An All-Solid State Nasicon Sodium Battery Operating at 200°C
Authors: Lalère Fabien , Leriche Jean-Bernard , Courty Matthieu , Boulineau Sylvain , Viallet Virginie , Masquelier Christian , Seznec Vincent 
Published: February 2020

Na-ion batteries have attracted recent interest and start now to be counted as viable alternatives vs. Li-ion technologies for specific applications. Indeed, recent works on phosphate-based Na-containing positive electrodes such as Na3V2(PO4)3
1 and Na3V2(PO4)2F3
2 have demonstrated excellent performances and can be considered as a new step on the way of sodium-ion technology development. However, like for the Li-ion technology, safety issues related to the use of flammable liquid electrolytes remain, especially due to the high reactivity of sodium with moisture and oxygen. All-solid state batteries, which use non-flammable solid electrolytes instead of organic liquid ones, have been proposed as strong candidates for alternative energy storage devices 3-5.
Following a recent approach developed for Li-ion all-solid state batteries6,7, we were able to assemble a monolithic all-solid state Na-ion battery using NASICON-type electrodes and electrolyte in a single 10’ step using the spark plasma sintering technique at 900°C (see Fig. 1). Na3V2(PO4)3 was used as both positive (V4+/V3+) and negative (V3+/V2+) electrodes while Na3Zr2Si2PO12 was used as the solid electrolyte. Both compositions present order-disorder phase transitions and present decent ionic conductivities of 1.5 x10-3 S cm-1 and 1.9 x10-4 S cm-1 at 200°C for Na3Zr2Si2PO12 and Na3V2(PO4)3, respectively.

Fig. 1: (top) Photo of the battery and (down) SEM backscattered electrons of the cross-section of the battery.
Thanks to a new experimental set-up, we report for the first time the electrochemical characteristics of an all-solid state Na-ion battery at temperatures as high as 200°C8. The potential limitations were selected so that the optimal capacity of Na3V2(PO4)3 could be attained at both negative and positive electrodes, given that it can be either reduced (Na3V2(PO4)3 → Na4V2(PO4)3 at 1.6 V vs. Na+/Na) or oxidized (Na3V2(PO4)3 → NaV2(PO4)3 at 3.4 V vs. Na+/Na), hence providing a theoretical voltage of 1.8 V for the symmetrical charged cell. The full battery supplies 85% of the theoretical capacity attained at C/10 with satisfactory capacity retention and low polarization, for an overall energy density of 1.87 x10-3 W h cm-2 and a capacity of 1.04 mA h cm-2(see Fig. 2).

Fig. 2: (top) Galvanostatic cycling at current rate of C/2 or C/10 with potential limitation of 2.2 V for the 3rd, 6th and 26thcycles and (down) capacity retention over cycling at 200°C.

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