Browsing by Author "Vara, Vilja"

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  • Atomikerroskasvatus nanorakenteiden valmistuksessa
    (2008) Vara, Vilja
     Kemian ja materiaalitieteiden tiedekunta | Bachelor's thesis
  • Fabrication of Li4Ti5O12 negative electrodes using water-based binders
    (2010) Vara, Vilja
     School of Chemical Engineering | Master's thesis
    Lithium-ion battery was developed to replace hazardous rechargeable metallic lithium battery. Most widely used materials for the negative and the positive electrode materials have been graphite and LiCoO2, respectively. These materials are constantly developed to find more efficient materials especially for high power density applications such as electric vehicles. Li4Ti5O12 is a very promising material for the negative electrode and possesses many advantages over conventionally used graphite: it is faster to charge, possesses longer life time, is environmentally friendlier and undergoes no volume change during charging and discharging which would otherwise lead to mechanical degradation of the battery. In the literature part discussed are the binding agents used in the Lithium-ion batteries. Binding agent binds electrode particles together and to the current collectors and brings mechanical stability to the electrode. Conventionally used fluorinated binders, PVDF (polyvinylidene fluoride) and Teflon, require hazardous and expensive organic solvents. On this account, water-based binders have drawn interest in the manufacturing of lithium-ion batteries. They are environmentally benign, non-toxic, and of low cost. Also, less amount of binder is required for sufficient battery performance than in the case of conventional binders, which leads to higher active material contents and the capacity of the battery increases. In the experimental part, the behaviour of Li4Ti5O12 negative electrodes prepared with water-based binders was studied. Different binder systems, including acryl, styrene butadiene latex and carboxyl methyl cellulose, and their amounts were investigated to find properly functioning batteries. The adhesion to aluminium current collector and the stability towards the electrolyte were studied. Electrodes with PVDF binder were fabricated for reference. The coin cells were cycled at different current rates to obtain their specific capacities. The best capacity results were obtained with acryl binders, whose amount in the electrode was 3 wt. %.