Composite Negative Electrode Research Articles

A metallic lithium anode for solid-state batteries with low volume change by utilizing a modified porous carbon host

Lithium metal is a promising negative electrode material for solid-state batteries (SSBs). However, uncontrolled lithium deposition and stripping cause several issues during cycling. Herein, the microporous carbon YP-50F and its modifications obtained by thermal ethene-based chemical vapor deposition (CVD) are investigated as 3D host to accommodate and control the deposition of metallic lithium. In half-cells vs. lithium, the CVD-YP composite electrode with Li6PS5Cl electrolyte shows significantly higher initial coulombic efficiency (79.5 %) than the pristine carbon (55.3 %) due to the reduction of side reactions. The metallic character of the deposited lithium is evidenced by 7Li Nuclear Magnetic Resonance spectroscopy. However, full cells with nickel-rich NCM (LiNi0.9Co0.05Mn0.05O2) positive electrode and CVD-YP composite negative electrode show reasonable performance over 50 cycles without occurrence of (micro-) short-circuits (in contrast to 2D reference electrodes). In addition, small prototype pouch cells are investigated and the thickness change during (dis)charging is less than one third compared to a bare lithium metal electrode. This demonstrates low breathing behavior of the CVD-YP electrode and confirms the reversible storage of metallic lithium within the 3D carbon-based composite electrode.

High-capacity, fast-charging and long-life magnesium/black phosphorous composite negative electrode for non-aqueous magnesium battery

Secondary non-aqueous magnesium-based batteries are a promising candidate for post-lithium-ion battery technologies. However, the uneven Mg plating behavior at the negative electrode leads to high overpotential and short cycle life. Here, to circumvent these issues, we report the preparation of a magnesium/black phosphorus (Mg@BP) composite and its use as a negative electrode for non-aqueous magnesium-based batteries. Via in situ and ex situ physicochemical measurements, we demonstrate that Mg ions are initially intercalated in black phosphorus two-dimensional structures, forming chemically stable MgxP intermediates. After the formation of the intermediates, Mg electrodeposition reaction became the predominant. When tested in the asymmetric coin cell configuration, the Mg@BP composite electrode allowed stable stripping/plating performances for 1600 h (800 cycles), a cumulative capacity of 3200 mAh cm−2, and a Coulombic efficiency of 99.98%. Assembly and testing of the Mg@BP | |nano-CuS coin cell enabled a discharge capacity of 398 mAh g−1 and an average cell discharge potential of about 1.15 V at a specific current of 560 mA g−1 with a low decay rate of 0.016% per cycle for 225 cycles at 25 °C.

Bi2O3@reduced graphene oxide and NiCo2@Ni3Co electrodes for all-electrodeposited high-performance supercapacitors

A novel α-Bi2O3@reduced graphene oxide (rGO) composite negative electrode is designed using an electrodeposition technique, exhibiting an activation process during the first 100 charge-discharge cycles. The bismuth compounds in an initial adsorbed state gradually transformed into a dissolved state, resulting in a distinctive morphological change and the formation of a porous nanosheet structure. At a current density of 1 A/g, the α-Bi2O3@rGO achieves a specific capacitance of 1144 F/g (317 mAh/g), representing 92.18 % of its theoretical value. Even when the current density is increased by 20 times, the capacitance still maintains at 91.71 %. Additionally, a multi-layered composite cathode of NiCo2@Ni3Co is prepared. Based on these two electrodes, an all-electrodeposited soft-packaged supercapacitor (AESPS) is assembled, reaching an energy density of 107.8 Wh/kg at a power density of 800 W/kg, and 73.8 Wh/kg at 16 kW/kg. These outstanding electrochemical performances strongly demonstrate their potential in novel energy storage devices.

Synthesis of Co@CoO/C by micro-tube method and their electrochemical performances

Lithium-ion batteries (LIBs) are promising secondary batteries that are widely used in portable electronic devices, electric vehicles and smart grids. The design and synthesis of high-performance electrode materials play a crucial role in achieving lithium-ion batteries with high energy density, prolonged cycle life, and superior safety. CoO has attracted significant attention as a negative electrode material for lithium-ion batteries due to its high theoretical capacity and abundant resources. However, its limited conductivity and suboptimal cycling performance impede its potential applications. The study proposes a novel micro-tube reaction method for the synthesis of Co@CoO/C, utilizing Kapok fiber as a template with a special hollow structure. The microstructure and composition of the samples were characterized using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After conducting electrochemical performance tests, it was discovered that at a current density of 100 mA/g and within the range of 0.01–3.0 V for 50 charge and discharge cycles. Co@CoO/C composite negative electrode exhibits a reversible lithium insertion specific capacity of 499.8 mAh/g and keep a discharge capacity retention rate of 97.6 %. The greatly improved lithium storage and stability performance of Co@CoO/C composite anode is mainly attributed to the synergistic effect between Co@CoO nanoparticles and the kapok carbon microtubule structure.

Investigation of The Failure Mechanisms of Li-Ion Pouch Cells with Si/Graphite Composite Negative Electrodes and Single Wall Carbon Nanotube Conducting Additive

Silicon-Graphite composite electrodes are a rapidly developing area of research and commercialization. Increasing the energy density of current Li-ion battery technology can be done by simply creating silicon-graphite composite electrodes. It is well known that the failure of these silicon-graphite composite electrodes stems from the expansion of the silicon during cycling that causes mechanical degradation, excessive SEI formation, and electrode shift loss. Here we explore the use and capacity loss mechanisms of a silicon-graphite composite anode employing CMC/SBR binder used in conjunction with single wall carbon nanotubes. These nanotubes are thought to be effective in increasing mechanical resiliency of the electrodes and increase the electrical connectivity between particles within the formed electrode. When the Si/graphite electrode cycles, it is believed that the SWCNTs help keep the active particles electrically connected and, hence, electrochemically active. Through dV/dQ analysis and in situ pressure monitoring, the pouch cells studied here are shown to exhibit minimal loss of active mass in the positive and negative electrodes but experience capacity loss due to continued negative electrode SEI growth leading to lithium inventory or shift loss.

Optimization of Si-containing and SiO based Anodes with Single-Walled Carbon Nanotubes for High Energy Density Applications

Lithium-ion batteries require a high energy density when being used in applications such as electric vehicles or portable electronics. This can be achieved on a large scale by improving packaging and implementation, or on a material scale by selecting more energy dense electrode active material. Silicon can be used as a replacement for graphite in negative electrodes if the detrimental volume expansions can be contained. These volume expansions cause continuous mechanical degradation capacity loss leading to short lifetimes that do not meet industry standards. These high-capacity high volume expansion materials such as silicon and SiO must be used in conjunction with more stable electrode materials like graphite to reduce the mechanical degradation caused by volume change. Single-walled carbon nanotubes are shown to be a simple yet effective drop in addition to improve electrical connectivity and increase capacity retention in these silicon-based composite negative electrodes. This added particle interconnectivity from the high tensile strength carbon nanotubes allows for the use of simple binders such as CMC/SBR to create composite electrodes with competitive performance without the use of expensive polymers or complex nanostructures.

Insights into mechanics and electrochemistry evolution of SiO/graphite anode by a composite electrode model

Silicon-based materials are crucial for high-capacity anodes, but their volume expansion in batteries due to the presence of silicon requires further analysis and research. Silicon monoxide/Graphite (SiO/C) is a composite material that combines the volume expansion of silicon oxide material with the practical application of carbon material. Therefore, understanding its behavior during actual use is important, particularly in full batteries and in pairs with high-capacity LiNi0.8Co0.15Al0.05O2 (NCA) cathode. There are fewer studies on this topic, which highlights the need for research. Thus, in this work, SiO/C composite negative electrodes are prepared with different compaction densities (CDs) of 1.38, 1.52, and 1.62 g cm−3. Pouch cells are assembled with NCA positive electrode to investigate the changes in battery thickness and internal resistance under different CDs and state of charge (SOC), as well as the Coulombic efficiency and cyclic performance of batteries are also examined. Additionally, the capacity-voltage curves, expansion curves under different CDs and SOC, particle stress change, and lithium concentration distribution under different CDs are comprehensively simulated. Thus, the evolution of lithium concentration distribution and electrodes volumetric strain during charge and discharge are directly presented. The established model through matching experimental data provides a research basis for predicting the performance of SiO/C negative electrodes, especially its electrochemical and mechanical performance evolution in high‑nickel full batteries. This study has important implications for the development of high-performance silicon-based anodes in practical applications.

High energy density pouch-type supercapacitor achieved by MOFs derived 3D hollow N-doped carbon with Fe2O3 and hierarchical CuCo2S4@NiFe-LDH core-shell nanostructures

The multicomponent rational control and distinctive architectural design of electrode materials remain critical factors for enhancing the energy density of supercapacitors. Herein, metal-organic framework (MOF)-derived three-dimensional (3D) hollow nitrogen-doped carbon (NHCs) with Fe2O3 core-shell composite negative electrode materials (NHCs@Fe2O3) were developed. In this framework, 1) the high specific surface area caused by the distinctive core-shell structure facilitated the electrolyte infiltration in the hollow skeleton, which shortened the ion transport path and enabled fast electron transfer; and 2) the synergistic effect of the nitrogen-containing groups of the hollow carbon and the reversible Faraday reaction of metal oxides increased the ratio of the pseudocapacitance. These phenomena were the primary reasons for the enhanced capacity of the core-shell electrode. Additionally, hierarchical CuCo2S4@layered double hydroxide (NiFe-LDH) nanobelt core-shell heterostructure arrays integrated on the nickel foam were used for the positive electrode materials. The asymmetric pouch-type supercapacitor assembled with NHCs@Fe2O3 (negative electrode) and CuCo2S4@NiFe-LDH (positive electrode) exhibited a high energy density of 68.6 W h kg–1 at a power density of 828.9 W kg–1. This work offers an effective strategy for fabricating multicomponent core-shell materials and optimizing the interactions between the components to enhance the electrochemical performance in energy storage applications.

Strategies of Practical Implementation of Chemical Pre-Lithiation Using Lithium Arene Complex Solutions: A Systematic Study on Silicon-Based Anodes

Currently, Lithium ion batteries (LIBs) are state-of-the-art (SOTA) energy storage systems. There is an urgent need for further improvements in terms of gravimetric and volumetric energy of LIBs, for a successful market penetration of electric vehicles. Therefore, development of advanced negative electrode materials is of high interest. Here, silicon (Si) is a promising active material to replace SOTA graphite due to its ~10-fold higher specific capacity and being also high abundant.However, Si undergoes severe volume changes up to 280% during (de-)lithiation, resulting in fast capacity fading and short cycle life due to the continuous re-formation of the solid electrolyte interphase (SEI), leading to active lithium losses (ALL). In order to counteract ALL, research is focusing on suitable pre-lithiation processes. Among different pre-lithiation methods, chemical pre-lithiation by application of lithium arene complex (LAC) solutions is promising as it is a fast, easy and cost-effective method.In this work, the stability of three different solvents to produce a 4,4’-dimethylbiphenyl (4,4’-DMBP) LAC is investigated via solid phase microextraction gas chromatography-mass spectrometry method (SPME-GC-MS). The optimized LAC solution is used to evaluate the stability of different binder systems with respect to electrode manufacturing. Based on these fundamental insights, different parameters such as the reaction temperature (T) and pre-lithiation time (PL-t) are systematically investigated regarding suitable degrees of pre-lithiation (DOPL) of the negative electrode. DOPLs up to a plateau of 55% can be obtained by using 0.5 M 4,4’-DMBP in tetrahydrofuran (THF) as LAC solution. Higher temperature during the reaction reduces the PL-t until achieving a pre-lithiation plateau. The impact of the parameters T and PL-t towards the electrochemical performance of Si-based LIB full cells is thoroughly investigated. It is shown that this approach improves the cycle life of a silicon nanowire graphite composite negative electrode up to 600% compared to the pristine electrodes

Enhancing heat-to-electricity conversion performance of the thermally regenerative electrochemical cycle using carbon-copper composite electrodes

Low-grade heat is ubiquitous but difficult to be recovered. Thermally regenerative electrochemical cycle (TREC) system is expected to be one of the technologies for efficient recovery of low-grade heat. However, due to the limited temperature coefficient and temperature difference, it is difficult to further improve the heat-to-electricity conversion performance of TREC system. Therefore, a TREC system with carbon-copper composite negative electrode is proposed. By studying various factors (acid treatment, current density, and electrolyte concentration) for the deposition of copper metal on carbon cloth, suitable conditions for the preparation of carbon-copper composite electrodes were determined. The proposed method increased the electrode reaction contact area, reduced the electrical energy charged during the TREC system cycle, and increased the heat-to-electricity conversion efficiency of the system to 1.3 times (from 2.97% to 3.86%) compared with the conventional system with copper sheet negative electrode.

A novel hierarchical heterostructure derived from alpha iron oxide supported carbon nano-network for high-performance supercapacitor application

Ferric oxide (Fe2O3) has gained immense attention as a favorable negatrode (negative electrode) material for high-performance supercapacitors for its low cost, high theoretical specific capacity, and abundance in nature. However, owing to its relatively large volume change during the long charge-discharge cycle and comparatively, low conductivity utterly hinders its electrochemical performance. Herein, a composite negative electrode consisting of Fe2O3 nanoparticles (NPs) decorated on CNT-graphene conductive networks (Fe2O3@GR-CNTs/NF) fabricated using a two-step approach is reported. The fabricated composite electrode exhibited a superior specific capacitance (114.2F/g) and good stability (64.2% after 2000 cycles) because of the unique structure of the composite material.

In situ form core-shell carbon nanotube-imide COF composite for high performance negative electrode of pseudocapacitor

High performance negative electrode material of pseudocapacitor is of paramount importance for the device energy storage capacity. Herein, a novel carbon nanotube-imide COF composite negative electrode material was successfully prepared by in situ growth of imide COF on the wall of nanotubes containing amine groups. FT-IR, XRD, SEM and HR-TEM verify that the core-shell composite was formed. Driven by the π-π interaction between carbon nanotube and imide COF, the composite exhibits high electron conductivity. N2 adsorption-desorption test further displays that the composite still possesses adequate porous structure with a high specific surface area of 386 m2 g−1. The unique core-shell structure enables the carbon nanotube-imide COF composite with high energy storage capacity, a high specific capacitance of 278 F g−1 at 0.5 A g−1 between -1 V to 0 V in the neutral electrolyte, among the best results for the recent reported high performance negative pseudocapacitance organic materials. Interestingly, the composite still gives a high specific capacitance of 72 F g−1 at high current density of 50 A g−1. These interesting energy storage properties should be attributed to the synergetic mechanism between carbon nanotube and COF. Moreover, the asymmetric device assumed with the carbon nanotube-imide COF composite as the negative material and the RuO2 as the positive material, displays high energy density of 25.9 W h kg−1 with a power density of 357.2 W kg−1. The composite negative material design idea would offer reference for other high performance energy storage materials.

Preparation of porous silicon/metal composite negative electrode materials and their application in high-energy lithium batteries

Abstract Porous silicon/metal composites have huge specific surface area, rich pore structure, tough framework system and low SEI film formation rate, and have great application prospects in the field of high-energy lithium batteries. Porous silicon/metal composites have abundant pore structure, which can greatly alleviate the volume effect of silicon during charging and discharging. The introduction of metal can increase the conduction rate and reduce the formation rate of SEI film. However, the development of a facile and rapid method to synthesize porous silicon/metal composites remains a challenge for current research. Based on the current research progress of porous silicon/metal composites and related literatures, in this paper, the preparation methods of porous silicon/metal composites in recent years are reviewed in detail, with a focus on their applications in the field of high-energy lithium batteries. Finally, the future development direction of porous silicon/metal composites is further prospected.

A rechargeable aqueous manganese-ion battery based on intercalation chemistry

Aqueous rechargeable metal batteries are intrinsically safe due to the utilization of low-cost and non-flammable water-based electrolyte solutions. However, the discharge voltages of these electrochemical energy storage systems are often limited, thus, resulting in unsatisfactory energy density. Therefore, it is of paramount importance to investigate alternative aqueous metal battery systems to improve the discharge voltage. Herein, we report reversible manganese-ion intercalation chemistry in an aqueous electrolyte solution, where inorganic and organic compounds act as positive electrode active materials for Mn2+ storage when coupled with a Mn/carbon composite negative electrode. In one case, the layered Mn0.18V2O5·nH2O inorganic cathode demonstrates fast and reversible Mn2+ insertion/extraction due to the large lattice spacing, thus, enabling adequate power performances and stable cycling behavior. In the other case, the tetrachloro-1,4-benzoquinone organic cathode molecules undergo enolization during charge/discharge processes, thus, contributing to achieving a stable cell discharge plateau at about 1.37 V. Interestingly, the low redox potential of the Mn/Mn2+ redox couple vs. standard hydrogen electrode (i.e., −1.19 V) enables the production of aqueous manganese metal cells with operational voltages higher than their zinc metal counterparts.

Design of ultrafine silicon structure for lithium battery and research progress of silicon-carbon composite negative electrode materials

As demand for high-performance electric vehicles, portable electronic equipment, and energy storage devices increases rapidly, the development of lithium-ion batteries with higher specific capacity and rate performance has become more and more urgent. As the main body of lithium storage, negative electrode materials have become the key to improving the performance of lithium batteries. The high specific capacity and low lithium insertion potential of silicon materials make them the best choice to replace traditional graphite negative electrodes. Pure silicon negative electrodes have huge volume expansion effects and SEI membranes (solid electrolyte interface) are easily damaged. Therefore, researchers have improved the performance of negative electrode materials through silicon-carbon composites. This article introduces the current design ideas of ultra-fine silicon structure for lithium batteries and the method of compounding with carbon materials, and reviews the research progress of the performance of silicon-carbon composite negative electrode materials. Ultra-fine silicon materials include disorderly dispersed ultra-fine silicon particles such as porous structures, hollow structures, and core-shell structures; and ordered ultra-fine silicon, such as silicon nanowire arrays, silicon nanotube arrays, and interconnected silicon nano-films. The article analyzes and compares the composite method of ultrafine silicon and carbon materials with different structural designs, and the effect of composite negative electrode materials on the specific capacity and cycle performance of the battery. Finally, the research direction of silicon-carbon composite negative electrode materials is prospected.

(Invited) Kinetic Analysis of Water-Stable Protected Graphite Electrode for High Rate Aqueous Lithium Ion Capacitors

The so-called water-stable protected Li anode is a composite negative electrode that is compatible with aqueous electrochemistry and has been successfully used for aqueous Li-O2 batteries.1,2 The multi-layered composite electrode is composed of a water stable lithium-ion conducting glass ceramic (e.g. LTAP, Li1+x+y Ti2-x Al x P3-y Si y O12), a Li electrode and a polymer electrolyte buffer layer to insulate the solid electrolyte from the Li electrode. We have applied the protected Li anode to aqueous hybrid supercapacitors, extending the cell voltage to 4 V and allowing the use of pseudocapacitive oxide electrodes such as RuO2 and MnO2.3,4 Later, protected Li anodes were expanded to pre-doped carbon (protected Li x C6 electrode), paving the way to the first aqueous lithium-ion capacitor.5 Despite the many advantageous of the aqueous lithium ion capacitor with pseudocapacitve positive electrodes, the protected anode suffers from large resistance due to its multi-component structure, leading to insufficient power density and energy efficiency. Improved protected negative electrodes were prepared by studying the effect of different buffer electrolytes, salts and ionic liquid additives, negative electrodes, binders, and solid electrolytes. The best performing protected anode so far is one incorporating a 50 μm thick LTAP with an alginate gel buffer layer and a pre-doped graphite electrode (Li x C6 | Alg-LiFSI/P13FSI | LTAP50). Overall, a 95% reduction in total resistance compared to our initial cell (Li | PEO-LiTFSI | LTAP150) was achieved.6 Protected Li x C6 negative electrodes with different LTAP thickness at various pre-lithiation ratio (x=0.1, 0.5, and 0.9) were characterized by electrochemical impedance spectroscopy (EIS) between 10 to 70°C. The total resistance and apparent activation energies E app calculated from EIS were more or less independent on pre-lithiation ratio. At low temperature (10°C), R grain was the main contributor to the total resistance, while at high temperature (70°C), R bulk became the major source of resistance. The E app, bulk was ~10 kJ/mol, which is 1/3 to 1/4 of E app, grain and E app, interface+ct, which have an E app~40 kJ/mol. The results from the EIS analysis implies that it is important to reduce R bulk to improve the high temperature performance, while for low temperature performance, R grain needs to be reduced. R bulk is the bulk resistance from the electrolytes (1.0 M Li2SO4 and Alg-LiFSI/P13FSI) and the intrinsic resistance of LTAP. R grain mainly comes from the grain boundary resistance of LTAP. Overall, the general message is that the solid electrolyte is at present the determining factor of the aqueous lithium-ion capacitor and development of a thin water stable solid electrolyte is important for improving the power density and energy efficiency of the 4 V- aqueous hybrid capacitor.This work was partially supported by an Advanced Low Carbon Technology Research Development Program (JST-ALCA, JPMJAL1008).[1] T. Zhang, N. Imanishi, S. Hasegawa, A. Hirano, J. Xie, Y. Takeda, O. Yamamoto, N. Sammes, J. Electrochem. Soc., 155, A965 (2008).[2] T. Zhang, N. Imanishi, S. Hasegawa, A. Hirano, J. Xie, Y. Takeda, O. Yamamoto, N. Sammes, Electrochem. Solid-State Lett., 12, A132 (2009).[3] S. Makino, Y. Shinohara, T. Ban, W. Shimizu, K. Takahashi, N. Imanishi, W. Sugimoto, RSC Advances, 2(32), 12144 (2012).[4] S. Makino, T. Ban, W. Sugimoto, Electrochemistry, 81(10), 795 (2013).[5] S. Makino, R. Yamamoto, S. Sugimoto, W. Sugimoto, J. Power Sources, 326, 711 (2016).[6] Y. Sato, S. Makino, D. Mochizuki, S. Hideshima, W. Sugimoto, Electrochemistry, 88(3), 139 (2020).

The preparation of graphite/silicon@carbon composites for lithium-ion batteries through molten salts electrolysis

High-specific-capacity materials are crucial for the high-energy-density lithium-ion secondary batteries as the automakers and customers are both eager to extend the cruising range of electric vehicles. The current commercial silicon/carbon composites are based on the mechanical mixture of silicon and graphite, but this weak combination is not suitable for the higher-capacity materials. Here, low-cost raw materials are used for the preparation of a graphite/silicon@carbon composite negative electrode material, which synergizes ball milling, molten salts electrolysis and carbon coating. Silica is in situ electrochemically reduced to silicon on the flaky graphite serving as the conducting substrate during the electrolysis process. It is found that ball milling increases the active sites on the basal plane of graphite, which is beneficial for the nucleation and growth of the silicon, and enhances the bonding of silicon particles and graphite. As for the electrochemical results of coin-type cells, this graphite/silicon@carbon composite material exhibits a better cycle performance than the commercial Si/C 650 silicon-based composite material.

Improving zinc porous electrode for secondary alkaline batteries: Toward a simple design of optimized 3D conductive network current collector

The internal migration of zinc within the thickness of porous composite negative electrodes for rechargeable zinc batteries causes detrimental shape change of the zinc electrode. It depends on various parameters linked to the electron conduction in the electrode: electronic percolation, conductive additives, primary current collector. This study highlights a simple solution, that drastically enhances the electrochemical performance of thick and porous zinc electrodes, by rethinking their architecture. Using a multiplicity of thin current collectors enables to create a 3D network of electronic percolation and a better repartition of the current lines within the electrode; as a result, the formation of multiple active zinc cores in the electrode volume is better controlled. This strategy allows to improve the management of zinc migration within the electrode structure, leading to minimal densification of each zinc core, and overall enables higher reversibility of zinc oxidation/reduction upon discharge/charge. It finally mitigates the initial drastic capacity fading observed on standard type calcium zincate negative electrode.

Understanding the Thermal Runaway of Ni-Rich Lithium-Ion Batteries

The main safety issue pertaining to operating lithium-ion batteries (LIBs) relates to their sensitivity to thermal runaway. This complex multiphysics phenomenon was observed in two commercial 18650 Ni-rich LIBs, namely a Panasonic NCR GA and a LG HG2, which were based on L i ( N i 0.8 C o 0.15 A l 0.05 ) O 2 (NCA) and L i ( N i 0.8 M n 0.1 C o 0.1 ) O 2 (NMC811), respectively, for positive electrodes, in combination with graphite-SiOx composite negative electrodes. At pristine state, the batteries were charged to different levels of state of charge (SOC) (100% and 50%) and were investigated through thermal abuse tests in quasi-adiabatic conditions of accelerating rate calorimetry (ARC). The results confirmed the proposed complete thermal runaway of exothermic chain reactions. The different factors impacting the thermal runaway kinetics were also studied by considering the intertwined impacts of SOC and the related properties of these highly reactive Ni-rich technologies. All tested cells started their accelerated thermal runaway stage at the same self-heating temperature rate of ~48 °C/min. Regardless of technology, cells at reduced SOC are less reactive. Regardless of SOC levels, the Panasonic NCR GA battery technology had a wider safe region than that of the LG HG2 battery. This technology also delayed the hard internal short circuit and shifted the final venting to a higher temperature. However, above this critical temperature, it exhibited the most severe irreversible self-heating stage, with the highest self-heating temperature rate over the longest duration.

Multiscale Multiphase Lithiation and Delithiation Mechanisms in a Composite Electrode Unraveled by Simultaneous Operando Small-Angle and Wide-Angle X-Ray Scattering.

The (de)lithiation process and resulting atomic and nanoscale morphological changes of an a-Si/c-FeSi2/graphite composite negative electrode are investigated within a Li-ion full cell at several current rates (C-rates) and after prolonged cycling by simultaneous operando synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS). WAXS allows the probing of the local crystalline structure. In particular, the observation of the graphite (de)lithiation process, revealed by the LixC6 Bragg reflections, enables access to the respective capacities of both graphite and active silicon. Simultaneously and independently, information on the silicon state of (de)lithiation and nanoscale morphology (1 to 60 nm) is obtained through SAXS. During lithiation, the SAXS intensity in the region corresponding to characteristic distances within the a-Si/c-FeSi2 domains increases. The combination of the SAXS/WAXS measurements over the course of several charge/discharge cycles, in pristine and aged electrodes, provides a complete picture of the C-rate-dependent sequential (de)lithiation mechanism of the a-Si/c-FeSi2/graphite anode. Our results indicate that, within the composite electrode, the active silicon volume does not increase linearly with lithium insertion and point toward the important role of the electrode morphology to accommodate the nanoscale silicon expansion, an effect that remains beneficial after cell aging and most probably explains the excellent performance of the composite material.