Improving the Charge-Discharge Capacity and Cycleability of Carbon Electrodes for Li-ion Batteries
06 June 2010
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| Charge and discharge curves of seven different materials studied. GMP40 (60:40 weight ratio of mixed mesophase pitch carbon and phenolic resin) produced the best results. Credit: ACS, Lin et al. Click to enlarge. |
As one of the many approaches under investigation to increase the power density, specific capacity, and cyclic efficiency of rechargeable lithium-ion batteries, researchers are seeking to develop higher-capacity anode materials (such as silicon- or tin-based materials). However, carbon remains the predominant commercial anode material solution at this point.
Researchers at Feng Chia University in Taiwan have developed a procedure to prepare surface-modified mesophase pitch carbon to increase the charge-discharge capacity and cycleability of carbon electrodes for lithium-ion batteries (LIBs).
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| SEM images of GMP40. Credit: ACS, Lin et al. Click to enlarge. |
After high-temperature treatment, GMP40 shows the highest first charge and discharge capacities of 426 and 322 mAh g-1, respectively, while mesophase pitch carbon shows the first charge and discharge capacities of 237 and 206 mAh g-1, respectively. A paper on their work appeared online 4 June in the ACS journal Energy & Fuels.
The GMP40 material also showed strong cycling performance, with capacity remaining above 250 mAh g-1 at the 60th cycle in comparison to less than 175 mAh g-1 for the mesophase pitch carbon.
Carbon materials—currently the predominant anode material for lithium-ion batteries—are categorized into three types, the researchers note: natural graphite, artificial graphite, and graphite-like carbon. Natural graphite is superior to other carbon candidates in terms of high capacity, low irreversible capacity at the first cycle, flat and low potential profile, large amounts of resources, and low cost.
Early studies showed that coke-coated graphite exhibits some smaller irreversible capacity and better cyclability than pristine graphite. The coke-coated graphite shows lower capacity than graphite, and it decreases the total reversible capacity for the anode of LIBs. Some studies have demonstrated that carbon coating of graphite improves the anode performance in LIBs.
Presently, we show a new material for the modified traditional anode of LIBs. We used mesophase pitch carbon as a precursor to coat with various concentrations of phenolic resin for application in the anode of LIBs. The core material is mesophase pitch carbon, which is highly crystalline.
—Lin et al.
The team produced seven different materials with different ratios of mesophase pitch carbon and phenolic resin ranging from pure mesophase pitch carbon (MGP) to carbon powder produced from pure phenolic resin (GPR). These were then fabricated into electrodes.
The remarkably improved electrochemical properties for the coated mesophase pitch carbon can be mainly attributed to the outer turbostratic structure, which provided more sites for Li ions. Further studies and evaluations are needed for commercial exploitation of the mesophase pitch carbon coated with phenolic resin as negative current collectors in LIBs.
—Lin et al.
Resources
Jui-Hsiang Lin, Tse-Hao Ko, Wen-Shyong Kuo and Chia-Hung Wei (2010) Mesophase Pitch Carbon Coated with Phenolic Resin for the Anode of Lithium-Ion Batteries. Energy Fuels, Article ASAP doi: 10.1021/ef1004122
Others are also doing valuable research. Shouldn't we acknowledge it?
Improved electrodes will lead to improved batteries.
Posted by: HarveyD | 08 June 2010 at 07:03 AM
The statement "GMP40 shows the highest first charge and discharge capacities of 426 and 322 mAh g-1, respectively,..." casts doubt on the viability of this material. What these data say is roughly 25% of the Li extracted from the cathode during the first charge will be trapped in the carbon and cannot participate further in the cell utilization. Considering the best graphite anodes exhibit an irreverible cycle1 capacity loss of 7-8%, 25% is an unacceptable penalty. Stated another way, GMP40 would reduce a 3Ah Li-ion cell to ca 2.4Ah, assuming the remainder of the battery chemistry is unchanged. Poor cycle1 efficiency is the downfall of nearly all high-capacity anode materials.
Posted by: Rik Howard | 09 June 2010 at 06:24 AM