Energy storage device

1. An energy storage device comprising:

at least one negative electrode comprising a mixed electrode comprising:

a region of a battery electrode material and a region of a capacitor electrode material in an amount of 1% to 15% by weight of the battery electrode material, and

at least one positive electrode, wherein the positive electrode comprises a positive battery electrode material mixed with a charging ability-increasing additive selected from one or a mixture of:

(a) carbon nanomaterial, vapour grown carbon fibre, fullerene, or a mixture thereof, and

(b) tin dioxide conductive materials,

and wherein the amount of the charging ability-increasing additive in the positive electrode material is between 0.05-10% by weight, based on the total weight of positive electrode material.

2. The energy storage device of claim 1 , wherein the amount of the charging ability-increasing additive is between 0.1% and 1.0% by weight.

3. The energy storage device of claim 1 , wherein the energy storage device is a lead-acid energy storage device, wherein the negative battery material is sponge lead, and the positive battery material is lead dioxide, and wherein the device further comprises sulphuric acid electrolyte.

4. The energy storage device of claim 3 , wherein the positive battery electrode material on the positive electrode is formed from a paste having a paste density of between 4.4 to 4.7 g/cm 3 .

5. The energy storage device of claim 3 , wherein the positive electrode comprises a current collector that is of between 0.8 and 2.2 mm in thickness.

6. The energy storage device of claim 3 , wherein the positive battery electrode material comprises an oxygen-suppressing additive.

7. The energy storage device of claim 6 , wherein the oxygen-suppressing additive is selected from one or more of the following:

an oxide, hydroxide or sulfate of antimony,

an oxide, hydroxide or sulfate of bismuth, and

an oxide, hydroxide or sulfate of arsenic.

8. The energy storage device of claim 7 , wherein the positive battery electrode material is formed from a paste of positive battery electrode material applied to the positive electrode, and wherein the oxygen-suppressing additive includes 100-1000 ppm bismuth.

9. The energy storage device of claim 3 , wherein the capacitor electrode material of the negative electrode comprises:

5-85 weight % carbon black

20-80 weight % activated carbon

0-25 weight % carbon material other than carbon black and activated carbon, and

0-30 weight % binder.

10. The energy storage device of claim 9 , including capacitor additive material in an amount of up to 20 weight % of the capacitor electrode material, the capacitor additive material selected from the group consisting of oxides, hydroxides or sulfates of zinc, cadmium, bismuth, lead and silver.

11. The energy storage device of claim 1 , wherein the mixed electrode comprises a current collector with two faces, the region of battery electrode material comprises a layer of battery electrode material covering the faces of the current collector creating two faces of the battery electrode material, and the region of capacitor electrode material is in the form of a layer of capacitor electrode material that overlies both faces of the battery electrode material.

12. The energy storage device of claim 11 , wherein the amount of the capacitor electrode material forming the region of capacitor electrode material is from 1% to 7% by weight of the battery electrode material.

13. The energy storage device of claim 1 , wherein the device comprises:

a plurality of said negative electrodes, each of said negative electrode comprising:

a negative current collector with two faces, with a coating of the negative battery electrode material on the faces of the current collector, wherein the negative battery electrode material comprises:

90-95% PbO

0.05-0.1% wt. % plastic fibre

1-2 wt. % BaSO 4

0.1-0.6% wt. % organic expander

0.5-3 wt. % carbon black

4-6 wt. % H 2 SO 4 , in which the PbO and H 2 SO 4 may be present as sponge lead following formation,

and a coating of the capacitor material on both faces of the negative battery electrode material at a level of 1-7 wt % based on the amount of negative battery electrode material, the capacitor material comprising:

5-85 wt. % carbon black

20-80 wt. % activated carbon

5-25 wt. % binder, and

a plurality of said positive electrodes, each of said positive electrodes comprising:

a positive current collector with two faces, with a coating of a positive capacitor material on the positive current collector, said positive capacitor material comprising:

5-85 wt. % carbon black

20-80 wt. % activated carbon

5-25 wt. % binder, and

a coating of said positive battery electrode material on both faces of the positive capacitor material, positive the battery electrode material comprising:

90-98 wt. % PbO

0.05-0.1 wt. % plastic fibre

3-7 wt. % H 2 SO 4 , and

0.1-10 wt. % of said charging ability-increasing additive,

in which the PbO and H 2 SO 4 may be present as lead dioxide following formation, and in which the amount of positive capacitor material on the positive electrode is between 1-6 wt. % based on the positive battery electrode material.

14. The energy storage device of claim 7 , wherein the positive battery electrode material is formed from a paste of positive battery electrode material applied to the positive electrode, and wherein the oxygen-suppressing additive includes either or both of the following:

up to 500 ppm antimony, and

up to 500 ppm arsenic,

wherein the ppm levels refer to parts per million based on lead oxide in the paste.

15. The energy storage device of claim 14 , wherein the positive battery electrode material is formed from a paste of positive battery electrode material applied to the positive electrode, and wherein the oxygen-suppressing additive includes 100-1000 ppm bismuth.

16. An energy storage device comprising at least one negative electrode and at least one positive electrode, wherein:

at least one negative electrode is a mixed electrode comprising a mixture of a battery electrode material and a capacitor electrode material, wherein the capacitor electrode material constitutes 2-10% by weight of the mixture of the battery electrode material and the capacitor electrode material,

each positive electrode comprises a positive battery electrode material mixed with a charging ability-increasing additive selected from one or a mixture of

(a) carbon nanomaterial, vapour grown carbon fibre, fullerene, or a mixture thereof, and

(b) tin dioxide conductive materials, and the amount of the charging ability-increasing additive in the positive electrode material is between 0.05-10% by weight, based on the total weight of positive electrode material.