Batteries | Issue Cover Collection Published in 2024

This paper describes a novel approach to determining a fast-charging profile for a lithium-ion battery by using a simplified single-particle electrochemical model and direct collocation methods for optimal control. An optimal control problem formulation and a direct solution approach were adopted to effectively address the issue. The results show that, in some cases, the optimal current profile resembles that of the constant current–constant voltage charging protocol. Several challenges and knowledge gaps were addressed in this work, including a reformulation of the optimal control problem, utilizing direct methods as an alternative to overcome the limitations of indirect methods employed in similar studies. The proposed formulation considers the minimum-time optimal control case, the trade-offs among the total charging time, the maximization of the lithium bulk concentration, and energy efficiency, along with inequality constraints and other factors not previously considered in the literature, which can be helpful in practical applications.

Lithium-ion batteries are well-established as traction batteries for electric vehicles. This has led to a growing market for second-life batteries that can be used in applications like home energy storage systems. Moreover, the recyclability and safe handling of aged or damaged cells and packs have become more important. While there are several indicators, like state of health (SOH), state of power (SOP), or state of safety (SOS), which describe the state of a battery before its defined end of life (EOL), there is no consistent classification methodology through which the usability of a cell or pack after its EOL is reached can be described. The proposed state of usability (SOU) provides a new indicator that accounts for the usability of a battery for a second life, recyclability, and the potential need for the safe handling of a lithium-ion battery after its first intended life cycle. This work presents a decision tree method, which in turn leads to five discrete usability levels, enabling a fast and rough determination of the SOU for practical use. Further, a calculation methodology for reasonable continuous regions of the SOU is proposed. Both methods are based on a literature-based rating of all of the relevant defect and aging mechanisms displayed in a risk matrix. Finally, some experimental methods that can be used for SOU determination are proposed. The developed methodology and the hands-on approach using a decision tree are well-suited for real-world applications in recycling companies and battery test laboratories.

Revolutionary and cost-effective state estimation techniques are crucial for advancing lithium-ion battery technology, especially in mobile applications. The accurate prediction of the battery state of health (SoH) enhances the state-of-charge estimation while providing valuable insights into performance, second-life utility, and safety. While recent machine learning developments show promise in SoH estimation, this paper addresses two challenges. First, many existing approaches depend on predefined charge/discharge cycles with constant current/constant voltage profiles, which limits their suitability for real-world scenarios. Second, pure time series forecasting methods require prior knowledge of the battery’s lifespan in order to formulate predictions within the time series. Our novel hybrid approach overcomes these limitations by classifying the current aging state of the cell rather than tracking the SoH. This is accomplished by analyzing current pulses filtered from authentic drive cycles. Our innovative solution employs a Long Short-Term Memory-based neural network for SoH prediction based on residual capacity, making it well-suited for online electric vehicle applications. By overcoming these challenges, our hybrid approach emerges as a reliable alternative for precise SoH estimation in electric vehicle batteries, marking a significant advancement in machine learning-based SoH estimation.

As the use of Li-ion batteries grows more widespread, incidents in large energy storage systems (stationary storage containers, etc.) or large-scale cell and battery storages (warehouses, recyclers, etc.), often leading to fire, are occurring on a more regular basis. Water remains one of the most efficient fire extinguishing agents for tackling such battery incidents, and large quantities are usually necessary. Since batteries contain various potentially harmful components (metals and their oxides or salts, solvents, etc.) and thermal runaway-induced battery incidents are accompanied by complex and potentially multistage fume emissions (containing both gas and particles), the potential impact of fire run-off waters on the environment should be considered and carefully assessed. The tests presented in this paper focus on analyzing the composition of the run-off waters used to spray NMC Li-ion modules under thermal runaway. It highlights that waters used for firefighting are susceptible to containing many metals, including Ni, Mn, Co, Li, and Al, mixed with other carbonaceous species (soot, tarballs) and sometimes undecomposed solvents used in electrolytes. Extrapolation of pollutant concentrations compared with PNEC values showed that, for large-scale incidents, run-off water could be potentially hazardous to the environment.

The global environmental crisis necessitates reliable, sustainable, and safe energy storage solutions. The current systems are nearing their capacity limits due to the reliance on conventional liquid electrolytes, which are fraught with stability and safety concerns, prompting the exploration of solid-state electrolytes, which enable the integration of metal electrodes. Solid-state sodium-ion batteries have emerged as an appealing option due to the abundance, low cost, and sustainability of sodium. However, low ionic conductivity and high interfacial resistance currently prevent their widespread adoption. This study explores polyvinyl-based polymers as wetting agents for the NASICON-type NZSP (Na₃Zr₂Si₂PO₁₂) solid electrolyte, resulting in a combined system with enhanced ionic conductivity suitable for sodium-ion solid-state full cells. Electrochemical impedance spectroscopy (EIS) performed on symmetric cells, employing NZSP paired with different wetting agent compositions, demonstrates a significant reduction in interfacial resistance with the use of poly(vinyl acetate) (PVAc)-based polymers, achieving an impressive ionic conductivity of 1.31 mS cm⁻¹ at room temperature, 63.8% higher than the pristine material, and notably reaching 7.36 mS cm⁻¹ at 90 °C. These results offer valuable insights into the potential of PVAc-based polymers for advancing high-performance solid-state sodium-ion batteries by reducing their total internal resistance.

As society becomes more reliant on Lithium-ion (Li-ion) batteries, state-of-health (SOH) estimation will need to become more accurate and reliable. Therefore, SOH modeling is in the process of shifting from using simple and continuous charge/discharge profiles to more dynamic profiles constructed to mimic real operation when aging the Li-ion batteries. However, in most cases, when aging the batteries, the same profile is just repeated until the battery reaches its end of life. Using data from batteries aged in this fashion to create a model, there is a very real possibility that the model will rely on the built-in repetitiveness of the profile. Therefore, this work will examine the dependence of the performance of multiple linear regression on the number of charges used to train the model, as well as their location within the profile used to age the batteries. The investigation shows that it is possible to train models using randomly selected partial charges while still reaching errors as low as 0.5%. Furthermore, it shows that only one randomly sampled partial charge is needed to achieve errors smaller than 1%. Lastly, as the number of randomly sampled partial charges used to train the model increases, the dependence on particular partial charges tends to decrease.

Cathode formulation, which describes the amount of cathode active material (CAM), conductive additives (CAs), and binders within a cathode compound, is decisive for the performance metrics of lithium-ion battery (LIB) cells. The direct measurement of electronic resistance can be an enabler for more time- and cost-efficient cathode formulation improvements. Within this work, we correlate the electronic resistance with the electrochemical performance of cathodes. Two different high-nickel NCM cathode materials and numerous CAs are used to validate the findings. A detailed look into the resistance reduction potential of carbon black (CB) and single-walled carbon nanotubes (SWCNTs) and their mixtures is carried out. Finally, an impact estimation of cathode formulation changes on LIB key performance factors, such as energy density and cost, is shown.

The effects of global warming highlight the urgent need for effective solutions to this problem. The electrification of society, which occurs through the widespread adoption of electric vehicles (EVs), is a critical strategy to combat climate change. Lithium-ion batteries (LIBs) are vital components of the global energy storage market for EVs, and sodium-ion batteries (SIBs) have gained renewed interest due to their potential for rapid growth. Improved safety and stability have also put solid-state batteries (SSBs) on the chart of top batteries in the world. This review examines the following three critical battery technologies: LIBs, SIBs, and SSBs. Although research has historically concentrated on heavier battery components, such as electrodes, to achieve high gravimetric density, binders, which comprise less than 5% of the battery weight, have demonstrated great promise for meeting the increasing need for energy storage. This review thoroughly explores various binders, focusing on their solubilities in water and organic solvents. Understanding binder mechanisms is crucial for developing binders that maintain a strong adhesion to electrodes, even during volume fluctuations caused by lithiation and delithiation. Therefore, we investigated the different mechanisms associated with binders. This review also discusses failure mechanisms and innovative design strategies to improve the performance of binders, such as composite, conductive, and self-healing binders. By investigating these fields, we hope to develop energy storage technologies that are more dependable and efficient while also helping to satisfy future energy needs.

LiFePO₄ (LFP) batteries are well known for their long cycle life. However, there have been many reports of significant capacity degradation in LFP battery packs after only three to five years of operation. This study assesses the second-life potential of commercial LFP batteries retired from electric vehicles (EVs) by evaluating their aging characteristics at the cell and module levels. Four LFP cells and four modules were subjected to aging tests under various conditions. The results indicate that LFP cells exhibit long life cycles with gradual capacity degradation and minimal internal resistance increase. Module-level analysis reveals significant balance issues which impact capacity recovery. Incremental capacity analysis (ICA) and post-mortem analysis identify the loss of active materials and lithium inventory as key aging mechanisms. This study provides the optimal working conditions for LFP batteries and suggests that, with proper balancing systems, LFP batteries can achieve extended second-life use in stationary energy storage applications, emphasizing the importance of effective balance management for sustainable battery utilization.

Lithium-ion batteries are currently one of the most important energy storage devices for various applications. However, it remains a great challenge to achieve both high energy density and high power density while reducing production costs. Cells with three-dimensional electrodes realized by laser ablation have been proven to have enhanced electrochemical performance compared to those with conventional two-dimensional electrodes, especially at fast charging/discharging. Nevertheless, the laser structuring of electrodes is still limited in terms of the achievable processing speed, and the upscaling of the laser structuring process is of great importance to gain a high technology readiness level. In the presented research, the impact of different laser structuring strategies on the electrochemical performance was investigated on aqueous processed Li(Ni_0.6Mn_0.2Co_0.2)O₂ cathodes with acid addition during the slurry mixing process. Rate capability analyses of cells with laser-structured aqueous processed electrodes exhibited enhanced performance, with capacity increases of up to 60 mAh/g at high current density, while a 65% decrease in ionic resistance was observed for cells with laser-structured electrodes. In addition, pouch cells with laser-structured acid-added electrodes maintained 29–38% higher cell capacity after 500 cycles, and their end of life was extended by a factor of about four, in contrast with the reference cells with two-dimensional electrodes containing common organic solvent-processed polyvinylidene fluoride binder.

The escalating demand for lithium has intensified the need to process critical lithium ores into battery-grade materials efficiently. This review paper provides an overview of the transformation processes and cost of converting critical lithium ores, primarily spodumene and brine, into high-purity battery-grade precursors. We systematically examine the study findings on various approaches for lithium recovery from spodumene and brine. Dense media separation (DMS) and froth flotation are the most often used processes for spodumene beneficiation. Magnetic separation (MS) and ore gravity concentration techniques in spodumene processing are also considered. To produce battery-grade lithium salts, the beneficiated, concentrated spodumene must be treated further, with or without heat, in the presence of acidic or alkaline media. As a result, various pyro and hydrometallurgical techniques are explored. Moreover, the process of extracting lithium from brine through precipitation, liquid–liquid extraction, and polymer inclusion membrane separation employing different organic, inorganic, and composite polymer sorbents is also reviewed.

When the concentration of a gas is below its lower flammable limit and the content of a liquid is below its minimum explosible concentration, their combined fuel mixture can be ignitable. The flammability characteristics and inhibition strategies for battery emission mixtures deserve further in-depth research attention. This article presents experimental research on the ignition characteristics and inhibition strategy for a venting emission mixture of a failed LiFePO₄ battery. By identifying the components of venting emissions, ignition experiments for gases, electrolyte mist, their combination fuels, and mixtures with additives can be performed to determine the flammable parameters, including ignition sensitivity and severity. The hybrid combination of non-flammable venting gases and electrolyte mist has the potential to induce ignition. However, there still exists a non-ignition region, where the gas concentration ratio (m_g) is below 0.15 and the liquid concentration ratio (m_l) is below 0.1. The following safety design principle can be proposed: increasing ignition temperature, prolonging ignition time, and reducing maximum pressure. Adhering to this principle, a non-flammable electrolyte consisting of 1 mol LiPF₆ in EC:DEC = 1:1 vol%, with FEC at 10% and VC at 1%, can be considered as an optimization strategy. In comparison to the original gas–liquid mixtures, the region where no ignition occurs becomes wider when the m_g is below 0.45 and the m_l is below 0.3. The new two-phase mixture has an ignition temperature of 835 °C, which is 50% higher than that of the original mixture. Overall, this experimental research demonstrates an innovative methodology for assessing the venting emission mixture safety of the battery while proposing a design principle for modifying non-flammable electrolyte functional materials. Consequently, these findings can contribute to formulating more suitable preventive and protective measures for commercial electric vehicles and battery energy storage systems’ thermal safety designs.