Probing Thermal and Chemical Stability of Na_xNi_1/3Fe_1/3Mn_1/3O₂ Cathode Material toward Safe Sodium-Ion Batteries

Abstract

Because of the low cost and high abundance of sodium, room-temperature sodium-ion batteries have recently been considered as an alternative power source to lithium-ion batteries. In contrast to the electrochemical performance of the batteries, safety has been paid much less attention, but safety is a critical consideration because sodium-ion batteries are intended for large-scale electrochemical energy storage applications. Herein, we have reported a NaNi 1/3 Fe 1/3 Mn 1/3 O 2 /hard carbon full cell with a good cycling performance and high Coulombic efficiency. The energy density of this pouch cell is close to 95 Wh/kg, and the capacity retention of the NFM full cell attained at 92.6% after 100 cycle numbers. Moreover, we have further used accelerating rate calorimetry, scanning electron microscopy, and operando synchrotron high-energy X-ray diffraction to investigate the thermal/chemical stability of charged Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 cathode material at both cell and component level. It is found that the thermal decomposition of desodiated Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 is a redox reaction that can be facilitated with the presence of either a reductive environment, such as electrolytes, or a strong oxidative environment that can result from a higher degree of desodiation. The findings presented in this work can guide future development of advanced sodium-ion batteries for practical application.

High‐Safety Nonaqueous Electrolytes and Interphases for Sodium‐Ion Batteries

“…The good thermal stability of SEI in NaPF 6 electrolytes was also confirmed by DSC analysis of Na 2 CO 3 mixed with NaPF 6 in EC/DEC ( Figure a), suggesting there are no Lewis acid species, e.g., PF 5 and HF in the solution at around 90 °C, unlike in the LIBs . More recent work reported thermal runaway behavior of Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 ||hard carbon full cell with an electrolyte of NaPF 6 ‐PC/EMC/FEC by Ma and co‐workers . The onset temperature of the battery self‐heating was located at 166.3 °C, corresponding to the exothermic reaction of SEI decomposition in the full cell, following with accelerate exothermal stage of the battery until thermal runaway.…”

High‐Abundance and Low‐Cost Metal‐Based Cathode Materials for Sodium‐Ion Batteries: Problems, Progress, and Key Technologies

“…The O3‐type iron‐ and manganese‐containing NaNi 1/3 Fe 1/3 Mn 1/3 O 2 and Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O 2 oxides have demonstrated the most realistic commercial perspectives for SIBs, since they can meet most of the requirements mentioned above and their full‐cell performances have been shown to be outstanding. Furthermore, in‐depth investigations of their hygroscopic properties, voltage decay mechanism, and full‐cell suitability/configuration are still urgently required to bring these low‐cost layered oxides to the commercial market …”

Materials Design for High‐Safety Sodium‐Ion Battery

“…i) Decomposition of SEI: Accelerating rate calorimetry (ARC) was employed to study the thermal runaway process of a Na‐ion pouch cell (developed by Sharp Laboratories of Europe with a capacity of 3000 mA h) composed of layered oxide cathode, polypropylene separator, Na + ‐conducting electrolyte, and hard carbon anode materials. [ 13–14 ] The first exothermic event initiated at ≈30 °C in the Na‐ion cell is assigned to be the initial breakdown of the SEI at the hard carbon surface. Compared with a commercial LCO pouch cell with similar energy density, it takes less time to approach the first exothermic event and the onset temperature is slightly lower for the Na‐ion cell, implying the SEI in Na‐based system is less stable at elevated temperatures.…”

“…For example, the T onset is between 30–50 °C for a 3000 mA h Na‐ion pouch cell with 1 m NaPF 6 in EC:DEC (1:1 in weight) electrolyte, [ 7 ] but 166.3 °C for a 1000 mA h pouch cell using 1.0 m NaPF 6 dissolved in propylene carbonate (PC) and ethyl methyl carbonate (EMC) (1:1 in volume) with 2 wt% fluoroethylene carbonate (FEC) as electrolyte. [ 13 ] 2)Thermal abuse temperature T e : T e is the temperature at the turning point between the second stage and the third stage of a thermal runaway event, which is the highest point for normally working and convenient escape. At this critical point, the cell temperature shows an exponential increment.…”

“…[ 11 ] So far, nonaqueous liquid electrolyte is still the primary option for SIBs because of wide electrochemical stable window, high ionic conductivity, and rapid mass transfer at the electrolyte‐electrode interface, yet giving rise to safety hazards. [ 12 ] Recent works demonstrate that sharp temperature rise, huge volume expansion, massive gas generation, and even fire accident occur during the thermal runaway event for SIBs, [ 7,13–14 ] therefore, the thermal failure is still a critical issue to tackle for developing a reliable Na‐ion battery system. [ 15–16 ]…”