Si Anode Research Articles

Overcoming low initial coulombic efficiencies of Si anodes through prelithiation in all-solid-state batteries

All-solid-state batteries using Si as the anode have shown promising performance without continual solid-electrolyte interface (SEI) growth. However, the first cycle irreversible capacity loss yields low initial Coulombic efficiency (ICE) of Si, limiting the energy density. To address this, we adopt a prelithiation strategy to increase ICE and conductivity of all-solid-state Si cells. A significant increase in ICE is observed for Li1Si anode paired with a lithium cobalt oxide (LCO) cathode. Additionally, a comparison with lithium nickel manganese cobalt oxide (NCM) reveals that performance improvements with Si prelithiation is only applicable for full cells dominated by high anode irreversibility. With this prelithiation strategy, 15% improvement in capacity retention is achieved after 1000 cycles compared to a pure Si. With Li1Si, a high areal capacity of up to 10 mAh cm–2 is attained using a dry-processed LCO cathode film, suggesting that the prelithiation method may be suitable for high-loading next-generation all-solid-state batteries.

Reduction‐Tolerance Electrolyte Design for High‐Energy Lithium Batteries

AbstractLithium batteries employing Li or silicon (Si) anodes hold promise for the next‐generation energy storage systems. However, their cycling behavior encounters rapid capacity degradation due to the vulnerability of solid electrolyte interphases (SEIs). Though anion‐derived SEIs mitigate this degradation, the unavoidable reduction of solvents introduces heterogeneity to SEIs, leading to fractures during cycling. Here, we elucidate how the reductive stability of solvents, dominated by the electrophilicity (EPT) and coordination ability (CDA), delineates the SEI formed on Li or Si anodes. Solvents exhibiting lower EPT and CDA demonstrate enhanced tolerance to reduction, resulting in inorganic‐rich SEIs with homogeneity. Guided by these criteria, we synthesized three promising solvents tailored for Li or Si anodes. The decomposition of these solvents is dictated by their EPTs under similar solvation structures, imparting distinct characteristics to SEIs and impacting battery performance. The optimized electrolyte, 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in N‐Pyrrolidine‐trifluoromethanesulfonamide (TFSPY), achieves 600 cycles of Si anodes with a capacity retention of 81 % (1910 mAh g−1). In anode‐free Cu||LiNi0.5Co0.2Mn0.3O2 (NCM523) pouch cells, this electrolyte sustains over 100 cycles with an 82 % capacity retention. These findings illustrate that reducing solvent decomposition benefits SEI formation, offering valuable insights for the designing electrolytes in high‐energy lithium batteries.

Reduction-Tolerance Electrolyte Design for High-Energy Lithium Batteries.

Lithium batteries employing Li or silicon (Si) anodes hold promise for the next-generation energy storage systems. However, their cycling behavior encounters rapid capacity degradation due to the vulnerability of solid electrolyte interphases (SEIs). Though anion-derived SEIs mitigate this degradation, the unavoidable reduction of solvents introduces heterogeneity to SEIs, leading to fractures during cycling. Here, we elucidate how the reductive stability of solvents, dominated by the electrophilicity (EPT) and coordination ability (CDA), delineates the SEI formed on Li or Si anodes. Solvents exhibiting lower EPT and CDA demonstrate enhanced tolerance to reduction, resulting in inorganic-rich SEIs with homogeneity. Guided by these criteria, we synthesized three promising solvents tailored for Li or Si anodes. The decomposition of these solvents is dictated by their EPTs under similar solvation structures, imparting distinct characteristics to SEIs and impacting battery performance. The optimized electrolyte, 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in N-Pyrrolidine-trifluoromethanesulfonamide (TFSPY), achieves 600 cycles of Si anodes with a capacity retention of 81 % (1910 mAh g-1). In anode-free Cu||LiNi0.5Co0.2Mn0.3O2 (NCM523) pouch cells, this electrolyte sustains over 100 cycles with an 82 % capacity retention. These findings illustrate that reducing solvent decomposition benefits SEI formation, offering valuable insights for the designing electrolytes in high-energy lithium batteries.

Inorganic/organic composite binder with self-healing property for silicon anode in lithium-ion battery

Silicon (Si) has garnered significant attention as a high-capacity anode material in high-energy density lithium-ion batteries (LIBs). Nevertheless, the huge volume variation of Si (>300%) during cycling results in rapid capacity deterioration, thereby impeding its commercial application. To confront this challenge, inorganic binder has been identified as a highly promising solution for Si anode due to its high bonding strength. Despite its effectiveness, the inorganic binder's limited elasticity hinders the rejuvenation of the impaired electrode structure. Hence, we devised an elasticity and self-healing composite binder, incorporating both inorganic and organic binders. The inorganic lithium metasilicate not only offers ample adhesion sites to Si but also establishes a protective coating layer on SiNPs. Simultaneously, the organic poly (vinyl alcohol) featuring a low glass transition temperature (72 °C) furnishes elasticity and a self-healing framework. Consequently, the Si anode shows exemplary cycling and rate performances. Additionally, the Si||NCM811 full cell attains a reversible capacity of 1.86 mAh/cm2 with a capacity retention of 67% after 50 cycles, indicating the commercial application potential of the composite binder. This study thus explores design strategies for composite binders, paving the way for high-performance Si anode.

Unraveling Morphology and Chemistry Dynamics in Fluoroethylene Carbonate Generated Silicon Anode Solid Electrolyte Interphase Across Delithiated and Lithiated States: Relative Cycling Stability Enabled by an Elastomeric Polymer Matrix

The silicon solid electrolyte interphase (SEI) faces cyclical cracking and reconstruction due to the ∼350% volume expansion. Understanding the SEI dynamic morphology and chemistry evolution from delithiated to lithiated states is thereby paramount to engineering a stable Si anode. Fluoroethylene carbonate (FEC) is a preferred additive with widely demonstrated enhancement of the Si cycling. Thus, insights into the dynamics of the FEC-SEI may provide hints toward engineering the Si interface. Herein, complementary ATR-FTIR, AFM, tip IR, and XPS probing reveal the presence of an elastomeric polycarbonate-like matrix in the FEC-generated SEI which is absent from the FEC-free SEI. Adding FEC to the baseline 1 M LiPF6 in EC:EMC (1:1) electrolyte promotes formation of a thinner and more conformal SEI, and subdues morphology and chemistry changes between consecutive half-cycles. From AFM, morphological stabilization of the FEC-SEI occurs earlier. Furthermore, conventional SEI biproducts such as Li2CO3 and LiEDC appear in reduced quantities in the FEC-SEI implying a reduced quantity of Li-consuming species. The thin polymeric FEC-SEI enables deeper (de)lithiation of silicon. In conclusion, the enhanced mechanical compliance, chemical invariance, and reduced Li inventory consumption of the FEC-SEI are logically the key features underlying the Si cycling enhancement by FEC.

Reduced graphene oxide assembled on the Si nanowire anode enabling low passivation and hydrogen evolution for long-life aqueous Si-air batteries

Silicon-air batteries (SABs), a new type of semiconductor air battery, have a high energy density. However, some side reactions in SABs cause Si anodes to be covered by a passivation layer to prevent continuous discharge, and the anode utilization rate is low. In this work, reduced graphene oxide (RGO) fabricated via high-temperature annealing or L-ascorbic acid (L.AA) reduction was first used to obtain Si nanowires/RGO-1000 (Si NWs/RGO-1000) and Si nanowires/RGO-L.AA (Si NWs/RGO-L.AA) composite anodes for SABs. It was found that RGO suppressed the passivation and self-corrosion reactions and that SABs using Si NWs/RGO-L.AA as the anode can discharge for more than 700 hours, breaking the previous performance of SABs, and that the specific capacity was increased by 90.8% compared to bare Si. This work provides a new solution for the design of high specific capacity SABs with nanostructures and anode protective layers.

Synergistically enhanced LiF–rich protective layer for highly stable silicon anodes

Silicon (Si) is considered as one of the most promising anode materials with an extremely high specific capacity (3579 mAh/g), which is beyond the limit of conventional graphite anodes in lithium (Li) ion batteries (LIBs). However, large volume changes during the lithiation/delithiation process and formation of an unstable solid electrolyte interface (SEI) layer hinder the practical application of Si anodes. To address these issues, constructing a stable protective layer at the interface between anode and electrolyte is a desirable strategy. In this study, a LiF-rich SEI inducing protective layer (LPL) comprising aluminum fluoride (AlF3) and poly(acrylic acid) (PAA) is introduced onto Si anode to construct a stable LiF–rich SEI layer and mitigate the volume changes of the Si anodes during cycling. Owing to the synergetic effects of AlF3 and PAA, a LiF-rich SEI layer with robust physicochemical properties is uniformly formed on the Si anode. As a result, the LPL coated Si (LPL@Si) anodes exhibit outstanding electrochemical properties in Li metal cell tests. In addition, a full-cell prepared with the LPL@Si anode and LiNi0.8Co0.1Mn0.1O2 as a cathode exhibits an excellent cycling performance and mitigated volume changes, demonstrating the potential of this strategy to protect the Si anodes for the development of high-energy–density LIBs.

Systematic Study of the Effect of Cycle Number and Crystal Structure on Si Anodes

AbstractThis paper shows that the number of cycles and the crystal structure play an important role in the capacity and cycling ability of lithium‐ion batteries. However, the detailed dynamics and continuity of the capacity decay mechanism caused by the number of cycles and crystal structure need to be further understood at the nanoscale. Molecular dynamics simulation was used to examine the microstructure development and deformation behavior of the Si anode in an electric field. The results show that the increase of the number of cycles leads to a large expansion of the volume of the Si electrode, which further leads to the loss of capacity and the decrease of cycle capacity, as well as the decrease of structural stability. The formation of Si crystal structure from diamond structure to amorphous depends on the depth of lithiation and desulfurization. Due to the presence of a large number of nanoscale voids, the Si anode has undergone volume expansion. The transformation associated with nanogap nucleation caused by the involuntary diffusion process is driven by more cycles, resulting in irreversible capacity loss of lithium‐ion batteries. The analysis model shows that the stress caused by diffusion is not only related to the position of the Si anode, but also to the cycle time.

Tailored Yolk-Shell Design to Silicon Microparticles via Scalable and Template-Free Synthesis for Superior Lithium Storage.

Micrometer-sized Si particles are beneficial to practical lithium-ion batteries in regard to low cost and high volumetric energy density in comparison with nanostructured Si anodes. However, both the issues of electrical contact loss and overgrowth of solid electrolyte interface for microscale Si induced by colossal volume change still remain to be addressed. Herein, a scalable and template-free method is introduced to fabricate yolk-shell structured Si anode from commercially available Si microparticles. The void is created via a one-step alkali etching process with the remaining silicon core as the yolk, and a double-walled shell is formed from simultaneous in situ growth of the conformal native oxide layer and subsequent carbon coating. In this configuration, the well-defined void spaces allow the Si core to expand without compromising structural integrity, while the double-walled shell acts as a static capsule to confine silicon fragments despite likely particle fracture. Therefore, electrical connectivity is maintained on both the particle and electrode level during deep galvanostatic cycling, and the solid-electrolyte interface is stabilized on the shell surface. Owing to the benefits of tailored design, excellent cycling stability (capacity retention of 95% after 100 cycles) and high coulombic efficiency (99.5%) are realized in a practical full-cell demonstration.

Conductive copper ion-reinforced sodium alginate aerogel based free-standing Si anode for Li-ion storage

Biomass materials with great advantages of wide accessibility, low cost and environmental benignity have favorable application prospects as Si anodes for lithium-ion batteries (LIBs). In order to alleviate the volume effect and improve the conductance of Si, we fabricated a conductive copper ion-reinforced sodium alginate (SA) aerogel based free-standing Si anode (Si@CNTs/Alg-Cu-II) containing silicon nanoparticles, sodium alginate aerogel, carbon nanotubes and Cu nanoparticles, via a simple, low-cost and sustainable process (under 1 × 10−1 Pa, 1 °C/min to 200 °C holding for 1 h). In the irregular lamellar porous aerogel, silicon particles with good dispersion are bound by macromolecular chains of SA via dynamic hydrogen bonds and subsequently restrained in the porous aerogel to release volume stress. The in situ generated Cu particles and well-dispersed carbon nanotubes (CNTs) construct the conductive network around Si particles to improve the electrical conductivity of the electrode. This unique structure delivers a capacity of 835.6 mAh/g after 100 cycles at 0.1 A/g based on the total mass of Si@CNTs/Alg-Cu-II composite (Si content of 25.62%). Moreover, it also shows outstanding stability under high current density (a capacity retention of 84.1% after 100 cycles at 0.5 A/g). The sustainable preparation method and excellent electrochemical performance of Si@CNTs/Alg-Cu-II provide a new strategy to develop high-performance free-standing Si-based anodes for LIBs.

Steric molecular combing effect enables Self-Healing binder for silicon anodes in Lithium-Ion batteries

Silicon is a promising anode material for lithium-ion batteries with its superior capacity. However, the volume change of the silicon anode seriously affects the electrode integrity and cycle stability. The waterborne guar gum (GG) binder has been regarded as one of the most promising binders for Si anodes. Here, a unique steric molecular combing approach based on guar gum, glycerol, and citric acid is proposed to develop a self-healing binder GGC, which would boost the structural stability of electrode materials. The GGC binder is mainly designed to weaken van der Waals' forces between polymers through the plasticizing effect of glycerol, combing and straightening the guar molecular chain of GG, and exposing the guar hydroxyl sites of GG and the carboxyl groups of citric acid. The condensation reaction between the hydroxyl sites of GG and the carboxyl groups of citric acid forms stronger hydrogen bonds, which can help achieve self-healing effect to cope with the severe volume expansion effect of silicone-based materials. Silicon electrode lithium-ion batteries prepared with GGC binders exhibit outstanding electrochemical performance, with a discharge capacity of up to 1579 mAh/g for 1200 cycles at 1 A/g, providing a high capacity retention rate of 96%. This paper demostrates the great potential of GGC binders in realizing electrochemical performance enhancement of silicon anode.

Electrolyte design for robust gradient solid-electrolyte interfaces to enable high-performance silicon anodes for pouch batteries

Silicon (Si) anodes has emerged as an ideal anode for the next generation of lithium-ion batteries owing to its high specific capacity. Nevertheless, Si particles undergo large volume expansion during cycling, inducing the continuous fragmentation/re-formation of the solid-electrolyte interphase (SEI) layer, which leads to rapid capacity decay and low Coulombic efficiency in EC-based carbonate electrolytes. Herein, a weakly solvating electrolyte with boric acid tris(hexafluoroisopropyl) ester (BTHE), 2,2,2-trifluoroethyl methyl carbonate (FDEC), and fluoroethylene carbonate (FEC) is developed to build a stable SEI. BTHE is introduced as a functional additive, which is induce anion and fluorinated solvent to form a gradient rigid–soft coupling SEI layer. In contrast to other anion-derived interfaces, weakly solvating electrolyte has been proven to construct a highly robust and stable –CF3-rich-organic outer layer and LiF-rich inner layer SEI on the Si anodes, resulting in approximately 99.9 % ultra-high Coulombic efficiency and ultra-high areal capacity (∼8.1 mAh cm−2). Beyond proof of concept, a 2.68 Ah Si||LiNi0.8Mn0.1Co0.1O2 pouch cell has an impressive 84.3 % capacity retention after 1000 cycles and could work normally at temperatures ranging from −30 °C to 100 °C based on this electrolyte, representing a pioneering report in pouch cells incorporating Si anodes.

Performance Optimization of Supercapbattery with Porous Modification on Silicon as Anode and Cathode Based on Al<sub>2</sub>O<sub>3</sub>/CuCrO<sub>2</sub>

The development of the supercapbattery has become the focus of energy storage research due to their potential to increase energy and power density. This research is focused on developing a modification of silicon (Si) porous as an anode with Al2O3/CuCrO2/AC composite as a cathode of supercapacitor. These electrodes were synthesized using LA133 binder with deionized water as solvent. The supercapacitor electrode uses an aluminum foil substrate, while the Si electrode uses a cupper foil substrate. The structural and morphological characterization of the electrodes were identified through XRD, FTIR, and SEM tests, while the electrochemical performance characterization using Galvanostatic Charge-Discharge (GCD) instruments. The results of XRD data analysis of thin film electrodes of supercapacitor showed diffraction peaks which indicated the phases Al2O3/CuCrO2/AC and Si porous. The absorption functional groups of Al2O3/CuCrO2/AC and Si porous were identified through FTIR characterization. The results of SEM showed the addition of CuCrO2 and structure modification of silicon into porous caused increasing value of porosity. The electrochemical performance of the optimum point at Al2O3/CuCrO2/AC condition, showing a specific capacitance of 50.3 F/g, an energy density of 36.499 Wh/kg, and a power density of 433.6 W/kg. The combination of Al2O3/CuCrO2/AC//Si Porous 16 for supercapbattery devices shows performance with a specific capacitance of 14.4 F/g, an energy density of 6.1 Wh/kg, and a power density of 33.6 W/kg. These results indicate an increase in electrochemical performance compared with Si anodes without modification.

Interfacial self-healing polymer electrolytes for Long-Cycle silicon anodes in High-Performance solid-state lithium batteries

For all-solid-state lithium-ion batteries (ASSLIBs), silicon (Si) stands out as an appealing anodes material due to its high energy density and improved safety compared to lithium metal. However, the substantial volume changes during cycling result in poor solid-state physical contact and electrolyte–electrode interface issues, leading to unsatisfactory electrochemical performance. In this study, we employed in-situ polymerization to construct an integrated Si anodes/self-healing polymer electrolyte for ASSLIBs. The polymer chain reorganization stems from numerous dynamic bonds in the constructed self-healing dynamic supermolecular elastomer electrolyte (SHDSE) molecular structure. Notably, SHDSE also serves as a Si anodes binder with enhanced adhesive capability. As a result, the well-structured Li|SHDSE|Si-SHDSE cell generates subtle electrolyte–electrode interface contacts at the molecular level, which can offer a continuous and stable Li+ transport pathway, reduce Si particle displacement, and mitigate electrode volume expansion. This further enhances cyclic stability (>500 cycles with 68.1 % capacity retention and >99.8 % Coulombic efficiency). More practically, the 2.0 Ah wave-shaped Si||LiCoO2 soft-pack battery with in-situ cured SHDSE exhibits strongly stabilized electrochemical performance (1.68 Ah after 700 cycles, 86.2 % capacity retention) in spite of a high operating temperatures up to 100 °C and in various bending tests. This represents a groundbreaking report in flexible solid-state soft-pack batteries containing Si anodes.

Stable operation of highly loaded pure Si-Fe anode under ambient pressure via carboxy silane-directed robust solid electrolyte interphase

Incorporation of higher content Si anode material beyond 5 wt% to Li-ion batteries (LIBs) is challenging, owing to large volume change, swelling, and solid electrolyte interphase (SEI) instability issues. Herein, a strategy of diacetoxydimethylsilane (DAMS) additive-directed SEI stabilization is proposed for a stable operation of Si-0.33FeSi2 (named as Si-Fe) anode without graphite, which provides siloxane inorganics and organics enrichment that compensate insufficient passivation of fluoroethylene carbonate (FEC) additive and reduce a dependence on FEC. Unprecedented stable cycling performance of highly loaded (3.5 mA h cm−2) pure Si-Fe anode is achieved with 2 wt% DAMS combined with 9 wt% FEC additives under ambient pressure, yielding high capacity 1270 mA h g−1 at 0.5 C and significantly improved capacity retention of 81% after 100 cycles, whereas short circuit and rapid capacity fade occur with FEC only additive. DAMS-directed robust SEI layer dramatically suppresses swelling and particles crossover through separator, and therefore prevents short circuit, demonstrating a possible operation of pure Si or Si-dominant anodes in the next-generation high-energy-density and safe LIBs.

High capacity and high rate capability Si anodes encapsulated with camphor-derived graphene for Li ion batteries

Future Li ion battery technologies demand novel design strategies for Li ion battery anode overlays with shorter ion diffusion channels, better interfacial resistance and enlarged electrode–electrolyte interface. This is especially significant when it comes to alloy anodes like Si, Ge etc where the ultra-high theoretical capacities are unable to be utilized owing to their huge volume expansion during the process and lower conductivity. A new strategy is introduced to synthesize Si nanoparticle based composite with graphene and carbon. Encapsulation of a homogeneous graphene layer imparts the anodes with high reversible capacity, outstanding stability and very high rate capability. The optimal samples exhibit an excellent capacity as high as 3327 mAhg-1and superior rate capability. The cyclic stability of the system was also outstanding with a capacity retention of 84% at the end of 100 cycles while neglecting the initial stabilizing period the capacity retention reaches upto 97%.

Elucidating the Role of Carbon Conductive Additive in the Processing and Electrochemical Behavior of Surface-Modified Si Anodes

Elucidating the Role of Carbon Conductive Additive in the Processing and Electrochemical Behavior of Surface-Modified Si Anodes

An easy-to-prepare flexible 3D network aqueous binder with gradient hydrogen bonding for high-performance silicon anodes

Although silicon (Si) anode has extremely high specific capacity, the damage to the electrode caused by the huge volume expansion greatly hinders its practical application in lithium-ion batteries. Aiming to alleviate this problem, a high-performance aqueous binder (AMNG) with gradient hydrogen bonding and flexible three-dimensional network structure is prepared by a one-pot method. Compared to the conventional linear polyacrylic acid (PAA) binder, the AMNG binder exhibits enhanced ionic conductivity and stress dissipation for Si nanoparticles, which is able to greatly reduce the side reactions caused by volume changes and considerably improve the electrochemical performance of Si anodes. As a result, the Si nanoparticles using the AMNG binder exhibit an initial discharge capacity as high as 3101 mAh g−1 with a Coulombic efficiency of 89.95%, and a capacity retention of 71.6% for 120 cycles, which are superior to the electrode using PAA, corresponding to 2832 mAh g−1, 88.37% and 28.1%, respectively. More prominently, the practical application of the AMNG binder is evaluated in high-mass-loading Si-based electrodes and even in full cells with LiFePO4, all showing satisfied performance. Therefore, this design approach is valuable as a reference for the preparation of commercial aqueous binders.

Unlocking High-Current Performance in Silicon Anode: Synergistic Phosphorus Doping and Nitrogen-Doped Carbon Encapsulation to Enhance Lithium Diffusivity.

The silicon (Si) offers enormous theoretical capacity as a lithium-ion battery (LIB) anode. However, the low charge mobility in Si particles hinders its application for high current loading. In this study, ball-milled phosphorus-doped Si nanoparticles encapsulated with nitrogen-doped carbon (P-Si@N-C) are employed as an anode for LIBs. P-doped Si nanoparticles are first obtained via ball-milling and calcination of Si with phosphoric acid. N-doped carbon encapsulation is then introduced via carbonization of the surfactant-assisted polymerization of pyrrole monomer on P-doped Si. While P dopant is required to support the stability at high current density, the encapsulation of Si particles with N-doped carbon is influential in enhancing the overall Li+ diffusivity of the Si anode. The combined approaches improve the anode's Li+ diffusivity up to tenfold compared to the untreated anode. It leads to exceptional anode stability at a high current, retaining 87 % of its initial capacity under a large current rate of 4000 mA g-1. The full-cell comprising P-Si@N-C anode and LiFePO4 cathode demonstrates 94 % capacity retention of its initial capacity after 100 cycles at 1 C. This study explores the effective strategies to improve Li+ diffusivity for high-rate Si-based anode.

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure

Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10−3 S cm−1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g−1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.