Surface-Bound Silicon Nanoparticles with a Planar-Oriented N-Type Polymer for Cycle-Stable Li-Ion Battery Anode

Polymer Coating Enabling a Durable Conductive Network for Si-Based Lithium-Ion Batteries

Silicon nanoparticles (SiNPs) have become a promising class of high-capacity silicon-based anodes. However, their large surface area intensifies severe interfacial side reactions, which impair kinetic performance. In this study, a uniform allyltrimethoxysilane-derived polymer (AP) coating is applied to SiNPs, enhancing the durability of the conductive network by strengthening triphasic contact integrity among SiNPs, conductive additives, and binders. This effectively mitigates electrical contact failure caused by volume fluctuations during cycling. The coating also improves the mechanical integrity of the entire electrode, while the robust solid electrolyte interphase (SEI) layer it induces prevents electrolyte penetration over long cycling. The optimized Si@AP anode exhibits an impressive reversible capacity of 1300 mAh g-1 after 200 cycles and delivers a rate capacity of 842 mAh g-1 at 5 C. This work underscores the significant potential of in situ polymer coatings for enhancing the mechanical and electrochemical performance of Si-based anodes.

Structural Design and Challenges of Micron-Scale Silicon-Based Lithium-ion Batteries

Currently, lithium-ion batteries (LIBs) are at the forefront of energy storage technologies. Silicon-based anodes, with their high capacity and low cost, present a promising alternative to traditional graphite anodes in LIBs, offering the potential for substantial improvements in energy density. However, the significant volumetric changes that silicon-based anodes undergo during charge and discharge cycles can lead to structural degradation. Furthermore, the formation of excessive solid-electrolyte interphases (SEIs) during cycling impedes the efficient migration of ions and electrons. This comprehensive review focuses on the structural design and optimization of micron-scale silicon-based anodes from both materials and systems perspectives. Significant progress is made in the development of advanced electrolytes, binders, and conductive additives that complement micron-scale silicon-based anodes in both half and full-cells. Moreover, advancements in system-level technologies, such as pre-lithiation techniques to mitigate irreversible Li+ loss, have enhanced the energy density and lifespan of micron-scale silicon-based full cells. This review concludes with a detailed classification of the underlying mechanisms, providing a comprehensive summary to guide the development of high-energy-density devices. It also offers strategic insights to address the challenges associated with the large-scale deployment of silicon-based LIBs.

Enhancing the Stability and Initial Coulombic Efficiency of Silicon Anodes through Coating with Glassy ZIF-4

The high capacity of electrodes allows for a lower mass of electrodes, which is essential for increasing the energy density of the batteries. According to this, silicon is a promising anode candidate for Li-ion batteries due to its high theoretical capacity. However, its practical application is hampered by the significant volume expansion of silicon during battery operation, resulting in pulverization and contact loss. In this study, we developed a stable Li-ion anode that not only solves the problem of the short lifetime of silicon but also preserves the initial efficiency by using silicon nanoparticles covered with glassy ZIF-4 (SZ-4). SZ-4 suppresses silicon pulverization, contact loss, etc. because the glassy ZIF-4 wrapped around the silicon nanoparticles prevents additional SEI formation outside the silicon surface due to the electrically insulating characteristics of glassy ZIF-4. The SZ-4 realized by a simple heat treatment method showed 74% capacity retention after 100 cycles and a high initial efficiency of 78.7%.

Prefabrication of "Trinity" Functional Binary Layers on a Silicon Surface to Develop High-Performance Lithium-Ion Batteries

The silicon (Si) anode is widely recognized as the most prospective next-generation anode. To promote the application of Si electrodes, it is imperative to address persistent interface side reactions caused by the huge volume expansion of Si particles. Herein, we introduce beneficial groups of the optimized binder and electrolyte on the Si surface by a co-dissolution method, realizing a "trinity" functional layer composed of azodicarbonamide and 4-nitrobenzenesulfonyl fluoride (AN). The "trinity" functional AN interfacial layer induces beneficial reductive decomposition reactions of the electrolyte and forms a hybrid solid-electrolyte interphase (SEI) skin layer with uniformly distributed organic/inorganic components, which can enhance the mechanical strength of the overall electrode, restrain harmful electrolyte depletion reactions, and maintain efficient ion/electron transport. Hence, the optimized Si@AN11 electrode retains 1407.9 mAh g^-1 after 500 cycles and still delivers 1773.5 mAh g^-1 at 10 C. In stark contrast, Si anodes have almost no reserved capacity at the same test conditions. Besides, the LiNi_0.5Co_0.2Mn_0.3O₂//Si@AN11 full-cell maintains 141.2 mAh g^-1 after 350 cycles. This work demonstrates the potential of developing multiple composite artificial layers to modulate the SEI properties of various next-generation electrodes.

In Situ Construction of a Multifunctional Interface Regulator with Amino-Modified Conjugated Diene toward High-Rate and Long-Cycle Silicon Anodes

Silicon (Si) is deemed to be the next-generation lithium-ion battery anode. However, on account of the poor electronic conductivity of Si materials and the instability of the solid electrolyte interphase layer, the electrochemical performance of Si anodes is far from reaching the application level. In this work, a multifunctional poly(propargylamine) (PPA) interlayer is constructed on the Si surface via a simple in situ polymerization method. Benefiting from the electronic conductivity, ionic conductivity, robust interphase interactions for hydrogen bonding, and stability of multifunctional PPA, the optimized Si@PPA-7% electrode shows improved lithium storage capability. A high capacity of 1316.3 mAh g^-1 is retained after 500 cycles at 2.1 A g^-1, and 2370.3 mAh g^-1 can be delivered at 42 A g^-1, which are in stark contrast to the unmodified Si electrode. Furthermore, the rate and cycle capabilities of the LiFePO₄//Si@PPA-7% full cell are also obviously better than those of LiFePO₄//Si.

Engineering of Silicon Core-Shell Structures for Li-ion Anodes

The amount of silicon in anode materials for Li-ion batteries is still limited by the huge volume changes during charge-discharge cycles. Such changes lead to the loss of electrical contacts, as well as mechanical and surface electrolyte interphase (SEI) instabilities, strongly reducing the cycle life. Core-shell structures have attracted a vast research interest due to the possibility of modifying some properties with a judicious choice of the shell. It is, for example, possible to improve the electronic conductivity and ionic diffusion, or buffer volume variations. This review gives a comprehensive overview of the recent developments and the different strategies used for the design, synthesis and electrochemical performance of silicon-based core-shells. It is based on a selection of the main types of silicon coatings reported in the literature, including carbon, inorganic, organic and double-layer coatings, Finally, a summary of the advantages and drawbacks of these different types of core-shells as anode materials for Li-ion batteries and some insightful suggestions in regards to their use are provided.

Building a Cycle-Stable Fe-Si Alloy/Carbon Nanocomposite Anode for Li-Ion Batteries through a Covalent-Bonding Method

Si is being intensively developed as a safe and high-performance anode for next-generation Li-ion batteries (LIBs); however, its battery application still remains challenging because of its low cycling Coulombic efficiency. To address this issue, we chose a conjugated polymer, polynaphthalene, as a carbon precursor and a low-cost commercial ferrosilicon (Fe-Si) alloy as the active phase to prepare a Fe-Si/C nanocomposite with a core-shell-like architecture through sand milling-assisted covalent-bonding method, followed by a carbonization reaction, thus forming a covalently bonded carbon coating on the surfaces of Fe-Si alloy nanoparticles. Benefitting from the greatly reduced volumetric expansion of Fe-Si alloy cores in the lithiation process and the stable interface provided by the outer carbon shell, the thus-prepared Fe-Si/C nanocomposite exhibits a high structural stability in repeated charge/discharge cycles. The experimental results reveal that the Fe-Si/C composite anode can demonstrate a high reversible capacity of 1316.2 mA h g^-1 with an active mass utilization of 82.6%, a long-term cycle stability of more than 1000 cycles even at a considerably high current rate of 2.0 A g^-1, and, in particular, a high cycling Coulombic efficiency of 99.7%, showing great prospect for application in practical LIBs.

Covalently Bonded Silicon/Carbon Nanocomposites as Cycle-Stable Anodes for Li-Ion Batteries

Carbon coating is a popular strategy to boost the cyclability of Si anodes for Li-ion batteries. However, most of the Si/C nanocomposite anodes fail to achieve stable cycling due to the easy separation and peeling off of the carbon layer from the Si surface during extended cycles. To overcome this problem, we develop a covalent modification strategy by chemically bonding a large conjugated polymer, poly-peri-naphthalene (PPN), on the surfaces of nano-Si particles through a mechanochemical method, followed by a carbonization reaction to convert the PPN polymer into carbon, thus forming a Si/C composite with a carbon coating layer tightly bonded on the Si surface. Due to the strong covalent bonding interaction of the Si surface with the PPN-derived carbon coating layer, the Si/C composite can keep its structural integrity and provide an effective surface protection during the fluctuating volume changes of the nano-Si cores. As a consequence, the thus-prepared Si/C composite anode demonstrates a reversible capacity of 1512.6 mA h g^-1, a stable cyclability over 500 cycles with a capacity retention of 74.2%, and a high cycling Coulombic efficiency of 99.5%, providing a novel insight for designing highly cyclable silicon anodes for new-generation Li-ion batteries.

Chemically Prelithiated Hard-Carbon Anode for High Power and High Capacity Li-Ion Batteries

Hard carbons (HC) have potential high capacities and power capability, prospectively serving as an alternative anode material for Li-ion batteries (LIB). However, their low initial coulombic efficiency (ICE) and the resulting poor cyclability hinder their practical applications. Herein, a facile and effective approach is developed to prelithiate hard carbons by a spontaneous chemical reaction with lithium naphthalenide (Li-Naph). Due to the mild reactivity and strong lithiation ability of Li-Naph, HC anode can be prelithiated rapidly in a few minutes and controllably to a desirable level by tuning the reaction time. The as-formed prelithiated hard carbon (pHC) has a thinner, denser, and more robust solid electrolyte interface layer consisting of uniformly distributed LiF, thus demonstrating a very high ICE, high power, and stable cyclability. When paired with the current commercial LiCoO₂ and LiFePO₄ cathodes, the assembled pHC/LiCoO₂ and pHC/LiFePO₄ full cells exhibit a high ICE of >95.0% and a nearly 100% utilization of electrode-active materials, confirming a practical application of pHC for a new generation of high capacity and high power LIBs.

A sandwich-like Si/SiC/nanographite sheet as a high performance anode for lithium-ion batteries

Silicon/carbon (Si/C) nanocomposite anodes have attracted great interest for their use in lithium-ion batteries (LIBs). However, Si nanoparticles are difficult to stabilize on a carbon surface. Herein, we solve this stabilization problem by designing a Si/silicon carbide/nanographite sheet (Si/SiC/NanoG) nanocomposite. The Si/SiC/NanoG nanocomposite is synthesized by the magnesium thermal reduction of a mixture of silica (SiO2) nanoparticles and NanoG at low temperature, which results in a sandwich-like structure in which the middle SiC layer serves as a linker to stabilize the Si nanoparticles on the surface of NanoGs. Electrochemical characterization shows that the Si/SiC/NanoG nanocomposite anode exhibits outstanding electrochemical performance (an initial reversible capacity of 1135.4 mA h g-1 and 80.4% capacity retention after 100 cycles at 100 mA g-1). This high capacity retention is due to the strong connection between Si and NanoG through the interfacial SiC layer, which buffers the volume changes during the Li-Si alloying-dealloying process. This research will contribute to the design of advanced Si/C anode materials of LIBs.

An Al2O3 coating layer on mesoporous Si nanospheres for stable solid electrolyte interphase and high-rate capacity for lithium ion batteries

The application of Si-based anode materials is hindered by their extreme volume change, poor cycling stability, and low coulombic efficiency. Solving these problems generally requires a combination of strategies, such as nanostructure designing or surface coating. However, these strategies increase the difficulty of the fabrication process. Herein, a simple and one-pot replacement reaction route was designed to produce an Al2O3 layer anchored on mesoporous Si nanospheres (Si@Al2O3) by employing Al nanospheres with a naturally formed Al2O3 layer as a reducing agent and self-sacrificial template. The obtained Si@Al2O3 was mesoporous, with enough porous space to buffer the volume change and provide a fast lithium ion transfer channel. Furthermore, the coated Al2O3 layer could stabilize the structure and SEI layer of the mesoporous Si nanospheres, endowing the Si@Al2O3 nanospheres with improved initial coulombic efficiency, cycling performance and rate capability. As a result, a high capacity of 1750.2 mA h g-1 at 0.5 A g-1 after 120 cycles and 1001.7 mA h g-1 at 2 A g-1 after 500 cycles were delivered for lithium ion batteries. The good performance could be attributed to the mesoporous structure and the outer-coated Al2O3 layer.