Due to its novel properties and unique utility, nitriles are attractive as an additive to lithium-ion battery electrolytes. However, when it is applied to high-voltage batteries, the effects and mechanisms are not clearly explained. In particular, we need to explore its mechanism. In this work, adiponitrile (ADN) has been employed as the additive in the electrolyte 1 M LiPF 6 -EC/DMC/EMC (1:1:1 by weight). The cycling tests for LiNi 0.5 Mn 1.5 O 4 half-cells after 150 cycles at 1 C (1 C = 147 mA/g) from 3.5 to 5.0 V show that adding 1 wt % ADN into the electrolyte can improve the capacity retention of the battery from 69.9% to 84.4%. Moreover, the rate performance can also be significantly improved. Based on the EIS measurement, a little ADN can stabilize the interfacial impedance avoiding a possible increase during cycling. To further clarify its mechanism, XRD, SEM, XPS measurements, and DFT calculations have been conducted, which display that when adding it into the liquid electrolyte, the cathode particles maintain good spinel shape and the molecule groups of ADN-S tend to be oxidized primarily to form a very thin film on the cathode surface. All these results indicate that ADN has potential applications in high performance electrolytes for storage systems.

Monoclinic and orthorhombic FeNbO4-based materials have been developed for many applications, including hydrogen sensors and solid oxide electrolysis cell (SOEC) electrodes. Here, we have employed density functional theory (DFT) calculations to investigate the bulk and surface properties of the monoclinic FeNbO4 structure, as well as water adsorption and dissociation on its pristine surfaces. Our calculations show that the high-spin state Fe3+ cations have a relatively smaller Bader charge than the Nb5+ cations, which accounts for Nb–O bonds that are stronger than Fe–O bonds. The analysis of the density of states (DOS) shows that the O 2p orbital occupies most of the valence band, including its maximum (VBM), with negligible contributions from the 4d and 3d orbitals of Nb and Fe cations, respectively. We found that the 3d orbitals of Fe occupy the conduction band minimum (CBM), which explains that electrons are conducted via the Fe–O–Fe framework. The calculation of the elastic constants demonstrates that pure monoclinic FeNbO4 is mechanically stable. We have also considered the thermodynamic stability and structures of the seven low-Miller-index surfaces and found that the (010) facet has the lowest surface energy and expresses the largest area in the Wulff crystal shape of the particle. Finally, we have simulated the interaction of water with the Fe3+ and Nb5+ sites of the four most stable surfaces and found that the dissociative adsorption of water takes place only on the (110) surface, which has important implications for the use of this material as a SOEC electrode.

Adiponitrile (ADN) has been applied into the lithium ion battery as an additive. However, how the amount of ADN impacts on the cycle and interface property of LiNi 0.5 Mn 1.5 O 4 is still unknown. In this work, we put different amount of ADN (0.5wt%, 1.0wt%, 2.0wt%, 5.0wt% and 10.0wt%) into the 1 M LiPF 6 -EC/DMC/EMC (1:1:1 by weight) to explore its effect and mechanism. The results of measurements show that the capacity retention of battery with 0.5% ADN has the highest value of 97.1% (126.3 mAh/g) at 0.1C after 50 cycles. While other systems' capacity drops down with the cycles obviously. Especially, when the amount of ADN increases, the polarization becomes serous and there occurs the dark passive film between particles. To explain why this situation happens, we carry out the XPS measurement and analog computation. Combining with these results, we draw a conclusion that as the amount increases, different groups such as (ADN+H) and (ADN-H) are produced and these groups can continue to participate in the film-forming reaction, which is responsible for the poor capacity and passive film.