1.Basic Principles and Structure

Ni-CD and Ni-Mh Batteries

Principle: Converts chemical energy into electrical energy through a chemical reaction. During discharge, cadmium (Cd) at the negative electrode is oxidized to cadmium ions (Cd²⁺), while nickel hydroxide (Ni(OH)₂) at the positive electrode is reduced to nickelous hydroxide (NiOOH).

Structure: Consists of an anode plate (cadmium), a cathode plate (nickel hydroxide), and an electrolyte (usually a potassium hydroxide solution), all enclosed in a metal casing. Nickel-metal hydride Battery

Principle: Similar to nickel-cadmium batteries, but the negative electrode material is a hydrogen storage alloy that reversibly absorbs and releases hydrogen.

Construction: Also includes an anode (hydrogen storage alloy), a cathode (nickel hydroxide), and an electrolyte (potassium hydroxide solution), but the overall design is more compact and has higher energy density.

Lithium-ion Battery

Principle: Relying on the movement of lithium ions between the positive and negative electrodes to store and release energy. During charging, lithium ions move from the positive electrode to the negative electrode; during discharging, the movement is reversed.

Construction: Typically consists of a positive electrode (such as lithium cobalt oxide or lithium iron phosphate), a negative electrode (graphite or other carbon materials), an electrolyte (lithium salt in an organic solvent), and a separator.

2.Performance Characteristics

Energy Density

Nickel-metal hydride batteries: Relatively low energy density, but heavy, making them unsuitable for applications requiring high energy density.

Ni-metal hydride batteries: Higher energy density than nickel-cadmium batteries, but still lower than lithium-ion batteries.
Lithium-ion batteries: Offer the highest energy density, providing long-term power while reducing device weight. Memory Effect

Nickel-cadmium batteries: They exhibit a significant memory effect, meaning that charging before fully discharging can cause their capacity to gradually decrease.

Nickel-metal hydride batteries: The memory effect is less pronounced, but care should still be taken to avoid frequent partial charging and discharging.

Lithium-ion batteries: They exhibit virtually no memory effect and can be charged and discharged at any time without affecting their capacity.

Self-discharge rate

Nickel-cadmium batteries: They have a high self-discharge rate and require regular charging when not in use for extended periods to prevent depletion.

Nickel-metal hydride batteries: They have a lower self-discharge rate and are superior to nickel-cadmium batteries.

Lithium-ion batteries: They have the lowest self-discharge rate and can retain a high charge even after long-term storage.

Safety

Nickel-cadmium batteries: They may produce toxic gases under high temperatures or short circuit conditions, and they pose a risk of overheating.

Nickel-metal hydride batteries: They are relatively safer, but care should still be taken to prevent overcharging and short circuiting.

Lithium-ion batteries: While technological advances have improved their safety, thermal runaway and even explosion can still occur under extreme conditions, so strict usage and maintenance procedures must be adhered to.

Cycle life

Nickel-cadmium batteries: They can typically last hundreds of charge and discharge cycles. Nickel-metal hydride batteries: Longer cycle life, typically reaching thousands of cycles.

Lithium-ion batteries: Longest cycle life, with high-quality products capable of thousands or even tens of thousands of charge and discharge cycles.

Environmental friendliness

Nickel-cadmium batteries: Contain the heavy metal cadmium, which is harmful to the environment and requires special handling and recycling.

Ni-metal hydride batteries: Free of heavy metals, they are relatively more environmentally friendly, but proper disposal of used batteries is still required.

Lithium-ion batteries: Although free of heavy metals, improper handling can lead to electrolyte leakage and environmental pollution, and thus require professional recycling.

3.Application

Ni-cadmium batteries: Due to their low cost and excellent impact resistance, they were once widely used in power tools, toys, and other fields. However, with technological advancements, they have gradually been replaced by other battery types.

Ni-metal hydride batteries: Suitable for devices such as digital cameras, portable audio systems, and flashlights, they are favored for their high energy density and low self-discharge rate. They are also commonly used in auxiliary power systems for hybrid and electric vehicles.

Lithium-ion batteries: Widely used in smartphones, tablets, laptops, drones, electric vehicles, and other fields. Due to its high energy density, long cycle life and low self-discharge rate, it has become the preferred energy solution for modern electronic devices and vehicles.