BMW i3: Battery System

Lithium-ion battery module structure, cooling/warm-up system

2017/04/17

Summary

 In addition to the 21.8 kWh lithium-ion battery featured on BMW's i3 EV that was available from the time the vehicle was launched, a 33.3 kWh version was released in 2016. The new battery extends the driving range of the European model by 1.5 times, from 190 km to 300 km. In either case, the battery case is the same size and located under the cabin. The batteries are supplied by Samsung SDI. This report will cover the 21.8 kWh battery system. It was generated by MarkLines in cooperation with the Detroit-based vehicle benchmark engineering company Munro. Munro produces reports based on teardown analyses of various vehicles. The company scrutinizes detailed specifications such as the weight and dimensions of various parts, as well as costs. For detailed information, please make an inquiry through the following site.



The BMW i3 battery unit

The drive module has the battery equipped on the bottom of the cabin The battery case as seen from the underside of the vehicle (central area)
The drive module has the battery equipped on the bottom of the cabin The battery case as seen from the underside of the vehicle (central area)

 The lithium-ion battery in the i3 is located in the center of the aluminum frame that carries the drive module powertrain and suspension unit. The central area of the vehicle is protected by the CFRP cabin that is joined to the top of the high rigidity frame, and deformation is kept to a minimum in the event of a collision by the impact-absorbing structure of the front and rear overhangs. The bottom of the battery case is connected to the front and rear diffusers to create an entirely flat underbody, thereby reducing air resistance and increasing stability during high speed driving.



Battery units with eight battery modules connected as a series

Battery module Eight battery modules are fitted within the battery unit
Battery module Eight battery modules are fitted within the battery unit

 The battery unit is located inside aluminum casing, and encompasses eight individual battery modules. The battery modules are connected to each other as a series via power terminals. Furthermore, each battery module features a control board. Aside from the power connection harness, a communication harness is connected to the control board and each battery module's performance is monitored. A battery control circuit unit is located behind the battery casing.



Battery modules composed of twelve battery cells

The battery module with the top cover open Two rows of six battery cells are in one battery module
The battery module with the top cover open Two rows of six battery cells are in one battery module

 The plastic battery module cover houses twelve battery cells. The battery cells are connected as a series via metal terminals. The terminal on the cell at the end of the battery module is connected to the adjoining battery module with a high-voltage harness. A thin wire harness is connected to each battery cell to monitor conditions, and then connects to a voltage sensor. The battery cell features an aluminum casing for reduced weight and cooling properties. The interior of the cells have a separator sandwiched between the positive and negative electrodes, which are flattened and thinly folded.



A battery cell The battery cell aluminum casing The inside of the battery cell (electrodes are flattened and rolled)
A battery cell The battery cell aluminum casing The inside of the battery cell (electrodes are flattened and rolled)

 The battery cell casings are made from aluminum to reduce weight, and also to take advantage of its cooling properties. The internal structure of the cells is composed of laminated layers of thin electrode foils.



Battery cooling/warm-up system featured on the bottom of the aluminum battery casing

Battery casing Battery casing top cover
Battery casing Battery casing top cover

 The top cover and battery casing are made from aluminum to reduce weight, and also to take advantage of its cooling properties. The casing is constructed of press-molded plates welded together.



Battery cooling/warm-up system
Battery cooling/warm-up system

 A cooling/warm-up system is installed on the bottom of the battery casing. Piping for the air conditioner refrigerant used for cooling and an electric heater are placed on top of one another.