IEEE Power & Energy Magazine - September/October 2017 - 23

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

A
e

Anode
-

Cathode
+

Electrolyte

e
e

Cu
Current Graphene Li+ Solvent
Molecule
Collector Structure

LiMO2
Layer
Structure

AI
Current
Collector

figure 2. A schematic of a discharging Li-ion battery
(Source: U.S. Department of Energy). Cu: copper; LiMO2:
Li metal oxide; Al: aluminum.

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. and standardized Li-ion battery production are also important
Also during charging, Li+ is deintercalated from the cathode for grid application because they determine the complexity of
oxide compound and inserted into the lattice of the anode. control and maintenance.
Emerging applications have motivated researchers to seek
The cathode has high potential and poor Li state, whereas
the anode has low potential and rich Li state. The process is advanced Li-ion battery technologies that are highly effireversed during discharge, as illustrated in Figure 2 (taking cient, safe, and low in cost. Significant developments have
as an example an anode with graphite and a cathode with a been accomplished in chemistry and materials science, such
as anode materials, cathode materials, and electrolytes. The
layered oxide compound).
Compared to other types of batteries (e.g., NiMH, NiCd, main characteristics of representative Li-ion batteries are conand lead-acid), Li-ion batteries have the advantages of high trasted in Table 2, where LMO represents Li-ion manganese
energy density (due to the high output voltage), high effi- oxide (i.e., LiMn2O4) batteries. It is worth mentioning that the
ciency, long cycle life, and environmental friendliness. Such Li-iron-phosphate (LFP) battery developed in 1997 remarkattractive attributes make Li-ion batteries ubiquitous in por- ably reduced the cost of Li-ion batteries for the first time,
table electronics. Li-ion batteries are also regarded as one of making large-scale commercial application possible. Furtherthe most promising traction batteries for next-generation EVs more, LFP is advantageous in thermal and cycling stability,
and plug-in HEVs (PHEVs). With the rapid development of safety, and environmental resilience, making it one of the
EVs and PHEVs, Li-ion battery technologies have made great most promising Li-ion batteries employed in the electric grid.
progress, providing a solid technical
foundation and industrial base for
table 2. The main characteristics of various types of Li-ion batteries.
energy storage applications.
Type
LMO
LFP
LNMC
LTO
Li-S
Besides the stringent requirements of power capability and enerEnergy density (Wh/kg)
160
120
200
70
500
gy capacity, e.g., in EVs and PHEVs,
Power density (W/kg)
200
200
200
1,000
-
large-scale commercial applications
Cycle life (100% depth
≥2,000
≥2,500
≥2,000
≥10,000 ~100
of Li-ion battery technologies are exof discharge)
pected to require a substantial price
Cost (US$/kWh)
~360
~360
~360
~860
-
reduction before they fit into largescale utility applications widely.
Safety
Good
Good
Good
Good
Good
Battery-cycle life is a key factor for
Maturity
Commercial Commercial Commercial Demo
R&D
grid application as well and affects
the economic viability of energy
Li-S: Li-sulphur; Demo: demonstration; R&D: research and development.
storage. The maturity of technology
september/october 2017

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