IEEE Power & Energy Magazine - Grid Edge 2023 - 55

energy density, realizes better environmental friendliness,
and is less prone to undergo memory effect. However, it
suffers from several technical downsides, such as high selfdischarge
rate, limited service life, and low Coulombic
efficiency (about 65%). Moreover, its ability to tolerate fast
charging and overcharge is very low. Particularly during
fast charging, massive amounts of heat may be generated,
and hydrogen buildup may cause cell rupture, leading to
considerable capacity decay. Its charging strategies, therefore,
must be meticulously designed.
As a small-format rechargeable cell, the NiMH battery
has been notably applied for portable consumer use. It began
to become popular for EVs and hybrid EVs (HEVs) in the
1990s and 2000s. Plug-in EVs (e.g., General Motors' EV1,
Honda's EV Plus, the Ford's Ranger EV, and the Vectrix
scooter) adopted NiMH battery packs, as did several HEVs,
such as the Toyota Prius, Honda Insight, and Ford Escape
and Chevrolet Malibu hybrids.
Li-Ion Battery
The Li-ion battery is an advanced rechargeable battery first
commercially developed by Sony in the early 1990s. During
charging, Li-ions are inserted into and deinserted from
the negative electrode and positive electrode, respectively.
Also during charging, Li+ is deintercalated from the cathode
oxide compound and inserted into the lattice of the anode.
The cathode has high potential and poor Li state, whereas
the anode has low potential and rich Li state. The process is
reversed during discharge, as illustrated in Figure 2 (taking
as an example an anode with graphite and a cathode with a
layered oxide compound).
Compared to other types of batteries (e.g., NiMH, NiCd,
and lead-acid), Li-ion batteries have the advantages of high
energy density (due to the high output voltage), high efficiency,
long cycle life, and environmental friendliness. Such
attractive attributes make Li-ion batteries ubiquitous in portable
electronics. Li-ion batteries are also regarded as one of
the most promising traction batteries for next-generation EVs
and plug-in HEVs (PHEVs). With the rapid development of
EVs and PHEVs, Li-ion battery technologies have made great
progress, providing a solid technical
foundation and industrial base for
energy storage applications.
Besides the stringent requireType
ments
of power capability and energy
capacity, e.g., in EVs and PHEVs,
large-scale commercial applications
of Li-ion battery technologies are expected
to require a substantial price
reduction before they fit into largescale
utility applications widely.
Battery-cycle life is a key factor for
grid application as well and affects
the economic viability of energy
storage. The maturity of technology
september/october 2017
A
e
e
e
e
e
e
Cu
Current
Collector
Graphene
Structure
Li+
Solvent
Molecule
LiMO2
Layer
Structure
figure 2. A schematic of a discharging Li-ion battery
(Source: U.S. Department of Energy). Cu: copper; LiMO2:
Li metal oxide; Al: aluminum.
and standardized Li-ion battery production are also important
for grid application because they determine the complexity of
control and maintenance.
Emerging applications have motivated researchers to seek
advanced Li-ion battery technologies that are highly efficient,
safe, and low in cost. Significant developments have
been accomplished in chemistry and materials science, such
as anode materials, cathode materials, and electrolytes. The
main characteristics of representative Li-ion batteries are contrasted
in Table 2, where LMO represents Li-ion manganese
oxide (i.e., LiMn2O4) batteries. It is worth mentioning that the
Li-iron-phosphate (LFP) battery developed in 1997 remarkably
reduced the cost of Li-ion batteries for the first time,
making large-scale commercial application possible. Furthermore,
LFP is advantageous in thermal and cycling stability,
safety, and environmental resilience, making it one of the
most promising Li-ion batteries employed in the electric grid.
Energy density (Wh/kg)
Power density (W/kg)
Cycle life (100% depth
of discharge)
Cost (US$/kWh)
Safety
Maturity
table 2. The main characteristics of various types of Li-ion batteries.
LMO
160
200
LFP
120
200
≥2,000
~360
Good
≥2,500
~360
Good
LNMC
200
200
≥2,000
~360
Good
Li-S: Li-sulphur; Demo: demonstration; R&D: research and development.
ieee power & energy magazine
55
LTO
70
Anode
-
Electrolyte
e
e
e
e
AI
Current
Collector
Cathode
+
e
Li-S
500
1,000 -
≥10,000 ~100
~860 -
Good
Good
Commercial Commercial Commercial Demo R&D
IEEE Power & Energy Magazine - Grid Edge 2023

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