Electrochemical properties of carbon nanofibers as the negative electrode in lithium-ion batteries

CARBON 57 (2013) 538– 540

539

New hybrid supercapacitors and their prospects

industries. The LIC will replace not only EDLCs but also other sec-

Katsuhiko Naoia,b, Yuki Naganoa, Wako Naoib

ondary batteries such as the lead acid battery or the LIB in many

a

industries in the near future.

Department of Applied Chemistry, Tokyo University of Agriculture and

Technology, Japan b

Division of Art & Innovative Technologies, K&W Inc., Japan

[TANSO 2013 (No. 256), 33–40.] doi:10.1016/j.carbon.2013.02.007

Electrochemical capacitors use activated carbons for both positive and negative electrodes that show a non-faradaic, double-layer charge–discharge mechanism in a symmetric configuration. Thus electrochemical capacitors are efficient energy storage devices that exhibit long lifespans and extremely rapid charge– discharge characteristics compared with batteries. Today, capacitor technology is regarded as promising and has an additional

Relevance of porosity and surface chemistry of superactivated carbons in capacitors D. Lozano-Castello´a, J.P. Marco-Lozara, M.J. Bleda-Martı´neza, F. Montillab, E. Morallo´nb, A. Linares-Solanoa, D. Cazorla-Amoro´sa

advantage with increasing effectiveness when combined with

a

Departamento de Quı´mica Inorga´nica, Universidad de Alicante, Spain

solar and wind regenerative energy sources. In recent years, com-

b

Departamento de Quı´mica Fı´sica and Instituto Universitario de

posite battery materials have been vigorously researched in the

Materiales, Universidad de Alicante, Spain

hope of improving their energy density. Hybridizing battery and capacitor materials overcomes the energy density limitation of

We show, through some examples, that chemical activation by

existing generation-I capacitors without much sacrifice of the

alkaline hydroxides permits the preparation of activated carbons

cycling performance. Normal battery-capacitor hybrids use a

with tailored pore volume, pore size distribution, pore structure

high-energy and sluggish redox electrode and low-energy and

and surface chemistry, which are useful for their application as

fast double-layer electrodes, possibly producing a larger working

electrodes in supercapacitors. Examples are presented discussing

voltage and higher overall capacitance. In order to smoothly oper-

the importance of each of these properties on the double layer

ate such asymmetric systems, however, the rates of the two dif-

capacitance, on the kinetics of the electric double-layer charge–

ferent electrodes must be highly balanced. Especially, the redox

discharge process and on the pseudo-capacitative contribution

rates of the battery electrodes must be substantially increased

from the surface functional groups or the addition of a conduct-

to the levels of double-layer process. In this perspective we sum-

ing polymer.

marize various hybrid systems and show representative aqueous and non-aqueous asymmetric configurations for their energy-

[TANSO 2013 (No. 256), 41–47.]

power improvement. We attempt to identify the essential issues

doi:10.1016/j.carbon.2013.02.008

for the realizable hybrids and suggest ways to overcome the rate increase by exemplifying ultrafast performance of the Li4Ti5O12 nanocrystal prepared by a unique in situ material processing technology under ultra-centrifugation.

Adsorption mechanism and electric double layer capacitances of porous and non-porous carbon electrode materials prepared

doi:10.1016/j.carbon.2013.02.006

by a hydroxide-activation method Hitoshi Kuwagaki Environmental Technique Service Co., United States

Development and applications of lithium ion capacitors Akio Hasebe Advanced Capacitor Technologies, Inc., Japan The lithium ion capacitor (LIC) is a new hybrid capacitor, in which the materials and the charge and discharge processes are different in the positive and negative electrodes. Generally, positive electrode materials are a kind of activated carbon as used for an EDLC electrode, and negative electrode materials are a kind of carbon materials as used for an LIB negative electrode. Also the

Various porous carbons were produced with a small mass-production scale hydroxide-activation furnace using different carbon materials. Some products derived from soft-carbons showed high electric double layer capacitances, large liquid phase iodine adsorption and large methanol vapor adsorption in spite of poor BET surface area. [TANSO 2013 (No. 256), 48–51.] doi:10.1016/j.carbon.2013.02.009

negative electrode of the LIC is doped in advance with lithium ions using a pre-doping process. Because of the difficulty of the pre-doping process, early LICs had a small capacitance, but the

Electrochemical properties of carbon nanofibers as the negative

development of a new pre-doping method is a breakthrough,

electrode in lithium-ion batteries

and the commercialization and mass production of a large capac-

Shohei

itance LIC has been accelerated. With the negative electrode

Tomokazu Fukutsukaa, Kohei Miyazakia, Takeshi Abea,

doped with lithium ions, the LIC achieves a four times higher

Takayuki Doib, Zempachi Ogumib

energy density than that of an EDLC, and also maintains the superior performance of EDLC, i.e., high power density and very long cycle life. The LIC has already started to be used in various industries such as the energy, electrical power and automobile

Maruyamaa, Guangzheng Zhuanga, Hongyu Wanga,

a

Graduate School of Engineering, Kyoto University, Japan

b

Office of Society-Academia Collaboration for Innovation, Kyoto Univer-

sity, Japan

540

CARBON 57 (2013) 538– 540

Carbon nanofibers were prepared by the exfoliation of natural

MgO-templated mesoporous carbons with different heat treat-

graphite flake in a propylene carbonate solution containing a lith-

ments are examined as both negative and positive electrodes in

ium salt and sonication. The electrochemical behavior of the car-

lithium-ion capacitors. MgO-templated carbon heated at 2200 °C

bon nanofibers used as the negative electrode in lithium-ion

has a specific surface area of 800 m2/g and a total pore volume

batteries was investigated. Carbon nanofibers heat-treated at

of 1.2 cm3/g, and shows superior performance as a negative elec-

600 °C had a diameter of several tens of nanometers. From X-

trode of a Li-ion capacitor when compared to artificial graphite.

ray diffraction measurements and Raman spectroscopy, it was

MgO-templated carbon heated at 1000 °C shows a larger capaci-

found that a graphitic structure derived from natural graphite

tance as a positive electrode than commercial activated carbons

flake remained in the carbon nanofibers. Carbon nanofibers

for an electric double layer capacitor. This unique performance

heat-treated at 400 °C showed a higher reversible capacity than

of MgO-template carbons is attributed to a combination of both

NG-7 (natural graphite powder) and a rapid response in the cyclic

high surface area and a highly uniform mesoporosity with a nar-

voltammogram. This is on account of the nanosize effect. The

row pore size distribution.

best electrochemical performance among all the carbon nanofibers was obtained by heat treatment at 400 °C. The rate perfor-

[TANSO 2013 (No. 256), 57–59.]

mance of the carbon nanofiber heat-treated at 400 °C was also

doi:10.1016/j.carbon.2013.02.011

examined. [TANSO 2013 (No. 256), 52–56.] doi:10.1016/j.carbon.2013.02.010

Performance of MgO-templated mesoporous carbons as electrode materials in lithium-ion capacitor Yasushi Sonedaa, Takafumi Yamaguchia, Kiyoaki Imotoa, Masaya Kodamaa, Takahiro Morishitab, Hironori Orikasab a

Energy Technology Research Institute, National Institute of Advanced

Industrial Science and Technology (AIST), Japan b

Advanced Carbon Technology Center, Toyo Tanso Co., Ltd., Japan