Capacity Fading Mechanism Research Articles

Regenerated Natural Minerals towards Double‐layers Heterojunctions Metal@metal‐sulfides with Remarkable Conductivity for Ultra‐fast Sodium‐ion Storage

AbstractAttracted by the high specific capacity and energy density, transition metal‐sulfides exhibit great application potential as sodium‐ion batteries anode, but still suffer from the uncontrolled separation of M/S phase and inferior conductivity. Herein, the flower‐like Fe1‐xS@Sb@C (FF) is rationally tailored, accompanied by double‐layer heterojunctions and C–S–Sb/Sb–S–Fe “bridge” bonds. Meanwhile, the bimetallic phases/boundary defects and built‐in electric fields are formed with a strong electronic coupling effect, effectively alleviating the separation of the M/S phase (Fe/Sb and S), and significantly enhancing ion/e− conductivity. As expected, FF delivers an ultra‐fast sodium‐ions storage rate capacity of 436.5/334.3 mAh g−1 even at 10.0/20.0 A g−1. When the operation temperature is lowered to ‐5 °C, the reversible capacity can still remain at ≈349.7 mAh g−1. Assisted by the detailed kinetic analysis and theoretical calculations, their great ion‐storage abilities mainly derive from improved interfacial Na+/e− transfer and surface/near‐surface redox behaviors. Moreover, the reassembling evolution of active phases is revealed by in/ex situ techniques, further demonstrating the stable adsorption/anchoring of intermediate reaction products Fe/Sb–S phases on the heterointerface, accompanying high reversible conversion‐alloying reaction. Given this, this interesting work is anticipated to offer an in‐depth insight into capacity fading mechanism, and effective strategy to design metal‐sulfur anodes for advanced sodium‐ion systems.

The Operation Window of Lithium Iron Phosphate/Graphite Cells Affects their Lifetime

Lithium iron phosphate (LFP) battery cells are ubiquitous in electric vehicles and stationary energy storage because they are cheap and have a long lifetime. This work compares LFP/graphite pouch cells undergoing charge-discharge cycles over five state of charge (SOC) windows (0%–25%, 0%–60%, 0%–80%, 0%–100%, and 75%–100%). Cycling LFP cells across a lower average SOC results in less capacity fade than cycling across a higher average SOC, regardless of depth of discharge. The primary capacity fade mechanism is lithium inventory loss due to: lithiated graphite reactivity with electrolyte, which increases incrementally with SOC, and lithium alkoxide species causing iron dissolution and deposition on the negative electrode at high SOC which further accelerates lithium inventory loss. Our results show that even low voltage LFP systems (3.65 V) have a tradeoff between average SOC and lifetime. Operating LFP cells at lower average SOC can extend their lifetime substantially in both EV and grid storage applications.

Ultra-Stable Sodium-Ion Battery Enabled by All-Solid-State Ferroelectric-Engineered Composite Electrolytes

HighlightsThe capacity fading mechanism of the conventional Na3V2(PO4)3//Na3V2(PO4)3 (NVP//NVP) cell has been investigated.All-solid-state ferroelectric-engineered composite electrolyte could improve the electrolyte–electrode interfacial stability as well as the interfacial ion conduction of the Na-ion battery using the NVP anode.Outstanding cyclic stability has been achieved in the all-solid-state Na-ion battery using the NVP anode, with a capacity fading rate as low as 0.005% per cycle.

A Review of Capacity Fade Mechanism and Promotion Strategies for Lithium Iron Phosphate Batteries

Commercialized lithium iron phosphate (LiFePO4) batteries have become mainstream energy storage batteries due to their incomparable advantages in safety, stability, and low cost. However, LiFePO4 (LFP) batteries still have the problems of capacity decline, poor low-temperature performance, etc. The problems are mainly caused by the following reasons: (1) the irreversible phase transition of LiFePO4; (2) the formation of the cathode–electrolyte interface (CEI) layer; (3) the dissolution of the iron elements; (4) the oxidative decomposition of the electrolyte; (5) the repeated growth and thickening of the solid–electrolyte interface (SEI) film on the anode electrode; (6) the structural deterioration of graphite anodes; (7) the growth of lithium dendrites. In order to eliminate the problems, methods such as the modification, doping, and coating of cathode materials, electrolyte design, and anode coating have been studied to effectively improve the electrochemical performance of LFP batteries. This review briefly describes the working principle of the LFP battery, the crystal structure of the LFP cathode material, and its electrochemical performance as a cathode. The performance degradation mechanism of LFP batteries is summarized in three aspects—cathode material, anode material, and electrolyte—and the research status of LFP material modification and electrolyte design is emphatically discussed. Finally, the challenges and future development of LFP batteries are prospected.

Unveiling Electrochemical Properties of Silicon for Stable Cycling Performance of Silicon Anode Materials

Research on silicon (Si) as an anode material for Li-ion batteries has spanned two decades; however, certain electrochemical properties of Si remain unclear. Specifically, the cyclic voltammogram (CV) pattern of Li/Si cells varies from case to case, influenced not only by the material but also by the experimental conditions. In this work, slow cyclic voltammetry is employed to investigate Li/Si cells, resulting in three distinct CV patterns. It is further observed that the CV pattern, particularly during the delithiation, is contingent on the state-of-lithiation (SOL) during lithiation and correlates with the capacity fade of Li/Si cells in subsequent cycles. Additionally, it is revealed that the primary mechanism for capacity fade differs between nano-sized silicon (Si-NP) and micro-sized silicon (Si-MP). In brief, capacity fade in Li/Si-NP cells predominantly arises from parasitic reactions between the highly lithiated Li-Si alloy and electrolyte solvents, exacerbated by the large specific surface area of Si-NP materials, whereas capacity fade in Li/Si-MP cells is primarily attributed to the Li electrode rather than the Si-MP electrode due to the restricted lithiation of Si-MP materials. Finally, this work concludes that limiting the SOL of Li/Si cells offers a straightforward and effective pathway to achieving stable cycling performance.

Experimental study of capacity fading mechanism in multiple overdischarge on LiNi0.5Co0.2Mn0.3O2&LiMn2O4/graphite lithium-ion batteries

Batteries can be overdischarged in practical applications, which does not pose safety risks. However, overdischarge can have a significant impact on battery performance. In this work, LiNi0.5Co0.2Mn0.3O2 (NCM)&LiMn2O4 (LMO)/graphite batteries are used as the main body. The failure mechanism of the batteries under different temperatures (−10 °C, 25 °C, 45 °C) and different depth of discharge (DOD) (105 % DOD and 110 % DOD) is studied systematically through the electrochemical methods, scanning electron microscopy (SEM), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that the deep overdischarge and high temperature accelerate the degradation of electrolyte, separator and collector, and cause rupture and recombination of solid electrolyte interphase (SEI) film. These result in the loss of conductivity, active substances and lithium ions, in which the loss of lithium ions plays a dominant role. Moreover, the attenuation of positive active material mainly comes from NCM. Our research results are of great significance for researchers to understand the failure mechanism of lithium batteries under different conditions and can provide important guidance for the safe design of lithium-ion batteries.

Unveiling the vacancy-mediated charge kinetics and capacity fading mechanism in Mn-based cathode for lithium-ion battery

In the recent past, Li2MnSiO4 (LMS) has been considered a promising cathode material for high energy density lithium-ion batteries (LIBs). Extraction of the maximum amount of Li from the host LMS and reversibility of Li insertion and extraction is still challenging, probably because of poor conductivity and, thereby, poor Li-kinetics. To improve the Li-diffusion and ionic conductivity, oxygen vacancies (OVs) in pristine LMS (LMS180) have been created, and then their impact on the Li-reactivity of LMS is studied. The quantity of OVs is determined by X-ray photoelectron spectroscopy (XPS) and calculated to be 6.8% in LMS180 heated at 300 ºC in Ar (LMSA300) and ∼ 8.2% in LMS180 heated at 500° C in Ar (LMSA500), subsequently it is supported and validate by the electron paramagnetic response (EPR) and high-resolution transmission electron microscopy (HR-TEM). The best sample, i.e., LMSA500, exhibits a total conductivity of 8.06×10−6 S/cm, resulting in an initial charge capacity of 292 (±5) mAh/g at 10 mA/g. The OVs are found to facilitate the facile lithium-ion movement by providing the lowest migration energy. Furthermore, knowing the impacts of OVs presence in LMS and their effect on Li-diffusion enables us to address traditional capacity fading processes in LMS.

Correlating Mn Dissolution and Capacity Fade in LiMn0.8Fe0.2PO4/Graphite Cells During Cycling and Storage at Elevated Temperature

LiMnxFe1−xPO4 is a promising positive electrode material for Li-ion batteries. In order to understand the failure mechanisms of this material, LiMn0.8Fe0.2PO4/graphite pouch cells were cycled at 40 or 55 °C over three voltage ranges: 2.5–3.6 V (Fe plateau), 3.6–4.2 V (Mn plateau), and 2.5–4.2 V (full voltage range). Cells cycled at higher temperature and over the full voltage range had the highest capacity fade. Differential voltage analysis showed that cells cycled over the Mn plateau and full voltage range had the highest Li inventory loss, and there was no active mass loss in any of the cells. Micro X-ray fluorescence spectroscopy showed that cells with higher levels of Mn deposition on the negative electrode had higher Li inventory loss. Constant voltage storage experiments at 55 °C showed rapid capacity loss for cells held at top of charge. Despite having similar Li inventory loss trends to the cycled cells, there was less Mn deposition on the negative electrodes. Thus, the capacity fade mechanisms are different for cells that undergo cycling and storage.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics for High-Throughput Flow Battery Characterization

The library of redox-active organics that are potential candidates for electrochemical energy storage in flow batteries is exceedingly vast, necessitating high-throughput characterization of molecular lifetimes. Demonstrated extremely stable chemistries require accurate yet rapid cell cycling tests, a demand often frustrated by time-denominated capacity fade mechanisms. We have developed a high-throughput setup for elevated temperature cycling of redox flow batteries, providing a new dimension in characterization parameter space to explore. We utilize it to evaluate capacity fade rates of aqueous redox-active organic molecules, as functions of temperature. We demonstrate Arrhenius-like behavior in the temporal capacity fade rates of multiple flow battery electrolytes, permitting extrapolation to lower operating temperatures. Collectively, these results highlight the importance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime flow batteries.

Solid-state synthesis and ion transport characteristics of the β-KSbF4 for all-solid-state fluoride-ion batteries

All-solid-state fluoride ion batteries (FIBs) have been recently considered as a post-lithium-ion battery system due to their high safety and high energy density. Just like all solid-state lithium batteries, the key to the development of FIBs lies in room-temperature electrolytes with high ionic conductivity. β-KSbF4 is a kind of promising solid-state electrolyte for FIBs owing to its rational ionic conductivity and relatively wide electrochemical stability window at room temperature. However, the previous synthesis routes of β-KSbF4 required the use of highly toxic hydrofluoric acid and the ionic conductivity of as-prepared product needs to be further improved. Herein, the β-KSbF4 sample with an ionic conductivity of 1.04 × 10−4 S cm−1 (30 °C) is synthesized through the simple solid-state route. In order to account for the high ionic conductivity of the as-synthesized β-KSbF4, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) are used to characterize the physicochemical properties. The results show that the as-synthesized β-KSbF4 exhibits higher carrier concentration of 1.0 × 10−6 S cm−1 Hz−1 K and hopping frequency of 1.31 × 106 Hz at 30 °C due to the formation of the fluorine vacancies. Meanwhile, the hopping frequency shows the same trend as the changes of ionic conductivity with the changes of temperature, while the carrier concentration is found to be almost constant. The two different trends indicate the hopping frequency is mainly responsible for the ionic conduction behavior within β-KSbF4. Furthermore, the all-solid-state FIBs, in which Ag and Pb + PbF2 are adopted as cathode and anode, and β-KSbF4 as fluoride ion conductor, are capable of reversible charge and discharge. The assembled FIBs show a discharge capacity of 108.4 mA h g−1 at 1st cycle and 74.2 mA h g−1 at 50th cycle. Based on an examination of the capacity decay mechanism, it has been found that deterioration of the electrolyte/electrode interface is an important reason for hindering the commercial application of FIBs. Hence, the in-depth comprehension of the ion transport characteristics in β-KSbF4 and the interpretation of the capacity fading mechanism will be conducive to promoting development of high-performance FIBs.

Solid-state Zn-ion batteries using composite cellulose polyethylene oxide materials-Illustration of reaction and capacity fading mechanisms

In this work, the composite materials of cellulose and poly(ethylene oxide) (PEO) materials as the solid-electrolyte separator was electrochemically and mechanically characterized before being incorporated into solid-state Zn-ion batteries (SSZIBs) with LiFePO4 cathode and Zn anode. As understanding fading mechanisms and operational settings is essential to developing long lasting batteries, we further investigated the mechanisms of LiFePO4 lithiation and de-lithiation in SSZIBs. The capacity fading mechanism was elucidated using ex-situ high energy synchrotron XANES measurements on our developed Zn-ion devices at varying charge rates. Long-term cycling was the focus of these investigations, which tracked and assessed chemical and structural changes. The results show that an increase in inactive FePO4 proportional to the loss of active lithium is the primary driver of capacity fading once the lithium source is depleted. XRD confirm that LiFePO4 exists in an olivine phase and reveal that the insertion and deinsertion behaviour of lithium ions in LiFePO4 changes with cycling. The two phases (LiFePO4, FePO4) and the loss of the lithium source may contribute to the reduced rate capability and capacity fading of LiFePO4 cells during prolonged cycling.

Magnetic Force Dilatometry of Silicon-NMC622 Lithium-Ion Coin Cells: The Effects of Binder, Capacity Ratio, and Electrolyte Selection

Operando cell expansion measurements on Si-NMC622 coin cells using a magnetic dilatometer were performed to understand the effects of electrode binder content, electrode formulation, negative-to-positive electrode capacity ratio (N/P ratio), and electrolyte selection on reversible and irreversible cell expansions. Our experiments reveal a complex relationship between cell properties, imparted by the selected cell parameters, and cell expansion. Reversible cell expansions scaled with cell discharge capacity and electrode mechanical properties, while irreversible cell expansions were sensitive to capacity fade, silicon utilization, and electrolyte decomposition mechanisms. Additionally, volumetric cell energy densities were calculated using the measured capacities and irreversible expansions over the life of the cells. We show that judicious selection of cell parameters can improve volumetric energy density after 200 charge/discharge cycles by approximately two-fold. Our work provides valuable insight, at an early stage of cell development, towards minimizing the effects of cell expansion on battery cell, pack, and module designs.

Facile Synthesis of Diazaanthraquinone Dimers as High-Capacity Organic Cathode Materials for Rechargeable Lithium Batteries.

Organic cathode materials (OCMs) have tremendous potential to construct sustainable and highly efficient batteries beyond conventional Li-ion batteries. Thereinto, quinone/pyrazine hybrids show significant advantages in material availability, energy density, and cycling stability. Herein, we propose a facile method to synthesize quinone/pyrazine hybrids, i.e., the condensation reaction between ortho-diamine and bromoacetyl groups. Based on it, we have successfully synthesized three 1,4-diazaanthraquinone (DAAQ) dimers, including 2,2'-bi(1,4-diazaanthraquinone) (BDAAQ) with an exceptional theoretical capacity of 512 mAh g-1 based on the eight-electron reaction. It can be fully utilized in Li batteries in a wide voltage range of 0.8-3.8 V, at the cost of inferior cycling stability. In an optimal voltage range of 1.4-3.8 V, BDAAQ exhibits one of the best comprehensive electrochemical performances for small-molecule OCMs, including a high specific capacity of 366 mAh g-1, an average discharge voltage of 2.26 V, as well as a respectable capacity retention of 59% after 500 cycles. Moreover, the in-depth investigations reveal the redox reaction mechanisms based on C═O and C═N groups as well as the capacity fading mechanisms based on dissolution-redeposition behaviors. In brief, this work provides an instructive synthesis method and mechanism understanding of high-performance OCMs based on a quinone/pyrazine hybrid structure.

Stress-dependent capacity fade behavior and mechanism of lithium-ion batteries

Understanding the behavior and mechanism of capacity fade in lithium-ion batteries can assist in promoting their wider commercial and industrial applications. We develop an Electrochemical-Thermal-Mechanical coupled Capacity Fade model (ETMCF) for nickel-manganese-cobalt (NMC111)/graphite (C) lithium-ion batteries. The main fade behaviors include SEI formation, lithium plating/stripping, SEI re-formation, and loss of active material. ETMCF model focuses on the influence of stress on capacity fade behaviors, improves the accuracy of predicting battery capacity fade at high charge/discharge rates (C-rates) and a wide temperature domain, and confirms that the stress effect in lithium-ion battery capacity fade is essential and cannot be ignored. We systematically examine the impact of C-rate, operating temperature, and coupling effects on the capacity fade mechanism and discover markedly distinct dominant fade behaviors under various C-rates and temperatures. Moreover, we also construct a phase diagram of the capacity loss ratio and elucidate the dependency of the C-tare, temperature, and capacity loss relationship. This work provides new insights into fast charging strategy and temperature regulation in battery management systems and offers a comprehensive analytical framework for predicting and evaluating battery capacity fade.

Quantifying effect of faradaic imbalance and crossover on capacity fade of vanadium redox flow battery

In this work, we aimed to reveal two main contributors to the capacity fade of a vanadium redox flow battery (VRFB). These contributors are the oxidative imbalance caused by the hydrogen evolution reaction (HER) competing with V3+ reduction during charging, and crossover, particularly the net transfer of vanadium ions from negolyte to posolyte. To investigate this, we performed VRFB cycling under various operation conditions with sequential monitoring of the electrolytes composition. We discovered that shortly after cycling starts, the crossover makes the negolyte capacity-limiting. This leads to high polarization of the negative electrode inducing HER and increasing average oxidation state (AOS) of the electrolyte. Our examination shows that the magnitude of the oxidative imbalance correlates with that of the crossover, both being dependent on the state-of-charge (SoC). Therefore, by changing operation conditions, we can slightly influence the crossover, while dramatically affect the oxidative imbalance. We also found that the resulting magnitude of the capacity fade is a trade-off between these two side-processes. This necessitates careful optimization of the battery and electrolyte composition, along with its cycling regime. From the data obtained, we conclude that the only proper approach to achieve lower capacity fade is by ensuring that the negolyte is capacity-limiting over long-term cycling. We hope that the data on the capacity fade mechanisms presented here will facilitate development of more stable and cost-effective VRFBs.

The capacity fading mechanism of high-capacity CrOx (x ≥ 2.5) cathode material for lithium-ion battery

The capacity fading mechanism of high-capacity CrOx (x ≥ 2.5) cathode material for lithium-ion battery

Structurally robust lithium-rich layered oxides for high-energy and long-lasting cathodes

O2-type lithium-rich layered oxides, known for mitigating irreversible transition metal migration and voltage decay, provide suitable framework for exploring the inherent properties of oxygen redox. Here, we present a series of O2-type lithium-rich layered oxides exhibiting minimal structural disordering and stable voltage retention even with high anionic redox participation based on the nominal composition. Notably, we observe a distinct asymmetric lattice breathing phenomenon within the layered framework driven by excessive oxygen redox, which includes substantial particle-level mechanical stress and the microcracks formation during cycling. This chemo-mechanical degradation can be effectively mitigated by balancing the anionic and cationic redox capabilities, securing both high discharge voltage (~ 3.43 V vs. Li/Li+) and capacity (~ 200 mAh g−1) over extended cycles. The observed correlation between the oxygen redox capability and the structural evolution of the layered framework suggests the distinct intrinsic capacity fading mechanism that differs from the previously proposed voltage fading mode.

Stable 2,5‐Dihydroxy‐1,4‐benzoquinone Based Organic Cathode Enabled by Coordination Polymer Formation and Binder Optimization

AbstractOrganic electrode materials are gaining increased attention in energy storage applications, but often encounter challenges such as low capacity and poor cycling stability. This paper explores the utilization of a 1‐D coordination polymer, copper(II)‐2,5‐dihydroxy‐1,4‐benzoquinone (Cu‐DHBQ), as a cathode material for Li‐ion batteries for the first time. Cu‐DHBQ is air‐stable, devoid of coordinated water molecules, and possesses a high theoretical capacity of 266 mAh g−1. With an optimal sodium alginate (SA) binder content of 25 wt%, the Cu‐DHBQ cathode demonstrates a notable initial capacity of 214 mAh g−1 and outstanding cycling stability, retaining 210 mAh g−1 (98% capacity retention) after 200 cycles at a current rate of 100 mA g−1. A comprehensive investigation into the capacity fading mechanisms, the bonding capability of the SA binder, and the interactions between Cu‐DHBQ and SA is conducted using scanning electron microscope (SEM), peel tests, and Fourier transform infrared spectroscopy (FTIR), respectively. Additionally, the electrochemical reaction mechanisms of Cu‐DHBQ are examined using ex situ X‐ray photoelectron spectroscopy (XPS) and FTIR. These findings offer valuable insights into understanding the electrochemical properties of coordination polymers and metal‐organic frameworks based on DHBQ, shedding light on their potential as materials for battery electrodes.

A Novel Approach for Post-Mortem Analysis in All-Solid-State Batteries: Isolating Solid Polymer Electrolytes from Lithium Anodes

Polymeric electrolytes are currently at the forefront of research for the next generation of lithium all-solid-state batteries. Polyethylene oxide (PEO), a commonly used polymer for these batteries, operates at elevated temperatures at which it reacts with active metal electrodes (e.g., lithium). Rich surface chemistry is developed at the Li-PEO interfaces, thereby controlling these batteries’ electrochemical behavior. Interfacial studies are essential to comprehend batteries’ stabilization or capacity fading mechanisms. For that, post-mortem analysis with an emphasis on interfaces is a necessary approach to underpinning these mechanisms. While it can be readily done with liquid electrolytes, post-mortem characterization of similar interfaces with solid electrolytes is hampered by the Li-PEO stack firm adhesion, which is impossible to separate. Here, various methods were attempted to separate polymer electrolytes from metallic anodes after Li symmetric cells’ operation, which is a necessary step for solid-state NMR characterization. By a simple method involving exposure to N2(g) atmosphere, PEO-based solid electrolyte samples were successfully isolated from lithium anodes while preserving their morphology and chemical characteristics to enable their direct analysis. This method’s concept was approved by Solid-state NMR spectroscopy. This work opens the door for post-operative analysis of many kinds of solid-state Li batteries.

H2O/HF Scavenging Mechanism in Cellulose-Based Separators for Lithium-Ion Batteries with Enhanced Cycle Life.

Lithium-ion batteries (LIBs) are increasingly being integrated into the transportation industry due to their high energy density, durability, and low cost. With the growing demand for transportation and other emerging applications, there is a concurrent rise in concern over LIB material sourcing and recycling. This urges the development of LIBs with extended cycle lifespans. One mechanism of capacity fading in LIBs is the dissolution of transition metals into the electrolyte after the cathode is etched with hydrofluoric acid (HF). HF is readily generated by the hydrolysis of the LIB electrolyte salt, lithium hexafluorophosphate (LiPF6), which makes minimizing moisture in the electrolyte a priority in manufacturing. In this study, a nonwoven, cellulose-based separator (CBS) is introduced as an alternative separator for battery technologies to scavenge residual water and HF from the electrolyte. The CBS is shown to be capable of scavenging varying amounts of water from the electrolyte based on different drying processes of the CBS, and a mechanism for this water scavenging is identified based on the materials present in the CBS. In addition, the chemical and electrochemical performance of the CBS in real battery conditions is investigated. Results suggest an effective H2O/HF scavenging capability in the CBS that allows LIB coin cells to have over 17% higher capacity retention than those with conventional separators. Furthermore, studies of the industrially manufactured, commercially relevant cylindrical and pouch cells show remarkable 761 and 103% improvements in the 60% capacity lifetime, respectively. The environmental friendliness, low cost, and easy application empowered by the cycle life improvements shown in this work make this nonwoven CBS a promising candidate for improving industry-level LIB performance.