Every nickel-metal hydride cell begins as a chemistry problem: how to pack a high-activity nickel hydroxide positive and an AB5 metal-hydride negative into a form that can be mass-produced with tight tolerances. The answer on modern lines is a sequence of coating, drying, pressing and winding steps that together determine a cell's capacity, discharge rate and service life almost as much as the chemistry itself. This article walks through the core NiMH manufacturing process and the quality variables that separate a good cell from a great one.
The active material does not come to the line as metal; it is prepared as a paste. The positive paste suspends nickel hydroxide (Ni(OH)2) particles — often with cobalt additives and conductive carbon — in a binder solution. The negative paste suspends the hydrogen-absorbing AB5 alloy (mischmetal, nickel, cobalt, manganese, aluminium). Binder selection matters: too little and the coating cracks during drying; too much and it insulates the active material and raises internal resistance.
Key variables at this stage:
The paste is coated onto a nickel-plated steel or nickel foam substrate — a continuous web that runs through the line at high speed. Paste weight per unit area is the single most important capacity lever: a heavier, more uniform coating raises capacity but a coating that is too thick or uneven causes poor rate capability, local hot spots and premature capacity fade.
After coating, the web passes through drying ovens to remove the solvent or water, then through calendering rolls that compress the electrode to a target thickness and porosity. Calendering does two things: it improves the electrical contact between active particles and the substrate, and it sets the porosity that the electrolyte will later occupy. Over-calendering crushes porosity and starves the electrode of electrolyte; under-calendering leaves high internal resistance.
For cylindrical cells the positive and negative electrodes are wound together with a separator into a jelly-roll. For prismatic cells, flat plates are stacked. In both cases the separator — typically a polyamide or polypropylene non-woven fabric treated to improve wetting — must separate the electrodes reliably while allowing the aqueous alkaline electrolyte, potassium hydroxide, to wet the active material uniformly.
Winding tension and alignment are critical. A misaligned or wrinkled electrode causes internal shorts, and an over-tight winding can strain the separator and reduce the electrolyte path. Modern winders use servo-controlled tension and optical alignment to hold electrode and separator edges within tight limits as layers build.
After the electrode assembly is inserted into the can, the cell is filled with KOH-based electrolyte, sealed (the safety vent is crimped in), and then subjected to formation — the first controlled charge-discharge cycles that activate the electrodes and establish the cell's initial capacity. Formation conditions, temperature and current profile influence the quality of the passivation layer and the cell's early cycle behaviour. Some manufacturers follow formation with a stabilising charge or storage to let the self-discharge characteristics settle.
For an OEM sourcing NiMH cells, the factory's process control is as important as the datasheet. Ask about coating-weight tolerance, formation standards, gas-generation rejection rates and incoming material traceability. A supplier that controls these variables delivers cells with consistent capacity and reliable life; one that does not ships whatever the line produces. When you buy from Weijiang Power you are buying a process that is engineered, measured and audited end to end — from powder to finished cell.
Want cells matched to your exact current, temperature and life requirements? Talk to our engineering team to align the manufacturing choices above with your application.
