| Rapid industrialization not only brings socio-economic development, but alsoleads to serious pollution detrimental to living environment. Consequently, cleanenergy devices such as lithium ion batteries (LIBs) have attracted enormous interestsdue to their environmental friendliness and sustainability. As a matter of fact, LIBsare deemed as one of the most attractive energy storage devices, because they possessa number of advantages like high energy density. Nowadays, most portable devicesare powered by LIBs, including mobile phones, digital cameras and laptops. Inaddition, they might also find potential applications in electric vehicles (EV), hybridelectric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV). However, one ofthe most noticeable defects for lithium ion batteries is their comparatively low powerdensity, which has adequately impeded their applications and prevented them frommeeting industrial requirements. In general, how to improve the power density inorder to exhibit better performance is the key to solve this problem. One of the mosteffective ways to improve the power performance of LIBs is to introduce nano-sizedmaterials. Theoretically, this strategy could largely shorten the diffusion length oflithium ion which certainly would simplify lithiation and de-lithiation processesinvolved. In this paper, samples with special morphologies were synthesized in thecondition of atmospheric pressure and high pressure and their electrochemical properties were also investigated.(1) LiMn2O4was synthesized by high temperature solid phase method indifferent temperatures utilized manganese dioxide and lithium hydroxide as rawmaterials and sodium chloride as flux. The test methods such as XRD, SEM, TEMwere used to confirm the structure and morphology of the sample. Results frommultiple aspects proved that we obtained LiMn2O4nanowires with diameter inapproximately40nm and the length of several microns in condition of700°C withflux. Electrochemical analysis showed that the sample synthesized at700°C in thepresence of flux afforded the highest initial discharge capacity of125.5mAh/g at0.2C rate and its capacity retention was85.6%after100cycles. There is no doubtthat the excellent properties and structure had a close relation of LiMn2O4nanowires.At the same time, we made a detailed mechanism explanation of the flux in reactionprocess.(2) For the first time, we used high temperature and high pressure hydrothermalmethod to synthesis LiMnO2. At the same time, the product which was obtained byhigh temperature in atmospheric pressure was selected as control group. Two methodsboth used two-step synthesis methods for synthesizing LiMnO2material. It should bepointed out that the lithium hydroxide was the excess component in this reaction, theexcess part would be used as flux in the whole system. The experimental resultsshowed that the raw material in molar ratio of Li:Mn=5:1exhibited the highest purityof the sample.(3) Porous hollow micro-ball samples with the diameter of about1μm wereobtained by high temperature solid phase method and high temperature and“”shaped materials were obtained via high temperature high pressure hydrothermal way.During the charging and discharging test, the spherical sample initial dischargecapacity reached128mAh/g. With the increase of cycling times, discharge capacityincreased gradually. It could rise at155mAh/g in the20th cycle. The initial dischargecapacity of high temperature high pressure hydrothermal method product afforded thevalue of104.5mAh/g and the maximum discharge capacity was112.7mAh/g. Wecan draw a conclusion by analyzing the cycle stability test that the electrochemical activity of the sample of high temperature tube furnace is higher than the other’s. Thisindicated that although the presence of pressure can inhibit the structural change in theelectrochemical process, chemical activity which was enhanced by the structure is stilldominant in the electrochemical process. |
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