Incorporating Nano-Si Particles Into Cellulose-Based Anodic Composites for Lithium-Ion Batteries

Incorporating Nano-Si Particles into Cellulose Fibers as a Way of Making Anodic Composites for Lithium-Ion Batteries

Joseph Wokpetah^{1, 2}, Simon Leijonmarck² and Goran Lindbergh²

¹The Pennsylvania State University, Department of Chemical Engineering, 212 Fenske Laboratory, University Park, PA 16802,USA

² KTH-Royal Institute of Technology, Division of Applied Electrochemistry, Teknikringen 42, 100 44 Stockholm, Sweden

Lithium-ion batteries are a class of rechargeable batteries in which lithium ions migrate from the cathode to the anode during discharge and vice versa during charging of the battery. These batteries have become if not the most important, one of the important batteries over the years and have grown from R&D interest to sales of over 4 billion units in 2009 [3]. Most devices and electronics that require multiple recharging cycles use lithium ion batteries since they can be recharged many times without losing their capacity. In addition, due to their high electric potential, one can store lots of energy per mass of lithium.

One of the many areas of lithium-ion batteries that are still being researched is the anode material. Silicon is becoming more preferred compared to carbon as the negative electrode material due to many factors and the most renowned being its capacity: '3579 mAh/g for silicon versus 372 mAh/g for carbon' [4]. This means that using silicon instead of carbon, as the anodic material for lithium-ion batteries will make the battery better in terms of storage of energy density and cycling.

Silicon is, however, known to fall off the cupper current collector during discharging and charging of the battery, due to the increase in its size as it forms complexes with the lithium ions. This effect decreases the capacity and lifetime of the battery. Sanchez et al have shown that binding these silicon particles on the surface of a cellulose fiber increases the batteries' performance[5]. This project aims to investigate how lithium-ion batteries will perform when silicon particles are incorporated in the pores of a cellulose fiber used in making the anodic material for the battery.

The method used involves continuous mixing of cellulose fibers with silicon and carbon particles in ethanol. Part of the mixture is solvent exchanged from ethanol to acetone and finally to pentane, whilst the other part is not solvent exchanged. The purpose of solvent exchange is to keep the fibers relatively open after drying. We hypothesize that after analysis of our final results, the battery's capacity and lifetime will increase compared to the conventional method which uses just silicon.

We were successful in building a functional lithium ion battery with a silicon-cellulose anodic material but had challenges with the battery's cyclability.

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[3] Edited by Thomas B. Reddy. Linden's Handbook of Batteries. Fourth edition. (2011)

[4] J.L. Gomez Camer, J. Morales and L. Sanchez. Nano-Si/Cellulose composites as anode materials for lithium-ion batteries. Electrochemical and solid-state Letters. (2008)

[5] J.L. Gomez Camer, J. Morales and L. Sanchez. Nano-Si/Cellulose composites as anode materials for lithium-ion batteries. Electrochemical and solid-state Letters. (2008)