Lithium Ion Cylindrical Cells Vs. Prismatic Cells

Cylindrical and Prismatic Cells are the most common options on the market for building Lithium Batteries. Before you purchase a battery for your application consider the following advantages and drawbacks of each type of cell.




Cylindrical Cells

Cylindrical cells are the most common cell type in use today. This design allows for better automation processes and techniques that increase consistency and lower cost.

Prismatic Cells

Prismatic cells have gained popularity because their large capacity and prismatic shape that make it easy to connect 4 cells together and create a 12V battery pack. 






Cylindrical Advantages

Compared to prismatic cells, cylindrical cells can be produced much faster so more KWh per cell can be produced every day equaling lower $ per KWh. The electrodes in a cylindrical cell are wound tightly and encased in a metal casing, This minimizes electrode material from breaking up from the mechanical vibrations, thermal cycling from charging and discharging and mechanical expansion of the current conductors inside from thermal cycling. Many cells are combined in series and in parallel to increase voltage and capacity of the battery pack. If one cell goes bad, the impact on the entire pack is low. With prismatic cells if one cell goes bad it can compromise the whole battery pack. Cylindrical cells radiate heat and control temperature more easily than prismatic cells.






Prismatic Disadvantages

Prismatic cells are made up of many positive and negative electrodes sandwiched together leaving more possibility for short circuit and inconsistency. The higher capacity makes it difficult for the BMS to protect each cell from over charging and dissipating heat. The larger cell size minimizes the possibility for automation leading to a lower degree of consistency. The internal electrodes can easily expand and contract causing deformation which can lead to a internal short circuit and are more prone to swelling similar to lead batteries.




Smart Battery Cell Safety Features and Design

The main issue with all lithium batteries is how to prevent a cell from overheating and rupturing if over charged. Smart Battery has several layers of safety redundancy systems at the cell level. The most notable safety feature is the internal thermal fuse between the anode and cathode that will shut down the cell before the temperature rises, preventing pressure build up and activating the 1.5Mpa safety vent. If the thermal fuse failed and pressure was released through the safety vent, the electrolyte has a flame retardant additive making the battery safe. These conditions would likely only occur if a charger or controller failed spiking current into the battery. The BPS is designed to protect the cells from this anomaly by opening at 15.8V and would have to fail in the closed state allowing excess current into the cells. The Group 31 - 12V 100AH is built with 80 cylindrical 3.2V 5AH (32650) cells combined with 4 sets of 20 cells in parallel and then combined in series. All 80 cells are matched by measuring 10 consistencies during several charge / discharge cycles at the end of production.



Thermal Fuse 

INTERNAL CELL SAFETY FUSE

Each cell has a built in thermal safety fuse between the anode and cathode that will break in the unlikely event the cell would begin to overheat.

safety vent 

HIGH PRESSURE SAFETY VENT

A high pressure safety vent will flip open to release energy and prevent explosion if exposed to extreme heat.

electrolyte
 

FLAME RETARDANT ELECTROLYTE

Our cells are manufactured with a flame retardant additive in the electrolyte making them safe.

explosion proof 

EXPLOSION PROOF STAINLESS STEEL

Every Smart Battery cell is manufactured in an explosion proof stainless steel cylindrical case.


Cell Matching Process


1. Consistency of Self Discharge

2. Consistency of Voltage

3. Consistency of Inner Impedance

4. Consistency of Capacity

5. Consistency of Cycle Life

6. Consistency of Platform

7. Consistency of Constant Current Rate

8. Consistency of Cell Power Control

9. Consistency of Parallel Module Control

10. Consistency of Finished Battery Module.



cell balancing
 

bolted  cells

LENGTHWAY BOARD
 

Circuit Protection 

The BMS balances the cells by sending more current through the length way circuit boards and into cells with a lower voltage. The BMS will also discharging cells that exceed 3.65V during charging.

Smart Battery cells positive and negative terminals are bolted vs the more common tab welded method. This creates a better connection for higher amperage loads and better current conductivity.

The Lengthway Circuit Boards have a unique function of over current and cross protection. The cells bolt through lengthway circuit board that provide balancing, even current flow, short circuit protection and add rigid strength to the battery pack.

If a cell over heats or if the battery is penetrated by a metal object the Lenghtway Circuit Board will disconnect the impacted cells allowing the rest of the battery to continue to function normally. 





Comments or Questions? let us know how we can help. 



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