Establishing a Resilient Conductive Binding Network for Si-Based Anodes via Molecular Engineering

Poly(ethylene) Oxide Electrolytes for All-Solid-State Lithium Batteries Using Microsized Silicon/Carbon Anodes with Enhanced Rate Capability and Cyclability

Silicon (Si) has been widely studied as one of the promising anodes for lithium-ion batteries (LIBs) because of its ultrahigh theoretical specific capacity and low working voltage. However, the poor interfacial stability of silicon against conventional liquid electrolytes has largely impeded its practical use. Therefore, the combination of silicon-based anodes and solid electrolytes has attracted a great deal of attention in recent years. Here, we demonstrate three types of microsized porous silicon/carbon (Si/C) electrodes (i.e., pristine, prelithiated by liquid electrolyte, and preinfiltrated by polymer electrolyte) that are paired with poly(ethylene) oxide (PEO)-based electrolytes for all-solid-state lithium batteries (ASSLBs). We found that when compared with ionic conductivity, the mechanical stability of the PEO electrolyte dominates the electrochemical performance of ASSLBs using Si/C electrodes at elevated temperature. Additionally, both prelithiated and preinfiltrated Si/C electrodes show higher specific capacity in comparison to the pristine electrode, which is attributed to continuous lithium-ion conducting pathways within the electrode and thus improved utilization of active material. Moreover, owing to good interfacial lithium-ion transport in the electrode, a solid-state half-cell with preinfiltrated Si/C electrode and PEO-lithium bis (trifluoromethanesulfonyl)imide electrolyte delivers a specific capacity of ∼1,000 mAh g-1 after 100 cycles under 800 mA g-1 at 60 °C with average Coulombic efficiency >98.9%. This work provides a strategy for rationally designing the microstructure of silicon-based electrodes with solid electrolytes for high-performance all-solid-state lithium batteries.

Lithiation Depth Regulation of Silicon Anodes toward Excellent Stability

Silicon (Si) is an appealing choice of anode for next-generation lithium ion batteries with high energy density, but its dramatic volume expansion makes it a tremendous challenge to achieve acceptable stability. Herein, we demonstrate that no capacity decay is observed during the testing period when the lithiation depth of Si nanoparticles is regulated at 2000 mAh g-1 or below, the fracture of Si anode films is well mitigated under suitable regulation of lithiation depth, and the cycled Si remains particulate without turning flocculent as under full lithiation. In addition, the solid electrolyte interphase (SEI) with a LiF-dominated outer region produced under lithiation regulation could better passivate the Si anodes and prevent further electrolyte decomposition than the mosaic-type SEI formed under full lithiation. Regulating lithiation depth proved to be a feasible solution to the pressing volume issues, and optimization of capacity utilization should be considered as much as materials-level optimization.

Neural Network Inspired Binder Enables Fast Li-Ion Transport and High Stress Adaptation for Si Anode

Extensive investigations have proven the effectiveness of elastic binders in settling the challenge of structural damage posed by volume expansion of high-capacity anode used in nanoscale silicon. However, the sluggish ionic conductivity of polymer binder severely restricts the electrode reactions, making it unsuitable for practical applications. Inspired by the biological tissues with rapid neurotransmission and robust muscles, we propose a biomimetic binder that contains ionic conductive polymer (by polymerization reaction of poly(ethylene glycol) diglycidyl ether and polyethylenimine) and rigid polymer backbone (polyacrylic acid), which can effectively mitigate both Li-ion transport resistance and lithiation stress to stabilize the silicon nanoparticles during cycles. Consequently, the silicon anode with biomimetic binder achieves a rate capability of 1897 mAh g-1 at 8.0 A g-1 and capacity retention of 87% after 150 cycles under areal capacity upon 3.0 mAh cm-2. These results demonstrate the possibility of decoupling ionic conductivity from mechanical properties toward practical high-capacity anodes for energy-dense batteries.

Constructing Matching Cathode-Anode Interphases with Improved Chemo-mechanical Stability for High-Energy Batteries

Coupling Ni-rich layered oxide cathodes with Si-based anodes is one of the most promising strategies to realize high-energy-density Li-ion batteries. However, unstable interfaces on both cathode and anode sides cause continuous parasitic reactions, resulting in structural degradation and capacity fading of full cells. Herein, lithium tetrafluoro(oxalato) phosphate is synthesized and applied as a multifunctional electrolyte additive to mitigate irreversible volume swing of the SiOx anode and suppress undesirable interfacial evolution of the LiNi0.83Co0.12Mn0.05O2 (NCM) cathode simultaneously, resulting in improved cycle life. Benefiting from its desirable redox thermodynamics and kinetics, the molecularly tailored additive facilitates matching interphases consisting of LiF, Li3PO4, and P-containing macromolecular polymer on both the NCM cathode and SiOx anode, respectively, modulating interfacial chemo-mechanical stability as well as charge transfer kinetics. More encouragingly, the proposed strategy enables 4.4 V 21700 cylindrical batteries (5 Ah) with excellent cycling stability (92.9% capacity retention after 300 cycles) under practical conditions. The key finding points out a fresh perspective on interfacial optimization for high-energy-density battery systems.

Universal F4-Modified Strategy on Metal-Organic Framework to Chemical Stabilize PVDF-HFP as Quasi-Solid-State Electrolyte

Solid-state electrolytes (SSEs) based on metal organic framework (MOF) and polymer mixed matrix membranes (MMMs) have shown great promotions in both lithium-ion conduction and interfacial resistance in lithium metal batteries (LMBs). However, the unwanted structural evolution and the and the obscure electrochemical reaction mechanism among two phases limit their further optimization and commercial application. Herein, fluorine-modified zirconium MOF with diverse F-quantities is synthesized, denoted as Zr-BDC-Fx (x = 0, 2, 4), to assemble high performance quais-solid-state electrolytes (QSSEs) with PVDF-HFP. The chemical complexation of F-sites in Zr-BDC-F4 stabilized PVDF-HFP chains in β-phase and disordered oscillation with enhanced charge transfer and Li transmit property. Besides, the porous confinement and electronegativity of F-groups enhanced the capture and dissociation of TFSI- anions and the homogeneous deposition of LiF solid electrolyte interphase (SEI), promoting the high-efficient transport of Li+ ions and inhibiting the growth of Li dendrites. The superb specific capacities in high-loaded Li.

Comprehensive Study of Lithium Diffusion in Si/C-Layer and Si/C3N4 Composites in a Faceted Crystalline Silicon Anode for Fast-Charging Lithium-Ion Batteries

By using silicon (Si) as an anode of lithium-ion batteries, the capacity can be significantly increased, but relatively large volume expansion limits the application as an efficient anode material. Huge volume expansion of the silicon anode during lithiation, however, leads to cracking and losing its connection with the current collector. This shortcoming can be improved by the deposition of a nanometric carbon- or nitrogen-doped carbon coating on the silicon surface, resulting in Si/C-layer and Si/C3N4 interfaces. In this work, Li+ diffusion in Si/C-layer and Si/C3N4 composite materials along three Si surfaces and various ion pathways were carefully analyzed by using density functional theory and ab initio molecular dynamic (AIMD) simulations. Both Si/C and Si/C3N4 interfaces and three Si surfaces of (100), (110), and (111) were investigated. The formation of nitrogen holes and monatomic carbon binders in the composite increases ion diffusivity and limits volume expansion. Furthermore, the Bader analysis shows that the type and orientation of the surfaces have important effects on ion distribution. The results indicated that the C3N4 composite increases Li+ diffusion in Si (100) from 7.82 × 10-5 to 3.17 × 10-4 cm2/s. The presented results provide a guide for the appropriate design of stable and safe high-energy-density batteries.

Unleashing the Potential of High-Capacity Anodes through an Interfacial Prelithiation Strategy

The scalable development of an environmentally adaptive and homogeneous Li+ supplementary route remains a formidable challenge for the existing prelithiation technologies, restricting the full potential of high-capacity anodes. In this study, we present a moisture-tolerant interfacial prelithiation approach through casting a hydrophobic poly(vinylidene-co-hexafluoropropylene) membrane blended with a deep-lithiated alloy (Li22Si5@C/PVDF-HFP) onto Si based anodes. This strategy could not only extend to various high-capacity anode systems (SiOx@C, hard carbon) but also align with industrial roll-to-roll assembly processes. By carefully adjusting the thickness of the prelithiation layer, the densely packed Si@C electrode (4.5 mAh cm-2) exhibits significantly improved initial Coulombic efficiency until a close-to-unit value, as well as extreme moisture tolerance (60% relative humidity). Furthermore, it achieves more than 10-fold enhancement of ionic conductivity across the electrode. As pairing the prelithiated Si@C anode with the LiNi0.8Co0.1Mn0.1O2 cathode, the 2 Ah pouch-format prototype balances an energy density of ∼371 Wh kg-1 and an extreme power output of 2450 W kg-1 as well as 83.8% capacity retention for 1000 cycles. The combined operando phase tracking and spatial arrangement analysis of the intermediate alloy elucidate that the enhanced Li utilization derives from the gradient stress dissipation model upon a spontaneous Li+ redistribution process.

Towards Practical Application of Li-S Battery with High Sulfur Loading and Lean Electrolyte: Will Carbon-Based Hosts Win This Race?

As the need for high-energy-density batteries continues to grow, lithium-sulfur (Li-S) batteries have become a highly promising next-generation energy solution due to their low cost and exceptional energy density compared to commercially available Li-ion batteries. Research into carbon-based sulfur hosts for Li-S batteries has been ongoing for over two decades, leading to a significant number of publications and patents. However, the commercialization of Li-S batteries has yet to be realized. This can be attributed, in part, to the instability of the Li metal anode. However, even when considering just the cathode side, there is still no consensus on whether carbon-based hosts will prove to be the best sulfur hosts for the industrialization of Li-S batteries. Recently, there has been controversy surrounding the use of carbon-based materials as the ideal sulfur hosts for practical applications of Li-S batteries under high sulfur loading and lean electrolyte conditions. To address this question, it is important to review the results of research into carbon-based hosts, assess their strengths and weaknesses, and provide a clear perspective. This review systematically evaluates the merits and mechanisms of various strategies for developing carbon-based host materials for high sulfur loading and lean electrolyte conditions. The review covers structural design and functional optimization strategies in detail, providing a comprehensive understanding of the development of sulfur hosts. The review also describes the use of efficient machine learning methods for investigating Li-S batteries. Finally, the outlook section lists and discusses current trends, challenges, and uncertainties surrounding carbon-based hosts, and concludes by presenting our standpoint and perspective on the subject.

Quantitative analysis of the structural evolution in Si anode via multi-scale image reconstruction

Despite the high theoretical capacity, silicon (Si) anode suffers from dramatical capacity loss, due to its massive volume swings (up to 300%) during cycling. Hence, thorough understanding of the structural evolution mechanism is necessary and essential for performance optimization of Si anode. Herein, a multi-scale three-dimensional (3D) image reconstruction technique is firstly applied to visualize the structural evolution process of Si anodes. Three key components (Si particles, inactive components, and voids) in the electrode are quantitatively analyzed by the focused ion beam and scanning electron microscope (FIB-SEM) technology. Furthermore, the average sizes of Si particles were run statistics during the cycling. By combining the componential observation within the electrode (macroscopic information) and the 3D models of the particle with solid electrolyte interphase (SEI) layer (microscopic information), the failure mechanism of Si anode is vividly demonstrated. This work establishes a new methodology to quantitatively analyze the structural and compositional evolution of Si anode, which could be further applied for the studies of many other electrode materials with similar issues.

Three-Dimensional Crosslinked PAA-TA Hybrid Binders for Long-Cycle-Life SiOx Anodes in Lithium-Ion Batteries

The large volume expansion hinders the commercial application of silicon oxide (SiO_x) anodes in lithium-ion batteries. Recent studies show that binders play a vital role in mitigating the volume change of SiO_x electrodes. Herein, we introduce the small molecule tannic acid (TA) with high branching into the linear poly(acrylic acid) (PAA) binder for SiO_x anodes. The three-dimensional (3D) crosslinked network with multiple hydrogen bonds is formed by the incorporation of abundant hydroxyl groups with unique carboxyl groups, which increases the interfacial adhesive strength with SiO_x particles. As a consequence, SiO_x electrodes based on the PAA-TA binder show an excellent cycling performance with a high specific capacity of 1025 mA h g^-1 at 500 mA g^-1 after 250 cycles. Moreover, the SiO_x||NCM811 full cell exhibits a reversible capacity of 143 mA h g^-1 corresponding to 87.4% capacity retention after 100 cycles.