Abstract:
The present invitation discloses a high capacity rechargeable battery, which comprises a carbon/manganese dioxide composite cathode; a zinc anode separated from cathode; an aqueous electrolyte contains zinc (Zn 2+ ) and manganese (Mn 2+ ) ions. The present invitation utilizes the oxidation/reduction of Mn 2+  ions on carbon/manganese dioxide composite to improve the capacity and the cycle life of the battery.

Description:
BACKGROUND 
       [0001]    This invention relates to rechargeable zinc ion batteries with high capacity and long cycle life. 
         [0002]    The US patent (U.S. Pat. No. 8,663,844 B2) invented a so-called zinc ion battery, which uses α-MnO 2  as cathode, zinc as anode and ZnSO 4  aqueous solution as the electrolyte. The battery chemistry of zinc ion battery is written as: 
         [0000]      Cathodic reaction: xZn 2+ +2Xe − +MnO 2           Zn x MnO 2    (1)
 
         [0000]      Anodic reaction: Zn         Zn 2+ +2e −   (2)
 
         [0003]    The advantage of zinc ion battery is ecofriendly, safety and low cost. However, the disadvantage of zinc ion battery is the low capacity of the battery. The capacity of MnO 2  is as low as 200 mAh g −1 , which preclude it from various applications for example electric vehicles. In addition, the cycle life of this battery is short. Therefore, it is necessary to discover new cathode active materials with a high capacity to further improve the energy density of zinc ion battery. 
       SUMMARY OF THE INVITATION 
       [0004]    The purpose of this patent is to invent a new battery with high capacity and long cycle life. 
         [0005]    Due to the energy crisis, our society requires rechargeable batteries with high capacity and long cycle life to power the portable electronics for further long time, to drive the electric vehicles rivaling cars powered by the combustion engine, and to store electricity generated by renewable sources. 
         [0006]    Carbon supporting manganese dioxide, which is simply denoted as carbon/MnO 2 , is worldwide interesting electrode material for the batteries or supercapcitors. The design of manganese dioxide deposited on the carbon support increases the conductivity of MnO 2  and improves the contact between MnO 2  and the electrolyte. As a result, the carbon/MnO 2  composite can obtain a better electrochemical behavior than pure MnO 2 . 
         [0007]    In addition, we firstly found in this application that there is the reversible manganese oxidation/reduction of Mn 2+  ions on the carbon/MnO 2  composites, which is simply written as: 
         [0000]      Mn 2 ++2H 2 O         MnO 2 +4H + +2e −   (3)
 
         [0008]    The cyclic voltammetry (CV) as shown in  FIG. 1  clearly shows the reversible manganese oxidation/reduction reaction on the carbon/MnO 2  composites. The manganese oxidation reaction from soluble Mn 2+  ions to MnO 2  deposits occurs at 1.58 vs. Zn 2+ /Zn and then extraction of Zn 2+  ions from MnO 2  occurs at 1.63 V vs. Zn 2+ /Zn, while insertion of Zn 2+  ions into MnO 2  and the manganese reduction reaction from MnO 2  to soluble Mn 2+  ions occur at 1.35 V and 1.20 V vs. Zn 2+ /Zn, respectively. 
         [0009]    There are synergistic reactions between manganese oxidation/reduction reaction (equation 1) and storage/release of Zn 2+  ions into/from MnO 2  (equation 3). The reversibility of manganese oxidation/reduction reaction can be improved to 100% by adding Mn 4+  source (MnO 2 ) in carbon/MnO 2  composites. Meanwhile, MnO 2  can reversibly store/release Zn 2+  ions during discharge/charge as shown in equation 1. Therefore, this invention utilizes the oxidation/reduction of Mn 2+  ions on carbon/manganese dioxide composites to improve the capacity and the cycle life of the battery. 
         [0010]    The rechargeable zinc ion battery comprise of a cathode composing of the active composite of carbon supporting manganese dioxide; a zinc anode; a separator for separating said cathode from said anode; and an aqueous electrolyte containing zinc ions (Zn 2+ ) and manganese (Mn 2+ ) ions. 
         [0011]    The said carbon supporting manganese dioxide is that the manganese dioxide is deposited on the carbon material, where carbon is as support for manganese dioxide. 
         [0012]    The said carbon material can be any shape of carbon element, for example, fullerene, carbon nanotube, graphene, carbon fiber, carbon foam. The said carbon material can be the composite of over two different carbon materials. 
         [0013]    The said manganese dioxide represents a general class of tunnel materials. The basic structural unit of manganese dioxide is MnO 6  octahedron. MnO 6  octahedra can share vertices and edges to form endless chains of MnO 6  octahedral subunits, which can in turn be linked to neighboring octahedral chains by sharing corners oredges. The piling up of MnO 6  units enables the building of one dimension (1D), two dimension (2D) or three dimension (3D) tunnels of manganese dioxide. 1D manganese dioxide is known as alpha type manganese dioxide (α-MnO 2 ), beta type manganese dioxide (β-MnO 2 ), gamma type manganese dioxide (γ-MnO 2 ), etc. 2D manganese dioxide is known as birnessite δ-MnO 2 . 2D manganese dioxide is known as λ-MnO 2 . In addition, manganese dioxide often contains foreign cations, physisorbed and structural water moleculars in its tunnel. There are many types of manganese dioxide containing various univalent and bivalent cations in its tunnels. For example, α-MnO 2  groups with 1D structure possess a large open tunnel structure including holladite group (Mg, Ca, Ba, K) Mn 8 O 16 , psilomelane group (Ca, Ba, K) Mn 5 O 10 .H 2 O and todorokite group (Mn, Ca, Mg) Mn 3 O 7 .H 2 O. 2D birnessite group minerals include chalcophanite ZnMn 3 O 7 .3H 2 O, buserite (Ca, Na) Mn 7 O 14 .3H 2 O and ranceite (Ca, Mn) Mn 4 O 9 .3H 2 O. And λ-MnO 2  groups with 3D tunnel include hetaerolite ZnMn 2 O 4 , hydroehetaerolite Zn 2 Mn 4 O 18 .H 2 O etc. 
         [0014]    The said carbon material can be composed of one uniform carbon materials for example carbon nanotube fabric, carbon fiber fabric, etc. 
         [0015]    The said zinc anode is in any shapes of pure zinc or zinc alloy, such as the foil, film, plat, grid, pillar, etc. 
         [0016]    The said zinc anode can also be a compressed mixture of pure zinc and/or zinc alloy particles, electrically conductive particles and a binder, and this compressed mixture is normally attached by the used binder on a current collector. 
         [0017]    The said binder is selected from the group consisting of natural and synthetic rubbers, polysulfone, acrylic polymers, epoxy resins, polystyrene and polytetrafluoroethylene. 
         [0018]    The said aqueous electrolyte comprises a solvent and a solute. The said solvent is water. The solute is the mixture of zinc slats and manganese salts. The said zinc slat is ZnSO 4 , Zn(NO 3 ) 2 , or ZnCl 2 , etc. and the said manganese slat is MnSO 4 , Mn(NO 3 ) 2 , or MnCl 2 , etc. 
         [0019]    The said separator is a thin layer of a suitable material, which can physically separate the said anode from the cathode. This separator is nonoxidizable and stable in the cell environment. 
         [0020]    The said rechargeable zinc ion battery can be configured as “button” cell, cylindrical cell or rectangular cell, etc. 
         [0021]    In addition, additives with specific function can be added in the anode, cathode or electrolyte to improve the performance of the batteries. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  Cyclic voltammetry of the reversible manganese oxidation/reduction reaction on the carbon/MnO 2  composites. 
           [0023]      FIG. 2  The discharge and charge curves of Cell 1 at a current density of 0.1 A g −1  (based on the positive active mass). 
           [0024]      FIG. 3  The discharge and charge curves of Cell 2 at a current density of 0.1 A g −1  (based on the positive active mass). 
           [0025]      FIG. 4  The discharge and charge curves of Cell 3 at a current density of 0.1 A g −1  (based on the positive active mass). 
           [0026]      FIG. 5  The discharge and charge curves of Cell 4 at a current density of 0.5 A g −1  (based on the positive active mass). 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Compositions of matter, articles of manufacture and methods for manufacture are set forth herein for preparation of carbon materials, battery electrodes, and the rechargeable battery. 
         [0028]    The synthesis of graphene/MnO 2  composites is shown in below. A 0.1 mol/L KMnO 4  aqueous solution was prepared by dissolving KMnO 4  (AR, 99%) in deionized water. An AOT/isooctane solution was prepared by adding 66.6 g surfactant of high purity sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT) to 1500 mL isooctane and stirring them well. 81 mL of 0.1 mol/L KMnO4 aqueous solution was then added in the AOT/isooctane solution, and 0.1244 g graphene was added into this mixture solution. Then it was ultrasound for 30 min to obtain a dark brown precipitate. The deposit was separated, washed with deionized water and ethanol several times, and dried at 90° for 12 h. 
         [0029]    The synthesis of MnO 2  is shown in below. A 0.1 mol/L KMnO 4  aqueous solution was prepared by dissolving KMnO 4  (AR, 99%) in deionized water. An AOT/isooctane solution was prepared by adding 66.6 g surfactant of high purity sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT) to 1500 mL isooctane and stirring them well. 81 mL of 0.1 mol/L KMnO4 aqueous solution was then added in the AOT/isooctane solution, and then ultrasound for 30 min to obtain a dark brown precipitate. The nano-sheet MnO 2  was separated, washed with deionized water and ethanol several times, and dried at 90° C. for 12 h. 
         [0030]    The electrode composing of graphene/MnO 2  composites is fabricated as following. Graphene/MnO 2  composites (70%), carbon black (20%) and LA133 binder (10%) were stirred 30 min to obtain the slurry. The slurry was coated on one side of the stainless steel foil current collector, and then dried at 90° C. for 10 h under vacuum. The electrode then was cut into a round shape with a diameter of 1.5 cm. This is graphene/MnO 2  cathode. The cyclic voltammetry of graphene/MnO 2  cathode in 1 molar per liter (M) ZnSO 4  and 2 M MnSO 4  aqueous solution is shown in  FIG. 1 . 
         [0031]    The MnO 2  cathode is fabricated as following. MnO 2  (70%), carbon black (20%) and LA133 binder (10%) were stirred 30 min to obtain the slurry. The slurry was coated on one side of the stainless steel foil current collector, and then dried at 90° C. for 10 h under vacuum. The electrode then was cut into a round shape with a diameter of 1.5 cm. 
         [0032]    The battery test used the coin cell assembly consisting of graphene electrode as cathode and zinc film (20 μm in thickness) as anode. A glass paper was used as the separator. The electrolyte is 1 M ZnSO 4  and 2 M MnSO 4  aqueous solution. This cell was denoted as Cell 1. The discharge and charge curves of Cell 1 are shown in  FIG. 2  at a current density of 0.1 A g −1  (based on the positive active mass). The capacity of this battery is over 4200 mAh g −1 . During cycling the Coloumbic efficiency of such battery is close to 100%. 
         [0033]    In order to demonstrate the effect of reversible manganese oxidation/reduction reaction on the carbon/MnO 2  composites, we assembled two other cells. The Cell 2 comprises of MnO 2  cathode, zinc film (20 μm in thickness) anode, and 1 M ZnSO 4  and 2 M MnSO 4  aqueous electrolyte. In addition, we assembled the Cell 3 without Mn 2+  ions in the electrolyte. The Cell 3 comprises of graphene/MnO 2  cathode, zinc film (20 μm in thickness) anode, and 1 M ZnSO 4  aqueous electrolyte. It is shown that in comparison with Cell 1, Cell 2 uses MnO 2  instead of carbon/MnO 2  composites as the cathode, while Cell 3 uses the aqueous electrolyte without Mn 2+  ions. The discharge and charge curves of Cell 2 and Cell 3 are shown in  FIG. 3  and  FIG. 4  at a current density of 0.1 A g −1  (based on the positive active mass), respectively. The capacities of Cell 2 and Cell 3 are 200 and 260 mAh g −1 . It is shown from the capacities of Cell 1, Cell 2, and Cell 3 that the capacity of the zinc ion battery is improved by the reversible manganese oxidation/reduction reaction on the carbon/MnO 2  composites. In addition, the cycle lives of Cell 1, Cell 2, and Cell 3 are 1000, 150, and 200 cycles. The reversible manganese oxidation/reduction reaction on the carbon/MnO 2  composites increases the cycle life of the zinc ion battery. 
         [0034]    The synthesis of carbon nanotube/MnO 2  composites is shown in below. A 0.1 mol/L KMnO 4  aqueous solution was prepared by dissolving KMnO 4  (AR, 99%) in deionized water. An AOT/isooctane solution was prepared by adding 66.6 g surfactant of high purity sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT) to 1500 mL isooctane and stirring them well. 81 mL of 0.1 mol/L KMnO 4  aqueous solution was then added in the AOT/isooctane solution, and 0.1244 g carbon nanotube was added into this mixture solution. Then it was ultrasound for 30 min to obtain a dark brown precipitate. The deposit was separated, washed with deionized water and ethanol several times, and dried at 90° C. for 12 h. 
         [0035]    The electrode composing of carbon nanotube /MnO 2  composites is fabricated as following. Carbon nanotube /MnO 2  composites (70%), carbon black (20%) and LA133 binder (10%) were stirred 30 min to obtain the slurry. The slurry was coated on one side of the stainless steel foil current collector, and then dried at 90° C. for 10 h under vacuum. The electrode then was cut into a round shape with a diameter of 1.5 cm. This is carbon nanotube /MnO 2  cathode. 
         [0036]    The battery test used the coin cell assembly consisting of carbon nanotube/MnO 2  electrode as cathode and zinc film (20 μm in thickness) as anode. A glass paper was used as the separator. The electrolyte is 1 M ZnSO 4  and 1 M MnSO 4  aqueous solution. This cell was denoted as Cell 4. The discharge and charge curves of Cell 4 are shown in  FIG. 5  at a current density of 0.1 A g −1  (based on the positive active mass). The capacity of this battery is over 1935 mAh g −1 . During cycling the coloumbic efficiency of such battery is close to 100%.