Charles Delacourt

Toward Understanding of Electrical Limitations (Electronic, Ionic) in LiMPO4 (M = Fe , Mn) Electrode Materials

To better understand the factors responsible for the poor electrochemical performances of the olivine-type LiMnPO 4 , various experiments such as chemical delithiation, galvanostatic charge and discharge, cyclic voltamperometry, and impedance conductivity, were carried out on both LiFePO 4 and LiMnPO 4 . Chemical delithiation experiments confirmed a topotactic two-phase electrochemical mechanism between LiMnPO 4 and the fully delithiated phase MnPO 4 (a = 5.909(5) A, b = 9.64(1) A, and c = 4.768(6) A). We conclude that the limiting factor in the MnPO 4 /LiMnPO 4 electrochemical reaction is nested mostly in the ionic and/or electronic transport within the LiMnPO 4 particles themselves rather than in charge transfer kinetics or structural instability of the MnPO 4 phase. For instance, the electrical conductivity of LiMnPO 4 (σ ∼ 3.10 - 9 S cm - 1 at 573 K, ΔE ∼ 1.1 eV) was found to be several orders of magnitude lower than that of LiFePO 4 (σ ∼ 10 - 9 S cm - 1 at 298 K, ΔE ∼ 0.6 eV).

Size Effects on Carbon-Free LiFePO4 Powders The Key to Superior Energy Density

C-free LiFePO 4 crystalline powders were prepared by a synthesis method based on direct precipitation under atmospheric pressure. The particle size distribution is extremely narrow, centered on ca. 140 nm. A soft thermal treatment, typically at 500°C for 3 h under slight reducing conditions was shown to be necessary to obtain satisfactory electrochemical Li + deinsertion/insertion properties. This thermal treatment does not lead to grain growth or sintering of the particles, and does not alter the surface of the particles. The electrochemical performances of the powders obtained by this synthesis method are excellent, in terms of specific capacity (147 mAh g -1 at 5C-rate) as well as in terms of cyclability (no significant capacity fade after more than 400 cycles), without the need of carbon coating.

A 3.6 V lithium-based fluorosulphate insertion positive electrode for lithium-ion batteries

Li-ion batteries have contributed to the commercial success of portable electronics, and are now in a position to influence higher-volume applications such as plug-in hybrid electric vehicles. Most commercial Li-ion batteries use positive electrodes based on lithium cobalt oxides. Despite showing a lower voltage than cobalt-based systems (3.45 V versus 4 V) and a lower energy density, LiFePO(4) has emerged as a promising contender owing to the cost sensitivity of higher-volume markets. LiFePO(4) also shows intrinsically low ionic and electronic transport, necessitating nanosizing and/or carbon coating. Clearly, there is a need for inexpensive materials with higher energy densities. Although this could in principle be achieved by introducing fluorine and by replacing phosphate groups with more electron-withdrawing sulphate groups, this avenue has remained unexplored. Herein, we synthesize and show promising electrode performance for LiFeSO(4)F. This material shows a slightly higher voltage (3.6 V versus Li) than LiFePO(4) and suppresses the need for nanosizing or carbon coating while sharing the same cost advantage. This work not only provides a positive-electrode contender to rival LiFePO(4), but also suggests that broad classes of fluoro-oxyanion materials could be discovered.

Multimodal Physics-Based Aging Model for Life Prediction of Li-Ion Batteries

An isothermal, multimodal, physics-based aging model for life prediction of Li-ion batteries is developed, for which a solvent-decomposition reaction leading to the growth of a solid electrolyte interphase (SEI) at the carbonaceous anode material is considered as the source of capacity fade. The rate of SEI film growth depends on both solvent diffusion through the SEI film and solvent-reduction kinetics at the carbon surface. The model is able to simulate a wide variety of battery aging profiles, e.g., open-circuit and constant-voltage storage, charge/discharge cycling, etc. An analysis of capacity-fade data from the literature reveals that the same set of aging parameters may be used for predicting cycling and constant-voltage storage. The use of this set of parameters for predicting storage under open-circuit voltage points out that part of the self-discharge is reversible.

Modeling of a Commercial Graphite/LiFePO4 Cell

An isothermal model for the electrochemical behavior of a commercial graphite/LiFePO 4 cell at 25 and 45°C is developed. Although it does not embed any special feature of the porous electrodes and of the two-phase process of the LiFePO 4 electrode, proper account of the experimental charge/discharge (from C/10 to 1C) and path-dependence effects of the commercial cell is achieved. The LiFePO 4 electrode is treated based on a resistive-reactant concept with multiple particles whereas a single-particle approach is used to model the graphite electrode. In order to refine the model parameters for each electrode, half cells are made either from the recovered LiFePO 4 or graphite electrodes vs. a Li counterelectrode. A detailed experiment/simulation analysis of half-cell and complete-cell data unfolds the impact of uniaxial pressure on the galvanostatic charge/discharge limitation and path dependence of the LiFePO 4 electrode in the coin cell and the commercial cell.

Mathematical Modeling of Lithium Iron Phosphate Electrode: Galvanostatic Charge/Discharge and Path Dependence

Based on the resistive-reactant concept, a simple mathematical model for lithium intercalation/deintercalation in a lithium iron phosphate electrode is developed. Demonstrative experiments are provided to shed light on the resistive-reactant feature of this electrode. Without embedding any special feature of the two-phase process, the model consists of regular concentration-dependent lithium diffusion inside four groups of active-material particles that have different connectivities to the conductive matrix of the electrode. Model-experiment comparisons reveal the effectiveness of the resistive-reactant concept for a quantitative description of the charge/discharge as well as the path dependence observed in lithium iron phosphate electrodes.

Life-Prediction Methods for Lithium-Ion Batteries Derived from a Fatigue Approach I. Introduction: Capacity-Loss Prediction Based on Damage Accumulation

The possibility of using mechanical-fatigue life-prognostic methods for the life prediction of Li-ion batteries is evaluated. To this end, a physics-based model of a battery experiencing a single source of aging, i.e., the growth of a solid electrolyte interphase at the carbonaceous anode material, is employed as a surrogate battery. Dummy aging data sets, consisting of current microcycles at a nearly constant state of charge, are readily generated and used to evaluate the prediction capability of damage-accumulation relationships, among which is the Palmgren-Miner (PM) rule, which is well known in the field of mechanical fatigue. The PM rule is slightly more accurate than the regular damage accumulation over time. A complete methodology for predicting the aging of a battery experiencing a complex current profile is proposed in a second paper.

LiZnSO4F Made in an Ionic Liquid: A Ceramic Electrolyte Composite for Solid-State Lithium Batteries

The search for good solid electrolytes constitutes a major goal towards the development of safer lithium batteries. A few candidates do exist, but they suffer either from narrow electrochemical window stability or too low ionic conductivity. Herein we report the ionic-liquid-assisted synthesis of a novel LiZnSO4F fluorosulfate phase having a sillimanite LiTiOPO4-type structure, which on simply pressed samples shows a room-temperature ionic conductivity of 10 – 10 7 Scm 1 together with a 0–5 V electrochemical stability window range, while ionic-liquid-free LiZnSO4F shows an ionic conductivity four orders of magnitude lower (10 11 Scm ). While robustly reproducible but not yet fully understood, this finding offers new opportunities to tailor inorganic composites with higher ionic conductivity. The origin of such results is demonstrated to be rooted in a surface effect associated with the grafting of a lithium-containing ionic liquid layer. This finding opens up new opportunities for the design of ceramic composites with higher ionic conductivity and should serve as an impetus for further exploiting the chemistry of ionic liquid grafting on oxides. Renewable energy sources and electric automotive transportation are popular topics in today s energy-conscious society, hence placing rechargeable batteries as one of the major technological sciences in this new century. Advances in energy storage are a tribute to chemists abilities to design new and better materials. In the hunt for novel electrode materials, notions of sustainability must be considered. This is the reason why LiFePO4, which is made of inexpensive and abundant chemical elements, has attracted the attention of the research community despite its poor conducting properties. By particle downsizing and carbon nanocoating, LiFePO4/C composite overcomes transport limitations and is capable of reversibly and rapidly intercalating 0.9 Li (ca. 160 mA hg ) at a redox voltage of 3.43 V versus Li. Thus, it has become one of the most praised electrode materials for the next generation of rechargeable batteries for high-volume applications. Further exploring the chemistry of polyanionic-based insertion electrodes, we recently synthesized, by an ionothermal process, a novel 3.6 V LiFeSO4F electrode showing a reversible capacity nearing 140 mAh g 1 (theoretical capacity = 151 mAh g ), good rate capability, and cycling stability. This fluorosulfate was found to crystallize in a tavorite structure (space group P 1) with three-dimensional channels for Li diffusion as opposed to the one-dimensional channels in LiFePO4. Most likely, from the 3D versus 1D change in the conduction path, the use of LiFeSO4F powders will obviate the need for nanosizing or carbon coating, while the same cost and environmental advantages are maintained. Since our early report, we have considerably enlarged the fluorosulfate family with the discovery of AMSO4F (A = Li, Na and M = Co, Ni, Mn, etc.) homologues. This new family of materials, practically unknown a year ago, counts no less than 20 members showing related structures with either promising electrochemical or attractive ionic properties. Among them, the sodium-based 3d-metal fluorosulfates, which crystallize in a titanite structure (derived from the tavorite structure, space group P21/c) and have localized positions for the Na ions, were found to show a four-fold increase in ionic conductivity as compared to their Li-based counterparts on cold-pressed powders (10 7 S cm 1 for Na vs. 10 11 Scm 1 for Li at room temperature). While far from the hallmark solid-state electrolytes for future Li batteries such as Li1.5Al0.5Ge1.5(PO4)3 (LAG), Li1.3Al0.3Ti1.7(PO4)3 (LAT), and Li3+xPO4 xNx (LIPON), which have room-temperature conductivities of 2.8 10 4 Scm , 10 3 S cm , and 10 6 S cm , respectively, such a finding was an impetus to look for further fluorosulfate members as part of the effort to develop new ceramic electrolyte materials with increased conductivity, thus allowing a switch from thin-film to bulk technology in all solid-state batteries. Besides high ionic conductivity, a pivotal figure of merit for solid-state electrolytes is the width of their electrochemical stability window. This window is limited for ionic conducting ceramics containing 3d-metal elements, such as Li1.3Al0.3Ti1.7(PO4)3, owing to the reduction of Ti 4+ in Ti at approximately 2.4 V. So our strategy was to search for other members of the fluorosulfate AMSO4F family containing divalent metals that cannot be easily reduced or oxidized. Besides LiMgSO4F, the first reported fluorosulfate, [7] other attractive candidates could enlist lead, tin, or zinc to prepare AMSO4F phases. Mindful of the previously reported struc[*] Dr. P. Barpanda, Dr. J.-N. Chotard, Dr. C. Delacourt, M. Reynaud, Prof. M. Armand, Prof. J.-M. Tarascon Laboratoire de R activit et Chimie des Solides Universit de Picardie Jules Verne, CNRS UMR 6007 33, rue Saint Leu, 80039 Amiens (France) E-mail: jean-marie.tarascon@sc.u-picardie.fr Homepage: http://jmtarascon.tech.officelive.com

Measurement of Lithium Diffusion Coefficient in LiyFeSO4F

Lithium diffusion coefficient (D) in LiyFeSO 4 F is investigated by means of three electrochemical techniques, namely potentiostatic intermittent titration technique (PITT), galvanostatic intermittent titration technique (GITT), and galvanostatic charge/discharge at different C-rates. The analytic equations used for analyzing PITT and GITT are based on radial diffusion in spherical particles, which is more suitable to the type of electrode studied here than the original equations derived by Wen et al. [J. Electrochem. Soc., 126, 2258 (1979).] for a slab geometry. While PITT and GITT analyses with the analytic equations are only valid in the partial solid solution regions (y ≤ 0.29 and y > 0.83 in Li y FeSO 4 F), the analysis of galvanostatic charge/discharge with a mathematical model allows for the determination of D over the entire lithium composition range. The average D values found with PITT and GITT analyses are in good agreement with each other, and of the same order as those reported for Li y FePO 4 in the literature (ca. 10 ―14 cm2/s); However, D is larger for Li y FeSO 4 F in the Li-rich composition range than in the Li-poor one, whereas it is the opposite for Li y FePO 4 . This result could explain why Li y FeSO 4 F has a better rate capability on discharge than Li y FePO 4 .

Life Prediction Methods for Lithium-Ion Batteries Derived from a Fatigue Approach II. Capacity-Loss Prediction of Batteries Subjected to Complex Current Profiles

A methodology for predicting the capacity loss of a battery under a complex current profile is provided. The prediction is based upon a set of elementary aging experiments, which are herein generated by a physics-based model featuring a surrogate battery, for which the source of aging is the growth of a solid-electrolyte interphase at the anode. Empirical correlations of the capacity loss as a function of the aging time and of the aging time as a function of the capacity loss are developed based on 12 dummy elementary aging experiments under different conditions of state of charge and current. Those correlations are used together with the relationship for loss accumulation over time or the Palmgren-Miner rule (both introduced in Part I) to predict the aging of a complex current profile. The prediction accuracy is assessed by a direct simulation of the complex profile by using the physics-based model featuring the surrogate battery.