Preparation, Characterization and Physicochemical Properties of Alkali Bis(polyfluoroalkyloxysulfonyl)imides and Electrochemical Properties of the Lithium Salts†

doi:10.7503/cjcu20131151

Abstract

Abstract:

Two series of alkali salts of bis(polyfluoroalkyloxysulfonyl)imides, alkali bis(2,2,2-trifluoroetho-xysulfonyl)imides{M[N(SO₂OCH₂CF₃)₂], MTFESI} and alkali bis[(1,1,1,3,3,3-hexafluoro-2-propoxy)sulfonyl]imides(M{N[SO₂OCH(CF₃)₂]₂}, MHFPSI)(M=Li, Na, K, Rb, Cs), were prepared and characterized by NMR, IR and elemental analysis. Thermal properties of the neat salts were investigated by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA). The fundamental physicochemical properties of nonaqueous electrolytes of lithium bis(polyfluoroalkyloxysulfonyl)imides are studied. The results indicate that the alkali bis(polyfluoroalkyloxysulfonyl)imides show high thermal stability and low melting point. The electrolytes of 1.0 mol/L lithium salt in a mixture of ethylene carbonate(EC)/ethyl methyl carbonate(EMC)(3:7, volume ratio) show medium conductivities, high oxidation potentials and do not corrode Al in the high potential region of 3—5 V(vs. Li⁺/Li).

Key words: Bis(2,2,2-trifluoroethoxysulfonyl)imide, Bis[(1,1,1,3,3,3-hexafluoro-2-propoxy)sulfonyl]-imide, Alkali salt, Nonaqueous electrolyte, Lithium-ion battery

CLC Number:

O646

TrendMD:

ZHANG Heng, LIU Chengyong, GONG Shouzhe, FENG Wenfang, XU Fei, NIE Jin, ZHOU Zhibin. Preparation, Characterization and Physicochemical Properties of Alkali Bis(polyfluoroalkyloxysulfonyl)imides and Electrochemical Properties of the Lithium Salts^†[J]. Chem. J. Chinese Universities, 2014, 35(4): 804.

Figures/Tables 10

Table 1 Thermal properties of alkali salts of bis(polyfluoroalkyloxysulfonyl)imide

Salt	T_s-s/℃	T_m/℃	ΔH_m/(J·g^-1)	T_d/℃	Salt	T_s-s/℃	T_m/℃	ΔH_m/(J·g^-1)	T_d/℃
LiTFESI	67	174	37.0	246	LiHFPSI		211	35.8	217
NaTFESI	134	183	32.3	283	NaHFPSI		210	10.3	312
KTFESI	47	159	19.0	298	KHFPSI		175	40.9	319
RbTFESI	93	141	2.6	298	RbHFPSI	142	169	10.4	262
CsTFESI		174	47.1	290	CsHFPSI		117	21.8	315

Fig.1 DSC curves of alkali salts of TFESI-(A) and HFPSI-(B) (A) a. LiTFESI; b. NaTFESI; c. KTFESI; d. RbTFESI; e. CsTFESI. (B) a. LiHFPSI; b. NaHFPSI; c. KHFPSI; d. RbHFPSI; e. CsHFPSI.

Fig.2 Melting temperature of alkali salts of HFPSI-(a) and TFESI-(b) versus the identity of cation

Fig.3 Thermogravimetric curves of alkali salts of TFESI-(A) and HFPSI-(B)

Fig.4 Decomposition temperature of alkali salts of TFESI-(a) and HFPSI-(b) versus the identity of cation

Table 2 Viscosity(η), glass transition temperatures(Tg), ionic conductivity(σ), oxidation potential and Al corrosion of 1.0 mol/L lithium salt in EC/EMC(3:7, volume ratio) at 25 ℃

Salt	10³η/(Pa·s)	T_g/℃	σ/(mS·cm^-1)	Oxidation potential/V	Al corrosion
LiTFESI	3.2	-106	4.2	5.6	No
LiHFPSI^*	5.7	-100	3.3	5.7	No

Fig.5 Arrhenius plots of specific conductivity of 1.0 mol/L LiTFESI, LiHFPSI, LiPF6, LiTFSI, LiClO4, and LiBF4 in a mixture of EC/EMC(3:7, volume ratio)

Fig.6 Cyclic voltammograms obtained on Pt in 1.0 mol/L LiTFESI in a mixture of EC/EMC(3:7, volume ratio) at a scan rate of 5 mV/s

Fig.7 Cyclic voltammograms for Al foil in 1.0 mol/L LiTFESI(A) and LiTFSI(B) in a mixture of EC/EMC(3:7, volume ratio) at a scan rate of 5 mV/s

Fig.8 SEM images of Al electrodes after the potential cycling in electrolytes of 1.0 mol/L LiTFESI(A) and LiTFSI(B) in a mixture of EC/EMC(3:7, volume ratio)

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