High-Nickel Technology for High-Energy-Density 21700 Battery

Blog | Published by Alex on October 8, 2025

High-Nickel Boost the Energy Density of 21700 Battery

In recent years, the rapid growth of EVs, ESS, power banks, and high-end power tools has driven the demand for lithium-ion batteries with higher energy density. Among various cell formats, the 21700 battery has emerged as a new standard following the 18650 battery, offering improved capacity, better thermal management, and greater energy density.
Among all factors affecting energy density, the cathode material plays the most decisive role. Conventional cathode chemistries such as NCM523 and NCM622 have approached their theoretical limits, prompting the industry to shift toward high-nickel materials—notably NCM811 and NCA—to achieve further gains in energy density.

Definition and Characteristics of High-Nickel Materials

High-nickel cathode materials generally refer to lithium nickel cobalt manganese oxide (LiNiₓCoᵧMn₁₋ₓ₋ᵧO₂, with x ≥ 0.8) or lithium nickel cobalt aluminum oxide (LiNi₀.₈Co₀.₁₅Al₀.₀₅O₂, or NCA).
Nickel contributes the majority of the energy storage capacity through redox reactions, while cobalt and manganese (or aluminum) are used to stabilize the crystal structure and enhance cycling performance.

Key advantages of high-nickel cathodes:
(1) High specific capacity – Around 200–220mAh/g, which is 15–20% higher than medium-nickel materials like NCM622.
(2) Higher voltage plateau – Operating voltage above 3.7V increases the total discharge energy.
(3) Cost reduction potential – Reduced cobalt content helps lower raw material cost as cobalt prices fluctuate.

Main challenges:
(1) Structural instability – High nickel content can cause crystal collapse during cycling.
(2) Increased side reactions – The highly active surface reacts more easily with electrolytes.
(3) Lower thermal stability – High-nickel cathodes release oxygen under high temperature or overcharge conditions, posing safety risks.

Advantages of High-Nickel Cathodes in 21700 Battery

The 21700 battery format (21 mm diameter, 70 mm height) provides an ideal platform for utilizing high-nickel materials effectively. Compared with 18650 battery, 21700 battery offers higher packing efficiency, enabling the full exploitation of high-nickel cathodes.

1. Higher Energy Density
When paired with a silicon-carbon anode, high-nickel NCM811 21700 battery can achieve 280–300Wh/kg, compared with only 240–260Wh/kg for traditional NCM622. This directly translates into longer driving ranges for EVs and extended operating time for tools.

2. Better Volumetric Utilization and System Integration
The volumetric energy density of 21700 battery is about 30% higher than that of 18650 battery. Combined with high-nickel cathodes, the energy density of battery packs can reach 800–900Wh/L, supporting more compact and efficient designs for vehicles and ESS applications.

3. Lower System Complexity and Cost
Fewer cells are required to achieve the same capacity, which simplifies the BMS (battery management system), reduces wiring and connections, and ultimately lowers the overall system cost.

Mechanism Behind Energy Density Improvement

1. Nickel Redox Contribution
The main capacity comes from the reversible Ni²⁺/Ni⁴⁺ redox reaction. A higher nickel content means more active sites for electron transfer, thus increasing the theoretical capacity per gram.

2. Optimized Lattice Spacing
High-nickel compositions expand the interlayer spacing within the crystal structure, improving lithium-ion diffusion and reducing internal resistance, which enhances both energy output and rate capability.

3. Surface Coating and Doping Stabilization
Applying protective coatings such as Al₂O₃ or ZrO₂, or doping elements like Mg or Ti, can stabilize the surface and mitigate side reactions under high voltage. These methods help maintain structural integrity and allow safe operation at higher charge voltages.

Technical Challenges and Improvement Strategies

1. Residual Alkaline Compounds
During calcination, LiOH and Li₂CO₃ residues may form on the particle surface and react with electrolytes, causing gas generation and swelling. This can be resolved by optimizing firing atmospheres and post-treatment cleaning processes.

2. Microcracks and Particle Fracture
High-nickel particles tend to develop microcracks due to volume changes and lattice stress during cycling, accelerating degradation. Solutions include primary particle coating, elastic binders, and optimized particle morphology design.

3. Thermal Stability and Safety Risks
High-nickel cathodes decompose at lower temperatures than NCM622 or NCM523. Ceramic-coated separators, flame-retardant additives, and surface-modified cathodes are used to enhance thermal stability.

4. Manufacturing Complexity
High-nickel materials require higher purity raw materials, strict humidity control, and precise stoichiometric management, increasing initial production cost and process difficulty.

Typical Applications and Development Trends

1. Electric Vehicles
Tesla’s Model 3 and Model Y use 21700 battery based on high-nickel NCA chemistry, achieving a balance between high energy density and cycle stability through electrolyte optimization and coating technologies.

2. Energy Storage and Power Tools
High-nickel 21700 battery are widely adopted in lightweight ESS, drones, and high-end cordless tools, providing longer runtime in limited space.
Chinese manufacturers such as LISHEN, JOINSUN, and BAK have also launched NCM811-based 21700 battery.

3. Future Trends: Solid-State and High-Voltage Systems
The next phase of innovation will combine high-nickel cathodes with solid-state electrolytes or high-voltage electrolyte systems, potentially pushing energy density beyond 350Wh/kg by 2030.

Summary

High-nickel cathode technology represents one of the most critical pathways for improving the energy density of 21700 battery (lithium-ion). By increasing nickel content and applying advanced stabilization methods such as surface coating and element doping, these materials can significantly enhance specific capacity and overall energy output. Although high-nickel cathodes introduce challenges in structural stability, thermal management, and manufacturing, continuous progress in material science and battery engineering is rapidly addressing these issues. High-nickel 21700 battery are leading the next generation of high-energy lithium-ion cells, enabling longer driving ranges, lighter systems, and more efficient energy storage solutions across multiple industries.

Related Articles

What is the NCM811 and its Advantages?