KN 18 Gaberscek

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Routes towards high-capacity and high-rate Li ion insertion batteries Miran Gaberšček1,2 1National Institute of Chemistry, Ljubljana, Slovenia 2Faculty of Chemistry and Chem. Technol., University of Ljubljana, Slovenia

Development of Li-ion batteries : 

Development of Li-ion batteries Small electronic devices and small batteries Higher energy density Higher power density Higher safety Environmentally friendly

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Anode: Cathode: C6 + xLi+ + xe-  LixC6 LiCoO6  LixCoO6 + (1-x) Li+ + (1-x)e- Principle of Li ion battery operation

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Overview of Li ion battery materials

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LixM2-yMyO4 Good candidates: Ge, Sb, As, P, Si, Ti Our choice No 1: M = Si M = transition element Li2MSiO4 Promising candidates for high capacity Our choice No 2: M = Ti Li2MTiO4 M=Fe, Mn, Ni, V

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Orthorhombic unit cell, space group Pmn21 STRUCTURE 1

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Li2FeTiO4 - LFT Li2MnTiO4 - LMT Li2NiTiO4 - LNT STRUCTURE 2 (cubic rock-salt structure with cationic disorder, space group Fm3m) - oxygen Multicoloured balls - Li, Fe, Ti

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Do we observe exchange of more than 1 Li in Li2MSiO4 or in Li2MTiO4 ?

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Increasing capacity Increasing voltage Note: Capacity depends on the voltage window

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Cycling stability is moderate

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In-situ XRD nanosized LFT Voltage-limited experiment ox. red. 1.4 % contraction of unit-cell volume single phase insertion mechanism

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In-situ Mössbauer spectroscopy for nanosized LFT no change in Fe ox. state in last two spectra reversible SEI formation additional capacity above 3.9 V was observed end of reduction complete oxidation Fe2+ to Fe3+ + Time-limited experiment

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In-situ XAS for nanosized LFT (EXAFS spectra) 3+3 octahedral deformation (as-prepared sample) 4+2 octahedral deformation (completely oxidized sample) Jahn-Teller octahedral deformation on the induvidual crystallographic site

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Partial conclusion Silicates and titanates can give high reversible capacities (< 300 mAh/g) No direct proof that more than 1 e- is exchanged (example: in Li2MnTiO4 only 1 Li is exchanged = 150 mAh/g) 3. At high and low potential additional reversible capacity is observed 4. The origin of additional capacity is still unclear

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Polarization (due to internal “resistance”) 1C =170 mA/g Electric power: P = UI Electric power density: p = UI m U=f(I) , URI Special case: PROBLEM OF BATTERY POWER

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Major sources of internal resistance

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1-30 m How to decrease resistance inside solid particles?

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Reversible capacity LiFePO4 (ca. 100 nm) Impact of particle size (example: LiFePO4)

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Measured Electrode Resistance, Rm (U/I) as a function of particle diameter LiFePO4 with ad-mixed carbon black carbon-coated LiFePO4 with ad-mixed carbon black THEORY:

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Can we further decrease particle size?

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Problem Heating leads to pronounced particle growth and agglomeration TiO2 nanotubes TiO2 anatase nanoparticles heating 8-10 nm 15-20 nm 10 nm

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Problem solution TiO2 nanotubes TiO2 anatase nanoparticles heating 8-10 nm 4-7 nm TEOS (silica precursor)

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Impact of surface treatment on morphology development

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Impact of morphology on power capability and capacity J. Jamnik, R. Dominko, B. Erjavec, M. Remskar, A. Pintar, M. Gaberscek, Adv. Mater. 21, 2715 (2009).

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Impact on cycling and on current density Increasing current density J. Jamnik, R. Dominko, B. Erjavec, M. Remskar, A. Pintar, M. Gaberscek, Adv. Mater. 21, 2715 (2009).

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Why do we always see hysteresis between charge and discharge? W.Dreyer, J. Jamnik, ..and M. Gaberscek, Nature Materials 9, 448 (2010).

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Two main assumptions: (i) The chemical potential of the individual particle is a non-monotone function of the Li mole fraction. (ii) Network consists of many particles. Model assumptions W.Dreyer, J. Jamnik, ..and M. Gaberscek, Nature Materials 9, 448 (2010).