Capacity Fading Mechanism Research Articles

Improving cycle life of layered lithium transition metal oxide (Li M O 2 ) based positive electrodes for Li ion batteries by smart selection of the electrochemical charge conditions

Abstract Increasing the specific energy of a lithium ion battery and maintaining its cycle life is a predominant goal and major challenge for electrochemical energy storage applications. Focusing on the positive electrode as the specific energy bottleneck, cycle life characteristics of promising layered oxide type active materials (Li M O 2 ) has been thoroughly investigated. Comparing the variety of Li M O 2 compositions, it could be shown that the “Ni-rich” (Ni ≥ 60% for M in Li M O 2 ) electrodes expectably revealed best performance compromises between specific energy and cycle life at 20 °C, but only LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) could also maintain sufficient cycle performance at elevated temperatures. Focusing on NMC622, it could be demonstrated that the applied electrochemical conditions (charge capacity, delithiation amount) in the formation cycles significantly influence the subsequent cycling performance. Moreover, the insignificant transition metal dissolution, demonstrated by means of total X-ray fluorescence (TXRF) technique, and unchanged lithiation degree in the discharged state, determined by the measurement of the Li + content by means of the inductively coupled plasma optical emission spectroscopy (ICP-OES) technique, pointed to a delithiation (charge) hindrance capacity fade mechanism. Considering these insights, thoughtful modifications of the electrochemical charge conditions could significantly prolong the cycle life.

Reaction and Capacity-Fading Mechanisms of Tin Nanoparticles in Potassium-Ion Batteries

In this article, we report a study of the electrochemical performance and degradation mechanism of tin (Sn) nanoparticle anodes in potassium-ion batteries (KIBs). A high capacity of 197 mAh/g was found for the Sn nanoparticles in KIBs. In situ transmission electron microscopy characterization revealed a two-step potassiation mechanism: formation of a KSn phase after full potassiation and reversible nanopore formation during the cycling of Sn nanoparticles. However, significant capacity fading occurred after a few cycles, which was caused by the severe pulverization of the Sn nanoparticles. This work offers a fundamental understanding of the reaction and degradation mechanisms of alloying-type anodes for KIBs, shedding light on the development of high-performance KIBs.

Degradation Identification of Individual Components in the LiyNi1/3Co1/3Mn1/3O2-LiyMn2O4 Blended Cathode for Large Format Lithium Ion Battery

The degradation behaviors of individual components in the LiyNi1/3Co1/3Mn1/3O2(NCM)–LiyMn2O4(LMO) blended cathode are investigated in this paper. A prognostic/mechanistic model is applied to quantitatively analyze the capacity fading mechanism of the lithium ion battery with blended cathode. NCM and LMO are considered to be connected in parallel with a same potential during cycling. Current is distributed between NCM and LMO based on the dQ/dV curves, and the capacities of NCM and LMO can thus be quantitatively identified, respectively. The identified model parameters show that both NCM and LMO suffer loss of active material (LAM), but NCM degrades faster than LMO. Loss of lithium inventory also contributes to the capacity degradation, whereas anode shows little LAM until 330 cycles. The identified capacity degradation mechanism is validated by the coin cells test data, as the capacity degradation of the coin cells assembled with the aged electrodes compared with those made of fresh electrodes are consistent with the identified results.

A Comprehensive Understanding on How Ultrathin Coating Layers on Active Particles Enhance Battery Performance Significantly

The Atomic Layer Deposition (ALD) coating strategy on active materials of Li-ion battery is known as an effective way than other coating techniques to enhance battery performance, but there is still substantial uncertainty about how these coating layers are the origin of the enhanced performance. A comprehensive model is developed based on experimental measurements and theoretical analysis to study how different coating strategies affect the mechanical and electrochemical responses of a battery system. Although it appears that a thicker coating helps to provide higher capacity and cycle life improvement, but a too-thick layer may act as a migration barriers and facilitate much slower lithium transport, resulting in capacity decrease. Further, the developed model quantitatively predicts the capacity retention of coated particles by mitigating the transition metal ion dissolution, which is one critical capacity fade mechanism of the metal oxide cathode materials. This quantitative study reveals the trade-off mechanism of ALD coating between the species transport (capacity) and protection (lifetime), which could be an important guidance for thin-coating based strategies for battery performance enhancement.

Understanding Capacity Fading of LiNi0.8Co0.15Al0.05O2 Via Long-Term Operando X-Ray Diffraction Studies

Layered lithium transition metal oxides are promising high-capacity cathode materials for Li-ion batteries. However, capacity fading has restricted the practical capacity to less than 70% of the theoretical capacity. Higher initial capacity can be achieved by charging to a higher voltage, yet this initial gain in capacity is quickly offset by the rapid fade in capacity. Understanding the capacity fading mechanism will help develop strategies to mitigate this problem. We used operando X-ray powder diffraction to follow the reactions of the layered LiNi0.8Co0.15Al0.05O2 over extended charge-discharge cycles at a slow current rate. The operando result shows that the capacity loss can be explained by the heterogeneity developed in the electrode after extended charge-discharge cycles.

Toward cyclic durable core/shell nanostructure of Sn-C composite anodes for stable lithium storage by simulating its lithiation-induced internal strain

Abstract To explore the capacity fading mechanism during long-term cycling of the milled Sn-C lithium storage anodes, the structural stability of the cycled Sn-C electrodes has been investigated using internal strain distribution as indicator by simulation with different two-dimensional core/shell nanostructure models solved by Lagrangian description, combining with experimental results. It is revealed that the Sn-C composite of a double-coating structure with the smaller Sn coated by a stiff layer Li2O and embedding in graphite sustains less deformation, and has higher structural stability than the single-coating one. Due to the lithiation-induced stress and strain effect, Sn particles aggregate and the Sn whiskers grow in the cycled Sn-C electrodes that observed by SEM and TEM, which is closely related to the Sn transportation. This strain induced structural damage causes the capacity fading of Sn anodes. Based on the simulation of strain distribution induced by lithiation, the nanostructure has been designed for Sn-C electrodes of smaller Sn particles embedded in matrix with large elastic modulus and proper thickness to obtain optimized combination of capacity and cycleability. It would provide a guideline for designing material and microstructure of anodes for lithium ion batteries.

Anisotropic Lattice Strain and Mechanical Degradation of High- and Low-Nickel NCM Cathode Materials for Li-Ion Batteries

In the near future, the targets for lithium-ion batteries concerning specific energy and cost can advantageously be met by introducing layered LiNixCoyMnzO2 (NCM) cathode materials with a high Ni content (x ≥ 0.6). Increasing the Ni content allows for the utilization of more lithium at a given cell voltage, thereby improving the specific capacity but at the expense of cycle life. Here, the capacity-fading mechanisms of both typical low-Ni NCM (x = 0.33, NCM111) and high-Ni NCM (x = 0.8, NCM811) cathodes are investigated and compared from crystallographic and microstructural viewpoints. In situ X-ray diffraction reveals that the unit cells undergo different volumetric changes of around 1.2 and 5.1% for NCM111 and NCM811, respectively, when cycled between 3.0 and 4.3 V vs Li/Li+. Volume changes for NCM811 are largest for x(Li) < 0.5 because of the severe decrease in interlayer lattice parameter c from 14.467(1) to 14.030(1) A. In agreement, in situ light microscopy reveals that delithiation leads to differe...

Mechanism of capacity fading caused by Mn (II) deposition on anodes for spinel lithium manganese oxide cell

The capacity fade of spinel lithium manganese oxide in lithium-ion batteries is a bottleneck challenge for the large-scale application. The traditional opinion is that Mn(II) ions in the anode are reduced to the metallic manganese that helps for catalyzing electrolyte decomposition. This could poison and damage the solid electrolyte interface (SEI) film, leading to the the capacity fade in Li-ion batteries. We propose a new mechanism that Mn(II) deposites at the anode hinders and/or blocks the intercalation/de-intercalation of lithium ions,which leads to the capacity fade in Li-ion batteries. Based on the new mechanism assumption, a kind of new structure with core-shell characteristic is designed to inhabit manganese ion dissolution, thus improving electrochemical cycle performance of the cell. By the way, this mechanism hypothesis is also supported by the results of these experiments. The LiMn2-xTixO4 shell layer enhances cathode resistance to corrosion attack and effectively suppresses dissolution of Mn, then improves battery cycle performance with LiMn2O4 cathode, even at high rate and elevated temperature.

Changing Established Belief on Capacity Fade Mechanisms: Thorough Investigation of LiNi1/3Co1/3Mn1/3O2 (NCM111) under High Voltage Conditions

The further development of lithium ion batteries operating at high voltages requires basic understanding of the occurring capacity fade mechanisms. In this work, the overall specific capacity loss with regard to reversible and irreversible processes for LiNi1/3Co1/3Mn1/3O2 (NCM111)/Li half cells, cycled at a charge cutoff potential of 4.6 V vs Li/Li+, has been investigated in detail. By means of total X-ray fluorescence (TXRF) technique it was shown that specific capacity losses associated with the amount of dissolved transition metals are negligible, implying a still intact NCM111 active material after 53 cycles. It was demonstrated that the specific capacity fade during cycling at constant specific currents can be mainly attributed to the increase of the delithiation (charge) hindrance, whereas lithiation (discharge) hindrance is only present after a specific current increase, leading to apparent specific capacity losses and to decreased Coulombic efficiencies. This could be proven by the determination ...

Electrochemical in situ X-ray probing in lithium-ion and sodium-ion batteries

In situ X-ray diffraction (XRD), as a widely used tool in probing the structure evolution in electrochemical process as well as the energy storage and capacity fading mechanism, has shown great effects with optimizing and building better batteries. Based on the research progresses of in situ XRD in recent years, we give a review of the development and the utilization of this powerful tool in understanding the complex electrochemical mechanisms. The studies on in situ XRD are divided into three sections based on the reaction mechanisms: alloying, conversion, and intercalation reactions in lithium-ion batteries. The alloying reaction, in which lithium ions insert into Si, Sb, and Ge is firstly reviewed, followed by a discussion about the recent development of in situ XRD on conversion reaction materials (including metal oxides and metal sulfides) and intercalation reaction materials (including cathode materials and some structure-stable anode materials). As for sodium-ion batteries, we divide these researches on structure evolution into two categories: cathode and anode materials. Finally, the future development of in situ XRD is discussed.

Mechanism of Capacity Fade in Sodium Storage and the Strategies of Improvement for FeS2 Anode.

Pyrite FeS2 has attracted extensive interest as anode material for sodium-ion batteries due to its high capacity, low cost, and abundant resource. However, the micron-sized FeS2 usually suffers from poor cyclability, which stems from structure collapse, exfoliation of active materials, and sulfur dissolution. Here, we use a synergistic approach to enhance the sodium storage performance of the micron-sized FeS2 through voltage control (0.5-3 V), binder choice, and graphene coating. The FeS2 electrode with the synergistic approach exhibits high specific capacity (524 mA h g-1), long cycle life (87.8% capacity retention after 800 cycles), and excellent rate capability (323 mA h g-1 at 5 A g-1). The results prove that a synergistic approach can be applied in the micron-sized sulfides to achieve high electrochemical performance.

Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells

Continuous operation of full cells with layered transition metal (TM) oxide positive electrodes (NCM523) leads to dissolution of TM ions and their migration and incorporation into the solid electrolyte interphase (SEI) of the graphite-based negative electrode. These processes correlate with cell capacity fade and accelerate markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥4.4 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. As Mn ions become incorporated into the SEI, the kinetics of lithium trapping change from power to linear at the higher UCVs, indicating a large effect of these ions on SEI growth and implicating (electro)catalytic reactions. We estimate that each MnII ion deposited in the SEI causes trapping of ∼102 additional Li+ ions thereby hastening the depletion of cyclable lithium ions. Using these results, we sketch a mechanism for cell capacity fade, emphasizing the conceptual picture over the chemical detail.

Research Progress on the Capacity Fading Mechanisms of High-Nickel Ternary Layered Oxide Cathode Materials

Research Progress on the Capacity Fading Mechanisms of High-Nickel Ternary Layered Oxide Cathode Materials

Study of Li Metal Deposition in Lithium Ion Battery during Low-Temperature Cycle Using In Situ Solid-State 7Li Nuclear Magnetic Resonance

The influences of temperature and cell operation conditions on Li metal deposition in lithium ion batteries were studied by in-situ solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy. The rates of Li metal deposition during the low-temperature cycle with two charge–discharge operation modes, i.e., continuous current and pulse current, were estimated for temperatures of 5, 0, and −5°C. Close values of activation energies were obtained for the capacity fading rate and the Li metal deposition rate, suggesting that Li metal deposition is the main cause of capacity fading in low-temperature cycles. The amounts of Li stored in the negative electrode and Li metal deposited during the low-temperature cycle were estimated and are discussed to understand the capacity fading mechanism. The pulse current mode cycle did not lead to any Li metal deposition at low temperatures.

A SEI Modeling Approach Distinguishing between Capacity and Power Fade

In this paper we introduce a pseudo two-dimensional (P2D) model for a common lithium-nickel-cobalt-manganese-oxide versus graphite (NCM/graphite) cell with solid electrolyte interphase (SEI) growth as the dominating capacity fade mechanism on the anode and active material dissolution as the main aging mechanism on the cathode. The SEI implementation considers a growth due to non-ideal insulation properties during calendar as well as cyclic aging and a re-formation after cyclic cracking of the layer during graphite expansion. Additionally, our approach distinguishes between an electronic (σSEI) and an ionic (κSEI) conductivity of the SEI. This approach introduces the possibility to adapt the model to capacity as well as power fade. Simulation data show good agreement with an experimental aging study for NCM/graphite cells at different temperatures introduced in literature.

Membrane evaluation for vanadium flow batteries in a temperature range of −20–50 °C

Vanadium flow battery (VFB) is one of the most promising large-scale energy storage technologies because of super long lifespan and unlimited capacity. In depth study of the all-climate (wide temperature) properties of VFB is essential to the practical application of VFB around the whole globe. In this work, we established a wide temperature (−20–50°C) research platform for VFB single cell evaluation. A series of typical cation exchange membranes (i.e. the benchmark Nafion 115 and Nafion 212, the Selemion CMV, and the promising candidate SPEEK) and anion exchange membranes (i.e. the Selemion AMV and APS) are studied in terms of their VFB efficiencies, long-term cycling stability and capacity fading mechanism in a temperature range of −20–50°C. Moreover, the desirable membrane for VFB application under different temperature conditions is also discussed and suggested.

Using Thin Films to Study Capacity Fade Mechanisms Observed in Conventional LiV3O8 cathodes

Capacity fade mechanisms can be difficult to pinpoint in conventional composite cathodes for Li-ion batteries. Capacity fade associated with the cathode can be caused by: (1) irreversible reactions involving the active material, possibly with the electrolyte, (2) degraded integrity of the composite structure, or (3) anode contamination by cathode dissolution products. Post-cycling characterization can be difficult, because these potential capacity fade mechanisms would occur in a complicated cathode structure with: porosity, possible microcracks, irregular surfaces, and multiple particulate phases (active material, binder, and conducting additive). Thin film cathodes were used to study how LiV3O8 (LVO) microstructure affects cycling performance without the added complications associated with a conventional composite cathode structure. Thin film cathodes were produced by magnetron sputtering a Pt current collector layer and an LVO layer onto alumina disks. The thin film geometry with its uniform layered structure was well suited for analysis of pristine and cycled LVO cathodes by several characterization techniques, including transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The cycling performance of heat-treated thin film cathodes was directly compared to that of conventional composite cathodes with heat-treated sol-gel derived LVO powder. Thin film and sol-gel derived LVO cathodes showed excellent microstructural and electrochemical agreement as a function of heat-treatment temperature. Depending on heat-treatment temperature, the microstructure ranged from amorphous (as-deposited or low temperature heat-treatment) to coarse-grained crystalline material (higher temperature). The maximum specific capacity and the maximum capacity fade were both observed for LVO nanocrystalline material fired at intermediate temperature, where reduced capacity and reduced capacity fade were observed for higher and lower firing temperatures. Capacity fade was linked to vanadium dissolution, where amorphous LVO cathodes showed much lower vanadium dissolution than nanocrystalline LVO material. This work was supported as part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012673.

Battery Degradation and Cost Analysis of a Lithium Ion Battery System for a 1 MW Green Energy Hub (GEH)

Studying higher renewable energy penetrations during the electricity generation phase, the Future Renewable Electric Energy Delivery and Management (FREEDM) Systems Center has focused on supporting the battery degradation and cost analysis portion of a commercial 1 MW green energy hub (GEH). Cost analysis and battery degradation modeling will be used as part of a coupled approach and consist of the following software applications: NREL's System Advisor Model (SAM) - for identification of load requirement and summarization of PV productions; COMSOL Multiphysics - for determination of efficient electrochemical battery energy storage system (BESS); and MATLAB – for the implementation of state of charge (SOC), state of health (SOH), and peak shaving algorithms. The GEH will provide for various grid services using 20% renewable energy penetration and a Lithium ion based (Li-ion) BESS. Preliminary results using a LiFePO4 based BESS are presented below. Technical Approach with Preliminary Results The LiFePO4 battery was cycled to determine SOC and SOH using the Versastat 4 Potentiostat with the measured data being used as a baseline for the development of the COMSOL model. SAM The System Advisor Model (SAM) is a model developed by the U.S. Department of Energy and National Renewable Energy Laboratory to analyze sustainable energy systems. The SAM was used to determine the photovoltaic footprint capable of supporting 20% penetration. Fig 1. COMSOL COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. COMSOL was used to model battery degradation and the affect of multiple cycling characteristics in a LiFePO4 cell. Fig 2. MATLAB MATLAB is matrix-based software that uses programming language for numerical computation. MATLAB was used for computation and data analysis of the peak shaving algorithm. Fig 3. Acknowledgement This work was supported by the FREEDM ERC program of the National Science Foundation under award number EEC-08212121. References Dubarry, Matthieu, Liaw, Bor Y. (2009). Identify capacity fading mechanism in a commercial LiFePO4 cell Journal of Power Sources Vol 194, pg 541-549.Kim, Jae-Hun, Woo, Sang C., Park, Min-Sik, Kim, Ki J., Yim, Taeeun, Kim, Jeom-Soo, Kim, Young-Jun. (2013). Capacity Fading Mechanism of LiFePO4 Based Lithium Secondary Batteries for Stationary Energy Storage, Journal of Power Sources Vol 229, pg 190-197.Yang, Ye, Li, Hui, Aichhorn, Andreas, Zheng, Jianping, Greenleaf, Michael. (2014). Sizing Strategy of Distributed Battery Storage System With High Penetration of Photovoltaic for Voltage Regulation and Peak Load Shaving. IEEE Transaction on Smart Grid, Vol 5, No2, pg 982 – 991. Figure 1

Change of Average and Local Structures for 0.5Li2MnO3-0.5LiMn1/3Ni1/3Co1/3O2 in First Charge Process of Different Rate

In recent years, there is an increasing demand for lithium ion batteries. It was used in small devices such as mobile phones. Recently, the expansion of the intended use of electric vehicles and power storage equipment has been expected. However, it is necessary to improve high energy density. The solid solution material Li2MnO3 –Li（Mn,Ni,Co）O2 have attracted attention because they deliver high discharge capacity. On the other hand, it was reported such a problem that this material shows large irreversible capacity in the first cycle and discharge capacity greatly decreased at the high rate. It has been considered that irreversible capacity is due to oxygen removal to take place during the initial charge process above 4.5 V. But the mechanism of the discharge capacity fade is not clear. To commercialize the solid solution materials, it is necessary to solve the problem. We focused on the above problem. Our previous report described a transition metal rearrangement that occurs between 4.6 and 3.3 V during the initial discharge process at low rate [1]. In this study, we focused on the change of average and local structures of 0.5Li2MnO3 -0.5LiMn1/3Ni1/3Co1/3O2, layered solid solution material, during the initial charge process to clarify the arrangements of formation at the different rates. First, the change of average structures of 0.5Li2MnO3 -0.5LiMn1/3Ni1/3Co1/3O2, layered solid solution material during the initial charge process was clarified the arrangements of formation at different rates using Synchrotron X-ray [BL02B2, SPring-8, Japan] and neutron diffractions [iMATERIA, J-PARC, Japan}. The refined site occupancy in the charging process showed different results from before charge. The Mn occupancy localized to 4g site after charge at 1C rate whearas that moved from 4g site to 2b site at 3C rate. Although the both 4g and 2b sites were occupied by Co in the charging process at 1C rate, the only 4g site was occupied by Co in the charge at 3C rate. It was revealed that the differentiation of charge rate induced the atomic arrangement in the transition metal layer. Second, to clarify the mechanism local atomic arrangement change, we carried out PDF analysis using powder neutron diffraction measurements and synchrotron X-ray total scattering measurement [BL04B2, SPring-8, Japan]. In addition, first-principle calculation (VASP-code) used to determine the initial structure when performing PDF analysis. The λ and σ2 of optimal model was calculated after PDF analysis, in order to investigate the distortion of the crystal structure of the charging process of different rates.In the pristine, distortion of MnO6 octahedra is small compared to NiO6 and CoO6 octahedra. Comparing MnO6 and CoO6 octahedra distortion in the initial charging process at 1C rate, MnO6 octahedra showed an increasing trend. At 3C rate, CoO6 octahedra showed an increasing trend. In λ and σ2 of NiO6 octahedra entered the Li layer by cation mixing in the charging process at 3C rate increased . This was related to the trend of localization of Mn and Co of average structure. Perhaps, MO6 octahedra to localize tend to distorted in the charging process and localized element is different by the charging rate. Acknowledgement This work was supported in part by JSPS KAKENHI Grant Number 25420718. [1] Y. Idemoto et al, Electrochimica Acta, , 153, 399(2015).

A Semi-Empirical Capacity Fade Model for Li-NCA Cathode

Lithium Nickel-Cobalt-Aluminum (NCA) is a popular cathode material for Li-ion cells due to its high energy density and moderate cost. Cycling experiments confirmed that the cathode capacity fade is the dominant capacity fade mechanism [1] in such cells. Electron energy loss spectroscopy (EELS) and X-Ray Absorption Fine Structure (XAFS) analysis of the aged LiNCA particles exhibit the formation of a NiO type layer, which is inactive to Li intercalation, at the surface of the particles. Estimated amount of this inactive layer is found to match with the capacity loss of the cell. Therefore, a physics based model with one empirically determined parameter has been constructed for this reaction and it has been implemented on Li-ion battery electrochemical model [3]. The model predicts the relative capacity of a Li-NCA cell cycles at different temperatures with high accuracy (Fig.1). For constant current condition, a simple closed form solution for the capacity fade has been derived and validated. On extension this model can effectively predict the remaining useful life.