Li battery: concept and its application in NEV

The lithium-ion Battery (LiB) features numerous advantages such as high energy density, high discharge voltage, minimal self-discharge, long cycle life and no memory effect. These have resulted in a wide use as the power source for New Electric Vehicles (NEV).

Typically, the LiB pack is placed at the bottom of the chassis. During the charging and discharging process, the battery produces a certain amount of heat. If the heat cannot be effectively dissapated in time, its accumulation will lead to rising the temperature of the battery, thereby deteriorating its performance and even causing a potential battery thermal runaway. This performance deterioration is related to the optimum operating temperature of an LiB which is in the range of 20~40 ℃. This calls for a better design of the Battery Thermal Management System (BTMS) which includes as well the choice of the appropriate coolant.

Today's mainstream technology for indirect cooling LiB batteries involves using a water/MEG based coolant, flowing through channels within a coolant plate or belt.

Electrode materials play a key role in LiB performance. In addition, they can play an important role in safety challenges. At this moment, an LiB battery can simply be classified into two categories based on the used cell chemistry, i.e., NCM and LFP. NCM stands for Ni, Co and Mn whereas LFP means Lithium iron (ferrous) phosphate. Each material has its own characteristics, for example. NCM has a higher energy density which means longer mileage; however its weakness is that it can lead to a thermal runaway - which is a safety concern. LFP on the other hand has a lower energy density but is considered be safer. Additionally, it is less costly. Nevertheless, both technologies have already evolved and have undergone a lot of progress.

Another classification of LiB can be made, broadly speaking, by dividing them into three groups in terms of shape - namely, Cylindric, Prismatic and Pouch. Among them, the prismatic one has the biggest marketing share due to its ease of production, vehicle layout flexibility and safety considerations.

Regarding cylindric cooling: a twisty cooling belt is closely attached to the cylindric battery array in which coolant flow to transfer the heat. For prismatic and pouch battery very often a bottom placed coolant plate is used in combination with vertical cooling plate in between the pouch cells/modules.