Lithium-ion battery cathode material synthesis and modification of LiMn_2O_4

Title: Lithium-ion battery cathode material synthesis and modification of LiMn_2O_4
　　Author: Cao Na occasion
　　Degree-granting unit: Zhejiang University
　　Keywords: lithium-ion battery;; spinel LiMn_2O_4;; cathode material;; doping;; coated;; electrochemical properties
　　Summary:
　　Spinel LiMn_2O_4 for a low cost, easy synthesis, high voltage, high safety, environmental pollution and has high capacity and other advantages, is considered a very promising cathode material for lithium-ion battery. However, spinels LiMn_2O_4 capacity fade during the cycle more serious, especially in temperatures above 50 ℃ or high-current Strong magnets charge and discharge, the capacity of rapid decay, a serious impediment to its commercial application, especially in the electric vehicle power and other large-scale applications on battery power. In this paper, by optimizing the synthesis of metal ions by means of doping and surface modification to explore LiMn_2O_4 stable spinel structure during the cycle, thereby to increase its temperature and high temperature electrochemical performance of the way. This paper studies the results are as follows:
　　1, spinel lithium manganese oxide nano-technology. In this paper, citric acid as a chelating agent, sol-gel synthesis of high lithium manganese oxide nano-crystalline, with an average particle size of about 109 nm. The synthesis of the spinel crystal grain LiMn_2O_4 more complete, clear sharp edges and corners, the state was typical of spinel, grain array comparison rules, and the high degree of particle orientation. This high degree of crystallinity LiMn_2O_4, can slow down the process of charging and discharging materials, structural changes are conducive to the freedom of de-intercalation of lithium ions to enhance its presence in the room temperature and high temperature cycle performance. Room temperature after 80 cycles, the capacity of 108 mAh / g, single-cycle capacity loss rate of 0.135 mAh / g; and remain at a high temperature 55 ℃ good cycle performance, capacity retention after 80 cycles was maintained 99 mAh / g.
　　2, spinel lithium manganese oxide doped rare earth elements. By spray-drying method and calcined at 750 ℃, synthesis of rare earth (La, Nd)-doped lithium manganese oxide spinel. Microstructure observed synthesis of rare-earth doped lithium manganese oxide hollow ball-like structure was reunited, and the nanorod diameter 60-100 nm interspersed in http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php the hollow ball. The study found that relative to the La-doped samples, Nd-doped lithium manganese oxide lattice into the higher levels, the specimen is more slender in the nanorods and the greater number, indicating that the formation and incorporation of nano-rod lattice directly related to the amount of rare earth elements. Electrochemical tests showed that, Nd-doped materials effectively improved discharge capacity and cycle performance, the nominal composition of LiNd_ (0.01) Mn_ (1.99) O_4 sample rate at 10 C under still about 110 mAh / g of reversible capacity; 1C magnification after 300 cycles, the capacity remains at 100 mAh / g or more. Description of rare earth doped nanorods and hollow spheres containing particles stable spinel structure, improve the material properties and the high rate charge and discharge cycle stability, have a significant role.
　　3, spinel lithium manganese oxide coated fluoride modified. With the commonly used oxide-coated materials, fluoride does not react with the electrolyte, the electrolyte is more stable. In this paper, co-precipitation method in a different spinel coated fluoride (LaF_3, YF_3), studied the fluoride surface modification of materials structure and electrochemical properties. The results showed that fluoride (YF_3, LaF_3) coating can effectively reduce the manganese ions dissolved in the spinel, stable spinel structure lithium manganese oxide inhibition of the Jahn-Teller distortion effect. In addition, fluoride surface coating can also inhibit the manganese dissolved in the electrolyte ions in the spinel crystal surface re-deposition of the electrode to ensure good electrical contact and physical contact, reducing the battery in the cycle of polarization, improve the material's structure and electrochemical stability. Electrochemical performance measurements show that coated 0.5mol% LaF3 samples often warm after 80 cycles with a 113 mAh / g capacity, 50 ℃ after the next 80 cycles the capacity was still 98 mAh / g or more.
　　4, the oxide cathode materials exploratory study. This sol-gel synthesis of mismatch type and K-doped oxide Ca_3Co_4O_9 Ca_ (2.95) K_ (0.05) Co_4O_9, and its lithium deintercalation characteristics of the exploratory research. The results show that, Ca_3Co_4O_9 good performance lithium-ion deintercalation, the theoretical capacity of 643 mAh / g. K doping not only improves its initial discharge capacity (about 1120 mAh / g), and improved its recycling performance. After 50 cycles, can still maintain 223 mAh / g capacity, about 2 times the undoped sample.
　　Degree Year: 2010