Exploring the Ni redox activity in polyanionic compounds as conceivable high potential cathodes for Na rechargeable batteries

Abstract

Although nickel-based polyanionic compounds are expected to exhibit a high operating voltage for batteries based on the Ni 2+/3+ redox couple activity, some rare experimental studies on the electrochemical performance of these materials are reported, resulting from the poor kinetics of the bulk materials in both Li and Na nonaqueous systems. Herein, the electrochemical activity of the Ni 2+/3+ redox couple in the mixed-polyanionic framework Na 4 Ni 3 (PO 4 ) 2 (P 2 O 7 ) is reported for the first time. This novel material exhibits a remarkably high operating voltage when cycled in sodium cells in both carbonate-and ionic liquid-based electrolytes. The application of a carbon coating and the use of an ionic liquid-based electrolyte enable the reversible sodium ion (de-)insertion in the host structure accompanied by the redox activity of Ni 2+/3+ at operating voltages as high as 4.8 V vs Na/Na + . These results present the realization of Ni-based mixed polyanionic compounds with improved electrochemical activity and pave the way for the discovery of new Na-based high potential cathode materials. NPG Asia Materials (2017) 9, e370; doi:10.1038/am.2017.41; published online 31 March 2017 INTRODUCTION Lithium-ion batteries have been largely recognized as the most efficient electrochemical energy storage devices for both portable electronics and electric vehicle applications. 1,2 However, the growth and diversification of the energy storage market trigger interest in low-cost and environmentally friendly alternative systems. In addition, recent concerns over the cost and future availability of lithium highlight the urgent need to exploit alternative energy storage systems. 3 In these terms, sodium (Na)-ion batteries are attractive candidates because of the electrochemistry that is similar to the well-established lithium-ion technology. 4 To date, the LiFePO 4 olivine with (PO 4 ) 3 − polyanionic framework, owing to its superior thermal stability and low cost, is considered to be one of the best electrode materials for lithium-ion batteries, mostly in view of its stable operating voltage and satisfactory specific capacity. However, the intrinsic tunability of the operating voltage of polyanionic compounds because of the presence of different transition metals such as Mn, Co and Ni 5-7 has triggered interest in alternative frameworks exhibiting higher cell voltages. According to theoretical prediction, lithium nickel phosphate has a remarkably high working potential (~5.1 V vs Li + /Li) because of the Ni 2+/3+ redox activity. 8 Unfortunately, several studies have demonstrated that the implementation of this material is restricted by several drawbacks such as the intrinsic sluggish kinetics attributable to the low electronic conductivity, the poor lithium transport in commonly used electrolyte systems and the structural

Progress in High‐Voltage Cathode Materials for Rechargeable Sodium‐Ion Batteries

“…The theoretical output voltage of olivine NaNiPO 4 was calculated to be 4.58 V; [45a] nevertheless, its electrochemical activity has never been verified experimentally. According to recent reports, [54] NaNiPO 4 F and Na 2 NiP 2 O 7 did not show any electrochemical activity up to 5.0 V, implying that the redox energies of Ni 2+/3+ in these frameworks were as high as >5.0 V, which needs to be further confirmed employing a electrochemically stable electrolyte at such a high potential. Passerini and co-workers [54a] reported the Ni 2+ / 3+ redox activity in the mixed-phosphate host of Na 4 Ni 3 (PO 4 ) 2 P 2 O 7 for the first time, which crystallized into an orthorhombic structure (Pn2 1 a), isostructural to Na 4 Co 3 (PO 4 ) 2 (P 2 O 7 ).…”

Impact of the Acid Treatment on Lignocellulosic Biomass Hard Carbon for Sodium‐Ion Battery Anodes

“…Indeed, despite the outstanding performance of LIB systems, growingc oncerns relatedt ot he global lithium supply and its geopolitical distribution have led to an increasing interest in alternative chemistries to lithium,not necessarily competing with LIBs in all the application fields, butr epresenting together with an efficient recycling process of lithium, a viable alternative for am ore sustainable future. [25][26][27][28] So far,agreat number of studies have proposed advanced electrode materials with promisinge lectrochemical performances both at the anode [25,26,29] and cathode [30][31][32][33] side. The accelerated gained knowledge is most likely ar esult of the fact that the Na-ion chemistry is based on the same rocking chair principle as LIBs.…”

Crystallization of the Na2FexNi1−xP2O7 Glass and Ability of Cathode for Sodium-Ion Batteries

“…In the 1st chargedischarge process of Na 2 NiP 2 O 7 , there was none redox peak exhibited out, which showed the same result with Zhang et al (2017). However, in the 2nd charge process, there was an oxidation peak of Ni 2+/3+ at about 4.6 V (Zhang et al, 2017) exhibited. In addition, in the discharge process of Na 2 Fe 0.25 Ni 0.75 P 2 O 7 , despite there could be a weak electrolytic solution decomposition potential at about 4.3 V, it still exhibited the potential of Ni 3+/2+ at about 4.3 and 4.4 V. As a result, Na 2 Fe x Ni 1−x P 2 O 7 with the Fe substitution up to x = 0.25 will activate the Ni 3+/2+ .…”

“…To check the redox peaks in the process of charge and discharge, dQ/dV plots that transformed from the chargedischarge curves are shown in Figure 10B. In the 1st chargedischarge process of Na 2 NiP 2 O 7 , there was none redox peak exhibited out, which showed the same result with Zhang et al (2017). However, in the 2nd charge process, there was an oxidation peak of Ni 2+/3+ at about 4.6 V (Zhang et al, 2017) exhibited.…”

“…Hence the Ni 2+ based on the stable threedimensional framework composed of (P 2 O 7 ) 4− with Na ions is expected to exhibit a higher potential than that of Fe 2+ . Unfortunately, Na 2 NiP 2 O 7 was reported that Ni was not active in the pyrophosphate framework under the electric test (Zhang et al, 2017).…”