Lithium Cycling Efficiency Research Articles

Influence of Electrolyte on Lithium Cycling Efficiency with Pressurized Electrode Stack

The dependence of lithium cycling efficiency on stack pressure was studied for several electrolytes. To evaluate the cycling efficiency , we calculated the figure of merit of lithium as . The effect of solvents on the change with pressure was examined for solute electrolytes containing 2‐methyltetrahydrofuran (2MeTHF), ethylene carbonate (EC)/2MeTHF, propylene carbonate (PC), or EC/PC. The electrolyte showed the largest (80 at 125 kg/cm2). With the electrolytes and , was less dependent on stack pressure than it was with the electrolytes and EC/2MeTHF, probably because a different separator was used for the former electrolytes. Examining the effect of the solute on the change with pressure showed that the for reached maximum values at 50 and 75 kg/cm2, respectively, and that the values for increased with increasing stack pressure up to at least 125 kg/cm2.

Lithium-cycling efficiency in inorganic electrolyte solution

Lithium-cycling efficiencies and corrosion rates were measured in half cells. The elaborated inorganic electrolyte solution, consisting mainly of LiAlCl 4 and SO 2, has a conductivity of 2.2 mS/cm at −25 °C and 98 mS/cm at 60 °C. Lithium-cycling efficiencies of about 98% at 40 mA/cm 2 for at least 50 cycles were achieved. Depending on improved electrolyte preparation, the current density for the lithium corrosion could be reduced from 12.1 to 6.5 μA/cm 2. The results indicate stability, compatibility and high rate capability of the system lithium/inorganic electrolyte solution.

Thermal Stability Study of LiAsF6 Electrolytes Using Accelerating Rate Calorimetry

Binary and ternary electrolytes containing solvent mixtures of cyclic esters and cyclic ethers and lithium hexafluoroarsenate as the electrolyte salt have been popular for some time for use in secondary lithium batteries because of their good conductivity and lithium cycling efficiency. The main concern regarding safety of lithium batteries is the initiation of self‐heating when the cell is under abusive conditions which in the extreme case can lead to a thermal runaway. There are a number of processes contributing to the self‐heating; such as reactions between the electrolyte and electrode materials and thermal decomposition of the electrolyte. Heating resulting from chemical reactions and thermal decompositions can also involve reaction products. Accelerating rate calorimetry is a simple technique which allows the study of self‐heating, in particlar the thermal decomposition of the electrolyte. In the work reported here, the effect of the addition of a cyclic ether to an electrolyte consisting of salt dissolved in a mixture of cyclic esters and the replacement of by lithium triflate salt on the thermal stability of the electrolyte, were determined. To establish the effect of at least one abusive condition such as battery overcharge, the thermal stabilities of the oxidized forms of two electrolytes containing electrolyte salt and cyclic ester/ether solvent mixtures were also measured.

A high performance Li xMnO y cathode material for rechargeable lithium cells

Lithiated α-MnO 2 has been synthetized and used as cathode material for rechargeable lithium cells. Coin cells have been used to test the material cycleability and characteristics with 1 M LiCF 3SO 3/PC—EC—DME electrolyte. Reversible capacity has been demonstrated for 130 cycles with 160 A h/kg with 3.6 to 2 V cycling cutoff voltages without important capacity loss. Pilot industrial batches have been used to realize prototype ‘C’-size cells; their cycling leads to performances as high as 200 A h/kg of Li χMnO y (α) in the first cycles corresponding to 2.4 A h for a cell capacity with discharge voltage of 2.87 V. To date, 60 cycles have been achieved with an anode excess of 2.6, which corresponds to a lithium cycling efficiency > 95%.

The Influence of Water on the Cycleability of Lithium in 2‐Methyltetrahydrofuran‐Based Electrolytes

The cycling efficiency of lithium in solutions of and in 2‐methyltetrahydrofuran was investigated by galvanostatic experiments and cyclic voltammetry. Traces of water lower the cycling efficiency of solutions, but produce an increase of the cycling efficiency of solutions, diminishing at water content above 500 ppm. Addition of 2‐methylfuran shows no effect. An increase of the lithium cycling efficiency of was observed after addition of small amounts of .

The Impedance of Lithium Electrodes in LiPF6 ‐ Based Electrolytes

The impedance spectrum of a lithium electrode in an electrolyte exhibits one or two semicircles. The variation of the two semicircles with immersion time indicates the presence of two kinds of passivating surface films. The change in resistance (Δ R1) associated with the first film during the first 24 h immersion time increased with increasing concentration. The large value of Δ R1 in a degraded electrolyte indicated that the decomposition of would lead to the formation of a thick passivating film. Δ R1 was well correlated with the oxidation potential of the solvent, which measures the stability of the solvent against lithium. The change in resistance (Δ R2) of the second film over 24 h was smaller than for the first film. The most effective solvent for decreasing Δ R1 was an ethylene carbonate (EC)/2‐methyl‐tetrahydrofuran (2MeTHF) mixed solvent. The lithium cycling efficiency in various solvent systems was demonstrated to increase with a decrease in Δ R1. The efficiency of the electrolyte varied significantly with concentration.

Effect of sodium cation on lithium corrosion in aprotic media

The present paper discusses the effect of Na + on the characteristics of lithium cells. The lithium cycling efficiency and the capacity retention of cathodically deposited lithium and of Li/MnO 2 and Li/Bi 2O 3 cells are much lower in electrolytes containing Na +. This deterioration in characteristics is accounted for by an enhancement of lithium anode corrosion in the presence of Na + in the electrolyte. The corrosion mechanism is described.

Dependence of Li/Cu 2V 2O 7 cell characteristics on electrolytic properties

The dependence of Li/Cu 2V 2O 7 cell characteristics such as rate performance and cycle life on electrolytic properties is investigated in several organic electrolytes. The electrolyte dependence of rate capability in Li/Cu 2V 2O 7 system is mainly determined by cation diffusion in the pore electrolyte phase. It is suggested that rate performance is improved by selecting an electrolyte with higher limiting molar conductivity for Li + ions. Cycle lives of cells with various electrolytes are shorter than the value expected from the Li half-cell data. The reason for this phenomenon is considered to be inactivity of the lithium electrode due to copper ions being dissolved upon charging, ie increased overvoltage, decreased lithium cycling efficiency and the possibility of causing internal soft-shorts.

An Improved Li / LixCoO2 Rechargeable Cell

Improvement of the cycling behavior of the cell has been brought about by the use of esters and alkyl carbonate‐based mixed solvents, and by physical modifications of the cathode structure. Binary solvent mixtures of methyl formate with either dimethyl carbonate, diethyl carbonate, or and electrolyte exhibit superior resistance towards solvent oxidation as well as improved lithium cycling efficiencies. Use of these mixed solvents with newly developed thin cathodes has resulted in stable cells which can be cycled more than 100 times at current densities of 1–10 mA cm−2, and at an average cell discharge voltage of between 3.9 and 3.7 V. Due to the high rate of solid‐state diffusion of Li+, the cathode can be charged at rates of up to 2 mA cm−2 over at least 100 deep charge and discharge cycles.

ChemInform Abstract: Lithium Cycling Efficiency on the Aluminum Substrate in Blended Sulfolane‐Ether Systems.

AbstractThe cycling efficiency of a Li secondary electrode on an Al substrate is found to depend on the cycling charge and current density as well as on the blended cosolvent ether (DME, THF) and on the electrolytic salt (LiClO4, LiBF4, LiPF6).

Lithium Cycling Efficiency on the Aluminum Substrate in Blended Sulfolane‐Ether Systems

The cycling characteristics of lithium (Li) secondary electrode with an Al substrate have been investigated in sulfolane (S)‐based electrolytes. The cycling efficiency varied with the charge‐discharge conditions: the cycling charge and the cycling rate (current density). The efficiency also depended on the blended cosolvent ether and on the electrolytic salt. The highest efficiency was obtained in the system of . The Li cycling characteristics on the Al substrate were compared with those on the Ni substrate. The current efficiency for the electroplating of Li on the substrates suggested that the coulombic loss of the efficiency on the Al substrate was mainly caused by the insufficient plating of Li during the charge while the loss at the Ni substrate was based on some undesirable chemical reaction of plated Li with the electrolyte.

Lithium cycling efficiency and conductivity for high dielectric solvent/low viscosity solvent mixed systems

Lithium cycling efficiency on a lithium substrate (Li-on-Li cycling) and conductivity for various mixed solvent systems of high dielectric solvent (HDS) and low viscosity solvent (LVS) were examined for secondary lithium batteries. For the HDS, sulfolane, dimethylsulfoxide, γ-lactones, propylene carbonate (PC) and ethylene carbonate (EC) were used. For the LVS, tetrahydrofuran (THF), 2-methyl-THF, 1,2-dialkoxyethanes and 1,3-dioxolane (DOL) were used. For the solute, LiAsF 6, LiBF 4, LiCF 3CO 3 and LiClO 4 were used. Lithium cycling efficiencies newly measured on a Li substrate ( E a ) for EC/LVS or PC/LVS were ca 5% or 15% higher than those previously obtained by simple cycling of Li on a Pt substrate, while the order of Li cycling efficiencies to LVS change is similar in both cases, except for EC/DOL or PC/DOL. The reasons seem to be that the Li-on-Li cycling minimizes the influence of electrochemical Li/Pt alloying and partial solvent oxidation during the cycle on Li cycling efficiency. The E a values in HDS/LVS mixed systems incorporating LiAsF 6 or LiClO 4 tended to increase with a decrease in the reactivity to Li, of not only LVS but also HDS. EC/THF systems incorporating LiAsF 6 or LiClO 4 showed high E a values of ca 95% even by Li-on-Li cycling, the value being higher than those (ca 92%) for LiBF 4 or LiCF 3SO 3 systems. In addition, for all the HDS/LVS mixed systems examined in this work, conductivities were higher than those for HDS or LVS single solvent systems. In regard to both conductivity and Li cycling efficiency, HDS/LVS mixed systems are considered to be effective in various lithium battery applications.

Lithium cycling efficiency and conductivity for ?-lactone-based electrolytes

Lithium cycling efficiency on a lithium substrate as well as conductivity were examined forγ-lactonebased electrolytes incorporating LiClO4 for use in nonaqueous lithium secondary batteries.γ-butyrolactone (BL),γ-valerolactone andγ-octanoiclactone were used. Conductivity increased with a decrease in viscosity for lactone. Lithium cycling efficiency tended to increase with a decrease in reactivity between lithium and lactone, which would be expected from the oxidation potential for lactone. In order to decrease viscosity, tetrahydrofuran (THF) was mixed with lactone. Conductivity for lactone/THF was higher than those for systems using either lactone or THF alone. For example, 1 M LiClO4-BL/THF (mixing volume ratio =1∶1) showed conductivity of 13.0 × 10−3 S cm−1, approximately 20% higher than that for BL. Lithium cycling efficiency for BL/THF, which exceeded 90%, was also higher than that for BL. Morphology of the deposited lithium in BL/THF was smoother than that in BL and similar to that in THF, as observed with a scanning electron microscope. The reason for the enhancement of the lithium cycling efficiency for BL/THF seems to be the adsorption of THF or THF-Li+ around the deposited Li, which has lower reactivity to Li and higher solvation power to Li+ than BL.

The cycling behaviour and stability of the lithium electrode in propylene carbonate and acetonitrile electrolytes

The conductivity and chemical stability with lithium of various electrolytes containing propylene carbonate (PC) and acetonitrile (AN) were determined. Addition of AN improved the conductivity of LiClO 4/PC and LiAsF 6/PC electrolytes, and the LiAsF 6/PC-AN electrolyte showed remarkable chemical stability in contact with lithium. The lithium cycling efficiency was determined on nickel and aluminium substrates in the various electrolytes over a range of current density. While the efficiencies observed on nickel substrates were very poor for all AN-containing electrolytes, efficiencies approaching those for electrolytes containing only PC were obtained with the LiAsF 6/PC-AN electrolyte at low current densities (∼1 mA cm −2) on aluminium substrates. It was concluded that the LiAsF 6/PC-AN electrolyte had generally favourable characteristics and may prove suitable for primary battery applications.

Behavior of Secondary Lithium and Aluminum‐Lithium Electrodes in Propylene Carbonate

The improvement of the lithium cycling efficiency obtained by substituting an aluminum substrate for a lithium substrate is explained by means of morphological and kinetic studies of the electrodes in the molar solution. SEM observations show that the insertion rate of the lithium deposit into aluminum can be sufficiently high so as to avoid dendritic growth; ESCA analysis reveals that propylene carbonate leads to a chemical formation of a polymeric membrane on the electrodes, which is less important on the aluminum than on the lithium substrate. Electrochemical impedance measurements associated with polarization curve data point out that most of the surface is active, giving rise to an exchange current density of about 17 mA/cm2; these studies also demonstrate that diffusion processes in the passivating layer and in the bulk of the electrode are responsible for the limited lithium cycling performances with the aluminum substrate.