High cycle life all-solid-state fluoride ion battery with La2NiO4+d high voltage cathode

Abstract

Fluoride ion batteries (FIBs) are a recent alternative all-solid-state battery technology. However, the FIB systems proposed so far suffer from poor cycling performance. In this work, we report La 2 NiO 4.13 with a Ruddlesden-Popper type structure as an intercalation-based active cathode material in all solid-state FIB with excellent cycling performance. The critical charging conditions to maintain the conductivity of the cell were determined, which seems to be a major obstacle towards improving the cycling stability of FIBs. For optimized operating conditions, a cycle life of about 60 cycles and over 220 cycles for critical cutoff capacities of 50 mAh/g and 30 mAh/g, respectively, could be achieved, with average Coulombic efficiencies between 95-99%. Cycling of the cell is a result of fluorination/de-fluorination into and from the La 2 NiO 4+d cathode, and it is revealed that La 2 NiO 4.13 is a multivalent electrode material. Our findings suggest that La 2 NiO 4.13 is a promising high energy cathode for FIBs.

Fluoride ion batteries – past, present, and future

“…This change in the oxidation state of Ni is also confirmed by XANES analysis. 151 In the case of La2CoO4.16, the number of inserted fluoride ions calculated (based on the effective charge capacity) is around 1.2 F − per formula unit. Furthermore, a separation between the side reaction of the carbon additive and the desired electrochemical redox reaction can be observed in the charge curves of La2CoO4+d which has been reported to be in favor controlling the degree of the side reactions taking place.…”

“…134 Unlike the fluorination of LaSrMnO4, which takes place in a layer-wise manner, the transformation of the Ruddlesden-Popper-type compounds La2NiO4+d and La2CoO4+d to La2MO4+dFy (1 ≤ y ≤ 2) occurs in only one step, and no stage-ordered fluorinated La2MO4+dF1 phase could be observed during the charging (electrochemical fluorination) step. 29,151 For the charged La2NiO4+d particles, the data obtained from electron diffraction tomography (ADT) suggests that 1.59 to 1.72 fluoride ions can be inserted within the interlayers of a La2NiO4+d unit cell, which corresponds to a change in the oxidation state of Ni from close to +2 for un-fluorinated particles to almost +4 for the fluorinated particles. This change in the oxidation state of Ni is also confirmed by XANES analysis.…”

“…Furthermore, a separation between the side reaction of the carbon additive and the desired electrochemical redox reaction can be observed in the charge curves of La2CoO4+d which has been reported to be in favor controlling the degree of the side reactions taking place. 29 Based on the extended cycling experiments on La2NiO4+d and La2CoO4+d, it is reported 29,151 that the choice of the cutoff criteria (capacity and potential) can significantly influence the cycling stability of cathodes with Ruddlesden-Popper-type structures. For instance, higher charging cutoff capacities such as 120 or 80 mAh g -1 would significantly deteriorate the cyclic stability of La2NiO4+d (as can be seen in Figure 17a), while at a lower cutoff capacity of 50 mAh g -1 the cyclic stability becomes much better (~ 60 cycles) and a cycle life of more than 220 cycles with a Coulombic efficiency of close to 100 % is reported for the cutoff capacity of 30 mAh g -1 (see Figure 17a).…”

“…The effect of the counter electrode (anode material) on the hysteresis potentials have also been found for the La2NiO4+d intercalation-based system. 151 In fact, by using anode materials with a lower intrinsic volume change during the redox reactions, less overpotentials would be introduced to the La2NiO4+d system, and therefore the cycling stability of the cell may be improved especially at higher cutoff capacities (Figure 18a). However, such a strategy does not improve the cycling stability of the La2CoO4.16 cathode material.…”

“…Furthermore, a high degree of structural reversibility has been observed over a routine discharging process for La2NiO4.13 and La2CoO4.16: After a discharge step, there is no sign of the high fluorine content phase with an extended c-parameter (up to ~ 15.2 Å) and the initial La2MO4+d structure could be recovered. 29,151 Figure 21. Discharge profiles of some of the so far proposed intercalation-based cathode materials for FIBs.…”