Transition Metal Oxide Cathode Research Articles

Quasi-Solid-State Conversion with Fast Redox Kinetics Enabled by a Sulfonamide-Based Electrolyte in Li-Organic Batteries.

The serious dissolution of organic electrode materials (e.g., perylene-3,4,9,10-tetracarboxylic dianhydride, PTCDA) in electrolytes is a major challenge, deteriorating their electrochemical performances and hindering the interpretation of the fundamental redox reaction mechanisms including the intrinsic kinetics and the solvent cointercalation. To address these issues, we propose a rationally designed sulfonamide-based electrolyte to enable a quasi-solid-state conversion (QSSC) of the PTCDA cathode by effectively suppressing its dissolution in the electrolyte. Benefiting from the QSSC, the Li||PTCDA cells can retain ∼95.8% of the original capacity after 300 cycles with both high and stable energy efficiencies >95%, even comparable to the layered transition-metal oxide cathodes, greatly outperforming an ether-based electrolyte with a high PTCDA solubility. The high energy efficiencies indicate that the QSSC of PTCDA has intrinsic fast redox kinetics. Furthermore, the solvent cointercalation mechanism was investigated by density functional theory/molecular dynamic calculations. This work develops a strategy for designing electrolytes for highly stable and efficient Li-organic batteries.

Progress and Perspective of High‐Entropy Strategy Applied in Layered Transition Metal Oxide Cathode Materials for High‐Energy and Long Cycle Life Sodium‐Ion Batteries

AbstractLayered transition metal oxide (LTMO) cathode materials of sodium‐ion batteries (SIBs) have shown great potential in large‐scale energy storage applications owing to their distinctive periodic layered structure and 2D ion diffusion channels. However, several challenges have hindered their widespread application, including phase transition complexities, interface instability, and susceptibility to air exposure. Fortunately, an impactful solution has emerged in the form of a high‐entropy doping strategy employed in energy storage research. Through the implementation of high‐entropy doping, LTMOs can overcome the aforementioned limitations, thereby elevating LTMO materials to a highly competitive and attractive option for next‐generation cathodes of SIBs. Thus, a comprehensive overview of the origins, definition, and characteristics of high‐entropy doping is provided. Additionally, the challenges associated with LTMOs in SIBs are explored, and discussed various modification methods to address these challenges. This review places significant emphasis on conducting a thorough analysis of the research advancements about high‐entropy LTMOs utilized in SIBs. Furthermore, a meticulous assessment of the future development trajectory is undertaken, heralding valuable research insights for the design and synthesis of advanced energy storage materials.

The Role and Substitution of Cobalt in the Cobalt‐Lean/Free Nickel‐Based Layered Transition Metal Oxides for Lithium Ion Batteries

AbstractThe Nickel‐based layered transition metal oxide cathode represented by NCM (LiNixCoyMnzO2, x+y+z=1) and NCA (LiNixCoyAlzO2, x+y+z=1) is widely used in the electric vehicle market due to its specific capacity and high working potential, in which Cobalt (Co) plays a huge role in improving the structural stability during the cycle. However, the limited supply of Co, due to its scarcity and the influence of geopolitics, poses a significant constraint on the further advancement of the Nickel‐based layered transition metal oxide cathode in the field of energy storage. In this paper, the mechanism of Co in the Nickel‐based layered transition metal oxides is reviewed, including its critical role for structural stability such as the inhibition of cationic mixing and the release of lattice oxygen et al. Subsequently, it outlines various strategies to enhance the performance of Co‐lean/free materials, such as ion doping, including single‐ion doping and multi‐ion co‐doping, and various surface coating strategies, so as to eliminate the adverse effects of Co loss on materials. Ultimately, this paper offers a glimpse into the promising future of Cobalt‐free strategies for high performance of Nickel‐based layered transition metal oxides.

Investigation on the Necessity of Low Rates Activation toward Lithium‐Sulfur Batteries

AbstractLow rate activation process is always used in conventional transition metal oxide cathode and fully activates active substances/electrolyte to achieve stable electrochemical performance. However, the related working mechanism in lithium‐sulfur (Li‐ battery is unclear due to the multiple complex chemical reaction steps including the redox of sulfur and the dissolution of polysulfides intermediate. Hence, the influencing mechanism of activation process on Li‐S battery is explored by adopting different current densities of 0.05, 0.2, and 1 C in initial three cycles before long‐term cycling tests at 0.2 C (denoted by 0.05, 0.2, and 1‐battery). 0.05‐battery presents the highest initial capacity in activation process, while 0.2‐battery presents superior electrochemical performances after 150 cycles. The similar trend can be found in more long‐term cycling rates such as 0.02, 0.1, 0.5, and 1 C. Potentiostatically Li2S precipitation test demonstrates that rapid generation of Li2S is achieved at higher current density, and S8‐Li2Sn‐Li2S conversion is accelerated according to Tafel plots. However, interfacial electrochemical and physical characterizations suggest that serious lithium dendrite growth will be induced under high current density. Therefore, considering the reaction kinetics and interfacial properties, low rate activation process is unnecessary when cycling current lower than 1 C for Li‐S battery.

Chemo-mechanical instabilities in lithium cobalt oxide at higher state-of-charge in Li-Ion batteries

Transition metal oxide cathodes are widely used in commercial Li-ion batteries. However, their practical charge capacity is limited due to severe chemo-mechanical instabilities at higher charge voltage, and state-of-charge condition. Here, in situ stress and strain measurements were synchronized to probe mechanical deformations in the lithium cobalt oxide (LCO) cathode via a multi-beam stress sensor and digital image correlation, respectively. In situ mechanical measurements revealed how Li removal from the electrode structure induces deformations on the LCO composite cathodes during cycling. The structure and morphology of the LCO cathodes were further investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies. Two distinct electrochemical and mechanical behaviors were identified when the LCO was charged up to 4.65 V. The LCO undergoes a compressive stress generation when charged up to 4.2 V and surface fractures on the LCO particles were detected by SEM. LCO cathode experienced significantly large contractions (negative strains) when charged up to 4.65 V, where intergranular crack formation and phase transformation were detected on the LCO particles via SEM and XRD, respectively. Overall, the study bridges complicated structural deformations with in situ analysis of mechanical degradations in LCO cathodes charged at higher voltages. The correlation is vital to understanding instability mechanisms in transition metal oxides at high voltages for alkali metal ion batteries.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Solvent-mediated oxide hydrogenation in layered cathodes.

Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. We demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries.

Microstrain screening towards defect-less layered transition metal oxide cathodes.

Microstrain and the associated surface-to-bulk propagation of structural defects are known to be major roadblocks to developing high-energy and long-life batteries. However, the origin and effects of microstrain during the synthesis of battery materials remain largely unknown. Here we perform microstrain screening during real-time and realistic synthesis of sodium layered oxide cathodes. Evidence gathered from multiscale in situ synchrotron X-ray diffraction and microscopy characterization collectively reveals that the spatial distribution of transition metals within individual precursor particles strongly governs the nanoscale phase transformation, local charge heterogeneity and accumulation of microstrain during synthesis. This unexpected dominance of transition metals results in a counterintuitive outward propagation of defect nucleation and growth. These insights direct a more rational synthesis route to reduce the microstrain and crystallographic defects within the bulk lattice, leading to significantly improved structural stability. The present work on microstrain screening represents a critical step towards synthesis-by-design of defect-less battery materials.

Electrochemical Performance of Lithium-Ion Cells with Lithium- and Manganese- Rich Oxide Cathodes

State-of the-art (SOA) lithium-ion batteries (LIBs) being developed for transportation applications contain a transition metal (TM) oxide cathode and a graphite anode; both serve as host-matrices to house lithium ions during battery operation. The cathodes typically contains Li1+xNiaCobAlcO2 (NCA) or Li1+xNiaMnbCocO2 (NMC) oxides: both oxide chemistries contain Co, which is known to preserve the layered structure during lithium extraction/insertion reactions. However, the possibility of a global Co shortage and soaring costs has galvanized the LIB community to explore sustainable cathode chemistries, while maintaining cell performance (energy/power densities), safety and cycle/calendar life. In this context the U.S. Department of Energy (DOE) initiated the Earth-Abundant Cathode Active Material (EaCAM) Program for the development of sustainable cathode chemistries, based on earth-abundant elements.Materials of particular interest to the EaCAM program are the x Li2MnO3 ● (1-x) LiMnaNibZcO2 composites; here Z refers to various elements that could be included in the oxide structure. These lithium- and manganese- rich materials are considered attractive candidates because of their high specific capacities, zero cobalt content, and lower costs compared to the SOA oxides. We have been examining the electrochemical behavior of cells with these oxides, with a particular focus on the 0.3 Li2MnO3 ● 0.7 LiMn0.5Ni0.5O2 (LMR) compound.During this presentation, we will show results from battery cells, containing LMR cathodes and either graphite or lithium-titanate anodes. In particular, the use of a microprobe reference electrode to monitor the cathode and anode potentials will be discussed. The effect of activation on cell performance and the performance loss characteristics during cycling will be highlighted. We will show how cell impedance is affected by voltage hysteresis and the voltage fade that results from cycling. Our ultimate goal is to identify constituents and mechanisms responsible for the cell performance loss and develop solutions to mitigate this degradation.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Scalable and Non-Destructive Analysis of Battery Degradation and Performance

Electrochemical processes occurring during battery operation are highly complex. Thermodynamic, kinetic and transport-based phenomena all play a significant role in the dynamic evolution of the time-based electrochemical response of any battery system. Researchers have long sought to quantify these various interconnected phenomena, but to-date elucidating the role these mechanisms play in the performance of battery systems has been challenging or impossible. To aid researchers in uncovering the mechanistic behavior of their systems, we have developed a novel testing protocol and corresponding data analysis method that is scalable and non-destructive (SAND). This protocol and analysis can be applied to any battery system, in any form factor, at any point in the battery life cycle; including R&D, manufacturing, and second life battery screening to name a few.The testing protocol is based on a series of galvanostatic current pulses at a variety of currents and/or times. By utilizing the natural differences in time-constant of the various electrochemical phenomena inside a battery, this technique can probe each mechanism to glean novel insight using standard battery cycling equipment. Specifically, the insights this technique can provide include: the electrochemical potential of each phase during lithiation and delithiation quantification of electrode kinetics at various states-of-charge (including exchange current density estimation from the Butler-Volmer model)quantitative estimation of transport-based polarization losses from both the electrodes and the electrolyte. This analysis provides an un-parallelled level of mechanistic insight into the inner workings of any battery, at any point, spanning small-scale R&D cells to large format cells in mass production.To demonstrate the capabilities of this technique this presentation will focus on the analysis of multiple cells (same model) from a Tier 1 supplier containing a lithium transition metal oxide cathode material cycled at various temperatures. These results have led to an extensive set of conclusions. For brevity a few of these conclusions are: The initial exchange current density of these cells is calculated to be 25.5 A/m2. The H2→H3 phase transition during charging is the least efficient phase, exhibiting the largest power loss during chargingThe inefficiencies in the H2→H3 phase transition are dominated by solid-state lithium atom diffusion within the electrodes. At low current densities the overpotential associated with transport is the dominant source of losses, while at higher currents kinetic overpotentials become the dominant source. In summary, we have developed a novel characterization technique requiring only standard battery cycling equipment that can be easily and quickly performed by researchers around the world. Whether on small-scale coin cells or large-format pouch cells, the analysis from this technique will give the battery community insight into the thermodynamic, kinetic, and transport properties of their system. Moreover, this technique can be applied in a variety of contexts related to battery development, including understanding degradation mechanisms, performing root-cause analysis of manufacturing defects, or providing more accurate parameters for computational modeling.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Continued efforts towards the decarbonization of the power sector through an uptake of renewable energy generation, namely solar and wind, play a key role in the fight against climate change. However, due to their variable nature, the simultaneous implementation of energy storage solutions capable of ensuring a reliable delivery of energy at any time of day is of the utmost importance. Aqueous rechargeable zinc-ion batteries (RZIBs) are a promising technology for this end. Offering several advantages over lithium-ion batteries in terms of cost, environmental impact, and material abundance, the investment in RZIB research continues to grow. However, the realization of commercial RZIBs is currently hindered by the lack of cathode materials with adequate performance for long-term storage solutions. This is the case for manganese (e.g., MnO2, Mn2O3, Mn3O4) and vanadium (e.g., V2O5, VO2) based oxides, which exhibit considerable capacity fade during realistic charge and discharge times. While simple transition metal oxides (MyOx, M=transition metal) are one of the most studied classes of materials for RZIB cathodes, a literature survey shows that there are still many unexplored redox active elements and redox pairs which may be employed in next-generation RZIBs. Therefore, to accelerate the discovery of these novel cathode systems, we mapped the theoretical Zn intercalation potential for simple oxides from 12 different transition metals using Density Functional Theory (DFT) calculated thermodynamic properties. The screened elements were chosen upon considering their commercial availability, toxicity, price, and existence of previously reported structures containing zinc. During the present analysis, the feasibility of Zn intercalation for each system was accounted for by analyzing the atomic arrangement in the charged and discharged phases. Experimentally obtained Pourbaix Diagrams were also used to probe the electrochemical stability of the cathodes in aqueous solution, with the possibility of electrolyte degradation (oxygen or hydrogen evolution reaction) and competing reactions (metal dissolution or solid phase change) also considered. Experimental validation of the computationally predicted potentials was also done for select materials. The result for the 35+ redox pairs evaluated in this study provides a clear roadmap for the future development of RZIBs cathodes.

Scalable One-Pot Synthesis of Nanostructured P2-Type Na2/3Ni1/3Mn2/3O2 Cathode Material for High-Performance Na-Ion Batteries

Sodium-ion batteries (SIBs) based on sodium transition metal oxides are considered as a viable alternative to lithium-ion batteries (LIBs) for grid-scale energy storage. This is because the critical elements used in these SIBs, such as sodium, manganese, and nickel, are abundantly available, and their supply chain does not pose any geopolitical risk like lithium and cobalt used in common LIB cathodes.1 Among sodium transition metal oxide cathodes, the P2-type Na2/3[Ni1/3Mn2/3]O2 (NNMO) is a promising material due to its high operating voltage (up to 4.5 V vs Na/Na+) and high capacity. When cycled between 2-4.5 V vs Na/Na+, it has a capacity of 173 mAh/g.2 This combination of high operating voltage and high capacity allows NNMO to outperform common LIBs in terms of energy density. Therefore, SIBs based on NNMO cathode are a scalable alternative to LIBs.Unfortunately, the current method used to produce NNMO through solid-state conversion is a time and energy-intensive process. It requires a temperature above 800 degrees Celsius and takes at least 12 hours to make a single batch of NNMO. Moreover, NNMO formed using this method has large particle sizes of a few micrometers. In my presentation, I will introduce a new and highly scalable method for synthesizing NNMO. This method can create NNMO in less than 20 minutes, which is much faster than the usual 12+ hours required by existing methods. Additionally, our protocol produces Nano-NNMO particles with size in the sub-200 nm. Nanoscale NNMO is crucial because it enhances the electrochemical performance of the materials, which I will also discuss. Key words: Sodium-ion batteries, Na2/3[Ni1/3Mn2/3]O2, high capacity, nanoparticles, rapid synthesis. References (1) Wang, C.; Liu, L.; Zhao, S.; Liu, Y.; Yang, Y.; Yu, H.; Lee, S.; Lee, G.-H.; Kang, Y.-M.; Liu, R.; et al. Tuning local chemistry of P2 layered-oxide cathode for high energy and long cycles of sodium-ion battery. Nature Communications 2021, 12 (1), 2256. DOI: 10.1038/s41467-021-22523-3.(2) Zhang, J.; Wang, W.; Wang, W.; Wang, S.; Li, B. Comprehensive Review of P2-Type Na2/3Ni1/3Mn2/3O2, a Potential Cathode for Practical Application of Na-Ion Batteries. ACS Applied Materials & Interfaces 2019, 11 (25), 22051-22066. DOI: 10.1021/acsami.9b03937.

Formation and Cycling of Microscale Silicon Anodes at Elevated Temperatures with FEC-Based and EC-Based Electrolytes

Silicon is a promising candidate to replace graphite (372 mAh g-1) as anode material in lithium-ion batteries (LIBs) due to its high theoretical gravimetric capacity of 3589 mAh g-1.1 Graphite is already partially substituted by silicon in commercial battery applications in order to increase the energy density of LIBs.2 However, a complete transition to silicon is still hindered by the extreme volume expansion of up to 300% upon complete electrochemical lithiation to Li15Si4.3 This causes particle cracking, electrical contact loss of active material, and the continuous (re-)formation of the solid electrolyte interphase (SEI) on the newly formed surface, leading to a continuous loss of cyclable lithium and a fast capacity fading of the cell.One approach to mitigate Si particle cracking is the partial lithiation of microscale silicon, limiting the capacity to ~1200 mAh g-1, i.e., one-third of the theoretical capacity, enabling a cycle-life of more than 200 cycles before reaching 80% state-of-health (SOH).4 While electronic disconnection of lithiated silicon contributes to the overall cyclable lithium losses, the continuous formation of the SEI remains one of the major challenges that limit the lifetime.5 Fluoroethylene carbonate (FEC) has been shown to be one of the most suitable additives for silicon-containing cells to ensure the formation of a suitable SEI and comparably stable cycling performance.6,7 However, especially at elevated temperatures, FEC decomposes to form vinylene carbonate and hydrogen fluoride, which is detrimental to the SEI.8 This study investigated temperature-dependent cycle-life stability of microscale-silicon dominant anodes with EC-based and FEC-based electrolytes at room and elevated temperature. The electrodes consist of 70% silicon (Wacker Chemie AG) with an LiPAA binder (8%) and conductive carbon (2%). Additionally, graphite (8% KS6L, Imerys) was added to enhance the electronic conductivity, whereby within the operating voltage range of the anode, only a minor capacity of the graphite is used. As electrolytes, either 1 M LiPF6 in EC:DEC 1:2 v:v (EC-based) or 1 M LiPF6 in FEC:DEC 2:8 v:v (FEC-based) were used. Full-cells were cycled with a nickel-rich transition metal oxide cathode active material (LiNi0.83Co0.12Mn0.05O2 (NCM831205), BASF SE) based cathode at 25 °C and 45 °C. As shown in Figure 1, cycling in coin cells revealed the expected decreased cycle-life of cells with the FEC-based electrolyte at 45 °C (light blue) compared to 25 °C (dark blue).8 However, cycling cells with the FEC-free, EC-based electrolyte (green) at elevated temperatures, showed the opposite trend. The cycle-life until 80% SOH increased by 110 cycles (+100%), surpassing that of the cells with the FEC-based electrolyte at 45 °C. The charge-averaged mean voltages for both charge and discharge were investigated to identify the main failure mechanisms. This allowed us to differentiate between the loss of cyclable lithium and internal cell resistance build-up.To better understand the contributions of anode and cathode to capacity fading, we assembled Swagelok® T-Cells with the same cell chemistry and cycled them analogously. While the resistance of the cathode remained nearly constant over the whole course of cycling, the resistance of the anode showed an increase with decreasing cell capacity. Furthermore, online electrochemical mass spectrometry (OEMS) was performed to determine the gases evolved during formation with the EC-based electrolyte at 25 °C and 45 °C. This allowed us to gain insights into the overall SEI formation mechanism and to differentiate the formation of suitable SEI components.

A High-Entropy Intergrowth Layered-Oxide Cathode with Enhanced Stability for Sodium-Ion Batteries.

Layered transition metal oxides are widely considered as ideal cathode materials for SIBs. However, the existing P2 and O3 structures possess specific issues, which limit their practical applications. To address these issues, this work designed a novel intergrowth layered oxide cathode with P2 and O3 phases by implementing Cu and Ti into the structure with the formation of high-entropy cathode materials with superior performance for SIBs. The electrochemical test results show that the optimized high-entropy cathode with the P2/O3 intergrowth structure possesses a high initial discharge capacity of 157.85 mAh g-1 at 0.1 C, an excellent rate performance of 84.41 mAh g-1 at 10 C, and long-term stability with capacity retention of 83.25 % after 500 cycles at 5 C. Furthermore, the analysis results of ex situ XRD and in situ XRD indicate that the adverse phase transition of P2-O2 under high voltage is effectively suppressed. This work indicates that the integration of high-entropy strategy with the two-phase intergrowth structure can effectively stabilize the layered structure, suppress the slipping of transition metal layers, and improve electrochemical performance, which provides a new approach for designing high-performance and practical layered transition metal oxide cathode materials for advanced SIBs.

Influence of Cathode Calendering Density on the Cycling Stability of Li-Ion Batteries Using NMC811 Single or Poly Crystalline Particles

Calendering of battery electrodes is a commonly used manufacturing process that enhances electrode packing density and therefore improves the volumetric energy density. While calendering is standard industrial practice, it is known to crack cathode particles, thereby increasing the electrode surface area. The latter is particularly problematic for new Ni-rich layered transition metal oxide cathodes, such as NMC811, which are known to have substantial surface-driven degradation processes. To establish appropriate calendering practices for these new cathode materials, we conducted a comparative analysis of uncalendered electrodes with electrodes that have a 35% porosity (industrial standard), and 25% porosity (highly calendered) for both single crystal (SC) and polycrystalline (PC) NMC811. PC cathodes show clear signs of cracking and decrease in rate capability when calendered to 25% porosity, whereas SC NMC811 cathodes, achieve better cycling stability and no penalty in rate performance at these high packing densities. These findings suggest that SC NMC811 cathodes should be calendered more densely, and we provide a comprehensive overview of both electrochemical and material characterisation methods that corroborate why PC and SC electrodes show such different degradation behaviour. Overall, this work is important because it shows how new single-crystal cathode materials can offer additional advantages both in terms of rate performance and cycling stability by calendaring them more densely.

An Active Strategy to Reduce Residual Alkali for High-Performance Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Residual alkali is one of the biggest challenges for the commercialization of sodium-based layered transition metal oxide cathode materials since it can even inevitably appear during the production process. Herein, taking O3-type Na0.9Ni0.25Mn0.4Fe0.2Mg0.1Ti0.05O2 as an example, an active strategy is proposed to reduce residual alkali by slowing the cooling rate, which can be achieved in one-step preparation method. It is suggested that slow cooling can significantly enhance the internal uniformity of the material, facilitating the reintegration of Na+ into the bulk material during the calcination cooling phase, therefore substantially reducing residual alkali. The strategy can remarkably suppress the slurry gelation and gas evolution and enhance the structural stability. Compared to naturally cooled cathode materials, the capacity retention of the slowly cooled electrode material increases from 76.2% to 85.7% after 300 cycles at 1C. This work offers a versatile approach to the development of advanced cathode materials toward practical applications.

Rational design of practical layered transition metal oxide cathode materials for sodium-ion batteries

Rational design of practical layered transition metal oxide cathode materials for sodium-ion batteries

Multiphase riveting structure constructed by slight molybdenum for enhanced P3/O3 layer-structured oxide cathode material

Phase engineering has been efficiently employed to improve the performance of transition metal oxide cathode materials by alleviating the Jahn-Teller effects and optimizing the ions diffusion pathway. The second-order Jahn-Teller effects by slight molybdenum substitution was confirmed to activate a new phase formation and to construct a multiphase riveting structure. A P3/O3 riveting-structured NaNi0.3Mn0.52Mo0.03Cu0.1Ti0.05O2 cathode material was successfully synthesized for sodium ion batteries, which undergoes a reversible phase transition from P3/O3 → P3 → Hex.O3′ when charged to 4.25 V and most of the materials will transform into P3 phase after the first charge–discharge cycle. Due to the high reversibility and crystal structure stability, it indicates 155.0 mAh g−1 discharge capacity with a high up to 99.65 % initial Coulomb efficiency. This P3/O3 riveting structure can alleviate the rigid failure caused by phase transition. Meanwhile, O3/P3 phases provide the main storage sites for Na+ as skeletons and the existence of P3 phase provides a better diffusion pathway for ion transport.

Understanding and Design of Cathode–Electrolyte Interphase in High‐Voltage Lithium–Metal Batteries

AbstractThe development of lithium–metal batteries (LMBs) has emerged as a mainstream approach for achieving high‐energy‐density energy storage devices. The stability of electrochemical interfaces plays an essential role in realizing stable and long‐life LMBs. Despite extensive and comprehensive research on the lithium anode interface, there is limited focus on the cathode interface, particularly regarding high‐voltage transition metal oxide cathode materials. In this review, the challenges associated with developing stable high‐voltage cathode materials are first discussed. Characterization techniques for understanding the composition and structure of the cathode–electrolyte interphase (CEI) are then introduced. Subsequently, recent developments in electrolyte design and interface modification for constructing a stable CEI are summarized. Finally, perspectives on future research trends for understanding and developing the high‐voltage CEI are discussed. This review can offer valuable guidance for understanding and designing the high‐voltage CEI, pushing forward the development of high‐energy‐density LMBs.

Depletion of Electrolyte Salt Upon Calendaric Aging of Lithium-Ion Batteries and its Effect on Cell Performance

The trend for increased nickel content in layered transition metal oxide cathode active materials and increasing charging cut-off voltages aggravates aging of lithium-ion battery cells at high state of charge (SOC). We investigate the calendaric aging behavior of large-format automotive prototype cells and laboratory single-layer pouch cells at high but realistic cell voltages/SOCs and demonstrate that electrolyte oxidation in combination with follow-up reactions can cause a significant loss of the LiPF6 salt in the electrolyte. For this, we analyze the LiPF6 concentration in aged cells, the generation of H2 upon storage, and the cell resistance for different aging conditions. We show that the LiPF6 loss is a critical aging phenomenon, as it cannot readily be detected by capacity fading measurements at low/medium C-rates or by cell resistance measurements, while it severely reduces rate and fast-charging capability. Under certain circumstances, LiPF6 loss can even lead to a temporary capacity increase due to conversion of the conducting salt in the electrolyte to cyclable lithium in the active material. Finally, we suggest a possible reaction mechanism and a simple accounting model to keep track of how different side reactions involved in LiPF6 loss change the cyclable lithium inventory of a lithium-ion cell.