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Preparation and properties of oxide cathode material of lithium thermal battery embedded design

Author: LiZhiYou
Tutor: HuangBoYun；QuXuanHui
School: Central South University
Course: Materials Science
Keywords: Thermal battery Cathode Lithium-intercalation Lithium-cobalt oxide Lithium-manganese oxide Lithium-vanadium oxide
CLC: TM911
Type: PhD thesis
Year: 2001
Downloads: 270
Quote: 3
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Abstract


The voltage of lithium-intercalation reaction, impedance and structural stability of intercalation-type cathode material were analysed and calculated. Theoritical results show that the reaction voltage depends on the content of lithium and the bond energy, and that the key ways to lower the electrode impedance are to increase the electronic conductivity of the electrode and the diffusion coefficient of lithium ion in the host and to decrease the size of powder. In addition, the thermal stability of lithium-insertion structure can be improved by using crystallographic co-lattice theory and doping treatment. Based on these, due structure and physical and chemical properties of an excellent cathode material are presented. And oxides of high-valence cobalt, manganese and vanadium as lithium-insertion host were chosen as experimental model. The sol-gel method and solid-state thermal reaction technique were used to prepare the composite oxides with variable lithium content. The doping treatments of some compounds were conducted. DTA and TG were used to analyse synthesis mechanism, XRD to analyse phase composition, SEM to observe morphology, Li-B/LiCl-KCl/oxide simulated thermal cells to analyse the lithium-intercalation mechanism and properties of cathode material.Experimental results show that, the single-phase material of LixCoO2(x^ 1) can’t be synthesized by the sol-gel and the solid-state thermal reaction. Instead, the resultants consist of LiCoOi and Co3O4 phases. // m-level powder can be produced using sol-gel method, and powder will be finer if the alkaline solvent is used. When the resultant with Li/Co atomic ratio of 0.8 is electrochemically intercalated with lithium at 500癈, its peak-voltage is 2.4V (vs Li-B alloy) and the available capacity is above 200A ?s ?g"1, all of them are less than that of FeS2.With the increase of lithium, MnO2 may change from/?-MnO2 phase to spinel LiMn2O4 via Lithiated MnO2 (Li2MnOs) after being lithiated at 410癈. The lithiated resultants with less lithium content turn to MnaOs and high-crystallinity LiMn2C>4 after exposed at a high temperature for a long time. All the resultants can turn to LiMn2C>4 when they are electrochemically lithiated at 500 癈. Theirpeak-voltage is about 2.3V, which is not sensitive to crystallographic structure and initial valence of Mn. If lithium ions are required to insert quickly, the output voltage depends on Li+ diffusion channel. Where, a MnO2/LiMn2O4 two-phase material with Li/Mn ratio of 1/4, prepared by oxiding the Mn203/LiMn2O4, shows the most steady output voltage and the highest available capacity 220A ?s ?g"1, which are still lower than those of FeS2. -phase vanadium oxides containing alkali ions (Li\ Na K+) have been synthesized by sol-gel method. If they are calcined in air, Lio.3V2Os can be oxided to LiV3Og and V2Os, but Nao.33V2Os and Ko.2sV2O5 remain stable. Inside the -phase crystals, there are three kinds of oxygen polyhedral which can accept lithium intercalation. When lithium ions insert into these sites quickly, the voltage relies on the energy decrease and the occupation possibility of every lithium-intercalation site. The peak voltage is 2.7V, and the available capacity is about 610A ?s ?g"1 for Lio.3V2Os. These properties are above 10% to FeS2.V2MoOs is prepared at high temperature if MoO3 is doped into V2Os. A lithium-rich Mo-containing solid-solution phase Lii+xVsOg is obtained when V2MoOg is lithiated. If Lii+^VsOg is doped with MoOs, it will change to lithium-rich Mo-containing Lii+^VsOg solid-solution and lithium-poor Lio.o4Vi.96Moo.o4Os solid-solution; with increasing P2C>5 content, V3O8 layered two-dimension network may be destroyed, low-lithium ft -Lio.3V2Os and a -V2Os are produced, in which three-dimension network characteristics become evident more and more.There are four kinds of oxygen octahedral inside y-Lii+jVaOg crystal, any kind of them can’t be occupied completely in the process of chemical intercalation. The peak voltage for electrochemical intercalation reaction comes to 2.8V (0.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Chemical power sources,batteries, fuel cells
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