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In the structural design of battery packs and energy storage modules, flame-retardant copper foil tape often appears in the BOM: shielding and grounding are required between battery cells, insulation and electromagnetic isolation are required inside the module, and copper foil tape has become a common auxiliary material due to its simultaneous conductivity, shielding, and certain flame retardancy.
During the selection review, the supplier provided a test report for "UL94 V-0" and the material passed. Engineers classify this tape as a "flame retardant material" psychologically, and in the design discussion of thermal runaway protection, it is considered as part of a "flame retardant barrier". This classification is not problematic at the compliance level, but there is a boundary that needs to be clarified at the functional level: V-0 proves "self extinguishing upon leaving the fire", not "blocking heat".
Test conditions for V-0: small flame, short contact, vertical combustion
The testing method for UL94 V-0 involves hanging the sample vertically, contacting the lower end of the sample with a standard methane flame (approximately 50W) for 10 seconds, then moving the flame away and recording the remaining flame time. The qualification criteria are: residual flame ≤ 10 seconds per test, total residual flame ≤ 50 seconds for 5 samples, and no dripping igniting cotton fibers.
Questions to be answered by V-0
This test assesses the self extinguishing ability of materials after short-term contact with small flames. The power of the flame is about 50W, the contact time is 10 seconds, and the total amount of heat input is limited. The question V-0 needs to answer is: Will the material continue to burn after being ignited, and will it spread the fire to other places.
Thermal runaway condition: above 1000 ° C, lasting for tens of seconds to minutes
The working condition of thermal runaway of battery cells is not on the same level as V-0 testing. Taking ternary lithium battery cells as an example, after thermal runaway is triggered, the internal temperature of the cell can quickly rise to over 800 ° C-1000 ° C. The flame and high-temperature particles sprayed from the pressure relief valve can reach a temperature of over 1000 ° C, with a duration ranging from tens of seconds to minutes, and a heat flux density much higher than that of a small flame of 50W.
Under such heat input, the material is not facing the problem of "whether it will self extinguish", but the problem of "how long it will burn through and whether the heat will be transferred to adjacent cells". The testing conditions for V-0 do not include the term 'sustained high-temperature heat flow', therefore the test results of V-0 cannot be used to infer the insulation time or blocking ability of the material under thermal runaway flames.
The real role boundary of flame-retardant copper foil tape in battery packs
By clarifying the meaning of V-0, the role of flame-retardant copper foil tape in battery packs can be more accurately positioned.
It can do it
Provide shielding and grounding functions in scenarios where the battery cell is operating normally and experiencing localized overheating; In the event of a localized small-scale fire (such as connector ignition or wire harness short circuit), the material itself does not actively support combustion, self extinguishes upon ignition, and does not become additional fuel for flame propagation; Provide certain electrical insulation and electromagnetic isolation inside the module.
It can't do it
Block the high-temperature flames and particles that cause thermal runaway of battery cells; Maintain structural integrity and insulation capability under sustained high temperature heat flow; It can replace professional thermal barrier materials such as aerogel, mica plate and ceramic silicone rubber. Placing flame-retardant copper foil tape in a position that blocks the spread of thermal runaway is a misuse of its ability. It should be placed in the position of "shielding, grounding, and insulation assistance", and the thermal barrier function is undertaken by specialized thermal barrier materials.
Another issue with copper foil in thermal runaway scenarios: thermal conductivity rather than insulation
Copper foil is an excellent thermal conductor with a thermal conductivity of approximately 400 W/(m · K). In the scenario of thermal runaway, this characteristic is negative: if the copper foil tape crosses the area between the thermal runaway cell and adjacent cells, the copper foil will quickly conduct heat from the thermal runaway area to the adjacent area, accelerating heat propagation rather than blocking it.
This is two independent dimensions from 'flame retardancy'. V-0 assesses combustion behavior, not thermal conductivity behavior. A V-0 copper foil tape may become a "bridge" for heat propagation in thermal runaway scenarios due to the high thermal conductivity of the copper foil. This is also why in the design of thermal runaway protection, the use of copper foil materials needs to be coordinated with thermal barrier materials, rather than solely responsible for insulation function.
Selection judgment based on "grade x thermal barrier x position"
Firstly, position UL94 V-0 as a "compliance attribute" rather than a "thermal barrier performance"
V-0 is a certification of the combustion behavior of materials under specific testing conditions, which answers "whether the material is easy to sustain combustion" and does not answer "how much heat the material can block". In the design discussion of thermal runaway protection, V-0 cannot replace thermal barrier performance data (such as thermal conductivity, specific heat capacity, burn through time, back temperature rise curve).
Secondly, differentiate the functional requirements of materials based on their application locations, rather than covering all locations with one material
The shielding and grounding positions between battery cells, as well as the conductivity and V-0 compliance of flame-retardant copper foil tape, are the main requirements; Professional thermal barrier materials such as aerogel, mica board or ceramic materials are required at the blocking position of heat runaway transmission between the electric core and the electric core. The two materials play their respective roles in the structure, and "V-0 copper foil tape" cannot replace thermal barrier materials.
Thirdly, when using copper foil tape across regions, evaluate the impact of its thermal conductivity path on heat propagation
If the copper foil tape crosses the area between the high-risk zone of thermal runaway and adjacent cells, the thermal conductivity of the copper foil may accelerate heat propagation. In this case, it is necessary to consider adding thermal blocking design on the copper foil path (such as disconnecting the copper foil, adding insulation layer), or using conductive materials with lower thermal conductivity.
Fourthly, in the overall thermal runaway protection design of the battery pack, flame-retardant copper foil tape should be managed as an "auxiliary material" rather than a "safety barrier"
Its V-0 compliance helps to pass the entire package's combustion testing and material compliance review, but it does not assume the function of blocking the spread of thermal runaway. The safety boundary for thermal runaway protection is determined by specialized thermal barrier materials and structural design.
Advanced Institute (Shenzhen) Technology Co., LtdThe flame retardant copper foil tape product line covers a phosphorus based halogen-free flame retardant adhesive layer system, with single and double conductive structures available. It can provide compliance data for "V-0 @ specified thickness", instructions for the adhesive layer flame retardant system, and evaluation recommendations for copper foil thickness and thermal conductivity path.
The product is positioned as a shielding, grounding, and insulation auxiliary function in battery packs and energy storage modules, helping engineers make a clear distinction between compliance and functional positioning. For more technical information, please visithttp://www.avanzado.cn/.