High damage tolerance of electrochemically lithiated silicon

Dual-Functional Photonic Battery Enabling Dynamic Radiative Thermal Management and Power Supply

Dynamic thermal management materials are pivotal for advancing energy-efficient buildings and promoting global sustainability. However, existing materials typically offer only a single-function of temperature regulation, lacking the integrated power supply capability essential for sustaining indoor activities and building sustainability, particularly in the face of frequent power outages. A photonic battery that combines all-season dynamic radiative thermoregulation with electrical power supply in a single silicon-based unit is demonstrated. This device delivers dual functionality with high infrared emissivity regulation (0.53 at 8-13 µm) and superior energy storage performance, featuring a high specific capacity (≈3271 mAh g-1), areal capacity (≈0.38 mAh cm-2), and efficient energy recycling (71.6%). A reversible ion-interaction-induced phase change mechanism, enabling continuous and non-volatile electro-optical-thermal transformation and significant infrared tunability, is proposed. Our simulations indicate that the implementation of these dynamic materials into buildings could significantly reduce energy consumption by up to 18.4%, equating to 544.8 GJ, and achieve an annual reduction in CO2 emissions of 124.1 tons. This work paves the way for the development of energy-saving electro-driven dynamic materials, marking a significant step forward in global sustainability initiatives.

Dynamic Thermosetting Resins with Synergistic Enhanced Strength and Toughness through Combination with Rigid and Soft Microdomains

Preparation of materials that possess highly strong and tough properties simultaneously is a great challenge. Thermosetting resins as a type of widely used polymeric materials without synergistic strength and toughness limit their applications in some special fields. In this report, an effective strategy to prepare thermosetting resins with synergistic strength and toughness, is presented. In this method, the soft and rigid microspheres with dynamic hemiaminal bonds are fabricated first, followed by hot-pressing to crosslink at the interfaces. Specifically, the rigid or soft microspheres are prepared via precipitation polymerization. After hot-pressing, the resulting rigid-soft blending materials exhibit superior strength and toughness, simultaneously. As compared with the precursor rigid or soft materials, the toughness of the rigid-soft blending films (RSBFs) is improved to 240% and 2100%, respectively, while the strength is comparable to the rigid precursor. As compared with the traditional crushing, blending, and hot-pressing of rigid or soft materials to get the nonuniform materials, the strength and toughness of the RSBFs are improved to 168% and 255%, respectively. This approach holds significant promise for the fabrication of polymer thermosets with a unique combination of strength and toughness.

Si-Based High-Entropy Anode for Lithium-Ion Batteries

Up to now, only a small portion of Si has been utilized in the anode for commercial lithium-ion batteries (LIBs) despite its high energy density. The main challenge of using micron-sized Si anode is the particle crack and pulverization due to the volume expansion during cycling. This work proposes a type of Si-based high-entropy alloy (HEA) materials with high structural stability for the LIB anode. Micron-sized HEA-Si anode can deliver a capacity of 971 mAhg-1 and retains 93.5% of its capacity after 100 cycles. In contrast, the silicon-germanium anode only retains 15% of its capacity after 20 cycles. This study has discovered that including HEA elements in Si-based anode can decrease its anisotropic stress and consequently enhance ductility at discharged state. By utilizing in situ X-ray diffraction and transmission electron microscopy analyses, a high-entropy transition metal doped Lix (Si/Ge) phase is found at lithiated anode, which returns to the pristine HEA phase after delithiation. The reversible lithiation and delithiation process between the HEA phases leads to intrinsic stability during cycling. These findings suggest that incorporating high-entropy modification is a promising approach in designing anode materials toward high-energy density LIBs.

Mechanics-based design of lithium-ion batteries: a perspective

From the overall framework of battery development, the battery structures have not received enough attention compared to the chemical components in batteries. The mechanical-electrochemical coupling behavior is a starting point for investigation on battery structures and the subsequent battery design. This perspective systematically reviews the efforts on the mechanics-based design for lithium-ion batteries (LIBs). Two typical types of mechanics-based LIB designs, namely the design at the preparation stage and that at the cycling stage, have been discussed, respectively. The former systemizes the structure design of multiscale battery components from the particle level to the cell level. The latter focuses on the external mechanics-related control, including external pressures and charge-discharge protocols, of in-service LIBs. Moreover, the general problems currently being faced in the mechanics-based LIB design are summarized, followed by the outlook of possible solutions.

Mechanical studies of the solid electrolyte interphase on anodes in lithium and lithium ion batteries

A stable solid electrolyte interphase (SEI) layer is key to high performing lithium ion and lithium metal batteries for metrics such as calendar and cycle life. The SEI must be mechanically robust to withstand large volumetric changes in anode materials such as lithium and silicon, so understanding the mechanical properties and behavior of the SEI is essential for the rational design of artificial SEI and anode form factors. The mechanical properties and mechanical failure of the SEI are challenging to study, because the SEI is thin at only ~10-200 nm thick and is air sensitive. Furthermore, the SEI changes as a function of electrode material, electrolyte and additives, temperature, potential, and formation protocols. A variety ofin situandex situtechniques have been used to study the mechanics of the SEI on a variety of lithium ion battery anode candidates; however, there has not been a succinct review of the findings thus far. Because of the difficulty of isolating the true SEI and its mechanical properties, there have been a limited number of studies that can fully de-convolute the SEI from the anode it forms on. A review of past research will be helpful for culminating current knowledge and helping to inspire new innovations to better quantify and understand the mechanical behavior of the SEI. This review will summarize the different experimental and theoretical techniques used to study the mechanics of SEI on common lithium battery anodes and their strengths and weaknesses.

A First Molecular Dynamics Study for Modeling the Microstructure and Mechanical Behavior of Si Nanopillars during Lithiation

This is the first study that employs large-scale atomistic simulations to examine the stress generation and deformation mechanisms of various Si nanopillars (SiNPs) during Li-ion insertion. First, a new robust and effective minimization approach is proposed to relax a lithiated amorphous SiNP (a-SiNP), which outperforms the known methods. Using this new method, our simulations are able to successfully capture the experimental morphological changes and volume expansions that SiNPs, hollow a-SiNPs, and solid crystalline SiNPs (c-SiNPs) experience upon maximum lithiation. These simulations enable us to selectively track the displacement of Si atoms and their atomic shear strain in the Li_3.75Si alloy region, allowing us to observe the plastic flow and illustrate the atomistic mechanism of lithiation-induced deformation for various SiNPs for the first time. Based on the simulation results, a simple fracture mechanistic model is used to determine the fracture resistance of SiNPs, showing that the hollow a-SiNP is the optimal form of Si as an anode because it has the highest fracture resistance. The crack propagation simulation suggests that the preexisting dislocations in pristine c-Si can contribute toward the fracture of c-SiNPs during lithiation. These findings can guide the design of new Si-based anode geometries for the next-generation Li-ion batteries.

Addressing Unfavorable Influence of Particle Cracking with a Strengthened Shell Layer in Ni-Rich Cathodes

Ni-rich layered materials are widely accepted as pivotal cathode materials to realize low-cost high-energy-density batteries. However, they still suffer from the intrinsic mechanically induced degradation due to the large lattice deformation. Here, we fabricate a strengthened shell layer on polycrystalline secondary particles to address the unfavorable influence of particle cracking instead of suppressing their bulky pulverization. This tough layer, constructed via welding LiNi_0.8Co_0.1Mn_0.1O₂ primary particles with a Nb-based ceramic, increases Young's modulus of the particles 2.6 times. This layer allows the particles work properly with the intact spherical morphology even after bulk cracking. It seems that this tough skin stops the bulky flaws growing into perforated fissures and keeps the electrodes from quick polarization. This approach demonstrates that, besides addressing the intrinsic challenges directly, appropriate particle engineering is another efficient way to exploit the potentials of Ni-rich cathodes and power batteries made out of them.

Low-cost batteries based on industrial waste Al-Si microparticles and LiFePO4 for stationary energy storage

Owing to their high capacity and low working potential, Si-based anodes are regarded as potential alternatives to graphite anodes to meet the higher requirements of Li-ion batteries (LIBs). However, high volume change causes the fracturing and pulverization of the bulk anode and continuous side reactions, which are more severe in large-particle Si anodes, limiting its practical application. Herein, to build a low-cost battery system, we chose a common industrial waste product, Al-Si microparticles (Al-SiMPs, ∼30 μm), as the anode for LIBs and coupled it with a 2.0 M LiFP6 2-MeTHF electrolyte to support its operation. The Al-SiMP anode showed a high specific capacity and a significantly improved electronic conductivity, ensuring high energy and power densities. An ultra-high initial coulombic efficiency (iCE) of 91.6% and a cycling CE of ∼99.9% were obtained in the half-cells, which delivered a capacity of 1300 mA h g-1 and maintained 95.3% after 100 cycles. Paired with low-cost and high-safety LiFePO4 as the cathode, the LFP||Al-SiMP full cells showed decent cycling stability and exhibited a considerable cost advantage, demonstrating a competitive solution for stationary energy storage.

Mechanoelectrochemical issues involved in current lithium-ion batteries

The volume change and concurrent stress evolution of electrode materials during the cycling of lithium-ion batteries can cause severe mechanical issues such as the fracture of active materials and electrodes, thus leading to safety issues and capacity fading. Recent years have witnessed a thriving interest to gain a complete understanding of battery electrode materials from the viewpoint of mechanics. This review paper aims at discussing battery electrode materials from a mechanical perspective to provide an overview of the recent innovative efforts in this field. On the one hand, we introduce the mechanical issues of active materials and electrodes in the electrochemical processes, along with a focus on the strategies developed for enhancing the mechanical strength of electrode materials and constructing mechanically robust electrodes. On the other hand, experimental and theoretical studies on the stress-regulated effects on electrochemical processes are discussed to demonstrate the intriguing role of mechanical stress as an enabler in electrochemistry. We also give an outlook on the promising research topics for understanding the material mechanical issues, reinforcing electrode materials and improving battery performance.

Strong stress-composition coupling in lithium alloy nanoparticles

The stress inevitably imposed during electrochemical reactions is expected to fundamentally affect the electrochemistry, phase behavior and morphology of electrodes in service. Here, we show a strong stress-composition coupling in lithium binary alloys during the lithiation of tin-tin oxide core-shell nanoparticles. Using in situ graphene liquid cell electron microscopy imaging, we visualise the generation of a non-uniform composition field in the nanoparticles during lithiation. Stress models based on density functional theory calculations show that the composition gradient is proportional to the applied stress. Based on this coupling, we demonstrate that we can directionally control the lithium distribution by applying different stresses to lithium alloy materials. Our results provide insights into stress-lithium electrochemistry coupling at the nanoscale and suggest potential applications of lithium alloy nanoparticles.

Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research

The increasing demands of energy storage require the significant improvement of current Li-ion battery electrode materials and the development of advanced electrode materials. Thus, it is necessary to gain an in-depth understanding of the reaction processes, degradation mechanism, and thermal decomposition mechanisms under realistic operation conditions. This understanding can be obtained by in situ/operando characterization techniques, which provide information on the structure evolution, redox mechanism, solid-electrolyte interphase (SEI) formation, side reactions, and Li-ion transport properties under operating conditions. Here, the recent developments in the in situ/operando techniques employed for the investigation of the structural stability, dynamic properties, chemical environment changes, and morphological evolution are described and summarized. The experimental approaches reviewed here include X-ray, electron, neutron, optical, and scanning probes. The experimental methods and operating principles, especially the in situ cell designs, are described in detail. Representative studies of the in situ/operando techniques are summarized, and finally the major current challenges and future opportunities are discussed. Several important battery challenges are likely to benefit from these in situ/operando techniques, including the inhomogeneous reactions of high-energy-density cathodes, the development of safe and reversible Li metal plating, and the development of stable SEI.

Two-dimensional porous silicon nanosheets as anode materials for high performance lithium-ion batteries

In this paper, silicon nanosheets (Si-NSs) are chemically synthesized by using graphene oxide nanosheets as the template. The obtained Si-NSs, which are aggregations of silicon nanocrystals with a size of ∼10 nm, are applied directly as the anode material for lithium ion batteries, delivering a reversible capacity of 800 mA h g-1 after 900 cycles at a rate as high as 8400 mA g-1. Ex situ measurements and in situ observations show the positive effect of the mesoporous structure on the structural stability of Si-NSs. The evolution and survivability of the porous structures during lithiation and delithiation processes are investigated by molecular dynamics simulations, demonstrating that the porous structure can enhance the amount of "active" Li atoms during the stable stage of cycling and therefore promote mass capacity. The longer the survival of the porous structure, the longer the high mass capacity can be retained.

Anisotropic Compositional Expansion and Chemical Potential of Lithiated SiO2 Electrodes: Multiscale Mechanical Analysis

The use of high-capacity electrode materials (i.e., Si) in Li-ion batteries is hindered by their mechanical degradation. Thus, oxides (i.e., SiO₂) are commonly used to obtain high expected capacities and long-term cycle performances. Despite extensive studies of the electrochemical-mechanical behaviors of high-capacity energy storage materials, the mechanical behaviors of amorphous SiO₂ during electrochemical reaction remain largely unknown. Here, we systematically investigate the stress evolution, electronic structure, and mechanical deformation of lithiated SiO₂ through first-principles computation and the finite element method. The structural and thermodynamic role of O in the amorphous Li-O-Si system is reported and compared with that in Si. Strong Si-O bonds in SiO₂ show high mechanical strength and brittle behavior, but as Li is inserted, the Li-rich SiO₂ phases become mechanically softened. The relaxation kinetics of SiO₂, inducing deviatoric inelastic strains under mechanical constraints, is also compared with that of Si. The finite element model including the kinetic model for anisotropic expansion demonstrates that the long-term cycling stability of core-shell Si-SiO₂ nanoparticles mainly arises from the reaction kinetics and high mechanical strength of SiO₂. These results provide fundamental insights into the chemomechanical behavior of SiO₂ for practical use.

A facile method to fabricate a porous Si/C composite with excellent cycling stability for use as the anode in a lithium ion battery

Porous Si/C with excellent cycling stability has been fabricated by dehydrating Si/sucrose mixed powder with concentrated H₂SO₄.

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

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

"Self-Peel-Off" Transfer Produces Ultrathin Polyvinylidene-Fluoride-Based Flexible Nanodevices

Here, a new strategy, self-peel-off transfer, for the preparation of ultrathin flexible nanodevices made from polyvinylidene-fluoride (PVDF) is reported. In this process, a functional pattern of nanoparticles is transferred via peeling from a temporary substrate to the final PVDF film. This peeling process takes advantage of the differences in the work of adhesion between the various layers (the PVDF layer, the nanoparticle-pattern layer and the substrate layer) and of the high stresses generated by the differential thermal expansion of the layers. The work of adhesion is mainly guided by the basic physical/chemical properties of these layers and is highly sensitive to variations in temperature and moisture in the environment. The peeling technique is tested on a variety of PVDF-based functional films using gold/palladium nanoparticles, carbon nanotubes, graphene oxide, and lithium iron phosphate. Several PVDF-based flexible nanodevices are prepared, including a single-sided wireless flexible humidity sensor in which PVDF is used as the substrate and a double-sided flexible capacitor in which PVDF is used as the ferroelectric layer and the carrier layer. Results show that the nanodevices perform with high repeatability and stability. Self-peel-off transfer is a viable preparation strategy for the design and fabrication of flexible, ultrathin, and light-weight nanodevices.

Tuning the Outward to Inward Swelling in Lithiated Silicon Nanotubes via Surface Oxide Coating

Electrochemically induced mechanical degradation hinders the application of Si anodes in advanced lithium-ion batteries. Hollow structures and surface coatings have been often used to mitigate the degradation of Si-based anodes. However, the structural change and degradation mechanism during lithiation/delithiation of hollow Si structures with coatings remain unclear. Here, we combine in situ TEM experiment and chemomechanical modeling to study the electrochemically induced swelling of amorphous-Si (a-Si) nanotubes with different thicknesses of surface SiOx layers. Surprisingly, we find that no inward expansion occurs at the inner surface during lithiation of a-Si nanotubes with native oxides. In contrast, inward expansion can be induced by increasing the thickness of SiOx on the outer surface, thus reducing the overall outward swelling of the lithiated nanotube. Moreover, both the sandwich lithiation mechanism and the two-stage lithiation process in a-Si nanotubes remain unchanged with the increasing thickness of surface coatings. Our chemomechanical modeling reveals the mechanical confinement effects in lithiated a-Si nanotubes with and without SiOx coatings. This work not only provides insights into the degradation of nanotube anodes with surface coatings but also sheds light onto the optimal design of hollow anodes for high-performance lithium-ion batteries.