While the concept of lithium-ion batteries is not newer than that of nickel-cadmium batteries, their practical application came relatively late. Due to the reactive chemical properties of lithium, safety hazards existed during production, use, and transportation. However, technological advancements have gradually alleviated these concerns, and lithium-ion batteries have become the mainstream of modern battery technology.
In practical applications, lithium-ion batteries have actually developed by gradually surpassing nickel-metal hydride batteries. The overall advantages of lithium-ion batteries are convenience and durability. The following is a comparison of the differences between lithium-ion batteries and nickel-metal hydride batteries:
1. High energy density
Nickel-metal hydride (NiMH) batteries are sized between nickel-cadmium (NiCd) and lithium-ion (Li-ion) batteries, reflecting their commercial viability. Due to their different energy densities—that is, the energy stored in the same volume—lithium-ion batteries provide three times the energy of NiMH batteries.
2. Self-discharge
Self-discharge refers to the loss of electrical power by a battery when it is not in use. While nickel-metal hydride (NiMH) and lithium-ion batteries have relatively low self-discharge rates, NiMH batteries are more prone to self-discharge, which shortens battery life and causes premature termination. Therefore, about ten years ago, the low self-discharge of NiMH batteries was a highlight in their promotion, while the self-discharge of lithium-ion batteries was almost negligible due to the natural differences in chemical properties caused by the materials used.
3. Memoryless effect
Nickel-metal hydride (NiMH) batteries exhibit a significant memory effect. Just as human memory is the impression left by the brain, NiMH batteries also suffer from this effect. Incomplete discharge or unsatisfactory charging over time will cause the battery to only remember the incomplete and unsatisfactory states, resulting in capacity decay. Lithium-ion batteries, on the other hand, do not. Therefore, NiMH batteries require a thorough deep discharge periodically to clear these residual memories, similar to brainwashing in humans. Lithium-ion batteries, however, can be recharged at any time, making them a "happy battery" for users.
4. High-charge-discharge platform
A single lithium-ion battery has a voltage of 3.6V, while a single nickel-metal hydride (NiMH) battery has a voltage of 1.2V. Lithium-ion batteries are charged by setting a terminal voltage, typically 4.2V per cell, while NiMH batteries do not have voltage rise/fall. The charging method for lithium-ion batteries is called voltage and current limiting (V/C), while NiMH batteries have a low voltage plateau and are typically charged by constant current (DC). Because their charging methods are different, lithium-ion battery chargers and NiMH battery chargers cannot be used together.
5. Standardized Specificity
Nickel-metal hydride (NiMH) batteries are commonly referred to as NiMH batteries, while lithium-ion batteries are rarely called NiMH batteries. This is because lithium-ion batteries are primarily used in products with large market volumes. Applying them to products with small market volumes presents not only technical challenges but also significant cost-sharing issues. While still addressing technological and market scale issues, some companies in the lithium-ion battery industry are actively moving into new areas of lithium battery application. For example, Dongguan Yanyou Electronics Co., Ltd., originally a custom lithium-ion battery manufacturer, has launched a dedicated R&D and production line for these batteries. This is a concrete measure to adapt to this trend, and it is believed that similar practices will become commonplace in the industry in the near future.
The five differences mentioned above all highlight the advantages of lithium-ion batteries. However, due to their different chemical properties, different types of battery products have their own inherent advantages and therefore will not be completely replaced by other types of batteries.
For example, in applications involving high-current instantaneous discharge, nickel-metal hydride (NiMH) batteries outperform lithium-ion batteries, including in medical devices, emergency equipment, and power tools. In broader applications, NiMH batteries could also be used in new energy hybrid vehicles, although further research in this area is needed.
