Hybrid and Aqueous Li + –Ni Metal Batteries

Open AccessCCS ChemistryRESEARCH ARTICLE1 Sep 2021Hybrid and Aqueous Li+–Ni Metal Batteries Jing Zhao†, Xu Yang†, Shuyue Li, Nan Chen, Chunzhong Wang, Yi Zeng and Fei Du Jing Zhao† College of Materials Science and Engineering, Key Laboratory of Automobile Materials, Ministry of Education, Jilin University, Changchun 130012 Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education, College of Physics, Jilin University, Changchun 130012 , Xu Yang† College of Science, Shenyang Aerospace University, Shenyang 110000 , Shuyue Li Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education, College of Physics, Jilin University, Changchun 130012 , Nan Chen Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education, College of Physics, Jilin University, Changchun 130012 , Chunzhong Wang Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education, College of Physics, Jilin University, Changchun 130012 , Yi Zeng *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] College of Materials Science and Engineering, Key Laboratory of Automobile Materials, Ministry of Education, Jilin University, Changchun 130012 and Fei Du *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Physics and Technology for Advanced Batteries Ministry of Education, College of Physics, Jilin University, Changchun 130012 https://doi.org/10.31635/ccschem.020.202000507 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Aqueous metal batteries have attracted particular attention due to their low cost, environmental friendliness, and high safety. However, they still face challenges that hinder practical applications, including the oxygen and hydrogen evolution and formation of the dendrite. Herein, we propose a novel hybrid-ion battery with Ni metal as the anode. Due to the electrostatic shielding effect of Li+, the surface of deposited Ni is smooth and dendrite-free, which enables an ultralong lifespan of over 4000 h and high coulombic efficiency over 99.5%. When coupled with spinel LiMn2O4 cathode, Li+ is the dominant charge carrier undergoing deintercalation and intercalation at the LiMn2O4 cathode, whereas Ni2+ is stripped from or deposited on the Ni anode. The proposed hybrid cell achieves high-capacity retention of 81% after 1000 cycles at 500 mA g−1, a superior rate performance with a specific capacity of 64 mAh g−1 at 2000 mA g−1, and good temperature tolerance. In addition, the hybrid pouch cell shows excellent electrochemical performances that further demonstrate its great potential as a new energy storage system. Download figure Download PowerPoint Introduction Rechargeable aqueous ion batteries have been popularly recommended as the promising energy storage system for the smart grid because of their potential low cost, environmental friendliness, and high safety.1–7 Due to the high ionic conductivity of the aqueous electrolyte and decreased energy barriers of hydrated ions, aqueous batteries usually demonstrate better high-rate capability and a longer lifespan in comparison with the organic electrolyte system.8–16 Beyond the well-developed lithium-ion and sodium-ion batteries, aqueous multivalent ion batteries including Zn-ion, Mg-ion, and so forth are receiving increasing attention in recent years owing to the multielectron reaction.17–25 Both Zn and Mg metals are chemically stable in water, which enables safer handling at ambient atmosphere and direct use as the anode in aqueous media. This unique advantage circumvents the usage of inactive components in the electrode, including conducting additive and binder, which beneficially decreases the battery weight, and thus increases the energy density. Recently, Wu et al.26 proposed Fe2+ as a novel charge carrier that shuttles between the Prussian blue cathode and Fe anode in a FeSO4 electrolyte. Repetitive Fe plating and stripping processes exhibit excellent stability without battery short circuit. Therefore, earth-abundant and cost-effective metal anodes are of great interest for developing novel metal anodes in aqueous metal batteries. Among all the 3d transition metals, nickel is highly competitive, yet often neglected. First, Ni metal is chemically stable in air and water, which renders it capable of being handled without additional safety measures.27,28 Second, nickel delivers the highest volumetric capacity of 8136 mAh cm−3 ( Supporting Information Table S1), and third, its high melting point is beneficial to thermal safety, especially in the case of short circuits for a large-scale energy storage device. More importantly, nickel is not likely to form dendrite or byproducts of nickel salts. Finally, its high coulombic efficiency during reversible platting and stripping is superior to its competitor, Zn metal.29,30 The pioneering work exploiting Ni2+ as the charge carrier was done by Xu et al.31 and Wang et al.,32 who employed MnO2 and K0.25Cu[Fe(CN)6]0.75·xH2O as the host materials. Though a certain amount of reversible capacity was achieved, the low average working potentials (<0.8 V) strongly decreased the output energy density of Ni-ion battery, thus, limiting its applications in the smart grid. Since 2013, hybrid aqueous ion batteries have been developed by taking advantage of different ionic electrochemistry.33–43 For example, the Li–Zn hybrid system using LiMn2O4 cathode and Zn anode in ZnCl2/LiCl hybrid electrolyte demonstrated a high discharge voltage of 1.8 V, higher than the pure aqueous Zn-ion battery.43 An aqueous Mg–Zn hybrid battery, constructed with MgMn2O4/ZnSO4 + MgSO4 + MnSO4/Zn, showed a highly stable capacity of 269 mAh g−1 with an enhanced operating voltage of 1.5 V.44 Besides the applicable performance, the charge transport is of great interest and still of concern because there are two charge carriers in the aqueous media. So far, two kinds of transfer processes were reported: the first is the single ion-selective mechanism. In the Zn/LiMn2O4 hybrid battery, Li+ can be inserted into and extracted from the spinel lattice of LiMn2O4; whereas, Zn2+ is stripped and platted on the surface of the metal anode.45–47 In contrast, dual ions could also be co-intercalated into the cathode side. As reported by Soundharrajan et al.,44 both Zn2+ and Mg2+ can undergo deintercalation from and intercalation into MgMn2O4, whereas only Zn2+ is simultaneously dissolved from and deposited on the Zn anode. Note that answers to the question of which process is determinative is strongly relevant to selective cation channels of host materials, the ionic size, and charge compatibility. Herein, we employ the strategy of hybrid-ion transportation to construct a Li+–Ni hybrid battery with Ni metal and high-voltage LiMn2O4 material as the anode and cathode, respectively. Impressively, nickel anode delivers an extremely long lifespan over 4000 h and high coulombic efficiency of 99.5% with no sign of dendrite formation or byproducts, which renders nickel as an ideal anode for aqueous batteries. The hybrid battery shows an operating voltage of 1.1 V, high reversible capacity (81% capacity retention after 1000 cycles), and excellent rate capability (64 mAh g−1 at 2000 mA g−1), which becomes a promising alternative to the existing rechargeable batteries to power the smart grid of the future. Experimental Methods Materials Lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) and nickel(II) trifluoromethanesulfonate [Ni(OTf)2] were purchased from DoDoChem (Suzhou, China) and Aladdin (Shanghai, China), respectively. The electrolyte was prepared by dissolving LiTFSI and Ni(OTf)2 in water to a concentration of 21 mol kg−1 LiTFSI and 1 mol kg−1 Ni(OTf)2 . Commercially available nickel foam (Taobao, Jinghong New Energy Technology Co., LTD, Zhengzhou, China) with a thickness of 1.0 mm was flattened by a jack with 20 MPa pressure before use. LiMn2O4 powders were purchased from Hunan Shanshan Advanced Material Co., Ltd. (Hunan, China) Titanium foil (0.01 mm thick) was purchased from Taobao (Aerospace metal materials, (Shenzhen, China)). Materials characterizations The structural analysis of the LiMn2O4 material was performed by X-ray diffraction (XRD) using a RigaKu D/max-2550 diffractometer with Cu Kα source. A Hitachi SU8020-type scanning electron microscope (SEM) was used to investigate the morphological property, and an FEI Tecnai G2-type transmission electron microscope (TEM) was employed for the microstructure analysis. All the samples for ex situ SEM and TEM were recovered from a full aqueous battery in a 2032 coin-cell configuration after electrochemical cycling. Raman spectroscopy was carried out using a Renishaw inVia Raman system with an Ar-ion laser excitation (λ = 514.5 nm). X-ray photoelectron spectra were measured via a VG scientific ESCALAB-250 spectrometer. Electrochemical measurements The electrochemical tests were carried out using coin-type cells (CR2032). Li+–Ni hybrid aqueous batteries were assembled using flat Ni foam as the counter electrode; LiMn2O4 as the working electrode, which was fabricated by coating a slurry prepared from a mixture of the active material; Super P conductive additive; and poly(vinylidene difluoride) (PVDF) binder, dissolved in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 7∶2∶1, on a Ti foil current collector. Then the electrode films were dried in a vacuum oven at 80 °C for 12 h. After patterning the electrode film into a circle of diameter 1.0 cm, the coin cells were assembled in the air. The loading mass of the materials was 1.4–2.0 mg cm−2. Glass fiber filters (Whatman GF/C) were used as separators for the cells. The electrolyte solution was prepared by dissolving LiTFSI and Ni(OTf)2 in water(21 and 1 m, respectively). Galvanostatic charge–discharge (GCD) tests were carried out with a voltage range of 0.1–1.7 V at room temperature using a Land-2001A (Wuhan, China) automatic battery tester. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out using a VSP multichannel potentiation–galvanostatic system (Bio-Logic SAS, Claix, France). For the three-electrode setup, Ni metal, saturated calomel electrode (SCE), and Ti foil were employed as working, reference, and counter electrodes, respectively. The corrosion potential and current were evaluated from Tafel fit plots in the electrochemical workstation. For the pouch cell (length 4.0 cm × wide 3.0 cm), the three-in-one vacuum sealing machine (MSK-115-III) was used to seal and vacuum, and then prepared per the coin-cell preparation process. The active mass loading for cathode materials was 2.5–3.0 mg cm−2. The capacity of Ni||LiMn2O4 battery is calculated based on the mass of LiMn2O4. Results and Discussion It is well known that the cell failure mechanism of aqueous batteries is intimately correlated with the hydrogen and oxygen evolution reactions of the aqueous electrolyte, as well as the corrosion reactions between the metal anode and electrolyte. To achieve the most suitable electrolyte for the newly designed Li+–Ni hybrid system, the composition and concentration of salts in water were first optimized. As shown in Supporting Information Figure S1a, the solution remains transparent even when the concentration of LiTFSI reaches 21 mol kg−1 (m). Then, the corresponding electrochemical stable windows of different electrolytes ( Supporting Information Figure S1b) were comprehensively investigated, where the initial voltage window of 1 m Ni(OTf)2 electrolyte is 1.8 V. As the concentration of LiTFSI increased, the voltage range simultaneously expanded, and finally reached 2.8 V for the 21 m LiTFSI + 1 m Ni(OTf)2 hybrid electrolyte (21 m Li + 1 m Ni). It has been reported that the cations and anions in the water-in-salts electrolyte effectivly bind the free water molecules and thus suppress the water splitting.48–50 Subsequently, the pH value of electrolytes rose from 1.9 to 6.5 as the concentration of LiTFSI increased ( Supporting Information Figure S2). The decreased acidity led to weakened corrosion of hydrogen ions on the Ni foam. After soaking in 21 m Li + 1 m Ni electrolyte for 10 days, the surface of Ni was still fresh and metal-lustered, in sharp contrast to the corroded Ni with a dark surface in 1 m Ni electrolyte ( Supporting Information Figure S3). The corrosions of metallic Ni in different electrolytes were further evaluated using potentiodynamic polarization tests ( Supporting Information Figure S4). Among the potential electrolytes, Ni in 21 m Li + 1 m Ni electrolyte showed the most positive corrosion potential of −0.95 V versus SCE and the smallest corrosion current of 0.12 mA. This phenomenon indicated a low tendency of corrosion reaction and low corrosion rate in the concentrated electrolyte, usually induced by hydrogen evolution and dissolved oxygen passivation.51,52 Thus, the concentrated electrolyte is more suitable for this system than others. The electrochemical Ni plating and stripping behavior were evaluated via CV in a three-electrode cell, where Ni foil, SCE, and Ti foil serve as the working, reference , and counter electrode, respectively. As shown in Supporting Information Figure S5, the cathodic and anodic peaks are observed at −0.50 and −0.05 V versus SCE corresponding to the Ni plating and stripping process, respectively. The coulombic efficiency of metal plating and stripping was then examined via GCD measurements in asymmetrical Ti||Ni cells. As shown in Figures 1a and 1b, cyclic stability was studied at a current density of 0.1 mA cm−2 with a 0.1 mAh cm−2 plating capacity set. The initial coulombic efficiency is 77%, which could be attributed to insufficient electrolyte infiltration or formation of surface or interface on Ni. Remarkably, a highly stable coulombic efficiency of 99.5% was maintained for 700 cycles, suggesting that all the deposited Ni on Ti could be recovered during the subsequent stripping process, which is competitive with Zn metal anodes ( Supporting Information Table S2). For comparison, in diluted electrolytes, coulombic efficiency of 1 m Ni, 1 m Li + 1 m Ni, and 10 m Li + 1 m Ni were ∼60%, ∼95%, and ∼97%, respectively ( Supporting Information Figures S6–S8). The increasing coulombic efficiency trend is attributed to the concentrated electrolyte suppressing the side reactions, such as hydrogen evolution or electrode corrosion, thus increasing the coulombic efficiency. The electrochemical behavior of Ni in 21 m Li + 1 m Ni was further investigated using a Ni||Ni symmetric cell under galvanostatic condition. The GCD profiles show no obvious potential fluctuation over 4000 h (Figure 1c), which is comparable with the state-of-the-art Zn-ion batteries ( Supporting Information Table S3). Furtheromore, the plating and stripping behavior of Ni||Ni batteries was also examined (Figure 1d). The overpotential remained almost unchanged as the current densities increased from 0.1 to 0.5 mA cm−2, indicating fast plating and stripping kinetics. Compared with the plating and stripping behavior of Ni using 1 m Ni electrolyte ( Supporting Information Figure S9), the platforms in GCD profiles of Ni||Ni cell using 21 m Li + 1 m Ni electrolyte are much flatter, indicating the electrochemically stable Ni deposition process. Figure 1 | Characterizations of the Ni anode in 21 m LiTFSI + 1 m Ni(OTf)2 electrolytes. (a) The GCD potential profiles of Ti||Ni asymmetrical cell at 0.1 mA cm−2. (b) The corresponding plating and stripping coulombic efficiency. (c) Galvanostatic Ni stripping and plating in a Ni||Ni symmetrical cell at 0.1 mA cm−2, each half-cycle lasts for 1 h. (d) Rate performance of Ni||Ni symmetrical cell at current densities from 0.1 to 0.5 mA cm−2. Download figure Download PowerPoint In addition, the morphology change of deposited Ni metal was investigated using SEM. As shown in Figures 2a and 2b, both the surfaces of Ni in 1 m Ni and 21 m Li + 1 m Ni electrolytes were smooth, indicating uniform Ni deposition at a current density of 0.1 mA cm−2. Whereas, the surface of Ni using 1 m Ni electrolyte (Figure 2c) became rough and showed characteristics of scattered sphere-like particles when current density increased to 0.5 mA cm−2, also observed in Zn and other metal anodes.53,54 In the presence of 21 m LiTFSI, the surface of Ni (Figure 2d) became smoother and the sphere-like particles were smaller and more uniform. As illustrated in Figure 2e, larger current density usually led to the formation of the crystal core of Ni. The Ni-ions preferred to deposit on the surface of the Ni core, thus forming large sphere-like particles. The reduction potential of Li+ is lower than that of Ni2+, thus a large amount of Li+ was likely adsorbed on the Ni core, which worked as an electrostatic shielding layer to prevent deposition of Ni2+ on the Ni core. Even though growth of the Ni core was suppressed, Ni2+ would deposit where the electrostatic shielding effect was weak. After 500 cycles at a current density of 0.1 A cm−2, the surface of Ni using 1 m Ni electrolyte became rough, whereas that of 21 m Li + 1 m Ni electrolyte remained smooth ( Supporting Information Figure S10), indicating the constant effects of LiTFSI on protecting the anode. Furthermore, the XRD patterns of Ni after 500 cycles ( Supporting Information Figure S11) show a pure Ni phase without any byproducts indicative of the high stability of the Ni anode. Figure 2 | Morphology evolution of Ni electrodes after cycling at different current densities. (a) 1 m Ni(OTf)2 and (b) 21 m LiTFSI + 1 m Ni(OTf)2 electrolytes at 0.1 mA cm−2. (c) 1 m Ni(OTf)2 and (d) 21 m LiTFSI + 1 m Ni(OTf)2 at 0.5 mA cm−2. (e) Illustration of Ni deposition process in 1 m Ni(OTf)2 and 21 m LiTFSI + 1 m Ni(OTf)2 electrolytes. Download figure Download PowerPoint Subsequently, the coin-type Ni||LiMn2O4 full cell was fabricated as a hybrid electrolyte. As illustrated in Figure 3a, Li+ was extracted from LiMn2O4 and the equivalent charge of Ni2+ was deposited onto Ni anode during charge; the process was reversed during discharge. The Ni||LiMn2O4 hybrid cell delivered a specific capacity of 123 mAh g−1 with an average discharge potential of 1.1 V (Figure 3b). When using delithiated LiMn2O4 (i.e., Li1-xMn2O4) cathode and 1 m Ni(OTf)2 electrolyte, the battery showed a negligible capacity, indicating that Ni2+ could hardly intercalate into the lattice of Li1-xMn2O4. Three-electrode battery was then employed to synchronously detect the potential change of the LiMn2O4 working electrode, Ni counter electrode, and voltage of the full cell. As shown in Supporting Information Figure S12, the charge and discharge curves indicate characteristic intercalation-type cathode and plating and stripping anode behavior with good reversibility. To further investigate the energy storage mechanism of the cathode, in situ XRD patterns were employed. As shown in Figure 3c, the diffraction peaks of (111), (311), (222), and (400) planes consistently shift to their larger angles during the charging process, indicating decreasing d spacing between corresponding planes with Li+ deintercalation. In the discharge process, the diffraction peaks shift back to their original position, which agrees well with the electrochemical behavior of LiMn2O4 in other literature.43,45 The cell parameters of LiMn2O4 ( Supporting Information Figure S13) at various states of charge and discharge also show that the intercalation of Li+ is highly reversible. Also, it is important to determine whether Ni2+ could be stored in LiMn2O4 or not. According to the reported structural refinement of LiNi0.5Mn1.5O2,55,56 even with a large amount of Ni2+ in the lattice, the occupancy of Ni2+ in the 8a site could be ignored, which indicates that Ni2+ could hardly be stored in 8a sites. Furthermore, Raman spectra (Figure 3d) suggest only peaks at 625 cm−1, corresponding to symmetric Mn–O stretching vibration of MnO6 groups, could be detected. The reversible shifts of peak agree well with the trend of in situ XRD. The absence of peaks at 500 cm−1 corresponding to Ni–O vibration indicates that Ni2+ in electrolytes could not be stored in 16d sites of LiMn2O4. situ X-ray photoelectron spectroscopy and the of ions increased with Li+ deintercalation and with Li+ As for Ni ions ( Supporting Information Figure only Ni2+ was which could be attributed to electrolyte on LiMn2O4. The absence of the storage of Ni ions in 16d sites. Thus, it could be the cathode and intercalation of Li+ and Ni2+ plating and stripping process in the anode side. Figure | (a) figure of hybrid Ni||LiMn2O4 aqueous (b) and discharge curves of using hybrid m LiTFSI + 1 m and 1 m Ni(OTf)2 electrolytes. (c) In situ XRD patterns of LiMn2O4 cathode at various of charge and discharge in the first and (d) situ Raman of LiMn2O4 and of LiMn2O4 Download figure Download PowerPoint The battery showed a specific capacity of 123 mAh g−1 at mA g−1 on the mass of with a high coulombic efficiency of (Figure When the current density increased to 2000 mAh g−1, it still delivered a capacity of 64 mAh g−1, which is of the value at mA g−1 (Figure and Supporting Information Figure suggesting a superior rate The stability of the proposed hybrid cell was examined at 500 mA g−1, where a capacity retention of 81% and coulombic efficiency of was after 1000 cycles, indicative of its high TEM and XRD show that LiMn2O4 remains unchanged after cycles, excellent structural ( Supporting Information Figures and situ XRD and SEM also suggest the pure phase and morphology of Ni anode after cycles ( Supporting Information Figure The reversible energy storage mechanism and side reactions the good performance of the Ni||LiMn2O4 Figure | Electrochemical performance of the hybrid Ni||LiMn2O4 aqueous (a) performance at mA (b) rate performance at current densities from to 2000 mA (c) stability at 500 mA (d) Rate and performance at different Download figure Download PowerPoint The energy storage performance at various is an important for the aqueous Supporting Information Figure shows the GCD profiles of Ni||LiMn2O4 at mA When the temperature increased from to °C , the of charge transfer thus to an enhanced discharge capacity of mAh g−1 and a lower which to the smaller overpotential of Ni plating and stripping in high temperature at different current densities ( Supporting Information Figure the the capacity decreased to mAh g−1 at which could from the larger overpotential of Ni plating and stripping ( Supporting Information Figure that both the and increased as the temperature decreased ( Supporting Information Figure The the capability of battery, at higher current density (Figure In addition, the coulombic efficiency was low at °C due to water as by the presence of a in the GCD ( Supporting Information Figure at V. the current density there was for electrolyte so the coulombic efficiency (Figure becomes at thus the battery showed higher efficiency. The Ni plating and stripping efficiency reached after cycles at and °C ( Supporting Information Figure suggesting that the temperature cathode and electrolyte than the plating and stripping due to the presence of the point of electrolyte thus the cell still worked at and after it even delivered the capacity as that at In the excellent temperature of the proposed hybrid battery renders it as a promising energy storage system. that the aqueous electrolyte is and the hybrid system not and The pouch cell was further assembled in the air with a three-in-one vacuum sealing As shown in Figure the pouch cell showed a charge and discharge as of the coin cell, for a lower capacity of mAh The initial coulombic efficiency was and then reached after two The cell also showed stable performance with a capacity retention of after cycles (Figure When current density increased to 1000 mA g−1, the pouch cell delivered a capacity of mAh g−1, of that at mA After the current density to mA g−1, it still delivered a stable capacity of mAh g−1 after cycles (Figure A was when pouch cells in (Figure Figure | Ni||LiMn2O4 hybrid aqueous (a) GCD profiles between 0.1 and V at mA (b) (c) Rate performance at current densities from to 1000 mA (d) of the by pouch cells in Download figure Download PowerPoint A novel hybrid aqueous Ni||LiMn2O4 battery system is proposed and The use of concentrated hybrid electrolyte m LiTFSI + 1 m not only a wide voltage also the uniform deposition of Ni2+ by electrostatic shielding of A of tests suggest that the cathode an intercalation the anode is and stripped of Ni. The coin-type Ni||LiMn2O4 cell shows an operating voltage of 1.1 V, capacity of 123 mAh g−1 at mA g−1, superior rate capability with a specific capacity of 64 mAh g−1 at 2000 mA g−1, a long lifespan of 1000 cycles, as well as good temperature tolerance. cells are also fabricated and show performance as that of the coin cell. It be that this is a work on of energy storage new with higher voltage and capacity and Ni anodes are in work to the energy density of the that this strategy of a hybrid cell a new of a battery with a and stable metal anode. Supporting Information Supporting Information is of is no of interest to This work was by Science of with The would to the from the Science and Technology Jilin and and the for the Rechargeable Li and Chen of Rechargeable Batteries for the of Aqueous Batteries by in the Li Lithium Batteries with Aqueous Energy for the A of