Mesocrystalline Positive Electrode Materials for Lithium-Ion Battery
EMSL Project ID
46897
Abstract
The applied use of nanoparticles has been the subject of intense research over the past several decades due to the novel properties and tunable functions of nanoparticles that can be utilized in a wide range of applications. A great deal of recent studies in the fields of colloidal and crystal chemistry have focused on ordered nanoparticle superstructures with a vast range of architectures, particularly mesocrystals. Mesocrystals, short for mesoscopically structured crystals, are crystallographically oriented nanoparticle superstructures and have received much attention since first being introduced by Colfen et al. Until recently, mesocrystals were only studied in biomineral materials but current research efforts have shifted on the development of mesocrystalline organic molecules, metal oxides, and other functional materials. Mesocrystals can be classified by their high degree of crystallinity, high porosity, and subunit alignment along a crystallographic register. These highly desirable properties are due in part to mesocrystal formation mechanisms, which are still poorly understood, and make mesocrystals the ideal material candidates for catalysis, sensing, and energy storage and conversion applications. Porous materials with large specific surface areas have been shown to enhance the performance of lithium-ion battery cathode because of more prevalent and uniform pores that ease intercalation by decreasing the Li-ion diffusion distance. Secondary battery cathodes constructed out of mesocrystalline materials could benefit tremendously from the inherent and uniform porosity with which the nanoparticles orient themselves.
Lithium iron phosphate (LiFePO4) and vanadium oxide are among the leading potential candidates of cathode materials for the next generation of lithium-ion batteries. VO2(B) has a theoretical capacity of 323 mAh/g making it an excellent potential candidate for lithium-ion battery cathode material; however, reports of VO2(B) have suffered from capacity fading upon cycling. LiFePO4 has been highly regarded due to its high theoretical capacity of 170mAh/g, flat voltage at ~3.4V, abundant raw material resources, and excellent thermal and chemical stability; however, LiFePO4 suffers from performance issues related to its low ionic and electronic conductivity values. The synthesis of cathodic material mesocrystals could potentially overcome stability and performance related issues due to the decreased lithium ion diffusion lengths and inherent pore network.
Utilizing additive-free solution-based processing methods, VO2(B) nanostars were developed from the reduction of commercially available V2O5 and oxalic acid. LiFePO4 was also synthesized following a simple solvothermal method with the end results being LiFePO4 mesocrystals displaying dumbbell morphology. In order to clearly establish this astounding structure as mesocrystalline, it is necessary to collect clear HRTEM images showing the crystalline nature and SAED patterns validating the single crystalline characteristics. Efforts carried out, to date, at the University of Washington have proven less than fruitful. Proper characterization of mesocrystals is often a difficult task because the oriented assembly of nanoparticles leads to the formation of mesocrystals where the constituting crystallites are arranged in a crystallographic register and the product particles demonstrate single crystal behavior. While identification of mesocrystals has proven to be difficult it can be achieved via the detection of a number of features including high porosity/large surface area and evidence of mesoscopic subunits as viewed from transmission electron microscopy (TEM). It is the aim of this proposal to successfully carry out TEM characterization of VO2(B) and LiFePO4 mesocrystals using the facilities and personnel available at Pacific Northwest National Laboratory (PNNL).
Project Details
Project type
Exploratory Research
Start Date
2012-03-05
End Date
2013-03-17
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Uchaker ED, M Gu, N Zhou, Y Li, CM Wang, and G Cao. 2013. "Enhanced Intercalation Dynamics And Stability Of Engineered Micro/nano-structured Electrode Materials: Vanadium Oxide Mesocrystals." Abstract submitted to Small . PNNL-SA-94412. Published in Enhanced Intercalation Dynamics and Stability of Engineered Micro/Nano-Structured Electrode Materials: Vanadium Oxide Mesocrystals. WILEY-VCH Verlag GmbH & Co., Weinheim.