Alkaline Manganese Cells
The alkaline manganese cell is a variant on the Leclanche cell that utilizes electrodes of zinc and manganese dioxide, but uses potassium hydroxide (KOH) instead of acidic ammonium chloride or zinc chloride as the electrolyte.
These batteries are widely used for portable audio and electronic equipment, such as battery-operated toys and torches. They are also used for powering small devices such as alarm clocks, electric shavers, and remote controls.
Positive Electrode
The positive electrode of an alkaline manganese cell consists of a mixture of powdered manganese dioxide, carbon powder, and other additives to enhance the conductivity and stability of the cathode. These are either pressed into the stainless steel can of the battery or deposited as pre-molded rings on the bottom surface of the can.
The cathode is protected from contamination and short circuiting by a separator. This can be a layer of non-woven cellulose or a synthetic polymer that is designed to conduct the ions in the electrolyte and remain stable.
In rechargeable alkaline batteries, the electrolyte is a solution of concentrated potassium hydroxide. This is also the electrolyte used for dry cells. It is a 35-40% solution of KOH in water, with varying concentrations depending on the application and the type of electrode materials.
During discharge, the active compounds of the battery system are oxidized by direct current to high-energy charge states. In the rechargeable battery, this is done by oxidation of the manganese oxyhydroxide in the discharged positive electrode to manganese dioxide and oxidation of the zinc oxide in the discharged negative electrode to metallic zinc.
The battery cycle life of an alkaline manganese cell can range from a few hundreds of cycles to several thousands of cycles under favorable conditions. This is largely determined by the depth of discharge and the temperature, but can be increased if the cell is charged to a high rate capacity.
A rechargeable battery based on this technology is commonly referred to as a RAM (rechargeable alkaline manganese) battery. It is constructed with a similar negative and positive electrodes as a primary battery, but has multilayered or semipermeable membrane separators that minimize zinc dendrite formation during charging.
The cathode of an alkaline manganese cell is made from pellets containing a mix of powdered manganese dioxide, a hygroscopic additive to increase the cumulative capacity, and a small amount of a hydrophobic binder to make the pellets uniform in consistency. This small amount does not impair the performance of the cell, but does provide a desired consistency for automated production.
Negative Electrode
The negative electrode of an alkaline manganese cell is made from a mixture of solids that includes both an active material and electrically conductive particles. The amount of the conductive material used in the mixture can be adjusted to achieve the desired electrical resistivity and specific capacity. The quantity of the binder used to hold the conductive material in place can also be adjusted to improve the electrical conductivity of the formed electrode.
The conductive particles of the solid mixture can be any type or combination of materials with a high electrical conductivity, including graphite, aluminum oxide, boron nitride, calcium nitride and titanium dioxide. They are combined to reduce the overall resistivity of the mixture, resulting in a high power discharge capacity.
Because the electrical resistivity of the formed positive electrode is dependent on the amount of the conductive material and the binder, it is important to ensure that the optimum ratios of these materials are utilized during the manufacturing process. This is a crucial step in achieving the maximum capacity of the electrode.
Another important factor in determining the electrical resistivity of the positive electrode is its porosity, which is the percentage of the volume of the formed solid mixture that is void of electrolyte. The higher the porosity of the formed solid mixture, the more electrolyte can be contained within the electrode.
It is also important to consider the density of the formed solid mixture during the production process. If the density of the solid mixture is too low, the formed electrode will not be able to contain a sufficient quantity of the electrolyte to provide good voltage regulation during charge and discharge.
A high density, well-packed alkaline manganese cell solid mixture will provide a high gravimetric density and volumetric density in the formed electrode. The volumetric density of the formed solid mixture will also be a significant factor in determining the volumetric discharge capacity of the battery.
The discharge capacity of the cell can be determined by a number of factors, including the rate of current flow and polarization. There are three distinct polarization characteristics that contribute to the total discharge capacity of the cell: activation polarization, ohmic polarization and concentration polarization.
Cathode Collector
A cathode collector is a metal that protrudes into an alkaline manganese cell’s anode and serves as a means of collecting current. Specifically, it collects the positive alkaline manganese cell ions that are produced from the anode and distributes them to the negative electrode of the cell.
The anode and the cathode are physically separated by a separator, which is made from a material that is electrically conductive. Typically, this material is graphite, but it may be another material that conducts electricity. It is important to use a conductive material for the anode as it helps prevent rust from forming at the anode’s surface and also provides a safety measure in case of a fire caused by the anode or if the anode breaks down.
An alkaline cell has a cathode consisting of powdered zinc mixed with manganese dioxide and potassium hydroxide in an electrolyte solution. This mixture is placed inside the steel shell of a cylindrical battery.
After the anode is filled with the powdered zinc and inserted into the cathode, a separate piece of separator material is added to physically isolate the anode from the cathode while still allowing ion transport between the two. This separator can be formed by placing strips of conductive material perpendicular to one another, extending out from the cathode.
In order to improve the performance of a cell, it is important to use the most suitable material for its components. Specifically, the anode of an alkaline cell should be made from the same type of zinc alloy used to make the cathode’s powder zinc. This will help eliminate the possibility of gassing between the anode and the cathode which can occur in undischarged or partially discharged cells.
It is important to also use a different material for the current collector of an alkaline battery as it will help increase its power capacity. This material can be any metal that conducts electricity, such as copper.
However, it is important to note that the use of a metal such as copper for the anode of an alkaline battery can lead to degradation in the cell’s anodic current collector. This degradation is primarily caused by the applied potential (over-discharge) and interactions with the cell’s electrolyte and microstructure. It is possible to mitigate the degradation of a copper current collector by increasing the cell’s temperature and applying an adequate press rate for the metal.
Anode
An alkaline manganese cell is a battery that contains an anode, a cathode and an electrolyte. The anode is made of zinc powder, while the cathode is composed of manganese dioxide and carbon.
The anode is the positive electrode, and it receives the charge from the cathode. It is important to use a good quality anode to provide the correct performance.
It can be made from either a gell or a porous material. It must be very pure to get the best results. It is also a very important part of the battery, as it controls the polarity.
Gelled anodes are a common type of anode in alkaline batteries. They contain a relatively high amount of zinc, typically around 76%, with the other elements being mercury and sodium carboxymethyl cellulose. This mixture is extruded into the battery and sealed in place by a sealant.
Another common type of anode is the solid phase anode. These can be prepared by mixing manganese oxide with carbon in a solution of water, or they can be a preformed powder that can be compressed into the cell using plungers or similar compacting devices forming a solid cathode mass in contact with the cell casing.
This type of anode is less expensive and more environmentally friendly than the gelled anode. It is also easier to work with and provides more current capacity at low discharge rates.
A phosphide-based anode is a promising alternative to the gelled anode for LIBs because of its high cycling performance and its potential to be charged using a separate cell. It has the advantage of a stable anode during oxidation and reduction, but there are some drawbacks to this type of anode, including its short lifetime.
Phosphide anodes are also prone to rapid corrosion. Therefore, they should be treated with caution when used in applications where the anode will be exposed to strong oxidants such as hydrocarbons.
The chemistry of the anode is also crucial to its performance, as it determines how well the battery will perform during charging and discharge. The anode must be designed to allow ions to flow freely between the cathode and the anode, while maintaining a good balance between insulating properties and ion conductivity.
