WO2022077058A1

WO2022077058A1 - Multi-chamber rechargeable zinc manganese dioxide battery

Info

Publication number: WO2022077058A1
Application number: PCT/AU2021/051193
Authority: WO
Inventors: Rose Mendoza
Original assignee: Sendai Holdings Pty Ltd
Current assignee: Sendai Holdings Pty Ltd
Priority date: 2020-10-14
Filing date: 2021-10-13
Publication date: 2022-04-21
Anticipated expiration: 2023-04-14

Abstract

A rechargeable zinc manganese dioxide battery with a manganese dioxide cathode and zinc anode with a water-based aqueous electrolyte. The embodiment is an aqueous secondary rechargeable zinc manganese dioxide battery that utilizes an aqueous acidic,alkaline and neutral electrolyte for the cathodic, anodic and electrolyte chambers,respectively. The embodiment also utilizes ion exchange membranes to isolate the cathodic, anodic and electrolyte compartments effectively addressing the persistent dendrite formation in zinc manganese dioxide systems which negatively affects its efficiency and capacity.

Description

MULTI-CHAMBER RECHARGEABLE ZINC MANGANESE DIOXIDE BATTERY

FIELD OF THE INVENTION

[0001] The present invention relates to a multi-chamber rechargeable zinc manganese dioxide battery with a manganese dioxide cathode and zinc anode with a water-based aqueous electrolyte.

BACKGROUND TO THE INVENTION

[0002] The electrochemical performance and cyclability of zinc ion batteries are highly dependent on the stability and reversibility of the reaction occurring in both anode and cathode. During discharge, the zinc metal oxidizes into Zn2+ and dissolves in the electrolyte. The Zn2+ in the electrolyte travels towards the cathode and inserts itself into the cathode layer. This process is formally known as “zinc intercalation”. The amount of zinc intercalation, on the other hand, was found to be affected by the surface morphology of the cathode. During discharge, the zinc interacted into the cathode must leave the cathode (zinc de-intercalation) and travel back to the anode and is then reduced into Zn metal again. This process is reversible and takes place until the cathode is exhausted [N. Zhang, Y. Dong, Y. Wang, Y. Wang, J. Li, J. Xu, Y. Liu, L. Jiao, and F. Cheng. ACS Appl. Mater. Interfaces, 2019, 11 , 32978-32986]. During charging, the structure of the cathode MnO2 transform into several phases: (1 ) spinellike trivalent (Mn3+) phase (ZnMn2O4), (2) a layered divalent (Mn2+) phase (ZnxMnO2), and the (3) tunnel-type Mn phase (ZnxMnO2) which takes charge of the efficient intercalation-deintercalation process. The mutual conversion process of Mn4+, Mn3+, Mn2+ dictates the conversion of chemical energy to electrical energy.

[0003] In applications using zinc manganese dioxide batteries zinc-dendrite formation is one of the most significant phenomena that are threatening the efficiency and capacity of the battery. Dendritic growth is a product of the repeated charge and discharge cycles of the battery. When the battery is in a state of discharge, zinc dissolves unevenly due to the irregularities and small differences in the surface of the zinc anode. This makes the zinc anode rougher increasing irregularities during charge and discharge cycles, to the extent of deforming the electrode. During charging, zinc deposits grows into a tree-branch-like or spike-like structures called dendrites. These dendrites continuously grow through the repeated charge and discharge cycles, then ultimately pierces the separators which allows electrolyte leakage into the cathode which inevitably eventually results in internal short circuiting. This catastrophic reaction of the cathodic materials and the electrolyte causes H2 gas generation and typically results in electrolyte exhaustion, which speeds up electrode polarization.

[0004] Some methods used to address the main problem on dendritic formation is the use of alloys of homogeneous mixtures of various metal and zinc (US Patent No. 5034291 A), the use of zinc oxides and improved particle size and surface function [Duan, J.X., Xiong, X., Hu, J.H. and Wang,, H., Journal of Power and Energy Engineering, 3, 11-18] and the use of combinations of electrolytes solutions [D. Chao, W. Zhou, C. Ye, Q. Zhang, Y. Chen, L. Gu, K. Davey, S.-Z. Qiao, Angew. Chem. Int. Ed. 2019, 58, 7823] as well as electrolyte additives (PCT Application No. CA98/00627 WO 99/00861 ) to enhance electrochemical reactions inside the zinc manganese dioxide battery.

[0005] The manganese dioxide cathode in a typical aqueous zinc manganese dioxide battery also poses threat to the battery performance since its surface tend to easily get deteriorated, inhibit the free mass and charge transfer and slows the rate of electrochemical reaction. As this takes place, the production of zinc-salt hydrates influences the pH of the solution, destabilizing the pH of the system and later affects the manganese dissolution decreasing manganese content of the system. With this process occurring over repeated charge and discharge cycle, the cell capacity also tends to decrease.

[0006] The zinc anode deformation, dendritic formation and growth as well as gas evolution, electrolyte exhaustion and manganese content decrease over repeated cycles threaten the reversibility of reactions and stability of the battery which must be avoided. To address these detrimental issues on zinc manganese dioxide batteries, particularly the aforementioned dendritic piercing of the separators and internal short circuiting, it is necessary to alter and enhance the cell charge and discharge mechanism and/or develop novel materials that will enhance the electrochemistry of the battery or use high strength separators capable of competing with dendrite formation.

[0007] The object of this invention is to provide a zinc manganese dioxide battery that effectively addresses the persistent dendrite formation which negatively affects its efficiency and capacity. SUMMARY OF THE INVENTION

[0008] In a first aspect the invention provides a multi-chamber rechargeable zinc manganese battery comprising 3 chambers: an anodic chamber, an electrolyte chamber, and a cathodic chamber.

[0009] Preferably the battery further provides: a zinc anode; a manganese dioxide cathode; and ion exchange membranes that selectively allow the passage of ions and that serves as separators totally isolating the anodic compartment from the cathodic compartment, wherein: the anodic chamber contains an aqueous alkaline electrolyte containing zinc ions with a pH maintained at 13 and above; the cathodic chamber contains an aqueous acidic electrolyte containing manganese ions with a pH range of 2.5 to 3.0; and the electrolyte chamber contains a neutral salt electrolyte with pH range of 6.9 to 7.4.

[0010] In preference the zinc anode comprises zinc powder and carbon nanotubes as the electrically conductive substance, and a binder, and the manganese dioxide cathode comprises manganese dioxide electrodeposited onto an activated graphite film.

[0011] Preferably the activated graphite film is composed of approximately 70% silicon dioxide, 12% carbon nanotubes, 12% graphite powder and 4% PVDF.

[0012] Preferably the sulfonic acid cation exchange membrane is placed approximately 2.5mm from the zinc anode and the quaternary ammonium anion exchange membrane is placed approximately 2.5mm from the manganese dioxide cathode.

[0013] In preference the electrolyte chamber spans approximately 1 mm between the anodic chamber and the cathodic chamber.

[0014] It should be noted that any one of the aspects mentioned above may include any of the features of any of the other aspects mentioned above and may include any of the features of any of the embodiments described below as appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows.

[0016] Figure 1 displays the actual cell assembly of the rechargeable zinc manganese dioxide battery embodiment

[0017] Figure 2 illustrates the chamber isolation mechanism of the SRU of the rechargeable zinc manganese-dioxide battery embodiment.

[0018] Figure 3 illustrates the half cell and the overall stoichiometric reactions of the rechargeable zinc manganese oxide battery.

DRAWING COMPONENTS

[0019] The drawings include the following integers.

10 rechargeable zinc manganese dioxide battery

21 negative cover plate

22 wave spring

23 graphite plate

24 zinc anode

25 alkaline (anode) chamber

26 cation exchange member

27 neutral (electrolyte) chamber,

28 anion exchange member

29 acidic (cathode) chamber

30 manganese dioxide cathode

31 graphite plate

32 positive cover plate

40 SRU (single repeating unit)

41 cations

42 anions

DETAILED DESCRIPTION OF THE INVENTION

[0020] The following detailed description of the invention refers to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Dimensions of certain parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

[0021] The purpose of the present invention relates to the reduction of the dendritic formation on existing zinc manganese dioxide batteries which will result in improved capacity and higher working and cell voltage. The use of cation and anion exchange membranes results in a zinc manganese battery made up of 3 chambers, through which the electrolyte is isolated and prevented from interacting with the cathodic and anodic electrolyte, avoiding dendrite formation and occurrence of irreversible electrochemical reactions that are detrimental to the battery, and which will negatively be impacting the battery efficiency and capacity.

[0022] The invention provides a rechargeable aqueous zinc manganese dioxide battery with the structure zinc electrode/alkaline electrolyte/ion exchange membrane/neutral electrolyte/ion exchange membrane/acidic electrolyte/manganese dioxide cathode.

[0023] The zinc anode can be prepared from pure zinc paste or powder, compressed onto an electrically conductive carbon normally by a binder on a current collector. Zinc foil or film can be used directly.

[0024] The anodic electrolyte is an alkaline liquid electrolyte composed of primary and secondary alkaline electrolyte. The primary alkaline electrolyte may include strong bases in aqueous solution such as potassium hydroxide, sodium hydroxide, copper hydroxide and silver hydroxide with a mildly basic zinc oxide solution as the secondary electrolyte.

[0025] The ion exchange membrane adjacent to the anode includes a cation exchange membrane that containing sulfonic acid anions that will selectively allow the passage of cations.

[0026] The neutral electrolyte can be sodium sulfate, potassium sulfate, copper sulfate and silver sulfate. The neutral electrolyte isolates the anodic electrolytes from the cathodic electrolytes

[0027] The ion exchange membrane adjacent to the cathode is an anionic membrane that contains quaternary ammonium cations that will selectively allow the passage of anions. [0028] The cathodic electrolyte is an acidic liquid electrolyte composed of primary and secondary acid electrolyte. The primary acid electrolyte in aqueous solution may include one or combinations of hydrochloric acid, sulfuric acid, nitric acid, boric acid and phosphoric acid solution and manganese sulfate as secondary acid electrolyte.

[0029] The cathode is composed of compressed mixture of manganese dioxide pressed into electrically conductive carbon.

[0030] The set of anion and cation exchange membranes serve as separators that will isolate the electrolyte from the anodic and cathodic compartment. The ion selectivity of the ion exchange membranes ensures that there will be cross contamination of the acidic electrolyte with the alkaline electrolyte and vice versa which will result in the formation of irreversible products that will reduce the efficiency and capacity if the battery.

[0031] The multi-chamber rechargeable zinc manganese battery can be configured as “button” or disc cell and/or rectangular cell, etc.

[0032] The battery is formed according to the full structure zinc anode/alkaline chamber/ion exchange membrane/neutral electrolyte/ion exchange membrane/acidic chamber/ manganese-dioxide cathode in the button cell configuration in Figure 1 including current collectors and backplates, with an SRU detailed in Figure 2.

[0033] Figure 1 displays the cell assembly of the rechargeable zinc manganese dioxide battery (10) according to a preferred embodiment of the invention. Utilizing the button cell configuration, conductive graphite plates (23, 31) are used as current collectors. The alkaline chamber (25), neutral chamber (27) and acidic chambers (29) are also equipped with gaskets to prevent leakage of electrolytes. The anion exchange membrane (28) and cation exchange membrane (26) isolate the three chambers from each other. The zinc anode (24), alkaline chamber (25), cationic exchange membrane (26), neutral chamber (27), anion exchange membrane (28), the acidic chamber (29) and the manganese dioxide cathode (30) define the single repeating unit (SRU) of the cell. The inner cell components are held into place using a stainless-steel wave spring (22). The inner cell structure is sealed by standard stainless-steel negative cover plate (21 ) and positive cover plate (32).

[0034] Figure 2 illustrates the chamber isolation mechanism of the SRU (40) of the rechargeable zinc manganese-dioxide battery (10). Cations (41 ) from the alkaline chamber (25) enter and exit the neutral chamber (27) via the cation exchange membrane (26). Anions (42) from the acidic chamber (29) enter and exit the neutral chamber (27) through the anion exchange membrane (28).

[0035] The zinc anode in this embodiment preferably uses 80%w zinc powder, 10%w carbon nanotubes, 10%w polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone (NMP) as the solvent. The mixture is homogenized and pressed on titanium foil as zinc electrode.

[0036] The primary alkaline electrolyte in the alkaline chamber is preferably potassium hydroxide. The concentration of the primary alkaline electrolyte is 300 g/L to 400 g/L. The concentration of the primary electrolyte is related to the pH of the solution. A decrease in the concentration range of the primary electrolyte will lower down the pH of the solution and will lower the battery voltage which will affect the degree of dissolution of the zinc electrode (24) and can accelerate anodic corrosion. A concentration range of 330 g/L to 390 g/L balances the electrolyte conductivity. The optimum concentration range of the secondary alkaline electrolyte-zinc oxide is 16 g/L to 21 g/L, these concentration range ensures that the pH of the secondary electrolyte will not reduce or increase the alkaline electrolyte pH which will cause significant reduction to the operating voltage or speeding up of anodic corrosion.

[0037] The cation exchange membrane (26) can be a sulfonic acid-based polymer membrane which includes but is not limited to Fumatech FKD, Fumatech FKS, Nation 117, Neosepta CM-1 and PCCell PC-SK. Fumatech FKD is preferred due to its capability to withstand alkaline dialysis, lower area resistance and higher ion exchange capacity.

[0038] The cation exchange membrane (26) will ensure that hydroxides from the alkaline chamber (25) will never interact with the substances in the electrolyte acidic chamber (29). At an optimal distance from the anode the cations will adequately transit to the electrolyte chamber (27) balancing its pH and maintaining electrolyte efficient cathodic and anodic electrochemistry. Thus, preventing the admixing of the neutral electrolyte (27) and that of the alkaline electrolyte (25) as illustrated in Figure 2. When the membrane is too far from the anode, internal resistance of the cell becomes higher due to thicker cell geometry. When the membrane is too close to the anode the rate of ion exchange and the migration of ions are increased which can cause membrane polarization, increasing current requirement and affecting the capacity and stability of the battery.

[0039] The neutral electrolyte in this embodiment is potassium sulfate in optimum concentration range of 17 g/L to 25 g/L. The pH of the electrolyte is maintained near neutral to prevent changes in pH that might affect the battery voltage and capacity.

[0040] The anion exchange membrane in this embodiment can be Fumatech FAS, FAD, Neosepta AM-1 , AFN and PC Cell - SA. Preferably, the battery in this embodiment uses Fumatech FAD which is an anion membrane with minimal thickness, low area resistance and high ion exchange capacity. The anion exchange membrane will only allow the passage of positive ions that will react with the negative ions transiting from the anodic chamber, which chemically balances the pH of the electrolyte and the system. The anion exchange membrane is placed at an optimum distance from the cathode to maintain efficient electrochemical reactions. Should the anionic membrane be too far from the cathode, the cell geometry becomes thicker and internal cell resistance becomes higher. Conversely, should the membrane be too near to the cathode, the distance for the transport of ions becomes shorter, thus allowing faster polarization of the membrane which increases cell resistance and at the same time varies the pH of the neutral electrolyte affecting cell efficiency and capacity.

[0041] The concentration of the acidic electrolyte, sulfuric acid is 200 g/L to 400 g/L. To achieve proper acidity of the acid electrolyte, the concentration of the acidic electrolyte must be maintained at a pH range of 2.5 to 3.0. Decreasing the pH of the acidic electrolyte further will affect the rate of dissolution of manganese oxide which in turn will result in low electrolyte conductivity, impending molecular motion. The changes in the rate of chemical reaction in the cathode will impact greatly the cell voltage and capacity.

[0042] To ensure that the acidic electrolyte performs optimally, a concentration range of 300 g/L to 350 g/L is required. The secondary electrolyte is preferably manganese sulfate at an optimum concentration range of 15 g/L to 25 g/L.

[0043] The manganese dioxide for this embodiment is preferably from manganese sulfate monohydrate electrodeposited onto conductive activated graphite film. The carbon slurry is prepared using 70%w silicon dioxide, 12%w carbon nanotubes (CNT), 12%w graphite powder, 4%w PVDF using NMP as the solvent and coated on graphite paper; and then dried at 80°C for 2 hours to remove NMP and other volatile impurities. The resulting film is then immersed in 10%w hydrofluoric acid to remove the silicon dioxide, washed with deionized water several times then dried at 80°C for 2 hours. This is called the activated graphite film.

[0044] The manganese dioxide cathode is prepared by the electrodeposition using equal amounts of manganese sulfate monohydrate and sulfuric acid which is at most 30% of the final solution, and using the activated graphite film as the working and counter electrode. A fixed cell voltage of 2.5V over a period of 28 minutes is used. The anode sheet is then removed from the cell, washed with deionized water and dried at 80°C for 6 hours.

[0045] The theoretical energy density of the zinc manganese dioxide battery embodiment utilizing the overall electrochemical reaction in Figure 3 is approximately 768.79 Wh kg^-1 of active electrode (cathode and anode) mass, calculated based on a 2- electron transfer mechanism for the manganese dioxide cathode [D. Chao, W. Zhou, C. Ye, Q. Zhang, Y. Chen, L. Gu, K. Davey, S.-Z. Qiao, Angew. Chem. Int. Ed. 2019, 58, 7823]. The theoretical energy density of the anode and the cathode is determined based on an approximation model [J. Shin, J-K Seo, R. Yaylian, A. Huang & Y-S. Meng, International Materials Reviews 2019] utilizing the amounts of zinc anode and manganese dioxide used and their theoretical capacity.

[0046] The rechargeable zinc manganese dioxide battery has a high theoretical voltage of 2.43V which sets the optimal voltage window at 2.5V to 2.7V.

[0047] The reader will now appreciate the present invention which provides a zinc manganese dioxide battery that effectively addresses the persistent dendrite formation which negatively affects its efficiency and capacity.

[0048] Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in this field. [0049] In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

Claims

1 . A multi-chamber rechargeable zinc manganese battery comprising 3 chambers: an anodic chamber, an electrolyte chamber, and a cathodic chamber.

2. A battery as in claim 1 further comprising: a zinc anode; a manganese dioxide cathode; and ion exchange membranes that selectively allow the passage of ions and that serves as separators totally isolating the anodic compartment from the cathodic compartment, wherein: the anodic chamber contains an aqueous alkaline electrolyte containing zinc ions with a pH maintained at 13 and above; the cathodic chamber contains an aqueous acidic electrolyte containing manganese ions with a pH range of 2.5 to 3.0; and the electrolyte chamber contains a neutral salt electrolyte with pH range of 6.9 to 7.4.

3. A battery as in claim 2, wherein the zinc anode comprises zinc powder and carbon nanotubes as the electrically conductive substance, and a binder.

4. A battery as in claim 2, wherein the manganese dioxide cathode comprises manganese dioxide electrodeposited onto an activated graphite film.

5. A battery as in claim 2, wherein the activated graphite film is composed of approximately 70% silicon dioxide, 12% carbon nanotubes, 12% graphite powder and 4% PVDF.

6. A battery as in claim 2, wherein the sulfonic acid cation exchange membrane is placed approximately 2.5mm from the zinc anode.

7. A battery as in claim 2, wherein the quaternary ammonium anion exchange membrane is placed approximately 2.5mm from the manganese dioxide cathode.

8. A battery as in claim 2, wherein the electrolyte chamber spans approximately

1 mm between the anodic chamber and the cathodic chamber.