| Spinel-type LiMn2O4material has been widely applied duo to the advantages of high-voltage, environment-friendly, abundant resources.The main problem of spinel-typeLiMn2O4as cathode in rechargeable lithium-ion batteries is the unsatisfied cyclestability.We hope to improve its cycle stability by element substitution. Thethree-dimensional nano TiO2micro-electrode has attracted more attention due to its simplepreparation, structural stability and more safety. Nano TiO2as the miniature power sourcesystem meets the needs of micro-electro-mechanical systems (MEMS).Besides, we alsoattempted to study the following two direction: the plasma treatment of natural graphite(NG) electrode and LiNi0.5Co0.2Mn0.3O2samples’ after treatment.The conclusions havebeen summarized as following:1、The modification of LiMn2O4material（1）The Li1-xNaxMn2O4（x=0-0.10）samples were synthesized via high-temperaturesolid state reaction and the electrochemical properties of Li1-xNaxMn2O4（x=0-0.10）werestudied. The LiMn2O4has the worst cycle stability. The cyclic stability is obviouslyimproved after partial substitution of Li by Na.As the Na content increases from x=0.00upto x=0.06, the capacity-fading becomes slower during cycling. Li0.94Na0.06Mn2O4has thebest capacity retention during cycling.（2）Synthesis temperature and Na content were optimized based on the abovementioned work. We got Li1-xNaxMn2O4（x=0，0.03，0.06，0.10）samples by preheating(470℃,10h)and calcined(750℃,20h).The partical size gets smaller after partialsubstitution of Li by Na. The cyclic stability is obviously improved. Besides, the samplesshow an improved cyclic performance at high temperature and rate capability. All thingsconsinderd, Li0.94Na0.06Mn2O4has the best performance.（3）The Li1-xKxMn2O4（x=0，0.06，0.10）samples were synthesized viahigh-temperature solid state reaction.The initial discharge capacity and cycle performanceare improved after partial substitution of Li by K. Besides, the samples show an improved cyclic performance at high temperature and rate capability compared with the as-preparedsample.（4）Based on the previous work,we have done an in-depth modification.We tried tomodify the Li0.94Na0.06Mn2O4sample by adding La/Ce oxides. Rate capability curvesresults show that the electrochemical properties of materials after adding La oxides havenot been improved；but we can find samples’specific capacity have a increase at10C afteradding Ce oxides.Besides, Li0.94Na0.06Mn2-xAlxO4(x=0,0.05,0.10) were prepared and theirelectrochemical properties were studied roughly. Results show that the cyclic stability isobviously improved after the substitution of Mn byAl.2、The assembled natural graphite(NG) electrode was directly treated with plasmatechnique in oxygen，MMA and AA atmosphere. The electrochemical properties of NGelectrode were studied.The effective capacity of the NG electrode has been successfullyimproved.3、The electrochemical properties of LiNi0.5Co0.2Mn0.3O2samples which weresynthesized at different temperatures (900℃、930℃、950℃、980℃、1000℃)were studied.From the charge-discharge tests and cycle performance curves we can find, samples weresynthesized at900℃and930℃have a higher initial discharge capacity but cycleperformance are not better; samples were synthesized at980℃and1000℃have a lowerinitial discharge capacity but cycle performance are better.The sample (synthesized at900℃) was calcined at900℃again, charge-discharge tests results in different cut-offvoltages show that the sample’s cyclic stability is obviously improved.4、We synthesized the TiO2nanotube array electrode by an electrochemical method.Two phases, anatase TiO2and Ti simple substance are clearly visible. After6000charging-discharging cycles, the phase structure remains unchanged and the tube walllooks like to be fatter. The capacity degradation is very small.The phase and microstructureis very stable after6000cycles. |
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