Multivalent Batteries Research Articles

(Invited) Multivalent Metal/Sulfur Chemistries for High Energy Density Rechargeable Batteries

The increasing demand for high energy density batteries urges the community to seek novel chemistries. Among them, Li/S and Li-O2 have received the most attentions due to their great potential and the community's extensive experience in Li chemistry. In contrast, multivalent chemistries (Mg and Al) attract less attention despite of their unique and remarkable advantages. Although their higher reduction potentials (Mg=-2.36V vs SHE; Al=-1.3V vs SHE) compromises battery voltages, their less reactive nature has enabled a better (elec)chemical compatibility at the metal/electrolyte interface, which eliminates any surface layer and leads to a high coulombic efficiency (100%) for metal deposition/striping. This is crucial for a rechargeable battery chemistry based on metal anode, because the formation of surface layer would cause continuous consumption of electrolyte during repeated cycling. Furthermore, the deposition of multivalent metal (Mg and Al) shows uniform morphology with no whiskers (‘dendrite’) below Sand’s time, which eliminates the possibility of whiskers penetrating through separators and internal short circuit of the battery. This feature allows multivalent metal batteries to function in a much safer manner than Li metal batteries.The success of multivalent battery chemistry relies on development of proper electrolytes and cathode materials. While great progress has been made regarding the former, few advance was seen in the latter. In this presentation, we will introduce our latest achievement in tackling the cathode challenges. Our study has focused on metal/sulfur chemistries, because 1) they provide close or even higher volumetric energy density than Li/S chemistry; 2) the potentially fast reaction kinetics of the non-topotactic reaction compared with intercalation reaction.

Study of the Zn Insertion into Nanostructured d-MnO2 in Non-Aqueous Metal Batteries Using in-Situ X-Ray Absorption Spectroscopy

Nonaqueous multivalent battery chemistries provide high theoretical volumetric capacity, limited dendrite formation, and wide electrochemical windows that are a promising alternative to traditional lithium-based energy storage materials. However, transport limitations and volume change have often restricted cathodes to nanophase materials. To better understand these structural changes, we have studied Zn intercalation in δ-MnO2 cathodes using X-ray absorption spectroscopy during charge and discharge. When paired with a zinc metal anode and a AN-Zn(TFSI)2 electrolyte, the MnO2 cathode provides excellent reversibility (~100% Coulombic efficiency) and stability for 50+ cycles with ~100 mAhg-1 capacity with an operating voltage of 1.2 V vs. Zn/Zn2+. In situ x-ray absorption spectroscopy (XAS) provides element-specific characterization of both crystalline and amorphous phases and enables direct correlations between electrochemical performance and structural/redox changes associated with Mn and Zn species while cycling. By looking at the main edge of the Mn K-edge XANES spectra, the δ-MnO2 samples show clear reversible changes in redox state upon Zn insertion and deinsertion which allows Mn absorption edge shifts systematically from left to the right while cycling. These redox changes can be correlated to the local structure at the Mn site using extended X-ray absorption fine structure (EXAFS). We find a substantial decrease in the first two coordination shells upon discharge and nearly complete recovery upon charge, which we attribute to Jahn-Teller distortions during reduction to Mn3+.

Mechanism of Zn Insertion into Nanostructured δ-MnO2: A Nonaqueous Rechargeable Zn Metal Battery

Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured δ-MnO2 cathode in association with a nonaqueous acetonitrile–Zn(TFSI)2 electrolyte and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte–electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any s...

Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges.

The rapidly expanding field of nonaqueous multivalent intercalation batteries offers a promising way to overcome safety, cost, and energy density limitations of state-of-the-art Li-ion battery technology. We present a critical and rigorous analysis of the increasing volume of multivalent battery research, focusing on a wide range of intercalation cathode materials and the mechanisms of multivalent ion insertion and migration within those frameworks. The present analysis covers a wide variety of material chemistries, including chalcogenides, oxides, and polyanions, highlighting merits and challenges of each class of materials as multivalent cathodes. The review underscores the overlap of experiments and theory, ranging from charting the design metrics useful for developing the next generation of MV-cathodes to targeted in-depth studies rationalizing complex experimental results. On the basis of our critical review of the literature, we provide suggestions for future multivalent cathode studies, including a strong emphasis on the unambiguous characterization of the intercalation mechanisms.

Ab initio study of Li, Mg and Al insertion into rutile VO2: fast diffusion and enhanced voltages for multivalent batteries.

Vanadium oxides are among the most promising materials that can be used as electrodes in rechargeable metal-ion batteries. In this work, we systematically investigate thermodynamic, electronic, and kinetic properties associated with the insertion of Li, Mg and Al atoms into rutile VO2. Using first-principles calculations, we systematically study the structural evolution and voltage curves of LixVO2, MgxVO2 and AlxVO2 (0 < x < 1) compounds. The calculated lithium intercalation voltage starts at 3.50 V for single-atom insertion and decreases to 2.23 V for full lithiation, to the LiVO2 compound, which agrees well with the experimental results. The Mg insertion features a plateau about 1.6 V up to Mg0.5VO2 and then another plateau-like region at around 0.5 V up to Mg1VO2. The predicted voltage curve for Al insertion starts at 1.98 V, followed by two plateaus at 1.48 V and 1.17 V. The diffusion barrier of Li, Mg and Al in the tunnel structure of VO2 is 0.06, 0.33 and 0.50 eV, respectively. The demonstrated excellent Li, Mg and Al mobility, high structural stability and high specific capacity suggest promising potential of rutile VO2 electrodes especially for multivalent batteries.

Design Strategies for Multivalent Energy Dense Cathode Materials

Multi-valent (MV) ion intercalation batteries that replace Li+ ions with MV cations such as Mg2+, Zn2+ and Ca2+ constitute a promising strategy to meet the energy density requirements of the next generation of electrical devices. One of the most pressing obstacles to the development of high-energy density MV-ion systems is the discovery of cathode materials offering sufficiently high voltage and, most importantly, high MV cation mobility. To date, there have only been a limited number of examples demonstrating the feasibility of rechargeable multivalent batteries, with most of the focus placed on Mg-cycling. Thus, it is important to assess the feasibility of several chemical spaces as multivalent intercalation cathodes. We will present a detailed analysis, based on first-principles DFT calculations, of multivalent ion intercalation in various promising candidates such as the spinel AnB2X4 (A = MV as Mg, Zn or Ca, B = transition metal and X = O2- or S2-), olivine AnFePO4 and various vanadium pentoxide AnV2O5 polymorphs [1-5]. Emphasis will be given to host structures exhibiting enhanced Mg or Zn mobility, and in particular to the chemical and structural descriptors which govern this property. Our findings show that matching the MV site preference to the diffusion topology of the host controls the ionic mobility, more significantly than any other factor, providing design guidelines to find fast-diffusing MV conductors. For example, Zn ions are expected to diffuse well in hosts where Zn ions are in non-preferred but stable octahedral sites and migrate through favored unstable tetrahedral site. We will also show some experimental data that validates these design rules. The results demonstrate that computational materials science is a powerful tool to enable the successful development and optimization of new materials for energy dense multivalent batteries. The work is entirely supported by the Department of Energy as part of the Joint Center for Energy Storage Research (JCESR). [1] Z. Rong, R. Malik, P. Canepa, G. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Materials Design Rules for Multi-Valent Ion Mobility in Intercalation Structures, Chem. Mat. 2015, 27, 6016. [2] M. Liu, Z. Rong, R. Malik, P. Canepa, A. Jain, G. Ceder and K. Persson, Spinel compounds as multivalent battery cathodes: a systematic evaluation based on ab initio calculations, Energy Environ. Sci. 2015, 8, 964. [3] G. Gautam, P. Canepa, A. Abdellahi, A. Urban, R. Malik and G. Ceder, Intercalation phase diagram of Mg in V2O5 from first principles, Chem. Mat. 2015, 27, 3733. [4] G. Gautam, P. Canepa, R. Malik, M. Liu, K. Persson and G. Ceder, First-principles evaluation of multi-valent cation insertion into orthorhombic V2O5, Chem. Comm. 2015, 51, 13619. [5] G. Gautam, P. Canepa, W. D. Richards, R. Malik and G. Ceder, Role of structural H2O in intercalation electrodes: the case of Mg in Nanocrystalline Xerogel-V2O5, Nano. Lett. 2016, 16, 2426–2431.

Low Cost Membrane-Free Single Chamber Zinc Bromine Battery for Grid-Scale Electrochemical Energy Storage Applications

Climate change is a major global concern which can potentially be addressed by integrating renewable energy sources and low cost grid scale electrochemical energy storage (EES) systems. Most research efforts to improve energy storage have been directed to redox flow, lithium-ion and next generation sodium and multivalent batteries. The focus has been on incremental improvements in cost, and efficiency of electrode active materials and electrolytes. Most of these batteries still employ traditional cell designs with expensive passive components. Unfortunately, this approach results in the balance-of-plant costs far outweighing the cost of electrochemically active materials. Techno-economic analyses indicate that the cost of energy storage must be <$100/kWh and power cost <$600/kW. Commercially available EES systems today do not meet these targets. In addition, battery life and energy efficiencies must be over 10,000 cycles and 70%, respectively, to be a sustainable option. Based on these targets, a more holistic approach is needed when considering new energy storage system materials and designs. Here, we discuss the design and working principle of a membrane free, non-flowing single-chamber zinc-bromine (SC-Zn-Br2) battery that utilizes the physical properties of liquid bromine, a porous carbon foam electrode, and also allows zinc dendrites to form freely. With this design, we eliminate the need to use failure prone and expensive passive components such as membrane separators, bromine complexing agents, flow-rated hardware, and control software as employed in traditional Zn-Br2 redox flow batteries (RFB). The ultimate figure of merit for feasibility in grid-scale EES system is $/kWh over its lifetime (cycles) at a given energy efficiency, or levelized cost of energy stored (LCOES). We demonstrate an SC-Zn-Br2 system with a maximum specific capacity of 89 mAh/g and energy density >150 Wh/kg (normalized to the mass of ZnBr2 salt in the electrolyte) and cell cost of $94/kWh including passive components. We achieve coulombic and energy efficiencies of up to 95% and 75%, respectively, for over 1000 cycles. The LCOES of SC-Zn-Br2 is shown to be an order of magnitude better than Zn-Br2 and vanadium RFB, as well as grid-scale lead-acid batteries and Li-ion batteries.

First-Principles Screening and Evaluation of Sulfide Compounds for Multivalent Battery Cathode Applications

The rapid growth of portable consumer electronics and electric vehicles demands new battery technologies with greater energy stored at a reduced cost. Energy storage solutions based on multivalent metals, such as Mg, could significantly increase the energy density as compared to lithium-ion based technology. In this work, we use recent advances in high-throughput first-principles calculations to systematically evaluate the performance of a group of 3d transition-metal sulfide compounds for multivalent cathode applications. We estimate the insertion voltage, capacity, thermodynamic stability of charged and discharged states, as well as the intercalating ion mobility and use these properties to evaluate promising directions. From our calculations, we identified sulfide compounds that exhibit improved Mg2+ mobility with feasible low diffusion activation energy; lower than their oxide counterparts, however the improved mobility comes at the expense of lower voltage and thereby lower theoretical specific energy. We also identified a Ca2+ intercalating sulfide compound which exhibits a low diffusion activation barrier of ~500 meV and a voltage of ~2V, revealing a potential cathode for use in Ca ion rechargeable batteries. We also present several general trends and design insights extracted from our evaluation for this category of materials.

High Throughput Approach to Accelerate Electrolyte Discovery for Post Li-Ion Batteries

Transforming transportation and electricity grid with high performance, low cost energy storage require development of post Li-ion technology and innovations in electrodes and electrolytes, alike. A non-aqueous multivalent (e.g., Mg2+, Ca2+ and Zn2+) metal cell is one of the potential candidates for a post-lithium-ion battery. The theoretical volumetric capacity of a metal anode coupled with the lack of dendrite formation at a multivalent metal anode provide an attractive opportunity in energy storage.1 The ability of Mg batteries to provide much higher volumetric capacity, particularly on the anode side where the Mg metal can theoretically provide 3833 mA h/cc as compared to the Li counterpart graphite (∼ 800 mA h/cc) at a lower cost makes the technology an attractive candidate for future batteries. On the other hand Zn metal anodes coupled with a reversible intercalation cathode chemistry have a number of promising features: (1) highly efficient (≥ 99%) reversible Zn deposition on Zn metal anode in high performance nonaqueous Zn electrolytes (e.g., high anodic stability (maximum ∼ 3.8 V) and ionic conductivity) (2) relatively lower activation barrier energy for migration of Zn2+ ions in a variety of cathode materials (e.g., FePO4, NiO2, and V2O5) (3) similar ionic radius compared with Li+ and Mg2+ ions (4) much higher volumetric capacity compared to other multivalent metals, such as Mg and Ca. However, development and commercialization of multivalent batteries require not only improved electrode discovery and development but also novel electrolytes, which are compatible with both the multivalent metal as well as the multivalent cathode. Thus a fundamental understanding of molecular level properties of these electrolytes is required to improve the electrochemical stability and the charge transfer properties. An automatic High-throughput computational infrastructure has been constructed for the electrolyte genome project supported by the US Joint Center for Energy Storage Research (JCESR) coupled with experimental analysis2. In this work, we present a multi-scale modelling approach for multivalent salts in various solvents. We uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potential, e.g., at the metal anode1. We elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. We find that Mg electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. Specifically, we observe that, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+→Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI− exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. We uncover the origin of anodic stability for a range of nonaqueous zinc electrolytes. By examination of electrochemical, structural, and transport properties of nonaqueous zinc electrolytes with varying concentrations, it is demonstrated that the acetonitrile−Zn(TFSI)2 , acetonitrile− Zn(CF3SO3)2 , and propylene carbonate− Zn(TFSI)2 electrolytes can not only support highly reversible Zn deposition behavior on a Zn metal anode (≥ 99% of Coulombic efficiency) but also provide high anodic stability (up to ∼ 3.8 V vs Zn/Zn2+ ).3 The combination of multi-scale modeling with experimental techniques provides unprecedented insight into the origin of the electrochemical, structural, and transport properties in multivalent electrolytes.

An efficient algorithm for finding the minimum energy path for cation migration in ionic materials.

The Nudged Elastic Band (NEB) is an established method for finding minimum-energy paths and energy barriers of ion migration in materials, but has been hampered in its general application by its significant computational expense when coupled with density functional theory (DFT) calculations. Typically, an NEB calculation is initialized from a linear interpolation of successive intermediate structures (also known as images) between known initial and final states. However, the linear interpolation introduces two problems: (1) slow convergence of the calculation, particularly in cases where the final path exhibits notable curvature; (2) divergence of the NEB calculations if any intermediate image comes too close to a non-diffusing species, causing instabilities in the ensuing calculation. In this work, we propose a new scheme to accelerate NEB calculations through an improved path initialization and associated energy estimation workflow. We demonstrate that for cation migration in an ionic framework, initializing the diffusion path as the minimum energy path through a static potential built upon the DFT charge density reproduces the true NEB path within a 0.2 Å deviation and yields up to a 25% improvement in typical NEB runtimes. Furthermore, we find that the locally relaxed energy barrier derived from this initialization yields a good approximation of the NEB barrier, with errors within 20 meV of the true NEB value, while reducing computational expense by up to a factor of 5. Finally, and of critical importance for the automation of migration path calculations in high-throughput studies, we find that the new approach significantly enhances the stability of the calculation by avoiding unphysical image initialization. Our algorithm promises to enable efficient calculations of diffusion pathways, resolving a long-standing obstacle to the computational screening of intercalation compounds for Li-ion and multivalent batteries.

Synthesis, Structure, and Properties of the New Intercalation Cathode Material MoO2.8F0.2

The widespread adoption of multivalent batteries is hampered by the lack of stable, reliable, high voltage cathodes that can reversibly intercalate divalent cations. In lithium-based systems, molybdenum trioxide has been studied for several years as a high capacity cathode material. Although its voltage is lower than other systems, e.g. V2O5, it has advantages including crystallographic stability on cycling. A key issue that is believed to limit its performance is that, as a d0 metal oxide, it has limited electronic conductivity at top of charge.1 In this poster we will be discussing the role of fluoride incorporation into the layered charged cathode MoO3 and its effect on the materials physical properties. Utilizing synthetic methodologies developed in our lab we have studied the fluoride solubility in the host material as a way to induce electronic conductivity across the whole range of use. We have shown that the maximum fluoride incorporation in the material yields a stoichiometry of MoO2.8F0.2. Incorporation above this value results in isolation of the perovskite phase MoO2.6F0.4. We have evaluated the material using multiple intercalating cations and compared it to the undoped parent material. While the electrochemical activity of the material using a lithium-based electrolyte is similar, remarkable differences have been observed when Mg is used as the cation. While the undoped material has little or no activity, the fluorinated materials shows excellent cycleability and structural reversibility.2

Kinetics of Alloying and Deposition in Multivalent Battery Anodes Using Real-Time X-Ray Diffraction

A multivalent successor to lithium ion batteries will likely incorporate a metal anode. However, many electrodeposition processes are prone to energy losses from side reactions and overpotentials for plating or stripping. To develop a link between the kinetics of crystal growth/dissolution with electrochemical data, we have followed electrodeposition of Mg and Zn with operando x-ray diffraction using a variety of electrolytes and current collectors. In some cases we find that alloying or passivation competes with metal deposition and can dramatically alter the morphology of the deposited metal, as seen by texture analysis of the diffraction.

Chemical Intercalation and De-Intercalation Studies on Multivalent Ion Cathodes

As the lithium ion battery technology matures, it becomes apparent that the energy density is more limited by the materials used. Beyond-Li ion battery technology is now garnering more interest, and, as such, the search for new greater energy storage materials is underway. For us we are pursuing multivalent batteries [1] and are investigating new cathode materials, in hopes of discovering and designing new (de)intercalation hosts, or possibly cathodes that hold multivalent cations (Mg2+, Zn2+, Ca2+) by other storage mechanisms as well at high voltages. In particular, oxide cathodes, for example bilayer-V2O5 (BL-V2O5) [2]or alpha-MnO2(hollandite, 2x2 tunnel structure) [3], have been explored for high voltage intercalation. Unfortunately many problems abound, such as poor diffusion of multivalent cations due to strong electrostatic interactions with the oxide lattice. The development of multivalent ion electrolytes is also at its infancy and it is required to exhibit high voltage stability, compatibility with cathode and inactivity towards cell components. Viable electrolytes for this battery task are hard to find, and thus limit our productivity. Nevertheless, the search and evaluation and synthesis will require the means to chemically cycle the materials. A few reagents like di-n-butyl magnesium, di-ethyl zinc have been reported to intercalate Mg2+ and Zn2+ions [4],[5]. In this work and poster, we will discuss and demonstrate a new method of utilizing novel reagents to intercalate multivalent cations into a variety of host materials.

Understanding Divalent Cation Intercalation into a Spinel-Type Mn2O4 Host Framework

Li-ion batteries dominate the mobile device market due their high energy density; and their application is being extended to the automotive and grid storage industries. However, charge storage limitations limit the applicability of classic Li-ion technologies into these new markets, thus triggering interest in new energy storage concepts. Multivalent ion intercalation is an attractive alternative because, while conceptually similar to Li-ion, they store more charge per intercalated species and observe less dramatic structural rearrangement in the host. Recently, reversible electrochemical Mg intercalation into spinel-type Mn2O4 has been reported, where Mg2+ ions occupy vacant tetrahedral sites [1]. First principles calculations by Lui et al. argue that other multivalent ions (i.e. Ca2+, Zn2+, Al3+, Y3+) may be intercalated into spinel host framework to yield high voltage cathode materials for multivalent batteries [2]. In this work, cubic phase Mn2O4 was prepared electrochemically by delithiating commercially available spinel-type LiMn2O4 in a non-aqueous environment. Following, Mn2O4electrodes were reduced in concentrated aqueous solutions of Ca-, Mg- and Zn nitrate to -0.4 V/SCE. As-prepared electrodes were characterized using powder x-ray diffraction. As shown in the figure, the cubic structure is preserved upon delithiation and significant structural changes occurred upon reduction; indicating the formation of a tetragonal spinel (likely tetrahedral site occupation) in addition to the parent cubic phase. X-ray absorption spectroscopy and atomic resolution microscopic methods will also be used to help understand the structural changes as these divalent cations are intercalated into a spinel host framework.

Investigation of Novel Tunnel Structured Zeta-V2O5 nanowire As a Potential Cathode for Li and Mg Ion Intercalation Using in Situ TEM and Aberration Corrected STEM

Li ion battery technology continues to be the leader in energy storage applications, however growing demand for higher capacity, longer lifetime and more cost effective options has motivated researchers to both improve existing Li ion technology and also explore multivalent battery technology. From consumer electronics to electric cars, designing better models for future calls for a vast improvement in the existing battery technology. [1] Of course, traditional intercalation compounds are drawing up interest as potential cathode candidates. V2O5 has been a promising cathode for Li ion batteries. Several first principle studies have also concluded that V2O5 could be a potential cathode for Mg ion intercalation.[2] The unique structure of V2O5 consisting of layers of VO5 square pyramids held by weak bonds along the interlayer direction facilitates ion intercalation between the layers. [3] According to a recent paper, a new tunnel structured polymorph of V2O5 [zeta-V2O5] has been stabilized which can accommodate both Li and Mg ions. [4] In this talk, I will present results using in-situ TEM “open cell battery” approach to study in situ lithiation of these tunnel structured zeta-V2O5 nanowires to better understand the reaction kinetics and progression of lithiation as well as study lithiation induced changes in the structure at an atomic scale. I will compare these results with previous results we obtained studying in situ lithiation of orthorhombic alpha-V2O5 nanowires using electron diffraction and electron energy loss spectroscopy.[5] I will also use aberration corrected scanning transmission electron microscopy (STEM) imaging to study the magnesium intercalated beta structure and present the results as well, again comparing with previous results we have obtained studying electrochemically cycled thin film orthorhombic V2O5 with Mg metal anode.[6][7] Figure 1(a) shows typical TEM image of the zeta-V2O5 nanowire, electron diffraction pattern in Figure 1(b) can be indexed using XRD data for zeta-V2O5. The tunnel framework of zeta- V2O5 can be identified in the filtered High angle annular dark field (HAADF) image presented in Fig 1(c), and the electron energy loss spectra presented in Fig 1(d) establishes the valence state of Vanadium as V5+ (as expected in V2O5) by confirming the energy difference between V L3and O K edges as 9.8 eV. References 1) Noorden, R V, The rechargeable revolution: A better battery, Nature, 2014, 507, 26-28 2) B. Zhou, H. Shi, R. Cao, X. Zhang, Z. Jiang, Theoretical study on the initial stage of a magnesium battery based on a V2O5 cathode, Phys Chem Chem Phys, 2014,16,18578 3) G S Gautam, P. Canepa, A.Abdellahi, A.Urban, R.Malik, G. Ceder, The Intercalation Phase Diagram of Mg in V2O5 from First-Principles, Chem Mat, 2015 4) P.M Marley, T. A Abtew, K. E Farley, G.A Horrocks, R.V Dennis, P. Zhang, S Banerjee, Emptying and Filling a Tunnel Bronze, Chem. Sci, 2015, 6, 1712 5)A Mukherjee, H A Ardakani, T Yi, J Cabana, R S Yassar, R F Klie, Investigation of Li intercalation mechanism into V2O5nanowire cathode using in situ Transmission Electron Microscopy methods[Manuscript in preparation] 6) A. Mukherjee, N.Sa, P J Phillips, A Burrell, R F Klie.Investigation of Mg intercalation into thin film orthorhombic V2O5cathode using Aberration corrected STEM and EELS[Manuscript in preparation] 7) This work is supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy (DOE),Office of Science, Basic Energy Sciences. Figure 1

A Brief Review on Multivalent Intercalation Batteries with Aqueous Electrolytes.

Rapidly growing global demand for high energy density rechargeable batteries has driven the research toward developing new chemistries and battery systems beyond Li-ion batteries. Due to the advantages of delivering more than one electron and giving more charge capacity, the multivalent systems have gained considerable attention. At the same time, affordability, ease of fabrication and safety aspects have also directed researchers to focus on aqueous electrolyte based multivalent intercalation batteries. There have been a decent number of publications disclosing capabilities and challenges of several multivalent battery systems in aqueous electrolytes, and while considering an increasing interest in this area, here, we present a brief overview of their recent progress, including electrode chemistries, functionalities and challenges.

Evaluation of sulfur spinel compounds for multivalent battery cathode applications

Promising sulfur spinel systems with facile cation mobility are revealed for multivalent cathode applications based on systematical calculation and screening.

Utilization of Ca K-Edge X-ray Absorption Near Edge Structure to Identify Intercalation in Potential Multivalent Battery Materials

Multivalent-ion batteries have been under investigation as a technology that can provide energy densities beyond that provided by lithium ion batteries. An emerging cation of interest is calcium, as it has similar electrochemical properties and size to sodium, and systems incorporating it have high theoretical density. Common techniques used to investigate intercalation, such as NMR, are currently unable to distinguish calcium's role in energy storage materials. In this work, we investigated the ability of calcium XANES to provide fingerprint identification of intercalated species using Ca ion exchanged NaxCoO2 and a Ca(PF6)2-based electrolyte as a case study. Ca XANES was able to detect intercalation down to concentrations of ∼1 Ca per 950 Å3, even with residual electrolyte on the surface. The ability to observe the structure of the intercalated ion will enable the discovery of new electrolytes and intercalation cathodes by helping to confirm theoretical predictions, allowing multivalent batteries to become a viable high energy density storage technology.

Dual‐Salt Mg‐Based Batteries with Conversion Cathodes

Mg batteries as the most typical multivalent batteries are attracting increasing attention because of resource abundance, high volumetric energy density, and smooth plating/stripping of Mg anodes. However, current limitations for the progress of Mg batteries come from the lack of high voltage electrolytes and fast Mg‐insertable structure prototypes. In order to improve their energy or power density, hybrid systems combining Li‐driven cathode reaction with Mg anode process appear to be a potential solution by bypassing the aforementioned limitations. Here, FeS x (x = 1 or 2) is employed as conversion cathode with 2–4 electron transfers to achieve a maximum energy density close to 400 Wh kg−1, which is comparable with that of Li‐ion batteries but without serious dendrite growth and polysulphide dissolution. In situ formation of solid electrolyte interfaces on both sulfide and Mg electrodes is likely responsible for long‐life cycling and suppression of S‐species passivation at Mg anodes. Without any decoration on the cathode, electrolyte additive, or anode protection, a reversible capacity of more than 200 mAh g−1 is still preserved for Mg/FeS2 after 200 cycles.

Materials Design Rules for Multivalent Ion Mobility in Intercalation Structures

The diffusion of ions in solid materials plays an important role in many aspects of materials science such as the geological evolution of minerals, materials synthesis, and in device performance across several technologies. For example, the realization of multivalent (MV) batteries, which offer a realistic route to superseding the electrochemical performance of Li-ion batteries, hinges on the discovery of host materials that possess adequate mobility of the MV intercalant to support reasonable charge and discharge times. This has proven especially challenging, motivating the current investigation of ion mobility (Li+, Mg2+, Zn2+, Ca2+, and Al3+) in spinel Mn2O4, olivine FePO4, layered NiO2, and orthorhombic δ-V2O5. In this study, we not only quantitatively assess these structures as candidate cathode materials, but also isolate the chemical and structural descriptors that govern MV diffusion. Our finding that matching the intercalant site preference to the diffusion path topology of the host structure controls mobility more than any other factor leads to practical and implementable guidelines to find fast-diffusing MV ion conductors.