Methylphosphonoyloxymethane as Electrolyte Component

Abstract

An electrolyte composition and an electrochemical cell that includes the electrolyte composition are included. The electrolyte composition includes: at least one aprotic organic solvent; at least one conducting salt; methylphosphonoyloxymethane; and optionally one or more additives. The use of methylphosphonoyloxymethane in an electrolyte composition for electrochemical cells is also included.

Claims

1. An electrolyte composition comprising: at least one aprotic organic solvent; at least one conducting salt; and methylphosphonoyloxymethane.

2. The electrolyte composition of claim 1, wherein the electrolyte composition comprises 0.01 to 5 wt.-% methylphosphonoyloxymethane based on a total weight of the electrolyte composition.

3. The electrolyte composition of claim 1, wherein the electrolyte composition comprises 0.05 to 1 wt.-% methylphosphonoyloxymethane based on a total weight of the electrolyte composition.

4. The electrolyte composition of claim 1, wherein the at least one aprotic organic solvent is selected from cyclic and acyclic organic carbonates, di-C.sub.1-C.sub.10-alkylethers, di-C.sub.1-C.sub.4-alkyl-C.sub.2-C.sub.6-alkylene ethers and polyethers, cyclic ethers, cyclic and acyclic acetals and ketals, orthocarboxylic acids esters, cyclic and acyclic esters of carboxylic acids, cyclic and acyclic sulfones, and cyclic and acyclic nitriles and dinitriles.

5. The electrolyte composition according of claim 1, wherein the at least one aprotic organic solvent is selected from cyclic and acyclic organic carbonates and cyclic and acyclic esters of carboxylic acids.

6. The electrolyte composition according claim 1, wherein the at least one conducting salt is selected from lithium salts.

7. The electrolyte composition of claim 1, wherein at least one conducting salt is selected from LiPF.sub.6, LiAsF.sub.6, LiSbF.sub.6, LiCF.sub.3SO.sub.3, LiBF.sub.4, lithium bis(oxalato) borate, lithium difluoro(oxalato) borate, LiClO.sub.4, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2F).sub.2, and LiPF.sub.3(CF.sub.2CF.sub.3).sub.3.

8. The electrolyte composition of claim 1, wherein the electrolyte composition further comprises at least one additive.

9. The electrolyte composition of claim 8, wherein the at least one additive is selected from cyclic carbonates comprising at least one double bond, and cyclic esters of sulfur comprising acids.

10. The electrolyte composition of claim 9, wherein the electrolyte composition comprises at least 74.99 wt.-% of the at least one organic aprotic solvent; 0.1 to 25 wt.-% of the at least one conducting salt; 0.1 to 5 wt.-% the methylphosphonoyloxymethane; and 0 to 25 wt.-% of the at least one additive, based on a total weight of the electrolyte composition.

11. Use of methylphosphonoyloxymethane in an electrolyte composition for electrochemical cells.

12. An electrochemical cell comprising an electrolyte composition wherein the electrolyte composition comprises: at least one aprotic organic solvent; at least one conducting salt; and methylphosphonoyloxymethane.

13. The electrochemical cell of claim 12, wherein the electrochemical cell is a lithium battery, a double layer capacitor, or a lithium ion capacitor.

14. The electrochemical cell of claim 12, wherein the electrochemical cell is a lithium cell comprising an anode including an anode active material selected from carbonaceous materials, lithium ion intercalating oxides of Ti, and/or silicon based materials.

15. The electrochemical cell of claim 12, wherein the electrochemical cell comprises a cathode containingincluding at least one cathode active material selected from lithium intercalating transition metal oxides and lithiated transition metal phosphates.

Description

1. ELECTROLYTE COMPOSITIONS

[0127] Electrolyte compositions were prepared from methylphosphonoyloxymethane (MPOM), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), lithium hexafluorophosphate (LiPF.sub.6), and vinylene carbonate (VC). The exact compositions are shown in Tables 1 and 2. Wt.-% are based on the total weight of the electrolyte composition.

[0128] MPOM was prepared according to the following procedure. To a cold solution (0 C.) of CH.sub.3PC.sub.12 (1.0 eq, 390 mmol, 50.66 g) in tetrahydrofurane (THF) (abs., 200 mL) was carefully added a dry mixture of methanol (2.5 eq., 980 mmol, 31.24 g) and triethylamine (1.02 eq., 400 mmol, 40.66 g) in THF (abs., 100 mL) and the reaction temperature was kept between 0 C. and 5 C. After complete addition, the reaction mixture was heated to 50 C. for 60 min, cooled to room temperature and the formed precipitate was filtered off. The filtrate was concentrated and distilled (2 mbar, 46 C.) to obtain MPOP as a colorless oil (25.8 g, 270 mmol, 70% yield).

[0129] 2. Electrochemical tests

2. ELECTROCHEMICAL PERFORMANCE

[0130] Differential capacity:

[0131] Button cells were fabricated using lithium nickel cobalt manganese oxide (Li(Ni.sub.0.33Co.sub.0.33Mn.sub.0.33)O.sub.2, NCM 111) electrodes with a capacity of 2 mAh/cm.sup.2 and a graphite electrode with a capacity of 2.15 mAh/cm.sup.2. A glass-fiber filter separator (Whatmann GF/D) was used as separator, which was soaked with 100 l of the respective electrolyte composition. The cells were charged with a rate of C/5. The differential capacity plot was measured at 25 C. in climate chambers. The reaction potential of the additive was determined by an increase of differential capacity (mAh/V) within a voltage range of 2.5 V to 3.1 V above a value of 0.5 mAh/V. The additive Methylphosphonoyloxymethane shows its decomposition reaction already at 2.65V. The decomposition leads to a passivation of the graphite electrode and the typical reaction of VC at 2.9V is not observed. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Differential capacity Reaction Electrolyte composition onset in V Example 1: 1M LiPF.sub.6 in EC:EMC 1:1 by wt. + 2.65 2 wt.-% VC + 5 wt.-% MPOM Comparative example 1: 1M LiPF.sub.6 in EC:EMC 1:1 by wt. + 2.92 2 wt.-% VC

[0132] Battery Test

[0133] Pouch cells (220mAh) were fabricated using lithium nickel cobalt manganese oxide (Li(Nio.sub.0.6Co.sub.0.2Mn.sub.0.2)O.sub.2, NCM 622), electrode density 3.4 g/ccm, mass loading 17 mg/cm.sup.2) with graphite anodes (artificial graphite, electrode density 1.4 g/ccm, mass loading 10 mg/cm.sup.2) using a 12 m thick polyolefin separator. The cell was filled with 700 l of electrolyte stored for 6 h and then evacuated and sealed. The formation of the cells was done by charging at a charge rate of 0.2 C and the storing the cells in a fully charged condition for 5 days at 45 C. After the formation first the capacity of the cells was checked by a 0.2 C charge and discharge step followed by a discharge rate test at 1 C charge and discharge rates of 1 C, 2 C and 3 C. After this the cells were either stored at 60 C. for 20 days in a fully charged state (4.2 V) or cycled at 45 C. at 1 C charge and discharge rate (4.2 V cut-off) for 100 cycles. The resistance of the cells was measured before cycling and storage and afterwards by applying 1 C, 2 C and a 3 C pulse (at 3.6 V) and measuring the voltage drop. The results are summarized in Table 2.

TABLE-US-00002 TABLE 2 DC Capacity DC resistance Capacity resistance recovery after increase after recovery increase 20 days of 20 days of after 100 after 100 Electrolyte storage at storage at cycles at cycles at composition 60 C. (*) 60 C. 45 C. (**) 45 C. Example 2 1.15M LiPF.sub.6 in 92.4% 1% 89% 92% EC:EMC:DEC 3:1:6 by volume + 0.1 wt % MPOM Example 3 1.15M LiPF.sub.6 in 97.2% 0% 94% 67% EC:EMC:DEC 3:1:6 by volume + 0.1 wt % MPOM + 1.5 wt.-% VC Comparative 1.15M LiPF.sub.6 in 94.2% 36% 84% 116% example 2 EC:EMC:DEC 3:1:6 by volume + 1.5 wt % VC (*): Capacity recovery is based on the C/5 discharge capacity after storage compared to the initial C/5 discharge capacity (**): Capacity recovery is based on the C/5 discharge capacity after 100 cycles compared to the initial C/5 discharge capacity