Multi-layered carbon coated Si-based composite as anode for lithium-ion batteries

Si@nitrogen-doped porous carbon derived from covalent organic framework for enhanced Li-storage

Due to ultra-high theoretical capacity (4200 mAh g^-1), silicon (Si) is an excellent candidate for the anode of lithium-ion batteries (LIBs). However, the application of Si is severely limited by its volume expansion of approximately 300% during the charge/discharge process. Herein, nitrogen-doped porous carbon (NC) capped nano-Si particles (Si@NC) composites with a core-shell structure were obtained by calcination of covalent organic frameworks (COFs) encapsulated nano-Si. COFs is a crystalline material with well-ordered structures, adjustable and ordered pores and abundant N atoms. After carbonization, the well-ordered pores and frameworks were kept well. Compared with other Si@NC composites, the well-ordered NC framework shell derived from COFs possesses high elasticity and well-ordered pores, which provides space for the volume expansion of nano-Si, and a channel to transfer Li⁺. The core-shell Si@NC composite exhibited good performances when applied as the anode of LIBs. At a current density of 100 mA g^-1, it exhibited a discharge-specific capacity of 1534.8 mAh g^-1 after 100 cycles with a first-coulomb efficiency of 69.7%. The combination of COFs with nano-Si is a better strategy for the preparation of anode materials of LIBs.

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.

Research Progress on Coating Structure of Silicon Anode Materials for Lithium-Ion Batteries

Silicon, which has been widely studied by virtue of its extremely high theoretical capacity and abundance, is recognized as one of the most promising anode materials for the next generation of lithium-ion batteries. However, silicon undergoes tremendous volume change during cycling, which leads to the destruction of the electrode structure and irreversible capacity loss, so the promotion of silicon materials in commercial applications is greatly hampered. In recent years, many strategies have been proposed to address these shortcomings of silicon. This Review focused on different coatings materials (e. g., carbon-based materials, metals, oxides, conducting polymers, etc.) for silicon materials. The role of different types of materials in the modification of silicon-based material encapsulation structure was reviewed to confirm the feasibility of the protective layer strategy. Finally, the future research direction of the silicon-based material coating structure design for the next-generation lithium-ion battery was summarized.

Recovery of porous silicon from waste crystalline silicon solar panels for high-performance lithium-ion battery anodes

A low-cost and easy-available silicon (Si) feedstock is of great significance for developing high-performance lithium-ion battery (LIB) anode materials. Herein, we employ waste crystalline Si solar panels as silicon raw materials, and transform micro-sized Si (m-Si) into porous Si (p-Si) by an alloying/dealloying approach in molten salt where Li⁺ was first reduced and simultaneously alloyed with m-Si to generate Li-Si alloy at the cathode. Subsequently, the as-prepared Li-Si alloy served as the anode in the same molten salt to release Li⁺ into the molten salt, resulting in the production of p-Si by taking advantage of the volume expansion/contraction effect. In the whole process, Li⁺ was shuttled between the electrodes in molten LiCl-KCl, without consuming Li salt. The obtained p-Si was applied as an anode in a half-type LIBs that delivered a capacity of 2427.7 mAh g^-1 at 1 A g^-1 after 200 cycles with a capacity retention rate of 91.5% (1383.3 mAh g^-1 after 500 cycles). Overall, this work offers a straightforward way to convent waste Si panels to high-performance Si anodes for LIBs, giving retired Si a second life and alleviating greenhouse gas emissions caused by Si production.

SiO x /C Composite Anode of Lithium-Ion Batteries with Enhanced Performances Using Multicomponent Binders

A silicon suboxide-carbon (SiO x /C, 1 ≤ x ≤ 2) composite anode of lithium-ion batteries (LIBs) with enhanced performance is prepared using an aqueous multicomponent binder technology. Considering the adhesive force, electrolyte absorption, and stability, different binders including sodium alginate (SA), polyacrylamide gel (PAM), polytetrafluoroethylene (PTFE), and their composites are evaluated. It is indicated that compared to other anodes with single- or multicomponent binders, the SiO x /C composite anode with PAM/SA/PTFE663 (PSAP663) binders exhibits strong adhesion, moderate electrolyte absorption ability, and a specific capacity of 427 mA h g-1 charge-discharged at 0.5 A g-1 after 300 cycles. The improvement of electrochemical performance is attributed to the comprehensive effects of composite binders, including the adhesion of active substances, surface protection, solution adsorption, conductive path, and so on. These results show that the PSAP663 binder has promising potential for application, which not only gives alternative practical schemes of the green binders for the SiO x /C anodes but also provides ideas to develop a high-performance adhesive technology for LIBs.

Flexible Carbon Nanotubes Confined Yolk-Shelled Silicon-Based Anode with Superior Conductivity for Lithium Storage

The further deployment of silicon-based anode materials is hindered by their poor rate and cycling abilities due to the inferior electrical conductivity and large volumetric changes. Herein, we report a silicon/carbon nanotube (Si/CNT) composite made of an externally grown flexible carbon nanotube (CNT) network to confine inner multiple Silicon (Si) nanoparticles (Si NPs). The in situ generated outer CNTs networks, not only accommodate the large volume changes of inside Si NPs but also to provide fast electronic/ionic diffusion pathways, resulting in a significantly improved cycling stability and rate performance. This Si/CNT composite demonstrated outstanding cycling performance, with 912.8 mAh g-1 maintained after 100 cycles at 100 mA g-1, and excellent rate ability of 650 mAh g-1 at 1 A g-1 after 1000 cycles. Furthermore, the facial and scalable preparation method created in this work will make this new Si-based anode material promising for practical application in the next generation Li-ion batteries.

Spherical Li4Ti5O12/NiO Composite With Enhanced Capacity and Rate Performance as Anode Material for Lithium-Ion Batteries

Compositing with metal oxides is proved to be an efficient strategy to improve electrochemical performance of anode material Li₄Ti₅O₁₂ for lithium-ion batteries. Herein, spherical Li₄Ti₅O₁₂/NiO composite powders have been successfully prepared via a spray drying method. X-ray diffraction and high-resolution transmission electron microscopy results demonstrate that crystal structure of the powders is spinel. Scanning electron microscopy results show that NiO uniformly distributes throughout Li₄Ti₅O₁₂ matrix. It is found that compositing with NiO increases both discharge platform capacity and rate stability of Li₄Ti₅O₁₂. The as-prepared Li₄Ti₅O₁₂/NiO (5%) exhibits a high initial discharge capacity of 381.3 mAh g⁻¹ at 0.1 C, and a discharge capacity of 194.7 mAh g⁻¹ at an ultrahigh rate of 20 C.

Si/a-C Nanocomposites with a Multiple Buffer Structure via One-Step Magnetron Sputtering for Ultrahigh-Stability Lithium-Ion Battery Anodes

Large volume expansion and serious pulverization of silicon are two major challenges for Si-based anode batteries. Herein, a high-mass-load (3.0 g cm^-3) silicon-doped amorphous carbon (Si/a-C) nanocomposite with a hierarchical buffer structure is prepared by one-step magnetron sputtering. The uniform mixing of silicon and carbon is realized on the several-nanometer scale by cosputter deposition of silicon and carbon. The boundary of the primary particles, made up of nanocarbon and nanosilicon, and the boundary of the secondary particles aggregated by the primary particles can provide accommodation space for the volume expansion of silicon and effectively buffer the volume expansion of silicon. Meanwhile, the continuous and uniformly distributed amorphous carbon enhances the conductivity of the Si/a-C nanocomposites. Typically, the 20% Si/a-C cell shows a superior initial discharge capacity of 845.3 mAh g^-1 and achieves excellent cycle performance of up to 1000 cycles (609.4 mAh g^-1) at the current density of 1 A g^-1. Furthermore, the 20% Si/a-C cell exhibits a high capacity of 602.8 mAh g^-1 with the stable discharge/charge rate performance in several extreme conditions (-40-70 °C). In view of the validity and mass productivity of the magnetron sputtering, a potential route for the industrial preparation of the Si/a-C anode nanocomposites is therefore highlighted by this study.

Adding Metal Carbides to Suppress the Crystalline Li15Si4 Formation: A Route toward Cycling Durable Si-Based Anodes for Lithium-Ion Batteries

In addition to large volume change and sluggish kinetics, the capacity decay of silicon anodes is also related to the formation of a crystalline Li₁₅Si₄ phase during cycling. Herein, we have demonstrated that refining cheap coarse-grained Si by ball milling with metal carbides (Mo₂C, Cr₂C₃, etc.) can reduce the Si crystallite size significantly and can thus suppress the formation of the crystalline Li₁₅Si₄ during cycling, which increases the life of Si-based anode materials significantly. Si-Cr₃C₂@few-layer graphene (SC@G) composite anode materials were designed and prepared by plasma milling (P-milling) to achieve a considerable capacity of 881.8 mA h g^-1 after 300 cycles at 1 A g^-1. A study of the microstructure of the SC@G indicated that the refined amorphous-nanocrystal Si grains were distributed uniformly around multiscale Cr₃C₂ particles, which were covered by few-layer graphenes. The rigid Cr₃C₂ skeleton, which acts as a good conductive material, can increase the conductivity of the SC@G composite, avoid the agglomeration of refined Si, and regenerate Si nanosized grains during lithiation and delithiation. These results showed that the SC@G anode material exhibited an excellent overall performance based on its high capacity and long cycle stability, as well as excellent lithium-ion diffusion kinetics for lithium storage.

Synthesis and Redox Mechanism of Cation-Disordered, Rock-Salt Cathode-Material Li-Ni-Ti-Nb-O Compounds for a Li-Ion Battery

Cation-disordered oxide materials working as cathodes for Li-ion batteries have been at a standstill because of their structurally limited specific capacities (below 175 mAh g^-1 in most cases). In this work, we have introduced 4d⁰ Nb⁵⁺ into host material LiNi_0.5Ti_0.5O₂ to synthesize Ni-based cation-disordered Fm3̅m Li-Ni-Ti-Nb-O compounds of Li_1+x/100Ni_1/2-x/100Ti_1/2-x/100Nb_x/100O₂ (x = 0, 5, 10, 15, 20) through a sol-gel method, showing particle sizes of less than 200 nm. Taking Li_1.2Ni_0.3Ti_0.3Nb_0.2O₂ with the best performance (an average voltage of ∼2.7 V and high discharge capacity of 221.5 mAh g^-1) among oxides as a model, we study the relationship between the structure, morphology, redox mechanism, and electrochemical performance of cation-disordered oxides through a combination of X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy tests and in situ XRD with electrochemistry. The obtained results indicate that the improved capacity is mainly ascribed to Nb⁵⁺, which optimizes the Ni²⁺/Ni⁴⁺ practical capacity and effectively stabilizes the O^2-/O^- redox reaction. The results emphasize that Li-Ni-Ti-Nb-O compounds are promising members in the family of cation-disordered transition-metal oxide materials.

The Effects of Reversibility of H2-H3 Phase Transition on Ni-Rich Layered Oxide Cathode for High-Energy Lithium-Ion Batteries

Although LiNi_0.8Co_0.1Mn_0.1O₂ is attracting increasing attention on account of its high specific capacity, the moderate cycle lifetime still hinders its large-scale commercialization applications. Herein, the Ti-doped LiNi_0.8Co_0.1Mn_0.1O₂ compounds are successfully synthesized. The Li(Ni_0.8Co_0.1Mn_0.1)_0.99Ti_0.01O₂ sample exhibits the best electrochemical performance. Under the voltage range of 2.7–4.3 V, it maintains a reversible capacity of 151.01 mAh·g⁻¹ with the capacity retention of 83.98% after 200 cycles at 1 C. Electrochemical impedance spectroscopy (EIS) and differential capacity profiles during prolonged cycling demonstrate that the Ti doping could enhance both the abilities of electronic transition and Li ion diffusion. More importantly, Ti doping can also improve the reversibility of the H2-H3 phase transitions during charge-discharge cycles, thus improving the electrochemical performance of Ni-rich cathodes.

Dual Carbonaceous Materials Synergetic Protection Silicon as a High-Performance Free-Standing Anode for Lithium-Ion Battery

Silicon is the one of the most promising anode material alternatives for next-generation lithium-ion batteries. However, the low electronic conductivity, unstable formation of solid electrolyte interphase, and the extremely high volume expansion (up to 300%) which results in pulverization of Si and rapid fading of its capacity have been identified as primary reasons for hindering its application. In this work, we put forward to introduce dual carbonaceous materials synergetic protection to overcome the drawbacks of the silicon anode. The silicon nanoparticle was coated by pyrolysed carbon, and meanwhile anchored on the surface of reduced graphene oxide, to form a self-standing film composite (C@Si/rGO). The C@Si/rGO film electrode displays high flexibility and an ordered porous structure, which could not only buffer the Si nanoparticle expansion during lithiation/delithiation processes, but also provides the channels for fast electron transfer and lithium ion transport. Therefore, the self-standing C@Si/rGO film electrode shows a high reversible capacity of 1002 mAh g-1 over 100 cycles and exhibits much better rate capability, validating it as a promising anode for constructing high performance lithium-ion batteries.

Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K⁺, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g^-1 at 0.1 C and 108 mAh g^-1 at 5 C and maintains over 193 mAh g^-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K⁺ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K_0.3MnO₂ cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g^-1 at 20 mA g^-1. This work is expected to promote the application of KIBs in wearable electronics.

High Performance and Structural Stability of K and Cl Co-Doped LiNi0.5Co0.2Mn0.3O2 Cathode Materials in 4.6 Voltage

The high energy density lithium ion batteries are being pursued because of their extensive application in electric vehicles with a large mileage and storage energy station with a long life. So, increasing the charge voltage becomes a strategy to improve the energy density. But it brings some harmful to the structural stability. In order to find the equilibrium between capacity and structure stability, the K and Cl co-doped LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) cathode materials are designed based on defect theory, and prepared by solid state reaction. The structure is investigated by means of X-ray diffraction (XRD), rietveld refinements, scanning electron microscope (SEM), XPS, EDS mapping and transmission electron microscope (TEM). Electrochemical properties are measured through electrochemical impedance spectroscopy (EIS), cyclic voltammogram curves (CV), charge/discharge tests. The results of XRD, EDS mapping, and XPS show that K and Cl are successfully incorporated into the lattice of NCM cathode materials. Rietveld refinements along with TEM analysis manifest K and Cl co-doping can effectively reduce cation mixing and make the layered structure more complete. After 100 cycles at 1 C, the K and Cl co-doped NCM retains a more integrated layered structure compared to the pristine NCM. It indicates the co-doping can effectively strengthen the layer structure and suppress the phase transition to some degree during repeated charge and discharge process. Through CV curves, it can be found that K and Cl co-doping can weaken the electrode polarization and improve the electrochemical performance. Electrochemical tests show that the discharge capacity of Li_0.99K_0.01(Ni_0.5Co_0.3Mn_0.2)O_1.99Cl_0.01 (KCl-NCM) are far higher than NCM at 5 C, and capacity retention reaches 78.1% after 100 cycles at 1 C. EIS measurement indicates that doping K and Cl contributes to the better lithium ion diffusion and the lower charge transfer resistance.

High Performance Composite Polymer Electrolytes Doped With Spherical-Like and Honeycomb Structural Li0.1Ca0.9TiO3 Particles

The spherical-like and honeycomb structural Li_0.1Ca_0.9TiO₃ particles are prepared by spray drying combined with following calcination confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS). The poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))-based composite polymer electrolytes (CPEs) modified with the particles are fabricated by phase inversion and activation processes. The characterization results show that the as-prepared CPE membranes possess the smoothest surface and most abundant micropores with the lowest crystallinity with adding the particles into the polymer matrix, which results in high ionic conductivity (3.947 mS cm^-1) and lithium ion transference number (0.4962) at ambient temperature. The interfacial resistance can be quickly stabilized at 508 Ω after 5 days storage and the electrochemical working window is up to 5.2 V. Moreover, the mechanical strength of the membranes gains significant improvement without lowering the ionic conductivity. Furthermore, the assembled coin cell can also deliver high discharge specific capacity and preserve steady cycle performance at different current densities. Those outstanding properties may be ascribed to the distinctive structure of the tailored spherical-like and honeycomb structural Li_0.1Ca_0.9TiO₃ particles, which can guarantee the desirable CPEs as a new promising candidate for the polymer electrolyte.

Li2O-Reinforced Solid Electrolyte Interphase on Three-Dimensional Sponges for Dendrite-Free Lithium Deposition

Lithium (Li) metal, with ultra-high theoretical capacity and low electrochemical potential, is the ultimate anode for next-generation Li metal batteries. However, the undesirable Li dendrite growth usually results in severe safety hazards and low Coulombic efficiency. In this work, we design a three-dimensional CuO@Cu submicron wire sponge current collector with high mechanical strength SEI layer dominated by Li₂O during electrochemical reaction process. The 3D CuO@Cu current collector realizes an enhanced CE of above 91% for an ultrahigh current of 10 mA cm^-2 after 100 cycles, and yields decent cycle stability at 5 C for the full cell. The exceptional performances of CuO@Cu submicron wire sponge current collector hold promise for further development of the next-generation metal-based batteries.

Cryptomelane-Type KMn8O16 as Potential Cathode Material - for Aqueous Zinc Ion Battery

Aqueous battery has been gained much more interest for large-scale energy storage fields due to its excellent safety, high power density and low cost. Cryptomelane-type KMn₈O₁₆ confirmed by X-ray diffraction (XRD) was successfully synthesized by a modified hydrothermal method, followed by annealed at 400°C for 3 h. The morphology and microstructure of as-prepared KMn₈O₁₆ investigated by field-emission scanning electron microscopy (FE-SEM) with the energy spectrum analysis (EDS) and transmission electron microscopy (TEM) demonstrate that one-dimensional nano rods with the length of about 500 nm constitute the microspheres with the diameter about 0.5~2 μm. The cyclic voltammetry measurement displays that the abundant intercalation of zinc ions on the cathode takes place during the initial discharge process, indicating that cryptomelane-type KMn₈O₁₆ can be used as the potential cathode material for aqueous zinc ion batteries. The electrode shows a good cycling performance with a reversible capacity of up to 77.0 mAh/g even after 100 cycles and a small self-discharge phenomenon.

Porous Hollow Superlattice NiMn2O4/NiCo2O4 Mesocrystals as a Highly Reversible Anode Material for Lithium-Ion Batteries

As a promising high-capacity anode material for Li-ion batteries, NiMn₂O₄ always suffers from the poor intrinsic conductivity and the architectural collapse originating from the volume expansion during cycle. Herein, a combined structure and architecture modulation is proposed to tackle concurrently the two handicaps, via a facile and well-controlled solvothermal approach to synthesize NiMn₂O₄/NiCo₂O₄ mesocrystals with superlattice structure and hollow multi-porous architecture. It is demonstrated that the obtained NiCo_1.5Mn_0.5O₄ sample is made up of a new mixed-phase NiMn₂O₄/NiCo₂O₄ compound system, with a high charge capacity of 532.2 mAh g⁻¹ with 90.4% capacity retention after 100 cycles at a current density of 1 A g⁻¹. The enhanced electrochemical performance can be attributed to the synergistic effects of the superlattice structure and the hollow multi-porous architecture of the NiMn₂O₄/NiCo₂O₄ compound. The superlattice structure can improve ionic conductivity to enhance charge transport kinetics of the bulk material, while the hollow multi-porous architecture can provide enough void spaces to alleviate the architectural change during cycling, and shorten the lithium ions diffusion and electron-transportation distances.

Fluidized bed reaction towards crystalline embedded amorphous Si anode with much enhanced cycling stability

The fluidized bed reaction route was introduced for the first time to prepare amorphous–crystalline silicon anode materials with excellent cycle stabilities.

Walnut-structure Si–G/C materials with high coulombic efficiency for long-life lithium ion batteries

Nano-sized silicon is a potential high energy density anode material for lithium ion batteries.