Preparation And Characterization Of Lithium Manganese Oxides As Cathode Materials Doping With Anion And Cation Ions For Lithium-ion Batteries By Low Heating Solid-state Coordination Method

Due to its relatively high energy density and low toxicity, the spinel lithium manganese oxide is promising to be cathode for lithium-ion battery. At present, the material is usually synthesized by high temperature solid-state method or sol-gel method. High temperature solid-state method has the disadvantages of long calcination and poor electrochemical performance. Because of high cost, complicated processes, sol-gel method is not suitable for commercial use. Here, low heating solid-state coordination method is adopted to synthesize the materials for its advantages of low calcination temperature and simple manipulation. The capacity of lithium manganese oxide fades rapidly in the charge-discharge cycle process for the reason such as, Jahn-Teller distortion, dissolution of manganese into the electrolyte and decomposition of the electrolyte. To overcome the capacity fading of LiMn2O4, the manganese site was replaced by some of metals such as Li, Cr and Al to enhance structural stability. Anion substitution (F,Cl,Br) can reduce the Mn oxidation state and improves the capacity. In this paper, the content mainly includes three parts: the study of Cl and Al (Cr) substitution, the study of Li, F substitution, as well as the study of Br and Al (Cr) substitution.1. Li1+xMn2O4-yFy (x=0, 0.05, 0.1; y=0, 0.05, 0.1) materials were successfully prepared. All the samples were identified as a single-phase spinel with a space group Fd3m in the whole composition range Li1+xMn2O4-yFy (x=0, 0.05, 0.1; y=0, 0.05, 0.1) by XRD. Transmission electron microscopy (TEM) images of the same samples, exhibited that powders were composed of ultrafine particles with uniformly distributed size of 30-50 nm. Charge-discharge test indicated that the samples possess satisfying electrochemical properties. The Li1.05Mn2O3.95F0.05 gives an initial capacity of 128 mAh/g and remains to be 112 mAh/g at the 100th cycle between the potential range 3.0 and 4.35 V and from 129 mAh/g to 106 mAh/g between 3.0 and 4.8 V.2. LiMexMn2-xO4-yCly (Me = Al,Cr) (x=0, 0.05, 0.10, 0.15; y=0, 0.05, 0.10) materials were successfully prepared. The diffraction peaks of XRD for all samples corresponded to a single phase spinel structure and no other impure peaks were detected. From the scanning electron micrograph (SEM) photographs, it is found that all of the as-prepared particles had the similar spherical morphology with uniform size distribution and the geometric diameter for the as-prepared powders ranging from the 400 nm to 600 nm. Cl-doping can cause severe capacity lose so Al and Cr were selected as co-dopants. LiAl0.05Mn1.95O3.90Cl0.10 has the initial capacity of 117 mAh/g and 95 mAh/g after 50 cycles. LiCr0.05Mn1.95O3.90Cl0.10 deliveres an initial capacity of 120 mAh/g and remains 83 mAh/g after 50 cycles.3. LiMexMn2-xO4-yBry (Me = Al, Cr) (x=0, 0.05, 0.10, 0.15; y=0, 0.05, 0.10) are synthesized via low heating solid-state coordination method. Br-substitution can result in increasing initial discharge capacity. Br and Al (Cr) codoping can result an desiring improvement in electrochemical performance. The initial capacity of LiMn1.95Al0.05O3.95Br0.05 is 127 mAh/g and 97 mAh/g is left after 100 cycles. LiMn1.95Cr0.05O3.95Br0.05 has an initial capacity of 124 mAh/g and remains to be 105 mAh/g after 100 cycles.