1. Overview and Background

In recent years, the drone market has continued to thrive, with the demand for drones in both civilian and military sectors constantly on the rise. The recent market growth has driven rapid technological advancements in drones, making them an indispensable part of various applications. This strong demand has led to the rapid iteration of drone products and has also spurred the development of supporting technologies such as avionics systems, navigation systems, data link systems, and power systems.

The Importance of Lithium Polymer Batteries

It is particularly worth noting that lithium polymer batteries, due to their high energy density, have a significant impact on the range and flight time of drones. Their performance directly affects the range and flight time of drones, thus becoming a key factor restricting the development and application of drones.

3. Principles of Lithium Polymer Batteries

Basic Characteristics

Lithium polymer batteries, also known as polymer lithium-ion batteries, represent the latest generation of lithium battery technology. They offer numerous advantages, such as high energy density, light weight, flexibility, and the ability to be customized into any shape. In the same volume, the capacity of lithium polymer batteries can reach twice that of conventional lithium batteries, and they are more cost-effective and safer. These batteries are typically packaged in aluminum-plastic or fire-resistant plastic.

Although lithium polymer batteries have a similar structure to liquid lithium batteries, the key difference lies in the type of electrolyte. Lithium polymer batteries use polymer materials in at least one of the positive electrode, negative electrode, or electrolyte. In current technological development, polymer materials are mainly applied to the positive electrode and electrolyte. The positive electrode materials have a wide range of options, including conductive polymer materials and inorganic compounds commonly used in lithium-ion batteries. The reaction process of lithium polymer batteries involves the interaction between lithium and intercalation compounds of carbon.

4. Key Performance Indicators

Voltage and Capacity

The voltage characteristic of a battery is one of the important indicators for evaluating its performance. The voltage characteristic is crucial for the battery performance and needs to be precisely controlled and monitored. For a single cell, its rated voltage is usually set at 3.7V. The unit of battery capacity is commonly expressed in Ah or mAh. For example, a battery labeled as 22000mAh can theoretically last for 2.2 hours when operating at a current of 1A.

Energy and Density

Increasing energy density can significantly enhance the battery's endurance. Energy density refers to the energy released by a unit volume or mass of the battery. Measured by unit volume, it is called volumetric energy density and is usually referred to as energy density, with units of Wh/L. For example, a lithium battery weighing 300g has a rated voltage of 3.7V and a capacity of 10Ah, so its specific energy is 123 Wh/kg.

Discharge Rate

Discharge rate (C) is an indicator for measuring the current required to discharge the battery's rated capacity within a specified time. It represents the multiple of the battery's rated capacity. The discharge rate affects the battery's instantaneous current output capability. For example, a battery with a capacity of 24Ah and a discharge rate of 5C can have a discharge current of up to 120A.

State of Charge and Internal Resistance

State of Charge (SOC) represents the ratio of the remaining capacity of the battery after discharge to its fully charged state. Its value ranges from 0 to 1. Accurate state of charge and low internal resistance are key to the efficient operation of the battery. The unit of internal resistance is typically milliohms (mΩ). Batteries with higher internal resistance generate more internal power consumption during charging and discharging, limiting the application of high discharge rates.

Self-Discharge and Lifespan

Self-discharge refers to the phenomenon where the battery's voltage gradually decreases when it is left in an open circuit state. This phenomenon is influenced by various factors such as manufacturing process, material selection, and storage environment. Self-discharge has a significant impact on battery capacity and lifespan is an important consideration for batteries. Lifespan of the battery involves two parameters: cycle life and calendar life. Cycle life refers to the number of times the battery can be charged and discharged, while calendar life refers to the time span experienced in a specific usage environment.

4. Development of Unmanned Aerial Vehicle Lithium Batteries

Generalization and Challenges

As unmanned aerial vehicle technology continues to develop, although general polymer lithium batteries are flexible and cost-effective, they face many usage challenges. Generalized polymer lithium batteries have gradually become the new favorite in the unmanned aerial vehicle field. These batteries not only have excellent performance but also can be flexibly applied to different weight classes of unmanned aerial vehicles. However, this battery cannot monitor the battery's charge level in real time, increasing the risk of crashing.

Intelligent Improvement

To address the usage pain points of generalized polymer lithium batteries, improving battery usage efficiency and safety through intelligent management systems is the current development trend. Intelligent polymer lithium batteries have undergone comprehensive optimization design. Through deep integration with the unmanned aerial vehicle flight control system and optimizing the battery management system, intelligent management and precise control of the battery are achieved.

Solidification Prospects

The development of solid-state lithium batteries has a bright prospect and will greatly improve the shortcomings of existing battery performance. Solid-state lithium-ion batteries have much higher energy density. By using all-solid-state electrolytes, lithium batteries can break away from the dependence on graphite anode embedded with lithium and directly use lithium metal as the anode. We expect to continuously promote the advancement of lithium battery technology through continuous innovation and reform, thereby injecting new impetus into the development of unmanned aircraft.