Liquid Metal Batteries Research Articles

Understanding high-temperature corrosion behavior of an AlN/Mo functionally graded material exposed to Li/LiF-LiCl-LiBr vapor

The high-temperature corrosion behavior of an AlN/Mo functionally graded material (FGM) under the Li/LiF-LiCl-LiBr vapor has been investigated. It is suggested that the Li vapor diffuses along the AlN and AlN/Mo grain boundaries and enters the interior of adjacent AlN grains, leading to the disintegration of AlN grains and subsequent failures. The 3D Mo networks are barely corroded, thus preventing cracking that may occur due to the inconsistent deformation inside the FGM. This work unravels the high-temperature corrosion mechanisms for the AlN/Mo FGM. Meanwhile, the operating temperature threshold for the liquid metal batteries employing Mo/AlN/Mo seals is determined to be ∼ 600 °C.

The future capacity prediction using a hybrid data-driven approach and aging analysis of liquid metal batteries

Liquid metal batteries (LMBs) are wildly considered for large-scale energy storage due to the advantages of simple construction, low cost, and long life. It is of great importance to find a reliable and accurate approach to predict the future capacity for battery management and failure evaluation. A hybrid data-driven framework is presented to predict not only the long-term capacity degradation but also the local regeneration. Firstly, the Empirical mode decomposition (EMD) method is employed to decompose original battery capacity data into a residual and some intrinsic mode functions (IMFs). Then based on the data characteristics, Gaussian Process Regression (GPR) and Relevance Vector Machine (RVM) with combined kernel function is utilized to predict the local fluctuations caused by regeneration phenomena and the capacity degradation, respectively. Furtherly, we can obtain accurate capacity prediction by adding individual predicted results. Finally, the aging process and the mechanism of capacity plunge are analyzed by the incremental capacity analysis (ICA) method. The Root Mean Square Error (RMSE) of prediction is 0.117 Ah for a 20 Ah battery and 0.141 Ah for a 50 Ah battery by using the proposed framework. Compared with existing mainstream methods, the proposed framework has a more accurate prediction performance to capture the degradation tendency before the capacity plunge, which indicates the positive promise for practical applications of this framework.

Modelling the effects of areal capacity on mass transport in liquid metal batteries

Liquid metal batteries (LMBs) are formed from three molten layers, and the interaction of thermal, compositional and electromagnetic forces influences their performance and stability. The coupled behaviour of these forces in LMBs remains uncharacterised, so in this study, a three-layer numerical model was developed to investigate this interaction in lab-scale to grid-scale batteries; areal capacities 0.9–7.5 Ah/cm2. Thermal convection was modelled first, and Rayleigh-Bénard convection, a flow observed in the anode, only developed in batteries larger than current grid-scale batteries. Electro-vortex flow was introduced and found to suppress thermal convection in the anode and electrolyte layers. Thermally stratifying temperature gradients in the cathode had some effect on electro-vortex flow, but compositional effects from mass transport were dominant. Finally, a background magnetic field was used to induce swirl flow, and the coupled effects of this flow with thermal gradients was studied. Swirl flow also suppressed thermal convection, and stratifying temperature gradients had little effect on the flow; however, compositional gradients in the cathode decelerated the poloidal velocity of swirl flow during discharge. These results show that electromagnetic flows are dominant in LMBs, and mixing compositional gradients in the cathodes of large areal capacity batteries remains a challenge in the field.

Stability theory for metal pad roll in cylindrical liquid metal batteries

When liquid metal batteries are charged or discharged, strong electrical currents are passing through the three liquid layers that we find in their interior. This may result in the metal pad roll instability that drives gravity waves on the interfaces between the layers. In this paper, we investigate theoretically metal pad roll instability in idealised cylindrical liquid metal batteries that were simulated previously by Weber et al. (Phys. Fluids, vol. 29, no. 5, 2017b, 054101) and Horstmann et al. (J. Fluid Mech., vol. 845, 2018, pp. 1–35). Near the instability threshold, we expect weakly destabilised gravity waves, and in this parameter regime, we can use perturbation methods to find explicit formulas for the growth rate of all possible waves. This perturbative approach also allows us to include dissipative effects, hence we can locate the instability threshold with good precision. We show that our theoretical growth rates are in quantitative agreement with previous and new direct numerical simulations. We explain how our theory can be used to estimate a lower bound on cell size beneath which metal pad roll instability is unlikely.

Enroute to sub-300 °C operating Sn–Zn||Pb–Bi liquid metal battery by compositional engineering

Liquid metal battery (LMB) is considered a potential contender for grid-scale energy storage systems. However, high operating temperatures (>400 °C) leading to higher operational costs limit its commercial application. Therefore, the current work focuses on reducing the melting temperature of electrodes and electrolytes below 300 °C by compositional engineering. Moreover, this study utilizes earth-abundant elements like Zn (with less reliance on Li), in Zn–Sn||Bi–Pb LMB system. The composition of LiCl in the electrolyte is varied to optimize the battery performance, especially the energy efficiency and overpotential while maintaining an operating temperature of <275 °C. It is found that as the LiCl content in the electrolyte salt increases (5–30 Mol%), the overpotential of the battery decreases (0.9–0.3 V), and the energy efficiency of the charge-discharge process improves (14.5%–80.9%) owing to the better ionic conductivity of LiCl. For the optimized LiCl concentration of 30 Mol% LiCl in the electrolyte, the fabricated LMB exhibit good cyclability (no degradation till 100 cycles), a high discharging voltage plateau of 0.92 V, 24.6 mAh charge storage capacity, and a low operating temperature of 275 °C, which is the lowest operating temperature reported so far in a Zn-based LMB system.

In-depth Li+ transportation in three-dimensionalized nanodiamond network for improved liquid and solid lithium metal batteries

Confining lithium (Li) deposition in three-dimensional scaffold is commonly employed to suppress Li dendrite and enhance the cycling stability of next generation Li metal batteries (LMBs). However, the efficiency of this strategy is often degraded under lean-Li conditions, due to the serious precipitation of deposited Li on the top surface of the electronic conducting scaffold such as carbon or metal matrix. Here it is found that building an insulating interlayer on the scaffold but with a high Li+ transfer dynamism, can be a promising strategy to address the above challenge. We successfully three-dimensionalize an insulating and robust nanodiamond (ND) network on carbon paper (CP) via chemical vapor deposition, which not only retards the electron transfer to avoid the top Li precipitation, but also exhibits impressive Li affinity and mobility to undergo an in-depth Li+ transportation throughout the scaffold. Based on this advanced three-dimensionalized ND network, the Li anode performance in CP@ND significantly exceeds that in the traditional carbon fiber matrix, particularly under lean-Li conditions. Furthermore, the application of CP@ND leads to a sharply improved cyclability of all-solid-state LMBs, establishing a novel guideline of protecting Li anode in the electrolyte-mobility-limited environment.

A novel sorting method for liquid metal batteries based on deep learning and sequential features

Energy storage system (ESS) is considered to be an effective solution for renewable energy consumption. Liquid metal battery (LMB), which is a newly emerged battery technology, has great potential in ESS applications and battery sorting is required to improve LMBs' overall performance in the group application. However, current sorting methods that focus on Lithium ion batteries could not meet the requirements of LMBs due to LMB's unique characteristics and data source. Therefore, a rapid battery sorting method based on deep learning and two-dimensional sequential features is proposed in this paper. It adopts a LSTM-CONV1D (long short-term memory unit and one-dimensional convolutional layer) neural network to establish the relationship between the input time series features extracted from the LMB activation dataset and the battery capacity. While the network is trained on segments from discharging curves, the estimation is made based on all the segments of a given discharging curve, which improves the precision of estimation. The model is trained and evaluated on the 50 Ah Li||Sb-Sn LMB's activation dataset, which has achieved an overall RMSE (root mean square error) of 0.3762 on batteries of the test set and an overall 90.77 % accuracy in the sorting application. Since the battery activation dataset utilized in this study is a typical combination of historical data and partial charge-discharge testing data, the proposed sorting method has the potential to be transferred to various forms of datasets such as fast testing (partial constant current charging or discharging test) dataset and different types of batteries.

Route Optimization Equalization Scheme Based on Graph Theory for Liquid Metal Battery Strings

In order to solve the inconsistency problem of series connected liquid metal battery (LMB) strings, a route optimization equalization scheme is proposed in this article. In terms of balancing topology, a modular double-layer cell-to-cell balancing topology based on inductor and flyback multi-winding transformer is designed, which can transfer energy between any two batteries within or among modules. For control strategy, an equalization strategy based on graph theory and ant colony optimization (ACO) is proposed, which has been compared with the traditional maximum/minimum equalization control strategy. The static condition simulation results show that compared with traditional equalization strategy, the balancing speed of the route optimization control strategy is improved by 88.62%, and the balancing efficiency is increased by 19.43%. Moreover, the inconsistency problem of the battery strings can be significantly improved under both static and dynamic conditions. Therefore, by improving the balancing effect, the proposed scheme can not only effectively avoid overcharging or discharging problems, but also increase the consistency, available capacity and service life of liquid metal battery strings.

Progress and perspectives of liquid metal batteries

Progress and perspectives of liquid metal batteries

Sb-Cu alloy cathode with a novel lithiation mechanism of ternary intermetallic formation: Enabling high energy density and superior rate capability of liquid metal battery

Sb-Cu alloy cathode with a novel lithiation mechanism of ternary intermetallic formation: Enabling high energy density and superior rate capability of liquid metal battery

The Joining of Alumina to Hastelloy by a TiZrCuNi Filler Metal: Wettability and Interfacial Reactivity

A systematic microstructural characterization of alumina joined to Hastelloy C22® by means of a commercial active TiZrCuNi alloy, named BTi-5, as a filler metal is reviewed and discussed. The contact angles of the liquid BTi-5 alloy measured at 900°C for the two materials to be joined are 12° and 47° for alumina and Hastelloy C22® after 5 min, respectively, thus demonstrating good wetting and adhesion at 900 °C with very little interfacial reactivity or interdiffusion. The thermomechanical stresses caused by the difference in the coefficient of thermal expansion (CTE) between the Hastelloy C22® superalloy (≈15.3 × 10-6 K-1) and its alumina counterpart (≈8 × 10-6 K-1) were the key issues that had to be resolved to avoid failure in this joint. In this work, a circular configuration of the Hastelloy C22®/alumina joint was specifically designed to produce a feedthrough for sodium-based liquid metal batteries operating at high temperatures (up to 600 °C). In this configuration, adhesion between the metal and ceramic components was enhanced after cooling by compressive forces created on the joined area due to the difference in CTE between the two materials.

Electrochemical performance and application prospect analysis of Li||Sb-Bi-Sn liquid metal batteries

Li||Sb-Bi-Sn liquid metal batteries (LMBs) exhibit excellent cycle stability due to the self-healing action of Sb-Bi-Sn cathode, but there are still many electrochemical conditions to be considered and determined before practical applications. Herein, the effects of different operating temperatures and charge–discharge regimes on cell performance have been investigated systematically. 500 °C is preferred as the optimal operating temperature of Li|LiF-LiCl-LiBr|Sb45Bi45Sn10 LMBs, and the batteries exhibit excellent rate capability and anti-pulse interference ability. Meanwhile, the energy density of the batteries is calculated to be 265 Wh kg−1, and the electrode costs are only 58.62 $ kWh−1. We propose that this work can pave a new direction toward assessing high-performance LMBs for practical applications.

Corrosion performance and possible mechanism of aluminium nitride-molybdenum gradient material in a simulated liquid metal battery environment

After being fabricated successfully by spark plasma sintering technology, corrosion performance of aluminum nitride-molybdenum gradient material was investigated using X-ray diffraction, scanning electron microscope, XPS techniques, etc. in a simulated liquid metal battery environment with LiF–LiBr–LiCl eutectic salt as electrolyte. The research results indicated that low temperature corrosion at 550 °C occurs mainly in pure aluminum nitride region with the corrosion products grown on the grain boundaries including alumina, nitrogen-lithium, aluminum-lithium intermediate phase or their complex compounds. Moreover, the formed corrosion product morphology is influenced significantly by aluminum nitride distribution. As the gradient compositions developed towards the pure molybdenum zone, the product morphologies tended to evolve in a sequence of sphere, flake and octahedron. At temperatures higher than 600 °C, alumina tends to be dissolved in molten salt vapor and molybdenum starts to be corroded simultaneously resulting in a substitute of the formed lithium aluminum molybdenum oxide phases for alumina in the final corrosion products. Mass change study on the samples suggested both the holding time and temperature have significant influences on the corrosion behavior of aluminum nitride-molybdenum gradient material. At temperatures higher than 700 °C, sudden change in sample mass accompanied by interface cracking would happen within the holding time of 100 h. Therefore, under long-term isothermal conditions, the serviced temperature of aluminum nitride-molybdenum functional gradient materials is suggested to be lower than 600 °C.

In Situ Transition Layer Design Based on Ti Additive Enabling High-Performance Liquid Metal Batteries

Liquid metal batteries (LMBs), with the merits of long lifespan and low cost, are deemed as one of the most promising energy storage technologies for large-scale energy storage applications due to the use of liquid metal electrodes and molten salt electrolytes. However, the consequent problem is that the poor wettability between graphite-based collectors and the liquid metal/alloy electrodes leads to large contact resistance, which limits the efficiency and stability of the battery. In this work, a transition layer in situ formed on a graphite-based positive electrode current collector by Ti additive is designed for the first time, which increases the wettability between the positive alloy and the current collector and improves the voltage efficiency of the Li||Sb-Sn cell from 85.6 to 88.4%. These results provide new ideas for the design of high-efficiency LMBs.

Accelerated design of electrodes for liquid metal battery by machine learning

The electrochemical performance of liquid metal batteries (LMBs) mainly relies on the rational design of electrode materials. Nevertheless, the traditional ways of optimizing electrode materials via trial-and-error methods consume much time and effort. Herein, we present an experimentally validated machine learning approach with a self-correction function to expedite the discovery of novel multi-element electrodes with optimal electrochemical properties for LMBs, where the alloy-related, LMB-related, and creative features are established as effective input parameters. LMBs dataset, augmented from 814 original data to 2158 efficacious data, successfully predicts the quaternary alloy electrodes with discharge voltage, discharge energy and energy density. Four screened alloy electrodes are successfully synthesized and confirmed to have superior performance. Experimental results reveal the as-designed LMBs show high coulombic efficiency (∼99%), high energy efficiency (∼87%), high energy density (∼280 Wh kg−1), and low energy cost (∼70 $ kWh−1), achieving good agreement with the predictions. This method opens up exciting new possibilities for the speedy screening of optimal electrode materials for maximizing LMBs performance.

A new method to suppress the MHD instability of cylindrical liquid metal batteries

The magnetohydrodynamics (MHD) instabilities of liquid metal batteries (LMBs) severely limit the wide application and commercialization of LMB. A new technology is proposed, which is called the gridstructure (GS), so as to achieve the suppression effect of the MHD instabilities in LMB. The GS is composed of electrically and magnetically insulated partitions, which fully contact the negative electrode and extended to the positive electrode of the battery. It is found that the GS inserted inside the LMBs can change the distribution of the circumferential induced magnetic field inside the battery, effectively reduce the induced magnetic field and Lorentz force, and thus improve the stability of the LMB.

Storage of wind power energy: main facts and feasibility − hydrogen as an option

The befalling of natural disasters has been experienced at an alarming level in the last decade due to discharging excessive amounts of CO2 into the atmosphere. The world needs to decarbonise itself sooner than later. To combat environmental impact and the climate change, several key initiatives were taken by countries like the UK, Japan, Europe, and Canada. That includes decarbonising the power sector entirely by bringing in renewable energy in place of fossil fuel on an agreed timeline. Many countries have committed to zero emission by 2050. However, it will not be easy to depend on 100% of renewable energy grid without renewable energy storage capability to assure grid stability. Therefore, this publication's key fundamental objective is to discuss the most suitable energy storage for energy generated by wind. A review of the available storage methods for renewable energy and specifically for possible storage for wind energy is accomplished. Factors that are needed to be considered for storage selection and the requirements are discussed. Wind farm capacity is one of the essential parameters that could affect selection procedures. It is recommended that detailed calculations be made of available energy and the excess power amount to be stored. However, the article discusses the most viable storage options such as liquid metal batteries grid embedded storage for frequency and voltage stability and produces green Hydrogen from surplus wind energy, especially in Sri Lanka.

Operando formation of multi-channel positive electrode achieved via tellurium alloying in liquid metal battery

Liquid metal batteries (LMBs), with long life, low cost, and high safety, are promising large-scale energy storage technology to achieve better utilization of intermittent renewable energy. However, there is often a trade-off between the energy density and rate capability in LMBs with binary alloy positive electrode. The poor rate capability is still an impediment to meet the demand for practical applications. Herein, in virtue of various electromotive force of Te, Sb, Bi alloying with Li, we propose a strategy of operando formation of Li 2 Te with multi-channel structure on the surface of positive electrode. Such structure of positive electrode benefits ion transport during cycling and leads to the better rate capability. The achieved Li || Sb-Bi-Te s5 (the subscript ‘s’ stands for ‘structure’, which means that Te is only for operando formation of multi-structure and doesn't provide cell capacity) cell exhibits superior rate performance with the capacity retention of 84.4% and energy density of 143 Wh kg −1 at 1000 mA cm −2 while they are only 43.8% and 76.56 Wh kg −1 in the Li || Sb-Bi cell. This facile strategy can provide guidance for design of novel electrode materials with benign energy density and rate capability for LMBs.

A yolk-shell eGaSn@Void@SiO2 nanodroplet design for high-performance cathodes in room temperature liquid metal batteries

Gallium-based liquid alloys that exhibit high capacity and self-healing properties have been demonstrated to be promising cathodes for room temperature liquid metal batteries (RTLMBs). However, the electrochemical performances of these alloys are poor due to severe volume expansion and an unstable solid electrolyte interface layer during the lithiation process. Here, a sol-gel strategy was performed to construct yolk-shell structure nanodroplets (eGaSn@Void@SiO2) that contain sufficient void space by amorphous silicon oxide, which generated a liquid metal electrode with a high performance. The amorphous SiO2 shells not only play an important role in building stable SEI films, providing efficient electron/ion conduction channels and preventing agglomeration of active substances, but exhibit good elastic behavior during charging/discharging. Due to the appropriate voids in the yolk-shell structure, the eGaSn nanodroplets can expand freely without breaking or disrupting the electrode structure; thus, the resulting eGaSn@Void@SiO2 NDs exhibited high capacities of 538, 454, and 338 mA h g−1 at current rates of 0.2, 1 and 5 C, respectively. No obvious decay was observed with more than 500 cycles and a capacity of 377 mA h g−1 at 2 C. Interestingly, the density functional theory (DFT) calculations revealed that the effective chemisorption between the discharge products and SiO2 provides sufficient electrical contact sites with a significant drop in electrochemical impedance during cycling. The causes of the superior electrodes performance were investigated in depth using in situ X-ray diffraction and theoretical calculations. Our rational design may shed unprecedented light on the development of liquid alloy-based cathodes for high-performance RTLMBs.

A multi-input single-output thermal management system design for liquid metal batteries

Liquid metal battery, with three-liquid-layer structure and high operating temperature, is a novel battery technology that shows great potential in grid energy storage. However, unlike lithium-ion batteries, liquid metal batteries are supposed to be heated to a high temperature before operation. Both temperature uniformity among cells and total energy consumption minimization is demanded in the preheating process. In this paper, an efficient thermal management controller design is proposed to optimize the temperature uniformity and energy consumption. Different from previous work, this design replaces the conventional single-input single-output controller with a multi-input single-output controller, which samples temperatures at different locations to control the heating rate. Experimental results show that the final controller error reaches a value of 1.2%. Based on the thermal management system design, a preheating strategy is further proposed to achieve the optimal balance between temperature uniformity and energy consumption. Compared with common strategies, the maximum temperature difference is reduced by 13.7% to 49.85 °C, and the energy consumption is reduced by 6.7% of the total module energy to 6.33 kWh. It is demonstrated in this study that the proposed thermal management system and heating strategy essentially improves the heating process of liquid metal battery stack.