Cycling Behavior of NCM523/Graphite Lithium-Ion Cells in the 3–4.4 V Range: Diagnostic Studies of Full Cells and Harvested Electrodes

Abstract

Energy density of full cells containing layered-oxide positive electrodes can be increased by raising the upper cutoff voltage above the present 4.2 V limit. In this article we examine aging behavior of cells, containing LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523)-based positive and graphite-based negative electrodes, which underwent up to ∼400 cycles in the 3-4.4 V range. Electrochemistry results from electrodes harvested from the cycled cells were obtained to identify causes of cell performance loss; these results were complemented with data from X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurements. Our experiments indicate that the full cell capacity fade increases linearly with cycle number and results from irreversible lithium loss in the negative electrode solid electrolyte interphase (SEI) layer. The accompanying electrode potential shift reduces utilization of active material in both electrodes and causes the positive electrode to cycle at higher states-of-charge. Full cell impedance rise on aging arises primarily at the positive electrode and results mainly from changes at the electrode-electrolyte interface; the small growth in negative electrode impedance reflects changes in the SEI layer. Our results indicate that cell performance loss could be mitigated by modifying the electrode-electrolyte interfaces through use of appropriate electrode coatings and/or electrolyte additives. The pursuit of high energy density lithium-ion batteries for transportation applications continues in order to increase the driving range of vehicles on a single charge. Because graphite (Gr) remains the active material of choice in the negative electrode, the search mainly revolves around layered oxides for the positive electrode. In recent years there has been immense interest in the lithium and manganese-rich layered oxides which are capable of delivering high energy density cells. [1][2][3][4][5][6][7][8][9][10] This interest has ebbed somewhat because the voltage fade exhibited by these oxides lowers the usable energy, and complicates state-ofcharge determination, of the battery cells. In this article we focus our attention on the NCM523 oxide which has been the subject of several recent articles. For example, Bak et al. conducted in situ X-ray diffraction studies on various (delithiated) Li x Ni a Co b Mn c O 2 materials and concluded that NCM523 is an optimized composition offering the thermal stability of lower-Ni oxides (such as NCM333) while displaying capacities closer to the higher-Ni oxides (such as NCM811).27 From AC impedance and DC polarization studies Amin and Chiang reported that the electronic conductivity of NCM523 increases with decreasing Li-content, from 10 −7 S/cm for a fully-lithiated oxide (Li 1.0 ) to 10 −2 S/cm for a significantly delithiated (Li 0.25 ) oxide.28 Dixit et al. confirmed from first * Electrochemical Society Member. z E-mail: abraham@anl.gov principle-based simulation studies that during oxide delithiation Ni oxidizes first, followed by Co, while Mn rem...

Toward Low-Cost, High-Energy Density, and High-Power Density Lithium-Ion Batteries

“…100 Also, high-voltage cycling results in decomposition of current generation electrolytes and in the buildup of a surface reaction layer. 99,100 Ni 4+ , in particular, is not stable in contact with electrolyte. 100,101 This complex interplay among electrolyte degradation, phase changes, and transition metal dissolution from the cathode surface have spurred investigations of the cathode electrolyte interface (CEI) in recent years.…”

“…98 High-voltage cycling results in impedance rise and capacity loss. 99 The impedance rise is partly attributed to a rock-salt surface reconstruction layer resulting from oxygen loss and reduction of the transition metal oxidation states. 100 Also, high-voltage cycling results in decomposition of current generation electrolytes and in the buildup of a surface reaction layer.…”

Selecting the Best Graphite for Long-Life, High-Energy Li-Ion Batteries

“…For example, the feature belonging to (CH 2 OCOOLi) 2 was stronger in the cycled SLC 1520T graphite anode, while both MAGE and MAGE3 graphite showed much stronger Li 2 CO 3 signals (Figure 6d). In A12, APS, SCMG-BH, and SLC 1520T, CH 3 OLi showed the strongest signal. Though inorganic species in the SEI layer make it more insulating and make Li diffusion more difficult, the actual thickness of the SEI layers was difficult to estimate.…”

“…Despite the recent progress in Si 1 and Li metal 2 as future anode materials, graphite still remains the active material of choice for the negative electrode. 3,4 Lithium ions can be intercalated into graphite sheets at various stages like Li x C 12 and Li x C 6 , providing a high specific capacity of 372 mAh/g (∼2.5 times higher than LiCoO 2 ) and high volumetric capacity (similar to LiCoO 2 ) corresponding to LiC 6 . 5,6 In addition to its low cost and non-toxicity, graphite has a lowest average voltage (150 mV vs. Li/Li + ) and the flat voltage profile, rendering a high overall cell voltage.…”

Tris(trimethylsilyl) Phosphite (TMSPi) and Triethyl Phosphite (TEPi) as Electrolyte Additives for Lithium Ion Batteries: Mechanistic Insights into Differences during LiNi0.5Mn0.3Co0.2O2-Graphite Full Cell Cycling

“…12 In order to explore aging mechanisms, electrodes were obtained from cycled cells that were disassembled in an argon-atmosphere glove box. The positive electrodes were lightly rinsed with dimethyl carbonate (DMC, Sigma Aldrich, >99%, anhydrous) and examined using a PHI 5000 VersaProbe II XPS system from Physical Electronics; details of instrumentation and analysis procedures are available in Ref.…”