U.S. patent application number 17/431728 was filed with the patent office on 2022-05-12 for powderous solid electrolyte compound for solid-state rechargeable lithium ion battery.
The applicant listed for this patent is POSTECH ACADEMY-INDUSTRY FOUNDATION, UMICORE, UMICORE KOREA LTD.. Invention is credited to Byoungwoo KANG, Seung-Jun WOO.
Application Number | 20220149427 17/431728 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-12 |
United States Patent
Application |
20220149427 |
Kind Code |
A1 |
KANG; Byoungwoo ; et
al. |
May 12, 2022 |
POWDEROUS SOLID ELECTROLYTE COMPOUND FOR SOLID-STATE RECHARGEABLE
LITHIUM ION BATTERY
Abstract
A solid solution electrolyte suitable for solid-state
rechargeable lithium ion battery comprising a compound having a
general formula
L.sub.i(3.5+L+x)Si.sub.(0.5+s-x)P.sub.(0.5+p-x)Ge.sub.2xO.sub.4+a
wherein -0.10.ltoreq.L.ltoreq.0.10, -0.10.ltoreq.s.ltoreq.0.10,
-0.10.ltoreq.p.ltoreq.0.10, -0.40.ltoreq.a.ltoreq.0.40, and
0.0<x.ltoreq.0.30, preferably 0.05.ltoreq.x.ltoreq.0.30.
Inventors: |
KANG; Byoungwoo;
(Gyeongsangbuk-do, KR) ; WOO; Seung-Jun;
(Gyeongsangbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UMICORE
UMICORE KOREA LTD.
POSTECH ACADEMY-INDUSTRY FOUNDATION |
Brussels
Chungcheongnam-do
Gyeongsangbuk-do |
|
BE
KR
KR |
|
|
Appl. No.: |
17/431728 |
Filed: |
February 19, 2020 |
PCT Filed: |
February 19, 2020 |
PCT NO: |
PCT/IB2020/051354 |
371 Date: |
August 18, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62807833 |
Feb 20, 2019 |
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62807863 |
Feb 20, 2019 |
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International
Class: |
H01M 10/0562 20060101
H01M010/0562; H01M 10/0525 20060101 H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2019 |
EP |
19162577.1 |
Mar 13, 2019 |
EP |
19162591.2 |
May 24, 2019 |
EP |
19176362.2 |
Claims
1-12. (canceled)
13. A solid solution electrolyte suitable for solid-state
rechargeable lithium ion battery comprising a compound having a
general formula
Li.sub.(3.5+L+x)Si.sub.(0.5+s-x)P.sub.(0.5+p-x)Ge.sub.2xO.sub.4+a
wherein -0.10.ltoreq.L.ltoreq.0.10, -0.10.ltoreq.s.ltoreq.0.10,
-0.10.ltoreq.p.ltoreq.0.10, -0.40.ltoreq.a.ltoreq.0.40, and
0.0<x.ltoreq.0.30.
14. The solid solution electrolyte according to claim 13 wherein
said compound has a general formula:
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4.
15. The solid solution electrolyte according to claim 13, having a
lithium ionic conductivity of at least 10.sup.-5 S/cm at room
temperature.
16. The solid solution electrolyte according to claim 13, wherein
0.15.ltoreq.x.ltoreq.0.30.
17. The solid solution electrolyte according to claim 13, having a
lithium ionic conductivity at room temperature superior or equal to
2.0.times.10.sup.-5 S/cm and inferior or equal to
3.0.times.10.sup.-5 S/cm.
18. The solid solution electrolyte according to claim 13,
comprising a crystal structure having an XRD pattern measured at a
wavelength of 1.5418 .ANG. comprising a first peak having a first
intensity and a second peak having a second intensity, said first
and second peaks being present in a range of 2.theta. superior or
equal to 27.5 and inferior or equal to 30.0.+-.0.5.degree., said
XRD pattern being furthermore free of peaks at
37.0.+-.0.5.degree..ltoreq.2.theta..ltoreq.47.0.+-.0.5.degree.
having an intensity superior to said first or second intensity.
19. The solid solution electrolyte according to claim 13,
comprising a crystal structure having an XRD pattern measured at a
wavelength of 1.5418 .ANG. comprising a first peak having a first
intensity and a second peak having a second intensity, said first
and second peaks being present in a first range of 2.theta.
superior or equal to 27.5 and inferior or equal to
30.0.+-.0.5.degree., wherein in a second range of 2.theta. superior
or equal to 21.0 and inferior or equal to 25.0.+-.0.5.degree., said
XRD pattern has no more than three peaks, each of said three peaks
having an intensity superior to said first or second intensity.
20. The solid solution electrolyte according to claim 13,
comprising a crystal structure having an XRD pattern measured at a
wavelength of 1.5418 .ANG. comprising a first peak having a first
intensity and a second peak having a second intensity, said first
and second peaks being present in a first range of 2.theta.
superior or equal to 27.5 and inferior or equal to
30.0.+-.0.5.degree., wherein in a second range of 2.theta. superior
or equal to 34.0 and inferior or equal to 36.0.+-.0.5.degree., said
XRD pattern has no more than three peaks, each of said three peaks
having an intensity superior to said first or second intensity.
21. A solid-state rechargeable lithium ion battery comprising the
solid solution electrolyte according to claim 13.
22. A solid-state rechargeable lithium ion battery comprising a
negative electrode having a Li metal-base anode contacting the
solid solution electrolyte according to claim 13.
23. The solid-state battery according to claim 21 wherein the
battery is configured to have an operating voltage superior or
equal to 200 V and inferior or equal to 500 V such that the battery
is suitable for use in an electric car.
24. A catholyte comprising the solid solution electrolyte according
claim 13, and a cathode material having the general formula:
Li.sub.1+kM'.sub.i-kO.sub.2 where
M'=Ni.sub.1-x'-y'-z'Mn.sub.x'Co.sub.y'.ANG..sub.z' with
-0.05.ltoreq.k.ltoreq.0.05, 0.ltoreq.x'.ltoreq.0.40,
0.05.ltoreq.y'.ltoreq.0.40, and 0.ltoreq.z'.ltoreq.0.05, wherein A
is a doping element which is different to Li, M' and O, said
positive active material powder comprising particles having a
layered R-3m crystal structure, said catholyte having a
D99.ltoreq.50 .mu.m and an ionic conductivity of at least
1.0.times.10.sup.-6 S/m.
Description
TECHNICAL FIELD AND BACKGROUND
[0001] This invention relates to a solid electrolyte (SE) for
solid-state rechargeable lithium-ion batteries suitable for
electric vehicle (EV) applications. The solid electrolyte according
to the invention has an improved lithium ionic conductivity.
[0002] Along with the developments of EVs, it comes also a demand
for lithium-ion batteries as a possible constant source of power
for such applications.
[0003] Aside the zero-emission aspect, additional requirements
rendering a battery eligible for EV applications should therefore
include: high capacity, longer cycle lives, lower cost, and better
safety.
[0004] Most of the past and ongoing research on batteries usually
emphasizes on the use of a liquid electrolyte, since such an
electrolyte has a high lithium ionic conductivity of around
10.sup.-2 S/cm at room temperature (measured for an electrolyte
composed of ethylene carbonate/dimethyl carbonate EC/DMC 1M
LiPF.sub.6) and provides a good contact with electrodes through
wetting. However, batteries containing liquid electrolytes imply
concerns since liquid electrolytes are usually flammable.
[0005] Solid electrolyte-based batteries are considerably safer and
can be an alternative to liquid electrolyte-based batteries for the
power source of electric vehicles. Since the decomposition
temperature of SE is higher than the liquid electrolyte, an EV
comprising such a SE-based battery, instead of a liquid
electrolyte-based battery, would be safer and its battery
manufacturing would also be safer. Aside from the clear advantage
that a SE-based battery is much safer than a liquid
electrolyte-based battery, a SE-based battery is also more compact
than liquid electrolyte-based batteries, and therefore lead to
higher power densities
[0006] However, it is also true that, compared to liquid
electrolyte, a SE has a lower lithium ionic conductivity (typically
included between 10.sup.-7 to 10.sup.-6 S/cm). The lower lithium
ionic conductivity in a SE is due to the higher migration energy of
lithium ions.
[0007] Well-known (inorganic) types of SE suitable for solid-state
rechargeable lithium-ion batteries (SSB) which have been mainly
explored are the La, Zr comprising garnet and the LSPO (lithium
silicon phosphorus oxide) LISICON (lithium superionic conductor)
electrolyte having a general formula:
Li.sub.4.+-.xSi.sub.1-xP.sub.xO.sub.4. The La, Zr comprising
garnet, especially the cubic garnet
(Li.sub.7La.sub.3Zr.sub.2O.sub.12), shows a high conductivity.
However, those materials are expensive due to the La and Zr
content. This compound also needs to be synthesized at a
temperature higher than 1000.degree. C. which is not desired
because of the volatility of lithium at the high temperature. The
LSPO is well-known for its high chemical and electrochemical
stability, high mechanical strength, and high electrochemical
oxidation voltage, making such an electrolyte a promising candidate
for EV applications.
[0008] LSPO compounds, like Li.sub.3.5Si.sub.0.5P.sub.0.5O.sub.4,
have a relatively low lithium ionic conductivity.
Li.sub.3.5Si.sub.0.5P.sub.0.5O.sub.4, is a solid solution of
Li.sub.4SiO.sub.4 and Li.sub.3PO.sub.4 having a crystal structure
of .gamma.-Li.sub.3PO.sub.4 with orthorhombic unit cell and
tetrahedrally coordinated cations. In the scope of the present
invention, a solid solution (also called solid-state solution)
refers to a multi-component solid-state solution as a result of a
mixture of one or more solutes in a solvent. In particular, the
solutes can be atoms or groups of atoms (or compounds). Such a
multi-component system is considered a solution rather than a
compound when the crystal structure of the solvent remains
unchanged by addition of the solutes, and when the chemical
components remain in a single homogeneous phase. In the system, the
solvent usually is a component with the largest portion and in this
case is Li.sub.3PO.sub.4. The crystal structure of the solvent
component is maintained after blending whereas the other component
(solute, e.g. Li.sub.4SiO.sub.4) dissolves in the solvent structure
instead of forming a distinct compound having a structure that
deviates from the structure of the solvent.
[0009] In Solid State Ionics (2015), 283, 109-114, Wang, Dawei et
al. studied the enhancement of lithium ionic conductivity of LSPO
by an addition of Li.sub.3BO.sub.3. The highest lithium ionic
conductivity was 6.5.times.10.sup.-6 S/cm at 20% of
Li.sub.3BO.sub.3 addition compared to 3.6.times.10.sup.-6 S/cm for
0% addition. Another study conducted by Choi, Ji-won et al. in
Solid State Ionics (2016), 289, 173-179, explored the effect of Al
cation substitution in 0.7Li.sub.4SiO.sub.4+0.3Li.sub.3PO.sub.4
solid solution system. The lithium ionic conductivity of
7.7.times.10.sup.-6 S/cm was achieved at room temperature by the
addition of 10 mol % Al.
[0010] Sokseiha et al. in Chem. Mater. (2018), 30, 5573-5582 and
Kamphorst et. al. in Solid State Ionics (1980), 1, 187-197 specify
that L 4S O4-U3PO3 solid solutions have a lower conductivity than
Li.sub.4GeO.sub.4--Li.sub.3PO.sub.3 teaching away from a possible
substitution of Ge with Si.
[0011] Burmakin et. al. in Russian Journal of Electrochemistry
(2010), 46, No. 2, 243-246 discloses a lithium germanium phosphate
solid electrolyte doped with a tetravalent cation, Zr like:
Li.sub.3.75Ge.sub.0.70Zr.sub.0.05P.sub.0.25O.sub.4,
Li.sub.3.50Zn.sub.0.125Ge.sub.0.75P.sub.0.25O.sub.4, respectively.
The Ge content in these formulation would not allow the obtention
of a solid solution in a LSPO-based SE.
[0012] Although noticeable, these attempts to achieve a solid
solution of a LSPO-based electrolyte are still below a desired
threshold of at least 0.50.times.10.sup.-5 (or 5.0.times.10.sup.-6)
S/cm required so that a solid-state battery made from said
electrolyte is a tangible alternative to current liquid
electrolyte-based batteries.
[0013] Certainly, there is a need for improving the lithium ionic
conductivity of LSPO-based electrolyte so as to render the use of
solid-state batteries made from such an electrolyte more performant
and therefore more attractive in the field of EV applications.
[0014] It is therefore an object of the present invention to
provide a LSPO-based SE having an improved lithium ionic
conductivity whilst retaining a solid solution, which is a
prerequisite for the use of such a SE in a solid-state secondary
battery suitable for EV applications.
[0015] Metallic Li can be used in the scope of the present
invention as an anode of a SSB comprising the electrolyte according
to the invention.
[0016] Provided that the SE according to the present invention can
be destined to be contacted to a Li metal-based anode, it must
therefore be compatible to said Li metal-based anode of the SSB,
meaning that the SE while contacting said anode must remain
chemically stable.
SUMMARY OF THE INVENTION
[0017] A solid electrolyte having an improved lithium ionic
conductivity whilst retaining a solid solution and being chemically
and thermally stable while contacting a Li metal anode is achieved
by providing a solid solution according to claim 1 which comprises
a LSPO-based electrolyte comprising germanium (Ge) up to 60 mol %.
A Ge doped LSPO is referenced hereunder as "LSPGO".
[0018] If a LSPGO-based electrolyte comprises Ge of superior to 60
mol %, it comprises at least one impurity phase (i.e.
Li.sub.2SiO.sub.3), and such a Li.sub.2SiO.sub.3-bearing
LSPGO-based electrolyte is not a solid solution according to the
present invention. A similar impurity phase is observed in Burmakin
et. al. (Li.sub.2ZrO.sub.3 in this case) for a high content of
Ge.
[0019] In the framework of the present invention, it has been
observed that by integrating up to 60 mol % of Ge in a solid
solution of LSPO-based electrolyte it was possible to preserve said
solid solution property together with a noticeable improvement of
the lithium ionic conduction to a minimal value of
0.50.times.10.sup.-5 S/cm, which constitutes a significant
contribution to what is currently known from the prior art.
[0020] It has also been demonstrated that the electrolyte according
to the present invention is stable in presence of a Li metal foil,
confirming its suitability in a SSB wherein a Li metal foil is used
as an anode.
[0021] The present invention concerns the following
embodiments:
[0022] 1. --A solid solution electrolyte suitable for solid-state
rechargeable lithium ion battery comprising a compound having a
general formula
Li.sub.(3.5+L+x)Si.sub.(0.5+s-x)P.sub.(0.5+p-x)Ge.sub.2xO.sub.4+a
wherein -0.10.ltoreq.L.ltoreq.0.10, -0.10.ltoreq.s.ltoreq.0.10,
-0.10.ltoreq.p.ltoreq.0.10, -0.40.ltoreq.a.ltoreq.0.40, and
0.00<x.ltoreq.0.30.
[0023] In a first aspect of the embodiment 1,
0.05.ltoreq.x.ltoreq.0.30, preferably
0.10.ltoreq.x.ltoreq.0.30.
[0024] In a second aspect of the embodiment 1,
0.15.ltoreq.x.ltoreq.0.30, preferably
0.20.ltoreq.x.ltoreq.0.30.
[0025] 2. --The solid solution electrolyte according to embodiment
1 wherein said compound has a general formula:
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4.
[0026] 3. --The solid solution electrolyte according to the
embodiment 1 or 2, having a lithium ionic conductivity of at least
10.sup.-5 S/cm at 25.degree. C.
[0027] 4. --The solid solution electrolyte according to any of the
preceding embodiments, wherein 0.25.ltoreq.x.ltoreq.0.30.
[0028] 5. --The solid solution electrolyte according to any of the
preceding embodiments, having a lithium ionic conductivity measured
at 25.degree. C. superior or equal to 2.0.times.10.sup.-5 S/cm and
inferior or equal to 3.0.times.10.sup.-5 S/cm, preferably superior
or equal to 2.5.times.10.sup.-5 S/cm and inferior or equal to
3.0.times.10.sup.-5 S/cm.
[0029] 6. --The solid solution electrolyte according to any of the
preceding embodiments, comprising a crystal structure having an XRD
pattern measured at 25.degree. C. and at a wavelength of 1.5418
.ANG. comprising a first peak having a first intensity and a second
peak having a second intensity, said first and second peaks being
present in a range of 2.theta. superior or equal to 27.5 and
inferior or to 30.0.+-.0.5.degree., said XRD pattern being
furthermore free of peaks at 2.theta.>37.0.+-.0.5.degree. having
an intensity superior to said first or second intensity.
[0030] 7. --The solid solution electrolyte according to any of the
preceding embodiments, comprising a crystal structure having an XRD
pattern measured at 25.degree. C. and at a wavelength of 1.5418
.ANG. comprising a first peak having a first intensity and a second
peak having a second intensity, said first and second peaks being
present in a first range of 2.theta. superior or equal to 27.5 and
inferior or to 30.0.+-.0.5.degree., wherein in a second range of
2.theta. superior or equal to 21.0 and inferior or to
25.0.+-.0.5.degree. said XRD pattern has no more than three
additional peaks, each of said three additional peaks having an
intensity superior to said first or second intensity.
[0031] 8. --The solid solution electrolyte according to any of the
preceding embodiments, comprising a crystal structure having an XRD
pattern measured at 25.degree. C. and at a wavelength of 1.5418
.ANG. comprising a first peak having a first intensity and a second
peak having a second intensity, said first and second peaks being
present in a first range of 2.theta. superior or equal to 27.5 and
inferior or to 30.0.+-.0.5.degree., wherein in a second range of
2.theta. superior or equal to 34.0 and inferior or to
36.0.+-.0.5.degree., said XRD pattern has no more than three
additional peaks, each of said three additional peaks having an
intensity superior to said first or second intensity.
[0032] 9. --A solid-state rechargeable lithium ion battery
comprising the solid solution electrolyte according to any of the
previous embodiments.
[0033] 10. --A solid-state rechargeable lithium ion battery
comprising a negative electrode having a Li metal-base anode
contacting the solid solution electrolyte according to any of the
embodiments 1 to 9.
[0034] 11. --Use of the solid-state battery according to the
embodiment 9 or 10 in an electric vehicle, in particular in an
electric car, wherein the operating voltage of said battery is
superior or equal to 200 V and inferior or equal to 500 V.
[0035] 12. --A catholyte comprising the solid solution electrolyte
according to any of the preceding embodiments and a cathode
material having the general formula: Li.sub.1+kM'.sub.1-kO.sub.2
where M'=Ni.sub.1-x'-y'-z'Mn.sub.x'Co.sub.y'A.sub.z' with
-0.05.ltoreq.k.ltoreq.0.05, 0.ltoreq.x'.ltoreq.0.40,
0.05.ltoreq.y'.ltoreq.0.40, and 0.ltoreq.z'.ltoreq.0.05, wherein A
is a doping element which is different to Li, M' and O, said
positive active material powder comprising particles having a
layered R-3m crystal structure, said catholyte having a
D99.ltoreq.50 .mu.m and an ionic conductivity of at least
1.0.times.10.sup.-6 S/m
BRIEF DESCRIPTION OF THE FIGURES
[0036] FIG. 1. Comparison of Electrochemical Impedance Spectra
(EIS) for sample with various Ge dopants (x in
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4+a) in
Example 1 and Comparative Example 1
[0037] FIG. 2. Variation of lithium ionic conductivity versus the
amount of Ge dopants (x in
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4+a) in
Example 1 and Comparative Example 1 FIG. 3. Comparison of X-ray
diffraction pattern of Example 1 and Comparative Example 1
[0038] FIG. 4. Fourier-transform infrared spectrum of EX1-A, EX1-B,
EX1-C, and Comparative Example 1 showing transmittance in (%) and
wavenumber in (cm.sup.-1)
[0039] FIG. 5. Comparison of X-ray diffraction pattern of
Comparative Examples 1 and 2
[0040] FIG. 6. Comparison of X-ray diffraction pattern of LSPO (a)
before exposure to molten Li metal at 250.degree. C. and (b) after
15 minutes exposure
[0041] FIG. 7. Comparison of voltage vs. capacity graph of
EX2-CAT-A and CEX3-CAT-B
DETAILED DESCRIPTION
[0042] In the following detailed description, preferred embodiments
are detailed so as to enable practice of the invention. Although
the invention is described with reference to these specific
preferred embodiments, it will be understood that the invention is
not limited to these embodiments. To the contrary, the invention
includes numerous alternatives, modifications and equivalents as
will become apparent from consideration of the following detailed
description.
[0043] This invention discloses a germanium bearing LSPO compounds
having a general formula
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4+a (LSPGO)
wherein 0.00<x.ltoreq.0.30 and -0.40.ltoreq.a.ltoreq.0.40. It is
a solid solution of Li.sub.4GeO.sub.4, Li.sub.3PO.sub.4, and
Li.sub.4SiO.sub.4. When Ge equally substitutes Si and P in a LSPO
compound, it is observed that the lithium ionic conductivity of the
compound according to claim 1 significantly increases (reaching at
least 10.sup.-5 S/cm) for x values higher or equal to 0.10.
Moreover, the conductivity of
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4+a wherein
0.10.ltoreq.x.ltoreq.0.30 gradually increases and it is maximized
when x is 0.30. In particular, the conductivity of the compound
according to claim 1 is unexpectedly higher (higher than 2.0
10.sup.-5 S/cm) for the narrow range: 0.20<x.ltoreq.0.30, in
particular for 0.25.ltoreq.x.ltoreq.0.30. Compared to the broader
range of Ge content of claim 1, this narrower range leads to an
increase of the lithium ionic conductivity by a 1.5 to 3.0 factor,
which is remarkable.
[0044] Such a high conductivity of at least 10.sup.-5 S/cm has
never been reported yet for solid solution LSPO type of
electrolytes.
[0045] In addition, compatibility of the electrolyte according to
the present invention with a Li metal anode.
[0046] This invention is also inclusive of a catholyte compound
made from a mixture of a NMC type of positive electrode active
material and the germanium bearing LSPO compound according to the
present invention.
[0047] Both polycrystalline and monolithic NMC can be used as a
positive electrode active material in the catholyte according to
the present invention. A "monolithic" morphology refers here to a
morphology where a secondary particle contains basically only one
primary particle. In the literature they are also called single
crystal material, mono-crystal material, and one-body material. The
preferred shape of the primary particle could be described as
pebble stone shaped. The monolithic morphology can be achieved by
using a high sintering temperature, a longer sintering time, and
the use of a higher excess of lithium. A "polycrystalline"
morphology refers to a morphology where a secondary particle
contains more than one primary particles.
[0048] The (solid-state) catholyte material is prepared by mixing
the germanium bearing LSPO compound with the NMC composition so as
to produce the catholyte which is subjected to a heat treatment at
600.degree. C..about.800.degree. C. for 1.about.20 hours under
oxidizing atmosphere. In particular, the method for producing said
catholyte is a co-sintering-based process wherein the germanium
bearing LSPO and the NMC compositions are blended so as to provide
a mixture which is then sintered.
[0049] There are several ways to obtain each of the compositions of
the germanium bearing LSPO and NMC positive electrode active
material in the catholyte. Whereas the difference of the median
particle sizes (D50) between the solid electrolyte and positive
electrode active material in the catholyte is superior or equal to
2 .mu.m, they can be separated using a classifier such the elbow
jet air classifier
(https://elcanindustries.com/elbow-jet-air-classifier/). The
compositions of separate particles are measured according to the
protocol disclosed in the section F) Inductively Coupled Plasma
method so as to determine each of the compositions of the germanium
bearing LSPO material and NMC positive electrode active material in
the catholyte.
[0050] The use of an Electron Energy Loss Spectroscopy (EELS) in a
Transmission Electron Microscope (TEM) is another example for
obtaining each of the compositions of the germanium bearing LSPO
material and NMC positive electrode active material in the
catholyte. The elements and their atomic amount can be obtained
directly by measuring the EELS of cross-sectional germanium bearing
LSPO particles and NMC positive electrode active material particles
separately.
[0051] The following analysis methods are used in the Examples:
[0052] A) Electrochemical Impedance Spectroscopy (EIS)
[0053] A cylindrical pellet is prepared by following procedure.
0.175 g of a powderous solid electrolyte compound sample is put on
a mold having a diameter of 1.275 cm. A pressure of 230 MPa is
applied to the mold. The pellet is sintered at 700.degree. C. for 3
hours in oxygen atmosphere. Silver paste is painted on both sides
of the pellet to have a sample configuration of Ag/pellet/Ag in
order to allow EIS measurements. Standard deviation of this
measurement is 2.0.times.10.sup.-8.
[0054] EIS is performed using an Ivium-n-Stat instrument, a
potentiostat/galvanostat with an integrated frequency response
analyzer. This instrument is common to be used in the battery/fuel
cell-testing to collect impedance response against frequency sweep.
The measurement frequency range is from 10.sup.6 Hz to 10.sup.-1
Hz. The setting point/decade is 10 and the setting voltage is
0.05V. Measurement is conducted at room temperature (at 25.degree.
C.). The lithium ionic conductivity is calculated by below
equation:
.sigma. = L R .times. A ##EQU00001##
[0055] where L is the thickness of the pellet, A is the area of the
sample, and R is the resistance obtained by the electrochemical
impedance spectroscopy.
[0056] B) X-Ray Diffraction Test
[0057] A cylindrical pellet is prepared by following procedure.
0.175 g of a powderous solid electrolyte compound sample is put on
a mold having a diameter of 1.275 cm. A pressure of 230 MPa is
applied to the mold. The pellet is sintered at 700.degree. C. for 3
hours in oxygen atmosphere.
[0058] The X-ray diffraction pattern of the pellet sample is
collected with a Rigaku X-Ray Diffractometer (D/MAX-2500/PC) using
a Cu K.alpha. radiation source emitting at a wavelength of 1.5418
.ANG.. The instrument configuration is set at: 1.degree. Soller
slit (SS), 1.degree. divergence slit (DS) and 0.15 mm reception
slit (RS). Diffraction patterns are obtained in the range of
10-70.degree. (2.theta.) with a scan speed of 4.degree. per a
minute. Obtained XRD patterns are analyzed by the Rietveld
refinement method using X'Pert HighScore Plus software. The
software is a powder pattern analysis tool with reliable Rietveld
refinement analysis results.
[0059] C) Fourier-Transform Infrared (FTIR) Spectrometry
[0060] FTIR transmission spectrum for the LSPGO powder is collected
using Thermo Scientific FTIR Spectrometer (Nicolet iS 50) in the
wave number range of 1200 to 500 cm.sup.-1, with a resolution of 4
cm.sup.-1, and scan cycle of 32 scan.
[0061] D) Particle Size Distribution
[0062] The catholyte powder samples used in the particle-size
distribution (psd) measurements are prepared by hand grinding the
catholyte powder samples using agate mortar and pestle. The psd is
measured by using a Malvern Mastersizer 3000 with Hydro MV wet
dispersion accessory after having dispersed each of the catholyte
powder samples in an aqueous medium. In order to improve the
dispersion of the catholyte powder, sufficient ultrasonic
irradiation and stirring is applied, and an appropriate surfactant
is introduced. D50 and D99 are defined as the particle size at 50%
and 99% of the cumulative volume % distributions obtained from the
Malvern Mastersizer 3000 with Hydro MV measurements.
[0063] E) Coin Cell Test
[0064] For the preparation of a positive electrode, a catholyte
containing 0.16 g of NMC, 0.03 g conductor (Super P), and 0.125 g
of 8 wt % PVDF binder are mixed in NMP solvent using a planetary
centrifugal mixer (Thinky mixer) for 20 minutes. The homogenized
slurry is spread on one side of an aluminum foil using a doctor
blade coater with a 15 .mu.m gap. The slurry-coated foil is dried
and punched as 8 mm diameter circular shape. A Swagelok cell is
assembled in an argon-filled glove box with the configuration of
positive electrode, separator having a diameter of 13 mm, and
lithium foil having a diameter of 11 mm as a negative electrode. 1M
LiPF.sub.6 in EC/DMC (1:1 wt %) is used as electrolyte. Each cell
is cycled at 25.degree. C. using automatic battery cycler
Wonatech-WBCS3000. The coin cell testing at 0.1 C in the
4.3.about.2.5V/Li metal window range.
[0065] F) Inductively Coupled Plasma (ICP)
[0066] The composition of a positive electrode active material, a
solid electrolyte, and a catholyte is measured by the inductively
coupled plasma (ICP) method using an Agillent ICP 720-ES. 1 gram of
a powder sample is dissolved into 50 mL high purity hydrochloric
acid (at least 37 wt % of HCl with respect to the total amount of
solution) in an Erlenmeyer flask. The flask is covered by a watch
glass and heated on a hot plate at 380.degree. C. until complete
dissolution of the powder. After being cooled to room temperature,
the solution from the Erlenmeyer flask is poured into a 250 mL
volumetric flask. Afterwards, the volumetric flask is filled with
deionized water up to the 250 mL mark, followed by a complete
homogenization. An appropriate amount of solution is taken out by a
pipette and transferred into a 250 mL volumetric flask for a second
dilution, where the volumetric flask is filled with internal
standard and 10% hydrochloric acid up to the 250 mL mark and then
homogenized. Finally, this solution is used for ICP
measurement.
[0067] The invention is further exemplified in the examples below.
The following samples were prepared:
Comparative Example 1
[0068] CEX1 having a general formula
Li.sub.3.50Si.sub.0.50P.sub.0.60O.sub.4 was prepared by the
following steps:
[0069] 1) Mixing: Li.sub.2CO.sub.3, SiO.sub.2, and
(NH.sub.4).sub.2HPO.sub.4 with total weight of around 6.0 g
according to the corresponding molar ratio were put on a 250 ml
bottle with 140 ml of deionized water and each 100 g of Y doped
ZrO.sub.2 balls having 3, 5, and 10 mm diameter. The bottle was
rotated in a conventional ball mill equipment with 300 RPM for 24
hours. The homogeneously mixed slurry was dried at 90.degree. C.
for 12 hours.
[0070] 2) Calcination: the dried mixture was calcined at
900.degree. C. for 6 hours in Ar atmosphere.
[0071] 3) Pulverization: 1.4 g of calcined powder was put on a 45
ml bottle with 30 ml of acetone and 3.4 g of Y doped ZrO.sub.2
balls having a dimeter of 1 mm. The bottle was rotated in a
conventional ball mill equipment with 500 RPM for 6 hours. The
pulverized powder was dried at 70.degree. C. for 6 hours.
[0072] 4) Sintering: The dried powder was sintered at 700.degree.
C. for 3 hours in oxygen atmosphere to get the final LSPO solid
electrolyte compound.
Example 1
[0073] Ge doped LSPO samples having a general formula
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4 were
prepared in the same manner as CEX1 except that different amount of
GeO.sub.2 was added and the amount of Li.sub.2CO.sub.3, SiO.sub.2,
and (NH.sub.4).sub.2HPO.sub.4 were adjusted in the mixing step
according to the target molar ratios. EX1-A, EX1-B, EX1-C, EX1-D,
EX1-E, and EX1-F had the x of 0.05, 0.10, 0.15, 0.20, 0.25, and
0.30, respectively.
Comparative Example 2
[0074] S doped LSPO samples CEX2-A1 and CEX2-A2 having a general
formula Li.sub.(3.5-30
x)Si.sub.(0.5-x)P.sub.(0.5-x)S.sub.2xO.sub.4+a were prepared in the
same manner as samples in the Example 1 except that different
amount of Li.sub.2SO.sub.4 was added instead of GeO.sub.2. CEX2-A1
and CEX2-A2 had the x of 0.05 and 0.10, respectively.
[0075] Ga doped LSPO sample CEX2-B having a general formula
Li.sub.(3.5-30 x)Si.sub.(0.5-x)P.sub.(0.5-x)Ga.sub.2xO.sub.4+a was
prepared in the same manner as samples in the Example 1 except that
Ga.sub.2O.sub.3 was added instead of GeO.sub.2. CEX2-B had the x of
0.05.
Explanatory Example 1
[0076] To examine the stability of electrolyte with Li metal, LSPGO
samples of EX1-B is directly contacted with molten Li metal under
Ar atmosphere. To this end, pellet of EX1-B is made by pressing
0.175 g of EX1-A powder under 2349.7 kgf/cm.sup.2 pressure,
followed by a sintering at 700.degree. C. for 3 h under 02
atmosphere. A stripe of Li foil is placed on a stainless-steel
plate heated on 250.degree. C. hot plate (under controlled
non-oxidizing atmosphere). The obtained molten Li is directly
poured on the prepared EX1-B pellets and the pellets are observed
for 15 minutes. This explanatory experiment is conducted in a glove
box with Ar atmosphere. The pellet is visually observed/monitored
so as to detect an eventual thermal runaway and the structure is
examined using X-Ray Diffraction.
[0077] Results
TABLE-US-00001 TABLE 1 List of Examples and Comparative Examples
with their properties Sample Conductivity Volume Examples ID
Composition x - (S/cm) (As) Comparative CEX1
Li.sub.3.50Si.sub.0.50P.sub.0.50O.sub.4 0.00 4.4 .times. 10.sup.-6
324.15 example 1 Example 1 EX1-A
Li.sub.3.55Si.sub.0.45P.sub.0.45Ge.sub.0.10O.sub.4 0.05 7.2 .times.
10.sup.-6 327.11 EX1-B
Li.sub.3.60Si.sub.0.40P.sub.0.40Ge.sub.0.20O.sub.4 0.10 1.0 .times.
10.sup.-5 329.96 EX1-C
Li.sub.3.65Si.sub.0.35P.sub.0.35Ge.sub.0.30O.sub.4 0.15 1.4 .times.
10.sup.-5 332.93 EX1-D
Li.sub.3.70Si.sub.0.30P.sub.0.30Ge.sub.0.40O.sub.4 0.20 1.5 .times.
10.sup.-5 335.73 EX1-E
Li.sub.3.75Si.sub.0.25P.sub.0.25Ge.sub.0.50O.sub.4 0.25 2.7 .times.
10.sup.-5 338.83 EX1-F
Li.sub.3.75Si.sub.0.25P.sub.0.25Ge.sub.0.50O.sub.4 0.30 2.4 .times.
10.sup.-5 340.76 Comparative CEX2-
Li.sub.3.35Si.sub.0.45P.sub.0.45S.sub.0.10O.sub.4 0.05 2.3 .times.
10.sup.-6 324.27 A1 example 2 CEX2-
Li.sub.3.20Si.sub.0.40P.sub.0.40S.sub.0.20O.sub.4 0.10 3.9 .times.
10.sup.-7 323.58 A2 CEX2-B
Li.sub.3.65Si.sub.0.45P.sub.0.45S.sub.0.10O.sub.4 0.05 3.5 .times.
10.sup.-6 No solid solution (*x in CEX1 and EX1-A to EX1-F with
formula Li.sub.(3.5x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2.times.04,
in CEX2-A1 and CEX2-A2 with formula
Li.sub.(3.5-3x)Si.sub.(0.5-x)P.sub.(0.5-x)S.sub.2xO.sub.4, and in
CEX2-B with formula
Li.sub.(3.5+303x)Si.sub.(0.5-x)P.sub.(0.5-x)Ga.sub.2xO.sub.4.)
[0078] Enhanced Conductivity of the LSPGO According to the Present
Invention
[0079] Table 1 summarizes the list of example and comparative
example samples. It can be seen that LSPGO samples at x=0.05-0.30
(EX1-A to EX1-F) have higher lithium ionic conductivity than the
LSPO sample (CEX1). As for S and Ga bearing LSPO (CEX2-A1, CEX2-A2,
and CEX2-B), the lithium ionic conductivities are lower.
[0080] FIG. 1 shows a typical Nyquist plot from EIS measurement
Li.sub.(3.5+x)Si.sub.(0.5-x)P.sub.(0.5-x)Ge.sub.2xO.sub.4+a (x=0.00
to 0.30). The plot is composed of real part of impedance in X axis
and imaginary part in Y axis. High frequency measurement appears on
the left side of the graph forms a semicircle that is followed by a
low angle spike as the result of the low frequency measurement. The
semicircle formation corresponded to the lithium conduction in SE.
The lithium ionic conductivity of CEX1 is 4.4.times.10.sup.-6 at
room temperature that is comparable with the earlier published
works on LSPO. The reduction of the semicircle diameter with the
higher Ge amount indicating lower resistance of sample suggesting a
better conductivity.
[0081] FIG. 2 shows the improvement of lithium ionic conductivity
where the value increases proportionally with more Ge in the
structure. The highest lithium ionic conductivity is
2.7.times.10.sup.-5 at x=0.25 which is about 6 times of CEX1. When
x is 0.30, the value reduces to 2.4.times.10.sup.-5, concluding
that 0.25 is an optimal concentration.
[0082] Retention of the Solid Solution in the Ge-Doped LSPO
According to the Invention
[0083] FIG. 3 shows the XRD patterns of CEX1 (undoped electrolyte)
and EX1-A to EX1-F. It is observed that Ge bearing LSPO samples
have a single LISICON phase without impurity, demonstrating that Ge
is well doped. In all graphs, the .gamma.-Li.sub.3PO.sub.4
structure is maintained, indicated by the characteristic double
peak at 28.degree.-29.degree. representing (121) and (200) planes
as well as four consecutive peaks at 34.degree.-36.degree.
correspond to (220), (131), (211), and (002) planes. The shifted
peak positions to the left related with the larger crystal volume
showed in Table 1. The observed single phase also acts as an
evidence of solid solution formation for the Ge bearing LSPO.
[0084] Additionally, FTIR measurement is displayed in FIG. 4 with
the vibration bands of P--O, Si--O, and Ge--O marked. The vibration
bands at 580 cm.sup.-1, 910 cm.sup.-1, and around 1050 cm.sup.-1
correspond to the vibration modes of tetrahedron P--O while band in
area of 985-1005 cm.sup.-1 corresponds to the vibration modes of
Si--O, also in tetrahedral structure. All bands show transmittance
signal increase along with the addition of Ge in the structure. On
the other hand, transmittance of 790 cm.sup.-1 band which
corresponds to Ge--O vibration decreases with the more Ge in the
structure. It is concluded that the atomic substitution of Ge
successfully occurred at Si and P sites without changing the
structure. This observation matches with that of XRD where the
structure of LSPO is maintained upon doping.
[0085] XRD of CEX2 are compared with CEX1 in FIG. 5. The S bearing
LSPO structure (CEX2-A) is still well maintained while Ga bearing
LSPO structure (CEX2-B) has multiple impurity peaks marked with (*)
in the graph. This indicating Ga is not easy to be doped in the
LSPO system and solid solution is failed to form for CEX2-B.
[0086] Chemical Stability of the LSPGO with a Li Metal Foil
[0087] Chemical stability of LSPGO with Li metal was examined
through a direct contact with the molten Li metal.
[0088] LSPGO pellet XRD diffraction pattern after exposure with
molten Li metal is compared with the original pattern before
exposure as displayed in FIG. 6. Both measurement produced
diffractogram with the same peak location indicating the structure
remain the same (there is no structural change as the result of
reaction with Li metal). The pellet is also observed to be very
stable upon contact without thermal runaway or any exothermic
reaction.
Example 2 (Catholyte)
[0089] A M-NMC622 compound having the target formula of
Li(Ni.sub.0.60Mn.sub.0.20Co.sub.0.20)O.sub.2 and a monolithic
morphology is obtained through a double sintering process and a wet
milling process running as follows:
[0090] 1) Co-precipitation: mixed transition metal hydroxides with
D50 of around 4 .mu.m are prepared by the process described in
KR101547972B1 (from page 6 line 25 to page 7 line 32).
[0091] 2) 1.sup.st blending: to obtain a lithium deficient sintered
precursor, Li.sub.2CO.sub.3 and the co-precipitation product are
homogenously blended with a Li/M' ratio of 0.85 in a Henschel mixer
for 30 minutes so as to obtain a 1.sup.st blend.
[0092] 3) 1.sup.st sintering: the 1.sup.st blend is sintered at
935.degree. C. for 10 hours under an oxygen containing atmosphere.
The product obtained from this step is a powderous lithium
deficient sintered precursor with Li/M'=0.85.
[0093] 4) Blending: the lithium deficient sintered precursor is
blended with LiOH.H.sub.2O to correct the Li stoichiometry to
Li/M'=1.01. The blending is performed in a mixer for 30 minutes so
as to obtain a 2.sup.nd blend.
[0094] 5) 2.sup.nd sintering: the 2.sup.nd blend is sintered at
890.degree. C. for 10 hours in an oxygen containing atmosphere in a
roller hearth kiln (RHK). The sintered blocks are crushed by a jaw
crushing equipment.
[0095] 6) Wet milling: To break the agglomerated intermediate
particles into monolithic primary particles, a wet ball milling
process is applied. 5 L bottle is filled with 1 L of deionized
water, 5.4 kg ZrO.sub.2 balls, and 1 kg of 2.sup.nd sintering
product from process number 5. The bottle is rotated on a
commercial ball mill equipment.
[0096] 7) Healing firing step (3rd sintering): The wet milled
product is heated at 750.degree. C. for 10 hours under oxygen
containing atmosphere in a furnace. The sintered compound is
sieved.
[0097] A catholyte material EX2-CAT-A is made by mixing M-NMC622
and EX1-B (Li.sub.3.60Si.sub.0.40P.sub.0.40Ge.sub.0.20O.sub.4)
according to a mixing ratio of 1:1 by weight, followed by a heat
treatment at 700.degree. C. for 3 hours in an oxygen atmosphere
(i.e. like air). EX1-B has a median particle size (D50) of 2
.mu.m.
[0098] A catholyte material EX2-CAT-B is obtained through a similar
manner as the preparation of EX2-CAT-A except that the mixture is
heated at 600.degree. C.
Comparative Example 3 (Catholyte)
[0099] CEX3-CAT-A and CEX3-CAT-B are obtained through a similar
manner as the preparation of EX2-CAT-A except that the mixture is
heated at 500.degree. C., 900.degree. C., respectively, as
displayed in Table 2.
TABLE-US-00002 TABLE 2 Particle size distribution and ionic
conductivity of EX2 and CEX3 material Co-sintering Ionic First
discharge Sample temperature D50 D99 conductivity capacity ID*
(.degree. C.) (.mu.m) (.mu.m) (S/cm) (mAh/g) EX2-CAT-A 700 10.2
34.7 1 .times. 10-5 176.4 EX2-CAT-B 600 10.3 31.0 2 .times. 10-6
_** CEX3-CAT-A 500 10.4 28.1 1 .times. 10-7 _** CEX3-CAT-B 900 10.5
143.0 9 .times. 10-4 133.8 *-CAT- stands for "catholyte". ** - :
not measured.
[0100] The results of the size distribution measurement as
displayed in the Table 2 show that EX2-CAT-A, EX2-CAT-B,
CEX3-CAT-A, and CEX3-CAT-B have a similar D50 at around 10.2-10.5
.mu.m. However, the D99 values are larger at the higher
co-sintering temperature. For instance, the D99 of EX2-CAT-A
(resulting from a sintering at 700.degree. C.) is 34.7 .mu.m while
the D99 of CEX3-CAT-B (resulting from a co-sintering at 900.degree.
C.) is 143.0 .mu.m. The coin cell characterization of EX2-CAT-A and
CEX3-CAT-B as displayed in FIG. 7 shows the effect of the
co-sintering temperature to the electrochemical performance. Here,
CEX3-CAT-B sintered at 900.degree. C. clearly shows a lower
discharge capacity comparing to EX2-CAT-A sintered at 700.degree.
C.
[0101] On the other hand, co-sintering temperature lower than
600.degree. C. is also unpreferable. The ionic conductivity data
provided in Table 2 also demonstrate that the ionic conductivity of
the catholyte depends upon the co-sintering temperature, wherein
the catholyte is more conductive at a higher co-sintering
temperature. EX2-CAT-A which results from a co-sintering prepared
at 700.degree. C. has an ionic conductivity of 10.sup.-5 S/cm while
CEX3-CAT-A (resulting from a co-sintering at 500.degree. C.) has an
ionic conductivity of 10.sup.-7 S/cm, i.e. a decrease of .times.100
is observed for this sample with respect to CEX3-CAT-A's ionic
conductivity.
* * * * *
References