Christian M. Julien

Review of 5-V electrodes for Li-ion batteries: status and trends

Lithium-ion batteries have dominated the battery industry for the past several years in portable electronic devices due to their high volumetric and gravimetric energy densities. The success of these batteries in small-scale applications translates to large-scale applications, with an important impact in the future of the environment by improving energy efficiency and reduction of pollution. We present the progress that allows several lithium-intercalation compounds to become the active cathode element of a new generation of Li-ion batteries, namely the 5-V cathodes, which are promising to improve the technology of energy storage and electric transportation, and address the replacement of gasoline engine by meeting the increasing demand for green energy power sources. The compounds considered here include spinel LiNi0.5Mn1.5O4 and its related doped-structures, olivine LiCoPO4, inverse spinel LiNiVO4 and fluorophosphate Li2CoPO4F. LiNi0.5Mn1.5O4 thin films, nanoscale prepared materials and surface-modified cathode particles are also considered. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of these materials as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed.

Surface modifications of electrode materials for lithium-ion batteries: status and trends

The research on the electrodes of Li-ion batteries aims to increase the energy density and the power density, improve the calendar and the cycling life, without sacrificing the safety issues. A constant progress through the years has been obtained owing to the surface treatment of the particles, in particular the coating of the particles with a layer that protects the core region from side reactions with the electrolyte, prevents the loss of oxygen, and the dissolution of the metal ions in the electrolyte, or simply improve the conductivity of the powder. The purpose of the present work is to review the different surface modifications that have been tried in the past for the different electrodes that are currently commercialized, or considered as promising, including the three families of positive electrodes (lamellar, spinel, and olivine families) and the three negative electrodes (carbon, Li4Ti5O12, and silicon). The role of the different coats used to improve either the surface conductivity, or the thermal stability, or the structural integrity is discussed. The limits in the efficiency of these different coats are also analyzed along with the understanding of the surface modifications that have been proposed.

Rechargeable lithium batteries for energy storage in smart grids

Abstract The move to “fuel-free” power mainly under the form of wind and solar photovoltaic makes a bigger challenge than ever before, because of the need to use energy storage for easy electricity transmission and distribution. That is why the integration of new primary sources requires more attention in the design, control, and management of the electric grid. This chapter provides an overview of energy storage systems applied to smart-grid applications. Several technologies are possible and a comparison in terms of effectiveness and prices is given for each of them in order to help the decision makers to make a choice. Special attention is given to lithium-ion batteries used in large facilities to support energy storage, the load leveling, and frequency regulation. With its ability to inject electricity contained in the batteries of cars on the grid, the vehicle-to-grid technology is also considered.

Diffusion of Li+ Ions in LiNi1/3Mn1/3Co1/3O2

Electrochemical properties of LiNi1/3Mn1/3Co1/3O2 powders have been investigated for a sample free on any impurity and cation mixing reduced to 1.3%. The discharge capacity decreases from 174 mAh/g (0.01C) to 133 mAh/g when cycled at a high current density of 3Crate. The sample reaches high capacity of 146 mAh/g after 90 cycles when using 1C-rate for discharging, with high capacity retention of 97%. The diffusion coefficient of the Li+ ions has been determined as a function of the delithiation rate by GIT and EIS analysis. The diffusion coefficient is in the range 1011-1012 cm2/s, and goes through a maximum at intermediate delithiation rate.

Electrolytes and Separators for Lithium Batteries

The current commercial Li-ion batteries are based on organic liquids, i.e., ethyl carbonates that have a high dielectric constant and thus are good solvents for salts. They also show a fairly large electrochemical window of stability. However, these organic solvents have high vapor pressures and in case of accidental battery shorts or thermal runaway, can lead to fires and explosions. The objective of the present chapter is to summarize the state of the art of nonaqueous electrolytes with development on control the SEI formation, safety concerns with Li salts, protection against overcharge and fire retardants.

Safety Aspects of Li-Ion Batteries

The carbon-coated LiFePO4 Li-ion oxide cathode was studied for its electrochemical, thermal, and safety performance. This electrode exhibited a reversible capacity corresponding to more than 89 % of the theoretical capacity when cycled between 2.5 and 4.0 V. Cylindrical 18650 cells with carbon-coated LiFePO4 also showed good capacity retention at higher discharge rates up to 5C rate with 99.3 % coulombic efficiency, implying that the carbon coating improves the electronic conductivity. Hybrid pulse power characterization (HPPC) test performed on LiFePO4 18650 cell indicated the suitability of this carbon-coated LiFePO4 for high power HEV applications. The heat generation during charge and discharge at 0.5C rate, studied using an isothermal microcalorimeter (IMC), indicated cell temperature is maintained in near ambient conditions in the absence of external cooling. Thermal studies were also investigated by Differential Scanning Calorimeter (DSC) and Accelerating Rate Calorimeter (ARC), which showed that LiFePO4 is safer, upon thermal and electrochemical abuse, than the commonly used lithium metal oxide cathodes with layered and spinel structures. Safety tests, such as nail penetration and crush test, were performed on LiFePO4 and LiCoO2 cathode based cells, to investigate on the safety hazards of the cells upon severe physical abuse and damage.

Self-assembled layer-by-layer partially reduced graphene oxide–sulfur composites as lithium–sulfur battery cathodes

Constructing a reliable conductive carbon matrix is essential for the sulfur-containing cathode materials of lithium–sulfur batteries. A ready-made conductive matrix infiltrated with sulfur as the cathode is the usual solution. Here, a partially reduced graphene oxide–sulfur composite (prGO/S) with an ordered self-assembled layer-by-layer structure is introduced as a Li–S battery cathode. The prGO/S composites are synthesized through a facile one-step self-assembly liquid route. An appropriate amount of sulfur is in situ deposited on the surface of the prGO nanosheets by adjusting the reduction degree of the GO nanosheets. The combined effect of the electrostatic repulsions and surface energy makes the sulfur wrapped prGO nanosheets self-assemble to form an ordered layer-by-layer structure, which not only ensures the uniform distribution of sulfur but also accommodates the volume change of the sulfur species during cycling. Moreover, the conductivity of the prGO/S composites improves when the reduction time increases. XPS spectra confirm that sulfur is still chemically bonded to the prGO. After applying the prGO coating of the prGO/S composite particle and as an interlayer in a lithium–sulfur battery configuration, a high initial discharge capacity of 1275.8 mA h g−1 is achieved and the discharge capacity of the 100th cycle is 1013.8 mA h g−1 at 0.1C rate.

A comprehensive review of lithium salts and beyond for rechargeable batteries: Progress and perspectives

Abstract The increasing need for energy storage has been the motivation for intensive research in batteries with different chemistries in the recent past. Among the elements of the batteries, the salts and their solvent play an important role. In particular, the cathodic stability at low potential depends importantly on the choice of the cation, while the stability at high potentials is mainly due to oxidation of anions and the ion mobility and dissociation depend primarily on the delocalization of the anion, so that many attempts are made to find the optimum choice of both the cations and anions of the salts, and their solvents. Although lithium-based batteries are almost exclusively used today, efforts are currently made to explore batteries based on sodium, aluminum, magnesium, calcium, potassium. The purpose of the present work is to review the salts and solvents that have been proposed in these different batteries and discuss their properties and their ability to be used in the near future and in the next generation of batteries.

Chemical and Electrochemical Stability of Copper in Molten KF-2HF

Fluorine is produced from electrolysis of KF/HF mixtures at around 95°C. In the cell configuration, carbon anodes are screwed onto a copper busbar. Much attention has been paid to the stability of copper since the corrosion and re-deposition of this metal on the cathodes is one of the main factors (side reaction) which limit the production yield of fluorine gas, the lifetime of the cells and the development of new electrolyzers. Therefore, in the frame of this study, various experiments were carried out to determine the corrosion rate of copper for a wide range of HF ratio and temperature. A statistics approach of the electrochemical data allowed us to predict the corrosion rate for many the operating conditions. At OCV, copper shows a good corrosion resistance even for high HF ratios. However, under a 6 V anodic polarization, copper corrosion rate raises drastically with an increase of the temperature and / or the HF ratio. Characterization techniques have shown that only a thin copper fluoride layer has been detected on copper at OCV. By contrast, two types of copper fluorides were evidenced at the electrode surface (CuF2 and KCuF3) when a potential was applied to Cu. Under anodic polarization, a thin CuF2 layer is formed at the copper surface whereas KCuF3 is detected at on the electrode surface resulting from the precipitation of Cu2+. For a better interpretation of the results, erosion-corrosion phenomenon issued from the fluorine bubbles impacts and electrolyte movements has been highlighted by weight losses of copper pieces. The breakdown of the passivation layer on copper and the exposition of the surface to the corrosive medium imply a quicker degradation of the metallic pieces.

Nanotechnology for Energy Storage

While lithium-ion batteries are currently the workhorses of portable electronics and power tools, the technology is just beginning to move up for power density applications such as electric drive vehicles and future energy storage options such as smart grids and back-up power systems. The later requires much higher charge rates that can be achieved to some extend by the use of nanomaterials. Two main reasons for electrochemical improvement are commonly evoked by designing electrode materials into the nanoscale domain: (1) the shorter diffusion lengths for the lithium ion across the active particle and (2) the increasing contact area between electrode and electrolyte. The purpose of this chapter is to draw attention to the technologies involved in the synthesis, layout and optimization of nano materials used as active components in Li-ion batteries. We present several nanostructured compounds such as lamellar compounds, manganese oxides and iron phosphates. Functional nanomaterials are also examined such are nanofibers, nanorods, nanocomposites, and nanocrystals.