5
The Evolion is a single 48 V module. The main components include a 14 cell pack of VL80E and two main electronic printed circuit
boards. A
Battery Management System Telecom (BMST)
is built into each module. With its microprocessor combined with the BMST
software (or firmware), the BMST optimizes the performance and protects the Evolion against situations like over charge, over and
under discharge, over and under temperature or over current. No external BMS is used. Each Evolion can be installed and operated
independently regardless of the number connected on the same power bus.
The BMST also allows communication via RS485 bus with the Saft Evolion Toolbox supervision software, for diagnostics or application
controller and its software, for feedback control. It can also integrate to the application alarm panel using a dry contact signal.
3. Evolion construction
A spirally wound electrode coil is used. The electrodes are made by depositing the active materials, mixed with a binder and
conductive agents, on a current collector. A metallic copper is used for the negative current collector and a metallic aluminum is
used for the positive current collector. A non-conductive separator material is interleaved in the coil to prevent short-circuiting of the
positive and negative and allow the electrolyte to conduct the lithium ions.
The electrolyte consists of a proprietary mixture of alkyl carbonates and lithium salt. A vinylene carbonate additive is used for negative
electrode SEI formation (Solid-Electrolyte Interface). The electrolyte is non-aqueous. The electrolyte conducts lithium ions from the
positive to the negative during charge and discharge.
The Li-ion electrochemistry accepts charge current with approximately 100 % coulombic efficiency over all temperature ranges. Unlike
aqueous battery technologies (Ni-Cd and Lead acid), the Li-ion electrochemistry does not use side reactions, like water electrolysis,
even when fully charged. Overcharging will not occur with Li-ion technology. Once the cell is fully charged, an insignificant amount of
charge current will be accepted by the cells. The Saft NCA lithium ion cell is sealed and does not produce or exhaust any gases during
normal operation.
The reaction mechanism of lithium-ion batteries is represented by Figure 1. The positive and negative materials facilitate intercalation
of lithium ions. The net effect of the charge and discharge reaction is the movement of lithium ions back and forth between the
electrodes. The corresponding flow of electrons in the external circuit is proportional to the ion flow between the electrodes. There is
no lithium metal formed in the NCA Li-ion electrochemistry used in the Evolion and therefore there are no hazards associated to that.
The Li-ion cell pack operates in a system combined with electronics (see section Evolion construction). The system is designed with
redundant safety functions to make sure the cells never exceed a preset operating level. One of the main safety factors is the cell
temperature limits. The Evolion operates normally and safely in the temperature range from - 40°C to + 75°C (- 40°F to + 167°F).
Important note: Chemical instability begins at above +
80°C (+
176°F).
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