Synthesis And Modification Of LiNi(1/3) Co_1/3 Mn_1/3 O₂ Cathode Material For Lithium Ion Batteries

LiNi_1/3Co_1/3Mn_1/3O₂ with layered structure is considered as the excellent cathode material including advantages of the three materials of LiNiOO₂,LiCoOO₂ and LiMn2O4. It has been attracted many attentions as the possible replacement to the LiCoOO₂ for its advantages such as the higher specific capacity, the milder thermal stability, the lower cost and less toxicity than that of the domain cathode material LiCoOO₂. In this paper, Co-precipitation and Solid-state method are applied to synthesize LiNi_1/3Co_1/3Mn_1/3O₂, respectively. The products synthesized by Co-precipitation method are modified by coating with ZnO layer and dope of Li+, and also, self-synthesizedα-MnOO₂ nanorod is used to improve the performances of the products synthesized by solid-state method. Good performances have been obtained for LiNi_1/3Co_1/3Mn_1/3O₂ improved by all these measures mentioned above. Powder X-ray diffraction (XRD), Transmission electron microscope (TEM), field emission Scan electron microscope (SEM), X-ray photo-electron spectrometry (XPS), inductively coupled plasma (ICP) with atomic emission spectroscopy (ICP-AES), electrochemical impedance spectroscopy (EIS) and the battery testing system are applied to characterize the as-prepared LiNi_1/3Co_1/3Mn_1/3O₂ and its modified products. The influences of ZnO coating layer, dope of Li+ and the different raw material on the composition, morphology, structure and electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ are investigated systemically. And more, relationships between these infects and the electrochemical properties are obtained by analysis of the characterizing results.In the chapter 1, the progress and importance of investigating the LiNi_1/3Co_1/3Mn_1/3O₂ has been introduced. The structure, synthesizing method, modifying method and the applying area are summarized. And more, the development of LiNi_1/3Co_1/3Mn_1/3O₂ in the future is also related.In the chapter 2, the working process and applied areas of the related apparatuses are introduced, and also, the processes of preparing electrode and asselmbling the cells are mentioned.In the chapter 3, influences of the ZnO coating layer on the structure, composition, morphology and electrochemical properties have been investigated. XRD results show that both of the pristine material and modified material have the hexagonalα-NaFeOO₂ structure without impurity, and the crystal parameters (a, c) are changed by the modifying measure. The pictures of SEM and TEM prove that the ZnO coating layer with sale of 20 nm on the surface of pristine LiNi_1/3Co_1/3Mn_1/3O₂ changes its morphology. The charge-discharge tests are performed at 70 mA g^-1 in the potential range of 2.5-4.3 V. It revels that the ZnO coating layer can improve the cycling performance of the LiNi_1/3Co_1/3Mn_1/3O₂ but decreasing its initial discharge specific capacity. It attributes to the inactive ZnO coating layer which increases the surface layer impedance.In the chapter 4, the structure, composition, morphology and high rate charge-discharge properties of prepared Li_8/7(Ni_1/3Co_1/3Mn_1/3)_6/7OO₂ have been investigated. The XPS results prove that the Ni²⁺ ions are changed to Ni³⁺ by doping excess Li+. The XRD result shows that Li_8/7(Ni_1/3Co_1/3Mn_1/3)_6/7OO₂ have highly ordered layer structure. The prepared Li_8/7(Ni_1/3Co_1/3Mn_1/3)_6/7OO₂ consists of submicron and nano-scaled particles with an average particle size of 0.15μm. The charge-discharge tests are performed at high rate of 1000 mA g^-1 and 2000 mA g^-1 (2.5-4.5 V), and excellent electrochemical properties are obtained. The average full-charge time of this material is less than 6 min at 5 C and 3 min at 10 C, indicating the promising application in lithium power batteries of this material.In the chapter 5, purchased MnOO₂ and the self-prepared nanorod MnOO₂ are used to synthesize LiNi_1/3Co_1/3Mn_1/3O₂ via Solid-state method, and the influence of temperature using nanorod MnOO₂ as the raw material is investigated. The XRD results show that impurity of NiO appears in the product synthesized by purchased MnOO₂. However, LiNi_1/3Co_1/3Mn_1/3O₂ with pure phase can be obtained by calcined at 850-900 0C using self-prepared nanorod MnOO₂, NiO, Co2O3, Li2CO3 as the raw material. The charge-discharge tests are performed at 1000 mA g^-1 in the potential range of 2.5-4.5 V. Excellent electrochemical properties are obtained, and the average full-charge time of this material is less than 6 min, indicating the pure phase LiNi_1/3Co_1/3Mn_1/3O₂ synthesized by this technology is suitable for applying in lithium power batteries.