Hideya Yoshitake

Improved performance in micron-sized silicon anodes by in situ polymerization of acrylic acid-based slurry

The interactions between silicon particles and polymeric binders are a key factor during the course of manufacturing high-capacity Si anodes for lithium-ion batteries. Polymeric binders usually compensate for the volumetric over-changes of silicon particles, and then prevent electrode deformation while keeping the integrity of electron and ion pathways. This work explores an efficient synthesis method to directly anchor a reliable binder tightly on the surface of Si particles by in situ polymerization of an acrylic acid monomer in the mixing process of Si-based slurry. The resultant Si composite electrode possesses a highly elastic structure, which can provide a highly extensible space accommodating volume expansion/contraction of Si particles during lithiation/delithiation. Moreover, the cross-linked acrylic acid network results in a strong cohesive force between Si particles and auxiliary materials, such as conductive agent and copper foil. Accordingly, a satisfactory electrochemical performance of the Si anode can be gained, including a high initial coulombic efficiency of ∼73% and stable cycling performance (∼82% retention over 300 cycles at a current density of 4 A g−1). Such a novel and facile fabrication process represents an appealing method for manufacturing high-performance Si-based anodes using micron-sized Si particles with low cost.

A micro-sized Si–CNT anode for practical application via a one-step, low-cost and green method

Silicon (Si) has been used in Li-ion batteries (LIBs), and considerable progress has been achieved in design and engineering with improved capacity and cycling. However, large-scale application of Si-based anodes is hindered owing to the wide use of toxic raw materials, high manufacturing cost, limited capacity and unpalatable tap density. Herein, we describe a low-cost and green route to solve these problems. Composite Si–carbon nanotube (CNT) spheres were synthesized using a scalable method: rotary spray drying. These spheres were interspersed by many CNTs and wrapped Si nanoparticles (SiNPs) within them. Due to slightly rigid structure of CNTs, many void spaces in spheres could be preserved during the agglomeration of spheres. These voids could accommodate the volume expansion of Si particles and promote a stable integral structure during cycling. Importantly, this micron-grade material could improve the volume density and tap density to achieve high energy density. The prepared material showed promising reversible capacity of 2500 mA h g−1 with retention of 98% during 500 cycles. Ultra-fast discharge–charge (900 mA h g−1 at 20C) was achieved owing to the crosslinking effect between CNTs and SiNPs in these spheres. Moreover, a high-performance Si material was actualized via a simple industrial method rather than a complex synthesis.

Formation of thermally resistant films induced by vinylene carbonate additive on a hard carbon anode for lithium ion batteries at elevated temperature

Vinylene carbonate (VC)-induced film formation in a LiFePO4/hard carbon (HC) cell is clarified based on mass spectroscopic analysis. VC is found to induce the formation of different types of thermally resistant organophosphates on the HC surface for different solvents and their formation mechanisms are elucidated. Formation of the organophosphates is also found to contribute to the improved cycle performance at elevated temperature due to their thermally stable characteristics.