Stabilizing Capacity Retention in NMC811/Graphite Full Cells via TMSPi Electrolyte Additives

Abstract

Developing high-energy-density cathodes with prolonged cycling life is crucial to the continuing success of lithium-ion batteries. In particular, nickel-rich layered LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes are receiving growing interest due to their high reversible capacities in the range of 160−200 mAh/g and reduced content of critical and expensive cobalt. Nevertheless, nickel-rich NMC materials still encounter several challenges limiting their long-term cyclability, such as irreversible structural rearrangements, transitionmetal dissolution, high surface reactivity, and parasitic oxidation of organic electrolyte at the surface of delithiated Li 1−z Ni x Mn y Co 1−x−y O 2 at high voltages. Here, we investigate the use of several electrolyte additives that can alleviate capacity fading through the formation of a protective layer passivating the surface of nickel-rich NMC811. Film-forming cathode additives should decompose prior to the solvents and cover the electrode surface with a protection layer which prevents further oxidative decomposition of the electrolyte and minimizes surface side reactions. We find that the addition of 1 vol. % tris(trimethylsilyl)phosphite (TMSPi) in combination with 1 vol. % vinylene carbonate (VC) to a standard electrolyte consisting of 1 M LiPF 6 in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 vol.) significantly enhances the capacity retention of NMC811/graphite full cells. Remarkably, a discharge capacity retention of 91% is achieved after 200 cycles at C/3. KEYWORDS: LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathodes, electrolyte additives, tris(trimethylsilyl)phosphite, vinylene carbonate, lithium-ion batteries

Visualization and Chemical Characterization of the Cathode Electrolyte Interphase Using He-Ion Microscopy and In Situ Time-of-Flight Secondary Ion Mass Spectrometry

“…It should be noted that a previous study of high voltage CEI layers has attributed 59 u/e in cycled electrodes to 7 Li 3 19 F 2 + . 25 It is possible that the 59 u/e peak from the cycled electrode contains both Co + and 7 Li 3 19 F 2 + and that the broad peak could also be attributed to Li-6 and Li-7 isotopes of 7 Li 3 19 F 2 + . It is possible that 7 Li 3 19 F 2 + contributes to some of the intensity of the 59 u/e peak.…”

Magnesium Substitution in Ni‐Rich NMC Layered Cathodes for High‐Energy Lithium Ion Batteries

“…H and M refer to hexagonal and monoclinic phases, respectively. [ 24 ] In the voltage range below 3.6 V, the reduction of electrolyte at the graphite anode and the formation of the solid electrolyte interphase (SEI [ 25 ] ) occur, followed by the lithium intercalation into graphite (C 6 → Li x C 6 ) at ≈3.45 V. [ 26 ] Although the characteristic plateaus along with sharp peaks in the d Q /d V versus voltage plot related to lithium/vacancy ordering processes upon (de‐)lithiation are clearly visible for all cells, the inclusion of Mg within the 3a sites disturbs the lithium ordering and causes less pronounced anodic peaks in the corresponding d Q /d V versus voltage plots (from 3.8 to 4.2 V), giving evidence of suppressed phase transitions. [ 27 ] These observations have been reported for similar materials and are particularly evident in the H 2 –H 3 phase transition region peak at high voltages, which is believed to be the responsible of an abrupt unit cell volume contraction and structure collapse due to the lattice mismatch between H 2 and H 3 phases.…”

Improved Lithium-Ion Transport Within the LiNi0.8Co0.15Al0.05O2 Secondary Cathode Particles Through a Template-Assisted Synthesis Route

“…67 The anodic peak below 3.0 V is associated to the decomposition of the electrolyte and the VC additive, 68 and the peak around 3.48 V is indicating the lithium insertion into graphite negative electrode. 69 The reversible multiphase transition of hexagonal phases (H3 to H2) and (H2 to M) occurs only at slightly lower voltages, at 4.07 and 3.85 V, respectively, indicating the high structural stability due to Al content. 70 The specific capacity versus voltage profile of the first cycle of the cells in Figure 8b reveals a similar charging profile for all three sampleswith a shoulder at ∼3.45 V attributed to Li + ion insertion to the graphite electrode upon delithiation of the NCA electrode and a small hump at ≈3.6−3.65 V upon (H1 to M) phase transformation of the NCA electrodes, 69 deliverable capacity of ≈149 mA h g −1 , which is quite lower than to that of the LC-NCA (169 mA h g −1 ) and HC-NCA (166 mA h g −1 ), probably due to the local structural collapses induced by the Ni 2+ oxidization into Ni 3+ that prevents further Li + shuttling into the electrode.…”