Lithium batteries are widely used in electronic products, electric vehicles and other fields, and their safety has become the focus of national regulatory agencies. As an important market and regulatory maker in the world, EU puts forward strict requirements on the design, manufacture and management of lithium batteries according to relevant directives of battery products. Among them, the EU Battery Directive (Battery Directive,2006/66/EC and its revised version) clearly stipulates the safety performance, environmental protection and recycling of batteries. This article focuses on the requirements of the EU Battery Directive, focusing on whether lithium batteries need to be equipped with Secondary Protection devices (Secondary Protection Device,SPD), from regulatory compliance, analyze and explain the security assurance and technical implementation perspectives.

I. Overview of EU Battery Directive

the EU Battery Directive was originally issued in 2006, aiming at regulating the production, sale and recycling of batteries, reducing the impact of batteries on the environment and improving the safety and efficiency of battery use. This instruction covers the construction, identification, component limitation, waste recycling and other aspects of the battery. In recent years, with the popularization of lithium batteries and the occurrence of safety accidents, the EU has increasingly strict safety standards and testing requirements for lithium batteries, especially emphasizing that batteries should have effective protection measures to prevent overcharge, overdischarge, short Circuit, abnormal temperature and other situations that may cause safety accidents.

II. Classification of protection devices in lithium batteries

in the safety design of lithium batteries, common protection devices mainly include:

1. 
   it usually refers to the internal safety mechanism of the battery, such as safety valve, diaphragm, thermal cutoff, etc. These are physical or chemical safety measures provided by the lithium battery body to prevent the battery from explosion or combustion caused by internal abnormalities.

2. Secondary Protection (Secondary Protection)
   also known as secondary protection device, it usually refers to the Electronic Protection Board (Battery Management System,BMS) or protection circuit module (PCM) of the external circuit, which is responsible for monitoring the voltage, current and temperature of the Battery, cut off the abnormal circuit in time to prevent dangerous states such as overcharge, overdischarge, and short circuit.

In lithium battery products, whether the protection device must contain secondary protection device depends on the application scenario, capacity, rated voltage and regulatory requirements of the battery.

III. Requirements of EU Battery Directive on secondary protection devices

although the EU Battery Directive does not explicitly stipulate that "secondary protection devices must be installed" one by one, its overall requirements on the safety performance of lithium batteries actually indirectly promote the popularization of secondary protection devices:

• safety Performance Standard
  the EU Battery Directive requires batteries to meet relevant safety testing standards, such as IEC 62133 series standards, which clearly stipulate that lithium batteries are being set upThe plan shall include protection measures that can prevent safety risks such as overcharge, overdischarge, and short circuit. The secondary protection device of modern lithium batteries is the key component that meets this standard.

• Producer Responsibility
  the directive emphasizes the need for producers to ensure that batteries are safe and reliable under normal and reasonably predictable use conditions. In order to meet this clause, producers usually adopt secondary protection devices to reduce the probability of safety accidents.

• Market access requirements
  lithium battery products entering the EU market need to meet the compliance testing of battery directives and relevant standards, and lithium batteries without reasonable protection devices are difficult to pass the certification process.

To sum up, although the instruction text does not directly require "secondary protection devices must be equipped", in order to meet the safety performance and compliance requirements, most lithium battery products must be equipped with corresponding protection circuits.

IV. Why do lithium batteries need secondary protection devices

1. Prevent overcharge and overdischarge

the safety margins voltage range of lithium battery is relatively narrow. Overcharging may lead to out-of-control chemical reaction inside the battery, resulting in gas, expansion and even combustion. Overdischarging damages the negative electrode structure, resulting in irreversible loss of capacity. The secondary protection device monitors the battery voltage in real time to ensure that it works within a safe range.2. Prevent overcurrent and short circuit

when the battery encounters a short circuit, it will generate a large current and release a large amount of energy instantly, which is easy to cause fire. The secondary protection device can quickly detect abnormal current, cut off the circuit in time, and protect the safety of batteries and equipment.

3. Temperature Monitoring

battery overheating is one of the security risks. The secondary protection device detects the battery temperature through the temperature sensor and takes protective measures when it exceeds the set threshold to avoid thermal runaway.

4. Battery balance

lithium battery pack consists of multiple single batteries in series. Unbalanced charging and discharging will shorten the battery life. The secondary protection device adjusts the monomer voltage through the equalization function to improve the overall performance and service life of the battery pack.

V. Application Scope and exceptions of secondary protection devices

although most lithium battery pack (especially battery packs with large capacity, which are used in electric vehicles, energy storage systems and other fields) must be equipped with secondary protection devices, in some small or specific applicationsIn this scenario, there are exceptions to the secondary protection device:

• small capacity battery
  lithium batteries with very small capacity (such as some built-in batteries of consumer electronics products) may rely on primary protection devices, and their application scenarios are relatively safe. In some cases, regulations allow them not to be equipped with complex secondary protection circuits.

• Integrated Device Protection
  in the design of some equipment, the protection function is undertaken by the circuit system of the equipment itself. The battery body is not equipped with secondary protection device alone, but the overall safety system meets the requirements of the European Union.

It should be noted that no matter whether it is equipped with secondary protection device or not, lithium battery must pass the safety performance test stipulated by EU to ensure its safety and reliability.

EU Battery Directive for lithium battery the safety performance of the lithium battery has put forward strict requirements. Although it is not clearly stipulated that the lithium battery must be equipped with secondary protection devices, its overall safety standards and market access requirements make the secondary protection devices become the standard configuration of lithium battery design. The secondary protection device greatly improves the safety and stability of lithium batteries by preventing multiple safety risks such as overcharge, overdischarge, overcurrent, short circuit and temperature abnormality, ensuring that the batteries conform to EU regulations and standards.