Flexible asymmetric electrochemical cells using nano graphene platelet as an electrode material

1. A flexible hybrid electrochemical cell comprising:

(I) a first electrochemical cell comprising:

(a) a sheet of spacer-modified graphene paper thinner than 1 mm as first electrode, said paper comprising (i) nano graphene platelets having a thickness smaller than 10 nm and (ii) discrete, non-continuous, and non-metallic particles, having a size no less than 2 nm, bonded to a surface or both surfaces of said nano graphene platelets as spacer particles to produce electrolyte-accessible pores having a size greater than 2 nm and less than 10 nm and having a specific surface area greater than 100 m 2 /g, and (iii) a binder that bonds said nano graphene platelets together and wherein said particles consist of a material selected from the group consisting of metal carbide, metal nitride, metal halide, and combinations thereof; and wherein said first electrode has a first specific capacitance C1,

(b) a thin-film first separator thinner than 1 mm and electrolyte;

(c) a thin-film second electrode thinner than 1 mm which is different in composition than the first electrode wherein said second electrode comprises a lithium foil or lithium-intercalated material; and wherein said separator is sandwiched between the first and second electrode to form a flexible laminate configuration;

(d) a second separator containing electrolyte, wherein said second separator is in physical contact with said second electrode;

(e) a third thin-film electrode, having a thickness less than 1 mm, in contact with said second separator and having a second specific capacitance C2 and wherein the C1/C2 ratio is greater than 3 which is used as a supercapacitor; and

(II) a second energy storage or conversion cell in a working relation to said first electrochemical cell, wherein said energy storage or conversion cell is selected from a battery, a fuel cell, a photovoltaic or solar cell, or a combination thereof.

2. The flexible hybrid electrochemical cell of claim 1 further comprising a third electrochemical cell in a working relation to said first electrochemical cell or said second energy storage or conversion cell.

3. A flexible hybrid electrochemical cell comprising:

(I) a first electrochemical cell comprising:

(a) a sheet of graphene paper as first electrode comprising nano graphene platelets having a platelet thickness less than 1 nm, wherein said first electrode has electrolyte-accessible pores, wherein said first electrode comprises a transition metal carbide coated on or bonded to at least one of the nano graphene platelets;

(b) a thin-film first separator thinner than 1 mm and electrolyte; and

(c) a thin-film or paper-like second electrode thinner than 1 mm which is different in composition than the first electrode; wherein said second electrode comprises a lithium foil or lithium-intercalated material; and wherein said separator is sandwiched between the first and second electrode to form a flexible laminate configuration; and

(II) a second energy storage or conversion cell in a working relation to said first electrochemical cell, wherein said energy storage or conversion cell is selected from a battery, a fuel cell, a photovoltaic or solar cell, or a combination thereof.

4. The flexible hybrid electrochemical cell of claim 3 further comprising a third electrochemical cell in a working relation to said first electrochemical cell or said second energy storage or conversion cell.

5. A flexible hybrid electrochemical cell comprising:

I. a first electrochemical capacitor comprising:

(a) a spacer-modified first thin-film electrode having a thickness lower than 1 mm, comprising (i) nano graphene platelets having a thickness smaller than 1 nm; (ii) discrete, non-continuous, and non-metallic particles having a size no less than 2 nm and selected from the group consisting of metal carbides, metal nitrides, metal halides, and combinations thereof, and wherein said particles are bonded to a surface or both surfaces of said nano graphene platelets to produce electrolyte-accessible pores having a size greater than 2 nm but less than 10 nm; and (iii) a binder that bonds said nano graphene platelets together, and wherein said first electrode has a specific surface area greater than about 100 m 2 /g and a first specific capacitance C1;

(b) a second thin-film electrode having a thickness lower than 1 mm, comprising nano graphene platelets and a plurality of interconnected pores accessible by an electrolyte, and wherein said second electrode has a specific surface area greater than about 100 m 2 /g and a second specific capacitance C2 and wherein the C1/C2 ratio is greater than 3; and

(c) a thin-film or porous electrode separator having a thickness lower than 0.1 mm disposed between the first and second electrodes, said separator comprising said electrolyte; and

II. a second energy storage or conversion cell in a working relation to said first electrochemical capacitor, wherein said energy storage or conversion cell is selected from a battery, a fuel cell, a photovoltaic or solar cell, or a combination thereof.

6. The flexible hybrid electrochemical cell of claim 5 further comprising a third electrochemical cell in a working relation to said first electrochemical capacitor or said second energy storage or conversion cell.

7. The flexible hybrid electrochemical cell of claim 5 , wherein said electrolyte comprises a room temperature ionic liquid.

8. The flexible hybrid electrochemical cell of claim 5 , wherein said first electrode further comprises fibrous elements selected from the group consisting of carbon nano-fibers, graphitic nano-fibers, carbon nano-tubes, carbon-graphite fibers, cellulose fibers, glass fibers, polymer fibers, ceramic fibers, metal fibers, and combinations thereof.

9. A flexible hybrid electrochemical cell comprising:

I. a flexible electrochemical capacitor or supercapacitor, comprising:

(a) a first paper-like electrode, comprising nano graphene platelets and a plurality of pores accessible by an electrolyte wherein said first electrode has a specific surface area greater than about 100 m 2 /g, wherein said first electrode comprises a transition metal carbide coated on or bonded to at least one of the nano graphene platelets;

(b) a second paper-like electrode, comprising nano graphene platelets and a plurality of pores accessible by said electrolyte wherein said second electrode has a specific surface area greater than about 100 m 2 /g; and

(c) a paper-like or porous electrode separator disposed between the first and second electrodes, said separator comprising said electrolyte; and

II. a second energy storage or conversion cell in a working relation to said first electrochemical capacitor, wherein said energy storage or conversion cell is selected from a battery, a fuel cell, a photovoltaic or solar cell, or a combination thereof.