Development of Nanosized Cathode Materials and Functional additive of Polymeric Binder for Silicon Anodes in Lithium Ion Batteries

Abstract

1. Synthesis of Nano-sized Urchin Shaped LiFePO4 for Lithium Ion Batteries

We present the synthesis of the nano-sized urchin shaped LiFePO4 by a thermal decomposition method of metal-surfactant complexes. The morphology of LiFePO4 particles could be controlled by the injection of oleylamine with other surfactants and phosphoric acid. The injection of oleylamine and/or phosphoric acid was a key issue to control the morphology of LiFePO4 particles, which definitely changed the morphology from nano sphere to different types of the urchin shaped nanoparticles. The lengths of urchin shaped LiFePO4 particles were varied ranging from 300 nm to 2 µm and a lot of thin nano-rods attached from the urchin shaped nanoparticles ranging from 5 nm to 20 nm. These hierarchical nanostructures of the urchin shaped LiFePO4 particles could not only improve low tap density problems, but the nano-rods below 20 nm from the edge of the urchin shaped nanoparticles also enhance electron transport pathway.

2. Thermally Cross-linkable Diamino-PEG Additive with PAA Polymeric Binder for Stable Cyclability of Silicon Nanoparticles based Negative Electrodes in Lithium Ion Batteries

Silicon has received substantial interest due to extremely high theoretical specific capacity of 3579 mAh g-1 for Li15Si4 as 280% volumetric expansion. But during lithium ion insertion and extraction into silicon particles volume expansion and contraction are inevitably occurred. After long cycling retention, a mechanical instability arisen from cracking and pulverization of silicon particles results in loss of electrical contacts in silicon composite negative electrodes. Here, we developed a new type of additive with poly(acrylic acid) (PAA) for stable cycling retention of silicon anodes. Diamino Poly Ethylene Glycol (diamino-PEG), 4-7-10-trioxa-1, 13-tridecanediamine, is used as a thermally curable additive with PAA polymeric binder for silicon nanoparticles based negative electrodes. Amino groups of the diamino-PEG form amide bonds with carboxylic acid groups of PAA binder, which gives strong binding force even in high humidity condition. The highly cross linked amide bonds between diamino-PEG and PAA binder in silicon nanoparticles based negative electrodes contributes to reduce electrical contact loss of silicon particles during electrochemical reaction and supports stable cycling performances, also enhances specific capacity compared to the silicon anode PAA binder only used.