Patent Application
20130309555
Currently, the only batteries (rechargeable or non-rechargeable) commercially available with ZnMn chemistries are round bobbin cells. ZnMn chemistries are low cost and lightweight, are environmentally benign, and have a very long charge retention. Round bobbin cells have a positive electrode that is stamped or pressed into a cylindrical hollow pellet and seated into a can, and the negative electrode is a gel that is filled into the center void of the positive electrode.
The high internal resistance of low capacity round bobbin cells limits the currents (i.e., power) that they can deliver. In contrast, flat plate (electrode) cells can be scaled up to large sizes providing high currents and storage capacities.
CA 2 389 907 A1 relates to a method of producing flat plate electrodes in a small format that exhibit high current densities, higher utilization of the active materials, and better rechargeability. The method of forming the electrodes requires the active materials, binders, thickening agents, additives, and an alkaline electrolyte to form a paste that is applied to a current collector. CA 2 389 907 A1 provides is a flat plate rechargeable alkaline manganese dioxide-zinc cell.
What is needed are low cost, lightweight, environmentally friendly batteries that can be used, for example, for large power back-up systems, which are primarily currently served by lead acid and NiCd chemistries. Such batteries should exhibit improvements in, for example, current density, memory effect (i.e., capacity fade), shelf life, charge retention (e.g., at higher operation temperatures), and voltage level of discharge curve over known round bobbin and flat plate cells.
Provided is a flat plate electrode cell. The flat plate electrode cell comprises positive electrode plates and negative electrode plates. The positive electrode plates each comprise manganese and compressed metal foam. The negative electrode plates each comprise zinc and compressed metal foam. The positive electrode plates can have aligned tabs and the negative electrode plates can have aligned tabs, and the flat plate electrode cell can further comprise a positive terminal formed from the aligned tabs of the positive electrode plates and a negative terminal formed from the aligned tabs of the negative electrode plates.
The rechargeable flat plate electrode cell of the present disclosure provides improvements in, for example, current density, memory effect (i.e., capacity fade), shelf life, charge retention (e.g., at higher operation temperatures), and voltage level of discharge curve over known round bobbin and flat plate cells. In particular, the rechargeable flat plate electrode cell of the present disclosure provides longer cycle life with reduced capacity fade as compared with known round bobbin and flat plate cells.
The rechargeable flat plate electrode cell of the present disclosure achieves such benefits primarily through unique electrode formation. In particular, both the positive and negative electrode of the rechargeable flat plate electrode cell of the present disclosure are formed from compressed metal foam, which provides both low resistance and high rate performance to the electrodes and the cell.
The rechargeable flat plate electrode cell of the present disclosure reduces the material costs, weight, toxicity (regulated limitations), volume, and maintenance of known batteries (e.g., batteries used for stationary power back-up applications), while increasing charge retention and reliability. The rechargeable flat plate electrode cell of the present disclosure can be used wherever high capacity DC power storage is required, can replace lead acid or NiCd large format batteries or other high power electric back-up systems, and can be used directly in applications that can accept a wide voltage range and in conjunction with a voltage stabilizing system when the application requires a narrower voltage range.
The rechargeable flat plate electrode cell of the present disclosure comprises one or more anode plates comprising anode paste and one or more cathode plates comprising cathode paste. The anode and cathode pastes each comprises active material metal powders (e.g., zinc and manganese, respectively) mixed with aqueous or organic binder to create a paste that can be consistently coated on one or both sides of a substrate. The substrate holds the active material (i.e., the paste) and acts as a current collector. In an embodiment, the substrate is made of a conductive material such as steel, Ni, or Cu, and may be plated with indium or Ni (i.e., a material that is non-active relative to MnO2) for the cathode and Cu (i.e., a non-active material relative to zinc) for the anode. In an embodiment, the substrate comprises a porous conductive substrate such as, for example, perforated metal, metal foam, metal felt, expanded metal, or carbon foam. More specifically, the substrate comprises nickel foam and/or copper plated nickel foam. Accordingly, the anode or cathode paste is coated on and throughout the foam mesh.
The coated substrate is dried and sized (i.e., compressed) to create a highly conductive, dense, porous flat plate electrode. The flat plate electrodes are wrapped and sealed in a layer of barrier and separator material to prevent short circuits and dendrite growth. The wrapped and sealed flat plate electrodes are stacked in an alternating cathode and anode pattern that is repeated until a desired capacity of the cell is reached. Tabs (collectors) of the flat plate cathode electrodes are connected together and tabs of the flat plate anode electrodes are connected together. In an embodiment, the rechargeable flat plate electrode cell of the present disclosure is bi-polar. Such bipolar batteries use a substrate to hold the positive active materials on one side and negative active materials on the other and the substrate acts as a cell wall. The cell walls are sealed either peripherally or tangentially to hold internal pressure and electrolyte.
In metal foams, typically 75-95% of the volume consists of void spaces. As such, the use of metal foams allows for thicker electrode substrates without increasing the resistance of the electrode substrates. Target compression from sizing for this embodiment is between about 42% and 45%, which gives desirable porosity, required for low resistance/high rate performance of the rechargeable flat plate electrode cell.
Without wishing to be bound by any theories, it is believed that the high density of compression reduces the resistance within the paste by reducing the distance between active particles in the active material and reduces the resistance to the substrate by bringing the active particles closer to it. The high density reduces the volume so the energy density is increased. The high density also reduces the void volume in the active material which reduces the amount of electrolyte required to fill the electrode which in turn reduces the rate at which dendrites are formed which protects the cell from shorting and increases cycle life. The density level is critical since over-compression will cause dry spots in the active material where electrolyte cannot get to. These dry spots are very high resistance which reduces performance and can create gassing areas which cause cell failure.
Without sizing, desired energy density and high power capability are not achieved. The target coated sized thickness for the cathode is less than about 0.0300 inches. Coated sized thickness for the cathode greater than about 0.0300 inches results in rate capability (power) losses, while coated sized thickness for the cathode less than about 0.0200 inches results in energy density losses, due to excess inter electrode spacing and substrate relative to active material.
The anode paste comprises about 75-98 weight %, for example, about 83.1 weight %, zinc active material; about 0.01-1.0 weight %, for example, about 0.27 weight %, polymeric binder; and about 0-20 weight %, for example, about 16.6 weight %, solid zinc oxide. Exemplary zinc active materials include lead-free zinc and zinc alloy, such as, for example, in metallic, powder, granular, particulate, fibrous, or flake form.
The cathode paste comprises about 70-90 weight % electrolytic manganese dioxide; about 2-15 weight %, for example, about 7.5 weight %, graphite and/or carbon black; about 3-10 weight %, for example, about 6 weight %, polymeric binder; about 1-15 weight %, for example, about 5 weight %, barium compound; and about 0.01-10 weight %, for example, about 5 weight %, hydrogen recombination catalyst. Exemplary barium compounds include barium oxide, barium hydroxide, and barium sulfate. Exemplary hydrogen recombination catalysts include silver, silver oxides, and hydrogen absorbing alloys. The cathode paste may further comprise indium.
Exemplary polymeric binders of either the cathode paste or anode paste include carboxymethyl cellulose (CMC), polyacrylic acid, starch, starch derivatives, polyisobutylene, polytetrafluoroethylene, polyamide, polyethylene, and a metal stearate. The polymeric binder of either the cathode paste or anode paste can include conductive graphite, for example, conductive graphite having an average particle size between 2 and 6 microns.
The rechargeable flat plate electrode cell of the present disclosure differs from currently commercially available rechargeable ZnMn batteries in that the flat plate electrodes of the cell:
The rechargeable flat plate electrode cell of the present disclosure further differs from currently commercially available batteries in that:
Advantages of the rechargeable flat plate electrode cell of the present disclosure include:
As illustrated in
With further reference to
Additionally performance characteristics of the rechargeable flat plate electrode cell of the present disclosure can include capacity of greater than 5 Ahr, cycle life exceeding 200 cycles at 80% DOD above 50% initial capacity, power exceeding C/2 rate to 1 V at 50% initial capacity and 2C rate to 1V at 25% initial capacity, energy density exceeding 90 Whr/kg, and power density exceeding 180 W/kg. DOD, or depth of discharge, is a measure of how much energy has been withdrawn from a battery, expressed as a percentage of full capacity. C/2 rate refers to a discharge rate of 50% of one hour capacity.
The rechargeable flat plate electrode cell of the present disclosure can be utilized in a vehicle for starting a internal combustion engine, or in a more portable format can be used in power tools, cell phones, computers, and portable electronic devices.
The following illustrative examples are intended to be non-limiting.
With regard to formation of the flat plate anode electrodes, 360 grams of Zn, 72 grams of ZnO, and 59.88 grams of 2% CMC gel were mixed to form a paste comprising 83.1 weight % zinc active material (i.e., Zn), 16.6 weight % solid zinc oxide, and 0.27 weight % polymeric binder. The paste was applied to one side of copper plated nickel foam and pressed/worked in. The copper was plated on the nickel foam via copper plating 1A for 30 minutes. Water was evaporated from the paste, and the dried pasted foam was pressed to approximately 50% of its original thickness. A 0.15 inch strip at the top of each flat plate anode electrode was coined for attachment of a tab. Further details of formed flat plate anode electrodes can be found in Table 1, below. With regard to the capacity calculations in Table 1, the capacity of 0.625g Zn is 512 mAh.
With regard to formation of the flat plate cathode electrodes, 41.90 grams of 2% CMC gel and 100 grams of cathode powder ground down to 1/10th of the initial particle size were mixed to form a paste. The cathode powder comprised electrolytic manganese dioxide, 7.5 weight % graphite/carbon black, 5 weight % polymeric binding agent, 5 weight % barium compound, and 5 weight % hydrogen recombination catalyst, and is pressed to form high density initial particles. The 2% CMC gel provided an additional 1 weight % polymeric binding agent to provide a paste with a total of 6 weight % polymeric binding agent. The paste was applied to one side of nickel foam having a weight basis of 0.255 g/in2. Water was evaporated from the paste, and the dried pasted foam was pressed to approximately 50% of its original thickness. A 0.15 inch strip at the top of each flat plate cathode electrode was coined for attachment of a tab. Further details of formed flat plate cathode electrodes can be found in Table 2, below.
Many modifications of the exemplary embodiments disclosed herein will readily occur to those of skill in the art. Accordingly, the rechargeable flat plate electrode cell of the present disclosure is to be construed as including all structure and methods that fall within the scope of the appended claims.
This application is a continuation of application Ser. No. 13/120,441, filed Mar. 23, 2011, which claims priority under 35 USC 1.119(e) to U.S. Provisional Application No. 61/100,318 filed on Sep. 26, 2008, all of the foregoing being hereby incorporated in their entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61100318 | Sep 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13120441 | Mar 2011 | US |
| Child | 13953369 | US |
