Studies On Electrode Materials For Lithium-Ion Batteries

Abstract

In the early 1970s, research carried out on rechargeable lithium batteries at the Exxon Laboratories in the US established that lithium ions can be intercalated electrochemically into certain layered transition-metal sulphides, the most promising being titanium disulphide. Stemming from this discovery for titanium disulphide, there has been increased interest on lithium-ion intercalation compounds for application in rechargeable batteries. The first rechargeable lithium cell was commercialized in late 1980s by Moli Energy Corporation in Canada. The cell comprised a spirally wound lithium foil as the anode, a separator and MoS2 as the cathode. The cell had a nominal voltage of 1.8 V and an attractive value of specific energy, which was 2 to 3 times greater than either lead-acid or nickel-cadmium cells. However, the battery was withdrawn from the market after safety problems were experienced. This paved way for the discovery of lithium-ion battery.

The origin of lithium-ion battery lies in the discovery that Li+-ions can be reversibly intercalated within or deintercalated from the van der Walls gap between graphene sheets of carbon materials at a potential close to the Li/Li+ electrode. Thus, lithium metal is replaced by carbon as the anode material for rechargeable lithium-ion batteries, and the problems associated with metallic lithium mitigated. Complimentary investigations on intercalation compounds based on transition metals resulted in establishing LiCoO2 and LiNiO2 as promising cathode materials. By employing aforesaid intercalation materials, namely carbon and LiCoO2 respectively, as negative and positive electrodes in a non-aqueous lithium-salt electrolyte, a Li-ion cell with a voltage value of about 3.5 V resulted. These findings led to a novel rechargeable battery technology.

Lithium-ion batteries were first introduced commercially in 1991 by the Sony Corporation in Japan. Other Japanese manufacturers soon entered the market, followed closely by American and European companies. The subsequent growth in sales of the batteries was truly phenomenal. Beginning from 1991, the lithium-ion battery market has grown from an R&D interest to sales of over 400 million units in 1999. The global market value for lithium-ion batteries at original equipment manufacturer level was estimated to be $1.86 billion in 2000. By 2006, the market is expected to grow to over 1.2 billion units with value of over $4 billion, while the average unit price is expected to fall.

Initially, realizable specific energy of commercial Li-ion battery was only about 120 Wh kg-1. However, with continuing improvements in various cell components, present day Li-ion batteries can provide a specific energy density of about 200 Wh kg-1. With the ‘holy grail’ far to be realized, the current R&D efforts are focussed on furthering the specific energy of lithium-ion batteries in conjunction with safety, environmental compatibility, and cost effectiveness.

In the Li-ion cell, all of its electrochemical constituents, namely anode, cathode and electrolyte are central to its performance. This thesis describes some novel studies on cathode and anode materials for lithium-ion Batteries.