanocomposite anodes using a scalable layer-by-layer atomization spray deposition technique. We show that particulate C interlayers between the current collector and the Si/SiO _x layer and between the separator and the Si/SiO _x layer improved electrical contact and reduced irreversible pulverization of the Si/SiO _x significantly. Overall, the multiscale approach based on microstructuring at the electrode level combined with nanoengineering at the material level improved the capacity, rate capability, and cycling stability compared to that of an anode comprising a random mixture of the same materials.

Si/Ag/C Nanohybrids with in Situ Incorporation of Super-Small Silver Nanoparticles: Tiny Amount, Huge Impact

Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are in situ synthesized and homogeneously embedded in the in situ formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent I-V behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes.

In situ analytical techniques for battery interface analysis

Interface is a key to high performance and safe lithium-ion batteries or lithium batteries.

Self-Rearrangement of Silicon Nanoparticles Embedded in Micro-Carbon Sphere Framework for High-Energy and Long-Life Lithium-Ion Batteries

Despite its highest theoretical capacity, the practical applications of the silicon anode are still limited by severe capacity fading, which is due to pulverization of the Si particles through volume change during charge and discharge. In this study, silicon nanoparticles are embedded in micron-sized porous carbon spheres (Si-MCS) via a facile hydrothermal process in order to provide a stiff carbon framework that functions as a cage to hold the pulverized silicon pieces. The carbon framework subsequently allows these silicon pieces to rearrange themselves in restricted domains within the sphere. Unlike current carbon coating methods, the Si-MCS electrode is immune to delamination. Hence, it demonstrates unprecedented excellent cyclability (capacity retention: 93.5% after 500 cycles at 0.8 A g^-1), high rate capability (with a specific capacity of 880 mAh g^-1 at the high discharge current density of 40 A g^-1), and high volumetric capacity (814.8 mAh cm^-3) on account of increased tap density. The lithium-ion battery using the new Si-MCS anode and commercial LiNi_0.6Co_0.2Mn_0.2O₂ cathode shows a high specific energy density above 300 Wh kg^-1, which is considerably higher than that of commercial graphite anodes.