Researchers at the University of St. Andrews in Scotland have devised a new approach to synthesize an electrode material for lithium-ion batteries that provides superior power and charge retention. They describe their results in the latest issue of Advanced Materials.
Lithium-ion battery electrodes use intercalation materials. These materials are composed of a solid network of lithium atoms together with other metals, such as cobalt, nickel, or manganese meshed together with oxygen atoms.
When you charge a lithium-ion battery, the charging current pulls the positive lithium ions out of this network. Then, when you use the battery, it discharges as these lithium ions migrate back into the electrode, pulling electrons as they go, and so generating a current.
The challenge is to make new electrode materials that deliver high power (fast discharge) and high energy storage. To address these issues, Kuthanapillil Shaju and Peter Bruce developed a new way of synthesizing a particular lithium intercalation compound (Li(Co1/3Ni1/3Mn1/3)O2). As a bonus, they hoped to be able to simplify the complicated manufacturing process.
The St Andrews team approach involves simply mixing the necessary precursor compounds—organic salts of the individual metals—with a solvent in a single step. This is in contrast to the conventional multi-step process used for making the compound. Using this technique, they were able to make highly uniform lithium oxide intercalation materials in which nickel, cobalt, and manganese ions are embedded at regular intervals in the solid, which also contains pores for the electrolyte.
The highly porous nature of the new material is crucial to its electrical properties. The pores allow the electrolyte to make intimate contact with the electrode surface resulting in high rates of discharge and high energy storage.
The St Andrews team has tested their new lithium electrode material by incorporating it into a prototype battery and found that it gives the battery far superior power and charge retention.
Increasing the rate by 1,000%, so that the battery can be discharged in just six minutes, reduces the discharge capacity by only 12%. The test results suggest that this approach to rechargeable batteries could be used to make even higher power batteries for vehicles and power tools.
There’s an added bonus in that replacing a proportion of the cobalt used in the traditional lithium-cobalt-oxide electrodes with manganese improves safety by reducing the risk of overheating.
“Macroporous Li(Ni1/3Co1/3Mn1/3)O2: A High-Power and High-Energy Cathode for Rechargeable Lithium Batteries” K. M. Shaju, P. G. Bruce; Advanced Materials, Volume 18, Issue 17 , Pages 2330 - 2334