Research on Direct Current Resistance,
Direct Current,

▍What is CTIA CERTIFICATION?

CTIA, the abbreviation of Cellular Telecommunications and Internet Association, is a non-profit civic organization established in 1984 for the purpose of guaranteeing benefit of operators, manufacturers and users. CTIA consists of all U.S. operators and manufacturers from mobile radio services, as well as from wireless data services and products. Supported by FCC (Federal Communications Commission) and Congress, CTIA performs a large part of duties and functions that were used to be conducted by the government. In 1991, CTIA created an unbiased, independent and centralized product evaluation and certification system for wireless industry. Under the system, all wireless products in consumer grade shall take compliance tests and those complying with the relevant standards will be granted to utilize CTIA marking and hit store shelves of North American communication market.

CATL (CTIA Authorized Testing Laboratory) represents labs accredited by CTIA for testing and review. Testing reports issued from CATL would be all approved by CTIA. While other testing reports and results from non-CATL will not be recognized or have no access to CTIA. CATL accredited by CTIA varies in industries and certifications. Only CATL which is qualified for battery compliance test and inspection has access to battery certification for compliance to  IEEE1725.

▍CTIA Battery Testing Standards

a) Certification Requirement for Battery system Compliance to IEEE1725— Applicable to Battery Systems with single cell or multiple cells connected in parallel;

b) Certification Requirement for Battery system Compliance to IEEE1625— Applicable to Battery Systems with multiple cells connected in parallel or in both parallel and series;

Warm tips: Select above certification standards properly for batteries used in mobile phones and computers. Do not misuse IEE1725 for batteries in mobile phones or IEEE1625 for batteries in computers.

▍Why MCM？

● Hard Technology: Since 2014, MCM has been attending battery pack conference held by CTIA in US annually, and is able to obtain latest update and understand new policy trends about CTIA in a more prompt, accurate and active way. 

●Qualification: MCM is CATL accredited by CTIA and is qualified to perform all processes related to certification including testing, factory audit and report uploading.

During charging and discharging of batteries, the capacity will be influenced by the overvoltage caused by internal resistance. As a critical parameter of battery, internal resistance is worth research for analyzing battery degradation. The internal resistance of a battery contains:
Ohm internal resistance (RΩ) –The resistance from tabs, electrolyte, separator and other components.Charges transmission internal resistance (Rct) – The resistance of ions passing tabs and electrolyte. This represents the difficulty of tabs reaction. Normally we can increase the conductivity to reduce this resistance.Polarization Resistance (Rmt) is the internal resistance caused by density uneven of lithium ions between cathode and anode. Polarization Resistance will be higher in situations like charging in low temperature or high rated charge.Normally we measure the ACIR or DCIR. ACIR is the internal resistance measured in 1k Hz AC current. This internal resistance is also known as Ohm resistance. The shortage of the data is that it cannot directly show the performance of a battery. DCIR is measured by a forced constant current in a short time, in which the voltage continuously changes. If the instantaneous current is I, and the change of voltage in that short term is ΔＵ, according to Ohm law Ｒ＝ΔＵ／Ｉ We can get the DCIR. DCIR is not about only Ohm internal resistance, but also charge transfer resistance and polarization resistance.It’s always a difficulty on the research of DCIR of a lithium-ion battery. It’s mainly because the internal resistance of a lithium-ion battery is very small, usually just some mΩ. Meanwhile as an active component, it is hard to measure the internal resistance directly. Besides, the internal resistance is influenced by the status of environment, like temperature and charges status. Below are standards that have mentioned about how to test DCIR.