LOW COST RECHARGEABLE BATTERY AND THE METHOD FOR MAKING THE SAME

Abstract

Low-cost electrochemical energy storage devices having electrochemical cells containing zinc electrodes in aqueous electrolytes, which exhibit superior cycle performance, preferably comprise the following elements: (a) a cathode formed of manganese dioxide particles, preferably doped with at least one of magnesium, strontium, barium, calcium, and lanthanum, wherein the manganese dioxide particles preferably form at least one of (1) a delta manganese dioxide structure and (2) a todokorite manganese dioxide structure; (b) an anode formed of particles comprising zinc, wherein the particles are preferably treated with at least one of bismuth, indium, gallium, antimony, and tin; (c) a mixed ion electrolyte solution with a pH greater than or equal to three and less than or equal to seven, wherein the solution preferably comprises at least one monovalent salt and at least one divalent salt; and (d) a mesh as cathode current collector comprising at least one of titanium, stainless steel, tantalum, and niobium, wherein the mesh is preferably coated by an electrically conductive and yet oxidation resistant material comprising but not limited to carbon.

Claims

1. An electrochemical cell, comprising: a cathode formed of at least one of: manganese dioxide; and manganese dioxide modified by at least one of magnesium, strontium, barium, calcium, and lanthanum; an anode formed of particles comprising zinc, wherein the particles are modified by at least one of bismuth, indium, gallium, antimony, and tin; a mixed ion electrolyte solution with a pH ranging from 3 to 7, wherein the solution comprises both monovalent salts and divalent salts; and a mesh current collector for the cathode comprising at least one of titanium, stainless steel, tantalum, and niobium, wherein the member is coated in an electrically conductive and yet oxidation resistant material comprising carbon.

2. The electrochemical cell of claim 1, wherein the manganese dioxide cathode forms at least one of: a delta manganese dioxide structure; and a todokorite manganese dioxide structure.

3. The electrochemical cell of claim 2, wherein the manganese dioxide cathode is modified with a metal.

4. The electrochemical cell of claim 3 wherein the metal is selected from the group consisting of magnesium, strontium, barium, calcium, and lanthanum.

5. An electrochemical cell, comprising: a cathode formed, at least in part, of manganese dioxide; and an anode formed, at least in part, of zinc; wherein the zinc is modified by a first metal.

6. The electrochemical cell of claim 5, wherein manganese dioxide is modified by a second metal.

7. The electrochemical cell of claim 6, wherein the second metal comprises at least one of magnesium, strontium, barium, calcium, and lanthanum.

8. The electrochemical cell of claim 5, further comprising an electrolyte solution with a pH ranging from 3 to 7.

9. The electrochemical cell of claim 8, wherein the electrolyte solution comprises both monovalent salts and divalent salts.

10. The electrochemical cell of claim 5, further comprising a current collector, coupled to the cathode, coated with electrically conductive and yet oxidation resistant material.

11. The electrochemical cell of claim 10, wherein the current collector is a mesh comprising at least one of titanium, stainless steel, tantalum, and niobium.

12. The electrochemical cell of claim 5, wherein the first metal comprises at least one of bismuth, indium, gallium, antimony and tin.

13. The electrochemical cell of claim 5, further comprising an electrolyte solution with a pH ranging from 3 to 7.

14. The electrochemical cell of claim 13, wherein the electrolyte solution comprises both monovalent salts and divalent salts.

15. The electrochemical cell of claim 13, further comprising a current collector, coupled to the cathode, coated with electrically conductive and yet oxidation resistant material.

16. The electrochemical cell of claim 15, wherein the current collector is a mesh comprising at least one of titanium, stainless steel, tantalum, and niobium.

17. The electrochemical cell of claim 5, wherein the manganese dioxide forms at least one of a todokorite manganese dioxide structure and a delta manganese dioxide structure.

18. The electrochemical cell of claim 17, wherein the first metal comprises at least one of bismuth, indium, gallium, antimony and tin.

19. The electrochemical cell of claim 17, further comprising a mixed ion electrolyte solution with a pH ranging from 3 to 7.

20. The electrochemical cell of claim 19, further comprising a current collector, coupled to the cathode, coated with electrically conductive and yet oxidation resistant material.

21. The electrochemical cell of claim 20, wherein the current collector is a mesh comprising at least one of titanium, stainless steel, tantalum, and niobium.

22. The electrochemical cell of claim 17, wherein the manganese dioxide is modified by a second metal.

23. The electrochemical cell of claim 22, wherein the second metal comprises at least one of magnesium, strontium, barium, calcium, and lanthanum.

24. The electrochemical cell of claim 22, further comprising a mixed ion electrolyte solution with a pH ranging from 3 to 7.

25. The electrochemical cell of claim 24, further comprising a current collector, coupled to the cathode, coated with electrically conductive and yet oxidation resistant material.

26. The electrochemical cell of claim 25, wherein the current collector is a mesh comprising at least one of titanium, stainless steel, tantalum, and niobium.

27. An electrochemical cell, comprising: a cathode comprising manganese dioxide; an anode comprising zinc; and a mixed ion electrolyte solution with a pH ranging from 3 to 7, wherein the solution comprises both monovalent salts and divalent salts.

28. The electrochemical cell of claim 27, wherein the monovalent salt comprises at least one of lithium, sodium, potassium, ammonium, rubidium and cesium.

29. The electrochemical cell of claim 28, wherein the divalent salt comprises at least one of zinc, manganese, barium, and magnesium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] This invention may be more readily understood by reference to the following drawings wherein:

[0032] FIGS. 1A and 1B are transmission electron microscope images of various structures of manganese dioxide.

[0033] FIG. 2 is a graph showing Cyclic Voltammetries (CVs) of ZnO electrodes with and without Bi treatment.

[0034] FIG. 3 shows the long-term cycling performance of an electrochemical cell made with Mg doped δ-MnO.sub.2 and Bi treated Zinc electrodes.

[0035] FIG. 4 shows the long-term cycling performance of an electrochemical cell made with Mg doped δ-MnO.sub.2 electrode with graphite coated Ti mesh current collector and Bi treated Zinc electrode.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present disclosed concepts may take form in various components and arrangements of components, and in various techniques, methods, or procedures and arrangements of steps. The referenced drawings are only for the purpose of illustrated embodiments, and are not to be construed as limiting the present invention. Various inventive features are described below that can each be used independently of one another or in combination with other features. Furthermore, as used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

[0037] FIGS. 1A and 1B are transmission electron microscope images of various structures of manganese dioxide. FIG. 1A is a transmission electron microscope image of a magnesium doped delta-manganese dioxide crystalline structure. Typically, delta-manganese dioxide is a poorly organized, densely packed crystalline structure having small tunnels, which generally make it difficult for particles, such as zinc, to intercalate into when used in a rechargeable battery. As a result, persons of ordinary skill in the art often overlook this structure as a potential material in a manganese dioxide electrode. However, as shown in FIG. 1A, magnesium doped delta-manganese dioxide exhibits a considerably well organized, large tunnel, yet densely packed structure, having tunnels large enough for the intercalation of ions within the structure, while being densely packed enough to allow reactivity of the ions within the structure. As a result, magnesium doped delta-manganese dioxide has shown great success for use in rechargeable electrochemical cells that utilize the intercalation of zinc ions during charge and discharge.

[0038] FIG. 1B is a transmission electron microscope image of an alpha-manganese dioxide crystalline structure. Without metal doping, in contrast to the delta-manganese dioxide structure, an alpha-manganese dioxide structure contains considerably larger tunnels allowing for greater intercalation of zinc in a rechargeable battery. As a result, alpha-manganese dioxide has attracted considerably more attention for use as electrode material in rechargeable batteries. Conversely, however, the metal doped structure of delta-manganese dioxide has proven to be considerably better than alpha-manganese dioxide under substantially identical circumstances.

[0039] Thus, metal doping has been shown to yield unpredictable results in the value each of the various structures of manganese dioxide. When manganese dioxide is doped with one or more metals, different structures have proven to exhibit considerably improved performance in various electrochemical cells, including rechargeable zinc batteries.

TABLE-US-00001 TABLE 1 Summary of synthesized MnO.sub.2 with different phase structures Sample # ID Reactants & Products 1 120513-1 δ (or amo)- 8 KMnO.sub.4 + C.sub.6H.sub.12O.sub.6 (glucose) Mn.sub.2 2 120913-1 α-MnO.sub.2 2KMnO.sub.4 + 3MnSO.sub.4 + 2H.sub.2O + HAc 3 121013-1 δ (or amo)- KMnO.sub.4 + C.sub.3H.sub.5(OH).sub.3 (glycerol) MnO.sub.2 4 121113-1 β-MnO.sub.2 2MnSO.sub.4 + 4KOH + O.sub.2 5 121913-1 α-MnO.sub.2 2Mn(NO.sub.3).sub.2 + 3NaOH + (NH.sub.4).sub.2S.sub.2O.sub.8 6 121913-2 α-MnO.sub.2 2Mn(Ac).sub.2 + 4NaOH + (NH.sub.4).sub.2S.sub.2O.sub.8 7 121913-3 Todorokite- 2MnSO.sub.4 + 4NaOH + (NH.sub.4).sub.2S.sub.2O.sub.8 + MnO.sub.2 MgSO.sub.4 8 122313-1 α-MnO.sub.2 2Mn(NO.sub.3).sub.2 + 3NaOH +(NH.sub.4).sub.2S.sub.2O.sub.8 9 122413-1 Todorokite- 2MnSO.sub.4 + 4NaOH + (NH.sub.4).sub.2S.sub.2O.sub.8 + MnO.sub.2 MgSO.sub.4 10 122713-1 Todorokite- KMnO.sub.4 + C.sub.3H.sub.5(OH).sub.3 (glycerol) + MnO.sub.2 MgSO.sub.4 11 123113-1 Todorokite- 2MnSO.sub.4 + 4KOH + (NH.sub.4).sub.2S.sub.2O.sub.8 + MnO.sub.2 MgSO.sub.4 12 010814-1 α-MnO.sub.2 2KMnO.sub.4 + 3MnSO.sub.4 +2H.sub.2O 13 010814-3 amorphous- 2KMnO.sub.4 + i-PrOH MnO.sub.2 14 010814-4 amorphous- 2KMnO.sub.4 + oxalic acid + 2H.sub.2O MnO.sub.2 15 011014-1 Zn doped MnSO.sub.4 + 2KMnO.sub.4 + 3MnSO.sub.4 + α-MnO.sub.2 2H.sub.2O 16 011314-1 Bi doped Bi(NO.sub.3).sub.3 + 2KMnO.sub.4 + 3MnSO.sub.4 + α-MnO.sub.2 2H.sub.2O 17 011614-1 Bi doped Bi(ac).sub.3 + HAc + 2KMnO.sub.4 + PrOH + α-MnO.sub.2 2H.sub.2O

[0040] Different types of manganese dioxide (MnO.sub.2) materials (Table 1), including, but not limited to, alpha (α)-; beta (β-), delta (δ-), amorphous (amo-), and todorokite (Tod-) phase manganese dioxide may be prepared according to methods known in the art. The phase and particle size of the materials may be checked using x-ray diffraction (XRD) and transmission electron microscopy (TEM).

[0041] Since Mg doped Tod-MnO.sub.2 has shown excellent specific capacity, its preparation method is briefly described. Mg doped Tod-MnO.sub.2 was prepared by two-step method by combining synthesis technique for making poorly crystallized layered δ-MnO.sub.2 and Tod-MnO.sub.2. Briefly, δ-MnO.sub.2 was first prepared by reduction of KMnO.sub.4 with glycerol in aqueous solution and stirred for 2 hours. The δ-MnO.sub.2 was ion-changed with Mg (II) ion by centrifuge separation and addition of 1M MgSO.sub.4 solution and stirring for 12 hours. δ-MnO.sub.2 was then turned into Mg doped Tod-MnO.sub.2 by transferring the δ-MnO.sub.2 slurry into a Teflon-lined stainless steel autoclave, and being heated in oven at 180° C. for another 12 hours. After cooling, the product was washed three times with distilled water and one time with iso-propanol, finally dried in an oven at 75° C. for overnight. The dry powder is then collected for use.

[0042] As shown in FIGS. 1A and 1B, δ-MnO.sub.2 contains most of nano-needles with an average width of ˜7 nm and length of ˜200 nm, while α-MnO.sub.2 mainly consists of nano-needle with a diameter of ˜10-12 nm and a length of 200-300 nm. A metal doped MnO.sub.2-based metal oxide cathode can be depicted with the molecular formula Mn.sub.1-xM.sub.xO.sub.2, where the dopant M can be, for instance, Mg, Sr, Ba, Ca, La or mixture; MnO.sub.2 base can be, for instance, α, β, δ or Todorokite phase structure. Further, the dopant amount x can have many concentrations, including, but not limited to from 0 to 0.3; with 0 to 0.1 being the optimum concentration. Mg, Sr, Ba, Ca, La or mixed thereof doped δ-MnO.sub.2 or doped. Todorokite MnO.sub.2; can have multiple dopant percentages, including, but not limited to, from 0.01 percent to 30 percent; with 5 to 10 percent the optimum percentage.

[0043] Thus, in an embodiment, the electrochemical cell includes a cathode. In an embodiment, the cathode is formed of manganese dioxide particles. Persons of ordinary skill in the art will understand that manganese dioxide can exist in various crystalline structures, including, but not limited to alpha manganese dioxide, beta manganese dioxide, delta manganese dioxide, amorphous manganese dioxide, and todokorite manganese dioxide. Accordingly, in an embodiment, the cathode is formed of alpha-manganese dioxide. In another embodiment, the cathode is formed of beta manganese dioxide. In yet another embodiment, the cathode is formed of delta manganese dioxide. In another embodiment, the cathode is formed of amorphous manganese dioxide. In another embodiment, the cathode is formed of todokorite-manganese dioxide

[0044] In various embodiments of the invention, the manganese dioxide particles are not doped or doped with one or more metals. For instance, in an embodiment, the manganese dioxide particles are doped with magnesium, strontium, barium, calcium, and lanthanum, among other metals. For instance, cathodes formed of magnesium doped delta-manganese dioxide are shown to have a very high specific capacity, making such cathodes highly desirable for use in zinc rechargeable batteries.

Mixed Ion Electrolyte

[0045] Both the phase of active cathode materials and electrolyte formulation can affect the electrode specific capacity and cycle stability. For instance, in a cathode containing α-MnO.sub.2 active material, the specific capacity of the active material may be only about 150 mAh/g-MnO.sub.2, which is consistent with prior data as listed in U.S. patent application 2012/0034515 A1. In 1 M MgSO.sub.4 electrolyte, the specific capacity of the electrode dropped quickly to 113 mAh/g-MnO.sub.2 after a 5th cycle,

[0046] On the other hand, δ-MnO.sub.2, Mg-doped δ-MnO.sub.2 and Mg-doped Tod-MnO.sub.2 have exhibited stable specific capacity of 180 mAh/g, 180 mAh/g and 200 mAh/g respectively in 1 M MgSO.sub.4 electrolyte.

[0047] By using mixed monovalent and divalent salt electrolyte containing 1 M MgSO.sub.4 1 M Li.sub.2SO.sub.40.7 M ZnSO.sub.4 and 0.3 M MnSO.sub.4, both δ-MnO.sub.2 and Mg-doped δ-MnO.sub.2 demonstrated stable specific capacity as high as 300 mAh/g. While not to be bounded by theory, it appears that mixed ion intercalation into the structure of MnO.sub.2 stabilizes the material structure during cycling.

[0048] Hence, in various embodiments of this invention, an electrochemical cell may include an aqueous electrolyte solution containing mixed monovalent and divalent ions salts. In an embodiment, monovalent ions, including but not limited to lithium, sodium, potassium, or caesium form various salts in the solution, including, but not limited to, lithium sulfate, sodium sulfate, potassium sulfate, or caesium sulfate. Divalent salts containing magnesium, zinc, and manganese, such as but not limited to, magnesium sulfate, zinc sulfate, and manganese sulfate, can stabilize electrode cycle performance.

Metal-Modification for Zinc Electrode

[0049] In various embodiments of the invention, a metal-doped zinc electrode is disclosed. In an embodiment, the electrode is an anode that includes zinc particles modified by one or more metals. Such metals can include, but are not limited to, bismuth, indium, aluminum, and tin.

[0050] The metal-doped zinc electrode can be formed in various configurations and structures in accordance with various embodiments. For instance, in an embodiment, the electrode may be formed of electroplated zinc. In another embodiment, the electrode may be formed of zinc powder, zinc alloy powder, and zinc oxide.

[0051] In many instances, zinc-based cells fail because the charging voltage reaches their limit (2.2 V). Surprisingly, cells made with used zinc electrode and new MnO.sub.2 do not work well, while cells made with used MnO.sub.2 electrode and new zinc electrode can continue to cycle. Also, white precipitation on the zinc electrode, which is likely ZnO, plays a role in reduced cycle stability. This leads to the conclusion that due to the hydrogen evolution and resulting pH change of the electrolyte, zinc ions deposit as ZnO on the zinc electrode. Such ZnO can hardly be charged back to zinc in the subsequent charging process, which could lead to the early cell failure.

[0052] While not bounded by theory, the metal modified Zn electrode can dramatically improve the reversibility in electrolyte with pH ranging from 3 to 7.

[0053] FIG. 2 is a cyclic voltammetry (CV graph showing current versus voltage) of ZnO electrodes with and without Bi treatment. During the discharge process of the battery, small amount of Zn ions will be converted to ZnO via the side reaction. As shown in FIG. 2, as voltage is increasingly applied to a ZnO electrode, there is little change in current. Further, it does not change over time. For instance, at cycle 1, ZnO exhibits a nearly identical lack of reactivity as it does at cycle 5. Therefore, the electrochemical activity of the Zn electrode in the battery decreases cycle-by-cycle.

[0054] In contrast, bismuth treated ZnO (Bi—ZnO) exhibits a considerably high degree of activity. Although the ZnO formed during discharge process, it can be charged back to Zn when Bi exists. Notably, after 50 cycles, Bi—ZnO is able to maintain activity at a high level and to a nearly identical extent as at cycle 1. These results have led to the conclusion that metal modified ZnO particles, particularly particles treated with bismuth, allow for a drastically increased cycle life, cycle stability, and specific capacity.

[0055] As shown in the CV study (FIG. 2), it is clear that ZnO is highly irreversible in neutral electrolyte while ZnO electrode treated Bi solution showed excellent reversibility in the neutral electrolyte. In an embodiment, the ZnO is treated with one or more metals, such as, for instance, bismuth.

[0056] For the Bi treatment, Zn electrodes were quickly immersed into a diluted Bi(NO.sub.3).sub.2 solution and then dried in the oven.

[0057] As shown FIGS. 3 and 4, the cell made of Mg doped δ-MnO.sub.2 and Bi treated zinc electrode demonstrates fast charging rates and very long cycle numbers (over 1200 cycles). In comparison, the cells made with Mg doped δ-MnO.sub.02 and conventional zinc electrode exhibit less than 50 cycles even with mixed ion electrolyte.

Conductive Material Coated Metal Mesh as a Current Collector

[0058] In accordance with various embodiments of the invention, a metal member may be used as a current collector. In various embodiments, the metal member may include titanium, stainless steel, and/or niobium. Thus, in an embodiment, the metal member is coupled to an electrode. For instance, the metal member may be coupled to the cathode. To increase the electrochemical stability, an electrically conductive material may be coated onto the metal member. In another embodiment, the structure of the metal member may be in the form of a mesh. The conductive material may be made of carbon materials, including, but not limited to, graphite and carbon black. In another embodiment, the conductive material may include, but not be limited to, titanium suboxide, metal nitride, and metal carbide.

[0059] In various embodiments, the electrically conductive material is a conductive ink. The conductive ink may be formed of an electrically conductive material, one or more polymer binders, including, but not limited to, thermoplastics such as polyvinylidene fluoride (PVDF) and polyamide-imides (Torlon) and various solvents, such as, but not limited to, n-methyl-2-pyrrolidone (NMP), dimethylformamide, and dimethyl sulfoxide. In various embodiments, the conductive ink is sprayed, painted, or otherwise incorporated onto the mesh, which is coupled to the electrode.

[0060] In the prototype development effort, it was recognized that current collector development for the MnO.sub.2 electrode is of great importance. An ideal current collector should: 1) have high electric conductivity; 2) be capable of high material loading; 3) be oxidation resistant; and 4) have high oxygen evolution over-potential. Metal meshes, which were widely used in the alkaline systems, could be a solution. However, many of them cannot meet the above requirements. The cells with Ti mesh exhibited increasing resistance and charging voltage. In this invention, we have successfully developed carbon (e.g. graphite) coated metal mesh (e.g. Ti, stainless steel) as the current collector for MnO.sub.2 electrode. Specifically, carbon (e.g. graphite power or carbon black) is mixed with polymer binders (e.g. PVDF or Torlon) in NMP solvent to form an ink. The mesh is then coated with brush or any other means known in the art with the ink. After drying in the oven, a thin conductive layer can be formed on the surface of the metal current collector, which can meet the requirements for ideal current collector.

[0061] The cells assembled with the cathode containing graphite ink coated Ti mesh current collector acid Bi treated zinc electrode has demonstrated over 4000 cycles (FIG. 4). In comparison, the cell with the same cathode containing stainless steel 304 mesh as current collector can only cycle for less than 10 cycles; while the cell with the same cathode containing titanium mesh current collector can only cycle for less than 50 cycles. Further, as compared with carbon cloth current collector, the coated mesh current collector has much lower cost and can be pressed at high compact pressure.

[0062] Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.