<s>
A	O
nickel	B-Device
metal	I-Device
hydride	I-Device
battery	I-Device
(	O
NiMH	B-Device
or	O
Ni	O
–	O
MH	O
)	O
is	O
a	O
type	O
of	O
rechargeable	B-Architecture
battery	I-Architecture
.	O
</s>
<s>
However	O
,	O
the	O
negative	O
electrodes	O
use	O
a	O
hydrogen-absorbing	O
alloy	B-Application
instead	O
of	O
cadmium	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
can	O
have	O
two	O
to	O
three	O
times	O
the	O
capacity	O
of	O
NiCd	O
batteries	O
of	O
the	O
same	O
size	O
,	O
with	O
significantly	O
higher	O
energy	O
density	O
,	O
although	O
much	O
less	O
than	O
lithium-ion	O
batteries	O
.	O
</s>
<s>
They	O
are	O
typically	O
used	O
as	O
a	O
substitute	O
for	O
similarly	O
shaped	O
non-rechargeable	O
alkaline	B-Algorithm
batteries	I-Algorithm
,	O
as	O
they	O
feature	O
a	O
slightly	O
lower	O
but	O
generally	O
compatible	O
cell	O
voltage	O
,	O
and	O
are	O
less	O
prone	O
to	O
leaking	O
.	O
</s>
<s>
Work	O
on	O
NiMH	B-Device
batteries	I-Device
began	O
at	O
the	O
Battelle-Geneva	O
Research	O
Center	O
following	O
the	O
technology	O
's	O
invention	O
in	O
1967	O
.	O
</s>
<s>
It	O
was	O
based	O
on	O
sintered	O
Ti2Ni+TiNi+x	O
alloys	B-Application
and	O
NiOOH	O
electrodes	O
.	O
</s>
<s>
The	O
batteries	O
 '	O
specific	O
energy	O
reached	O
50W·	O
h/kg	O
(	O
180kJ/kg	O
)	O
,	O
specific	O
power	O
up	O
to	O
1000W/kg	O
and	O
a	O
life	O
of	O
500	O
charge	B-Algorithm
cycles	I-Algorithm
(	O
at	O
100%	O
depth	B-Algorithm
of	I-Algorithm
discharge	I-Algorithm
)	O
.	O
</s>
<s>
Interest	O
grew	O
in	O
the	O
1970s	O
with	O
the	O
commercialisation	O
of	O
the	O
nickel	B-Algorithm
–	I-Algorithm
hydrogen	I-Algorithm
battery	I-Algorithm
for	O
satellite	O
applications	O
.	O
</s>
<s>
Research	O
carried	O
out	O
by	O
Philips	O
Laboratories	O
and	O
France	O
's	O
CNRS	O
developed	O
new	O
high-energy	O
hybrid	O
alloys	B-Application
incorporating	O
rare-earth	O
metals	O
for	O
the	O
negative	O
electrode	O
.	O
</s>
<s>
However	O
,	O
these	O
suffered	O
from	O
alloy	B-Application
instability	O
in	O
alkaline	O
electrolyte	O
and	O
consequently	O
insufficient	O
cycle	B-Algorithm
life	I-Algorithm
.	O
</s>
<s>
In	O
1987	O
,	O
Willems	O
and	O
Buschow	O
demonstrated	O
a	O
successful	O
battery	O
based	O
on	O
this	O
approach	O
(	O
using	O
a	O
mixture	O
of	O
La0.8Nd0.2Ni2.5Co2.4Si0.1	O
)	O
,	O
which	O
kept	O
84%	O
of	O
its	O
charge	O
capacity	O
after	O
4000	O
charge	O
–	O
discharge	O
cycles	B-Algorithm
.	O
</s>
<s>
More	O
economically	O
viable	O
alloys	B-Application
using	O
mischmetal	O
instead	O
of	O
lanthanum	O
were	O
soon	O
developed	O
.	O
</s>
<s>
Modern	O
NiMH	B-Device
cells	I-Device
were	O
based	O
on	O
this	O
design	O
.	O
</s>
<s>
The	O
first	O
consumer-grade	O
NiMH	B-Device
cells	I-Device
became	O
commercially	O
available	O
in	O
1989	O
.	O
</s>
<s>
In	O
1998	O
,	O
Ovonic	O
Battery	O
Co	O
.	O
improved	O
the	O
Ti	O
–	O
Ni	O
alloy	B-Application
structure	O
and	O
composition	O
and	O
patented	O
its	O
innovations	O
.	O
</s>
<s>
In	O
2008	O
,	O
more	O
than	O
two	O
million	O
hybrid	O
cars	O
worldwide	O
were	O
manufactured	O
with	O
NiMH	B-Device
batteries	I-Device
.	O
</s>
<s>
In	O
the	O
European	O
Union	O
due	O
to	O
its	O
Battery	O
Directive	O
,	O
nickel	B-Device
metal	I-Device
hydride	I-Device
batteries	I-Device
replaced	O
Ni	O
–	O
Cd	O
batteries	O
for	O
portable	O
consumer	O
use	O
.	O
</s>
<s>
About	O
22%	O
of	O
portable	O
rechargeable	B-Architecture
batteries	I-Architecture
sold	O
in	O
Japan	O
in	O
2010	O
were	O
NiMH	B-Device
.	O
</s>
<s>
This	O
percentage	O
has	O
fallen	O
over	O
time	O
due	O
to	O
the	O
increase	O
in	O
manufacture	O
of	O
lithium-ion	O
batteries	O
:	O
in	O
2000	O
,	O
almost	O
half	O
of	O
all	O
portable	O
rechargeable	B-Architecture
batteries	I-Architecture
sold	O
in	O
Japan	O
were	O
NiMH	B-Device
.	O
</s>
<s>
In	O
2015	O
BASF	O
produced	O
a	O
modified	O
microstructure	O
that	O
helped	O
make	O
NiMH	B-Device
batteries	I-Device
more	O
durable	O
,	O
in	O
turn	O
allowing	O
changes	O
to	O
the	O
cell	O
design	O
that	O
saved	O
considerable	O
weight	O
,	O
allowing	O
the	O
specific	O
energy	O
to	O
reach	O
140	O
watt-hours	O
per	O
kilogram	O
.	O
</s>
<s>
The	O
metal	O
M	O
in	O
the	O
negative	O
electrode	O
of	O
a	O
NiMH	B-Device
cell	I-Device
is	O
an	O
intermetallic	O
compound	O
.	O
</s>
<s>
The	O
most	O
common	O
is	O
AB5	O
,	O
where	O
A	O
is	O
a	O
rare-earth	O
mixture	O
of	O
lanthanum	O
,	O
cerium	O
,	O
neodymium	O
,	O
praseodymium	O
,	O
and	O
B	O
is	O
nickel	O
,	O
cobalt	B-Algorithm
,	O
manganese	O
,	O
or	O
aluminium	O
.	O
</s>
<s>
Some	O
cells	O
use	O
higher-capacity	O
negative	O
electrode	O
materials	O
based	O
on	O
AB2	O
compounds	O
,	O
where	O
A	O
is	O
titanium	O
or	O
vanadium	O
,	O
and	O
B	O
is	O
zirconium	O
or	O
nickel	O
,	O
modified	O
with	O
chromium	B-Language
,	O
cobalt	B-Algorithm
,	O
iron	O
,	O
or	O
manganese	O
.	O
</s>
<s>
NiMH	B-Device
cells	I-Device
have	O
an	O
alkaline	O
electrolyte	O
,	O
usually	O
potassium	O
hydroxide	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
of	O
bipolar	O
design	O
(	O
bipolar	O
batteries	O
)	O
are	O
being	O
developed	O
because	O
they	O
offer	O
some	O
advantages	O
for	O
applications	O
as	O
storage	O
systems	O
for	O
electric	O
vehicles	O
.	O
</s>
<s>
When	O
fast-charging	O
,	O
it	O
is	O
advisable	O
to	O
charge	O
the	O
NiMH	B-Device
cells	I-Device
with	O
a	O
smart	O
battery	B-Application
charger	I-Application
to	O
avoid	O
overcharging	O
,	O
which	O
can	O
damage	O
cells	O
.	O
</s>
<s>
The	O
Panasonic	O
NiMH	B-Device
charging	O
manual	O
warns	O
that	O
overcharging	O
for	O
long	O
enough	O
can	O
damage	O
a	O
battery	O
and	O
suggests	O
limiting	O
the	O
total	O
charging	O
time	O
to	O
10	O
–	O
20	O
hours	O
.	O
</s>
<s>
Some	O
chargers	O
do	O
this	O
after	O
the	O
charge	B-Algorithm
cycle	I-Algorithm
,	O
to	O
offset	O
natural	O
self-discharge	B-Algorithm
.	O
</s>
<s>
Panasonic	O
's	O
handbook	O
recommends	O
that	O
NiMH	B-Device
batteries	I-Device
on	O
standby	O
be	O
charged	O
by	O
a	O
lower	O
duty	O
cycle	O
approach	O
,	O
where	O
a	O
pulse	O
of	O
a	O
higher	O
current	O
is	O
used	O
whenever	O
the	O
battery	O
's	O
voltage	O
drops	O
below	O
1.3V	O
.	O
</s>
<s>
To	O
prevent	O
cell	O
damage	O
,	O
fast	O
chargers	O
must	O
terminate	O
their	O
charge	B-Algorithm
cycle	I-Algorithm
before	O
overcharging	O
occurs	O
.	O
</s>
<s>
However	O
,	O
the	O
voltage	O
drop	O
is	O
much	O
less	O
pronounced	O
for	O
NiMH	B-Device
and	O
can	O
be	O
non-existent	O
at	O
low	O
charge	O
rates	O
,	O
which	O
can	O
make	O
the	O
approach	O
unreliable	O
.	O
</s>
<s>
Modern	O
NiMH	B-Device
cells	I-Device
contain	O
catalysts	O
to	O
handle	O
gases	O
produced	O
by	O
over-charging	O
(	O
2H2{}	O
+	O
O2	O
->[\text{catalyst}]	O
2H2O	O
)	O
.	O
</s>
<s>
A	O
method	O
for	O
very	O
rapid	O
charging	O
called	O
in-cell	B-Algorithm
charge	I-Algorithm
control	I-Algorithm
involves	O
an	O
internal	O
pressure	O
switch	O
in	O
the	O
cell	O
,	O
which	O
disconnects	O
the	O
charging	O
current	O
in	O
the	O
event	O
of	O
overpressure	O
.	O
</s>
<s>
One	O
inherent	O
risk	O
with	O
NiMH	B-Device
chemistry	O
is	O
that	O
overcharging	O
causes	O
hydrogen	O
gas	O
to	O
form	O
,	O
potentially	O
rupturing	O
the	O
cell	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
are	O
made	O
of	O
environmentally	O
friendly	O
materials	O
.	O
</s>
<s>
Voltage	B-Algorithm
depression	I-Algorithm
(	O
often	O
mistakenly	O
attributed	O
to	O
the	O
memory	B-Algorithm
effect	I-Algorithm
)	O
from	O
repeated	O
partial	O
discharge	O
can	O
occur	O
,	O
but	O
is	O
reversible	O
with	O
a	O
few	O
full	O
discharge/charge	O
cycles	O
.	O
</s>
<s>
Under	O
a	O
light	O
load	O
(	O
0.5	O
amperes	O
)	O
,	O
the	O
starting	O
voltage	O
of	O
a	O
freshly	O
charged	O
AA	B-Algorithm
NiMH	B-Device
cell	I-Device
in	O
good	O
condition	O
is	O
about	O
1.4	O
volts	O
.	O
</s>
<s>
This	O
situation	O
can	O
occur	O
in	O
the	O
common	O
arrangement	O
of	O
four	O
AA	B-Algorithm
cells	I-Algorithm
in	O
series	O
in	O
a	O
digital	B-Device
camera	I-Device
,	O
where	O
one	O
cell	O
completely	O
discharges	O
before	O
the	O
others	O
due	O
to	O
small	O
differences	O
in	O
capacity	O
among	O
the	O
cells	O
.	O
</s>
<s>
Some	O
cameras	O
,	O
GPS	O
receivers	O
and	O
PDAs	B-Application
detect	O
the	O
safe	O
end-of-discharge	O
voltage	O
of	O
the	O
series	O
cells	O
and	O
perform	O
an	O
auto-shutdown	O
,	O
but	O
devices	O
such	O
as	O
flashlights	O
and	O
some	O
toys	O
do	O
not	O
.	O
</s>
<s>
Historically	O
,	O
NiMH	B-Device
cells	I-Device
have	O
had	O
a	O
somewhat	O
higher	O
self-discharge	B-Algorithm
rate	O
(	O
equivalent	O
to	O
internal	O
leakage	O
)	O
than	O
NiCd	O
cells	O
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
rate	O
varies	O
greatly	O
with	O
temperature	O
,	O
where	O
lower	O
storage	O
temperature	O
leads	O
to	O
slower	O
discharge	O
and	O
longer	O
battery	O
life	O
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
is	O
on	O
the	O
first	O
day	O
and	O
stabilizes	O
around	O
per	O
day	O
at	O
room	O
temperature	O
.	O
</s>
<s>
The	O
low	O
self-discharge	B-Algorithm
nickel	B-Device
metal	I-Device
hydride	I-Device
battery	I-Device
(	O
LSD	O
NiMH	B-Device
)	O
has	O
a	O
significantly	O
lower	O
rate	O
of	O
self-discharge	B-Algorithm
.	O
</s>
<s>
By	O
using	O
improvements	O
to	O
electrode	O
separator	O
,	O
positive	O
electrode	O
,	O
and	O
other	O
components	O
,	O
manufacturers	O
claim	O
the	O
cells	O
retain	O
70	O
–	O
85%	O
of	O
their	O
capacity	O
when	O
stored	O
for	O
one	O
year	O
at	O
,	O
compared	O
to	O
about	O
half	O
for	O
normal	O
NiMH	B-Device
batteries	I-Device
.	O
</s>
<s>
They	O
are	O
otherwise	O
similar	O
to	O
standard	O
NiMH	B-Device
batteries	I-Device
,	O
and	O
can	O
be	O
charged	O
in	O
standard	O
NiMH	B-Device
chargers	O
.	O
</s>
<s>
These	O
cells	O
are	O
marketed	O
as	O
"	O
hybrid	O
"	O
,	O
"	O
ready-to-use	O
"	O
or	O
"	O
pre-charged	O
"	O
rechargeables	B-Architecture
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
rate	O
depends	O
upon	O
separator	O
thickness	O
;	O
thicker	O
separators	O
reduce	O
self-discharge	B-Algorithm
,	O
but	O
also	O
reduce	O
capacity	O
as	O
they	O
leave	O
less	O
space	O
for	O
active	O
components	O
,	O
and	O
thin	O
separators	O
lead	O
to	O
higher	O
self-discharge	B-Algorithm
.	O
</s>
<s>
Low-self-discharge	O
cells	O
have	O
somewhat	O
lower	O
capacity	O
than	O
otherwise	O
equivalent	O
NiMH	B-Device
cells	I-Device
because	O
of	O
the	O
larger	O
volume	O
of	O
the	O
separator	O
.	O
</s>
<s>
The	O
highest-capacity	O
low-self-discharge	O
AA	B-Algorithm
cells	I-Algorithm
have	O
2500mAh	O
capacity	O
,	O
compared	O
to	O
2700mAh	O
for	O
high-capacity	O
AA	B-Algorithm
NiMH	B-Device
cells	I-Device
.	O
</s>
<s>
corrosion	O
capabilities	O
)	O
,	O
and	O
addition	O
of	O
Al2(SO4 )	O
3	O
into	O
electrolyte	O
(	O
causing	O
reduction	O
in	O
MH	O
alloy	B-Application
corrosion	O
)	O
.	O
</s>
<s>
NiMH	B-Device
cells	I-Device
are	O
often	O
used	O
in	O
digital	B-Device
cameras	I-Device
and	O
other	O
high-drain	O
devices	O
,	O
where	O
over	O
the	O
duration	O
of	O
single-charge	O
use	O
they	O
outperform	O
primary	O
(	O
such	O
as	O
alkaline	O
)	O
batteries	O
.	O
</s>
<s>
NiMH	B-Device
cells	I-Device
are	O
advantageous	O
for	O
high-current-drain	O
applications	O
,	O
largely	O
due	O
to	O
their	O
lower	O
internal	O
resistance	O
.	O
</s>
<s>
Typical	O
alkaline	O
AA-size	O
batteries	O
,	O
which	O
offer	O
approximately	O
2600mAh	O
capacity	O
at	O
low	O
current	O
demand	O
(	O
25mA	O
)	O
,	O
provide	O
only	O
1300mAh	O
capacity	O
with	O
a	O
500mA	O
load	O
.	O
</s>
<s>
Digital	B-Device
cameras	I-Device
with	O
LCDs	O
and	O
flashlights	O
can	O
draw	O
over	O
1000mA	O
,	O
quickly	O
depleting	O
them	O
.	O
</s>
<s>
NiMH	B-Device
cells	I-Device
can	O
deliver	O
these	O
current	O
levels	O
without	O
similar	O
loss	O
of	O
capacity	O
.	O
</s>
<s>
Devices	O
that	O
were	O
designed	O
to	O
operate	O
using	O
primary	O
alkaline	O
chemistry	O
(	O
or	O
zinc	O
–	O
carbon/chloride	O
)	O
cells	O
may	O
not	O
function	O
with	O
NiMH	B-Device
cells	I-Device
.	O
</s>
<s>
However	O
,	O
most	O
devices	O
compensate	O
for	O
the	O
voltage	O
drop	O
of	O
an	O
alkaline	B-Algorithm
battery	I-Algorithm
as	O
it	O
discharges	O
down	O
to	O
about	O
1volt	O
.	O
</s>
<s>
Low	O
internal	O
resistance	O
allows	O
NiMH	B-Device
cells	I-Device
to	O
deliver	O
a	O
nearly	O
constant	O
voltage	O
until	O
they	O
are	O
almost	O
completely	O
discharged	O
.	O
</s>
<s>
Thus	O
battery-level	O
indicators	O
designed	O
to	O
read	O
alkaline	B-Algorithm
cells	I-Algorithm
overstate	O
the	O
remaining	O
charge	O
when	O
used	O
with	O
NiMH	B-Device
cells	I-Device
,	O
as	O
the	O
voltage	O
of	O
alkaline	B-Algorithm
cells	I-Algorithm
decreases	O
steadily	O
during	O
most	O
of	O
the	O
discharge	O
cycle	O
.	O
</s>
<s>
Lithium-ion	O
batteries	O
have	O
a	O
higher	O
specific	O
energy	O
than	O
nickel	B-Device
metal	I-Device
hydride	I-Device
batteries	I-Device
,	O
but	O
they	O
are	O
significantly	O
more	O
expensive	O
.	O
</s>
<s>
They	O
also	O
produce	O
a	O
higher	O
voltage	O
(	O
3.2	O
–	O
3.7V	O
nominal	O
)	O
,	O
and	O
are	O
thus	O
not	O
a	O
drop-in	O
replacement	O
for	O
alkaline	B-Algorithm
batteries	I-Algorithm
without	O
circuitry	O
to	O
reduce	O
voltage	O
.	O
</s>
<s>
,	O
nickel	B-Device
metal	I-Device
hydride	I-Device
batteries	I-Device
constituted	O
three	O
percent	O
of	O
the	O
battery	O
market	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
have	O
replaced	O
NiCd	O
for	O
many	O
roles	O
,	O
notably	O
small	O
rechargeable	B-Architecture
batteries	I-Architecture
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
are	O
commonly	O
available	O
in	O
AA	B-Algorithm
(	O
penlight-size	O
)	O
batteries	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
nominally	O
operate	O
at	O
1.2V	O
per	O
cell	O
,	O
somewhat	O
lower	O
than	O
conventional	O
1.5V	O
cells	O
,	O
but	O
can	O
operate	O
many	O
devices	O
designed	O
for	O
that	O
voltage	O
.	O
</s>
<s>
NiMH	B-Device
batteries	I-Device
were	O
frequently	O
used	O
in	O
prior-generation	O
electric	O
and	O
hybrid-electric	O
vehicles	O
;	O
as	O
of	O
2020	O
they	O
have	O
been	O
superseded	O
almost	O
entirely	O
by	O
lithium-ion	O
batteries	O
in	O
all-electric	O
and	O
plug-in	O
hybrid	O
vehicles	O
,	O
but	O
they	O
remain	O
in	O
use	O
in	O
some	O
hybrid	O
vehicles	O
(	O
2020	O
Toyota	O
Highlander	O
,	O
for	O
example	O
)	O
.	O
</s>
<s>
Every	O
first	O
generation	O
hybrid	O
vehicle	O
used	O
NIMH	B-Device
batteries	I-Device
,	O
most	O
notably	O
the	O
Toyota	O
Prius	O
and	O
Honda	O
Insight	O
,	O
as	O
well	O
as	O
later	O
models	O
including	O
the	O
Ford	O
Escape	O
Hybrid	O
,	O
Chevrolet	O
Malibu	O
Hybrid	O
and	O
Honda	O
Civic	O
Hybrid	O
also	O
use	O
them	O
.	O
</s>
<s>
Stanford	O
R	O
.	O
Ovshinsky	O
invented	O
and	O
patented	O
a	O
popular	O
improvement	O
of	O
the	O
NiMH	B-Device
battery	I-Device
and	O
founded	O
Ovonic	O
Battery	O
Company	O
in	O
1982	O
.	O
</s>
<s>
By	O
the	O
late	O
1990s	O
,	O
NiMH	B-Device
batteries	I-Device
were	O
being	O
used	O
successfully	O
in	O
many	O
fully	O
electric	O
vehicles	O
,	O
such	O
as	O
the	O
General	O
Motors	O
EV1	O
and	O
Dodge	O
Caravan	O
EPIC	O
minivan	O
.	O
</s>
<s>
Cobasys	O
control	O
of	O
NiMH	B-Device
batteries	I-Device
created	O
a	O
patent	O
encumbrance	O
for	O
large	O
automotive	O
NiMH	B-Device
batteries	I-Device
.	O
</s>
