Extreme Fast Charging Research Articles

Covalent Carbide Interconnects Enable Robust Interfaces and Thin SEI for Graphite Anode Stability under Extreme Fast Charging.

Carbonaceous and carbon-coated electrodes are ubiquitous in electrochemical energy storage and conversion technologies due to their electrochemical stability, lightweight nature, and relatively low cost. However, traditional reliance on conductive additives and binders leads to impermanent electrical pathways. Here, a general approach is presented to fabricate robust electrodes with a progressive failure mechanism by introducing carbide-based interconnects grown via carbothermal conversion of (5 wt%) titanium hydride nanoparticles. This method concurrently enhances both electrical and mechanical properties within the electrode architecture. The resulting chemical bonding between active materials establishes a novel mechanism to maintain stable electrical pathways during cycling. Employed as Li-ion battery anodes, these electrodes exhibit improved cyclability, achieving 80% capacity retention after 800 fast-charge cycles at moderate loading (1 mAh cm- 2). High loading cells with areal capacity of 3 mAh cm-2 show significantly improved cycle lifeover the same number of cycles. This performance improvement is attributed to the absence of significant impedance growth and a thinner solid electrolyte interphase (SEI) layer formed at high current densities (4C) as demonstrated by X-ray photoelectron spectroscopy and transmission electron microscopy studies. The enhanced conductivity facilitates SEI formation, lowering ionic impedance and mitigating lithium plating, ultimately leading to the reported extended cycle life.

Multistage Linkage Internal Exclusion External Electrolyte Tactic Unlocks Extreme Fast Charge Lithium Metal Batteries.

Lithium metal batteries are booming because of their inherent preponderance, but a negative electric field from concentration dipolarization and slow solid-phase transfer at the electrode interface become blocking modules for extreme fast charging. Achieving an anion-rich solvation shell with a high dielectric constant (ε) is a feasible strategy to bootstrap an interface microenvironment for mass-transport reaction, but it is still an uncultivated field. Herein, the superposition, including the donor number values, the high ε, and the spatial potential resistance, are complementarily considered; we propose a low-cost electrolyte with an internal excluding external tactic to answer the above issue. Explanatorily, an optimized solvation shell follows the cascading exclusion relationship of nitrate ion (NO3-) → tetraglyme → ethylene carbonate → dimethyl carbonate. And the culminated bilayer structure establishes ideal conditions for Li+ transfer-reaction kinetics, of which an anion-rich internal shell facilitates solid-phase transport and a high-ε external shell slashes the negative electric field.

(Energy Technology Division Graduate Student Award sponsored by BioLogic) In-Situ, Non-Destructive, 3D Neutron Imaging of Lithium Plating Following Extreme Fast-Charging of Full-Cell Lithium-Ion Batteries

One of the primary challenges impeding extreme fast-charging (XFC) of current lithium-ion batteries (LIBs) for electric vehicles (EVs) within 10–15 minutes is the deposition of Li metal on graphite known as “Li plating”.1-2 After Li plates, it either re-intercalates into the graphite electrode or is stripped off during battery discharging to form “active Li”or becomes electronically disconnected resulting in “dead Li.” Previous studies have indicated that dead Li is the main contributor to the XFC-related capacity loss of LIBs. However, mechanistic understanding of the 3D morphological behavior and spatial heterogeneities of dead Li; and how they differ from those of plated and active Li during the XFC is not well understood.3-4 Here, we present an in-situ, non-destructive 3D characterization of the morphological behavior and spatial heterogeneities of plated, dead, and active Li on graphite electrodes in full-cell LIBs using high-resolution neutron micro-computed tomography. We performed neutron µCT5 (pixel size: ~ 5.74 µm; effective spatial resolution: ~10-15 µm) at the ICON beamline6 at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. We imaged two batteries in the charged and discharged states: (1) after 4 cycles of 1C charging and (2) after 6 cycles of 6C charging.Our results show that Li plates at and around the edges of the graphite electrodes, indicating that graphite edges and the areas around these edges are the most susceptible to Li plating. However, certain edges and areas around these edges formed dead Li whereas others formed active Li, suggesting 3D spatial heterogeneities in the formation of dead and active Li at both 1C and 6C. Mainly, we discuss these heterogeneities at four regions: (1) near the Cu CC, (2) in the middle of the graphite electrode, (3) near the graphite-separator interface, and (4) in the separator. Specifically, we found that Li near the Cu CC remains active whereas most of the plated Li at the graphite-separator interface and in the separator becomes dead at both 1C and 6C.Morphologically, we observed porous nature of plated and dead Li at both 1C and 6C. Our 3D visualizations noticeably show nodules of varying densities of metallic Li. However, we observed different 3D behavior of Li plating at 1C and 6C. For example, tip-like Li deposits were seen laterally closer to the center of the graphite electrode, near the graphite-separator interface, and into the separator at 6C. In contrast, at 1C, no tip-like Li deposits were observed near the graphite-separator interface and into the separator. Based on our findings, we concluded that higher XFC-charging rate and cycling number (6 cycles of 6C charging) cause the formation of tip-like Li deposits as compared to the relatively slower XFC-charging rate and cycling number (4 cycles of 1C charging). We believe that insights derived from this work will guide the design of thick graphite electrodes with minimized-plating for fast-charged EVs.

Prelithiated Silicon Anodes for High-Energy and High-Power Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are pivotal in powering modern electronic devices and next-generation land and air electric vehicles. Silicon-based anodes are considered the next technology to replace traditional graphite anodes due to their high theoretical capacity. However, the inherent challenges associated with their large volume expansion and high irreversible capacity loss (IRCL) limit their practical application. This abstract explores our patented strategy of prelithiation as a viable approach to mitigate the IRCL limitations of SiOx dominant anodes. Prelithiation involves the precise addition of supplemental lithium into the anode, mitigating the adverse effects of initial lithiation and enhancing overall cyclability, energy, power, and extreme fast charge capability for silicon oxide dominant LIBs. Various prelithiation techniques, including Li powder, Li slurry, Li-foil, and the chemical doping of SiOx are examined to evaluate their effectiveness in providing supplemental lithium. The effectiveness of the prelithiation process is assessed by examining the impact on the structural stability, cycling performance, power capability, and rate capability of SiOx dominant anodes integrated into high-capacity (~30 Ah) pouch cells. Our focus is to emphasize prelithiation as a practical and scalable solution to enhance the electrochemical performance of SiOx dominant anodes, contributing to the development of high-energy and high-power LIBs enabling advanced air mobility and high-performance electric vehicles. The findings presented in this abstract contribute to the growing body of knowledge aimed at advancing the fundamental understanding and practical implementation of prelithiation as an enabler for SiOx-based anodes in LIBs. Figure 1

Ionblox’s SiOx-Based, High-Energy, High-Power Li-Ion Battery for Performance Electric Vehicles and Electric Aviation

Demands on land-based, high-performance electric vehicles (EVs) and electric aviation, by means of electric conventional takeoff and landing aircraft (eCTOLs) and electric vertical takeoff and landing aircraft (eVTOLs) demand more on a secondary cell chemistry than ever before. There are many secondary cells on the market that offer energy density, power density, fast-charge capability, or cycle life, but few, if any other manufacturing-ready cells, offer a combination of all four. IONBLOX has solved this by pairing it’s patented, Pre-lithiated SiOx anode with a high nickel, NMC cathode to produce cells exceeding 330 wh/kg. Herein we describe the performance of our 32 Ah cell, featuring high-energy density, high-power density, extreme fast charge capability, and good cycle life, within a package that is already in production.In particular, challenges for the eVTOL market will be addressed, which require peak power demand on the cell at low state-of-charge, without reducing the energy density. Methods for characterizing cells for such high-power applications will be further explored. DCIR pulse characterization and more customized testing like usable energy testing, which is important for identifying the applicable energy density for high-power use cases, will be demonstrated. Additionally, extreme fast charge capability is described on our large format cells with 5 min charge to >60% total cell capacity, over 1000 cycles. This shows such a cell is up to the expectations of a consumer familiar with the timing of a standard gasoline pump. Contribution from the information presented herein demonstrates the state of Si-based anode chemistry and can serve as useful guidelines to the academic community as future technologies are pursued for similar applications Figure 1

Investigation of 40 Ah Prismatic Batteries Operating Under Fast-Charge Conditions Using Operando Synchrotron XRD Technique

The pressing challenges posed by the energy crisis and the impact of climate change have forced a gradual replacement of traditional internal combustion engine (ICE) automobile powertrains with electrochemical energy storage devices. However, a boost of the electric vehicles (EVs) market, by significant battery performance enhancements are consistently required, primarily due to numerous persistent concerns. One of the key features targeted by battery and EVs industries is the rapid charging capability, making EVs more competitive with the quick refueling of traditional gasoline vehicles. Notably, despite the clear benefits of fast charging technology, the accelerated battery degradation after fast and extreme fast charging raises on top of the drawbacks of this technology. Therefore, understanding of heterogeneity and structural transformations within battery systems is of high interest.In this regard, we attempt to investigate the structural properties of a LiNi1/3Mn1/3Co1/3O2 (NMC111) /graphite fresh industrial prismatic cell using synchrotron XRD under fast charge conditions. The investigated battery is a PHEV cell with an experimental capacity of 40 Ah. It was taken from a range rover vehicle pack after being disassembled. The evolution of the composite anode and cathode structures was followed by operando wide-angle X-ray scattering (WAXS). Using this approach, we were able to measure and quantify the different phases of graphite and NMC111 lithiation/delithiation at various potentials by analyzing the corresponding Bragg peaks. By that, we were able to detect some heterogeneities in the degree of lithiation/delithiation within the cell upon charge. In addition, a comparison between a fresh cell and another aged cell, with a state of health (SOH) of 88%, was made in order to investigate the effect of aging under fast charging conditions on the performance of the industrial LIBs.

Ferrocene-Based Polymer Organic Cathode for Extreme Fast Charging Lithium-Ion Batteries with Ultralong Lifespans.

To meet the growing demand for energy storage, lithium-ion batteries (LIBs) with fast charging capabilities has emerged as a critical technology. The electrode materials affect the rate performance significantly. Organic electrodes with structural flexibility support fast lithium-ion transport and are considered promising candidates for fast-charging LIBs. However, it is a challenge to create organic electrodes that can cycle steadily and reach high energy density in a few minutes. To solve this issue, accelerating the transport of electrons and lithium ions in the electrode is the key. Here, it is demonstrated that a ferrocene-based polymer electrode (Fc-SO3Li) can be used as a fast-charging organic electrode for LIBs. Thanks to its molecular architecture, LIBs with Fc-SO3Li show exceptional cycling stability (99.99% capacity retention after 10 000 cycles) and reach an energy density of 183Wh kg-1 in 72 seconds. Moreover, the composite material through insitu polymerization with Fc-SO3Li and 50 wt % carbon nanotube (denoted as Fc-SO3Li-CNT50) achieved optimized electron and ion transport pathways. After 10000 cycles at a high current density of 50C, it delivered a high energy density of 304Wh kg-1. This study provides valuable insights into designing cathode materials for LIBs that combine high power and ultralong cycle life.

Extreme Fast Charging of Lithium Metal Batteries Enabled by a Molten-Salt-Derived Nanocrystal Interphase.

The extreme fast charging performance of lithium metal batteries (LMBs) with a long life is an important focus in the development of next-generation battery technologies. The friable solid electrolyte interphase and dendritic lithium growth are major problems. The formation of an inorganic nanocrystal-dominant interphase produced by preimmersing the Li in molten lithium bis(fluorosulfonyl)imide that suppresses the overgrowth of the usual interphase is reported. Its high surface modulus combined with fast Li+ diffusivity enables a reversible dendrite-proof deposition under ultrahigh-rate conditions. It gives a record-breaking cumulative plating/stripping capacity of >240000 mAh cm-2 at 30mA cm-2@30 mAh cm-2 for a symmetric cell and an extreme fast charging performance at 6 C for 500 cycles for a Li||LiCoO2 full cell with a high-areal-capacity, thus expanding the use of LMBs to high-loading and power-intensive scenarios. Its usability both in roll-to-roll production and in different electrolytes indicating the scalable and industrial potential of this process for high-performance LMBs.

Temperature-dependence vanadium regulation for extreme fast charging LiFePO4 cathode materials with multilevel core-shell structure

Lithium-ion batteries (LIBs) with LiFePO4 cathode are widely used in electric vehicles and energy storage systems owing to their cost-effectiveness and safety. However, this type of LIBs is limited by poor fast-charging capabilities owing to the inherent poor electronic conductivity and one-dimensional ionic pathways. Herein, we show that the approach of temperature-dependence vanadium (V) regulation can greatly improve the Li+ diffusion dynamics both in bulk and at interface, leading to the achievement of ultrafast charging/discharging capability of LiFePO4-based LIBs. The formation of V3+ doping induced Fe-site vacancy in bulk and Li3V2(PO4)3 phase at interface with high ionic conductivity can be achieved at the optimal conditions of 700°C and 0.10 V content. Additionally, this regulatory V effect endows the LiFe1-3/2xVxPO4 (LFVP) materials with a specific multilevel core-shell structure. Consequently, the optimal LFVP-0.10-700 sample delivers high specific capacities of 169.6 mAh g−1 at 0.1 C with an excellent capacity retention of 97.5 % after 200 cycles at 1 C, as well as ∼100 mAh g−1 at an ultrahigh rate of 50 C for 3500 cycles. These performances make LiFePO4 cathode possible for extreme fast charging LIBs.

Fast-Charging Phosphorus-Based Anodes: Promises, Challenges, and Pathways for Improvement.

Fast-charging batteries are highly sought after. However, the current battery industry has used carbon as the preferred anode, which can suffer from dendrite formation problems at high current density, causing failure after prolonged cycling and posing safety hazards. The phosphorus (P) anode is being considered as a promising successor to graphite due to its safe lithiation potential, low ion diffusion energy barrier, and high theoretical storage capacity. Since 2019, fast-charging P-based anodes have realized the goals of extreme fast charging (XFC), which enables a 10 min recharging time to deliver a capacity retention larger than 80%. Rechargeable battery technologies that use P-based anodes, along with high-capacity conversion-type cathodes or high-voltage insertion-type cathodes, have thus garnered substantial attention from both the academic and industry communities. In spite of this activity, there remains a rather sparse range of high-performance and fast-charging P-based cell configurations. Herein, we first systematically examine four challenges for fast-charging P-based anodes, including the volumetric variation during the cycling process, the electrode interfacial instability, the dissolution of polyphosphides, and the long-lasting P/electrolyte side reactions. Next, we summarize a range of strategies with the potential to circumvent these challenges and rationally control electrochemical reaction processes at the P anode. We also consider both binders and electrode structures. We also propose other remaining issues and corresponding strategies for the improvement and understanding of the fast-charging P anode. Finally, we review and discuss the existing full cell configurations based on P anodes and forecast the potential feasibility of recycling spent P-based full cells according to the trajectory of recent developments in batteries. We hope this review affords a fresh perspective on P science and engineering toward fast-charging energy storage devices.

Dominant Solvent-Separated Ion Pairs in Electrolytes Enable Superhigh Conductivity for Fast-Charging and Low-Temperature Lithium Ion Batteries.

The low ionic conductivities of aprotic electrolytes hinder the development of extreme fast charging technologies and applications at low temperatures for lithium-ion batteries (LIBs). Herein, we present an electrolyte with LiFSI in acetone (DMK). In DMK electrolytes, the solvation number is three, and solvent-separated ion pairs (SSIPs) are the dominant structure, which is largely different from other linear aprotic electrolytes where salts primarily exist as contact ion pairs (CIPs). With incompact solvation structures due to the weak solvation ability of DMK with Li+, the ionic conductivity reaches 45 mS/cm at room temperature. The percentage of SSIPs increases as temperatures decrease in DMK electrolytes, which is totally different from the carbonate-based electrolytes but greatly beneficial to low-temperature ionic conductivity. With the appropriate addition of VC and FEC, DMK-based electrolytes still exhibit a superhigh ionic conductivity. Even at -40 °C, the ionic conductivity is greater than 10 mS/cm. With DMK-based electrolytes, LIBs with thick LiFePO4 electrodes can be cycled at high rates and at low temperatures.

Multilayered Energy Management Framework for Extreme Fast Charging Stations Considering Demand Charges, Battery Degradation, and Forecast Uncertainties

To achieve a cost-effective and expeditious charging experience for extreme fast charging station (XFCS) owners and electric vehicle (EV) users, the optimal operation of XFCS is crucial. It is however challenging to simultaneously manage the profit from energy arbitrage, the cost of demand charges, and the degradation of a battery energy storage system (BESS) under uncertainties. This paper, therefore, proposes a multi-layered multi-time scale energy flow management framework for an XFCS by considering long- and short-term forecast uncertainties, monthly demand charges reduction, and BESS life degradation. In the proposed approach, an upper scheduling layer (USL) ensures the overall operation economy and yields optimal scheduling of the energy resources on a rolling horizon basis, thereby considering the long-term forecast errors. A lower dispatch layer (LDL) takes the short-term forecast errors into account during the real-time operation of the XFCS. Per the latest research, monthly demand charges can be as high as 90% of the total monthly bills for EV fast charging stations; to this end, this paper takes the first attempt at the reduction of demand charges cost by considering the trade-off between the energy cost and monthly demand charges. Contrasting literature, this work allocates an energy reserve in the BESS stored energy to deal with the impact of short-term forecast errors on the optimized real-time operation of the XFCS. Moreover, degradation modeling considers the trade-off between short-term benefits and long-term BESS life degradation. Lastly, case studies and a comparative analysis prove the efficacy of the proposed framework.

Decoupling Interfacial Kinetics Realizes 5C Fast Charging of Potassium‐Ion Batteries Using Graphite Anode

AbstractImproving interfacial kinetics is the key to realizing extreme fast charging (XFC) of graphite‐based potassium ion batteries (PIBs). The electrolyte engineering is commonly used for solid electrolyte interphase (SEI) design. However, this strategy adjusts both ion solvation structure and (de)solvation kinetics simultaneously, thus making it difficult to explicitly reveal the linkage between SEI properties and interfacial kinetics. Herein, the content of inorganic species in preformed SEI on graphite surface is precisely regulated and uncovered its critical role in improving the interfacial kinetics. The charge transfer kinetics on graphite/electrolyte interphase is found to be the rate limitation step upon XFC. Meanwhile, the increased inorganic species in SEI plays a decisive role in optimizing the charge transfer rather than the kinetics of naked K+ crossing SEI. Through unlocking the anodic charge transfer limitation with ultra‐inorganic rich SEI, the graphite//Prussian blue analogs full cells achieve a superior XFC ability (13 min charge to 80%) with a specific capacity of 103 mAh g−1 at 5 C. This work provides a fundamental understanding of the relationship between SEI properties and interfacial kinetics during XFC, which enables the rational design of SEI chemistry for fast‐charging PIBs.

A multi-functional electrolyte additive for fast-charging and flame-retardant lithium-ion batteries

A multi-functional electrolyte additive, namely ethoxy(pentafluoro)cyclotriphosphazene, is explored to realize extreme fast charging of lithium-ion batteries with enhanced safety.

Covalently Joined Electrode Architectures for Extreme Fast Charging Li-Ion Batteries

Li-ion batteries are the backbone of all electric vehicles (EVs) in production today [1]. However, they compete poorly against the few-minute refueling time of fossil fuel powered vehicles [2, 3]. To successfully replace fossil fuel powered vehicles, the EV batteries must support charging rates under the 15-minute mark as determined by the eXtreme Fast Charging (XFC) standard defined by the U.S. Department of Energy [4]. When subjected to XFC charging rates, well-known problems of lithium plating and delamination plague graphite anodes due to local potential gradients and binder degradation respectively [5].Our work replaces the traditional polymer binder with conductive titanium carbide interconnects that covalently join graphite particles as well as bond them to the current collector [6]. This new architecture demonstrates ~400% increase in electrical conductivity compared to traditional architectures with polymer binders while maintaining interparticle integrity and improving adhesion. The adhesion and mechanical properties are provided by conductive chemical bonds mitigating delamination as these novel bonds suffer less mechanical and chemical degradation under high current rates than adhesion provided by polymer binders. The improved conductivity was also utilized to form a solid electrolyte interphase (SEI) at rates up to 4C reducing the ionic impedance of the SEI interface significantly [7]. The improved graphite electrodes can sustain 15-minute charge maintaining 80% of the specific capacity of the graphite particles for 800 cycles at commercially relevant loadings. Our studies introduce an effective strategy to engineer Li-ion battery electrode architectures that simultaneously improve electrical and ionic conductivity mitigating lithium plating and delamination under XFC charging rate needed for the mass adoption of EVs. Habib, A.A., S. Motakabber, and M.I. Ibrahimy. A comparative study of electrochemical battery for electric vehicles applications. in 2019 IEEE International Conference on Power, Electrical, and Electronics and Industrial Applications (PEEIACON). 2019. IEEE.Balali, Y. and S. Stegen, Review of energy storage systems for vehicles based on technology, environmental impacts, and costs. Renewable and Sustainable Energy Reviews, 2021. 135: p. 110185.Andwari, A.M., et al., A review of Battery Electric Vehicle technology and readiness levels. Renewable and Sustainable Energy Reviews, 2017. 78: p. 414-430.Dufek, E.J., et al., Developing extreme fast charge battery protocols–A review spanning materials to systems. Journal of Power Sources, 2022: p. 231129.Ahmed, S., et al., Enabling fast charging–A battery technology gap assessment. Journal of Power Sources, 2017. 367: p. 250-262.Rangom, Y., Covalently Joined Carbonaceous and Mettalloid Powders by Carbide-Based Interconnects and Method of Fabrication for High-Performance Electrodes. 2021: United States preliminary patent #63/248,293.Rangom, Y., T.T. Duignan, and X. Zhao, Lithium-ion transport behavior in thin-film graphite electrodes with SEI layers formed at different current densities. ACS Applied Materials & Interfaces, 2021. 13(36): p. 42662-42669. Figure 1

3D Progression of Dead Li on Graphite Electrodes during Extended Fast Charging

Long charging times of commercial lithium-ion batteries (LIBs) constitute one of the critical remaining bottlenecks in the widespread deployment of electric vehicles (EVs). Therefore, there is a global push towards extreme fast charging (XFC)1in 10–15 minutes for 80% of the pack capacity. However, existing LIBs cannot achieve these XFC goals without significant capacity fade during cycling over battery lifetime.2 One of the key XFC degradation mechanisms is “Li plating,” which occurs when Li metal forms on the graphite electrode due the liquid electrolyte and solid-phase (graphite) mass transport limitations and sluggish charge-transfer kinetics of the Li intercalation reaction.3 This is mostly attributed to the formation of dead Li,4 which is the irreversibly plated Li that has become electronically disconnected from the graphite electrode. Since dead Li constitutes most of the XFC-related capacity loss, it is extremely important to unravel the link between its morphological evolution/progression, and battery capacity fade during extended XFC cycling.In this work, we report non-destructive, in-situ three-dimensional (3D) characterization of dead Li on graphite electrodes in full-cell LIBs during extended XFC using high-resolution (pixel size: ~ 7.8 µm; effective spatial resolution: ~25-30 µm) neutron micro-computed tomography (µCT). Specifically, we imaged batteries in the discharged state at the following cycle numbers at 6C charging rate: 10, 25, 50, and 150 cycles. Neutron µCT is promising for in-situ 3D Li detection on graphite electrodes because it provides strong contrast between Li and C (~ 71.87: 5.55 barns5). To leverage high-resolution neutron µCT for this work, we designed a custom neutron-friendly LIB coin-cell that provided exceptional neutron transmission at the graphite-separator-electrolyte interface as well as standard XFC performance at 6C between 3.0 and 4.1 V. We performed these imaging experiments at the MARS (CG-1D) beamline6 at the High Flux Isotope Reactor, Oak Ridge National Laboratory.Our results reveal 3D evolution of dead Li morphology from isolated plated deposits on only one edge of the graphite electrode after 25 cycles at 6C charging, to increasingly mossy-like covering the entire circumference of the graphite electrode after 150 cycles. Based on our imaging data, we did not observe any dead Li after only 10 XFC cycles. However, we noticed that dead Li started to nucleate around a partial edge of the graphite electrode after 25 XFC cycles, and then grew to the other edges after 50 XFC cycles, eventually forming a complete ring after 150 XFC cycles. At 150 XFC cycles, we also observed the dead Li ring outgrowths away from the edges of the graphite electrode onto the separator. In the extended XFC-cycled samples, 50 and 150 XFC cycles, we found significant dried out salt deposits on the separator, spacers, spring, and casing, which may be due to other parasitic reactions occurring at increased XFC cycling. Lastly, we determined quantitative relationships between the amount of dead Li in 3D, XFC cycling number, and XFC-related capacity loss of the battery.In conclusion, this work contributed to the advanced understanding of the 3D progression of dead Li and its relationship with XFC-related capacity loss on graphite electrodes during extended XFC cycling. We believe insights from this work will help develop improved 3D graphite electrode architectures that will minimize Li plating during repeated XFC cycling in fast-charged LIBs.

Optimizing Extreme Fast Charging Strategy for Lithium-Ion Batteries: A Model Predictive Control Approach

With the increasing demand for extreme fast charging (XFC) in electric vehicles (EVs), there is an urgent need to develop health-conscious fast charging strategies for lithium-ion batteries. However, simply increasing the charging current can disproportionately accelerate battery aging, resulting in severe capacity and performance loss, while posing unacceptable safety risks during operation. In addition, the battery management system (BMS) needs to know the state of each cell for reliable and accurate management, but this involves significant computational burden. In other words, new fast charging strategies need to be developed to solve the dilemma between charging rate, battery aging, and computational complexity.In this work, we propose a novel framework for modelling, estimating, and balancing different types of state heterogeneities in a multi-cell battery module. This framework facilitates the development of optimal fast charging strategies based on battery electrochemical models and model predictive control (MPC). First, an electrochemical and thermal coupling model is formulated at the unit cell level, and a module model is formulated at the system level, taking into account various factors such as connection resistances and system terminals. Then, a non-linear MPC is used to achieve fast charging while considering the health of the battery module. Battery performance is tracked by accurately estimating the battery's internal state, which can support the balancing of all state heterogeneity types represented in the model by controlling the charging current according to the internal state. The proposed framework has three main advantages: (1) The modelling strategy has a flexible and configurable structure that can be applied to battery modules of any size. Using this, (2) the internal state of the battery can be estimated with reduced computational complexity. (3) MPC can be applied to cell-to-cell balancing and XFC strategy. The results of the proposed method provide important insights for achieving XFC and show promise for real-time online estimation and control. Figure 1

3D Morphological Evolution of Dead and Active Lithium at the Graphite-Separator-Electrolyte Interface during Fast Charging

Lithium-ion batteries (LIBs) have profoundly advanced the development of electric vehicles (EV). However, one of the remaining bottlenecks in the widespread adoption of EVs is the long charging time required for commercial LIBs. There is a global push towards extreme fast charging (XFC) to reduce charging times to 10-15 minutes.1 However, XFC results in rapid degradation in the electrochemical performance of batteries, mainly due to Li plating. This plating refers to the loss of active Li, where it either becomes dead meaning electronically disconnected after plating on the anode, or it becomes inactive due to the irreversible reaction of Li with the electrolyte to form a solid electrolyte interphase. Dead Li contributes significantly to capacity loss during XFC;3 thus, differentiating dead and inactive from active Li is extremely important to unravel their link with battery capacity fade. However, owing to the complexity of these competing electrochemical reactions in addition to the intricacy of detecting Li at the buried graphite-separator-electrolyte interface, a comprehensive understanding of Li plating remains a challenge.In this work, we conducted non-destructive, in-situ three-dimensional (3D) characterization of dead and active Li on energy-dense graphite electrodes during XFC using high-resolution neutron micro-computed tomography (µCT). Thick or industry-relevant (negative and positive electrodes ~ 130 μm) graphite electrodes are promising battery materials because they store higher amounts of energy. However, they plate Li faster and at lower XFC cycle numbers, and hence experience higher loss in battery capacity due to Li plating.To characterize Li plating on thick graphite electrodes, we performed high-resolution neutron µCT4 (pixel size: ~ 5.74 µm; effective spatial resolution: ~10-15 µm) at the ICON beamline5 at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. Neutron µCT was used because it provides high relative neutron contrast between Li and C (~ 71.87: 5.55 barns6) for in-situ 3D imaging. Therefore, to leverage high-resolution neutron µCT for in-situ Li detection, we designed a neutron-friendly LIB. Our designed battery enabled excellent neutron transmission at the graphite-separator-electrolyte interface while exhibiting similar XFC performance at a 6C charging-rate between 3.0 and 4.1V. We imaged three batteries in the charged and discharged states under the following conditions: 4 cycles at 1C charging; 4 and 6 cycles at 6C charging. Here, we note that since inactive Li was below the spatial resolution of the ICON beamline, only dead, active, and plated Li were investigated in this work.Our results reveal changes in dead Li morphologies from isolated deposits after 4 cycles at 1C charging to increasingly mossy-like dense deposits covering the entire circumference of the graphite electrode after 6 cycles at 6C charging. Furthermore, as the XFC cycle number increased from four to six at 6C charging, the amount of dead Li increased significantly. After 6 cycles at 6C charging, we also observed dead Li outgrowths in a circular geometry onto the separator around the graphite electrode. Using our imaging data, we determined a quantitative link between the amounts of dead and active Li with the capacity loss of the battery. Our analysis suggests that the amounts of plated and dead Li increase with the charging rate and cycle number. Finally, we developed quantitative relationships in 3D between the amounts of dead, active, and plated Li, and XFC-related capacity loss of the battery.In conclusion, this work contributed to the advanced understanding of the morphological evolution of dead, active, and plated Li and their relationship with XFC-related capacity loss on thick graphite electrodes. We believe these insights will help inform rational 3D designs of thick graphite electrodes that will minimize Li plating in fast-charged LIBs.

Towards Extreme Fast Charging of 4.6 V LiCoO2 Viamitigating High-Voltage Kinetic Hindrance

High-voltage LiCoO2 (LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries (LIBs) in the 3 C markets. However, the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that the kinetic limitations can be mitigated by a facial Mg2++Gd3+ co-doping method. The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage, making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process. The homogeneity enables the structural stability of LCO at a high-rate current density, inhibiting stress accumulation and irreversible phase transition. When used in combination with a Li metal anode, the doped LCO shows an extreme fast charging (XFC) capability, with a superior high capacity of 193.1 mAh g−1 even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C. This work provides a new insight to prepare XFC high-voltage LCO cathode materials. Figure 1

Extreme Fast Charging of High Energy Density Lithium Ion Battery

The demand for high-energy-density batteries using Ni-rich cathodes is increasing due to the continuous expansion of the electric vehicle (EV) market. U.S. Department of Energy has stated the need for extreme-fast-charging (XFC) batteries that achieve an 80% state of charge (SOC) in less than 15 min. However, Ni-rich cathodes tend to lose capacity quickly under XFC conditions, which compromises their structural integrity. In addition, XFC conditions rapidly generate significant heat due to the high current applied to the cell, leading to the degradation of cell components. It is challenging to create Ni-rich cathodes that can withstand XFC conditions while still maintaining maximum energy density and long-term cycling performance. In this study, a cathode called Li[Ni0.92Co0.06Al0.01Nb0.01]O2 (Nb-NCA93) is introduced, which has a high energy density of 869 Wh kg-1. The presence of Nb in the cathode induces grain refinement in its secondary particles, reducing internal stress and preventing heterogeneity of Li concentration during cycling. When used in a full-cell, the Nb-NCA93 cathode reaches full charge within 12 minutes and retains 85.3% of its initial capacity after 1000 cycles, cycled at full depth of discharge. Furthermore, the refined microstructure of the Nb-NCA93 cathode limits heat generation under XFC conditions. References H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155 C. S. Yoon, H.-H. Ryu, G.-T. Park, J.-H Kim, K.-H. Kim, Y.-K Sun, J. Mater. Chem. A 2018, 6, 4126 U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2019, 9, 1803902