Cycles For Lithium-ion Batteries Research Articles

Lithium Plating at the Cell Edge Induced by Anode Overhang during Cycling in Lithium-Ion Batteries: Part I. Modeling and Mechanism

The anode overhang is usually cited to prevent lithium plating at the cell edges of lithium-ion batteries. Still, numerous reports in the literature show lithium plating at the cell edge, which is typically referred to as edge plating. Edge plating is often attributed to inhomogeneous lithium distribution, thermal gradients, or pressure-dependent effects. This work presents an easy-to-implement two-dimensional electrochemical model demonstrating inhomogeneous lithiation induced by the anode overhang, which can explain experimentally observed edge plating. First, the mechanism of inhomogeneous lithiation due to the anode overhang is explained in detail. Then, a parameter study on charge protocol and geometric cell properties is presented, and the implications for cell applications are analyzed. Finally, the findings are discussed and put into a broader perspective of cell design, manufacturing, and fast charging application. In Part II of this work, the simulation is validated experimentally using multi-reference electrode single-layer pouch cells.

An Ultralow-concentration and Moisture-resistant Electrolyte of Lithium Difluoro(oxalato)borate in Carbonate Solvents for Stable Cycling in Practical Lithium-ion Batteries.

The electrolyte concentration not only impacts the battery performance but also affects the battery cost and manufacturing. Currently, most studies focus on high-concentration (>3 M) or localized high-concentration electrolytes (~1 M); however, the expensive lithium salt imposes a major concern. Most recently, ultralow concentration electrolytes (<0.3 M) have emerged as intriguing alternatives for battery applications, which feature low cost, low viscosity, and extreme-temperature operation. However, at such an early development stage, many works are urgently needed to further understand the electrolyte properties. Herein, we introduce an ultralow concentration electrolyte of 2 wt % (0.16 M) lithium difluoro(oxalato)borate (LiDFOB) in standard carbonate solvents. This electrolyte exhibits a record-low salt/solvent mass ratio reported to date, thus pointing to a superior low cost. Furthermore, this electrolyte is highly compatible with commercial Li-ion materials, forming stable and inorganic-rich interphases on the lithium cobalt oxide (LiCoO2) cathode and graphite anode. Consequently, the LiCoO2-graphite full cell demonstrates excellent cycling performance. Besides, this electrolyte is moisture-resistant and effectively suppresses the generation of hydrogen fluoride, which will markedly facilitate the battery assembly and recycling process under ambient conditions.

Unveiling voltage evolution during Li plating-relaxation-Li stripping cycling of lithium-ion batteries

The unwanted Li plating on graphite anode surface in lithium-ion batteries causes poor cycling performance along with raised safety risk once Li dendrites penetrate separator. Voltage characteristics during relaxation and discharging have been recognized as the most direct and convenient indictor for Li plating detection, where unveiling voltage evolution during plating-relaxation-stripping cycling needs to be emphasized to facilitate Li plating detection. This study fabricates Li|graphite cells to implement Li plating-relaxation-stripping protocols through over-lithiation before internal short circuit, and the Li nucleation-growth process is linked to voltage evolution assisting with the post-mortem approaches. The Li plating voltage initially displays continuous decline indicated as Li nucleation, until the formation of Li plating plateau indicated as Li growth. The plating-relaxation-stripping voltage patterns show highly correlation that the occurrence of Li plating plateau exactly corresponds to the appearance of a mixed relaxation plateau attributed to the equilibrium of Li stripping and Li re-intercalation into graphite, while the disappearance of the mixed relaxation plateau just corresponds to the advent of Li stripping plateau. Three stages are finally divided associated with characteristic Li plating -relaxation-stripping voltage patterns, where Stage I indicates the occurrence of Li plating plateau behaving as predominant LixC6; Stage II is characterized as the occurrence of mixed relaxation plateau manifested as Li coexisting with LixC6; Stage III is distinguished by the appearance of Li stripping plateau indicated as predominant Li and dead Li. This work proposes underlying evolution mechanism of Li plating-relaxation-stripping cycling, which contributes to sufficient evidence for reliable Li plating detection.

Trifluoromethylated Lithium Borates as Electrolyte Salts for High‐Energy‐Density Lithium‐Ion Batteries with High‐Voltage LiNi0.5Mn1.5O4 Positive Electrodes

AbstractLiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for high‐energy‐density lithium‐ion batteries (LIBs) because of its high working voltage; however, its practical application is hindered by the insufficient oxidation resistance of LIB electrolytes. In this study, we aimed to address this issue by evaluating two trifluoromethylated lithium borate compounds lithium difluoro (perfluoropinacolato) borate (PFP‐F2) and lithium difluoro(2‐hydroxy‐3,3,3,3′,3′,3′‐hexafluoroisobutylato) borate (HHIB‐F2) as electrolyte salts for high‐potential LIBs (4.8 V vs. Li/Li+) with LNMO positive electrodes. In full‐cell tests, the cyclability of LIBs containing these salts is superior (60 °C) to that of the cell with lithium tetrafluoroborate (LiBF4) as the reference electrolyte salt, which is ascribed to the formation of a positive electrode passivation layer that inhibits the oxidative decomposition of the electrolyte salt and solvent in the former case. Moreover, the oxidative decomposition of trifluoromethylated borates at 4.8 V affords a passivation layer on the negative electrode. Thus, the examined borates hold great promise for the commercialization of high‐energy‐density LNMO‐based LIBs, and the formation of a solid electrolyte interphase (SEI) at the negative electrode resulting from the oxidative decomposition products of electrolyte salts is a promising new way to enhance the performance of high‐potential positive electrode LIBs beyond existing levels.

Stable cycling and low-temperature operation utilizing amorphous carbon-coated graphite anodes for lithium-ion batteries.

With the continuous expansion of the lithium-ion battery market, addressing the critical issues of stable cycling and low-temperature operation of lithium-ion batteries (LIBs) has become an urgent necessity. The high anisotropy and poor kinetics of pristine graphite in LIBs contribute to the formation of precipitated lithium dendrites, especially during rapid charging or low-temperature operation. In this study, we design a graphite coated with amorphous carbon (GC) through the Chemical Vapor Deposition (CVD) method. The coated carbon layer at the graphite interface exhibits enhanced reaction kinetics and expanded lithium-ion diffusion pathways, thereby reduction in polarization effectively alleviates the risk of lithium precipitation during rapid charging and low-temperature operation. The pouch cell incorporating GC‖LiCoO2 exhibits exceptional durability, retaining 87% of its capacity even after 1200 cycles at a high charge/discharge rate of 5C/5C. Remarkably, at -20 °C, the GC-2 maintains a specific capacity of 163 mA h g-1 at 0.5C, higher than that of pristine graphite (65 mA h g-1). Even at -40 °C, the GC-2‖LiCoO2 pouch cell still shows excellent capacity retention. This design realizes the practical application of graphite anode in extreme environments, and have a promising prospect of application.

Rapid Test and Assessment of Lithium-ion Battery Cycle Life Based on Transfer Learning

Rapid Test and Assessment of Lithium-ion Battery Cycle Life Based on Transfer Learning

Speciation of Transition Metal Dissolution in Electrolyte from Common Cathode Materials

Significant capacity loss has been observed across extended cycling of lithium-ion batteries to high temperatures and high voltages. This occurs due to transition metal dissolution from the high voltage spinel or layered oxide cathode material, ion migration through the electrolyte, and deposition on the solid-electrolyte interphase (SEI) on the anode. While much research has been done to track the oxidation state of the transition metal in the cathode material or deposited on the anode, there have been mixed reports on the chemical state of the transition metal ions dissolved in the electrolyte depending on the type of cathode used. X-ray absorption near edge spectroscopy (XANES) was performed on electrolytes extracted from full cells built with four different cathode materials that were cycled at either high or standard voltages to determine the chemical state of Mn and Ni in solution. Inductively coupled plasma-mass spectrometry (ICP-MS) was performed on the anodes from these cells to determine the concentration of deposited metal ions.

Significance of electrolyte additive molecule structure in stabilizing interphase in LiNi0.8Co0.1Mn0.1O2/artificial graphite pouch cells at high temperature

Electrolyte additives are pivotal for stable cycling of rechargeable lithium ion batteries (LIBs), which dictate the creation of the protective interphases on electrodes. Many additives have been proposed but less knowledge is available on the relationship between their molecular structure and interphase stability. This research compares three electrolyte additives with systematic changes in their cyclic ethylene sulfate structures, i.e. 1,3,2−dioxathiolane−2,2−dioxide (DTD), 4−methyl−1,3,2−dioxathiolane−2,2− dioxide (MDTD) and 4−propyl−[1,3,2] dioxathiolane−2,2−dioxide (PDTD) to investigate their effects on the performance of LiNi0.8Co0.1Mn0.1O2/artificial graphite lithium ion pouch cells at high temperature. Comprehensive characterizations reveal that all these additives exhibit similar oxidative and reductive activity, but they lead to diverse long−term cycling performance at 55 °C. The sulfate species derived from the propyl functionalized PDTD form the most effective cathode and anode interphases in preventing electrolyte decomposition and improving cycling capabilities, with capacity retention of 85 % after 900 cycles at 55 °C. Meanwhile, a super stable (3000 cycles), high−capacity (1668 mAh) pouch cell is constructed at 25 °C. This work paves a road to design electrolyte additive more efficiently for high−energy−density LIBs at elevated temperature.

Speciation of Transition Metal Dissolution in Electrolyte from Common Cathode Materials.

Significant capacity loss has been observed across extended cycling of lithium-ion batteries cycled to high potential. One of the sources of capacity fade is transition metal dissolution from the cathode active material, ion migration through the electrolyte, and deposition on the solid-electrolyte interphase on the anode. While much research has been conducted on the oxidation state of the transition metal in the cathode active material or deposited on the anode, there have been limited investigations of the oxidation state of the transition metal ions dissolved in the electrolyte. In this work, X-ray absorption spectroscopy has been performed on electrolytes extracted from cells built with four different cathode active materials (LiMn2 O4 (LMO), LiNi0.5 Mn1.5 O4 (LNMO), LiNi0.8 Mn0.1 Co0.1 O2 (NMC811), and (x Li2 MnO3 *(1-x) LiNia Mnb Coc O2 , with a+b+c=1) (LMRNMC)) that were cycled at either high or standard potentials to determine the oxidation state of Mn and Ni in solution. Inductively coupled plasma-mass spectrometry has been performed on the anodes from these cells to determine the concentration of deposited transition metal ions. While transition metal ions were found dissolved in all electrolytes, the oxidation state(s) of Mn and Ni were determined to be dependent on the cathode material and independent of cycling potential.

Interfacial Engineering of MoS2/V2O3@C-rGO Composites with Pseudocapacitance-Enhanced Li/Na-Ion Storage Kinetics.

Molybdenum sulfide has been widely investigated as a prospective anode material for Li+/Na+ storage because of its unique layered structure and high theoretical capacity. However, the enormous volume variation and poor conductivity limit the development of molybdenum sulfide. The rational design of a heterogeneous interface is of great importance to improve the structure stability and electrical conductivity of electrode materials. Herein, a high-temperature mixing method is implemented in the hydrothermal process to synthesize the hybrid structure of MoS2/V2O3@carbon-graphene (MoS2/V2O3@C-rGO). The MoS2/V2O3@C-rGO composites exhibit superior Li+/Na+ storage performance due to the construction of the interface between the MoS2 and V2O3 components and the introduction of carbon materials, delivering a prominent reversible capacity of 564 mAh g-1 at 1 A g-1 after 600 cycles for lithium-ion batteries and 376.3 mAh g-1 at 1 A g-1 after 450 cycles for sodium-ion batteries. Theoretical calculations confirm that the construction of the interface between the MoS2 and V2O3 components can accelerate the reaction kinetics and enhance the charge-ionic transport of molybdenum sulfide. The results illustrate that interfacial engineering may be an effective guide to obtain high-performance electrode materials for Li+/Na+ storage.

Study of temperature cycling of commercial rechargeable lithium-ion batteries

Lithium-ion batteries, a popular electric energy storage device, have high energy density and impressive working performance. However, the temperature affects its life cycle, capacity, and performance. Different effects are generated inside the battery for the different temperature conditions. It is necessary to study their thermal and electric characteristics in various thermal conditions since electric energy storage devices are used in various applications at low or high temperatures. In this study, the experimental analysis was performed to observe how a battery cell behaves above room temperature for a different 18650 cylindrical battery cell with a capacity of 5200 mAh. The testing temperature for this experiment was at 28˚C, 50˚C, 60˚C, 70˚C, and 100˚C. It is noted that the capacity of the battery cell fades drastically at high temperatures compared to low temperatures due to internal short circuits occurring at high temperatures.

Hollow sea urchin-like microspheres of the dual transition metal oxides NiO/Co3O4 immobilized on rGO enhance lithium-ion battery cycling and rate performance

The serious volume expansion and unsatisfying electronic conductivity during charge/discharge of transition metal oxides with relatively high capacity and low cost have limited their development as anode materials for lithium-ion batteries (LIBs). Herein, elaborately designed dual transition metal oxides NiO/Co3O4 immobilized on reduced graphene oxide (NiO/Co3O4 @rGO) with unique hollow sea urchin-like microspheres are employed as a modulated material for satisfying structural integrity and high capacity. On the one hand, the radioactive spines outside of sea urchin material inhibit its’ agglomeration, enlarge surface area for electrolyte infiltration, and shorten the Li+ transport path during the lithiation/delithiation process, but they also alleviate the side effects caused by volume change during cycling. On the other hand, rGO, with its good electronic conductivity and flexibility, provides physical protection for the material structure. Thanks to these merits, the NiO/Co3O4 @rGO anode exhibited a remarkable reversible discharge (1845 mAh g−1 upon 100 cycles at 0.1 A g−1), outstanding rate capacity, and desirable cycling stability (1252 mAh g−1 up to 400 cycles at 1 A g−1) in LIBs, demonstrating the enormous potential of NiO/Co3O4 @rGO for feasible synthesis, high performance, and inexpensive LIBs.

A Rapid Test Method Based on Prediction with Swarm Intelligent Optimization and Monte Carlo Expansion for Lithium-Ion Battery Cycle Life

The cycle life test offers significant sustainment for utilization and maintenance of lithium-ion batteries. The traditional way is continuous charge-discharge testing without interruption, which often takes one year or even longer. Therefore, this paper proposes a rapid cycle life test method based on intelligent prediction to replace the continuous test, which shortens the test period and accelerates product replacement. The original capacity data is decoupled into the short-term regeneration trajectory and the long-term degradation trajectory, which are predicted by the long-short term memory model optimized by swarm intelligent algorithm. The data expansion technique based on Monte Carlo sampling is used to increase the diversity of training data to improve the prediction accuracy. The feasibility and effectiveness are proved by NASA data sets. The results show that the cycle life test time reduced by at least 90% with the error less than 3 cycles.

Long Short-Term Memory Network with Transfer Learning for Lithium-ion Battery Capacity Fade and Cycle Life Prediction

Machine Learning (ML) is a promising technique for battery health estimation and prediction. However, with more and more types of batteries entering the market, building an ML model from scratch for each new battery requires collecting a large amount of data, which is very expensive and time-consuming. This paper proposes a transfer learning approach to reduce the amount of data that needs to be recollected for a new battery. The key idea is to train an ML model for a new battery of interest (i.e., target battery) with a limited amount of data by transferring the knowledge contained in a well-studied battery (i.e., source battery) with sufficient data. We illustrate this approach using two types of batteries, i.e., the battery with Li0.86Ni0.86Co0.11Al0.03O2-based positive electrode (NCA battery, source battery) and the battery with Li0.84Ni0.83Co0.11Mn0.07O2-based positive electrode (NCM battery, target battery), which have similar degradation patterns but dramatically different cycle life. Specifically, we first pre-train a long short-term memory (LSTM) network, using cycling data of 20 NCA cells at 25 °C and at 45 °C, to predict the following capacity fade based on the previous capacity sequence. Then, to make the model applicable to NCM cells, we employ the transfer learning method to retrain the model, using cycling data of only 2 NCM cells at 25 °C, and propose a two-stage approach to further improve the model performance. The proposed two-stage model can predict the cycle life of NCM cells at 45 °C using the capacities of the first 13 cycles and obtain a cycle life root-mean-squared-error (RMSE) of 25.23 cycles and a capacity trajectory RMSE of 17.80 mAh (0.51 %).

A Phosphorofluoridate-Based Multifunctional Electrolyte Additive Enables Long Cycling of High-Energy Lithium-Ion Batteries.

Ni-rich layered oxides are regarded as key components for realizing post Li-ion batteries (LIBs). However, high-valence Ni, which acts as an oxidant in deeply delithiated states, aggravates the oxidation of the electrolyte at the cathode, causing cell impedance to increase. Additionally, the leaching of transition metal (TM) ions from Ni-rich cathodes by acidic compounds such as Brønsted-acidic HF produced through LiPF6 hydrolysis aggravates the structural instability of the cathode and renders the electrode-electrolyte interface unstable. Herein, we present a multifunctional electrolyte additive, bis(trimethylsilyl) phosphorofluoridate (BTSPFA), to attain enhanced interfacial stability of graphite anodes and Ni-rich cathodes in Li-ion cells. BTSPFA eliminates the corrosive HF molecules by cleaving silyl ether bonds and enables the formation of a polar P-O- and P-F-enriched cathode electrolyte interface (CEI) on the Ni-rich cathode. It also promotes the creation of a solid electrolyte interphase composed of inorganic-rich species, which suppresses the reduction of the electrolyte during battery operation. The synergistic effect of the HF scavenging ability of BTSPFA and the stable BTSPFA-promoted CEI effectively suppresses the TM leaching from the Ni-rich cathode while also preventing unwanted TM deposition on the anode. LiNi0.8Co0.1Mn0.1O2/graphite full cells with 1 wt % BTSPFA exhibited an enhanced discharge capacity retention of 79.8% after 500 cycles at 1C and 45 °C. These unique features of BTSPFA are useful for resolving the interfacial deterioration issue of high-capacity Ni-rich cathodes paired with graphite anodes.

Prelithiated rigid polymer with high ionic conductivity as silicon-based anode binder for lithium-ion battery

Silicon-based electrodes suffer from rapid performance degradation derived from a severe volume expansion during cycling in lithium-ion batteries, and using elaborately designed polymer binders is deemed an efficient tactic to tackle the above thorny issues. In this study, a water-soluble rigid-rod poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT) polymer is described and employed as the binder for Si-based electrodes for the first time. The nematic rigid PBDT bundles wrapped around the Si nanoparticles by hydrogen bonding effectively inhibit the volume expansion of the Si and promote the formation of stable solid electrolyte interfaces (SEI). Moreover, the prelithiated PBDT binder with high ionic conductivity (3.2 × 10−4 S cm−1) not only improves the Li-ions transportation behaviors in the electrode but can also partially compensate for the irreversible Li source consumption during SEI formation. Consequently, the cycling stability and initial coulombic efficiency of the Si-based electrodes with the PBDT binder are remarkably enhanced compared to that with the PVDF binder. This work demonstrates the molecular structure and prelithiation strategy of the polymer binder that play a crucial role in improving the performance of Si-based electrodes with high-volume expansion.

Early prediction of lithium-ion battery cycle life based on voltage-capacity discharge curves

Accurately predicting the lifetime of lithium-ion batteries is critical for accelerating technological advancements and applications. Nevertheless, the complex aging mechanisms and dynamic operating conditions of lithium-ion batteries have remained major challenges. This paper proposes a method for early predicting lithium-ion batteries cycle life based on weighted least squares support vector machine (WLS-SVM) with health indicators (HIs) as input. The HIs are extracted from lithium-ion batteries voltage-capacity discharge curves, since these curves are easy to measure and strongly correlate to battery cycle life. Taking into account the nonlinearity of batteries cycle life, a support vector machine (SVM) that is capable of strong generalization is used to predict cycle life. As a solution to the problem of misleading results from outlier data in SVM, error square term combined with weight functions is used in this study to improve robustness and prediction accuracy. The datasets of 41 cells are used to verify the proposed early prediction method. The results show that the root mean square error (RMSE) and mean absolute error (MAE) of cycle life prediction results by the proposed method are much lower, and the cycle life early prediction errors of the test cells are all <9 %, which notes that the proposed method is accurate and valid for cycle life early prediction.

Cyclotetrabenzil Derivatives for Electrochemical Lithium-Ion Storage.

Organic electrode materials could revolutionize batteries because of their high energy densities, the use of Earth-abundant elements, and structural diversity which allows fine-tuning of electrochemical properties. However, small organic molecules and intermediates formed during their redox cycling in lithium-ion batteries (LIBs) have high solubility in organic electrolytes, leading to rapid decay of cycling performance. We report the use of three cyclotetrabenzil octaketone macrocycles as cathode materials for LIBs. The rigid and insoluble naphthalene-based cyclotetrabenzil reversibly accepts eight electrons in a two-step process with a specific capacity of 279 mAh g-1 and a stable cycling performance with ≈65 % capacity retention after 135 cycles. DFT calculations indicate that its reduction increases both ring strain and ring rigidity, as demonstrated by computed high distortion energies, repulsive regions in NCI plots, and close [C⋅⋅⋅C] contacts between the naphthalenes. This work highlights the importance of shape-persistency and ring strain in the design of redox-active macrocycles that maintain very low solubility in various redox states.

Point-cavity-like carbon layer coated SnS nanotubes with improved energy storage capacity for lithium/sodium ion batteries

Tin monosulfide (SnS) is known as a prospective anode material for lithium/sodium ion batteries due to its high capacity, low cost, and easy preparation. Carbon coating is a powerful strategy to improve poor electronic conductivity and alleviate the large volume expansion of the SnS, thus achieving high electrochemical performances. However, the commonly used carbon coatings strategies usually generate interstices between the SnS and carbonaceous material, interrupting electron and ion transfer and unsatisfied accommodation of volume expansion. Herein, point-cavity-like carbon coated SnS nanotubes (CN/SnS) were synthesized by a close-knit mechanism using polyvinylpyrrolidone (PVP) and carbon nitride (g-C3N4) as carbon sources. The carbonyl group in PVP can form hexahydroxylated stannyl compound with Sn2+, and the amine group can generate CN bond with the g-C3N4 template in an aqueous solution, respectively. The unique construction of CN/SnS can successfully reinforce the electron and ion transfer capability and accommodate volume expansion. The reformative effectivity dramatically improves the energy storage properties of SnS electrode for LIBs/SIBs. The CN/SnS electrode can deliver high specific capacities of 547.7 mAh g−1 at 1.0 A g−1 after 300 cycles for lithium-ion batteries and 298.2 mAh g−1 at 0.1 A g−1 after 200 cycles for sodium-ion batteries, respectively. The structure design is practical and feasible, which could be used to develop high-performance transition metal sulfide/carbon composite anodes for LIBs and SIBs.

Influence of lithium plating on lithium-ion battery aging at high temperature

Lithium plating is an important issue for lithium-ion battery safety and cycle life that can be caused by cycle at low temperature. In this study, we investigated battery aging over an extended low-temperature cycle and at high temperature after the low-temperature cycle. Nondestructive and destructive analysis methods were used to study battery electrochemical dynamics and changes to the materials, and the results indicated that battery aging over the extended low-temperature cycle could be divided into two stages. The mechanism of the first stage is that of “dead lithium,” which causes significant capacity fading, whereas that of the second stage is solid electrolyte interphase (SEI) growth. It was also found that plated lithium accelerates battery aging at high temperature; part of it is intercalated into anode, another part of it reacts with the electrolyte, thus consuming the plated lithium. Thus, electrolyte decomposition and SEI growth are the primary aging mechanisms at high temperature after low-temperature cycling. The plated lithium content and charge/discharge rate affected plated lithium consumption during the high-temperature cycle. Plated lithium was not depleted for the battery with significant amounts of plated lithium or upon charging with high current and discharging with both high and low current when the state of health (SOH) decreased to 70%. The factors affecting battery aging ranked in order of importance are charge current > plated lithium content > high temperature > discharge current.