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

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.

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

Effect of particle size on LiMnPO4 cathodes

Paul Bowen, Nam Hee Kwon

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.

2007

Atomic doping & coating for Electrocatalysis & Li-ion batteries

Albert Claude Jean-Pierre Daubry

molybdenum atomic-doping on bio-waste derived nitrogen-doped conductive carbon electrocatalyst was synthesized and investigated for the dinitrogen reduction to ammonia in alkaline media. The assessment of the catalytic activity was found to be non-trivial as nearly any external source can be the cause of ammonia contamination. In a closed-cell set-up using isotopically labelled 15N2 as feed gas for 48h chronoamperometry at -0.1 V vs RHE that the current density was correlated to the availability of the gas. Non-precious metals were incorporated in an oxidized carbon black conductive matrix and investigated for their activity towards oxygen evolution reaction in 0.1 M H2SO4, 0.5 M H2SO4 and 0.1 M HClO4. The stability of the deposited catalyst was insufficient and their deterioration was attributed to the oxidation of the carbon support as well as the dissolution of the metal ions upon high anodic potentials.The same metal-incorporated oxidized conductive carbon black agents were investigated for the enhancement of the performance of Si/C anodes in lithium-ion batteries. It was found that cobalt incorporation in the oxidized matrix displayed a significant influence in the electrochemical kinetics and consequent rate performances. With 0.8% cobalt ions by mass incorporated in oxidized KetJen Black the average capacity of the Si/C anode was increased by 180% at 1.5 A.g-1. This metal incorporation approach was extended to other ionic species (copper, iron and nickel) and other carbon conductive agents (SuperP). The electrolyte affinity, the desolvation process and the improved electronic conductivity synergistically improved the rate performance without compromising the gravimetric capacity of the electrode.The deposition of ultra-thin aluminium oxide by atomic layered deposition on the surface of LiNi0.5Co0.2Mn0.3O2 cathode material in lithium-ion batteries for the improvement of cyclic performances at high voltages (4.3-4.6 V) was investigated. One source of the failure mechanisms of the battery comes from unwanted side reactions between surface species and the electrolyte. The aluminium oxide layers of 1.42 nm and 2,36 nm were found to be beneficial at current densities exceeding 1.0 C (1 C = 170 mAh.g-1), and especially at 5.0 C with an increase of about 20 mAh.g-1 and 35 mAh.g-1 compared to uncoated NCM523, respectively. The capacity retention was found to be improved for all coated samples compared to pristine upon 140 cycles at 1.0 C. Mitigating side reactions and increasing the specific capacity at higher C-rates by atomically controlled layered deposition of inexpensive metal oxides is desirable for the implementation next-generation of safer and stable fast-charging high-voltage lithium-ion batteries.