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Views: 0 Author: Site Editor Publish Time: 2025-12-27 Origin: Site
Nickel–metal hydride (NiMH) batteries are one of the most important rechargeable battery technologies in modern history. Positioned between the earlier nickel–cadmium (NiCd) batteries and today’s dominant lithium-ion systems, NiMH batteries have played a crucial role in driving the evolution of portable electronics, hybrid vehicles, and consumer power solutions. They are known for their reliability, environmental advantages compared with older chemistries, and balanced performance across safety, cost, and energy density. This article offers a comprehensive exploration of the origins and development of NiMH batteries, explains their working principles, and analyzes their internal structure.
Before the introduction of NiMH batteries, nickel–cadmium batteries dominated the rechargeable battery market. NiCd batteries offered good cycle life and high discharge capability, but they had two major drawbacks:
Cadmium toxicity, which posed significant environmental hazards.
Memory effect, where repeated partial charging degraded usable capacity.
As environmental regulations tightened and performance demands increased, researchers began searching for alternative nickel-based rechargeable battery systems that could maintain efficiency while eliminating cadmium.
Research on metal hydride storage materials in hydrogen energy systems during the 1960s and 1970s became the foundation of NiMH technology. Scientists discovered that certain alloys could reversibly absorb and release hydrogen, functioning as efficient hydrogen reservoirs. This breakthrough inspired the concept of replacing the cadmium negative electrode in NiCd batteries with hydrogen-absorbing alloys.
By the 1980s, technological refinements in hydrogen storage alloys, sealing techniques, and electrolytes allowed nickel–metal hydride batteries to transition from laboratory research to commercial production. Major companies such as Sanyo, Panasonic, and General Electric contributed significantly to industrialization and standardization.
In the 1990s and early 2000s, NiMH batteries reached their golden era. They were widely applied in:
Portable electronics such as cameras, flashlights, and handheld devices
Rechargeable household batteries (AA/AAA formats)
Hybrid electric vehicles (HEVs) such as Toyota Prius, which brought NiMH into large-scale automotive applications
NiMH batteries earned recognition for their safety stability, robustness, and environmental advantages compared with NiCd.
Although lithium-ion batteries eventually surpassed NiMH in energy density and became dominant in consumer electronics, NiMH batteries remain relevant today. They continue to play a major role in:
Hybrid vehicles
Power tools
High-drain household rechargeable batteries
Backup power systems
Rather than disappearing, NiMH batteries evolved to complement lithium-ion systems by offering safer and more stable performance in specific environments.
NiMH batteries operate based on electrochemical reactions between the nickel oxyhydroxide (NiOOH) cathode and hydrogen-absorbing alloy anode in an alkaline electrolyte.
During discharge, the following reactions occur:
Cathode (positive electrode) reaction:
Nickel oxyhydroxide is reduced to nickel hydroxide
NiOOH + H₂O + e⁻ → Ni(OH)₂ + OH⁻
Anode (negative electrode) reaction:
Hydrogen stored in the metal hydride alloy is oxidized
MH + OH⁻ → M + H₂O + e⁻
Overall cell reaction:
NiOOH + MH → Ni(OH)₂ + M
During charging, the reaction is reversed. Hydrogen is reabsorbed into the alloy structure, while nickel hydroxide is converted back into nickel oxyhydroxide.
Reversible hydrogen storage: The metal hydride alloy allows hydrogen to be repeatedly absorbed and released, enabling rechargeability.
Stable voltage platform: Nominal voltage is around 1.2 V, similar to NiCd, which ensures compatibility with traditional battery designs.
Good high-current discharge capability: Suitable for devices requiring continuous or burst power.
Although packaging formats may differ, the fundamental structure of NiMH batteries remains consistent.
Material: Nickel oxyhydroxide (NiOOH) supported by nickel hydroxide
Function: Serves as an electron acceptor during discharge and a donor during charging
Design: Porous structure enhances reaction surface area and efficiency
Material: Hydrogen-absorbing alloy, commonly rare-earth-based (LaNi5-type) or titanium–nickel-based
Function: Stores hydrogen during charging and releases it during discharge
Advantages: Eliminates cadmium toxicity found in NiCd systems
Typically potassium hydroxide (KOH) alkaline electrolyte
Provides ionic conductivity and stabilizes electrochemical operation
Acts as an insulating barrier preventing short circuits while allowing ion transfer
Must be chemically stable in alkaline environments
Cylindrical or prismatic metal casing ensures mechanical stability
Pressure relief valves prevent gas buildup, enhancing safety
Higher capacity than NiCd batteries
Environmentally friendlier, with no toxic cadmium
Strong current delivery capability
Good cycle life, typically hundreds to over a thousand charge cycles
Excellent safety stability, with lower risk of combustion compared with lithium-ion batteries
Lower energy density than lithium-ion batteries
Self-discharge rate higher than some modern chemistries, though improved low self-discharge NiMH designs now exist
Performance may decline at very high or very low temperatures
Rechargeable household batteries (AA/AAA)
Digital cameras and photography devices
Hybrid fuel vehicles
Industrial and emergency backup power
Medical and communication devices
Although lithium-ion and emerging solid-state batteries dominate advanced technology markets, NiMH continues to evolve:
Improved hydrogen storage alloys for higher capacity
Enhanced low self-discharge technology
Better cycle durability for hybrid vehicles
Environmentally optimized manufacturing and recycling systems
NiMH batteries are expected to maintain relevance in fields prioritizing safety reliability, moderate cost, and environmental balance.
Nickel–metal hydride batteries represent an important milestone in battery development. Originating from hydrogen storage technology breakthroughs, NiMH batteries successfully replaced environmentally harmful NiCd batteries and achieved widespread commercial success. Their working principle is based on reversible hydrogen absorption and nickel redox reactions, while their structure integrates advanced electrode materials, alkaline electrolytes, and secure sealing systems.
Even in the era dominated by lithium-ion batteries, NiMH technology continues to hold value due to its stability, safety, environmental friendliness, and balanced cost-performance ratio. Looking ahead, ongoing technological improvements and expanding application scenarios ensure that NiMH batteries will remain a vital part of the global energy ecosystem for years to come.
