Battery & Electrification Technology - May/June 2024 - 26

Cobalt-Free Electrodes Achieved with Nickel Ions
A new nickel-based electrode material opens avenues to cobalt-free batteries for electric vehicles.
Yokohama National University, Japan
M
any electric vehicles are powered
by lithium-ion (Li-ion) batteries
that rely on cobalt - a
scarce, expensive metal with high
environmental and social costs. A
team of researchers from Japanese
and French universities have now
developed a practical nickel-based
electrode material that opens new
avenues to cobalt-free batteries for
electric vehicles.
The researchers detailed their findings
in a study published in the journal
Energy Storage Materials.
" There is an undeniable need for
cobalt-free, high-energy electrode
materials for lithium-ion batteries, "
said Naoaki Yabuuchi from Yokohama
National University.
Li-ion batteries can be recharged
Repulsive electrostatic interaction
Ni migration suppression and
improved reversibility without
Co ions
×
Ni ion in
Li layer
when Li-ions flow from a positively
charged electrode to a negatively
charged electrode. In most Li-ion batteries
for portable electronics, the positive
electrode contains lithium cobalt oxide
(LiCoO2
chain of cobalt creates a bottleneck for
large-scale batteries, including the ones
used in electric vehicles. In addition, cobalt
extraction generates toxic waste
that contaminates land, air, and water.
To address these issues, lithium nickel
oxide (LiNiO2) - which is similar in
structure to LiCoO2
- often serves as a
cobalt-free alternative for electrode material.
However, key instability issues
plague the compound, specifically a
gradual loss of capacity at the high-voltage
region, which is associated with
nickel-ion migration.
To improve electrode reversibility,
nickel ions have been partially substituted
by other metal ions, including reintroduced
cobalt ions as well as manganese,
aluminum, and magnesium, to create
" nickel-enriched layered materials " to
serve as positive electrode materials.
" So far, 10-20 percent cobalt ions
were necessary for nickel-based elec26
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
(anti-site
defect)
Li0.975
Ni1.025
O2
LiFSA/DMC
50 mA g-1
. 2.5 - 4.5 v
10th
50th
100th
500 nm
50
100
10 μm
150
Capacity / mAh g-1
Repulsive electrostatic interaction leads to Ni ion migration suppression and improved reversibility
without cobalt (Co) ions. (Image: Yokohama National University)
), a chemical compound that offers
high stability and energy density.
However, the limited, fraught supply
trode materials, " Yabuuchi said. This, according
to Yabuuchi, is still too much,
and a unified understanding of how
metal substitution can improve the process
has not yet been established.
To address this knowledge gap,
Yabuuchi and collaborators dug deeper
into the problematic phase transition.
When Li-ions leave the cathode under
the influence of an external field,
nickel ions migrate to specific sites
within the lithium layers. Although this
process is reversible, the reversibility
gradually degrades through continuous
cycles until the capacity is completely
lost - a phenomenon not seen in cobalt-ion
migration.
Previous studies reported that tungsten
doping in LiNiO2 is an efficient approach
to suppressing the detrimental
phase transitions at high-voltage regions.
Yabuuchi and collaborators tested
the hypothesis that heavy, expensive
tungsten ions could be substituted with
other elements, specifically phosphorous
- a lighter, more abundant element.
After detailed analysis on LiNiO2
integrated
with nanosized lithium phosphate
(Li3PO4
), the researchers observed
that, under certain conditions, problematic
nickel-ion migration was effectively
suppressed due to repulsive electrostatic
interaction from the extra nickel
ions within the Li layers. Moreover, from
these findings, Li-deficient LiNiO2
Li0.975Ni1.025O2, with the extra nickel
ions in Li layers, is also synthesized
using a simple methodology without
phosphorus integration. Results also
showed how Li0.975Ni1.025O2 can effectively
mitigate unfavorable nickel-ion
migration and deliver consistent reversibility
without cobalt ions.
" These findings open a new direction
to develop high performance and practical
cobalt-free nickel-based electrode
materials with an extremely simple and
cost-effective methodology, " Yabuuchi
said. " This material achieved the ultimate
goal for high-performance nickel-based
electrode materials. "
In future endeavors, the researchers
plan to investigate the feasibility of a
nickel-free material to support Li-ion
batteries.
For more information, contact Akiko
Tsumura at kenkyu-koho@ynu.ac.jp;
+81-453-393-213.
Battery & Electrification Technology, May/June 2024
Excellent
stability
200
250
,
Voltage / V

Battery & Electrification Technology - May/June 2024

Table of Contents for the Digital Edition of Battery & Electrification Technology - May/June 2024