Nickel-based battery technologies have seen significant advancements since 2000, with innovations in alloy compositions, electrode structures, and manufacturing processes driving improvements in energy density, cycle life, and cost efficiency. This survey examines key patents in nickel battery technology, focusing on nickel-metal hydride (NiMH), nickel-cadmium (NiCd), and nickel-zinc (NiZn) systems.

### **Alloy Compositions for Nickel-Metal Hydride Batteries**
A major area of innovation in NiMH batteries involves the development of advanced hydrogen storage alloys for the negative electrode. Patents from the early 2000s introduced multi-component alloys, such as AB₅-type (lanthanum-based) and AB₂-type (titanium/zirconium-based) materials, optimized for higher capacity and corrosion resistance.

One notable advancement is the incorporation of rare-earth elements like cerium and praseodymium into the alloy matrix to enhance hydrogen absorption kinetics. For example, patents filed by battery manufacturers in Japan and China describe modified AB₅ alloys with cobalt and manganese substitutions, improving cycle stability by reducing pulverization during charge-discharge cycles.

Another trend involves the use of nanostructured alloys. Patents from the late 2010s disclose methods for producing ultrafine alloy powders with controlled crystallinity, increasing surface area for faster electrochemical reactions. Some formulations integrate small amounts of aluminum or copper to suppress oxidation, further extending battery lifespan.

### **Electrode Structures for Nickel-Based Batteries**
Innovations in electrode design have played a crucial role in enhancing the performance of nickel-based batteries. In NiMH systems, patents highlight porous nickel foam substrates with high surface area coatings, improving active material utilization. Some designs incorporate conductive additives like carbon nanotubes or graphene to reduce internal resistance.

For NiCd batteries, recent patents focus on reducing cadmium toxicity while maintaining performance. One approach involves hybrid electrodes combining cadmium with alternative materials such as iron or zinc. Another strategy employs layered electrode architectures, where cadmium is confined within a protective matrix to minimize electrode swelling.

In NiZn batteries, a key challenge has been zinc electrode degradation due to dendrite formation and shape change. Patents from the 2010s propose solutions such as three-dimensional zinc electrodes with polymer binders or additives like bismuth oxide to stabilize the electrode structure. Some designs integrate ion-selective membranes to prevent zinc migration.

### **Manufacturing and Process Innovations**
Several patents address manufacturing improvements for nickel-based batteries. Roll-to-roll electrode production techniques, adapted from lithium-ion battery manufacturing, have been applied to NiMH and NiCd systems to reduce costs. Dry electrode processing methods, eliminating solvent use in slurry preparation, have also been patented for nickel battery production.

Another area of focus is electrolyte optimization. Advanced alkaline electrolytes with additives such as lithium hydroxide or sodium silicate have been patented to enhance conductivity and suppress gas evolution during cycling. Some formulations include organic inhibitors to reduce corrosion of nickel electrodes.

### **High-Performance and Specialty Applications**
Nickel-based batteries remain relevant in applications requiring high durability and safety. Patents from aerospace and defense sectors describe ruggedized NiCd and NiMH cells with enhanced thermal stability for extreme environments. Innovations include hermetically sealed designs and reinforced separators to withstand mechanical stress.

For electric vehicles and hybrid systems, patents disclose NiMH batteries with improved high-rate performance. These designs often feature optimized electrode thickness and graded porosity to balance power and energy density. Some hybrid configurations combine nickel-based chemistry with supercapacitors for rapid energy delivery.

### **Emerging Trends and Future Directions**
Recent patents indicate ongoing research into next-generation nickel batteries, including nickel-hydrogen (NiH₂) systems for space applications and nickel-iron (NiFe) batteries for grid storage. Innovations in recycling processes, such as hydrometallurgical recovery of nickel and rare-earth metals, are also gaining attention.

In summary, nickel battery technology has evolved significantly since 2000, with key patents driving progress in materials, electrode engineering, and manufacturing. While lithium-ion batteries dominate many markets, nickel-based systems continue to offer advantages in specific applications, supported by ongoing innovation.