DESCRIPTION
POROUS SILICON-BASED ANODE ACTIVE MATERIAL, METHOD OF
PREPARING THE SAME, AND LITHIUM SECONDARY BATTERY INCLUDING
5 THE ANODE ACTIVE MATERIAL
TECHNICAL FIELD
[0001] .The present invention relates to a porous sil:i(:onbased
anode active .material, a method of preparing the same,
10 and a lithium secondary battery including the porous siliconbased
anode active material.
BACKGROUND ART
[0002] Recently, in line with miniaturization, 1i'ghtwe:~gh.t~
thin profile, and portable trends in electronic devices
15 according to the development of information and
telecommunications industry, the need for high energy dens:i.ty
ba.tteries used as power sources of such elec-tronic: devices
has increased. Currently, research ,i,nto 1i:thium seconda.ry
batteries, as batteries that may best satisfy the above need,
20 has actively conducted.
[0003] Graphite' is mainly used as an anode material .of the
lithium' secondary battery. However, graphite has a ].ow
capacity per unit mass of 372 mAh/g and a high-capac::i:ty
lithium secondary battery may be difficult to be prepared by
25 using graphite.
[0004] However, since a silicon-based material has a
capacity (4,190 mAh/g) 11 times or more higher than a
theoretical capacity (37.2 mAh/g) of a carbon-based anode
active material, the silicon-based material is on the
5 spotlight as a material for. replacing the carbon-based anode
active material. However, since volume expansion of .the
silicon-based material during the intercalation of. li.th:ium
ions is 3 times or more when silicon is only used, the
capacity of a battery tends to decrease as charging and
10 discharging of .the bat'tery proceed and safety issues may a:Lso
oc.cur. Thus, many techniques are required to cornmerc~~al:i.ze
the silicon-based material.
[0005] Therefore, a significant amount of research. in.1:o an
increase in the capacity of an anode active material, such as
15 silicon, i.e., a decrease in a volume expansion coefficient
by alloying of silicon, has been conducted. However, since a
metal, such as silicon (Si) , . tin (Sn), and aluminum (Al), i.s
alloyed with lithium during charge and disdharge, volume
expansion and contraction may occur. Thus, cyc:l.e
20 characteristics of the battery may degrade.
[0006] Although silicon is known as an element that may most
likely provide high capacity, it may be very difflicu:l:t to
amorphize silicon itself alone and it may be also di:E:E:i.cu:l:t
to amorphize. an alloy including silicon as a main componen.L.
25 However, a method of easily amorphizing a sil-icon-based
material has recently been developed by using mechanical
alloying.
[00071 For example, as a method of preparing an anode active
material for a lithium secondary battery using a s:i.:Licon
5 alloy, a method of preparing an anode active material. has
been developed, in which powders of a silicon element and an
element M (where M is nickel (Ni), cobalt (Co), boron (B),
chromium (Cr) , copper (Cu) , iron (Fe) , manganese (Mn) ,
ti.tanium (Ti), or, yttrium (Y) ) are alloyed by mechanical
10 alloying to form a SiM alloy, the SiM alloy is heat treated,
and .the heat-treated SiM alloy is then alloyed with powder of
an element X . (where X is silver (Ag) , copper (Cu) , and gold
(Au)) by mechanical alloying to obtain a SiMX alloy.
[0008] However, with respect to the anode active materfial
15 :for a lithium secondary battery prepared by the above method,
its charge and discharge capacity may be decreased due .to the
degradation of silicon as charge and discharge cycles proceed.
With respect to the mechanical alloying, since .the
destruction of an alloy structure may occur due .to the
20 intercalation and deintercalation of lithium, .the cyc:Le
characteristics may degrade.
[0009] Therefore, there is a need to develop an anode act:i.ve.
material which may replace a typical anode active mater~al
3 and may improve discharge capacity, efficiency,. and life
25 characteristics when used in the lithium secondary battery.
[0010] Prior Art Documents
[0011] [Patent Document]
[0012] KR 1114492 B1
5
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0013] The present invention provides a porous silicon-based
anode active material which may efficien.tly control volume
10 expansion occurred during charge and discharge o:f a 3.ith:iurn
secondary battery.
[0014] The present invention also provides a method of
preparing the porous silicon-based anode active materi.a:l..
[0015] The present invention also provides an anode and a
15 , lithium secondary battery including the porous silicon-based
anode active material.
TECHNICAL SOLUTION
[0016] According to an aspect of the present invention,
there is provided a porous silicon-based anode active
20 material including crystalline silicon (Si) particles; and a
plurality of pores on surfaces, or the surfaces and inside of
the crystalline silicon particles, wherein at least one plane
of crystal planes of at least a portion of the p1ural:i.t~ o:t
pores includes a (110) plane.
25 [0017] According to another aspect of the present inventson,
there is provided a method of preparing a porous siliconbased
anode active material including the steps of: (i)
depositing metal partic1e.s on a surface .of a silicon wafer;
(ii) etching the silicon wafer by dipping .the surface o:f 'the
5 silicon wafer having the metal particles deposit'ed thereon in
an etching soiu.tion to form pores on the surface, or the
surface and inside of the silicon wafer; and, (iii) con.t:ac.t:i.ng
.the silicon wafer having the pores formed thereon with a
metal removal solution to remove the metal particles and
10 grinding the silicon wafer thus , obtained to obtain
crystalline silicon particles.
[0018] According to another aspect of the present invention,
there is provided an anode including the anode active
material. . .
15 [0019] According to another aspect of the present inven.ti.on,
there is provided a lithium secondary batte:rry including a
cat:hode, the anode, a separator disposed between the cathode
and .the anode, and an electrolyte in ;which a 1i:l:hium sa1l.t :i.s
dissolved.
20 ADVANTAGEOUS EFFECTS
[00201 Since a porous silicon-based anode active ma-ter:ial
according to an embodiment of the present invention may alLow
volume expansion, which is occurred during charge and.
discharge of a lithium secondary battery, to be concentrated
25 on pores instead of the outside of the anode active ma-terial.,
1
the porous silicon-based anode active material may imp:rove
li.:fe charac.teristics of the lithium secondary ba.t.te.ry by
efficiently controlling the volume. expansi-on.
[00211 A porous silicon-based anode active materi-al.
5 according to another embodiment of the present invention may
not only provide enhanced mechanical properties as well as
excellent electrical conductivity even after an electrode
expands while charge and discharge. proceed by further
including a carbon coating layer on silicon particles, but
10 may also further improve .the performance of a 1i:th:ium
secondary battery by suppressing side reactions with an
electrolyte solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The following drawings attached to the specificatfion
15 illustrate preferred examples of the present invention by
example, and serve to enable technical concepts of .the
present invention to be further understood together wfith
detailed description of the invention given below, and
therefore the present invention should not be interpre.ked
20 only with matters in such drawings.
[0023] FIG. 1 is a schematic view illustrating fo:rms o:f
volume expansion according to the degree of lithiatfion o:f!
silicon nanowires;
[0024] FIG. 2 is an exemplary view, illustrating the
25 direction of volume expansion of a porous silicon-based anode
active material including crystalline silicon . particles ~
having an axla1 direction of according to an embodiment
.of the present invention;
[0025] FIG. 3 is an exemplary view ill.us.trat:iny ,the
5 direc.tion of volume expansion of a porous sili-con-based anode
active material including crystalline sil-icon par.t:ic:l.es
having an axial direction of <110> according to an embodiment
of the. present invention;
[0026] FIG. 4 is an exemplary view illustrating 'the
10 direction of volume expansion of a porous sil-icon-based anode
ac.tive material including crystalline silicon , partic::les
having an axial direction of according to an embodiment
of the present invention;
[0027] FIGS. 5 and 6 are .schematic views illustrat-i.ng the
15 degree of volume expan'sion (changes in form) accordi-ng .to a
ratio of a length of a plurality of pores i.n a. (110) plan(-?
direction to a length of ,the pores i.n a plane d:irec.t:ion o'ther
.than the (11.0) plane direction in porous sili-con-based anode
active materials under the assumption that the same volume of
20 pores is included.
,MODE FOR CARRYING OUT THE. INVENTION
[0028] Hereinafter, the present invention will be described
in more detai'l to allow for a clearer understanding of the
present invention.
25 [0029] It will be understood that words or terms used in .the
-
specification and claims shall not be interpreted as che
meaning defined in commonly used dictionaries. It wil.1. be
further understood that the words or terms should be
interpreted as having a meaning that is consistent with their
5 meaning in Lhe context of the relevant art and the technical
idea of the invention, based on the principle that an
inventor may properly define the meaning of the words or
terms to best explain the invention.
10 [0030] A porous silicon-based anode active mater:ial
according to an embodiment of the present invention i.nc:Ludes
crystalline silicon (Si) particles and a plu:ral.i.ty of po:ces
on surfaces, or the surfaces and inside of the crystall:i.ne
silicon particles, wherein ,at least one plane of crys.ta:L
1.5 planes of a.t least a portion of the plurality of pores
includes a (110) plane.
[0031] In the porous silicon-based anode active ma.l-.er:ial
according to the embodiment of the present invention, since a
(110) plane is included in at least one plane of the crystal
20 planes of at least a portion of the plurality of po:res,
volume expansion occurred during charge and discharge .o:i:' a
lithium secondary battery is allowed to be c:oncent:rated on
.the pores instead of the outside of .the anode active mater:i.al..
Thus, the porous silicon-based anode ac-tive ma.teria:l. may
25 improve life characterist.ics of the secondsry battery by
efficiently controlling the volume expansion.,
[0032] In general, a Si-based material exhibits higher
caph~it:t~h an a carbon-based material, but the volume o.fi the
Si-based ma.teria1 may expand because a crystal st:ruc.tb:re
5 thereof may be changed when absorbing and storfing lithium.
When the Si-based material absorbs and sto.res .the maximum
amount of li-thium, the Si-based material may be transformed
into Li4.4Si and the volume of Li4.4Si may expand due Lo
charging. With respect to the rate of increase in volume due
10 to the charging, the volume may expand up to about 4.12 times
the volume of silicon before the volume expansion.
[0033] However, wit'h respect to crystalline silicon, .the
volume expansion of the silicon during the intercalation of
lithium ions is generally severe in a specific direc.ti.on o : C a
15 c.rys.tal plane of the silicon.
[do341 In .this regard, the crystal plane of .I-.he crysta:L:l.:i.rlc+
silicon may be identified by various me.thods, and for examp:l.e,
may be measured by. X-ray dif f raction, a transmission elec.t:ron
microscope (TEM) , or nuclear magnetic resonance.
20 [0035] FIG. 1 is a schematic view illustrating forms of
volume expansion according to the degree of lithiation of
silicon nanowires having different orientations, such as a
, <110>, or direction.
[0036] That is, FIG. 1 illustrates high magnification images
25 (d to f) of partially lithiated crystall.ine si.licon nanowires
a.t 120 mV vs Li/LiC; high magnification images (g to i.) ' o-:f:.
fully lithiated crystalline silicon nanowires at 10 mV vs
Li/~i+; and low magnification images (j to 1) of fu:L:l.y
lithiated crystalline silicon nanowires with respect to each
5 of a crystalline silicon nanowire (a) oriented in a <100>
axis direction (plane direction); a crystalline. silicon
nanowire (b) oriented in a <110> axis direction; and a
crystalline silicon nanowire (c) oriented i.n .a axis
direction.
10 [0037] As illustrated in m to o of FIG'. 1, when the
schematic views of crystal orientations of outer walls o f the
crystalline silicon nanowires oriented in the , <110>,
and axis directions are examined, crystal planes of .the
crystalline silicon nanowire (a) oriented in the
15 direction may include (110) planes and (100) planes (crys-tal
planes) (m) . Also, crystal planes of the crystalline si.:Licon
nanowire oriented in the <110> direction may include (1.00)
pl-anes, (111) planes, and (110) planes (n), and al.1 crystal.
planes of th'e crystalline silicon nanowire oriented in the
20 <].].I> direction may be (110) planes (0) .
[0038] In FIG. 1, with respect to the crystalline s:i.:Licon
nanowire (a) oriented in the axis direction, i.t may be
observed that volume expansion is severe in cruci:t'orm ( - I - )
di-rec-tions as the crystalline silicon nanowire (a) . :i.s
25 partially or fully lithiated (d, g, and j). In this case, i't
may 'be understood that 6 cruciform (+) directions
co:rrespond to the (110) planes among .the crystal planes of
the crystalline silicon nanowire (m).
[00391 Similarly,, with respect to the crystalline siLicon
5 nanowire (b) oriented in the <110> axis direction, the volume
of .the crystalline silicon nanowire severely expands in
directions of about 34.5 degrees as the crystalline silicon
nanowire (b) is partially or fully lithiated (e, h, and k).
In this case, the directions of the volume expans:i.on
10 correspond to the (110) planes among the crystal planes of
the crystalline silicon nanowire (n) . ,
[00401 Also, with respect to the crystalline sil.icon
nanowire (c) oriented in the axis direction, it may be
observed that the volume of .the crystalline silicon nanow:i..re
15 severely expands in all directions as the crysta1:L:ine s:i.:Ll.con
nanowire (c) is fully lithiated (f, i, and 1) . In t:hi.s cilse,
it may be understood that the directions of the volume
expansion correspond to the (110) planes which are a l l
crystal planes of the crystalline silicon nanowire (0).
20 [0041] According to the present invention, since the
plurality of pores are formed on the surfaces or the surfaces
and inside of the crystalline silicon particles and the at
least one plane of the crystal planes of at least a portfion
of the plurality of pores iricludes a (110) plane, .the volume
25 expansion occurred during the charge and dfischarge of the
lithium secondary battery is allowed to be concentrated cjn
the pores instead of the outside of the anode active material.
Thus, an apparent volume expansion of the anode active
material may be minimized.
5 [0042] The anode active material according to the embodiment
of the present invention may include a plurality of
honeycomb-shaped pores on at least the surfaces or the
surfaces and inside of the crystalline silicon particzles. In
this case, a diameter of the pore is in a range of 10 rim to 2
10 pm and preferably, in a range of 100 nm to 1 pm. In the case
that the diameter of the pore is less than 10 nm, since the
diameter of the pore is excessively small, it may be
insufficient to accommodate the volume expansion. Thus, the
effects of the present invention may be insignificant. I:n
15 the case in which the diameter of the pore is greater than 2
pm, since the pores may remain even after accommodating the
volume expansion, energy density of the active material may
be reduced.
[0043] Also, the at leas't one plane of the c.rys.t:a:L planes o:f!
20 at least a portion of the plurality of pores may :inc:lude a
(1.10) Plane, a total number of the crystal planes of .the pore
may be 6 to 8, and among them, 2 planes, 4 planes, o:r 6
planes may include (110) planes.
[0044] In order for the at least one plane of the crystal
25 planes of the pores to be a (110) plane, the crys.ta:Ll:irle
12
I P Q DEk-HI 0 6 - Q h - 2 0 1 5 17 164
silicon particles according to the embodiment of the present
inven.tion may include at least one or more si:Licon part:ic:l.es
having an axial direction of <110>, , or <11.1>.
[0045] An average .particle diameter ( D S o ) of the po:rous
5 silicon-based anode active material according .to '(-.he
embodiment of the present invention is in a range of 100 nm
to 50 pm and preferably, in a range of 100 nm to 20 pm.
[0046] In the present invention, the average par.ticle
diameter ( D S o ) of the porous silicon-based anode actfive
10 material may be defined as a particle diameter at 50% in a
cumulative particle diameter distribution. For example, the
average particle diameter ( D S 0 ) of the porous silicon-based
anode active material according to the embodiment o:E .the
present invention may be measured by using a laser
. ,
15 diffraction method. The laser diffraction method may
generally measure a particle diameter ranging from a
submicron level to a few mrn, and may obtain highly repea.tab1.e
and high resolution results.
[0047] In the case that the average particle diameter
20 is greater than 50 m a uniform volume expansion may be
difficult even if pores are included in the inside o:E the
particles, and thus, life characteristics may degrade. In
the case in which the average particle diameter ( D S 0 ) is less
than 100 nm, since the particle diameter is excessive sma:Ll.,
25 a uniform electrode configuration with a binder and a
----- - ~. .- - --- .. -- - --- -- - .~ ...- . -- ..-. ~ - . - - . z,p J-$ :' -- .D. fLH.. >. .I, QjE.- -0.2-; 2s I,5 I.,?Q .4;
conductive agent may not be realized.
[0048] F I G . 2 is an exemplary view illustrating the
direction of volume expansion of a porous silicon-based anode
active material including crystalline sil.i.con pa.r.t/ic:I.es
5 having an axial direction of according to an embodiment
I of the present invention.
1 [0049] As illustrated in F I G . 2,. since all crystal planes o:E
pores of the crystalline silicon particles having an ax:i.s:L
di.:rection of include (110) planes, the volume expans:i.on
-10 may be concentrated in all directions of ..the crystal' planes
o:f:' the po:res when lithiation occurs during the intercala,l-.:i.on
of lfithium ions. Thus, the volume expansion may 'be minimized.
[0050] Similarly, according to another embodiment o:E .the
present invention, as illustrated in F I G . 3, the porous
15 silicon-based anode acthe material may include crys.tall:ir?e
silicon particles having an axial direction of <].lo>.
[0051] Referring to F I G . 3, with respect -to the crystall./ine
si-licon part.icles having an axial direc.tion of <11.0>, vol-umc-?
expansion may be concentrated in a diagonal direc.tion, YL. (-2 ..,
20 directions of (110) planes which is tilted about 34.5 deg:rrec-,s
with respect to a (111) plane.
[0052] Also, 'as illustrated in F I G . 4 according to anoLhe:r
embodiment of the present invention, the porous silicon-based
anode active material may include crystalline s.i:Li.con
25 particles having an axial direction of .
LBO DELHE 0 6 - Q 2 , - 2615 17' $El4
[0053] Referring to FIG. 4, with respect to !:he crysta.L.!..inc.:
silicon particles having an axial direction of , volume
expansion may be concentrated. in cruciform ( I - direc:t:ions,
i. e., directions of (110) planes.
5 [0054] That is, according to an embodiment o'f .the present
invention, the volume expansion of .the porous silicon-based
anode active material may be concentrated in (110) plane
d:irect'ions during the intercalation of lithium ions.
, [0055] According 'to an embodiment of the present inven-tion,
10 since the anode active material of the present 'invention is
used, a volume expansion coefficient during the intercalation
of lithium :ions may be reduced by about 20% to about 80% in
comparison to the case of using a typical silicon-based anode
active materAal .
15 [0056] . An internal porosity of the po.rous si1:icon-based
anode active material according to the embodiment o f .the
p:resent invention is in a range of 5% to 90%, p:referably, i n . .
a range of 20% to 70%, and more preferably, in a range o f 20%
to 50% based on a total volume of the porous silicon-based
20 anode active material.
[0057] Herein, the internal porosity. may . be defined as
follows :
[0058] Internal porosity = volume of pores. per unit
mass/(spec:~fic volume + volume of pores per un.i.t mass)
I 25 [0059] The measurement of the internal porosity :i.s not-. I
particularly limited. ~ c ~ o ~ d itho g a n embodiment of the
present invention, the internal porosity, for example, may be
measured by a Brunauer-Emmett-Teller (BET) method or mercury
(Hg) porosimetry.
5 [0060] In the case that the internal porosity of the porous
silicon-based anode active material is less than 5%, volume
expansion o.f the anode active material. during charge and
discharge may not be suppressed. In 'the case in which the
internal porosity of the porous silicon-based anode ac.t:i.ve
1 0 ma.kerial is greater than 90%, mechanical strength may be
decreased due to a plurality of pores included in .the anodce
active material, and' thus, the anode active material may be
fractured during manufacturing processes (slurry mixing,
pressing after coating, etc.) of a battery.
15 [0061] A specific surface area of the. porous silicon-based
anode active material according to the embodiment o.I' .(-.he
present inven-tion is in a range of 0.5 m2/g .to 100 m2/g and
p:referably, :in a range of 2 m2/g to 50 m2/g. :!:n the case t h a t
.the specific surface area is greater than 100 m2/g, a side
20 reaction with an electrolyte solution may be difficult .t:o be
controlled due to the wide specific surface area. :C'n 'the
case i.n which the specific surface area is less than 0.5 m2/g,
sufficient pores may not be formed, and thus, the volume
expansion during the charge and discharge of a lithfium
25 secondary battery may not be effectively accommodated.
16
[00621 I n t h e porous s i l i c o n - b a s e d anode a c t i v e mate rr i a:!.
according t o t h e embodiment of t h e . p r e s e n t invent:ion, -the
p l u r a l i t y of pores may f u r t h e r extend i n a (110) plane
d i r e c t i o n of .the p o r e s .
5 [00631 In t h i s r e g a r d , FIGS. 5 and 6 a r e schematic views
i l l u s t r a t i n g che degree of volume expansion (changes i n form)
according t o a r a t i o of a l e n g t h of a p l u r a l i t y of pores i n a
(3.10) plane d i r e c t i o n t o a l e n g t h of t h e pores i n a plane
d i r e c t i o n o t h e r than t h e (110) plane d i r e c t i o n i n porous
10 s i l i c o n - b a s e d anode. a c t i v e m a t e r i a l s under t h e assumpt:ion
t h a t the same volume of pores is i n c l u d e d .
[00641 Spec/ifi.cally, i n the porous si.:licon-based arlode
a c t i v e ma.ter:i.al as i l l u s t r a t e d i n FIG. 5, i n t h e case t h a t
the l e n g t h of t h e p l u r a l i t y of pores i n a (110) plane
15 d i r e c t i o n is . r e l a t i v e l y s m a l l e r than the l e n g t h of .the pores
i n a plane d . i r e c . t i o n . o t h e r than the (110) plane d:i.recti..on, .
e . g . , a 1.eng.th of the pores i n a ( 100) plane d i r e c t f i o n , s i n c e
a s u f f i c i e n t i n t e r n a l space f o r a c t u a l ,expansion may be
secured, a g r e a t e r volume r e d u c t i o n e f f e c t may be obtained a t . .
20 t h e same pore s i z e and volume.
[0065] In c o n t r a s t , as i l l u s t r a t e d i n ' F I G . 6, i n t h e case i n
which t h e l e n g t h of t h e p l u r a l i t y of pores i n a (110) pi-ane
di.:rec.t:ion i.s r e l ' a t i v e l y g r e a t e r than t h e l e n g t h o:f .the. pores
.i.n a plane d i r e c t i o n o t h e r than t h e (11.0) plane d:irec:.tior!,
25 e . g . , a l e n g t h of t h e pbres i n a (100) plane dirc-,c:~l-.~.on,ii
space f o r a c t u a l expansion is i n s u f f i c i e n t , and even.tually,
expansion may occur t o t h e o u t s i d e of a S i p a r t i c l e .
[0066] The porous s i l i c o n - b a s e d anode a c t i v e ma.ter:ia:I.
according t o t h e embodiment of t h e p r e s e n t i n v e n t i o n may
5 f u r t h e r i n c l u d e a carbon c o a t i n g l a y e r on .the c r y s t a l l f i n e
s i l i c o n p a r t i c l e s .
[0067] According .to an embodiment of t h e present: invenl-.:iLon,
s i n c e .the carbon c o a t i n g l a y e r on t h e c r y s t a l l i n e siLi(:on
p a r t i c l e s i s f u r t h e r included, mechanical p:roper.t:ic-,s . a r e
10 f u r t h e r enhanced. Thus, a p a r t i c l e shape r,ay not only be
s t a b l y maintai'ned while t h e p a r t i c l e s a r e not f r a c t u r e d even
during r o l l i n g , but a l s o e l e c t r i c a l c o n d u c t i v i t y may be
f u r t h e r improved by i n c l u d i n g t h e carbon c o a t i n g l a y e r having
e x c e l l e n t c o n d u c t i v i t y on t h e o u t e r walls of t h e p a . r t i c l e s .
15 [0068] A t h i c k n e s s of t h e carbon coating l a y e r is i n a .range
of 5 nm t o 100 nm and p r e f e r a b l y , i n a range o f 5 nm t o 50 nm.
In t h e case t h a t t h e t h i c k n e s s of t h e carbon c o a t i n g 1.ayer is
l e s s than. 5 nm, an e f f e c t of i n c r e a s i n g e:I.ec.t:.rica:l.
c o n d u c t i v i t y due -to t h e carbon c o a t i n g ' l a y e r may be
20 i . n s i g n i f ic:an.t-. and .the r e a c t i v i t y with t h e elec:t:ro:l.y'te
sol.ution durr~ng t h e a p p l i c a t i o n of t h e a c t i v e material. may be
high. Thus, an i n i t i a l e f f i c i e n c y may be reduced. In .the
c a s e . i n which t h e t h i c k n e s s of t h e carbon c o a t i n g l a y e r is
g r e a t e r than 100 nm, s i n c e t h e t h i c k n e s s of t h e carbon
25 c o a t i n g l a y e r may be e x c e s s i v e l y i n c r e a s e d t o a c t as a
barrier to the mobility of lithium. ions, resistance may
increase and there may be difficulties in e1ect:rode
processing due to the hard surface.
[0069] Also, .t:he present invention provides a me.thod of
5 preparing a porous silicon-based anode active materfial
including the steps of (i) depositing metal particles on a
surface of a silicon wafer; (ii) etching .the silicon wafer by
dipping the surface of the. silicon wafer having the metal
particles deposited thereon in an etching solution to form
10 pores on the, .surface, or the surface and inside of .the
sil-icon wafer; and (iii) contacting the silicon wafer having
the pores formed thereon with a metal removal solu't:/ion to
remove the metal particles and grinding the silicon wa:l:'e:r
thus obtained to obtain crystalline silicon particles.
r -
15 [0070] Specifically, in the method of preparing a po:~ous
silicon-based anode active material, step (i) is deposfit:i.ny
metal particles on a surface of a silicon wafer.
[0071] In step (i), the method of depositing metal par.t::ic:l.es
may include various methods, for example, vacuum-based
20 deposition and solution deposition methods. The vacuum-based
deposition method is a method of using high vacuum equipment
such as thermal evaporation, electron beam evaporation, and
spu.ttering. The vacuum-based deposition me.t-.hod .has .
advantages in that a high quality thin metal :film may be
25 deposited to a precise thickness. In the solution depos:i'I::i.on
method, such as electrode deposition, electroless deposition,
and self assembly, a surface of silicon may be plated by
electrochemically reducing metal ions or metal nanopar.t/ic:Les
dispersed in a solvent may be fixed to the surface of silicon.
5 The solution deposition method has advantages in tha-t it is
:relatively simple and low cost in comparison to the expens:i.ve
and complicated vacuum deposition method.
[0072] According .to an embodiment of the present i-nventfion,
a fluorinated solution and a metal precursor soluti.on are
10 mixed and a mixed solution is then in contact with a silicon
wafer to deposit metal particles of the metal precursor
sol-ution on the silicon wafer.
LO0731 In this case, the silicon wafer emits electrons due
to the fluorinated solution and metal ions in the solut:i.on
\- I
15 receive electrons to be reduced and deposited on the surface
of the silicon wafer. Once the metal particles are deposited
on the surface of the si-licon wafer, con.tinuous depos:i.l::i.on
may occur as the metal particle itself becomes a <:ata.:i.ys.t
site.
20 [0074] I* order for at least one plane of the crystal p:Lanes
of .the pores of the porous silicon-based anode ac.t:i.ve
material to include a (110) plane according to an embod:iment
of the present invention, a silicon wafer having an axial
direction of <110> in which 2 planes of crystal. pl-ancis of
25 pores are (110) planes; a silicon wafer having an axfial..
direc-tion of in irlliich '4.' planes of crys.t:al planes i):f!
po.res are (110) planes; or a silicon wafer having an ax:i.al.
direction of in which 6 planes of crystal. planes of
pores are (11.0) planes may be used as the above silicon wa:fier
5 For example, a silicon wafer having an axial direction of
or may be used as the above silicon wafer.
Commercial silicon wafers may be purchased and used.
[0075] At least one selected from the group consisting of
hydrogen fluoride (HE), hydrofluosilicic acid (H2SiEG,) and
10 ammonium fluoride (NH4F) may be used as .the fluorinated . .
solution. 'I'he metal precursor solution may include at leas't
one me.tal particle selected from the group consis.tiny. o:f:' .
silver (Ag), gold (Au), platinum (Pt), and copper (Cu), anti
may be a s'al-t form'. An anion of .the salt may inc:Lude n:i.t::c:i.c
:. $?
15 acfid (NO3-,) sulfuric acid SO^^-) , iodine (IT,) per(:hl_o.rat:e
(Clog-), acetic acid (CH3COO-), or a combination thereof. '.[.'he
diameter of the formed pore may be determined according to a
diameter of the metal particles, and the diameter of the
metal particles may be in a range of 10 nm to 20 pm.
20 [0076] According. to an embodiment of .the present inven-t:.i.tan,
the fluorinated solution and the metal precursor solution may
be mixed in a weight ratio of 10:90 to 90:lO. In the case
that .the weight ra.tio of the fluorinated solu.t:ion incl.udetl :i.s
less than 10, an amount of the metal particles deposited on
25 .the surface of .the silicon wafer may be small and a .reac.t:i.or!
rate may be very slow, and thus, a -preparation ti-me may
increase. In the case in which the weight ratio of .the
fluorinated solution included is greater than 90, deposit:ion
rate of the metal particles on .the surface of .the silicon
5 wafer may be very fast, and thus, uniform and small-sized
metal particles may not be deposited on the silicon wafer.
[0077] Al.so, an amount of the metal particles deposi.ted on
the silicon wafer may be controlled according .I:o a
concentration of the fluorinated soluti.on and a con.tac,t .i-.:i.me
10 of the surface of the silicon wafer with the metal precursor
solution. An amount of the contacted silicon wafer may be in
a range of 0.001 parts by weight to 50 parts by weight based
on 100 parts by weight of the mixed solution o f the
fluorinated solution and the metal precursor solution.
15 [0078] According to an embodiment of the presen-t invention,
step (ii) is etching the silicon wafer by dipping the su.r:l:'ace
of:' the silicon wafer having the metal part-icles deposi-ted
thereon in an etching solution to form pores on the sur.€ace,
or .the surface and inside of the silicon wafer. Nanopo:res,
20 mesopores, and macropores may be formed through .the above
etching prodess. H
[.0079] The etching of the silicon wafer is performed as
follows. For. example, metal particles become metal ions by
being oxidized by H202 , the silicon wafer is con.ti.nuous:l.y
25 dissolved while transferring electrons 'to the metal par.t:i.c:l.es
a.t interfaces between the silicon wafer and the me.t:al
particles, and the reduction of the above-described me.i:a:l.
i.ons, which are oxidized from the metal particles deposit:ed
on the surface of the silicon wafer,' o.ccurs. ~ccordin~'l~,
5 the silicon wafer in contact with the metal particles may be
continuously etched to form a honeycomb-shaped porous
structure at least on the surface thereof, and the diameter
of the metal particles may increase because the me,t:al.
particles have a strong tendency of agglomeration wi.th [:he
10 adjacen-t me.tal particles in the etching solu-tion during .the
[0080] That is, the metal particles may act as a t:emp:Lat:e,
and the diameter of pores in the final etched product may be
cont.rol.led by controlling the diameter and shape of t:he me.ta:i.
15 pa.rt:ic:Les.
[0081] A mixed solution of a HF solution and a hydrogen
peroxide ( H 2 0 2 ) solution may be used as the etching sol.ution,
and an amount of the HE solution included may vary acco.rd:i.ny
to the degree of etching. However, the H F . solution and the
20 1-1202 solution may be mixed in a weight ratio of 10:90 .to
90: 10. In .this case, the amount of H202 plays an important
role in the formation of pores in silicon.
[0082] Also, the etching may be performed for 10 minu.tes .to
5 hours. In the case that the etching is performed less .t'rlar!
25 10 minutes, the formation of pores may be insignifican-i:. I:n
the case in which the etching is performed greater than 5
hours, the silicon wafer is excessively etched, and thus,
mechanical properties 0.f the anode active material may be
deteriorated.
5
[0083] In the method of preparing a porous silicon-based
anode active ma.teria1 according to the embodiment o f the
presen-t invention, step (iii) is contac.ting the silicon wafer
having the pores formed,thereon with a metal removal solution
10 .to remove the metal particles and grinding the silicon wafer
thus obtained to obtain crystalline silicon particles.
[0084] The metal removal solution used may bo at least one
selected from the group consisting of nitric acid ( H N 0 3 ) ,
sulfuric acid (H2SO4) , and hydrochloric acid (HC1) .
15 [0085] The grinding, for example, may be per:to:rmed us:i.nq a
roll-mill, a ball-mill (including wet and dry .types), and a
jet-mill, and the grinding may be performed .to ob.tai.n a
diameter of the anode active material of 100 nm to 50 pm.
[0086] Also, according to the method of preparing a porous
20 silicon-based anode active material according to .the
embodiment of the present invention, after step (iii), t:he
method may further include coating surfaces of .the
c:rystalline silicon particles with carbon by mixing .the
crystalline silicon particles with a carbon precursor and
. 2 5 then performing a heat treatment, and thus, '.the porous
si.licon-based anode active material may further incl-ude a
carbon coating layer on the surfaces of the crystal1:ine
silicon particles
[00871 According to an embodiment of the present invention,
5 the coating may include coating with .pyrolytic carbon usfing
at least one gas or liquid carbon source selected from %he
'g.roup consisting of hydrocarbon gas, me.thane, ethane,
ethylene, butane, acetylene, carbon monoxide, propane, and
propylene; or coa.ting with liquid or solid pitch..
10 [0088] Also, the carbon .coating layer according to an
embodiment of the present invention may be ob-tafined by
dispersing the carbon precursor in a sol.vent, mixing .the
di-spersion with the crystalline silicon particles, and then
drying and performing a heat treatment.
15 [0089] Any carbon precursor may be used without 1'imita.t:i.on
so long as it may form carbon by a heat treatment, and .:!:'o:r
example, pitch or a hydrocarbon-based material. may be usc?tl.
Examples of the hydrocarbon-based material may be fur:fu:ryl.
alcohol or a phenol-based resin.
20 [0090] Also, for example, tetrahydrofuran (TI-IF) and a:l.coho:L
may be used as the solvent for forming the carbon coa'l::i.ng
layer, and the coating may be performed by sintering i.n a
heat treatment temperature range of 300°C to i,400°C.
[0091] The present invention may also provide an anode
25 including the porous silicon-based anode active material.
[00921 Furthermore, the present invention may provide a
lithium secondary battery including a ca.thode, an anode, a .
sepa:rator disposed between the cathode and -the anode, and an
electroly'te i.n which a lithium salt is dissolved, wherefin the
5 anode includes the porous silicon-based anode active mate:r:i.a:l..
[0093] An anode active material according to an embodiment
of .the present invention may be used in a secondary ba-t.l-.e:ry
by mixing the porous silicon-based anode active material with
a typically used anode active material, and the typi.ca:l.:l.y
10 used anode active material may be at least one selected from
the group co~sisting of graphite, soft carbon, hard carbon,
and lithium .titanium oxide.
[0094] The anode active material thus prepared may be used
.to prepare an anode by a typical method in .the art. E'o:r
15 example, the anode active material according to t h e
embodiment of the present invention is mixed with a bi.nde:r, a
sol.vent, and a conductive agent and a dispersant if necessary,
and sti.rred .to prepare a slurry. Then, a current co1:Lec'to:r
may be coated with the slurry and pressed to prepare an anode.
20 [0095] Various types of binder polymers, such as a
polyvinylidene fluoride-hexafluoropropylene copolymer (I?VDE'-
co-HEP) , polyvinylidene fluoride, polyacryloni trile,
polymethyl.methacrylate, - polyvinyl alcohol, carboxyme-thy1
cellulose (CMC), starch, hydroxypropyl cellulose, regenerated
25 cellulose, po.lyvinylpyrrolidone, .t-.etra:f:'luoroe.thy:l.ene,
polye.thylene, polypropylene, an ethylene-propylene-diene
monomer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber
(SBR), a fluorine rubber, poly acrylic acid, and a polymer
having hydrogen thereof substituted wi.th lithium (:Li), sod:i.um
5 (Na), and calcium (Ca), or various copolymers, may be used as
the binder. N-methyl pyrrolidone, acetone; or water may be
used as the solvent.
[0096] Any conductive agent may be used without par.i::i.cu:l.ar
limitation so long as it, has suitable conductivity without
10 causing adverse chemical changes in the batteries. fi'o r
example, the conductive agent may include a conduc.1::i.ve
material such as: graphite such as natural. graphfite and
artificial graphite; carbon black such as acetylene black,
.. Ketjen black, channel black, furnace black, lamp black, and
15 thermal black; conductive fibers such as carbon fibers and
metal fibers; conductive tubes such as carbon nanotubes;
metal powder such as fluorocarbon powder, aluminum powdc-,:r,
and nickel. powder; conductive whiskers such as zinc ox:ide
whiskers . and, potassium .titanate whiskers; conducti.ve me.ta:l.
20 oxide such as titanium oxide; or polyphenylene derivatives.
[00971 An aqueous-based dispersant or an organic dispersant,
such as N-methyl-2-pyrrolidone, may be used as the di.spe:rsan.i:.
[00981 Similar .to the preparation of the anode, a cathode
.active material, a conductive agent, a binder, and a so:Lvent
25 are mixed to prepare a slurry, and a cathode may then be
7 '
prepared by d i r e c t l y coating a metal current. c o l l e c t o r with
.(-.he s l u r r y o r by c a s t i n g t h e s l u r r y on a sepa:ra.te suppo.r-t,a nd
lamina-Ling a ca.thode a c t i v e m a t e r i a l f i l m s e p a r a t e d f :rom 'the
support on a metal c u r r e n t c o l l e c t o r .
5 [0099] Examples of t h e cathode a c - t i v e m a t e r i a l may be a
l a y e r e d compound, such as l i t h i u m coba1.t oxide (:L:i-(:o07),
l i t h i u m n i c k e l oxide (LiNi02) , L i [Ni,CoyMn,M,] O2 (where M :is
any one s e l e c t e d from t h e group c o n s i s t i n g of aluminum (Al),
g a l l i u m ( G a ) , and indium ( I n ) , o r two o r more elements
10 t h e r e o f ; and 0.35x<0.1, OIy, 250.5, 0 5 ~ 1 0 . 1 , and x+y-1-z-I-v=l),
L i ( LiaMb-a-b'Mb' f ) 02-cAc (where 02a10.2, 0.61b51, Osb' 50.2, and
O1c<0.2; M i n c l u d e s manganese (Mn) and a.t l e a s t one se:Le<:t:ed
from t h e group c o n s i s t i n g of n i c k e l ( N i ) , c o b a l t (Co), i..ron
(re), chromium ( C r ) , vanadium ( V ) , copper (Cu), z i n c .(Zn),
c ..
IS and t i t a n i u m ( T i ) ; M' is a t l e a s t one s e l e c t e d :Ir':rom t h e group
c o n s i s t i n g of Al., magnesium (Mg), and boron ( R ) ; and A i s a,i:
l e a s t one select'ed from t h e group c o n s i s . t i n g of phospho:rus
(P), f l u o r i n e ( F ) , s u l f u r ( S ) , and n i t r o g e n ( N ) ) , or a
compound s u b s t i t u t e d with a t l e a s t one t r a n s i t i o n metal;
20 . l i t h i u m manganese oxides such as t h e chemical formu:l.a
L,il+,Mn2-,0~ (where y ranges from 0 t o 0.33) , LiMn03, :LiMn203,
and LiMnO2.; l i t h i u m copper oxide (Li2Cu02); vanadium oxides
such as LiV308, LiFe304, V2O5, and Cu2V207; N i - s i t e type lithfium
n i c k e l o x i d e e x p r e s s e d by t h e chemical formula LiNil.-,My&
25 (where M is Co, Mn, A l , Cu, Fe, Mg, R, or Ga, and y .ranges
:from 0.01 to 0.3) ; lithium manganese complex oxfide expres-sed
by the chemical formula LiMnz-,M,Oz (where M is Co, Nil Fe, Cr,
Zn, or ta.ntalum (Ta), and y ranges from 0.01 to 0.1.) or
Li2Mn3M08 (where M is Fe, Co, Ni, Cu, or Zn) ; L,iMn204 having a
5 part of lithium (Li) being substituted with alkaline earth
me.tal ions; a disulfide compound; and a complex oxide formed
of Fe2(Mo04)3. However, the cathode act'ive material is not
I.imi.ted there.to.
[00100] A typical porous polymer film used as a .typ.i..cal.
10 separator, for: example, a porous polymer film prepared from a
polyolefln-based polymer, such as an ethylene homopolymer, a
propylene homopolymer, an ethylene/butene copolymer, an
ethylene/hexene copolymer, and an ethylene/methacrylate
copolymer, may be used alone or in a lamination therewith as
15 .the separator. Also, a typical porous nonwoven fabric:, :for
example, a nonwoven fabric formed of high meltfing point glass
fibers or pol.ye thylene terephthalate fibers, and a' polymer
separa.tor base material. having at least one surface thereof
coated with ceramic may be used. Howeve:r, the presen-t
20 invention is not limited 'thereto.
[00101] In an electrolyte solution used in an ernbodimen.l-.o :f:'
the present :i.nvention, _a lithium .salt, which may be i.nc:Luded
as .tile electrolyte, may be used without limitation so long as
i.t is typically. used in an electrolyte solution for a
25 secondary, battery. For example, one selected from the group
c o n s i s t i n g of F-, C1-, I-, NO3-, N ( C N ) 2 - l BF4-, C104-,
5 (CF3CF2S022)N - may. be used as a n a n i o n o f t h e lyithium sa:l:t.
[001021 In the e l e c t r o l y t e s o l u t i o n used i n an embodiment of
t h e p r e s e n t i n v e n t i o n , an organic s o l v e n t included i n .the
e l - e c t r o l y t e s o l u t i o n may be used without l i m i t a t i o n so long
as it is t y p i c a l l y used. T y p i c a l l y , any one s e l e c t e d from
10 t h e group c o n s i s t i n g of propylene c a r b o n a t e , e t h y l e n e
carbonate, d i e t h y l carbonate, dimethyl c a r b o n a t e , ethylmethyl
carbonate, methylpropyl carbonate, d i p r o p y l carbona.te,
:f.l.uoro-ethylene carbonate, dimethyl sulfoxfide, ac:etorii:kfiri.:Le,
d.i.methoxyethane, ' . dietkioxyethane, vinylenc carbonate,
15 s u l f o l a n e , y-butyrolactone, propylene s u :I. :E :i. t e ,
. t e ~ t r a h y d r o f u r a n , methyl f ormate, me thy1 a c e ' t a t e , e!:hy~I..
ace-ta'te, i s o p r o p y l a c e t a t e , isoamyl. a c e t a t e , me.thyl.
p:rop:ionatf+,'' e t h y l p r o p i o n a t e , p r o p y l p r o p i o n a t e , b u t y l
p r o p i o n a t e , meth.y l . b u t y l a t e , and e t h y l b u t y l a t e , or a mixtu:re
20 of two or more t h e r e o f may be used.
[001031 I n p a r t i c u l a r , e t h y l e n e carbonate and .propylerie
carbonate, r i n g - t y p e carbonates among t h e carbonate-based
organic s o l v e n t s , well d i s s o c i a t e t h e , l i t h i u r n s a l t i n the
e l . e c t r o l y t e due .to high d i e l e c t r i c cons.t:an.ts as high-
25 v i s c o s i t y o r g a n i c s o l v e n t s , and t h u s , t h e ring-.type ca:rboriate
may be u s e d . S i n c e an e l e c t r o l y t e having high e l e c t r i c a l
c o n d u c t i v i t y may be prepared when t h e r i n g - t y p e carbonate :i.s
mixed w i t h l o w - v i s c o s i t y , l o w - d i e . l e c t r i c c o n s t a n t l i n e a r
carbonate, such as dimethyl carbonate and d i e . t h y l carbona,t:e,
5 i n an a p p r o p r i a t e r a t i o , ' t h e r i n g - t y p e c a r b o n a t e , f o r example,
may be used.
[00104] S e l e c t i v e l y , t h e e l e c t r o l y t e s t o r e d according to t h e
p r e s e n t i n v e n t i o n may f u r t h e r include an addit:ive, such as an
overcharge i n h i b i t o r , included i n a t y p i c a l e l e c t r o l y t e .
10 [00105] A s e p a r a t o r is disposed between t h e cathode and the
anode 110 form an e l e c t r o d e assembly, the e l e c t r o d e assembly
is put i n a c y l i n d r i c a l b a t t e r y case or pri.sma.tic ba.t-tery
case or aluminum pouch, and a secondary b a t t e r y is .then
completed 'when t h e e l e c t r o l y t e i s i n j e ' c t e d t h e r e i n t o . Al.so,,
5 ,the e l e c t r o d e . assembly is stacked and impregna-ted with .the
e l e c t r o l y t e s o l u t i o n , and a l i t h i u m secondary b a t ' t e r y 1.s .then
comple.l-.ed when t h e product thus obtained i s put i.n a ba.t.:-.e:ry
case and s e a l e d
[00106] The l i t h i u m secondary b a t t e r y accordiing t o t h e .
20 p r e s e n t i n v e n t i o n may not only be used i n a b a t t e r y cc-,l:l. [iha.t
i s use,d a s a power source of a s m a l l d e v i c e , but may a l s o be
used as a ur1i.t c e l l i n a medium and l a r g e s i z e d ba.t-..ke.ry
module i n c l u d i n g a p l u r a l i t y of b a t t e r y c e l l s . Pre:t'e:r:red
examples of t h e medium and l a r g e s i z e d device may be an
25 e l e c t r i c v e h i c l e , a hybrid e l e c t r i c v e h i c l e , a p l u g - i n hybrid
e i - e c t r i c v e h i c l e , or a power s t o r a g e system, b u t t h e medium
and l a r g e s i z e d device is not l i m i t e d t h e r e t o .
[00107] H e r e i n a f t e r , t h e p r e s e n t i n v e n t i o n w i l . 1 be described
i n de.tai1, according t o s p e c i f i c exampl-es. The i n v e n t i o n may,
5 however, be embodied i n many d i f f e r e n t forms , and should not
be c o n s t r u e d as being l i m i t e d t o .the embodiments sets f o r t h
h e r e i n . Rather, t h e s e example embodiments a r e provided so
t h a t t h i s d e s c r i p t i o n w i l l be thorough and complete, and w i l l
f u l l y convey t h e scope of t h e p r e s e n t i n v e n t i v e concept ,to
10 those s k i l l e d i n . t h e a r t .
[00108] Examples
[00109] Example 1: Preparation of Porous Silicon-based Anode
Active Material in which All 6 Planes of Crystal' planes of
15 Pores are (110) Planes
[00110] < Step (1.) : Depositing Metal P a r t i c l e s on .the Su:r:Eiicc-?
of S i l i c o n Wafer>
[00111] 300 mP of a 10 mol% hydrogen f l u o r i d e (HF) sol.ut:~on
and 300 mP of a 10 mM s i l v e r n i t r a t e ( A ~ N O ~s)o l u t i o n were
20 mixed f o r 10 minutes. A s i l i c o n wafer (LG S i l t r o n ) having a n
axial. d i r e c t i o n of was added t o t h e s o l u t , i o n , i n wh:i.ch
HE and s i l v e r n i t r a t e were' mixed, and mixed f o r 5 minutes.
Then, t h e s o l u t i o n was f i l t e r e d , washed,. and d r i e d t o . depos:it
Ay on the s u r f a c e of t h e s i l i c o n wafer.
[00112]
[00113] 200 mP of a 5 mol% HF s o l u t i o n and 100 mP of a 1..5
wt:% hydrogen peroxide (H202) s o l u t i o n were mixed o : 1.0
minutes. The s i l i c o n wafer having Ag p a r - t i c l e s d e p o s i t e d
5 thereon, which had been obtained i n s t e p (i), was added t o
t h e e t c h i n g sol.ution, i n which HF and hydrogen peroxide were
. .
mixed, and m.i.xed f o r 30 minutes. . Then, t h e soluti.on was
: f j . l t k r e d , washed, and d r i e d t o form pores on t h e sur:f;ice and
i n s i d e of t h e s i l i c o n wafer.
[00114]
[00115] 100 mP of 60 mol% n i t r i c a c i d (HN03) was heated t:o
5 0 " ~an d t h e porous s i l i c o n wafer obtained i n s t e p (ii)w as
.then added t h e r e t o and mixed f o r 2 hours. Then, .the solu.l::i.on
15 was f i l t e r e d , washed, and d r i e d t o remove Ay. The po:rous
s i l i c o n wafer was ground t o an a p p r o p r i a t e s i z e using a
mortar, t h e ground porous s i l i c o n wafer was then bal.1 m:i.l:l.ed
i n a n ' argon ( A r ) atmosphere, , and t h e bal.:l.-mi:Lled po:rol.:!s
s i l i c o n wafer was f i n a l l y sieved (625 mesh s i e v e : 20 ym mesh
20 s i z e ) t o prepare a porous s i l i c o n anode a c t i v e mate:rial..
[00116] In t h e prepared porous s i l i c o n anode a c t i v e ma.t-.e.ria:l.,
a l l 6 planes of c r y s t a l planes of pores were (110) p l a n e s .
[00117] Example 2: Preparation of Porous Silicon-based' Anode
25 ~ctive Material in which 4 Planes among Crystal Planes of
Pores are (110) Planes
[00118] A porous silicon-based anode ac.tive materfial . was
prepared in .the same manner as in Example 1 except tha't a
silicon wafer (LG Siltron) having an axial direction o:ff
5 was used, instead of the silicon wafer having an axial
direction of in step (i) of Example 1. In the prepared
porous silicon anode active material, 4 planes among crystal
planes of pores were (110) planes.
10 [00119] Example 3 : Preparation of Porous Silicon-based Anode
Active Material in which 2 Planes among Crystal Planes of
Pores are (110) Planes
[00120] A porous silicon-based anode active rna.ter:ial was
prepared in the same manner as in Example 1 excep.t .i-.ha'ta- .
15 silicon wafer (LG Siltron) having an axial direc-tion of <11.0>
was used instead of the silicon wafer having an axi.al. . -
di:rec.tion of in step (i) of Example 1. :Cn the prepared
porous silicon anode active material, 2 planes among crys-tal.
planes of pores were (110) planes.
20
[00121] Example 4: Preparation of Secondary Battery
[00122] The porous silicon anode active material prepared i.n
Example 1,. acetylene black as a conductive agent:, and :I-:i:th:i.um
polyacrylate as a binder were mixed at a weight ra't:i.o o:f
25 70:10:20, and the mixture was. mixed with a N-methy1-2-
p y r r o l i d o n e s o l v e n t . t o prepare a s l u r r y . One s u r f a c e o:f a
copper currek.t c o l l e c t o r was , c o a t e d with t h e prepared s1ur:ry
.to a t h i c k n e s s of 30 pm, d r i e d , and r o l l e d . Then, an anode
was prepared by punching i n t o a predetermined s i z e .
5 [00123] 10 w t % f l u o r o e t h y l e n e carbonate based on a t o t a l
weight of an e l e c - t r o l y t e soluti.on. was added .to, a mixed
solvent:, which i n c l u d e s 1 . 0 'M LiPF6 and an o r g a n i c solvent
pcepa:red by mixing e t h y l e n e carbonate and d i e - t h y l ca;rbona'te
a.t a weight r a t i o of 30:70, t o prepare a non-aqueobs
[00124] A l i t h i u m f o i l was used as a counter e l e c t r o d e , a
p o l y o l e f i n s e p a r a t o r was disposed between both elecisrodes,
and a coin-type secondary b a t t e r y was then prepared by
i n j e c t i n g t h e e l e c t r o l y t e s o l u t i o n .
15
[00125] E x a m p l e s 5 and 6: P r e p a r a t i o n of S e c o n d a r y B a t t e r y
[00126] Secondary b a t t e r i e s were r e s p e c t i v e l y prepared i n the
same manner a s i n Example 4 except t h a t t h e anode ac.L:i.ve
m a t e r i a l s prepared i n Examples 2 and 3 were used i.ns.i:ead o.E
., 20 using the porous s i l i c o n anode a c t i v e m a t e r i a l prc-?pared :i.r~
Example 1 .
[00127] C o m p a r a t i v e Example 1: P r e p a r a t i o n of S i l i c o n Anode ,
A c t i v e M a t e r i a l w i t h o u t P o r e s
25 [00128] A s i l i c o n wafer (LG S i l t r o n ) having an ax:i.a1.
d i r e c . t i o n of was ground t o an appropria.!-.e s i z e us.i.ng a
mortar, t h e ground s i l i c o n water was then b a l l m i l l e d i n an
A.r atmosphere, and .the b a l l - m i l l e d s i l i c o n wafer was fina:L:l.y
sieved (625 mesh s i e v e : 20 pm mesh s i z e ) .to prepare 'a s i l i c o n
5 anode a c t i v e m a t e r i a l without p o r e s .
[00129] Comparative Example 2: Preparation of. Secondary
Battery
[00130] A secondary b a t t e r y was prepared i n t h e same manner
10 as i n Example 4 except t h a t t h e anode a c t i v e ma.te:r?ial
prepared :in Compara.tive Example I was. used i n s t e a d o:fr' using
the porous s i l i c o n anode a c t i v e m a t e r i a l prepared i n Examp:l.e
1.
15 [00131] Experimental Example 1: Analysis of Shape and Crystal
Structure of Porous Silicon-based Anode Active Material
[00132] An X-ray d i f f r a c ' t i o n (XRD) a n a l y s i s was performed to
i n v e s t i g a t e t h e shape and c r y s t a l s t r u c t u r e of t h e porous
s i l i c o n - b a s e d anode a c t i v e m a t e r i a l ' a c c o r d i n g .to .the
20 embodiment of t h e p r e s e n t i n v e n t i o n .
[00133] Experimental Example 2: Life Characteristics, and
Thickness Change ~ a t e ' ~ n a 1 ~ s i s
[00134] The following experiments were performed i.n o r d e r to
25 i n v e s t i g a . t e l i f e c h a r a c t e r i s t i c s and t h i c k n e s s change :rakes
01 the secondary batte'ri'es -prepared in Examples 4 to 6 and
Comparative Example 2.
[00135] Life characteristics of each battery were measured by
performing charge and discharge at 0.1 C in a first cycle and
5. .the life characteristics .were represented as a ra.ti.0 of
discharge capacity in a 49th cycle .to .the fi:rs.t' cyc1.e
discharge capacity. Each secondary battery was disassemb:l.ed
in a charge state of a 50th cycle and a thickness of an
electrode was measured. Then, a thickness change rate was
10 obtained by comparing the above thickness with a thickness of
the electrode before the first cycle.
[00136] The following Table 1 presents internal porosil:ies,
'life characteristics, and thickness change rates of t,he
. .
1 secondary' batteries prepared in Examples 4 to 6 and
Comparative Example 2 . . ,
Examples
Example 4
Example 5
Example 6
Comparative
Example 2
Internal
Porosity ( % )
5 1
4 8
5 0
0
Life
characteristics
( % -
9 6
9 3
8 5
13
Thickness change
rate ( % ) .
--
7 5
8 9
142
320
[001381 - Life characteristics: (discharge capaci.ty in a 49th
cycle/ first cycle discharge capacity).~10 0
[001391 - Thickness change rate: (electrode thickness in a
5 charge state of a 50th cycle - electrode thickness before a
first cycle)/ electrode thickness before the first cycle x
[00140] - Internal porosity = volume of pores per ur1:i:t:
7
mass/(speci,fic vol-ume I- volume of pores per unit mass)
10 [00141] (use BELSORP (BET instrument) by EEL Japan Ink., use
values calculated by the Barrett-Joyner-Halenda (BJ'II) me.thod,
l.e., a mesopore measurement method)
' [00142] As illustrated in Table 1, the li.thium seconda.ry
15 batteries of Examples 4 to 6 using the anode active ma.terial.s,
'in which at least one plane of crystal planes o.f po:res
included a (110) plane according. to the present invention,
exhibited significant differences in life characteris~tics and
I
thickness change rate in comparison to the li-thium secondary
20 battery of Comparative Example 2 using .the anode acl-.:i.ve
material without pores.
[00143] Specifically, with respect to the 1i.chium sc:.c:onda:ry
batteries of Examples 4 to 6 of the presen.t .i,nven.tion,si n(:(:.
the at least one plane of the crystal planes of the pores in
25 the porous silicon anode active materia'l included .the (11.0)
t . '
p l a n e , t h e volume expansion occurred during the charge and
d i s c h a r g e of t h e secondary b a t t e r y .was alilowed .to be
c o n c e n t r a t e d on t h e pores of t h e anode a c t i v e m a . t e r i a l . '.l.'hus,
t h e volume expans jon may be e f f i c i e n t l y c o n t r o l l e d t o about
5 25% or more. Therefore, it may be confirmed t h a t t h e
.i-.hicikness change r a . t e s of Examples 4 t o 6 were signi:lr'i.cant-.:l-y
lower .than t h a t of Comparative Example 2 without p o r e s , and
accordingly, t h e l i f e c h a r a c t e r i s t i c s were improved by about
70% or more.
10 INDUSTRIAL APPLICABILITY
[00144] Since a porous s i l i c o n - b a s e d anode a c t i v e mater:ial
according t o an embodiment of t h e p r e s e n t i n v e n t i o n may allow
volume expansion, which is occurred d u r i n g charqe and
d i s c h a r g e of a li-thium secondary b a t t e r y , ,to be concent:rated
15 on pores i n s t e a d of t h e o u t s i d e of t h e anode a c t i v e ma.te:r?:.a:l.,
t h e porous sili.con-based anode a c t i v e m a t e r i a l may imp:rovc-!
' l i f e ' c h a r a c ' t e r i s t i c s of t h e l i t h i u m . secondary baL.i:c-,.ry by
ef:'.f:'iciently c o n t r o l l i n g .the volume expansion.
CLAIMS
1. A porous silicon-based anode active mate.r:i.al
comprising:
5 crystalline silicon (Si) particles; and
a plurality of pores on surfaces, or the surfaces and
. .
inside of the crystalline silicon particles,
wherein at least one plane of crystal. planes o:fi at
least a portion of the plurality of pores compri-ses a (11.0)
10 plane.
2. The porous silicon-based anode ac.tive material o:l! c::La:i.m
1, wherein 2 planes, 4 planes, or 6 planes of the crystal.
planes of the at least a portion of 'the plurality of pores
15 comprise (110) planes.
3. The porous silicon-based anode active ma-terial C):E c1.a.i.m
I., wherein the crystalline silicon particles comprise silicon
pa.rtic1.e~h av:ing an axial direction of <110>, <100>, o.r .
4. The porous silicon-based anode active material o:fi c:La:i.m
1, wherein a diame.ter of the pore is in a range o:E 1.0 nm to 2
I-lm -
25 5. The porous silicon-based anode active ma.teria1 o:f! c1.a:i.m
- 1., wherein 2n average p a r t i c l e diameter (DS0) of t h e porous
s i l i c o n - b a s e d anode a c t i v e m a t e r i a l is i n a r a n g e o f 100 nm
t o 50 pm.
5 6 . The porous s i l i c o n - b a s e d anode a c t i v e ma-terial. o:f c::La:i.m
I., wherefin a s p e c i f i c s u r f a c e a r e a of t h e porous silficonbased
anode a c t i v e m a t e r i a l i s i n a range of 0 . 5 m2/g t o 1.00
m2/g.
10 7 . .The porous s i l i c o n - b a s e d anode a c t i v e m a - t e r i a l o.f claim
1, wherein an i n t e r n a l p o r o s i t y of t h e . porous s i l i c o n - b a s e d
anode a c t i v e m a t e r i a l is i n a range o£ 5% t o 90%.
8. The porous s i l i c o n - b a s e d anode a c t i v e m a t e r i a l of c1a:i.m
15 1, wherein a volume of t h e porous s i l i c o n - b a s e d anode acl::i.ve
m a t e r i a l expands i n a (.110) p l a n e dfirection of .(-.he po:r:es
du:ring i n t e r c a l a . t i o n of l i t h i u m i o n s .
9 . The porous silicon.-based anode a c t i v e m a t e r i a l of claim
2.0 1, wherein t h e p l u r a l i t y of pores f u r t h e r -extend i n a (113)
plane d i r e c t i o n of t h e p o r e s . ' .
10. The porous s i l i c o n - b a s e d anode a c t i v e . m a t e r i a l o:f claim
9, wherein a l e n g t h of t h e p l u r a l i t y of pores i n .the (1.1.0)
25 plane d i r e c t i o n of t h e pores i s r e l a - L i v e l y s m a l L : .than a 1
length of the pores in a plane direction other Lhan the (1.10)
plane direction.
11. The porous silicon-based anode active material 0% claim
5 1, further comprising a carbon coating layer on .the
crystalline silicon particles.
12. The porous silicon-based anode active ma.cerial o:f c1a:i.m
1.1., wherein a thickness of the carbon coating layer i.s i.n a
10 range of 5 nm to 100 nm.
13. A method of preparing a porous silicon-based anode
active material, the method comprising the steps of:
(i) depositing metal particles on a surface of a
15 sj.l.i.c:on wafer;.
(ii) etching the silicon wafer by dipping the su.r.fiace
of the silicon wafer having the metal partficles deposiked
thereon in an etching solution to form pores on the surface,
or the surface and inside of the si.licon wafer;'and
20 (iii) contacting .the silicon wafer having .the po:res
:formed thereon with. a metal removal soluti.on .to remove .i-.i.?e
meta:L par-ticles and grinding the silicon wafer -thus obl-.afinc-?d
to obtain crystalline silicon particles.
25 14. The method of. claim 13, wherein the silicon wafer has
an a x i a l d i r e c t i o n of < l l O > , , o r .
15. 'The method of claim 1 4 , wherein the s i l - i c o n wafer has
an a x i a l d i r e c t i o n of <100> o r < I l l > .
16. The method of claim 13, wherein t h e d e p o s i . t i n g of the
metal p a r t i c l e s is performed by mixing a f l u o r i n a t e d s o l u t i o n
and a metal p r e c u r s o r s o l u t i o n , and c o n t a c t i n g t h e s i l i c o n
wafer with . t h e mixed s o l u t i o n .
1.7. The method of claim 16, wherein t h e f l u o r i n a . t e d
so:l.ution comprises a t l e a s t one s e l e c t e d :from .the group
c o n s i s t i n g of hydrogen f l u o r i d e ( H E ) , hydrofluosi1ici.c: a c i d
(I-l2SiF6,) and a&nium f l u o r i d e (NH4E) . .. .
15
1.13. :l?he me.thod of claim 16, wherein -the rne.ta:i. p:r(-,c:u:rsor
s o l u t i o n comprises a t l e a s t one metal p a r t i c l e s e l e c t e d from
.the gr'oup c o n s i s t i n g of s i l v e r , gold, platinum, and coppe:r.
20 1 9 . . The method of claim 16, where'in' t h e . f l u o r i n a . t e d
s o l u t i o n and t h e metal p r e c u r s o r s o l u t i o n a r e -mixed i n a
weight r a f i o of 10:90 t o 90:lO.
20. The method of claim 16, wherein an amount o:E :the
25 .contacted s i l i c o n wafer is i n a range of 0.001 p a r t s by
weight to 50 parts by weight based on 100 parts by weight of
the mixed solution of the fluorinated solution and the metal
precursor solution.
5 21. The method of claim 13, wherein the etching solution is
a mixed solution of a HE solution and a hydrogen perox:i.de .'
22. The method of claim 21, wherein the HF solu'ti'on and 'the
10 I-IzOz sol-ution are mixed in a weight ratio of 10: 90 to 90: 10: ' .
23. 'The me'thod of claim 13, wherein the etchfiny :is
performed for 10 minutes to 5.hours.
15 24. The' method of claim 13, wherein the metal 'remova:l.
solution comprises at least one selected from the group
consisting of nitric acid, sulfuric acid, and hydroch1o.r:~~
a c i. d .
20 25. 'The me.thod of ,claim 14, further comprising (:oat:i.ng
surfaces of the crystalline silicon particles with carbon by
mixing the crystalline silicon .particles with a carbon
precursor and pe.rforming .a heat treatment, after step (iii) . ,
25 26. 'The method of claim 25, wherein the carbon prec:ursor .
comprises pi-tch o r a hydrocarbon-based ma-terial..
27. The method of claim 25, wherein t h e heat treatmen-t i.s
perfoymed i n a tempera.ture range of 300°C t o 1,400"C.
28. An anode comprising t h e porous s i l i c o n - b a s e d anode
a c t i v e m a t e r i a l of claim 1.
2 9 . A l i t h i u m secondary b a t t e r y comprising:
' a cathode;
an anode;
a, s e p a r a t o r disposed between t h e cathode and [:he anode;
and
an e l e c t r o l y t e i n which a l i t h i u m s a l t is dissol.ved,
1 S wherein t h e anode is t.he anode of claim 28.