Bachtin, K.

Bekaert, E.

Chakravadhanula, V.S.K.

Chen, R.

Ehrenberg, H.

Indris, S.

Nikolowski, K.

Roth, C.

Wohlfahrt-Mehrens, M.

English

Chakravadhanula, V. S. K.

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association Figure 4: XRD patterns of the pure LiFeTiO4 powder  (blue curve) and of the electrospun electrode (red curve). References 1. Chen, R., Heinzmann, R., Witte, R., Lebedkin, S., Hahn, H., Indris, S., Bunsentagung 2013 - 112th General Assembly of the German Bunsen Society for Physical Chemistry, Karlsruhe, May 9-11, 2013  2. Saiful Islam, M., Dominko, R., Masquelier,C., Sirisopanaporn,C., Armstrongd, A.R., Bruced, P.,  J. Mater. Chem., 21 (2011) 9811-9818 3. Küzma, M., Dominko, R., Meden, A., Makovec, D., Bele, M., Jamnik, J., & Gaberšček, M. Journal of Power Sources 189 (2009) 81–88   Discussion and Conclusion  Above results appear to be quite promising. It seems that the structuring of the cathode improves the cyclling efficiency (ratio between discharge and charge capacity) and the cyclability. The better cycling stability may be the result of reduction of the cycling related strain by the fiber matrix. The improved efficiency may be due to the above mentioned active particle separation by the fibrous structure. However to study the correlation between the electrode structure and the battery performance in detail further investigations are planned.  1 µm Electrospun LiFeTiO4 3D structured cathode material for lithium ion batteries  Introduction  LiFeTiO4 as well as Li2FexMnySiO4  are promising cathode materials for lithium-ion-batteries (high voltage vs. Li and high theoretical capacity) [1,2]. However, they exhibit various handling difficulties when the electrodes are prepared  by coating Al foils with a suspension of a powder mixture. Moreover it is assumed that the low electronic as well as low ionic conductivity of these materials keeps them from achieving their full theoretical capacity. One suggested strategy to allow the full ion insertion is the separation of active particles from each other [3]. Thus, the use of 3D fiber structured electrodes (made e.g. by electrospinning method) may improve their electrochmical performance. Electrospinning offers the following advantages: comparatively facile and fast electrode production, preparation of electrodes where the active particles are embedded into an electron conductive fiber matrix with no need for binder and current collectors. In the present investigation we make an effort to demonstrate the advantages of 3D-fiber structured over traditionally prepared cathodes.    Krystyna Bachtin a,b, Ruiyong Chen c, Sylvio Indris c, Kristian Nikolowski  a,b Venkata Sai Kiran Chakravadhanula a, Emilie Bekaerta, Margret Wohlfahrt-Mehrensa,Christina Roth d, Helmut Ehrenberg b,a  aHelmholtz-Institute Ulm for Electrochemical Energy Storage (HIU), Albert-Einstein-Allee 11, 89081 Ulm, Germany bInstitute for Applied Materials – Energy Storage Systems (IAM-ESS),Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany c Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany d Freie Universität Berlin (FUB), Physical Chemistry, Takustraße 3, 14195 Berlin, Germany Results titanate T carbonization Figure 1: Electrospinning apparatus, its working principle and an example of the electrode preparation process. Electrospinning solution polymer + liquid precursor syringe 750°C, 1h argon Fiber mat Electrode Battery test 1 µm Electrospinning solution polymer + nanopowder ø = 12 mm m = 5 mg Results silicate Experimental The traditonal powder electrode was prepared by grinding and mixing the cathode material with carbon black, graphite and PVdF binder (Polyvinylidene fluoride). An Al current collector foil was coated with a slurry of that powder mixture dissolved in NMP (N-Methyl-2-pyrrolidone). Afterwards, the electrodes were cut out from that foil and pressed at 7t. The fiber mat electrodes were prepared by electrospinning a viscous dispersion consisting of either a powder or a precursor in a 10% polymer solution of PAN (Polyacrylonitrile) in DMF (Dimethylformamide). The obtained fiber mat was then thermally treated in argon gas atmosphere in order to carbonize the polymer.  Electrospun material after carbonization  pure LiFeTiO4 powder (Fd-3m)   2θ [°] (Co Kα) Charge capacity electrospun electrode Figure 2: SEM image (left) and STEM image (right) of the electrospun electrode, the active  material is supported by fibers. The LiFeTiO4 particles are well dispersed in the  fibers, however, there are also larger agglomerates included in the fibers.   Magnification: 10.000x for the left and 60.000x for the right image. Figure 3: SEM images of the „classic“ powder electrode. The small particles are the cathode      powder/carbon black mixture, the large grains are graphite particles. The powder      layer  was not very homogeneous and it showed only weak adhesion to the Al foil.     Magnification: 10.000x for the left and 50.000x for the right image 200 nm Discharge capacity electrospun electrode Charge capacity powder electrode Discharge capacity powder electrode  cell capacity [mAh] Figure 5: Cycling efficiency of the electrospun and of the   powder electrode measured at different currents.  normed cell capacity [%] Cycle number Cycle number % % % % i1= 0,05 mA i2= 2i1 i3= 2i2 i4= 2i3 i5= 2i4 i1 Charge capacity electrospun electrode Discharge capacity electrospun electrode Charge capacity powder electrode Discharge capacity powder electrode Figure 6: SEM images of the electrospun and of the powder electrode.     Magnification: 50.000x for the left and for the right image. Figure 7: Cycling stability of the electrospun and of the powder electrode  measured at i = 0,3 [mA]. The electrodes have been cycled  between 4,8 V and 1,5 V vs. Li. The capacity of the powder  electrode decrease continuously while the electrospun one seems to  be stable over the cycling number. 200 nm 200 nm The TEM work was carried out with the support of the Karlsruhe Nano Micro Facility, a Helmholtz Research Infrastructure at KIT Campus North. 

Electrospun LiFeTiO₄ 3D structured cathode material for lithium ion batteries

https://publikationen.bibliothek.kit.edu/220091858/3816312

Electrospun LiFeTiO₄ 3D structured cathode material for lithium ion batteries

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