Michel Gauthier

Hierarchically porous LiFePO4/nitrogen-doped carbon nanotubes composite as a cathode for lithium ion batteries

A porous composite of LiFePO4/nitrogen-doped carbon nanotubes (N-CNTs) with hierarchical structure was prepared by a sol–gel method without templates or surfactants. Highly conductive and uniformly dispersed N-CNTs incorporated into three dimensional interlaced porous LiFePO4 can facilitate the electronic and lithium ion diffusion rate. The LiFePO4/N-CNTs composites deliver a reversible discharge capacity of 138 mA h g−1 at a current density of 17 mA g−1 while the LiFePO4/CNTs composites only deliver 113 mA h g−1, demonstrating N-CNTs modified composites can act as a promising cathode for high-performance lithium-ion batteries.

LiFePO4/gel/natural graphite cells for the BATT program

LiFePO{sub 4}/gel/natural graphite (NG) cells have been prepared and cycled under a fixed protocol for cycle and calendar life determination. Cell compression of 10 psi was found to represent an optimal balance between cell impedance and the first cycle losses on the individual electrodes with the gel electrolyte. Cells with a Li anode showed capacities of 160 and 78 mAh/g-LiFePO{sub 4} for C/25 and 2C discharge rates, respectively. Rapid capacity and power fade were observed in the LiFePO{sub 4}/gel/NG cells during cycling and calendar life studies. Diagnostic evaluations point to the consumption of cycleable Li though a side reaction as the reason for performance fade with minimal degradation of the individual electrodes.

Size-dependent surface phase change of lithium iron phosphate during carbon coating

Carbon coating is a simple, effective and common technique for improving the conductivity of active materials in lithium ion batteries. However, carbon coating provides a strong reducing atmosphere and many factors remain unclear concerning the interface nature and underlying interaction mechanism that occurs between carbon and the active materials. Here, we present a size-dependent surface phase change occurring in lithium iron phosphate during the carbon coating process. Intriguingly, nanoscale particles exhibit an extremely high stability during the carbon coating process, whereas microscale particles display a direct visualization of surface phase changes occurring at the interface at elevated temperatures. Our findings provide a comprehensive understanding of the effect of particle size during carbon coating and the interface interaction that occurs on carbon-coated battery material--allowing for further improvement in materials synthesis and manufacturing processes for advanced battery materials.

LiFePO4 synthesized via melt synthesis using low-cost iron precursors

LiFePO4/C material has been prepared using fast-melt synthesis method followed by grinding and carbon coating. The low-cost iron ore concentrate (IOC) and purified iron ore concentrate (IOP) were used as iron precursors in the melt process to reduce significantly the cost of LiFePO4/C. The same product was also synthesized using pure Fe2O3 under similar conditions as reference. The physical-chemical and electrochemical properties of samples were investigated. The X-ray Diffraction (XRD) results confirm the formation of an olivine structure of LiFePO4 with a minor amount of Li3PO4 and Li4P2O7 impurities for all the samples but no Fe2P. The power performances of LiFePO4/C using low-cost iron precursors were close to the sample using pure Fe2O3 precursor although capacity in mAh g−1 is somewhat lower. With the inherent presence of silicon and other metals species, multi-substitution may take place when using IOC as source of iron leading to a Li(Fe1-yMy)(P1-xSix)O4 general composition. Multi-substitution, however, allows a better cycling stability. Therefore, these iron precursors present a promising option in this field to reduce the cost of a large-scale synthesis of LiFePO4/C for Li-ion batteries application.

Expanded metal a novel anode for Li-ion polymer batteries

Abstract An electrochemical cell using an electrode of expanded metal (EXMET ® ) is demonstrated. The sheet of EXMET ® contains voids with open volume and geometric arrangement that are capable of locally absorbing any lateral expansion. Consequently, all cumulative changes in the plane of the EXMET ® , when an Li–Al alloy is initially formed, are avoided. Three configurations of electrochemical generators utilizing cathodes of V 2 O 5 , FePO 4 and LiCoO 2 are described. Studies of alloy and dense anode sheets with local stress relaxation were demonstrated by in situ optical microscopy (OM) and scanning electron microscopy (SEM) using expanded metal. These studies indicate that a dense anode offers advantages for application in SPE-cells, including safety, long life and reliability.

Production of Lithium-Ion Cathode Material for Automotive Batteries Using Melting Casting Process

In the 1990s, LiFePO4 (LFP) was discovered as a cathode material for lithium ion batteries and was successfully used in the variety of devices such as power tools, E-bikes and grid accumulators. New challenges associated with use of lithium ion batteries for automotive applications demand higher performance and operating requirements, yet these requirements need to be achieved at affordable cost and without compromising vehicle safety. The advantages of LFP as a cathode material include thermal stability, limited environmental impact and potential of low cost as compared to the cathode chemistries containing cobalt. Currently, solid state and hydrothermal processes are used to synthesize LFP at the industrial scale. However, they require multiple, time-consuming steps and costly precursors. Recently, a melting-casting process to produce LFP cathode material was investigated. The motivation behind this new process is the great flexibility of raw materials including chemical makeup and particle size, and the use of lower cost, commodity chemicals, with the benefits of increased kinetics in the molten state and energy efficiencies leading to overall process cost savings. Also, if successful this process could represent a novel application of conventional casting. Melting lithium-, iron- and phosphorus-bearing precursors in near stoichiometric ratios and casting LFP material that forms around 1000 °C requires fewer processing steps and shorter reaction time. Initially, electric resistance furnaces were utilized to melt the precursors to synthesize LFP. In this investigation, induction furnace was utilized to significantly reduce the melting cycle time. Various precursors and process parameters were tested from small laboratory samples of less than 1 kg to pilot-scale casting of approximately 40 kg. Cast LFP samples were evaluated using SEM/EDX microscope, differential scanning calorimetry, thermal analysis, X-ray diffraction and battery assemblies in coin cells, and compared against commercial LFP product.