Mass production
of an electric
vehicle-worthy
lithium-silicon
battery is at least
five years away,
but progress
is being made.
Sila expects
its lithium silicon
anodes, within
their lithium
batteries,
to be used
in wireless
earbuds and
smart watches
within a year.
Advano expects
to have lithium silicon
anode lithium batteries
placed in some small
consumer electronics
within a year.
The long-term goal
is higher energy density
electric vehicle batteries,
but the first experiment
will be small consumer
devices.
It's been a slow road
to develop lithium silicon
anode electric vehicle
batteries, with 20% to 50%
more energy per battery
than today's conventional
lithium batteries with
their graphite anodes.
“The pace of battery
development is not as fast
as other technology areas,
such as computing,”
says Matthew McDowell,
a materials scientist
at the Georgia Institute
of Technology.
The reason:
There is a complex interplay
of the variables involved
when swapping out graphite
for silicon in lithium battery
anodes, to get higher
battery energy density:
-- The higher energy density
must justify higher cost.
-- Thermal stability
can not be reduced,
-- The charging rate
must not be slowed.
-- The battery lifespan
must not be reduced.
Additional electric vehicle
challenges are tough:
- Batteries must consistently
last more than one decade
- Batteries must be able
to handle daily recharging,
- Batteries must be able
to handle a very wide range
of outdoor temperatures.
- Other unique automobile stresses,
include jolts from potholes, and
constant vibration.
Building a
lithium-silicon
anode battery
that retains
its high energy
for over
one decade
may be
the biggest
challenge.
That's why only
small consumer
electronics will use
the first wave
of silicon-lithium
batteries.
Gadgets that
only need to last
for a few years.
Gene Berdichevsky,
employee number seven
at Tesla, led the team
that designed the
lithium-ion battery pack
for the company’s first car,
the Roadster.
There’s still a trade-off
between the shelf life
of Tesla batteries, and
the amount of energy
packed into them.
Berdichevsky founded
Sila Nanotechnologies
in 2011 to build
a better battery.
His secret ingredient
is nano-engineered
particles of silicon,
which can supercharge
lithium-ion cells
when they’re used
as the battery’s
negative electrode,
or anode.
Sila is among
just a few companies
trying to bring
lithium-silicon batteries
out of the lab and
into the real world,.
In one year Berdichevsky
plans to have the first
lithium-silicon batteries
in consumer electronics,
which he says
will make them
last 20% longer
per charge.
Your favorite
portable device
— phone, laptop,
or smart watch —
is powered
by a lithium-ion
battery eager
to provide electrons,
plus a silicon-soaked
circuit board
that routes them
where they need to go.
But if you combine
lithium and silicon
in a battery,
it can create
all sorts
of problems.
When a
lithium-ion
battery
is charging,
lithium ions flow
to the anode,
which is
typically made
of a type of carbon
called graphite.
If you
swap graphite
for silicon,
then far more
lithium ions
can be stored
in the anode,
which increases
the energy capacity
of the battery.
But packing
all these
lithium ions
into the electrode
causes it to swell
like a balloon --
it can grow up to
four times larger.
The swollen anode
can pulverize the
nano-engineered
silicon particles
and rupture the
protective barrier
between the anode
and the battery’s
electrolyte, which
ferries lithium ions
between the electrodes.
Over time,
"crud"
builds up
at the boundary
between the anode
and electrolyte,
blocking the
efficient transfer
of lithium ions.
The "crud" kills
any performance
improvements
the silicon anode
provided.
Tesla's "solution"
is to sprinkle
small amounts
of silicon oxide
—better known
as sand—
throughout
a graphite anode.
The silicon oxide
comes
"pre-puffed",
so it reduces
the stress
on the anode
from swelling
during charging.
But it also limits
the amount of lithium
that can be stored
in the anode.
Tesla improving
a battery this way
does not produce
double-digit
performance gains,
but it helps.
Cary Hayner, cofounder
and CTO of NanoGraf,
thinks it’s possible
to get the best of silicon
and graphite without
the loss of energy capacity
from silicon oxide.
NanoGraf is boosting
the energy of carbon-silicon
batteries by embedding
silicon particles in graphene.
Their design
uses a graphene matrix
to give silicon room
to swell and to
protect the anode
from damaging reactions
with the electrolyte.
A graphene-silicon
anode can increase
the amount of energy
in a lithium-ion battery
by up to 30%.
For a 40% to 50%
energy density
improvement ,
you have to
eliminate
graphite.
Scientists
have known
how to make
silicon anodes
for years
Sila was one of
the first companies
to figure out how to
mass-manufacture
silicon nanoparticles.
Their solution
involves
packing silicon
nanoparticles
into a rigid shell,
which protects them
from damaging
interactions
with the battery’s
electrolyte.
The inside of the shell
is like a silicon sponge,
and its porosity means
it can accommodate
the swelling when
the battery is charging.
Materials manufacturer
Advano produces
silicon nanoparticles
by the ton in its
New Orleans factory.
To lower the costs,
Advano sources
its raw material
from silicon wafer
scrap from companies
that make solar panels
and other electronics.
The Advano factory
uses a chemical process
to grind the wafers down
into highly engineered
nanoparticles
that can be used
for battery anodes.
“The real problem is not
‘Can we get a battery
that is powerful?’
It’s ‘Can we make
that battery cheap enough
to build trillions of them?’”
says Alexander Girau,
Advano’s founder and CEO.
With this clever
scrap-to-anode
pipeline,
Girau believes
he has a solution.