High Performance Pillared Vanadium Oxide Xerogel Cathode for Lithium Ion Batteries

Abstract

Lithium ion batteries commonly utilize layered oxide materials as the cathode, where lithium is intercalated and deintercalated between the layers in the crystal structure during cycling. The repeated lithium insertion and extraction can cause stress on the material, leading to fracture. Additionally, the extent of lithiation may cause phase changes in the layered structure that are sometimes irreversible. These changes to the material cause capacity loss and reduce the battery cycle life. This research focuses on nanostructuring layered oxides to enhance their cyclability and power capabilities. In particular, vanadium oxide xerogels were modified by adding pillaring molecules between the layers to increase the interlayer spacing. Vanadium oxide xerogels possess attractive capacities but suffer from significant capacity fade due to distortion of the crystal structure. We hypothesize that the pillars will enhance thermal and mechanical stability by reducing the strain on the structure and increasing lithium ion mobility, thereby increasing the cycle life and high rate capacities. Aluminum Keggin ions were used as pillaring agents for the vanadium oxide xerogels. X-ray diffraction showed an interlayer spacing increase from 1.14 to 1.32 nm after pillaring, consistent with the size of the keggin ions (~1.3 nm), while still maintaining the layered V 2 O 5 xerogel crystalline structure (Figure 1). Elemental analysis indicated an aluminum loading of 9 wt% in the pillared material. The pillared materials also demonstrate increased thermal stability and rate capabilities during cycling in coin cells, with capacities over 60% higher than those of the unpillared V 2 O 5 xerogel. Additionally, the pillared materials retained more capacity during cycling at C/2. Pillaring the layered vanadium oxide xerogels improved both capacity retention and battery lifetime. Figure 1. Diffraction patterns for V 2 O 5 xerogel (a), pillared V 2 O 5 xerogel (b), and pillared V 2 O 5 xerogel after heat treatment in either air (c) or nitrogen (d). The dotted line is intended as a guide for the eye. Figure 1