Batteries

Hannu Jääskeläinen

This is a preview of the paper, limited to some initial content. Full access requires DieselNet subscription.
Please log in to view the complete version of this paper.

Abstract: Lithium-ion batteries are the dominant type of battery for vehicle applications. Many variations of Li-ion batteries are possible that utilize different electrode and electrolyte materials. With the focus on improving the driving range and reducing costs of electric vehicles, battery technology has seen significant advances focusing on improving battery capacity and safety while minimizing increases in mass and reducing cost.

Introduction

The battery is arguably the most critical component of electric vehicles. With the increased focus on improving the driving range and reducing costs of electric vehicles, battery technology has seen significant advances since the 1990s. Much of the focus has been on improving battery capacity and safety while minimizing increases in mass and reducing cost.

Li-ion batteries are the dominant type of battery for vehicle applications. Many variations of Li-ion batteries are possible depending on electrode and electrolyte materials selected.

Battery Basics

Figure 1 shows some details of a typical Li-ion battery cell. The main components are a graphite anode, a lithium metal oxide cathode and an electrolyte. The cathode in this illustration is lithium cobalt oxide (LCO), LiCoO2, but other cathode materials are possible as well. The anode incorporates a copper current collector and the cathode an aluminum current collector. In this example, a liquid electrolyte of a lithium salt and an organic solvent are used (e.g., LiPF6 salt with ethylene carbonate electrolyte). A separator, such as a microporous polymer membrane (e.g., polyolefin resins such as polyethylene (PE), polypropylene (PP) or their composites are common), prevents physical contact of the electrodes while allowing the exchange of lithium ions between the electrodes.

[SVG image]
Figure 1. Li-ion cell structure

In practice, the components can be manufactured as thin foils that can be packaged into different configurations such as the cylindrical, pouch and prismatic geometries, Figure 2 [5197]. Pouch cells are typically packaged in a soft aluminum plastic film. Prismatic cells are rectangular in shape but have a hard shell.

[schematic]
Figure 2. Battery cell configurations

(Adapted from Lidbeck [5197])

During charging, electrons are released from the cathode and collected at the anode via an external circuit and Li ions move from the cathode (deintercalate) to the anode (intercalate) via the electrolyte. For an LCO battery:

Cathode: LiyCoO2 ↔ Liy-xCoO2 + xLi+ + xe-(1)

Anode: C6 + xLi+ + xe- ↔ LixC6(2)

During discharging, the reverse reactions occur. Further discussion of Li-ion battery basics can be found elsewhere [5198]. For LCO, only partial deintercation of Li from the cathode is possible before the cathode is irreversibly damaged and a practical value of x = 0.5.

###