Preparation Of Manganese-based Materials As Cathodes For Lithium-ion Battery

Rechargeable lithium-ion batteries are the dominant power sources not only for applications in portable consumer electronics but especially for energy conversion and storage devices such as electric vehicles (EVs), and hybrid electric vehicles (HEVs) because of their high energy densities and long cycle life. However, current lithium-ion battery technologies are still far from satisfactory to meet the increasingly diverse ranges of applications. To advance battery technologies, it is of great importance to explore novel cathodes with large specific capacity or high operating potential, to match them reasonably and to investigate their electrochemical performances. In this paper, the main points are summarized as follows:1. A facile and general approach has been presented to fabricate one dimensional porous hierarchical micro/nanostructured 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 lithium-rich materials. Specifically, metal oxalate hydrate precursors (MC2O4x·H2O, M= Mn, Ni, Co, Li) with one-dimensional microrod structures were first prepared via a novel ethanol-mediated co-precipitation method at room temperature, and followed by post-annealing treatment to obtain the 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 electrode materials. Moreover, through controlling the volume ratio of ethanol/water in the co-precipitation reaction, MC2O4·xH2O precursors with different aspect ratios are synthesized. The electrochemical results indicate that the as-prepared sample, which is prepared at the volume ratio of ethanol/water of 5:1, exhibits a high reversible capacity, excellent rate capability and good cycle stability. It delivers a discharge capacity of 297.1 mAh g-1 at 0.1 C rate, and 151.0 mAh g-1 even at as high as 10 C rate and with capacity retention of 97% at 2 C over 100 cycles. The unique porous hierarchical micro/nanostructured architecture favors for shortening the electron and lithium diffusion lengths, providing appropriate contact area between active materials and electrolyte, facilitating the efficient diffusion of electrolyte into the inner region of the electrode and accomodating the volume change associated with repeated Li+ insertion/extraction.2. MCO3·xH2O, (M= Mn, Ni) microspheres as precursors have been synthesized beforehand based on a co-precipitation method with NaHCO3 and Na2CO3 as the precipitating agent, respectively. After the impregnation of LiOH·H2O and post-annealing treatment, LiNi0.5Mn1.5O4 hollow microspheres and LiNi0.5Mn1.5O4 microparticles are obtained. The LiNi0.5Mn1.5O4 hollow microspheres display discharge capacities of 128.9 mAh·g-1 at 0.1 C rate,120.0 and 100.0 mAh·g-1 even at 20 C and 30 C rate, respectively, and also demonstrate good cycling stability from 0.5 C to 10 C. In addition, the LiNi0.5Mn1.5O4 hollow microspheres deliver a specific capacities of 125.3 and 113.5 mAh·g-1 at 0.1 C at 0℃ and -20℃, which are 97% and 87% of the capacity 25℃, respectively. The excellent rate performances and low-temperature capability are mainly attributed to its hollow micro/nano-structure, which can shorten Li+ions diffusion path and buffer the volume change during repeated Li+insertion/extraction processes.3. A new lithium-ion battery has been successfully assembled based on high energy CuO nanorod array anode and high voltage spinel LiNi0.5Mn1.5O4 cathode. Electrochemical tests of the CuO nanorod array grown on copper substrate demonstrate that the CuO/Li half cell can deliver discharge capacities of 787 and 560 mAh g-1 at 0.1 and 10C rates. Different from the traditional prelithiation of transition metal oxides anodes, a CuO-limited full cell has been assembled directly by adjusting the positive/negative capacity ratio of 1.2:1, which could deliver a discharge capacity of 660 mAh g-1 with estimated energy density of about 217 Wh kg-1 at 0.1 C rate. The CuO/LiNi0.5Mn1.5O4 full cell exhibits good cycle stability (with capacity retention of 84% at 0.5 C over 100 cycles) and superior rate capability (about 240 mAh g-1 at a high rate of 10 C), which are mainly resulted from the reasonable match between CuO arrays directly constructed on copper substrate and the hierarchical structured LiNi0.5Mn1.5O4 cathode materials.