Lithium Cycling Efficiency Research Articles

Improvement in lithium cycling efficiency by using lithium powder anode

A lithium metal rechargeable battery system has been developed using a compacted lithium powder electrode. Lithium powders were made by the droplet emulsion technique (DET). The cycle life of a compacted lithium powder cell was more than double and the internal resistance was lower than those of a lithium foil cell, respectively. Also, the cycling efficiency of a compacted lithium powder cell was considerably improved in comparison with a lithium foil cell.

Characterization of Lithium Electrode in Lithium Imides/Ethylene Carbonate, and Cyclic Ether Electrolytes : I. Surface Morphology and Lithium Cycling Efficiency

The surface and cross-sectional morphologies of deposited lithium on a nickel substrate in (LiBETI) electrolytes with ethylene carbonate (THP), dimethoxyethane, dimethylcarbonate (DMC), propylenecarbonate (PC), γ-butyrolactone (GBL) (1:1) binary solvents were investigated by scanning electron microscopy observation. Dendritic morphology of deposited lithium was observed in DMC-, PC-, and GBL-containing solvents. However, deposited lithium in a electrolyte exhibited a fine particle-like morphology and had a thinner surface film. The electrolyte provided excellent performance based on the results of cycling characteristics using a cell and Li/Ni cell. The morphology of deposited lithium in an electrolyte was strongly influenced by the kind of solutes. In LiBETI electrolyte, freshly deposited lithium exhibited uniform and fine particle-like morphology. In contrast, dendritic morphology was observed in (LiTFSI) electrolyte, resulting in a subsequent decrease in the lithium cycling efficiency. Electrolyte temperature was also an important factor influencing the lithium surface and efficiency. The use of LiTFSI electrolyte at elevated temperatures could suppress dendritic formation, resulting in excellent efficiency and cycling characteristics. We confirmed that the lithium surface morphology correlated well with the lithium cycling efficiency and the efficiency was strongly influenced by combinations of solvents and solutes. © 2004 The Electrochemical Society. All rights reserved.

Glyme-based nonaqueous electrolytes for rechargeable lithium cells

Poly(ethylene glycol)dimethyl ethers [(CH 3O(CH 2CH 2O) n CH 3, n = 1, 2, 3, and 4)] are generally known as “glymes”. This study examines the conductivity, lithium ion solvation state and charge–discharge cycling efficiency of lithium metal anodes in glyme-based electrolytes for rechargeable lithium cells. 1 M (M: mol l −1) LiPF 6 was used as the solute. The properties of the glymes were investigated by using a ternary mixed solvent consisting of n-glyme, ethylene carbonate (EC) and methylethylcarbonate (MEC). This was because the solubility of LiPF 6 is far less than 1 M in an n-glyme single solvent. The glyme solutions exhibited higher conductivity and higher lithium cycling efficiency than EC/MEC. The conductivity tended to increase with decreases in ethylene oxide chain number ( n) and solution viscosity. The decrease in the solution viscosity resulted from the change in the lithium ion solvation structure that occurred when a glyme was added to EC/MEC. The selective solvation of the glyme with respect to lithium ions was clearly demonstrated by 13 C -NMR measurements. The lithium cycling efficiency value depended on the charge–discharge current ( I ps). When n increased there was an increase in lithium cycling efficiency at a low I ps and a decrease in the reduction potential of the glymes. When the conductivities including those at low temperature (below 0 °C), and charge–discharge cycling at a high current are taken into account, di- or tri-glyme is superior to the other glymes tested here.

Effect of vinylene carbonate as additive to electrolyte for lithium metal anode

The cycling efficiencies and cycling performance of a lithium metal anode in a vinylene carbonate (VC)-containing electrolyte were evaluated using Li/Ni and LiCoO 2/Li coin type cells. The cycling efficiencies of deposited lithium on a nickel substrate in an EC + DMC (1:1) electrolyte containing LiPF 6, LiBF 4, LiN(SO 2CF 3) 2 (LiTFSI), or LiN(SO 2C 2F 5) (LiBETI) at 25 and 50 °C were improved by presence of VC. However, the lithium cycling efficiencies at low temperature (0 °C) decreased by adding VC to the EC+DMC (1:1) electrolyte. The deposited lithium at low temperature exhibited a dendritic morphology and a thicker surface film. The lithium ion conductivity of the VC derived surface film was lower than that of the VC-free surface film at low temperature. Therefore, we concluded that the cycling efficiency decreased with decreasing temperature. On the other hand, the cell containing VC additive has excellent performance at elevated temperature. The deposited lithium at 50 °C in the VC-containing electrolyte exhibited a particulate morphology and formed a thinner surface film. The VC derived surface film, which consists of polymeric species, suppressed the deleterious reaction between the deposited lithium and the electrolyte.

A study of cross-linked PEO gel polymer electrolytes using bisphenol A ethoxylate diacrylate: ionic conductivity and mechanical properties

Ionic conductivity, mechanical stability and electrochemical property were examined on the poly ethyleneoxide (PEO) based cross-linked gel polymer electrolyte. Bisphenol A ethoxylate diacrylates (BPAEDA) with different numbers of ethylene oxide units ( n=4, 15) were used as cross-linkers. The curing kinetics of the cross-linker was examined by an FT-IR study with two types of initiators and at different curing temperatures. Higher conductivity was observed for the longer ethylene oxide unit. Conductivity of the polymer electrolyte prepared from BPAEDA ( n=15) and liquid electrolyte (70 wt.%) was 3.47×10 −3 S/cm at 30 °C. Improved tensile strength and elongation at break were realized from the polymer electrolyte using BPAEDA as a cross-linker. Electrolyte having higher cross-linking density showed higher tensile strength, but showed decreased flexibility. The stability of the polymer electrolyte against electrochemical oxidation could be extended to larger than 4.5 V (versus Li/Li +). Lithium cycling efficiency of the polymer electrolyte was about 80%.

Influence of electrolyte additives on safety and cycle life of rechargeable lithium cells

The influence of electrolyte additives on the safety and cycle life of 4V-class lithium cells is examined. The electrolyte solution employed was 1 M LiClO4-propylene carbonate, the most widely used electrolyte in lithium battery research. The additives studied were ten organic aromatic compounds including biphenyl, cyclohexylbenzene and hydrogenated diphenyleneoxide. For safety, focus was given to the overcharging tolerance of the lithium cells. Biphenyl is well-known as an overcharge protection additive. The purpose of this work was to find additives with a higher oxidation potential and longer charge–discharge cycle life than biphenyl. The oxidation potentials and currents of the additives were measured to determine whether or not these compounds work as overcharge protection additives. Charge–discharge cycling efficiencies were examined for lithium metal anodes. The results showed that cyclohexylbenzene and hydrogenated diphenyleneoxide have a higher oxidation potential and a higher lithium cycling efficiency than biphenyl.

A lithium battery electrolyte based on gelled polyethylene oxide

Gel polymer electrolytes (GPEs) were prepared by dipping a polyethylene oxide (PEO)-based solid polymer electrolyte in lithium triflate/propylene carbonate (PC) liquid electrolyte solutions. The quantity of the liquid electrolyte gelled in the polymer was monitored as a function of dipping time in several liquid electrolytic solutions characterized by a different salt concentration. The GPE conductivity was measured as a function of the salt concentration and the liquid fraction content. The Li/GPE interface properties were evaluated by monitoring the charge transfer resistance at open circuit voltage and the lithium cycling efficiency under dynamic conditions. Chronopotentiometry measurements were used to study the variations of the lithium ion concentration in the electrolyte near the electrode surface. The transition time and the lithium diffusion coefficient were calculated as a function of the salt concentration of the liquid electrolyte used to swell the polymer electrolyte. The GPE electrochemical stability was measured by slow scan voltammetry sweep. Battery cells were assembled by sandwiching a GPE between a lithium disk and a gelled PEO-based composite cathode. The battery performance was evaluated at various discharge rates, while the rechargeability was tested under galvanostatic conditions at the C/10 rate.

Electrochemical properties of tetrahydropyran-based ternary electrolytes for 4 V Lithium metal rechargeable batteries

In order to improve low-temperature performance of ethylene carbonate (EC)+tetrahydropyran (THP) (5:5) electrolyte with 1 mol dm −3 lithium bisperfluoroethylsulfonyl imide (LiN(SO 2C 2F 5) 2) as solute, propylene carbonate (PC) solvent was mixed with this electrolyte. It was found that the electrochemical properties of the resultant ternary electrolytes depended strongly on the solvent composition and 1 mol dm −3 (LiN(SO 2C 2F 5) 2)/EC+PC+THP (3:3:4) electrolyte had not only promising freezing point of −36°C but also high lithium cycling efficiency of 95.2%. Furthermore, lithium cycling efficiency was improved to 99.0% by decreasing lithium deposition current density to 0.2 mA cm −2. At the temperature ranging from 25 to −10°C, Li/LiMn 2O 4 coin cell with 1 mol dm −3 (LiN(SO 2C 2F 5) 2)/EC+PC+THP (3:3:4) electrolyte showed the satisfactory cycling performance. Thermal tests further disclosed that this ternary electrolyte showed good thermal stability even with the existence of lithium metal.

Lithium Imide Electrolytes with Two‐Oxygen‐Atom‐Containing Cycloalkane Solvents for 4 V Lithium Metal Rechargeable Batteries

Lithium bisperfluoroethylsulfonyl imide electrolytes with five‐, six‐, and seven‐membered cycloalkane solvents containing two oxygen atoms were characterized in order to develop the organic electrolytes for 4 V lithium metal rechargeable batteries. Among the examined electrolytes, ethylene carbonate (EC) and 1,3‐dioxane (DOX) mixed electrolyte (5:5) with as solute were found to be the most advantegeous, with high cycling efficiency (95.2%), good oxidation stability (>5 V), promising freezing point (−21°C), and high boiling point, (105%C) of DOX solvent. Furthermore, only a slight decline in discharge capacity was observed for a coin cell with this electrolyte. Lithium cycling efficiency was also found to increase with decreasing deposition current density. Especially at deposition/dissolution current density of , lithium cycling efficiency in (5:5) electrolyte achieved above 99%. Thermal tests disclosed that this mixed electrolyte showed good thermal stability even with the existence of lithium metal. © 2000 The Electrochemical Society. All rights reserved.

Electrochemical Behavior of Lithium Imide/Cyclic Ether Electrolytes for 4 V Lithium Metal Rechargeable Batteries

To develop organic electrolytes for 4 V lithium metal rechargeable batteries, electrolytes with five‐, six‐, and seven‐ membered cyclic ether solvents were characterized. Among these examined electrolytes, /tetrahydropyran (THP) electrolyte was found to possess the most advantages, such as high cycling efficiency, good oxidation stability, and high boiling point. Furthermore, lithium cycling efficiency and conductivity were improved by mixing 50% ethylene carbonate (EC) in electrolyte. By using solute as an alternative to electrolyte, corrosion of the aluminum current collector was inhibited and therefore, excellent cycling performance of a coin cell was realized. It was also found that lithium cycling efficiency increased with decreasing deposition current density or increasing dissolution current density. Especially at deposition/dissolution current densities of , the observed lithium cycling efficiency in electrolyte was above 99%. Thermal tests further disclosed that this mixed electrolyte has good thermal stability even in the presence of lithium metal or cathode materials. © 1999 The Electrochemical Society. All rights reserved.

Chelate complexes with boron as lithium salts for lithium battery electrolytes

The electrolytic conductivity and charge–discharge characteristics of lithium electrodes are examined in propylene carbonate (PC)- and ethylene carbonate (EC)-based binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)-O,O′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)-O,O′]borate (LBNB) and lithium bis[2,2′-biphenyldiolato(2-)-O,O′]borate (LBBPB). The LBBPB exhibits high thermal and electrochemical stability compared with LBBB and LBNB. Conductivities in PC-THF and EC-THF binary solvent electrolytes at X THF (mole fraction of tetrahydrofuran, THF)=0.5 containing 0.5 M LBBB and LBNB are nearly equal to that in 0.5 M LiCF 3 SO 3 electrolyte as a typical lithium battery electrolyte. The conductivity in 0.3 M LBBPB/PC-DME (DME: 1,2-dimethoxyethane) electrolyte is fairly low compared with that in other electrolytes. The energy density with the LBNB electrolyte is higher than that with LBBB or LBBPB electrolyte. In general, lithium cycling efficiencies in THF-based LBBB and LBNB electrolytes become higher than those in DME-based electrolytes. The 0.5 M LBNB/PC-THF electrolyte is a moderately rechargeable lithium battery electrolyte. The 0.3 M LBBPB/PC-DME equimolar solvent electrolyte displays the highest cycling efficiency, viz., >70%, at a high range of cycle number.

Mixed solvent electrolyte for high voltage lithium metal secondary cells

We have examined various solvents and solutes as electrolytes for high voltage lithium metal secondary cells in terms of the oxidation potential, specific conductivity and cycling performance of Li/LiMn 1.9Co 0.1O 4 cells. We selected propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME) and 1,2-diethoxyethane (DEE) as the solvents, and LiClO 4, LiPF 6, LiAsF 4 and LiBF 4 as the solutes. Of the mixed solvent electrolytes we used, 1.0 mol dm −3 LiPF 6 in a mixture of EC and DMC with a ratio of 1:1, provided a high figure of merit (FOM) of 43.5 for lithium cycling efficiency with Li/LiMn 1.9Co 0.1O 4 cells as well as a high potential of over 5 V vs. Li/Li + and a high specific conductivity of 3.1 mS cm −1 at −20°C and 18.7 mS cm −1 at 60°C.

Effect of purification of 2-methyltetrahydrofuran/ethylene carbonate mixed solvent electrolytes on cyclability of lithium metal anodes for rechargeable cells

The effects of the purification of LiAsF6–2-methyl tetrahydrofuran (2MeTHF)/ethylene carbonate (EC) mixed solvent organic electrolytes on the charge–discharge cyclability of lithium metal anodes has been investigated by using an accelerated method for evaluating lithium cycling efficiency. This method involves cycle tests on coin cells with an amorphous V2O5–P2O5 (95:5 molar ratio) cathode and an anode containing a small amount of lithium. Using this method, the cycle life of the cell was determined over a short period simply from the lithium cycling efficiency. The lithium cycling efficiency in LiAsF6–2MeTHF/EC was improved by removing both water and organic impurities such as peroxides. An electrolyte containing less than 14ppm of water and 20ppm of organic impurities had a high lithium cycling efficiency of 97.2%.

Electrochemical characterization of a composite polymer electrolyte with improved lithium metal electrode interfacial properties

In the development of rechargeable lithium polymer batteries it is of paramount importance to control the passivation phenomena occurring at the lithium electrode interface. It is well estabilished that the type and the growth of the lithium passivation layer is unpredictably influenced by the presence of liquid components and/or impurities in the electrolyte. Therefore, one approach to improve the stability of the lithium interface is the use of liquid-free, highly pure electrolytes. The electrochemical properties of a composite polymer electrolyte obtained by hot pressing a mixture of polyethylene oxide (PEO), a lithium salt (lithium tetrafluoroborate, LiBF4) and a powdered ceramic additive (γ-LiAlO2), will be presented and discussed. The electrochemical characterization included the determination of the ionic conductivity, the anodic break-down voltage and, most importantly, the stability of the lithium metal electrode interface and the lithium stripping-plating process efficiency. The main feature of this dry, true solid-state electrolyte is a very good compatibility with the lithium metal electrode, demonstrated by a very high lithium cycling efficiency, which approaches a value of 99%.

Multi-component nonaqueous electrolytes for rechargeable lithium cells

In this paper we examine the influence of various mixed-solvent electrolytes on the discharge capacity and charge–discharge cycle life of coin-type lithium (Li) metal/amorphous (a-) V 2 O 5 –P 2 O 5 (95:5 in molar ratio) cells. The solvents used were ethylene carbonate (EC), propylene carbonate (PC), 2-methyl-tetrahydrofuran (2MeTHF), THF, 1,2-diethoxyethane and 4-methyl-1,3-dioxolane, LiAsF 6 and LiCF 3 SO 3 were used as the solute. The electrolyte solutions examined here contain binary, ternary and quaternary mixed solvent systems. The purpose of this work is to obtain an electrolyte solution which provides lithium cells with a higher rate capability than the previously studied EC/PC/2MeTHF ternary mixed system while suppressing the reduction in the cycle life. The stack pressure effect on the lithium cycling efficiency is minimized by the spacious internal electrode structure of the coin cell used in this work in order to investigate the influence of the electrolyte materials on the cell properties. Among the electrolyte systems examined here, the EC/PC/2MeTHF/THF (15:70:7.5:7.5 in volume) four-solvent mixed system provided the best cell performance. Its rate capability at 5 mA cm −2 discharge was about twice that of EC/PC/2MeTHF ternary mixed solvent electrolyte with almost the same rechargeability.

Improvement in lithium cycling efficiency by using additives in lithium metal

The main reason for the reduction in lithium (Li) cycling efficiency at a low-discharge current density is the accumulation of electrochemically inert Li (dead Li) which is isolated from the Li anode. In this work, we investigated the effect of benzene or toluene as additives and their effect of an Li metal sheet with conductive carbon powder on Li-cycling efficiency. Li-cycling efficiency is improved by using the folded Li sheet with benzene adsorbed between the Li layers. This improvement results from the formation of a new film on and in Li. The cycling efficiency of Li with carbon power is also improved. The improvement is considered as a result from the recombination of dead Li through an electrical path made of carbon powder.

Lithium cycling efficiency of ternary solvent electrolytes with ethylene carbonate—dimethyl carbonate mixture

Lithium cycling efficiency for ternary solvent (mol ratio 1:1:1) electrolytes of different molar conductivities containing LiPF 6 and LiClO 4 with ethylene carbonate (EC)—dimethyl carbonate (DMC) binary mixture of constant mixed ratio (mol ratio 1:1) was investigated by galvanostatic experiments at 25 °C. The solvents applied to the EC-DMC mixture are 1,2-dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF) and ethylmethyl carbonate (EMC). The molar conductivity of the EC-DMC-DME ternary solvent electrolytes gradually increased with the addition of DME. However, the molar conductivities of the EC-DMC-2-MeTHF and EC-DMC-EMC ternary solvent electrolytes gradually decreased with the addition of 2-MeTHF and EMC. The decrease of the molar conductivity for these solutions is attributed to a decrease of the dissociation degree for electrolytes versus a decrease of the dielectric constant rather than that of the viscosity of the EC-DMC-2-MeTHF and EC-DMC-EMC ternary solvent mixtures. The lithium cycling efficiency of every ternary electrolyte containing LiPF 6 was larger than those of the EC-DME, EC-EMC and EC-DMC binary electrolytes containing LiPF 6 at about 20 cycles. Especially, the efficiency of LiPF 6/EC-DMC-DME electrolyte became about 80% at 40 cycles. The nickel (working) electrode surface in binary and ternary electrolytes after dissolution by cyclic voltammetry was observed by atomic force microscopy. The formation of lithium dendrite was already observed during the first cycle in the LiPF 6/EC-DMC electrolyte. However, it was found that the addition of ethers such as DME and 2-MeTHF to the LiPF 6/EC-DMC electrolyte was helpful to suppress the formation of lithium dendrite on the nickel electrode.

Application to Lithium Batteries of Ternary Solvent Electrolytes with Ethylene Carbonate – 1,2-Dimethoxyethane Mixture

ABSTRACTThe electrolytic conductivity, the lithium cycling efficiency of lithium electrode and the energy density for Li/V2O5(2025) coin-type cell were examined in ternary solvent electrolytes containing LiPF6and LiClO4with ethylene carbonate(EC) – 1,2-dimethoxyethane(DME) equimolar binary mixture at 25°C. The solvents applied to EC – DME mixture are dimethyl carbonate(DMC), ethyl methyl carbonate(EMC), diethyl carbonate(DEC), 1,3-dioxolane(DOL), 2,2-bis(trifluoromethyl)-1,3-dioxolane(TFMDOL), 1,3-dimethy1–2-imidazolidinone(DMI) and 1-methyl-2-pyrrolidinone(NMP). The order of decrease of the molar conductivities in ternary solvents electrolytes except DMI and NMP systems is agreement with that of increase in viscosities of the solvents applied to EC – DME binary mixture. The molar conductivities in ternary solvent electrolytes containing DMI and NMP are mainly affected by the dielectric constants rather than viscosities of mixed solvents. The energy density of Li/V2O5(2025) coin-type cell in LiPF6/EC – DME – DOL electrolyte with the highest molar conductivity was 500 Wh kg−1, which is the highest value in every ternary electrolyte. The lithium cycling efficiency(charge - discharge coulombic cycling efficiency of lithium electrode) in EC – DME – EMC, EC – DME – DMI and EC – DME – TFMDOL electrolytes containing LiPF6is more than 75% at 40 cycle numbers. The lithium electrodeposition on the Ni(working) electrode surface in ternary solvent electrolytes by cyclic voltammetry was observed by atomic force microscopy(AFM) and scanning electron microscope(SEM).

ChemInform Abstract: Effect of Additives on Lithium Cycling Efficiency.

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Effect of Additives on Lithium Cycling Efficiency

Lithium cycling efficiency was evaluated for mixed‐solvent electrolyte with several additives: tetraalkylammonium chlorides with a long n‐alkyl chain and three methyl groups. The ammonium chlorides with n‐alkyl group longer than increased lithium cycling efficiency. Cetyltrimethylammonium chloride (CTAC) produced the best improvement in lithium cycling efficiency. A figure of merit (FOM) of lithium for 0.01M CTAC was 46, which was 1.5 times the FOM for the corresponding additive‐free electrolyte. The with CTAC showed an increase in FOM with stack pressure, but the effect was less than that for the additive‐free . Scanning electron microscope observation showed that the addition of CTAC decreased the needle‐like lithium deposition and increased particulate lithium deposition. This deposition morphology may be the main cause of the increase in FOM. The additive had no effect on rate capability for cell cycling at 3 mA/cm2discharge and 1 mA/cm2 charge.