Rechargeable lithium-ion battery (LIB) cathodes consist of transition metal oxide material, which reversibly (de)intercalates lithium at a high potential difference versus a carbon anode. Manganese oxide cathode material offers lower cost and toxicity than the normally used cobalt. However, LiMn2O4 suffers from capacity fading, Mn dissolution at high temperatures, and poor high rate capability. Its ultimate performance, however, depends on the morphology and electrochemical properties. In this work, Au alloyed with Fe, Pd, and Pt, respectively, was synthesized and used to improve the microstructure and catalytic activities by functionalizing LiMn2O4 via a coprecipitation calcination method. The pristine LiMn2O4 and modified materials were examined using a combination of spectroscopic and microscopic techniques along with in-detail galvanostatic charge–discharge tests. Microscopic results revealed that the modified composite cathode materials had high phase purity, highly crystallized particles, and more regular morphological structures with narrow size distributions. Galvanostatic charge–discharge testing indicated that the initial discharge capacities of LiMxMn2-xO4 at 0.1 C for M0.02=PtAu, FeAu, and PdAu were 147, 155.5, and 160.2 mAh g−1, respectively. The enhancement of the capacity retention and higher electrode coulombic efficiency of the modified materials were significant, especially at high C rate. At enlarged cycling potential ranges, the Li(M)0.02Mn1.98O4 samples delivered relevant discharge capacities (70, 80, and 90 mAh g-1) compared to LiMn2O4 (45 mAh g-1).
Part of the book: Alkali-ion Batteries
The performance of the battery cathode depends on the electrode microstructure and morphology, as well as the inherent electrochemical properties of the cathode materials. The spinel LiMn2O4 is the most promising candidate as a cathode material because of its low cost and nontoxicity compared with commercial LiCoO2. However, there is still a challenge to synthesize high-quality single-crystal nanostructured cathode materials. Nanowires offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. To enhance the activity and stability, flexible spinel nanowires are synthesized, via α-MnO2 nanowire precursor method. Ultrathin LiMn2O4 nanowires with cubic spinel structure were synthesized by using a solvothermal reaction to produce α-MnO2 nanowire followed by solid-state lithiation. LiMn2O4 nanowires have diameters less than 10 nm and lengths of several micrometers. The LiMn2O4 nanowires are used as stabilizing support during the electrochemical redox processes. The unique nanoporous material effectively accommodates structural transformation during Li+ ion insertion and effectively reduces Li+ diffusion distances, reducing the volumetric changes and lattice stresses during charge and discharge. Galvanostatic battery testing showed that LiMn2O4 nanowires delivered 146 mAh/g in a large potential window. The electrochemical and spectrochemical interrogation techniques demonstrated that LiMn2O4 nanowires are promising cathode materials for lithium ion batteries as apposed to LiMn2O4 powders.
Part of the book: Nanowires