Energy Density Lithium-ion Batteries Research Articles

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

A Scalable Approach to Synthesize Cobalt-Free LNMO Cathode Materials for High Energy Density Lithium Ion Batteries

The rapid growing demand for electric vehicles (EVs) has highlighted the need for high-energy-density batteries. The cathode material plays a vital role in achieving this goal[1]. As the limitations of cathode capacity improvement are approached, the pursuit for high-voltage materials becomes a viable option[2]. Lithium nickel manganese oxide LNMO (LiNi0.5Mn1.5O4) stands out due to its remarkable attributes including a substantial reversible capacity, excellent thermal stability, cost-effectiveness, environmental friendliness, and a high energy density[3]. Moreover, its cobalt-free composition aligns with sustainability objectives. Despite extensive research, the large-scale production and deployment of LNMO remain formidable challenges.In this study an industrially applicable co-precipitation method-based scalable synthesis strategy is introduced. The LNMO spheres with controlled various sizes and morphologies were successfully fabricated by adjusting the pH environment during synthesis carefully (Fig. 1A). Scanning electron microscopy (SEM) revealed the presence of uniformly spherical particles with dimensions of appr. 6, 9, and 14 µm and unique morphological characteristics (Fig. 1Ad-f). Synchrotron X-ray diffraction (SXRD) of LNMO samples revealed a deviation from the optimal Ni-to-Mn ratio of 1:3 (Fig. 1B)[4,5]. This variation results from the pH-dependent metal ion precipitation dynamics during synthesis, introducing a fascinating dimension to LNMO material fabrication. As potential cathode materials for lithium-ion batteries, these samples underwent a thorough electrochemical evaluation as part of our research. Among the synthesized LNMO samples, LNMO-9 demonstrated the most promising specific capacity, surpassing approximately 138 mAh/g and working under high voltage of 4.75 V (Fig. 1C). Furthermore, the characterizations of the materials were also thoroughly investigated by a variety of advanced characterization techniques, including Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM).This research reveals a strategy for synthesizing LNMO materials with certain regulated features and presents a successful strategy for industrial manufacturing as well. Particularly in the context of the EV industry, this research acquires critical significance in answering the growing demand for high-performance, sustainable energy storage systems. Fig. 1 (A) Illustration of the synthesis process of LNMO-x samples with SEM images of (a‒c) NiMn-x precursors and (d‒f) LNMO-x products. (B) SXRD patterns with Rietveld refinements and (C) charge/discharge profile of LNMO-x samples. Reference [1] H.-H. Ryu, G.-C. Kang, R. Ismoyojati, G.-T. Park, F. Maglia, Y.-K. Sun, Intrinsic weaknesses of Co-free Ni–Mn layered cathodes for electric vehicles, Materials Today. (2022) S1369702122000645. https://doi.org/10.1016/j.mattod.2022.03.005.[2] T. Liu, A. Dai, J. Lu, Y. Yuan, Y. Xiao, L. Yu, M. Li, J. Gim, L. Ma, J. Liu, C. Zhan, L. Li, J. Zheng, Y. Ren, T. Wu, R. Shahbazian-Yassar, J. Wen, F. Pan, K. Amine, Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery, Nat Commun. 10 (2019) 4721. https://doi.org/10.1038/s41467-019-12626-3.[3] Y. Xue, L.-L. Zheng, J. Wang, J.-G. Zhou, F.-D. Yu, G.-J. Zhou, Z.-B. Wang, Improving Electrochemical Performance of High-Voltage Spinel LiNi 0.5 Mn 1.5 O 4 Cathode by Cobalt Surface Modification, ACS Appl. Energy Mater. 2 (2019) 2982–2989. https://doi.org/10.1021/acsaem.9b00564.[4] A. Gomez, G. Dina, S. Kycia, The high-energy x-ray diffraction and scattering beamline at the Canadian Light Source, Review of Scientific Instruments. 89 (2018) 063301. https://doi.org/10.1063/1.5017613.[5] H.M. Rietveld, A profile refinement method for nuclear and magnetic structures, J Appl Crystallogr. 2 (1969) 65–71. https://doi.org/10.1107/S0021889869006558. Figure 1

Approach for Mitigating Interfacial Degradation in Silicon-Based Electrodes to Enhance Cycling Stability of Lithium-Ion Batteries and Capacitors

The growing demand for high energy density in lithium-ion batteries has led to extensive investigations on silicon negative electrodes. In this study, we propose a novel approach to address the interfacial degradation of electrodes caused by volume expansion during lithium insertion/extraction. The approach involves a sandwich structure consisting of a carbon nanofiber (CNF) undercoating electrode and a CNF-coated separator. The CNF is treated with acid to form carboxyl and hydroxyl groups on its surface, which improves the dispersion of the coating slurry and enhances adhesion to the electrode. Through electrochemical testing, the improved silicon electrode shows a high retention rate of 82% compared to the initial capacity after 100 cycles, and high electrochemical performance when applied to both lithium-ion batteries and lithium-ion capacitors. These results are attributed to the improved adhesion between the electrode and current collector, as well as the formation of a stable solid electrolyte interphase layer on the electrode surface. These findings suggest that the conductive coating process, applied to the separator and current collector, effectively mitigates interfacial issues that are associated with silicon-based electrodes. This approach has the potential to overcome the degradation characteristics of silicon electrodes and significantly contribute to improving the cycling stability of lithium-ion batteries and capacitors.

Simulation of Lithium-Sulfur Batteries and Optimization of Cathode Structure

Recently, the spread of the mobile devices and clean energy, the demand for high-power and high-capacity secondary batteries has been growing. However, the energy density of lithium-ion batteries (LiB) that is widely used nowadays is reaching its design limit. Instead of LiB, lithium-sulfur batteries (LiSB) are expected as one of the next-generation secondary batteries. Compared to LiB, LiSB has the advantages of higher energy density, lower cost, and easier weight saving. In LiB, the driving force is the insertion and desorption reaction of lithium ions between the cathode and anode, while in LiSB, is the complex sulfur dissolution and precipitation reaction. In LiSB, the electrolyte determines the dissolution and precipitation of sulfur, which is thought to have a significant impact on battery characteristics. Therefore, new electrolyte systems are being developed daily and techniques to elucidate the reaction mechanisms are needed. Furthermore, the effect of carbon black, a conductive material, on battery characteristics has also been considered. In this study, we investigated the optimal initial lithium ion concentration and calculation focused on the precipitation form of each carbon species for the design of optimal electrode structures.Kumaresan's one-dimensional model [1] based on porous electrode theory was used. Sulfur was used as the cathode active material and lithium metal as the anode active material. Electron and ionic potentials were calculated from the electro-neutrality condition, concentration distribution in the electrolyte was calculated from the non-stationary mass balance equation, and electrochemical reactions at the interface between active material and electrolyte were calculated using the Butler-Volmer equation. Furthermore, stepwise reactions were considered by incorporating the electrochemical reaction of sulfur and the dissolution and precipitation reactions into the concentration distribution and the interfacial reactions. The temperature in the electrode layer was assumed to be constant, and no heat loss or side reactions due to overvoltage were assumed to occur. In LiSB, sulfur dissolved in the electrolyte on the cathode surface is sequentially reduced as polysulfide ions as the discharge progresses. It then combines with lithium ions transferred from the anode and expands to about 1.8 times. Therefore, based on our previous research [2], the effect of the expansion and contraction of the electrode particles was reflected by dynamic changes in the structural properties of the electrode layer.Ionic conductivity and transport number are important parameters that affect the properties of the electrolyte. The higher the lithium ion concentration, the higher the transport number, but the lower the ionic conductivity [3]. In this study, we focused on sulfolane-based electrolyte and investigated the effect of initial lithium ion concentration on discharge capacity by incorporating the relationship between ionic conductivity and transport number into a model. As a result, the discharge capacity reached its maximum when the initial lithium ion concentration was 3.0 M. In the static state, the ionic conductivity was highest around 1.6 M, but considering the operating conditions during discharge, the concentration distribution became be more remarkable due to the low transport number, which may have resulted in excessive Li2S precipitation near the separator. As an extension to the microstructure of the electrode layer, we focused on carbon black (CB). Two types of CB (KB, MCND) were targeted. When MCND and KB were used as CB under the same conditions in the experiment, it was confirmed that the discharge characteristics of MCND were significantly better than those of KB. In LiSB, Li2S precipitation has a significant effect on discharge characteristics. Therefore, we focused on the pores of both CBs. We reconstructed the binarized structure from X-ray CT images of both CBs, hypothetically precipitated Li2S in the pores, and calculated the relative conductivity. The relative conductivity represents the transport property and is highly dependent on the structure of the electrode layer. As a calculation result, the relative conductivity of KB became significantly smaller as the porosity decreased. From the above, the transport properties in both CBs were confirmed by calculation.As described above, it was suggested that an optimum lithium ion concentration exists, and the effect of different CB structures on transport properties was qualitatively evaluated. In the future, it is necessary to confirm the validity of the optimal concentration through experiments and to quantitatively evaluate the effect of different CB.AcknowledgmentThis study was supported by JST ALCA-SPRING Grant JPMJAL1301, Japan.

Doped Micron Silicon and Mxene Based Composite Anodes for High-Performance Li-Ion Batteries

With the world's energy needs constantly increasing, renewable energy sources must be technologically advanced and integrated with energy storage devices to ensure their uninterrupted operation. In recent decades, researchers have devoted substantial efforts to improve the energy density of lithium-ion batteries (LIBs) [1]. While graphite remains the commercial anode in LIBs, it’s very low theoretical capacity (372 mAh g-1) restricts its use in high-energy applications. Silicon (Si), owing to its high theoretical capacity of 4200 mAh g-1, natural abundance, and appropriate Li uptake potential (0.4 V vs Li/Li+), is a promising anode material [2]. However, its massive volume expansion restricts its practical use.In this study, micron-sized Si particles are combined with graphite. Micron Si is less expensive, and the synthesis process is simpler. The well-ground mixture (Si-G) is mixed with a polymer solution to generate pyrolytic carbon (upon carbonising). This aids in the buffering of mechanical stresses caused by Si volume expansion. Furthermore, direct exposure of Si to the electrolyte is avoided, stabilising the solid electrolyte interphase (SEI). The addition of a dopant improves the intrinsic conductivity of the material, resulting in increased capacity by providing electron and Li-ion transport channels. To further enhance the composite's performance, synthesized Mxene is added to promote the charge transport between micron Si. Using various techniques such as SEM-EDAX, XRD, Raman, and XPS spectroscopy, the composite's morphology and structure is studied which reveals uniformly distributed Si, C, and Mxene sheets that retain the sheet architecture.As an anode, the composite exhibits outstanding electrochemical performance which was evident by its impressive lithium storage specific capacity of 2003 mAh g-1 (based on weight of Si) even after long term cycling (at 1C rate). Additionally, the composite demonstrates superior rate performance with a specific capacity of 2439 mAh g-1 at 10 C rate, highlighting its potential for high-power applications. Moreover, the electrode displayed a low charge transfer impedance and fast electron transport, which improved the electrochemical performance. The reason for this improved performance is the unique structure consisting of Mxene and doping, which significantly increased the Li ion diffusion and the active sites. Also, low-cost micron Si is used which has a high tap density. Thus, this work provides an approach to develop high-capacity LIBs based on silicon. Keywords: Lithium-ion battery, micron silicon anode, Mxene, doping. References Liu, L. Kang, J. Hu, E. Jung, J. Zhang, S.C. Jun, Y. Yamauchi, Unlocking the Potential of Oxygen-Deficient Copper-Doped Co 3 O 4 Nanocrystals Confined in Carbon as an Advanced Electrode for Flexible Solid-State Supercapacitors, ACS Energy Lett. 6 (2021) 3011–3019. https://doi.org/10.1021/acsenergylett.1c01373.Zhou, Y. Liu, C. Du, Y. Ren, T. Mu, P. Zuo, G. Yin, Y. Ma, X. Cheng, Y. Gao, Polyaniline-encapsulated silicon on three-dimensional carbon nanotubes foam with enhanced electrochemical performance for lithium-ion batteries, Journal of Power Sources. 381 (2018) 156–163. https://doi.org/10.1016/j.jpowsour.2018.02.009.

(Invited) Safety of Li-Ion Batteries: Current Challenges in a Policy Context

Batteries are a key technology required to meet our objective for climate neutrality, to reduce dependency on fuel imports as well as to ensure maximum use of renewable electricity. Over 80 GW / 160 GWh of stationary batteries and over 50 million electric vehicles are expected in the EU by 2030. Lithium-ion batteries are expected to dominate the market well beyond 2030, while developments in other technologies will continue in parallel. Battery-related policies are currently of high interest and have to evolve quickly in order to facilitate and accommodate technological progress.With increasing numbers of electric vehicles and batteries in operation and the parallel rise of energy density in lithium-ion batteries, risks related to battery safety e.g., through battery fires, increase. The Joint Research Centre (JRC) carries out research on battery safety to support policymaking and develop fit-for-purpose testing methodologies: the recently proposed Batteries Regulation, aiming at a sustainable battery value chain, foresees new safety requirements for stationary batteries. Another example is the Global Technical Regulation on Electric Vehicle Safety, where a thermal propagation test procedure is being developed with international partners.In this context, thermal runaway initiation methods and criteria for thermal runaway events had been analysed. A rapid heating method and suitable criteria for thermal runaway were applied in a thermal propagation test campaign on full electric vehicles and corresponding battery packs. While a high degree of reproducibility was observed, a difference in severity between pack and vehicle-level tests was found, and gas emissions from the tests are currently being analysed. Figure 1

Understanding of Polyacrylic Acid as Binder for High Silicon Containing Anodes and Ni-Rich Cathodes

With the increased demand on electric vehicles, portable devices and energy storage systems, a great attention is being drawn to improve the energy density of lithium-ion batteries (LiBs) [1]. The commercial LiBs anodes are usually consisted of graphite-based material, which limits the energy density due to its relatively low theoretical capacities. Silicon (Si) has been recognized as an alternative anode material with its high theoretical capacity, natural abundance, and low discharge potential. Despite the above-mentioned advantages, Si undergoes a substantial volume expansion (300% approximately) during the battery operation [2]. There are some approaches to mitigate the adverse of expansion, whereas the cost and scalability of these techniques are the bottlenecks to solve this issue [3]. In this work, we focus on maintaining the structural integrity, along with the coordination of Li as functional binder which could be an effective solution to the abovementioned challenges.In addition to the energy density and capacity targets, considering more environmentally friendly approaches is also one of the key topics for battery manufacturing. Aqueous processing of the anodes is already state-of-the-art whilst, the cathode has its own challenges to be overcome. Ni-rich transition oxide active materials, such as LiNi0.8MN0.1Co0.1 (NMC811), are attractive for high-capacity target applications. Due to the high reactive surface of the active material, during the slurry processing, NMC811 reacts with water, which leads to Li+/H+ exchange [4]. Thus, the slurry results in high pH which can corrode the aluminum foil current collector and cause poor capacity due to Li loss. The advantage of using polyacrylic acid (PAA) is to employ COOH, in which the leached Li+ can bond to the backbone. Hence, the pH of slurry is maintained on desirable coating range and the capacity loss can be reduced due to the proposed aqueous processing.In this study, we explore the utilization of a well-known polymer, polyacrylic acid, as binder for both negative and positive electrodes. On the anode, PAA is functionalized with Li+ and used LiPAA prior to electrode production. It is highly crucial to observe how the dynamics of Si and LiPAA impacts the anode performance during the cycling. To comprehend this, post mortem, scanning electron microscopy (SEM) was performed to detect the positioning and concentration of Si on pristine and cycled anodes. On the cathode side, the focus is to utilize the leached Li+ during the slurry processing by having PAA as binder. This technique has been already successfully implemented by our group on the research pilot scale [5]. The idea is to make pH stable slurry without using any additional acid, in conjunction with creating in situ functional binder (LiPAA). Deep understanding of functional binders is to serve as a guide for the rational design of Si-electrode and aqueous NMC811 cathodes for LiBs.

Solvent-Driven Degradation of Ni-Rich Cathodes Probed by Operando Gas Analysis

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling stability, which is exacerbated by increased cell voltage due to higher interfacial reactivity than their lower Ni-content analogues. Here, we study the pivotal role of electrolyte solvents in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells (1, 2). Operando gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte oxidation. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 is charged above 4.3 V vs Li/Li+ - the observed onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. The gas analysis also reveals the crosstalk effect caused by the products of the nascent oxygen from the NMC811 lattice and the electrolyte solvent, showing anodic reactivity. In contrast, NMC111, which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown. Oxygen loss is suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. W. M. Dose et al., Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries. ACS Energy Letters 7, 3524-3530 (2022).W. M. Dose et al., Electrolyte Reactivity at the Charged Ni-Rich Cathode Interface and Degradation in Li-Ion Batteries. ACS Applied Materials & Interfaces 14, 13206-13222 (2022). Figure 1

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

(Invited) A Chemical Mechanism of Carbonate Electrolyte Failure at Silicon Anode Interface for New Electrolyte Design

Silicon (Si) anode has tremendous potential for the next-generation high energy density lithium-ion battery, but the development of devices with sufficient capacity retention and calendar life remains elusive. While numerous studies have characterized the composition and dynamics of the solid-electrolyte-interface (SEI) on silicon anodes, the chemical mechanisms that produce the identified species remain largely speculative and conflicting. In this presentation, we demonstrate the use of trimethylsilyllithium as a model compound to study the chemical mechanisms of electrolyte failure unique to silicon anodes. The insights from this mechanistic study led to the rational design of new electrolytes that outperform traditional EC-based carbonate electrolytes demonstrated in NMC811/Si full cells.

(Keynote) Rapid Thermal Management for Fast Charging of Energy-Dense Lithium-Ion Batteries

Charging time trauma refers to the pain experienced by electric vehicle (EV) owners when the ‘refill’ time is significantly longer than that of traditional internal combustion engine vehicles. Worsening this trauma is the inconsistency of EV charging; for example, the same EV may take five times longer to charge on a cold day. Faster charging will alleviate this pain point and aid in the mass adoption of EVs, crucial for meeting near-term carbon emission goals. Reaching this goal will require smarter and more rapid thermal management to provide significantly faster safe charging.The results from the 2022 Nature article “Fast charging of energy-dense lithium-ion batteries” (DOI 10.1038/s41586-022-05281-0) where 265 Wh/kg lithium-ion pouch cells were charged from 0-70% in less than 12 minutes, 2,000 times in a row before end-of-life, will be presented. These cells used only proven materials, including a liquid electrolyte made from industrially-used components, and energy-dense, EV-grade electrodes. Key to success was smart cell thermal management. More recent advancements, including multi-cell battery-level data, will also be discussed. Figure 1

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium-Ion Batteries with Enhanced Cycle Life and Thermal Safety.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8 Co0.1 Mn0.1 O2 /SiOx -graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6 -carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

Elucidating in-situ heat generation of LiFePO4 semi-solid lithium slurry battery under specific cycling protocols

Semi-solid lithium slurry battery combines the advantages of the high energy density of lithium-ion battery and the flowability of flow battery electrodes and has attracted attention in energy storage. Elucidating the heat generation during cycling is crucial for evaluating the safety. However, there is a relative lack of research in this field of semi-solid lithium slurry battery. Herein, the heat generation of lithium iron phosphate (LiFePO4) semi-solid lithium slurry battery during cycling under specific cycling protocols is investigated in this work. The results show that the battery has lower heat generation when cycling at an ambient temperature of 35–50 ℃ and a charging cutoff voltage below 4.0 V, meanwhile, it maintains considerable capacity. However, when the charging cutoff voltage exceeds 4.4 V, the cyclic heat generation of the battery increases significantly, and the capacity attenuates significantly. Meanwhile, the classical equation for calculating battery heat generation of lithium-ion battery is no longer reliable. This is mainly because the electrolyte content of the semi-solid lithium slurry battery is too high (over 80 %), and at high charging cutoff voltage, the side decomposition reactions of the electrolyte increase significantly. Subsequent characterization of electrode materials also confirms this inference. This study can provide a clearer understanding of the safety of semi-solid lithium slurry battery and has guiding implications for industrial applications.

Electrochemical performance of lithium-ion batteries with two-layer gradient electrode architectures

Thick electrodes whose active materials have high areal density may improve the energy densities of lithium-ion batteries. However, the weakened rate abilities and cycle lifetimes of such electrodes significantly limit their practical applications. In this study, a modified two-dimensional model was built to evaluate the influence of the electrode structure on the lithiation process. Gradient electrodes with different particle sizes along the thickness direction are designed and fabricated via a two-layer coating process. The gradient design in the thickness direction is confirmed by three-dimensional digital microscopy, energy-dispersive spectroscopy, X-ray diffraction, and scanning electron microscopy. Galvanostatic charge/discharge cycling tests and electrochemical impedance spectroscopy are performed to investigate the electrochemical properties of the fabricated gradient electrodes. The simulation results indicate that the gradient electrode structure can enhance the utilization of electrode particles on the current collector side and alleviate the nonuniformity of the solid-phase Li concentration along the thickness direction. High electrochemical performance and long-term cycling stability of the designed gradient electrodes are verified by electrochemical test. The gradient structure fabricated via multi-layer coating processes can be used to improve the electrochemical performance of thick electrodes.

An Electrolyte with Less Space-Occupying Diluent at Cathode Inner Helmholtz Plane for Stable 4.6 V Lithium-Ion Batteries.

Reasonably elevating the working voltage (≥4.4 V vs. Li/Li+ ) of the cathode is one of the efficient approaches to maximize the energy density of lithium-ion batteries (LIBs). As a preferred partner for high-voltage LIB systems, localized high-concentration electrolyte (LHCE), characterized by a stronger Li solvation structure, less free solvent, and robust electrode/electrolyte interphase has attracted much attention in academic circles. Herein, we systematically studied the role of the diluent in LHCE on the formation of the cathode electrolyte interphase (CEI) and elucidated that the existing anion-diluent pairing in the inner Helmholtz plane (IHP) results in an uneven CEI and subsequent battery degradation under high voltage. A m-fluorotoluene (mFT) diluent was further employed in the LHCE containing lithium difluoro(oxalato)borate (LiDFOB) to facilitate a uniform and rich-anion-derived CEI, since the weaker interaction of HmFT -BDFOB - , as compared to the HHhydrofluoroether -BDFOB - , reduces the influence of mFT in IHP or initial CEI formation. Consequently, the mFT-dominated LHCE propels the high-voltage performance of LIBs one step forward, endowing a 4.6 V-class 1.2-Ah graphite||LiNi0.8 Co0.1 Mn0.1 O2 pouch cells a 90.4 % capacity retention after 130 cycles. Our study thus describes a new index affecting the CEI formation and proposes novel strategies to deeply optimize the high-voltage LIBs.

10 μm-Level TiNb2 O7 Secondary Particles for Fast-Charging Lithium-Ion Batteries.

TiNb2 O7 with Wadsley-Roth phase delivers double theoretical specific capacity and similar working potential in comparison to spinel Li4 Ti5 O12 , the commercial high-rate anode material, and thus can enable much higher energy density of lithium-ion batteries. However, the inter-particle resistance within the high-mass-loading TiNb2 O7 electrode would impede the capacity release for practical application, especially under fast-charging conditions. Herein, 10-20 μm-size carbon-coated TiNb2 O7 secondary particle (SP-TiNb2 O7 ) consisting of initial micro-scale TiNb2 O7 particles (MP-TiNb2 O7 ) was fabricated. The high crystallinity of active material could enable fast-charge diffusion and electrochemical reaction rate within particles, and the small number of stacking layers of SP-TiNb2 O7 could reduce the large inter-particle resistance that regular particle electrode often possess and achieve high compaction density of electrodes with high mass loading. The investigation on materials structure and electrochemical reaction kinetics verified the advances of the as-fabricated SP-TiNb2 O7 in achieving superior electrochemical performance. The SP-TiNb2 O7 exhibited high reversible capacity of 292.7 mAh g-1 in the potential range of 1-3 V (Li+ /Li) at 0.1 C, delivering high-capacity release of 94.3 %, and high capacity retention of 86 % at 0.5 C for 250 cycles in half cell configuration. Particularly, the advances of such an anode were verified in practical 5 Ah-level laminated full pouch cell. The as-assembled LiFePO4 ||TiNb2 O7 full cell exhibited a high capacity of 5.08 Ah at high charging rate of 6 C (77.9 % of that at 0.2 C of 6.52 Ah), as well as an ultralow capacity decay rate of 0.0352 % for 250 cycles at 1 C, suggesting the great potential for practical fast-charging lithium-ion batteries.

Trends in the Gravimetric and Volumetric Energy Densities of Lithium-Ion Batteries over the Past Decade

Trends in the Gravimetric and Volumetric Energy Densities of Lithium-Ion Batteries over the Past Decade

Ultraviolet-thermal coupling cross-linked fabricate polymer/ceramic composite solid electrolyte for room temperature quasi solid state lithium ion batteries

Polymer-based electrolyte, as a key component of lithium ion solid state battery, has good adaptability to lithium metal anode, and has received extensive attention in recent years. However, the low conductivity, limited thermal stability and poor mechanical strength of polymer-based solid electrolytes restricting its commercial application. Herein, We reveal experimentally that the Polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li1.3Al0.3Ti1.7(PO4)3 (LATP) composite solid electrolyte can be prepared by means of ultraviolet and thermal coupling curing (UV-TC) process, and the electrolyte film has better electrochemical performance than that prepared by means of thermal curing (TC) process. Therefore, the carefully designed electrolyte film is efficiently prepared by UV-TC curing process to improve the specific capacity (152.34 mAhg−1), the rate performance (89.04 mAhg−1 at 1 C) and good cycle performance (92.3 % retention rate in 100 cycles at 0.1 C) at room temperature for Li||PVDF-HFP/LATP||LFP solid state battery. The ionic conductivity of the solid electrolyte film prepared by the UV-TC method (4.3 × 10−4 S cm−1) is more encouraging than that of the TC method (9.2 × 10−5 S cm−1). This work shows that the polymer/ceramic composite solid electrolyte films (CSEs) prepared by simple and efficient UV-TC method has great prospects in realizing high energy density and high safety room temperature quasi solid state lithium ion batteries.

A computational analysis of effects of electrode thickness on the energy density of lithium-ion batteries

Elevated energy density is a prime requirement for many lithium-ion battery (LIB) applications, including electric vehicles (EVs). At the cell level, the enhanced energy density of LIBs is achievable by designing thicker electrodes, which decreases the weight of the inactive materials. This work proposed a reduced order electrochemical model (ROEM), which is an extended single particle model (extended SPM), by incorporating the existing order reduction techniques of Pseudo-Two-Dimensional (P2D) model. The proposed model was used to predict the energy density values of a nickel cobalt manganese (NCM) cell with respect to the cathode thickness. The validation of the model was performed by using MATLAB at 0.05C, 1C, 2C, 3C and 5C rates by comparing the simulation results with the experimental data obtained from the Stanford Energy Control Laboratory. The verified model was then used to simulate the effect of varying thicknesses of the cathode on energy density of the NCM cell at C/5, C/2, 1C, and 2C rates of discharge. The simulation results illustrate that increasing the cathode thickness has a profound positive impact on the energy density of the cell. The prediction of the model demonstrates a total of around 20 % increase in energy density for the increment of cathode thickness from 75 μm to 600 μm. The proposed model can replicate energy density for thicker electrodes up to 2C rate reasonably correctly. However, the incorporation of thermal characteristics and other influential parameters of LIB cells into the proposed model can yield a better prediction of energy density of thicker electrodes at higher C-rates, which is recommended for further study.

Clarifying the limiting factor of material utilization in thick electrodes of lithium-ion batteries

Improving the energy density of lithium-ion batteries is a goal pursued in state-of-the-art batteries, and the use of thick electrodes with high active material loading densities is one of the most effective and direct methods. Most studies indicate that the hindrance to the practical application of thick electrodes is mainly attributed to the slow charge kinetics, resulting in very low utilization of active materials. Here, this work shows that the thermodynamic properties of the electrode material also have a significant impact on the electrode reaction behavior. When the equilibrium potential of the electrode material has a strong dependence on the state of charge, it promotes the uniform reaction of the electrode active material. By simulating the full battery under low and high load conditions, the reaction behavior of the thin electrodes is dominated by the equilibrium potential curve. However, the reaction behavior of thick electrodes is regulated by both kinetics and thermodynamics and depends on the strength of the relationship between these two properties. Meanwhile, the graphite anode limits the release of the full battery capacity to a greater extent. This work points out a new direction for the practical development and application of thick electrodes.