Carbon Nanotube Enhanced Lithium Ion Composite Cathodes

Abstract

Batteries are sought that can deliver high energy density and high power density over thousands of cycles, with minimum environmental impact and cost. Invariably no one material can achieve all of these requirements. Lithium Iron Phosphate (LFP) satisfies most of these requirements reasonably well with the exception of power density. Two coincident methods have been utilized to increase the power capability and cycle life of battery cathodes by reducing the electrode resistance to the reaction site and increasing the diffusion coefficient for ions and electrons. Electrode resistance is typically reduced by a combination of surface coatings and carbon additives in the composites. Recent work has demonstrated that spray deposition with PVdF as binder increases the cathode capacity resilience over extended cycling.1 Likewise, incorporation of carbon nanotubes (CNT) has demonstrated decreased cathode fade over many life cycles as well.2-3 Since capacity fade has been experimentally connected to loss of electrode contact, it stands to reason that a battery made with a process that optimizes the binder contact and utilizes a resilient and highly conductive carbon additive would have extended capacity life, with the potential added benefit of higher energy density from a small inactive material content in the cathode.4 In this work, we investigate the properties of the CNT, the processing of CNTs in cathode films made using slurry and spray deposition techniques with LiFePO4 as the cathode material, and the synthesis of the materials with CNTs. We demonstrate that with an optimized processing method composites with minimal inactive material (10%) can perform with rate capabilities comparable to 20% carbon black (25% inactive material) without capacity fade.