Patrick Charest

Effect of Carbon Source as Additives in LiFePO4 as Positive Electrode for Lithium-Ion Batteries

The electrochemical properties of LiFePO4 cathodes with different carbon contents were studied to determine the role of carbon as conductive additive. LiFePO4 cathodes containing from 0 to 12% of conductive additive ~carbon black or mixture of carbon black and graphite! were cycled at different C rates. The capacity of the LiFePO4 cathode increased as conductive additive content increased. Carbon increased the utilization of active material and the electrical conductivity of electrode, but decreased volumetric capacity of electrode. This composition ~LiFePO4 with 3 wt % of carbon and 3 wt % of Graphite! is suitable for HEV application.

Redox Behaviors of Ni and Cr with Different Counter Cations in Spinel Cathodes for Li-Ion Batteries

The electrochemical performances of the spinels Li[Ni 0.5 M 1.5 ]O 4 , Li[CrM]O 4 , and Li[MnM]O 4 with M = Mn(IV) vs Ti(IV) as cathodes for Li-ion batteries are compared. With M = Mn(IV), reversible access to the valence states Ni(IV) to Ni(II) and Cr(IV) to Cr(III) is possible at a voltage V ≈ 4.7 and 4.85 V (vs Li + /Li), respectively. The solid electrolyte interface (SEI) layer formed with M = Mn(IV) at voltages V > 4.3 V are Li-permeable. The disproportionation reaction 3Cr(IV) = 2Cr(III) + Cr(VI) contributes to the loss of capacity in Li[CrMn]O 4 - With M = Ti(IV), reversible charge/discharge curves were not obtained between 3.5 and 4.9 V (vs Li + /Li). The cathode Fermi energy E FC is lowered by about 0.2 eV on charging from M = Mn(IV) to M = Ti(IV), but this lowering is not sufficient to cause O 2 evolution from the spinel on charge with M = Ti(IV). Whereas Li-permeable SEI layers are formed with M = Mn(IV), we conclude that the SEI layers formed with M = Ti(IV) are Li-blocking. The SEI layer may be a Li-poor, Ti-rich phase formed at the surface of the cathode particle during charge rather than an SEI layer formed by a reaction with the electrolyte.

Temperature Effect on LiFePO4 Cathode Performance

Two forms of LiFePO4 material were evaluated in lithium cells. One type of LiFePO4 (PI) that has a particle size ranging from 1-5 µm is compared to LiFePO4 (P-II) consisting of nano-particles. Coated electrodes on Al-carbon with thickness varying from 18 to 25 µm were used in this study. The addition of VGCF carbon fiber greatly improved the rate capability at low temperature. This suggests a good conductivity networking and wettability in the cathode. LiFePO4 (P-II) has improved the low- and high-rate discharge capacity. When VGCF fibers were combined with LiFePO4 (P-II) in the same composite cathode, the high rate capacity at 12C was increased by 51% compared to LiFePO4 (P-I) cathode with carbon black. At -10°C and at 2C rate, 90 mAh/g was delivered from the cell. Cycling at 60°C occurred with negligible capacity fade after 400 cycles. Furthermore, the cell was capable of good performance at high rate with 120 mAh/g at 10C, and it still has a good reserve at 25C with 73mAh/g.

HQ Asymmetric Super Capacitor: Graphite-Li4Ti5O12/Ionic Liquid/Carbon

Introduction Electrodes containing Li4Ti5O12 have good Liion intercalation and de-intercalation reversibility and exhibit no structural change (zero-strain insertion material) during charge–discharge cycling. Thus, Li4Ti5O12 is an interesting candidate in negative electrodes for solid-state [1] and liquid-type [2] lithiumion batteries. This active material has a middischarge voltage close to 1.55 V versus Li/Li, which is very promising for electrodes in a large number of battery applications [3, 5]. It can be used as an anode with: (a) high-voltage cathodes in Li-ion batteries, and (b) carbon electrodes in hybrid supercapacitors, which was suggested for the first time by Zaghib and Armand [3,4]. . The CLi4Ti5O12 powder was characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observations. The electrochemical discharge and charge of asymmetric supercapacitor (ASC) behaviour was determined in a liquid electrolyte and ionic liquid (molten salt). Some comparisons between electrode processes using PVDF versus water-soluble binder (WSB) are presented. The performance ASC using new negative based on multilayer Graphite Li4Ti5O12 at 0. 25 and 60°C will be presented

Olivine Coated Spinel: 5-Volt System for High Energy Lithium Batteries

The cyclability of Li ion transfer in Li-ion rechargeable batteries depends mainly on the dimensional stability of the host material during insertion and deinsertion of Li+. Recently, it was found that redox reactions of non stoichiometric or doped LiMyMn2−yO4 (M=Li, Co, Cr, Ni, Al, etc.) spinels are much better than that of the pure LiMn2O4 ceramics, which exhibit a slight capacity fading. These materials have been investigated to improve the cycling performance of LiMn2O4, showing a tetragonal distortion induced by the excess of Mn Jahn–Teller ions in deeply discharged electrode. However, all the reported doping methods have led to a decreased specific charge compared to the undoped LiMn2O4 materials so far. The search of high-voltage material electrodes has been focused on two categories: the inverse spinels, e.g., LiMVO4, and the normal spinels, LiMyMn2−yO4. Recent investigations have shown that, among the Ni-substituted LiMn2O4 spinels, the composition LiNi0.5Mn1.5O4 possesses specific electrochemical characteristics such as a high capacity of 130–140 mAh/g associated with a highvoltage plateau in the 5-V range Gao et al. [1] investigated the origin of the voltage profile for LiNiyMn2−yO4. For the same system, Zhong et al. [2] showed the effects of the synthesis route (sol-gel vs. solid state) on some structural and electrochemical properties. The almost flat voltage profile was confirmed by Ohzuku et al. [3]. All these works only reported on structural and electrochemical information, Also the cycle life was find very poor due the instability of the electrolyte at high voltage (5V). The olivine coated spinel (5V) was not reported before. The stability of the electrolyte is one the most important key for cycling the cell at high voltage. The aim of this communication is the growth and characterization of the LMN : LiNi0.5Mn1.5O4 (spinel) materials prepared by different techniques. Because the standard electrolyte is very stable in contact with olivine, we applied the olivine coated spinel 5 V system for high energy lithium batteries. Figure 1 shows the voltage profile of LiFePO4 (LFP) coated LMN, the LFP show a voltage activity at 3.5 V and the spinel material at 4. 7 V. The capacity with non coated is 103 mAh/g , the first coulombic efficiency (1 CE) is 67 %, for the LFP coated LMN, the capacity is 120 mAh/g and the 1 CE is 76 %. The olivine coating increases the reversible capacity and also the 1 CE %. Figure 2 shows the comparison of the rate performances of uncoated and LFP coated spinel. The LFP coated spinel increases the capacity at high rate. The high power performance was improved with LFP-coated LMN. For the safety of point of view, the DSC peaks (not shown) is shifted to high temperature side by olivine coating spinel. LFP coating has more shifted than LiMnPO4, LiNiPO4, or LiCoPO4. Thermal stability is improved by LFP coating LMN.