Study On Key Materials In Silicon Based Lithium Ion Battery Anode

Structures of lithium ion battery are mainly composed of electrode, electrolyte and separator. As the core subassembly of lithium ion battery, electrodes directly result to the performance of lithium ion battery. Electrode mainly composed of active materials, conductive materials and binder. As the core material of lithium ion battery, active materials were attracted much attention in previous studies. But conductive additive and binder have attracted less attention because the very small amount in lithium ion battery. Although the dosages of conductive additive and binder are small in the lithium ion battery, the important role of there cannot be neglected. Conductive additive and binder is especially important in high capacity anode.In High capacity anode, the large volume changes of active materials in the charging and discharging cycles led to the break of conductive path, the separate between current collectors and active composite layer. This caused the serious capacity fade in lithium ion battery. Improve the conductive additive and binder can relieve or solve these problems and without impact the cost of lithium ion battery. Thus, our studies were focus on improve the conductive additive and binder to improve the electricity performance of Lithium ion battery.First, our studies determined a basic battery assembly process apply to the high capacity active materials. Previous study shows the different structure change in the charge and discharge process between conventional carbon-based materials and high capacity new materials, conventional preparation processes of lithium ion battery electrode cannot exploiting the performance of high capacity anode. Thus, we determined the battery assembly process which apply to the high capacity active materials though many times test. And, doing the following study based on this battery assembly process.In conductive materials field, we developed a composite conductive include three dimensional nanomaterials and two dimensional nanomaterials to accommodate the high capacity anode. We choices the carboxyl group functionalized Multi-walled nanotubes(a- MWCNTS) as the two dimensional nanomaterials. Preparation the a- MWCNTS, the outer tube wall was embedded defect and incorporates the functionalized group like hydroxyl and carboxyl, a- MWCNTS can conduction electrons in the internal tube wall. The introduction of carboxyl group caused two role, one role is improve the dispersion performance of MWCNT in the water and ensured the open of long-rang electrical conductivity networks, the other is improve the binding force between binder and conductive materials. We choices SP as the three dimensional nanomaterials because SP has large surface area. Thus, add SP in electrode can improve the contact area between active materials and conductive materials.Comparison to the conventional conductive materials the mixed-conductive materials had improve the discharge specific capacity for the first time from 1938 m Ah g-1 to 2927 m Ah g-1, improve the Coulomb efficiency for the first time from 79.2% to 81.9%. After 100 hundred cycles of charge and discharge, the capacity retention improves from 59% to 74.3%.In binder field, We have demonstrated that anion polyacrylamide(APAM) could serve as an effective binder for Si anode of Lithium ion batteries for the first time. APAM has the following advantages. First is good water solubility, can reduce pollution. Second is have carboxyl group, can improve the binding force between APAM and metal material. Third is large molecular weight, can buffer the volume expansion of active material. Fourth is large number of amide group in APAM, caused APAM have large number of intermolecular and intramolecular hydrogen bonding, can improve the self- health capability of APAM.Our studies compare the effect of different molecular weight of APAM and different material ratio in Nano-size silicon based electrode. Experimental results show that when we use the APAM with 16 million molecular(APAM16) weight, the discharge specific capacity for the first time had improved from 2005.8 m Ah g-1 to 3485 m Ah g-1; the Coulomb efficiency for the first time had improve from 78.6% to 85.9%.