Font Size: a A A

Preparation And Properties Of Nickel - Manganese - Based Lithium Ion Battery Cathode Materials

Posted on:2017-01-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:F S FengFull Text:PDF
GTID:1101330488964682Subject:Non-ferrous metallurgy
Abstract/Summary:PDF Full Text Request
Lithium-ion batteries are widely used in portable electronic products, because of its high voltage, high specific energy, long cycle life, low self-discharge, no memory effect, environmental-friendly characteristics, etc. However, in order to further broaden the application range of the lithium-ion batteries, it is necessary to improve the power density and energy density of lithium-ion batteries whose performance largely depends on cathode material. Therefore, this article reviewed the current status of cathode materials for the lithium-ion batteries, both the high voltage spinel LiNi0.5Mn1.5O4 and high capacity lithium rich layered 0.3Li2Mn03-0.7LiNi0.5Mn0.5O2 cathode materials were studied.LiNi0.5Mn1.5O4 cathode materials were prepared by a high temperature solid-state method and a low temperature solid-state method, the effect of heating rate (5℃/min、 10℃/min、20℃/min、30℃/min) on structure, crystal size, morphology and electrochemical performance of the obtained sample was studied. The results showed that the structure, crystal morphology and chemical properties of the as-prepared LiNi0.5Mn1.5O4 were effectively controlled by the heating rate. When the heating rate was 20 ℃min-1, the obtained samples either by high-temperature solid-state method or low-temperature solid-state method showed a high capacity and an excellent rate capability. Particularly, the as-prepared LiNi0.5Mn1.5O4 synthesized by a low temperature solid-state method showed the best cycling stability and maximum capacity, its discharge capacity decayed from the initial 137.0 mAh·g-1 to 125.0 mAh·g-1, capacity retention rate of 91.2% after 100 cycles. At 10 C rate, the capacity could still reach 125.0 mAh·g-1 or more.Spinel LiNi0.5Mn1.5O4 samples were prepared by a low temperature solid-state method. The effect of raw materials on structure, crystal size and morphology, and electrochemical performance of LiNi0.5Mn1.5O4 cathode material were comparatively investigated. The results showed that the LiNi0.5Mn1.5O4 prepared from chlorides shows relatively bigger crystals with a well-developed octahedral shape with{111} faces, while the LiNi0.5Mn1.5O4 prepared from acetates (without chlorides) displayed a quasi octahedral shape whose edges and corners were not fully developed. Such a difference in crystal size and morphology affected their electrochemical performance. The octahedral LiNi0.5Mn1.5O4 prepared from chlorides has higher capacity, much better rate capability and cycling performance.Li-rich layer 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 samples were prepared by a high temperature solid-state method, and the effects of temperature, low-temperature presintering precursor and cooling rate way on structure and electrochemical performance of 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 cathode material were studied. The results showed that the structural integration of Li2MnO3 and LiNi0.5Mn0.5O2 and electrochemical performance of the obtained 0.3Li2MnO3-0.7LiNi0.5Mn0.5O2 samples were highly influenced by temperature, low-temperature presintering precursor and cooling way. These are beneficial to the structural integration of Li2MnO3 and LiNi0.5Mn0.5O2 and the grain size grow up for 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 samples by elevating temperature. At 900℃, the obtained 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 samples have high composite due to the structural integration of Li2MnO3 and LiNi0.5Mn0.5O2, and showed clearly increase in electrochemical performance. In the process of charge/discharge, the stable structure of the obtained 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 slowed down the voltage decays of the electrode and decreased first irreversible capacity loss.The different decomposition degree on Li, Mn and Ni salt of the precursor can be attribute to different low presintering temperature, which led to different ordered distribution between Li2MnO3 phase in LiNi0.5Mn0.5O2 matrix, and finally impacted electrochemical performance of the sample 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2. The precursor was sintered under 400℃ presintering processing to obtain sample 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2, Li2MnO3 phase could be orderly distributed in LiNi0.5Mn0.5O2 phase matrix. However, at 500℃, the primary crystal Li2MnO3 will form in a subsequent high-temperature sintering process, which contributed to unordered distribution of Li2NiMnO3 in LiNi0.5Mn0.5O2 phase matrix, and resulted in phase separation between Li2MnO3 and LiNi0.5Mn0.5O2 with relatively low integration of the two phase structure. At 600 ℃, the obtained sample was only a single phase of layered materials. When presintered temperature at 400℃, the obtained sample exhibited typical characteristic of lithium rich cathode material, and its initial discharge capacity reached 173.3 mAh·g-1 and first irreversible capacity loss was 71.2 mAh·g-1, capacity retention rate was 90.9% after 10 times cycle.Li-rich layer 0.3Li2MnO3-0.7LiNi0.5Mn0.5O2 was prepared by a solid-state method with a two-step heating process, and the effect of cooling rate after the first-step heating (400℃) on structure and electrochemical behavior of the obtained material was studied. The result showed that the sample prepared with a slow cooling had much better electrochemical performance due to its better structural integration between Li2MnO3 and LiNi0.5Mn0.5O2 than the sample obtained with a quick cooling. The sample prepared with a slow cooling showed high initial charge and discharge capacity that could reach 251.3 mAh·g-1 and 171.8 mAh·g-1, respectively, but the sample obtained with a quick cooling only showed 38.2 mAh·g-1.
Keywords/Search Tags:Lithium-ion batteries, Cathode materials, LiNi0.5Mn1.5O4, Li-rich materials, Li2MnO3
PDF Full Text Request
Related items