Surface Modification of Silicon Nanoparticles by an "Ink" Layer for Advanced Lithium Ion Batteries

Solid-solution reaction suppresses the Jahn-Teller effect of potassium manganese hexacyanoferrate in potassium-ion batteries

Potassium manganese hexacyanoferrate (KMnHCF) suffers from poor cycling stability in potassium-ion batteries due to the Jahn-Teller effect, and experiences destabilizing asymmetric expansions and contractions during cycling. Herein, hollow nanospheres consisting of ultrasmall KMnHCF nanocube subunits (KMnHCF-S) are developed by a facile strategy. In situ XRD analysis demonstrates that the traditional phase transition for KMnHCF is replaced by a single-phase solid-solution reaction for KMnHCF-S, which effectively suppresses the Jahn-Teller effect. From DFT calculations, it was found that the calculated reaction energy for K+ extraction in the solid-solution reaction is much lower than that in the phase transition, indicating easier K+ extraction during the solid-solution reaction. KMnHCF-S delivers high capacity, outstanding rate capability, and superior cycling performance. Impressively, the K-ion full cell composed of the KMnHCF-S cathode and graphite anode also displays excellent cycling stability. The solid-solution reaction not only suppresses the Jahn-Teller effect of KMnHCF-S but also provides a strategy to enhance the electrochemical performance of other electrodes which undergo phase transitions.

Recent Applications of Molecular Structures at Silicon Anode Interfaces

Silicon (Si) is a promising anode material to realize many-fold higher anode capacity in next-generation lithium-ion batteries (LIBs). Si electrochemistry has strong dependence on the property of the Si interface, and therefore, Si surface engineering has attracted considerable research interest to address the challenges of Si electrodes such as dramatic volume changes and the high reactivity of Si surface. Molecular nanostructures, including metal–organic frameworks (MOFs), covalent–organic frameworks (COFs) and monolayers, have been employed in recent years to decorate or functionalize Si anode surfaces to improve their electrochemical performance. These materials have the advantages of facile preparation, nanoscale controllability and structural diversity, and thus could be utilized as versatile platforms for Si surface modification. This review aims to summarize the recent applications of MOFs, COFs and monolayers for Si anode development. The functionalities and common design strategies of these molecular structures are demonstrated.

Recycling of Lignin and Si Waste for Advanced Si/C Battery Anodes

The ever-increasing silicon photovoltaics industry produces a huge annual production of silicon waste (2.03 × 10⁵ tons in 2019), while lignin is one of the main waste materials in the traditional paper industry (7.0 × 10⁷ tons annually), which lead to not only enormous wastage of resources but also serious environment pollution. Lithium-ion batteries (LIBs) are the dominating power sources for portable electronics and electric vehicles. Silicon (Si)-based material is the most promising anode choice for the next-generation high-energy-density LIBs due to its much higher capacity than the commercial graphite anode. Here, we proposed the use of these silicon and lignin waste as sustainable raw materials to fabricate high-capacity silicon/carbon (Si/C) anode materials for LIBs via a facile coprecipitation method utilizing electrostatic attracting force, followed by a thermal annealing process. The as-achieved Si/C composite featured an advanced material structure with micrometer-sized secondary particles and Si nanoparticles embedded in the carbon matrix, which could tackle the inherent challenges of Si materials, including low conductivity and large volume change during the lithiation/delithiation processes. As expected, the obtained Si/C composite displayed an initial charge capacity of 1016.8 mAh g^-1, which was 3 times that of a commercial graphite anode in the state-of-the-art LIBs, as well as a high capacity retention of 74.5% at 0.2 A g^-1 after 100 cycles. In addition, this Si/C composite delivered superior rate capability with a high capacity of 575.9 mAh g^-1 at 2 A g^-1, 63.4% of the capacity at 0.2 A g^-1. The utilization of industrial Si and lignin waste provides a sustainable route for the fabrication of advanced high-capacity anode materials for the next-generation LIBs with high economic and environmental feasibility.

Silicon-nanoparticle-based composites for advanced lithium-ion battery anodes

Lithium-ion batteries (LIBs) play an important role in modern society. The low capacity of graphite cannot meet the demands of LIBs calling for high power and energy densities. Silicon (Si) is one of the most promising materials instead of graphite, because of its high theoretical capacity, low discharge voltage, low cost, etc. However, Si shows low conductivity of both ions and electrons and exhibits a severe volume change during cycles. Fabricating nano-sized Si and Si-based composites is an effective method to enhance the electrochemical performance of LIB anodes. Using a small size of Si nanoparticles (SiNPs) is likely to avoid the cracking of this material. One critical issue is to disclose different types and electrochemical effects of various coupled materials in the Si-based composites for anode fabrication and optimization. Hence, this paper reviews diverse SiNP-based composites for advanced LIBs from the perspective of composition and electrochemical effects. Almost all kinds of materials that have been coupled with SiNPs for LIB applications are summarized, along with their electrochemical influences on the composites. The integrated materials, including carbon materials, metals, metal oxides, polymers, Si-based materials, transition metal nitrides, carbides, dichalcogenides, alloys, and metal-organic frameworks (MOFs), are comprehensively presented.

Saclike-silicon nanoparticles anchored in ZIF-8 derived spongy matrix as high-performance anode for lithium-ion batteries

The carbon layer with good electrical conductivity and outstanding mechanical stability are essential in designing high-performance silicon/carbon (Si/C) anodes to replace the commercial graphite in lithium-ion batteries (LIBs). In terms of solving the two inherent defects of poor conductivity and big volume change of silicon, we fabricate a spongy carbon matrix derived from ZIF-8 to anchor saclike silicon synthesized by molten salt magnesiothermic reduction method. This spongy matrix can anchor saclike silicon to provide a stable reaction interface and support fast electronic transmission. At the same time, buffer space in saclike Si nanoparticles and spongy matrix can synergistically accommodate the volume change of Si to maintain the integrity of the electrode. The resulting composite with a high Si content of 77.58% exhibits good capacities of 1448 mAh g^-1 at 2 A g^-1 and 848 mAh g^-1 at 4 A g^-1 after 500 cycles. High initial coulombic efficiency of 84% at 0.2 A g^-1 is also exhibited in the first three activation cycles. Therefore, this novel multifunctional N-doped spongy matrix can supply multifaceted benefits in accommodation of volumetric variation, enhancement of conductivity, and integrity of structure during cycling.

Cathode materials with mixed phases of orthorhombic MoO3 and Li0.042MoO3 for lithium-ion batteries

MoO3 is a promising cathode candidate for lithium-ion batteries and its electronic conductivity is usually improved by MoO3lithiation via reaction of MoO3 with LiCl solutions. However, this process might increase the manufacturing complexity and result in surface breakage of MoO3 cathodes. In this paper, by introducing lithium source into MoO3 synthesis, MoO3 can be lithiated through introduction of the Li0.042MoO3 phase into the MoO3 structure. XRD and ICP results indicate that the phase composition and lithium content can be regulated by changing the amount of lithium source in the reaction solutions. FESEM and specific surface area measurements show that the particle size becomes more uniform and the surface area is increased when the degree of MoO3 lithiation is higher. The lithiated MoO3 sample shows better cycling performance than that of pristine MoO3, which is mainly due to the enhanced conductivity and increased surface area of the lithiated MoO3.