Next-generation Electric Vehicles Research Articles

UV cross-linked highly stable polymer garnet composite electrolyte with improved interphase for lithium metal batteries

The next-generation electric vehicles heavily rely on high-energy–density lithium metal batteries with enhanced safety. Replacing liquid electrolytes with solid-state polymer electrolytes offers superior protection, high flexibility, and stability. However, inadequate ionic conductivity and poor compatibility at the interfaces with the electrodes hinder the practical application of solid-state electrolytes. In this work, we developed a polyethylene glycol-based, highly cross-linked polymer electrolyte with a garnet-type, fast Li+ conductive Li6.2Al0.24La3Zr2O12 (Al-LLZO) filler. The Al-LLZO filler was incorporated into a cross-linking functional polymeric matrix of polyethylene glycol diacrylate, pentaerythritol tetrakis (3-mercaptopropionate), and lithium perchlorate salt. The cross-linked polymer garnet composite electrolyte (CPGCE) was prepared via UV-induced photo-polymerization. The resulting CPGCE exhibits superior free-standing flexibility, a desired ionic conductivity of 4.4 × 10−4 S cm−1, and a wide potential window up to 4.2 V. The Li|CPGCE|Li symmetric cell underwent stripping and plating at varying current densities of 0.05 to 0.3 mA cm−2, displaying a low overpotential range from ±0.02 V to ±0.08 V over 500 cycles. Similarly, the as-cycled Li|CPGCE|Li showed excellent stripping and plating performance at 0.1 mA cm−2 for 500 cycles at 60 °C. The incorporation of the Al-LLZO nanofiller provided active sites with continuous Li+ conducting pathways, suppressing the growth of dead lithium dendrites. The Li|CPGCE|LiFePO₄ full cell exhibited a discharge capacity of 155 mAh g−1 at a rate of 0.1C, with a coulombic efficiency of 96 % over 50 cycles at 25 °C. This work offers a straightforward and convenient approach to creating highly durable polymer composite electrolytes with enhanced interfacial stability, advancing the implementation of all-solid-state lithium metal batteries.

Dynamic mechanical behaviors of load-bearing battery structure upon low-velocity impact loading in electric vehicles

As the electrification trend of vehicles continues, new energy vehicles such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) are being equipped with new functional energy storage devices demanding a trade-off between electrical and mechanical property. Accordingly, composite-battery integrated structures which simultaneously carry mechanical resistance and energy-storage capacity, are being explored to offer great potential for the next generation of EVs or PHEVs. Herein, the dynamic responses and failure mechanisms of the integrated structure under the commonly occurring low-velocity impact events are studied both experimentally and numerically. A macro-scale finite element (FE) model was developed by implementing constitutive models of component materials, including lithium‐ion polymer (LiPo) battery cells, polymer foams, and carbon fiber-reinforced polymers (CFRP). The numerical method demonstrates good feasibility and accurately predicts impact behaviors, with the maximum error of the peak impact load not exceeding 8 %. The integrated structures are proven to reduce mechanical damage while maintaining mechanical and electrochemical performance within a range of impacts. The electrical and mechanical behaviors and their correlations were revealed. Sensitivity of the mechanical behaviors and electrical failure to battery arrangement were discussed as well as the structure design on energy absorption capacity. These results hold significant potential for the safety and lightweight design of energy storage composite structures incorporating lithium-ion batteries.

Rest in phase transition: Should charging habits in next generation EVs be adapted?

Nickel-rich cathode materials are a popular cathode for high energy lithium ion batteries in the current and next generation of electric vehicles. While nickel-rich cathodes offer high energy density, their cycle-life is compromised due to several factors directly related to their (de)lithiation behavior. At high state of charge the nickel-rich cathode experiences a hexagonal-hexagonal transition which is accompanied by drastic changes in the unit cell parameters. This phenomenon is detrimental for cycle-life of a battery cell. This work elucidates on the effect of storing LiNi0.8Mn0.1Co0.1O2‖Graphite cells at 95 % state of charge corresponding to the above-mentioned transition for 10 h every six cycles. The results are compared to cells cycled without a rest at high state of charge and cells cycled to 100 % state of charge. Analysis of the obtained cycling data shows that resting lithium ion cells based nickel-rich cathode based cells is detrimental leading to higher impedance growth and capacity decay than cycling to 100 % state of charge.

Guest Editorial: Special Issue on Advanced Charging Technologies for Next-Generation Electric Vehicles

Guest Editorial: Special Issue on Advanced Charging Technologies for Next-Generation Electric Vehicles

Mechanical engineering in automotive innovation: A review of electric vehicles and future trends

This paper provides a succinct overview of the extensive landscape of automotive innovation within the realm of mechanical engineering, focusing on the transformative emergence of electric vehicles (EVs) and the anticipated future trends in this dynamic field. As the automotive industry undergoes a paradigm shift towards sustainable and eco-friendly transportation solutions, the role of mechanical engineering in shaping the future of mobility becomes increasingly pivotal. The review begins by delving into the evolution of electric vehicles, tracing their historical development and highlighting key milestones that have propelled them from niche alternatives to mainstream contenders in the automotive market. A comprehensive examination of the underlying mechanical engineering principles governing EV design and performance is presented, emphasizing advancements in battery technology, electric drivetrains, and energy management systems. The document scrutinizes current challenges and opportunities associated with electric vehicles, addressing issues such as range anxiety, charging infrastructure, and the environmental impact of battery production and disposal. It explores ongoing research efforts within the field of mechanical engineering aimed at overcoming these challenges and enhancing the overall efficiency, safety, and sustainability of electric vehicles. Furthermore, the paper outlines the anticipated future trends in automotive innovation, providing insights into cutting-edge technologies and methodologies poised to shape the next generation of electric vehicles. Topics include advancements in materials science for lightweight construction, artificial intelligence integration for autonomous driving, and the integration of renewable energy sources to further enhance the environmental footprint of EVs. This review underscores the pivotal role of mechanical engineering in the ongoing revolution of automotive technology, emphasizing the transformative impact of electric vehicles and offering a glimpse into the exciting future trends that will define the landscape of sustainable mobility.

Designing electrolytesand interphases for high-energy lithium batteries.

High-energy and stable lithium-ion batteries are desired for next-generation electric devices and vehicles. To achieve their development, the formation of stable interfaces on high-capacity anodes and high-voltage cathodes is crucial. However, such interphases in certain commercialized Li-ion batteries are not stable. Due to internal stresses during operation, cracks are formed in the interphase and electrodes; the presence of such cracks allows for the formation of Li dendrites and new interphases, resulting in a decay of the energy capacity. In this Review, we highlight electrolyte design strategies to form LiF-rich interphases in different battery systems. In aqueous electrolytes, the hydrophobic LiF can extend the electrochemical stability window of aqueous electrolytes. In organic liquid electrolytes, the highly lithiophobic LiF can suppress Li dendrite formation and growth. Electrolyte design aimed at forming LiF-rich interphases has substantially advanced high-energy aqueous and non-aqueous Li-ion batteries. The electrolyte and interphase design principles discussed here are also applicable to solid-state batteries, as a strategy to achieve long cycle life under low stack pressure, as well as to construct other metal batteries.

A New Ternary Co-Free Layered Cathode, Li[Ni1-x-yTixAly]O2, for High-Energy Lithium-Ion Batteries

For the sustainable development of Li[NixCoyMn1−x−y]O2 and Li[NixCoyAl1−x−y]O2 cathodes, reducing the reliance on cobalt, which is extremely expensive with a fluctuating price and supply uncertainty, is considered essential. In this study, we propose a highly stable Co-free Ni-rich layered cathode developed through a new doping strategy that incorporates heteroelements at different doping stages, including the introduction of Ti during Ni(OH)2 synthesis and doping excess amounts of Al during the lithiation step. The multi-stage engineering strategy guarantees structural durability and electrochemical cycling stability of the inherently unstable LNO to a commercially viable level. Combined with particle surface protection, the Li[Ni0.951Ti0.008Al0.041]O2 cathode retains 72.0% of its initial capacity after 3500 cycles, which is unprecedented among previously reported Co-free cathodes. The proposed Co-free cathodes can meet the energy density required for next-generation electric vehicles, as the cathode delivers 890 Wh kgcathode-1, and presents a clear breakthrough for the development of commercially viable LNO cathode.

Artificial Neural Network Modeling to Predict Thermal and Electrical Performances of Batteries with Direct Oil Cooling

The limitations of existing commercial indirect liquid cooling have drawn attention to direct liquid cooling for battery thermal management in next-generation electric vehicles. To commercialize direct liquid cooling for battery thermal management, an extensive database reflecting performance and operating parameters needs to be established. The development of prediction models could generate this reference database to design an effective cooling system with the least experimental effort. In the present work, artificial neural network (ANN) modeling is demonstrated to predict the thermal and electrical performances of batteries with direct oil cooling based on various operating conditions. The experiments are conducted on an 18650 battery module with direct oil cooling to generate the learning data for the development of neural network models. The neural network models are developed considering oil temperature, oil flow rate, and discharge rate as the input operating conditions and maximum temperature, temperature difference, heat transfer coefficient, and voltage as the output thermal and electrical performances. The proposed neural network models comprise two algorithms, the Levenberg–Marquardt (LM) training variant with the Tangential-Sigmoidal (Tan-Sig) transfer function and that with the Logarithmic-Sigmoidal (Log-Sig) transfer function. The ANN_LM-Tan algorithm with a structure of 3-10-10-4 shows accurate prediction of thermal and electrical performances under all operating conditions compared to the ANN_LM-Log algorithm with the same structure. The maximum prediction errors for the ANN_LM-Tan and ANN_LM-Log algorithms are restricted within ±0.97% and ±4.81%, respectively, considering all input and output parameters. The ANN_LM-Tan algorithm is suggested to accurately predict the thermal and electrical performances of batteries with direct oil cooling based on a maximum determination coefficient (R2) and variance coefficient (COV) of 0.99 and 1.65, respectively.

Trifunctional composite thermal barrier mitigates the thermal runaway propagation of large-format prismatic lithium-ion batteries

With the increasing energy density and capacity of lithium ion batteries (LIB), the safety problems caused by thermal runaway propagation (TRP) has become the most predominant hazard for electric vehicles (EVs) and energy storage systems (ESSs). Mitigating the TRP is significant for large-format LIB application. This study proposed a novel thermal barrier with nano-ceramic fiber, phase change materials (PCM) and mica cross skeleton. A 3 mm thermal barrier can effectively prevent the TRP behavior of a 153 Ah Li(Ni0.5Co0.2Mn0.3) (NCM523) battery module. The enthalpy of heat absorption of PCM is 1958 J/g. Besides, the mica skeleton can resist the extrusion pressure from the batteries, and the remaining nano-ceramic fiber provides insulation capacity. Moreover, the thermal barrier still maintains desirable heat insulation under pressure and high temperature operations, exhibiting high compressive strength. Furthermore, the thermal barrier can reduce the maximum temperature of the battery by about 10 °C during 2C charging and discharging conditions. This study guides the safety design of thermal barrier for large capacity LIB systems, contributing to the potential safety protection of next-generation EVs and ESSs.

Challenges and approaches of single-crystal Ni-rich layered cathodes in lithium batteries.

High energy density and high safety are incompatible with each other in a lithium battery, which challenges today's energy storage and power applications. Ni-rich layered transition metal oxides (NMCs) have been identified as the primary cathode candidate for powering next-generation electric vehicles and have been extensively studied in the last two decades, leading to the fast growth of their market share, including both polycrystalline and single-crystal NMC cathodes. Single-crystal NMCs appear to be superior to polycrystalline NMCs, especially at low Ni content (≤60%). However, Ni-rich single-crystal NMC cathodes experience even faster capacity decay than polycrystalline NMC cathodes, rendering them unsuitable for practical application. Accordingly, this work will systematically review the attenuation mechanism of single-crystal NMCs and generate fresh insights into valuable research pathways. This perspective will provide a direction for the development of Ni-rich single-crystal NMC cathodes.

Multifunctional Additive Ethoxy(pentafluoro)Cyclotriphosphazene Enables Safe Carbonate Electrolyte for SiOx-Graphite/NMC811 Batteries

The silicon or silicon monoxide (SiO x )-graphite/nickel-rich (≥80% Ni) LiNi x Mn y Co z O2 (x+y+z = 1, NMC) cell chemistry is widely regarded as one of the most promising chemistries for next-generation electric vehicle batteries for due to its higher energy density compared to state-of-the-art graphite/Ni-rich NMC batteries. However, the drastic volume change during lithiation and delithiation of silicon poses a significant challenge to realize its high capacity with a practical cycle life. Besides performance degradation, it is desirable to address safety risks stemming from, e.g., the high flammability of carbonate solvents and oxygen release from highly delithiated Ni-rich NMC materials.To address these problems, one of the most effective methods is to develop advanced electrolytes that combine flame-retardant properties and excellent electrochemical performance. Generally, in consideration of the balanced trade-offs between cost, scalability, safety, and electrochemical compatibility, the use of flame retardants is a very promising approach to realize the next-generation nonflammable electrolytes.However, it is still a huge challenge to optimize the electrolyte composition to stabilize Si-based and Ni-rich lithium-ion batteries.Here, the compatibility of the flame retardant ethoxy(pentafluoro)cyclotriphosphazene (PFPN) as additive for carbonate electrolytes is studied, for the first time, in the SiO x -graphite/NMC811 full cells. [1] A synergistic effect is found between PFPN and lithium hexafluorophosphate (LiPF6) for the flame retardancy, and a modified electrolyte (1.35M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7 by vol.) with 10 wt.% fluoroethylene carbonate (FEC) and 5 wt.% PFPN) displays a very low self-extinguishing time of only 3 s/g while also maintaining a high ionic conductivity of 8.4 mS/cm at 25 °C. Furthermore, the morphology evolution and interphase composition of both anode and cathode are investigated, gaining important insights into the decomposition mechanism of PFPN to stabilize the electrode-electrolyte interfaces. Meanwhile, the wetting properties of the modified electrolyte are also improved due to the excellent wettability of PFPN. As a result, half and full coin cells with SiO x -graphite anode and NMC811 cathode display better capacity retention during long-term cycling with the modified electrolyte than with 1M LiPF6 in EC:EMC (3:7 by vol.) with 10 wt.% FEC. In addition, the enhanced cycling performance with the modified PFPN-contained electrolyte is also confirmed for 1 Ah SiO x -graphite/NMC811 pouch cells cycled under various pressures. These results open a promising avenue for the development of safe and high-performance electrolytes for silicon-based lithium-ion batteries.

Crack resistant pure and Co-doped LiNiO2 cathodes synthesized by nanosheet precursors

High-Ni materials LiNiO2 or LiNi1-xMxO2 (x < 0.1), whose energy density is over 800 Wh kg−1 (discharge capacity >220 mAh g−1, average discharge voltage ∼3.8 V), are promising candidates as cathode for next-generation electric vehicle batteries. However, commercial applications of high-Ni cathodes have been hindered by their fast capacity fading with cycling. Herein, we synthesized a series of high-Ni materials (LiNiO2, LiNi0.95Co0.05O2 and LiNi0.9Co0.1O2) by adopting nanosheet hydroxide precursors. The obtained high-Ni materials with micro-spheres made up of nanorod grains can sustain the large volume deformation and eliminates cracking during charge-discharge. Owing to the hierarchical structure, our as-synthesized high-Ni cathodes exhibit excellent cycling stability up to 4.7 V and under high temperatures, and the corresponding full cells show superior long cycling stability suitable for practical applications, such as 94% and 83% capacity retention after 300 and 500 cycles, respectively for a LiNi0.95Co0.05O2||graphite cell. Overall, this study offers a facile approach to address the poor cycling stability of high-Ni materials.

A Review of Advanced Cooling Strategies for Battery Thermal Management Systems in Electric Vehicles

Electric vehicles (EVs) offer a potential solution to face the global energy crisis and climate change issues in the transportation sector. Currently, lithium-ion (Li-ion) batteries have gained popularity as a source of energy in EVs, owing to several benefits including higher power density. To compete with internal combustion (IC) engine vehicles, the capacity of Li-ion batteries is continuously increasing to improve the efficiency and reliability of EVs. The performance characteristics and safe operations of Li-ion batteries depend on their operating temperature which demands the effective thermal management of Li-ion batteries. The commercially employed cooling strategies have several obstructions to enable the desired thermal management of high-power density batteries with allowable maximum temperature and symmetrical temperature distribution. The efforts are striving in the direction of searching for advanced cooling strategies which could eliminate the limitations of current cooling strategies and be employed in next-generation battery thermal management systems. The present review summarizes numerous research studies that explore advanced cooling strategies for battery thermal management in EVs. Research studies on phase change material cooling and direct liquid cooling for battery thermal management are comprehensively reviewed over the time period of 2018–2023. This review discusses the various experimental and numerical works executed to date on battery thermal management based on the aforementioned cooling strategies. Considering the practical feasibility and drawbacks of phase change material cooling, the focus of the present review is tilted toward the explanation of current research works on direct liquid cooling as an emerging battery thermal management technique. Direct liquid cooling has the potential to achieve the desired battery performance under normal as well as extreme operating conditions. However, extensive research still needs to be executed to commercialize direct liquid cooling as an advanced battery thermal management technique in EVs. The present review would be referred to as one that gives concrete direction in the search for a suitable advanced cooling strategy for battery thermal management in the next generation of EVs.

Simultaneous B/W dual coating on ultra-high nickel single crystal cathode material for lithium-ion batteries

The ultra-high nickel LiNixCoyMn1-x-yO2 (x > 0.9) cathode material is a prime candidate for powering next-generation electric vehicles. However, its inherent structural instability and complicated interface side-reactions limit its commercialization. Here, the LiNi0.92Co0.04Mn0.04O2 single-crystal cathode material with an average particle size of 1.69 μm is prepared via a simple temperature fluctuation method combined with B and W surface modification. As-formed surface Li–B–O and Li2WO4 lithium ion conductors can successfully enhance the discharge capacity of single crystal LiNi0.92Co0.04Mn0.04O2 from 219.9 to 226.5 mAh g−1 by facilitating lithium ion diffusion. At 4.5 V, the B and W surface modification significantly enhances the cycle retention from 71.8% to 87.1% at 1 C after 100 cycles due to the construction of a uniform boron-rich cathode/electrolyte interface (CEI) layer. The specific composition of the as-formed CEI film is clearly identified. The analysis results of B and W modifications show that the presence of boron-rich CEI and Li2WO4 coating layer protects the particles from electrolyte erosion under high voltage and enhances lithium-ion diffusion on the particle surface. Therefore, the chemical states of Ni within the particle for B- and W-modified samples are distributed more homogeneously after long cycling.

Nano-Confined Tin Oxide in Carbon Nanotube Electrodes via Electrostatic Spray Deposition for Lithium-Ion Batteries.

The development of novel materials is essential for the next generation of electric vehicles and portable devices. Tin oxide (SnO2), with its relatively high theoretical capacity, has been considered as a promising anode material for applications in energy storage devices. However, the SnO2 anode material suffers from poor conductivity and huge volume expansion during charge/discharge cycles. In this study, we evaluated an approach to control the conductivity and volume change of SnO2 through a controllable and effective method by confining different percentages of SnO2 nanoparticles into carbon nanotubes (CNTs). The binder-free confined SnO2 in CNT composite was deposited via an electrostatic spray deposition technique. The morphology of the synthesized and deposited composite was evaluated by scanning electron microscopy and high-resolution transmission electron spectroscopy. The binder-free 20% confined SnO2 in CNT anode delivered a high reversible capacity of 770.6 mAh g-1. The specific capacity of the anode increased to 1069.7 mAh g-1 after 200 cycles, owing to the electrochemical milling effect. The delivered specific capacity after 200 cycles shows that developed novel anode material is suitable for lithium-ion batteries (LIBs).

Design of active-material/solid-electrolyte composite particles with conductive additives for all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (ASSLIBs) are promising candidates for next-generation electric vehicle batteries. The contact interface between the active material (AM) and solid electrolyte (SE) is an important factor that affects the performance of ASSLIB. Composite particles, which are SE-coated AM particles, can form electrodes with large AM-SE contact interfaces. However, they can decrease in cell capacity because of the SE coating layer with electrical non-conductance. This study designed composite particles with conductive additives (CAs) using dry-coating. Acetylene black (AB) and vapor-grown carbon fiber (VGCF) were used as typical CAs, and the composite particles with these CAs were compared with those without CAs and simple mixture. Although the addition of CAs improved the cell capacity and decreased internal resistance, the type of CA significantly affected the rate performance. Because the VGCFs were barely incorporated into the SE coating layer, the incorporation of VGCFs did not improve the rate performance. However, the ABs were effectively incorporated into SE coating layer, resulting in the best rate performance in this study. This difference was due to the ease of supplying electrons to the AM particles. Therefore, AB was suitable for the CA of the composite particles to improve the performance of the ASSLIB.

Chemically and Microstructurally Tailored Concentration Gradient Layered Cathode for Advanced Li-Ion Batteries

The recharging capability of Ni-rich layered cathodes deteriorates rapidly upon cycling, mainly from mechanical instability caused by removing a large amount of Li ions from the host structure.1,2 The resulting microcracks expose the cathode particle interior to electrolyte attack in addition to undermining the mechanical integrity of the cathode particle. In this study, we develop a Ni-rich layered cathode by combining precursor engineering and a new doping strategy during lithiation that generates minimal microcracking and exhibits substantially improved cycling stability. Excess Al is deliberately introduced into a concentration-gradient (CG) hydroxide precursor, which exhibits a highly oriented geometry in which elongated primary particles are aligned in the radial direction of a spherical secondary particles. The excess Al ions enable the refinement of the primary particles in a controlled manner and the precise tailoring of their morphology and orientation. It is demonstrated that the chemical and microstructural engineering of a Li[NixCoyAl1–x–y]O2 (NCA) cathode starting from its precursor stage produces a unique structure that relieves the detrimental mechanical strain and significantly extends the battery life. Thus, the designed CG Li[Ni0.86Co0.1Al0.04]O2 retains 86.5% of the initial capacity after 2000 cycles and an unprecedented 78.0% even at a severe operation condition of 45 oC. The proposed CG Li[Ni0.86Co0.1Al0.04]O2 represents a new class of Ni-rich NCA cathodes that can meet the energy density required for next-generation electric vehicles, without compromising the battery life and safety. Reference s : [1] S. Watanabe, M. Kinoshita, T. Hosokawa, K. Morigaki, K. Nakura, J. Power Sources 258 (2014) 210–217.[2] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 30 (2018) 1155–1163.

Exploring the Interplay between Composite Cathode Design and Cell Performance for Solid-State Lithium Batteries

To accelerate the mass market adaptation of electric vehicles (EVs), raising the gravimetric energy density of batteries to > 250 Wh/kg while maintaining a cost target of < $ 120/kWh is of critical importance (the ultimate targets of the U.S. Department and the advanced battery consortium).[1] Solid-state batteries are widely recognized as excellent prospects for application in the next generation of EVs and other energy storage devices, with the promise to realize higher energy densities, superior safety and environmentally friendly characteristics. At the cell level, the development of SSBs has been hampered by challenges with the interface originating from the poor interfacial stability between the solid-state electrolytes (SSE) and the electrodes. By eliminating the liquid electrolyte, conductive pathways throughout the whole thickness of the positive electrode and at the solid-solid interface become less efficient causing large polarization and diminished cell performance. This can be exacerbated by the current urge to use thicker electrodes in an attempt to increase the energy density which is a common practice in the currently widely adapted lithium ion batteries employing liquid electrolytes. Notably, increasing cathode thickness beyond a certain limit leads to a point of diminishing returns in terms of energy density. This is mainly attributed to the dominating effect of porosity at higher cathode thickness.[2,3] For instance, it has been found that cells with NMC cathodes thinner than 155 μm (< 6.5 mAh cm-2) showed excellent cycling stability and no capacity losses for C-rates up to 0.5C.[4] To address this challenge, one approach is to formulate the cathode (positive electrode) using a small fraction of ionic conductors (Catholyte) that are mostly derived from the solid electrolyte formulation. In addition, this approach could be complemented with the application of a 10 μm intermediate SSE coating at the cathode surface. The use of catholytes has a second advantage of replacing the non-green polymer polyvinylidene fluoride (PVDF) which is currently the most commonly used binder. Having fluorine in its structure, PVDF is non-recyclable and a potential source of environmentally harmful fluorocarbons.[5] We have begun studying the interfacial stability between composite cathodes using LiFePO4 (LFP), a safe, environmentally-friendly, 3.4 V cathode material, and different SSEs including ceramic electrolytes, polymer electrolytes and polymer-ceramic composite electrolytes. In this work, an optimally designed DOE was planned to study the impact of varying active material mass loading in composite cathodes, and the significance of intermediate coating on SSB electrochemical performance. The SSE used is a plasticized polymer electrolyte with the following optimized formula: 77 % PEO, 13% LiTFSI and 10% Succinonitrile (SN) while the composite cathode was composed of 86% LFP, 4% C65 conductive carbon and 10% of the aforementioned SSE as the catholyte. The active material mass loading was varied between 1 – 12 mg cm-2 in 1 mg cm-2 increments and all composite cathodes were tested with and without the intermediate coating layer. This powerful and contemporary statistical approach aims to provide an enhanced design strategy for a popular and very promising SSB chemistry (Li/PEO/LFP). Finally, our findings shed light on a new approach that can be adopted to explore other battery chemistry with higher voltages such as oxide cathodes, non-oxide solid or semi-solid electrolytes.

Uncovering Unique Interfacial Properties in Different Lithium Fluoride Phases: A First-Principles Prediction

Electrolytes are susceptible to reductive decomposition on the surface of negative electrodes leading to the formation and growth of solid-electrolyte interphase (SEI) layer [1]. Stable SEI can be beneficial as a protective layer, given that it can provide insulation to electron transport from the anode to electrolyte, prevent solvent molecules from reaching the anode, and at the same time allow transport of Li+ [2]. Thus, the SEI can contribute critically to the safety and operability of lithium-ion batteries (LIBs), but its functionality heavily depends on the conditions under which it gets synthesized [3]. This can have a significant effect on battery performance. For instance, nucleation and growth of lithium dendrites during cycling is known to result in continuous electrolyte degradation, destruction of the SEI, agglomeration of so-called “dead lithium”, and short-circuiting of the battery [4]. This greatly affects next-generation electric vehicles (EVs), for which all-solid-state lithium-metal batteries (ASSLMBs) have garnered significant attention due to their superior energy storage capacity and safety over LIBs [5]. However, the considerable interfacial impedance originating from poor physical contact and/or parasitic reactions at the Li/SSE interface hinders the development of ASSLMBs. Alternative approaches towards achieving a stable protective interface have been pursued: like use of electrolyte additives to manipulate the constituents and compositions of SEI or designing artificial protective layers to improve performance. For instance, admixture of optimum amounts of fluorine-rich additives like fluoroethylene carbonate (FEC) to traditional carbonate electrolytes (like EC/DMC) has been seen to generate a robust LiF-rich SEI. However, the intrinsic role of LiF remains a topic of uncertainty. Conventional understanding would posit that dominance of LiF leaves the SEI susceptible to poor lithium-ion transport properties. Previously, theoretical works reported significantly lower ionic conductivities in crystalline LiF when compared to other common inorganic SEI materials like Li2O and Li2CO3. Underwhelming transport properties pose serious rate limitations in its effectiveness as a serious candidate for interfacial protection in ASSLMBs. To potentially overcome such bottleneck, this study systematically investigates different phases of LiF: their structures, stabilities and interfacial properties are described using first principles calculations. Careful analysis of the structural models reveals that unlike the widely studied rock salt ordered counterpart, certain phases of LiF exhibit excellent Li+ transport properties with a high predicted diffusivity at room temperature. Mechanically too, improved interfacial qualities are demonstrated with increased flexibility and fracture resistance, opening up important avenues for structural and compositional stability over cell cycling while maintaining its desirable electron-blocking characteristics. However, it is also important to take a step back and note that the rock salt phase is the most energetically stable among LiF phases, which thereby exhibit a propensity for phase transformation under ambient conditions. To overcome this, a strategy of incorporating hetero dopants as impurities to stabilize the host matrix is discussed. By increasing the dopant concentration up to an optimum amount, relative thermodynamic stability of the interface-friendly phases of LiF is achieved. Our examination of the structure reveals unique lithium-dopant interactions which help sustain such LiF phases in the host matrix. The combination of excellent Li-ion transport properties and electron blocking ability makes such LiF-rich composites an excellent candidate for use as an interfacial protective layer that can effectively suppress electrolyte decomposition and Li dendrite propagation, while simultaneously improving the contact and compatibility of the electrode/electrolyte interface. These unique and exceptional traits make them materials of great promise for protecting critical interfaces in ASSLMBs and LIBs.[1] M. Gauthier, T.J. Carney, A. Grimaud, L. Giordano, N. Pour, H.-H. Chang, D.P. Fenning, S.F. Lux, O. Paschos, C. Bauer, F. Maglia, S. Lupart, P. Lamp, Y. Shao-Horn, Electrode−Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights, J. Phys. Chem. Lett. 6 (2015) 4653−4672. https://doi.org/10.1021/acs.jpclett.5b01727[2] D. Bedrov, O. Borodin, J.B. Hooper, Li+ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations, J. Phys. Chem. C 121 (2017) 16098–16109. https://doi.org/10.1021/acs.jpcc.7b04247[3] D. Aurbach, B. Markovsky, I. Weissman, E. Levi, Y. Ein-Eli, On the Correlation Between Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries, Electrochim. Acta 45 (1999) 67−86. https://doi.org/10.1016/S0013-4686(99)00194-2[4] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.G. Zhang, Lithium Metal Anodes for Rechargeable Batteries, Energy Environ. Sci. 7 (2014) 513−537. https://doi.org/10.1039/C3EE40795K[5] J. G. Kim, B. Son, S. Mukherjee, N. Schuppert, A. Bates, O. Kwon, M. J. Choi, H. Y. Chung, S. Park, A review of lithium and non-lithium based solid state batteries, J. Power Sources 282 (2015) 299−322. https://doi.org/10.1016/j.jpowsour.2015.02.054

(Digital Presentation) Temperature Rise during High-Power Pulses of Lithium-Ion Batteries

Lithium-ion batteries currently dominate the light-duty electric vehicle (EV) market due to their high energy density, low self-discharge, and high efficiency. Because of these advantages, Li-ion batteries are now being explored for next-generation EV applications like heavy trucks and aerial vehicles. The new applications present design challenges somewhat different from light-duty, road vehicles. For instance, aerial EVs during take-off and landing or heavy trucks on lengthy inclines/declines require high power (or regenerative) pulses for >1 minute. These long-duration, high power pulses may lead to significant temperature rise that could damage the battery and/or produce unsafe conditions resulting in thermal runaway. Accurate estimations of the temperature rise during these pulses are important for initial studies focused on assessing the validity of Li-ion batteries in these and other applications.This work starts by demonstrating how the accuracy of approximating the temperature rise using Joule heating – i.e., I2R, where I is the applied current and R is the electrochemical resistance – decays considerably for high power pulses. A 3-D thermal-electrochemical model of an NMC532-Graphite pouch cell is then used to explain the causes of the deviation. It is shown that a combination of transport in the electrolyte and self-heating cause variations in the resistance during the pulse, which invalidate the Joule heating approximation. Insights from these results are used to develop a correlation for the temperature rise during high power pulses. The correlation provides an improved estimation of the temperature using minimal experimental data for the area specific resistance of the cell.