An additive-free silicon anode in nanotube morphology as a model lithium ion battery material

"Nanoskeleton" Si-SiOx/C Anodes toward Highly Stable Lithium-Ion Batteries

A fragile solid-electrolyte interphase (SEI) layer due to the volume expansion of silicon cannot sufficiently prevent side reactions and electrolyte consumption and restricts the application of silicon anodes in lithium-ion batteries with high cycling stability. Herein, a carbon nanotube (CNT) supported "nanoskeleton" structure with robust mechanical properties and improved conductive pathways is designed by twining CNTs with in situ grown SiOx/C and carbon-wrapped Si nanoparticles. The CNT "nanoskeleton" can improve electrical contact between particles, promoting the formation of a denser and more homogeneous SEI layer. Moreover, the buffer region granted by the CNTs can tolerate the volume expansions of Si, avoiding the repeated destruction of the SEI layer during the continuous lithiation and delithiation processes. Combined with these advantages, the anode with optimal CNT content can deliver both a high capacity (918 mAh·g-1 at 200 mA·g-1) and high-capacity retention (74% after 300 cycles) with relieved volume expansion (71.4%). The capacity of the NMC111 full cell with the synthesized Si-SiOx/C anode is retained at 71 mAh·g-1 after 500 cycles at 100 mAh·g-1 with a capacity retention of 72%.

Preparation of Buffered Nano-Submicron Hierarchical Structure Hollow SiOx @C Anodes for Lithium-Ion Battery Materials with Carboxymethyl Chitosan

Silicon-based materials are among the most promising anode materials for next-generation lithium-ion batteries. However, the volume expansion and poor conductivity of silicon-based materials during the charge and discharge process seriously hinder their practical application in the field of anodes. Here, we choose carboxymethyl chitosan (CMCS) as the carbon source coating and binding on the surface of nano silicon and hollow silicon dioxide (H-SiO2 ) to form a hierarchical buffered structure of nano-hollow SiOx @C. The hollow H-SiO2 can alleviate the volume expansion of nano silicon during the lithiation process under continuous cycling. Meanwhile, the carbon layer carbonized by CMCS containing N-doping further regulates the silicon's expansion and improves the conductivity of the active materials. The as- prepared SiOx @C material exhibits an initial discharge capacity of 985.4 mAh g-1 with the decay rate of 0.27 % per cycle in 150 cycles under the current density of 0.2 A g-1 . It is proved that the hierarchical buffer structure nano-hollow SiOx @C anode material has practical application potential.

Large areal capacity all-in-one lithium-ion battery based on boron-doped silicon/carbon hybrid anode material and cellulose framework

Si, featuring ultra-large theoretical specific capacity, is a very promising alternative to graphite for Li-ion batteries (LIBs). However, Si suffers from intrinsic low electrical conductivity and structural instability upon lithiation, thereby severely deteriorating its electrochemical performance. To address these issues, B-doping into Si, N-doped carbon coating layer, and carbon nanotube conductive network are combined in this work. The obtained Si/C hybrid anode material can be "grown" onto the Cu foil without using any binder and delivers large specific capacity (2328 mAh g^-1 at 0.2 A g^-1), great rate capability (1296.8 mAh g^-1 at 4 A g^-1), and good cyclability (76.7% capacity retention over 500 cycles). Besides, a cellulose separator derived from cotton is found to be superior to traditional polypropylene separator. By using cellulose as both the separator host and the mechanical skeleton of two electrodes, a flexible all-in-one paper-like LIB is assembled via a facile layer-by-layer filtration method. In this all-in-one LIB, all the components are integrated together with robust interfaces. This LIB is able to offer commercial-level areal capacity of 3.47 mAh cm^-2 (corresponding to 12.73 mWh cm^-2 and 318.3 mWh cm^-3) and good cycling stability even under bending. This study offers a new route for optimizing Si-based anode materials and constructing flexible energy storage devices with a large areal capacity.