Research on Direct Current Resistance,
Direct Current,

▍Vietnam MIC Certification

Circular 42/2016/TT-BTTTT stipulated that batteries installed in mobile phones, tablets and notebooks are not allowed to be exported to Vietnam unless  they are subjected to DoC certifctaion since Oct.1,2016. DoC will also be required to provide when applying Type Approval for end products (mobile phones, tablets and notebooks).

MIC released new Circular 04/2018/TT-BTTTT in May,2018 which stipulates that no more IEC 62133:2012 report issued by overseas accredited laboratory is accepted in July 1, 2018. Local test is necessity while applying for ADoC certificate.

▍Testing Standard

QCVN101：2016/BTTTT（refer to IEC 62133：2012)

▍PQIR

The Vietnamese government issued a new decree No. 74/2018 / ND-CP on May 15, 2018 to stipulate that two types of products imported into Vietnam are subject to PQIR (Product Quality Inspection Registration) application when being imported to Vietnam.

Based on this law, the Ministry of Information and Communication (MIC) of Vietnam issued the official document 2305/BTTTT-CVT on July 1, 2018, stipulating that the products under its control (including batteries) must be applied for PQIR when being imported into Vietnam. SDoC shall be submitted to complete the customs clearance process. The official date of entry into force of this regulation is August 10, 2018. PQIR is applicable to a single import to Vietnam, that is, every time an importer imports goods, he shall apply for PQIR (batch inspection) + SDoC.

However, for importers who are urgent to import goods without SDOC, VNTA will temporarily verify PQIR and facilitate customs clearance. But importers need to submit SDoC to VNTA to complete the entire customs clearance process within 15 working days after customs clearance. (VNTA will no longer issue the previous ADOC which is only applicable to Vietnam Local Manufacturers)

▍Why MCM?

● Sharer of Latest Information

● Co-founder of Quacert battery testing laboratory 

MCM thus becomes the sole agent of this lab in Mainland China, Hong Kong, Macau and Taiwan.

● One-stop Agency Service

MCM, an ideal one-stop agency, provides testing, certification and agent service for clients.

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.
International standard:
IEC 61960-3: 2017: Secondary cells and batteries containing alkaline or other non-acid electrolytes – Secondary lithium cells and batteries for portable applications – Part 3: Prismatic and cylindrical lithium secondary cells and batteries made from them.
IEC 62620:2014: Secondary cells and batteries containing alkaline or other non-acid electrolytes – Secondary lithium cells and batteries for use in industrial applications.