Manufacturing of LiNi_0.5Mn_1.5O₄Positive Composite Electrodes with Industry-Relevant Surface Capacities for Lithium Ion-Cells

Abstract

Influence of the electrode formulation on the cyclability of LiNi 0.5 Mn 1.5 O 4 was studied for industry-relevant surface capacities (i.e. up to ∼3 mAh cm −2 ) with two mixing methods at the lab scale: ball milling and magnetic stirring. The inactive binder and carbon additives content were varied, as well as the type of those. A more homogeneous distribution of additives is observed in ball milled electrodes compared to stirred ones. The cycle life of the former is degraded with lower coulombic efficiency at first cycle, as a consequence of higher specific surface area of the electrodes and increased parasitic reactions. The coulombic efficiency stabilizes at 99.25% after several cycles, irrespective of the electrode formulation used. The fading of the capacity is minimized by increasing the amount of conductive additives or by substituting part of carbon black for carbon nanofibers. However, the cyclability of the electrodes with high active mass loading is severely decreased. The best result found is capacity retention of 85% after 300 cycles. The electrodes prepared in water with carboxylmethyl cellulose (CMC) exhibit poorer cyclability compared to the ones prepared in N-Methylpyrrolidone (NMP) with Polyvinylidene Fluorine (PVdF). Finally, electrodes with optimized formulation was prepared at the pilot scale and evaluated. LiNi 0.5 Mn 1.5 O 4 (LNMO) shows very good structural stability upon cycling. 1-7 As a positive electrode active material, its large reversible capacity of ca 135 mAh/g and high working voltage results in higher specific energy than that of LiFePO 4 , undoped-LiMn 2 O 4 and LiCoO 2 . Moreover, LNMO can be a high rate electrode material even in the form of micron-size particles. 8 This material is thus envisioned for electric vehicles as it meets the performance/cost requirements needed. Its advantages are, however, largely counter-balanced by the instability of several of the cell constituents at the high working voltage of this positive electrode, which is beyond the thermodynamic stability window of common organic electrolytes. As a consequence, parasitic reactions occur at the surface of the active material with the electrolyte that decompose and form surface films deposit including lithium salts and organic carbonates. 9 As a result, large irreversible capacity at the first cycle and low coulombic efficiency (CE) are usually observed for LNMO with conventional electrolytes, which prohibit the use of LNMO for electric vehicle application. 10 Through accurate measurements, Dahn and co-workers showed the CE decreases proportionally to the increase in charge-discharge cycle time indicating that parasitic reactions at the positive electrode occur at a fixed rate at a given temperature. It was found that for LNMO-based cells, time and temperature, and not the cycle number, determine the parasitic reactions and the calendar life. 11 In that regard, the influence of the particle size has been studied, in general by varying the temperature of the material's synthesis. 9-13 The observed trend sh...

Graphite//LiNi0.5Mn1.5O4 Cells Based on Environmentally Friendly Made‐in‐Water Electrodes

“…Graphite‐composite electrodes featuring 90 wt % graphite (SLP 30, Imerys), 5 wt % Super C45 (C45, Imerys), and 5 wt % CMC binder were prepared by a pre‐pilot automated coated line, as shown in Ref. . Disk electrodes (1.13 cm 2 geometric area) with a mass loading of active material in the range of 3.0–4.0 mg cm −2 (ca.…”

“…tective film formed on the cathode surface andt he better dispersion of composite-electrode components than in those made with PVdF should reduce the contact between LNMO and electrolyte, thus effectively suppressing Ni and Mn dissolution over 100 cycles even at high temperature. [7] Nguyen et al [8] reported that aqueous processed LNMO electrodes with CMC binder showedp oorer cycling performance than those with PVdF binderi nE C/DMC-1 m LiPF 6 owing to the presence of trace impurities of water in the composite electrodes that can lead to HF formation, whichi sd etrimental for the electrode's cycling performance. The electrode-drying step crucially affects the electrochemical performance of made-in-water LNMO electrodes.…”

Alternative binders for sustainable electrochemical energy storage – the transition to aqueous electrode processing and bio-derived polymers

“…22 As for LFP, the main reasons for such improved performance were identified to be the well maintained electrode microstructure, a lower internal resistance and faster de-/lithiation kinetics, a higher peeling strength, and less swelling of the binder by the liquid organic electrolyte, 162,[164][165][166] while the proper drying of in-waterprocessed electrodes is apparently crucial. 18,170 Once more, the use of PAA was reported to result in the formation of a very homogeneous surface coating of the active material particles, 169 which is, in light of the high lithium de-/insertion potential of LNMO and the rather limited oxidative stability of common organic-carbonate-based electrolytes, of even greater relevance compared to LFP and LMO, since it turned out to stabilize the electrode/electrolyte interface, thus preventing or at least lowering the continuous electrolyte decomposition. Another very interesting aspect of the study of Pieczonka et al 169 was that the therein utilized Li-PAA may also as a Li + reservoir, which simultaneously allows for buffering the acidity of the electrolyte due to the corresponding exchange of lithium cations (from the binder) and protons (from the electrolyte), which mitigates parasitic side reactions at the interface.…”

AC Magnetron Sputtering: An Industrial Approach for High‐Voltage and High‐Performance Thin‐Film Cathodes for Li‐Ion Batteries

“…In contrast, the reduced cycle life of the LNMO_comm electrodes can be assigned to the following factors: low electroactive material density, loss of contact of the different electrode components, and the detrimental effect of parasitic reactions of the electrode additives, as, for example, electrolyte reactions with carbon particles. [ 50 ] This latter effect is avoided in the case of LNMO thin‐films that are 100% electroactive material.…”