Effect of electrolyte and additives on performance of LiNi 0.5 Mn 1.5 O 4 Brett L. Lucht Department of Chemistry University of Rhode Island
Source of Energy Fade of Lithium-ion Batteries Poor calendar life and performance loss upon thermal abuse, accelerated aging, or extended cycling of Lithium-ion batteries Three primary sources have been reported Thermal decomposition of the electrolyte (LiPF 6 /Carbonate) Thermal deterioration of protective SEI on anode and reactions of electrolyte with anode Reaction of electrolyte with cathode to form surface films composed of LiF/Li x PF y /Li x POF y, PEO, Polycarbonate, ROCO 2 OLi Aurbach, D. J. Power Sources 119-121, 497 (2003) Zhang, X. et. al. J. Electrochem. Soc. 148, A463 (2001) Abraham, D. P. et. al. J. Power Sources 119-121, 511 (2003) 2
Efficiency, % Investigation of Electrolytes for HV Spinel Research suggests two primary mechanisms of performance loss due to electrolyte (LiPF 6 in Carbonates) Oxidation of the electrolyte on cathode surface Metal ion dissolution due to acidic electrolyte decomposition products Investigation of novel electrolytes to Improve Performance of LiNi 0.5 Mn 1.5 O 4 cathodes cycled to high Voltage Cathode Film forming additives which generate a passivation layer inhibiting electrolyte oxidation Lewis Basic Additives which inhibit Mn dissolution Capacity, mah g -1 160 140 120 100 80 Room Temperature 80 60 75 40 70 20 Elevated 55 o C 65 0 0 10 20 30 40 50 60 70 Cycle No. Very little capacity fade at RT followed by dramatic capacity fade at 55 o C for graphite/linimno 4 cells Cathode laminate may be damaged (Oh J. Power Sources 215, 312, 2012) 100 95 90 85 3
Q, mah I, ma Storage Experiments of Ni 0.5 Mn 1.5 O 3 with Electrolyte Investigation of the reactions of the electrolyte with the cathode surface. Ni 0.5 Mn 1.5 O 3 /Li cells were stored at various voltages between 4.0 and 5.3 V vs Li for one week. At low voltages, below 4.7 V, there is very little current flow through the cells. As the voltage surpasses 4.7 V vs Li there is a significant increase in charge flow through the cells. The increased charge flow is consistent with electrolyte oxidation on the surface of the cathode at high potential. Similar results were observed for LiNi 0.5 Mn 1.5 O 4 4 3 2 1 Q, 4.0 V Q, 4.3 V Q, 4.7 V Q, 5.0 V Q, 5.3 V I, 4.0 V I. 4.3 V I, 4.7 V I, 5.0 V I, 5.3 V 0 0 0.01 0.1 1 10 100 1000 time, hr Oxidation of the electrolyte solution (1 M LiPF 6 in 1:1:1 (EC:DEC:DMC) at various potentials with a Ni 0.5 Mn 1.5 O 3 /Li half cell. 4 3 2 1 Yang, Ravdel & Lucht Electrochem. Solid State Lett 13, A95 (2010) 4
Ex-Situ Surface Analysis of LiNi 0.5 Mn 1.5 O 4 cathodes with LiPF 6 in EC/DMC/DEC (1/1/1 vol) 4.0 V O-C C1s C-O O1s Metal Oxide F1s P2p EPDM EPDM 4.0V EPDM 4.3V EPDM 5.0V EPDM 5.3V EPDM, EC free electrolyte Li x PF y O z Li x PF y 4.3 V C=O Li x PF y Li x PF y O z Li x PF y O z PEC 4.7 V O=C 5.0 V 5.3 V 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 292 290 288 286 284 282 280 538 536 534 532 530 528 140 138 136 134 132 130 692 690 688 686 684 682 Wavenumber (cm -1 ) X Axis Title XPS Suggests Metal oxide covered with polyethylene carbonate (PEC) at high voltage. Polyethylene carbonate and oxalate generation supported by IR 5
Impedance before and after cycling at elevated temperature, ET cycling RT cycling ET cycling ET cycling RT cycling (a) (b) RT cycling (c) full cell anode half cell cathode half cell Half cells were prepared from electrode extracted from cells cycled at ET Most of the impedance growth occurs on the cathode 6
XPS Spectra of Cycled Cathodes fresh C-O C=O C 1s O 1s C-C Li 2 CO 3 O=C O-M PVDF F 1s P 2p Li x PO y F z Mn 2p Ni 2p Li 2 CO 3 O-C LiF STD RT STD ET 294 291 288 285 282 540 537 534 531 528 525693 690 687 684 681141 138 135 132 129 670 660 650 640 630 900 890 880 870 860 850 840 Significant electrolyte decomposition occurs upon cycling at 55 o C Decomposition products include polyethylene carbonate and lithium alkyl carbonates and lithium oxalate Mn and Ni content at surface is decreased 7
SEM Images of Cathodes Fresh cathode Cathode half cell after cycled at RT The changes to the morphology of the bulk cathodes upon cycling is small Cathode half cell after continuously cycled at ET, and RT again. 8
XPS Spectra of Anodes C 1s C-O C-C O 1s PVDF F 1s Li x PO y F z P 2p Mn 3p fresh C=O Li 2 CO 3 Li 2 CO 3 O-C O=C LiF Li x PO y F z STD RT STD ET 291 288 285 282 279 537 534 531 528 525693 690 687 684 681 138 135 132 129 126 60 55 50 45 40 Significant electrolyte decomposition occurs upon cycling at 55 o C Decomposition products include lithium alkyl carbonates, Li 2 CO 3, LiF, and Li x PF y O z No change to bulk material by SEM, but delamination is observed Mn is also present on the anode surface (ICP-MS) 9
Efficiency, % Effect of Electrolyte Additives on Cycling Behavior 180 100 160 140 120 RT ET RT 80 100 60 Capacity, mah g -1 80 60 40 40 20 STD Add 1.5% LiBOB 20 0 0 10 20 30 40 50 60 70 80 Cycle No. 0 Incorporation of electrolyte additive(s) results in dramatic decrease in capacity fade upon cycling at 55 o C for graphite/lini 0.5 Mn 1.5 O 4 cells 10
XPS Spectra of Anodes Changes to cathode surface are small upon incorporation of additive 11
XPS Spectra of Cycled Cathodes Additive inhibits LiF formation on Anode Mn deposition is also inhibited 12
Investigating the performance of LiNi 0.5 Mn 1.5 O 4 cathodes cycled to high voltage Discovered that the two leading sources of performance fade are electrolyte oxidation and Mn dissolution Electrolyte oxidation below 4.9 V lesser contributor, thermal effects are larger contributor. Both the anode and cathode are damaged from cycling at 55 o C. Additives have been developed that inhibit Mn dissolution and improve performance of high voltage cathodes Novel electrolyte formulations can improve the cycling performance of LiNi 0.5 Mn 1.5 O 4 cathodes at high voltage (4.9 V vs Li) 13
Acknowledgments BASF SE, Arnd Garsuch Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No 6879235 under the Batteries for Advanced Transportation Technologies (BATT) Program Boris Ravdel and Frank Puglia, Yardney Technical Products/Lithion. Mike Platek, Sensors and Surface Technology Partnership at URI for assistance with XPS and SEM. 14
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