Unraveling the New Role of Metal-Organic Frameworks in Designing Silicon Hollow Nanocages for High-Energy Lithium-Ion Batteries

Synergistic Protecting-Etching Synthesis of Carbon Nanoboxes@Silicon for High-Capacity Lithium-Ion Battery

Silicon (Si) is considered as the most likely choice for the high-capacity lithium-ion batteries owing to its ultrahigh theoretical capacity (4200 mA h g-1) being over 10 times than that of traditional graphite anode materials (372 mA h g-1). However, its widespread application is limited by problems such as a large volume expansion and low electrical conductivity. Herein, we design a hollow nitrogen-doped carbon-coated silicon (Si@Co-HNC) composite in a water-based system via a synergistic protecting-etching strategy of tannic acid. The prepared Si@Co-HNC composite can effectively mitigate the volume change of silicon and improve the electrical conductivity. Moreover, the abundant voids inside the carbon layer and the porous carbon layer accelerate the transport of electrons and lithium ions, resulting in excellent electrochemical performance. The reversible discharge capacity of 1205 mA h g-1 can be retained after 120 cycles at a current density of 0.5 A g-1. In particular, the discharge capacity can be maintained at 1066 mA h g-1 after 300 cycles at a high current density of 1 A g-1. This study provides a new strategy for the design of Si-based anode materials with excellent electrical conductivity and structural stability.

Chelation-Assisted formation of carbon nanotubes interconnected Yolk-Shell Silicon/Carbon anodes for High-Performance Lithium-ion batteries

As a viable replacement to commercial graphite anodes, silicon (Si) anodes have gained much attention from academics because of their considerable theoretical specific capacity and appropriate reaction voltage. Nevertheless, some limitations still exist in developing silicon anodes, including significant volume expansion and poor electrical conductivity. Herein, the carbon nanotubes (CNTs) interconnected yolk-shell silicon/carbon anodes (YS-Si@CoNC) were prepared via the chelation competition induced polymerization (CCIP) approach. The YS-Si@CoNC anode, designed in this study, demonstrates improved performance. At the current density of 0.5 A g^-1 and 1 A g^-1, a capacity of 1001 mAh g^-1 and 956.5 mAh g^-1 can be achieved after 150 cycles and after 300 cycles, respectively. In particular, at the current density of 5 A g^-1, the reversible specific capacity of 688 mAh g^-1 is realized. The exceptional outcomes are mainly attributed to the internal voids that adequately alleviate the volumetric expansion and the CNTs and carbon shells that provide an efficient conducting matrix to fasten the diffusion of electrons and lithium-ions. Our research presents a convenient way of designing Si/C anode materials with a yolk-shell structure to guarantee impressive electrical conductivity and robust structural integrity for high-performance LIBs.

Lithiophilic hollow Co3[Co(CN)6]2 embedded carbon nanotube film for dendrite-free lithium metal anodes

Lithium metal is considered to be an ideal anode material due to its ultra-high theoretical capacity and extremely low electric potential. Unfortunately, the infinite volume expansion and unregulated formation of lithium dendrites in the plating/stripping process restrict its practical utilization. Herein, we designed a hollow Co₃[Co(CN)₆]₂ (CoCoPBA) embedded high-conductivity carbon film as a three-dimensional (3D) lithiophilic current collector (h-CoCoPBAs@SWCNT). The interwoven carbon nanotubes with hollow nanoparticles can effectively promote electron transfer and reduce local current density, adapting to the huge volume expansion in long-term electrochemical cycling. At the same time, lithiophilic hollow CoCoPBA nanoparticles provide abundant active sites due to their large surface area, efficiently reducing nucleation overpotential and making lithium deposition easier and more uniform, both confirmed by theoretical calculation and experiment. Accordingly, compared with bare Cu electrodes, h-CoCoPBAs@SWCNT electrodes have a flat and uniform Li deposition morphology, which is beneficial to enhance the cycle life of lithium metal anodes. And the symmetrical cell assembled by h-CoCoPBAs@SWCNT shows stable cycling performance of more than 500 h at 2 mA cm^-2 with 1 mAh cm^-2. Besides, the assembled lithium-sulfur full cell also has higher cycle stability and rate performance.

Design of a Dual-Electrolyte Battery System Based on a High-Energy NCM811-Si/C Full Battery Electrode-Compatible Electrolyte

Rechargeable lithium-ion batteries using high-capacity anodes and high-voltage cathodes can deliver the highest possible energy densities among all electrochemical devices. However, there is no single electrolyte with a wide and stable electrochemical window that can accommodate both a high-voltage cathode and a low-voltage anode so far. Here, we propose that a strategy of using a hybrid electrolyte should be applied to realize the full potential of a Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)-silicon/carbon (Si/C) full cell by simultaneously achieving optimal redox chemistry at both the NCM811 cathode and the Si/C anode. The hybrid-electrolyte design spatially separates the cathodic electrolytes from anodic electrolytes by a Nafion-based separator. The ionic liquid electrolyte (LiTFSI-Pyr₁₃TFSI) on the cathode side can stand high work potentials and form a stable cathodic electrolyte intermediate (CEI) on NCM811. Meanwhile, a stable solid electrolyte intermediate (SEI) and high cycling stability can also be achieved on the anode side, enabled by a localized high concentration of ether-based electrolytes (LiTFSI-DME/HFE). The decoupled NCM811-Si/C full cell exhibits excellent long-term cycling performance with ultrahigh capacity retention for over 1000 cycles, thanks to the synergy of the cathode-side and anode-side electrolytes. This hybrid-electrolyte strategy has been proven to be applicable for other high-performance battery systems such as dual-ion batteries (DIB).