Engineering the interlayer spacing by pre-intercalation for high performance supercapacitor MXene electrodes in room temperature ionic liquid

1 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof, and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the intercalant comprises an alkyl-ammonium (AA) cation selected from a formula [(CH 3 ) 3 NC n H 2n+1 ] + , wherein n is in a range of 3-30.

2 . The supercapacitor of claim 1 , wherein the alkyl-ammonium (AA) cation comprises [(CH 3 ) 3 NC 12 H 25 ] + .

3 . The supercapacitor of claim 1 , wherein the M is selected from the group of Ti, Nb, Sc, V, Cr, Y, Zr, Mo, Hf, Ta, W, and a combination thereof.

4 . The supercapacitor of claim 1 , wherein the room-temperature ionic liquid (RTIL) comprises an organic cation selected from the group of 1-ethyl-3-methyl imidazolium (EMIM + ), 1-alkyl-3-methyl-imidazolium, 1-alkyl-2,3-methyl-imidazolium, tetraalkylammonium, trialkylsulfonium, tetraalkylphosphonium, 1-alkylpyridinium, N-alkyl-N-methyl-morpholinium, 1-alkyl-1-methyl-piperidinium, 1-alkyl-1-methyl-pyrrolidinium, 3-methylpyridinium, 1-methylimidazolium, or a combination thereof, wherein the alkyl is a C 1 -C 50 alkyl.

5 . The supercapacitor of claim 1 , wherein the room-temperature ionic liquid (RTIL) comprises an organic anion selected from bis-(trifluoromethylsulfonyl)-imide (TFSI − ), dicyanamide (N(CN) 2 − ), hexafluorophosphate (PF 6 − ), tetrachloroaluminate, thiocyanate (SCN − ), halides, tetrafluoroborate, hexafluorophosphate, tris(pentafluoroethyl) Trifluorophosphate, alkylsulfate, methanesulfonate, trifluoromethanesulfonate, bis(fluorosulfonyl)imide, (fluorosulfonyl) (trifluoromethanesulfonyl)imide, bis(trifluoromethanesulfonyl)imide, dicyanamide, bis(oxalato)borate, or a combination thereof, wherein the alkyl comprises a C 1 -C 50 alkyl.

6 . The supercapacitor of claim 1 , wherein the M n+1 X n T x layers have a d-spacing in a range of about 1.0-20 nm, and the difference in d-spacing, Δd, between pristine M n+1 X n T x layers and the M n+1 X n T x layers including the intercalant is in a range of about 0.1-20 nm.

7 . The supercapacitor of claim 1 , wherein the RTIL comprises 1-ethyl-3-methyl imidazolium bis-(trifluoromethylsulfonyl)-imide (EMIMTFSI).

8 . The supercapacitor of claim 1 , wherein the M n+1 X n T x layers comprise Ti 3 C 2 T x layers.

9 . The supercapacitor of claim 1 , wherein the M n+1 X n T x layers comprise Nb 2 CT x layers.

10 . A method of preparing a supercapacitor according to claim 1 , the method comprising:

incorporating into the electrode the electrode material comprising the M n+1 X n T x layers having interlayers therebetween and the intercalant located in at least a portion of the interlayers,

incorporating the electrode into the supercapacitor; and

incorporating the electrolyte comprising the room-temperature ionic liquid (RTIL) into the supercapacitor.

11 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof; and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the M n+1 X n T x layers have a unit cell and the amount of the intercalant located in the interlayers of the M n+1 X n T x layers is in a range of about 0.01-1 intercalant cations per M n+1 X n T x unit cell.

12 . The supercapacitor of claim 11 , wherein the M n+1 X n T x layers comprise Ti 3 C 2 T x layers, the intercalant comprises an alkylammonium (AA) cation, and the amount of the alkylammonium cation located in the interlayers of the Ti 3 C 2 T x layers is in a range of about 0.01-1 of the alkylammonium cations per Ti 3 C 2 T x unit cell.

13 . The supercapacitor of claim 11 , wherein the M n+1 X n T x layers comprise Nb 2 CT x layers, the intercalant comprises an alkylammonium (AA) cation, and the amount of the alkylammonium cation located in the interlayers of the Nb 2 CT x layers is in a range of about 0.01-1 of the alkylammonium cation per Nb 2 CT x unit cell.

14 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof; and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the room temperature ionic liquid (RTIL) comprises a blend of 1-butylimidazole (BuIM) and bis(trifluoromethanesulfonyl)imide (HNTf 2 ) solution in a molecular ratio in a range of about 0.6:0.4 to 0.9:0.1.

15 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof; and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the RTIL comprises an organic cation, and the electrode material further comprises the organic cation located in the interlayers of the M n+1 X n T x layers in a density in a range of about 50-1500 kg/m 3 .

16 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof; and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the RTIL comprises an organic anion, and the electrode material further comprises the organic anion located in the interlayers of the M n+1 X n T x layers in a density in a range of about 50-2000 kg/m 3 .

17 . An electrode material comprising:

M n+1 X n T x layers having interlayers therebetween and an intercalant located in at least a portion of the interlayers, wherein the intercalant comprises an alkyl-ammonium (AA) cation selected from a formula [(CH 3 ) 3 NC n H 2n+1 ] + , wherein n is in a range of 3-30,

wherein M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (Cl), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof, and

the M n+1 X n T x layers further comprising an organic cation of an RTIL located in at least a portion of the interlayers.

18 . A supercapacitor comprising:

an electrode comprising an electrode material, the electrode material comprising:

M n+1 X n T x layers having interlayers therebetween,

wherein the M is selected from the group of Group 3, 4, 5, 6, and 7 transition metals and a combination thereof,

wherein X is C, N, or a combination thereof,

wherein n is 1, 2, 3, or 4,

wherein T x comprises a termination group selected from the group of alkoxide, alkyl, carboxylate, halide, fluorine (F), chlorine (CI), hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, sulfonate, thiol, and a combination thereof; and

an intercalant located in at least a portion of the interlayers; and

an electrolyte comprising a room temperature ionic liquid (RTIL), wherein the RTIL is neat such that it is not combined with a solvent.

19 . The supercapacitor of claim 18 , wherein the intercalant comprises an alkyl-ammonium (AA) cation.

20 . The supercapacitor of claim 19 , wherein the alkyl-ammonium (AA) cation is selected from a formula [(CH 3 ) 3 NC n H 2n+1 ] + , wherein n is in a range of 3-30.