Rational Design of Ion-Conductive Layer on Si Anode Enables Superior-Stable Lithium-Ion Batteries.

Silicon (Si) is considered a promising commercial material for the next-generation of high-energy density lithium-ion battery (LIB) due to its high theoretical capacity. However, the severe volume changes and the poor conductivity hinder the practical application of Si anode. Herein, a novel core-shell heterostructure, Si as the core and V3 O4 @C as the shell (Si@V3 O4 @C), is proposed by a facile solvothermal reaction. Theoretical simulations have shown that the in-situ-formed V3 O4 layer facilitates the rapid Li+ diffusion and lowers the energy barrier of Li transport from the carbon shell to the inner core. The 3D network structure constructed by amorphous carbon can effectively improve electronic conductivity and structural stability. Benefiting from the rationally designed structure, the optimized Si@V3 O4 @C electrode exhibits an excellent cycling stability of 1061.1 mAh g-1 at 0.5 A g-1 over 700 cycles (capacity retention of 70.0%) with an average Coulombic efficiency of 99.3%. In addition, the Si@V3 O4 @C||LiFePO4 full cell shows a superior capacity retention of 78.7% after 130 cycles at 0.5 C. This study opens a novel way for designing high-performance silicon anode for advanced LIBs.

In Situ Constructing of Rigid-Soft Coupling Solid-Electrolyte Interphase on Silicon Electrode toward High-Performance Lithium Ion Batteries.

The application of Si anodes is hindered by some critical issues such as large volume changes of bare Si and fragile solid-electrolyte interface (SEI), resulting in low coulombic efficiency and rapid capacity decay. Herein, a multifunctional SEI film with high content of LiF is in situ constructed via the surface grafting of carbon-fluorine functionalized groups on silicon nanoparticles (SiNPs) during cycling. Mechanical study demonstrates that the incorporation of LiF with high modulus and unbroken carbon-fluorine groups with highly elastic guarantee the rigid-soft coupling SEI film on Si electrode. Furthermore, it is demonstrated that the rigid-soft coupling SEI film can effectively accommodate the volume expansion of Si nanoparticles during lithiation process, with the electrode expanding rate of only 114.16% after 100 cycles (263.87% for bare Si without surface modification). Afterward, with the aid of well-designed rigid-soft coupling SEI, the initial Coulomb efficiency of 89.8% is achieved, showing a reversible capacity of 1477 mAh g-1 after 200 cycles at 1.2 A g-1 . This work provides a simple and efficient solution that can potentially facilitate the practical application of Si anodes.

Bamboo Inspired Silicon Anodes with Ultrahigh Initial Coulombic Efficiency and High Capacity for the Li-Ion Batteries.

Silicon is regarded as the most promising candidate due to its ultrahigh theoretical energy density (4200 mAh g-1). However, the large volume expansion of silicon nanoparticles would result in the destruction of electrodes and a shortened cycle lifetime. Here, inspired by the natural structure of bamboo, the silicon anode with vascular bundle-like structure is proposed to improve the electrochemical performance for the first time. The dense channel wall in the silicon anode can accommodate the volume change of silicon nanoparticles and the transport of ions and electrons is also enhanced. The obtained silicon anodes display excellent mechanical properties (50% compression resilience and the average peel force of 4.34 N) and good wettability. What more, the silicon anodes exhibit high initial coulombic efficiency (94.5%), excellent cycle stability (2100 mAh g-1 after 300 cycles) which stands out among the silicon anodes. Specially, the silicon anode with impressive areal capacity of 36.36 mAh cm-2 and initial coulombic efficiency of 84% is also achieved. This work offers a novel and efficient strategy for the preparation of the flexible electrodes with outstanding performance.

Interlayer Engineering and Prelithiation: Empowering Si Anodes for Low-Pressure-Operating All-Solid-State Batteries.

Silicon (Si) anodes, free from the dendritic growth concerns found in lithium (Li) metal anodes, offer a promising alternative for high-energy all-solid-state batteries (ASSBs). However, most advancements in Si anodes have been achieved under impractical high operating pressures, which can mask detrimental electrochemo-mechanical issues. Herein, we effectively address the challenges related to the low-pressure operation of Si anodes in ASSBs by introducing an silver (Ag) interlayer between the solid electrolyte layer (Li6PS5Cl) and anode and prelithiating the anodes. The Si composite electrodes, consisting of Si/polyvinylidene fluoride/carbon nanotubes, are optimized for suitable mechanical properties and electrical connectivity. Although the impact of the Ag interlayer is insignificant at an exceedingly high operating pressure of 70 MPa, it substantially enhances the interfacial contacts under a practical low operating pressure of 15 MPa. Thus, Ag-coated Si anodes outperform bare Si anodes (discharge capacity: 2430 vs 1560 mA h g-1). The robust interfacial contact is attributed to the deformable, adhesive properties and protective role of the in situ lithiated Ag interlayer, as evidenced by comprehensive ex situ analyses. Operando electrochemical pressiometry is used effectively to probe the strong interface for Ag-coated Si anodes. Furthermore, prelithiation through the thermal evaporation deposition of Li metal significantly improves the cycling performance.

Engineering of Siloxanes for Stabilizing Silicon Anode Materials.

Silicon (Si) is considered the most promising anode material for the next generation of lithium-ion batteries (LIBs) because of its high theoretical specific capacity and abundant reserves. However, the volume expansion of silicon in the cycling process causes the destruction of the electrode structure and irreversible capacity loss. As a result, the commercial application of silicon materials is greatly hindered. In recent years, siloxane-based organosilicon materials have been widely used in silicon anode of LIBs because of their unique structure and physical and chemical properties, and have shown excellent electrochemical properties. The comprehensive achievement of siloxanes in silicon-based LIBs can be understood better through a systematic summary, which is necessary to guide the design of electrodes and achieve better electrochemical performance. This paper systematically introduces the unique advantages of siloxane materials in electrode, surface/interface modification, binder, and electrolyte. The challenges and future directions for siloxane materials are presented to enhance their performance and expand their application in silicon-based LIBs.

Nano Silicon Anode without Electrolyte Adding for Sulfide-Based All-Solid-State Lithium-Ion Batteries.

All-solid-state lithium-ion batteries (ASSLBs) employing silicon (Si) anode and sulfide electrolyte attract much attention, since they can achieve both high energy density and safety. For large-scale application, sheet-type Si anode matching sulfide based ASSLBs is preferred. Here, a LiAlO2 layer coated Si (Si@LiAlO2 ) is reported for sheet-type electrode. This electrode employs conventional slurry coating methods without adding any sulfide electrolyte. The effect of LiAlO2 coating on the electrochemical performance and morphology evolution of Si electrode is investigated. Since the high mechanical strength and ionic conductivity of LiAlO2 layer can sufficiently relieve the huge expansion of Si and promote the Li+ diffusion, the electrochemical performance is significantly enhanced. The Si@LiAlO2 electrodes deliver high coulombic efficiency exceeding 80% and hold considerable specific capacity of 1205 mAh g-1 (150 cycles, 0.33 C). The Si@LiAlO2 | LiNi0.83 Co0.11 Mn0.06 O2 full-cells exhibit a high reversible capacity of 147 mAh g-1 (0.28 mA cm-2 ) and a considerable capacity retention of 80.2% (62 cycles, 2.8 mA cm-2 ). This work demonstrates promising practicability and provides a new route for the scalable preparation of Si electrode sheets for ASSLBs with extended lifespan.

Molecular-Cling-Effect of Fluoroethylene Carbonate Characterized via Ethoxy(pentafluoro)cyclotriphosphazene on SiOx/C Anode Materials - A New Perspective for Formerly Sub-Sufficient SEI Forming Additive Compounds.

Effective electrolyte compositions are of primary importance in raising the performance of lithium-ion batteries (LIBs). Recently, fluorinated cyclic phosphazenes in combination with fluoroethylene carbonate (FEC) have been introduced as promising electrolyte additives, which can decompose to form an effective dense, uniform, and thin protective layer on the surface of electrodes. Although the basic electrochemical aspects of cyclic fluorinated phosphazenes combined with FEC were introduced, it is still unclear how these two compounds interact constructively during operation. This study investigates the complementary effect of FEC and ethoxy(pentafluoro)cyclotriphosphazene (EtPFPN) in aprotic organic electrolyte in LiNi0.5 Co0.2 Mn0.3 O ∥ SiOx /C full cells. The formation mechanism of lithium ethyl methyl carbonate (LEMC)-EtPFPN interphasial intermediate products and the reaction mechanism of lithium alkoxide with EtPFPN are proposed and supported by Density Functional Theory calculations. A novel property of FEC is also discussed here, called molecular-cling-effect (MCE). To the best knowledge, the MCE has not been reported in the literature, although FEC belongs to one of the most investigated electrolyte additives. The beneficial MCE of FEC toward the sub-sufficient solid-electrolyte interphase forming additive compound EtPFPN is investigated via gas chromatography-mass spectrometry, gas chromatography high resolution-accurate mass spectrometry, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy, and scanning electron microscopy.

Partially Carbonized Polymer Binder with Polymer Dots for Silicon Anodes in Lithium-Ion Batteries.

Large-scale applications of conventional conductive binders for silicon (Si) anodes are challenging to accomplish due to their complex synthesis steps and high cost. Herein, a carbonized polymer dots-assisted polyvinyl alcohol-chitosan (PVA-CS-CPDs) binder is developed through a simple and low-cost hydrothermal method. Through rational design, the PVA-CS-CPDs binder retains rich polar groups while forming conjugated structures. The conjugated structure endows the PVA-CS-CPDs with high electronic conductivity, and the retained polar groups maintain strong binding strength. The proposed water-soluble binding system acts as both a binder and conductive additive, enabling stable cycling for high-Si-content (90 wt.%) anodes without any other conductive additives.

Self-Repairable Silicon Anodes Using a Multifunctional Binder for High-Performance Lithium-Ion Batteries.

Despite of extremely high theoretical capacity of Si (3579 mAh g-1 ), Si anodes suffer from pulverization and delamination of the electrodes induced by large volume change during charge/discharge cycles. To address those issues, herein, self-healable and highly stretchable multifunctional binders, polydioxythiophene:polyacrylic acid:phytic acid (PEDOT:PAA: PA, PDPP) that provide Si anodes with self-healability and excellent structural integrity is designed. By utilizing the self-healing binder, Si anodes self-repair cracks and damages of Si anodes generated during cycling. For the first time, it is demonstrated that Si anodes autonomously self-heal artificially created cracks in electrolytes under practical battery operating conditions. Consequently, this self-healable Si anode can still deliver a reversible capacity of 2312 mAh g-1 after 100 cycles with remarkable initial Coulombic efficiency of 94%, which is superior to other reported Si anodes. Moreover, the self-healing binder possesses enhanced Li-ion diffusivity with additional electronic conductivity, providing excellent rate capability with a capacity of 2084 mAh g-1 at a very high C-rate of 5 C.

Carbon Nanotube-Reinforced Dual Carbon Stress-Buffering for Highly Stable Silicon Anode Material in Lithium-Ion Battery.

Silicon (Si) anode suffers from huge volume expansion which causes poor structural stability in terms of electrode material, solid electrolyte interface, and electrode, limiting its practical application in high-energy-density lithium-ion batteries. Rationally designing architectures to optimize the stress distribution of Si/carbon (Si/C) composites has been proven to be effective in enhancing their structural stability and cycling stability, but this remains a big challenge. Here, metal-organic frameworks (ZIF-67)-derived carbon nanotube-reinforced carbon framework is employed as an outer protective layer to encapsulate the inner carbon-coated Si nanoparticles (Si@C@CNTs), which features dual carbon stress-buffering to enhance the structural stability of Si/C composite and prolong their cycling lifetime. Finite element simulation proves the structural advantage of dual carbon stress-buffering through significantly relieving stress concentration when Si lithiation. The outer carbon framework also accelerates the charge transfer efficiency during charging/discharging by the improvement of lithium-ion diffusion and electron transport. As a result, the Si@C@CNTs electrode exhibits excellent long-term lifetime and good rate capability, showing a specific capacity of 680 mAh g-1 even at a high rate of 1 A g-1 after 1000 cycles. This work provides insight into the design of robust architectures for Si/C composites by stress optimization.

Silicon Cutting Waste Derived Silicon Nanosheets with Adjustable Native SiO2 Shell for Highly-Stable Lithiation/Delithiation.

Silicon is an excellent candidate for the next generation of ultra-high performance anode materials, with the rapid iteration of the lithium-ion battery industry. High-quality silicon sources are the cornerstone of the development of silicon anodes, and silicon cutting waste (SCW) is one of them while still faces the problems of poor performance and unclear structure-activity relationship. Herein, a simple, efficient, and inexpensive purification method is implemented to reduce impurities in SCW and expose the morphology of nanosheets therein. Furthermore, HF is used to modulate the abundant native O in SCW after thermodynamic and kinetic considerations, realizing the mechanical support for the internal Si in the form of an amorphous SiO2 shell. Afterward, SCNS@SiO2 -2.5 with a 1.0 nm thick SiO2 shell exhibits a reversible capacity of 1583.3 mAh g-1 after 200 cycles at 0.8 A g-1 . Ultimately, the molecular dynamics simulations profoundly reveal that the amorphous SiO2 shell is transformed into the extremely ductile Lix SiOy shell to ditch stress and relieve strain during the lithiation/delithiation process.

A Uniform Self-Reinforced Organic/Inorganic Hybrid SEI Chelation Strategy on Microscale Silicon Surfaces for Stable-Cycling Anodes in Lithium-Ion Batteries.

A promising anode material for Li-ion batteries, silicon (Si) suffers from volume expansion-induced pulverization and solid electrolyte interface (SEI) instability. Microscale Si with high tap density and high initial Coulombic efficiency (ICE) has become a more anticipated choice, but it will exacerbate the above issues. In this work, the polymer polyhedral oligomeric silsesquioxane-lithium bis (allylmalonato) borate (PSLB) is constructed by in situ chelation on microscale Si surfaces via click chemistry. This polymerized nanolayer has an "organic/inorganic hybrid flexible cross-linking" structure that can accommodate the volume change of Si. Under the stable framework formed by PSLB, a large number of oxide anions on the chain segment preferentially adsorb LiPF6 and further induce the integration of inorganic-rich, dense SEI, which improves the mechanical stability of SEI and provides accelerated kinetics for Li+ transfer. Therefore, the Si4@PSLB anode exhibits significantly enhanced long-cycle performance. After 300 cycles at 1 A g-1 , it can still provide a specific capacity of 1083 mAh g-1 . Cathode-coupled with LiNi0.9 Co0.05 Mn0.05 O2 (NCM90) in the full cell retains 80.8% of its capacity after 150 cycles at 0.5 C.

Sponge-Like Porous-Conductive Polymer Coating for Ultrastable Silicon Anodes in Lithium-Ion Batteries.

Urgent calls for reversible cycling performance of silicon (Si) requires an efficient solution to maintain the silicon-electrolyte interface stable. Herein, a conductive biphenyl-polyoxadiazole (bPOD) layer is coated on Si particles to enhance the electrochemical process and prolong the cells lifespan. The conformal bPOD coatings are mixed ionicelectronic conductors, which not only inhibit the infinite growth of solid electrolyte interphase (SEI) but also endow electrodes with outstanding ion/electrons transport capacity. The superior 3D porous structure in the continuous phase allows the bPOD layers to act like a sponge to buffer volume variation, resulting in high structural stability. The in situ polymerized bPOD coating and it-driven thin LiF-rich SEI layer remarkably improve the lithium storage performance of Si anodes, showing a high reversible specific capacity of 1600 mAh g-1 even after 500 cycles at 1 A g-1 along with excellent rate capacity of over 1500 mAh g-1 at 3 A g-1 . It should be noticed that a long cycle life of 800 cycles with 1065 mAh g-1 at 3 A g-1 can also be achieved with a capacity retention of more than 80%. Therefore,  we  believe this unique polymer coating design paves the way for the widespread adoption of next-generation lithium-ion batteries.

Roll-Pressed Silicon Anodes with High Reversible Volumetric Capacity Achieved by Interfacial Stabilization and Mechanical Strengthening of a Silicon/Graphene Hybrid Assembly.

Application of Si anodes is hindered by severe capacity fading due to pulverization of Si particles during the large volume changes of Si during charge/discharge and repeated formation of the solid-electrolyte interphase. To address these issues, considerable efforts have been devoted to the development of Si composites with conductive carbons (Si/C composites). However, Si/C composites with high C content inevitably show low volumetric capacity because of low electrode density. For practical applications, the volumetric capacity of a Si/C composite electrode is more important than gravimetric capacity, but volumetric capacity in pressed electrodes is rarely reported. Herein, a novel synthesis strategy is demonstrate for a compact Si nanoparticle/graphene microspherical assembly with interfacial stability and mechanical strength achieved by consecutively formed chemical bonds using 3-aminopropyltriethoxysilane and sucrose. The unpressed electrode (density: 0.71 g cm-3 ) shows a reversible specific capacity of 1470 mAh g-1 with a high initial coulombic efficiency of 83.7% at a current density of 1 C-rate. The corresponding pressed electrode (density: 1.32 g cm-3 ) exhibits high reversible volumetric capacity of 1405 mAh cm-3 and gravimetric capacity of 1520 mAh g-1 with a high initial coulombic efficiency of 80.4% and excellent cycling stability of 83% over 100 cycles at 1 C-rate.

Benchmarking the Effect of Particle Size on Silicon Anode Materials for Lithium-Ion Batteries.

High-capacity silicon has been regarded as one of the most promising anodes for high-energy lithium-ion batteries. However, it suffers from severe volume expansion, particle pulverization, and repeated solid electrolyte interphase (SEI) growth, which leads to rapid electrochemical failure, while the particle size also plays key role here and its effects remain elusive. In this paper, through multiple-physical, chemical, and synchrotron-based characterizations, the evolutions of the composition, structure, morphology, and surface chemistry of silicon anodes with the particle size ranging from 50 to 5 µm upon cycling are benchmarked, which greatly link to their electrochemical failure discrepancies. It is found that the nano- and micro-silicon anodes undergo similar crystal to amorphous phase transition, but quite different composition transition upon de-/lithiation; at the same time, the nano- and 1 µm-silicon samples present obviously different mechanochemical behaviors from the 5 µm-silicon sample, such as electrode crack, particle pulverization/crack as well as volume expansion; in addition, the micro-silicon samples possess much thinner SEI layer than the nano-silicon samples upon cycling, and also differences in SEI compositions. It is hoped this comprehensive study and understanding should offer critical insights into the exclusive and customized modification strategies to diverse silicon anodes ranging from nano to microscale.

Gradient H-Bonding Supports Highly Adaptable and Rapidly Self-Healing Composite Binders with High Ionic Conductivity for Silicon Anodes in Lithium-Ion Batteries.

An ideal binder for high-energy-density lithium-ion batteries (LIBs) should effectively inhibit volume effects, exhibit specific functional properties (e.g., self-repair capabilities and high ionic conductivity), and require low-cost, environmentally friendly mass production processes. This study adopts a synergistic strategy involving gradient (strong-weak) hydrogen bonding to construct a hard/soft polymer composite binder with self-healing abilities and high battery cell environments adaptability in LIBs. The meticulously designed 3D network structure comprising continuous electron transport pathways buffers the mechanical stresses caused by changes in silicon volume and improves the overall stability of the solid electrolyte interphase film. The Si-based anode with a polymer composite binder poly(acrylic acid-g-ureido pyrimidinone5% )/polyethylene oxide (Si/PAA-UPy5% /PEO) achieves a reversible capacity of 1245 mAh g-1 after 200 cycles at 0.5 C, which is 6.6 times higher than that of the Si/PAA anode. After 200 cycles at 0.2 A g-1 , a half-cell comprising Si/C anode with a polymer composite binder (Si/C/PAA-UPy5% /PEO) has a remaining specific capacity of 420 mAh g-1 and a capacity retention rate of 79%. The corresponding full cell with a Li-based cathode (LiFePO4 /Si/C/PAA-UPy5% /PEO) has an initial area capacity of 0.96 mAh cm-2 and retains an area capacity of 0.90 mAh cm-2 (capacity retention rate = 93%) after 100 cycles at 0.2 A g-1 .

A Review on Recent Advances for Boosting Initial Coulombic Efficiency of Silicon Anodic Lithium Ion batteries.

Rechargeable silicon anode lithium ion batteries (SLIBs) have attracted tremendous attention because of their merits, including a high theoretical capacity, low working potential, and abundant natural sources. The past decade has witnessed significant developments in terms of extending the lifespan and maintaining high capacities of SLIBs. However, the detrimental issue of low initial Coulombic efficiency (ICE) toward SLIBs is causing more and more attention in recent years because ICE value is a core index in full battery design that profoundly determines the utilization of active materials and the weight of an assembled battery. Herein, a comprehensive review is presented of recent advances in solutions for improving ICE of SLIBs. From design perspectives, the strategies for boosting ICE of silicon anodes are systematically categorized into several aspects covering structure regulation, prelithiation, interfacial design, binder design, and electrolyte additives. The merits and challenges of various approaches are highlighted and discussed in detail, which provides valuable insights into the rational design and development of state-of-the-art techniques to deal with the deteriorative issue of low ICE of SLIBs. Furthermore, conclusions and future promising research prospects for lifting ICE of SLIBs are proposed at the end of the review.

A Hierarchical Si/C Nanocomposite of Stable Conductive Network Formed Through Thermal Phase Separation of Asphaltenes for High-Performance Li-Ion Batteries.

Silicon is one of the most promising anode materials for lithium-ion batteries. However, the huge volume change of silicon during lithiation/delithiation triggers continuous growth of solid-electrolyte interphase, loss of conductive contacts and structural collapse of the electrode, which causes a rapid deterioration of battery capacities. Inspired by the polyaromatic molecular nature and phase separation of asphaltenes in bitumen during thermal cracking, a hierarchical Si/C nanocomposite of robust carbon coatings and a firmly connected carbon framework on the silicon surface is synthesized by controlling the concentration of asphaltenes as carbon source and hence desired phase separation during the subsequent carbonization. The electrode made using this special Si/C nanocomposite exhibits a high reversible capacity of 1149 mAh g-1 after 600 cycles with a capacity retention of 98.5% and the operation ability at a high mass loading over 10 mg cm-2 or an area capacity of 23.8 mAh cm-2 , which represents one of the highest area capacities reported in open literature but with much more stable and prolonged operations. This simple and efficient strategy is easy to scale up for commercial production to meet the rapid growth of the electric vehicle industry.

Constructing a Reinforced and Gradient Solid Electrolyte Interphase on Si Nanoparticles by In-Situ Thiol-Ene Click Reaction for Long Cycling Lithium-Ion Batteries.

Constructing a stable solid electrolyte interphase (SEI) on high-specific-capacity silicon (Si) anode is one of the most effective methods to reduce the crack of SEI and improve the cycling performance of Si anode. Herein, the authors construct a reinforced and gradient SEI on Si nanoparticles by an in-situ thiol-ene click reaction. Mercaptopropyl trimethoxysilane (MPTMS) with thiol functional groups (SH) is first grafted on the Si nanoparticles through condensation reaction, which then in-situ covalently bonds with vinylene carbonate (VC) to form a reinforced and uniform SEI on Si nanoparticles. The modified SEI with sufficient elastic Lix SiOy can homogenize the stress and strain during the lithiation of Si nanoparticles to reduce their expansion and prevent the SEI from cracking. The Si nanoparticles-graphite blending anode with the reinforced SEI exhibits excellent performance with an initial coulombic efficiency of ≈90%, a capacity of 1053.3 mA h g-1 after 500 cycles and a high capacity of 852.8 mA h g-1 even at a high current density of 3 A g-1 . Moreover, the obtained anode shows superior cycling stability under both high loadings and lean electrolyte. The in-situ thiol-ene click reaction is a practical method to construct reinforced SEI on Si nanoparticles for next-generation high-energy-density lithium-ion batteries.

The Latest Trends in Electric Vehicles Batteries.

Global energy demand is rapidly increasing due to population and economic growth, especially in large emerging countries, which will account for 90% of energy demand growth to 2035. Electric vehicles (EVs) play a paramount role in the electrification revolution towards the reduction of the carbon footprint. Here, we review all the major trends in Li-ion batteries technologies used in EVs. We conclude that only five types of cathodes are used and that most of the EV companies use Nickel Manganese Cobalt oxide (NMC). Most of the Li-ion batteries anodes are graphite-based. Positive and negative electrodes are reviewed in detail as well as future trends such as the effort to reduce the Cobalt content. The electrolyte is a liquid/gel flammable solvent usually containing a LiFeP6 salt. The electrolyte makes the battery and battery pack unsafe, which drives the research and development to replace the flammable liquid by a solid electrolyte.