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Research on Modification of Li[Li0.2Mn0.54Ni0.13Co0.13]O2Cathode Material for Lithium-ion Batteries

Author: YangFei
Tutor: DuKe
School: Central South University
Course: Metallurgical Engineering
Keywords: Manganese based solid solution surface modification irreversible capacity loss sodium additive
CLC: TM912
Type: Master's thesis
Year: 2013
Downloads: 41
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Abstract


xLi2MnO3·(1-x)LiM’O2has became an attractive cathode material for lithium ion batteries, due to the high capacity, low cost and environment friendly characteristic. However, its application is limited because of the low efficiency, poor ionic conductivity and bad electrochemical performance on high rates. In this paper, we used the method of sodium additive and pretreatment on Li[Li0.2Mno.54Ni0.13Co0.13]O2and studied the mechanism of modification.We used NiSO4-6H2O, CoSO4·7H2O, MnSO4·H2O, Na2CO3, NH4HCO3as raw materials to synthetize [Mn0.54Ni0.13Co0.13]CO3. Li[Li0.2Mn0.54Ni0.13Co0.13]02was obtained by mixing [Mn0.54Ni0.13Co0.13]CO3with lithium hydroxide and sintering. It has a high capacity at0.1C (243.6mAh·g-1) but the initial charge/discharge efficiency is very low (only63.5%) and rate performance is poor (149.5and66.3mAh·g-1at1C and5C respectively). The effects of sodium additive on the microstructure and electrochemical properties of Li[Li0.2Mn0.54Ni0.13Co0.13]02-based material were investigated. XRD patterns of NaxLi1.2-x[Mn0.54Ni0.13Co0.13]O2(0≤x≤1.2) showed that the sodium additive did not incorporate into the Li[Li0.2Mn0.2Ni0.13Co0.13]O2lattice but induced a dispersed secondary phase Nao.7MnO2.05.The two-phase composite showed an improved rate performance compared with the single phase of Li[Li0.2Mn0.54Ni0.13Co0.13]O2, especially when x=0.2, Nao.2Li1.0[Mn0.54Ni0.13Co0.13]02showed174.5mAh·-g-1at1C and135.6mAh·g-1at5C.In order to improve the initial charge/discharge efficiency of Li[Li0.2Mno.54Ni0.13Co0.13]02, we used deionized water, ammonium sulfate and phosphoric acid to treat Li[Li0.2Mn0.54Ni0.13Co0.13]O2. Test results showed that the deionized water couldn’t improve the electrochemical properties but phosphoric acid and ammonium sulfate could improve the initial efficiency to86.3%and85.0%respectively. Voltage and cycle performance declined for phosphoric acid treated sample. The cathode material, which has been treated with20%ammonium sulfate, showed much better electrochemical performance.Citric acid and ammonium citrate tribasic were used to study the modification mechanism. ICP-AES analysis showed that a part of lithium,16.37wt%and13.14wt%for citric acid and ammonium citrate tribasic treated samples respectively was dissolved out during the pretreatment stage. Also a small amount of transition metals were desorpted in this process. The charging/discharging test revealed that the materials treated by20%of citric acid and ammonium citrate tribasic performed improved initial efficiency (80.2%and80.7%). After40at0.2C, the capacity retention rate increased to97.42%and92.70%from91.43%and the capacity at1C increased to179.5mAh·g-1,181.5mAh·g-1respectively. The results showed that after the treatment of citric acid and ammonium citrate tribasic cycle stability and the rate performance of Li[Li0.2Mn0.54Ni0.13Co0.13]02were both improved. Figers:22, tables:16, references:123.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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