Concentrated LiPF6/PC electrolyte solutions for 5-V LiNi0.5Mn1.5O4 positive electrode in lithium-ion batteries

Abstract

Charge and discharge properties of spinel LiNi 0.5 Mn 1.5 O 4 positive electrodes were investigated using propylene carbonate (PC)-based concentrated electrolyte solutions in the range of 0.83 (ca. 1 mol dm-3) to 4.45 (nearly saturated) mol kg-1. The solvation state of PC in the concentrated electrolyte solution was studied by Raman spectroscopy. The HOMO energy of PC in Li + (PC) n was evaluated by first-principle calculation to assess the oxidative stability of PC molecules solvating lithium ion. Charge and discharge measurements revealed that the irreversible capacity due to solvent decomposition decreased with increasing the concentration of LiPF 6 , while discharge capacity increased. In addition, cycle performance of LiNi 0.5 Mn 1.5 O 4 positive electrodes was remarkably improved by the use of graphitized Ketjenblack as a conductive additive.

Dilution of Highly Concentrated LiBF4/Propylene Carbonate Electrolyte Solution with Fluoroalkyl Ethers for 5-V LiNi0.5Mn1.5O4Positive Electrodes

“…The HOMO energy of PC remarkably drops by solvation, and is further lowered with lowering the solvating number (−15.3, −15.7, −16.3 and −16.9 eV for Li + (PC) 4 , Li + (PC) 3 , Li + (PC) 2 and Li + (PC), respectively), and hence the oxidative stability of PC is enhanced by decreasing the PC/Li molar ratio in concentrated LiBF 4 /PC solutions as shown in our previous study. 10 In Fig. 3, an increase in the volume fraction of HFE decreased the viscosity, but increased the PC/Li ratio, the latter of which means an increase in free PC molecules owing to a lower solubility of LiBF 4 .…”

“…Solvation structures of lithium ion and atoms, Li + (PC) n , were obtained at MP2 6-31G(d). 10 Initial structures of Li + (PC) n were randomly generated for each solvation number (n) and then the geometries were fully optimized at the MP2 6-31G(d) level. Calculation of the vibrational frequency was performed with the basis sets to confirm that the geometries are at the minimum of the potential energy surface.…”

“…Recently highly concentrated electrolyte solutions are attracting much attention of battery researchers because of many unique characteristics, which include remarkably enhanced oxidative stability of ether-and carbonate ester-based concentrated electrolyte solutions. [8][9][10][11] We previously reported that highly concentrated propylene carbonate (PC)-based electrolyte solutions are highly stable against oxidation at LiNi 0.5 Mn 1.5 O 4 positive electrodes. 10,11 The use of nearly saturated LiPF 6 /PC and LiBF 4 /PC solutions resulted in high charge/discharge performance of LiNi 0.5 Mn 1.5 O 4 positive electrodes, whereas the co-intercalation reaction of PC at graphite was not fully suppressed even at the nearly saturating concentration.…”

“…[8][9][10][11] We previously reported that highly concentrated propylene carbonate (PC)-based electrolyte solutions are highly stable against oxidation at LiNi 0.5 Mn 1.5 O 4 positive electrodes. 10,11 The use of nearly saturated LiPF 6 /PC and LiBF 4 /PC solutions resulted in high charge/discharge performance of LiNi 0.5 Mn 1.5 O 4 positive electrodes, whereas the co-intercalation reaction of PC at graphite was not fully suppressed even at the nearly saturating concentration. However, concentrated electrolyte solutions commonly have a serious problem, that is, very high viscosities.…”

Electrolytes for electrochemical energy storage

“…207,218 Thanks to the unique solution structure with anions and solvent molecules coordinating strongly to Li + ions, HCEs exhibit enhanced oxidative stability, and inhibit the dissolution of the Al current collector. [221][222][223][224][225] It was shown that the 4.45 mol L ─1 LiPF6/PC electrolyte improved the cycling performance of the 5.0 V LiNi0.5Mn1.5O4 positrode, while the corresponding dilute electrolyte was easily oxidised and decomposed at such high positive potentials. 221 Specially, the simple formulation of the superconcentrated LiN(SO2F2)2/DMC (LiFSA/DMC) electrolyte exhibited remarkably high anodic stability at 5.5 V vs. Li + /Li.…”