U.S. patent application number 16/565153 was filed with the patent office on 2020-06-04 for solid electrolyte glass for lithium or sodium ions conduction.
This patent application is currently assigned to UNIVERSIDADE DO PORTO. The applicant listed for this patent is UNIVERSIDADE DO PORTO LABORATORIO NACIONAL DE ENERGIA E GEOLOGIA. Invention is credited to Jose Jorge DO AMARAL FERREIRA, Maria Helena SOUSA SOARES DE OLIVEIRA BRAGA.
Application Number | 20200176813 16/565153 |
Document ID | / |
Family ID | 52808081 |
Filed Date | 2020-06-04 |
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United States Patent
Application |
20200176813 |
Kind Code |
A1 |
SOUSA SOARES DE OLIVEIRA BRAGA;
Maria Helena ; et al. |
June 4, 2020 |
SOLID ELECTROLYTE GLASS FOR LITHIUM OR SODIUM IONS CONDUCTION
Abstract
Glassy electrolyte for lithium or sodium ions conduction The
present disclosure relates to the development and improvement of
sodium or lithium-ion electrochemical devices, in particular to the
development of a new glassy electrolyte comprising high ionic
conductivity for batteries, capacitors, and other electrochemical
devices comprising a solid electrolyte glass comprising the formula
R.sub.3-2xM.sub.xHalO wherein R is selected from the group
consisting of lithium or sodium: M is selected from the group
consisting of magnesium, calcium, strontium or barium; Hal is
selected from the group consisting of flourine, chlorine, bromine,
iodine or mixtures thereof; X is the number of moles of M and
0.ltoreq.x.ltoreq.0.01 and the solid electrolyte glass has a glass
transition point.
Inventors: |
SOUSA SOARES DE OLIVEIRA BRAGA;
Maria Helena; (Porto, PT) ; DO AMARAL FERREIRA; Jose
Jorge; (Amadora, PT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNIVERSIDADE DO PORTO
LABORATORIO NACIONAL DE ENERGIA E GEOLOGIA |
Porto
Amadora |
|
PT
PT |
|
|
Assignee: |
UNIVERSIDADE DO PORTO
Porto
PT
LABORATORIO NACIONAL DE ENERGIA E GEOLOGIA
Amadora
PT
|
Family ID: |
52808081 |
Appl. No.: |
16/565153 |
Filed: |
September 9, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15121678 |
Aug 25, 2016 |
10411293 |
|
|
PCT/IB2015/051440 |
Feb 26, 2015 |
|
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16565153 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 16/00 20130101;
Y02E 60/13 20130101; H01G 11/84 20130101; H01G 11/56 20130101; H01G
9/15 20130101; H01M 10/0525 20130101; H01M 10/052 20130101; H01M
10/054 20130101; H01M 2300/0071 20130101; H01M 10/0562
20130101 |
International
Class: |
H01M 10/0562 20060101
H01M010/0562; H01M 10/054 20060101 H01M010/054; H01G 11/56 20060101
H01G011/56; H01G 11/84 20060101 H01G011/84; H01M 10/052 20060101
H01M010/052; H01M 16/00 20060101 H01M016/00; H01G 9/15 20060101
H01G009/15; H01M 10/0525 20060101 H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2014 |
PT |
107482 |
Claims
1. A solid electrolyte glass comprising compound of formula
R.sub.3-2xM.sub.xHalO wherein R is selected from the group
consisting of lithium or sodium; M is selected from the group
consisting of magnesium, calcium, strontium or barium; Hal is
selected from the group consisting of fluorine, chlorine, bromine,
iodine or mixtures thereof; X is the number of moles of M and
0.ltoreq.x.ltoreq.0.01; and wherein the solid electrolyte glass has
a glassy phase.
2. The electrolyte glass according to claim 1 wherein R is
lithium.
3. The electrolyte glass according to claim 1 wherein R is
sodium.
4. The electrolyte glass according to claim 1, comprising an ionic
conductivity of at least 13 mScm.sup.-1 at 25.degree. C.
5. (canceled)
6. (canceled)
7. The electrolyte glass according to claim 1, comprising an ionic
conductivity of at least 17 mScm.sup.-1 at 25.degree. C.
8. (canceled)
9. (canceled)
10. The electrolyte glass according to claim 1, wherein X is 0.002,
0.005; 0.007 or 0.01.
11. The electrolyte glass according to claim 1, wherein Hal is a
mixture of chlorine and iodine.
12. The electrolyte glass according to claim 1, wherein Hal is
Hal=0.5Cl+0.51.
13. (canceled)
14. The electrolyte glass according to claim 1, wherein R is
lithium, M is barium, Hal is chlorine and x is 0.005.
15. (canceled)
16. (canceled)
17. An electrolyte composition comprising a compound of formula
Na.sub.3-2xM.sub.xHalO wherein M is selected from the group
consisting of magnesium, calcium, strontium or barium; Hal is
selected from the group consisting of fluorine, chlorine, bromine,
iodine or mixtures thereof; X is the number of moles of M and
0<x.ltoreq.0.01.
18. The composition according to claim 17, wherein M is barium, Hal
is chlorine and x is 0.005.
19. An electrochemical device comprising the electrolyte glass
according to claim 1 or the electrolyte composition according to
claim 17.
20. A capacitor comprising the electrolyte glass according to claim
1 or the electrolyte composition according to claim 17.
21. A battery comprising the electrolyte glass according to claim 1
or the electrolyte composition according to claim 17.
22. An electrochemical device comprising at least one capacitor
according to claim 20.
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
28. (canceled)
29. An ionic conductivity and/or an electrochemical window of
stability enhancer for a material mixture comprising the
electrolyte glass according to claim 1 or the electrolyte
composition according to claim 17.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 15/121,678 filed Aug. 25, 2016, which is a
U.S. National Stage Application under 35 U.S.C. .sctn. 371 of
International Patent Application No. PCT/1132015/051440, both of
which are hereby incorporated by reference in their respective
entireties.
TECHNICAL FIELD
[0002] The present disclosure relates to the development and
improvement of sodium or lithium-ion electrochemical devices, in
particular to the development of a new solid electrolyte glass
comprising a high ionic conductivity and/or a high electrochemical
window of stability.
BACKGROUND
[0003] Four types of next generation batteries are currently being
envisaged among the international community: lithium-sulfur,
metal-air, and metal-sodium batteries, multivalent cation batteries
and all-solid-state battery concepts (M. Tatsumisago and Hayashi,
A. Sol. Stat. Ionics, 2012, 225, 342). These battery designs
require high-performance, safe and cost effective electrolytes that
are compatible with optimized electrode materials. Solid
electrolytes have not yet been extensively employed in commercial
batteries as they suffer poor ionic conduction at acceptable
temperatures and insufficient stability with respect to
lithium-metal.
[0004] Chen and co-workers (Z. Chen, Y. Qini, Y. Ren, W. Lu, C.
Orendorff, E. P. Roth and K. Amine, Energy Environ. Sci. 2011, 4,
4023) showed that higher graphite negative electrode surface area
in a lithium-ion cell can result in more solid electrolyte
interphase (SEI) and therefore more heat generation during thermal
decomposition. This initial reaction, which occurs at
.about.110.degree. C., can further trigger other exothermal
reactions in the cell. Therefore, the latest work on graphitic
anodes mainly focuses on the development of a stable artificial
solid electrolyte interphase to stabilize the lithiated graphite
and improve both safety and cycling performance.
[0005] Recently, lithium batteries using oxygen from air at the
positive electrode (lithium-air batteries) have attracted
world-wide attention. In this open system, the use of electrolytes
with low volatility is strictly required. For the lithium-air
batteries a major focus of attention has been the lithium-metal
anode protected by a lithium-ion conducting ceramic electrolyte
(N.-S. Choi, Z. Chen, S. A. Freunberger, X. Ji, Y.-K. Sun, K.
Amine, G. Yushin, L. F. Nazar, J. Cho and P. G. Bruce, Angew. Chem.
Int. 2012, 51, 9994). LISICON
(Li.sub.(1+x+y)Al.sub.xTi.sub.2-xSi.sub.yP.sub.(3-y)O.sub.12)
(Ohara Inc. 2013) has been used for the previous purpose with a
major inconvenient related to--LISICON being reduced in contact
with Li-metal--following-on a Li/ceramic interface difficult to
cycle (N.-S. Choi, Z. Chen, S. A. Freunberger, X. Ji, Y.-K. Sun, K.
Amine, G. Yushin, L. F. Nazar, J. Cho and P. G. Bruce, Angew. Chem.
Int. 2012, 51, 9994).
[0006] Promising results were recently obtained with a
Li.sub.10GeP.sub.2S.sub.12 solid electrolyte N. Kamaya, K. Homma,
Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y.
Kato, S. Hama, K. Kawamoto and A. A. Mitsui, Nature Mat. 2011, 10,
682). In this solid electrolyte medium, Li.sup.+ ions are conducted
at 0.012 mScm.sup.-1 and 12 mScm.sup.-1 at -100.degree. C. and
25.degree. C., respectively, which is considered to be a high
conductivity. Mo et al (Y. Mo, S. P. Ong and G. Ceder, Chem. Mater.
2012, 24, 15) found that Li.sub.10GeP.sub.2S.sub.12 is not stable
against reduction by lithium at low voltage or extraction of Li
with decomposition at high voltage.
[0007] On a different front, sulfide glasses have been studied due
to their high ionic conductivity. A glass of the
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2 system is formed at ambient
pressure by quenching
0.03Li.sub.3PO.sub.4-0.59Li.sub.2S-0.38SiS.sub.2 in liquid
nitrogen. Its conductivity at room temperature is 0.69 mScm.sup.-1
(S. Kondo, K. Takada and Y. Yamamura, Sol. Stat. Ionics 1992,
53-56(2), 1183) and its stability against electrochemical reduction
is as wide as 10 V (A. Hayashi, H. Yamashita, M. Tatsumisago and T.
Minami, Sol. Stat. Ionics 2002, 148, 381).
[0008] On the other hand, for lithium-ion or sodium-ion
electrochemical devices such as capacitors and especially
batteries, the safety issue remains a major barrier. Battery
manufacturers are now able to produce high-quality lithium-ion
cells for consumer electronics, with less than one reported safety
incident for every one million cells produced. However, this
failure rate is still too high for applications in plug-in hybrid
electric vehicles and pure electric vehicles, since several hundred
of lithium-ion cells will be needed to power a vehicle. The failure
of a single cell can generate a large amount of heat and flame,
both of which can then trigger thermal runaway of neighbouring
cells, leading to failure throughout the battery pack.
Consequently, there is a wide effort to tackle the safety issue of
lithium batteries.
[0009] Typically, the conductivity of liquid state of the art
electrolytes at room temperature (20.degree. C.) is about 10
mScm.sup.-1, and it increases by approximately 30-40% at 40.degree.
C. The electrochemical window of stability of liquid electrolytes
is usually equal or smaller than 4 V, not enabling their use with
all the pairs of electrodes.
[0010] The stability of the electrolyte is related to its
electrochemical window which is directly related with the
electrical band gap. The calculated electronic energy band gap for
Li.sub.3ClO crystalline solid is 6.44 eV and does not change more
than the decimal value of an eV with low dopant levels up to 0.7 at
%. Cyclic voltammetry experiments conducted to determine the window
of stability of the glassy samples at 130.degree. C. have shown a
stability range of more than 8 V, which allows the application of
our electrolyte in next generation high voltage battery cells (5
V).
[0011] These facts are disclosed in order to illustrate the
technical problem addressed by the present disclosure.
GENERAL DESCRIPTION
[0012] The present disclosure relies on a novel type of glasses,
which is a disordered amorphous phase presenting a glass transition
and showing the highest ionic conductivity of at least 13
mScm.sup.-1 at 25.degree. C. for Li-ion and at least 17 mScm.sup.-1
for Na-ion at 25.degree. C. These glassy electrolytes for
lithium/sodium batteries are inexpensive, light, recyclable,
non-flammable and non-toxic. Moreover, they present a wide
electrochemical window (higher than 8 V) and thermal stability
within the application range of temperatures.
[0013] A lithium-ion or sodium-ion battery is a rechargeable type
of battery, wherein lithium/sodium ions move, through the
electrolyte, from the negative electrode to the positive electrode
during the discharge process and back during the charging process.
The battery's electrochemistry is governed by an overall reaction
occurring at the positive and negative electrodes and the battery's
maximum open circuit potential difference is determined by the
cited reaction.
[0014] A lithium-ion or sodium-ion electrical double layer
capacitor (EDLC) is a supercapacitor, wherein lithium/sodium ions
move, through the electrolyte towards the negative electrode
accumulating at the interface and forming a nanometric spaced
capacitor with the electrode's negative ions or electrons during
charge. At the opposite interface, electrode's positive ions form
another EDLC with the negative ions of the electrolyte (which are
negative due to lack of Li or Na cations). The capacitor's
operating potential difference is determined by the electrolyte's
electrochemical window of stability.
[0015] The lithium-ion or sodium-ion batteries and capacitors are
lightweight, high energy density power sources for a variety of
devices, such as portable devices, power tools, electric vehicles,
and electrical grid storage; contain no toxic metals and are
therefore characterized as non-hazardous waste.
[0016] The disclosed subject-matter relates to a glassy electrolyte
for Li-ion or Na-ion (Lit and Nat, respectively). The glass is
synthesized from a compound with stoichiometry
R.sub.3-2xM.sub.xHalO, wherein R is lithium (Li) or sodium (Na); M
is magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba);
Hal is fluorine (F), chlorine (Cl), bromine (Br) or iodine (I), or
a mixture between these elements; O is oxygen. Furthermore,
0.ltoreq.x.ltoreq.0.01, preferably with
0.002.ltoreq.x.ltoreq.0.007; preferably with
0.003.ltoreq.x.ltoreq.0.005.
[0017] The glassy electrolyte, after reaching the vitreous state,
is a Li.sup.+ ion or Na.sup.+ ion superconductor in addition to
being an electrical insulator demonstrating the essential
functional characteristics of an electrolyte. The ionic
conductivity in the disclose glassy electrolyte, comprising
Li.sup.+ ion or Na.sup.+ ion, improves at least two orders of
magnitude comparing with the crystalline material. The
electrochemical window becomes also wider from 6 V to more than 8
V. It can, therefore, be applied between the negative and positive
electrodes of a lithium battery or capacitor if R in the formula of
the compound mentioned above is lithium, or to a sodium battery or
capacitor if R in the same formula is sodium.
[0018] This glass has proved to be anti-flammable, to have
lightweight, being recyclable, easy to synthesize and of low
cost.
[0019] An embodiment of the disclosed subject-matter is relate to
solid electrolyte glass comprising formula R.sub.3-2xM.sub.xHalO
wherein [0020] R is selected from the group consisting of lithium
or sodium; [0021] M is selected from the group consisting of
magnesium, calcium, strontium or barium; [0022] Hal is selected
from the group consisting of fluorine, chlorine, bromine, iodine or
mixtures thereof; [0023] X is the number of moles of M and
0.ltoreq.x.ltoreq.0.01; [0024] and the solid electrolyte glass has
a glass transition point.
[0025] In an embodiment the solid electrolyte glass does not have a
peak with a half-value width of 0.64.degree. or less in a range of
31.degree..ltoreq.2.theta..ltoreq.34.degree. in measurement by an
X-ray diffraction method using a CuK.alpha. ray.
[0026] In an embodiment the Li.sub.3-2x0.005Ba.sub.0.005ClO glassy
electrolyte does not have a peak with a half-value width of 0.64 or
less in a range of 31.degree..ltoreq.2.theta..ltoreq.34.degree. in
measurement by an X-ray diffraction method using a CuK.alpha.
ray.
[0027] In an embodiment the solid electrolyte glass of the present
disclosure has a ionic conductivity of at least 13 mScm.sup.-1 at
25.degree. C. wherein R is a ion lithium; preferably an ionic
conductivity of 13-60 mScm.sup.-1 at 25.degree. C., more preferably
an ionic conductivity of at least 25 mScm.sup.-1 at 25.degree.
C.
[0028] In an embodiment the solid electrolyte glass of the present
disclosure has a ionic conductivity of at least 17 mScm.sup.-1 at
25.degree. C. wherein R is a ion sodium; preferably an ionic
conductivity of 17-105 mScm.sup.-1 at 25.degree. C., more
preferably an ionic conductivity of at least 31 mScm.sup.-1 at
25.degree. C.
[0029] The ionic conductivity can be measured by standard methods,
namely by Electrochemical Impedance Spectroscopy (EIS) at
25.degree. C.
[0030] In an embodiment the solid electrolyte glass of the present
disclosure X in the formula may be 0.002, 0.005, 0.007 or 0.01.
[0031] In an embodiment the solid electrolyte glass of the present
disclosure Hal may be a mixture of chloride and iodine.
[0032] In an embodiment the solid electrolyte glass of the present
disclosure Hal may be Hal=0.5Cl+0.51.
[0033] In an embodiment the solid electrolyte glass of the present
disclosure wherein R is lithium:
M is barium, Hal is chlorine and x is 0.005 or; M is barium, Hal is
a mixture of chlorine and iodine, x is 0.005.
[0034] In an embodiment the solid electrolyte glass of the present
disclosure wherein R is sodium, M is Ba, Hal is Cl and x is
0.005.
[0035] Another aspect of the present disclosure is related to a
electrolyte composition, in particular a solid electrolyte glass
composition, of the formula Na.sub.3-2xM.sub.xHalO wherein [0036] M
is selected from the group consisting of magnesium, calcium,
strontium or barium; [0037] Hal is selected from the group
consisting of fluorine, chlorine, bromine, iodine or mixtures
thereof; [0038] X is the number of moles of M and
0<x.ltoreq.0.01.
[0039] Another aspect of the present disclosure is related to an
electrochemical device comprising a glassy electrolyte describes in
the present disclosure.
[0040] Another aspect of the present disclosure is related to a
battery comprising a glassy electrolyte describes in the present
disclosure.
[0041] Another aspect of the present disclosure is related to a
capacitor comprising the glassy electrolyte describes in the
present disclosure.
[0042] Another aspect of the present disclosure is related to an
electrochemical device comprising at least one capacitor of the
present describes in the present disclosure and at least one
battery describes in the present disclosure.
[0043] Another aspect of the present disclosure is related to a
method for synthetizing a conductive glass electrolyte, in
particular for preparing 5 g, comprising a compound of the formula
R.sub.3-2xM.sub.xHalO wherein [0044] R is lithium; [0045] M is
selected from the group consisting of magnesium, calcium, strontium
or barium; [0046] Hal is selected from the group consisting of
fluorine, chlorine, bromine, iodine or mixtures thereof, in
particular Cl; [0047] X is the number of moles of M and
0.ltoreq.x.ltoreq.0.01; [0048] comprising the following steps:
[0049] mixing a stoichiometric quantity of LiHal, LiOH, and one of
the following compounds: Mg(OH).sub.2; Ca(OH).sub.2, Sr(OH).sub.2
or Ba(OH).sub.2; [0050] adding to said mixture deionized water and
mixing to form a solution in a closed container; [0051] heating
said solution up to 250.degree. C. during 2-8 h; [0052] opening the
container to evaporate the excess of water in the heated
product.
[0053] In one embodiment, the method for synthetizing any of the
compounds of the previous paragraph may comprise the following
step: [0054] introducing the synthetized glassy material between
electrodes the electrodes of an electrochemical device; [0055]
heating the glassy material up to 170-240.degree. C. and
cooling.
[0056] In one embodiment, the method for synthetizing any of the
compounds of the previous paragraph may comprise the following
step: [0057] a stoichiometry mixture of LiCl, LiOH, and one of the
following compounds: Mg(OH).sub.2; Ca(OH).sub.2, Sr(OH).sub.2 or
Ba(OH).sub.2, is used; the mixture is introduced in a Teflon
reactor with 1-2 drops of deionized water and mixing to form a
homogenous paste which is kept closed in the reactor and introduced
in a sand bath; [0058] the mixture is heated up to 250.degree. C.
and kept for at least 4 h; [0059] the reactor is opened to let the
excess of water evaporate; [0060] a glass material synthetized is
introduced between two gold square electrodes with 1 cm wide and
pressed with the aid of a clip for the electrolyte to gain a
regular thickness equal to 1-3 mm; [0061] the glass material
produced is heated up to 230.degree. C. and cooled down in the sand
bath, 2-5 times under the action of a variable potential difference
between -10 V and 10 V with variable frequencies between 100 Hz and
5 MHz.
[0062] Another aspect of the present disclosure is related to a
method for synthetizing a conductive glass electrolyte, in
particular for preparing 5 g, comprising a compound of the formula
R.sub.3-2xM.sub.xHalO wherein [0063] R is sodium; [0064] M is
selected from the group consisting of magnesium, calcium, strontium
and barium; [0065] Hal is selected from the group consisting of
fluorine, chlorine, bromine, iodine or mixtures thereof; [0066] X
is the number of moles of M and 0.ltoreq.x.ltoreq.0.01 of [0067]
comprising the following steps: [0068] mixing a stoichiometry
quantity of NaHal, NaOH and one of the following compounds:
Mg(OH).sub.2; Ca(OH).sub.2; Sr(OH).sub.2 or Ba(OH).sub.2; [0069]
adding to said mixture deionized water and mixing to form a
solution in a closed container; [0070] heating the solution up to
70-90.degree. C. for 2-8 h; [0071] increasing the temperature up to
190-250.degree. C. for 2-8 h, maintaining said temperature for at
least 2 h; [0072] opening the container to evaporate the excess
water in the heated product.
[0073] In one embodiment, the method for synthetizing any of the
compounds of the previous paragraph may comprise the following
step:
[0074] introducing the synthetized glass material between
electrodes;
[0075] heating the glass up to 190-230.degree. C. and cooling.
[0076] In one embodiment, the method for synthetizing any of the
compounds of the previous paragraph may comprise the following
step:
[0077] a stoichiometry mixture of NaCl, NaOH and one of the
following compounds: Mg(OH).sub.2; Ca(OH).sub.2; Sr(OH).sub.2 or
Ba(OH).sub.2 or a stoichiometry mixture of NaCl, NaF, NaOH and one
of the following compounds: Mg(OH).sub.2; Ca(OH).sub.2;
Sr(OH).sub.2 or Ba(OH).sub.2 is used; [0078] the mixture is
introduced in a reactor with 1-2 drops of deionized water and mixed
to form a homogenous paste which is kept closed in the reactor and
introduced in a sand bath; [0079] the mixture is heated up to
80.degree. C. for 2 h; [0080] the temperature is increased to
120.degree. C. for 24 h; [0081] the temperature is increased to
245.degree. C. for 24 h; [0082] the temperature is maintained for
at least 4 h; [0083] the reactor is opened to let the excess of
water evaporate; [0084] a glassy material synthetized is introduced
between two gold square electrodes with 1 cm wide and pressed with
the aid of a clip for the electrolyte to gain a regular thickness
equal to 1-3 mm; [0085] the glass material produced is heated up to
230.degree. C. and cooled down in the sand bath; [0086] the glass
material is heated up to 140.degree. C. and cooled down in the sand
bath 2-5 times under the action of a variable potential difference
between -10 V and 10 V with variable frequencies between 100 Hz and
5 MHz.
[0087] Another aspect of the present disclosure is related to a
method for synthetizing a ion conductive glassy electrolyte, in
particular for preparing 5 g, comprising a compound of the formula
R.sub.3-2xM.sub.xHalO wherein [0088] R is lithium; [0089] M is
selected from the group consisting of magnesium, calcium, strontium
or barium; [0090] Hal is selected from the group consisting of
fluorine, chlorine, bromine, iodine or mixtures thereof; [0091] X
is the number of moles of M and 0.ltoreq.x.ltoreq.0.01 of [0092]
comprising the following steps: [0093] mixing a stoichiometry
quantity of LiCl, LiOH and one of the following compounds:
Mg(OH).sub.2; Ca(OH).sub.2; Sr(OH).sub.2 or Ba(OH).sub.2; [0094]
adding to said mixture deionized water, in particular 5-25 ml or
1-2 drops, and mixed to form a solution, in particular an
homogeneous paste, in a closed container; [0095] heating said
solution up to 250.degree. C. during 2-8 h; [0096] opening the
container to evaporate the excess of water in the product; [0097]
introducing the glass material synthetized between the electrodes,
in particular a glass material synthetized is introduced between
two gold square electrodes with 1 cm wide and pressed with the aid
of a clip for the electrolyte to gain a regular thickness equal to
1-3 mm; [0098] the glass obtained is heated up to 170-240.degree.
C. and cooled down, in particular 2-5 times under the action of a
variable potential difference between -10 V and 10 V with variable
frequencies between 100 Hz and 5 MHz.
[0099] Another aspect of the present disclosure is related to the
use of the composition of the formula R.sub.3-2xM.sub.xHalO wherein
[0100] R is selected from the group consisting of lithium or
sodium; [0101] M is selected from the group consisting of
magnesium, calcium, barium or strontium; [0102] Hal is selected
from the group consisting of fluorine, chlorine, bromine, iodine or
mixtures thereof; [0103] X is the number of moles of M and
0.ltoreq.x.ltoreq.0.01; as an enhancer of the ionic conductivity of
an electrolyte and/or of the electrochemical window of stability of
an electrolyte.
[0104] The disclosed subject matter relates to a glassy electrolyte
optimized with ultra-fast ionic conduction based on an
R.sub.3-2xM.sub.xHalO stoichiometry, in which R is lithium or
sodium ion, M is a higher valent cation such as Mg.sup.2+,
Ca.sup.2+, Sr.sup.2+, Ba.sup.2+; and Hal is a halide anion like
F.sup.-, Cl.sup.-, Br.sup.- or I.sup.- or a mixture of halides
anions.
[0105] The glass-liquid transition is the reversible transition in
amorphous materials from a hard and relatively brittle state into a
molten or rubber-like state. The glass transition of a liquid to a
solid-like state may occur with either cooling or compression. The
transition comprises a relatively smooth increase in the viscosity
of a material of about 17 orders of magnitude without any
pronounced change in material structure. The consequence of this
dramatic increase is a glass exhibiting solid-like mechanical
properties on the timescale of practical observation. While glasses
are often thought of as rigid and completely immobile, it is well
known that relaxation processes of one type or another continue to
be measurable all the way down to the cryogenic range. Hundreds of
degrees below T.sub.g, on the other hand, there is frequently an
important source of dielectric loss in ordinary glass insulators.
This is attributed to mobile alkali ions and, to a lesser extent,
protons, in the anionic network. In many cases, for example in
solid electrolytes, these quasi-free modes of motion are the focus
of special materials interest such as advanced solid electrolytes
based on freely mobile cations.
[0106] A more operative classification for the glass transition
temperature is that at this temperature--or within a few degrees up
to for example 50.degree. C.--the specific heat, the coefficient of
thermal expansion and eventually the dielectric constant change
abruptly. In the Differential Scanning calorimetry (DSC)
experiment, T.sub.g is expressed by a change in the base line,
indicating a change in the heat capacity of the material. Usually,
no enthalpy (latent heat change) is associated with this transition
(it is a second order transition); therefore, the effect in a DSC
curve is slender and is distinguishable only if the instrument is
sensitive.
[0107] These solid electrolytes undergo a viscous liquid to a
solid-like transition, at T.sub.g. Above T.sub.g a non-Arrhenius
conductivity regime is observed [T.sub.g(Li.sub.3ClO) 119.degree.
C., T.sub.g(Li.sub.3-2*0.005Mg.sub.0.005ClO).apprxeq.109.degree.
C., T.sub.g(Li.sub.3-2*0.005Ca.sub.0.005ClO) 99.degree. C.,
T.sub.g(Li.sub.3-2*0.005Ba.sub.0.005ClO) 75.degree. C., T.sub.g
(Li.sub.3-2*0.005Ba.sub.0.005Cl.sub.0.5I.sub.0.5O) 38.degree. C.].
One variant of the solid electrolyte developed by us,
Li.sub.3-2xBa.sub.xClO (x=0.005), has a conductivity of 25
mScm.sup.-1, 38 mScm.sup.-1 and 240 mScm.sup.-1 at 25.degree. C.,
75.degree. C. and 100.degree. C., respectively, in the glassy state
or supercooled liquid state. Another variant,
Li.sub.3-2xBa.sub.xCl.sub.0.5I.sub.0.5O (x=0.005), has a
conductivity of 121 mScm.sup.-1 at 50.degree. C. in the supercooled
liquid state.
[0108] Antiperovskite hydroxides, most of them following the
general formula Li.sub.3-n(OH.sub.n)Hal or Li.sub.4(OH).sub.3Cl
present ionic conductivities which are surprisingly smaller than
the Li.sub.3-2*xM.sub.xHalO vitreous electrolytes, achieving the
highest ionic conductivity, 0.010 Scm.sup.-1, at 250.degree. C.
(for Li.sub.5(OH).sub.3Cl.sub.2). Nevertheless, they are observed
in our samples prior to the formation of the glasses and they may
have an surprisingly important role in glass formation since the
translational symmetry characteristic of a homogeneous fluid is
broken by exposure to an external force field, in the vicinity of a
confining surface (which may be regarded as the source of an
external field), or in the presence of an interface between
coexisting phases.
DESCRIPTION OF THE FIGURES
[0109] For a better understanding of the solution, the attached
figures are joined, which represent preferred embodiments of the
invention which, however, these figures are not intended to limit
the scope of the present invention.
[0110] FIG. 1: XRD diffractogram of a sample of Li.sub.3ClO at room
temperature. There is evidence of small amount of an hydroxide
phase, possibly Li.sub.5(OH).sub.2Cl.sub.3, due to sample
manipulation. At 180.degree. C. (graph right above, FIG. 1 (1)),
there is little evidence of the hydroxide but the presence of
crystalline Li.sub.3ClO is still clear, although an amorphous phase
becomes visible. At 230.degree. C. (graph right above, FIG. 1 (2)),
only an amorphous phase is clearly distinguishable. The XRD
radiation used was CuK.sub..alpha..
[0111] FIG. 2: XRD diffractogram of a Li.sub.3ClO--crystalline
sample (the same as in FIG. 1 (1)) and of
Li.sub.3-2*0.005Ba.sub.0.005ClO glassy (2) at room temperature
after EIS measurements (after six cycles of heating/cooling).
Compton's scatter, which is inelastic scattering and amorphous
scatter related with the glass is observed. There is evidence of
the presence of an hydroxide phase, possibly
Li.sub.5Cl.sub.3(OH).sub.2 (the same as in FIG. 1), that due to
sample's air exposed manipulation is inevitable and starts to form
at the surface.
[0112] FIG. 3: Differential Scanning calorimetry (DSC). DSC curves
for a sample of Li.sub.3-2*0.005Mg.sub.0.005ClO during heating and
cooling, at 5.degree. C./min, eventually showing the glass
transition (baseline anomaly) and first order transition
temperatures (melting corresponds to endothermic incidents (heating
curve) and to an exothermic incident on the cooling curve).
[0113] FIG. 4: EIS experimental and fitted data using the
equivalent circuit previously described. Nyquist impedance and
correspondent fitting curve for the 2.sup.nd cycle of a sample
containing Li.sub.3-2*0.005Ba.sub.0.005ClO, at 25.degree. C. A is
the surface area, A=1.76 cm.sup.2 and d the thickness, d=0.2
cm.
[0114] FIG. 5: EIS experimental and fitted data using the
equivalent circuit previously described. Nyquist impedance for the
2.sup.nd cycle of a sample containing
Li.sub.3-2*0.005Ba.sub.0.005ClO, at different temperatures after
the glass transition. A is the surface area and d the
thickness.
[0115] FIG. 6: Photograph of a glassy sample of
Li.sub.3-2*0.005Ca.sub.0.005ClO.
[0116] FIG. 7A-C: Electrical properties of plain and doped
Li.sub.3ClO. FIG. 7A: Calculated electronic band structure for the
Li.sub.3-2*0.04Ca.sub.0.04ClO solid crystal within the Brillouin
zone directions, using DFT-GGA as implemented in VASP. The band gap
of 4.74 eV is highlighted after the Fermi level which corresponds
to 0 eV. FIG. 7B: Li.sub.3ClO calculated electronic band structure
within the Brillouin zone directions, using HSE06. The band gap of
6.44 eV highlights the difference between Eg calculated with
DFT-GGA and HSE06.
[0117] FIG. 7C: Voltammetry for different cells and doped
electrolytes, at 130.degree. C., emphasizing the stability of the
electrolytes up to 8 V.
[0118] FIG. 8: Glass transition temperature versus ionic radius (of
the Li.sup.+ ion, in Li.sub.3ClO, of the doping ion (M) in
Li.sub.3-2*0.005M.sub.0.005ClO, M=Mg.sup.2+, Ca.sup.2+, Sr.sup.2+,
Ba.sup.2+ and of Li.sub.3-2*0.005M.sub.0.005Cl.sub.0.5I.sub.0.5O).
Excluding Sr.sup.2+, all glass transition temperatures were
obtained by Electrochemical Impedance Spectroscopy (EIS). Ionic
radiuses were obtained from the literature.
[0119] FIG. 9A-B: Ionic conductivities of plain and doped
Li.sub.3ClO. FIG. 9A: Logarithm of the ionic conductivity of
Li.sub.3ClO, Li.sub.3-2*0.005Mg.sub.0.005ClO and
Li.sub.3-2*0.005Ca.sub.0.005ClO versus 1000/T [K] during heating
and cooling. FIG. 9B: Comparison between the logarithm of the ionic
conductivities of hydroxides that can be formed during
Li.sub.3-2*xM.sub.xHalO synthesis; some known solid electrolytes
and a gel electrolyte commonly used in Li-ion batteries;
Li.sub.3ClO and Li.sub.3-2*0.005M0.005ClO (M=Mg, Ca, Sr, and Ba)
during heating. Line and symbols +, x for
Li.sub.3-2*0.005Ba.sub.0.005ClO glassy samples in their 2.sup.nd,
3.sup.rd and 4.sup.th heating/cooling cycles, respectively. EIS
measurements were performed during heating.
[0120] FIG. 10A-B: Log(.sigma.T) versus 1000/T graphs, to highlight
identical values for the extrapolated data of the .sigma.T term in
the solid-like glass and supercooled liquid domains when the
temperature, T, approaches infinity; FIG. 10 A: for a sample of
Li.sub.3ClO; FIG. 10B: for a sample of
Li.sub.3-2*0.005Ca.sub.0.005ClO.
[0121] FIG. 11: Pseudo-Arrhenius plot and "apparent" activation
energies for a Li.sub.3-2*0.005Ba.sub.0.005ClO sample during the
4.sup.th heating/cooling cycle. The sample was submitted to an EIS
cycle on every heating. The sample was glassy and therefore it is
not expected an Arrhenius behaviour at least above T.sub.g.
[0122] FIG. 12: Ionic conductivities of plain and doped
Li.sub.3ClO. Logarithm of the ionic conductivity of Li.sub.3ClO (Y.
Zhao and L. L. Daemen, J. Am. Chem. Soc. 2012, 134, 15042),
Li.sub.3Cl.sub.0.5Br.sub.0.5O (Y. Zhao and L. L. Daemen, J. Am.
Chem. Soc. 2012, 134, 15042), Agl (H. Mehrer, Diffusion in Solids
Fundamentals, Methods, Materials, Diffusion-Controlled Processes,
Springer Series in Solid-State Sciences, Vol. 155, 1st ed. 2007),
Li.sub.3-2*0.005Ba.sub.0.005ClO (1.sup.st and 4.sup.th cycles) and
Li.sub.3-2*0.005Ba.sub.0.005Cl.sub.0.5I.sub.0.5O (1.sup.st to
3.sup.rd cycles) versus 1000/T [K] during heating.
[0123] FIG. 13: The experimental ionic conductivity versus
concentration for Li.sub.3-2*xCa.sub.xClO and
Li.sub.3-2*xMg.sub.xClO. These results were obtained in the
stainless steel non-optimized cell. Electrodes were of stainless
steel. The sample cannot be pressure tight as in the gold cell, and
most likely the samples did not become glasses.
[0124] FIG. 14A-B: Cycle stability of the solid electrolyte versus
Li-metal. FIG. 14A: Chronopotentiometry emphasizing cycling
stability of a Li/Li.sub.3-2*0.005Ca.sub.0.005ClO/Li cell at
44.degree. C. V.sub.ac stands for open circuit voltage. The applied
current (I.sub.app)=.+-.0.1mAcm.sup.-2 FIG. 14B: Zoom of the graph
in FIG. 14A (bottom right graph) showing the stability of the
Li/Li.sub.3-2*0.005Ca.sub.0.005ClO/Li cell.
[0125] FIG. 15: Lattice vibration spectra of the Li.sub.3ClO.
Above: the calculated spectrum and IINS for a
brass/Li.sub.3ClO/brass cell (blocking electrodes). Below: the IINS
for a Li/Li.sub.3ClO/Li cell. The dependence from the applied
frequency of the intensity of the spectra peaks highlights the jump
frequency. This effect is notorious for the peaks around 350
cm.sup.-1. In the calculated spectra, incoherent cross-sections of
each element were not weighed. Additionally, calculations did not
take into account the overtones.
DETAILED DESCRIPTION
[0126] The present disclosure describe the novel type of glasses,
and method of obtain thereof.
[0127] Synthesis, Characterization and Neutron Scattering
[0128] In an embodiment, the preparation of Li.sub.3ClO and
corresponding doped solid electrolyte samples consisted in
pre-drying LiCl, and Li, Mg, Ca or Ba hydroxides since most of them
are highly hygroscopic, weighing the stoichiometric amounts and
mixing them. Then, by adding a few deionized water drops, a paste
was formed and introduced in a Teflon reactor, which was closed.
The reactor was heated at 230-260.degree. C. for 2-3 hours before
it was opened to let the water evaporate for approximately 1 h.
Then it was closed in glassware and allowed to cool to room
temperature. A vacuum pump was used to dry the water out. A few
hours are needed for the sample to become 100% of the amorphous
Li.sub.3ClO or its doped homolog. Pellets were obtained as well
(with a cold press).
[0129] The part of the sample designated for EIS experiments was
manipulated in air, after synthesis, since it proportionated the
formation of hydroxides that were beneficial to glass
formation.
[0130] The cooling processes took place in the sand bath, it was
slow, in the screw pressed cell, and most of the times EIS
experiments were performed during cooling. Glasses were obtained
after hydroxides ran out (eventually this phase works as a
confining surface, helping glass formation).
[0131] In an embodiment, samples were submitted to X-ray
Diffraction (XRD) in a Panalytical instrument, using CuK.sub.a
radiation, to determine the amount of the product present in the
sample as observed in FIG. 1. XRD measurements were also performed
after EIS experiments to determine if the material was amorphous.
An example of the latter measurements can be observed in FIG. 2.
Mg, Ca, Sr or Ba quantitative analysis was performed by means of
Atomic Absorption Spectroscopy (AAS).
[0132] The high sensitivity of ionic conductivity of glasses to
chemical composition is well known, therefore different doping
elements and compositions Li.sub.3-2*xM.sub.xHalO (for example, x=0
in Li.sub.3ClO; x=0.002, 0.005, 0.007 and 0.01 for M=Mg and Ca;
x=0.005 for M=Ba and Hal=Cl or Hal=0.5Cl+0.5I) were synthesized. To
obtain glasses, the samples were mounted into a gold cell
(described in ionic and electronic conductivity measurements), in
air atmosphere, and performed heating-cooling cycles up to
250.degree. C. Eventually, after the first heating-cooling cycle
(sample was slowly cooled down and protected from moisture), the
ionic conductivity grows abruptly.
[0133] Differential Scanning calorimetry experiments (DSC) in
alumina closed crucibles and Ar flowing atmosphere, using dried
powder and slightly pressed powder, show that after the first
cycle, the hydroxide's melting peak cannot be distinguished
anymore. The latter also shows a baseline anomaly that is probably
due to the glassy transition and a clear first order transition
corresponding to the melting peak of Li.sub.3-0.01Mg.sub.000.5ClO
as it can be distinguished in FIG. 3. A Labsys-Setaram instrument
was used to perform the latter measurements.
[0134] The role of the lattice during hopping and diffusion was
established by means of neutron inelastic incoherent scattering
(IINS). A sample holder stick and a lithium-metal symmetric battery
cell (screw brass collectors, quartz glass tube with approximately
2.5 cm of diameter, and about 3 cm of sample--distance between
lithium electrodes) were prepared for these experiments at the Los
Alamos Neutron Scattering Center (LANSCE). Temperature, current and
applied frequency could vary.
[0135] Ionic and Electronic Conductivity Measurements
[0136] Electrochemical Impedance Spectroscopy (EIS) was performed
in a cell using either gold or stainless steel (blocking
electrodes) that was heated up in a sand bath, in air atmosphere or
in a glovebox in Ar and/or air (water vapour <10%). Our gold
symmetric cell has about 1.77 cm.sup.2 of surface area. It
consisted of two disk foils of gold separated by the sample with a
thickness of about less than 5 mm (usually 1-3.0 mm) and it was
pressed tightly with a screw. Our stainless steel cell was bulky
and could contain a sample with the same dimensions as the gold
one. In the latter cell, blocking electrodes could be stainless
steel or copper (just for temperatures near room temperature). This
cell was seldom used. The instrument used is a Bio-Logic SP240.
Experiments were conducted in the temperature range 25 to
255.degree. C. The frequency range was 5 MHz-0.1 Hz. Ionic
conductivity was calculated using Nyquist impedance of an
equivalent circuit containing a passive resistance in series with a
constant phase element in series with circuit containing a
capacitor in parallel with a resistance. The latter resistance is
the solid electrolyte's resistance which plays the role of the
dielectric in an ideal parallel-plate capacitor. When the
resistance to ionic conduction becomes too small and Faraday's
induction caused by the cables unavoidable and prominent at high
frequencies, a non-ideal inductive element was added in series to
the previous circuit. FIGS. 4 and 5 show EIS measurements' data for
a sample containing Li.sub.3-2*0.005Ba.sub.0.005ClO tested in a
symmetric gold cell as previously described, for different cycles
and temperatures. Tests in the empty cell and with Agl were
performed to control the procedures and establish analysis
methods.
[0137] Cyclic voltammetry tests were performed in the stainless
steel cell with a lithium electrode as reference electrode and a
counter electrode of copper or stainless steel. Chronopotentiometry
was performed in a lithium symmetric cell equivalent to the gold
one previously described. Three measurements intercalated by an
open circuit interval were performed containing 20 cycles each of
40 minutes (20 minutes at a positive current and 20 minutes at a
negative current). Measurements were performed in an Ar-dry glove
box.
[0138] Calculations
[0139] In an embodiment, density Functional Theory (DFT)
calculations with Projector Augmented Wave (PAW) pseudopotentials
as implemented in the Vienna Ab initio Simulation Package (VASP)
code, were performed. A plane wave cut-off of 500 eV, and k-mesh of
4.times.4.times.4 were used. Calculations were implemented for
crystalline electrolytes in real space and were performed within
the P1 space group supercells containing at least 134 atoms. Some
supercells contained as many atoms as possible, 270 atoms or more,
to allow better approximations with the real Ba.sup.2+, Ca.sup.2+
or Mg.sup.2+ concentrations. The Generalized Gradient Approximation
(GGA), and the PerdewBurkeErnzerhof (PBE) functional were used, and
no magnetic moments were included in the model. The
Heyd-Scuseria-Erznerhof (HSE06) functional was used to calculate
band structure and electronic Density of States (DOS) to determine
the lowest unoccupied molecular orbital (LUMO) and the highest
occupied molecular orbital (HOMO).
[0140] Ionic conduction in solids occurs by ion hopping from a
crystal lattice site to another by vacancy mechanism; therefore it
is convenient to have a partial occupancy of energetically
equivalent or near-equivalent sites. In favourable structures, the
defects may be mobile, leading to high ionic conductivity. While
the rate of ion transport in a crystalline solid is dictated by the
diffusivity and concentration of the vacancies mediating ion
transport, the open structure of inorganic glassy materials
facilitates the process of ionic hopping and results in enhanced
conductivity. Inorganic glasses thus represent an attractive
material class for electrolyte applications. An advantage of
inorganic glasses is single-cation conduction; they belong to the
so-called decoupled systems in which the mode of ionic conduction
relaxation is decoupled from the mode of structural relaxation.
[0141] Comparing the temperature dependence of the relaxation time
of the structure and conduction for inorganic glassy liquids with,
say, organic polymers shows that the former exhibit a decoupling
character capable of yielding higher single ion conduction in the
glassy state (FIG. 6). Single cation conduction is associated with
fewer side reactions and significantly wider electrochemical
stability windows, which can be up to 10 V.
[0142] Electronic properties, such as the band structure and
Density of States (DOS) were also calculated by means of DFT using
the GGA functionals and the Hyed-Scuseria-Erznerhof (HSE06)
functionals. In FIG. 7a, electronic band structure calculations
using GGA are shown as well as the correspondent band gap of 4.74
eV. FIG. 7b shows a HSE06 calculation and its correspondent band
gap, E.sub.g, value of 6.44 eV, which indicates a wide range of
electrochemical stability for the crystalline material. (The band
gap calculated using HSE06 hybrid functional seems to agree more
with experiments than the one calculated using GGA functional as
generally expected. FIG. 7c shows voltammetry graphs correspondent
to four experiments in which it can be observed that no substantial
oxidation of Li.sub.3ClO or Li.sub.3-2*0.005Ba.sub.0.005ClO at
130.degree. C. can be detected up to 8 V, which covers all the
negative-positive electrode-pair voltage windows for Li batteries.
The electrical conductivity was obtained from these voltammetry
cycles using the HebbWagner (H-W) method. In a polarization
measurement, under steady state conditions, in a Li/Li.sub.3ClO/Cu
cell with a ion blocking electrode such as Cu, a
.differential.I/.differential.V=-A.sigma.e/d where I is the
electrical current, V is the applied voltage (E in FIG. 7c), A the
cross-sectional area of the electrolyte (with j=I/A), d the
thickness of the electrolyte and .sigma.e its electronic
conductivity. The derivative .differential.I/.differential.V yields
de electronic conductivity in the electrolyte near the end adjacent
to the blocking electrode.
[0143] For Li.sub.3ClO at 130.degree. C. in the 1.4-2.5 V interval,
.sigma..sub.e=9.2.times.10-9 Scm.sup.-1, and in the interval
2.55-2.82 V, .sigma..sub.e=1.18.times.10-7 Scm.sup.-1. For
Li.sub.3-2*0.005Ba.sub.0.005ClO at 130.degree. C. for the first
cycle and over the interval 4.1-5.97 V,
.sigma..sub.e=6.77.times.10.sup.-8 Scm.sup.-1. For the second
cycle, and in the range 2.07-5.37 V,
.sigma..sub.e=1.05.times.10.sup.-8 Scm.sup.-1. The latter yields a
transport number,
t.sub.i=.sigma..sub.i/(.sigma..sub.i+.sigma..sub.e), near unity as
required for good quality solid electrolytes; .sigma..sub.i is the
ionic conductivity.
[0144] From the experimental study and DFT analysis, it was
observed that the ionic radius of the doping atom plays an
important role in the liquid/solid-like transition; namely, the
larger the doping ion radius the lower the glass transition
temperature as it is shown in FIG. 8. This effect arises due to the
disorder that the impurity introduces in the crystal structure,
especially the part related to the enthalpy. Consequently, very
high ionic conductivities can be obtained at relatively low
temperatures, e.g. 25.degree. C. or lower, in high ionic radius
doped glassy samples.
[0145] FIG. 9 shows the ionic conductivities for solid-like and
supercooled liquid samples of plain and doped electrolytes. In FIG.
9a, not only can the glass transitions be observed, but also the
ionic conductivity hysteresis resulting from heating the followed
by cooling.
[0146] A peak immediately before the ergodicity breaking transition
is observed as well. Ionic conductivity dispersion, probably due to
decoupling of diffusivity from viscosity, is observed in the
non-Arrhenius regime in FIGS. 9a and 9b. For a material with ionic
conductivity, a, that can be measured above and below T.sub.g, the
extrapolated data for the .sigma.T term in the two domains should
give identical values when the temperature, T, approaches infinity.
This finding is verified in the current work and can be observed in
FIGS. 10A-10B.
[0147] Li.sub.3ClO behaves as a solid-like glass (following
Arrhenius law) below T.sub.g; above T.sub.g it becomes a
supercooled liquid showing a non-Arrhenius behaviour. It was
observed a similar kind of behaviour for the doped material,
although this behaviour depends on the history of the material as
well (as it may be observed from the comparisons between the
2.sup.nd and 4.sup.th cycles in FIG. 9b for
Li.sub.3-2*0.005Ba.sub.0.005ClO. Moreover, doping is not necessary
to obtain a glass, but it is helpful to get it at lower
temperatures.
[0148] A Li.sub.3-2*0.005Ba.sub.0.005ClO sample that slowly cooled
down after the 3rd heating/cooling cycle submitted to EIS
measurements on heating shows unusually high ionic conductivity at
25.degree. C. as expected and as it is shown on FIG. 9b (+
symbols). In FIG. 11 the pseudo-Arrhenius curve for the latter
sample in the 4.sup.th cycle can be observed. Although linear
behaviour it is not expected, at least above T.sub.g, activation
energies as low as 0.06 eV can be observed in the temperature range
of 35.degree. C. to 74.degree. C. The glass transition can be
observed in FIG. 9b (x symbols) and in FIG. 11, although it is much
smoother than in previous cycles, probably indicating higher
similitude between the supercooled liquid and the solid-like
material highlighting that the glass dynamics depends very highly
of the cooling rate, among other factors.
[0149] Nonetheless, for lithium batteries, the glassy phase,
Li.sub.3-2*xM.sub.xHalO, offers higher ionic conductivity as it is
shown in FIG. 9b and superior chemical stability compared with
those materials, as shown in FIG. 7. Furthermore, unlike Ti and Ge
containing materials, Li.sub.3-2*xM.sub.xHalO does not react with
lithium-metal and offers a wider window of electrochemical
stability.
[0150] Moreover, from the air, the only element that should be
avoided--at least after synthesizing a highly conductive
glass--should be water vapour, which makes our electrolyte an
excellent candidate to be used in lithium-air batteries with
lithium-metal anode.
[0151] Doping with Ba.sup.2+ enhances this effect even further
since larger doping ion radius in this case results in higher
anisotropy of the lattice, and this seems to be in favour of higher
ionic conductivity. However, such an enhancement is limited by
other mechanisms such as the hopping ion trapping in the vicinity
of the doping ion; which is less likely to occur in
Li.sub.3-2*0.005Ba.sub.0.005Cl.sub.0.5I.sub.0.5O since the presence
of I.sup.- in the centre of the cube will expand the lattice, as
described to occur in Li.sub.3Cl.sub.0.5Br.sub.0.5O. FIG. 13 shows
an optimal composition (x) for Li.sub.3-2xMg.sub.xClO and
Li.sub.3-2xCa.sub.xClO.
[0152] A symmetric Li/Li.sub.3-2*0.005Ca.sub.0.005ClO/Li cell was
configured to demonstrate the cyclability and long-term
compatibility of Li.sub.3-2*0.005Ca.sub.0.005ClO with metallic
lithium. FIGS. 14a and b shows the voltage profile of the cell
cycled near room temperature, at 44.degree. C. At this temperature,
the cell presented a voltage of 46.0 mV at a current density of 0.1
mAcm.sup.-2. The direct current (dc) conductivity derived from the
symmetric cell was 0.27 mScm.sup.-1--obtained by
chronopotentiometry as shown in FIGS. 14a and 14b--which is
relatively close to the alternating-current (ac) conductivity of
0.85 mScm.sup.-1 obtained from electrochemical impedance
spectroscopy measurements extrapolated for 44.degree. C. Small
interfacial resistance between the lithium electrode and the solid
electrolyte was observed, further confirming that the
Li.sub.3-2*0.005Ca.sub.0.005ClO is completely compatible with
metallic lithium. The cell showed excellent cyclability at
44.degree. C. as illustrated in FIGS. 14a and 14b, not showing
signs of resistance increase during more than 460 h being much more
stable than many other electrolytes. These results prove the
ability of the glass to be used in Li batteries for electronic
device.
[0153] Moreover, the ionic conductivity increases until above 220
h, as shown in FIG. 14a, indicating that, even at 44.degree. C.,
the sample will become partially amorphous eventually due to
electrochemical cycling.
[0154] The solid electrolyte Li.sub.3ClO structure employs abundant
Li.sup.+ (high concentration of mobile charge carriers) and
non-toxic elements and is easily processed, using wet chemistry at
relatively low temperatures (240.degree. C. to 310.degree. C.),
which is another argument for inexpensive and
environmentally-friendly fabrication. Samples were annealed in a
pressure tight wafer of Au--in the cell setup--at up to 250.degree.
C. Seldom was it needed more than one cycle for the sample to
become partially vitreous and highly conductor. A glassy surface
and structure is visible to the eyesight after heating and cooling
in FIG. 6 and as denoted in FIG. 2. The sample can become
transparent on melting.
[0155] It is likely that the precursor hydroxides have an important
role in product formation promoting the contact between the reagent
compounds powders. These hydroxides are antiperovskite structures,
most of them following the general formula Li.sub.3-n(OH.sub.n)Hal.
Their ionic conductivities are considerably smaller than the
Li.sub.3-2*xM.sub.xHalO vitreous electrolytes. In fact, the
hydroxide recurrently formed was Li.sub.5(OH).sub.3Cl.sub.2 and/or
Li.sub.4(OH).sub.3Cl but it transforms into Li.sub.3-2*xM.sub.xHalO
after the first cycle as it can be inferred from Differential
Scanning calorimeter (DSC) measurements shown in FIG. 3.
[0156] The glass transition of Li.sub.3-2*0.005Mg.sub.0.005ClO in
DSC measurements seems to occur at T.sub.g.about.136.degree. C. as
observed in FIG. 3, which is in agreement with the ionic
conductivity results. Melting of Li.sub.3-2*0.005Mg.sub.0.005ClO
occurs at T.sub.m=269.degree. C. as the correspondent endothermic
peak demonstrates in FIG. 3. A glass transition, T.sub.g, is linked
via an empirical relationship with the melting temperature T.sub.m,
T.sub.g.about.(2/3)T.sub.m. We obtained,
T.sub.g/T.sub.m.about.0.75, by means of DSC, and T.sub.g/T.sub.m
0.71, by conductivity measurements, which is a good approximation
to the empirical factor of 0.67.
[0157] The phonon density of states was calculated using DFT and
compared with Incoherent Inelastic Neutron Spectroscopy (IINS)
spectra. The role of the lattice during hopping and diffusion was
established experimentally as a function of electrodes'
temperature, voltage and applied frequency. Most of the vibration
modes maintain a constant intensity with the applied frequency as
observed in FIG. 15. The effect is likely to be associated with the
crystalline behaviour since the experimental conditions were not
favourable to glass formation.
[0158] For 320-380 cm.sup.-1 wavenumbers (.about.1013 Hz), the
intensity varies with the applied frequency, being higher at f=100
Hz and lower at f=104 Hz.
[0159] This is most likely the jump frequency (.about.1013 Hz) as
the eigenvectors associated with phonons suggest, which implies
that at higher frequencies more ions have jumped already.
[0160] It is important to mention that the Li.sub.3ClO-crystalline
density is as low as 2.07 gcm.sup.-3
(Li.sub.3-2*0.005Ca0.005ClO-crystalline is 2.09 gcm.sup.-3 and
Li.sub.3-2*0.005Ba.sub.0.005ClO-crystalline is 2.28 gcm.sup.-3). At
200.degree. C. Li.sub.3ClO density is 1.96 gcm.sup.-3. Liquid
electrolytes in lithium-ion batteries consist of lithium salts,
such as LiPF.sub.6 (1.50 gcm.sup.-3) or LiClO.sub.4 (2.42
gcm.sup.-3) in an organic solvent, such as ethylene carbonate (1.3
gcm.sup.-3) or dimethyl carbonate (1.07 gcm.sup.-3).
[0161] Although the cell will not be lighter just by replacing the
liquid by equal volume of the solid electrolyte and even if
moisture has to be avoided likewise; merely a thin film of solid
electrolyte is needed with no separator or sophisticated packaging
resulting in a lighter battery.
[0162] The present results show that the new Li.sub.3-2xM.sub.xHalO
glassy electrolyte or Na.sub.3-2xM.sub.xHalO glassy electrolyte (in
which M is a higher valent cation like Ca.sup.2+ Sr.sup.2+,
Mg.sup.+2 or Ba.sup.2+, and Hal is a halide like Cl.sup.-, or a
mixture of halide ions like F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-)
has an extremely high ionic conductivity that is well above the
lithium-ion conductivity of any other superionic conductor at
T=25.degree. C. (25 mScm.sup.-1).
[0163] It is the first time that a glass formed from an
antiperovskite crystal is presented.
[0164] In addition, this new electrolyte is chemically very stable
with respect to Li-metal (more than 260 cycles), proving that it
can be used in consumer electronic devices, and it is a light, good
electronic insulator, non-flammable and contains no pollutants.
Moreover, this novel electrolyte is easy to synthesize, thermally
stable and electrochemical stable at least up to 8 V. It is thus
promising for applications requiring batteries with high powers and
energy densities, especially, for hybrid electric and pure electric
vehicles.
[0165] The present invention is not, obviously, in any way
restricted to the herein described embodiments and a person with
average knowledge in the area can predict many possibilities of
modification of the same invention and substitutions of technical
characteristics by others equivalent, depending on the requirements
of each situation, as defined in the appended claims.
[0166] The embodiments described above can be combined with each
other. The following claims further define the preferred
embodiments of the present invention.
* * * * *