KR20230056935A - Zn-MnO2 Secondary Cell Comprising hydrophilic Carbon Coated Separator - Google Patents

Abstract

The present invention relates to a zinc-manganese dioxide secondary battery including a hydrophilic carbon coating as a separator. The invention relates to the zinc-manganese dioxide secondary battery, comprising: a cathode containing zinc; an anode containing manganese dioxide; and a separator between the cathode and the anode. The separator includes a porous substrate and a carbon coating layer coated on the surface of the porous substrate, the carbon coating layer includes carbon powder and a binder, and the carbon powder includes at least one hydrophilic functional group including C=O, O-C=O, C-O, O-H, -NO_2, O-NO_2, and C-OH on the surface. Accordingly, the present invention can provide a zinc-manganese dioxide battery with a separator structure which reactivates eluted manganese ions to suppress active material loss and improve battery capacity and lifespan.

Description

Zinc-manganese dioxide secondary battery containing hydrophilic carbon coating as a separator {Zn-MnO2 Secondary Cell Comprising hydrophilic Carbon Coated Separator}

The present invention relates to a zinc - manganese dioxide secondary battery, and more particularly, to a zinc - manganese dioxide secondary battery including a hydrophilic carbon coating as a separator.

As the global climate change problem emerges, there is a movement to reduce fossil fuels, and accordingly, an energy storage system (ESS) is attracting attention to efficiently use electrical energy. Lithium ion batteries have been mainly used as batteries for ESS, but due to the nature of using oil-based electrolytes, recent explosions and fire accidents occur frequently. For this reason, in order to increase stability, a battery using an inexpensive Zn-based aqueous electrolyte solution is being developed.

A Zn-MnO ₂ battery is one of the most promising battery candidates for ESS. However, there is a problem in that understanding of the driving mechanism of the battery is not complete, and Mn ²⁺ ions are eluted during charging and discharging, resulting in loss of active material and thus reduction in lifespan. In addition, the Zn sulfate formed on the surface of the electrode cannot be properly removed, resulting in a decrease in lifespan due to an increase in resistance.

Conventionally, in order to solve these problems, research has been conducted from the viewpoint of cathode materials or electrolytes, and there is no approach from the viewpoint of separators.

(1) KR 10-2191807 B

In order to solve the problems of the prior art, an object of the present invention is to provide a zinc-manganese dioxide battery having a separator structure that suppresses active material loss.

In addition, an object of the present invention is to provide a zinc-manganese dioxide battery having a separator structure that is used as an active site for Mn ions eluted in an electrolyte and can promote the decomposition of Zn sulfate generated during a discharge process.

In addition, an object of the present invention is to provide a method for manufacturing a separator of the above-described zinc-manganese dioxide battery.

In order to achieve the above technical problem, the present invention provides a zinc-manganese dioxide secondary battery including a negative electrode containing zinc, a positive electrode containing manganese dioxide, and a separator between the negative electrode and the positive electrode, wherein the separator includes a porous substrate and the porous substrate It includes a carbon coating layer coated on a surface, wherein the carbon coating layer includes carbon powder and a binder, and the carbon powder has C=O, OC=O, CO, OH, -NO ₂ , O-NO ₂ , and It provides a zinc-manganese dioxide secondary battery characterized in that it comprises at least one hydrophilic functional group containing C-OH.

In the present invention, the hydrophilic functional group of the carbon powder is preferably formed by acid treatment.

In order to achieve the above other technical problem, the present invention provides a method for manufacturing a zinc-manganese dioxide secondary battery, comprising the steps of acid-treating carbon powder; preparing a coating slurry containing acid-treated carbon powder and a binder; and coating the slurry on the pore channels of the porous substrate of the separator. In this case, the porous substrate may include glass fibers.

In addition, the acid treatment step is preferably performed by supporting the carbon powder in a mixed aqueous solution of sulfuric acid and nitric acid.

In the present invention, the pH of the mixed aqueous solution is 0.1 to 2 It is desirable to be In addition, at this time, the acid treatment is 2 It is preferable to perform over time.

In order to achieve the above another technical problem, the present invention provides a method for manufacturing a zinc-manganese dioxide secondary battery, comprising the steps of acid-treating carbon powder; Preparing a coating slurry containing an acid-treated porous substrate, carbon powder and a binder; and coating the slurry on one surface of the separator.

According to the present invention, it is possible to provide a zinc-manganese dioxide battery having a separator structure that reactivates eluted manganese ions to suppress active material loss and to improve battery capacity and life.

In addition, the present invention can provide a zinc-manganese dioxide battery that is used as an active site for Mn ions eluted in an electrolyte and promotes the decomposition of Zn sulfate generated during a discharge process to increase battery capacity and battery life.

1 is a view schematically showing the structure of a zinc-manganese dioxide secondary battery according to an embodiment of the present invention.
Figure 2 is a photograph of observing the dispersion state (Acid-C) of the powder in the electrolyte according to an embodiment of the present invention.
3a and 3b are graphs showing XPS analysis results for aSP powder prepared according to an embodiment of the present invention.
4 is a photograph of a wettability test result of a carbon coating layer manufactured according to an embodiment of the present invention.
5a to 5f are graphs showing the results of evaluating the electrical properties of the carbon coating layer prepared according to an embodiment of the present invention.
6a to 6f are graphs showing the results of measuring the long-term cycle characteristics of the SEM picture, surface XRD data, and long-term cycle characteristics of the cell after cycle driving of the cell to which the separator according to an embodiment of the present invention is applied.

The present invention will be described in detail by describing preferred embodiments of the present invention with reference to the following drawings.

The present invention, a problem of zinc-manganese dioxide battery, which is a problem of Mn ²⁺ ion elution problem, by introducing a carbon coating film in which a specific functional group is formed by surface treatment to the separator, reactivates the eluted manganese to contribute to improving capacity and lifespan characteristics. suggest a way to Since the present invention uses carbon activated with specific functional groups, thick electrodes can be sufficiently activated, and since carbon has conductive properties, it can be used as an active site for eluted Mn ²⁺ ions. In particular, Zn generated during the discharge process Sulfate, in particular, can promote the decomposition of zinc hydroxide sulfate (ZHS), contributing to the increase in capacity and lifespan of the battery.

1 is a view schematically showing the structure of a zinc-manganese dioxide secondary battery according to an embodiment of the present invention.

Referring to FIG. 1 , a zinc-manganese dioxide (Zn-MnO ₂ ) secondary battery 100 of the present invention includes a negative electrode 110, a positive electrode 110, a separator 130 and an electrolyte 140, and the separator 130 ), the cathode 110 and the anode 120 are disposed to face each other.

In the present invention, the positive electrode 120 includes manganese dioxide of various phases, such as α-, β-, γ-, and δ-, as an active material. The positive electrode may include a binder such as a carbon material and PVdF in addition to an active material. The anode 110 includes zinc, and for example, zinc metal or an alloy thereof may be used.

The separator includes a porous substrate and a carbon coating layer formed on a surface of the separator and/or an internal pore channel of the porous substrate.

In the present invention, a porous substrate, for example, a substrate made of a fiber material such as paper or glass fiber may be used as the substrate of the separator.

In addition, in the present invention, the separation membrane 130 includes a carbon coating layer activated to have a predetermined functional group on the surface of the pore channel formed by the porous substrate. In the present invention, the functional group on the surface of the carbon coating layer may include at least one selected from the group consisting of C=O, OC=O, CO, OH, -NO ₂ , O-NO ₂ , and C-OH.

Carbon powder constituting the carbon coating layer is Ketjen black. Carbon Nanotube, Acetylene black, Carbon black, Graphene, Graphene oxide (GO), Reduced graphene oxide (rGO), Super-P P), carbon nanofibers, and one or more types of powder selected from graphite, but is not limited thereto.

In the present invention, the carbon powder constituting the carbon coating layer may be activated by acid treatment. For example, the acid treatment may be performed by supporting the carbon material in a mixed solution of hydrochloric acid (HCl) and nitric acid (HNO ₃ ) for 2 hours or more.

In the present invention, one or two or more acids selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid may be used as the acid of the acid treatment solution. In addition, at this time, the acid concentration (pH) in the acid treatment aqueous solution is preferably 0.1 to 2.

Meanwhile, in the present invention, the carbon coating layer may be deposited in the separator itself, that is, in the pore channels formed in the porous substrate of the separator.

Alternatively or in parallel with this, the carbon coating layer may be coated as a separate layer added to one side or both sides of the separator. In this case, the carbon coating layer may include a separate support and may include a carbon material and a binder, and the support may be porous, and may be implemented by, for example, fibers such as cellulose fibers. In this way, when the carbon coating layer is provided on one surface of the separator, the carbon coating layer is preferably formed on a surface facing the anode among the two surfaces of the separator. This can facilitate the trap of Mn ions diffusing from the anode and the decomposition of ZHS.

Meanwhile, the carbon coating layer may be used for controlling Zn dendrites and decomposing Zn sulfate formed on the surface of a Zn cathode. In this case, it is preferable that the carbon coating layer is formed on a surface facing the cathode.

In the present invention, the electrolyte 140 may be a weak acid electrolyte. In the present invention, for example, ZnSO ₄ or Zn(CF ₃ SO ₃ ) ₂ may be used as the weak acid electrolyte. At this time, the concentration of the salt is preferably 1M to 3M. In addition, the electrolyte 140 may further include an additive. The additive may be MnSO ₄ or Mn(CF ₃ SO ₃ ) ₂ , and the additive salt may be included in a concentration of 0.1M to 0.5M. At this time, when the concentration of the additive is lower than 0.1M, it does not greatly affect the performance improvement of the battery system, and when it is higher than 0.5M, unwanted reactants are generated on the surface of the negative electrode 110, and battery performance may be reduced.

<Acid treatment of carbon material used for carbon coating layer>

A mixed aqueous solution of 37% HCl and 60% HNO ₃ (weight ratio 1: 1) was prepared, and the mixed aqueous solution and super p black (hereinafter referred to as 'SP') powder were weighed so that the weight ratio was 1: 1 After that, it was immersed in the mixed aqueous solution for 2 days. Thereafter, after filtering the solution, the powder was washed and subjected to vacuum heat treatment to prepare an acid-treated SP (hereinafter referred to as 'aSP') powder.

The prepared aSP powder was dispersed in an electrolyte solution. Figure 2 is a photograph of observing the dispersion state (Acid-C) of the powder in the electrolyte. For comparison, the dispersion state (Prestine-C) of the SP powder was also photographed. As the electrolyte, 3M ZnSO ₄ + 0.1M MnSO ₄ aqueous solution was used.

The prepared aSP powder was subjected to XPS analysis. For comparison, XPS analysis was also performed on the SP powder not treated with acid.

3a and 3b are graphs showing the results of XPS analysis of the prepared aSP powder.

Referring to FIGS. 3A and 3B , in the aSP powder, -NO ₂ and -O-NO ₂ are observed as functional groups not observed in the SP powder.

<Manufacture of carbon coating layer>

Nippon Kodoshi Co. (NKK) cellulose separator (MPF30AC) as a support, aSP powder and a binder (PVDF) are mixed in a ratio of 8: 2 to prepare a slurry, and then the prepared slurry is cast on one side of the separator, and then vacuum dried Thus, a carbon coating layer having a thickness of 3 to 5 μm was formed. For comparison, a slurry was prepared in the same manner, except that SP powder was used instead of aSP powder, and then cast on one side of the separator to form a coating layer.

A wettability test of the electrolyte solution was performed on the surface of the prepared carbon coating layer. As the electrolyte, 3M ZnSO ₄ + 0.1M MnSO ₄ aqueous solution was used.

4 is a photograph of a wettability test result. The pictures on the left of FIG. 4 are taken immediately after dropping the droplet of the electrolyte, and the pictures on the right are taken 15 minutes after dropping the droplet of the electrolyte. It can be seen from FIG. 4 that the wettability of the acid-treated carbon is greatly improved compared to that of the untreated carbon.

<Evaluation of electrical properties of carbon coating layer>

Electrical characteristics of the prepared carbon coating film according to the electrode surface area were evaluated in a 3M ZnSO ₄ + 0.1M MnSO ₄ electrolyte solution. For this evaluation, a cell was constructed using zinc metal as the negative electrode, glass fiber as the separator, and stainless steel (SS) foil and carbon paper (CP) as the positive electrode. At this time, a sample (aCSL) in which a carbon coating layer using cellulose (MPF30AC) as a support was formed between the separator and the anode, and a sample (SL) in which a cellulose separator (MPF30AC) was placed between the separator and the anode were produced.

Figure 5a is a graph showing the results of measuring the amount of charge. In FIG. 5A, SS indicates a cell using stainless steel foil as an anode, and CP indicates a cell using carbon paper as an anode, where CP has a larger surface area than SS.

Referring to FIG. 5A, the data shows that the sample in which CP and aCSL are grafted shows the largest charging capacity because aCSL is included and provides more reaction sites capable of precipitating Mn ²⁺ ions dissolved in the electrolyte. It is judged as

5B is a graph showing ICP analysis results after charging. In the electrolyte of each cell, the Mn2+ concentration decreased compared to the initial state (Prestine), and it can be seen that the amount of Mn ²⁺ ions dissolved in the electrolyte of the CP/aCSL cell decreased the most. This means that aCSL was used to trap Mn ²⁺ ions. Thanks to these effects, cells to which aCSL is applied show improved capacity and coulombic efficiency than cells without it. FIG. 5C is a graph showing the calculation results of capacity and coulombic efficiency.

5D and 5E are graphs showing voltage profile analysis results for SL and aCSL, respectively, and FIG. 5F is a graph divided into sections D1 and D2 in FIG. 5E.

Referring to the figure, it can be seen that D1 and D2 are maintained constant in the aCSL cell compared to the SL cell, and in particular, the D2 retention rate related to ZHS generation is significantly improved compared to the SL cell. This means that reaction sites related to the generation/decomposition of ZHS are still active even when the cycle progresses, which means that aCSL contributes to the effective generation/decomposition of ZHS during charging and discharging.

<Evaluation of cell characteristics with carbon coating layer separator applied>

In order to confirm that the effect of the carbon-coated separator is maintained even during long-term cycle driving, SEM analysis was performed. For this analysis, a cell was constructed using a zinc metal cathode, a glass fiber separator, an aCSL interlayer, and a manganese dioxide anode. As the electrolyte, 3M ZnSO ₄ + 0.1M MnSO ₄ aqueous solution was used.

Referring to FIG. 6 , it can be seen that when a cell including aCSL is driven, ZHS is reversibly generated/removed from the surface of the aCSL (see (a) and (b) of FIG. 6 ). In FIG. 6A , C denotes charging, D denotes discharging, and the preceding number denotes the number of charge/discharge cycles.

On the other hand, since ZHS can be effectively removed, cells grafted with aCSL show greatly improved lifespan characteristics (see FIG. 6(c)) and output characteristics (see FIG. 6(d)) compared to the control group. And regardless of the current density, it shows improved capacity retention characteristics compared to the control SL cell (see (e) and (f) of FIG. 6).

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements that can be made by those skilled in the art using the basic concept of the present invention defined in the following claims It will also be appreciated that it falls within the scope of the present invention.

Claims (8)

In a zinc-manganese dioxide secondary battery comprising a negative electrode containing zinc, a positive electrode containing manganese dioxide, and a separator between the negative electrode and the positive electrode,
The separator includes a porous substrate and a carbon coating layer coated on the surface of the porous substrate,
The carbon coating layer includes carbon powder and a binder,
The carbon powder is a zinc-manganese dioxide secondary, characterized in that it contains at least one hydrophilic functional group including C = O, OC = O, CO, OH, -NO ₂ , O-NO ₂ , and C-OH on the surface battery. According to claim 1,
The carbon powder is a zinc-manganese dioxide secondary battery, characterized in that acid treatment. In the method for manufacturing a zinc-manganese dioxide secondary battery,
Acid treating the carbon powder;
preparing a coating slurry containing acid-treated carbon powder and a binder; and
A method for producing a zinc-manganese dioxide secondary battery comprising the step of coating the slurry on the pore channels of the porous substrate of the separator. According to claim 1,
The porous substrate is a zinc-manganese dioxide secondary battery, characterized in that it comprises glass fibers. According to claim 1,
The acid treatment step is a zinc-manganese dioxide secondary battery, characterized in that carried out by supporting the carbon powder in a mixed aqueous solution of sulfuric acid and nitric acid. According to claim 5,
Zinc-manganese dioxide secondary battery, characterized in that the pH of the mixed aqueous solution is 0.1 to 2. According to claim 5,
Zinc-manganese dioxide secondary battery, characterized in that the acid treatment is carried out for 2 hours or more. In the method for manufacturing a zinc-manganese dioxide secondary battery,
Acid treating the carbon powder;
Preparing a coating slurry containing an acid-treated porous support, carbon powder and a binder; and
A method for producing a zinc-manganese dioxide secondary battery, comprising the step of coating the slurry on one side of the separator.

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