| Summary: | 碩士 === 輔仁大學 === 化學系 === 102 === There are three parts in this study which is based on co-precipitation with an innovative dual-continue reactor. The following are three parts in the experiment of this study：
1. This study conducts the co-precipitation method to design a dual-continue reactor and prepare a high tap-density LiNi0.8Co0.2O2 (LNC). The precursor of LNC cathode material can grow to be a large particle in the first reactor with a low pH condition (pH=10.5), and then the precursor of LNC can continually grow to be a dense particle in the second reactor with a high pH condition (pH=11.5). The physical and electrochemical performances of material from first reactor were then compared with second reactor. The particle sizes of LNC were 10-13μm. The tap-density of LNC from first reactor and second reactor were 2.18 and 2.35 g/cm3, respectively. Electrochemical test included charged-discharge capacity. The energy density of volume for second LNC (455.42 mAh/cm3) was higher than first LNC (411.07 mAh/cm3).
2. This study added a function of cathode material modification in this system. As same as the first part, the precursor of LNC cathode material can grow to be a large particle in the first reactor with low pH condition (pH=10.5), then it can continually grow to be a dense particle and modified the surface of the precursor by using Mg(OH)2 in the second reactor with high pH condition (pH=11.2). In this way, the Ni0.8Co0.2(OH)2 (NC) and Mg(OH)2-Ni0.8Co0.2(OH)2 (Mg-NC) precursor were synthesized simultaneously. Next they were sintered to LNC and homogeneously Mg doped LiNi0.8Co0.2O2 (Mg-LNC), respectively. The average of Mg doping concentration in the Mg-LNC was 2.5 mol%. After analyzing physical properties, it confirmed that Mg element has homogeneously doped in the structure of Mg-LNC. Moreover, the Mg-LNC has higher tap-density than the pristine LNC cathode material. In terms of electrochemical and thermal analysis of LNC and Mg-LNC, it showed that Mg-LNC has lower capacity, but better rate capacity, cycle life, and thermal stability because the electrochemically inactive Mg doped the cathode material. On the contrary, Mg was effective in stabilizing the structure of the cathode material.
3. This study replaced magnesium with manganese in the second reactor, and synthesized the Mn(OH)2-Ni0.8Co0.2(OH)2 (Mn-NC) precursor. Respecting the low diffusion rate of metal ions, this study expected to synthesize heterogeneously Mn modified LiNi0.8Co0.2O2 (Mn-LNC) after calcination. It had different composition of the particles from the surface to the core: high concentration at the surface but kept the core as LNC. The average of Mn concentration in the Mn-LNC is 12 mol%. Then the physical, electrochemical and thermal examinations of Mn-LNC were compared with homogeneous LiNi0.7Co0.2Mn0.1O2 (LNCM). The capacity of Mn-LNC was lower than LNCM, this attributed to the heterogeneous Mn content of Mn-LNC particles, but this method improved the electrochemical characteristics enhanced the cycle life and thermal stability.
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