Minoru Handa

Application of Lithium Organoborate with Salicylic Ligand to Lithium Battery Electrolyte

The thermal characteristics of lithium bis[salicylato(2-)]borate (LBSB) and its novel derivatives synthesized by us, such as lithium bis[3-methylsalicylato(2-)]borate (3-MLBSB), lithium bis[3,5-dichlorosalicylato(2-)]borate (DCLBSB), and lithium bis[3,5,6-trichlorosalicylato(2-)]borate (TCLBSB) were examined by thermogravimetric analysis (TG). The thermal decomposition in air begins at 260, 290, 310, and 320°C for TCLBSB, LBSB, DCLBSB, and 3-MLBSB, respectively. The thermal stabilities of 3-MLBSB and DCLBSB are nearly equal to those of LiN(CF 3 SO 2 ) 2 and LiN(C 2 F 5 SO 2 ) 2 . The order of the stability toward oxidation of these organoborates is TCLBSB DCLBSB > LBSB > 3-MLBSB, which differs from the thermal stability. Ionic dissociation properties of LBSB and its derivatives were examined by conductivity measurements in ethylene carbonate-1,2-dimethoxyethane (EC-DME) equimolar binary dilute solutions. The conductivities of the 0.1 mol dm -3 DCLBSB and TCLBSB electrolytes become higher than those in the LBSB and 3-MLBSB electrolytes. It means that DCLBSB and TCLBSB have high dissociating abilities in EC-DME mixture. The 0.5 mol dm -3 LBSB/EC-DME equimolar binary solution exhibits the highest lithium electrode cycling efficiency of more than 85% in the higher range of cycle numbers. This is a good electrolyte for rechargeable batteries.

Chelate complexes with boron as lithium salts for lithium battery electrolytes

Abstract 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.

Application to lithium battery electrolyte of lithium chelate compound with boron

Abstract The electrolytic conductivities and charge–discharge characteristics of lithium electrode are examined in propylene carbonate (PC)- and ethylene carbonate (EC) tetrahydrofurans, such as 2-methyltetrahydrofuran (2-MeTHF) and 2,5-dimethyltetrahydrofuran (2,5-DMeTHF), binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)- O , O ′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)- O , O ′]borate (LBNB), lithium bis[2,2′-biphenyldiolato(2-)- O , O ′]borate (LBBPB) and lithium bis[salicylato(2-)]borate (LBSB). The order of specific conductivities in PC- and EC-based equimolar binary solutions containing these organoborates is LBBB≥LBNB>LBSB>LBBPB. The conductivity in LBNB electrolyte with higher viscosity than that in LBSB electrolyte becomes high. The PC–2-MeTHF and PC–2,5-DMeTHF equimolar binary solutions containing LBSB and a mixed electrolyte (LBBPB+LiPF 6 ) show very high cycling efficiencies more than 90% at a higher range of cycle number. The EC–THF and EC–2-MeTHF equimolar binary solutions are moderate electrolytes with about 80% cycling efficiencies. It is found by using scanning electron microscope (SEM) that the films formed on the electrode in PC–2-MeTHF and PC–2,5-DMeTHF electrolytes with higher cycling efficiencies have a homogeneous surface with uniform grain size.

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 LiPF6 and LiClO4 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 LiPF6 was larger than those of the EC-DME, EC-EMC and EC-DMC binary electrolytes containing LiPF6 at about 20 cycles. Especially, the efficiency of LiPF6/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 LiPF6/EC-DMC electrolyte. However, it was found that the addition of ethers such as DME and 2-MeTHF to the LiPF6/EC-DMC electrolyte was helpful to suppress the formation of lithium dendrite on the nickel electrode.

Formation of acetylacetonato iron complexes in acetonitrile and their resonance Raman spectra

Formation of acetylacetonato from complexes in acetonitrile, Fe(acac)2+, Fe(acac)2+ and Fe(acac)3, (the expression represents the solvated species: acac- is the 2, 4-pentanedionate ion), were spectrophotometrically studied. On addition of Hacac to an acetonitrile solution of Fe(ClO4)3, Fe(acac)2+ was quantitatively formed. When excess Hacac was added, only Fe(acac)2+ was obtained without forming Fe(acac)3. On the other hand, Fe(acac)2+ was quantitatively obtained by adding HClO4 to an acetonitrile solution of Fe(acac)3, and Fe(acac)2+ was also formed by adding an excess of HClO4. All the species of acetylacetonato complexes: Fe(acac)2+, Fe(acac)2+ and Fe(acac)3 were formed in the system of Fe(ClO4)3 with an addition of tetraethylammonium acetylacetonate. The resonance Raman spectra of the obtained solutions of Fe(acac)2+ and Fe(acac)2+ and of the solution of Fe(acac)3 were measured. The peaks mainly associated with v(FeO) and v(CO) are observed near 450 and 1600 cm-1, respectively. The order of v(FeO) is Fe(acac)2+ (474 cm-1) > Fe(acac)2+ (462 cm-1) > Fe(acac)3 (451 cm-1) and that of v(CO) is Fe(acac)2+ (1554 cm-1) < Fe(acac)2+ (1578 cm-1) < Fe(acac)3 (1603 cm-1). These results indicate that the coordination strength of acac- to Fe becomes weaker, because the Lewis acidity of the metal decreases as the number of coordinated acac- increases.

Solvent effects on acetylacetonato iron complexes

Abstract Interactions of various solvents with Fe(acac) 2+ , Fe(acac) 2 + and Fe(acac) 3 (the expression represents the solvated species: acac t- is the 2,4-pentanedionate ion, acetylacetonate ion) were investigated through observing v (FeO) and v (CO) in resonance Raman spectra. In the Fe(acac) 2+ system, both v (CO) and v (FeO) correlate with donor number ( DN ): the v (CO) band shifts toward high frequency with the increase in DN , while the v (FeO) band exhibits the inverse trend. The relation between v (CO) and v (FeO) in different solvents is a good example of the bond length variation rules (the donor-acceptor concept). In the Fe(acac)3 system, i.e. the non-direct solvation system, v (CO) shifts toward low frequency with increase in the relative dielectric constant (ϵ r ) of the solvent, whereas v (FeO) is constant, independent of ϵ r These facts indicate that the CO bond of the acacligand is lengthened by the polarizability effect of the solvents, while the FeO bond in the inside of the complex is not influenced. On the other hand, v (CO) and v (FeO) do not correlate with ϵ r in the Fe(acac) 2+ system. They indicate that the direct effect (donor effect) of the solvent molecules on the metal is larger than macroscopic effects such as polarizability. In the Fe(acac) 2 + system, the v (CO) shift exhibits a similar trend to that in Fe(acac)3, whereas the shift of v(FeO) is similar to that in Fe(acac) 2 + . The results suggest that Fe(acac) 2 + is influenced by both the macroscopic and direct effects of the solvents. To confirm this in the Fe(acac) 2 + system, solid samples were prepared by freeze drying the solutions and measuring their resonance Raman spectra.

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm−1. Thev(C-O) peak (around 1580 cm−1) is shifted to low frequency with an increase in the dielectric constant ɛT of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm−1) are constant, independent of ɛT. It implies that the C-O bond in the acac− ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.