Energy Density of Polymer Batteries

The energy density of polymer batteries refers to the amount of electrical energy stored per unit mass or unit volume. It is one of the core 

factors for evaluating battery performance, directly determining the battery's endurance and potential for miniaturization.

Core Classification and Definitions

1. Gravimetric Energy Density (Specific Energy)

Definition: The electrical energy contained per unit mass of the battery. The unit is typically Wh/kg (Watt-hours per kilogram).

Significance: Determines the degree of "lightweighting" of the battery. For example, given batteries of the same capacity, the higher the 

gravimetric energy density, the lighter the weight. This makes it more suitable for weight-sensitive devices such as drones and laptops.

2. Volumetric Energy Density (Specific Capacity)

Definition: The electrical energy contained per unit volume of the battery. The unit is typically Wh/L (Watt-hours per liter).

Significance: Determines the degree of "miniaturization" of the battery. The higher the volumetric energy density, the smaller the physical size 

for the same capacity, making it suitable for products with high space requirements, such as mobile phones and smart wearable devices.

Characteristics of Polymer Battery Energy Density

Polymer batteries generally refer to Lithium Polymer (Li-Polymer) batteries. Their energy density has a distinct advantage compared to traditional 

lithium-ion batteries. The core reasons for this are:

Lighter Construction: The electrolyte is solid or gel-like, eliminating the need for a metal casing. This allows for a lightweight, thin, and compact 

structure using aluminum-plastic film pouch packaging.

Higher Space Utilization: The cells can be customized into any shape, resulting in higher space utilization and indirectly boosting volumetric 

energy density.

Currently, the gravimetric energy density of consumer-grade lithium polymer batteries is approximately 200–300 Wh/kg, while the volumetric 

energy density is about 500–700 Wh/L. In contrast, power-type lithium polymer batteries (used in electric vehicles and energy storage devices) 

have a slightly lower energy density of around 150–250 Wh/kg, as they prioritize safety and cycle life.

Key Factors Affecting Energy Density

Cathode Materials: Ternary materials (NCM/NCA) have higher energy density than Lithium Iron Phosphate (LFP), making them the mainstream 

choice for high-energy-density batteries.

Anode Materials: Silicon-based anodes offer higher lithium storage capacity compared to traditional graphite anodes, significantly boosting 

energy density.

Cell Design: Utilizing high-nickel cathodes paired with silicon-based anodes, thinning the electrode sheets, and optimizing the stacking process 

can all increase energy density.

Packaging Technology: Compared to cylindrical or prismatic hard-shell packaging, pouch packaging is lighter and offers higher space utilization.

Balancing Energy Density with Other Performance Metrics

Energy density is not the higher the better; it must be balanced with other critical factors such as safety, cycle life, and cost.