Fast Charging Conditions Research Articles

Effect of Disorder and Doping on Electronic Structure and Diffusion Properties of Li3V2O5

V2O5 in its ω phase (Li3V2O5) with excess lithium is a potential alternative to the graphite anode for lithium-ion batteries at low temperature and fast charging conditions owing to its safer voltage (0.6 V vs Li+/Li(s)) and high lithium transport rate. In-operando cationic disorder, as observed in most ordered materials, can produce significant changes in charge compensation mechanisms, anionic activity, lithium diffusion, and operational voltages. In this work, we report the variation in structural distortion, electronic structure, and migration barrier accompanied by disorder using first-principles calculations. Owing to the segregation of lithium atoms in the disordered state, we observe greater distortion, emergence of metallic behavior, and potential anionic activity from nonbonding oxygen states near the Fermi level. Redox capacity can be tuned by doping with 3d metals, which can adjust the participating cationic states, and by fluorine substitution, which can stabilize or suppress anionic states. Moreover, the suppression of anionic activity is found to decrease structural distortion, which is crucial for mitigating voltage fade and hysteresis. Diffusion barrier calculations in the presence of disorder indicate the activation of the remaining 3D paths for lithium hopping which are unavailable in the ordered configuration, explaining its fast-charging ability observed in experiments.

Atomistic modeling of LiF microstructure ionic conductivity and its influence on nucleation and plating

The formation and degradation of the solid electrolyte interphase (SEI) and its underlying transport properties play an essential role in the overall performance of lithium-ion batteries. This paper presents classical molecular dynamics studies on polycrystalline inorganic lithium fluoride (LiF) layers to model and predict the SEI transport properties. The ionic conductivity is obtained from the lithium-ion diffusivity in polycrystalline structures of LiF using the Nernst-Einstein relation. The predicted molecular dynamics data are used in a continuum scale phase-field model to evaluate the plating kinetics under fast charging conditions. The analysis emphasizes that the SEI ionic conductivity properties impact the plating dynamics, where SEI's low ion conductivity value is prone to large plating and subsequent capacity degradation. The combination of atomic and continuum scale studies shown herein lays a foundation to tune in SEI transport properties to decrease the amount of lithium plating and improve the performance of fast-charging batteries.

Effects of Fast Charging Modes on Thermal Performance of Lithium‐Ion Battery

Fast charging technology can greatly increase the charging speed and shorten the charging time of electric vehicles, but the heat generation and temperature rise of the lithium‐ion battery during the fast charging process seriously affect its electrochemical characteristics and cycle life and even cause safety issues. Therefore, it is necessary to analyze the thermal performance of the lithium‐ion battery under fast charging conditions and investigate the effects of different fast charging modes on it. Herein, an NMC lithium‐ion cell is taken as the object, and the electrochemical–thermal coupling model is built and verified. Based on this model, the heat generations and temperature rises of the cell in different fast charging modes are analyzed and compared, including constant current (CC) charging, constant voltage (CV) charging, CC–CV charging, stage CC charging, and pulse charging. It is found that the peak temperature of the cell appears at different moments in the above charging modes. The peak temperature and total heat generation during CV charging are much greater than those during charging of other modes. The results can provide references for the design and selection of charging modes and battery thermal management systems toward fast charging technology.

Remaining useful life prediction method of EV power battery for DC fast charging condition

To realize the online rapid prediction of the remaining useful life (RUL) of electric vehicle (EV) power battery under direct current (DC) fast charging conditions and reduce the influence of complex health indicator (HI) on the prediction accuracy, an adaptive prediction method of the RUL of EV power battery based on whale swarm algorithm–long short-term memory (WSA-LSTM) algorithm is proposed in this paper. Firstly, a complete set of HI is built based on a dynamic data-driven application system (DDDAS) to ensure the real-time combination of condition monitoring data and simulation systems. Then, combined with the calculation of Pearson and Spearman correlation coefficients and the entropy weight method, the main features that affect the battery capacity are screened out to reduce the interference of secondary HI on RUL prediction. Thirdly, the whale swarm algorithm is used to globally optimize the hyperparameters of the long short-term memory to achieve rapid RUL prediction. Finally, we conduct simulation experiments based on real-time data under EV DC charging conditions. The simulation results show that the HI screening method proposed in this paper is effective, and the RUL prediction method can achieve a fast and accurate prediction of DC fast charging conditions.

Development of a hybrid battery thermal management system coupled with phase change material under fast charging conditions

A compact battery thermal management system (BTMS) coupled with a phase change material (PCM) is proposed to improve its performance under fast charging conditions. A battery thermal model and two-phase PCM simulation model were developed and validated through experimental data, and a parametric study was conducted by changing the parameters of the PCM and operating conditions of the liquid cooling system. As a result, in the proposed system, the highest maximum temperature of the battery module was 38.4 °C and maximum temperature difference was 3.9 °C during the charge–discharge cycle, and both of these values were simultaneously maintained within the proper range. The aforementioned values were 13.2 °C and 10.8 °C lower than the corresponding values for the conventional liquid cooling method. In addition, through the optimal operating conditions, sufficient heat dissipation was achieved while shortening the operating time of the liquid cooling system by 12.4 % of the total time. Finally, the heat absorbed by the PCM was dissipated sufficiently during the cycle. Therefore, the proposed BTMS is not only effective in terms of its cooling performance but also sufficiently usable in the continuous cycle.

Investigation of Graphite Electrode Degradation in Lithium-Ion Cells Using 4D-STEM

The development of longer lasting and faster charging lithium-ion batteries (LIBs) remains a critical engineering priority for the U.S. Department of Energy. To enable the next-generation technology, it is essential to understand the nature and extent of materials failure during battery operation. Under fast-charging conditions, it has been shown that graphite particles, which comprise the active material of the LIB anode, suffer irreversible material degradation that limits ultimate battery performance. This damage to the graphite manifests as turbostratic lattice disorder, severe morphological roughening, and anode swelling [1]. While these findings are essential to understand the nature of damage to the anode under fast-charge conditions, it remains to be seen whether such damage occurs at slower rates or is instead accelerated by extreme rate conditions and aging. In this regard, the recent advances in high-resolution electron microscopy (HREM) and four-dimensional scanning transmission electron microscopy (4D-STEM) methods provide the essential tools to enable nanoscopic quantification of battery degradation [2], [3].In this work, we use advanced analytical electron microscopy and diffraction strategies to analyze nanoscopic degradation of graphite anode material under different cycling rate and aging conditions. The results of this work will demonstrate novel strategies for identifying nanoscale structural disorder that arise in battery materials as well as provide key understanding of graphite material failure to aid in the development of high-performance anode materials. We study (in post-mortem) the graphite particle cross-sections harvested from LIBs at different aging conditions for both C/2 (i.e., 2 hours to full charge) and 6C (i.e., 10 minutes to full charge) rate. At the nano- to atomic-scale, we rely primarily on aberration-corrected STEM for imaging and diffraction acquisition for each sample (see Figure 1 for the results). High resolution imaging reveals the extent of lattice disorder and amorphous character localized at graphite pore edges. The 4D-STEM data helps to further quantify the extent and distribution of nanoscale structural disorder (including permanent strain and turbostratic disorder). The experimental methods employed to acquire the datasets and the strategies employed to interpret the data to understand the nature of the resulting damage, including recent progress into Cepstral STEM, will be discussed. Additional supporting evidences of graphite disorder from Raman spectroscopy studies and rate-dependent anode swelling from scanning electron microscopy will also be presented. References : [1] S. Pidaparthy, M.-T. F. Rodrigues, J.-M. Zuo, and D. P. Abraham, “Increased Disorder at Graphite Particle Edges Revealed by Multi-length Scale Characterization of Anodes from Fast-Charged Lithium-Ion Cells,” J. Electrochem. Soc., vol. 168, no. 10, p. 100509, 2021.[2] J.-M. Zuo et al., “Data-Driven Electron Microscopy: Electron Diffraction Imaging of Materials Structural Properties,” arXiv Prepr. arXiv2110.02070, 2021.[3] E. Padgett et al., “The exit-wave power-cepstrum transform for scanning nanobeam electron diffraction: robust strain mapping at subnanometer resolution and subpicometer precision,” Ultramicroscopy, vol. 214, p. 112994, 2020. Acknowledgements: SP acknowledges support from the U. S. Department of Energy Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the U. S. Department of Energy under contract number DE‐SC0014664. This work was carried out in part in the Materials Research Laboratory Central Research Facilities, University of Illinois. DA and MTFR acknowledge support from DOE’s Vehicle Technologies Office. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Figure 1

Electrolyte Development for Safe Li-Ion Battery Fast Charging: Decreasing Inactive Li on Graphite

Fast charging of lithium-ion batteries is limited primarily by the risks from lithium plating on the graphite anode. Plated lithium can become electrically isolated from the graphite (‘inactive Li’), causing rapid capacity fade and raising safety concerns. Thus, many studies have focused on detecting Li plating and designing operating conditions or materials to avoid it. Here we explore the reversibility of the lithium plating reaction as a tunable electrolyte property to mitigate inactive Li. We report a novel cycling technique to rigorously estimate the Li plating reversibility on graphite in Li/Graphite cells and then apply it to understand how additives, amount plated, and current density affect reversibility. Electrolyte compositions with reported high reversibility are tested under fast charging conditions in graphite/NMC cells, showing superior cycling performance and less inactive Li quantified by hydrogen gas evolution of extracted anodes. Finally, we consider limitations of reversibility measurements for Li plating/stripping on graphite and offer ways to address them.

(Invited) Enabling Fast Charging of Lithium-Ion Batteries without Lithium Plating

Today’s Li-ion technology is highly optimized for performance at relatively slow charging operation. However, significant challenges still present for fast charging conditions (> 4C). In state-of-the-art Li-ion batteries (LIBs) with high energy densities, the electrodes are relatively thick (> 100 μm), which leads to a tradeoff between energy density and high-power performance. In addition, the electrochemical potential of the anode can easily become more negative than Li/Li+ during fast charging, resulting in Li plating [1]. Therefore, new approaches are needed to overcome these energy/power tradeoffs in LIBsIn this talk, I will introduce three strategies to enable fast charging LIBs, using industrially-relevant pouch cells with thick (>3 mAh/cm2) electrode loadings. In the first strategy, vertical channels are introduced into post-calendared electrodes using laser ablation patterning [2]. The resulting 3-D anode architecture consists of a hexagonal close-packed array of vertical channels that serve as linear pathways for rapid ionic diffusion through the electrode thickness. This allows for a more homogeneous flux of Li throughout the volume of the electrode. As a result, the accessible capacity of the electrode during fast charging increases, and Li plating is eliminated.In the second strategy, the energy/power tradeoffs in carbonaceous anode materials are overcome by forming hybrid blends of graphite and hard carbon [3]. This allows for a balance between the higher energy density of graphite with the faster rate performance of hard carbon. By controlling the graphite/hard carbon ratio, we identify an optimal blend for fast charging.In the third strategy, we demonstrate the potential to eliminate Li plating and enabling 4C fast charging purely through interfacial control. This is achieved by coating the surface of graphite with a solid-state electrolyte material using Atomic Layer Deposition (ALD) [4]. These coatings eliminate electrolyte decomposition during the formation cycle, resulting in an “artificial SEI” with a resistance that is 75% lower than the natural SEI that forms in carbonate electrolytes. This challenges the fundamental assumption that fast charging of thick graphite anodes must be solved by improving mass transport, highlighting the critical role of the SEI on fast-charge performance.[1] Y. Chen, K.-H. Chen, A. J. Sanchez, E. Kazyak, V. Goel, Y. Gorlin, J. Christensen, K. Thornton, N. P. Dasgupta, J. Mater Chem. A 9, 23522 (2021).[2] K.-H. Chen, M. Namkoong, V. Goel, C. Yang, S. Kazemiabnavi, S. M. Mortuza, E. Kazyak, J. Mazumder, K. Thornton, J. Sakamoto, N. P. Dasgupta, J. Power Sources 471, 228475 (2020).[3] K.-H. Chen, V. Goel, M. J. Namkoong, M. Wied, S. Müller, V. Wood, J. Sakamoto, K. Thornton, N. P. Dasgupta, Adv. Energy Mater. 11, 2003336 (2020).[4] E. Kazyak, K.-H. Chen, Y. Chen, T. H. Cho, N. P. Dasgupta, Adv. Energy Mater, In Press (2021).

Thermal-Switchable, Trifunctional Ceramic-Hydrogel Nanocomposites Enable Full-Lifecycle Security in Practical Battery Systems.

Thermal runaway (TR) failures of large-format lithium-ion battery systems related to fires and explosions have become a growing concern. Here, we design a smart ceramic-hydrogel nanocomposite that provides integrated thermal management, cooling, and fire insulation functionalities and enables full-lifecycle security. The glass-ceramic nanobelt sponges exhibit high mechanical flexibility with 80% reversible compressibility and high fatigue resistance, which can firmly couple with the polymer-nanoparticle hydrogels and form thermal-switchable nanocomposites. In the operating mode, the high enthalpy of the nanocomposites enables efficient thermal management, thereby preventing local temperature spikes and overheating under extremely fast charging conditions. In the case of mechanical or thermal abuse, the stored water can be immediately released, leaving behind a highly flexible ceramic matrix with low thermal conductivity (42 mW m-1 K-1 at 200 °C) and high-temperature resistance (up to 1300 °C), thus effectively cooling the TR battery and alleviating the devastating TR propagation. The versatility, self-adaptivity, environmental friendliness, and manufacturing scalability make this material highly attractive for practical safety assurance applications.

Two-stage aging trajectory prediction of LFP lithium-ion battery based on transfer learning with the cycle life prediction

With the wide application of the LFP lithium-ion batteries, more attention is paid to the battery life and future aging behaviors as the safety and performance of the battery are guaranteed by accurate battery aging monitoring. In recent years, long-term aging trajectory prediction of the lithium-ion battery is always a challenge due to its complex nonlinear aging behaviors especially the aging behaviors in the two aging stages are quite different when the battery experiences the two-stage aging process under fast-charging conditions. Thus, it is harder to achieve accurate long-term aging trajectory prediction of the LFP lithium-ion batteries on the condition of the two-stage aging process. To address it, a novel transfer learning strategy combined with the cycle life prediction technology is presented in this paper. Specifically, a new cycle life prediction method is proposed based on feature extraction and deep learning technology and achieves accurate cycle life prediction. The transfer learning is started by developing a base aging model offline to learn the information of the two-stage aging process. Then, taking the predicted cycle life as its prior information, the Bayesian model migration technology is employed to predict the aging trajectory accurately, and the uncertainty of the aging trajectory is quantified. Two batches of the battery datasets are used for performance evaluation and comparison with two benchmarks. It is novel to combine the cycle life prediction and transfer learning technique to achieve accurate two-stage aging trajectory prediction with only a few data available (first 30%).

Bilayer hybrid graphite anodes via freeze tape casting for extreme fast charging applications

Extreme fast charging (XFC) of lithium-ion batteries is critical for continuous market adoption of electric vehicles. However, mass transport limitations and sluggish kinetics lead to lithium plating in graphite anodes under fast charging conditions. One approach to address the mass transport limitation in graphite is to design low-tortuosity electrodes to enhance ionic transport. In this study, a bilayer hybrid structured electrode with directionally aligned channels was developed via freeze tape casting, which enables faster lithium ion diffusion through the graphite electrode. A scalable roll-to-roll process was designed in which slurry can be cast on any substrates for simple processing. Electrochemical impedance spectroscopy measurements indicated that the bilayer hybrid coating had both low tortuosity and short diffusion pathways, enabling XFC charging. Rate testing for the bilayer hybrid electrode indicated superior performance over the other coatings, exhibiting a ∼20% improvement in the charge capacity compared with the conventional coating at 5C and 10 min total charging time. The bilayer hybrid electrode also demonstrated a 10% improvement in capacity retention compared with the conventional electrode after 1000 cycles at XFC conditions. This study demonstrates freeze tape casting as a scalable way to fabricate low-tortuosity electrodes for XFC applications.

Liquid cooling vs hybrid cooling for fast charging lithium-ion batteries: A comparative numerical study

Lithium-ion batteries (LIBs) rely on efficient thermal management systems for their safe and reliable operation. Issues like overheating of LIBs due to excessive heat generation, thermal runaway and thermal propagation are still a challenge for engineers. To address the challenge, numerous cooling methods viz. liquid cooling, air cooling, cooling using phase change materials (PCMs), hybrid cooling (i.e., combining liquid and PCM cooling), etc., have been proposed by different authors in the past. Though all the above methods are best suited for LIBs under normal charging/discharging operations, their suitability for cooling fast charging LIBs remains unexplored. In general, the heat generation and risks due to thermal runaway in LIBs are relatively more during fast charging than normal charging. As regards hybrid cooling employing PCMs, the method is yet to be benchmarked, as PCMs themselves suffer from low thermal conductivity issues that may affect their overall thermal performance. The present work is an attempt to address the above-stated aspects. Detailed 3D numerical simulations on three different design configurations (D1-D3) of a prismatic LIB module consisting of four 10 Ah batteries fast charged at 8C rate are reported herein. Two different cooling methods viz. (i) liquid cooling employing a dielectric liquid coolant (STO-50) and (ii) hybrid cooling combining liquid dielectric and a PCM (RT35) are investigated, and their performances compared. The results reveal interesting facts on the ability of liquid cooling (D2) over hybrid cooling (D3) for fast charging LIBs. Parametric studies show that the coolant flow direction (horizontal/vertical) and thermal conductivity of the PCM (kpcm) have a profound influence on the cooling obtained compared to PCM’s melting temperature (Tm) and latent heat (λ). It is concluded that PCM based hybrid cooling is not suitable for cooling LIBs under fast charging unless kpcm is enhanced to 1 W/mK or above. A minimum coolant flow rate of 2 lpm is needed to limit the battery temperatures to 40 °C or below for the module under fast charging conditions. An increase in PCMs latent heat from 160 to 200 kJ/kg has no significant influence on the cooling achieved.

An optimal thermal management system heating control strategy for electric vehicles under low-temperature fast charging conditions

• An improving fast charging protocol is proposed to avoid lithium plating. • A multi-stage heating control strategy based on the battery temperature is developed. • Dual crucial objectives, heating energy consumption and charging time are balanced. • An optimal heating control strategy for low-temperature fast charging is proposed. • The optimal control strategy can reduce heating energy consumption by 11.61%. Electric vehicle thermal management system (EVTMS) and its corresponding control strategy are essential to ensure the battery performance at low temperatures. Due to the complexity of the low-temperature fast charging process, it is necessary to comprehensively consider the battery heating and charging performance when developing the heating strategy. However, most studies only focus on the charging time. In this context, an EVTMS is investigated in this paper, and the simulation models are established. In addition, the battery heating and charging performance under low-temperature fast charging conditions are analyzed by experiment and simulation. An improved fast charging protocol for reducing the battery-lifetime degradation is proposed. Moreover, an EVTMS multi-stage heating control strategy is developed to realize the cooperative control with the improved charging strategy. Taking dual crucial yet conflicting factors, heating energy consumption and charging time, as the optimization objectives, the proposed EVTMS control strategy is optimized using genetic algorithm. And an optimal heating control strategy is obtained. The results show that compared with the strategy only considering the charging time, the optimal strategy can reduce the heating energy consumption by 11.61% and increase the charging efficiency by 1.2%, only with the increase of the charging time by 2.98 min.

Prevention of lithium deposition reaction in Li-ion batteries using a non-invasive approach, Part I: Separation of the negative electrode contributions

Many Li-ion cell aging mechanisms take place at the electrodes. Among these mechanisms, there is the deposit of lithium at the graphite electrode in fast charging conditions of LIBs. This mechanism can be avoided by having a control on the potential of the graphite electrode. This is difficult to achieve because this potential is mixed to others contributions in the battery voltage. In the present paper, we propose a method to separate the potential of the graphite electrode to the battery voltage using a model and characterization of the battery that is non-invasive and easy to implement. The method has been applied to a LiFePO4/graphite battery. The contributions of the SEI, the charge transfer and diffusion of the graphite electrode have been estimated in the battery voltage. The proposed method can be adapted to other Li-ion batteries or other battery technologies using carbon as negative active-material (e.g. sodium ion batteries).

State of health estimation for fast-charging lithium-ion battery based on incremental capacity analysis

Recently, lithium-ion batteries with fast-charging capability up to 3C rate are progressively equipped in modern consumer products. State of health (SOH) estimation specifically developed for fast-charging batteries is still an open-question, and the majority of the published methods is for batteries under lower charging rate below 1C. This study proposes a novel SOH method in particular for fast-charging batteries based on the incremental capacity (IC) analysis and Gaussian process regression (GPR). Firstly, the battery aging under fast-charging conditions is discussed according to the IC analysis, and a different characteristic of the IC curve is found for fast-charging batteries beyond the one observed under a lower charging rate. Then a novel feature extracted from the IC curves is introduced for SOH estimation of fast-charging batteries, and this novel feature is further identified and verified both from physical mechanism analysis and from quantitative comparison with classical features on battery aging correlation. Finally, a GPR model is established and trained with the dataset of extracted features for SOH estimation of fast-charging batteries. The proposed method is demonstrated on two fast-charging batteries Datasets, in which one of them simulates the real-life application, and the proposed method can achieve more than 90% reduction on mean absolute percentage error.

Adaptive online capacity prediction based on transfer learning for fast charging lithium-ion batteries

The aging of the battery is complicated and depends on both internal and external factors. Fast charging will amplify the cell-to-cell differences and make battery capacity prediction more challenging. In this paper, a long short-term memory network-based transfer learning model is proposed for adaptive online capacity prediction under fast charging. First, a novel voltage feature of charging to 80% state of charge in about 10 min is introduced. A sliding window is designed to integrate the voltage feature and the cycle number. The feature is highly practical and can be easily measured in all fast charging conditions. Second, to deal with the cell-to-cell differences and improve the model adaptivity, a cross-validation method with both high- and low-similarity tasks is performed to derive optimal hyperparameters. Then, the offline model can be trained using the existing complete battery lifespan data. Third, with the arrival of new battery data, the model can be finetuned at the full connected layer. The well-adjusted model can be applied for online capacity prediction. The other four features are compared to prove the superiority of the proposed feature. Six experiments with different fast charging conditions are carried out to verify the effectiveness and adaptability of the proposed method.

Electrolyte Effects on the Stabilization of Prussian Blue Analogue Electrodes in Aqueous Sodium-Ion Batteries.

Aqueous sodium-ion batteries based on Prussian Blue Analogues (PBA) are considered as promising and scalable candidates for stationary energy storage systems, where longevity and cycling stability are assigned utmost importance to maintain economic viability. Although degradation due to active material dissolution is a common issue of battery electrodes, it is hardly observable directly due to a lack of in operando techniques, making it challenging to optimize the performance of electrodes. By operating Na2Ni[Fe(CN)6] and Na2Co[Fe(CN)6] model electrodes in a flow-cell setup connected to an inductively coupled plasma mass spectrometer, in this work, the dynamics of constituent transition-metal dissolution during the charge-discharge cycles was monitored in real time. At neutral pHs, the extraction of nickel and cobalt was found to drive the degradation process during charge-discharge cycles. It was also found that the nature of anions present in the electrolytes has a significant impact on the degradation rate, determining the order ClO4- > NO3- > Cl- > SO42- with decreasing stability from the perchlorate to sulfate electrolytes. It is proposed that the dissolution process is initiated by detrimental specific adsorption of anions during the electrode oxidation, therefore scaling with their respective chemisorption affinity. This study involves an entire comparison of the effectiveness of common stabilization strategies for PBAs under very fast (dis)charging conditions at 300C, emphasizing the superiority of highly concentrated NaClO4 with almost no capacity loss after 10 000 cycles for Na2Ni[Fe(CN)6].

IC Curve-Based Lithium-Ion Battery SOC Estimation at High Rate Charging Current

The safety of battery operation requires a reliable battery management system (BMS) with an accurate and rapid estimation of battery state of charge (SOC), especially at fast charging scenarios. This article proposes an incremental capacity (IC) curve-based battery SOC estimation method at a high rate charging current, where SOC-IC functions are derived to estimate battery SOC using the measured IC value. Moreover, various charging currents and battery packs with different battery numbers are used to validate the effectiveness of the proposed method. Results demonstrate that the proposed method can provide accurate battery SOC estimation results at high rate charging current and can be easily adopted for varying charging current and battery pack. With its accuracy and computational efficiency, the proposed method can be incorporated into battery BMS for providing reliable SOC estimation at fast charging conditions.

Operando Analysis of Gas Evolution in TiNb2O7 (TNO)-Based Anodes for Advanced High-Energy Lithium-Ion Batteries under Fast Charging.

TiNb2O7 (TNO) is regarded as one of the promising next-generation anode materials for lithium-ion batteries (LIBs) due to its high rate capabilities, higher theoretical capacity, and higher lithiation voltage. This enables the cycling of TNO-based anodes under extreme fast charging (XFC) conditions with a minimal risk of lithium plating compared to that of graphite anodes. Here, the gas evolution in real time with TNO-based pouch cells is first reported via operando mass spectrometry. The main gases are identified to be CO2, C2H4, and O2. A solid-electrolyte interphase is detected on TNO, which continues evolving, forming, and dissolving with the lithiation and delithiation of TNO. The gas evolution can be significantly reduced when a protective coating is applied on the TNO particles, reducing the CO2 and C2H4 evolution by ∼2 and 5 times, respectively, at 0.1C in a half-cell configuration. The reduction on gas generation in full cells is even more pronounced. The surface coating also enables 20% improvement in capacity under XFC conditions.

Engineering Graphitic Structure Via Molten Salt Assisted Low Temperature Electrocatalytic Graphitization for High Capacity Anode Application

Graphite, a successfully commercialized anode for lithium-ion batteries (LIBs), is conventionally synthesized via the Acheson process at ~3000 °C. Because of sluggish lithium diffusion kinetics, synthetic graphite exhibits abysmal electrochemical performance under fast-charging conditions, which is an essential prerequisite for boosting electric mobility. Herein, we demonstrated engineering the graphitic structure via molten salt assisted electrocatalytic graphitization of amorphous carbon feedstocks to afford nano-flake graphite with tunable interlayer spacing to accelerate lithium diffusion kinetics at ~800-850 °C. The beauty of our strategy for engineering the graphitic structure is that it results in high-performing nano- flake graphite at much lower temperature with a short synthesis time, resulting in a significant increase in energy savings. The resulting graphite with unique nanoarchitecture exhibits outstanding electrochemical performance at fast charging conditions and outscored state of the art’s commercial graphite. The results demonstrated that such a strategy could enhance the energy density of fast-charging batteries that could boost electromobility.