Charge Cutoff Research Articles

Maximizing the Structural Stability of the Na-Rich Prussian Blue Analogue Electrode through Charge Cutoff Voltage Regulation.

Prussian blue and its analogues (PB/PBAs) are promising sodium-ion battery cathode materials due to their easy synthesis and excellent discharge capacity. However, their low structural stability poses a challenge. One critical factor affecting stability is the charge cutoff voltage. Increasing this voltage can enhance lithium-ion battery capacity but may reduce cycle retention due to intensified electrode-electrolyte interface reactions. This study investigates whether this phenomenon also applies to sodium-ion batteries and proposes an optimal voltage to improve both the capacity and stability. By cycling between 3.8 and 4.2 V, the charge/discharge profiles and redox reaction intensity were analyzed. The correlation between structural stability and charge cutoff voltage was re-evaluated based on these findings. An optimal charge cutoff voltage of 4.1 V was identified, creating an additional plateau during initial charging and altering Na+ ion positioning to enhance capacity. Enhanced mobility of ions and electrons was observed through a stable solid-electrolyte interphase (SEI) formation. Ex situ X-ray diffraction (XRD) confirmed reversible phase transitions and excellent structural stability. This study underscores the strategic use of charge cutoff voltage to enhance both discharge capacity and structural stability, offering insights for advancing PB/PBA cathode materials with improved stability and capacity.

Study on the impact of cutoff voltage on structural and electrochemical stability of sodium-ion layered cathodes

NaNi1/3Fe1/3Mn1/3O2 is recognized for its relatively high theoretical specific capacity and operating voltage, rendering it a sodium-ion cathode material with significant commercial potential. A higher cutoff voltage typically enables more sodium ion deintercalation, thereby achieving higher capacity. However, this increased deintercalation can introduce challenges such as structural instability and side reactions with the electrolyte, leading to electrochemical performance degradation. This study focuses on the migration process of transition metal ions under conditions of high charging cutoff voltage and high sodium removal. At a voltage of 4.3 V, the migration of Ni ions facilitates more charge compensation but is accompanied by irreversible Ni migration, inducing an irreversible phase transition to the O’ phase. Conversely, at a cutoff voltage of 4.1 V, the P3 and O3 phases with high sodium removal demonstrate excellent cycling stability. The specific capacities before and after 150 cycles (at 0.5C) are 142.3 and 113.7 mAh/g, respectively, indicating a tolerable internal structural stress within these high sodium removal phases. This contrasts with the differentiated internal structural stresses generated by the P3, O3, and O’ phases during phase transitions at a cutoff voltage of 4.3 V. The research underscores the importance of regulating reversible crystal phases within the tolerance range of internal stress and avoiding irreversible crystal phases to enhance the cycling stability of cathode materials. These findings provide crucial insights for optimizing NNFMO cathode materials and hold significant implications for the design of high-performance, long-life sodium-ion batteries.

Push-Pull Electrolyte Design Strategy Enables High-Voltage Low-Temperature Lithium Metal Batteries.

Lithium (Li) metal batteries hold significant promise in elevating energy density, yet their performance at ultralow temperatures remains constrained by sluggish charge transport kinetics and the formation of unstable interphases. In conventional electrolyte systems, lithium ions are tightly locked in the solvation structure, thereby engendering difficulty in the desolvation process and further exacerbating solvent decomposition. Herein, we propose a new push-pull electrolyte design strategy, utilizing molecular electrostatic potential (ESP) screening to identify 2,2-difluoroethyl trifluoromethanesulfonate (DTF) as an optimal cosolvent. Importantly, DTF exhibits a moderate ESP minimum (-21.0 kcal mol-1) to strike a balance between overly strong and overly weak Li ion affinity, which allows the sulfonyl group to effectively pull Li ions without disrupting the anion-rich solvation structure. Simultaneously, the difluoromethyl group, with a high ESP maximum (37.3 kcal mol-1), pushes solvent molecules via competitive hydrogen bonding. This design reconstructs existing solvation structures and expedites Li ion desolvation. Furthermore, fluorinated DTF demonstrates excellent stability at elevated voltage and facilitates the formation of robust inorganic-rich interphases. Impressively, rapid charge transfer kinetics can be achieved employing designed electrolyte, and the LiNi0.8Mn0.1Co0.1O2 (NMC811)||Li cells demonstrate excellent charge-discharge cycling stability with a high capacity exceeding 153 mAh g-1 even at -40 °C, retaining over 93% of initial capacity after 100 cycles under a 4.8 V charging cutoff. This work provides insights into the design of low-temperature electrolytes with a wide electrochemical window, advancing the development of batteries for extreme conditions.

Investigation of the Roles of Functional Solvents in Performance Stability of High Voltage Lithium Batteries

Li-ion batteries (LIBs) have become prevalent for portable and large-scale applications, such as personal electronic devices, unmanned aircraft systems, electric vehicles, and power grids.1 However, LIBs are approaching an asymptotic limit in specific energy (~250 Wh kg-1 at cell level); therefore, they are insufficient to meet future applications that require higher battery specific energies.2 Ni-rich cathodes, such as LiNi0.8Co0.1Mn0.1O2 (NMC811), have the potential to provide much higher specific energies for next-generation LIBs (e.g., >350 Wh kg-1) and, therefore, are considered the most promising low-cost cathode materials.3 Nevertheless, Ni-rich cathode based LIBs with conventional carbonate solvent based electrolytes face severe technical challenges, especially when cycled at high upper cutoff voltages, due to electrolyte decomposition, parasitic oxidation reactions at the electrolyte/cathode interface, irreversible phase changes in the cathodes, and dissolution of transition metals into electrolytes.4 Therefore, R&D efforts are needed to tackle the above technical challenges of Ni-rich cathode based LIBs before they become commercially viable.In our previous study,5 a ternary of fluorinated solvents was used to formulate a high voltage stable electrolyte (HVE) which was used in Ni-rich cathode based, high-voltage lithium batteries. These HVE-based batteries demonstrated a significant improvement in cycle stability when operated at a charge cutoff voltage of 4.5 V (vs Li/Li+). In this study, we investigated the roles of single-solvents and co-solvents in the cycle stability of the high-voltage lithium batteries. Several families of organic solvents, such as fluorinated carbonates and organosilicon based solvents were investigated. Our preliminary data showed that some unique combinations of the functional solvents could lead to exceptionally stable cycle performance in the high-voltage lithium batteries. We will discuss possible fundamental mechanisms responsible for the observed performance stability of the high-voltage lithium batteries using ex-situ XPS, density functional theory calculations, and other characterization techniques. References (1) Li, J.; Fleetwood, J.; Hawley, W. B.; Kays, W. From materials to cell: state-of-the-art and prospective technologies for lithium-ion battery electrode processing. Chemical Reviews 2021, 122 (1), 903-956.(2) Khan, F. N. U.; Rasul, M. G.; Sayem, A.; Mandal, N. K. Design and optimization of lithium-ion battery as an efficient energy storage device for electric vehicles: A comprehensive review. Journal of Energy Storage 2023, 71, 108033.(3) Xue, W.; Huang, M.; Li, Y.; Zhu, Y. G.; Gao, R.; Xiao, X.; Zhang, W.; Li, S.; Xu, G.; Yu, Y. Ultra-high-voltage Ni-rich layered cathodes in practical Li metal batteries enabled by a sulfonamide-based electrolyte. Nature Energy 2021, 6 (5), 495-505.(4) Yang, J.; Liang, X.; Ryu, H.-H.; Yoon, C. S.; Sun, Y.-K. Ni-Rich Layered Cathodes for Lithium-Ion Batteries: From Challenges to the Future. Energy Storage Materials 2023, 102969.(5) Poches, C.; Razzaq, A. A.; Studer, H.; Ogilvie, R.; Lama, B.; Paudel, T. R.; Li, X.; Pupek, K.; Xing, W. Fluorinated High-Voltage Electrolytes To Stabilize Nickel-Rich Lithium Batteries. ACS Applied Materials & Interfaces 2023, 15 (37), 43648-43655. Acknowledgement This work was supported by the following funding sources. The Larry and Linda Pearson Endowed Chair at the Department of Mechanical Engineering, South Dakoda School of Mines and Technology. The Naval Air Warfare Center Weapons Division, China Lake, CA under Contract No N6893622C0017. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Naval Air Warfare Center Weapons Division, China Lake, CA. TP acknowledges the support from the SDBOR Governor Research Center for the Electrochemical Energy Storage and NASA EPSCOR-80NSSC23M0072.

Regulations of Bulk and Interfacial Chemistry of Mn-Based Cathode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) show the great potential to achieve large-scale energy storage due to their low cost and good safety as well as abundant resources of sodium. Among the cathode materials for SIBs, manganese-based layered oxides with adjustable structure have been attached great interest for the high energy density and low-cost SIBs. . Particularly, P2-type Mn-based materials exhibit anionic redox during charge and discharge processes, which can not only elevate the battery potential but also provide extra capacity, drastically boosting the energy density of the batteries. However, the irreversible phase transition, Jahn-Teller effect of manganese and interphase degradation at high charge cutoff voltage during anionic redox largely affect the cyclic stability of the cathodes. Therefore, it is essential to develop effective strategies to regulate the structural and interfacial chemistry for suppressing the phase transition and voltage hysteresis as well as increasing the cycle life of cathode materials. In this work, various electrochemical inert/active elements have been introduced into Mn-based P2 type cathode materials for regulating the electronic structure of the cathodes to promote more anionic redox and improve the structural stability. In addition, a new type of ionic liquid is introduced to build a stable interphase and improve the high voltage stability of the cathode material. Multi-model synchrotron-based X-ray characterization techniques combined with first-principles calculation are used to reveal the effectiveness of different strategies on the electrochemical properties of SIBs. The results provide valuable information for the development of high-performance cathode materials. Acknowledgement This work at Shanghai Jiao Tong University was financially supported by the National Natural Science Foundation of China (No. 22209106).

Long-Cycle Lithium Batteries with LiNi0.8Co0.1Mn0.1O2 Cathodes above 4.5V Enabled by Uniform Coating of Nanosized Garnet Electrolytes

Abstract The pursuit of high-energy cathode materials has been focused on raising the charging cutoff voltage of nickel (Ni)-rich layered oxide cathode such as LiNi0.8Co0.1Mn0.1O2 (NCM811). However, the NCM811 suffers from rapid capacity fading upon cycling at cutoff voltage higher than 4.5 V, owing to their structural degradation and labile surface reactivity. Surface-coating with solid electrolytes has been recognized as an effective method to mitigate the performance failure of NCM811 at high voltage. Herein, the nano-sized Li6.4La3Ta0.6Zr1.4O12 (LLZTO) is uniformly coated on the surface of single-crystal NCM811 particles, accompanied with the long-range Ta5+ diffusion into the transition metal layer of NCM811 lattice. It is revealed that the LLZTO coating can not only inhibit the surface reactions of NCM811 with liquid electrolytes but also play an important role in suppressing the bulk microcracking within the NCM811 particles. The incorporation of Ta5+ ion expands the lattice spacing and thereby improves the homogeneity of the Li+ diffusion in the single-crystal NCM811, which alleviates the mechanical strain and intragranular cracks caused by nonuniform phases-transformation at high charging voltage. The synergy of surface protection and structural stabilization realized by LLZTO coating enables the NCM811-based lithium batteries to achieve a remarkable electrochemical performance. Typically, LLZTO coated NCM811 delivers a high reversible specific capacity of 202.1 mAh⋅g−1 with an excellent capacity retention as high as 70% over 1000 cycles upon charging to 4.5 V at 1 C.

Cut-off voltage influencing the voltage decay of single crystal lithium-rich manganese-based cathode materials in lithium-ion batteries

The voltage decay of Li-rich layered oxide cathode materials results in the deterioration of cycling performance and continuous energy loss, which seriously hinders their application in the high-energy–density lithium-ion battery (LIB) market. However, the origin of the voltage decay mechanism remains controversial due to the complex influences of transition metal (TM) migration, oxygen release, indistinguishable surface/bulk reactions and the easy intra/inter-crystalline cracking during cycling. We investigated the direct cause of voltage decay in micrometer-scale single-crystal Li1.2Mn0.54Ni0.13Co0.13O2 (SC-LNCM) cathode materials by regulating the cut-off voltage. The redox of TM and O2− ions can be precisely controlled by setting different voltage windows, while the cracking can be restrained, and surface/bulk structural evaluation can be monitored because of the large single crystal size. The results show that the voltage decay of SC-LNCM is related to the combined effect of cation rearrangement and oxygen release. Maintaining the discharge cutoff voltage at 3 V or the charging cutoff voltage at 4.5 V effectively mitigates the voltage decay, which provides a solution for suppressing the voltage decay of Li-rich and Mn-based layered oxide cathode materials. Our work provides significant insights into the origin of the voltage decay mechanism and an easily achievable strategy to restrain the voltage decay for Li-rich and Mn-based cathode materials.

Superior stable high‐voltage LiCoO2 enabled by modification with a layer of lithiated polyvinylidene fluoride‐derived LiF

AbstractHigh‐voltage LiCoO2 (LCO) can deliver a high capacity and therefore significantly boost the energy density of Li‐ion batteries (LIBs). However, its cyclability is still a major problem in terms of commercial applications. Herein, we propose a simple but effective method to greatly improve the high‐voltage cyclability of an LCO cathode by constructing a surface LiF modification layer via pyrolysis of the lithiated polyvinylidene fluoride (Li‐PVDF) coating under air atmosphere. Benefitting from the good film‐forming and strong adhesion ability of Li‐PVDF, the thus‐obtained LiF layer is uniform, dense, and conformal; therefore, it is capable of acting as a barrier layer to effectively protect the LCO surface from direct exposure to the electrolyte, thus suppressing the interfacial side reactions and surface structure deterioration. Consequently, the high‐voltage stability of the LCO electrode is significantly enhanced. Under a high charge cutoff voltage of 4.6 V, the LiF‐modified LCO (LiF@LCO) cathode demonstrates a high capacity of 201 mA h g−1 at 0.1 C and a stable cycling performance at 0.5 C with 80.5% capacity retention after 700 cycles, outperforming the vast majority of high‐voltage LCO cathodes reported so far.

Surface engineering of Li3V2(PO4)3-based cathode materials with enhanced performance for lithium-ion batteries working in a wide temperature range

Operating at extreme temperatures is the biggest challenge for lithium-ion batteries (LIBs) in practical applications, as both the capacity and cycling stability of LIBs are largely decreased due to the sluggish reaction kinetics of the cathodes. Therefore, developing suitable cathode materials is the key point to tackling this challenge. Lithium vanadium phosphate [Li3V2(PO4)3, LVP] is a promising cathode with good features of a high working voltage, high intrinsic ionic diffusion coefficiency, and stable olivine structure in a wide temperature range, although it is perplexed by the low electronic conductivity. To tackle this issue, a series of nitrogen-doped carbon network (NC) coated LVP composites were synthesized using a hydrothermal-assisted sol-gel method. Among them, the LVP@NC-0.8 sample exhibited a remarkable tolerance at a high charging cutoff voltage of 4.8 V in a wide temperature range. Full cells of LVP@NC-0.8||graphite exhibited superior performance at different current rates. Moreover, the reaction mechanism of the LVP@NC-0.8 electrode was proved by in-situ X-ray diffraction technique, demonstrating that temperature was a critical factor that contributed to the sluggish phase transformation with high voltage hysteresis at low temperature and severe crystal structure distortion at high temperature. Theoretical calculations further demonstrated the superiority of the NC for high electronic conductivity and reduced lithium transportation barriers. The enhanced electrochemical performances of LVP-based cathode materials have provided the possible application of LIBs in a wide temperature range.

A synergistic duo for enhanced cathode stability in high-voltage lithium-ion batteries

Lithium-ion batteries with high-nickel cathode materials are promising candidates for achieving significantly higher energy densities. However, when Ni-rich subjected to higher charging cutoff voltages accelerates both electrolyte decomposition and structural degradation, leading to compromised cycling stability and reduced lifespan. In this study, we have developed a dual-additive strategy using lithium difluoro bisoxalate phosphate (LiDFBOP), and 1,3-divinyl-1,1,3,3-tetramethyldisilazane (DTDS) to address these challenges and improve the battery's performance. Theoretical calculations and experimental results indicate that the LiDFBOP regulates Li⁺ solvation for robust CEI formation, while DTDS scavenges impurities and promotes the formation of an inorganic/organic interphase. The synergistic effect of these additives combination allows Li||NCM811 coin cell to retain a capacity retention 87.9 % at 4.6 V and Graphite||NCM811full cell achieved 90.5 % capacity retention at 4.5 V. Moreover, the 1Ah pouch full cells exhibit excellent cycling stability, with a capacity retention of 91.4 % after 610 cycles at a constant current of 500 mA and voltage of 4.5 V. This work offers guidance on designing multifunctional additives to achieve synergistic electrolyte engineering for high-energy lithium-ion batteries.

Suppressed Electrolyte Decomposition Behavior to Improve Cycling Performance of LiCoO2 under 4.6V through the Regulation of Interfacial Adsorption Forces.

Alleviating the decomposition of the electrolyte is of great significance to improving the cycle stability of cathodes, especially for LiCoO2 (LCO), its volumetric energy density can be effectively promoted by increasing the charge cutoff voltage to 4.6V, thereby supporting the large-scale application of clean energy. However, the rapid decomposition of the electrolyte under 4.6V conditions not only loses the transport carrier for lithium ion, but also produces HF and insulators that destroy the interface of LCO and increase impedance. In this work, the decomposition of electrolyte is effectively suppressed by changing the adsorption force between LCO interface and EC. Density functional theory illustrates the LCO coated with lower electronegativity elements has a weaker adsorption force with the electrolyte, the adsorption energy between LCO@Mg and EC (0.49eV) is weaker than that of LCO@Ti (0.73eV). Meanwhile, based on the results of time of flight secondary ion mass spectrometry, conductivity-atomic force microscopy, in situ differential electrochemical mass spectrometry, soft X-ray absorption spectroscopy, and nuclear magnetic resonance, as the adsorption force increases, the electrolyte decomposes more seriously. This work provides a new perspective on the interaction between electrolyte and the interface of cathode and further improves the understanding of electrolyte decomposition.

Mg/Al Double-Pillared LiNiO2 as a Co-Free Ternary Cathode Material Ensuring Stable Cycling at 4.6 V.

Cobalt-free (Co-free) and nickel-rich (Ni-rich) cathode materials have attracted significant attention and undergone extensive studies due to their affordability and superior energy density. However, the commercialization of these Co-free materials is hindered by challenges such as cation disorder, irreversible phase changes, and inadequate high-voltage performance. To overcome these challenges, a Co-free ternary cathode material of Mg/Al double-pillared LiNiO2 (NMA) synthesized via a wet-coating and lithiation-sintering technique is proposed. Fundamental studies reveal that Mg and Al have the potential to form a distinctive double-pillar structure within the layered cathode, enhancing its structural stability. To be specific, the strategic placement of Mg and Al in Li and Ni layers, respectively, effectively reduces Li+/Ni2+ disorder and prevents irreversible phase transitions. Additionally, the inclusion of Mg and Al refines the primary grains and compacts the secondary grains in the cathode material, reducing stress from cyclic usage and preventing material cracking, thereby mitigating electrolyte erosion. As a result, NMA demonstrates exceptional electrochemical performance under a high charge cutoff voltage of 4.6 V. It maintains 70% of initial specific capacity after 500 cycles at 1 C and exhibits excellent rate performance, with a capacity of 162 mAh g-1 at 5 C and 149 mAh g-1 at 10 C. As a whole, the produced NMA achieves a high structural stability in cases of excessive delithiation, providing a groundbreaking solution for the development of cost-effective and high-energy-density cathode materials for lithium-ion batteries.

Electrolyte Regulation in Stabilizing the Interface of a Cobalt-Free Layered Cathode for 4.8 V High-Voltage Lithium-Ion Batteries.

The cobalt-free layered oxide cathode of LiNi0.65Mn0.35O2 is promising for high-energy-density lithium-ion batteries (LIBs). However, under high-voltage conditions, severe side reactions between the Co-free cathode and electrolyte, as well as grain boundary cracks and pulverization of particles, hinder its practical applications. Herein, an electrolyte regulation strategy is proposed by adding fluoroethylene carbonate (FEC) and LiPO2F2 as electrolyte additives in carbonate-based electrolytes to address the above issues. As a result, a homogeneous and dense organic-inorganic hybrid cathode electrolyte interface (CEI) film is formed on the cathode surface. The CEI film consists of C-F, LiF, Li2CO3, and LixPOyFz species, which is proven to be highly conductive and effective in suppressing structure damage and alleviating the interfacial reactions between the cathode and electrolyte. With such a CEI film, the interfacial stability of the Co-free cathode and the high-voltage cycling performance of Li||LiNi0.65Mn0.35O2 are greatly improved. A reversible capacity of 155.1 mAh g-1 and a capacity retention of 81.3% over 150 cycles are attained at a 4.8 V charge cutoff voltage with the tamed electrolyte, whereas the cell without the additives only retains 76.1% capacity retention. Therefore, our work demonstrates the synergistic effect of FEC and LiPO2F2 in stabilizing the interface of Co-free cathode materials and provides an alternative strategy for the electrolyte design of high-voltage LIBs.

Stabilization of LiCoO2 Cathodes in High Voltage Lithium Metal Batteries Through 2-(Trifluoromethyl)Benzamide (2-TFMBA) Electrolyte Additives.

Increasing the charging cutoff voltage of LiCoO2 to 4.6V is significant for enhancing battery density. However, the practical application of Li‖LiCoO2 batteries with a 4.6V cutoff voltage faces significant impediments due to the detrimental changes under high voltage. This study presents a novel bifunctional electrolyte additive, 2-(trifluoromethyl)benzamide (2-TFMBA), which is employed to establish a stable and dense cathode-electrolyte interface (CEI). Characterization results reveal that an optimized CEI is achieved through the synergistic effects of the amide groups and trifluoromethyl groups within 2-TFMBA. The resulting CEI not only enhances the structural stability of LiCoO2 but also serves as a high-speed lithium-ion conduction channel, which expedites the insertion and extraction of lithium ions. The Li‖LiCoO2 batteries with 0.5wt% 2-TFMBA achieves an 84.7% capacity retention rate after enduring 300 cycles at a current rate of 1C, under a cut-off voltage of 4.6V. This study provides valuable strategic insights into the stabilization of cathode materials in high-voltage batteries.

Implementation of Constant Temperature–Constant Voltage Charging Method with Energy Loss Minimization for Lithium-Ion Batteries

Effective charging techniques must consider factors such as charging efficiency, lifecycle, charging time (CT), and battery temperature. Currently, most charging strategies primarily focus on CT and charging losses (CL), overlooking the crucial influence of battery temperature on battery life. Therefore, this study proposes a constant temperature–constant voltage (CT-CV) charging method based on minimizing energy losses. The charging process is primarily divided into three stages. In the first stage, a constant current (CC) charging is implemented using a 2C rate that aims to expedite battery charging but may result in a rapid temperature increase. The second stage involves constant temperature charging, where the charging current is regulated based on battery temperature feedback using a PID controller to maintain a stable battery temperature. The third stage is constant voltage (CV) charging, where a fixed current is applied continuously until the current drops below the charging cutoff current. After completion of the charging process, the charging time can be calculated, and charging losses can be determined by incorporating the battery equivalent circuit model (ECM). To determine the optimal transition time, the paper employs Coulomb counting and the battery ECM, considering both CT and losses to simulate the transition time with minimal CL. This approach achieves optimization of transition points by establishing ECM, measuring internal impedance of the battery, and simulating various charging scenarios, and eliminates the need for multiple actual experiments. Experimental results show that the charging time (CT) should be reduced and the maximum temperature rise (TR) should be reduced under the same average TR condition of the proposed method. At the same CT, the average TR and the maximum TR should both decrease. The charging method proposed in this study exhibits the following advantages: (1) simultaneous consideration of the battery’s equivalent circuit model and charging time; (2) the achieved transition point demonstrates characteristics of minimized charging losses; (3) eliminates the need for multiple experimental iterations.

Suppressing Surface Ligand-to-Metal Charge Transfer toward Stable High-Voltage LiCoO2.

Increasing the charging cutoff voltage is a viable approach to push the energy density limits of LiCoO2 and meet the requirements of the rapid development of 3C electronics. However, an irreversible oxygen redox is readily triggered by the high charging voltage, which severely restricts practical applications of high-voltage LiCoO2. In this study, we propose a modification strategy via suppressing surface ligand-to-metal charge transfer to inhibit the oxygen redox-induced structure instability. A d0 electronic structure Zr4+ is selected as the charge transfer insulator and successfully doped into the surface lattice of LiCoO2. Using a combination of theoretical calculations, ex situ X-ray absorption spectra, and in situ differential electrochemical mass spectrometry analysis, our results show that the modified LiCoO2 exhibits suppressed oxygen redox activity and stable redox electrochemistry. As a result, it demonstrates a robust long-cycle lattice structure with a practically eliminated voltage decay (0.17 mV/cycle) and an excellent capacity retention of 89.4% after 100 cycles at 4.6 V. More broadly, this work provides a new perspective on suppressing the oxygen redox activity through modulating surface ligand-to-metal charge transfer for achieving a stable high-voltage ion storage structure.

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

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

Extending phase-variation voltage zones in P2-type sodium cathodes through high-entropy doping for enhanced cycling stability and rate capability

P2-type layered sodium oxides hold great promise for grid-scale energy storage applications owing to their low-cost merit, while their detrimental structural and chemical transition lead to low reversible capacities and poor cycling stability. Herein, we leverage a high-entropy (HE) doping strategy to stabilize the P2-type Na0.667Mn0.667Ni0.167Co0.167O2 (NMNC) cathode. A novel Na0.667Mn0.667Ni0.167Co0.117Ti0.01Mg0.01Cu0.01Mo0.01Nb0.01O2 (HE-NMNC) composite, with five equal content (1 at %) of cation substitution and exhibiting a pure P63/mmc space group structure, is proposed. Interestingly, a reversible P2-type phase variation is identified for HE-NMNC at high degrees of charge, but such phase variation occurs in a wider voltage region and is much slower than that in the NMNC baseline. It is demonstrated that the HE-NMNC delivers outstanding rate capability and cycling stability under a charging cutoff voltage of 4.5 V, achieving a reversible capacity of 111 mAh/g at 5 C and retaining around 130 mAh/g after 100 cycles at 1 C. Apart from the charge compensation of main transition metals (Ni, Co, and Mn), the reversible redox of lattice oxygen also contributes to the capacity of HE-NMNC upon cycling. The proposed high-entropy doping strategy and reaction mechanism may provide new insights for developing advanced cathode materials.

Surface Passivation of LiCoO2 by Solid Electrolyte Nanoshell for High Interfacial Stability and Conductivity.

The practical application of lithium cobalt oxide (LiCoO2 ) cathodes at high voltages is hindered by the instability of the surface structure and side reactions with the electrolyte. Herein, we prepared a multifunctional hierarchical core@double-shell structured LiCoO2 (MS-LCO) cathode material using a scalable sol-gel method. The MS-LCO cathode material comprised an outer shell with fast lithium-ion conductivity, a La/Zr co-doped inner shell, and a bulk LiCoO2 core. The outermost shell prevented direct contact between the electrolyte and LiCoO2 core, which alleviated the electrolyte decomposition and loss of active cobalt, while the La/Zr co-doped shell improved the structural stability at higher voltages in a half-cell with a liquid electrolyte. The MS-LCO cathode exhibited a stable capacity of 163.1 mAh g-1 after 500 cycles at 0.5 C, and a high specific capacity of 166.8 mAh g-1 at 2 C. In addition, a solid lithium battery with the surface-passivated MS-LCO cathode and a polyethylene oxide (PEO)-based inorganic/organic composite electrolyte retained 85.8 % of its initial discharge capacity after 150 cycles at a charging cutoff voltage of 4.3 V. Thus, the introduction of a surface-passivating shell can effectively suppress the decomposition of PEO caused by highly reactive oxygen species in LiCoO2 at high voltages.

Ca-Zr co-doping enabled electrochemical reversibility of O3-type NaCrO2 for sodium-ion batteries with high-voltage characteristics

O3-type NaCrO2 has been researched as a promising cathode material for sodium-ion batteries (SIBs), however, it suffers from serious irreversible phase transitions when charged to 3.8 V, thereby resulting in a severe decline of reversible capacity. To improve the structural stability, small amounts of Ca2+ and Zr4+ ions are introduced into the O3-type NaCrO2 via a facile solid-state reaction in this work. In the voltage range of 1.5–3.8 V, O3-type Na0.94Ca0.03Cr0.97Zr0.03O2 delivers ∼ 120 mAh g−1 with a capacity retention of 64.6% after 500 cycles and a reversible capacity of 76 mAh g−1 at 20C, much better than those of O3-type NaCrO2. The improved performance of O3-type Na0.94Ca0.03Cr0.97Zr0.03O2 is attributed to the better structural reversibility and electrochemical reaction kinetics at the high charge cutoff voltage enabled by Ca and Zr co-doping. Our findings benefit the development of cathode materials with high energy density and high cycling stability for SIBs.