One of the
factors that determine the success of electric vehicles is the availability of
batteries that can be charged quickly and retain enough charge to make long
distance travel possible per charge. Researchers at the Indian Institute of
Science Education and Research (IISER) Pune have synthesised a new type of
anode material to make such a battery possible.
Unlike graphite
anode-containing lithium ion batteries that have capacity of just 372mAh/gram,
the anode synthesised by IISER researchers has double the capacity of about
720mAh/gram. The capacity remained the same even after 1,000 charge-discharge
cycles.
The high
capacity was seen when the rate of charging/discharging was 100mA/gram. But
when the battery was charged quickly (1A/gram), the capacity reduced by about
20% (about 580mAh/gram).
“So even when
the battery is charged quickly, it can still store about 80% charge,” says
Prof. Ramanathan Vaidhyanathan from the Department of Chemistry at IISER Pune.
“And even when
the battery was charged rapidly (2A/gram), the capacity was still around
500mAh/gram, which is much higher than the graphite-containing battery.” He is
one of the corresponding authors of a paper published in the journal Advanced
Energy Materials.
“The performance
of the anode material is good in terms of capacity and stability,” says Dr.
Satishchandra Ogale from the Department of Physics at IISER Pune and the other
corresponding author. “Graphite is cheaper and lithium ions can easily be
inserted into graphite. But unlike the novel anode material, graphite can’t be
tuned.”
Testing the
anode
The researchers
tested the capacity by replacing the graphite anode with the novel material
(covalent organic framework) and used lithium metal as the cathode and not
lithium cobaltate (LiCoO2), which is normally used as the cathode.
“We had tested
the anode using a half-cell configuration. To realise the full potential of the
novel material it has to be tested in a full-cell configuration,” he says.
When tested in a
full-cell configuration, the charge will be lower than what has been observed
by the researchers. This is because the kinetics of lithium diffusion will be
different depending on the cathode material used and the configuration of the
battery.
“The capacity of
a graphite anode in a full-cell configuration will be only about 150mAh/gram if
the battery is charged quickly (rate of charge is 1A/gram). So with our anode
material, even if the capacity drops by 50% in a full-cell configuration, the
capacity will be about 360mAh/gram, which is much higher than graphite. This
can be confirmed only when we carry out an experiment using full-cell
configuration,” says Prof. Vaidhyanathan.
The anode made
of a few-layer thick (6-8 layers) nanosheets has pores lined by functional
groups capable of interacting with lithium ions. The pores provide an easy path
for diffusion of lithium ions and helps access the functional groups, which are
sites of lithium ion interaction.
“Optimal
interactions allow lithium ions to go in and come out of the nanosheets with
ease allowing the anode to discharge easily,” says Sattwick Haldar from the
Department of Chemistry, IISER Pune and first author of the paper.
Charging and
capacity
The ease with
which lithium ions go in and come out of the nanosheet anode changes when the
time taken to charge the battery changes. When it is charged quickly, the
efficiency of lithium ions diffusion drops and capacity of the battery reduces.
“In our case, whether the battery charging time is short or long (50mA/gram or
2A/gram), the capacity does not change much,” says Prof. Vaidhyanathan.
The anode was
tested in a coin cell and not a bigger battery that would typically be used in
electric automobiles. The researchers are trying to scale-up the battery so
that it can potentially be used for applications that need higher battery output.
Source:Source: THE HINDU-10th December,2017
