U.S. patent application number 12/965850 was filed with the patent office on 2011-12-08 for lithium battery cathode composite material.
This patent application is currently assigned to HON HAI PRECISION INDUSTRY CO., LTD.. Invention is credited to JIAN GAO, XIANG-MING HE, CHANG-YIN JIANG, JIAN-JUN LI, GAI YANG, JIE-RONG YING.
Application Number | 20110300446 12/965850 |
Document ID | / |
Family ID | 45063769 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110300446 |
Kind Code |
A1 |
YANG; GAI ; et al. |
December 8, 2011 |
LITHIUM BATTERY CATHODE COMPOSITE MATERIAL
Abstract
A lithium battery cathode composite material includes a number
of composite particles. Each of the composite particles includes
one lithium vanadium phosphate particle and a lithium iron
phosphate layer. The lithium iron phosphate layer is disposed on a
surface of the lithium vanadium phosphate particle. The lithium
iron phosphate layer includes a number of uniformly disposed
lithium iron phosphate particles.
Inventors: |
YANG; GAI; (Beijing, CN)
; JIANG; CHANG-YIN; (Beijing, CN) ; GAO; JIAN;
(Beijing, CN) ; YING; JIE-RONG; (Beijing, CN)
; LI; JIAN-JUN; (Beijing, CN) ; HE;
XIANG-MING; (Beijing, CN) |
Assignee: |
HON HAI PRECISION INDUSTRY CO.,
LTD.
Tu-Cheng
TW
TSINGHUA UNIVERSITY
Beijing
CN
|
Family ID: |
45063769 |
Appl. No.: |
12/965850 |
Filed: |
December 11, 2010 |
Current U.S.
Class: |
429/221 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 4/5825 20130101; H01M 10/052 20130101 |
Class at
Publication: |
429/221 |
International
Class: |
H01M 4/52 20100101
H01M004/52 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2010 |
CN |
201010191050.4 |
Jun 3, 2010 |
CN |
201010191051.9 |
Jun 3, 2010 |
CN |
201010191130.X |
Jun 3, 2010 |
CN |
201010191251.4 |
Claims
1. A lithium battery cathode composite material comprising a
plurality of composite particles, each of the composite particles
comprising a lithium vanadium phosphate particle and a lithium iron
phosphate layer disposed on a surface of the lithium vanadium
phosphate particle, wherein the lithium iron phosphate layer
comprises a plurality of lithium iron phosphate particles.
2. The lithium battery cathode composite material of claim 1,
wherein the composite particles have core-shell structures.
3. The lithium battery cathode composite material of claim 1,
wherein the lithium vanadium phosphate particle in each compound
particle is substantially ball-shaped, and a diameter of the
lithium vanadium phosphate particle is in a range from about 1
micrometer to about 50 micrometers.
4. The lithium battery cathode composite material of claim 1,
wherein the lithium iron phosphate layer comprises a plurality of
pores defined by the lithium iron phosphate particles.
5. The lithium battery cathode composite material of claim 1,
wherein the lithium iron phosphate particles are substantially
ball-shaped, and diameters of the lithium vanadium phosphate
particle are in a range from about 50 nanometers to about 10
micrometers.
6. The lithium battery cathode composite material of claim 1,
wherein a weight ratio between the lithium iron phosphate layer and
the lithium vanadium phosphate particle is larger than 1.5.
7. The lithium battery cathode composite material of claim 1,
wherein a thickness of the lithium iron phosphate layer is less
than or equal to 10 micrometers.
8. The lithium battery cathode composite material of claim 1,
wherein the composite particle comprises carbon material disposed
therein, and a weight ratio between the carbon material in each
composite particle and the lithium vanadium phosphate particle is
in a range from about 0.005 to about 0.1.
9. The lithium battery cathode composite material of claim 8,
wherein the carbon material exists as a carbon layer disposed
between the lithium vanadium phosphate particle and the lithium
iron phosphate layer.
10. The lithium battery cathode composite material of claim 8,
wherein the carbon material exists as a carbon layer disposed on a
surface of each of the lithium iron phosphate particles.
11. The lithium battery cathode composite material of claim 8,
wherein the carbon material exists as carbon particles disposed in
the lithium iron phosphate layer.
12. The lithium battery cathode composite material of claim 1,
wherein the lithium iron phosphate particles are doped by metal
ions.
13. The lithium battery cathode composite material of claim 12,
wherein the lithium iron phosphate particles comprise a plurality
of iron ions (Fe.sup.2+), nickel ions (Ni.sup.2+), cobaltco ions
(Co.sup.3+), magnesium irons (Mg.sup.2+), or vanadium ions
(V.sup.3+).
14. The lithium battery cathode composite material of claim 13,
wherein a chemical formula of the lithium iron phosphate particles
doped with the metal ions is LiFe.sub.(1-xy/2)M.sub.xPO.sub.4,
wherein M is a metal doped in the lithium iron phosphate particles,
X is a number of M ion in one lithium iron phosphate molecule, and
Y is a charge number of one M ion.
15. The lithium battery cathode composite material of claim 14,
wherein X is in a range from about 0.01 to about 0.08.
16. A lithium battery cathode composite material comprising a
plurality of composite particles, each of the composite particles
having a core and a shell, wherein the core comprises one lithium
vanadium phosphate particle, and the shell comprises a lithium iron
phosphate layer defining a plurality of pores.
17. The lithium battery cathode composite material of claim 16,
wherein the lithium iron phosphate layer comprises a plurality of
lithium iron phosphate particles dispersed uniformly on a surface
of the lithium vanadium phosphate particle.
18. The lithium battery cathode composite material of claim 17,
wherein the lithium iron phosphate particles are doped by metal
ions.
19. The lithium battery cathode composite material of claim 18,
wherein the lithium iron phosphate particles are doped by vanadium
ions (V.sup.3+).
20. A lithium battery cathode composite material comprising a
plurality of composite particles, each of the composite particles
having a core and a shell, wherein the core is a lithium vanadium
phosphate particle, the shell is a lithium iron phosphate layer
comprised of a plurality of lithium iron phosphate particles, and a
plurality of pores are defined by the plurality of lithium iron
phosphate particles.
Description
RELATED APPLICATIONS
[0001] This application claims all benefits accruing under 35
U.S.C. .sctn.119 from China Patent Applications No. 201010191050.4,
filed on Jun. 3, 2010; No. 201010191051.9, filed on Jun. 3, 2010;
201010191130.X, filed on Jun. 3, 2010; and 201010191251.4, filed on
Jun. 3, 2010, in the China Intellectual Property Office, the
contents of which are hereby incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to cathode material of
lithium batteries and methods for fabricating the same.
[0004] 2. Description of Related Art
[0005] Lithium batteries are used in various portable devices, such
as notebook PCs, mobile phones, and digital cameras because of
their small weight, high discharge voltage, long cyclic life, and
high energy density compared with conventional lead storage
batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and
nickel-zinc batteries.
[0006] Among various cathode materials, transition metal oxides and
mixed transition metal oxides have received much attention because
of their relatively high charge/discharge capacities in the lithium
batteries. Lithium iron phosphate (e.g. LiFePO.sub.4), and lithium
vanadium phosphate (e.g. Li.sub.3V.sub.2(PO.sub.4).sub.3) are two
widely used cathode active materials. Lithium iron phosphate has
the advantage of high specific capacity, but has the disadvantage
of bad performance at low temperatures. Lithium vanadium phosphate
has good performance at low temperatures, but low specific
capacity. As such, there is a composite cathode material including
both lithium iron phosphate and lithium vanadium phosphate provided
in, "Improving electrochemical properties of lithium iron phosphate
by addition of vanadium," Yang M R, Ke W, Wu S H. J Power Sources,
2007, 165: 646-650. However, in the composite cathode material,
lithium iron phosphate and lithium vanadium phosphate are
disorderly disposed, which means that some of the lithium iron
phosphate cannot contact with the electrolyte when used in a
lithium battery. As such, lithium iron phosphate cannot be
dispersed in the electrolyte easily and quickly, thereby negatively
impacting electrochemical properties of the electrode material of
the lithium battery.
[0007] What is needed, therefore, is a lithium battery cathode
composite material and method for making the same that can overcome
the above-described shortcomings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Many aspects of the embodiments can be better understood
with reference to the following drawings. The components in the
drawings are not necessarily drawn to scale, the emphasis instead
being placed upon clearly illustrating the principles of the
embodiments. Moreover, in the drawings, like reference numerals
designate corresponding parts throughout the several views.
[0009] FIG. 1 is a schematic view of a lithium battery cathode
composite material structure according to a first embodiment.
[0010] FIG. 2 is a Scanning Electron Microscope (SEM) Image of the
lithium battery cathode composite material in FIG. 1.
[0011] FIG. 3 is a schematic view of a lithium battery cathode
composite material doped with carbon structure according to a
second embodiment.
[0012] FIG. 4 is a test graph showing charge/discharge specific
capacities at 0.1 Coulomb (C) rates of the lithium battery cathode
composite material according to the first embodiment and a lithium
battery cathode composite material doped with vanadium according to
a third embodiment.
[0013] FIG. 5 is a test graph showing charge/discharge specific
capacities at different rates of the lithium battery cathode
composite material according to the first embodiment and the
lithium battery cathode composite material doped with vanadium
according to the third embodiment.
[0014] FIG. 6 is a flow chart of a method for making the lithium
battery cathode composite material according to one embodiment.
[0015] FIG. 7 is an SEM image of a lithium vanadium phosphate
material according to one embodiment.
[0016] FIG. 8 is an SEM image of lithium iron phosphate precursor
particles according to one embodiment.
[0017] FIG. 9 is a Transmission Electron Microscope (TEM) image of
lithium iron phosphate precursor particles according to one
embodiment.
[0018] FIG. 10 is an SEM image of lithium iron phosphate particles
according to one embodiment.
[0019] FIG. 11 is a test graph showing the relationship between
specific capacity and cycling capability at 0.1 C rate of the
lithium battery cathode composite material according to another
embodiment.
[0020] FIG. 12 is a chart comparing discharging specific capacity
at 0.1 C between the lithium iron phosphate particles in FIG. 10
and the lithium battery cathode composite material according to one
embodiment.
[0021] FIG. 13 is a chart comparing discharging specific capacity
at 1 C between the lithium iron phosphate particles in FIG. 10 and
the lithium battery cathode composite material in FIG. 12.
[0022] FIG. 14 is a chart comparing discharging specific capacity
at 5 C between the lithium iron phosphate particles in FIG. 10 and
the lithium battery cathode composite material in FIG. 12.
[0023] FIG. 15 is a chart comparing discharging specific capacity
at 10 C between the lithium iron phosphate particles in FIG. 10 and
the lithium battery cathode composite material in FIG. 12.
[0024] FIG. 16 is an SEM image of lithium iron phosphate precursor
particles without vanadium doping according to one embodiment.
[0025] FIG. 17 is an SEM image of lithium iron phosphate precursor
particles doped with vanadium according to another embodiment.
[0026] FIG. 18 is an SEM image of lithium iron phosphate particles
doped with vanadium according to yet another embodiment.
[0027] FIG. 19 is s a test graph showing the relationship between
specific capacity and cycling capability at 1 C rate of the lithium
iron phosphate particles doped with Vanadium according to another
embodiment.
[0028] FIG. 20 is a chart comparing X-ray diffraction patterns
between the lithium iron phosphate particles in FIG. 16 and lithium
iron materials doped with vanadium.
[0029] FIG. 21 is a chart comparing discharging specific capacity
at 0.1 C between lithium iron phosphate particles doped with
vanadium and lithium battery cathode composite material doped with
vanadium according to one embodiment.
[0030] FIG. 22 is a chart comparing discharging specific capacity
at 1 C between lithium iron phosphate particles doped with vanadium
and lithium battery cathode composite material doped with vanadium
in FIG. 19.
[0031] FIG. 23 is a chart comparing discharging specific capacity
at 5 C between lithium iron phosphate particles doped with vanadium
and lithium battery cathode composite material doped with vanadium
in FIG. 19.
[0032] FIG. 24 is a chart comparing discharging specific capacity
at 10 C between lithium iron phosphate particles doped with
vanadium and lithium battery cathode composite material doped with
vanadium in FIG. 19.
DETAILED DESCRIPTION
[0033] The disclosure is illustrated by way of example and not by
way of limitation in the figures of the accompanying drawings in
which like references indicate similar elements. It should be noted
that references to "an" or "one" embodiment in this disclosure are
not necessarily to the same embodiment, and such references mean at
least one.
[0034] Referring to FIGS. 1 and 2, a lithium battery cathode
composite material 10 according to a first embodiment is shown. The
lithium battery cathode composite material 10 includes a plurality
of composite particles 100. The composite particles 100 have
core-shell structures. Each composite particle 100 includes one
lithium vanadium phosphate particle 102 and a lithium iron
phosphate layer 104 covering the lithium vanadium phosphate
particle 102. The lithium vanadium phosphate particle 102 can be
considered a "core," and the lithium iron phosphate layer 104 can
be considered a "shell."
[0035] The lithium vanadium phosphate particle 102 can be
ball-shaped or almost ball-shaped. A diameter of the lithium
vanadium phosphate particle 102 is in a range from about 1
micrometer to about 50 micrometers. In other embodiments, the
diameter of the lithium vanadium phosphate particle 102 is in a
range from about 5 micrometers to about 20 micrometers. In the
embodiment according to FIGS. 1 and 2, the diameter of the lithium
vanadium phosphate particle 102 is about 10 micrometers.
[0036] A weight ratio between the lithium iron phosphate layer 104
and the lithium vanadium phosphate particle 102 is larger than 1.5.
The lithium iron phosphate layer 104 includes a plurality of
lithium iron phosphate particles 1042. The plurality of lithium
iron phosphate particles 1042 is disposed on an outer surface of
the lithium vanadium phosphate particle 102. Each of the lithium
iron phosphate particles 1042 can be ball-shaped or almost
ball-shaped. A diameter of each lithium iron phosphate particle
1042 can be in a range from about 50 nanometers to about 10
micrometers. In other embodiments, the diameter of the lithium iron
phosphate particles 1042 can be in a range from about 100
nanometers to about 500 nanometers. The diameter of the lithium
iron particles 1042 cannot be too large in the instance the lithium
iron particles 1042 fall off the lithium vanadium particle 102. In
the embodiment according to FIGS. 1 and 2, the diameter of the
lithium iron phosphate particles 1042 is in a range from about 100
nanometers to about 200 nanometers. The lithium iron phosphate
layer 104 has a large specific surface area because the lithium
iron phosphate particles 1042 are ball-shaped or almost ball-shaped
and have small diameter.
[0037] A thickness of the lithium iron phosphate layer 104 can be
less than 10 micrometers. In one embodiment according to FIGS. 1
and 2, the thickness of the lithium iron phosphate layer 104 is
about 2 micrometers. The lithium iron phosphate layer 104 further
includes a plurality of pores defined by adjacent lithium iron
phosphate particles 1042.
[0038] In the composite particles 100 having core-shell structures,
because the "shell" (lithium iron phosphate layer) 104 has a large
specific surface area, the "shell" 104 has a large contact area
with an electrolyte when the lithium battery cathode composite
material 10 is used in a battery, and the lithium iron phosphate
particles 1042 can be dispersed easily and quickly in the
electrolyte. Further, the shell 104 includes a plurality of pores
which can ensure the contact area between the composite particles
100 and the electrolyte is sufficient, and the "core" (lithium
vanadium phosphate particle) 102 can also contact the electrolyte.
As such, the lithium ions in the lithium battery cathode composite
material 10 can be fully dispersed in the electrolyte. Furthermore,
the core 102 can be considered an active supporter of the shell
104, which further ensures the lithium iron phosphate particles
1042 inside the shell 104 also disperse in the electrolyte. As
such, the lithium battery cathode composite material 10 can be well
dispersed in the electrolyte.
[0039] Referring to FIG. 3, a lithium battery cathode composite
material 20 according to a second embodiment is shown. The lithium
battery cathode composite material 20 includes a plurality of
composite particles 200. The composite particles 200 have
core-shell structures. Every composite particle 200 includes one
lithium vanadium phosphate particle 202 and a lithium iron
phosphate layer 204 covering the lithium vanadium phosphate
particle 202. The lithium iron phosphate layer 204 includes a
plurality of lithium iron phosphate particles 2042.
[0040] Each of the composite particles 200 includes carbon
material. The carbon material in the composite particles 200 can
exist as a carbon layer or carbon particles. A weight ratio between
the carbon material in each composite particle 200 and the lithium
vanadium phosphate particle 202 can be in a range from about 0.005
to about 0.1, particularly, the weight ratio between the carbon
material and the lithium vanadium phosphate particle 202 can be in
a range from about 0.02 to about 0.05.
[0041] In one example, the composite particle 200 can include a
carbon layer 208 disposed between the lithium vanadium phosphate
particle 202 and the lithium iron phosphate layer 204. The carbon
layer 208 is disposed on an outer surface of the lithium vanadium
phosphate particle 202. The carbon layer 208 can improve the
conductivity of the composite particle 200, and further improve the
conductivity of the lithium battery cathode composite material
20.
[0042] In another example, the lithium iron phosphate layer 204 can
further include a plurality of carbon particles 206 dispersed in
the lithium iron phosphate particles 2042. Each of the carbon
particles 206 can be disposed between adjacent lithium iron
phosphate particles 2042. The carbon particles 206 can improve the
conductivity of the lithium battery cathode composite material 20.
The carbon particles 206 can improve the conductivity of the
lithium iron phosphate layer 204, and further improve the
conductivity of the lithium battery cathode composite material
20.
[0043] In yet another example, each of the lithium iron particle
2042 can further include a carbon layer 2046 disposed on an outer
surface of the lithium iron particle 2042. The carbon layer 2046
can improve the conductivity of lithium iron phosphate layer 204,
and further improve the conductivity of the lithium battery cathode
composite material 20.
[0044] A lithium battery cathode composite material according to a
third embodiment is disclosed. The lithium battery cathode
composite material has the same structure as the lithium battery
cathode composite material 10 disclosed in the first embodiment
except for certain characteristics of the lithium iron phosphate
layer.
[0045] In the third embodiment, the lithium iron phosphate layer of
the composite particle can be doped with different metal ions
instead of iron ions (Fe.sup.2+) in the lithium iron phosphate
particles. The metal ions can be nickel ions (Ni.sup.2+), cobalt
ions (Co.sup.3+), magnesium irons (Mg.sup.2+), or vanadium ions
(V.sup.3+). The chemical formula of the lithium iron phosphate
doped with the metal ions can be LiFe.sub.(1-xy/2)M.sub.xPO.sub.4,
wherein M is the metal doping material in the lithium iron
phosphate, X is the number of M ions per one lithium iron phosphate
molecule, Y is charge number of one M ion. X can be in a range from
about 0.01 to about 0.08. Doping with the metal ions can decrease
the chemical bonding force of Li--O in lithium iron phosphate, and
the lithium ions can be dispersed easily in the electrolyte. As
such, the rate capability and the cycling capability of the lithium
battery cathode composite material 20 can be improved. In the third
embodiment, the metal doping material in the lithium iron phosphate
is vanadium, and the chemical formula of the lithium iron phosphate
doped with the vanadium ions is LiFe.sub.0.97V.sub.0.03PO.sub.4.
FIG. 4 shows that, at the same rate, the charge/discharge specific
capacity of the lithium battery cathode composite material
according to the third embodiment is better than the lithium
battery cathode composite material without doping. FIG. 5 shows
that, at different rates, the charge/discharge specific capacity of
the lithium battery cathode composite material according to the
third embodiment is better than the lithium battery cathode
composite material without doping.
[0046] A method for making a lithium battery cathode composite
material according to one embodiment is provided. The method
includes the following steps:
[0047] Step one, providing a plurality of lithium vanadium
phosphate particles; and
[0048] Step two, forming a lithium iron phosphate layer on an outer
surface of each lithium vanadium phosphate particle.
[0049] Step one includes the following substeps of:
[0050] S1: providing a solution including a lithium source
material, a vanadium material, a phosphate source material
solution, and a solvent, wherein the lithium source material, the
vanadium material, and the phosphate source material solution are
dispersed in the solvent;
[0051] S2, dispersing a carbon source compound into the solution to
form a sol mixture;
[0052] S3, spray drying the sol mixture to form a plurality of
lithium vanadium precursor particles; and
[0053] S4, heating the precursor particles, thereby forming a
plurality of lithium vanadium phosphate particles.
[0054] In step S1, a mol ratio between lithium, vanadium, and
phosphate can be about .alpha.:2:3, and .alpha. is in a range from
3 to 3.3. The vanadium in the solution is vanadium ions (V.sup.5+).
The lithium source material and the phosphate source material can
be dissolved in water. The lithium source material can be lithium
hydroxide or lithium salt. The lithium salt can be lithium
carbonate, lithium sulfate, lithium nitrate, or lithium chlorinate.
The phosphate source material can be phosphateic acid, ammonium
di-hydrogen phosphate, or DAP. The vanadium source material can be
ammonium metavanadate, vanadium pentoxide, hypovanadic oxide, or
vanadium tetrachloride. The solvent can be water, ethanol, or
acetone. The water can be deionized water or distilled water. In
one embodiment, the lithium source material is lithium hydroxide,
the vanadium source material is ammonium metavanadate, and the
phosphate source material is phosphateic acid. The mol ratio
between lithium, vanadium, and phosphate can be about 3:2:3. The
solution can be stirred about 2 hours to ensure the lithium source,
the vanadium source material, and the phosphate source material are
uniformly dissolved in the solvent.
[0055] In step S2, the carbon source compound is organic material,
which can undergo schizolysis to form carbon material, such as
saccharose, dextrose, phenolic resin, polyacrylic acid,
polyacrylonitrile, polyethyleneglycol, and polyvinylalcohol. The
carbon source compound can be a reductive agent, and V.sup.5+ in
the solution is reduced to V.sup.3+. A mol ratio between vanadium
and carbon can be in a range from about 1:1 to about 1:1.3. In
order to get a uniform sol mixture, before adding the carbon source
compound or during dispersing the carbon source compound, the
solution can be heated to a temperature of about 60.degree. C. to
about 85.degree. C., resulting in partial evaporation of the
solvent. In the heating process, the solution can be stirred using
a magnetic agitating method, a ball milling method, or ultrasonic
concussion.
[0056] In one embodiment, the carbon source compound is saccharose
and the mol ratio in the sol mixture is about 1:1.2. The detail
process of the step S2 includes:
[0057] heating the solution to about 80.degree. C.;
[0058] maintaining the temperature and agitating the solution using
the magnetic agitating method for about 2 hours until the solution
becomes the sol mixture; and
[0059] adding saccharose into the sol mixture and agitating the sol
mixture until the saccharose is dissolved in the sol mixture.
[0060] In step S3, the sol mixture can be dried using a spray dry
method. The spray dry method can be achieved using an airflow spray
dryer. The spray dryer includes an atomizer and a peristaltic pump.
The atomizer includes a two-fluid nozzle. The step S3 includes the
following substeps of:
[0061] S3a, filling the sol mixture into the spray dryer using the
peristaltic pump;
[0062] S3b, atomizing the sol mixture using the atomizer under a
certain air pressure, thereby forming a plurality of vaporific
liquid drops; and
[0063] S3c, heating the liquid drops in hot air, thereby forming a
plurality of lithium vanadium precursor particles.
[0064] In step s3b, the plurality of vaporific liquid drops has
extremely small diameters. Accordingly, the liquid drops have large
specific surface areas and rapid heat exchange can occur between
the hot air and the vaporific liquid drops. Therefore, solvent in
the liquid drops can be rapidly vaporized, thereby forming the
lithium vanadium precursor particles. The lithium vanadium
precursor particles are ball-shaped and porous. The diameters of
the lithium vanadium precursor particles can be in a range from
about 5 micrometers to about 20 micrometers. Each of the lithium
vanadium precursor particles is a compound mixture of vanadium
source material, lithium source material, carbon source compound,
and phosphor source material.
[0065] In step S4, the lithium vanadium phosphate precursor
particles are heated in an inert gas from about 10 hours to about
20 hours at a temperature ranging from about 500 degrees Celsius to
about 1000 degrees Celsius. In one embodiment, the heating
temperature is about 800 degrees Celsius and the heating time is
about 16 hours. After the heating process, the lithium vanadium
precursor particles become lithium vanadium phosphate particles. In
the heating process, the carbon source compound is pyrolyzed to
form carbon, and V.sup.5+ ions are reduced to V.sup.3+ ions by
carbon, and carbon is oxidized to carbon dioxide or carbon
monoxide. As such, carbon may be present in the lithium vanadium
phosphate particles. Referring to FIG. 7, the lithium vanadium
particles are formed directly from the lithium vanadium precursor
particles which are ball-shaped or almost ball-shaped, and the
lithium vanadium phosphate particles are ball-shaped or almost
ball-shaped.
[0066] The step two includes the following substeps of:
[0067] M1, providing a lithium iron phosphate precursor slurry;
[0068] M2, dispersing the lithium vanadium phosphate particles in
the lithium iron phosphate precursor slurry, coating the outer
surface of each lithium vanadium phosphate particle with the
lithium iron phosphate precursor slurry to form a plurality of
compound precursor particles, and then solidifying the compound
precursor particles; and
[0069] M3, heat treating the compound precursor particles to form a
plurality of compound particles, thereby forming the lithium
battery cathode composite material.
[0070] In step M1, a method for making the lithium iron phosphate
precursor slurry can be a coprecipitation method or a sol-gel
method. In one embodiment, the method for making the lithium iron
phosphate precursor slurry includes steps of:
[0071] M1a, providing a solution including a solvent, an iron salt
material, and a phosphate material;
[0072] M1b, providing a reactor, adding the solution and a
plurality of micro particles into the reactor, and adding an
alkaline solution into the solution until a pH value of the
solution ranges from about 1.5 to 5, and stirring the solution to
form a plurality of iron phosphate precursor particles, wherein the
plurality of iron phosphate precursor particles is disposed in the
solution to form a liquid mixture; and
[0073] M1c, adding a lithium source solution and a reducing agent
into the liquid mixture to form a lithium iron phosphate precursor
slurry.
[0074] In step M1a, a ratio between the iron and the phosphate can
be in a range from about 1:0.8 to about 1:1.2. The iron salt and
the phosphate source material can be both dissolved in the solvent
to form a solution. The iron salt can be iron chloride, iron
nitrate, or iron sulfate. The phosphate source material can be
phosphateic acid, ammonium hydrogen phosphate, or ammonium
di-hydrogen phosphate. The phosphate source material is dissolved
in the solvent to form a plurality of phosphate anions
(PO.sub.4).sup.3-. The solvent can be water, ethanol, or acetone.
The water can be deionized water or distilled water. In the liquid
mixture, a mol ratio of the iron salt is in a range from about 0.1
mol/L to about 3 mol/L, and a mol ratio of the phosphate source
material is in a range from about 0.1 mol/L to about 3 mol/L. In
one embodiment, the iron salt is iron nitrate, the phosphate source
material is phosphateic acid, and the mol ratio of the iron nitrate
and the phosphateic acid are both 0.2 mol/L.
[0075] In the step M1b, the plurality of micro particles is made of
rigid material that is not dissolved in the solvent. The micro
particles do not react with the iron salt and the phosphate source
material. The material of the micro particles can be ceramic,
quartz, or glass. The diameters of the micro particles can be in a
range from about 20 micrometers to about 1 millimeter. A volume
percentage of the micro particles in the solution can be in a range
from about 15% to about 50%.
[0076] In the step M1b, the solution can be transported
continuously in the reactor at a flow rate of about 100 ml/hour to
about 150 ml/hour. In one embodiment, the flow rate is about 120
ml/hour. The solution can be added in the reactor from a bottom
part of the reactor. A solvent material can be added into the
reactor before the solution is added in the reactor. The solvent
material can be the same as the solvent in the solution. In one
embodiment, the solvent material is deionized water and a volume
ratio of the solvent material in the reactor is about 60%.
[0077] In the step M1b, the micro particles can be added in the
reactor before the solution is transported or during transportation
of the solution into the reactor. The solution and the micro
particles can be agitated using magnetic agitation, ball milling,
or ultrasonic concussion. In one embodiment, the solution and the
micro particles are magnetically agitated, the power of the
magnetic agitator can be in a range from about 50 W/L to about 60
W/L.
[0078] In the step M1b, the alkaline solution can be ammonia water
or sodium hydroxide. In one embodiment, the pH value of the
solution after the alkaline solution has been added is about 2.3.
The iron salt reacts with the phosphate source material to form a
plurality of iron phosphate hydrate particles. Because the solution
is added into the reactor continuously, the iron phosphate hydrate
particles overflow from the reactor continuously. Iron phosphate
hydrate particles can be collected from the overflowing
materials.
[0079] In step M1b, during the stirring process, the micro
particles are used as stirrers to enhance reaction between the iron
salt and the phosphate source material. The micro particles can
also be used to control diameters of the iron phosphate precursor
particles, and preventing the iron phosphate precursor particles
from clumping together during formation. The micro particles can be
omitted in the step.
[0080] Other parameters can be used to control diameters of the
iron phosphate hydrate particles, such as the temperature of the
reactor, flow speed of the solution, and reaction time between the
iron salt and the phosphate source material. The temperature of the
reactor can be in a range from about 25.degree. C. to about
50.degree. C. The reaction time can be in a range from about 40
minutes to about 2 hours. The reaction time can be controlled by
changing the flow velocity of the solution. The higher the
temperature, the larger the diameters of the iron phosphate
particles. The longer the reaction time, the larger the diameters
of the iron phosphate precursor particles. In one embodiment, the
temperature of the reactor is about 25.degree. C. and the reaction
time is about 1 hour.
[0081] The step M1b can further include the step of washing the
iron phosphate hydrate particles. The overflowing materials
collected are washed using a centrifugation method. The iron
phosphate precursor particles are dried at a temperature of about
70.degree. C. to about 100.degree. C. for about 2 hours to about 4
hours. The diameters of the iron phosphate hydrate particles are in
a range from about 20 nanometers to about 10 micrometers. The
diameters of the iron phosphate hydrate particles are smaller than
the micro particles. The iron phosphate hydrate particles and the
micro particles can be separated by filtering.
[0082] Referring to FIGS. 8 and 9, the diameters of the iron
phosphate hydrate particles can be in a range from about 20
nanometers to about 10 micrometers. The shapes of the iron
phosphate hydrate particles can be ball-shaped or almost
ball-shaped. In one embodiment, the diameters of the iron phosphate
hydrate particles are in a range from about 100 nanometers to about
200 nanometers. Characteristics such as the diameters and
dispersivity of the iron phosphate hydrate particles determine the
characteristics of the lithium battery cathode composite
material.
[0083] The iron phosphate hydrate particles can be further heated
to a temperature of about 400.degree. C. to about 700.degree. C. in
a protective gas atmosphere to remove the crystal water in the iron
phosphate hydrate particles, thereby forming iron phosphate
precursor particles without crystal water. The protective gas can
be inert gases or nitrogen. The temperature is maintained for about
2 hours to about 24 hours. In one embodiment, the iron phosphate
hydrate particles are heated to about 520.degree. C. for about 10
hours to remove crystal water to form the iron phosphate precursor
particles.
[0084] In the step M1c, the lithium source material can be lithium
hydroxide or lithium salt. The lithium salt can be lithium
carbonate, lithium sulfate, lithium nitrate, or lithium
chlorination. The solvent can be water, ethanol, or acetone. The
water can be deionized water or distilled water. The reducing agent
can be a carbon source compound, which is an organic material and
can undergo schizolysis to form carbon material, such as
saccharose, dextrose, phenolic resin, polyacrylic acid,
polyacrylonitrile, polyethyleneglycol, and polyvinylalcohol. A mol
ratio between lithium in the lithium source material, phosphate in
the iron phosphate precursor particles, and carbon in the carbon
compound material can be in a range from about 1:1:1 to about
1.2:1:1.3. In one embodiment, the lithium source material is
lithium hydroxide, and the reducing agent is saccharose.
[0085] In the step M1c, after the lithium source material and the
reducing agent are added in the liquid mixture, the liquid mixture
can be agitated by a magnetic agitating method, ball milling
method, or ultrasonic concussion. In one embodiment, the liquid
mixture is agitated by the ball milling method for about 2
hours.
[0086] In the step M1c, the lithium iron phosphate precursor slurry
is a mixture including iron phosphate precursor particles, lithium
source material, and reducing agent.
[0087] In the step M1, in another embodiment, after the lithium
iron phosphate precursor slurry is formed, the lithium iron
phosphate precursor slurry can be dried and then heat-treated at a
temperature in a range from about 500.degree. C. to about
850.degree. for about 8 hours to about 40 hours to form a plurality
of lithium iron phosphate particles. In this process, the reducing
agent undergoes schizolysis to form carbon material, and the
Fe.sup.3+ ions in the iron phosphate precursor particles are
reduced to Fe.sup.2+ ions by the carbon material. The Fe.sup.2+
ions react with the lithium source material to form lithium iron
phosphate material, a plurality of lithium iron phosphate
particles. The carbon material can control diameters of the lithium
iron phosphate particles and prevent the lithium iron phosphate
particles from clumping together. The lithium iron phosphate
particles made by the method in this embodiment can be used as a
cathode material in a lithium battery separately.
[0088] The step M2 further includes substeps of:
[0089] M2a, dividing the lithium iron phosphate precursor slurry
into a first part, a second part, and a third part;
[0090] M2b, dispersing the lithium vanadium phosphate particles in
the first part, to coat the surface of each of the lithium vanadium
phosphate particles with the first part;
[0091] M2c, separating the coated lithium vanadium phosphate
particles from the first part, and drying the coated lithium
vanadium phosphate particles to form a plurality of first compound
particles;
[0092] M2d, dispersing the first compound particles in the second
part, and repeating steps M2b and M2c to form a plurality of second
compound particles;
[0093] M2e, dispersing the second compound particles in the third
part, and repeating steps M2b and M2c to form a plurality of
compound precursor particles.
[0094] In the step M2b, the lithium vanadium phosphate particles
and the first part lithium iron phosphate precursor slurry are
agitated to ensure uniform coating of each of the lithium vanadium
phosphate particles.
[0095] In the step M2b, a water-soluble adhesive can be added into
the lithium iron phosphate precursor slurry. The lithium iron
phosphate precursor slurry with the water-soluble adhesive can
tightly combine with the lithium vanadium phosphate particles.
[0096] In the step M2c, the lithium vanadium phosphate particles
coated with the lithium iron phosphate precursor slurry are dried
at a temperature in a range from about 60.degree. C. to about
90.degree. C. for about 10 minutes to about 30 minutes.
[0097] In the step M2e, each compound precursor particle includes a
lithium vanadium phosphate particle and a lithium iron phosphate
precursor layer. The lithium iron phosphate precursor layer
includes iron phosphate precursor particles, lithium source
material, and reducing agent. A weight ratio between the iron
phosphate precursor particles and the lithium vanadium phosphate
particles in the compound precursor particles can be in a range
from about 5.5:4 to about 6.5:4.
[0098] In the step M3, the compound precursor particles are
heat-treated at a temperature in a range from about 500.degree. C.
to about 850.degree. for about 8 hours to about 40 hours. In this
process, the reducing agent undergoes schizolysis to form carbon
material, and the Fe.sup.3+ ions in the iron phosphate precursor
particles are reduced to Fe.sup.2+ ions by the carbon material. The
Fe.sup.2+ ions react with the lithium source material to form
lithium iron phosphate material, and as such a plurality of lithium
iron phosphate particles is formed, whereby the compound precursor
particles become compound particles. Each of the compound particles
includes a lithium vanadium phosphate particle and a lithium iron
phosphate layer disposed on the surface of the lithium vanadium
phosphate particle. The lithium iron phosphate layer includes a
plurality of lithium iron phosphate particles. The carbon material
can control the diameters of the lithium iron phosphate particles
and prevent the lithium iron phosphate particles from clumping
together. The carbon material disposed on surfaces of the lithium
iron phosphate particles can improve the conductivity of the
lithium iron phosphate particles.
[0099] The lithium battery cathode composite material formed by
this method has a core-shell structure, because the "shell"
(lithium iron phosphate layer) has a large specific surface area,
the shell has a large contact area with an electrolyte when the
lithium battery cathode composite material is used in a battery,
and the lithium iron phosphate particles can be dispersed easily
and quickly in the electrolyte. The method for making the lithium
battery cathode composite material is an oxido-reduction method
which is simple and has a short cycle. The reducing agent is carbon
compound material, which is relatively cheap, thus the method is
low-cost.
[0100] The lithium iron phosphate particles disposed on the
surfaces of the lithium vanadium phosphate particles can be used as
the electrode material of a lithium battery separately. Referring
to FIG. 11, at a 1 Coulomb (C) rate, the lithium iron phosphate
particles made by this method, which have diameters of about 100
nanometers to about 200 nanometers, have a specific capacity of
about 106.4 mAh/g in the first cycle, and the specific capacity of
the lithium battery cathode composite material is decreased about
95 mAh/g at the fiftieth cycle, which is down about 10% from the
first cycle. Thus, the lithium iron phosphate particles having
small diameters have good cycling capability. Referring to FIGS.
12-15, at a voltage of about 2.5V to about 4.3V, the lithium
battery cathode composite material made by the present method has a
higher specific capacity than the lithium iron phosphate particles
at different rates. FIGS. 12-15 shows that the lithium battery
cathode composite material having core-shell structures have better
characteristics than just lithium iron phosphate particles, because
the lithium iron phosphate particles in the lithium battery cathode
composite material is essentially a "shell" having a large specific
surface area, and the lithium iron phosphate particles 1042 can be
dispersed easily and quickly in the electrolyte.
[0101] A method for making a lithium battery cathode composite
material doped with vanadium ions is provided. The method includes
the following steps:
[0102] Step I, providing a plurality of lithium vanadium phosphate
particles; and
[0103] Step II, forming a lithium iron phosphate layer doped with
vanadium ions on an outer surface of each lithium vanadium
phosphate particle.
[0104] In step I, the detailed process of providing the plurality
of lithium vanadium phosphate particles is the same as step one of
the method for making a lithium battery cathode composite
material.
[0105] Step II includes the following substeps of:
[0106] N1, providing a slurry of lithium iron phosphate precursor
doped with vanadium ions;
[0107] N2, dispersing the lithium vanadium phosphate particles in
the lithium iron phosphate precursor slurry, to coat the outer
surface of each lithium vanadium phosphate particle to form a
plurality of compound precursor particles, and then solidifying the
compound precursor particles; and
[0108] N3, heat treating the compound precursor particles to form a
plurality of compound particles doped with vanadium, thereby
forming the lithium battery cathode composite material doped with
vanadium.
[0109] In step N1, a method for making the slurry of lithium iron
phosphate precursor doped with vanadium includes steps of: N1a,
providing a solution including a solvent, a vanadium source
material, an iron salt material, and a phosphate material; N1b,
providing a reactor, adding the solution and a plurality of micro
particles into the reactor, adding an alkaline solution in the
solution until the solution has a pH value ranging from about 1.5
to 5, and stirring the solution to form a plurality of iron
phosphate precursor particles, wherein the plurality of iron
phosphate precursor particles is disposed in the solution to form a
liquid mixture; and N1c, adding a lithium source solution and a
reducing agent into the liquid mixture to form a slurry of lithium
iron phosphate precursor doped with vanadium.
[0110] In step N1a, a mol ratio between the mol sum of vanadium,
iron, and the phosphate can be in a range from about 1:0.8 to about
1:1.2. Other characteristics of step N1a are the same as those
disclosed in the step M1a above.
[0111] In step N1b, the iron salt reacts with the phosphate source
material and vanadium source material to form a plurality of iron
phosphate hydrate particles doped with vanadium. The detailed
process is the same as the step M1b disclosed herein.
[0112] In step N1c, the detailed process is the same as the step
M1c disclosed herein. In the step N1c, the slurry of lithium iron
phosphate precursor doped with vanadium is a mixture including iron
hydrate particles doped with vanadium, lithium source material, and
reducing agent. Referring to FIGS. 16 and 17, the iron phosphate
hydrate particles doped with vanadium have smaller diameters and
better dispersivity than the iron phosphate hydrate particles
without vanadium.
[0113] In the step N1, after the slurry of lithium iron phosphate
precursor doped with vanadium is formed, the slurry of lithium iron
phosphate precursor doped with vanadium can be dried and then
heat-treated at a temperature in a range from about 500.degree. C.
to about 850.degree. for about 8 hours to about 40 hours to form a
plurality of lithium iron phosphate particles doped with vanadium.
In this process, the reducing agent undergoes schizolysis to form
carbon material, the Fe.sup.3+ ions in the iron phosphate precursor
particles are reduced to Fe.sup.2+ ions by the carbon material, and
the V.sup.5+ ions are reduced to V.sup.3+. The Fe.sup.2+ ions and
the V.sup.3+ ions react with the lithium source material to form
lithium iron phosphate material doped with vanadium, and as such, a
plurality of lithium iron phosphate particles doped with vanadium
is formed. In the present embodiment, the chemical formula of the
lithium iron phosphate particles doped with vanadium is
LiFe.sub.0.97V.sub.0.03PO.sub.4. The carbon material can control
diameters of the lithium iron phosphate particles doped with
vanadium and prevent the lithium iron phosphate particles doped
with vanadium from clumping together. Referring to FIG. 18, lithium
iron phosphate particles doped with vanadium are ball-shaped or
almost ball-shaped and have small diameters. The lithium iron
phosphate particles doped with vanadium can be used as cathode
material in a lithium battery separately. Referring to FIG. 19, at
a voltage of about 2.5V to about 4.2V and at a 1 C rate, the
lithium iron phosphate particles doped with vanadium
(LiFe.sub.0.97V.sub.0.03PO.sub.4) has a specific capacity of about
135.3 mAh/g at the first cycle, and a specific capacity of about
124.4 mAh/G after 50 cycles. Therefore the lithium iron phosphate
particles doped with vanadium have a high specific capacity and
good cycling capacity.
[0114] In step N2, the detailed process is the same as the step M2
disclosed herein.
[0115] In step N3, the detailed process is the same as the step M3
disclosed herein. In step N3, each of the compound particles doped
with vanadium includes a lithium vanadium phosphate particle and a
lithium iron phosphate disposed on the surface of the lithium
vanadium phosphate particle. The lithium iron phosphate layer
includes a plurality of lithium iron phosphate particles doped with
vanadium. Each of the lithium iron phosphate particles is doped
with vanadium. Referring to FIG. 20, the comparison of X-ray
diffraction patterns between the lithium iron phosphate particles
and lithium iron phosphate particles doped with vanadium shows that
the two X-ray diffraction patterns are almost the same, which
proves that vanadium in the lithium iron phosphate particles exists
as vanadium ions instead of iron ions in the lithium iron phosphate
particles, and there are no impurities brought by the vanadium in
the lithium iron phosphate particles doped with vanadium.
[0116] The lithium iron phosphate particles doped with vanadium
disclosed above can be used as an electrode material separately.
Referring to FIGS. 21-24, at a voltage of about 2.5V to about 4.3V,
the lithium iron phosphate particles doped with vanadium have
specific capacities of 148.6 mAh/g at 0.1 C rate, 135.3 mAh/g at 1
C rate, 105.0 mAh/g at 5 C rate, and 74.3 mAh/g at 10 C rate. At a
voltage of about 2.5V to about 4.3V, the lithium battery cathode
composite material doped with vanadium has specific capacities of
145.0 mAh/g at 0.1 C rate, 136.2 mAh/g at 1 C rate, 115.0 mAh/g at
5 C rate, and 89.0 mAh/g at 10 C rate. FIGS. 21-24 show that the
lithium battery cathode composite material doped with vanadium has
almost the same specific capacity as the lithium iron phosphate
particles doped with vanadium at lower rates (0.1 C and 1 C), but
has higher specific capacity than the lithium iron phosphate
particles doped with vanadium at higher rates (5 C and 10 C).
[0117] It is to be understood that the above-described embodiments
are intended to illustrate rather than limit the disclosure.
Variations may be made to the embodiments without departing from
the spirit of the disclosure as claimed. It is understood that any
element of any one embodiment is considered to be disclosed to be
incorporated with any other embodiment. The above-described
embodiments illustrate the scope of the invention but do not
restrict the scope of the disclosure.
[0118] Depending on the embodiment, certain of the steps of methods
described may be removed, others may be added, and the sequence of
steps may be altered. It is also to be understood that the
description and the claims drawn to a method may include some
indication in reference to certain steps. However, the indication
used is only to be viewed for identification purposes and not as a
suggestion as to an order for the steps.
* * * * *