Freestanding LiFe 0.2 Mn 0.8 PO 4 /rGO nanocomposites as high energy density fast charging cathodes for lithium-ion batteries F. Zoller a, b , D. B € ohm a, c , J. Luxa d , M. D € oblinger c , Z. Sofer d , D. Semenenko e , T. Bein c , D. Fattakhova-Rohlfing a, b, e, * a Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-1): Materials Synthesis and Processing, Wilhelm-Johnen-Straße, 52425 Jülich, Germany b Faculty of Engineering and Center for Nanointegration Duisburg-Essen (CENIDE), Universit€ at Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany c Department of Chemistry and Center for NanoScience (CeNS), Ludwig-Maximilians-Universit€ at München (LMU Munich), Butenandtstrasse 5-13 (E), 81377 Munich, Germany d Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technick a 5, 166 28 Prague 6, Czech Republic e Laboratory of Physical and Chemical Processes in Post Li-ion Batteries, Moscow Institute of Physics and Technology, Institutsky Lane 9, Moscow District, 141700 Dolgoprudny, Russia article info Article history: Received 12 March 2020 Received in revised form 8 April 2020 Accepted 9 April 2020 Available online xxx Keywords: Cathode materials Lithium manganese phosphate Freestanding electrodes Nanoparticles abstract Freestanding electrodes for lithium ion batteries are considered as a promising option to increase the total gravimetric energy density of the cells due to a decreased weight of electrochemically inactive materials. We report a simple procedure for the fabrication of freestanding LiFe 0.2 Mn 0.8 PO 4 (LFMP)/rGO electrodes with a very high loading of active material of 83 wt%, high total loading of up to 8 mg cm 2 , high energy density, excellent cycling stability and at the same time very fast charging rate, with a total performance significantly exceeding the values reported in the literature. The keys to the improved electrode performance are optimization of LFMP nanoparticles via nanoscaling and doping; the use of graphene oxide (GO) with its high concentration of surface functional groups favoring the adhesion of high amounts of LFMP nanoparticles, and freeze-casting of the GO-based nanocomposites to prevent the morphology collapse and provide a unique fluffy open microstructure of the freestanding electrodes. The rate and the cycling performance of the obtained freestanding electrodes are superior compared to their Al-foil coated equivalents, especially when calculated for the entire weight of the electrode, due to the extremely reduced content of electrochemically inactive material (17 wt% of electrochemically inactive material in case of the freestanding compared to 90 wt% for the Al-foil based electrode), resulting in 120 mAh g 1 electrode in contrast to 10 mAh g 1 electrode at 0.2 C. The electrochemical performance of the freestanding LFMP/rGO electrodes is also considerably better than the values reported in literature for freestanding LFMP and LMP composites, and can even keep up with those of LFP-based analogues. The freestanding LFMP/rGO reported in this work is additionally attractive due to its high gravimetric energy density (604 Wh kg 1 LFMP at 0.2C). The obtained results demonstrate the advantage of freestanding LiFe 0.2 Mn 0.8 PO 4 /rGO electrodes and their great potential for applications in lithium ion batteries. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Olivine-structured lithium transition-metal phosphates LiMPO 4 (M ¼ Fe, Mn, Co, Ni) attract significant interest as cathode materials in Li-ion batteries (LIBs) due to their high theoretical specific ca- pacities of around 170 mAh g 1 , good chemical and thermal sta- bility, safety and low cost. Particularly, LiFePO 4 (LFP) has been already successfully commercialized [1e3]. Nevertheless, LFP has a rather low operating potential of 3.45 V vs. Li/Li þ and a corre- sponding low energy density (568 Wh kg 1 ), which hampers its application in high power and/or high energy devices [1]. Mn, Co or Ni based analogues gain increasing attention as promising alter- natives having a similar theoretical specific capacity but higher energy densities of 701 Wh kg 1 , 802 Wh kg 1 and 867 Wh kg 1 for * Corresponding author. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-1): Materials Synthesis and Processing, Wilhelm-Joh- nen-Straße, 52425 Jülich, Germany. E-mail address: d.fattakhova@fz-juelich.de (D. Fattakhova-Rohlfing). Contents lists available at ScienceDirect Materials Today Energy journal homepage: www.journals.elsevier.com/materials-today-energy/ https://doi.org/10.1016/j.mtener.2020.100416 2468-6069/© 2020 Elsevier Ltd. All rights reserved. Materials Today Energy 16 (2020) 100416