Luciana Gomes Chagas

Water sensitivity of layered P2/P3-NaxNi0.22Co0.11Mn0.66O2 cathode material

Sodium-based layered oxides undergo several structural changes upon the (de-)sodiation process and reveal a strong tendency towards water intercalation at lower sodium contents. However, valuable information about their handling during the investigation are still rare. Herein, we report an investigation of the water sensitivity of layered NaxNi0.22Co0.11Mn0.66O2 with mixed P2/P3 structure via X-ray diffraction. At lower sodium contents, i.e. below x ≈ 0.33 or above 3.6 V vs. Na/Na+, a strong tendency for the uptake of water is observed, supported by the appearance of new diffraction peaks confirming a dramatically increased interlayer distance. However, at high sodium content (x > 0.33) the material can be processed in open air without major changes.

P-type NaxNi0.22Co0.11Mn0.66O2 materials: linking synthesis with structure and electrochemical performance

P-type layered oxides are promising cathode materials for sodium-ion batteries and a wide variety of compounds have been investigated so far. Nevertheless, detailed studies on how to link synthesis temperature, structure and electrochemistry are still rare. Herein, we present a study on P-type NaxNi0.22Co0.11Mn0.66O2 materials, investigating the influence of synthesis temperature on their structure and electrochemical performance. The change of annealing temperature leads to various materials of different morphologies and either P3-type (700 °C), P3/P2-type (750 °C) or P2-type (800–900 °C) structure. Galvanostatic cycling of P3-type materials revealed high initial capacities but also a high capacity fade per cycle leading to a poor long-term cycling performance. In contrast, pure P2-type NaxNi0.22Co0.11Mn0.66O2, synthesized at 800 °C, exhibits lower initial capacities but a stable cycling performance, underlined by a good rate capability, high coulombic efficiencies and high average discharge capacity (117 mA h g−1) and discharge voltage (3.30 V vs. Na/Na+) for 200 cycles.

Aqueous Processing of Na0.44MnO2 Cathode Material for the Development of Greener Na-Ion Batteries

The implementation of aqueous electrode processing of cathode materials is a key for the development of greener Na-ion batteries. Herein, the development and optimization of the aqueous electrode processing for the ecofriendly Na0.44MnO2 (NMO) cathode material, employing carboxymethyl cellulose (CMC) as binder, are reported for the first time. The characterization of such an electrode reveals that the performances are strongly affected by the employed electrolyte solution, especially, the sodium salt and the use of electrolytes additives. In particular, the best results are obtained using the 1 M solution of NaPF6 in EC/DEC (ethylene carbonate/diethyl carbonate) 3:7 (v/v) + 2 wt % FEC (fluoroethylene carbonate). With this electrolyte, the outstanding capacity of 99.7 mA h g-1 is delivered by the CMC-NMO cathode after 800 cycles at a 1C charge/discharge rate. On the basis of this excellent long-term performance, a full sodium cell, composed of a CMC-based NMO cathode and hard carbon from biowaste (corn cob), has been assembled and tested. The cell delivers excellent performances in terms of specific capacity, capacity retention, and long-term cycling stability. After 75 cycles at a C/5 rate, the capacity of the NMO in the full-cell approaches 109 mA h g-1 with a Coulombic efficiency of 99.9%.

Non-aqueous semi-solid flow battery based on Na-ion chemistry. P2-type NaₓNi₀̣₂₂Co₀̣₁₁Mn₀̣₆₆O₂-NaTi₂(PO₄)₃

We report the first proof of concept for a non-aqueous semi-solid flow battery (SSFB) based on Na-ion chemistry using P2-type NaxNi0.22Co0.11Mn0.66O2 and NaTi2(PO4)3 as positive and negative electrodes, respectively. This concept opens the door for developing a new low-cost type of non-aqueous semi-solid flow batteries based on the rich chemistry of Na-ion intercalating compounds.