Effect of particle size on LiMnPO4 cathodes

LiMnPO4 was synthesized using a sol–gel method and tested as a cathode material for lithium ion batteries. After calcination at temperatures between 520 and 600 ◦C, primary particle sizes in the range of 140–220 nm were achieved. Subsequent dry ball milling reduced the primary particle diameters from 130 to 90 nm, depending on time of ball milling. Reversible capacities of 156 mAh g−1 at C/100 and 134 mAh g−1 at C/10 were measured. At 92% and 79% of the theoretical values, respectively, these are the highest values reported to date for this material. At faster charging rates, the electrochemical performance was found to be improved when smaller LiMnPO4 particles were used.

Mesoscopic manganese based cathode materials for high voltage lithium ion batteries

Nam Hee Kwon

Alternative cathode materials were investigated for application to high voltage lithium ion batteries. Manganese based materials were considered due to the low cost and environmentally sustainable impact. Layer-structured oxide and phospho-olivine materials were prepared by a sol-gel method to obtain mesoscopic particles. The particle size of the layered Li1.15Mn0.545Ni0.245Al0.06O2 material was 200 nm. A ball-milling process reduced the particle size to 60 nm. Doping with Ni and Al in the layered Li1.15Mn0.545Ni0.245Al0.06O2 material provided a redox potential at 4.1 V vs. Li+/Li. The specific capacities of 60 and 200 nm particle sized materials were 150 and 125 mAh/g, respectively at C/10. The 60 nm sized material showed a higher lithium intercalation rate than the 200 nm sized material. Particularly, at high charge-discharge rates (1C and 5C), 127 and 85 mAh/g, respectively compared to 95 and 10 mAh/g at 1C and 5C, respectively of 200 nm material. However, the 60 nm sized material degraded faster upon cycling after 80 cycles. The increased impedance indicates a large resistance associated with the interface reaction in the cycled 60 nm particlels. Two types of electrolytes were investigated in the same cathode material. 3-methoxypropionitrile (MPN) with 1M LiN(SO2CF3)2 electrolyte showed faster Li intercalation than ethylene carbonate/dimethyl carbonate (EC/DMC) with 1M LiPF6 at 1C and 5C in complete cells. LiMnPO4 was synthesized by a sol-gel method using glycolic acid. The decomposition temperature was lower in the dried gel prepared under strong acid conditions. Finally, highly ordered crystallites were formed between 520 and 570°C with particle sizes in the range of 140 to 160 nm. Subsequent dry ballmilling reduced the diameter to 130 ± 10 nm and also improved the carbon coating on the active material. LiMnPO4 material provided a redox potential of 4.1 V vs. Li+/Li. Reversible capacities of 156 mAh/g at C/100 and 134 mAh/g at C/10 were measured. At 92 and 79 % of the theoretical value, respectively, these are the highest values reported to date for this material. At faster charging rates, the electrochemical performance was found to be improved when smaller LiMnPO4 particles were used. The LiMnPO4 material showed an excellent capacity retention upon cycling as phosphate framwork is chemically and thermodynamically stable.

EPFL2006

LiMnPO4 as an Advanced Cathode Material for Rechargeable Lithium Batteries

Gianluca Deghenghi

LiMnPO4 nanoparticles synthesized by the polyol method were examined as a cathode material for advanced Li-ion batteries. The structure, surface morphology, and performance were characterized by X-ray diffraction, high resolution scanning electron microscopy, high resolution transmission electron microscopy, Raman, Fourier transform IR, and photoelectron spectroscopies, and standard electrochemical techniques. A stable reversible capacity up to 145 mAh g(-1) could be measured at discharge potentials > 4 V vs Li/Li+, with a reasonable capacity retention during prolonged charge/discharge cycling. The rate capability of the LiMnPO4 electrodes studied herein was higher than that of LiNi0.5Mn0.5O2 and LiNi0.8Co0.15Al0.05O2 (NCA) in similar experiments and measurements. The active mass studied herein seems to be the least surface reactive in alkyl carbonate/LiPF6 solutions. We attribute the low surface activity of this material, compared to the lithiated transition-metal oxides that are examined and used as cathode materials for Li-ion batteries, to the relatively low basicity and nucleophilicity of the oxygen atoms in the olivine compounds. The thermal stability of the LiMnPO4 material in solutions (measured by differential scanning calorimetry) is much higher compared to that of transition-metal oxide cathodes. This is demonstrated herein by a comparison with NCA electrodes. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3125765] All rights reserved.

2009

Enhanced rate performance of lithium-ion battery anodes using a cobalt-incorporated carbon conductive agent

Albert Claude Jean-Pierre Daubry, Xile Hu, Ming Yang

Lithium-ion batteries with enhanced rate performance are of crucial importance for practical applications. Extensive studies on the structural design and surface modification of electrode materials with the aim of improving the rate performance have been reported. Here we describe a new concept to enhance the rate capability by incorporating a tiny amount of metal species into the electron conductive agent. We show that the Si/C composite anode exhibits increased capabilities at high current densities when oxidized Ketjen black (KJB) with incorporated cobalt (Co-ox-KJB) is used as the electron conductive agent. Compared with the pristine KJB, the reversible capacities of the Si/C electrode with the Co-ox-KJB are increased by 180% on average at 1.50 A g(-1) (279 mA h g(-1)vs. 73 mA h g(-1), respectively). A synergistic contribution from enhanced electron conductivity by Co incorporation, improved affinity towards the electrolyte and an enhanced desolvation process by surface functional groups is responsible for the improved electrochemical performance. This approach is applicable for super P-based electron conductive agents as well.

ROYAL SOC CHEMISTRY2022

Mesoscopic manganese based cathode materials for high voltage lithium ion batteries

Nam Hee Kwon

EPFL2006