| Nowdays, with the rapid development of electric vehicles (EVs) and hybrid electric vehicles (HEVs), it has become a prevailing trend to exploit lithium ion batteries (LIBs) with high energy density, high power density and long cycling life.However, the electrochemical performance of LIBs currently developed could not meet the increasing demand for applications. Usually, the synthesis procedures of electrode materials are relative tedious and there are high requirements for equipments and rigorous control of process parameters. Therefore, it is highly necessary to develop a general, simple and mild method to synthesize electrode materials for LIBs. In this work, we report the preparation and morphology control of a series of manganese-based electrode materials from tuning reaction kinetics. For the first time, a general and mild synthesis method based on ethanol/water solvent was developed to prepare a wide range of one dimensional manganese-based electrode materials for high performance LIBs. The main points are summarized as follows:1. The kinetics of the fast reaction between multi-metal ions and oxalic acid in ethanol/water solvent was investigated by measuring the turbidity changes with time,taking the synthesis of Li-rich manganese-based electrode material as a sample. It is found that the addition of ethanol into water can not only accelerate the reaction kinetics, but also change the relative reaction rate of nickel, cobalt and manganese acetate with oxalic acid, respectively. Besides, ethanol plays an important role in tuning the oxalate precursors' morphology. We have successfully expanded the apporoach to synthesize a series of uniform 1D electrode materials, such as Li-rich Li1.2Nio.13Coo.13Mno.54O2, Li1.2Ni0.1Mn0,6O2, spinel LiNi0.5Mn1.5O4 cathode materials and spinel NiMn2O4,ZnMn2O4 anode materials. The as-synthsized electrode materials exhibited great electrochemical properties. Li1.2Ni0.13Co0.13Mn0.54O2 can deliver a discharge capacity of 297.1 and 151.0 mAh g-1 at the rate of 0.1 C and 10 C and it can maintain a capacity retention of 97% after 100 cycles at 2 C rate. The excellent rate properties can be ascribed to be that the unique porous micro- and nanostructured architecture favors for shortening the electron and lithium diffusion lengths, facilitating the efficient diffusion of electrolyte into the inner region of the electrode. Moreover, the great cycling performance is related to the reason that the uniform micro- and nanostructured architecture could maintain a consistent state of charge and discharge and accomodate the volume change associated with repeated Li+ insertion/extraction.2. In ethanol/water mixed solvent,a stepwise co-precitation was adopted to synthesize uniform oxalate precursors and LiNi1/3Co1/3Mn1/3O2 was obtained after calcination of the oxalate precursors. By fixing the amount of Mn(Ac)2 added in the first step and adjusting the ratio of [Ni2++Co2+]1/[Ni2++Co2+]2 added in first and second step,four different LiNi1/3Co1/3Mn1/3O2 precursors can be obtained. The result indicated that the aspect ratio of oxalate precursors increased with the increased ratio of [Ni2++Co2+]1/[Ni2++Co2+]2. Even more, we also studied the influence of the addition of LiAc on the aspect ratio of oxalate precursors. The result indicated that the aspect ratio of oxalate precursors increased with the increased amount of LiAc.We compared the electrochemical properties of 1D micro- and nanostructured LiNi1/3Co1/3Mn1/3O2 microbars with LiNi1/3Co1/3Mn1/3O2 nanoparticles,and found that the electrochemical properties of LiNi1/3Co1/3Mn1/3O2 microbars were better than those of LiNi1/3Co1/3Mn1/3O2 nanoparticles. LiNi1/3Co1/3Mn1/3O2 microbars can deliver a discharge capacity of 162.8 and 111.9 mAh g-1 at the rate of 0.2 C and 20 C with a coulombic efficiency of 87.1% and it can maintain a capacity retention of 87.3% after 500 cycles at 0.5 C rate.3. Co-precipitation approach was taken to prepare oxalate compounds MC2O4·xH2O (M=Ni?Cu?Ag) in ethanol/water mixed solution, which were calcined in Ar/H2 atmosphere. M/MnO (M=Ni?Cu?Ag) can be obtained and the metals were distributed homogenously around MnO. Simply by adjusting the molar ratio of manganese to other metals, the coating amount of a conducting metal outside MnO electrode materials could be precisely controlled. The obtained product Ni/MnO was applicated in lithium ion batteries and exhibited better rate and cycling properties compared with pure MnO. At the optimal ratio of Ni:MnO=1:10, the electrode material exhibited an initial coulomb efficiency of 53.5% and a discharge capacity of 635.5 mAh g-1 at 0.5 C rate. Even at high rate of 10 C, it can still maintain a discharge capacity of 195.9 mAh g-1, indicating its superior rate performance.Meanwhile, the electrode material can maintain a discharge capacity of 785.7 mAh g'1 after 45 cycles at 0.5 C rate. In summary, the electrochemical performance could be effectively promoted by the approach of metal coating modification on MnO electrode materials. |
PDF Full Text Request