| Lithium ion battery (LIB) is regarded as an attractive power source, which can be usedfor portable electronic devices, power tools, electric vehicles, and industrial energy storage.The critical requirements of LIB’s performance promote the development of anode materialswith high capacity. The anode materials are limited in practice, because of severe volumechanges during insertion and extraction of Lithium ion, which leads to capacity fading andthe breakage of anode materials. To this end, a novel copper current collector with surfacestructures of micro-blind holes and micro-balls were proposed in this thesis. The design,fabrication, mechanism and effects on LIB of the surface structure were symmetricallystudied, The main contents in this thesis were as follows:1. Pulverization model of anode materials with high capacityThe stress in electrode materials was analyzed based on difusion law of lithium ions inanode materials which were supposed as linear elastic material. The expansion caused bydifusion of lithium ions was equivalent as thermal expansion. The stress functionwasobtained by mechanical analysis of anode materials. The fracture failure was discussed basedon the K criterion of linear elastic material brittle fracture, and the key function of materialfailure was obtained.2. The design and mathematical model of surface structuresThe stress growed when difusion. A novel copper current collector with surfacestructures of micro-blind holes and micro-balls were proposed to avoid electrode failure. Thestructures could providedbinding force. Therefore, structure models were built. The modelsindicated that: the bigger the ratio of depth to width, the bigger the binding force, and thebetter the effect of restricted expansion at the same holes. Cone holes, cylinder holes andspherical holeshad the better function in turn. The model of micro-balls was same as themodel of spherical holes, they had the same function theoretically.3. Fabrication of micro-blind holes by laser processing and micro-balls by sinteringThe copper current collector with micro-blind holes was fabricated by laser system. Inthis thesis, the processing programme of concentric circles scanning-fixed beam wasproposed to increase processing quality. The experimental results show that: the values of laser out power, laser scanning speed,pulse frequency of laser and laser focuses should be20W,500mm/s,20kHz and10μm for better structures.The copper current collector with micro-balls was fabricated by solid phase sinterprocessing, sintering process was formulated. The experimental results show that: thesintering temperature is proportional to thesintering neckat the under of the condition ofconstant of sintering time and the copper powder diameter. The higher sintering temperature,the bigger thesintering neck andsintering strength. At the under of the condition of constant ofsintering time and the copper powder diameter, the longer sintering time, the biggerthesintering neck andsintering strength. Sintering temperature1000℃and sintering time3hwas the best sintering process.4. Performance test of copper current collector, Performance test of LIB withcopper current collectorElectrochemical performance, surface wettability and tensile performance of coppercurrent collector were investigated by cyclic voltammetry test, contact angle test and tensiletest. The results indicated: the copper current collector with surface structures were stable inthe electrolyte, and the anode potential should be under3.5V vs. Li+/Li. The surfacestructures effected on surface wettability slightly. The tensile strength of copper currentcollector with micro-blind holes was to meet the requirements of industry, but the tensilestrength of copper current collector with micro-balls was lower.LIBs fabricated by copper current collector with micro-balls and copper current collectorwith micro-blind holes were test by Charge-Discharge cycling. The results show that: thesurface structures could provide reasonable binding force to increase cycle performance ofLIB. The increasing depth of micro-blind hole help to increase cycle performance of LIB atthe same diameter. The smaller the diameter, the better performance the LIB at the samedepth. The bigger diameter of copper powders was advantageous to performance of LIB. |
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