Electrolyte Additives For Lithium Ion Batteries Research Articles

Phosphorus derivatives as electrolyte additives for lithium-ion battery: The removal of O2 generated from lithium-rich layered oxide cathode

Direct internal pressure measurements of the cylindrical Li-ion cells with a mixture of LiCoO2 and Li1.167Ni0.233Co0.1Mn0.467Mo0.033O2 (a solid solution between 0.4 Li2Mn0.8Ni0.1Mo0.1O3 and 0.6 LiNi0.4Co0.2Mn0.4O2) as cathode and graphite as anode have been performed during cell charging. Cell internal pressure at the end of charging is greatly reduced from 2.85 to 0.84–1.84 bar by adding a small amount of phosphorus derivatives such as triphenyl phosphine (TPP), ethyl diphenylphosphinite (EDP), and triethyl phosphite (TEP) into a carbonate-based electrolyte. The phosphorus derivatives are supposed to react with O2 generated from the decomposition of the Li2MnO3 component. The chemical states of additive molecules before and after the charging process have been characterized with a nuclear magnetic resonance (NMR) spectroscopy and gas chromatography–mass spectrometry (GC–MS). It has also been shown that those additives improve the cycle life when applied in coin full cells.

Synthesis of aminoalkylsilanes with oligo(ethylene oxide) unit as multifunctional electrolyte additives for lithium-ion batteries

Aminoalkylsilanes with oligo(ethylene oxide) units were designed and synthesized as multifunctional electrolyte additives for lithium-ion batteries. The chemical structures were fully characterized by nuclear magnetic resonance (NMR) spectroscopy and their thermal properties, viscosities, electrochemical windows, and ionic conductivities were systematically measured. With adding one of these compounds (1 vol. %, DSC3N1) in the baseline electrolyte 1.0 M LiPF6 in EC: DEC (1:1, in volume), Li/LiCoO2 half cell tests showed an improved cyclability after 100 cycles and improved rate capability at 5C rate condition. Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopic (EDS) analysis confirmed the acid scavenging function and film forming capability of DSC3N1. These results demonstrated that the multifunctional organosilicon compounds have considerable potential as additives for use in lithium-ion batteries.

Effect of Anion Receptor Additives on Electrochemical Performance of Lithium-Ion Batteries

Four boron-based anion receptors were investigated as electrolyte additives for lithium-ion batteries. The electrochemical performance of lithium-ion cells was found to strongly depend on the structure of the anion receptor added to the electrolyte. The capacity retention of the lithium-ion cell was slightly improved by adding 0.07 M bis(1,1,1,3,3,3-hexafluoroisopropyl)pentafluorophenylboronate additive, whereas the addition of 2,5-bis(trifluoromethylphenyl)tetrafluoro-1,3,2-benzodioxaborole dramatically deteriorated the electrochemical performance. The addition of a certain type of anion receptor can promote the electrochemical decomposition of the electrolyte, resulting in high interfacial impedance and accelerated capacity fading of lithium-ion cells. Ab initio calculations showed that the electrochemical performance of anion receptors had good correlation to the degree of localization of the lowest unoccupied molecular orbital at the boron center of anion receptors, which can potentially be used in th...

Functional electrolytes: Synergetic effect of electrolyte additives for lithium-ion battery

We have found that certain combinations of specific additives show a very interesting behavior in Li-ion batteries. During the course of investigating further improvements in the performance of the triple-bonded compounds, which we very recently reported, a novel and unique effect of an additive combination was observed. The combination of the triple-bonded compounds and the double-bonded compounds has proven to show a much improved battery performance, especially in cycleability and gas evolution than the case when they are singly used. Especially, the synergetic effect of propargyl methanesulfonate and vinylene carbonate is remarkable. To clarify the synergetic effect, the electrochemical properties of the additives and the electrode analyses were investigated. It is assumed that the higher battery performance of the combination effect resulted not only from the thin and dense SEI on the negative electrode but also from the positive electrode surface co-polymerized film produced by the synergetic decomposition of the additives. We suggest that the keys for producing the synergetic functions are (1) a structural difference in the unsaturated moiety, and (2) a greater difference in the reduction potential.

Isocyanate compounds as electrolyte additives for lithium-ion batteries

Several isocyanate compounds have been investigated with regard to their performance as film forming electrolyte additives in propylene carbonate (PC) and EC/EMC-based electrolytes. In situ and ex situ analytical methods were applied to understand the differences in performance. Particular attention was paid to the differences of aromatic and linear isocyanate compounds.

Theoretical Studies on the Reductive Decompositions of Solvents and Additives for Lithium-Ion Batteries near Lithium Anodes

The reduction reactions of various solvents and additives for lithium-ion battery electrolytes have been investigated by ab initio calculations in the presence of the lithium anode at the Hartree-Fock level. The solvents and the additives studied included ethylene carbonate, propylene carbonate, vinylene carbonate, vinylethylene carbonate, ethylene sulfite, and tetrahydrofuran. Vinyl vinylene carbonate was also examined as a model compound. A cluster of 15 lithium atoms was used to model a lithium electrode to explicitly include the interactions of the solvent molecules with the lithium metal. The transition state in the reduction reaction was determined for each solvent or additive by searching for the saddle point of the potential energy surface. Internal reaction coordinate calculations were performed both to verify the transition state and also to locate the reactant and the product of the reduction reaction. From the calculations, the activation barrier and the reaction energy were determined. The reaction mechanism was also discussed in terms of the solid electrolyte interface film formation characteristics of each solvent and additive.

Effects of Aromatic Esters as Propylene Carbonate-Based Electrolyte Additives in Lithium-Ion Batteries

The role of aromatic esters as additives in propylene carbonate (PC) based electrolytes used in lithium-ion batteries has been investigated. The addition of aromatic esters into the 1.0 M -PC:DEC (3:2 in volume) suppresses the co-intercalation of PC and solvated ions and inhibits the further decomposition of electrolytes during the first lithium intercalation process. A graphitic anode (MCMB-2528, mesocarbon microbeads) in a PC-based electrolyte with the aromatic esters exhibits a high reversible capacity. Scanning electron microscopy and the first discharge curve results show that the aromatic esters decompose and form a proper solid electrolyte interphase (SEI) film on the MCMB surface to not only prevent exfoliation of the graphite electrode but also stabilize the electrolyte. Both cyclic voltammogram and the lowest unoccupied molecular orbital energy level show that the aromatic esters have higher reduction potentials than that of the electrolyte solvents. An increase in reverse capacity may be achieved by increasing the addition. However, when the addition exceeds a certain critical value, the SEI film inhibits the intercalation of lithium ions and lowers the capacity. Furthermore, the percentage of the aromatic esters in electrolytes directly influences the low-temperature performance and the rate capability of the cells. An optimal result may be obtained when the addition is approximately 2-4%.

Butyrolactone derivatives as electrolyte additives for lithium-ion batteries with graphite anodes

A series of butyrolactone derivatives with various side chains mainly at the 5-position were used as additives in 1 M LiClO 4–propylene carbonate (PC) electrolyte for lithium-ion batteries with graphite anodes. When more than 0.3 M of 2-acetyloxy-4,4-dimethyl-4-butanolide (AcBL1) was added to 1 M LiClO 4–PC solution, exfoliation of graphite, co-intercalation and decomposition of PC was suppressed and lithium insertion and extraction into/from graphite anode proceeded. 13 C NMR measurements suggested that the suppression of PC co-intercalation and decomposition was due to the decrease of the number of PC molecules coordinated to the lithium ion and increase of AcBL1 coordination. Addition of butyrolactone derivatives with acetoxyl or carbonate groups at the 5-position into 1 M LiClO 4–PC solution led to better charge–discharge anode performance.