Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells

Sophie Solchenbach, Morten Wetjen, Daniel Pritzl, K. Uta Schwenke, Hubert A. Gasteiger
2018 Journal of the Electrochemical Society  
In the present study, we explore the use of lithium oxalate as a "sacrificial salt" in combination with lithium nickel manganese spinel (LNMO) cathodes. By online electrochemical mass spectrometry (OEMS), we demonstrate that the oxidation of lithium oxalate to CO 2 (corresponding to 525 mAh/g) occurs quantitatively around 4.7 V vs. Li/Li + . LNMO/graphite cells containing 2.5 or 5 wt% lithium oxalate show an up to ∼11% higher initial discharge capacity and less capacity fade over 300 cycles
more » ... over 300 cycles (12% and 8% vs. 19%) compared to cells without lithium oxalate. In LNMO/SiG full-cells with an FEC-containing electrolyte solution, lithium oxalate leads to a better capacity retention (45% vs 20% after 250 cycles) and a higher coulombic efficiency throughout cycling (∼1%) compared to cells without lithium oxalate. When CO 2 from lithium oxalate oxidation is removed after formation, a similar capacity fading as in LNMO/SiG cells without lithium oxalate is observed. Hence, we attribute the improved cycling performance to the presence of CO 2 in the cells. Further analysis (e.g., FEC consumption by 19 F-NMR) indicate that CO 2 is an effective SEI-forming additive for SiG anodes, and that a combination of FEC and CO 2 has a synergistic effect on the lifetime of full-cells with SiG anodes. Experimental Lithium oxalate/carbon black electrode preparation.-2 g Commercial lithium oxalate (99% purity, average particle size ∼40 μm, Alfa Aesar, United States) was ballmilled with zirconia balls (Ø 3 mm, 30 g) at 400 rpm for 1 h without solvent (dry), then for 1.5 h in 2 mL N-methyl pyrrolidone (NMP, anhydrous, Sigma-Aldrich, United States) until an average particle size of 0.2 μm was reached. The particle sizes before and after ballmilling were quantified by ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 207.241.231.82
doi:10.1149/2.0611803jes fatcat:wcvugfdqdnb3fm52twuwoe7qx4