Honghe Zheng

Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes

A conductive polymer is developed for solving the long-standing volume change issue in lithium battery electrodes. A combination of synthesis, spectroscopy and simulation techniques tailors the electronic structure of the polymer to enable in situ lithium doping. Composite anodes based on this polymer and commercial Si particles exhibit 2100 mAh g -1 in Si after 650 cycles without any conductive additive. Copyright

Hard carbon: a promising lithium-ion battery anode for high temperature applications with ionic electrolyte

Electrochemical behavior of a hard carbon plate in an electrolyte based on a room temperature ionic liquid consisting of trimethyl-n-hexylammonium (TMHA) cation and bis(trifluoromethanesulfone) imide (TFSI) anion was investigated. Hard carbon is found to be less prone to passivation due to the high electrochemical stability of the ionic liquid. Lithiation and de-lithiation of the carbon anode is strongly affected by temperature. At room temperature, the hard carbon is difficult to lithiate and a high potential hysteresis is observed between charge and discharge curves. Increasing temperature contributes to higher reversible capacity, higher coulombic efficiency, and lower potential hysteresis. At 80 °C, a reversible capacity of 16.2 mAh cm−2 (equivalent to 675.0 mAh g−1) was obtained with 73.6% of the first cycle coulombic efficiency. Considering that graphitic anodes do not work at this temperature due to the decomposition of the solid electrolyte interphase (SEI), the combination of hard carbon with ionic electrolyte can meet some special requirements for high temperature applications with improved safety. The activation energy for Li-ion transfer across the hard carbon/ionic electrolyte interface was measured by ac impedance spectroscopy; a value of 80 ± 5 kJ mol−1 was obtained. The large activation energy implies a high barrier of activation at the electrode/electrolyte interface, which accounts for the poor rate performance of the hard carbon anode in the ionic electrolyte.

Quantitative Characterization of the Surface Evolution for LiNi0.5Co0.2Mn0.3O2/Graphite Cell during Long-Term Cycling

Many factors have been brought forward to explain the capacity degradation mechanisms of LiNixCoyMnzO2 (NCM)/graphite cells at extreme conditions such as under high temperature or with high cutoff voltage. However, the main factors dominating the long-term cycling performance under normal operations remain elusive. Quantitative analyses of the electrode surface evolution for a commercial 18650 LiNi0.5Co0.2Mn0.3O2 (NCM523)/graphite cell during ca. 3000 cycles under normal operation are presented. Electrochemical analyses and inductively coupled plasma-optical emission spectroscopy (ICP-OES) confirm lithium inventory loss makes up for ca. 60% of the cells capacity loss. Electrochemical deterioration of the NCM523 cathode is identified to be another important factor, which accounts for more than 30% of the capacity decay. Irregular primary particle cracking due to the mechanical stress and the phase change aroused from Li-Ni mixing during repetitive cycles are identified to be the main contributors for the NCM cathode deterioration. The amount of transition metal dissolved into electrolyte is determined to be quite low, and the resulting impedance rise after about 3000 cycles is obtained to be twice that of the reference cell, which are not very significant affecting the long-term cycling performance under normal operations.

Effect of Vinylene Carbonate on Graphite Anode Cycling Efficiency

Effect of Vinylene Carbonate on Graphite Anode Cycling Efficiency Paul Ridgway, Honghe Zheng, Gao L i u , Xiangun Song, Philip Ross, Vincent Battaglia Advanced Energy Technologies Department, Lawrence Berkeley National Laboratory, Berkeley, C A 94720 Vinylene Carbonate ( V C ) was added to the electrolyte in graphite-lithium half-cells. W e report its effect on the coulombic efficiency (as capacity shift) o f graphite electrodes under various formation cycling conditions. Cyclic voltammetry on glassy carbon showed that V C passivates the electrode against electrolyte reduction. The dQ/dV plots o f the first lithiation o f the graphite suggest that V C alters the SEI layer, and that by varying the cell formation rate, the initial ratio o f ethylene carbonate to V C in the SEI layer can be controlled. V C was found to decrease first cycle efficiency and reversible capacity (in ongoing cycling) when used to excess. However, experiments with V C additive used with various formation rates did not show any decrease in capacity shift. Introduction Carbonaceous materials, graphite formulations in particular, are the current standard for battery anodes in electric vehicle lithium-ion batteries (1). To attain performance suitable for plug-in hybrid and all-electric vehicles, improvement i n longevity o f the graphite anode is needed. Electrolyte additives have proven useful for this purpose. For example, vinylene carbonate ( V C ) added to Propylene Carbonate/LiPF6 electrolyte forms a Solvent-Electrolyte Interphase (SEI) layer on graphite anodes, preventing P C intercolation and reduction (and subsequent graphite exfoliaton) [2]. The addition o f V C to EC-based LiPF6 electrolytes is reported to improve performance o f graphite anodes by reducing irreversible capacity, suppressing gas formation, and improving cycling behavior [3-7]. A n important aspect o f anode performance is the effectiveness o f the SEI layer in inhibiting the side reactions which form it. The continuation o f these side reactions reduces cycling efficiency and consumes electrolyte which reduces the lifetime o f the cell. We probe the effect o f V C and various rates o f formation on these continuing side reactions by measuring the fractional capacity shift (8). HydroQuebecs SNG-12 anode graphite was chosen for this study because its relatively high capacity shift is a performance problem i n need o f a solution. In the results section, we begin by studying the effect of V C on the electrochemistry o f glassy carbon in EC-based L i P F 6 electrolyte. Then we determine a basis for choosing the concentration o f V C in the cell. This leads to our measurements o f the reversible capacity o f graphite in lithium half-cells as a function of V C concentration, followed by an examination o f the effect o f V C on the dQ/dV curves o f the first lithiation o f graphite.

Fabrication procedure for LiMn2O4/Graphite-based Lithium-ionRechargeable Pouch Cells

Procedures were developed at LBNL specifically for making electrodes and batteries of LiMn{sub 2}O{sub 4} (spinel) and MCMB (meso carbon micro beads) graphite for high-power applications (HEVs). Electrode performance can be very dependent on the materials used so it is pointed out that Toda M809 was used for the cathode active material and MCMB 10-28 from Osaka Gas was used for the anode active material. The conductive additives were Dankon black, an acetylene black, and SFG-6, a micron-size graphite. The binder used was PVdF (Kureha 1100). More details of these procedures can be found in the lab notebook of Gao Liu. These procedures are documented here but are continuously being refined, and should therefore be considered a work in progress.

Performance of Lithium Ion Cell Anode Graphites Under Various Cycling Conditions

Lawrence Berkeley National Laboratory 1 Cyclotron Rd. MS 70R011G, Berkeley, CA 94720 Performance of Lithium Ion Cell Anode Graphites Under Various Cycling Conditions Paul Ridgway 1 , Honghe Zheng 1 , Gao Liu 1 , Xiangun Song 1 , Abdelbast Guerfi 2 , Patrick Charest 2 , Karim Zaghib 2 , Vincent Battaglia 1 Lawrence Berkeley National Laboratory, MS70-108B, 1 Cyclotron Rd., Berkeley, CA 94720 Institut de Recherche dHydro-Quebec, 1800 Lionel Boulet, Varennes, QC, Canada, J3X 1S1 Graphites MCMB-2810 and OMAC-15 (made by Osaka Gas Inc.), and SNG12 (Hydro Quebec, Inc.) were evaluated (in coin cells with lithium counter electrodes) as anode materials for lithium-ion cells intended for use in hybrid electric vehicles. Though the reversible capacity obtained for SNG was slightly higher than that of OMAC or MCMB, its 1 st cycle efficiency was lower. Voltage vs capacity plots of cycling data show that the discharge and charge limits shift to higher capacity values due to continuation of anode side reactions. Varying the cycle charge and discharge limits was found to have no significant effect on fractional capacity shift per cycle. Introduction Carbonaceous materials, graphite formulations in particular, are the current standard for lithium-ion anodes for electric vehicle batteries(1). Until recently, Osaka Gas product MCMB was considered by many to be the industry standard for this application. As this material is no longer produced, an acceptable alternative is needed. In this work two graphite materials are evaluated along with MCMB in “lithium half-cells” (cells with lithium counter electrodes) by comparing their reversible capacities and first cycle efficiencies. Another aspect of anode performance is the effectiveness of the Solid-Electrolyte Interphase (SEI) layer in inhibiting the side reactions which form it. The continuation of these side reactions reduces cycling efficiency and consumes electrolyte which reduces the lifetime of the cell. We compare the extent of these continuing side reactions in the three materials by measuring the “fractional capacity shift” as explained in the Results section. In comparing the performance of the three anodes, the cells were cycled between a cell charge (anode lithiation) limit of 5mV and a discharge (delithiation) limit of 1V. Use of these or similar limits is convenient but are not the cycle limits experienced by anodes in commercial cells. Therefore, we also measured the capacity shift under cycle limits modified to simulate those to which the anode is more likely subjected in a commercial cell.