U.S. patent application number 16/560270 was filed with the patent office on 2019-12-26 for sulfide and oxy-sulfide glass and glass-ceramic films for batteries incorporating metallic anodes.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Han NGUYEN, James R. SALVADOR, Thomas A. YERSAK.
Application Number | 20190393549 16/560270 |
Document ID | / |
Family ID | 63711304 |
Filed Date | 2019-12-26 |
United States Patent
Application |
20190393549 |
Kind Code |
A1 |
YERSAK; Thomas A. ; et
al. |
December 26, 2019 |
SULFIDE AND OXY-SULFIDE GLASS AND GLASS-CERAMIC FILMS FOR BATTERIES
INCORPORATING METALLIC ANODES
Abstract
A solid state electrolyte including an oxy-sulfide glass or
glass ceramic, solid state electrolyte layer having a thickness in
the range of ten micrometers to two hundred micrometers is provide.
The composition of the electrolyte layer is the reaction product of
a mixture initially including either a glass former including
sulfur or a glass co-former including sulfur, and a glass modifier
including Li.sub.2O or Na.sub.2O. The solid-state electrolyte layer
is further characterized as having a wholly amorphous
microstructure or as having small recrystallized regions separated
from each other in an amorphous matrix, the recrystallized regions
having a size of up to five micrometers. The solid-state
electrolyte layer includes mobile lithium ions or mobile sodium
ions associated with sulfur anions chemically anchored in the
microstructure.
Inventors: |
YERSAK; Thomas A.;
(Ferndale, MI) ; SALVADOR; James R.; (Royal Oak,
MI) ; NGUYEN; Han; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
63711304 |
Appl. No.: |
16/560270 |
Filed: |
September 4, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15480505 |
Apr 6, 2017 |
|
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16560270 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/0562 20130101;
H01M 2300/0071 20130101; C03B 17/062 20130101; C03C 4/18 20130101;
C03B 32/02 20130101; H01M 2300/0068 20130101; C03B 19/09 20130101;
H01M 10/052 20130101; C03B 25/025 20130101; C03C 3/321 20130101;
C03B 2201/86 20130101; C03C 10/00 20130101 |
International
Class: |
H01M 10/0562 20060101
H01M010/0562; C03C 3/32 20060101 C03C003/32; C03C 10/00 20060101
C03C010/00; C03C 4/18 20060101 C03C004/18; C03B 25/02 20060101
C03B025/02 |
Claims
1. A solid state electrolyte comprising a sulfide or an oxy-sulfide
glass or glass ceramic, solid state electrolyte layer having a
thickness in the range of 10 .mu.m to 200 .mu.m, the composition of
the electrolyte layer being the reaction product of a mixture
initially comprising: a glass former comprising a glass-forming
sulfide or oxide; and a glass modifier comprising an alkali
metal-containing sulfide or oxide, wherein at least one of the
glass former and glass modifier comprise a sulfide, and wherein the
solid-state electrolyte layer is further characterized as having a
wholly amorphous microstructure or as having small recrystallized
regions separated from each other in an amorphous matrix, the
recrystallized regions having a size of up to five micrometers, the
solid-state electrolyte layer comprising mobile lithium ions or
mobile sodium ions associated with sulfur anions chemically
anchored in the microstructure.
2. The solid state electrolyte according to claim 1, wherein the
glass modifier comprises Li.sub.2O.
3. The solid state electrolyte according to claim 1, comprising the
glass former comprising sulfur, the glass former being selected
from the group consisting of P.sub.2S.sub.5, SiS.sub.2, GeS.sub.2,
SnS.sub.2, As.sub.2S.sub.3, and combinations thereof.
4. The solid state electrolyte according to claim 3, wherein the
glass modifier further comprises Li.sub.2S.
5. The solid state electrolyte according to claim 3, wherein the
mixture further comprises: a glass co-former selected from the
group consisting of P.sub.2O.sub.5, B.sub.2O.sub.3, SiO.sub.2,
Al.sub.2O.sub.3, and combinations thereof.
6. The solid state electrolyte according to claim 1, comprising a
glass co-former comprising sulfur, the glass co-former being
selected from the group consisting of P.sub.2S.sub.5, SiS.sub.2,
GeS.sub.2, SnS.sub.2, As.sub.2S.sub.3, and combinations thereof,
the mixture further comprising a glass former selected from the
group consisting of P.sub.2O.sub.5, B.sub.2O.sub.3, SiO.sub.2,
Al.sub.2O.sub.3, and combinations thereof.
7. The solid state electrolyte according to claim 1, wherein the
glass modifier comprises Na.sub.2O.
8. A battery cell comprising the solid state electrolyte according
to claim 1.
9. A solid state electrolyte comprising the reaction product of a
mixture comprising: a glass former comprising sulfur; and a glass
modifier comprising Li.sub.2O or Na.sub.2O, wherein the solid state
electrolyte has a non-crystalline microstructure having a glass
transition temperature.
10. The solid state electrolyte according to claim 9, wherein the
solid state electrolyte is in a layer having a thickness of 10
.mu.m to 200 .mu.m.
11. The solid state electrolyte according to claim 9, wherein the
glass former comprises P.sub.2S.sub.5, SiS.sub.2, GeS.sub.2,
SnS.sub.2, As.sub.2S.sub.3, or a combination thereof.
12. The solid state electrolyte according to claim 11, wherein the
mixture further comprises a glass co-former selected from the group
consisting of P.sub.2O.sub.5, B.sub.2O.sub.3, SiO.sub.2,
Al.sub.2O.sub.3, and combinations thereof.
13. The solid state electrolyte according to claim 9, wherein the
mixture further comprises: a glass dopant.
14. The solid state electrolyte according to claim 9, wherein the
solid state electrolyte has a porosity of up to 15%.
15. The solid state electrolyte according to claim 9, wherein the
solid state electrolyte is positioned between a cathode and an
anode.
16. A solid state electrolyte comprising the reaction product of a
mixture comprising: a glass former comprising oxygen; a glass
co-former comprising sulfur; and a glass modifier comprising
Li.sub.2O or Na.sub.2O, wherein the solid state electrolyte has a
non-crystalline microstructure having a glass transition
temperature.
17. The solid state electrolyte according to claim 16, wherein the
glass former comprises P.sub.2O.sub.5, B.sub.2O.sub.3, SiO.sub.2,
Al.sub.2O.sub.3, or a combination thereof.
18. The solid state electrolyte according to claim 17, wherein the
mixture further comprises a glass co-former selected from the group
consisting of P.sub.2S.sub.5, SiS.sub.2, GeS.sub.2, SnS.sub.2,
As.sub.2S.sub.3, and combinations thereof.
19. The solid state electrolyte according to claim 16, further
comprising a glass dopant.
20. The solid state electrolyte according to claim 16, wherein the
solid state electrolyte is a layer that is interposed between an
anode and a cathode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/480,505 filed on Apr. 6, 2017. The entire disclosure of
the above application is incorporated herein by reference.
TECHNICAL FIELD
[0002] Methods are provided for preparing sulfide and oxy-sulfide
glass and glass-ceramic solid-state electrolytes for batteries
having a metallic anode substantially consisting of lithium or
sodium. Dense sulfur-containing glasses are prepared which enable
the formation of energy dense metal anode batteries while
preventing penetration of metallic dendrites into the solid-state
electrolyte/separator.
INTRODUCTION
[0003] Lithium batteries are finding increasing use in automotive
vehicles and many other consumer products and sodium batteries are
receiving favorable consideration for such applications. Exemplary
batteries may employ a lithium metal anode in combination with a
suitable liquid or solid electrolyte and a compatible active
cathode material. For example, lithium batteries utilizing lithium
metal anodes could enable the formation of energy-dense
lithium-lithium manganese oxide electrochemical cells,
lithium-sulfur cells, and lithium-air cells.
[0004] In many lithium-metal batteries and proposed sodium-metal
batteries it would be desirable to use a solid-state electrolyte
(SSE) which could enable the transport of metal ions between the
anode layer and cathode layer while also physically separating
these electrodes. Some glass compositions which act as both an
electrolyte and a separator have been proposed for use with lithium
electrodes. Such glass compositions serve both to transport lithium
ions and also form a physical barrier between the lithium anode and
the rest of the cell components. Sulfide glasses have fair to
excellent lithium ion conductivity but have been difficult to form
as electrolyte/separator structures and have been vulnerable to
cell failure due to penetration by lithium dendrites formed on and
from the lithium anode during repeated cycling of the battery
cell(s).
[0005] There remains a need for methods of forming thin
sulfide-based or oxy-sulfide electrolyte films suitable for
prolonged use in lithium metal electrochemical cells. The
solid-state electrolyte must contribute to both suitable energy
capacity of the cell and to mechanically prevent dendritic lithium
shorting of the cell.
SUMMARY
[0006] Sulfide and oxy-sulfide glasses may be formed by combining
three classes of materials: i) one or more glass formers,
including, for example, P.sub.2S.sub.5, SiS.sub.2, GeS.sub.2,
SnS.sub.2, P.sub.2O.sub.5, B.sub.2O.sub.3, SiO.sub.2,
Al.sub.2O.sub.3; ii) one or more glass modifiers, including, for
example, Li.sub.2S, Na.sub.2S, Li.sub.2O, Na.sub.2O, and; iii) one
or more dopants, for improving glass formability and/or stability,
including, for example, LiI, Li.sub.3PO.sub.4, Li.sub.4SiO.sub.4.
It will be understood that the compositions associated with
particular material classes are exemplary and neither limiting nor
exclusionary.
[0007] For a sulfide glass both the glass former and the glass
modifier will contain sulfur (e.g. Li.sub.2S--P.sub.2S.sub.5). An
oxy-sulfide glass may combine an oxide-forming system with a
sulfide co-former (for example, and without limitation
Li.sub.2O--P.sub.2O.sub.5--P.sub.2S.sub.5) or a sulfide-forming
system with an oxide co-former (for example, and without limitation
Li.sub.2S--P.sub.2S.sub.5--P.sub.2O.sub.5).
[0008] In the following description, at least one component must
contain sulfur to support the intended electrolyte activity.
Particularly, at least one of the glass formers must contain sulfur
to be a sulfide or oxy-sulfide glass but the glass modifier, as
noted in the above illustrative example may contain either sulfur
or oxygen (in the above non-limiting examples, Li.sub.2S,
Li.sub.2O)
[0009] These constituent precursors react to form a unique
composition that enables the formation of mobile alkali metal
cations. For convenience, any compositions detailed in subsequent
sections will be described in terms of the atomic proportions of
their constituents (for example. 70Li.sub.2S-30P.sub.2S.sub.5).
These constituents, when processed, will however form a glass whose
empirical composition is Li.sub.7P.sub.3S.sub.11 which possesses a
structure with mobile lithium ions and anchored phosphorus sulfide
tetrahedral anion structural units (PS.sub.4.sup.3-).
[0010] The resulting sulfur-containing glass compositions
achievable with suitable combinations of these constituents
include, without limitation, lithium phosphorous (oxy)sulfide,
lithium boron (oxy)sulfide, lithium boron phosphorous oxy-sulfide,
lithium silicon (oxy)sulfide, lithium germanium (oxy)sulfide,
lithium arsenic (oxy)sulfide, lithium selenium (oxy)sulfide, and
lithium aluminum (oxy)sulfide, individually or in combination. The
term (oxy)sulfide represents that both an oxygen-free sulfide
composition or an oxygen-containing oxy-sulfide may be
prepared.
[0011] An example of a suitable composition is
xLi.sub.2S.(100-x)P.sub.2S.sub.5 where x has a value in the range
of 50-90. The composition is formed by preparing a melt of
dilithium sulfide and phosphorus pentasulfide at a temperature of
about 700.degree. C. The glass former and glass modifier interact
to form a glassy composition containing mobile lithium ions. In an
aspect, applicable to cells in which sodium ions are the conductive
entities, disodium sulfide may appropriately be substituted for
dilithium sulfide to form a sodium ion-conducting solid
electrolyte. Such a sodium ion-conducting electrolyte may be
prepared by following the steps described below for a lithium
ion-conducting electrolyte with appropriate substitution of
sodium-containing constituents for the recited lithium-containing
constituents.
[0012] In an embodiment of the invention, an initial
lithium-containing sulfide glass composition is in the form of
small particles (a powder) having amorphous glassy microstructures.
The particles are applied to a quartz substrate layer (or a like
material resistant to moderate temperatures of less than about
350.degree. C. and non-reactive with the glass particles) in a thin
layer of generally uniform thickness and over an area predetermined
for finished formation of the glass electrode/separator layers. The
amorphous glass particles are then heated on, and consolidated
against, the substrate to form a fully integral consolidated glass
layer, 10 micrometers to 200 micrometers thick, still having a
non-crystalline microstructure. The supported thin glass layer is
then annealed to reduce any localized stresses induced in the
consolidated microstructure and, if desired, to introduce small
isolated crystal phases in the non-crystalline matrix.
[0013] The glass layer is carefully removed from the substrate and
processed as necessary into individual lithium-conducting
electrode/separator layers for assembly into lithium-based
batteries utilizing a lithium metal anode layer. Generally, the
as-fabricated glass layer thickness will be pre-determined to be
suitable for its intended battery use. But because it is intended
that the width of the substrate will be greater than the dimension
required of a battery electrolyte, and that, preferably, the
fabrication process will be continuous, the fabricated thin glass
layer sheet may need to be cut, sliced or otherwise apportioned
into suitably-sized electrolyte portions.
[0014] The intention is to produce a thin, transparent to
translucent, glass electrode/separator layer that can function
cooperatively with a metallic lithium or sodium anode layer and
efficiently accommodate the transport of lithium or sodium ions
between the anode layer and an engaging, or nearby, cathode layer.
Further, the thin glass layer remains resistant to penetration of
metallic dendrites which may form on the anode during repeated
cycling of the battery cell.
[0015] In a second embodiment, a melt of the interacted
constituents is applied to a pre-heated, smooth flat surface of a
smooth substrate. The substrate is selected to both be non-reactive
by the melt and wettable by the melt so that the melt may freely
spread across the substrate surface. A suitable substrate is
quartz. The surface area of the substrate and the quantity of
applied melt cooperate to form a molten layer of predetermined
thickness of between 10 and 200 micrometers and corresponding to
the intended thickness of the conductor/separator. The molten layer
is then quickly cooled at a rate sufficient to render an amorphous
solid as a thin glassy film or layer.
[0016] Following an annealing treatment to remove residual stresses
and, optionally, partially crystallize the layer, the layer may be
removed from its supporting substrate. Again, it is anticipated
that the as-fabricated layer will be cut or otherwise sectioned
into appropriately-sized portions suited for application as
electrolytes in a battery or cell.
[0017] In an aspect, this melt-derived glass layer may be
pulverized to form the glassy powder precursor for the powder-based
process described in the first embodiment. Such pulverization may
be practiced after the melt has been solidified or after the
solidified melt has been annealed.
[0018] Other features of the disclosure will be apparent from the
following detailed descriptions and illustrations which make
reference to the drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a process for forming a compacted
lithium-containing sulfide or oxy-sulfide glass film from sulfide
or oxy-sulfide powder. The process may be conducted as a continuous
process.
[0020] FIGS. 2A-C schematically illustrate the microstructural
evolution experienced by a glassy powder compact during
consolidation.
[0021] FIG. 3 illustrates a continuous or semi-continuous process
for forming a thin layer of sulfide and oxy-sulfide glass film from
a lithium-containing sulfide or oxy-sulfide melt.
DETAILED DESCRIPTION
[0022] Sulfide-based or oxy-sulfide-based glasses containing
lithium ions offer promise as solid electrolytes in electrochemical
cells which employ an alkali metal, particularly lithium or sodium,
as an anode. For convenience, the following description will detail
methods for forming a thin layer of a lithium ion-conducting solid
electrolyte for use in cells comprising a metallic lithium anode,
but similar methods may be practiced to prepare sodium
ion-conducting electrolytes by substituting sodium-based
compositions for the corresponding lithium-based compositions.
[0023] Suitably thin films or sheets of these sulfide or
oxy-sulfide compositions may be interposed between the lithium
metal anode, possibly in conjunction with a liquid,
lithium-conducting electrolyte, and an opposing cathode and serve
to separate these opposing electrodes and prevent direct electrical
interconnection of anode and cathode in such cells.
[0024] The separator function of the film is as important as its
electrolytic properties since a lithium metal anode, initially of
uniform thickness, develops local variation in thickness with
successive discharge-charge cycles. These local thickness
variations manifest themselves as dendrites, elongated, spear-like
features which protrude from the bulk lithium metal layer and, if
suitably extensive may bridge the gap between anode and cathode to
produce a short circuit. Thus, the thin glass film should be
suitably robust to mechanically obstruct such dendrites. In
addition, the film should be resistant to chemical or metallurgical
infiltration of lithium to prevent formation of a lithium metal
`bridge` through the electrolyte/separator which would likewise
enable direct electrical interconnection of anode and cathode.
Resistance to such chemical and metallurgical infiltration is
conferred by the absence of grain boundaries in amorphous
structures.
[0025] A wide range of sulfide and oxy-sulfide compositions may be
employed, each incorporating a glass former and a
lithium-containing glass modifier Li.sub.4SiO.sub.4,
Li.sub.3PO.sub.4, lithium halides and their sodium-based
counterparts are dopants which may be used to improve glass
formability and/or stability as well as enhancing ionic
conductivity. Suitable sulfide-based glass formers include
P.sub.2S.sub.5, GeS.sub.2, SiS.sub.2, As.sub.2S.sub.3 and SnS.sub.2
which may be combined with Li.sub.2S etc. As stated earlier, for a
sulfide glass both the glass former and the glass modifier will
contain sulfur (e.g. Li.sub.2S--P.sub.2S.sub.5). For an oxy-sulfide
glass it will either be an oxide-forming system with a sulfide
co-former (e.g. Li.sub.2O--P.sub.2O.sub.5--P.sub.2S.sub.5) or a
sulfide-forming system with an oxide co-former (e.g.
Li.sub.2S--P.sub.2S.sub.5--P.sub.2O.sub.5).
[0026] An exemplary, but non-limiting glass-forming system may be
based on P.sub.2S.sub.5 (diphosphorus pentasulfide) as the glass
former and Li.sub.2S (dilithium sulfide) as the glass modifier. Of
course, Li.sub.2S also serves to contribute the Li.sup.+ lithium
ions to the resulting glass and impart the desired lithium ion
conductivity to the glass. A wide range of proportions of these
constituents may yield suitable glasses. One exemplary, but
non-limiting, composition is 70Li.sub.2S.30P.sub.2S.sub.5.
[0027] As noted, a major consequence of the relative proportions of
the glass former and the lithium-containing glass modifier is to
vary the concentration of Li.sup.+ lithium ions in, and
consequently the conductivity of, the resulting glass. In addition,
the viscosity of the resulting glass and fluidity of the glass melt
are also affected by the relative concentration of glass former and
modifier, or equivalently, by the glass composition with processing
consequences which will be covered below.
[0028] Suitable exemplary methods for fabrication of thin glass
films from a glassy powder precursor are described below in
conjunction with FIGS. 1 and 3. FIG. 1 illustrates a process which
employs, as its starting material, previously-prepared glassy
powders with the composition of the intended thin glass film while
FIG. 3 illustrates a process which employs a melt of the intended
glass film composition. The process of FIG. 3 may also be used as a
high-throughput process for preparing `bulk` glassy layers which
may be pulverized to prepare powders, suitable for the process of
FIG. 1, of the glassy films. FIG. 2 illustrates the microstructural
evolution occurring during the powder process illustrated in FIG.
1.
[0029] FIG. 1 details a continuous process for preparing continuous
lengths of such thin glass films which would subsequently be cut or
otherwise fragmented into a plurality of discrete conductor sheets
suitably sized for the electro-chemical cell in which they are to
be incorporated. However, those of skill in the art will appreciate
that such a continuous process may readily be adapted to be
conducted as a batch process, in which the individual steps may be
conducted independently of one another and/or asynchronously to
prepare a plurality of individual conductor sheets, not necessarily
pre-sized for the electrochemical cell. For example, the processing
steps may be performed at a series of individual stations with the
in-process conductor sheets transported from station-to-station by
pick-and-place automation, robots, conveyor belts or other suitable
equipment.
[0030] In an embodiment as shown at FIG. 1, the thin glassy films
are fabricated on a substrate, a portion 10 of which is shown.
Substrate portion 10 is carried on, and advances in, the direction
of arrow 30 by the action of rollers 12, 12'. Substrate portion 10
may be a portion of a continuous belt which, at roller 12' loops
under (not shown) substrate portion 10 and is carried in a
direction opposite that of arrow 30 from roller 12' to roller 12
until it loops upwardly (not shown) at roller 12 to again
participate in the process to be described. Alternatively,
substrate 10 may be a portion of a large diameter annular disc
which is supported and carried on radially oriented rollers 12
continually advancing in a single direction until a surface portion
of substrate 10 completes a full revolution and returns to its
starting point ready for re-use. It will be further appreciated
that, in operation of such a continuous device there may be need
for cleaning or surface treatment stations (not shown) to restore
the substrate surface to a suitable condition for re-use. These
features and characteristics are not illustrated and the following
description will focus primarily on the sequence of fabrication
steps occurring in fabrication zone 100 on substrate portion 10 as
substrate portion 10 traverses the fabrication zone.
[0031] Substrate portion 10, with a smooth surface 18, is advanced
by support rollers 12, 12' in the direction of arrow 30 so that it
is progressively carried into fabrication zone 100. As will be
described more fully below, the material of substrate portion 110
is subjected to a range of temperatures that generally do not
exceed 350.degree. C. Accordingly, a wide range of materials may be
considered for use as a substrate. Generally, the choice of
substrate material should be informed by the requirement that it
exhibit suitable structural strength at the maximum temperature of
interest, and that it be non-reactive with the sulfide/oxy-sulfide
glass powder. Exemplary materials include quartz, stainless steels,
and generally, metals and alloys with melting points of
1000.degree. C. or greater. In some applications, it may be
feasible to use a high temperature, possibly reinforced polymer
such as polytetrafluoroethylene (Teflon) or polyetheretherketone
(PEEK).
[0032] As substrate portion 10 advances, it passes below hopper 22
containing particles of solid glassy materials 40 and dispensing
nozzle 16, both of which cooperate to apply, by gravity, glass
powder 40, as a substantially uniformly thick powder layer 20, to
the surface 18 of substrate portion 10. Although a single hopper 22
and nozzle 16 are shown, it may be appropriate to employ multiple
dispensing nozzles 16, fed by a single or multiple hoppers 22 to
more uniformly apply powder layer 20 to the full width of substrate
portion 10. Those of skill in the art will appreciate that various
additional pieces of conventional equipment such as screw
conveyers, vibratory screens etc. (not shown) may be employed to
assure a uniform and continuous flow of such particulate
matter.
[0033] Similarly, to achieve a generally uniform distribution and
thickness of the powder particles on substrate portion 10 a device
such as a doctor blade (not shown) or a vibratory exciter (not
shown) may be used to more completely level the applied powder and
render a generally uniform powder layer 20 downstream of hopper 22.
Although not shown, it will be appreciated that powder may also be
applied as a paste containing a volatile solvent that may be
evaporated after deposition, by spray deposition, by electrostatic
deposition or any other suitable means known to those of skill in
the art.
[0034] Suitable solid glassy particles may be formed, for example
by ball milling a bulk, solid glassy material. Bulk glassy material
prepared by any suitable method including the process illustrated
in FIG. 3 which will be described later, or from batch processed
material. The powder preferably includes particles from a large
number of size ranges to enable more complete packing of the power
particles but the maximum particle size should be limited to no
more than 15% of the thickness of powder layer 20.
[0035] It is intended that powder layer 20 be heated and compacted
to form fully dense glassy layer 20'. Compaction may be effected by
passing powder layer 20 between opposed, heated rollers 42. In an
aspect, powder layer 20 may optionally be preheated in an oven or
furnace 34 (shown in ghost), or, rollers 42 may serve to both heat
and compact the particles. For simplicity, only one set of rollers
42 is illustrated but a series of such heated rollers, each
applying a predetermined degree of compaction until full or
near-full density is achieved, may be employed. Of course, full
density is most readily achieved when the packing fraction of
powder layer 20 is highest, which, as noted, is promoted by
accepting a wide range of a particle sizes, including fines, in
powder 40. The term full density is intended to encompass a
compacted body containing up to 15% residual porosity.
[0036] Suitable time-temperature-pressure combinations to achieve
full density are related to the viscosity of the glass which must
be sufficiently low that the glassy particles will flow under
pressure, rather than fracturing. Hence, the glass be maintained
above its T.sub.g, its glass transition temperature. Typically, the
viscosity of liquids, and supercooled amorphous alloys, will
decrease with increasing temperature suggesting that increased
temperature will be beneficial. However, to maintain the glassy
layer in a compactable but fully amorphous state, the compaction
temperature may not exceed T.sub.c, the crystallization temperature
of the selected glass composition. Also, for production efficiency,
the compaction time, or the time spent by powder layer 20 between
the gap of rolls 42 cannot be excessive. Suitably the compaction
temperature should be selected to be about 40.degree. C. above
T.sub.g but below T.sub.c both of which temperatures will vary with
glass composition. Glasses compacted in this temperature range may
be compacted in about 5-3600 seconds under a pressure of 0.1 to 360
MPa. Some suitable glass compositions include
xLi.sub.2S.(100-x-y)P.sub.2S.sub.5.yP.sub.2O.sub.5 (x=50-90 and
y=0-20) and which exhibit a T.sub.g of between 210.degree. C. and
220.degree. C. and a T.sub.c of between 220.degree. C. and
280.degree. C.
[0037] After compaction, compacted glassy layer 20' will exhibit
internal stress(es) which, if not relieved may promote spontaneous
fracture and fragmentation of the glassy sheet. To relieve the
resulting internal stress, compacted glassy layer 20' passes
through annealing furnace 28. The annealing time and temperature
may be selected to relieve internal stresses while retaining either
an amorphous microstructure or a partially crystallized
microstructure. When a fully amorphous or glassy layer is desired,
the annealing temperature should be maintained above T.sub.g but
below T.sub.c to render a glassy layer 20'' substantially free of
internal stresses. As long as the temperature is less than T.sub.c
the annealing time may be selected consistent with the annealing
temperature, with shorter annealing times being appropriate for
higher annealing temperatures and longer annealing times being
required for lower annealing temperature, as is well known to those
of skill in the art.
[0038] In some aspects, it may be preferred that the microstructure
in the glass layer 20'' be partially crystalline. A partially
crystalline microstructure comprising isolated, discontinuous
nanometer-sized or micrometer-sized crystalline regions surrounded
by amorphous material has been demonstrated to exhibit higher ionic
conductivity and better resistance to penetration than a
like-dimensioned fully amorphous body. The requirement that the
crystalline phase be discontinuous limits the maximum fraction, by
volume, of crystalline phase to be less than 60% with volumes as
low as 1% being feasibly achieved. In a preferred aspect, the
volume fraction of crystalline material should range from 20% to
40%. The development of such a microstructure requires that the
annealing temperature be increased to above T.sub.c for at least a
brief period.
[0039] The development of crystalline regions will occur by a
nucleation and growth process in which a plurality of
nanometer-sized or micrometer-sized crystalline regions develop in
the amorphous material and slowly grow until the entirety of the
amorphous layer is transformed to a crystalline phase. It is
preferred to develop the desired microstructure of nanometer-sized
or micrometer-sized islands of crystalline phase encapsulated in a
continuous amorphous matrix. Such a structure may be developed by
selecting an annealing temperature which is above, but close to
T.sub.c, to limit the number of nuclei and hence increase their
separation. An annealing temperature close to T.sub.c will also
serve to reduce diffusion (relative to a higher annealing
temperature) and so slow the growth of the crystalline regions
enabling more flexibility in controlling of the process.
Optionally, a multi(temperature)-zone furnace 28 may be employed to
at least partially decouple the nucleation process from the growth
process, for example by heating to above T.sub.c before decreasing
the temperature below T.sub.c point for continued annealing to
promote more controllable growth of the crystalline regions.
[0040] The mechanical and thermal cycles to which the glass powder
20 is subjected are shown schematically at FIGS. 2A-C. At FIG. 2A,
a portion of powder layer 20 is shown and comprises a plurality of
layered glassy particles 220 of varying sizes separated by
interparticle voids 250. The particles are maintained in close
proximity by application of pressure P. On heating to a temperature
greater than T.sub.g, the glassy material will begin to exhibit
macroscopic flow in response to pressure P. Also, some atom
transport will occur through diffusion. The combination of
macroscopic flow and diffusion, under the urging of applied
pressure P will compact and consolidate the particles, eliminating
many of the interparticle voids and consolidating the particles
into amorphous or glassy body 320 incorporating remnant void 250'
shown at FIG. 2B. For ease of comparing FIGS. 2A and 2B, the
remnant internal particle boundaries are shown in as dashed lines
in the interior of body 320, but, absent some surface contamination
or other marker initially present on the particle surface the
amorphous boundary regions will be indistinguishable from the
amorphous particle interiors and so will not be identifiable.
[0041] FIG. 2C is illustrative of the two microstructures which may
be developed during annealing. Note that in both cases remnant void
250' remaining after compaction is retained in the resulting
microstructure. If the annealing temperature T.sub.A is chosen to
be less than T.sub.c only stress relief will occur and body 320,
although substantially stress-free will be, microstructurally,
identical to body 320 at the end of the compaction step as shown at
FIG. 2B. If, however, the annealing temperature T.sub.A is chosen
to be greater than T.sub.c then not only will the stresses be
relieved but small, irregularly-shaped, but generally equi-axed
crystalline regions 340 will develop in body 320'. The size of
these, generally equi-axed crystalline regions may be characterized
by a characteristic dimension which may be the diameter of a sphere
sufficient to circumscribe the crystalline region.
[0042] On exiting the annealing furnace 28 the layer 20'' slowly
cools, by radiation as indicated at 32 in FIG. 1, to room
temperature or about 20-25.degree. C. At this stage, the glassy
layer may be removed from the substrate and processed appropriately
to prepare it for use in an electrochemical cell. Since, the
required processing temperatures are generally low to moderate, the
smooth substrate surface 18 is not expected to react, bond to or
otherwise engage with the glass layer. Thus, the glassy layer 20''
may be readily separated from substrate portion surface 18 without
introducing any deformation or damage to either the glassy layer
20'' or of substrate portion surface 18. Thus, substrate portion
surface 18 will, possibly absent some minor cleaning etc., be
immediately available for re-use to enable the continued production
of the continuous layer glassy layer 20''.
[0043] It will be appreciated that the specific features of the
above-described device are illustrative and not limiting. For
example, the use of heated rollers to compact the powder and the
relationships of the heating devices to the substrate portion is a
consequence of the desire to operate the process continuously.
However, the process may be conducted in batch mode where, for
example, a suitable quantity of, optionally pre-heated, powder
could be confined between the (optionally heated) platens of a
press or other pressure-inducing device and heated until
consolidated, then transferred to a local or remote oven and
annealed to produce a discrete glass sheet generally conforming in
size to the press platen dimensions. Alternatively, the entire
press or like apparatus could be contained within an oven and the
temperature adjusted appropriately for the particular process step.
These and other alternative implementations of the above-described
process steps are comprehended in the above disclosure.
[0044] The above process requires an initial lithium-containing (or
sodium-containing) (oxy)sulfide glass precursor composition powder
with an amorphous glassy microstructure.
[0045] Such a powder may be formed in several ways. One method is
to combine suitable proportions of a glass-former constituent and a
lithium-containing (or sodium-containing) glass-modifier
constituent and heat them to form a melt. The melt may then be
rapidly quenched, for example by melt spinning to form a ribbon or
splat cooled to prepare flattened particles of `bulk` amorphous
solid.
[0046] The melting and quenching may also be conducted in a closed
vessel or ampoule. This minimizes issues related to the reactivity
and volatility of melts of these compositions. However, this
approach limits the quench rate that may be achieved and limits the
volume of material which may be rendered amorphous.
[0047] Ball milling may also serve to promote chemical interaction
between the constituents nominally at room temperature obviating
concerns over reaction with the atmosphere or selective
volatilization. This procedure, generally known as mechanochemical
milling, requires only bringing together the constituent
glass-former and glass-modifier, which may be dispersed in an inert
aprotic carrier liquid such as ethers, alkanes, possibly ketones or
ester based liquids. More preferably, however, the precursors are
dry milled in the absence of solvent. in a ball mill and continuing
to mill these constituents until the reaction goes to completion
and an appropriate particle size distribution is achieved.
[0048] All of the above approaches however are small throughput
processes, and, even if several such processes were conducted in
parallel, ill-suited for providing a continuous stream of glassy
powder precursor to feed the continuous powder-based process
described above. An approach to preparing, in a continuous or
semi-continuous process a significant quantity of an amorphous
glassy layer is shown in FIG. 3.
[0049] The process of FIG. 3 will be described as it may be
practiced to form an ionic conductor layer, but, as will become
apparent, minimal modification is required to render the process
suitable for the preparation of feedstock suited for the practice
of the above-described powder process.
[0050] Analogously to the powder compaction process shown at FIG.
1, the process shown at FIG. 3 illustrates a fabrication zone 200
though which passes a substrate portion 110 transported on rollers
112, 112' in a direction indicated by arrow 130. As before,
substrate portion 110 may be a portion of a continuous belt which,
at roller 112' loops under (not shown) the section shown and is
carried in the direction from roller 112' to roller 112 until it
loops upwardly (not shown) at roller 112 to again participate in
the process. Alternatively, substrate 110 may be a portion of a
large diameter annular disc which is supported and carried on
radially oriented rollers 112 continually advancing in a single
direction until a surface portion of substrate 110 completes a full
revolution and returns to its starting point ready for re-use. It
will be further appreciated that, in operation of such a continuous
device there may be need for cleaning or surface treatment stations
(not shown) to restore the substrate surface to a suitable
condition for re-use.
[0051] Substrate portion 110 may be fabricated from a material
which may be wetted by a glass melt without reacting or otherwise
interacting with the melt. Since the melting point of typical glass
compositions is about 700.degree. C., only a limited number of
suitable substrate materials may be used. Preferably substrate
surface 118 is fabricated of quartz. If substrate portion 110 is a
section of a belt as described above it cannot be fabricated of a
continuous sheet of brittle quartz but must instead be fabricated
of a series of pivotably attached plates arranged to flex and bend
in a manner generally analogous to a tank tread or caterpillar
track. In this arrangement, it may be more convenient to use metal
`plates` to form the `tread` or `track` with each `tread` or
`track` carrying an individual, smooth-bottomed, flat-bottomed,
shallow quartz dish rather than trying to achieve a smooth
continuous quartz surface.
[0052] Substrate portion 110, on entering fabrication zone 200
first enters a heating zone 114 which may comprise a furnace or
other heating device adapted to heat the substrate to temperature
at or slightly above the melt temperature of the glass melt.
Typically, this may be between 650.degree. C. and 1000.degree. C.
On continued advance of substrate portion 110 it receives, from
dispensing device 122 through nozzle 116, a flow of the liquid
glass melt 140. Although only a single dispenser 122 and nozzle 116
are shown, it may be appropriate to employ multiple nozzles 116 fed
by a single dispenser 122 or to employ a plurality of nozzles 116
each fed by a dedicated dispenser 122 to more uniformly coat the
substrate surface 118. Because the melt compositions are reactive
and volatile as described previously the liquid should be
maintained under a 0.1-1 MPa overpressure of non-reactive gas such
as vaporized sulfur, phosphorus and/or inert gas such as argon such
the that partial equilibrium vapor pressures of the more volatile
species in the glass melt is less than the over pressure provided
to minimize contamination and achieve consistency of composition.
It may be appropriate to at least partially enclose (enclosure, or
the like, not shown) that portion of the process involving liquid
melt to facilitate atmosphere control. To limit the extent of, or
need for, such atmosphere control, dispenser nozzle 116 should be
positioned as close as possible to substrate surface 118, and
coolant spray nozzle 124, which serves to cool and solidify the
melt (described further below), should be placed as close as
possible to where the melt is dispensed from nozzle 116.
[0053] Because the glass melt wets the substrate portion surface
118 the glass melt spreads over substrate surface 118 to produce a
thin, substantially uniform, layer of melt 120 supported by
substrate 110. As noted earlier, the glass composition will affect
the fluidity of the glass melt. Since the spreading of the liquid
melt will be influenced by the viscosity of the melt, the choice of
glass composition may be informed by a requirement for a preferred
fluidity range, generally a range which promotes the rapid
distribution and levelling of the melt. The thickness of the melt
may be adjusted by adjusting the volume flow rate of melt onto the
substrate. Generally, it is preferred that the melt thickness range
from 10 micrometers to 200 micrometers.
[0054] Further advance of substrate portion 10 will expose the
underside of substrate portion 110 to coolant 126 applied through
spray nozzle 124. Coolant 126, which, before dispensing, may be
passed through a cooler (not shown) to increase its effectiveness,
may be drawn from storage unit 136 as shown, or from some other
suitable source, including a municipal water supply. Coolant 126 is
applied at a flow rate sufficient to rapidly extract heat locally
from substrate portion 110 so that liquid melt 120 is cooled by
conduction through its contact with substrate portion 110 at a rate
sufficient to suppress crystallization and render a glassy or
amorphous solid glass layer 120'.
[0055] The aggressive cooling applied to liquid melt 120 may result
in non-uniform cooling of liquid melt 120 and possibly induce
residual stresses in solid glass layer 120'. Residual stresses may
also be induced by differences in the thermal expansion coefficient
of the glass layer 120' and the supporting quartz substrate portion
110. Thus, continued advance of substrate portion 10 carries the
substrate portion and its supported solid glass layer 20' into a
furnace, oven or other suitable heating device 28 where the solid
glass layer may be raised to an elevated temperature for a time
suitable to relax and relieve the residual stresses to render a
substantially stress-free solid glass layer 20'' at the furnace 28
exit.
[0056] The temperature of the furnace 28 and the annealing
temperature to which solid glass layer 20' is subjected should be
sufficiently high to promote stress relaxation in a reasonable
time. As before, the annealing temperature may be selected to
render either an amorphous, glassy layer or a layer comprising
discontinuous nanometer-sized or micrometer-sized crystalline
regions. A suitable annealing temperature will depend on the glass
composition, but, by way of illustration and not limitation, an
annealing temperature of between about 220.degree. C. and
320.degree. C. is appropriate for some ranges of glass compositions
because many they exhibit crystallization temperatures of 270-370
.degree. C.
[0057] On exiting the annealing furnace 128 the layer 120'' slowly
cools, by radiation as indicated at 132, to room temperature or
about 20-25.degree. C. At this stage, the glassy layer may be
removed from the substrate and processed appropriately to prepare
it for use in an electrochemical cell. Since, as noted earlier, the
substrate surface 118 is particularly selected not to react with
the glass melt it is expected that no appreciable deformation of
the layer or damage to the substrate surface 118 will occur on
separation and that substrate portion surface 118 will, possibly
absent some minor cleaning etc., be immediately available for
re-use.
[0058] If it is intended to operate this process to prepare `bulk`
glassy material for subsequent pulverization to power and use in
the powder-based solid electrolyte production process of FIG. 1
some modifications may be made to the melt-based process of FIG. 3.
First, the thickness of the dispensed liquid layer may be increased
to up to 10,000 micrometers while still achieving a quench rate
satisfactory to render the melt amorphous. Second, any annealing
should be conducted below T.sub.c so maintain the final
microstructure as amorphous. Third, it may be possible to eliminate
the annealing step entirely. By eliminating the annealing step the
quenched structure may possess sufficiently high residual
stress(es) that it will spontaneously fragment. Such fragmentation,
since the glassy material is to be pulverized, is perfectly
suitable for its intended process, but may create handling or
cleaning issues which minimize or obviate any energy advantage
gained by eliminating the annealing step.
[0059] The above description of exemplary embodiments and specific
examples are merely descriptive in nature; they are not intended to
limit the scope of the claims that follow. Each of the terms used
in the appended claims should be given its ordinary and customary
meaning unless specifically and unambiguously stated otherwise in
the specification.
* * * * *